]> This is edition 2.9 of the GNU Emacs Lisp Reference Manual,corresponding to Emacs version 22.1.Copyright © 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free SoftwareFoundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being “GNU General Public License,” with the Front-Cover texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.” (a) The FSF's Back-Cover Text is: “You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.” Emacs Lisp This Info file contains edition 2.9 of the GNU Emacs Lisp Reference Manual, corresponding to GNU Emacs version 22.1. <setfilename>../info/intro</setfilename> Introduction Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere “extension language”; it is a full computer programming language in its own right. You can use it as you would any other programming language. Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables. This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information. Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing. This is edition 2.9 of the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 22.1. Caveats bugs in this manual This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few topics that are not covered, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written. Because we are not able to deal with them completely, we have left out several parts intentionally. This includes most information about usage on VMS. The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says—from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know. As you use this manual, we ask that you send corrections as soon as you find them. If you think of a simple, real life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the node name and function or variable name, as appropriate. Also state the number of the edition you are criticizing. bugs suggestions Please mail comments and corrections to bug-lisp-manual@gnu.org We let mail to this list accumulate unread until someone decides to apply the corrections. Months, and sometimes years, go by between updates. So please attach no significance to the lack of a reply—your mail will be acted on in due time. If you want to contact the Emacs maintainers more quickly, send mail to bug-gnu-emacs@gnu.org. Lisp History Lisp history Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it ideal for other purposes as well, such as writing editing commands. Maclisp Common Lisp Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960s at MIT's Project MAC. Eventually the implementors of the descendants of Maclisp came together and developed a standard for Lisp systems, called Common Lisp. In the meantime, Gerry Sussman and Guy Steele at MIT developed a simplified but very powerful dialect of Lisp, called Scheme. GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don't know Common Lisp, don't worry about it; this manual is self-contained. cl A certain amount of Common Lisp emulation is available via the cl library. *note Overview: (cl)Top. Emacs Lisp is not at all influenced by Scheme; but the GNU project has an implementation of Scheme, called Guile. We use Guile in all new GNU software that calls for extensibility. Conventions This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later. Some Terms Throughout this manual, the phrases “the Lisp reader” and “the Lisp printer” refer to those routines in Lisp that convert textual representations of Lisp objects into actual Lisp objects, and vice versa. See , for more details. You, the person reading this manual, are thought of as “the programmer” and are addressed as “you.” “The user” is the person who uses Lisp programs, including those you write. fonts in this manual Examples of Lisp code are formatted like this: (list 1 2 3). Names that represent metasyntactic variables, or arguments to a function being described, are formatted like this: first-number. nil and t truth value boolean nil false In Lisp, the symbol nil has three separate meanings: it is a symbol with the name ‘nil’; it is the logical truth value false; and it is the empty list—the list of zero elements. When used as a variable, nil always has the value nil. As far as the Lisp reader is concerned, ‘()’ and ‘nil’ are identical: they stand for the same object, the symbol nil. The different ways of writing the symbol are intended entirely for human readers. After the Lisp reader has read either ‘()’ or ‘nil’, there is no way to determine which representation was actually written by the programmer. In this manual, we write () when we wish to emphasize that it means the empty list, and we write nil when we wish to emphasize that it means the truth value false. That is a good convention to use in Lisp programs also. (cons 'foo ()) ; Emphasize the empty list (setq foo-flag nil) ; Emphasize the truth value false t true In contexts where a truth value is expected, any non-nil value is considered to be true. However, t is the preferred way to represent the truth value true. When you need to choose a value which represents true, and there is no other basis for choosing, use t. The symbol t always has the value t. In Emacs Lisp, nil and t are special symbols that always evaluate to themselves. This is so that you do not need to quote them to use them as constants in a program. An attempt to change their values results in a setting-constant error. See . booleanp — Function: booleanp object Return non-nil iff object is one of the two canonical booleanvalues: t or nil. Evaluation Notation evaluation notation documentation notation notation A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with ‘=>’: (car '(1 2)) => 1 You can read this as “(car '(1 2)) evaluates to 1.” When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with ‘==>’. We may or may not show the result of the evaluation of the expanded form. (third '(a b c)) ==> (car (cdr (cdr '(a b c)))) => c Sometimes to help describe one form we show another form that produces identical results. The exact equivalence of two forms is indicated with ‘==’. (make-sparse-keymap) == (list 'keymap) Printing Notation printing notation Many of the examples in this manual print text when they are evaluated. If you execute example code in a Lisp Interaction buffer (such as the buffer ‘*scratch*’), the printed text is inserted into the buffer. If you execute the example by other means (such as by evaluating the function eval-region), the printed text is displayed in the echo area. Examples in this manual indicate printed text with ‘-|’, irrespective of where that text goes. The value returned by evaluating the form (here bar) follows on a separate line with ‘=>’. (progn (prin1 'foo) (princ "\n") (prin1 'bar)) -| foo -| bar => bar Error Messages error message notation Some examples signal errors. This normally displays an error message in the echo area. We show the error message on a line starting with ‘error-->’. Note that ‘error-->’ itself does not appear in the echo area. (+ 23 'x) error--> Wrong type argument: number-or-marker-p, x Buffer Text Notation buffer text notation Some examples describe modifications to the contents of a buffer, by showing the “before” and “after” versions of the text. These examples show the contents of the buffer in question between two lines of dashes containing the buffer name. In addition, ‘-!-’ indicates the location of point. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is currently located.) ---------- Buffer: foo ---------- This is the -!-contents of foo. ---------- Buffer: foo ---------- (insert "changed ") => nil ---------- Buffer: foo ---------- This is the changed -!-contents of foo. ---------- Buffer: foo ---------- Format of Descriptions description format Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category—function, variable, or whatever—appears at the beginning of the line. The description follows on succeeding lines, sometimes with examples. A Sample Function Description function descriptions command descriptions macro descriptions special form descriptions In a function description, the name of the function being described appears first. It is followed on the same line by a list of argument names. These names are also used in the body of the description, to stand for the values of the arguments. The appearance of the keyword &optional in the argument list indicates that the subsequent arguments may be omitted (omitted arguments default to nil). Do not write &optional when you call the function. The keyword &rest (which must be followed by a single argument name) indicates that any number of arguments can follow. The single argument name following &rest will receive, as its value, a list of all the remaining arguments passed to the function. Do not write &rest when you call the function. Here is a description of an imaginary function foo: foo — Function: foo integer1 &optional integer2 &rest integers The function foo subtracts integer1 from integer2,then adds all the rest of the arguments to the result. If integer2is not supplied, then the number 19 is used by default. (foo 1 5 3 9) => 16 (foo 5) => 14 More generally, (foo w x y…) == (+ (- x w) y…) Any argument whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. Arguments named object may be of any type. (See , for a list of Emacs object types.) Arguments with other sorts of names (e.g., new-file) are discussed specifically in the description of the function. In some sections, features common to the arguments of several functions are described at the beginning. See , for a more complete description of optional and rest arguments. Command, macro, and special form descriptions have the same format, but the word `Function' is replaced by `Command', `Macro', or `Special Form', respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way. Special form descriptions use a more complex notation to specify optional and repeated arguments because they can break the argument list down into separate arguments in more complicated ways. ‘[optional-arg]’ means that optional-arg is optional and ‘repeated-args…’ stands for zero or more arguments. Parentheses are used when several arguments are grouped into additional levels of list structure. Here is an example: count-loop — Special Form: count-loop ( var [ from to [ inc ] ] ) body … This imaginary special form implements a loop that executes thebody forms and then increments the variable var on eachiteration. On the first iteration, the variable has the valuefrom; on subsequent iterations, it is incremented by one (or byinc if that is given). The loop exits before executing bodyif var equals to. Here is an example: (count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri)) If from and to are omitted, var is bound tonil before the loop begins, and the loop exits if var isnon-nil at the beginning of an iteration. Here is an example: (count-loop (done) (if (pending) (fixit) (setq done t))) In this special form, the arguments from and to areoptional, but must both be present or both absent. If they are present,inc may optionally be specified as well. These arguments aregrouped with the argument var into a list, to distinguish themfrom body, which includes all remaining elements of the form. A Sample Variable Description variable descriptions option descriptions A variable is a name that can hold a value. Although nearly all variables can be set by the user, certain variables exist specifically so that users can change them; these are called user options. Ordinary variables and user options are described using a format like that for functions except that there are no arguments. Here is a description of the imaginary electric-future-map variable. electric-future-map — Variable: electric-future-map The value of this variable is a full keymap used by Electric CommandFuture mode. The functions in this map allow you to edit commands youhave not yet thought about executing. User option descriptions have the same format, but `Variable' is replaced by `User Option'. Version Information These facilities provide information about which version of Emacs is in use. emacs-version — Command: emacs-version &optional here This function returns a string describing the version of Emacs that isrunning. It is useful to include this string in bug reports. (emacs-version) => "GNU Emacs 20.3.5 (i486-pc-linux-gnulibc1, X toolkit) of Sat Feb 14 1998 on psilocin.gnu.org" If here is non-nil, it inserts the text in the bufferbefore point, and returns nil. Called interactively, thefunction prints the same information in the echo area, but giving aprefix argument makes here non-nil. emacs-build-time — Variable: emacs-build-time The value of this variable indicates the time at which Emacs was builtat the local site. It is a list of three integers, like the valueof current-time (see ). emacs-build-time => (13623 62065 344633) emacs-version — Variable: emacs-version The value of this variable is the version of Emacs being run. It is astring such as "20.3.1". The last number in this string is notreally part of the Emacs release version number; it is incremented eachtime you build Emacs in any given directory. A value with four numericcomponents, such as "20.3.9.1", indicates an unreleased testversion. The following two variables have existed since Emacs version 19.23: emacs-major-version — Variable: emacs-major-version The major version number of Emacs, as an integer. For Emacs version20.3, the value is 20. emacs-minor-version — Variable: emacs-minor-version The minor version number of Emacs, as an integer. For Emacs version20.3, the value is 3. Acknowledgements This manual was written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc. Corrections were supplied by Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Per Starbäck, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn. <setfilename>../info/objects</setfilename> Lisp Data Types object Lisp object type data type A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects. Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for “the” type of an object. primitive type A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, hash-table, subr, and byte-code function, plus several special types, such as buffer, that are related to editing. (See .) Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type. Note that Lisp is unlike many other languages in that Lisp objects are self-typing: the primitive type of the object is implicit in the object itself. For example, if an object is a vector, nothing can treat it as a number; Lisp knows it is a vector, not a number. In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatever value you store in it, type and all. (Actually, a small number of Emacs Lisp variables can only take on values of a certain type. See .) This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters. Printed Representation and Read Syntax printed representation read syntax The printed representation of an object is the format of the output generated by the Lisp printer (the function prin1) for that object. Every data type has a unique printed representation. The read syntax of an object is the format of the input accepted by the Lisp reader (the function read) for that object. This is not necessarily unique; many kinds of object have more than one syntax. See . hash notation In most cases, an object's printed representation is also a read syntax for the object. However, some types have no read syntax, since it does not make sense to enter objects of these types as constants in a Lisp program. These objects are printed in hash notation, which consists of the characters ‘#<’, a descriptive string (typically the type name followed by the name of the object), and a closing ‘>’. For example: (current-buffer) => #<buffer objects.texi> Hash notation cannot be read at all, so the Lisp reader signals the error invalid-read-syntax whenever it encounters ‘#<’. invalid-read-syntax In other languages, an expression is text; it has no other form. In Lisp, an expression is primarily a Lisp object and only secondarily the text that is the object's read syntax. Often there is no need to emphasize this distinction, but you must keep it in the back of your mind, or you will occasionally be very confused. When you evaluate an expression interactively, the Lisp interpreter first reads the textual representation of it, producing a Lisp object, and then evaluates that object (see ). However, evaluation and reading are separate activities. Reading returns the Lisp object represented by the text that is read; the object may or may not be evaluated later. See , for a description of read, the basic function for reading objects. Comments comments ‘;’ in comment A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a semicolon (‘;’) starts a comment if it is not within a string or character constant. The comment continues to the end of line. The Lisp reader discards comments; they do not become part of the Lisp objects which represent the program within the Lisp system. The ‘#@count’ construct, which skips the next count characters, is useful for program-generated comments containing binary data. The Emacs Lisp byte compiler uses this in its output files (see ). It isn't meant for source files, however. See , for conventions for formatting comments. Programming Types programming types There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp. Integer Type The range of values for integers in Emacs Lisp is −268435456 to 268435455 (29 bits; i.e., -2**28 to 2**28 - 1) on most machines. (Some machines may provide a wider range.) It is important to note that the Emacs Lisp arithmetic functions do not check for overflow. Thus (1+ 268435455) is −268435456 on most machines. The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading ‘+’ or a final ‘.’. -1 ; The integer -1. 1 ; The integer 1. 1. ; Also the integer 1. +1 ; Also the integer 1. 536870913 ; Also the integer 1 on a 29-bit implementation. See , for more information. Floating Point Type Floating point numbers are the computer equivalent of scientific notation; you can think of a floating point number as a fraction together with a power of ten. The precise number of significant figures and the range of possible exponents is machine-specific; Emacs uses the C data type double to store the value, and internally this records a power of 2 rather than a power of 10. The printed representation for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent. See , for more information. Character Type ASCII character codes A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65. Individual characters are used occasionally in programs, but it is more common to work with strings, which are sequences composed of characters. See . Characters in strings, buffers, and files are currently limited to the range of 0 to 524287—nineteen bits. But not all values in that range are valid character codes. Codes 0 through 127 are ASCII codes; the rest are non-ASCII (see ). Characters that represent keyboard input have a much wider range, to encode modifier keys such as Control, Meta and Shift. There are special functions for producing a human-readable textual description of a character for the sake of messages. See . Basic Char Syntax read syntax for characters printed representation for characters syntax for characters ‘?’ in character constant question mark in character constant Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is not clear programming. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark. The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, ‘?A’ for the character A, ‘?B’ for the character B, and ‘?a’ for the character a. For example: ?Q => 81 ?q => 113 You can use the same syntax for punctuation characters, but it is often a good idea to add a ‘\’ so that the Emacs commands for editing Lisp code don't get confused. For example, ‘?\(’ is the way to write the open-paren character. If the character is ‘\’, you must use a second ‘\’ to quote it: ‘?\\’. whitespace bell character ‘\a’ backspace ‘\b’ tab (ASCII character) ‘\t’ vertical tab ‘\v’ formfeed ‘\f’ newline ‘\n’ return (ASCII character) ‘\r’ escape (ASCII character) ‘\e’ space (ASCII character) ‘\s’ You can express the characters control-g, backspace, tab, newline, vertical tab, formfeed, space, return, del, and escape as ‘?\a’, ‘?\b’, ‘?\t’, ‘?\n’, ‘?\v’, ‘?\f’, ‘?\s’, ‘?\r’, ‘?\d’, and ‘?\e’, respectively. (‘?\s’ followed by a dash has a different meaning—it applies the “super” modifier to the following character.) Thus, ?\a => 7 ; control-g, C-g ?\b => 8 ; backspace, BS, C-h ?\t => 9 ; tab, TAB, C-i ?\n => 10 ; newline, C-j ?\v => 11 ; vertical tab, C-k ?\f => 12 ; formfeed character, C-l ?\r => 13 ; carriage return, RET, C-m ?\e => 27 ; escape character, ESC, C-[ ?\s => 32 ; space character, SPC ?\\ => 92 ; backslash character, \ ?\d => 127 ; delete character, DEL escape sequence These sequences which start with backslash are also known as escape sequences, because backslash plays the role of an “escape character”; this terminology has nothing to do with the character ESC. ‘\s’ is meant for use in character constants; in string constants, just write the space. A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, ‘?\+’ is equivalent to ‘?+’. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters ‘()\|;'`"#.,’ to avoid confusing the Emacs commands for editing Lisp code. You can also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as ‘\t’ or ‘\s’, instead of an actual whitespace character such as a tab or a space. (If you do write backslash followed by a space, you should write an extra space after the character constant to separate it from the following text.) General Escape Syntax In addition to the specific excape sequences for special important control characters, Emacs provides general categories of escape syntax that you can use to specify non-ASCII text characters. unicode character escape For instance, you can specify characters by their Unicode values. ?\unnnn represents a character that maps to the Unicode code point ‘U+nnnn’. There is a slightly different syntax for specifying characters with code points above #xFFFF; \U00nnnnnn represents the character whose Unicode code point is ‘U+nnnnnn’, if such a character is supported by Emacs. If the corresponding character is not supported, Emacs signals an error. This peculiar and inconvenient syntax was adopted for compatibility with other programming languages. Unlike some other languages, Emacs Lisp supports this syntax in only character literals and strings. ‘\’ in character constant backslash in character constant octal character code The most general read syntax for a character represents the character code in either octal or hex. To use octal, write a question mark followed by a backslash and the octal character code (up to three octal digits); thus, ‘?\101’ for the character A, ‘?\001’ for the character C-a, and ?\002 for the character C-b. Although this syntax can represent any ASCII character, it is preferred only when the precise octal value is more important than the ASCII representation. ?\012 => 10 ?\n => 10 ?\C-j => 10 ?\101 => 65 ?A => 65 To use hex, write a question mark followed by a backslash, ‘x’, and the hexadecimal character code. You can use any number of hex digits, so you can represent any character code in this way. Thus, ‘?\x41’ for the character A, ‘?\x1’ for the character C-a, and ?\x8e0 for the Latin-1 character ‘a’ with grave accent. Control-Character Syntax control characters Control characters can be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both ‘?\^I’ and ‘?\^i’ are valid read syntax for the character C-i, the character whose value is 9. Instead of the ‘^’, you can use ‘C-’; thus, ‘?\C-i’ is equivalent to ‘?\^I’ and to ‘?\^i’: ?\^I => 9 ?\C-I => 9 In strings and buffers, the only control characters allowed are those that exist in ASCII; but for keyboard input purposes, you can turn any character into a control character with ‘C-’. The character codes for these non-ASCII control characters include the 2**26 bit as well as the code for the corresponding non-control character. Ordinary terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using X and other window systems. For historical reasons, Emacs treats the DEL character as the control equivalent of ?: ?\^? => 127 ?\C-? => 127 As a result, it is currently not possible to represent the character Control-?, which is a meaningful input character under X, using ‘\C-’. It is not easy to change this, as various Lisp files refer to DEL in this way. For representing control characters to be found in files or strings, we recommend the ‘^’ syntax; for control characters in keyboard input, we prefer the ‘C-’ syntax. Which one you use does not affect the meaning of the program, but may guide the understanding of people who read it. Meta-Character Syntax meta characters A meta character is a character typed with the META modifier key. The integer that represents such a character has the 2**27 bit set. We use high bits for this and other modifiers to make possible a wide range of basic character codes. In a string, the 2**7 bit attached to an ASCII character indicates a meta character; thus, the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ASCII characters. (In Emacs versions 18 and older, this convention was used for characters outside of strings as well.) The read syntax for meta characters uses ‘\M-’. For example, ‘?\M-A’ stands for M-A. You can use ‘\M-’ together with octal character codes (see below), with ‘\C-’, or with any other syntax for a character. Thus, you can write M-A as ‘?\M-A’, or as ‘?\M-\101’. Likewise, you can write C-M-b as ‘?\M-\C-b’, ‘?\C-\M-b’, or ‘?\M-\002’. Other Character Modifier Bits The case of a graphic character is indicated by its character code; for example, ASCII distinguishes between the characters ‘a’ and ‘A’. But ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the 2**25 bit to indicate that the shift key was used in typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary terminals do not report the distinction to the computer in any way. The Lisp syntax for the shift bit is ‘\S-’; thus, ‘?\C-\S-o’ or ‘?\C-\S-O’ represents the shifted-control-o character. hyper characters super characters alt characters The X Window System defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are ‘\H-’, ‘\s-’ and ‘\A-’. (Case is significant in these prefixes.) Thus, ‘?\H-\M-\A-x’ represents Alt-Hyper-Meta-x. (Note that ‘\s’ with no following ‘-’ represents the space character.) Numerically, the bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper. Symbol Type A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary Lisp use, with one single obarray (see , a symbol's name is unique—no two symbols have the same name. A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently. A symbol whose name starts with a colon (‘:’) is called a keyword symbol. These symbols automatically act as constants, and are normally used only by comparing an unknown symbol with a few specific alternatives. ‘\’ in symbols backslash in symbols A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters ‘-+=*/’. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a ‘\’ at the beginning of the name to force interpretation as a symbol.) The characters ‘_~!@$%^&:<>{}?’ are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, ‘\t’ represents a tab character; in the name of a symbol, however, ‘\t’ merely quotes the letter ‘t’. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing. CL note—case of letters Common Lisp note: In Common Lisp, lower case letters are always “folded” to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct. Here are several examples of symbol names. Note that the ‘+’ in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the fourth example because the rest of the name makes it invalid as a number. foo ; A symbol named ‘foo’. FOO ; A symbol named ‘FOO’, different from ‘foo’. char-to-string ; A symbol named ‘char-to-string’. 1+ ; A symbol named ‘1+’ ; (not ‘+1’, which is an integer). \+1 ; A symbol named ‘+1’ ; (not a very readable name). \(*\ 1\ 2\) ; A symbol named ‘(* 1 2)’ (a worse name). +-*/_~!@$%^&=:<>{} ; A symbol named ‘+-*/_~!@$%^&=:<>{}’. ; These characters need not be escaped. ‘#:’ read syntax Normally the Lisp reader interns all symbols (see ). To prevent interning, you can write ‘#:’ before the name of the symbol. Sequence Types A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence. Arrays are further subdivided into strings, vectors, char-tables and bool-vectors. Vectors can hold elements of any type, but string elements must be characters, and bool-vector elements must be t or nil. Char-tables are like vectors except that they are indexed by any valid character code. The characters in a string can have text properties like characters in a buffer (see ), but vectors do not support text properties, even when their elements happen to be characters. Lists, strings and the other array types are different, but they have important similarities. For example, all have a length l, and all have elements which can be indexed from zero to l minus one. Several functions, called sequence functions, accept any kind of sequence. For example, the function elt can be used to extract an element of a sequence, given its index. See . It is generally impossible to read the same sequence twice, since sequences are always created anew upon reading. If you read the read syntax for a sequence twice, you get two sequences with equal contents. There is one exception: the empty list () always stands for the same object, nil. Cons Cell and List Types address field of register decrement field of register pointers A cons cell is an object that consists of two slots, called the car slot and the cdr slot. Each slot can hold or refer to any Lisp object. We also say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr. A note to C programmers: in Lisp, we do not distinguish between “holding” a value and “pointing to” the value, because pointers in Lisp are implicit. A list is a series of cons cells, linked together so that the cdr slot of each cons cell holds either the next cons cell or the empty list. The empty list is actually the symbol nil. See , for functions that work on lists. Because most cons cells are used as part of lists, the phrase list structure has come to refer to any structure made out of cons cells. atoms Because cons cells are so central to Lisp, we also have a word for “an object which is not a cons cell.” These objects are called atoms. parenthesis ‘(…)’ in lists The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis. Here are examples of lists: (A 2 "A") ; A list of three elements. () ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string "A ()". (A ()) ; A list of two elements: A and the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element ; (which is a list of three elements). Upon reading, each object inside the parentheses becomes an element of the list. That is, a cons cell is made for each element. The car slot of the cons cell holds the element, and its cdr slot refers to the next cons cell of the list, which holds the next element in the list. The cdr slot of the last cons cell is set to hold nil. The names car and cdr derive from the history of Lisp. The original Lisp implementation ran on an IBM 704 computer which divided words into two parts, called the “address” part and the “decrement”; car was an instruction to extract the contents of the address part of a register, and cdr an instruction to extract the contents of the decrement. By contrast, “cons cells” are named for the function cons that creates them, which in turn was named for its purpose, the construction of cells. Drawing Lists as Box Diagrams box diagrams, for lists diagrams, boxed, for lists A list can be illustrated by a diagram in which the cons cells are shown as pairs of boxes, like dominoes. (The Lisp reader cannot read such an illustration; unlike the textual notation, which can be understood by both humans and computers, the box illustrations can be understood only by humans.) This picture represents the three-element list (rose violet buttercup): --- --- --- --- --- --- | | |--> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | --> rose --> violet --> buttercup In this diagram, each box represents a slot that can hold or refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow represents a reference to a Lisp object, either an atom or another cons cell. In this example, the first box, which holds the car of the first cons cell, refers to or “holds” rose (a symbol). The second box, holding the cdr of the first cons cell, refers to the next pair of boxes, the second cons cell. The car of the second cons cell is violet, and its cdr is the third cons cell. The cdr of the third (and last) cons cell is nil. Here is another diagram of the same list, (rose violet buttercup), sketched in a different manner: --------------- ---------------- ------------------- | car | cdr | | car | cdr | | car | cdr | | rose | o-------->| violet | o-------->| buttercup | nil | | | | | | | | | | --------------- ---------------- ------------------- nil as a list empty list A list with no elements in it is the empty list; it is identical to the symbol nil. In other words, nil is both a symbol and a list. Here is the list (A ()), or equivalently (A nil), depicted with boxes and arrows: --- --- --- --- | | |--> | | |--> nil --- --- --- --- | | | | --> A --> nil Here is a more complex illustration, showing the three-element list, ((pine needles) oak maple), the first element of which is a two-element list: --- --- --- --- --- --- | | |--> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | | --> oak --> maple | | --- --- --- --- --> | | |--> | | |--> nil --- --- --- --- | | | | --> pine --> needles The same list represented in the second box notation looks like this: -------------- -------------- -------------- | car | cdr | | car | cdr | | car | cdr | | o | o------->| oak | o------->| maple | nil | | | | | | | | | | | -- | --------- -------------- -------------- | | | -------------- ---------------- | | car | cdr | | car | cdr | ------>| pine | o------->| needles | nil | | | | | | | -------------- ---------------- Dotted Pair Notation dotted pair notation ‘.’ in lists Dotted pair notation is a general syntax for cons cells that represents the car and cdr explicitly. In this syntax, (a . b) stands for a cons cell whose car is the object a and whose cdr is the object b. Dotted pair notation is more general than list syntax because the cdr does not have to be a list. However, it is more cumbersome in cases where list syntax would work. In dotted pair notation, the list ‘(1 2 3)’ is written as ‘(1 . (2 . (3 . nil)))’. For nil-terminated lists, you can use either notation, but list notation is usually clearer and more convenient. When printing a list, the dotted pair notation is only used if the cdr of a cons cell is not a list. Here's an example using boxes to illustrate dotted pair notation. This example shows the pair (rose . violet): --- --- | | |--> violet --- --- | | --> rose You can combine dotted pair notation with list notation to represent conveniently a chain of cons cells with a non-nil final cdr. You write a dot after the last element of the list, followed by the cdr of the final cons cell. For example, (rose violet . buttercup) is equivalent to (rose . (violet . buttercup)). The object looks like this: --- --- --- --- | | |--> | | |--> buttercup --- --- --- --- | | | | --> rose --> violet The syntax (rose . violet . buttercup) is invalid because there is nothing that it could mean. If anything, it would say to put buttercup in the cdr of a cons cell whose cdr is already used for violet. The list (rose violet) is equivalent to (rose . (violet)), and looks like this: --- --- --- --- | | |--> | | |--> nil --- --- --- --- | | | | --> rose --> violet Similarly, the three-element list (rose violet buttercup) is equivalent to (rose . (violet . (buttercup))). It looks like this: --- --- --- --- --- --- | | |--> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | --> rose --> violet --> buttercup Association List Type An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the car is considered a key, and the cdr is considered an associated value. (In some cases, the associated value is stored in the car of the cdr.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list. For example, (setq alist-of-colors '((rose . red) (lily . white) (buttercup . yellow))) sets the variable alist-of-colors to an alist of three elements. In the first element, rose is the key and red is the value. See , for a further explanation of alists and for functions that work on alists. See , for another kind of lookup table, which is much faster for handling a large number of keys. Array Type An array is composed of an arbitrary number of slots for holding or referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes approximately the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.) Emacs defines four types of array: strings, vectors, bool-vectors, and char-tables. A string is an array of characters and a vector is an array of arbitrary objects. A bool-vector can hold only t or nil. These kinds of array may have any length up to the largest integer. Char-tables are sparse arrays indexed by any valid character code; they can hold arbitrary objects. The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The largest possible index value is one less than the length of the array. Once an array is created, its length is fixed. All Emacs Lisp arrays are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with nested one-dimensional arrays.) Each type of array has its own read syntax; see the following sections for details. The array type is a subset of the sequence type, and contains the string type, the vector type, the bool-vector type, and the char-table type. String Type A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string. See , for functions that operate on strings. Syntax for Strings ‘"’ in strings double-quote in strings ‘\’ in strings backslash in strings The read syntax for strings is a double-quote, an arbitrary number of characters, and another double-quote, "like this". To include a double-quote in a string, precede it with a backslash; thus, "\"" is a string containing just a single double-quote character. Likewise, you can include a backslash by preceding it with another backslash, like this: "this \\ is a single embedded backslash". newline in strings The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline—one that is preceded by ‘\’—does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. An escaped space ‘\ ’ is likewise ignored. "It is useful to include newlines in documentation strings, but the newline is \ ignored if escaped." => "It is useful to include newlines in documentation strings, but the newline is ignored if escaped." Non-ASCII Characters in Strings You can include a non-ASCII international character in a string constant by writing it literally. There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte. If the string constant is read from a multibyte source, such as a multibyte buffer or string, or a file that would be visited as multibyte, then the character is read as a multibyte character, and that makes the string multibyte. If the string constant is read from a unibyte source, then the character is read as unibyte and that makes the string unibyte. You can also represent a multibyte non-ASCII character with its character code: use a hex escape, ‘\xnnnnnnn’, with as many digits as necessary. (Multibyte non-ASCII character codes are all greater than 256.) Any character which is not a valid hex digit terminates this construct. If the next character in the string could be interpreted as a hex digit, write ‘\ ’ (backslash and space) to terminate the hex escape—for example, ‘\x8e0\ ’ represents one character, ‘a’ with grave accent. ‘\ ’ in a string constant is just like backslash-newline; it does not contribute any character to the string, but it does terminate the preceding hex escape. You can represent a unibyte non-ASCII character with its character code, which must be in the range from 128 (0200 octal) to 255 (0377 octal). If you write all such character codes in octal and the string contains no other characters forcing it to be multibyte, this produces a unibyte string. However, using any hex escape in a string (even for an ASCII character) forces the string to be multibyte. You can also specify characters in a string by their numeric values in Unicode, using ‘\u’ and ‘\U’ (see ). See , for more information about the two text representations. Nonprinting Characters in Strings You can use the same backslash escape-sequences in a string constant as in character literals (but do not use the question mark that begins a character constant). For example, you can write a string containing the nonprinting characters tab and C-a, with commas and spaces between them, like this: "\t, \C-a". See , for a description of the read syntax for characters. However, not all of the characters you can write with backslash escape-sequences are valid in strings. The only control characters that a string can hold are the ASCII control characters. Strings do not distinguish case in ASCII control characters. Properly speaking, strings cannot hold meta characters; but when a string is to be used as a key sequence, there is a special convention that provides a way to represent meta versions of ASCII characters in a string. If you use the ‘\M-’ syntax to indicate a meta character in a string constant, this sets the 2**7 bit of the character in the string. If the string is used in define-key or lookup-key, this numeric code is translated into the equivalent meta character. See . Strings cannot hold characters that have the hyper, super, or alt modifiers. Text Properties in Strings A string can hold properties for the characters it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to copy the text's properties with no special effort. See , for an explanation of what text properties mean. Strings with text properties use a special read and print syntax: #("characters" property-data...) where property-data consists of zero or more elements, in groups of three as follows: beg end plist The elements beg and end are integers, and together specify a range of indices in the string; plist is the property list for that range. For example, #("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic)) represents a string whose textual contents are ‘foo bar’, in which the first three characters have a face property with value bold, and the last three have a face property with value italic. (The fourth character has no text properties, so its property list is nil. It is not actually necessary to mention ranges with nil as the property list, since any characters not mentioned in any range will default to having no properties.) Vector Type A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.) The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation. [1 "two" (three)] ; A vector of three elements. => [1 "two" (three)] See , for functions that work with vectors. Char-Table Type A char-table is a one-dimensional array of elements of any type, indexed by character codes. Char-tables have certain extra features to make them more useful for many jobs that involve assigning information to character codes—for example, a char-table can have a parent to inherit from, a default value, and a small number of extra slots to use for special purposes. A char-table can also specify a single value for a whole character set. The printed representation of a char-table is like a vector except that there is an extra ‘#^’ at the beginning. See , for special functions to operate on char-tables. Uses of char-tables include: Case tables (see ). Character category tables (see ). Display tables (see ). Syntax tables (see ). Bool-Vector Type A bool-vector is a one-dimensional array of elements that must be t or nil. The printed representation of a bool-vector is like a string, except that it begins with ‘#&’ followed by the length. The string constant that follows actually specifies the contents of the bool-vector as a bitmap—each “character” in the string contains 8 bits, which specify the next 8 elements of the bool-vector (1 stands for t, and 0 for nil). The least significant bits of the character correspond to the lowest indices in the bool-vector. (make-bool-vector 3 t) => #&3"^G" (make-bool-vector 3 nil) => #&3"^@" These results make sense, because the binary code for ‘C-g’ is 111 and ‘C-@’ is the character with code 0. If the length is not a multiple of 8, the printed representation shows extra elements, but these extras really make no difference. For instance, in the next example, the two bool-vectors are equal, because only the first 3 bits are used: (equal #&3"\377" #&3"\007") => t Hash Table Type A hash table is a very fast kind of lookup table, somewhat like an alist in that it maps keys to corresponding values, but much faster. Hash tables have no read syntax, and print using hash notation. See , for functions that operate on hash tables. (make-hash-table) => #<hash-table 'eql nil 0/65 0x83af980> Function Type Lisp functions are executable code, just like functions in other programming languages. In Lisp, unlike most languages, functions are also Lisp objects. A non-compiled function in Lisp is a lambda expression: that is, a list whose first element is the symbol lambda (see ). In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression can be called as a function even though it has no name; to emphasize this, we also call it an anonymous function (see ). A named function in Lisp is just a symbol with a valid function in its function cell (see ). Most of the time, functions are called when their names are written in Lisp expressions in Lisp programs. However, you can construct or obtain a function object at run time and then call it with the primitive functions funcall and apply. See . Macro Type A Lisp macro is a user-defined construct that extends the Lisp language. It is represented as an object much like a function, but with different argument-passing semantics. A Lisp macro has the form of a list whose first element is the symbol macro and whose cdr is a Lisp function object, including the lambda symbol. Lisp macro objects are usually defined with the built-in defmacro function, but any list that begins with macro is a macro as far as Emacs is concerned. See , for an explanation of how to write a macro. Warning: Lisp macros and keyboard macros (see ) are entirely different things. When we use the word “macro” without qualification, we mean a Lisp macro, not a keyboard macro. Primitive Function Type special forms A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word “subr” is derived from “subroutine.”) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see ). It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to redefine a primitive with a function written in Lisp. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. Therefore, we discourage redefinition of primitive functions. The term function refers to all Emacs functions, whether written in Lisp or C. See , for information about the functions written in Lisp. Primitive functions have no read syntax and print in hash notation with the name of the subroutine. (symbol-function 'car) ; Access the function cell ; of the symbol. => #<subr car> (subrp (symbol-function 'car)) ; Is this a primitive function? => t ; Yes. Byte-Code Function Type The byte compiler produces byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. See , for information about the byte compiler. The printed representation and read syntax for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’. Autoload Type An autoload object is a list whose first element is the symbol autoload. It is stored as the function definition of a symbol, where it serves as a placeholder for the real definition. The autoload object says that the real definition is found in a file of Lisp code that should be loaded when necessary. It contains the name of the file, plus some other information about the real definition. After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file. An autoload object is usually created with the function autoload, which stores the object in the function cell of a symbol. See , for more details. Editing Types editing types The types in the previous section are used for general programming purposes, and most of them are common to most Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing. Buffer Type A buffer is an object that holds text that can be edited (see ). Most buffers hold the contents of a disk file (see ) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see ). But a buffer need not be displayed in any window. The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, you can insert text efficiently into an existing buffer, altering the buffer's contents, whereas “inserting” text into a string requires concatenating substrings, and the result is an entirely new string object. Each buffer has a designated position called point (see ). At any time, one buffer is the current buffer. Most editing commands act on the contents of the current buffer in the neighborhood of point. Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (see ). Several other data structures are associated with each buffer: a local syntax table (see ); a local keymap (see ); and, a list of buffer-local variable bindings (see ). overlays (see ). text properties for the text in the buffer (see ). The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs. A buffer may be indirect, which means it shares the text of another buffer, but presents it differently. See . Buffers have no read syntax. They print in hash notation, showing the buffer name. (current-buffer) => #<buffer objects.texi> Marker Type A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer's text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer. Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer. (point-marker) => #<marker at 10779 in objects.texi> See , for information on how to test, create, copy, and move markers. Window Type A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows. Though many windows may exist simultaneously, at any time one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case. Windows are grouped on the screen into frames; each window belongs to one and only one frame. See . Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently. (selected-window) => #<window 1 on objects.texi> See , for a description of the functions that work on windows. Frame Type A frame is a screen area that contains one or more Emacs windows; we also use the term “frame” to refer to the Lisp object that Emacs uses to refer to the screen area. Frames have no read syntax. They print in hash notation, giving the frame's title, plus its address in core (useful to identify the frame uniquely). (selected-frame) => #<frame emacs@psilocin.gnu.org 0xdac80> See , for a description of the functions that work on frames. Window Configuration Type window layout in a frame A window configuration stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later. Window configurations do not have a read syntax; their print syntax looks like ‘#<window-configuration>’. See , for a description of several functions related to window configurations. Frame Configuration Type screen layout window layout, all frames A frame configuration stores information about the positions, sizes, and contents of the windows in all frames. It is actually a list whose car is frame-configuration and whose cdr is an alist. Each alist element describes one frame, which appears as the car of that element. See , for a description of several functions related to frame configurations. Process Type The word process usually means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by the Emacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of Emacs, extend the capabilities of Emacs. An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess. Process objects have no read syntax. They print in hash notation, giving the name of the process: (process-list) => (#<process shell>) See , for information about functions that create, delete, return information about, send input or signals to, and receive output from processes. Stream Type A stream is an object that can be used as a source or sink for characters—either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a *Help* buffer, or to the echo area. The object nil, in addition to its other meanings, may be used as a stream. It stands for the value of the variable standard-input or standard-output. Also, the object t as a stream specifies input using the minibuffer (see ) or output in the echo area (see ). Streams have no special printed representation or read syntax, and print as whatever primitive type they are. See , for a description of functions related to streams, including parsing and printing functions. Keymap Type A keymap maps keys typed by the user to commands. This mapping controls how the user's command input is executed. A keymap is actually a list whose car is the symbol keymap. See , for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings. Overlay Type An overlay specifies properties that apply to a part of a buffer. Each overlay applies to a specified range of the buffer, and contains a property list (a list whose elements are alternating property names and values). Overlay properties are used to present parts of the buffer temporarily in a different display style. Overlays have no read syntax, and print in hash notation, giving the buffer name and range of positions. See , for how to create and use overlays. Read Syntax for Circular Objects circular structure, read syntax shared structure, read syntax ‘#n=’ read syntax ‘#n#’ read syntax To represent shared or circular structures within a complex of Lisp objects, you can use the reader constructs ‘#n=’ and ‘#n#’. Use #n= before an object to label it for later reference; subsequently, you can use #n# to refer the same object in another place. Here, n is some integer. For example, here is how to make a list in which the first element recurs as the third element: (#1=(a) b #1#) This differs from ordinary syntax such as this ((a) b (a)) which would result in a list whose first and third elements look alike but are not the same Lisp object. This shows the difference: (prog1 nil (setq x '(#1=(a) b #1#))) (eq (nth 0 x) (nth 2 x)) => t (setq x '((a) b (a))) (eq (nth 0 x) (nth 2 x)) => nil You can also use the same syntax to make a circular structure, which appears as an “element” within itself. Here is an example: #1=(a #1#) This makes a list whose second element is the list itself. Here's how you can see that it really works: (prog1 nil (setq x '#1=(a #1#))) (eq x (cadr x)) => t The Lisp printer can produce this syntax to record circular and shared structure in a Lisp object, if you bind the variable print-circle to a non-nil value. See . Type Predicates type checking wrong-type-argument The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do so, since function arguments in Lisp do not have declared data types, as they do in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that the function can use. All built-in functions do check the types of their actual arguments when appropriate, and signal a wrong-type-argument error if an argument is of the wrong type. For example, here is what happens if you pass an argument to + that it cannot handle: (+ 2 'a) error--> Wrong type argument: number-or-marker-p, a type predicates testing types If you want your program to handle different types differently, you must do explicit type checking. The most common way to check the type of an object is to call a type predicate function. Emacs has a type predicate for each type, as well as some predicates for combinations of types. A type predicate function takes one argument; it returns t if the argument belongs to the appropriate type, and nil otherwise. Following a general Lisp convention for predicate functions, most type predicates' names end with ‘p’. Here is an example which uses the predicates listp to check for a list and symbolp to check for a symbol. (defun add-on (x) (cond ((symbolp x) ;; If X is a symbol, put it on LIST. (setq list (cons x list))) ((listp x) ;; If X is a list, add its elements to LIST. (setq list (append x list))) (t ;; We handle only symbols and lists. (error "Invalid argument %s in add-on" x)))) Here is a table of predefined type predicates, in alphabetical order, with references to further information. atom See atom. arrayp See arrayp. bool-vector-p See bool-vector-p. bufferp See bufferp. byte-code-function-p See byte-code-function-p. case-table-p See case-table-p. char-or-string-p See char-or-string-p. char-table-p See char-table-p. commandp See commandp. consp See consp. display-table-p See display-table-p. floatp See floatp. frame-configuration-p See frame-configuration-p. frame-live-p See frame-live-p. framep See framep. functionp See functionp. hash-table-p See hash-table-p. integer-or-marker-p See integer-or-marker-p. integerp See integerp. keymapp See keymapp. keywordp See . listp See listp. markerp See markerp. wholenump See wholenump. nlistp See nlistp. numberp See numberp. number-or-marker-p See number-or-marker-p. overlayp See overlayp. processp See processp. sequencep See sequencep. stringp See stringp. subrp See subrp. symbolp See symbolp. syntax-table-p See syntax-table-p. user-variable-p See user-variable-p. vectorp See vectorp. window-configuration-p See window-configuration-p. window-live-p See window-live-p. windowp See windowp. booleanp See booleanp. string-or-null-p See string-or-null-p. The most general way to check the type of an object is to call the function type-of. Recall that each object belongs to one and only one primitive type; type-of tells you which one (see ). But type-of knows nothing about non-primitive types. In most cases, it is more convenient to use type predicates than type-of. type-of — Function: type-of object This function returns a symbol naming the primitive type ofobject. The value is one of the symbols symbol,integer, float, string, cons, vector,char-table, bool-vector, hash-table, subr,compiled-function, marker, overlay, window,buffer, frame, process, orwindow-configuration. (type-of 1) => integer (type-of 'nil) => symbol (type-of '()) ; () is nil. => symbol (type-of '(x)) => cons Equality Predicates equality Here we describe two functions that test for equality between any two objects. Other functions test equality between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type. eq — Function: eq object1 object2 This function returns t if object1 and object2 arethe same object, nil otherwise.eq returns t if object1 and object2 areintegers with the same value. Also, since symbol names are normallyunique, if the arguments are symbols with the same name, they areeq. For other types (e.g., lists, vectors, strings), twoarguments with the same contents or elements are not necessarilyeq to each other: they are eq only if they are the sameobject, meaning that a change in the contents of one will be reflectedby the same change in the contents of the other. (eq 'foo 'foo) => t (eq 456 456) => t (eq "asdf" "asdf") => nil (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (setq foo '(1 (2 (3)))) => (1 (2 (3))) (eq foo foo) => t (eq foo '(1 (2 (3)))) => nil (eq [(1 2) 3] [(1 2) 3]) => nil (eq (point-marker) (point-marker)) => nil The make-symbol function returns an uninterned symbol, distinctfrom the symbol that is used if you write the name in a Lisp expression.Distinct symbols with the same name are not eq. See . (eq (make-symbol "foo") 'foo) => nil equal — Function: equal object1 object2 This function returns t if object1 and object2 haveequal components, nil otherwise. Whereas eq tests if itsarguments are the same object, equal looks inside nonidenticalarguments to see if their elements or contents are the same. So, if twoobjects are eq, they are equal, but the converse is notalways true. (equal 'foo 'foo) => t (equal 456 456) => t (equal "asdf" "asdf") => t (eq "asdf" "asdf") => nil (equal '(1 (2 (3))) '(1 (2 (3)))) => t (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (equal [(1 2) 3] [(1 2) 3]) => t (eq [(1 2) 3] [(1 2) 3]) => nil (equal (point-marker) (point-marker)) => t (eq (point-marker) (point-marker)) => nil Comparison of strings is case-sensitive, but does not take account oftext properties—it compares only the characters in the strings. Fortechnical reasons, a unibyte string and a multibyte string areequal if and only if they contain the same sequence ofcharacter codes and all these codes are either in the range 0 through127 (ASCII) or 160 through 255 (eight-bit-graphic).(see ). (equal "asdf" "ASDF") => nil However, two distinct buffers are never considered equal, even iftheir textual contents are the same. The test for equality is implemented recursively; for example, given two cons cells x and y, (equal x y) returns t if and only if both the expressions below return t: (equal (car x) (car y)) (equal (cdr x) (cdr y)) Because of this recursive method, circular lists may therefore cause infinite recursion (leading to an error). <setfilename>../info/numbers</setfilename> Numbers integers numbers GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as −3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as −4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, ‘e2’ stands for ten to the second power, and that is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision. Integer Basics The range of values for an integer depends on the machine. The minimum range is −268435456 to 268435455 (29 bits; i.e., -2**28 to 2**28 - 1), but some machines may provide a wider range. Many examples in this chapter assume an integer has 29 bits. overflow The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period. 1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer −1. 536870913 ; Also the integer 1, due to overflow. 0 ; The integer 0. -0 ; The integer 0. integers in specific radix radix for reading an integer base for reading an integer hex numbers octal numbers reading numbers in hex, octal, and binary The syntax for integers in bases other than 10 uses ‘#’ followed by a letter that specifies the radix: ‘b’ for binary, ‘o’ for octal, ‘x’ for hex, or ‘radixr’ to specify radix radix. Case is not significant for the letter that specifies the radix. Thus, ‘#binteger’ reads integer in binary, and ‘#radixrinteger’ reads integer in radix radix. Allowed values of radix run from 2 to 36. For example: #b101100 => 44 #o54 => 44 #x2c => 44 #24r1k => 44 To understand how various functions work on integers, especially the bitwise operators (see ), it is often helpful to view the numbers in their binary form. In 29-bit binary, the decimal integer 5 looks like this: 0 0000 0000 0000 0000 0000 0000 0101 (We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.) The integer −1 looks like this: 1 1111 1111 1111 1111 1111 1111 1111 two's complement −1 is represented as 29 ones. (This is called two's complement notation.) The negative integer, −5, is creating by subtracting 4 from −1. In binary, the decimal integer 4 is 100. Consequently, −5 looks like this: 1 1111 1111 1111 1111 1111 1111 1011 In this implementation, the largest 29-bit binary integer value is 268,435,455 in decimal. In binary, it looks like this: 0 1111 1111 1111 1111 1111 1111 1111 Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 268,435,455, the value is the negative integer −268,435,456: (+ 1 268435455) => -268435456 => 1 0000 0000 0000 0000 0000 0000 0000 Many of the functions described in this chapter accept markers for arguments in place of numbers. (See .) Since the actual arguments to such functions may be either numbers or markers, we often give these arguments the name number-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored. most-positive-fixnum — Variable: most-positive-fixnum The value of this variable is the largest integer that Emacs Lispcan handle. most-negative-fixnum — Variable: most-negative-fixnum The value of this variable is the smallest integer that Emacs Lisp canhandle. It is negative. Floating Point Basics Floating point numbers are useful for representing numbers that are not integral. The precise range of floating point numbers is machine-specific; it is the same as the range of the C data type double on the machine you are using. The read-syntax for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in ‘-1.0’. IEEE floating point positive infinity negative infinity infinity NaN Most modern computers support the IEEE floating point standard, which provides for positive infinity and negative infinity as floating point values. It also provides for a class of values called NaN or “not-a-number”; numerical functions return such values in cases where there is no correct answer. For example, (/ 0.0 0.0) returns a NaN. For practical purposes, there's no significant difference between different NaN values in Emacs Lisp, and there's no rule for precisely which NaN value should be used in a particular case, so Emacs Lisp doesn't try to distinguish them (but it does report the sign, if you print it). Here are the read syntaxes for these special floating point values: positive infinity ‘1.0e+INF’ negative infinity ‘-1.0e+INF’ Not-a-number ‘0.0e+NaN’ or ‘-0.0e+NaN’. To test whether a floating point value is a NaN, compare it with itself using =. That returns nil for a NaN, and t for any other floating point value. The value -0.0 is distinguishable from ordinary zero in IEEE floating point, but Emacs Lisp equal and = consider them equal values. You can use logb to extract the binary exponent of a floating point number (or estimate the logarithm of an integer): logb — Function: logb number This function returns the binary exponent of number. Moreprecisely, the value is the logarithm of number base 2, roundeddown to an integer. (logb 10) => 3 (logb 10.0e20) => 69 Type Predicates for Numbers predicates for numbers The functions in this section test for numbers, or for a specific type of number. The functions integerp and floatp can take any type of Lisp object as argument (they would not be of much use otherwise), but the zerop predicate requires a number as its argument. See also integer-or-marker-p and number-or-marker-p, in . floatp — Function: floatp object This predicate tests whether its argument is a floating pointnumber and returns t if so, nil otherwise.floatp does not exist in Emacs versions 18 and earlier. integerp — Function: integerp object This predicate tests whether its argument is an integer, and returnst if so, nil otherwise. numberp — Function: numberp object This predicate tests whether its argument is a number (either integer orfloating point), and returns t if so, nil otherwise. wholenump — Function: wholenump object natural numbersThe wholenump predicate (whose name comes from the phrase“whole-number-p”) tests to see whether its argument is a nonnegativeinteger, and returns t if so, nil otherwise. 0 isconsidered non-negative. natnumpnatnump is an obsolete synonym for wholenump. zerop — Function: zerop number This predicate tests whether its argument is zero, and returns tif so, nil otherwise. The argument must be a number.(zerop x) is equivalent to (= x 0). Comparison of Numbers number comparison comparing numbers To test numbers for numerical equality, you should normally use =, not eq. There can be many distinct floating point number objects with the same numeric value. If you use eq to compare them, then you test whether two values are the same object. By contrast, = compares only the numeric values of the objects. At present, each integer value has a unique Lisp object in Emacs Lisp. Therefore, eq is equivalent to = where integers are concerned. It is sometimes convenient to use eq for comparing an unknown value with an integer, because eq does not report an error if the unknown value is not a number—it accepts arguments of any type. By contrast, = signals an error if the arguments are not numbers or markers. However, it is a good idea to use = if you can, even for comparing integers, just in case we change the representation of integers in a future Emacs version. Sometimes it is useful to compare numbers with equal; it treats two numbers as equal if they have the same data type (both integers, or both floating point) and the same value. By contrast, = can treat an integer and a floating point number as equal. See . There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here's a function to do this: (defvar fuzz-factor 1.0e-6) (defun approx-equal (x y) (or (and (= x 0) (= y 0)) (< (/ (abs (- x y)) (max (abs x) (abs y))) fuzz-factor))) CL note—integers vrs eq Common Lisp note: Comparing numbers in Common Lisp always requires = because Common Lisp implements multi-word integers, and two distinct integer objects can have the same numeric value. Emacs Lisp can have just one integer object for any given value because it has a limited range of integer values. = — Function: = number-or-marker1 number-or-marker2 This function tests whether its arguments are numerically equal, andreturns t if so, nil otherwise. eql — Function: eql value1 value2 This function acts like eq except when both arguments arenumbers. It compares numbers by type and numeric value, so that(eql 1.0 1) returns nil, but (eql 1.0 1.0) and(eql 1 1) both return t. /= — Function: /= number-or-marker1 number-or-marker2 This function tests whether its arguments are numerically equal, andreturns t if they are not, and nil if they are. < — Function: < number-or-marker1 number-or-marker2 This function tests whether its first argument is strictly less thanits second argument. It returns t if so, nil otherwise. <= — Function: <= number-or-marker1 number-or-marker2 This function tests whether its first argument is less than or equalto its second argument. It returns t if so, nilotherwise. > — Function: > number-or-marker1 number-or-marker2 This function tests whether its first argument is strictly greaterthan its second argument. It returns t if so, nilotherwise. >= — Function: >= number-or-marker1 number-or-marker2 This function tests whether its first argument is greater than orequal to its second argument. It returns t if so, nilotherwise. max — Function: max number-or-marker &rest numbers-or-markers This function returns the largest of its arguments.If any of the arguments is floating-point, the value is returnedas floating point, even if it was given as an integer. (max 20) => 20 (max 1 2.5) => 2.5 (max 1 3 2.5) => 3.0 min — Function: min number-or-marker &rest numbers-or-markers This function returns the smallest of its arguments.If any of the arguments is floating-point, the value is returnedas floating point, even if it was given as an integer. (min -4 1) => -4 abs — Function: abs number This function returns the absolute value of number. Numeric Conversions rounding in conversions number conversions converting numbers To convert an integer to floating point, use the function float. float — Function: float number This returns number converted to floating point.If number is already a floating point number, float returnsit unchanged. There are four functions to convert floating point numbers to integers; they differ in how they round. All accept an argument number and an optional argument divisor. Both arguments may be integers or floating point numbers. divisor may also be nil. If divisor is nil or omitted, these functions convert number to an integer, or return it unchanged if it already is an integer. If divisor is non-nil, they divide number by divisor and convert the result to an integer. An arith-error results if divisor is 0. truncate — Function: truncate number &optional divisor This returns number, converted to an integer by rounding towardszero. (truncate 1.2) => 1 (truncate 1.7) => 1 (truncate -1.2) => -1 (truncate -1.7) => -1 floor — Function: floor number &optional divisor This returns number, converted to an integer by rounding downward(towards negative infinity).If divisor is specified, this uses the kind of divisionoperation that corresponds to mod, rounding downward. (floor 1.2) => 1 (floor 1.7) => 1 (floor -1.2) => -2 (floor -1.7) => -2 (floor 5.99 3) => 1 ceiling — Function: ceiling number &optional divisor This returns number, converted to an integer by rounding upward(towards positive infinity). (ceiling 1.2) => 2 (ceiling 1.7) => 2 (ceiling -1.2) => -1 (ceiling -1.7) => -1 round — Function: round number &optional divisor This returns number, converted to an integer by rounding towards thenearest integer. Rounding a value equidistant between two integersmay choose the integer closer to zero, or it may prefer an even integer,depending on your machine. (round 1.2) => 1 (round 1.7) => 2 (round -1.2) => -1 (round -1.7) => -2 Arithmetic Operations arithmetic operations Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used. All of these functions except % return a floating point value if any argument is floating. It is important to note that in Emacs Lisp, arithmetic functions do not check for overflow. Thus (1+ 268435455) may evaluate to −268435456, depending on your hardware. 1+ — Function: 1+ number-or-marker This function returns number-or-marker plus 1.For example, (setq foo 4) => 4 (1+ foo) => 5 This function is not analogous to the C operator ++—it does notincrement a variable. It just computes a sum. Thus, if we continue, foo => 4 If you want to increment the variable, you must use setq,like this: (setq foo (1+ foo)) => 5 1- — Function: 1- number-or-marker This function returns number-or-marker minus 1. + — Function: + &rest numbers-or-markers This function adds its arguments together. When given no arguments,+ returns 0. (+) => 0 (+ 1) => 1 (+ 1 2 3 4) => 10 - — Function: - &optional number-or-marker &rest more-numbers-or-markers The - function serves two purposes: negation and subtraction.When - has a single argument, the value is the negative of theargument. When there are multiple arguments, - subtracts each ofthe more-numbers-or-markers from number-or-marker,cumulatively. If there are no arguments, the result is 0. (- 10 1 2 3 4) => 0 (- 10) => -10 (-) => 0 * — Function: * &rest numbers-or-markers This function multiplies its arguments together, and returns theproduct. When given no arguments, * returns 1. (*) => 1 (* 1) => 1 (* 1 2 3 4) => 24 / — Function: / dividend divisor &rest divisors This function divides dividend by divisor and returns thequotient. If there are additional arguments divisors, then itdivides dividend by each divisor in turn. Each argument may be anumber or a marker.If all the arguments are integers, then the result is an integer too.This means the result has to be rounded. On most machines, the resultis rounded towards zero after each division, but some machines may rounddifferently with negative arguments. This is because the Lisp function/ is implemented using the C division operator, which alsopermits machine-dependent rounding. As a practical matter, all knownmachines round in the standard fashion. arith-error in divisionIf you divide an integer by 0, an arith-error error is signaled.(See .) Floating point division by zero returns eitherinfinity or a NaN if your machine supports IEEE floating point;otherwise, it signals an arith-error error. (/ 6 2) => 3 (/ 5 2) => 2 (/ 5.0 2) => 2.5 (/ 5 2.0) => 2.5 (/ 5.0 2.0) => 2.5 (/ 25 3 2) => 4 (/ -17 6) => -2 (could in theory be −3 on some machines) % — Function: % dividend divisor remainderThis function returns the integer remainder after division of dividendby divisor. The arguments must be integers or markers.For negative arguments, the remainder is in principle machine-dependentsince the quotient is; but in practice, all known machines behave alike.An arith-error results if divisor is 0. (% 9 4) => 1 (% -9 4) => -1 (% 9 -4) => 1 (% -9 -4) => -1 For any two integers dividend and divisor, (+ (% dividend divisor) (* (/ dividend divisor) divisor)) always equals dividend. mod — Function: mod dividend divisor modulusThis function returns the value of dividend modulo divisor;in other words, the remainder after division of dividendby divisor, but with the same sign as divisor.The arguments must be numbers or markers.Unlike %, mod returns a well-defined result for negativearguments. It also permits floating point arguments; it rounds thequotient downward (towards minus infinity) to an integer, and uses thatquotient to compute the remainder.An arith-error results if divisor is 0. (mod 9 4) => 1 (mod -9 4) => 3 (mod 9 -4) => -3 (mod -9 -4) => -1 (mod 5.5 2.5) => .5 For any two numbers dividend and divisor, (+ (mod dividend divisor) (* (floor dividend divisor) divisor)) always equals dividend, subject to rounding error if eitherargument is floating point. For floor, see . Rounding Operations rounding without conversion The functions ffloor, fceiling, fround, and ftruncate take a floating point argument and return a floating point result whose value is a nearby integer. ffloor returns the nearest integer below; fceiling, the nearest integer above; ftruncate, the nearest integer in the direction towards zero; fround, the nearest integer. ffloor — Function: ffloor float This function rounds float to the next lower integral value, andreturns that value as a floating point number. fceiling — Function: fceiling float This function rounds float to the next higher integral value, andreturns that value as a floating point number. ftruncate — Function: ftruncate float This function rounds float towards zero to an integral value, andreturns that value as a floating point number. fround — Function: fround float This function rounds float to the nearest integral value,and returns that value as a floating point number. Bitwise Operations on Integers bitwise arithmetic logical arithmetic In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern “moved over.” The bitwise operations in Emacs Lisp apply only to integers. lsh — Function: lsh integer1 count logical shiftlsh, which is an abbreviation for logical shift, shifts thebits in integer1 to the left count places, or to the rightif count is negative, bringing zeros into the vacated bits. Ifcount is negative, lsh shifts zeros into the leftmost(most-significant) bit, producing a positive result even ifinteger1 is negative. Contrast this with ash, below.Here are two examples of lsh, shifting a pattern of bits oneplace to the left. We show only the low-order eight bits of the binarypattern; the rest are all zero. (lsh 5 1) => 10 ;; Decimal 5 becomes decimal 10. 00000101 => 00001010 (lsh 7 1) => 14 ;; Decimal 7 becomes decimal 14. 00000111 => 00001110 As the examples illustrate, shifting the pattern of bits one place tothe left produces a number that is twice the value of the previousnumber.Shifting a pattern of bits two places to the left produces resultslike this (with 8-bit binary numbers): (lsh 3 2) => 12 ;; Decimal 3 becomes decimal 12. 00000011 => 00001100 On the other hand, shifting one place to the right looks like this: (lsh 6 -1) => 3 ;; Decimal 6 becomes decimal 3. 00000110 => 00000011 (lsh 5 -1) => 2 ;; Decimal 5 becomes decimal 2. 00000101 => 00000010 As the example illustrates, shifting one place to the right divides thevalue of a positive integer by two, rounding downward.The function lsh, like all Emacs Lisp arithmetic functions, doesnot check for overflow, so shifting left can discard significant bitsand change the sign of the number. For example, left shifting268,435,455 produces −2 on a 29-bit machine: (lsh 268435455 1) ; left shift => -2 In binary, in the 29-bit implementation, the argument looks like this: ;; Decimal 268,435,455 0 1111 1111 1111 1111 1111 1111 1111 which becomes the following when left shifted: ;; Decimal −2 1 1111 1111 1111 1111 1111 1111 1110 ash — Function: ash integer1 count arithmetic shiftash (arithmetic shift) shifts the bits in integer1to the left count places, or to the right if countis negative.ash gives the same results as lsh except wheninteger1 and count are both negative. In that case,ash puts ones in the empty bit positions on the left, whilelsh puts zeros in those bit positions.Thus, with ash, shifting the pattern of bits one place to the rightlooks like this: (ash -6 -1) => -3 ;; Decimal −6 becomes decimal −3. 1 1111 1111 1111 1111 1111 1111 1010 => 1 1111 1111 1111 1111 1111 1111 1101 In contrast, shifting the pattern of bits one place to the right withlsh looks like this: (lsh -6 -1) => 268435453 ;; Decimal −6 becomes decimal 268,435,453. 1 1111 1111 1111 1111 1111 1111 1010 => 0 1111 1111 1111 1111 1111 1111 1101 Here are other examples: ; 29-bit binary values (lsh 5 2) ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 => 20 ; = 0 0000 0000 0000 0000 0000 0001 0100 (ash 5 2) => 20 (lsh -5 2) ; -5 = 1 1111 1111 1111 1111 1111 1111 1011 => -20 ; = 1 1111 1111 1111 1111 1111 1110 1100 (ash -5 2) => -20 (lsh 5 -2) ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 => 1 ; = 0 0000 0000 0000 0000 0000 0000 0001 (ash 5 -2) => 1 (lsh -5 -2) ; -5 = 1 1111 1111 1111 1111 1111 1111 1011 => 134217726 ; = 0 0111 1111 1111 1111 1111 1111 1110 (ash -5 -2) ; -5 = 1 1111 1111 1111 1111 1111 1111 1011 => -2 ; = 1 1111 1111 1111 1111 1111 1111 1110 logand — Function: logand &rest ints-or-markers This function returns the “logical and” of the arguments: thenth bit is set in the result if, and only if, the nth bit isset in all the arguments. (“Set” means that the value of the bit is 1rather than 0.)For example, using 4-bit binary numbers, the “logical and” of 13 and12 is 12: 1101 combined with 1100 produces 1100.In both the binary numbers, the leftmost two bits are set (i.e., theyare 1's), so the leftmost two bits of the returned value are set.However, for the rightmost two bits, each is zero in at least one ofthe arguments, so the rightmost two bits of the returned value are 0's.Therefore, (logand 13 12) => 12 If logand is not passed any argument, it returns a value of−1. This number is an identity element for logandbecause its binary representation consists entirely of ones. Iflogand is passed just one argument, it returns that argument. ; 29-bit binary values (logand 14 13) ; 14 = 0 0000 0000 0000 0000 0000 0000 1110 ; 13 = 0 0000 0000 0000 0000 0000 0000 1101 => 12 ; 12 = 0 0000 0000 0000 0000 0000 0000 1100 (logand 14 13 4) ; 14 = 0 0000 0000 0000 0000 0000 0000 1110 ; 13 = 0 0000 0000 0000 0000 0000 0000 1101 ; 4 = 0 0000 0000 0000 0000 0000 0000 0100 => 4 ; 4 = 0 0000 0000 0000 0000 0000 0000 0100 (logand) => -1 ; -1 = 1 1111 1111 1111 1111 1111 1111 1111 logior — Function: logior &rest ints-or-markers This function returns the “inclusive or” of its arguments: the nth bitis set in the result if, and only if, the nth bit is set in at leastone of the arguments. If there are no arguments, the result is zero,which is an identity element for this operation. If logior ispassed just one argument, it returns that argument. ; 29-bit binary values (logior 12 5) ; 12 = 0 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 => 13 ; 13 = 0 0000 0000 0000 0000 0000 0000 1101 (logior 12 5 7) ; 12 = 0 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0 0000 0000 0000 0000 0000 0000 0111 => 15 ; 15 = 0 0000 0000 0000 0000 0000 0000 1111 logxor — Function: logxor &rest ints-or-markers This function returns the “exclusive or” of its arguments: thenth bit is set in the result if, and only if, the nth bit isset in an odd number of the arguments. If there are no arguments, theresult is 0, which is an identity element for this operation. Iflogxor is passed just one argument, it returns that argument. ; 29-bit binary values (logxor 12 5) ; 12 = 0 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 => 9 ; 9 = 0 0000 0000 0000 0000 0000 0000 1001 (logxor 12 5 7) ; 12 = 0 0000 0000 0000 0000 0000 0000 1100 ; 5 = 0 0000 0000 0000 0000 0000 0000 0101 ; 7 = 0 0000 0000 0000 0000 0000 0000 0111 => 14 ; 14 = 0 0000 0000 0000 0000 0000 0000 1110 lognot — Function: lognot integer This function returns the logical complement of its argument: the nthbit is one in the result if, and only if, the nth bit is zero ininteger, and vice-versa. (lognot 5) => -6 ;; 5 = 0 0000 0000 0000 0000 0000 0000 0101 ;; becomes ;; -6 = 1 1111 1111 1111 1111 1111 1111 1010 Standard Mathematical Functions transcendental functions mathematical functions floating-point functions These mathematical functions allow integers as well as floating point numbers as arguments. sin — Function: sin arg cos — Function: cos arg tan — Function: tan arg These are the ordinary trigonometric functions, with argument measuredin radians. asin — Function: asin arg The value of (asin arg) is a number between−pi/2andpi/2(inclusive) whose sine is arg; if, however, arg is out ofrange (outside [−1, 1]), it signals a domain-error error. acos — Function: acos arg The value of (acos arg) is a number between 0 andpi(inclusive) whose cosine is arg; if, however, arg is outof range (outside [−1, 1]), it signals a domain-error error. atan — Function: atan y &optional x The value of (atan y) is a number between−pi/2andpi/2(exclusive) whose tangent is y. If the optional secondargument x is given, the value of (atan y x) is theangle in radians between the vector [x, y] and theX axis. exp — Function: exp arg This is the exponential function; it returnseto the power arg.eis a fundamental mathematical constant also called the base of naturallogarithms. log — Function: log arg &optional base This function returns the logarithm of arg, with base base.If you don't specify base, the baseeis used. If arg is negative, it signals a domain-errorerror. log10 — Function: log10 arg This function returns the logarithm of arg, with base 10. Ifarg is negative, it signals a domain-error error.(log10 x) == (log x 10), at leastapproximately. expt — Function: expt x y This function returns x raised to power y. If botharguments are integers and y is positive, the result is aninteger; in this case, overflow causes truncation, so watch out. sqrt — Function: sqrt arg This returns the square root of arg. If arg is negative,it signals a domain-error error. Random Numbers random numbers A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series. In Emacs, pseudo-random numbers are generated from a “seed” number. Starting from any given seed, the random function always generates the same sequence of numbers. Emacs always starts with the same seed value, so the sequence of values of random is actually the same in each Emacs run! For example, in one operating system, the first call to (random) after you start Emacs always returns −1457731, and the second one always returns −7692030. This repeatability is helpful for debugging. If you want random numbers that don't always come out the same, execute (random t). This chooses a new seed based on the current time of day and on Emacs's process ID number. random — Function: random &optional limit This function returns a pseudo-random integer. Repeated calls return aseries of pseudo-random integers.If limit is a positive integer, the value is chosen to benonnegative and less than limit.If limit is t, it means to choose a new seed based on thecurrent time of day and on Emacs's process ID number. On some machines, any integer representable in Lisp may be the resultof random. On other machines, the result can never be largerthan a certain maximum or less than a certain (negative) minimum. <setfilename>../info/strings</setfilename> Strings and Characters strings character arrays characters bytes A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files; to send messages to users; to hold text being copied between buffers; and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters. See , for special considerations for strings of keyboard character events. String and Character Basics Characters are represented in Emacs Lisp as integers; whether an integer is a character or not is determined only by how it is used. Thus, strings really contain integers. The length of a string (like any array) is fixed, and cannot be altered once the string exists. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ASCII code 0.) Since strings are arrays, and therefore sequences as well, you can operate on them with the general array and sequence functions. (See .) For example, you can access or change individual characters in a string using the functions aref and aset (see ). There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte (see ). An ASCII character always occupies one byte in a string; in fact, when a string is all ASCII, there is no real difference between the unibyte and multibyte representations. For most Lisp programming, you don't need to be concerned with these two representations. Sometimes key sequences are represented as strings. When a string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are large integers) rather than character codes in the range 128 to 255. Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no other control characters. They do not distinguish case in ASCII control characters. If you want to store such characters in a sequence, such as a key sequence, you must use a vector instead of a string. See , for more information about the representation of meta and other modifiers for keyboard input characters. Strings are useful for holding regular expressions. You can also match regular expressions against strings with string-match (see ). The functions match-string (see ) and replace-match (see ) are useful for decomposing and modifying strings after matching regular expressions against them. Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See . All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied. See , for information about functions that display strings or copy them into buffers. See , and , for information about the syntax of characters and strings. See , for functions to convert between text representations and to encode and decode character codes. The Predicates for Strings For more information about general sequence and array predicates, see , and . stringp — Function: stringp object This function returns t if object is a string, nilotherwise. string-or-null-p — Function: string-or-null-p object This function returns t if object is a string or nil,nil otherwise. char-or-string-p — Function: char-or-string-p object This function returns t if object is a string or acharacter (i.e., an integer), nil otherwise. Creating Strings The following functions create strings, either from scratch, or by putting strings together, or by taking them apart. make-string — Function: make-string count character This function returns a string made up of count repetitions ofcharacter. If count is negative, an error is signaled. (make-string 5 ?x) => "xxxxx" (make-string 0 ?x) => "" Other functions to compare with this one include char-to-string(see ), make-vector (see ), andmake-list (see ). string — Function: string &rest characters This returns a string containing the characters characters. (string ?a ?b ?c) => "abc" substring — Function: substring string start &optional end This function returns a new string which consists of those charactersfrom string in the range from (and including) the character at theindex start up to (but excluding) the character at the indexend. The first character is at index zero. (substring "abcdefg" 0 3) => "abc" Here the index for ‘a’ is 0, the index for ‘b’ is 1, and theindex for ‘c’ is 2. Thus, three letters, ‘abc’, are copiedfrom the string "abcdefg". The index 3 marks the characterposition up to which the substring is copied. The character whose indexis 3 is actually the fourth character in the string.A negative number counts from the end of the string, so that −1signifies the index of the last character of the string. For example: (substring "abcdefg" -3 -1) => "ef" In this example, the index for ‘e’ is −3, the index for‘f’ is −2, and the index for ‘g’ is −1.Therefore, ‘e’ and ‘f’ are included, and ‘g’ is excluded.When nil is used for end, it stands for the length of thestring. Thus, (substring "abcdefg" -3 nil) => "efg" Omitting the argument end is equivalent to specifying nil.It follows that (substring string 0) returns a copy of allof string. (substring "abcdefg" 0) => "abcdefg" But we recommend copy-sequence for this purpose (see ).If the characters copied from string have text properties, theproperties are copied into the new string also. See .substring also accepts a vector for the first argument.For example: (substring [a b (c) "d"] 1 3) => [b (c)] A wrong-type-argument error is signaled if start is notan integer or if end is neither an integer nor nil. Anargs-out-of-range error is signaled if start indicates acharacter following end, or if either integer is out of rangefor string.Contrast this function with buffer-substring (see ), which returns a string containing a portion of the text inthe current buffer. The beginning of a string is at index 0, but thebeginning of a buffer is at index 1. substring-no-properties — Function: substring-no-properties string &optional start end This works like substring but discards all text properties fromthe value. Also, start may be omitted or nil, which isequivalent to 0. Thus, (substring-no-propertiesstring) returns a copy of string, with all textproperties removed. concat — Function: concat &rest sequences copying strings concatenating stringsThis function returns a new string consisting of the characters in thearguments passed to it (along with their text properties, if any). Thearguments may be strings, lists of numbers, or vectors of numbers; theyare not themselves changed. If concat receives no arguments, itreturns an empty string. (concat "abc" "-def") => "abc-def" (concat "abc" (list 120 121) [122]) => "abcxyz" ;; nil is an empty sequence. (concat "abc" nil "-def") => "abc-def" (concat "The " "quick brown " "fox.") => "The quick brown fox." (concat) => "" The concat function always constructs a new string that isnot eq to any existing string.In Emacs versions before 21, when an argument was an integer (not asequence of integers), it was converted to a string of digits making upthe decimal printed representation of the integer. This obsolete usageno longer works. The proper way to convert an integer to its decimalprinted form is with format (see ) ornumber-to-string (see ).For information about other concatenation functions, see thedescription of mapconcat in ,vconcat in , and append in . split-string — Function: split-string string &optional separators omit-nulls This function splits string into substrings at matches for theregular expression separators. Each match for separatorsdefines a splitting point; the substrings between the splitting pointsare made into a list, which is the value returned bysplit-string.If omit-nulls is nil, the result contains null stringswhenever there are two consecutive matches for separators, or amatch is adjacent to the beginning or end of string. Ifomit-nulls is t, these null strings are omitted from theresult.If separators is nil (or omitted),the default is the value of split-string-default-separators.As a special case, when separators is nil (or omitted),null strings are always omitted from the result. Thus: (split-string " two words ") => ("two" "words") The result is not ("" "two" "words" ""), which would rarely beuseful. If you need such a result, use an explicit value forseparators: (split-string " two words " split-string-default-separators) => ("" "two" "words" "") More examples: (split-string "Soup is good food" "o") => ("S" "up is g" "" "d f" "" "d") (split-string "Soup is good food" "o" t) => ("S" "up is g" "d f" "d") (split-string "Soup is good food" "o+") => ("S" "up is g" "d f" "d") Empty matches do count, except that split-string will not lookfor a final empty match when it already reached the end of the stringusing a non-empty match or when string is empty: (split-string "aooob" "o*") => ("" "a" "" "b" "") (split-string "ooaboo" "o*") => ("" "" "a" "b" "") (split-string "" "") => ("") However, when separators can match the empty string,omit-nulls is usually t, so that the subtleties in thethree previous examples are rarely relevant: (split-string "Soup is good food" "o*" t) => ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") (split-string "Nice doggy!" "" t) => ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") (split-string "" "" t) => nil Somewhat odd, but predictable, behavior can occur for certain“non-greedy” values of separators that can prefer emptymatches over non-empty matches. Again, such values rarely occur inpractice: (split-string "ooo" "o*" t) => nil (split-string "ooo" "\\|o+" t) => ("o" "o" "o") split-string-default-separators — Variable: split-string-default-separators The default value of separators for split-string. Itsusual value is "[ \f\t\n\r\v]+". Modifying Strings The most basic way to alter the contents of an existing string is with aset (see ). (aset string idx char) stores char into string at index idx. Each character occupies one or more bytes, and if char needs a different number of bytes from the character already present at that index, aset signals an error. A more powerful function is store-substring: store-substring — Function: store-substring string idx obj This function alters part of the contents of the string string, bystoring obj starting at index idx. The argument objmay be either a character or a (smaller) string.Since it is impossible to change the length of an existing string, it isan error if obj doesn't fit within string's actual length,or if any new character requires a different number of bytes from thecharacter currently present at that point in string. To clear out a string that contained a password, use clear-string: clear-string — Function: clear-string string This makes string a unibyte string and clears its contents tozeros. It may also change string's length. Comparison of Characters and Strings string equality char-equal — Function: char-equal character1 character2 This function returns t if the arguments represent the samecharacter, nil otherwise. This function ignores differencesin case if case-fold-search is non-nil. (char-equal ?x ?x) => t (let ((case-fold-search nil)) (char-equal ?x ?X)) => nil string= — Function: string= string1 string2 This function returns t if the characters of the two stringsmatch exactly. Symbols are also allowed as arguments, in which casetheir print names are used.Case is always significant, regardless of case-fold-search. (string= "abc" "abc") => t (string= "abc" "ABC") => nil (string= "ab" "ABC") => nil The function string= ignores the text properties of the twostrings. When equal (see ) compares twostrings, it uses string=.For technical reasons, a unibyte and a multibyte string areequal if and only if they contain the same sequence ofcharacter codes and all these codes are either in the range 0 through127 (ASCII) or 160 through 255 (eight-bit-graphic).However, when a unibyte string gets converted to a multibyte string,all characters with codes in the range 160 through 255 get convertedto characters with higher codes, whereas ASCII charactersremain unchanged. Thus, a unibyte string and its conversion tomultibyte are only equal if the string is all ASCII.Character codes 160 through 255 are not entirely proper in multibytetext, even though they can occur. As a consequence, the situationwhere a unibyte and a multibyte string are equal without bothbeing all ASCII is a technical oddity that very few EmacsLisp programmers ever get confronted with. See . string-equal — Function: string-equal string1 string2 string-equal is another name for string=. lexical comparison string< — Function: string< string1 string2 This function compares two strings a character at a time. Itscans both the strings at the same time to find the first pair of correspondingcharacters that do not match. If the lesser character of these two isthe character from string1, then string1 is less, and thisfunction returns t. If the lesser character is the one fromstring2, then string1 is greater, and this function returnsnil. If the two strings match entirely, the value is nil.Pairs of characters are compared according to their character codes.Keep in mind that lower case letters have higher numeric values in theASCII character set than their upper case counterparts; digits andmany punctuation characters have a lower numeric value than upper caseletters. An ASCII character is less than any non-ASCIIcharacter; a unibyte non-ASCII character is always less than anymultibyte non-ASCII character (see ). (string< "abc" "abd") => t (string< "abd" "abc") => nil (string< "123" "abc") => t When the strings have different lengths, and they match up to thelength of string1, then the result is t. If they match upto the length of string2, the result is nil. A string ofno characters is less than any other string. (string< "" "abc") => t (string< "ab" "abc") => t (string< "abc" "") => nil (string< "abc" "ab") => nil (string< "" "") => nil Symbols are also allowed as arguments, in which case their print namesare used. string-lessp — Function: string-lessp string1 string2 string-lessp is another name for string<. compare-strings — Function: compare-strings string1 start1 end1 string2 start2 end2 &optional ignore-case This function compares the specified part of string1 with thespecified part of string2. The specified part of string1runs from index start1 up to index end1 (nil meansthe end of the string). The specified part of string2 runs fromindex start2 up to index end2 (nil means the end ofthe string).The strings are both converted to multibyte for the comparison(see ) so that a unibyte string and itsconversion to multibyte are always regarded as equal. Ifignore-case is non-nil, then case is ignored, so thatupper case letters can be equal to lower case letters.If the specified portions of the two strings match, the value ist. Otherwise, the value is an integer which indicates how manyleading characters agree, and which string is less. Its absolute valueis one plus the number of characters that agree at the beginning of thetwo strings. The sign is negative if string1 (or its specifiedportion) is less. assoc-string — Function: assoc-string key alist &optional case-fold This function works like assoc, except that key must be astring or symbol, and comparison is done using compare-strings.Symbols are converted to strings before testing.If case-fold is non-nil, it ignores case differences.Unlike assoc, this function can also match elements of the alistthat are strings or symbols rather than conses. In particular, alist canbe a list of strings or symbols rather than an actual alist.See . See also the compare-buffer-substrings function in , for a way to compare text in buffers. The function string-match, which matches a regular expression against a string, can be used for a kind of string comparison; see . Conversion of Characters and Strings conversion of strings This section describes functions for conversions between characters, strings and integers. format (see ) and prin1-to-string (see ) can also convert Lisp objects into strings. read-from-string (see ) can “convert” a string representation of a Lisp object into an object. The functions string-make-multibyte and string-make-unibyte convert the text representation of a string (see ). See , for functions that produce textual descriptions of text characters and general input events (single-key-description and text-char-description). These are used primarily for making help messages. char-to-string — Function: char-to-string character character to stringThis function returns a new string containing one character,character. This function is semi-obsolete because the functionstring is more general. See . string-to-char — Function: string-to-char string string to character This function returns the first character in string. If thestring is empty, the function returns 0. The value is also 0 when thefirst character of string is the null character, ASCII code0. (string-to-char "ABC") => 65 (string-to-char "xyz") => 120 (string-to-char "") => 0 (string-to-char "\000") => 0 This function may be eliminated in the future if it does not seem usefulenough to retain. number-to-string — Function: number-to-string number integer to string integer to decimalThis function returns a string consisting of the printed base-tenrepresentation of number, which may be an integer or a floatingpoint number. The returned value starts with a minus sign if the argument isnegative. (number-to-string 256) => "256" (number-to-string -23) => "-23" (number-to-string -23.5) => "-23.5" int-to-stringint-to-string is a semi-obsolete alias for this function.See also the function format in . string-to-number — Function: string-to-number string &optional base string to numberThis function returns the numeric value of the characters instring. If base is non-nil, it must be an integerbetween 2 and 16 (inclusive), and integers are converted in that base.If base is nil, then base ten is used. Floating pointconversion only works in base ten; we have not implemented otherradices for floating point numbers, because that would be much morework and does not seem useful. If string looks like an integerbut its value is too large to fit into a Lisp integer,string-to-number returns a floating point result.The parsing skips spaces and tabs at the beginning of string,then reads as much of string as it can interpret as a number inthe given base. (On some systems it ignores other whitespace at thebeginning, not just spaces and tabs.) If the first character afterthe ignored whitespace is neither a digit in the given base, nor aplus or minus sign, nor the leading dot of a floating point number,this function returns 0. (string-to-number "256") => 256 (string-to-number "25 is a perfect square.") => 25 (string-to-number "X256") => 0 (string-to-number "-4.5") => -4.5 (string-to-number "1e5") => 100000.0 string-to-intstring-to-int is an obsolete alias for this function. Here are some other functions that can convert to or from a string: concat concat can convert a vector or a list into a string.See . vconcat vconcat can convert a string into a vector. See . append append can convert a string into a list. See . Formatting Strings formatting strings strings, formatting them Formatting means constructing a string by substitution of computed values at various places in a constant string. This constant string controls how the other values are printed, as well as where they appear; it is called a format string. Formatting is often useful for computing messages to be displayed. In fact, the functions message and error provide the same formatting feature described here; they differ from format only in how they use the result of formatting. format — Function: format string &rest objects This function returns a new string that is made by copyingstring and then replacing any format specificationin the copy with encodings of the corresponding objects. Thearguments objects are the computed values to be formatted.The characters in string, other than the format specifications,are copied directly into the output, including their text properties,if any. ‘%’ in format format specification A format specification is a sequence of characters beginning with a ‘%’. Thus, if there is a ‘%d’ in string, the format function replaces it with the printed representation of one of the values to be formatted (one of the arguments objects). For example: (format "The value of fill-column is %d." fill-column) => "The value of fill-column is 72." Since format interprets ‘%’ characters as format specifications, you should never pass an arbitrary string as the first argument. This is particularly true when the string is generated by some Lisp code. Unless the string is known to never include any ‘%’ characters, pass "%s", described below, as the first argument, and the string as the second, like this: (format "%s" arbitrary-string) If string contains more than one format specification, the format specifications correspond to successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause an error. Any extra values to be formatted are ignored. Certain format specifications require values of particular types. If you supply a value that doesn't fit the requirements, an error is signaled. Here is a table of valid format specifications: ‘%s’ Replace the specification with the printed representation of the object,made without quoting (that is, using princ, notprin1—see ). Thus, strings are representedby their contents alone, with no ‘"’ characters, and symbols appearwithout ‘\’ characters.If the object is a string, its text properties arecopied into the output. The text properties of the ‘%s’ itselfare also copied, but those of the object take priority. ‘%S’ Replace the specification with the printed representation of the object,made with quoting (that is, using prin1—see ). Thus, strings are enclosed in ‘"’ characters, and‘\’ characters appear where necessary before special characters. ‘%o’ integer to octalReplace the specification with the base-eight representation of aninteger. ‘%d’ Replace the specification with the base-ten representation of aninteger. ‘%x’‘%X’ integer to hexadecimalReplace the specification with the base-sixteen representation of aninteger. ‘%x’ uses lower case and ‘%X’ uses upper case. ‘%c’ Replace the specification with the character which is the value given. ‘%e’ Replace the specification with the exponential notation for a floatingpoint number. ‘%f’ Replace the specification with the decimal-point notation for a floatingpoint number. ‘%g’ Replace the specification with notation for a floating point number,using either exponential notation or decimal-point notation, whicheveris shorter. ‘%%’ Replace the specification with a single ‘%’. This formatspecification is unusual in that it does not use a value. For example,(format "%% %d" 30) returns "% 30". Any other format character results in an ‘Invalid format operation’ error. Here are several examples: (format "The name of this buffer is %s." (buffer-name)) => "The name of this buffer is strings.texi." (format "The buffer object prints as %s." (current-buffer)) => "The buffer object prints as strings.texi." (format "The octal value of %d is %o, and the hex value is %x." 18 18 18) => "The octal value of 18 is 22, and the hex value is 12." field width padding A specification can have a width, which is a signed decimal number between the ‘%’ and the specification character. If the printed representation of the object contains fewer characters than this width, format extends it with padding. The padding goes on the left if the width is positive (or starts with zero) and on the right if the width is negative. The padding character is normally a space, but it's ‘0’ if the width starts with a zero. Some of these conventions are ignored for specification characters for which they do not make sense. That is, ‘%s’, ‘%S’ and ‘%c’ accept a width starting with 0, but still pad with spaces on the left. Also, ‘%%’ accepts a width, but ignores it. Here are some examples of padding: (format "%06d is padded on the left with zeros" 123) => "000123 is padded on the left with zeros" (format "%-6d is padded on the right" 123) => "123 is padded on the right" If the width is too small, format does not truncate the object's printed representation. Thus, you can use a width to specify a minimum spacing between columns with no risk of losing information. In the following three examples, ‘%7s’ specifies a minimum width of 7. In the first case, the string inserted in place of ‘%7s’ has only 3 letters, it needs 4 blank spaces as padding. In the second case, the string "specification" is 13 letters wide but is not truncated. In the third case, the padding is on the right. (format "The word `%7s' actually has %d letters in it." "foo" (length "foo")) => "The word ` foo' actually has 3 letters in it." (format "The word `%7s' actually has %d letters in it." "specification" (length "specification")) => "The word `specification' actually has 13 letters in it." (format "The word `%-7s' actually has %d letters in it." "foo" (length "foo")) => "The word `foo ' actually has 3 letters in it." precision in format specifications All the specification characters allow an optional precision before the character (after the width, if present). The precision is a decimal-point ‘.’ followed by a digit-string. For the floating-point specifications (‘%e’, ‘%f’, ‘%g’), the precision specifies how many decimal places to show; if zero, the decimal-point itself is also omitted. For ‘%s’ and ‘%S’, the precision truncates the string to the given width, so ‘%.3s’ shows only the first three characters of the representation for object. Precision has no effect for other specification characters. flags in format specifications Immediately after the ‘%’ and before the optional width and precision, you can put certain “flag” characters. ‘+’ as a flag inserts a plus sign before a positive number, so that it always has a sign. A space character as flag inserts a space before a positive number. (Otherwise, positive numbers start with the first digit.) Either of these two flags ensures that positive numbers and negative numbers use the same number of columns. These flags are ignored except for ‘%d’, ‘%e’, ‘%f’, ‘%g’, and if both flags are used, the ‘+’ takes precedence. The flag ‘#’ specifies an “alternate form” which depends on the format in use. For ‘%o’ it ensures that the result begins with a ‘0’. For ‘%x’ and ‘%X’, it prefixes the result with ‘0x’ or ‘0X’. For ‘%e’, ‘%f’, and ‘%g’, the ‘#’ flag means include a decimal point even if the precision is zero. Case Conversion in Lisp upper case lower case character case case conversion in Lisp The character case functions change the case of single characters or of the contents of strings. The functions normally convert only alphabetic characters (the letters ‘A’ through ‘Z’ and ‘a’ through ‘z’, as well as non-ASCII letters); other characters are not altered. You can specify a different case conversion mapping by specifying a case table (see ). These functions do not modify the strings that are passed to them as arguments. The examples below use the characters ‘X’ and ‘x’ which have ASCII codes 88 and 120 respectively. downcase — Function: downcase string-or-char This function converts a character or a string to lower case.When the argument to downcase is a string, the function createsand returns a new string in which each letter in the argument that isupper case is converted to lower case. When the argument todowncase is a character, downcase returns thecorresponding lower case character. This value is an integer. If theoriginal character is lower case, or is not a letter, then the valueequals the original character. (downcase "The cat in the hat") => "the cat in the hat" (downcase ?X) => 120 upcase — Function: upcase string-or-char This function converts a character or a string to upper case.When the argument to upcase is a string, the function createsand returns a new string in which each letter in the argument that islower case is converted to upper case.When the argument to upcase is a character, upcasereturns the corresponding upper case character. This value is an integer.If the original character is upper case, or is not a letter, then thevalue returned equals the original character. (upcase "The cat in the hat") => "THE CAT IN THE HAT" (upcase ?x) => 88 capitalize — Function: capitalize string-or-char capitalizationThis function capitalizes strings or characters. Ifstring-or-char is a string, the function creates and returns a newstring, whose contents are a copy of string-or-char in which eachword has been capitalized. This means that the first character of eachword is converted to upper case, and the rest are converted to lowercase.The definition of a word is any sequence of consecutive characters thatare assigned to the word constituent syntax class in the current syntaxtable (see ).When the argument to capitalize is a character, capitalizehas the same result as upcase. (capitalize "The cat in the hat") => "The Cat In The Hat" (capitalize "THE 77TH-HATTED CAT") => "The 77th-Hatted Cat" (capitalize ?x) => 88 upcase-initials — Function: upcase-initials string-or-char If string-or-char is a string, this function capitalizes theinitials of the words in string-or-char, without altering anyletters other than the initials. It returns a new string whosecontents are a copy of string-or-char, in which each word hashad its initial letter converted to upper case.The definition of a word is any sequence of consecutive characters thatare assigned to the word constituent syntax class in the current syntaxtable (see ).When the argument to upcase-initials is a character,upcase-initials has the same result as upcase. (upcase-initials "The CAT in the hAt") => "The CAT In The HAt" See , for functions that compare strings; some of them ignore case differences, or can optionally ignore case differences. The Case Table You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the case conversion functions for Lisp objects (see the previous section) and those that apply to text in the buffer (see ). Each buffer has a case table; there is also a standard case table which is used to initialize the case table of new buffers. A case table is a char-table (see ) whose subtype is case-table. This char-table maps each character into the corresponding lower case character. It has three extra slots, which hold related tables: upcase The upcase table maps each character into the corresponding uppercase character. canonicalize The canonicalize table maps all of a set of case-related charactersinto a particular member of that set. equivalences The equivalences table maps each one of a set of case-related charactersinto the next character in that set. In simple cases, all you need to specify is the mapping to lower-case; the three related tables will be calculated automatically from that one. For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both lower case and upper case. The extra table canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character. For example, since ‘a’ and ‘A’ are related by case-conversion, they should have the same canonical equivalent character (which should be either ‘a’ for both of them, or ‘A’ for both of them). The extra table equivalences is a map that cyclically permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map ‘a’ into ‘A’ and ‘A’ into ‘a’, and likewise for each set of equivalent characters.) When you construct a case table, you can provide nil for canonicalize; then Emacs fills in this slot from the lower case and upper case mappings. You can also provide nil for equivalences; then Emacs fills in this slot from canonicalize. In a case table that is actually in use, those components are non-nil. Do not try to specify equivalences without also specifying canonicalize. Here are the functions for working with case tables: case-table-p — Function: case-table-p object This predicate returns non-nil if object is a valid casetable. set-standard-case-table — Function: set-standard-case-table table This function makes table the standard case table, so that it willbe used in any buffers created subsequently. standard-case-table — Function: standard-case-table This returns the standard case table. current-case-table — Function: current-case-table This function returns the current buffer's case table. set-case-table — Function: set-case-table table This sets the current buffer's case table to table. with-case-table — Macro: with-case-table table body … The with-case-table macro saves the current case table, makestable the current case table, evaluates the body forms,and finally restores the case table. The return value is the value ofthe last form in body. The case table is restored even in caseof an abnormal exit via throw or error (see ). Some language environments may modify the case conversions of ASCII characters; for example, in the Turkish language environment, the ASCII character ‘I’ is downcased into a Turkish “dotless i”. This can interfere with code that requires ordinary ASCII case conversion, such as implementations of ASCII-based network protocols. In that case, use the with-case-table macro with the variable ascii-case-table, which stores the unmodified case table for the ASCII character set. ascii-case-table — Variable: ascii-case-table The case table for the ASCII character set. This should not bemodified by any language environment settings. The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify the specified case table case-table; they also modify the standard syntax table. See . Normally you would use these functions to change the standard case table. set-case-syntax-pair — Function: set-case-syntax-pair uc lc case-table This function specifies a pair of corresponding letters, one upper caseand one lower case. set-case-syntax-delims — Function: set-case-syntax-delims l r case-table This function makes characters l and r a matching pair ofcase-invariant delimiters. set-case-syntax — Function: set-case-syntax char syntax case-table This function makes char case-invariant, with syntaxsyntax. describe-buffer-case-table — Command: describe-buffer-case-table This command displays a description of the contents of the currentbuffer's case table. <setfilename>../info/lists</setfilename> Lists lists element (of list) A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list. Lists and Cons Cells lists and cons cells Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object that represents an ordered pair. That is, it has two slots, and each slot holds, or refers to, some Lisp object. One slot is known as the car, and the other is known as the cdr. (These names are traditional; see .) cdr is pronounced “could-er.” We say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr. A list is a series of cons cells “chained together,” so that each cell refers to the next one. There is one cons cell for each element of the list. By convention, the cars of the cons cells hold the elements of the list, and the cdrs are used to chain the list: the cdr slot of each cons cell refers to the following cons cell. The cdr of the last cons cell is nil. This asymmetry between the car and the cdr is entirely a matter of convention; at the level of cons cells, the car and cdr slots have the same characteristics. true list Since nil is the conventional value to put in the cdr of the last cons cell in the list, we call that case a true list. In Lisp, we consider the symbol nil a list as well as a symbol; it is the list with no elements. For convenience, the symbol nil is considered to have nil as its cdr (and also as its car). Therefore, the cdr of a true list is always a true list. dotted list circular list If the cdr of a list's last cons cell is some other value, neither nil nor another cons cell, we call the structure a dotted list, since its printed representation would use ‘.’. There is one other possibility: some cons cell's cdr could point to one of the previous cons cells in the list. We call that structure a circular list. For some purposes, it does not matter whether a list is true, circular or dotted. If the program doesn't look far enough down the list to see the cdr of the final cons cell, it won't care. However, some functions that operate on lists demand true lists and signal errors if given a dotted list. Most functions that try to find the end of a list enter infinite loops if given a circular list. list structure Because most cons cells are used as part of lists, the phrase list structure has come to mean any structure made out of cons cells. The cdr of any nonempty true list l is a list containing all the elements of l except the first. See , for the read and print syntax of cons cells and lists, and for “box and arrow” illustrations of lists. Predicates on Lists The following predicates test whether a Lisp object is an atom, whether it is a cons cell or is a list, or whether it is the distinguished object nil. (Many of these predicates can be defined in terms of the others, but they are used so often that it is worth having all of them.) consp — Function: consp object This function returns t if object is a cons cell, nilotherwise. nil is not a cons cell, although it is a list. atom — Function: atom object This function returns t if object is an atom, nilotherwise. All objects except cons cells are atoms. The symbolnil is an atom and is also a list; it is the only Lisp objectthat is both. (atom object) == (not (consp object)) listp — Function: listp object This function returns t if object is a cons cell ornil. Otherwise, it returns nil. (listp '(1)) => t (listp '()) => t nlistp — Function: nlistp object This function is the opposite of listp: it returns t ifobject is not a list. Otherwise, it returns nil. (listp object) == (not (nlistp object)) null — Function: null object This function returns t if object is nil, andreturns nil otherwise. This function is identical to not,but as a matter of clarity we use null when object isconsidered a list and not when it is considered a truth value(see not in ). (null '(1)) => nil (null '()) => t Accessing Elements of Lists list elements car — Function: car cons-cell This function returns the value referred to by the first slot of thecons cell cons-cell. Expressed another way, this functionreturns the car of cons-cell.As a special case, if cons-cell is nil, then caris defined to return nil; therefore, any list is a valid argumentfor car. An error is signaled if the argument is not a cons cellor nil. (car '(a b c)) => a (car '()) => nil cdr — Function: cdr cons-cell This function returns the value referred to by the second slot ofthe cons cell cons-cell. Expressed another way, this functionreturns the cdr of cons-cell.As a special case, if cons-cell is nil, then cdris defined to return nil; therefore, any list is a valid argumentfor cdr. An error is signaled if the argument is not a cons cellor nil. (cdr '(a b c)) => (b c) (cdr '()) => nil car-safe — Function: car-safe object This function lets you take the car of a cons cell while avoidingerrors for other data types. It returns the car of object ifobject is a cons cell, nil otherwise. This is in contrastto car, which signals an error if object is not a list. (car-safe object) == (let ((x object)) (if (consp x) (car x) nil)) cdr-safe — Function: cdr-safe object This function lets you take the cdr of a cons cell whileavoiding errors for other data types. It returns the cdr ofobject if object is a cons cell, nil otherwise.This is in contrast to cdr, which signals an error ifobject is not a list. (cdr-safe object) == (let ((x object)) (if (consp x) (cdr x) nil)) pop — Macro: pop listname This macro is a way of examining the car of a list,and taking it off the list, all at once.It operates on the list which is stored in the symbol listname.It removes this element from the list by setting listnameto the cdr of its old value—but it also returns the carof that list, which is the element being removed. x => (a b c) (pop x) => a x => (b c) nth — Function: nth n list This function returns the nth element of list. Elementsare numbered starting with zero, so the car of list iselement number zero. If the length of list is n or less,the value is nil.If n is negative, nth returns the first element oflist. (nth 2 '(1 2 3 4)) => 3 (nth 10 '(1 2 3 4)) => nil (nth -3 '(1 2 3 4)) => 1 (nth n x) == (car (nthcdr n x)) The function elt is similar, but applies to any kind of sequence.For historical reasons, it takes its arguments in the opposite order.See . nthcdr — Function: nthcdr n list This function returns the nth cdr of list. In otherwords, it skips past the first n links of list and returnswhat follows.If n is zero or negative, nthcdr returns all oflist. If the length of list is n or less,nthcdr returns nil. (nthcdr 1 '(1 2 3 4)) => (2 3 4) (nthcdr 10 '(1 2 3 4)) => nil (nthcdr -3 '(1 2 3 4)) => (1 2 3 4) last — Function: last list &optional n This function returns the last link of list. The car ofthis link is the list's last element. If list is null,nil is returned. If n is non-nil, thenth-to-last link is returned instead, or the whole of listif n is bigger than list's length. safe-length — Function: safe-length list This function returns the length of list, with no risk of eitheran error or an infinite loop. It generally returns the number ofdistinct cons cells in the list. However, for circular lists,the value is just an upper bound; it is often too large.If list is not nil or a cons cell, safe-lengthreturns 0. The most common way to compute the length of a list, when you are not worried that it may be circular, is with length. See . caar — Function: caar cons-cell This is the same as (car (car cons-cell)). cadr — Function: cadr cons-cell This is the same as (car (cdr cons-cell))or (nth 1 cons-cell). cdar — Function: cdar cons-cell This is the same as (cdr (car cons-cell)). cddr — Function: cddr cons-cell This is the same as (cdr (cdr cons-cell))or (nthcdr 2 cons-cell). butlast — Function: butlast x &optional n This function returns the list x with the last element,or the last n elements, removed. If n is greaterthan zero it makes a copy of the list so as not to damage theoriginal list. In general, (append (butlast x n)(last x n)) will return a list equal to x. nbutlast — Function: nbutlast x &optional n This is a version of butlast that works by destructivelymodifying the cdr of the appropriate element, rather thanmaking a copy of the list. Building Cons Cells and Lists cons cells building lists Many functions build lists, as lists reside at the very heart of Lisp. cons is the fundamental list-building function; however, it is interesting to note that list is used more times in the source code for Emacs than cons. cons — Function: cons object1 object2 This function is the most basic function for building new liststructure. It creates a new cons cell, making object1 thecar, and object2 the cdr. It then returns the newcons cell. The arguments object1 and object2 may be anyLisp objects, but most often object2 is a list. (cons 1 '(2)) => (1 2) (cons 1 '()) => (1) (cons 1 2) => (1 . 2) consingcons is often used to add a single element to the front of alist. This is called consing the element onto the list. There is no strictly equivalent way to add an element tothe end of a list. You can use (append listname (listnewelt)), which creates a whole new list by copying listnameand adding newelt to its end. Or you can use (nconclistname (list newelt)), which modifies listnameby following all the cdrs and then replacing the terminatingnil. Compare this to adding an element to the beginning of alist with cons, which neither copies nor modifies the list. For example: (setq list (cons newelt list)) Note that there is no conflict between the variable named listused in this example and the function named list described below;any symbol can serve both purposes. list — Function: list &rest objects This function creates a list with objects as its elements. Theresulting list is always nil-terminated. If no objectsare given, the empty list is returned. (list 1 2 3 4 5) => (1 2 3 4 5) (list 1 2 '(3 4 5) 'foo) => (1 2 (3 4 5) foo) (list) => nil make-list — Function: make-list length object This function creates a list of length elements, in which eachelement is object. Compare make-list withmake-string (see ). (make-list 3 'pigs) => (pigs pigs pigs) (make-list 0 'pigs) => nil (setq l (make-list 3 '(a b)) => ((a b) (a b) (a b)) (eq (car l) (cadr l)) => t append — Function: append &rest sequences copying listsThis function returns a list containing all the elements ofsequences. The sequences may be lists, vectors,bool-vectors, or strings, but the last one should usually be a list.All arguments except the last one are copied, so none of the argumentsis altered. (See nconc in , for a way to joinlists with no copying.)More generally, the final argument to append may be any Lispobject. The final argument is not copied or converted; it becomes thecdr of the last cons cell in the new list. If the final argumentis itself a list, then its elements become in effect elements of theresult list. If the final element is not a list, the result is adotted list since its final cdr is not nil as requiredin a true list.In Emacs 20 and before, the append function also allowedintegers as (non last) arguments. It converted them to strings ofdigits, making up the decimal print representation of the integer, andthen used the strings instead of the original integers. This obsoleteusage no longer works. The proper way to convert an integer to adecimal number in this way is with format (see ) or number-to-string (see ). Here is an example of using append: (setq trees '(pine oak)) => (pine oak) (setq more-trees (append '(maple birch) trees)) => (maple birch pine oak) trees => (pine oak) more-trees => (maple birch pine oak) (eq trees (cdr (cdr more-trees))) => t You can see how append works by looking at a box diagram. The variable trees is set to the list (pine oak) and then the variable more-trees is set to the list (maple birch pine oak). However, the variable trees continues to refer to the original list: more-trees trees | | | --- --- --- --- -> --- --- --- --- --> | | |--> | | |--> | | |--> | | |--> nil --- --- --- --- --- --- --- --- | | | | | | | | --> maple -->birch --> pine --> oak An empty sequence contributes nothing to the value returned by append. As a consequence of this, a final nil argument forces a copy of the previous argument: trees => (pine oak) (setq wood (append trees nil)) => (pine oak) wood => (pine oak) (eq wood trees) => nil This once was the usual way to copy a list, before the function copy-sequence was invented. See . Here we show the use of vectors and strings as arguments to append: (append [a b] "cd" nil) => (a b 99 100) With the help of apply (see ), we can append all the lists in a list of lists: (apply 'append '((a b c) nil (x y z) nil)) => (a b c x y z) If no sequences are given, nil is returned: (append) => nil Here are some examples where the final argument is not a list: (append '(x y) 'z) => (x y . z) (append '(x y) [z]) => (x y . [z]) The second example shows that when the final argument is a sequence but not a list, the sequence's elements do not become elements of the resulting list. Instead, the sequence becomes the final cdr, like any other non-list final argument. reverse — Function: reverse list This function creates a new list whose elements are the elements oflist, but in reverse order. The original argument list isnot altered. (setq x '(1 2 3 4)) => (1 2 3 4) (reverse x) => (4 3 2 1) x => (1 2 3 4) copy-tree — Function: copy-tree tree &optional vecp This function returns a copy of the tree tree. If tree is acons cell, this makes a new cons cell with the same car andcdr, then recursively copies the car and cdr in thesame way.Normally, when tree is anything other than a cons cell,copy-tree simply returns tree. However, if vecp isnon-nil, it copies vectors too (and operates recursively ontheir elements). number-sequence — Function: number-sequence from &optional to separation This returns a list of numbers starting with from andincrementing by separation, and ending at or just beforeto. separation can be positive or negative and defaultsto 1. If to is nil or numerically equal to from,the value is the one-element list (from). If to isless than from with a positive separation, or greater thanfrom with a negative separation, the value is nilbecause those arguments specify an empty sequence.If separation is 0 and to is neither nil nornumerically equal to from, number-sequence signals anerror, since those arguments specify an infinite sequence.All arguments can be integers or floating point numbers. However,floating point arguments can be tricky, because floating pointarithmetic is inexact. For instance, depending on the machine, it mayquite well happen that (number-sequence 0.4 0.6 0.2) returnsthe one element list (0.4), whereas(number-sequence 0.4 0.8 0.2) returns a list with threeelements. The nth element of the list is computed by the exactformula (+ from (* n separation)). Thus, ifone wants to make sure that to is included in the list, one canpass an expression of this exact type for to. Alternatively,one can replace to with a slightly larger value (or a slightlymore negative value if separation is negative).Some examples: (number-sequence 4 9) => (4 5 6 7 8 9) (number-sequence 9 4 -1) => (9 8 7 6 5 4) (number-sequence 9 4 -2) => (9 7 5) (number-sequence 8) => (8) (number-sequence 8 5) => nil (number-sequence 5 8 -1) => nil (number-sequence 1.5 6 2) => (1.5 3.5 5.5) Modifying List Variables These functions, and one macro, provide convenient ways to modify a list which is stored in a variable. push — Macro: push newelt listname This macro provides an alternative way to write(setq listname (cons newelt listname)). (setq l '(a b)) => (a b) (push 'c l) => (c a b) l => (c a b) Two functions modify lists that are the values of variables. add-to-list — Function: add-to-list symbol element &optional append compare-fn This function sets the variable symbol by consing elementonto the old value, if element is not already a member of thatvalue. It returns the resulting list, whether updated or not. Thevalue of symbol had better be a list already before the call.add-to-list uses compare-fn to compare elementagainst existing list members; if compare-fn is nil, ituses equal.Normally, if element is added, it is added to the front ofsymbol, but if the optional argument append isnon-nil, it is added at the end.The argument symbol is not implicitly quoted; add-to-listis an ordinary function, like set and unlike setq. Quotethe argument yourself if that is what you want. Here's a scenario showing how to use add-to-list: (setq foo '(a b)) => (a b) (add-to-list 'foo 'c) ;; Add c. => (c a b) (add-to-list 'foo 'b) ;; No effect. => (c a b) foo ;; foo was changed. => (c a b) An equivalent expression for (add-to-list 'var value) is this: (or (member value var) (setq var (cons value var))) add-to-ordered-list — Function: add-to-ordered-list symbol element &optional order This function sets the variable symbol by insertingelement into the old value, which must be a list, at theposition specified by order. If element is already amember of the list, its position in the list is adjusted accordingto order. Membership is tested using eq.This function returns the resulting list, whether updated or not.The order is typically a number (integer or float), and theelements of the list are sorted in non-decreasing numerical order.order may also be omitted or nil. Then the numeric orderof element stays unchanged if it already has one; otherwise,element has no numeric order. Elements without a numeric listorder are placed at the end of the list, in no particular order.Any other value for order removes the numeric order of elementif it already has one; otherwise, it is equivalent to nil.The argument symbol is not implicitly quoted;add-to-ordered-list is an ordinary function, like setand unlike setq. Quote the argument yourself if that is whatyou want.The ordering information is stored in a hash table on symbol'slist-order property. Here's a scenario showing how to use add-to-ordered-list: (setq foo '()) => nil (add-to-ordered-list 'foo 'a 1) ;; Add a. => (a) (add-to-ordered-list 'foo 'c 3) ;; Add c. => (a c) (add-to-ordered-list 'foo 'b 2) ;; Add b. => (a b c) (add-to-ordered-list 'foo 'b 4) ;; Move b. => (a c b) (add-to-ordered-list 'foo 'd) ;; Append d. => (a c b d) (add-to-ordered-list 'foo 'e) ;; Add e . => (a c b e d) foo ;; foo was changed. => (a c b e d) Modifying Existing List Structure destructive list operations You can modify the car and cdr contents of a cons cell with the primitives setcar and setcdr. We call these “destructive” operations because they change existing list structure. CL note—rplaca vs setcar rplacarplacdCommon Lisp note: Common Lisp uses functions rplaca and rplacd to alter list structure; they change structure the same way as setcar and setcdr, but the Common Lisp functions return the cons cell while setcar and setcdr return the new car or cdr. Altering List Elements with setcar Changing the car of a cons cell is done with setcar. When used on a list, setcar replaces one element of a list with a different element. setcar — Function: setcar cons object This function stores object as the new car of cons,replacing its previous car. In other words, it changes thecar slot of cons to refer to object. It returns thevalue object. For example: (setq x '(1 2)) => (1 2) (setcar x 4) => 4 x => (4 2) When a cons cell is part of the shared structure of several lists, storing a new car into the cons changes one element of each of these lists. Here is an example: ;; Create two lists that are partly shared. (setq x1 '(a b c)) => (a b c) (setq x2 (cons 'z (cdr x1))) => (z b c) ;; Replace the car of a shared link. (setcar (cdr x1) 'foo) => foo x1 ; Both lists are changed. => (a foo c) x2 => (z foo c) ;; Replace the car of a link that is not shared. (setcar x1 'baz) => baz x1 ; Only one list is changed. => (baz foo c) x2 => (z foo c) Here is a graphical depiction of the shared structure of the two lists in the variables x1 and x2, showing why replacing b changes them both: --- --- --- --- --- --- x1---> | | |----> | | |--> | | |--> nil --- --- --- --- --- --- | --> | | | | | | --> a | --> b --> c | --- --- | x2--> | | |-- --- --- | | --> z Here is an alternative form of box diagram, showing the same relationship: x1: -------------- -------------- -------------- | car | cdr | | car | cdr | | car | cdr | | a | o------->| b | o------->| c | nil | | | | -->| | | | | | -------------- | -------------- -------------- | x2: | -------------- | | car | cdr | | | z | o---- | | | -------------- Altering the CDR of a List The lowest-level primitive for modifying a cdr is setcdr: setcdr — Function: setcdr cons object This function stores object as the new cdr of cons,replacing its previous cdr. In other words, it changes thecdr slot of cons to refer to object. It returns thevalue object. Here is an example of replacing the cdr of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the car of the list, and is not reached via the cdr. (setq x '(1 2 3)) => (1 2 3) (setcdr x '(4)) => (4) x => (1 4) You can delete elements from the middle of a list by altering the cdrs of the cons cells in the list. For example, here we delete the second element, b, from the list (a b c), by changing the cdr of the first cons cell: (setq x1 '(a b c)) => (a b c) (setcdr x1 (cdr (cdr x1))) => (c) x1 => (a c) Here is the result in box notation: -------------------- | | -------------- | -------------- | -------------- | car | cdr | | | car | cdr | -->| car | cdr | | a | o----- | b | o-------->| c | nil | | | | | | | | | | -------------- -------------- -------------- The second cons cell, which previously held the element b, still exists and its car is still b, but it no longer forms part of this list. It is equally easy to insert a new element by changing cdrs: (setq x1 '(a b c)) => (a b c) (setcdr x1 (cons 'd (cdr x1))) => (d b c) x1 => (a d b c) Here is this result in box notation: -------------- ------------- ------------- | car | cdr | | car | cdr | | car | cdr | | a | o | -->| b | o------->| c | nil | | | | | | | | | | | | --------- | -- | ------------- ------------- | | ----- -------- | | | --------------- | | | car | cdr | | -->| d | o------ | | | --------------- Functions that Rearrange Lists rearrangement of lists modification of lists Here are some functions that rearrange lists “destructively” by modifying the cdrs of their component cons cells. We call these functions “destructive” because they chew up the original lists passed to them as arguments, relinking their cons cells to form a new list that is the returned value. See delq, in , for another function that modifies cons cells. nconc — Function: nconc &rest lists concatenating lists joining listsThis function returns a list containing all the elements of lists.Unlike append (see ), the lists arenot copied. Instead, the last cdr of each of thelists is changed to refer to the following list. The last of thelists is not altered. For example: (setq x '(1 2 3)) => (1 2 3) (nconc x '(4 5)) => (1 2 3 4 5) x => (1 2 3 4 5) Since the last argument of nconc is not itself modified, it isreasonable to use a constant list, such as '(4 5), as in theabove example. For the same reason, the last argument need not be alist: (setq x '(1 2 3)) => (1 2 3) (nconc x 'z) => (1 2 3 . z) x => (1 2 3 . z) However, the other arguments (all but the last) must be lists.A common pitfall is to use a quoted constant list as a non-lastargument to nconc. If you do this, your program will changeeach time you run it! Here is what happens: (defun add-foo (x) ; We want this function to add (nconc '(foo) x)) ; foo to the front of its arg. (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo)) x)) (setq xx (add-foo '(1 2))) ; It seems to work. => (foo 1 2) (setq xy (add-foo '(3 4))) ; What happened? => (foo 1 2 3 4) (eq xx xy) => t (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo 1 2 3 4) x))) nreverse — Function: nreverse list reversing a list This function reverses the order of the elements of list.Unlike reverse, nreverse alters its argument by reversingthe cdrs in the cons cells forming the list. The cons cell thatused to be the last one in list becomes the first cons cell of thevalue. For example: (setq x '(a b c)) => (a b c) x => (a b c) (nreverse x) => (c b a) ;; The cons cell that was first is now last. x => (a) To avoid confusion, we usually store the result of nreverseback in the same variable which held the original list: (setq x (nreverse x)) Here is the nreverse of our favorite example, (a b c),presented graphically: Original list head: Reversed list: ------------- ------------- ------------ | car | cdr | | car | cdr | | car | cdr | | a | nil |<-- | b | o |<-- | c | o | | | | | | | | | | | | | | ------------- | --------- | - | -------- | - | | | | ------------- ------------ sort — Function: sort list predicate stable sort sorting listsThis function sorts list stably, though destructively, andreturns the sorted list. It compares elements using predicate. Astable sort is one in which elements with equal sort keys maintain theirrelative order before and after the sort. Stability is important whensuccessive sorts are used to order elements according to differentcriteria.The argument predicate must be a function that accepts twoarguments. It is called with two elements of list. To get anincreasing order sort, the predicate should return non-nil if thefirst element is “less than” the second, or nil if not.The comparison function predicate must give reliable results forany given pair of arguments, at least within a single call tosort. It must be antisymmetric; that is, if a isless than b, b must not be less than a. It must betransitive—that is, if a is less than b, and bis less than c, then a must be less than c. If youuse a comparison function which does not meet these requirements, theresult of sort is unpredictable.The destructive aspect of sort is that it rearranges the conscells forming list by changing cdrs. A nondestructive sortfunction would create new cons cells to store the elements in theirsorted order. If you wish to make a sorted copy without destroying theoriginal, copy it first with copy-sequence and then sort.Sorting does not change the cars of the cons cells in list;the cons cell that originally contained the element a inlist still has a in its car after sorting, but it nowappears in a different position in the list due to the change ofcdrs. For example: (setq nums '(1 3 2 6 5 4 0)) => (1 3 2 6 5 4 0) (sort nums '<) => (0 1 2 3 4 5 6) nums => (1 2 3 4 5 6) Warning: Note that the list in nums no longer contains0; this is the same cons cell that it was before, but it is no longerthe first one in the list. Don't assume a variable that formerly heldthe argument now holds the entire sorted list! Instead, save the resultof sort and use that. Most often we store the result back intothe variable that held the original list: (setq nums (sort nums '<)) See , for more functions that perform sorting.See documentation in , for auseful example of sort. Using Lists as Sets lists as sets sets A list can represent an unordered mathematical set—simply consider a value an element of a set if it appears in the list, and ignore the order of the list. To form the union of two sets, use append (as long as you don't mind having duplicate elements). You can remove equal duplicates using delete-dups. Other useful functions for sets include memq and delq, and their equal versions, member and delete. CL note—lack union, intersection Common Lisp note: Common Lisp has functions union (which avoids duplicate elements) and intersection for set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish. memq — Function: memq object list membership in a listThis function tests to see whether object is a member oflist. If it is, memq returns a list starting with thefirst occurrence of object. Otherwise, it returns nil.The letter ‘q’ in memq says that it uses eq tocompare object against the elements of the list. For example: (memq 'b '(a b c b a)) => (b c b a) (memq '(2) '((1) (2))) ; (2) and (2) are not eq. => nil delq — Function: delq object list deleting list elementsThis function destructively removes all elements eq toobject from list. The letter ‘q’ in delq saysthat it uses eq to compare object against the elements ofthe list, like memq and remq. When delq deletes elements from the front of the list, it does so simply by advancing down the list and returning a sublist that starts after those elements: (delq 'a '(a b c)) == (cdr '(a b c)) When an element to be deleted appears in the middle of the list, removing it involves changing the cdrs (see ). (setq sample-list '(a b c (4))) => (a b c (4)) (delq 'a sample-list) => (b c (4)) sample-list => (a b c (4)) (delq 'c sample-list) => (a b (4)) sample-list => (a b (4)) Note that (delq 'c sample-list) modifies sample-list to splice out the third element, but (delq 'a sample-list) does not splice anything—it just returns a shorter list. Don't assume that a variable which formerly held the argument list now has fewer elements, or that it still holds the original list! Instead, save the result of delq and use that. Most often we store the result back into the variable that held the original list: (setq flowers (delq 'rose flowers)) In the following example, the (4) that delq attempts to match and the (4) in the sample-list are not eq: (delq '(4) sample-list) => (a c (4)) If you want to delete elements that are equal to a given value, use delete (see below). remq — Function: remq object list This function returns a copy of list, with all elements removedwhich are eq to object. The letter ‘q’ in remqsays that it uses eq to compare object against the elementsof list. (setq sample-list '(a b c a b c)) => (a b c a b c) (remq 'a sample-list) => (b c b c) sample-list => (a b c a b c) memql — Function: memql object list The function memql tests to see whether object is a memberof list, comparing members with object using eql,so floating point elements are compared by value.If object is a member, memql returns a list starting withits first occurrence in list. Otherwise, it returns nil.Compare this with memq: (memql 1.2 '(1.1 1.2 1.3)) ; 1.2 and 1.2 are eql. => (1.2 1.3) (memq 1.2 '(1.1 1.2 1.3)) ; 1.2 and 1.2 are not eq. => nil The following three functions are like memq, delq and remq, but use equal rather than eq to compare elements. See . member — Function: member object list The function member tests to see whether object is a memberof list, comparing members with object using equal.If object is a member, member returns a list starting withits first occurrence in list. Otherwise, it returns nil.Compare this with memq: (member '(2) '((1) (2))) ; (2) and (2) are equal. => ((2)) (memq '(2) '((1) (2))) ; (2) and (2) are not eq. => nil ;; Two strings with the same contents are equal. (member "foo" '("foo" "bar")) => ("foo" "bar") delete — Function: delete object sequence If sequence is a list, this function destructively removes allelements equal to object from sequence. For lists,delete is to delq as member is to memq: ituses equal to compare elements with object, likemember; when it finds an element that matches, it cuts theelement out just as delq would.If sequence is a vector or string, delete returns a copyof sequence with all elements equal to objectremoved.For example: (setq l '((2) (1) (2))) (delete '(2) l) => ((1)) l => ((2) (1)) ;; If you want to change l reliably, ;; write (setq l (delete elt l)). (setq l '((2) (1) (2))) (delete '(1) l) => ((2) (2)) l => ((2) (2)) ;; In this case, it makes no difference whether you set l, ;; but you should do so for the sake of the other case. (delete '(2) [(2) (1) (2)]) => [(1)] remove — Function: remove object sequence This function is the non-destructive counterpart of delete. Itreturns a copy of sequence, a list, vector, or string, withelements equal to object removed. For example: (remove '(2) '((2) (1) (2))) => ((1)) (remove '(2) [(2) (1) (2)]) => [(1)] Common Lisp note: The functions member, delete and remove in GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not use equal to compare elements. member-ignore-case — Function: member-ignore-case object list This function is like member, except that object shouldbe a string and that it ignores differences in letter-case and textrepresentation: upper-case and lower-case letters are treated asequal, and unibyte strings are converted to multibyte prior tocomparison. delete-dups — Function: delete-dups list This function destructively removes all equal duplicates fromlist, stores the result in list and returns it. Ofseveral equal occurrences of an element in list,delete-dups keeps the first one. See also the function add-to-list, in , for a way to add an element to a list stored in a variable and used as a set. Association Lists association list alist An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the car of each cons cell is the key, and the cdr is the associated value.This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items. Here is an example of an alist. The key pine is associated with the value cones; the key oak is associated with acorns; and the key maple is associated with seeds. ((pine . cones) (oak . acorns) (maple . seeds)) Both the values and the keys in an alist may be any Lisp objects. For example, in the following alist, the symbol a is associated with the number 1, and the string "b" is associated with the list (2 3), which is the cdr of the alist element: ((a . 1) ("b" 2 3)) Sometimes it is better to design an alist to store the associated value in the car of the cdr of the element. Here is an example of such an alist: ((rose red) (lily white) (buttercup yellow)) Here we regard red as the value associated with rose. One advantage of this kind of alist is that you can store other related information—even a list of other items—in the cdr of the cdr. One disadvantage is that you cannot use rassq (see below) to find the element containing a given value. When neither of these considerations is important, the choice is a matter of taste, as long as you are consistent about it for any given alist. The same alist shown above could be regarded as having the associated value in the cdr of the element; the value associated with rose would be the list (red). Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one. In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases. Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See , for a comparison of property lists and association lists. assoc — Function: assoc key alist This function returns the first association for key inalist, comparing key against the alist elements usingequal (see ). It returns nil if noassociation in alist has a car equal to key.For example: (setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assoc 'oak trees) => (oak . acorns) (cdr (assoc 'oak trees)) => acorns (assoc 'birch trees) => nil Here is another example, in which the keys and values are not symbols: (setq needles-per-cluster '((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine"))) (cdr (assoc 3 needles-per-cluster)) => ("Pitch Pine") (cdr (assoc 2 needles-per-cluster)) => ("Austrian Pine" "Red Pine") The function assoc-string is much like assoc except that it ignores certain differences between strings. See . rassoc — Function: rassoc value alist This function returns the first association with value value inalist. It returns nil if no association in alist hasa cdr equal to value.rassoc is like assoc except that it compares the cdr ofeach alist association instead of the car. You can think ofthis as “reverse assoc,” finding the key for a given value. assq — Function: assq key alist This function is like assoc in that it returns the firstassociation for key in alist, but it makes the comparisonusing eq instead of equal. assq returns nilif no association in alist has a car eq to key.This function is used more often than assoc, since eq isfaster than equal and most alists use symbols as keys.See . (setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assq 'pine trees) => (pine . cones) On the other hand, assq is not usually useful in alists where thekeys may not be symbols: (setq leaves '(("simple leaves" . oak) ("compound leaves" . horsechestnut))) (assq "simple leaves" leaves) => nil (assoc "simple leaves" leaves) => ("simple leaves" . oak) rassq — Function: rassq value alist This function returns the first association with value value inalist. It returns nil if no association in alist hasa cdr eq to value.rassq is like assq except that it compares the cdr ofeach alist association instead of the car. You can think ofthis as “reverse assq,” finding the key for a given value.For example: (setq trees '((pine . cones) (oak . acorns) (maple . seeds))) (rassq 'acorns trees) => (oak . acorns) (rassq 'spores trees) => nil rassq cannot search for a value stored in the carof the cdr of an element: (setq colors '((rose red) (lily white) (buttercup yellow))) (rassq 'white colors) => nil In this case, the cdr of the association (lily white) is notthe symbol white, but rather the list (white). Thisbecomes clearer if the association is written in dotted pair notation: (lily white) == (lily . (white)) assoc-default — Function: assoc-default key alist &optional test default This function searches alist for a match for key. For eachelement of alist, it compares the element (if it is an atom) orthe element's car (if it is a cons) against key, by callingtest with two arguments: the element or its car, andkey. The arguments are passed in that order so that you can getuseful results using string-match with an alist that containsregular expressions (see ). If test is omittedor nil, equal is used for comparison.If an alist element matches key by this criterion,then assoc-default returns a value based on this element.If the element is a cons, then the value is the element's cdr.Otherwise, the return value is default.If no alist element matches key, assoc-default returnsnil. copy-alist — Function: copy-alist alist copying alistsThis function returns a two-level deep copy of alist: it creates anew copy of each association, so that you can alter the associations ofthe new alist without changing the old one. (setq needles-per-cluster '((2 . ("Austrian Pine" "Red Pine")) (3 . ("Pitch Pine")) (5 . ("White Pine")))) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (setq copy (copy-alist needles-per-cluster)) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (eq needles-per-cluster copy) => nil (equal needles-per-cluster copy) => t (eq (car needles-per-cluster) (car copy)) => nil (cdr (car (cdr needles-per-cluster))) => ("Pitch Pine") (eq (cdr (car (cdr needles-per-cluster))) (cdr (car (cdr copy)))) => t This example shows how copy-alist makes it possible to changethe associations of one copy without affecting the other: (setcdr (assq 3 copy) '("Martian Vacuum Pine")) (cdr (assq 3 needles-per-cluster)) => ("Pitch Pine") assq-delete-all — Function: assq-delete-all key alist This function deletes from alist all the elements whose caris eq to key, much as if you used delq to deleteeach such element one by one. It returns the shortened alist, andoften modifies the original list structure of alist. Forcorrect results, use the return value of assq-delete-all ratherthan looking at the saved value of alist. (setq alist '((foo 1) (bar 2) (foo 3) (lose 4))) => ((foo 1) (bar 2) (foo 3) (lose 4)) (assq-delete-all 'foo alist) => ((bar 2) (lose 4)) alist => ((foo 1) (bar 2) (lose 4)) rassq-delete-all — Function: rassq-delete-all value alist This function deletes from alist all the elements whose cdris eq to value. It returns the shortened alist, andoften modifies the original list structure of alist.rassq-delete-all is like assq-delete-all except that itcompares the cdr of each alist association instead of thecar. Managing a Fixed-Size Ring of Objects ring data structure This section describes functions for operating on rings. A ring is a fixed-size data structure that supports insertion, deletion, rotation, and modulo-indexed reference and traversal. make-ring — Function: make-ring size This returns a new ring capable of holding size objects.size should be an integer. ring-p — Function: ring-p object This returns t if object is a ring, nil otherwise. ring-size — Function: ring-size ring This returns the maximum capacity of the ring. ring-length — Function: ring-length ring This returns the number of objects that ring currently contains.The value will never exceed that returned by ring-size. ring-elements — Function: ring-elements ring This returns a list of the objects in ring, in order, newest first. ring-copy — Function: ring-copy ring This returns a new ring which is a copy of ring.The new ring contains the same (eq) objects as ring. ring-empty-p — Function: ring-empty-p ring This returns t if ring is empty, nil otherwise. The newest element in the ring always has index 0. Higher indices correspond to older elements. Indices are computed modulo the ring length. Index −1 corresponds to the oldest element, −2 to the next-oldest, and so forth. ring-ref — Function: ring-ref ring index This returns the object in ring found at index index.index may be negative or greater than the ring length. Ifring is empty, ring-ref signals an error. ring-insert — Function: ring-insert ring object This inserts object into ring, making it the newestelement, and returns object.If the ring is full, insertion removes the oldest element tomake room for the new element. ring-remove — Function: ring-remove ring &optional index Remove an object from ring, and return that object. Theargument index specifies which item to remove; if it isnil, that means to remove the oldest item. If ring isempty, ring-remove signals an error. ring-insert-at-beginning — Function: ring-insert-at-beginning ring object This inserts object into ring, treating it as the oldestelement. The return value is not significant.If the ring is full, this function removes the newest element to makeroom for the inserted element. fifo data structure If you are careful not to exceed the ring size, you can use the ring as a first-in-first-out queue. For example:(let ((fifo (make-ring 5))) (mapc (lambda (obj) (ring-insert fifo obj)) '(0 one "two")) (list (ring-remove fifo) t (ring-remove fifo) t (ring-remove fifo))) => (0 t one t "two") <setfilename>../info/sequences</setfilename> Sequences, Arrays, and Vectors sequence Recall that the sequence type is the union of two other Lisp types: lists and arrays. In other words, any list is a sequence, and any array is a sequence. The common property that all sequences have is that each is an ordered collection of elements. An array is a single primitive object that has a slot for each of its elements. All the elements are accessible in constant time, but the length of an existing array cannot be changed. Strings, vectors, char-tables and bool-vectors are the four types of arrays. A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements. The following diagram shows the relationship between these types: _____________________________________________ | | | Sequence | | ______ ________________________________ | | | | | | | | | List | | Array | | | | | | ________ ________ | | | |______| | | | | | | | | | | Vector | | String | | | | | |________| |________| | | | | ____________ _____________ | | | | | | | | | | | | | Char-table | | Bool-vector | | | | | |____________| |_____________| | | | |________________________________| | |_____________________________________________| The elements of vectors and lists may be any Lisp objects. The elements of strings are all characters. Sequences In Emacs Lisp, a sequence is either a list or an array. The common property of all sequences is that they are ordered collections of elements. This section describes functions that accept any kind of sequence. sequencep — Function: sequencep object Returns t if object is a list, vector, string,bool-vector, or char-table, nil otherwise. length — Function: length sequence string length list length vector length sequence length char-table lengthThis function returns the number of elements in sequence. Ifsequence is a dotted list, a wrong-type-argument error issignaled. Circular lists may cause an infinite loop. For achar-table, the value returned is always one more than the maximumEmacs character code.See , for the related function safe-length. (length '(1 2 3)) => 3 (length ()) => 0 (length "foobar") => 6 (length [1 2 3]) => 3 (length (make-bool-vector 5 nil)) => 5 See also string-bytes, in . elt — Function: elt sequence index elements of sequencesThis function returns the element of sequence indexed byindex. Legitimate values of index are integers rangingfrom 0 up to one less than the length of sequence. Ifsequence is a list, out-of-range values behave as fornth. See . Otherwise, out-of-range valuestrigger an args-out-of-range error. (elt [1 2 3 4] 2) => 3 (elt '(1 2 3 4) 2) => 3 ;; We use string to show clearly which character elt returns. (string (elt "1234" 2)) => "3" (elt [1 2 3 4] 4) error--> Args out of range: [1 2 3 4], 4 (elt [1 2 3 4] -1) error--> Args out of range: [1 2 3 4], -1 This function generalizes aref (see ) andnth (see ). copy-sequence — Function: copy-sequence sequence copying sequencesReturns a copy of sequence. The copy is the same type of objectas the original sequence, and it has the same elements in the same order.Storing a new element into the copy does not affect the originalsequence, and vice versa. However, the elements of the newsequence are not copies; they are identical (eq) to the elementsof the original. Therefore, changes made within these elements, asfound via the copied sequence, are also visible in the originalsequence.If the sequence is a string with text properties, the property list inthe copy is itself a copy, not shared with the original's propertylist. However, the actual values of the properties are shared.See .This function does not work for dotted lists. Trying to copy acircular list may cause an infinite loop.See also append in , concat in, and vconcat in ,for other ways to copy sequences. (setq bar '(1 2)) => (1 2) (setq x (vector 'foo bar)) => [foo (1 2)] (setq y (copy-sequence x)) => [foo (1 2)] (eq x y) => nil (equal x y) => t (eq (elt x 1) (elt y 1)) => t ;; Replacing an element of one sequence. (aset x 0 'quux) x => [quux (1 2)] y => [foo (1 2)] ;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x => [quux (69 2)] y => [foo (69 2)] Arrays array An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, an element of a list requires access time that is proportional to the position of the element in the list. Emacs defines four types of array, all one-dimensional: strings, vectors, bool-vectors and char-tables. A vector is a general array; its elements can be any Lisp objects. A string is a specialized array; its elements must be characters. Each type of array has its own read syntax. See , and . All four kinds of array share these characteristics: The first element of an array has index zero, the second element hasindex 1, and so on. This is called zero-origin indexing. Forexample, an array of four elements has indices 0, 1, 2, and 3. The length of the array is fixed once you create it; you cannotchange the length of an existing array. For purposes of evaluation, the array is a constant—in other words,it evaluates to itself. The elements of an array may be referenced or changed with the functionsaref and aset, respectively (see ). When you create an array, other than a char-table, you must specify its length. You cannot specify the length of a char-table, because that is determined by the range of character codes. In principle, if you want an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons: They occupy one-fourth the space of a vector of the same elements. Strings are printed in a way that shows the contents more clearlyas text. Strings can hold text properties. See . Many of the specialized editing and I/O facilities of Emacs accept onlystrings. For example, you cannot insert a vector of characters into abuffer the way you can insert a string. See . By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See . Functions that Operate on Arrays In this section, we describe the functions that accept all types of arrays. arrayp — Function: arrayp object This function returns t if object is an array (i.e., avector, a string, a bool-vector or a char-table). (arrayp [a]) => t (arrayp "asdf") => t (arrayp (syntax-table)) ;; A char-table. => t aref — Function: aref array index array elementsThis function returns the indexth element of array. Thefirst element is at index zero. (setq primes [2 3 5 7 11 13]) => [2 3 5 7 11 13] (aref primes 4) => 11 (aref "abcdefg" 1) => 98 ; ‘b’ is ASCII code 98. See also the function elt, in . aset — Function: aset array index object This function sets the indexth element of array to beobject. It returns object. (setq w [foo bar baz]) => [foo bar baz] (aset w 0 'fu) => fu w => [fu bar baz] (setq x "asdfasfd") => "asdfasfd" (aset x 3 ?Z) => 90 x => "asdZasfd" If array is a string and object is not a character, awrong-type-argument error results. The function converts aunibyte string to multibyte if necessary to insert a character. fillarray — Function: fillarray array object This function fills the array array with object, so thateach element of array is object. It returns array. (setq a [a b c d e f g]) => [a b c d e f g] (fillarray a 0) => [0 0 0 0 0 0 0] a => [0 0 0 0 0 0 0] (setq s "When in the course") => "When in the course" (fillarray s ?-) => "------------------" If array is a string and object is not a character, awrong-type-argument error results. The general sequence functions copy-sequence and length are often useful for objects known to be arrays. See . Vectors vector (type) Arrays in Lisp, like arrays in most languages, are blocks of memory whose elements can be accessed in constant time. A vector is a general-purpose array of specified length; its elements can be any Lisp objects. (By contrast, a string can hold only characters as elements.) Vectors in Emacs are used for obarrays (vectors of symbols), and as part of keymaps (vectors of commands). They are also used internally as part of the representation of a byte-compiled function; if you print such a function, you will see a vector in it. In Emacs Lisp, the indices of the elements of a vector start from zero and count up from there. Vectors are printed with square brackets surrounding the elements. Thus, a vector whose elements are the symbols a, b and a is printed as [a b a]. You can write vectors in the same way in Lisp input. A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See . Here are examples illustrating these principles: (setq avector [1 two '(three) "four" [five]]) => [1 two (quote (three)) "four" [five]] (eval avector) => [1 two (quote (three)) "four" [five]] (eq avector (eval avector)) => t Functions for Vectors Here are some functions that relate to vectors: vectorp — Function: vectorp object This function returns t if object is a vector. (vectorp [a]) => t (vectorp "asdf") => nil vector — Function: vector &rest objects This function creates and returns a vector whose elements are thearguments, objects. (vector 'foo 23 [bar baz] "rats") => [foo 23 [bar baz] "rats"] (vector) => [] make-vector — Function: make-vector length object This function returns a new vector consisting of length elements,each initialized to object. (setq sleepy (make-vector 9 'Z)) => [Z Z Z Z Z Z Z Z Z] vconcat — Function: vconcat &rest sequences copying vectorsThis function returns a new vector containing all the elements of thesequences. The arguments sequences may be true lists,vectors, strings or bool-vectors. If no sequences are given, anempty vector is returned.The value is a newly constructed vector that is not eq to anyexisting vector. (setq a (vconcat '(A B C) '(D E F))) => [A B C D E F] (eq a (vconcat a)) => nil (vconcat) => [] (vconcat [A B C] "aa" '(foo (6 7))) => [A B C 97 97 foo (6 7)] The vconcat function also allows byte-code function objects asarguments. This is a special feature to make it easy to access the entirecontents of a byte-code function object. See .In Emacs versions before 21, the vconcat function allowedintegers as arguments, converting them to strings of digits, but thatfeature has been eliminated. The proper way to convert an integer toa decimal number in this way is with format (see ) or number-to-string (see ).For other concatenation functions, see mapconcat in , concat in , and appendin . The append function also provides a way to convert a vector into a list with the same elements: (setq avector [1 two (quote (three)) "four" [five]]) => [1 two (quote (three)) "four" [five]] (append avector nil) => (1 two (quote (three)) "four" [five]) Char-Tables char-tables extra slots of char-table A char-table is much like a vector, except that it is indexed by character codes. Any valid character code, without modifiers, can be used as an index in a char-table. You can access a char-table's elements with aref and aset, as with any array. In addition, a char-table can have extra slots to hold additional data not associated with particular character codes. Char-tables are constants when evaluated. subtype of char-table Each char-table has a subtype which is a symbol. The subtype has two purposes: to distinguish char-tables meant for different uses, and to control the number of extra slots. For example, display tables are char-tables with display-table as the subtype, and syntax tables are char-tables with syntax-table as the subtype. A valid subtype must have a char-table-extra-slots property which is an integer between 0 and 10. This integer specifies the number of extra slots in the char-table. parent of char-table A char-table can have a parent, which is another char-table. If it does, then whenever the char-table specifies nil for a particular character c, it inherits the value specified in the parent. In other words, (aref char-table c) returns the value from the parent of char-table if char-table itself specifies nil. default value of char-table A char-table can also have a default value. If so, then (aref char-table c) returns the default value whenever the char-table does not specify any other non-nil value. make-char-table — Function: make-char-table subtype &optional init Return a newly created char-table, with subtype subtype. Eachelement is initialized to init, which defaults to nil. Youcannot alter the subtype of a char-table after the char-table iscreated.There is no argument to specify the length of the char-table, becauseall char-tables have room for any valid character code as an index. char-table-p — Function: char-table-p object This function returns t if object is a char-table,otherwise nil. char-table-subtype — Function: char-table-subtype char-table This function returns the subtype symbol of char-table. set-char-table-default — Function: set-char-table-default char-table char new-default This function sets the default value of generic character charin char-table to new-default.There is no special function to access default values in a char-table.To do that, use char-table-range (see below). char-table-parent — Function: char-table-parent char-table This function returns the parent of char-table. The parent isalways either nil or another char-table. set-char-table-parent — Function: set-char-table-parent char-table new-parent This function sets the parent of char-table to new-parent. char-table-extra-slot — Function: char-table-extra-slot char-table n This function returns the contents of extra slot n ofchar-table. The number of extra slots in a char-table isdetermined by its subtype. set-char-table-extra-slot — Function: set-char-table-extra-slot char-table n value This function stores value in extra slot n ofchar-table. A char-table can specify an element value for a single character code; it can also specify a value for an entire character set. char-table-range — Function: char-table-range char-table range This returns the value specified in char-table for a range ofcharacters range. Here are the possibilities for range: nil Refers to the default value. char Refers to the element for character char(supposing char is a valid character code). charset Refers to the value specified for the whole character setcharset (see ). generic-char A generic character stands for a character set, or a row of acharacter set; specifying the generic character as argument isequivalent to specifying the character set name. See , for a description of generic characters. set-char-table-range — Function: set-char-table-range char-table range value This function sets the value in char-table for a range ofcharacters range. Here are the possibilities for range: nil Refers to the default value. t Refers to the whole range of character codes. char Refers to the element for character char(supposing char is a valid character code). charset Refers to the value specified for the whole character setcharset (see ). generic-char A generic character stands for a character set; specifying the genericcharacter as argument is equivalent to specifying the character setname. See , for a description of generic characters. map-char-table — Function: map-char-table function char-table This function calls function for each element of char-table.function is called with two arguments, a key and a value. The keyis a possible range argument for char-table-range—eithera valid character or a generic character—and the value is(char-table-range char-table key).Overall, the key-value pairs passed to function describe all thevalues stored in char-table.The return value is always nil; to make this function useful,function should have side effects. For example,here is how to examine each element of the syntax table: (let (accumulator) (map-char-table #'(lambda (key value) (setq accumulator (cons (list key value) accumulator))) (syntax-table)) accumulator) => ((475008 nil) (474880 nil) (474752 nil) (474624 nil) ... (5 (3)) (4 (3)) (3 (3)) (2 (3)) (1 (3)) (0 (3))) Bool-vectors Bool-vectors A bool-vector is much like a vector, except that it stores only the values t and nil. If you try to store any non-nil value into an element of the bool-vector, the effect is to store t there. As with all arrays, bool-vector indices start from 0, and the length cannot be changed once the bool-vector is created. Bool-vectors are constants when evaluated. There are two special functions for working with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays. make-bool-vector — Function: make-bool-vector length initial Return a new bool-vector of length elements,each one initialized to initial. bool-vector-p — Function: bool-vector-p object This returns t if object is a bool-vector,and nil otherwise. Here is an example of creating, examining, and updating a bool-vector. Note that the printed form represents up to 8 boolean values as a single character. (setq bv (make-bool-vector 5 t)) => #&5"^_" (aref bv 1) => t (aset bv 3 nil) => nil bv => #&5"^W" These results make sense because the binary codes for control-_ and control-W are 11111 and 10111, respectively. <setfilename>../info/hash</setfilename> Hash Tables hash tables lookup tables A hash table is a very fast kind of lookup table, somewhat like an alist (see ) in that it maps keys to corresponding values. It differs from an alist in these ways: Lookup in a hash table is extremely fast for large tables—in fact, thetime required is essentially independent of how many elements arestored in the table. For smaller tables (a few tens of elements)alists may still be faster because hash tables have a more-or-lessconstant overhead. The correspondences in a hash table are in no particular order. There is no way to share structure between two hash tables,the way two alists can share a common tail. Emacs Lisp provides a general-purpose hash table data type, along with a series of functions for operating on them. Hash tables have no read syntax, and print in hash notation, like this: (make-hash-table) => #<hash-table 'eql nil 0/65 0x83af980> (The term “hash notation” refers to the initial ‘#’ character—see —and has nothing to do with the term “hash table.”) Obarrays are also a kind of hash table, but they are a different type of object and are used only for recording interned symbols (see ). Creating Hash Tables creating hash tables The principal function for creating a hash table is make-hash-table. make-hash-table — Function: make-hash-table &rest keyword-args This function creates a new hash table according to the specifiedarguments. The arguments should consist of alternating keywords(particular symbols recognized specially) and values corresponding tothem.Several keywords make sense in make-hash-table, but the only twothat you really need to know about are :test and :weakness. :test test This specifies the method of key lookup for this hash table. Thedefault is eql; eq and equal are otheralternatives: eql Keys which are numbers are “the same” if they are equal, thatis, if they are equal in value and either both are integers or bothare floating point numbers; otherwise, two distinct objects are never“the same.” eq Any two distinct Lisp objects are “different” as keys. equal Two Lisp objects are “the same,” as keys, if they are equalaccording to equal. You can use define-hash-table-test (see ) todefine additional possibilities for test. :weakness weak The weakness of a hash table specifies whether the presence of a key orvalue in the hash table preserves it from garbage collection.The value, weak, must be one of nil, key,value, key-or-value, key-and-value, or twhich is an alias for key-and-value. If weak is keythen the hash table does not prevent its keys from being collected asgarbage (if they are not referenced anywhere else); if a particular keydoes get collected, the corresponding association is removed from thehash table.If weak is value, then the hash table does not preventvalues from being collected as garbage (if they are not referencedanywhere else); if a particular value does get collected, thecorresponding association is removed from the hash table.If weak is key-and-value or t, both the key andthe value must be live in order to preserve the association. Thus,the hash table does not protect either keys or values from garbagecollection; if either one is collected as garbage, that removes theassociation.If weak is key-or-value, either the key orthe value can preserve the association. Thus, associations areremoved from the hash table when both their key and value would becollected as garbage (if not for references from weak hash tables).The default for weak is nil, so that all keys and valuesreferenced in the hash table are preserved from garbage collection. :size size This specifies a hint for how many associations you plan to store in thehash table. If you know the approximate number, you can make things alittle more efficient by specifying it this way. If you specify toosmall a size, the hash table will grow automatically when necessary, butdoing that takes some extra time.The default size is 65. :rehash-size rehash-size When you add an association to a hash table and the table is “full,”it grows automatically. This value specifies how to make the hash tablelarger, at that time.If rehash-size is an integer, it should be positive, and the hashtable grows by adding that much to the nominal size. Ifrehash-size is a floating point number, it had better be greaterthan 1, and the hash table grows by multiplying the old size by thatnumber.The default value is 1.5. :rehash-threshold threshold This specifies the criterion for when the hash table is “full” (soit should be made larger). The value, threshold, should be apositive floating point number, no greater than 1. The hash table is“full” whenever the actual number of entries exceeds this fractionof the nominal size. The default for threshold is 0.8. makehash — Function: makehash &optional test This is equivalent to make-hash-table, but with a different styleargument list. The argument test specifies the methodof key lookup.This function is obsolete. Use make-hash-table instead. Hash Table Access This section describes the functions for accessing and storing associations in a hash table. In general, any Lisp object can be used as a hash key, unless the comparison method imposes limits. Any Lisp object can also be used as the value. gethash — Function: gethash key table &optional default This function looks up key in table, and returns itsassociated value—or default, if key has noassociation in table. puthash — Function: puthash key value table This function enters an association for key in table, withvalue value. If key already has an association intable, value replaces the old associated value. remhash — Function: remhash key table This function removes the association for key from table, ifthere is one. If key has no association, remhash doesnothing.Common Lisp note: In Common Lisp, remhash returnsnon-nil if it actually removed an association and nilotherwise. In Emacs Lisp, remhash always returns nil. clrhash — Function: clrhash table This function removes all the associations from hash table table,so that it becomes empty. This is also called clearing the hashtable.Common Lisp note: In Common Lisp, clrhash returns the emptytable. In Emacs Lisp, it returns nil. maphash — Function: maphash function table This function calls function once for each of the associations intable. The function function should accept twoarguments—a key listed in table, and its associatedvalue. maphash returns nil. Defining Hash Comparisons hash code define hash comparisons You can define new methods of key lookup by means of define-hash-table-test. In order to use this feature, you need to understand how hash tables work, and what a hash code means. You can think of a hash table conceptually as a large array of many slots, each capable of holding one association. To look up a key, gethash first computes an integer, the hash code, from the key. It reduces this integer modulo the length of the array, to produce an index in the array. Then it looks in that slot, and if necessary in other nearby slots, to see if it has found the key being sought. Thus, to define a new method of key lookup, you need to specify both a function to compute the hash code from a key, and a function to compare two keys directly. define-hash-table-test — Function: define-hash-table-test name test-fn hash-fn This function defines a new hash table test, named name.After defining name in this way, you can use it as the testargument in make-hash-table. When you do that, the hash tablewill use test-fn to compare key values, and hash-fn to computea “hash code” from a key value.The function test-fn should accept two arguments, two keys, andreturn non-nil if they are considered “the same.”The function hash-fn should accept one argument, a key, and returnan integer that is the “hash code” of that key. For good results, thefunction should use the whole range of integer values for hash codes,including negative integers.The specified functions are stored in the property list of nameunder the property hash-table-test; the property value's form is(test-fn hash-fn). sxhash — Function: sxhash obj This function returns a hash code for Lisp object obj.This is an integer which reflects the contents of objand the other Lisp objects it points to.If two objects obj1 and obj2 are equal, then (sxhashobj1) and (sxhash obj2) are the same integer.If the two objects are not equal, the values returned by sxhashare usually different, but not always; once in a rare while, by luck,you will encounter two distinct-looking objects that give the sameresult from sxhash. This example creates a hash table whose keys are strings that are compared case-insensitively. (defun case-fold-string= (a b) (compare-strings a nil nil b nil nil t)) (defun case-fold-string-hash (a) (sxhash (upcase a))) (define-hash-table-test 'case-fold 'case-fold-string= 'case-fold-string-hash) (make-hash-table :test 'case-fold) Here is how you could define a hash table test equivalent to the predefined test value equal. The keys can be any Lisp object, and equal-looking objects are considered the same key. (define-hash-table-test 'contents-hash 'equal 'sxhash) (make-hash-table :test 'contents-hash) Other Hash Table Functions Here are some other functions for working with hash tables. hash-table-p — Function: hash-table-p table This returns non-nil if table is a hash table object. copy-hash-table — Function: copy-hash-table table This function creates and returns a copy of table. Only the tableitself is copied—the keys and values are shared. hash-table-count — Function: hash-table-count table This function returns the actual number of entries in table. hash-table-test — Function: hash-table-test table This returns the test value that was given when table wascreated, to specify how to hash and compare keys. Seemake-hash-table (see ). hash-table-weakness — Function: hash-table-weakness table This function returns the weak value that was specified for hashtable table. hash-table-rehash-size — Function: hash-table-rehash-size table This returns the rehash size of table. hash-table-rehash-threshold — Function: hash-table-rehash-threshold table This returns the rehash threshold of table. hash-table-size — Function: hash-table-size table This returns the current nominal size of table. <setfilename>../info/symbols</setfilename> Symbols symbol A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see , and . For the precise read syntax for symbols, see . You can test whether an arbitrary Lisp object is a symbol with symbolp: symbolp — Function: symbolp object This function returns t if object is a symbol, nilotherwise. Symbol Components symbol components Each symbol has four components (or “cells”), each of which references another object: Print name print name cellThe print name cell holds a string that names the symbol forreading and printing. See symbol-name in . Value value cellThe value cell holds the current value of the symbol as avariable. When a symbol is used as a form, the value of the form is thecontents of the symbol's value cell. See symbol-value in. Function function cellThe function cell holds the function definition of the symbol.When a symbol is used as a function, its function definition is used inits place. This cell is also used to make a symbol stand for a keymapor a keyboard macro, for editor command execution. Because each symbolhas separate value and function cells, variables names and function names donot conflict. See symbol-function in . Property list property list cellThe property list cell holds the property list of the symbol. Seesymbol-plist in . The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object. The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this lookup uses a hashing algorithm and an obarray; see .) The value cell holds the symbol's value as a variable (see ). That is what you get if you evaluate the symbol as a Lisp expression (see ). Any Lisp object is a legitimate value. Certain symbols have values that cannot be changed; these include nil and t, and any symbol whose name starts with ‘:’ (those are called keywords). See . We often refer to “the function foo” when we really mean the function stored in the function cell of the symbol foo. We make the distinction explicit only when necessary. In normal usage, the function cell usually contains a function (see ) or a macro (see ), as that is what the Lisp interpreter expects to see there (see ). Keyboard macros (see ), keymaps (see ) and autoload objects (see ) are also sometimes stored in the function cells of symbols. The property list cell normally should hold a correctly formatted property list (see ), as a number of functions expect to see a property list there. The function cell or the value cell may be void, which means that the cell does not reference any object. (This is not the same thing as holding the symbol void, nor the same as holding the symbol nil.) Examining a function or value cell that is void results in an error, such as ‘Symbol's value as variable is void’. The four functions symbol-name, symbol-value, symbol-plist, and symbol-function return the contents of the four cells of a symbol. Here as an example we show the contents of the four cells of the symbol buffer-file-name: (symbol-name 'buffer-file-name) => "buffer-file-name" (symbol-value 'buffer-file-name) => "/gnu/elisp/symbols.texi" (symbol-function 'buffer-file-name) => #<subr buffer-file-name> (symbol-plist 'buffer-file-name) => (variable-documentation 29529) Because this symbol is the variable which holds the name of the file being visited in the current buffer, the value cell contents we see are the name of the source file of this chapter of the Emacs Lisp Manual. The property list cell contains the list (variable-documentation 29529) which tells the documentation functions where to find the documentation string for the variable buffer-file-name in the DOC-version file. (29529 is the offset from the beginning of the DOC-version file to where that documentation string begins—see .) The function cell contains the function for returning the name of the file. buffer-file-name names a primitive function, which has no read syntax and prints in hash notation (see ). A symbol naming a function written in Lisp would have a lambda expression (or a byte-code object) in this cell. Defining Symbols definitions of symbols A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently. A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable. defvar and defconst are special forms that define a symbol as a global variable. They are documented in detail in . For defining user option variables that can be customized, use defcustom (see ). defun defines a symbol as a function, creating a lambda expression and storing it in the function cell of the symbol. This lambda expression thus becomes the function definition of the symbol. (The term “function definition,” meaning the contents of the function cell, is derived from the idea that defun gives the symbol its definition as a function.) defsubst and defalias are two other ways of defining a function. See . defmacro defines a symbol as a macro. It creates a macro object and stores it in the function cell of the symbol. Note that a given symbol can be a macro or a function, but not both at once, because both macro and function definitions are kept in the function cell, and that cell can hold only one Lisp object at any given time. See . In Emacs Lisp, a definition is not required in order to use a symbol as a variable or function. Thus, you can make a symbol a global variable with setq, whether you define it first or not. The real purpose of definitions is to guide programmers and programming tools. They inform programmers who read the code that certain symbols are intended to be used as variables, or as functions. In addition, utilities such as etags and make-docfile recognize definitions, and add appropriate information to tag tables and the DOC-version file. See . Creating and Interning Symbols reading symbols To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion. symbol name hashing hashing obarray bucket (in obarray) When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it “hashes” those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code. (The same idea is used for general Emacs hash tables, but they are a different data type; see .) interning If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol. Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray. Interning usually happens automatically in the reader, but sometimes other programs need to do it. For example, after the M-x command obtains the command name as a string using the minibuffer, it then interns the string, to get the interned symbol with that name. symbol equality uninterned symbol No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable. Creating an uninterned symbol is useful in generating Lisp code, because an uninterned symbol used as a variable in the code you generate cannot clash with any variables used in other Lisp programs. In Emacs Lisp, an obarray is actually a vector. Each element of the vector is a bucket; its value is either an interned symbol whose name hashes to that bucket, or 0 if the bucket is empty. Each interned symbol has an internal link (invisible to the user) to the next symbol in the bucket. Because these links are invisible, there is no way to find all the symbols in an obarray except using mapatoms (below). The order of symbols in a bucket is not significant. In an empty obarray, every element is 0, so you can create an obarray with (make-vector length 0). This is the only valid way to create an obarray. Prime numbers as lengths tend to result in good hashing; lengths one less than a power of two are also good. Do not try to put symbols in an obarray yourself. This does not work—only intern can enter a symbol in an obarray properly. CL note—symbol in obarrays Common Lisp note: In Common Lisp, a single symbol may be interned in several obarrays. Most of the functions below take a name and sometimes an obarray as arguments. A wrong-type-argument error is signaled if the name is not a string, or if the obarray is not a vector. symbol-name — Function: symbol-name symbol This function returns the string that is symbol's name. For example: (symbol-name 'foo) => "foo" Warning: Changing the string by substituting characters doeschange the name of the symbol, but fails to update the obarray, so don'tdo it! make-symbol — Function: make-symbol name This function returns a newly-allocated, uninterned symbol whose name isname (which must be a string). Its value and function definitionare void, and its property list is nil. In the example below,the value of sym is not eq to foo because it is adistinct uninterned symbol whose name is also ‘foo’. (setq sym (make-symbol "foo")) => foo (eq sym 'foo) => nil intern — Function: intern name &optional obarray This function returns the interned symbol whose name is name. Ifthere is no such symbol in the obarray obarray, interncreates a new one, adds it to the obarray, and returns it. Ifobarray is omitted, the value of the global variableobarray is used. (setq sym (intern "foo")) => foo (eq sym 'foo) => t (setq sym1 (intern "foo" other-obarray)) => foo (eq sym1 'foo) => nil CL note—interning existing symbol Common Lisp note: In Common Lisp, you can intern an existing symbol in an obarray. In Emacs Lisp, you cannot do this, because the argument to intern must be a string, not a symbol. intern-soft — Function: intern-soft name &optional obarray This function returns the symbol in obarray whose name isname, or nil if obarray has no symbol with that name.Therefore, you can use intern-soft to test whether a symbol witha given name is already interned. If obarray is omitted, thevalue of the global variable obarray is used.The argument name may also be a symbol; in that case,the function returns name if name is internedin the specified obarray, and otherwise nil. (intern-soft "frazzle") ; No such symbol exists. => nil (make-symbol "frazzle") ; Create an uninterned one. => frazzle (intern-soft "frazzle") ; That one cannot be found. => nil (setq sym (intern "frazzle")) ; Create an interned one. => frazzle (intern-soft "frazzle") ; That one can be found! => frazzle (eq sym 'frazzle) ; And it is the same one. => t obarray — Variable: obarray This variable is the standard obarray for use by intern andread. mapatoms — Function: mapatoms function &optional obarray This function calls function once with each symbol in the obarrayobarray. Then it returns nil. If obarray isomitted, it defaults to the value of obarray, the standardobarray for ordinary symbols. (setq count 0) => 0 (defun count-syms (s) (setq count (1+ count))) => count-syms (mapatoms 'count-syms) => nil count => 1871 See documentation in , for anotherexample using mapatoms. unintern — Function: unintern symbol &optional obarray This function deletes symbol from the obarray obarray. Ifsymbol is not actually in the obarray, unintern doesnothing. If obarray is nil, the current obarray is used.If you provide a string instead of a symbol as symbol, it standsfor a symbol name. Then unintern deletes the symbol (if any) inthe obarray which has that name. If there is no such symbol,unintern does nothing.If unintern does delete a symbol, it returns t. Otherwiseit returns nil. Property Lists property list plist A property list (plist for short) is a list of paired elements stored in the property list cell of a symbol. Each of the pairs associates a property name (usually a symbol) with a property or value. Property lists are generally used to record information about a symbol, such as its documentation as a variable, the name of the file where it was defined, or perhaps even the grammatical class of the symbol (representing a word) in a language-understanding system. Character positions in a string or buffer can also have property lists. See . The property names and values in a property list can be any Lisp objects, but the names are usually symbols. Property list functions compare the property names using eq. Here is an example of a property list, found on the symbol progn when the compiler is loaded: (lisp-indent-function 0 byte-compile byte-compile-progn) Here lisp-indent-function and byte-compile are property names, and the other two elements are the corresponding values. Property Lists and Association Lists plist vs. alist alist vs. plist property lists vs association lists Association lists (see ) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct. Property lists are better than association lists for attaching information to various Lisp function names or variables. If your program keeps all of its associations in one association list, it will typically need to search that entire list each time it checks for an association. This could be slow. By contrast, if you keep the same information in the property lists of the function names or variables themselves, each search will scan only the length of one property list, which is usually short. This is why the documentation for a variable is recorded in a property named variable-documentation. The byte compiler likewise uses properties to record those functions needing special treatment. However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by beginning the property name with the program's usual name-prefix for variables and functions.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list. Property List Functions for Symbols symbol-plist — Function: symbol-plist symbol This function returns the property list of symbol. setplist — Function: setplist symbol plist This function sets symbol's property list to plist.Normally, plist should be a well-formed property list, but this isnot enforced. The return value is plist. (setplist 'foo '(a 1 b (2 3) c nil)) => (a 1 b (2 3) c nil) (symbol-plist 'foo) => (a 1 b (2 3) c nil) For symbols in special obarrays, which are not used for ordinarypurposes, it may make sense to use the property list cell in anonstandard fashion; in fact, the abbrev mechanism does so(see ). get — Function: get symbol property This function finds the value of the property named property insymbol's property list. If there is no such property, nilis returned. Thus, there is no distinction between a value ofnil and the absence of the property.The name property is compared with the existing property namesusing eq, so any object is a legitimate property.See put for an example. put — Function: put symbol property value This function puts value onto symbol's property list underthe property name property, replacing any previous property value.The put function returns value. (put 'fly 'verb 'transitive) =>'transitive (put 'fly 'noun '(a buzzing little bug)) => (a buzzing little bug) (get 'fly 'verb) => transitive (symbol-plist 'fly) => (verb transitive noun (a buzzing little bug)) Property Lists Outside Symbols These functions are useful for manipulating property lists that are stored in places other than symbols: plist-get — Function: plist-get plist property This returns the value of the property propertystored in the property list plist. For example, (plist-get '(foo 4) 'foo) => 4 (plist-get '(foo 4 bad) 'foo) => 4 (plist-get '(foo 4 bad) 'bar) => wrong-type-argument error It accepts a malformed plist argument and always returns nilif property is not found in the plist. For example, (plist-get '(foo 4 bad) 'bar) => nil plist-put — Function: plist-put plist property value This stores value as the value of the property property inthe property list plist. It may modify plist destructively,or it may construct a new list structure without altering the old. Thefunction returns the modified property list, so you can store that backin the place where you got plist. For example, (setq my-plist '(bar t foo 4)) => (bar t foo 4) (setq my-plist (plist-put my-plist 'foo 69)) => (bar t foo 69) (setq my-plist (plist-put my-plist 'quux '(a))) => (bar t foo 69 quux (a)) You could define put in terms of plist-put as follows: (defun put (symbol prop value) (setplist symbol (plist-put (symbol-plist symbol) prop value))) lax-plist-get — Function: lax-plist-get plist property Like plist-get except that it compares propertiesusing equal instead of eq. lax-plist-put — Function: lax-plist-put plist property value Like plist-put except that it compares propertiesusing equal instead of eq. plist-member — Function: plist-member plist property This returns non-nil if plist contains the givenproperty. Unlike plist-get, this allows you to distinguishbetween a missing property and a property with the value nil.The value is actually the tail of plist whose car isproperty. <setfilename>../info/eval</setfilename> Evaluation evaluation interpreter interpreter value of expression The evaluation of expressions in Emacs Lisp is performed by the Lisp interpreter—a program that receives a Lisp object as input and computes its value as an expression. How it does this depends on the data type of the object, according to rules described in this chapter. The interpreter runs automatically to evaluate portions of your program, but can also be called explicitly via the Lisp primitive function eval. Introduction to Evaluation The Lisp interpreter, or evaluator, is the program that computes the value of an expression that is given to it. When a function written in Lisp is called, the evaluator computes the value of the function by evaluating the expressions in the function body. Thus, running any Lisp program really means running the Lisp interpreter. How the evaluator handles an object depends primarily on the data type of the object. forms expression A Lisp object that is intended for evaluation is called an expression or a form. The fact that expressions are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often. It is very common to read a Lisp expression and then evaluate the expression, but reading and evaluation are separate activities, and either can be performed alone. Reading per se does not evaluate anything; it converts the printed representation of a Lisp object to the object itself. It is up to the caller of read whether this object is a form to be evaluated, or serves some entirely different purpose. See . Do not confuse evaluation with command key interpretation. The editor command loop translates keyboard input into a command (an interactively callable function) using the active keymaps, and then uses call-interactively to invoke the command. The execution of the command itself involves evaluation if the command is written in Lisp, but that is not a part of command key interpretation itself. See . recursive evaluation Evaluation is a recursive process. That is, evaluation of a form may call eval to evaluate parts of the form. For example, evaluation of a function call first evaluates each argument of the function call, and then evaluates each form in the function body. Consider evaluation of the form (car x): the subform x must first be evaluated recursively, so that its value can be passed as an argument to the function car. Evaluation of a function call ultimately calls the function specified in it. See . The execution of the function may itself work by evaluating the function definition; or the function may be a Lisp primitive implemented in C, or it may be a byte-compiled function (see ). environment The evaluation of forms takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables.This definition of “environment” is specifically not intended to include all the data that can affect the result of a program. Whenever a form refers to a variable without creating a new binding for it, the value of the variable's binding in the current environment is used. See . side effect Evaluation of a form may create new environments for recursive evaluation by binding variables (see ). These environments are temporary and vanish by the time evaluation of the form is complete. The form may also make changes that persist; these changes are called side effects. An example of a form that produces side effects is (setq foo 1). The details of what evaluation means for each kind of form are described below (see ). Kinds of Forms A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and “all other types.” This section describes all three kinds, one by one, starting with the “all other types” which are self-evaluating forms. Self-Evaluating Forms vector evaluation literal evaluation self-evaluating form A self-evaluating form is any form that is not a list or symbol. Self-evaluating forms evaluate to themselves: the result of evaluation is the same object that was evaluated. Thus, the number 25 evaluates to 25, and the string "foo" evaluates to the string "foo". Likewise, evaluation of a vector does not cause evaluation of the elements of the vector—it returns the same vector with its contents unchanged. '123 ; A number, shown without evaluation. => 123 123 ; Evaluated as usual---result is the same. => 123 (eval '123) ; Evaluated ``by hand''---result is the same. => 123 (eval (eval '123)) ; Evaluating twice changes nothing. => 123 It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there's no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example: ;; Build an expression containing a buffer object. (setq print-exp (list 'print (current-buffer))) => (print #<buffer eval.texi>) ;; Evaluate it. (eval print-exp) -| #<buffer eval.texi> => #<buffer eval.texi> Symbol Forms symbol evaluation When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see . In the following example, we set the value of a symbol with setq. Then we evaluate the symbol, and get back the value that setq stored. (setq a 123) => 123 (eval 'a) => 123 a => 123 The symbols nil and t are treated specially, so that the value of nil is always nil, and the value of t is always t; you cannot set or bind them to any other values. Thus, these two symbols act like self-evaluating forms, even though eval treats them like any other symbol. A symbol whose name starts with ‘:’ also self-evaluates in the same way; likewise, its value ordinarily cannot be changed. See . Classification of List Forms list form evaluation A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form. The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme. Symbol Function Indirection symbol function indirection indirection for functions void function If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See , for more information about using a symbol as a name for a function stored in the function cell of the symbol. One possible consequence of this process is an infinite loop, in the event that a symbol's function cell refers to the same symbol. Or a symbol may have a void function cell, in which case the subroutine symbol-function signals a void-function error. But if neither of these things happens, we eventually obtain a non-symbol, which ought to be a function or other suitable object. invalid-function More precisely, we should now have a Lisp function (a lambda expression), a byte-code function, a primitive function, a Lisp macro, a special form, or an autoload object. Each of these types is a case described in one of the following sections. If the object is not one of these types, the error invalid-function is signaled. The following example illustrates the symbol indirection process. We use fset to set the function cell of a symbol and symbol-function to get the function cell contents (see ). Specifically, we store the symbol car into the function cell of first, and the symbol first into the function cell of erste. ;; Build this function cell linkage: ;; ------------- ----- ------- ------- ;; | #<subr car> | <-- | car | <-- | first | <-- | erste | ;; ------------- ----- ------- ------- (symbol-function 'car) => #<subr car> (fset 'first 'car) => car (fset 'erste 'first) => first (erste '(1 2 3)) ; Call the function referenced by erste. => 1 By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol. ((lambda (arg) (erste arg)) '(1 2 3)) => 1 Executing the function itself evaluates its body; this does involve symbol function indirection when calling erste. The built-in function indirect-function provides an easy way to perform symbol function indirection explicitly. indirect-function — Function: indirect-function function &optional noerror This function returns the meaning of function as a function. Iffunction is a symbol, then it finds function's functiondefinition and starts over with that value. If function is not asymbol, then it returns function itself.This function signals a void-function error if the final symbolis unbound and optional argument noerror is nil oromitted. Otherwise, if noerror is non-nil, it returnsnil if the final symbol is unbound.It signals a cyclic-function-indirection error if there is aloop in the chain of symbols.Here is how you could define indirect-function in Lisp: (defun indirect-function (function) (if (symbolp function) (indirect-function (symbol-function function)) function)) Evaluation of Function Forms function form evaluation function call If the first element of a list being evaluated is a Lisp function object, byte-code object or primitive function object, then that list is a function call. For example, here is a call to the function +: (+ 1 x) The first step in evaluating a function call is to evaluate the remaining elements of the list from left to right. The results are the actual argument values, one value for each list element. The next step is to call the function with this list of arguments, effectively using the function apply (see ). If the function is written in Lisp, the arguments are used to bind the argument variables of the function (see ); then the forms in the function body are evaluated in order, and the value of the last body form becomes the value of the function call. Lisp Macro Evaluation macro call evaluation If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results. Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions. Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is evaluated. For example, given a macro defined as follows: (defmacro cadr (x) (list 'car (list 'cdr x))) an expression such as (cadr (assq 'handler list)) is a macro call, and its expansion is: (car (cdr (assq 'handler list))) Note that the argument (assq 'handler list) appears in the expansion. See , for a complete description of Emacs Lisp macros. Special Forms special form evaluation A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do. Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments. Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described. and see catch see cond see condition-case see defconst see defmacro see defun see defvar see function see if see interactive see letlet* see or see prog1prog2progn see quote see save-current-buffer see save-excursion see save-restriction see save-window-excursion see setq see setq-default see track-mouse see unwind-protect see while see with-output-to-temp-buffer see CL note—special forms compared Common Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp. setq, if, and catch are special forms in both Emacs Lisp and Common Lisp. defun is a special form in Emacs Lisp, but a macro in Common Lisp. save-excursion is a special form in Emacs Lisp, but doesn't exist in Common Lisp. throw is a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values). Autoloading The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol's function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. See . Quoting The special form quote returns its single argument, as written, without evaluating it. This provides a way to include constant symbols and lists, which are not self-evaluating objects, in a program. (It is not necessary to quote self-evaluating objects such as numbers, strings, and vectors.) quote — Special Form: quote object This special form returns object, without evaluating it. ‘'’ for quoting quoting using apostrophe apostrophe for quoting Because quote is used so often in programs, Lisp provides a convenient read syntax for it. An apostrophe character (‘'’) followed by a Lisp object (in read syntax) expands to a list whose first element is quote, and whose second element is the object. Thus, the read syntax 'x is an abbreviation for (quote x). Here are some examples of expressions that use quote: (quote (+ 1 2)) => (+ 1 2) (quote foo) => foo 'foo => foo ''foo => (quote foo) '(quote foo) => (quote foo) ['foo] => [(quote foo)] Other quoting constructs include function (see ), which causes an anonymous lambda expression written in Lisp to be compiled, and ‘`’ (see ), which is used to quote only part of a list, while computing and substituting other parts. Eval Most often, forms are evaluated automatically, by virtue of their occurrence in a program being run. On rare occasions, you may need to write code that evaluates a form that is computed at run time, such as after reading a form from text being edited or getting one from a property list. On these occasions, use the eval function. The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see ). It is generally cleaner and more flexible to store a function in a data structure, and call it with funcall or apply, than to store an expression in the data structure and evaluate it. Using functions provides the ability to pass information to them as arguments. eval — Function: eval form This is the basic function evaluating an expression. It evaluatesform in the current environment and returns the result. How theevaluation proceeds depends on the type of the object (see ).Since eval is a function, the argument expression that appearsin a call to eval is evaluated twice: once as preparation beforeeval is called, and again by the eval function itself.Here is an example: (setq foo 'bar) => bar (setq bar 'baz) => baz ;; Here eval receives argument foo (eval 'foo) => bar ;; Here eval receives argument bar, which is the value of foo (eval foo) => baz The number of currently active calls to eval is limited tomax-lisp-eval-depth (see below). eval-region — Command: eval-region start end &optional stream read-function This function evaluates the forms in the current buffer in the regiondefined by the positions start and end. It reads forms fromthe region and calls eval on them until the end of the region isreached, or until an error is signaled and not handled.By default, eval-region does not produce any output. However,if stream is non-nil, any output produced by outputfunctions (see ), as well as the values thatresult from evaluating the expressions in the region are printed usingstream. See .If read-function is non-nil, it should be a function,which is used instead of read to read expressions one by one.This function is called with one argument, the stream for readinginput. You can also use the variable load-read-function(see How Programs Do Loading)to specify this function, but it is more robust to use theread-function argument.eval-region does not move point. It always returns nil. evaluation of buffer contents eval-buffer — Command: eval-buffer &optional buffer-or-name stream filename unibyte print This is similar to eval-region, but the arguments providedifferent optional features. eval-buffer operates on theentire accessible portion of buffer buffer-or-name.buffer-or-name can be a buffer, a buffer name (a string), ornil (or omitted), which means to use the current buffer.stream is used as in eval-region, unless stream isnil and print non-nil. In that case, values thatresult from evaluating the expressions are still discarded, but theoutput of the output functions is printed in the echo area.filename is the file name to use for load-history(see ), and defaults to buffer-file-name(see ). If unibyte is non-nil,read converts strings to unibyte whenever possible. eval-current-buffereval-current-buffer is an alias for this command. max-lisp-eval-depth — Variable: max-lisp-eval-depth This variable defines the maximum depth allowed in calls to eval,apply, and funcall before an error is signaled (with errormessage "Lisp nesting exceeds max-lisp-eval-depth").This limit, with the associated error when it is exceeded, is one wayEmacs Lisp avoids infinite recursion on an ill-defined function. Ifyou increase the value of max-lisp-eval-depth too much, suchcode can cause stack overflow instead. Lisp nesting errorThe depth limit counts internal uses of eval, apply, andfuncall, such as for calling the functions mentioned in Lispexpressions, and recursive evaluation of function call arguments andfunction body forms, as well as explicit calls in Lisp code.The default value of this variable is 300. If you set it to a valueless than 100, Lisp will reset it to 100 if the given value is reached.Entry to the Lisp debugger increases the value, if there is little roomleft, to make sure the debugger itself has room to execute.max-specpdl-size provides another limit on nesting.See Local Variables. values — Variable: values The value of this variable is a list of the values returned by all theexpressions that were read, evaluated, and printed from buffers(including the minibuffer) by the standard Emacs commands which dothis. (Note that this does not include evaluation in‘*ielm*’ buffers, nor evaluation using C-j inlisp-interaction-mode.) The elements are ordered most recentfirst. (setq x 1) => 1 (list 'A (1+ 2) auto-save-default) => (A 3 t) values => ((A 3 t) 1 …) This variable is useful for referring back to values of forms recentlyevaluated. It is generally a bad idea to print the value ofvalues itself, since this may be very long. Instead, examineparticular elements, like this: ;; Refer to the most recent evaluation result. (nth 0 values) => (A 3 t) ;; That put a new element on, ;; so all elements move back one. (nth 1 values) => (A 3 t) ;; This gets the element that was next-to-most-recent ;; before this example. (nth 3 values) => 1 <setfilename>../info/control</setfilename> Control Structures special forms for control structures control structures A Lisp program consists of expressions or forms (see ). We control the order of execution of these forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain. The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code—the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b. The result of evaluating b becomes the value of the function. Explicit control structures make possible an order of execution other than sequential. Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see ). Sequencing Evaluating forms in the order they appear is the most common way control passes from one form to another. In some contexts, such as in a function body, this happens automatically. Elsewhere you must use a control structure construct to do this: progn, the simplest control construct of Lisp. A progn special form looks like this: (progn a b c …) and it says to execute the forms a, b, c, and so on, in that order. These forms are called the body of the progn form. The value of the last form in the body becomes the value of the entire progn. (progn) returns nil. implicit progn In the early days of Lisp, progn was the only way to execute two or more forms in succession and use the value of the last of them. But programmers found they often needed to use a progn in the body of a function, where (at that time) only one form was allowed. So the body of a function was made into an “implicit progn”: several forms are allowed just as in the body of an actual progn. Many other control structures likewise contain an implicit progn. As a result, progn is not used as much as it was many years ago. It is needed now most often inside an unwind-protect, and, or, or in the then-part of an if. progn — Special Form: progn forms … This special form evaluates all of the forms, in textualorder, returning the result of the final form. (progn (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The third form" Two other control constructs likewise evaluate a series of forms but return a different value: prog1 — Special Form: prog1 form1 forms … This special form evaluates form1 and all of the forms, intextual order, returning the result of form1. (prog1 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The first form" Here is a way to remove the first element from a list in the variablex, then return the value of that former element: (prog1 (car x) (setq x (cdr x))) prog2 — Special Form: prog2 form1 form2 forms … This special form evaluates form1, form2, and all of thefollowing forms, in textual order, returning the result ofform2. (prog2 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The second form" Conditionals conditional evaluation Conditional control structures choose among alternatives. Emacs Lisp has four conditional forms: if, which is much the same as in other languages; when and unless, which are variants of if; and cond, which is a generalized case statement. if — Special Form: if condition then-form else-forms … if chooses between the then-form and the else-formsbased on the value of condition. If the evaluated condition isnon-nil, then-form is evaluated and the result returned.Otherwise, the else-forms are evaluated in textual order, and thevalue of the last one is returned. (The else part of if isan example of an implicit progn. See .)If condition has the value nil, and no else-forms aregiven, if returns nil.if is a special form because the branch that is not selected isnever evaluated—it is ignored. Thus, in the example below,true is not printed because print is never called. (if nil (print 'true) 'very-false) => very-false when — Macro: when condition then-forms … This is a variant of if where there are no else-forms,and possibly several then-forms. In particular, (when condition a b c) is entirely equivalent to (if condition (progn a b c) nil) unless — Macro: unless condition forms … This is a variant of if where there is no then-form: (unless condition a b c) is entirely equivalent to (if condition nil a b c) cond — Special Form: cond clause … cond chooses among an arbitrary number of alternatives. Eachclause in the cond must be a list. The car of thislist is the condition; the remaining elements, if any, thebody-forms. Thus, a clause looks like this: (condition body-forms…) cond tries the clauses in textual order, by evaluating thecondition of each clause. If the value of condition isnon-nil, the clause “succeeds”; then cond evaluates itsbody-forms, and the value of the last of body-forms becomesthe value of the cond. The remaining clauses are ignored.If the value of condition is nil, the clause “fails,” sothe cond moves on to the following clause, trying itscondition.If every condition evaluates to nil, so that every clausefails, cond returns nil.A clause may also look like this: (condition) Then, if condition is non-nil when tested, the value ofcondition becomes the value of the cond form.The following example has four clauses, which test for the cases wherethe value of x is a number, string, buffer and symbol,respectively: (cond ((numberp x) x) ((stringp x) x) ((bufferp x) (setq temporary-hack x) ; multiple body-forms (buffer-name x)) ; in one clause ((symbolp x) (symbol-value x))) Often we want to execute the last clause whenever none of the previousclauses was successful. To do this, we use t as thecondition of the last clause, like this: (tbody-forms). The form t evaluates to t, which isnever nil, so this clause never fails, provided the condgets to it at all.For example, (setq a 5) (cond ((eq a 'hack) 'foo) (t "default")) => "default" This cond expression returns foo if the value of ais hack, and returns the string "default" otherwise. Any conditional construct can be expressed with cond or with if. Therefore, the choice between them is a matter of style. For example: (if a b c) == (cond (a b) (t c)) Constructs for Combining Conditions This section describes three constructs that are often used together with if and cond to express complicated conditions. The constructs and and or can also be used individually as kinds of multiple conditional constructs. not — Function: not condition This function tests for the falsehood of condition. It returnst if condition is nil, and nil otherwise.The function not is identical to null, and we recommendusing the name null if you are testing for an empty list. and — Special Form: and conditions … The and special form tests whether all the conditions aretrue. It works by evaluating the conditions one by one in theorder written.If any of the conditions evaluates to nil, then the resultof the and must be nil regardless of the remainingconditions; so and returns nil right away, ignoringthe remaining conditions.If all the conditions turn out non-nil, then the value ofthe last of them becomes the value of the and form. Just(and), with no conditions, returns t, appropriatebecause all the conditions turned out non-nil. (Thinkabout it; which one did not?)Here is an example. The first condition returns the integer 1, which isnot nil. Similarly, the second condition returns the integer 2,which is not nil. The third condition is nil, so theremaining condition is never evaluated. (and (print 1) (print 2) nil (print 3)) -| 1 -| 2 => nil Here is a more realistic example of using and: (if (and (consp foo) (eq (car foo) 'x)) (message "foo is a list starting with x")) Note that (car foo) is not executed if (consp foo) returnsnil, thus avoiding an error.and expressions can also be written using either if orcond. Here's how: (and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3)))) or — Special Form: or conditions … The or special form tests whether at least one of theconditions is true. It works by evaluating all theconditions one by one in the order written.If any of the conditions evaluates to a non-nil value, thenthe result of the or must be non-nil; so or returnsright away, ignoring the remaining conditions. The value itreturns is the non-nil value of the condition just evaluated.If all the conditions turn out nil, then the orexpression returns nil. Just (or), with noconditions, returns nil, appropriate because all theconditions turned out nil. (Think about it; which onedid not?)For example, this expression tests whether x is eithernil or the integer zero: (or (eq x nil) (eq x 0)) Like the and construct, or can be written in terms ofcond. For example: (or arg1 arg2 arg3) == (cond (arg1) (arg2) (arg3)) You could almost write or in terms of if, but not quite: (if arg1 arg1 (if arg2 arg2 arg3)) This is not completely equivalent because it can evaluate arg1 orarg2 twice. By contrast, (or arg1 arg2arg3) never evaluates any argument more than once. Iteration iteration recursion Iteration means executing part of a program repetitively. For example, you might want to repeat some computation once for each element of a list, or once for each integer from 0 to n. You can do this in Emacs Lisp with the special form while: while — Special Form: while condition forms … while first evaluates condition. If the result isnon-nil, it evaluates forms in textual order. Then itreevaluates condition, and if the result is non-nil, itevaluates forms again. This process repeats until conditionevaluates to nil.There is no limit on the number of iterations that may occur. The loopwill continue until either condition evaluates to nil oruntil an error or throw jumps out of it (see ).The value of a while form is always nil. (setq num 0) => 0 (while (< num 4) (princ (format "Iteration %d." num)) (setq num (1+ num))) -| Iteration 0. -| Iteration 1. -| Iteration 2. -| Iteration 3. => nil To write a “repeat...until” loop, which will execute something on eachiteration and then do the end-test, put the body followed by theend-test in a progn as the first argument of while, asshown here: (while (progn (forward-line 1) (not (looking-at "^$")))) This moves forward one line and continues moving by lines until itreaches an empty line. It is peculiar in that the while has nobody, just the end test (which also does the real work of moving point). The dolist and dotimes macros provide convenient ways to write two common kinds of loops. dolist — Macro: dolist ( var list [ result ] ) body … This construct executes body once for each element oflist, binding the variable var locally to hold the currentelement. Then it returns the value of evaluating result, ornil if result is omitted. For example, here is how youcould use dolist to define the reverse function: (defun reverse (list) (let (value) (dolist (elt list value) (setq value (cons elt value))))) dotimes — Macro: dotimes ( var count [ result ] ) body … This construct executes body once for each integer from 0(inclusive) to count (exclusive), binding the variable varto the integer for the current iteration. Then it returns the valueof evaluating result, or nil if result is omitted.Here is an example of using dotimes to do something 100 times: (dotimes (i 100) (insert "I will not obey absurd orders\n")) Nonlocal Exits nonlocal exits A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited. Explicit Nonlocal Exits: catch and throw Most control constructs affect only the flow of control within the construct itself. The function throw is the exception to this rule of normal program execution: it performs a nonlocal exit on request. (There are other exceptions, but they are for error handling only.) throw is used inside a catch, and jumps back to that catch. For example: (defun foo-outer () (catch 'foo (foo-inner))) (defun foo-inner () … (if x (throw 'foo t)) …) The throw form, if executed, transfers control straight back to the corresponding catch, which returns immediately. The code following the throw is not executed. The second argument of throw is used as the return value of the catch. The function throw finds the matching catch based on the first argument: it searches for a catch whose first argument is eq to the one specified in the throw. If there is more than one applicable catch, the innermost one takes precedence. Thus, in the above example, the throw specifies foo, and the catch in foo-outer specifies the same symbol, so that catch is the applicable one (assuming there is no other matching catch in between). Executing throw exits all Lisp constructs up to the matching catch, including function calls. When binding constructs such as let or function calls are exited in this way, the bindings are unbound, just as they are when these constructs exit normally (see ). Likewise, throw restores the buffer and position saved by save-excursion (see ), and the narrowing status saved by save-restriction and the window selection saved by save-window-excursion (see ). It also runs any cleanups established with the unwind-protect special form when it exits that form (see ). The throw need not appear lexically within the catch that it jumps to. It can equally well be called from another function called within the catch. As long as the throw takes place chronologically after entry to the catch, and chronologically before exit from it, it has access to that catch. This is why throw can be used in commands such as exit-recursive-edit that throw back to the editor command loop (see ). CL note—only throw in Emacs Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially: return, return-from, and go, for example. Emacs Lisp has only throw. catch — Special Form: catch tag body … tag on run time stackcatch establishes a return point for the throw function.The return point is distinguished from other such return points bytag, which may be any Lisp object except nil. The argumenttag is evaluated normally before the return point is established.With the return point in effect, catch evaluates the forms of thebody in textual order. If the forms execute normally (withouterror or nonlocal exit) the value of the last body form is returned fromthe catch.If a throw is executed during the execution of body,specifying the same value tag, the catch form exitsimmediately; the value it returns is whatever was specified as thesecond argument of throw. throw — Function: throw tag value The purpose of throw is to return from a return point previouslyestablished with catch. The argument tag is used to chooseamong the various existing return points; it must be eq to the valuespecified in the catch. If multiple return points match tag,the innermost one is used.The argument value is used as the value to return from thatcatch. no-catchIf no return point is in effect with tag tag, then a no-catcherror is signaled with data (tag value). Examples of catch and throw One way to use catch and throw is to exit from a doubly nested loop. (In most languages, this would be done with a “go to.”) Here we compute (foo i j) for i and j varying from 0 to 9: (defun search-foo () (catch 'loop (let ((i 0)) (while (< i 10) (let ((j 0)) (while (< j 10) (if (foo i j) (throw 'loop (list i j))) (setq j (1+ j)))) (setq i (1+ i)))))) If foo ever returns non-nil, we stop immediately and return a list of i and j. If foo always returns nil, the catch returns normally, and the value is nil, since that is the result of the while. Here are two tricky examples, slightly different, showing two return points at once. First, two return points with the same tag, hack: (defun catch2 (tag) (catch tag (throw 'hack 'yes))) => catch2 (catch 'hack (print (catch2 'hack)) 'no) -| yes => no Since both return points have tags that match the throw, it goes to the inner one, the one established in catch2. Therefore, catch2 returns normally with value yes, and this value is printed. Finally the second body form in the outer catch, which is 'no, is evaluated and returned from the outer catch. Now let's change the argument given to catch2: (catch 'hack (print (catch2 'quux)) 'no) => yes We still have two return points, but this time only the outer one has the tag hack; the inner one has the tag quux instead. Therefore, throw makes the outer catch return the value yes. The function print is never called, and the body-form 'no is never evaluated. Errors errors When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error. When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer. In complicated programs, simple termination may not be what you want. For example, the program may have made temporary changes in data structures, or created temporary buffers that should be deleted before the program is finished. In such cases, you would use unwind-protect to establish cleanup expressions to be evaluated in case of error. (See .) Occasionally, you may wish the program to continue execution despite an error in a subroutine. In these cases, you would use condition-case to establish error handlers to recover control in case of error. Resist the temptation to use error handling to transfer control from one part of the program to another; use catch and throw instead. See . How to Signal an Error signaling errors Signaling an error means beginning error processing. Error processing normally aborts all or part of the running program and returns to a point that is set up to handle the error (see ). Here we describe how to signal an error. Most errors are signaled “automatically” within Lisp primitives which you call for other purposes, such as if you try to take the car of an integer or move forward a character at the end of the buffer. You can also signal errors explicitly with the functions error and signal. Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See . Every error specifies an error message, one way or another. The message should state what is wrong (“File does not exist”), not how things ought to be (“File must exist”). The convention in Emacs Lisp is that error messages should start with a capital letter, but should not end with any sort of punctuation. error — Function: error format-string &rest args This function signals an error with an error message constructed byapplying format (see ) toformat-string and args.These examples show typical uses of error: (error "That is an error -- try something else") error--> That is an error -- try something else (error "You have committed %d errors" 10) error--> You have committed 10 errors error works by calling signal with two arguments: theerror symbol error, and a list containing the string returned byformat.Warning: If you want to use your own string as an error messageverbatim, don't just write (error string). If stringcontains ‘%’, it will be interpreted as a format specifier, withundesirable results. Instead, use (error "%s" string). signal — Function: signal error-symbol data This function signals an error named by error-symbol. Theargument data is a list of additional Lisp objects relevant tothe circumstances of the error.The argument error-symbol must be an error symbol—a symbolbearing a property error-conditions whose value is a list ofcondition names. This is how Emacs Lisp classifies different sorts oferrors. See , for a description of error symbols,error conditions and condition names.If the error is not handled, the two arguments are used in printingthe error message. Normally, this error message is provided by theerror-message property of error-symbol. If data isnon-nil, this is followed by a colon and a comma separated listof the unevaluated elements of data. For error, theerror message is the car of data (that must be a string).Subcategories of file-error are handled specially.The number and significance of the objects in data depends onerror-symbol. For example, with a wrong-type-arg error,there should be two objects in the list: a predicate that describes the typethat was expected, and the object that failed to fit that type.Both error-symbol and data are available to any errorhandlers that handle the error: condition-case binds a localvariable to a list of the form (error-symbol .data) (see ).The function signal never returns (though in older Emacs versionsit could sometimes return). (signal 'wrong-number-of-arguments '(x y)) error--> Wrong number of arguments: x, y (signal 'no-such-error '("My unknown error condition")) error--> peculiar error: "My unknown error condition" CL note—no continuable errors Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors. How Emacs Processes Errors When an error is signaled, signal searches for an active handler for the error. A handler is a sequence of Lisp expressions designated to be executed if an error happens in part of the Lisp program. If the error has an applicable handler, the handler is executed, and control resumes following the handler. The handler executes in the environment of the condition-case that established it; all functions called within that condition-case have already been exited, and the handler cannot return to them. If there is no applicable handler for the error, it terminates the current command and returns control to the editor command loop. (The command loop has an implicit handler for all kinds of errors.) The command loop's handler uses the error symbol and associated data to print an error message. You can use the variable command-error-function to control how this is done: command-error-function — Variable: command-error-function This variable, if non-nil, specifies a function to use tohandle errors that return control to the Emacs command loop. Thefunction should take three arguments: data, a list of the sameform that condition-case would bind to its variable;context, a string describing the situation in which the erroroccurred, or (more often) nil; and caller, the Lispfunction which called the primitive that signaled the error. debug-on-erroruse An error that has no explicit handler may call the Lisp debugger. The debugger is enabled if the variable debug-on-error (see ) is non-nil. Unlike error handlers, the debugger runs in the environment of the error, so that you can examine values of variables precisely as they were at the time of the error. Writing Code to Handle Errors error handler handling errors The usual effect of signaling an error is to terminate the command that is running and return immediately to the Emacs editor command loop. You can arrange to trap errors occurring in a part of your program by establishing an error handler, with the special form condition-case. A simple example looks like this: (condition-case nil (delete-file filename) (error nil)) This deletes the file named filename, catching any error and returning nil if an error occurs. The second argument of condition-case is called the protected form. (In the example above, the protected form is a call to delete-file.) The error handlers go into effect when this form begins execution and are deactivated when this form returns. They remain in effect for all the intervening time. In particular, they are in effect during the execution of functions called by this form, in their subroutines, and so on. This is a good thing, since, strictly speaking, errors can be signaled only by Lisp primitives (including signal and error) called by the protected form, not by the protected form itself. The arguments after the protected form are handlers. Each handler lists one or more condition names (which are symbols) to specify which errors it will handle. The error symbol specified when an error is signaled also defines a list of condition names. A handler applies to an error if they have any condition names in common. In the example above, there is one handler, and it specifies one condition name, error, which covers all errors. The search for an applicable handler checks all the established handlers starting with the most recently established one. Thus, if two nested condition-case forms offer to handle the same error, the inner of the two gets to handle it. If an error is handled by some condition-case form, this ordinarily prevents the debugger from being run, even if debug-on-error says this error should invoke the debugger. See . If you want to be able to debug errors that are caught by a condition-case, set the variable debug-on-signal to a non-nil value. When an error is handled, control returns to the handler. Before this happens, Emacs unbinds all variable bindings made by binding constructs that are being exited and executes the cleanups of all unwind-protect forms that are exited. Once control arrives at the handler, the body of the handler is executed. After execution of the handler body, execution returns from the condition-case form. Because the protected form is exited completely before execution of the handler, the handler cannot resume execution at the point of the error, nor can it examine variable bindings that were made within the protected form. All it can do is clean up and proceed. The condition-case construct is often used to trap errors that are predictable, such as failure to open a file in a call to insert-file-contents. It is also used to trap errors that are totally unpredictable, such as when the program evaluates an expression read from the user. Error signaling and handling have some resemblance to throw and catch (see ), but they are entirely separate facilities. An error cannot be caught by a catch, and a throw cannot be handled by an error handler (though using throw when there is no suitable catch signals an error that can be handled). condition-case — Special Form: condition-case var protected-form handlers … This special form establishes the error handlers handlers aroundthe execution of protected-form. If protected-form executeswithout error, the value it returns becomes the value of thecondition-case form; in this case, the condition-case hasno effect. The condition-case form makes a difference when anerror occurs during protected-form.Each of the handlers is a list of the form (conditionsbody…). Here conditions is an error condition nameto be handled, or a list of condition names; body is one or moreLisp expressions to be executed when this handler handles an error.Here are examples of handlers: (error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file")) Each error that occurs has an error symbol that describes whatkind of error it is. The error-conditions property of thissymbol is a list of condition names (see ). Emacssearches all the active condition-case forms for a handler thatspecifies one or more of these condition names; the innermost matchingcondition-case handles the error. Within thiscondition-case, the first applicable handler handles the error.After executing the body of the handler, the condition-casereturns normally, using the value of the last form in the handler bodyas the overall value. error descriptionThe argument var is a variable. condition-case does notbind this variable when executing the protected-form, only when ithandles an error. At that time, it binds var locally to anerror description, which is a list giving the particulars of theerror. The error description has the form (error-symbol. data). The handler can refer to this list to decide what todo. For example, if the error is for failure opening a file, the filename is the second element of data—the third element of theerror description.If var is nil, that means no variable is bound. Then theerror symbol and associated data are not available to the handler. error-message-string — Function: error-message-string error-description This function returns the error message string for a given errordescriptor. It is useful if you want to handle an error by printing theusual error message for that error. See . arith-errorexample Here is an example of using condition-case to handle the error that results from dividing by zero. The handler displays the error message (but without a beep), then returns a very large number. (defun safe-divide (dividend divisor) (condition-case err ;; Protected form. (/ dividend divisor) ;; The handler. (arith-error ; Condition. ;; Display the usual message for this error. (message "%s" (error-message-string err)) 1000000))) => safe-divide (safe-divide 5 0) -| Arithmetic error: (arith-error) => 1000000 The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus, (safe-divide nil 3) error--> Wrong type argument: number-or-marker-p, nil Here is a condition-case that catches all kinds of errors, including those signaled with error: (setq baz 34) => 34 (condition-case err (if (eq baz 35) t ;; This is a call to the function error. (error "Rats! The variable %s was %s, not 35" 'baz baz)) ;; This is the handler; it is not a form. (error (princ (format "The error was: %s" err)) 2)) -| The error was: (error "Rats! The variable baz was 34, not 35") => 2 Error Symbols and Condition Names error symbol error name condition name user-defined error error-conditions When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language. These narrow classifications are grouped into a hierarchy of wider classes called error conditions, identified by condition names. The narrowest such classes belong to the error symbols themselves: each error symbol is also a condition name. There are also condition names for more extensive classes, up to the condition name error which takes in all kinds of errors (but not quit). Thus, each error has one or more condition names: error, the error symbol if that is distinct from error, and perhaps some intermediate classifications. In order for a symbol to be an error symbol, it must have an error-conditions property which gives a list of condition names. This list defines the conditions that this kind of error belongs to. (The error symbol itself, and the symbol error, should always be members of this list.) Thus, the hierarchy of condition names is defined by the error-conditions properties of the error symbols. Because quitting is not considered an error, the value of the error-conditions property of quit is just (quit). peculiar error In addition to the error-conditions list, the error symbol should have an error-message property whose value is a string to be printed when that error is signaled but not handled. If the error symbol has no error-message property or if the error-message property exists, but is not a string, the error message ‘peculiar error’ is used. See . Here is how we define a new error symbol, new-error: (put 'new-error 'error-conditions '(error my-own-errors new-error)) => (error my-own-errors new-error) (put 'new-error 'error-message "A new error") => "A new error" This error has three condition names: new-error, the narrowest classification; my-own-errors, which we imagine is a wider classification; and error, which is the widest of all. The error string should start with a capital letter but it should not end with a period. This is for consistency with the rest of Emacs. Naturally, Emacs will never signal new-error on its own; only an explicit call to signal (see ) in your code can do this: (signal 'new-error '(x y)) error--> A new error: x, y This error can be handled through any of the three condition names. This example handles new-error and any other errors in the class my-own-errors: (condition-case foo (bar nil t) (my-own-errors nil)) The significant way that errors are classified is by their condition names—the names used to match errors with handlers. An error symbol serves only as a convenient way to specify the intended error message and list of condition names. It would be cumbersome to give signal a list of condition names rather than one error symbol. By contrast, using only error symbols without condition names would seriously decrease the power of condition-case. Condition names make it possible to categorize errors at various levels of generality when you write an error handler. Using error symbols alone would eliminate all but the narrowest level of classification. See , for a list of all the standard error symbols and their conditions. Cleaning Up from Nonlocal Exits The unwind-protect construct is essential whenever you temporarily put a data structure in an inconsistent state; it permits you to make the data consistent again in the event of an error or throw. (Another more specific cleanup construct that is used only for changes in buffer contents is the atomic change group; .) unwind-protect — Special Form: unwind-protect body-form cleanup-forms … cleanup forms protected forms error cleanup unwindingunwind-protect executes body-form with a guarantee thatthe cleanup-forms will be evaluated if control leavesbody-form, no matter how that happens. body-form maycomplete normally, or execute a throw out of theunwind-protect, or cause an error; in all cases, thecleanup-forms will be evaluated.If body-form finishes normally, unwind-protect returns thevalue of body-form, after it evaluates the cleanup-forms.If body-form does not finish, unwind-protect does notreturn any value in the normal sense.Only body-form is protected by the unwind-protect. If anyof the cleanup-forms themselves exits nonlocally (via athrow or an error), unwind-protect is notguaranteed to evaluate the rest of them. If the failure of one of thecleanup-forms has the potential to cause trouble, then protectit with another unwind-protect around that form.The number of currently active unwind-protect forms counts,together with the number of local variable bindings, against the limitmax-specpdl-size (see Local Variables). For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing: (save-excursion (let ((buffer (get-buffer-create " *temp*"))) (set-buffer buffer) (unwind-protect body-form (kill-buffer buffer)))) You might think that we could just as well write (kill-buffer (current-buffer)) and dispense with the variable buffer. However, the way shown above is safer, if body-form happens to get an error after switching to a different buffer! (Alternatively, you could write another save-excursion around body-form, to ensure that the temporary buffer becomes current again in time to kill it.) Emacs includes a standard macro called with-temp-buffer which expands into more or less the code shown above (see Current Buffer). Several of the macros defined in this manual use unwind-protect in this way. ftp-login Here is an actual example derived from an FTP package. It creates a process (see ) to try to establish a connection to a remote machine. As the function ftp-login is highly susceptible to numerous problems that the writer of the function cannot anticipate, it is protected with a form that guarantees deletion of the process in the event of failure. Otherwise, Emacs might fill up with useless subprocesses. (let ((win nil)) (unwind-protect (progn (setq process (ftp-setup-buffer host file)) (if (setq win (ftp-login process host user password)) (message "Logged in") (error "Ftp login failed"))) (or win (and process (delete-process process))))) This example has a small bug: if the user types C-g to quit, and the quit happens immediately after the function ftp-setup-buffer returns but before the variable process is set, the process will not be killed. There is no easy way to fix this bug, but at least it is very unlikely. <setfilename>../info/variables</setfilename> Variables variable A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols. In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See . The Lisp objects that constitute a Lisp program determine the textual form of the program—it is simply the read syntax for those Lisp objects. This is why, for example, a variable in a textual Lisp program is written using the read syntax for the symbol that represents the variable. Global Variables global variable The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable. You specify a value for a symbol with setq. For example, (setq x '(a b)) gives the variable x the value (a b). Note that setq does not evaluate its first argument, the name of the variable, but it does evaluate the second argument, the new value. Once the variable has a value, you can refer to it by using the symbol by itself as an expression. Thus, x => (a b) assuming the setq form shown above has already been executed. If you do set the same variable again, the new value replaces the old one: x => (a b) (setq x 4) => 4 x => 4 Variables that Never Change setting-constant keyword symbol variable with constant value constant variables symbol that evaluates to itself symbol with constant value In Emacs Lisp, certain symbols normally evaluate to themselves. These include nil and t, as well as any symbol whose name starts with ‘:’ (these are called keywords). These symbols cannot be rebound, nor can their values be changed. Any attempt to set or bind nil or t signals a setting-constant error. The same is true for a keyword (a symbol whose name starts with ‘:’), if it is interned in the standard obarray, except that setting such a symbol to itself is not an error. nil == 'nil => nil (setq nil 500) error--> Attempt to set constant symbol: nil keywordp — Function: keywordp object function returns t if object is a symbol whose namestarts with ‘:’, interned in the standard obarray, and returnsnil otherwise. Local Variables binding local variables local variables local binding global binding Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily—only until a certain part of the program finishes. These values are called local, and the variables so used are called local variables. For example, when a function is called, its argument variables receive new local values that last until the function exits. The let special form explicitly establishes new local values for specified variables; these last until exit from the let form. shadowing of variables Establishing a local value saves away the previous value (or lack of one) of the variable. When the life span of the local value is over, the previous value is restored. In the mean time, we say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see ). If you set a variable (such as with setq) while it is local, this replaces the local value; it does not alter the global value, or previous local values, that are shadowed. To model this behavior, we speak of a local binding of the variable as well as a local value. The local binding is a conceptual place that holds a local value. Entry to a function, or a special form such as let, creates the local binding; exit from the function or from the let removes the local binding. As long as the local binding lasts, the variable's value is stored within it. Use of setq or set while there is a local binding stores a different value into the local binding; it does not create a new binding. We also speak of the global binding, which is where (conceptually) the global value is kept. current binding A variable can have more than one local binding at a time (for example, if there are nested let forms that bind it). In such a case, the most recently created local binding that still exists is the current binding of the variable. (This rule is called dynamic scoping; see .) If there are no local bindings, the variable's global binding is its current binding. We sometimes call the current binding the most-local existing binding, for emphasis. Ordinary evaluation of a symbol always returns the value of its current binding. The special forms let and let* exist to create local bindings. let — Special Form: let ( bindings … ) forms … This special form binds variables according to bindings and thenevaluates all of the forms in textual order. The let-formreturns the value of the last form in forms.Each of the bindings is either (i) a symbol, in which casethat symbol is bound to nil; or (ii) a list of the form(symbol value-form), in which case symbol isbound to the result of evaluating value-form. If value-formis omitted, nil is used.All of the value-forms in bindings are evaluated in theorder they appear and before binding any of the symbols to them.Here is an example of this: z is bound to the old value ofy, which is 2, not the new value of y, which is 1. (setq y 2) => 2 (let ((y 1) (z y)) (list y z)) => (1 2) let* — Special Form: let* ( bindings … ) forms … This special form is like let, but it binds each variable rightafter computing its local value, before computing the local value forthe next variable. Therefore, an expression in bindings canreasonably refer to the preceding symbols bound in this let*form. Compare the following example with the example above forlet. (setq y 2) => 2 (let* ((y 1) (z y)) ; Use the just-established value of y. (list y z)) => (1 1) Here is a complete list of the other facilities that create local bindings: Function calls (see ). Macro calls (see ). condition-case (see ). Variables can also have buffer-local bindings (see ) and frame-local bindings (see ); a few variables have terminal-local bindings (see ). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on “where” you are in Emacs, rather than localized in time. max-specpdl-size — Variable: max-specpdl-size variable limit error evaluation error infinite recursionThis variable defines the limit on the total number of local variablebindings and unwind-protect cleanups (see Cleaning Up from Nonlocal Exits) that are allowed before signaling anerror (with data "Variable binding depth exceedsmax-specpdl-size").This limit, with the associated error when it is exceeded, is one waythat Lisp avoids infinite recursion on an ill-defined function.max-lisp-eval-depth provides another limit on depth of nesting.See Eval.The default value is 1000. Entry to the Lisp debugger increases thevalue, if there is little room left, to make sure the debugger itselfhas room to execute. When a Variable is “Void” void-variable void variable If you have never given a symbol any value as a global variable, we say that that symbol's global value is void. In other words, the symbol's value cell does not have any Lisp object in it. If you try to evaluate the symbol, you get a void-variable error rather than a value. Note that a value of nil is not the same as void. The symbol nil is a Lisp object and can be the value of a variable just as any other object can be; but it is a value. A void variable does not have any value. After you have given a variable a value, you can make it void once more using makunbound. makunbound — Function: makunbound symbol This function makes the current variable binding of symbol void.Subsequent attempts to use this symbol's value as a variable will signalthe error void-variable, unless and until you set it again.makunbound returns symbol. (makunbound 'x) ; Make the global value of x void. => x x error--> Symbol's value as variable is void: x If symbol is locally bound, makunbound affects the mostlocal existing binding. This is the only way a symbol can have a voidlocal binding, since all the constructs that create local bindingscreate them with values. In this case, the voidness lasts at most aslong as the binding does; when the binding is removed due to exit fromthe construct that made it, the previous local or global binding isreexposed as usual, and the variable is no longer void unless the newlyreexposed binding was void all along. (setq x 1) ; Put a value in the global binding. => 1 (let ((x 2)) ; Locally bind it. (makunbound 'x) ; Void the local binding. x) error--> Symbol's value as variable is void: x x ; The global binding is unchanged. => 1 (let ((x 2)) ; Locally bind it. (let ((x 3)) ; And again. (makunbound 'x) ; Void the innermost-local binding. x)) ; And refer: it's void. error--> Symbol's value as variable is void: x (let ((x 2)) (let ((x 3)) (makunbound 'x)) ; Void inner binding, then remove it. x) ; Now outer let binding is visible. => 2 A variable that has been made void with makunbound is indistinguishable from one that has never received a value and has always been void. You can use the function boundp to test whether a variable is currently void. boundp — Function: boundp variable boundp returns t if variable (a symbol) is not void;more precisely, if its current binding is not void. It returnsnil otherwise. (boundp 'abracadabra) ; Starts out void. => nil (let ((abracadabra 5)) ; Locally bind it. (boundp 'abracadabra)) => t (boundp 'abracadabra) ; Still globally void. => nil (setq abracadabra 5) ; Make it globally nonvoid. => 5 (boundp 'abracadabra) => t Defining Global Variables variable definition You may announce your intention to use a symbol as a global variable with a variable definition: a special form, either defconst or defvar. In Emacs Lisp, definitions serve three purposes. First, they inform people who read the code that certain symbols are intended to be used a certain way (as variables). Second, they inform the Lisp system of these things, supplying a value and documentation. Third, they provide information to utilities such as etags and make-docfile, which create data bases of the functions and variables in a program. The difference between defconst and defvar is primarily a matter of intent, serving to inform human readers of whether the value should ever change. Emacs Lisp does not restrict the ways in which a variable can be used based on defconst or defvar declarations. However, it does make a difference for initialization: defconst unconditionally initializes the variable, while defvar initializes it only if it is void. defvar — Special Form: defvar symbol [ value [ doc-string ] ] This special form defines symbol as a variable and can alsoinitialize and document it. The definition informs a person readingyour code that symbol is used as a variable that might be set orchanged. Note that symbol is not evaluated; the symbol to bedefined must appear explicitly in the defvar.If symbol is void and value is specified, defvarevaluates it and sets symbol to the result. But if symbolalready has a value (i.e., it is not void), value is not evenevaluated, and symbol's value remains unchanged. If valueis omitted, the value of symbol is not changed in any case.If symbol has a buffer-local binding in the current buffer,defvar operates on the default value, which is buffer-independent,not the current (buffer-local) binding. It sets the default value ifthe default value is void. See .When you evaluate a top-level defvar form with C-M-x inEmacs Lisp mode (eval-defun), a special feature ofeval-defun arranges to set the variable unconditionally, withouttesting whether its value is void.If the doc-string argument appears, it specifies the documentationfor the variable. (This opportunity to specify documentation is one ofthe main benefits of defining the variable.) The documentation isstored in the symbol's variable-documentation property. TheEmacs help functions (see ) look for this property.If the variable is a user option that users would want to setinteractively, you should use ‘*’ as the first character ofdoc-string. This lets users set the variable conveniently usingthe set-variable command. Note that you should nearly alwaysuse defcustom instead of defvar to define thesevariables, so that users can use M-x customize and relatedcommands to set them. See .Here are some examples. This form defines foo but does notinitialize it: (defvar foo) => foo This example initializes the value of bar to 23, and givesit a documentation string: (defvar bar 23 "The normal weight of a bar.") => bar The following form changes the documentation string for bar,making it a user option, but does not change the value, since baralready has a value. (The addition (1+ nil) would get an errorif it were evaluated, but since it is not evaluated, there is no error.) (defvar bar (1+ nil) "*The normal weight of a bar.") => bar bar => 23 Here is an equivalent expression for the defvar special form: (defvar symbol value doc-string) == (progn (if (not (boundp 'symbol)) (setq symbol value)) (if 'doc-string (put 'symbol 'variable-documentation 'doc-string)) 'symbol) The defvar form returns symbol, but it is normally usedat top level in a file where its value does not matter. defconst — Special Form: defconst symbol value [ doc-string ] This special form defines symbol as a value and initializes it.It informs a person reading your code that symbol has a standardglobal value, established here, that should not be changed by the useror by other programs. Note that symbol is not evaluated; thesymbol to be defined must appear explicitly in the defconst.defconst always evaluates value, and sets the value ofsymbol to the result. If symbol does have a buffer-localbinding in the current buffer, defconst sets the default value,not the buffer-local value. (But you should not be makingbuffer-local bindings for a symbol that is defined withdefconst.)Here, pi is a constant that presumably ought not to be changedby anyone (attempts by the Indiana State Legislature notwithstanding).As the second form illustrates, however, this is only advisory. (defconst pi 3.1415 "Pi to five places.") => pi (setq pi 3) => pi pi => 3 user-variable-p — Function: user-variable-p variable user optionThis function returns t if variable is a user option—avariable intended to be set by the user for customization—andnil otherwise. (Variables other than user options exist for theinternal purposes of Lisp programs, and users need not know about them.)User option variables are distinguished from other variables eitherthough being declared using defcustom They may also bedeclared equivalently in cus-start.el. or by the first characterof their variable-documentation property. If the property existsand is a string, and its first character is ‘*’, then the variableis a user option. Aliases of user options are also user options. variable-interactive If a user option variable has a variable-interactive property, the set-variable command uses that value to control reading the new value for the variable. The property's value is used as if it were specified in interactive (see ). However, this feature is largely obsoleted by defcustom (see ). Warning: If the defconst and defvar special forms are used while the variable has a local binding (made with let, or a function argument), they set the local-binding's value; the top-level binding is not changed. This is not what you usually want. To prevent it, use these special forms at top level in a file, where normally no local binding is in effect, and make sure to load the file before making a local binding for the variable. Tips for Defining Variables Robustly When you define a variable whose value is a function, or a list of functions, use a name that ends in ‘-function’ or ‘-functions’, respectively. There are several other variable name conventions; here is a complete list: ‘…-hook’ The variable is a normal hook (see ). ‘…-function’ The value is a function. ‘…-functions’ The value is a list of functions. ‘…-form’ The value is a form (an expression). ‘…-forms’ The value is a list of forms (expressions). ‘…-predicate’ The value is a predicate—a function of one argument that returnsnon-nil for “good” arguments and nil for “bad”arguments. ‘…-flag’ The value is significant only as to whether it is nil or not. ‘…-program’ The value is a program name. ‘…-command’ The value is a whole shell command. ‘…-switches’ The value specifies options for a command. When you define a variable, always consider whether you should mark it as “risky”; see . When defining and initializing a variable that holds a complicated value (such as a keymap with bindings in it), it's best to put the entire computation of the value into the defvar, like this: (defvar my-mode-map (let ((map (make-sparse-keymap))) (define-key map "\C-c\C-a" 'my-command) … map) docstring) This method has several benefits. First, if the user quits while loading the file, the variable is either still uninitialized or initialized properly, never in-between. If it is still uninitialized, reloading the file will initialize it properly. Second, reloading the file once the variable is initialized will not alter it; that is important if the user has run hooks to alter part of the contents (such as, to rebind keys). Third, evaluating the defvar form with C-M-x will reinitialize the map completely. Putting so much code in the defvar form has one disadvantage: it puts the documentation string far away from the line which names the variable. Here's a safe way to avoid that: (defvar my-mode-map nil docstring) (unless my-mode-map (let ((map (make-sparse-keymap))) (define-key map "\C-c\C-a" 'my-command) … (setq my-mode-map map))) This has all the same advantages as putting the initialization inside the defvar, except that you must type C-M-x twice, once on each form, if you do want to reinitialize the variable. But be careful not to write the code like this: (defvar my-mode-map nil docstring) (unless my-mode-map (setq my-mode-map (make-sparse-keymap)) (define-key my-mode-map "\C-c\C-a" 'my-command) …) This code sets the variable, then alters it, but it does so in more than one step. If the user quits just after the setq, that leaves the variable neither correctly initialized nor void nor nil. Once that happens, reloading the file will not initialize the variable; it will remain incomplete. Accessing Variable Values The usual way to reference a variable is to write the symbol which names it (see ). This requires you to specify the variable name when you write the program. Usually that is exactly what you want to do. Occasionally you need to choose at run time which variable to reference; then you can use symbol-value. symbol-value — Function: symbol-value symbol This function returns the value of symbol. This is the value inthe innermost local binding of the symbol, or its global value if ithas no local bindings. (setq abracadabra 5) => 5 (setq foo 9) => 9 ;; Here the symbol abracadabra ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value 'abracadabra)) => foo ;; Here, the value of abracadabra, ;; which is foo, ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value abracadabra)) => 9 (symbol-value 'abracadabra) => 5 A void-variable error is signaled if the current binding ofsymbol is void. How to Alter a Variable Value The usual way to change the value of a variable is with the special form setq. When you need to compute the choice of variable at run time, use the function set. setq — Special Form: setq [ symbol form ] … This special form is the most common method of changing a variable'svalue. Each symbol is given a new value, which is the result ofevaluating the corresponding form. The most-local existingbinding of the symbol is changed.setq does not evaluate symbol; it sets the symbol that youwrite. We say that this argument is automatically quoted. The‘q’ in setq stands for “quoted.”The value of the setq form is the value of the last form. (setq x (1+ 2)) => 3 x ; x now has a global value. => 3 (let ((x 5)) (setq x 6) ; The local binding of x is set. x) => 6 x ; The global value is unchanged. => 3 Note that the first form is evaluated, then the firstsymbol is set, then the second form is evaluated, then thesecond symbol is set, and so on: (setq x 10 ; Notice that x is set before y (1+ x)) ; the value of y is computed. => 11 set — Function: set symbol value This function sets symbol's value to value, then returnsvalue. Since set is a function, the expression written forsymbol is evaluated to obtain the symbol to set.The most-local existing binding of the variable is the binding that isset; shadowed bindings are not affected. (set one 1) error--> Symbol's value as variable is void: one (set 'one 1) => 1 (set 'two 'one) => one (set two 2) ; two evaluates to symbol one. => 2 one ; So it is one that was set. => 2 (let ((one 1)) ; This binding of one is set, (set 'one 3) ; not the global value. one) => 3 one => 2 If symbol is not actually a symbol, a wrong-type-argumenterror is signaled. (set '(x y) 'z) error--> Wrong type argument: symbolp, (x y) Logically speaking, set is a more fundamental primitive thansetq. Any use of setq can be trivially rewritten to useset; setq could even be defined as a macro, given theavailability of set. However, set itself is rarely used;beginners hardly need to know about it. It is useful only for choosingat run time which variable to set. For example, the commandset-variable, which reads a variable name from the user and thensets the variable, needs to use set. CL note—set local Common Lisp note: In Common Lisp, set always changes the symbol's “special” or dynamic value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are dynamic, so set always affects the most local existing binding. Scoping Rules for Variable Bindings A given symbol foo can have several local variable bindings, established at different places in the Lisp program, as well as a global binding. The most recently established binding takes precedence over the others. scope extent dynamic scoping lexical scoping Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. “Indefinite scope” means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. “Dynamic extent” means that the binding lasts as long as the activation of the construct that established it. The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be located textually within the function or block that binds the variable. CL note—special variables Common Lisp note: Variables declared “special” in Common Lisp are dynamically scoped, like all variables in Emacs Lisp. Scope Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions: (defun binder (x) ; x is bound in binder. (foo 5)) ; foo is some other function. (defun user () ; x is used ``free'' in user. (list x)) In a lexically scoped language, the binding of x in binder would never be accessible in user, because user is not textually contained within the function binder. However, in dynamically-scoped Emacs Lisp, user may or may not refer to the binding of x established in binder, depending on the circumstances: If we call user directly without calling binder at all,then whatever binding of x is found, it cannot come frombinder. If we define foo as follows and then call binder, then thebinding made in binder will be seen in user: (defun foo (lose) (user)) However, if we define foo as follows and then call binder,then the binding made in binder will not be seen inuser: (defun foo (x) (user)) Here, when foo is called by binder, it binds x.(The binding in foo is said to shadow the one made inbinder.) Therefore, user will access the x boundby foo instead of the one bound by binder. Emacs Lisp uses dynamic scoping because simple implementations of lexical scoping are slow. In addition, every Lisp system needs to offer dynamic scoping at least as an option; if lexical scoping is the norm, there must be a way to specify dynamic scoping instead for a particular variable. It might not be a bad thing for Emacs to offer both, but implementing it with dynamic scoping only was much easier. Extent Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. “Local” or “automatic” variables in most languages, including C and Pascal, have dynamic extent. One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not. To illustrate this, the function below, make-add, returns a function that purports to add n to its own argument m. This would work in Common Lisp, but it does not do the job in Emacs Lisp, because after the call to make-add exits, the variable n is no longer bound to the actual argument 2. (defun make-add (n) (function (lambda (m) (+ n m)))) ; Return a function. => make-add (fset 'add2 (make-add 2)) ; Define function add2 ; with (make-add 2). => (lambda (m) (+ n m)) (add2 4) ; Try to add 2 to 4. error--> Symbol's value as variable is void: n closures not available Some Lisp dialects have “closures,” objects that are like functions but record additional variable bindings. Emacs Lisp does not have closures. Implementation of Dynamic Scoping deep binding A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems. Suppose there is a stack of bindings, which are variable-value pairs. At entry to a function or to a let form, we can push bindings onto the stack for the arguments or local variables created there. We can pop those bindings from the stack at exit from the binding construct. We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding. As you can see, a function's bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite. shallow binding The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found—the value cell of the symbol. In shallow binding, setting the variable works by storing a value in the value cell. Creating a new binding works by pushing the old value (belonging to a previous binding) onto a stack, and storing the new local value in the value cell. Eliminating a binding works by popping the old value off the stack, into the value cell. We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding. Proper Use of Dynamic Scoping Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique: Use or bind the variable only in a few related functions, written closetogether in one file. Such a variable is used for communication withinone program.You should write comments to inform other programmers that they can seeall uses of the variable before them, and to advise them not to add useselsewhere. Give the variable a well-defined, documented meaning, and make allappropriate functions refer to it (but not bind it or set it) whereverthat meaning is relevant. For example, the variablecase-fold-search is defined as “non-nil means ignore casewhen searching”; various search and replace functions refer to itdirectly or through their subroutines, but do not bind or set it.Then you can bind the variable in other programs, knowing reliably whatthe effect will be. In either case, you should define the variable with defvar. This helps other people understand your program by telling them to look for inter-function usage. It also avoids a warning from the byte compiler. Choose the variable's name to avoid name conflicts—don't use short names like x. Buffer-Local Variables variable, buffer-local buffer-local variables Global and local variable bindings are found in most programming languages in one form or another. Emacs, however, also supports additional, unusual kinds of variable binding: buffer-local bindings, which apply only in one buffer, and frame-local bindings, which apply only in one frame. Having different values for a variable in different buffers and/or frames is an important customization method. This section describes buffer-local bindings; for frame-local bindings, see the following section, . (A few variables have bindings that are local to each terminal; see .) Introduction to Buffer-Local Variables A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so its other bindings are unchanged. This means that the change is visible only in the buffer where you made it. The variable's ordinary binding, which is not associated with any specific buffer, is called the default binding. In most cases, this is the global binding. A variable can have buffer-local bindings in some buffers but not in other buffers. The default binding is shared by all the buffers that don't have their own bindings for the variable. (This includes all newly-created buffers.) If you set the variable in a buffer that does not have a buffer-local binding for it, this sets the default binding (assuming there are no frame-local bindings to complicate the matter), so the new value is visible in all the buffers that see the default binding. The most common use of buffer-local bindings is for major modes to change variables that control the behavior of commands. For example, C mode and Lisp mode both set the variable paragraph-start to specify that only blank lines separate paragraphs. They do this by making the variable buffer-local in the buffer that is being put into C mode or Lisp mode, and then setting it to the new value for that mode. See . The usual way to make a buffer-local binding is with make-local-variable, which is what major mode commands typically use. This affects just the current buffer; all other buffers (including those yet to be created) will continue to share the default value unless they are explicitly given their own buffer-local bindings. automatically buffer-local A more powerful operation is to mark the variable as automatically buffer-local by calling make-variable-buffer-local. You can think of this as making the variable local in all buffers, even those yet to be created. More precisely, the effect is that setting the variable automatically makes the variable local to the current buffer if it is not already so. All buffers start out by sharing the default value of the variable as usual, but setting the variable creates a buffer-local binding for the current buffer. The new value is stored in the buffer-local binding, leaving the default binding untouched. This means that the default value cannot be changed with setq in any buffer; the only way to change it is with setq-default. Warning: When a variable has buffer-local or frame-local bindings in one or more buffers, let rebinds the binding that's currently in effect. For instance, if the current buffer has a buffer-local value, let temporarily rebinds that. If no buffer-local or frame-local bindings are in effect, let rebinds the default value. If inside the let you then change to a different current buffer in which a different binding is in effect, you won't see the let binding any more. And if you exit the let while still in the other buffer, you won't see the unbinding occur (though it will occur properly). Here is an example to illustrate: (setq foo 'g) (set-buffer "a") (make-local-variable 'foo) (setq foo 'a) (let ((foo 'temp)) ;; foo => 'temp ; let binding in buffer ‘a’ (set-buffer "b") ;; foo => 'g ; the global value since foo is not local in ‘b’ body…) foo => 'g ; exiting restored the local value in buffer ‘a’, ; but we don't see that in buffer ‘b’ (set-buffer "a") ; verify the local value was restored foo => 'a Note that references to foo in body access the buffer-local binding of buffer ‘b’. When a file specifies local variable values, these become buffer-local values when you visit the file. See See section ``File Variables'' in The GNU Emacs Manual. Creating and Deleting Buffer-Local Bindings make-local-variable — Command: make-local-variable variable This function creates a buffer-local binding in the current buffer forvariable (a symbol). Other buffers are not affected. The valuereturned is variable. The buffer-local value of variable starts out as the same valuevariable previously had. If variable was void, it remainsvoid. ;; In buffer ‘b1’: (setq foo 5) ; Affects all buffers. => 5 (make-local-variable 'foo) ; Now it is local in ‘b1’. => foo foo ; That did not change => 5 ; the value. (setq foo 6) ; Change the value => 6 ; in ‘b1’. foo => 6 ;; In buffer ‘b2’, the value hasn't changed. (save-excursion (set-buffer "b2") foo) => 5 Making a variable buffer-local within a let-binding for thatvariable does not work reliably, unless the buffer in which you do thisis not current either on entry to or exit from the let. This isbecause let does not distinguish between different kinds ofbindings; it knows only which variable the binding was made for.If the variable is terminal-local, this function signals an error. Suchvariables cannot have buffer-local bindings as well. See .Warning: do not use make-local-variable for a hookvariable. The hook variables are automatically made buffer-local asneeded if you use the local argument to add-hook orremove-hook. make-variable-buffer-local — Command: make-variable-buffer-local variable This function marks variable (a symbol) automaticallybuffer-local, so that any subsequent attempt to set it will make itlocal to the current buffer at the time.A peculiar wrinkle of this feature is that binding the variable (withlet or other binding constructs) does not create a buffer-localbinding for it. Only setting the variable (with set orsetq), while the variable does not have a let-stylebinding that was made in the current buffer, does so.If variable does not have a default value, then calling thiscommand will give it a default value of nil. If variablealready has a default value, that value remains unchanged.Subsequently calling makunbound on variable will resultin a void buffer-local value and leave the default value unaffected.The value returned is variable.Warning: Don't assume that you should usemake-variable-buffer-local for user-option variables, simplybecause users might want to customize them differently indifferent buffers. Users can make any variable local, when they wishto. It is better to leave the choice to them.The time to use make-variable-buffer-local is when it is crucialthat no two buffers ever share the same binding. For example, when avariable is used for internal purposes in a Lisp program which dependson having separate values in separate buffers, then usingmake-variable-buffer-local can be the best solution. local-variable-p — Function: local-variable-p variable &optional buffer This returns t if variable is buffer-local in bufferbuffer (which defaults to the current buffer); otherwise,nil. local-variable-if-set-p — Function: local-variable-if-set-p variable &optional buffer This returns t if variable will become buffer-local inbuffer buffer (which defaults to the current buffer) if it isset there. buffer-local-value — Function: buffer-local-value variable buffer This function returns the buffer-local binding of variable (asymbol) in buffer buffer. If variable does not have abuffer-local binding in buffer buffer, it returns the defaultvalue (see ) of variable instead. buffer-local-variables — Function: buffer-local-variables &optional buffer This function returns a list describing the buffer-local variables inbuffer buffer. (If buffer is omitted, the current buffer isused.) It returns an association list (see ) inwhich each element contains one buffer-local variable and its value.However, when a variable's buffer-local binding in buffer is void,then the variable appears directly in the resulting list. (make-local-variable 'foobar) (makunbound 'foobar) (make-local-variable 'bind-me) (setq bind-me 69) (setq lcl (buffer-local-variables)) ;; First, built-in variables local in all buffers: => ((mark-active . nil) (buffer-undo-list . nil) (mode-name . "Fundamental") … ;; Next, non-built-in buffer-local variables. ;; This one is buffer-local and void: foobar ;; This one is buffer-local and nonvoid: (bind-me . 69)) Note that storing new values into the cdrs of cons cells in thislist does not change the buffer-local values of the variables. kill-local-variable — Command: kill-local-variable variable This function deletes the buffer-local binding (if any) forvariable (a symbol) in the current buffer. As a result, thedefault binding of variable becomes visible in this buffer. Thistypically results in a change in the value of variable, since thedefault value is usually different from the buffer-local value justeliminated.If you kill the buffer-local binding of a variable that automaticallybecomes buffer-local when set, this makes the default value visible inthe current buffer. However, if you set the variable again, that willonce again create a buffer-local binding for it.kill-local-variable returns variable.This function is a command because it is sometimes useful to kill onebuffer-local variable interactively, just as it is useful to createbuffer-local variables interactively. kill-all-local-variables — Function: kill-all-local-variables This function eliminates all the buffer-local variable bindings of thecurrent buffer except for variables marked as “permanent.” As aresult, the buffer will see the default values of most variables.This function also resets certain other information pertaining to thebuffer: it sets the local keymap to nil, the syntax table to thevalue of (standard-syntax-table), the case table to(standard-case-table), and the abbrev table to the value offundamental-mode-abbrev-table.The very first thing this function does is run the normal hookchange-major-mode-hook (see below).Every major mode command begins by calling this function, which has theeffect of switching to Fundamental mode and erasing most of the effectsof the previous major mode. To ensure that this does its job, thevariables that major modes set should not be marked permanent.kill-all-local-variables returns nil. change-major-mode-hook — Variable: change-major-mode-hook The function kill-all-local-variables runs this normal hookbefore it does anything else. This gives major modes a way to arrangefor something special to be done if the user switches to a differentmajor mode. It is also useful for buffer-specific minor modesthat should be forgotten if the user changes the major mode.For best results, make this variable buffer-local, so that it willdisappear after doing its job and will not interfere with thesubsequent major mode. See . permanent local variable A buffer-local variable is permanent if the variable name (a symbol) has a permanent-local property that is non-nil. Permanent locals are appropriate for data pertaining to where the file came from or how to save it, rather than with how to edit the contents. The Default Value of a Buffer-Local Variable default value The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable. The functions default-value and setq-default access and change a variable's default value regardless of whether the current buffer has a buffer-local binding. For example, you could use setq-default to change the default setting of paragraph-start for most buffers; and this would work even when you are in a C or Lisp mode buffer that has a buffer-local value for this variable. The special forms defvar and defconst also set the default value (if they set the variable at all), rather than any buffer-local or frame-local value. default-value — Function: default-value symbol This function returns symbol's default value. This is the valuethat is seen in buffers and frames that do not have their own values forthis variable. If symbol is not buffer-local, this is equivalentto symbol-value (see ). default-boundp — Function: default-boundp symbol The function default-boundp tells you whether symbol'sdefault value is nonvoid. If (default-boundp 'foo) returnsnil, then (default-value 'foo) would get an error.default-boundp is to default-value as boundp is tosymbol-value. setq-default — Special Form: setq-default [ symbol form ] … This special form gives each symbol a new default value, which isthe result of evaluating the corresponding form. It does notevaluate symbol, but does evaluate form. The value of thesetq-default form is the value of the last form.If a symbol is not buffer-local for the current buffer, and is notmarked automatically buffer-local, setq-default has the sameeffect as setq. If symbol is buffer-local for the currentbuffer, then this changes the value that other buffers will see (as longas they don't have a buffer-local value), but not the value that thecurrent buffer sees. ;; In buffer ‘foo’: (make-local-variable 'buffer-local) => buffer-local (setq buffer-local 'value-in-foo) => value-in-foo (setq-default buffer-local 'new-default) => new-default buffer-local => value-in-foo (default-value 'buffer-local) => new-default ;; In (the new) buffer ‘bar’: buffer-local => new-default (default-value 'buffer-local) => new-default (setq buffer-local 'another-default) => another-default (default-value 'buffer-local) => another-default ;; Back in buffer ‘foo’: buffer-local => value-in-foo (default-value 'buffer-local) => another-default set-default — Function: set-default symbol value This function is like setq-default, except that symbol isan ordinary evaluated argument. (set-default (car '(a b c)) 23) => 23 (default-value 'a) => 23 Frame-Local Variables frame-local variables Just as variables can have buffer-local bindings, they can also have frame-local bindings. These bindings belong to one frame, and are in effect when that frame is selected. Frame-local bindings are actually frame parameters: you create a frame-local binding in a specific frame by calling modify-frame-parameters and specifying the variable name as the parameter name. To enable frame-local bindings for a certain variable, call the function make-variable-frame-local. make-variable-frame-local — Command: make-variable-frame-local variable Enable the use of frame-local bindings for variable. This doesnot in itself create any frame-local bindings for the variable; however,if some frame already has a value for variable as a frameparameter, that value automatically becomes a frame-local binding.If variable does not have a default value, then calling thiscommand will give it a default value of nil. If variablealready has a default value, that value remains unchanged.If the variable is terminal-local, this function signals an error,because such variables cannot have frame-local bindings as well.See . A few variables that are implementedspecially in Emacs can be buffer-local, but can never be frame-local.This command returns variable. Buffer-local bindings take precedence over frame-local bindings. Thus, consider a variable foo: if the current buffer has a buffer-local binding for foo, that binding is active; otherwise, if the selected frame has a frame-local binding for foo, that binding is active; otherwise, the default binding of foo is active. Here is an example. First we prepare a few bindings for foo: (setq f1 (selected-frame)) (make-variable-frame-local 'foo) ;; Make a buffer-local binding for foo in ‘b1’. (set-buffer (get-buffer-create "b1")) (make-local-variable 'foo) (setq foo '(b 1)) ;; Make a frame-local binding for foo in a new frame. ;; Store that frame in f2. (setq f2 (make-frame)) (modify-frame-parameters f2 '((foo . (f 2)))) Now we examine foo in various contexts. Whenever the buffer ‘b1’ is current, its buffer-local binding is in effect, regardless of the selected frame: (select-frame f1) (set-buffer (get-buffer-create "b1")) foo => (b 1) (select-frame f2) (set-buffer (get-buffer-create "b1")) foo => (b 1) Otherwise, the frame gets a chance to provide the binding; when frame f2 is selected, its frame-local binding is in effect: (select-frame f2) (set-buffer (get-buffer "*scratch*")) foo => (f 2) When neither the current buffer nor the selected frame provides a binding, the default binding is used: (select-frame f1) (set-buffer (get-buffer "*scratch*")) foo => nil When the active binding of a variable is a frame-local binding, setting the variable changes that binding. You can observe the result with frame-parameters: (select-frame f2) (set-buffer (get-buffer "*scratch*")) (setq foo 'nobody) (assq 'foo (frame-parameters f2)) => (foo . nobody) Possible Future Local Variables We have considered the idea of bindings that are local to a category of frames—for example, all color frames, or all frames with dark backgrounds. We have not implemented them because it is not clear that this feature is really useful. You can get more or less the same results by adding a function to after-make-frame-functions, set up to define a particular frame parameter according to the appropriate conditions for each frame. It would also be possible to implement window-local bindings. We don't know of many situations where they would be useful, and it seems that indirect buffers (see ) with buffer-local bindings offer a way to handle these situations more robustly. If sufficient application is found for either of these two kinds of local bindings, we will provide it in a subsequent Emacs version. File Local Variables file local variables A file can specify local variable values; Emacs uses these to create buffer-local bindings for those variables in the buffer visiting that file. See See section ``Local Variables in Files'' in The GNU Emacs Manual, for basic information about file local variables. This section describes the functions and variables that affect processing of file local variables. enable-local-variables — User Option: enable-local-variables This variable controls whether to process file local variables.The possible values are: t (the default) Set the safe variables, and query (once) about any unsafe variables. :safe Set only the safe variables and do not query. :all Set all the variables and do not query. nil Don't set any variables. anything else Query (once) about all the variables. hack-local-variables — Function: hack-local-variables &optional mode-only This function parses, and binds or evaluates as appropriate, any localvariables specified by the contents of the current buffer. The variableenable-local-variables has its effect here. However, thisfunction does not look for the ‘mode:’ local variable in the‘-*-’ line. set-auto-mode does that, also takingenable-local-variables into account (see ).If the optional argument mode-only is non-nil, then allthis function does is return t if the ‘-*-’ line orthe local variables list specifies a mode and nil otherwise.It does not set the mode nor any other file local variable. If a file local variable could specify a function that would be called later, or an expression that would be executed later, simply visiting a file could take over your Emacs. Emacs takes several measures to prevent this. safe local variable You can specify safe values for a variable with a safe-local-variable property. The property has to be a function of one argument; any value is safe if the function returns non-nil given that value. Many commonly encountered file variables standardly have safe-local-variable properties, including fill-column, fill-prefix, and indent-tabs-mode. For boolean-valued variables that are safe, use booleanp as the property value. Lambda expressions should be quoted so that describe-variable can display the predicate. safe-local-variable-values — User Option: safe-local-variable-values This variable provides another way to mark some variable values assafe. It is a list of cons cells (var . val),where var is a variable name and val is a value which issafe for that variable.When Emacs asks the user whether or not to obey a set of file localvariable specifications, the user can choose to mark them as safe.Doing so adds those variable/value pairs tosafe-local-variable-values, and saves it to the user's customfile. safe-local-variable-p — Function: safe-local-variable-p sym val This function returns non-nil if it is safe to give symthe value val, based on the above criteria. Some variables are considered risky. A variable whose name ends in any of ‘-command’, ‘-frame-alist’, ‘-function’, ‘-functions’, ‘-hook’, ‘-hooks’, ‘-form’, ‘-forms’, ‘-map’, ‘-map-alist’, ‘-mode-alist’, ‘-program’, or ‘-predicate’ is considered risky. The variables ‘font-lock-keywords’, ‘font-lock-keywords’ followed by a digit, and ‘font-lock-syntactic-keywords’ are also considered risky. Finally, any variable whose name has a non-nil risky-local-variable property is considered risky. risky-local-variable-p — Function: risky-local-variable-p sym This function returns non-nil if sym is a risky variable,based on the above criteria. If a variable is risky, it will not be entered automatically into safe-local-variable-values as described above. Therefore, Emacs will always query before setting a risky variable, unless the user explicitly allows the setting by customizing safe-local-variable-values directly. ignored-local-variables — Variable: ignored-local-variables This variable holds a list of variables that should not be given localvalues by files. Any value specified for one of these variables iscompletely ignored. The ‘Eval:’ “variable” is also a potential loophole, so Emacs normally asks for confirmation before handling it. enable-local-eval — User Option: enable-local-eval This variable controls processing of ‘Eval:’ in ‘-*-’ linesor local variableslists in files being visited. A value of t means process themunconditionally; nil means ignore them; anything else means askthe user what to do for each file. The default value is maybe. safe-local-eval-forms — User Option: safe-local-eval-forms This variable holds a list of expressions that are safe toevaluate when found in the ‘Eval:’ “variable” in a filelocal variables list. If the expression is a function call and the function has a safe-local-eval-function property, the property value determines whether the expression is safe to evaluate. The property value can be a predicate to call to test the expression, a list of such predicates (it's safe if any predicate succeeds), or t (always safe provided the arguments are constant). Text properties are also potential loopholes, since their values could include functions to call. So Emacs discards all text properties from string values specified for file local variables. Variable Aliases variable aliases It is sometimes useful to make two variables synonyms, so that both variables always have the same value, and changing either one also changes the other. Whenever you change the name of a variable—either because you realize its old name was not well chosen, or because its meaning has partly changed—it can be useful to keep the old name as an alias of the new one for compatibility. You can do this with defvaralias. defvaralias — Function: defvaralias new-alias base-variable &optional docstring This function defines the symbol new-alias as a variable aliasfor symbol base-variable. This means that retrieving the valueof new-alias returns the value of base-variable, andchanging the value of new-alias changes the value ofbase-variable. The two aliased variable names always share thesame value and the same bindings.If the docstring argument is non-nil, it specifies thedocumentation for new-alias; otherwise, the alias gets the samedocumentation as base-variable has, if any, unlessbase-variable is itself an alias, in which case new-alias getsthe documentation of the variable at the end of the chain of aliases.This function returns base-variable. Variable aliases are convenient for replacing an old name for a variable with a new name. make-obsolete-variable declares that the old name is obsolete and therefore that it may be removed at some stage in the future. make-obsolete-variable — Function: make-obsolete-variable obsolete-name current-name &optional when This function makes the byte-compiler warn that the variableobsolete-name is obsolete. If current-name is a symbol, it isthe variable's new name; then the warning message says to usecurrent-name instead of obsolete-name. If current-nameis a string, this is the message and there is no replacement variable.If provided, when should be a string indicating when thevariable was first made obsolete—for example, a date or a releasenumber. You can make two variables synonyms and declare one obsolete at the same time using the macro define-obsolete-variable-alias. define-obsolete-variable-alias — Macro: define-obsolete-variable-alias obsolete-name current-name &optional when docstring This macro marks the variable obsolete-name as obsolete and alsomakes it an alias for the variable current-name. It isequivalent to the following: (defvaralias obsolete-name current-name docstring) (make-obsolete-variable obsolete-name current-name when) indirect-variable — Function: indirect-variable variable This function returns the variable at the end of the chain of aliasesof variable. If variable is not a symbol, or if variable isnot defined as an alias, the function returns variable.This function signals a cyclic-variable-indirection error ifthere is a loop in the chain of symbols. (defvaralias 'foo 'bar) (indirect-variable 'foo) => bar (indirect-variable 'bar) => bar (setq bar 2) bar => 2 foo => 2 (setq foo 0) bar => 0 foo => 0 Variables with Restricted Values Ordinary Lisp variables can be assigned any value that is a valid Lisp object. However, certain Lisp variables are not defined in Lisp, but in C. Most of these variables are defined in the C code using DEFVAR_LISP. Like variables defined in Lisp, these can take on any value. However, some variables are defined using DEFVAR_INT or DEFVAR_BOOL. See Writing Emacs Primitives, in particular the description of functions of the type syms_of_filename, for a brief discussion of the C implementation. Variables of type DEFVAR_BOOL can only take on the values nil or t. Attempting to assign them any other value will set them to t: (let ((display-hourglass 5)) display-hourglass) => t byte-boolean-vars — Variable: byte-boolean-vars This variable holds a list of all variables of type DEFVAR_BOOL. Variables of type DEFVAR_INT can only take on integer values. Attempting to assign them any other value will result in an error: (setq window-min-height 5.0) error--> Wrong type argument: integerp, 5.0 <setfilename>../info/functions</setfilename> Functions A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them. What Is a Function? In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures. Here are important terms for functions in Emacs Lisp and for other function-like objects. function functionIn Emacs Lisp, a function is anything that can be applied toarguments in a Lisp program. In some cases, we use it morespecifically to mean a function written in Lisp. Special forms andmacros are not functions. primitive primitive subr built-in functionA primitive is a function callable from Lisp that is written in C,such as car or append. These functions are also calledbuilt-in functions, or subrs. (Special forms are alsoconsidered primitives.)Usually the reason we implement a function as a primitive is eitherbecause it is fundamental, because it provides a low-level interfaceto operating system services, or because it needs to run fast.Primitives can be modified or added only by changing the C sources andrecompiling the editor. See . lambda expression A lambda expression is a function written in Lisp.These are described in the following section.See . special form A special form is a primitive that is like a function but does notevaluate all of its arguments in the usual way. It may evaluate onlysome of the arguments, or may evaluate them in an unusual order, orseveral times. Many special forms are described in . macro macroA macro is a construct defined in Lisp by the programmer. Itdiffers from a function in that it translates a Lisp expression that youwrite into an equivalent expression to be evaluated instead of theoriginal expression. Macros enable Lisp programmers to do the sorts ofthings that special forms can do. See , for how to define anduse macros. command commandA command is an object that command-execute can invoke; itis a possible definition for a key sequence. Some functions arecommands; a function written in Lisp is a command if it contains aninteractive declaration (see ). Such a functioncan be called from Lisp expressions like other functions; in this case,the fact that the function is a command makes no difference.Keyboard macros (strings and vectors) are commands also, even thoughthey are not functions. A symbol is a command if its functiondefinition is a command; such symbols can be invoked with M-x.The symbol is a function as well if the definition is a function.See . keystroke command keystroke commandA keystroke command is a command that is bound to a key sequence(typically one to three keystrokes). The distinction is made heremerely to avoid confusion with the meaning of “command” in non-Emacseditors; for Lisp programs, the distinction is normally unimportant. byte-code function A byte-code function is a function that has been compiled by thebyte compiler. See . functionp — Function: functionp object This function returns t if object is any kind offunction, or a special form, or, recursively, a symbol whose functiondefinition is a function or special form. (This does not includemacros.) Unlike functionp, the next three functions do not treat a symbol as its function definition. subrp — Function: subrp object This function returns t if object is a built-in function(i.e., a Lisp primitive). (subrp 'message) ; message is a symbol, => nil ; not a subr object. (subrp (symbol-function 'message)) => t byte-code-function-p — Function: byte-code-function-p object This function returns t if object is a byte-codefunction. For example: (byte-code-function-p (symbol-function 'next-line)) => t subr-arity — Function: subr-arity subr This function provides information about the argument list of aprimitive, subr. The returned value is a pair(min . max). min is the minimum number ofargs. max is the maximum number or the symbol many, for afunction with &rest arguments, or the symbol unevalled ifsubr is a special form. Lambda Expressions lambda expression A function written in Lisp is a list that looks like this: (lambda (arg-variables…) [ documentation-string ] [ interactive-declaration ] body-forms…) Such a list is called a lambda expression. In Emacs Lisp, it actually is valid as an expression—it evaluates to itself. In some other Lisp dialects, a lambda expression is not a valid expression at all. In either case, its main use is not to be evaluated as an expression, but to be called as a function. Components of a Lambda Expression A function written in Lisp (a “lambda expression”) is a list that looks like this: (lambda (arg-variables…) [documentation-string] [interactive-declaration] body-forms…) lambda list The first element of a lambda expression is always the symbol lambda. This indicates that the list represents a function. The reason functions are defined to start with lambda is so that other lists, intended for other uses, will not accidentally be valid as functions. The second element is a list of symbols—the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See . The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See . The interactive declaration is a list of the form (interactive code-string). This declares how to provide arguments if the function is used interactively. Functions with this declaration are called commands; they can be called using M-x or bound to a key. Functions not intended to be called in this way should not have interactive declarations. See , for how to write an interactive declaration. body of function The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The value returned by the function is the value returned by the last element of the body. A Simple Lambda-Expression Example Consider for example the following function: (lambda (a b c) (+ a b c)) We can call this function by writing it as the car of an expression, like this: ((lambda (a b c) (+ a b c)) 1 2 3) This call evaluates the body of the lambda expression with the variable a bound to 1, b bound to 2, and c bound to 3. Evaluation of the body adds these three numbers, producing the result 6; therefore, this call to the function returns the value 6. Note that the arguments can be the results of other function calls, as in this example: ((lambda (a b c) (+ a b c)) 1 (* 2 3) (- 5 4)) This evaluates the arguments 1, (* 2 3), and (- 5 4) from left to right. Then it applies the lambda expression to the argument values 1, 6 and 1 to produce the value 8. It is not often useful to write a lambda expression as the car of a form in this way. You can get the same result, of making local variables and giving them values, using the special form let (see ). And let is clearer and easier to use. In practice, lambda expressions are either stored as the function definitions of symbols, to produce named functions, or passed as arguments to other functions (see ). However, calls to explicit lambda expressions were very useful in the old days of Lisp, before the special form let was invented. At that time, they were the only way to bind and initialize local variables. Other Features of Argument Lists wrong-number-of-arguments argument binding binding arguments argument lists, features Our simple sample function, (lambda (a b c) (+ a b c)), specifies three argument variables, so it must be called with three arguments: if you try to call it with only two arguments or four arguments, you get a wrong-number-of-arguments error. It is often convenient to write a function that allows certain arguments to be omitted. For example, the function substring accepts three arguments—a string, the start index and the end index—but the third argument defaults to the length of the string if you omit it. It is also convenient for certain functions to accept an indefinite number of arguments, as the functions list and + do. optional arguments rest arguments &optional &rest To specify optional arguments that may be omitted when a function is called, simply include the keyword &optional before the optional arguments. To specify a list of zero or more extra arguments, include the keyword &rest before one final argument. Thus, the complete syntax for an argument list is as follows: (required-vars… [ &optional optional-vars… ] [ &rest rest-var ] ) The square brackets indicate that the &optional and &rest clauses, and the variables that follow them, are optional. A call to the function requires one actual argument for each of the required-vars. There may be actual arguments for zero or more of the optional-vars, and there cannot be any actual arguments beyond that unless the lambda list uses &rest. In that case, there may be any number of extra actual arguments. If actual arguments for the optional and rest variables are omitted, then they always default to nil. There is no way for the function to distinguish between an explicit argument of nil and an omitted argument. However, the body of the function is free to consider nil an abbreviation for some other meaningful value. This is what substring does; nil as the third argument to substring means to use the length of the string supplied. CL note—default optional arg Common Lisp note: Common Lisp allows the function to specify what default value to use when an optional argument is omitted; Emacs Lisp always uses nil. Emacs Lisp does not support “supplied-p” variables that tell you whether an argument was explicitly passed. For example, an argument list that looks like this: (a b &optional c d &rest e) binds a and b to the first two actual arguments, which are required. If one or two more arguments are provided, c and d are bound to them respectively; any arguments after the first four are collected into a list and e is bound to that list. If there are only two arguments, c is nil; if two or three arguments, d is nil; if four arguments or fewer, e is nil. There is no way to have required arguments following optional ones—it would not make sense. To see why this must be so, suppose that c in the example were optional and d were required. Suppose three actual arguments are given; which variable would the third argument be for? Would it be used for the c, or for d? One can argue for both possibilities. Similarly, it makes no sense to have any more arguments (either required or optional) after a &rest argument. Here are some examples of argument lists and proper calls: ((lambda (n) (1+ n)) ; One required: 1) ; requires exactly one argument. => 2 ((lambda (n &optional n1) ; One required and one optional: (if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments. 1 2) => 3 ((lambda (n &rest ns) ; One required and one rest: (+ n (apply '+ ns))) ; 1 or more arguments. 1 2 3 4 5) => 15 Documentation Strings of Functions documentation of function A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See , for how the documentation-string is accessed. It is a good idea to provide documentation strings for all the functions in your program, even those that are called only from within your program. Documentation strings are like comments, except that they are easier to access. The first line of the documentation string should stand on its own, because apropos displays just this first line. It should consist of one or two complete sentences that summarize the function's purpose. The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. That is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands. You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation. The last line of the documentation string can specify calling conventions different from the actual function arguments. Write text like this: \(fn arglist) following a blank line, at the beginning of the line, with no newline following it inside the documentation string. (The ‘\’ is used to avoid confusing the Emacs motion commands.) The calling convention specified in this way appears in help messages in place of the one derived from the actual arguments of the function. This feature is particularly useful for macro definitions, since the arguments written in a macro definition often do not correspond to the way users think of the parts of the macro call. Naming a Function function definition named function function name In most computer languages, every function has a name; the idea of a function without a name is nonsensical. In Lisp, a function in the strictest sense has no name. It is simply a list whose first element is lambda, a byte-code function object, or a primitive subr-object. However, a symbol can serve as the name of a function. This happens when you put the function in the symbol's function cell (see ). Then the symbol itself becomes a valid, callable function, equivalent to the list or subr-object that its function cell refers to. The contents of the function cell are also called the symbol's function definition. The procedure of using a symbol's function definition in place of the symbol is called symbol function indirection; see . In practice, nearly all functions are given names in this way and referred to through their names. For example, the symbol car works as a function and does what it does because the primitive subr-object #<subr car> is stored in its function cell. We give functions names because it is convenient to refer to them by their names in Lisp expressions. For primitive subr-objects such as #<subr car>, names are the only way you can refer to them: there is no read syntax for such objects. For functions written in Lisp, the name is more convenient to use in a call than an explicit lambda expression. Also, a function with a name can refer to itself—it can be recursive. Writing the function's name in its own definition is much more convenient than making the function definition point to itself (something that is not impossible but that has various disadvantages in practice). We often identify functions with the symbols used to name them. For example, we often speak of “the function car,” not distinguishing between the symbol car and the primitive subr-object that is its function definition. For most purposes, the distinction is not important. Even so, keep in mind that a function need not have a unique name. While a given function object usually appears in the function cell of only one symbol, this is just a matter of convenience. It is easy to store it in several symbols using fset; then each of the symbols is equally well a name for the same function. A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict. (Some Lisp dialects, such as Scheme, do not distinguish between a symbol's value and its function definition; a symbol's value as a variable is also its function definition.) If you have not given a symbol a function definition, you cannot use it as a function; whether the symbol has a value as a variable makes no difference to this. Defining Functions defining a function We usually give a name to a function when it is first created. This is called defining a function, and it is done with the defun special form. defun — Special Form: defun name argument-list body-forms defun is the usual way to define new Lisp functions. Itdefines the symbol name as a function that looks like this: (lambda argument-list . body-forms) defun stores this lambda expression in the function cell ofname. It returns the value name, but usually we ignore thisvalue.As described previously, argument-list is a list of argumentnames and may include the keywords &optional and &rest(see ). Also, the first two of thebody-forms may be a documentation string and an interactivedeclaration.There is no conflict if the same symbol name is also used as avariable, since the symbol's value cell is independent of the functioncell. See .Here are some examples: (defun foo () 5) => foo (foo) => 5 (defun bar (a &optional b &rest c) (list a b c)) => bar (bar 1 2 3 4 5) => (1 2 (3 4 5)) (bar 1) => (1 nil nil) (bar) error--> Wrong number of arguments. (defun capitalize-backwards () "Upcase the last letter of a word." (interactive) (backward-word 1) (forward-word 1) (backward-char 1) (capitalize-word 1)) => capitalize-backwards Be careful not to redefine existing functions unintentionally.defun redefines even primitive functions such as carwithout any hesitation or notification. Redefining a function alreadydefined is often done deliberately, and there is no way to distinguishdeliberate redefinition from unintentional redefinition. function aliases defalias — Function: defalias name definition &optional docstring This special form defines the symbol name as a function, withdefinition definition (which can be any valid Lisp function).It returns definition.If docstring is non-nil, it becomes the functiondocumentation of name. Otherwise, any documentation provided bydefinition is used.The proper place to use defalias is where a specific functionname is being defined—especially where that name appears explicitly inthe source file being loaded. This is because defalias recordswhich file defined the function, just like defun(see ).By contrast, in programs that manipulate function definitions for otherpurposes, it is better to use fset, which does not keep suchrecords. See . You cannot create a new primitive function with defun or defalias, but you can use them to change the function definition of any symbol, even one such as car or x-popup-menu whose normal definition is a primitive. However, this is risky: for instance, it is next to impossible to redefine car without breaking Lisp completely. Redefining an obscure function such as x-popup-menu is less dangerous, but it still may not work as you expect. If there are calls to the primitive from C code, they call the primitive's C definition directly, so changing the symbol's definition will have no effect on them. See also defsubst, which defines a function like defun and tells the Lisp compiler to open-code it. See . Calling Functions function invocation calling a function Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation. The most common way of invoking a function is by evaluating a list. For example, evaluating the list (concat "a" "b") calls the function concat with arguments "a" and "b". See , for a description of evaluation. When you write a list as an expression in your program, you specify which function to call, and how many arguments to give it, in the text of the program. Usually that's just what you want. Occasionally you need to compute at run time which function to call. To do that, use the function funcall. When you also need to determine at run time how many arguments to pass, use apply. funcall — Function: funcall function &rest arguments funcall calls function with arguments, and returnswhatever function returns.Since funcall is a function, all of its arguments, includingfunction, are evaluated before funcall is called. Thismeans that you can use any expression to obtain the function to becalled. It also means that funcall does not see theexpressions you write for the arguments, only their values.These values are not evaluated a second time in the act ofcalling function; the operation of funcall is like thenormal procedure for calling a function, once its arguments havealready been evaluated.The argument function must be either a Lisp function or aprimitive function. Special forms and macros are not allowed, becausethey make sense only when given the “unevaluated” argumentexpressions. funcall cannot provide these because, as we sawabove, it never knows them in the first place. (setq f 'list) => list (funcall f 'x 'y 'z) => (x y z) (funcall f 'x 'y '(z)) => (x y (z)) (funcall 'and t nil) error--> Invalid function: #<subr and> Compare these examples with the examples of apply. apply — Function: apply function &rest arguments apply calls function with arguments, just likefuncall but with one difference: the last of arguments is alist of objects, which are passed to function as separatearguments, rather than a single list. We say that applyspreads this list so that each individual element becomes anargument.apply returns the result of calling function. As withfuncall, function must either be a Lisp function or aprimitive function; special forms and macros do not make sense inapply. (setq f 'list) => list (apply f 'x 'y 'z) error--> Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) => 10 (apply '+ '(1 2 3 4)) => 10 (apply 'append '((a b c) nil (x y z) nil)) => (a b c x y z) For an interesting example of using apply, see . functionals It is common for Lisp functions to accept functions as arguments or find them in data structures (especially in hook variables and property lists) and call them using funcall or apply. Functions that accept function arguments are often called functionals. Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function: identity — Function: identity arg This function returns arg and has no side effects. ignore — Function: ignore &rest args This function ignores any arguments and returns nil. Mapping Functions mapping functions A mapping function applies a given function (not a special form or macro) to each element of a list or other collection. Emacs Lisp has several such functions; mapcar and mapconcat, which scan a list, are described here. See , for the function mapatoms which maps over the symbols in an obarray. See , for the function maphash which maps over key/value associations in a hash table. These mapping functions do not allow char-tables because a char-table is a sparse array whose nominal range of indices is very large. To map over a char-table in a way that deals properly with its sparse nature, use the function map-char-table (see ). mapcar — Function: mapcar function sequence mapcar applies function to each element of sequencein turn, and returns a list of the results.The argument sequence can be any kind of sequence except achar-table; that is, a list, a vector, a bool-vector, or a string. Theresult is always a list. The length of the result is the same as thelength of sequence. For example: (mapcar 'car '((a b) (c d) (e f))) => (a c e) (mapcar '1+ [1 2 3]) => (2 3 4) (mapcar 'char-to-string "abc") => ("a" "b" "c") ;; Call each function in my-hooks. (mapcar 'funcall my-hooks) (defun mapcar* (function &rest args) "Apply FUNCTION to successive cars of all ARGS. Return the list of results." ;; If no list is exhausted, (if (not (memq nil args)) ;; apply function to cars. (cons (apply function (mapcar 'car args)) (apply 'mapcar* function ;; Recurse for rest of elements. (mapcar 'cdr args))))) (mapcar* 'cons '(a b c) '(1 2 3 4)) => ((a . 1) (b . 2) (c . 3)) mapc — Function: mapc function sequence mapc is like mapcar except that function is used forside-effects only—the values it returns are ignored, not collectedinto a list. mapc always returns sequence. mapconcat — Function: mapconcat function sequence separator mapconcat applies function to each element ofsequence: the results, which must be strings, are concatenated.Between each pair of result strings, mapconcat inserts the stringseparator. Usually separator contains a space or comma orother suitable punctuation.The argument function must be a function that can take oneargument and return a string. The argument sequence can be anykind of sequence except a char-table; that is, a list, a vector, abool-vector, or a string. (mapconcat 'symbol-name '(The cat in the hat) " ") => "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") => "IBM.9111" Anonymous Functions anonymous function In Lisp, a function is a list that starts with lambda, a byte-code function compiled from such a list, or alternatively a primitive subr-object; names are “extra.” Although usually functions are defined with defun and given names at the same time, it is occasionally more concise to use an explicit lambda expression—an anonymous function. Such a list is valid wherever a function name is. Any method of creating such a list makes a valid function. Even this: (setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x)))) => (lambda (x) (+ 12 x)) This computes a list that looks like (lambda (x) (+ 12 x)) and makes it the value (not the function definition!) of silly. Here is how we might call this function: (funcall silly 1) => 13 (It does not work to write (silly 1), because this function is not the function definition of silly. We have not given silly any function definition, just a value as a variable.) Most of the time, anonymous functions are constants that appear in your program. For example, you might want to pass one as an argument to the function mapcar, which applies any given function to each element of a list. Here we define a function change-property which uses a function as its third argument: (defun change-property (symbol prop function) (let ((value (get symbol prop))) (put symbol prop (funcall function value)))) Here we define a function that uses change-property, passing it a function to double a number: (defun double-property (symbol prop) (change-property symbol prop '(lambda (x) (* 2 x)))) In such cases, we usually use the special form function instead of simple quotation to quote the anonymous function, like this: (defun double-property (symbol prop) (change-property symbol prop (function (lambda (x) (* 2 x))))) Using function instead of quote makes a difference if you compile the function double-property. For example, if you compile the second definition of double-property, the anonymous function is compiled as well. By contrast, if you compile the first definition which uses ordinary quote, the argument passed to change-property is the precise list shown: (lambda (x) (* x 2)) The Lisp compiler cannot assume this list is a function, even though it looks like one, since it does not know what change-property will do with the list. Perhaps it will check whether the car of the third element is the symbol *! Using function tells the compiler it is safe to go ahead and compile the constant function. Nowadays it is possible to omit function entirely, like this: (defun double-property (symbol prop) (change-property symbol prop (lambda (x) (* 2 x)))) This is because lambda itself implies function. We sometimes write function instead of quote when quoting the name of a function, but this usage is just a sort of comment: (function symbol) == (quote symbol) == 'symbol ‘#'’ syntax The read syntax #' is a short-hand for using function. For example, #'(lambda (x) (* x x)) is equivalent to (function (lambda (x) (* x x))) function — Special Form: function function-object function quotingThis special form returns function-object without evaluating it.In this, it is equivalent to quote. However, it serves as anote to the Emacs Lisp compiler that function-object is intendedto be used only as a function, and therefore can safely be compiled.Contrast this with quote, in . See , for a realistic example using function and an anonymous function. Accessing Function Cell Contents The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols. See also the function indirect-function. See . symbol-function — Function: symbol-function symbol void-functionThis returns the object in the function cell of symbol. If thesymbol's function cell is void, a void-function error issignaled.This function does not check that the returned object is a legitimatefunction. (defun bar (n) (+ n 2)) => bar (symbol-function 'bar) => (lambda (n) (+ n 2)) (fset 'baz 'bar) => bar (symbol-function 'baz) => bar void function cell If you have never given a symbol any function definition, we say that that symbol's function cell is void. In other words, the function cell does not have any Lisp object in it. If you try to call such a symbol as a function, it signals a void-function error. Note that void is not the same as nil or the symbol void. The symbols nil and void are Lisp objects, and can be stored into a function cell just as any other object can be (and they can be valid functions if you define them in turn with defun). A void function cell contains no object whatsoever. You can test the voidness of a symbol's function definition with fboundp. After you have given a symbol a function definition, you can make it void once more using fmakunbound. fboundp — Function: fboundp symbol This function returns t if the symbol has an object in itsfunction cell, nil otherwise. It does not check that the objectis a legitimate function. fmakunbound — Function: fmakunbound symbol This function makes symbol's function cell void, so that asubsequent attempt to access this cell will cause avoid-function error. It returns symbol. (See alsomakunbound, in .) (defun foo (x) x) => foo (foo 1) =>1 (fmakunbound 'foo) => foo (foo 1) error--> Symbol's function definition is void: foo fset — Function: fset symbol definition This function stores definition in the function cell ofsymbol. The result is definition. Normallydefinition should be a function or the name of a function, butthis is not checked. The argument symbol is an ordinary evaluatedargument.There are three normal uses of this function: Copying one symbol's function definition to another—in other words,making an alternate name for a function. (If you think of this as thedefinition of the new name, you should use defalias instead offset; see .) Giving a symbol a function definition that is not a list and thereforecannot be made with defun. For example, you can use fsetto give a symbol s1 a function definition which is another symbols2; then s1 serves as an alias for whatever definitions2 presently has. (Once again use defalias instead offset if you think of this as the definition of s1.) In constructs for defining or altering functions. If defunwere not a primitive, it could be written in Lisp (as a macro) usingfset. Here are examples of these uses: ;; Save foo's definition in old-foo. (fset 'old-foo (symbol-function 'foo)) ;; Make the symbol car the function definition of xfirst. ;; (Most likely, defalias would be better than fset here.) (fset 'xfirst 'car) => car (xfirst '(1 2 3)) => 1 (symbol-function 'xfirst) => car (symbol-function (symbol-function 'xfirst)) => #<subr car> ;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") => "\^u2\^k" ;; Here is a function that alters other functions. (defun copy-function-definition (new old) "Define NEW with the same function definition as OLD." (fset new (symbol-function old))) fset is sometimes used to save the old definition of a function before redefining it. That permits the new definition to invoke the old definition. But it is unmodular and unclean for a Lisp file to redefine a function defined elsewhere. If you want to modify a function defined by another package, it is cleaner to use defadvice (see ). Declaring Functions Obsolete You can use make-obsolete to declare a function obsolete. This indicates that the function may be removed at some stage in the future. make-obsolete — Function: make-obsolete obsolete-name current-name &optional when This function makes the byte compiler warn that the functionobsolete-name is obsolete. If current-name is a symbol, thewarning message says to use current-name instead ofobsolete-name. current-name does not need to be an alias forobsolete-name; it can be a different function with similarfunctionality. If current-name is a string, it is the warningmessage.If provided, when should be a string indicating when the functionwas first made obsolete—for example, a date or a release number. You can define a function as an alias and declare it obsolete at the same time using the macro define-obsolete-function-alias. define-obsolete-function-alias — Macro: define-obsolete-function-alias obsolete-name current-name &optional when docstring This macro marks the function obsolete-name obsolete and alsodefines it as an alias for the function current-name. It isequivalent to the following: (defalias obsolete-name current-name docstring) (make-obsolete obsolete-name current-name when) Inline Functions inline functions defsubst You can define an inline function by using defsubst instead of defun. An inline function works just like an ordinary function except for one thing: when you compile a call to the function, the function's definition is open-coded into the caller. Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them. Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline. Also, inline functions do not behave well with respect to debugging, tracing, and advising (see ). Since ease of debugging and the flexibility of redefining functions are important features of Emacs, you should not make a function inline, even if it's small, unless its speed is really crucial, and you've timed the code to verify that using defun actually has performance problems. It's possible to define a macro to expand into the same code that an inline function would execute. (See .) But the macro would be limited to direct use in expressions—a macro cannot be called with apply, mapcar and so on. Also, it takes some work to convert an ordinary function into a macro. To convert it into an inline function is very easy; simply replace defun with defsubst. Since each argument of an inline function is evaluated exactly once, you needn't worry about how many times the body uses the arguments, as you do for macros. (See .) Inline functions can be used and open-coded later on in the same file, following the definition, just like macros. Determining whether a Function is Safe to Call function safety safety of functions Some major modes such as SES call functions that are stored in user files. (*note (ses)Top::, for more information on SES.) User files sometimes have poor pedigrees—you can get a spreadsheet from someone you've just met, or you can get one through email from someone you've never met. So it is risky to call a function whose source code is stored in a user file until you have determined that it is safe. unsafep — Function: unsafep form &optional unsafep-vars Returns nil if form is a safe Lisp expression, orreturns a list that describes why it might be unsafe. The argumentunsafep-vars is a list of symbols known to have temporarybindings at this point; it is mainly used for internal recursivecalls. The current buffer is an implicit argument, which provides alist of buffer-local bindings. Being quick and simple, unsafep does a very light analysis and rejects many Lisp expressions that are actually safe. There are no known cases where unsafep returns nil for an unsafe expression. However, a “safe” Lisp expression can return a string with a display property, containing an associated Lisp expression to be executed after the string is inserted into a buffer. This associated expression can be a virus. In order to be safe, you must delete properties from all strings calculated by user code before inserting them into buffers. Other Topics Related to Functions Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here. apply See . autoload See . call-interactively See . commandp See . documentation See . eval See . funcall See . function See . ignore See . indirect-function See . interactive See . interactive-p See . mapatoms See . mapcar See . map-char-table See . mapconcat See . undefined See . <setfilename>../info/macros</setfilename> Macros macros Macros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro. Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them. If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See . A Simple Example of a Macro Suppose we would like to define a Lisp construct to increment a variable value, much like the ++ operator in C. We would like to write (inc x) and have the effect of (setq x (1+ x)). Here's a macro definition that does the job: inc (defmacro inc (var) (list 'setq var (list '1+ var))) When this is called with (inc x), the argument var is the symbol x—not the value of x, as it would be in a function. The body of the macro uses this to construct the expansion, which is (setq x (1+ x)). Once the macro definition returns this expansion, Lisp proceeds to evaluate it, thus incrementing x. Expansion of a Macro Call expansion of macros macro call A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro. Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list. Having obtained the arguments, Lisp invokes the macro definition just as a function is invoked. The argument variables of the macro are bound to the argument values from the macro call, or to a list of them in the case of a &rest argument. And the macro body executes and returns its value just as a function body does. The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro. Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual. You can see the expansion of a given macro call by calling macroexpand. macroexpand — Function: macroexpand form &optional environment macro expansionThis function expands form, if it is a macro call. If the resultis another macro call, it is expanded in turn, until something which isnot a macro call results. That is the value returned bymacroexpand. If form is not a macro call to begin with, itis returned as given.Note that macroexpand does not look at the subexpressions ofform (although some macro definitions may do so). Even if theyare macro calls themselves, macroexpand does not expand them.The function macroexpand does not expand calls to inline functions.Normally there is no need for that, since a call to an inline function isno harder to understand than a call to an ordinary function.If environment is provided, it specifies an alist of macrodefinitions that shadow the currently defined macros. Byte compilationuses this feature. (defmacro inc (var) (list 'setq var (list '1+ var))) => inc (macroexpand '(inc r)) => (setq r (1+ r)) (defmacro inc2 (var1 var2) (list 'progn (list 'inc var1) (list 'inc var2))) => inc2 (macroexpand '(inc2 r s)) => (progn (inc r) (inc s)) ; inc not expanded here. macroexpand-all — Function: macroexpand-all form &optional environment macroexpand-all expands macros like macroexpand, butwill look for and expand all macros in form, not just at thetop-level. If no macros are expanded, the return value is eqto form.Repeating the example used for macroexpand above withmacroexpand-all, we see that macroexpand-all doesexpand the embedded calls to inc: (macroexpand-all '(inc2 r s)) => (progn (setq r (1+ r)) (setq s (1+ s))) Macros and Byte Compilation byte-compiling macros You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation. When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself—they would be computed at compile time, which is not useful. In order for compilation of macro calls to work, the macros must already be defined in Lisp when the calls to them are compiled. The compiler has a special feature to help you do this: if a file being compiled contains a defmacro form, the macro is defined temporarily for the rest of the compilation of that file. To make this feature work, you must put the defmacro in the same file where it is used, and before its first use. Byte-compiling a file executes any require calls at top-level in the file. This is in case the file needs the required packages for proper compilation. One way to ensure that necessary macro definitions are available during compilation is to require the files that define them (see ). To avoid loading the macro definition files when someone runs the compiled program, write eval-when-compile around the require calls (see ). Defining Macros A Lisp macro is a list whose car is macro. Its cdr should be a function; expansion of the macro works by applying the function (with apply) to the list of unevaluated argument-expressions from the macro call. It is possible to use an anonymous Lisp macro just like an anonymous function, but this is never done, because it does not make sense to pass an anonymous macro to functionals such as mapcar. In practice, all Lisp macros have names, and they are usually defined with the special form defmacro. defmacro — Special Form: defmacro name argument-list body-forms … defmacro defines the symbol name as a macro that lookslike this: (macro lambda argument-list . body-forms) (Note that the cdr of this list is a function—a lambda expression.)This macro object is stored in the function cell of name. Thevalue returned by evaluating the defmacro form is name, butusually we ignore this value.The shape and meaning of argument-list is the same as in afunction, and the keywords &rest and &optional may be used(see ). Macros may have a documentation string, butany interactive declaration is ignored since macros cannot becalled interactively. The body of the macro definition can include a declare form, which can specify how TAB should indent macro calls, and how to step through them for Edebug. declare — Macro: declare specs … A declare form is used in a macro definition to specify variousadditional information about it. Two kinds of specification arecurrently supported: (debug edebug-form-spec) Specify how to step through macro calls for Edebug.See . (indent indent-spec) Specify how to indent calls to this macro. See ,for more details. A declare form only has its special effect in the body of adefmacro form if it immediately follows the documentationstring, if present, or the argument list otherwise. (Strictlyspeaking, several declare forms can follow thedocumentation string or argument list, but since a declare formcan have several specs, they can always be combined into asingle form.) When used at other places in a defmacro form, oroutside a defmacro form, declare just returns nilwithout evaluating any specs. No macro absolutely needs a declare form, because that form has no effect on how the macro expands, on what the macro means in the program. It only affects secondary features: indentation and Edebug. Backquote backquote (list substitution) ` (list substitution) ` Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the ‘`’ syntax (usually called backquote). Backquote allows you to quote a list, but selectively evaluate elements of that list. In the simplest case, it is identical to the special form quote (see ). For example, these two forms yield identical results: `(a list of (+ 2 3) elements) => (a list of (+ 2 3) elements) '(a list of (+ 2 3) elements) => (a list of (+ 2 3) elements) , (with backquote) The special marker ‘,’ inside of the argument to backquote indicates a value that isn't constant. Backquote evaluates the argument of ‘,’ and puts the value in the list structure: (list 'a 'list 'of (+ 2 3) 'elements) => (a list of 5 elements) `(a list of ,(+ 2 3) elements) => (a list of 5 elements) Substitution with ‘,’ is allowed at deeper levels of the list structure also. For example: (defmacro t-becomes-nil (variable) `(if (eq ,variable t) (setq ,variable nil))) (t-becomes-nil foo) == (if (eq foo t) (setq foo nil)) ,@ (with backquote) splicing (with backquote) You can also splice an evaluated value into the resulting list, using the special marker ‘,@’. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ‘`’ is often unreadable. Here are some examples: (setq some-list '(2 3)) => (2 3) (cons 1 (append some-list '(4) some-list)) => (1 2 3 4 2 3) `(1 ,@some-list 4 ,@some-list) => (1 2 3 4 2 3) (setq list '(hack foo bar)) => (hack foo bar) (cons 'use (cons 'the (cons 'words (append (cdr list) '(as elements))))) => (use the words foo bar as elements) `(use the words ,@(cdr list) as elements) => (use the words foo bar as elements) In old Emacs versions, before version 19.29, ‘`’ used a different syntax which required an extra level of parentheses around the entire backquote construct. Likewise, each ‘,’ or ‘,@’ substitution required an extra level of parentheses surrounding both the ‘,’ or ‘,@’ and the following expression. The old syntax required whitespace between the ‘`’, ‘,’ or ‘,@’ and the following expression. This syntax is still accepted, for compatibility with old Emacs versions, but we recommend not using it in new programs. Common Problems Using Macros The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble. Wrong Time The most common problem in writing macros is doing some of the real work prematurely—while expanding the macro, rather than in the expansion itself. For instance, one real package had this macro definition: (defmacro my-set-buffer-multibyte (arg) (if (fboundp 'set-buffer-multibyte) (set-buffer-multibyte arg))) With this erroneous macro definition, the program worked fine when interpreted but failed when compiled. This macro definition called set-buffer-multibyte during compilation, which was wrong, and then did nothing when the compiled package was run. The definition that the programmer really wanted was this: (defmacro my-set-buffer-multibyte (arg) (if (fboundp 'set-buffer-multibyte) `(set-buffer-multibyte ,arg))) This macro expands, if appropriate, into a call to set-buffer-multibyte that will be executed when the compiled program is actually run. Evaluating Macro Arguments Repeatedly When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple “for” loop such as one might find in Pascal. for (defmacro for (var from init to final do &rest body) "Execute a simple \"for\" loop. For example, (for i from 1 to 10 do (print i))." (list 'let (list (list var init)) (cons 'while (cons (list '<= var final) (append body (list (list 'inc var))))))) => for (for i from 1 to 3 do (setq square (* i i)) (princ (format "\n%d %d" i square))) ==> (let ((i 1)) (while (<= i 3) (setq square (* i i)) (princ (format "\n%d %d" i square)) (inc i))) -|1 1 -|2 4 -|3 9 => nil The arguments from, to, and do in this macro are “syntactic sugar”; they are entirely ignored. The idea is that you will write noise words (such as from, to, and do) in those positions in the macro call. Here's an equivalent definition simplified through use of backquote: (defmacro for (var from init to final do &rest body) "Execute a simple \"for\" loop. For example, (for i from 1 to 10 do (print i))." `(let ((,var ,init)) (while (<= ,var ,final) ,@body (inc ,var)))) Both forms of this definition (with backquote and without) suffer from the defect that final is evaluated on every iteration. If final is a constant, this is not a problem. If it is a more complex form, say (long-complex-calculation x), this can slow down the execution significantly. If final has side effects, executing it more than once is probably incorrect. macro argument evaluation A well-designed macro definition takes steps to avoid this problem by producing an expansion that evaluates the argument expressions exactly once unless repeated evaluation is part of the intended purpose of the macro. Here is a correct expansion for the for macro: (let ((i 1) (max 3)) (while (<= i max) (setq square (* i i)) (princ (format "%d %d" i square)) (inc i))) Here is a macro definition that creates this expansion: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." `(let ((,var ,init) (max ,final)) (while (<= ,var max) ,@body (inc ,var)))) Unfortunately, this fix introduces another problem, described in the following section. Local Variables in Macro Expansions In the previous section, the definition of for was fixed as follows to make the expansion evaluate the macro arguments the proper number of times: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." `(let ((,var ,init) (max ,final)) (while (<= ,var max) ,@body (inc ,var)))) The new definition of for has a new problem: it introduces a local variable named max which the user does not expect. This causes trouble in examples such as the following: (let ((max 0)) (for x from 0 to 10 do (let ((this (frob x))) (if (< max this) (setq max this))))) The references to max inside the body of the for, which are supposed to refer to the user's binding of max, really access the binding made by for. The way to correct this is to use an uninterned symbol instead of max (see ). The uninterned symbol can be bound and referred to just like any other symbol, but since it is created by for, we know that it cannot already appear in the user's program. Since it is not interned, there is no way the user can put it into the program later. It will never appear anywhere except where put by for. Here is a definition of for that works this way: (defmacro for (var from init to final do &rest body) "Execute a simple for loop: (for i from 1 to 10 do (print i))." (let ((tempvar (make-symbol "max"))) `(let ((,var ,init) (,tempvar ,final)) (while (<= ,var ,tempvar) ,@body (inc ,var))))) This creates an uninterned symbol named max and puts it in the expansion instead of the usual interned symbol max that appears in expressions ordinarily. Evaluating Macro Arguments in Expansion Another problem can happen if the macro definition itself evaluates any of the macro argument expressions, such as by calling eval (see ). If the argument is supposed to refer to the user's variables, you may have trouble if the user happens to use a variable with the same name as one of the macro arguments. Inside the macro body, the macro argument binding is the most local binding of this variable, so any references inside the form being evaluated do refer to it. Here is an example: (defmacro foo (a) (list 'setq (eval a) t)) => foo (setq x 'b) (foo x) ==> (setq b t) => t ; and b has been set. ;; but (setq a 'c) (foo a) ==> (setq a t) => t ; but this set a, not c. It makes a difference whether the user's variable is named a or x, because a conflicts with the macro argument variable a. Another problem with calling eval in a macro definition is that it probably won't do what you intend in a compiled program. The byte-compiler runs macro definitions while compiling the program, when the program's own computations (which you might have wished to access with eval) don't occur and its local variable bindings don't exist. To avoid these problems, don't evaluate an argument expression while computing the macro expansion. Instead, substitute the expression into the macro expansion, so that its value will be computed as part of executing the expansion. This is how the other examples in this chapter work. How Many Times is the Macro Expanded? Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded. Therefore, you should avoid side effects in computation of the macro expansion, unless you really know what you are doing. One special kind of side effect can't be avoided: constructing Lisp objects. Almost all macro expansions include constructed lists; that is the whole point of most macros. This is usually safe; there is just one case where you must be careful: when the object you construct is part of a quoted constant in the macro expansion. If the macro is expanded just once, in compilation, then the object is constructed just once, during compilation. But in interpreted execution, the macro is expanded each time the macro call runs, and this means a new object is constructed each time. In most clean Lisp code, this difference won't matter. It can matter only if you perform side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid side effects on objects constructed by macro definitions. Here is an example of how such side effects can get you into trouble:(defmacro empty-object () (list 'quote (cons nil nil)))(defun initialize (condition) (let ((object (empty-object))) (if condition (setcar object condition)) object)) If initialize is interpreted, a new list (nil) is constructed each time initialize is called. Thus, no side effect survives between calls. If initialize is compiled, then the macro empty-object is expanded during compilation, producing a single “constant” (nil) that is reused and altered each time initialize is called. One way to avoid pathological cases like this is to think of empty-object as a funny kind of constant, not as a memory allocation construct. You wouldn't use setcar on a constant such as '(nil), so naturally you won't use it on (empty-object) either. Indenting Macros You can use the declare form in the macro definition to specify how to TAB should indent indent calls to the macro. You write it like this: (declare (indent indent-spec)) Here are the possibilities for indent-spec: nil This is the same as no property—use the standard indentation pattern. defun Handle this function like a ‘def’ construct: treat the secondline as the start of a body. an integer, number The first number arguments of the function aredistinguished arguments; the rest are considered the bodyof the expression. A line in the expression is indented according towhether the first argument on it is distinguished or not. If theargument is part of the body, the line is indented lisp-body-indentmore columns than the open-parenthesis starting the containingexpression. If the argument is distinguished and is either the firstor second argument, it is indented twice that many extra columns.If the argument is distinguished and not the first or second argument,the line uses the standard pattern. a symbol, symbol symbol should be a function name; that function is called tocalculate the indentation of a line within this expression. Thefunction receives two arguments: state The value returned by parse-partial-sexp (a Lisp primitive forindentation and nesting computation) when it parses up to thebeginning of this line. pos The position at which the line being indented begins. It should return either a number, which is the number of columns ofindentation for that line, or a list whose car is such a number. Thedifference between returning a number and returning a list is that anumber says that all following lines at the same nesting level shouldbe indented just like this one; a list says that following lines mightcall for different indentations. This makes a difference when theindentation is being computed by C-M-q; if the value is anumber, C-M-q need not recalculate indentation for the followinglines until the end of the list. <setfilename>../info/customize</setfilename> Writing Customization Definitions customization definitions This chapter describes how to declare user options for customization, and also customization groups for classifying them. We use the term customization item to include both kinds of customization definitions—as well as face definitions (see ). Common Item Keywords customization keywords All kinds of customization declarations (for variables and groups, and for faces) accept keyword arguments for specifying various information. This section describes some keywords that apply to all kinds. All of these keywords, except :tag, can be used more than once in a given item. Each use of the keyword has an independent effect. The keyword :tag is an exception because any given item can only display one name. :tag label tag, customization keywordUse label, a string, instead of the item's name, to label theitem in customization menus and buffers. Don't use a tagwhich is substantially different from the item's real name; that wouldcause confusion. One legitimate case for use of :tag is tospecify a dash where normally a hyphen would be converted to a space: (defcustom cursor-in-non-selected-windows … :tag "Cursor In Non-selected Windows" group, customization keyword :group group Put this customization item in group group. When you use:group in a defgroup, it makes the new group a subgroup ofgroup.If you use this keyword more than once, you can put a single item intomore than one group. Displaying any of those groups will show thisitem. Please don't overdo this, since the result would be annoying. :link link-data link, customization keywordInclude an external link after the documentation string for this item.This is a sentence containing an active field which references someother documentation.There are several alternatives you can use for link-data: (custom-manual info-node) Link to an Info node; info-node is a string which specifies thenode name, as in "(emacs)Top". The link appears as‘[Manual]’ in the customization buffer and enters the built-inInfo reader on info-node. (info-link info-node) Like custom-manual except that the link appearsin the customization buffer with the Info node name. (url-link url) Link to a web page; url is a string which specifies theURL. The link appears in the customization buffer asurl and invokes the WWW browser specified bybrowse-url-browser-function. (emacs-commentary-link library) Link to the commentary section of a library; library is a stringwhich specifies the library name. (emacs-library-link library) Link to an Emacs Lisp library file; library is a string whichspecifies the library name. (file-link file) Link to a file; file is a string which specifies the name of thefile to visit with find-file when the user invokes this link. (function-link function) Link to the documentation of a function; function is a stringwhich specifies the name of the function to describe withdescribe-function when the user invokes this link. (variable-link variable) Link to the documentation of a variable; variable is a stringwhich specifies the name of the variable to describe withdescribe-variable when the user invokes this link. (custom-group-link group) Link to another customization group. Invoking it creates a newcustomization buffer for group. You can specify the text to use in the customization buffer by adding:tag name after the first element of the link-data;for example, (info-link :tag "foo" "(emacs)Top") makes a link tothe Emacs manual which appears in the buffer as ‘foo’.An item can have more than one external link; however, most items havenone at all. :load file load, customization keywordLoad file file (a string) before displaying this customizationitem. Loading is done with load-library, and only if the file isnot already loaded. :require feature require, customization keywordExecute (require 'feature) when your saved customizationsset the value of this item. feature should be a symbol.The most common reason to use :require is when a variable enablesa feature such as a minor mode, and just setting the variable won't haveany effect unless the code which implements the mode is loaded. :version version version, customization keywordThis keyword specifies that the item was first introduced in Emacsversion version, or that its default value was changed in thatversion. The value version must be a string. :package-version '(package . version) package-version, customization keywordThis keyword specifies that the item was first introduced inpackage version version, or that its meaning or defaultvalue was changed in that version. The value of package is asymbol and version is a string.This keyword takes priority over :version.package should be the official name of the package, such as MH-Eor Gnus. If the package package is released as part of Emacs,package and version should appear in the value ofcustomize-package-emacs-version-alist. Packages distributed as part of Emacs that use the :package-version keyword must also update the customize-package-emacs-version-alist variable. customize-package-emacs-version-alist — Variable: customize-package-emacs-version-alist This alist provides a mapping for the versions of Emacs that areassociated with versions of a package listed in the:package-version keyword. Its elements look like this: (package (pversion . eversion)…) For each package, which is a symbol, there are one or moreelements that contain a package version pversion with anassociated Emacs version eversion. These versions are strings.For example, the MH-E package updates this alist with the following: (add-to-list 'customize-package-emacs-version-alist '(MH-E ("6.0" . "22.1") ("6.1" . "22.1") ("7.0" . "22.1") ("7.1" . "22.1") ("7.2" . "22.1") ("7.3" . "22.1") ("7.4" . "22.1") ("8.0" . "22.1"))) The value of package needs to be unique and it needs to matchthe package value appearing in the :package-versionkeyword. Since the user might see the value in a error message, a goodchoice is the official name of the package, such as MH-E or Gnus. Defining Customization Groups define customization group customization groups, defining Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twelve or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups. The package's main or only group should be a member of one or more of the standard customization groups. (To display the full list of them, use M-x customize.) Choose one or more of them (but not too many), and add your group to each of them using the :group keyword. The way to declare new customization groups is with defgroup. defgroup — Macro: defgroup group members doc [ keyword value ] … Declare group as a customization group containing members.Do not quote the symbol group. The argument doc specifiesthe documentation string for the group.The argument members is a list specifying an initial set ofcustomization items to be members of the group. However, most oftenmembers is nil, and you specify the group's members byusing the :group keyword when defining those members.If you want to specify group members through members, each elementshould have the form (name widget). Here nameis a symbol, and widget is a widget type for editing that symbol.Useful widgets are custom-variable for a variable,custom-face for a face, and custom-group for a group.When you introduce a new group into Emacs, use the :versionkeyword in the defgroup; then you need not use it forthe individual members of the group.In addition to the common keywords (see ), you canalso use this keyword in defgroup: :prefix prefix prefix, defgroup keywordIf the name of an item in the group starts with prefix, then thetag for that item is constructed (by default) by omitting prefix.One group can have any number of prefixes. The prefix-discarding feature is currently turned off, which means that :prefix currently has no effect. We did this because we found that discarding the specified prefixes often led to confusing names for options. This happened because the people who wrote the defgroup definitions for various groups added :prefix keywords whenever they make logical sense—that is, whenever the variables in the library have a common prefix. In order to obtain good results with :prefix, it would be necessary to check the specific effects of discarding a particular prefix, given the specific items in a group and their names and documentation. If the resulting text is not clear, then :prefix should not be used in that case. It should be possible to recheck all the customization groups, delete the :prefix specifications which give unclear results, and then turn this feature back on, if someone would like to do the work. Defining Customization Variables define customization options customization variables, how to define Use defcustom to declare user-customizable variables. defcustom — Macro: defcustom option standard doc [ keyword value ] … This construct declares option as a customizable user optionvariable. You should not quote option. The argument docspecifies the documentation string for the variable. There is no needto start it with a ‘*’, because defcustom automaticallymarks option as a user option (see ).The argument standard is an expression that specifies thestandard value for option. Evaluating the defcustom formevaluates standard, but does not necessarily install thestandard value. If option already has a default value,defcustom does not change it. If the user has saved acustomization for option, defcustom installs the user'scustomized value as option's default value. If neither of thosecases applies, defcustom installs the result of evaluatingstandard as the default value.The expression standard can be evaluated at various other times,too—whenever the customization facility needs to know option'sstandard value. So be sure to use an expression which is harmless toevaluate at any time. We recommend avoiding backquotes instandard, because they are not expanded when editing the value,so list values will appear to have the wrong structure.Every defcustom should specify :group at least once.If you specify the :set keyword, to make the variable take otherspecial actions when set through the customization buffer, thevariable's documentation string should tell the user specifically howto do the same job in hand-written Lisp code.When you evaluate a defcustom form with C-M-x in Emacs Lispmode (eval-defun), a special feature of eval-defunarranges to set the variable unconditionally, without testing whetherits value is void. (The same feature applies to defvar.)See . defcustom accepts the following additional keywords: :type type Use type as the data type for this option. It specifies whichvalues are legitimate, and how to display the value.See , for more information. :options value-list options, defcustom keywordSpecify the list of reasonable values for use in thisoption. The user is not restricted to using only these values, but theyare offered as convenient alternatives.This is meaningful only for certain types, currently includinghook, plist and alist. See the definition of theindividual types for a description of how to use :options. :set setfunction set, defcustom keywordSpecify setfunction as the way to change the value of thisoption. The function setfunction should take two arguments, asymbol (the option name) and the new value, and should do whatever isnecessary to update the value properly for this option (which may notmean simply setting the option as a Lisp variable). The default forsetfunction is set-default. :get getfunction get, defcustom keywordSpecify getfunction as the way to extract the value of thisoption. The function getfunction should take one argument, asymbol, and should return whatever customize should use as the“current value” for that symbol (which need not be the symbol's Lispvalue). The default is default-value.You have to really understand the workings of Custom to use:get correctly. It is meant for values that are treated inCustom as variables but are not actually stored in Lisp variables. Itis almost surely a mistake to specify getfunction for a valuethat really is stored in a Lisp variable. :initialize function initialize, defcustom keywordfunction should be a function used to initialize the variablewhen the defcustom is evaluated. It should take two arguments,the option name (a symbol) and the value. Here are some predefinedfunctions meant for use in this way: custom-initialize-set Use the variable's :set function to initialize the variable, butdo not reinitialize it if it is already non-void. custom-initialize-default Like custom-initialize-set, but use the functionset-default to set the variable, instead of the variable's:set function. This is the usual choice for a variable whose:set function enables or disables a minor mode; with this choice,defining the variable will not call the minor mode function, butcustomizing the variable will do so. custom-initialize-reset Always use the :set function to initialize the variable. Ifthe variable is already non-void, reset it by calling the :setfunction using the current value (returned by the :get method).This is the default :initialize function. custom-initialize-changed Use the :set function to initialize the variable, if it isalready set or has been customized; otherwise, just useset-default. custom-initialize-safe-setcustom-initialize-safe-default These functions behave like custom-initialize-set(custom-initialize-default, respectively), but catch errors.If an error occurs during initialization, they set the variable tonil using set-default, and throw no error.These two functions are only meant for options defined in pre-loadedfiles, where some variables or functions used to compute the option'svalue may not yet be defined. The option normally gets updated instartup.el, ignoring the previously computed value. Because ofthis typical usage, the value which these two functions computenormally only matters when, after startup, one unsets the option'svalue and then reevaluates the defcustom. By that time, the necessaryvariables and functions will be defined, so there will not be an error. :set-after variables set-after, defcustom keywordWhen setting variables according to saved customizations, make sure toset the variables variables before this one; in other words, delaysetting this variable until after those others have been handled. Use:set-after if setting this variable won't work properly unlessthose other variables already have their intended values. The :require keyword is useful for an option that turns on the operation of a certain feature. Assuming that the package is coded to check the value of the option, you still need to arrange for the package to be loaded. You can do that with :require. See . Here is an example, from the library saveplace.el: (defcustom save-place nil "Non-nil means automatically save place in each file..." :type 'boolean :require 'saveplace :group 'save-place) If a customization item has a type such as hook or alist, which supports :options, you can add additional values to the list from outside the defcustom declaration by calling custom-add-frequent-value. For example, if you define a function my-lisp-mode-initialization intended to be called from emacs-lisp-mode-hook, you might want to add that to the list of reasonable values for emacs-lisp-mode-hook, but not by editing its definition. You can do it thus: (custom-add-frequent-value 'emacs-lisp-mode-hook 'my-lisp-mode-initialization) custom-add-frequent-value — Function: custom-add-frequent-value symbol value For the customization option symbol, add value to thelist of reasonable values.The precise effect of adding a value depends on the customization typeof symbol. Internally, defcustom uses the symbol property standard-value to record the expression for the standard value, and saved-value to record the value saved by the user with the customization buffer. Both properties are actually lists whose car is an expression which evaluates to the value. Customization Types customization types When you define a user option with defcustom, you must specify its customization type. That is a Lisp object which describes (1) which values are legitimate and (2) how to display the value in the customization buffer for editing. type, defcustom keyword You specify the customization type in defcustom with the :type keyword. The argument of :type is evaluated, but only once when the defcustom is executed, so it isn't useful for the value to vary. Normally we use a quoted constant. For example: (defcustom diff-command "diff" "The command to use to run diff." :type '(string) :group 'diff) In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (see ). Some of the type symbols do not use any arguments; those are called simple types. For a simple type, if you do not use any keyword-value pairs, you can omit the parentheses around the type symbol. For example just string as a customization type is equivalent to (string). All customization types are implemented as widgets; see See section ``Introduction'' in The Emacs Widget Library, for details. Simple Types This section describes all the simple customization types. sexp The value may be any Lisp object that can be printed and read back. Youcan use sexp as a fall-back for any option, if you don't want totake the time to work out a more specific type to use. integer The value must be an integer, and is represented textuallyin the customization buffer. number The value must be a number (floating point or integer), and isrepresented textually in the customization buffer. float The value must be a floating point number, and is representedtextually in the customization buffer. string The value must be a string, and the customization buffer shows just thecontents, with no delimiting ‘"’ characters and no quoting with‘\’. regexp Like string except that the string must be a valid regularexpression. character The value must be a character code. A character code is actually aninteger, but this type shows the value by inserting the character in thebuffer, rather than by showing the number. file The value must be a file name, and you can do completion withM-TAB. (file :must-match t) The value must be a file name for an existing file, and you can docompletion with M-TAB. directory The value must be a directory name, and you can do completion withM-TAB. hook The value must be a list of functions (or a single function, but that isobsolete usage). This customization type is used for hook variables.You can use the :options keyword in a hook variable'sdefcustom to specify a list of functions recommended for use inthe hook; see . alist The value must be a list of cons-cells, the car of each cellrepresenting a key, and the cdr of the same cell representing anassociated value. The user can add and delete key/value pairs, andedit both the key and the value of each pair.You can specify the key and value types like this: (alist :key-type key-type :value-type value-type) where key-type and value-type are customization typespecifications. The default key type is sexp, and the defaultvalue type is sexp.The user can add any key matching the specified key type, but you cangive some keys a preferential treatment by specifying them with the:options (see ). The specified keyswill always be shown in the customize buffer (together with a suitablevalue), with a checkbox to include or exclude or disable the key/valuepair from the alist. The user will not be able to edit the keysspecified by the :options keyword argument.The argument to the :options keywords should be a list ofspecifications for reasonable keys in the alist. Ordinarily, they aresimply atoms, which stand for themselves as. For example: :options '("foo" "bar" "baz") specifies that there are three “known” keys, namely "foo","bar" and "baz", which will always be shown first.You may want to restrict the value type for specific keys, forexample, the value associated with the "bar" key can only be aninteger. You can specify this by using a list instead of an atom inthe list. The first element will specify the key, like before, whilethe second element will specify the value type. For example: :options '("foo" ("bar" integer) "baz") Finally, you may want to change how the key is presented. By default,the key is simply shown as a const, since the user cannot changethe special keys specified with the :options keyword. However,you may want to use a more specialized type for presenting the key, likefunction-item if you know it is a symbol with a function binding.This is done by using a customization type specification instead of asymbol for the key. :options '("foo" ((function-item some-function) integer) "baz") Many alists use lists with two elements, instead of cons cells. Forexample, (defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3)) "Each element is a list of the form (KEY VALUE).") instead of (defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3)) "Each element is a cons-cell (KEY . VALUE).") Because of the way lists are implemented on top of cons cells, you cantreat list-alist in the example above as a cons cell alist, wherethe value type is a list with a single element containing the realvalue. (defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3)) "Each element is a list of the form (KEY VALUE)." :type '(alist :value-type (group integer))) The group widget is used here instead of list only becausethe formatting is better suited for the purpose.Similarly, you can have alists with more values associated with eachkey, using variations of this trick: (defcustom person-data '(("brian" 50 t) ("dorith" 55 nil) ("ken" 52 t)) "Alist of basic info about people. Each element has the form (NAME AGE MALE-FLAG)." :type '(alist :value-type (group integer boolean))) (defcustom pets '(("brian") ("dorith" "dog" "guppy") ("ken" "cat")) "Alist of people's pets. In an element (KEY . VALUE), KEY is the person's name, and the VALUE is a list of that person's pets." :type '(alist :value-type (repeat string))) plist The plist custom type is similar to the alist (see above),except that the information is stored as a property list, i.e. a list ofthis form: (key value key value key value …) The default :key-type for plist is symbol,rather than sexp. symbol The value must be a symbol. It appears in the customization buffer asthe name of the symbol. function The value must be either a lambda expression or a function name. Whenit is a function name, you can do completion with M-TAB. variable The value must be a variable name, and you can do completion withM-TAB. face The value must be a symbol which is a face name, and you can docompletion with M-TAB. boolean The value is boolean—either nil or t. Note that byusing choice and const together (see the next section),you can specify that the value must be nil or t, but alsospecify the text to describe each value in a way that fits the specificmeaning of the alternative. coding-system The value must be a coding-system name, and you can do completion withM-TAB. color The value must be a valid color name, and you can do completion withM-TAB. A sample is provided. Composite Types Composite Types (customization) When none of the simple types is appropriate, you can use composite types, which build new types from other types or from specified data. The specified types or data are called the arguments of the composite type. The composite type normally looks like this: (constructor arguments…) but you can also add keyword-value pairs before the arguments, like this: (constructor { keyword value } … arguments…) Here is a table of constructors and how to use them to write composite types: (cons car-type cdr-type) The value must be a cons cell, its car must fit car-type, andits cdr must fit cdr-type. For example, (cons stringsymbol) is a customization type which matches values such as("foo" . foo).In the customization buffer, the car and the cdr aredisplayed and edited separately, each according to the typethat you specify for it. (list element-types…) The value must be a list with exactly as many elements as theelement-types given; and each element must fit thecorresponding element-type.For example, (list integer string function) describes a list ofthree elements; the first element must be an integer, the second astring, and the third a function.In the customization buffer, each element is displayed and editedseparately, according to the type specified for it. (vector element-types…) Like list except that the value must be a vector instead of alist. The elements work the same as in list. (choice alternative-types…) The value must fit at least one of alternative-types.For example, (choice integer string) allows either aninteger or a string.In the customization buffer, the user selects an alternativeusing a menu, and can then edit the value in the usual way for thatalternative.Normally the strings in this menu are determined automatically from thechoices; however, you can specify different strings for the menu byincluding the :tag keyword in the alternatives. For example, ifan integer stands for a number of spaces, while a string is text to useverbatim, you might write the customization type this way, (choice (integer :tag "Number of spaces") (string :tag "Literal text")) so that the menu offers ‘Number of spaces’ and ‘Literal text’.In any alternative for which nil is not a valid value, other thana const, you should specify a valid default for that alternativeusing the :value keyword. See .If some values are covered by more than one of the alternatives,customize will choose the first alternative that the value fits. Thismeans you should always list the most specific types first, and themost general last. Here's an example of proper usage: (choice (const :tag "Off" nil) symbol (sexp :tag "Other")) This way, the special value nil is not treated like othersymbols, and symbols are not treated like other Lisp expressions. (radio element-types…) This is similar to choice, except that the choices are displayedusing `radio buttons' rather than a menu. This has the advantage ofdisplaying documentation for the choices when applicable and so is oftena good choice for a choice between constant functions(function-item customization types). (const value) The value must be value—nothing else is allowed.The main use of const is inside of choice. For example,(choice integer (const nil)) allows either an integer ornil.:tag is often used with const, inside of choice.For example, (choice (const :tag "Yes" t) (const :tag "No" nil) (const :tag "Ask" foo)) describes a variable for which t means yes, nil means no,and foo means “ask.” (other value) This alternative can match any Lisp value, but if the user chooses thisalternative, that selects the value value.The main use of other is as the last element of choice.For example, (choice (const :tag "Yes" t) (const :tag "No" nil) (other :tag "Ask" foo)) describes a variable for which t means yes, nil means no,and anything else means “ask.” If the user chooses ‘Ask’ fromthe menu of alternatives, that specifies the value foo; but anyother value (not t, nil or foo) displays as‘Ask’, just like foo. (function-item function) Like const, but used for values which are functions. Thisdisplays the documentation string as well as the function name.The documentation string is either the one you specify with:doc, or function's own documentation string. (variable-item variable) Like const, but used for values which are variable names. Thisdisplays the documentation string as well as the variable name. Thedocumentation string is either the one you specify with :doc, orvariable's own documentation string. (set types…) The value must be a list, and each element of the list must match one ofthe types specified.This appears in the customization buffer as a checklist, so that each oftypes may have either one corresponding element or none. It isnot possible to specify two different elements that match the same oneof types. For example, (set integer symbol) allows oneinteger and/or one symbol in the list; it does not allow multipleintegers or multiple symbols. As a result, it is rare to usenonspecific types such as integer in a set.Most often, the types in a set are const types, asshown here: (set (const :bold) (const :italic)) Sometimes they describe possible elements in an alist: (set (cons :tag "Height" (const height) integer) (cons :tag "Width" (const width) integer)) That lets the user specify a height value optionallyand a width value optionally. (repeat element-type) The value must be a list and each element of the list must fit the typeelement-type. This appears in the customization buffer as alist of elements, with ‘[INS]’ and ‘[DEL]’ buttons for addingmore elements or removing elements. (restricted-sexp :match-alternatives criteria) This is the most general composite type construct. The value may beany Lisp object that satisfies one of criteria. criteriashould be a list, and each element should be one of thesepossibilities: A predicate—that is, a function of one argument that has no sideeffects, and returns either nil or non-nil according tothe argument. Using a predicate in the list says that objects for whichthe predicate returns non-nil are acceptable. A quoted constant—that is, 'object. This sort of elementin the list says that object itself is an acceptable value. For example, (restricted-sexp :match-alternatives (integerp 't 'nil)) allows integers, t and nil as legitimate values.The customization buffer shows all legitimate values using their readsyntax, and the user edits them textually. Here is a table of the keywords you can use in keyword-value pairs in a composite type: :tag tag Use tag as the name of this alternative, for user communicationpurposes. This is useful for a type that appears inside of achoice. :match-alternatives criteria match-alternatives, customization keywordUse criteria to match possible values. This is used only inrestricted-sexp. :args argument-list args, customization keywordUse the elements of argument-list as the arguments of the typeconstruct. For instance, (const :args (foo)) is equivalent to(const foo). You rarely need to write :args explicitly,because normally the arguments are recognized automatically aswhatever follows the last keyword-value pair. Splicing into Lists The :inline feature lets you splice a variable number of elements into the middle of a list or vector. You use it in a set, choice or repeat type which appears among the element-types of a list or vector. Normally, each of the element-types in a list or vector describes one and only one element of the list or vector. Thus, if an element-type is a repeat, that specifies a list of unspecified length which appears as one element. But when the element-type uses :inline, the value it matches is merged directly into the containing sequence. For example, if it matches a list with three elements, those become three elements of the overall sequence. This is analogous to using ‘,@’ in the backquote construct. For example, to specify a list whose first element must be baz and whose remaining arguments should be zero or more of foo and bar, use this customization type: (list (const baz) (set :inline t (const foo) (const bar))) This matches values such as (baz), (baz foo), (baz bar) and (baz foo bar). When the element-type is a choice, you use :inline not in the choice itself, but in (some of) the alternatives of the choice. For example, to match a list which must start with a file name, followed either by the symbol t or two strings, use this customization type: (list file (choice (const t) (list :inline t string string))) If the user chooses the first alternative in the choice, then the overall list has two elements and the second element is t. If the user chooses the second alternative, then the overall list has three elements and the second and third must be strings. Type Keywords You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings: :value default This is used for a type that appears as an alternative inside ofchoice; it specifies the default value to use, at first, if andwhen the user selects this alternative with the menu in thecustomization buffer.Of course, if the actual value of the option fits this alternative, itwill appear showing the actual value, not default.If nil is not a valid value for the alternative, then it isessential to specify a valid default with :value. :format format-string format, customization keywordThis string will be inserted in the buffer to represent the valuecorresponding to the type. The following ‘%’ escapes are availablefor use in format-string: ‘%[button%]’ Display the text button marked as a button. The :actionattribute specifies what the button will do if the user invokes it;its value is a function which takes two arguments—the widget whichthe button appears in, and the event.There is no way to specify two different buttons with differentactions. ‘%{sample%}’ Show sample in a special face specified by :sample-face. ‘%v’ Substitute the item's value. How the value is represented depends onthe kind of item, and (for variables) on the customization type. ‘%d’ Substitute the item's documentation string. ‘%h’ Like ‘%d’, but if the documentation string is more than one line,add an active field to control whether to show all of it or just thefirst line. ‘%t’ Substitute the tag here. You specify the tag with the :tagkeyword. ‘%%’ Display a literal ‘%’. :action action action, customization keywordPerform action if the user clicks on a button. :button-face face button-face, customization keywordUse the face face (a face name or a list of face names) for buttontext displayed with ‘%[…%]’. :button-prefix prefix:button-suffix suffix button-prefix, customization keyword button-suffix, customization keywordThese specify the text to display before and after a button.Each can be: nil No text is inserted. a string The string is inserted literally. a symbol The symbol's value is used. :tag tag Use tag (a string) as the tag for the value (or part of the value)that corresponds to this type. :doc doc doc, customization keywordUse doc as the documentation string for this value (or part of thevalue) that corresponds to this type. In order for this to work, youmust specify a value for :format, and use ‘%d’ or ‘%h’in that value.The usual reason to specify a documentation string for a type is toprovide more information about the meanings of alternatives inside a:choice type or the parts of some other composite type. :help-echo motion-doc help-echo, customization keywordWhen you move to this item with widget-forward orwidget-backward, it will display the string motion-doc inthe echo area. In addition, motion-doc is used as the mousehelp-echo string and may actually be a function or form evaluatedto yield a help string. If it is a function, it is called with oneargument, the widget. :match function match, customization keywordSpecify how to decide whether a value matches the type. Thecorresponding value, function, should be a function that acceptstwo arguments, a widget and a value; it should return non-nil ifthe value is acceptable. Defining New Types In the previous sections we have described how to construct elaborate type specifications for defcustom. In some cases you may want to give such a type specification a name. The obvious case is when you are using the same type for many user options: rather than repeat the specification for each option, you can give the type specification a name, and use that name each defcustom. The other case is when a user option's value is a recursive data structure. To make it possible for a datatype to refer to itself, it needs to have a name. Since custom types are implemented as widgets, the way to define a new customize type is to define a new widget. We are not going to describe the widget interface here in details, see See section ``Introduction'' in The Emacs Widget Library, for that. Instead we are going to demonstrate the minimal functionality needed for defining new customize types by a simple example. (define-widget 'binary-tree-of-string 'lazy "A binary tree made of cons-cells and strings." :offset 4 :tag "Node" :type '(choice (string :tag "Leaf" :value "") (cons :tag "Interior" :value ("" . "") binary-tree-of-string binary-tree-of-string))) (defcustom foo-bar "" "Sample variable holding a binary tree of strings." :type 'binary-tree-of-string) The function to define a new widget is called define-widget. The first argument is the symbol we want to make a new widget type. The second argument is a symbol representing an existing widget, the new widget is going to be defined in terms of difference from the existing widget. For the purpose of defining new customization types, the lazy widget is perfect, because it accepts a :type keyword argument with the same syntax as the keyword argument to defcustom with the same name. The third argument is a documentation string for the new widget. You will be able to see that string with the M-x widget-browse RET binary-tree-of-string RET command. After these mandatory arguments follow the keyword arguments. The most important is :type, which describes the data type we want to match with this widget. Here a binary-tree-of-string is described as being either a string, or a cons-cell whose car and cdr are themselves both binary-tree-of-string. Note the reference to the widget type we are currently in the process of defining. The :tag attribute is a string to name the widget in the user interface, and the :offset argument is there to ensure that child nodes are indented four spaces relative to the parent node, making the tree structure apparent in the customization buffer. The defcustom shows how the new widget can be used as an ordinary customization type. The reason for the name lazy is that the other composite widgets convert their inferior widgets to internal form when the widget is instantiated in a buffer. This conversion is recursive, so the inferior widgets will convert their inferior widgets. If the data structure is itself recursive, this conversion is an infinite recursion. The lazy widget prevents the recursion: it convert its :type argument only when needed. <setfilename>../info/loading</setfilename> Loading loading library Lisp library Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file. The load functions evaluate all the expressions in a file just as the eval-buffer function evaluates all the expressions in a buffer. The difference is that the load functions read and evaluate the text in the file as found on disk, not the text in an Emacs buffer. top-level form The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions. A file containing Lisp code is often called a library. Thus, the “Rmail library” is a file containing code for Rmail mode. Similarly, a “Lisp library directory” is a directory of files containing Lisp code. How Programs Do Loading Emacs Lisp has several interfaces for loading. For example, autoload creates a placeholder object for a function defined in a file; trying to call the autoloading function loads the file to get the function's real definition (see ). require loads a file if it isn't already loaded (see ). Ultimately, all these facilities call the load function to do the work. load — Function: load filename &optional missing-ok nomessage nosuffix must-suffix This function finds and opens a file of Lisp code, evaluates all theforms in it, and closes the file.To find the file, load first looks for a file namedfilename.elc, that is, for a file whose name isfilename with the extension ‘.elc’ appended. If such afile exists, it is loaded. If there is no file by that name, thenload looks for a file named filename.el. If thatfile exists, it is loaded. Finally, if neither of those names isfound, load looks for a file named filename with nothingappended, and loads it if it exists. (The load function is notclever about looking at filename. In the perverse case of afile named foo.el.el, evaluation of (load "foo.el") willindeed find it.)If Auto Compression mode is enabled, as it is by default, then ifload can not find a file, it searches for a compressed versionof the file before trying other file names. It decompresses and loadsit if it exists. It looks for compressed versions by appending eachof the suffixes in jka-compr-load-suffixes to the file name.The value of this variable must be a list of strings. Its standardvalue is (".gz").If the optional argument nosuffix is non-nil, thenload does not try the suffixes ‘.elc’ and ‘.el’. Inthis case, you must specify the precise file name you want, exceptthat, if Auto Compression mode is enabled, load will still usejka-compr-load-suffixes to find compressed versions. Byspecifying the precise file name and using t fornosuffix, you can prevent perverse file names such asfoo.el.el from being tried.If the optional argument must-suffix is non-nil, thenload insists that the file name used must end in either‘.el’ or ‘.elc’ (possibly extended with a compressionsuffix), unless it contains an explicit directory name.If filename is a relative file name, such as foo orbaz/foo.bar, load searches for the file using the variableload-path. It appends filename to each of the directorieslisted in load-path, and loads the first file it finds whose namematches. The current default directory is tried only if it is specifiedin load-path, where nil stands for the default directory.load tries all three possible suffixes in the first directory inload-path, then all three suffixes in the second directory, andso on. See .If you get a warning that foo.elc is older than foo.el, itmeans you should consider recompiling foo.el. See .When loading a source file (not compiled), load performscharacter set translation just as Emacs would do when visiting the file.See .Messages like ‘Loading foo...’ and ‘Loading foo...done’ appearin the echo area during loading unless nomessage isnon-nil. load errorsAny unhandled errors while loading a file terminate loading. If theload was done for the sake of autoload, any function definitionsmade during the loading are undone. file-errorIf load can't find the file to load, then normally it signals theerror file-error (with ‘Cannot open load filefilename’). But if missing-ok is non-nil, thenload just returns nil.You can use the variable load-read-function to specify a functionfor load to use instead of read for reading expressions.See below.load returns t if the file loads successfully. load-file — Command: load-file filename This command loads the file filename. If filename is arelative file name, then the current default directory is assumed.This command does not use load-path, and does not appendsuffixes. However, it does look for compressed versions (if AutoCompression Mode is enabled). Use this command if you wish to specifyprecisely the file name to load. load-library — Command: load-library library This command loads the library named library. It is equivalent toload, except in how it reads its argument interactively. load-in-progress — Variable: load-in-progress This variable is non-nil if Emacs is in the process of loading afile, and it is nil otherwise. load-read-function — Variable: load-read-function This variable specifies an alternate expression-reading function forload and eval-region to use instead of read.The function should accept one argument, just as read does.Normally, the variable's value is nil, which means thosefunctions should use read.Instead of using this variable, it is cleaner to use another, newerfeature: to pass the function as the read-function argument toeval-region. See Eval. For information about how load is used in building Emacs, see . Load SuffixesWe now describe some technical details about the exact suffixes that load tries. load-suffixes — Variable: load-suffixes This is a list of suffixes indicating (compiled or source) Emacs Lispfiles. It should not include the empty string. load usesthese suffixes in order when it appends Lisp suffixes to the specifiedfile name. The standard value is (".elc" ".el") which producesthe behavior described in the previous section. load-file-rep-suffixes — Variable: load-file-rep-suffixes This is a list of suffixes that indicate representations of the samefile. This list should normally start with the empty string.When load searches for a file it appends the suffixes in thislist, in order, to the file name, before searching for another file.Enabling Auto Compression mode appends the suffixes injka-compr-load-suffixes to this list and disabling AutoCompression mode removes them again. The standard value ofload-file-rep-suffixes if Auto Compression mode is disabled is(""). Given that the standard value ofjka-compr-load-suffixes is (".gz"), the standard valueof load-file-rep-suffixes if Auto Compression mode is enabledis ("" ".gz"). get-load-suffixes — Function: get-load-suffixes This function returns the list of all suffixes that load shouldtry, in order, when its must-suffix argument is non-nil.This takes both load-suffixes and load-file-rep-suffixesinto account. If load-suffixes, jka-compr-load-suffixesand load-file-rep-suffixes all have their standard values, thisfunction returns (".elc" ".elc.gz" ".el" ".el.gz") if AutoCompression mode is enabled and (".elc" ".el") if AutoCompression mode is disabled. To summarize, load normally first tries the suffixes in the value of (get-load-suffixes) and then those in load-file-rep-suffixes. If nosuffix is non-nil, it skips the former group, and if must-suffix is non-nil, it skips the latter group. Library Search library search find library When Emacs loads a Lisp library, it searches for the library in a list of directories specified by the variable load-path. load-path — User Option: load-path EMACSLOADPATH environment variableThe value of this variable is a list of directories to search whenloading files with load. Each element is a string (which must bea directory name) or nil (which stands for the current workingdirectory). The value of load-path is initialized from the environment variable EMACSLOADPATH, if that exists; otherwise its default value is specified in emacs/src/epaths.h when Emacs is built. Then the list is expanded by adding subdirectories of the directories in the list. The syntax of EMACSLOADPATH is the same as used for PATH; ‘:’ (or ‘;’, according to the operating system) separates directory names, and ‘.’ is used for the current default directory. Here is an example of how to set your EMACSLOADPATH variable from a csh .login file: setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp Here is how to set it using sh: export EMACSLOADPATH EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp Here is an example of code you can place in your init file (see ) to add several directories to the front of your default load-path: (setq load-path (append (list nil "/user/bil/emacs" "/usr/local/lisplib" "~/emacs") load-path)) In this example, the path searches the current working directory first, followed then by the /user/bil/emacs directory, the /usr/local/lisplib directory, and the ~/emacs directory, which are then followed by the standard directories for Lisp code. Dumping Emacs uses a special value of load-path. If the value of load-path at the end of dumping is unchanged (that is, still the same special value), the dumped Emacs switches to the ordinary load-path value when it starts up, as described above. But if load-path has any other value at the end of dumping, that value is used for execution of the dumped Emacs also. Therefore, if you want to change load-path temporarily for loading a few libraries in site-init.el or site-load.el, you should bind load-path locally with let around the calls to load. The default value of load-path, when running an Emacs which has been installed on the system, includes two special directories (and their subdirectories as well): "/usr/local/share/emacs/version/site-lisp" and "/usr/local/share/emacs/site-lisp" The first one is for locally installed packages for a particular Emacs version; the second is for locally installed packages meant for use with all installed Emacs versions. There are several reasons why a Lisp package that works well in one Emacs version can cause trouble in another. Sometimes packages need updating for incompatible changes in Emacs; sometimes they depend on undocumented internal Emacs data that can change without notice; sometimes a newer Emacs version incorporates a version of the package, and should be used only with that version. Emacs finds these directories' subdirectories and adds them to load-path when it starts up. Both immediate subdirectories and subdirectories multiple levels down are added to load-path. Not all subdirectories are included, though. Subdirectories whose names do not start with a letter or digit are excluded. Subdirectories named RCS or CVS are excluded. Also, a subdirectory which contains a file named .nosearch is excluded. You can use these methods to prevent certain subdirectories of the site-lisp directories from being searched. If you run Emacs from the directory where it was built—that is, an executable that has not been formally installed—then load-path normally contains two additional directories. These are the lisp and site-lisp subdirectories of the main build directory. (Both are represented as absolute file names.) locate-library — Command: locate-library library &optional nosuffix path interactive-call This command finds the precise file name for library library. Itsearches for the library in the same way load does, and theargument nosuffix has the same meaning as in load: don'tadd suffixes ‘.elc’ or ‘.el’ to the specified namelibrary.If the path is non-nil, that list of directories is usedinstead of load-path.When locate-library is called from a program, it returns the filename as a string. When the user runs locate-libraryinteractively, the argument interactive-call is t, and thistells locate-library to display the file name in the echo area. Loading Non-ASCII Characters When Emacs Lisp programs contain string constants with non-ASCII characters, these can be represented within Emacs either as unibyte strings or as multibyte strings (see ). Which representation is used depends on how the file is read into Emacs. If it is read with decoding into multibyte representation, the text of the Lisp program will be multibyte text, and its string constants will be multibyte strings. If a file containing Latin-1 characters (for example) is read without decoding, the text of the program will be unibyte text, and its string constants will be unibyte strings. See . To make the results more predictable, Emacs always performs decoding into the multibyte representation when loading Lisp files, even if it was started with the ‘--unibyte’ option. This means that string constants with non-ASCII characters translate into multibyte strings. The only exception is when a particular file specifies no decoding. The reason Emacs is designed this way is so that Lisp programs give predictable results, regardless of how Emacs was started. In addition, this enables programs that depend on using multibyte text to work even in a unibyte Emacs. Of course, such programs should be designed to notice whether the user prefers unibyte or multibyte text, by checking default-enable-multibyte-characters, and convert representations appropriately. In most Emacs Lisp programs, the fact that non-ASCII strings are multibyte strings should not be noticeable, since inserting them in unibyte buffers converts them to unibyte automatically. However, if this does make a difference, you can force a particular Lisp file to be interpreted as unibyte by writing ‘-*-unibyte: t;-*-’ in a comment on the file's first line. With that designator, the file will unconditionally be interpreted as unibyte, even in an ordinary multibyte Emacs session. This can matter when making keybindings to non-ASCII characters written as ?vliteral. Autoload autoload The autoload facility allows you to make a function or macro known in Lisp, but put off loading the file that defines it. The first call to the function automatically reads the proper file to install the real definition and other associated code, then runs the real definition as if it had been loaded all along. There are two ways to set up an autoloaded function: by calling autoload, and by writing a special “magic” comment in the source before the real definition. autoload is the low-level primitive for autoloading; any Lisp program can call autoload at any time. Magic comments are the most convenient way to make a function autoload, for packages installed along with Emacs. These comments do nothing on their own, but they serve as a guide for the command update-file-autoloads, which constructs calls to autoload and arranges to execute them when Emacs is built. autoload — Function: autoload function filename &optional docstring interactive type This function defines the function (or macro) named function so asto load automatically from filename. The string filenamespecifies the file to load to get the real definition of function.If filename does not contain either a directory name, or thesuffix .el or .elc, then autoload insists on addingone of these suffixes, and it will not load from a file whose name isjust filename with no added suffix. (The variableload-suffixes specifies the exact required suffixes.)The argument docstring is the documentation string for thefunction. Specifying the documentation string in the call toautoload makes it possible to look at the documentation withoutloading the function's real definition. Normally, this should beidentical to the documentation string in the function definitionitself. If it isn't, the function definition's documentation stringtakes effect when it is loaded.If interactive is non-nil, that says function can becalled interactively. This lets completion in M-x work withoutloading function's real definition. The complete interactivespecification is not given here; it's not needed unless the useractually calls function, and when that happens, it's time to loadthe real definition.You can autoload macros and keymaps as well as ordinary functions.Specify type as macro if function is really a macro.Specify type as keymap if function is really akeymap. Various parts of Emacs need to know this information withoutloading the real definition.An autoloaded keymap loads automatically during key lookup when a prefixkey's binding is the symbol function. Autoloading does not occurfor other kinds of access to the keymap. In particular, it does nothappen when a Lisp program gets the keymap from the value of a variableand calls define-key; not even if the variable name is the samesymbol function. function cell in autoloadIf function already has a non-void function definition that is notan autoload object, autoload does nothing and returns nil.If the function cell of function is void, or is already an autoloadobject, then it is defined as an autoload object like this: (autoload filename docstring interactive type) For example, (symbol-function 'run-prolog) => (autoload "prolog" 169681 t nil) In this case, "prolog" is the name of the file to load, 169681refers to the documentation string in theemacs/etc/DOC-version file (see ),t means the function is interactive, and nil that it isnot a macro or a keymap. autoload errors The autoloaded file usually contains other definitions and may require or provide one or more features. If the file is not completely loaded (due to an error in the evaluation of its contents), any function definitions or provide calls that occurred during the load are undone. This is to ensure that the next attempt to call any function autoloading from this file will try again to load the file. If not for this, then some of the functions in the file might be defined by the aborted load, but fail to work properly for the lack of certain subroutines not loaded successfully because they come later in the file. If the autoloaded file fails to define the desired Lisp function or macro, then an error is signaled with data "Autoloading failed to define function function-name". update-file-autoloads update-directory-autoloads magic autoload comment autoload cookie A magic autoload comment (often called an autoload cookie) consists of ‘;;;###autoload’, on a line by itself, just before the real definition of the function in its autoloadable source file. The command M-x update-file-autoloads writes a corresponding autoload call into loaddefs.el. Building Emacs loads loaddefs.el and thus calls autoload. M-x update-directory-autoloads is even more powerful; it updates autoloads for all files in the current directory. The same magic comment can copy any kind of form into loaddefs.el. If the form following the magic comment is not a function-defining form or a defcustom form, it is copied verbatim. “Function-defining forms” include define-skeleton, define-derived-mode, define-generic-mode and define-minor-mode as well as defun and defmacro. To save space, a defcustom form is converted to a defvar in loaddefs.el, with some additional information if it uses :require. You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but M-x update-file-autoloads copies it to loaddefs.el, where it is executed while building Emacs. The following example shows how doctor is prepared for autoloading with a magic comment: ;;;###autoload (defun doctor () "Switch to *doctor* buffer and start giving psychotherapy." (interactive) (switch-to-buffer "*doctor*") (doctor-mode)) Here's what that produces in loaddefs.el: (autoload (quote doctor) "doctor" "\ Switch to *doctor* buffer and start giving psychotherapy. \(fn)" t nil) fn in function's documentation string The backslash and newline immediately following the double-quote are a convention used only in the preloaded uncompiled Lisp files such as loaddefs.el; they tell make-docfile to put the documentation string in the etc/DOC file. See . See also the commentary in lib-src/make-docfile.c. ‘(fn)’ in the usage part of the documentation string is replaced with the function's name when the various help functions (see ) display it. If you write a function definition with an unusual macro that is not one of the known and recognized function definition methods, use of an ordinary magic autoload comment would copy the whole definition into loaddefs.el. That is not desirable. You can put the desired autoload call into loaddefs.el instead by writing this: ;;;###autoload (autoload 'foo "myfile") (mydefunmacro foo ...) Repeated Loading repeated loading You can load a given file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from. When you load or reload files, bear in mind that the load and load-library functions automatically load a byte-compiled file rather than a non-compiled file of similar name. If you rewrite a file that you intend to save and reinstall, you need to byte-compile the new version; otherwise Emacs will load the older, byte-compiled file instead of your newer, non-compiled file! If that happens, the message displayed when loading the file includes, ‘(compiled; note, source is newer)’, to remind you to recompile it. When writing the forms in a Lisp library file, keep in mind that the file might be loaded more than once. For example, think about whether each variable should be reinitialized when you reload the library; defvar does not change the value if the variable is already initialized. (See .) The simplest way to add an element to an alist is like this: (push '(leif-mode " Leif") minor-mode-alist) But this would add multiple elements if the library is reloaded. To avoid the problem, write this: (or (assq 'leif-mode minor-mode-alist) (push '(leif-mode " Leif") minor-mode-alist)) or this: (add-to-list '(leif-mode " Leif") minor-mode-alist) Occasionally you will want to test explicitly whether a library has already been loaded. Here's one way to test, in a library, whether it has been loaded before: (defvar foo-was-loaded nil) (unless foo-was-loaded execute-first-time-only (setq foo-was-loaded t)) If the library uses provide to provide a named feature, you can use featurep earlier in the file to test whether the provide call has been executed before. See . Features features requiring features providing features provide and require are an alternative to autoload for loading files automatically. They work in terms of named features. Autoloading is triggered by calling a specific function, but a feature is loaded the first time another program asks for it by name. A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn't been loaded already. To require the presence of a feature, call require with the feature name as argument. require looks in the global variable features to see whether the desired feature has been provided already. If not, it loads the feature from the appropriate file. This file should call provide at the top level to add the feature to features; if it fails to do so, require signals an error. load error with require For example, in emacs/lisp/prolog.el, the definition for run-prolog includes the following code: (defun run-prolog () "Run an inferior Prolog process, with I/O via buffer *prolog*." (interactive) (require 'comint) (switch-to-buffer (make-comint "prolog" prolog-program-name)) (inferior-prolog-mode)) The expression (require 'comint) loads the file comint.el if it has not yet been loaded. This ensures that make-comint is defined. Features are normally named after the files that provide them, so that require need not be given the file name. The comint.el file contains the following top-level expression: (provide 'comint) This adds comint to the global features list, so that (require 'comint) will henceforth know that nothing needs to be done. byte-compiling require When require is used at top level in a file, it takes effect when you byte-compile that file (see ) as well as when you load it. This is in case the required package contains macros that the byte compiler must know about. It also avoids byte-compiler warnings for functions and variables defined in the file loaded with require. Although top-level calls to require are evaluated during byte compilation, provide calls are not. Therefore, you can ensure that a file of definitions is loaded before it is byte-compiled by including a provide followed by a require for the same feature, as in the following example. (provide 'my-feature) ; Ignored by byte compiler, ; evaluated by load. (require 'my-feature) ; Evaluated by byte compiler. The compiler ignores the provide, then processes the require by loading the file in question. Loading the file does execute the provide call, so the subsequent require call does nothing when the file is loaded. provide — Function: provide feature &optional subfeatures This function announces that feature is now loaded, or beingloaded, into the current Emacs session. This means that the facilitiesassociated with feature are or will be available for other Lispprograms.The direct effect of calling provide is to add feature tothe front of the list features if it is not already in the list.The argument feature must be a symbol. provide returnsfeature.If provided, subfeatures should be a list of symbols indicatinga set of specific subfeatures provided by this version offeature. You can test the presence of a subfeature usingfeaturep. The idea of subfeatures is that you use them when apackage (which is one feature) is complex enough to make ituseful to give names to various parts or functionalities of thepackage, which might or might not be loaded, or might or might not bepresent in a given version. See , foran example. features => (bar bish) (provide 'foo) => foo features => (foo bar bish) When a file is loaded to satisfy an autoload, and it stops due to anerror in the evaluation of its contents, any function definitions orprovide calls that occurred during the load are undone.See . require — Function: require feature &optional filename noerror This function checks whether feature is present in the currentEmacs session (using (featurep feature); see below). Theargument feature must be a symbol.If the feature is not present, then require loads filenamewith load. If filename is not supplied, then the name ofthe symbol feature is used as the base file name to load.However, in this case, require insists on finding featurewith an added ‘.el’ or ‘.elc’ suffix (possibly extended witha compression suffix); a file whose name is just feature won'tbe used. (The variable load-suffixes specifies the exactrequired Lisp suffixes.)If noerror is non-nil, that suppresses errors from actualloading of the file. In that case, require returns nilif loading the file fails. Normally, require returnsfeature.If loading the file succeeds but does not provide feature,require signals an error, ‘Required feature featurewas not provided’. featurep — Function: featurep feature &optional subfeature This function returns t if feature has been provided inthe current Emacs session (i.e., if feature is a member offeatures.) If subfeature is non-nil, then thefunction returns t only if that subfeature is provided as well(i.e. if subfeature is a member of the subfeatureproperty of the feature symbol.) features — Variable: features The value of this variable is a list of symbols that are the featuresloaded in the current Emacs session. Each symbol was put in this listwith a call to provide. The order of the elements in thefeatures list is not significant. Which File Defined a Certain Symbol symbol-file — Function: symbol-file symbol &optional type This function returns the name of the file that defined symbol.If type is nil, then any kind of definition isacceptable. If type is defun or defvar, thatspecifies function definition only or variable definition only.The value is normally an absolute file name. It can also benil, if the definition is not associated with any file. The basis for symbol-file is the data in the variable load-history. load-history — Variable: load-history This variable's value is an alist connecting library file names with thenames of functions and variables they define, the features they provide,and the features they require.Each element is a list and describes one library. The car of thelist is the absolute file name of the library, as a string. The restof the list elements have these forms: var The symbol var was defined as a variable. (defun . fun) The function fun was defined. (t . fun) The function fun was previously an autoload before this libraryredefined it as a function. The following element is always(defun . fun), which represents defining fun as afunction. (autoload . fun) The function fun was defined as an autoload. (require . feature) The feature feature was required. (provide . feature) The feature feature was provided. The value of load-history may have one element whose car isnil. This element describes definitions made witheval-buffer on a buffer that is not visiting a file. The command eval-region updates load-history, but does so by adding the symbols defined to the element for the file being visited, rather than replacing that element. See . Unloading unloading packages You can discard the functions and variables loaded by a library to reclaim memory for other Lisp objects. To do this, use the function unload-feature: unload-feature — Command: unload-feature feature &optional force This command unloads the library that provided feature feature.It undefines all functions, macros, and variables defined in thatlibrary with defun, defalias, defsubst,defmacro, defconst, defvar, and defcustom.It then restores any autoloads formerly associated with those symbols.(Loading saves these in the autoload property of the symbol.) unload-feature-special-hooksBefore restoring the previous definitions, unload-feature runsremove-hook to remove functions in the library from certainhooks. These hooks include variables whose names end in ‘hook’or ‘-hooks’, plus those listed inunload-feature-special-hooks. This is to prevent Emacs fromceasing to function because important hooks refer to functions thatare no longer defined. feature-unload-hookIf these measures are not sufficient to prevent malfunction, a librarycan define an explicit unload hook. If feature-unload-hookis defined, it is run as a normal hook before restoring the previousdefinitions, instead of the usual hook-removing actions. Theunload hook ought to undo all the global state changes made by thelibrary that might cease to work once the library is unloaded.unload-feature can cause problems with libraries that fail to dothis, so it should be used with caution.Ordinarily, unload-feature refuses to unload a library on whichother loaded libraries depend. (A library a depends on libraryb if a contains a require for b.) If theoptional argument force is non-nil, dependencies areignored and you can unload any library. The unload-feature function is written in Lisp; its actions are based on the variable load-history. unload-feature-special-hooks — Variable: unload-feature-special-hooks This variable holds a list of hooks to be scanned before unloading alibrary, to remove functions defined in the library. Hooks for Loading loading hooks hooks for loading You can ask for code to be executed if and when a particular library is loaded, by calling eval-after-load. eval-after-load — Function: eval-after-load library form This function arranges to evaluate form at the end of loadingthe file library, each time library is loaded. Iflibrary is already loaded, it evaluates form right away.Don't forget to quote form!You don't need to give a directory or extension in the file namelibrary—normally you just give a bare file name, like this: (eval-after-load "edebug" '(def-edebug-spec c-point t)) To restrict which files can trigger the evaluation, include adirectory or an extension or both in library. Only a file whoseabsolute true name (i.e., the name with all symbolic links chased out)matches all the given name components will match. In the followingexample, my_inst.elc or my_inst.elc.gz in some directory..../foo/bar will trigger the evaluation, but notmy_inst.el: (eval-after-load "foo/bar/my_inst.elc" …) library can also be a feature (i.e. a symbol), in which caseform is evaluated when (provide library) is called.An error in form does not undo the load, but does preventexecution of the rest of form. In general, well-designed Lisp programs should not use this feature. The clean and modular ways to interact with a Lisp library are (1) examine and set the library's variables (those which are meant for outside use), and (2) call the library's functions. If you wish to do (1), you can do it immediately—there is no need to wait for when the library is loaded. To do (2), you must load the library (preferably with require). But it is OK to use eval-after-load in your personal customizations if you don't feel they must meet the design standards for programs meant for wider use. after-load-alist — Variable: after-load-alist This variable, an alist built by eval-after-load, holds theexpressions to evaluate when particular libraries are loaded. Eachelement looks like this: (regexp-or-feature forms…) The key regexp-or-feature is either a regular expression or asymbol, and the value is a list of forms. The forms are evaluated whenthe key matches the absolute true name of the file beingloaded or the symbol being provided. <setfilename>../info/compile</setfilename> Byte Compilation byte compilation byte-code compilation (Emacs Lisp) Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter. Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code. Compiling a Lisp file with the Emacs byte compiler always reads the file as multibyte text, even if Emacs was started with ‘--unibyte’, unless the file specifies otherwise. This is so that compilation gives results compatible with running the same file without compilation. See . In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true. no-byte-compile If you do not want a Lisp file to be compiled, ever, put a file-local variable binding for no-byte-compile into it, like this: ;; -*-no-byte-compile: t; -*- See , for how to investigate errors occurring in byte compilation. Performance of Byte-Compiled Code A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example: (defun silly-loop (n) "Return time before and after N iterations of a loop." (let ((t1 (current-time-string))) (while (> (setq n (1- n)) 0)) (list t1 (current-time-string)))) => silly-loop (silly-loop 100000) => ("Fri Mar 18 17:25:57 1994" "Fri Mar 18 17:26:28 1994") ; 31 seconds (byte-compile 'silly-loop) => [Compiled code not shown] (silly-loop 100000) => ("Fri Mar 18 17:26:52 1994" "Fri Mar 18 17:26:58 1994") ; 6 seconds In this example, the interpreted code required 31 seconds to run, whereas the byte-compiled code required 6 seconds. These results are representative, but actual results will vary greatly. The Compilation Functions compilation functions You can byte-compile an individual function or macro definition with the byte-compile function. You can compile a whole file with byte-compile-file, or several files with byte-recompile-directory or batch-byte-compile. The byte compiler produces error messages and warnings about each file in a buffer called ‘*Compile-Log*’. These report things in your program that suggest a problem but are not necessarily erroneous. macro compilation Be careful when writing macro calls in files that you may someday byte-compile. Macro calls are expanded when they are compiled, so the macros must already be defined for proper compilation. For more details, see . If a program does not work the same way when compiled as it does when interpreted, erroneous macro definitions are one likely cause (see ). Inline (defsubst) functions are less troublesome; if you compile a call to such a function before its definition is known, the call will still work right, it will just run slower. Normally, compiling a file does not evaluate the file's contents or load the file. But it does execute any require calls at top level in the file. One way to ensure that necessary macro definitions are available during compilation is to require the file that defines them (see ). To avoid loading the macro definition files when someone runs the compiled program, write eval-when-compile around the require calls (see ). byte-compile — Function: byte-compile symbol This function byte-compiles the function definition of symbol,replacing the previous definition with the compiled one. The functiondefinition of symbol must be the actual code for the function;i.e., the compiler does not follow indirection to another symbol.byte-compile returns the new, compiled definition ofsymbol. If symbol's definition is a byte-code function object,byte-compile does nothing and returns nil. Lisp recordsonly one function definition for any symbol, and if that is alreadycompiled, non-compiled code is not available anywhere. So there is noway to “compile the same definition again.” (defun factorial (integer) "Compute factorial of INTEGER." (if (= 1 integer) 1 (* integer (factorial (1- integer))))) => factorial (byte-compile 'factorial) => #[(integer) "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207" [integer 1 * factorial] 4 "Compute factorial of INTEGER."] The result is a byte-code function object. The string it contains isthe actual byte-code; each character in it is an instruction or anoperand of an instruction. The vector contains all the constants,variable names and function names used by the function, except forcertain primitives that are coded as special instructions.If the argument to byte-compile is a lambda expression,it returns the corresponding compiled code, but does not storeit anywhere. compile-defun — Command: compile-defun &optional arg This command reads the defun containing point, compiles it, andevaluates the result. If you use this on a defun that is actually afunction definition, the effect is to install a compiled version of thatfunction.compile-defun normally displays the result of evaluation in theecho area, but if arg is non-nil, it inserts the resultin the current buffer after the form it compiled. byte-compile-file — Command: byte-compile-file filename &optional load This function compiles a file of Lisp code named filename into afile of byte-code. The output file's name is made by changing the‘.el’ suffix into ‘.elc’; if filename does not end in‘.el’, it adds ‘.elc’ to the end of filename.Compilation works by reading the input file one form at a time. If itis a definition of a function or macro, the compiled function or macrodefinition is written out. Other forms are batched together, then eachbatch is compiled, and written so that its compiled code will beexecuted when the file is read. All comments are discarded when theinput file is read.This command returns t if there were no errors and nilotherwise. When called interactively, it prompts for the file name.If load is non-nil, this command loads the compiled fileafter compiling it. Interactively, load is the prefix argument. % ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el (byte-compile-file "~/emacs/push.el") => t % ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el -rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc byte-recompile-directory — Command: byte-recompile-directory directory &optional flag force library compilationThis command recompiles every ‘.el’ file in directory (orits subdirectories) that needs recompilation. A file needsrecompilation if a ‘.elc’ file exists but is older than the‘.el’ file.When a ‘.el’ file has no corresponding ‘.elc’ file,flag says what to do. If it is nil, this command ignoresthese files. If flag is 0, it compiles them. If it is neithernil nor 0, it asks the user whether to compile each such file,and asks about each subdirectory as well.Interactively, byte-recompile-directory prompts fordirectory and flag is the prefix argument.If force is non-nil, this command recompiles every‘.el’ file that has a ‘.elc’ file.The returned value is unpredictable. batch-byte-compile — Function: batch-byte-compile &optional noforce This function runs byte-compile-file on files specified on thecommand line. This function must be used only in a batch execution ofEmacs, as it kills Emacs on completion. An error in one file does notprevent processing of subsequent files, but no output file will begenerated for it, and the Emacs process will terminate with a nonzerostatus code.If noforce is non-nil, this function does not recompilefiles that have an up-to-date ‘.elc’ file. % emacs -batch -f batch-byte-compile *.el byte-code — Function: byte-code code-string data-vector max-stack byte-code interpreterThis function actually interprets byte-code. A byte-compiled functionis actually defined with a body that calls byte-code. Don't callthis function yourself—only the byte compiler knows how to generatevalid calls to this function.In Emacs version 18, byte-code was always executed by way of a call tothe function byte-code. Nowadays, byte-code is usually executedas part of a byte-code function object, and only rarely through anexplicit call to byte-code. Documentation Strings and Compilation dynamic loading of documentation Functions and variables loaded from a byte-compiled file access their documentation strings dynamically from the file whenever needed. This saves space within Emacs, and makes loading faster because the documentation strings themselves need not be processed while loading the file. Actual access to the documentation strings becomes slower as a result, but this normally is not enough to bother users. Dynamic access to documentation strings does have drawbacks: If you delete or move the compiled file after loading it, Emacs can nolonger access the documentation strings for the functions and variablesin the file. If you alter the compiled file (such as by compiling a new version),then further access to documentation strings in this file willprobably give nonsense results. If your site installs Emacs following the usual procedures, these problems will never normally occur. Installing a new version uses a new directory with a different name; as long as the old version remains installed, its files will remain unmodified in the places where they are expected to be. However, if you have built Emacs yourself and use it from the directory where you built it, you will experience this problem occasionally if you edit and recompile Lisp files. When it happens, you can cure the problem by reloading the file after recompiling it. You can turn off this feature at compile time by setting byte-compile-dynamic-docstrings to nil; this is useful mainly if you expect to change the file, and you want Emacs processes that have already loaded it to keep working when the file changes. You can do this globally, or for one source file by specifying a file-local binding for the variable. One way to do that is by adding this string to the file's first line: -*-byte-compile-dynamic-docstrings: nil;-*- byte-compile-dynamic-docstrings — Variable: byte-compile-dynamic-docstrings If this is non-nil, the byte compiler generates compiled filesthat are set up for dynamic loading of documentation strings. ‘#@count’ ‘#$’ The dynamic documentation string feature writes compiled files that use a special Lisp reader construct, ‘#@count’. This construct skips the next count characters. It also uses the ‘#$’ construct, which stands for “the name of this file, as a string.” It is usually best not to use these constructs in Lisp source files, since they are not designed to be clear to humans reading the file. Dynamic Loading of Individual Functions dynamic loading of functions lazy loading When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn't fully read the function definitions in the file. Instead, each function definition contains a place-holder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder. The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate user-callable functions, if using one of them does not imply you will probably also use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides. The dynamic loading feature has certain disadvantages: If you delete or move the compiled file after loading it, Emacs can nolonger load the remaining function definitions not already loaded. If you alter the compiled file (such as by compiling a new version),then trying to load any function not already loaded will usually yieldnonsense results. These problems will never happen in normal circumstances with installed Emacs files. But they are quite likely to happen with Lisp files that you are changing. The easiest way to prevent these problems is to reload the new compiled file immediately after each recompilation. The byte compiler uses the dynamic function loading feature if the variable byte-compile-dynamic is non-nil at compilation time. Do not set this variable globally, since dynamic loading is desirable only for certain files. Instead, enable the feature for specific source files with file-local variable bindings. For example, you could do it by writing this text in the source file's first line: -*-byte-compile-dynamic: t;-*- byte-compile-dynamic — Variable: byte-compile-dynamic If this is non-nil, the byte compiler generates compiled filesthat are set up for dynamic function loading. fetch-bytecode — Function: fetch-bytecode function If function is a byte-code function object, this immediatelyfinishes loading the byte code of function from itsbyte-compiled file, if it is not fully loaded already. Otherwise,it does nothing. It always returns function. Evaluation During Compilation These features permit you to write code to be evaluated during compilation of a program. eval-and-compile — Special Form: eval-and-compile body … This form marks body to be evaluated both when you compile thecontaining code and when you run it (whether compiled or not).You can get a similar result by putting body in a separate fileand referring to that file with require. That method ispreferable when body is large. Effectively require isautomatically eval-and-compile, the package is loaded both whencompiling and executing.autoload is also effectively eval-and-compile too. It'srecognized when compiling, so uses of such a function don't produce“not known to be defined” warnings.Most uses of eval-and-compile are fairly sophisticated.If a macro has a helper function to build its result, and that macrois used both locally and outside the package, theneval-and-compile should be used to get the helper both whencompiling and then later when running.If functions are defined programmatically (with fset say), theneval-and-compile can be used to have that done at compile-timeas well as run-time, so calls to those functions are checked (andwarnings about “not known to be defined” suppressed). eval-when-compile — Special Form: eval-when-compile body … This form marks body to be evaluated at compile time but not whenthe compiled program is loaded. The result of evaluation by thecompiler becomes a constant which appears in the compiled program. Ifyou load the source file, rather than compiling it, body isevaluated normally. compile-time constantIf you have a constant that needs some calculation to produce,eval-when-compile can do that at compile-time. For example,(defvar my-regexp (eval-when-compile (regexp-opt '("aaa" "aba" "abb")))) macros, at compile timeIf you're using another package, but only need macros from it (thebyte compiler will expand those), then eval-when-compile can beused to load it for compiling, but not executing. For example,(eval-when-compile (require 'my-macro-package)) ;; only macros needed from thisThe same sort of thing goes for macros and defsubst functionsdefined locally and only for use within the file. They are needed forcompiling the file, but in most cases they are not needed forexecution of the compiled file. For example,(eval-when-compile (unless (fboundp 'some-new-thing) (defmacro 'some-new-thing () (compatibility code))))This is often good for code that's only a fallback for compatibilitywith other versions of Emacs.Common Lisp Note: At top level, eval-when-compile is analogous to the CommonLisp idiom (eval-when (compile eval) …). Elsewhere, theCommon Lisp ‘#.’ reader macro (but not when interpreting) is closerto what eval-when-compile does. Compiler Errors compiler errors Byte compilation outputs all errors and warnings into the buffer ‘*Compile-Log*’. The messages include file names and line numbers that identify the location of the problem. The usual Emacs commands for operating on compiler diagnostics work properly on these messages. However, the warnings about functions that were used but not defined are always “located” at the end of the file, so these commands won't find the places they are really used. To do that, you must search for the function names. You can suppress the compiler warning for calling an undefined function func by conditionalizing the function call on an fboundp test, like this: (if (fboundp 'func) ...(func ...)...) The call to func must be in the then-form of the if, and func must appear quoted in the call to fboundp. (This feature operates for cond as well.) Likewise, you can suppress a compiler warning for an unbound variable variable by conditionalizing its use on a boundp test, like this: (if (boundp 'variable) ...variable...) The reference to variable must be in the then-form of the if, and variable must appear quoted in the call to boundp. You can suppress any compiler warnings using the construct with-no-warnings: with-no-warnings — Special Form: with-no-warnings body … In execution, this is equivalent to (progn body...),but the compiler does not issue warnings for anything that occursinside body.We recommend that you use this construct around the smallestpossible piece of code. Byte-Code Function Objects compiled function byte-code function Byte-compiled functions have a special data type: they are byte-code function objects. Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’. A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements have any normal use. They are: arglist The list of argument symbols. byte-code The string containing the byte-code instructions. constants The vector of Lisp objects referenced by the byte code. These includesymbols used as function names and variable names. stacksize The maximum stack size this function needs. docstring The documentation string (if any); otherwise, nil. The value maybe a number or a list, in case the documentation string is stored in afile. Use the function documentation to get the realdocumentation string (see ). interactive The interactive spec (if any). This can be a string or a Lispexpression. It is nil for a function that isn't interactive. Here's an example of a byte-code function object, in printed representation. It is the definition of the command backward-sexp. #[(&optional arg) "^H\204^F^@\301^P\302^H[!\207" [arg 1 forward-sexp] 2 254435 "p"] The primitive way to create a byte-code object is with make-byte-code: make-byte-code — Function: make-byte-code &rest elements This function constructs and returns a byte-code function objectwith elements as its elements. You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope). You can access the elements of a byte-code object using aref; you can also use vconcat to create a vector with the same elements. Disassembled Byte-Code disassembled byte-code People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into humanly readable form. The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function. In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack. disassemble — Command: disassemble object &optional buffer-or-name This command displays the disassembled code for object. Ininteractive use, or if buffer-or-name is nil or omitted,the output goes in a buffer named ‘*Disassemble*’. Ifbuffer-or-name is non-nil, it must be a buffer or thename of an existing buffer. Then the output goes there, at point, andpoint is left before the output.The argument object can be a function name, a lambda expressionor a byte-code object. If it is a lambda expression, disassemblecompiles it and disassembles the resulting compiled code. Here are two examples of using the disassemble function. We have added explanatory comments to help you relate the byte-code to the Lisp source; these do not appear in the output of disassemble. These examples show unoptimized byte-code. Nowadays byte-code is usually optimized, but we did not want to rewrite these examples, since they still serve their purpose. (defun factorial (integer) "Compute factorial of an integer." (if (= 1 integer) 1 (* integer (factorial (1- integer))))) => factorial (factorial 4) => 24 (disassemble 'factorial) -| byte-code for factorial: doc: Compute factorial of an integer. args: (integer) 0 constant 1 ; Push 1 onto stack. 1 varref integer ; Get value of integer ; from the environment ; and push the value ; onto the stack. 2 eqlsign ; Pop top two values off stack, ; compare them, ; and push result onto stack. 3 goto-if-nil 10 ; Pop and test top of stack; ; if nil, go to 10, ; else continue. 6 constant 1 ; Push 1 onto top of stack. 7 goto 17 ; Go to 17 (in this case, 1 will be ; returned by the function). 10 constant * ; Push symbol * onto stack. 11 varref integer ; Push value of integer onto stack. 12 constant factorial ; Push factorial onto stack. 13 varref integer ; Push value of integer onto stack. 14 sub1 ; Pop integer, decrement value, ; push new value onto stack. ; Stack now contains: ; − decremented value of integer ; − factorial ; − value of integer ; − * 15 call 1 ; Call function factorial using ; the first (i.e., the top) element ; of the stack as the argument; ; push returned value onto stack. ; Stack now contains: ; − result of recursive ; call to factorial ; − value of integer ; − * 16 call 2 ; Using the first two ; (i.e., the top two) ; elements of the stack ; as arguments, ; call the function *, ; pushing the result onto the stack. 17 return ; Return the top element ; of the stack. => nil The silly-loop function is somewhat more complex: (defun silly-loop (n) "Return time before and after N iterations of a loop." (let ((t1 (current-time-string))) (while (> (setq n (1- n)) 0)) (list t1 (current-time-string)))) => silly-loop (disassemble 'silly-loop) -| byte-code for silly-loop: doc: Return time before and after N iterations of a loop. args: (n) 0 constant current-time-string ; Push ; current-time-string ; onto top of stack. 1 call 0 ; Call current-time-string ; with no argument, ; pushing result onto stack. 2 varbind t1 ; Pop stack and bind t1 ; to popped value. 3 varref n ; Get value of n from ; the environment and push ; the value onto the stack. 4 sub1 ; Subtract 1 from top of stack. 5 dup ; Duplicate the top of the stack; ; i.e., copy the top of ; the stack and push the ; copy onto the stack. 6 varset n ; Pop the top of the stack, ; and bind n to the value. ; In effect, the sequence dup varset ; copies the top of the stack ; into the value of n ; without popping it. 7 constant 0 ; Push 0 onto stack. 8 gtr ; Pop top two values off stack, ; test if n is greater than 0 ; and push result onto stack. 9 goto-if-nil-else-pop 17 ; Goto 17 if n <= 0 ; (this exits the while loop). ; else pop top of stack ; and continue 12 constant nil ; Push nil onto stack ; (this is the body of the loop). 13 discard ; Discard result of the body ; of the loop (a while loop ; is always evaluated for ; its side effects). 14 goto 3 ; Jump back to beginning ; of while loop. 17 discard ; Discard result of while loop ; by popping top of stack. ; This result is the value nil that ; was not popped by the goto at 9. 18 varref t1 ; Push value of t1 onto stack. 19 constant current-time-string ; Push ; current-time-string ; onto top of stack. 20 call 0 ; Call current-time-string again. 21 list2 ; Pop top two elements off stack, ; create a list of them, ; and push list onto stack. 22 unbind 1 ; Unbind t1 in local environment. 23 return ; Return value of the top of stack. => nil <setfilename>../info/advising</setfilename> Advising Emacs Lisp Functions advising functions The advice feature lets you add to the existing definition of a function, by advising the function. This is a cleaner method for a library to customize functions defined within Emacs—cleaner than redefining the whole function. piece of advice Each function can have multiple pieces of advice, separately defined. Each defined piece of advice can be enabled or disabled explicitly. All the enabled pieces of advice for any given function actually take effect when you activate advice for that function, or when you define or redefine the function. Note that enabling a piece of advice and activating advice for a function are not the same thing. Usage Note: Advice is useful for altering the behavior of existing calls to an existing function. If you want the new behavior for new calls, or for key bindings, you should define a new function (or a new command) which uses the existing function. Usage note: Advising a function can cause confusion in debugging, since people who debug calls to the original function may not notice that it has been modified with advice. Therefore, if you have the possibility to change the code of that function (or ask someone to do so) to run a hook, please solve the problem that way. Advice should be reserved for the cases where you cannot get the function changed. In particular, this means that a file in Emacs should not put advice on a function in Emacs. There are currently a few exceptions to this convention, but we aim to correct them. A Simple Advice Example The command next-line moves point down vertically one or more lines; it is the standard binding of C-n. When used on the last line of the buffer, this command inserts a newline to create a line to move to if next-line-add-newlines is non-nil (its default is nil.) Suppose you wanted to add a similar feature to previous-line, which would insert a new line at the beginning of the buffer for the command to move to (when next-line-add-newlines is non-nil). How could you do this? You could do it by redefining the whole function, but that is not modular. The advice feature provides a cleaner alternative: you can effectively add your code to the existing function definition, without actually changing or even seeing that definition. Here is how to do this: (defadvice previous-line (before next-line-at-end (&optional arg try-vscroll)) "Insert an empty line when moving up from the top line." (if (and next-line-add-newlines (= arg 1) (save-excursion (beginning-of-line) (bobp))) (progn (beginning-of-line) (newline)))) This expression defines a piece of advice for the function previous-line. This piece of advice is named next-line-at-end, and the symbol before says that it is before-advice which should run before the regular definition of previous-line. (&optional arg try-vscroll) specifies how the advice code can refer to the function's arguments. When this piece of advice runs, it creates an additional line, in the situation where that is appropriate, but does not move point to that line. This is the correct way to write the advice, because the normal definition will run afterward and will move back to the newly inserted line. Defining the advice doesn't immediately change the function previous-line. That happens when you activate the advice, like this: (ad-activate 'previous-line) This is what actually begins to use the advice that has been defined so far for the function previous-line. Henceforth, whenever that function is run, whether invoked by the user with C-p or M-x, or called from Lisp, it runs the advice first, and its regular definition second. This example illustrates before-advice, which is one class of advice: it runs before the function's base definition. There are two other advice classes: after-advice, which runs after the base definition, and around-advice, which lets you specify an expression to wrap around the invocation of the base definition. Defining Advice defining advice advice, defining To define a piece of advice, use the macro defadvice. A call to defadvice has the following syntax, which is based on the syntax of defun and defmacro, but adds more: defadvice (defadvice function (class name [ position ] [ arglist ] flags...) [ documentation-string ] [ interactive-form ] body-forms...) Here, function is the name of the function (or macro or special form) to be advised. From now on, we will write just “function” when describing the entity being advised, but this always includes macros and special forms. In place of the argument list in an ordinary definition, an advice definition calls for several different pieces of information. class of advice before-advice after-advice around-advice class specifies the class of the advice—one of before, after, or around. Before-advice runs before the function itself; after-advice runs after the function itself; around-advice is wrapped around the execution of the function itself. After-advice and around-advice can override the return value by setting ad-return-value. ad-return-value — Variable: ad-return-value While advice is executing, after the function's original definition hasbeen executed, this variable holds its return value, which willultimately be returned to the caller after finishing all the advice.After-advice and around-advice can arrange to return some other valueby storing it in this variable. The argument name is the name of the advice, a non-nil symbol. The advice name uniquely identifies one piece of advice, within all the pieces of advice in a particular class for a particular function. The name allows you to refer to the piece of advice—to redefine it, or to enable or disable it. The optional position specifies where, in the current list of advice of the specified class, this new advice should be placed. It should be either first, last or a number that specifies a zero-based position (first is equivalent to 0). If no position is specified, the default is first. Position values outside the range of existing positions in this class are mapped to the beginning or the end of the range, whichever is closer. The position value is ignored when redefining an existing piece of advice. The optional arglist can be used to define the argument list for the sake of advice. This becomes the argument list of the combined definition that is generated in order to run the advice (see ). Therefore, the advice expressions can use the argument variables in this list to access argument values. The argument list used in advice need not be the same as the argument list used in the original function, but must be compatible with it, so that it can handle the ways the function is actually called. If two pieces of advice for a function both specify an argument list, they must specify the same argument list. See , for more information about argument lists and advice, and a more flexible way for advice to access the arguments. The remaining elements, flags, are symbols that specify further information about how to use this piece of advice. Here are the valid symbols and their meanings: activate Activate the advice for function now. Changes in a function'sadvice always take effect the next time you activate advice for thefunction; this flag says to do so, for function, immediately afterdefining this piece of advice. forward adviceThis flag has no immediate effect if function itself is not defined yet (asituation known as forward advice), because it is impossible toactivate an undefined function's advice. However, definingfunction will automatically activate its advice. protect Protect this piece of advice against non-local exits and errors inpreceding code and advice. Protecting advice places it as a cleanup inan unwind-protect form, so that it will execute even if theprevious code gets an error or uses throw. See . compile Compile the combined definition that is used to run the advice. Thisflag is ignored unless activate is also specified.See . disable Initially disable this piece of advice, so that it will not be usedunless subsequently explicitly enabled. See . preactivate Activate advice for function when this defadvice iscompiled or macroexpanded. This generates a compiled advised definitionaccording to the current advice state, which will be used duringactivation if appropriate. See .This is useful only if this defadvice is byte-compiled. The optional documentation-string serves to document this piece of advice. When advice is active for function, the documentation for function (as returned by documentation) combines the documentation strings of all the advice for function with the documentation string of its original function definition. The optional interactive-form form can be supplied to change the interactive behavior of the original function. If more than one piece of advice has an interactive-form, then the first one (the one with the smallest position) found among all the advice takes precedence. The possibly empty list of body-forms specifies the body of the advice. The body of an advice can access or change the arguments, the return value, the binding environment, and perform any other kind of side effect. Warning: When you advise a macro, keep in mind that macros are expanded when a program is compiled, not when a compiled program is run. All subroutines used by the advice need to be available when the byte compiler expands the macro. ad-unadvise — Command: ad-unadvise function This command deletes the advice from function. ad-unadvise-all — Command: ad-unadvise-all This command deletes all pieces of advice from all functions. Around-Advice Around-advice lets you “wrap” a Lisp expression “around” the original function definition. You specify where the original function definition should go by means of the special symbol ad-do-it. Where this symbol occurs inside the around-advice body, it is replaced with a progn containing the forms of the surrounded code. Here is an example: (defadvice foo (around foo-around) "Ignore case in `foo'." (let ((case-fold-search t)) ad-do-it)) Its effect is to make sure that case is ignored in searches when the original definition of foo is run. ad-do-it — Variable: ad-do-it This is not really a variable, rather a place-holder that looks like avariable. You use it in around-advice to specify the place to run thefunction's original definition and other “earlier” around-advice. If the around-advice does not use ad-do-it, then it does not run the original function definition. This provides a way to override the original definition completely. (It also overrides lower-positioned pieces of around-advice). If the around-advice uses ad-do-it more than once, the original definition is run at each place. In this way, around-advice can execute the original definition (and lower-positioned pieces of around-advice) several times. Another way to do that is by using ad-do-it inside of a loop. Computed Advice The macro defadvice resembles defun in that the code for the advice, and all other information about it, are explicitly stated in the source code. You can also create advice whose details are computed, using the function ad-add-advice. ad-add-advice — Function: ad-add-advice function advice class position Calling ad-add-advice adds advice as a piece of advice tofunction in class class. The argument advice hasthis form: (name protected enabled definition) Here protected and enabled are flags, and definitionis the expression that says what the advice should do. If enabledis nil, this piece of advice is initially disabled(see ).If function already has one or more pieces of advice in thespecified class, then position specifies where in the listto put the new piece of advice. The value of position can eitherbe first, last, or a number (counting from 0 at thebeginning of the list). Numbers outside the range are mapped to thebeginning or the end of the range, whichever is closer. Theposition value is ignored when redefining an existing piece ofadvice.If function already has a piece of advice with the samename, then the position argument is ignored and the old advice isreplaced with the new one. Activation of Advice activating advice advice, activating By default, advice does not take effect when you define it—only when you activate advice for the function that was advised. However, the advice will be activated automatically if you define or redefine the function later. You can request the activation of advice for a function when you define the advice, by specifying the activate flag in the defadvice. But normally you activate the advice for a function by calling the function ad-activate or one of the other activation commands listed below. Separating the activation of advice from the act of defining it permits you to add several pieces of advice to one function efficiently, without redefining the function over and over as each advice is added. More importantly, it permits defining advice for a function before that function is actually defined. When a function's advice is first activated, the function's original definition is saved, and all enabled pieces of advice for that function are combined with the original definition to make a new definition. (Pieces of advice that are currently disabled are not used; see .) This definition is installed, and optionally byte-compiled as well, depending on conditions described below. In all of the commands to activate advice, if compile is t (or anything but nil or a negative number), the command also compiles the combined definition which implements the advice. If it is nil or a negative number, what happens depends on ad-default-compilation-action as described below. ad-activate — Command: ad-activate function &optional compile This command activates all the advice defined for function. Activating advice does nothing if function's advice is already active. But if there is new advice, added since the previous time you activated advice for function, it activates the new advice. ad-deactivate — Command: ad-deactivate function This command deactivates the advice for function. deactivating advice ad-update — Command: ad-update function &optional compile This command activates the advice for functionif its advice is already activated. This is usefulif you change the advice. ad-activate-all — Command: ad-activate-all &optional compile This command activates the advice for all functions. ad-deactivate-all — Command: ad-deactivate-all This command deactivates the advice for all functions. ad-update-all — Command: ad-update-all &optional compile This command activates the advice for all functionswhose advice is already activated. This is usefulif you change the advice of some functions. ad-activate-regexp — Command: ad-activate-regexp regexp &optional compile This command activates all pieces of advice whose names matchregexp. More precisely, it activates all advice for any functionwhich has at least one piece of advice that matches regexp. ad-deactivate-regexp — Command: ad-deactivate-regexp regexp This command deactivates all pieces of advice whose names matchregexp. More precisely, it deactivates all advice for anyfunction which has at least one piece of advice that matchesregexp. ad-update-regexp — Command: ad-update-regexp regexp &optional compile This command activates pieces of advice whose names match regexp,but only those for functions whose advice is already activated. reactivating adviceReactivating a function's advice is useful for putting into effect allthe changes that have been made in its advice (including enabling anddisabling specific pieces of advice; see ) since thelast time it was activated. ad-start-advice — Command: ad-start-advice Turn on automatic advice activation when a function is defined orredefined. This is the default mode. ad-stop-advice — Command: ad-stop-advice Turn off automatic advice activation when a function is defined orredefined. ad-default-compilation-action — User Option: ad-default-compilation-action This variable controls whether to compile the combined definitionthat results from activating advice for a function.A value of always specifies to compile unconditionally.A value of never specifies never compile the advice.A value of maybe specifies to compile if the byte-compiler isalready loaded. A value of like-original specifies to compilethe advice if the original definition of the advised function iscompiled or a built-in function.This variable takes effect only if the compile argument ofad-activate (or any of the above functions) did not forcecompilation. If the advised definition was constructed during “preactivation” (see ), then that definition must already be compiled, because it was constructed during byte-compilation of the file that contained the defadvice with the preactivate flag. Enabling and Disabling Advice enabling advice advice, enabling and disabling disabling advice Each piece of advice has a flag that says whether it is enabled or not. By enabling or disabling a piece of advice, you can turn it on and off without having to undefine and redefine it. For example, here is how to disable a particular piece of advice named my-advice for the function foo: (ad-disable-advice 'foo 'before 'my-advice) This function by itself only changes the enable flag for a piece of advice. To make the change take effect in the advised definition, you must activate the advice for foo again: (ad-activate 'foo) ad-disable-advice — Command: ad-disable-advice function class name This command disables the piece of advice named name in classclass on function. ad-enable-advice — Command: ad-enable-advice function class name This command enables the piece of advice named name in classclass on function. You can also disable many pieces of advice at once, for various functions, using a regular expression. As always, the changes take real effect only when you next reactivate advice for the functions in question. ad-disable-regexp — Command: ad-disable-regexp regexp This command disables all pieces of advice whose names matchregexp, in all classes, on all functions. ad-enable-regexp — Command: ad-enable-regexp regexp This command enables all pieces of advice whose names matchregexp, in all classes, on all functions. Preactivation preactivating advice advice, preactivating Constructing a combined definition to execute advice is moderately expensive. When a library advises many functions, this can make loading the library slow. In that case, you can use preactivation to construct suitable combined definitions in advance. To use preactivation, specify the preactivate flag when you define the advice with defadvice. This defadvice call creates a combined definition which embodies this piece of advice (whether enabled or not) plus any other currently enabled advice for the same function, and the function's own definition. If the defadvice is compiled, that compiles the combined definition also. When the function's advice is subsequently activated, if the enabled advice for the function matches what was used to make this combined definition, then the existing combined definition is used, thus avoiding the need to construct one. Thus, preactivation never causes wrong results—but it may fail to do any good, if the enabled advice at the time of activation doesn't match what was used for preactivation. Here are some symptoms that can indicate that a preactivation did not work properly, because of a mismatch. Activation of the advisedfunction takes longer than usual. The byte-compiler getsloaded while an advised function gets activated. byte-compile is included in the value of features eventhough you did not ever explicitly use the byte-compiler. Compiled preactivated advice works properly even if the function itself is not defined until later; however, the function needs to be defined when you compile the preactivated advice. There is no elegant way to find out why preactivated advice is not being used. What you can do is to trace the function ad-cache-id-verification-code (with the function trace-function-background) before the advised function's advice is activated. After activation, check the value returned by ad-cache-id-verification-code for that function: verified means that the preactivated advice was used, while other values give some information about why they were considered inappropriate. Warning: There is one known case that can make preactivation fail, in that a preconstructed combined definition is used even though it fails to match the current state of advice. This can happen when two packages define different pieces of advice with the same name, in the same class, for the same function. But you should avoid that anyway. Argument Access in Advice The simplest way to access the arguments of an advised function in the body of a piece of advice is to use the same names that the function definition uses. To do this, you need to know the names of the argument variables of the original function. While this simple method is sufficient in many cases, it has a disadvantage: it is not robust, because it hard-codes the argument names into the advice. If the definition of the original function changes, the advice might break. Another method is to specify an argument list in the advice itself. This avoids the need to know the original function definition's argument names, but it has a limitation: all the advice on any particular function must use the same argument list, because the argument list actually used for all the advice comes from the first piece of advice for that function. A more robust method is to use macros that are translated into the proper access forms at activation time, i.e., when constructing the advised definition. Access macros access actual arguments by position regardless of how these actual arguments get distributed onto the argument variables of a function. This is robust because in Emacs Lisp the meaning of an argument is strictly determined by its position in the argument list. ad-get-arg — Macro: ad-get-arg position This returns the actual argument that was supplied at position. ad-get-args — Macro: ad-get-args position This returns the list of actual arguments supplied starting atposition. ad-set-arg — Macro: ad-set-arg position value This sets the value of the actual argument at position tovalue ad-set-args — Macro: ad-set-args position value-list This sets the list of actual arguments starting at position tovalue-list. Now an example. Suppose the function foo is defined as (defun foo (x y &optional z &rest r) ...) and is then called with (foo 0 1 2 3 4 5 6) which means that x is 0, y is 1, z is 2 and r is (3 4 5 6) within the body of foo. Here is what ad-get-arg and ad-get-args return in this case: (ad-get-arg 0) => 0 (ad-get-arg 1) => 1 (ad-get-arg 2) => 2 (ad-get-arg 3) => 3 (ad-get-args 2) => (2 3 4 5 6) (ad-get-args 4) => (4 5 6) Setting arguments also makes sense in this example: (ad-set-arg 5 "five") has the effect of changing the sixth argument to "five". If this happens in advice executed before the body of foo is run, then r will be (3 4 "five" 6) within that body. Here is an example of setting a tail of the argument list: (ad-set-args 0 '(5 4 3 2 1 0)) If this happens in advice executed before the body of foo is run, then within that body, x will be 5, y will be 4, z will be 3, and r will be (2 1 0) inside the body of foo. These argument constructs are not really implemented as Lisp macros. Instead they are implemented specially by the advice mechanism. Advising Primitives advising primitives Advising a primitive function (also called a “subr”) is risky. Some primitive functions are used by the advice mechanism; advising them could cause an infinite recursion. Also, many primitive functions are called directly from C code. Calls to the primitive from Lisp code will take note of the advice, but calls from C code will ignore the advice. When the advice facility constructs the combined definition, it needs to know the argument list of the original function. This is not always possible for primitive functions. When advice cannot determine the argument list, it uses (&rest ad-subr-args), which always works but is inefficient because it constructs a list of the argument values. You can use ad-define-subr-args to declare the proper argument names for a primitive function: ad-define-subr-args — Function: ad-define-subr-args function arglist This function specifies that arglist should be used as theargument list for function function. For example, (ad-define-subr-args 'fset '(sym newdef)) specifies the argument list for the function fset. The Combined Definition Suppose that a function has n pieces of before-advice (numbered from 0 through n−1), m pieces of around-advice and k pieces of after-advice. Assuming no piece of advice is protected, the combined definition produced to implement the advice for a function looks like this: (lambda arglist [ [ advised-docstring ] [ (interactive ...) ] ] (let (ad-return-value) before-0-body-form ... .... before- n−1-body-form ... around-0-body-form ... around-1-body-form ... .... around- m−1-body-form ... (setq ad-return-value apply original definition to arglist ) end-of-around- m−1-body-form ... .... end-of-around-1-body-form ... end-of-around-0-body-form ... after-0-body-form ... .... after- k−1-body-form ... ad-return-value)) Macros are redefined as macros, which means adding macro to the beginning of the combined definition. The interactive form is present if the original function or some piece of advice specifies one. When an interactive primitive function is advised, advice uses a special method: it calls the primitive with call-interactively so that it will read its own arguments. In this case, the advice cannot access the arguments. The body forms of the various advice in each class are assembled according to their specified order. The forms of around-advice l are included in one of the forms of around-advice l − 1. The innermost part of the around advice onion is apply original definition to arglist whose form depends on the type of the original function. The variable ad-return-value is set to whatever this returns. The variable is visible to all pieces of advice, which can access and modify it before it is actually returned from the advised function. The semantic structure of advised functions that contain protected pieces of advice is the same. The only difference is that unwind-protect forms ensure that the protected advice gets executed even if some previous piece of advice had an error or a non-local exit. If any around-advice is protected, then the whole around-advice onion is protected as a result. <setfilename>../info/debugging</setfilename> Debugging Lisp Programs There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears. If the problem occurs when you run the program, you can use a Lispdebugger to investigate what is happening during execution. In additionto the ordinary debugger, Emacs comes with a source-level debugger,Edebug. This chapter describes both of them. If the problem is syntactic, so that Lisp cannot even read the program,you can use the Emacs facilities for editing Lisp to localize it. If the problem occurs when trying to compile the program with the bytecompiler, you need to know how to examine the compiler's input buffer. Another useful debugging tool is the dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See . For debugging problems in terminal descriptions, the open-termscript function can be useful. See . The Lisp Debugger debugger for Emacs Lisp Lisp debugger break The ordinary Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See . Entering the Debugger on an Error error debugging debugging errors The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error. However, entry to the debugger is not a normal consequence of an error. Many commands frequently cause Lisp errors when invoked inappropriately (such as C-f at the end of the buffer), and during ordinary editing it would be very inconvenient to enter the debugger each time this happens. So if you want errors to enter the debugger, set the variable debug-on-error to non-nil. (The command toggle-debug-on-error provides an easy way to do this.) debug-on-error — User Option: debug-on-error This variable determines whether the debugger is called when an error issignaled and not handled. If debug-on-error is t, allkinds of errors call the debugger (except those listed indebug-ignored-errors). If it is nil, none call thedebugger.The value can also be a list of error conditions that should call thedebugger. For example, if you set it to the list(void-variable), then only errors about a variable that has novalue invoke the debugger.When this variable is non-nil, Emacs does not create an errorhandler around process filter functions and sentinels. Therefore,errors in these functions also invoke the debugger. See . debug-ignored-errors — User Option: debug-ignored-errors This variable specifies certain kinds of errors that should not enterthe debugger. Its value is a list of error condition symbols and/orregular expressions. If the error has any of those condition symbols,or if the error message matches any of the regular expressions, thenthat error does not enter the debugger, regardless of the value ofdebug-on-error.The normal value of this variable lists several errors that happen oftenduring editing but rarely result from bugs in Lisp programs. However,“rarely” is not “never”; if your program fails with an error thatmatches this list, you will need to change this list in order to debugthe error. The easiest way is usually to setdebug-ignored-errors to nil. eval-expression-debug-on-error — User Option: eval-expression-debug-on-error If this variable has a non-nil value, thendebug-on-error is set to t when evaluating with thecommand eval-expression. Ifeval-expression-debug-on-error is nil, then the value ofdebug-on-error is not changed. See See section ``Evaluating Emacs-Lisp Expressions'' in The GNU Emacs Manual. debug-on-signal — User Option: debug-on-signal Normally, errors that are caught by condition-case never run thedebugger, even if debug-on-error is non-nil. In otherwords, condition-case gets a chance to handle the error beforethe debugger gets a chance.If you set debug-on-signal to a non-nil value, then thedebugger gets the first chance at every error; an error will invoke thedebugger regardless of any condition-case, if it fits thecriteria specified by the values of debug-on-error anddebug-ignored-errors.Warning: This variable is strong medicine! Various parts ofEmacs handle errors in the normal course of affairs, and you may noteven realize that errors happen there. If you setdebug-on-signal to a non-nil value, those errors willenter the debugger.Warning: debug-on-signal has no effect whendebug-on-error is nil. To debug an error that happens during loading of the init file, use the option ‘--debug-init’. This binds debug-on-error to t while loading the init file, and bypasses the condition-case which normally catches errors in the init file. If your init file sets debug-on-error, the effect may not last past the end of loading the init file. (This is an undesirable byproduct of the code that implements the ‘--debug-init’ command line option.) The best way to make the init file set debug-on-error permanently is with after-init-hook, like this: (add-hook 'after-init-hook (lambda () (setq debug-on-error t))) Debugging Infinite Loops infinite loops loops, infinite quitting from infinite loop stopping an infinite loop When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes a quit. Ordinary quitting gives no information about why the program was looping. To get more information, you can set the variable debug-on-quit to non-nil. Quitting with C-g is not considered an error, and debug-on-error has no effect on the handling of C-g. Likewise, debug-on-quit has no effect on errors. Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem. debug-on-quit — User Option: debug-on-quit This variable determines whether the debugger is called when quitis signaled and not handled. If debug-on-quit is non-nil,then the debugger is called whenever you quit (that is, type C-g).If debug-on-quit is nil, then the debugger is not calledwhen you quit. See . Entering the Debugger on a Function Call function call debugging debugging specific functions To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller. debug-on-entry — Command: debug-on-entry function-name This function requests function-name to invoke the debugger eachtime it is called. It works by inserting the form(implement-debug-on-entry) into the function definition as thefirst form.Any function or macro defined as Lisp code may be set to break onentry, regardless of whether it is interpreted code or compiled code.If the function is a command, it will enter the debugger when calledfrom Lisp and when called interactively (after the reading of thearguments). You can also set debug-on-entry for primitive functions(i.e., those written in C) this way, but it only takes effect when theprimitive is called from Lisp code. Debug-on-entry is not allowed forspecial forms.When debug-on-entry is called interactively, it prompts forfunction-name in the minibuffer. If the function is already setup to invoke the debugger on entry, debug-on-entry does nothing.debug-on-entry always returns function-name.Warning: if you redefine a function after usingdebug-on-entry on it, the code to enter the debugger isdiscarded by the redefinition. In effect, redefining the functioncancels the break-on-entry feature for that function.Here's an example to illustrate use of this function: (defun fact (n) (if (zerop n) 1 (* n (fact (1- n))))) => fact (debug-on-entry 'fact) => fact (fact 3) ------ Buffer: *Backtrace* ------ Debugger entered--entering a function: * fact(3) eval((fact 3)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ------ Buffer: *Backtrace* ------ (symbol-function 'fact) => (lambda (n) (debug (quote debug)) (if (zerop n) 1 (* n (fact (1- n))))) cancel-debug-on-entry — Command: cancel-debug-on-entry &optional function-name This function undoes the effect of debug-on-entry onfunction-name. When called interactively, it prompts forfunction-name in the minibuffer. If function-name isomitted or nil, it cancels break-on-entry for all functions.Calling cancel-debug-on-entry does nothing to a function which isnot currently set up to break on entry. Explicit Entry to the Debugger You can cause the debugger to be called at a certain point in your program by writing the expression (debug) at that point. To do this, visit the source file, insert the text ‘(debug)’ at the proper place, and type C-M-x (eval-defun, a Lisp mode key binding). Warning: if you do this for temporary debugging purposes, be sure to undo this insertion before you save the file! The place where you insert ‘(debug)’ must be a place where an additional form can be evaluated and its value ignored. (If the value of (debug) isn't ignored, it will alter the execution of the program!) The most common suitable places are inside a progn or an implicit progn (see ). Using the Debugger When the debugger is entered, it displays the previously selected buffer in one window and a buffer named ‘*Backtrace*’ in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error). The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see ) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer. current stack frame The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame. If a line starts with a star, that means that exiting that frame will call the debugger again. This is useful for examining the return value of a function. If a function name is underlined, that means the debugger knows where its source code is located. You can click Mouse-2 on that name, or move to it and type RET, to visit the source code. The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted. Debugger Commands debugger command list The debugger buffer (in Debugger mode) provides special commands in addition to the usual Emacs commands. The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source for the function and type C-M-x on its definition.) You cannot use the Lisp debugger to step through a primitive function. Here is a list of Debugger mode commands: c Exit the debugger and continue execution. When continuing is possible,it resumes execution of the program as if the debugger had never beenentered (aside from any side-effects that you caused by changingvariable values or data structures while inside the debugger).Continuing is possible after entry to the debugger due to function entryor exit, explicit invocation, or quitting. You cannot continue if thedebugger was entered because of an error. d Continue execution, but enter the debugger the next time any Lispfunction is called. This allows you to step through thesubexpressions of an expression, seeing what values the subexpressionscompute, and what else they do.The stack frame made for the function call which enters the debugger inthis way will be flagged automatically so that the debugger will becalled again when the frame is exited. You can use the u commandto cancel this flag. b Flag the current frame so that the debugger will be entered when theframe is exited. Frames flagged in this way are marked with starsin the backtrace buffer. u Don't enter the debugger when the current frame is exited. Thiscancels a b command on that frame. The visible effect is toremove the star from the line in the backtrace buffer. j Flag the current frame like b. Then continue execution likec, but temporarily disable break-on-entry for all functions thatare set up to do so by debug-on-entry. e Read a Lisp expression in the minibuffer, evaluate it, and print thevalue in the echo area. The debugger alters certain importantvariables, and the current buffer, as part of its operation; etemporarily restores their values from outside the debugger, so you canexamine and change them. This makes the debugger more transparent. Bycontrast, M-: does nothing special in the debugger; it shows youthe variable values within the debugger. R Like e, but also save the result of evaluation in thebuffer ‘*Debugger-record*’. q Terminate the program being debugged; return to top-level Emacscommand execution.If the debugger was entered due to a C-g but you really wantto quit, and not debug, use the q command. r Return a value from the debugger. The value is computed by reading anexpression with the minibuffer and evaluating it.The r command is useful when the debugger was invoked due to exitfrom a Lisp call frame (as requested with b or by entering theframe with d); then the value specified in the r command isused as the value of that frame. It is also useful if you calldebug and use its return value. Otherwise, r has the sameeffect as c, and the specified return value does not matter.You can't use r when the debugger was entered due to an error. l Display a list of functions that will invoke the debugger when called.This is a list of functions that are set to break on entry by means ofdebug-on-entry. Warning: if you redefine such afunction and thus cancel the effect of debug-on-entry, it mayerroneously show up in this list. Invoking the Debugger Here we describe in full detail the function debug that is used to invoke the debugger. debug — Function: debug &rest debugger-args This function enters the debugger. It switches buffers to a buffernamed ‘*Backtrace*’ (or ‘*Backtrace*<2>’ if it is the secondrecursive entry to the debugger, etc.), and fills it with informationabout the stack of Lisp function calls. It then enters a recursiveedit, showing the backtrace buffer in Debugger mode.The Debugger mode c, d, j, and r commands exitthe recursive edit; then debug switches back to the previousbuffer and returns to whatever called debug. This is the onlyway the function debug can return to its caller.The use of the debugger-args is that debug displays therest of its arguments at the top of the ‘*Backtrace*’ buffer, sothat the user can see them. Except as described below, this is theonly way these arguments are used.However, certain values for first argument to debug have aspecial significance. (Normally, these values are used only by theinternals of Emacs, and not by programmers calling debug.) Hereis a table of these special values: lambda lambda in debugA first argument of lambda means debug was calledbecause of entry to a function when debug-on-next-call wasnon-nil. The debugger displays ‘Debuggerentered--entering a function:’ as a line of text at the top of thebuffer. debug debug as first argument means debug was called becauseof entry to a function that was set to debug on entry. The debuggerdisplays the string ‘Debugger entered--entering a function:’,just as in the lambda case. It also marks the stack frame forthat function so that it will invoke the debugger when exited. t When the first argument is t, this indicates a call todebug due to evaluation of a function call form whendebug-on-next-call is non-nil. The debugger displays‘Debugger entered--beginning evaluation of function call form:’as the top line in the buffer. exit When the first argument is exit, it indicates the exit of astack frame previously marked to invoke the debugger on exit. Thesecond argument given to debug in this case is the value beingreturned from the frame. The debugger displays ‘Debuggerentered--returning value:’ in the top line of the buffer, followed bythe value being returned. error error in debugWhen the first argument is error, the debugger indicates thatit is being entered because an error or quit was signaled andnot handled, by displaying ‘Debugger entered--Lisp error:’followed by the error signaled and any arguments to signal.For example, (let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Debugger entered--Lisp error: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------ If an error was signaled, presumably the variabledebug-on-error is non-nil. If quit was signaled,then presumably the variable debug-on-quit is non-nil. nil Use nil as the first of the debugger-args when you wantto enter the debugger explicitly. The rest of the debugger-argsare printed on the top line of the buffer. You can use this feature todisplay messages—for example, to remind yourself of the conditionsunder which debug is called. Internals of the Debugger This section describes functions and variables used internally by the debugger. debugger — Variable: debugger The value of this variable is the function to call to invoke thedebugger. Its value must be a function of any number of arguments, or,more typically, the name of a function. This function should invokesome kind of debugger. The default value of the variable isdebug.The first argument that Lisp hands to the function indicates why itwas called. The convention for arguments is detailed in the descriptionof debug (see ). backtrace — Command: backtrace run time stack call stackThis function prints a trace of Lisp function calls currently active.This is the function used by debug to fill up the‘*Backtrace*’ buffer. It is written in C, since it must have accessto the stack to determine which function calls are active. The returnvalue is always nil.In the following example, a Lisp expression calls backtraceexplicitly. This prints the backtrace to the streamstandard-output, which, in this case, is the buffer‘backtrace-output’.Each line of the backtrace represents one function call. The line showsthe values of the function's arguments if they are all known; if theyare still being computed, the line says so. The arguments of specialforms are elided. (with-output-to-temp-buffer "backtrace-output" (let ((var 1)) (save-excursion (setq var (eval '(progn (1+ var) (list 'testing (backtrace)))))))) => (testing nil) ----------- Buffer: backtrace-output ------------ backtrace() (list ...computing arguments...) (progn ...) eval((progn (1+ var) (list (quote testing) (backtrace)))) (setq ...) (save-excursion ...) (let ...) (with-output-to-temp-buffer ...) eval((with-output-to-temp-buffer ...)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ----------- Buffer: backtrace-output ------------ debug-on-next-call — Variable: debug-on-next-call eval, and debugging apply, and debugging funcall, and debuggingIf this variable is non-nil, it says to call the debugger beforethe next eval, apply or funcall. Entering thedebugger sets debug-on-next-call to nil.The d command in the debugger works by setting this variable. backtrace-debug — Function: backtrace-debug level flag This function sets the debug-on-exit flag of the stack frame levellevels down the stack, giving it the value flag. If flag isnon-nil, this will cause the debugger to be entered when thatframe later exits. Even a nonlocal exit through that frame will enterthe debugger.This function is used only by the debugger. command-debug-status — Variable: command-debug-status This variable records the debugging status of the current interactivecommand. Each time a command is called interactively, this variable isbound to nil. The debugger can set this variable to leaveinformation for future debugger invocations during the same commandinvocation.The advantage of using this variable rather than an ordinary globalvariable is that the data will never carry over to a subsequent commandinvocation. backtrace-frame — Function: backtrace-frame frame-number The function backtrace-frame is intended for use in Lispdebuggers. It returns information about what computation is happeningin the stack frame frame-number levels down.If that frame has not evaluated the arguments yet, or is a specialform, the value is (nil function arg-forms…).If that frame has evaluated its arguments and called its functionalready, the return value is (t functionarg-values…).In the return value, function is whatever was supplied as thecar of the evaluated list, or a lambda expression in thecase of a macro call. If the function has a &rest argument, thatis represented as the tail of the list arg-values.If frame-number is out of range, backtrace-frame returnsnil. Edebug Edebug debugging facility Edebug is a source-level debugger for Emacs Lisp programs with which you can: Step through evaluation, stopping before and after each expression. Set conditional or unconditional breakpoints. Stop when a specified condition is true (the global break event). Trace slow or fast, stopping briefly at each stop point, orat each breakpoint. Display expression results and evaluate expressions as if outside ofEdebug. Automatically re-evaluate a list of expressions anddisplay their results each time Edebug updates the display. Output trace info on function enter and exit. Stop when an error occurs. Display a backtrace, omitting Edebug's own frames. Specify argument evaluation for macros and defining forms. Obtain rudimentary coverage testing and frequency counts. The first three sections below should tell you enough about Edebug to enable you to use it. Using Edebug To debug a Lisp program with Edebug, you must first instrument the Lisp code that you want to debug. A simple way to do this is to first move point into the definition of a function or macro and then do C-u C-M-x (eval-defun with a prefix argument). See , for alternative ways to instrument code. Once a function is instrumented, any call to the function activates Edebug. Depending on which Edebug execution mode you have selected, activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands. The default execution mode is step, which stops execution. See . Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer, and it is temporarily read-only. An arrow in the left fringe indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself. If you instrument the definition of fac (shown below) and then execute (fac 3), here is what you would normally see. Point is at the open-parenthesis before if. (defun fac (n) =>-!-(if (< 0 n) (* n (fac (1- n))) 1)) stop points The places within a function where Edebug can stop execution are called stop points. These occur both before and after each subexpression that is a list, and also after each variable reference. Here we use periods to show the stop points in the function fac: (defun fac (n) .(if .(< 0 n.). .(* n. .(fac .(1- n.).).). 1).) The special commands of Edebug are available in the source code buffer in addition to the commands of Emacs Lisp mode. For example, you can type the Edebug command SPC to execute until the next stop point. If you type SPC once after entry to fac, here is the display you will see: (defun fac (n) =>(if -!-(< 0 n) (* n (fac (1- n))) 1)) When Edebug stops execution after an expression, it displays the expression's value in the echo area. Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands. Instrumenting for Edebug In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places. C-M-x eval-defun (Edebug) When you invoke command C-M-x (eval-defun) with a prefix argument on a function definition, it instruments the definition before evaluating it. (This does not modify the source code itself.) If the variable edebug-all-defs is non-nil, that inverts the meaning of the prefix argument: in this case, C-M-x instruments the definition unless it has a prefix argument. The default value of edebug-all-defs is nil. The command M-x edebug-all-defs toggles the value of the variable edebug-all-defs. eval-region (Edebug) eval-buffer (Edebug) eval-current-buffer (Edebug) If edebug-all-defs is non-nil, then the commands eval-region, eval-current-buffer, and eval-buffer also instrument any definitions they evaluate. Similarly, edebug-all-forms controls whether eval-region should instrument any form, even non-defining forms. This doesn't apply to loading or evaluations in the minibuffer. The command M-x edebug-all-forms toggles this option. edebug-eval-top-level-form Another command, M-x edebug-eval-top-level-form, is available to instrument any top-level form regardless of the values of edebug-all-defs and edebug-all-forms. While Edebug is active, the command I (edebug-instrument-callee) instruments the definition of the function or macro called by the list form after point, if is not already instrumented. This is possible only if Edebug knows where to find the source for that function; for this reading, after loading Edebug, eval-region records the position of every definition it evaluates, even if not instrumenting it. See also the i command (see ), which steps into the call after instrumenting the function. Edebug knows how to instrument all the standard special forms, interactive forms with an expression argument, anonymous lambda expressions, and other defining forms. However, Edebug cannot determine on its own what a user-defined macro will do with the arguments of a macro call, so you must provide that information using Edebug specifications; see , for details. When Edebug is about to instrument code for the first time in a session, it runs the hook edebug-setup-hook, then sets it to nil. You can use this to load Edebug specifications associated with a package you are using, but only when you use Edebug. eval-expression (Edebug) To remove instrumentation from a definition, simply re-evaluate its definition in a way that does not instrument. There are two ways of evaluating forms that never instrument them: from a file with load, and from the minibuffer with eval-expression (M-:). If Edebug detects a syntax error while instrumenting, it leaves point at the erroneous code and signals an invalid-read-syntax error. See , for other evaluation functions available inside of Edebug. Edebug Execution Modes Edebug execution modes Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping—whether it stops at each stop point, or continues to the next breakpoint, for example—and how much Edebug displays the progress of the evaluation before it stops. Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands; all except for S resume execution of the program, at least for a certain distance. S Stop: don't execute any more of the program, but wait for moreEdebug commands (edebug-stop). SPC Step: stop at the next stop point encountered (edebug-step-mode). n Next: stop at the next stop point encountered after an expression(edebug-next-mode). Also see edebug-forward-sexp in. t Trace: pause (normally one second) at each Edebug stop point(edebug-trace-mode). T Rapid trace: update the display at each stop point, but don't actuallypause (edebug-Trace-fast-mode). g Go: run until the next breakpoint (edebug-go-mode). See . c Continue: pause one second at each breakpoint, and then continue(edebug-continue-mode). C Rapid continue: move point to each breakpoint, but don't pause(edebug-Continue-fast-mode). G Go non-stop: ignore breakpoints (edebug-Go-nonstop-mode). Youcan still stop the program by typing S, or any editing command. In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list. While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else. If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input. keyboard macros (Edebug) Keyboard macros containing the commands in this section do not completely work: exiting from Edebug, to resume the program, loses track of the keyboard macro. This is not easy to fix. Also, defining or executing a keyboard macro outside of Edebug does not affect commands inside Edebug. This is usually an advantage. See also the edebug-continue-kbd-macro option (see ). When you enter a new Edebug level, the initial execution mode comes from the value of the variable edebug-initial-mode. (See .) By default, this specifies step mode. Note that you may reenter the same Edebug level several times if, for example, an instrumented function is called several times from one command. edebug-sit-for-seconds — User Option: edebug-sit-for-seconds This option specifies how many seconds to wait between execution stepsin trace mode. The default is 1 second. Jumping The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See , for the details on breakpoints. These commands may fail to work as expected in case of nonlocal exit, as that can bypass the temporary breakpoint where you expected the program to stop. h Proceed to the stop point near where point is (edebug-goto-here). f Run the program for one expression(edebug-forward-sexp). o Run the program until the end of the containing sexp. i Step into the function or macro called by the form after point. The h command proceeds to the stop point at or after the current location of point, using a temporary breakpoint. The f command runs the program forward over one expression. More precisely, it sets a temporary breakpoint at the position that C-M-f would reach, then executes in go mode so that the program will stop at breakpoints. With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression. You must check that the position C-M-f finds is a place that the program will really get to. In cond, for example, this may not be true. For flexibility, the f command does forward-sexp starting at point, rather than at the stop point. If you want to execute one expression from the current stop point, first type w, to move point there, and then type f. The o command continues “out of” an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp. The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late. The i command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it. Miscellaneous Edebug Commands Some miscellaneous Edebug commands are described here. ? Display the help message for Edebug (edebug-help). C-] Abort one level back to the previous command level(abort-recursive-edit). q Return to the top level editor command loop (top-level). Thisexits all recursive editing levels, including all levels of Edebugactivity. However, instrumented code protected withunwind-protect or condition-case forms may resumedebugging. Q Like q, but don't stop even for protected code(top-level-nonstop). r Redisplay the most recently known expression result in the echo area(edebug-previous-result). d Display a backtrace, excluding Edebug's own functions for clarity(edebug-backtrace).You cannot use debugger commands in the backtrace buffer in Edebug asyou would in the standard debugger.The backtrace buffer is killed automatically when you continueexecution. You can invoke commands from Edebug that activate Edebug again recursively. Whenever Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d. Breaks Edebug's step mode stops execution when the next stop point is reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints. Edebug Breakpoints breakpoints (Edebug) While using Edebug, you can specify breakpoints in the program you are testing: these are places where execution should stop. You can set a breakpoint at any stop point, as defined in . For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints: b Set a breakpoint at the stop point at or after point(edebug-set-breakpoint). If you use a prefix argument, thebreakpoint is temporary—it turns off the first time it stops theprogram. u Unset the breakpoint (if any) at the stop point at or afterpoint (edebug-unset-breakpoint). x condition RET Set a conditional breakpoint which stops the program only ifevaluating condition produces a non-nil value(edebug-set-conditional-breakpoint). With a prefix argument,the breakpoint is temporary. B Move point to the next breakpoint in the current definition(edebug-next-breakpoint). While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect. Re-evaluating or reinstrumenting a definition removes all of its previous breakpoints. A conditional breakpoint tests a condition each time the program gets there. Any errors that occur as a result of evaluating the condition are ignored, as if the result were nil. To set a conditional breakpoint, use x, and specify the condition expression in the minibuffer. Setting a conditional breakpoint at a stop point that has a previously established conditional breakpoint puts the previous condition expression in the minibuffer so you can edit it. You can make a conditional or unconditional breakpoint temporary by using a prefix argument with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset. Edebug always stops or pauses at a breakpoint, except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely. To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer. Global Break Condition stopping on events global break condition A global break condition stops execution when a specified condition is satisfied, no matter where that may occur. Edebug evaluates the global break condition at every stop point; if it evaluates to a non-nil value, then execution stops or pauses depending on the execution mode, as if a breakpoint had been hit. If evaluating the condition gets an error, execution does not stop. edebug-set-global-break-condition The condition expression is stored in edebug-global-break-condition. You can specify a new expression using the X command from the source code buffer while Edebug is active, or using C-x X X from any buffer at any time, as long as Edebug is loaded (edebug-set-global-break-condition). The global break condition is the simplest way to find where in your code some event occurs, but it makes code run much more slowly. So you should reset the condition to nil when not using it. Source Breakpoints edebug source breakpoints All breakpoints in a definition are forgotten each time you reinstrument it. If you wish to make a breakpoint that won't be forgotten, you can write a source breakpoint, which is simply a call to the function edebug in your source code. You can, of course, make such a call conditional. For example, in the fac function, you can insert the first line as shown below, to stop when the argument reaches zero: (defun fac (n) (if (= n 0) (edebug)) (if (< 0 n) (* n (fac (1- n))) 1)) When the fac definition is instrumented and the function is called, the call to edebug acts as a breakpoint. Depending on the execution mode, Edebug stops or pauses there. If no instrumented code is being executed when edebug is called, that function calls debug. Trapping Errors Emacs normally displays an error message when an error is signaled and not handled with condition-case. While Edebug is active and executing instrumented code, it normally responds to all unhandled errors. You can customize this with the options edebug-on-error and edebug-on-quit; see . When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, and within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case, you might want to display a full backtrace (see ). If you change debug-on-error or debug-on-quit while Edebug is active, these changes will be forgotten when Edebug becomes inactive. Furthermore, during Edebug's recursive edit, these variables are bound to the values they had outside of Edebug. Edebug Views These Edebug commands let you view aspects of the buffer and window status as they were before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug. v Switch to viewing the outside window configuration(edebug-view-outside). Type C-x X w to return to Edebug. p Temporarily display the outside current buffer with point at itsoutside position (edebug-bounce-point), pausing for one secondbefore returning to Edebug. With a prefix argument n, pause forn seconds instead. w Move point back to the current stop point in the source code buffer(edebug-where).If you use this command in a different window displaying the samebuffer, that window will be used instead to display the currentdefinition in the future. W Toggle whether Edebug saves and restores the outside windowconfiguration (edebug-toggle-save-windows).With a prefix argument, W only toggles saving and restoring ofthe selected window. To specify a window that is not displaying thesource code buffer, you must use C-x X W from the global keymap. You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed. After moving point, you may wish to jump back to the stop point. You can do that with w from a source code buffer. You can jump back to the stop point in the source code buffer from any buffer using C-x X w. Each time you use W to turn saving off, Edebug forgets the saved outside window configuration—so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of ‘*edebug*’ and ‘*edebug-trace*’ may conflict with the buffers you wish to see unless you have enough windows open. Evaluation While within Edebug, you can evaluate expressions “as if” Edebug were not running. Edebug tries to be invisible to the expression's evaluation and printing. Evaluation of expressions that cause side effects will work as expected, except for changes to data that Edebug explicitly saves and restores. See , for details on this process. e exp RET Evaluate expression exp in the context outside of Edebug(edebug-eval-expression). That is, Edebug tries to minimize itsinterference with the evaluation. M-: exp RET Evaluate expression exp in the context of Edebug itself. C-x C-e Evaluate the expression before point, in the context outside of Edebug(edebug-eval-last-sexp). lexical binding (Edebug) Edebug supports evaluation of expressions containing references to lexically bound symbols created by the following constructs in cl.el (version 2.03 or later): lexical-let, macrolet, and symbol-macrolet. Evaluation List Buffer You can use the evaluation list buffer, called ‘*edebug*’, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display. E Switch to the evaluation list buffer ‘*edebug*’(edebug-visit-eval-list). In the ‘*edebug*’ buffer you can use the commands of Lisp Interaction mode (see See section ``Lisp Interaction'' in The GNU Emacs Manual) as well as these special commands: C-j Evaluate the expression before point, in the outside context, and insertthe value in the buffer (edebug-eval-print-last-sexp). C-x C-e Evaluate the expression before point, in the context outside of Edebug(edebug-eval-last-sexp). C-c C-u Build a new evaluation list from the contents of the buffer(edebug-update-eval-list). C-c C-d Delete the evaluation list group that point is in(edebug-delete-eval-item). C-c C-w Switch back to the source code buffer at the current stop point(edebug-where). You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as you would in ‘*scratch*’; but they are evaluated in the context outside of Edebug. The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops. evaluation list group To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines. The command C-c C-u (edebug-update-eval-list) rebuilds the evaluation list, scanning the buffer and using the first expression of each group. (The idea is that the second expression of the group is the value previously computed and displayed.) Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged. If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions that use variables not currently valid do not interrupt your debugging. Here is an example of what the evaluation list window looks like after several expressions have been added to it: (current-buffer) #<buffer *scratch*> ;--------------------------------------------------------------- (selected-window) #<window 16 on *scratch*> ;--------------------------------------------------------------- (point) 196 ;--------------------------------------------------------------- bad-var "Symbol's value as variable is void: bad-var" ;--------------------------------------------------------------- (recursion-depth) 0 ;--------------------------------------------------------------- this-command eval-last-sexp ;--------------------------------------------------------------- To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, insert a new comment line, then type C-c C-u. You need not insert dashes in the comment line—its contents don't matter. After selecting ‘*edebug*’, you can return to the source code buffer with C-c C-w. The ‘*edebug*’ buffer is killed when you continue execution, and recreated next time it is needed. Printing in Edebug printing (Edebug) printing circular structures cust-print If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it. One way to cope with circular structure is to set print-length or print-level to truncate the printing. Edebug does this for you; it binds print-length and print-level to 50 if they were nil. (Actually, the variables edebug-print-length and edebug-print-level specify the values to use within Edebug.) See . edebug-print-length — User Option: edebug-print-length If non-nil, Edebug binds print-length to this value whileprinting results. The default value is 50. edebug-print-level — User Option: edebug-print-level If non-nil, Edebug binds print-level to this value whileprinting results. The default value is 50. You can also print circular structures and structures that share elements more informatively by binding print-circle to a non-nil value. Here is an example of code that creates a circular structure: (setq a '(x y)) (setcar a a) Custom printing prints this as ‘Result: #1=(#1# y)’. The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’ notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors. edebug-print-circle — User Option: edebug-print-circle If non-nil, Edebug binds print-circle to this value whileprinting results. The default value is t. Other programs can also use custom printing; see cust-print.el for details. Trace Buffer trace buffer Edebug can record an execution trace, storing it in a buffer named ‘*edebug-trace*’. This is a log of function calls and returns, showing the function names and their arguments and values. To enable trace recording, set edebug-trace to a non-nil value. Making a trace buffer is not the same thing as using trace execution mode (see ). When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record consists of ‘::::{’, followed by the function name and argument values. A function exit record consists of ‘::::}’, followed by the function name and result of the function. The number of ‘:’s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls. edebug-print-trace-before edebug-print-trace-after You can customize trace recording for function entry and exit by redefining the functions edebug-print-trace-before and edebug-print-trace-after. edebug-tracing — Macro: edebug-tracing string body … This macro requests additional trace information around the executionof the body forms. The argument string specifies textto put in the trace buffer, after the ‘{’ or ‘}’. Allthe arguments are evaluated, and edebug-tracing returns thevalue of the last form in body. edebug-trace — Function: edebug-trace format-string &rest format-args This function inserts text in the trace buffer. It computes the textwith (apply 'format format-string format-args).It also appends a newline to separate entries. edebug-tracing and edebug-trace insert lines in the trace buffer whenever they are called, even if Edebug is not active. Adding text to the trace buffer also scrolls its window to show the last lines inserted. Coverage Testing coverage testing (Edebug) frequency counts performance analysis Edebug provides rudimentary coverage testing and display of execution frequency. Coverage testing works by comparing the result of each expression with the previous result; each form in the program is considered “covered” if it has returned two different values since you began testing coverage in the current Emacs session. Thus, to do coverage testing on your program, execute it under various conditions and note whether it behaves correctly; Edebug will tell you when you have tried enough different conditions that each form has returned two different values. Coverage testing makes execution slower, so it is only done if edebug-test-coverage is non-nil. Frequency counting is performed for all execution of an instrumented function, even if the execution mode is Go-nonstop, and regardless of whether coverage testing is enabled. C-x X = edebug-temp-display-freq-count Use C-x X = (edebug-display-freq-count) to display both the coverage information and the frequency counts for a definition. Just = (edebug-temp-display-freq-count) displays the same information temporarily, only until you type another key. edebug-display-freq-count — Command: edebug-display-freq-count This command displays the frequency count data for each line of thecurrent definition.The frequency counts appear as comment lines after each line of code,and you can undo all insertions with one undo command. Thecounts appear under the ‘(’ before an expression or the ‘)’after an expression, or on the last character of a variable. Tosimplify the display, a count is not shown if it is equal to thecount of an earlier expression on the same line.The character ‘=’ following the count for an expression says thatthe expression has returned the same value each time it was evaluated.In other words, it is not yet “covered” for coverage testing purposes.To clear the frequency count and coverage data for a definition,simply reinstrument it with eval-defun. For example, after evaluating (fac 5) with a source breakpoint, and setting edebug-test-coverage to t, when the breakpoint is reached, the frequency data looks like this: (defun fac (n) (if (= n 0) (edebug)) ;#6 1 = =5 (if (< 0 n) ;#5 = (* n (fac (1- n))) ;# 5 0 1)) ;# 0 The comment lines show that fac was called 6 times. The first if statement returned 5 times with the same result each time; the same is true of the condition on the second if. The recursive call of fac did not return at all. The Outside Context Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent. Checking Whether to Stop Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program. max-lisp-eval-depth and max-specpdl-size are bothincremented once to reduce Edebug's impact on the stack. You could,however, still run out of stack space when using Edebug. The state of keyboard macro execution is saved and restored. WhileEdebug is active, executing-kbd-macro is bound to nilunless edebug-continue-kbd-macro is non-nil. Edebug Display Update When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from “outside” Edebug (see ). When you exit Edebug (by continuing the program), it restores the previous window configuration. Emacs redisplays only when it pauses. Usually, when you continue execution, the program re-enters Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the “outside” configuration. Consequently, what you see is the same window configuration as the last time Edebug was active, with no interruption. Entry to Edebug for displaying something also saves and restores the following data (though some of them are deliberately not restored if an error or quit signal occurs). current buffer point and mark (Edebug)Which buffer is current, and the positions of point and the mark in thecurrent buffer, are saved and restored. window configuration (Edebug)The outside window configuration is saved and restored ifedebug-save-windows is non-nil (see ).The window configuration is not restored on error or quit, but theoutside selected window is reselected even on error or quit incase a save-excursion is active. If the value ofedebug-save-windows is a list, only the listed windows are savedand restored.The window start and horizontal scrolling of the source code buffer arenot restored, however, so that the display remains coherent within Edebug. The value of point in each displayed buffer is saved and restored ifedebug-save-displayed-buffer-points is non-nil. The variables overlay-arrow-position andoverlay-arrow-string are saved and restored. So you can safelyinvoke Edebug from the recursive edit elsewhere in the same buffer. cursor-in-echo-area is locally bound to nil so thatthe cursor shows up in the window. Edebug Recursive Edit When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data: The current match data. See . The variables last-command, this-command,last-command-char, last-input-char,last-input-event, last-command-event,last-event-frame, last-nonmenu-event, andtrack-mouse. Commands used within Edebug do not affect thesevariables outside of Edebug.Executing commands within Edebug can change the key sequence thatwould be returned by this-command-keys, and there is no way toreset the key sequence from Lisp.Edebug cannot save and restore the value ofunread-command-events. Entering Edebug while this variable has anontrivial value can interfere with execution of the program you aredebugging. Complex commands executed while in Edebug are added to the variablecommand-history. In rare cases this can alter execution. Within Edebug, the recursion depth appears one deeper than the recursiondepth outside Edebug. This is not true of the automatically updatedevaluation list window. standard-output and standard-input are bound to nilby the recursive-edit, but Edebug temporarily restores them duringevaluations. The state of keyboard macro definition is saved and restored. WhileEdebug is active, defining-kbd-macro is bound toedebug-continue-kbd-macro. Edebug and Macros To make Edebug properly instrument expressions that call macros, some extra care is needed. This subsection explains the details. Instrumenting Macro Calls When Edebug instruments an expression that calls a Lisp macro, it needs additional information about the macro to do the job properly. This is because there is no a-priori way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.) Therefore, you must define an Edebug specification for each macro that Edebug will encounter, to explain the format of calls to that macro. To do this, add a debug declaration to the macro definition. Here is a simple example that shows the specification for the for example macro (see ). (defmacro for (var from init to final do &rest body) "Execute a simple \"for\" loop. For example, (for i from 1 to 10 do (print i))." (declare (debug (symbolp "from" form "to" form "do" &rest form))) ...) The Edebug specification says which parts of a call to the macro are forms to be evaluated. For simple macros, the specification often looks very similar to the formal argument list of the macro definition, but specifications are much more general than macro arguments. See , for more explanation of the declare form. You can also define an edebug specification for a macro separately from the macro definition with def-edebug-spec. Adding debug declarations is preferred, and more convenient, for macro definitions in Lisp, but def-edebug-spec makes it possible to define Edebug specifications for special forms implemented in C. def-edebug-spec — Macro: def-edebug-spec macro specification Specify which expressions of a call to macro macro are forms to beevaluated. specification should be the edebug specification.Neither argument is evaluated.The macro argument can actually be any symbol, not just a macroname. Here is a table of the possibilities for specification and how each directs processing of arguments. t All arguments are instrumented for evaluation. 0 None of the arguments is instrumented. a symbol The symbol must have an Edebug specification which is used instead.This indirection is repeated until another kind of specification isfound. This allows you to inherit the specification from another macro. a list The elements of the list describe the types of the arguments of acalling form. The possible elements of a specification list aredescribed in the following sections. edebug-eval-macro-args If a macro has no Edebug specification, neither through a debug declaration nor through a def-edebug-spec call, the variable edebug-eval-macro-args comes into play. If it is nil, the default, none of the arguments is instrumented for evaluation. If it is non-nil, all arguments are instrumented. Specification List Edebug specification list A specification list is required for an Edebug specification if some arguments of a macro call are evaluated while others are not. Some elements in a specification list match one or more arguments, but others modify the processing of all following elements. The latter, called specification keywords, are symbols beginning with ‘&’ (such as &optional). A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords apply only to the remainder of the sublist or group they are contained in. When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. See , for more details. Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications. Here's a table of the possible elements of a specification list, with their meanings (see , for the referenced examples): sexp A single unevaluated Lisp object, which is not instrumented. form A single evaluated expression, which is instrumented. place edebug-unwrapA place to store a value, as in the Common Lisp setf construct. body Short for &rest form. See &rest below. function-form A function form: either a quoted function symbol, a quoted lambdaexpression, or a form (that should evaluate to a function symbol orlambda expression). This is useful when an argument that's a lambdaexpression might be quoted with quote rather thanfunction, since it instruments the body of the lambda expressioneither way. lambda-expr A lambda expression with no quoting. &optional All following elements in the specification list are optional; as soonas one does not match, Edebug stops matching at this level.To make just a few elements optional followed by non-optional elements,use [&optional specs…]. To specify that severalelements must all match or none, use &optional[specs…]. See the defun example. &rest All following elements in the specification list are repeated zero ormore times. In the last repetition, however, it is not a problem if theexpression runs out before matching all of the elements of thespecification list.To repeat only a few elements, use [&rest specs…].To specify several elements that must all match on every repetition, use&rest [specs…]. &or Each of the following elements in the specification list is analternative. One of the alternatives must match, or the &orspecification fails.Each list element following &or is a single alternative. Togroup two or more list elements as a single alternative, enclose them in[…]. &not Each of the following elements is matched as alternatives as if by using&or, but if any of them match, the specification fails. If noneof them match, nothing is matched, but the &not specificationsucceeds. &define Indicates that the specification is for a defining form. The definingform itself is not instrumented (that is, Edebug does not stop before andafter the defining form), but forms inside it typically will beinstrumented. The &define keyword should be the first element ina list specification. nil This is successful when there are no more arguments to match at thecurrent argument list level; otherwise it fails. See sublistspecifications and the backquote example. gate preventing backtrackingNo argument is matched but backtracking through the gate is disabledwhile matching the remainder of the specifications at this level. Thisis primarily used to generate more specific syntax error messages. See, for more details. Also see the let example. other-symbol indirect specificationsAny other symbol in a specification list may be a predicate or anindirect specification.If the symbol has an Edebug specification, this indirectspecification should be either a list specification that is used inplace of the symbol, or a function that is called to process thearguments. The specification may be defined with def-edebug-specjust as for macros. See the defun example.Otherwise, the symbol should be a predicate. The predicate is calledwith the argument and the specification fails if the predicate returnsnil. In either case, that argument is not instrumented.Some suitable predicates include symbolp, integerp,stringp, vectorp, and atom. [elements…] […] (Edebug)A vector of elements groups the elements into a single groupspecification. Its meaning has nothing to do with vectors. "string" The argument should be a symbol named string. This specificationis equivalent to the quoted symbol, 'symbol, where the nameof symbol is the string, but the string form is preferred. (vector elements…) The argument should be a vector whose elements must match theelements in the specification. See the backquote example. (elements…) Any other list is a sublist specification and the argument must bea list whose elements match the specification elements. dotted lists (Edebug)A sublist specification may be a dotted list and the corresponding listargument may then be a dotted list. Alternatively, the last cdr of adotted list specification may be another sublist specification (via agrouping or an indirect specification, e.g., (spec . [(morespecs…)])) whose elements match the non-dotted list arguments.This is useful in recursive specifications such as in the backquoteexample. Also see the description of a nil specificationabove for terminating such recursion.Note that a sublist specification written as (specs . nil)is equivalent to (specs), and (specs .(sublist-elements…)) is equivalent to (specssublist-elements…). Here is a list of additional specifications that may appear only after &define. See the defun example. name The argument, a symbol, is the name of the defining form.A defining form is not required to have a name field; and it may havemultiple name fields. :name This construct does not actually match an argument. The elementfollowing :name should be a symbol; it is used as an additionalname component for the definition. You can use this to add a unique,static component to the name of the definition. It may be used morethan once. arg The argument, a symbol, is the name of an argument of the defining form.However, lambda-list keywords (symbols starting with ‘&’)are not allowed. lambda-list lambda-list (Edebug)This matches a lambda list—the argument list of a lambda expression. def-body The argument is the body of code in a definition. This is likebody, described above, but a definition body must be instrumentedwith a different Edebug call that looks up information associated withthe definition. Use def-body for the highest level list of formswithin the definition. def-form The argument is a single, highest-level form in a definition. This islike def-body, except use this to match a single form rather thana list of forms. As a special case, def-form also means thattracing information is not output when the form is executed. See theinteractive example. Backtracking in Specifications backtracking syntax error (Edebug) If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument. When a syntax error is detected, it might not be reported until much later after higher-level alternatives have been exhausted, and with the point positioned further from the real error. But if backtracking is disabled when an error occurs, it can be reported immediately. Note that backtracking is also reenabled automatically in several situations; it is reenabled when a new alternative is established by &optional, &rest, or &or, or at the start of processing a sublist, group, or indirect specification. The effect of enabling or disabling backtracking is limited to the remainder of the level currently being processed and lower levels. Backtracking is disabled while matching any of the form specifications (that is, form, body, def-form, and def-body). These specifications will match any form so any error must be in the form itself rather than at a higher level. Backtracking is also disabled after successfully matching a quoted symbol or string specification, since this usually indicates a recognized construct. But if you have a set of alternative constructs that all begin with the same symbol, you can usually work around this constraint by factoring the symbol out of the alternatives, e.g., ["foo" &or [first case] [second case] ...]. Most needs are satisfied by these two ways that backtracking is automatically disabled, but occasionally it is useful to explicitly disable backtracking by using the gate specification. This is useful when you know that no higher alternatives could apply. See the example of the let specification. Specification Examples It may be easier to understand Edebug specifications by studying the examples provided here. A let special form has a sequence of bindings and a body. Each of the bindings is either a symbol or a sublist with a symbol and optional expression. In the specification below, notice the gate inside of the sublist to prevent backtracking once a sublist is found. (def-edebug-spec let ((&rest &or symbolp (gate symbolp &optional form)) body)) Edebug uses the following specifications for defun and defmacro and the associated argument list and interactive specifications. It is necessary to handle interactive forms specially since an expression argument is actually evaluated outside of the function body. (def-edebug-spec defmacro defun) ; Indirect ref to defun spec. (def-edebug-spec defun (&define name lambda-list [&optional stringp] ; Match the doc string, if present. [&optional ("interactive" interactive)] def-body)) (def-edebug-spec lambda-list (([&rest arg] [&optional ["&optional" arg &rest arg]] &optional ["&rest" arg] ))) (def-edebug-spec interactive (&optional &or stringp def-form)) ; Notice: def-form The specification for backquote below illustrates how to match dotted lists and use nil to terminate recursion. It also illustrates how components of a vector may be matched. (The actual specification defined by Edebug does not support dotted lists because doing so causes very deep recursion that could fail.) (def-edebug-spec ` (backquote-form)) ; Alias just for clarity. (def-edebug-spec backquote-form (&or ([&or "," ",@"] &or ("quote" backquote-form) form) (backquote-form . [&or nil backquote-form]) (vector &rest backquote-form) sexp)) Edebug Options These options affect the behavior of Edebug: edebug-setup-hook — User Option: edebug-setup-hook Functions to call before Edebug is used. Each time it is set to a newvalue, Edebug will call those functions once and thenedebug-setup-hook is reset to nil. You could use this toload up Edebug specifications associated with a package you are usingbut only when you also use Edebug.See . edebug-all-defs — User Option: edebug-all-defs If this is non-nil, normal evaluation of defining forms such asdefun and defmacro instruments them for Edebug. Thisapplies to eval-defun, eval-region, eval-buffer,and eval-current-buffer.Use the command M-x edebug-all-defs to toggle the value of thisoption. See . edebug-all-forms — User Option: edebug-all-forms If this is non-nil, the commands eval-defun,eval-region, eval-buffer, and eval-current-bufferinstrument all forms, even those that don't define anything.This doesn't apply to loading or evaluations in the minibuffer.Use the command M-x edebug-all-forms to toggle the value of thisoption. See . edebug-save-windows — User Option: edebug-save-windows If this is non-nil, Edebug saves and restores the windowconfiguration. That takes some time, so if your program does not carewhat happens to the window configurations, it is better to set thisvariable to nil.If the value is a list, only the listed windows are saved andrestored.You can use the W command in Edebug to change this variableinteractively. See . edebug-save-displayed-buffer-points — User Option: edebug-save-displayed-buffer-points If this is non-nil, Edebug saves and restores point in alldisplayed buffers.Saving and restoring point in other buffers is necessary if you aredebugging code that changes the point of a buffer which is displayed ina non-selected window. If Edebug or the user then selects the window,point in that buffer will move to the window's value of point.Saving and restoring point in all buffers is expensive, since itrequires selecting each window twice, so enable this only if you needit. See . edebug-initial-mode — User Option: edebug-initial-mode If this variable is non-nil, it specifies the initial executionmode for Edebug when it is first activated. Possible values arestep, next, go, Go-nonstop, trace,Trace-fast, continue, and Continue-fast.The default value is step.See . edebug-trace — User Option: edebug-trace If this is non-nil, trace each function entry and exit.Tracing output is displayed in a buffer named ‘*edebug-trace*’, onefunction entry or exit per line, indented by the recursion level.Also see edebug-tracing, in . edebug-test-coverage — User Option: edebug-test-coverage If non-nil, Edebug tests coverage of all expressions debugged.See . edebug-continue-kbd-macro — User Option: edebug-continue-kbd-macro If non-nil, continue defining or executing any keyboard macrothat is executing outside of Edebug. Use this with caution since it is notdebugged.See . edebug-on-error — User Option: edebug-on-error Edebug binds debug-on-error to this value, ifdebug-on-error was previously nil. See . edebug-on-quit — User Option: edebug-on-quit Edebug binds debug-on-quit to this value, ifdebug-on-quit was previously nil. See . If you change the values of edebug-on-error or edebug-on-quit while Edebug is active, their values won't be used until the next time Edebug is invoked via a new command. edebug-global-break-condition — User Option: edebug-global-break-condition If non-nil, an expression to test for at every stop point. Ifthe result is non-nil, then break. Errors are ignored.See . Debugging Invalid Lisp Syntax debugging invalid Lisp syntax The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error “End of file during parsing” in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, “Invalid read syntax: ")"” indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change? If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun. unbalanced parentheses parenthesis mismatch, debugging However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. (In addition, just moving point through the code with Show Paren mode enabled might find the mismatch.) Excess Open Parentheses The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to go to the end of the file and type C-u C-M-u. This will move you to the beginning of the first defun that is unbalanced. The next step is to determine precisely what is wrong. There is no way to be sure of this except by studying the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves. But don't do this yet! Keep reading, first. Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced. Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses. After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything. Excess Close Parentheses To deal with an excess close parenthesis, first go to the beginning of the file, then type C-u -1 C-M-u to find the end of the first unbalanced defun. Then find the actual matching close parenthesis by typing C-M-f at the beginning of that defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity. If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses. After you think you have fixed the problem, use C-M-q again. If the old indentation actually fits the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything. Test Coverage coverage testing testcover-start testcover-mark-all testcover-next-mark You can do coverage testing for a file of Lisp code by loading the testcover library and using the command M-x testcover-start RET file RET to instrument the code. Then test your code by calling it one or more times. Then use the command M-x testcover-mark-all to display colored highlights on the code to show where coverage is insufficient. The command M-x testcover-next-mark will move point forward to the next highlighted spot. Normally, a red highlight indicates the form was never completely evaluated; a brown highlight means it always evaluated to the same value (meaning there has been little testing of what is done with the result). However, the red highlight is skipped for forms that can't possibly complete their evaluation, such as error. The brown highlight is skipped for forms that are expected to always evaluate to the same value, such as (setq x 14). For difficult cases, you can add do-nothing macros to your code to give advice to the test coverage tool. 1value — Macro: 1value form Evaluate form and return its value, but inform coverage testingthat form's value should always be the same. noreturn — Macro: noreturn form Evaluate form, informing coverage testing that form shouldnever return. If it ever does return, you get a run-time error. Edebug also has a coverage testing feature (see ). These features partly duplicate each other, and it would be cleaner to combine them. Debugging Problems in Compilation debugging byte compilation problems When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the ‘*Compile-Log*’ buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred. What you should do is switch to the buffer ‘ *Compiler Input*’. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read. If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error. If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can't localize the error precisely, but can still show you which function to check. <setfilename>../info/streams</setfilename> Reading and Printing Lisp Objects Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in . This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing). Introduction to Reading and Printing Lisp reader printing reading Reading a Lisp object means parsing a Lisp expression in textual form and producing a corresponding Lisp object. This is how Lisp programs get into Lisp from files of Lisp code. We call the text the read syntax of the object. For example, the text ‘(a . 5)’ is the read syntax for a cons cell whose car is a and whose cdr is the number 5. Printing a Lisp object means producing text that represents that object—converting the object to its printed representation (see ). Printing the cons cell described above produces the text ‘(a . 5)’. Reading and printing are more or less inverse operations: printing the object that results from reading a given piece of text often produces the same text, and reading the text that results from printing an object usually produces a similar-looking object. For example, printing the symbol foo produces the text ‘foo’, and reading that text returns the symbol foo. Printing a list whose elements are a and b produces the text ‘(a b)’, and reading that text produces a list (but not the same list) with elements a and b. However, these two operations are not precisely inverse to each other. There are three kinds of exceptions: Printing can produce text that cannot be read. For example, buffers,windows, frames, subprocesses and markers print as text that startswith ‘#’; if you try to read this text, you get an error. There isno way to read those data types. One object can have multiple textual representations. For example,‘1’ and ‘01’ represent the same integer, and ‘(a b)’ and‘(a . (b))’ represent the same list. Reading will accept any ofthe alternatives, but printing must choose one of them. Comments can appear at certain points in the middle of an object'sread sequence without affecting the result of reading it. Input Streams stream (for reading) input stream Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream: buffer buffer input streamThe input characters are read from buffer, starting with thecharacter directly after point. Point advances as characters are read. marker marker input streamThe input characters are read from the buffer that marker is in,starting with the character directly after the marker. The markerposition advances as characters are read. The value of point in thebuffer has no effect when the stream is a marker. string string input streamThe input characters are taken from string, starting at the firstcharacter in the string and using as many characters as required. function function input streamThe input characters are generated by function, which must supporttwo kinds of calls: When it is called with no arguments, it should return the next character. When it is called with one argument (always a character), functionshould save the argument and arrange to return it on the next call.This is called unreading the character; it happens when the Lispreader reads one character too many and wants to “put it back where itcame from.” In this case, it makes no difference what valuefunction returns. t t input streamt used as a stream means that the input is read from theminibuffer. In fact, the minibuffer is invoked once and the textgiven by the user is made into a string that is then used as theinput stream. If Emacs is running in batch mode, standard input is usedinstead of the minibuffer. For example, (message "%s" (read t)) will read a Lisp expression from standard input and print the resultto standard output. nil nil input streamnil supplied as an input stream means to use the value ofstandard-input instead; that value is the default inputstream, and must be a non-nil input stream. symbol A symbol as input stream is equivalent to the symbol's functiondefinition (if any). Here is an example of reading from a stream that is a buffer, showing where point is located before and after: ---------- Buffer: foo ---------- This-!- is the contents of foo. ---------- Buffer: foo ---------- (read (get-buffer "foo")) => is (read (get-buffer "foo")) => the ---------- Buffer: foo ---------- This is the-!- contents of foo. ---------- Buffer: foo ---------- Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text. Here is an example of reading from a stream that is a marker, initially positioned at the beginning of the buffer shown. The value read is the symbol This. ---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (setq m (set-marker (make-marker) 1 (get-buffer "foo"))) => #<marker at 1 in foo> (read m) => This m => #<marker at 5 in foo> ;; Before the first space. Here we read from the contents of a string: (read "(When in) the course") => (When in) The following example reads from the minibuffer. The prompt is: ‘Lisp expression: ’. (That is always the prompt used when you read from the stream t.) The user's input is shown following the prompt. (read t) => 23 ---------- Buffer: Minibuffer ---------- Lisp expression: 23 RET ---------- Buffer: Minibuffer ---------- Finally, here is an example of a stream that is a function, named useless-stream. Before we use the stream, we initialize the variable useless-list to a list of characters. Then each call to the function useless-stream obtains the next character in the list or unreads a character by adding it to the front of the list. (setq useless-list (append "XY()" nil)) => (88 89 40 41) (defun useless-stream (&optional unread) (if unread (setq useless-list (cons unread useless-list)) (prog1 (car useless-list) (setq useless-list (cdr useless-list))))) => useless-stream Now we read using the stream thus constructed: (read 'useless-stream) => XY useless-list => (40 41) Note that the open and close parentheses remain in the list. The Lisp reader encountered the open parenthesis, decided that it ended the input, and unread it. Another attempt to read from the stream at this point would read ‘()’ and return nil. get-file-char — Function: get-file-char This function is used internally as an input stream to read from theinput file opened by the function load. Don't use this functionyourself. Input Functions This section describes the Lisp functions and variables that pertain to reading. In the functions below, stream stands for an input stream (see the previous section). If stream is nil or omitted, it defaults to the value of standard-input. end-of-file An end-of-file error is signaled if reading encounters an unterminated list, vector, or string. read — Function: read &optional stream This function reads one textual Lisp expression from stream,returning it as a Lisp object. This is the basic Lisp input function. read-from-string — Function: read-from-string string &optional start end string to objectThis function reads the first textual Lisp expression from the text instring. It returns a cons cell whose car is that expression,and whose cdr is an integer giving the position of the nextremaining character in the string (i.e., the first one not read).If start is supplied, then reading begins at index start inthe string (where the first character is at index 0). If you specifyend, then reading is forced to stop just before that index, as ifthe rest of the string were not there.For example: (read-from-string "(setq x 55) (setq y 5)") => ((setq x 55) . 11) (read-from-string "\"A short string\"") => ("A short string" . 16) ;; Read starting at the first character. (read-from-string "(list 112)" 0) => ((list 112) . 10) ;; Read starting at the second character. (read-from-string "(list 112)" 1) => (list . 5) ;; Read starting at the seventh character, ;; and stopping at the ninth. (read-from-string "(list 112)" 6 8) => (11 . 8) standard-input — Variable: standard-input This variable holds the default input stream—the stream thatread uses when the stream argument is nil.The default is t, meaning use the minibuffer. Output Streams stream (for printing) output stream An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream: buffer buffer output streamThe output characters are inserted into buffer at point.Point advances as characters are inserted. marker marker output streamThe output characters are inserted into the buffer that markerpoints into, at the marker position. The marker position advances ascharacters are inserted. The value of point in the buffer has no effecton printing when the stream is a marker, and this kind of printingdoes not move point (except that if the marker points at or before theposition of point, point advances with the surrounding text, asusual). function function output streamThe output characters are passed to function, which is responsiblefor storing them away. It is called with a single character asargument, as many times as there are characters to be output, andis responsible for storing the characters wherever you want to put them. t t output streamThe output characters are displayed in the echo area. nil nil output streamnil specified as an output stream means to use the value ofstandard-output instead; that value is the default outputstream, and must not be nil. symbol A symbol as output stream is equivalent to the symbol's functiondefinition (if any). Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore more a matter of how you use a Lisp object, than of different types of object. Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the ‘h’ in ‘the’. At the end, point is located directly before that same ‘h’. print example ---------- Buffer: foo ---------- This is t-!-he contents of foo. ---------- Buffer: foo ---------- (print "This is the output" (get-buffer "foo")) => "This is the output" ---------- Buffer: foo ---------- This is t "This is the output" -!-he contents of foo. ---------- Buffer: foo ---------- Now we show a use of a marker as an output stream. Initially, the marker is in buffer foo, between the ‘t’ and the ‘h’ in the word ‘the’. At the end, the marker has advanced over the inserted text so that it remains positioned before the same ‘h’. Note that the location of point, shown in the usual fashion, has no effect. ---------- Buffer: foo ---------- This is the -!-output ---------- Buffer: foo ---------- (setq m (copy-marker 10)) => #<marker at 10 in foo> (print "More output for foo." m) => "More output for foo." ---------- Buffer: foo ---------- This is t "More output for foo." he -!-output ---------- Buffer: foo ---------- m => #<marker at 34 in foo> The following example shows output to the echo area: (print "Echo Area output" t) => "Echo Area output" ---------- Echo Area ---------- "Echo Area output" ---------- Echo Area ---------- Finally, we show the use of a function as an output stream. The function eat-output takes each character that it is given and conses it onto the front of the list last-output (see ). At the end, the list contains all the characters output, but in reverse order. (setq last-output nil) => nil (defun eat-output (c) (setq last-output (cons c last-output))) => eat-output (print "This is the output" 'eat-output) => "This is the output" last-output => (10 34 116 117 112 116 117 111 32 101 104 116 32 115 105 32 115 105 104 84 34 10) Now we can put the output in the proper order by reversing the list: (concat (nreverse last-output)) => " \"This is the output\" " Calling concat converts the list to a string so you can see its contents more clearly. Output Functions This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation. ‘"’ in printing ‘\’ in printing quoting characters in printing escape characters in printing Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See , for full details. You specify quoting or no quoting by the choice of printing function. If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting. Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation: (setq foo (list nil)) => (nil) (setcar foo foo) => (#0) In the functions below, stream stands for an output stream. (See the previous section for a description of output streams.) If stream is nil or omitted, it defaults to the value of standard-output. print — Function: print object &optional stream Lisp printerThe print function is a convenient way of printing. It outputsthe printed representation of object to stream, printing inaddition one newline before object and another after it. Quotingcharacters are used. print returns object. For example: (progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" => " came back" prin1 — Function: prin1 object &optional stream This function outputs the printed representation of object tostream. It does not print newlines to separate output asprint does, but it does use quoting characters just likeprint. It returns object. (progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" => " came back" princ — Function: princ object &optional stream This function outputs the printed representation of object tostream. It returns object.This function is intended to produce output that is readable by people,not by read, so it doesn't insert quoting characters and doesn'tput double-quotes around the contents of strings. It does not add anyspacing between calls. (progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" => " in the \"hat\"" terpri — Function: terpri &optional stream newline in printThis function outputs a newline to stream. The name standsfor “terminate print.” write-char — Function: write-char character &optional stream This function outputs character to stream. It returnscharacter. prin1-to-string — Function: prin1-to-string object &optional noescape object to stringThis function returns a string containing the text that prin1would have printed for the same argument. (prin1-to-string 'foo) => "foo" (prin1-to-string (mark-marker)) => "#<marker at 2773 in strings.texi>" If noescape is non-nil, that inhibits use of quotingcharacters in the output. (This argument is supported in Emacs versions19 and later.) (prin1-to-string "foo") => "\"foo\"" (prin1-to-string "foo" t) => "foo" See format, in , for other ways to obtainthe printed representation of a Lisp object as a string. with-output-to-string — Macro: with-output-to-string body … This macro executes the body forms with standard-output setup to feed output into a string. Then it returns that string.For example, if the current buffer name is ‘foo’, (with-output-to-string (princ "The buffer is ") (princ (buffer-name))) returns "The buffer is foo". Variables Affecting Output output-controlling variables standard-output — Variable: standard-output The value of this variable is the default output stream—the streamthat print functions use when the stream argument is nil.The default is t, meaning display in the echo area. print-quoted — Variable: print-quoted If this is non-nil, that means to print quoted forms usingabbreviated reader syntax. (quote foo) prints as 'foo,(function foo) as #'foo, and backquoted forms printusing modern backquote syntax. print-escape-newlines — Variable: print-escape-newlines ‘\n’ in print escape charactersIf this variable is non-nil, then newline characters in stringsare printed as ‘\n’ and formfeeds are printed as ‘\f’.Normally these characters are printed as actual newlines and formfeeds.This variable affects the print functions prin1 and printthat print with quoting. It does not affect princ. Here is anexample using prin1: (prin1 "a\nb") -| "a -| b" => "a b" (let ((print-escape-newlines t)) (prin1 "a\nb")) -| "a\nb" => "a b" In the second expression, the local binding ofprint-escape-newlines is in effect during the call toprin1, but not during the printing of the result. print-escape-nonascii — Variable: print-escape-nonascii If this variable is non-nil, then unibyte non-ASCIIcharacters in strings are unconditionally printed as backslash sequencesby the print functions prin1 and print that print withquoting.Those functions also use backslash sequences for unibyte non-ASCIIcharacters, regardless of the value of this variable, when the outputstream is a multibyte buffer or a marker pointing into one. print-escape-multibyte — Variable: print-escape-multibyte If this variable is non-nil, then multibyte non-ASCIIcharacters in strings are unconditionally printed as backslash sequencesby the print functions prin1 and print that print withquoting.Those functions also use backslash sequences for multibytenon-ASCII characters, regardless of the value of this variable,when the output stream is a unibyte buffer or a marker pointing intoone. print-length — Variable: print-length printing limitsThe value of this variable is the maximum number of elements to print inany list, vector or bool-vector. If an object being printed has morethan this many elements, it is abbreviated with an ellipsis.If the value is nil (the default), then there is no limit. (setq print-length 2) => 2 (print '(1 2 3 4 5)) -| (1 2 ...) => (1 2 ...) print-level — Variable: print-level The value of this variable is the maximum depth of nesting ofparentheses and brackets when printed. Any list or vector at a depthexceeding this limit is abbreviated with an ellipsis. A value ofnil (which is the default) means no limit. eval-expression-print-length — User Option: eval-expression-print-length eval-expression-print-level — User Option: eval-expression-print-level These are the values for print-length and print-levelused by eval-expression, and thus, indirectly, by manyinteractive evaluation commands (see See section ``Evaluating Emacs-Lisp Expressions'' in The GNU Emacs Manual). These variables are used for detecting and reporting circular and shared structure: print-circle — Variable: print-circle If non-nil, this variable enables detection of circularand shared structure in printing. print-gensym — Variable: print-gensym If non-nil, this variable enables detection of uninterned symbols(see ) in printing. When this is enabled,uninterned symbols print with the prefix ‘#:’, which tells the Lispreader to produce an uninterned symbol. print-continuous-numbering — Variable: print-continuous-numbering If non-nil, that means number continuously across print calls.This affects the numbers printed for ‘#n=’ labels and‘#m#’ references.Don't set this variable with setq; you should only bind ittemporarily to t with let. When you do that, you shouldalso bind print-number-table to nil. print-number-table — Variable: print-number-table This variable holds a vector used internally by printing to implementthe print-circle feature. You should not use it exceptto bind it to nil when you bind print-continuous-numbering. float-output-format — Variable: float-output-format This variable specifies how to print floating point numbers. Itsdefault value is nil, meaning use the shortest outputthat represents the number without losing information.To control output format more precisely, you can put a string in thisvariable. The string should hold a ‘%’-specification to be usedin the C function sprintf. For further restrictions on whatyou can use, see the variable's documentation string. <setfilename>../info/minibuf</setfilename> Minibuffers arguments, reading complex arguments minibuffer A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the frame, in the same place as the echo area (see ), but only while it is in use for reading an argument. Introduction to Minibuffers In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ‘ *Minibuf-number*’, and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometimes frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see .) The text in the minibuffer always starts with the prompt string, the text that was specified by the program that is using the minibuffer to tell the user what sort of input to type. This text is marked read-only so you won't accidentally delete or change it. It is also marked as a field (see ), so that certain motion functions, including beginning-of-line, forward-word, forward-sentence, and forward-paragraph, stop at the boundary between the prompt and the actual text. (In older Emacs versions, the prompt was displayed using a special mechanism and was not part of the buffer contents.) The minibuffer's window is normally a single line; it grows automatically if necessary if the contents require more space. You can explicitly resize it temporarily with the window sizing commands; it reverts to its normal size when the minibuffer is exited. You can resize it permanently by using the window sizing commands in the frame's other window, when the minibuffer is not active. If the frame contains just a minibuffer, you can change the minibuffer's size by changing the frame's size. Use of the minibuffer reads input events, and that alters the values of variables such as this-command and last-command (see ). Your program should bind them around the code that uses the minibuffer, if you do not want that to change them. If a command uses a minibuffer while there is an active minibuffer, this is called a recursive minibuffer. The first minibuffer is named ‘ *Minibuf-0*’. Recursive minibuffers are named by incrementing the number at the end of the name. (The names begin with a space so that they won't show up in normal buffer lists.) Of several recursive minibuffers, the innermost (or most recently entered) is the active minibuffer. We usually call this “the” minibuffer. You can permit or forbid recursive minibuffers by setting the variable enable-recursive-minibuffers or by putting properties of that name on command symbols (see ). Like other buffers, a minibuffer uses a local keymap (see ) to specify special key bindings. The function that invokes the minibuffer also sets up its local map according to the job to be done. See , for the non-completion minibuffer local maps. See , for the minibuffer local maps for completion. When Emacs is running in batch mode, any request to read from the minibuffer actually reads a line from the standard input descriptor that was supplied when Emacs was started. Reading Text Strings with the Minibuffer Most often, the minibuffer is used to read text as a string. It can also be used to read a Lisp object in textual form. The most basic primitive for minibuffer input is read-from-minibuffer; it can do either one. There are also specialized commands for reading commands, variables, file names, etc. (see ). In most cases, you should not call minibuffer input functions in the middle of a Lisp function. Instead, do all minibuffer input as part of reading the arguments for a command, in the interactive specification. See . read-from-minibuffer — Function: read-from-minibuffer prompt-string &optional initial-contents keymap read hist default inherit-input-method This function is the most general way to get input through theminibuffer. By default, it accepts arbitrary text and returns it as astring; however, if read is non-nil, then it usesread to convert the text into a Lisp object (see ).The first thing this function does is to activate a minibuffer anddisplay it with prompt-string as the prompt. This value must be astring. Then the user can edit text in the minibuffer.When the user types a command to exit the minibuffer,read-from-minibuffer constructs the return value from the text inthe minibuffer. Normally it returns a string containing that text.However, if read is non-nil, read-from-minibufferreads the text and returns the resulting Lisp object, unevaluated.(See , for information about reading.)The argument default specifies a default value to make availablethrough the history commands. It should be a string, or nil.If non-nil, the user can access it usingnext-history-element, usually bound in the minibuffer toM-n. If read is non-nil, then default isalso used as the input to read, if the user enters empty input.(If read is non-nil and default is nil, emptyinput results in an end-of-file error.) However, in the usualcase (where read is nil), read-from-minibufferignores default when the user enters empty input and returns anempty string, "". In this respect, it is different from allthe other minibuffer input functions in this chapter.If keymap is non-nil, that keymap is the local keymap touse in the minibuffer. If keymap is omitted or nil, thevalue of minibuffer-local-map is used as the keymap. Specifyinga keymap is the most important way to customize the minibuffer forvarious applications such as completion.The argument hist specifies which history list variable to usefor saving the input and for history commands used in the minibuffer.It defaults to minibuffer-history. See .If the variable minibuffer-allow-text-properties isnon-nil, then the string which is returned includes whatever textproperties were present in the minibuffer. Otherwise all the textproperties are stripped when the value is returned.If the argument inherit-input-method is non-nil, then theminibuffer inherits the current input method (see ) andthe setting of enable-multibyte-characters (see ) from whichever buffer was current before entering theminibuffer.Use of initial-contents is mostly deprecated; we recommend usinga non-nil value only in conjunction with specifying a cons cellfor hist. See . read-string — Function: read-string prompt &optional initial history default inherit-input-method This function reads a string from the minibuffer and returns it. Thearguments prompt, initial, history andinherit-input-method are used as in read-from-minibuffer.The keymap used is minibuffer-local-map.The optional argument default is used as inread-from-minibuffer, except that, if non-nil, it alsospecifies a default value to return if the user enters null input. Asin read-from-minibuffer it should be a string, or nil,which is equivalent to an empty string.This function is a simplified interface to theread-from-minibuffer function: (read-string prompt initial history default inherit) == (let ((value (read-from-minibuffer prompt initial nil nil history default inherit))) (if (and (equal value "") default) default value)) minibuffer-allow-text-properties — Variable: minibuffer-allow-text-properties If this variable is nil, then read-from-minibuffer stripsall text properties from the minibuffer input before returning it.This variable also affects read-string. However,read-no-blanks-input (see below), as well asread-minibuffer and related functions (see Reading Lisp Objects With the Minibuffer), and allfunctions that do minibuffer input with completion, discard textproperties unconditionally, regardless of the value of this variable. minibuffer-local-map — Variable: minibuffer-local-map This is the default local keymap for reading from the minibuffer. Bydefault, it makes the following bindings: C-j exit-minibuffer RET exit-minibuffer C-g abort-recursive-edit M-nDOWN next-history-element M-pUP previous-history-element M-s next-matching-history-element M-r previous-matching-history-element read-no-blanks-input — Function: read-no-blanks-input prompt &optional initial inherit-input-method This function reads a string from the minibuffer, but does not allowwhitespace characters as part of the input: instead, those charactersterminate the input. The arguments prompt, initial, andinherit-input-method are used as in read-from-minibuffer.This is a simplified interface to the read-from-minibufferfunction, and passes the value of the minibuffer-local-ns-mapkeymap as the keymap argument for that function. Since the keymapminibuffer-local-ns-map does not rebind C-q, it ispossible to put a space into the string, by quoting it.This function discards text properties, regardless of the value ofminibuffer-allow-text-properties. (read-no-blanks-input prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial minibuffer-local-ns-map)) minibuffer-local-ns-map — Variable: minibuffer-local-ns-map This built-in variable is the keymap used as the minibuffer local keymapin the function read-no-blanks-input. By default, it makes thefollowing bindings, in addition to those of minibuffer-local-map: SPC SPC in minibufferexit-minibuffer TAB TAB in minibufferexit-minibuffer ? ? in minibufferself-insert-and-exit Reading Lisp Objects with the Minibuffer This section describes functions for reading Lisp objects with the minibuffer. read-minibuffer — Function: read-minibuffer prompt &optional initial This function reads a Lisp object using the minibuffer, and returns itwithout evaluating it. The arguments prompt and initial areused as in read-from-minibuffer.This is a simplified interface to theread-from-minibuffer function: (read-minibuffer prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial nil t)) Here is an example in which we supply the string "(testing)" asinitial input: (read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ---------- The user can type RET immediately to use the initial input as adefault, or can edit the input. eval-minibuffer — Function: eval-minibuffer prompt &optional initial This function reads a Lisp expression using the minibuffer, evaluatesit, then returns the result. The arguments prompt andinitial are used as in read-from-minibuffer.This function simply evaluates the result of a call toread-minibuffer: (eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial)) edit-and-eval-command — Function: edit-and-eval-command prompt form This function reads a Lisp expression in the minibuffer, and thenevaluates it. The difference between this command andeval-minibuffer is that here the initial form is notoptional and it is treated as a Lisp object to be converted to printedrepresentation rather than as a string of text. It is printed withprin1, so if it is a string, double-quote characters (‘"’)appear in the initial text. See .The first thing edit-and-eval-command does is to activate theminibuffer with prompt as the prompt. Then it inserts the printedrepresentation of form in the minibuffer, and lets the user edit it.When the user exits the minibuffer, the edited text is read withread and then evaluated. The resulting value becomes the valueof edit-and-eval-command.In the following example, we offer the user an expression with initialtext which is a valid form already: (edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ---------- Typing RET right away would exit the minibuffer and evaluate theexpression, thus moving point forward one word.edit-and-eval-command returns nil in this example. Minibuffer History minibuffer history history list A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. A history list is actually a symbol, not a list; it is a variable whose value is a list of strings (previous inputs), most recent first. There are many separate history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer. You specify the history list with the optional hist argument to either read-from-minibuffer or completing-read. Here are the possible values for it: variable Use variable (a symbol) as the history list. (variable . startpos) Use variable (a symbol) as the history list, and assume that theinitial history position is startpos (a nonnegative integer).Specifying 0 for startpos is equivalent to just specifying thesymbol variable. previous-history-element will displaythe most recent element of the history list in the minibuffer. If youspecify a positive startpos, the minibuffer history functionsbehave as if (elt variable (1- STARTPOS)) were thehistory element currently shown in the minibuffer.For consistency, you should also specify that element of the historyas the initial minibuffer contents, using the initial argumentto the minibuffer input function (see ). If you don't specify hist, then the default history list minibuffer-history is used. For other standard history lists, see below. You can also create your own history list variable; just initialize it to nil before the first use. Both read-from-minibuffer and completing-read add new elements to the history list automatically, and provide commands to allow the user to reuse items on the list. The only thing your program needs to do to use a history list is to initialize it and to pass its name to the input functions when you wish. But it is safe to modify the list by hand when the minibuffer input functions are not using it. Emacs functions that add a new element to a history list can also delete old elements if the list gets too long. The variable history-length specifies the maximum length for most history lists. To specify a different maximum length for a particular history list, put the length in the history-length property of the history list symbol. The variable history-delete-duplicates specifies whether to delete duplicates in history. add-to-history — Function: add-to-history history-var newelt &optional maxelt keep-all This function adds a new element newelt, if it isn't the emptystring, to the history list stored in the variable history-var,and returns the updated history list. It limits the list length tothe value of maxelt (if non-nil) or history-length(described below). The possible values of maxelt have the samemeaning as the values of history-length.Normally, add-to-history removes duplicate members from thehistory list if history-delete-duplicates is non-nil.However, if keep-all is non-nil, that says not to removeduplicates, and to add newelt to the list even if it is empty. history-add-new-input — Variable: history-add-new-input If the value of this variable is nil, standard functions thatread from the minibuffer don't add new elements to the history list.This lets Lisp programs explicitly manage input history by usingadd-to-history. By default, history-add-new-input isset to a non-nil value. history-length — Variable: history-length The value of this variable specifies the maximum length for allhistory lists that don't specify their own maximum lengths. If thevalue is t, that means there no maximum (don't delete oldelements). The value of history-length property of the historylist variable's symbol, if set, overrides this variable for thatparticular history list. history-delete-duplicates — Variable: history-delete-duplicates If the value of this variable is t, that means when adding anew history element, all previous identical elements are deleted. Here are some of the standard minibuffer history list variables: minibuffer-history — Variable: minibuffer-history The default history list for minibuffer history input. query-replace-history — Variable: query-replace-history A history list for arguments to query-replace (and similararguments to other commands). file-name-history — Variable: file-name-history A history list for file-name arguments. buffer-name-history — Variable: buffer-name-history A history list for buffer-name arguments. regexp-history — Variable: regexp-history A history list for regular expression arguments. extended-command-history — Variable: extended-command-history A history list for arguments that are names of extended commands. shell-command-history — Variable: shell-command-history A history list for arguments that are shell commands. read-expression-history — Variable: read-expression-history A history list for arguments that are Lisp expressions to evaluate. Initial Input Several of the functions for minibuffer input have an argument called initial or initial-contents. This is a mostly-deprecated feature for specifying that the minibuffer should start out with certain text, instead of empty as usual. If initial is a string, the minibuffer starts out containing the text of the string, with point at the end, when the user starts to edit the text. If the user simply types RET to exit the minibuffer, it will use the initial input string to determine the value to return. We discourage use of a non-nil value for initial, because initial input is an intrusive interface. History lists and default values provide a much more convenient method to offer useful default inputs to the user. There is just one situation where you should specify a string for an initial argument. This is when you specify a cons cell for the hist or history argument. See . initial can also be a cons cell of the form (string . position). This means to insert string in the minibuffer but put point at position within the string's text. As a historical accident, position was implemented inconsistently in different functions. In completing-read, position's value is interpreted as origin-zero; that is, a value of 0 means the beginning of the string, 1 means after the first character, etc. In read-minibuffer, and the other non-completion minibuffer input functions that support this argument, 1 means the beginning of the string 2 means after the first character, etc. Use of a cons cell as the value for initial arguments is deprecated in user code. Completion completion Completion is a feature that fills in the rest of a name starting from an abbreviation for it. Completion works by comparing the user's input against a list of valid names and determining how much of the name is determined uniquely by what the user has typed. For example, when you type C-x b (switch-to-buffer) and then type the first few letters of the name of the buffer to which you wish to switch, and then type TAB (minibuffer-complete), Emacs extends the name as far as it can. Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names. The try-completion function is the basic primitive for completion: it returns the longest determined completion of a given initial string, with a given set of strings to match against. The function completing-read provides a higher-level interface for completion. A call to completing-read specifies how to determine the list of valid names. The function then activates the minibuffer with a local keymap that binds a few keys to commands useful for completion. Other functions provide convenient simple interfaces for reading certain kinds of names with completion. Basic Completion Functions The completion functions try-completion, all-completions and test-completion have nothing in themselves to do with minibuffers. We describe them in this chapter so as to keep them near the higher-level completion features that do use the minibuffer. If you store a completion alist in a variable, you should mark the variable as “risky” with a non-nil risky-local-variable property. try-completion — Function: try-completion string collection &optional predicate This function returns the longest common substring of all possiblecompletions of string in collection. The value ofcollection must be a list of strings or symbols, an alist, anobarray, a hash table, or a function that implements a virtual set ofstrings (see below).Completion compares string against each of the permissiblecompletions specified by collection; if the beginning of thepermissible completion equals string, it matches. If no permissiblecompletions match, try-completion returns nil. If onlyone permissible completion matches, and the match is exact, thentry-completion returns t. Otherwise, the value is thelongest initial sequence common to all the permissible completions thatmatch.If collection is an alist (see ), thepermissible completions are the elements of the alist that are eitherstrings, symbols, or conses whose car is a string or symbol.Symbols are converted to strings using symbol-name. Otherelements of the alist are ignored. (Remember that in Emacs Lisp, theelements of alists do not have to be conses.) In particular, alist of strings or symbols is allowed, even though we usually do notthink of such lists as alists. obarray in completionIf collection is an obarray (see ), the namesof all symbols in the obarray form the set of permissible completions. Theglobal variable obarray holds an obarray containing the names ofall interned Lisp symbols.Note that the only valid way to make a new obarray is to create itempty and then add symbols to it one by one using intern.Also, you cannot intern a given symbol in more than one obarray.If collection is a hash table, then the keys that are stringsare the possible completions. Other keys are ignored.You can also use a symbol that is a function as collection. Thenthe function is solely responsible for performing completion;try-completion returns whatever this function returns. Thefunction is called with three arguments: string, predicateand nil. (The reason for the third argument is so that the samefunction can be used in all-completions and do the appropriatething in either case.) See .If the argument predicate is non-nil, then it must be afunction of one argument, unless collection is a hash table, inwhich case it should be a function of two arguments. It is used totest each possible match, and the match is accepted only ifpredicate returns non-nil. The argument given topredicate is either a string or a cons cell (the car ofwhich is a string) from the alist, or a symbol (not a symbolname) from the obarray. If collection is a hash table,predicate is called with two arguments, the string key and theassociated value.In addition, to be acceptable, a completion must also match all theregular expressions in completion-regexp-list. (Unlesscollection is a function, in which case that function has tohandle completion-regexp-list itself.)In the first of the following examples, the string ‘foo’ ismatched by three of the alist cars. All of the matches begin withthe characters ‘fooba’, so that is the result. In the secondexample, there is only one possible match, and it is exact, so the valueis t. (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) => "fooba" (try-completion "foo" '(("barfoo" 2) ("foo" 3))) => t In the following example, numerous symbols begin with the characters‘forw’, and all of them begin with the word ‘forward’. Inmost of the symbols, this is followed with a ‘-’, but not in all,so no more than ‘forward’ can be completed. (try-completion "forw" obarray) => "forward" Finally, in the following example, only two of the three possiblematches pass the predicate test (the string ‘foobaz’ istoo short). Both of those begin with the string ‘foobar’. (defun test (s) (> (length (car s)) 6)) => test (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => "foobar" all-completions — Function: all-completions string collection &optional predicate nospace This function returns a list of all possible completions ofstring. The arguments to this function (aside fromnospace) are the same as those of try-completion. Also,this function uses completion-regexp-list in the same way thattry-completion does. The optional argument nospace onlymatters if string is the empty string. In that case, ifnospace is non-nil, completions that start with a spaceare ignored.If collection is a function, it is called with three arguments:string, predicate and t; then all-completionsreturns whatever the function returns. See .Here is an example, using the function test shown in theexample for try-completion: (defun test (s) (> (length (car s)) 6)) => test (all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => ("foobar1" "foobar2") test-completion — Function: test-completion string collection &optional predicate This function returns non-nil if string is a validcompletion possibility specified by collection andpredicate. The arguments are the same as intry-completion. For instance, if collection is a list ofstrings, this is true if string appears in the list andpredicate is satisfied.This function uses completion-regexp-list in the sameway that try-completion does.If predicate is non-nil and if collection containsseveral strings that are equal to each other, as determined bycompare-strings according to completion-ignore-case,then predicate should accept either all or none of them.Otherwise, the return value of test-completion is essentiallyunpredictable.If collection is a function, it is called with three arguments,the values string, predicate and lambda; whateverit returns, test-completion returns in turn. completion-ignore-case — Variable: completion-ignore-case If the value of this variable is non-nil, Emacs does notconsider case significant in completion. completion-regexp-list — Variable: completion-regexp-list This is a list of regular expressions. The completion functions onlyconsider a completion acceptable if it matches all regular expressionsin this list, with case-fold-search (see )bound to the value of completion-ignore-case. lazy-completion-table — Macro: lazy-completion-table var fun This macro provides a way to initialize the variable var as acollection for completion in a lazy way, not computing its actualcontents until they are first needed. You use this macro to produce avalue that you store in var. The actual computation of theproper value is done the first time you do completion using var.It is done by calling fun with no arguments. Thevalue fun returns becomes the permanent value of var.Here is an example of use: (defvar foo (lazy-completion-table foo make-my-alist)) Completion and the Minibuffer minibuffer completion reading from minibuffer with completion This section describes the basic interface for reading from the minibuffer with completion. completing-read — Function: completing-read prompt collection &optional predicate require-match initial hist default inherit-input-method This function reads a string in the minibuffer, assisting the user byproviding completion. It activates the minibuffer with promptprompt, which must be a string.The actual completion is done by passing collection andpredicate to the function try-completion. This happensin certain commands bound in the local keymaps used for completion.Some of these commands also call test-completion. Thus, ifpredicate is non-nil, it should be compatible withcollection and completion-ignore-case. See .If require-match is nil, the exit commands work regardlessof the input in the minibuffer. If require-match is t, theusual minibuffer exit commands won't exit unless the input completes toan element of collection. If require-match is neithernil nor t, then the exit commands won't exit unless theinput already in the buffer matches an element of collection.However, empty input is always permitted, regardless of the value ofrequire-match; in that case, completing-read returnsdefault, or "", if default is nil. Thevalue of default (if non-nil) is also available to theuser through the history commands.The function completing-read usesminibuffer-local-completion-map as the keymap ifrequire-match is nil, and usesminibuffer-local-must-match-map if require-match isnon-nil. See .The argument hist specifies which history list variable to use forsaving the input and for minibuffer history commands. It defaults tominibuffer-history. See .The argument initial is mostly deprecated; we recommend using anon-nil value only in conjunction with specifying a cons cellfor hist. See . For default input, usedefault instead.If the argument inherit-input-method is non-nil, then theminibuffer inherits the current input method (see ) and the setting of enable-multibyte-characters(see ) from whichever buffer was current beforeentering the minibuffer.If the built-in variable completion-ignore-case isnon-nil, completion ignores case when comparing the inputagainst the possible matches. See . In this modeof operation, predicate must also ignore case, or you will getsurprising results.Here's an example of using completing-read: (completing-read "Complete a foo: " '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) nil t "fo") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Complete a foo: fo-!- ---------- Buffer: Minibuffer ---------- If the user then types DEL DEL b RET,completing-read returns barfoo.The completing-read function binds variables to passinformation to the commands that actually do completion.They are described in the following section. Minibuffer Commands that Do Completion This section describes the keymaps, commands and user options used in the minibuffer to do completion. The description refers to the situation when Partial Completion mode is disabled (as it is by default). When enabled, this minor mode uses its own alternatives to some of the commands described below. See See section ``Completion Options'' in The GNU Emacs Manual, for a short description of Partial Completion mode. minibuffer-completion-table — Variable: minibuffer-completion-table The value of this variable is the collection used for completion inthe minibuffer. This is the global variable that contains whatcompleting-read passes to try-completion. It is used byminibuffer completion commands such as minibuffer-complete-word. minibuffer-completion-predicate — Variable: minibuffer-completion-predicate This variable's value is the predicate that completing-readpasses to try-completion. The variable is also used by the otherminibuffer completion functions. minibuffer-completion-confirm — Variable: minibuffer-completion-confirm When the value of this variable is non-nil, Emacs asks forconfirmation of a completion before exiting the minibuffer.completing-read binds this variable, and the functionminibuffer-complete-and-exit checks the value before exiting. minibuffer-complete-word — Command: minibuffer-complete-word This function completes the minibuffer contents by at most a singleword. Even if the minibuffer contents have only one completion,minibuffer-complete-word does not add any characters beyond thefirst character that is not a word constituent. See . minibuffer-complete — Command: minibuffer-complete This function completes the minibuffer contents as far as possible. minibuffer-complete-and-exit — Command: minibuffer-complete-and-exit This function completes the minibuffer contents, and exits ifconfirmation is not required, i.e., ifminibuffer-completion-confirm is nil. If confirmationis required, it is given by repeating this commandimmediately—the command is programmed to work without confirmationwhen run twice in succession. minibuffer-completion-help — Command: minibuffer-completion-help This function creates a list of the possible completions of thecurrent minibuffer contents. It works by calling all-completionsusing the value of the variable minibuffer-completion-table asthe collection argument, and the value ofminibuffer-completion-predicate as the predicate argument.The list of completions is displayed as text in a buffer named‘*Completions*’. display-completion-list — Function: display-completion-list completions &optional common-substring This function displays completions to the stream instandard-output, usually a buffer. (See , for moreinformation about streams.) The argument completions is normallya list of completions just returned by all-completions, but itdoes not have to be. Each element may be a symbol or a string, eitherof which is simply printed. It can also be a list of two strings,which is printed as if the strings were concatenated. The first ofthe two strings is the actual completion, the second string serves asannotation.The argument common-substring is the prefix that is common toall the completions. With normal Emacs completion, it is usually thesame as the string that was completed. display-completion-listuses this to highlight text in the completion list for better visualfeedback. This is not needed in the minibuffer; for minibuffercompletion, you can pass nil.This function is called by minibuffer-completion-help. Themost common way to use it is together withwith-output-to-temp-buffer, like this: (with-output-to-temp-buffer "*Completions*" (display-completion-list (all-completions (buffer-string) my-alist) (buffer-string))) completion-auto-help — User Option: completion-auto-help If this variable is non-nil, the completion commandsautomatically display a list of possible completions whenever nothingcan be completed because the next character is not uniquely determined. minibuffer-local-completion-map — Variable: minibuffer-local-completion-map completing-read uses this value as the local keymap when anexact match of one of the completions is not required. By default, thiskeymap makes the following bindings: ? minibuffer-completion-help SPC minibuffer-complete-word TAB minibuffer-complete with other characters bound as in minibuffer-local-map(see ). minibuffer-local-must-match-map — Variable: minibuffer-local-must-match-map completing-read uses this value as the local keymap when anexact match of one of the completions is required. Therefore, no keysare bound to exit-minibuffer, the command that exits theminibuffer unconditionally. By default, this keymap makes the followingbindings: ? minibuffer-completion-help SPC minibuffer-complete-word TAB minibuffer-complete C-j minibuffer-complete-and-exit RET minibuffer-complete-and-exit with other characters bound as in minibuffer-local-map. minibuffer-local-filename-completion-map — Variable: minibuffer-local-filename-completion-map This is like minibuffer-local-completion-mapexcept that it does not bind SPC. This keymap is used by thefunction read-file-name. minibuffer-local-must-match-filename-map — Variable: minibuffer-local-must-match-filename-map This is like minibuffer-local-must-match-mapexcept that it does not bind SPC. This keymap is used by thefunction read-file-name. High-Level Completion Functions This section describes the higher-level convenient functions for reading certain sorts of names with completion. In most cases, you should not call these functions in the middle of a Lisp function. When possible, do all minibuffer input as part of reading the arguments for a command, in the interactive specification. See . read-buffer — Function: read-buffer prompt &optional default existing This function reads the name of a buffer and returns it as a string.The argument default is the default name to use, the value toreturn if the user exits with an empty minibuffer. If non-nil,it should be a string or a buffer. It is mentioned in the prompt, butis not inserted in the minibuffer as initial input.The argument prompt should be a string ending with a colon and aspace. If default is non-nil, the function inserts it inprompt before the colon to follow the convention for reading fromthe minibuffer with a default value (see ).If existing is non-nil, then the name specified must bethat of an existing buffer. The usual commands to exit the minibufferdo not exit if the text is not valid, and RET does completion toattempt to find a valid name. If existing is neither nilnor t, confirmation is required after completion. (However,default is not checked for validity; it is returned, whatever itis, if the user exits with the minibuffer empty.)In the following example, the user enters ‘minibuffer.t’, andthen types RET. The argument existing is t, and theonly buffer name starting with the given input is‘minibuffer.texi’, so that name is the value. (read-buffer "Buffer name: " "foo" t) ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Buffer name (default foo): -!- ---------- Buffer: Minibuffer ---------- ;; The user types minibuffer.t RET. => "minibuffer.texi" read-buffer-function — Variable: read-buffer-function This variable specifies how to read buffer names. For example, if youset this variable to iswitchb-read-buffer, all Emacs commandsthat call read-buffer to read a buffer name will actually use theiswitchb package to read it. read-command — Function: read-command prompt &optional default This function reads the name of a command and returns it as a Lispsymbol. The argument prompt is used as inread-from-minibuffer. Recall that a command is anything forwhich commandp returns t, and a command name is a symbolfor which commandp returns t. See .The argument default specifies what to return if the user entersnull input. It can be a symbol or a string; if it is a string,read-command interns it before returning it. If default isnil, that means no default has been specified; then if the userenters null input, the return value is (intern ""), that is, asymbol whose name is an empty string. (read-command "Command name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ---------- If the user types forward-c RET, then this function returnsforward-char.The read-command function is a simplified interface tocompleting-read. It uses the variable obarray so as tocomplete in the set of extant Lisp symbols, and it uses thecommandp predicate so as to accept only command names: commandp example (read-command prompt) == (intern (completing-read prompt obarray 'commandp t nil)) read-variable — Function: read-variable prompt &optional default This function reads the name of a user variable and returns it as asymbol.The argument default specifies what to return if the user entersnull input. It can be a symbol or a string; if it is a string,read-variable interns it before returning it. If defaultis nil, that means no default has been specified; then if theuser enters null input, the return value is (intern ""). (read-variable "Variable name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Variable name? -!- ---------- Buffer: Minibuffer ---------- If the user then types fill-p RET, read-variablereturns fill-prefix.In general, read-variable is similar to read-command,but uses the predicate user-variable-p instead ofcommandp: user-variable-p example (read-variable prompt) == (intern (completing-read prompt obarray 'user-variable-p t nil)) See also the functions read-coding-system and read-non-nil-coding-system, in , and read-input-method-name, in . Reading File Names read file names prompt for file name Here is another high-level completion function, designed for reading a file name. It provides special features including automatic insertion of the default directory. read-file-name — Function: read-file-name prompt &optional directory default existing initial predicate This function reads a file name in the minibuffer, prompting withprompt and providing completion.If existing is non-nil, then the user must specify the nameof an existing file; RET performs completion to make the namevalid if possible, and then refuses to exit if it is not valid. If thevalue of existing is neither nil nor t, thenRET also requires confirmation after completion. Ifexisting is nil, then the name of a nonexistent file isacceptable.read-file-name usesminibuffer-local-filename-completion-map as the keymap ifexisting is nil, and usesminibuffer-local-must-match-filename-map if existing isnon-nil. See .The argument directory specifies the directory to use forcompletion of relative file names. It should be an absolute directoryname. If insert-default-directory is non-nil,directory is also inserted in the minibuffer as initial input.It defaults to the current buffer's value of default-directory. If you specify initial, that is an initial file name to insertin the buffer (after directory, if that is inserted). In thiscase, point goes at the beginning of initial. The default forinitial is nil—don't insert any file name. To see whatinitial does, try the command C-x C-v. Pleasenote: we recommend using default rather than initial inmost cases.If default is non-nil, then the function returnsdefault if the user exits the minibuffer with the same non-emptycontents that read-file-name inserted initially. The initialminibuffer contents are always non-empty ifinsert-default-directory is non-nil, as it is bydefault. default is not checked for validity, regardless of thevalue of existing. However, if existing isnon-nil, the initial minibuffer contents should be a valid file(or directory) name. Otherwise read-file-name attemptscompletion if the user exits without any editing, and does not returndefault. default is also available through the historycommands.If default is nil, read-file-name tries to find asubstitute default to use in its place, which it treats in exactly thesame way as if it had been specified explicitly. If default isnil, but initial is non-nil, then the default isthe absolute file name obtained from directory andinitial. If both default and initial are niland the buffer is visiting a file, read-file-name uses theabsolute file name of that file as default. If the buffer is notvisiting a file, then there is no default. In that case, if the usertypes RET without any editing, read-file-name simplyreturns the pre-inserted contents of the minibuffer.If the user types RET in an empty minibuffer, this functionreturns an empty string, regardless of the value of existing.This is, for instance, how the user can make the current buffer visitno file using M-x set-visited-file-name.If predicate is non-nil, it specifies a function of oneargument that decides which file names are acceptable completionpossibilities. A file name is an acceptable value if predicatereturns non-nil for it.read-file-name does not automatically expand file names. Youmust call expand-file-name yourself if an absolute file name isrequired.Here is an example: (read-file-name "The file is ") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ---------- Typing manual TAB results in the following: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ---------- If the user types RET, read-file-name returns the file nameas the string "/gp/gnu/elisp/manual.texi". read-file-name-function — Variable: read-file-name-function If non-nil, this should be a function that accepts the samearguments as read-file-name. When read-file-name iscalled, it calls this function with the supplied arguments instead ofdoing its usual work. read-file-name-completion-ignore-case — Variable: read-file-name-completion-ignore-case If this variable is non-nil, read-file-name ignores casewhen performing completion. read-directory-name — Function: read-directory-name prompt &optional directory default existing initial This function is like read-file-name but allows only directorynames as completion possibilities.If default is nil and initial is non-nil,read-directory-name constructs a substitute default bycombining directory (or the current buffer's default directoryif directory is nil) and initial. If bothdefault and initial are nil, this function usesdirectory as substitute default, or the current buffer's defaultdirectory if directory is nil. insert-default-directory — User Option: insert-default-directory This variable is used by read-file-name, and thus, indirectly,by most commands reading file names. (This includes all commands thatuse the code letters ‘f’ or ‘F’ in their interactive form.See Code Characters for interactive.) Itsvalue controls whether read-file-name starts by placing thename of the default directory in the minibuffer, plus the initial filename if any. If the value of this variable is nil, thenread-file-name does not place any initial input in theminibuffer (unless you specify initial input with the initialargument). In that case, the default directory is still used forcompletion of relative file names, but is not displayed.If this variable is nil and the initial minibuffer contents areempty, the user may have to explicitly fetch the next history elementto access a default value. If the variable is non-nil, theinitial minibuffer contents are always non-empty and the user canalways request a default value by immediately typing RET in anunedited minibuffer. (See above.)For example: ;; Here the minibuffer starts out with the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ---------- Programmed Completion programmed completion Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion. To use this feature, pass a symbol with a function definition as the collection argument to completing-read. The function completing-read arranges to pass your completion function along to try-completion and all-completions, which will then let your function do all the work. The completion function should accept three arguments: The string to be completed. The predicate function to filter possible matches, or nil ifnone. Your function should call the predicate for each possible match,and ignore the possible match if the predicate returns nil. A flag specifying the type of operation. There are three flag values for three operations: nil specifies try-completion. The completion functionshould return the completion of the specified string, or t if thestring is a unique and exact match already, or nil if the stringmatches no possibility.If the string is an exact match for one possibility, but also matchesother longer possibilities, the function should return the string, nott. t specifies all-completions. The completion functionshould return a list of all possible completions of the specifiedstring. lambda specifies test-completion. The completionfunction should return t if the specified string is an exactmatch for some possibility; nil otherwise. It would be consistent and clean for completion functions to allow lambda expressions (lists that are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables already have other meanings, and it would be unreliable to treat one differently just because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol. Emacs uses programmed completion when completing file names. See . dynamic-completion-table — Macro: dynamic-completion-table function This macro is a convenient way to write a function that can act asprogrammed completion function. The argument function should bea function that takes one argument, a string, and returns an alist ofpossible completions of it. You can think ofdynamic-completion-table as a transducer between that interfaceand the interface for programmed completion functions. Yes-or-No Queries asking the user questions querying the user yes-or-no questions This section describes functions used to ask the user a yes-or-no question. The function y-or-n-p can be answered with a single character; it is useful for questions where an inadvertent wrong answer will not have serious consequences. yes-or-no-p is suitable for more momentous questions, since it requires three or four characters to answer. If either of these functions is called in a command that was invoked using the mouse—more precisely, if last-nonmenu-event (see ) is either nil or a list—then it uses a dialog box or pop-up menu to ask the question. Otherwise, it uses keyboard input. You can force use of the mouse or use of keyboard input by binding last-nonmenu-event to a suitable value around the call. Strictly speaking, yes-or-no-p uses the minibuffer and y-or-n-p does not; but it seems best to describe them together. y-or-n-p — Function: y-or-n-p prompt This function asks the user a question, expecting input in the echoarea. It returns t if the user types y, nil if theuser types n. This function also accepts SPC to mean yesand DEL to mean no. It accepts C-] to mean “quit,” likeC-g, because the question might look like a minibuffer and forthat reason the user might try to use C-] to get out. The answeris a single character, with no RET needed to terminate it. Upperand lower case are equivalent.“Asking the question” means printing prompt in the echo area,followed by the string ‘(y or n) ’. If the input is not one ofthe expected answers (y, n, SPC,DEL, or something that quits), the function responds‘Please answer y or n.’, and repeats the request.This function does not actually use the minibuffer, since it does notallow editing of the answer. It actually uses the echo area (see ), which uses the same screen space as the minibuffer. Thecursor moves to the echo area while the question is being asked.The answers and their meanings, even ‘y’ and ‘n’, are nothardwired. The keymap query-replace-map specifies them.See .In the following example, the user first types q, which isinvalid. At the next prompt the user types y. (y-or-n-p "Do you need a lift? ") ;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area: ---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ---------- ;; If the user then types q, the following appears: ---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ---------- ;; When the user types a valid answer, ;; it is displayed after the question: ---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ---------- We show successive lines of echo area messages, but only one actuallyappears on the screen at a time. y-or-n-p-with-timeout — Function: y-or-n-p-with-timeout prompt seconds default-value Like y-or-n-p, except that if the user fails to answer withinseconds seconds, this function stops waiting and returnsdefault-value. It works by setting up a timer; see .The argument seconds may be an integer or a floating point number. yes-or-no-p — Function: yes-or-no-p prompt This function asks the user a question, expecting input in theminibuffer. It returns t if the user enters ‘yes’,nil if the user types ‘no’. The user must type RET tofinalize the response. Upper and lower case are equivalent.yes-or-no-p starts by displaying prompt in the echo area,followed by ‘(yes or no) ’. The user must type one of theexpected responses; otherwise, the function responds ‘Please answeryes or no.’, waits about two seconds and repeats the request.yes-or-no-p requires more work from the user thany-or-n-p and is appropriate for more crucial decisions.Here is an example: (yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ---------- If the user first types y RET, which is invalid because thisfunction demands the entire word ‘yes’, it responds by displayingthese prompts, with a brief pause between them: ---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ---------- Asking Multiple Y-or-N Questions When you have a series of similar questions to ask, such as “Do you want to save this buffer” for each buffer in turn, you should use map-y-or-n-p to ask the collection of questions, rather than asking each question individually. This gives the user certain convenient facilities such as the ability to answer the whole series at once. map-y-or-n-p — Function: map-y-or-n-p prompter actor list &optional help action-alist no-cursor-in-echo-area This function asks the user a series of questions, reading asingle-character answer in the echo area for each one.The value of list specifies the objects to ask questions about.It should be either a list of objects or a generator function. If it isa function, it should expect no arguments, and should return either thenext object to ask about, or nil meaning stop asking questions.The argument prompter specifies how to ask each question. Ifprompter is a string, the question text is computed like this: (format prompter object) where object is the next object to ask about (as obtained fromlist).If not a string, prompter should be a function of one argument(the next object to ask about) and should return the question text. Ifthe value is a string, that is the question to ask the user. Thefunction can also return t meaning do act on this object (anddon't ask the user), or nil meaning ignore this object (and don'task the user).The argument actor says how to act on the answers that the usergives. It should be a function of one argument, and it is called witheach object that the user says yes for. Its argument is always anobject obtained from list.If the argument help is given, it should be a list of this form: (singular plural action) where singular is a string containing a singular noun thatdescribes the objects conceptually being acted on, plural is thecorresponding plural noun, and action is a transitive verbdescribing what actor does.If you don't specify help, the default is ("object""objects" "act on").Each time a question is asked, the user may enter y, Y, orSPC to act on that object; n, N, or DEL to skipthat object; ! to act on all following objects; ESC orq to exit (skip all following objects); . (period) to act onthe current object and then exit; or C-h to get help. These arethe same answers that query-replace accepts. The keymapquery-replace-map defines their meaning for map-y-or-n-pas well as for query-replace; see .You can use action-alist to specify additional possible answersand what they mean. It is an alist of elements of the form(char function help), each of which defines oneadditional answer. In this element, char is a character (theanswer); function is a function of one argument (an object fromlist); help is a string.When the user responds with char, map-y-or-n-p callsfunction. If it returns non-nil, the object is considered“acted upon,” and map-y-or-n-p advances to the next object inlist. If it returns nil, the prompt is repeated for thesame object.Normally, map-y-or-n-p binds cursor-in-echo-area whileprompting. But if no-cursor-in-echo-area is non-nil, itdoes not do that.If map-y-or-n-p is called in a command that was invoked using themouse—more precisely, if last-nonmenu-event (see ) is either nil or a list—then it uses a dialog boxor pop-up menu to ask the question. In this case, it does not usekeyboard input or the echo area. You can force use of the mouse or useof keyboard input by binding last-nonmenu-event to a suitablevalue around the call.The return value of map-y-or-n-p is the number of objects acted on. Reading a Password passwords, reading To read a password to pass to another program, you can use the function read-passwd. read-passwd — Function: read-passwd prompt &optional confirm default This function reads a password, prompting with prompt. It doesnot echo the password as the user types it; instead, it echoes ‘.’for each character in the password.The optional argument confirm, if non-nil, says to read thepassword twice and insist it must be the same both times. If it isn'tthe same, the user has to type it over and over until the last twotimes match.The optional argument default specifies the default password toreturn if the user enters empty input. If default is nil,then read-passwd returns the null string in that case. Minibuffer Commands This section describes some commands meant for use in the minibuffer. exit-minibuffer — Command: exit-minibuffer This command exits the active minibuffer. It is normally bound tokeys in minibuffer local keymaps. self-insert-and-exit — Command: self-insert-and-exit This command exits the active minibuffer after inserting the lastcharacter typed on the keyboard (found in last-command-char;see ). previous-history-element — Command: previous-history-element n This command replaces the minibuffer contents with the value of thenth previous (older) history element. next-history-element — Command: next-history-element n This command replaces the minibuffer contents with the value of thenth more recent history element. previous-matching-history-element — Command: previous-matching-history-element pattern n This command replaces the minibuffer contents with the value of thenth previous (older) history element that matches pattern (aregular expression). next-matching-history-element — Command: next-matching-history-element pattern n This command replaces the minibuffer contents with the value of thenth next (newer) history element that matches pattern (aregular expression). Minibuffer Windows minibuffer windows These functions access and select minibuffer windows and test whether they are active. active-minibuffer-window — Function: active-minibuffer-window This function returns the currently active minibuffer window, ornil if none is currently active. minibuffer-window — Function: minibuffer-window &optional frame This function returns the minibuffer window used for frame frame.If frame is nil, that stands for the current frame. Notethat the minibuffer window used by a frame need not be part of thatframe—a frame that has no minibuffer of its own necessarily uses someother frame's minibuffer window. set-minibuffer-window — Function: set-minibuffer-window window This function specifies window as the minibuffer window to use.This affects where the minibuffer is displayed if you put text in itwithout invoking the usual minibuffer commands. It has no effect onthe usual minibuffer input functions because they all start bychoosing the minibuffer window according to the current frame. window-minibuffer-p — Function: window-minibuffer-p &optional window This function returns non-nil if window is a minibufferwindow.window defaults to the selected window. It is not correct to determine whether a given window is a minibuffer by comparing it with the result of (minibuffer-window), because there can be more than one minibuffer window if there is more than one frame. minibuffer-window-active-p — Function: minibuffer-window-active-p window This function returns non-nil if window, assumed to bea minibuffer window, is currently active. Minibuffer Contents These functions access the minibuffer prompt and contents. minibuffer-prompt — Function: minibuffer-prompt This function returns the prompt string of the currently activeminibuffer. If no minibuffer is active, it returns nil. minibuffer-prompt-end — Function: minibuffer-prompt-end This function returns the currentposition of the end of the minibuffer prompt, if a minibuffer iscurrent. Otherwise, it returns the minimum valid buffer position. minibuffer-prompt-width — Function: minibuffer-prompt-width This function returns the current display-width of the minibufferprompt, if a minibuffer is current. Otherwise, it returns zero. minibuffer-contents — Function: minibuffer-contents This function returns the editablecontents of the minibuffer (that is, everything except the prompt) asa string, if a minibuffer is current. Otherwise, it returns theentire contents of the current buffer. minibuffer-contents-no-properties — Function: minibuffer-contents-no-properties This is like minibuffer-contents, except that it does not copy textproperties, just the characters themselves. See . minibuffer-completion-contents — Function: minibuffer-completion-contents This is like minibuffer-contents, except that it returns onlythe contents before point. That is the part that completion commandsoperate on. See . delete-minibuffer-contents — Function: delete-minibuffer-contents This function erases the editable contents of the minibuffer (that is,everything except the prompt), if a minibuffer is current. Otherwise,it erases the entire current buffer. Recursive Minibuffers recursive minibuffers These functions and variables deal with recursive minibuffers (see ): minibuffer-depth — Function: minibuffer-depth This function returns the current depth of activations of theminibuffer, a nonnegative integer. If no minibuffers are active, itreturns zero. enable-recursive-minibuffers — User Option: enable-recursive-minibuffers If this variable is non-nil, you can invoke commands (such asfind-file) that use minibuffers even while the minibuffer windowis active. Such invocation produces a recursive editing level for a newminibuffer. The outer-level minibuffer is invisible while you areediting the inner one.If this variable is nil, you cannot invoke minibuffercommands when the minibuffer window is active, not even if you switch toanother window to do it. If a command name has a property enable-recursive-minibuffers that is non-nil, then the command can use the minibuffer to read arguments even if it is invoked from the minibuffer. A command can also achieve this by binding enable-recursive-minibuffers to t in the interactive declaration (see ). The minibuffer command next-matching-history-element (normally M-s in the minibuffer) does the latter. Minibuffer Miscellany minibufferp — Function: minibufferp &optional buffer-or-name This function returns non-nil if buffer-or-name is aminibuffer. If buffer-or-name is omitted, it tests the currentbuffer. minibuffer-setup-hook — Variable: minibuffer-setup-hook This is a normal hook that is run whenever the minibuffer is entered.See . minibuffer-exit-hook — Variable: minibuffer-exit-hook This is a normal hook that is run whenever the minibuffer is exited.See . minibuffer-help-form — Variable: minibuffer-help-form The current value of this variable is used to rebind help-formlocally inside the minibuffer (see ). minibuffer-scroll-window — Variable: minibuffer-scroll-window If the value of this variable is non-nil, it should be a windowobject. When the function scroll-other-window is called in theminibuffer, it scrolls this window. minibuffer-selected-window — Function: minibuffer-selected-window This function returns the window which was selected when theminibuffer was entered. If selected window is not a minibufferwindow, it returns nil. max-mini-window-height — User Option: max-mini-window-height This variable specifies the maximum height for resizing minibufferwindows. If a float, it specifies a fraction of the height of theframe. If an integer, it specifies a number of lines. minibuffer-message — Function: minibuffer-message string This function displays string temporarily at the end of theminibuffer text, for two seconds, or until the next input eventarrives, whichever comes first. <setfilename>../info/commands</setfilename> Command Loop editor command loop command loop When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them. Command Loop Overview The first thing the command loop must do is read a key sequence, which is a sequence of events that translates into a command. It does this by calling the function read-key-sequence. Your Lisp code can also call this function (see ). Lisp programs can also do input at a lower level with read-event (see ) or discard pending input with discard-input (see ). The key sequence is translated into a command through the currently active keymaps. See , for information on how this is done. The result should be a keyboard macro or an interactively callable function. If the key is M-x, then it reads the name of another command, which it then calls. This is done by the command execute-extended-command (see ). To execute a command requires first reading the arguments for it. This is done by calling command-execute (see ). For commands written in Lisp, the interactive specification says how to read the arguments. This may use the prefix argument (see ) or may read with prompting in the minibuffer (see ). For example, the command find-file has an interactive specification which says to read a file name using the minibuffer. The command's function body does not use the minibuffer; if you call this command from Lisp code as a function, you must supply the file name string as an ordinary Lisp function argument. If the command is a string or vector (i.e., a keyboard macro) then execute-kbd-macro is used to execute it. You can call this function yourself (see ). To terminate the execution of a running command, type C-g. This character causes quitting (see ). pre-command-hook — Variable: pre-command-hook The editor command loop runs this normal hook before each command. Atthat time, this-command contains the command that is about torun, and last-command describes the previous command.See . post-command-hook — Variable: post-command-hook The editor command loop runs this normal hook after each command(including commands terminated prematurely by quitting or by errors),and also when the command loop is first entered. At that time,this-command refers to the command that just ran, andlast-command refers to the command before that. Quitting is suppressed while running pre-command-hook and post-command-hook. If an error happens while executing one of these hooks, it terminates execution of the hook, and clears the hook variable to nil so as to prevent an infinite loop of errors. A request coming into the Emacs server (see See section ``Emacs Server'' in The GNU Emacs Manual) runs these two hooks just as a keyboard command does. Defining Commands defining commands commands, defining functions, making them interactive interactive function A Lisp function becomes a command when its body contains, at top level, a form that calls the special form interactive. This form does nothing when actually executed, but its presence serves as a flag to indicate that interactive calling is permitted. Its argument controls the reading of arguments for an interactive call. Using interactive arguments, interactive entry This section describes how to write the interactive form that makes a Lisp function an interactively-callable command, and how to examine a command's interactive form. interactive — Special Form: interactive arg-descriptor This special form declares that the function in which it appears is acommand, and that it may therefore be called interactively (viaM-x or by entering a key sequence bound to it). The argumentarg-descriptor declares how to compute the arguments to thecommand when the command is called interactively.A command may be called from Lisp programs like any other function, butthen the caller supplies the arguments and arg-descriptor has noeffect.The interactive form has its effect because the command loop(actually, its subroutine call-interactively) scans through thefunction definition looking for it, before calling the function. Oncethe function is called, all its body forms including theinteractive form are executed, but at this timeinteractive simply returns nil without even evaluating itsargument. There are three possibilities for the argument arg-descriptor: It may be omitted or nil; then the command is called with noarguments. This leads quickly to an error if the command requires oneor more arguments. It may be a string; then its contents should consist of a code characterfollowed by a prompt (which some code characters use and some ignore).The prompt ends either with the end of the string or with a newline.Here is a simple example: (interactive "bFrobnicate buffer: ") The code letter ‘b’ says to read the name of an existing buffer,with completion. The buffer name is the sole argument passed to thecommand. The rest of the string is a prompt.If there is a newline character in the string, it terminates the prompt.If the string does not end there, then the rest of the string shouldcontain another code character and prompt, specifying another argument.You can specify any number of arguments in this way. The prompt string can use ‘%’ to include previous argument values(starting with the first argument) in the prompt. This is done usingformat (see ). For example, here is howyou could read the name of an existing buffer followed by a new name togive to that buffer: (interactive "bBuffer to rename: \nsRename buffer %s to: ") ‘*’ in interactive read-only buffers in interactiveIf the first character in the string is ‘*’, then an error issignaled if the buffer is read-only. ‘@’ in interactive If the first character in the string is ‘@’, and if the keysequence used to invoke the command includes any mouse events, thenthe window associated with the first of those events is selectedbefore the command is run.You can use ‘*’ and ‘@’ together; the order does not matter.Actual reading of arguments is controlled by the rest of the promptstring (starting with the first character that is not ‘*’ or‘@’). It may be a Lisp expression that is not a string; then it should be aform that is evaluated to get a list of arguments to pass to thecommand. Usually this form will call various functions to read inputfrom the user, most often through the minibuffer (see )or directly from the keyboard (see ).Providing point or the mark as an argument value is also common, butif you do this and read input (whether using the minibuffer ornot), be sure to get the integer values of point or the mark afterreading. The current buffer may be receiving subprocess output; ifsubprocess output arrives while the command is waiting for input, itcould relocate point and the mark.Here's an example of what not to do: (interactive (list (region-beginning) (region-end) (read-string "Foo: " nil 'my-history))) Here's how to avoid the problem, by examining point and the mark afterreading the keyboard input: (interactive (let ((string (read-string "Foo: " nil 'my-history))) (list (region-beginning) (region-end) string))) Warning: the argument values should not include any datatypes that can't be printed and then read. Some facilities savecommand-history in a file to be read in the subsequentsessions; if a command's arguments contain a data type that printsusing ‘#<…>’ syntax, those facilities won't work.There are, however, a few exceptions: it is ok to use a limited set ofexpressions such as (point), (mark),(region-beginning), and (region-end), because Emacsrecognizes them specially and puts the expression (rather than itsvalue) into the command history. To see whether the expression youwrote is one of these exceptions, run the command, then examine(car command-history). examining the interactiveform interactive-form — Function: interactive-form function This function returns the interactive form of function.If function is an interactively callable function(see ), the value is the command'sinteractive form (interactive spec), whichspecifies how to compute its arguments. Otherwise, the value isnil. If function is a symbol, its function definition isused. Code Characters for interactive interactive code description description for interactive codes codes, interactive, description of characters for interactive codes The code character descriptions below contain a number of key words, defined here as follows: Completion interactive completionProvide completion. TAB, SPC, and RET perform namecompletion because the argument is read using completing-read(see ). ? displays a list of possible completions. Existing Require the name of an existing object. An invalid name is notaccepted; the commands to exit the minibuffer do not exit if the currentinput is not valid. Default default argument stringA default value of some sort is used if the user enters no text in theminibuffer. The default depends on the code character. No I/O This code letter computes an argument without reading any input.Therefore, it does not use a prompt string, and any prompt string yousupply is ignored.Even though the code letter doesn't use a prompt string, you must followit with a newline if it is not the last code character in the string. Prompt A prompt immediately follows the code character. The prompt ends eitherwith the end of the string or with a newline. Special This code character is meaningful only at the beginning of theinteractive string, and it does not look for a prompt or a newline.It is a single, isolated character. reading interactive arguments Here are the code character descriptions for use with interactive: ‘*’ Signal an error if the current buffer is read-only. Special. ‘@’ Select the window mentioned in the first mouse event in the keysequence that invoked this command. Special. ‘a’ A function name (i.e., a symbol satisfying fboundp). Existing,Completion, Prompt. ‘b’ The name of an existing buffer. By default, uses the name of thecurrent buffer (see ). Existing, Completion, Default,Prompt. ‘B’ A buffer name. The buffer need not exist. By default, uses the name ofa recently used buffer other than the current buffer. Completion,Default, Prompt. ‘c’ A character. The cursor does not move into the echo area. Prompt. ‘C’ A command name (i.e., a symbol satisfying commandp). Existing,Completion, Prompt. ‘d’ position argumentThe position of point, as an integer (see ). No I/O. ‘D’ A directory name. The default is the current default directory of thecurrent buffer, default-directory (see ).Existing, Completion, Default, Prompt. ‘e’ The first or next mouse event in the key sequence that invoked the command.More precisely, ‘e’ gets events that are lists, so you can look atthe data in the lists. See . No I/O.You can use ‘e’ more than once in a single command's interactivespecification. If the key sequence that invoked the command hasn events that are lists, the nth ‘e’ provides thenth such event. Events that are not lists, such as function keysand ASCII characters, do not count where ‘e’ is concerned. ‘f’ A file name of an existing file (see ). The defaultdirectory is default-directory. Existing, Completion, Default,Prompt. ‘F’ A file name. The file need not exist. Completion, Default, Prompt. ‘G’ A file name. The file need not exist. If the user enters just adirectory name, then the value is just that directory name, with nofile name within the directory added. Completion, Default, Prompt. ‘i’ An irrelevant argument. This code always supplies nil asthe argument's value. No I/O. ‘k’ A key sequence (see ). This keeps reading eventsuntil a command (or undefined command) is found in the current keymaps. The key sequence argument is represented as a string or vector.The cursor does not move into the echo area. Prompt.If ‘k’ reads a key sequence that ends with a down-event, it alsoreads and discards the following up-event. You can get access to thatup-event with the ‘U’ code character.This kind of input is used by commands such as describe-key andglobal-set-key. ‘K’ A key sequence, whose definition you intend to change. This works like‘k’, except that it suppresses, for the last input event in the keysequence, the conversions that are normally used (when necessary) toconvert an undefined key into a defined one. ‘m’ marker argumentThe position of the mark, as an integer. No I/O. ‘M’ Arbitrary text, read in the minibuffer using the current buffer's inputmethod, and returned as a string (see See section ``Input Methods'' in The GNU Emacs Manual). Prompt. ‘n’ A number, read with the minibuffer. If the input is not a number, theuser has to try again. ‘n’ never uses the prefix argument.Prompt. ‘N’ The numeric prefix argument; but if there is no prefix argument, reada number as with n. The value is always a number. See . Prompt. ‘p’ numeric prefix argument usageThe numeric prefix argument. (Note that this ‘p’ is lower case.)No I/O. ‘P’ raw prefix argument usageThe raw prefix argument. (Note that this ‘P’ is upper case.) NoI/O. ‘r’ region argumentPoint and the mark, as two numeric arguments, smallest first. This isthe only code letter that specifies two successive arguments rather thanone. No I/O. ‘s’ Arbitrary text, read in the minibuffer and returned as a string(see ). Terminate the input with eitherC-j or RET. (C-q may be used to include either ofthese characters in the input.) Prompt. ‘S’ An interned symbol whose name is read in the minibuffer. Any whitespacecharacter terminates the input. (Use C-q to include whitespace inthe string.) Other characters that normally terminate a symbol (e.g.,parentheses and brackets) do not do so here. Prompt. ‘U’ A key sequence or nil. Can be used after a ‘k’ or‘K’ argument to get the up-event that was discarded (if any)after ‘k’ or ‘K’ read a down-event. If no up-event has beendiscarded, ‘U’ provides nil as the argument. No I/O. ‘v’ A variable declared to be a user option (i.e., satisfying thepredicate user-variable-p). This reads the variable usingread-variable. See . Existing,Completion, Prompt. ‘x’ A Lisp object, specified with its read syntax, terminated with aC-j or RET. The object is not evaluated. See . Prompt. ‘X’ evaluated expression argumentA Lisp form's value. ‘X’ reads as ‘x’ does, then evaluatesthe form so that its value becomes the argument for the command.Prompt. ‘z’ A coding system name (a symbol). If the user enters null input, theargument value is nil. See . Completion,Existing, Prompt. ‘Z’ A coding system name (a symbol)—but only if this command has a prefixargument. With no prefix argument, ‘Z’ provides nil as theargument value. Completion, Existing, Prompt. Examples of Using interactive examples of using interactive interactive, examples of using Here are some examples of interactive: (defun foo1 () ; foo1 takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) => foo1 (defun foo2 (n) ; foo2 takes one argument, (interactive "p") ; which is the numeric prefix. (forward-word (* 2 n))) => foo2 (defun foo3 (n) ; foo3 takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) => foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) => three-b (three-b "*scratch*" "declarations.texi" "*mail*") => nil Interactive Call interactive call After the command loop has translated a key sequence into a command it invokes that command using the function command-execute. If the command is a function, command-execute calls call-interactively, which reads the arguments and calls the command. You can also call these functions yourself. commandp — Function: commandp object &optional for-call-interactively Returns t if object is suitable for calling interactively;that is, if object is a command. Otherwise, returns nil.The interactively callable objects include strings and vectors (treatedas keyboard macros), lambda expressions that contain a top-level call tointeractive, byte-code function objects made from such lambdaexpressions, autoload objects that are declared as interactive(non-nil fourth argument to autoload), and some of theprimitive functions.A symbol satisfies commandp if its function definitionsatisfies commandp. Keys and keymaps are not commands.Rather, they are used to look up commands (see ).If for-call-interactively is non-nil, thencommandp returns t only for objects thatcall-interactively could call—thus, not for keyboard macros.See documentation in , for arealistic example of using commandp. call-interactively — Function: call-interactively command &optional record-flag keys This function calls the interactively callable function command,reading arguments according to its interactive calling specifications.It returns whatever command returns. An error is signaled ifcommand is not a function or if it cannot be calledinteractively (i.e., is not a command). Note that keyboard macros(strings and vectors) are not accepted, even though they areconsidered commands, because they are not functions. If commandis a symbol, then call-interactively uses its function definition. record command historyIf record-flag is non-nil, then this command and itsarguments are unconditionally added to the list command-history.Otherwise, the command is added only if it uses the minibuffer to readan argument. See .The argument keys, if given, should be a vector which specifiesthe sequence of events to supply if the command inquires which eventswere used to invoke it. If keys is omitted or nil, thedefault is the return value of this-command-keys-vector.See . command-execute — Function: command-execute command &optional record-flag keys special keyboard macro executionThis function executes command. The argument command mustsatisfy the commandp predicate; i.e., it must be an interactivelycallable function or a keyboard macro.A string or vector as command is executed withexecute-kbd-macro. A function is passed tocall-interactively, along with the optional record-flagand keys.A symbol is handled by using its function definition in its place. Asymbol with an autoload definition counts as a command if it wasdeclared to stand for an interactively callable function. Such adefinition is handled by loading the specified library and thenrechecking the definition of the symbol.The argument special, if given, means to ignore the prefixargument and not clear it. This is used for executing special events(see ). execute-extended-command — Command: execute-extended-command prefix-argument read command nameThis function reads a command name from the minibuffer usingcompleting-read (see ). Then it usescommand-execute to call the specified command. Whatever thatcommand returns becomes the value of execute-extended-command. execute with prefix argumentIf the command asks for a prefix argument, it receives the valueprefix-argument. If execute-extended-command is calledinteractively, the current raw prefix argument is used forprefix-argument, and thus passed on to whatever command is run. M-xexecute-extended-command is the normal definition of M-x,so it uses the string ‘M-x ’ as a prompt. (It would be betterto take the prompt from the events used to invokeexecute-extended-command, but that is painful to implement.) Adescription of the value of the prefix argument, if any, also becomespart of the prompt. (execute-extended-command 3) ---------- Buffer: Minibuffer ---------- 3 M-x forward-word RET ---------- Buffer: Minibuffer ---------- => t interactive-p — Function: interactive-p This function returns t if the containing function (the onewhose code includes the call to interactive-p) was called indirect response to user input. This means that it was called with thefunction call-interactively, and that a keyboard macro isnot running, and that Emacs is not running in batch mode.If the containing function was called by Lisp evaluation (or withapply or funcall), then it was not called interactively. The most common use of interactive-p is for deciding whether to give the user additional visual feedback (such as by printing an informative message). For example: ;; Here's the usual way to use interactive-p. (defun foo () (interactive) (when (interactive-p) (message "foo"))) => foo ;; This function is just to illustrate the behavior. (defun bar () (interactive) (setq foobar (list (foo) (interactive-p)))) => bar ;; Type M-x foo. -| foo ;; Type M-x bar. ;; This does not display a message. foobar => (nil t) If you want to test only whether the function was called using call-interactively, add an optional argument print-message which should be non-nil in an interactive call, and use the interactive spec to make sure it is non-nil. Here's an example: (defun foo (&optional print-message) (interactive "p") (when print-message (message "foo"))) Defined in this way, the function does display the message when called from a keyboard macro. We use "p" because the numeric prefix argument is never nil. called-interactively-p — Function: called-interactively-p This function returns t when the calling function was calledusing call-interactively.When possible, instead of using this function, you should use themethod in the example above; that method makes it possible for acaller to “pretend” that the function was called interactively. Information from the Command Loop The editor command loop sets several Lisp variables to keep status records for itself and for commands that are run. last-command — Variable: last-command This variable records the name of the previous command executed by thecommand loop (the one before the current command). Normally the valueis a symbol with a function definition, but this is not guaranteed.The value is copied from this-command when a command returns tothe command loop, except when the command has specified a prefixargument for the following command.This variable is always local to the current terminal and cannot bebuffer-local. See . real-last-command — Variable: real-last-command This variable is set up by Emacs just like last-command,but never altered by Lisp programs. this-command — Variable: this-command current commandThis variable records the name of the command now being executed bythe editor command loop. Like last-command, it is normally a symbolwith a function definition.The command loop sets this variable just before running a command, andcopies its value into last-command when the command finishes(unless the command specified a prefix argument for the followingcommand). kill command repetitionSome commands set this variable during their execution, as a flag forwhatever command runs next. In particular, the functions for killing textset this-command to kill-region so that any kill commandsimmediately following will know to append the killed text to theprevious kill. If you do not want a particular command to be recognized as the previous command in the case where it got an error, you must code that command to prevent this. One way is to set this-command to t at the beginning of the command, and set this-command back to its proper value at the end, like this: (defun foo (args…) (interactive …) (let ((old-this-command this-command)) (setq this-command t) …do the work… (setq this-command old-this-command))) We do not bind this-command with let because that would restore the old value in case of error—a feature of let which in this case does precisely what we want to avoid. this-original-command — Variable: this-original-command This has the same value as this-command except when commandremapping occurs (see ). In that case,this-command gives the command actually run (the result ofremapping), and this-original-command gives the command thatwas specified to run but remapped into another command. this-command-keys — Function: this-command-keys This function returns a string or vector containing the key sequencethat invoked the present command, plus any previous commands thatgenerated the prefix argument for this command. Any events read by thecommand using read-event without a timeout get tacked on to the end.However, if the command has called read-key-sequence, itreturns the last read key sequence. See . Thevalue is a string if all events in the sequence were characters thatfit in a string. See . (this-command-keys) ;; Now use C-u C-x C-e to evaluate that. => "^U^X^E" this-command-keys-vector — Function: this-command-keys-vector Like this-command-keys, except that it always returns the eventsin a vector, so you don't need to deal with the complexities of storinginput events in a string (see ). clear-this-command-keys — Function: clear-this-command-keys &optional keep-record This function empties out the table of events forthis-command-keys to return. Unless keep-record isnon-nil, it also empties the records that the functionrecent-keys (see ) will subsequently return.This is useful after reading a password, to prevent the password fromechoing inadvertently as part of the next command in certain cases. last-nonmenu-event — Variable: last-nonmenu-event This variable holds the last input event read as part of a key sequence,not counting events resulting from mouse menus.One use of this variable is for telling x-popup-menu where to popup a menu. It is also used internally by y-or-n-p(see ). last-command-event — Variable: last-command-event last-command-char — Variable: last-command-char This variable is set to the last input event that was read by thecommand loop as part of a command. The principal use of this variableis in self-insert-command, which uses it to decide whichcharacter to insert. last-command-event ;; Now use C-u C-x C-e to evaluate that. => 5 The value is 5 because that is the ASCII code for C-e.The alias last-command-char exists for compatibility withEmacs version 18. last-event-frame — Variable: last-event-frame This variable records which frame the last input event was directed to.Usually this is the frame that was selected when the event wasgenerated, but if that frame has redirected input focus to anotherframe, the value is the frame to which the event was redirected.See .If the last event came from a keyboard macro, the value is macro. Adjusting Point After Commands adjusting point invisible/intangible text, and point display property, and point display composition property, and point display It is not easy to display a value of point in the middle of a sequence of text that has the display, composition or intangible property, or is invisible. Therefore, after a command finishes and returns to the command loop, if point is within such a sequence, the command loop normally moves point to the edge of the sequence. A command can inhibit this feature by setting the variable disable-point-adjustment: disable-point-adjustment — Variable: disable-point-adjustment If this variable is non-nil when a command returns to thecommand loop, then the command loop does not check for those textproperties, and does not move point out of sequences that have them.The command loop sets this variable to nil before each command,so if a command sets it, the effect applies only to that command. global-disable-point-adjustment — Variable: global-disable-point-adjustment If you set this variable to a non-nil value, the feature ofmoving point out of these sequences is completely turned off. Input Events events input events The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail. eventp — Function: eventp object This function returns non-nil if object is an input eventor event type.Note that any symbol might be used as an event or an event type.eventp cannot distinguish whether a symbol is intended by Lispcode to be used as an event. Instead, it distinguishes whether thesymbol has actually been used in an event that has been read as input inthe current Emacs session. If a symbol has not yet been so used,eventp returns nil. Keyboard Events keyboard events There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. The event type of a character event is the character itself (an integer); see . modifier bits (of input character) basic code (of input character) An input character event consists of a basic code between 0 and 524287, plus any or all of these modifier bits: meta The2**27bit in the character code indicates a charactertyped with the meta key held down. control The2**26bit in the character code indicates a non-ASCIIcontrol character.ascii control characters such as C-a have special basiccodes of their own, so Emacs needs no special bit to indicate them.Thus, the code for C-a is just 1.But if you type a control combination not in ASCII, such as% with the control key, the numeric value you get is the codefor % plus2**26(assuming the terminal supports non-ASCIIcontrol characters). shift The2**25bit in the character code indicates an ASCII controlcharacter typed with the shift key held down.For letters, the basic code itself indicates upper versus lower case;for digits and punctuation, the shift key selects an entirely differentcharacter with a different basic code. In order to keep within theASCII character set whenever possible, Emacs avoids using the2**25bit for those characters.However, ASCII provides no way to distinguish C-A fromC-a, so Emacs uses the2**25bit in C-A and not inC-a. hyper The2**24bit in the character code indicates a charactertyped with the hyper key held down. super The2**23bit in the character code indicates a charactertyped with the super key held down. alt The2**22bit in the character code indicates a character typed withthe alt key held down. (On some terminals, the key labeled ALTis actually the meta key.) It is best to avoid mentioning specific bit numbers in your program. To test the modifier bits of a character, use the function event-modifiers (see ). When making key bindings, you can use the read syntax for characters with modifier bits (‘\C-’, ‘\M-’, and so on). For making key bindings with define-key, you can use lists such as (control hyper ?x) to specify the characters (see ). The function event-convert-list converts such a list into an event type (see ). Function Keys function keys Most keyboards also have function keys—keys that have names or symbols that are not characters. Function keys are represented in Emacs Lisp as symbols; the symbol's name is the function key's label, in lower case. For example, pressing a key labeled F1 places the symbol f1 in the input stream. The event type of a function key event is the event symbol itself. See . Here are a few special cases in the symbol-naming convention for function keys: backspace, tab, newline, return, delete These keys correspond to common ASCII control characters that havespecial keys on most keyboards.In ASCII, C-i and TAB are the same character. If theterminal can distinguish between them, Emacs conveys the distinction toLisp programs by representing the former as the integer 9, and thelatter as the symbol tab.Most of the time, it's not useful to distinguish the two. So normallyfunction-key-map (see ) is set up to maptab into 9. Thus, a key binding for character code 9 (thecharacter C-i) also applies to tab. Likewise for the othersymbols in this group. The function read-char likewise convertsthese events into characters.In ASCII, BS is really C-h. But backspaceconverts into the character code 127 (DEL), not into code 8(BS). This is what most users prefer. left, up, right, down Cursor arrow keys kp-add, kp-decimal, kp-divide, … Keypad keys (to the right of the regular keyboard). kp-0, kp-1, … Keypad keys with digits. kp-f1, kp-f2, kp-f3, kp-f4 Keypad PF keys. kp-home, kp-left, kp-up, kp-right, kp-down Keypad arrow keys. Emacs normally translates these into thecorresponding non-keypad keys home, left, … kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-delete Additional keypad duplicates of keys ordinarily found elsewhere. Emacsnormally translates these into the like-named non-keypad keys. You can use the modifier keys ALT, CTRL, HYPER, META, SHIFT, and SUPER with function keys. The way to represent them is with prefixes in the symbol name: ‘A-’ The alt modifier. ‘C-’ The control modifier. ‘H-’ The hyper modifier. ‘M-’ The meta modifier. ‘S-’ The shift modifier. ‘s-’ The super modifier. Thus, the symbol for the key F3 with META held down is M-f3. When you use more than one prefix, we recommend you write them in alphabetical order; but the order does not matter in arguments to the key-binding lookup and modification functions. Mouse Events Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The car of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see ). The rest of the list elements give position and time information. For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the ‘e’ interactive code. See . A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer—that is entirely under the control of the command binding of the key sequence. Click Events click event mouse click event When the user presses a mouse button and releases it at the same location, that generates a click event. All mouse click event share the same format: (event-type position click-count) event-type This is a symbol that indicates which mouse button was used. It isone of the symbols mouse-1, mouse-2, …, where thebuttons are numbered left to right.You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’,‘S-’ and ‘s-’ for modifiers alt, control, hyper, meta, shiftand super, just as you would with function keys.This symbol also serves as the event type of the event. Key bindingsdescribe events by their types; thus, if there is a key binding formouse-1, that binding would apply to all events whoseevent-type is mouse-1. position This is the position where the mouse click occurred. The actualformat of position depends on what part of a window was clickedon. The various formats are described below. click-count This is the number of rapid repeated presses so far of the same mousebutton. See . For mouse click events in the text area, mode line, header line, or in the marginal areas, position has this form: (window pos-or-area (x . y) timestamp object text-pos (col . row) image (dx . dy) (width . height)) window This is the window in which the click occurred. pos-or-area This is the buffer position of the character clicked on in the textarea, or if clicked outside the text area, it is the window area inwhich the click occurred. It is one of the symbols mode-line,header-line, vertical-line, left-margin,right-margin, left-fringe, or right-fringe. x, y These are the pixel-denominated coordinates of the click, relative tothe top left corner of window, which is (0 . 0).For the mode or header line, y does not have meaningful data.For the vertical line, x does not have meaningful data. timestamp This is the time at which the event occurred, in milliseconds. object This is the object on which the click occurred. It is eithernil if there is no string property, or it has the form(string . string-pos) when there is a string-type textproperty at the click position. string This is the string on which the click occurred, including anyproperties. string-pos This is the position in the string on which the click occurred,relevant if properties at the click need to be looked up. text-pos For clicks on a marginal area or on a fringe, this is the bufferposition of the first visible character in the corresponding line inthe window. For other events, it is the current buffer position inthe window. col, row These are the actual coordinates of the glyph under the x,y position, possibly padded with default character widthglyphs if x is beyond the last glyph on the line. image This is the image object on which the click occurred. It is eithernil if there is no image at the position clicked on, or it isan image object as returned by find-image if click was in an image. dx, dy These are the pixel-denominated coordinates of the click, relative tothe top left corner of object, which is (0 . 0). Ifobject is nil, the coordinates are relative to the topleft corner of the character glyph clicked on. For mouse clicks on a scroll-bar, position has this form: (window area (portion . whole) timestamp part) window This is the window whose scroll-bar was clicked on. area This is the scroll bar where the click occurred. It is one of thesymbols vertical-scroll-bar or horizontal-scroll-bar. portion This is the distance of the click from the top or left end ofthe scroll bar. whole This is the length of the entire scroll bar. timestamp This is the time at which the event occurred, in milliseconds. part This is the part of the scroll-bar which was clicked on. It is oneof the symbols above-handle, handle, below-handle,up, down, top, bottom, and end-scroll. In one special case, buffer-pos is a list containing a symbol (one of the symbols listed above) instead of just the symbol. This happens after the imaginary prefix keys for the event are inserted into the input stream. See . Drag Events drag event mouse drag event With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this: (event-type (window1 buffer-pos1 (x1 . y1) timestamp1) (window2 buffer-pos2 (x2 . y2) timestamp2) click-count) For a drag event, the name of the symbol event-type contains the prefix ‘drag-’. For example, dragging the mouse with button 2 held down generates a drag-mouse-2 event. The second and third elements of the event give the starting and ending position of the drag. Aside from that, the data have the same meanings as in a click event (see ). You can access the second element of any mouse event in the same way, with no need to distinguish drag events from others. The ‘drag-’ prefix follows the modifier key prefixes such as ‘C-’ and ‘M-’. If read-key-sequence receives a drag event that has no key binding, and the corresponding click event does have a binding, it changes the drag event into a click event at the drag's starting position. This means that you don't have to distinguish between click and drag events unless you want to. Button-Down Events button-down event Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released. If you want to take action as soon as a button is pressed, you need to handle button-down events.Button-down is the conservative antithesis of drag. These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see ), except that the event-type symbol name contains the prefix ‘down-’. The ‘down-’ prefix follows modifier key prefixes such as ‘C-’ and ‘M-’. The function read-key-sequence ignores any button-down events that don't have command bindings; therefore, the Emacs command loop ignores them too. This means that you need not worry about defining button-down events unless you want them to do something. The usual reason to define a button-down event is so that you can track mouse motion (by reading motion events) until the button is released. See . Repeat Events repeat events double-click events triple-click events mouse events, repeated If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses. The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events). The event type of a double-click event contains the prefix ‘double-’. Thus, a double click on the second mouse button with meta held down comes to the Lisp program as M-double-mouse-2. If a double-click event has no binding, the binding of the corresponding ordinary click event is used to execute it. Thus, you need not pay attention to the double click feature unless you really want to. When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click. This is convenient, if the meaning of a double click somehow “builds on” the meaning of a single click—which is recommended user interface design practice for double clicks. If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains ‘double-drag’ instead of just ‘drag’. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag. Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains ‘double-down’ instead of just ‘down’. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored. To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event. If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain ‘triple’ instead of ‘double’. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event. If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed. event-click-count — Function: event-click-count event This function returns the number of consecutive button presses that ledup to event. If event is a double-down, double-click ordouble-drag event, the value is 2. If event is a triple event,the value is 3 or greater. If event is an ordinary mouse event(not a repeat event), the value is 1. double-click-fuzz — User Option: double-click-fuzz To generate repeat events, successive mouse button presses must be atapproximately the same screen position. The value ofdouble-click-fuzz specifies the maximum number of pixels themouse may be moved (horizontally or vertically) between two successiveclicks to make a double-click.This variable is also the threshold for motion of the mouse to countas a drag. double-click-time — User Option: double-click-time To generate repeat events, the number of milliseconds betweensuccessive button presses must be less than the value ofdouble-click-time. Setting double-click-time tonil disables multi-click detection entirely. Setting it tot removes the time limit; Emacs then detects multi-clicks byposition only. Motion Events motion event mouse motion events Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this: (mouse-movement (window buffer-pos (x . y) timestamp)) The second element of the list describes the current position of the mouse, just as in a click event (see ). The special form track-mouse enables generation of motion events within its body. Outside of track-mouse forms, Emacs does not generate events for mere motion of the mouse, and these events do not appear. See . Focus Events focus event Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See . Focus events are represented in Lisp as lists that look like this: (switch-frame new-frame) where new-frame is the frame switched to. Most X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Emacs appears to do this, because it changes the cursor to solid in the new frame. However, there is no need for the Lisp program to know about the focus change until some other kind of input arrives. So Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event. A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it. Miscellaneous System Events A few other event types represent occurrences within the system. delete-frame event(delete-frame (frame)) This kind of event indicates that the user gave the window managera command to delete a particular window, which happens to be an Emacs frame.The standard definition of the delete-frame event is to delete frame. iconify-frame event (iconify-frame (frame)) This kind of event indicates that the user iconified frame usingthe window manager. Its standard definition is ignore; since theframe has already been iconified, Emacs has no work to do. The purposeof this event type is so that you can keep track of such events if youwant to. make-frame-visible event (make-frame-visible (frame)) This kind of event indicates that the user deiconified frame usingthe window manager. Its standard definition is ignore; since theframe has already been made visible, Emacs has no work to do. wheel-up event wheel-down event (wheel-up position)(wheel-down position) These kinds of event are generated by moving a mouse wheel. Theirusual meaning is a kind of scroll or zoom.The element position is a list describing the position of theevent, in the same format as used in a mouse-click event.This kind of event is generated only on some kinds of systems. On somesystems, mouse-4 and mouse-5 are used instead. Forportable code, use the variables mouse-wheel-up-event andmouse-wheel-down-event defined in mwheel.el to determinewhat event types to expect for the mouse wheel. drag-n-drop event (drag-n-drop position files) This kind of event is generated when a group of files isselected in an application outside of Emacs, and then dragged anddropped onto an Emacs frame.The element position is a list describing the position of theevent, in the same format as used in a mouse-click event, andfiles is the list of file names that were dragged and dropped.The usual way to handle this event is by visiting these files.This kind of event is generated, at present, only on some kinds ofsystems. help-echo event help-echo This kind of event is generated when a mouse pointer moves onto aportion of buffer text which has a help-echo text property.The generated event has this form: (help-echo frame help window object pos) The precise meaning of the event parameters and the way theseparameters are used to display the help-echo text are described in. sigusr1 event sigusr2 event user signals sigusr1sigusr2 These events are generated when the Emacs process receivesthe signals SIGUSR1 and SIGUSR2. They contain noadditional data because signals do not carry additional information.To catch a user signal, bind the corresponding event to an interactivecommand in the special-event-map (see ).The command is called with no arguments, and the specific signal event isavailable in last-input-event. For example: (defun sigusr-handler () (interactive) (message "Caught signal %S" last-input-event)) (define-key special-event-map [sigusr1] 'sigusr-handler) To test the signal handler, you can make Emacs send a signal to itself: (signal-process (emacs-pid) 'sigusr1) If one of these events arrives in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it. Event Examples If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this: (down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320)) (mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180)) While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here: (C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)) (C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219) (#<window 18 on NEWS> 3510 (0 . 28) -729648)) While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these: (M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)) (M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844) (#<window 20 on carlton-sanskrit.tex> 161 (33 . 3) -453816)) To handle a SIGUSR1 signal, define an interactive function, and bind it to the signal usr1 event sequence: (defun usr1-handler () (interactive) (message "Got USR1 signal")) (global-set-key [signal usr1] 'usr1-handler) Classifying Events event type Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the car of the list. Thus, the event type is always a symbol or a character. Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act. Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the META key, regardless of which other key or mouse button was used. The functions event-modifiers and event-basic-type are provided to get such information conveniently. event-modifiers — Function: event-modifiers event This function returns a list of the modifiers that event has. Themodifiers are symbols; they include shift, control,meta, alt, hyper and super. In addition,the modifiers list of a mouse event symbol always contains one ofclick, drag, and down. For double or tripleevents, it also contains double or triple.The argument event may be an entire event object, or just anevent type. If event is a symbol that has never been used in anevent that has been read as input in the current Emacs session, thenevent-modifiers can return nil, even when eventactually has modifiers.Here are some examples: (event-modifiers ?a) => nil (event-modifiers ?A) => (shift) (event-modifiers ?\C-a) => (control) (event-modifiers ?\C-%) => (control) (event-modifiers ?\C-\S-a) => (control shift) (event-modifiers 'f5) => nil (event-modifiers 's-f5) => (super) (event-modifiers 'M-S-f5) => (meta shift) (event-modifiers 'mouse-1) => (click) (event-modifiers 'down-mouse-1) => (down) The modifiers list for a click event explicitly contains click,but the event symbol name itself does not contain ‘click’. event-basic-type — Function: event-basic-type event This function returns the key or mouse button that eventdescribes, with all modifiers removed. The event argument is asin event-modifiers. For example: (event-basic-type ?a) => 97 (event-basic-type ?A) => 97 (event-basic-type ?\C-a) => 97 (event-basic-type ?\C-\S-a) => 97 (event-basic-type 'f5) => f5 (event-basic-type 's-f5) => f5 (event-basic-type 'M-S-f5) => f5 (event-basic-type 'down-mouse-1) => mouse-1 mouse-movement-p — Function: mouse-movement-p object This function returns non-nil if object is a mouse movementevent. event-convert-list — Function: event-convert-list list This function converts a list of modifier names and a basic event typeto an event type which specifies all of them. The basic event typemust be the last element of the list. For example, (event-convert-list '(control ?a)) => 1 (event-convert-list '(control meta ?a)) => -134217727 (event-convert-list '(control super f1)) => C-s-f1 Accessing Events mouse events, data in This section describes convenient functions for accessing the data in a mouse button or motion event. These two functions return the starting or ending position of a mouse-button event, as a list of this form: (window pos-or-area (x . y) timestamp object text-pos (col . row) image (dx . dy) (width . height)) event-start — Function: event-start event This returns the starting position of event.If event is a click or button-down event, this returns thelocation of the event. If event is a drag event, this returns thedrag's starting position. event-end — Function: event-end event This returns the ending position of event.If event is a drag event, this returns the position where the userreleased the mouse button. If event is a click or button-downevent, the value is actually the starting position, which is the onlyposition such events have. mouse position list, accessing These functions take a position list as described above, and return various parts of it. posn-window — Function: posn-window position Return the window that position is in. posn-area — Function: posn-area position Return the window area recorded in position. It returns nilwhen the event occurred in the text area of the window; otherwise, itis a symbol identifying the area in which the event occurred. posn-point — Function: posn-point position Return the buffer position in position. When the event occurredin the text area of the window, in a marginal area, or on a fringe,this is an integer specifying a buffer position. Otherwise, the valueis undefined. posn-x-y — Function: posn-x-y position Return the pixel-based x and y coordinates in position, as acons cell (x . y). These coordinates are relativeto the window given by posn-window.This example shows how to convert these window-relative coordinatesinto frame-relative coordinates: (defun frame-relative-coordinates (position) "Return frame-relative coordinates from POSITION." (let* ((x-y (posn-x-y position)) (window (posn-window position)) (edges (window-inside-pixel-edges window))) (cons (+ (car x-y) (car edges)) (+ (cdr x-y) (cadr edges))))) posn-col-row — Function: posn-col-row position Return the row and column (in units of the frame's default characterheight and width) of position, as a cons cell (col .row). These are computed from the x and y valuesactually found in position. posn-actual-col-row — Function: posn-actual-col-row position Return the actual row and column in position, as a cons cell(col . row). The values are the actual row numberin the window, and the actual character number in that row. It returnsnil if position does not include actual positions values.You can use posn-col-row to get approximate values. posn-string — Function: posn-string position Return the string object in position, either nil, or acons cell (string . string-pos). posn-image — Function: posn-image position Return the image object in position, either nil, or animage (image ...). posn-object — Function: posn-object position Return the image or string object in position, eithernil, an image (image ...), or a cons cell(string . string-pos). posn-object-x-y — Function: posn-object-x-y position Return the pixel-based x and y coordinates relative to the upper leftcorner of the object in position as a cons cell (dx. dy). If the position is a buffer position, return therelative position in the character at that position. posn-object-width-height — Function: posn-object-width-height position Return the pixel width and height of the object in position as acons cell (width . height). If the positionis a buffer position, return the size of the character at that position. timestamp of a mouse event posn-timestamp — Function: posn-timestamp position Return the timestamp in position. This is the time at which theevent occurred, in milliseconds. These functions compute a position list given particular buffer position or screen position. You can access the data in this position list with the functions described above. posn-at-point — Function: posn-at-point &optional pos window This function returns a position list for position pos inwindow. pos defaults to point in window;window defaults to the selected window.posn-at-point returns nil if pos is not visible inwindow. posn-at-x-y — Function: posn-at-x-y x y &optional frame-or-window whole This function returns position information corresponding to pixelcoordinates x and y in a specified frame or window,frame-or-window, which defaults to the selected window.The coordinates x and y are relative to theframe or window used.If whole is nil, the coordinates are relativeto the window text area, otherwise they are relative tothe entire window area including scroll bars, margins and fringes. These functions are useful for decoding scroll bar events. scroll-bar-event-ratio — Function: scroll-bar-event-ratio event This function returns the fractional vertical position of a scroll barevent within the scroll bar. The value is a cons cell(portion . whole) containing two integers whose ratiois the fractional position. scroll-bar-scale — Function: scroll-bar-scale ratio total This function multiplies (in effect) ratio by total,rounding the result to an integer. The argument ratio is not anumber, but rather a pair (num . denom)—typically avalue returned by scroll-bar-event-ratio.This function is handy for scaling a position on a scroll bar into abuffer position. Here's how to do that: (+ (point-min) (scroll-bar-scale (posn-x-y (event-start event)) (- (point-max) (point-min)))) Recall that scroll bar events have two integers forming a ratio, in placeof a pair of x and y coordinates. Putting Keyboard Events in Strings keyboard events in strings strings with keyboard events In most of the places where strings are used, we conceptualize the string as containing text characters—the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible. We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that: Use vectors instead of strings for key sequences, when you plan to usethem for anything other than as arguments to lookup-key anddefine-key. For example, you can useread-key-sequence-vector instead of read-key-sequence, andthis-command-keys-vector instead of this-command-keys. Use vectors to write key sequence constants containing meta characters,even when passing them directly to define-key. When you have to look at the contents of a key sequence that might be astring, use listify-key-sequence (see )first, to convert it to a list. The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases. The earliest GNU Emacs versions represented meta characters as codes in the range of 128 to 255. At that time, the basic character codes ranged from 0 to 127, so all keyboard character codes did fit in a string. Many Lisp programs used ‘\M-’ in string constants to stand for meta characters, especially in arguments to define-key and similar functions, and key sequences and sequences of events were always represented as strings. When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is 2**27 and such numbers cannot be included in a string. To support programs with ‘\M-’ in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters: If the keyboard character value is in the range of 0 to 127, it can goin the string unchanged. The meta variants of those characters, with codes in the range of2**27to2**27+127,can also go in the string, but you must change theirnumeric values. You must set the2**7bit instead of the2**27bit, resulting in a value between 128 and 255. Only a unibyte stringcan include these codes. Non-ASCII characters above 256 can be included in a multibyte string. Other keyboard character events cannot fit in a string. This includeskeyboard events in the range of 128 to 255. Functions such as read-key-sequence that construct strings of keyboard input characters follow these rules: they construct vectors instead of strings, when the events won't fit in a string. When you use the read syntax ‘\M-’ in a string, it produces a code in the range of 128 to 255—the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings. However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section. Reading Input read input keyboard input The editor command loop reads key sequences using the function read-key-sequence, which uses read-event. These and other functions for event input are also available for use in Lisp programs. See also momentary-string-display in , and sit-for in . See , for functions and variables for controlling terminal input modes and debugging terminal input. For higher-level input facilities, see . Key Sequence Input key sequence input The command loop reads input a key sequence at a time, by calling read-key-sequence. Lisp programs can also call this function; for example, describe-key uses it to read the key to describe. read-key-sequence — Function: read-key-sequence prompt &optional continue-echo dont-downcase-last switch-frame-ok command-loop This function reads a key sequence and returns it as a string orvector. It keeps reading events until it has accumulated a complete keysequence; that is, enough to specify a non-prefix command using thecurrently active keymaps. (Remember that a key sequence that startswith a mouse event is read using the keymaps of the buffer in thewindow that the mouse was in, not the current buffer.)If the events are all characters and all can fit in a string, thenread-key-sequence returns a string (see ).Otherwise, it returns a vector, since a vector can hold all kinds ofevents—characters, symbols, and lists. The elements of the string orvector are the events in the key sequence.Reading a key sequence includes translating the events in variousways. See .The argument prompt is either a string to be displayed in theecho area as a prompt, or nil, meaning not to display a prompt.The argument continue-echo, if non-nil, means to echothis key as a continuation of the previous key.Normally any upper case event is converted to lower case if theoriginal event is undefined and the lower case equivalent is defined.The argument dont-downcase-last, if non-nil, means do notconvert the last event to lower case. This is appropriate for readinga key sequence to be defined.The argument switch-frame-ok, if non-nil, means that thisfunction should process a switch-frame event if the userswitches frames before typing anything. If the user switches framesin the middle of a key sequence, or at the start of the sequence butswitch-frame-ok is nil, then the event will be put offuntil after the current key sequence.The argument command-loop, if non-nil, means that thiskey sequence is being read by something that will read commands oneafter another. It should be nil if the caller will read justone key sequence.In the following example, Emacs displays the prompt ‘?’ in theecho area, and then the user types C-x C-f. (read-key-sequence "?") ---------- Echo Area ---------- ?C-x C-f ---------- Echo Area ---------- => "^X^F" The function read-key-sequence suppresses quitting: C-gtyped while reading with this function works like any other character,and does not set quit-flag. See . read-key-sequence-vector — Function: read-key-sequence-vector prompt &optional continue-echo dont-downcase-last switch-frame-ok command-loop This is like read-key-sequence except that it alwaysreturns the key sequence as a vector, never as a string.See . upper case key sequence downcasing in lookup-key If an input character is upper-case (or has the shift modifier) and has no key binding, but its lower-case equivalent has one, then read-key-sequence converts the character to lower case. Note that lookup-key does not perform case conversion in this way. The function read-key-sequence also transforms some mouse events. It converts unbound drag events into click events, and discards unbound button-down events entirely. It also reshuffles focus events and miscellaneous window events so that they never appear in a key sequence with any other events. header-lineprefix key mode-lineprefix key vertical-lineprefix key horizontal-scroll-barprefix key vertical-scroll-barprefix key menu-barprefix key mouse events, in special parts of frame When mouse events occur in special parts of a window, such as a mode line or a scroll bar, the event type shows nothing special—it is the same symbol that would normally represent that combination of mouse button and modifier keys. The information about the window part is kept elsewhere in the event—in the coordinates. But read-key-sequence translates this information into imaginary “prefix keys,” all of which are symbols: header-line, horizontal-scroll-bar, menu-bar, mode-line, vertical-line, and vertical-scroll-bar. You can define meanings for mouse clicks in special window parts by defining key sequences using these imaginary prefix keys. For example, if you call read-key-sequence and then click the mouse on the window's mode line, you get two events, like this: (read-key-sequence "Click on the mode line: ") => [mode-line (mouse-1 (#<window 6 on NEWS> mode-line (40 . 63) 5959987))] num-input-keys — Variable: num-input-keys This variable's value is the number of key sequences processed so far inthis Emacs session. This includes key sequences read from the terminaland key sequences read from keyboard macros being executed. Reading One Event reading a single event event, reading only one The lowest level functions for command input are those that read a single event. None of the three functions below suppresses quitting. read-event — Function: read-event &optional prompt inherit-input-method seconds This function reads and returns the next event of command input, waitingif necessary until an event is available. Events can come directly fromthe user or from a keyboard macro.If the optional argument prompt is non-nil, it should be astring to display in the echo area as a prompt. Otherwise,read-event does not display any message to indicate it is waitingfor input; instead, it prompts by echoing: it displays descriptions ofthe events that led to or were read by the current command. See .If inherit-input-method is non-nil, then the current inputmethod (if any) is employed to make it possible to enter anon-ASCII character. Otherwise, input method handling is disabledfor reading this event.If cursor-in-echo-area is non-nil, then read-eventmoves the cursor temporarily to the echo area, to the end of any messagedisplayed there. Otherwise read-event does not move the cursor.If seconds is non-nil, it should be a number specifyingthe maximum time to wait for input, in seconds. If no input arriveswithin that time, read-event stops waiting and returnsnil. A floating-point value for seconds means to waitfor a fractional number of seconds. Some systems support only a wholenumber of seconds; on these systems, seconds is rounded down.If seconds is nil, read-event waits as long asnecessary for input to arrive.If seconds is nil, Emacs is considered idle while waitingfor user input to arrive. Idle timers—those created withrun-with-idle-timer (see )—can run during thisperiod. However, if seconds is non-nil, the state ofidleness remains unchanged. If Emacs is non-idle whenread-event is called, it remains non-idle throughout theoperation of read-event; if Emacs is idle (which can happen ifthe call happens inside an idle timer), it remains idle.If read-event gets an event that is defined as a help character,then in some cases read-event processes the event directly withoutreturning. See . Certain other events, calledspecial events, are also processed directly withinread-event (see ).Here is what happens if you call read-event and then press theright-arrow function key: (read-event) => right read-char — Function: read-char &optional prompt inherit-input-method seconds This function reads and returns a character of command input. If theuser generates an event which is not a character (i.e. a mouse click orfunction key event), read-char signals an error. The argumentswork as in read-event.In the first example, the user types the character 1 (ASCIIcode 49). The second example shows a keyboard macro definition thatcalls read-char from the minibuffer using eval-expression.read-char reads the keyboard macro's very next character, whichis 1. Then eval-expression displays its return value inthe echo area. (read-char) => 49 ;; We assume here you use M-: to evaluate this. (symbol-function 'foo) => "^[:(read-char)^M1" (execute-kbd-macro 'foo) -| 49 => nil read-char-exclusive — Function: read-char-exclusive &optional prompt inherit-input-method seconds This function reads and returns a character of command input. If theuser generates an event which is not a character,read-char-exclusive ignores it and reads another event, until itgets a character. The arguments work as in read-event. num-nonmacro-input-events — Variable: num-nonmacro-input-events This variable holds the total number of input events received so farfrom the terminal—not counting those generated by keyboard macros. Modifying and Translating Input Events Emacs modifies every event it reads according to extra-keyboard-modifiers, then translates it through keyboard-translate-table (if applicable), before returning it from read-event. extra-keyboard-modifiers — Variable: extra-keyboard-modifiers This variable lets Lisp programs “press” the modifier keys on thekeyboard. The value is a character. Only the modifiers of thecharacter matter. Each time the user types a keyboard key, it isaltered as if those modifier keys were held down. For instance, ifyou bind extra-keyboard-modifiers to ?\C-\M-a, then allkeyboard input characters typed during the scope of the binding willhave the control and meta modifiers applied to them. The character?\C-@, equivalent to the integer 0, does not count as a controlcharacter for this purpose, but as a character with no modifiers.Thus, setting extra-keyboard-modifiers to zero cancels anymodification.When using a window system, the program can “press” any of themodifier keys in this way. Otherwise, only the CTL and METAkeys can be virtually pressed.Note that this variable applies only to events that really come fromthe keyboard, and has no effect on mouse events or any other events. keyboard-translate-table — Variable: keyboard-translate-table This variable is the translate table for keyboard characters. It letsyou reshuffle the keys on the keyboard without changing any commandbindings. Its value is normally a char-table, or else nil.(It can also be a string or vector, but this is considered obsolete.)If keyboard-translate-table is a char-table(see ), then each character read from the keyboard islooked up in this char-table. If the value found there isnon-nil, then it is used instead of the actual input character.Note that this translation is the first thing that happens to acharacter after it is read from the terminal. Record-keeping featuressuch as recent-keys and dribble files record the characters aftertranslation.Note also that this translation is done before the characters aresupplied to input methods (see ). Usetranslation-table-for-input (see ),if you want to translate characters after input methods operate. keyboard-translate — Function: keyboard-translate from to This function modifies keyboard-translate-table to translatecharacter code from into character code to. It createsthe keyboard translate table if necessary. Here's an example of using the keyboard-translate-table to make C-x, C-c and C-v perform the cut, copy and paste operations: (keyboard-translate ?\C-x 'control-x) (keyboard-translate ?\C-c 'control-c) (keyboard-translate ?\C-v 'control-v) (global-set-key [control-x] 'kill-region) (global-set-key [control-c] 'kill-ring-save) (global-set-key [control-v] 'yank) On a graphical terminal that supports extended ASCII input, you can still get the standard Emacs meanings of one of those characters by typing it with the shift key. That makes it a different character as far as keyboard translation is concerned, but it has the same usual meaning. See , for mechanisms that translate event sequences at the level of read-key-sequence. Invoking the Input Method The event-reading functions invoke the current input method, if any (see ). If the value of input-method-function is non-nil, it should be a function; when read-event reads a printing character (including SPC) with no modifier bits, it calls that function, passing the character as an argument. input-method-function — Variable: input-method-function If this is non-nil, its value specifies the current input methodfunction.Warning: don't bind this variable with let. It is oftenbuffer-local, and if you bind it around reading input (which is exactlywhen you would bind it), switching buffers asynchronously whileEmacs is waiting will cause the value to be restored in the wrongbuffer. The input method function should return a list of events which should be used as input. (If the list is nil, that means there is no input, so read-event waits for another event.) These events are processed before the events in unread-command-events (see ). Events returned by the input method function are not passed to the input method function again, even if they are printing characters with no modifier bits. If the input method function calls read-event or read-key-sequence, it should bind input-method-function to nil first, to prevent recursion. The input method function is not called when reading the second and subsequent events of a key sequence. Thus, these characters are not subject to input method processing. The input method function should test the values of overriding-local-map and overriding-terminal-local-map; if either of these variables is non-nil, the input method should put its argument into a list and return that list with no further processing. Quoted Character Input quoted character input You can use the function read-quoted-char to ask the user to specify a character, and allow the user to specify a control or meta character conveniently, either literally or as an octal character code. The command quoted-insert uses this function. read-quoted-char — Function: read-quoted-char &optional prompt octal character input control characters, reading nonprinting characters, readingThis function is like read-char, except that if the firstcharacter read is an octal digit (0-7), it reads any number of octaldigits (but stopping if a non-octal digit is found), and returns thecharacter represented by that numeric character code. If thecharacter that terminates the sequence of octal digits is RET,it is discarded. Any other terminating character is used as inputafter this function returns.Quitting is suppressed when the first character is read, so that theuser can enter a C-g. See .If prompt is supplied, it specifies a string for prompting theuser. The prompt string is always displayed in the echo area, followedby a single ‘-’.In the following example, the user types in the octal number 177 (whichis 127 in decimal). (read-quoted-char "What character") ---------- Echo Area ---------- What character 1 7 7- ---------- Echo Area ---------- => 127 Miscellaneous Event Input Features This section describes how to “peek ahead” at events without using them up, how to check for pending input, and how to discard pending input. See also the function read-passwd (see ). unread-command-events — Variable: unread-command-events next input peeking at inputThis variable holds a list of events waiting to be read as commandinput. The events are used in the order they appear in the list, andremoved one by one as they are used.The variable is needed because in some cases a function reads an eventand then decides not to use it. Storing the event in this variablecauses it to be processed normally, by the command loop or by thefunctions to read command input. prefix argument unreadingFor example, the function that implements numeric prefix arguments readsany number of digits. When it finds a non-digit event, it must unreadthe event so that it can be read normally by the command loop.Likewise, incremental search uses this feature to unread events with nospecial meaning in a search, because these events should exit the searchand then execute normally.The reliable and easy way to extract events from a key sequence so as toput them in unread-command-events is to uselistify-key-sequence (see ).Normally you add events to the front of this list, so that the eventsmost recently unread will be reread first.Events read from this list are not normally added to the currentcommand's key sequence (as returned by e.g. this-command-keys),as the events will already have been added once as they were read forthe first time. An element of the form (t . event)forces event to be added to the current command's key sequence. listify-key-sequence — Function: listify-key-sequence key This function converts the string or vector key to a list ofindividual events, which you can put in unread-command-events. unread-command-char — Variable: unread-command-char This variable holds a character to be read as command input.A value of -1 means “empty.”This variable is mostly obsolete now that you can useunread-command-events instead; it exists only to support programswritten for Emacs versions 18 and earlier. input-pending-p — Function: input-pending-p waiting for command key inputThis function determines whether any command input is currentlyavailable to be read. It returns immediately, with value t ifthere is available input, nil otherwise. On rare occasions itmay return t when no input is available. last-input-event — Variable: last-input-event last-input-char — Variable: last-input-char This variable records the last terminal input event read, whetheras part of a command or explicitly by a Lisp program.In the example below, the Lisp program reads the character 1,ASCII code 49. It becomes the value of last-input-event,while C-e (we assume C-x C-e command is used to evaluatethis expression) remains the value of last-command-event. (progn (print (read-char)) (print last-command-event) last-input-event) -| 49 -| 5 => 49 The alias last-input-char exists for compatibility withEmacs version 18. while-no-input — Macro: while-no-input body … This construct runs the body forms and returns the value of thelast one—but only if no input arrives. If any input arrives duringthe execution of the body forms, it aborts them (working muchlike a quit). The while-no-input form returns nil ifaborted by a real quit, and returns t if aborted by arrival ofother input.If a part of body binds inhibit-quit to non-nil,arrival of input during those parts won't cause an abort untilthe end of that part.If you want to be able to distinguish all possible values computedby body from both kinds of abort conditions, write the codelike this: (while-no-input (list (progn . body))) discard-input — Function: discard-input flushing input discarding input keyboard macro, terminatingThis function discards the contents of the terminal input buffer andcancels any keyboard macro that might be in the process of definition.It returns nil.In the following example, the user may type a number of characters rightafter starting the evaluation of the form. After the sleep-forfinishes sleeping, discard-input discards any characters typedduring the sleep. (progn (sleep-for 2) (discard-input)) => nil Special Events special events Special events are handled at a very low level—as soon as they are read. The read-event function processes these events itself, and never returns them. Instead, it keeps waiting for the first event that is not special and returns that one. Events that are handled in this way do not echo, they are never grouped into key sequences, and they never appear in the value of last-command-event or (this-command-keys). They do not discard a numeric argument, they cannot be unread with unread-command-events, they may not appear in a keyboard macro, and they are not recorded in a keyboard macro while you are defining one. These events do, however, appear in last-input-event immediately after they are read, and this is the way for the event's definition to find the actual event. The events types iconify-frame, make-frame-visible, delete-frame, drag-n-drop, and user signals like sigusr1 are normally handled in this way. The keymap which defines how to handle special events—and which events are special—is in the variable special-event-map (see ). Waiting for Elapsed Time or Input waiting The wait functions are designed to wait for a certain amount of time to pass or until there is input. For example, you may wish to pause in the middle of a computation to allow the user time to view the display. sit-for pauses and updates the screen, and returns immediately if input comes in, while sleep-for pauses without updating the screen. sit-for — Function: sit-for seconds &optional nodisp This function performs redisplay (provided there is no pending inputfrom the user), then waits seconds seconds, or until input isavailable. The usual purpose of sit-for is to give the usertime to read text that you display. The value is t ifsit-for waited the full time with no input arriving(see ). Otherwise, the value is nil.The argument seconds need not be an integer. If it is a floatingpoint number, sit-for waits for a fractional number of seconds.Some systems support only a whole number of seconds; on these systems,seconds is rounded down.The expression (sit-for 0) is equivalent to (redisplay),i.e. it requests a redisplay, without any delay, if there is no pending input.See .If nodisp is non-nil, then sit-for does notredisplay, but it still returns as soon as input is available (or whenthe timeout elapses).In batch mode (see ), sit-for cannot beinterrupted, even by input from the standard input descriptor. It isthus equivalent to sleep-for, which is described below.It is also possible to call sit-for with three arguments,as (sit-for seconds millisec nodisp),but that is considered obsolete. sleep-for — Function: sleep-for seconds &optional millisec This function simply pauses for seconds seconds without updatingthe display. It pays no attention to available input. It returnsnil.The argument seconds need not be an integer. If it is a floatingpoint number, sleep-for waits for a fractional number of seconds.Some systems support only a whole number of seconds; on these systems,seconds is rounded down.The optional argument millisec specifies an additional waitingperiod measured in milliseconds. This adds to the period specified byseconds. If the system doesn't support waiting fractions of asecond, you get an error if you specify nonzero millisec.Use sleep-for when you wish to guarantee a delay. See , for functions to get the current time. Quitting C-g quitting interrupt Lisp functions Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop. Typing C-g while the command loop is waiting for keyboard input does not cause a quit; it acts as an ordinary input character. In the simplest case, you cannot tell the difference, because C-g normally runs the command keyboard-quit, whose effect is to quit. However, when C-g follows a prefix key, they combine to form an undefined key. The effect is to cancel the prefix key as well as any prefix argument. In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly. When C-g does directly quit, it does so by setting the variable quit-flag to t. Emacs checks this variable at appropriate times and quits if it is not nil. Setting quit-flag non-nil in any way thus causes a quit. At the level of C code, quitting cannot happen just anywhere; only at the special places that check quit-flag. The reason for this is that quitting at other places might leave an inconsistency in Emacs's internal state. Because quitting is delayed until a safe place, quitting cannot make Emacs crash. Certain functions such as read-key-sequence or read-quoted-char prevent quitting entirely even though they wait for input. Instead of quitting, C-g serves as the requested input. In the case of read-key-sequence, this serves to bring about the special behavior of C-g in the command loop. In the case of read-quoted-char, this is so that C-q can be used to quote a C-g. preventing quitting You can prevent quitting for a portion of a Lisp function by binding the variable inhibit-quit to a non-nil value. Then, although C-g still sets quit-flag to t as usual, the usual result of this—a quit—is prevented. Eventually, inhibit-quit will become nil again, such as when its binding is unwound at the end of a let form. At that time, if quit-flag is still non-nil, the requested quit happens immediately. This behavior is ideal when you wish to make sure that quitting does not happen within a “critical section” of the program. read-quoted-char quitting In some functions (such as read-quoted-char), C-g is handled in a special way that does not involve quitting. This is done by reading the input with inhibit-quit bound to t, and setting quit-flag to nil before inhibit-quit becomes nil again. This excerpt from the definition of read-quoted-char shows how this is done; it also shows that normal quitting is permitted after the first character of input. (defun read-quoted-char (&optional prompt) "…documentation…" (let ((message-log-max nil) done (first t) (code 0) char) (while (not done) (let ((inhibit-quit first) …) (and prompt (message "%s-" prompt)) (setq char (read-event)) (if inhibit-quit (setq quit-flag nil))) …set the variable code… ) code)) quit-flag — Variable: quit-flag If this variable is non-nil, then Emacs quits immediately, unlessinhibit-quit is non-nil. Typing C-g ordinarily setsquit-flag non-nil, regardless of inhibit-quit. inhibit-quit — Variable: inhibit-quit This variable determines whether Emacs should quit when quit-flagis set to a value other than nil. If inhibit-quit isnon-nil, then quit-flag has no special effect. with-local-quit — Macro: with-local-quit body … This macro executes body forms in sequence, but allows quitting, atleast locally, within body even if inhibit-quit wasnon-nil outside this construct. It returns the value of thelast form in body, unless exited by quitting, in which caseit returns nil.If inhibit-quit is nil on entry to with-local-quit,it only executes the body, and setting quit-flag causesa normal quit. However, if inhibit-quit is non-nil sothat ordinary quitting is delayed, a non-nil quit-flagtriggers a special kind of local quit. This ends the execution ofbody and exits the with-local-quit body withquit-flag still non-nil, so that another (ordinary) quitwill happen as soon as that is allowed. If quit-flag isalready non-nil at the beginning of body, the local quithappens immediately and the body doesn't execute at all.This macro is mainly useful in functions that can be called fromtimers, process filters, process sentinels, pre-command-hook,post-command-hook, and other places where inhibit-quit isnormally bound to t. keyboard-quit — Command: keyboard-quit This function signals the quit condition with (signal 'quitnil). This is the same thing that quitting does. (See signalin .) You can specify a character other than C-g to use for quitting. See the function set-input-mode in . Prefix Command Arguments prefix argument raw prefix argument numeric prefix argument Most Emacs commands can use a prefix argument, a number specified before the command itself. (Don't confuse prefix arguments with prefix keys.) The prefix argument is at all times represented by a value, which may be nil, meaning there is currently no prefix argument. Each command may use the prefix argument or ignore it. There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation. Here are the possible values of a raw prefix argument: nil, meaning there is no prefix argument. Its numeric value is1, but numerous commands make a distinction between nil and theinteger 1. An integer, which stands for itself. A list of one element, which is an integer. This form of prefixargument results from one or a succession of C-u's with nodigits. The numeric value is the integer in the list, but somecommands make a distinction between such a list and an integer alone. The symbol -. This indicates that M– or C-u - wastyped, without following digits. The equivalent numeric value is−1, but some commands make a distinction between the integer−1 and the symbol -. We illustrate these possibilities by calling the following function with various prefixes: (defun display-prefix (arg) "Display the value of the raw prefix arg." (interactive "P") (message "%s" arg)) Here are the results of calling display-prefix with various raw prefix arguments: M-x display-prefix -| nil C-u M-x display-prefix -| (4) C-u C-u M-x display-prefix -| (16) C-u 3 M-x display-prefix -| 3 M-3 M-x display-prefix -| 3 ; (Same as C-u 3.) C-u - M-x display-prefix -| - M-- M-x display-prefix -| - ; (Same as C-u -.) C-u - 7 M-x display-prefix -| -7 M-- 7 M-x display-prefix -| -7 ; (Same as C-u -7.) Emacs uses two variables to store the prefix argument: prefix-arg and current-prefix-arg. Commands such as universal-argument that set up prefix arguments for other commands store them in prefix-arg. In contrast, current-prefix-arg conveys the prefix argument to the current command, so setting it has no effect on the prefix arguments for future commands. Normally, commands specify which representation to use for the prefix argument, either numeric or raw, in the interactive specification. (See .) Alternatively, functions may look at the value of the prefix argument directly in the variable current-prefix-arg, but this is less clean. prefix-numeric-value — Function: prefix-numeric-value arg This function returns the numeric meaning of a valid raw prefix argumentvalue, arg. The argument may be a symbol, a number, or a list.If it is nil, the value 1 is returned; if it is -, thevalue −1 is returned; if it is a number, that number is returned;if it is a list, the car of that list (which should be a number) isreturned. current-prefix-arg — Variable: current-prefix-arg This variable holds the raw prefix argument for the currentcommand. Commands may examine it directly, but the usual method foraccessing it is with (interactive "P"). prefix-arg — Variable: prefix-arg The value of this variable is the raw prefix argument for thenext editing command. Commands such as universal-argumentthat specify prefix arguments for the following command work by settingthis variable. last-prefix-arg — Variable: last-prefix-arg The raw prefix argument value used by the previous command. The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason. universal-argument — Command: universal-argument This command reads input and specifies a prefix argument for thefollowing command. Don't call this command yourself unless you knowwhat you are doing. digit-argument — Command: digit-argument arg This command adds to the prefix argument for the following command. Theargument arg is the raw prefix argument as it was before thiscommand; it is used to compute the updated prefix argument. Don't callthis command yourself unless you know what you are doing. negative-argument — Command: negative-argument arg This command adds to the numeric argument for the next command. Theargument arg is the raw prefix argument as it was before thiscommand; its value is negated to form the new prefix argument. Don'tcall this command yourself unless you know what you are doing. Recursive Editing recursive command loop recursive editing level command loop, recursive The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command. The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.) All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop. minibuffer input Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands. throw example exit exit recursive editing aborting To invoke a recursive editing level, call the function recursive-edit. This function contains the command loop; it also contains a call to catch with tag exit, which makes it possible to exit the recursive editing level by throwing to exit (see ). If you throw a value other than t, then recursive-edit returns normally to the function that called it. The command C-M-c (exit-recursive-edit) does this. Throwing a t value causes recursive-edit to quit, so that control returns to the command loop one level up. This is called aborting, and is done by C-] (abort-recursive-edit). Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit “recursively,” create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.) Recursive edits are useful in debugging. You can insert a call to debug into a function definition as a sort of breakpoint, so that you can look around when the function gets there. debug invokes a recursive edit but also provides the other features of the debugger. Recursive editing levels are also used when you type C-r in query-replace or use C-x q (kbd-macro-query). recursive-edit — Function: recursive-edit suspend evaluationThis function invokes the editor command loop. It is calledautomatically by the initialization of Emacs, to let the user beginediting. When called from a Lisp program, it enters a recursive editinglevel.If the current buffer is not the same as the selected window's buffer,recursive-edit saves and restores the current buffer. Otherwise,if you switch buffers, the buffer you switched to is current afterrecursive-edit returns.In the following example, the function simple-rec firstadvances point one word, then enters a recursive edit, printing out amessage in the echo area. The user can then do any editing desired, andthen type C-M-c to exit and continue executing simple-rec. (defun simple-rec () (forward-word 1) (message "Recursive edit in progress") (recursive-edit) (forward-word 1)) => simple-rec (simple-rec) => nil exit-recursive-edit — Command: exit-recursive-edit This function exits from the innermost recursive edit (includingminibuffer input). Its definition is effectively (throw 'exitnil). abort-recursive-edit — Command: abort-recursive-edit This function aborts the command that requested the innermost recursiveedit (including minibuffer input), by signaling quitafter exiting the recursive edit. Its definition is effectively(throw 'exit t). See . top-level — Command: top-level This function exits all recursive editing levels; it does not return avalue, as it jumps completely out of any computation directly back tothe main command loop. recursion-depth — Function: recursion-depth This function returns the current depth of recursive edits. When norecursive edit is active, it returns 0. Disabling Commands disabled command Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident. disabled The low-level mechanism for disabling a command is to put a non-nil disabled property on the Lisp symbol for the command. These properties are normally set up by the user's init file (see ) with Lisp expressions such as this: (put 'upcase-region 'disabled t) For a few commands, these properties are present by default (you can remove them in your init file if you wish). If the value of the disabled property is a string, the message saying the command is disabled includes that string. For example: (put 'delete-region 'disabled "Text deleted this way cannot be yanked back!\n") See See section ``Disabling'' in The GNU Emacs Manual, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs. enable-command — Command: enable-command command Allow command (a symbol) to be executed without specialconfirmation from now on, and alter the user's init file (see ) so that this will apply to future sessions. disable-command — Command: disable-command command Require special confirmation to execute command from now on, andalter the user's init file so that this will apply to future sessions. disabled-command-function — Variable: disabled-command-function The value of this variable should be a function. When the userinvokes a disabled command interactively, this function is calledinstead of the disabled command. It can use this-command-keysto determine what the user typed to run the command, and thus find thecommand itself.The value may also be nil. Then all commands work normally,even disabled ones.By default, the value is a function that asks the user whether toproceed. Command History command history complex command history of commands The command loop keeps a history of the complex commands that have been executed, to make it convenient to repeat these commands. A complex command is one for which the interactive argument reading uses the minibuffer. This includes any M-x command, any M-: command, and any command whose interactive specification reads an argument from the minibuffer. Explicit use of the minibuffer during the execution of the command itself does not cause the command to be considered complex. command-history — Variable: command-history This variable's value is a list of recent complex commands, eachrepresented as a form to evaluate. It continues to accumulate allcomplex commands for the duration of the editing session, but when itreaches the maximum size (see ), the oldestelements are deleted as new ones are added. command-history => ((switch-to-buffer "chistory.texi") (describe-key "^X^[") (visit-tags-table "~/emacs/src/") (find-tag "repeat-complex-command")) This history list is actually a special case of minibuffer history (see ), with one special twist: the elements are expressions rather than strings. There are a number of commands devoted to the editing and recall of previous commands. The commands repeat-complex-command, and list-command-history are described in the user manual (see See section ``Repetition'' in The GNU Emacs Manual). Within the minibuffer, the usual minibuffer history commands are available. Keyboard Macros keyboard macros A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (see ). execute-kbd-macro — Function: execute-kbd-macro kbdmacro &optional count loopfunc This function executes kbdmacro as a sequence of events. Ifkbdmacro is a string or vector, then the events in it are executedexactly as if they had been input by the user. The sequence isnot expected to be a single key sequence; normally a keyboardmacro definition consists of several key sequences concatenated.If kbdmacro is a symbol, then its function definition is used inplace of kbdmacro. If that is another symbol, this process repeats.Eventually the result should be a string or vector. If the result isnot a symbol, string, or vector, an error is signaled.The argument count is a repeat count; kbdmacro is executed thatmany times. If count is omitted or nil, kbdmacro isexecuted once. If it is 0, kbdmacro is executed over and over until itencounters an error or a failing search.If loopfunc is non-nil, it is a function that is called,without arguments, prior to each iteration of the macro. Ifloopfunc returns nil, then this stops execution of the macro.See , for an example of using execute-kbd-macro. executing-kbd-macro — Variable: executing-kbd-macro This variable contains the string or vector that defines the keyboardmacro that is currently executing. It is nil if no macro iscurrently executing. A command can test this variable so as to behavedifferently when run from an executing macro. Do not set this variableyourself. defining-kbd-macro — Variable: defining-kbd-macro This variable is non-nil if and only if a keyboard macro isbeing defined. A command can test this variable so as to behavedifferently while a macro is being defined. The value isappend while appending to the definition of an existing macro.The commands start-kbd-macro, kmacro-start-macro andend-kbd-macro set this variable—do not set it yourself.The variable is always local to the current terminal and cannot bebuffer-local. See . last-kbd-macro — Variable: last-kbd-macro This variable is the definition of the most recently defined keyboardmacro. Its value is a string or vector, or nil.The variable is always local to the current terminal and cannot bebuffer-local. See . kbd-macro-termination-hook — Variable: kbd-macro-termination-hook This normal hook (see ) is run when a keyboardmacro terminates, regardless of what caused it to terminate (reachingthe macro end or an error which ended the macro prematurely). <setfilename>../info/keymaps</setfilename> Keymaps keymap The command bindings of input events are recorded in data structures called keymaps. Each entry in a keymap associates (or binds) an individual event type, either to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup. Key Sequences key keystroke key sequence A key sequence, or key for short, is a sequence of one or more input events that form a unit. Input events include characters, function keys, and mouse actions (see ). The Emacs Lisp representation for a key sequence is a string or vector. Unless otherwise stated, any Emacs Lisp function that accepts a key sequence as an argument can handle both representations. In the string representation, alphanumeric characters ordinarily stand for themselves; for example, "a" represents a and "2" represents 2. Control character events are prefixed by the substring "\C-", and meta characters by "\M-"; for example, "\C-x" represents the key C-x. In addition, the TAB, RET, ESC, and DEL events are represented by "\t", "\r", "\e", and "\d" respectively. The string representation of a complete key sequence is the concatenation of the string representations of the constituent events; thus, "\C-xl" represents the key sequence C-x l. Key sequences containing function keys, mouse button events, or non-ASCII characters such as C-= or H-a cannot be represented as strings; they have to be represented as vectors. In the vector representation, each element of the vector represents an input event, in its Lisp form. See . For example, the vector [?\C-x ?l] represents the key sequence C-x l. For examples of key sequences written in string and vector representations, See section ``Init Rebinding'' in The GNU Emacs Manual. kbd — Macro: kbd keyseq-text This macro converts the text keyseq-text (a string constant)into a key sequence (a string or vector constant). The contents ofkeyseq-text should describe the key sequence using almost the samesyntax used in this manual. More precisely, it uses the same syntaxthat Edit Macro mode uses for editing keyboard macros (see See section ``Edit Keyboard Macro'' in The GNU Emacs Manual); you must surroundfunction key names with ‘<…>’. (kbd "C-x") => "\C-x" (kbd "C-x C-f") => "\C-x\C-f" (kbd "C-x 4 C-f") => "\C-x4\C-f" (kbd "X") => "X" (kbd "RET") => "\^M" (kbd "C-c SPC") => "\C-c " (kbd "<f1> SPC") => [f1 32] (kbd "C-M-<down>") => [C-M-down] This macro is not meant for use with arguments that vary—onlywith string constants. Keymap Basics key binding binding of a key complete key undefined key A keymap is a Lisp data structure that specifies key bindings for various key sequences. A single keymap directly specifies definitions for individual events. When a key sequence consists of a single event, its binding in a keymap is the keymap's definition for that event. The binding of a longer key sequence is found by an iterative process: first find the definition of the first event (which must itself be a keymap); then find the second event's definition in that keymap, and so on until all the events in the key sequence have been processed. If the binding of a key sequence is a keymap, we call the key sequence a prefix key. Otherwise, we call it a complete key (because no more events can be added to it). If the binding is nil, we call the key undefined. Examples of prefix keys are C-c, C-x, and C-x 4. Examples of defined complete keys are X, RET, and C-x 4 C-f. Examples of undefined complete keys are C-x C-g, and C-c 3. See , for more details. The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit—it is not really one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence. The set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness. At any time, several primary keymaps are active—that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See , for details. Format of Keymaps format of keymaps keymap format full keymap sparse keymap Each keymap is a list whose car is the symbol keymap. The remaining elements of the list define the key bindings of the keymap. A symbol whose function definition is a keymap is also a keymap. Use the function keymapp (see below) to test whether an object is a keymap. Several kinds of elements may appear in a keymap, after the symbol keymap that begins it: (type . binding) This specifies one binding, for events of type type. Eachordinary binding applies to events of a particular event type,which is always a character or a symbol. See .In this kind of binding, binding is a command. (type item-name [cache] . binding) This specifies a binding which is also a simple menu item thatdisplays as item-name in the menu. cache, if present,caches certain information for display in the menu. See . (type item-name help-string [cache] . binding) This is a simple menu item with help string help-string. (type menu-item . details) This specifies a binding which is also an extended menu item. Thisallows use of other features. See . (t . binding) default key bindingThis specifies a default key binding; any event not bound by otherelements of the keymap is given binding as its binding. Defaultbindings allow a keymap to bind all possible event types without havingto enumerate all of them. A keymap that has a default bindingcompletely masks any lower-precedence keymap, except for eventsexplicitly bound to nil (see below). char-table If an element of a keymap is a char-table, it counts as holdingbindings for all character events with no modifier bits(see ): element n is the binding for thecharacter with code n. This is a compact way to record lots ofbindings. A keymap with such a char-table is called a fullkeymap. Other keymaps are called sparse keymaps. string keymap prompt string overall prompt string prompt string of keymapAside from elements that specify bindings for keys, a keymap can alsohave a string as an element. This is called the overall promptstring and makes it possible to use the keymap as a menu.See . When the binding is nil, it doesn't constitute a definition but it does take precedence over a default binding or a binding in the parent keymap. On the other hand, a binding of nil does not override lower-precedence keymaps; thus, if the local map gives a binding of nil, Emacs uses the binding from the global map. meta characters lookup Keymaps do not directly record bindings for the meta characters. Instead, meta characters are regarded for purposes of key lookup as sequences of two characters, the first of which is ESC (or whatever is currently the value of meta-prefix-char). Thus, the key M-a is internally represented as ESC a, and its global binding is found at the slot for a in esc-map (see ). This conversion applies only to characters, not to function keys or other input events; thus, M-end has nothing to do with ESC end. Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for DEL and TAB, plus C-c C-l, M-C-q, and M-C-x. lisp-mode-map => (keymap (3 keymap ;; C-c C-z (26 . run-lisp)) (27 keymap ;; M-C-x, treated as ESC C-x (24 . lisp-send-defun) keymap ;; M-C-q, treated as ESC C-q (17 . indent-sexp)) ;; This part is inherited from lisp-mode-shared-map. keymap ;; DEL (127 . backward-delete-char-untabify) (27 keymap ;; M-C-q, treated as ESC C-q (17 . indent-sexp)) (9 . lisp-indent-line)) keymapp — Function: keymapp object This function returns t if object is a keymap, nilotherwise. More precisely, this function tests for a list whosecar is keymap, or for a symbol whose function definitionsatisfies keymapp. (keymapp '(keymap)) => t (fset 'foo '(keymap)) (keymapp 'foo) => t (keymapp (current-global-map)) => t Creating Keymaps creating keymaps Here we describe the functions for creating keymaps. make-sparse-keymap — Function: make-sparse-keymap &optional prompt This function creates and returns a new sparse keymap with no entries.(A sparse keymap is the kind of keymap you usually want.) The newkeymap does not contain a char-table, unlike make-keymap, anddoes not bind any events. (make-sparse-keymap) => (keymap) If you specify prompt, that becomes the overall prompt stringfor the keymap. You should specify this only for menu keymaps(see ). A keymap with an overall prompt string willalways present a mouse menu or a keyboard menu if it is active forlooking up the next input event. Don't specify an overall prompt stringfor the main map of a major or minor mode, because that would causethe command loop to present a keyboard menu every time. make-keymap — Function: make-keymap &optional prompt This function creates and returns a new full keymap. That keymapcontains a char-table (see ) with slots for allcharacters without modifiers. The new keymap initially binds allthese characters to nil, and does not bind any other kind ofevent. The argument prompt specifies aprompt string, as in make-sparse-keymap. (make-keymap) => (keymap #^[t nil nil nil … nil nil keymap]) A full keymap is more efficient than a sparse keymap when it holdslots of bindings; for just a few, the sparse keymap is better. copy-keymap — Function: copy-keymap keymap This function returns a copy of keymap. Any keymaps thatappear directly as bindings in keymap are also copied recursively,and so on to any number of levels. However, recursive copying does nottake place when the definition of a character is a symbol whose functiondefinition is a keymap; the same symbol appears in the new copy. (setq map (copy-keymap (current-local-map))) => (keymap ;; (This implements meta characters.) (27 keymap (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) (eq map (current-local-map)) => nil (equal map (current-local-map)) => t Inheritance and Keymaps keymap inheritance inheriting a keymap's bindings A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this: (keymap elements… . parent-keymap) The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with elements. If you change the bindings in parent-keymap using define-key or other key-binding functions, these changed bindings are visible in the inheriting keymap, unless shadowed by the bindings made by elements. The converse is not true: if you use define-key to change bindings in the inheriting keymap, these changes are recorded in elements, but have no effect on parent-keymap. The proper way to construct a keymap with a parent is to use set-keymap-parent; if you have code that directly constructs a keymap with a parent, please convert the program to use set-keymap-parent instead. keymap-parent — Function: keymap-parent keymap This returns the parent keymap of keymap. If keymaphas no parent, keymap-parent returns nil. set-keymap-parent — Function: set-keymap-parent keymap parent This sets the parent keymap of keymap to parent, and returnsparent. If parent is nil, this function giveskeymap no parent at all.If keymap has submaps (bindings for prefix keys), they too receivenew parent keymaps that reflect what parent specifies for thoseprefix keys. Here is an example showing how to make a keymap that inherits from text-mode-map: (let ((map (make-sparse-keymap))) (set-keymap-parent map text-mode-map) map) A non-sparse keymap can have a parent too, but this is not very useful. A non-sparse keymap always specifies something as the binding for every numeric character code without modifier bits, even if it is nil, so these character's bindings are never inherited from the parent keymap. Prefix Keys prefix key A prefix key is a key sequence whose binding is a keymap. The keymap defines what to do with key sequences that extend the prefix key. For example, C-x is a prefix key, and it uses a keymap that is also stored in the variable ctl-x-map. This keymap defines bindings for key sequences starting with C-x. Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables: esc-map ESC-prefixesc-map is the global keymap for the ESC prefix key. Thus,the global definitions of all meta characters are actually found here.This map is also the function definition of ESC-prefix. C-hhelp-map is the global keymap for the C-h prefix key. C-c mode-specific-mapmode-specific-map is the global keymap for the prefix keyC-c. This map is actually global, not mode-specific, but its nameprovides useful information about C-c in the output of C-h b(display-bindings), since the main use of this prefix key is formode-specific bindings. C-x ctl-x-map Control-X-prefixctl-x-map is the global keymap used for the C-x prefix key.This map is found via the function cell of the symbolControl-X-prefix. C-x RET mule-keymapmule-keymap is the global keymap used for the C-x RETprefix key. C-x 4 ctl-x-4-mapctl-x-4-map is the global keymap used for the C-x 4 prefixkey. C-x 5 ctl-x-5-mapctl-x-5-map is the global keymap used for the C-x 5 prefixkey. C-x 6 2C-mode-map2C-mode-map is the global keymap used for the C-x 6 prefixkey. C-x v vc-prefix-mapvc-prefix-map is the global keymap used for the C-x v prefixkey. M-o facemenu-keymapfacemenu-keymap is the global keymap used for the M-oprefix key. The other Emacs prefix keys are M-g, C-x @, C-x a i,C-x ESC and ESC ESC. They use keymapsthat have no special names. The keymap binding of a prefix key is used for looking up the event that follows the prefix key. (It may instead be a symbol whose function definition is a keymap. The effect is the same, but the symbol serves as a name for the prefix key.) Thus, the binding of C-x is the symbol Control-X-prefix, whose function cell holds the keymap for C-x commands. (The same keymap is also the value of ctl-x-map.) Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and ESC as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See . If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map. In the following example, we make C-p a prefix key in the local keymap, in such a way that C-p is identical to C-x. Then the binding for C-p C-f is the function find-file, just like C-x C-f. The key sequence C-p 6 is not found in any active keymap. (use-local-map (make-sparse-keymap)) => nil (local-set-key "\C-p" ctl-x-map) => nil (key-binding "\C-p\C-f") => find-file (key-binding "\C-p6") => nil define-prefix-command — Function: define-prefix-command symbol &optional mapvar prompt prefix commandThis function prepares symbol for use as a prefix key's binding:it creates a sparse keymap and stores it as symbol's functiondefinition. Subsequently binding a key sequence to symbol willmake that key sequence into a prefix key. The return value is symbol.This function also sets symbol as a variable, with the keymap asits value. But if mapvar is non-nil, it sets mapvaras a variable instead.If prompt is non-nil, that becomes the overall promptstring for the keymap. The prompt string should be given for menu keymaps(see ). Active Keymaps active keymap global keymap local keymap Emacs normally contains many keymaps; at any given time, just a few of them are active, meaning that they participate in the interpretation of user input. All the active keymaps are used together to determine what command to execute when a key is entered. Normally the active keymaps are the keymap property keymap, the keymaps of any enabled minor modes, the current buffer's local keymap, and the global keymap, in that order. Emacs searches for each input key sequence in all these keymaps. See , for more details of this procedure. When the key sequence starts with a mouse event (optionally preceded by a symbolic prefix), the active keymaps are determined based on the position in that event. If the event happened on a string embedded with a display, before-string, or after-string property (see ), the non-nil map properties of the string override those of the buffer. The global keymap holds the bindings of keys that are defined regardless of the current buffer, such as C-f. The variable global-map holds this keymap, which is always active. Each buffer may have another keymap, its local keymap, which may contain new or overriding definitions for keys. The current buffer's local keymap is always active except when overriding-local-map overrides it. The local-map text or overlay property can specify an alternative local keymap for certain parts of the buffer; see . Each minor mode can have a keymap; if it does, the keymap is active when the minor mode is enabled. Modes for emulation can specify additional active keymaps through the variable emulation-mode-map-alists. The highest precedence normal keymap comes from the keymap text or overlay property. If that is non-nil, it is the first keymap to be processed, in normal circumstances. However, there are also special ways for programs to substitute other keymaps for some of those. The variable overriding-local-map, if non-nil, specifies a keymap that replaces all the usual active keymaps except the global keymap. Another way to do this is with overriding-terminal-local-map; it operates on a per-terminal basis. These variables are documented below. major mode keymap Since every buffer that uses the same major mode normally uses the same local keymap, you can think of the keymap as local to the mode. A change to the local keymap of a buffer (using local-set-key, for example) is seen also in the other buffers that share that keymap. The local keymaps that are used for Lisp mode and some other major modes exist even if they have not yet been used. These local keymaps are the values of variables such as lisp-mode-map. For most major modes, which are less frequently used, the local keymap is constructed only when the mode is used for the first time in a session. The minibuffer has local keymaps, too; they contain various completion and exit commands. See . Emacs has other keymaps that are used in a different way—translating events within read-key-sequence. See . See , for a list of standard keymaps. current-active-maps — Function: current-active-maps &optional olp This returns the list of active keymaps that would be used by thecommand loop in the current circumstances to look up a key sequence.Normally it ignores overriding-local-map andoverriding-terminal-local-map, but if olp isnon-nil then it pays attention to them. key-binding — Function: key-binding key &optional accept-defaults no-remap position This function returns the binding for key according to thecurrent active keymaps. The result is nil if key isundefined in the keymaps.The argument accept-defaults controls checking for defaultbindings, as in lookup-key (see ).When commands are remapped (see ),key-binding normally processes command remappings so as toreturns the remapped command that will actually be executed. However,if no-remap is non-nil, key-binding ignoresremappings and returns the binding directly specified for key.If key starts with a mouse event (perhaps following a prefixevent), the maps to be consulted are determined based on the event'sposition. Otherwise, they are determined based on the value of point.However, you can override either of them by specifying position.If position is non-nil, it should be either a bufferposition or an event position like the value of event-start.Then the maps consulted are determined based on position.An error is signaled if key is not a string or a vector. (key-binding "\C-x\C-f") => find-file Searching the Active Keymaps searching active keymaps for keys After translation of event subsequences (see ) Emacs looks for them in the active keymaps. Here is a pseudo-Lisp description of the order and conditions for searching them:(or (if overriding-terminal-local-map ( find-in overriding-terminal-local-map) (if overriding-local-map (find-in overriding-local-map) (or (find-in (get-char-property (point) 'keymap)) (find-in-any emulation-mode-map-alists) (find-in-any minor-mode-overriding-map-alist) (find-in-any minor-mode-map-alist) (if (get-text-property (point) 'local-map) (find-in (get-char-property (point) 'local-map)) (find-in (current-local-map)))))) (find-in (current-global-map))) The find-in and find-in-any are pseudo functions that search in one keymap and in an alist of keymaps, respectively. (Searching a single keymap for a binding is called key lookup; see .) If the key sequence starts with a mouse event, or a symbolic prefix event followed by a mouse event, that event's position is used instead of point and the current buffer. Mouse events on an embedded string use non-nil text properties from that string instead of the buffer. The function finally found may be remapped(see ). Characters that are bound to self-insert-command are translatedaccording to translation-table-for-input before insertion. current-active-maps returns a list of thecurrently active keymaps at point. When a match is found (see ), if the binding in thekeymap is a function, the search is over. However if the keymap entryis a symbol with a value or a string, Emacs replaces the input keysequences with the variable's value or the string, and restarts thesearch of the active keymaps. Controlling the Active Keymaps global-map — Variable: global-map This variable contains the default global keymap that maps Emacskeyboard input to commands. The global keymap is normally thiskeymap. The default global keymap is a full keymap that bindsself-insert-command to all of the printing characters.It is normal practice to change the bindings in the global keymap, but youshould not assign this variable any value other than the keymap it startsout with. current-global-map — Function: current-global-map This function returns the current global keymap. This is thesame as the value of global-map unless you change one or theother. (current-global-map) => (keymap [set-mark-command beginning-of-line … delete-backward-char]) current-local-map — Function: current-local-map This function returns the current buffer's local keymap, or nilif it has none. In the following example, the keymap for the‘*scratch*’ buffer (using Lisp Interaction mode) is a sparse keymapin which the entry for ESC, ASCII code 27, is another sparsekeymap. (current-local-map) => (keymap (10 . eval-print-last-sexp) (9 . lisp-indent-line) (127 . backward-delete-char-untabify) (27 keymap (24 . eval-defun) (17 . indent-sexp))) current-minor-mode-maps — Function: current-minor-mode-maps This function returns a list of the keymaps of currently enabled minor modes. use-global-map — Function: use-global-map keymap This function makes keymap the new current global keymap. Itreturns nil.It is very unusual to change the global keymap. use-local-map — Function: use-local-map keymap This function makes keymap the new local keymap of the currentbuffer. If keymap is nil, then the buffer has no localkeymap. use-local-map returns nil. Most major modecommands use this function. minor-mode-map-alist — Variable: minor-mode-map-alist This variable is an alist describing keymaps that may or may not beactive according to the values of certain variables. Its elements looklike this: (variable . keymap) The keymap keymap is active whenever variable has anon-nil value. Typically variable is the variable thatenables or disables a minor mode. See .Note that elements of minor-mode-map-alist do not have the samestructure as elements of minor-mode-alist. The map must be thecdr of the element; a list with the map as the second element willnot do. The cdr can be either a keymap (a list) or a symbol whosefunction definition is a keymap.When more than one minor mode keymap is active, the earlier one inminor-mode-map-alist takes priority. But you should designminor modes so that they don't interfere with each other. If you dothis properly, the order will not matter.See , for more information about minormodes. See also minor-mode-key-binding (see ). minor-mode-overriding-map-alist — Variable: minor-mode-overriding-map-alist This variable allows major modes to override the key bindings forparticular minor modes. The elements of this alist look like theelements of minor-mode-map-alist: (variable. keymap).If a variable appears as an element ofminor-mode-overriding-map-alist, the map specified by thatelement totally replaces any map specified for the same variable inminor-mode-map-alist.minor-mode-overriding-map-alist is automatically buffer-local inall buffers. overriding-local-map — Variable: overriding-local-map If non-nil, this variable holds a keymap to use instead of thebuffer's local keymap, any text property or overlay keymaps, and anyminor mode keymaps. This keymap, if specified, overrides all othermaps that would have been active, except for the current global map. overriding-terminal-local-map — Variable: overriding-terminal-local-map If non-nil, this variable holds a keymap to use instead ofoverriding-local-map, the buffer's local keymap, text propertyor overlay keymaps, and all the minor mode keymaps.This variable is always local to the current terminal and cannot bebuffer-local. See . It is used to implementincremental search mode. overriding-local-map-menu-flag — Variable: overriding-local-map-menu-flag If this variable is non-nil, the value ofoverriding-local-map or overriding-terminal-local-map canaffect the display of the menu bar. The default value is nil, sothose map variables have no effect on the menu bar.Note that these two map variables do affect the execution of keysequences entered using the menu bar, even if they do not affect themenu bar display. So if a menu bar key sequence comes in, you shouldclear the variables before looking up and executing that key sequence.Modes that use the variables would typically do this anyway; normallythey respond to events that they do not handle by “unreading” them andexiting. special-event-map — Variable: special-event-map This variable holds a keymap for special events. If an event type has abinding in this keymap, then it is special, and the binding for theevent is run directly by read-event. See . emulation-mode-map-alists — Variable: emulation-mode-map-alists This variable holds a list of keymap alists to use for emulationsmodes. It is intended for modes or packages using multiple minor-modekeymaps. Each element is a keymap alist which has the same format andmeaning as minor-mode-map-alist, or a symbol with a variablebinding which is such an alist. The “active” keymaps in each alistare used before minor-mode-map-alist andminor-mode-overriding-map-alist. Key Lookup key lookup keymap entry Key lookup is the process of finding the binding of a key sequence from a given keymap. The execution or use of the binding is not part of key lookup. Key lookup uses just the event type of each event in the key sequence; the rest of the event is ignored. In fact, a key sequence used for key lookup may designate a mouse event with just its types (a symbol) instead of the entire event (a list). See . Such a “key sequence” is insufficient for command-execute to run, but it is sufficient for looking up or rebinding a key. When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap. Let's use the term keymap entry to describe the value found by looking up an event type in a keymap. (This doesn't include the item string and other extra elements in a keymap element for a menu item, because lookup-key and other key lookup functions don't include them in the returned value.) While any Lisp object may be stored in a keymap as a keymap entry, not all make sense for key lookup. Here is a table of the meaningful types of keymap entries: nil nil in keymapnil means that the events used so far in the lookup form anundefined key. When a keymap fails to mention an event type at all, andhas no default binding, that is equivalent to a binding of nilfor that event type. command command in keymapThe events used so far in the lookup form a complete key,and command is its binding. See . array string in keymapThe array (either a string or a vector) is a keyboard macro. The eventsused so far in the lookup form a complete key, and the array is itsbinding. See , for more information. keymap keymap in keymapThe events used so far in the lookup form a prefix key. The nextevent of the key sequence is looked up in keymap. list list in keymapThe meaning of a list depends on what it contains: If the car of list is the symbol keymap, then the listis a keymap, and is treated as a keymap (see above). lambda in keymapIf the car of list is lambda, then the list is alambda expression. This is presumed to be a function, and is treatedas such (see above). In order to execute properly as a key binding,this function must be a command—it must have an interactivespecification. See . If the car of list is a keymap and the cdr is an eventtype, then this is an indirect entry: (othermap . othertype) When key lookup encounters an indirect entry, it looks up instead thebinding of othertype in othermap and uses that.This feature permits you to define one key as an alias for another key.For example, an entry whose car is the keymap called esc-mapand whose cdr is 32 (the code for SPC) means, “Use the globalbinding of Meta-SPC, whatever that may be.” symbol symbol in keymapThe function definition of symbol is used in place ofsymbol. If that too is a symbol, then this process is repeated,any number of times. Ultimately this should lead to an object that isa keymap, a command, or a keyboard macro. A list is allowed if it is akeymap or a command, but indirect entries are not understood when foundvia symbols.Note that keymaps and keyboard macros (strings and vectors) are notvalid functions, so a symbol with a keymap, string, or vector as itsfunction definition is invalid as a function. It is, however, valid asa key binding. If the definition is a keyboard macro, then the symbolis also valid as an argument to command-execute(see ). undefined in keymapThe symbol undefined is worth special mention: it means to treatthe key as undefined. Strictly speaking, the key is defined, and itsbinding is the command undefined; but that command does the samething that is done automatically for an undefined key: it rings the bell(by calling ding) but does not signal an error. preventing prefix keyundefined is used in local keymaps to override a global keybinding and make the key “undefined” locally. A local binding ofnil would fail to do this because it would not override theglobal binding. anything else If any other type of object is found, the events used so far in thelookup form a complete key, and the object is its binding, but thebinding is not executable as a command. In short, a keymap entry may be a keymap, a command, a keyboard macro, a symbol that leads to one of them, or an indirection or nil. Here is an example of a sparse keymap with two characters bound to commands and one bound to another keymap. This map is the normal value of emacs-lisp-mode-map. Note that 9 is the code for TAB, 127 for DEL, 27 for ESC, 17 for C-q and 24 for C-x. (keymap (9 . lisp-indent-line) (127 . backward-delete-char-untabify) (27 keymap (17 . indent-sexp) (24 . eval-defun))) Functions for Key Lookup Here are the functions and variables pertaining to key lookup. lookup-key — Function: lookup-key keymap key &optional accept-defaults This function returns the definition of key in keymap. Allthe other functions described in this chapter that look up keys uselookup-key. Here are examples: (lookup-key (current-global-map) "\C-x\C-f") => find-file (lookup-key (current-global-map) (kbd "C-x C-f")) => find-file (lookup-key (current-global-map) "\C-x\C-f12345") => 2 If the string or vector key is not a valid key sequence accordingto the prefix keys specified in keymap, it must be “too long”and have extra events at the end that do not fit into a single keysequence. Then the value is a number, the number of events at the frontof key that compose a complete key. If accept-defaults is non-nil, then lookup-keyconsiders default bindings as well as bindings for the specific eventsin key. Otherwise, lookup-key reports only bindings forthe specific sequence key, ignoring default bindings except whenyou explicitly ask about them. (To do this, supply t as anelement of key; see .)If key contains a meta character (not a function key), thatcharacter is implicitly replaced by a two-character sequence: the valueof meta-prefix-char, followed by the corresponding non-metacharacter. Thus, the first example below is handled by conversion intothe second example. (lookup-key (current-global-map) "\M-f") => forward-word (lookup-key (current-global-map) "\ef") => forward-word Unlike read-key-sequence, this function does not modify thespecified events in ways that discard information (see ). In particular, it does not convert letters to lower case andit does not change drag events to clicks. undefined — Command: undefined Used in keymaps to undefine keys. It calls ding, but doesnot cause an error. local-key-binding — Function: local-key-binding key &optional accept-defaults This function returns the binding for key in the currentlocal keymap, or nil if it is undefined there. The argument accept-defaults controls checking for default bindings,as in lookup-key (above). global-key-binding — Function: global-key-binding key &optional accept-defaults This function returns the binding for command key in thecurrent global keymap, or nil if it is undefined there. The argument accept-defaults controls checking for default bindings,as in lookup-key (above). minor-mode-key-binding — Function: minor-mode-key-binding key &optional accept-defaults This function returns a list of all the active minor mode bindings ofkey. More precisely, it returns an alist of pairs(modename . binding), where modename is thevariable that enables the minor mode, and binding is key'sbinding in that mode. If key has no minor-mode bindings, thevalue is nil.If the first binding found is not a prefix definition (a keymap or asymbol defined as a keymap), all subsequent bindings from other minormodes are omitted, since they would be completely shadowed. Similarly,the list omits non-prefix bindings that follow prefix bindings.The argument accept-defaults controls checking for defaultbindings, as in lookup-key (above). meta-prefix-char — Variable: meta-prefix-char ESCThis variable is the meta-prefix character code. It is used fortranslating a meta character to a two-character sequence so it can belooked up in a keymap. For useful results, the value should be aprefix event (see ). The default value is 27, which isthe ASCII code for ESC.As long as the value of meta-prefix-char remains 27, key lookuptranslates M-b into ESC b, which is normally definedas the backward-word command. However, if you were to setmeta-prefix-char to 24, the code for C-x, then Emacs willtranslate M-b into C-x b, whose standard binding is theswitch-to-buffer command. (Don't actually do this!) Here is anillustration of what would happen: meta-prefix-char ; The default value. => 27 (key-binding "\M-b") => backward-word ?\C-x ; The print representation => 24 ; of a character. (setq meta-prefix-char 24) => 24 (key-binding "\M-b") => switch-to-buffer ; Now, typing M-b is ; like typing C-x b. (setq meta-prefix-char 27) ; Avoid confusion! => 27 ; Restore the default value! This translation of one event into two happens only for characters, notfor other kinds of input events. Thus, M-F1, a functionkey, is not converted into ESC F1. Changing Key Bindings changing key bindings rebinding The way to rebind a key is to change its entry in a keymap. If you change a binding in the global keymap, the change is effective in all buffers (though it has no direct effect in buffers that shadow the global binding with a local one). If you change the current buffer's local map, that usually affects all buffers using the same major mode. The global-set-key and local-set-key functions are convenient interfaces for these operations (see ). You can also use define-key, a more general function; then you must specify explicitly the map to change. When choosing the key sequences for Lisp programs to rebind, please follow the Emacs conventions for use of various keys (see ). meta character key constants control character key constants In writing the key sequence to rebind, it is good to use the special escape sequences for control and meta characters (see ). The syntax ‘\C-’ means that the following character is a control character and ‘\M-’ means that the following character is a meta character. Thus, the string "\M-x" is read as containing a single M-x, "\C-f" is read as containing a single C-f, and "\M-\C-x" and "\C-\M-x" are both read as containing a single C-M-x. You can also use this escape syntax in vectors, as well as others that aren't allowed in strings; one example is ‘[?\C-\H-x home]’. See . The key definition and lookup functions accept an alternate syntax for event types in a key sequence that is a vector: you can use a list containing modifier names plus one base event (a character or function key name). For example, (control ?a) is equivalent to ?\C-a and (hyper control left) is equivalent to C-H-left. One advantage of such lists is that the precise numeric codes for the modifier bits don't appear in compiled files. The functions below signal an error if keymap is not a keymap, or if key is not a string or vector representing a key sequence. You can use event types (symbols) as shorthand for events that are lists. The kbd macro (see ) is a convenient way to specify the key sequence. define-key — Function: define-key keymap key binding This function sets the binding for key in keymap. (Ifkey is more than one event long, the change is actually madein another keymap reached from keymap.) The argumentbinding can be any Lisp object, but only certain types aremeaningful. (For a list of meaningful types, see .)The value returned by define-key is binding.If key is [t], this sets the default binding inkeymap. When an event has no binding of its own, the Emacscommand loop uses the keymap's default binding, if there is one. invalid prefix key error key sequence errorEvery prefix of key must be a prefix key (i.e., bound to a keymap)or undefined; otherwise an error is signaled. If some prefix ofkey is undefined, then define-key defines it as a prefixkey so that the rest of key can be defined as specified.If there was previously no binding for key in keymap, thenew binding is added at the beginning of keymap. The order ofbindings in a keymap makes no difference for keyboard input, but itdoes matter for menu keymaps (see ). This example creates a sparse keymap and makes a number of bindings in it: (setq map (make-sparse-keymap)) => (keymap) (define-key map "\C-f" 'forward-char) => forward-char map => (keymap (6 . forward-char)) ;; Build sparse submap for C-x and bind f in that. (define-key map (kbd "C-x f") 'forward-word) => forward-word map => (keymap (24 keymap ; C-x (102 . forward-word)) ; f (6 . forward-char)) ; C-f ;; Bind C-p to the ctl-x-map. (define-key map (kbd "C-p") ctl-x-map) ;; ctl-x-map => [nil … find-file … backward-kill-sentence] ;; Bind C-f to foo in the ctl-x-map. (define-key map (kbd "C-p C-f") 'foo) => 'foo map => (keymap ; Note foo in ctl-x-map. (16 keymap [nil … foo … backward-kill-sentence]) (24 keymap (102 . forward-word)) (6 . forward-char)) Note that storing a new binding for C-p C-f actually works by changing an entry in ctl-x-map, and this has the effect of changing the bindings of both C-p C-f and C-x C-f in the default global map. The function substitute-key-definition scans a keymap for keys that have a certain binding and rebinds them with a different binding. Another feature which is cleaner and can often produce the same results to remap one command into another (see ). substitute-key-definition — Function: substitute-key-definition olddef newdef keymap &optional oldmap replace bindingsThis function replaces olddef with newdef for any keys inkeymap that were bound to olddef. In other words,olddef is replaced with newdef wherever it appears. Thefunction returns nil.For example, this redefines C-x C-f, if you do it in an Emacs withstandard bindings: (substitute-key-definition 'find-file 'find-file-read-only (current-global-map)) If oldmap is non-nil, that changes the behavior ofsubstitute-key-definition: the bindings in oldmap determinewhich keys to rebind. The rebindings still happen in keymap, notin oldmap. Thus, you can change one map under the control of thebindings in another. For example, (substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map) puts the special deletion command in my-map for whichever keysare globally bound to the standard deletion command.Here is an example showing a keymap before and after substitution: (setq map '(keymap (?1 . olddef-1) (?2 . olddef-2) (?3 . olddef-1))) => (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1)) (substitute-key-definition 'olddef-1 'newdef map) => nil map => (keymap (49 . newdef) (50 . olddef-2) (51 . newdef)) suppress-keymap — Function: suppress-keymap keymap &optional nodigits self-insert-command overrideThis function changes the contents of the full keymap keymap byremapping self-insert-command to the command undefined(see ). This has the effect of undefining allprinting characters, thus making ordinary insertion of text impossible.suppress-keymap returns nil.If nodigits is nil, then suppress-keymap definesdigits to run digit-argument, and - to runnegative-argument. Otherwise it makes them undefined like therest of the printing characters. yank suppression quoted-insert suppressionThe suppress-keymap function does not make it impossible tomodify a buffer, as it does not suppress commands such as yankand quoted-insert. To prevent any modification of a buffer, makeit read-only (see ).Since this function modifies keymap, you would normally use iton a newly created keymap. Operating on an existing keymapthat is used for some other purpose is likely to cause trouble; forexample, suppressing global-map would make it impossible to usemost of Emacs.Most often, suppress-keymap is used to initialize localkeymaps of modes such as Rmail and Dired where insertion of text is notdesirable and the buffer is read-only. Here is an example taken fromthe file emacs/lisp/dired.el, showing how the local keymap forDired mode is set up: (setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) … Remapping Commands remapping commands A special kind of key binding, using a special “key sequence” which includes a command name, has the effect of remapping that command into another. Here's how it works. You make a key binding for a key sequence that starts with the dummy event remap, followed by the command name you want to remap. Specify the remapped definition as the definition in this binding. The remapped definition is usually a command name, but it can be any valid definition for a key binding. Here's an example. Suppose that My mode uses special commands my-kill-line and my-kill-word, which should be invoked instead of kill-line and kill-word. It can establish this by making these two command-remapping bindings in its keymap: (define-key my-mode-map [remap kill-line] 'my-kill-line) (define-key my-mode-map [remap kill-word] 'my-kill-word) Whenever my-mode-map is an active keymap, if the user types C-k, Emacs will find the standard global binding of kill-line (assuming nobody has changed it). But my-mode-map remaps kill-line to my-kill-line, so instead of running kill-line, Emacs runs my-kill-line. Remapping only works through a single level. In other words, (define-key my-mode-map [remap kill-line] 'my-kill-line) (define-key my-mode-map [remap my-kill-line] 'my-other-kill-line) does not have the effect of remapping kill-line into my-other-kill-line. If an ordinary key binding specifies kill-line, this keymap will remap it to my-kill-line; if an ordinary binding specifies my-kill-line, this keymap will remap it to my-other-kill-line. command-remapping — Function: command-remapping command &optional position keymaps This function returns the remapping for command (a symbol),given the current active keymaps. If command is not remapped(which is the usual situation), or not a symbol, the function returnsnil. position can optionally specify a buffer positionor an event position to determine the keymaps to use, as inkey-binding.If the optional argument keymaps is non-nil, itspecifies a list of keymaps to search in. This argument is ignored ifposition is non-nil. Keymaps for Translating Sequences of Events keymaps for translating events This section describes keymaps that are used during reading a key sequence, to translate certain event sequences into others. read-key-sequence checks every subsequence of the key sequence being read, as it is read, against function-key-map and then against key-translation-map. function-key-map — Variable: function-key-map This variable holds a keymap that describes the character sequences sentby function keys on an ordinary character terminal. This keymap has thesame structure as other keymaps, but is used differently: it specifiestranslations to make while reading key sequences, rather than bindingsfor key sequences.If function-key-map “binds” a key sequence k to a vectorv, then when k appears as a subsequence anywhere in akey sequence, it is replaced with the events in v.For example, VT100 terminals send ESC O P when thekeypad PF1 key is pressed. Therefore, we want Emacs to translatethat sequence of events into the single event pf1. We accomplishthis by “binding” ESC O P to [pf1] infunction-key-map, when using a VT100.Thus, typing C-c PF1 sends the character sequence C-cESC O P; later the function read-key-sequence translatesthis back into C-c PF1, which it returns as the vector[?\C-c pf1].Entries in function-key-map are ignored if they conflict withbindings made in the minor mode, local, or global keymaps. The intentis that the character sequences that function keys send should not havecommand bindings in their own right—but if they do, the ordinarybindings take priority.The value of function-key-map is usually set up automaticallyaccording to the terminal's Terminfo or Termcap entry, but sometimesthose need help from terminal-specific Lisp files. Emacs comes withterminal-specific files for many common terminals; their main purpose isto make entries in function-key-map beyond those that can bededuced from Termcap and Terminfo. See . key-translation-map — Variable: key-translation-map This variable is another keymap used just like function-key-mapto translate input events into other events. It differs fromfunction-key-map in two ways: key-translation-map goes to work after function-key-map isfinished; it receives the results of translation byfunction-key-map. Non-prefix bindings in key-translation-map override actual keybindings. For example, if C-x f has a non-prefix binding inkey-translation-map, that translation takes effect even thoughC-x f also has a key binding in the global map. Note however that actual key bindings can have an effect onkey-translation-map, even though they are overridden by it.Indeed, actual key bindings override function-key-map and thusmay alter the key sequence that key-translation-map receives.Clearly, it is better to avoid this type of situation.The intent of key-translation-map is for users to map onecharacter set to another, including ordinary characters normally boundto self-insert-command. key translation function You can use function-key-map or key-translation-map for more than simple aliases, by using a function, instead of a key sequence, as the “translation” of a key. Then this function is called to compute the translation of that key. The key translation function receives one argument, which is the prompt that was specified in read-key-sequence—or nil if the key sequence is being read by the editor command loop. In most cases you can ignore the prompt value. If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define C-c h to turn the character that follows into a Hyper character: (defun hyperify (prompt) (let ((e (read-event))) (vector (if (numberp e) (logior (lsh 1 24) e) (if (memq 'hyper (event-modifiers e)) e (add-event-modifier "H-" e)))))) (defun add-event-modifier (string e) (let ((symbol (if (symbolp e) e (car e)))) (setq symbol (intern (concat string (symbol-name symbol)))) (if (symbolp e) symbol (cons symbol (cdr e))))) (define-key function-key-map "\C-ch" 'hyperify) If you have enabled keyboard character set decoding using set-keyboard-coding-system, decoding is done after the translations listed above. See . However, in future Emacs versions, character set decoding may be done at an earlier stage. Commands for Binding Keys This section describes some convenient interactive interfaces for changing key bindings. They work by calling define-key. People often use global-set-key in their init files (see ) for simple customization. For example, (global-set-key (kbd "C-x C-\\") 'next-line) or (global-set-key [?\C-x ?\C-\\] 'next-line) or (global-set-key [(control ?x) (control ?\\)] 'next-line) redefines C-x C-\ to move down a line. (global-set-key [M-mouse-1] 'mouse-set-point) redefines the first (leftmost) mouse button, entered with the Meta key, to set point where you click. non-ASCII text in keybindings Be careful when using non-ASCII text characters in Lisp specifications of keys to bind. If these are read as multibyte text, as they usually will be in a Lisp file (see ), you must type the keys as multibyte too. For instance, if you use this: (global-set-key "ö" 'my-function) ; bind o-umlaut or (global-set-key ?ö 'my-function) ; bind o-umlaut and your language environment is multibyte Latin-1, these commands actually bind the multibyte character with code 2294, not the unibyte Latin-1 character with code 246 (M-v). In order to use this binding, you need to enter the multibyte Latin-1 character as keyboard input. One way to do this is by using an appropriate input method (see See section ``Input Methods'' in The GNU Emacs Manual). If you want to use a unibyte character in the key binding, you can construct the key sequence string using multibyte-char-to-unibyte or string-make-unibyte (see ). global-set-key — Command: global-set-key key binding This function sets the binding of key in the current global mapto binding. (global-set-key key binding) == (define-key (current-global-map) key binding) global-unset-key — Command: global-unset-key key unbinding keysThis function removes the binding of key from the currentglobal map.One use of this function is in preparation for defining a longer keythat uses key as a prefix—which would not be allowed ifkey has a non-prefix binding. For example: (global-unset-key "\C-l") => nil (global-set-key "\C-l\C-l" 'redraw-display) => nil This function is implemented simply using define-key: (global-unset-key key) == (define-key (current-global-map) key nil) local-set-key — Command: local-set-key key binding This function sets the binding of key in the current localkeymap to binding. (local-set-key key binding) == (define-key (current-local-map) key binding) local-unset-key — Command: local-unset-key key This function removes the binding of key from the currentlocal map. (local-unset-key key) == (define-key (current-local-map) key nil) Scanning Keymaps This section describes functions used to scan all the current keymaps for the sake of printing help information. accessible-keymaps — Function: accessible-keymaps keymap &optional prefix This function returns a list of all the keymaps that can be reached (viazero or more prefix keys) from keymap. The value is anassociation list with elements of the form (key .map), where key is a prefix key whose definition inkeymap is map.The elements of the alist are ordered so that the key increasesin length. The first element is always ([] . keymap),because the specified keymap is accessible from itself with a prefix ofno events.If prefix is given, it should be a prefix key sequence; thenaccessible-keymaps includes only the submaps whose prefixes startwith prefix. These elements look just as they do in the value of(accessible-keymaps); the only difference is that some elementsare omitted.In the example below, the returned alist indicates that the keyESC, which is displayed as ‘^[’, is a prefix key whosedefinition is the sparse keymap (keymap (83 . center-paragraph)(115 . foo)). (accessible-keymaps (current-local-map)) =>(([] keymap (27 keymap ; Note this keymap for ESC is repeated below. (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) ("^[" keymap (83 . center-paragraph) (115 . foo))) In the following example, C-h is a prefix key that uses a sparsekeymap starting with (keymap (118 . describe-variable)…).Another prefix, C-x 4, uses a keymap which is also the value ofthe variable ctl-x-4-map. The event mode-line is one ofseveral dummy events used as prefixes for mouse actions in special partsof a window. (accessible-keymaps (current-global-map)) => (([] keymap [set-mark-command beginning-of-line … delete-backward-char]) ("^H" keymap (118 . describe-variable) … (8 . help-for-help)) ("^X" keymap [x-flush-mouse-queue … backward-kill-sentence]) ("^[" keymap [mark-sexp backward-sexp … backward-kill-word]) ("^X4" keymap (15 . display-buffer) …) ([mode-line] keymap (S-mouse-2 . mouse-split-window-horizontally) …)) These are not all the keymaps you would see in actuality. map-keymap — Function: map-keymap function keymap The function map-keymap calls function oncefor each binding in keymap. It passes two arguments,the event type and the value of the binding. If keymaphas a parent, the parent's bindings are included as well.This works recursively: if the parent has itself a parent, then thegrandparent's bindings are also included and so on.This function is the cleanest way to examine all the bindingsin a keymap. where-is-internal — Function: where-is-internal command &optional keymap firstonly noindirect no-remap This function is a subroutine used by the where-is command(see See section ``Help'' in The GNU Emacs Manual). It returns a listof all key sequences (of any length) that are bound to command in aset of keymaps.The argument command can be any object; it is compared with allkeymap entries using eq.If keymap is nil, then the maps used are the current activekeymaps, disregarding overriding-local-map (that is, pretendingits value is nil). If keymap is a keymap, then themaps searched are keymap and the global keymap. If keymapis a list of keymaps, only those keymaps are searched.Usually it's best to use overriding-local-map as the expressionfor keymap. Then where-is-internal searches precisely thekeymaps that are active. To search only the global map, pass(keymap) (an empty keymap) as keymap.If firstonly is non-ascii, then the value is a singlevector representing the first key sequence found, rather than a list ofall possible key sequences. If firstonly is t, then thevalue is the first key sequence, except that key sequences consistingentirely of ASCII characters (or meta variants of ASCIIcharacters) are preferred to all other key sequences and that thereturn value can never be a menu binding.If noindirect is non-nil, where-is-internal doesn'tfollow indirect keymap bindings. This makes it possible to search foran indirect definition itself.When command remapping is in effect (see ),where-is-internal figures out when a command will be run due toremapping and reports keys accordingly. It also returns nil ifcommand won't really be run because it has been remapped to someother command. However, if no-remap is non-nil.where-is-internal ignores remappings. (where-is-internal 'describe-function) => ([8 102] [f1 102] [help 102] [menu-bar help-menu describe describe-function]) describe-bindings — Command: describe-bindings &optional prefix buffer-or-name This function creates a listing of all current key bindings, anddisplays it in a buffer named ‘*Help*’. The text is grouped bymodes—minor modes first, then the major mode, then global bindings.If prefix is non-nil, it should be a prefix key; then thelisting includes only keys that start with prefix.The listing describes meta characters as ESC followed by thecorresponding non-meta character.When several characters with consecutive ASCII codes have thesame definition, they are shown together, as‘firstchar..lastchar’. In this instance, you need toknow the ASCII codes to understand which characters this means.For example, in the default global map, the characters ‘SPC.. ~’ are described by a single line. SPC is ASCII 32,~ is ASCII 126, and the characters between them include allthe normal printing characters, (e.g., letters, digits, punctuation,etc.); all these characters are bound to self-insert-command.If buffer-or-name is non-nil, it should be a buffer or abuffer name. Then describe-bindings lists that buffer's bindings,instead of the current buffer's. Menu Keymaps menu keymaps A keymap can operate as a menu as well as defining bindings for keyboard keys and mouse buttons. Menus are usually actuated with the mouse, but they can function with the keyboard also. If a menu keymap is active for the next input event, that activates the keyboard menu feature. Defining Menus defining menus menu prompt string prompt string (of menu) A keymap acts as a menu if it has an overall prompt string, which is a string that appears as an element of the keymap. (See .) The string should describe the purpose of the menu's commands. Emacs displays the overall prompt string as the menu title in some cases, depending on the toolkit (if any) used for displaying menus.It is required for menus which do not use a toolkit, e.g. under MS-DOS. Keyboard menus also display the overall prompt string. The easiest way to construct a keymap with a prompt string is to specify the string as an argument when you call make-keymap, make-sparse-keymap (see ), or define-prefix-command (see ). If you do not want the keymap to operate as a menu, don't specify a prompt string for it. keymap-prompt — Function: keymap-prompt keymap This function returns the overall prompt string of keymap,or nil if it has none. The menu's items are the bindings in the keymap. Each binding associates an event type to a definition, but the event types have no significance for the menu appearance. (Usually we use pseudo-events, symbols that the keyboard cannot generate, as the event types for menu item bindings.) The menu is generated entirely from the bindings that correspond in the keymap to these events. The order of items in the menu is the same as the order of bindings in the keymap. Since define-key puts new bindings at the front, you should define the menu items starting at the bottom of the menu and moving to the top, if you care about the order. When you add an item to an existing menu, you can specify its position in the menu using define-key-after (see ). Simple Menu Items The simpler (and original) way to define a menu item is to bind some event type (it doesn't matter what event type) to a binding like this: (item-string . real-binding) The car, item-string, is the string to be displayed in the menu. It should be short—preferably one to three words. It should describe the action of the command it corresponds to. Note that it is not generally possible to display non-ASCII text in menus. It will work for keyboard menus and will work to a large extent when Emacs is built with the Gtk+ toolkit.In this case, the text is first encoded using the utf-8 coding system and then rendered by the toolkit as it sees fit. You can also supply a second string, called the help string, as follows: (item-string help . real-binding) help specifies a “help-echo” string to display while the mouse is on that item in the same way as help-echo text properties (see ). As far as define-key is concerned, item-string and help-string are part of the event's binding. However, lookup-key returns just real-binding, and only real-binding is used for executing the key. If real-binding is nil, then item-string appears in the menu but cannot be selected. If real-binding is a symbol and has a non-nil menu-enable property, that property is an expression that controls whether the menu item is enabled. Every time the keymap is used to display a menu, Emacs evaluates the expression, and it enables the menu item only if the expression's value is non-nil. When a menu item is disabled, it is displayed in a “fuzzy” fashion, and cannot be selected. The menu bar does not recalculate which items are enabled every time you look at a menu. This is because the X toolkit requires the whole tree of menus in advance. To force recalculation of the menu bar, call force-mode-line-update (see ). You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this: (item-string [ help ] (key-binding-data) . real-binding) Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't mention keyboard equivalents in the item strings themselves, since that is redundant. Extended Menu Items menu-item An extended-format menu item is a more flexible and also cleaner alternative to the simple format. You define an event type with a binding that's a list starting with the symbol menu-item. For a non-selectable string, the binding looks like this: (menu-item item-name) A string starting with two or more dashes specifies a separator line; see . To define a real menu item which can be selected, the extended format binding looks like this: (menu-item item-name real-binding . item-property-list) Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information. When an equivalent keyboard key binding is cached, the extended menu item binding looks like this: (menu-item item-name real-binding (key-binding-data) . item-property-list) Here is a table of the properties that are supported: :enable form The result of evaluating form determines whether the item isenabled (non-nil means yes). If the item is not enabled,you can't really click on it. :visible form The result of evaluating form determines whether the item shouldactually appear in the menu (non-nil means yes). If the itemdoes not appear, then the menu is displayed as if this item werenot defined at all. :help help The value of this property, help, specifies a “help-echo” stringto display while the mouse is on that item. This is displayed in thesame way as help-echo text properties (see ).Note that this must be a constant string, unlike the help-echoproperty for text and overlays. :button (type . selected) This property provides a way to define radio buttons and toggle buttons.The car, type, says which: it should be :toggle or:radio. The cdr, selected, should be a form; theresult of evaluating it says whether this button is currently selected.A toggle is a menu item which is labeled as either “on” or “off”according to the value of selected. The command itself shouldtoggle selected, setting it to t if it is nil,and to nil if it is t. Here is how the menu itemto toggle the debug-on-error flag is defined: (menu-item "Debug on Error" toggle-debug-on-error :button (:toggle . (and (boundp 'debug-on-error) debug-on-error))) This works because toggle-debug-on-error is defined as a commandwhich toggles the variable debug-on-error.Radio buttons are a group of menu items, in which at any time oneand only one is “selected.” There should be a variable whose valuesays which one is selected at any time. The selected form foreach radio button in the group should check whether the variable has theright value for selecting that button. Clicking on the button shouldset the variable so that the button you clicked on becomes selected. :key-sequence key-sequence This property specifies which key sequence is likely to be bound to thesame command invoked by this menu item. If you specify the right keysequence, that makes preparing the menu for display run much faster.If you specify the wrong key sequence, it has no effect; before Emacsdisplays key-sequence in the menu, it verifies thatkey-sequence is really equivalent to this menu item. :key-sequence nil This property indicates that there is normally no key binding which isequivalent to this menu item. Using this property saves time inpreparing the menu for display, because Emacs does not need to searchthe keymaps for a keyboard equivalent for this menu item.However, if the user has rebound this item's definition to a keysequence, Emacs ignores the :keys property and finds the keyboardequivalent anyway. :keys string This property specifies that string is the string to displayas the keyboard equivalent for this menu item. You can usethe ‘\\[...]’ documentation construct in string. :filter filter-fn This property provides a way to compute the menu item dynamically.The property value filter-fn should be a function of one argument;when it is called, its argument will be real-binding. Thefunction should return the binding to use instead.Emacs can call this function at any time that it does redisplay oroperates on menu data structures, so you should write it so it cansafely be called at any time. Menu Separators menu separators A menu separator is a kind of menu item that doesn't display any text—instead, it divides the menu into subparts with a horizontal line. A separator looks like this in the menu keymap: (menu-item separator-type) where separator-type is a string starting with two or more dashes. In the simplest case, separator-type consists of only dashes. That specifies the default kind of separator. (For compatibility, "" and - also count as separators.) Certain other values of separator-type specify a different style of separator. Here is a table of them: "--no-line""--space" An extra vertical space, with no actual line. "--single-line" A single line in the menu's foreground color. "--double-line" A double line in the menu's foreground color. "--single-dashed-line" A single dashed line in the menu's foreground color. "--double-dashed-line" A double dashed line in the menu's foreground color. "--shadow-etched-in" A single line with a 3D sunken appearance. This is the default,used separators consisting of dashes only. "--shadow-etched-out" A single line with a 3D raised appearance. "--shadow-etched-in-dash" A single dashed line with a 3D sunken appearance. "--shadow-etched-out-dash" A single dashed line with a 3D raised appearance. "--shadow-double-etched-in" Two lines with a 3D sunken appearance. "--shadow-double-etched-out" Two lines with a 3D raised appearance. "--shadow-double-etched-in-dash" Two dashed lines with a 3D sunken appearance. "--shadow-double-etched-out-dash" Two dashed lines with a 3D raised appearance. You can also give these names in another style, adding a colon after the double-dash and replacing each single dash with capitalization of the following word. Thus, "--:singleLine", is equivalent to "--single-line". Some systems and display toolkits don't really handle all of these separator types. If you use a type that isn't supported, the menu displays a similar kind of separator that is supported. Alias Menu Items Sometimes it is useful to make menu items that use the “same” command but with different enable conditions. The best way to do this in Emacs now is with extended menu items; before that feature existed, it could be done by defining alias commands and using them in menu items. Here's an example that makes two aliases for toggle-read-only and gives them different enable conditions: (defalias 'make-read-only 'toggle-read-only) (put 'make-read-only 'menu-enable '(not buffer-read-only)) (defalias 'make-writable 'toggle-read-only) (put 'make-writable 'menu-enable 'buffer-read-only) When using aliases in menus, often it is useful to display the equivalent key bindings for the “real” command name, not the aliases (which typically don't have any key bindings except for the menu itself). To request this, give the alias symbol a non-nil menu-alias property. Thus, (put 'make-read-only 'menu-alias t) (put 'make-writable 'menu-alias t) causes menu items for make-read-only and make-writable to show the keyboard bindings for toggle-read-only. Menus and the Mouse The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice—see .) If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.) It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button. A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with ‘@’. The rest of the item string becomes the name of the pane. See the file lisp/mouse.el for an example of this. Any ordinary bindings with ‘@’-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps. X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with ‘@’ or not. In a toolkit version of Emacs, the only thing special about ‘@’ at the beginning of an item string is that the ‘@’ doesn't appear in the menu item. Multiple keymaps that define the same menu prefix key produce separate panes or separate submenus. Menus and the Keyboard When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the keymap operates as a keyboard menu; the user specifies the next event by choosing a menu item with the keyboard. Emacs displays the keyboard menu with the map's overall prompt string, followed by the alternatives (the item strings of the map's bindings), in the echo area. If the bindings don't all fit at once, the user can type SPC to see the next line of alternatives. Successive uses of SPC eventually get to the end of the menu and then cycle around to the beginning. (The variable menu-prompt-more-char specifies which character is used for this; SPC is the default.) When the user has found the desired alternative from the menu, he or she should type the corresponding character—the one whose binding is that alternative. This way of using menus in an Emacs-like editor was inspired by the Hierarkey system. menu-prompt-more-char — Variable: menu-prompt-more-char This variable specifies the character to use to ask to seethe next line of a menu. Its initial value is 32, the codefor SPC. Menu Example menu definition example Here is a complete example of defining a menu keymap. It is the definition of the ‘Replace’ submenu in the ‘Edit’ menu in the menu bar, and it uses the extended menu item format (see ). First we create the keymap, and give it a name: (defvar menu-bar-replace-menu (make-sparse-keymap "Replace")) Next we define the menu items: (define-key menu-bar-replace-menu [tags-repl-continue] '(menu-item "Continue Replace" tags-loop-continue :help "Continue last tags replace operation")) (define-key menu-bar-replace-menu [tags-repl] '(menu-item "Replace in tagged files" tags-query-replace :help "Interactively replace a regexp in all tagged files")) (define-key menu-bar-replace-menu [separator-replace-tags] '(menu-item "--")) ;; … Note the symbols which the bindings are “made for”; these appear inside square brackets, in the key sequence being defined. In some cases, this symbol is the same as the command name; sometimes it is different. These symbols are treated as “function keys,” but they are not real function keys on the keyboard. They do not affect the functioning of the menu itself, but they are “echoed” in the echo area when the user selects from the menu, and they appear in the output of where-is and apropos. The menu in this example is intended for use with the mouse. If a menu is intended for use with the keyboard, that is, if it is bound to a key sequence ending with a keyboard event, then the menu items should be bound to characters or “real” function keys, that can be typed with the keyboard. The binding whose definition is ("--") is a separator line. Like a real menu item, the separator has a key symbol, in this case separator-replace-tags. If one menu has two separators, they must have two different key symbols. Here is how we make this menu appear as an item in the parent menu: (define-key menu-bar-edit-menu [replace] (list 'menu-item "Replace" menu-bar-replace-menu)) Note that this incorporates the submenu keymap, which is the value of the variable menu-bar-replace-menu, rather than the symbol menu-bar-replace-menu itself. Using that symbol in the parent menu item would be meaningless because menu-bar-replace-menu is not a command. If you wanted to attach the same replace menu to a mouse click, you can do it this way: (define-key global-map [C-S-down-mouse-1] menu-bar-replace-menu) The Menu Bar menu bar Most window systems allow each frame to have a menu bar—a permanently displayed menu stretching horizontally across the top of the frame. The items of the menu bar are the subcommands of the fake “function key” menu-bar, as defined in the active keymaps. To add an item to the menu bar, invent a fake “function key” of your own (let's call it key), and make a binding for the key sequence [menu-bar key]. Most often, the binding is a menu keymap, so that pressing a button on the menu bar item leads to another menu. When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined menu containing all the subcommands of that item—the global subcommands, the local subcommands, and the minor mode subcommands. The variable overriding-local-map is normally ignored when determining the menu bar contents. That is, the menu bar is computed from the keymaps that would be active if overriding-local-map were nil. See . In order for a frame to display a menu bar, its menu-bar-lines parameter must be greater than zero. Emacs uses just one line for the menu bar itself; if you specify more than one line, the other lines serve to separate the menu bar from the windows in the frame. We recommend 1 or 2 as the value of menu-bar-lines. See . Here's an example of setting up a menu bar item: (modify-frame-parameters (selected-frame) '((menu-bar-lines . 2))) ;; Make a menu keymap (with a prompt string) ;; and make it the menu bar item's definition. (define-key global-map [menu-bar words] (cons "Words" (make-sparse-keymap "Words"))) ;; Define specific subcommands in this menu. (define-key global-map [menu-bar words forward] '("Forward word" . forward-word)) (define-key global-map [menu-bar words backward] '("Backward word" . backward-word)) A local keymap can cancel a menu bar item made by the global keymap by rebinding the same fake function key with undefined as the binding. For example, this is how Dired suppresses the ‘Edit’ menu bar item: (define-key dired-mode-map [menu-bar edit] 'undefined) edit is the fake function key used by the global map for the ‘Edit’ menu bar item. The main reason to suppress a global menu bar item is to regain space for mode-specific items. menu-bar-final-items — Variable: menu-bar-final-items Normally the menu bar shows global items followed by items defined by thelocal maps.This variable holds a list of fake function keys for items to display atthe end of the menu bar rather than in normal sequence. The defaultvalue is (help-menu); thus, the ‘Help’ menu item normally appearsat the end of the menu bar, following local menu items. menu-bar-update-hook — Variable: menu-bar-update-hook This normal hook is run by redisplay to update the menu bar contents,before redisplaying the menu bar. You can use it to update submenuswhose contents should vary. Since this hook is run frequently, weadvise you to ensure that the functions it calls do not take much timein the usual case. Tool bars tool bar A tool bar is a row of icons at the top of a frame, that execute commands when you click on them—in effect, a kind of graphical menu bar. The frame parameter tool-bar-lines (X resource ‘toolBar’) controls how many lines' worth of height to reserve for the tool bar. A zero value suppresses the tool bar. If the value is nonzero, and auto-resize-tool-bars is non-nil, the tool bar expands and contracts automatically as needed to hold the specified contents. If the value of auto-resize-tool-bars is grow-only, the tool bar expands automatically, but does not contract automatically. To contract the tool bar, the user has to redraw the frame by entering C-l. The tool bar contents are controlled by a menu keymap attached to a fake “function key” called tool-bar (much like the way the menu bar is controlled). So you define a tool bar item using define-key, like this: (define-key global-map [tool-bar key] item) where key is a fake “function key” to distinguish this item from other items, and item is a menu item key binding (see ), which says how to display this item and how it behaves. The usual menu keymap item properties, :visible, :enable, :button, and :filter, are useful in tool bar bindings and have their normal meanings. The real-binding in the item must be a command, not a keymap; in other words, it does not work to define a tool bar icon as a prefix key. The :help property specifies a “help-echo” string to display while the mouse is on that item. This is displayed in the same way as help-echo text properties (see ). In addition, you should use the :image property; this is how you specify the image to display in the tool bar: :image image images is either a single image specification or a vector of fourimage specifications. If you use a vector of four,one of them is used, depending on circumstances: item 0 Used when the item is enabled and selected. item 1 Used when the item is enabled and deselected. item 2 Used when the item is disabled and selected. item 3 Used when the item is disabled and deselected. If image is a single image specification, Emacs draws the tool bar button in disabled state by applying an edge-detection algorithm to the image. The default tool bar is defined so that items specific to editing do not appear for major modes whose command symbol has a mode-class property of special (see ). Major modes may add items to the global bar by binding [tool-bar foo] in their local map. It makes sense for some major modes to replace the default tool bar items completely, since not many can be accommodated conveniently, and the default bindings make this easy by using an indirection through tool-bar-map. tool-bar-map — Variable: tool-bar-map By default, the global map binds [tool-bar] as follows: (global-set-key [tool-bar] '(menu-item "tool bar" ignore :filter (lambda (ignore) tool-bar-map))) Thus the tool bar map is derived dynamically from the value of variabletool-bar-map and you should normally adjust the default (global)tool bar by changing that map. Major modes may replace the global barcompletely by making tool-bar-map buffer-local and set to akeymap containing only the desired items. Info mode provides anexample. There are two convenience functions for defining tool bar items, as follows. tool-bar-add-item — Function: tool-bar-add-item icon def key &rest props This function adds an item to the tool bar by modifyingtool-bar-map. The image to use is defined by icon, whichis the base name of an XPM, XBM or PBM image file to be located byfind-image. Given a value ‘"exit"’, say, exit.xpm,exit.pbm and exit.xbm would be searched for in that orderon a color display. On a monochrome display, the search order is‘.pbm’, ‘.xbm’ and ‘.xpm’. The binding to use is thecommand def, and key is the fake function key symbol in theprefix keymap. The remaining arguments props are additionalproperty list elements to add to the menu item specification.To define items in some local map, bind tool-bar-map withlet around calls of this function: (defvar foo-tool-bar-map (let ((tool-bar-map (make-sparse-keymap))) (tool-bar-add-item …) … tool-bar-map)) tool-bar-add-item-from-menu — Function: tool-bar-add-item-from-menu command icon &optional map &rest props This function is a convenience for defining tool bar items which areconsistent with existing menu bar bindings. The binding ofcommand is looked up in the menu bar in map (defaultglobal-map) and modified to add an image specification foricon, which is found in the same way as bytool-bar-add-item. The resulting binding is then placed intool-bar-map, so use this function only for global tool baritems.map must contain an appropriate keymap bound to[menu-bar]. The remaining arguments props are additionalproperty list elements to add to the menu item specification. tool-bar-local-item-from-menu — Function: tool-bar-local-item-from-menu command icon in-map &optional from-map &rest props This function is used for making non-global tool bar items. Use itlike tool-bar-add-item-from-menu except that in-mapspecifies the local map to make the definition in. The argumentfrom-map is like the map argument oftool-bar-add-item-from-menu. auto-resize-tool-bar — Variable: auto-resize-tool-bar If this variable is non-nil, the tool bar automatically resizes toshow all defined tool bar items—but not larger than a quarter of theframe's height.If the value is grow-only, the tool bar expands automatically,but does not contract automatically. To contract the tool bar, theuser has to redraw the frame by entering C-l. auto-raise-tool-bar-buttons — Variable: auto-raise-tool-bar-buttons If this variable is non-nil, tool bar items displayin raised form when the mouse moves over them. tool-bar-button-margin — Variable: tool-bar-button-margin This variable specifies an extra margin to add around tool bar items.The value is an integer, a number of pixels. The default is 4. tool-bar-button-relief — Variable: tool-bar-button-relief This variable specifies the shadow width for tool bar items.The value is an integer, a number of pixels. The default is 1. tool-bar-border — Variable: tool-bar-border This variable specifies the height of the border drawn below the toolbar area. An integer value specifies height as a number of pixels.If the value is one of internal-border-width (the default) orborder-width, the tool bar border height corresponds to thecorresponding frame parameter. You can define a special meaning for clicking on a tool bar item with the shift, control, meta, etc., modifiers. You do this by setting up additional items that relate to the original item through the fake function keys. Specifically, the additional items should use the modified versions of the same fake function key used to name the original item. Thus, if the original item was defined this way, (define-key global-map [tool-bar shell] '(menu-item "Shell" shell :image (image :type xpm :file "shell.xpm"))) then here is how you can define clicking on the same tool bar image with the shift modifier: (define-key global-map [tool-bar S-shell] 'some-command) See , for more information about how to add modifiers to function keys. Modifying Menus When you insert a new item in an existing menu, you probably want to put it in a particular place among the menu's existing items. If you use define-key to add the item, it normally goes at the front of the menu. To put it elsewhere in the menu, use define-key-after: define-key-after — Function: define-key-after map key binding &optional after Define a binding in map for key, with value binding,just like define-key, but position the binding in map afterthe binding for the event after. The argument key should beof length one—a vector or string with just one element. Butafter should be a single event type—a symbol or a character, nota sequence. The new binding goes after the binding for after. Ifafter is t or is omitted, then the new binding goes last, atthe end of the keymap. However, new bindings are added before anyinherited keymap.Here is an example: (define-key-after my-menu [drink] '("Drink" . drink-command) 'eat) makes a binding for the fake function key DRINK and puts itright after the binding for EAT.Here is how to insert an item called ‘Work’ in the ‘Signals’menu of Shell mode, after the item break: (define-key-after (lookup-key shell-mode-map [menu-bar signals]) [work] '("Work" . work-command) 'break) <setfilename>../info/modes</setfilename> Major and Minor Modes mode A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually. This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see , and . Hooks hooks A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the init file (see ), but Lisp programs can set them also. See , for a list of standard hook variables. normal hook Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. By convention, whenever the hook name ends in ‘-hook’, that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way. Every major mode function is supposed to run a normal hook called the mode hook as the one of the last steps of initialization. This makes it easy for a user to customize the behavior of the mode, by overriding the buffer-local variable assignments already made by the mode. Most minor mode functions also run a mode hook at the end. But hooks are used in other contexts too. For example, the hook suspend-hook runs just before Emacs suspends itself (see ). The recommended way to add a hook function to a normal hook is by calling add-hook (see below). The hook functions may be any of the valid kinds of functions that funcall accepts (see ). Most normal hook variables are initially void; add-hook knows how to deal with this. You can add hooks either globally or buffer-locally with add-hook. abnormal hook If the hook variable's name does not end with ‘-hook’, that indicates it is probably an abnormal hook. That means the hook functions are called with arguments, or their return values are used in some way. The hook's documentation says how the functions are called. You can use add-hook to add a function to an abnormal hook, but you must write the function to follow the hook's calling convention. By convention, abnormal hook names end in ‘-functions’ or ‘-hooks’. If the variable's name ends in ‘-function’, then its value is just a single function, not a list of functions. Here's an example that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode: (add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill) At the appropriate time, Emacs uses the run-hooks function to run particular hooks. run-hooks — Function: run-hooks &rest hookvars This function takes one or more normal hook variable names asarguments, and runs each hook in turn. Each argument should be asymbol that is a normal hook variable. These arguments are processedin the order specified.If a hook variable has a non-nil value, that value should be alist of functions. run-hooks calls all the functions, one byone, with no arguments.The hook variable's value can also be a single function—either alambda expression or a symbol with a function definition—whichrun-hooks calls. But this usage is obsolete. run-hook-with-args — Function: run-hook-with-args hook &rest args This function is the way to run an abnormal hook and always call allof the hook functions. It calls each of the hook functions one byone, passing each of them the arguments args. run-hook-with-args-until-failure — Function: run-hook-with-args-until-failure hook &rest args This function is the way to run an abnormal hook until one of the hookfunctions fails. It calls each of the hook functions, passing each ofthem the arguments args, until some hook function returnsnil. It then stops and returns nil. If none of thehook functions return nil, it returns a non-nil value. run-hook-with-args-until-success — Function: run-hook-with-args-until-success hook &rest args This function is the way to run an abnormal hook until a hook functionsucceeds. It calls each of the hook functions, passing each of themthe arguments args, until some hook function returnsnon-nil. Then it stops, and returns whatever was returned bythe last hook function that was called. If all hook functions returnnil, it returns nil as well. add-hook — Function: add-hook hook function &optional append local This function is the handy way to add function function to hookvariable hook. You can use it for abnormal hooks as well as fornormal hooks. function can be any Lisp function that can acceptthe proper number of arguments for hook. For example, (add-hook 'text-mode-hook 'my-text-hook-function) adds my-text-hook-function to the hook called text-mode-hook.If function is already present in hook (comparing usingequal), then add-hook does not add it a second time.It is best to design your hook functions so that the order in which theyare executed does not matter. Any dependence on the order is “askingfor trouble.” However, the order is predictable: normally,function goes at the front of the hook list, so it will beexecuted first (barring another add-hook call). If the optionalargument append is non-nil, the new hook function goes atthe end of the hook list and will be executed last.add-hook can handle the cases where hook is void or itsvalue is a single function; it sets or changes the value to a list offunctions.If local is non-nil, that says to add function tothe buffer-local hook list instead of to the global hook list. Ifneeded, this makes the hook buffer-local and adds t to thebuffer-local value. The latter acts as a flag to run the hookfunctions in the default value as well as in the local value. remove-hook — Function: remove-hook hook function &optional local This function removes function from the hook variablehook. It compares function with elements of hookusing equal, so it works for both symbols and lambdaexpressions.If local is non-nil, that says to remove functionfrom the buffer-local hook list instead of from the global hook list. Major Modes major mode Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time. For each major mode there is a function to switch to that mode in the current buffer; its name should end in ‘-mode’. These functions work by setting buffer-local variable bindings and other data associated with the buffer, such as a local keymap. The effect lasts until you switch to another major mode in the same buffer. Major Mode Basics Fundamental mode The least specialized major mode is called Fundamental mode. This mode has no mode-specific definitions or variable settings, so each Emacs command behaves in its default manner, and each option is in its default state. All other major modes redefine various keys and options. For example, Lisp Interaction mode provides special key bindings for C-j (eval-print-last-sexp), TAB (lisp-indent-line), and other keys. When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult). If the new mode is similar to an old one, it is often unwise to modify the old one to serve two purposes, since it may become harder to use and maintain. Instead, copy and rename an existing major mode definition and alter the copy—or use define-derived-mode to define a derived mode (see ). For example, Rmail Edit mode is a major mode that is very similar to Text mode except that it provides two additional commands. Its definition is distinct from that of Text mode, but uses that of Text mode. Even if the new mode is not an obvious derivative of any other mode, it is convenient to use define-derived-mode with a nil parent argument, since it automatically enforces the most important coding conventions for you. For a very simple programming language major mode that handles comments and fontification, you can use define-generic-mode. See . Rmail Edit mode offers an example of changing the major mode temporarily for a buffer, so it can be edited in a different way (with ordinary Emacs commands rather than Rmail commands). In such cases, the temporary major mode usually provides a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using an alternative major mode avoids this limitation. See . The standard GNU Emacs Lisp library directory tree contains the code for several major modes, in files such as text-mode.el, texinfo.el, lisp-mode.el, c-mode.el, and rmail.el. They are found in various subdirectories of the lisp directory. You can study these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode. Major Mode Conventions major mode conventions conventions for writing major modes The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode. (Fundamental mode is an exception to many of these conventions, because its definition is to present the global state of Emacs.) This list of conventions is only partial, because each major mode should aim for consistency in general with other Emacs major modes. This makes Emacs as a whole more coherent. It is impossible to list here all the possible points where this issue might come up; if the Emacs developers point out an area where your major mode deviates from the usual conventions, please make it compatible. Define a command whose name ends in ‘-mode’, with no arguments,that switches to the new mode in the current buffer. This commandshould set up the keymap, syntax table, and buffer-local variables in anexisting buffer, without changing the buffer's contents. Write a documentation string for this command that describes thespecial commands available in this mode. C-h m(describe-mode) in your mode will display this string.The documentation string may include the special documentationsubstrings, ‘\[command]’, ‘\{keymap}’, and‘\<keymap>’, which enable the documentation to adaptautomatically to the user's own key bindings. See . The major mode command should start by callingkill-all-local-variables. This runs the normal hookchange-major-mode-hook, then gets rid of the buffer-localvariables of the major mode previously in effect. See . The major mode command should set the variable major-mode to themajor mode command symbol. This is how describe-mode discoverswhich documentation to print. The major mode command should set the variable mode-name to the“pretty” name of the mode, as a string. This string appears in themode line. functions in modesSince all global names are in the same name space, all the globalvariables, constants, and functions that are part of the mode shouldhave names that start with the major mode name (or with an abbreviationof it if the name is long). See . In a major mode for editing some kind of structured text, such as aprogramming language, indentation of text according to structure isprobably useful. So the mode should set indent-line-functionto a suitable function, and probably customize other variablesfor indentation. keymaps in modesThe major mode should usually have its own keymap, which is used as thelocal keymap in all buffers in that mode. The major mode command shouldcall use-local-map to install this local map. See , for more information.This keymap should be stored permanently in a global variable namedmodename-mode-map. Normally the library that defines themode sets this variable.See , for advice about how to write the code to setup the mode's keymap variable. The key sequences bound in a major mode keymap should usually start withC-c, followed by a control character, a digit, or {,}, <, >, : or ;. The other punctuationcharacters are reserved for minor modes, and ordinary letters arereserved for users.A major mode can also rebind the keys M-n, M-p andM-s. The bindings for M-n and M-p should normallybe some kind of “moving forward and backward,” but this does notnecessarily mean cursor motion.It is legitimate for a major mode to rebind a standard key sequence ifit provides a command that does “the same job” in a way bettersuited to the text this mode is used for. For example, a major modefor editing a programming language might redefine C-M-a to“move to the beginning of a function” in a way that works better forthat language.It is also legitimate for a major mode to rebind a standard keysequence whose standard meaning is rarely useful in that mode. Forinstance, minibuffer modes rebind M-r, whose standard meaning israrely of any use in the minibuffer. Major modes such as Dired orRmail that do not allow self-insertion of text can reasonably redefineletters and other printing characters as special commands. Major modes modes for editing text should not define RET to doanything other than insert a newline. However, it is ok forspecialized modes for text that users don't directly edit, such asDired and Info modes, to redefine RET to do something entirelydifferent. Major modes should not alter options that are primarily a matter of userpreference, such as whether Auto-Fill mode is enabled. Leave this toeach user to decide. However, a major mode should customize othervariables so that Auto-Fill mode will work usefully if the userdecides to use it. syntax tables in modesThe mode may have its own syntax table or may share one with otherrelated modes. If it has its own syntax table, it should store this ina variable named modename-mode-syntax-table. See . If the mode handles a language that has a syntax for comments, it shouldset the variables that define the comment syntax. See See section ``Options Controlling Comments'' in The GNU Emacs Manual. abbrev tables in modesThe mode may have its own abbrev table or may share one with otherrelated modes. If it has its own abbrev table, it should store thisin a variable named modename-mode-abbrev-table. If themajor mode command defines any abbrevs itself, it should pass tfor the system-flag argument to define-abbrev.See . The mode should specify how to do highlighting for Font Lock mode, bysetting up a buffer-local value for the variablefont-lock-defaults (see ). The mode should specify how Imenu should find the definitions orsections of a buffer, by setting up a buffer-local value for thevariable imenu-generic-expression, for the two variablesimenu-prev-index-position-function andimenu-extract-index-name-function, or for the variableimenu-create-index-function (see ). The mode can specify a local value foreldoc-documentation-function to tell ElDoc mode how to handlethis mode. Use defvar or defcustom to set mode-related variables, sothat they are not reinitialized if they already have a value. (Suchreinitialization could discard customizations made by the user.) buffer-local variables in modesTo make a buffer-local binding for an Emacs customization variable, usemake-local-variable in the major mode command, notmake-variable-buffer-local. The latter function would make thevariable local to every buffer in which it is subsequently set, whichwould affect buffers that do not use this mode. It is undesirable for amode to have such global effects. See .With rare exceptions, the only reasonable way to usemake-variable-buffer-local in a Lisp package is for a variablewhich is used only within that package. Using it on a variable used byother packages would interfere with them. mode hook major mode hookEach major mode should have a normal mode hook namedmodename-mode-hook. The very last thing the major mode commandshould do is to call run-mode-hooks. This runs the mode hook,and then runs the normal hook after-change-major-mode-hook.See . The major mode command may start by calling some other major modecommand (called the parent mode) and then alter some of itssettings. A mode that does this is called a derived mode. Therecommended way to define one is to use define-derived-mode,but this is not required. Such a mode should call the parent modecommand inside a delay-mode-hooks form. (Usingdefine-derived-mode does this automatically.) See , and . If something special should be done if the user switches a buffer fromthis mode to any other major mode, this mode can set up a buffer-localvalue for change-major-mode-hook (see ). If this mode is appropriate only for specially-prepared text, then themajor mode command symbol should have a property named mode-classwith value special, put on as follows: mode-class (property) special (put 'funny-mode 'mode-class 'special) This tells Emacs that new buffers created while the current buffer isin Funny mode should not inherit Funny mode, in casedefault-major-mode is nil. Modes such as Dired, Rmail,and Buffer List use this feature. If you want to make the new mode the default for files with certainrecognizable names, add an element to auto-mode-alist to selectthe mode for those file names (see ). If youdefine the mode command to autoload, you should add this element inthe same file that calls autoload. If you use an autoloadcookie for the mode command, you can also use an autoload cookie forthe form that adds the element (see ). If you donot autoload the mode command, it is sufficient to add the element inthe file that contains the mode definition. In the comments that document the file, you should provide a sampleautoload form and an example of how to add toauto-mode-alist, that users can include in their init files(see ). mode loadingThe top-level forms in the file defining the mode should be written sothat they may be evaluated more than once without adverse consequences.Even if you never load the file more than once, someone else will. How Emacs Chooses a Major Mode major mode, automatic selection Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited. It also processes local variables specified in the file text. fundamental-mode — Command: fundamental-mode Fundamental mode is a major mode that is not specialized for anythingin particular. Other major modes are defined in effect by comparisonwith this one—their definitions say what to change, starting fromFundamental mode. The fundamental-mode function does notrun any mode hooks; you're not supposed to customize it. (If you want Emacsto behave differently in Fundamental mode, change the globalstate of Emacs.) normal-mode — Command: normal-mode &optional find-file This function establishes the proper major mode and buffer-local variablebindings for the current buffer. First it calls set-auto-mode(see below), then it runs hack-local-variables to parse, andbind or evaluate as appropriate, the file's local variables(see ).If the find-file argument to normal-mode is non-nil,normal-mode assumes that the find-file function is callingit. In this case, it may process local variables in the ‘-*-’line or at the end of the file. The variableenable-local-variables controls whether to do so. See See section ``Local Variables in Files'' in The GNU Emacs Manual,for the syntax of the local variables section of a file.If you run normal-mode interactively, the argumentfind-file is normally nil. In this case,normal-mode unconditionally processes any file local variables.If normal-mode processes the local variables list and this listspecifies a major mode, that mode overrides any mode chosen byset-auto-mode. If neither set-auto-mode norhack-local-variables specify a major mode, the buffer stays inthe major mode determined by default-major-mode (see below). file mode specification errornormal-mode uses condition-case around the call to themajor mode function, so errors are caught and reported as a ‘Filemode specification error’, followed by the original error message. set-auto-mode — Function: set-auto-mode &optional keep-mode-if-same visited file mode This function selects the major mode that is appropriate for thecurrent buffer. It bases its decision (in order of precedence) onthe ‘-*-’ line, on the ‘#!’ line (usinginterpreter-mode-alist), on the text at the beginning of thebuffer (using magic-mode-alist), and finally on the visitedfile name (using auto-mode-alist). See See section ``How Major Modes are Chosen'' in The GNU Emacs Manual. However, thisfunction does not look for the ‘mode:’ local variable near theend of a file; the hack-local-variables function does that.If enable-local-variables is nil, set-auto-modedoes not check the ‘-*-’ line for a mode tag either.If keep-mode-if-same is non-nil, this function does notcall the mode command if the buffer is already in the proper majormode. For instance, set-visited-file-name sets this tot to avoid killing buffer local variables that the user mayhave set. default-major-mode — User Option: default-major-mode This variable holds the default major mode for new buffers. Thestandard value is fundamental-mode.If the value of default-major-mode is nil, Emacs usesthe (previously) current buffer's major mode as the default major modeof a new buffer. However, if that major mode symbol has a mode-classproperty with value special, then it is not used for new buffers;Fundamental mode is used instead. The modes that have this property arethose such as Dired and Rmail that are useful only with text that hasbeen specially prepared. set-buffer-major-mode — Function: set-buffer-major-mode buffer This function sets the major mode of buffer to the value ofdefault-major-mode; if that variable is nil, it uses thecurrent buffer's major mode (if that is suitable). As an exception,if buffer's name is ‘*scratch*’, it sets the mode toinitial-major-mode.The low-level primitives for creating buffers do not use this function,but medium-level commands such as switch-to-buffer andfind-file-noselect use it whenever they create buffers. initial-major-mode — User Option: initial-major-mode ‘*scratch*’The value of this variable determines the major mode of the initial‘*scratch*’ buffer. The value should be a symbol that is a majormode command. The default value is lisp-interaction-mode. interpreter-mode-alist — Variable: interpreter-mode-alist This variable specifies major modes to use for scripts that specify acommand interpreter in a ‘#!’ line. Its value is an alist withelements of the form (interpreter . mode); forexample, ("perl" . perl-mode) is one element present bydefault. The element says to use mode mode if the filespecifies an interpreter which matches interpreter. magic-mode-alist — Variable: magic-mode-alist This variable's value is an alist with elements of the form(regexp . function), where regexp is aregular expression and function is a function or nil.After visiting a file, set-auto-mode calls function ifthe text at the beginning of the buffer matches regexp andfunction is non-nil; if function is nil,auto-mode-alist gets to decide the mode. magic-fallback-mode-alist — Variable: magic-fallback-mode-alist This works like magic-mode-alist, except that it is handledonly if auto-mode-alist does not specify a mode for this file. auto-mode-alist — Variable: auto-mode-alist This variable contains an association list of file name patterns(regular expressions) and corresponding major mode commands. Usually,the file name patterns test for suffixes, such as ‘.el’ and‘.c’, but this need not be the case. An ordinary element of thealist looks like (regexp . mode-function).For example, (("\\`/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) …) When you visit a file whose expanded file name (see ), with version numbers and backup suffixes removed usingfile-name-sans-versions (see ), matchesa regexp, set-auto-mode calls the correspondingmode-function. This feature enables Emacs to select the propermajor mode for most files.If an element of auto-mode-alist has the form (regexpfunction t), then after calling function, Emacs searchesauto-mode-alist again for a match against the portion of the filename that did not match before. This feature is useful foruncompression packages: an entry of the form ("\\.gz\\'"function t) can uncompress the file and then put the uncompressedfile in the proper mode according to the name sans ‘.gz’.Here is an example of how to prepend several pattern pairs toauto-mode-alist. (You might use this sort of expression in yourinit file.) (setq auto-mode-alist (append ;; File name (within directory) starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("[^\\./]*\\'" . fundamental-mode) ;; File name ends in ‘.C’. ("\\.C\\'" . c++-mode)) auto-mode-alist)) Getting Help about a Major Mode mode help help for major mode documentation for major mode The describe-mode function is used to provide information about major modes. It is normally called with C-h m. The describe-mode function uses the value of major-mode, which is why every major mode function needs to set the major-mode variable. describe-mode — Command: describe-mode This function displays the documentation of the current major mode.The describe-mode function calls the documentationfunction using the value of major-mode as an argument. Thus, itdisplays the documentation string of the major mode function.(See .) major-mode — Variable: major-mode This buffer-local variable holds the symbol for the current buffer'smajor mode. This symbol should have a function definition that is thecommand to switch to that major mode. The describe-modefunction uses the documentation string of the function as thedocumentation of the major mode. Defining Derived Modes derived mode It's often useful to define a new major mode in terms of an existing one. An easy way to do this is to use define-derived-mode. define-derived-mode — Macro: define-derived-mode variant parent name docstring keyword-args … body … This construct defines variant as a major mode command, usingname as the string form of the mode name. variant andparent should be unquoted symbols.The new command variant is defined to call the functionparent, then override certain aspects of that parent mode: The new mode has its own sparse keymap, namedvariant-map. define-derived-modemakes the parent mode's keymap the parent of the new map, unlessvariant-map is already set and already has a parent. The new mode has its own syntax table, kept in the variablevariant-syntax-table, unless you override this using the:syntax-table keyword (see below). define-derived-modemakes the parent mode's syntax-table the parent ofvariant-syntax-table, unless the latter is already setand already has a parent different from the standard syntax table. The new mode has its own abbrev table, kept in the variablevariant-abbrev-table, unless you override this using the:abbrev-table keyword (see below). The new mode has its own mode hook, variant-hook. Itruns this hook, after running the hooks of its ancestor modes, withrun-mode-hooks, as the last thing it does. See . In addition, you can specify how to override other aspects ofparent with body. The command variantevaluates the forms in body after setting up all its usualoverrides, just before running the mode hooks.You can also specify nil for parent. This gives the newmode no parent. Then define-derived-mode behaves as describedabove, but, of course, omits all actions connected with parent.The argument docstring specifies the documentation string forthe new mode. define-derived-mode adds some generalinformation about the mode's hook, followed by the mode's keymap, atthe end of this docstring. If you omit docstring,define-derived-mode generates a documentation string.The keyword-args are pairs of keywords and values. The valuesare evaluated. The following keywords are currently supported: :syntax-table You can use this to explicitly specify a syntax table for the newmode. If you specify a nil value, the new mode uses the samesyntax table as parent, or the standard syntax table ifparent is nil. (Note that this does not followthe convention used for non-keyword arguments that a nil valueis equivalent with not specifying the argument.) :abbrev-table You can use this to explicitly specify an abbrev table for the newmode. If you specify a nil value, the new mode uses the sameabbrev table as parent, or fundamental-mode-abbrev-tableif parent is nil. (Again, a nil value isnot equivalent to not specifying this keyword.) :group If this is specified, the value should be the customization group forthis mode. (Not all major modes have one.) Only the (stillexperimental and unadvertised) command customize-mode currentlyuses this. define-derived-mode does not automaticallydefine the specified customization group. Here is a hypothetical example: (define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link) Do not write an interactive spec in the definition;define-derived-mode does that automatically. Generic Modes generic mode Generic modes are simple major modes with basic support for comment syntax and Font Lock mode. To define a generic mode, use the macro define-generic-mode. See the file generic-x.el for some examples of the use of define-generic-mode. define-generic-mode — Macro: define-generic-mode mode comment-list keyword-list font-lock-list auto-mode-list function-list &optional docstring This macro defines a generic mode command named mode (a symbol,not quoted). The optional argument docstring is thedocumentation for the mode command. If you do not supply it,define-generic-mode generates one by default.The argument comment-list is a list in which each element iseither a character, a string of one or two characters, or a cons cell.A character or a string is set up in the mode's syntax table as a“comment starter.” If the entry is a cons cell, the car is setup as a “comment starter” and the cdr as a “comment ender.”(Use nil for the latter if you want comments to end at the endof the line.) Note that the syntax table mechanism has limitationsabout what comment starters and enders are actually possible.See .The argument keyword-list is a list of keywords to highlightwith font-lock-keyword-face. Each keyword should be a string.Meanwhile, font-lock-list is a list of additional expressions tohighlight. Each element of this list should have the same form as anelement of font-lock-keywords. See .The argument auto-mode-list is a list of regular expressions toadd to the variable auto-mode-alist. They are added by the executionof the define-generic-mode form, not by expanding the macro call.Finally, function-list is a list of functions for the modecommand to call for additional setup. It calls these functions justbefore it runs the mode hook variable mode-hook. Mode Hooks Every major mode function should finish by running its mode hook and the mode-independent normal hook after-change-major-mode-hook. It does this by calling run-mode-hooks. If the major mode is a derived mode, that is if it calls another major mode (the parent mode) in its body, it should do this inside delay-mode-hooks so that the parent won't run these hooks itself. Instead, the derived mode's call to run-mode-hooks runs the parent's mode hook too. See . Emacs versions before Emacs 22 did not have delay-mode-hooks. When user-implemented major modes have not been updated to use it, they won't entirely follow these conventions: they may run the parent's mode hook too early, or fail to run after-change-major-mode-hook. If you encounter such a major mode, please correct it to follow these conventions. When you defined a major mode using define-derived-mode, it automatically makes sure these conventions are followed. If you define a major mode “by hand,” not using define-derived-mode, use the following functions to handle these conventions automatically. run-mode-hooks — Function: run-mode-hooks &rest hookvars Major modes should run their mode hook using this function. It issimilar to run-hooks (see ), but it also runsafter-change-major-mode-hook.When this function is called during the execution of adelay-mode-hooks form, it does not run the hooks immediately.Instead, it arranges for the next call to run-mode-hooks to runthem. delay-mode-hooks — Macro: delay-mode-hooks body … When one major mode command calls another, it should do so inside ofdelay-mode-hooks.This macro executes body, but tells all run-mode-hookscalls during the execution of body to delay running their hooks.The hooks will actually run during the next call torun-mode-hooks after the end of the delay-mode-hooksconstruct. after-change-major-mode-hook — Variable: after-change-major-mode-hook This is a normal hook run by run-mode-hooks. It is run at thevery end of every properly-written major mode function. Major Mode Examples Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from text-mode.el that illustrate many of the conventions listed above: ;; Create the syntax table for this mode. (defvar text-mode-syntax-table (let ((st (make-syntax-table))) (modify-syntax-entry ?\" ". " st) (modify-syntax-entry ?\\ ". " st) ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. (modify-syntax-entry ?' "w p" st) st) "Syntax table used while in `text-mode'.") ;; Create the keymap for this mode. (defvar text-mode-map (let ((map (make-sparse-keymap))) (define-key map "\e\t" 'ispell-complete-word) (define-key map "\es" 'center-line) (define-key map "\eS" 'center-paragraph) map) "Keymap for `text-mode'. Many other modes, such as Mail mode, Outline mode and Indented Text mode, inherit all the commands defined in this map.") Here is how the actual mode command is defined now: (define-derived-mode text-mode nil "Text" "Major mode for editing text written for humans to read. In this mode, paragraphs are delimited only by blank or white lines. You can thus get the full benefit of adaptive filling (see the variable `adaptive-fill-mode'). \\{text-mode-map} Turning on Text mode runs the normal hook `text-mode-hook'." (make-local-variable 'text-mode-variant) (setq text-mode-variant t) ;; These two lines are a feature added recently. (set (make-local-variable 'require-final-newline) mode-require-final-newline) (set (make-local-variable 'indent-line-function) 'indent-relative)) (The last line is redundant nowadays, since indent-relative is the default value, and we'll delete it in a future version.) Here is how it was defined formerly, before define-derived-mode existed: ;; This isn't needed nowadays, since define-derived-mode does it. (defvar text-mode-abbrev-table nil "Abbrev table used while in text mode.") (define-abbrev-table 'text-mode-abbrev-table ()) (defun text-mode () "Major mode for editing text intended for humans to read... Special commands: \\{text-mode-map} Turning on text-mode runs the hook `text-mode-hook'." (interactive) (kill-all-local-variables) (use-local-map text-mode-map) (setq local-abbrev-table text-mode-abbrev-table) (set-syntax-table text-mode-syntax-table) ;; These four lines are absent from the current version ;; not because this is done some other way, but rather ;; because nowadays Text mode uses the normal definition of paragraphs. (make-local-variable 'paragraph-start) (setq paragraph-start (concat "[ \t]*$\\|" page-delimiter)) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) (make-local-variable 'indent-line-function) (setq indent-line-function 'indent-relative-maybe) (setq mode-name "Text") (setq major-mode 'text-mode) (run-mode-hooks 'text-mode-hook)) ; Finally, this permits the user to ; customize the mode with a hook. lisp-mode.el The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from lisp-mode.el that illustrate how these modes are written. syntax table example ;; Create mode-specific table variables. (defvar lisp-mode-syntax-table nil "") (defvar lisp-mode-abbrev-table nil "") (defvar emacs-lisp-mode-syntax-table (let ((table (make-syntax-table))) (let ((i 0)) ;; Set syntax of chars up to ‘0’ to say they are ;; part of symbol names but not words. ;; (The digit ‘0’ is 48 in the ASCII character set.) (while (< i ?0) (modify-syntax-entry i "_ " table) (setq i (1+ i))) ;; … similar code follows for other character ranges. ;; Then set the syntax codes for characters that are special in Lisp. (modify-syntax-entry ? " " table) (modify-syntax-entry ?\t " " table) (modify-syntax-entry ?\f " " table) (modify-syntax-entry ?\n "> " table) ;; Give CR the same syntax as newline, for selective-display. (modify-syntax-entry ?\^m "> " table) (modify-syntax-entry ?\; "< " table) (modify-syntax-entry ?` "' " table) (modify-syntax-entry ?' "' " table) (modify-syntax-entry ?, "' " table) ;; …likewise for many other characters… (modify-syntax-entry ?\( "() " table) (modify-syntax-entry ?\) ")( " table) (modify-syntax-entry ?\[ "(] " table) (modify-syntax-entry ?\] ")[ " table)) table)) ;; Create an abbrev table for lisp-mode. (define-abbrev-table 'lisp-mode-abbrev-table ()) The three modes for Lisp share much of their code. For instance, each calls the following function to set various variables: (defun lisp-mode-variables (lisp-syntax) (when lisp-syntax (set-syntax-table lisp-mode-syntax-table)) (setq local-abbrev-table lisp-mode-abbrev-table) … In Lisp and most programming languages, we want the paragraph commands to treat only blank lines as paragraph separators. And the modes should undestand the Lisp conventions for comments. The rest of lisp-mode-variables sets this up: (make-local-variable 'paragraph-start) (setq paragraph-start (concat page-delimiter "\\|$" )) (make-local-variable 'paragraph-separate) (setq paragraph-separate paragraph-start) … (make-local-variable 'comment-indent-function) (setq comment-indent-function 'lisp-comment-indent)) … Each of the different Lisp modes has a slightly different keymap. For example, Lisp mode binds C-c C-z to run-lisp, but the other Lisp modes do not. However, all Lisp modes have some commands in common. The following code sets up the common commands: (defvar shared-lisp-mode-map () "Keymap for commands shared by all sorts of Lisp modes.") ;; Putting this if after the defvar is an older style. (if shared-lisp-mode-map () (setq shared-lisp-mode-map (make-sparse-keymap)) (define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp) (define-key shared-lisp-mode-map "\177" 'backward-delete-char-untabify)) And here is the code to set up the keymap for Lisp mode: (defvar lisp-mode-map () "Keymap for ordinary Lisp mode...") (if lisp-mode-map () (setq lisp-mode-map (make-sparse-keymap)) (set-keymap-parent lisp-mode-map shared-lisp-mode-map) (define-key lisp-mode-map "\e\C-x" 'lisp-eval-defun) (define-key lisp-mode-map "\C-c\C-z" 'run-lisp)) Finally, here is the complete major mode function definition for Lisp mode. (defun lisp-mode () "Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp. Commands: Delete converts tabs to spaces as it moves back. Blank lines separate paragraphs. Semicolons start comments. \\{lisp-mode-map} Note that `run-lisp' may be used either to start an inferior Lisp job or to switch back to an existing one. Entry to this mode calls the value of `lisp-mode-hook' if that value is non-nil." (interactive) (kill-all-local-variables) (use-local-map lisp-mode-map) ; Select the mode's keymap. (setq major-mode 'lisp-mode) ; This is how describe-mode ; finds out what to describe. (setq mode-name "Lisp") ; This goes into the mode line. (lisp-mode-variables t) ; This defines various variables. (make-local-variable 'comment-start-skip) (setq comment-start-skip "\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *") (make-local-variable 'font-lock-keywords-case-fold-search) (setq font-lock-keywords-case-fold-search t) (setq imenu-case-fold-search t) (set-syntax-table lisp-mode-syntax-table) (run-mode-hooks 'lisp-mode-hook)) ; This permits the user to use a ; hook to customize the mode. Minor Modes minor mode A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named “generally available, optional feature modes,” except that such a name would be unwieldy. A minor mode is not usually meant as a variation of a single major mode. Usually they are general and can apply to many major modes. For example, Auto Fill mode works with any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do. A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect. Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier than it used to be. minor-mode-list — Variable: minor-mode-list The value of this variable is a list of all minor mode commands. Conventions for Writing Minor Modes minor mode conventions conventions for writing minor modes There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, the use of a hook at the end of the initialization function, and the use of keymaps and other tables. In addition, there are several conventions that are specific to minor modes. (The easiest way to follow all the conventions is to use the macro define-minor-mode; .) mode variableMake a variable whose name ends in ‘-mode’ to control the minormode. We call this the mode variable. The minor mode commandshould set this variable (nil to disable; anything else toenable).If possible, implement the mode so that setting the variableautomatically enables or disables the mode. Then the minor mode commanddoes not need to do anything except set the variable.This variable is used in conjunction with the minor-mode-alist todisplay the minor mode name in the mode line. It can also enableor disable a minor mode keymap. Individual commands or hooks can alsocheck the variable's value.If you want the minor mode to be enabled separately in each buffer,make the variable buffer-local. Define a command whose name is the same as the mode variable.Its job is to enable and disable the mode by setting the variable.The command should accept one optional argument. If the argument isnil, it should toggle the mode (turn it on if it is off, andoff if it is on). It should turn the mode on if the argument is apositive integer, the symbol t, or a list whose car is oneof those. It should turn the mode off if the argument is a negativeinteger or zero, the symbol -, or a list whose car is anegative integer or zero. The meaning of other arguments is notspecified.Here is an example taken from the definition of transient-mark-mode.It shows the use of transient-mark-mode as a variable that enables ordisables the mode's behavior, and also shows the proper way to toggle,enable or disable the minor mode based on the raw prefix argument value. (setq transient-mark-mode (if (null arg) (not transient-mark-mode) (> (prefix-numeric-value arg) 0))) Add an element to minor-mode-alist for each minor mode(see ), if you want to indicate theminor mode in the mode line. This element should be a list of thefollowing form: (mode-variable string) Here mode-variable is the variable that controls enabling of theminor mode, and string is a short string, starting with a space,to represent the mode in the mode line. These strings must be short sothat there is room for several of them at once.When you add an element to minor-mode-alist, use assq tocheck for an existing element, to avoid duplication. For example: (unless (assq 'leif-mode minor-mode-alist) (setq minor-mode-alist (cons '(leif-mode " Leif") minor-mode-alist))) or like this, using add-to-list (see ): (add-to-list 'minor-mode-alist '(leif-mode " Leif")) Global minor modes distributed with Emacs should if possible support enabling and disabling via Custom (see ). To do this, the first step is to define the mode variable with defcustom, and specify :type boolean. If just setting the variable is not sufficient to enable the mode, you should also specify a :set method which enables the mode by invoking the mode command. Note in the variable's documentation string that setting the variable other than via Custom may not take effect. Also mark the definition with an autoload cookie (see ), and specify a :require so that customizing the variable will load the library that defines the mode. This will copy suitable definitions into loaddefs.el so that users can use customize-option to enable the mode. For example: ;;;###autoload (defcustom msb-mode nil "Toggle msb-mode. Setting this variable directly does not take effect; use either \\[customize] or the function `msb-mode'." :set 'custom-set-minor-mode :initialize 'custom-initialize-default :version "20.4" :type 'boolean :group 'msb :require 'msb) Keymaps and Minor Modes Each minor mode can have its own keymap, which is active when the mode is enabled. To set up a keymap for a minor mode, add an element to the alist minor-mode-map-alist. See . self-insert-command, minor modes One use of minor mode keymaps is to modify the behavior of certain self-inserting characters so that they do something else as well as self-insert. In general, this is the only way to do that, since the facilities for customizing self-insert-command are limited to special cases (designed for abbrevs and Auto Fill mode). (Do not try substituting your own definition of self-insert-command for the standard one. The editor command loop handles this function specially.) The key sequences bound in a minor mode should consist of C-c followed by one of .,/?`'"[]\|~!#$%^&*()-_+=. (The other punctuation characters are reserved for major modes.) Defining Minor Modes The macro define-minor-mode offers a convenient way of implementing a mode in one self-contained definition. define-minor-mode — Macro: define-minor-mode mode doc [ init-value [ lighter [ keymap ] ] ] keyword-args … body … This macro defines a new minor mode whose name is mode (asymbol). It defines a command named mode to toggle the minormode, with doc as its documentation string. It also defines avariable named mode, which is set to t or nil byenabling or disabling the mode. The variable is initialized toinit-value. Except in unusual circumstances (see below), thisvalue must be nil.The string lighter says what to display in the mode linewhen the mode is enabled; if it is nil, the mode is not displayedin the mode line.The optional argument keymap specifies the keymap for the minor mode.It can be a variable name, whose value is the keymap, or it can be an alistspecifying bindings in this form: (key-sequence . definition) The above three arguments init-value, lighter, andkeymap can be (partially) omitted when keyword-args areused. The keyword-args consist of keywords followed bycorresponding values. A few keywords have special meanings: :group group Custom group name to use in all generated defcustom forms.Defaults to mode without the possible trailing ‘-mode’.Warning: don't use this default group name unless you havewritten a defgroup to define that group properly. See . :global global If non-nil, this specifies that the minor mode should be globalrather than buffer-local. It defaults to nil.One of the effects of making a minor mode global is that themode variable becomes a customization variable. Toggling itthrough the Custom interface turns the mode on and off, and its valuecan be saved for future Emacs sessions (see See section ``Saving Customizations'' in The GNU Emacs Manual. For the savedvariable to work, you should ensure that the define-minor-modeform is evaluated each time Emacs starts; for packages that are notpart of Emacs, the easiest way to do this is to specify a:require keyword. :init-value init-value This is equivalent to specifying init-value positionally. :lighter lighter This is equivalent to specifying lighter positionally. :keymap keymap This is equivalent to specifying keymap positionally. Any other keyword arguments are passed directly to thedefcustom generated for the variable mode.The command named mode first performs the standard actions suchas setting the variable named mode and then executes thebody forms, if any. It finishes by running the mode hookvariable mode-hook. The initial value must be nil except in cases where (1) the mode is preloaded in Emacs, or (2) it is painless for loading to enable the mode even though the user did not request it. For instance, if the mode has no effect unless something else is enabled, and will always be loaded by that time, enabling it by default is harmless. But these are unusual circumstances. Normally, the initial value must be nil. easy-mmode-define-minor-mode The name easy-mmode-define-minor-mode is an alias for this macro. Here is an example of using define-minor-mode: (define-minor-mode hungry-mode "Toggle Hungry mode. With no argument, this command toggles the mode. Non-null prefix argument turns on the mode. Null prefix argument turns off the mode. When Hungry mode is enabled, the control delete key gobbles all preceding whitespace except the last. See the command \\[hungry-electric-delete]." ;; The initial value. nil ;; The indicator for the mode line. " Hungry" ;; The minor mode bindings. '(("\C-\^?" . hungry-electric-delete)) :group 'hunger) This defines a minor mode named “Hungry mode,” a command named hungry-mode to toggle it, a variable named hungry-mode which indicates whether the mode is enabled, and a variable named hungry-mode-map which holds the keymap that is active when the mode is enabled. It initializes the keymap with a key binding for C-DEL. It puts the variable hungry-mode into custom group hunger. There are no body forms—many minor modes don't need any. Here's an equivalent way to write it: (define-minor-mode hungry-mode "Toggle Hungry mode. With no argument, this command toggles the mode. Non-null prefix argument turns on the mode. Null prefix argument turns off the mode. When Hungry mode is enabled, the control delete key gobbles all preceding whitespace except the last. See the command \\[hungry-electric-delete]." ;; The initial value. :init-value nil ;; The indicator for the mode line. :lighter " Hungry" ;; The minor mode bindings. :keymap '(("\C-\^?" . hungry-electric-delete) ("\C-\M-\^?" . (lambda () (interactive) (hungry-electric-delete t)))) :group 'hunger) define-globalized-minor-mode — Macro: define-globalized-minor-mode global-mode mode turn-on keyword-args … This defines a global toggle named global-mode whose meaning isto enable or disable the buffer-local minor mode mode in allbuffers. To turn on the minor mode in a buffer, it uses the functionturn-on; to turn off the minor mode, it calls mode with−1 as argument.Globally enabling the mode also affects buffers subsequently createdby visiting files, and buffers that use a major mode other thanFundamental mode; but it does not detect the creation of a new bufferin Fundamental mode.This defines the customization option global-mode (see ),which can be toggled in the Custom interface to turn the minor mode onand off. As with define-minor-mode, you should ensure that thedefine-globalized-minor-mode form is evaluated each time Emacsstarts, for example by providing a :require keyword.Use :group group in keyword-args to specify thecustom group for the mode variable of the global minor mode. Mode-Line Format mode line Each Emacs window (aside from minibuffer windows) typically has a mode line at the bottom, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and major and minor modes. A window can also have a header line, which is much like the mode line but appears at the top of the window. This section describes how to control the contents of the mode line and header line. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes. Mode Line Basics mode-line-format is a buffer-local variable that holds a mode line construct, a kind of template, which controls what is displayed on the mode line of the current buffer. The value of header-line-format specifies the buffer's header line in the same way. All windows for the same buffer use the same mode-line-format and header-line-format. For efficiency, Emacs does not continuously recompute the mode line and header line of a window. It does so when circumstances appear to call for it—for instance, if you change the window configuration, switch buffers, narrow or widen the buffer, scroll, or change the buffer's modification status. If you modify any of the variables referenced by mode-line-format (see ), or any other variables and data structures that affect how text is displayed (see ), you may want to force an update of the mode line so as to display the new information or display it in the new way. force-mode-line-update — Function: force-mode-line-update &optional all Force redisplay of the current buffer's mode line and header line.The next redisplay will update the mode line and header line based onthe latest values of all relevant variables. With optionalnon-nil all, force redisplay of all mode lines and headerlines.This function also forces recomputation of the menu bar menusand the frame title. The selected window's mode line is usually displayed in a different color using the face mode-line. Other windows' mode lines appear in the face mode-line-inactive instead. See . The Data Structure of the Mode Line mode-line construct The mode-line contents are controlled by a data structure called a mode-line construct, made up of lists, strings, symbols, and numbers kept in buffer-local variables. Each data type has a specific meaning for the mode-line appearance, as described below. The same data structure is used for constructing frame titles (see ) and header lines (see ). A mode-line construct may be as simple as a fixed string of text, but it usually specifies how to combine fixed strings with variables' values to construct the text. Many of these variables are themselves defined to have mode-line constructs as their values. Here are the meanings of various data types as mode-line constructs: percent symbol in mode linestring A string as a mode-line construct appears verbatim except for%-constructs in it. These stand for substitution ofother data; see .If parts of the string have face properties, they controldisplay of the text just as they would text in the buffer. Anycharacters which have no face properties are displayed, bydefault, in the face mode-line or mode-line-inactive(see See section ``Standard Faces'' in The GNU Emacs Manual). Thehelp-echo and local-map properties in string havespecial meanings. See . symbol A symbol as a mode-line construct stands for its value. The value ofsymbol is used as a mode-line construct, in place of symbol.However, the symbols t and nil are ignored, as is anysymbol whose value is void.There is one exception: if the value of symbol is a string, it isdisplayed verbatim: the %-constructs are not recognized.Unless symbol is marked as “risky” (i.e., it has anon-nil risky-local-variable property), all textproperties specified in symbol's value are ignored. Thisincludes the text properties of strings in symbol's value, aswell as all :eval and :propertize forms in it. (Thereason for this is security: non-risky variables could be setautomatically from file variables without prompting the user.) (string rest…)(list rest…) A list whose first element is a string or list means to process all theelements recursively and concatenate the results. This is the mostcommon form of mode-line construct. (:eval form) A list whose first element is the symbol :eval says to evaluateform, and use the result as a string to display. Make sure thisevaluation cannot load any files, as doing so could cause infiniterecursion. (:propertize elt props…) A list whose first element is the symbol :propertize says toprocess the mode-line construct elt recursively, then add the textproperties specified by props to the result. The argumentprops should consist of zero or more pairs text-propertyvalue. (This feature is new as of Emacs 22.1.) (symbol then else) A list whose first element is a symbol that is not a keyword specifiesa conditional. Its meaning depends on the value of symbol. Ifsymbol has a non-nil value, the second element,then, is processed recursively as a mode-line element.Otherwise, the third element, else, is processed recursively.You may omit else; then the mode-line element displays nothingif the value of symbol is nil or void. (width rest…) A list whose first element is an integer specifies truncation orpadding of the results of rest. The remaining elementsrest are processed recursively as mode-line constructs andconcatenated together. When width is positive, the result isspace filled on the right if its width is less than width. Whenwidth is negative, the result is truncated on the right to−width columns if its width exceeds −width.For example, the usual way to show what percentage of a buffer is abovethe top of the window is to use a list like this: (-3 "%p"). The Top Level of Mode Line Control The variable in overall control of the mode line is mode-line-format. mode-line-format — Variable: mode-line-format The value of this variable is a mode-line construct that controls thecontents of the mode-line. It is always buffer-local in all buffers.If you set this variable to nil in a buffer, that buffer doesnot have a mode line. (A window that is just one line tall neverdisplays a mode line.) The default value of mode-line-format is designed to use the values of other variables such as mode-line-position and mode-line-modes (which in turn incorporates the values of the variables mode-name and minor-mode-alist). Very few modes need to alter mode-line-format itself. For most purposes, it is sufficient to alter some of the variables that mode-line-format either directly or indirectly refers to. If you do alter mode-line-format itself, the new value should use the same variables that appear in the default value (see ), rather than duplicating their contents or displaying the information in another fashion. This way, customizations made by the user or by Lisp programs (such as display-time and major modes) via changes to those variables remain effective. Here is an example of a mode-line-format that might be useful for shell-mode, since it contains the host name and default directory. (setq mode-line-format (list "-" 'mode-line-mule-info 'mode-line-modified 'mode-line-frame-identification "%b--" ;; Note that this is evaluated while making the list. ;; It makes a mode-line construct which is just a string. (getenv "HOST") ":" 'default-directory " " 'global-mode-string " %[(" '(:eval (mode-line-mode-name)) 'mode-line-process 'minor-mode-alist "%n" ")%]--" '(which-func-mode ("" which-func-format "--")) '(line-number-mode "L%l--") '(column-number-mode "C%c--") '(-3 "%p") "-%-")) (The variables line-number-mode, column-number-mode and which-func-mode enable particular minor modes; as usual, these variable names are also the minor mode command names.) Variables Used in the Mode Line This section describes variables incorporated by the standard value of mode-line-format into the text of the mode line. There is nothing inherently special about these variables; any other variables could have the same effects on the mode line if mode-line-format's value were changed to use them. However, various parts of Emacs set these variables on the understanding that they will control parts of the mode line; therefore, practically speaking, it is essential for the mode line to use them. mode-line-mule-info — Variable: mode-line-mule-info This variable holds the value of the mode-line construct that displaysinformation about the language environment, buffer coding system, andcurrent input method. See . mode-line-modified — Variable: mode-line-modified This variable holds the value of the mode-line construct that displayswhether the current buffer is modified.The default value of mode-line-modified is ("%1*%1+").This means that the mode line displays ‘**’ if the buffer ismodified, ‘--’ if the buffer is not modified, ‘%%’ if thebuffer is read only, and ‘%*’ if the buffer is read only andmodified.Changing this variable does not force an update of the mode line. mode-line-frame-identification — Variable: mode-line-frame-identification This variable identifies the current frame. The default value is" " if you are using a window system which can show multipleframes, or "-%F " on an ordinary terminal which shows only oneframe at a time. mode-line-buffer-identification — Variable: mode-line-buffer-identification This variable identifies the buffer being displayed in the window. Itsdefault value is ("%12b"), which displays the buffer name, paddedwith spaces to at least 12 columns. mode-line-position — Variable: mode-line-position This variable indicates the position in the buffer. Here is asimplified version of its default value. The actual default valuealso specifies addition of the help-echo text property. ((-3 "%p") (size-indication-mode (8 " of %I")) (line-number-mode ((column-number-mode (10 " (%l,%c)") (6 " L%l"))) ((column-number-mode (5 " C%c"))))) This means that mode-line-position displays at least the bufferpercentage and possibly the buffer size, the line number and the columnnumber. vc-mode — Variable: vc-mode The variable vc-mode, buffer-local in each buffer, recordswhether the buffer's visited file is maintained with version control,and, if so, which kind. Its value is a string that appears in the modeline, or nil for no version control. mode-line-modes — Variable: mode-line-modes This variable displays the buffer's major and minor modes. Here is asimplified version of its default value. The real default value alsospecifies addition of text properties. ("%[(" mode-name mode-line-process minor-mode-alist "%n" ")%]--") So mode-line-modes normally also displays the recursive editinglevel, information on the process status and whether narrowing is ineffect. The following three variables are used in mode-line-modes: mode-name — Variable: mode-name This buffer-local variable holds the “pretty” name of the currentbuffer's major mode. Each major mode should set this variable so that themode name will appear in the mode line. mode-line-process — Variable: mode-line-process This buffer-local variable contains the mode-line information on processstatus in modes used for communicating with subprocesses. It isdisplayed immediately following the major mode name, with no interveningspace. For example, its value in the ‘*shell*’ buffer is(":%s"), which allows the shell to display its status alongwith the major mode as: ‘(Shell:run)’. Normally this variableis nil. minor-mode-alist — Variable: minor-mode-alist This variable holds an association list whose elements specify how themode line should indicate that a minor mode is active. Each element ofthe minor-mode-alist should be a two-element list: (minor-mode-variable mode-line-string) More generally, mode-line-string can be any mode-line spec. Itappears in the mode line when the value of minor-mode-variableis non-nil, and not otherwise. These strings should begin withspaces so that they don't run together. Conventionally, theminor-mode-variable for a specific mode is set to anon-nil value when that minor mode is activated.minor-mode-alist itself is not buffer-local. Each variablementioned in the alist should be buffer-local if its minor mode can beenabled separately in each buffer. global-mode-string — Variable: global-mode-string This variable holds a mode-line spec that, by default, appears in themode line just after the which-func-mode minor mode if set,else after mode-line-modes. The command display-timesets global-mode-string to refer to the variabledisplay-time-string, which holds a string containing the timeand load information.The ‘%M’ construct substitutes the value ofglobal-mode-string, but that is obsolete, since the variable isincluded in the mode line from mode-line-format. The variable default-mode-line-format is where mode-line-format usually gets its value: default-mode-line-format — Variable: default-mode-line-format This variable holds the default mode-line-format for buffersthat do not override it. This is the same as (default-value'mode-line-format).Here is a simplified version of the default value ofdefault-mode-line-format. The real default value alsospecifies addition of text properties. ("-" mode-line-mule-info mode-line-modified mode-line-frame-identification mode-line-buffer-identification " " mode-line-position (vc-mode vc-mode) " " mode-line-modes (which-func-mode ("" which-func-format "--")) (global-mode-string ("--" global-mode-string)) "-%-") %-Constructs in the Mode Line Strings used as mode-line constructs can use certain %-constructs to substitute various kinds of data. Here is a list of the defined %-constructs, and what they mean. In any construct except ‘%%’, you can add a decimal integer after the ‘%’ to specify a minimum field width. If the width is less, the field is padded with spaces to the right. %b The current buffer name, obtained with the buffer-name function.See . %c The current column number of point. %e When Emacs is nearly out of memory for Lisp objects, a brief messagesaying so. Otherwise, this is empty. %f The visited file name, obtained with the buffer-file-namefunction. See . %F The title (only on a window system) or the name of the selected frame.See . %i The size of the accessible part of the current buffer; basically(- (point-max) (point-min)). %I Like ‘%i’, but the size is printed in a more readable way by using‘k’ for 10^3, ‘M’ for 10^6, ‘G’ for 10^9, etc., toabbreviate. %l The current line number of point, counting within the accessible portionof the buffer. %n ‘Narrow’ when narrowing is in effect; nothing otherwise (seenarrow-to-region in ). %p The percentage of the buffer text above the top of window, or‘Top’, ‘Bottom’ or ‘All’. Note that the defaultmode-line specification truncates this to three characters. %P The percentage of the buffer text that is above the bottom ofthe window (which includes the text visible in the window, as well asthe text above the top), plus ‘Top’ if the top of the buffer isvisible on screen; or ‘Bottom’ or ‘All’. %s The status of the subprocess belonging to the current buffer, obtained withprocess-status. See . %t Whether the visited file is a text file or a binary file. This is ameaningful distinction only on certain operating systems (see ). %z The mnemonics of keyboard, terminal, and buffer coding systems. %Z Like ‘%z’, but including the end-of-line format. %* ‘%’ if the buffer is read only (see buffer-read-only); ‘*’ if the buffer is modified (see buffer-modified-p); ‘-’ otherwise. See . %+ ‘*’ if the buffer is modified (see buffer-modified-p); ‘%’ if the buffer is read only (see buffer-read-only); ‘-’ otherwise. This differs from ‘%*’ only for a modifiedread-only buffer. See . %& ‘*’ if the buffer is modified, and ‘-’ otherwise. %[ An indication of the depth of recursive editing levels (not countingminibuffer levels): one ‘[’ for each editing level.See . %] One ‘]’ for each recursive editing level (not counting minibufferlevels). %- Dashes sufficient to fill the remainder of the mode line. %% The character ‘%’—this is how to include a literal ‘%’ in astring in which %-constructs are allowed. The following two %-constructs are still supported, but they are obsolete, since you can get the same results with the variables mode-name and global-mode-string. %m The value of mode-name. %M The value of global-mode-string. Properties in the Mode Line text properties in the mode line Certain text properties are meaningful in the mode line. The face property affects the appearance of text; the help-echo property associates help strings with the text, and local-map can make the text mouse-sensitive. There are four ways to specify text properties for text in the mode line: Put a string with a text property directly into the mode-line datastructure. Put a text property on a mode-line %-construct such as ‘%12b’; thenthe expansion of the %-construct will have that same text property. Use a (:propertize elt props…) construct togive elt a text property specified by props. Use a list containing :eval form in the mode-line datastructure, and make form evaluate to a string that has a textproperty. You can use the local-map property to specify a keymap. This keymap only takes real effect for mouse clicks; binding character keys and function keys to it has no effect, since it is impossible to move point into the mode line. When the mode line refers to a variable which does not have a non-nil risky-local-variable property, any text properties given or specified within that variable's values are ignored. This is because such properties could otherwise specify functions to be called, and those functions could come from file local variables. Window Header Lines header line (of a window) window header line A window can have a header line at the top, just as it can have a mode line at the bottom. The header line feature works just like the mode-line feature, except that it's controlled by different variables. header-line-format — Variable: header-line-format This variable, local in every buffer, specifies how to display theheader line, for windows displaying the buffer. The format of the valueis the same as for mode-line-format (see ). default-header-line-format — Variable: default-header-line-format This variable holds the default header-line-format for buffersthat do not override it. This is the same as (default-value'header-line-format).It is normally nil, so that ordinary buffers have no header line. A window that is just one line tall never displays a header line. A window that is two lines tall cannot display both a mode line and a header line at once; if it has a mode line, then it does not display a header line. Emulating Mode-Line Formatting You can use the function format-mode-line to compute the text that would appear in a mode line or header line based on a certain mode-line specification. format-mode-line — Function: format-mode-line format &optional face window buffer This function formats a line of text according to format as ifit were generating the mode line for window, but instead ofdisplaying the text in the mode line or the header line, it returnsthe text as a string. The argument window defaults to theselected window. If buffer is non-nil, all theinformation used is taken from buffer; by default, it comes fromwindow's buffer.The value string normally has text properties that correspond to thefaces, keymaps, etc., that the mode line would have. And any characterfor which no face property is specified gets a defaultvalue which is usually face. (If face is t,that stands for either mode-line if window is selected,otherwise mode-line-inactive. If face is nil oromitted, that stands for no face property.)However, if face is an integer, the value has no text properties.For example, (format-mode-line header-line-format) returns thetext that would appear in the selected window's header line (""if it has no header line). (format-mode-line header-line-format'header-line) returns the same text, with each charactercarrying the face that it will have in the header line itself. Imenu Imenu Imenu is a feature that lets users select a definition or section in the buffer, from a menu which lists all of them, to go directly to that location in the buffer. Imenu works by constructing a buffer index which lists the names and buffer positions of the definitions, or other named portions of the buffer; then the user can choose one of them and move point to it. Major modes can add a menu bar item to use Imenu using imenu-add-to-menubar. imenu-add-to-menubar — Function: imenu-add-to-menubar name This function defines a local menu bar item named nameto run Imenu. The user-level commands for using Imenu are described in the Emacs Manual (see See section ``Imenu'' in the Emacs Manual). This section explains how to customize Imenu's method of finding definitions or buffer portions for a particular major mode. The usual and simplest way is to set the variable imenu-generic-expression: imenu-generic-expression — Variable: imenu-generic-expression This variable, if non-nil, is a list that specifies regularexpressions for finding definitions for Imenu. Simple elements ofimenu-generic-expression look like this: (menu-title regexp index) Here, if menu-title is non-nil, it says that the matchesfor this element should go in a submenu of the buffer index;menu-title itself specifies the name for the submenu. Ifmenu-title is nil, the matches for this element go directlyin the top level of the buffer index.The second item in the list, regexp, is a regular expression(see ); anything in the buffer that it matchesis considered a definition, something to mention in the buffer index.The third item, index, is a non-negative integer that indicateswhich subexpression in regexp matches the definition's name.An element can also look like this: (menu-title regexp index function arguments…) Each match for this element creates an index item, and when the indexitem is selected by the user, it calls function with argumentsconsisting of the item name, the buffer position, and arguments.For Emacs Lisp mode, imenu-generic-expression could look likethis: ((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Types*" "^\\s-*\ (def\\(type\\|struct\\|class\\|ine-condition\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2)) Setting this variable makes it buffer-local in the current buffer. imenu-case-fold-search — Variable: imenu-case-fold-search This variable controls whether matching against the regularexpressions in the value of imenu-generic-expression iscase-sensitive: t, the default, means matching should ignorecase.Setting this variable makes it buffer-local in the current buffer. imenu-syntax-alist — Variable: imenu-syntax-alist This variable is an alist of syntax table modifiers to use whileprocessing imenu-generic-expression, to override the syntax tableof the current buffer. Each element should have this form: (characters . syntax-description) The car, characters, can be either a character or a string.The element says to give that character or characters the syntaxspecified by syntax-description, which is passed tomodify-syntax-entry (see ).This feature is typically used to give word syntax to characters whichnormally have symbol syntax, and thus to simplifyimenu-generic-expression and speed up matching.For example, Fortran mode uses it this way: (setq imenu-syntax-alist '(("_$" . "w"))) The imenu-generic-expression regular expressions can then use‘\\sw+’ instead of ‘\\(\\sw\\|\\s_\\)+’. Note that thistechnique may be inconvenient when the mode needs to limit the initialcharacter of a name to a smaller set of characters than are allowed inthe rest of a name.Setting this variable makes it buffer-local in the current buffer. Another way to customize Imenu for a major mode is to set the variables imenu-prev-index-position-function and imenu-extract-index-name-function: imenu-prev-index-position-function — Variable: imenu-prev-index-position-function If this variable is non-nil, its value should be a function thatfinds the next “definition” to put in the buffer index, scanningbackward in the buffer from point. It should return nil if itdoesn't find another “definition” before point. Otherwise it shouldleave point at the place it finds a “definition” and return anynon-nil value.Setting this variable makes it buffer-local in the current buffer. imenu-extract-index-name-function — Variable: imenu-extract-index-name-function If this variable is non-nil, its value should be a function toreturn the name for a definition, assuming point is in that definitionas the imenu-prev-index-position-function function would leaveit.Setting this variable makes it buffer-local in the current buffer. The last way to customize Imenu for a major mode is to set the variable imenu-create-index-function: imenu-create-index-function — Variable: imenu-create-index-function This variable specifies the function to use for creating a bufferindex. The function should take no arguments, and return an indexalist for the current buffer. It is called withinsave-excursion, so where it leaves point makes no difference.The index alist can have three types of elements. Simple elementslook like this: (index-name . index-position) Selecting a simple element has the effect of moving to positionindex-position in the buffer. Special elements look like this: (index-name index-position function arguments…) Selecting a special element performs: (funcall function index-name index-position arguments…) A nested sub-alist element looks like this: (menu-title sub-alist) It creates the submenu menu-title specified by sub-alist.The default value of imenu-create-index-function isimenu-default-create-index-function. This function calls thevalue of imenu-prev-index-position-function and the value ofimenu-extract-index-name-function to produce the index alist.However, if either of these two variables is nil, the defaultfunction uses imenu-generic-expression instead.Setting this variable makes it buffer-local in the current buffer. Font Lock Mode Font Lock mode Font Lock mode is a feature that automatically attaches face properties to certain parts of the buffer based on their syntactic role. How it parses the buffer depends on the major mode; most major modes define syntactic criteria for which faces to use in which contexts. This section explains how to customize Font Lock for a particular major mode. Font Lock mode finds text to highlight in two ways: through syntactic parsing based on the syntax table, and through searching (usually for regular expressions). Syntactic fontification happens first; it finds comments and string constants and highlights them. Search-based fontification happens second. Font Lock Basics There are several variables that control how Font Lock mode highlights text. But major modes should not set any of these variables directly. Instead, they should set font-lock-defaults as a buffer-local variable. The value assigned to this variable is used, if and when Font Lock mode is enabled, to set all the other variables. font-lock-defaults — Variable: font-lock-defaults This variable is set by major modes, as a buffer-local variable, tospecify how to fontify text in that mode. It automatically becomesbuffer-local when you set it. If its value is nil, Font-Lockmode does no highlighting, and you can use the ‘Faces’ menu(under ‘Edit’ and then ‘Text Properties’ in the menu bar) toassign faces explicitly to text in the buffer.If non-nil, the value should look like this: (keywords [keywords-only [case-fold [syntax-alist [syntax-begin other-vars…]]]]) The first element, keywords, indirectly specifies the value offont-lock-keywords which directs search-based fontification.It can be a symbol, a variable or a function whose value is the listto use for font-lock-keywords. It can also be a list ofseveral such symbols, one for each possible level of fontification.The first symbol specifies how to do level 1 fontification, the secondsymbol how to do level 2, and so on. See .The second element, keywords-only, specifies the value of thevariable font-lock-keywords-only. If this is omitted ornil, syntactic fontification (of strings and comments) is alsoperformed. If this is non-nil, such fontification is notperformed. See .The third element, case-fold, specifies the value offont-lock-keywords-case-fold-search. If it is non-nil,Font Lock mode ignores case when searching as directed byfont-lock-keywords.If the fourth element, syntax-alist, is non-nil, itshould be a list of cons cells of the form (char-or-string. string). These are used to set up a syntax table forsyntactic fontification (see ). Theresulting syntax table is stored in font-lock-syntax-table.The fifth element, syntax-begin, specifies the value offont-lock-beginning-of-syntax-function. We recommend settingthis variable to nil and using syntax-begin-functioninstead.All the remaining elements (if any) are collectively calledother-vars. Each of these elements should have the form(variable . value)—which means, makevariable buffer-local and then set it to value. You canuse these other-vars to set other variables that affectfontification, aside from those you can control with the first fiveelements. See . If your mode fontifies text explicitly by adding font-lock-face properties, it can specify (nil t) for font-lock-defaults to turn off all automatic fontification. However, this is not required; it is possible to fontify some things using font-lock-face properties and set up automatic fontification for other parts of the text. Search-based Fontification The most important variable for customizing Font Lock mode is font-lock-keywords. It specifies the search criteria for search-based fontification. You should specify the value of this variable with keywords in font-lock-defaults. font-lock-keywords — Variable: font-lock-keywords This variable's value is a list of the keywords to highlight. Becareful when composing regular expressions for this list; a poorlywritten pattern can dramatically slow things down! Each element of font-lock-keywords specifies how to find certain cases of text, and how to highlight those cases. Font Lock mode processes the elements of font-lock-keywords one by one, and for each element, it finds and handles all matches. Ordinarily, once part of the text has been fontified already, this cannot be overridden by a subsequent match in the same text; but you can specify different behavior using the override element of a subexp-highlighter. Each element of font-lock-keywords should have one of these forms: regexp Highlight all matches for regexp usingfont-lock-keyword-face. For example, ;; Highlight occurrences of the word ‘foo’ ;; using font-lock-keyword-face. "\\<foo\\>" The function regexp-opt (see ) is usefulfor calculating optimal regular expressions to match a number ofdifferent keywords. function Find text by calling function, and highlight the matchesit finds using font-lock-keyword-face.When function is called, it receives one argument, the limit ofthe search; it should begin searching at point, and not search beyond thelimit. It should return non-nil if it succeeds, and set thematch data to describe the match that was found. Returning nilindicates failure of the search.Fontification will call function repeatedly with the same limit,and with point where the previous invocation left it, untilfunction fails. On failure, function need not reset pointin any particular way. (matcher . subexp) In this kind of element, matcher is either a regularexpression or a function, as described above. The cdr,subexp, specifies which subexpression of matcher should behighlighted (instead of the entire text that matcher matched). ;; Highlight the ‘bar’ in each occurrence of ‘fubar’, ;; using font-lock-keyword-face. ("fu\\(bar\\)" . 1) If you use regexp-opt to produce the regular expressionmatcher, you can use regexp-opt-depth (see ) to calculate the value for subexp. (matcher . facespec) In this kind of element, facespec is an expression whose valuespecifies the face to use for highlighting. In the simplest case,facespec is a Lisp variable (a symbol) whose value is a facename. ;; Highlight occurrences of ‘fubar’, ;; using the face which is the value of fubar-face. ("fubar" . fubar-face) However, facespec can also evaluate to a list of this form: (face face prop1 val1 prop2 val2…) to specify the face face and various additional text propertiesto put on the text that matches. If you do this, be sure to add theother text property names that you set in this way to the value offont-lock-extra-managed-props so that the properties will alsobe cleared out when they are no longer appropriate. Alternatively,you can set the variable font-lock-unfontify-region-function toa function that clears these properties. See . (matcher . subexp-highlighter) In this kind of element, subexp-highlighter is a listwhich specifies how to highlight matches found by matcher.It has the form: (subexp facespec [[override [laxmatch]]) The car, subexp, is an integer specifying which subexpressionof the match to fontify (0 means the entire matching text). The secondsubelement, facespec, is an expression whose value specifies theface, as described above.The last two values in subexp-highlighter, override andlaxmatch, are optional flags. If override is t,this element can override existing fontification made by previouselements of font-lock-keywords. If it is keep, theneach character is fontified if it has not been fontified already bysome other element. If it is prepend, the face specified byfacespec is added to the beginning of the font-lock-faceproperty. If it is append, the face is added to the end of thefont-lock-face property.If laxmatch is non-nil, it means there should be no errorif there is no subexpression numbered subexp in matcher.Obviously, fontification of the subexpression numbered subexp willnot occur. However, fontification of other subexpressions (and otherregexps) will continue. If laxmatch is nil, and thespecified subexpression is missing, then an error is signaled whichterminates search-based fontification.Here are some examples of elements of this kind, and what they do: ;; Highlight occurrences of either ‘foo’ or ‘bar’, using ;; foo-bar-face, even if they have already been highlighted. ;; foo-bar-face should be a variable whose value is a face. ("foo\\|bar" 0 foo-bar-face t) ;; Highlight the first subexpression within each occurrence ;; that the function fubar-match finds, ;; using the face which is the value of fubar-face. (fubar-match 1 fubar-face) (matcher . anchored-highlighter) In this kind of element, anchored-highlighter specifies how tohighlight text that follows a match found by matcher. So amatch found by matcher acts as the anchor for further searchesspecified by anchored-highlighter. anchored-highlighteris a list of the following form: (anchored-matcher pre-form post-form subexp-highlighters…) Here, anchored-matcher, like matcher, is either a regularexpression or a function. After a match of matcher is found,point is at the end of the match. Now, Font Lock evaluates the formpre-form. Then it searches for matches ofanchored-matcher and uses subexp-highlighters to highlightthese. A subexp-highlighter is as described above. Finally,Font Lock evaluates post-form.The forms pre-form and post-form can be used to initializebefore, and cleanup after, anchored-matcher is used. Typically,pre-form is used to move point to some position relative to thematch of matcher, before starting with anchored-matcher.post-form might be used to move back, before resuming withmatcher.After Font Lock evaluates pre-form, it does not search foranchored-matcher beyond the end of the line. However, ifpre-form returns a buffer position that is greater than theposition of point after pre-form is evaluated, then the positionreturned by pre-form is used as the limit of the search instead.It is generally a bad idea to return a position greater than the endof the line; in other words, the anchored-matcher search shouldnot span lines.For example, ;; Highlight occurrences of the word ‘item’ following ;; an occurrence of the word ‘anchor’ (on the same line) ;; in the value of item-face. ("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face)) Here, pre-form and post-form are nil. Thereforesearching for ‘item’ starts at the end of the match of‘anchor’, and searching for subsequent instances of ‘anchor’resumes from where searching for ‘item’ concluded. (matcher highlighters…) This sort of element specifies several highlighter lists for asingle matcher. A highlighter list can be of the typesubexp-highlighter or anchored-highlighter as describedabove.For example, ;; Highlight occurrences of the word ‘anchor’ in the value ;; of anchor-face, and subsequent occurrences of the word ;; ‘item’ (on the same line) in the value of item-face. ("\\<anchor\\>" (0 anchor-face) ("\\<item\\>" nil nil (0 item-face))) (eval . form) Here form is an expression to be evaluated the first timethis value of font-lock-keywords is used in a buffer.Its value should have one of the forms described in this table. Warning: Do not design an element of font-lock-keywords to match text which spans lines; this does not work reliably. For details, see See . You can use case-fold in font-lock-defaults to specify the value of font-lock-keywords-case-fold-search which says whether search-based fontification should be case-insensitive. font-lock-keywords-case-fold-search — Variable: font-lock-keywords-case-fold-search Non-nil means that regular expression matching for the sake offont-lock-keywords should be case-insensitive. Customizing Search-Based Fontification You can use font-lock-add-keywords to add additional search-based fontification rules to a major mode, and font-lock-remove-keywords to removes rules. font-lock-add-keywords — Function: font-lock-add-keywords mode keywords &optional how This function adds highlighting keywords, for the current bufferor for major mode mode. The argument keywords should be alist with the same format as the variable font-lock-keywords.If mode is a symbol which is a major mode command name, such asc-mode, the effect is that enabling Font Lock mode inmode will add keywords to font-lock-keywords.Calling with a non-nil value of mode is correct only inyour ~/.emacs file.If mode is nil, this function adds keywords tofont-lock-keywords in the current buffer. This way of callingfont-lock-add-keywords is usually used in mode hook functions.By default, keywords are added at the beginning offont-lock-keywords. If the optional argument how isset, they are used to replace the value offont-lock-keywords. If how is any other non-nilvalue, they are added at the end of font-lock-keywords.Some modes provide specialized support you can use in additionalhighlighting patterns. See the variablesc-font-lock-extra-types, c++-font-lock-extra-types,and java-font-lock-extra-types, for example.Warning: major mode functions must not callfont-lock-add-keywords under any circumstances, either directlyor indirectly, except through their mode hooks. (Doing so would leadto incorrect behavior for some minor modes.) They should set up theirrules for search-based fontification by settingfont-lock-keywords. font-lock-remove-keywords — Function: font-lock-remove-keywords mode keywords This function removes keywords from font-lock-keywordsfor the current buffer or for major mode mode. As infont-lock-add-keywords, mode should be a major modecommand name or nil. All the caveats and requirements forfont-lock-add-keywords apply here too. For example, this code (font-lock-add-keywords 'c-mode '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))) adds two fontification patterns for C mode: one to fontify the word ‘FIXME’, even in comments, and another to fontify the words ‘and’, ‘or’ and ‘not’ as keywords. That example affects only C mode proper. To add the same patterns to C mode and all modes derived from it, do this instead: (add-hook 'c-mode-hook (lambda () (font-lock-add-keywords nil '(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend) ("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face))))) Other Font Lock Variables This section describes additional variables that a major mode can set by means of other-vars in font-lock-defaults (see ). font-lock-mark-block-function — Variable: font-lock-mark-block-function If this variable is non-nil, it should be a function that iscalled with no arguments, to choose an enclosing range of text forrefontification for the command M-o M-o(font-lock-fontify-block).The function should report its choice by placing the region around it.A good choice is a range of text large enough to give proper results,but not too large so that refontification becomes slow. Typical valuesare mark-defun for programming modes or mark-paragraph fortextual modes. font-lock-extra-managed-props — Variable: font-lock-extra-managed-props This variable specifies additional properties (other thanfont-lock-face) that are being managed by Font Lock mode. Itis used by font-lock-default-unfontify-region, which normallyonly manages the font-lock-face property. If you want FontLock to manage other properties as well, you must specify them in afacespec in font-lock-keywords as well as add them tothis list. See . font-lock-fontify-buffer-function — Variable: font-lock-fontify-buffer-function Function to use for fontifying the buffer. The default value isfont-lock-default-fontify-buffer. font-lock-unfontify-buffer-function — Variable: font-lock-unfontify-buffer-function Function to use for unfontifying the buffer. This is used whenturning off Font Lock mode. The default value isfont-lock-default-unfontify-buffer. font-lock-fontify-region-function — Variable: font-lock-fontify-region-function Function to use for fontifying a region. It should take twoarguments, the beginning and end of the region, and an optional thirdargument verbose. If verbose is non-nil, thefunction should print status messages. The default value isfont-lock-default-fontify-region. font-lock-unfontify-region-function — Variable: font-lock-unfontify-region-function Function to use for unfontifying a region. It should take twoarguments, the beginning and end of the region. The default value isfont-lock-default-unfontify-region. Levels of Font Lock Many major modes offer three different levels of fontification. You can define multiple levels by using a list of symbols for keywords in font-lock-defaults. Each symbol specifies one level of fontification; it is up to the user to choose one of these levels. The chosen level's symbol value is used to initialize font-lock-keywords. Here are the conventions for how to define the levels of fontification: Level 1: highlight function declarations, file directives (such as include orimport directives), strings and comments. The idea is speed, so onlythe most important and top-level components are fontified. Level 2: in addition to level 1, highlight all language keywords,including type names that act like keywords, as well as named constantvalues. The idea is that all keywords (either syntactic or semantic)should be fontified appropriately. Level 3: in addition to level 2, highlight the symbols being defined infunction and variable declarations, and all builtin function names,wherever they appear. Precalculated Fontification In addition to using font-lock-defaults for search-based fontification, you may use the special character property font-lock-face (see ). This property acts just like the explicit face property, but its activation is toggled when the user calls M-x font-lock-mode. Using font-lock-face is especially convenient for special modes which construct their text programmatically, such as list-buffers and occur. If your mode does not use any of the other machinery of Font Lock (i.e. it only uses the font-lock-face property), it should not set the variable font-lock-defaults. Faces for Font Lock faces for font lock font lock faces You can make Font Lock mode use any face, but several faces are defined specifically for Font Lock mode. Each of these symbols is both a face name, and a variable whose default value is the symbol itself. Thus, the default value of font-lock-comment-face is font-lock-comment-face. This means you can write font-lock-comment-face in a context such as font-lock-keywords where a face-name-valued expression is used. font-lock-comment-face font-lock-comment-faceUsed (typically) for comments. font-lock-comment-delimiter-face font-lock-comment-delimiter-faceUsed (typically) for comments delimiters. font-lock-doc-face font-lock-doc-faceUsed (typically) for documentation strings in the code. font-lock-string-face font-lock-string-faceUsed (typically) for string constants. font-lock-keyword-face font-lock-keyword-faceUsed (typically) for keywords—names that have special syntacticsignificance, like for and if in C. font-lock-builtin-face font-lock-builtin-faceUsed (typically) for built-in function names. font-lock-function-name-face font-lock-function-name-faceUsed (typically) for the name of a function being defined or declared,in a function definition or declaration. font-lock-variable-name-face font-lock-variable-name-faceUsed (typically) for the name of a variable being defined or declared,in a variable definition or declaration. font-lock-type-face font-lock-type-faceUsed (typically) for names of user-defined data types,where they are defined and where they are used. font-lock-constant-face font-lock-constant-faceUsed (typically) for constant names. font-lock-preprocessor-face font-lock-preprocessor-faceUsed (typically) for preprocessor commands. font-lock-negation-char-face font-lock-negation-char-faceUsed (typically) for easily-overlooked negation characters. font-lock-warning-face font-lock-warning-faceUsed (typically) for constructs that are peculiar, or that greatlychange the meaning of other text. For example, this is used for‘;;;###autoload’ cookies in Emacs Lisp, and for #errordirectives in C. Syntactic Font Lock syntactic font lock Syntactic fontification uses the syntax table to find comments and string constants (see ). It highlights them using font-lock-comment-face and font-lock-string-face (see ), or whatever font-lock-syntactic-face-function chooses. There are several variables that affect syntactic fontification; you should set them by means of font-lock-defaults (see ). font-lock-keywords-only — Variable: font-lock-keywords-only Non-nil means Font Lock should not do syntactic fontification;it should only fontify based on font-lock-keywords. The normalway for a mode to set this variable to t is withkeywords-only in font-lock-defaults. font-lock-syntax-table — Variable: font-lock-syntax-table This variable holds the syntax table to use for fontification ofcomments and strings. Specify it using syntax-alist infont-lock-defaults. If this is nil, fontification usesthe buffer's syntax table. font-lock-beginning-of-syntax-function — Variable: font-lock-beginning-of-syntax-function If this variable is non-nil, it should be a function to movepoint back to a position that is syntactically at “top level” andoutside of strings or comments. Font Lock uses this when necessaryto get the right results for syntactic fontification.This function is called with no arguments. It should leave point atthe beginning of any enclosing syntactic block. Typical values arebeginning-of-line (used when the start of the line is known tobe outside a syntactic block), or beginning-of-defun forprogramming modes, or backward-paragraph for textual modes.If the value is nil, Font Lock usessyntax-begin-function to move back outside of any comment,string, or sexp. This variable is semi-obsolete; we recommend settingsyntax-begin-function instead.Specify this variable using syntax-begin infont-lock-defaults. font-lock-syntactic-face-function — Variable: font-lock-syntactic-face-function A function to determine which face to use for a given syntacticelement (a string or a comment). The function is called with oneargument, the parse state at point returned byparse-partial-sexp, and should return a face. The defaultvalue returns font-lock-comment-face for comments andfont-lock-string-face for strings.This can be used to highlighting different kinds of strings orcomments differently. It is also sometimes abused together withfont-lock-syntactic-keywords to highlight constructs that spanmultiple lines, but this is too esoteric to document here.Specify this variable using other-vars infont-lock-defaults. Setting Syntax Properties Font Lock mode can be used to update syntax-table properties automatically (see ). This is useful in languages for which a single syntax table by itself is not sufficient. font-lock-syntactic-keywords — Variable: font-lock-syntactic-keywords This variable enables and controls updating syntax-tableproperties by Font Lock. Its value should be a list of elements ofthis form: (matcher subexp syntax override laxmatch) The parts of this element have the same meanings as in the correspondingsort of element of font-lock-keywords, (matcher subexp facespec override laxmatch) However, instead of specifying the value facespec to use for theface property, it specifies the value syntax to use forthe syntax-table property. Here, syntax can be a string(as taken by modify-syntax-entry), a syntax table, a cons cell(as returned by string-to-syntax), or an expression whose valueis one of those two types. override cannot be prepend orappend.For example, an element of the form: ("\\$\\(#\\)" 1 ".") highlights syntactically a hash character when following a dollarcharacter, with a SYNTAX of "." (meaning punctuation syntax).Assuming that the buffer syntax table specifies hash characters tohave comment start syntax, the element will only highlight hashcharacters that do not follow dollar characters as commentssyntactically.An element of the form: ("\\('\\).\\('\\)" (1 "\"") (2 "\"")) highlights syntactically both single quotes which surround a singlecharacter, with a SYNTAX of "\"" (meaning string quote syntax).Assuming that the buffer syntax table does not specify single quotesto have quote syntax, the element will only highlight single quotes ofthe form ‘'c'’ as strings syntactically. Other forms, suchas ‘foo'bar’ or ‘'fubar'’, will not be highlighted asstrings.Major modes normally set this variable with other-vars infont-lock-defaults. Multiline Font Lock Constructs multiline font lock Normally, elements of font-lock-keywords should not match across multiple lines; that doesn't work reliably, because Font Lock usually scans just part of the buffer, and it can miss a multi-line construct that crosses the line boundary where the scan starts. (The scan normally starts at the beginning of a line.) Making elements that match multiline constructs work properly has two aspects: correct identification and correct rehighlighting. The first means that Font Lock finds all multiline constructs. The second means that Font Lock will correctly rehighlight all the relevant text when a multiline construct is changed—for example, if some of the text that was previously part of a multiline construct ceases to be part of it. The two aspects are closely related, and often getting one of them to work will appear to make the other also work. However, for reliable results you must attend explicitly to both aspects. There are three ways to ensure correct identification of multiline constructs: Add a function to font-lock-extend-region-functions that doesthe identification and extends the scan so that the scannedtext never starts or ends in the middle of a multiline construct. Use the font-lock-fontify-region-function hook similarly toextend the scan so that the scanned text never starts or ends in themiddle of a multiline construct. Somehow identify the multiline construct right when it gets insertedinto the buffer (or at any point after that but before font-locktries to highlight it), and mark it with a font-lock-multilinewhich will instruct font-lock not to start or end the scan in themiddle of the construct. There are three ways to do rehighlighting of multiline constructs: Place a font-lock-multiline property on the construct. Thiswill rehighlight the whole construct if any part of it is changed. Insome cases you can do this automatically by setting thefont-lock-multiline variable, which see. Make sure jit-lock-contextually is set and rely on it doing itsjob. This will only rehighlight the part of the construct thatfollows the actual change, and will do it after a short delay.This only works if the highlighting of the various parts of yourmultiline construct never depends on text in subsequent lines.Since jit-lock-contextually is activated by default, this canbe an attractive solution. Place a jit-lock-defer-multiline property on the construct.This works only if jit-lock-contextually is used, and with thesame delay before rehighlighting, but like font-lock-multiline,it also handles the case where highlighting depends onsubsequent lines. Font Lock Multiline One way to ensure reliable rehighlighting of multiline Font Lock constructs is to put on them the text property font-lock-multiline. It should be present and non-nil for text that is part of a multiline construct. When Font Lock is about to highlight a range of text, it first extends the boundaries of the range as necessary so that they do not fall within text marked with the font-lock-multiline property. Then it removes any font-lock-multiline properties from the range, and highlights it. The highlighting specification (mostly font-lock-keywords) must reinstall this property each time, whenever it is appropriate. Warning: don't use the font-lock-multiline property on large ranges of text, because that will make rehighlighting slow. font-lock-multiline — Variable: font-lock-multiline If the font-lock-multiline variable is set to t, FontLock will try to add the font-lock-multiline propertyautomatically on multiline constructs. This is not a universalsolution, however, since it slows down Font Lock somewhat. It canmiss some multiline constructs, or make the property larger or smallerthan necessary.For elements whose matcher is a function, the function shouldensure that submatch 0 covers the whole relevant multiline construct,even if only a small subpart will be highlighted. It is often just aseasy to add the font-lock-multiline property by hand. The font-lock-multiline property is meant to ensure proper refontification; it does not automatically identify new multiline constructs. Identifying the requires that Font-Lock operate on large enough chunks at a time. This will happen by accident on many cases, which may give the impression that multiline constructs magically work. If you set the font-lock-multiline variable non-nil, this impression will be even stronger, since the highlighting of those constructs which are found will be properly updated from then on. But that does not work reliably. To find multiline constructs reliably, you must either manually place the font-lock-multiline property on the text before Font-Lock looks at it, or use font-lock-fontify-region-function. Region to Fontify after a Buffer Change When a buffer is changed, the region that Font Lock refontifies is by default the smallest sequence of whole lines that spans the change. While this works well most of the time, sometimes it doesn't—for example, when a change alters the syntactic meaning of text on an earlier line. You can enlarge (or even reduce) the region to fontify by setting one the following variables: font-lock-extend-after-change-region-function — Variable: font-lock-extend-after-change-region-function This buffer-local variable is either nil or a function forFont-Lock to call to determine the region to scan and fontify.The function is given three parameters, the standard beg,end, and old-len from after-change-functions(see ). It should return either a cons of thebeginning and end buffer positions (in that order) of the region tofontify, or nil (which means choose the region in the standardway). This function needs to preserve point, the match-data, and thecurrent restriction. The region it returns may start or end in themiddle of a line.Since this function is called after every buffer change, it should bereasonably fast. Desktop Save Mode desktop save mode Desktop Save Mode is a feature to save the state of Emacs from one session to another. The user-level commands for using Desktop Save Mode are described in the GNU Emacs Manual (see See section ``Saving Emacs Sessions'' in the GNU Emacs Manual). Modes whose buffers visit a file, don't have to do anything to use this feature. For buffers not visiting a file to have their state saved, the major mode must bind the buffer local variable desktop-save-buffer to a non-nil value. desktop-save-buffer — Variable: desktop-save-buffer If this buffer-local variable is non-nil, the buffer will haveits state saved in the desktop file at desktop save. If the value isa function, it is called at desktop save with argumentdesktop-dirname, and its value is saved in the desktop file alongwith the state of the buffer for which it was called. When file namesare returned as part of the auxiliary information, they should beformatted using the call (desktop-file-name file-name desktop-dirname) For buffers not visiting a file to be restored, the major mode must define a function to do the job, and that function must be listed in the alist desktop-buffer-mode-handlers. desktop-buffer-mode-handlers — Variable: desktop-buffer-mode-handlers Alist with elements (major-mode . restore-buffer-function) The function restore-buffer-function will be called withargument list (buffer-file-name buffer-name desktop-buffer-misc) and it should return the restored buffer.Here desktop-buffer-misc is the value returned by the functionoptionally bound to desktop-save-buffer. <setfilename>../info/help</setfilename> Documentation documentation strings GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation. Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion. For commands to display documentation strings, see See section ``Help'' in The GNU Emacs Manual. For the conventions for writing documentation strings, see . Documentation Basics documentation conventions writing a documentation string string, writing a doc string A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable. When you write a documentation string, make the first line a complete sentence (or two complete sentences) since some commands, such as apropos, show only the first line of a multi-line documentation string. Also, you should not indent the second line of a documentation string, if it has one, because that looks odd when you use C-h f (describe-function) or C-h v (describe-variable) to view the documentation string. There are many other conventions for doc strings; see . Documentation strings can contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See .) emacs-lisp-docstring-fill-column Emacs Lisp mode fills documentation strings to the width specified by emacs-lisp-docstring-fill-column. In Emacs Lisp, a documentation string is accessible through the function or variable that it describes: function-documentationThe documentation for a function is usually stored in the functiondefinition itself (see ). The functiondocumentation knows how to extract it. You can also putfunction documentation in the function-documentation propertyof the function name. That is useful with definitions such askeyboard macros that can't hold a documentation string. variable-documentationThe documentation for a variable is stored in the variable's propertylist under the property name variable-documentation. Thefunction documentation-property knows how to retrieve it. DOC-version(documentation) file To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the file emacs/etc/DOC-version—not inside Emacs. The documentation strings for functions and variables loaded during the Emacs session from byte-compiled files are stored in those files (see ). The data structure inside Emacs has an integer offset into the file, or a list containing a file name and an integer, in place of the documentation string. The functions documentation and documentation-property use that information to fetch the documentation string from the appropriate file; this is transparent to the user. The emacs/lib-src directory contains two utilities that you can use to print nice-looking hardcopy for the file emacs/etc/DOC-version. These are sorted-doc and digest-doc. Access to Documentation Strings documentation-property — Function: documentation-property symbol property &optional verbatim This function returns the documentation string that is recorded insymbol's property list under property property. Itretrieves the text from a file if the value calls for that. If theproperty value isn't nil, isn't a string, and doesn't refer totext in a file, then it is evaluated to obtain a string.The last thing this function does is pass the string throughsubstitute-command-keys to substitute actual key bindings,unless verbatim is non-nil. (documentation-property 'command-line-processed 'variable-documentation) => "Non-nil once command line has been processed" (symbol-plist 'command-line-processed) => (variable-documentation 188902) (documentation-property 'emacs 'group-documentation) => "Customization of the One True Editor." documentation — Function: documentation function &optional verbatim This function returns the documentation string of function.documentation handles macros, named keyboard macros, andspecial forms, as well as ordinary functions.If function is a symbol, this function first looks for thefunction-documentation property of that symbol; if that has anon-nil value, the documentation comes from that value (if thevalue is not a string, it is evaluated). If function is not asymbol, or if it has no function-documentation property, thendocumentation extracts the documentation string from the actualfunction definition, reading it from a file if called for.Finally, unless verbatim is non-nil, it callssubstitute-command-keys so as to return a value containing theactual (current) key bindings.The function documentation signals a void-function errorif function has no function definition. However, it is OK ifthe function definition has no documentation string. In that case,documentation returns nil. face-documentation — Function: face-documentation face This function returns the documentation string of face as aface. Here is an example of using the two functions, documentation and documentation-property, to display the documentation strings for several symbols in a ‘*Help*’ buffer. (defun describe-symbols (pattern) "Describe the Emacs Lisp symbols matching PATTERN. All symbols that have PATTERN in their name are described in the `*Help*' buffer." (interactive "sDescribe symbols matching: ") (let ((describe-func (function (lambda (s) ;; Print description of symbol. (if (fboundp s) ; It is a function. (princ (format "%s\t%s\n%s\n\n" s (if (commandp s) (let ((keys (where-is-internal s))) (if keys (concat "Keys: " (mapconcat 'key-description keys " ")) "Keys: none")) "Function") (or (documentation s) "not documented")))) (if (boundp s) ; It is a variable. (princ (format "%s\t%s\n%s\n\n" s (if (user-variable-p s) "Option " "Variable") (or (documentation-property s 'variable-documentation) "not documented"))))))) sym-list) ;; Build a list of symbols that match pattern. (mapatoms (function (lambda (sym) (if (string-match pattern (symbol-name sym)) (setq sym-list (cons sym sym-list)))))) ;; Display the data. (with-output-to-temp-buffer "*Help*" (mapcar describe-func (sort sym-list 'string<)) (print-help-return-message)))) The describe-symbols function works like apropos, but provides more information. (describe-symbols "goal") ---------- Buffer: *Help* ---------- goal-column Option *Semipermanent goal column for vertical motion, as set by … set-goal-column Keys: C-x C-n Set the current horizontal position as a goal for C-n and C-p. Those commands will move to this position in the line moved to rather than trying to keep the same horizontal position. With a non-nil argument, clears out the goal column so that C-n and C-p resume vertical motion. The goal column is stored in the variable `goal-column'. temporary-goal-column Variable Current goal column for vertical motion. It is the column where point was at the start of current run of vertical motion commands. When the `track-eol' feature is doing its job, the value is 9999. ---------- Buffer: *Help* ---------- The asterisk ‘*’ as the first character of a variable's doc string, as shown above for the goal-column variable, means that it is a user option; see the description of defvar in . Snarf-documentation — Function: Snarf-documentation filename This function is used only during Emacs initialization, just beforethe runnable Emacs is dumped. It finds the file offsets of thedocumentation strings stored in the file filename, and recordsthem in the in-core function definitions and variable property lists inplace of the actual strings. See .Emacs reads the file filename from the emacs/etc directory.When the dumped Emacs is later executed, the same file will be lookedfor in the directory doc-directory. Usually filename is"DOC-version". doc-directory — Variable: doc-directory This variable holds the name of the directory which should contain thefile "DOC-version" that contains documentation strings forbuilt-in and preloaded functions and variables.In most cases, this is the same as data-directory. They may bedifferent when you run Emacs from the directory where you built it,without actually installing it. See .In older Emacs versions, exec-directory was used for this. Substituting Key Bindings in Documentation documentation, keys in keys in documentation strings substituting keys in documentation When documentation strings refer to key sequences, they should use the current, actual key bindings. They can do so using certain special text sequences described below. Accessing documentation strings in the usual way substitutes current key binding information for these special sequences. This works by calling substitute-command-keys. You can also call that function yourself. Here is a list of the special sequences and what they mean: \[command] stands for a key sequence that will invoke command, or ‘M-xcommand’ if command has no key bindings. \{mapvar} stands for a summary of the keymap which is the value of the variablemapvar. The summary is made using describe-bindings. \<mapvar> stands for no text itself. It is used only for a side effect: itspecifies mapvar's value as the keymap for any following‘\[command]’ sequences in this documentation string. \= quotes the following character and is discarded; thus, ‘\=\[’ puts‘\[’ into the output, and ‘\=\=’ puts ‘\=’ into theoutput. Please note: Each ‘\’ must be doubled when written in a string in Emacs Lisp. substitute-command-keys — Function: substitute-command-keys string This function scans string for the above special sequences andreplaces them by what they stand for, returning the result as a string.This permits display of documentation that refers accurately to theuser's own customized key bindings. Here are examples of the special sequences: (substitute-command-keys "To abort recursive edit, type: \\[abort-recursive-edit]") => "To abort recursive edit, type: C-]" (substitute-command-keys "The keys that are defined for the minibuffer here are: \\{minibuffer-local-must-match-map}") => "The keys that are defined for the minibuffer here are: ? minibuffer-completion-help SPC minibuffer-complete-word TAB minibuffer-complete C-j minibuffer-complete-and-exit RET minibuffer-complete-and-exit C-g abort-recursive-edit " (substitute-command-keys "To abort a recursive edit from the minibuffer, type\ \\<minibuffer-local-must-match-map>\\[abort-recursive-edit].") => "To abort a recursive edit from the minibuffer, type C-g." There are other special conventions for the text in documentation strings—for instance, you can refer to functions, variables, and sections of this manual. See , for details. Describing Characters for Help Messages describe characters and events These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself. key-description — Function: key-description sequence &optional prefix Emacs event standard notationThis function returns a string containing the Emacs standard notationfor the input events in sequence. If prefix isnon-nil, it is a sequence of input events leading up tosequence and is included in the return value. Both argumentsmay be strings, vectors or lists. See , for moreinformation about valid events. (key-description [?\M-3 delete]) => "M-3 <delete>" (key-description [delete] "\M-3") => "M-3 <delete>" See also the examples for single-key-description, below. single-key-description — Function: single-key-description event &optional no-angles event printing character printing control character printing meta character printingThis function returns a string describing event in the standardEmacs notation for keyboard input. A normal printing characterappears as itself, but a control character turns into a stringstarting with ‘C-’, a meta character turns into a string startingwith ‘M-’, and space, tab, etc. appear as ‘SPC’,‘TAB’, etc. A function key symbol appears inside angle brackets‘<…>’. An event that is a list appears as the name of thesymbol in the car of the list, inside angle brackets.If the optional argument no-angles is non-nil, the anglebrackets around function keys and event symbols are omitted; this isfor compatibility with old versions of Emacs which didn't use thebrackets. (single-key-description ?\C-x) => "C-x" (key-description "\C-x \M-y \n \t \r \f123") => "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" (single-key-description 'delete) => "<delete>" (single-key-description 'C-mouse-1) => "<C-mouse-1>" (single-key-description 'C-mouse-1 t) => "C-mouse-1" text-char-description — Function: text-char-description character This function returns a string describing character in thestandard Emacs notation for characters that appear in text—likesingle-key-description, except that control characters arerepresented with a leading caret (which is how control characters inEmacs buffers are usually displayed). Another difference is thattext-char-description recognizes the 2**7 bit as the Metacharacter, whereas single-key-description uses the 2**27 bitfor Meta. (text-char-description ?\C-c) => "^C" (text-char-description ?\M-m) => "\xed" (text-char-description ?\C-\M-m) => "\x8d" (text-char-description (+ 128 ?m)) => "M-m" (text-char-description (+ 128 ?\C-m)) => "M-^M" read-kbd-macro — Function: read-kbd-macro string &optional need-vector This function is used mainly for operating on keyboard macros, but itcan also be used as a rough inverse for key-description. Youcall it with a string containing key descriptions, separated by spaces;it returns a string or vector containing the corresponding events.(This may or may not be a single valid key sequence, depending on whatevents you use; see .) If need-vector isnon-nil, the return value is always a vector. Help Functions Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see See section ``Help'' in The GNU Emacs Manual. Here we describe some program-level interfaces to the same information. apropos — Command: apropos pattern &optional do-all This function finds all “meaningful” symbols whose names contain amatch for the apropos pattern pattern. An apropos pattern iseither a word to match, a space-separated list of words of which atleast two must match, or a regular expression (if any special regularexpression characters occur). A symbol is “meaningful” if it has adefinition as a function, variable, or face, or has properties.The function returns a list of elements that look like this: (symbol score fn-doc var-doc plist-doc widget-doc face-doc group-doc) Here, score is an integer measure of how important the symbolseems to be as a match, and the remaining elements are documentationstrings for symbol's various roles (or nil).It also displays the symbols in a buffer named ‘*Apropos*’, eachwith a one-line description taken from the beginning of itsdocumentation string. If do-all is non-nil, or if the user optionapropos-do-all is non-nil, then apropos alsoshows key bindings for the functions that are found; it also showsall interned symbols, not just meaningful ones (and it liststhem in the return value as well). help-map — Variable: help-map The value of this variable is a local keymap for characters following theHelp key, C-h. help-command — Prefix Command: help-command This symbol is not a function; its function definition cell holds thekeymap known as help-map. It is defined in help.el asfollows: (define-key global-map (char-to-string help-char) 'help-command) (fset 'help-command help-map) print-help-return-message — Function: print-help-return-message &optional function This function builds a string that explains how to restore the previousstate of the windows after a help command. After building the message,it applies function to it if function is non-nil.Otherwise it calls message to display it in the echo area.This function expects to be called inside awith-output-to-temp-buffer special form, and expectsstandard-output to have the value bound by that special form.For an example of its use, see the long example in . help-char — Variable: help-char The value of this variable is the help character—the character thatEmacs recognizes as meaning Help. By default, its value is 8, whichstands for C-h. When Emacs reads this character, ifhelp-form is a non-nil Lisp expression, it evaluates thatexpression, and displays the result in a window if it is a string.Usually the value of help-form is nil. Then thehelp character has no special meaning at the level of command input, andit becomes part of a key sequence in the normal way. The standard keybinding of C-h is a prefix key for several general-purpose helpfeatures.The help character is special after prefix keys, too. If it has nobinding as a subcommand of the prefix key, it runsdescribe-prefix-bindings, which displays a list of all thesubcommands of the prefix key. help-event-list — Variable: help-event-list The value of this variable is a list of event types that serve asalternative “help characters.” These events are handled just like theevent specified by help-char. help-form — Variable: help-form If this variable is non-nil, its value is a form to evaluatewhenever the character help-char is read. If evaluating the formproduces a string, that string is displayed.A command that calls read-event or read-char probablyshould bind help-form to a non-nil expression while itdoes input. (The time when you should not do this is when C-h hassome other meaning.) Evaluating this expression should result in astring that explains what the input is for and how to enter it properly.Entry to the minibuffer binds this variable to the value ofminibuffer-help-form (see ). prefix-help-command — Variable: prefix-help-command This variable holds a function to print help for a prefix key. Thefunction is called when the user types a prefix key followed by the helpcharacter, and the help character has no binding after that prefix. Thevariable's default value is describe-prefix-bindings. describe-prefix-bindings — Function: describe-prefix-bindings This function calls describe-bindings to display a list of allthe subcommands of the prefix key of the most recent key sequence. Theprefix described consists of all but the last event of that keysequence. (The last event is, presumably, the help character.) The following two functions are meant for modes that want to provide help without relinquishing control, such as the “electric” modes. Their names begin with ‘Helper’ to distinguish them from the ordinary help functions. Helper-describe-bindings — Command: Helper-describe-bindings This command pops up a window displaying a help buffer containing alisting of all of the key bindings from both the local and global keymaps.It works by calling describe-bindings. Helper-help — Command: Helper-help This command provides help for the current mode. It prompts the userin the minibuffer with the message ‘Help (Type ? for furtheroptions)’, and then provides assistance in finding out what the keybindings are, and what the mode is intended for. It returns nil.This can be customized by changing the map Helper-help-map. data-directory — Variable: data-directory This variable holds the name of the directory in which Emacs findscertain documentation and text files that come with Emacs. In olderEmacs versions, exec-directory was used for this. make-help-screen — Macro: make-help-screen fname help-line help-text help-map This macro defines a help command named fname that acts like aprefix key that shows a list of the subcommands it offers.When invoked, fname displays help-text in a window, thenreads and executes a key sequence according to help-map. Thestring help-text should describe the bindings available inhelp-map.The command fname is defined to handle a few events itself, byscrolling the display of help-text. When fname reads one ofthose special events, it does the scrolling and then reads anotherevent. When it reads an event that is not one of those few, and whichhas a binding in help-map, it executes that key's binding andthen returns.The argument help-line should be a single-line summary of thealternatives in help-map. In the current version of Emacs, thisargument is used only if you set the option three-step-help tot.This macro is used in the command help-for-help which is thebinding of C-h C-h. three-step-help — User Option: three-step-help If this variable is non-nil, commands defined withmake-help-screen display their help-line strings in theecho area at first, and display the longer help-text strings onlyif the user types the help character again. <setfilename>../info/files</setfilename> Files In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in , and those related to backups and auto-saving are described in . Many of the file functions take one or more arguments that are file names. A file name is actually a string. Most of these functions expand file name arguments by calling expand-file-name, so that ~ is handled correctly, as are relative file names (including ‘../’). These functions don't recognize environment variable substitutions such as ‘$HOME’. See . When file I/O functions signal Lisp errors, they usually use the condition file-error (see ). The error message is in most cases obtained from the operating system, according to locale system-message-locale, and decoded using coding system locale-coding-system (see ). Visiting Files finding files visiting files Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file “the visited file” of the buffer. A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file. In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, “I am editing a file,” rather than, “I am editing a buffer that I will soon save as a file of the same name.” Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind. Functions for Visiting Files This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with ‘find-’ rather than ‘visit-’. See , for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name. In a Lisp program, if you want to look at the contents of a file but not alter it, the fastest way is to use insert-file-contents in a temporary buffer. Visiting the file is not necessary and takes longer. See . find-file — Command: find-file filename &optional wildcards This command selects a buffer visiting the file filename,using an existing buffer if there is one, and otherwise creating anew buffer and reading the file into it. It also returns that buffer.Aside from some technical details, the body of the find-filefunction is basically equivalent to: (switch-to-buffer (find-file-noselect filename nil nil wildcards)) (See switch-to-buffer in .)If wildcards is non-nil, which is always true in aninteractive call, then find-file expands wildcard characters infilename and visits all the matching files.When find-file is called interactively, it prompts forfilename in the minibuffer. find-file-noselect — Function: find-file-noselect filename &optional nowarn rawfile wildcards This function is the guts of all the file-visiting functions. Itreturns a buffer visiting the file filename. You may make thebuffer current or display it in a window if you wish, but thisfunction does not do so.The function returns an existing buffer if there is one; otherwise itcreates a new buffer and reads the file into it. Whenfind-file-noselect uses an existing buffer, it first verifiesthat the file has not changed since it was last visited or saved inthat buffer. If the file has changed, this function asks the userwhether to reread the changed file. If the user says ‘yes’, anyedits previously made in the buffer are lost.Reading the file involves decoding the file's contents (see ), including end-of-line conversion, and format conversion(see ). If wildcards is non-nil,then find-file-noselect expands wildcard characters infilename and visits all the matching files.This function displays warning or advisory messages in various peculiarcases, unless the optional argument nowarn is non-nil. Forexample, if it needs to create a buffer, and there is no file namedfilename, it displays the message ‘(New file)’ in the echoarea, and leaves the buffer empty.The find-file-noselect function normally callsafter-find-file after reading the file (see ). That function sets the buffer major mode, parses localvariables, warns the user if there exists an auto-save file more recentthan the file just visited, and finishes by running the functions infind-file-hook.If the optional argument rawfile is non-nil, thenafter-find-file is not called, and thefind-file-not-found-functions are not run in case of failure.What's more, a non-nil rawfile value suppresses codingsystem conversion and format conversion.The find-file-noselect function usually returns the buffer thatis visiting the file filename. But, if wildcards are actuallyused and expanded, it returns a list of buffers that are visiting thevarious files. (find-file-noselect "/etc/fstab") => #<buffer fstab> find-file-other-window — Command: find-file-other-window filename &optional wildcards This command selects a buffer visiting the file filename, butdoes so in a window other than the selected window. It may use anotherexisting window or split a window; see .When this command is called interactively, it prompts forfilename. find-file-read-only — Command: find-file-read-only filename &optional wildcards This command selects a buffer visiting the file filename, likefind-file, but it marks the buffer as read-only. See , for related functions and variables.When this command is called interactively, it prompts forfilename. view-file — Command: view-file filename This command visits filename using View mode, returning to theprevious buffer when you exit View mode. View mode is a minor mode thatprovides commands to skim rapidly through the file, but does not let youmodify the text. Entering View mode runs the normal hookview-mode-hook. See .When view-file is called interactively, it prompts forfilename. find-file-wildcards — User Option: find-file-wildcards If this variable is non-nil, then the various find-filecommands check for wildcard characters and visit all the files thatmatch them (when invoked interactively or when their wildcardsargument is non-nil). If this option is nil, thenthe find-file commands ignore their wildcards argumentand never treat wildcard characters specially. find-file-hook — Variable: find-file-hook The value of this variable is a list of functions to be called after afile is visited. The file's local-variables specification (if any) willhave been processed before the hooks are run. The buffer visiting thefile is current when the hook functions are run.This variable is a normal hook. See . find-file-not-found-functions — Variable: find-file-not-found-functions The value of this variable is a list of functions to be called whenfind-file or find-file-noselect is passed a nonexistentfile name. find-file-noselect calls these functions as soon asit detects a nonexistent file. It calls them in the order of the list,until one of them returns non-nil. buffer-file-name isalready set up.This is not a normal hook because the values of the functions areused, and in many cases only some of the functions are called. Subroutines of Visiting The find-file-noselect function uses two important subroutines which are sometimes useful in user Lisp code: create-file-buffer and after-find-file. This section explains how to use them. create-file-buffer — Function: create-file-buffer filename This function creates a suitably named buffer for visitingfilename, and returns it. It uses filename (sans directory)as the name if that name is free; otherwise, it appends a string such as‘<2>’ to get an unused name. See also .Please note: create-file-buffer does notassociate the new buffer with a file and does not select the buffer.It also does not use the default major mode. (create-file-buffer "foo") => #<buffer foo> (create-file-buffer "foo") => #<buffer foo<2>> (create-file-buffer "foo") => #<buffer foo<3>> This function is used by find-file-noselect.It uses generate-new-buffer (see ). after-find-file — Function: after-find-file &optional error warn noauto after-find-file-from-revert-buffer nomodes This function sets the buffer major mode, and parses local variables(see ). It is called by find-file-noselectand by the default revert function (see ). new file message file open errorIf reading the file got an error because the file does not exist, butits directory does exist, the caller should pass a non-nil valuefor error. In that case, after-find-file issues a warning:‘(New file)’. For more serious errors, the caller should usually notcall after-find-file.If warn is non-nil, then this function issues a warningif an auto-save file exists and is more recent than the visited file.If noauto is non-nil, that says not to enable or disableAuto-Save mode. The mode remains enabled if it was enabled before.If after-find-file-from-revert-buffer is non-nil, thatmeans this call was from revert-buffer. This has no directeffect, but some mode functions and hook functions check the valueof this variable.If nomodes is non-nil, that means don't alter the buffer'smajor mode, don't process local variables specifications in the file,and don't run find-file-hook. This feature is used byrevert-buffer in some cases.The last thing after-find-file does is call all the functionsin the list find-file-hook. Saving Buffers saving buffers When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file. save-buffer — Command: save-buffer &optional backup-option This function saves the contents of the current buffer in its visitedfile if the buffer has been modified since it was last visited or saved.Otherwise it does nothing.save-buffer is responsible for making backup files. Normally,backup-option is nil, and save-buffer makes a backupfile only if this is the first save since visiting the file. Othervalues for backup-option request the making of backup files inother circumstances: With an argument of 4 or 64, reflecting 1 or 3 C-u's, thesave-buffer function marks this version of the file to bebacked up when the buffer is next saved. With an argument of 16 or 64, reflecting 2 or 3 C-u's, thesave-buffer function unconditionally backs up the previousversion of the file before saving it. With an argument of 0, unconditionally do not make any backup file. save-some-buffers — Command: save-some-buffers &optional save-silently-p pred This command saves some modified file-visiting buffers. Normally itasks the user about each buffer. But if save-silently-p isnon-nil, it saves all the file-visiting buffers without queryingthe user.The optional pred argument controls which buffers to ask about(or to save silently if save-silently-p is non-nil).If it is nil, that means to ask only about file-visiting buffers.If it is t, that means also offer to save certain other non-filebuffers—those that have a non-nil buffer-local value ofbuffer-offer-save (see ). A user who says‘yes’ to saving a non-file buffer is asked to specify the filename to use. The save-buffers-kill-emacs function passes thevalue t for pred.If pred is neither t nor nil, then it should bea function of no arguments. It will be called in each buffer to decidewhether to offer to save that buffer. If it returns a non-nilvalue in a certain buffer, that means do offer to save that buffer. write-file — Command: write-file filename &optional confirm This function writes the current buffer into file filename, makesthe buffer visit that file, and marks it not modified. Then it renamesthe buffer based on filename, appending a string like ‘<2>’if necessary to make a unique buffer name. It does most of this work bycalling set-visited-file-name (see ) andsave-buffer.If confirm is non-nil, that means to ask for confirmationbefore overwriting an existing file. Interactively, confirmation isrequired, unless the user supplies a prefix argument.If filename is an existing directory, or a symbolic link to one,write-file uses the name of the visited file, in directoryfilename. If the buffer is not visiting a file, it uses thebuffer name instead. Saving a buffer runs several hooks. It also performs format conversion (see ), and may save text properties in “annotations” (see ). write-file-functions — Variable: write-file-functions The value of this variable is a list of functions to be called beforewriting out a buffer to its visited file. If one of them returnsnon-nil, the file is considered already written and the rest ofthe functions are not called, nor is the usual code for writing the fileexecuted.If a function in write-file-functions returns non-nil, itis responsible for making a backup file (if that is appropriate).To do so, execute the following code: (or buffer-backed-up (backup-buffer)) You might wish to save the file modes value returned bybackup-buffer and use that (if non-nil) to set the modebits of the file that you write. This is what save-buffernormally does. See Making Backup Files.The hook functions in write-file-functions are also responsiblefor encoding the data (if desired): they must choose a suitable codingsystem and end-of-line conversion (see ),perform the encoding (see ), and setlast-coding-system-used to the coding system that was used(see ).If you set this hook locally in a buffer, it is assumed to beassociated with the file or the way the contents of the buffer wereobtained. Thus the variable is marked as a permanent local, so thatchanging the major mode does not alter a buffer-local value. On theother hand, calling set-visited-file-name will reset it.If this is not what you want, you might like to usewrite-contents-functions instead.Even though this is not a normal hook, you can use add-hook andremove-hook to manipulate the list. See . write-contents-functions — Variable: write-contents-functions This works just like write-file-functions, but it is intendedfor hooks that pertain to the buffer's contents, not to the particularvisited file or its location. Such hooks are usually set up by majormodes, as buffer-local bindings for this variable. This variableautomatically becomes buffer-local whenever it is set; switching to anew major mode always resets this variable, but callingset-visited-file-name does not.If any of the functions in this hook returns non-nil, the fileis considered already written and the rest are not called and neitherare the functions in write-file-functions. before-save-hook — User Option: before-save-hook This normal hook runs before a buffer is saved in its visited file,regardless of whether that is done normally or by one of the hooksdescribed above. For instance, the copyright.el program usesthis hook to make sure the file you are saving has the current year inits copyright notice. after-save-hook — User Option: after-save-hook This normal hook runs after a buffer has been saved in its visited file.One use of this hook is in Fast Lock mode; it uses this hook to save thehighlighting information in a cache file. file-precious-flag — User Option: file-precious-flag If this variable is non-nil, then save-buffer protectsagainst I/O errors while saving by writing the new file to a temporaryname instead of the name it is supposed to have, and then renaming it tothe intended name after it is clear there are no errors. This procedureprevents problems such as a lack of disk space from resulting in aninvalid file.As a side effect, backups are necessarily made by copying. See . Yet, at the same time, saving a precious file always breaksall hard links between the file you save and other file names.Some modes give this variable a non-nil buffer-local valuein particular buffers. require-final-newline — User Option: require-final-newline This variable determines whether files may be written out that donot end with a newline. If the value of the variable ist, then save-buffer silently adds a newline at the end ofthe file whenever the buffer being saved does not already end in one.If the value of the variable is non-nil, but not t, thensave-buffer asks the user whether to add a newline each time thecase arises.If the value of the variable is nil, then save-bufferdoesn't add newlines at all. nil is the default value, but a fewmajor modes set it to t in particular buffers. See also the function set-visited-file-name (see ). Reading from Files reading from files You can copy a file from the disk and insert it into a buffer using the insert-file-contents function. Don't use the user-level command insert-file in a Lisp program, as that sets the mark. insert-file-contents — Function: insert-file-contents filename &optional visit beg end replace This function inserts the contents of file filename into thecurrent buffer after point. It returns a list of the absolute file nameand the length of the data inserted. An error is signaled iffilename is not the name of a file that can be read.The function insert-file-contents checks the file contentsagainst the defined file formats, and converts the file contents ifappropriate. See . It also calls the functions inthe list after-insert-file-functions; see . Normally, one of the functions in theafter-insert-file-functions list determines the coding system(see ) used for decoding the file's contents,including end-of-line conversion.If visit is non-nil, this function additionally marks thebuffer as unmodified and sets up various fields in the buffer so that itis visiting the file filename: these include the buffer's visitedfile name and its last save file modtime. This feature is used byfind-file-noselect and you probably should not use it yourself.If beg and end are non-nil, they should be integersspecifying the portion of the file to insert. In this case, visitmust be nil. For example, (insert-file-contents filename nil 0 500) inserts the first 500 characters of a file.If the argument replace is non-nil, it means to replace thecontents of the buffer (actually, just the accessible portion) with thecontents of the file. This is better than simply deleting the buffercontents and inserting the whole file, because (1) it preserves somemarker positions and (2) it puts less data in the undo list.It is possible to read a special file (such as a FIFO or an I/O device)with insert-file-contents, as long as replace andvisit are nil. insert-file-contents-literally — Function: insert-file-contents-literally filename &optional visit beg end replace This function works like insert-file-contents except that it doesnot do format decoding (see ), does not docharacter code conversion (see ), does not runfind-file-hook, does not perform automatic uncompression, and soon. If you want to pass a file name to another process so that another program can read the file, use the function file-local-copy; see . Writing to Files writing to files You can write the contents of a buffer, or part of a buffer, directly to a file on disk using the append-to-file and write-region functions. Don't use these functions to write to files that are being visited; that could cause confusion in the mechanisms for visiting. append-to-file — Command: append-to-file start end filename This function appends the contents of the region delimited bystart and end in the current buffer to the end of filefilename. If that file does not exist, it is created. Thisfunction returns nil.An error is signaled if filename specifies a nonwritable file,or a nonexistent file in a directory where files cannot be created.When called from Lisp, this function is completely equivalent to: (write-region start end filename t) write-region — Command: write-region start end filename &optional append visit lockname mustbenew This function writes the region delimited by start and endin the current buffer into the file specified by filename.If start is nil, then the command writes the entire buffercontents (not just the accessible portion) to the file andignores end. If start is a string, then write-region writes or appendsthat string, rather than text from the buffer. end is ignored inthis case.If append is non-nil, then the specified text is appendedto the existing file contents (if any). If append is aninteger, write-region seeks to that byte offset from the startof the file and writes the data from there.If mustbenew is non-nil, then write-region asksfor confirmation if filename names an existing file. Ifmustbenew is the symbol excl, then write-regiondoes not ask for confirmation, but instead it signals an errorfile-already-exists if the file already exists.The test for an existing file, when mustbenew is excl, usesa special system feature. At least for files on a local disk, there isno chance that some other program could create a file of the same namebefore Emacs does, without Emacs's noticing.If visit is t, then Emacs establishes an associationbetween the buffer and the file: the buffer is then visiting that file.It also sets the last file modification time for the current buffer tofilename's modtime, and marks the buffer as not modified. Thisfeature is used by save-buffer, but you probably should not useit yourself. If visit is a string, it specifies the file name to visit. Thisway, you can write the data to one file (filename) while recordingthe buffer as visiting another file (visit). The argumentvisit is used in the echo area message and also for file locking;visit is stored in buffer-file-name. This feature is usedto implement file-precious-flag; don't use it yourself unless youreally know what you're doing.The optional argument lockname, if non-nil, specifies thefile name to use for purposes of locking and unlocking, overridingfilename and visit for that purpose.The function write-region converts the data which it writes tothe appropriate file formats specified by buffer-file-format.See . It also calls the functions in the listwrite-region-annotate-functions; see .Normally, write-region displays the message ‘Wrotefilename’ in the echo area. If visit is neither tnor nil nor a string, then this message is inhibited. Thisfeature is useful for programs that use files for internal purposes,files that the user does not need to know about. with-temp-file — Macro: with-temp-file file body … The with-temp-file macro evaluates the body forms with atemporary buffer as the current buffer; then, at the end, it writes thebuffer contents into file file. It kills the temporary bufferwhen finished, restoring the buffer that was current before thewith-temp-file form. Then it returns the value of the last formin body.The current buffer is restored even in case of an abnormal exit viathrow or error (see ).See also with-temp-buffer in The Current Buffer. File Locks file locks lock file When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. (File locks are not implemented on Microsoft systems.) Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do. The file lock is really a file, a symbolic link with a special name, stored in the same directory as the file you are editing. When you access files using NFS, there may be a small probability that you and another user will both lock the same file “simultaneously.” If this happens, it is possible for the two users to make changes simultaneously, but Emacs will still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see . file-locked-p — Function: file-locked-p filename This function returns nil if the file filename is notlocked. It returns t if it is locked by this Emacs process, andit returns the name of the user who has locked it if it is locked bysome other job. (file-locked-p "foo") => nil lock-buffer — Function: lock-buffer &optional filename This function locks the file filename, if the current buffer ismodified. The argument filename defaults to the current buffer'svisited file. Nothing is done if the current buffer is not visiting afile, or is not modified, or if the system does not support locking. unlock-buffer — Function: unlock-buffer This function unlocks the file being visited in the current buffer,if the buffer is modified. If the buffer is not modified, thenthe file should not be locked, so this function does nothing. It alsodoes nothing if the current buffer is not visiting a file, or if thesystem does not support locking. File locking is not supported on some systems. On systems that do not support it, the functions lock-buffer, unlock-buffer and file-locked-p do nothing and return nil. ask-user-about-lock — Function: ask-user-about-lock file other-user This function is called when the user tries to modify file, but itis locked by another user named other-user. The defaultdefinition of this function asks the user to say what to do. The valuethis function returns determines what Emacs does next: A value of t says to grab the lock on the file. Thenthis user may edit the file and other-user loses the lock. A value of nil says to ignore the lock and let thisuser edit the file anyway. file-lockedThis function may instead signal a file-locked error, in whichcase the change that the user was about to make does not take place.The error message for this error looks like this: error--> File is locked: file other-user where file is the name of the file and other-user is thename of the user who has locked the file. If you wish, you can replace the ask-user-about-lock functionwith your own version that makes the decision in another way. The codefor its usual definition is in userlock.el. Information about Files file, information about The functions described in this section all operate on strings that designate file names. With a few exceptions, all the functions have names that begin with the word ‘file’. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted. Testing Accessibility accessibility of a file file accessibility These functions test for permission to access a file in specific ways. Unless explicitly stated otherwise, they recursively follow symbolic links for their file name arguments, at all levels (at the level of the file itself and at all levels of parent directories). file-exists-p — Function: file-exists-p filename This function returns t if a file named filename appearsto exist. This does not mean you can necessarily read the file, onlythat you can find out its attributes. (On Unix and GNU/Linux, this istrue if the file exists and you have execute permission on thecontaining directories, regardless of the protection of the fileitself.)If the file does not exist, or if fascist access control policiesprevent you from finding the attributes of the file, this functionreturns nil.Directories are files, so file-exists-p returns t whengiven a directory name. However, symbolic links are treatedspecially; file-exists-p returns t for a symbolic linkname only if the target file exists. file-readable-p — Function: file-readable-p filename This function returns t if a file named filename existsand you can read it. It returns nil otherwise. (file-readable-p "files.texi") => t (file-exists-p "/usr/spool/mqueue") => t (file-readable-p "/usr/spool/mqueue") => nil file-executable-p — Function: file-executable-p filename This function returns t if a file named filename exists andyou can execute it. It returns nil otherwise. On Unix andGNU/Linux, if the file is a directory, execute permission means you cancheck the existence and attributes of files inside the directory, andopen those files if their modes permit. file-writable-p — Function: file-writable-p filename This function returns t if the file filename can be writtenor created by you, and nil otherwise. A file is writable if thefile exists and you can write it. It is creatable if it does not exist,but the specified directory does exist and you can write in thatdirectory.In the third example below, foo is not writable because theparent directory does not exist, even though the user could create sucha directory. (file-writable-p "~/foo") => t (file-writable-p "/foo") => nil (file-writable-p "~/no-such-dir/foo") => nil file-accessible-directory-p — Function: file-accessible-directory-p dirname This function returns t if you have permission to open existingfiles in the directory whose name as a file is dirname;otherwise (or if there is no such directory), it returns nil.The value of dirname may be either a directory name (such as/foo/) or the file name of a file which is a directory(such as /foo, without the final slash).Example: after the following, (file-accessible-directory-p "/foo") => nil we can deduce that any attempt to read a file in /foo/ willgive an error. access-file — Function: access-file filename string This function opens file filename for reading, then closes it andreturns nil. However, if the open fails, it signals an errorusing string as the error message text. file-ownership-preserved-p — Function: file-ownership-preserved-p filename This function returns t if deleting the file filename andthen creating it anew would keep the file's owner unchanged. It alsoreturns t for nonexistent files.If filename is a symbolic link, then, unlike the other functionsdiscussed here, file-ownership-preserved-p does notreplace filename with its target. However, it does recursivelyfollow symbolic links at all levels of parent directories. file-newer-than-file-p — Function: file-newer-than-file-p filename1 filename2 file age file modification timeThis function returns t if the file filename1 isnewer than file filename2. If filename1 does notexist, it returns nil. If filename1 does exist, butfilename2 does not, it returns t.In the following example, assume that the file aug-19 was writtenon the 19th, aug-20 was written on the 20th, and the fileno-file doesn't exist at all. (file-newer-than-file-p "aug-19" "aug-20") => nil (file-newer-than-file-p "aug-20" "aug-19") => t (file-newer-than-file-p "aug-19" "no-file") => t (file-newer-than-file-p "no-file" "aug-19") => nil You can use file-attributes to get a file's last modificationtime as a list of two numbers. See . Distinguishing Kinds of Files This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files. file-symlink-p — Function: file-symlink-p filename file symbolic linksIf the file filename is a symbolic link, thefile-symlink-p function returns the (non-recursive) link targetas a string. (Determining the file name that the link points to fromthe target is nontrivial.) First, this function recursively followssymbolic links at all levels of parent directories.If the file filename is not a symbolic link (or there is no such file),file-symlink-p returns nil. (file-symlink-p "foo") => nil (file-symlink-p "sym-link") => "foo" (file-symlink-p "sym-link2") => "sym-link" (file-symlink-p "/bin") => "/pub/bin" The next two functions recursively follow symbolic links at all levels for filename. file-directory-p — Function: file-directory-p filename This function returns t if filename is the name of anexisting directory, nil otherwise. (file-directory-p "~rms") => t (file-directory-p "~rms/lewis/files.texi") => nil (file-directory-p "~rms/lewis/no-such-file") => nil (file-directory-p "$HOME") => nil (file-directory-p (substitute-in-file-name "$HOME")) => t file-regular-p — Function: file-regular-p filename This function returns t if the file filename exists and isa regular file (not a directory, named pipe, terminal, orother I/O device). Truenames truename (of file) The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away ‘.’ and ‘..’ appearing as name components. This results in a sort of canonical name for the file. A file does not always have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation. file-truename — Function: file-truename filename The function file-truename returns the truename of the filefilename. The argument must be an absolute file name.This function does not expand environment variables. Onlysubstitute-in-file-name does that. See .If you may need to follow symbolic links preceding ‘..’appearing as a name component, you should make sure to callfile-truename without prior direct or indirect calls toexpand-file-name, as otherwise the file name componentimmediately preceding ‘..’ will be “simplified away” beforefile-truename is called. To eliminate the need for a call toexpand-file-name, file-truename handles ‘~’ in thesame way that expand-file-name does. See Functions that Expand Filenames. file-chase-links — Function: file-chase-links filename &optional limit This function follows symbolic links, starting with filename,until it finds a file name which is not the name of a symbolic link.Then it returns that file name. This function does not followsymbolic links at the level of parent directories.If you specify a number for limit, then after chasing throughthat many links, the function just returns what it has even if that isstill a symbolic link. To illustrate the difference between file-chase-links and file-truename, suppose that /usr/foo is a symbolic link to the directory /home/foo, and /home/foo/hello is an ordinary file (or at least, not a symbolic link) or nonexistent. Then we would have: (file-chase-links "/usr/foo/hello") ;; This does not follow the links in the parent directories. => "/usr/foo/hello" (file-truename "/usr/foo/hello") ;; Assuming that /home is not a symbolic link. => "/home/foo/hello" See , for related information. Other Information about Files This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification. file-modes — Function: file-modes filename permission file attributesThis function returns the mode bits of filename, as an integer.The mode bits are also called the file permissions, and they specifyaccess control in the usual Unix fashion. If the low-order bit is 1,then the file is executable by all users, if the second-lowest-order bitis 1, then the file is writable by all users, etc.The highest value returnable is 4095 (7777 octal), meaning thateveryone has read, write, and execute permission, that the SUID bitis set for both others and group, and that the sticky bit is set.If filename does not exist, file-modes returns nil.This function recursively follows symbolic links at all levels. (file-modes "~/junk/diffs") => 492 ; Decimal integer. (format "%o" 492) => "754" ; Convert to octal. (set-file-modes "~/junk/diffs" 438) => nil (format "%o" 438) => "666" ; Convert to octal. % ls -l diffs -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs If the filename argument to the next two functions is a symbolic link, then these function do not replace it with its target. However, they both recursively follow symbolic links at all levels of parent directories. file-nlinks — Function: file-nlinks filename This functions returns the number of names (i.e., hard links) thatfile filename has. If the file does not exist, then this functionreturns nil. Note that symbolic links have no effect on thisfunction, because they are not considered to be names of the files theylink to. % ls -l foo* -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 (file-nlinks "foo") => 2 (file-nlinks "doesnt-exist") => nil file-attributes — Function: file-attributes filename &optional id-format This function returns a list of attributes of file filename. Ifthe specified file cannot be opened, it returns nil.The optional parameter id-format specifies the preferred formatof attributes UID and GID (see below)—thevalid values are 'string and 'integer. The latter isthe default, but we plan to change that, so you should specify anon-nil value for id-format if you use the returnedUID or GID.The elements of the list, in order, are: t for a directory, a string for a symbolic link (the namelinked to), or nil for a text file. The number of names the file has. Alternate names, also known as hardlinks, can be created by using the add-name-to-file function(see ). The file's UID, normally as a string. However, if it doesnot correspond to a named user, the value is an integer or a floatingpoint number. The file's GID, likewise. The time of last access, as a list of two integers.The first integer has the high-order 16 bits of time,the second has the low 16 bits. (This is similar to thevalue of current-time; see .) The time of last modification as a list of two integers (as above). modification time of file The time of last status change as a list of two integers (as above). The size of the file in bytes. If the size is too large to fit in aLisp integer, this is a floating point number. The file's modes, as a string of ten letters or dashes,as in ‘ls -l’. t if the file's GID would change if file weredeleted and recreated; nil otherwise. The file's inode number. If possible, this is an integer. If the inodenumber is too large to be represented as an integer in Emacs Lisp, thenthe value has the form (high . low), where lowholds the low 16 bits. The file system number of the file system that the file is in.Depending on the magnitude of the value, this can be either an integeror a cons cell, in the same manner as the inode number. This elementand the file's inode number together give enough information todistinguish any two files on the system—no two files can have the samevalues for both of these numbers. For example, here are the file attributes for files.texi: (file-attributes "files.texi" 'string) => (nil 1 "lh" "users" (8489 20284) (8489 20284) (8489 20285) 14906 "-rw-rw-rw-" nil 129500 -32252) and here is how the result is interpreted: nil is neither a directory nor a symbolic link. 1 has only one name (the name files.texi in the current defaultdirectory). "lh" is owned by the user with name "lh". "users" is in the group with name "users". (8489 20284) was last accessed on Aug 19 00:09. (8489 20284) was last modified on Aug 19 00:09. (8489 20285) last had its inode changed on Aug 19 00:09. 14906 is 14906 bytes long. (It may not contain 14906 characters, though,if some of the bytes belong to multibyte sequences.) "-rw-rw-rw-" has a mode of read and write access for the owner, group, and world. nil would retain the same GID if it were recreated. 129500 has an inode number of 129500. -32252 is on file system number -32252. How to Locate Files in Standard Places locate file in path find file in path This section explains how to search for a file in a list of directories (a path). One example is when you need to look for a program's executable file, e.g., to find out whether a given program is installed on the user's system. Another example is the search for Lisp libraries (see ). Such searches generally need to try various possible file name extensions, in addition to various possible directories. Emacs provides a function for such a generalized search for a file. locate-file — Function: locate-file filename path &optional suffixes predicate This function searches for a file whose name is filename in alist of directories given by path, trying the suffixes insuffixes. If it finds such a file, it returns the fullabsolute file name of the file (see );otherwise it returns nil.The optional argument suffixes gives the list of file-namesuffixes to append to filename when searching.locate-file tries each possible directory with each of thesesuffixes. If suffixes is nil, or (""), then thereare no suffixes, and filename is used only as-is. Typicalvalues of suffixes are exec-suffixes (see exec-suffixes), load-suffixes,load-file-rep-suffixes and the return value of the functionget-load-suffixes (see ).Typical values for path are exec-path (see exec-path) when looking for executable programs orload-path (see load-path) when looking forLisp files. If filename is absolute, path has no effect,but the suffixes in suffixes are still tried.The optional argument predicate, if non-nil, specifiesthe predicate function to use for testing whether a candidate file issuitable. The predicate function is passed the candidate file name asits single argument. If predicate is nil or unspecified,locate-file uses file-readable-p as the defaultpredicate. Useful non-default predicates includefile-executable-p, file-directory-p, and otherpredicates described in .For compatibility, predicate can also be one of the symbolsexecutable, readable, writable, exists, ora list of one or more of these symbols. executable-find — Function: executable-find program This function searches for the executable file of the namedprogram and returns the full absolute name of the executable,including its file-name extensions, if any. It returns nil ifthe file is not found. The functions searches in all the directoriesin exec-path and tries all the file-name extensions inexec-suffixes. Changing File Names and Attributes copying files deleting files linking files setting modes of files The functions in this section rename, copy, delete, link, and set the modes of files. In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists: Signal a file-already-exists error ifok-if-already-exists is nil. Request confirmation if ok-if-already-exists is a number. Replace the old file without confirmation if ok-if-already-existsis any other value. The next four commands all recursively follow symbolic links at all levels of parent directories for their first argument, but, if that argument is itself a symbolic link, then only copy-file replaces it with its (recursive) target. add-name-to-file — Command: add-name-to-file oldname newname &optional ok-if-already-exists file with multiple names file hard linkThis function gives the file named oldname the additional namenewname. This means that newname becomes a new “hardlink” to oldname.In the first part of the following example, we list two files,foo and foo3. % ls -li fo* 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Now we create a hard link, by calling add-name-to-file, then listthe files again. This shows two names for one file, foo andfoo2. (add-name-to-file "foo" "foo2") => nil % ls -li fo* 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3 Finally, we evaluate the following: (add-name-to-file "foo" "foo3" t) and list the files again. Now there are three namesfor one file: foo, foo2, and foo3. The oldcontents of foo3 are lost. (add-name-to-file "foo1" "foo3") => nil % ls -li fo* 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3 This function is meaningless on operating systems where multiple namesfor one file are not allowed. Some systems implement multiple namesby copying the file instead.See also file-nlinks in . rename-file — Command: rename-file filename newname &optional ok-if-already-exists This command renames the file filename as newname.If filename has additional names aside from filename, itcontinues to have those names. In fact, adding the name newnamewith add-name-to-file and then deleting filename has thesame effect as renaming, aside from momentary intermediate states. copy-file — Command: copy-file oldname newname &optional ok-if-exists time preserve-uid-gid This command copies the file oldname to newname. Anerror is signaled if oldname does not exist. If newnamenames a directory, it copies oldname into that directory,preserving its final name component.If time is non-nil, then this function gives the new filethe same last-modified time that the old one has. (This works on onlysome operating systems.) If setting the time gets an error,copy-file signals a file-date-error error. In aninteractive call, a prefix argument specifies a non-nil valuefor time.This function copies the file modes, too.If argument preserve-uid-gid is nil, we let the operatingsystem decide the user and group ownership of the new file (this isusually set to the user running Emacs). If preserve-uid-gid isnon-nil, we attempt to copy the user and group ownership of thefile. This works only on some operating systems, and only if you havethe correct permissions to do so. make-symbolic-link — Command: make-symbolic-link filename newname &optional ok-if-exists ln file-already-existsThis command makes a symbolic link to filename, namednewname. This is like the shell command ‘ln -sfilename newname’.This function is not available on systems that don't support symboliclinks. delete-file — Command: delete-file filename rmThis command deletes the file filename, like the shell command‘rm filename’. If the file has multiple names, it continuesto exist under the other names.A suitable kind of file-error error is signaled if the file doesnot exist, or is not deletable. (On Unix and GNU/Linux, a file isdeletable if its directory is writable.)If filename is a symbolic link, delete-file does notreplace it with its target, but it does follow symbolic links at alllevels of parent directories.See also delete-directory in . define-logical-name — Function: define-logical-name varname string This function defines the logical name varname to have the valuestring. It is available only on VMS. set-file-modes — Function: set-file-modes filename mode This function sets mode bits of filename to mode (whichmust be an integer). Only the low 12 bits of mode are used.This function recursively follows symbolic links at all levels forfilename. set-default-file-modes — Function: set-default-file-modes mode umaskThis function sets the default file protection for new files created byEmacs and its subprocesses. Every file created with Emacs initially hasthis protection, or a subset of it (write-region will not give afile execute permission even if the default file protection allowsexecute permission). On Unix and GNU/Linux, the default protection isthe bitwise complement of the “umask” value.The argument mode must be an integer. On most systems, only thelow 9 bits of mode are meaningful. You can use the Lisp constructfor octal character codes to enter mode; for example, (set-default-file-modes ?\644) Saving a modified version of an existing file does not count as creatingthe file; it preserves the existing file's mode, whatever that is. Sothe default file protection has no effect. default-file-modes — Function: default-file-modes This function returns the current default protection value. set-file-times — Function: set-file-times filename &optional time This function sets the access and modification times of filenameto time. The return value is t if the times are successfullyset, otherwise it is nil. time defaults to the currenttime and must be in the format returned by current-time(see ). MS-DOS and file modes file modes and MS-DOS On MS-DOS, there is no such thing as an “executable” file mode bit. So Emacs considers a file executable if its name ends in one of the standard executable extensions, such as .com, .bat, .exe, and some others. Files that begin with the Unix-standard ‘#!’ signature, such as shell and Perl scripts, are also considered as executable files. This is reflected in the values returned by file-modes and file-attributes. Directories are also reported with executable bit set, for compatibility with Unix. File Names file names Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument. In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names. The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory. On MS-DOS and MS-Windows, these functions (like the function that actually operate on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate the components, as well as Unix syntax; but they always return Unix syntax. On VMS, these functions (and the ones that operate on files) understand both VMS file-name syntax and Unix syntax. This enables Lisp programs to specify file names in Unix syntax and work properly on all systems without change. File Name Components directory part (of file name) nondirectory part (of file name) version number (in file name) The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name. On most systems, the directory part is everything up to and including the last slash (backslash is also allowed in input on MS-DOS or MS-Windows); the nondirectory part is the rest. The rules in VMS syntax are complicated. For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On most systems, only backup files have version numbers in their names. On VMS, every file has a version number, but most of the time the file name actually used in Emacs omits the version number, so that version numbers in Emacs are found mostly in directory lists. file-name-directory — Function: file-name-directory filename This function returns the directory part of filename, as adirectory name (see ), or nil iffilename does not include a directory part.On GNU and Unix systems, a string returned by this function alwaysends in a slash. On MS-DOS it can also end in a colon. On VMS, itreturns a string ending in one of the three characters ‘:’,‘]’, or ‘>’. (file-name-directory "lewis/foo") ; Unix example => "lewis/" (file-name-directory "foo") ; Unix example => nil (file-name-directory "[X]FOO.TMP") ; VMS example => "[X]" file-name-nondirectory — Function: file-name-nondirectory filename This function returns the nondirectory part of filename. (file-name-nondirectory "lewis/foo") => "foo" (file-name-nondirectory "foo") => "foo" (file-name-nondirectory "lewis/") => "" ;; The following example is accurate only on VMS. (file-name-nondirectory "[X]FOO.TMP") => "FOO.TMP" file-name-sans-versions — Function: file-name-sans-versions filename &optional keep-backup-version This function returns filename with any file version numbers,backup version numbers, or trailing tildes discarded.If keep-backup-version is non-nil, then true file versionnumbers understood as such by the file system are discarded from thereturn value, but backup version numbers are kept. (file-name-sans-versions "~rms/foo.~1~") => "~rms/foo" (file-name-sans-versions "~rms/foo~") => "~rms/foo" (file-name-sans-versions "~rms/foo") => "~rms/foo" ;; The following example applies to VMS only. (file-name-sans-versions "foo;23") => "foo" file-name-extension — Function: file-name-extension filename &optional period This function returns filename's final “extension,” if any,after applying file-name-sans-versions to remove anyversion/backup part. The extension, in a file name, is the part thatstarts with the last ‘.’ in the last name component (minusany version/backup part).This function returns nil for extensionless file names such asfoo. It returns "" for null extensions, as infoo.. If the last component of a file name begins with a‘.’, that ‘.’ doesn't count as the beginning of anextension. Thus, .emacs's “extension” is nil, not‘.emacs’.If period is non-nil, then the returned value includesthe period that delimits the extension, and if filename has noextension, the value is "". file-name-sans-extension — Function: file-name-sans-extension filename This function returns filename minus its extension, if any. Theversion/backup part, if present, is only removed if the file has anextension. For example, (file-name-sans-extension "foo.lose.c") => "foo.lose" (file-name-sans-extension "big.hack/foo") => "big.hack/foo" (file-name-sans-extension "/my/home/.emacs") => "/my/home/.emacs" (file-name-sans-extension "/my/home/.emacs.el") => "/my/home/.emacs" (file-name-sans-extension "~/foo.el.~3~") => "~/foo" (file-name-sans-extension "~/foo.~3~") => "~/foo.~3~" Note that the ‘.~3~’ in the two last examples is the backup part,not an extension. Absolute and Relative File Names absolute file name relative file name All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix and GNU/Linux, an absolute file name starts with a slash or a tilde (‘~’), and a relative one does not. On MS-DOS and MS-Windows, an absolute file name starts with a slash or a backslash, or with a drive specification ‘x:/’, where x is the drive letter. The rules on VMS are complicated. file-name-absolute-p — Function: file-name-absolute-p filename This function returns t if file filename is an absolutefile name, nil otherwise. On VMS, this function understands bothUnix syntax and VMS syntax. (file-name-absolute-p "~rms/foo") => t (file-name-absolute-p "rms/foo") => nil (file-name-absolute-p "/user/rms/foo") => t Given a possibly relative file name, you can convert it to an absolute name using expand-file-name (see ). This function converts absolute file names to relative names: file-relative-name — Function: file-relative-name filename &optional directory This function tries to return a relative name that is equivalent tofilename, assuming the result will be interpreted relative todirectory (an absolute directory name or directory file name).If directory is omitted or nil, it defaults to thecurrent buffer's default directory.On some operating systems, an absolute file name begins with a devicename. On such systems, filename has no relative equivalent basedon directory if they start with two different device names. Inthis case, file-relative-name returns filename in absoluteform. (file-relative-name "/foo/bar" "/foo/") => "bar" (file-relative-name "/foo/bar" "/hack/") => "../foo/bar" Directory Names directory name file name of directory A directory name is the name of a directory. A directory is actually a kind of file, so it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On GNU and Unix systems, this is simple: a directory name ends in a slash, whereas the directory's name as a file lacks that slash. On MS-DOS and VMS, the relationship is more complicated. The difference between a directory name and its name as a file is subtle but crucial. When an Emacs variable or function argument is described as being a directory name, a file name of a directory is not acceptable. When file-name-directory returns a string, that is always a directory name. The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as ‘$HOME’, and the constructs ‘~’, ‘.’ and ‘..’. file-name-as-directory — Function: file-name-as-directory filename This function returns a string representing filename in a formthat the operating system will interpret as the name of a directory. Onmost systems, this means appending a slash to the string (if it does notalready end in one). On VMS, the function converts a string of the form[X]Y.DIR.1 to the form [X.Y]. (file-name-as-directory "~rms/lewis") => "~rms/lewis/" directory-file-name — Function: directory-file-name dirname This function returns a string representing dirname in a form thatthe operating system will interpret as the name of a file. On mostsystems, this means removing the final slash (or backslash) from thestring. On VMS, the function converts a string of the form [X.Y]to [X]Y.DIR.1. (directory-file-name "~lewis/") => "~lewis" Given a directory name, you can combine it with a relative file name using concat: (concat dirname relfile) Be sure to verify that the file name is relative before doing that. If you use an absolute file name, the results could be syntactically invalid or refer to the wrong file. If you want to use a directory file name in making such a combination, you must first convert it to a directory name using file-name-as-directory: (concat (file-name-as-directory dirfile) relfile) Don't try concatenating a slash by hand, as in ;;; Wrong! (concat dirfile "/" relfile) because this is not portable. Always use file-name-as-directory. directory name abbreviation Directory name abbreviations are useful for directories that are normally accessed through symbolic links. Sometimes the users recognize primarily the link's name as “the name” of the directory, and find it annoying to see the directory's “real” name. If you define the link name as an abbreviation for the “real” name, Emacs shows users the abbreviation instead. directory-abbrev-alist — Variable: directory-abbrev-alist The variable directory-abbrev-alist contains an alist ofabbreviations to use for file directories. Each element has the form(from . to), and says to replace from withto when it appears in a directory name. The from string isactually a regular expression; it should always start with ‘^’.The to string should be an ordinary absolute directory name. Donot use ‘~’ to stand for a home directory in that string. Thefunction abbreviate-file-name performs these substitutions.You can set this variable in site-init.el to describe theabbreviations appropriate for your site.Here's an example, from a system on which file system /home/fsfand so on are normally accessed through symbolic links named /fsfand so on. (("^/home/fsf" . "/fsf") ("^/home/gp" . "/gp") ("^/home/gd" . "/gd")) To convert a directory name to its abbreviation, use this function: abbreviate-file-name — Function: abbreviate-file-name filename This function applies abbreviations from directory-abbrev-alistto its argument, and substitutes ‘~’ for the user's homedirectory. You can use it for directory names and for file names,because it recognizes abbreviations even as part of the name. Functions that Expand Filenames expansion of file names Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as ./ and name/../. expand-file-name — Function: expand-file-name filename &optional directory This function converts filename to an absolute file name. Ifdirectory is supplied, it is the default directory to start withif filename is relative. (The value of directory shoulditself be an absolute directory name or directory file name; it maystart with ‘~’.) Otherwise, the current buffer's value ofdefault-directory is used. For example: (expand-file-name "foo") => "/xcssun/users/rms/lewis/foo" (expand-file-name "../foo") => "/xcssun/users/rms/foo" (expand-file-name "foo" "/usr/spool/") => "/usr/spool/foo" (expand-file-name "$HOME/foo") => "/xcssun/users/rms/lewis/$HOME/foo" If the part of the combined file name before the first slash is‘~’, it expands to the value of the HOME environmentvariable (usually your home directory). If the part before the firstslash is ‘~user’ and if user is a valid login name,it expands to user's home directory.Filenames containing ‘.’ or ‘..’ are simplified to theircanonical form: (expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo" In some cases, a leading ‘..’ component can remain in the output: (expand-file-name "../home" "/") => "/../home" This is for the sake of filesystems that have the concept of a“superroot” above the root directory /. On other filesystems,/../ is interpreted exactly the same as /.Note that expand-file-name does not expand environmentvariables; only substitute-in-file-name does that.Note also that expand-file-name does not follow symbolic linksat any level. This results in a difference between the wayfile-truename and expand-file-name treat ‘..’.Assuming that ‘/tmp/bar’ is a symbolic link to the directory‘/tmp/foo/bar’ we get: (file-truename "/tmp/bar/../myfile") => "/tmp/foo/myfile" (expand-file-name "/tmp/bar/../myfile") => "/tmp/myfile" If you may need to follow symbolic links preceding ‘..’, youshould make sure to call file-truename without prior direct orindirect calls to expand-file-name. See . default-directory — Variable: default-directory The value of this buffer-local variable is the default directory for thecurrent buffer. It should be an absolute directory name; it may startwith ‘~’. This variable is buffer-local in every buffer.expand-file-name uses the default directory when its secondargument is nil.Aside from VMS, the value is always a string ending with a slash. default-directory => "/user/lewis/manual/" substitute-in-file-name — Function: substitute-in-file-name filename This function replaces environment variable references infilename with the environment variable values. Followingstandard Unix shell syntax, ‘$’ is the prefix to substitute anenvironment variable value. If the input contains ‘$$’, that isconverted to ‘$’; this gives the user a way to “quote” a‘$’.The environment variable name is the series of alphanumeric characters(including underscores) that follow the ‘$’. If the character followingthe ‘$’ is a ‘{’, then the variable name is everything up to thematching ‘}’.Calling substitute-in-file-name on output produced bysubstitute-in-file-name tends to give incorrect results. Forinstance, use of ‘$$’ to quote a single ‘$’ won't workproperly, and ‘$’ in an environment variable's value could leadto repeated substitution. Therefore, programs that call this functionand put the output where it will be passed to this function need todouble all ‘$’ characters to prevent subsequent incorrectresults. Here we assume that the environment variable HOME, which holdsthe user's home directory name, has value ‘/xcssun/users/rms’. (substitute-in-file-name "$HOME/foo") => "/xcssun/users/rms/foo" After substitution, if a ‘~’ or a ‘/’ appears immediatelyafter another ‘/’, the function discards everything before it (upthrough the immediately preceding ‘/’). (substitute-in-file-name "bar/~/foo") => "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") => "/xcssun/users/rms/foo" ;; /usr/local/ has been discarded. On VMS, ‘$’ substitution is not done, so this function does nothingon VMS except discard superfluous initial components as shown above. Generating Unique File Names Some programs need to write temporary files. Here is the usual way to construct a name for such a file: (make-temp-file name-of-application) The job of make-temp-file is to prevent two different users or two different jobs from trying to use the exact same file name. make-temp-file — Function: make-temp-file prefix &optional dir-flag suffix This function creates a temporary file and returns its name. Emacscreates the temporary file's name by adding to prefix somerandom characters that are different in each Emacs job. The result isguaranteed to be a newly created empty file. On MS-DOS, this functioncan truncate the string prefix to fit into the 8+3 file-namelimits. If prefix is a relative file name, it is expandedagainst temporary-file-directory. (make-temp-file "foo") => "/tmp/foo232J6v" When make-temp-file returns, the file has been created and isempty. At that point, you should write the intended contents into thefile.If dir-flag is non-nil, make-temp-file creates anempty directory instead of an empty file. It returns the file name,not the directory name, of that directory. See .If suffix is non-nil, make-temp-file adds it atthe end of the file name.To prevent conflicts among different libraries running in the sameEmacs, each Lisp program that uses make-temp-file should have itsown prefix. The number added to the end of prefixdistinguishes between the same application running in different Emacsjobs. Additional added characters permit a large number of distinctnames even in one Emacs job. The default directory for temporary files is controlled by the variable temporary-file-directory. This variable gives the user a uniform way to specify the directory for all temporary files. Some programs use small-temporary-file-directory instead, if that is non-nil. To use it, you should expand the prefix against the proper directory before calling make-temp-file. In older Emacs versions where make-temp-file does not exist, you should use make-temp-name instead: (make-temp-name (expand-file-name name-of-application temporary-file-directory)) make-temp-name — Function: make-temp-name string This function generates a string that can be used as a unique filename. The name starts with string, and has several randomcharacters appended to it, which are different in each Emacs job. Itis like make-temp-file except that it just constructs a name,and does not create a file. Another difference is that stringshould be an absolute file name. On MS-DOS, this function cantruncate the string prefix to fit into the 8+3 file-name limits. temporary-file-directory — Variable: temporary-file-directory TMPDIR environment variable TMP environment variable TEMP environment variableThis variable specifies the directory name for creating temporary files.Its value should be a directory name (see ), but itis good for Lisp programs to cope if the value is a directory's filename instead. Using the value as the second argument toexpand-file-name is a good way to achieve that.The default value is determined in a reasonable way for your operatingsystem; it is based on the TMPDIR, TMP and TEMPenvironment variables, with a fall-back to a system-dependent name ifnone of these variables is defined.Even if you do not use make-temp-file to create the temporaryfile, you should still use this variable to decide which directory toput the file in. However, if you expect the file to be small, youshould use small-temporary-file-directory first if that isnon-nil. small-temporary-file-directory — Variable: small-temporary-file-directory This variable specifies the directory name forcreating certain temporary files, which are likely to be small.If you want to write a temporary file which is likely to be small, youshould compute the directory like this: (make-temp-file (expand-file-name prefix (or small-temporary-file-directory temporary-file-directory))) File Name Completion file name completion subroutines completion, file name This section describes low-level subroutines for completing a file name. For higher level functions, see . file-name-all-completions — Function: file-name-all-completions partial-filename directory This function returns a list of all possible completions for a filewhose name starts with partial-filename in directorydirectory. The order of the completions is the order of the filesin the directory, which is unpredictable and conveys no usefulinformation.The argument partial-filename must be a file name containing nodirectory part and no slash (or backslash on some systems). The currentbuffer's default directory is prepended to directory, ifdirectory is not absolute.In the following example, suppose that ~rms/lewis is the currentdefault directory, and has five files whose names begin with ‘f’:foo, file~, file.c, file.c.~1~, andfile.c.~2~. (file-name-all-completions "f" "") => ("foo" "file~" "file.c.~2~" "file.c.~1~" "file.c") (file-name-all-completions "fo" "") => ("foo") file-name-completion — Function: file-name-completion filename directory &optional predicate This function completes the file name filename in directorydirectory. It returns the longest prefix common to all file namesin directory directory that start with filename. Ifpredicate is non-nil then it ignores possible completionsthat don't satisfy predicate, after calling that functionwith one argument, the expanded absolute file name.If only one match exists and filename matches it exactly, thefunction returns t. The function returns nil if directorydirectory contains no name starting with filename.In the following example, suppose that the current default directoryhas five files whose names begin with ‘f’: foo,file~, file.c, file.c.~1~, andfile.c.~2~. (file-name-completion "fi" "") => "file" (file-name-completion "file.c.~1" "") => "file.c.~1~" (file-name-completion "file.c.~1~" "") => t (file-name-completion "file.c.~3" "") => nil completion-ignored-extensions — User Option: completion-ignored-extensions file-name-completion usually ignores file names that end in anystring in this list. It does not ignore them when all the possiblecompletions end in one of these suffixes. This variable has no effecton file-name-all-completions.A typical value might look like this: completion-ignored-extensions => (".o" ".elc" "~" ".dvi") If an element of completion-ignored-extensions ends in a slash‘/’, it signals a directory. The elements which do not endin a slash will never match a directory; thus, the above value will notfilter out a directory named foo.elc. Standard File Names Most of the file names used in Lisp programs are entered by the user. But occasionally a Lisp program needs to specify a standard file name for a particular use—typically, to hold customization information about each user. For example, abbrev definitions are stored (by default) in the file ~/.abbrev_defs; the completion package stores completions in the file ~/.completions. These are two of the many standard file names used by parts of Emacs for certain purposes. Various operating systems have their own conventions for valid file names and for which file names to use for user profile data. A Lisp program which reads a file using a standard file name ought to use, on each type of system, a file name suitable for that system. The function convert-standard-filename makes this easy to do. convert-standard-filename — Function: convert-standard-filename filename This function alters the file name filename to fit the conventionsof the operating system in use, and returns the result as a new string. The recommended way to specify a standard file name in a Lisp program is to choose a name which fits the conventions of GNU and Unix systems, usually with a nondirectory part that starts with a period, and pass it to convert-standard-filename instead of using it directly. Here is an example from the completion package: (defvar save-completions-file-name (convert-standard-filename "~/.completions") "*The file name to save completions to.") On GNU and Unix systems, and on some other systems as well, convert-standard-filename returns its argument unchanged. On some other systems, it alters the name to fit the system's conventions. For example, on MS-DOS the alterations made by this function include converting a leading ‘.’ to ‘_’, converting a ‘_’ in the middle of the name to ‘.’ if there is no other ‘.’, inserting a ‘.’ after eight characters if there is none, and truncating to three characters after the ‘.’. (It makes other changes as well.) Thus, .abbrev_defs becomes _abbrev.def, and .completions becomes _complet.ion. Contents of Directories directory-oriented functions file names in directory A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system. Emacs can list the names of the files in a directory as a Lisp list, or display the names in a buffer using the ls shell command. In the latter case, it can optionally display information about each file, depending on the options passed to the ls command. directory-files — Function: directory-files directory &optional full-name match-regexp nosort This function returns a list of the names of the files in the directorydirectory. By default, the list is in alphabetical order.If full-name is non-nil, the function returns the files'absolute file names. Otherwise, it returns the names relative tothe specified directory.If match-regexp is non-nil, this function returns onlythose file names that contain a match for that regular expression—theother file names are excluded from the list. On case-insensitivefilesystems, the regular expression matching is case-insensitive. If nosort is non-nil, directory-files does not sortthe list, so you get the file names in no particular order. Use this ifyou want the utmost possible speed and don't care what order the filesare processed in. If the order of processing is visible to the user,then the user will probably be happier if you do sort the names. (directory-files "~lewis") => ("#foo#" "#foo.el#" "." ".." "dired-mods.el" "files.texi" "files.texi.~1~") An error is signaled if directory is not the name of a directorythat can be read. directory-files-and-attributes — Function: directory-files-and-attributes directory &optional full-name match-regexp nosort id-format This is similar to directory-files in deciding which filesto report on and how to report their names. However, insteadof returning a list of file names, it returns for each file alist (filename . attributes), where attributesis what file-attributes would return for that file.The optional argument id-format has the same meaning as thecorresponding argument to file-attributes (see ). file-name-all-versions — Function: file-name-all-versions file dirname This function returns a list of all versions of the file namedfile in directory dirname. It is only available on VMS. file-expand-wildcards — Function: file-expand-wildcards pattern &optional full This function expands the wildcard pattern pattern, returninga list of file names that match it.If pattern is written as an absolute file name,the values are absolute also.If pattern is written as a relative file name, it is interpretedrelative to the current default directory. The file names returned arenormally also relative to the current default directory. However, iffull is non-nil, they are absolute. insert-directory — Function: insert-directory file switches &optional wildcard full-directory-p This function inserts (in the current buffer) a directory listing fordirectory file, formatted with ls according toswitches. It leaves point after the inserted text.switches may be a string of options, or a list of stringsrepresenting individual options.The argument file may be either a directory name or a filespecification including wildcard characters. If wildcard isnon-nil, that means treat file as a file specification withwildcards.If full-directory-p is non-nil, that means the directorylisting is expected to show the full contents of a directory. Youshould specify t when file is a directory and switches donot contain ‘-d’. (The ‘-d’ option to ls says todescribe a directory itself as a file, rather than showing itscontents.)On most systems, this function works by running a directory listingprogram whose name is in the variable insert-directory-program.If wildcard is non-nil, it also runs the shell specified byshell-file-name, to expand the wildcards.MS-DOS and MS-Windows systems usually lack the standard Unix programls, so this function emulates the standard Unix program lswith Lisp code.As a technical detail, when switches contains the long‘--dired’ option, insert-directory treats it specially,for the sake of dired. However, the normally equivalent short‘-D’ option is just passed on to insert-directory-program,as any other option. insert-directory-program — Variable: insert-directory-program This variable's value is the program to run to generate a directory listingfor the function insert-directory. It is ignored on systemswhich generate the listing with Lisp code. Creating and Deleting Directories creating and deleting directories Most Emacs Lisp file-manipulation functions get errors when used on files that are directories. For example, you cannot delete a directory with delete-file. These special functions exist to create and delete directories. make-directory — Function: make-directory dirname &optional parents This function creates a directory named dirname.If parents is non-nil, as is always the case in aninteractive call, that means to create the parent directories first,if they don't already exist. delete-directory — Function: delete-directory dirname This function deletes the directory named dirname. The functiondelete-file does not work for files that are directories; youmust use delete-directory for them. If the directory containsany files, delete-directory signals an error.This function only follows symbolic links at the level of parentdirectories. Making Certain File Names “Magic” magic file names You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing remote file names (see See section ``Remote Files'' in The GNU Emacs Manual). To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match. The variable file-name-handler-alist holds a list of handlers, together with regular expressions that determine when to apply each handler. Each element has this form: (regexp . handler) All the Emacs primitives for file access and file name transformation check the given file name against file-name-handler-alist. If the file name matches regexp, the primitives handle that file by calling handler. The first argument given to handler is the name of the primitive, as a symbol; the remaining arguments are the arguments that were passed to that primitive. (The first of these arguments is most often the file name itself.) For example, if you do this: (file-exists-p filename) and filename has handler handler, then handler is called like this: (funcall handler 'file-exists-p filename) When a function takes two or more arguments that must be file names, it checks each of those names for a handler. For example, if you do this: (expand-file-name filename dirname) then it checks for a handler for filename and then for a handler for dirname. In either case, the handler is called like this: (funcall handler 'expand-file-name filename dirname) The handler then needs to figure out whether to handle filename or dirname. If the specified file name matches more than one handler, the one whose match starts last in the file name gets precedence. This rule is chosen so that handlers for jobs such as uncompression are handled first, before handlers for jobs such as remote file access. Here are the operations that a magic file name handler gets to handle: access-file, add-name-to-file, byte-compiler-base-file-name, copy-file, delete-directory, delete-file, diff-latest-backup-file, directory-file-name, directory-files, directory-files-and-attributes, dired-call-process, dired-compress-file, dired-uncache, expand-file-name, file-accessible-directory-p, file-attributes, file-directory-p, file-executable-p, file-exists-p, file-local-copy, file-remote-p, file-modes, file-name-all-completions, file-name-as-directory, file-name-completion, file-name-directory, file-name-nondirectory, file-name-sans-versions, file-newer-than-file-p, file-ownership-preserved-p, file-readable-p, file-regular-p, file-symlink-p, file-truename, file-writable-p, find-backup-file-name, find-file-noselect, get-file-buffer, insert-directory, insert-file-contents, load, make-auto-save-file-name, make-directory, make-directory-internal, make-symbolic-link, rename-file, set-file-modes, set-file-times, set-visited-file-modtime, shell-command, substitute-in-file-name, unhandled-file-name-directory, vc-registered, verify-visited-file-modtime, write-region. Handlers for insert-file-contents typically need to clear the buffer's modified flag, with (set-buffer-modified-p nil), if the visit argument is non-nil. This also has the effect of unlocking the buffer if it is locked. The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself—when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation “in the usual way.” It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this: (defun my-file-handler (operation &rest args) ;; First check for the specific operations ;; that we have special handling for. (cond ((eq operation 'insert-file-contents) …) ((eq operation 'write-region) …) … ;; Handle any operation we don't know about. (t (let ((inhibit-file-name-handlers (cons 'my-file-handler (and (eq inhibit-file-name-operation operation) inhibit-file-name-handlers))) (inhibit-file-name-operation operation)) (apply operation args))))) When a handler function decides to call the ordinary Emacs primitive for the operation at hand, it needs to prevent the primitive from calling the same handler once again, thus leading to an infinite recursion. The example above shows how to do this, with the variables inhibit-file-name-handlers and inhibit-file-name-operation. Be careful to use them exactly as shown above; the details are crucial for proper behavior in the case of multiple handlers, and for operations that have two file names that may each have handlers. safe-magic (property) Handlers that don't really do anything special for actual access to the file—such as the ones that implement completion of host names for remote file names—should have a non-nil safe-magic property. For instance, Emacs normally “protects” directory names it finds in PATH from becoming magic, if they look like magic file names, by prefixing them with ‘/:’. But if the handler that would be used for them has a non-nil safe-magic property, the ‘/:’ is not added. operations (property) A file name handler can have an operations property to declare which operations it handles in a nontrivial way. If this property has a non-nil value, it should be a list of operations; then only those operations will call the handler. This avoids inefficiency, but its main purpose is for autoloaded handler functions, so that they won't be loaded except when they have real work to do. Simply deferring all operations to the usual primitives does not work. For instance, if the file name handler applies to file-exists-p, then it must handle load itself, because the usual load code won't work properly in that case. However, if the handler uses the operations property to say it doesn't handle file-exists-p, then it need not handle load nontrivially. inhibit-file-name-handlers — Variable: inhibit-file-name-handlers This variable holds a list of handlers whose use is presently inhibitedfor a certain operation. inhibit-file-name-operation — Variable: inhibit-file-name-operation The operation for which certain handlers are presently inhibited. find-file-name-handler — Function: find-file-name-handler file operation This function returns the handler function for file name file,or nil if there is none. The argument operation shouldbe the operation to be performed on the file—the value you will passto the handler as its first argument when you call it. Ifoperation equals inhibit-file-name-operation, or if it isnot found in the operations property of the handler, thisfunction returns nil. file-local-copy — Function: file-local-copy filename This function copies file filename to an ordinary non-magic fileon the local machine, if it isn't on the local machine already. Magicfile names should handle the file-local-copy operation if theyrefer to files on other machines. A magic file name that is used forother purposes than remote file access should not handlefile-local-copy; then this function will treat the file aslocal.If filename is local, whether magic or not, this function doesnothing and returns nil. Otherwise it returns the file nameof the local copy file. file-remote-p — Function: file-remote-p filename This function tests whether filename is a remote file. Iffilename is local (not remote), the return value is nil.If filename is indeed remote, the return value is a string thatidentifies the remote system.This identifier string can include a host name and a user name, aswell as characters designating the method used to access the remotesystem. For example, the remote identifier string for the filename/ssh:user@host:/some/file is /ssh:user@host:.If file-remote-p returns the same identifier for two differentfilenames, that means they are stored on the same file system and canbe accessed locally with respect to each other. This means, forexample, that it is possible to start a remote process accessing bothfiles at the same time. Implementors of file handlers need to ensurethis principle is valid. unhandled-file-name-directory — Function: unhandled-file-name-directory filename This function returns the name of a directory that is not magic. Ituses the directory part of filename if that is not magic. For amagic file name, it invokes the file name handler, which thereforedecides what value to return.This is useful for running a subprocess; every subprocess must have anon-magic directory to serve as its current directory, and this functionis a good way to come up with one. File Format Conversion file format conversion encoding file formats decoding file formats The variable format-alist defines a list of file formats, which describe textual representations used in files for the data (text, text-properties, and possibly other information) in an Emacs buffer. Emacs performs format conversion if appropriate when reading and writing files. format-alist — Variable: format-alist This list contains one format definition for each defined file format. format definition Each format definition is a list of this form: (name doc-string regexp from-fn to-fn modify mode-fn) Here is what the elements in a format definition mean: name The name of this format. doc-string A documentation string for the format. regexp A regular expression which is used to recognize files represented inthis format. from-fn A shell command or function to decode data in this format (to convertfile data into the usual Emacs data representation).A shell command is represented as a string; Emacs runs the command as afilter to perform the conversion.If from-fn is a function, it is called with two arguments, beginand end, which specify the part of the buffer it should convert.It should convert the text by editing it in place. Since this canchange the length of the text, from-fn should return the modifiedend position.One responsibility of from-fn is to make sure that the beginningof the file no longer matches regexp. Otherwise it is likely toget called again. to-fn A shell command or function to encode data in this format—that is, toconvert the usual Emacs data representation into this format.If to-fn is a string, it is a shell command; Emacs runs thecommand as a filter to perform the conversion.If to-fn is a function, it is called with three arguments:begin and end, which specify the part of the buffer itshould convert, and buffer, which specifies which buffer. Thereare two ways it can do the conversion: By editing the buffer in place. In this case, to-fn shouldreturn the end-position of the range of text, as modified. By returning a list of annotations. This is a list of elements of theform (position . string), where position is aninteger specifying the relative position in the text to be written, andstring is the annotation to add there. The list must be sorted inorder of position when to-fn returns it.When write-region actually writes the text from the buffer to thefile, it intermixes the specified annotations at the correspondingpositions. All this takes place without modifying the buffer. modify A flag, t if the encoding function modifies the buffer, andnil if it works by returning a list of annotations. mode-fn A minor-mode function to call after visiting a file converted from thisformat. The function is called with one argument, the integer 1;that tells a minor-mode function to enable the mode. The function insert-file-contents automatically recognizes file formats when it reads the specified file. It checks the text of the beginning of the file against the regular expressions of the format definitions, and if it finds a match, it calls the decoding function for that format. Then it checks all the known formats over again. It keeps checking them until none of them is applicable. Visiting a file, with find-file-noselect or the commands that use it, performs conversion likewise (because it calls insert-file-contents); it also calls the mode function for each format that it decodes. It stores a list of the format names in the buffer-local variable buffer-file-format. buffer-file-format — Variable: buffer-file-format This variable states the format of the visited file. More precisely,this is a list of the file format names that were decoded in the courseof visiting the current buffer's file. It is always buffer-local in allbuffers. When write-region writes data into a file, it first calls the encoding functions for the formats listed in buffer-file-format, in the order of appearance in the list. format-write-file — Command: format-write-file file format &optional confirm This command writes the current buffer contents into the filefile in format format, and makes that format the defaultfor future saves of the buffer. The argument format is a listof format names. Except for the format argument, this commandis similar to write-file. In particular, confirm has thesame meaning and interactive treatment as the corresponding argumentto write-file. See . format-find-file — Command: format-find-file file format This command finds the file file, converting it according toformat format. It also makes format the default if thebuffer is saved later.The argument format is a list of format names. If format isnil, no conversion takes place. Interactively, typing justRET for format specifies nil. format-insert-file — Command: format-insert-file file format &optional beg end This command inserts the contents of file file, converting itaccording to format format. If beg and end arenon-nil, they specify which part of the file to read, as ininsert-file-contents (see ).The return value is like what insert-file-contents returns: alist of the absolute file name and the length of the data inserted(after conversion).The argument format is a list of format names. If format isnil, no conversion takes place. Interactively, typing justRET for format specifies nil. buffer-auto-save-file-format — Variable: buffer-auto-save-file-format This variable specifies the format to use for auto-saving. Its value isa list of format names, just like the value ofbuffer-file-format; however, it is used instead ofbuffer-file-format for writing auto-save files. If the valueis t, the default, auto-saving uses the same format as aregular save in the same buffer. This variable is always buffer-localin all buffers. <setfilename>../info/backups</setfilename> Backups and Auto-Saving backups and auto-saving Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session. Backup Files backup file A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Thus, normally, the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists. Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it. By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically. Making Backup Files backup-buffer — Function: backup-buffer This function makes a backup of the file visited by the currentbuffer, if appropriate. It is called by save-buffer beforesaving the buffer the first time.If a backup was made by renaming, the return value is a cons cell ofthe form (modes . backupname), where modes are themode bits of the original file, as returned by file-modes(see Other Information about Files), andbackupname is the name of the backup. In all other cases, thatis, if a backup was made by copying or if no backup was made, thisfunction returns nil. buffer-backed-up — Variable: buffer-backed-up This buffer-local variable says whether this buffer's file hasbeen backed up on account of this buffer. If it is non-nil,the backup file has been written. Otherwise, the file should be backedup when it is next saved (if backups are enabled). This is apermanent local; kill-all-local-variables does not alter it. make-backup-files — User Option: make-backup-files This variable determines whether or not to make backup files. If itis non-nil, then Emacs creates a backup of each file when it issaved for the first time—provided that backup-inhibitedis nil (see below).The following example shows how to change the make-backup-filesvariable only in the Rmail buffers and not elsewhere. Setting itnil stops Emacs from making backups of these files, which maysave disk space. (You would put this code in your init file.) (add-hook 'rmail-mode-hook (function (lambda () (make-local-variable 'make-backup-files) (setq make-backup-files nil)))) backup-enable-predicate — Variable: backup-enable-predicate This variable's value is a function to be called on certain occasions todecide whether a file should have backup files. The function receivesone argument, an absolute file name to consider. If the function returnsnil, backups are disabled for that file. Otherwise, the othervariables in this section say whether and how to make backups. normal-backup-enable-predicateThe default value is normal-backup-enable-predicate, which checksfor files in temporary-file-directory andsmall-temporary-file-directory. backup-inhibited — Variable: backup-inhibited If this variable is non-nil, backups are inhibited. It recordsthe result of testing backup-enable-predicate on the visited filename. It can also coherently be used by other mechanisms that inhibitbackups based on which file is visited. For example, VC sets thisvariable non-nil to prevent making backups for files managedwith a version control system.This is a permanent local, so that changing the major mode does not loseits value. Major modes should not set this variable—they should setmake-backup-files instead. backup-directory-alist — Variable: backup-directory-alist This variable's value is an alist of filename patterns and backupdirectory names. Each element looks like (regexp . directory) Backups of files with names matching regexp will be made indirectory. directory may be relative or absolute. If it isabsolute, so that all matching files are backed up into the samedirectory, the file names in this directory will be the full name of thefile backed up with all directory separators changed to ‘!’ toprevent clashes. This will not work correctly if your filesystemtruncates the resulting name.For the common case of all backups going into one directory, the alistshould contain a single element pairing ‘"."’ with the appropriatedirectory name.If this variable is nil, or it fails to match a filename, thebackup is made in the original file's directory.On MS-DOS filesystems without long names this variable is alwaysignored. make-backup-file-name-function — Variable: make-backup-file-name-function This variable's value is a function to use for making backups insteadof the default make-backup-file-name. A value of nilgives the default make-backup-file-name behavior.See Naming Backup Files.This could be buffer-local to do something special for specificfiles. If you define it, you may need to changebackup-file-name-p and file-name-sans-versions too. Backup by Renaming or by Copying? backup files, rename or copy There are two ways that Emacs can make a backup file: Emacs can rename the original file so that it becomes a backup file, andthen write the buffer being saved into a new file. After thisprocedure, any other names (i.e., hard links) of the original file nowrefer to the backup file. The new file is owned by the user doing theediting, and its group is the default for new files written by the userin that directory. Emacs can copy the original file into a backup file, and then overwritethe original file with new contents. After this procedure, any othernames (i.e., hard links) of the original file continue to refer to thecurrent (updated) version of the file. The file's owner and group willbe unchanged. The first method, renaming, is the default. The variable backup-by-copying, if non-nil, says to use the second method, which is to copy the original file and overwrite it with the new buffer contents. The variable file-precious-flag, if non-nil, also has this effect (as a sideline of its main significance). See . backup-by-copying — User Option: backup-by-copying If this variable is non-nil, Emacs always makes backup files bycopying. The following three variables, when non-nil, cause the second method to be used in certain special cases. They have no effect on the treatment of files that don't fall into the special cases. backup-by-copying-when-linked — User Option: backup-by-copying-when-linked If this variable is non-nil, Emacs makes backups by copying forfiles with multiple names (hard links).This variable is significant only if backup-by-copying isnil, since copying is always used when that variable isnon-nil. backup-by-copying-when-mismatch — User Option: backup-by-copying-when-mismatch If this variable is non-nil, Emacs makes backups by copying in caseswhere renaming would change either the owner or the group of the file.The value has no effect when renaming would not alter the owner orgroup of the file; that is, for files which are owned by the user andwhose group matches the default for a new file created there by theuser.This variable is significant only if backup-by-copying isnil, since copying is always used when that variable isnon-nil. backup-by-copying-when-privileged-mismatch — User Option: backup-by-copying-when-privileged-mismatch This variable, if non-nil, specifies the same behavior asbackup-by-copying-when-mismatch, but only for certain user-idvalues: namely, those less than or equal to a certain number. You setthis variable to that number.Thus, if you set backup-by-copying-when-privileged-mismatchto 0, backup by copying is done for the superuser only,when necessary to prevent a change in the owner of the file.The default is 200. Making and Deleting Numbered Backup Files If a file's name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, …, foo.~259~, and so on. version-control — User Option: version-control This variable controls whether to make a single non-numbered backupfile or multiple numbered backups. nil Make numbered backups if the visited file already has numbered backups;otherwise, do not. This is the default. never Do not make numbered backups. anything else Make numbered backups. The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them. kept-new-versions — User Option: kept-new-versions The value of this variable is the number of newest versions to keepwhen a new numbered backup is made. The newly made backup is includedin the count. The default value is 2. kept-old-versions — User Option: kept-old-versions The value of this variable is the number of oldest versions to keepwhen a new numbered backup is made. The default value is 2. If there are backups numbered 1, 2, 3, 5, and 7, and both of these variables have the value 2, then the backups numbered 1 and 2 are kept as old versions and those numbered 5 and 7 are kept as new versions; backup version 3 is excess. The function find-backup-file-name (see ) is responsible for determining which backup versions to delete, but does not delete them itself. delete-old-versions — User Option: delete-old-versions If this variable is t, then saving a file deletes excessbackup versions silently. If it is nil, that meansto ask for confirmation before deleting excess backups.Otherwise, they are not deleted at all. dired-kept-versions — User Option: dired-kept-versions This variable specifies how many of the newest backup versions to keepin the Dired command . (dired-clean-directory). That's thesame thing kept-new-versions specifies when you make a new backupfile. The default is 2. Naming Backup Files The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest. backup-file-name-p — Function: backup-file-name-p filename This function returns a non-nil value if filename is apossible name for a backup file. It just checks the name, not whethera file with the name filename exists. (backup-file-name-p "foo") => nil (backup-file-name-p "foo~") => 3 The standard definition of this function is as follows: (defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~\\'" file)) Thus, the function returns a non-nil value if the file name endswith a ‘~’. (We use a backslash to split the documentationstring's first line into two lines in the text, but produce just oneline in the string itself.)This simple expression is placed in a separate function to make it easyto redefine for customization. make-backup-file-name — Function: make-backup-file-name filename This function returns a string that is the name to use for anon-numbered backup file for file filename. On Unix, this is justfilename with a tilde appended.The standard definition of this function, on most operating systems, isas follows: (defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE..." (concat file "~")) You can change the backup-file naming convention by redefining thisfunction. The following example redefines make-backup-file-nameto prepend a ‘.’ in addition to appending a tilde: (defun make-backup-file-name (filename) (expand-file-name (concat "." (file-name-nondirectory filename) "~") (file-name-directory filename))) (make-backup-file-name "backups.texi") => ".backups.texi~" Some parts of Emacs, including some Dired commands, assume that backupfile names end with ‘~’. If you do not follow that convention, itwill not cause serious problems, but these commands may giveless-than-desirable results. find-backup-file-name — Function: find-backup-file-name filename This function computes the file name for a new backup file forfilename. It may also propose certain existing backup files fordeletion. find-backup-file-name returns a list whose car isthe name for the new backup file and whose cdr is a list of backupfiles whose deletion is proposed. The value can also be nil,which means not to make a backup.Two variables, kept-old-versions and kept-new-versions,determine which backup versions should be kept. This function keepsthose versions by excluding them from the cdr of the value.See .In this example, the value says that ~rms/foo.~5~ is the nameto use for the new backup file, and ~rms/foo.~3~ is an “excess”version that the caller should consider deleting now. (find-backup-file-name "~rms/foo") => ("~rms/foo.~5~" "~rms/foo.~3~") file-newest-backup — Function: file-newest-backup filename This function returns the name of the most recent backup file forfilename, or nil if that file has no backup files.Some file comparison commands use this function so that they canautomatically compare a file with its most recent backup. Auto-Saving Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See See section ``Auto-Saving: Protection Against Disasters'' in The GNU Emacs Manual, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them. buffer-auto-save-file-name — Variable: buffer-auto-save-file-name This buffer-local variable is the name of the file used forauto-saving the current buffer. It is nil if the buffershould not be auto-saved. buffer-auto-save-file-name => "/xcssun/users/rms/lewis/#backups.texi#" auto-save-mode — Command: auto-save-mode arg When used interactively without an argument, this command is a toggleswitch: it turns on auto-saving of the current buffer if it is off, andvice versa. With an argument arg, the command turns auto-savingon if the value of arg is t, a nonempty list, or a positiveinteger. Otherwise, it turns auto-saving off. auto-save-file-name-p — Function: auto-save-file-name-p filename This function returns a non-nil value if filename is astring that could be the name of an auto-save file. It assumesthe usual naming convention for auto-save files: a name thatbegins and ends with hash marks (‘#’) is a possible auto-save filename. The argument filename should not contain a directory part. (make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#" (auto-save-file-name-p "#backups.texi#") => 0 (auto-save-file-name-p "backups.texi") => nil The standard definition of this function is as follows: (defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename)) This function exists so that you can customize it if you wish tochange the naming convention for auto-save files. If you redefine it,be sure to redefine the function make-auto-save-file-namecorrespondingly. make-auto-save-file-name — Function: make-auto-save-file-name This function returns the file name to use for auto-saving the currentbuffer. This is just the file name with hash marks (‘#’) prependedand appended to it. This function does not look at the variableauto-save-visited-file-name (described below); callers of thisfunction should check that variable first. (make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#" Here is a simplified version of the standard definition of thisfunction: (defun make-auto-save-file-name () "Return file name to use for auto-saves \ of current buffer.." (if buffer-file-name (concat (file-name-directory buffer-file-name) "#" (file-name-nondirectory buffer-file-name) "#") (expand-file-name (concat "#%" (buffer-name) "#")))) This exists as a separate function so that you can redefine it tocustomize the naming convention for auto-save files. Be sure tochange auto-save-file-name-p in a corresponding way. auto-save-visited-file-name — User Option: auto-save-visited-file-name If this variable is non-nil, Emacs auto-saves buffers inthe files they are visiting. That is, the auto-save is done in the samefile that you are editing. Normally, this variable is nil, soauto-save files have distinct names that are created bymake-auto-save-file-name.When you change the value of this variable, the new value does not takeeffect in an existing buffer until the next time auto-save mode isreenabled in it. If auto-save mode is already enabled, auto-savescontinue to go in the same file name until auto-save-mode iscalled again. recent-auto-save-p — Function: recent-auto-save-p This function returns t if the current buffer has beenauto-saved since the last time it was read in or saved. set-buffer-auto-saved — Function: set-buffer-auto-saved This function marks the current buffer as auto-saved. The buffer willnot be auto-saved again until the buffer text is changed again. Thefunction returns nil. auto-save-interval — User Option: auto-save-interval The value of this variable specifies how often to do auto-saving, interms of number of input events. Each time this many additional inputevents are read, Emacs does auto-saving for all buffers in which that isenabled. Setting this to zero disables autosaving based on thenumber of characters typed. auto-save-timeout — User Option: auto-save-timeout The value of this variable is the number of seconds of idle time thatshould cause auto-saving. Each time the user pauses for this long,Emacs does auto-saving for all buffers in which that is enabled. (Ifthe current buffer is large, the specified timeout is multiplied by afactor that increases as the size increases; for a million-bytebuffer, the factor is almost 4.)If the value is zero or nil, then auto-saving is not done as aresult of idleness, only after a certain number of input events asspecified by auto-save-interval. auto-save-hook — Variable: auto-save-hook This normal hook is run whenever an auto-save is about to happen. auto-save-default — User Option: auto-save-default If this variable is non-nil, buffers that are visiting fileshave auto-saving enabled by default. Otherwise, they do not. do-auto-save — Command: do-auto-save &optional no-message current-only This function auto-saves all buffers that need to be auto-saved. Itsaves all buffers for which auto-saving is enabled and that have beenchanged since the previous auto-save.If any buffers are auto-saved, do-auto-save normally displays amessage saying ‘Auto-saving...’ in the echo area whileauto-saving is going on. However, if no-message isnon-nil, the message is inhibited.If current-only is non-nil, only the current bufferis auto-saved. delete-auto-save-file-if-necessary — Function: delete-auto-save-file-if-necessary &optional force This function deletes the current buffer's auto-save file ifdelete-auto-save-files is non-nil. It is called everytime a buffer is saved.Unless force is non-nil, this function only deletes thefile if it was written by the current Emacs session since the lasttrue save. delete-auto-save-files — User Option: delete-auto-save-files This variable is used by the functiondelete-auto-save-file-if-necessary. If it is non-nil,Emacs deletes auto-save files when a true save is done (in the visitedfile). This saves disk space and unclutters your directory. rename-auto-save-file — Function: rename-auto-save-file This function adjusts the current buffer's auto-save file name if thevisited file name has changed. It also renames an existing auto-savefile, if it was made in the current Emacs session. If the visitedfile name has not changed, this function does nothing. buffer-saved-size — Variable: buffer-saved-size The value of this buffer-local variable is the length of the currentbuffer, when it was last read in, saved, or auto-saved. This isused to detect a substantial decrease in size, and turn off auto-savingin response.If it is −1, that means auto-saving is temporarily shut off inthis buffer due to a substantial decrease in size. Explicitly savingthe buffer stores a positive value in this variable, thus reenablingauto-saving. Turning auto-save mode off or on also updates thisvariable, so that the substantial decrease in size is forgotten. auto-save-list-file-name — Variable: auto-save-list-file-name This variable (if non-nil) specifies a file for recording thenames of all the auto-save files. Each time Emacs does auto-saving, itwrites two lines into this file for each buffer that has auto-savingenabled. The first line gives the name of the visited file (it's emptyif the buffer has none), and the second gives the name of the auto-savefile.When Emacs exits normally, it deletes this file; if Emacs crashes, youcan look in the file to find all the auto-save files that might containwork that was otherwise lost. The recover-session command usesthis file to find them.The default name for this file specifies your home directory and startswith ‘.saves-’. It also contains the Emacs process ID and thehost name. auto-save-list-file-prefix — Variable: auto-save-list-file-prefix After Emacs reads your init file, it initializesauto-save-list-file-name (if you have not already set itnon-nil) based on this prefix, adding the host name and processID. If you set this to nil in your init file, then Emacs doesnot initialize auto-save-list-file-name. Reverting If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file with the revert-buffer command. See See section ``Reverting a Buffer'' in The GNU Emacs Manual. revert-buffer — Command: revert-buffer &optional ignore-auto noconfirm preserve-modes This command replaces the buffer text with the text of the visitedfile on disk. This action undoes all changes since the file was visitedor saved.By default, if the latest auto-save file is more recent than the visitedfile, and the argument ignore-auto is nil,revert-buffer asks the user whether to use that auto-saveinstead. When you invoke this command interactively, ignore-autois t if there is no numeric prefix argument; thus, theinteractive default is not to check the auto-save file.Normally, revert-buffer asks for confirmation before it changesthe buffer; but if the argument noconfirm is non-nil,revert-buffer does not ask for confirmation.Normally, this command reinitializes the buffer's major and minor modesusing normal-mode. But if preserve-modes isnon-nil, the modes remain unchanged.Reverting tries to preserve marker positions in the buffer by using thereplacement feature of insert-file-contents. If the buffercontents and the file contents are identical before the revertoperation, reverting preserves all the markers. If they are notidentical, reverting does change the buffer; in that case, it preservesthe markers in the unchanged text (if any) at the beginning and end ofthe buffer. Preserving any additional markers would be problematical. You can customize how revert-buffer does its work by setting the variables described in the rest of this section. revert-without-query — User Option: revert-without-query This variable holds a list of files that should be reverted withoutquery. The value is a list of regular expressions. If the visited filename matches one of these regular expressions, and the file has changedon disk but the buffer is not modified, then revert-bufferreverts the file without asking the user for confirmation. Some major modes customize revert-buffer by making buffer-local bindings for these variables: revert-buffer-function — Variable: revert-buffer-function The value of this variable is the function to use to revert thisbuffer. If non-nil, it should be a function with two optionalarguments to do the work of reverting. The two optional arguments,ignore-auto and noconfirm, are the arguments thatrevert-buffer received. If the value is nil, revertingworks the usual way.Modes such as Dired mode, in which the text being edited does notconsist of a file's contents but can be regenerated in some otherfashion, can give this variable a buffer-local value that is a function toregenerate the contents. revert-buffer-insert-file-contents-function — Variable: revert-buffer-insert-file-contents-function The value of this variable, if non-nil, specifies the function to use toinsert the updated contents when reverting this buffer. The functionreceives two arguments: first the file name to use; second, t ifthe user has asked to read the auto-save file.The reason for a mode to set this variable instead ofrevert-buffer-function is to avoid duplicating or replacing therest of what revert-buffer does: asking for confirmation,clearing the undo list, deciding the proper major mode, and running thehooks listed below. before-revert-hook — Variable: before-revert-hook This normal hook is run by revert-buffer beforeinserting the modified contents—but only ifrevert-buffer-function is nil. after-revert-hook — Variable: after-revert-hook This normal hook is run by revert-buffer after insertingthe modified contents—but only if revert-buffer-function isnil. <setfilename>../info/buffers</setfilename> Buffers buffer A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows. Buffer Basics A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. Although several buffers normally exist, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows. Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. See . A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function. Buffer-specific information that is directly accessible is stored in buffer-local variable bindings, which are variable values that are effective only in a particular buffer. This feature allows each buffer to override the values of certain variables. Most major modes override variables such as fill-column or comment-column in this way. For more information about buffer-local variables and functions related to them, see . For functions and variables related to visiting files in buffers, see and . For functions and variables related to the display of buffers in windows, see . bufferp — Function: bufferp object This function returns t if object is a buffer,nil otherwise. The Current Buffer selecting a buffer changing to another buffer current buffer There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see ). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can temporarily designate any buffer as current in order to operate on its contents, without changing what is displayed on the screen. The way to designate a current buffer in a Lisp program is by calling set-buffer. The specified buffer remains current until a new one is designated. When an editing command returns to the editor command loop, the command loop designates the buffer displayed in the selected window as current, to prevent confusion: the buffer that the cursor is in when Emacs reads a command is the buffer that the command will apply to. (See .) Therefore, set-buffer is not the way to switch visibly to a different buffer so that the user can edit it. For that, you must use the functions described in . Warning: Lisp functions that change to a different current buffer should not depend on the command loop to set it back afterwards. Editing commands written in Emacs Lisp can be called from other programs as well as from the command loop; it is convenient for the caller if the subroutine does not change which buffer is current (unless, of course, that is the subroutine's purpose). Therefore, you should normally use set-buffer within a save-current-buffer or save-excursion (see ) form that will restore the current buffer when your function is done. Here is an example, the code for the command append-to-buffer (with the documentation string abridged): (defun append-to-buffer (buffer start end) "Append to specified buffer the text of the region. …" (interactive "BAppend to buffer: \nr") (let ((oldbuf (current-buffer))) (save-current-buffer (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) This function binds a local variable to record the current buffer, and then save-current-buffer arranges to make it current again. Next, set-buffer makes the specified buffer current. Finally, insert-buffer-substring copies the string from the original current buffer to the specified (and now current) buffer. If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed. If you make local bindings (with let or function arguments) for a variable that may also have buffer-local bindings, make sure that the same buffer is current at the beginning and at the end of the local binding's scope. Otherwise you might bind it in one buffer and unbind it in another! There are two ways to do this. In simple cases, you may see that nothing ever changes the current buffer within the scope of the binding. Otherwise, use save-current-buffer or save-excursion to make sure that the buffer current at the beginning is current again whenever the variable is unbound. Do not rely on using set-buffer to change the current buffer back, because that won't do the job if a quit happens while the wrong buffer is current. Here is what not to do: (let (buffer-read-only (obuf (current-buffer))) (set-buffer …) … (set-buffer obuf)) Using save-current-buffer, as shown here, handles quitting, errors, and throw, as well as ordinary evaluation. (let (buffer-read-only) (save-current-buffer (set-buffer …) …)) current-buffer — Function: current-buffer This function returns the current buffer. (current-buffer) => #<buffer buffers.texi> set-buffer — Function: set-buffer buffer-or-name This function makes buffer-or-name the current buffer. This doesnot display the buffer in any window, so the user cannot necessarily seethe buffer. But Lisp programs will now operate on it.This function returns the buffer identified by buffer-or-name.An error is signaled if buffer-or-name does not identify anexisting buffer. save-current-buffer — Special Form: save-current-buffer body … The save-current-buffer special form saves the identity of thecurrent buffer, evaluates the body forms, and finally restoresthat buffer as current. The return value is the value of the lastform in body. The current buffer is restored even in case of anabnormal exit via throw or error (see ).If the buffer that used to be current has been killed by the time ofexit from save-current-buffer, then it is not made current again,of course. Instead, whichever buffer was current just before exitremains current. with-current-buffer — Macro: with-current-buffer buffer-or-name body … The with-current-buffer macro saves the identity of the currentbuffer, makes buffer-or-name current, evaluates the bodyforms, and finally restores the buffer. The return value is the valueof the last form in body. The current buffer is restored evenin case of an abnormal exit via throw or error (see ).An error is signaled if buffer-or-name does not identify anexisting buffer. with-temp-buffer — Macro: with-temp-buffer body … The with-temp-buffer macro evaluates the body formswith a temporary buffer as the current buffer. It saves the identity ofthe current buffer, creates a temporary buffer and makes it current,evaluates the body forms, and finally restores the previouscurrent buffer while killing the temporary buffer. By default, undoinformation (see ) is not recorded in the buffer created bythis macro (but body can enable that, if needed).The return value is the value of the last form in body. You canreturn the contents of the temporary buffer by using(buffer-string) as the last form.The current buffer is restored even in case of an abnormal exit viathrow or error (see ).See also with-temp-file in Writing to Files. Buffer Names buffer names Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name. hidden buffers buffers without undo information Buffers that are ephemeral and generally uninteresting to the user have names starting with a space, so that the list-buffers and buffer-menu commands don't mention them (but if such a buffer visits a file, it is mentioned). A name starting with space also initially disables recording undo information; see . buffer-name — Function: buffer-name &optional buffer This function returns the name of buffer as a string. Ifbuffer is not supplied, it defaults to the current buffer.If buffer-name returns nil, it means that bufferhas been killed. See . (buffer-name) => "buffers.texi" (setq foo (get-buffer "temp")) => #<buffer temp> (kill-buffer foo) => nil (buffer-name foo) => nil foo => #<killed buffer> rename-buffer — Command: rename-buffer newname &optional unique This function renames the current buffer to newname. An erroris signaled if newname is not a string. Ordinarily, rename-buffer signals an error if newname isalready in use. However, if unique is non-nil, it modifiesnewname to make a name that is not in use. Interactively, you canmake unique non-nil with a numeric prefix argument.(This is how the command rename-uniquely is implemented.)This function returns the name actually given to the buffer. get-buffer — Function: get-buffer buffer-or-name This function returns the buffer specified by buffer-or-name.If buffer-or-name is a string and there is no buffer with thatname, the value is nil. If buffer-or-name is a buffer, itis returned as given; that is not very useful, so the argument is usuallya name. For example: (setq b (get-buffer "lewis")) => #<buffer lewis> (get-buffer b) => #<buffer lewis> (get-buffer "Frazzle-nots") => nil See also the function get-buffer-create in . generate-new-buffer-name — Function: generate-new-buffer-name starting-name &optional ignore This function returns a name that would be unique for a new buffer—butdoes not create the buffer. It starts with starting-name, andproduces a name not currently in use for any buffer by appending anumber inside of ‘<…>’. It starts at 2 and keepsincrementing the number until it is not the name of an existing buffer.If the optional second argument ignore is non-nil, itshould be a string, a potential buffer name. It means to considerthat potential buffer acceptable, if it is tried, even it is the nameof an existing buffer (which would normally be rejected). Thus, ifbuffers named ‘foo’, ‘foo<2>’, ‘foo<3>’ and‘foo<4>’ exist, (generate-new-buffer-name "foo") => "foo<5>" (generate-new-buffer-name "foo" "foo<3>") => "foo<3>" (generate-new-buffer-name "foo" "foo<6>") => "foo<5>" See the related function generate-new-buffer in . Buffer File Name visited file buffer file name file name of buffer The buffer file name is the name of the file that is visited in that buffer. When a buffer is not visiting a file, its buffer file name is nil. Most of the time, the buffer name is the same as the nondirectory part of the buffer file name, but the buffer file name and the buffer name are distinct and can be set independently. See . buffer-file-name — Function: buffer-file-name &optional buffer This function returns the absolute file name of the file thatbuffer is visiting. If buffer is not visiting any file,buffer-file-name returns nil. If buffer is notsupplied, it defaults to the current buffer. (buffer-file-name (other-buffer)) => "/usr/user/lewis/manual/files.texi" buffer-file-name — Variable: buffer-file-name This buffer-local variable contains the name of the file being visitedin the current buffer, or nil if it is not visiting a file. Itis a permanent local variable, unaffected bykill-all-local-variables. buffer-file-name => "/usr/user/lewis/manual/buffers.texi" It is risky to change this variable's value without doing various otherthings. Normally it is better to use set-visited-file-name (seebelow); some of the things done there, such as changing the buffer name,are not strictly necessary, but others are essential to avoid confusingEmacs. buffer-file-truename — Variable: buffer-file-truename This buffer-local variable holds the abbreviated truename of the filevisited in the current buffer, or nil if no file is visited.It is a permanent local, unaffected bykill-all-local-variables. See , and. buffer-file-number — Variable: buffer-file-number This buffer-local variable holds the file number and directory devicenumber of the file visited in the current buffer, or nil if nofile or a nonexistent file is visited. It is a permanent local,unaffected by kill-all-local-variables.The value is normally a list of the form (filenumdevnum). This pair of numbers uniquely identifies the file amongall files accessible on the system. See the functionfile-attributes, in , for more informationabout them.If buffer-file-name is the name of a symbolic link, then bothnumbers refer to the recursive target. get-file-buffer — Function: get-file-buffer filename This function returns the buffer visiting file filename. Ifthere is no such buffer, it returns nil. The argumentfilename, which must be a string, is expanded (see ), then compared against the visited file names of all livebuffers. Note that the buffer's buffer-file-name must matchthe expansion of filename exactly. This function will notrecognize other names for the same file. (get-file-buffer "buffers.texi") => #<buffer buffers.texi> In unusual circumstances, there can be more than one buffer visitingthe same file name. In such cases, this function returns the firstsuch buffer in the buffer list. find-buffer-visiting — Function: find-buffer-visiting filename &optional predicate This is like get-file-buffer, except that it can return anybuffer visiting the file possibly under a different name. Thatis, the buffer's buffer-file-name does not need to match theexpansion of filename exactly, it only needs to refer to thesame file. If predicate is non-nil, it should be afunction of one argument, a buffer visiting filename. Thebuffer is only considered a suitable return value if predicatereturns non-nil. If it can not find a suitable buffer toreturn, find-buffer-visiting returns nil. set-visited-file-name — Command: set-visited-file-name filename &optional no-query along-with-file If filename is a non-empty string, this function changes thename of the file visited in the current buffer to filename. (If thebuffer had no visited file, this gives it one.) The next timethe buffer is saved it will go in the newly-specified file.This command marks the buffer as modified, since it does not (as faras Emacs knows) match the contents of filename, even if itmatched the former visited file. It also renames the buffer tocorrespond to the new file name, unless the new name is already inuse.If filename is nil or the empty string, that stands for“no visited file.” In this case, set-visited-file-name marksthe buffer as having no visited file, without changing the buffer'smodified flag.Normally, this function asks the user for confirmation if therealready is a buffer visiting filename. If no-query isnon-nil, that prevents asking this question. If there alreadyis a buffer visiting filename, and the user confirms orquery is non-nil, this function makes the new buffer nameunique by appending a number inside of ‘<…>’ to filename.If along-with-file is non-nil, that means to assume thatthe former visited file has been renamed to filename. In thiscase, the command does not change the buffer's modified flag, nor thebuffer's recorded last file modification time as reported byvisited-file-modtime (see ). Ifalong-with-file is nil, this function clears the recordedlast file modification time, after which visited-file-modtimereturns zero. When the function set-visited-file-name is called interactively, itprompts for filename in the minibuffer. list-buffers-directory — Variable: list-buffers-directory This buffer-local variable specifies a string to display in a bufferlisting where the visited file name would go, for buffers that don'thave a visited file name. Dired buffers use this variable. Buffer Modification buffer modification modification flag (of buffer) Emacs keeps a flag called the modified flag for each buffer, to record whether you have changed the text of the buffer. This flag is set to t whenever you alter the contents of the buffer, and cleared to nil when you save it. Thus, the flag shows whether there are unsaved changes. The flag value is normally shown in the mode line (see ), and controls saving (see ) and auto-saving (see ). Some Lisp programs set the flag explicitly. For example, the function set-visited-file-name sets the flag to t, because the text does not match the newly-visited file, even if it is unchanged from the file formerly visited. The functions that modify the contents of buffers are described in . buffer-modified-p — Function: buffer-modified-p &optional buffer This function returns t if the buffer buffer has been modifiedsince it was last read in from a file or saved, or nilotherwise. If buffer is not supplied, the current bufferis tested. set-buffer-modified-p — Function: set-buffer-modified-p flag This function marks the current buffer as modified if flag isnon-nil, or as unmodified if the flag is nil.Another effect of calling this function is to cause unconditionalredisplay of the mode line for the current buffer. In fact, thefunction force-mode-line-update works by doing this: (set-buffer-modified-p (buffer-modified-p)) restore-buffer-modified-p — Function: restore-buffer-modified-p flag Like set-buffer-modified-p, but does not force redisplayof mode lines. not-modified — Command: not-modified &optional arg This command marks the current buffer as unmodified, and not needingto be saved. If arg is non-nil, it marks the buffer asmodified, so that it will be saved at the next suitable occasion.Interactively, arg is the prefix argument.Don't use this function in programs, since it prints a message in theecho area; use set-buffer-modified-p (above) instead. buffer-modified-tick — Function: buffer-modified-tick &optional buffer This function returns buffer's modification-count. This is acounter that increments every time the buffer is modified. Ifbuffer is nil (or omitted), the current buffer is used.The counter can wrap around occasionally. buffer-chars-modified-tick — Function: buffer-chars-modified-tick &optional buffer This function returns buffer's character-change modification-count.Changes to text properties leave this counter unchanged; however, eachtime text is inserted or removed from the buffer, the counter is resetto the value that would be returned buffer-modified-tick.By comparing the values returned by two buffer-chars-modified-tickcalls, you can tell whether a character change occurred in that bufferin between the calls. If buffer is nil (or omitted), thecurrent buffer is used. Buffer Modification Time comparing file modification time modification time of buffer Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file. (See , for how to examine a file's modification time.) verify-visited-file-modtime — Function: verify-visited-file-modtime buffer This function compares what buffer has recorded for themodification time of its visited file against the actual modificationtime of the file as recorded by the operating system. The two should bethe same unless some other process has written the file since Emacsvisited or saved it.The function returns t if the last actual modification time andEmacs's recorded modification time are the same, nil otherwise.It also returns t if the buffer has no recorded lastmodification time, that is if visited-file-modtime would returnzero.It always returns t for buffers that are not visiting a file,even if visited-file-modtime returns a non-zero value. Forinstance, it always returns t for dired buffers. It returnst for buffers that are visiting a file that does not exist andnever existed, but nil for file-visiting buffers whose file hasbeen deleted. clear-visited-file-modtime — Function: clear-visited-file-modtime This function clears out the record of the last modification time ofthe file being visited by the current buffer. As a result, the nextattempt to save this buffer will not complain of a discrepancy infile modification times.This function is called in set-visited-file-name and otherexceptional places where the usual test to avoid overwriting a changedfile should not be done. visited-file-modtime — Function: visited-file-modtime This function returns the current buffer's recorded last filemodification time, as a list of the form (high low).(This is the same format that file-attributes uses to returntime values; see .)If the buffer has no recorded last modification time, this functionreturns zero. This case occurs, for instance, if the buffer is notvisiting a file or if the time has been explicitly cleared byclear-visited-file-modtime. Note, however, thatvisited-file-modtime returns a list for some non-file bufferstoo. For instance, in a Dired buffer listing a directory, it returnsthe last modification time of that directory, as recorded by Dired.For a new buffer visiting a not yet existing file, high is−1 and low is 65535, that is,2**16 - 1. set-visited-file-modtime — Function: set-visited-file-modtime &optional time This function updates the buffer's record of the last modification timeof the visited file, to the value specified by time if timeis not nil, and otherwise to the last modification time of thevisited file.If time is neither nil nor zero, it should have the form(high . low) or (high low), ineither case containing two integers, each of which holds 16 bits of thetime.This function is useful if the buffer was not read from the filenormally, or if the file itself has been changed for some known benignreason. ask-user-about-supersession-threat — Function: ask-user-about-supersession-threat filename This function is used to ask a user how to proceed after an attempt tomodify an buffer visiting file filename when the file is newerthan the buffer text. Emacs detects this because the modificationtime of the file on disk is newer than the last save-time of thebuffer. This means some other program has probably altered the file. file-supersessionDepending on the user's answer, the function may return normally, inwhich case the modification of the buffer proceeds, or it may signal afile-supersession error with data (filename), in whichcase the proposed buffer modification is not allowed.This function is called automatically by Emacs on the properoccasions. It exists so you can customize Emacs by redefining it.See the file userlock.el for the standard definition.See also the file locking mechanism in . Read-Only Buffers read-only buffer buffer, read-only If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing. Read-only buffers are used in two kinds of situations: A buffer visiting a write-protected file is normally read-only.Here, the purpose is to inform the user that editing the buffer with theaim of saving it in the file may be futile or undesirable. The user whowants to change the buffer text despite this can do so after clearingthe read-only flag with C-x C-q. Modes such as Dired and Rmail make buffers read-only when altering thecontents with the usual editing commands would probably be a mistake.The special commands of these modes bind buffer-read-only tonil (with let) or bind inhibit-read-only tot around the places where they themselves change the text. buffer-read-only — Variable: buffer-read-only This buffer-local variable specifies whether the buffer is read-only.The buffer is read-only if this variable is non-nil. inhibit-read-only — Variable: inhibit-read-only If this variable is non-nil, then read-only buffers and,depending on the actual value, some or all read-only characters may bemodified. Read-only characters in a buffer are those that havenon-nil read-only properties (either text properties oroverlay properties). See , for more informationabout text properties. See , for more information aboutoverlays and their properties.If inhibit-read-only is t, all read-only characterproperties have no effect. If inhibit-read-only is a list, thenread-only character properties have no effect if they are membersof the list (comparison is done with eq). toggle-read-only — Command: toggle-read-only &optional arg This command toggles whether the current buffer is read-only. It isintended for interactive use; do not use it in programs. At any givenpoint in a program, you should know whether you want the read-only flagon or off; so you can set buffer-read-only explicitly to theproper value, t or nil.If arg is non-nil, it should be a raw prefix argument.toggle-read-only sets buffer-read-only to t ifthe numeric value of that prefix argument is positive and tonil otherwise. See . barf-if-buffer-read-only — Function: barf-if-buffer-read-only This function signals a buffer-read-only error if the currentbuffer is read-only. See , for another way tosignal an error if the current buffer is read-only. The Buffer List buffer list The buffer list is a list of all live buffers. The order of the buffers in the list is based primarily on how recently each buffer has been displayed in a window. Several functions, notably other-buffer, use this ordering. A buffer list displayed for the user also follows this order. Creating a buffer adds it to the end of the buffer list, and killing a buffer removes it. Buffers move to the front of the list when they are selected for display in a window (see ), and to the end when they are buried (see bury-buffer, below). There are no functions available to the Lisp programmer which directly manipulate the buffer list. In addition to the fundamental Emacs buffer list, each frame has its own version of the buffer list, in which the buffers that have been selected in that frame come first, starting with the buffers most recently selected in that frame. (This order is recorded in frame's buffer-list frame parameter; see .) The buffers that were never selected in frame come afterward, ordered according to the fundamental Emacs buffer list. buffer-list — Function: buffer-list &optional frame This function returns the buffer list, including all buffers, even thosewhose names begin with a space. The elements are actual buffers, nottheir names.If frame is a frame, this returns frame's buffer list. Ifframe is nil, the fundamental Emacs buffer list is used:all the buffers appear in order of most recent selection, regardless ofwhich frames they were selected in. (buffer-list) => (#<buffer buffers.texi> #<buffer *Minibuf-1*> #<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>) ;; Note that the name of the minibuffer ;; begins with a space! (mapcar (function buffer-name) (buffer-list)) => ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS") The list that buffer-list returns is constructed specifically by buffer-list; it is not an internal Emacs data structure, and modifying it has no effect on the order of buffers. If you want to change the order of buffers in the frame-independent buffer list, here is an easy way: (defun reorder-buffer-list (new-list) (while new-list (bury-buffer (car new-list)) (setq new-list (cdr new-list)))) With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer. To change the order or value of a frame's buffer list, set the frame's buffer-list frame parameter with modify-frame-parameters (see ). other-buffer — Function: other-buffer &optional buffer visible-ok frame This function returns the first buffer in the buffer list other thanbuffer. Usually this is the buffer selected most recently (inframe frame or else the currently selected frame, see ), aside from buffer. Buffers whose names start with aspace are not considered at all.If buffer is not supplied (or if it is not a buffer), thenother-buffer returns the first buffer in the selected frame'sbuffer list that is not now visible in any window in a visible frame.If frame has a non-nil buffer-predicate parameter,then other-buffer uses that predicate to decide which buffers toconsider. It calls the predicate once for each buffer, and if the valueis nil, that buffer is ignored. See . If visible-ok is nil, other-buffer avoids returninga buffer visible in any window on any visible frame, except as a lastresort. If visible-ok is non-nil, then it does not matterwhether a buffer is displayed somewhere or not.If no suitable buffer exists, the buffer ‘*scratch*’ is returned(and created, if necessary). bury-buffer — Command: bury-buffer &optional buffer-or-name This function puts buffer-or-name at the end of the buffer list,without changing the order of any of the other buffers on the list.This buffer therefore becomes the least desirable candidate forother-buffer to return. The argument can be either a bufferitself or the name of one.bury-buffer operates on each frame's buffer-list parameteras well as the frame-independent Emacs buffer list; therefore, thebuffer that you bury will come last in the value of (buffer-listframe) and in the value of (buffer-list nil).If buffer-or-name is nil or omitted, this means to bury thecurrent buffer. In addition, if the buffer is displayed in the selectedwindow, this switches to some other buffer (obtained usingother-buffer) in the selected window. But if the buffer isdisplayed in some other window, it remains displayed there.To replace a buffer in all the windows that display it, usereplace-buffer-in-windows. See . Creating Buffers creating buffers buffers, creating This section describes the two primitives for creating buffers. get-buffer-create creates a buffer if it finds no existing buffer with the specified name; generate-new-buffer always creates a new buffer and gives it a unique name. Other functions you can use to create buffers include with-output-to-temp-buffer (see ) and create-file-buffer (see ). Starting a subprocess can also create a buffer (see ). get-buffer-create — Function: get-buffer-create name This function returns a buffer named name. It returns a livebuffer with that name, if one exists; otherwise, it creates a newbuffer. The buffer does not become the current buffer—this functiondoes not change which buffer is current.If name is a buffer instead of a string, it is returned, even ifit is dead. An error is signaled if name is neither a stringnor a buffer. (get-buffer-create "foo") => #<buffer foo> The major mode for a newly created buffer is set to Fundamental mode.(The variable default-major-mode is handled at a higher level;see .) If the name begins with a space, thebuffer initially disables undo information recording (see ). generate-new-buffer — Function: generate-new-buffer name This function returns a newly created, empty buffer, but does not makeit current. If there is no buffer named name, then that is thename of the new buffer. If that name is in use, this function addssuffixes of the form ‘<n>’ to name, where n is aninteger. It tries successive integers starting with 2 until it finds anavailable name.An error is signaled if name is not a string. (generate-new-buffer "bar") => #<buffer bar> (generate-new-buffer "bar") => #<buffer bar<2>> (generate-new-buffer "bar") => #<buffer bar<3>> The major mode for the new buffer is set to Fundamental mode. Thevariable default-major-mode is handled at a higher level.See .See the related function generate-new-buffer-name in . Killing Buffers killing buffers buffers, killing Killing a buffer makes its name unknown to Emacs and makes the memory space it occupied available for other use. The buffer object for the buffer that has been killed remains in existence as long as anything refers to it, but it is specially marked so that you cannot make it current or display it. Killed buffers retain their identity, however; if you kill two distinct buffers, they remain distinct according to eq although both are dead. If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See . If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well. The buffer-name of a killed buffer is nil. You can use this feature to test whether a buffer has been killed: (defun buffer-killed-p (buffer) "Return t if BUFFER is killed." (not (buffer-name buffer))) kill-buffer — Command: kill-buffer buffer-or-name This function kills the buffer buffer-or-name, freeing all itsmemory for other uses or to be returned to the operating system. Ifbuffer-or-name is nil, it kills the current buffer.Any processes that have this buffer as the process-buffer aresent the SIGHUP signal, which normally causes them to terminate.(The basic meaning of SIGHUP is that a dialup line has beendisconnected.) See .If the buffer is visiting a file and contains unsaved changes,kill-buffer asks the user to confirm before the buffer is killed.It does this even if not called interactively. To prevent the requestfor confirmation, clear the modified flag before callingkill-buffer. See .Killing a buffer that is already dead has no effect.This function returns t if it actually killed the buffer. Itreturns nil if the user refuses to confirm or ifbuffer-or-name was already dead. (kill-buffer "foo.unchanged") => t (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) yes ---------- Buffer: Minibuffer ---------- => t kill-buffer-query-functions — Variable: kill-buffer-query-functions After confirming unsaved changes, kill-buffer calls the functionsin the list kill-buffer-query-functions, in order of appearance,with no arguments. The buffer being killed is the current buffer whenthey are called. The idea of this feature is that these functions willask for confirmation from the user. If any of them returns nil,kill-buffer spares the buffer's life. kill-buffer-hook — Variable: kill-buffer-hook This is a normal hook run by kill-buffer after asking all thequestions it is going to ask, just before actually killing the buffer.The buffer to be killed is current when the hook functions run.See . This variable is a permanent local, so its local bindingis not cleared by changing major modes. buffer-offer-save — Variable: buffer-offer-save This variable, if non-nil in a particular buffer, tellssave-buffers-kill-emacs and save-some-buffers (if thesecond optional argument to that function is t) to offer tosave that buffer, just as they offer to save file-visiting buffers.See . The variablebuffer-offer-save automatically becomes buffer-local when setfor any reason. See . buffer-save-without-query — Variable: buffer-save-without-query This variable, if non-nil in a particular buffer, tellssave-buffers-kill-emacs and save-some-buffers to savethis buffer (if it's modified) without asking the user. The variableautomatically becomes buffer-local when set for any reason. buffer-live-p — Function: buffer-live-p object This function returns t if object is a buffer which hasnot been killed, nil otherwise. Indirect Buffers indirect buffers base buffer An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer. The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves. In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, independent values of point, independent narrowing, independent markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), independent major modes, and independent buffer-local variable bindings. An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer. Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer. make-indirect-buffer — Command: make-indirect-buffer base-buffer name &optional clone This creates and returns an indirect buffer named name whosebase buffer is base-buffer. The argument base-buffer maybe a live buffer or the name (a string) of an existing buffer. Ifname is the name of an existing buffer, an error is signaled.If clone is non-nil, then the indirect buffer originallyshares the “state” of base-buffer such as major mode, minormodes, buffer local variables and so on. If clone is omittedor nil the indirect buffer's state is set to the default statefor new buffers.If base-buffer is an indirect buffer, its base buffer is used asthe base for the new buffer. If, in addition, clone isnon-nil, the initial state is copied from the actual basebuffer, not from base-buffer. clone-indirect-buffer — Function: clone-indirect-buffer newname display-flag &optional norecord This function creates and returns a new indirect buffer that sharesthe current buffer's base buffer and copies the rest of the currentbuffer's attributes. (If the current buffer is not indirect, it isused as the base buffer.)If display-flag is non-nil, that means to display the newbuffer by calling pop-to-buffer. If norecord isnon-nil, that means not to put the new buffer to the front ofthe buffer list. buffer-base-buffer — Function: buffer-base-buffer &optional buffer This function returns the base buffer of buffer, which defaultsto the current buffer. If buffer is not indirect, the value isnil. Otherwise, the value is another buffer, which is never anindirect buffer. The Buffer Gap Emacs buffers are implemented using an invisible gap to make insertion and deletion faster. Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, this means that the gap must first be moved to the locus of the insertion or deletion. Emacs moves the gap only when you try to insert or delete. This is why your first editing command in one part of a large buffer, after previously editing in another far-away part, sometimes involves a noticeable delay. This mechanism works invisibly, and Lisp code should never be affected by the gap's current location, but these functions are available for getting information about the gap status. gap-position — Function: gap-position This function returns the current gap position in the current buffer. gap-size — Function: gap-size This function returns the current gap size of the current buffer. <setfilename>../info/windows</setfilename> Windows This chapter describes most of the functions and variables related to Emacs windows. See , for information on how text is displayed in windows. Basic Concepts of Emacs Windows window selected window A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant. Emacs groups windows into frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple nonoverlapping Emacs windows. In each frame, at any time, one and only one window is designated as selected within the frame. The frame's cursor appears in that window, but the other windows have “non-selected” cursors, normally less visible. At any time, one frame is the selected frame; and the window selected within that frame is the selected window. The selected window's buffer is usually the current buffer (except when set-buffer has been used). See . cursor-in-non-selected-windows — Variable: cursor-in-non-selected-windows If this variable is nil, Emacs displays only one cursor,in the selected window. Other windows have no cursor at all. For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (See .) Each window has the following attributes: containing frame window height window width window edges with respect to the screen or frame the buffer it displays position within the buffer at the upper left of the window amount of horizontal scrolling, in columns point the mark how recently the window was selected fringe settings display margins scroll-bar settings multiple windows Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached. The meaning of “window” in Emacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame. terminal screen screen of terminal tiled windows Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows and resizes them, not all conceivable tilings of windows on an Emacs frame are actually possible. See , and . See , for information on how the contents of the window's buffer are displayed in the window. windowp — Function: windowp object This function returns t if object is a window. Splitting Windows splitting windows window splitting The functions described here are the primitives used to split a window into two windows. Two higher level functions sometimes split a window, but not always: pop-to-buffer and display-buffer (see ). The functions described here do not accept a buffer as an argument. The two “halves” of the split window initially display the same buffer previously visible in the window that was split. split-window — Command: split-window &optional window size horizontal This function splits a new window out of window's screen area.It returns the new window.If horizontal is non-nil, then window splits intotwo side by side windows. The original window window keeps theleftmost size columns, and gives the rest of the columns to thenew window. Otherwise, it splits into windows one above the other, andwindow keeps the upper size lines and gives the rest of thelines to the new window. The original window is therefore theleft-hand or upper of the two, and the new window is the right-hand orlower.If window is omitted or nil, that stands for the selectedwindow. When you split the selected window, it remains selected.If size is omitted or nil, then window is dividedevenly into two parts. (If there is an odd line, it is allocated tothe new window.) When split-window is called interactively,all its arguments are nil.If splitting would result in making a window that is smaller thanwindow-min-height or window-min-width, the functionsignals an error and does not split the window at all.The following example starts with one window on a screen that is 50lines high by 80 columns wide; then it splits the window. (setq w (selected-window)) => #<window 8 on windows.texi> (window-edges) ; Edges in order: => (0 0 80 50) ; left--top--right--bottom ;; Returns window created (setq w2 (split-window w 15)) => #<window 28 on windows.texi> (window-edges w2) => (0 15 80 50) ; Bottom window; ; top is line 15 (window-edges w) => (0 0 80 15) ; Top window The screen looks like this: __________ | | line 0 | w | |__________| | | line 15 | w2 | |__________| line 50 column 0 column 80 Next, split the top window horizontally: (setq w3 (split-window w 35 t)) => #<window 32 on windows.texi> (window-edges w3) => (35 0 80 15) ; Left edge at column 35 (window-edges w) => (0 0 35 15) ; Right edge at column 35 (window-edges w2) => (0 15 80 50) ; Bottom window unchanged Now the screen looks like this: column 35 __________ | | | line 0 | w | w3 | |___|______| | | line 15 | w2 | |__________| line 50 column 0 column 80 Normally, Emacs indicates the border between two side-by-side windowswith a scroll bar (see Scroll Bars) or ‘|’characters. The display table can specify alternative bordercharacters; see . split-window-vertically — Command: split-window-vertically &optional size This function splits the selected window into two windows, one above theother, leaving the upper of the two windows selected, with sizelines. (If size is negative, then the lower of the two windowsgets − size lines and the upper window gets the rest, butthe upper window is still the one selected.) However, ifsplit-window-keep-point (see below) is nil, then eitherwindow can be selected.In other respects, this function is similar to split-window.In particular, the upper window is the original one and the returnvalue is the new, lower window. split-window-keep-point — User Option: split-window-keep-point If this variable is non-nil (the default), thensplit-window-vertically behaves as described above.If it is nil, then split-window-vertically adjusts pointin each of the two windows to avoid scrolling. (This is useful onslow terminals.) It selects whichever window contains the screen linethat point was previously on.This variable only affects the behavior of split-window-vertically.It has no effect on the other functions described here. split-window-horizontally — Command: split-window-horizontally &optional size This function splits the selected window into two windowsside-by-side, leaving the selected window on the left with sizecolumns. If size is negative, the rightmost window gets− size columns, but the leftmost window still remainsselected.This function is basically an interface to split-window.You could define a simplified version of the function like this: (defun split-window-horizontally (&optional arg) "Split selected window into two windows, side by side..." (interactive "P") (let ((size (and arg (prefix-numeric-value arg)))) (and size (< size 0) (setq size (+ (window-width) size))) (split-window nil size t))) one-window-p — Function: one-window-p &optional no-mini all-frames This function returns non-nil if there is only one window. Theargument no-mini, if non-nil, means don't count theminibuffer even if it is active; otherwise, the minibuffer window iscounted when it is active.The argument all-frames specifies which frames to consider. Hereare the possible values and their meanings: nil Count the windows in the selected frame, plus the minibuffer usedby that frame even if it lies in some other frame. t Count all windows in all existing frames. visible Count all windows in all visible frames. 0 Count all windows in all visible or iconified frames. anything else Count precisely the windows in the selected frame, and no others. Deleting Windows deleting windows A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see ). Restoring a window configuration also deletes any windows that aren't part of that configuration. When you delete a window, the space it took up is given to one adjacent sibling. window-live-p — Function: window-live-p window This function returns nil if window is deleted, andt otherwise.Warning: Erroneous information or fatal errors may result fromusing a deleted window as if it were live. delete-window — Command: delete-window &optional window This function removes window from display, and returns nil.If window is omitted, then the selected window is deleted. Anerror is signaled if there is only one window when delete-windowis called. delete-other-windows — Command: delete-other-windows &optional window This function makes window the only window on its frame, bydeleting the other windows in that frame. If window is omitted ornil, then the selected window is used by default.The return value is nil. delete-windows-on — Command: delete-windows-on buffer-or-name &optional frame This function deletes all windows showing buffer-or-name. Ifthere are no windows showing buffer-or-name, it does nothing.buffer-or-name must be a buffer or the name of an existingbuffer.delete-windows-on operates frame by frame. If a frame hasseveral windows showing different buffers, then those showingbuffer-or-name are removed, and the others expand to fill thespace. If all windows in some frame are showing buffer-or-name(including the case where there is only one window), then the framewinds up with a single window showing another buffer chosen withother-buffer. See .The argument frame controls which frames to operate on. Thisfunction does not use it in quite the same way as the other functionswhich scan all windows; specifically, the values t and nilhave the opposite of their meanings in other functions. Here are thefull details: If it is nil, operate on all frames. If it is t, operate on the selected frame. If it is visible, operate on all visible frames. If it is 0, operate on all visible or iconified frames. If it is a frame, operate on that frame. This function always returns nil. Selecting Windows selecting a window When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it. selected-window — Function: selected-window This function returns the selected window. This is the window inwhich the cursor appears and to which many commands apply. select-window — Function: select-window window &optional norecord This function makes window the selected window. The cursor thenappears in window (on redisplay). Unless window wasalready selected, select-window makes window's buffer thecurrent buffer.Normally window's selected buffer is moved to the front of thebuffer list, but if norecord is non-nil, the buffer listorder is unchanged.The return value is window. (setq w (next-window)) (select-window w) => #<window 65 on windows.texi> save-selected-window — Macro: save-selected-window forms … This macro records the selected frame, as well as the selected windowof each frame, executes forms in sequence, then restores theearlier selected frame and windows. It also saves and restores thecurrent buffer. It returns the value of the last form in forms.This macro does not save or restore anything about the sizes,arrangement or contents of windows; therefore, if the formschange them, the change persists. If the previously selected windowof some frame is no longer live at the time of exit from forms,that frame's selected window is left alone. If the previouslyselected window is no longer live, then whatever window is selected atthe end of forms remains selected. with-selected-window — Macro: with-selected-window window forms … This macro selects window (without changing the buffer list),executes forms in sequence, then restores the previouslyselected window and current buffer. It is just likesave-selected-window, except that it explicitly selectswindow, also without altering the buffer list sequence. finding windows The following functions choose one of the windows on the screen, offering various criteria for the choice. get-lru-window — Function: get-lru-window &optional frame dedicated This function returns the window least recently “used” (that is,selected). If any full-width windows are present, it only considersthese. The selected window is always the most recently used window.The selected window can be the least recently used window if it is theonly window. A newly created window becomes the least recently usedwindow until it is selected. A minibuffer window is never acandidate. Dedicated windows are never candidates unless thededicated argument is non-nil, so if allexisting windows are dedicated, the value is nil.The argument frame controls which windows are considered. If it is nil, consider windows on the selected frame. If it is t, consider windows on all frames. If it is visible, consider windows on all visible frames. If it is 0, consider windows on all visible or iconified frames. If it is a frame, consider windows on that frame. get-largest-window — Function: get-largest-window &optional frame dedicated This function returns the window with the largest area (height timeswidth). If there are no side-by-side windows, then this is the windowwith the most lines. A minibuffer window is never a candidate.Dedicated windows are never candidates unless thededicated argument is non-nil, so if all existing windowsare dedicated, the value is nil.If there are two candidate windows of the same size, this functionprefers the one that comes first in the cyclic ordering of windows(see following section), starting from the selected window.The argument frame controls which set of windows toconsider. See get-lru-window, above. window that satisfies a predicate conditional selection of windows get-window-with-predicate — Function: get-window-with-predicate predicate &optional minibuf all-frames default This function returns a window satisfying predicate. It cyclesthrough all visible windows using walk-windows (see ), calling predicate on each one of themwith that window as its argument. The function returns the firstwindow for which predicate returns a non-nil value; ifthat never happens, it returns default.The optional arguments minibuf and all-frames specify theset of windows to include in the scan. See the description ofnext-window in , for details. Cyclic Ordering of Windows cyclic ordering of windows ordering of windows, cyclic window ordering, cyclic When you use the command C-x o (other-window) to select the next window, it moves through all the windows on the screen in a specific cyclic order. For any given configuration of windows, this order never varies. It is called the cyclic ordering of windows. This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split. If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom. next-window — Function: next-window &optional window minibuf all-frames minibuffer window, and next-windowThis function returns the window following window in the cyclicordering of windows. This is the window that C-x o would selectif typed when window is selected. If window is the onlywindow visible, then this function returns window. If omitted,window defaults to the selected window.The value of the argument minibuf determines whether theminibuffer is included in the window order. Normally, whenminibuf is nil, the minibuffer is included if it iscurrently active; this is the behavior of C-x o. (The minibufferwindow is active while the minibuffer is in use. See .)If minibuf is t, then the cyclic ordering includes theminibuffer window even if it is not active.If minibuf is neither t nor nil, then the minibufferwindow is not included even if it is active.The argument all-frames specifies which frames to consider. Hereare the possible values and their meanings: nil Consider all the windows in window's frame, plus the minibufferused by that frame even if it lies in some other frame. If theminibuffer counts (as determined by minibuf), then all windows onall frames that share that minibuffer count too. t Consider all windows in all existing frames. visible Consider all windows in all visible frames. (To get useful results, youmust ensure window is in a visible frame.) 0 Consider all windows in all visible or iconified frames. a frame Consider all windows on that frame. anything else Consider precisely the windows in window's frame, and no others. This example assumes there are two windows, both displaying thebuffer ‘windows.texi’: (selected-window) => #<window 56 on windows.texi> (next-window (selected-window)) => #<window 52 on windows.texi> (next-window (next-window (selected-window))) => #<window 56 on windows.texi> previous-window — Function: previous-window &optional window minibuf all-frames This function returns the window preceding window in the cyclicordering of windows. The other arguments specify which windows toinclude in the cycle, as in next-window. other-window — Command: other-window count &optional all-frames This function selects the countth following window in the cyclicorder. If count is negative, then it moves back −countwindows in the cycle, rather than forward. It returns nil.The argument all-frames has the same meaning as innext-window, but the minibuf argument of next-windowis always effectively nil.In an interactive call, count is the numeric prefix argument. walk-windows — Function: walk-windows proc &optional minibuf all-frames This function cycles through all windows. It calls the functionproc once for each window, with the window as its soleargument.The optional arguments minibuf and all-frames specify theset of windows to include in the scan. See next-window, above,for details. window-list — Function: window-list &optional frame minibuf window This function returns a list of the windows on frame, startingwith window. If frame is nil or omitted,window-list uses the selected frame instead; if window isnil or omitted, it uses the selected window.The value of minibuf determines if the minibuffer window isincluded in the result list. If minibuf is t, the resultalways includes the minibuffer window. If minibuf is nilor omitted, that includes the minibuffer window if it is active. Ifminibuf is neither nil nor t, the result neverincludes the minibuffer window. Buffers and Windows examining windows windows, controlling precisely buffers, controlled in windows This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See , for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control. set-window-buffer — Function: set-window-buffer window buffer-or-name &optional keep-margins This function makes window display buffer-or-name as itscontents. It returns nil. buffer-or-name must be abuffer, or the name of an existing buffer. This is the fundamentalprimitive for changing which buffer is displayed in a window, and allways of doing that call this function. (set-window-buffer (selected-window) "foo") => nil Normally, displaying buffer in window resets the window'sdisplay margins, fringe widths, scroll bar settings, and positionbased on the local variables of buffer. However, ifkeep-margins is non-nil, the display margins and fringewidths of window remain unchanged. See . buffer-display-count — Variable: buffer-display-count This buffer-local variable records the number of times a buffer isdisplayed in a window. It is incremented each timeset-window-buffer is called for the buffer. window-buffer — Function: window-buffer &optional window This function returns the buffer that window is displaying. Ifwindow is omitted, this function returns the buffer for theselected window. (window-buffer) => #<buffer windows.texi> get-buffer-window — Function: get-buffer-window buffer-or-name &optional all-frames This function returns a window currently displayingbuffer-or-name, or nil if there is none. If there areseveral such windows, then the function returns the first one in thecyclic ordering of windows, starting from the selected window.See .The argument all-frames controls which windows to consider. If it is nil, consider windows on the selected frame. If it is t, consider windows on all frames. If it is visible, consider windows on all visible frames. If it is 0, consider windows on all visible or iconified frames. If it is a frame, consider windows on that frame. get-buffer-window-list — Function: get-buffer-window-list buffer-or-name &optional minibuf all-frames This function returns a list of all the windows currently displayingbuffer-or-name.The two optional arguments work like the optional arguments ofnext-window (see ); they are notlike the single optional argument of get-buffer-window. Perhapswe should change get-buffer-window in the future to make itcompatible with the other functions. buffer-display-time — Variable: buffer-display-time This variable records the time at which a buffer was last made visiblein a window. It is always local in each buffer; each timeset-window-buffer is called, it sets this variable to(current-time) in the specified buffer (see ).When a buffer is first created, buffer-display-time starts outwith the value nil. Displaying Buffers in Windows switching to a buffer displaying a buffer In this section we describe convenient functions that choose a window automatically and use it to display a specified buffer. These functions can also split an existing window in certain circumstances. We also describe variables that parameterize the heuristics used for choosing a window. See , for low-level functions that give you more precise control. All of these functions work by calling set-window-buffer. Do not use the functions in this section in order to make a buffer current so that a Lisp program can access or modify it; they are too drastic for that purpose, since they change the display of buffers in windows, which would be gratuitous and surprise the user. Instead, use set-buffer and save-current-buffer (see ), which designate buffers as current for programmed access without affecting the display of buffers in windows. switch-to-buffer — Command: switch-to-buffer buffer-or-name &optional norecord This function makes buffer-or-name the current buffer, and alsodisplays the buffer in the selected window. This means that a human cansee the buffer and subsequent keyboard commands will apply to it.Contrast this with set-buffer, which makes buffer-or-namethe current buffer but does not display it in the selected window.See .If buffer-or-name does not identify an existing buffer, then a newbuffer by that name is created. The major mode for the new buffer isset according to the variable default-major-mode. See . If buffer-or-name is nil,switch-to-buffer chooses a buffer using other-buffer.Normally the specified buffer is put at the front of the buffer list(both the selected frame's buffer list and the frame-independent bufferlist). This affects the operation of other-buffer. However, ifnorecord is non-nil, this is not done. See .The switch-to-buffer function is often used interactively, asthe binding of C-x b. It is also used frequently in programs. Itreturns the buffer that it switched to. The next two functions are similar to switch-to-buffer, except for the described features. switch-to-buffer-other-window — Command: switch-to-buffer-other-window buffer-or-name &optional norecord This function makes buffer-or-name the current buffer anddisplays it in a window not currently selected. It then selects thatwindow. The handling of the buffer is the same as inswitch-to-buffer.The currently selected window is absolutely never used to do the job.If it is the only window, then it is split to make a distinct window forthis purpose. If the selected window is already displaying the buffer,then it continues to do so, but another window is nonetheless found todisplay it in as well.This function updates the buffer list just like switch-to-bufferunless norecord is non-nil. pop-to-buffer — Function: pop-to-buffer buffer-or-name &optional other-window norecord This function makes buffer-or-name the current buffer andswitches to it in some window, preferably not the window previouslyselected. The “popped-to” window becomes the selected window withinits frame. The return value is the buffer that was switched to.If buffer-or-name is nil, that means to choose someother buffer, but you don't specify which.If the variable pop-up-frames is non-nil,pop-to-buffer looks for a window in any visible frame alreadydisplaying the buffer; if there is one, it returns that window and makesit be selected within its frame. If there is none, it creates a newframe and displays the buffer in it.If pop-up-frames is nil, then pop-to-bufferoperates entirely within the selected frame. (If the selected frame hasjust a minibuffer, pop-to-buffer operates within the mostrecently selected frame that was not just a minibuffer.)If the variable pop-up-windows is non-nil, windows maybe split to create a new window that is different from the originalwindow. For details, see .If other-window is non-nil, pop-to-buffer finds orcreates another window even if buffer-or-name is already visiblein the selected window. Thus buffer-or-name could end updisplayed in two windows. On the other hand, if buffer-or-name isalready displayed in the selected window and other-window isnil, then the selected window is considered sufficient displayfor buffer-or-name, so that nothing needs to be done.All the variables that affect display-buffer affectpop-to-buffer as well. See .If buffer-or-name is a string that does not name an existingbuffer, a buffer by that name is created. The major mode for the newbuffer is set according to the variable default-major-mode.See .This function updates the buffer list just like switch-to-bufferunless norecord is non-nil. replace-buffer-in-windows — Command: replace-buffer-in-windows buffer-or-name This function replaces buffer-or-name with some other buffer in allwindows displaying it. It chooses the other buffer withother-buffer. In the usual applications of this function, youdon't care which other buffer is used; you just want to make sure thatbuffer-or-name is no longer displayed.This function returns nil. Choosing a Window for Display This section describes the basic facility that chooses a window to display a buffer in—display-buffer. All the higher-level functions and commands use this subroutine. Here we describe how to use display-buffer and how to customize it. display-buffer — Command: display-buffer buffer-or-name &optional not-this-window frame This command makes buffer-or-name appear in some window, likepop-to-buffer, but it does not select that window and does notmake the buffer current. The identity of the selected window isunaltered by this function. buffer-or-name must be a buffer, orthe name of an existing buffer.If not-this-window is non-nil, it means to display thespecified buffer in a window other than the selected one, even if it isalready on display in the selected window. This can cause the buffer toappear in two windows at once. Otherwise, if buffer-or-name isalready being displayed in any window, that is good enough, so thisfunction does nothing.display-buffer returns the window chosen to displaybuffer-or-name.If the argument frame is non-nil, it specifies which framesto check when deciding whether the buffer is already displayed. If thebuffer is already displayed in some window on one of these frames,display-buffer simply returns that window. Here are the possiblevalues of frame: If it is nil, consider windows on the selected frame.(Actually, the last non-minibuffer frame.) If it is t, consider windows on all frames. If it is visible, consider windows on all visible frames. If it is 0, consider windows on all visible or iconified frames. If it is a frame, consider windows on that frame. Precisely how display-buffer finds or creates a window depends onthe variables described below. display-buffer-reuse-frames — User Option: display-buffer-reuse-frames If this variable is non-nil, display-buffer searchesexisting frames for a window displaying the buffer. If the buffer isalready displayed in a window in some frame, display-buffer makesthe frame visible and raises it, to use that window. If the buffer isnot already displayed, or if display-buffer-reuse-frames isnil, display-buffer's behavior is determined by othervariables, described below. pop-up-windows — User Option: pop-up-windows This variable controls whether display-buffer makes new windows.If it is non-nil and there is only one window, then that windowis split. If it is nil, then display-buffer does notsplit the single window, but uses it whole. split-height-threshold — User Option: split-height-threshold This variable determines when display-buffer may split a window,if there are multiple windows. display-buffer always splits thelargest window if it has at least this many lines. If the largestwindow is not this tall, it is split only if it is the sole window andpop-up-windows is non-nil. even-window-heights — User Option: even-window-heights This variable determines if display-buffer should even out windowheights if the buffer gets displayed in an existing window, above orbeneath another existing window. If even-window-heights ist, the default, window heights will be evened out. Ifeven-window-heights is nil, the original window heightswill be left alone. pop-up-frames — User Option: pop-up-frames This variable controls whether display-buffer makes new frames.If it is non-nil, display-buffer looks for an existingwindow already displaying the desired buffer, on any visible frame. Ifit finds one, it returns that window. Otherwise it makes a new frame.The variables pop-up-windows and split-height-threshold donot matter if pop-up-frames is non-nil.If pop-up-frames is nil, then display-buffer eithersplits a window or reuses one.See , for more information. pop-up-frame-function — User Option: pop-up-frame-function This variable specifies how to make a new frame if pop-up-framesis non-nil.Its value should be a function of no arguments. Whendisplay-buffer makes a new frame, it does so by calling thatfunction, which should return a frame. The default value of thevariable is a function that creates a frame using parameters frompop-up-frame-alist. pop-up-frame-alist — User Option: pop-up-frame-alist This variable holds an alist specifying frame parameters used whendisplay-buffer makes a new frame. See , formore information about frame parameters. special-display-buffer-names — User Option: special-display-buffer-names A list of buffer names for buffers that should be displayed specially.If the buffer's name is in this list, display-buffer handles thebuffer specially.By default, special display means to give the buffer a dedicated frame.If an element is a list, instead of a string, then the car of thelist is the buffer name, and the rest of the list says how to createthe frame. There are two possibilities for the rest of the list (itscdr). It can be an alist, specifying frame parameters, or it cancontain a function and arguments to give to it. (The function's firstargument is always the buffer to be displayed; the arguments from thelist come after that.)For example: (("myfile" (minibuffer) (menu-bar-lines . 0))) specifies to display a buffer named ‘myfile’ in a dedicated framewith specified minibuffer and menu-bar-lines parameters.The list of frame parameters can also use the phony frame parameterssame-frame and same-window. If the specified frameparameters include (same-window . value) and valueis non-nil, that means to display the buffer in the currentselected window. Otherwise, if they include (same-frame .value) and value is non-nil, that means to displaythe buffer in a new window in the currently selected frame. special-display-regexps — User Option: special-display-regexps A list of regular expressions that specify buffers that should bedisplayed specially. If the buffer's name matches any of the regularexpressions in this list, display-buffer handles the bufferspecially.By default, special display means to give the buffer a dedicated frame.If an element is a list, instead of a string, then the car of thelist is the regular expression, and the rest of the list says how tocreate the frame. See above, under special-display-buffer-names. special-display-p — Function: special-display-p buffer-name This function returns non-nil if displaying a buffernamed buffer-name with display-buffer wouldcreate a special frame. The value is t if it woulduse the default frame parameters, or else the specified listof frame parameters. special-display-function — Variable: special-display-function This variable holds the function to call to display a buffer specially.It receives the buffer as an argument, and should return the window inwhich it is displayed.The default value of this variable isspecial-display-popup-frame. special-display-popup-frame — Function: special-display-popup-frame buffer &optional args This function makes buffer visible in a frame of its own. Ifbuffer is already displayed in a window in some frame, it makesthe frame visible and raises it, to use that window. Otherwise, itcreates a frame that will be dedicated to buffer. Thisfunction returns the window it used.If args is an alist, it specifies frame parameters for the newframe.If args is a list whose car is a symbol, then (carargs) is called as a function to actually create and set up theframe; it is called with buffer as first argument, and (cdrargs) as additional arguments.This function always uses an existing window displaying buffer,whether or not it is in a frame of its own; but if you set up the abovevariables in your init file, before buffer was created, thenpresumably the window was previously made by this function. special-display-frame-alist — User Option: special-display-frame-alist This variable holds frame parameters forspecial-display-popup-frame to use when it creates a frame. same-window-buffer-names — User Option: same-window-buffer-names A list of buffer names for buffers that should be displayed in theselected window. If the buffer's name is in this list,display-buffer handles the buffer by switching to it in theselected window. same-window-regexps — User Option: same-window-regexps A list of regular expressions that specify buffers that should bedisplayed in the selected window. If the buffer's name matches any ofthe regular expressions in this list, display-buffer handles thebuffer by switching to it in the selected window. same-window-p — Function: same-window-p buffer-name This function returns t if displaying a buffernamed buffer-name with display-buffer wouldput it in the selected window. display-buffer-function — Variable: display-buffer-function This variable is the most flexible way to customize the behavior ofdisplay-buffer. If it is non-nil, it should be a functionthat display-buffer calls to do the work. The function shouldaccept two arguments, the first two arguments that display-bufferreceived. It should choose or create a window, display the specifiedbuffer in it, and then return the window.This hook takes precedence over all the other options and hooksdescribed above. dedicated window A window can be marked as “dedicated” to its buffer. Then display-buffer will not try to use that window to display any other buffer. window-dedicated-p — Function: window-dedicated-p window This function returns non-nil if window is marked asdedicated; otherwise nil. set-window-dedicated-p — Function: set-window-dedicated-p window flag This function marks window as dedicated if flag isnon-nil, and nondedicated otherwise. Windows and Point window position window point position in window point in window Each window has its own value of point, independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer. The window point is established when a window is first created; it isinitialized from the buffer's point, or from the window point of anotherwindow opened on the buffer if such a window exists. Selecting a window sets the value of point in its buffer from thewindow's value of point. Conversely, deselecting a window sets thewindow's value of point from that of the buffer. Thus, when you switchbetween windows that display a given buffer, the point value for theselected window is in effect in the buffer, while the point values forthe other windows are stored in those windows. As long as the selected window displays the current buffer, the window'spoint and the buffer's point always move together; they remain equal. See , for more details on buffer positions. cursor As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer. window-point — Function: window-point &optional window This function returns the current position of point in window.For a nonselected window, this is the value point would have (in thatwindow's buffer) if that window were selected. If window isnil, the selected window is used.When window is the selected window and its buffer is also thecurrent buffer, the value returned is the same as point in that buffer.Strictly speaking, it would be more correct to return the“top-level” value of point, outside of any save-excursionforms. But that value is hard to find. set-window-point — Function: set-window-point window position This function positions point in window at positionposition in window's buffer. It returns position.If window is selected, and its buffer is current,this simply does goto-char. The Window Start Position window start position Each window contains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line. window-start — Function: window-start &optional window window top lineThis function returns the display-start position of windowwindow. If window is nil, the selected window isused. For example, (window-start) => 7058 When you create a window, or display a different buffer in it, thedisplay-start position is set to a display-start position recently usedfor the same buffer, or 1 if the buffer doesn't have any.Redisplay updates the window-start position (if you have not specifiedit explicitly since the previous redisplay)—for example, to make surepoint appears on the screen. Nothing except redisplay automaticallychanges the window-start position; if you move point, do not expect thewindow-start position to change in response until after the nextredisplay.For a realistic example of using window-start, see thedescription of count-lines. See . window-end — Function: window-end &optional window update This function returns the position of the end of the display in windowwindow. If window is nil, the selected window isused.Simply changing the buffer text or moving point does not update thevalue that window-end returns. The value is updated only whenEmacs redisplays and redisplay completes without being preempted.If the last redisplay of window was preempted, and did not finish,Emacs does not know the position of the end of display in that window.In that case, this function returns nil.If update is non-nil, window-end always returns anup-to-date value for where the window ends, based on the currentwindow-start value. If the saved value is valid,window-end returns that; otherwise it computes the correctvalue by scanning the buffer text.Even if update is non-nil, window-end does notattempt to scroll the display if point has moved off the screen, theway real redisplay would do. It does not alter thewindow-start value. In effect, it reports where the displayedtext will end if scrolling is not required. set-window-start — Function: set-window-start window position &optional noforce This function sets the display-start position of window toposition in window's buffer. It returns position.The display routines insist that the position of point be visible when abuffer is displayed. Normally, they change the display-start position(that is, scroll the window) whenever necessary to make point visible.However, if you specify the start position with this function usingnil for noforce, it means you want display to start atposition even if that would put the location of point off thescreen. If this does place point off screen, the display routines movepoint to the left margin on the middle line in the window.For example, if point is 1 and you set the start of the window to2, then point would be “above” the top of the window. The displayroutines will automatically move point if it is still 1 when redisplayoccurs. Here is an example: ;; Here is what ‘foo’ looks like before executing ;; the set-window-start expression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) => 2 ;; Here is what ‘foo’ looks like after executing ;; the set-window-start expression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ---------- If noforce is non-nil, and position would place pointoff screen at the next redisplay, then redisplay computes a new window-startposition that works well with point, and thus position is not used. pos-visible-in-window-p — Function: pos-visible-in-window-p &optional position window partially This function returns non-nil if position is within therange of text currently visible on the screen in window. Itreturns nil if position is scrolled vertically out ofview. Locations that are partially obscured are not consideredvisible unless partially is non-nil. The argumentposition defaults to the current position of point inwindow; window, to the selected window.If position is t, that means to check the last visibleposition in window.The pos-visible-in-window-p function considers only verticalscrolling. If position is out of view only because windowhas been scrolled horizontally, pos-visible-in-window-p returnsnon-nil anyway. See .If position is visible, pos-visible-in-window-p returnst if partially is nil; if partially isnon-nil, and the character after position is fullyvisible, it returns a list of the form (x y), wherex and y are the pixel coordinates relative to the top leftcorner of the window; otherwise it returns an extended list of theform (x y rtop rbot rowhvpos), where the rtop and rbot specify the numberof off-window pixels at the top and bottom of the row atposition, rowh specifies the visible height of that row,and vpos specifies the vertical position (zero-based row number)of that row.Here is an example: ;; If point is off the screen now, recenter it now. (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0)) window-line-height — Function: window-line-height &optional line window This function returns information about text line line in window.If line is one of header-line or mode-line,window-line-height returns information about the correspondingline of the window. Otherwise, line is a text line numberstarting from 0. A negative number counts from the end of the window.The argument line defaults to the current line in window;window, to the selected window.If the display is not up to date, window-line-height returnsnil. In that case, pos-visible-in-window-p may be usedto obtain related information.If there is no line corresponding to the specified line,window-line-height returns nil. Otherwise, it returnsa list (height vpos ypos offbot),where height is the height in pixels of the visible part of theline, vpos and ypos are the vertical position in lines andpixels of the line relative to the top of the first text line, andoffbot is the number of off-window pixels at the bottom of thetext line. If there are off-window pixels at the top of the (first)text line, ypos is negative. Textual Scrolling textual scrolling scrolling textually Textual scrolling means moving the text up or down through a window. It works by changing the value of the window's display-start location. It may also change the value of window-point to keep point on the screen. Textual scrolling was formerly called “vertical scrolling,” but we changed its name to distinguish it from the new vertical fractional scrolling feature (see ). In the commands scroll-up and scroll-down, the directions “up” and “down” refer to the motion of the text in the buffer at which you are looking through the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at text in the middle of a buffer and repeatedly call scroll-down, you will eventually see the beginning of the buffer. Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then “down” commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view. The textual scrolling functions (aside from scroll-other-window) have unpredictable results if the current buffer is different from the buffer that is displayed in the selected window. See . If the window contains a row which is taller than the height of the window (for example in the presence of a large image), the scroll functions will adjust the window vscroll to scroll the partially visible row. To disable this feature, Lisp code may bind the variable `auto-window-vscroll' to nil (see ). scroll-up — Command: scroll-up &optional count This function scrolls the text in the selected window upwardcount lines. If count is negative, scrolling is actuallydownward.If count is nil (or omitted), then the length of scrollis next-screen-context-lines lines less than the usable height ofthe window (not counting its mode line).scroll-up returns nil, unless it gets an errorbecause it can't scroll any further. scroll-down — Command: scroll-down &optional count This function scrolls the text in the selected window downwardcount lines. If count is negative, scrolling is actuallyupward.If count is omitted or nil, then the length of the scrollis next-screen-context-lines lines less than the usable height ofthe window (not counting its mode line).scroll-down returns nil, unless it gets an error becauseit can't scroll any further. scroll-other-window — Command: scroll-other-window &optional count This function scrolls the text in another window upward countlines. Negative values of count, or nil, are handledas in scroll-up.You can specify which buffer to scroll by setting the variableother-window-scroll-buffer to a buffer. If that buffer isn'talready displayed, scroll-other-window displays it in somewindow.When the selected window is the minibuffer, the next window is normallythe one at the top left corner. You can specify a different window toscroll, when the minibuffer is selected, by setting the variableminibuffer-scroll-window. This variable has no effect when anyother window is selected. When it is non-nil and theminibuffer is selected, it takes precedence overother-window-scroll-buffer. See .When the minibuffer is active, it is the next window if the selectedwindow is the one at the bottom right corner. In this case,scroll-other-window attempts to scroll the minibuffer. If theminibuffer contains just one line, it has nowhere to scroll to, so theline reappears after the echo area momentarily displays the message‘Beginning of buffer’. other-window-scroll-buffer — Variable: other-window-scroll-buffer If this variable is non-nil, it tells scroll-other-windowwhich buffer to scroll. scroll-margin — User Option: scroll-margin This option specifies the size of the scroll margin—a minimum numberof lines between point and the top or bottom of a window. Wheneverpoint gets within this many lines of the top or bottom of the window,redisplay scrolls the text automatically (if possible) to move pointout of the margin, closer to the center of the window. scroll-conservatively — User Option: scroll-conservatively This variable controls how scrolling is done automatically when pointmoves off the screen (or into the scroll margin). If the value is apositive integer n, then redisplay scrolls the text up ton lines in either direction, if that will bring point back intoproper view. This action is called conservative scrolling.Otherwise, scrolling happens in the usual way, under the control ofother variables such as scroll-up-aggressively andscroll-down-aggressively.The default value is zero, which means that conservative scrollingnever happens. scroll-down-aggressively — User Option: scroll-down-aggressively The value of this variable should be either nil or a fractionf between 0 and 1. If it is a fraction, that specifies where onthe screen to put point when scrolling down. More precisely, when awindow scrolls down because point is above the window start, the newstart position is chosen to put point f part of the windowheight from the top. The larger f, the more aggressive thescrolling.A value of nil is equivalent to .5, since its effect is to centerpoint. This variable automatically becomes buffer-local when set in anyfashion. scroll-up-aggressively — User Option: scroll-up-aggressively Likewise, for scrolling up. The value, f, specifies how farpoint should be placed from the bottom of the window; thus, as withscroll-up-aggressively, a larger value scrolls more aggressively. scroll-step — User Option: scroll-step This variable is an older variant of scroll-conservatively. Thedifference is that it if its value is n, that permits scrollingonly by precisely n lines, not a smaller number. This featuredoes not work with scroll-margin. The default value is zero. scroll-preserve-screen-position — User Option: scroll-preserve-screen-position If this option is t, scrolling which would move the currentpoint position out of the window chooses the new position of pointso that the vertical position of the cursor is unchanged, if possible.If it is non-nil and not t, then the scrolling functionsalways preserve the vertical position of point, if possible. next-screen-context-lines — User Option: next-screen-context-lines The value of this variable is the number of lines of continuity toretain when scrolling by full screens. For example, scroll-upwith an argument of nil scrolls so that this many lines at thebottom of the window appear instead at the top. The default value is2. recenter — Command: recenter &optional count centering pointThis function scrolls the text in the selected window so that point isdisplayed at a specified vertical position within the window. It doesnot “move point” with respect to the text.If count is a nonnegative number, that puts the line containingpoint count lines down from the top of the window. Ifcount is a negative number, then it counts upward from thebottom of the window, so that −1 stands for the last usableline in the window. If count is a non-nil list, then itstands for the line in the middle of the window.If count is nil, recenter puts the line containingpoint in the middle of the window, then clears and redisplays the entireselected frame.When recenter is called interactively, count is the rawprefix argument. Thus, typing C-u as the prefix sets thecount to a non-nil list, while typing C-u 4 setscount to 4, which positions the current line four lines from thetop.With an argument of zero, recenter positions the current line atthe top of the window. This action is so handy that some people make aseparate key binding to do this. For example, (defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window) Vertical Fractional Scrolling vertical fractional scrolling Vertical fractional scrolling means shifting the image in the window up or down by a specified multiple or fraction of a line. Each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero. The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height. What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image. window-vscroll — Function: window-vscroll &optional window pixels-p This function returns the current vertical scroll position ofwindow. If window is nil, the selected window isused. If pixels-p is non-nil, the return value ismeasured in pixels, rather than in units of the normal line height. (window-vscroll) => 0 set-window-vscroll — Function: set-window-vscroll window lines &optional pixels-p This function sets window's vertical scroll position tolines. The argument lines should be zero or positive; ifnot, it is taken as zero.If window is nil, the selected window is used.The actual vertical scroll position must always correspondto an integral number of pixels, so the value you specifyis rounded accordingly.The return value is the result of this rounding. (set-window-vscroll (selected-window) 1.2) => 1.13 If pixels-p is non-nil, lines specifies a number ofpixels. In this case, the return value is lines. auto-window-vscroll — Variable: auto-window-vscroll If this variable is non-nil, the line-move, scroll-up, andscroll-down functions will automatically modify the window vscroll toscroll through display rows that are taller that the height of thewindow, for example in the presence of large images. Horizontal Scrolling horizontal scrolling Horizontal scrolling means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a horizontal scroll position, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero. The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line. Because we read from side to side in the “inner loop,” and from top to bottom in the “outer loop,” the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of each line to go off screen. Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge. auto-hscroll-mode If auto-hscroll-mode is set, redisplay automatically alters the horizontal scrolling of a window as necessary to ensure that point is always visible. However, you can still set the horizontal scrolling value explicitly. The value you specify serves as a lower bound for automatic scrolling, i.e. automatic scrolling will not scroll a window to a column less than the specified one. scroll-left — Command: scroll-left &optional count set-minimum This function scrolls the selected window count columns to theleft (or to the right if count is negative). The defaultfor count is the window width, minus 2.The return value is the total amount of leftward horizontal scrolling ineffect after the change—just like the value returned bywindow-hscroll (below).Once you scroll a window as far right as it can go, back to its normalposition where the total leftward scrolling is zero, attempts to scrollany farther right have no effect.If set-minimum is non-nil, the new scroll amount becomesthe lower bound for automatic scrolling; that is, automatic scrollingwill not scroll a window to a column less than the value returned bythis function. Interactive calls pass non-nil forset-minimum. scroll-right — Command: scroll-right &optional count set-minimum This function scrolls the selected window count columns to theright (or to the left if count is negative). The defaultfor count is the window width, minus 2. Aside from the directionof scrolling, this works just like scroll-left. window-hscroll — Function: window-hscroll &optional window This function returns the total leftward horizontal scrolling ofwindow—the number of columns by which the text in windowis scrolled left past the left margin.The value is never negative. It is zero when no horizontal scrollinghas been done in window (which is usually the case).If window is nil, the selected window is used. (window-hscroll) => 0 (scroll-left 5) => 5 (window-hscroll) => 5 set-window-hscroll — Function: set-window-hscroll window columns This function sets horizontal scrolling of window. The value ofcolumns specifies the amount of scrolling, in terms of columnsfrom the left margin. The argument columns should be zero orpositive; if not, it is taken as zero. Fractional values ofcolumns are not supported at present.Note that set-window-hscroll may appear not to work if you testit by evaluating a call with M-: in a simple way. What happensis that the function sets the horizontal scroll value and returns, butthen redisplay adjusts the horizontal scrolling to make point visible,and this overrides what the function did. You can observe thefunction's effect if you call it while point is sufficiently far fromthe left margin that it will remain visible.The value returned is columns. (set-window-hscroll (selected-window) 10) => 10 Here is how you can determine whether a given position position is off the screen due to horizontal scrolling: (defun hscroll-on-screen (window position) (save-excursion (goto-char position) (and (>= (- (current-column) (window-hscroll window)) 0) (< (- (current-column) (window-hscroll window)) (window-width window))))) The Size of a Window window size size of window An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of ‘|’ characters that separates side-by-side windows. The following three functions return size information about a window: window-height — Function: window-height &optional window This function returns the number of lines in window, includingits mode line and header line, if any. If window fills itsentire frame except for the echo area, this is typically one less thanthe value of frame-height on that frame.If window is nil, the function uses the selected window. (window-height) => 23 (split-window-vertically) => #<window 4 on windows.texi> (window-height) => 11 window-body-height — Function: window-body-height &optional window Like window-height but the value does not include themode line (if any) or the header line (if any). window-width — Function: window-width &optional window This function returns the number of columns in window. Ifwindow fills its entire frame, this is the same as the value offrame-width on that frame. The width does not include thewindow's scroll bar or the column of ‘|’ characters that separatesside-by-side windows.If window is nil, the function uses the selected window. (window-width) => 80 window-edges — Function: window-edges &optional window This function returns a list of the edge coordinates of window.If window is nil, the selected window is used.The order of the list is (left top rightbottom), all elements relative to 0, 0 at the top left corner ofthe frame. The element right of the value is one more than therightmost column used by window, and bottom is one more thanthe bottommost row used by window and its mode-line.The edges include the space used by the window's scroll bar, displaymargins, fringes, header line, and mode line, if it has them. Also,if the window has a neighbor on the right, its right edge valueincludes the width of the separator line between the window and thatneighbor. Since the width of the window does not include thisseparator, the width does not usually equal the difference between theright and left edges. window-inside-edges — Function: window-inside-edges &optional window This is similar to window-edges, but the edge valuesit returns include only the text area of the window. Theydo not include the header line, mode line, scroll bar orvertical separator, fringes, or display margins. Here are the results obtained on a typical 24-line terminal with just one window, with menu bar enabled: (window-edges (selected-window)) => (0 1 80 23) (window-inside-edges (selected-window)) => (0 1 80 22) The bottom edge is at line 23 because the last line is the echo area. The bottom inside edge is at line 22, which is the window's mode line. If window is at the upper left corner of its frame, and there is no menu bar, then bottom returned by window-edges is the same as the value of (window-height), right is almost the same as the value of (window-width), and top and left are zero. For example, the edges of the following window are ‘0 0 8 5’. Assuming that the frame has more than 8 columns, the last column of the window (column 7) holds a border rather than text. The last row (row 4) holds the mode line, shown here with ‘xxxxxxxxx’. 0 _______ 0 | | | | | | | | xxxxxxxxx 4 7 In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are ‘0 0 4 3’ and the edges of the right window are ‘4 0 7 3’. The inside edges of the left window are ‘0 0 3 2’, and the inside edges of the right window are ‘4 0 7 2’, ___ ___ | | | | | | xxxxxxxxx 0 34 7 window-pixel-edges — Function: window-pixel-edges &optional window This function is like window-edges except that, on a graphicaldisplay, the edge values are measured in pixels instead of incharacter lines and columns. window-inside-pixel-edges — Function: window-inside-pixel-edges &optional window This function is like window-inside-edges except that, on agraphical display, the edge values are measured in pixels instead ofin character lines and columns. Changing the Size of a Window window resizing resize window changing window size window size, changing The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing one window affects other windows. enlarge-window — Command: enlarge-window size &optional horizontal This function makes the selected window size lines taller,stealing lines from neighboring windows. It takes the lines from onewindow at a time until that window is used up, then takes from another.If a window from which lines are stolen shrinks belowwindow-min-height lines, that window disappears.If horizontal is non-nil, this function makeswindow wider by size columns, stealing columns instead oflines. If a window from which columns are stolen shrinks belowwindow-min-width columns, that window disappears.If the requested size would exceed that of the window's frame, then thefunction makes the window occupy the entire height (or width) of theframe.If there are various other windows from which lines or columns can bestolen, and some of them specify fixed size (usingwindow-size-fixed, see below), they are left untouched whileother windows are “robbed.” If it would be necessary to alter thesize of a fixed-size window, enlarge-window gets an errorinstead.If size is negative, this function shrinks the window by−size lines or columns. If that makes the window smallerthan the minimum size (window-min-height andwindow-min-width), enlarge-window deletes the window.enlarge-window returns nil. enlarge-window-horizontally — Command: enlarge-window-horizontally columns This function makes the selected window columns wider.It could be defined as follows: (defun enlarge-window-horizontally (columns) (interactive "p") (enlarge-window columns t)) shrink-window — Command: shrink-window size &optional horizontal This function is like enlarge-window but negates the argumentsize, making the selected window smaller by giving lines (orcolumns) to the other windows. If the window shrinks belowwindow-min-height or window-min-width, then it disappears.If size is negative, the window is enlarged by −sizelines or columns. shrink-window-horizontally — Command: shrink-window-horizontally columns This function makes the selected window columns narrower.It could be defined as follows: (defun shrink-window-horizontally (columns) (interactive "p") (shrink-window columns t)) adjust-window-trailing-edge — Function: adjust-window-trailing-edge window delta horizontal This function makes the selected window delta lines taller ordelta columns wider, by moving the bottom or right edge. Thisfunction does not delete other windows; if it cannot make therequested size adjustment, it signals an error. On success, thisfunction returns nil. fit-window-to-buffer — Function: fit-window-to-buffer &optional window max-height min-height This function makes window the right height to display itscontents exactly. If window is omitted or nil, it usesthe selected window.The argument max-height specifies the maximum height the windowis allowed to be; nil means use the frame height. The argumentmin-height specifies the minimum height for the window;nil means use window-min-height. All these heightvalues include the mode-line and/or header-line. shrink-window-if-larger-than-buffer — Command: shrink-window-if-larger-than-buffer &optional window This command shrinks window vertically to be as small aspossible while still showing the full contents of its buffer—but notless than window-min-height lines. If window is notgiven, it defaults to the selected window.However, the command does nothing if the window is already too small todisplay the whole text of the buffer, or if part of the contents arecurrently scrolled off screen, or if the window is not the full width ofits frame, or if the window is the only window in its frame.This command returns non-nil if it actually shrank the windowand nil otherwise. window-size-fixed — Variable: window-size-fixed If this variable is non-nil, in any given buffer,then the size of any window displaying the buffer remains fixedunless you explicitly change it or Emacs has no other choice.If the value is height, then only the window's height is fixed;if the value is width, then only the window's width is fixed.Any other non-nil value fixes both the width and the height.This variable automatically becomes buffer-local when set.Explicit size-change functions such as enlarge-windowget an error if they would have to change a window size which is fixed.Therefore, when you want to change the size of such a window,you should bind window-size-fixed to nil, like this: (let ((window-size-fixed nil)) (enlarge-window 10)) Note that changing the frame size will change the size of afixed-size window, if there is no other alternative. minimum window size The following two variables constrain the window-structure-changing functions to a minimum height and width. window-min-height — User Option: window-min-height The value of this variable determines how short a window may becomebefore it is automatically deleted. Making a window smaller thanwindow-min-height automatically deletes it, and no window maybe created shorter than this. The default value is 4.The absolute minimum window height is one; actions that change windowsizes reset this variable to one if it is less than one. window-min-width — User Option: window-min-width The value of this variable determines how narrow a window may becomebefore it is automatically deleted. Making a window smaller thanwindow-min-width automatically deletes it, and no window may becreated narrower than this. The default value is 10.The absolute minimum window width is two; actions that change windowsizes reset this variable to two if it is less than two. Coordinates and Windows This section describes how to relate screen coordinates to windows. window-at — Function: window-at x y &optional frame This function returns the window containing the specified cursorposition in the frame frame. The coordinates x and yare measured in characters and count from the top left corner of theframe. If they are out of range, window-at returns nil.If you omit frame, the selected frame is used. coordinates-in-window-p — Function: coordinates-in-window-p coordinates window This function checks whether a particular frame position falls withinthe window window.The argument coordinates is a cons cell of the form (x. y). The coordinates x and y are measured incharacters, and count from the top left corner of the screen or frame.The value returned by coordinates-in-window-p is non-nilif the coordinates are inside window. The value also indicateswhat part of the window the position is in, as follows: (relx . rely) The coordinates are inside window. The numbers relx andrely are the equivalent window-relative coordinates for thespecified position, counting from 0 at the top left corner of thewindow. mode-line The coordinates are in the mode line of window. header-line The coordinates are in the header line of window. vertical-line The coordinates are in the vertical line between window and itsneighbor to the right. This value occurs only if the window doesn'thave a scroll bar; positions in a scroll bar are considered outside thewindow for these purposes. left-fringeright-fringe The coordinates are in the left or right fringe of the window. left-marginright-margin The coordinates are in the left or right margin of the window. nil The coordinates are not in any part of window. The function coordinates-in-window-p does not require a frame asargument because it always uses the frame that window is on. The Window Tree window tree A window tree specifies the layout, size, and relationship between all windows in one frame. window-tree — Function: window-tree &optional frame This function returns the window tree for frame frame.If frame is omitted, the selected frame is used.The return value is a list of the form (root mini),where root represents the window tree of the frame'sroot window, and mini is the frame's minibuffer window.If the root window is not split, root is the root window itself.Otherwise, root is a list (dir edges w1w2 ...) where dir is nil for a horizontal split,and t for a vertical split, edges gives the combined size andposition of the subwindows in the split, and the rest of the elementsare the subwindows in the split. Each of the subwindows may again bea window or a list representing a window split, and so on. Theedges element is a list (left top right bottom)similar to the value returned by window-edges. Window Configurations window configurations saving window information A window configuration records the entire layout of one frame—all windows, their sizes, which buffers they contain, what part of each buffer is displayed, and the values of point and the mark; also their fringes, margins, and scroll bar settings. It also includes the values of window-min-height, window-min-width and minibuffer-scroll-window. An exception is made for point in the selected window for the current buffer; its value is not saved in the window configuration. You can bring back an entire previous layout by restoring a window configuration previously saved. If you want to record all frames instead of just one, use a frame configuration instead of a window configuration. See . current-window-configuration — Function: current-window-configuration &optional frame This function returns a new object representing frame's currentwindow configuration. If frame is omitted, the selected frameis used. set-window-configuration — Function: set-window-configuration configuration This function restores the configuration of windows and buffers asspecified by configuration, for the frame that configurationwas created for.The argument configuration must be a value that was previouslyreturned by current-window-configuration. This configuration isrestored in the frame from which configuration was made, whetherthat frame is selected or not. This always counts as a window sizechange and triggers execution of the window-size-change-functions(see ), because set-window-configuration doesn'tknow how to tell whether the new configuration actually differs from theold one.If the frame which configuration was saved from is dead, all thisfunction does is restore the three variables window-min-height,window-min-width and minibuffer-scroll-window. In thiscase, the function returns nil. Otherwise, it returns t.Here is a way of using this function to get the same effectas save-window-excursion: (let ((config (current-window-configuration))) (unwind-protect (progn (split-window-vertically nil) …) (set-window-configuration config))) save-window-excursion — Special Form: save-window-excursion forms … This special form records the window configuration, executes formsin sequence, then restores the earlier window configuration. The windowconfiguration includes, for each window, the value of point and theportion of the buffer that is visible. It also includes the choice ofselected window. However, it does not include the value of point inthe current buffer; use save-excursion also, if you wish topreserve that.Don't use this construct when save-selected-window is sufficient.Exit from save-window-excursion always triggers execution of thewindow-size-change-functions. (It doesn't know how to tellwhether the restored configuration actually differs from the one ineffect at the end of the forms.)The return value is the value of the final form in forms.For example: (split-window) => #<window 25 on control.texi> (setq w (selected-window)) => #<window 19 on control.texi> (save-window-excursion (delete-other-windows w) (switch-to-buffer "foo") 'do-something) => do-something ;; The screen is now split again. window-configuration-p — Function: window-configuration-p object This function returns t if object is a window configuration. compare-window-configurations — Function: compare-window-configurations config1 config2 This function compares two window configurations as regards thestructure of windows, but ignores the values of point and mark and thesaved scrolling positions—it can return t even if thoseaspects differ.The function equal can also compare two window configurations; itregards configurations as unequal if they differ in any respect, even asaved point or mark. window-configuration-frame — Function: window-configuration-frame config This function returns the frame for which the window configurationconfig was made. Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file winner.el for some more operations on windows configurations. Hooks for Window Scrolling and Changes hooks for window operations This section describes how a Lisp program can take action whenever a window displays a different part of its buffer or a different buffer. There are three actions that can change this: scrolling the window, switching buffers in the window, and changing the size of the window. The first two actions run window-scroll-functions; the last runs window-size-change-functions. window-scroll-functions — Variable: window-scroll-functions This variable holds a list of functions that Emacs should call beforeredisplaying a window with scrolling. It is not a normal hook, becauseeach function is called with two arguments: the window, and its newdisplay-start position.Displaying a different buffer in the window also runs these functions.These functions must be careful in using window-end(see ); if you need an up-to-date value, you must usethe update argument to ensure you get it.Warning: don't use this feature to alter the way the windowis scrolled. It's not designed for that, and such use probably won'twork. window-size-change-functions — Variable: window-size-change-functions This variable holds a list of functions to be called if the size of anywindow changes for any reason. The functions are called just once perredisplay, and just once for each frame on which size changes haveoccurred.Each function receives the frame as its sole argument. There is nodirect way to find out which windows on that frame have changed size, orprecisely how. However, if a size-change function records, at eachcall, the existing windows and their sizes, it can also compare thepresent sizes and the previous sizes.Creating or deleting windows counts as a size change, and thereforecauses these functions to be called. Changing the frame size alsocounts, because it changes the sizes of the existing windows.It is not a good idea to use save-window-excursion (see ) in these functions, because that always counts as asize change, and it would cause these functions to be called over andover. In most cases, save-selected-window (see ) is what you need here. redisplay-end-trigger-functions — Variable: redisplay-end-trigger-functions This abnormal hook is run whenever redisplay in a window uses text thatextends past a specified end trigger position. You set the end triggerposition with the function set-window-redisplay-end-trigger. Thefunctions are called with two arguments: the window, and the end triggerposition. Storing nil for the end trigger position turns off thefeature, and the trigger value is automatically reset to nil justafter the hook is run. set-window-redisplay-end-trigger — Function: set-window-redisplay-end-trigger window position This function sets window's end trigger position atposition. window-redisplay-end-trigger — Function: window-redisplay-end-trigger &optional window This function returns window's current end trigger position.If window is nil or omitted, it uses the selected window. window-configuration-change-hook — Variable: window-configuration-change-hook A normal hook that is run every time you change the window configurationof an existing frame. This includes splitting or deleting windows,changing the sizes of windows, or displaying a different buffer in awindow. The frame whose window configuration has changed is theselected frame when this hook runs. <setfilename>../info/frames</setfilename> Frames frame In Emacs editing, A frame is a screen object that contains one or more Emacs windows. It's the kind of object that is called a “window” in the terminology of graphical environments; but we can't call it a “window” here, because Emacs uses that word in a different way. A frame initially contains a single main window and/or a minibuffer window; you can subdivide the main window vertically or horizontally into smaller windows. In Emacs Lisp, a frame object is a Lisp object that represents a frame on the screen. terminal frame When Emacs runs on a text-only terminal, it starts with one terminal frame. If you create additional ones, Emacs displays one and only one at any given time—on the terminal screen, of course. window frame When Emacs communicates directly with a supported window system, such as X, it does not have a terminal frame; instead, it starts with a single window frame, but you can create more, and Emacs can display several such frames at once as is usual for window systems. framep — Function: framep object This predicate returns a non-nil value if object is aframe, and nil otherwise. For a frame, the value indicates whichkind of display the frame uses: x The frame is displayed in an X window. t A terminal frame on a character display. mac The frame is displayed on a Macintosh. w32 The frame is displayed on MS-Windows 9X/NT. pc The frame is displayed on an MS-DOS terminal. See , for information about the related topic of controlling Emacs redisplay. Creating Frames To create a new frame, call the function make-frame. make-frame — Function: make-frame &optional alist This function creates and returns a new frame, displaying the currentbuffer. If you are using a supported window system, it makes a windowframe; otherwise, it makes a terminal frame.The argument is an alist specifying frame parameters. Any parametersnot mentioned in alist default according to the value of thevariable default-frame-alist; parameters not specified even theredefault from the standard X resources or whatever is used instead onyour system.The set of possible parameters depends in principle on what kind ofwindow system Emacs uses to display its frames. See , for documentation of individual parameters you can specify.This function itself does not make the new frame the selected frame.See . The previously selected frame remains selected.However, the window system may select the new frame for its own reasons,for instance if the frame appears under the mouse pointer and yoursetup is for focus to follow the pointer. before-make-frame-hook — Variable: before-make-frame-hook A normal hook run by make-frame before it actually creates theframe. after-make-frame-functions — Variable: after-make-frame-functions An abnormal hook run by make-frame after it creates the frame.Each function in after-make-frame-functions receives one argument, theframe just created. Multiple Displays multiple X displays displays, multiple A single Emacs can talk to more than one X display. Initially, Emacs uses just one display—the one chosen with the DISPLAY environment variable or with the ‘--display’ option (see See section ``Initial Options'' in The GNU Emacs Manual). To connect to another display, use the command make-frame-on-display or specify the display frame parameter when you create the frame. Emacs treats each X server as a separate terminal, giving each one its own selected frame and its own minibuffer windows. However, only one of those frames is “the selected frame” at any given moment, see . A few Lisp variables are terminal-local; that is, they have a separate binding for each terminal. The binding in effect at any time is the one for the terminal that the currently selected frame belongs to. These variables include default-minibuffer-frame, defining-kbd-macro, last-kbd-macro, and system-key-alist. They are always terminal-local, and can never be buffer-local (see ) or frame-local. A single X server can handle more than one screen. A display name ‘host:server.screen’ has three parts; the last part specifies the screen number for a given server. When you use two screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard, and it treats them as a single terminal. Note that some graphical terminals can output to more than a one monitor (or other output device) at the same time. On these “multi-monitor” setups, a single display value controls the output to all the physical monitors. In this situation, there is currently no platform-independent way for Emacs to distinguish between the different physical monitors. make-frame-on-display — Command: make-frame-on-display display &optional parameters This creates and returns a new frame on display display, takingthe other frame parameters from parameters. Aside from thedisplay argument, it is like make-frame (see ). x-display-list — Function: x-display-list This returns a list that indicates which X displays Emacs has aconnection to. The elements of the list are strings, and each one isa display name. x-open-connection — Function: x-open-connection display &optional xrm-string must-succeed This function opens a connection to the X display display. Itdoes not create a frame on that display, but it permits you to checkthat communication can be established with that display.The optional argument xrm-string, if not nil, is astring of resource names and values, in the same format used in the.Xresources file. The values you specify override the resourcevalues recorded in the X server itself; they apply to all Emacs framescreated on this display. Here's an example of what this string mightlook like: "*BorderWidth: 3\n*InternalBorder: 2\n" See See section ``X Resources'' in The GNU Emacs Manual.If must-succeed is non-nil, failure to open the connectionterminates Emacs. Otherwise, it is an ordinary Lisp error. x-close-connection — Function: x-close-connection display This function closes the connection to display display. Beforeyou can do this, you must first delete all the frames that were open onthat display (see ). Frame Parameters frame parameters A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses. Frame parameters exist mostly for the sake of window systems. A terminal frame has a few parameters, mostly for compatibility's sake; only the height, width, name, title, menu-bar-lines, buffer-list and buffer-predicate parameters do something special. If the terminal supports colors, the parameters foreground-color, background-color, background-mode and display-type are also meaningful. Access to Frame Parameters These functions let you read and change the parameter values of a frame. frame-parameter — Function: frame-parameter frame parameter This function returns the value of the parameter parameter (asymbol) of frame. If frame is nil, it returns theselected frame's parameter. If frame has no setting forparameter, this function returns nil. frame-parameters — Function: frame-parameters &optional frame The function frame-parameters returns an alist listing all theparameters of frame and their values. If frame isnil or omitted, this returns the selected frame's parameters modify-frame-parameters — Function: modify-frame-parameters frame alist This function alters the parameters of frame frame based on theelements of alist. Each element of alist has the form(parm . value), where parm is a symbol naming aparameter. If you don't mention a parameter in alist, its valuedoesn't change. If frame is nil, it defaults to the selectedframe. modify-all-frames-parameters — Function: modify-all-frames-parameters alist This function alters the frame parameters of all existing framesaccording to alist, then modifies default-frame-alist(and, if necessary, initial-frame-alist) to apply the sameparameter values to frames that will be created henceforth. Initial Frame Parameters You can specify the parameters for the initial startup frame by setting initial-frame-alist in your init file (see ). initial-frame-alist — Variable: initial-frame-alist This variable's value is an alist of parameter values used when creatingthe initial window frame. You can set this variable to specify theappearance of the initial frame without altering subsequent frames.Each element has the form: (parameter . value) Emacs creates the initial frame before it reads your initfile. After reading that file, Emacs checks initial-frame-alist,and applies the parameter settings in the altered value to the alreadycreated initial frame.If these settings affect the frame geometry and appearance, you'll seethe frame appear with the wrong ones and then change to the specifiedones. If that bothers you, you can specify the same geometry andappearance with X resources; those do take effect before the frame iscreated. See See section ``X Resources'' in The GNU Emacs Manual.X resource settings typically apply to all frames. If you want tospecify some X resources solely for the sake of the initial frame, andyou don't want them to apply to subsequent frames, here's how to achievethis. Specify parameters in default-frame-alist to override theX resources for subsequent frames; then, to prevent these from affectingthe initial frame, specify the same parameters ininitial-frame-alist with values that match the X resources. If these parameters specify a separate minibuffer-only frame with (minibuffer . nil), and you have not created one, Emacs creates one for you. minibuffer-frame-alist — Variable: minibuffer-frame-alist This variable's value is an alist of parameter values used when creatingan initial minibuffer-only frame—if such a frame is needed, accordingto the parameters for the main initial frame. default-frame-alist — Variable: default-frame-alist This is an alist specifying default values of frame parameters for allEmacs frames—the first frame, and subsequent frames. When using the XWindow System, you can get the same results by means of X resourcesin many cases.Setting this variable does not affect existing frames. See also special-display-frame-alist. See . If you use options that specify window appearance when you invoke Emacs, they take effect by adding elements to default-frame-alist. One exception is ‘-geometry’, which adds the specified position to initial-frame-alist instead. See See section ``Command Line Arguments for Emacs Invocation'' in The GNU Emacs Manual. Window Frame Parameters Just what parameters a frame has depends on what display mechanism it uses. This section describes the parameters that have special meanings on some or all kinds of terminals. Of these, name, title, height, width, buffer-list and buffer-predicate provide meaningful information in terminal frames, and tty-color-mode is meaningful only in terminal frames. Basic Parameters These frame parameters give the most basic information about the frame. title and name are meaningful on all terminals. display The display on which to open this frame. It should be a string of theform "host:dpy.screen", just like theDISPLAY environment variable. display-type This parameter describes the range of possible colors that can be usedin this frame. Its value is color, grayscale ormono. title If a frame has a non-nil title, it appears in the window system'sborder for the frame, and also in the mode line of windows in that frameif mode-line-frame-identification uses ‘%F’(see ). This is normally the case when Emacs is notusing a window system, and can only display one frame at a time.See . name The name of the frame. The frame name serves as a default for the frametitle, if the title parameter is unspecified or nil. Ifyou don't specify a name, Emacs sets the frame name automatically(see ).If you specify the frame name explicitly when you create the frame, thename is also used (instead of the name of the Emacs executable) whenlooking up X resources for the frame. Position Parameters Position parameters' values are normally measured in pixels, but on text-only terminals they count characters or lines instead. left The screen position of the left edge, in pixels, with respect to theleft edge of the screen. The value may be a positive number pos,or a list of the form (+ pos) which permits specifying anegative pos value.A negative number −pos, or a list of the form (-pos), actually specifies the position of the right edge of thewindow with respect to the right edge of the screen. A positive valueof pos counts toward the left. Reminder: if theparameter is a negative integer −pos, then pos ispositive.Some window managers ignore program-specified positions. If you want tobe sure the position you specify is not ignored, specify anon-nil value for the user-position parameter as well. top The screen position of the top edge, in pixels, with respect to thetop edge of the screen. It works just like left, except verticallyinstead of horizontally. icon-left The screen position of the left edge of the frame's icon, inpixels, counting from the left edge of the screen. This takes effect ifand when the frame is iconified.If you specify a value for this parameter, then you must also specifya value for icon-top and vice versa. The window manager mayignore these two parameters. icon-top The screen position of the top edge of the frame's icon, inpixels, counting from the top edge of the screen. This takes effect ifand when the frame is iconified. user-position When you create a frame and specify its screen position with theleft and top parameters, use this parameter to say whetherthe specified position was user-specified (explicitly requested in someway by a human user) or merely program-specified (chosen by a program).A non-nil value says the position was user-specified.Window managers generally heed user-specified positions, and some heedprogram-specified positions too. But many ignore program-specifiedpositions, placing the window in a default fashion or letting the userplace it with the mouse. Some window managers, including twm,let the user specify whether to obey program-specified positions orignore them.When you call make-frame, you should specify a non-nilvalue for this parameter if the values of the left and topparameters represent the user's stated preference; otherwise, usenil. Size Parameters Size parameters' values are normally measured in pixels, but on text-only terminals they count characters or lines instead. height The height of the frame contents, in characters. (To get the height inpixels, call frame-pixel-height; see .) width The width of the frame contents, in characters. (To get the height inpixels, call frame-pixel-width; see .) user-size This does for the size parameters height and width whatthe user-position parameter (see above) does for the positionparameters top and left. fullscreen Specify that width, height or both shall be set to the size of the screen.The value fullwidth specifies that width shall be the size of thescreen. The value fullheight specifies that height shall be thesize of the screen. The value fullboth specifies that both thewidth and the height shall be set to the size of the screen. Layout Parameters These frame parameters enable or disable various parts of the frame, or control their sizes. border-width The width in pixels of the frame's border. internal-border-width The distance in pixels between text (or fringe) and the frame's border. vertical-scroll-bars Whether the frame has scroll bars for vertical scrolling, and which sideof the frame they should be on. The possible values are left,right, and nil for no scroll bars. scroll-bar-width The width of vertical scroll bars, in pixels, or nil meaning touse the default width. left-fringeright-fringe The default width of the left and right fringes of windows in thisframe (see ). If either of these is zero, that effectivelyremoves the corresponding fringe. A value of nil stands forthe standard fringe width, which is the width needed to display thefringe bitmaps.The combined fringe widths must add up to an integral number ofcolumns, so the actual default fringe widths for the frame may belarger than the specified values. The extra width needed to reach anacceptable total is distributed evenly between the left and rightfringe. However, you can force one fringe or the other to a precisewidth by specifying that width as a negative integer. If both widths arenegative, only the left fringe gets the specified width. menu-bar-lines The number of lines to allocate at the top of the frame for a menubar. The default is 1. A value of nil means don't display amenu bar. See . (The X toolkit and GTK allow at most onemenu bar line; they treat larger values as 1.) tool-bar-lines The number of lines to use for the tool bar. A value of nilmeans don't display a tool bar. (GTK allows at most one tool bar line;it treats larger values as 1.) line-spacing Additional space to leave below each text line, in pixels (a positiveinteger). See , for more information. Buffer Parameters These frame parameters, meaningful on all kinds of terminals, deal with which buffers have been, or should, be displayed in the frame. minibuffer Whether this frame has its own minibuffer. The value t meansyes, nil means no, only means this frame is just aminibuffer. If the value is a minibuffer window (in some other frame),the new frame uses that minibuffer. buffer-predicate The buffer-predicate function for this frame. The functionother-buffer uses this predicate (from the selected frame) todecide which buffers it should consider, if the predicate is notnil. It calls the predicate with one argument, a buffer, once foreach buffer; if the predicate returns a non-nil value, itconsiders that buffer. buffer-list A list of buffers that have been selected in this frame,ordered most-recently-selected first. unsplittable If non-nil, this frame's window is never split automatically. Window Management Parameters window manager, and frame parameters These frame parameters, meaningful only on window system displays, interact with the window manager. visibility The state of visibility of the frame. There are three possibilities:nil for invisible, t for visible, and icon foriconified. See . auto-raise Whether selecting the frame raises it (non-nil means yes). auto-lower Whether deselecting the frame lowers it (non-nil means yes). icon-type The type of icon to use for this frame when it is iconified. If thevalue is a string, that specifies a file containing a bitmap to use.Any other non-nil value specifies the default bitmap icon (apicture of a gnu); nil specifies a text icon. icon-name The name to use in the icon for this frame, when and if the iconappears. If this is nil, the frame's title is used. window-id The number of the window-system window used by the frameto contain the actual Emacs windows. outer-window-id The number of the outermost window-system window used for the whole frame. wait-for-wm If non-nil, tell Xt to wait for the window manager to confirmgeometry changes. Some window managers, including versions of Fvwm2and KDE, fail to confirm, so Xt hangs. Set this to nil toprevent hanging with those window managers. Cursor Parameters This frame parameter controls the way the cursor looks. cursor-type How to display the cursor. Legitimate values are: box Display a filled box. (This is the default.) hollow Display a hollow box. nil Don't display a cursor. bar Display a vertical bar between characters. (bar . width) Display a vertical bar width pixels wide between characters. hbar Display a horizontal bar. (hbar . height) Display a horizontal bar height pixels high. cursor-type The buffer-local variable cursor-type overrides the value of the cursor-type frame parameter, but if it is t, that means to use the cursor specified for the frame. blink-cursor-alist — Variable: blink-cursor-alist This variable specifies how to blink the cursor. Each element has theform (on-state . off-state). Whenever the cursortype equals on-state (comparing using equal), thecorresponding off-state specifies what the cursor looks likewhen it blinks “off.” Both on-state and off-stateshould be suitable values for the cursor-type frame parameter.There are various defaults for how to blink each type of cursor, ifthe type is not mentioned as an on-state here. Changes in thisvariable do not take effect immediately, because the variable isexamined only when you specify the cursor-type parameter. Color Parameters These frame parameters control the use of colors. background-mode This parameter is either dark or light, accordingto whether the background color is a light one or a dark one. tty-color-mode standard colors for character terminalsThis parameter overrides the terminal's color support as given by thesystem's terminal capabilities database in that this parameter's valuespecifies the color mode to use in terminal frames. The value can beeither a symbol or a number. A number specifies the number of colorsto use (and, indirectly, what commands to issue to produce eachcolor). For example, (tty-color-mode . 8) specifies use of theANSI escape sequences for 8 standard text colors. A value of -1 turnsoff color support.If the parameter's value is a symbol, it specifies a number throughthe value of tty-color-mode-alist, and the associated number isused instead. screen-gamma gamma correctionIf this is a number, Emacs performs “gamma correction” which adjuststhe brightness of all colors. The value should be the screen gamma ofyour display, a floating point number.Usual PC monitors have a screen gamma of 2.2, so color values inEmacs, and in X windows generally, are calibrated to display properlyon a monitor with that gamma value. If you specify 2.2 forscreen-gamma, that means no correction is needed. Other valuesrequest correction, designed to make the corrected colors appear onyour screen the way they would have appeared without correction on anordinary monitor with a gamma value of 2.2.If your monitor displays colors too light, you should specify ascreen-gamma value smaller than 2.2. This requests correctionthat makes colors darker. A screen gamma value of 1.5 may give goodresults for LCD color displays. These frame parameters are semi-obsolete in that they are automatically equivalent to particular face attributes of particular faces. font The name of the font for displaying text in the frame. This is astring, either a valid font name for your system or the name of an Emacsfontset (see ). It is equivalent to the fontattribute of the default face. foreground-color The color to use for the image of a character. It is equivalent tothe :foreground attribute of the default face. background-color The color to use for the background of characters. It is equivalent tothe :background attribute of the default face. mouse-color The color for the mouse pointer. It is equivalent to the :backgroundattribute of the mouse face. cursor-color The color for the cursor that shows point. It is equivalent to the:background attribute of the cursor face. border-color The color for the border of the frame. It is equivalent to the:background attribute of the border face. scroll-bar-foreground If non-nil, the color for the foreground of scroll bars. It isequivalent to the :foreground attribute of thescroll-bar face. scroll-bar-background If non-nil, the color for the background of scroll bars. It isequivalent to the :background attribute of thescroll-bar face. Frame Size And Position size of frame screen size frame size resize frame You can read or change the size and position of a frame using the frame parameters left, top, height, and width. Whatever geometry parameters you don't specify are chosen by the window manager in its usual fashion. Here are some special features for working with sizes and positions. (For the precise meaning of “selected frame” used by these functions, see .) set-frame-position — Function: set-frame-position frame left top This function sets the position of the top left corner of frame toleft and top. These arguments are measured in pixels, andnormally count from the top left corner of the screen.Negative parameter values position the bottom edge of the window up fromthe bottom edge of the screen, or the right window edge to the left ofthe right edge of the screen. It would probably be better if the valueswere always counted from the left and top, so that negative argumentswould position the frame partly off the top or left edge of the screen,but it seems inadvisable to change that now. frame-height — Function: frame-height &optional frame frame-width — Function: frame-width &optional frame These functions return the height and width of frame, measured inlines and columns. If you don't supply frame, they use theselected frame. screen-height — Function: screen-height screen-width — Function: screen-width These functions are old aliases for frame-height andframe-width. When you are using a non-window terminal, the sizeof the frame is normally the same as the size of the terminal screen. frame-pixel-height — Function: frame-pixel-height &optional frame frame-pixel-width — Function: frame-pixel-width &optional frame These functions return the height and width of frame, measured inpixels. If you don't supply frame, they use the selected frame. frame-char-height — Function: frame-char-height &optional frame frame-char-width — Function: frame-char-width &optional frame These functions return the height and width of a character inframe, measured in pixels. The values depend on the choice offont. If you don't supply frame, these functions use the selectedframe. set-frame-size — Function: set-frame-size frame cols rows This function sets the size of frame, measured in characters;cols and rows specify the new width and height.To set the size based on values measured in pixels, useframe-char-height and frame-char-width to convertthem to units of characters. set-frame-height — Function: set-frame-height frame lines &optional pretend This function resizes frame to a height of lines lines. Thesizes of existing windows in frame are altered proportionally tofit.If pretend is non-nil, then Emacs displays lineslines of output in frame, but does not change its value for theactual height of the frame. This is only useful for a terminal frame.Using a smaller height than the terminal actually implements may beuseful to reproduce behavior observed on a smaller screen, or if theterminal malfunctions when using its whole screen. Setting the frameheight “for real” does not always work, because knowing the correctactual size may be necessary for correct cursor positioning on aterminal frame. set-frame-width — Function: set-frame-width frame width &optional pretend This function sets the width of frame, measured in characters.The argument pretend has the same meaning as inset-frame-height. set-screen-height set-screen-width The older functions set-screen-height and set-screen-width were used to specify the height and width of the screen, in Emacs versions that did not support multiple frames. They are semi-obsolete, but still work; they apply to the selected frame. Geometry Here's how to examine the data in an X-style window geometry specification: x-parse-geometry — Function: x-parse-geometry geom geometry specificationThe function x-parse-geometry converts a standard X windowgeometry string to an alist that you can use as part of the argument tomake-frame.The alist describes which parameters were specified in geom, andgives the values specified for them. Each element looks like(parameter . value). The possible parametervalues are left, top, width, and height.For the size parameters, the value must be an integer. The positionparameter names left and top are not totally accurate,because some values indicate the position of the right or bottom edgesinstead. These are the value possibilities for the positionparameters: an integer A positive integer relates the left edge or top edge of the window tothe left or top edge of the screen. A negative integer relates theright or bottom edge of the window to the right or bottom edge of thescreen. (+ position) This specifies the position of the left or top edge of the windowrelative to the left or top edge of the screen. The integerposition may be positive or negative; a negative value specifies aposition outside the screen. (- position) This specifies the position of the right or bottom edge of the windowrelative to the right or bottom edge of the screen. The integerposition may be positive or negative; a negative value specifies aposition outside the screen. Here is an example: (x-parse-geometry "35x70+0-0") => ((height . 70) (width . 35) (top - 0) (left . 0)) Frame Titles frame title Every frame has a name parameter; this serves as the default for the frame title which window systems typically display at the top of the frame. You can specify a name explicitly by setting the name frame property. Normally you don't specify the name explicitly, and Emacs computes the frame name automatically based on a template stored in the variable frame-title-format. Emacs recomputes the name each time the frame is redisplayed. frame-title-format — Variable: frame-title-format This variable specifies how to compute a name for a frame when you havenot explicitly specified one. The variable's value is actually a modeline construct, just like mode-line-format, except that the‘%c’ and ‘%l’ constructs are ignored. See . icon-title-format — Variable: icon-title-format This variable specifies how to compute the name for an iconified frame,when you have not explicitly specified the frame title. This titleappears in the icon itself. multiple-frames — Variable: multiple-frames This variable is set automatically by Emacs. Its value is t whenthere are two or more frames (not counting minibuffer-only frames orinvisible frames). The default value of frame-title-format usesmultiple-frames so as to put the buffer name in the frame titleonly when there is more than one frame.The value of this variable is not guaranteed to be accurate exceptwhile processing frame-title-format oricon-title-format. Deleting Frames deleting frames Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. delete-frame — Command: delete-frame &optional frame force delete-frame-functionsThis function deletes the frame frame. Unless frame is atooltip, it first runs the hook delete-frame-functions (eachfunction gets one argument, frame). By default, frame isthe selected frame.A frame cannot be deleted if its minibuffer is used by other frames.Normally, you cannot delete a frame if all other frames are invisible,but if the force is non-nil, then you are allowed to do so. frame-live-p — Function: frame-live-p frame The function frame-live-p returns non-nil if the frameframe has not been deleted. The possible non-nil returnvalues are like those of framep. See . Some window managers provide a command to delete a window. These work by sending a special message to the program that operates the window. When Emacs gets one of these commands, it generates a delete-frame event, whose normal definition is a command that calls the function delete-frame. See . Finding All Frames frames, scanning all frame-list — Function: frame-list The function frame-list returns a list of all the frames thathave not been deleted. It is analogous to buffer-list forbuffers, and includes frames on all terminals. The list that you get isnewly created, so modifying the list doesn't have any effect on theinternals of Emacs. visible-frame-list — Function: visible-frame-list This function returns a list of just the currently visible frames.See . (Terminal frames always count as“visible,” even though only the selected one is actually displayed.) next-frame — Function: next-frame &optional frame minibuf The function next-frame lets you cycle conveniently through allthe frames on the current display from an arbitrary starting point. Itreturns the “next” frame after frame in the cycle. Ifframe is omitted or nil, it defaults to the selected frame(see ).The second argument, minibuf, says which frames to consider: nil Exclude minibuffer-only frames. visible Consider all visible frames. 0 Consider all visible or iconified frames. a window Consider only the frames using that particular window as theirminibuffer. anything else Consider all frames. previous-frame — Function: previous-frame &optional frame minibuf Like next-frame, but cycles through all frames in the oppositedirection. See also next-window and previous-window, in . Frames and Windows Each window is part of one and only one frame; you can get the frame with window-frame. window-frame — Function: window-frame window This function returns the frame that window is on. All the non-minibuffer windows in a frame are arranged in a cyclic order. The order runs from the frame's top window, which is at the upper left corner, down and to the right, until it reaches the window at the lower right corner (always the minibuffer window, if the frame has one), and then it moves back to the top. See . frame-first-window — Function: frame-first-window &optional frame This returns the topmost, leftmost window of frame frame.If omitted or nil, frame defaults to the selected frame. At any time, exactly one window on any frame is selected within the frame. The significance of this designation is that selecting the frame also selects this window. You can get the frame's current selected window with frame-selected-window. frame-selected-window — Function: frame-selected-window &optional frame This function returns the window on frame that is selectedwithin frame. If omitted or nil, frame defaults tothe selected frame. set-frame-selected-window — Function: set-frame-selected-window frame window This sets the selected window of frame frame to window.If frame is nil, it operates on the selected frame. Ifframe is the selected frame, this makes window theselected window. This function returns window. Conversely, selecting a window for Emacs with select-window also makes that window selected within its frame. See . Another function that (usually) returns one of the windows in a given frame is minibuffer-window. See . Minibuffers and Frames Normally, each frame has its own minibuffer window at the bottom, which is used whenever that frame is selected. If the frame has a minibuffer, you can get it with minibuffer-window (see ). However, you can also create a frame with no minibuffer. Such a frame must use the minibuffer window of some other frame. When you create the frame, you can specify explicitly the minibuffer window to use (in some other frame). If you don't, then the minibuffer is found in the frame which is the value of the variable default-minibuffer-frame. Its value should be a frame that does have a minibuffer. If you use a minibuffer-only frame, you might want that frame to raise when you enter the minibuffer. If so, set the variable minibuffer-auto-raise to t. See . default-minibuffer-frame — Variable: default-minibuffer-frame This variable specifies the frame to use for the minibuffer window, bydefault. It does not affect existing frames. It is always local tothe current terminal and cannot be buffer-local. See . Input Focus input focus At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame. When Emacs displays its frames on several terminals (see ), each terminal has its own selected frame. But only one of these is “the selected frame”: it's the frame that belongs to the terminal from which the most recent input came. That is, when Emacs runs a command that came from a certain terminal, the selected frame is the one of that terminal. Since Emacs runs only a single command at any given time, it needs to consider only one selected frame at a time; this frame is what we call the selected frame in this manual. The display on which the selected frame is displayed is the selected frame's display. selected-frame — Function: selected-frame This function returns the selected frame. Some window systems and window managers direct keyboard input to the window object that the mouse is in; others require explicit clicks or commands to shift the focus to various window objects. Either way, Emacs automatically keeps track of which frame has the focus. To switch to a different frame from a Lisp function, call select-frame-set-input-focus. Lisp programs can also switch frames “temporarily” by calling the function select-frame. This does not alter the window system's concept of focus; rather, it escapes from the window manager's control until that control is somehow reasserted. When using a text-only terminal, only one frame can be displayed at a time on the terminal, so after a call to select-frame, the next redisplay actually displays the newly selected frame. This frame remains selected until a subsequent call to select-frame or select-frame-set-input-focus. Each terminal frame has a number which appears in the mode line before the buffer name (see ). select-frame-set-input-focus — Function: select-frame-set-input-focus frame This function makes frame the selected frame, raises it (shouldit happen to be obscured by other frames) and tries to give it the Xserver's focus. On a text-only terminal, the next redisplay displaysthe new frame on the entire terminal screen. The return value of thisfunction is not significant. select-frame — Function: select-frame frame This function selects frame frame, temporarily disregarding thefocus of the X server if any. The selection of frame lasts untilthe next time the user does something to select a different frame, oruntil the next time this function is called. (If you are using awindow system, the previously selected frame may be restored as theselected frame after return to the command loop, because it still mayhave the window system's input focus.) The specified framebecomes the selected frame, as explained above, and the terminal thatframe is on becomes the selected terminal. This functionreturns frame, or nil if frame has been deleted.In general, you should never use select-frame in a way that couldswitch to a different terminal without switching back when you're done. Emacs cooperates with the window system by arranging to select frames as the server and window manager request. It does so by generating a special kind of input event, called a focus event, when appropriate. The command loop handles a focus event by calling handle-switch-frame. See . handle-switch-frame — Command: handle-switch-frame frame This function handles a focus event by selecting frame frame.Focus events normally do their job by invoking this command.Don't call it for any other reason. redirect-frame-focus — Function: redirect-frame-focus frame &optional focus-frame This function redirects focus from frame to focus-frame.This means that focus-frame will receive subsequent keystrokes andevents intended for frame. After such an event, the value oflast-event-frame will be focus-frame. Also, switch-frameevents specifying frame will instead select focus-frame.If focus-frame is omitted or nil, that cancels any existingredirection for frame, which therefore once again receives its ownevents.One use of focus redirection is for frames that don't have minibuffers.These frames use minibuffers on other frames. Activating a minibufferon another frame redirects focus to that frame. This puts the focus onthe minibuffer's frame, where it belongs, even though the mouse remainsin the frame that activated the minibuffer.Selecting a frame can also change focus redirections. Selecting framebar, when foo had been selected, changes any redirectionspointing to foo so that they point to bar instead. Thisallows focus redirection to work properly when the user switches fromone frame to another using select-window.This means that a frame whose focus is redirected to itself is treateddifferently from a frame whose focus is not redirected.select-frame affects the former but not the latter.The redirection lasts until redirect-frame-focus is called tochange it. focus-follows-mouse — User Option: focus-follows-mouse This option is how you inform Emacs whether the window manager transfersfocus when the user moves the mouse. Non-nil says that it does.When this is so, the command other-frame moves the mouse to aposition consistent with the new selected frame. (This option has noeffect on MS-Windows, where the mouse pointer is always automaticallymoved by the OS to the selected frame.) Visibility of Frames visible frame invisible frame iconified frame frame visibility A window frame may be visible, invisible, or iconified. If it is visible, you can see its contents, unless other windows cover it. If it is iconified, the frame's contents do not appear on the screen, but an icon does. If the frame is invisible, it doesn't show on the screen, not even as an icon. Visibility is meaningless for terminal frames, since only the selected one is actually displayed in any case. make-frame-visible — Command: make-frame-visible &optional frame This function makes frame frame visible. If you omitframe, it makes the selected frame visible. This does not raisethe frame, but you can do that with raise-frame if you wish(see ). make-frame-invisible — Command: make-frame-invisible &optional frame force This function makes frame frame invisible. If you omitframe, it makes the selected frame invisible.Unless force is non-nil, this function refuses to makeframe invisible if all other frames are invisible.. iconify-frame — Command: iconify-frame &optional frame This function iconifies frame frame. If you omit frame, iticonifies the selected frame. frame-visible-p — Function: frame-visible-p frame This returns the visibility status of frame frame. The value ist if frame is visible, nil if it is invisible, andicon if it is iconified.On a text-only terminal, all frames are considered visible, whetherthey are currently being displayed or not, and this function returnst for all frames. The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See . The user can iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See . Raising and Lowering Frames Most window systems use a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from “highest” to “lowest.” Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it. lowering a frame A window's place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it “up,” to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen. You can raise and lower Emacs frame Windows with these functions: raise-frame — Command: raise-frame &optional frame This function raises frame frame (default, the selected frame).If frame is invisible or iconified, this makes it visible. lower-frame — Command: lower-frame &optional frame This function lowers frame frame (default, the selected frame). minibuffer-auto-raise — User Option: minibuffer-auto-raise If this is non-nil, activation of the minibuffer raises the framethat the minibuffer window is in. You can also enable auto-raise (raising automatically when a frame is selected) or auto-lower (lowering automatically when it is deselected) for any frame using frame parameters. See . Frame Configurations frame configuration A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (See .) current-frame-configuration — Function: current-frame-configuration This function returns a frame configuration list that describesthe current arrangement of frames and their contents. set-frame-configuration — Function: set-frame-configuration configuration &optional nodelete This function restores the state of frames described inconfiguration. However, this function does not restore deletedframes.Ordinarily, this function deletes all existing frames not listed inconfiguration. But if nodelete is non-nil, theunwanted frames are iconified instead. Mouse Tracking mouse tracking Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves. The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever—only until some other event, such as the release of a button. track-mouse — Special Form: track-mouse body … This special form executes body, with generation of mouse motionevents enabled. Typically body would use read-event toread the motion events and modify the display accordingly. See , for the format of mouse motion events.The value of track-mouse is that of the last form in body.You should design body to return when it sees the up-event thatindicates the release of the button, or whatever kind of event meansit is time to stop tracking. The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position. In many cases, you can avoid the need to track the mouse by using the mouse-face text property (see ). That works at a much lower level and runs more smoothly than Lisp-level mouse tracking. Mouse Position mouse position position of mouse The functions mouse-position and set-mouse-position give access to the current position of the mouse. mouse-position — Function: mouse-position This function returns a description of the position of the mouse. Thevalue looks like (frame x . y), where xand y are integers giving the position in characters relative tothe top left corner of the inside of frame. mouse-position-function — Variable: mouse-position-function If non-nil, the value of this variable is a function formouse-position to call. mouse-position calls thisfunction just before returning, with its normal return value as thesole argument, and it returns whatever this function returns to it.This abnormal hook exists for the benefit of packages likext-mouse.el that need to do mouse handling at the Lisp level. set-mouse-position — Function: set-mouse-position frame x y This function warps the mouse to position x, y inframe frame. The arguments x and y are integers,giving the position in characters relative to the top left corner of theinside of frame. If frame is not visible, this functiondoes nothing. The return value is not significant. mouse-pixel-position — Function: mouse-pixel-position This function is like mouse-position except that it returnscoordinates in units of pixels rather than units of characters. set-mouse-pixel-position — Function: set-mouse-pixel-position frame x y This function warps the mouse like set-mouse-position except thatx and y are in units of pixels rather than units ofcharacters. These coordinates are not required to be within the frame.If frame is not visible, this function does nothing. The returnvalue is not significant. Pop-Up Menus When using a window system, a Lisp program can pop up a menu so that the user can choose an alternative with the mouse. x-popup-menu — Function: x-popup-menu position menu This function displays a pop-up menu and returns an indication ofwhat selection the user makes.The argument position specifies where on the screen to put thetop left corner of the menu. It can be either a mouse button event(which says to put the menu where the user actuated the button) or alist of this form: ((xoffset yoffset) window) where xoffset and yoffset are coordinates, measured inpixels, counting from the top left corner of window. windowmay be a window or a frame.If position is t, it means to use the current mouseposition. If position is nil, it means to precompute thekey binding equivalents for the keymaps specified in menu,without actually displaying or popping up the menu.The argument menu says what to display in the menu. It can be akeymap or a list of keymaps (see ). In this case, thereturn value is the list of events corresponding to the user's choice.(This list has more than one element if the choice occurred in asubmenu.) Note that x-popup-menu does not actually execute thecommand bound to that sequence of events.Alternatively, menu can have the following form: (title pane1 pane2...) where each pane is a list of form (title item1 item2...) Each item should normally be a cons cell (line . value),where line is a string, and value is the value to return ifthat line is chosen. An item can also be a string; this makes anon-selectable line in the menu.If the user gets rid of the menu without making a valid choice, forinstance by clicking the mouse away from a valid choice or by typingkeyboard input, then this normally results in a quit andx-popup-menu does not return. But if position is a mousebutton event (indicating that the user invoked the menu with themouse) then no quit occurs and x-popup-menu returns nil. Usage note: Don't use x-popup-menu to display a menu if you could do the job with a prefix key defined with a menu keymap. If you use a menu keymap to implement a menu, C-h c and C-h a can see the individual items in that menu and provide help for them. If instead you implement the menu by defining a command that calls x-popup-menu, the help facilities cannot know what happens inside that command, so they cannot give any help for the menu's items. The menu bar mechanism, which lets you switch between submenus by moving the mouse, cannot look within the definition of a command to see that it calls x-popup-menu. Therefore, if you try to implement a submenu using x-popup-menu, it cannot work with the menu bar in an integrated fashion. This is why all menu bar submenus are implemented with menu keymaps within the parent menu, and never with x-popup-menu. See . If you want a menu bar submenu to have contents that vary, you should still use a menu keymap to implement it. To make the contents vary, add a hook function to menu-bar-update-hook to update the contents of the menu keymap as necessary. Dialog Boxes dialog boxes A dialog box is a variant of a pop-up menu—it looks a little different, it always appears in the center of a frame, and it has just one level and one or more buttons. The main use of dialog boxes is for asking questions that the user can answer with “yes,” “no,” and a few other alternatives. With a single button, they can also force the user to acknowledge important information. The functions y-or-n-p and yes-or-no-p use dialog boxes instead of the keyboard, when called from commands invoked by mouse clicks. x-popup-dialog — Function: x-popup-dialog position contents &optional header This function displays a pop-up dialog box and returns an indication ofwhat selection the user makes. The argument contents specifiesthe alternatives to offer; it has this format: (title (string . value)…) which looks like the list that specifies a single pane forx-popup-menu.The return value is value from the chosen alternative.As for x-popup-menu, an element of the list may be just astring instead of a cons cell (string . value).That makes a box that cannot be selected.If nil appears in the list, it separates the left-hand items fromthe right-hand items; items that precede the nil appear on theleft, and items that follow the nil appear on the right. If youdon't include a nil in the list, then approximately half theitems appear on each side.Dialog boxes always appear in the center of a frame; the argumentposition specifies which frame. The possible values are as inx-popup-menu, but the precise coordinates or the individualwindow don't matter; only the frame matters.If header is non-nil, the frame title for the box is‘Information’, otherwise it is ‘Question’. The former is usedfor message-box (see ).In some configurations, Emacs cannot display a real dialog box; soinstead it displays the same items in a pop-up menu in the center of theframe.If the user gets rid of the dialog box without making a valid choice,for instance using the window manager, then this produces a quit andx-popup-dialog does not return. Pointer Shape pointer shape mouse pointer shape You can specify the mouse pointer style for particular text or images using the pointer text property, and for images with the :pointer and :map image properties. The values you can use in these properties are text (or nil), arrow, hand, vdrag, hdrag, modeline, and hourglass. text stands for the usual mouse pointer style used over text. Over void parts of the window (parts that do not correspond to any of the buffer contents), the mouse pointer usually uses the arrow style, but you can specify a different style (one of those above) by setting void-text-area-pointer. void-text-area-pointer — Variable: void-text-area-pointer This variable specifies the mouse pointer style for void text areas.These include the areas after the end of a line or below the last linein the buffer. The default is to use the arrow (non-text)pointer style. You can specify what the text pointer style really looks like by setting the variable x-pointer-shape. x-pointer-shape — Variable: x-pointer-shape This variable specifies the pointer shape to use ordinarily in theEmacs frame, for the text pointer style. x-sensitive-text-pointer-shape — Variable: x-sensitive-text-pointer-shape This variable specifies the pointer shape to use when the mouseis over mouse-sensitive text. These variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also installs the current value of those two variables. See . The values you can use, to specify either of these pointer shapes, are defined in the file lisp/term/x-win.el. Use M-x apropos RET x-pointer RET to see a list of them. Window System Selections selection (for window systems) The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type. x-set-selection — Command: x-set-selection type data This function sets a “selection” in the X server. It takes twoarguments: a selection type type, and the value to assign to it,data. If data is nil, it means to clear out theselection. Otherwise, data may be a string, a symbol, an integer(or a cons of two integers or list of two integers), an overlay, or acons of two markers pointing to the same buffer. An overlay or a pairof markers stands for text in the overlay or between the markers.The argument data may also be a vector of valid non-vectorselection values.Each possible type has its own selection value, which changesindependently. The usual values of type are PRIMARY,SECONDARY and CLIPBOARD; these are symbols with upper-casenames, in accord with X Window System conventions. If type isnil, that stands for PRIMARY.This function returns data. x-get-selection — Function: x-get-selection &optional type data-type This function accesses selections set up by Emacs or by other Xclients. It takes two optional arguments, type anddata-type. The default for type, the selection type, isPRIMARY.The data-type argument specifies the form of data conversion touse, to convert the raw data obtained from another X client into Lispdata. Meaningful values include TEXT, STRING,UTF8_STRING, TARGETS, LENGTH, DELETE,FILE_NAME, CHARACTER_POSITION, NAME,LINE_NUMBER, COLUMN_NUMBER, OWNER_OS,HOST_NAME, USER, CLASS, ATOM, andINTEGER. (These are symbols with upper-case names in accordwith X conventions.) The default for data-type isSTRING. cut buffer The X server also has a set of eight numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them. Cut buffers are numbered from 0 to 7. x-get-cut-buffer — Function: x-get-cut-buffer &optional n This function returns the contents of cut buffer number n.If omitted n defaults to 0. x-set-cut-buffer — Function: x-set-cut-buffer string &optional push This function stores string into the first cut buffer (cut buffer0). If push is nil, only the first cut buffer is changed.If push is non-nil, that says to move the values downthrough the series of cut buffers, much like the way successive kills inEmacs move down the kill ring. In other words, the previous value ofthe first cut buffer moves into the second cut buffer, and the second tothe third, and so on through all eight cut buffers. selection-coding-system — Variable: selection-coding-system This variable specifies the coding system to use when reading andwriting selections or the clipboard. See . The default is compound-text-with-extensions, whichconverts to the text representation that X11 normally uses. clipboard support (for MS-Windows) When Emacs runs on MS-Windows, it does not implement X selections in general, but it does support the clipboard. x-get-selection and x-set-selection on MS-Windows support the text data type only; if the clipboard holds other types of data, Emacs treats the clipboard as empty. scrap support (for Mac OS) On Mac OS, selection-like data transfer between applications is performed through a mechanism called scraps. The clipboard is a particular scrap named com.apple.scrap.clipboard. Types of scrap data are called scrap flavor types, which are identified by four-char codes such as TEXT. Emacs associates a selection with a scrap, and a selection type with a scrap flavor type via mac-scrap-name and mac-ostype properties, respectively. (get 'CLIPBOARD 'mac-scrap-name) => "com.apple.scrap.clipboard" (get 'com.apple.traditional-mac-plain-text 'mac-ostype) => "TEXT" Conventionally, selection types for scrap flavor types on Mac OS have the form of UTI (Uniform Type Identifier) such as com.apple.traditional-mac-plain-text, public.utf16-plain-text, and public.file-url. x-select-enable-clipboard — User Option: x-select-enable-clipboard If this is non-nil, the Emacs yank functions consult theclipboard before the primary selection, and the kill functions store inthe clipboard as well as the primary selection. Otherwise they do notaccess the clipboard at all. The default is nil on most systems,but t on MS-Windows and Mac. Drag and Drop x-dnd-test-function x-dnd-known-types When a user drags something from another application over Emacs, that other application expects Emacs to tell it if Emacs can handle the data that is dragged. The variable x-dnd-test-function is used by Emacs to determine what to reply. The default value is x-dnd-default-test-function which accepts drops if the type of the data to be dropped is present in x-dnd-known-types. You can customize x-dnd-test-function and/or x-dnd-known-types if you want Emacs to accept or reject drops based on some other criteria. x-dnd-types-alist If you want to change the way Emacs handles drop of different types or add a new type, customize x-dnd-types-alist. This requires detailed knowledge of what types other applications use for drag and drop. dnd-protocol-alist When an URL is dropped on Emacs it may be a file, but it may also be another URL type (ftp, http, etc.). Emacs first checks dnd-protocol-alist to determine what to do with the URL. If there is no match there and if browse-url-browser-function is an alist, Emacs looks for a match there. If no match is found the text for the URL is inserted. If you want to alter Emacs behavior, you can customize these variables. Color Names color names specify color numerical RGB color specification A color name is text (usually in a string) that specifies a color. Symbolic names such as ‘black’, ‘white’, ‘red’, etc., are allowed; use M-x list-colors-display to see a list of defined names. You can also specify colors numerically in forms such as ‘#rgb’ and ‘RGB:r/g/b’, where r specifies the red level, g specifies the green level, and b specifies the blue level. You can use either one, two, three, or four hex digits for r; then you must use the same number of hex digits for all g and b as well, making either 3, 6, 9 or 12 hex digits in all. (See the documentation of the X Window System for more details about numerical RGB specification of colors.) These functions provide a way to determine which color names are valid, and what they look like. In some cases, the value depends on the selected frame, as described below; see , for the meaning of the term “selected frame.” color-defined-p — Function: color-defined-p color &optional frame This function reports whether a color name is meaningful. It returnst if so; otherwise, nil. The argument frame sayswhich frame's display to ask about; if frame is omitted ornil, the selected frame is used.Note that this does not tell you whether the display you are usingreally supports that color. When using X, you can ask for any definedcolor on any kind of display, and you will get some result—typically,the closest it can do. To determine whether a frame can really displaya certain color, use color-supported-p (see below). x-color-defined-pThis function used to be called x-color-defined-p,and that name is still supported as an alias. defined-colors — Function: defined-colors &optional frame This function returns a list of the color names that are definedand supported on frame frame (default, the selected frame).If frame does not support colors, the value is nil. x-defined-colorsThis function used to be called x-defined-colors,and that name is still supported as an alias. color-supported-p — Function: color-supported-p color &optional frame background-p This returns t if frame can really display the colorcolor (or at least something close to it). If frame isomitted or nil, the question applies to the selected frame.Some terminals support a different set of colors for foreground andbackground. If background-p is non-nil, that means you areasking whether color can be used as a background; otherwise youare asking whether it can be used as a foreground.The argument color must be a valid color name. color-gray-p — Function: color-gray-p color &optional frame This returns t if color is a shade of gray, as defined onframe's display. If frame is omitted or nil, thequestion applies to the selected frame. If color is not a validcolor name, this function returns nil. color-values — Function: color-values color &optional frame rgb valueThis function returns a value that describes what color shouldideally look like on frame. If color is defined, thevalue is a list of three integers, which give the amount of red, theamount of green, and the amount of blue. Each integer ranges inprinciple from 0 to 65535, but some displays may not use the fullrange. This three-element list is called the rgb values of thecolor.If color is not defined, the value is nil. (color-values "black") => (0 0 0) (color-values "white") => (65280 65280 65280) (color-values "red") => (65280 0 0) (color-values "pink") => (65280 49152 51968) (color-values "hungry") => nil The color values are returned for frame's display. Ifframe is omitted or nil, the information is returned forthe selected frame's display. If the frame cannot display colors, thevalue is nil. x-color-valuesThis function used to be called x-color-values,and that name is still supported as an alias. Text Terminal Colors colors on text-only terminals Text-only terminals usually support only a small number of colors, and the computer uses small integers to select colors on the terminal. This means that the computer cannot reliably tell what the selected color looks like; instead, you have to inform your application which small integers correspond to which colors. However, Emacs does know the standard set of colors and will try to use them automatically. The functions described in this section control how terminal colors are used by Emacs. Several of these functions use or return rgb values, described in . These functions accept a display (either a frame or the name of a terminal) as an optional argument. We hope in the future to make Emacs support more than one text-only terminal at one time; then this argument will specify which terminal to operate on (the default being the selected frame's terminal; see ). At present, though, the frame argument has no effect. tty-color-define — Function: tty-color-define name number &optional rgb frame This function associates the color name name withcolor number number on the terminal.The optional argument rgb, if specified, is an rgb value, a listof three numbers that specify what the color actually looks like.If you do not specify rgb, then this color cannot be used bytty-color-approximate to approximate other colors, becauseEmacs will not know what it looks like. tty-color-clear — Function: tty-color-clear &optional frame This function clears the table of defined colors for a text-only terminal. tty-color-alist — Function: tty-color-alist &optional frame This function returns an alist recording the known colors supported by atext-only terminal.Each element has the form (name number . rgb)or (name number). Here, name is the colorname, number is the number used to specify it to the terminal.If present, rgb is a list of three color values (for red, green,and blue) that says what the color actually looks like. tty-color-approximate — Function: tty-color-approximate rgb &optional frame This function finds the closest color, among the known colorssupported for display, to that described by the rgb valuergb (a list of color values). The return value is an element oftty-color-alist. tty-color-translate — Function: tty-color-translate color &optional frame This function finds the closest color to color among the knowncolors supported for display and returns its index (an integer).If the name color is not defined, the value is nil. X Resources x-get-resource — Function: x-get-resource attribute class &optional component subclass The function x-get-resource retrieves a resource value from the XWindow defaults database.Resources are indexed by a combination of a key and a class.This function searches using a key of the form‘instance.attribute’ (where instance is the nameunder which Emacs was invoked), and using ‘Emacs.class’ asthe class.The optional arguments component and subclass add to the keyand the class, respectively. You must specify both of them or neither.If you specify them, the key is‘instance.component.attribute’, and the class is‘Emacs.class.subclass’. x-resource-class — Variable: x-resource-class This variable specifies the application name that x-get-resourceshould look up. The default value is "Emacs". You can examine Xresources for application names other than “Emacs” by binding thisvariable to some other string, around a call to x-get-resource. x-resource-name — Variable: x-resource-name This variable specifies the instance name that x-get-resourceshould look up. The default value is the name Emacs was invoked with,or the value specified with the ‘-name’ or ‘-rn’ switches. To illustrate some of the above, suppose that you have the line: xterm.vt100.background: yellow in your X resources file (whose name is usually ~/.Xdefaults or ~/.Xresources). Then: (let ((x-resource-class "XTerm") (x-resource-name "xterm")) (x-get-resource "vt100.background" "VT100.Background")) => "yellow" (let ((x-resource-class "XTerm") (x-resource-name "xterm")) (x-get-resource "background" "VT100" "vt100" "Background")) => "yellow" See See section ``X Resources'' in The GNU Emacs Manual. Display Feature Testing display feature testing The functions in this section describe the basic capabilities of a particular display. Lisp programs can use them to adapt their behavior to what the display can do. For example, a program that ordinarily uses a popup menu could use the minibuffer if popup menus are not supported. The optional argument display in these functions specifies which display to ask the question about. It can be a display name, a frame (which designates the display that frame is on), or nil (which refers to the selected frame's display, see ). See , , for other functions to obtain information about displays. display-popup-menus-p — Function: display-popup-menus-p &optional display This function returns t if popup menus are supported ondisplay, nil if not. Support for popup menus requires thatthe mouse be available, since the user cannot choose menu items withouta mouse. display-graphic-p — Function: display-graphic-p &optional display This function returns t if display is a graphic displaycapable of displaying several frames and several different fonts atonce. This is true for displays that use a window system such as X, andfalse for text-only terminals. display-mouse-p — Function: display-mouse-p &optional display mouse, availabilityThis function returns t if display has a mouse available,nil if not. display-color-p — Function: display-color-p &optional display x-display-color-pThis function returns t if the screen is a color screen.It used to be called x-display-color-p, and that nameis still supported as an alias. display-grayscale-p — Function: display-grayscale-p &optional display This function returns t if the screen can display shades of gray.(All color displays can do this.) display-supports-face-attributes-p — Function: display-supports-face-attributes-p attributes &optional display This function returns non-nil if all the face attributes inattributes are supported (see ).The definition of `supported' is somewhat heuristic, but basicallymeans that a face containing all the attributes in attributes,when merged with the default face for display, can be represented in away that's different in appearance than the default face, and `close in spirit' to what the attributes specify, if not exact. Point (2) implies that a :weight black attribute will besatisfied by any display that can display bold, as will:foreground "yellow" as long as some yellowish color can bedisplayed, but :slant italic will not be satisfied bythe tty display code's automatic substitution of a `dim' face foritalic. display-selections-p — Function: display-selections-p &optional display This function returns t if display supports selections.Windowed displays normally support selections, but they may also besupported in some other cases. display-images-p — Function: display-images-p &optional display This function returns t if display can display images.Windowed displays ought in principle to handle images, but somesystems lack the support for that. On a display that does not supportimages, Emacs cannot display a tool bar. display-screens — Function: display-screens &optional display This function returns the number of screens associated with the display. display-pixel-height — Function: display-pixel-height &optional display This function returns the height of the screen in pixels.On a character terminal, it gives the height in characters.For graphical terminals, note that on “multi-monitor” setups thisrefers to the pixel width for all physical monitors associated withdisplay. See . display-pixel-width — Function: display-pixel-width &optional display This function returns the width of the screen in pixels.On a character terminal, it gives the width in characters.For graphical terminals, note that on “multi-monitor” setups thisrefers to the pixel width for all physical monitors associated withdisplay. See . display-mm-height — Function: display-mm-height &optional display This function returns the height of the screen in millimeters,or nil if Emacs cannot get that information. display-mm-width — Function: display-mm-width &optional display This function returns the width of the screen in millimeters,or nil if Emacs cannot get that information. display-mm-dimensions-alist — Variable: display-mm-dimensions-alist This variable allows the user to specify the dimensions of graphicaldisplays returned by display-mm-height anddisplay-mm-width in case the system provides incorrect values. display-backing-store — Function: display-backing-store &optional display This function returns the backing store capability of the display.Backing store means recording the pixels of windows (and parts ofwindows) that are not exposed, so that when exposed they can bedisplayed very quickly.Values can be the symbols always, when-mapped, ornot-useful. The function can also return nilwhen the question is inapplicable to a certain kind of display. display-save-under — Function: display-save-under &optional display This function returns non-nil if the display supports theSaveUnder feature. That feature is used by pop-up windowsto save the pixels they obscure, so that they can pop downquickly. display-planes — Function: display-planes &optional display This function returns the number of planes the display supports.This is typically the number of bits per pixel.For a tty display, it is log to base two of the number of colors supported. display-visual-class — Function: display-visual-class &optional display This function returns the visual class for the screen. The value is oneof the symbols static-gray, gray-scale,static-color, pseudo-color, true-color, anddirect-color. display-color-cells — Function: display-color-cells &optional display This function returns the number of color cells the screen supports. These functions obtain additional information specifically about X displays. x-server-version — Function: x-server-version &optional display This function returns the list of version numbers of the X serverrunning the display. The value is a list of three integers: the majorand minor version numbers of the X protocol, and thedistributor-specific release number of the X server software itself. x-server-vendor — Function: x-server-vendor &optional display This function returns the “vendor” that provided the X serversoftware (as a string). Really this means whoever distributes the Xserver.When the developers of X labelled software distributors as“vendors,” they showed their false assumption that no system couldever be developed and distributed noncommercially. <setfilename>../info/positions</setfilename> Positions position (in buffer) A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character “at” a position, meaning the character after that position. Positions are usually represented as integers starting from 1, but can also be represented as markers—special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. Functions that expect an argument to be a position (an integer), but accept a marker as a substitute, normally ignore which buffer the marker points into; they convert the marker to an integer, and use that integer, exactly as if you had passed the integer as the argument, even if the marker points to the “wrong” buffer. A marker that points nowhere cannot convert to an integer; using it instead of an integer causes an error. See . See also the “field” feature (see ), which provides functions that are used by many cursor-motion commands. Point point Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places. Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits. point with narrowing The value of point is a number no less than 1, and no greater than the buffer size plus 1. If narrowing is in effect (see ), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it). Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See , for more details. point — Function: point current buffer positionThis function returns the value of point in the current buffer,as an integer. (point) => 175 point-min — Function: point-min This function returns the minimum accessible value of point in thecurrent buffer. This is normally 1, but if narrowing is in effect, itis the position of the start of the region that you narrowed to.(See .) point-max — Function: point-max This function returns the maximum accessible value of point in thecurrent buffer. This is (1+ (buffer-size)), unless narrowing isin effect, in which case it is the position of the end of the regionthat you narrowed to. (See .) buffer-end — Function: buffer-end flag This function returns (point-max) if flag is greater than0, (point-min) otherwise. The argument flag must be anumber. buffer-size — Function: buffer-size &optional buffer This function returns the total number of characters in the currentbuffer. In the absence of any narrowing (see ),point-max returns a value one larger than this.If you specify a buffer, buffer, then the value is thesize of buffer. (buffer-size) => 35 (point-max) => 36 Motion motion by chars, words, lines, lists Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See . Motion by Characters These functions move point based on a count of characters. goto-char is the fundamental primitive; the other functions use that. goto-char — Command: goto-char position This function sets point in the current buffer to the valueposition. If position is less than 1, it moves point to thebeginning of the buffer. If position is greater than the lengthof the buffer, it moves point to the end.If narrowing is in effect, position still counts from thebeginning of the buffer, but point cannot go outside the accessibleportion. If position is out of range, goto-char movespoint to the beginning or the end of the accessible portion.When this function is called interactively, position is thenumeric prefix argument, if provided; otherwise it is read from theminibuffer.goto-char returns position. forward-char — Command: forward-char &optional count This function moves point count characters forward, towards theend of the buffer (or backward, towards the beginning of the buffer, ifcount is negative). If count is nil, the defaultis 1.If this attempts to move past the beginning or end of the buffer (orthe limits of the accessible portion, when narrowing is in effect), itsignals an error with error symbol beginning-of-buffer orend-of-buffer.In an interactive call, count is the numeric prefix argument. backward-char — Command: backward-char &optional count This is just like forward-char except that it movesin the opposite direction. Motion by Words These functions for parsing words use the syntax table to decide whether a given character is part of a word. See . forward-word — Command: forward-word &optional count This function moves point forward count words (or backward ifcount is negative). If count is nil, it movesforward one word.“Moving one word” means moving until point crosses aword-constituent character and then encounters a word-separatorcharacter. However, this function cannot move point past the boundaryof the accessible portion of the buffer, or across a field boundary(see ). The most common case of a field boundary is the endof the prompt in the minibuffer.If it is possible to move count words, without being stoppedprematurely by the buffer boundary or a field boundary, the value ist. Otherwise, the return value is nil and point stops atthe buffer boundary or field boundary.If inhibit-field-text-motion is non-nil,this function ignores field boundaries.In an interactive call, count is specified by the numeric prefixargument. If count is omitted or nil, it defaults to 1. backward-word — Command: backward-word &optional count This function is just like forward-word, except that it movesbackward until encountering the front of a word, rather than forward. words-include-escapes — Variable: words-include-escapes This variable affects the behavior of forward-word and everythingthat uses it. If it is non-nil, then characters in the“escape” and “character quote” syntax classes count as part ofwords. Otherwise, they do not. inhibit-field-text-motion — Variable: inhibit-field-text-motion If this variable is non-nil, certain motion functions includingforward-word, forward-sentence, andforward-paragraph ignore field boundaries. Motion to an End of the Buffer move to beginning or end of buffer To move point to the beginning of the buffer, write: (goto-char (point-min)) Likewise, to move to the end of the buffer, use: (goto-char (point-max)) Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area. beginning-of-buffer — Command: beginning-of-buffer &optional n This function moves point to the beginning of the buffer (or the limitsof the accessible portion, when narrowing is in effect), setting themark at the previous position (except in Transient Mark mode, ifthe mark is already active, it does not set the mark.)If n is non-nil, then it puts point n tenths of theway from the beginning of the accessible portion of the buffer. In aninteractive call, n is the numeric prefix argument, if provided;otherwise n defaults to nil.Warning: Don't use this function in Lisp programs! end-of-buffer — Command: end-of-buffer &optional n This function moves point to the end of the buffer (or the limits ofthe accessible portion, when narrowing is in effect), setting the markat the previous position (except in Transient Mark mode when the markis already active). If n is non-nil, then it puts pointn tenths of the way from the end of the accessible portion ofthe buffer.In an interactive call, n is the numeric prefix argument,if provided; otherwise n defaults to nil.Warning: Don't use this function in Lisp programs! Motion by Text Lines lines Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed. goto-line — Command: goto-line line This function moves point to the front of the lineth line,counting from line 1 at beginning of the buffer. If line is lessthan 1, it moves point to the beginning of the buffer. If line isgreater than the number of lines in the buffer, it moves point to theend of the buffer—that is, the end of the last line of thebuffer. This is the only case in which goto-line does notnecessarily move to the beginning of a line.If narrowing is in effect, then line still counts from thebeginning of the buffer, but point cannot go outside the accessibleportion. So goto-line moves point to the beginning or end of theaccessible portion, if the line number specifies an inaccessibleposition.The return value of goto-line is the difference betweenline and the line number of the line to which point actually wasable to move (in the full buffer, before taking account of narrowing).Thus, the value is positive if the scan encounters the real end of thebuffer before finding the specified line. The value is zero if scanencounters the end of the accessible portion but not the real end of thebuffer.In an interactive call, line is the numeric prefix argument ifone has been provided. Otherwise line is read in the minibuffer. beginning-of-line — Command: beginning-of-line &optional count This function moves point to the beginning of the current line. With anargument count not nil or 1, it moves forwardcount−1 lines and then to the beginning of the line.This function does not move point across a field boundary(see ) unless doing so would move beyond there to adifferent line; therefore, if count is nil or 1, andpoint starts at a field boundary, point does not move. To ignorefield boundaries, either bind inhibit-field-text-motion tot, or use the forward-line function instead. Forinstance, (forward-line 0) does the same thing as(beginning-of-line), except that it ignores field boundaries.If this function reaches the end of the buffer (or of the accessibleportion, if narrowing is in effect), it positions point there. No erroris signaled. line-beginning-position — Function: line-beginning-position &optional count Return the position that (beginning-of-line count)would move to. end-of-line — Command: end-of-line &optional count This function moves point to the end of the current line. With anargument count not nil or 1, it moves forwardcount−1 lines and then to the end of the line.This function does not move point across a field boundary(see ) unless doing so would move beyond there to adifferent line; therefore, if count is nil or 1, andpoint starts at a field boundary, point does not move. To ignorefield boundaries, bind inhibit-field-text-motion to t.If this function reaches the end of the buffer (or of the accessibleportion, if narrowing is in effect), it positions point there. No erroris signaled. line-end-position — Function: line-end-position &optional count Return the position that (end-of-line count)would move to. forward-line — Command: forward-line &optional count beginning of lineThis function moves point forward count lines, to the beginning ofthe line. If count is negative, it moves point−count lines backward, to the beginning of a line. Ifcount is zero, it moves point to the beginning of the currentline. If count is nil, that means 1.If forward-line encounters the beginning or end of the buffer (orof the accessible portion) before finding that many lines, it sets pointthere. No error is signaled.forward-line returns the difference between count and thenumber of lines actually moved. If you attempt to move down five linesfrom the beginning of a buffer that has only three lines, point stops atthe end of the last line, and the value will be 2.In an interactive call, count is the numeric prefix argument. count-lines — Function: count-lines start end lines in regionThis function returns the number of lines between the positionsstart and end in the current buffer. If start andend are equal, then it returns 0. Otherwise it returns at least1, even if start and end are on the same line. This isbecause the text between them, considered in isolation, must contain atleast one line unless it is empty.Here is an example of using count-lines: (defun current-line () "Return the vertical position of point…" (+ (count-lines (window-start) (point)) (if (= (current-column) 0) 1 0))) line-number-at-pos — Function: line-number-at-pos &optional pos line numberThis function returns the line number in the current buffercorresponding to the buffer position pos. If pos is nilor omitted, the current buffer position is used. Also see the functions bolp and eolp in . These functions do not move point, but test whether it is already at the beginning or end of a line. Motion by Screen Lines The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines. In some cases, text lines are truncated on the screen rather than continued onto additional screen lines. In these cases, vertical-motion moves point much like forward-line. See . Because the width of a given string depends on the flags that control the appearance of certain characters, vertical-motion behaves differently, for a given piece of text, depending on the buffer it is in, and even on the selected window (because the width, the truncation flag, and display table may vary between windows). See . These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. See cache-long-line-scans. vertical-motion — Function: vertical-motion count &optional window This function moves point to the start of the screen line countscreen lines down from the screen line containing point. If countis negative, it moves up instead.vertical-motion returns the number of screen lines over which itmoved point. The value may be less in absolute value than countif the beginning or end of the buffer was reached.The window window is used for obtaining parameters such as thewidth, the horizontal scrolling, and the display table. Butvertical-motion always operates on the current buffer, even ifwindow currently displays some other buffer. count-screen-lines — Function: count-screen-lines &optional beg end count-final-newline window This function returns the number of screen lines in the text frombeg to end. The number of screen lines may be differentfrom the number of actual lines, due to line continuation, the displaytable, etc. If beg and end are nil or omitted,they default to the beginning and end of the accessible portion of thebuffer.If the region ends with a newline, that is ignored unless the optionalthird argument count-final-newline is non-nil.The optional fourth argument window specifies the window forobtaining parameters such as width, horizontal scrolling, and so on.The default is to use the selected window's parameters.Like vertical-motion, count-screen-lines always uses thecurrent buffer, regardless of which buffer is displayed inwindow. This makes possible to use count-screen-lines inany buffer, whether or not it is currently displayed in some window. move-to-window-line — Command: move-to-window-line count This function moves point with respect to the text currently displayedin the selected window. It moves point to the beginning of the screenline count screen lines from the top of the window. Ifcount is negative, that specifies a position−count lines from the bottom (or the last line of thebuffer, if the buffer ends above the specified screen position).If count is nil, then point moves to the beginning of theline in the middle of the window. If the absolute value of countis greater than the size of the window, then point moves to the placethat would appear on that screen line if the window were tall enough.This will probably cause the next redisplay to scroll to bring thatlocation onto the screen.In an interactive call, count is the numeric prefix argument.The value returned is the window line number point has moved to, withthe top line in the window numbered 0. compute-motion — Function: compute-motion from frompos to topos width offsets window This function scans the current buffer, calculating screen positions.It scans the buffer forward from position from, assuming that isat screen coordinates frompos, to position to or coordinatestopos, whichever comes first. It returns the ending bufferposition and screen coordinates.The coordinate arguments frompos and topos are cons cells ofthe form (hpos . vpos).The argument width is the number of columns available to displaytext; this affects handling of continuation lines. nil meansthe actual number of usable text columns in the window, which isequivalent to the value returned by (window-width window).The argument offsets is either nil or a cons cell of theform (hscroll . tab-offset). Here hscroll isthe number of columns not being displayed at the left margin; mostcallers get this by calling window-hscroll. Meanwhile,tab-offset is the offset between column numbers on the screen andcolumn numbers in the buffer. This can be nonzero in a continuationline, when the previous screen lines' widths do not add up to a multipleof tab-width. It is always zero in a non-continuation line.The window window serves only to specify which display table touse. compute-motion always operates on the current buffer,regardless of what buffer is displayed in window.The return value is a list of five elements: (pos hpos vpos prevhpos contin) Here pos is the buffer position where the scan stopped, vposis the vertical screen position, and hpos is the horizontal screenposition.The result prevhpos is the horizontal position one character backfrom pos. The result contin is t if the last linewas continued after (or within) the previous character.For example, to find the buffer position of column col of screen lineline of a certain window, pass the window's display start locationas from and the window's upper-left coordinates as frompos.Pass the buffer's (point-max) as to, to limit the scan tothe end of the accessible portion of the buffer, and pass line andcol as topos. Here's a function that does this: (defun coordinates-of-position (col line) (car (compute-motion (window-start) '(0 . 0) (point-max) (cons col line) (window-width) (cons (window-hscroll) 0) (selected-window)))) When you use compute-motion for the minibuffer, you need to useminibuffer-prompt-width to get the horizontal position of thebeginning of the first screen line. See . Moving over Balanced Expressions sexp motion Lisp expression motion list motion balanced parenthesis motion Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see . See , for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see See section ``Commands for Editing with Parentheses'' in The GNU Emacs Manual. forward-list — Command: forward-list &optional arg This function moves forward across arg (default 1) balanced groups ofparentheses. (Other syntactic entities such as words or paired stringquotes are ignored.) backward-list — Command: backward-list &optional arg This function moves backward across arg (default 1) balanced groups ofparentheses. (Other syntactic entities such as words or paired stringquotes are ignored.) up-list — Command: up-list &optional arg This function moves forward out of arg (default 1) levels of parentheses.A negative argument means move backward but still to a less deep spot. down-list — Command: down-list &optional arg This function moves forward into arg (default 1) levels ofparentheses. A negative argument means move backward but still godeeper in parentheses (−arg levels). forward-sexp — Command: forward-sexp &optional arg This function moves forward across arg (default 1) balanced expressions.Balanced expressions include both those delimited by parentheses andother kinds, such as words and string constants.See . For example, ---------- Buffer: foo ---------- (concat-!- "foo " (car x) y z) ---------- Buffer: foo ---------- (forward-sexp 3) => nil ---------- Buffer: foo ---------- (concat "foo " (car x) y-!- z) ---------- Buffer: foo ---------- backward-sexp — Command: backward-sexp &optional arg This function moves backward across arg (default 1) balanced expressions. beginning-of-defun — Command: beginning-of-defun &optional arg This function moves back to the argth beginning of a defun. Ifarg is negative, this actually moves forward, but it still movesto the beginning of a defun, not to the end of one. arg defaultsto 1. end-of-defun — Command: end-of-defun &optional arg This function moves forward to the argth end of a defun. Ifarg is negative, this actually moves backward, but it still movesto the end of a defun, not to the beginning of one. arg defaultsto 1. defun-prompt-regexp — User Option: defun-prompt-regexp If non-nil, this buffer-local variable holds a regularexpression that specifies what text can appear before theopen-parenthesis that starts a defun. That is to say, a defun beginson a line that starts with a match for this regular expression,followed by a character with open-parenthesis syntax. open-paren-in-column-0-is-defun-start — User Option: open-paren-in-column-0-is-defun-start If this variable's value is non-nil, an open parenthesis incolumn 0 is considered to be the start of a defun. If it isnil, an open parenthesis in column 0 has no special meaning.The default is t. beginning-of-defun-function — Variable: beginning-of-defun-function If non-nil, this variable holds a function for finding thebeginning of a defun. The function beginning-of-defuncalls this function instead of using its normal method. end-of-defun-function — Variable: end-of-defun-function If non-nil, this variable holds a function for finding the end ofa defun. The function end-of-defun calls this function insteadof using its normal method. Skipping Characters skipping characters The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see . These functions convert the set string to multibyte if the buffer is multibyte, and they convert it to unibyte if the buffer is unibyte, as the search functions do (see ). skip-chars-forward — Function: skip-chars-forward character-set &optional limit This function moves point in the current buffer forward, skipping over agiven set of characters. It examines the character following point,then advances point if the character matches character-set. Thiscontinues until it reaches a character that does not match. Thefunction returns the number of characters moved over.The argument character-set is a string, like the inside of a‘[…]’ in a regular expression except that ‘]’ does notterminate it, and ‘\’ quotes ‘^’, ‘-’ or ‘\’.Thus, "a-zA-Z" skips over all letters, stopping before thefirst nonletter, and "^a-zA-Z" skips nonletters stopping beforethe first letter. See See . Character classescan also be used, e.g. "[:alnum:]". See see .If limit is supplied (it must be a number or a marker), itspecifies the maximum position in the buffer that point can be skippedto. Point will stop at or before limit.In the following example, point is initially located directly before the‘T’. After the form is evaluated, point is located at the end ofthat line (between the ‘t’ of ‘hat’ and the newline). Thefunction skips all letters and spaces, but not newlines. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (skip-chars-forward "a-zA-Z ") => nil ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- skip-chars-backward — Function: skip-chars-backward character-set &optional limit This function moves point backward, skipping characters that matchcharacter-set, until limit. It is just likeskip-chars-forward except for the direction of motion.The return value indicates the distance traveled. It is an integer thatis zero or less. Excursions excursion It is often useful to move point “temporarily” within a localized portion of the program, or to switch buffers temporarily. This is called an excursion, and it is done with the save-excursion special form. This construct initially remembers the identity of the current buffer, and its values of point and the mark, and restores them after the completion of the excursion. The forms for saving and restoring the configuration of windows are described elsewhere (see , and see ). save-excursion — Special Form: save-excursion body … mark excursion point excursionThe save-excursion special form saves the identity of the currentbuffer and the values of point and the mark in it, evaluatesbody, and finally restores the buffer and its saved values ofpoint and the mark. All three saved values are restored even in case ofan abnormal exit via throw or error (see ).The save-excursion special form is the standard way to switchbuffers or move point within one part of a program and avoid affectingthe rest of the program. It is used more than 4000 times in the Lispsources of Emacs.save-excursion does not save the values of point and the mark forother buffers, so changes in other buffers remain in effect aftersave-excursion exits. window excursionsLikewise, save-excursion does not restore window-buffercorrespondences altered by functions such as switch-to-buffer.One way to restore these correspondences, and the selected window, is touse save-window-excursion inside save-excursion(see ).The value returned by save-excursion is the result of the lastform in body, or nil if no body forms were given. (save-excursion forms) == (let ((old-buf (current-buffer)) (old-pnt (point-marker)) (old-mark (copy-marker (mark-marker)))) (unwind-protect (progn forms) (set-buffer old-buf) (goto-char old-pnt) (set-marker (mark-marker) old-mark))) Warning: Ordinary insertion of text adjacent to the saved point value relocates the saved value, just as it relocates all markers. More precisely, the saved value is a marker with insertion type nil. See . Therefore, when the saved point value is restored, it normally comes before the inserted text. Although save-excursion saves the location of the mark, it does not prevent functions which modify the buffer from setting deactivate-mark, and thus causing the deactivation of the mark after the command finishes. See . Narrowing narrowing restriction (in a buffer) accessible portion (of a buffer) Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer. Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion. Values such as positions or line numbers, which usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible. The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing. narrow-to-region — Command: narrow-to-region start end This function sets the accessible portion of the current buffer to startat start and end at end. Both arguments should be characterpositions.In an interactive call, start and end are set to the boundsof the current region (point and the mark, with the smallest first). narrow-to-page — Command: narrow-to-page &optional move-count This function sets the accessible portion of the current buffer toinclude just the current page. An optional first argumentmove-count non-nil means to move forward or backward bymove-count pages and then narrow to one page. The variablepage-delimiter specifies where pages start and end(see ).In an interactive call, move-count is set to the numeric prefixargument. widen — Command: widen wideningThis function cancels any narrowing in the current buffer, so that theentire contents are accessible. This is called widening.It is equivalent to the following expression: (narrow-to-region 1 (1+ (buffer-size))) save-restriction — Special Form: save-restriction body … This special form saves the current bounds of the accessible portion,evaluates the body forms, and finally restores the saved bounds,thus restoring the same state of narrowing (or absence thereof) formerlyin effect. The state of narrowing is restored even in the event of anabnormal exit via throw or error (see ).Therefore, this construct is a clean way to narrow a buffer temporarily.The value returned by save-restriction is that returned by thelast form in body, or nil if no body forms were given. Caution: it is easy to make a mistake when using thesave-restriction construct. Read the entire description herebefore you try it.If body changes the current buffer, save-restriction stillrestores the restrictions on the original buffer (the buffer whoserestrictions it saved from), but it does not restore the identity of thecurrent buffer.save-restriction does not restore point and the mark; usesave-excursion for that. If you use both save-restrictionand save-excursion together, save-excursion should comefirst (on the outside). Otherwise, the old point value would berestored with temporary narrowing still in effect. If the old pointvalue were outside the limits of the temporary narrowing, this wouldfail to restore it accurately.Here is a simple example of correct use of save-restriction: ---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo-!- ---------- Buffer: foo ---------- (save-excursion (save-restriction (goto-char 1) (forward-line 2) (narrow-to-region 1 (point)) (goto-char (point-min)) (replace-string "foo" "bar"))) ---------- Buffer: foo ---------- This is the contents of bar This is the contents of bar This is the contents of foo-!- ---------- Buffer: foo ---------- <setfilename>../info/markers</setfilename> Markers markers A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it. Overview of Markers A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. In that case, the marker's buffer is normally ignored. Of course, a marker used in this way usually points to a position in the buffer that the function operates on, but that is entirely the programmer's responsibility. See , for a complete description of positions. A marker has three attributes: the marker position, the marker buffer, and the insertion type. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker. marker relocation Deleting text around a marker's position leaves the marker between the characters immediately before and after the deleted text. Inserting text at the position of a marker normally leaves the marker either in front of or after the new text, depending on the marker's insertion type (see )—unless the insertion is done with insert-before-markers (see ). marker garbage collection Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere. markers as numbers Because it is common to perform arithmetic operations on a marker position, most of the arithmetic operations (including + and -) accept markers as arguments. In such cases, the marker stands for its current position. Here are examples of creating markers, setting markers, and moving point to markers: ;; Make a new marker that initially does not point anywhere: (setq m1 (make-marker)) => #<marker in no buffer> ;; Set m1 to point between the 99th and 100th characters ;; in the current buffer: (set-marker m1 100) => #<marker at 100 in markers.texi> ;; Now insert one character at the beginning of the buffer: (goto-char (point-min)) => 1 (insert "Q") => nil ;; m1 is updated appropriately. m1 => #<marker at 101 in markers.texi> ;; Two markers that point to the same position ;; are not eq, but they are equal. (setq m2 (copy-marker m1)) => #<marker at 101 in markers.texi> (eq m1 m2) => nil (equal m1 m2) => t ;; When you are finished using a marker, make it point nowhere. (set-marker m1 nil) => #<marker in no buffer> Predicates on Markers You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers. markerp — Function: markerp object This function returns t if object is a marker, nilotherwise. Note that integers are not markers, even though manyfunctions will accept either a marker or an integer. integer-or-marker-p — Function: integer-or-marker-p object This function returns t if object is an integer or a marker,nil otherwise. number-or-marker-p — Function: number-or-marker-p object This function returns t if object is a number (eitherinteger or floating point) or a marker, nil otherwise. Functions that Create Markers When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker. The next four functions all return markers with insertion type nil. See . make-marker — Function: make-marker This function returns a newly created marker that does not pointanywhere. (make-marker) => #<marker in no buffer> point-marker — Function: point-marker This function returns a new marker that points to the present positionof point in the current buffer. See . For an example, seecopy-marker, below. point-min-marker — Function: point-min-marker This function returns a new marker that points to the beginning of theaccessible portion of the buffer. This will be the beginning of thebuffer unless narrowing is in effect. See . point-max-marker — Function: point-max-marker This function returns a new marker that points to the end of theaccessible portion of the buffer. This will be the end of the bufferunless narrowing is in effect. See .Here are examples of this function and point-min-marker, shown ina buffer containing a version of the source file for the text of thischapter. (point-min-marker) => #<marker at 1 in markers.texi> (point-max-marker) => #<marker at 15573 in markers.texi> (narrow-to-region 100 200) => nil (point-min-marker) => #<marker at 100 in markers.texi> (point-max-marker) => #<marker at 200 in markers.texi> copy-marker — Function: copy-marker marker-or-integer &optional insertion-type If passed a marker as its argument, copy-marker returns anew marker that points to the same place and the same buffer as doesmarker-or-integer. If passed an integer as its argument,copy-marker returns a new marker that points to positionmarker-or-integer in the current buffer.The new marker's insertion type is specified by the argumentinsertion-type. See .If passed an integer argument less than 1, copy-marker returns anew marker that points to the beginning of the current buffer. Ifpassed an integer argument greater than the length of the buffer,copy-marker returns a new marker that points to the end of thebuffer. (copy-marker 0) => #<marker at 1 in markers.texi> (copy-marker 20000) => #<marker at 7572 in markers.texi> An error is signaled if marker is neither a marker nor aninteger. Two distinct markers are considered equal (even though not eq) to each other if they have the same position and buffer, or if they both point nowhere. (setq p (point-marker)) => #<marker at 2139 in markers.texi> (setq q (copy-marker p)) => #<marker at 2139 in markers.texi> (eq p q) => nil (equal p q) => t Information from Markers This section describes the functions for accessing the components of a marker object. marker-position — Function: marker-position marker This function returns the position that marker points to, ornil if it points nowhere. marker-buffer — Function: marker-buffer marker This function returns the buffer that marker points into, ornil if it points nowhere. (setq m (make-marker)) => #<marker in no buffer> (marker-position m) => nil (marker-buffer m) => nil (set-marker m 3770 (current-buffer)) => #<marker at 3770 in markers.texi> (marker-buffer m) => #<buffer markers.texi> (marker-position m) => 3770 buffer-has-markers-at — Function: buffer-has-markers-at position This function returns t if one or more markerspoint at position position in the current buffer. Marker Insertion Types insertion type of a marker When you insert text directly at the place where a marker points, there are two possible ways to relocate that marker: it can point before the inserted text, or point after it. You can specify which one a given marker should do by setting its insertion type. Note that use of insert-before-markers ignores markers' insertion types, always relocating a marker to point after the inserted text. set-marker-insertion-type — Function: set-marker-insertion-type marker type This function sets the insertion type of marker marker totype. If type is t, marker will advance whentext is inserted at its position. If type is nil,marker does not advance when text is inserted there. marker-insertion-type — Function: marker-insertion-type marker This function reports the current insertion type of marker. Most functions that create markers, without an argument allowing to specify the insertion type, create them with insertion type nil. Also, the mark has, by default, insertion type nil. Moving Marker Positions This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs. set-marker — Function: set-marker marker position &optional buffer This function moves marker to positionin buffer. If buffer is not provided, it defaults tothe current buffer.If position is less than 1, set-marker moves markerto the beginning of the buffer. If position is greater than thesize of the buffer, set-marker moves marker to the end of thebuffer. If position is nil or a marker that pointsnowhere, then marker is set to point nowhere.The value returned is marker. (setq m (point-marker)) => #<marker at 4714 in markers.texi> (set-marker m 55) => #<marker at 55 in markers.texi> (setq b (get-buffer "foo")) => #<buffer foo> (set-marker m 0 b) => #<marker at 1 in foo> move-marker — Function: move-marker marker position &optional buffer This is another name for set-marker. The Mark mark, the mark ring One special marker in each buffer is designated the mark. It specifies a position to bound a range of text for commands such as kill-region and indent-rigidly. Lisp programs should set the mark only to values that have a potential use to the user, and never for their own internal purposes. For example, the replace-regexp command sets the mark to the value of point before doing any replacements, because this enables the user to move back there conveniently after the replace is finished. Many commands are designed to operate on the text between point and the mark when called interactively. If you are writing such a command, don't examine the mark directly; instead, use interactive with the ‘r’ specification. This provides the values of point and the mark as arguments to the command in an interactive call, but permits other Lisp programs to specify arguments explicitly. See . Each buffer has a marker which represents the value of the mark in that buffer, independent of any other buffer. When a buffer is newly created, this marker exists but does not point anywhere. That means the mark “doesn't exist” in that buffer as yet. Once the mark “exists” in a buffer, it normally never ceases to exist. However, it may become inactive, if Transient Mark mode is enabled. The variable mark-active, which is always buffer-local in all buffers, indicates whether the mark is active: non-nil means yes. A command can request deactivation of the mark upon return to the editor command loop by setting deactivate-mark to a non-nil value (but this causes deactivation only if Transient Mark mode is enabled). The main motivation for using Transient Mark mode is that this mode also enables highlighting of the region when the mark is active. See . In addition to the mark, each buffer has a mark ring which is a list of markers containing previous values of the mark. When editing commands change the mark, they should normally save the old value of the mark on the mark ring. The variable mark-ring-max specifies the maximum number of entries in the mark ring; once the list becomes this long, adding a new element deletes the last element. There is also a separate global mark ring, but that is used only in a few particular user-level commands, and is not relevant to Lisp programming. So we do not describe it here. mark — Function: mark &optional force current buffer markThis function returns the current buffer's mark position as an integer,or nil if no mark has ever been set in this buffer.If Transient Mark mode is enabled, and mark-even-if-inactive isnil, mark signals an error if the mark is inactive.However, if force is non-nil, then mark disregardsinactivity of the mark, and returns the mark position anyway (ornil). mark-marker — Function: mark-marker This function returns the marker that represents the current buffer'smark. It is not a copy, it is the marker used internally. Therefore,changing this marker's position will directly affect the buffer'smark. Don't do that unless that is the effect you want. (setq m (mark-marker)) => #<marker at 3420 in markers.texi> (set-marker m 100) => #<marker at 100 in markers.texi> (mark-marker) => #<marker at 100 in markers.texi> Like any marker, this marker can be set to point at any buffer youlike. If you make it point at any buffer other than the one of whichit is the mark, it will yield perfectly consistent, but rather odd,results. We recommend that you not do it! set-mark — Function: set-mark position This function sets the mark to position, and activates the mark.The old value of the mark is not pushed onto the mark ring.Please note: Use this function only if you want the user tosee that the mark has moved, and you want the previous mark position tobe lost. Normally, when a new mark is set, the old one should go on themark-ring. For this reason, most applications should usepush-mark and pop-mark, not set-mark.Novice Emacs Lisp programmers often try to use the mark for the wrongpurposes. The mark saves a location for the user's convenience. Anediting command should not alter the mark unless altering the mark ispart of the user-level functionality of the command. (And, in thatcase, this effect should be documented.) To remember a location forinternal use in the Lisp program, store it in a Lisp variable. Forexample: (let ((beg (point))) (forward-line 1) (delete-region beg (point))). push-mark — Function: push-mark &optional position nomsg activate This function sets the current buffer's mark to position, andpushes a copy of the previous mark onto mark-ring. Ifposition is nil, then the value of point is used.push-mark returns nil.The function push-mark normally does not activate themark. To do that, specify t for the argument activate.A ‘Mark set’ message is displayed unless nomsg isnon-nil. pop-mark — Function: pop-mark This function pops off the top element of mark-ring and makesthat mark become the buffer's actual mark. This does not move point inthe buffer, and it does nothing if mark-ring is empty. Itdeactivates the mark.The return value is not meaningful. transient-mark-mode — User Option: transient-mark-mode This variable if non-nil enables Transient Mark mode, in whichevery buffer-modifying primitive sets deactivate-mark. Theconsequence of this is that commands that modify the buffer normallymake the mark inactive.Lisp programs can set transient-mark-mode to only toenable Transient Mark mode for the following command only. Duringthat following command, the value of transient-mark-mode isidentity. If it is still identity at the end of thecommand, it changes to nil. mark-even-if-inactive — User Option: mark-even-if-inactive If this is non-nil, Lisp programs and the Emacs user can use themark even when it is inactive. This option affects the behavior ofTransient Mark mode. When the option is non-nil, deactivation ofthe mark turns off region highlighting, but commands that use the markbehave as if the mark were still active. deactivate-mark — Variable: deactivate-mark If an editor command sets this variable non-nil, then the editorcommand loop deactivates the mark after the command returns (ifTransient Mark mode is enabled). All the primitives that change thebuffer set deactivate-mark, to deactivate the mark when thecommand is finished.To write Lisp code that modifies the buffer without causingdeactivation of the mark at the end of the command, binddeactivate-mark to nil around the code that does themodification. For example: (let (deactivate-mark) (insert " ")) deactivate-mark — Function: deactivate-mark This function deactivates the mark, if Transient Mark mode is enabled.Otherwise it does nothing. mark-active — Variable: mark-active The mark is active when this variable is non-nil. This variableis always buffer-local in each buffer. activate-mark-hook — Variable: activate-mark-hook deactivate-mark-hook — Variable: deactivate-mark-hook These normal hooks are run, respectively, when the mark becomes activeand when it becomes inactive. The hook activate-mark-hook isalso run at the end of a command if the mark is active and it ispossible that the region may have changed. mark-ring — Variable: mark-ring The value of this buffer-local variable is the list of saved formermarks of the current buffer, most recent first. mark-ring => (#<marker at 11050 in markers.texi> #<marker at 10832 in markers.texi> …) mark-ring-max — User Option: mark-ring-max The value of this variable is the maximum size of mark-ring. Ifmore marks than this are pushed onto the mark-ring,push-mark discards an old mark when it adds a new one. The Region region (between point and mark) The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here. The next two functions signal an error if the mark does not point anywhere. If Transient Mark mode is enabled and mark-even-if-inactive is nil, they also signal an error if the mark is inactive. region-beginning — Function: region-beginning This function returns the position of the beginning of the region (asan integer). This is the position of either point or the mark,whichever is smaller. region-end — Function: region-end This function returns the position of the end of the region (as aninteger). This is the position of either point or the mark, whichever islarger. Few programs need to use the region-beginning and region-end functions. A command designed to operate on a region should normally use interactive with the ‘r’ specification to find the beginning and end of the region. This lets other Lisp programs specify the bounds explicitly as arguments. (See .) <setfilename>../info/text</setfilename> Text text This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often operating at point or on text adjacent to point. Many are interactive. All the functions that change the text provide for undoing the changes (see ). Many text-related functions operate on a region of text defined by two buffer positions passed in arguments named start and end. These arguments should be either markers (see ) or numeric character positions (see ). The order of these arguments does not matter; it is all right for start to be the end of the region and end the beginning. For example, (delete-region 1 10) and (delete-region 10 1) are equivalent. An args-out-of-range error is signaled if either start or end is outside the accessible portion of the buffer. In an interactive call, point and the mark are used for these arguments. buffer contents Throughout this chapter, “text” refers to the characters in the buffer, together with their properties (when relevant). Keep in mind that point is always between two characters, and the cursor appears on the character after point. Examining Text Near Point text near point Many functions are provided to look at the characters around point. Several simple functions are described here. See also looking-at in . In the following four functions, “beginning” or “end” of buffer refers to the beginning or end of the accessible portion. char-after — Function: char-after &optional position This function returns the character in the current buffer at (i.e.,immediately after) position position. If position is out ofrange for this purpose, either before the beginning of the buffer, or ator beyond the end, then the value is nil. The default forposition is point.In the following example, assume that the first character in thebuffer is ‘@’: (char-to-string (char-after 1)) => "@" char-before — Function: char-before &optional position This function returns the character in the current buffer immediatelybefore position position. If position is out of range forthis purpose, either at or before the beginning of the buffer, or beyondthe end, then the value is nil. The default forposition is point. following-char — Function: following-char This function returns the character following point in the currentbuffer. This is similar to (char-after (point)). However, ifpoint is at the end of the buffer, then following-char returns 0.Remember that point is always between characters, and the cursornormally appears over the character following point. Therefore, thecharacter returned by following-char is the character thecursor is over.In this example, point is between the ‘a’ and the ‘c’. ---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (char-to-string (preceding-char)) => "a" (char-to-string (following-char)) => "c" preceding-char — Function: preceding-char This function returns the character preceding point in the currentbuffer. See above, under following-char, for an example. Ifpoint is at the beginning of the buffer, preceding-char returns0. bobp — Function: bobp This function returns t if point is at the beginning of thebuffer. If narrowing is in effect, this means the beginning of theaccessible portion of the text. See also point-min in. eobp — Function: eobp This function returns t if point is at the end of the buffer.If narrowing is in effect, this means the end of accessible portion ofthe text. See also point-max in See . bolp — Function: bolp This function returns t if point is at the beginning of a line.See . The beginning of the buffer (or of its accessibleportion) always counts as the beginning of a line. eolp — Function: eolp This function returns t if point is at the end of a line. Theend of the buffer (or of its accessible portion) is always consideredthe end of a line. Examining Buffer Contents This section describes functions that allow a Lisp program to convert any portion of the text in the buffer into a string. buffer-substring — Function: buffer-substring start end This function returns a string containing a copy of the text of theregion defined by positions start and end in the currentbuffer. If the arguments are not positions in the accessible portion ofthe buffer, buffer-substring signals an args-out-of-rangeerror.It is not necessary for start to be less than end; thearguments can be given in either order. But most often the smallerargument is written first.Here's an example which assumes Font-Lock mode is not enabled: ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo\n" If the text being copied has any text properties, these are copied intothe string along with the characters they belong to. See . However, overlays (see ) in the buffer andtheir properties are ignored, not copied.For example, if Font-Lock mode is enabled, you might get results likethese: (buffer-substring 1 10) => #("This is t" 0 1 (fontified t) 1 9 (fontified t)) buffer-substring-no-properties — Function: buffer-substring-no-properties start end This is like buffer-substring, except that it does not copy textproperties, just the characters themselves. See . filter-buffer-substring — Function: filter-buffer-substring start end &optional delete noprops This function passes the buffer text between start and endthrough the filter functions specified by the variablebuffer-substring-filters, and returns the value from the lastfilter function. If buffer-substring-filters is nil,the value is the unaltered text from the buffer, whatbuffer-substring would return.If delete is non-nil, this function deletes the textbetween start and end after copying it, likedelete-and-extract-region.If noprops is non-nil, the final string returned does notinclude text properties, while the string passed through the filtersstill includes text properties from the buffer text.Lisp code should use this function instead of buffer-substring,buffer-substring-no-properties,or delete-and-extract-region when copying into user-accessibledata structures such as the kill-ring, X clipboard, and registers.Major and minor modes can add functions tobuffer-substring-filters to alter such text as it is copied outof the buffer. buffer-substring-filters — Variable: buffer-substring-filters This variable should be a list of functions that accept a singleargument, a string, and return a string.filter-buffer-substring passes the buffer substring to thefirst function in this list, and the return value of each function ispassed to the next function. The return value of the last function isused as the return value of filter-buffer-substring.As a special convention, point is set to the start of the buffer textbeing operated on (i.e., the start argument forfilter-buffer-substring) before these functions are called.If this variable is nil, no filtering is performed. buffer-string — Function: buffer-string This function returns the contents of the entire accessible portion ofthe current buffer as a string. It is equivalent to (buffer-substring (point-min) (point-max)) ---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) => "This is the contents of buffer foo\n" current-word — Function: current-word &optional strict really-word This function returns the symbol (or word) at or near point, as a string.The return value includes no text properties.If the optional argument really-word is non-nil, it finds aword; otherwise, it finds a symbol (which includes both wordcharacters and symbol constituent characters).If the optional argument strict is non-nil, then pointmust be in or next to the symbol or word—if no symbol or word isthere, the function returns nil. Otherwise, a nearby symbol orword on the same line is acceptable. thing-at-point — Function: thing-at-point thing Return the thing around or next to point, as a string.The argument thing is a symbol which specifies a kind of syntacticentity. Possibilities include symbol, list, sexp,defun, filename, url, word, sentence,whitespace, line, page, and others. ---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (thing-at-point 'word) => "Peace" (thing-at-point 'line) => "Gentlemen may cry ``Peace! Peace!,''\n" (thing-at-point 'whitespace) => nil Comparing Text comparing buffer text This function lets you compare portions of the text in a buffer, without copying them into strings first. compare-buffer-substrings — Function: compare-buffer-substrings buffer1 start1 end1 buffer2 start2 end2 This function lets you compare two substrings of the same buffer or twodifferent buffers. The first three arguments specify one substring,giving a buffer (or a buffer name) and two positions within thebuffer. The last three arguments specify the other substring in thesame way. You can use nil for buffer1, buffer2, orboth to stand for the current buffer.The value is negative if the first substring is less, positive if thefirst is greater, and zero if they are equal. The absolute value ofthe result is one plus the index of the first differing characterswithin the substrings.This function ignores case when comparing charactersif case-fold-search is non-nil. It always ignorestext properties.Suppose the current buffer contains the text ‘foobarbarhaha!rara!’; then in this example the two substrings are ‘rbar ’and ‘rara!’. The value is 2 because the first substring is greaterat the second character. (compare-buffer-substrings nil 6 11 nil 16 21) => 2 Inserting Text insertion of text text insertion insertion before point before point, insertion Insertion means adding new text to a buffer. The inserted text goes at point—between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point. Insertion relocates markers that point at positions after the insertion point, so that they stay with the surrounding text (see ). When a marker points at the place of insertion, insertion may or may not relocate the marker, depending on the marker's insertion type (see ). Certain special functions such as insert-before-markers relocate all such markers to point after the inserted text, regardless of the markers' insertion type. Insertion functions signal an error if the current buffer is read-only or if they insert within read-only text. These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text. The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa—if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See . insert — Function: insert &rest args This function inserts the strings and/or characters args into thecurrent buffer, at point, moving point forward. In other words, itinserts the text before point. An error is signaled unless allargs are either strings or characters. The value is nil. insert-before-markers — Function: insert-before-markers &rest args This function inserts the strings and/or characters args into thecurrent buffer, at point, moving point forward. An error is signaledunless all args are either strings or characters. The value isnil.This function is unlike the other insertion functions in that itrelocates markers initially pointing at the insertion point, to pointafter the inserted text. If an overlay begins at the insertion point,the inserted text falls outside the overlay; if a nonempty overlayends at the insertion point, the inserted text falls inside thatoverlay. insert-char — Function: insert-char character count &optional inherit This function inserts count instances of character into thecurrent buffer before point. The argument count should be aninteger, and character must be a character. The value is nil.This function does not convert unibyte character codes 128 through 255to multibyte characters, not even if the current buffer is a multibytebuffer. See .If inherit is non-nil, then the inserted characters inheritsticky text properties from the two characters before and after theinsertion point. See . insert-buffer-substring — Function: insert-buffer-substring from-buffer-or-name &optional start end This function inserts a portion of buffer from-buffer-or-name(which must already exist) into the current buffer before point. Thetext inserted is the region between start and end. (Thesearguments default to the beginning and end of the accessible portion ofthat buffer.) This function returns nil.In this example, the form is executed with buffer ‘bar’ as thecurrent buffer. We assume that buffer ‘bar’ is initially empty. ---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) => nil ---------- Buffer: bar ---------- We hold these truth-!- ---------- Buffer: bar ---------- insert-buffer-substring-no-properties — Function: insert-buffer-substring-no-properties from-buffer-or-name &optional start end This is like insert-buffer-substring except that it does notcopy any text properties. See , for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties. User-Level Insertion Commands This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs. insert-buffer — Command: insert-buffer from-buffer-or-name This command inserts the entire accessible contents offrom-buffer-or-name (which must exist) into the current bufferafter point. It leaves the mark after the inserted text. The valueis nil. self-insert-command — Command: self-insert-command count character insertion self-insertionThis command inserts the last character typed; it does so counttimes, before point, and returns nil. Most printing charactersare bound to this command. In routine use, self-insert-commandis the most frequently called function in Emacs, but programs rarely useit except to install it on a keymap.In an interactive call, count is the numeric prefix argument.Self-insertion translates the input character throughtranslation-table-for-input. See .This command calls auto-fill-function whenever that isnon-nil and the character inserted is in the tableauto-fill-chars (see ). This command performs abbrev expansion if Abbrev mode is enabled andthe inserted character does not have word-constituentsyntax. (See , and .) It is alsoresponsible for calling blink-paren-function when the insertedcharacter has close parenthesis syntax (see ).Do not try substituting your own definition ofself-insert-command for the standard one. The editor commandloop handles this function specially. newline — Command: newline &optional number-of-newlines This command inserts newlines into the current buffer before point.If number-of-newlines is supplied, that many newline charactersare inserted. newline and Auto Fill modeThis function calls auto-fill-function if the current columnnumber is greater than the value of fill-column andnumber-of-newlines is nil. Typically whatauto-fill-function does is insert a newline; thus, the overallresult in this case is to insert two newlines at different places: oneat point, and another earlier in the line. newline does notauto-fill if number-of-newlines is non-nil.This command indents to the left margin if that is not zero.See .The value returned is nil. In an interactive call, countis the numeric prefix argument. overwrite-mode — Variable: overwrite-mode This variable controls whether overwrite mode is in effect. The valueshould be overwrite-mode-textual, overwrite-mode-binary,or nil. overwrite-mode-textual specifies textualoverwrite mode (treats newlines and tabs specially), andoverwrite-mode-binary specifies binary overwrite mode (treatsnewlines and tabs like any other characters). Deleting Text text deletion deleting text vs killing Deletion means removing part of the text in a buffer, without saving it in the kill ring (see ). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see ). Some deletion functions do save text in the kill ring in some special cases. All of the deletion functions operate on the current buffer. erase-buffer — Command: erase-buffer This function deletes the entire text of the current buffer(not just the accessible portion), leaving itempty. If the buffer is read-only, it signals a buffer-read-onlyerror; if some of the text in it is read-only, it signals atext-read-only error. Otherwise, it deletes the text withoutasking for any confirmation. It returns nil.Normally, deleting a large amount of text from a buffer inhibits furtherauto-saving of that buffer “because it has shrunk.” However,erase-buffer does not do this, the idea being that the futuretext is not really related to the former text, and its size should notbe compared with that of the former text. delete-region — Command: delete-region start end This command deletes the text between positions start andend in the current buffer, and returns nil. If point wasinside the deleted region, its value afterward is start.Otherwise, point relocates with the surrounding text, as markers do. delete-and-extract-region — Function: delete-and-extract-region start end This function deletes the text between positions start andend in the current buffer, and returns a string containing thetext just deleted.If point was inside the deleted region, its value afterward isstart. Otherwise, point relocates with the surrounding text, asmarkers do. delete-char — Command: delete-char count &optional killp This command deletes count characters directly after point, orbefore point if count is negative. If killp isnon-nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, andkillp is the unprocessed prefix argument. Therefore, if a prefixargument is supplied, the text is saved in the kill ring. If no prefixargument is supplied, then one character is deleted, but not saved inthe kill ring.The value returned is always nil. delete-backward-char — Command: delete-backward-char count &optional killp deleting previous charThis command deletes count characters directly before point, orafter point if count is negative. If killp isnon-nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, andkillp is the unprocessed prefix argument. Therefore, if a prefixargument is supplied, the text is saved in the kill ring. If no prefixargument is supplied, then one character is deleted, but not saved inthe kill ring.The value returned is always nil. backward-delete-char-untabify — Command: backward-delete-char-untabify count &optional killp tab deletionThis command deletes count characters backward, changing tabsinto spaces. When the next character to be deleted is a tab, it isfirst replaced with the proper number of spaces to preserve alignmentand then one of those spaces is deleted instead of the tab. Ifkillp is non-nil, then the command saves the deletedcharacters in the kill ring.Conversion of tabs to spaces happens only if count is positive.If it is negative, exactly −count characters after pointare deleted.In an interactive call, count is the numeric prefix argument, andkillp is the unprocessed prefix argument. Therefore, if a prefixargument is supplied, the text is saved in the kill ring. If no prefixargument is supplied, then one character is deleted, but not saved inthe kill ring.The value returned is always nil. backward-delete-char-untabify-method — User Option: backward-delete-char-untabify-method This option specifies how backward-delete-char-untabify shoulddeal with whitespace. Possible values include untabify, thedefault, meaning convert a tab to many spaces and delete one;hungry, meaning delete all tabs and spaces before point withone command; all meaning delete all tabs, spaces and newlinesbefore point, and nil, meaning do nothing special forwhitespace characters. User-Level Deletion Commands This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs. delete-horizontal-space — Command: delete-horizontal-space &optional backward-only deleting whitespaceThis function deletes all spaces and tabs around point. It returnsnil.If backward-only is non-nil, the function deletesspaces and tabs before point, but not after point.In the following examples, we call delete-horizontal-space fourtimes, once on each line, with point between the second and thirdcharacters on the line each time. ---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ---------- delete-indentation — Command: delete-indentation &optional join-following-p This function joins the line point is on to the previous line, deletingany whitespace at the join and in some cases replacing it with onespace. If join-following-p is non-nil,delete-indentation joins this line to the following lineinstead. The function returns nil.If there is a fill prefix, and the second of the lines being joinedstarts with the prefix, then delete-indentation deletes thefill prefix before joining the lines. See .In the example below, point is located on the line starting‘events’, and it makes no difference if there are trailing spacesin the preceding line. ---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ---------- After the lines are joined, the function fixup-whitespace isresponsible for deciding whether to leave a space at the junction. fixup-whitespace — Command: fixup-whitespace This function replaces all the horizontal whitespace surrounding pointwith either one space or no space, according to the context. Itreturns nil.At the beginning or end of a line, the appropriate amount of space isnone. Before a character with close parenthesis syntax, or after acharacter with open parenthesis or expression-prefix syntax, no space isalso appropriate. Otherwise, one space is appropriate. See .In the example below, fixup-whitespace is called the first timewith point before the word ‘spaces’ in the first line. For thesecond invocation, point is directly after the ‘(’. ---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ---------- just-one-space — Command: just-one-space &optional n This command replaces any spaces and tabs around point with a singlespace, or n spaces if n is specified. It returnsnil. delete-blank-lines — Command: delete-blank-lines This function deletes blank lines surrounding point. If point is on ablank line with one or more blank lines before or after it, then all butone of them are deleted. If point is on an isolated blank line, then itis deleted. If point is on a nonblank line, the command deletes allblank lines immediately following it.A blank line is defined as a line containing only tabs and spaces.delete-blank-lines returns nil. The Kill Ring kill ring Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have ‘kill-’ in their name. By contrast, the functions whose names start with ‘delete-’ normally do not save text for yanking (though they can still be undone); these are “deletion” functions. Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See . Killed text is saved for later yanking in the kill ring. This is a list that holds a number of recent kills, not just the last text kill. We call this a “ring” because yanking treats it as having elements in a cyclic order. The list is kept in the variable kill-ring, and can be operated on with the usual functions for lists; there are also specialized functions, described in this section, that treat it as a ring. Some people think this use of the word “kill” is unfortunate, since it refers to operations that specifically do not destroy the entities “killed.” This is in sharp contrast to ordinary life, in which death is permanent and “killed” entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term “cut ring” makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now. Kill Ring Concepts The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this: ("some text" "a different piece of text" "even older text") When the list reaches kill-ring-max entries in length, adding a new entry automatically deletes the last entry. When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one. For yanking, one entry in the kill ring is designated the “front” of the ring. Some yank commands “rotate” the ring by designating a different element as the “front.” But this virtual rotation doesn't change the list itself—the most recent entry always comes first in the list. Functions for Killing kill-region is the usual subroutine for killing text. Any command that calls this function is a “kill command” (and should probably have ‘kill’ in its name). kill-region puts the newly killed text in a new element at the beginning of the kill ring or adds it to the most recent element. It determines automatically (using last-command) whether the previous command was a kill command, and if so appends the killed text to the most recent entry. kill-region — Command: kill-region start end &optional yank-handler This function kills the text in the region defined by start andend. The text is deleted but saved in the kill ring, along withits text properties. The value is always nil.In an interactive call, start and end are point andthe mark. If the buffer or text is read-only, kill-region modifies the killring just the same, then signals an error without modifying the buffer.This is convenient because it lets the user use a series of killcommands to copy text from a read-only buffer into the kill ring.If yank-handler is non-nil, this puts that value ontothe string of killed text, as a yank-handler text property.See . Note that if yank-handler is nil, anyyank-handler properties present on the killed text are copiedonto the kill ring, like other text properties. kill-read-only-ok — User Option: kill-read-only-ok If this option is non-nil, kill-region does not signal anerror if the buffer or text is read-only. Instead, it simply returns,updating the kill ring but not changing the buffer. copy-region-as-kill — Command: copy-region-as-kill start end This command saves the region defined by start and end onthe kill ring (including text properties), but does not delete the textfrom the buffer. It returns nil.The command does not set this-command to kill-region, so asubsequent kill command does not append to the same kill ring entry.Don't call copy-region-as-kill in Lisp programs unless you aim tosupport Emacs 18. For newer Emacs versions, it is better to usekill-new or kill-append instead. See . Yanking Yanking means inserting text from the kill ring, but it does not insert the text blindly. Yank commands and some other commands use insert-for-yank to perform special processing on the text that they copy into the buffer. insert-for-yank — Function: insert-for-yank string This function normally works like insert except that it doesn'tinsert the text properties in the yank-excluded-propertieslist. However, if any part of string has a non-nilyank-handler text property, that property can do variousspecial processing on that part of the text being inserted. insert-buffer-substring-as-yank — Function: insert-buffer-substring-as-yank buf &optional start end This function resembles insert-buffer-substring except that itdoesn't insert the text properties in theyank-excluded-properties list. You can put a yank-handler text property on all or part of the text to control how it will be inserted if it is yanked. The insert-for-yank function looks for that property. The property value must be a list of one to four elements, with the following format (where elements after the first may be omitted): (function param noexclude undo) Here is what the elements do: function When function is present and non-nil, it is called instead ofinsert to insert the string. function takes oneargument—the string to insert. param If param is present and non-nil, it replaces string(or the part of string being processed) as the object passed tofunction (or insert); for example, if function isyank-rectangle, param should be a list of strings toinsert as a rectangle. noexclude If noexclude is present and non-nil, the normal removal of theyank-excluded-properties is not performed; instead function isresponsible for removing those properties. This may be necessaryif function adjusts point before or after inserting the object. undo If undo is present and non-nil, it is a function that will becalled by yank-pop to undo the insertion of the current object.It is called with two arguments, the start and end of the currentregion. function can set yank-undo-function to overridethe undo value. Functions for Yanking This section describes higher-level commands for yanking, which are intended primarily for the user but useful also in Lisp programs. Both yank and yank-pop honor the yank-excluded-properties variable and yank-handler text property (see ). yank — Command: yank &optional arg inserting killed textThis command inserts before point the text at the front of thekill ring. It positions the mark at the beginning of that text, andpoint at the end.If arg is a non-nil list (which occurs interactively whenthe user types C-u with no digits), then yank inserts thetext as described above, but puts point before the yanked text andputs the mark after it.If arg is a number, then yank inserts the argthmost recently killed text—the argth element of the kill ringlist, counted cyclically from the front, which is considered thefirst element for this purpose.yank does not alter the contents of the kill ring, unless itused text provided by another program, in which case it pushes that textonto the kill ring. However if arg is an integer different fromone, it rotates the kill ring to place the yanked string at the front.yank returns nil. yank-pop — Command: yank-pop &optional arg This command replaces the just-yanked entry from the kill ring with adifferent entry from the kill ring.This is allowed only immediately after a yank or anotheryank-pop. At such a time, the region contains text that was justinserted by yanking. yank-pop deletes that text and inserts inits place a different piece of killed text. It does not add the deletedtext to the kill ring, since it is already in the kill ring somewhere.It does however rotate the kill ring to place the newly yanked string atthe front.If arg is nil, then the replacement text is the previouselement of the kill ring. If arg is numeric, the replacement isthe argth previous kill. If arg is negative, a more recentkill is the replacement.The sequence of kills in the kill ring wraps around, so that after theoldest one comes the newest one, and before the newest one goes theoldest.The return value is always nil. yank-undo-function — Variable: yank-undo-function If this variable is non-nil, the function yank-pop usesits value instead of delete-region to delete the textinserted by the previous yank oryank-pop command. The value must be a function of twoarguments, the start and end of the current region.The function insert-for-yank automatically sets this variableaccording to the undo element of the yank-handlertext property, if there is one. Low-Level Kill Ring These functions and variables provide access to the kill ring at a lower level, but still convenient for use in Lisp programs, because they take care of interaction with window system selections (see ). current-kill — Function: current-kill n &optional do-not-move The function current-kill rotates the yanking pointer, whichdesignates the “front” of the kill ring, by n places (from newerkills to older ones), and returns the text at that place in the ring.If the optional second argument do-not-move is non-nil,then current-kill doesn't alter the yanking pointer; it justreturns the nth kill, counting from the current yanking pointer.If n is zero, indicating a request for the latest kill,current-kill calls the value ofinterprogram-paste-function (documented below) beforeconsulting the kill ring. If that value is a function and calling itreturns a string, current-kill pushes that string onto the killring and returns it. It also sets the yanking pointer to point tothat new entry, regardless of the value of do-not-move.Otherwise, current-kill does not treat a zero value for nspecially: it returns the entry pointed at by the yanking pointer anddoes not move the yanking pointer. kill-new — Function: kill-new string &optional replace yank-handler This function pushes the text string onto the kill ring andmakes the yanking pointer point to it. It discards the oldest entryif appropriate. It also invokes the value ofinterprogram-cut-function (see below).If replace is non-nil, then kill-new replaces thefirst element of the kill ring with string, rather than pushingstring onto the kill ring.If yank-handler is non-nil, this puts that value ontothe string of killed text, as a yank-handler property.See . Note that if yank-handler is nil, thenkill-new copies any yank-handler properties present onstring onto the kill ring, as it does with other text properties. kill-append — Function: kill-append string before-p &optional yank-handler This function appends the text string to the first entry in thekill ring and makes the yanking pointer point to the combined entry.Normally string goes at the end of the entry, but ifbefore-p is non-nil, it goes at the beginning. Thisfunction also invokes the value of interprogram-cut-function(see below). This handles yank-handler just likekill-new, except that if yank-handler is different fromthe yank-handler property of the first entry of the kill ring,kill-append pushes the concatenated string onto the kill ring,instead of replacing the original first entry with it. interprogram-paste-function — Variable: interprogram-paste-function This variable provides a way of transferring killed text from otherprograms, when you are using a window system. Its value should benil or a function of no arguments.If the value is a function, current-kill calls it to get the“most recent kill.” If the function returns a non-nil value,then that value is used as the “most recent kill.” If it returnsnil, then the front of the kill ring is used.The normal use of this hook is to get the window system's primaryselection as the most recent kill, even if the selection belongs toanother application. See . interprogram-cut-function — Variable: interprogram-cut-function This variable provides a way of communicating killed text to otherprograms, when you are using a window system. Its value should benil or a function of one required and one optional argument.If the value is a function, kill-new and kill-append callit with the new first element of the kill ring as the first argument.The second, optional, argument has the same meaning as the pushargument to x-set-cut-buffer (see ) and only affects the second and later cut buffers.The normal use of this hook is to set the window system's primaryselection (and first cut buffer) from the newly killed text.See . Internals of the Kill Ring The variable kill-ring holds the kill ring contents, in the form of a list of strings. The most recent kill is always at the front of the list. The kill-ring-yank-pointer variable points to a link in the kill ring list, whose car is the text to yank next. We say it identifies the “front” of the ring. Moving kill-ring-yank-pointer to a different link is called rotating the kill ring. We call the kill ring a “ring” because the functions that move the yank pointer wrap around from the end of the list to the beginning, or vice-versa. Rotation of the kill ring is virtual; it does not change the value of kill-ring. Both kill-ring and kill-ring-yank-pointer are Lisp variables whose values are normally lists. The word “pointer” in the name of the kill-ring-yank-pointer indicates that the variable's purpose is to identify one element of the list for use by the next yank command. The value of kill-ring-yank-pointer is always eq to one of the links in the kill ring list. The element it identifies is the car of that link. Kill commands, which change the kill ring, also set this variable to the value of kill-ring. The effect is to rotate the ring so that the newly killed text is at the front. Here is a diagram that shows the variable kill-ring-yank-pointer pointing to the second entry in the kill ring ("some text" "a different piece of text" "yet older text"). kill-ring ---- kill-ring-yank-pointer | | | v | --- --- --- --- --- --- --> | | |------> | | |--> | | |--> nil --- --- --- --- --- --- | | | | | | | | -->"yet older text" | | | --> "a different piece of text" | --> "some text" This state of affairs might occur after C-y (yank) immediately followed by M-y (yank-pop). kill-ring — Variable: kill-ring This variable holds the list of killed text sequences, most recentlykilled first. kill-ring-yank-pointer — Variable: kill-ring-yank-pointer This variable's value indicates which element of the kill ring is at the“front” of the ring for yanking. More precisely, the value is a tailof the value of kill-ring, and its car is the kill stringthat C-y should yank. kill-ring-max — User Option: kill-ring-max The value of this variable is the maximum length to which the killring can grow, before elements are thrown away at the end. The defaultvalue for kill-ring-max is 60. Undo redo Most buffers have an undo list, which records all changes made to the buffer's text so that they can be undone. (The buffers that don't have one are usually special-purpose buffers for which Emacs assumes that undoing is not useful. In particular, any buffer whose name begins with a space has its undo recording off by default; see .) All the primitives that modify the text in the buffer automatically add elements to the front of the undo list, which is in the variable buffer-undo-list. buffer-undo-list — Variable: buffer-undo-list This buffer-local variable's value is the undo list of the currentbuffer. A value of t disables the recording of undo information. Here are the kinds of elements an undo list can have: position This kind of element records a previous value of point; undoing thiselement moves point to position. Ordinary cursor motion does notmake any sort of undo record, but deletion operations use these entriesto record where point was before the command. (beg . end) This kind of element indicates how to delete text that was inserted.Upon insertion, the text occupied the range beg–end in thebuffer. (text . position) This kind of element indicates how to reinsert text that was deleted.The deleted text itself is the string text. The place toreinsert it is (abs position). If position ispositive, point was at the beginning of the deleted text, otherwise itwas at the end. (t high . low) This kind of element indicates that an unmodified buffer becamemodified. The elements high and low are two integers, eachrecording 16 bits of the visited file's modification time as of when itwas previously visited or saved. primitive-undo uses thosevalues to determine whether to mark the buffer as unmodified once again;it does so only if the file's modification time matches those numbers. (nil property value beg . end) This kind of element records a change in a text property.Here's how you might undo the change: (put-text-property beg end property value) (marker . adjustment) This kind of element records the fact that the marker marker wasrelocated due to deletion of surrounding text, and that it movedadjustment character positions. Undoing this element movesmarker − adjustment characters. (apply funname . args) This is an extensible undo item, which is undone by callingfunname with arguments args. (apply delta beg end funname . args) This is an extensible undo item, which records a change limited to therange beg to end, which increased the size of the bufferby delta. It is undone by calling funname with argumentsargs.This kind of element enables undo limited to a region to determinewhether the element pertains to that region. nil This element is a boundary. The elements between two boundaries arecalled a change group; normally, each change group corresponds toone keyboard command, and undo commands normally undo an entire group asa unit. undo-boundary — Function: undo-boundary This function places a boundary element in the undo list. The undocommand stops at such a boundary, and successive undo commands undoto earlier and earlier boundaries. This function returns nil.The editor command loop automatically creates an undo boundary beforeeach key sequence is executed. Thus, each undo normally undoes theeffects of one command. Self-inserting input characters are anexception. The command loop makes a boundary for the first suchcharacter; the next 19 consecutive self-inserting input characters donot make boundaries, and then the 20th does, and so on as long asself-inserting characters continue.All buffer modifications add a boundary whenever the previous undoablechange was made in some other buffer. This is to ensure thateach command makes a boundary in each buffer where it makes changes.Calling this function explicitly is useful for splitting the effects ofa command into more than one unit. For example, query-replacecalls undo-boundary after each replacement, so that the user canundo individual replacements one by one. undo-in-progress — Variable: undo-in-progress This variable is normally nil, but the undo commands bind it tot. This is so that various kinds of change hooks can tell whenthey're being called for the sake of undoing. primitive-undo — Function: primitive-undo count list This is the basic function for undoing elements of an undo list.It undoes the first count elements of list, returningthe rest of list.primitive-undo adds elements to the buffer's undo list when itchanges the buffer. Undo commands avoid confusion by saving the undolist value at the beginning of a sequence of undo operations. Then theundo operations use and update the saved value. The new elements addedby undoing are not part of this saved value, so they don't interfere withcontinuing to undo.This function does not bind undo-in-progress. Maintaining Undo Lists This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big. Recording of undo information in a newly created buffer is normally enabled to start with; but if the buffer name starts with a space, the undo recording is initially disabled. You can explicitly enable or disable undo recording with the following two functions, or by setting buffer-undo-list yourself. buffer-enable-undo — Command: buffer-enable-undo &optional buffer-or-name This command enables recording undo information for bufferbuffer-or-name, so that subsequent changes can be undone. If noargument is supplied, then the current buffer is used. This functiondoes nothing if undo recording is already enabled in the buffer. Itreturns nil.In an interactive call, buffer-or-name is the current buffer.You cannot specify any other buffer. buffer-disable-undo — Command: buffer-disable-undo &optional buffer-or-name disabling undoThis function discards the undo list of buffer-or-name, and disablesfurther recording of undo information. As a result, it is no longerpossible to undo either previous changes or any subsequent changes. Ifthe undo list of buffer-or-name is already disabled, this functionhas no effect.This function returns nil. As editing continues, undo lists get longer and longer. To prevent them from using up all available memory space, garbage collection trims them back to size limits you can set. (For this purpose, the “size” of an undo list measures the cons cells that make up the list, plus the strings of deleted text.) Three variables control the range of acceptable sizes: undo-limit, undo-strong-limit and undo-outer-limit. In these variables, size is counted as the number of bytes occupied, which includes both saved text and other data. undo-limit — User Option: undo-limit This is the soft limit for the acceptable size of an undo list. Thechange group at which this size is exceeded is the last one kept. undo-strong-limit — User Option: undo-strong-limit This is the upper limit for the acceptable size of an undo list. Thechange group at which this size is exceeded is discarded itself (alongwith all older change groups). There is one exception: the very latestchange group is only discarded if it exceeds undo-outer-limit. undo-outer-limit — User Option: undo-outer-limit If at garbage collection time the undo info for the current commandexceeds this limit, Emacs discards the info and displays a warning.This is a last ditch limit to prevent memory overflow. undo-ask-before-discard — User Option: undo-ask-before-discard If this variable is non-nil, when the undo info exceedsundo-outer-limit, Emacs asks in the echo area whether todiscard the info. The default value is nil, which means todiscard it automatically.This option is mainly intended for debugging. Garbage collection isinhibited while the question is asked, which means that Emacs mightleak memory if the user waits too long before answering the question. Filling filling text Filling means adjusting the lengths of lines (by moving the line breaks) so that they are nearly (but no greater than) a specified maximum width. Additionally, lines can be justified, which means inserting spaces to make the left and/or right margins line up precisely. The width is controlled by the variable fill-column. For ease of reading, lines should be no longer than 70 or so columns. You can use Auto Fill mode (see ) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly. Most of the commands in this section return values that are not meaningful. All the functions that do filling take note of the current left margin, current right margin, and current justification style (see ). If the current justification style is none, the filling functions don't actually do anything. Several of the filling functions have an argument justify. If it is non-nil, that requests some kind of justification. It can be left, right, full, or center, to request a specific style of justification. If it is t, that means to use the current justification style for this part of the text (see current-justification, below). Any other value is treated as full. When you call the filling functions interactively, using a prefix argument implies the value full for justify. fill-paragraph — Command: fill-paragraph justify This command fills the paragraph at or after point. Ifjustify is non-nil, each line is justified as well.It uses the ordinary paragraph motion commands to find paragraphboundaries. See See section ``Paragraphs'' in The GNU Emacs Manual. fill-region — Command: fill-region start end &optional justify nosqueeze to-eop This command fills each of the paragraphs in the region from startto end. It justifies as well if justify isnon-nil.If nosqueeze is non-nil, that means to leave whitespaceother than line breaks untouched. If to-eop is non-nil,that means to keep filling to the end of the paragraph—or the next hardnewline, if use-hard-newlines is enabled (see below).The variable paragraph-separate controls how to distinguishparagraphs. See . fill-individual-paragraphs — Command: fill-individual-paragraphs start end &optional justify citation-regexp This command fills each paragraph in the region according to itsindividual fill prefix. Thus, if the lines of a paragraph were indentedwith spaces, the filled paragraph will remain indented in the samefashion.The first two arguments, start and end, are the beginningand end of the region to be filled. The third and fourth arguments,justify and citation-regexp, are optional. Ifjustify is non-nil, the paragraphs are justified aswell as filled. If citation-regexp is non-nil, it means thefunction is operating on a mail message and therefore should not fillthe header lines. If citation-regexp is a string, it is used asa regular expression; if it matches the beginning of a line, that lineis treated as a citation marker.Ordinarily, fill-individual-paragraphs regards each change inindentation as starting a new paragraph. Iffill-individual-varying-indent is non-nil, then onlyseparator lines separate paragraphs. That mode can handle indentedparagraphs with additional indentation on the first line. fill-individual-varying-indent — User Option: fill-individual-varying-indent This variable alters the action of fill-individual-paragraphs asdescribed above. fill-region-as-paragraph — Command: fill-region-as-paragraph start end &optional justify nosqueeze squeeze-after This command considers a region of text as a single paragraph and fillsit. If the region was made up of many paragraphs, the blank linesbetween paragraphs are removed. This function justifies as well asfilling when justify is non-nil.If nosqueeze is non-nil, that means to leave whitespaceother than line breaks untouched. If squeeze-after isnon-nil, it specifies a position in the region, and means don'tcanonicalize spaces before that position.In Adaptive Fill mode, this command calls fill-context-prefix tochoose a fill prefix by default. See . justify-current-line — Command: justify-current-line &optional how eop nosqueeze This command inserts spaces between the words of the current line sothat the line ends exactly at fill-column. It returnsnil.The argument how, if non-nil specifies explicitly the styleof justification. It can be left, right, full,center, or none. If it is t, that means to dofollow specified justification style (see current-justification,below). nil means to do full justification.If eop is non-nil, that means do only left-justificationif current-justification specifies full justification. This isused for the last line of a paragraph; even if the paragraph as awhole is fully justified, the last line should not be.If nosqueeze is non-nil, that means do not change interiorwhitespace. default-justification — User Option: default-justification This variable's value specifies the style of justification to use fortext that doesn't specify a style with a text property. The possiblevalues are left, right, full, center, ornone. The default value is left. current-justification — Function: current-justification This function returns the proper justification style to use for fillingthe text around point.This returns the value of the justification text property atpoint, or the variable default-justification if there is no suchtext property. However, it returns nil rather than noneto mean “don't justify”. sentence-end-double-space — User Option: sentence-end-double-space If this variable is non-nil, a period followed by just one spacedoes not count as the end of a sentence, and the filling functionsavoid breaking the line at such a place. sentence-end-without-period — User Option: sentence-end-without-period If this variable is non-nil, a sentence can end without aperiod. This is used for languages like Thai, where sentences endwith a double space but without a period. sentence-end-without-space — User Option: sentence-end-without-space If this variable is non-nil, it should be a string ofcharacters that can end a sentence without following spaces. fill-paragraph-function — Variable: fill-paragraph-function This variable provides a way for major modes to override the filling ofparagraphs. If the value is non-nil, fill-paragraph callsthis function to do the work. If the function returns a non-nilvalue, fill-paragraph assumes the job is done, and immediatelyreturns that value.The usual use of this feature is to fill comments in programminglanguage modes. If the function needs to fill a paragraph in the usualway, it can do so as follows: (let ((fill-paragraph-function nil)) (fill-paragraph arg)) use-hard-newlines — Variable: use-hard-newlines If this variable is non-nil, the filling functions do not deletenewlines that have the hard text property. These “hardnewlines” act as paragraph separators. Margins for Filling fill-prefix — User Option: fill-prefix This buffer-local variable, if non-nil, specifies a string oftext that appears at the beginning of normal text lines and should bedisregarded when filling them. Any line that fails to start with thefill prefix is considered the start of a paragraph; so is any linethat starts with the fill prefix followed by additional whitespace.Lines that start with the fill prefix but no additional whitespace areordinary text lines that can be filled together. The resulting filledlines also start with the fill prefix.The fill prefix follows the left margin whitespace, if any. fill-column — User Option: fill-column This buffer-local variable specifies the maximum width of filled lines.Its value should be an integer, which is a number of columns. All thefilling, justification, and centering commands are affected by thisvariable, including Auto Fill mode (see ).As a practical matter, if you are writing text for other people toread, you should set fill-column to no more than 70. Otherwisethe line will be too long for people to read comfortably, and this canmake the text seem clumsy. default-fill-column — Variable: default-fill-column The value of this variable is the default value for fill-column inbuffers that do not override it. This is the same as(default-value 'fill-column).The default value for default-fill-column is 70. set-left-margin — Command: set-left-margin from to margin This sets the left-margin property on the text from from toto to the value margin. If Auto Fill mode is enabled, thiscommand also refills the region to fit the new margin. set-right-margin — Command: set-right-margin from to margin This sets the right-margin property on the text from fromto to to the value margin. If Auto Fill mode is enabled,this command also refills the region to fit the new margin. current-left-margin — Function: current-left-margin This function returns the proper left margin value to use for fillingthe text around point. The value is the sum of the left-marginproperty of the character at the start of the current line (or zero ifnone), and the value of the variable left-margin. current-fill-column — Function: current-fill-column This function returns the proper fill column value to use for fillingthe text around point. The value is the value of the fill-columnvariable, minus the value of the right-margin property of thecharacter after point. move-to-left-margin — Command: move-to-left-margin &optional n force This function moves point to the left margin of the current line. Thecolumn moved to is determined by calling the functioncurrent-left-margin. If the argument n is non-nil,move-to-left-margin moves forward n−1 lines first.If force is non-nil, that says to fix the line'sindentation if that doesn't match the left margin value. delete-to-left-margin — Function: delete-to-left-margin &optional from to This function removes left margin indentation from the text betweenfrom and to. The amount of indentation to delete isdetermined by calling current-left-margin. In no case does thisfunction delete non-whitespace. If from and to are omitted,they default to the whole buffer. indent-to-left-margin — Function: indent-to-left-margin This function adjusts the indentation at the beginning of the currentline to the value specified by the variable left-margin. (Thatmay involve either inserting or deleting whitespace.) This functionis value of indent-line-function in Paragraph-Indent Text mode. left-margin — Variable: left-margin This variable specifies the base left margin column. In Fundamentalmode, C-j indents to this column. This variable automaticallybecomes buffer-local when set in any fashion. fill-nobreak-predicate — Variable: fill-nobreak-predicate This variable gives major modes a way to specify not to break a lineat certain places. Its value should be a list of functions. Wheneverfilling considers breaking the line at a certain place in the buffer,it calls each of these functions with no arguments and with pointlocated at that place. If any of the functions returnsnon-nil, then the line won't be broken there. Adaptive Fill Mode When Adaptive Fill Mode is enabled, Emacs determines the fill prefix automatically from the text in each paragraph being filled rather than using a predetermined value. During filling, this fill prefix gets inserted at the start of the second and subsequent lines of the paragraph as described in , and in . adaptive-fill-mode — User Option: adaptive-fill-mode Adaptive Fill mode is enabled when this variable is non-nil.It is t by default. fill-context-prefix — Function: fill-context-prefix from to This function implements the heart of Adaptive Fill mode; it chooses afill prefix based on the text between from and to,typically the start and end of a paragraph. It does this by lookingat the first two lines of the paragraph, based on the variablesdescribed below. Usually, this function returns the fill prefix, a string. However,before doing this, the function makes a final check (not speciallymentioned in the following) that a line starting with this prefixwouldn't look like the start of a paragraph. Should this happen, thefunction signals the anomaly by returning nil instead.In detail, fill-context-prefix does this: It takes a candidate for the fill prefix from the first line—ittries first the function in adaptive-fill-function (if any),then the regular expression adaptive-fill-regexp (see below).The first non-nil result of these, or the empty string ifthey're both nil, becomes the first line's candidate. If the paragraph has as yet only one line, the function tests thevalidity of the prefix candidate just found. The function thenreturns the candidate if it's valid, or a string of spaces otherwise.(see the description of adaptive-fill-first-line-regexp below). When the paragraph already has two lines, the function next looks fora prefix candidate on the second line, in just the same way it did forthe first line. If it doesn't find one, it returns nil. The function now compares the two candidate prefixes heuristically: ifthe non-whitespace characters in the line 2 candidate occur in thesame order in the line 1 candidate, the function returns the line 2candidate. Otherwise, it returns the largest initial substring whichis common to both candidates (which might be the empty string). adaptive-fill-regexp — User Option: adaptive-fill-regexp Adaptive Fill mode matches this regular expression against the textstarting after the left margin whitespace (if any) on a line; thecharacters it matches are that line's candidate for the fill prefix.The default value matches whitespace with certain punctuationcharacters intermingled. adaptive-fill-first-line-regexp — User Option: adaptive-fill-first-line-regexp Used only in one-line paragraphs, this regular expression acts as anadditional check of the validity of the one available candidate fillprefix: the candidate must match this regular expression, or matchcomment-start-skip. If it doesn't, fill-context-prefixreplaces the candidate with a string of spaces “of the same width”as it.The default value of this variable is "\\`[ \t]*\\'", whichmatches only a string of whitespace. The effect of this default is toforce the fill prefixes found in one-line paragraphs always to be purewhitespace. adaptive-fill-function — User Option: adaptive-fill-function You can specify more complex ways of choosing a fill prefixautomatically by setting this variable to a function. The function iscalled with point after the left margin (if any) of a line, and itmust preserve point. It should return either “that line's” fillprefix or nil, meaning it has failed to determine a prefix. Auto Filling filling, automatic Auto Fill mode Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see . Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See . auto-fill-function — Variable: auto-fill-function The value of this buffer-local variable should be a function (of noarguments) to be called after self-inserting a character from the tableauto-fill-chars. It may be nil, in which case nothingspecial is done in that case.The value of auto-fill-function is do-auto-fill whenAuto-Fill mode is enabled. That is a function whose sole purpose is toimplement the usual strategy for breaking a line. In older Emacs versions, this variable was named auto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed to auto-fill-function in version 19. normal-auto-fill-function — Variable: normal-auto-fill-function This variable specifies the function to use forauto-fill-function, if and when Auto Fill is turned on. Majormodes can set buffer-local values for this variable to alter how AutoFill works. auto-fill-chars — Variable: auto-fill-chars A char table of characters which invoke auto-fill-function whenself-inserted—space and newline in most language environments. Theyhave an entry t in the table. Sorting Text sorting text The sorting functions described in this section all rearrange text in a buffer. This is in contrast to the function sort, which rearranges the order of the elements of a list (see ). The values returned by these functions are not meaningful. sort-subr — Function: sort-subr reverse nextrecfun endrecfun &optional startkeyfun endkeyfun predicate This function is the general text-sorting routine that subdivides abuffer into records and then sorts them. Most of the commands in thissection use this function.To understand how sort-subr works, consider the whole accessibleportion of the buffer as being divided into disjoint pieces calledsort records. The records may or may not be contiguous, but theymust not overlap. A portion of each sort record (perhaps all of it) isdesignated as the sort key. Sorting rearranges the records in order bytheir sort keys.Usually, the records are rearranged in order of ascending sort key.If the first argument to the sort-subr function, reverse,is non-nil, the sort records are rearranged in order ofdescending sort key.The next four arguments to sort-subr are functions that arecalled to move point across a sort record. They are called many timesfrom within sort-subr. nextrecfun is called with point at the end of a record. Thisfunction moves point to the start of the next record. The first recordis assumed to start at the position of point when sort-subr iscalled. Therefore, you should usually move point to the beginning ofthe buffer before calling sort-subr.This function can indicate there are no more sort records by leavingpoint at the end of the buffer. endrecfun is called with point within a record. It moves point tothe end of the record. startkeyfun is called to move point from the start of a record tothe start of the sort key. This argument is optional; if it is omitted,the whole record is the sort key. If supplied, the function shouldeither return a non-nil value to be used as the sort key, orreturn nil to indicate that the sort key is in the bufferstarting at point. In the latter case, endkeyfun is called tofind the end of the sort key. endkeyfun is called to move point from the start of the sort keyto the end of the sort key. This argument is optional. Ifstartkeyfun returns nil and this argument is omitted (ornil), then the sort key extends to the end of the record. Thereis no need for endkeyfun if startkeyfun returns anon-nil value. The argument predicate is the function to use to compare keys.If keys are numbers, it defaults to <; otherwise it defaults tostring<.As an example of sort-subr, here is the complete functiondefinition for sort-lines: ;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order),\ BEG and END (region to sort). The variable `sort-fold-case' determines\ whether alphabetic case affects the sort order." (interactive "P\nr") (save-excursion (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (let ((inhibit-field-text-motion t)) (sort-subr reverse 'forward-line 'end-of-line))))) Here forward-line moves point to the start of the next record,and end-of-line moves point to the end of record. We do not passthe arguments startkeyfun and endkeyfun, because the entirerecord is used as the sort key.The sort-paragraphs function is very much the same, except thatits sort-subr call looks like this: (sort-subr reverse (function (lambda () (while (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1)))) 'forward-paragraph) Markers pointing into any sort records are left with no usefulposition after sort-subr returns. sort-fold-case — User Option: sort-fold-case If this variable is non-nil, sort-subr and the otherbuffer sorting functions ignore case when comparing strings. sort-regexp-fields — Command: sort-regexp-fields reverse record-regexp key-regexp start end This command sorts the region between start and endalphabetically as specified by record-regexp and key-regexp.If reverse is a negative integer, then sorting is in reverseorder.Alphabetical sorting means that two sort keys are compared bycomparing the first characters of each, the second characters of each,and so on. If a mismatch is found, it means that the sort keys areunequal; the sort key whose character is less at the point of firstmismatch is the lesser sort key. The individual characters are comparedaccording to their numerical character codes in the Emacs character set.The value of the record-regexp argument specifies how to dividethe buffer into sort records. At the end of each record, a search isdone for this regular expression, and the text that matches it is takenas the next record. For example, the regular expression ‘^.+$’,which matches lines with at least one character besides a newline, wouldmake each such line into a sort record. See , fora description of the syntax and meaning of regular expressions.The value of the key-regexp argument specifies what part of eachrecord is the sort key. The key-regexp could match the wholerecord, or only a part. In the latter case, the rest of the record hasno effect on the sorted order of records, but it is carried along whenthe record moves to its new position.The key-regexp argument can refer to the text matched by asubexpression of record-regexp, or it can be a regular expressionon its own.If key-regexp is: ‘\digit’ then the text matched by the digitth ‘\(...\)’ parenthesisgrouping in record-regexp is the sort key. ‘\&’ then the whole record is the sort key. a regular expression then sort-regexp-fields searches for a match for the regularexpression within the record. If such a match is found, it is the sortkey. If there is no match for key-regexp within a record thenthat record is ignored, which means its position in the buffer is notchanged. (The other records may move around it.) For example, if you plan to sort all the lines in the region by thefirst word on each line starting with the letter ‘f’, you shouldset record-regexp to ‘^.*$’ and set key-regexp to‘\<f\w*\>’. The resulting expression looks like this: (sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end)) If you call sort-regexp-fields interactively, it prompts forrecord-regexp and key-regexp in the minibuffer. sort-lines — Command: sort-lines reverse start end This command alphabetically sorts lines in the region betweenstart and end. If reverse is non-nil, the sortis in reverse order. sort-paragraphs — Command: sort-paragraphs reverse start end This command alphabetically sorts paragraphs in the region betweenstart and end. If reverse is non-nil, the sortis in reverse order. sort-pages — Command: sort-pages reverse start end This command alphabetically sorts pages in the region betweenstart and end. If reverse is non-nil, the sortis in reverse order. sort-fields — Command: sort-fields field start end This command sorts lines in the region between start andend, comparing them alphabetically by the fieldth fieldof each line. Fields are separated by whitespace and numbered startingfrom 1. If field is negative, sorting is by the−fieldth field from the end of the line. This commandis useful for sorting tables. sort-numeric-fields — Command: sort-numeric-fields field start end This command sorts lines in the region between start andend, comparing them numerically by the fieldth field ofeach line. Fields are separated by whitespace and numbered startingfrom 1. The specified field must contain a number in each line of theregion. Numbers starting with 0 are treated as octal, and numbersstarting with ‘0x’ are treated as hexadecimal.If field is negative, sorting is by the−fieldth field from the end of the line. Thiscommand is useful for sorting tables. sort-numeric-base — User Option: sort-numeric-base This variable specifies the default radix forsort-numeric-fields to parse numbers. sort-columns — Command: sort-columns reverse &optional beg end This command sorts the lines in the region between beg andend, comparing them alphabetically by a certain range ofcolumns. The column positions of beg and end bound therange of columns to sort on.If reverse is non-nil, the sort is in reverse order.One unusual thing about this command is that the entire linecontaining position beg, and the entire line containing positionend, are included in the region sorted.Note that sort-columns rejects text that contains tabs, becausetabs could be split across the specified columns. Use M-xuntabify to convert tabs to spaces before sorting.When possible, this command actually works by calling the sortutility program. Counting Columns columns counting columns horizontal position The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line). These functions count each character according to the number of columns it occupies on the screen. This means control characters count as occupying 2 or 4 columns, depending upon the value of ctl-arrow, and tabs count as occupying a number of columns that depends on the value of tab-width and on the column where the tab begins. See . Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0. They also ignore overlays and text properties, aside from invisibility. current-column — Function: current-column This function returns the horizontal position of point, measured incolumns, counting from 0 at the left margin. The column position is thesum of the widths of all the displayed representations of the charactersbetween the start of the current line and point.For an example of using current-column, see the description ofcount-lines in . move-to-column — Function: move-to-column column &optional force This function moves point to column in the current line. Thecalculation of column takes into account the widths of thedisplayed representations of the characters between the start of theline and point.If column column is beyond the end of the line, point moves to theend of the line. If column is negative, point moves to thebeginning of the line.If it is impossible to move to column column because that is inthe middle of a multicolumn character such as a tab, point moves to theend of that character. However, if force is non-nil, andcolumn is in the middle of a tab, then move-to-columnconverts the tab into spaces so that it can move precisely to columncolumn. Other multicolumn characters can cause anomalies despiteforce, since there is no way to split them.The argument force also has an effect if the line isn't longenough to reach column column; if it is t, that means toadd whitespace at the end of the line to reach that column.If column is not an integer, an error is signaled.The return value is the column number actually moved to. Indentation indentation The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin. Indentation Primitives This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See , for related functions. current-indentation — Function: current-indentation This function returns the indentation of the current line, which isthe horizontal position of the first nonblank character. If thecontents are entirely blank, then this is the horizontal position of theend of the line. indent-to — Command: indent-to column &optional minimum This function indents from point with tabs and spaces until columnis reached. If minimum is specified and non-nil, then atleast that many spaces are inserted even if this requires going beyondcolumn. Otherwise the function does nothing if point is alreadybeyond column. The value is the column at which the insertedindentation ends.The inserted whitespace characters inherit text properties from thesurrounding text (usually, from the preceding text only). See . indent-tabs-mode — User Option: indent-tabs-mode If this variable is non-nil, indentation functions can inserttabs as well as spaces. Otherwise, they insert only spaces. Settingthis variable automatically makes it buffer-local in the current buffer. Indentation Controlled by Major Mode An important function of each major mode is to customize the TAB key to indent properly for the language being edited. This section describes the mechanism of the TAB key and how to control it. The functions in this section return unpredictable values. indent-line-function — Variable: indent-line-function This variable's value is the function to be used by TAB (andvarious commands) to indent the current line. The commandindent-according-to-mode does no more than call this function.In Lisp mode, the value is the symbol lisp-indent-line; in Cmode, c-indent-line; in Fortran mode, fortran-indent-line.The default value is indent-relative. indent-according-to-mode — Command: indent-according-to-mode This command calls the function in indent-line-function toindent the current line in a way appropriate for the current major mode. indent-for-tab-command — Command: indent-for-tab-command This command calls the function in indent-line-function to indentthe current line; however, if that function isindent-to-left-margin, insert-tab is called instead. (Thatis a trivial command that inserts a tab character.) newline-and-indent — Command: newline-and-indent This function inserts a newline, then indents the new line (the onefollowing the newline just inserted) according to the major mode.It does indentation by calling the current indent-line-function.In programming language modes, this is the same thing TAB does,but in some text modes, where TAB inserts a tab,newline-and-indent indents to the column specified byleft-margin. reindent-then-newline-and-indent — Command: reindent-then-newline-and-indent This command reindents the current line, inserts a newline at point,and then indents the new line (the one following the newline justinserted).This command does indentation on both lines according to the currentmajor mode, by calling the current value of indent-line-function.In programming language modes, this is the same thing TAB does,but in some text modes, where TAB inserts a tab,reindent-then-newline-and-indent indents to the column specifiedby left-margin. Indenting an Entire Region This section describes commands that indent all the lines in the region. They return unpredictable values. indent-region — Command: indent-region start end to-column This command indents each nonblank line starting between start(inclusive) and end (exclusive). If to-column isnil, indent-region indents each nonblank line by callingthe current mode's indentation function, the value ofindent-line-function.If to-column is non-nil, it should be an integerspecifying the number of columns of indentation; then this functiongives each line exactly that much indentation, by either adding ordeleting whitespace.If there is a fill prefix, indent-region indents each lineby making it start with the fill prefix. indent-region-function — Variable: indent-region-function The value of this variable is a function that can be used byindent-region as a short cut. It should take two arguments, thestart and end of the region. You should design the function sothat it will produce the same results as indenting the lines of theregion one by one, but presumably faster.If the value is nil, there is no short cut, andindent-region actually works line by line.A short-cut function is useful in modes such as C mode and Lisp mode,where the indent-line-function must scan from the beginning ofthe function definition: applying it to each line would be quadratic intime. The short cut can update the scan information as it moves throughthe lines indenting them; this takes linear time. In a mode whereindenting a line individually is fast, there is no need for a short cut.indent-region with a non-nil argument to-column hasa different meaning and does not use this variable. indent-rigidly — Command: indent-rigidly start end count This command indents all lines starting between start(inclusive) and end (exclusive) sideways by count columns.This “preserves the shape” of the affected region, moving it as arigid unit. Consequently, this command is useful not only for indentingregions of unindented text, but also for indenting regions of formattedcode.For example, if count is 3, this command adds 3 columns ofindentation to each of the lines beginning in the region specified.In Mail mode, C-c C-y (mail-yank-original) usesindent-rigidly to indent the text copied from the message beingreplied to. indent-code-rigidly — Function: indent-code-rigidly start end columns &optional nochange-regexp This is like indent-rigidly, except that it doesn't alter linesthat start within strings or comments.In addition, it doesn't alter a line if nochange-regexp matches atthe beginning of the line (if nochange-regexp is non-nil). Indentation Relative to Previous Lines This section describes two commands that indent the current line based on the contents of previous lines. indent-relative — Command: indent-relative &optional unindented-ok This command inserts whitespace at point, extending to the samecolumn as the next indent point of the previous nonblank line. Anindent point is a non-whitespace character following whitespace. Thenext indent point is the first one at a column greater than the currentcolumn of point. For example, if point is underneath and to the left ofthe first non-blank character of a line of text, it moves to that columnby inserting whitespace.If the previous nonblank line has no next indent point (i.e., none at agreat enough column position), indent-relative either doesnothing (if unindented-ok is non-nil) or callstab-to-tab-stop. Thus, if point is underneath and to the rightof the last column of a short line of text, this command ordinarilymoves point to the next tab stop by inserting whitespace.The return value of indent-relative is unpredictable.In the following example, point is at the beginning of the secondline: This line is indented twelve spaces. -!-The quick brown fox jumped. Evaluation of the expression (indent-relative nil) produces thefollowing: This line is indented twelve spaces. -!-The quick brown fox jumped. In this next example, point is between the ‘m’ and ‘p’ of‘jumped’: This line is indented twelve spaces. The quick brown fox jum-!-ped. Evaluation of the expression (indent-relative nil) produces thefollowing: This line is indented twelve spaces. The quick brown fox jum -!-ped. indent-relative-maybe — Command: indent-relative-maybe This command indents the current line like the previous nonblank line,by calling indent-relative with t as theunindented-ok argument. The return value is unpredictable.If the previous nonblank line has no indent points beyond the currentcolumn, this command does nothing. Adjustable “Tab Stops” tabs stops for indentation This section explains the mechanism for user-specified “tab stops” and the mechanisms that use and set them. The name “tab stops” is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see ). Note that the TAB character as input uses this tab stop feature only in a few major modes, such as Text mode. See See section ``Tab Stops'' in The GNU Emacs Manual. tab-to-tab-stop — Command: tab-to-tab-stop This command inserts spaces or tabs before point, up to the next tabstop column defined by tab-stop-list. It searches the list foran element greater than the current column number, and uses that elementas the column to indent to. It does nothing if no such element isfound. tab-stop-list — User Option: tab-stop-list This variable is the list of tab stop columns used bytab-to-tab-stops. The elements should be integers in increasingorder. The tab stop columns need not be evenly spaced.Use M-x edit-tab-stops to edit the location of tab stopsinteractively. Indentation-Based Motion Commands These commands, primarily for interactive use, act based on the indentation in the text. back-to-indentation — Command: back-to-indentation This command moves point to the first non-whitespace character in thecurrent line (which is the line in which point is located). It returnsnil. backward-to-indentation — Command: backward-to-indentation &optional arg This command moves point backward arg lines and then to thefirst nonblank character on that line. It returns nil.If arg is omitted or nil, it defaults to 1. forward-to-indentation — Command: forward-to-indentation &optional arg This command moves point forward arg lines and then to the firstnonblank character on that line. It returns nil.If arg is omitted or nil, it defaults to 1. Case Changes case conversion in buffers The case change commands described here work on text in the current buffer. See , for case conversion functions that work on strings and characters. See , for how to customize which characters are upper or lower case and how to convert them. capitalize-region — Command: capitalize-region start end This function capitalizes all words in the region defined bystart and end. To capitalize means to convert each word'sfirst character to upper case and convert the rest of each word to lowercase. The function returns nil.If one end of the region is in the middle of a word, the part of theword within the region is treated as an entire word.When capitalize-region is called interactively, start andend are point and the mark, with the smallest first. ---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ---------- downcase-region — Command: downcase-region start end This function converts all of the letters in the region defined bystart and end to lower case. The function returnsnil.When downcase-region is called interactively, start andend are point and the mark, with the smallest first. upcase-region — Command: upcase-region start end This function converts all of the letters in the region defined bystart and end to upper case. The function returnsnil.When upcase-region is called interactively, start andend are point and the mark, with the smallest first. capitalize-word — Command: capitalize-word count This function capitalizes count words after point, moving pointover as it does. To capitalize means to convert each word's firstcharacter to upper case and convert the rest of each word to lower case.If count is negative, the function capitalizes the−count previous words but does not move point. The valueis nil.If point is in the middle of a word, the part of the word before pointis ignored when moving forward. The rest is treated as an entire word.When capitalize-word is called interactively, count isset to the numeric prefix argument. downcase-word — Command: downcase-word count This function converts the count words after point to all lowercase, moving point over as it does. If count is negative, itconverts the −count previous words but does not move point.The value is nil.When downcase-word is called interactively, count is setto the numeric prefix argument. upcase-word — Command: upcase-word count This function converts the count words after point to all uppercase, moving point over as it does. If count is negative, itconverts the −count previous words but does not move point.The value is nil.When upcase-word is called interactively, count is set tothe numeric prefix argument. Text Properties text properties attributes of text properties of text Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see ). The properties belong to a particular character at a particular place, such as, the letter ‘T’ at the beginning of this sentence or the first ‘o’ in ‘foo’—if the same character occurs in two different places, the two occurrences in general have different properties. Each property has a name and a value. Both of these can be any Lisp object, but the name is normally a symbol. Typically each property name symbol is used for a particular purpose; for instance, the text property face specifies the faces for displaying the character (see ). The usual way to access the property list is to specify a name and ask what value corresponds to it. If a character has a category property, we call it the property category of the character. It should be a symbol. The properties of the symbol serve as defaults for the properties of the character. Copying text between strings and buffers preserves the properties along with the characters; this includes such diverse functions as substring, insert, and buffer-substring. Examining Text Properties The simplest way to examine text properties is to ask for the value of a particular property of a particular character. For that, use get-text-property. Use text-properties-at to get the entire property list of a character. See , for functions to examine the properties of a number of characters at once. These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1. get-text-property — Function: get-text-property pos prop &optional object This function returns the value of the prop property of thecharacter after position pos in object (a buffer orstring). The argument object is optional and defaults to thecurrent buffer.If there is no prop property strictly speaking, but the characterhas a property category that is a symbol, then get-text-property returnsthe prop property of that symbol. get-char-property — Function: get-char-property position prop &optional object This function is like get-text-property, except that it checksoverlays first and then text properties. See .The argument object may be a string, a buffer, or a window. If itis a window, then the buffer displayed in that window is used for textproperties and overlays, but only the overlays active for that windoware considered. If object is a buffer, then all overlays in thatbuffer are considered, as well as text properties. If object is astring, only text properties are considered, since strings never haveoverlays. get-char-property-and-overlay — Function: get-char-property-and-overlay position prop &optional object This is like get-char-property, but gives extra informationabout the overlay that the property value comes from.Its value is a cons cell whose car is the property value, thesame value get-char-property would return with the samearguments. Its cdr is the overlay in which the property wasfound, or nil, if it was found as a text property or not foundat all.If position is at the end of object, both the car andthe cdr of the value are nil. char-property-alias-alist — Variable: char-property-alias-alist This variable holds an alist which maps property names to a list ofalternative property names. If a character does not specify a directvalue for a property, the alternative property names are consulted inorder; the first non-nil value is used. This variable takesprecedence over default-text-properties, and categoryproperties take precedence over this variable. text-properties-at — Function: text-properties-at position &optional object This function returns the entire property list of the character atposition in the string or buffer object. If object isnil, it defaults to the current buffer. default-text-properties — Variable: default-text-properties This variable holds a property list giving default values for textproperties. Whenever a character does not specify a value for aproperty, neither directly, through a category symbol, or throughchar-property-alias-alist, the value stored in this list isused instead. Here is an example: (setq default-text-properties '(foo 69) char-property-alias-alist nil) ;; Make sure character 1 has no properties of its own. (set-text-properties 1 2 nil) ;; What we get, when we ask, is the default value. (get-text-property 1 'foo) => 69 Changing Text Properties The primitives for changing properties apply to a specified range of text in a buffer or string. The function set-text-properties (see end of section) sets the entire property list of the text in that range; more often, it is useful to add, change, or delete just certain properties specified by name. Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (see ). Positions in a string start from 0, whereas positions in a buffer start from 1. put-text-property — Function: put-text-property start end prop value &optional object This function sets the prop property to value for the textbetween start and end in the string or buffer object.If object is nil, it defaults to the current buffer. add-text-properties — Function: add-text-properties start end props &optional object This function adds or overrides text properties for the text betweenstart and end in the string or buffer object. Ifobject is nil, it defaults to the current buffer.The argument props specifies which properties to add. It shouldhave the form of a property list (see ): a list whoseelements include the property names followed alternately by thecorresponding values.The return value is t if the function actually changed someproperty's value; nil otherwise (if props is nil orits values agree with those in the text).For example, here is how to set the comment and faceproperties of a range of text: (add-text-properties start end '(comment t face highlight)) remove-text-properties — Function: remove-text-properties start end props &optional object This function deletes specified text properties from the text betweenstart and end in the string or buffer object. Ifobject is nil, it defaults to the current buffer.The argument props specifies which properties to delete. Itshould have the form of a property list (see ): a listwhose elements are property names alternating with corresponding values.But only the names matter—the values that accompany them are ignored.For example, here's how to remove the face property. (remove-text-properties start end '(face nil)) The return value is t if the function actually changed someproperty's value; nil otherwise (if props is nil orif no character in the specified text had any of those properties).To remove all text properties from certain text, useset-text-properties and specify nil for the new propertylist. remove-list-of-text-properties — Function: remove-list-of-text-properties start end list-of-properties &optional object Like remove-text-properties except thatlist-of-properties is a list of property names only, not analternating list of property names and values. set-text-properties — Function: set-text-properties start end props &optional object This function completely replaces the text property list for the textbetween start and end in the string or buffer object.If object is nil, it defaults to the current buffer.The argument props is the new property list. It should be a listwhose elements are property names alternating with corresponding values.After set-text-properties returns, all the characters in thespecified range have identical properties.If props is nil, the effect is to get rid of all propertiesfrom the specified range of text. Here's an example: (set-text-properties start end nil) Do not rely on the return value of this function. The easiest way to make a string with text properties is with propertize: propertize — Function: propertize string &rest properties This function returns a copy of string which has the textproperties properties. These properties apply to all thecharacters in the string that is returned. Here is an example thatconstructs a string with a face property and a mouse-faceproperty: (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) => #("foo" 0 3 (mouse-face bold-italic face italic)) To put different properties on various parts of a string, you canconstruct each part with propertize and then combine them withconcat: (concat (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) " and " (propertize "bar" 'face 'italic 'mouse-face 'bold-italic)) => #("foo and bar" 0 3 (face italic mouse-face bold-italic) 3 8 nil 8 11 (face italic mouse-face bold-italic)) See also the function buffer-substring-no-properties (see ) which copies text from the buffer but does not copy its properties. Text Property Search Functions In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value. Here are functions you can use to do this. They use eq for comparing property values. In all cases, object defaults to the current buffer. For high performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change. These functions do not move point; instead, they return a position (or nil). Remember that a position is always between two characters; the position returned by these functions is between two characters with different properties. next-property-change — Function: next-property-change pos &optional object limit The function scans the text forward from position pos in thestring or buffer object till it finds a change in some textproperty, then returns the position of the change. In other words, itreturns the position of the first character beyond pos whoseproperties are not identical to those of the character just afterpos.If limit is non-nil, then the scan ends at positionlimit. If there is no property change before that point,next-property-change returns limit.The value is nil if the properties remain unchanged all the wayto the end of object and limit is nil. If the valueis non-nil, it is a position greater than or equal to pos.The value equals pos only when limit equals pos.Here is an example of how to scan the buffer by chunks of text withinwhich all properties are constant: (while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) Process text from point to next-change… (goto-char next-change))) previous-property-change — Function: previous-property-change pos &optional object limit This is like next-property-change, but scans back from posinstead of forward. If the value is non-nil, it is a positionless than or equal to pos; it equals pos only if limitequals pos. next-single-property-change — Function: next-single-property-change pos prop &optional object limit The function scans text for a change in the prop property, thenreturns the position of the change. The scan goes forward fromposition pos in the string or buffer object. In otherwords, this function returns the position of the first characterbeyond pos whose prop property differs from that of thecharacter just after pos.If limit is non-nil, then the scan ends at positionlimit. If there is no property change before that point,next-single-property-change returns limit.The value is nil if the property remains unchanged all the way tothe end of object and limit is nil. If the value isnon-nil, it is a position greater than or equal to pos; itequals pos only if limit equals pos. previous-single-property-change — Function: previous-single-property-change pos prop &optional object limit This is like next-single-property-change, but scans back frompos instead of forward. If the value is non-nil, it is aposition less than or equal to pos; it equals pos only iflimit equals pos. next-char-property-change — Function: next-char-property-change pos &optional limit This is like next-property-change except that it considersoverlay properties as well as text properties, and if no change isfound before the end of the buffer, it returns the maximum bufferposition rather than nil (in this sense, it resembles thecorresponding overlay function next-overlay-change, rather thannext-property-change). There is no object operandbecause this function operates only on the current buffer. It returnsthe next address at which either kind of property changes. previous-char-property-change — Function: previous-char-property-change pos &optional limit This is like next-char-property-change, but scans back frompos instead of forward, and returns the minimum bufferposition if no change is found. next-single-char-property-change — Function: next-single-char-property-change pos prop &optional object limit This is like next-single-property-change except that itconsiders overlay properties as well as text properties, and if nochange is found before the end of the object, it returns themaximum valid position in object rather than nil. Unlikenext-char-property-change, this function does have anobject operand; if object is not a buffer, onlytext-properties are considered. previous-single-char-property-change — Function: previous-single-char-property-change pos prop &optional object limit This is like next-single-char-property-change, but scans backfrom pos instead of forward, and returns the minimum validposition in object if no change is found. text-property-any — Function: text-property-any start end prop value &optional object This function returns non-nil if at least one character betweenstart and end has a property prop whose value isvalue. More precisely, it returns the position of the first suchcharacter. Otherwise, it returns nil.The optional fifth argument, object, specifies the string orbuffer to scan. Positions are relative to object. The defaultfor object is the current buffer. text-property-not-all — Function: text-property-not-all start end prop value &optional object This function returns non-nil if at least one character betweenstart and end does not have a property prop with valuevalue. More precisely, it returns the position of the first suchcharacter. Otherwise, it returns nil.The optional fifth argument, object, specifies the string orbuffer to scan. Positions are relative to object. The defaultfor object is the current buffer. Properties with Special Meanings Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like. Note: the properties composition, display, invisible and intangible can also cause point to move to an acceptable place, after each Emacs command. See . property category of text character category (text property)category If a character has a category property, we call it theproperty category of the character. It should be a symbol. Theproperties of this symbol serve as defaults for the properties of thecharacter. face face codes of text face (text property)You can use the property face to control the font and color oftext. See , for more information.In the simplest case, the value is a face name. It can also be a list;then each element can be any of these possibilities; A face name (a symbol or string). A property list of face attributes. This has theform (keyword value …), where each keyword is aface attribute name and value is a meaningful value for thatattribute. With this feature, you do not need to create a face eachtime you want to specify a particular attribute for certain text.See . A cons cell with the form (foreground-color . color-name) or(background-color . color-name). These elements specifyjust the foreground color or just the background color. See , for the supported forms of color-name.A cons cell of (foreground-color . color-name) is equivalent tospecifying (:foreground color-name); likewise for thebackground. You can use Font Lock Mode (see ), to dynamicallyupdate face properties based on the contents of the text. font-lock-face font-lock-face (text property)The font-lock-face property is the same in all respects as theface property, but its state of activation is controlled byfont-lock-mode. This can be advantageous for special bufferswhich are not intended to be user-editable, or for static areas oftext which are always fontified in the same way.See .Strictly speaking, font-lock-face is not a built-in textproperty; rather, it is implemented in Font Lock mode usingchar-property-alias-alist. See .This property is new in Emacs 22.1. mouse-face mouse-face (text property)The property mouse-face is used instead of face when themouse is on or near the character. For this purpose, “near” meansthat all text between the character and where the mouse is have the samemouse-face property value. fontified fontified (text property)This property says whether the text is ready for display. Ifnil, Emacs's redisplay routine calls the functions infontification-functions (see ) to prepare thispart of the buffer before it is displayed. It is used internally bythe “just in time” font locking code. display This property activates various features that change theway text is displayed. For example, it can make text appear talleror shorter, higher or lower, wider or narrow, or replaced with an image.See . help-echo help-echo (text property) tooltipIf text has a string as its help-echo property, then when youmove the mouse onto that text, Emacs displays that string in the echoarea, or in the tooltip window (see See section ``Tooltips'' in The GNU Emacs Manual).If the value of the help-echo property is a function, thatfunction is called with three arguments, window, object andpos and should return a help string or nil fornone. The first argument, window is the window in whichthe help was found. The second, object, is the buffer, overlay orstring which had the help-echo property. The posargument is as follows: If object is a buffer, pos is the position in the buffer. If object is an overlay, that overlay has a help-echoproperty, and pos is the position in the overlay's buffer. If object is a string (an overlay string or a string displayedwith the display property), pos is the position in thatstring. If the value of the help-echo property is neither a function nora string, it is evaluated to obtain a help string.You can alter the way help text is displayed by setting the variableshow-help-function (see ).This feature is used in the mode line and for other active text. keymap keymap of character keymap (text property)The keymap property specifies an additional keymap forcommands. When this keymap applies, it is used for key lookup beforethe minor mode keymaps and before the buffer's local map.See . If the property value is a symbol, thesymbol's function definition is used as the keymap.The property's value for the character before point applies if it isnon-nil and rear-sticky, and the property's value for thecharacter after point applies if it is non-nil andfront-sticky. (For mouse clicks, the position of the click is usedinstead of the position of point.) local-map local-map (text property)This property works like keymap except that it specifies akeymap to use instead of the buffer's local map. For mostpurposes (perhaps all purposes), it is better to use the keymapproperty. syntax-table The syntax-table property overrides what the syntax table saysabout this particular character. See . read-only read-only character read-only (text property)If a character has the property read-only, then modifying thatcharacter is not allowed. Any command that would do so gets an error,text-read-only. If the property value is a string, that stringis used as the error message.Insertion next to a read-only character is an error if insertingordinary text there would inherit the read-only property due tostickiness. Thus, you can control permission to insert next toread-only text by controlling the stickiness. See .Since changing properties counts as modifying the buffer, it is notpossible to remove a read-only property unless you know thespecial trick: bind inhibit-read-only to a non-nil valueand then remove the property. See . invisible invisible (text property)A non-nil invisible property can make a character invisibleon the screen. See , for details. intangible intangible (text property)If a group of consecutive characters have equal and non-nilintangible properties, then you cannot place point between them.If you try to move point forward into the group, point actually moves tothe end of the group. If you try to move point backward into the group,point actually moves to the start of the group.If consecutive characters have unequal non-nilintangible properties, they belong to separate groups; eachgroup is separately treated as described above.When the variable inhibit-point-motion-hooks is non-nil,the intangible property is ignored. field field (text property)Consecutive characters with the same field property constitute afield. Some motion functions including forward-word andbeginning-of-line stop moving at a field boundary.See . cursor cursor (text property)Normally, the cursor is displayed at the end of any overlay and textproperty strings present at the current window position. You canplace the cursor on any desired character of these strings by givingthat character a non-nil cursor text property. pointer pointer (text property)This specifies a specific pointer shape when the mouse pointer is overthis text or image. See , for possible pointershapes. line-spacing line-spacing (text property)A newline can have a line-spacing text or overlay property thatcontrols the height of the display line ending with that newline. Theproperty value overrides the default frame line spacing and the bufferlocal line-spacing variable. See . line-height line-height (text property)A newline can have a line-height text or overlay property thatcontrols the total height of the display line ending in that newline.See . modification-hooks change hooks for a character hooks for changing a character modification-hooks (text property)If a character has the property modification-hooks, then itsvalue should be a list of functions; modifying that character calls allof those functions. Each function receives two arguments: the beginningand end of the part of the buffer being modified. Note that if aparticular modification hook function appears on several charactersbeing modified by a single primitive, you can't predict how many timesthe function will be called.If these functions modify the buffer, they should bindinhibit-modification-hooks to t around doing so, toavoid confusing the internal mechanism that calls these hooks.Overlays also support the modification-hooks property, but thedetails are somewhat different (see ). insert-in-front-hooksinsert-behind-hooks insert-in-front-hooks (text property) insert-behind-hooks (text property)The operation of inserting text in a buffer also calls the functionslisted in the insert-in-front-hooks property of the followingcharacter and in the insert-behind-hooks property of thepreceding character. These functions receive two arguments, thebeginning and end of the inserted text. The functions are calledafter the actual insertion takes place.See also , for other hooks that are calledwhen you change text in a buffer. point-enteredpoint-left hooks for motion of point point-entered (text property) point-left (text property)The special properties point-entered and point-leftrecord hook functions that report motion of point. Each time pointmoves, Emacs compares these two property values: the point-left property of the character after the old location,and the point-entered property of the character after the newlocation. If these two values differ, each of them is called (if not nil)with two arguments: the old value of point, and the new one.The same comparison is made for the characters before the old and newlocations. The result may be to execute two point-left functions(which may be the same function) and/or two point-enteredfunctions (which may be the same function). In any case, all thepoint-left functions are called first, followed by all thepoint-entered functions.It is possible with char-after to examine characters at variousbuffer positions without moving point to those positions. Only anactual change in the value of point runs these hook functions. inhibit-point-motion-hooks — Variable: inhibit-point-motion-hooks When this variable is non-nil, point-left andpoint-entered hooks are not run, and the intangibleproperty has no effect. Do not set this variable globally; bind it withlet. show-help-function — Variable: show-help-function If this variable is non-nil, it specifies afunction called to display help strings. These may be help-echoproperties, menu help strings (see ,see ), or tool bar help strings (see ). The specified function is called with one argument, the helpstring to display. Tooltip mode (see See section ``Tooltips'' in The GNU Emacs Manual) provides an example. composition composition (text property)This text property is used to display a sequence of characters as asingle glyph composed from components. For instance, in Thai a baseconsonant is composed with the following combining vowel as a singleglyph. The value should be a character or a sequence (vector, list,or string) of integers. If it is a character, it means to display that character instead ofthe text in the region. If it is a string, it means to display that string's contents insteadof the text in the region. If it is a vector or list, the elements are characters interleavedwith internal codes specifying how to compose the following characterwith the previous one. Formatted Text Properties These text properties affect the behavior of the fill commands. They are used for representing formatted text. See , and . hard If a newline character has this property, it is a “hard” newline.The fill commands do not alter hard newlines and do not move wordsacross them. However, this property takes effect only if theuse-hard-newlines minor mode is enabled. See See section ``Hard and Soft Newlines'' in The GNU Emacs Manual. right-margin This property specifies an extra right margin for filling this part of thetext. left-margin This property specifies an extra left margin for filling this part of thetext. justification This property specifies the style of justification for filling this partof the text. Stickiness of Text Properties sticky text properties inheritance of text properties Self-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties. In a Lisp program, you can do insertion with inheritance or without, depending on your choice of insertion primitive. The ordinary text insertion functions such as insert do not inherit any properties. They insert text with precisely the properties of the string being inserted, and no others. This is correct for programs that copy text from one context to another—for example, into or out of the kill ring. To insert with inheritance, use the special primitives described in this section. Self-inserting characters inherit properties because they work using these primitives. When you do insertion with inheritance, which properties are inherited, and from where, depends on which properties are sticky. Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. When both sides offer different sticky values for the same property, the previous character's value takes precedence. By default, a text property is rear-sticky but not front-sticky; thus, the default is to inherit all the properties of the preceding character, and nothing from the following character. You can control the stickiness of various text properties with two specific text properties, front-sticky and rear-nonsticky, and with the variable text-property-default-nonsticky. You can use the variable to specify a different default for a given property. You can use those two text properties to make any specific properties sticky or nonsticky in any particular part of the text. If a character's front-sticky property is t, then all its properties are front-sticky. If the front-sticky property is a list, then the sticky properties of the character are those whose names are in the list. For example, if a character has a front-sticky property whose value is (face read-only), then insertion before the character can inherit its face property and its read-only property, but no others. The rear-nonsticky property works the opposite way. Most properties are rear-sticky by default, so the rear-nonsticky property says which properties are not rear-sticky. If a character's rear-nonsticky property is t, then none of its properties are rear-sticky. If the rear-nonsticky property is a list, properties are rear-sticky unless their names are in the list. text-property-default-nonsticky — Variable: text-property-default-nonsticky This variable holds an alist which defines the default rear-stickinessof various text properties. Each element has the form(property . nonstickiness), and it defines thestickiness of a particular text property, property.If nonstickiness is non-nil, this means that the propertyproperty is rear-nonsticky by default. Since all properties arefront-nonsticky by default, this makes property nonsticky in bothdirections by default.The text properties front-sticky and rear-nonsticky, whenused, take precedence over the default nonstickiness specified intext-property-default-nonsticky. Here are the functions that insert text with inheritance of properties: insert-and-inherit — Function: insert-and-inherit &rest strings Insert the strings strings, just like the function insert,but inherit any sticky properties from the adjoining text. insert-before-markers-and-inherit — Function: insert-before-markers-and-inherit &rest strings Insert the strings strings, just like the functioninsert-before-markers, but inherit any sticky properties from theadjoining text. See , for the ordinary insertion functions which do not inherit. Saving Text Properties in Files text properties in files saving text properties You can save text properties in files (along with the text itself), and restore the same text properties when visiting or inserting the files, using these two hooks: write-region-annotate-functions — Variable: write-region-annotate-functions This variable's value is a list of functions for write-region torun to encode text properties in some fashion as annotations to the textbeing written in the file. See .Each function in the list is called with two arguments: the start andend of the region to be written. These functions should not alter thecontents of the buffer. Instead, they should return lists indicatingannotations to write in the file in addition to the text in thebuffer.Each function should return a list of elements of the form(position . string), where position is aninteger specifying the relative position within the text to be written,and string is the annotation to add there.Each list returned by one of these functions must be already sorted inincreasing order by position. If there is more than one function,write-region merges the lists destructively into one sorted list.When write-region actually writes the text from the buffer to thefile, it intermixes the specified annotations at the correspondingpositions. All this takes place without modifying the buffer. after-insert-file-functions — Variable: after-insert-file-functions This variable holds a list of functions for insert-file-contentsto call after inserting a file's contents. These functions should scanthe inserted text for annotations, and convert them to the textproperties they stand for.Each function receives one argument, the length of the inserted text;point indicates the start of that text. The function should scan thattext for annotations, delete them, and create the text properties thatthe annotations specify. The function should return the updated lengthof the inserted text, as it stands after those changes. The valuereturned by one function becomes the argument to the next function.These functions should always return with point at the beginning ofthe inserted text.The intended use of after-insert-file-functions is for convertingsome sort of textual annotations into actual text properties. But otheruses may be possible. We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs. We suggest not trying to handle arbitrary Lisp objects as text property names or values—because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode. See , for a related feature. Lazy Computation of Text Properties Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them. The primitive that extracts text from the buffer along with its properties is buffer-substring. Before examining the properties, this function runs the abnormal hook buffer-access-fontify-functions. buffer-access-fontify-functions — Variable: buffer-access-fontify-functions This variable holds a list of functions for computing text properties.Before buffer-substring copies the text and text properties for aportion of the buffer, it calls all the functions in this list. Each ofthe functions receives two arguments that specify the range of thebuffer being accessed. (The buffer itself is always the currentbuffer.) The function buffer-substring-no-properties does not call these functions, since it ignores text properties anyway. In order to prevent the hook functions from being called more than once for the same part of the buffer, you can use the variable buffer-access-fontified-property. buffer-access-fontified-property — Variable: buffer-access-fontified-property If this variable's value is non-nil, it is a symbol which is usedas a text property name. A non-nil value for that text propertymeans, “the other text properties for this character have already beencomputed.”If all the characters in the range specified for buffer-substringhave a non-nil value for this property, buffer-substringdoes not call the buffer-access-fontify-functions functions. Itassumes these characters already have the right text properties, andjust copies the properties they already have.The normal way to use this feature is that thebuffer-access-fontify-functions functions add this property, aswell as others, to the characters they operate on. That way, they avoidbeing called over and over for the same text. Defining Clickable Text clickable text Clickable text is text that can be clicked, with either the the mouse or via keyboard commands, to produce some result. Many major modes use clickable text to implement features such as hyper-links. The button package provides an easy way to insert and manipulate clickable text. See . In this section, we will explain how to manually set up clickable text in a buffer using text properties. This involves two things: (1) indicating clickability when the mouse moves over the text, and (2) making RET or a mouse click on that text do something. Indicating clickability usually involves highlighting the text, and often involves displaying helpful information about the action, such as which mouse button to press, or a short summary of the action. This can be done with the mouse-face and help-echo text properties. See . Here is an example of how Dired does it: (condition-case nil (if (dired-move-to-filename) (add-text-properties (point) (save-excursion (dired-move-to-end-of-filename) (point)) '(mouse-face highlight help-echo "mouse-2: visit this file in other window"))) (error nil)) The first two arguments to add-text-properties specify the beginning and end of the text. The usual way to make the mouse do something when you click it on this text is to define mouse-2 in the major mode's keymap. The job of checking whether the click was on clickable text is done by the command definition. Here is how Dired does it: (defun dired-mouse-find-file-other-window (event) "In Dired, visit the file or directory name you click on." (interactive "e") (let (window pos file) (save-excursion (setq window (posn-window (event-end event)) pos (posn-point (event-end event))) (if (not (windowp window)) (error "No file chosen")) (set-buffer (window-buffer window)) (goto-char pos) (setq file (dired-get-file-for-visit))) (if (file-directory-p file) (or (and (cdr dired-subdir-alist) (dired-goto-subdir file)) (progn (select-window window) (dired-other-window file))) (select-window window) (find-file-other-window (file-name-sans-versions file t))))) The reason for the save-excursion construct is to avoid changing the current buffer. In this case, Dired uses the functions posn-window and posn-point to determine which buffer the click happened in and where, and in that buffer, dired-get-file-for-visit to determine which file to visit. Instead of defining a mouse command for the major mode, you can define a key binding for the clickable text itself, using the keymap text property: (let ((map (make-sparse-keymap))) (define-key map [mouse-2] 'operate-this-button) (put-text-property (point) (save-excursion (dired-move-to-end-of-filename) (point)) 'keymap map)) This method makes it possible to define different commands for various clickable pieces of text. Also, the major mode definition (or the global definition) remains available for the rest of the text in the buffer. Links and Mouse-1 follow links mouse-1 The normal Emacs command for activating text in read-only buffers is Mouse-2, which includes following textual links. However, most graphical applications use Mouse-1 for following links. For compatibility, Mouse-1 follows links in Emacs too, when you click on a link quickly without moving the mouse. The user can customize this behavior through the variable mouse-1-click-follows-link. To define text as a link at the Lisp level, you should bind the mouse-2 event to a command to follow the link. Then, to indicate that Mouse-1 should also follow the link, you should specify a follow-link condition either as a text property or as a key binding: follow-link property If the clickable text has a non-nil follow-link text or overlayproperty, that specifies the condition. follow-link event If there is a binding for the follow-link event, either on theclickable text or in the local keymap, the binding is the condition. Regardless of how you set the follow-link condition, its value is used as follows to determine whether the given position is inside a link, and (if so) to compute an action code saying how Mouse-1 should handle the link. mouse-face If the condition is mouse-face, a position is inside a link ifthere is a non-nil mouse-face property at that position.The action code is always t.For example, here is how Info mode handles Mouse-1: (define-key Info-mode-map [follow-link] 'mouse-face) a function If the condition is a valid function, func, then a positionpos is inside a link if (func pos) evaluatesto non-nil. The value returned by func serves as theaction code.For example, here is how pcvs enables Mouse-1 to follow links onfile names only: (define-key map [follow-link] (lambda (pos) (eq (get-char-property pos 'face) 'cvs-filename-face))) anything else If the condition value is anything else, then the position is inside alink and the condition itself is the action code. Clearly you shouldonly specify this kind of condition on the text that constitutes alink. The action code tells Mouse-1 how to follow the link: a string or vector If the action code is a string or vector, the Mouse-1 event istranslated into the first element of the string or vector; i.e., theaction of the Mouse-1 click is the local or global binding ofthat character or symbol. Thus, if the action code is "foo",Mouse-1 translates into f. If it is [foo],Mouse-1 translates into foo. anything else For any other non-nil action code, the mouse-1 event istranslated into a mouse-2 event at the same position. To define Mouse-1 to activate a button defined with define-button-type, give the button a follow-link property with a value as specified above to determine how to follow the link. For example, here is how Help mode handles Mouse-1: (define-button-type 'help-xref 'follow-link t 'action #'help-button-action) To define Mouse-1 on a widget defined with define-widget, give the widget a :follow-link property with a value as specified above to determine how to follow the link. For example, here is how the link widget specifies that a Mouse-1 click shall be translated to RET: (define-widget 'link 'item "An embedded link." :button-prefix 'widget-link-prefix :button-suffix 'widget-link-suffix :follow-link "\C-m" :help-echo "Follow the link." :format "%[%t%]") mouse-on-link-p — Function: mouse-on-link-p pos This function returns non-nil if position pos in thecurrent buffer is on a link. pos can also be a mouse eventlocation, as returned by event-start (see ). Defining and Using Fields fields A field is a range of consecutive characters in the buffer that are identified by having the same value (comparing with eq) of the field property (either a text-property or an overlay property). This section describes special functions that are available for operating on fields. You specify a field with a buffer position, pos. We think of each field as containing a range of buffer positions, so the position you specify stands for the field containing that position. When the characters before and after pos are part of the same field, there is no doubt which field contains pos: the one those characters both belong to. When pos is at a boundary between fields, which field it belongs to depends on the stickiness of the field properties of the two surrounding characters (see ). The field whose property would be inherited by text inserted at pos is the field that contains pos. There is an anomalous case where newly inserted text at pos would not inherit the field property from either side. This happens if the previous character's field property is not rear-sticky, and the following character's field property is not front-sticky. In this case, pos belongs to neither the preceding field nor the following field; the field functions treat it as belonging to an empty field whose beginning and end are both at pos. In all of these functions, if pos is omitted or nil, the value of point is used by default. If narrowing is in effect, then pos should fall within the accessible portion. See . field-beginning — Function: field-beginning &optional pos escape-from-edge limit This function returns the beginning of the field specified by pos.If pos is at the beginning of its field, andescape-from-edge is non-nil, then the return value isalways the beginning of the preceding field that ends at pos,regardless of the stickiness of the field properties aroundpos.If limit is non-nil, it is a buffer position; if thebeginning of the field is before limit, then limit will bereturned instead. field-end — Function: field-end &optional pos escape-from-edge limit This function returns the end of the field specified by pos.If pos is at the end of its field, and escape-from-edge isnon-nil, then the return value is always the end of the followingfield that begins at pos, regardless of the stickiness ofthe field properties around pos.If limit is non-nil, it is a buffer position; if the endof the field is after limit, then limit will be returnedinstead. field-string — Function: field-string &optional pos This function returns the contents of the field specified by pos,as a string. field-string-no-properties — Function: field-string-no-properties &optional pos This function returns the contents of the field specified by pos,as a string, discarding text properties. delete-field — Function: delete-field &optional pos This function deletes the text of the field specified by pos. constrain-to-field — Function: constrain-to-field new-pos old-pos &optional escape-from-edge only-in-line inhibit-capture-property This function “constrains” new-pos to the field thatold-pos belongs to—in other words, it returns the positionclosest to new-pos that is in the same field as old-pos.If new-pos is nil, then constrain-to-field usesthe value of point instead, and moves point to the resulting positionas well as returning it.If old-pos is at the boundary of two fields, then the acceptablefinal positions depend on the argument escape-from-edge. Ifescape-from-edge is nil, then new-pos must be inthe field whose field property equals what new charactersinserted at old-pos would inherit. (This depends on thestickiness of the field property for the characters before andafter old-pos.) If escape-from-edge is non-nil,new-pos can be anywhere in the two adjacent fields.Additionally, if two fields are separated by another field with thespecial value boundary, then any point within this specialfield is also considered to be “on the boundary.”Commands like C-a with no argumemt, that normally move backwardto a specific kind of location and stay there once there, probablyshould specify nil for escape-from-edge. Other motioncommands that check fields should probably pass t.If the optional argument only-in-line is non-nil, andconstraining new-pos in the usual way would move it to a differentline, new-pos is returned unconstrained. This used in commandsthat move by line, such as next-line andbeginning-of-line, so that they respect field boundaries only inthe case where they can still move to the right line.If the optional argument inhibit-capture-property isnon-nil, and old-pos has a non-nil property of thatname, then any field boundaries are ignored.You can cause constrain-to-field to ignore all field boundaries(and so never constrain anything) by binding the variableinhibit-field-text-motion to a non-nil value. Why Text Properties are not Intervals intervals Some editors that support adding attributes to text in the buffer do so by letting the user specify “intervals” within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification. If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property. Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two. Suppose we “fix” this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two. Insertion of text at the border between intervals also raises questions that have no satisfactory answer. However, it is easy to arrange for editing to behave consistently for questions of the form, “What are the properties of this character?” So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end. In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See . Emacs also provides explicit intervals as a presentation feature; see . Substituting for a Character Code The following functions replace characters within a specified region based on their character codes. subst-char-in-region — Function: subst-char-in-region start end old-char new-char &optional noundo replace charactersThis function replaces all occurrences of the character old-charwith the character new-char in the region of the current bufferdefined by start and end. undo avoidanceIf noundo is non-nil, then subst-char-in-region doesnot record the change for undo and does not mark the buffer as modified.This was useful for controlling the old selective display feature(see ).subst-char-in-region does not move point and returnsnil. ---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) => nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ---------- translate-region — Function: translate-region start end table This function applies a translation table to the characters in thebuffer between positions start and end.The translation table table is a string or a char-table;(aref table ochar) gives the translated charactercorresponding to ochar. If table is a string, anycharacters with codes larger than the length of table are notaltered by the translation.The return value of translate-region is the number ofcharacters that were actually changed by the translation. This doesnot count characters that were mapped into themselves in thetranslation table. Registers registers A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ASCII characters and their meta variants (but with the exception of C-g) can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by the character that is its name. register-alist — Variable: register-alist This variable is an alist of elements of the form (name .contents). Normally, there is one element for each Emacsregister that has been used.The object name is a character (an integer) identifying theregister. The contents of a register can have several possible types: a number A number stands for itself. If insert-register finds a numberin the register, it converts the number to decimal. a marker A marker represents a buffer position to jump to. a string A string is text saved in the register. a rectangle A rectangle is represented by a list of strings. (window-configuration position) This represents a window configuration to restore in one frame, and aposition to jump to in the current buffer. (frame-configuration position) This represents a frame configuration to restore, and a positionto jump to in the current buffer. (file filename) This represents a file to visit; jumping to this value visits filefilename. (file-query filename position) This represents a file to visit and a position in it; jumping to thisvalue visits file filename and goes to buffer positionposition. Restoring this type of position asks the user forconfirmation first. The functions in this section return unpredictable values unless otherwise stated. get-register — Function: get-register reg This function returns the contents of the registerreg, or nil if it has no contents. set-register — Function: set-register reg value This function sets the contents of register reg to value.A register can be set to any value, but the other register functionsexpect only certain data types. The return value is value. view-register — Command: view-register reg This command displays what is contained in register reg. insert-register — Command: insert-register reg &optional beforep This command inserts contents of register reg into the currentbuffer.Normally, this command puts point before the inserted text, and themark after it. However, if the optional second argument beforepis non-nil, it puts the mark before and point after.You can pass a non-nil second argument beforep to thisfunction interactively by supplying any prefix argument.If the register contains a rectangle, then the rectangle is insertedwith its upper left corner at point. This means that text is insertedin the current line and underneath it on successive lines.If the register contains something other than saved text (a string) ora rectangle (a list), currently useless things happen. This may bechanged in the future. Transposition of Text This subroutine is used by the transposition commands. transpose-regions — Function: transpose-regions start1 end1 start2 end2 &optional leave-markers This function exchanges two nonoverlapping portions of the buffer.Arguments start1 and end1 specify the bounds of one portionand arguments start2 and end2 specify the bounds of theother portion.Normally, transpose-regions relocates markers with the transposedtext; a marker previously positioned within one of the two transposedportions moves along with that portion, thus remaining between the sametwo characters in their new position. However, if leave-markersis non-nil, transpose-regions does not do this—it leavesall markers unrelocated. Base 64 Encoding base 64 encoding Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of ASCII graphic characters. It is defined in Internet RFC An RFC, an acronym for Request for Comments, is a numbered Internet informational document describing a standard. RFCs are usually written by technical experts acting on their own initiative, and are traditionally written in a pragmatic, experience-driven manner. 2045. This section describes the functions for converting to and from this code. base64-encode-region — Function: base64-encode-region beg end &optional no-line-break This function converts the region from beg to end into base64 code. It returns the length of the encoded text. An error issignaled if a character in the region is multibyte, i.e. in amultibyte buffer the region must contain only characters from thecharsets ascii, eight-bit-control andeight-bit-graphic.Normally, this function inserts newline characters into the encodedtext, to avoid overlong lines. However, if the optional argumentno-line-break is non-nil, these newlines are not added, sothe output is just one long line. base64-encode-string — Function: base64-encode-string string &optional no-line-break This function converts the string string into base 64 code. Itreturns a string containing the encoded text. As forbase64-encode-region, an error is signaled if a character in thestring is multibyte.Normally, this function inserts newline characters into the encodedtext, to avoid overlong lines. However, if the optional argumentno-line-break is non-nil, these newlines are not added, sothe result string is just one long line. base64-decode-region — Function: base64-decode-region beg end This function converts the region from beg to end from base64 code into the corresponding decoded text. It returns the length ofthe decoded text.The decoding functions ignore newline characters in the encoded text. base64-decode-string — Function: base64-decode-string string This function converts the string string from base 64 code intothe corresponding decoded text. It returns a unibyte string containing thedecoded text.The decoding functions ignore newline characters in the encoded text. MD5 Checksum MD5 checksum message digest computation MD5 cryptographic checksums, or message digests, are 128-bit “fingerprints” of a document or program. They are used to verify that you have an exact and unaltered copy of the data. The algorithm to calculate the MD5 message digest is defined in Internet RFC For an explanation of what is an RFC, see the footnote in . 1321. This section describes the Emacs facilities for computing message digests. md5 — Function: md5 object &optional start end coding-system noerror This function returns the MD5 message digest of object, whichshould be a buffer or a string.The two optional arguments start and end are characterpositions specifying the portion of object to compute themessage digest for. If they are nil or omitted, the digest iscomputed for the whole of object.The function md5 does not compute the message digest directlyfrom the internal Emacs representation of the text (see ). Instead, it encodes the text using a codingsystem, and computes the message digest from the encoded text. Theoptional fourth argument coding-system specifies which codingsystem to use for encoding the text. It should be the same codingsystem that you used to read the text, or that you used or will usewhen saving or sending the text. See , for moreinformation about coding systems.If coding-system is nil or omitted, the default dependson object. If object is a buffer, the default forcoding-system is whatever coding system would be chosen bydefault for writing this text into a file. If object is astring, the user's most preferred coding system (see See section ``the description of@code{prefer-coding-system}'' in GNU Emacs Manual) is used.Normally, md5 signals an error if the text can't be encodedusing the specified or chosen coding system. However, ifnoerror is non-nil, it silently uses raw-textcoding instead. Atomic Change Groups atomic changes In data base terminology, an atomic change is an indivisible change—it can succeed entirely or it can fail entirely, but it cannot partly succeed. A Lisp program can make a series of changes to one or several buffers as an atomic change group, meaning that either the entire series of changes will be installed in their buffers or, in case of an error, none of them will be. To do this for one buffer, the one already current, simply write a call to atomic-change-group around the code that makes the changes, like this: (atomic-change-group (insert foo) (delete-region x y)) If an error (or other nonlocal exit) occurs inside the body of atomic-change-group, it unmakes all the changes in that buffer that were during the execution of the body. This kind of change group has no effect on any other buffers—any such changes remain. If you need something more sophisticated, such as to make changes in various buffers constitute one atomic group, you must directly call lower-level functions that atomic-change-group uses. prepare-change-group — Function: prepare-change-group &optional buffer This function sets up a change group for buffer buffer, whichdefaults to the current buffer. It returns a “handle” thatrepresents the change group. You must use this handle to activate thechange group and subsequently to finish it. To use the change group, you must activate it. You must do this before making any changes in the text of buffer. activate-change-group — Function: activate-change-group handle This function activates the change group that handle designates. After you activate the change group, any changes you make in that buffer become part of it. Once you have made all the desired changes in the buffer, you must finish the change group. There are two ways to do this: you can either accept (and finalize) all the changes, or cancel them all. accept-change-group — Function: accept-change-group handle This function accepts all the changes in the change group specified byhandle, making them final. cancel-change-group — Function: cancel-change-group handle This function cancels and undoes all the changes in the change groupspecified by handle. Your code should use unwind-protect to make sure the group is always finished. The call to activate-change-group should be inside the unwind-protect, in case the user types C-g just after it runs. (This is one reason why prepare-change-group and activate-change-group are separate functions, because normally you would call prepare-change-group before the start of that unwind-protect.) Once you finish the group, don't use the handle again—in particular, don't try to finish the same group twice. To make a multibuffer change group, call prepare-change-group once for each buffer you want to cover, then use nconc to combine the returned values, like this: (nconc (prepare-change-group buffer-1) (prepare-change-group buffer-2)) You can then activate the multibuffer change group with a single call to activate-change-group, and finish it with a single call to accept-change-group or cancel-change-group. Nested use of several change groups for the same buffer works as you would expect. Non-nested use of change groups for the same buffer will get Emacs confused, so don't let it happen; the first change group you start for any given buffer should be the last one finished. Change Hooks change hooks hooks for text changes These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also , for how to detect changes to specific parts of the text. The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them. before-change-functions — Variable: before-change-functions This variable holds a list of functions to call before any buffermodification. Each function gets two arguments, the beginning and endof the region that is about to change, represented as integers. Thebuffer that is about to change is always the current buffer. after-change-functions — Variable: after-change-functions This variable holds a list of functions to call after any buffermodification. Each function receives three arguments: the beginning andend of the region just changed, and the length of the text that existedbefore the change. All three arguments are integers. The buffer that'sabout to change is always the current buffer.The length of the old text is the difference between the buffer positionsbefore and after that text as it was before the change. As for thechanged text, its length is simply the difference between the first twoarguments. Output of messages into the ‘*Messages*’ buffer does not call these functions. combine-after-change-calls — Macro: combine-after-change-calls body … The macro executes body normally, but arranges to call theafter-change functions just once for a series of several changes—ifthat seems safe.If a program makes several text changes in the same area of the buffer,using the macro combine-after-change-calls around that part ofthe program can make it run considerably faster when after-change hooksare in use. When the after-change hooks are ultimately called, thearguments specify a portion of the buffer including all of the changesmade within the combine-after-change-calls body.Warning: You must not alter the values ofafter-change-functions withinthe body of a combine-after-change-calls form.Warning: if the changes you combine occur in widely scatteredparts of the buffer, this will still work, but it is not advisable,because it may lead to inefficient behavior for some change hookfunctions. The two variables above are temporarily bound to nil during the time that any of these functions is running. This means that if one of these functions changes the buffer, that change won't run these functions. If you do want a hook function to make changes that run these functions, make it bind these variables back to their usual values. One inconvenient result of this protective feature is that you cannot have a function in after-change-functions or before-change-functions which changes the value of that variable. But that's not a real limitation. If you want those functions to change the list of functions to run, simply add one fixed function to the hook, and code that function to look in another variable for other functions to call. Here is an example: (setq my-own-after-change-functions nil) (defun indirect-after-change-function (beg end len) (let ((list my-own-after-change-functions)) (while list (funcall (car list) beg end len) (setq list (cdr list))))) (add-hooks 'after-change-functions 'indirect-after-change-function) first-change-hook — Variable: first-change-hook This variable is a normal hook that is run whenever a buffer is changedthat was previously in the unmodified state. inhibit-modification-hooks — Variable: inhibit-modification-hooks If this variable is non-nil, all of the change hooks aredisabled; none of them run. This affects all the hook variablesdescribed above in this section, as well as the hooks attached tocertain special text properties (see ) and overlayproperties (see ). <setfilename>../info/characters</setfilename> Non-ASCII Characters multibyte characters characters, multi-byte non-ASCII characters This chapter covers the special issues relating to non-ASCII characters and how they are stored in strings and buffers. Text Representations text representations Emacs has two text representations—two ways to represent text in a string or buffer. These are called unibyte and multibyte. Each string, and each buffer, uses one of these two representations. For most purposes, you can ignore the issue of representations, because Emacs converts text between them as appropriate. Occasionally in Lisp programming you will need to pay attention to the difference. unibyte text In unibyte representation, each character occupies one byte and therefore the possible character codes range from 0 to 255. Codes 0 through 127 are ASCII characters; the codes from 128 through 255 are used for one non-ASCII character set (you can choose which character set by setting the variable nonascii-insert-offset). leading code multibyte text trailing codes In multibyte representation, a character may occupy more than one byte, and as a result, the full range of Emacs character codes can be stored. The first byte of a multibyte character is always in the range 128 through 159 (octal 0200 through 0237). These values are called leading codes. The second and subsequent bytes of a multibyte character are always in the range 160 through 255 (octal 0240 through 0377); these values are trailing codes. Some sequences of bytes are not valid in multibyte text: for example, a single isolated byte in the range 128 through 159 is not allowed. But character codes 128 through 159 can appear in multibyte text, represented as two-byte sequences. All the character codes 128 through 255 are possible (though slightly abnormal) in multibyte text; they appear in multibyte buffers and strings when you do explicit encoding and decoding (see ). In a buffer, the buffer-local value of the variable enable-multibyte-characters specifies the representation used. The representation for a string is determined and recorded in the string when the string is constructed. enable-multibyte-characters — Variable: enable-multibyte-characters This variable specifies the current buffer's text representation.If it is non-nil, the buffer contains multibyte text; otherwise,it contains unibyte text.You cannot set this variable directly; instead, use the functionset-buffer-multibyte to change a buffer's representation. default-enable-multibyte-characters — Variable: default-enable-multibyte-characters This variable's value is entirely equivalent to (default-value'enable-multibyte-characters), and setting this variable changes thatdefault value. Setting the local binding ofenable-multibyte-characters in a specific buffer is not allowed,but changing the default value is supported, and it is a reasonablething to do, because it has no effect on existing buffers.The ‘--unibyte’ command line option does its job by setting thedefault value to nil early in startup. position-bytes — Function: position-bytes position Return the byte-position corresponding to buffer positionposition in the current buffer. This is 1 at the start of thebuffer, and counts upward in bytes. If position is out ofrange, the value is nil. byte-to-position — Function: byte-to-position byte-position Return the buffer position corresponding to byte-positionbyte-position in the current buffer. If byte-position isout of range, the value is nil. multibyte-string-p — Function: multibyte-string-p string Return t if string is a multibyte string. string-bytes — Function: string-bytes string string, number of bytesThis function returns the number of bytes in string.If string is a multibyte string, this can be greater than(length string). Converting Text Representations Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, though this conversion loses information. In general these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation. Emacs chooses the representation for a string based on the text that it is constructed from. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has. When inserting text into a buffer, Emacs converts the text to the buffer's representation, as specified by enable-multibyte-characters in that buffer. In particular, when you insert multibyte text into a unibyte buffer, Emacs converts the text to unibyte, even though this conversion cannot in general preserve all the characters that might be in the multibyte text. The other natural alternative, to convert the buffer contents to multibyte, is not acceptable because the buffer's representation is a choice made by the user that cannot be overridden automatically. Converting unibyte text to multibyte text leaves ASCII characters unchanged, and likewise character codes 128 through 159. It converts the non-ASCII codes 160 through 255 by adding the value nonascii-insert-offset to each character code. By setting this variable, you specify which character set the unibyte characters correspond to (see ). For example, if nonascii-insert-offset is 2048, which is (- (make-char 'latin-iso8859-1) 128), then the unibyte non-ASCII characters correspond to Latin 1. If it is 2688, which is (- (make-char 'greek-iso8859-7) 128), then they correspond to Greek letters. Converting multibyte text to unibyte is simpler: it discards all but the low 8 bits of each character code. If nonascii-insert-offset has a reasonable value, corresponding to the beginning of some character set, this conversion is the inverse of the other: converting unibyte text to multibyte and back to unibyte reproduces the original unibyte text. nonascii-insert-offset — Variable: nonascii-insert-offset This variable specifies the amount to add to a non-ASCII characterwhen converting unibyte text to multibyte. It also applies whenself-insert-command inserts a character in the unibytenon-ASCII range, 128 through 255. However, the functionsinsert and insert-char do not perform this conversion.The right value to use to select character set cs is (-(make-char cs) 128). If the value ofnonascii-insert-offset is zero, then conversion actually uses thevalue for the Latin 1 character set, rather than zero. nonascii-translation-table — Variable: nonascii-translation-table This variable provides a more general alternative tononascii-insert-offset. You can use it to specify independentlyhow to translate each code in the range of 128 through 255 into amultibyte character. The value should be a char-table, or nil.If this is non-nil, it overrides nonascii-insert-offset. The next three functions either return the argument string, or a newly created string with no text properties. string-make-unibyte — Function: string-make-unibyte string This function converts the text of string to unibyterepresentation, if it isn't already, and returns the result. Ifstring is a unibyte string, it is returned unchanged. Multibytecharacter codes are converted to unibyte according tononascii-translation-table or, if that is nil, usingnonascii-insert-offset. If the lookup in the translation tablefails, this function takes just the low 8 bits of each character. string-make-multibyte — Function: string-make-multibyte string This function converts the text of string to multibyterepresentation, if it isn't already, and returns the result. Ifstring is a multibyte string or consists entirely ofASCII characters, it is returned unchanged. In particular,if string is unibyte and entirely ASCII, the returnedstring is unibyte. (When the characters are all ASCII,Emacs primitives will treat the string the same way whether it isunibyte or multibyte.) If string is unibyte and containsnon-ASCII characters, the functionunibyte-char-to-multibyte is used to convert each unibytecharacter to a multibyte character. string-to-multibyte — Function: string-to-multibyte string This function returns a multibyte string containing the same sequenceof character codes as string. Unlikestring-make-multibyte, this function unconditionally returns amultibyte string. If string is a multibyte string, it isreturned unchanged. multibyte-char-to-unibyte — Function: multibyte-char-to-unibyte char This convert the multibyte character char to a unibytecharacter, based on nonascii-translation-table andnonascii-insert-offset. unibyte-char-to-multibyte — Function: unibyte-char-to-multibyte char This convert the unibyte character char to a multibytecharacter, based on nonascii-translation-table andnonascii-insert-offset. Selecting a Representation Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa. set-buffer-multibyte — Function: set-buffer-multibyte multibyte Set the representation type of the current buffer. If multibyteis non-nil, the buffer becomes multibyte. If multibyteis nil, the buffer becomes unibyte.This function leaves the buffer contents unchanged when viewed as asequence of bytes. As a consequence, it can change the contents viewedas characters; a sequence of two bytes which is treated as one characterin multibyte representation will count as two characters in unibyterepresentation. Character codes 128 through 159 are an exception. Theyare represented by one byte in a unibyte buffer, but when the buffer isset to multibyte, they are converted to two-byte sequences, and viceversa.This function sets enable-multibyte-characters to record whichrepresentation is in use. It also adjusts various data in the buffer(including overlays, text properties and markers) so that they cover thesame text as they did before.You cannot use set-buffer-multibyte on an indirect buffer,because indirect buffers always inherit the representation of thebase buffer. string-as-unibyte — Function: string-as-unibyte string This function returns a string with the same bytes as string buttreating each byte as a character. This means that the value may havemore characters than string has.If string is already a unibyte string, then the value isstring itself. Otherwise it is a newly created string, with notext properties. If string is multibyte, any characters itcontains of charset eight-bit-control or eight-bit-graphicare converted to the corresponding single byte. string-as-multibyte — Function: string-as-multibyte string This function returns a string with the same bytes as string buttreating each multibyte sequence as one character. This means that thevalue may have fewer characters than string has.If string is already a multibyte string, then the value isstring itself. Otherwise it is a newly created string, with notext properties. If string is unibyte and contains any individual8-bit bytes (i.e. not part of a multibyte form), they are converted tothe corresponding multibyte character of charset eight-bit-controlor eight-bit-graphic. Character Codes character codes The unibyte and multibyte text representations use different character codes. The valid character codes for unibyte representation range from 0 to 255—the values that can fit in one byte. The valid character codes for multibyte representation range from 0 to 524287, but not all values in that range are valid. The values 128 through 255 are not entirely proper in multibyte text, but they can occur if you do explicit encoding and decoding (see ). Some other character codes cannot occur at all in multibyte text. Only the ASCII codes 0 through 127 are completely legitimate in both representations. char-valid-p — Function: char-valid-p charcode &optional genericp This returns t if charcode is valid (either for unibytetext or for multibyte text). (char-valid-p 65) => t (char-valid-p 256) => nil (char-valid-p 2248) => t If the optional argument genericp is non-nil, thisfunction also returns t if charcode is a genericcharacter (see ). Character Sets character sets Emacs classifies characters into various character sets, each of which has a name which is a symbol. Each character belongs to one and only one character set. In general, there is one character set for each distinct script. For example, latin-iso8859-1 is one character set, greek-iso8859-7 is another, and ascii is another. An Emacs character set can hold at most 9025 characters; therefore, in some cases, characters that would logically be grouped together are split into several character sets. For example, one set of Chinese characters, generally known as Big 5, is divided into two Emacs character sets, chinese-big5-1 and chinese-big5-2. ASCII characters are in character set ascii. The non-ASCII characters 128 through 159 are in character set eight-bit-control, and codes 160 through 255 are in character set eight-bit-graphic. charsetp — Function: charsetp object Returns t if object is a symbol that names a character set,nil otherwise. charset-list — Variable: charset-list The value is a list of all defined character set names. charset-list — Function: charset-list This function returns the value of charset-list. It is onlyprovided for backward compatibility. char-charset — Function: char-charset character This function returns the name of the character set that characterbelongs to, or the symbol unknown if character is not avalid character. charset-plist — Function: charset-plist charset This function returns the charset property list of the character setcharset. Although charset is a symbol, this is not the sameas the property list of that symbol. Charset properties are used forspecial purposes within Emacs. list-charset-chars — Command: list-charset-chars charset This command displays a list of characters in the character setcharset. Characters and Bytes bytes and characters introduction sequence (of character) dimension (of character set) In multibyte representation, each character occupies one or more bytes. Each character set has an introduction sequence, which is normally one or two bytes long. (Exception: the ascii character set and the eight-bit-graphic character set have a zero-length introduction sequence.) The introduction sequence is the beginning of the byte sequence for any character in the character set. The rest of the character's bytes distinguish it from the other characters in the same character set. Depending on the character set, there are either one or two distinguishing bytes; the number of such bytes is called the dimension of the character set. charset-dimension — Function: charset-dimension charset This function returns the dimension of charset; at present, thedimension is always 1 or 2. charset-bytes — Function: charset-bytes charset This function returns the number of bytes used to represent a characterin character set charset. This is the simplest way to determine the byte length of a character set's introduction sequence: (- (charset-bytes charset) (charset-dimension charset)) Splitting Characters character as bytes The functions in this section convert between characters and the byte values used to represent them. For most purposes, there is no need to be concerned with the sequence of bytes used to represent a character, because Emacs translates automatically when necessary. split-char — Function: split-char character Return a list containing the name of the character set ofcharacter, followed by one or two byte values (integers) whichidentify character within that character set. The number of bytevalues is the character set's dimension.If character is invalid as a character code, split-charreturns a list consisting of the symbol unknown and character. (split-char 2248) => (latin-iso8859-1 72) (split-char 65) => (ascii 65) (split-char 128) => (eight-bit-control 128) generate characters in charsets make-char — Function: make-char charset &optional code1 code2 This function returns the character in character set charset whoseposition codes are code1 and code2. This is roughly theinverse of split-char. Normally, you should specify either oneor both of code1 and code2 according to the dimension ofcharset. For example, (make-char 'latin-iso8859-1 72) => 2248 Actually, the eighth bit of both code1 and code2 is zeroedbefore they are used to index charset. Thus you may use, forinstance, an ISO 8859 character code rather than subtracting 128, asis necessary to index the corresponding Emacs charset. generic characters If you call make-char with no byte-values, the result is a generic character which stands for charset. A generic character is an integer, but it is not valid for insertion in the buffer as a character. It can be used in char-table-range to refer to the whole character set (see ). char-valid-p returns nil for generic characters. For example: (make-char 'latin-iso8859-1) => 2176 (char-valid-p 2176) => nil (char-valid-p 2176 t) => t (split-char 2176) => (latin-iso8859-1 0) The character sets ascii, eight-bit-control, and eight-bit-graphic don't have corresponding generic characters. If charset is one of them and you don't supply code1, make-char returns the character code corresponding to the smallest code in charset. Scanning for Character Sets Sometimes it is useful to find out which character sets appear in a part of a buffer or a string. One use for this is in determining which coding systems (see ) are capable of representing all of the text in question. charset-after — Function: charset-after &optional pos This function return the charset of a character in the current bufferat position pos. If pos is omitted or nil, itdefaults to the current value of point. If pos is out of range,the value is nil. find-charset-region — Function: find-charset-region beg end &optional translation This function returns a list of the character sets that appear in thecurrent buffer between positions beg and end.The optional argument translation specifies a translation table tobe used in scanning the text (see ). If itis non-nil, then each character in the region is translatedthrough this table, and the value returned describes the translatedcharacters instead of the characters actually in the buffer. find-charset-string — Function: find-charset-string string &optional translation This function returns a list of the character sets that appear in thestring string. It is just like find-charset-region, exceptthat it applies to the contents of string instead of part of thecurrent buffer. Translation of Characters character translation tables translation tables A translation table is a char-table that specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems. For instance, the coding-system utf-8 has a translation table that maps characters of various charsets (e.g., latin-iso8859-x) into Unicode character sets. This way, it can encode Latin-2 characters into UTF-8. Meanwhile, unify-8859-on-decoding-mode operates by specifying standard-translation-table-for-decode to translate Latin-x characters into corresponding Unicode characters. make-translation-table — Function: make-translation-table &rest translations This function returns a translation table based on the argumenttranslations. Each element of translations should be alist of elements of the form (from . to); this saysto translate the character from into to.The arguments and the forms in each argument are processed in order,and if a previous form already translates to to some othercharacter, say to-alt, from is also translated toto-alt.You can also map one whole character set into another character set withthe same dimension. To do this, you specify a generic character (whichdesignates a character set) for from (see ).In this case, if to is also a generic character, its characterset should have the same dimension as from's. Then thetranslation table translates each character of from's characterset into the corresponding character of to's character set. Iffrom is a generic character and to is an ordinarycharacter, then the translation table translates every character offrom's character set into to. In decoding, the translation table's translations are applied to the characters that result from ordinary decoding. If a coding system has property translation-table-for-decode, that specifies the translation table to use. (This is a property of the coding system, as returned by coding-system-get, not a property of the symbol that is the coding system's name. See Basic Concepts of Coding Systems.) Otherwise, if standard-translation-table-for-decode is non-nil, decoding uses that table. In encoding, the translation table's translations are applied to the characters in the buffer, and the result of translation is actually encoded. If a coding system has property translation-table-for-encode, that specifies the translation table to use. Otherwise the variable standard-translation-table-for-encode specifies the translation table. standard-translation-table-for-decode — Variable: standard-translation-table-for-decode This is the default translation table for decoding, forcoding systems that don't specify any other translation table. standard-translation-table-for-encode — Variable: standard-translation-table-for-encode This is the default translation table for encoding, forcoding systems that don't specify any other translation table. translation-table-for-input — Variable: translation-table-for-input Self-inserting characters are translated through this translationtable before they are inserted. Search commands also translate theirinput through this table, so they can compare more reliably withwhat's in the buffer.set-buffer-file-coding-system sets this variable so that yourkeyboard input gets translated into the character sets that the bufferis likely to contain. This variable automatically becomesbuffer-local when set. Coding Systems coding system When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular coding system. How to define a coding system is an arcane matter, and is not documented here. Basic Concepts of Coding Systems character code conversion Character code conversion involves conversion between the encoding used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8. Most coding systems specify a particular character code for conversion, but some of them leave the choice unspecified—to be chosen heuristically for each file, based on the data. In general, a coding system doesn't guarantee roundtrip identity: decoding a byte sequence using coding system, then encoding the resulting text in the same coding system, can produce a different byte sequence. However, the following coding systems do guarantee that the byte sequence will be the same as what you originally decoded: chinese-big5 chinese-iso-8bit cyrillic-iso-8bit emacs-mule greek-iso-8bit hebrew-iso-8bit iso-latin-1 iso-latin-2 iso-latin-3 iso-latin-4 iso-latin-5 iso-latin-8 iso-latin-9 iso-safe japanese-iso-8bit japanese-shift-jis korean-iso-8bit raw-text Encoding buffer text and then decoding the result can also fail to reproduce the original text. For instance, if you encode Latin-2 characters with utf-8 and decode the result using the same coding system, you'll get Unicode characters (of charset mule-unicode-0100-24ff). If you encode Unicode characters with iso-latin-2 and decode the result with the same coding system, you'll get Latin-2 characters. EOL conversion end-of-line conversion line end conversion End of line conversion handles three different conventions used on various systems for representing end of line in files. The Unix convention is to use the linefeed character (also called newline). The DOS convention is to use a carriage-return and a linefeed at the end of a line. The Mac convention is to use just carriage-return. base coding system variant coding system Base coding systems such as latin-1 leave the end-of-line conversion unspecified, to be chosen based on the data. Variant coding systems such as latin-1-unix, latin-1-dos and latin-1-mac specify the end-of-line conversion explicitly as well. Most base coding systems have three corresponding variants whose names are formed by adding ‘-unix’, ‘-dos’ and ‘-mac’. The coding system raw-text is special in that it prevents character code conversion, and causes the buffer visited with that coding system to be a unibyte buffer. It does not specify the end-of-line conversion, allowing that to be determined as usual by the data, and has the usual three variants which specify the end-of-line conversion. no-conversion is equivalent to raw-text-unix: it specifies no conversion of either character codes or end-of-line. The coding system emacs-mule specifies that the data is represented in the internal Emacs encoding. This is like raw-text in that no code conversion happens, but different in that the result is multibyte data. coding-system-get — Function: coding-system-get coding-system property This function returns the specified property of the coding systemcoding-system. Most coding system properties exist for internalpurposes, but one that you might find useful is mime-charset.That property's value is the name used in MIME for the character codingwhich this coding system can read and write. Examples: (coding-system-get 'iso-latin-1 'mime-charset) => iso-8859-1 (coding-system-get 'iso-2022-cn 'mime-charset) => iso-2022-cn (coding-system-get 'cyrillic-koi8 'mime-charset) => koi8-r The value of the mime-charset property is also definedas an alias for the coding system. Encoding and I/O The principal purpose of coding systems is for use in reading and writing files. The function insert-file-contents uses a coding system for decoding the file data, and write-region uses one to encode the buffer contents. You can specify the coding system to use either explicitly (see ), or implicitly using a default mechanism (see ). But these methods may not completely specify what to do. For example, they may choose a coding system such as undefined which leaves the character code conversion to be determined from the data. In these cases, the I/O operation finishes the job of choosing a coding system. Very often you will want to find out afterwards which coding system was chosen. buffer-file-coding-system — Variable: buffer-file-coding-system This buffer-local variable records the coding system that was used to visitthe current buffer. It is used for saving the buffer, and for writing partof the buffer with write-region. If the text to be writtencannot be safely encoded using the coding system specified by thisvariable, these operations select an alternative encoding by callingthe function select-safe-coding-system (see ). If selecting a different encoding requires to askthe user to specify a coding system, buffer-file-coding-systemis updated to the newly selected coding system.buffer-file-coding-system does not affect sending textto a subprocess. save-buffer-coding-system — Variable: save-buffer-coding-system This variable specifies the coding system for saving the buffer (byoverriding buffer-file-coding-system). Note that it is not usedfor write-region.When a command to save the buffer starts out to usebuffer-file-coding-system (or save-buffer-coding-system),and that coding system cannot handlethe actual text in the buffer, the command asks the user to chooseanother coding system (by calling select-safe-coding-system).After that happens, the command also updatesbuffer-file-coding-system to represent the coding system thatthe user specified. last-coding-system-used — Variable: last-coding-system-used I/O operations for files and subprocesses set this variable to thecoding system name that was used. The explicit encoding and decodingfunctions (see ) set it too.Warning: Since receiving subprocess output sets this variable,it can change whenever Emacs waits; therefore, you should copy thevalue shortly after the function call that stores the value you areinterested in. The variable selection-coding-system specifies how to encode selections for the window system. See . file-name-coding-system — Variable: file-name-coding-system The variable file-name-coding-system specifies the codingsystem to use for encoding file names. Emacs encodes file names usingthat coding system for all file operations. Iffile-name-coding-system is nil, Emacs uses a defaultcoding system determined by the selected language environment. In thedefault language environment, any non-ASCII characters infile names are not encoded specially; they appear in the file systemusing the internal Emacs representation. Warning: if you change file-name-coding-system (or the language environment) in the middle of an Emacs session, problems can result if you have already visited files whose names were encoded using the earlier coding system and are handled differently under the new coding system. If you try to save one of these buffers under the visited file name, saving may use the wrong file name, or it may get an error. If such a problem happens, use C-x C-w to specify a new file name for that buffer. Coding Systems in Lisp Here are the Lisp facilities for working with coding systems: coding-system-list — Function: coding-system-list &optional base-only This function returns a list of all coding system names (symbols). Ifbase-only is non-nil, the value includes only thebase coding systems. Otherwise, it includes alias and variant codingsystems as well. coding-system-p — Function: coding-system-p object This function returns t if object is a coding systemname or nil. check-coding-system — Function: check-coding-system coding-system This function checks the validity of coding-system.If that is valid, it returns coding-system.Otherwise it signals an error with condition coding-system-error. coding-system-eol-type — Function: coding-system-eol-type coding-system This function returns the type of end-of-line (a.k.a. eol)conversion used by coding-system. If coding-systemspecifies a certain eol conversion, the return value is an integer 0,1, or 2, standing for unix, dos, and mac,respectively. If coding-system doesn't specify eol conversionexplicitly, the return value is a vector of coding systems, each onewith one of the possible eol conversion types, like this:(coding-system-eol-type 'latin-1) => [latin-1-unix latin-1-dos latin-1-mac]If this function returns a vector, Emacs will decide, as part of thetext encoding or decoding process, what eol conversion to use. Fordecoding, the end-of-line format of the text is auto-detected, and theeol conversion is set to match it (e.g., DOS-style CRLF format willimply dos eol conversion). For encoding, the eol conversion istaken from the appropriate default coding system (e.g.,default-buffer-file-coding-system forbuffer-file-coding-system), or from the default eol conversionappropriate for the underlying platform. coding-system-change-eol-conversion — Function: coding-system-change-eol-conversion coding-system eol-type This function returns a coding system which is like coding-systemexcept for its eol conversion, which is specified by eol-type.eol-type should be unix, dos, mac, ornil. If it is nil, the returned coding system determinesthe end-of-line conversion from the data.eol-type may also be 0, 1 or 2, standing for unix,dos and mac, respectively. coding-system-change-text-conversion — Function: coding-system-change-text-conversion eol-coding text-coding This function returns a coding system which uses the end-of-lineconversion of eol-coding, and the text conversion oftext-coding. If text-coding is nil, it returnsundecided, or one of its variants according to eol-coding. find-coding-systems-region — Function: find-coding-systems-region from to This function returns a list of coding systems that could be used toencode a text between from and to. All coding systems inthe list can safely encode any multibyte characters in that portion ofthe text.If the text contains no multibyte characters, the function returns thelist (undecided). find-coding-systems-string — Function: find-coding-systems-string string This function returns a list of coding systems that could be used toencode the text of string. All coding systems in the list cansafely encode any multibyte characters in string. If the textcontains no multibyte characters, this returns the list(undecided). find-coding-systems-for-charsets — Function: find-coding-systems-for-charsets charsets This function returns a list of coding systems that could be used toencode all the character sets in the list charsets. detect-coding-region — Function: detect-coding-region start end &optional highest This function chooses a plausible coding system for decoding the textfrom start to end. This text should be a byte sequence(see ).Normally this function returns a list of coding systems that couldhandle decoding the text that was scanned. They are listed in order ofdecreasing priority. But if highest is non-nil, then thereturn value is just one coding system, the one that is highest inpriority.If the region contains only ASCII characters except for suchISO-2022 control characters ISO-2022 as ESC, the value isundecided or (undecided), or a variant specifyingend-of-line conversion, if that can be deduced from the text. detect-coding-string — Function: detect-coding-string string &optional highest This function is like detect-coding-region except that itoperates on the contents of string instead of bytes in the buffer. See Process Information, in particular the description of the functions process-coding-system and set-process-coding-system, for how to examine or set the coding systems used for I/O to a subprocess. User-Chosen Coding Systems select safe coding system select-safe-coding-system — Function: select-safe-coding-system from to &optional default-coding-system accept-default-p file This function selects a coding system for encoding specified text,asking the user to choose if necessary. Normally the specified textis the text in the current buffer between from and to. Iffrom is a string, the string specifies the text to encode, andto is ignored.If default-coding-system is non-nil, that is the firstcoding system to try; if that can handle the text,select-safe-coding-system returns that coding system. It canalso be a list of coding systems; then the function tries each of themone by one. After trying all of them, it next tries the currentbuffer's value of buffer-file-coding-system (if it is notundecided), then the value ofdefault-buffer-file-coding-system and finally the user's mostpreferred coding system, which the user can set using the commandprefer-coding-system (see See section ``Recognizing Coding Systems'' in The GNU Emacs Manual).If one of those coding systems can safely encode all the specifiedtext, select-safe-coding-system chooses it and returns it.Otherwise, it asks the user to choose from a list of coding systemswhich can encode all the text, and returns the user's choice.default-coding-system can also be a list whose first element ist and whose other elements are coding systems. Then, if no codingsystem in the list can handle the text, select-safe-coding-systemqueries the user immediately, without trying any of the threealternatives described above.The optional argument accept-default-p, if non-nil,should be a function to determine whether a coding system selectedwithout user interaction is acceptable. select-safe-coding-systemcalls this function with one argument, the base coding system of theselected coding system. If accept-default-p returns nil,select-safe-coding-system rejects the silently selected codingsystem, and asks the user to select a coding system from a list ofpossible candidates. select-safe-coding-system-accept-default-pIf the variable select-safe-coding-system-accept-default-p isnon-nil, its value overrides the value ofaccept-default-p.As a final step, before returning the chosen coding system,select-safe-coding-system checks whether that coding system isconsistent with what would be selected if the contents of the regionwere read from a file. (If not, this could lead to data corruption ina file subsequently re-visited and edited.) Normally,select-safe-coding-system uses buffer-file-name as thefile for this purpose, but if file is non-nil, it usesthat file instead (this can be relevant for write-region andsimilar functions). If it detects an apparent inconsistency,select-safe-coding-system queries the user before selecting thecoding system. Here are two functions you can use to let the user specify a coding system, with completion. See . read-coding-system — Function: read-coding-system prompt &optional default This function reads a coding system using the minibuffer, prompting withstring prompt, and returns the coding system name as a symbol. Ifthe user enters null input, default specifies which coding systemto return. It should be a symbol or a string. read-non-nil-coding-system — Function: read-non-nil-coding-system prompt This function reads a coding system using the minibuffer, prompting withstring prompt, and returns the coding system name as a symbol. Ifthe user tries to enter null input, it asks the user to try again.See . Default Coding Systems This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them. The idea of these variables is that you set them once and for all to the defaults you want, and then do not change them again. To specify a particular coding system for a particular operation in a Lisp program, don't change these variables; instead, override them using coding-system-for-read and coding-system-for-write (see ). auto-coding-regexp-alist — Variable: auto-coding-regexp-alist This variable is an alist of text patterns and corresponding codingsystems. Each element has the form (regexp. coding-system); a file whose first few kilobytes matchregexp is decoded with coding-system when its contents areread into a buffer. The settings in this alist take priority overcoding: tags in the files and the contents offile-coding-system-alist (see below). The default value is setso that Emacs automatically recognizes mail files in Babyl format andreads them with no code conversions. file-coding-system-alist — Variable: file-coding-system-alist This variable is an alist that specifies the coding systems to use forreading and writing particular files. Each element has the form(pattern . coding), where pattern is a regularexpression that matches certain file names. The element applies to filenames that match pattern.The cdr of the element, coding, should be either a codingsystem, a cons cell containing two coding systems, or a function name (asymbol with a function definition). If coding is a coding system,that coding system is used for both reading the file and writing it. Ifcoding is a cons cell containing two coding systems, its carspecifies the coding system for decoding, and its cdr specifies thecoding system for encoding.If coding is a function name, the function should take oneargument, a list of all arguments passed tofind-operation-coding-system. It must return a coding systemor a cons cell containing two coding systems. This value has the samemeaning as described above. process-coding-system-alist — Variable: process-coding-system-alist This variable is an alist specifying which coding systems to use for asubprocess, depending on which program is running in the subprocess. Itworks like file-coding-system-alist, except that pattern ismatched against the program name used to start the subprocess. The codingsystem or systems specified in this alist are used to initialize thecoding systems used for I/O to the subprocess, but you can specifyother coding systems later using set-process-coding-system. Warning: Coding systems such as undecided, which determine the coding system from the data, do not work entirely reliably with asynchronous subprocess output. This is because Emacs handles asynchronous subprocess output in batches, as it arrives. If the coding system leaves the character code conversion unspecified, or leaves the end-of-line conversion unspecified, Emacs must try to detect the proper conversion from one batch at a time, and this does not always work. Therefore, with an asynchronous subprocess, if at all possible, use a coding system which determines both the character code conversion and the end of line conversion—that is, one like latin-1-unix, rather than undecided or latin-1. network-coding-system-alist — Variable: network-coding-system-alist This variable is an alist that specifies the coding system to use fornetwork streams. It works much like file-coding-system-alist,with the difference that the pattern in an element may be either aport number or a regular expression. If it is a regular expression, itis matched against the network service name used to open the networkstream. default-process-coding-system — Variable: default-process-coding-system This variable specifies the coding systems to use for subprocess (andnetwork stream) input and output, when nothing else specifies what todo.The value should be a cons cell of the form (input-coding. output-coding). Here input-coding applies to input fromthe subprocess, and output-coding applies to output to it. auto-coding-functions — Variable: auto-coding-functions This variable holds a list of functions that try to determine acoding system for a file based on its undecoded contents.Each function in this list should be written to look at text in thecurrent buffer, but should not modify it in any way. The buffer willcontain undecoded text of parts of the file. Each function shouldtake one argument, size, which tells it how many characters tolook at, starting from point. If the function succeeds in determininga coding system for the file, it should return that coding system.Otherwise, it should return nil.If a file has a ‘coding:’ tag, that takes precedence, so thesefunctions won't be called. find-operation-coding-system — Function: find-operation-coding-system operation &rest arguments This function returns the coding system to use (by default) forperforming operation with arguments. The value has thisform: (decoding-system . encoding-system) The first element, decoding-system, is the coding system to usefor decoding (in case operation does decoding), andencoding-system is the coding system for encoding (in caseoperation does encoding).The argument operation is a symbol, one of write-region,start-process, call-process, call-process-region,insert-file-contents, or open-network-stream. These arethe names of the Emacs I/O primitives that can do character code andeol conversion.The remaining arguments should be the same arguments that might be givento the corresponding I/O primitive. Depending on the primitive, oneof those arguments is selected as the target. For example, ifoperation does file I/O, whichever argument specifies the filename is the target. For subprocess primitives, the process name is thetarget. For open-network-stream, the target is the service nameor port number.Depending on operation, this function looks up the target infile-coding-system-alist, process-coding-system-alist,or network-coding-system-alist. If the target is found in thealist, find-operation-coding-system returns its association inthe alist; otherwise it returns nil.If operation is insert-file-contents, the argumentcorresponding to the target may be a cons cell of the form(filename . buffer)). In that case, filenameis a file name to look up in file-coding-system-alist, andbuffer is a buffer that contains the file's contents (not yetdecoded). If file-coding-system-alist specifies a function tocall for this file, and that function needs to examine the file'scontents (as it usually does), it should examine the contents ofbuffer instead of reading the file. Specifying a Coding System for One Operation You can specify the coding system for a specific operation by binding the variables coding-system-for-read and/or coding-system-for-write. coding-system-for-read — Variable: coding-system-for-read If this variable is non-nil, it specifies the coding system touse for reading a file, or for input from a synchronous subprocess.It also applies to any asynchronous subprocess or network stream, but ina different way: the value of coding-system-for-read when youstart the subprocess or open the network stream specifies the inputdecoding method for that subprocess or network stream. It remains inuse for that subprocess or network stream unless and until overridden.The right way to use this variable is to bind it with let for aspecific I/O operation. Its global value is normally nil, andyou should not globally set it to any other value. Here is an exampleof the right way to use the variable: ;; Read the file with no character code conversion. ;; Assume crlf represents end-of-line. (let ((coding-system-for-read 'emacs-mule-dos)) (insert-file-contents filename)) When its value is non-nil, this variable takes precedence overall other methods of specifying a coding system to use for input,including file-coding-system-alist,process-coding-system-alist andnetwork-coding-system-alist. coding-system-for-write — Variable: coding-system-for-write This works much like coding-system-for-read, except that itapplies to output rather than input. It affects writing to files,as well as sending output to subprocesses and net connections.When a single operation does both input and output, as docall-process-region and start-process, bothcoding-system-for-read and coding-system-for-writeaffect it. inhibit-eol-conversion — Variable: inhibit-eol-conversion When this variable is non-nil, no end-of-line conversion is done,no matter which coding system is specified. This applies to all theEmacs I/O and subprocess primitives, and to the explicit encoding anddecoding functions (see ). Explicit Encoding and Decoding encoding in coding systems decoding in coding systems All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section. The result of encoding, and the input to decoding, are not ordinary text. They logically consist of a series of byte values; that is, a series of characters whose codes are in the range 0 through 255. In a multibyte buffer or string, character codes 128 through 159 are represented by multibyte sequences, but this is invisible to Lisp programs. The usual way to read a file into a buffer as a sequence of bytes, so you can decode the contents explicitly, is with insert-file-contents-literally (see ); alternatively, specify a non-nil rawfile argument when visiting a file with find-file-noselect. These methods result in a unibyte buffer. The usual way to use the byte sequence that results from explicitly encoding text is to copy it to a file or process—for example, to write it with write-region (see ), and suppress encoding by binding coding-system-for-write to no-conversion. Here are the functions to perform explicit encoding or decoding. The encoding functions produce sequences of bytes; the decoding functions are meant to operate on sequences of bytes. All of these functions discard text properties. encode-coding-region — Command: encode-coding-region start end coding-system This command encodes the text from start to end accordingto coding system coding-system. The encoded text replaces theoriginal text in the buffer. The result of encoding is logically asequence of bytes, but the buffer remains multibyte if it was multibytebefore.This command returns the length of the encoded text. encode-coding-string — Function: encode-coding-string string coding-system &optional nocopy This function encodes the text in string according to codingsystem coding-system. It returns a new string containing theencoded text, except when nocopy is non-nil, in whichcase the function may return string itself if the encodingoperation is trivial. The result of encoding is a unibyte string. decode-coding-region — Command: decode-coding-region start end coding-system This command decodes the text from start to end accordingto coding system coding-system. The decoded text replaces theoriginal text in the buffer. To make explicit decoding useful, the textbefore decoding ought to be a sequence of byte values, but bothmultibyte and unibyte buffers are acceptable.This command returns the length of the decoded text. decode-coding-string — Function: decode-coding-string string coding-system &optional nocopy This function decodes the text in string according to codingsystem coding-system. It returns a new string containing thedecoded text, except when nocopy is non-nil, in whichcase the function may return string itself if the decodingoperation is trivial. To make explicit decoding useful, the contentsof string ought to be a sequence of byte values, but a multibytestring is acceptable. decode-coding-inserted-region — Function: decode-coding-inserted-region from to filename &optional visit beg end replace This function decodes the text from from to to as ifit were being read from file filename using insert-file-contentsusing the rest of the arguments provided.The normal way to use this function is after reading text from a filewithout decoding, if you decide you would rather have decoded it.Instead of deleting the text and reading it again, this time withdecoding, you can call this function. Terminal I/O Encoding Emacs can decode keyboard input using a coding system, and encode terminal output. This is useful for terminals that transmit or display text using a particular encoding such as Latin-1. Emacs does not set last-coding-system-used for encoding or decoding for the terminal. keyboard-coding-system — Function: keyboard-coding-system This function returns the coding system that is in use for decodingkeyboard input—or nil if no coding system is to be used. set-keyboard-coding-system — Command: set-keyboard-coding-system coding-system This command specifies coding-system as the coding system touse for decoding keyboard input. If coding-system is nil,that means do not decode keyboard input. terminal-coding-system — Function: terminal-coding-system This function returns the coding system that is in use for encodingterminal output—or nil for no encoding. set-terminal-coding-system — Command: set-terminal-coding-system coding-system This command specifies coding-system as the coding system to usefor encoding terminal output. If coding-system is nil,that means do not encode terminal output. MS-DOS File Types DOS file types MS-DOS file types Windows file types file types on MS-DOS and Windows text files and binary files binary files and text files On MS-DOS and Microsoft Windows, Emacs guesses the appropriate end-of-line conversion for a file by looking at the file's name. This feature classifies files as text files and binary files. By “binary file” we mean a file of literal byte values that are not necessarily meant to be characters; Emacs does no end-of-line conversion and no character code conversion for them. On the other hand, the bytes in a text file are intended to represent characters; when you create a new file whose name implies that it is a text file, Emacs uses DOS end-of-line conversion. buffer-file-type — Variable: buffer-file-type This variable, automatically buffer-local in each buffer, records thefile type of the buffer's visited file. When a buffer does not specifya coding system with buffer-file-coding-system, this variable isused to determine which coding system to use when writing the contentsof the buffer. It should be nil for text, t for binary.If it is t, the coding system is no-conversion.Otherwise, undecided-dos is used.Normally this variable is set by visiting a file; it is set tonil if the file was visited without any actual conversion. file-name-buffer-file-type-alist — User Option: file-name-buffer-file-type-alist This variable holds an alist for recognizing text and binary files.Each element has the form (regexp . type), whereregexp is matched against the file name, and type may benil for text, t for binary, or a function to call tocompute which. If it is a function, then it is called with a singleargument (the file name) and should return t or nil.When running on MS-DOS or MS-Windows, Emacs checks this alist to decidewhich coding system to use when reading a file. For a text file,undecided-dos is used. For a binary file, no-conversionis used.If no element in this alist matches a given file name, thendefault-buffer-file-type says how to treat the file. default-buffer-file-type — User Option: default-buffer-file-type This variable says how to handle files for whichfile-name-buffer-file-type-alist says nothing about the type.If this variable is non-nil, then these files are treated asbinary: the coding system no-conversion is used. Otherwise,nothing special is done for them—the coding system is deduced solelyfrom the file contents, in the usual Emacs fashion. Input Methods input methods Input methods provide convenient ways of entering non-ASCII characters from the keyboard. Unlike coding systems, which translate non-ASCII characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (See See section ``Input Methods'' in The GNU Emacs Manual, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them. Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names. current-input-method — Variable: current-input-method This variable holds the name of the input method now active in thecurrent buffer. (It automatically becomes local in each buffer when setin any fashion.) It is nil if no input method is active in thebuffer now. default-input-method — User Option: default-input-method This variable holds the default input method for commands that choose aninput method. Unlike current-input-method, this variable isnormally global. set-input-method — Command: set-input-method input-method This command activates input method input-method for the currentbuffer. It also sets default-input-method to input-method.If input-method is nil, this command deactivates any inputmethod for the current buffer. read-input-method-name — Function: read-input-method-name prompt &optional default inhibit-null This function reads an input method name with the minibuffer, promptingwith prompt. If default is non-nil, that is returnedby default, if the user enters empty input. However, ifinhibit-null is non-nil, empty input signals an error.The returned value is a string. input-method-alist — Variable: input-method-alist This variable defines all the supported input methods.Each element defines one input method, and should have the form: (input-method language-env activate-func title description args...) Here input-method is the input method name, a string;language-env is another string, the name of the languageenvironment this input method is recommended for. (That serves only fordocumentation purposes.)activate-func is a function to call to activate this method. Theargs, if any, are passed as arguments to activate-func. Alltold, the arguments to activate-func are input-method andthe args.title is a string to display in the mode line while this method isactive. description is a string describing this method and whatit is good for. The fundamental interface to input methods is through the variable input-method-function. See , and . Locales locale POSIX defines a concept of “locales” which control which language to use in language-related features. These Emacs variables control how Emacs interacts with these features. locale-coding-system — Variable: locale-coding-system keyboard input decoding on XThis variable specifies the coding system to use for decoding systemerror messages and—on X Window system only—keyboard input, forencoding the format argument to format-time-string, and fordecoding the return value of format-time-string. system-messages-locale — Variable: system-messages-locale This variable specifies the locale to use for generating system errormessages. Changing the locale can cause messages to come out in adifferent language or in a different orthography. If the variable isnil, the locale is specified by environment variables in theusual POSIX fashion. system-time-locale — Variable: system-time-locale This variable specifies the locale to use for formatting time values.Changing the locale can cause messages to appear according to theconventions of a different language. If the variable is nil, thelocale is specified by environment variables in the usual POSIX fashion. locale-info — Function: locale-info item This function returns locale data item for the current POSIXlocale, if available. item should be one of these symbols: codeset Return the character set as a string (locale item CODESET). days Return a 7-element vector of day names (locale itemsDAY_1 through DAY_7); months Return a 12-element vector of month names (locale items MON_1through MON_12). paper Return a list (width height) for the default papersize measured in millimeters (locale items PAPER_WIDTH andPAPER_HEIGHT). If the system can't provide the requested information, or ifitem is not one of those symbols, the value is nil. Allstrings in the return value are decoded usinglocale-coding-system. See See section ``Locales'' in The GNU Libc Manual,for more information about locales and locale items. <setfilename>../info/searching</setfilename> Searching and Matching searching GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it. The ‘skip-chars…’ functions also perform a kind of searching. See . To search for changes in character properties, see . Searching for Strings string search These are the primitive functions for searching through the text in a buffer. They are meant for use in programs, but you may call them interactively. If you do so, they prompt for the search string; the arguments limit and noerror are nil, and repeat is 1. These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. See . search-forward — Command: search-forward string &optional limit noerror repeat This function searches forward from point for an exact match forstring. If successful, it sets point to the end of the occurrencefound, and returns the new value of point. If no match is found, thevalue and side effects depend on noerror (see below). In the following example, point is initially at the beginning of theline. Then (search-forward "fox") moves point after the lastletter of ‘fox’: ---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ---------- The argument limit specifies the upper bound to the search. (Itmust be a position in the current buffer.) No match extending afterthat position is accepted. If limit is omitted or nil, itdefaults to the end of the accessible portion of the buffer. search-failedWhat happens when the search fails depends on the value ofnoerror. If noerror is nil, a search-failederror is signaled. If noerror is t, search-forwardreturns nil and does nothing. If noerror is neithernil nor t, then search-forward moves point to theupper bound and returns nil. (It would be more consistent now toreturn the new position of point in that case, but some existingprograms may depend on a value of nil.)The argument noerror only affects valid searches which fail tofind a match. Invalid arguments cause errors regardless ofnoerror.If repeat is supplied (it must be a positive number), then thesearch is repeated that many times (each time starting at the end of theprevious time's match). If these successive searches succeed, thefunction succeeds, moving point and returning its new value. Otherwisethe search fails, with results depending on the value ofnoerror, as described above. search-backward — Command: search-backward string &optional limit noerror repeat This function searches backward from point for string. It isjust like search-forward except that it searches backwards andleaves point at the beginning of the match. word-search-forward — Command: word-search-forward string &optional limit noerror repeat This function searches forward from point for a “word” match forstring. If it finds a match, it sets point to the end of thematch found, and returns the new value of point. Word matching regards string as a sequence of words, disregardingpunctuation that separates them. It searches the buffer for the samesequence of words. Each word must be distinct in the buffer (searchingfor the word ‘ball’ does not match the word ‘balls’), but thedetails of punctuation and spacing are ignored (searching for ‘ballboy’ does match ‘ball. Boy!’).In this example, point is initially at the beginning of the buffer; thesearch leaves it between the ‘y’ and the ‘!’. ---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ---------- If limit is non-nil, it must be a position in the currentbuffer; it specifies the upper bound to the search. The match foundmust not extend after that position.If noerror is nil, then word-search-forward signalsan error if the search fails. If noerror is t, then itreturns nil instead of signaling an error. If noerror isneither nil nor t, it moves point to limit (or theend of the accessible portion of the buffer) and returns nil.If repeat is non-nil, then the search is repeated that manytimes. Point is positioned at the end of the last match. word-search-backward — Command: word-search-backward string &optional limit noerror repeat This function searches backward from point for a word match tostring. This function is just like word-search-forwardexcept that it searches backward and normally leaves point at thebeginning of the match. Searching and Case searching and case By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for ‘FOO’, then ‘Foo’ or ‘foo’ is also considered a match. This applies to regular expressions, too; thus, ‘[aB]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’. If you do not want this feature, set the variable case-fold-search to nil. Then all letters must match exactly, including case. This is a buffer-local variable; altering the variable affects only the current buffer. (See .) Alternatively, you may change the value of default-case-fold-search, which is the default value of case-fold-search for buffers that do not override it. Note that the user-level incremental search feature handles case distinctions differently. When given a lower case letter, it looks for a match of either case, but when given an upper case letter, it looks for an upper case letter only. But this has nothing to do with the searching functions used in Lisp code. case-replace — User Option: case-replace This variable determines whether the higher level replacementfunctions should preserve case. If the variable is nil, thatmeans to use the replacement text verbatim. A non-nil valuemeans to convert the case of the replacement text according to thetext being replaced.This variable is used by passing it as an argument to the functionreplace-match. See . case-fold-search — User Option: case-fold-search This buffer-local variable determines whether searches should ignorecase. If the variable is nil they do not ignore case; otherwisethey do ignore case. default-case-fold-search — Variable: default-case-fold-search The value of this variable is the default value forcase-fold-search in buffers that do not override it. This is thesame as (default-value 'case-fold-search). Regular Expressions regular expression regexp A regular expression (regexp, for short) is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them. re-builder regular expressions, developing For convenient interactive development of regular expressions, you can use the M-x re-builder command. It provides a convenient interface for creating regular expressions, by giving immediate visual feedback in a separate buffer. As you edit the regexp, all its matches in the target buffer are highlighted. Each parenthesized sub-expression of the regexp is shown in a distinct face, which makes it easier to verify even very complex regexps. Syntax of Regular Expressions Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘^’, ‘$’, and ‘\’; no new special characters will be defined in the future. The character ‘]’ is special if it ends a character alternative (see later). The character ‘-’ is special inside a character alternative. A ‘[:’ and balancing ‘:]’ enclose a character class inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it. For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘fg’, but it does match a part of that string.) Likewise, ‘o’ is a regular expression that matches only ‘o’. Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string. As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something more powerful, you need to use one of the special regular expression constructs. Special Characters in Regular Expressions Here is a list of the characters that are special in a regular expression. ‘.’ (Period) ‘.’ in regexpis a special character that matches any single character except a newline.Using concatenation, we can make regular expressions like ‘a.b’, whichmatches any three-character string that begins with ‘a’ and ends with‘b’. ‘*’ ‘*’ in regexpis not a construct by itself; it is a postfix operator that means tomatch the preceding regular expression repetitively as many times aspossible. Thus, ‘o*’ matches any number of ‘o’s (including no‘o’s).‘*’ always applies to the smallest possible precedingexpression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.The matcher processes a ‘*’ construct by matching, immediately, asmany repetitions as can be found. Then it continues with the rest ofthe pattern. If that fails, backtracking occurs, discarding some of thematches of the ‘*’-modified construct in the hope that that willmake it possible to match the rest of the pattern. For example, inmatching ‘ca*ar’ against the string ‘caaar’, the ‘a*’first tries to match all three ‘a’s; but the rest of the pattern is‘ar’ and there is only ‘r’ left to match, so this try fails.The next alternative is for ‘a*’ to match only two ‘a’s. Withthis choice, the rest of the regexp matches successfully.Warning: Nested repetition operators can run for anindefinitely long time, if they lead to ambiguous matching. Forexample, trying to match the regular expression ‘\(x+y*\)*a’against the string ‘xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz’ couldtake hours before it ultimately fails. Emacs must try each way ofgrouping the ‘x’s before concluding that none of them can work.Even worse, ‘\(x*\)*’ can match the null string in infinitelymany ways, so it causes an infinite loop. To avoid these problems,check nested repetitions carefully, to make sure that they do notcause combinatorial explosions in backtracking. ‘+’ ‘+’ in regexpis a postfix operator, similar to ‘*’ except that it must matchthe preceding expression at least once. So, for example, ‘ca+r’matches the strings ‘car’ and ‘caaaar’ but not the string‘cr’, whereas ‘ca*r’ matches all three strings. ‘?’ ‘?’ in regexpis a postfix operator, similar to ‘*’ except that it must match thepreceding expression either once or not at all. For example,‘ca?r’ matches ‘car’ or ‘cr’; nothing else. ‘*?’, ‘+?’, ‘??’ These are “non-greedy” variants of the operators ‘*’, ‘+’and ‘?’. Where those operators match the largest possiblesubstring (consistent with matching the entire containing expression),the non-greedy variants match the smallest possible substring(consistent with matching the entire containing expression).For example, the regular expression ‘c[ad]*a’ when applied to thestring ‘cdaaada’ matches the whole string; but the regularexpression ‘c[ad]*?a’, applied to that same string, matches just‘cda’. (The smallest possible match here for ‘[ad]*?’ thatpermits the whole expression to match is ‘d’.) ‘[ … ]’ character alternative (in regexp) ‘[’ in regexp ‘]’ in regexpis a character alternative, which begins with ‘[’ and isterminated by ‘]’. In the simplest case, the characters betweenthe two brackets are what this character alternative can match.Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s(including the empty string), from which it follows that ‘c[ad]*r’matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.You can also include character ranges in a character alternative, bywriting the starting and ending characters with a ‘-’ between them.Thus, ‘[a-z]’ matches any lower-case ASCII letter.Ranges may be intermixed freely with individual characters, as in‘[a-z$%.]’, which matches any lower case ASCII letteror ‘$’, ‘%’ or period.Note that the usual regexp special characters are not special inside acharacter alternative. A completely different set of characters isspecial inside character alternatives: ‘]’, ‘-’ and ‘^’.To include a ‘]’ in a character alternative, you must make it thefirst character. For example, ‘[]a]’ matches ‘]’ or ‘a’.To include a ‘-’, write ‘-’ as the first or last character ofthe character alternative, or put it after a range. Thus, ‘[]-]’matches both ‘]’ and ‘-’.To include ‘^’ in a character alternative, put it anywhere but atthe beginning.The beginning and end of a range of multibyte characters must be inthe same character set (see ). Thus,"[\x8e0-\x97c]" is invalid because character 0x8e0 (‘a’with grave accent) is in the Emacs character set for Latin-1 but thecharacter 0x97c (‘u’ with diaeresis) is in the Emacs characterset for Latin-2. (We use Lisp string syntax to write that example,and a few others in the next few paragraphs, in order to include hexescape sequences in them.)If a range starts with a unibyte character c and ends with amultibyte character c2, the range is divided into two parts: oneis ‘c..?\377’, the other is ‘c1..c2’, wherec1 is the first character of the charset to which c2belongs.You cannot always match all non-ASCII characters with the regularexpression "[\200-\377]". This works when searching a unibytebuffer or string (see ), but not in a multibytebuffer or string, because many non-ASCII characters have codesabove octal 0377. However, the regular expression "[^\000-\177]"does match all non-ASCII characters (see below regarding ‘^’),in both multibyte and unibyte representations, because only theASCII characters are excluded.A character alternative can also specify namedcharacter classes (see ). This is a POSIX feature whosesyntax is ‘[:class:]’. Using a character class is equivalentto mentioning each of the characters in that class; but the latter isnot feasible in practice, since some classes include thousands ofdifferent characters. ‘[^ … ]’ ‘^’ in regexp‘[^’ begins a complemented character alternative. Thismatches any character except the ones specified. Thus,‘[^a-z0-9A-Z]’ matches all characters except letters anddigits.‘^’ is not special in a character alternative unless it is the firstcharacter. The character following the ‘^’ is treated as if itwere first (in other words, ‘-’ and ‘]’ are not special there).A complemented character alternative can match a newline, unless newline ismentioned as one of the characters not to match. This is in contrast tothe handling of regexps in programs such as grep. ‘^’ beginning of line in regexpWhen matching a buffer, ‘^’ matches the empty string, but only at thebeginning of a line in the text being matched (or the beginning of theaccessible portion of the buffer). Otherwise it fails to matchanything. Thus, ‘^foo’ matches a ‘foo’ that occurs at thebeginning of a line.When matching a string instead of a buffer, ‘^’ matches at thebeginning of the string or after a newline character.For historical compatibility reasons, ‘^’ can be used only at thebeginning of the regular expression, or after ‘\(’, ‘\(?:’or ‘\|’. ‘$’ ‘$’ in regexp end of line in regexpis similar to ‘^’ but matches only at the end of a line (or theend of the accessible portion of the buffer). Thus, ‘x+$’matches a string of one ‘x’ or more at the end of a line.When matching a string instead of a buffer, ‘$’ matches at the endof the string or before a newline character.For historical compatibility reasons, ‘$’ can be used only at theend of the regular expression, or before ‘\)’ or ‘\|’. ‘\’ ‘\’ in regexphas two functions: it quotes the special characters (including‘\’), and it introduces additional special constructs.Because ‘\’ quotes special characters, ‘\$’ is a regularexpression that matches only ‘$’, and ‘\[’ is a regularexpression that matches only ‘[’, and so on.Note that ‘\’ also has special meaning in the read syntax of Lispstrings (see ), and must be quoted with ‘\’. Forexample, the regular expression that matches the ‘\’ character is‘\\’. To write a Lisp string that contains the characters‘\\’, Lisp syntax requires you to quote each ‘\’ with another‘\’. Therefore, the read syntax for a regular expression matching‘\’ is "\\\\". Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears. As a ‘\’ is not special inside a character alternative, it can never remove the special meaning of ‘-’ or ‘]’. So you should not quote these characters when they have no special meaning either. This would not clarify anything, since backslashes can legitimately precede these characters where they have special meaning, as in ‘[^\]’ ("[^\\]" for Lisp string syntax), which matches any single character except a backslash. In practice, most ‘]’ that occur in regular expressions close a character alternative and hence are special. However, occasionally a regular expression may try to match a complex pattern of literal ‘[’ and ‘]’. In such situations, it sometimes may be necessary to carefully parse the regexp from the start to determine which square brackets enclose a character alternative. For example, ‘[^][]]’ consists of the complemented character alternative ‘[^][]’ (which matches any single character that is not a square bracket), followed by a literal ‘]’. The exact rules are that at the beginning of a regexp, ‘[’ is special and ‘]’ not. This lasts until the first unquoted ‘[’, after which we are in a character alternative; ‘[’ is no longer special (except when it starts a character class) but ‘]’ is special, unless it immediately follows the special ‘[’ or that ‘[’ followed by a ‘^’. This lasts until the next special ‘]’ that does not end a character class. This ends the character alternative and restores the ordinary syntax of regular expressions; an unquoted ‘[’ is special again and a ‘]’ not. Character Classes character classes in regexp Here is a table of the classes you can use in a character alternative, and what they mean: ‘[:ascii:]’ This matches any ASCII character (codes 0–127). ‘[:alnum:]’ This matches any letter or digit. (At present, for multibytecharacters, it matches anything that has word syntax.) ‘[:alpha:]’ This matches any letter. (At present, for multibyte characters, itmatches anything that has word syntax.) ‘[:blank:]’ This matches space and tab only. ‘[:cntrl:]’ This matches any ASCII control character. ‘[:digit:]’ This matches ‘0’ through ‘9’. Thus, ‘[-+[:digit:]]’matches any digit, as well as ‘+’ and ‘-’. ‘[:graph:]’ This matches graphic characters—everything except ASCII controlcharacters, space, and the delete character. ‘[:lower:]’ This matches any lower-case letter, as determined bythe current case table (see ). ‘[:multibyte:]’ This matches any multibyte character (see ). ‘[:nonascii:]’ This matches any non-ASCII character. ‘[:print:]’ This matches printing characters—everything except ASCII controlcharacters and the delete character. ‘[:punct:]’ This matches any punctuation character. (At present, for multibytecharacters, it matches anything that has non-word syntax.) ‘[:space:]’ This matches any character that has whitespace syntax(see ). ‘[:unibyte:]’ This matches any unibyte character (see ). ‘[:upper:]’ This matches any upper-case letter, as determined bythe current case table (see ). ‘[:word:]’ This matches any character that has word syntax (see ). ‘[:xdigit:]’ This matches the hexadecimal digits: ‘0’ through ‘9’, ‘a’through ‘f’ and ‘A’ through ‘F’. Backslash Constructs in Regular Expressions For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: certain two-character sequences starting with ‘\’ that have special meanings. (The character after the ‘\’ in such a sequence is always ordinary when used on its own.) Here is a table of the special ‘\’ constructs. ‘\|’ ‘|’ in regexp regexp alternativespecifies an alternative.Two regular expressions a and b with ‘\|’ inbetween form an expression that matches anything that either a orb matches.Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’but no other string.‘\|’ applies to the largest possible surrounding expressions. Only asurrounding ‘\( … \)’ grouping can limit the grouping power of‘\|’.If you need full backtracking capability to handle multiple uses of‘\|’, use the POSIX regular expression functions (see ). ‘\{m\}’ is a postfix operator that repeats the previous pattern exactly mtimes. Thus, ‘x\{5\}’ matches the string ‘xxxxx’and nothing else. ‘c[ad]\{3\}r’ matches string such as‘caaar’, ‘cdddr’, ‘cadar’, and so on. ‘\{m,n\}’ is a more general postfix operator that specifies repetition with aminimum of m repeats and a maximum of n repeats. If mis omitted, the minimum is 0; if n is omitted, there is nomaximum.For example, ‘c[ad]\{1,2\}r’ matches the strings ‘car’,‘cdr’, ‘caar’, ‘cadr’, ‘cdar’, and ‘cddr’, andnothing else.‘\{0,1\}’ or ‘\{,1\}’ is equivalent to ‘?’. ‘\{0,\}’ or ‘\{,\}’ is equivalent to ‘*’. ‘\{1,\}’ is equivalent to ‘+’. ‘\( … \)’ ‘(’ in regexp ‘)’ in regexp regexp groupingis a grouping construct that serves three purposes: To enclose a set of ‘\|’ alternatives for other operations. Thus,the regular expression ‘\(foo\|bar\)x’ matches either ‘foox’or ‘barx’. To enclose a complicated expression for the postfix operators ‘*’,‘+’ and ‘?’ to operate on. Thus, ‘ba\(na\)*’ matches‘ba’, ‘bana’, ‘banana’, ‘bananana’, etc., with anynumber (zero or more) of ‘na’ strings. To record a matched substring for future reference with‘\digit’ (see below). This last application is not a consequence of the idea of aparenthetical grouping; it is a separate feature that was assigned as asecond meaning to the same ‘\( … \)’ construct because, inpractice, there was usually no conflict between the two meanings. Butoccasionally there is a conflict, and that led to the introduction ofshy groups. ‘\(?: … \)’ is the shy group construct. A shy group serves the first twopurposes of an ordinary group (controlling the nesting of otheroperators), but it does not get a number, so you cannot refer back toits value with ‘\digit’.Shy groups are particularly useful for mechanically-constructed regularexpressions because they can be added automatically without altering thenumbering of any ordinary, non-shy groups. ‘\digit’ matches the same text that matched the digitth occurrence of agrouping (‘\( … \)’) construct.In other words, after the end of a group, the matcher remembers thebeginning and end of the text matched by that group. Later on in theregular expression you can use ‘\’ followed by digit tomatch that same text, whatever it may have been.The strings matching the first nine grouping constructs appearing inthe entire regular expression passed to a search or matching functionare assigned numbers 1 through 9 in the order that the openparentheses appear in the regular expression. So you can use‘\1’ through ‘\9’ to refer to the text matched by thecorresponding grouping constructs.For example, ‘\(.*\)\1’ matches any newline-free string that iscomposed of two identical halves. The ‘\(.*\)’ matches the firsthalf, which may be anything, but the ‘\1’ that follows must matchthe same exact text.If a ‘\( … \)’ construct matches more than once (which canhappen, for instance, if it is followed by ‘*’), only the lastmatch is recorded.If a particular grouping construct in the regular expression was nevermatched—for instance, if it appears inside of an alternative thatwasn't used, or inside of a repetition that repeated zero times—thenthe corresponding ‘\digit’ construct never matchesanything. To use an artificial example,, ‘\(foo\(b*\)\|lose\)\2’cannot match ‘lose’: the second alternative inside the largergroup matches it, but then ‘\2’ is undefined and can't matchanything. But it can match ‘foobb’, because the firstalternative matches ‘foob’ and ‘\2’ matches ‘b’. ‘\w’ ‘\w’ in regexpmatches any word-constituent character. The editor syntax tabledetermines which characters these are. See . ‘\W’ ‘\W’ in regexpmatches any character that is not a word constituent. ‘\scode’ ‘\s’ in regexpmatches any character whose syntax is code. Here code is acharacter that represents a syntax code: thus, ‘w’ for wordconstituent, ‘-’ for whitespace, ‘(’ for open parenthesis,etc. To represent whitespace syntax, use either ‘-’ or a spacecharacter. See , for a list of syntax codes andthe characters that stand for them. ‘\Scode’ ‘\S’ in regexpmatches any character whose syntax is not code. ‘\cc’ matches any character whose category is c. Here c is acharacter that represents a category: thus, ‘c’ for Chinesecharacters or ‘g’ for Greek characters in the standard categorytable. ‘\Cc’ matches any character whose category is not c. The following regular expression constructs match the empty string—that is, they don't use up any characters—but whether they match depends on the context. For all, the beginning and end of the accessible portion of the buffer are treated as if they were the actual beginning and end of the buffer. ‘\`’ ‘\`’ in regexpmatches the empty string, but only at the beginningof the buffer or string being matched against. ‘\'’ ‘\'’ in regexpmatches the empty string, but only at the end ofthe buffer or string being matched against. ‘\=’ ‘\=’ in regexpmatches the empty string, but only at point.(This construct is not defined when matching against a string.) ‘\b’ ‘\b’ in regexpmatches the empty string, but only at the beginning orend of a word. Thus, ‘\bfoo\b’ matches any occurrence of‘foo’ as a separate word. ‘\bballs?\b’ matches‘ball’ or ‘balls’ as a separate word.‘\b’ matches at the beginning or end of the buffer (or string)regardless of what text appears next to it. ‘\B’ ‘\B’ in regexpmatches the empty string, but not at the beginning orend of a word, nor at the beginning or end of the buffer (or string). ‘\<’ ‘\<’ in regexpmatches the empty string, but only at the beginning of a word.‘\<’ matches at the beginning of the buffer (or string) only if aword-constituent character follows. ‘\>’ ‘\>’ in regexpmatches the empty string, but only at the end of a word. ‘\>’matches at the end of the buffer (or string) only if the contents endwith a word-constituent character. ‘\_<’ ‘\_<’ in regexpmatches the empty string, but only at the beginning of a symbol. Asymbol is a sequence of one or more word or symbol constituentcharacters. ‘\_<’ matches at the beginning of the buffer (orstring) only if a symbol-constituent character follows. ‘\_>’ ‘\_>’ in regexpmatches the empty string, but only at the end of a symbol. ‘\_>’matches at the end of the buffer (or string) only if the contents endwith a symbol-constituent character. invalid-regexp Not every string is a valid regular expression. For example, a string that ends inside a character alternative without terminating ‘]’ is invalid, and so is a string that ends with a single ‘\’. If an invalid regular expression is passed to any of the search functions, an invalid-regexp error is signaled. Complex Regexp Example Here is a complicated regexp which was formerly used by Emacs to recognize the end of a sentence together with any whitespace that follows. (Nowadays Emacs uses a similar but more complex default regexp constructed by the function sentence-end. See .) First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. ‘\"’ stands for a double-quote as part of the string, ‘\\’ for a backslash as part of the string, ‘\t’ for a tab and ‘\n’ for a newline. "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" In contrast, if you evaluate this string, you will see the following: "[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*" => "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[ ]*" In this output, tab and newline appear as themselves. This regular expression contains four parts in succession and can be deciphered as follows: [.?!] The first part of the pattern is a character alternative that matchesany one of three characters: period, question mark, and exclamationmark. The match must begin with one of these three characters. (Thisis one point where the new default regexp used by Emacs differs fromthe old. The new value also allows some non-ASCIIcharacters that end a sentence without any following whitespace.) []\"')}]* The second part of the pattern matches any closing braces and quotationmarks, zero or more of them, that may follow the period, question markor exclamation mark. The \" is Lisp syntax for a double-quote ina string. The ‘*’ at the end indicates that the immediatelypreceding regular expression (a character alternative, in this case) may berepeated zero or more times. \\($\\| $\\|\t\\| \\) The third part of the pattern matches the whitespace that follows theend of a sentence: the end of a line (optionally with a space), or atab, or two spaces. The double backslashes mark the parentheses andvertical bars as regular expression syntax; the parentheses delimit agroup and the vertical bars separate alternatives. The dollar sign isused to match the end of a line. [ \t\n]* Finally, the last part of the pattern matches any additional whitespacebeyond the minimum needed to end a sentence. Regular Expression Functions These functions operate on regular expressions. regexp-quote — Function: regexp-quote string This function returns a regular expression whose only exact match isstring. Using this regular expression in looking-at willsucceed only if the next characters in the buffer are string;using it in a search function will succeed if the text being searchedcontains string.This allows you to request an exact string match or search when callinga function that wants a regular expression. (regexp-quote "^The cat$") => "\\^The cat\\$" One use of regexp-quote is to combine an exact string match withcontext described as a regular expression. For example, this searchesfor the string that is the value of string, surrounded bywhitespace: (re-search-forward (concat "\\s-" (regexp-quote string) "\\s-")) regexp-opt — Function: regexp-opt strings &optional paren This function returns an efficient regular expression that will matchany of the strings in the list strings. This is useful when youneed to make matching or searching as fast as possible—for example,for Font Lock mode.If the optional argument paren is non-nil, then thereturned regular expression is always enclosed by at least oneparentheses-grouping construct. If paren is words, thenthat construct is additionally surrounded by ‘\<’ and ‘\>’.This simplified definition of regexp-opt produces aregular expression which is equivalent to the actual value(but not as efficient): (defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren))) regexp-opt-depth — Function: regexp-opt-depth regexp This function returns the total number of grouping constructs(parenthesized expressions) in regexp. (This does not includeshy groups.) Regular Expression Searching regular expression searching regexp searching searching for regexp In GNU Emacs, you can search for the next match for a regular expression either incrementally or not. For incremental search commands, see See section ``Regular Expression Search'' in The GNU Emacs Manual. Here we describe only the search functions useful in programs. The principal one is re-search-forward. These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. See . re-search-forward — Command: re-search-forward regexp &optional limit noerror repeat This function searches forward in the current buffer for a string oftext that is matched by the regular expression regexp. Thefunction skips over any amount of text that is not matched byregexp, and leaves point at the end of the first match found.It returns the new value of point.If limit is non-nil, it must be a position in the currentbuffer. It specifies the upper bound to the search. No matchextending after that position is accepted.If repeat is supplied, it must be a positive number; the searchis repeated that many times; each repetition starts at the end of theprevious match. If all these successive searches succeed, the searchsucceeds, moving point and returning its new value. Otherwise thesearch fails. What re-search-forward does when the searchfails depends on the value of noerror: nil Signal a search-failed error. t Do nothing and return nil. anything else Move point to limit (or the end of the accessible portion of thebuffer) and return nil. In the following example, point is initially before the ‘T’.Evaluating the search call moves point to the end of that line (betweenthe ‘t’ of ‘hat’ and the newline). ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ---------- re-search-backward — Command: re-search-backward regexp &optional limit noerror repeat This function searches backward in the current buffer for a string oftext that is matched by the regular expression regexp, leavingpoint at the beginning of the first text found.This function is analogous to re-search-forward, but they are notsimple mirror images. re-search-forward finds the match whosebeginning is as close as possible to the starting point. Ifre-search-backward were a perfect mirror image, it would find thematch whose end is as close as possible. However, in fact it finds thematch whose beginning is as close as possible (and yet ends before thestarting point). The reason for this is that matching a regularexpression at a given spot always works from beginning to end, andstarts at a specified beginning position.A true mirror-image of re-search-forward would require a specialfeature for matching regular expressions from end to beginning. It'snot worth the trouble of implementing that. string-match — Function: string-match regexp string &optional start This function returns the index of the start of the first match forthe regular expression regexp in string, or nil ifthere is no match. If start is non-nil, the search startsat that index in string.For example, (string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 The index of the first character of thestring is 0, the index of the second character is 1, and so on.After this function returns, the index of the first character beyondthe match is available as (match-end 0). See . (string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32 looking-at — Function: looking-at regexp This function determines whether the text in the current buffer directlyfollowing point matches the regular expression regexp. “Directlyfollowing” means precisely that: the search is “anchored” and it cansucceed only starting with the first character following point. Theresult is t if so, nil otherwise.This function does not move point, but it updates the match data, whichyou can access using match-beginning and match-end.See .In this example, point is located directly before the ‘T’. If itwere anywhere else, the result would be nil. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t looking-back — Function: looking-back regexp &optional limit This function returns t if regexp matches text beforepoint, ending at point, and nil otherwise.Because regular expression matching works only going forward, this isimplemented by searching backwards from point for a match that ends atpoint. That can be quite slow if it has to search a long distance.You can bound the time required by specifying limit, which saysnot to search before limit. In this case, the match that isfound must begin at or after limit. ---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-back "read \"" 3) => t (looking-back "read \"" 4) => nil search-spaces-regexp — Variable: search-spaces-regexp If this variable is non-nil, it should be a regular expressionthat says how to search for whitespace. In that case, any group ofspaces in a regular expression being searched for stands for use ofthis regular expression. However, spaces inside of constructs such as‘[…]’ and ‘*’, ‘+’, ‘?’ are not affected bysearch-spaces-regexp.Since this variable affects all regular expression search and matchconstructs, you should bind it temporarily for as small as possiblea part of the code. POSIX Regular Expression Searching The usual regular expression functions do backtracking when necessary to handle the ‘\|’ and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found. This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match. The POSIX search and match functions do not properly support the non-greedy repetition operators. This is because POSIX backtracking conflicts with the semantics of non-greedy repetition. posix-search-forward — Function: posix-search-forward regexp &optional limit noerror repeat This is like re-search-forward except that it performs the fullbacktracking specified by the POSIX standard for regular expressionmatching. posix-search-backward — Function: posix-search-backward regexp &optional limit noerror repeat This is like re-search-backward except that it performs the fullbacktracking specified by the POSIX standard for regular expressionmatching. posix-looking-at — Function: posix-looking-at regexp This is like looking-at except that it performs the fullbacktracking specified by the POSIX standard for regular expressionmatching. posix-string-match — Function: posix-string-match regexp string &optional start This is like string-match except that it performs the fullbacktracking specified by the POSIX standard for regular expressionmatching. The Match Data match data Emacs keeps track of the start and end positions of the segments of text found during a search; this is called the match data. Thanks to the match data, you can search for a complex pattern, such as a date in a mail message, and then extract parts of the match under control of the pattern. Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten. Replacing the Text that Matched replace matched text This function replaces all or part of the text matched by the last search. It works by means of the match data. case in replacements replace-match — Function: replace-match replacement &optional fixedcase literal string subexp This function replaces the text in the buffer (or in string) thatwas matched by the last search. It replaces that text withreplacement.If you did the last search in a buffer, you should specify nilfor string and make sure that the current buffer when you callreplace-match is the one in which you did the searching ormatching. Then replace-match does the replacement by editingthe buffer; it leaves point at the end of the replacement text, andreturns t.If you did the search in a string, pass the same string as string.Then replace-match does the replacement by constructing andreturning a new string.If fixedcase is non-nil, then replace-match usesthe replacement text without case conversion; otherwise, it convertsthe replacement text depending upon the capitalization of the text tobe replaced. If the original text is all upper case, this convertsthe replacement text to upper case. If all words of the original textare capitalized, this capitalizes all the words of the replacementtext. If all the words are one-letter and they are all upper case,they are treated as capitalized words rather than all-upper-casewords.If literal is non-nil, then replacement is insertedexactly as it is, the only alterations being case changes as needed.If it is nil (the default), then the character ‘\’ is treatedspecially. If a ‘\’ appears in replacement, then it must bepart of one of the following sequences: ‘\&’ ‘&’ in replacement‘\&’ stands for the entire text being replaced. ‘\n’ ‘\n’ in replacement‘\n’, where n is a digit, stands for the text thatmatched the nth subexpression in the original regexp.Subexpressions are those expressions grouped inside ‘\(…\)’.If the nth subexpression never matched, an empty string is substituted. ‘\\’ ‘\’ in replacement‘\\’ stands for a single ‘\’ in the replacement text. These substitutions occur after case conversion, if any,so the strings they substitute are never case-converted.If subexp is non-nil, that says to replace justsubexpression number subexp of the regexp that was matched, notthe entire match. For example, after matching ‘foo \(ba*r\)’,calling replace-match with 1 as subexp means to replacejust the text that matched ‘\(ba*r\)’. Simple Match Data Access This section explains how to use the match data to find out what was matched by the last search or match operation, if it succeeded. You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which. If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want. Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, ‘\(…\)’. The countth subexpression is found by counting occurrences of ‘\(’ from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions—after a simple string search, the only information available is about the entire match. Every successful search sets the match data. Therefore, you should query the match data immediately after searching, before calling any other function that might perform another search. Alternatively, you may save and restore the match data (see ) around the call to functions that could perform another search. A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future. So don't try to rely on the value of the match data after a failing search. match-string — Function: match-string count &optional in-string This function returns, as a string, the text matched in the last searchor match operation. It returns the entire text if count is zero,or just the portion corresponding to the countth parentheticalsubexpression, if count is positive.If the last such operation was done against a string withstring-match, then you should pass the same string as theargument in-string. After a buffer search or match,you should omit in-string or pass nil for it; but youshould make sure that the current buffer when you callmatch-string is the one in which you did the searching ormatching.The value is nil if count is out of range, or for asubexpression inside a ‘\|’ alternative that wasn't used or arepetition that repeated zero times. match-string-no-properties — Function: match-string-no-properties count &optional in-string This function is like match-string except that the resulthas no text properties. match-beginning — Function: match-beginning count This function returns the position of the start of text matched by thelast regular expression searched for, or a subexpression of it.If count is zero, then the value is the position of the start ofthe entire match. Otherwise, count specifies a subexpression inthe regular expression, and the value of the function is the startingposition of the match for that subexpression.The value is nil for a subexpression inside a ‘\|’alternative that wasn't used or a repetition that repeated zero times. match-end — Function: match-end count This function is like match-beginning except that it returns theposition of the end of the match, rather than the position of thebeginning. Here is an example of using the match data, with a comment showing the positions within the text: (string-match "\\(qu\\)\\(ick\\)" "The quick fox jumped quickly.") ;0123456789 => 4 (match-string 0 "The quick fox jumped quickly.") => "quick" (match-string 1 "The quick fox jumped quickly.") => "qu" (match-string 2 "The quick fox jumped quickly.") => "ick" (match-beginning 1) ; The beginning of the match => 4 ; with ‘qu’ is at index 4. (match-beginning 2) ; The beginning of the match => 6 ; with ‘ick’ is at index 6. (match-end 1) ; The end of the match => 6 ; with ‘qu’ is at index 6. (match-end 2) ; The end of the match => 9 ; with ‘ick’ is at index 9. Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word ‘in’. The beginning of the entire match is at the 9th character of the buffer (‘T’), and the beginning of the match for the first subexpression is at the 13th character (‘c’). (list (re-search-forward "The \\(cat \\)") (match-beginning 0) (match-beginning 1)) => (9 9 13) ---------- Buffer: foo ---------- I read "The cat -!-in the hat comes back" twice. ^ ^ 9 13 ---------- Buffer: foo ---------- (In this case, the index returned is a buffer position; the first character of the buffer counts as 1.) Accessing the Entire Match Data The functions match-data and set-match-data read or write the entire match data, all at once. match-data — Function: match-data &optional integers reuse reseat This function returns a list of positions (markers or integers) thatrecord all the information on what text the last search matched.Element zero is the position of the beginning of the match for thewhole expression; element one is the position of the end of the matchfor the expression. The next two elements are the positions of thebeginning and end of the match for the first subexpression, and so on.In general, elementnumber 2ncorresponds to (match-beginning n); andelementnumber 2n + 1corresponds to (match-end n).Normally all the elements are markers or nil, but ifintegers is non-nil, that means to use integers insteadof markers. (In that case, the buffer itself is appended as anadditional element at the end of the list, to facilitate completerestoration of the match data.) If the last match was done on astring with string-match, then integers are always used,since markers can't point into a string.If reuse is non-nil, it should be a list. In that case,match-data stores the match data in reuse. That is,reuse is destructively modified. reuse does not need tohave the right length. If it is not long enough to contain the matchdata, it is extended. If it is too long, the length of reusestays the same, but the elements that were not used are set tonil. The purpose of this feature is to reduce the need forgarbage collection.If reseat is non-nil, all markers on the reuse listare reseated to point to nowhere.As always, there must be no possibility of intervening searches betweenthe call to a search function and the call to match-data that isintended to access the match data for that search. (match-data) => (#<marker at 9 in foo> #<marker at 17 in foo> #<marker at 13 in foo> #<marker at 17 in foo>) set-match-data — Function: set-match-data match-list &optional reseat This function sets the match data from the elements of match-list,which should be a list that was the value of a previous call tomatch-data. (More precisely, anything that has the same formatwill work.)If match-list refers to a buffer that doesn't exist, you don't getan error; that sets the match data in a meaningless but harmless way.If reseat is non-nil, all markers on the match-list listare reseated to point to nowhere. store-match-datastore-match-data is a semi-obsolete alias for set-match-data. Saving and Restoring the Match Data When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data: (re-search-forward "The \\(cat \\)") => 48 (foo) ; Perhaps foo does ; more searching. (match-end 0) => 61 ; Unexpected result---not 48! You can save and restore the match data with save-match-data: save-match-data — Macro: save-match-data body … This macro executes body, saving and restoring the matchdata around it. The return value is the value of the last form inbody. You could use set-match-data together with match-data to imitate the effect of the special form save-match-data. Here is how: (let ((data (match-data))) (unwind-protect … ; Ok to change the original match data. (set-match-data data))) Emacs automatically saves and restores the match data when it runs process filter functions (see ) and process sentinels (see ). Search and Replace replacement after search searching and replacing If you want to find all matches for a regexp in part of the buffer, and replace them, the best way is to write an explicit loop using re-search-forward and replace-match, like this: (while (re-search-forward "foo[ \t]+bar" nil t) (replace-match "foobar")) See Replacing the Text that Matched, for a description of replace-match. However, replacing matches in a string is more complex, especially if you want to do it efficiently. So Emacs provides a function to do this. replace-regexp-in-string — Function: replace-regexp-in-string regexp rep string &optional fixedcase literal subexp start This function copies string and searches it for matches forregexp, and replaces them with rep. It returns themodified copy. If start is non-nil, the search formatches starts at that index in string, so matches startingbefore that index are not changed.This function uses replace-match to do the replacement, and itpasses the optional arguments fixedcase, literal andsubexp along to replace-match.Instead of a string, rep can be a function. In that case,replace-regexp-in-string calls rep for each match,passing the text of the match as its sole argument. It collects thevalue rep returns and passes that to replace-match as thereplacement string. The match-data at this point are the resultof matching regexp against a substring of string. If you want to write a command along the lines of query-replace, you can use perform-replace to do the work. perform-replace — Function: perform-replace from-string replacements query-flag regexp-flag delimited-flag &optional repeat-count map start end This function is the guts of query-replace and relatedcommands. It searches for occurrences of from-string in thetext between positions start and end and replaces some orall of them. If start is nil (or omitted), point is usedinstead, and the end of the buffer's accessible portion is used forend.If query-flag is nil, it replaces alloccurrences; otherwise, it asks the user what to do about each one.If regexp-flag is non-nil, then from-string isconsidered a regular expression; otherwise, it must match literally. Ifdelimited-flag is non-nil, then only replacementssurrounded by word boundaries are considered.The argument replacements specifies what to replace occurrenceswith. If it is a string, that string is used. It can also be a list ofstrings, to be used in cyclic order.If replacements is a cons cell, (function. data), this means to call function after each match toget the replacement text. This function is called with two arguments:data, and the number of replacements already made.If repeat-count is non-nil, it should be an integer. Thenit specifies how many times to use each of the strings in thereplacements list before advancing cyclically to the next one.If from-string contains upper-case letters, thenperform-replace binds case-fold-search to nil, andit uses the replacements without altering the case of them.Normally, the keymap query-replace-map defines the possibleuser responses for queries. The argument map, ifnon-nil, specifies a keymap to use instead ofquery-replace-map. query-replace-map — Variable: query-replace-map This variable holds a special keymap that defines the valid userresponses for perform-replace and the commands that use it, aswell as y-or-n-p and map-y-or-n-p. This map is unusualin two ways: The “key bindings” are not commands, just symbols that are meaningfulto the functions that use this map. Prefix keys are not supported; each key binding must be for asingle-event key sequence. This is because the functions don't useread-key-sequence to get the input; instead, they read a singleevent and look it up “by hand.” Here are the meaningful “bindings” for query-replace-map. Several of them are meaningful only for query-replace and friends. act Do take the action being considered—in other words, “yes.” skip Do not take action for this question—in other words, “no.” exit Answer this question “no,” and give up on the entire series ofquestions, assuming that the answers will be “no.” act-and-exit Answer this question “yes,” and give up on the entire series ofquestions, assuming that subsequent answers will be “no.” act-and-show Answer this question “yes,” but show the results—don't advance yetto the next question. automatic Answer this question and all subsequent questions in the series with“yes,” without further user interaction. backup Move back to the previous place that a question was asked about. edit Enter a recursive edit to deal with this question—instead of anyother action that would normally be taken. delete-and-edit Delete the text being considered, then enter a recursive edit to replaceit. recenter Redisplay and center the window, then ask the same question again. quit Perform a quit right away. Only y-or-n-p and related functionsuse this answer. help Display some help, then ask again. Standard Regular Expressions Used in Editing regexps used standardly in editing standard regexps used in editing This section describes some variables that hold regular expressions used for certain purposes in editing: page-delimiter — Variable: page-delimiter This is the regular expression describing line-beginnings that separatepages. The default value is "^\014" (i.e., "^^L" or"^\C-l"); this matches a line that starts with a formfeedcharacter. The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that ‘^’ would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes where a left margin is never used. paragraph-separate — Variable: paragraph-separate This is the regular expression for recognizing the beginning of a linethat separates paragraphs. (If you change this, you may have tochange paragraph-start also.) The default value is"[ \t\f]*$", which matches a line that consists entirely ofspaces, tabs, and form feeds (after its left margin). paragraph-start — Variable: paragraph-start This is the regular expression for recognizing the beginning of a linethat starts or separates paragraphs. The default value is"\f\\|[ \t]*$", which matches a line containing onlywhitespace or starting with a form feed (after its left margin). sentence-end — Variable: sentence-end If non-nil, the value should be a regular expression describingthe end of a sentence, including the whitespace following thesentence. (All paragraph boundaries also end sentences, regardless.)If the value is nil, the default, then the functionsentence-end has to construct the regexp. That is why youshould always call the function sentence-end to obtain theregexp to be used to recognize the end of a sentence. sentence-end — Function: sentence-end This function returns the value of the variable sentence-end,if non-nil. Otherwise it returns a default value based on thevalues of the variables sentence-end-double-space(see ),sentence-end-without-period andsentence-end-without-space. <setfilename>../info/syntax</setfilename> Syntax Tables parsing buffer text syntax table text parsing A syntax table specifies the syntactic textual function of each character. This information is used by the parsing functions, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see ) and the list motion functions (see ), as well as the functions in this chapter. Syntax Table Concepts A syntax table provides Emacs with the information that determines the syntactic use of each character in a buffer. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see ) and the list motion functions (see ) as well as the functions in this chapter. A syntax table is a char-table (see ). The element at index c describes the character with code c. The element's value should be a list that encodes the syntax of the character in question. Syntax tables are used only for moving across text, not for the Emacs Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed. (Some Lisp systems provide ways to redefine the read syntax, but we decided to leave this feature out of Emacs Lisp for simplicity.) Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character ‘;’ begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer that uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See , for an example of how to set up a syntax table. A syntax table can inherit the data for some characters from the standard syntax table, while specifying other characters itself. The “inherit” syntax class means “inherit this character's syntax from the standard syntax table.” Just changing the standard syntax for a character affects all syntax tables that inherit from it. syntax-table-p — Function: syntax-table-p object This function returns t if object is a syntax table. Syntax Descriptors syntax class This section describes the syntax classes and flags that denote the syntax of a character, and how they are represented as a syntax descriptor, which is a Lisp string that you pass to modify-syntax-entry to specify the syntax you want. The syntax table specifies a syntax class for each character. There is no necessary relationship between the class of a character in one syntax table and its class in any other table. Each class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually the designator character is one that is often assigned that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has. Thus, ‘\’ as a designator character always gives “escape character” syntax, regardless of what syntax ‘\’ currently has. syntax descriptor A syntax descriptor is a Lisp string that specifies a syntax class, a matching character (used only for the parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient. For example, the syntax descriptor for the character ‘*’ in C mode is ‘. 23’ (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of a comment-ender), and the entry for ‘/’ is ‘. 14’ (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender). Table of Syntax Classes Here is a table of syntax classes, the characters that stand for them, their meanings, and examples of their use. whitespace character — Syntax class: whitespace character Whitespace characters (designated by ‘ ’ or ‘-’)separate symbols and words from each other. Typically, whitespacecharacters have no other syntactic significance, and multiple whitespacecharacters are syntactically equivalent to a single one. Space, tab,newline and formfeed are classified as whitespace in almost all majormodes. word constituent — Syntax class: word constituent Word constituents (designated by ‘w’) are parts of words inhuman languages, and are typically used in variable and command namesin programs. All upper- and lower-case letters, and the digits, aretypically word constituents. symbol constituent — Syntax class: symbol constituent Symbol constituents (designated by ‘_’) are the extracharacters that are used in variable and command names along with wordconstituents. For example, the symbol constituents class is used inLisp mode to indicate that certain characters may be part of symbolnames even though they are not part of English words. These charactersare ‘$&*+-_<>’. In standard C, the only non-word-constituentcharacter that is valid in symbols is underscore (‘_’). punctuation character — Syntax class: punctuation character Punctuation characters (designated by ‘.’) are thosecharacters that are used as punctuation in English, or are used in someway in a programming language to separate symbols from one another.Some programming language modes, such as Emacs Lisp mode, have nocharacters in this class since the few characters that are not symbol orword constituents all have other uses. Other programming language modes,such as C mode, use punctuation syntax for operators. open parenthesis character — Syntax class: open parenthesis character close parenthesis character — Syntax class: close parenthesis character parenthesis syntaxOpen and close parenthesis characters are characters used indissimilar pairs to surround sentences or expressions. Such a groupingis begun with an open parenthesis character and terminated with a close.Each open parenthesis character matches a particular close parenthesischaracter, and vice versa. Normally, Emacs indicates momentarily thematching open parenthesis when you insert a close parenthesis.See .The class of open parentheses is designated by ‘(’, and that ofclose parentheses by ‘)’.In English text, and in C code, the parenthesis pairs are ‘()’,‘[]’, and ‘{}’. In Emacs Lisp, the delimiters for lists andvectors (‘()’ and ‘[]’) are classified as parenthesischaracters. string quote — Syntax class: string quote String quote characters (designated by ‘"’) are used inmany languages, including Lisp and C, to delimit string constants. Thesame string quote character appears at the beginning and the end of astring. Such quoted strings do not nest.The parsing facilities of Emacs consider a string as a single token.The usual syntactic meanings of the characters in the string aresuppressed.The Lisp modes have two string quote characters: double-quote (‘"’)and vertical bar (‘|’). ‘|’ is not used in Emacs Lisp, but itis used in Common Lisp. C also has two string quote characters:double-quote for strings, and single-quote (‘'’) for characterconstants.English text has no string quote characters because English is not aprogramming language. Although quotation marks are used in English,we do not want them to turn off the usual syntactic properties ofother characters in the quotation. escape-syntax character — Syntax class: escape-syntax character An escape character (designated by ‘\’) starts an escapesequence such as is used in C string and character constants. Thecharacter ‘\’ belongs to this class in both C and Lisp. (In C, itis used thus only inside strings, but it turns out to cause no troubleto treat it this way throughout C code.)Characters in this class count as part of words ifwords-include-escapes is non-nil. See . character quote — Syntax class: character quote A character quote character (designated by ‘/’) quotes thefollowing character so that it loses its normal syntactic meaning. Thisdiffers from an escape character in that only the character immediatelyfollowing is ever affected.Characters in this class count as part of words ifwords-include-escapes is non-nil. See .This class is used for backslash in &tex; mode. paired delimiter — Syntax class: paired delimiter Paired delimiter characters (designated by ‘$’) are likestring quote characters except that the syntactic properties of thecharacters between the delimiters are not suppressed. Only &tex; modeuses a paired delimiter presently—the ‘$’ that both enters andleaves math mode. expression prefix — Syntax class: expression prefix An expression prefix operator (designated by ‘'’) is used forsyntactic operators that are considered as part of an expression if theyappear next to one. In Lisp modes, these characters include theapostrophe, ‘'’ (used for quoting), the comma, ‘,’ (used inmacros), and ‘#’ (used in the read syntax for certain data types). comment starter — Syntax class: comment starter comment ender — Syntax class: comment ender comment syntaxThe comment starter and comment ender characters are used invarious languages to delimit comments. These classes are designatedby ‘<’ and ‘>’, respectively.English text has no comment characters. In Lisp, the semicolon(‘;’) starts a comment and a newline or formfeed ends one. inherit standard syntax — Syntax class: inherit standard syntax This syntax class does not specify a particular syntax. It says to lookin the standard syntax table to find the syntax of this character. Thedesignator for this syntax class is ‘@’. generic comment delimiter — Syntax class: generic comment delimiter A generic comment delimiter (designated by ‘!’) startsor ends a special kind of comment. Any generic comment delimitermatches any generic comment delimiter, but they cannot matcha comment starter or comment ender; generic comment delimiters can onlymatch each other.This syntax class is primarily meant for use with thesyntax-table text property (see ). You canmark any range of characters as forming a comment, by giving the firstand last characters of the range syntax-table propertiesidentifying them as generic comment delimiters. generic string delimiter — Syntax class: generic string delimiter A generic string delimiter (designated by ‘|’) starts or endsa string. This class differs from the string quote class in that anygeneric string delimiter can match any other generic string delimiter; butthey do not match ordinary string quote characters.This syntax class is primarily meant for use with thesyntax-table text property (see ). You canmark any range of characters as forming a string constant, by giving thefirst and last characters of the range syntax-table propertiesidentifying them as generic string delimiters. Syntax Flags syntax flags In addition to the classes, entries for characters in a syntax table can specify flags. There are seven possible flags, represented by the characters ‘1’, ‘2’, ‘3’, ‘4’, ‘b’, ‘n’, and ‘p’. All the flags except ‘n’ and ‘p’ are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as ‘*’ in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (‘/*’), and the first character of an end-of-comment sequence (‘*/’). Here is a table of the possible flags for a character c, and what they mean: ‘1’ means c is the start of a two-character comment-startsequence. ‘2’ means c is the second character of such a sequence. ‘3’ means c is the start of a two-character comment-endsequence. ‘4’ means c is the second character of such a sequence. ‘b’ means that c as a comment delimiter belongs to thealternative “b” comment style.Emacs supports two comment styles simultaneously in any one syntaxtable. This is for the sake of C++. Each style of comment syntax hasits own comment-start sequence and its own comment-end sequence. Eachcomment must stick to one style or the other; thus, if it starts withthe comment-start sequence of style “b,” it must also end with thecomment-end sequence of style “b.”The two comment-start sequences must begin with the same character; onlythe second character may differ. Mark the second character of the“b”-style comment-start sequence with the ‘b’ flag.A comment-end sequence (one or two characters) applies to the “b”style if its first character has the ‘b’ flag set; otherwise, itapplies to the “a” style.The appropriate comment syntax settings for C++ are as follows: ‘/’ ‘124b’ ‘*’ ‘23’ newline ‘>b’ This defines four comment-delimiting sequences: ‘/*’ This is a comment-start sequence for “a” style because thesecond character, ‘*’, does not have the ‘b’ flag. ‘//’ This is a comment-start sequence for “b” style because the secondcharacter, ‘/’, does have the ‘b’ flag. ‘*/’ This is a comment-end sequence for “a” style because the firstcharacter, ‘*’, does not have the ‘b’ flag. newline This is a comment-end sequence for “b” style, because the newlinecharacter has the ‘b’ flag. ‘n’ on a comment delimiter character specifiesthat this kind of comment can be nested. For a two-charactercomment delimiter, ‘n’ on either character makes itnestable. ‘p’ identifies an additional “prefix character” for Lisp syntax.These characters are treated as whitespace when they appear betweenexpressions. When they appear within an expression, they are handledaccording to their usual syntax classes.The function backward-prefix-chars moves back over thesecharacters, as well as over characters whose primary syntax class isprefix (‘'’). See . Syntax Table Functions In this section we describe functions for creating, accessing and altering syntax tables. make-syntax-table — Function: make-syntax-table &optional table This function creates a new syntax table, with all values initializedto nil. If table is non-nil, it becomes theparent of the new syntax table, otherwise the standard syntax table isthe parent. Like all char-tables, a syntax table inherits from itsparent. Thus the original syntax of all characters in the returnedsyntax table is determined by the parent. See .Most major mode syntax tables are created in this way. copy-syntax-table — Function: copy-syntax-table &optional table This function constructs a copy of table and returns it. Iftable is not supplied (or is nil), it returns a copy of thestandard syntax table. Otherwise, an error is signaled if table isnot a syntax table. modify-syntax-entry — Command: modify-syntax-entry char syntax-descriptor &optional table This function sets the syntax entry for char according tosyntax-descriptor. The syntax is changed only for table,which defaults to the current buffer's syntax table, and not in anyother syntax table. The argument syntax-descriptor specifies thedesired syntax; this is a string beginning with a class designatorcharacter, and optionally containing a matching character and flags aswell. See .This function always returns nil. The old syntax information inthe table for this character is discarded.An error is signaled if the first character of the syntax descriptor is notone of the seventeen syntax class designator characters. An error is alsosignaled if char is not a character. Examples: ;; Put the space character in class whitespace. (modify-syntax-entry ?\s " ") => nil ;; Make ‘$’ an open parenthesis character, ;; with ‘^’ as its matching close. (modify-syntax-entry ?$ "(^") => nil ;; Make ‘^’ a close parenthesis character, ;; with ‘$’ as its matching open. (modify-syntax-entry ?^ ")$") => nil ;; Make ‘/’ a punctuation character, ;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode. (modify-syntax-entry ?/ ". 14") => nil char-syntax — Function: char-syntax character This function returns the syntax class of character, representedby its mnemonic designator character. This returns only theclass, not any matching parenthesis or flags.An error is signaled if char is not a character.The following examples apply to C mode. The first example shows thatthe syntax class of space is whitespace (represented by a space). Thesecond example shows that the syntax of ‘/’ is punctuation. Thisdoes not show the fact that it is also part of comment-start and -endsequences. The third example shows that open parenthesis is in the classof open parentheses. This does not show the fact that it has a matchingcharacter, ‘)’. (string (char-syntax ?\s)) => " " (string (char-syntax ?/)) => "." (string (char-syntax ?\()) => "(" We use string to make it easier to see the character returned bychar-syntax. set-syntax-table — Function: set-syntax-table table This function makes table the syntax table for the current buffer.It returns table. syntax-table — Function: syntax-table This function returns the current syntax table, which is the table forthe current buffer. with-syntax-table — Macro: with-syntax-table table body … This macro executes body using table as the current syntaxtable. It returns the value of the last form in body, afterrestoring the old current syntax table.Since each buffer has its own current syntax table, we should make thatmore precise: with-syntax-table temporarily alters the currentsyntax table of whichever buffer is current at the time the macroexecution starts. Other buffers are not affected. Syntax Properties syntax-table (text property) When the syntax table is not flexible enough to specify the syntax of a language, you can use syntax-table text properties to override the syntax table for specific character occurrences in the buffer. See . You can use Font Lock mode to set syntax-table text properties. See . The valid values of syntax-table text property are: syntax-table If the property value is a syntax table, that table is used instead ofthe current buffer's syntax table to determine the syntax for thisoccurrence of the character. (syntax-code . matching-char) A cons cell of this format specifies the syntax for thisoccurrence of the character. (see ) nil If the property is nil, the character's syntax is determined fromthe current syntax table in the usual way. parse-sexp-lookup-properties — Variable: parse-sexp-lookup-properties If this is non-nil, the syntax scanning functions pay attentionto syntax text properties. Otherwise they use only the current syntaxtable. Motion and Syntax This section describes functions for moving across characters that have certain syntax classes. skip-syntax-forward — Function: skip-syntax-forward syntaxes &optional limit This function moves point forward across characters having syntaxclasses mentioned in syntaxes (a string of syntax classcharacters). It stops when it encounters the end of the buffer, orposition limit (if specified), or a character it is not supposedto skip.If syntaxes starts with ‘^’, then the function skipscharacters whose syntax is not in syntaxes.The return value is the distance traveled, which is a nonnegativeinteger. skip-syntax-backward — Function: skip-syntax-backward syntaxes &optional limit This function moves point backward across characters whose syntaxclasses are mentioned in syntaxes. It stops when it encountersthe beginning of the buffer, or position limit (if specified), ora character it is not supposed to skip.If syntaxes starts with ‘^’, then the function skipscharacters whose syntax is not in syntaxes.The return value indicates the distance traveled. It is an integer thatis zero or less. backward-prefix-chars — Function: backward-prefix-chars This function moves point backward over any number of characters withexpression prefix syntax. This includes both characters in theexpression prefix syntax class, and characters with the ‘p’ flag. Parsing Expressions This section describes functions for parsing and scanning balanced expressions, also known as sexps. Basically, a sexp is either a balanced parenthetical grouping, a string, or a symbol name (a sequence of characters whose syntax is either word constituent or symbol constituent). However, characters whose syntax is expression prefix are treated as part of the sexp if they appear next to it. The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See , for convenient higher-level functions for moving over balanced expressions. A character's syntax controls how it changes the state of the parser, rather than describing the state itself. For example, a string delimiter character toggles the parser state between “in-string” and “in-code,” but the syntax of characters does not directly say whether they are inside a string. For example (note that 15 is the syntax code for generic string delimiters), (put-text-property 1 9 'syntax-table '(15 . nil)) does not tell Emacs that the first eight chars of the current buffer are a string, but rather that they are all string delimiters. As a result, Emacs treats them as four consecutive empty string constants. Motion Commands Based on Parsing This section describes simple point-motion functions that operate based on parsing expressions. scan-lists — Function: scan-lists from count depth This function scans forward count balanced parenthetical groupingsfrom position from. It returns the position where the scan stops.If count is negative, the scan moves backwards.If depth is nonzero, parenthesis depth counting begins from thatvalue. The only candidates for stopping are places where the depth inparentheses becomes zero; scan-lists counts count suchplaces and then stops. Thus, a positive value for depth means goout depth levels of parenthesis.Scanning ignores comments if parse-sexp-ignore-comments isnon-nil.If the scan reaches the beginning or end of the buffer (or itsaccessible portion), and the depth is not zero, an error is signaled.If the depth is zero but the count is not used up, nil isreturned. scan-sexps — Function: scan-sexps from count This function scans forward count sexps from position from.It returns the position where the scan stops. If count isnegative, the scan moves backwards.Scanning ignores comments if parse-sexp-ignore-comments isnon-nil.If the scan reaches the beginning or end of (the accessible part of) thebuffer while in the middle of a parenthetical grouping, an error issignaled. If it reaches the beginning or end between groupings butbefore count is used up, nil is returned. forward-comment — Function: forward-comment count This function moves point forward across count complete comments (that is, including the starting delimiter and the terminatingdelimiter if any), plus any whitespace encountered on the way. Itmoves backward if count is negative. If it encounters anythingother than a comment or whitespace, it stops, leaving point at theplace where it stopped. This includes (for instance) finding the endof a comment when moving forward and expecting the beginning of one.The function also stops immediately after moving over the specifiednumber of complete comments. If count comments are found asexpected, with nothing except whitespace between them, it returnst; otherwise it returns nil.This function cannot tell whether the “comments” it traverses areembedded within a string. If they look like comments, it treats themas comments. To move forward over all comments and whitespace following point, use (forward-comment (buffer-size)). (buffer-size) is a good argument to use, because the number of comments in the buffer cannot exceed that many. Finding the Parse State for a Position For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic state corresponding to a given buffer position. This function does that conveniently. syntax-ppss — Function: syntax-ppss &optional pos This function returns the parser state (see next section) that theparser would reach at position pos starting from the beginningof the buffer. This is equivalent to (parse-partial-sexp(point-min) pos), except that syntax-ppss uses a cacheto speed up the computation. Due to this optimization, the 2nd value(previous complete subexpression) and 6th value (minimum parenthesisdepth) of the returned parser state are not meaningful. syntax-ppss automatically hooks itself to before-change-functions to keep its cache consistent. But updating can fail if syntax-ppss is called while before-change-functions is temporarily let-bound, or if the buffer is modified without obeying the hook, such as when using inhibit-modification-hooks. For this reason, it is sometimes necessary to flush the cache manually. syntax-ppss-flush-cache — Function: syntax-ppss-flush-cache beg This function flushes the cache used by syntax-ppss, starting atposition beg. Major modes can make syntax-ppss run faster by specifying where it needs to start parsing. syntax-begin-function — Variable: syntax-begin-function If this is non-nil, it should be a function that moves to anearlier buffer position where the parser state is equivalent tonil—in other words, a position outside of any comment,string, or parenthesis. syntax-ppss uses it to furtheroptimize its computations, when the cache gives no help. Parser State parser state A parser state is a list of ten elements describing the final state of parsing text syntactically as part of an expression. The parsing functions in the following sections return a parser state as the value, and in some cases accept one as an argument also, so that you can resume parsing after it stops. Here are the meanings of the elements of the parser state: The depth in parentheses, counting from 0. Warning: this canbe negative if there are more close parens than open parens betweenthe start of the defun and point. innermost containing parenthesesThe character position of the start of the innermost parentheticalgrouping containing the stopping point; nil if none. previous complete subexpressionThe character position of the start of the last complete subexpressionterminated; nil if none. inside stringNon-nil if inside a string. More precisely, this is thecharacter that will terminate the string, or t if a genericstring delimiter character should terminate it. inside commentt if inside a comment (of either style),or the comment nesting level if inside a kind of commentthat can be nested. quote charactert if point is just after a quote character. The minimum parenthesis depth encountered during this scan. What kind of comment is active: nil for a comment of style“a” or when not inside a comment, t for a comment of style“b,” and syntax-table for a comment that should be ended by ageneric comment delimiter character. The string or comment start position. While inside a comment, this isthe position where the comment began; while inside a string, this is theposition where the string began. When outside of strings and comments,this element is nil. Internal data for continuing the parsing. The meaning of thisdata is subject to change; it is used if you pass this listas the state argument to another call. Elements 1, 2, and 6 are ignored in a state which you pass as an argument to continue parsing, and elements 8 and 9 are used only in trivial cases. Those elements serve primarily to convey information to the Lisp program which does the parsing. One additional piece of useful information is available from a parser state using this function: syntax-ppss-toplevel-pos — Function: syntax-ppss-toplevel-pos state This function extracts, from parser state state, the lastposition scanned in the parse which was at top level in grammaticalstructure. “At top level” means outside of any parentheses,comments, or strings.The value is nil if state represents a parse which hasarrived at a top level position. We have provided this access function rather than document how the data is represented in the state, because we plan to change the representation in the future. Low-Level Parsing The most basic way to use the expression parser is to tell it to start at a given position with a certain state, and parse up to a specified end position. parse-partial-sexp — Function: parse-partial-sexp start limit &optional target-depth stop-before state stop-comment This function parses a sexp in the current buffer starting atstart, not scanning past limit. It stops at positionlimit or when certain criteria described below are met, and setspoint to the location where parsing stops. It returns a parser statedescribing the status of the parse at the point where it stops. parenthesis depthIf the third argument target-depth is non-nil, parsingstops if the depth in parentheses becomes equal to target-depth.The depth starts at 0, or at whatever is given in state.If the fourth argument stop-before is non-nil, parsingstops when it comes to any character that starts a sexp. Ifstop-comment is non-nil, parsing stops when it comes to thestart of a comment. If stop-comment is the symbolsyntax-table, parsing stops after the start of a comment or astring, or the end of a comment or a string, whichever comes first.If state is nil, start is assumed to be at the toplevel of parenthesis structure, such as the beginning of a functiondefinition. Alternatively, you might wish to resume parsing in themiddle of the structure. To do this, you must provide a stateargument that describes the initial status of parsing. The valuereturned by a previous call to parse-partial-sexp will donicely. Parameters to Control Parsing multibyte-syntax-as-symbol — Variable: multibyte-syntax-as-symbol If this variable is non-nil, scan-sexps treats allnon-ASCII characters as symbol constituents regardlessof what the syntax table says about them. (However, text propertiescan still override the syntax.) parse-sexp-ignore-comments — User Option: parse-sexp-ignore-comments skipping commentsIf the value is non-nil, then comments are treated aswhitespace by the functions in this section and by forward-sexp,scan-lists and scan-sexps. parse-sexp-lookup-properties The behavior of parse-partial-sexp is also affected by parse-sexp-lookup-properties (see ). You can use forward-comment to move forward or backward over one comment or several comments. Some Standard Syntax Tables Most of the major modes in Emacs have their own syntax tables. Here are several of them: standard-syntax-table — Function: standard-syntax-table This function returns the standard syntax table, which is the syntaxtable used in Fundamental mode. text-mode-syntax-table — Variable: text-mode-syntax-table The value of this variable is the syntax table used in Text mode. c-mode-syntax-table — Variable: c-mode-syntax-table The value of this variable is the syntax table for C-mode buffers. emacs-lisp-mode-syntax-table — Variable: emacs-lisp-mode-syntax-table The value of this variable is the syntax table used in Emacs Lisp modeby editing commands. (It has no effect on the Lisp readfunction.) Syntax Table Internals syntax table internals Lisp programs don't usually work with the elements directly; the Lisp-level syntax table functions usually work with syntax descriptors (see ). Nonetheless, here we document the internal format. This format is used mostly when manipulating syntax properties. Each element of a syntax table is a cons cell of the form (syntax-code . matching-char). The car, syntax-code, is an integer that encodes the syntax class, and any flags. The cdr, matching-char, is non-nil if a character to match was specified. This table gives the value of syntax-code which corresponds to each syntactic type. Integer Class Integer Class Integer Class 0 whitespace 5 close parenthesis 10 character quote 1 punctuation 6 expression prefix 11 comment-start 2 word 7 string quote 12 comment-end 3 symbol 8 paired delimiter 13 inherit 4 open parenthesis 9 escape 14 generic comment 15 generic string For example, the usual syntax value for ‘(’ is (4 . 41). (41 is the character code for ‘)’.) The flags are encoded in higher order bits, starting 16 bits from the least significant bit. This table gives the power of two which corresponds to each syntax flag. Prefix Flag Prefix Flag Prefix Flag ‘1’ (lsh 1 16) ‘4’ (lsh 1 19) ‘b’ (lsh 1 21) ‘2’ (lsh 1 17) ‘p’ (lsh 1 20) ‘n’ (lsh 1 22) ‘3’ (lsh 1 18) string-to-syntax — Function: string-to-syntax desc This function returns the internal form corresponding to the syntaxdescriptor desc, a cons cell (syntax-code. matching-char). syntax-after — Function: syntax-after pos This function returns the syntax code of the character in the bufferafter position pos, taking account of syntax properties as wellas the syntax table. If pos is outside the buffer's accessibleportion (see accessible portion), this function returnsnil. syntax-class — Function: syntax-class syntax This function returns the syntax class of the syntax codesyntax. (It masks off the high 16 bits that hold the flagsencoded in the syntax descriptor.) If syntax is nil, itreturns nil; this is so evaluating the expression (syntax-class (syntax-after pos)) where pos is outside the buffer's accessible portion, willyield nil without throwing errors or producing wrong syntaxclass codes. Categories categories of characters character categories Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories. category table Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes. Each category has a name, which is an ASCII printing character in the range ‘ ’ to ‘~’. You specify the name of a category when you define it with define-category. The category table is actually a char-table (see ). The element of the category table at index c is a category set—a bool-vector—that indicates which categories character c belongs to. In this category set, if the element at index cat is t, that means category cat is a member of the set, and that character c belongs to category cat. For the next three functions, the optional argument table defaults to the current buffer's category table. define-category — Function: define-category char docstring &optional table This function defines a new category, with name char anddocumentation docstring, for the category table table. category-docstring — Function: category-docstring category &optional table This function returns the documentation string of category categoryin category table table. (category-docstring ?a) => "ASCII" (category-docstring ?l) => "Latin" get-unused-category — Function: get-unused-category &optional table This function returns a category name (a character) which is notcurrently defined in table. If all possible categories are in usein table, it returns nil. category-table — Function: category-table This function returns the current buffer's category table. category-table-p — Function: category-table-p object This function returns t if object is a category table,otherwise nil. standard-category-table — Function: standard-category-table This function returns the standard category table. copy-category-table — Function: copy-category-table &optional table This function constructs a copy of table and returns it. Iftable is not supplied (or is nil), it returns a copy of thestandard category table. Otherwise, an error is signaled if tableis not a category table. set-category-table — Function: set-category-table table This function makes table the category table for the currentbuffer. It returns table. make-category-table — Function: make-category-table This creates and returns an empty category table. In an empty categorytable, no categories have been allocated, and no characters belong toany categories. make-category-set — Function: make-category-set categories This function returns a new category set—a bool-vector—whose initialcontents are the categories listed in the string categories. Theelements of categories should be category names; the new categoryset has t for each of those categories, and nil for allother categories. (make-category-set "al") => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" char-category-set — Function: char-category-set char This function returns the category set for character char in thecurrent buffer's category table. This is the bool-vector whichrecords which categories the character char belongs to. Thefunction char-category-set does not allocate storage, becauseit returns the same bool-vector that exists in the category table. (char-category-set ?a) => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0" category-set-mnemonics — Function: category-set-mnemonics category-set This function converts the category set category-set into a stringcontaining the characters that designate the categories that are membersof the set. (category-set-mnemonics (char-category-set ?a)) => "al" modify-category-entry — Function: modify-category-entry character category &optional table reset This function modifies the category set of character in categorytable table (which defaults to the current buffer's categorytable).Normally, it modifies the category set by adding category to it.But if reset is non-nil, then it deletes categoryinstead. describe-categories — Command: describe-categories &optional buffer-or-name This function describes the category specifications in the currentcategory table. It inserts the descriptions in a buffer, and thendisplays that buffer. If buffer-or-name is non-nil, itdescribes the category table of that buffer instead. <setfilename>../info/abbrevs</setfilename> Abbrevs and Abbrev Expansion abbrev An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing. The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used. An abbrev table is represented as an obarray containing a symbol for each abbreviation. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function to do the expansion (see ); its property list cell typically contains the use count, the number of times the abbreviation has been expanded. Alternatively, the use count is on the count property and the system-abbrev flag is on the system-type property. Abbrevs with a non-nil system-type property are called “system” abbrevs. They are usually defined by modes or packages, instead of by the user, and are treated specially in certain respects. Because the symbols used for abbrevs are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way. See . For the user-level commands for abbrevs, see See section ``Abbrev Mode'' in The GNU Emacs Manual. Setting Up Abbrev Mode Abbrev mode is a minor mode controlled by the value of the variable abbrev-mode. abbrev-mode — Variable: abbrev-mode A non-nil value of this variable turns on the automatic expansionof abbrevs when their abbreviations are inserted into a buffer.If the value is nil, abbrevs may be defined, but they are notexpanded automatically.This variable automatically becomes buffer-local when set in any fashion. default-abbrev-mode — Variable: default-abbrev-mode This is the value of abbrev-mode for buffers that do not override it.This is the same as (default-value 'abbrev-mode). Abbrev Tables This section describes how to create and manipulate abbrev tables. make-abbrev-table — Function: make-abbrev-table This function creates and returns a new, empty abbrev table—an obarraycontaining no symbols. It is a vector filled with zeros. clear-abbrev-table — Function: clear-abbrev-table table This function undefines all the abbrevs in abbrev table table,leaving it empty. It always returns nil. copy-abbrev-table — Function: copy-abbrev-table table This function returns a copy of abbrev table table—a newabbrev table that contains the same abbrev definitions. The onlydifference between table and the returned copy is that thisfunction sets the property lists of all copied abbrevs to 0. define-abbrev-table — Function: define-abbrev-table tabname definitions This function defines tabname (a symbol) as an abbrev tablename, i.e., as a variable whose value is an abbrev table. It definesabbrevs in the table according to definitions, a list ofelements of the form (abbrevname expansionhook usecount system-flag). If an element ofdefinitions has length less than five, omitted elements defaultto nil. A value of nil for usecount is equivalentto zero. The return value is always nil.If this function is called more than once for the same tabname,subsequent calls add the definitions in definitions totabname, rather than overriding the entire original contents.(A subsequent call only overrides abbrevs explicitly redefined orundefined in definitions.) abbrev-table-name-list — Variable: abbrev-table-name-list This is a list of symbols whose values are abbrev tables.define-abbrev-table adds the new abbrev table name to this list. insert-abbrev-table-description — Function: insert-abbrev-table-description name &optional human This function inserts before point a description of the abbrev tablenamed name. The argument name is a symbol whose value is anabbrev table. The return value is always nil.If human is non-nil, the description is human-oriented.System abbrevs are listed and identified as such. Otherwise thedescription is a Lisp expression—a call to define-abbrev-tablethat would define name as it is currently defined, but withoutthe system abbrevs. (The mode or package using name is supposedto add these to name separately.) Defining Abbrevs define-abbrev is the low-level basic function for defining an abbrev in a specified abbrev table. When major modes predefine standard abbrevs, they should call define-abbrev and specify t for system-flag. Be aware that any saved non-“system” abbrevs are restored at startup, i.e. before some major modes are loaded. Major modes should therefore not assume that when they are first loaded their abbrev tables are empty. define-abbrev — Function: define-abbrev table name expansion &optional hook count system-flag This function defines an abbrev named name, in table, toexpand to expansion and call hook. The return value isname.The value of count, if specified, initializes the abbrev'susage-count. If count is not specified or nil, the usecount is initialized to zero.The argument name should be a string. The argumentexpansion is normally the desired expansion (a string), ornil to undefine the abbrev. If it is anything but a string ornil, then the abbreviation “expands” solely by runninghook.The argument hook is a function or nil. If hook isnon-nil, then it is called with no arguments after the abbrev isreplaced with expansion; point is located at the end ofexpansion when hook is called. no-self-insert propertyIf hook is a non-nil symbol whose no-self-insertproperty is non-nil, hook can explicitly control whetherto insert the self-inserting input character that triggered theexpansion. If hook returns non-nil in this case, thatinhibits insertion of the character. By contrast, if hookreturns nil, expand-abbrev also returns nil, asif expansion had not really occurred.If system-flag is non-nil, that marks the abbrev as a“system” abbrev with the system-type property. Unlesssystem-flag has the value force, a “system” abbrev willnot overwrite an existing definition for a non-“system” abbrev of thesame name.Normally the function define-abbrev sets the variableabbrevs-changed to t, if it actually changes the abbrev.(This is so that some commands will offer to save the abbrevs.) Itdoes not do this for a “system” abbrev, since those won't be savedanyway. only-global-abbrevs — User Option: only-global-abbrevs If this variable is non-nil, it means that the user plans to useglobal abbrevs only. This tells the commands that define mode-specificabbrevs to define global ones instead. This variable does not alter thebehavior of the functions in this section; it is examined by theircallers. Saving Abbrevs in Files A file of saved abbrev definitions is actually a file of Lisp code. The abbrevs are saved in the form of a Lisp program to define the same abbrev tables with the same contents. Therefore, you can load the file with load (see ). However, the function quietly-read-abbrev-file is provided as a more convenient interface. User-level facilities such as save-some-buffers can save abbrevs in a file automatically, under the control of variables described here. abbrev-file-name — User Option: abbrev-file-name This is the default file name for reading and saving abbrevs. quietly-read-abbrev-file — Function: quietly-read-abbrev-file &optional filename This function reads abbrev definitions from a file named filename,previously written with write-abbrev-file. If filename isomitted or nil, the file specified in abbrev-file-name isused. save-abbrevs is set to t so that changes will besaved.This function does not display any messages. It returns nil. save-abbrevs — User Option: save-abbrevs A non-nil value for save-abbrevs means that Emacs shouldoffer the user to save abbrevs when files are saved. If the value issilently, Emacs saves the abbrevs without asking the user.abbrev-file-name specifies the file to save the abbrevs in. abbrevs-changed — Variable: abbrevs-changed This variable is set non-nil by defining or altering anyabbrevs (except “system” abbrevs). This serves as a flag forvarious Emacs commands to offer to save your abbrevs. write-abbrev-file — Command: write-abbrev-file &optional filename Save all abbrev definitions (except “system” abbrevs), for all abbrevtables listed in abbrev-table-name-list, in the filefilename, in the form of a Lisp program that when loaded willdefine the same abbrevs. If filename is nil or omitted,abbrev-file-name is used. This function returns nil. Looking Up and Expanding Abbreviations Abbrevs are usually expanded by certain interactive commands, including self-insert-command. This section describes the subroutines used in writing such commands, as well as the variables they use for communication. abbrev-symbol — Function: abbrev-symbol abbrev &optional table This function returns the symbol representing the abbrev namedabbrev. The value returned is nil if that abbrev is notdefined. The optional second argument table is the abbrev tableto look it up in. If table is nil, this function triesfirst the current buffer's local abbrev table, and second the globalabbrev table. abbrev-expansion — Function: abbrev-expansion abbrev &optional table This function returns the string that abbrev would expand into (asdefined by the abbrev tables used for the current buffer). Ifabbrev is not a valid abbrev, the function returns nil.The optional argument table specifies the abbrev table to use,as in abbrev-symbol. expand-abbrev — Command: expand-abbrev This command expands the abbrev before point, if any. If point does notfollow an abbrev, this command does nothing. The command returns theabbrev symbol if it did expansion, nil otherwise.If the abbrev symbol has a hook function which is a symbol whoseno-self-insert property is non-nil, and if the hookfunction returns nil as its value, then expand-abbrevreturns nil even though expansion did occur. abbrev-prefix-mark — Command: abbrev-prefix-mark &optional arg This command marks the current location of point as the beginning ofan abbrev. The next call to expand-abbrev will use the textfrom here to point (where it is then) as the abbrev to expand, ratherthan using the previous word as usual.First, this command expands any abbrev before point, unless argis non-nil. (Interactively, arg is the prefix argument.)Then it inserts a hyphen before point, to indicate the start of thenext abbrev to be expanded. The actual expansion removes the hyphen. abbrev-all-caps — User Option: abbrev-all-caps When this is set non-nil, an abbrev entered entirely in uppercase is expanded using all upper case. Otherwise, an abbrev enteredentirely in upper case is expanded by capitalizing each word of theexpansion. abbrev-start-location — Variable: abbrev-start-location The value of this variable is a buffer position (an integer or a marker)for expand-abbrev to use as the start of the next abbrev to beexpanded. The value can also be nil, which means to use theword before point instead. abbrev-start-location is set tonil each time expand-abbrev is called. This variable isalso set by abbrev-prefix-mark. abbrev-start-location-buffer — Variable: abbrev-start-location-buffer The value of this variable is the buffer for whichabbrev-start-location has been set. Trying to expand an abbrevin any other buffer clears abbrev-start-location. This variableis set by abbrev-prefix-mark. last-abbrev — Variable: last-abbrev This is the abbrev-symbol of the most recent abbrev expanded. Thisinformation is left by expand-abbrev for the sake of theunexpand-abbrev command (see See section ``Expanding Abbrevs'' in The GNU Emacs Manual). last-abbrev-location — Variable: last-abbrev-location This is the location of the most recent abbrev expanded. This containsinformation left by expand-abbrev for the sake of theunexpand-abbrev command. last-abbrev-text — Variable: last-abbrev-text This is the exact expansion text of the most recent abbrev expanded,after case conversion (if any). Its value is nil if the abbrevhas already been unexpanded. This contains information left byexpand-abbrev for the sake of the unexpand-abbrev command. pre-abbrev-expand-hook — Variable: pre-abbrev-expand-hook This is a normal hook whose functions are executed, in sequence, justbefore any expansion of an abbrev. See . Since it is a normalhook, the hook functions receive no arguments. However, they can findthe abbrev to be expanded by looking in the buffer before point.Running the hook is the first thing that expand-abbrev does, andso a hook function can be used to change the current abbrev table beforeabbrev lookup happens. (Although you have to do this carefully. Seethe example below.) The following sample code shows a simple use of pre-abbrev-expand-hook. It assumes that foo-mode is a mode for editing certain files in which lines that start with ‘#’ are comments. You want to use Text mode abbrevs for those lines. The regular local abbrev table, foo-mode-abbrev-table is appropriate for all other lines. Then you can put the following code in your .emacs file. See , for the definitions of local-abbrev-table and text-mode-abbrev-table. (defun foo-mode-pre-abbrev-expand () (when (save-excursion (forward-line 0) (eq (char-after) ?#)) (let ((local-abbrev-table text-mode-abbrev-table) ;; Avoid infinite loop. (pre-abbrev-expand-hook nil)) (expand-abbrev)) ;; We have already called `expand-abbrev' in this hook. ;; Hence we want the "actual" call following this hook to be a no-op. (setq abbrev-start-location (point-max) abbrev-start-location-buffer (current-buffer)))) (add-hook 'foo-mode-hook #'(lambda () (add-hook 'pre-abbrev-expand-hook 'foo-mode-pre-abbrev-expand nil t))) Note that foo-mode-pre-abbrev-expand just returns nil without doing anything for lines not starting with ‘#’. Hence abbrevs expand normally using foo-mode-abbrev-table as local abbrev table for such lines. Standard Abbrev Tables Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs. global-abbrev-table — Variable: global-abbrev-table This is the abbrev table for mode-independent abbrevs. The abbrevsdefined in it apply to all buffers. Each buffer may also have a localabbrev table, whose abbrev definitions take precedence over those in theglobal table. local-abbrev-table — Variable: local-abbrev-table The value of this buffer-local variable is the (mode-specific)abbreviation table of the current buffer. fundamental-mode-abbrev-table — Variable: fundamental-mode-abbrev-table This is the local abbrev table used in Fundamental mode; in other words,it is the local abbrev table in all buffers in Fundamental mode. text-mode-abbrev-table — Variable: text-mode-abbrev-table This is the local abbrev table used in Text mode. lisp-mode-abbrev-table — Variable: lisp-mode-abbrev-table This is the local abbrev table used in Lisp mode and Emacs Lisp mode. <setfilename>../info/processes</setfilename> Processes child process parent process subprocess process In the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process. A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process.” Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it. processp — Function: processp object This function returns t if object is a process,nil otherwise. Functions that Create Subprocesses There are three functions that create a new subprocess in which to run a program. One of them, start-process, creates an asynchronous process and returns a process object (see ). The other two, call-process and call-process-region, create a synchronous process and do not return a process object (see ). Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here. execute program PATH environment variable HOME environment variable In all cases, the function's program argument specifies the program to be run. An error is signaled if the file is not found or cannot be executed. If the file name is relative, the variable exec-path contains a list of directories to search. Emacs initializes exec-path when it starts up, based on the value of the environment variable PATH. The standard file name constructs, ‘~’, ‘.’, and ‘..’, are interpreted as usual in exec-path, but environment variable substitutions (‘$HOME’, etc.) are not recognized; use substitute-in-file-name to perform them (see ). nil in this list refers to default-directory. Executing a program can also try adding suffixes to the specified name: exec-suffixes — Variable: exec-suffixes This variable is a list of suffixes (strings) to try adding to thespecified program file name. The list should include "" if youwant the name to be tried exactly as specified. The default value issystem-dependent. Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use args to provide those. Each of the subprocess-creating functions has a buffer-or-name argument which specifies where the standard output from the program will go. It should be a buffer or a buffer name; if it is a buffer name, that will create the buffer if it does not already exist. It can also be nil, which says to discard the output unless a filter function handles it. (See , and .) Normally, you should avoid having multiple processes send output to the same buffer because their output would be intermixed randomly. program arguments All three of the subprocess-creating functions have a &rest argument, args. The args must all be strings, and they are supplied to program as separate command line arguments. Wildcard characters and other shell constructs have no special meanings in these strings, since the strings are passed directly to the specified program. The subprocess gets its current directory from the value of default-directory (see ). environment variables, subprocesses The subprocess inherits its environment from Emacs, but you can specify overrides for it with process-environment. See . exec-directory — Variable: exec-directory movemailThe value of this variable is a string, the name of a directory thatcontains programs that come with GNU Emacs, programs intended for Emacsto invoke. The program movemail is an example of such a program;Rmail uses it to fetch new mail from an inbox. exec-path — User Option: exec-path The value of this variable is a list of directories to search forprograms to run in subprocesses. Each element is either the name of adirectory (i.e., a string), or nil, which stands for the defaultdirectory (which is the value of default-directory). program directoriesThe value of exec-path is used by call-process andstart-process when the program argument is not an absolutefile name. Shell Arguments arguments for shell commands shell command arguments Lisp programs sometimes need to run a shell and give it a command that contains file names that were specified by the user. These programs ought to be able to support any valid file name. But the shell gives special treatment to certain characters, and if these characters occur in the file name, they will confuse the shell. To handle these characters, use the function shell-quote-argument: shell-quote-argument — Function: shell-quote-argument argument This function returns a string which represents, in shell syntax,an argument whose actual contents are argument. It shouldwork reliably to concatenate the return value into a shell commandand then pass it to a shell for execution.Precisely what this function does depends on your operating system. Thefunction is designed to work with the syntax of your system's standardshell; if you use an unusual shell, you will need to redefine thisfunction. ;; This example shows the behavior on GNU and Unix systems. (shell-quote-argument "foo > bar") => "foo\\ \\>\\ bar" ;; This example shows the behavior on MS-DOS and MS-Windows. (shell-quote-argument "foo > bar") => "\"foo > bar\"" Here's an example of using shell-quote-argument to constructa shell command: (concat "diff -c " (shell-quote-argument oldfile) " " (shell-quote-argument newfile)) Creating a Synchronous Process synchronous subprocess After a synchronous process is created, Emacs waits for the process to terminate before continuing. Starting Dired on GNU or UnixOn other systems, Emacs uses a Lisp emulation of ls; see . is an example of this: it runs ls in a synchronous process, then modifies the output slightly. Because the process is synchronous, the entire directory listing arrives in the buffer before Emacs tries to do anything with it. While Emacs waits for the synchronous subprocess to terminate, the user can quit by typing C-g. The first C-g tries to kill the subprocess with a SIGINT signal; but it waits until the subprocess actually terminates before quitting. If during that time the user types another C-g, that kills the subprocess instantly with SIGKILL and quits immediately (except on MS-DOS, where killing other processes doesn't work). See . The synchronous subprocess functions return an indication of how the process terminated. The output from a synchronous subprocess is generally decoded using a coding system, much like text read from a file. The input sent to a subprocess by call-process-region is encoded using a coding system, much like text written into a file. See . call-process — Function: call-process program &optional infile destination display &rest args This function calls program in a separate process and waits forit to finish.The standard input for the process comes from file infile ifinfile is not nil, and from the null device otherwise.The argument destination says where to put the process output.Here are the possibilities: a buffer Insert the output in that buffer, before point. This includes both thestandard output stream and the standard error stream of the process. a string Insert the output in a buffer with that name, before point. t Insert the output in the current buffer, before point. nil Discard the output. 0 Discard the output, and return nil immediately without waitingfor the subprocess to finish.In this case, the process is not truly synchronous, since it can run inparallel with Emacs; but you can think of it as synchronous in thatEmacs is essentially finished with the subprocess as soon as thisfunction returns.MS-DOS doesn't support asynchronous subprocesses, so this option doesn'twork there. (real-destination error-destination) Keep the standard output stream separate from the standard error stream;deal with the ordinary output as specified by real-destination,and dispose of the error output according to error-destination.If error-destination is nil, that means to discard theerror output, t means mix it with the ordinary output, and astring specifies a file name to redirect error output into.You can't directly specify a buffer to put the error output in; that istoo difficult to implement. But you can achieve this result by sendingthe error output to a temporary file and then inserting the file into abuffer. If display is non-nil, then call-process redisplaysthe buffer as output is inserted. (However, if the coding system chosenfor decoding output is undecided, meaning deduce the encodingfrom the actual data, then redisplay sometimes cannot continue oncenon-ASCII characters are encountered. There are fundamentalreasons why it is hard to fix this; see .)Otherwise the function call-process does no redisplay, and theresults become visible on the screen only when Emacs redisplays thatbuffer in the normal course of events.The remaining arguments, args, are strings that specify commandline arguments for the program.The value returned by call-process (unless you told it not towait) indicates the reason for process termination. A number gives theexit status of the subprocess; 0 means success, and any other valuemeans failure. If the process terminated with a signal,call-process returns a string describing the signal.In the examples below, the buffer ‘foo’ is current. (call-process "pwd" nil t) => 0 ---------- Buffer: foo ---------- /usr/user/lewis/manual ---------- Buffer: foo ---------- (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") => 0 ---------- Buffer: bar ---------- lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh ---------- Buffer: bar ---------- Here is a good example of the use of call-process, which used tobe found in the definition of insert-directory: (call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file)) process-file — Function: process-file program &optional infile buffer display &rest args This function processes files synchronously in a separate process. Itis similar to call-process but may invoke a file handler basedon the value of the variable default-directory. The currentworking directory of the subprocess is default-directory.The arguments are handled in almost the same way as forcall-process, with the following differences:Some file handlers may not support all combinations and forms of thearguments infile, buffer, and display. For example,some file handlers might behave as if display were nil,regardless of the value actually passed. As another example, somefile handlers might not support separating standard output and erroroutput by way of the buffer argument.If a file handler is invoked, it determines the program to run basedon the first argument program. For instance, consider that ahandler for remote files is invoked. Then the path that is used forsearching the program might be different than exec-path.The second argument infile may invoke a file handler. The filehandler could be different from the handler chosen for theprocess-file function itself. (For example,default-directory could be on a remote host, whereasinfile is on another remote host. Or default-directorycould be non-special, whereas infile is on a remote host.)If buffer is a list of the form (real-destinationerror-destination), and error-destination names a file,then the same remarks as for infile apply.The remaining arguments (args) will be passed to the processverbatim. Emacs is not involved in processing file names that arepresent in args. To avoid confusion, it may be best to avoidabsolute file names in args, but rather to specify all filenames as relative to default-directory. The functionfile-relative-name is useful for constructing such relativefile names. call-process-region — Function: call-process-region start end program &optional delete destination display &rest args This function sends the text from start to end asstandard input to a process running program. It deletes the textsent if delete is non-nil; this is useful whendestination is t, to insert the output in the currentbuffer in place of the input.The arguments destination and display control what to dowith the output from the subprocess, and whether to update the displayas it comes in. For details, see the description ofcall-process, above. If destination is the integer 0,call-process-region discards the output and returns nilimmediately, without waiting for the subprocess to finish (this onlyworks if asynchronous subprocesses are supported).The remaining arguments, args, are strings that specify commandline arguments for the program.The return value of call-process-region is just like that ofcall-process: nil if you told it to return withoutwaiting; otherwise, a number or string which indicates how thesubprocess terminated.In the following example, we use call-process-region to run thecat utility, with standard input being the first five charactersin buffer ‘foo’ (the word ‘input’). cat copies itsstandard input into its standard output. Since the argumentdestination is t, this output is inserted in the currentbuffer. ---------- Buffer: foo ---------- input-!- ---------- Buffer: foo ---------- (call-process-region 1 6 "cat" nil t) => 0 ---------- Buffer: foo ---------- inputinput-!- ---------- Buffer: foo ---------- The shell-command-on-region command usescall-process-region like this: (call-process-region start end shell-file-name ; Name of program. nil ; Do not delete region. buffer ; Send output to buffer. nil ; No redisplay during output. "-c" command) ; Arguments for the shell. call-process-shell-command — Function: call-process-shell-command command &optional infile destination display &rest args This function executes the shell command command synchronouslyin a separate process. The final arguments args are additionalarguments to add at the end of command. The other argumentsare handled as in call-process. shell-command-to-string — Function: shell-command-to-string command This function executes command (a string) as a shell command,then returns the command's output as a string. Creating an Asynchronous Process asynchronous subprocess After an asynchronous process is created, Emacs and the subprocess both continue running immediately. The process thereafter runs in parallel with Emacs, and the two can communicate with each other using the functions described in the following sections. However, communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only when Emacs is waiting for input or for a time delay. Here we describe how to create an asynchronous process. start-process — Function: start-process name buffer-or-name program &rest args This function creates a new asynchronous subprocess and starts theprogram program running in it. It returns a process object thatstands for the new subprocess in Lisp. The argument namespecifies the name for the process object; if a process with this namealready exists, then name is modified (by appending ‘<1>’,etc.) to be unique. The buffer buffer-or-name is the buffer toassociate with the process.The remaining arguments, args, are strings that specify commandline arguments for the program.In the example below, the first process is started and runs (rather,sleeps) for 100 seconds. Meanwhile, the second process is started, andgiven the name ‘my-process<1>’ for the sake of uniqueness. Itinserts the directory listing at the end of the buffer ‘foo’,before the first process finishes. Then it finishes, and a message tothat effect is inserted in the buffer. Much later, the first processfinishes, and another message is inserted in the buffer for it. (start-process "my-process" "foo" "sleep" "100") => #<process my-process> (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin") => #<process my-process<1>> ---------- Buffer: foo ---------- total 2 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon Process my-process<1> finished Process my-process finished ---------- Buffer: foo ---------- start-process-shell-command — Function: start-process-shell-command name buffer-or-name command &rest command-args This function is like start-process except that it uses a shellto execute the specified command. The argument command is a shellcommand name, and command-args are the arguments for the shellcommand. The variable shell-file-name specifies which shell touse.The point of running a program through the shell, rather than directlywith start-process, is so that you can employ shell features suchas wildcards in the arguments. It follows that if you include anarbitrary user-specified arguments in the command, you should quote itwith shell-quote-argument first, so that any special shellcharacters do not have their special shell meanings. See . process-connection-type — Variable: process-connection-type pipes PTYsThis variable controls the type of device used to communicate withasynchronous subprocesses. If it is non-nil, then PTYs areused, when available. Otherwise, pipes are used.PTYs are usually preferable for processes visible to the user, asin Shell mode, because they allow job control (C-c, C-z,etc.) to work between the process and its children, whereas pipes donot. For subprocesses used for internal purposes by programs, it isoften better to use a pipe, because they are more efficient. Inaddition, the total number of PTYs is limited on many systems andit is good not to waste them.The value of process-connection-type takes effect whenstart-process is called. So you can specify how to communicatewith one subprocess by binding the variable around the call tostart-process. (let ((process-connection-type nil)) ; Use a pipe. (start-process …)) To determine whether a given subprocess actually got a pipe or aPTY, use the function process-tty-name (see ). Deleting Processes deleting processes Deleting a process disconnects Emacs immediately from the subprocess. Processes are deleted automatically after they terminate, but not necessarily right away. You can delete a process explicitly at any time. If you delete a terminated process explicitly before it is deleted automatically, no harm results. Deleting a running process sends a signal to terminate it (and its child processes if any), and calls the process sentinel if it has one. See . When a process is deleted, the process object itself continues to exist as long as other Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted processes, but those that do I/O or send signals will report an error. The process mark continues to point to the same place as before, usually into a buffer where output from the process was being inserted. delete-exited-processes — User Option: delete-exited-processes This variable controls automatic deletion of processes that haveterminated (due to calling exit or to a signal). If it isnil, then they continue to exist until the user runslist-processes. Otherwise, they are deleted immediately afterthey exit. delete-process — Function: delete-process process This function deletes a process, killing it with a SIGKILLsignal. The argument may be a process, the name of a process, abuffer, or the name of a buffer. (A buffer or buffer-name stands forthe process that get-buffer-process returns.) Callingdelete-process on a running process terminates it, updates theprocess status, and runs the sentinel (if any) immediately. If theprocess has already terminated, calling delete-process has noeffect on its status, or on the running of its sentinel (which willhappen sooner or later). (delete-process "*shell*") => nil Process Information Several functions return information about processes. list-processes is provided for interactive use. list-processes — Command: list-processes &optional query-only This command displays a listing of all living processes. In addition,it finally deletes any process whose status was ‘Exited’ or‘Signaled’. It returns nil.If query-only is non-nil then it lists only processeswhose query flag is non-nil. See . process-list — Function: process-list This function returns a list of all processes that have not been deleted. (process-list) => (#<process display-time> #<process shell>) get-process — Function: get-process name This function returns the process named name, or nil ifthere is none. An error is signaled if name is not a string. (get-process "shell") => #<process shell> process-command — Function: process-command process This function returns the command that was executed to startprocess. This is a list of strings, the first string being theprogram executed and the rest of the strings being the arguments thatwere given to the program. (process-command (get-process "shell")) => ("/bin/csh" "-i") process-id — Function: process-id process This function returns the PID of process. This is aninteger that distinguishes the process process from all otherprocesses running on the same computer at the current time. ThePID of a process is chosen by the operating system kernel when theprocess is started and remains constant as long as the process exists. process-name — Function: process-name process This function returns the name of process. process-status — Function: process-status process-name This function returns the status of process-name as a symbol.The argument process-name must be a process, a buffer, aprocess name (string) or a buffer name (string).The possible values for an actual subprocess are: run for a process that is running. stop for a process that is stopped but continuable. exit for a process that has exited. signal for a process that has received a fatal signal. open for a network connection that is open. closed for a network connection that is closed. Once a connectionis closed, you cannot reopen it, though you might be able to opena new connection to the same place. connect for a non-blocking connection that is waiting to complete. failed for a non-blocking connection that has failed to complete. listen for a network server that is listening. nil if process-name is not the name of an existing process. (process-status "shell") => run (process-status (get-buffer "*shell*")) => run x => #<process xx<1>> (process-status x) => exit For a network connection, process-status returns one of the symbolsopen or closed. The latter means that the other sideclosed the connection, or Emacs did delete-process. process-exit-status — Function: process-exit-status process This function returns the exit status of process or the signalnumber that killed it. (Use the result of process-status todetermine which of those it is.) If process has not yetterminated, the value is 0. process-tty-name — Function: process-tty-name process This function returns the terminal name that process is using forits communication with Emacs—or nil if it is using pipesinstead of a terminal (see process-connection-type in). process-coding-system — Function: process-coding-system process This function returns a cons cell describing the coding systems in usefor decoding output from process and for encoding input toprocess (see ). The value has this form: (coding-system-for-decoding . coding-system-for-encoding) set-process-coding-system — Function: set-process-coding-system process &optional decoding-system encoding-system This function specifies the coding systems to use for subsequent outputfrom and input to process. It will use decoding-system todecode subprocess output, and encoding-system to encode subprocessinput. Every process also has a property list that you can use to store miscellaneous values associated with the process. process-get — Function: process-get process propname This function returns the value of the propname propertyof process. process-put — Function: process-put process propname value This function sets the value of the propname propertyof process to value. process-plist — Function: process-plist process This function returns the process plist of process. set-process-plist — Function: set-process-plist process plist This function sets the process plist of process to plist. Sending Input to Processes process input Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the “standard input” of the subprocess. Some operating systems have limited space for buffered input in a PTY. On these systems, Emacs sends an EOF periodically amidst the other characters, to force them through. For most programs, these EOFs do no harm. Subprocess input is normally encoded using a coding system before the subprocess receives it, much like text written into a file. You can use set-process-coding-system to specify which coding system to use (see ). Otherwise, the coding system comes from coding-system-for-write, if that is non-nil; or else from the defaulting mechanism (see ). Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters, sentinels and timers to run—so take account of that in writing your code. In these functions, the process argument can be a process or the name of a process, or a buffer or buffer name (which stands for a process via get-buffer-process). nil means the current buffer's process. process-send-string — Function: process-send-string process string This function sends process the contents of string asstandard input. If it is nil, the current buffer's process is used. The function returns nil. (process-send-string "shell<1>" "ls\n") => nil ---------- Buffer: *shell* ---------- ... introduction.texi syntax-tables.texi~ introduction.texi~ text.texi introduction.txt text.texi~ ... ---------- Buffer: *shell* ---------- process-send-region — Function: process-send-region process start end This function sends the text in the region defined by start andend as standard input to process.An error is signaled unless both start and end areintegers or markers that indicate positions in the current buffer. (Itis unimportant which number is larger.) process-send-eof — Function: process-send-eof &optional process This function makes process see an end-of-file in itsinput. The EOF comes after any text already sent to it.The function returns process. (process-send-eof "shell") => "shell" process-running-child-p — Function: process-running-child-p process This function will tell you whether a subprocess has given control ofits terminal to its own child process. The value is t if this istrue, or if Emacs cannot tell; it is nil if Emacs can be certainthat this is not so. Sending Signals to Processes process signals sending signals signals Sending a signal to a subprocess is a way of interrupting its activities. There are several different signals, each with its own meaning. The set of signals and their names is defined by the operating system. For example, the signal SIGINT means that the user has typed C-c, or that some analogous thing has happened. Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects. You can send signals explicitly by calling the functions in this section. Emacs also sends signals automatically at certain times: killing a buffer sends a SIGHUP signal to all its associated processes; killing Emacs sends a SIGHUP signal to all remaining processes. (SIGHUP is a signal that usually indicates that the user hung up the phone.) Each of the signal-sending functions takes two optional arguments: process and current-group. The argument process must be either a process, a process name, a buffer, a buffer name, or nil. A buffer or buffer name stands for a process through get-buffer-process. nil stands for the process associated with the current buffer. An error is signaled if process does not identify a process. The argument current-group is a flag that makes a difference when you are running a job-control shell as an Emacs subprocess. If it is non-nil, then the signal is sent to the current process-group of the terminal that Emacs uses to communicate with the subprocess. If the process is a job-control shell, this means the shell's current subjob. If it is nil, the signal is sent to the process group of the immediate subprocess of Emacs. If the subprocess is a job-control shell, this is the shell itself. The flag current-group has no effect when a pipe is used to communicate with the subprocess, because the operating system does not support the distinction in the case of pipes. For the same reason, job-control shells won't work when a pipe is used. See process-connection-type in . interrupt-process — Function: interrupt-process &optional process current-group This function interrupts the process process by sending thesignal SIGINT. Outside of Emacs, typing the “interruptcharacter” (normally C-c on some systems, and DEL onothers) sends this signal. When the argument current-group isnon-nil, you can think of this function as “typing C-c”on the terminal by which Emacs talks to the subprocess. kill-process — Function: kill-process &optional process current-group This function kills the process process by sending thesignal SIGKILL. This signal kills the subprocess immediately,and cannot be handled by the subprocess. quit-process — Function: quit-process &optional process current-group This function sends the signal SIGQUIT to the processprocess. This signal is the one sent by the “quitcharacter” (usually C-b or C-\) when you are not insideEmacs. stop-process — Function: stop-process &optional process current-group This function stops the process process by sending thesignal SIGTSTP. Use continue-process to resume itsexecution.Outside of Emacs, on systems with job control, the “stop character”(usually C-z) normally sends this signal. Whencurrent-group is non-nil, you can think of this function as“typing C-z” on the terminal Emacs uses to communicate with thesubprocess. continue-process — Function: continue-process &optional process current-group This function resumes execution of the process process by sendingit the signal SIGCONT. This presumes that process wasstopped previously. signal-process — Function: signal-process process signal This function sends a signal to process process. The argumentsignal specifies which signal to send; it should be an integer.The process argument can be a system process ID; thatallows you to send signals to processes that are not children ofEmacs. Receiving Output from Processes process output output from processes There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output. If the process has no buffer and no filter function, its output is discarded. When a subprocess terminates, Emacs reads any pending output, then stops reading output from that subprocess. Therefore, if the subprocess has children that are still live and still producing output, Emacs won't receive that output. Output from a subprocess can arrive only while Emacs is waiting: when reading terminal input, in sit-for and sleep-for (see ), and in accept-process-output (see ). This minimizes the problem of timing errors that usually plague parallel programming. For example, you can safely create a process and only then specify its buffer or filter function; no output can arrive before you finish, if the code in between does not call any primitive that waits. process-adaptive-read-buffering — Variable: process-adaptive-read-buffering On some systems, when Emacs reads the output from a subprocess, theoutput data is read in very small blocks, potentially resulting invery poor performance. This behavior can be remedied to some extentby setting the variable process-adaptive-read-buffering to anon-nil value (the default), as it will automatically delay readingfrom such processes, thus allowing them to produce more output beforeEmacs tries to read it. It is impossible to separate the standard output and standard error streams of the subprocess, because Emacs normally spawns the subprocess inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If you want to keep the output to those streams separate, you should redirect one of them to a file—for example, by using an appropriate shell command. Process Buffers A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp. Unless the process has a filter function (see ), its output is inserted in the associated buffer. The position to insert the output is determined by the process-mark, which is then updated to point to the end of the text just inserted. Usually, but not always, the process-mark is at the end of the buffer. process-buffer — Function: process-buffer process This function returns the associated buffer of the processprocess. (process-buffer (get-process "shell")) => #<buffer *shell*> process-mark — Function: process-mark process This function returns the process marker for process, which is themarker that says where to insert output from the process.If process does not have a buffer, process-mark returns amarker that points nowhere.Insertion of process output in a buffer uses this marker to decide whereto insert, and updates it to point after the inserted text. That is whysuccessive batches of output are inserted consecutively.Filter functions normally should use this marker in the same fashionas is done by direct insertion of output in the buffer. A goodexample of a filter function that uses process-mark is found atthe end of the following section.When the user is expected to enter input in the process buffer fortransmission to the process, the process marker separates the new inputfrom previous output. set-process-buffer — Function: set-process-buffer process buffer This function sets the buffer associated with process tobuffer. If buffer is nil, the process becomesassociated with no buffer. get-buffer-process — Function: get-buffer-process buffer-or-name This function returns a nondeleted process associated with the bufferspecified by buffer-or-name. If there are several processesassociated with it, this function chooses one (currently, the one mostrecently created, but don't count on that). Deletion of a process(see delete-process) makes it ineligible for this function toreturn.It is usually a bad idea to have more than one process associated withthe same buffer. (get-buffer-process "*shell*") => #<process shell> Killing the process's buffer deletes the process, which kills thesubprocess with a SIGHUP signal (see ). Process Filter Functions filter function process filter A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process is passed to the filter. The process buffer is used directly for output from the process only when there is no filter. The filter function can only be called when Emacs is waiting for something, because process output arrives only at such times. Emacs waits when reading terminal input, in sit-for and sleep-for (see ), and in accept-process-output (see ). A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output. Quitting is normally inhibited within a filter function—otherwise, the effect of typing C-g at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a filter function, bind inhibit-quit to nil. In most cases, the right way to do this is with the macro with-local-quit. See . If an error happens during execution of a filter function, it is caught automatically, so that it doesn't stop the execution of whatever program was running when the filter function was started. However, if debug-on-error is non-nil, the error-catching is turned off. This makes it possible to use the Lisp debugger to debug the filter function. See . Many filter functions sometimes or always insert the text in the process's buffer, mimicking the actions of Emacs when there is no filter. Such filter functions need to use set-buffer in order to be sure to insert in that buffer. To avoid setting the current buffer semipermanently, these filter functions must save and restore the current buffer. They should also update the process marker, and in some cases update the value of point. Here is how to do these things: (defun ordinary-insertion-filter (proc string) (with-current-buffer (process-buffer proc) (let ((moving (= (point) (process-mark proc)))) (save-excursion ;; Insert the text, advancing the process marker. (goto-char (process-mark proc)) (insert string) (set-marker (process-mark proc) (point))) (if moving (goto-char (process-mark proc)))))) The reason to use with-current-buffer, rather than using save-excursion to save and restore the current buffer, is so as to preserve the change in point made by the second call to goto-char. To make the filter force the process buffer to be visible whenever new text arrives, insert the following line just before the with-current-buffer construct: (display-buffer (process-buffer proc)) To force point to the end of the new output, no matter where it was previously, eliminate the variable moving and call goto-char unconditionally. In earlier Emacs versions, every filter function that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for filter functions; they never need to do it explicitly. See . A filter function that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error. The expression (buffer-name (process-buffer process)) returns nil if the buffer is dead. The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output. set-process-filter — Function: set-process-filter process filter This function gives process the filter function filter. Iffilter is nil, it gives the process no filter. process-filter — Function: process-filter process This function returns the filter function of process, or nilif it has none. Here is an example of use of a filter function: (defun keep-output (process output) (setq kept (cons output kept))) => keep-output (setq kept nil) => nil (set-process-filter (get-process "shell") 'keep-output) => keep-output (process-send-string "shell" "ls ~/other\n") => nil kept => ("lewis@slug[8] % " "FINAL-W87-SHORT.MSS backup.otl kolstad.mss~ address.txt backup.psf kolstad.psf backup.bib~ david.mss resume-Dec-86.mss~ backup.err david.psf resume-Dec.psf backup.mss dland syllabus.mss " "#backups.mss# backup.mss~ kolstad.mss ") Decoding Process Output decode process output When Emacs writes process output directly into a multibyte buffer, it decodes the output according to the process output coding system. If the coding system is raw-text or no-conversion, Emacs converts the unibyte output to multibyte using string-to-multibyte, and inserts the resulting multibyte text. You can use set-process-coding-system to specify which coding system to use (see ). Otherwise, the coding system comes from coding-system-for-read, if that is non-nil; or else from the defaulting mechanism (see ). Warning: Coding systems such as undecided which determine the coding system from the data do not work entirely reliably with asynchronous subprocess output. This is because Emacs has to process asynchronous subprocess output in batches, as it arrives. Emacs must try to detect the proper coding system from one batch at a time, and this does not always work. Therefore, if at all possible, specify a coding system that determines both the character code conversion and the end of line conversion—that is, one like latin-1-unix, rather than undecided or latin-1. filter multibyte flag, of process process filter multibyte flag When Emacs calls a process filter function, it provides the process output as a multibyte string or as a unibyte string according to the process's filter multibyte flag. If the flag is non-nil, Emacs decodes the output according to the process output coding system to produce a multibyte string, and passes that to the process. If the flag is nil, Emacs puts the output into a unibyte string, with no decoding, and passes that. When you create a process, the filter multibyte flag takes its initial value from default-enable-multibyte-characters. If you want to change the flag later on, use set-process-filter-multibyte. set-process-filter-multibyte — Function: set-process-filter-multibyte process multibyte This function sets the filter multibyte flag of processto multibyte. process-filter-multibyte-p — Function: process-filter-multibyte-p process This function returns the filter multibyte flag of process. Accepting Output from Processes accept input from processes Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process. accept-process-output — Function: accept-process-output &optional process seconds millisec just-this-one This function allows Emacs to read pending output from processes. Theoutput is inserted in the associated buffers or given to their filterfunctions. If process is non-nil then this function doesnot return until some output has been received from process. The arguments seconds and millisec let you specify timeoutperiods. The former specifies a period measured in seconds and thelatter specifies one measured in milliseconds. The two time periodsthus specified are added together, and accept-process-outputreturns after that much time, whether or not there has been anysubprocess output.The argument millisec is semi-obsolete nowadays becauseseconds can be a floating point number to specify waiting afractional number of seconds. If seconds is 0, the functionaccepts whatever output is pending but does not wait. If process is a process, and the argument just-this-one isnon-nil, only output from that process is handled, suspending outputfrom other processes until some output has been received from thatprocess or the timeout expires. If just-this-one is an integer,also inhibit running timers. This feature is generally notrecommended, but may be necessary for specific applications, such asspeech synthesis.The function accept-process-output returns non-nil if itdid get some output, or nil if the timeout expired before outputarrived. Sentinels: Detecting Process Status Changes process sentinel sentinel (of process) A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event. The string describing the event looks like one of the following: "finished\n". "exited abnormally with code exitcode\n". "name-of-signal\n". "name-of-signal (core dumped)\n". A sentinel runs only while Emacs is waiting (e.g., for terminal input, or for time to elapse, or for process output). This avoids the timing errors that could result from running them at random places in the middle of other Lisp programs. A program can wait, so that sentinels will run, by calling sit-for or sleep-for (see ), or accept-process-output (see ). Emacs also allows sentinels to run when the command loop is reading input. delete-process calls the sentinel when it terminates a running process. Emacs does not keep a queue of multiple reasons to call the sentinel of one process; it records just the current status and the fact that there has been a change. Therefore two changes in status, coming in quick succession, can call the sentinel just once. However, process termination will always run the sentinel exactly once. This is because the process status can't change again after termination. Emacs explicitly checks for output from the process before running the process sentinel. Once the sentinel runs due to process termination, no further output can arrive from the process. A sentinel that writes the output into the buffer of the process should check whether the buffer is still alive. If it tries to insert into a dead buffer, it will get an error. If the buffer is dead, (buffer-name (process-buffer process)) returns nil. Quitting is normally inhibited within a sentinel—otherwise, the effect of typing C-g at command level or to quit a user command would be unpredictable. If you want to permit quitting inside a sentinel, bind inhibit-quit to nil. In most cases, the right way to do this is with the macro with-local-quit. See . If an error happens during execution of a sentinel, it is caught automatically, so that it doesn't stop the execution of whatever programs was running when the sentinel was started. However, if debug-on-error is non-nil, the error-catching is turned off. This makes it possible to use the Lisp debugger to debug the sentinel. See . While a sentinel is running, the process sentinel is temporarily set to nil so that the sentinel won't run recursively. For this reason it is not possible for a sentinel to specify a new sentinel. In earlier Emacs versions, every sentinel that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for sentinels; they never need to do it explicitly. See . set-process-sentinel — Function: set-process-sentinel process sentinel This function associates sentinel with process. Ifsentinel is nil, then the process will have no sentinel.The default behavior when there is no sentinel is to insert a message inthe process's buffer when the process status changes.Changes in process sentinel take effect immediately—if the sentinelis slated to be run but has not been called yet, and you specify a newsentinel, the eventual call to the sentinel will use the new one. (defun msg-me (process event) (princ (format "Process: %s had the event `%s'" process event))) (set-process-sentinel (get-process "shell") 'msg-me) => msg-me (kill-process (get-process "shell")) -| Process: #<process shell> had the event `killed' => #<process shell> process-sentinel — Function: process-sentinel process This function returns the sentinel of process, or nil if ithas none. waiting-for-user-input-p — Function: waiting-for-user-input-p While a sentinel or filter function is running, this function returnsnon-nil if Emacs was waiting for keyboard input from the user atthe time the sentinel or filter function was called, nil if itwas not. Querying Before Exit When Emacs exits, it terminates all its subprocesses by sending them the SIGHUP signal. Because subprocesses may be doing valuable work, Emacs normally asks the user to confirm that it is ok to terminate them. Each process has a query flag which, if non-nil, says that Emacs should ask for confirmation before exiting and thus killing that process. The default for the query flag is t, meaning do query. process-query-on-exit-flag — Function: process-query-on-exit-flag process This returns the query flag of process. set-process-query-on-exit-flag — Function: set-process-query-on-exit-flag process flag This function sets the query flag of process to flag. Itreturns flag. ;; Don't query about the shell process (set-process-query-on-exit-flag (get-process "shell") nil) => t process-kill-without-query — Function: process-kill-without-query process &optional do-query This function clears the query flag of process, so thatEmacs will not query the user on account of that process.Actually, the function does more than that: it returns the old value ofthe process's query flag, and sets the query flag to do-query.Please don't use this function to do those things any more—pleaseuse the newer, cleaner functions process-query-on-exit-flag andset-process-query-on-exit-flag in all but the simplest cases.The only way you should use process-kill-without-query nowadaysis like this: ;; Don't query about the shell process (process-kill-without-query (get-process "shell")) Transaction Queues transaction queue You can use a transaction queue to communicate with a subprocess using transactions. First use tq-create to create a transaction queue communicating with a specified process. Then you can call tq-enqueue to send a transaction. tq-create — Function: tq-create process This function creates and returns a transaction queue communicating withprocess. The argument process should be a subprocesscapable of sending and receiving streams of bytes. It may be a childprocess, or it may be a TCP connection to a server, possibly on anothermachine. tq-enqueue — Function: tq-enqueue queue question regexp closure fn &optional delay-question This function sends a transaction to queue queue. Specifying thequeue has the effect of specifying the subprocess to talk to.The argument question is the outgoing message that starts thetransaction. The argument fn is the function to call when thecorresponding answer comes back; it is called with two arguments:closure, and the answer received.The argument regexp is a regular expression that should matchtext at the end of the entire answer, but nothing before; that's howtq-enqueue determines where the answer ends.If the argument delay-question is non-nil, delay sending thisquestion until the process has finished replying to any previousquestions. This produces more reliable results with some processes.The return value of tq-enqueue itself is not meaningful. tq-close — Function: tq-close queue Shut down transaction queue queue, waiting for all pending transactionsto complete, and then terminate the connection or child process. Transaction queues are implemented by means of a filter function. See . Network Connections network connection TCP UDP Emacs Lisp programs can open stream (TCP) and datagram (UDP) network connections to other processes on the same machine or other machines. A network connection is handled by Lisp much like a subprocess, and is represented by a process object. However, the process you are communicating with is not a child of the Emacs process, so it has no process ID, and you can't kill it or send it signals. All you can do is send and receive data. delete-process closes the connection, but does not kill the program at the other end; that program must decide what to do about closure of the connection. Lisp programs can listen for connections by creating network servers. A network server is also represented by a kind of process object, but unlike a network connection, the network server never transfers data itself. When it receives a connection request, it creates a new network connection to represent the connection just made. (The network connection inherits certain information, including the process plist, from the server.) The network server then goes back to listening for more connection requests. Network connections and servers are created by calling make-network-process with an argument list consisting of keyword/argument pairs, for example :server t to create a server process, or :type 'datagram to create a datagram connection. See , for details. You can also use the open-network-stream function described below. You can distinguish process objects representing network connections and servers from those representing subprocesses with the process-status function. The possible status values for network connections are open, closed, connect, and failed. For a network server, the status is always listen. None of those values is possible for a real subprocess. See . You can stop and resume operation of a network process by calling stop-process and continue-process. For a server process, being stopped means not accepting new connections. (Up to 5 connection requests will be queued for when you resume the server; you can increase this limit, unless it is imposed by the operating system.) For a network stream connection, being stopped means not processing input (any arriving input waits until you resume the connection). For a datagram connection, some number of packets may be queued but input may be lost. You can use the function process-command to determine whether a network connection or server is stopped; a non-nil value means yes. open-network-stream — Function: open-network-stream name buffer-or-name host service This function opens a TCP connection, and returns a process objectthat represents the connection.The name argument specifies the name for the process object. Itis modified as necessary to make it unique.The buffer-or-name argument is the buffer to associate with theconnection. Output from the connection is inserted in the buffer,unless you specify a filter function to handle the output. Ifbuffer-or-name is nil, it means that the connection is notassociated with any buffer.The arguments host and service specify where to connect to;host is the host name (a string), and service is the name ofa defined network service (a string) or a port number (an integer). process-contact — Function: process-contact process &optional key This function returns information about how a network process was setup. For a connection, when key is nil, it returns(hostname service) which specifies what youconnected to.If key is t, the value is the complete status informationfor the connection or server; that is, the list of keywords and valuesspecified in make-network-process, except that some of thevalues represent the current status instead of what you specified: :buffer The associated value is the process buffer. :filter The associated value is the process filter function. :sentinel The associated value is the process sentinel function. :remote In a connection, the address in internal format of the remote peer. :local The local address, in internal format. :service In a server, if you specified t for service,this value is the actual port number. :local and :remote are included even if they were notspecified explicitly in make-network-process.If key is a keyword, the function returns the value correspondingto that keyword.For an ordinary child process, this function always returns t. Network Servers network servers You create a server by calling make-network-process with :server t. The server will listen for connection requests from clients. When it accepts a client connection request, that creates a new network connection, itself a process object, with the following parameters: The connection's process name is constructed by concatenating theserver process' name with a client identification string. Theclient identification string for an IPv4 connection looks like‘<a.b.c.d:p>’. Otherwise, it is aunique number in brackets, as in ‘<nnn>’. The numberis unique for each connection in the Emacs session. If the server's filter is non-nil, the connection process doesnot get a separate process buffer; otherwise, Emacs creates a newbuffer for the purpose. The buffer name is the server's buffer nameor process name, concatenated with the client identification string.The server's process buffer value is never used directly by Emacs, butit is passed to the log function, which can log connections byinserting text there. The communication type and the process filter and sentinel areinherited from those of the server. The server never directlyuses its filter and sentinel; their sole purpose is to initializeconnections made to the server. The connection's process contact info is set according to the client'saddressing information (typically an IP address and a port number).This information is associated with the process-contactkeywords :host, :service, :remote. The connection's local address is set up according to the portnumber used for the connection. The client process' plist is initialized from the server's plist. Datagrams datagrams A datagram connection communicates with individual packets rather than streams of data. Each call to process-send sends one datagram packet (see ), and each datagram received results in one call to the filter function. The datagram connection doesn't have to talk with the same remote peer all the time. It has a remote peer address which specifies where to send datagrams to. Each time an incoming datagram is passed to the filter function, the peer address is set to the address that datagram came from; that way, if the filter function sends a datagram, it will go back to that place. You can specify the remote peer address when you create the datagram connection using the :remote keyword. You can change it later on by calling set-process-datagram-address. process-datagram-address — Function: process-datagram-address process If process is a datagram connection or server, this functionreturns its remote peer address. set-process-datagram-address — Function: set-process-datagram-address process address If process is a datagram connection or server, this functionsets its remote peer address to address. Low-Level Network Access You can also create network connections by operating at a lower level than that of open-network-stream, using make-network-process. make-network-process The basic function for creating network connections and network servers is make-network-process. It can do either of those jobs, depending on the arguments you give it. make-network-process — Function: make-network-process &rest args This function creates a network connection or server and returns theprocess object that represents it. The arguments args are alist of keyword/argument pairs. Omitting a keyword is alwaysequivalent to specifying it with value nil, except for:coding, :filter-multibyte, and :reuseaddr. Hereare the meaningful keywords: :name name Use the string name as the process name. It is modified ifnecessary to make it unique. :type type Specify the communication type. A value of nil specifies astream connection (the default); datagram specifies a datagramconnection. Both connections and servers can be of either type. :server server-flag If server-flag is non-nil, create a server. Otherwise,create a connection. For a stream type server, server-flag maybe an integer which then specifies the length of the queue of pendingconnections to the server. The default queue length is 5. :host host Specify the host to connect to. host should be a host name orInternet address, as a string, or the symbol local to specifythe local host. If you specify host for a server, it mustspecify a valid address for the local host, and only clientsconnecting to that address will be accepted. :service service service specifies a port number to connect to, or, for a server,the port number to listen on. It should be a service name thattranslates to a port number, or an integer specifying the port numberdirectly. For a server, it can also be t, which means to letthe system select an unused port number. :family family family specifies the address (and protocol) family forcommunication. nil means determine the proper address familyautomatically for the given host and service.local specifies a Unix socket, in which case host isignored. ipv4 and ipv6 specify to use IPv4 and IPv6respectively. :local local-address For a server process, local-address is the address to listen on.It overrides family, host and service, and youmay as well not specify them. :remote remote-address For a connection, remote-address is the address to connect to.It overrides family, host and service, and youmay as well not specify them.For a datagram server, remote-address specifies the initialsetting of the remote datagram address.The format of local-address or remote-address depends onthe address family: An IPv4 address is represented as a five-element vector of four 8-bitintegers and one 16-bit integer[a b c d p] corresponding tonumeric IPv4 address a.b.c.d and port numberp. An IPv6 address is represented as a nine-element vector of 16-bitintegers [a b c d e fg h p] corresponding to numeric IPv6 addressa:b:c:d:e:f:g:h andport number p. A local address is represented as a string which specifies the addressin the local address space. An “unsupported family” address is represented by a cons(f . av), where f is the family number andav is a vector specifying the socket address using one elementper address data byte. Do not rely on this format in portable code,as it may depend on implementation defined constants, data sizes, anddata structure alignment. :nowait bool If bool is non-nil for a stream connection, returnwithout waiting for the connection to complete. When the connectionsucceeds or fails, Emacs will call the sentinel function, with asecond argument matching "open" (if successful) or"failed". The default is to block, so thatmake-network-process does not return until the connectionhas succeeded or failed. :stop stopped Start the network connection or server in the `stopped' state ifstopped is non-nil. :buffer buffer Use buffer as the process buffer. :coding coding Use coding as the coding system for this process. To specifydifferent coding systems for decoding data from the connection and forencoding data sent to it, specify (decoding .encoding) for coding.If you don't specify this keyword at all, the defaultis to determine the coding systems from the data. :noquery query-flag Initialize the process query flag to query-flag.See . :filter filter Initialize the process filter to filter. :filter-multibyte bool If bool is non-nil, strings given to the process filterare multibyte, otherwise they are unibyte. If you don't specify thiskeyword at all, the default is that the strings are multibyte ifdefault-enable-multibyte-characters is non-nil. :sentinel sentinel Initialize the process sentinel to sentinel. :log log Initialize the log function of a server process to log. The logfunction is called each time the server accepts a network connectionfrom a client. The arguments passed to the log function areserver, connection, and message, where serveris the server process, connection is the new process for theconnection, and message is a string describing what hashappened. :plist plist Initialize the process plist to plist. The original argument list, modified with the actual connectioninformation, is available via the process-contact function. Network Options The following network options can be specified when you create a network process. Except for :reuseaddr, you can also set or modify these options later, using set-network-process-option. For a server process, the options specified with make-network-process are not inherited by the client connections, so you will need to set the necessary options for each child connection as it is created. :bindtodevice device-name If device-name is a non-empty string identifying a networkinterface name (see network-interface-list), only handlepackets received on that interface. If device-name is nil(the default), handle packets received on any interface.Using this option may require special privileges on some systems. :broadcast broadcast-flag If broadcast-flag is non-nil for a datagram process, theprocess will receive datagram packet sent to a broadcast address, andbe able to send packets to a broadcast address. Ignored for a streamconnection. :dontroute dontroute-flag If dontroute-flag is non-nil, the process can only sendto hosts on the same network as the local host. :keepalive keepalive-flag If keepalive-flag is non-nil for a stream connection,enable exchange of low-level keep-alive messages. :linger linger-arg If linger-arg is non-nil, wait for successfultransmission of all queued packets on the connection before it isdeleted (see delete-process). If linger-arg is aninteger, it specifies the maximum time in seconds to wait for queuedpackets to be sent before closing the connection. Default isnil which means to discard unsent queued packets when theprocess is deleted. :oobinline oobinline-flag If oobinline-flag is non-nil for a stream connection,receive out-of-band data in the normal data stream. Otherwise, ignoreout-of-band data. :priority priority Set the priority for packets sent on this connection to the integerpriority. The interpretation of this number is protocolspecific, such as setting the TOS (type of service) field on IPpackets sent on this connection. It may also have system dependenteffects, such as selecting a specific output queue on the networkinterface. :reuseaddr reuseaddr-flag If reuseaddr-flag is non-nil (the default) for a streamserver process, allow this server to reuse a specific port number (see:service) unless another process on this host is alreadylistening on that port. If reuseaddr-flag is nil, theremay be a period of time after the last use of that port (by anyprocess on the host), where it is not possible to make a new server onthat port. set-network-process-option — Function: set-network-process-option process option value This function sets or modifies a network option for network processprocess. See make-network-process for details of optionsoption and their corresponding values value.The current setting of an option is available via theprocess-contact function. Testing Availability of Network Features To test for the availability of a given network feature, use featurep like this: (featurep 'make-network-process '(keyword value)) The result of the first form is t if it works to specify keyword with value value in make-network-process. The result of the second form is t if keyword is supported by make-network-process. Here are some of the keyword—value pairs you can test in this way. (:nowait t) Non-nil if non-blocking connect is supported. (:type datagram) Non-nil if datagrams are supported. (:family local) Non-nil if local (a.k.a. “UNIX domain”) sockets are supported. (:family ipv6) Non-nil if IPv6 is supported. (:service t) Non-nil if the system can select the port for a server. To test for the availability of a given network option, use featurep like this: (featurep 'make-network-process 'keyword) Here are some of the options you can test in this way. :bindtodevice:broadcast:dontroute:keepalive:linger:oobinline:priority:reuseaddr That particular network option is supported bymake-network-process and set-network-process-option. Misc Network Facilities These additional functions are useful for creating and operating on network connections. network-interface-list — Function: network-interface-list This function returns a list describing the network interfacesof the machine you are using. The value is an alist whoseelements have the form (name . address).address has the same form as the local-addressand remote-address arguments to make-network-process. network-interface-info — Function: network-interface-info ifname This function returns information about the network interface namedifname. The value is a list of the form(addr bcast netmask hwaddr flags). addr The Internet protocol address. bcast The broadcast address. netmask The network mask. hwaddr The layer 2 address (Ethernet MAC address, for instance). flags The current flags of the interface. format-network-address — Function: format-network-address address &optional omit-port This function converts the Lisp representation of a network address toa string.A five-element vector [a b c d p]represents an IPv4 address a.b.c.d and portnumber p. format-network-address converts that to thestring "a.b.c.d:p".A nine-element vector [a b c d ef g h p] represents an IPv6 address alongwith a port number. format-network-address converts that tothe string"[a:b:c:d:e:f:g:h]:p".If the vector does not include the port number, p, or ifomit-port is non-nil, the result does not include the:p suffix. Packing and Unpacking Byte Arrays byte packing and unpacking This section describes how to pack and unpack arrays of bytes, usually for binary network protocols. These functions convert byte arrays to alists, and vice versa. The byte array can be represented as a unibyte string or as a vector of integers, while the alist associates symbols either with fixed-size objects or with recursive sub-alists. serializing deserializing packing unpacking Conversion from byte arrays to nested alists is also known as deserializing or unpacking, while going in the opposite direction is also known as serializing or packing. Describing Data Layout To control unpacking and packing, you write a data layout specification, a special nested list describing named and typed fields. This specification controls length of each field to be processed, and how to pack or unpack it. We normally keep bindat specs in variables whose names end in ‘-bindat-spec’; that kind of name is automatically recognized as “risky.” endianness big endian little endian network byte ordering A field's type describes the size (in bytes) of the object that the field represents and, in the case of multibyte fields, how the bytes are ordered within the field. The two possible orderings are “big endian” (also known as “network byte ordering”) and “little endian.” For instance, the number #x23cd (decimal 9165) in big endian would be the two bytes #x23 #xcd; and in little endian, #xcd #x23. Here are the possible type values: u8byte Unsigned byte, with length 1. u16wordshort Unsigned integer in network byte order, with length 2. u24 Unsigned integer in network byte order, with length 3. u32dwordlong Unsigned integer in network byte order, with length 4.Note: These values may be limited by Emacs' integer implementation limits. u16ru24ru32r Unsigned integer in little endian order, with length 2, 3 and 4, respectively. str len String of length len. strz len Zero-terminated string, in a fixed-size field with length len. vec len [type] Vector of len elements of type type, or bytes if nottype is specified.The type is any of the simple types above, or another vectorspecified as a list (vec len [type]). ip Four-byte vector representing an Internet address. For example:[127 0 0 1] for localhost. bits len List of set bits in len bytes. The bytes are taken in bigendian order and the bits are numbered starting with 8 *len − 1 and ending with zero. For example: bits2 unpacks #x28 #x1c to (2 3 4 11 13) and#x1c #x28 to (3 5 10 11 12). (eval form) form is a Lisp expression evaluated at the moment the field isunpacked or packed. The result of the evaluation should be one of theabove-listed type specifications. For a fixed-size field, the length len is given as an integer specifying the number of bytes in the field. When the length of a field is not fixed, it typically depends on the value of a preceding field. In this case, the length len can be given either as a list (name ...) identifying a field name in the format specified for bindat-get-field below, or by an expression (eval form) where form should evaluate to an integer, specifying the field length. A field specification generally has the form ([name] handler). The square braces indicate that name is optional. (Don't use names that are symbols meaningful as type specifications (above) or handler specifications (below), since that would be ambiguous.) name can be a symbol or the expression (eval form), in which case form should evaluate to a symbol. handler describes how to unpack or pack the field and can be one of the following: type Unpack/pack this field according to the type specification type. eval form Evaluate form, a Lisp expression, for side-effect only. If thefield name is specified, the value is bound to that field name. fill len Skip len bytes. In packing, this leaves them unchanged,which normally means they remain zero. In unpacking, this meansthey are ignored. align len Skip to the next multiple of len bytes. struct spec-name Process spec-name as a sub-specification. This describes astructure nested within another structure. union form (tag spec)… Evaluate form, a Lisp expression, find the first tagthat matches it, and process its associated data layout specificationspec. Matching can occur in one of three ways: If a tag has the form (eval expr), evaluateexpr with the variable tag dynamically bound to the valueof form. A non-nil result indicates a match. tag matches if it is equal to the value of form. tag matches unconditionally if it is t. repeat count field-specs… Process the field-specs recursively, in order, then repeatstarting from the first one, processing all the specs counttimes overall. The count is given using the same formats as afield length—if an eval form is used, it is evaluated just once.For correct operation, each spec in field-specs must include a name. For the (eval form) forms used in a bindat specification, the form can access and update these dynamically bound variables during evaluation: last Value of the last field processed. bindat-raw The data as a byte array. bindat-idx Current index (within bindat-raw) for unpacking or packing. struct The alist containing the structured data that have been unpacked sofar, or the entire structure being packed. You can usebindat-get-field to access specific fields of this structure. countindex Inside a repeat block, these contain the maximum number ofrepetitions (as specified by the count parameter), and thecurrent repetition number (counting from 0). Setting count tozero will terminate the inner-most repeat block after the currentrepetition has completed. Functions to Unpack and Pack Bytes In the following documentation, spec refers to a data layout specification, bindat-raw to a byte array, and struct to an alist representing unpacked field data. bindat-unpack — Function: bindat-unpack spec bindat-raw &optional bindat-idx This function unpacks data from the unibyte string or bytearray bindat-rawaccording to spec. Normally this starts unpacking at thebeginning of the byte array, but if bindat-idx is non-nil, itspecifies a zero-based starting position to use instead.The value is an alist or nested alist in which each element describesone unpacked field. bindat-get-field — Function: bindat-get-field struct &rest name This function selects a field's data from the nested aliststruct. Usually struct was returned bybindat-unpack. If name corresponds to just one argument,that means to extract a top-level field value. Multiple namearguments specify repeated lookup of sub-structures. An integer nameacts as an array index.For example, if name is (a b 2 c), that means to findfield c in the third element of subfield b of fielda. (This corresponds to struct.a.b[2].c in C.) Although packing and unpacking operations change the organization of data (in memory), they preserve the data's total length, which is the sum of all the fields' lengths, in bytes. This value is not generally inherent in either the specification or alist alone; instead, both pieces of information contribute to its calculation. Likewise, the length of a string or array being unpacked may be longer than the data's total length as described by the specification. bindat-length — Function: bindat-length spec struct This function returns the total length of the data in struct,according to spec. bindat-pack — Function: bindat-pack spec struct &optional bindat-raw bindat-idx This function returns a byte array packed according to spec fromthe data in the alist struct. Normally it creates and fills anew byte array starting at the beginning. However, if bindat-rawis non-nil, it specifies a pre-allocated unibyte string or vector topack into. If bindat-idx is non-nil, it specifies the startingoffset for packing into bindat-raw.When pre-allocating, you should make sure (length bindat-raw)meets or exceeds the total length to avoid an out-of-range error. bindat-ip-to-string — Function: bindat-ip-to-string ip Convert the Internet address vector ip to a string in the usualdotted notation. (bindat-ip-to-string [127 0 0 1]) => "127.0.0.1" Examples of Byte Unpacking and Packing Here is a complete example of byte unpacking and packing:(defvar fcookie-index-spec '((:version u32) (:count u32) (:longest u32) (:shortest u32) (:flags u32) (:delim u8) (:ignored fill 3) (:offset repeat (:count) (:foo u32))) "Description of a fortune cookie index file's contents.")(defun fcookie (cookies &optional index) "Display a random fortune cookie from file COOKIES.Optional second arg INDEX specifies the associated indexfilename, which is by default constructed by appending\".dat\" to COOKIES. Display cookie text in possiblynew buffer \"*Fortune Cookie: BASENAME*\" where BASENAMEis COOKIES without the directory part." (interactive "fCookies file: ") (let* ((info (with-temp-buffer (insert-file-contents-literally (or index (concat cookies ".dat"))) (bindat-unpack fcookie-index-spec (buffer-string)))) (sel (random (bindat-get-field info :count))) (beg (cdar (bindat-get-field info :offset sel))) (end (or (cdar (bindat-get-field info :offset (1+ sel))) (nth 7 (file-attributes cookies))))) (switch-to-buffer (get-buffer-create (format "*Fortune Cookie: %s*" (file-name-nondirectory cookies)))) (erase-buffer) (insert-file-contents-literally cookies nil beg (- end 3))))(defun fcookie-create-index (cookies &optional index delim) "Scan file COOKIES, and write out its index file.Optional second arg INDEX specifies the index filename,which is by default constructed by appending \".dat\" toCOOKIES. Optional third arg DELIM specifies the unibytecharacter which, when found on a line of its own inCOOKIES, indicates the border between entries." (interactive "fCookies file: ") (setq delim (or delim ?%)) (let ((delim-line (format "\n%c\n" delim)) (count 0) (max 0) min p q len offsets) (unless (= 3 (string-bytes delim-line)) (error "Delimiter cannot be represented in one byte")) (with-temp-buffer (insert-file-contents-literally cookies) (while (and (setq p (point)) (search-forward delim-line (point-max) t) (setq len (- (point) 3 p))) (setq count (1+ count) max (max max len) min (min (or min max) len) offsets (cons (1- p) offsets)))) (with-temp-buffer (set-buffer-multibyte nil) (insert (bindat-pack fcookie-index-spec `((:version . 2) (:count . ,count) (:longest . ,max) (:shortest . ,min) (:flags . 0) (:delim . ,delim) (:offset . ,(mapcar (lambda (o) (list (cons :foo o))) (nreverse offsets)))))) (let ((coding-system-for-write 'raw-text-unix)) (write-file (or index (concat cookies ".dat"))))))) Following is an example of defining and unpacking a complex structure. Consider the following C structures: struct header { unsigned long dest_ip; unsigned long src_ip; unsigned short dest_port; unsigned short src_port; }; struct data { unsigned char type; unsigned char opcode; unsigned short length; /* In network byte order */ unsigned char id[8]; /* null-terminated string */ unsigned char data[/* (length + 3) & ~3 */]; }; struct packet { struct header header; unsigned long counters[2]; /* In little endian order */ unsigned char items; unsigned char filler[3]; struct data item[/* items */]; }; The corresponding data layout specification:(setq header-spec '((dest-ip ip) (src-ip ip) (dest-port u16) (src-port u16)))(setq data-spec '((type u8) (opcode u8) (length u16) ;; network byte order (id strz 8) (data vec (length)) (align 4)))(setq packet-spec '((header struct header-spec) (counters vec 2 u32r) ;; little endian order (items u8) (fill 3) (item repeat (items) (struct data-spec)))) A binary data representation:(setq binary-data [ 192 168 1 100 192 168 1 101 01 28 21 32 160 134 1 0 5 1 0 0 2 0 0 0 2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0 1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ]) The corresponding decoded structure:(setq decoded (bindat-unpack packet-spec binary-data)) =>((header (dest-ip . [192 168 1 100]) (src-ip . [192 168 1 101]) (dest-port . 284) (src-port . 5408)) (counters . [100000 261]) (items . 2) (item ((data . [1 2 3 4 5]) (id . "ABCDEF") (length . 5) (opcode . 3) (type . 2)) ((data . [6 7 8 9 10 11 12]) (id . "BCDEFG") (length . 7) (opcode . 4) (type . 1)))) Fetching data from this structure:(bindat-get-field decoded 'item 1 'id) => "BCDEFG" <setfilename>../info/display</setfilename> Emacs Display This chapter describes a number of features related to the display that Emacs presents to the user. Refreshing the Screen The function redraw-frame clears and redisplays the entire contents of a given frame (see ). This is useful if the screen is corrupted. redraw-frame — Function: redraw-frame frame This function clears and redisplays frame frame. Even more powerful is redraw-display: redraw-display — Command: redraw-display This function clears and redisplays all visible frames. This function calls for redisplay of certain windows, the next time redisplay is done, but does not clear them first. force-window-update — Function: force-window-update &optional object This function forces some or all windows to be updated on next redisplay.If object is a window, it forces redisplay of that window. Ifobject is a buffer or buffer name, it forces redisplay of allwindows displaying that buffer. If object is nil (oromitted), it forces redisplay of all windows. Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually—after all the input has been processed. Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption. no-redraw-on-reenter — Variable: no-redraw-on-reenter suspend (cf. no-redraw-on-reenter) resume (cf. no-redraw-on-reenter)This variable controls whether Emacs redraws the entire screen after ithas been suspended and resumed. Non-nil means there is no needto redraw, nil means redrawing is needed. The default is nil. Forcing Redisplay forcing redisplay Emacs redisplay normally stops if input arrives, and does not happen at all if input is available before it starts. Most of the time, this is exactly what you want. However, you can prevent preemption by binding redisplay-dont-pause to a non-nil value. redisplay-preemption-period — Variable: redisplay-preemption-period This variable specifies how many seconds Emacs waits between checksfor new input during redisplay. (The default is 0.1 seconds.) Ifinput has arrived when Emacs checks, it pre-empts redisplay andprocesses the available input before trying again to redisplay.If this variable is nil, Emacs does not check for input duringredisplay, and redisplay cannot be preempted by input.This variable is only obeyed on graphical terminals. Fortext terminals, see . redisplay-dont-pause — Variable: redisplay-dont-pause If this variable is non-nil, pending input does notprevent or halt redisplay; redisplay occurs, and finishes,regardless of whether input is available. redisplay — Function: redisplay &optional force This function performs an immediate redisplay provided there are nopending input events. This is equivalent to (sit-for 0).If the optional argument force is non-nil, it forces animmediate and complete redisplay even if input is available.Returns t if redisplay was performed, or nil otherwise. Truncation line wrapping line truncation continuation lines ‘$’ in display ‘\’ in display When a line of text extends beyond the right edge of a window, Emacs can continue the line (make it “wrap” to the next screen line), or truncate the line (limit it to one screen line). The additional screen lines used to display a long text line are called continuation lines. Continuation is not the same as filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See . On a graphical display, tiny arrow images in the window fringes indicate truncated and continued lines (see ). On a text terminal, a ‘$’ in the rightmost column of the window indicates truncation; a ‘\’ on the rightmost column indicates a line that “wraps.” (The display table can specify alternate characters to use for this; see ). truncate-lines — User Option: truncate-lines This buffer-local variable controls how Emacs displays lines that extendbeyond the right edge of the window. The default is nil, whichspecifies continuation. If the value is non-nil, then theselines are truncated.If the variable truncate-partial-width-windows is non-nil,then truncation is always used for side-by-side windows (within oneframe) regardless of the value of truncate-lines. default-truncate-lines — User Option: default-truncate-lines This variable is the default value for truncate-lines, forbuffers that do not have buffer-local values for it. truncate-partial-width-windows — User Option: truncate-partial-width-windows This variable controls display of lines that extend beyond the rightedge of the window, in side-by-side windows (see ).If it is non-nil, these lines are truncated; otherwise,truncate-lines says what to do with them. When horizontal scrolling (see ) is in use in a window, that forces truncation. If your buffer contains very long lines, and you use continuation to display them, just thinking about them can make Emacs redisplay slow. The column computation and indentation functions also become slow. Then you might find it advisable to set cache-long-line-scans to t. cache-long-line-scans — Variable: cache-long-line-scans If this variable is non-nil, various indentation and motionfunctions, and Emacs redisplay, cache the results of scanning thebuffer, and consult the cache to avoid rescanning regions of the bufferunless they are modified.Turning on the cache slows down processing of short lines somewhat.This variable is automatically buffer-local in every buffer. The Echo Area error display echo area The echo area is used for displaying error messages (see ), for messages made with the message primitive, and for echoing keystrokes. It is not the same as the minibuffer, despite the fact that the minibuffer appears (when active) in the same place on the screen as the echo area. The GNU Emacs Manual specifies the rules for resolving conflicts between the echo area and the minibuffer for use of that screen space (see See section ``The Minibuffer'' in The GNU Emacs Manual). You can write output in the echo area by using the Lisp printing functions with t as the stream (see ), or explicitly. Displaying Messages in the Echo Area display message in echo area This section describes the functions for explicitly producing echo area messages. Many other Emacs features display messages there, too. message — Function: message format-string &rest arguments This function displays a message in the echo area. The argumentformat-string is similar to a C language printf formatstring. See format in , for the detailson the conversion specifications. message returns theconstructed string.In batch mode, message prints the message text on the standarderror stream, followed by a newline.If format-string, or strings among the arguments, haveface text properties, these affect the way the message is displayed. If format-string is nil or the empty string,message clears the echo area; if the echo area has beenexpanded automatically, this brings it back to its normal size.If the minibuffer is active, this brings the minibuffer contents backonto the screen immediately. (message "Minibuffer depth is %d." (minibuffer-depth)) -| Minibuffer depth is 0. => "Minibuffer depth is 0." ---------- Echo Area ---------- Minibuffer depth is 0. ---------- Echo Area ---------- To automatically display a message in the echo area or in a pop-buffer,depending on its size, use display-message-or-buffer (see below). with-temp-message — Macro: with-temp-message message &rest body This construct displays a message in the echo area temporarily, duringthe execution of body. It displays message, executesbody, then returns the value of the last body form while restoringthe previous echo area contents. message-or-box — Function: message-or-box format-string &rest arguments This function displays a message like message, but may display itin a dialog box instead of the echo area. If this function is called ina command that was invoked using the mouse—more precisely, iflast-nonmenu-event (see ) is eithernil or a list—then it uses a dialog box or pop-up menu todisplay the message. Otherwise, it uses the echo area. (This is thesame criterion that y-or-n-p uses to make a similar decision; see.)You can force use of the mouse or of the echo area by bindinglast-nonmenu-event to a suitable value around the call. message-box — Function: message-box format-string &rest arguments This function displays a message like message, but uses a dialogbox (or a pop-up menu) whenever that is possible. If it is impossibleto use a dialog box or pop-up menu, because the terminal does notsupport them, then message-box uses the echo area, likemessage. display-message-or-buffer — Function: display-message-or-buffer message &optional buffer-name not-this-window frame This function displays the message message, which may be either astring or a buffer. If it is shorter than the maximum height of theecho area, as defined by max-mini-window-height, it is displayedin the echo area, using message. Otherwise,display-buffer is used to show it in a pop-up buffer.Returns either the string shown in the echo area, or when a pop-upbuffer is used, the window used to display it.If message is a string, then the optional argumentbuffer-name is the name of the buffer used to display it when apop-up buffer is used, defaulting to ‘*Message*’. In the casewhere message is a string and displayed in the echo area, it isnot specified whether the contents are inserted into the buffer anyway.The optional arguments not-this-window and frame are as fordisplay-buffer, and only used if a buffer is displayed. current-message — Function: current-message This function returns the message currently being displayed in theecho area, or nil if there is none. Reporting Operation Progress progress reporting When an operation can take a while to finish, you should inform the user about the progress it makes. This way the user can estimate remaining time and clearly see that Emacs is busy working, not hung. Functions listed in this section provide simple and efficient way of reporting operation progress. Here is a working example that does nothing useful: (let ((progress-reporter (make-progress-reporter "Collecting mana for Emacs..." 0 500))) (dotimes (k 500) (sit-for 0.01) (progress-reporter-update progress-reporter k)) (progress-reporter-done progress-reporter)) make-progress-reporter — Function: make-progress-reporter message min-value max-value &optional current-value min-change min-time This function creates and returns a progress reporter—anobject you will use as an argument for all other functions listedhere. The idea is to precompute as much data as possible to makeprogress reporting very fast.When this progress reporter is subsequently used, it will displaymessage in the echo area, followed by progress percentage.message is treated as a simple string. If you need it to dependon a filename, for instance, use format before calling thisfunction.min-value and max-value arguments stand for starting andfinal states of your operation. For instance, if you scan a buffer,they should be the results of point-min and point-maxcorrespondingly. It is required that max-value is greater thanmin-value. If you create progress reporter when some part ofthe operation has already been completed, then specifycurrent-value argument. But normally you should omit it or setit to nil—it will default to min-value then.Remaining arguments control the rate of echo area updates. Progressreporter will wait for at least min-change more percents of theoperation to be completed before printing next message.min-time specifies the minimum time in seconds to pass betweensuccessive prints. It can be fractional. Depending on Emacs andsystem capabilities, progress reporter may or may not respect thislast argument or do it with varying precision. Default value formin-change is 1 (one percent), for min-time—0.2(seconds.)This function calls progress-reporter-update, so the firstmessage is printed immediately. progress-reporter-update — Function: progress-reporter-update reporter value This function does the main work of reporting progress of youroperation. It displays the message of reporter, followed byprogress percentage determined by value. If percentage is zero,or close enough according to the min-change and min-timearguments, then it is omitted from the output.reporter must be the result of a call tomake-progress-reporter. value specifies the currentstate of your operation and must be between min-value andmax-value (inclusive) as passed tomake-progress-reporter. For instance, if you scan a buffer,then value should be the result of a call to point.This function respects min-change and min-time as passedto make-progress-reporter and so does not output new messageson every invocation. It is thus very fast and normally you should nottry to reduce the number of calls to it: resulting overhead will mostlikely negate your effort. progress-reporter-force-update — Function: progress-reporter-force-update reporter value &optional new-message This function is similar to progress-reporter-update exceptthat it prints a message in the echo area unconditionally.The first two arguments have the same meaning as forprogress-reporter-update. Optional new-message allowsyou to change the message of the reporter. Since this functionsalways updates the echo area, such a change will be immediatelypresented to the user. progress-reporter-done — Function: progress-reporter-done reporter This function should be called when the operation is finished. Itprints the message of reporter followed by word “done” in theecho area.You should always call this function and not hope forprogress-reporter-update to print “100%.” Firstly, it maynever print it, there are many good reasons for this not to happen.Secondly, “done” is more explicit. dotimes-with-progress-reporter — Macro: dotimes-with-progress-reporter ( var count [ result ] ) message body … This is a convenience macro that works the same way as dotimesdoes, but also reports loop progress using the functions describedabove. It allows you to save some typing.You can rewrite the example in the beginning of this node usingthis macro this way: (dotimes-with-progress-reporter (k 500) "Collecting some mana for Emacs..." (sit-for 0.01)) Logging Messages in ‘*Messages*’ logging echo-area messages Almost all the messages displayed in the echo area are also recorded in the ‘*Messages*’ buffer so that the user can refer back to them. This includes all the messages that are output with message. message-log-max — User Option: message-log-max This variable specifies how many lines to keep in the ‘*Messages*’buffer. The value t means there is no limit on how many lines tokeep. The value nil disables message logging entirely. Here'show to display a message and prevent it from being logged: (let (message-log-max) (message …)) To make ‘*Messages*’ more convenient for the user, the logging facility combines successive identical messages. It also combines successive related messages for the sake of two cases: question followed by answer, and a series of progress messages. A “question followed by an answer” means two messages like the ones produced by y-or-n-p: the first is ‘question’, and the second is ‘question...answer’. The first message conveys no additional information beyond what's in the second, so logging the second message discards the first from the log. A “series of progress messages” means successive messages like those produced by make-progress-reporter. They have the form ‘base...how-far’, where base is the same each time, while how-far varies. Logging each message in the series discards the previous one, provided they are consecutive. The functions make-progress-reporter and y-or-n-p don't have to do anything special to activate the message log combination feature. It operates whenever two consecutive messages are logged that share a common prefix ending in ‘...’. Echo Area Customization These variables control details of how the echo area works. cursor-in-echo-area — Variable: cursor-in-echo-area This variable controls where the cursor appears when a message isdisplayed in the echo area. If it is non-nil, then the cursorappears at the end of the message. Otherwise, the cursor appears atpoint—not in the echo area at all.The value is normally nil; Lisp programs bind it to tfor brief periods of time. echo-area-clear-hook — Variable: echo-area-clear-hook This normal hook is run whenever the echo area is cleared—either by(message nil) or for any other reason. echo-keystrokes — Variable: echo-keystrokes This variable determines how much time should elapse before commandcharacters echo. Its value must be an integer or floating point number,which specifies thenumber of seconds to wait before echoing. If the user types a prefixkey (such as C-x) and then delays this many seconds beforecontinuing, the prefix key is echoed in the echo area. (Once echoingbegins in a key sequence, all subsequent characters in the same keysequence are echoed immediately.)If the value is zero, then command input is not echoed. message-truncate-lines — Variable: message-truncate-lines Normally, displaying a long message resizes the echo area to displaythe entire message. But if the variable message-truncate-linesis non-nil, the echo area does not resize, and the message istruncated to fit it, as in Emacs 20 and before. The variable max-mini-window-height, which specifies the maximum height for resizing minibuffer windows, also applies to the echo area (which is really a special use of the minibuffer window. See . Reporting Warnings warnings Warnings are a facility for a program to inform the user of a possible problem, but continue running. Warning Basics severity level Every warning has a textual message, which explains the problem for the user, and a severity level which is a symbol. Here are the possible severity levels, in order of decreasing severity, and their meanings: :emergency A problem that will seriously impair Emacs operation soonif you do not attend to it promptly. :error A report of data or circumstances that are inherently wrong. :warning A report of data or circumstances that are not inherently wrong, butraise suspicion of a possible problem. :debug A report of information that may be useful if you are debugging. When your program encounters invalid input data, it can either signal a Lisp error by calling error or signal or report a warning with severity :error. Signaling a Lisp error is the easiest thing to do, but it means the program cannot continue processing. If you want to take the trouble to implement a way to continue processing despite the bad data, then reporting a warning of severity :error is the right way to inform the user of the problem. For instance, the Emacs Lisp byte compiler can report an error that way and continue compiling other functions. (If the program signals a Lisp error and then handles it with condition-case, the user won't see the error message; it could show the message to the user by reporting it as a warning.) warning type Each warning has a warning type to classify it. The type is a list of symbols. The first symbol should be the custom group that you use for the program's user options. For example, byte compiler warnings use the warning type (bytecomp). You can also subcategorize the warnings, if you wish, by using more symbols in the list. display-warning — Function: display-warning type message &optional level buffer-name This function reports a warning, using message as the messageand type as the warning type. level should be theseverity level, with :warning being the default.buffer-name, if non-nil, specifies the name of the bufferfor logging the warning. By default, it is ‘*Warnings*’. lwarn — Function: lwarn type level message &rest args This function reports a warning using the value of (formatmessage args...) as the message. In other respects it isequivalent to display-warning. warn — Function: warn message &rest args This function reports a warning using the value of (formatmessage args...) as the message, (emacs) as thetype, and :warning as the severity level. It exists forcompatibility only; we recommend not using it, because you shouldspecify a specific warning type. Warning Variables Programs can customize how their warnings appear by binding the variables described in this section. warning-levels — Variable: warning-levels This list defines the meaning and severity order of the warningseverity levels. Each element defines one severity level,and they are arranged in order of decreasing severity.Each element has the form (level stringfunction), where level is the severity level it defines.string specifies the textual description of this level.string should use ‘%s’ to specify where to put the warningtype information, or it can omit the ‘%s’ so as not to includethat information.The optional function, if non-nil, is a function to callwith no arguments, to get the user's attention.Normally you should not change the value of this variable. warning-prefix-function — Variable: warning-prefix-function If non-nil, the value is a function to generate prefix text forwarnings. Programs can bind the variable to a suitable function.display-warning calls this function with the warnings buffercurrent, and the function can insert text in it. That text becomesthe beginning of the warning message.The function is called with two arguments, the severity level and itsentry in warning-levels. It should return a list to use as theentry (this value need not be an actual member ofwarning-levels). By constructing this value, the function canchange the severity of the warning, or specify different handling fora given severity level.If the variable's value is nil then there is no functionto call. warning-series — Variable: warning-series Programs can bind this variable to t to say that the nextwarning should begin a series. When several warnings form a series,that means to leave point on the first warning of the series, ratherthan keep moving it for each warning so that it appears on the last one.The series ends when the local binding is unbound andwarning-series becomes nil again.The value can also be a symbol with a function definition. That isequivalent to t, except that the next warning will also callthe function with no arguments with the warnings buffer current. Thefunction can insert text which will serve as a header for the seriesof warnings.Once a series has begun, the value is a marker which points to thebuffer position in the warnings buffer of the start of the series.The variable's normal value is nil, which means to handleeach warning separately. warning-fill-prefix — Variable: warning-fill-prefix When this variable is non-nil, it specifies a fill prefix touse for filling each warning's text. warning-type-format — Variable: warning-type-format This variable specifies the format for displaying the warning typein the warning message. The result of formatting the type this waygets included in the message under the control of the string in theentry in warning-levels. The default value is " (%s)".If you bind it to "" then the warning type won't appear atall. Warning Options These variables are used by users to control what happens when a Lisp program reports a warning. warning-minimum-level — User Option: warning-minimum-level This user option specifies the minimum severity level that should beshown immediately to the user. The default is :warning, whichmeans to immediately display all warnings except :debugwarnings. warning-minimum-log-level — User Option: warning-minimum-log-level This user option specifies the minimum severity level that should belogged in the warnings buffer. The default is :warning, whichmeans to log all warnings except :debug warnings. warning-suppress-types — User Option: warning-suppress-types This list specifies which warning types should not be displayedimmediately for the user. Each element of the list should be a listof symbols. If its elements match the first elements in a warningtype, then that warning is not displayed immediately. warning-suppress-log-types — User Option: warning-suppress-log-types This list specifies which warning types should not be logged in thewarnings buffer. Each element of the list should be a list ofsymbols. If it matches the first few elements in a warning type, thenthat warning is not logged. Invisible Text invisible text You can make characters invisible, so that they do not appear on the screen, with the invisible property. This can be either a text property (see ) or a property of an overlay (see ). Cursor motion also partly ignores these characters; if the command loop finds point within them, it moves point to the other side of them. In the simplest case, any non-nil invisible property makes a character invisible. This is the default case—if you don't alter the default value of buffer-invisibility-spec, this is how the invisible property works. You should normally use t as the value of the invisible property if you don't plan to set buffer-invisibility-spec yourself. More generally, you can use the variable buffer-invisibility-spec to control which values of the invisible property make text invisible. This permits you to classify the text into different subsets in advance, by giving them different invisible values, and subsequently make various subsets visible or invisible by changing the value of buffer-invisibility-spec. Controlling visibility with buffer-invisibility-spec is especially useful in a program to display the list of entries in a database. It permits the implementation of convenient filtering commands to view just a part of the entries in the database. Setting this variable is very fast, much faster than scanning all the text in the buffer looking for properties to change. buffer-invisibility-spec — Variable: buffer-invisibility-spec This variable specifies which kinds of invisible propertiesactually make a character invisible. Setting this variable makes itbuffer-local. t A character is invisible if its invisible property isnon-nil. This is the default. a list Each element of the list specifies a criterion for invisibility; if acharacter's invisible property fits any one of these criteria,the character is invisible. The list can have two kinds of elements: atom A character is invisible if its invisible property valueis atom or if it is a list with atom as a member. (atom . t) A character is invisible if its invisible property value isatom or if it is a list with atom as a member. Moreover,a sequence of such characters displays as an ellipsis. Two functions are specifically provided for adding elements to buffer-invisibility-spec and removing elements from it. add-to-invisibility-spec — Function: add-to-invisibility-spec element This function adds the element element tobuffer-invisibility-spec. If buffer-invisibility-specwas t, it changes to a list, (t), so that text whoseinvisible property is t remains invisible. remove-from-invisibility-spec — Function: remove-from-invisibility-spec element This removes the element element frombuffer-invisibility-spec. This does nothing if elementis not in the list. A convention for use of buffer-invisibility-spec is that a major mode should use the mode's own name as an element of buffer-invisibility-spec and as the value of the invisible property: ;; If you want to display an ellipsis: (add-to-invisibility-spec '(my-symbol . t)) ;; If you don't want ellipsis: (add-to-invisibility-spec 'my-symbol) (overlay-put (make-overlay beginning end) 'invisible 'my-symbol) ;; When done with the overlays: (remove-from-invisibility-spec '(my-symbol . t)) ;; Or respectively: (remove-from-invisibility-spec 'my-symbol) line-move-ignore-invisible Ordinarily, functions that operate on text or move point do not care whether the text is invisible. The user-level line motion commands explicitly ignore invisible newlines if line-move-ignore-invisible is non-nil (the default), but only because they are explicitly programmed to do so. However, if a command ends with point inside or immediately before invisible text, the main editing loop moves point further forward or further backward (in the same direction that the command already moved it) until that condition is no longer true. Thus, if the command moved point back into an invisible range, Emacs moves point back to the beginning of that range, and then back one more character. If the command moved point forward into an invisible range, Emacs moves point forward up to the first visible character that follows the invisible text. Incremental search can make invisible overlays visible temporarily and/or permanently when a match includes invisible text. To enable this, the overlay should have a non-nil isearch-open-invisible property. The property value should be a function to be called with the overlay as an argument. This function should make the overlay visible permanently; it is used when the match overlaps the overlay on exit from the search. During the search, such overlays are made temporarily visible by temporarily modifying their invisible and intangible properties. If you want this to be done differently for a certain overlay, give it an isearch-open-invisible-temporary property which is a function. The function is called with two arguments: the first is the overlay, and the second is nil to make the overlay visible, or t to make it invisible again. Selective Display Selective display refers to a pair of related features for hiding certain lines on the screen. The first variant, explicit selective display, is designed for use in a Lisp program: it controls which lines are hidden by altering the text. This kind of hiding in some ways resembles the effect of the invisible property (see ), but the two features are different and do not work the same way. In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature. The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now hidden. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line. Selective display does not directly affect editing commands. For example, C-f (forward-char) moves point unhesitatingly into hidden text. However, the replacement of newline characters with carriage return characters affects some editing commands. For example, next-line skips hidden lines, since it searches only for newlines. Modes that use selective display can also define commands that take account of the newlines, or that control which parts of the text are hidden. When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing hidden. The selective display effect is seen only within Emacs. selective-display — Variable: selective-display This buffer-local variable enables selective display. This means thatlines, or portions of lines, may be made hidden. If the value of selective-display is t, then the charactercontrol-m marks the start of hidden text; the control-m, and the restof the line following it, are not displayed. This is explicit selectivedisplay. If the value of selective-display is a positive integer, thenlines that start with more than that many columns of indentation are notdisplayed. When some portion of a buffer is hidden, the vertical movementcommands operate as if that portion did not exist, allowing a singlenext-line command to skip any number of hidden lines.However, character movement commands (such as forward-char) donot skip the hidden portion, and it is possible (if tricky) to insertor delete text in an hidden portion.In the examples below, we show the display appearance of thebuffer foo, which changes with the value ofselective-display. The contents of the buffer do notchange. (setq selective-display nil) => nil ---------- Buffer: foo ---------- 1 on this column 2on this column 3n this column 3n this column 2on this column 1 on this column ---------- Buffer: foo ---------- (setq selective-display 2) => 2 ---------- Buffer: foo ---------- 1 on this column 2on this column 2on this column 1 on this column ---------- Buffer: foo ---------- selective-display-ellipses — Variable: selective-display-ellipses If this buffer-local variable is non-nil, then Emacs displays‘…’ at the end of a line that is followed by hidden text.This example is a continuation of the previous one. (setq selective-display-ellipses t) => t ---------- Buffer: foo ---------- 1 on this column 2on this column ... 2on this column 1 on this column ---------- Buffer: foo ---------- You can use a display table to substitute other text for the ellipsis(‘…’). See . Temporary Displays Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature. with-output-to-temp-buffer — Special Form: with-output-to-temp-buffer buffer-name forms … This function executes forms while arranging to insert any outputthey print into the buffer named buffer-name, which is firstcreated if necessary, and put into Help mode. Finally, the buffer isdisplayed in some window, but not selected.If the forms do not change the major mode in the output buffer,so that it is still Help mode at the end of their execution, thenwith-output-to-temp-buffer makes this buffer read-only at theend, and also scans it for function and variable names to make theminto clickable cross-references. See Tips for Documentation Strings, in particular the item on hyperlinks indocumentation strings, for more details.The string buffer-name specifies the temporary buffer, whichneed not already exist. The argument must be a string, not a buffer.The buffer is erased initially (with no questions asked), and it ismarked as unmodified after with-output-to-temp-buffer exits.with-output-to-temp-buffer binds standard-output to thetemporary buffer, then it evaluates the forms in forms. Outputusing the Lisp output functions within forms goes by default tothat buffer (but screen display and messages in the echo area, althoughthey are “output” in the general sense of the word, are not affected).See .Several hooks are available for customizing the behaviorof this construct; they are listed below.The value of the last form in forms is returned. ---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (with-output-to-temp-buffer "foo" (print 20) (print standard-output)) => #<buffer foo> ---------- Buffer: foo ---------- 20 #<buffer foo> ---------- Buffer: foo ---------- temp-buffer-show-function — Variable: temp-buffer-show-function If this variable is non-nil, with-output-to-temp-buffercalls it as a function to do the job of displaying a help buffer. Thefunction gets one argument, which is the buffer it should display.It is a good idea for this function to run temp-buffer-show-hookjust as with-output-to-temp-buffer normally would, inside ofsave-selected-window and with the chosen window and bufferselected. temp-buffer-setup-hook — Variable: temp-buffer-setup-hook This normal hook is run by with-output-to-temp-buffer beforeevaluating body. When the hook runs, the temporary buffer iscurrent. This hook is normally set up with a function to put thebuffer in Help mode. temp-buffer-show-hook — Variable: temp-buffer-show-hook This normal hook is run by with-output-to-temp-buffer afterdisplaying the temporary buffer. When the hook runs, the temporary bufferis current, and the window it was displayed in is selected. This hookis normally set up with a function to make the buffer read only, andfind function names and variable names in it, provided the major modeis Help mode. momentary-string-display — Function: momentary-string-display string position &optional char message This function momentarily displays string in the current buffer atposition. It has no effect on the undo list or on the buffer'smodification status.The momentary display remains until the next input event. If the nextinput event is char, momentary-string-display ignores itand returns. Otherwise, that event remains buffered for subsequent useas input. Thus, typing char will simply remove the string fromthe display, while typing (say) C-f will remove the string fromthe display and later (presumably) move point forward. The argumentchar is a space by default.The return value of momentary-string-display is not meaningful.If the string string does not contain control characters, you cando the same job in a more general way by creating (and then subsequentlydeleting) an overlay with a before-string property.See .If message is non-nil, it is displayed in the echo areawhile string is displayed in the buffer. If it is nil, adefault message says to type char to continue.In this example, point is initially located at the beginning of thesecond line: ---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ---------- Overlays overlays You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay. An overlay uses markers to record its beginning and end; thus, editing the text of the buffer adjusts the beginning and end of each overlay so that it stays with the text. When you create the overlay, you can specify whether text inserted at the beginning should be inside the overlay or outside, and likewise for the end of the overlay. Managing Overlays This section describes the functions to create, delete and move overlays, and to examine their contents. Overlay changes are not recorded in the buffer's undo list, since the overlays are not part of the buffer's contents. overlayp — Function: overlayp object This function returns t if object is an overlay. make-overlay — Function: make-overlay start end &optional buffer front-advance rear-advance This function creates and returns an overlay that belongs tobuffer and ranges from start to end. Both startand end must specify buffer positions; they may be integers ormarkers. If buffer is omitted, the overlay is created in thecurrent buffer.The arguments front-advance and rear-advance specify themarker insertion type for the start of the overlay and for the end ofthe overlay, respectively. See . If theyare both nil, the default, then the overlay extends to includeany text inserted at the beginning, but not text inserted at the end.If front-advance is non-nil, text inserted at thebeginning of the overlay is excluded from the overlay. Ifrear-advance is non-nil, text inserted at the end of theoverlay is included in the overlay. overlay-start — Function: overlay-start overlay This function returns the position at which overlay starts,as an integer. overlay-end — Function: overlay-end overlay This function returns the position at which overlay ends,as an integer. overlay-buffer — Function: overlay-buffer overlay This function returns the buffer that overlay belongs to. Itreturns nil if overlay has been deleted. delete-overlay — Function: delete-overlay overlay This function deletes overlay. The overlay continues to exist asa Lisp object, and its property list is unchanged, but it ceases to beattached to the buffer it belonged to, and ceases to have any effect ondisplay.A deleted overlay is not permanently disconnected. You can give it aposition in a buffer again by calling move-overlay. move-overlay — Function: move-overlay overlay start end &optional buffer This function moves overlay to buffer, and places its boundsat start and end. Both arguments start and endmust specify buffer positions; they may be integers or markers.If buffer is omitted, overlay stays in the same buffer itwas already associated with; if overlay was deleted, it goes intothe current buffer.The return value is overlay.This is the only valid way to change the endpoints of an overlay. Donot try modifying the markers in the overlay by hand, as that fails toupdate other vital data structures and can cause some overlays to be“lost.” remove-overlays — Function: remove-overlays &optional start end name value This function removes all the overlays between start andend whose property name has the value value. It canmove the endpoints of the overlays in the region, or split them.If name is omitted or nil, it means to delete all overlays inthe specified region. If start and/or end are omitted ornil, that means the beginning and end of the buffer respectively.Therefore, (remove-overlays) removes all the overlays in thecurrent buffer. Here are some examples: ;; Create an overlay. (setq foo (make-overlay 1 10)) => #<overlay from 1 to 10 in display.texi> (overlay-start foo) => 1 (overlay-end foo) => 10 (overlay-buffer foo) => #<buffer display.texi> ;; Give it a property we can check later. (overlay-put foo 'happy t) => t ;; Verify the property is present. (overlay-get foo 'happy) => t ;; Move the overlay. (move-overlay foo 5 20) => #<overlay from 5 to 20 in display.texi> (overlay-start foo) => 5 (overlay-end foo) => 20 ;; Delete the overlay. (delete-overlay foo) => nil ;; Verify it is deleted. foo => #<overlay in no buffer> ;; A deleted overlay has no position. (overlay-start foo) => nil (overlay-end foo) => nil (overlay-buffer foo) => nil ;; Undelete the overlay. (move-overlay foo 1 20) => #<overlay from 1 to 20 in display.texi> ;; Verify the results. (overlay-start foo) => 1 (overlay-end foo) => 20 (overlay-buffer foo) => #<buffer display.texi> ;; Moving and deleting the overlay does not change its properties. (overlay-get foo 'happy) => t Emacs stores the overlays of each buffer in two lists, divided around an arbitrary “center position.” One list extends backwards through the buffer from that center position, and the other extends forwards from that center position. The center position can be anywhere in the buffer. overlay-recenter — Function: overlay-recenter pos This function recenters the overlays of the current buffer aroundposition pos. That makes overlay lookup faster for positionsnear pos, but slower for positions far away from pos. A loop that scans the buffer forwards, creating overlays, can run faster if you do (overlay-recenter (point-max)) first. Overlay Properties Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. See , for comparison. Text properties are considered a part of the text; overlays and their properties are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay property changes are not recorded in the buffer's undo list. These functions read and set the properties of an overlay: overlay-get — Function: overlay-get overlay prop This function returns the value of property prop recorded inoverlay, if any. If overlay does not record any value forthat property, but it does have a category property which is asymbol, that symbol's prop property is used. Otherwise, the valueis nil. overlay-put — Function: overlay-put overlay prop value This function sets the value of property prop recorded inoverlay to value. It returns value. overlay-properties — Function: overlay-properties overlay This returns a copy of the property list of overlay. See also the function get-char-property which checks both overlay properties and text properties for a given character. See . Many overlay properties have special meanings; here is a table of them: priority priority (overlay property)This property's value (which should be a nonnegative integer number)determines the priority of the overlay. The priority matters when twoor more overlays cover the same character and both specify the sameproperty; the one whose priority value is larger takes priorityover the other. For the face property, the higher priorityvalue does not completely replace the other; instead, its faceattributes override the face attributes of the lower priorityface property.Currently, all overlays take priority over text properties. Pleaseavoid using negative priority values, as we have not yet decided justwhat they should mean. window window (overlay property)If the window property is non-nil, then the overlayapplies only on that window. category category (overlay property)If an overlay has a category property, we call it thecategory of the overlay. It should be a symbol. The propertiesof the symbol serve as defaults for the properties of the overlay. face face (overlay property)This property controls the way text is displayed—for example, whichfont and which colors. See , for more information.In the simplest case, the value is a face name. It can also be a list;then each element can be any of these possibilities: A face name (a symbol or string). A property list of face attributes. This has the form (keywordvalue …), where each keyword is a face attributename and value is a meaningful value for that attribute. Withthis feature, you do not need to create a face each time you want tospecify a particular attribute for certain text. See . A cons cell, either of the form (foreground-color . color-name) or(background-color . color-name). These elements specifyjust the foreground color or just the background color.(foreground-color . color-name) has the same effect as(:foreground color-name); likewise for the background. mouse-face mouse-face (overlay property)This property is used instead of face when the mouse is withinthe range of the overlay. display display (overlay property)This property activates various features that change theway text is displayed. For example, it can make text appear talleror shorter, higher or lower, wider or narrower, or replaced with an image.See . help-echo help-echo (overlay property)If an overlay has a help-echo property, then when you move themouse onto the text in the overlay, Emacs displays a help string in theecho area, or in the tooltip window. For details see . modification-hooks modification-hooks (overlay property)This property's value is a list of functions to be called if anycharacter within the overlay is changed or if text is inserted strictlywithin the overlay.The hook functions are called both before and after each change.If the functions save the information they receive, and compare notesbetween calls, they can determine exactly what change has been madein the buffer text.When called before a change, each function receives four arguments: theoverlay, nil, and the beginning and end of the text range to bemodified.When called after a change, each function receives five arguments: theoverlay, t, the beginning and end of the text range justmodified, and the length of the pre-change text replaced by that range.(For an insertion, the pre-change length is zero; for a deletion, thatlength is the number of characters deleted, and the post-changebeginning and end are equal.)If these functions modify the buffer, they should bindinhibit-modification-hooks to t around doing so, toavoid confusing the internal mechanism that calls these hooks.Text properties also support the modification-hooks property,but the details are somewhat different (see ). insert-in-front-hooks insert-in-front-hooks (overlay property)This property's value is a list of functions to be called before andafter inserting text right at the beginning of the overlay. The callingconventions are the same as for the modification-hooks functions. insert-behind-hooks insert-behind-hooks (overlay property)This property's value is a list of functions to be called before andafter inserting text right at the end of the overlay. The callingconventions are the same as for the modification-hooks functions. invisible invisible (overlay property)The invisible property can make the text in the overlayinvisible, which means that it does not appear on the screen.See , for details. intangible intangible (overlay property)The intangible property on an overlay works just like theintangible text property. See , for details. isearch-open-invisible This property tells incremental search how to make an invisible overlayvisible, permanently, if the final match overlaps it. See . isearch-open-invisible-temporary This property tells incremental search how to make an invisible overlayvisible, temporarily, during the search. See . before-string before-string (overlay property)This property's value is a string to add to the display at the beginningof the overlay. The string does not appear in the buffer in anysense—only on the screen. after-string after-string (overlay property)This property's value is a string to add to the display at the end ofthe overlay. The string does not appear in the buffer in anysense—only on the screen. evaporate evaporate (overlay property)If this property is non-nil, the overlay is deleted automaticallyif it becomes empty (i.e., if its length becomes zero). If you givean empty overlay a non-nil evaporate property, that deletesit immediately. local-map keymap of character (and overlays) local-map (overlay property)If this property is non-nil, it specifies a keymap for a portionof the text. The property's value replaces the buffer's local map, whenthe character after point is within the overlay. See . keymap keymap (overlay property)The keymap property is similar to local-map but overrides thebuffer's local map (and the map specified by the local-mapproperty) rather than replacing it. Searching for Overlays overlays-at — Function: overlays-at pos This function returns a list of all the overlays that cover thecharacter at position pos in the current buffer. The list is inno particular order. An overlay contains position pos if itbegins at or before pos, and ends after pos.To illustrate usage, here is a Lisp function that returns a list of theoverlays that specify property prop for the character at point: (defun find-overlays-specifying (prop) (let ((overlays (overlays-at (point))) found) (while overlays (let ((overlay (car overlays))) (if (overlay-get overlay prop) (setq found (cons overlay found)))) (setq overlays (cdr overlays))) found)) overlays-in — Function: overlays-in beg end This function returns a list of the overlays that overlap the regionbeg through end. “Overlap” means that at least onecharacter is contained within the overlay and also contained within thespecified region; however, empty overlays are included in the result ifthey are located at beg, or strictly between beg and end. next-overlay-change — Function: next-overlay-change pos This function returns the buffer position of the next beginning or endof an overlay, after pos. If there is none, it returns(point-max). previous-overlay-change — Function: previous-overlay-change pos This function returns the buffer position of the previous beginning orend of an overlay, before pos. If there is none, it returns(point-min). As an example, here's a simplified (and inefficient) version of the primitive function next-single-char-property-change (see ). It searches forward from position pos for the next position where the value of a given property prop, as obtained from either overlays or text properties, changes. (defun next-single-char-property-change (position prop) (save-excursion (goto-char position) (let ((propval (get-char-property (point) prop))) (while (and (not (eobp)) (eq (get-char-property (point) prop) propval)) (goto-char (min (next-overlay-change (point)) (next-single-property-change (point) prop))))) (point))) Width Since not all characters have the same width, these functions let you check the width of a character. See , and , for related functions. char-width — Function: char-width char This function returns the width in columns of the character char,if it were displayed in the current buffer and the selected window. string-width — Function: string-width string This function returns the width in columns of the string string,if it were displayed in the current buffer and the selected window. truncate-string-to-width — Function: truncate-string-to-width string width &optional start-column padding ellipsis This function returns the part of string that fits withinwidth columns, as a new string.If string does not reach width, then the result ends wherestring ends. If one multi-column character in stringextends across the column width, that character is not included inthe result. Thus, the result can fall short of width but cannotgo beyond it.The optional argument start-column specifies the starting column.If this is non-nil, then the first start-column columns ofthe string are omitted from the value. If one multi-column character instring extends across the column start-column, thatcharacter is not included.The optional argument padding, if non-nil, is a paddingcharacter added at the beginning and end of the result string, to extendit to exactly width columns. The padding character is used at theend of the result if it falls short of width. It is also used atthe beginning of the result if one multi-column character instring extends across the column start-column.If ellipsis is non-nil, it should be a string which willreplace the end of str (including any padding) if it extendsbeyond end-column, unless the display width of str isequal to or less than the display width of ellipsis. Ifellipsis is non-nil and not a string, it stands for"...". (truncate-string-to-width "\tab\t" 12 4) => "ab" (truncate-string-to-width "\tab\t" 12 4 ?\s) => " ab " Line Height line height The total height of each display line consists of the height of the contents of the line, plus optional additional vertical line spacing above or below the display line. The height of the line contents is the maximum height of any character or image on that display line, including the final newline if there is one. (A display line that is continued doesn't include a final newline.) That is the default line height, if you do nothing to specify a greater height. (In the most common case, this equals the height of the default frame font.) There are several ways to explicitly specify a larger line height, either by specifying an absolute height for the display line, or by specifying vertical space. However, no matter what you specify, the actual line height can never be less than the default. line-height (text property) A newline can have a line-height text or overlay property that controls the total height of the display line ending in that newline. If the property value is t, the newline character has no effect on the displayed height of the line—the visible contents alone determine the height. This is useful for tiling small images (or image slices) without adding blank areas between the images. If the property value is a list of the form (height total), that adds extra space below the display line. First Emacs uses height as a height spec to control extra space above the line; then it adds enough space below the line to bring the total line height up to total. In this case, the other ways to specify the line spacing are ignored. Any other kind of property value is a height spec, which translates into a number—the specified line height. There are several ways to write a height spec; here's how each of them translates into a number: integer If the height spec is a positive integer, the height value is that integer. float If the height spec is a float, float, the numeric height valueis float times the frame's default line height. (face . ratio) If the height spec is a cons of the format shown, the numeric heightis ratio times the height of face face. ratio canbe any type of number, or nil which means a ratio of 1.If face is t, it refers to the current face. (nil . ratio) If the height spec is a cons of the format shown, the numeric heightis ratio times the height of the contents of the line. Thus, any valid height spec determines the height in pixels, one way or another. If the line contents' height is less than that, Emacs adds extra vertical space above the line to achieve the specified total height. If you don't specify the line-height property, the line's height consists of the contents' height plus the line spacing. There are several ways to specify the line spacing for different parts of Emacs text. default-line-spacing You can specify the line spacing for all lines in a frame with the line-spacing frame parameter (see ). However, if the variable default-line-spacing is non-nil, it overrides the frame's line-spacing parameter. An integer value specifies the number of pixels put below lines on graphical displays. A floating point number specifies the spacing relative to the frame's default line height. line-spacing You can specify the line spacing for all lines in a buffer via the buffer-local line-spacing variable. An integer value specifies the number of pixels put below lines on graphical displays. A floating point number specifies the spacing relative to the default frame line height. This overrides line spacings specified for the frame. line-spacing (text property) Finally, a newline can have a line-spacing text or overlay property that overrides the default frame line spacing and the buffer local line-spacing variable, for the display line ending in that newline. One way or another, these mechanisms specify a Lisp value for the spacing of each line. The value is a height spec, and it translates into a Lisp value as described above. However, in this case the numeric height value specifies the line spacing, rather than the line height. Faces faces A face is a named collection of graphical attributes: font family, foreground color, background color, optional underlining, and many others. Faces are used in Emacs to control the style of display of particular parts of the text or the frame. See See section ``Standard Faces'' in The GNU Emacs Manual, for the list of faces Emacs normally comes with. face id Each face has its own face number, which distinguishes faces at low levels within Emacs. However, for most purposes, you refer to faces in Lisp programs by the symbols that name them. facep — Function: facep object This function returns t if object is a face name stringor symbol (or if it is a vector of the kind used internally to recordface data). It returns nil otherwise. Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish. Defining Faces The way to define a new face is with defface. This creates a kind of customization item (see ) which the user can customize using the Customization buffer (see See section ``Easy Customization'' in The GNU Emacs Manual). defface — Macro: defface face spec doc [ keyword value ] … This declares face as a customizable face that defaultsaccording to spec. You should not quote the symbol face,and it should not end in ‘-face’ (that would be redundant). Theargument doc specifies the face documentation. The keywords youcan use in defface are the same as in defgroup anddefcustom (see ).When defface executes, it defines the face according tospec, then uses any customizations that were read from theinit file (see ) to override that specification.The purpose of spec is to specify how the face should appear ondifferent kinds of terminals. It should be an alist whose elementshave the form (display atts). Each element'scar, display, specifies a class of terminals. (The firstelement, if its car is default, is special—it specifiesdefaults for the remaining elements). The element's cadr,atts, is a list of face attributes and their values; itspecifies what the face should look like on that kind of terminal.The possible attributes are defined in the value ofcustom-face-attributes.The display part of an element of spec determines whichframes the element matches. If more than one element of specmatches a given frame, the first element that matches is the one usedfor that frame. There are three possibilities for display: default This element of spec doesn't match any frames; instead, itspecifies defaults that apply to all frames. This kind of element, ifused, must be the first element of spec. Each of the followingelements can override any or all of these defaults. t This element of spec matches all frames. Therefore, anysubsequent elements of spec are never used. Normallyt is used in the last (or only) element of spec. a list If display is a list, each element should have the form(characteristic value…). Herecharacteristic specifies a way of classifying frames, and thevalues are possible classifications which display shouldapply to. Here are the possible values of characteristic: type The kind of window system the frame uses—either graphic (anygraphics-capable display), x, pc (for the MS-DOS console),w32 (for MS Windows 9X/NT/2K/XP), mac (for the Macintoshdisplay), or tty (a non-graphics-capable display).See window-system. class What kinds of colors the frame supports—either color,grayscale, or mono. background The kind of background—either light or dark. min-colors An integer that represents the minimum number of colors the frameshould support. This matches a frame if itsdisplay-color-cells value is at least the specified integer. supports Whether or not the frame can display the face attributes given invalue… (see ). See the documentationfor the function display-supports-face-attributes-p for moreinformation on exactly how this testing is done. See . If an element of display specifies more than one value for agiven characteristic, any of those values is acceptable. Ifdisplay has more than one element, each element should specify adifferent characteristic; then each characteristic of theframe must match one of the values specified for it indisplay. Here's how the standard face region is defined: (defface region '((((class color) (min-colors 88) (background dark)) :background "blue3") (((class color) (min-colors 88) (background light)) :background "lightgoldenrod2") (((class color) (min-colors 16) (background dark)) :background "blue3") (((class color) (min-colors 16) (background light)) :background "lightgoldenrod2") (((class color) (min-colors 8)) :background "blue" :foreground "white") (((type tty) (class mono)) :inverse-video t) (t :background "gray")) "Basic face for highlighting the region." :group 'basic-faces) Internally, defface uses the symbol property face-defface-spec to record the face attributes specified in defface, saved-face for the attributes saved by the user with the customization buffer, customized-face for the attributes customized by the user for the current session, but not saved, and face-documentation for the documentation string. frame-background-mode — User Option: frame-background-mode This option, if non-nil, specifies the background type to use forinterpreting face definitions. If it is dark, then Emacs treatsall frames as if they had a dark background, regardless of their actualbackground colors. If it is light, then Emacs treats all framesas if they had a light background. Face Attributes face attributes The effect of using a face is determined by a fixed set of face attributes. This table lists all the face attributes, and what they mean. You can specify more than one face for a given piece of text; Emacs merges the attributes of all the faces to determine how to display the text. See . Any attribute in a face can have the value unspecified. This means the face doesn't specify that attribute. In face merging, when the first face fails to specify a particular attribute, that means the next face gets a chance. However, the default face must specify all attributes. Some of these font attributes are meaningful only on certain kinds of displays—if your display cannot handle a certain attribute, the attribute is ignored. (The attributes :family, :width, :height, :weight, and :slant correspond to parts of an X Logical Font Descriptor.) :family Font family name, or fontset name (see ). If you specify afont family name, the wild-card characters ‘*’ and ‘?’ areallowed. :width Relative proportionate width, also known as the character set width orset width. This should be one of the symbols ultra-condensed,extra-condensed, condensed, semi-condensed,normal, semi-expanded, expanded,extra-expanded, or ultra-expanded. :height Either the font height, an integer in units of 1/10 point, a floatingpoint number specifying the amount by which to scale the height of anyunderlying face, or a function, which is called with the old height(from the underlying face), and should return the new height. :weight Font weight—a symbol from this series (from most dense to most faint):ultra-bold, extra-bold, bold, semi-bold,normal, semi-light, light, extra-light,or ultra-light.On a text-only terminal, any weight greater than normal is displayed asextra bright, and any weight less than normal is displayed ashalf-bright (provided the terminal supports the feature). :slant Font slant—one of the symbols italic, oblique, normal,reverse-italic, or reverse-oblique.On a text-only terminal, slanted text is displayed as half-bright, ifthe terminal supports the feature. :foreground Foreground color, a string. The value can be a system-defined colorname, or a hexadecimal color specification of the form‘#rrggbb’. (‘#000000’ is black,‘#ff0000’ is red, ‘#00ff00’ is green, ‘#0000ff’ isblue, and ‘#ffffff’ is white.) :background Background color, a string, like the foreground color. :inverse-video Whether or not characters should be displayed in inverse video. Thevalue should be t (yes) or nil (no). :stipple The background stipple, a bitmap.The value can be a string; that should be the name of a file containingexternal-format X bitmap data. The file is found in the directorieslisted in the variable x-bitmap-file-path.Alternatively, the value can specify the bitmap directly, with a listof the form (width height data). Here,width and height specify the size in pixels, anddata is a string containing the raw bits of the bitmap, row byrow. Each row occupies (width + 7) / 8 consecutive bytesin the string (which should be a unibyte string for best results).This means that each row always occupies at least one whole byte.If the value is nil, that means use no stipple pattern.Normally you do not need to set the stipple attribute, because it isused automatically to handle certain shades of gray. :underline Whether or not characters should be underlined, and in what color. Ifthe value is t, underlining uses the foreground color of theface. If the value is a string, underlining uses that color. Thevalue nil means do not underline. :overline Whether or not characters should be overlined, and in what color.The value is used like that of :underline. :strike-through Whether or not characters should be strike-through, and in whatcolor. The value is used like that of :underline. :inherit The name of a face from which to inherit attributes, or a list of facenames. Attributes from inherited faces are merged into the face like anunderlying face would be, with higher priority than underlying faces.If a list of faces is used, attributes from faces earlier in the listoverride those from later faces. :box Whether or not a box should be drawn around characters, its color, thewidth of the box lines, and 3D appearance. Here are the possible values of the :box attribute, and what they mean: nil Don't draw a box. t Draw a box with lines of width 1, in the foreground color. color Draw a box with lines of width 1, in color color. (:line-width width :color color :style style) This way you can explicitly specify all aspects of the box. The valuewidth specifies the width of the lines to draw; it defaults to 1.The value color specifies the color to draw with. The default isthe foreground color of the face for simple boxes, and the backgroundcolor of the face for 3D boxes.The value style specifies whether to draw a 3D box. If it isreleased-button, the box looks like a 3D button that is not beingpressed. If it is pressed-button, the box looks like a 3D buttonthat is being pressed. If it is nil or omitted, a plain 2D boxis used. In older versions of Emacs, before :family, :height, :width, :weight, and :slant existed, these attributes were used to specify the type face. They are now semi-obsolete, but they still work: :font This attribute specifies the font name. :bold A non-nil value specifies a bold font. :italic A non-nil value specifies an italic font. For compatibility, you can still set these “attributes,” even though they are not real face attributes. Here is what that does: :font You can specify an X font name as the “value” of this “attribute”;that sets the :family, :width, :height,:weight, and :slant attributes according to the font name.If the value is a pattern with wildcards, the first font that matchesthe pattern is used to set these attributes. :bold A non-nil makes the face bold; nil makes it normal.This actually works by setting the :weight attribute. :italic A non-nil makes the face italic; nil makes it normal.This actually works by setting the :slant attribute. x-bitmap-file-path — Variable: x-bitmap-file-path This variable specifies a list of directories for searchingfor bitmap files, for the :stipple attribute. bitmap-spec-p — Function: bitmap-spec-p object This returns t if object is a valid bitmap specification,suitable for use with :stipple (see above). It returnsnil otherwise. Face Attribute Functions This section describes the functions for accessing and modifying the attributes of an existing face. set-face-attribute — Function: set-face-attribute face frame &rest arguments This function sets one or more attributes of face face for frameframe. The attributes you specify this way override whateverthe defface says.The extra arguments arguments specify the attributes to set, andthe values for them. They should consist of alternating attribute names(such as :family or :underline) and corresponding values.Thus, (set-face-attribute 'foo nil :width 'extended :weight 'bold :underline "red") sets the attributes :width, :weight and :underlineto the corresponding values.If frame is t, this function sets the default attributesfor new frames. Default attribute values specified this way overridethe defface for newly created frames.If frame is nil, this function sets the attributes forall existing frames, and the default for new frames. face-attribute — Function: face-attribute face attribute &optional frame inherit This returns the value of the attribute attribute of faceface on frame. If frame is nil,that means the selected frame (see ).If frame is t, this returns whatever new-frames defaultvalue you previously specified with set-face-attribute for theattribute attribute of face. If you have not specifiedone, it returns nil.If inherit is nil, only attributes directly defined byface are considered, so the return value may beunspecified, or a relative value. If inherit isnon-nil, face's definition of attribute is mergedwith the faces specified by its :inherit attribute; however thereturn value may still be unspecified or relative. Ifinherit is a face or a list of faces, then the result is furthermerged with that face (or faces), until it becomes specified andabsolute.To ensure that the return value is always specified and absolute, usea value of default for inherit; this will resolve anyunspecified or relative values by merging with the default face(which is always completely specified).For example, (face-attribute 'bold :weight) => bold face-attribute-relative-p — Function: face-attribute-relative-p attribute value This function returns non-nil if value, when used as thevalue of the face attribute attribute, is relative. This meansit would modify, rather than completely override, any value that comesfrom a subsequent face in the face list or that is inherited fromanother face.unspecified is a relative value for all attributes.For :height, floating point values are also relative.For example: (face-attribute-relative-p :height 2.0) => t merge-face-attribute — Function: merge-face-attribute attribute value1 value2 If value1 is a relative value for the face attributeattribute, returns it merged with the underlying valuevalue2; otherwise, if value1 is an absolute value for theface attribute attribute, returns value1 unchanged. The functions above did not exist before Emacs 21. For compatibility with older Emacs versions, you can use the following functions to set and examine the face attributes which existed in those versions. They use values of t and nil for frame just like set-face-attribute and face-attribute. set-face-foreground — Function: set-face-foreground face color &optional frame set-face-background — Function: set-face-background face color &optional frame These functions set the foreground (or background, respectively) colorof face face to color. The argument color should be astring, the name of a color.Certain shades of gray are implemented by stipple patterns onblack-and-white screens. set-face-stipple — Function: set-face-stipple face pattern &optional frame This function sets the background stipple pattern of face faceto pattern. The argument pattern should be the name of astipple pattern defined by the X server, or actual bitmap data(see ), or nil meaning don't use stipple.Normally there is no need to pay attention to stipple patterns, becausethey are used automatically to handle certain shades of gray. set-face-font — Function: set-face-font face font &optional frame This function sets the font of face face. This actually setsthe attributes :family, :width, :height,:weight, and :slant according to the font namefont. set-face-bold-p — Function: set-face-bold-p face bold-p &optional frame This function specifies whether face should be bold. Ifbold-p is non-nil, that means yes; nil means no.This actually sets the :weight attribute. set-face-italic-p — Function: set-face-italic-p face italic-p &optional frame This function specifies whether face should be italic. Ifitalic-p is non-nil, that means yes; nil means no.This actually sets the :slant attribute. set-face-underline-p — Function: set-face-underline-p face underline &optional frame This function sets the underline attribute of face face.Non-nil means do underline; nil means don't.If underline is a string, underline with that color. set-face-inverse-video-p — Function: set-face-inverse-video-p face inverse-video-p &optional frame This function sets the :inverse-video attribute of faceface. invert-face — Function: invert-face face &optional frame This function swaps the foreground and background colors of faceface. These functions examine the attributes of a face. If you don't specify frame, they refer to the selected frame; t refers to the default data for new frames. They return the symbol unspecified if the face doesn't define any value for that attribute. face-foreground — Function: face-foreground face &optional frame inherit face-background — Function: face-background face &optional frame inherit These functions return the foreground color (or background color,respectively) of face face, as a string.If inherit is nil, only a color directly defined by the face isreturned. If inherit is non-nil, any faces specified by its:inherit attribute are considered as well, and if inheritis a face or a list of faces, then they are also considered, until aspecified color is found. To ensure that the return value is alwaysspecified, use a value of default for inherit. face-stipple — Function: face-stipple face &optional frame inherit This function returns the name of the background stipple pattern of faceface, or nil if it doesn't have one.If inherit is nil, only a stipple directly defined by theface is returned. If inherit is non-nil, any facesspecified by its :inherit attribute are considered as well, andif inherit is a face or a list of faces, then they are alsoconsidered, until a specified stipple is found. To ensure that thereturn value is always specified, use a value of default forinherit. face-font — Function: face-font face &optional frame This function returns the name of the font of face face. face-bold-p — Function: face-bold-p face &optional frame This function returns t if face is bold—that is, if it isbolder than normal. It returns nil otherwise. face-italic-p — Function: face-italic-p face &optional frame This function returns t if face is italic or oblique,nil otherwise. face-underline-p — Function: face-underline-p face &optional frame This function returns the :underline attribute of face face. face-inverse-video-p — Function: face-inverse-video-p face &optional frame This function returns the :inverse-video attribute of face face. Displaying Faces Here are the ways to specify which faces to use for display of text: With defaults. The default face is used as the ultimatedefault for all text. (In Emacs 19 and 20, the defaultface is used only when no other face is specified.) For a mode line or header line, the face mode-line ormode-line-inactive, or header-line, is merged in justbefore default. With text properties. A character can have a face property; ifso, the faces and face attributes specified there apply. See .If the character has a mouse-face property, that is used insteadof the face property when the mouse is “near enough” to thecharacter. With overlays. An overlay can have face and mouse-faceproperties too; they apply to all the text covered by the overlay. With a region that is active. In Transient Mark mode, the region ishighlighted with the face region (see See section ``Standard Faces'' in The GNU Emacs Manual). With special glyphs. Each glyph can specify a particular facenumber. See . If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. For each attribute, Emacs tries first the face of any special glyph; then the face for region highlighting, if appropriate; then the faces specified by overlays, followed by those specified by text properties, then the mode-line or mode-line-inactive or header-line face (if in a mode line or a header line), and last the default face. When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See . Font Selection Selecting a font means mapping the specified face attributes for a character to a font that is available on a particular display. The face attributes, as determined by face merging, specify most of the font choice, but not all. Part of the choice depends on what character it is. If the face specifies a fontset name, that fontset determines a pattern for fonts of the given charset. If the face specifies a font family, a font pattern is constructed. Emacs tries to find an available font for the given face attributes and character's registry and encoding. If there is a font that matches exactly, it is used, of course. The hard case is when no available font exactly fits the specification. Then Emacs looks for one that is “close”—one attribute at a time. You can specify the order to consider the attributes. In the case where a specified font family is not available, you can specify a set of mappings for alternatives to try. face-font-selection-order — Variable: face-font-selection-order This variable specifies the order of importance of the face attributes:width, :height, :weight, and :slant. Thevalue should be a list containing those four symbols, in order ofdecreasing importance.Font selection first finds the best available matches for the firstattribute listed; then, among the fonts which are best in that way, itsearches for the best matches in the second attribute, and so on.The attributes :weight and :width have symbolic values ina range centered around normal. Matches that are more extreme(farther from normal) are somewhat preferred to matches that areless extreme (closer to normal); this is designed to ensure thatnon-normal faces contrast with normal ones, whenever possible.The default is (:width :height :weight :slant), which means firstfind the fonts closest to the specified :width, then—among thefonts with that width—find a best match for the specified font height,and so on.One example of a case where this variable makes a difference is when thedefault font has no italic equivalent. With the default ordering, theitalic face will use a non-italic font that is similar to thedefault one. But if you put :slant before :height, theitalic face will use an italic font, even if its height is notquite right. face-font-family-alternatives — Variable: face-font-family-alternatives This variable lets you specify alternative font families to try, if agiven family is specified and doesn't exist. Each element should havethis form: (family alternate-families…) If family is specified but not available, Emacs will try the otherfamilies given in alternate-families, one by one, until it finds afamily that does exist. face-font-registry-alternatives — Variable: face-font-registry-alternatives This variable lets you specify alternative font registries to try, if agiven registry is specified and doesn't exist. Each element should havethis form: (registry alternate-registries…) If registry is specified but not available, Emacs will try theother registries given in alternate-registries, one by one,until it finds a registry that does exist. Emacs can make use of scalable fonts, but by default it does not use them, since the use of too many or too big scalable fonts can crash XFree86 servers. scalable-fonts-allowed — Variable: scalable-fonts-allowed This variable controls which scalable fonts to use. A value ofnil, the default, means do not use scalable fonts. tmeans to use any scalable font that seems appropriate for the text.Otherwise, the value must be a list of regular expressions. Then ascalable font is enabled for use if its name matches any regularexpression in the list. For example, (setq scalable-fonts-allowed '("muleindian-2$")) allows the use of scalable fonts with registry muleindian-2. face-font-rescale-alist — Variable: face-font-rescale-alist This variable specifies scaling for certain faces. Its value shouldbe a list of elements of the form (fontname-regexp . scale-factor) If fontname-regexp matches the font name that is about to beused, this says to choose a larger similar font according to thefactor scale-factor. You would use this feature to normalizethe font size if certain fonts are bigger or smaller than theirnominal heights and widths would suggest. Functions for Working with Faces Here are additional functions for creating and working with faces. make-face — Function: make-face name This function defines a new face named name, initially with allattributes nil. It does nothing if there is already a face namedname. face-list — Function: face-list This function returns a list of all defined face names. copy-face — Function: copy-face old-face new-name &optional frame new-frame This function defines a face named new-name as a copy of the existingface named old-face. It creates the face new-name if thatdoesn't already exist.If the optional argument frame is given, this function appliesonly to that frame. Otherwise it applies to each frame individually,copying attributes from old-face in each frame to new-facein the same frame.If the optional argument new-frame is given, then copy-facecopies the attributes of old-face in frame to new-namein new-frame. face-id — Function: face-id face This function returns the face number of face face. face-documentation — Function: face-documentation face This function returns the documentation string of face face, ornil if none was specified for it. face-equal — Function: face-equal face1 face2 &optional frame This returns t if the faces face1 and face2 have thesame attributes for display. face-differs-from-default-p — Function: face-differs-from-default-p face &optional frame This returns non-nil if the face face displaysdifferently from the default face. face alias A face alias provides an equivalent name for a face. You can define a face alias by giving the alias symbol the face-alias property, with a value of the target face name. The following example makes modeline an alias for the mode-line face. (put 'modeline 'face-alias 'mode-line) Automatic Face Assignment automatic face assignment faces, automatic choice This hook is used for automatically assigning faces to text in the buffer. It is part of the implementation of Font-Lock mode. fontification-functions — Variable: fontification-functions This variable holds a list of functions that are called by Emacsredisplay as needed to assign faces automatically to text in the buffer.The functions are called in the order listed, with one argument, abuffer position pos. Each function should attempt to assign facesto the text in the current buffer starting at pos.Each function should record the faces they assign by setting theface property. It should also add a non-nilfontified property for all the text it has assigned faces to.That property tells redisplay that faces have been assigned to that textalready.It is probably a good idea for each function to do nothing if thecharacter after pos already has a non-nil fontifiedproperty, but this is not required. If one function overrides theassignments made by a previous one, the properties as they areafter the last function finishes are the ones that really matter.For efficiency, we recommend writing these functions so that theyusually assign faces to around 400 to 600 characters at each call. Looking Up Fonts x-list-fonts — Function: x-list-fonts pattern &optional face frame maximum This function returns a list of available font names that matchpattern. If the optional arguments face and frame arespecified, then the list is limited to fonts that are the same size asface currently is on frame.The argument pattern should be a string, perhaps with wildcardcharacters: the ‘*’ character matches any substring, and the‘?’ character matches any single character. Pattern matchingof font names ignores case.If you specify face and frame, face should be a face name(a symbol) and frame should be a frame.The optional argument maximum sets a limit on how many fonts toreturn. If this is non-nil, then the return value is truncatedafter the first maximum matching fonts. Specifying a small valuefor maximum can make this function much faster, in cases wheremany fonts match the pattern. x-family-fonts — Function: x-family-fonts &optional family frame This function returns a list describing the available fonts for familyfamily on frame. If family is omitted or nil,this list applies to all families, and therefore, it contains allavailable fonts. Otherwise, family must be a string; it maycontain the wildcards ‘?’ and ‘*’.The list describes the display that frame is on; if frame isomitted or nil, it applies to the selected frame's display(see ).The list contains a vector of the following form for each font: [family width point-size weight slant fixed-p full registry-and-encoding] The first five elements correspond to face attributes; if youspecify these attributes for a face, it will use this font.The last three elements give additional information about the font.fixed-p is non-nil if the font is fixed-pitch.full is the full name of the font, andregistry-and-encoding is a string giving the registry andencoding of the font.The result list is sorted according to the current face font sort order. x-font-family-list — Function: x-font-family-list &optional frame This function returns a list of the font families available forframe's display. If frame is omitted or nil, itdescribes the selected frame's display (see ).The value is a list of elements of this form: (family . fixed-p) Here family is a font family, and fixed-p isnon-nil if fonts of that family are fixed-pitch. font-list-limit — Variable: font-list-limit This variable specifies maximum number of fonts to consider in fontmatching. The function x-family-fonts will not return more thanthat many fonts, and font selection will consider only that many fontswhen searching a matching font for face attributes. The default iscurrently 100. Fontsets A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the “font” for a frame or a face. Here is information about defining a fontset under Lisp program control. create-fontset-from-fontset-spec — Function: create-fontset-from-fontset-spec fontset-spec &optional style-variant-p noerror This function defines a new fontset according to the specificationstring fontset-spec. The string should have this format: fontpattern, [ charsetname:fontname ]… Whitespace characters before and after the commas are ignored.The first part of the string, fontpattern, should have the form ofa standard X font name, except that the last two fields should be‘fontset-alias’.The new fontset has two names, one long and one short. The long name isfontpattern in its entirety. The short name is‘fontset-alias’. You can refer to the fontset by eithername. If a fontset with the same name already exists, an error issignaled, unless noerror is non-nil, in which case thisfunction does nothing.If optional argument style-variant-p is non-nil, that saysto create bold, italic and bold-italic variants of the fontset as well.These variant fontsets do not have a short name, only a long one, whichis made by altering fontpattern to indicate the bold or italicstatus.The specification string also says which fonts to use in the fontset.See below for the details. The construct ‘charset:font’ specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string. For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces ‘fontset-alias’ with a value that names one character set. For the ASCII character set, ‘fontset-alias’ is replaced with ‘ISO8859-1’. In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does. Thus if fontpattern is this, -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24 the font specification for ASCII characters would be this: -*-fixed-medium-r-normal-*-24-*-ISO8859-1 and the font specification for Chinese GB2312 characters would be this: -*-fixed-medium-r-normal-*-24-*-gb2312*-* You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in the family field. In such a case, ‘Fontset-n’ can be specified as below: Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\ chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-* Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in the family field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ in the family field. set-fontset-font — Function: set-fontset-font name character fontname &optional frame This function modifies the existing fontset name touse the font name fontname for the character character.If name is nil, this function modifies the defaultfontset, whose short name is ‘fontset-default’.character may be a cons; (from . to), wherefrom and to are non-generic characters. In that case, usefontname for all characters in the range from and to(inclusive).character may be a charset. In that case, usefontname for all character in the charsets.fontname may be a cons; (family . registry),where family is a family name of a font (possibly including afoundry name at the head), registry is a registry name of a font(possibly including an encoding name at the tail).For instance, this changes the default fontset to use a font of whichregistry name is ‘JISX0208.1983’ for all characters belonging tothe charset japanese-jisx0208. (set-fontset-font nil 'japanese-jisx0208 '(nil . "JISX0208.1983")) char-displayable-p — Function: char-displayable-p char This function returns t if Emacs ought to be able to displaychar. More precisely, if the selected frame's fontset has afont to display the character set that char belongs to.Fontsets can specify a font on a per-character basis; when the fontsetdoes that, this function's value may not be accurate. Fringes fringes The fringes of a window are thin vertical strips down the sides that are used for displaying bitmaps that indicate truncation, continuation, horizontal scrolling, and the overlay arrow. Fringe Size and Position The following buffer-local variables control the position and width of the window fringes. fringes-outside-margins — Variable: fringes-outside-margins The fringes normally appear between the display margins and the windowtext. If the value is non-nil, they appear outside the displaymargins. See . left-fringe-width — Variable: left-fringe-width This variable, if non-nil, specifies the width of the leftfringe in pixels. A value of nil means to use the left fringewidth from the window's frame. right-fringe-width — Variable: right-fringe-width This variable, if non-nil, specifies the width of the rightfringe in pixels. A value of nil means to use the right fringewidth from the window's frame. The values of these variables take effect when you display the buffer in a window. If you change them while the buffer is visible, you can call set-window-buffer to display it once again in the same window, to make the changes take effect. set-window-fringes — Function: set-window-fringes window left &optional right outside-margins This function sets the fringe widths of window window.If window is nil, the selected window is used.The argument left specifies the width in pixels of the leftfringe, and likewise right for the right fringe. A value ofnil for either one stands for the default width. Ifoutside-margins is non-nil, that specifies that fringesshould appear outside of the display margins. window-fringes — Function: window-fringes &optional window This function returns information about the fringes of a windowwindow. If window is omitted or nil, the selectedwindow is used. The value has the form (left-widthright-width outside-margins). Fringe Indicators fringe indicators indicators, fringe The fringe indicators are tiny icons Emacs displays in the window fringe (on a graphic display) to indicate truncated or continued lines, buffer boundaries, overlay arrow, etc. indicate-empty-lines — User Option: indicate-empty-lines fringes, and empty line indicationWhen this is non-nil, Emacs displays a special glyph in thefringe of each empty line at the end of the buffer, on graphicaldisplays. See . This variable is automaticallybuffer-local in every buffer. indicate-buffer-boundaries — Variable: indicate-buffer-boundaries This buffer-local variable controls how the buffer boundaries andwindow scrolling are indicated in the window fringes.Emacs can indicate the buffer boundaries—that is, the first and lastline in the buffer—with angle icons when they appear on the screen.In addition, Emacs can display an up-arrow in the fringe to showthat there is text above the screen, and a down-arrow to showthere is text below the screen.There are three kinds of basic values: nil Don't display any of these fringe icons. left Display the angle icons and arrows in the left fringe. right Display the angle icons and arrows in the right fringe. any non-alist Display the angle icons in the left fringeand don't display the arrows. Otherwise the value should be an alist that specifies which fringeindicators to display and where. Each element of the alist shouldhave the form (indicator . position). Here,indicator is one of top, bottom, up,down, and t (which covers all the icons not yetspecified), while position is one of left, rightand nil.For example, ((top . left) (t . right)) places the top anglebitmap in left fringe, and the bottom angle bitmap as well as botharrow bitmaps in right fringe. To show the angle bitmaps in the leftfringe, and no arrow bitmaps, use ((top . left) (bottom . left)). default-indicate-buffer-boundaries — Variable: default-indicate-buffer-boundaries The value of this variable is the default value forindicate-buffer-boundaries in buffers that do not override it. fringe-indicator-alist — Variable: fringe-indicator-alist This buffer-local variable specifies the mapping from logical fringeindicators to the actual bitmaps displayed in the window fringes.These symbols identify the logical fringe indicators: Truncation and continuation line indicators: truncation, continuation. Buffer position indicators: up, down,top, bottom,top-bottom. Empty line indicator: empty-line. Overlay arrow indicator: overlay-arrow. Unknown bitmap indicator: unknown. The value is an alist where each element (indicator . bitmaps)specifies the fringe bitmaps used to display a specific logicalfringe indicator.Here, indicator specifies the logical indicator type, andbitmaps is list of symbols (left right[left1 right1]) which specifies the actual bitmap shownin the left or right fringe for the logical indicator.The left and right symbols specify the bitmaps shown inthe left and/or right fringe for the specific indicator. Theleft1 or right1 bitmaps are used only for the `bottom' and`top-bottom indicators when the last (only) line in has no finalnewline. Alternatively, bitmaps may be a single symbol which isused in both left and right fringes.When fringe-indicator-alist has a buffer-local value, and thereis no bitmap defined for a logical indicator, or the bitmap ist, the corresponding value from the (non-local)default-fringe-indicator-alist is used.To completely hide a specific indicator, set the bitmap to nil. default-fringe-indicator-alist — Variable: default-fringe-indicator-alist The value of this variable is the default value forfringe-indicator-alist in buffers that do not override it. Standard fringe bitmaps for indicators: left-arrow right-arrow up-arrow down-arrow left-curly-arrow right-curly-arrow left-triangle right-triangle top-left-angle top-right-angle bottom-left-angle bottom-right-angle left-bracket right-bracket filled-rectangle hollow-rectangle filled-square hollow-square vertical-bar horizontal-bar empty-line question-mark Fringe Cursors fringe cursors cursor, fringe When a line is exactly as wide as the window, Emacs displays the cursor in the right fringe instead of using two lines. Different bitmaps are used to represent the cursor in the fringe depending on the current buffer's cursor type. Logical cursor types: box , hollow, bar,hbar, hollow-small. The hollow-small type is used instead of hollow when the normal hollow-rectangle bitmap is too tall to fit on a specific display line. overflow-newline-into-fringe — Variable: overflow-newline-into-fringe If this is non-nil, lines exactly as wide as the window (notcounting the final newline character) are not continued. Instead,when point is at the end of the line, the cursor appears in the rightfringe. fringe-cursor-alist — Variable: fringe-cursor-alist This variable specifies the mapping from logical cursor type to theactual fringe bitmaps displayed in the right fringe. The value is analist where each element (cursor . bitmap) specifiesthe fringe bitmaps used to display a specific logical cursor type inthe fringe. Here, cursor specifies the logical cursor type andbitmap is a symbol specifying the fringe bitmap to be displayedfor that logical cursor type.When fringe-cursor-alist has a buffer-local value, and there isno bitmap defined for a cursor type, the corresponding value from the(non-local) default-fringes-indicator-alist is used. default-fringes-cursor-alist — Variable: default-fringes-cursor-alist The value of this variable is the default value forfringe-cursor-alist in buffers that do not override it. Standard bitmaps for displaying the cursor in right fringe: filled-rectangle hollow-rectangle filled-square hollow-square vertical-bar horizontal-bar Fringe Bitmaps fringe bitmaps bitmaps, fringe The fringe bitmaps are the actual bitmaps which represent the logical fringe indicators for truncated or continued lines, buffer boundaries, overlay arrow, etc. Fringe bitmap symbols have their own name space. The fringe bitmaps are shared by all frames and windows. You can redefine the built-in fringe bitmaps, and you can define new fringe bitmaps. The way to display a bitmap in the left or right fringes for a given line in a window is by specifying the display property for one of the characters that appears in it. Use a display specification of the form (left-fringe bitmap [face]) or (right-fringe bitmap [face]) (see ). Here, bitmap is a symbol identifying the bitmap you want, and face (which is optional) is the name of the face whose colors should be used for displaying the bitmap, instead of the default fringe face. face is automatically merged with the fringe face, so normally face need only specify the foreground color for the bitmap. fringe-bitmaps-at-pos — Function: fringe-bitmaps-at-pos &optional pos window This function returns the fringe bitmaps of the display linecontaining position pos in window window. The returnvalue has the form (left right ov), where leftis the symbol for the fringe bitmap in the left fringe (or nilif no bitmap), right is similar for the right fringe, and ovis non-nil if there is an overlay arrow in the left fringe.The value is nil if pos is not visible in window.If window is nil, that stands for the selected window.If pos is nil, that stands for the value of point inwindow. Customizing Fringe Bitmaps define-fringe-bitmap — Function: define-fringe-bitmap bitmap bits &optional height width align This function defines the symbol bitmap as a new fringe bitmap,or replaces an existing bitmap with that name.The argument bits specifies the image to use. It should beeither a string or a vector of integers, where each element (aninteger) corresponds to one row of the bitmap. Each bit of an integercorresponds to one pixel of the bitmap, where the low bit correspondsto the rightmost pixel of the bitmap.The height is normally the length of bits. However, youcan specify a different height with non-nil height. The widthis normally 8, but you can specify a different width with non-nilwidth. The width must be an integer between 1 and 16.The argument align specifies the positioning of the bitmaprelative to the range of rows where it is used; the default is tocenter the bitmap. The allowed values are top, center,or bottom.The align argument may also be a list (alignperiodic) where align is interpreted as described above.If periodic is non-nil, it specifies that the rows inbits should be repeated enough times to reach the specifiedheight. destroy-fringe-bitmap — Function: destroy-fringe-bitmap bitmap This function destroy the fringe bitmap identified by bitmap.If bitmap identifies a standard fringe bitmap, it actuallyrestores the standard definition of that bitmap, instead ofeliminating it entirely. set-fringe-bitmap-face — Function: set-fringe-bitmap-face bitmap &optional face This sets the face for the fringe bitmap bitmap to face.If face is nil, it selects the fringe face. Thebitmap's face controls the color to draw it in.face is merged with the fringe face, so normallyface should specify only the foreground color. The Overlay Arrow The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed. This feature has nothing to do with overlays (see ). overlay-arrow-string — Variable: overlay-arrow-string This variable holds the string to display to call attention to aparticular line, or nil if the arrow feature is not in use.On a graphical display the contents of the string are ignored; instead aglyph is displayed in the fringe area to the left of the display area. overlay-arrow-position — Variable: overlay-arrow-position This variable holds a marker that indicates where to display the overlayarrow. It should point at the beginning of a line. On a non-graphicaldisplay the arrow textappears at the beginning of that line, overlaying any text that wouldotherwise appear. Since the arrow is usually short, and the lineusually begins with indentation, normally nothing significant isoverwritten.The overlay-arrow string is displayed in any given buffer if the valueof overlay-arrow-position in that buffer points into thatbuffer. Thus, it works to can display multiple overlay arrow stringsby creating buffer-local bindings of overlay-arrow-position.However, it is usually cleaner to useoverlay-arrow-variable-list to achieve this result. You can do a similar job by creating an overlay with a before-string property. See . You can define multiple overlay arrows via the variable overlay-arrow-variable-list. overlay-arrow-variable-list — Variable: overlay-arrow-variable-list This variable's value is a list of variables, each of which specifiesthe position of an overlay arrow. The variableoverlay-arrow-position has its normal meaning because it is onthis list. Each variable on this list can have properties overlay-arrow-string and overlay-arrow-bitmap that specify an overlay arrow string (for text-only terminals) or fringe bitmap (for graphical terminals) to display at the corresponding overlay arrow position. If either property is not set, the default overlay-arrow-string or overlay-arrow fringe indicator is used. Scroll Bars scroll bars Normally the frame parameter vertical-scroll-bars controls whether the windows in the frame have vertical scroll bars, and whether they are on the left or right. The frame parameter scroll-bar-width specifies how wide they are (nil meaning the default). See . frame-current-scroll-bars — Function: frame-current-scroll-bars &optional frame This function reports the scroll bar type settings for frameframe. The value is a cons cell(vertical-type . horizontal-type), wherevertical-type is either left, right, or nil(which means no scroll bar.) horizontal-type is meant tospecify the horizontal scroll bar type, but since they are notimplemented, it is always nil. vertical-scroll-bar You can enable or disable scroll bars for a particular buffer, by setting the variable vertical-scroll-bar. This variable automatically becomes buffer-local when set. The possible values are left, right, t, which means to use the frame's default, and nil for no scroll bar. You can also control this for individual windows. Call the function set-window-scroll-bars to specify what to do for a specific window: set-window-scroll-bars — Function: set-window-scroll-bars window width &optional vertical-type horizontal-type This function sets the width and type of scroll bars for windowwindow.width specifies the scroll bar width in pixels (nil meansuse the width specified for the frame). vertical-type specifieswhether to have a vertical scroll bar and, if so, where. The possiblevalues are left, right and nil, just like thevalues of the vertical-scroll-bars frame parameter.The argument horizontal-type is meant to specify whether andwhere to have horizontal scroll bars, but since they are notimplemented, it has no effect. If window is nil, theselected window is used. window-scroll-bars — Function: window-scroll-bars &optional window Report the width and type of scroll bars specified for window.If window is omitted or nil, the selected window is used.The value is a list of the form (widthcols vertical-type horizontal-type). The valuewidth is the value that was specified for the width (which maybe nil); cols is the number of columns that the scrollbar actually occupies.horizontal-type is not actually meaningful. If you don't specify these values for a window with set-window-scroll-bars, the buffer-local variables scroll-bar-mode and scroll-bar-width in the buffer being displayed control the window's vertical scroll bars. The function set-window-buffer examines these variables. If you change them in a buffer that is already visible in a window, you can make the window take note of the new values by calling set-window-buffer specifying the same buffer that is already displayed. scroll-bar-mode — Variable: scroll-bar-mode This variable, always local in all buffers, controls whether and whereto put scroll bars in windows displaying the buffer. The possible valuesare nil for no scroll bar, left to put a scroll bar onthe left, and right to put a scroll bar on the right. window-current-scroll-bars — Function: window-current-scroll-bars &optional window This function reports the scroll bar type for window window.If window is omitted or nil, the selected window is used.The value is a cons cell(vertical-type . horizontal-type). Unlikewindow-scroll-bars, this reports the scroll bar type actuallyused, once frame defaults and scroll-bar-mode are taken intoaccount. scroll-bar-width — Variable: scroll-bar-width This variable, always local in all buffers, specifies the width of thebuffer's scroll bars, measured in pixels. A value of nil meansto use the value specified by the frame. The display Property display specification display (text property) The display text property (or overlay property) is used to insert images into text, and also control other aspects of how text displays. The value of the display property should be a display specification, or a list or vector containing several display specifications. Some kinds of display properties specify something to display instead of the text that has the property. In this case, “the text” means all the consecutive characters that have the same Lisp object as their display property; these characters are replaced as a single unit. By contrast, characters that have similar but distinct Lisp objects as their display properties are handled separately. Here's a function that illustrates this point: (defun foo () (goto-char (point-min)) (dotimes (i 5) (let ((string (concat "A"))) (put-text-property (point) (1+ (point)) 'display string) (forward-char 1) (put-text-property (point) (1+ (point)) 'display string) (forward-char 1)))) It gives each of the first ten characters in the buffer string "A" as the display property, but they don't all get the same string. The first two characters get the same string, so they together are replaced with one ‘A’. The next two characters get a second string, so they together are replaced with one ‘A’. Likewise for each following pair of characters. Thus, the ten characters appear as five A's. This function would have the same results: (defun foo () (goto-char (point-min)) (dotimes (i 5) (let ((string (concat "A"))) (put-text-property (point) (2+ (point)) 'display string) (put-text-property (point) (1+ (point)) 'display string) (forward-char 2)))) This illustrates that what matters is the property value for each character. If two consecutive characters have the same object as the display property value, it's irrelevant whether they got this property from a single call to put-text-property or from two different calls. The rest of this section describes several kinds of display specifications and what they mean. Specified Spaces spaces, specified height or width variable-width spaces To display a space of specified width and/or height, use a display specification of the form (space . props), where props is a property list (a list of alternating properties and values). You can put this property on one or more consecutive characters; a space of the specified height and width is displayed in place of all of those characters. These are the properties you can use in props to specify the weight of the space: :width width If width is an integer or floating point number, it specifiesthat the space width should be width times the normal characterwidth. width can also be a pixel width specification(see ). :relative-width factor Specifies that the width of the stretch should be computed from thefirst character in the group of consecutive characters that have thesame display property. The space width is the width of thatcharacter, multiplied by factor. :align-to hpos Specifies that the space should be wide enough to reach hpos.If hpos is a number, it is measured in units of the normalcharacter width. hpos can also be a pixel widthspecification (see ). You should use one and only one of the above properties. You can also specify the height of the space, with these properties: :height height Specifies the height of the space.If height is an integer or floating point number, it specifiesthat the space height should be height times the normal characterheight. The height may also be a pixel height specification(see ). :relative-height factor Specifies the height of the space, multiplying the ordinary heightof the text having this display specification by factor. :ascent ascent If the value of ascent is a non-negative number no greater than100, it specifies that ascent percent of the height of the spaceshould be considered as the ascent of the space—that is, the partabove the baseline. The ascent may also be specified in pixel unitswith a pixel ascent specification (see ). Don't use both :height and :relative-height together. The :width and :align-to properties are supported on non-graphic terminals, but the other space properties in this section are not. Pixel Specification for Spaces spaces, pixel specification The value of the :width, :align-to, :height, and :ascent properties can be a special kind of expression that is evaluated during redisplay. The result of the evaluation is used as an absolute number of pixels. The following expressions are supported: expr ::= num | (num) | unit | elem | pos | image | form num ::= integer | float | symbol unit ::= in | mm | cm | width | height elem ::= left-fringe | right-fringe | left-margin | right-margin | scroll-bar | text pos ::= left | center | right form ::= (num . expr) | (op expr ...) op ::= + | - The form num specifies a fraction of the default frame font height or width. The form (num) specifies an absolute number of pixels. If num is a symbol, symbol, its buffer-local variable binding is used. The in, mm, and cm units specify the number of pixels per inch, millimeter, and centimeter, respectively. The width and height units correspond to the default width and height of the current face. An image specification image corresponds to the width or height of the image. The left-fringe, right-fringe, left-margin, right-margin, scroll-bar, and text elements specify to the width of the corresponding area of the window. The left, center, and right positions can be used with :align-to to specify a position relative to the left edge, center, or right edge of the text area. Any of the above window elements (except text) can also be used with :align-to to specify that the position is relative to the left edge of the given area. Once the base offset for a relative position has been set (by the first occurrence of one of these symbols), further occurrences of these symbols are interpreted as the width of the specified area. For example, to align to the center of the left-margin, use :align-to (+ left-margin (0.5 . left-margin)) If no specific base offset is set for alignment, it is always relative to the left edge of the text area. For example, ‘:align-to 0’ in a header-line aligns with the first text column in the text area. A value of the form (num . expr) stands for the product of the values of num and expr. For example, (2 . in) specifies a width of 2 inches, while (0.5 . image) specifies half the width (or height) of the specified image. The form (+ expr ...) adds up the value of the expressions. The form (- expr ...) negates or subtracts the value of the expressions. Other Display Specifications Here are the other sorts of display specifications that you can use in the display text property. string Display string instead of the text that has this property.Recursive display specifications are not supported—string'sdisplay properties, if any, are not used. (image . image-props) This kind of display specification is an image descriptor (see ).When used as a display specification, it means to display the imageinstead of the text that has the display specification. (slice x y width height) This specification together with image specifies a slice(a partial area) of the image to display. The elements y andx specify the top left corner of the slice, within the image;width and height specify the width and height of theslice. Integer values are numbers of pixels. A floating point numberin the range 0.0–1.0 stands for that fraction of the width or heightof the entire image. ((margin nil) string) A display specification of this form means to display stringinstead of the text that has the display specification, at the sameposition as that text. It is equivalent to using just string,but it is done as a special case of marginal display (see ). (space-width factor) This display specification affects all the space characters within thetext that has the specification. It displays all of these spacesfactor times as wide as normal. The element factor shouldbe an integer or float. Characters other than spaces are not affectedat all; in particular, this has no effect on tab characters. (height height) This display specification makes the text taller or shorter.Here are the possibilities for height: (+ n) This means to use a font that is n steps larger. A “step” isdefined by the set of available fonts—specifically, those that matchwhat was otherwise specified for this text, in all attributes exceptheight. Each size for which a suitable font is available counts asanother step. n should be an integer. (- n) This means to use a font that is n steps smaller. a number, factor A number, factor, means to use a font that is factor timesas tall as the default font. a symbol, function A symbol is a function to compute the height. It is called with thecurrent height as argument, and should return the new height to use. anything else, form If the height value doesn't fit the previous possibilities, it isa form. Emacs evaluates it to get the new height, with the symbolheight bound to the current specified font height. (raise factor) This kind of display specification raises or lowers the textit applies to, relative to the baseline of the line.factor must be a number, which is interpreted as a multiple of theheight of the affected text. If it is positive, that means to displaythe characters raised. If it is negative, that means to display themlower down.If the text also has a height display specification, that doesnot affect the amount of raising or lowering, which is based on thefaces used for the text. You can make any display specification conditional. To do that, package it in another list of the form (when condition . spec). Then the specification spec applies only when condition evaluates to a non-nil value. During the evaluation, object is bound to the string or buffer having the conditional display property. position and buffer-position are bound to the position within object and the buffer position where the display property was found, respectively. Both positions can be different when object is a string. Displaying in the Margins display margins margins, display A buffer can have blank areas called display margins on the left and on the right. Ordinary text never appears in these areas, but you can put things into the display margins using the display property. To put text in the left or right display margin of the window, use a display specification of the form (margin right-margin) or (margin left-margin) on it. To put an image in a display margin, use that display specification along with the display specification for the image. Unfortunately, there is currently no way to make text or images in the margin mouse-sensitive. If you put such a display specification directly on text in the buffer, the specified margin display appears instead of that buffer text itself. To put something in the margin in association with certain buffer text without preventing or altering the display of that text, put a before-string property on the text and put the display specification on the contents of the before-string. Before the display margins can display anything, you must give them a nonzero width. The usual way to do that is to set these variables: left-margin-width — Variable: left-margin-width This variable specifies the width of the left margin.It is buffer-local in all buffers. right-margin-width — Variable: right-margin-width This variable specifies the width of the right margin.It is buffer-local in all buffers. Setting these variables does not immediately affect the window. These variables are checked when a new buffer is displayed in the window. Thus, you can make changes take effect by calling set-window-buffer. You can also set the margin widths immediately. set-window-margins — Function: set-window-margins window left &optional right This function specifies the margin widths for window window.The argument left controls the left margin andright controls the right margin (default 0). window-margins — Function: window-margins &optional window This function returns the left and right margins of windowas a cons cell of the form (left . right).If window is nil, the selected window is used. Images images in buffers To display an image in an Emacs buffer, you must first create an image descriptor, then use it as a display specifier in the display property of text that is displayed (see ). Emacs is usually able to display images when it is run on a graphical terminal. Images cannot be displayed in a text terminal, on certain graphical terminals that lack the support for this, or if Emacs is compiled without image support. You can use the function display-images-p to determine if images can in principle be displayed (see ). Emacs can display a number of different image formats; some of them are supported only if particular support libraries are installed on your machine. In some environments, Emacs can load image libraries on demand; if so, the variable image-library-alist can be used to modify the set of known names for these dynamic libraries (though it is not possible to add new image formats). The supported image formats include XBM, XPM (this requires the libraries libXpm version 3.4k and libz), GIF (requiring libungif 4.1.0), PostScript, PBM, JPEG (requiring the libjpeg library version v6a), TIFF (requiring libtiff v3.4), and PNG (requiring libpng 1.0.2). You specify one of these formats with an image type symbol. The image type symbols are xbm, xpm, gif, postscript, pbm, jpeg, tiff, and png. image-types — Variable: image-types This variable contains a list of those image type symbols that arepotentially supported in the current configuration.Potentially here means that Emacs knows about the image types,not necessarily that they can be loaded (they could depend onunavailable dynamic libraries, for example).To know which image types are really available, useimage-type-available-p. image-library-alist — Variable: image-library-alist This in an alist of image types vs external libraries needed todisplay them.Each element is a list (image-type library...),where the car is a supported image format from image-types, andthe rest are strings giving alternate filenames for the correspondingexternal libraries to load.Emacs tries to load the libraries in the order they appear on thelist; if none is loaded, the running session of Emacs won't supportthe image type. pbm and xbm don't need to be listed;they're always supported.This variable is ignored if the image libraries are statically linkedinto Emacs. image-type-available-p — Function: image-type-available-p type image-type-available-pThis function returns non-nil if image type type isavailable, i.e., if images of this type can be loaded and displayed inEmacs. type should be one of the types contained inimage-types.For image types whose support libraries are statically linked, thisfunction always returns t; for other image types, it returnst if the dynamic library could be loaded, nil otherwise. Image Descriptors image descriptor An image description is a list of the form (image . props), where props is a property list containing alternating keyword symbols (symbols whose names start with a colon) and their values. You can use any Lisp object as a property, but the only properties that have any special meaning are certain symbols, all of them keywords. Every image descriptor must contain the property :type type to specify the format of the image. The value of type should be an image type symbol; for example, xpm for an image in XPM format. Here is a list of other properties that are meaningful for all image types: :file file The :file property says to load the image from filefile. If file is not an absolute file name, it is expandedin data-directory. :data data The :data property says the actual contents of the image.Each image must use either :data or :file, but not both.For most image types, the value of the :data property should be astring containing the image data; we recommend using a unibyte string.Before using :data, look for further information in the sectionbelow describing the specific image format. For some image types,:data may not be supported; for some, it allows other data types;for some, :data alone is not enough, so you need to use otherimage properties along with :data. :margin margin The :margin property specifies how many pixels to add as anextra margin around the image. The value, margin, must be anon-negative number, or a pair (x . y) of suchnumbers. If it is a pair, x specifies how many pixels to addhorizontally, and y specifies how many pixels to add vertically.If :margin is not specified, the default is zero. :ascent ascent The :ascent property specifies the amount of the image'sheight to use for its ascent—that is, the part above the baseline.The value, ascent, must be a number in the range 0 to 100, orthe symbol center.If ascent is a number, that percentage of the image's height isused for its ascent.If ascent is center, the image is vertically centeredaround a centerline which would be the vertical centerline of text drawnat the position of the image, in the manner specified by the textproperties and overlays that apply to the image.If this property is omitted, it defaults to 50. :relief relief The :relief property, if non-nil, adds a shadow rectanglearound the image. The value, relief, specifies the width of theshadow lines, in pixels. If relief is negative, shadows are drawnso that the image appears as a pressed button; otherwise, it appears asan unpressed button. :conversion algorithm The :conversion property, if non-nil, specifies aconversion algorithm that should be applied to the image before it isdisplayed; the value, algorithm, specifies which algorithm. laplaceemboss Specifies the Laplace edge detection algorithm, which blurs out smalldifferences in color while highlighting larger differences. Peoplesometimes consider this useful for displaying the image for a“disabled” button. (edge-detection :matrix matrix :color-adjust adjust) Specifies a general edge-detection algorithm. matrix must beeither a nine-element list or a nine-element vector of numbers. A pixelat position x/y in the transformed image is computed fromoriginal pixels around that position. matrix specifies, for eachpixel in the neighborhood of x/y, a factor with which that pixelwill influence the transformed pixel; element 0 specifies thefactor for the pixel at x-1/y-1, element 1 the factor forthe pixel at x/y-1 etc., as shown below: (x-1/y-1 x/y-1 x+1/y-1 x-1/y x/y x+1/y x-1/y+1 x/y+1 x+1/y+1) The resulting pixel is computed from the color intensity of the colorresulting from summing up the RGB values of surrounding pixels,multiplied by the specified factors, and dividing that sum by the sumof the factors' absolute values.Laplace edge-detection currently uses a matrix of (1 0 0 0 0 0 9 9 -1) Emboss edge-detection uses a matrix of ( 2 -1 0 -1 0 1 0 1 -2) disabled Specifies transforming the image so that it looks “disabled.” :mask mask If mask is heuristic or (heuristic bg), builda clipping mask for the image, so that the background of a frame isvisible behind the image. If bg is not specified, or if bgis t, determine the background color of the image by looking atthe four corners of the image, assuming the most frequently occurringcolor from the corners is the background color of the image. Otherwise,bg must be a list (red green blue)specifying the color to assume for the background of the image.If mask is nil, remove a mask from the image, if it hasone. Images in some formats include a mask which can be removed byspecifying :mask nil. :pointer shape This specifies the pointer shape when the mouse pointer is over thisimage. See , for available pointer shapes. :map map This associates an image map of hot spots with this image.An image map is an alist where each element has the format(area id plist). An area is specifiedas either a rectangle, a circle, or a polygon.A rectangle is a cons(rect . ((x0 . y0) . (x1 . y1)))which specifies the pixel coordinates of the upper left and bottom rightcorners of the rectangle area.A circle is a cons(circle . ((x0 . y0) . r))which specifies the center and the radius of the circle; r maybe a float or integer.A polygon is a cons(poly . [x0 y0 x1 y1 ...])where each pair in the vector describes one corner in the polygon.When the mouse pointer lies on a hot-spot area of an image, theplist of that hot-spot is consulted; if it contains a help-echoproperty, that defines a tool-tip for the hot-spot, and if it containsa pointer property, that defines the shape of the mouse cursor whenit is on the hot-spot.See , for available pointer shapes.When you click the mouse when the mouse pointer is over a hot-spot, anevent is composed by combining the id of the hot-spot with themouse event; for instance, [area4 mouse-1] if the hot-spot'sid is area4. image-mask-p — Function: image-mask-p spec &optional frame This function returns t if image spec has a mask bitmap.frame is the frame on which the image will be displayed.frame nil or omitted means to use the selected frame(see ). XBM Images XBM To use XBM format, specify xbm as the image type. This image format doesn't require an external library, so images of this type are always supported. Additional image properties supported for the xbm image type are: :foreground foreground The value, foreground, should be a string specifying the imageforeground color, or nil for the default color. This color isused for each pixel in the XBM that is 1. The default is the frame'sforeground color. :background background The value, background, should be a string specifying the imagebackground color, or nil for the default color. This color isused for each pixel in the XBM that is 0. The default is the frame'sbackground color. If you specify an XBM image using data within Emacs instead of an external file, use the following three properties: :data data The value, data, specifies the contents of the image.There are three formats you can use for data: A vector of strings or bool-vectors, each specifying one line of theimage. Do specify :height and :width. A string containing the same byte sequence as an XBM file would contain.You must not specify :height and :width in this case,because omitting them is what indicates the data has the format of anXBM file. The file contents specify the height and width of the image. A string or a bool-vector containing the bits of the image (plus perhapssome extra bits at the end that will not be used). It should contain atleast width * height bits. In this case, you must specify:height and :width, both to indicate that the stringcontains just the bits rather than a whole XBM file, and to specify thesize of the image. :width width The value, width, specifies the width of the image, in pixels. :height height The value, height, specifies the height of the image, in pixels. XPM Images XPM To use XPM format, specify xpm as the image type. The additional image property :color-symbols is also meaningful with the xpm image type: :color-symbols symbols The value, symbols, should be an alist whose elements have theform (name . color). In each element, name isthe name of a color as it appears in the image file, and colorspecifies the actual color to use for displaying that name. GIF Images GIF For GIF images, specify image type gif. :index index You can use :index to specify one image from a GIF file thatcontains more than one image. This property specifies use of imagenumber index from the file. If the GIF file doesn't contain animage with index index, the image displays as a hollow box. PostScript Images postscript images To use PostScript for an image, specify image type postscript. This works only if you have Ghostscript installed. You must always use these three properties: :pt-width width The value, width, specifies the width of the image measured inpoints (1/72 inch). width must be an integer. :pt-height height The value, height, specifies the height of the image in points(1/72 inch). height must be an integer. :bounding-box box The value, box, must be a list or vector of four integers, whichspecifying the bounding box of the PostScript image, analogous to the‘BoundingBox’ comment found in PostScript files. %%BoundingBox: 22 171 567 738 Displaying PostScript images from Lisp data is not currently implemented, but it may be implemented by the time you read this. See the etc/NEWS file to make sure. Other Image Types PBM For PBM images, specify image type pbm. Color, gray-scale and monochromatic images are supported. For mono PBM images, two additional image properties are supported. :foreground foreground The value, foreground, should be a string specifying the imageforeground color, or nil for the default color. This color isused for each pixel in the XBM that is 1. The default is the frame'sforeground color. :background background The value, background, should be a string specifying the imagebackground color, or nil for the default color. This color isused for each pixel in the XBM that is 0. The default is the frame'sbackground color. For JPEG images, specify image type jpeg. For TIFF images, specify image type tiff. For PNG images, specify image type png. Defining Images The functions create-image, defimage and find-image provide convenient ways to create image descriptors. create-image — Function: create-image file-or-data &optional type data-p &rest props This function creates and returns an image descriptor which uses thedata in file-or-data. file-or-data can be a file name ora string containing the image data; data-p should be nilfor the former case, non-nil for the latter case.The optional argument type is a symbol specifying the image type.If type is omitted or nil, create-image tries todetermine the image type from the file's first few bytes, or elsefrom the file's name.The remaining arguments, props, specify additional imageproperties—for example, (create-image "foo.xpm" 'xpm nil :heuristic-mask t) The function returns nil if images of this type are notsupported. Otherwise it returns an image descriptor. defimage — Macro: defimage symbol specs &optional doc This macro defines symbol as an image name. The argumentsspecs is a list which specifies how to display the image.The third argument, doc, is an optional documentation string.Each argument in specs has the form of a property list, and eachone should specify at least the :type property and either the:file or the :data property. The value of :typeshould be a symbol specifying the image type, the value of:file is the file to load the image from, and the value of:data is a string containing the actual image data. Here is anexample: (defimage test-image ((:type xpm :file "~/test1.xpm") (:type xbm :file "~/test1.xbm"))) defimage tests each argument, one by one, to see if it isusable—that is, if the type is supported and the file exists. Thefirst usable argument is used to make an image descriptor which isstored in symbol.If none of the alternatives will work, then symbol is definedas nil. find-image — Function: find-image specs This function provides a convenient way to find an image satisfying oneof a list of image specifications specs.Each specification in specs is a property list with contentsdepending on image type. All specifications must at least contain theproperties :type type and either :file fileor :data DATA, where type is a symbol specifyingthe image type, e.g. xbm, file is the file to load theimage from, and data is a string containing the actual image data.The first specification in the list whose type is supported, andfile exists, is used to construct the image specification to bereturned. If no specification is satisfied, nil is returned.The image is looked for in image-load-path. image-load-path — Variable: image-load-path This variable's value is a list of locations in which to search forimage files. If an element is a string or a variable symbol whosevalue is a string, the string is taken to be the name of a directoryto search. If an element is a variable symbol whose value is a list,that is taken to be a list of directory names to search.The default is to search in the images subdirectory of thedirectory specified by data-directory, then the directoryspecified by data-directory, and finally in the directories inload-path. Subdirectories are not automatically included inthe search, so if you put an image file in a subdirectory, you have tosupply the subdirectory name explicitly. For example, to find theimage images/foo/bar.xpm within data-directory, youshould specify the image as follows: (defimage foo-image '((:type xpm :file "foo/bar.xpm"))) image-load-path-for-library — Function: image-load-path-for-library library image &optional path no-error This function returns a suitable search path for images used by theLisp package library.The function searches for image first using image-load-path,excluding data-directory/images, and then inload-path, followed by a path suitable for library, whichincludes ../../etc/images and ../etc/images relative tothe library file itself, and finally indata-directory/images.Then this function returns a list of directories which contains firstthe directory in which image was found, followed by the value ofload-path. If path is given, it is used instead ofload-path.If no-error is non-nil and a suitable path can't befound, don't signal an error. Instead, return a list of directories asbefore, except that nil appears in place of the image directory.Here is an example that uses a common idiom to provide compatibilitywith versions of Emacs that lack the variable image-load-path: (defvar image-load-path) ; shush compiler (let* ((load-path (image-load-path-for-library "mh-e" "mh-logo.xpm")) (image-load-path (cons (car load-path) (when (boundp 'image-load-path) image-load-path)))) (mh-tool-bar-folder-buttons-init)) Showing Images You can use an image descriptor by setting up the display property yourself, but it is easier to use the functions in this section. insert-image — Function: insert-image image &optional string area slice This function inserts image in the current buffer at point. Thevalue image should be an image descriptor; it could be a valuereturned by create-image, or the value of a symbol defined withdefimage. The argument string specifies the text to putin the buffer to hold the image. If it is omitted or nil,insert-image uses " " by default.The argument area specifies whether to put the image in a margin.If it is left-margin, the image appears in the left margin;right-margin specifies the right margin. If area isnil or omitted, the image is displayed at point within thebuffer's text.The argument slice specifies a slice of the image to insert. Ifslice is nil or omitted the whole image is inserted.Otherwise, slice is a list (x y widthheight) which specifies the x and y positions andwidth and height of the image area to insert. Integervalues are in units of pixels. A floating point number in the range0.0–1.0 stands for that fraction of the width or height of the entireimage.Internally, this function inserts string in the buffer, and givesit a display property which specifies image. See . insert-sliced-image — Function: insert-sliced-image image &optional string area rows cols This function inserts image in the current buffer at point, likeinsert-image, but splits the image into rowsxcolsequally sized slices. put-image — Function: put-image image pos &optional string area This function puts image image in front of pos in thecurrent buffer. The argument pos should be an integer or amarker. It specifies the buffer position where the image should appear.The argument string specifies the text that should hold the imageas an alternative to the default.The argument image must be an image descriptor, perhaps returnedby create-image or stored by defimage.The argument area specifies whether to put the image in a margin.If it is left-margin, the image appears in the left margin;right-margin specifies the right margin. If area isnil or omitted, the image is displayed at point within thebuffer's text.Internally, this function creates an overlay, and gives it abefore-string property containing text that has a displayproperty whose value is the image. (Whew!) remove-images — Function: remove-images start end &optional buffer This function removes images in buffer between positionsstart and end. If buffer is omitted or nil,images are removed from the current buffer.This removes only images that were put into buffer the wayput-image does it, not images that were inserted withinsert-image or in other ways. image-size — Function: image-size spec &optional pixels frame This function returns the size of an image as a pair(width . height). spec is an imagespecification. pixels non-nil means return sizesmeasured in pixels, otherwise return sizes measured in canonicalcharacter units (fractions of the width/height of the frame's defaultfont). frame is the frame on which the image will be displayed.frame null or omitted means use the selected frame (see ). max-image-size — Variable: max-image-size This variable is used to define the maximum size of image that Emacswill load. Emacs will refuse to load (and display) any image that islarger than this limit.If the value is an integer, it directly specifies the maximumimage height and width, measured in pixels. If it is a floatingpoint number, it specifies the maximum image height and widthas a ratio to the frame height and width. If the value isnon-numeric, there is no explicit limit on the size of images.The purpose of this variable is to prevent unreasonably large imagesfrom accidentally being loaded into Emacs. It only takes effect thefirst time an image is loaded. Once an image is placed in the imagecache, it can always be displayed, even if the value ofmax-image-size is subsequently changed (see ). Image Cache image cache Emacs stores images in an image cache when it displays them, so it can display them again more efficiently. It removes an image from the cache when it hasn't been displayed for a specified period of time. When an image is looked up in the cache, its specification is compared with cached image specifications using equal. This means that all images with equal specifications share the same image in the cache. image-cache-eviction-delay — Variable: image-cache-eviction-delay This variable specifies the number of seconds an image can remain in thecache without being displayed. When an image is not displayed for thislength of time, Emacs removes it from the image cache.If the value is nil, Emacs does not remove images from the cacheexcept when you explicitly clear it. This mode can be useful fordebugging. clear-image-cache — Function: clear-image-cache &optional frame This function clears the image cache. If frame is non-nil,only the cache for that frame is cleared. Otherwise all frames' cachesare cleared. Buttons buttons in buffers clickable buttons in buffers The button package defines functions for inserting and manipulating clickable (with the mouse, or via keyboard commands) buttons in Emacs buffers, such as might be used for help hyper-links, etc. Emacs uses buttons for the hyper-links in help text and the like. A button is essentially a set of properties attached (via text properties or overlays) to a region of text in an Emacs buffer. These properties are called button properties. One of these properties (action) is a function, which will be called when the user invokes it using the keyboard or the mouse. The invoked function may then examine the button and use its other properties as desired. In some ways the Emacs button package duplicates functionality offered by the widget package (see See section ``Introduction'' in The Emacs Widget Library), but the button package has the advantage that it is much faster, much smaller, and much simpler to use (for elisp programmers—for users, the result is about the same). The extra speed and space savings are useful mainly if you need to create many buttons in a buffer (for instance an *Apropos* buffer uses buttons to make entries clickable, and may contain many thousands of entries). Button Properties button properties Buttons have an associated list of properties defining their appearance and behavior, and other arbitrary properties may be used for application specific purposes. Some properties that have special meaning to the button package include: action action (button property)The function to call when the user invokes the button, which is passedthe single argument button. By default this is ignore,which does nothing. mouse-action mouse-action (button property)This is similar to action, and when present, will be usedinstead of action for button invocations resulting frommouse-clicks (instead of the user hitting RET). If notpresent, mouse-clicks use action instead. face face (button property)This is an Emacs face controlling how buttons of this type aredisplayed; by default this is the button face. mouse-face mouse-face (button property)This is an additional face which controls appearance duringmouse-overs (merged with the usual button face); by default this isthe usual Emacs highlight face. keymap keymap (button property)The button's keymap, defining bindings active within the buttonregion. By default this is the usual button region keymap, storedin the variable button-map, which defines RET andmouse-2 to invoke the button. type type (button property)The button-type of the button. When creating a button, this isusually specified using the :type keyword argument.See . help-echo help-index (button property)A string displayed by the Emacs tool-tip help system; by default,"mouse-2, RET: Push this button". follow-link follow-link (button property)The follow-link property, defining how a Mouse-1 click behaveson this button, See . button button (button property)All buttons have a non-nil button property, which may be usefulin finding regions of text that comprise buttons (which is what thestandard button functions do). There are other properties defined for the regions of text in a button, but these are not generally interesting for typical uses. Button Types button types Every button has a button type, which defines default values for the button's properties. Button types are arranged in a hierarchy, with specialized types inheriting from more general types, so that it's easy to define special-purpose types of buttons for specific tasks. define-button-type — Function: define-button-type name &rest properties Define a `button type' called name. The remaining argumentsform a sequence of property value pairs, specifying defaultproperty values for buttons with this type (a button's type may be setby giving it a type property when creating the button, usingthe :type keyword argument).In addition, the keyword argument :supertype may be used tospecify a button-type from which name inherits its defaultproperty values. Note that this inheritance happens only whenname is defined; subsequent changes to a supertype are notreflected in its subtypes. Using define-button-type to define default properties for buttons is not necessary—buttons without any specified type use the built-in button-type button—but it is encouraged, since doing so usually makes the resulting code clearer and more efficient. Making Buttons making buttons Buttons are associated with a region of text, using an overlay or text properties to hold button-specific information, all of which are initialized from the button's type (which defaults to the built-in button type button). Like all Emacs text, the appearance of the button is governed by the face property; by default (via the face property inherited from the button button-type) this is a simple underline, like a typical web-page link. For convenience, there are two sorts of button-creation functions, those that add button properties to an existing region of a buffer, called make-...button, and those that also insert the button text, called insert-...button. The button-creation functions all take the &rest argument properties, which should be a sequence of property value pairs, specifying properties to add to the button; see . In addition, the keyword argument :type may be used to specify a button-type from which to inherit other properties; see . Any properties not explicitly specified during creation will be inherited from the button's type (if the type defines such a property). The following functions add a button using an overlay (see ) to hold the button properties: make-button — Function: make-button beg end &rest properties This makes a button from beg to end in thecurrent buffer, and returns it. insert-button — Function: insert-button label &rest properties This insert a button with the label label at point,and returns it. The following functions are similar, but use Emacs text properties (see ) to hold the button properties, making the button actually part of the text instead of being a property of the buffer. Buttons using text properties do not create markers into the buffer, which is important for speed when you use extremely large numbers of buttons. Both functions return the position of the start of the new button: make-text-button — Function: make-text-button beg end &rest properties This makes a button from beg to end in the current buffer, usingtext properties. insert-text-button — Function: insert-text-button label &rest properties This inserts a button with the label label at point, using textproperties. Manipulating Buttons manipulating buttons These are functions for getting and setting properties of buttons. Often these are used by a button's invocation function to determine what to do. Where a button parameter is specified, it means an object referring to a specific button, either an overlay (for overlay buttons), or a buffer-position or marker (for text property buttons). Such an object is passed as the first argument to a button's invocation function when it is invoked. button-start — Function: button-start button Return the position at which button starts. button-end — Function: button-end button Return the position at which button ends. button-get — Function: button-get button prop Get the property of button button named prop. button-put — Function: button-put button prop val Set button's prop property to val. button-activate — Function: button-activate button &optional use-mouse-action Call button's action property (i.e., invoke it). Ifuse-mouse-action is non-nil, try to invoke the button'smouse-action property instead of action; if the buttonhas no mouse-action property, use action as normal. button-label — Function: button-label button Return button's text label. button-type — Function: button-type button Return button's button-type. button-has-type-p — Function: button-has-type-p button type Return t if button has button-type type, or one oftype's subtypes. button-at — Function: button-at pos Return the button at position pos in the current buffer, or nil. button-type-put — Function: button-type-put type prop val Set the button-type type's prop property to val. button-type-get — Function: button-type-get type prop Get the property of button-type type named prop. button-type-subtype-p — Function: button-type-subtype-p type supertype Return t if button-type type is a subtype of supertype. Button Buffer Commands button buffer commands These are commands and functions for locating and operating on buttons in an Emacs buffer. push-button is the command that a user uses to actually `push' a button, and is bound by default in the button itself to RET and to mouse-2 using a region-specific keymap. Commands that are useful outside the buttons itself, such as forward-button and backward-button are additionally available in the keymap stored in button-buffer-map; a mode which uses buttons may want to use button-buffer-map as a parent keymap for its keymap. If the button has a non-nil follow-link property, and mouse-1-click-follows-link is set, a quick Mouse-1 click will also activate the push-button command. See . push-button — Command: push-button &optional pos use-mouse-action Perform the action specified by a button at location pos.pos may be either a buffer position or a mouse-event. Ifuse-mouse-action is non-nil, or pos is amouse-event (see ), try to invoke the button'smouse-action property instead of action; if the buttonhas no mouse-action property, use action as normal.pos defaults to point, except when push-button is invokedinteractively as the result of a mouse-event, in which case, the mouseevent's position is used. If there's no button at pos, donothing and return nil, otherwise return t. forward-button — Command: forward-button n &optional wrap display-message Move to the nth next button, or nth previous button ifn is negative. If n is zero, move to the start of anybutton at point. If wrap is non-nil, moving past eitherend of the buffer continues from the other end. Ifdisplay-message is non-nil, the button's help-echo stringis displayed. Any button with a non-nil skip propertyis skipped over. Returns the button found. backward-button — Command: backward-button n &optional wrap display-message Move to the nth previous button, or nth next button ifn is negative. If n is zero, move to the start of anybutton at point. If wrap is non-nil, moving past eitherend of the buffer continues from the other end. Ifdisplay-message is non-nil, the button's help-echo stringis displayed. Any button with a non-nil skip propertyis skipped over. Returns the button found. next-button — Function: next-button pos &optional count-current previous-button — Function: previous-button pos &optional count-current Return the next button after (for next-button or before (forprevious-button) position pos in the current buffer. Ifcount-current is non-nil, count any button at posin the search, instead of starting at the next button. Abstract Display ewoc display, abstract display, arbitrary objects model/view/controller view part, model/view/controller The Ewoc package constructs buffer text that represents a structure of Lisp objects, and updates the text to follow changes in that structure. This is like the “view” component in the “model/view/controller” design paradigm. An ewoc is a structure that organizes information required to construct buffer text that represents certain Lisp data. The buffer text of the ewoc has three parts, in order: first, fixed header text; next, textual descriptions of a series of data elements (Lisp objects that you specify); and last, fixed footer text. Specifically, an ewoc contains information on: The buffer which its text is generated in. The text's start position in the buffer. The header and footer strings. A doubly-linked chain of nodes, each of which contains: A data element, a single Lisp object. Links to the preceding and following nodes in the chain. A pretty-printer function which is responsible forinserting the textual representation of a dataelement value into the current buffer. Typically, you define an ewoc with ewoc-create, and then pass the resulting ewoc structure to other functions in the Ewoc package to build nodes within it, and display it in the buffer. Once it is displayed in the buffer, other functions determine the correspondance between buffer positions and nodes, move point from one node's textual representation to another, and so forth. See . A node encapsulates a data element much the way a variable holds a value. Normally, encapsulation occurs as a part of adding a node to the ewoc. You can retrieve the data element value and place a new value in its place, like so:(ewoc-data node) => value (ewoc-set-data node new-value) => new-value You can also use, as the data element value, a Lisp object (list or vector) that is a container for the “real” value, or an index into some other structure. The example (see ) uses the latter approach. When the data changes, you will want to update the text in the buffer. You can update all nodes by calling ewoc-refresh, or just specific nodes using ewoc-invalidate, or all nodes satisfying a predicate using ewoc-map. Alternatively, you can delete invalid nodes using ewoc-delete or ewoc-filter, and add new nodes in their place. Deleting a node from an ewoc deletes its associated textual description from buffer, as well. Abstract Display Functions In this subsection, ewoc and node stand for the structures described above (see ), while data stands for an arbitrary Lisp object used as a data element. ewoc-create — Function: ewoc-create pretty-printer &optional header footer nosep This constructs and returns a new ewoc, with no nodes (and thus no dataelements). pretty-printer should be a function that takes oneargument, a data element of the sort you plan to use in this ewoc, andinserts its textual description at point using insert (and neverinsert-before-markers, because that would interfere with theEwoc package's internal mechanisms).Normally, a newline is automatically inserted after the header,the footer and every node's textual description. If nosepis non-nil, no newline is inserted. This may be useful fordisplaying an entire ewoc on a single line, for example, or formaking nodes “invisible” by arranging for pretty-printerto do nothing for those nodes.An ewoc maintains its text in the buffer that is current whenyou create it, so switch to the intended buffer before callingewoc-create. ewoc-buffer — Function: ewoc-buffer ewoc This returns the buffer where ewoc maintains its text. ewoc-get-hf — Function: ewoc-get-hf ewoc This returns a cons cell (header . footer)made from ewoc's header and footer. ewoc-set-hf — Function: ewoc-set-hf ewoc header footer This sets the header and footer of ewoc to the stringsheader and footer, respectively. ewoc-enter-first — Function: ewoc-enter-first ewoc data ewoc-enter-last — Function: ewoc-enter-last ewoc data These add a new node encapsulating data, putting it, respectively,at the beginning or end of ewoc's chain of nodes. ewoc-enter-before — Function: ewoc-enter-before ewoc node data ewoc-enter-after — Function: ewoc-enter-after ewoc node data These add a new node encapsulating data, adding it toewoc before or after node, respectively. ewoc-prev — Function: ewoc-prev ewoc node ewoc-next — Function: ewoc-next ewoc node These return, respectively, the previous node and the next node of nodein ewoc. ewoc-nth — Function: ewoc-nth ewoc n This returns the node in ewoc found at zero-based index n.A negative n means count from the end. ewoc-nth returnsnil if n is out of range. ewoc-data — Function: ewoc-data node This extracts the data encapsulated by node and returns it. ewoc-set-data — Function: ewoc-set-data node data This sets the data encapsulated by node to data. ewoc-locate — Function: ewoc-locate ewoc &optional pos guess This determines the node in ewoc which contains point (orpos if specified), and returns that node. If ewoc has nonodes, it returns nil. If pos is before the first node,it returns the first node; if pos is after the last node, it returnsthe last node. The optional third arg guessshould be a node that is likely to be near pos; this doesn'talter the result, but makes the function run faster. ewoc-location — Function: ewoc-location node This returns the start position of node. ewoc-goto-prev — Function: ewoc-goto-prev ewoc arg ewoc-goto-next — Function: ewoc-goto-next ewoc arg These move point to the previous or next, respectively, argth nodein ewoc. ewoc-goto-prev does not move if it is already atthe first node or if ewoc is empty, whereas ewoc-goto-nextmoves past the last node, returning nil. Excepting this specialcase, these functions return the node moved to. ewoc-goto-node — Function: ewoc-goto-node ewoc node This moves point to the start of node in ewoc. ewoc-refresh — Function: ewoc-refresh ewoc This function regenerates the text of ewoc. It works bydeleting the text between the header and the footer, i.e., all thedata elements' representations, and then calling the pretty-printerfunction for each node, one by one, in order. ewoc-invalidate — Function: ewoc-invalidate ewoc &rest nodes This is similar to ewoc-refresh, except that only nodes inewoc are updated instead of the entire set. ewoc-delete — Function: ewoc-delete ewoc &rest nodes This deletes each node in nodes from ewoc. ewoc-filter — Function: ewoc-filter ewoc predicate &rest args This calls predicate for each data element in ewoc anddeletes those nodes for which predicate returns nil.Any args are passed to predicate. ewoc-collect — Function: ewoc-collect ewoc predicate &rest args This calls predicate for each data element in ewocand returns a list of those elements for which predicatereturns non-nil. The elements in the list are orderedas in the buffer. Any args are passed to predicate. ewoc-map — Function: ewoc-map map-function ewoc &rest args This calls map-function for each data element in ewoc andupdates those nodes for which map-function returns non-nil.Any args are passed to map-function. Abstract Display Example Here is a simple example using functions of the ewoc package to implement a “color components display,” an area in a buffer that represents a vector of three integers (itself representing a 24-bit RGB value) in various ways. (setq colorcomp-ewoc nil colorcomp-data nil colorcomp-mode-map nil colorcomp-labels ["Red" "Green" "Blue"]) (defun colorcomp-pp (data) (if data (let ((comp (aref colorcomp-data data))) (insert (aref colorcomp-labels data) "\t: #x" (format "%02X" comp) " " (make-string (ash comp -2) ?#) "\n")) (let ((cstr (format "#%02X%02X%02X" (aref colorcomp-data 0) (aref colorcomp-data 1) (aref colorcomp-data 2))) (samp " (sample text) ")) (insert "Color\t: " (propertize samp 'face `(foreground-color . ,cstr)) (propertize samp 'face `(background-color . ,cstr)) "\n")))) (defun colorcomp (color) "Allow fiddling with COLOR in a new buffer. The buffer is in Color Components mode." (interactive "sColor (name or #RGB or #RRGGBB): ") (when (string= "" color) (setq color "green")) (unless (color-values color) (error "No such color: %S" color)) (switch-to-buffer (generate-new-buffer (format "originally: %s" color))) (kill-all-local-variables) (setq major-mode 'colorcomp-mode mode-name "Color Components") (use-local-map colorcomp-mode-map) (erase-buffer) (buffer-disable-undo) (let ((data (apply 'vector (mapcar (lambda (n) (ash n -8)) (color-values color)))) (ewoc (ewoc-create 'colorcomp-pp "\nColor Components\n\n" (substitute-command-keys "\n\\{colorcomp-mode-map}")))) (set (make-local-variable 'colorcomp-data) data) (set (make-local-variable 'colorcomp-ewoc) ewoc) (ewoc-enter-last ewoc 0) (ewoc-enter-last ewoc 1) (ewoc-enter-last ewoc 2) (ewoc-enter-last ewoc nil))) controller part, model/view/controller This example can be extended to be a “color selection widget” (in other words, the controller part of the “model/view/controller” design paradigm) by defining commands to modify colorcomp-data and to “finish” the selection process, and a keymap to tie it all together conveniently. (defun colorcomp-mod (index limit delta) (let ((cur (aref colorcomp-data index))) (unless (= limit cur) (aset colorcomp-data index (+ cur delta))) (ewoc-invalidate colorcomp-ewoc (ewoc-nth colorcomp-ewoc index) (ewoc-nth colorcomp-ewoc -1)))) (defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1)) (defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1)) (defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1)) (defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1)) (defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1)) (defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1)) (defun colorcomp-copy-as-kill-and-exit () "Copy the color components into the kill ring and kill the buffer. The string is formatted #RRGGBB (hash followed by six hex digits)." (interactive) (kill-new (format "#%02X%02X%02X" (aref colorcomp-data 0) (aref colorcomp-data 1) (aref colorcomp-data 2))) (kill-buffer nil)) (setq colorcomp-mode-map (let ((m (make-sparse-keymap))) (suppress-keymap m) (define-key m "i" 'colorcomp-R-less) (define-key m "o" 'colorcomp-R-more) (define-key m "k" 'colorcomp-G-less) (define-key m "l" 'colorcomp-G-more) (define-key m "," 'colorcomp-B-less) (define-key m "." 'colorcomp-B-more) (define-key m " " 'colorcomp-copy-as-kill-and-exit) m)) Note that we never modify the data in each node, which is fixed when the ewoc is created to be either nil or an index into the vector colorcomp-data, the actual color components. Blinking Parentheses parenthesis matching blinking parentheses balancing parentheses This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis. blink-paren-function — Variable: blink-paren-function The value of this variable should be a function (of no arguments) tobe called whenever a character with close parenthesis syntax is inserted.The value of blink-paren-function may be nil, in whichcase nothing is done. blink-matching-paren — User Option: blink-matching-paren If this variable is nil, then blink-matching-open doesnothing. blink-matching-paren-distance — User Option: blink-matching-paren-distance This variable specifies the maximum distance to scan for a matchingparenthesis before giving up. blink-matching-delay — User Option: blink-matching-delay This variable specifies the number of seconds for the cursor to remainat the matching parenthesis. A fraction of a second often givesgood results, but the default is 1, which works on all systems. blink-matching-open — Command: blink-matching-open This function is the default value of blink-paren-function. Itassumes that point follows a character with close parenthesis syntax andmoves the cursor momentarily to the matching opening character. If thatcharacter is not already on the screen, it displays the character'scontext in the echo area. To avoid long delays, this function does notsearch farther than blink-matching-paren-distance characters.Here is an example of calling this function explicitly. (defun interactive-blink-matching-open () "Indicate momentarily the start of sexp before point." (interactive) (let ((blink-matching-paren-distance (buffer-size)) (blink-matching-paren t)) (blink-matching-open))) Usual Display Conventions The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see ). Here are the usual display conventions: Character codes 32 through 126 map to glyph codes 32 through 126.Normally this means they display as themselves. Character code 9 is a horizontal tab. It displays as whitespaceup to a position determined by tab-width. Character code 10 is a newline. All other codes in the range 0 through 31, and code 127, display in oneof two ways according to the value of ctl-arrow. If it isnon-nil, these codes map to sequences of two glyphs, where thefirst glyph is the ASCII code for ‘^’. (A display table canspecify a glyph to use instead of ‘^’.) Otherwise, these codes mapjust like the codes in the range 128 to 255.On MS-DOS terminals, Emacs arranges by default for the character code127 to be mapped to the glyph code 127, which normally displays as anempty polygon. This glyph is used to display non-ASCII charactersthat the MS-DOS terminal doesn't support. See See section ``MS-DOS and MULE'' in The GNU Emacs Manual. Character codes 128 through 255 map to sequences of four glyphs, wherethe first glyph is the ASCII code for ‘\’, and the others aredigit characters representing the character code in octal. (A displaytable can specify a glyph to use instead of ‘\’.) Multibyte character codes above 256 are displayed as themselves, or as aquestion mark or empty box if the terminal cannot display thatcharacter. The usual display conventions apply even when there is a display table, for any character whose entry in the active display table is nil. Thus, when you set up a display table, you need only specify the characters for which you want special behavior. These display rules apply to carriage return (character code 13), when it appears in the buffer. But that character may not appear in the buffer where you expect it, if it was eliminated as part of end-of-line conversion (see ). These variables affect the way certain characters are displayed on the screen. Since they change the number of columns the characters occupy, they also affect the indentation functions. These variables also affect how the mode line is displayed; if you want to force redisplay of the mode line using the new values, call the function force-mode-line-update (see ). ctl-arrow — User Option: ctl-arrow control characters in displayThis buffer-local variable controls how control characters aredisplayed. If it is non-nil, they are displayed as a caretfollowed by the character: ‘^A’. If it is nil, they aredisplayed as a backslash followed by three octal digits: ‘\001’. default-ctl-arrow — Variable: default-ctl-arrow The value of this variable is the default value for ctl-arrow inbuffers that do not override it. See . tab-width — User Option: tab-width The value of this buffer-local variable is the spacing between tabstops used for displaying tab characters in Emacs buffers. The valueis in units of columns, and the default is 8. Note that this featureis completely independent of the user-settable tab stops used by thecommand tab-to-tab-stop. See . Display Tables display table You can use the display table feature to control how all possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set. The display table maps each character code into a sequence of glyphs, each glyph being a graphic that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table. Display tables affect how the mode line is displayed; if you want to force redisplay of the mode line using a new display table, call force-mode-line-update (see ). Display Table Format A display table is actually a char-table (see ) with display-table as its subtype. make-display-table — Function: make-display-table This creates and returns a display table. The table initially hasnil in all elements. The ordinary elements of the display table are indexed by character codes; the element at index c says how to display the character code c. The value should be nil or a vector of the glyphs to be output (see ). nil says to display the character c according to the usual display conventions (see ). Warning: if you use the display table to change the display of newline characters, the whole buffer will be displayed as one long “line.” The display table also has six “extra slots” which serve special purposes. Here is a table of their meanings; nil in any slot means to use the default for that slot, as stated below. 0 The glyph for the end of a truncated screen line (the default for thisis ‘$’). See . On graphical terminals, Emacs usesarrows in the fringes to indicate truncation, so the display table hasno effect. 1 The glyph for the end of a continued line (the default is ‘\’).On graphical terminals, Emacs uses curved arrows in the fringes toindicate continuation, so the display table has no effect. 2 The glyph for indicating a character displayed as an octal charactercode (the default is ‘\’). 3 The glyph for indicating a control character (the default is ‘^’). 4 A vector of glyphs for indicating the presence of invisible lines (thedefault is ‘...’). See . 5 The glyph used to draw the border between side-by-side windows (thedefault is ‘|’). See . This takes effect onlywhen there are no scroll bars; if scroll bars are supported and in use,a scroll bar separates the two windows. For example, here is how to construct a display table that mimics the effect of setting ctl-arrow to a non-nil value: (setq disptab (make-display-table)) (let ((i 0)) (while (< i 32) (or (= i ?\t) (= i ?\n) (aset disptab i (vector ?^ (+ i 64)))) (setq i (1+ i))) (aset disptab 127 (vector ?^ ??))) display-table-slot — Function: display-table-slot display-table slot This function returns the value of the extra slot slot ofdisplay-table. The argument slot may be a number from 0 to5 inclusive, or a slot name (symbol). Valid symbols aretruncation, wrap, escape, control,selective-display, and vertical-border. set-display-table-slot — Function: set-display-table-slot display-table slot value This function stores value in the extra slot slot ofdisplay-table. The argument slot may be a number from 0 to5 inclusive, or a slot name (symbol). Valid symbols aretruncation, wrap, escape, control,selective-display, and vertical-border. describe-display-table — Function: describe-display-table display-table This function displays a description of the display tabledisplay-table in a help buffer. describe-current-display-table — Command: describe-current-display-table This command displays a description of the current display table in ahelp buffer. Active Display Table active display table Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table. window-display-table — Function: window-display-table &optional window This function returns window's display table, or nilif window does not have an assigned display table. The defaultfor window is the selected window. set-window-display-table — Function: set-window-display-table window table This function sets the display table of window to table.The argument table should be either a display table ornil. buffer-display-table — Variable: buffer-display-table This variable is automatically buffer-local in all buffers; its value ina particular buffer specifies the display table for that buffer. If itis nil, that means the buffer does not have an assigned displaytable. standard-display-table — Variable: standard-display-table This variable's value is the default display table, used whenever awindow has no display table and neither does the buffer displayed inthat window. This variable is nil by default. If there is no display table to use for a particular window—that is, if the window specifies none, its buffer specifies none, and standard-display-table is nil—then Emacs uses the usual display conventions for all character codes in that window. See . A number of functions for changing the standard display table are defined in the library disp-table. Glyphs glyph A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Normally glyphs come from vectors in the display table (see ). A glyph is represented in Lisp as a glyph code. A glyph code can be simple or it can be defined by the glyph table. A simple glyph code is just a way of specifying a character and a face to output it in. See . The following functions are used to manipulate simple glyph codes: make-glyph-code — Function: make-glyph-code char &optional face This function returns a simple glyph code representing char charwith face face. glyph-char — Function: glyph-char glyph This function returns the character of simple glyph code glyph. glyph-face — Function: glyph-face glyph This function returns face of simple glyph code glyph, ornil if glyph has the default face (face-id 0). On character terminals, you can set up a glyph table to define the meaning of glyph codes (represented as small integers). glyph-table — Variable: glyph-table The value of this variable is the current glyph table. It should benil or a vector whose gth element defines glyph codeg.If a glyph code is greater than or equal to the length of the glyphtable, that code is automatically simple. If glyph-table isnil then all glyph codes are simple.The glyph table is used only on character terminals. On graphicaldisplays, all glyph codes are simple. Here are the meaningful types of elements in the glyph table: string Send the characters in string to the terminal to outputthis glyph code. code Define this glyph code as an alias for glyph code code createdby make-glyph-code. You can use such an alias to define asmall-numbered glyph code which specifies a character with a face. nil This glyph code is simple. create-glyph — Function: create-glyph string This function returns a newly-allocated glyph code which is set up todisplay by sending string to the terminal. Beeping bell This section describes how to make Emacs ring the bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use just beeping when signaling an error is more appropriate. (See .) ding — Function: ding &optional do-not-terminate keyboard macro terminationThis function beeps, or flashes the screen (see visible-bell below).It also terminates any keyboard macro currently executing unlessdo-not-terminate is non-nil. beep — Function: beep &optional do-not-terminate This is a synonym for ding. visible-bell — User Option: visible-bell This variable determines whether Emacs should flash the screen torepresent a bell. Non-nil means yes, nil means no. Thisis effective on graphical displays, and on text-only terminalsprovided the terminal's Termcap entry defines the visible bellcapability (‘vb’). ring-bell-function — Variable: ring-bell-function If this is non-nil, it specifies how Emacs should “ring thebell.” Its value should be a function of no arguments. If this isnon-nil, it takes precedence over the visible-bellvariable. Window Systems Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term “window,” but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all. window-system — Variable: window-system This variable tells Lisp programs what window system Emacs is runningunder. The possible values are x X Window SystemEmacs is displaying using X. pc Emacs is displaying using MS-DOS. w32 Emacs is displaying using Windows. mac Emacs is displaying using a Macintosh. nil Emacs is using a character-based terminal. window-setup-hook — Variable: window-setup-hook This variable is a normal hook which Emacs runs after handling theinitialization files. Emacs runs this hook after it has completedloading your init file, the default initialization file (ifany), and the terminal-specific Lisp code, and running the hookterm-setup-hook.This hook is used for internal purposes: setting up communication withthe window system, and creating the initial window. Users should notinterfere with it. <setfilename>../info/os</setfilename> Operating System Interface This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output, and flow control. See , for related information. See also , for additional operating system status information pertaining to the terminal and the screen. Starting Up Emacs This section describes what Emacs does when it is started, and how you can customize these actions. Summary: Sequence of Actions at Startup initialization of Emacs startup of Emacs startup.el The order of operations performed (in startup.el) by Emacs when it is started up is as follows: It adds subdirectories to load-path, by running the file namedsubdirs.el in each directory in the list. Normally this fileadds the directory's subdirectories to the list, and these will bescanned in their turn. The files subdirs.el are normallygenerated automatically by Emacs installation. It sets the language environment and the terminal coding system,if requested by environment variables such as LANG. It loads the initialization library for the window system, if you areusing a window system. This library's name isterm/windowsystem-win.el. It processes the initial options. (Some of them are handledeven earlier than this.) It initializes the window frame and faces, if appropriate. It runs the normal hook before-init-hook. It loads the library site-start (if any), unless the option‘-Q’ (or ‘--no-site-file’) was specified. The library's filename is usually site-start.el. site-start.el It loads your init file (usually ~/.emacs), unless the option‘-q’ (or ‘--no-init-file’), ‘-Q’, or ‘--batch’ wasspecified on the command line. The ‘-u’ option can specifyanother user whose home directory should be used instead of ~. It loads the library default (if any), unlessinhibit-default-init is non-nil. (This is not done in‘-batch’ mode, or if ‘-Q’ or ‘-q’ was specified on thecommand line.) The library's file name is usually default.el. default.el It runs the normal hook after-init-hook. It sets the major mode according to initial-major-mode, providedthe buffer ‘*scratch*’ is still current and still in Fundamentalmode. It loads the terminal-specific Lisp file, if any, except when in batchmode or using a window system. It displays the initial echo area message, unless you have suppressedthat with inhibit-startup-echo-area-message. It processes the action arguments from the command line. It runs emacs-startup-hook and then term-setup-hook. It calls frame-notice-user-settings, which modifies theparameters of the selected frame according to whatever the init filesspecify. It runs window-setup-hook. See . It displays copyleft, nonwarranty, and basic use information, providedthe value of inhibit-startup-message is nil, you didn'tspecify ‘--no-splash’ or ‘-Q’. inhibit-startup-message — User Option: inhibit-startup-message This variable inhibits the initial startup messages (the nonwarranty,etc.). If it is non-nil, then the messages are not printed.This variable exists so you can set it in your personal init file, onceyou are familiar with the contents of the startup message. Do not setthis variable in the init file of a new user, or in a way that affectsmore than one user, because that would prevent new users from receivingthe information they are supposed to see. inhibit-startup-echo-area-message — User Option: inhibit-startup-echo-area-message This variable controls the display of the startup echo area message.You can suppress the startup echo area message by adding text with thisform to your init file: (setq inhibit-startup-echo-area-message "your-login-name") Emacs explicitly checks for an expression as shown above in your initfile; your login name must appear in the expression as a Lisp stringconstant. Other methods of settinginhibit-startup-echo-area-message to the same value do notinhibit the startup message.This way, you can easily inhibit the message for yourself if you wish,but thoughtless copying of your init file will not inhibit the messagefor someone else. The Init File, .emacs init file .emacs When you start Emacs, it normally attempts to load your init file, a file in your home directory. Its normal name is .emacs, but you can also call it .emacs.el. Alternatively, you can use a file named init.el in a subdirectory .emacs.d. Whichever place you use, you can also compile the file (see ); then the actual file loaded will be .emacs.elc or init.elc. The command-line switches ‘-q’, ‘-Q’, and ‘-u’ control whether and where to find the init file; ‘-q’ (and the stronger ‘-Q’) says not to load an init file, while ‘-u user’ says to load user's init file instead of yours. See See section ``Entering Emacs'' in The GNU Emacs Manual. If neither option is specified, Emacs uses the LOGNAME environment variable, or the USER (most systems) or USERNAME (MS systems) variable, to find your home directory and thus your init file; this way, even if you have su'd, Emacs still loads your own init file. If those environment variables are absent, though, Emacs uses your user-id to find your home directory. default init file A site may have a default init file, which is the library named default.el. Emacs finds the default.el file through the standard search path for libraries (see ). The Emacs distribution does not come with this file; sites may provide one for local customizations. If the default init file exists, it is loaded whenever you start Emacs, except in batch mode or if ‘-q’ (or ‘-Q’) is specified. But your own personal init file, if any, is loaded first; if it sets inhibit-default-init to a non-nil value, then Emacs does not subsequently load the default.el file. Another file for site-customization is site-start.el. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option ‘--no-site-file’. site-run-file — Variable: site-run-file This variable specifies the site-customization file to load before theuser's init file. Its normal value is "site-start". The onlyway you can change it with real effect is to do so before dumpingEmacs. See See section ``Init File Examples'' in The GNU Emacs Manual, for examples of how to make various commonly desired customizations in your .emacs file. inhibit-default-init — User Option: inhibit-default-init This variable prevents Emacs from loading the default initializationlibrary file for your session of Emacs. If its value is non-nil,then the default library is not loaded. The default value isnil. before-init-hook — Variable: before-init-hook This normal hook is run, once, just before loading all the init files(the user's init file, default.el, and/or site-start.el).(The only way to change it with real effect is before dumping Emacs.) after-init-hook — Variable: after-init-hook This normal hook is run, once, just after loading all the init files(the user's init file, default.el, and/or site-start.el),before loading the terminal-specific library and processing thecommand-line action arguments. emacs-startup-hook — Variable: emacs-startup-hook This normal hook is run, once, just after handling the command linearguments, just before term-setup-hook. user-init-file — Variable: user-init-file This variable holds the absolute file name of the user's init file. If theactual init file loaded is a compiled file, such as .emacs.elc,the value refers to the corresponding source file. Terminal-Specific Initialization terminal-specific initialization Each terminal type can have its own Lisp library that Emacs loads when run on that type of terminal. The library's name is constructed by concatenating the value of the variable term-file-prefix and the terminal type (specified by the environment variable TERM). Normally, term-file-prefix has the value "term/"; changing this is not recommended. Emacs finds the file in the normal manner, by searching the load-path directories, and trying the ‘.elc’ and ‘.el’ suffixes. Termcap The usual function of a terminal-specific library is to enable special keys to send sequences that Emacs can recognize. It may also need to set or add to function-key-map if the Termcap or Terminfo entry does not specify all the terminal's function keys. See . When the name of the terminal type contains a hyphen, and no library is found whose name is identical to the terminal's name, Emacs strips from the terminal's name the last hyphen and everything that follows it, and tries again. This process is repeated until Emacs finds a matching library or until there are no more hyphens in the name (the latter means the terminal doesn't have any library specific to it). Thus, for example, if there are no ‘aaa-48’ and ‘aaa-30’ libraries, Emacs will try the same library term/aaa.el for terminal types ‘aaa-48’ and ‘aaa-30-rv’. If necessary, the library can evaluate (getenv "TERM") to find the full name of the terminal type. Your init file can prevent the loading of the terminal-specific library by setting the variable term-file-prefix to nil. This feature is useful when experimenting with your own peculiar customizations. You can also arrange to override some of the actions of the terminal-specific library by setting the variable term-setup-hook. This is a normal hook which Emacs runs using run-hooks at the end of Emacs initialization, after loading both your init file and any terminal-specific libraries. You can use this variable to define initializations for terminals that do not have their own libraries. See . term-file-prefix — Variable: term-file-prefix TERM environment variableIf the term-file-prefix variable is non-nil, Emacs loadsa terminal-specific initialization file as follows: (load (concat term-file-prefix (getenv "TERM"))) You may set the term-file-prefix variable to nil in yourinit file if you do not wish to load theterminal-initialization file. To do this, put the following inyour init file: (setq term-file-prefix nil).On MS-DOS, if the environment variable TERM is not set, Emacsuses ‘internal’ as the terminal type. term-setup-hook — Variable: term-setup-hook This variable is a normal hook that Emacs runs after loading yourinit file, the default initialization file (if any) and theterminal-specific Lisp file.You can use term-setup-hook to override the definitions made by aterminal-specific file. See window-setup-hook in , for a related feature. Command-Line Arguments command-line arguments You can use command-line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command-line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs. This section describes how Emacs processes command-line arguments, and how you can customize them. command-line — Function: command-line This function parses the command line that Emacs was called with,processes it, loads the user's init file and displays thestartup messages. command-line-processed — Variable: command-line-processed The value of this variable is t once the command line has beenprocessed.If you redump Emacs by calling dump-emacs, you may wish to setthis variable to nil first in order to cause the new dumped Emacsto process its new command-line arguments. command-switch-alist — Variable: command-switch-alist switches on command line options on command line command-line optionsThe value of this variable is an alist of user-defined command-lineoptions and associated handler functions. This variable exists so youcan add elements to it.A command-line option is an argument on the command line, whichhas the form: -option The elements of the command-switch-alist look like this: (option . handler-function) The car, option, is a string, the name of a command-lineoption (not including the initial hyphen). The handler-functionis called to handle option, and receives the option name as itssole argument.In some cases, the option is followed in the command line by anargument. In these cases, the handler-function can find all theremaining command-line arguments in the variablecommand-line-args-left. (The entire list of command-linearguments is in command-line-args.)The command-line arguments are parsed by the command-line-1function in the startup.el file. See also See section ``Command Line Arguments for Emacs Invocation'' in The GNU Emacs Manual. command-line-args — Variable: command-line-args The value of this variable is the list of command-line arguments passedto Emacs. command-line-functions — Variable: command-line-functions This variable's value is a list of functions for handling anunrecognized command-line argument. Each time the next argument to beprocessed has no special meaning, the functions in this list are called,in order of appearance, until one of them returns a non-nilvalue.These functions are called with no arguments. They can access thecommand-line argument under consideration through the variableargi, which is bound temporarily at this point. The remainingarguments (not including the current one) are in the variablecommand-line-args-left.When a function recognizes and processes the argument in argi, itshould return a non-nil value to say it has dealt with thatargument. If it has also dealt with some of the following arguments, itcan indicate that by deleting them from command-line-args-left.If all of these functions return nil, then the argument is usedas a file name to visit. Getting Out of Emacs exiting Emacs There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs—only when you are about to log out. Suspending is much more common. Killing Emacs killing Emacs Killing Emacs means ending the execution of the Emacs process. The parent process normally resumes control. The low-level primitive for killing Emacs is kill-emacs. kill-emacs — Function: kill-emacs &optional exit-data This function exits the Emacs process and kills it.If exit-data is an integer, then it is used as the exit statusof the Emacs process. (This is useful primarily in batch operation; see.)If exit-data is a string, its contents are stuffed into theterminal input buffer so that the shell (or whatever program next readsinput) can read them. All the information in the Emacs process, aside from files that have been saved, is lost when the Emacs process is killed. Because killing Emacs inadvertently can lose a lot of work, Emacs queries for confirmation before actually terminating if you have buffers that need saving or subprocesses that are running. This is done in the function save-buffers-kill-emacs, the higher level function from which kill-emacs is usually called. kill-emacs-query-functions — Variable: kill-emacs-query-functions After asking the standard questions, save-buffers-kill-emacscalls the functions in the list kill-emacs-query-functions, inorder of appearance, with no arguments. These functions can ask foradditional confirmation from the user. If any of them returnsnil, save-buffers-kill-emacs does not kill Emacs, anddoes not run the remaining functions in this hook. Callingkill-emacs directly does not run this hook. kill-emacs-hook — Variable: kill-emacs-hook This variable is a normal hook; once save-buffers-kill-emacs isfinished with all file saving and confirmation, it callskill-emacs which runs the functions in this hook.kill-emacs does not run this hook in batch mode.kill-emacs may be invoked directly (that is not viasave-buffers-kill-emacs) if the terminal is disconnected, or insimilar situations where interaction with the user is not possible.Thus, if your hook needs to interact with the user, put it onkill-emacs-query-functions; if it needs to run regardless ofhow Emacs is killed, put it on kill-emacs-hook. Suspending Emacs suspending Emacs Suspending Emacs means stopping Emacs temporarily and returning control to its superior process, which is usually the shell. This allows you to resume editing later in the same Emacs process, with the same buffers, the same kill ring, the same undo history, and so on. To resume Emacs, use the appropriate command in the parent shell—most likely fg. Some operating systems do not support suspension of jobs; on these systems, “suspension” actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs. Suspension is not useful with window systems, because the Emacs job may not have a parent that can resume it again, and in any case you can give input to some other job such as a shell merely by moving to a different window. Therefore, suspending is not allowed when Emacs is using a window system (X, MS Windows, or Mac). suspend-emacs — Function: suspend-emacs &optional string This function stops Emacs and returns control to the superior process.If and when the superior process resumes Emacs, suspend-emacsreturns nil to its caller in Lisp.If string is non-nil, its characters are sent to be readas terminal input by Emacs's superior shell. The characters instring are not echoed by the superior shell; only the resultsappear.Before suspending, suspend-emacs runs the normal hooksuspend-hook.After the user resumes Emacs, suspend-emacs runs the normal hooksuspend-resume-hook. See .The next redisplay after resumption will redraw the entire screen,unless the variable no-redraw-on-reenter is non-nil(see ).In the following example, note that ‘pwd’ is not echoed afterEmacs is suspended. But it is read and executed by the shell. (suspend-emacs) => nil (add-hook 'suspend-hook (function (lambda () (or (y-or-n-p "Really suspend? ") (error "Suspend canceled"))))) => (lambda nil (or (y-or-n-p "Really suspend? ") (error "Suspend canceled"))) (add-hook 'suspend-resume-hook (function (lambda () (message "Resumed!")))) => (lambda nil (message "Resumed!")) (suspend-emacs "pwd") => nil ---------- Buffer: Minibuffer ---------- Really suspend? y ---------- Buffer: Minibuffer ---------- ---------- Parent Shell ---------- lewis@slug[23] % /user/lewis/manual lewis@slug[24] % fg ---------- Echo Area ---------- Resumed! suspend-hook — Variable: suspend-hook This variable is a normal hook that Emacs runs before suspending. suspend-resume-hook — Variable: suspend-resume-hook This variable is a normal hook that Emacs runs on resumingafter a suspension. Operating System Environment operating system environment Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on. system-configuration — Variable: system-configuration This variable holds the standard GNU configuration name for thehardware/software configuration of your system, as a string. Theconvenient way to test parts of this string is withstring-match. system type and name system-type — Variable: system-type The value of this variable is a symbol indicating the type of operatingsystem Emacs is operating on. Here is a table of the possible values: alpha-vms VMS on the Alpha. aix-v3 AIX. berkeley-unix Berkeley BSD. cygwin Cygwin. dgux Data General DGUX operating system. gnu the GNU system (using the GNU kernel, which consists of the HURD and Mach). gnu/linux A GNU/Linux system—that is, a variant GNU system, using the Linuxkernel. (These systems are the ones people often call “Linux,” butactually Linux is just the kernel, not the whole system.) hpux Hewlett-Packard HPUX operating system. irix Silicon Graphics Irix system. ms-dos Microsoft MS-DOS “operating system.” Emacs compiled with DJGPP forMS-DOS binds system-type to ms-dos even when you run it onMS-Windows. next-mach NeXT Mach-based system. rtu Masscomp RTU, UCB universe. unisoft-unix UniSoft UniPlus. usg-unix-v AT&T System V. vax-vms VAX VMS. windows-nt Microsoft windows NT. The same executable supports Windows 9X, but thevalue of system-type is windows-nt in either case. xenix SCO Xenix 386. We do not wish to add new symbols to make finer distinctions unless itis absolutely necessary! In fact, we hope to eliminate some of thesealternatives in the future. We recommend usingsystem-configuration to distinguish between different operatingsystems. system-name — Function: system-name This function returns the name of the machine you are running on. (system-name) => "www.gnu.org" The symbol system-name is a variable as well as a function. In fact, the function returns whatever value the variable system-name currently holds. Thus, you can set the variable system-name in case Emacs is confused about the name of your system. The variable is also useful for constructing frame titles (see ). mail-host-address — Variable: mail-host-address If this variable is non-nil, it is used instead ofsystem-name for purposes of generating email addresses. Forexample, it is used when constructing the default value ofuser-mail-address. See . (Since this isdone when Emacs starts up, the value actually used is the one saved whenEmacs was dumped. See .) getenv — Command: getenv var environment variable accessThis function returns the value of the environment variable var,as a string. var should be a string. If var is undefinedin the environment, getenv returns nil. If returns‘""’ if var is set but null. Within Emacs, the environmentvariable values are kept in the Lisp variable process-environment. (getenv "USER") => "lewis" lewis@slug[10] % printenv PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin USER=lewis TERM=ibmapa16 SHELL=/bin/csh HOME=/user/lewis setenv — Command: setenv variable &optional value This command sets the value of the environment variable namedvariable to value. variable should be a string.Internally, Emacs Lisp can handle any string. However, normallyvariable should be a valid shell identifier, that is, a sequenceof letters, digits and underscores, starting with a letter orunderscore. Otherwise, errors may occur if subprocesses of Emacs tryto access the value of variable. If value is omitted ornil, setenv removes variable from the environment.Otherwise, value should be a string.setenv works by modifying process-environment; bindingthat variable with let is also reasonable practice.setenv returns the new value of variable, or nilif it removed variable from the environment. process-environment — Variable: process-environment This variable is a list of strings, each describing one environmentvariable. The functions getenv and setenv work by meansof this variable. process-environment => ("l=/usr/stanford/lib/gnuemacs/lisp" "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" "USER=lewis" "TERM=ibmapa16" "SHELL=/bin/csh" "HOME=/user/lewis") If process-environment contains “duplicate” elements thatspecify the same environment variable, the first of these elementsspecifies the variable, and the other “duplicates” are ignored. path-separator — Variable: path-separator This variable holds a string which says which character separatesdirectories in a search path (as found in an environment variable). Itsvalue is ":" for Unix and GNU systems, and ";" for MS-DOSand MS-Windows. parse-colon-path — Function: parse-colon-path path This function takes a search path string such as would be the value ofthe PATH environment variable, and splits it at the separators,returning a list of directory names. nil in this list stands for“use the current directory.” Although the function's name says“colon,” it actually uses the value of path-separator. (parse-colon-path ":/foo:/bar") => (nil "/foo/" "/bar/") invocation-name — Variable: invocation-name This variable holds the program name under which Emacs was invoked. Thevalue is a string, and does not include a directory name. invocation-directory — Variable: invocation-directory This variable holds the directory from which the Emacs executable wasinvoked, or perhaps nil if that directory cannot be determined. installation-directory — Variable: installation-directory If non-nil, this is a directory within which to look for thelib-src and etc subdirectories. This is non-nilwhen Emacs can't find those directories in their standard installedlocations, but can find them in a directory related somehow to the onecontaining the Emacs executable. load-average — Function: load-average &optional use-float This function returns the current 1-minute, 5-minute, and 15-minute loadaverages, in a list.By default, the values are integers that are 100 times the system loadaverages, which indicate the average number of processes trying to run.If use-float is non-nil, then they are returnedas floating point numbers and without multiplying by 100.If it is impossible to obtain the load average, this function signalsan error. On some platforms, access to load averages requiresinstalling Emacs as setuid or setgid so that it can read kernelinformation, and that usually isn't advisable.If the 1-minute load average is available, but the 5- or 15-minuteaverages are not, this function returns a shortened list containingthe available averages. (load-average) => (169 48 36) (load-average t) => (1.69 0.48 0.36) lewis@rocky[5] % uptime 11:55am up 1 day, 19:37, 3 users, load average: 1.69, 0.48, 0.36 emacs-pid — Function: emacs-pid This function returns the process ID of the Emacs process,as an integer. tty-erase-char — Variable: tty-erase-char This variable holds the erase character that was selectedin the system's terminal driver, before Emacs was started.The value is nil if Emacs is running under a window system. setprv — Function: setprv privilege-name &optional setp getprv This function sets or resets a VMS privilege. (It does not exist onother systems.) The first argument is the privilege name, as a string.The second argument, setp, is t or nil, indicatingwhether the privilege is to be turned on or off. Its default isnil. The function returns t if successful, nilotherwise.If the third argument, getprv, is non-nil, setprvdoes not change the privilege, but returns t or nilindicating whether the privilege is currently enabled. User Identification user identification init-file-user — Variable: init-file-user This variable says which user's init files should be used byEmacs—or nil if none. "" stands for the user whooriginally logged in. The value reflects command-line options such as‘-q’ or ‘-u user’.Lisp packages that load files of customizations, or any other sort ofuser profile, should obey this variable in deciding where to find it.They should load the profile of the user name found in this variable.If init-file-user is nil, meaning that the ‘-q’option was used, then Lisp packages should not load any customizationfiles or user profile. user-mail-address — Variable: user-mail-address This holds the nominal email address of the user who is using Emacs.Emacs normally sets this variable to a default value after reading yourinit files, but not if you have already set it. So you can set thevariable to some other value in your init file if you do notwant to use the default value. user-login-name — Function: user-login-name &optional uid If you don't specify uid, this function returns the name underwhich the user is logged in. If the environment variable LOGNAMEis set, that value is used. Otherwise, if the environment variableUSER is set, that value is used. Otherwise, the value is basedon the effective UID, not the real UID.If you specify uid, the value is the user name that correspondsto uid (which should be an integer), or nil if there isno such user. (user-login-name) => "lewis" user-real-login-name — Function: user-real-login-name This function returns the user name corresponding to Emacs's realUID. This ignores the effective UID and ignores theenvironment variables LOGNAME and USER. user-full-name — Function: user-full-name &optional uid This function returns the full name of the logged-in user—or the valueof the environment variable NAME, if that is set. (user-full-name) => "Bil Lewis" If the Emacs job's user-id does not correspond to any known user (andprovided NAME is not set), the value is "unknown".If uid is non-nil, then it should be a number (a user-id)or a string (a login name). Then user-full-name returns the fullname corresponding to that user-id or login name. If you specify auser-id or login name that isn't defined, it returns nil. user-full-name user-real-login-name user-login-name The symbols user-login-name, user-real-login-name and user-full-name are variables as well as functions. The functions return the same values that the variables hold. These variables allow you to “fake out” Emacs by telling the functions what to return. The variables are also useful for constructing frame titles (see ). user-real-uid — Function: user-real-uid This function returns the real UID of the user.The value may be a floating point number. (user-real-uid) => 19 user-uid — Function: user-uid This function returns the effective UID of the user.The value may be a floating point number. Time of Day This section explains how to determine the current time and the time zone. current-time-string — Function: current-time-string &optional time-value This function returns the current time and date as a human-readablestring. The format of the string is unvarying; the number of charactersused for each part is always the same, so you can reliably usesubstring to extract pieces of it. It is wise to count thecharacters from the beginning of the string rather than from the end, asadditional information may some day be added at the end. The argument time-value, if given, specifies a time to formatinstead of the current time. The argument should be a list whose firsttwo elements are integers. Thus, you can use times obtained fromcurrent-time (see below) and from file-attributes(see ). time-value can also bea cons of two integers, but this is considered obsolete. (current-time-string) => "Wed Oct 14 22:21:05 1987" current-time — Function: current-time This function returns the system's time value as a list of threeintegers: (high low microsec). The integershigh and low combine to give the number of seconds since0:00 January 1, 1970 UTC (Coordinated Universal Time), which ishigh * 2**16 + low.The third element, microsec, gives the microseconds since thestart of the current second (or 0 for systems that return time withthe resolution of only one second).The first two elements can be compared with file time values such as youget with the function file-attributes.See . current-time-zone — Function: current-time-zone &optional time-value This function returns a list describing the time zone that the user isin.The value has the form (offset name). Hereoffset is an integer giving the number of seconds ahead of UTC(east of Greenwich). A negative value means west of Greenwich. Thesecond element, name, is a string giving the name of the timezone. Both elements change when daylight saving time begins or ends;if the user has specified a time zone that does not use a seasonal timeadjustment, then the value is constant through time.If the operating system doesn't supply all the information necessary tocompute the value, the unknown elements of the list are nil.The argument time-value, if given, specifies a time to analyzeinstead of the current time. The argument should have the same formas for current-time-string (see above). Thus, you can usetimes obtained from current-time (see above) and fromfile-attributes. See . set-time-zone-rule — Function: set-time-zone-rule tz This function specifies the local time zone according to tz. Iftz is nil, that means to use an implementation-defineddefault time zone. If tz is t, that means to useUniversal Time. Otherwise, tz should be a string specifying atime zone rule. float-time — Function: float-time &optional time-value This function returns the current time as a floating-point number ofseconds since the epoch. The argument time-value, if given,specifies a time to convert instead of the current time. The argumentshould have the same form as for current-time-string (seeabove). Thus, it accepts the output of current-time andfile-attributes.Warning: Since the result is floating point, it may not beexact. Do not use this function if precise time stamps are required. Time Conversion These functions convert time values (lists of two or three integers) to calendrical information and vice versa. You can get time values from the functions current-time (see ) and file-attributes (see ). Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future. Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number −37 represents the Gregorian year 38 B.C. decode-time — Function: decode-time &optional time This function converts a time value into calendrical information. Ifyou don't specify time, it decodes the current time. The returnvalue is a list of nine elements, as follows: (seconds minutes hour day month year dow dst zone) Here is what the elements mean: seconds The number of seconds past the minute, as an integer between 0 and 59.On some operating systems, this is 60 for leap seconds. minutes The number of minutes past the hour, as an integer between 0 and 59. hour The hour of the day, as an integer between 0 and 23. day The day of the month, as an integer between 1 and 31. month The month of the year, as an integer between 1 and 12. year The year, an integer typically greater than 1900. dow The day of week, as an integer between 0 and 6, where 0 stands forSunday. dst t if daylight saving time is effect, otherwise nil. zone An integer indicating the time zone, as the number of seconds east ofGreenwich. Common Lisp Note: Common Lisp has different meanings fordow and zone. encode-time — Function: encode-time seconds minutes hour day month year &optional zone This function is the inverse of decode-time. It converts sevenitems of calendrical data into a time value. For the meanings of thearguments, see the table above under decode-time.Year numbers less than 100 are not treated specially. If you want themto stand for years above 1900, or years above 2000, you must alter themyourself before you call encode-time.The optional argument zone defaults to the current time zone andits daylight saving time rules. If specified, it can be either a list(as you would get from current-time-zone), a string as in theTZ environment variable, t for Universal Time, or aninteger (as you would get from decode-time). The specifiedzone is used without any further alteration for daylight saving time.If you pass more than seven arguments to encode-time, the firstsix are used as seconds through year, the last argument isused as zone, and the arguments in between are ignored. Thisfeature makes it possible to use the elements of a list returned bydecode-time as the arguments to encode-time, like this: (apply 'encode-time (decode-time …)) You can perform simple date arithmetic by using out-of-range values forthe seconds, minutes, hour, day, and montharguments; for example, day 0 means the day preceding the given month.The operating system puts limits on the range of possible time values;if you try to encode a time that is out of range, an error results.For instance, years before 1970 do not work on some systems;on others, years as early as 1901 do work. Parsing and Formatting Times These functions convert time values (lists of two or three integers) to text in a string, and vice versa. date-to-time — Function: date-to-time string This function parses the time-string string and returns thecorresponding time value. format-time-string — Function: format-time-string format-string &optional time universal This function converts time (or the current time, if time isomitted) to a string according to format-string. The argumentformat-string may contain ‘%’-sequences which say tosubstitute parts of the time. Here is a table of what the‘%’-sequences mean: ‘%a’ This stands for the abbreviated name of the day of week. ‘%A’ This stands for the full name of the day of week. ‘%b’ This stands for the abbreviated name of the month. ‘%B’ This stands for the full name of the month. ‘%c’ This is a synonym for ‘%x %X’. ‘%C’ This has a locale-specific meaning. In the default locale (named C), itis equivalent to ‘%A, %B %e, %Y’. ‘%d’ This stands for the day of month, zero-padded. ‘%D’ This is a synonym for ‘%m/%d/%y’. ‘%e’ This stands for the day of month, blank-padded. ‘%h’ This is a synonym for ‘%b’. ‘%H’ This stands for the hour (00-23). ‘%I’ This stands for the hour (01-12). ‘%j’ This stands for the day of the year (001-366). ‘%k’ This stands for the hour (0-23), blank padded. ‘%l’ This stands for the hour (1-12), blank padded. ‘%m’ This stands for the month (01-12). ‘%M’ This stands for the minute (00-59). ‘%n’ This stands for a newline. ‘%p’ This stands for ‘AM’ or ‘PM’, as appropriate. ‘%r’ This is a synonym for ‘%I:%M:%S %p’. ‘%R’ This is a synonym for ‘%H:%M’. ‘%S’ This stands for the seconds (00-59). ‘%t’ This stands for a tab character. ‘%T’ This is a synonym for ‘%H:%M:%S’. ‘%U’ This stands for the week of the year (01-52), assuming that weeksstart on Sunday. ‘%w’ This stands for the numeric day of week (0-6). Sunday is day 0. ‘%W’ This stands for the week of the year (01-52), assuming that weeksstart on Monday. ‘%x’ This has a locale-specific meaning. In the default locale (named‘C’), it is equivalent to ‘%D’. ‘%X’ This has a locale-specific meaning. In the default locale (named‘C’), it is equivalent to ‘%T’. ‘%y’ This stands for the year without century (00-99). ‘%Y’ This stands for the year with century. ‘%Z’ This stands for the time zone abbreviation (e.g., ‘EST’). ‘%z’ This stands for the time zone numerical offset (e.g., ‘-0500’). You can also specify the field width and type of padding for any ofthese ‘%’-sequences. This works as in printf: you writethe field width as digits in the middle of a ‘%’-sequences. If youstart the field width with ‘0’, it means to pad with zeros. If youstart the field width with ‘_’, it means to pad with spaces.For example, ‘%S’ specifies the number of seconds since the minute;‘%03S’ means to pad this with zeros to 3 positions, ‘%_3S’ topad with spaces to 3 positions. Plain ‘%3S’ pads with zeros,because that is how ‘%S’ normally pads to two positions.The characters ‘E’ and ‘O’ act as modifiers when used between‘%’ and one of the letters in the table above. ‘E’ specifiesusing the current locale's “alternative” version of the date and time.In a Japanese locale, for example, %Ex might yield a date formatbased on the Japanese Emperors' reigns. ‘E’ is allowed in‘%Ec’, ‘%EC’, ‘%Ex’, ‘%EX’, ‘%Ey’, and‘%EY’.‘O’ means to use the current locale's “alternative”representation of numbers, instead of the ordinary decimal digits. Thisis allowed with most letters, all the ones that output numbers.If universal is non-nil, that means to describe the time asUniversal Time; nil means describe it using what Emacs believesis the local time zone (see current-time-zone).This function uses the C library function strftime(see See section ``Formatting Calendar Time'' in The GNU C Library Reference Manual) to do most of the work. In order to communicate with thatfunction, it first encodes its argument using the coding systemspecified by locale-coding-system (see ); afterstrftime returns the resulting string,format-time-string decodes the string using that same codingsystem. seconds-to-time — Function: seconds-to-time seconds This function converts seconds, a floating point number ofseconds since the epoch, to a time value and returns that. To performthe inverse conversion, use float-time. Processor Run time processor run time get-internal-run-time — Function: get-internal-run-time This function returns the processor run time used by Emacs as a listof three integers: (high low microsec). Theintegers high and low combine to give the number ofseconds, which ishigh * 2**16 + low.The third element, microsec, gives the microseconds (or 0 forsystems that return time with the resolution of only one second).If the system doesn't provide a way to determine the processor runtime, get-internal-run-time returns the same time as current-time. Time Calculations These functions perform calendrical computations using time values (the kind of list that current-time returns). time-less-p — Function: time-less-p t1 t2 This returns t if time value t1 is less than time valuet2. time-subtract — Function: time-subtract t1 t2 This returns the time difference t1 − t2 betweentwo time values, in the same format as a time value. time-add — Function: time-add t1 t2 This returns the sum of two time values, one of which ought torepresent a time difference rather than a point in time.Here is how to add a number of seconds to a time value: (time-add time (seconds-to-time seconds)) time-to-days — Function: time-to-days time This function returns the number of days between the beginning of year1 and time. time-to-day-in-year — Function: time-to-day-in-year time This returns the day number within the year corresponding to time. date-leap-year-p — Function: date-leap-year-p year This function returns t if year is a leap year. Timers for Delayed Execution timer You can set up a timer to call a function at a specified future time or after a certain length of idleness. Emacs cannot run timers at any arbitrary point in a Lisp program; it can run them only when Emacs could accept output from a subprocess: namely, while waiting or inside certain primitive functions such as sit-for or read-event which can wait. Therefore, a timer's execution may be delayed if Emacs is busy. However, the time of execution is very precise if Emacs is idle. Emacs binds inhibit-quit to t before calling the timer function, because quitting out of many timer functions can leave things in an inconsistent state. This is normally unproblematical because most timer functions don't do a lot of work. Indeed, for a timer to call a function that takes substantial time to run is likely to be annoying. If a timer function needs to allow quitting, it should use with-local-quit (see ). For example, if a timer function calls accept-process-output to receive output from an external process, that call should be wrapped inside with-local-quit, to ensure that C-g works if the external process hangs. It is usually a bad idea for timer functions to alter buffer contents. When they do, they usually should call undo-boundary both before and after changing the buffer, to separate the timer's changes from user commands' changes and prevent a single undo entry from growing to be quite large. Timer functions should also avoid calling functions that cause Emacs to wait, such as sit-for (see ). This can lead to unpredictable effects, since other timers (or even the same timer) can run while waiting. If a timer function needs to perform an action after a certain time has elapsed, it can do this by scheduling a new timer. If a timer function calls functions that can change the match data, it should save and restore the match data. See . run-at-time — Command: run-at-time time repeat function &rest args This sets up a timer that calls the function function witharguments args at time time. If repeat is a number(integer or floating point), the timer is scheduled to run again everyrepeat seconds after time. If repeat is nil,the timer runs only once.time may specify an absolute or a relative time.Absolute times may be specified using a string with a limited varietyof formats, and are taken to be times today, even if already inthe past. The recognized forms are ‘xxxx’,‘x:xx’, or ‘xx:xx’ (military time),and ‘xxam’, ‘xxAM’, ‘xxpm’,‘xxPM’, ‘xx:xxam’,‘xx:xxAM’, ‘xx:xxpm’, or‘xx:xxPM’. A period can be used instead of a colonto separate the hour and minute parts.To specify a relative time as a string, use numbers followed by units.For example: ‘1 min’ denotes 1 minute from now. ‘1 min 5 sec’ denotes 65 seconds from now. ‘1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year’ denotes exactly 103 months, 123 days, and 10862 seconds from now. For relative time values, Emacs considers a month to be exactly thirtydays, and a year to be exactly 365.25 days.Not all convenient formats are strings. If time is a number(integer or floating point), that specifies a relative time measured inseconds. The result of encode-time can also be used to specifyan absolute value for time.In most cases, repeat has no effect on when first calltakes place—time alone specifies that. There is one exception:if time is t, then the timer runs whenever the time is amultiple of repeat seconds after the epoch. This is useful forfunctions like display-time.The function run-at-time returns a timer value that identifiesthe particular scheduled future action. You can use this value to callcancel-timer (see below). A repeating timer nominally ought to run every repeat seconds, but remember that any invocation of a timer can be late. Lateness of one repetition has no effect on the scheduled time of the next repetition. For instance, if Emacs is busy computing for long enough to cover three scheduled repetitions of the timer, and then starts to wait, it will immediately call the timer function three times in immediate succession (presuming no other timers trigger before or between them). If you want a timer to run again no less than n seconds after the last invocation, don't use the repeat argument. Instead, the timer function should explicitly reschedule the timer. timer-max-repeats — Variable: timer-max-repeats This variable's value specifies the maximum number of times to repeatcalling a timer function in a row, when many previously scheduledcalls were unavoidably delayed. with-timeout — Macro: with-timeout ( seconds timeout-forms … ) body … Execute body, but give up after seconds seconds. Ifbody finishes before the time is up, with-timeout returnsthe value of the last form in body. If, however, the execution ofbody is cut short by the timeout, then with-timeoutexecutes all the timeout-forms and returns the value of the lastof them.This macro works by setting a timer to run after seconds seconds. Ifbody finishes before that time, it cancels the timer. If thetimer actually runs, it terminates execution of body, thenexecutes timeout-forms.Since timers can run within a Lisp program only when the program calls aprimitive that can wait, with-timeout cannot stop executingbody while it is in the midst of a computation—only when itcalls one of those primitives. So use with-timeout only with abody that waits for input, not one that does a long computation. The function y-or-n-p-with-timeout provides a simple way to use a timer to avoid waiting too long for an answer. See . cancel-timer — Function: cancel-timer timer This cancels the requested action for timer, which should be atimer—usually, one previously returned by run-at-time orrun-with-idle-timer. This cancels the effect of that call toone of these functions; the arrival of the specified time will notcause anything special to happen. Idle Timers Here is how to set up a timer that runs when Emacs is idle for a certain length of time. Aside from how to set them up, idle timers work just like ordinary timers. run-with-idle-timer — Command: run-with-idle-timer secs repeat function &rest args Set up a timer which runs when Emacs has been idle for secsseconds. The value of secs may be an integer or a floating pointnumber; a value of the type returned by current-idle-timeis also allowed.If repeat is nil, the timer runs just once, the first timeEmacs remains idle for a long enough time. More often repeat isnon-nil, which means to run the timer each time Emacsremains idle for secs seconds.The function run-with-idle-timer returns a timer value which youcan use in calling cancel-timer (see ). idleness Emacs becomes “idle” when it starts waiting for user input, and it remains idle until the user provides some input. If a timer is set for five seconds of idleness, it runs approximately five seconds after Emacs first becomes idle. Even if repeat is non-nil, this timer will not run again as long as Emacs remains idle, because the duration of idleness will continue to increase and will not go down to five seconds again. Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, and even if there have been garbage collections and autosaves. When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one. current-idle-time — Function: current-idle-time This function returns the length of time Emacs has been idle, as alist of three integers: (high low microsec).The integers high and low combine to give the number ofseconds of idleness, which ishigh * 2**16 + low.The third element, microsec, gives the microseconds since thestart of the current second (or 0 for systems that return time withthe resolution of only one second).The main use of this function is when an idle timer function wants to“take a break” for a while. It can set up another idle timer tocall the same function again, after a few seconds more idleness.Here's an example: (defvar resume-timer nil "Timer that `timer-function' used to reschedule itself, or nil.") (defun timer-function () ;; If the user types a command while resume-timer ;; is active, the next time this function is called from ;; its main idle timer, deactivate resume-timer. (when resume-timer (cancel-timer resume-timer)) ...do the work for a while... (when taking-a-break (setq resume-timer (run-with-idle-timer ;; Compute an idle time break-length ;; more than the current value. (time-add (current-idle-time) (seconds-to-time break-length)) nil 'timer-function)))) Some idle timer functions in user Lisp packages have a loop that does a certain amount of processing each time around, and exits when (input-pending-p) is non-nil. That approach seems very natural but has two problems: It blocks out all process output (since Emacs accepts process outputonly while waiting). It blocks out any idle timers that ought to run during that time. To avoid these problems, don't use that technique. Instead, write such idle timers to reschedule themselves after a brief pause, using the method in the timer-function example above. Terminal Input terminal input This section describes functions and variables for recording or manipulating terminal input. See , for related functions. Input Modes input modes terminal input modes set-input-mode — Function: set-input-mode interrupt flow meta &optional quit-char This function sets the mode for reading keyboard input. Ifinterrupt is non-null, then Emacs uses input interrupts. If it isnil, then it uses cbreak mode. The default setting issystem-dependent. Some systems always use cbreak mode regardlessof what is specified.When Emacs communicates directly with X, it ignores this argument anduses interrupts if that is the way it knows how to communicate.If flow is non-nil, then Emacs uses xon/xoff(C-q, C-s) flow control for output to the terminal. Thishas no effect except in cbreak mode. The argument meta controls support for input character codesabove 127. If meta is t, Emacs converts characters withthe 8th bit set into Meta characters. If meta is nil,Emacs disregards the 8th bit; this is necessary when the terminal usesit as a parity bit. If meta is neither t nor nil,Emacs uses all 8 bits of input unchanged. This is good for terminalsthat use 8-bit character sets. If quit-char is non-nil, it specifies the character touse for quitting. Normally this character is C-g.See . The current-input-mode function returns the input mode settings Emacs is currently using. current-input-mode — Function: current-input-mode This function returns the current mode for reading keyboard input. Itreturns a list, corresponding to the arguments of set-input-mode,of the form (interrupt flow meta quit) inwhich: interrupt is non-nil when Emacs is using interrupt-driven input. Ifnil, Emacs is using cbreak mode. flow is non-nil if Emacs uses xon/xoff (C-q, C-s)flow control for output to the terminal. This value is meaningful onlywhen interrupt is nil. meta is t if Emacs treats the eighth bit of input characters asthe meta bit; nil means Emacs clears the eighth bit of everyinput character; any other value means Emacs uses all eight bits as thebasic character code. quit is the character Emacs currently uses for quitting, usually C-g. Recording Input recording input recent-keys — Function: recent-keys This function returns a vector containing the last 300 input events fromthe keyboard or mouse. All input events are included, whether or notthey were used as parts of key sequences. Thus, you always get the last100 input events, not counting events generated by keyboard macros.(These are excluded because they are less interesting for debugging; itshould be enough to see the events that invoked the macros.)A call to clear-this-command-keys (see )causes this function to return an empty vector immediately afterward. open-dribble-file — Command: open-dribble-file filename dribble fileThis function opens a dribble file named filename. When adribble file is open, each input event from the keyboard or mouse (butnot those from keyboard macros) is written in that file. Anon-character event is expressed using its printed representationsurrounded by ‘<…>’.You close the dribble file by calling this function with an argumentof nil.This function is normally used to record the input necessary totrigger an Emacs bug, for the sake of a bug report. (open-dribble-file "~/dribble") => nil See also the open-termscript function (see ). Terminal Output terminal output The terminal output functions send output to a text terminal, or keep track of output sent to the terminal. The variable baud-rate tells you what Emacs thinks is the output speed of the terminal. baud-rate — Variable: baud-rate This variable's value is the output speed of the terminal, as far asEmacs knows. Setting this variable does not change the speed of actualdata transmission, but the value is used for calculations such aspadding. It also affects decisions about whether to scroll part of thescreen or repaint on text terminals. See ,for the corresponding functionality on graphical terminals.The value is measured in baud. If you are running across a network, and different parts of the network work at different baud rates, the value returned by Emacs may be different from the value used by your local terminal. Some network protocols communicate the local terminal speed to the remote machine, so that Emacs and other programs can get the proper value, but others do not. If Emacs has the wrong value, it makes decisions that are less than optimal. To fix the problem, set baud-rate. baud-rate — Function: baud-rate This obsolete function returns the value of the variablebaud-rate. send-string-to-terminal — Function: send-string-to-terminal string This function sends string to the terminal without alteration.Control characters in string have terminal-dependent effects.This function operates only on text terminals.One use of this function is to define function keys on terminals thathave downloadable function key definitions. For example, this is how (oncertain terminals) to define function key 4 to move forward fourcharacters (by transmitting the characters C-u C-f to thecomputer): (send-string-to-terminal "\eF4\^U\^F") => nil open-termscript — Command: open-termscript filename termscript fileThis function is used to open a termscript file that will recordall the characters sent by Emacs to the terminal. It returnsnil. Termscript files are useful for investigating problemswhere Emacs garbles the screen, problems that are due to incorrectTermcap entries or to undesirable settings of terminal options moreoften than to actual Emacs bugs. Once you are certain which characterswere actually output, you can determine reliably whether they correspondto the Termcap specifications in use.You close the termscript file by calling this function with anargument of nil.See also open-dribble-file in . (open-termscript "../junk/termscript") => nil Sound Output sound To play sound using Emacs, use the function play-sound. Only certain systems are supported; if you call play-sound on a system which cannot really do the job, it gives an error. Emacs version 20 and earlier did not support sound at all. The sound must be stored as a file in RIFF-WAVE format (‘.wav’) or Sun Audio format (‘.au’). play-sound — Function: play-sound sound This function plays a specified sound. The argument, sound, hasthe form (sound properties...), where the propertiesconsist of alternating keywords (particular symbols recognizedspecially) and values corresponding to them.Here is a table of the keywords that are currently meaningful insound, and their meanings: :file file This specifies the file containing the sound to play.If the file name is not absolute, it is expanded againstthe directory data-directory. :data data This specifies the sound to play without need to refer to a file. Thevalue, data, should be a string containing the same bytes as asound file. We recommend using a unibyte string. :volume volume This specifies how loud to play the sound. It should be a number in therange of 0 to 1. The default is to use whatever volume has beenspecified before. :device device This specifies the system device on which to play the sound, as astring. The default device is system-dependent. Before actually playing the sound, play-soundcalls the functions in the list play-sound-functions.Each function is called with one argument, sound. play-sound-file — Function: play-sound-file file &optional volume device This function is an alternative interface to playing a sound filespecifying an optional volume and device. play-sound-functions — Variable: play-sound-functions A list of functions to be called before playing a sound. Each functionis called with one argument, a property list that describes the sound. Operating on X11 Keysyms X11 keysyms To define system-specific X11 keysyms, set the variable system-key-alist. system-key-alist — Variable: system-key-alist This variable's value should be an alist with one element for eachsystem-specific keysym. Each element has the form (code. symbol), where code is the numeric keysym code (notincluding the “vendor specific” bit,-2**28),and symbol is the name for the function key.For example (168 . mute-acute) defines a system-specific key (usedby HP X servers) whose numeric code is-2**28+ 168.It is not crucial to exclude from the alist the keysyms of other Xservers; those do no harm, as long as they don't conflict with the onesused by the X server actually in use.The variable is always local to the current terminal, and cannot bebuffer-local. See . You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables: x-alt-keysym — Variable: x-alt-keysym x-meta-keysym — Variable: x-meta-keysym x-hyper-keysym — Variable: x-hyper-keysym x-super-keysym — Variable: x-super-keysym The name of the keysym that should stand for the Alt modifier(respectively, for Meta, Hyper, and Super). For example, here ishow to swap the Meta and Alt modifiers within Emacs:(setq x-alt-keysym 'meta)(setq x-meta-keysym 'alt) Batch Mode batch mode The command-line option ‘-batch’ causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with ‘-l file’, which loads the library named file, or ‘-f function’, which calls function with no arguments, or ‘--eval form’. Any Lisp program output that would normally go to the echo area, either using message, or using prin1, etc., with t as the stream, goes instead to Emacs's standard error descriptor when in batch mode. Similarly, input that would normally come from the minibuffer is read from the standard input descriptor. Thus, Emacs behaves much like a noninteractive application program. (The echo area output that Emacs itself normally generates, such as command echoing, is suppressed entirely.) noninteractive — Variable: noninteractive This variable is non-nil when Emacs is running in batch mode. Session Management session manager Emacs supports the X Session Management Protocol for suspension and restart of applications. In the X Window System, a program called the session manager has the responsibility to keep track of the applications that are running. During shutdown, the session manager asks applications to save their state, and delays the actual shutdown until they respond. An application can also cancel the shutdown. When the session manager restarts a suspended session, it directs these applications to individually reload their saved state. It does this by specifying a special command-line argument that says what saved session to restore. For Emacs, this argument is ‘--smid session’. emacs-save-session-functions — Variable: emacs-save-session-functions Emacs supports saving state by using a hook calledemacs-save-session-functions. Each function in this hook iscalled when the session manager tells Emacs that the window system isshutting down. The functions are called with no arguments and with thecurrent buffer set to a temporary buffer. Each function can useinsert to add Lisp code to this buffer. At the end, Emacssaves the buffer in a file that a subsequent Emacs invocation willload in order to restart the saved session.If a function in emacs-save-session-functions returnsnon-nil, Emacs tells the session manager to cancel theshutdown. Here is an example that just inserts some text into ‘*scratch*’ when Emacs is restarted by the session manager. (add-hook 'emacs-save-session-functions 'save-yourself-test) (defun save-yourself-test () (insert "(save-excursion (switch-to-buffer \"*scratch*\") (insert \"I am restored\"))") nil) Emacs 21 Antinews For those users who live backwards in time, here is information about downgrading to Emacs version 21.4. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 22.1 features. Old Lisp Features in Emacs 21 Many unnecessary features of redisplay have been eliminated. (Theearlier major release, Emacs 20, will have a completely rewrittenredisplay engine, which will be even simpler.) The function redisplay has been removed. To update the displaywithout delay, call (sit-for 0). Since it is generallyconsidered wasteful to update the display if there are any pendinginput events, no replacement for (redisplay t) is provided. The function force-window-update has been removed. Itshouldn't be needed, since changes in window contents are detectedautomatically. In case they aren't, call redraw-display toredraw everything. Point no longer moves out from underneath invisible text at the end ofeach command. This allows the user to detect invisible text by movingthe cursor around—if the cursor gets stuck, there is somethinginvisible in the way. If you really want cursor motion to ignore thetext, try marking it as intangible. Support for image maps and image slices has been removed. Emacs wasalways meant for editing text, anyway. The mode line now accepts all text properties, as well as:propertize and :eval forms, regardless of therisky-local-variable property. The line-height and line-spacing properties no longerhave any meaning for newline characters. Such properties wouldn'tmake sense, since newlines are not really characters; they just tellyou where to break a line. Considerable simplifications have been made to the displayspecification (space . props), which is used fordisplaying a space of specified width and height. Pixel-basedspecifications and Lisp expressions are no longer accepted. Many features associated with the fringe areas have been removed, toencourage people to concentrate on the main editing area (the fringewill be completely removed in Emacs 20.) Arbitrary bitmaps can nolonger be displayed in the fringe; an overlay arrow can still bedisplayed, but there can only be one overlay arrow at a time (any morewould be confusing.) The fringe widths cannot be adjusted, andindividual windows cannot have their own fringe settings. A mouseclick on the fringe no longer generates a special event. Individual windows cannot have their own scroll-bar settings. You can no longer use ‘default’ in a defface to specifydefaults for subsequent faces. The function display-supports-face-attributes-p has beenremoved. In defface specifications, the supportspredicate is no longer supported. The functions merge-face-attribute andface-attribute-relative-p have been removed. The priority of faces in a list supplied by the :inherit faceattribute has been reversed. We like to make changes like this oncein a while, to keep Emacs Lisp programmers on their toes. The min-colors face attribute, used for tailoring faces tolimited-color displays, does not exist. If in doubt, use colors like“white” and “black,” which ought to be defined everywhere. The tty-color-mode frame parameter does not exist. You shouldjust trust the terminal capabilities database. Several simplifications have been made to mouse support: Clicking mouse-1 won't follow links, as that is alien to thespirit of Emacs. Therefore, the follow-link property doesn'thas any special meaning, and the function mouse-on-link-p hasbeen removed. The variable void-text-area-pointer has been removed, so themouse pointer shape remains unchanged when moving between valid textareas and void text areas. The pointer image and textproperties are no longer supported. Mouse events will no longer specify the timestamp, the object clicked,equivalent buffer positions (for marginal or fringe areas), glyphcoordinates, or relative pixel coordinates. Simplifications have also been made to the way Emacs handles keymapsand key sequences: The kbd macro is now obsolete and is no longer documented.It isn't that difficult to write key sequences using the string andvector representations, and we want to encourage users to learn. Emacs no longer supports key remapping. You can do pretty much thesame thing with substitute-key-definition, or by advising therelevant command. The keymap text and overlay property is now overridden by minormode keymaps, and will not work at the ends of text properties andoverlays. The functions map-keymap, keymap-prompt, andcurrent-active-maps have been removed. Process support has been pared down to a functional minimum. Thefunctions call-process-shell-command and process-filehave been deleted. Processes no longer maintain property lists, andthey won't ask any questions when the user tries to exit Emacs (whichwould simply be rude.) The function signal-process won'taccept a process object, only the process id; determining the processid from a process object is left as an exercise to the programmer. Networking has also been simplified: make-network-process andits various associated function have all been replaced with a singleeasy-to-use function, open-network-stream, which can't use UDP,can't act as a server, and can't set up non-blocking connections.Also, deleting a network process with delete-process won't callthe sentinel. Many programming shortcuts have been deleted, to provide you with theenjoyment of “rolling your own.” The macros while-no-input,with-local-quit, and with-selected-window, along withdynamic-completion-table and lazy-completion-table nolonger exist. Also, there are no built-in progress reporters;with Emacs, you can take progress for granted. Variable aliases are no longer supported. Aliases are for functions,not for variables. The variables most-positive-fixnum andmost-negative-fixnum do not exist. On 32 bit machines, themost positive integer is probably 134217727, and the most negativeinteger is probably -134217728. The functions eql and macroexpand-all are no longeravailable. However, you can find similar functions in the clpackage. The list returned by split-string won't include null substringsfor separators at the beginning or end of a string. If you want tocheck for such separators, do it separately. The function assoc-string has been removed. Useassoc-ignore-case or assoc-ignore-representation (whichare no longer obsolete.) The escape sequence ‘\s’ is always interpreted as a supermodifier, never a space. The variable buffer-save-without-query has been removed, toprevent Emacs from sneakily saving buffers. Also, the hookbefore-save-hook has been removed, so if you want something tobe done before saving, advise or redefine basic-save-buffer. The variable buffer-auto-save-file-format has been renamed toauto-save-file-format, and is no longer a permanent local. The function visited-file-modtime now returns a cons, insteadof a list of two integers. The primitive set-file-times hasbeen eliminated. The function file-remote-p is no longer available. When determining the filename extension, a leading dot in a filenameis no longer ignored. Thus, .emacs is considered to haveextension emacs, rather than being extensionless. Emacs looks for special file handlers in a more efficient manner: itwill choose the first matching handler infile-name-handler-alist, rather than trying to figure out whichprovides the closest match. The predicate argument for read-file-name has beenremoved, and so have the variables read-file-name-function andread-file-name-completion-ignore-case. The functionread-directory-name has also been removed. The functions all-completions and try-completion will nolonger accept lists of strings or hash tables (it will still acceptalists, obarrays, and functions.) In addition, the functiontest-completion is no longer available. The ‘G’ interactive code character is no longer supported.Use ‘F’ instead. Arbitrary Lisp functions can no longer be recorded intobuffer-undo-list. As a consequence, yank-undo-functionis obsolete, and has been removed. Emacs will never complain about commands that accumulate too much undoinformation, so you no longer have to worry about bindingbuffer-undo-list to t for such commands (though you maywant to do that anyway, to avoid taking up unnecessary memory space.) Atomic change groups are no longer supported. The list returned by (match-data t) no longer records thebuffer as a final element. The function looking-back has been removed, so we no longerhave the benefit of hindsight. The variable search-spaces-regexp does not exist. Spacesalways stand for themselves in regular expression searches. The functions skip-chars-forward and skip-chars-backwardno longer accepts character classes such as ‘[:alpha:]’. Allcharacters are created equal. The yank-handler text property no longer has any meaning.Also, yank-excluded-properties, insert-for-yank, andinsert-buffer-substring-as-yank have all been removed. The variable char-property-alias-alist has been deleted.Aliases are for functions, not for properties. The function get-char-property-and-overlay has been deleted.If you want the properties at a point, find the text properties at thepoint; then, find the overlays at the point, and find the propertieson those overlays. Font Lock mode only manages face properties; you can't usefont-lock keywords to specify arbitrary text properties for it tomanage. After all, it is called Font Lock mode, not ArbitraryProperties Lock mode. The arguments to remove-overlays are no longer optional. In replace-match, the replacement text now inherits propertiesfrom the surrounding text. The variable mode-line-format no longer supports the :propertize,%i, and %I constructs. The functionformat-mode-line has been removed. The functions window-inside-edges and window-body-heighthave been removed. You should do the relevant calculations yourself,starting with window-width and window-height. The functions window-pixel-edges andwindow-inside-pixel-edges have been removed. We prefer tothink in terms of lines and columns, not pixel coordinates. (Sometimein the distant past, we will do away with graphical terminalsentirely, in favor of text terminals.) For similar reasons, thefunctions posn-at-point, posn-at-x-y, andwindow-line-height have been removed, andpos-visible-in-window-p no longer worries about partiallyvisible rows. The macro save-selected-window only saves the selected windowof the selected frame, so don't try selecting windows in other frames. The function minibufferp is no longer available. The function modify-all-frames-parameters has been removed (wealways suspected the name was ungrammatical, anyway.) The line-spacing variable no longer accepts float values. The function tool-bar-local-item-from-menu has been deleted.If you need to make an entry in the tool bar, you can still usetool-bar-add-item-from-menu, but that modifies the binding inthe source keymap instead of copying it into the local keymap. When determining the major mode, the file name takes precedence overthe interpreter magic line. The variable magic-mode-alist,which associates certain buffer beginnings with major modes, has beeneliminated. The hook after-change-major-mode-hook is not defined, andneither are run-mode-hooks and delay-mode-hooks. The variable minor-mode-list has been removed. define-derived-mode will copy abbrevs from the parent mode'sabbrev table, instead of creating a new, empty abbrev table. There are no “system” abbrevs. When the user saves into the abbrevsfile, all abbrevs are saved. The Warnings facility has been removed. Just use error. Several hook variables have been renamed to flout the Emacs namingconventions. We feel that consistency is boring, and havingnon-standard hook names encourages users to check the documentationbefore using a hook. For instance, the normal hookfind-file-hook has been renamed to find-file-hooks, andthe abnormal hook delete-frame-functions has been renamed todelete-frame-hook. The function symbol-file does not exist. If you want to knowwhich file defined a function or variable, try grepping for it. The variable load-history records function definitions justlike variable definitions, instead of indicating which functions werepreviously autoloaded. There is a new variable, recursive-load-depth-limit, whichspecifies how many times files can recursively load themselves; it is50 by default, and nil means infinity. Previously, Emacs signaled anerror after just 3 recursive loads, which was boring. Byte-compiler warnings and error messages will leave out the line andcharacter positions, in order to exercise your debugging skills.Also, there is no with-no-warnings macro—instead ofsuppressing compiler warnings, fix your code to avoid them! The function unsafep has been removed. File local variables can now specify a string with text properties.Since arbitrary Lisp expressions can be embedded in text properties,this can provide you with a great deal of flexibility and power. Onthe other hand, safe-local-eval-forms and thesafe-local-eval-function function property have no specialmeaning. You can no longer use char-displayable-p to test if Emacs candisplay a certain character. The function string-to-multibyte is no longer available. The translation-table-for-input translation table has beenremoved. Also, translation hash tables are no longer available, so wedon't need the functions lookup-character andlookup-integer. The table argument to translate-region can no longer bea char-table; it has to be a string. The variable auto-coding-functions and the two functionsmerge-coding-systems and decode-coding-inserted-regionhave been deleted. The coding system propertymime-text-unsuitable no longer has any special meaning. If pure storage overflows while dumping, Emacs won't tell you how muchadditional pure storage it needs. Try adding in increments of 20000,until you have enough. The variables gc-elapsed, gcs-done, andpost-gc-hook have been garbage-collected. GNU Free Documentation License

Version 1.2, November 2002

Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. PREAMBLEThe purpose of this License is to make a manual, textbook, or otherfunctional and useful document “free” in the sense of freedom: toassure everyone the effective freedom to copy and redistribute it,with or without modifying it, either commercially or noncommercially.Secondarily, this License preserves for the author and publisher a wayto get credit for their work, while not being considered responsiblefor modifications made by others.This License is a kind of “copyleft,” which means that derivativeworks of the document must themselves be free in the same sense. Itcomplements the GNU General Public License, which is a copyleftlicense designed for free software.We have designed this License in order to use it for manuals for freesoftware, because free software needs free documentation: a freeprogram should come with manuals providing the same freedoms that thesoftware does. But this License is not limited to software manuals;it can be used for any textual work, regardless of subject matter orwhether it is published as a printed book. We recommend this Licenseprincipally for works whose purpose is instruction or reference. APPLICABILITY AND DEFINITIONSThis License applies to any manual or other work, in any medium, thatcontains a notice placed by the copyright holder saying it can bedistributed under the terms of this License. Such a notice grants aworld-wide, royalty-free license, unlimited in duration, to use thatwork under the conditions stated herein. The “Document,” below,refers to any such manual or work. Any member of the public is alicensee, and is addressed as “you.” You accept the license if youcopy, modify or distribute the work in a way requiring permissionunder copyright law.A “Modified Version” of the Document means any work containing theDocument or a portion of it, either copied verbatim, or withmodifications and/or translated into another language.A “Secondary Section” is a named appendix or a front-matter section ofthe Document that deals exclusively with the relationship of thepublishers or authors of the Document to the Document's overall subject(or to related matters) and contains nothing that could fall directlywithin that overall subject. (Thus, if the Document is in part atextbook of mathematics, a Secondary Section may not explain anymathematics.) The relationship could be a matter of historicalconnection with the subject or with related matters, or of legal,commercial, philosophical, ethical or political position regardingthem.The “Invariant Sections” are certain Secondary Sections whose titlesare designated, as being those of Invariant Sections, in the noticethat says that the Document is released under this License. If asection does not fit the above definition of Secondary then it is notallowed to be designated as Invariant. The Document may contain zeroInvariant Sections. If the Document does not identify any InvariantSections then there are none.The “Cover Texts” are certain short passages of text that are listed,as Front-Cover Texts or Back-Cover Texts, in the notice that says thatthe Document is released under this License. A Front-Cover Text maybe at most 5 words, and a Back-Cover Text may be at most 25 words.A “Transparent” copy of the Document means a machine-readable copy,represented in a format whose specification is available to thegeneral public, that is suitable for revising the documentstraightforwardly with generic text editors or (for images composed ofpixels) generic paint programs or (for drawings) some widely availabledrawing editor, and that is suitable for input to text formatters orfor automatic translation to a variety of formats suitable for inputto text formatters. A copy made in an otherwise Transparent fileformat whose markup, or absence of markup, has been arranged to thwartor discourage subsequent modification by readers is not Transparent.An image format is not Transparent if used for any substantial amountof text. A copy that is not “Transparent” is called “Opaque.”Examples of suitable formats for Transparent copies include plainASCII without markup, Texinfo input format, LaTeX input format, SGMLor XML using a publicly available DTD, and standard-conforming simpleHTML, PostScript or PDF designed for human modification. Examples oftransparent image formats include PNG, XCF and JPG. Opaque formatsinclude proprietary formats that can be read and edited only byproprietary word processors, SGML or XML for which the DTD and/orprocessing tools are not generally available, and themachine-generated HTML, PostScript or PDF produced by some wordprocessors for output purposes only.The “Title Page” means, for a printed book, the title page itself,plus such following pages as are needed to hold, legibly, the materialthis License requires to appear in the title page. For works informats which do not have any title page as such, “Title Page” meansthe text near the most prominent appearance of the work's title,preceding the beginning of the body of the text.A section “Entitled XYZ” means a named subunit of the Document whosetitle either is precisely XYZ or contains XYZ in parentheses followingtext that translates XYZ in another language. (Here XYZ stands for aspecific section name mentioned below, such as “Acknowledgements,”“Dedications,” “Endorsements,” or “History.”) To “Preserve the Title”of such a section when you modify the Document means that it remains asection “Entitled XYZ” according to this definition.The Document may include Warranty Disclaimers next to the notice whichstates that this License applies to the Document. These WarrantyDisclaimers are considered to be included by reference in thisLicense, but only as regards disclaiming warranties: any otherimplication that these Warranty Disclaimers may have is void and hasno effect on the meaning of this License. VERBATIM COPYINGYou may copy and distribute the Document in any medium, eithercommercially or noncommercially, provided that this License, thecopyright notices, and the license notice saying this License appliesto the Document are reproduced in all copies, and that you add no otherconditions whatsoever to those of this License. You may not usetechnical measures to obstruct or control the reading or furthercopying of the copies you make or distribute. However, you may acceptcompensation in exchange for copies. If you distribute a large enoughnumber of copies you must also follow the conditions in section 3.You may also lend copies, under the same conditions stated above, andyou may publicly display copies. COPYING IN QUANTITYIf you publish printed copies (or copies in media that commonly haveprinted covers) of the Document, numbering more than 100, and theDocument's license notice requires Cover Texts, you must enclose thecopies in covers that carry, clearly and legibly, all these CoverTexts: Front-Cover Texts on the front cover, and Back-Cover Texts onthe back cover. Both covers must also clearly and legibly identifyyou as the publisher of these copies. The front cover must presentthe full title with all words of the title equally prominent andvisible. You may add other material on the covers in addition.Copying with changes limited to the covers, as long as they preservethe title of the Document and satisfy these conditions, can be treatedas verbatim copying in other respects.If the required texts for either cover are too voluminous to fitlegibly, you should put the first ones listed (as many as fitreasonably) on the actual cover, and continue the rest onto adjacentpages.If you publish or distribute Opaque copies of the Document numberingmore than 100, you must either include a machine-readable Transparentcopy along with each Opaque copy, or state in or with each Opaque copya computer-network location from which the general network-usingpublic has access to download using public-standard network protocolsa complete Transparent copy of the Document, free of added material.If you use the latter option, you must take reasonably prudent steps,when you begin distribution of Opaque copies in quantity, to ensurethat this Transparent copy will remain thus accessible at the statedlocation until at least one year after the last time you distribute anOpaque copy (directly or through your agents or retailers) of thatedition to the public.It is requested, but not required, that you contact the authors of theDocument well before redistributing any large number of copies, to givethem a chance to provide you with an updated version of the Document. MODIFICATIONSYou may copy and distribute a Modified Version of the Document underthe conditions of sections 2 and 3 above, provided that you releasethe Modified Version under precisely this License, with the ModifiedVersion filling the role of the Document, thus licensing distributionand modification of the Modified Version to whoever possesses a copyof it. In addition, you must do these things in the Modified Version:A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.C. State on the Title page the name of the publisher of the Modified Version, as the publisher.D. Preserve all the copyright notices of the Document.E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.H. Include an unaltered copy of this License.I. Preserve the section Entitled “History,” Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.K. For any section Entitled “Acknowledgements” or “Dedications,” Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.M. Delete any section Entitled “Endorsements.” Such a section may not be included in the Modified Version.N. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.O. Preserve any Warranty Disclaimers.If the Modified Version includes new front-matter sections orappendices that qualify as Secondary Sections and contain no materialcopied from the Document, you may at your option designate some or allof these sections as invariant. To do this, add their titles to thelist of Invariant Sections in the Modified Version's license notice.These titles must be distinct from any other section titles.You may add a section Entitled “Endorsements,” provided it containsnothing but endorsements of your Modified Version by variousparties–for example, statements of peer review or that the text hasbeen approved by an organization as the authoritative definition of astandard.You may add a passage of up to five words as a Front-Cover Text, and apassage of up to 25 words as a Back-Cover Text, to the end of the listof Cover Texts in the Modified Version. Only one passage ofFront-Cover Text and one of Back-Cover Text may be added by (orthrough arrangements made by) any one entity. If the Document alreadyincludes a cover text for the same cover, previously added by you orby arrangement made by the same entity you are acting on behalf of,you may not add another; but you may replace the old one, on explicitpermission from the previous publisher that added the old one.The author(s) and publisher(s) of the Document do not by this Licensegive permission to use their names for publicity for or to assert orimply endorsement of any Modified Version. COMBINING DOCUMENTSYou may combine the Document with other documents released under thisLicense, under the terms defined in section 4 above for modifiedversions, provided that you include in the combination all of theInvariant Sections of all of the original documents, unmodified, andlist them all as Invariant Sections of your combined work in itslicense notice, and that you preserve all their Warranty Disclaimers.The combined work need only contain one copy of this License, andmultiple identical Invariant Sections may be replaced with a singlecopy. If there are multiple Invariant Sections with the same name butdifferent contents, make the title of each such section unique byadding at the end of it, in parentheses, the name of the originalauthor or publisher of that section if known, or else a unique number.Make the same adjustment to the section titles in the list ofInvariant Sections in the license notice of the combined work.In the combination, you must combine any sections Entitled “History”in the various original documents, forming one section Entitled“History”; likewise combine any sections Entitled “Acknowledgements,”and any sections Entitled “Dedications.” You must delete all sectionsEntitled “Endorsements.” COLLECTIONS OF DOCUMENTSYou may make a collection consisting of the Document and other documentsreleased under this License, and replace the individual copies of thisLicense in the various documents with a single copy that is included inthe collection, provided that you follow the rules of this License forverbatim copying of each of the documents in all other respects.You may extract a single document from such a collection, and distributeit individually under this License, provided you insert a copy of thisLicense into the extracted document, and follow this License in allother respects regarding verbatim copying of that document. AGGREGATION WITH INDEPENDENT WORKSA compilation of the Document or its derivatives with other separateand independent documents or works, in or on a volume of a storage ordistribution medium, is called an “aggregate” if the copyrightresulting from the compilation is not used to limit the legal rightsof the compilation's users beyond what the individual works permit.When the Document is included in an aggregate, this License does notapply to the other works in the aggregate which are not themselvesderivative works of the Document.If the Cover Text requirement of section 3 is applicable to thesecopies of the Document, then if the Document is less than one half ofthe entire aggregate, the Document's Cover Texts may be placed oncovers that bracket the Document within the aggregate, or theelectronic equivalent of covers if the Document is in electronic form.Otherwise they must appear on printed covers that bracket the wholeaggregate. TRANSLATIONTranslation is considered a kind of modification, so you maydistribute translations of the Document under the terms of section 4.Replacing Invariant Sections with translations requires specialpermission from their copyright holders, but you may includetranslations of some or all Invariant Sections in addition to theoriginal versions of these Invariant Sections. You may include atranslation of this License, and all the license notices in theDocument, and any Warranty Disclaimers, provided that you also includethe original English version of this License and the original versionsof those notices and disclaimers. In case of a disagreement betweenthe translation and the original version of this License or a noticeor disclaimer, the original version will prevail.If a section in the Document is Entitled “Acknowledgements,”“Dedications,” or “History,” the requirement (section 4) to Preserveits Title (section 1) will typically require changing the actualtitle. TERMINATIONYou may not copy, modify, sublicense, or distribute the Document exceptas expressly provided for under this License. Any other attempt tocopy, modify, sublicense or distribute the Document is void, and willautomatically terminate your rights under this License. However,parties who have received copies, or rights, from you under thisLicense will not have their licenses terminated so long as suchparties remain in full compliance. FUTURE REVISIONS OF THIS LICENSEThe Free Software Foundation may publish new, revised versionsof the GNU Free Documentation License from time to time. Such newversions will be similar in spirit to the present version, but maydiffer in detail to address new problems or concerns. Seehttp://www.gnu.org/copyleft/.Each version of the License is given a distinguishing version number.If the Document specifies that a particular numbered version of thisLicense “or any later version” applies to it, you have the option offollowing the terms and conditions either of that specified version orof any later version that has been published (not as a draft) by theFree Software Foundation. If the Document does not specify a versionnumber of this License, you may choose any version ever published (notas a draft) by the Free Software Foundation. ADDENDUM: How to use this License for your documents To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page: Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License.'' If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this: with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list. If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation. If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software. <setfilename>../info/gpl</setfilename> GNU General Public License

Version 2, June 1991

Copyright © 1989, 1991 Free Software Foundation, Inc. 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software—to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Lesser General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things. To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it. For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights. We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software. Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations. Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

This License applies to any program or other work which containsa notice placed by the copyright holder saying it may be distributedunder the terms of this General Public License. The “Program”, below,refers to any such program or work, and a “work based on the Program”means either the Program or any derivative work under copyright law:that is to say, a work containing the Program or a portion of it,either verbatim or with modifications and/or translated into anotherlanguage. (Hereinafter, translation is included without limitation inthe term “modification”.) Each licensee is addressed as “you”.Activities other than copying, distribution and modification are notcovered by this License; they are outside its scope. The act ofrunning the Program is not restricted, and the output from the Programis covered only if its contents constitute a work based on theProgram (independent of having been made by running the Program).Whether that is true depends on what the Program does. You may copy and distribute verbatim copies of the Program'ssource code as you receive it, in any medium, provided that youconspicuously and appropriately publish on each copy an appropriatecopyright notice and disclaimer of warranty; keep intact all thenotices that refer to this License and to the absence of any warranty;and give any other recipients of the Program a copy of this Licensealong with the Program.You may charge a fee for the physical act of transferring a copy, andyou may at your option offer warranty protection in exchange for a fee. You may modify your copy or copies of the Program or any portionof it, thus forming a work based on the Program, and copy anddistribute such modifications or work under the terms of Section 1above, provided that you also meet all of these conditions: You must cause the modified files to carry prominent noticesstating that you changed the files and the date of any change. You must cause any work that you distribute or publish, that inwhole or in part contains or is derived from the Program or anypart thereof, to be licensed as a whole at no charge to all thirdparties under the terms of this License. If the modified program normally reads commands interactivelywhen run, you must cause it, when started running for suchinteractive use in the most ordinary way, to print or display anannouncement including an appropriate copyright notice and anotice that there is no warranty (or else, saying that you providea warranty) and that users may redistribute the program underthese conditions, and telling the user how to view a copy of thisLicense. (Exception: if the Program itself is interactive butdoes not normally print such an announcement, your work based onthe Program is not required to print an announcement.) These requirements apply to the modified work as a whole. Ifidentifiable sections of that work are not derived from the Program,and can be reasonably considered independent and separate works inthemselves, then this License, and its terms, do not apply to thosesections when you distribute them as separate works. But when youdistribute the same sections as part of a whole which is a work basedon the Program, the distribution of the whole must be on the terms ofthis License, whose permissions for other licensees extend to theentire whole, and thus to each and every part regardless of who wrote it.Thus, it is not the intent of this section to claim rights or contestyour rights to work written entirely by you; rather, the intent is toexercise the right to control the distribution of derivative orcollective works based on the Program.In addition, mere aggregation of another work not based on the Programwith the Program (or with a work based on the Program) on a volume ofa storage or distribution medium does not bring the other work underthe scope of this License. You may copy and distribute the Program (or a work based on it,under Section 2) in object code or executable form under the terms ofSections 1 and 2 above provided that you also do one of the following: Accompany it with the complete corresponding machine-readablesource code, which must be distributed under the terms of Sections1 and 2 above on a medium customarily used for software interchange; or, Accompany it with a written offer, valid for at least threeyears, to give any third party, for a charge no more than yourcost of physically performing source distribution, a completemachine-readable copy of the corresponding source code, to bedistributed under the terms of Sections 1 and 2 above on a mediumcustomarily used for software interchange; or, Accompany it with the information you received as to the offerto distribute corresponding source code. (This alternative isallowed only for noncommercial distribution and only if youreceived the program in object code or executable form with suchan offer, in accord with Subsection b above.) The source code for a work means the preferred form of the work formaking modifications to it. For an executable work, complete sourcecode means all the source code for all modules it contains, plus anyassociated interface definition files, plus the scripts used tocontrol compilation and installation of the executable. However, as aspecial exception, the source code distributed need not includeanything that is normally distributed (in either source or binaryform) with the major components (compiler, kernel, and so on) of theoperating system on which the executable runs, unless that componentitself accompanies the executable.If distribution of executable or object code is made by offeringaccess to copy from a designated place, then offering equivalentaccess to copy the source code from the same place counts asdistribution of the source code, even though third parties are notcompelled to copy the source along with the object code. You may not copy, modify, sublicense, or distribute the Programexcept as expressly provided under this License. Any attemptotherwise to copy, modify, sublicense or distribute the Program isvoid, and will automatically terminate your rights under this License.However, parties who have received copies, or rights, from you underthis License will not have their licenses terminated so long as suchparties remain in full compliance. You are not required to accept this License, since you have notsigned it. However, nothing else grants you permission to modify ordistribute the Program or its derivative works. These actions areprohibited by law if you do not accept this License. Therefore, bymodifying or distributing the Program (or any work based on theProgram), you indicate your acceptance of this License to do so, andall its terms and conditions for copying, distributing or modifyingthe Program or works based on it. Each time you redistribute the Program (or any work based on theProgram), the recipient automatically receives a license from theoriginal licensor to copy, distribute or modify the Program subject tothese terms and conditions. You may not impose any furtherrestrictions on the recipients' exercise of the rights granted herein.You are not responsible for enforcing compliance by third parties tothis License. If, as a consequence of a court judgment or allegation of patentinfringement or for any other reason (not limited to patent issues),conditions are imposed on you (whether by court order, agreement orotherwise) that contradict the conditions of this License, they do notexcuse you from the conditions of this License. If you cannotdistribute so as to satisfy simultaneously your obligations under thisLicense and any other pertinent obligations, then as a consequence youmay not distribute the Program at all. For example, if a patentlicense would not permit royalty-free redistribution of the Program byall those who receive copies directly or indirectly through you, thenthe only way you could satisfy both it and this License would be torefrain entirely from distribution of the Program.If any portion of this section is held invalid or unenforceable underany particular circumstance, the balance of the section is intended toapply and the section as a whole is intended to apply in othercircumstances.It is not the purpose of this section to induce you to infringe anypatents or other property right claims or to contest validity of anysuch claims; this section has the sole purpose of protecting theintegrity of the free software distribution system, which isimplemented by public license practices. Many people have madegenerous contributions to the wide range of software distributedthrough that system in reliance on consistent application of thatsystem; it is up to the author/donor to decide if he or she is willingto distribute software through any other system and a licensee cannotimpose that choice.This section is intended to make thoroughly clear what is believed tobe a consequence of the rest of this License. If the distribution and/or use of the Program is restricted incertain countries either by patents or by copyrighted interfaces, theoriginal copyright holder who places the Program under this Licensemay add an explicit geographical distribution limitation excludingthose countries, so that distribution is permitted only in or amongcountries not thus excluded. In such case, this License incorporatesthe limitation as if written in the body of this License. The Free Software Foundation may publish revised and/or new versionsof the General Public License from time to time. Such new versions willbe similar in spirit to the present version, but may differ in detail toaddress new problems or concerns.Each version is given a distinguishing version number. If the Programspecifies a version number of this License which applies to it and “anylater version”, you have the option of following the terms and conditionseither of that version or of any later version published by the FreeSoftware Foundation. If the Program does not specify a version number ofthis License, you may choose any version ever published by the Free SoftwareFoundation. If you wish to incorporate parts of the Program into other freeprograms whose distribution conditions are different, write to the authorto ask for permission. For software which is copyrighted by the FreeSoftware Foundation, write to the Free Software Foundation; we sometimesmake exceptions for this. Our decision will be guided by the two goalsof preserving the free status of all derivatives of our free software andof promoting the sharing and reuse of software generally.

NO WARRANTY

BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTYFOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHENOTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIESPROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSEDOR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OFMERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK ASTO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THEPROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,REPAIR OR CORRECTION. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITINGWILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/ORREDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISINGOUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITEDTO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BYYOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHERPROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THEPOSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found. one line to give the program's name and a brief idea of what it does. Copyright (C) yyyy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) yyyy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘show w’ and ‘show c’; they could even be mouse-clicks or menu items—whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. <setfilename>../info/tips</setfilename> Tips and Conventions tips for writing Lisp standards of coding style coding standards This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow. You can automatically check some of the conventions described below by running the command M-x checkdoc RET when visiting a Lisp file. It cannot check all of the conventions, and not all the warnings it gives necessarily correspond to problems, but it is worth examining them all. Emacs Lisp Coding Conventions coding conventions in Emacs Lisp Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use: Simply loading the package should not change Emacs's editing behavior.Include a command or commands to enable and disable the feature,or to invoke it.This convention is mandatory for any file that includes customdefinitions. If fixing such a file to follow this convention requiresan incompatible change, go ahead and make the incompatible change;don't postpone it. Since all global variables share the same name space, and allfunctions share another name space, you should choose a short word todistinguish your program from other Lisp programs Thebenefits of a Common Lisp-style package system are considered not tooutweigh the costs. . Then take care to begin the names of all globalvariables, constants, and functions in your program with the chosenprefix. This helps avoid name conflicts.Occasionally, for a command name intended for users to use, it is moreconvenient if some words come before the package's name prefix. Andconstructs that define functions, variables, etc., work better if theystart with ‘defun’ or ‘defvar’, so put the name prefix lateron in the name.This recommendation applies even to names for traditional Lispprimitives that are not primitives in Emacs Lisp—such ascopy-list. Believe it or not, there is more than one plausibleway to define copy-list. Play it safe; append your name prefixto produce a name like foo-copy-list or mylib-copy-listinstead.If you write a function that you think ought to be added to Emacs undera certain name, such as twiddle-files, don't call it by that namein your program. Call it mylib-twiddle-files in your program,and send mail to ‘bug-gnu-emacs@gnu.org’ suggesting we addit to Emacs. If and when we do, we can change the name easily enough.If one prefix is insufficient, your package can use two or threealternative common prefixes, so long as they make sense.Separate the prefix from the rest of the symbol name with a hyphen,‘-’. This will be consistent with Emacs itself and with most EmacsLisp programs. Put a call to provide at the end of each separate Lisp file. If a file requires certain other Lisp programs to be loadedbeforehand, then the comments at the beginning of the file should sayso. Also, use require to make sure they are loaded. If one file foo uses a macro defined in another file bar,foo should contain this expression before the first use of themacro: (eval-when-compile (require 'bar)) (And the library bar should contain (provide 'bar),to make the require work.) This will cause bar to beloaded when you byte-compile foo. Otherwise, you risk compilingfoo without the necessary macro loaded, and that would producecompiled code that won't work right. See .Using eval-when-compile avoids loading bar whenthe compiled version of foo is used. Please don't require the cl package of Common Lisp extensions atrun time. Use of this package is optional, and it is not part of thestandard Emacs namespace. If your package loads cl at run time,that could cause name clashes for users who don't use that package.However, there is no problem with using the cl package atcompile time, with (eval-when-compile (require 'cl)). That'ssufficient for using the macros in the cl package, because thecompiler expands them before generating the byte-code. When defining a major mode, please follow the major modeconventions. See . When defining a minor mode, please follow the minor modeconventions. See . If the purpose of a function is to tell you whether a certain conditionis true or false, give the function a name that ends in ‘p’. Ifthe name is one word, add just ‘p’; if the name is multiple words,add ‘-p’. Examples are framep and frame-live-p. If a user option variable records a true-or-false condition, give it aname that ends in ‘-flag’. If the purpose of a variable is to store a single function, give it aname that ends in ‘-function’. If the purpose of a variable isto store a list of functions (i.e., the variable is a hook), pleasefollow the naming conventions for hooks. See . unloading packages, preparing forIf loading the file adds functions to hooks, define a functionfeature-unload-hook, where feature is the name ofthe feature the package provides, and make it undo any such changes.Using unload-feature to unload the file will run this function.See . It is a bad idea to define aliases for the Emacs primitives. Normallyyou should use the standard names instead. The case where an aliasmay be useful is where it facilitates backwards compatibility orportability. If a package needs to define an alias or a new function forcompatibility with some other version of Emacs, name it with the packageprefix, not with the raw name with which it occurs in the other version.Here is an example from Gnus, which provides many examples of suchcompatibility issues. (defalias 'gnus-point-at-bol (if (fboundp 'point-at-bol) 'point-at-bol 'line-beginning-position)) Redefining (or advising) an Emacs primitive is a bad idea. It may dothe right thing for a particular program, but there is no telling whatother programs might break as a result. In any case, it is a problemfor debugging, because the advised function doesn't do what its sourcecode says it does. If the programmer investigating the problem isunaware that there is advice on the function, the experience can bevery frustrating.We hope to remove all the places in Emacs that advise primitives.In the mean time, please don't add any more. It is likewise a bad idea for one Lisp package to advise a functionin another Lisp package. Likewise, avoid using eval-after-load (see ) in libraries and packages. This feature is meant forpersonal customizations; using it in a Lisp program is unclean,because it modifies the behavior of another Lisp file in a way that'snot visible in that file. This is an obstacle for debugging, muchlike advising a function in the other package. If a file does replace any of the functions or library programs ofstandard Emacs, prominent comments at the beginning of the file shouldsay which functions are replaced, and how the behavior of thereplacements differs from that of the originals. Constructs that define a function or variable should be macros,not functions, and their names should start with ‘def’. A macro that defines a function or variable should have a name thatstarts with ‘define-’. The macro should receive the name to bedefined as the first argument. That will help various tools find thedefinition automatically. Avoid constructing the names in the macroitself, since that would confuse these tools. Please keep the names of your Emacs Lisp source files to 13 charactersor less. This way, if the files are compiled, the compiled files' nameswill be 14 characters or less, which is short enough to fit on all kindsof Unix systems. In some other systems there is a convention of choosing variable namesthat begin and end with ‘*’. We don't use that convention in EmacsLisp, so please don't use it in your programs. (Emacs uses such namesonly for special-purpose buffers.) The users will find Emacs morecoherent if all libraries use the same conventions. If your program contains non-ASCII characters in string or characterconstants, you should make sure Emacs always decodes these charactersthe same way, regardless of the user's settings. There are two waysto do that: Use coding system emacs-mule, and specify that forcoding in the ‘-*-’ line or the local variables list. ;; XXX.el -*- coding: emacs-mule; -*- Use one of the coding systems based on ISO 2022 (such asiso-8859-n and iso-2022-7bit), and specify it with ‘!’ atthe end for coding. (The ‘!’ turns off any possiblecharacter translation.) ;; XXX.el -*- coding: iso-latin-2!; -*- Indent each function with C-M-q (indent-sexp) using thedefault indentation parameters. Don't make a habit of putting close-parentheses on lines by themselves;Lisp programmers find this disconcerting. Once in a while, when thereis a sequence of many consecutive close-parentheses, it may make senseto split the sequence in one or two significant places. Please put a copyright notice and copying permission notice on thefile if you distribute copies. Use a notice like this one: ;; Copyright (C) year name ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; This program is distributed in the hope that it will be ;; useful, but WITHOUT ANY WARRANTY; without even the implied ;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR ;; PURPOSE. See the GNU General Public License for more details. ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor, ;; Boston, MA 02110-1301 USA If you have signed papers to assign the copyright to the Foundation,then use ‘Free Software Foundation, Inc.’ as name.Otherwise, use your name. See also See . Key Binding Conventions key binding, conventions for mouse-2 references, followingSpecial major modes used for read-only text should usually redefinemouse-2 and RET to trace some sort of reference in the text.Modes such as Dired, Info, Compilation, and Occur redefine it in thisway.In addition, they should mark the text as a kind of “link” so thatmouse-1 will follow it also. See . reserved keys keys, reservedPlease do not define C-c letter as a key in Lisp programs.Sequences consisting of C-c and a letter (either upper or lowercase) are reserved for users; they are the only sequencesreserved for users, so do not block them.Changing all the Emacs major modes to respect this convention was alot of work; abandoning this convention would make that work go towaste, and inconvenience users. Please comply with it. Function keys F5 through F9 without modifier keys arealso reserved for users to define. Applications should not bind mouse events based on button 1 with theshift key held down. These events include S-mouse-1,M-S-mouse-1, C-S-mouse-1, and so on. They are reserved forusers. Sequences consisting of C-c followed by a control character or adigit are reserved for major modes. Sequences consisting of C-c followed by {, },<, >, : or ; are also reserved for major modes. Sequences consisting of C-c followed by any other punctuationcharacter are allocated for minor modes. Using them in a major mode isnot absolutely prohibited, but if you do that, the major mode bindingmay be shadowed from time to time by minor modes. Do not bind C-h following any prefix character (includingC-c). If you don't bind C-h, it is automatically availableas a help character for listing the subcommands of the prefix character. Do not bind a key sequence ending in ESC except followinganother ESC. (That is, it is OK to bind a sequence ending inESC ESC.)The reason for this rule is that a non-prefix binding for ESC inany context prevents recognition of escape sequences as function keys inthat context. Anything which acts like a temporary mode or state which the user canenter and leave should define ESC ESC orESC ESC ESC as a way to escape.For a state which accepts ordinary Emacs commands, or more generally anykind of state in which ESC followed by a function key or arrow keyis potentially meaningful, then you must not define ESCESC, since that would preclude recognizing an escape sequenceafter ESC. In these states, you should define ESCESC ESC as the way to escape. Otherwise, defineESC ESC instead. Emacs Programming Tips programming conventions Following these conventions will make your program fit better into Emacs when it runs. Don't use next-line or previous-line in programs; nearlyalways, forward-line is more convenient as well as morepredictable and robust. See . Don't call functions that set the mark, unless setting the mark is oneof the intended features of your program. The mark is a user-levelfeature, so it is incorrect to change the mark except to supply a valuefor the user's benefit. See .In particular, don't use any of these functions: beginning-of-buffer, end-of-buffer replace-string, replace-regexp insert-file, insert-buffer If you just want to move point, or replace a certain string, or inserta file or buffer's contents, without any of the other featuresintended for interactive users, you can replace these functions withone or two lines of simple Lisp code. Use lists rather than vectors, except when there is a particular reasonto use a vector. Lisp has more facilities for manipulating lists thanfor vectors, and working with lists is usually more convenient.Vectors are advantageous for tables that are substantial in size and areaccessed in random order (not searched front to back), provided there isno need to insert or delete elements (only lists allow that). The recommended way to show a message in the echo area is withthe message function, not princ. See . When you encounter an error condition, call the function error(or signal). The function error does not return.See .Do not use message, throw, sleep-for,or beep to report errors. An error message should start with a capital letter but should not endwith a period. A question asked in the minibuffer with y-or-n-p oryes-or-no-p should start with a capital letter and end with‘? ’. When you mention a default value in a minibuffer prompt,put it and the word ‘default’ inside parentheses.It should look like this: Enter the answer (default 42): In interactive, if you use a Lisp expression to produce a listof arguments, don't try to provide the “correct” default values forregion or position arguments. Instead, provide nil for thosearguments if they were not specified, and have the function bodycompute the default value when the argument is nil. Forinstance, write this: (defun foo (pos) (interactive (list (if specified specified-pos))) (unless pos (setq pos default-pos)) ...) rather than this: (defun foo (pos) (interactive (list (if specified specified-pos default-pos))) ...) This is so that repetition of the command will recomputethese defaults based on the current circumstances.You do not need to take such precautions when you use interactivespecs ‘d’, ‘m’ and ‘r’, because they make specialarrangements to recompute the argument values on repetition of thecommand. Many commands that take a long time to execute display a message thatsays something like ‘Operating...’ when they start, and change it to‘Operating...done’ when they finish. Please keep the style ofthese messages uniform: no space around the ellipsis, andno period after ‘done’. Try to avoid using recursive edits. Instead, do what the Rmail ecommand does: use a new local keymap that contains one command definedto switch back to the old local keymap. Or do what theedit-options command does: switch to another buffer and let theuser switch back at will. See . Tips for Making Compiled Code Fast execution speed speedups Here are ways of improving the execution speed of byte-compiled Lisp programs. profiling timing programs elp.elProfile your program with the elp library. See the fileelp.el for instructions. benchmark.el benchmarkingCheck the speed of individual Emacs Lisp forms using thebenchmark library. See the functions benchmark-run andbenchmark-run-compiled in benchmark.el. Use iteration rather than recursion whenever possible.Function calls are slow in Emacs Lisp even when a compiled functionis calling another compiled function. Using the primitive list-searching functions memq, member,assq, or assoc is even faster than explicit iteration. Itcan be worth rearranging a data structure so that one of these primitivesearch functions can be used. Certain built-in functions are handled specially in byte-compiled code,avoiding the need for an ordinary function call. It is a good idea touse these functions rather than alternatives. To see whether a functionis handled specially by the compiler, examine its byte-compileproperty. If the property is non-nil, then the function ishandled specially.For example, the following input will show you that aref iscompiled specially (see ): (get 'aref 'byte-compile) => byte-compile-two-args If calling a small function accounts for a substantial part of yourprogram's running time, make the function inline. This eliminatesthe function call overhead. Since making a function inline reducesthe flexibility of changing the program, don't do it unless it givesa noticeable speedup in something slow enough that users care aboutthe speed. See . Tips for Avoiding Compiler Warnings byte compiler warnings, how to avoid Try to avoid compiler warnings about undefined free variables, by addingdummy defvar definitions for these variables, like this: (defvar foo) Such a definition has no effect except to tell the compilernot to warn about uses of the variable foo in this file. If you use many functions and variables from a certain file, you canadd a require for that package to avoid compilation warningsfor them. For instance, (eval-when-compile (require 'foo)) If you bind a variable in one function, and use it or set it inanother function, the compiler warns about the latter function unlessthe variable has a definition. But adding a definition would beunclean if the variable has a short name, since Lisp packages shouldnot define short variable names. The right thing to do is to renamethis variable to start with the name prefix used for the otherfunctions and variables in your package. The last resort for avoiding a warning, when you want to do somethingthat usually is a mistake but it's not a mistake in this one case,is to put a call to with-no-warnings around it. Tips for Documentation Strings documentation strings, conventions and tips checkdoc-minor-mode Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command M-x checkdoc-minor-mode. Every command, function, or variable intended for users to know aboutshould have a documentation string. An internal variable or subroutine of a Lisp program might as well havea documentation string. In earlier Emacs versions, you could save spaceby using a comment instead of a documentation string, but that is nolonger the case—documentation strings now take up very little space ina running Emacs. Format the documentation string so that it fits in an Emacs window on an80-column screen. It is a good idea for most lines to be no wider than60 characters. The first line should not be wider than 67 charactersor it will look bad in the output of apropos.You can fill the text if that looks good. However, rather than blindlyfilling the entire documentation string, you can often make it much morereadable by choosing certain line breaks with care. Use blank linesbetween topics if the documentation string is long. The first line of the documentation string should consist of one or twocomplete sentences that stand on their own as a summary. M-xapropos displays just the first line, and if that line's contents don'tstand on their own, the result looks bad. In particular, start thefirst line with a capital letter and end with a period.For a function, the first line should briefly answer the question,“What does this function do?” For a variable, the first line shouldbriefly answer the question, “What does this value mean?”Don't limit the documentation string to one line; use as many lines asyou need to explain the details of how to use the function orvariable. Please use complete sentences for the rest of the text too. When the user tries to use a disabled command, Emacs displays just thefirst paragraph of its documentation string—everything through thefirst blank line. If you wish, you can choose which information toinclude before the first blank line so as to make this display useful. The first line should mention all the important arguments of thefunction, and should mention them in the order that they are writtenin a function call. If the function has many arguments, then it isnot feasible to mention them all in the first line; in that case, thefirst line should mention the first few arguments, including the mostimportant arguments. When a function's documentation string mentions the value of an argumentof the function, use the argument name in capital letters as if it werea name for that value. Thus, the documentation string of the functioneval refers to its second argument as ‘FORM’, because theactual argument name is form: Evaluate FORM and return its value. Also write metasyntactic variables in capital letters, such as when youshow the decomposition of a list or vector into subunits, some of whichmay vary. ‘KEY’ and ‘VALUE’ in the following exampleillustrate this practice: The argument TABLE should be an alist whose elements have the form (KEY . VALUE). Here, KEY is ... Never change the case of a Lisp symbol when you mention it in a docstring. If the symbol's name is foo, write “foo,” not“Foo” (which is a different symbol).This might appear to contradict the policy of writing functionargument values, but there is no real contradiction; the argumentvalue is not the same thing as the symbol which thefunction uses to hold the value.If this puts a lower-case letter at the beginning of a sentenceand that annoys you, rewrite the sentence so that the symbolis not at the start of it. Do not start or end a documentation string with whitespace. Do not indent subsequent lines of a documentation string sothat the text is lined up in the source code with the text of the firstline. This looks nice in the source code, but looks bizarre when usersview the documentation. Remember that the indentation before thestarting double-quote is not part of the string! When a documentation string refers to a Lisp symbol, write it as itwould be printed (which usually means in lower case), with single-quotesaround it. For example: ‘lambda’. There are two exceptions: writet and nil without single-quotes. (In this manual, we use a differentconvention, with single-quotes for all symbols.) hyperlinks in documentation stringsHelp mode automatically creates a hyperlink when a documentation stringuses a symbol name inside single quotes, if the symbol has either afunction or a variable definition. You do not need to do anythingspecial to make use of this feature. However, when a symbol has both afunction definition and a variable definition, and you want to refer tojust one of them, you can specify which one by writing one of the words‘variable’, ‘option’, ‘function’, or ‘command’,immediately before the symbol name. (Case makes no difference inrecognizing these indicator words.) For example, if you write This function sets the variable `buffer-file-name'. then the hyperlink will refer only to the variable documentation ofbuffer-file-name, and not to its function documentation.If a symbol has a function definition and/or a variable definition, butthose are irrelevant to the use of the symbol that you are documenting,you can write the words ‘symbol’ or ‘program’ before thesymbol name to prevent making any hyperlink. For example, If the argument KIND-OF-RESULT is the symbol `list', this function returns a list of all the objects that satisfy the criterion. does not make a hyperlink to the documentation, irrelevant here, of thefunction list.Normally, no hyperlink is made for a variable without variabledocumentation. You can force a hyperlink for such variables bypreceding them with one of the words ‘variable’ or‘option’.Hyperlinks for faces are only made if the face name is preceded orfollowed by the word ‘face’. In that case, only the facedocumentation will be shown, even if the symbol is also defined as avariable or as a function.To make a hyperlink to Info documentation, write the name of the Infonode (or anchor) in single quotes, preceded by ‘info node’,‘Info node’, ‘info anchor’ or ‘Info anchor’. The Infofile name defaults to ‘emacs’. For example, See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'. Finally, to create a hyperlink to URLs, write the URL in singlequotes, preceded by ‘URL’. For example, The home page for the GNU project has more information (see URL `http://www.gnu.org/'). Don't write key sequences directly in documentation strings. Instead,use the ‘\\[…]’ construct to stand for them. For example,instead of writing ‘C-f’, write the construct‘\\[forward-char]’. When Emacs displays the documentation string,it substitutes whatever key is currently bound to forward-char.(This is normally ‘C-f’, but it may be some other character if theuser has moved key bindings.) See . In documentation strings for a major mode, you will want to refer to thekey bindings of that mode's local map, rather than global ones.Therefore, use the construct ‘\\<…>’ once in thedocumentation string to specify which key map to use. Do this beforethe first use of ‘\\[…]’. The text inside the‘\\<…>’ should be the name of the variable containing thelocal keymap for the major mode.It is not practical to use ‘\\[…]’ very many times, becausedisplay of the documentation string will become slow. So use this todescribe the most important commands in your major mode, and then use‘\\{…}’ to display the rest of the mode's keymap. For consistency, phrase the verb in the first sentence of a function'sdocumentation string as an imperative—for instance, use “Return thecons of A and B.” in preference to “Returns the cons of A and B.”Usually it looks good to do likewise for the rest of the firstparagraph. Subsequent paragraphs usually look better if each sentenceis indicative and has a proper subject. The documentation string for a function that is a yes-or-no predicateshould start with words such as “Return t if,” to indicateexplicitly what constitutes “truth.” The word “return” avoidsstarting the sentence with lower-case “t,” which could be somewhatdistracting. If a line in a documentation string begins with an open-parenthesis,write a backslash before the open-parenthesis, like this: The argument FOO can be either a number \(a buffer position) or a string (a file name). This prevents the open-parenthesis from being treated as the start of adefun (see See section ``Defuns'' in The GNU Emacs Manual). Write documentation strings in the active voice, not the passive, and inthe present tense, not the future. For instance, use “Return a listcontaining A and B.” instead of “A list containing A and B will bereturned.” Avoid using the word “cause” (or its equivalents) unnecessarily.Instead of, “Cause Emacs to display text in boldface,” write just“Display text in boldface.” When a command is meaningful only in a certain mode or situation,do mention that in the documentation string. For example,the documentation of dired-find-file is: In Dired, visit the file or directory named on this line. When you define a variable that users ought to set interactively, younormally should use defcustom. However, if for some reason youuse defvar instead, start the doc string with a ‘*’.See . The documentation string for a variable that is a yes-or-no flag shouldstart with words such as “Non-nil means,” to make it clear thatall non-nil values are equivalent and indicate explicitly whatnil and non-nil mean. Tips on Writing Comments comments, Lisp convention for We recommend these conventions for where to put comments and how to indent them: ‘;’ Comments that start with a single semicolon, ‘;’, should all bealigned to the same column on the right of the source code. Suchcomments usually explain how the code on the same line does its job. InLisp mode and related modes, the M-; (indent-for-comment)command automatically inserts such a ‘;’ in the right place, oraligns such a comment if it is already present.This and following examples are taken from the Emacs sources. (setq base-version-list ; there was a base (assoc (substring fn 0 start-vn) ; version to which file-version-assoc-list)) ; this looks like ; a subversion ‘;;’ Comments that start with two semicolons, ‘;;’, should be aligned tothe same level of indentation as the code. Such comments usuallydescribe the purpose of the following lines or the state of the programat that point. For example: (prog1 (setq auto-fill-function … … ;; update mode line (force-mode-line-update))) We also normally use two semicolons for comments outside functions. ;; This Lisp code is run in Emacs ;; when it is to operate as a server ;; for other processes. Every function that has no documentation string (presumably one that isused only internally within the package it belongs to), should insteadhave a two-semicolon comment right before the function, explaining whatthe function does and how to call it properly. Explain precisely whateach argument means and how the function interprets its possible values. ‘;;;’ Comments that start with three semicolons, ‘;;;’, should start atthe left margin. These are used, occasionally, for comments withinfunctions that should start at the margin. We also use them sometimesfor comments that are between functions—whether to use two or threesemicolons depends on whether the comment should be considered a“heading” by Outline minor mode. By default, comments starting withat least three semicolons (followed by a single space and anon-whitespace character) are considered headings, comments startingwith two or less are not.Another use for triple-semicolon comments is for commenting out lineswithin a function. We use three semicolons for this precisely so thatthey remain at the left margin. By default, Outline minor mode doesnot consider a comment to be a heading (even if it starts with atleast three semicolons) if the semicolons are followed by at least twospaces. Thus, if you add an introductory comment to the commented outcode, make sure to indent it by at least two spaces after the threesemicolons. (defun foo (a) ;;; This is no longer necessary. ;;; (force-mode-line-update) (message "Finished with %s" a)) When commenting out entire functions, use two semicolons. ‘;;;;’ Comments that start with four semicolons, ‘;;;;’, should be alignedto the left margin and are used for headings of major sections of aprogram. For example: ;;;; The kill ring The indentation commands of the Lisp modes in Emacs, such as M-; (indent-for-comment) and TAB (lisp-indent-line), automatically indent comments according to these conventions, depending on the number of semicolons. See See section ``Manipulating Comments'' in The GNU Emacs Manual. Conventional Headers for Emacs Libraries header comments library header comments Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions. We'll start with an example, a package that is included in the Emacs distribution. Parts of this example reflect its status as part of Emacs; for example, the copyright notice lists the Free Software Foundation as the copyright holder, and the copying permission says the file is part of Emacs. When you write a package and post it, the copyright holder would be you (unless your employer claims to own it instead), and you should get the suggested copying permission from the end of the GNU General Public License itself. Don't say your file is part of Emacs if we haven't installed it in Emacs yet! With that warning out of the way, on to the example: ;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers ;; Copyright (C) 1992 Free Software Foundation, Inc. ;; Author: Eric S. Raymond <esr@snark.thyrsus.com> ;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com> ;; Created: 14 Jul 1992 ;; Version: 1.2 ;; Keywords: docs ;; This file is part of GNU Emacs. … ;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, ;; Boston, MA 02110-1301, USA. The very first line should have this format: ;;; filename --- description The description should be complete in one line. If the file needs a ‘-*-’ specification, put it after description. After the copyright notice come several header comment lines, each beginning with ‘;; header-name:’. Here is a table of the conventional possibilities for header-name: ‘Author’ This line states the name and net address of at least the principalauthor of the library.If there are multiple authors, you can list them on continuation linesled by ;; and a tab character, like this: ;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu> ;; Dave Sill <de5@ornl.gov> ;; Dave Brennan <brennan@hal.com> ;; Eric Raymond <esr@snark.thyrsus.com> ‘Maintainer’ This line should contain a single name/address as in the Author line, oran address only, or the string ‘FSF’. If there is no maintainerline, the person(s) in the Author field are presumed to be themaintainers. The example above is mildly bogus because the maintainerline is redundant.The idea behind the ‘Author’ and ‘Maintainer’ lines is to makepossible a Lisp function to “send mail to the maintainer” withouthaving to mine the name out by hand.Be sure to surround the network address with ‘<…>’ ifyou include the person's full name as well as the network address. ‘Created’ This optional line gives the original creation date of thefile. For historical interest only. ‘Version’ If you wish to record version numbers for the individual Lisp program, putthem in this line. ‘Adapted-By’ In this header line, place the name of the person who adapted thelibrary for installation (to make it fit the style conventions, forexample). ‘Keywords’ This line lists keywords for the finder-by-keyword help command.Please use that command to see a list of the meaningful keywords.This field is important; it's how people will find your package whenthey're looking for things by topic area. To separate the keywords, youcan use spaces, commas, or both. Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can't do any harm. We use additional stylized comments to subdivide the contents of the library file. These should be separated by blank lines from anything else. Here is a table of them: ‘;;; Commentary:’ This begins introductory comments that explain how the library works.It should come right after the copying permissions, terminated by a‘Change Log’, ‘History’ or ‘Code’ comment line. Thistext is used by the Finder package, so it should make sense in thatcontext. ‘;;; Documentation:’ This was used in some files in place of ‘;;; Commentary:’,but it is deprecated. ‘;;; Change Log:’ This begins change log information stored in the library file (if youstore the change history there). For Lisp files distributed with Emacs,the change history is kept in the file ChangeLog and not in thesource file at all; these files generally do not have a ‘;;; ChangeLog:’ line. ‘History’ is an alternative to ‘Change Log’. ‘;;; Code:’ This begins the actual code of the program. ‘;;; filename ends here’ This is the footer line; it appears at the very end of the file.Its purpose is to enable people to detect truncated versions of the filefrom the lack of a footer line. <setfilename>../info/internals</setfilename> GNU Emacs Internals This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers. Building Emacs building Emacs temacs This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance. Compilation of the C source files in the src directory produces an executable file called temacs, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands. loadup.el The command ‘temacs -l loadup’ uses temacs to create the real runnable Emacs executable. These arguments direct temacs to evaluate the Lisp files specified in the file loadup.el. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare. dumping Emacs It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; temacs can dump out an executable program called emacs that has these files preloaded. emacs starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed. To create emacs, use the command ‘temacs -batch -l loadup dump’. The purpose of ‘-batch’ here is to prevent temacs from trying to initialize any of its data on the terminal; this ensures that the tables of terminal information are empty in the dumped Emacs. The argument ‘dump’ tells loadup.el to dump a new executable named emacs. Some operating systems don't support dumping. On those systems, you must start Emacs with the ‘temacs -l loadup’ command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most—or once a week if you never log out—the extra time is not too severe a problem. site-load.el You can specify additional files to preload by writing a library named site-load.el that loads them. You may need to add a definition #define SITELOAD_PURESIZE_EXTRA n to make n added bytes of pure space to hold the additional files. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable. After loadup.el reads site-load.el, it finds the documentation strings for primitive and preloaded functions (and variables) in the file etc/DOC where they are stored, by calling Snarf-documentation (see Accessing Documentation). site-init.el preloading additional functions and variables You can specify other Lisp expressions to execute just before dumping by putting them in a library named site-init.el. This file is executed after the documentation strings are found. If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs: Arrange to scan these files when producing the etc/DOC file,and load them with site-load.el. Load the files with site-init.el, then copy the files into theinstallation directory for Lisp files when you install Emacs. Specify a non-nil value forbyte-compile-dynamic-docstrings as a local variable in each of thesefiles, and load them with either site-load.el orsite-init.el. (This method has the drawback that thedocumentation strings take up space in Emacs all the time.) It is not advisable to put anything in site-load.el or site-init.el that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with default.el, so that users can override your changes if they wish. See . In a package that can be preloaded, it is sometimes useful to specify a computation to be done when Emacs subsequently starts up. For this, use eval-at-startup: eval-at-startup — Macro: eval-at-startup body … This evaluates the body forms, either immediately if running inan Emacs that has already started up, or later when Emacs does startup. Since the value of the body forms is not necessarilyavailable when the eval-at-startup form is run, that formalways returns nil. dump-emacs — Function: dump-emacs to-file from-file unexecThis function dumps the current state of Emacs into an executable fileto-file. It takes symbols from from-file (this is normallythe executable file temacs).If you want to use this function in an Emacs that was already dumped,you must run Emacs with ‘-batch’. Pure Storage pure storage Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session are kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files—data that should never change during actual use of Emacs. Pure storage is allocated only while temacs is loading the standard preloaded Lisp libraries. In the file emacs, it is marked as read-only (on operating systems that permit this), so that the memory space can be shared by all the Emacs jobs running on the machine at once. Pure storage is not expandable; a fixed amount is allocated when Emacs is compiled, and if that is not sufficient for the preloaded libraries, temacs allocates dynamic memory for the part that didn't fit. If that happens, you should increase the compilation parameter PURESIZE in the file src/puresize.h and rebuild Emacs, even though the resulting image will work: garbage collection is disabled in this situation, causing a memory leak. Such an overflow normally won't happen unless you try to preload additional libraries or add features to the standard ones. Emacs will display a warning about the overflow when it starts. purecopy — Function: purecopy object This function makes a copy in pure storage of object, and returnsit. It copies a string by simply making a new string with the samecharacters, but without text properties, in pure storage. Itrecursively copies the contents of vectors and cons cells. It doesnot make copies of other objects such as symbols, but just returnsthem unchanged. It signals an error if asked to copy markers.This function is a no-op except while Emacs is being built and dumped;it is usually called only in the file emacs/lisp/loaddefs.el, buta few packages call it just in case you decide to preload them. pure-bytes-used — Variable: pure-bytes-used The value of this variable is the number of bytes of pure storageallocated so far. Typically, in a dumped Emacs, this number is veryclose to the total amount of pure storage available—if it were not,we would preallocate less. purify-flag — Variable: purify-flag This variable determines whether defun should make a copy of thefunction definition in pure storage. If it is non-nil, then thefunction definition is copied into pure storage.This flag is t while loading all of the basic functions forbuilding Emacs initially (allowing those functions to be sharable andnon-collectible). Dumping Emacs as an executable always writesnil in this variable, regardless of the value it actually hasbefore and after dumping.You should not change this flag in a running Emacs. Garbage Collection garbage collection memory allocation When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.) It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but “garbage recycler” might be a more intuitive metaphor for this facility.) The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible. When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second (“sweep”) phase of the garbage collector arranges to reuse them. free list The sweep phase puts unused cons cells onto a free list for future allocation; likewise for symbols and markers. It compacts the accessible strings so they occupy fewer 8k blocks; then it frees the other 8k blocks. Vectors, buffers, windows, and other large objects are individually allocated and freed using malloc and free. CL note—allocate more storage Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues until gc-cons-threshold bytes have been used. This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection). garbage-collect — Command: garbage-collect This command runs a garbage collection, and returns information onthe amount of space in use. (Garbage collection can also occurspontaneously if you use more than gc-cons-threshold bytes ofLisp data since the previous garbage collection.)garbage-collect returns a list containing the followinginformation: ((used-conses . free-conses) (used-syms . free-syms) (used-miscs . free-miscs) used-string-chars used-vector-slots (used-floats . free-floats) (used-intervals . free-intervals) (used-strings . free-strings)) Here is an example: (garbage-collect) => ((106886 . 13184) (9769 . 0) (7731 . 4651) 347543 121628 (31 . 94) (1273 . 168) (25474 . 3569)) Here is a table explaining each element: used-conses The number of cons cells in use. free-conses The number of cons cells for which space has been obtained from theoperating system, but that are not currently being used. used-syms The number of symbols in use. free-syms The number of symbols for which space has been obtained from theoperating system, but that are not currently being used. used-miscs The number of miscellaneous objects in use. These include markers andoverlays, plus certain objects not visible to users. free-miscs The number of miscellaneous objects for which space has been obtainedfrom the operating system, but that are not currently being used. used-string-chars The total size of all strings, in characters. used-vector-slots The total number of elements of existing vectors. used-floats The number of floats in use. free-floats The number of floats for which space has been obtained from theoperating system, but that are not currently being used. used-intervals The number of intervals in use. Intervals are an internaldata structure used for representing text properties. free-intervals The number of intervals for which space has been obtainedfrom the operating system, but that are not currently being used. used-strings The number of strings in use. free-strings The number of string headers for which the space was obtained from theoperating system, but which are currently not in use. (A stringobject consists of a header and the storage for the string textitself; the latter is only allocated when the string is created.) If there was overflow in pure space (see the previous section),garbage-collect returns nil, because a real garbagecollection can not be done in this situation. garbage-collection-messages — User Option: garbage-collection-messages If this variable is non-nil, Emacs displays a message at thebeginning and end of garbage collection. The default value isnil, meaning there are no such messages. post-gc-hook — Variable: post-gc-hook This is a normal hook that is run at the end of garbage collection.Garbage collection is inhibited while the hook functions run, so becareful writing them. gc-cons-threshold — User Option: gc-cons-threshold The value of this variable is the number of bytes of storage that mustbe allocated for Lisp objects after one garbage collection in order totrigger another garbage collection. A cons cell counts as eight bytes,a string as one byte per character plus a few bytes of overhead, and soon; space allocated to the contents of buffers does not count. Notethat the subsequent garbage collection does not happen immediately whenthe threshold is exhausted, but only the next time the Lisp evaluator iscalled.The initial threshold value is 400,000. If you specify a largervalue, garbage collection will happen less often. This reduces theamount of time spent garbage collecting, but increases total memory use.You may want to do this when running a program that creates lots ofLisp data.You can make collections more frequent by specifying a smaller value,down to 10,000. A value less than 10,000 will remain in effect onlyuntil the subsequent garbage collection, at which timegarbage-collect will set the threshold back to 10,000. gc-cons-percentage — User Option: gc-cons-percentage The value of this variable specifies the amount of consing before agarbage collection occurs, as a fraction of the current heap size.This criterion and gc-cons-threshold apply in parallel, andgarbage collection occurs only when both criteria are satisfied.As the heap size increases, the time to perform a garbage collectionincreases. Thus, it can be desirable to do them less frequently inproportion. The value returned by garbage-collect describes the amount of memory used by Lisp data, broken down by data type. By contrast, the function memory-limit provides information on the total amount of memory Emacs is currently using. memory-limit — Function: memory-limit This function returns the address of the last byte Emacs has allocated,divided by 1024. We divide the value by 1024 to make sure it fits in aLisp integer.You can use this to get a general idea of how your actions affect thememory usage. memory-full — Variable: memory-full This variable is t if Emacs is close to out of memory for Lispobjects, and nil otherwise. memory-use-counts — Function: memory-use-counts This returns a list of numbers that count the number of objectscreated in this Emacs session. Each of these counters increments fora certain kind of object. See the documentation string for details. gcs-done — Variable: gcs-done This variable contains the total number of garbage collectionsdone so far in this Emacs session. gc-elapsed — Variable: gc-elapsed This variable contains the total number of seconds of elapsed timeduring garbage collection so far in this Emacs session, as a floatingpoint number. Memory Usage memory usage These functions and variables give information about the total amount of memory allocation that Emacs has done, broken down by data type. Note the difference between these and the values returned by (garbage-collect); those count objects that currently exist, but these count the number or size of all allocations, including those for objects that have since been freed. cons-cells-consed — Variable: cons-cells-consed The total number of cons cells that have been allocated so farin this Emacs session. floats-consed — Variable: floats-consed The total number of floats that have been allocated so farin this Emacs session. vector-cells-consed — Variable: vector-cells-consed The total number of vector cells that have been allocated so farin this Emacs session. symbols-consed — Variable: symbols-consed The total number of symbols that have been allocated so farin this Emacs session. string-chars-consed — Variable: string-chars-consed The total number of string characters that have been allocated so farin this Emacs session. misc-objects-consed — Variable: misc-objects-consed The total number of miscellaneous objects that have been allocated sofar in this Emacs session. These include markers and overlays, pluscertain objects not visible to users. intervals-consed — Variable: intervals-consed The total number of intervals that have been allocated so farin this Emacs session. strings-consed — Variable: strings-consed The total number of strings that have been allocated so far in thisEmacs session. Writing Emacs Primitives primitive function internals writing Emacs primitives Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here. An example of a special form is the definition of or, from eval.c. (An ordinary function would have the same general appearance.) garbage collection protection DEFUN ("or", For, Sor, 0, UNEVALLED, 0, doc: /* Eval args until one of them yields non-nil, then return that value. The remaining args are not evalled at all. If all args return nil, return nil. usage: (or CONDITIONS ...) */) (args) Lisp_Object args; { register Lisp_Object val = Qnil; struct gcpro gcpro1; GCPRO1 (args); while (CONSP (args)) { val = Feval (XCAR (args)); if (!NILP (val)) break; args = XCDR (args); } UNGCPRO; return val; } DEFUN, C macro to define Lisp primitives Let's start with a precise explanation of the arguments to the DEFUN macro. Here is a template for them: DEFUN (lname, fname, sname, min, max, interactive, doc) lname This is the name of the Lisp symbol to define as the function name; inthe example above, it is or. fname This is the C function name for this function. This isthe name that is used in C code for calling the function. The name is,by convention, ‘F’ prepended to the Lisp name, with all dashes(‘-’) in the Lisp name changed to underscores. Thus, to call thisfunction from C code, call For. Remember that the arguments mustbe of type Lisp_Object; various macros and functions for creatingvalues of type Lisp_Object are declared in the filelisp.h. sname This is a C variable name to use for a structure that holds the data forthe subr object that represents the function in Lisp. This structureconveys the Lisp symbol name to the initialization routine that willcreate the symbol and store the subr object as its definition. Byconvention, this name is always fname with ‘F’ replaced with‘S’. min This is the minimum number of arguments that the function requires. Thefunction or allows a minimum of zero arguments. max This is the maximum number of arguments that the function accepts, ifthere is a fixed maximum. Alternatively, it can be UNEVALLED,indicating a special form that receives unevaluated arguments, orMANY, indicating an unlimited number of evaluated arguments (theequivalent of &rest). Both UNEVALLED and MANY aremacros. If max is a number, it may not be less than min andit may not be greater than eight. interactive This is an interactive specification, a string such as might be used asthe argument of interactive in a Lisp function. In the case ofor, it is 0 (a null pointer), indicating that or cannot becalled interactively. A value of "" indicates a function thatshould receive no arguments when called interactively. doc This is the documentation string. It uses C comment syntax ratherthan C string syntax because comment syntax requires nothing specialto include multiple lines. The ‘doc:’ identifies the commentthat follows as the documentation string. The ‘/*’ and ‘*/’delimiters that begin and end the comment are not part of thedocumentation string.If the last line of the documentation string begins with the keyword‘usage:’, the rest of the line is treated as the argument listfor documentation purposes. This way, you can use different argumentnames in the documentation string from the ones used in the C code.‘usage:’ is required if the function has an unlimited number ofarguments.All the usual rules for documentation strings in Lisp code(see ) apply to C code documentation stringstoo. After the call to the DEFUN macro, you must write the argument name list that every C function must have, followed by ordinary C declarations for the arguments. For a function with a fixed maximum number of arguments, declare a C argument for each Lisp argument, and give them all type Lisp_Object. When a Lisp function has no upper limit on the number of arguments, its implementation in C actually receives exactly two arguments: the first is the number of Lisp arguments, and the second is the address of a block containing their values. They have types int and Lisp_Object *. GCPRO and UNGCPRO protect C variables from garbage collection Within the function For itself, note the use of the macros GCPRO1 and UNGCPRO. GCPRO1 is used to “protect” a variable from garbage collection—to inform the garbage collector that it must look in that variable and regard its contents as an accessible object. GC protection is necessary whenever you call Feval or anything that can directly or indirectly call Feval. At such a time, any Lisp object that this function may refer to again must be protected somehow. It suffices to ensure that at least one pointer to each object is GC-protected; that way, the object cannot be recycled, so all pointers to it remain valid. Thus, a particular local variable can do without protection if it is certain that the object it points to will be preserved by some other pointer (such as another local variable which has a GCPRO)Formerly, strings were a special exception; in older Emacs versions, every local variable that might point to a string needed a GCPRO.. Otherwise, the local variable needs a GCPRO. The macro GCPRO1 protects just one local variable. If you want to protect two variables, use GCPRO2 instead; repeating GCPRO1 will not work. Macros GCPRO3, GCPRO4, GCPRO5, and GCPRO6 also exist. All these macros implicitly use local variables such as gcpro1; you must declare these explicitly, with type struct gcpro. Thus, if you use GCPRO2, you must declare gcpro1 and gcpro2. Alas, we can't explain all the tricky details here. UNGCPRO cancels the protection of the variables that are protected in the current function. It is necessary to do this explicitly. Built-in functions that take a variable number of arguments actually accept two arguments at the C level: the number of Lisp arguments, and a Lisp_Object * pointer to a C vector containing those Lisp arguments. This C vector may be part of a Lisp vector, but it need not be. The responsibility for using GCPRO to protect the Lisp arguments from GC if necessary rests with the caller in this case, since the caller allocated or found the storage for them. You must not use C initializers for static or global variables unless the variables are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See . Do not use static variables within functions—place all static variables at top level in the file. This is necessary because Emacs on some operating systems defines the keyword static as a null macro. (This definition is used because those systems put all variables declared static in a place that becomes read-only after dumping, whether they have initializers or not.) defsubr, Lisp symbol for a primitive Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this: defsubr (&subr-structure-name); Here subr-structure-name is the name you used as the third argument to DEFUN. If you add a new primitive to a file that already has Lisp primitives defined in it, find the function (near the end of the file) named syms_of_something, and add the call to defsubr there. If the file doesn't have this function, or if you create a new file, add to it a syms_of_filename (e.g., syms_of_myfile). Then find the spot in emacs.c where all of these functions are called, and add a call to syms_of_filename there. byte-boolean-vars defining Lisp variables in C DEFVAR_INT, DEFVAR_LISP, DEFVAR_BOOL The function syms_of_filename is also the place to define any C variables that are to be visible as Lisp variables. DEFVAR_LISP makes a C variable of type Lisp_Object visible in Lisp. DEFVAR_INT makes a C variable of type int visible in Lisp with a value that is always an integer. DEFVAR_BOOL makes a C variable of type int visible in Lisp with a value that is either t or nil. Note that variables defined with DEFVAR_BOOL are automatically added to the list byte-boolean-vars used by the byte compiler. staticpro, protection from GC If you define a file-scope C variable of type Lisp_Object, you must protect it from garbage-collection by calling staticpro in syms_of_filename, like this: staticpro (&variable); Here is another example function, with more complicated arguments. This comes from the code in window.c, and it demonstrates the use of macros and functions to manipulate Lisp objects. DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p, Scoordinates_in_window_p, 2, 2, "xSpecify coordinate pair: \nXExpression which evals to window: ", "Return non-nil if COORDINATES is in WINDOW.\n\ COORDINATES is a cons of the form (X . Y), X and Y being distances\n\ ... If they are on the border between WINDOW and its right sibling,\n\ `vertical-line' is returned.") (coordinates, window) register Lisp_Object coordinates, window; { int x, y; CHECK_LIVE_WINDOW (window, 0); CHECK_CONS (coordinates, 1); x = XINT (Fcar (coordinates)); y = XINT (Fcdr (coordinates)); switch (coordinates_in_window (XWINDOW (window), &x, &y)) { case 0: /* NOT in window at all. */ return Qnil; case 1: /* In text part of window. */ return Fcons (make_number (x), make_number (y)); case 2: /* In mode line of window. */ return Qmode_line; case 3: /* On right border of window. */ return Qvertical_line; default: abort (); } } Note that C code cannot call functions by name unless they are defined in C. The way to call a function written in Lisp is to use Ffuncall, which embodies the Lisp function funcall. Since the Lisp function funcall accepts an unlimited number of arguments, in C it takes two: the number of Lisp-level arguments, and a one-dimensional array containing their values. The first Lisp-level argument is the Lisp function to call, and the rest are the arguments to pass to it. Since Ffuncall can call the evaluator, you must protect pointers from garbage collection around the call to Ffuncall. The C functions call0, call1, call2, and so on, provide handy ways to call a Lisp function conveniently with a fixed number of arguments. They work by calling Ffuncall. eval.c is a very good file to look through for examples; lisp.h contains the definitions for some important macros and functions. If you define a function which is side-effect free, update the code in byte-opt.el which binds side-effect-free-fns and side-effect-and-error-free-fns so that the compiler optimizer knows about it. Object Internals object internals GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Pointers are thirty-two bits wide in most implementations. Depending on the operating system and type of machine for which you compile Emacs, twenty-nine bits are used to address the object, and the remaining three bits are used for the tag that identifies the object's type. Because Lisp objects are represented as tagged pointers, it is always possible to determine the Lisp data type of any object. The C data type Lisp_Object can hold any Lisp object of any data type. Ordinary variables have type Lisp_Object, which means they can hold any type of Lisp value; you can determine the actual data type only at run time. The same is true for function arguments; if you want a function to accept only a certain type of argument, you must check the type explicitly using a suitable predicate (see ). type checking internals Buffer Internals internals, of buffer buffer internals Buffers contain fields not directly accessible by the Lisp programmer. We describe them here, naming them by the names used in the C code. Many are accessible indirectly in Lisp programs via Lisp primitives. Two structures are used to represent buffers in C. The buffer_text structure contains fields describing the text of a buffer; the buffer structure holds other fields. In the case of indirect buffers, two or more buffer structures reference the same buffer_text structure. Here is a list of the struct buffer_text fields: beg This field contains the actual address of the buffer contents. gpt This holds the character position of the gap in the buffer.See . z This field contains the character position of the end of the buffertext. gpt_byte Contains the byte position of the gap. z_byte Holds the byte position of the end of the buffer text. gap_size Contains the size of buffer's gap. See . modiff This field counts buffer-modification events for this buffer. It isincremented for each such event, and never otherwise changed. save_modiff Contains the previous value of modiff, as of the last time abuffer was visited or saved in a file. overlay_modiff Counts modifications to overlays analogous to modiff. beg_unchanged Holds the number of characters at the start of the text that are knownto be unchanged since the last redisplay that finished. end_unchanged Holds the number of characters at the end of the text that are known tobe unchanged since the last redisplay that finished. unchanged_modified Contains the value of modiff at the time of the last redisplaythat finished. If this value matches modiff,beg_unchanged and end_unchanged contain no usefulinformation. overlay_unchanged_modified Contains the value of overlay_modiff at the time of the lastredisplay that finished. If this value matches overlay_modiff,beg_unchanged and end_unchanged contain no usefulinformation. markers The markers that refer to this buffer. This is actually a singlemarker, and successive elements in its marker chain are the othermarkers referring to this buffer text. intervals Contains the interval tree which records the text properties of thisbuffer. The fields of struct buffer are: next Points to the next buffer, in the chain of all buffers including killedbuffers. This chain is used only for garbage collection, in order tocollect killed buffers properly. Note that vectors, and most kinds ofobjects allocated as vectors, are all on one chain, but buffers are on aseparate chain of their own. own_text This is a struct buffer_text structure. In an ordinary buffer,it holds the buffer contents. In indirect buffers, this field is notused. text This points to the buffer_text structure that is used for thisbuffer. In an ordinary buffer, this is the own_text field above.In an indirect buffer, this is the own_text field of the basebuffer. pt Contains the character position of point in a buffer. pt_byte Contains the byte position of point in a buffer. begv This field contains the character position of the beginning of theaccessible range of text in the buffer. begv_byte This field contains the byte position of the beginning of theaccessible range of text in the buffer. zv This field contains the character position of the end of theaccessible range of text in the buffer. zv_byte This field contains the byte position of the end of theaccessible range of text in the buffer. base_buffer In an indirect buffer, this points to the base buffer. In an ordinarybuffer, it is null. local_var_flags This field contains flags indicating that certain variables are local inthis buffer. Such variables are declared in the C code usingDEFVAR_PER_BUFFER, and their buffer-local bindings are stored infields in the buffer structure itself. (Some of these fields aredescribed in this table.) modtime This field contains the modification time of the visited file. It isset when the file is written or read. Before writing the buffer into afile, this field is compared to the modification time of the file to seeif the file has changed on disk. See . auto_save_modified This field contains the time when the buffer was last auto-saved. auto_save_failure_time The time at which we detected a failure to auto-save, or -1 if we didn'thave a failure. last_window_start This field contains the window-start position in the buffer as ofthe last time the buffer was displayed in a window. clip_changed This flag is set when narrowing changes in a buffer. prevent_redisplay_optimizations_p this flag indicates that redisplay optimizations should not be usedto display this buffer. undo_list This field points to the buffer's undo list. See . name The buffer name is a string that names the buffer. It is guaranteed tobe unique. See . filename The name of the file visited in this buffer, or nil. directory The directory for expanding relative file names. save_length Length of the file this buffer is visiting, when last read or saved.This and other fields concerned with saving are not kept in thebuffer_text structure because indirect buffers are never saved. auto_save_file_name File name used for auto-saving this buffer. This is not in thebuffer_text because it's not used in indirect buffers at all. read_only Non-nil means this buffer is read-only. mark This field contains the mark for the buffer. The mark is a marker,hence it is also included on the list markers. See . local_var_alist This field contains the association list describing the buffer-localvariable bindings of this buffer, not including the built-inbuffer-local bindings that have special slots in the buffer object.(Those slots are omitted from this table.) See . major_mode Symbol naming the major mode of this buffer, e.g., lisp-mode. mode_name Pretty name of major mode, e.g., "Lisp". mode_line_format Mode line element that controls the format of the mode line. If thisis nil, no mode line will be displayed. header_line_format This field is analogous to mode_line_format for the modeline displayed at the top of windows. keymap This field holds the buffer's local keymap. See . abbrev_table This buffer's local abbrevs. syntax_table This field contains the syntax table for the buffer. See . category_table This field contains the category table for the buffer. case_fold_search The value of case-fold-search in this buffer. tab_width The value of tab-width in this buffer. fill_column The value of fill-column in this buffer. left_margin The value of left-margin in this buffer. auto_fill_function The value of auto-fill-function in this buffer. downcase_table This field contains the conversion table for converting text to lower case.See . upcase_table This field contains the conversion table for converting text to upper case.See . case_canon_table This field contains the conversion table for canonicalizing text forcase-folding search. See . case_eqv_table This field contains the equivalence table for case-folding search.See . truncate_lines The value of truncate-lines in this buffer. ctl_arrow The value of ctl-arrow in this buffer. selective_display The value of selective-display in this buffer. selective_display_ellipsis The value of selective-display-ellipsis in this buffer. minor_modes An alist of the minor modes of this buffer. overwrite_mode The value of overwrite_mode in this buffer. abbrev_mode The value of abbrev-mode in this buffer. display_table This field contains the buffer's display table, or nil if it doesn'thave one. See . save_modified This field contains the time when the buffer was last saved, as an integer.See . mark_active This field is non-nil if the buffer's mark is active. overlays_before This field holds a list of the overlays in this buffer that end at orbefore the current overlay center position. They are sorted in order ofdecreasing end position. overlays_after This field holds a list of the overlays in this buffer that end afterthe current overlay center position. They are sorted in order ofincreasing beginning position. overlay_center This field holds the current overlay center position. See . enable_multibyte_characters This field holds the buffer's local value ofenable-multibyte-characters—either t or nil. buffer_file_coding_system The value of buffer-file-coding-system in this buffer. file_format The value of buffer-file-format in this buffer. auto_save_file_format The value of buffer-auto-save-file-format in this buffer. pt_marker In an indirect buffer, or a buffer that is the base of an indirectbuffer, this holds a marker that records point for this buffer when thebuffer is not current. begv_marker In an indirect buffer, or a buffer that is the base of an indirectbuffer, this holds a marker that records begv for this bufferwhen the buffer is not current. zv_marker In an indirect buffer, or a buffer that is the base of an indirectbuffer, this holds a marker that records zv for this buffer whenthe buffer is not current. file_truename The truename of the visited file, or nil. invisibility_spec The value of buffer-invisibility-spec in this buffer. last_selected_window This is the last window that was selected with this buffer in it, or nilif that window no longer displays this buffer. display_count This field is incremented each time the buffer is displayed in a window. left_margin_width The value of left-margin-width in this buffer. right_margin_width The value of right-margin-width in this buffer. indicate_empty_lines Non-nil means indicate empty lines (lines with no text) with asmall bitmap in the fringe, when using a window system that can do it. display_time This holds a time stamp that is updated each time this buffer isdisplayed in a window. scroll_up_aggressively The value of scroll-up-aggressively in this buffer. scroll_down_aggressively The value of scroll-down-aggressively in this buffer. Window Internals internals, of window window internals Windows have the following accessible fields: frame The frame that this window is on. mini_p Non-nil if this window is a minibuffer window. parent Internally, Emacs arranges windows in a tree; each group of siblings hasa parent window whose area includes all the siblings. This field pointsto a window's parent.Parent windows do not display buffers, and play little role in displayexcept to shape their child windows. Emacs Lisp programs usually haveno access to the parent windows; they operate on the windows at theleaves of the tree, which actually display buffers.The following four fields also describe the window tree structure. hchild In a window subdivided horizontally by child windows, the leftmost child.Otherwise, nil. vchild In a window subdivided vertically by child windows, the topmost child.Otherwise, nil. next The next sibling of this window. It is nil in a window that isthe rightmost or bottommost of a group of siblings. prev The previous sibling of this window. It is nil in a window thatis the leftmost or topmost of a group of siblings. left This is the left-hand edge of the window, measured in columns. (Theleftmost column on the screen is column 0.) top This is the top edge of the window, measured in lines. (The top line onthe screen is line 0.) height The height of the window, measured in lines. width The width of the window, measured in columns. This width includes thescroll bar and fringes, and/or the separator line on the right of thewindow (if any). buffer The buffer that the window is displaying. This may change often duringthe life of the window. start The position in the buffer that is the first character to be displayedin the window. pointm window point internalsThis is the value of point in the current buffer when this window isselected; when it is not selected, it retains its previous value. force_start If this flag is non-nil, it says that the window has beenscrolled explicitly by the Lisp program. This affects what the nextredisplay does if point is off the screen: instead of scrolling thewindow to show the text around point, it moves point to a location thatis on the screen. frozen_window_start_p This field is set temporarily to 1 to indicate to redisplay thatstart of this window should not be changed, even if pointgets invisible. start_at_line_beg Non-nil means current value of start was the beginning of a linewhen it was chosen. too_small_ok Non-nil means don't delete this window for becoming “too small.” height_fixed_p This field is temporarily set to 1 to fix the height of the selectedwindow when the echo area is resized. use_time This is the last time that the window was selected. The functionget-lru-window uses this field. sequence_number A unique number assigned to this window when it was created. last_modified The modiff field of the window's buffer, as of the last timea redisplay completed in this window. last_overlay_modified The overlay_modiff field of the window's buffer, as of the lasttime a redisplay completed in this window. last_point The buffer's value of point, as of the last time a redisplay completedin this window. last_had_star A non-nil value means the window's buffer was “modified” when thewindow was last updated. vertical_scroll_bar This window's vertical scroll bar. left_margin_width The width of the left margin in this window, or nil not tospecify it (in which case the buffer's value of left-margin-widthis used. right_margin_width Likewise for the right margin. window_end_pos This is computed as z minus the buffer position of the last glyphin the current matrix of the window. The value is only valid ifwindow_end_valid is not nil. window_end_bytepos The byte position corresponding to window_end_pos. window_end_vpos The window-relative vertical position of the line containingwindow_end_pos. window_end_valid This field is set to a non-nil value if window_end_pos is trulyvalid. This is nil if nontrivial redisplay is preempted since in thatcase the display that window_end_pos was computed for did not getonto the screen. redisplay_end_trigger If redisplay in this window goes beyond this buffer position, it runsthe redisplay-end-trigger-hook. cursor A structure describing where the cursor is in this window. last_cursor The value of cursor as of the last redisplay that finished. phys_cursor A structure describing where the cursor of this window physically is. phys_cursor_type The type of cursor that was last displayed on this window. phys_cursor_on_p This field is non-zero if the cursor is physically on. cursor_off_p Non-zero means the cursor in this window is logically on. last_cursor_off_p This field contains the value of cursor_off_p as of the time ofthe last redisplay. must_be_updated_p This is set to 1 during redisplay when this window must be updated. hscroll This is the number of columns that the display in the window is scrolledhorizontally to the left. Normally, this is 0. vscroll Vertical scroll amount, in pixels. Normally, this is 0. dedicated Non-nil if this window is dedicated to its buffer. display_table The window's display table, or nil if none is specified for it. update_mode_line Non-nil means this window's mode line needs to be updated. base_line_number The line number of a certain position in the buffer, or nil.This is used for displaying the line number of point in the mode line. base_line_pos The position in the buffer for which the line number is known, ornil meaning none is known. region_showing If the region (or part of it) is highlighted in this window, this fieldholds the mark position that made one end of that region. Otherwise,this field is nil. column_number_displayed The column number currently displayed in this window's mode line, or nilif column numbers are not being displayed. current_matrix A glyph matrix describing the current display of this window. desired_matrix A glyph matrix describing the desired display of this window. Process Internals internals, of process process internals The fields of a process are: name A string, the name of the process. command A list containing the command arguments that were used to start thisprocess. filter A function used to accept output from the process instead of a buffer,or nil. sentinel A function called whenever the process receives a signal, or nil. buffer The associated buffer of the process. pid An integer, the operating system's process ID. childp A flag, non-nil if this is really a child process.It is nil for a network connection. mark A marker indicating the position of the end of the last output from thisprocess inserted into the buffer. This is often but not always the endof the buffer. kill_without_query If this is non-nil, killing Emacs while this process is stillrunning does not ask for confirmation about killing the process. raw_status_lowraw_status_high These two fields record 16 bits each of the process status returned bythe wait system call. status The process status, as process-status should return it. tickupdate_tick If these two fields are not equal, a change in the status of the processneeds to be reported, either by running the sentinel or by inserting amessage in the process buffer. pty_flag Non-nil if communication with the subprocess uses a PTY;nil if it uses a pipe. infd The file descriptor for input from the process. outfd The file descriptor for output to the process. subtty The file descriptor for the terminal that the subprocess is using. (Onsome systems, there is no need to record this, so the value isnil.) tty_name The name of the terminal that the subprocess is using,or nil if it is using pipes. decode_coding_system Coding-system for decoding the input from this process. decoding_buf A working buffer for decoding. decoding_carryover Size of carryover in decoding. encode_coding_system Coding-system for encoding the output to this process. encoding_buf A working buffer for encoding. encoding_carryover Size of carryover in encoding. inherit_coding_system_flag Flag to set coding-system of the process buffer from thecoding system used to decode process output. <setfilename>../info/errors</setfilename> Standard Errors standard errors Here is the complete list of the error symbols in standard Emacs, grouped by concept. The list includes each symbol's message (on the error-message property of the symbol) and a cross reference to a description of how the error can occur. Each error symbol has an error-conditions property that is a list of symbols. Normally this list includes the error symbol itself and the symbol error. Occasionally it includes additional symbols, which are intermediate classifications, narrower than error but broader than a single error symbol. For example, all the errors in accessing files have the condition file-error. If we do not say here that a certain error symbol has additional error conditions, that means it has none. As a special exception, the error symbol quit does not have the condition error, because quitting is not considered an error. See , for an explanation of how errors are generated and handled. symbol string; reference. error "error"See . quit "Quit"See . args-out-of-range "Args out of range"This happens when trying to access an element beyond the range of asequence or buffer.See , See . arith-error "Arithmetic error"See . beginning-of-buffer "Beginning of buffer"See . buffer-read-only "Buffer is read-only"See . coding-system-error "Invalid coding system"See . cyclic-function-indirection "Symbol's chain of function indirections\ contains a loop"See . cyclic-variable-indirection "Symbol's chain of variable indirections\ contains a loop"See . end-of-buffer "End of buffer"See . end-of-file "End of file during parsing"Note that this is not a subcategory of file-error,because it pertains to the Lisp reader, not to file I/O.See . file-already-exists This is a subcategory of file-error.See . file-date-error This is a subcategory of file-error. It occurs whencopy-file tries and fails to set the last-modification time ofthe output file.See . file-error We do not list the error-strings of this error and its subcategories,because the error message is normally constructed from the data itemsalone when the error condition file-error is present. Thus,the error-strings are not very relevant. However, these error symbolsdo have error-message properties, and if no data is provided,the error-message property is used.See . file-locked This is a subcategory of file-error.See . file-supersession This is a subcategory of file-error.See . ftp-error This is a subcategory of file-error, which results from problemsin accessing a remote file using ftp.See See section ``Remote Files'' in The GNU Emacs Manual. invalid-function "Invalid function"See . invalid-read-syntax "Invalid read syntax"See . invalid-regexp "Invalid regexp"See . mark-inactive "The mark is not active now"See . no-catch "No catch for tag"See . scan-error "Scan error"This happens when certain syntax-parsing functionsfind invalid syntax or mismatched parentheses.See , and . search-failed "Search failed"See . setting-constant "Attempt to set a constant symbol"The values of the symbols nil and t,and any symbols that start with ‘:’,may not be changed.See Variables that Never Change. text-read-only "Text is read-only"This is a subcategory of buffer-read-only.See . undefined-color "Undefined color"See . void-function "Symbol's function definition is void"See . void-variable "Symbol's value as variable is void"See . wrong-number-of-arguments "Wrong number of arguments"See . wrong-type-argument "Wrong type argument"See . These kinds of error, which are classified as special cases of arith-error, can occur on certain systems for invalid use of mathematical functions. domain-error "Arithmetic domain error"See . overflow-error "Arithmetic overflow error"This is a subcategory of domain-error.See . range-error "Arithmetic range error"See . singularity-error "Arithmetic singularity error"This is a subcategory of domain-error.See . underflow-error "Arithmetic underflow error"This is a subcategory of domain-error.See . <setfilename>../info/locals</setfilename> Buffer-Local Variables buffer-local variables, general-purpose standard buffer-local variables The table below lists the general-purpose Emacs variables that automatically become buffer-local in each buffer. Most become buffer-local only when set; a few of them are always local in every buffer. Many Lisp packages define such variables for their internal use, but we don't try to list them all here. Every buffer-specific minor mode defines a buffer-local variable named ‘modename-mode’. See . Minor mode variables will not be listed here. auto-fill-function See . buffer-auto-save-file-format See . buffer-auto-save-file-name See . buffer-backed-up See . buffer-display-count See . buffer-display-table See . buffer-display-time See . buffer-file-coding-system See . buffer-file-format See . buffer-file-name See . buffer-file-number See . buffer-file-truename See . buffer-file-type See . buffer-invisibility-spec See . buffer-offer-save See . buffer-save-without-query See . buffer-read-only See . buffer-saved-size See . buffer-undo-list See . cache-long-line-scans See . case-fold-search See . ctl-arrow See . cursor-type See . cursor-in-non-selected-windows See . comment-column See See section ``Comments'' in The GNU Emacs Manual. default-directory See . defun-prompt-regexp See . desktop-save-buffer See . enable-multibyte-characters . fill-column See . fill-prefix See . font-lock-defaults See . fringe-cursor-alist See . fringe-indicator-alist See . fringes-outside-margins See . goal-column See See section ``Moving Point'' in The GNU Emacs Manual. header-line-format See . indicate-buffer-boundaries See . indicate-empty-lines See . left-fringe-width See . left-margin See . left-margin-width See . line-spacing See . local-abbrev-table See . major-mode See . mark-active See . mark-ring See . mode-line-buffer-identification See . mode-line-format See . mode-line-modified See . mode-line-process See . mode-name See . point-before-scroll Used for communication between mouse commands and scroll-bar commands. right-fringe-width See . right-margin-width See . save-buffer-coding-system See . scroll-bar-width See . scroll-down-aggressively See . scroll-up-aggressively See . selective-display See . selective-display-ellipses See . tab-width See . truncate-lines See . vertical-scroll-bar See . window-size-fixed See . write-contents-functions See . <setfilename>../info/maps</setfilename> Standard Keymaps standard keymaps The following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are loaded only when their respective mode is used. This is not an exhaustive list. Several keymaps are used in the minibuffer. See . Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap. apropos-mode-map apropos-mode-mapA sparse keymap for apropos buffers. Buffer-menu-mode-map Buffer-menu-mode-mapA full keymap used by Buffer Menu mode. c-mode-map c-mode-mapA sparse keymap used by C mode. command-history-map command-history-mapA full keymap used by Command History mode. ctl-x-4-map A sparse keymap for subcommands of the prefix C-x 4. ctl-x-5-map A sparse keymap for subcommands of the prefix C-x 5. ctl-x-map A full keymap for C-x commands. custom-mode-map A full keymap for Custom mode. debugger-mode-map debugger-mode-mapA full keymap used by Debugger mode. dired-mode-map dired-mode-mapA full keymap for dired-mode buffers. edit-abbrevs-map edit-abbrevs-mapA sparse keymap used in edit-abbrevs. edit-tab-stops-map edit-tab-stops-mapA sparse keymap used in edit-tab-stops. electric-buffer-menu-mode-map electric-buffer-menu-mode-mapA full keymap used by Electric Buffer Menu mode. electric-history-map electric-history-mapA full keymap used by Electric Command History mode. emacs-lisp-mode-map emacs-lisp-mode-mapA sparse keymap used by Emacs Lisp mode. esc-map A full keymap for ESC (or Meta) commands. facemenu-menu facemenu-menuThe sparse keymap that displays the Text Properties menu. facemenu-background-menu facemenu-background-menuThe sparse keymap that displays the Background Color submenu of the TextProperties menu. facemenu-face-menu facemenu-face-menuThe sparse keymap that displays the Face submenu of the Text Properties menu. facemenu-foreground-menu facemenu-foreground-menuThe sparse keymap that displays the Foreground Color submenu of the TextProperties menu. facemenu-indentation-menu facemenu-indentation-menuThe sparse keymap that displays the Indentation submenu of the TextProperties menu. facemenu-justification-menu facemenu-justification-menuThe sparse keymap that displays the Justification submenu of the TextProperties menu. facemenu-special-menu facemenu-special-menuThe sparse keymap that displays the Special Props submenu of the TextProperties menu. function-key-map The keymap for translating keypad and function keys.If there are none, then it contains an empty sparse keymap.See . fundamental-mode-map fundamental-mode-mapThe sparse keymap for Fundamental mode.It is empty and should not be changed. global-map The full keymap containing default global key bindings.Modes should not modify the Global map. grep-mode-map grep-mode-mapThe keymap for grep-mode buffers. help-map The sparse keymap for the keys that follow the help character C-h. help-mode-map help-mode-mapThe sparse keymap for Help mode. Helper-help-map Helper-help-mapA full keymap used by the help utility package.It has the same keymap in its value cell and in its functioncell. Info-edit-map Info-edit-mapA sparse keymap used by the e command of Info. Info-mode-map Info-mode-mapA sparse keymap containing Info commands. isearch-mode-map isearch-mode-mapA keymap that defines the characters you can type within incrementalsearch. key-translation-map A keymap for translating keys. This one overrides ordinary keybindings, unlike function-key-map. See . kmacro-map kmacro-mapA sparse keymap for keys that follows the C-x C-k prefixsearch. lisp-interaction-mode-map lisp-interaction-mode-mapA sparse keymap used by Lisp Interaction mode. lisp-mode-map lisp-mode-mapA sparse keymap used by Lisp mode. menu-bar-edit-menu menu-bar-edit-menuThe keymap which displays the Edit menu in the menu bar. menu-bar-files-menu menu-bar-files-menuThe keymap which displays the Files menu in the menu bar. menu-bar-help-menu menu-bar-help-menuThe keymap which displays the Help menu in the menu bar. menu-bar-mule-menu menu-bar-mule-menuThe keymap which displays the Mule menu in the menu bar. menu-bar-search-menu menu-bar-search-menuThe keymap which displays the Search menu in the menu bar. menu-bar-tools-menu menu-bar-tools-menuThe keymap which displays the Tools menu in the menu bar. mode-specific-map The keymap for characters following C-c. Note, this is in theglobal map. This map is not actually mode specific: its name was chosento be informative for the user in C-h b (display-bindings),where it describes the main use of the C-c prefix key. occur-mode-map occur-mode-mapA sparse keymap used by Occur mode. query-replace-map A sparse keymap used for responses in query-replace and relatedcommands; also for y-or-n-p and map-y-or-n-p. The functionsthat use this map do not support prefix keys; they look up one event at atime. text-mode-map text-mode-mapA sparse keymap used by Text mode. tool-bar-map The keymap defining the contents of the tool bar. view-mode-map view-mode-mapA full keymap used by View mode. <setfilename>../info/hooks</setfilename> Standard Hooks standard hooks hook variables, list of The following is a list of hook variables that let you provide functions to be called from within Emacs on suitable occasions. Most of these variables have names ending with ‘-hook’. They are normal hooks, run by means of run-hooks. The value of such a hook is a list of functions; the functions are called with no arguments and their values are completely ignored. The recommended way to put a new function on such a hook is to call add-hook. See , for more information about using hooks. Every major mode defines a mode hook named ‘modename-mode-hook’. The major mode command runs this normal hook with run-mode-hooks as the very last thing it does. See . Most minor modes have mode hooks too. Mode hooks are omitted in the list below. The variables whose names end in ‘-hooks’ or ‘-functions’ are usually abnormal hooks; their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their values are used). The variables whose names end in ‘-function’ have single functions as their values. activate-mark-hook See . after-change-functions See . after-change-major-mode-hook See . after-init-hook See . after-insert-file-functions See . after-make-frame-functions See . after-revert-hook See . after-save-hook See . auto-fill-function See . auto-save-hook See . before-change-functions See . before-init-hook See . before-make-frame-hook See . before-revert-hook See . before-save-hook See . blink-paren-function See . buffer-access-fontify-functions See . calendar-load-hook See . change-major-mode-hook See . command-line-functions See . comment-indent-function See See section ``Options Controlling Comments'' in the GNU Emacs Manual. compilation-finish-functions Functions to call when a compilation process finishes. custom-define-hook Hook called after defining each customize option. deactivate-mark-hook See . desktop-after-read-hook Normal hook run after a successful desktop-read. May be usedto show a buffer list. See See section ``Saving Emacs Sessions'' in the GNU Emacs Manual. desktop-no-desktop-file-hook Normal hook run when desktop-read can't find a desktop file.May be used to show a dired buffer. See See section ``Saving Emacs Sessions'' in the GNU Emacs Manual. desktop-save-hook Normal hook run before the desktop is saved in a desktop file. Thisis useful for truncating history lists, for example. See See section ``Saving Emacs Sessions'' in the GNU Emacs Manual. diary-display-hook See . diary-hook List of functions called after the display of the diary. Can be usedfor appointment notification. disabled-command-function See . echo-area-clear-hook See . emacs-startup-hook See . find-file-hook See . find-file-not-found-functions See . first-change-hook See . font-lock-beginning-of-syntax-function See . font-lock-fontify-buffer-function See . font-lock-fontify-region-function See . font-lock-mark-block-function See . font-lock-syntactic-face-function See . font-lock-unfontify-buffer-function See . font-lock-unfontify-region-function See . initial-calendar-window-hook See . kbd-macro-termination-hook See . kill-buffer-hook See . kill-buffer-query-functions See . kill-emacs-hook See . kill-emacs-query-functions See . lisp-indent-function list-diary-entries-hook See . mail-setup-hook See See section ``Mail Mode Miscellany'' in the GNU Emacs Manual. mark-diary-entries-hook See . menu-bar-update-hook See . minibuffer-setup-hook See . minibuffer-exit-hook See . mouse-position-function See . nongregorian-diary-listing-hook See . nongregorian-diary-marking-hook See . occur-hook post-command-hook See . pre-abbrev-expand-hook See . pre-command-hook See . print-diary-entries-hook See . redisplay-end-trigger-functions See . scheme-indent-function suspend-hook See . suspend-resume-hook See . temp-buffer-setup-hook See . temp-buffer-show-function See . temp-buffer-show-hook See . term-setup-hook See . today-visible-calendar-hook See . today-invisible-calendar-hook See . window-configuration-change-hook See . window-scroll-functions See . window-setup-hook See . window-size-change-functions See . write-contents-functions See . write-file-functions See . write-region-annotate-functions See . <setfilename>../info/index</setfilename> xreflabel="Index" id="Index"> Index %, see ‘"’ in printing, see ‘"’ in strings, see ‘#$’, see ‘#'’ syntax, see ‘#:’ read syntax, see ‘#@count’, see ‘#n#’ read syntax, see ‘#n=’ read syntax, see ‘$’ in display, see ‘$’ in regexp, see ‘%’ in format, see ‘&’ in replacement, see ‘'’ for quoting, see ‘(…)’ in lists, see ‘(’ in regexp, see ‘)’ in regexp, see ‘*’ in interactive, see ‘*’ in regexp, see ‘*scratch*’, see ‘+’ in regexp, see ‘.’ in lists, see ‘.’ in regexp, see ‘;’ in comment, see ‘?’ in character constant, see ‘?’ in regexp, see ‘@’ in interactive, see ‘[’ in regexp, see ‘\’ in character constant, see ‘\’ in display, see ‘\’ in printing, see ‘\’ in regexp, see ‘\’ in replacement, see ‘\’ in strings, see ‘\’ in symbols, see ‘\'’ in regexp, see ‘\<’ in regexp, see ‘\=’ in regexp, see ‘\>’ in regexp, see ‘\_<’ in regexp, see ‘\_>’ in regexp, see ‘\`’ in regexp, see ‘\a’, see ‘\b’, see ‘\B’ in regexp, see ‘\b’ in regexp, see ‘\e’, see ‘\f’, see ‘\n’, see ‘\n’ in print, see ‘\n’ in replacement, see ‘\r’, see ‘\s’, see ‘\S’ in regexp, see ‘\s’ in regexp, see ‘\t’, see ‘\v’, see ‘\W’ in regexp, see ‘\w’ in regexp, see ‘]’ in regexp, see ‘^’ in regexp, see ‘|’ in regexp, see &optional, see &rest, see *, see +, see , (with backquote), see ,@ (with backquote), see -, see .emacs, see /, see /=, see 1+, see 1-, see 1value, see 2C-mode-map, see <, see <=, see =, see >, see >=, see ? in minibuffer, see […] (Edebug), see `, see ` (list substitution), see A abbrev, see abbrev tables in modes, see abbrev-all-caps, see abbrev-expansion, see abbrev-file-name, see abbrev-mode, see abbrev-prefix-mark, see abbrev-start-location, see abbrev-start-location-buffer, see abbrev-symbol, see abbrev-table-name-list, see abbreviate-file-name, see abbrevs-changed, see abnormal hook, see abort-recursive-edit, see aborting, see abs, see absolute file name, see accept input from processes, see accept-change-group, see accept-process-output, see access-file, see accessibility of a file, see accessible portion (of a buffer), see accessible-keymaps, see acos, see action (button property), see action, customization keyword, see activate-change-group, see activate-mark-hook, see activating advice, see active display table, see active keymap, see active-minibuffer-window, see ad-activate, see ad-activate-all, see ad-activate-regexp, see ad-add-advice, see ad-deactivate, see ad-deactivate-all, see ad-deactivate-regexp, see ad-default-compilation-action, see ad-define-subr-args, see ad-disable-advice, see ad-disable-regexp, see ad-do-it, see ad-enable-advice, see ad-enable-regexp, see ad-get-arg, see ad-get-args, see ad-return-value, see ad-set-arg, see ad-set-args, see ad-start-advice, see ad-stop-advice, see ad-unadvise, see ad-unadvise-all, see ad-update, see ad-update-all, see ad-update-regexp, see adaptive-fill-first-line-regexp, see adaptive-fill-function, see adaptive-fill-mode, see adaptive-fill-regexp, see add-hook, see add-name-to-file, see add-text-properties, see add-to-history, see add-to-invisibility-spec, see add-to-list, see add-to-ordered-list, see address field of register, see adjust-window-trailing-edge, see adjusting point, see advice, activating, see advice, defining, see advice, enabling and disabling, see advice, preactivating, see advising functions, see advising primitives, see after-advice, see after-change-functions, see after-change-major-mode-hook, see after-find-file, see after-init-hook, see after-insert-file-functions, see after-load-alist, see after-make-frame-functions, see after-revert-hook, see after-save-hook, see after-string (overlay property), see alist, see alist vs. plist, see all-completions, see alt characters, see and, see anonymous function, see apostrophe for quoting, see append, see append-to-file, see apply, see apply, and debugging, see apropos, see apropos-mode-map, see aref, see args, customization keyword, see argument binding, see argument lists, features, see arguments for shell commands, see arguments, interactive entry, see arguments, reading, see arith-error example, see arith-error in division, see arithmetic operations, see arithmetic shift, see around-advice, see array, see array elements, see arrayp, see ASCII character codes, see ascii-case-table, see aset, see ash, see asin, see ask-user-about-lock, see ask-user-about-supersession-threat, see asking the user questions, see assoc, see assoc-default, see assoc-string, see association list, see assq, see assq-delete-all, see asynchronous subprocess, see atan, see atom, see atomic changes, see atoms, see attributes of text, see Auto Fill mode, see auto-coding-functions, see auto-coding-regexp-alist, see auto-fill-chars, see auto-fill-function, see auto-hscroll-mode, see auto-mode-alist, see auto-raise-tool-bar-buttons, see auto-resize-tool-bar, see auto-save-default, see auto-save-file-name-p, see auto-save-hook, see auto-save-interval, see auto-save-list-file-name, see auto-save-list-file-prefix, see auto-save-mode, see auto-save-timeout, see auto-save-visited-file-name, see auto-window-vscroll, see autoload, see autoload cookie, see autoload errors, see automatic face assignment, see automatically buffer-local, see B back-to-indentation, see backquote (list substitution), see backslash in character constant, see backslash in strings, see backslash in symbols, see backspace, see backtrace, see backtrace-debug, see backtrace-frame, see backtracking, see backup file, see backup files, rename or copy, see backup-buffer, see backup-by-copying, see backup-by-copying-when-linked, see backup-by-copying-when-mismatch, see backup-by-copying-when-privileged-mismatch, see backup-directory-alist, see backup-enable-predicate, see backup-file-name-p, see backup-inhibited, see backups and auto-saving, see backward-button, see backward-char, see backward-delete-char-untabify, see backward-delete-char-untabify-method, see backward-list, see backward-prefix-chars, see backward-sexp, see backward-to-indentation, see backward-word, see balanced parenthesis motion, see balancing parentheses, see barf-if-buffer-read-only, see base 64 encoding, see base buffer, see base coding system, see base for reading an integer, see base64-decode-region, see base64-decode-string, see base64-encode-region, see base64-encode-string, see basic code (of input character), see batch mode, see batch-byte-compile, see baud-rate, see beep, see before point, insertion, see before-advice, see before-change-functions, see before-init-hook, see before-make-frame-hook, see before-revert-hook, see before-save-hook, see before-string (overlay property), see beginning of line, see beginning of line in regexp, see beginning-of-buffer, see beginning-of-defun, see beginning-of-defun-function, see beginning-of-line, see bell, see bell character, see benchmark.el, see benchmarking, see big endian, see binary files and text files, see bindat-get-field, see bindat-ip-to-string, see bindat-length, see bindat-pack, see bindat-unpack, see binding arguments, see binding local variables, see binding of a key, see bitmap-spec-p, see bitmaps, fringe, see bitwise arithmetic, see blink-cursor-alist, see blink-matching-delay, see blink-matching-open, see blink-matching-paren, see blink-matching-paren-distance, see blink-paren-function, see blinking parentheses, see bobp, see body of function, see bolp, see bool-vector-p, see Bool-vectors, see boolean, see booleanp, see boundp, see box diagrams, for lists, see break, see breakpoints (Edebug), see bucket (in obarray), see buffer, see buffer contents, see buffer file name, see buffer input stream, see buffer internals, see buffer list, see buffer modification, see buffer names, see buffer output stream, see buffer text notation, see buffer, read-only, see buffer-access-fontified-property, see buffer-access-fontify-functions, see buffer-auto-save-file-format, see buffer-auto-save-file-name, see buffer-backed-up, see buffer-base-buffer, see buffer-chars-modified-tick, see buffer-disable-undo, see buffer-display-count, see buffer-display-table, see buffer-display-time, see buffer-enable-undo, see buffer-end, see buffer-file-coding-system, see buffer-file-format, see buffer-file-name, see buffer-file-number, see buffer-file-truename, see buffer-file-type, see buffer-has-markers-at, see buffer-invisibility-spec, see buffer-list, see buffer-live-p, see buffer-local variables, see buffer-local variables in modes, see buffer-local variables, general-purpose, see buffer-local-value, see buffer-local-variables, see Buffer-menu-mode-map, see buffer-modified-p, see buffer-modified-tick, see buffer-name, see buffer-name-history, see buffer-offer-save, see buffer-read-only, see buffer-save-without-query, see buffer-saved-size, see buffer-size, see buffer-string, see buffer-substring, see buffer-substring-filters, see buffer-substring-no-properties, see buffer-undo-list, see bufferp, see buffers without undo information, see buffers, controlled in windows, see buffers, creating, see buffers, killing, see bugs, see bugs in this manual, see building Emacs, see building lists, see built-in function, see bury-buffer, see butlast, see button (button property), see button buffer commands, see button properties, see button types, see button-activate, see button-at, see button-down event, see button-end, see button-face, customization keyword, see button-get, see button-has-type-p, see button-label, see button-prefix, customization keyword, see button-put, see button-start, see button-suffix, customization keyword, see button-type, see button-type-get, see button-type-put, see button-type-subtype-p, see buttons in buffers, see byte compilation, see byte compiler warnings, how to avoid, see byte packing and unpacking, see byte-boolean-vars, see byte-boolean-vars, see byte-code, see byte-code, see byte-code function, see byte-code interpreter, see byte-code-function-p, see byte-compile, see byte-compile-dynamic, see byte-compile-dynamic-docstrings, see byte-compile-file, see byte-compiling macros, see byte-compiling require, see byte-recompile-directory, see byte-to-position, see bytes, see bytes and characters, see C-c, see C-g, see C-h, see C C-M-x, see c-mode-map, see c-mode-syntax-table, see C-x, see C-x 4, see C-x 5, see C-x 6, see C-x RET, see C-x v, see C-x X =, see caar, see cache-long-line-scans, see cadr, see call stack, see call-interactively, see call-process, see call-process-region, see call-process-shell-command, see called-interactively-p, see calling a function, see cancel-change-group, see cancel-debug-on-entry, see cancel-timer, see capitalization, see capitalize, see capitalize-region, see capitalize-word, see car, see car-safe, see case conversion in buffers, see case conversion in Lisp, see case in replacements, see case-fold-search, see case-replace, see case-table-p, see catch, see categories of characters, see category (overlay property), see category (text property), see category table, see category-docstring, see category-set-mnemonics, see category-table, see category-table-p, see cdar, see cddr, see cdr, see cdr-safe, see ceiling, see centering point, see change hooks, see change hooks for a character, see change-major-mode-hook, see changing key bindings, see changing to another buffer, see changing window size, see char-after, see char-before, see char-category-set, see char-charset, see char-displayable-p, see char-equal, see char-or-string-p, see char-property-alias-alist, see char-syntax, see char-table length, see char-table-extra-slot, see char-table-p, see char-table-parent, see char-table-range, see char-table-subtype, see char-tables, see char-to-string, see char-valid-p, see char-width, see character alternative (in regexp), see character arrays, see character as bytes, see character case, see character categories, see character classes in regexp, see character code conversion, see character codes, see character insertion, see character printing, see character quote, see character sets, see character to string, see character translation tables, see characters, see characters for interactive codes, see characters, multi-byte, see charset-after, see charset-bytes, see charset-dimension, see charset-list, see charset-plist, see charsetp, see check-coding-system, see checkdoc-minor-mode, see child process, see circular list, see circular structure, read syntax, see cl, see CL note—allocate more storage, see CL note—case of letters, see CL note—default optional arg, see CL note—integers vrs eq, see CL note—interning existing symbol, see CL note—lack union, intersection, see CL note—no continuable errors, see CL note—only throw in Emacs, see CL note—rplaca vs setcar, see CL note—set local, see CL note—special forms compared, see CL note—special variables, see CL note—symbol in obarrays, see class of advice, see cleanup forms, see clear-abbrev-table, see clear-image-cache, see clear-string, see clear-this-command-keys, see clear-visited-file-modtime, see click event, see clickable buttons in buffers, see clickable text, see clipboard support (for MS-Windows), see clone-indirect-buffer, see close parenthesis character, see closures not available, see clrhash, see codes, interactive, description of, see coding conventions in Emacs Lisp, see coding standards, see coding system, see coding-system-change-eol-conversion, see coding-system-change-text-conversion, see coding-system-eol-type, see coding-system-for-read, see coding-system-for-write, see coding-system-get, see coding-system-list, see coding-system-p, see color names, see color-defined-p, see color-gray-p, see color-supported-p, see color-values, see colors on text-only terminals, see columns, see combine-after-change-calls, see command, see command descriptions, see command history, see command in keymap, see command loop, see command loop, recursive, see command-debug-status, see command-error-function, see command-execute, see command-history, see command-history-map, see command-line, see command-line arguments, see command-line options, see command-line-args, see command-line-functions, see command-line-processed, see command-remapping, see command-switch-alist, see commandp, see commandp example, see commands, defining, see comment ender, see comment starter, see comment syntax, see comments, see comments, Lisp convention for, see Common Lisp, see compare-buffer-substrings, see compare-strings, see compare-window-configurations, see comparing buffer text, see comparing file modification time, see comparing numbers, see compilation (Emacs Lisp), see compilation functions, see compile-defun, see compile-time constant, see compiled function, see compiler errors, see complete key, see completing-read, see completion, see completion, file name, see completion-auto-help, see completion-ignore-case, see completion-ignored-extensions, see completion-regexp-list, see complex arguments, see complex command, see Composite Types (customization), see composition (text property), see composition property, and point display, see compute-motion, see concat, see concatenating lists, see concatenating strings, see cond, see condition name, see condition-case, see conditional evaluation, see conditional selection of windows, see cons, see cons cells, see cons-cells-consed, see consing, see consp, see constant variables, see constrain-to-field, see continuation lines, see continue-process, see control character key constants, see control character printing, see control characters, see control characters in display, see control characters, reading, see control structures, see Control-X-prefix, see controller part, model/view/controller, see conventions for writing major modes, see conventions for writing minor modes, see conversion of strings, see convert-standard-filename, see converting numbers, see coordinates-in-window-p, see copy-abbrev-table, see copy-alist, see copy-category-table, see copy-face, see copy-file, see copy-hash-table, see copy-keymap, see copy-marker, see copy-region-as-kill, see copy-sequence, see copy-syntax-table, see copy-tree, see copying alists, see copying files, see copying lists, see copying sequences, see copying strings, see copying vectors, see cos, see count-lines, see count-loop, see count-screen-lines, see counting columns, see coverage testing, see coverage testing (Edebug), see create-file-buffer, see create-fontset-from-fontset-spec, see create-glyph, see create-image, see creating and deleting directories, see creating buffers, see creating hash tables, see creating keymaps, see ctl-arrow, see ctl-x-4-map, see ctl-x-5-map, see ctl-x-map, see current binding, see current buffer, see current buffer mark, see current buffer point and mark (Edebug), see current buffer position, see current command, see current stack frame, see current-active-maps, see current-buffer, see current-case-table, see current-column, see current-fill-column, see current-frame-configuration, see current-global-map, see current-idle-time, see current-indentation, see current-input-method, see current-input-mode, see current-justification, see current-kill, see current-left-margin, see current-local-map, see current-message, see current-minor-mode-maps, see current-prefix-arg, see current-time, see current-time-string, see current-time-zone, see current-window-configuration, see current-word, see cursor, see cursor (text property), see cursor, fringe, see cursor-in-echo-area, see cursor-in-non-selected-windows, see cursor-type, see cust-print, see custom-add-frequent-value, see customization definitions, see customization groups, defining, see customization keywords, see customization types, see customization variables, how to define, see customize-package-emacs-version-alist, see cut buffer, see cyclic ordering of windows, see D data type, see data-directory, see datagrams, see date-leap-year-p, see date-to-time, see deactivate-mark, see deactivate-mark-hook, see deactivating advice, see debug, see debug-ignored-errors, see debug-on-entry, see debug-on-error, see debug-on-error use, see debug-on-next-call, see debug-on-quit, see debug-on-signal, see debugger, see debugger command list, see debugger for Emacs Lisp, see debugger-mode-map, see debugging byte compilation problems, see debugging errors, see debugging invalid Lisp syntax, see debugging specific functions, see declare, see decode process output, see decode-coding-inserted-region, see decode-coding-region, see decode-coding-string, see decode-time, see decoding file formats, see decoding in coding systems, see decrement field of register, see dedicated window, see deep binding, see def-edebug-spec, see defadvice, see defalias, see default argument string, see default init file, see default key binding, see default value, see default value of char-table, see default-abbrev-mode, see default-boundp, see default-buffer-file-type, see default-case-fold-search, see default-ctl-arrow, see default-directory, see default-enable-multibyte-characters, see default-file-modes, see default-fill-column, see default-frame-alist, see default-fringe-indicator-alist, see default-fringes-cursor-alist, see default-header-line-format, see default-indicate-buffer-boundaries, see default-input-method, see default-justification, see default-line-spacing, see default-major-mode, see default-minibuffer-frame, see default-mode-line-format, see default-process-coding-system, see default-text-properties, see default-truncate-lines, see default-value, see default.el, see defconst, see defcustom, see defface, see defgroup, see defimage, see define customization group, see define customization options, see define hash comparisons, see define-abbrev, see define-abbrev-table, see define-button-type, see define-category, see define-derived-mode, see define-fringe-bitmap, see define-generic-mode, see define-globalized-minor-mode, see define-hash-table-test, see define-key, see define-key-after, see define-logical-name, see define-minor-mode, see define-obsolete-function-alias, see define-obsolete-variable-alias, see define-prefix-command, see defined-colors, see defining a function, see defining advice, see defining commands, see defining Lisp variables in C, see defining menus, see defining-kbd-macro, see definitions of symbols, see defmacro, see defsubr, Lisp symbol for a primitive, see defsubst, see defun, see DEFUN, C macro to define Lisp primitives, see defun-prompt-regexp, see defvar, see DEFVAR_INT, DEFVAR_LISP, DEFVAR_BOOL, see defvaralias, see delay-mode-hooks, see delete, see delete-and-extract-region, see delete-auto-save-file-if-necessary, see delete-auto-save-files, see delete-backward-char, see delete-blank-lines, see delete-char, see delete-directory, see delete-dups, see delete-exited-processes, see delete-field, see delete-file, see delete-frame, see delete-frame event, see delete-frame-functions, see delete-horizontal-space, see delete-indentation, see delete-minibuffer-contents, see delete-old-versions, see delete-other-windows, see delete-overlay, see delete-process, see delete-region, see delete-to-left-margin, see delete-window, see delete-windows-on, see deleting files, see deleting frames, see deleting list elements, see deleting previous char, see deleting processes, see deleting text vs killing, see deleting whitespace, see deleting windows, see delq, see derived mode, see describe characters and events, see describe-bindings, see describe-buffer-case-table, see describe-categories, see describe-current-display-table, see describe-display-table, see describe-mode, see describe-prefix-bindings, see description for interactive codes, see description format, see deserializing, see desktop save mode, see desktop-buffer-mode-handlers, see desktop-save-buffer, see destroy-fringe-bitmap, see destructive list operations, see detect-coding-region, see detect-coding-string, see diagrams, boxed, for lists, see dialog boxes, see digit-argument, see dimension (of character set), see ding, see directory name, see directory name abbreviation, see directory part (of file name), see directory-abbrev-alist, see directory-file-name, see directory-files, see directory-files-and-attributes, see directory-oriented functions, see dired-kept-versions, see dired-mode-map, see disable-command, see disable-point-adjustment, see disabled, see disabled command, see disabled-command-function, see disabling advice, see disabling undo, see disassemble, see disassembled byte-code, see discard-input, see discarding input, see display (overlay property), see display (text property), see display feature testing, see display margins, see display message in echo area, see display property, and point display, see display specification, see display table, see display, abstract, see display, arbitrary objects, see display-backing-store, see display-buffer, see display-buffer-function, see display-buffer-reuse-frames, see display-color-cells, see display-color-p, see display-completion-list, see display-graphic-p, see display-grayscale-p, see display-images-p, see display-message-or-buffer, see display-mm-dimensions-alist, see display-mm-height, see display-mm-width, see display-mouse-p, see display-pixel-height, see display-pixel-width, see display-planes, see display-popup-menus-p, see display-save-under, see display-screens, see display-selections-p, see display-supports-face-attributes-p, see display-table-slot, see display-visual-class, see display-warning, see displaying a buffer, see displays, multiple, see dnd-protocol-alist, see do-auto-save, see doc, customization keyword, see doc-directory, see DOC-version (documentation) file, see documentation, see documentation conventions, see documentation for major mode, see documentation notation, see documentation of function, see documentation strings, see documentation strings, conventions and tips, see documentation, keys in, see documentation-property, see dolist, see DOS file types, see dotimes, see dotimes-with-progress-reporter, see dotted list, see dotted lists (Edebug), see dotted pair notation, see double-click events, see double-click-fuzz, see double-click-time, see double-quote in strings, see down-list, see downcase, see downcase-region, see downcase-word, see downcasing in lookup-key, see drag event, see drag-n-drop event, see dribble file, see dump-emacs, see dumping Emacs, see dynamic loading of documentation, see dynamic loading of functions, see dynamic scoping, see dynamic-completion-table, see E easy-mmode-define-minor-mode, see echo area, see echo-area-clear-hook, see echo-keystrokes, see edebug, see Edebug debugging facility, see Edebug execution modes, see Edebug specification list, see edebug-all-defs, see edebug-all-forms, see edebug-continue-kbd-macro, see edebug-display-freq-count, see edebug-eval-macro-args, see edebug-eval-top-level-form, see edebug-global-break-condition, see edebug-initial-mode, see edebug-on-error, see edebug-on-quit, see edebug-print-circle, see edebug-print-length, see edebug-print-level, see edebug-print-trace-after, see edebug-print-trace-before, see edebug-save-displayed-buffer-points, see edebug-save-windows, see edebug-set-global-break-condition, see edebug-setup-hook, see edebug-sit-for-seconds, see edebug-temp-display-freq-count, see edebug-test-coverage, see edebug-trace, see edebug-trace, see edebug-tracing, see edebug-unwrap, see edit-abbrevs-map, see edit-and-eval-command, see edit-tab-stops-map, see editing types, see editor command loop, see electric-buffer-menu-mode-map, see electric-future-map, see electric-history-map, see element (of list), see elements of sequences, see elp.el, see elt, see Emacs event standard notation, see emacs-build-time, see emacs-lisp-docstring-fill-column, see emacs-lisp-mode-map, see emacs-lisp-mode-syntax-table, see emacs-major-version, see emacs-minor-version, see emacs-pid, see emacs-save-session-functions, see emacs-startup-hook, see emacs-version, see EMACSLOADPATH environment variable, see empty list, see emulation-mode-map-alists, see enable-command, see enable-local-eval, see enable-local-variables, see enable-multibyte-characters, see enable-recursive-minibuffers, see enabling advice, see encode-coding-region, see encode-coding-string, see encode-time, see encoding file formats, see encoding in coding systems, see end of line in regexp, see end-of-buffer, see end-of-defun, see end-of-defun-function, see end-of-file, see end-of-line, see end-of-line conversion, see endianness, see enlarge-window, see enlarge-window-horizontally, see environment, see environment variable access, see environment variables, subprocesses, see eobp, see EOL conversion, see eolp, see eq, see eql, see equal, see equality, see erase-buffer, see error, see error cleanup, see error debugging, see error description, see error display, see error handler, see error in debug, see error message notation, see error name, see error symbol, see error-conditions, see error-message-string, see errors, see ESC, see esc-map, see ESC-prefix, see escape (ASCII character), see escape characters, see escape characters in printing, see escape sequence, see escape-syntax character, see eval, see eval, and debugging, see eval-after-load, see eval-and-compile, see eval-at-startup, see eval-buffer, see eval-buffer (Edebug), see eval-current-buffer, see eval-current-buffer (Edebug), see eval-defun (Edebug), see eval-expression (Edebug), see eval-expression-debug-on-error, see eval-expression-print-length, see eval-expression-print-level, see eval-minibuffer, see eval-region, see eval-region (Edebug), see eval-when-compile, see evaluated expression argument, see evaluation, see evaluation error, see evaluation list group, see evaluation notation, see evaluation of buffer contents, see evaporate (overlay property), see even-window-heights, see event printing, see event type, see event, reading only one, see event-basic-type, see event-click-count, see event-convert-list, see event-end, see event-modifiers, see event-start, see eventp, see events, see ewoc, see ewoc-buffer, see ewoc-collect, see ewoc-create, see ewoc-data, see ewoc-delete, see ewoc-enter-after, see ewoc-enter-before, see ewoc-enter-first, see ewoc-enter-last, see ewoc-filter, see ewoc-get-hf, see ewoc-goto-next, see ewoc-goto-node, see ewoc-goto-prev, see ewoc-invalidate, see ewoc-locate, see ewoc-location, see ewoc-map, see ewoc-next, see ewoc-nth, see ewoc-prev, see ewoc-refresh, see ewoc-set-data, see ewoc-set-hf, see examining the interactive form, see examining windows, see examples of using interactive, see excursion, see exec-directory, see exec-path, see exec-suffixes, see executable-find, see execute program, see execute with prefix argument, see execute-extended-command, see execute-kbd-macro, see executing-kbd-macro, see execution speed, see exit, see exit recursive editing, see exit-minibuffer, see exit-recursive-edit, see exiting Emacs, see exp, see expand-abbrev, see expand-file-name, see expansion of file names, see expansion of macros, see expression, see expression prefix, see expt, see extended-command-history, see extent, see extra slots of char-table, see extra-keyboard-modifiers, see F face (button property), see face (overlay property), see face (text property), see face alias, see face attributes, see face codes of text, see face id, see face-attribute, see face-attribute-relative-p, see face-background, see face-bold-p, see face-differs-from-default-p, see face-documentation, see face-documentation, see face-equal, see face-font, see face-font-family-alternatives, see face-font-registry-alternatives, see face-font-rescale-alist, see face-font-selection-order, see face-foreground, see face-id, see face-inverse-video-p, see face-italic-p, see face-list, see face-stipple, see face-underline-p, see facemenu-background-menu, see facemenu-face-menu, see facemenu-foreground-menu, see facemenu-indentation-menu, see facemenu-justification-menu, see facemenu-keymap, see facemenu-menu, see facemenu-special-menu, see facep, see faces, see faces for font lock, see faces, automatic choice, see false, see fboundp, see fceiling, see feature-unload-hook, see featurep, see features, see fetch-bytecode, see ffloor, see field (text property), see field width, see field-beginning, see field-end, see field-string, see field-string-no-properties, see fields, see fifo data structure, see file accessibility, see file age, see file attributes, see file format conversion, see file hard link, see file local variables, see file locks, see file mode specification error, see file modes and MS-DOS, see file modification time, see file name completion subroutines, see file name of buffer, see file name of directory, see file names, see file names in directory, see file open error, see file symbolic links, see file types on MS-DOS and Windows, see file with multiple names, see file, information about, see file-accessible-directory-p, see file-already-exists, see file-attributes, see file-chase-links, see file-coding-system-alist, see file-directory-p, see file-error, see file-executable-p, see file-exists-p, see file-expand-wildcards, see file-local-copy, see file-locked, see file-locked-p, see file-modes, see file-name-absolute-p, see file-name-all-completions, see file-name-all-versions, see file-name-as-directory, see file-name-buffer-file-type-alist, see file-name-coding-system, see file-name-completion, see file-name-directory, see file-name-extension, see file-name-history, see file-name-nondirectory, see file-name-sans-extension, see file-name-sans-versions, see file-newer-than-file-p, see file-newest-backup, see file-nlinks, see file-ownership-preserved-p, see file-precious-flag, see file-readable-p, see file-regular-p, see file-relative-name, see file-remote-p, see file-supersession, see file-symlink-p, see file-truename, see file-writable-p, see fill-column, see fill-context-prefix, see fill-individual-paragraphs, see fill-individual-varying-indent, see fill-nobreak-predicate, see fill-paragraph, see fill-paragraph-function, see fill-prefix, see fill-region, see fill-region-as-paragraph, see fillarray, see filling text, see filling, automatic, see filter function, see filter multibyte flag, of process, see filter-buffer-substring, see find file in path, see find library, see find-backup-file-name, see find-buffer-visiting, see find-charset-region, see find-charset-string, see find-coding-systems-for-charsets, see find-coding-systems-region, see find-coding-systems-string, see find-file, see find-file-hook, see find-file-name-handler, see find-file-noselect, see find-file-not-found-functions, see find-file-other-window, see find-file-read-only, see find-file-wildcards, see find-image, see find-operation-coding-system, see finding files, see finding windows, see first-change-hook, see fit-window-to-buffer, see fixup-whitespace, see flags in format specifications, see float, see float-output-format, see float-time, see floating-point functions, see floatp, see floats-consed, see floor, see flushing input, see fmakunbound, see fn in function's documentation string, see focus event, see focus-follows-mouse, see follow links, see follow-link (button property), see following-char, see font lock faces, see Font Lock mode, see font-list-limit, see font-lock-add-keywords, see font-lock-beginning-of-syntax-function, see font-lock-builtin-face, see font-lock-comment-delimiter-face, see font-lock-comment-face, see font-lock-constant-face, see font-lock-defaults, see font-lock-doc-face, see font-lock-extend-after-change-region-function, see font-lock-extra-managed-props, see font-lock-face (text property), see font-lock-fontify-buffer-function, see font-lock-fontify-region-function, see font-lock-function-name-face, see font-lock-keyword-face, see font-lock-keywords, see font-lock-keywords-case-fold-search, see font-lock-keywords-only, see font-lock-mark-block-function, see font-lock-multiline, see font-lock-negation-char-face, see font-lock-preprocessor-face, see font-lock-remove-keywords, see font-lock-string-face, see font-lock-syntactic-face-function, see font-lock-syntactic-keywords, see font-lock-syntax-table, see font-lock-type-face, see font-lock-unfontify-buffer-function, see font-lock-unfontify-region-function, see font-lock-variable-name-face, see font-lock-warning-face, see fontification-functions, see fontified (text property), see fonts in this manual, see foo, see for, see force-mode-line-update, see force-window-update, see forcing redisplay, see format, see format definition, see format of keymaps, see format specification, see format, customization keyword, see format-alist, see format-find-file, see format-insert-file, see format-mode-line, see format-network-address, see format-time-string, see format-write-file, see formatting strings, see formfeed, see forms, see forward advice, see forward-button, see forward-char, see forward-comment, see forward-line, see forward-list, see forward-sexp, see forward-to-indentation, see forward-word, see frame, see frame configuration, see frame parameters, see frame size, see frame title, see frame visibility, see frame-background-mode, see frame-char-height, see frame-char-width, see frame-current-scroll-bars, see frame-first-window, see frame-height, see frame-list, see frame-live-p, see frame-local variables, see frame-parameter, see frame-parameters, see frame-pixel-height, see frame-pixel-width, see frame-selected-window, see frame-title-format, see frame-visible-p, see frame-width, see framep, see frames, scanning all, see free list, see frequency counts, see fringe bitmaps, see fringe cursors, see fringe indicators, see fringe-bitmaps-at-pos, see fringe-cursor-alist, see fringe-indicator-alist, see fringes, see fringes, and empty line indication, see fringes-outside-margins, see fround, see fset, see ftp-login, see ftruncate, see full keymap, see funcall, see funcall, and debugging, see function, see function, see function aliases, see function call, see function call debugging, see function cell, see function cell in autoload, see function definition, see function descriptions, see function form evaluation, see function input stream, see function invocation, see function keys, see function name, see function output stream, see function quoting, see function safety, see function-documentation, see function-key-map, see functionals, see functionp, see functions in modes, see functions, making them interactive, see Fundamental mode, see fundamental-mode, see fundamental-mode-abbrev-table, see fundamental-mode-map, see G gamma correction, see gap-position, see gap-size, see garbage collection, see garbage collection protection, see garbage-collect, see garbage-collection-messages, see gc-cons-percentage, see gc-cons-threshold, see gc-elapsed, see GCPRO and UNGCPRO, see gcs-done, see generate characters in charsets, see generate-new-buffer, see generate-new-buffer-name, see generic characters, see generic comment delimiter, see generic mode, see generic string delimiter, see geometry specification, see get, see get, defcustom keyword, see get-buffer, see get-buffer-create, see get-buffer-process, see get-buffer-window, see get-buffer-window-list, see get-char-property, see get-char-property-and-overlay, see get-file-buffer, see get-file-char, see get-internal-run-time, see get-largest-window, see get-load-suffixes, see get-lru-window, see get-process, see get-register, see get-text-property, see get-unused-category, see get-window-with-predicate, see getenv, see gethash, see GIF, see global binding, see global break condition, see global keymap, see global variable, see global-abbrev-table, see global-disable-point-adjustment, see global-key-binding, see global-map, see global-mode-string, see global-set-key, see global-unset-key, see glyph, see glyph-char, see glyph-face, see glyph-table, see goto-char, see goto-line, see grep-mode-map, see group, customization keyword, see H hack-local-variables, see handle-switch-frame, see handling errors, see hash code, see hash notation, see hash tables, see hash-table-count, see hash-table-p, see hash-table-rehash-size, see hash-table-rehash-threshold, see hash-table-size, see hash-table-test, see hash-table-weakness, see hashing, see header comments, see header line (of a window), see header-line prefix key, see header-line-format, see help for major mode, see help-char, see help-command, see help-echo (overlay property), see help-echo (text property), see help-echo event, see help-echo, customization keyword, see help-event-list, see help-form, see help-index (button property), see help-map, see help-mode-map, see Helper-describe-bindings, see Helper-help, see Helper-help-map, see hex numbers, see hidden buffers, see history list, see history of commands, see history-add-new-input, see history-delete-duplicates, see history-length, see HOME environment variable, see hook variables, list of, see hooks, see hooks for changing a character, see hooks for loading, see hooks for motion of point, see hooks for text changes, see hooks for window operations, see horizontal position, see horizontal scrolling, see horizontal-scroll-bar prefix key, see hyper characters, see hyperlinks in documentation strings, see I icon-title-format, see iconified frame, see iconify-frame, see iconify-frame event, see identity, see idleness, see IEEE floating point, see if, see ignore, see ignored-local-variables, see image cache, see image descriptor, see image-cache-eviction-delay, see image-library-alist, see image-load-path, see image-load-path-for-library, see image-mask-p, see image-size, see image-type-available-p, see image-types, see images in buffers, see Imenu, see imenu-add-to-menubar, see imenu-case-fold-search, see imenu-create-index-function, see imenu-extract-index-name-function, see imenu-generic-expression, see imenu-prev-index-position-function, see imenu-syntax-alist, see implicit progn, see inc, see indent-according-to-mode, see indent-code-rigidly, see indent-for-tab-command, see indent-line-function, see indent-region, see indent-region-function, see indent-relative, see indent-relative-maybe, see indent-rigidly, see indent-tabs-mode, see indent-to, see indent-to-left-margin, see indentation, see indicate-buffer-boundaries, see indicate-empty-lines, see indicators, fringe, see indirect buffers, see indirect specifications, see indirect-function, see indirect-variable, see indirection for functions, see infinite loops, see infinite recursion, see infinity, see Info-edit-map, see Info-mode-map, see inherit standard syntax, see inheritance of text properties, see inheriting a keymap's bindings, see inhibit-default-init, see inhibit-eol-conversion, see inhibit-field-text-motion, see inhibit-file-name-handlers, see inhibit-file-name-operation, see inhibit-modification-hooks, see inhibit-point-motion-hooks, see inhibit-quit, see inhibit-read-only, see inhibit-startup-echo-area-message, see inhibit-startup-message, see init file, see init-file-user, see initial-frame-alist, see initial-major-mode, see initialization of Emacs, see initialize, defcustom keyword, see inline functions, see innermost containing parentheses, see input events, see input focus, see input methods, see input modes, see input stream, see input-method-alist, see input-method-function, see input-pending-p, see insert, see insert-abbrev-table-description, see insert-and-inherit, see insert-before-markers, see insert-before-markers-and-inherit, see insert-behind-hooks (overlay property), see insert-behind-hooks (text property), see insert-buffer, see insert-buffer-substring, see insert-buffer-substring-as-yank, see insert-buffer-substring-no-properties, see insert-button, see insert-char, see insert-default-directory, see insert-directory, see insert-directory-program, see insert-file-contents, see insert-file-contents-literally, see insert-for-yank, see insert-image, see insert-in-front-hooks (overlay property), see insert-in-front-hooks (text property), see insert-register, see insert-sliced-image, see insert-text-button, see inserting killed text, see insertion before point, see insertion of text, see insertion type of a marker, see inside comment, see inside string, see installation-directory, see int-to-string, see intangible (overlay property), see intangible (text property), see integer to decimal, see integer to hexadecimal, see integer to octal, see integer to string, see integer-or-marker-p, see integerp, see integers, see integers in specific radix, see interactive, see interactive call, see interactive code description, see interactive completion, see interactive function, see interactive, examples of using, see interactive-form, see interactive-p, see intern, see intern-soft, see internals, of buffer, see internals, of process, see internals, of window, see interning, see interpreter, see interpreter-mode-alist, see interprogram-cut-function, see interprogram-paste-function, see interrupt Lisp functions, see interrupt-process, see intervals, see intervals-consed, see introduction sequence (of character), see invalid prefix key error, see invalid-function, see invalid-read-syntax, see invalid-regexp, see invert-face, see invisible (overlay property), see invisible (text property), see invisible frame, see invisible text, see invisible/intangible text, and point, see invocation-directory, see invocation-name, see isearch-mode-map, see iteration, see J joining lists, see just-one-space, see justify-current-line, see K kbd, see kbd-macro-termination-hook, see kept-new-versions, see kept-old-versions, see key, see key binding, see key binding, conventions for, see key lookup, see key sequence, see key sequence error, see key sequence input, see key translation function, see key-binding, see key-description, see key-translation-map, see keyboard events, see keyboard events in strings, see keyboard input, see keyboard input decoding on X, see keyboard macro execution, see keyboard macro termination, see keyboard macro, terminating, see keyboard macros, see keyboard macros (Edebug), see keyboard-coding-system, see keyboard-quit, see keyboard-translate, see keyboard-translate-table, see keymap, see keymap (button property), see keymap (overlay property), see keymap (text property), see keymap entry, see keymap format, see keymap in keymap, see keymap inheritance, see keymap of character, see keymap of character (and overlays), see keymap prompt string, see keymap-parent, see keymap-prompt, see keymapp, see keymaps for translating events, see keymaps in modes, see keys in documentation strings, see keys, reserved, see keystroke, see keystroke command, see keyword symbol, see keywordp, see kill command repetition, see kill ring, see kill-all-local-variables, see kill-append, see kill-buffer, see kill-buffer-hook, see kill-buffer-query-functions, see kill-emacs, see kill-emacs-hook, see kill-emacs-query-functions, see kill-local-variable, see kill-new, see kill-process, see kill-read-only-ok, see kill-region, see kill-ring, see kill-ring-max, see kill-ring-yank-pointer, see killing buffers, see killing Emacs, see kmacro-map, see L lambda expression, see lambda in debug, see lambda in keymap, see lambda list, see lambda-list (Edebug), see last, see last-abbrev, see last-abbrev-location, see last-abbrev-text, see last-coding-system-used, see last-command, see last-command-char, see last-command-event, see last-event-frame, see last-input-char, see last-input-event, see last-kbd-macro, see last-nonmenu-event, see last-prefix-arg, see lax-plist-get, see lax-plist-put, see lazy loading, see lazy-completion-table, see leading code, see left-fringe-width, see left-margin, see left-margin-width, see length, see let, see let*, see lexical binding (Edebug), see lexical comparison, see lexical scoping, see library, see library compilation, see library header comments, see library search, see line end conversion, see line height, see line number, see line truncation, see line wrapping, see line-beginning-position, see line-end-position, see line-height (text property), see line-height (text property), see line-move-ignore-invisible, see line-number-at-pos, see line-spacing, see line-spacing (text property), see line-spacing (text property), see lines, see lines in region, see link, customization keyword, see linking files, see Lisp debugger, see Lisp expression motion, see Lisp history, see Lisp library, see Lisp nesting error, see Lisp object, see Lisp printer, see Lisp reader, see lisp-interaction-mode-map, see lisp-mode-abbrev-table, see lisp-mode-map, see lisp-mode.el, see list, see list elements, see list form evaluation, see list in keymap, see list length, see list motion, see list structure, see list-buffers-directory, see list-charset-chars, see list-processes, see listify-key-sequence, see listp, see lists, see lists and cons cells, see lists as sets, see literal evaluation, see little endian, see ln, see load, see load error with require, see load errors, see load, customization keyword, see load-average, see load-file, see load-file-rep-suffixes, see load-history, see load-in-progress, see load-library, see load-path, see load-read-function, see load-suffixes, see loading, see loading hooks, see loadup.el, see local binding, see local keymap, see local variables, see local-abbrev-table, see local-key-binding, see local-map (overlay property), see local-map (text property), see local-set-key, see local-unset-key, see local-variable-if-set-p, see local-variable-p, see locale, see locale-coding-system, see locale-info, see locate file in path, see locate-file, see locate-library, see lock file, see lock-buffer, see log, see log10, see logand, see logb, see logging echo-area messages, see logical arithmetic, see logical shift, see logior, see lognot, see logxor, see looking-at, see looking-back, see lookup tables, see lookup-key, see loops, infinite, see lower case, see lower-frame, see lowering a frame, see lsh, see lwarn, see M-o, see M-x, see M Maclisp, see macro, see macro argument evaluation, see macro call, see macro call evaluation, see macro compilation, see macro descriptions, see macro expansion, see macroexpand, see macroexpand-all, see macros, see macros, at compile time, see magic autoload comment, see magic file names, see magic-fallback-mode-alist, see magic-mode-alist, see mail-host-address, see major mode, see major mode conventions, see major mode hook, see major mode keymap, see major mode, automatic selection, see major-mode, see make-abbrev-table, see make-auto-save-file-name, see make-backup-file-name, see make-backup-file-name-function, see make-backup-files, see make-bool-vector, see make-button, see make-byte-code, see make-category-set, see make-category-table, see make-char, see make-char-table, see make-directory, see make-display-table, see make-face, see make-frame, see make-frame-invisible, see make-frame-on-display, see make-frame-visible, see make-frame-visible event, see make-glyph-code, see make-hash-table, see make-help-screen, see make-indirect-buffer, see make-keymap, see make-list, see make-local-variable, see make-marker, see make-network-process, see make-obsolete, see make-obsolete-variable, see make-overlay, see make-progress-reporter, see make-ring, see make-sparse-keymap, see make-string, see make-symbol, see make-symbolic-link, see make-syntax-table, see make-temp-file, see make-temp-name, see make-text-button, see make-translation-table, see make-variable-buffer-local, see make-variable-frame-local, see make-vector, see makehash, see making buttons, see makunbound, see manipulating buttons, see map-char-table, see map-keymap, see map-y-or-n-p, see mapatoms, see mapc, see mapcar, see mapconcat, see maphash, see mapping functions, see margins, display, see mark, see mark excursion, see mark ring, see mark, the, see mark-active, see mark-even-if-inactive, see mark-marker, see mark-ring, see mark-ring-max, see marker argument, see marker garbage collection, see marker input stream, see marker output stream, see marker relocation, see marker-buffer, see marker-insertion-type, see marker-position, see markerp, see markers, see markers as numbers, see match data, see match, customization keyword, see match-alternatives, customization keyword, see match-beginning, see match-data, see match-end, see match-string, see match-string-no-properties, see mathematical functions, see max, see max-image-size, see max-lisp-eval-depth, see max-mini-window-height, see max-specpdl-size, see md5, see MD5 checksum, see member, see member-ignore-case, see membership in a list, see memory allocation, see memory usage, see memory-full, see memory-limit, see memory-use-counts, see memq, see memql, see menu bar, see menu definition example, see menu keymaps, see menu prompt string, see menu separators, see menu-bar prefix key, see menu-bar-edit-menu, see menu-bar-files-menu, see menu-bar-final-items, see menu-bar-help-menu, see menu-bar-mule-menu, see menu-bar-search-menu, see menu-bar-tools-menu, see menu-bar-update-hook, see menu-item, see menu-prompt-more-char, see merge-face-attribute, see message, see message digest computation, see message-box, see message-log-max, see message-or-box, see message-truncate-lines, see meta character key constants, see meta character printing, see meta characters, see meta characters lookup, see meta-prefix-char, see min, see minibuffer, see minibuffer completion, see minibuffer history, see minibuffer input, see minibuffer window, and next-window, see minibuffer windows, see minibuffer-allow-text-properties, see minibuffer-auto-raise, see minibuffer-complete, see minibuffer-complete-and-exit, see minibuffer-complete-word, see minibuffer-completion-confirm, see minibuffer-completion-contents, see minibuffer-completion-help, see minibuffer-completion-predicate, see minibuffer-completion-table, see minibuffer-contents, see minibuffer-contents-no-properties, see minibuffer-depth, see minibuffer-exit-hook, see minibuffer-frame-alist, see minibuffer-help-form, see minibuffer-history, see minibuffer-local-completion-map, see minibuffer-local-filename-completion-map, see minibuffer-local-map, see minibuffer-local-must-match-filename-map, see minibuffer-local-must-match-map, see minibuffer-local-ns-map, see minibuffer-message, see minibuffer-prompt, see minibuffer-prompt-end, see minibuffer-prompt-width, see minibuffer-scroll-window, see minibuffer-selected-window, see minibuffer-setup-hook, see minibuffer-window, see minibuffer-window-active-p, see minibufferp, see minimum window size, see minor mode, see minor mode conventions, see minor-mode-alist, see minor-mode-key-binding, see minor-mode-list, see minor-mode-map-alist, see minor-mode-overriding-map-alist, see misc-objects-consed, see mod, see mode, see mode help, see mode hook, see mode line, see mode loading, see mode variable, see mode-class (property), see mode-line construct, see mode-line prefix key, see mode-line-buffer-identification, see mode-line-format, see mode-line-frame-identification, see mode-line-modes, see mode-line-modified, see mode-line-mule-info, see mode-line-position, see mode-line-process, see mode-name, see mode-specific-map, see model/view/controller, see modification flag (of buffer), see modification of lists, see modification time of buffer, see modification time of file, see modification-hooks (overlay property), see modification-hooks (text property), see modifier bits (of input character), see modify-all-frames-parameters, see modify-category-entry, see modify-frame-parameters, see modify-syntax-entry, see modulus, see momentary-string-display, see most-negative-fixnum, see most-positive-fixnum, see motion by chars, words, lines, lists, see motion event, see mouse click event, see mouse drag event, see mouse events, data in, see mouse events, in special parts of frame, see mouse events, repeated, see mouse motion events, see mouse pointer shape, see mouse position, see mouse position list, accessing, see mouse tracking, see mouse, availability, see mouse-1, see mouse-2, see mouse-action (button property), see mouse-face (button property), see mouse-face (overlay property), see mouse-face (text property), see mouse-movement-p, see mouse-on-link-p, see mouse-pixel-position, see mouse-position, see mouse-position-function, see move to beginning or end of buffer, see move-marker, see move-overlay, see move-to-column, see move-to-left-margin, see move-to-window-line, see movemail, see MS-DOS and file modes, see MS-DOS file types, see mule-keymap, see multibyte characters, see multibyte text, see multibyte-char-to-unibyte, see multibyte-string-p, see multibyte-syntax-as-symbol, see multiline font lock, see multiple windows, see multiple X displays, see multiple-frames, see N named function, see NaN, see narrow-to-page, see narrow-to-region, see narrowing, see natnump, see natural numbers, see nbutlast, see nconc, see negative infinity, see negative-argument, see network byte ordering, see network connection, see network servers, see network-coding-system-alist, see network-interface-info, see network-interface-list, see new file message, see newline, see newline, see newline and Auto Fill mode, see newline in print, see newline in strings, see newline-and-indent, see next input, see next-button, see next-char-property-change, see next-frame, see next-history-element, see next-matching-history-element, see next-overlay-change, see next-property-change, see next-screen-context-lines, see next-single-char-property-change, see next-single-property-change, see next-window, see nil, see nil as a list, see nil in keymap, see nil input stream, see nil output stream, see nlistp, see no-byte-compile, see no-catch, see no-redraw-on-reenter, see no-self-insert property, see non-ASCII characters, see non-ASCII text in keybindings, see nonascii-insert-offset, see nonascii-translation-table, see nondirectory part (of file name), see noninteractive, see nonlocal exits, see nonprinting characters, reading, see noreturn, see normal hook, see normal-auto-fill-function, see normal-backup-enable-predicate, see normal-mode, see not, see not-modified, see notation, see nreverse, see nth, see nthcdr, see null, see num-input-keys, see num-nonmacro-input-events, see number comparison, see number conversions, see number-or-marker-p, see number-sequence, see number-to-string, see numberp, see numbers, see numeric prefix argument, see numeric prefix argument usage, see numerical RGB color specification, see O obarray, see obarray in completion, see object, see object internals, see object to string, see occur-mode-map, see octal character code, see octal character input, see octal numbers, see one-window-p, see only-global-abbrevs, see open parenthesis character, see open-dribble-file, see open-network-stream, see open-paren-in-column-0-is-defun-start, see open-termscript, see operating system environment, see operations (property), see option descriptions, see optional arguments, see options on command line, see options, defcustom keyword, see or, see ordering of windows, cyclic, see other-buffer, see other-window, see other-window-scroll-buffer, see output from processes, see output stream, see output-controlling variables, see overall prompt string, see overflow, see overflow-newline-into-fringe, see overlay-arrow-position, see overlay-arrow-string, see overlay-arrow-variable-list, see overlay-buffer, see overlay-end, see overlay-get, see overlay-properties, see overlay-put, see overlay-recenter, see overlay-start, see overlayp, see overlays, see overlays-at, see overlays-in, see overriding-local-map, see overriding-local-map-menu-flag, see overriding-terminal-local-map, see overwrite-mode, see P package-version, customization keyword, see packing, see padding, see page-delimiter, see paired delimiter, see paragraph-separate, see paragraph-start, see parent of char-table, see parent process, see parenthesis, see parenthesis depth, see parenthesis matching, see parenthesis mismatch, debugging, see parenthesis syntax, see parse-colon-path, see parse-partial-sexp, see parse-sexp-ignore-comments, see parse-sexp-lookup-properties, see parse-sexp-lookup-properties, see parser state, see parsing buffer text, see passwords, reading, see PATH environment variable, see path-separator, see PBM, see peculiar error, see peeking at input, see percent symbol in mode line, see perform-replace, see performance analysis, see permanent local variable, see permission, see piece of advice, see pipes, see play-sound, see play-sound-file, see play-sound-functions, see plist, see plist vs. alist, see plist-get, see plist-member, see plist-put, see point, see point excursion, see point in window, see point with narrowing, see point-entered (text property), see point-left (text property), see point-marker, see point-max, see point-max-marker, see point-min, see point-min-marker, see pointer (text property), see pointer shape, see pointers, see pop, see pop-mark, see pop-to-buffer, see pop-up-frame-alist, see pop-up-frame-function, see pop-up-frames, see pop-up-windows, see pos-visible-in-window-p, see position (in buffer), see position argument, see position in window, see position of mouse, see position-bytes, see positive infinity, see posix-looking-at, see posix-search-backward, see posix-search-forward, see posix-string-match, see posn-actual-col-row, see posn-area, see posn-at-point, see posn-at-x-y, see posn-col-row, see posn-image, see posn-object, see posn-object-width-height, see posn-object-x-y, see posn-point, see posn-string, see posn-timestamp, see posn-window, see posn-x-y, see post-command-hook, see post-gc-hook, see postscript images, see pre-abbrev-expand-hook, see pre-command-hook, see preactivating advice, see preceding-char, see precision in format specifications, see predicates for numbers, see prefix argument, see prefix argument unreading, see prefix command, see prefix key, see prefix, defgroup keyword, see prefix-arg, see prefix-help-command, see prefix-numeric-value, see preloading additional functions and variables, see prepare-change-group, see preventing backtracking, see preventing prefix key, see preventing quitting, see previous complete subexpression, see previous-button, see previous-char-property-change, see previous-frame, see previous-history-element, see previous-matching-history-element, see previous-overlay-change, see previous-property-change, see previous-single-char-property-change, see previous-single-property-change, see previous-window, see primitive, see primitive function internals, see primitive type, see primitive-undo, see prin1, see prin1-to-string, see princ, see print, see print example, see print name cell, see print-circle, see print-continuous-numbering, see print-escape-multibyte, see print-escape-newlines, see print-escape-nonascii, see print-gensym, see print-help-return-message, see print-length, see print-level, see print-number-table, see print-quoted, see printed representation, see printed representation for characters, see printing, see printing (Edebug), see printing circular structures, see printing limits, see printing notation, see priority (overlay property), see process, see process filter, see process filter multibyte flag, see process input, see process internals, see process output, see process sentinel, see process signals, see process-adaptive-read-buffering, see process-buffer, see process-coding-system, see process-coding-system-alist, see process-command, see process-connection-type, see process-contact, see process-datagram-address, see process-environment, see process-exit-status, see process-file, see process-filter, see process-filter-multibyte-p, see process-get, see process-id, see process-kill-without-query, see process-list, see process-mark, see process-name, see process-plist, see process-put, see process-query-on-exit-flag, see process-running-child-p, see process-send-eof, see process-send-region, see process-send-string, see process-sentinel, see process-status, see process-tty-name, see processor run time, see processp, see profiling, see prog1, see prog2, see progn, see program arguments, see program directories, see programmed completion, see programming conventions, see programming types, see progress reporting, see progress-reporter-done, see progress-reporter-force-update, see progress-reporter-update, see prompt for file name, see prompt string (of menu), see prompt string of keymap, see properties of text, see propertize, see property category of text character, see property list, see property list cell, see property lists vs association lists, see protect C variables from garbage collection, see protected forms, see provide, see providing features, see PTYs, see punctuation character, see pure storage, see pure-bytes-used, see purecopy, see purify-flag, see push, see push-button, see push-mark, see put, see put-image, see put-text-property, see puthash, see Q query-replace-history, see query-replace-map, see querying the user, see question mark in character constant, see quietly-read-abbrev-file, see quit-flag, see quit-process, see quitting, see quitting from infinite loop, see quote, see quote character, see quoted character input, see quoted-insert suppression, see quoting characters in printing, see quoting using apostrophe, see R radix for reading an integer, see raise-frame, see random, see random numbers, see rassoc, see rassq, see rassq-delete-all, see raw prefix argument, see raw prefix argument usage, see re-builder, see re-search-backward, see re-search-forward, see reactivating advice, see read, see read command name, see read file names, see read input, see read syntax, see read syntax for characters, see read-buffer, see read-buffer-function, see read-char, see read-char-exclusive, see read-coding-system, see read-command, see read-directory-name, see read-event, see read-expression-history, see read-file-name, see read-file-name-completion-ignore-case, see read-file-name-function, see read-from-minibuffer, see read-from-string, see read-input-method-name, see read-kbd-macro, see read-key-sequence, see read-key-sequence-vector, see read-minibuffer, see read-no-blanks-input, see read-non-nil-coding-system, see read-only (text property), see read-only buffer, see read-only buffers in interactive, see read-only character, see read-passwd, see read-quoted-char, see read-quoted-char quitting, see read-string, see read-variable, see reading, see reading a single event, see reading from files, see reading from minibuffer with completion, see reading interactive arguments, see reading numbers in hex, octal, and binary, see reading symbols, see real-last-command, see rearrangement of lists, see rebinding, see recent-auto-save-p, see recent-keys, see recenter, see record command history, see recording input, see recursion, see recursion-depth, see recursive command loop, see recursive editing level, see recursive evaluation, see recursive minibuffers, see recursive-edit, see redirect-frame-focus, see redisplay, see redisplay-dont-pause, see redisplay-end-trigger-functions, see redisplay-preemption-period, see redo, see redraw-display, see redraw-frame, see references, following, see regexp, see regexp alternative, see regexp grouping, see regexp searching, see regexp-history, see regexp-opt, see regexp-opt-depth, see regexp-quote, see regexps used standardly in editing, see region (between point and mark), see region argument, see region-beginning, see region-end, see register-alist, see registers, see regular expression, see regular expression searching, see regular expressions, developing, see reindent-then-newline-and-indent, see relative file name, see remainder, see remapping commands, see remhash, see remove, see remove-from-invisibility-spec, see remove-hook, see remove-images, see remove-list-of-text-properties, see remove-overlays, see remove-text-properties, see remq, see rename-auto-save-file, see rename-buffer, see rename-file, see repeat events, see repeated loading, see replace bindings, see replace characters, see replace matched text, see replace-buffer-in-windows, see replace-match, see replace-regexp-in-string, see replacement after search, see require, see require, customization keyword, see require-final-newline, see requiring features, see reserved keys, see resize frame, see resize window, see rest arguments, see restore-buffer-modified-p, see restriction (in a buffer), see resume (cf. no-redraw-on-reenter), see return (ASCII character), see reverse, see reversing a list, see revert-buffer, see revert-buffer-function, see revert-buffer-insert-file-contents-function, see revert-without-query, see rgb value, see right-fringe-width, see right-margin-width, see ring data structure, see ring-bell-function, see ring-copy, see ring-elements, see ring-empty-p, see ring-insert, see ring-insert-at-beginning, see ring-length, see ring-p, see ring-ref, see ring-remove, see ring-size, see risky-local-variable-p, see rm, see round, see rounding in conversions, see rounding without conversion, see rplaca, see rplacd, see run time stack, see run-at-time, see run-hook-with-args, see run-hook-with-args-until-failure, see run-hook-with-args-until-success, see run-hooks, see run-mode-hooks, see run-with-idle-timer, see S safe local variable, see safe-length, see safe-local-eval-forms, see safe-local-variable-p, see safe-local-variable-values, see safe-magic (property), see safety of functions, see same-window-buffer-names, see same-window-p, see same-window-regexps, see save-abbrevs, see save-buffer, see save-buffer-coding-system, see save-current-buffer, see save-excursion, see save-match-data, see save-restriction, see save-selected-window, see save-some-buffers, see save-window-excursion, see saving buffers, see saving text properties, see saving window information, see scalable-fonts-allowed, see scan-lists, see scan-sexps, see scope, see scrap support (for Mac OS), see screen layout, see screen of terminal, see screen size, see screen-height, see screen-width, see scroll bars, see scroll-bar-event-ratio, see scroll-bar-mode, see scroll-bar-scale, see scroll-bar-width, see scroll-conservatively, see scroll-down, see scroll-down-aggressively, see scroll-left, see scroll-margin, see scroll-other-window, see scroll-preserve-screen-position, see scroll-right, see scroll-step, see scroll-up, see scroll-up-aggressively, see scrolling textually, see search-backward, see search-failed, see search-forward, see search-spaces-regexp, see searching, see searching active keymaps for keys, see searching and case, see searching and replacing, see searching for regexp, see seconds-to-time, see select safe coding system, see select-frame, see select-frame-set-input-focus, see select-safe-coding-system, see select-safe-coding-system-accept-default-p, see select-window, see selected window, see selected-frame, see selected-window, see selecting a buffer, see selecting a window, see selection (for window systems), see selection-coding-system, see selective-display, see selective-display-ellipses, see self-evaluating form, see self-insert-and-exit, see self-insert-command, see self-insert-command override, see self-insert-command, minor modes, see self-insertion, see send-string-to-terminal, see sending signals, see sentence-end, see sentence-end-double-space, see sentence-end-without-period, see sentence-end-without-space, see sentinel (of process), see sequence, see sequence length, see sequencep, see serializing, see session manager, see set, see set, defcustom keyword, see set-after, defcustom keyword, see set-auto-mode, see set-buffer, see set-buffer-auto-saved, see set-buffer-major-mode, see set-buffer-modified-p, see set-buffer-multibyte, see set-case-syntax, see set-case-syntax-delims, see set-case-syntax-pair, see set-case-table, see set-category-table, see set-char-table-default, see set-char-table-extra-slot, see set-char-table-parent, see set-char-table-range, see set-default, see set-default-file-modes, see set-display-table-slot, see set-face-attribute, see set-face-background, see set-face-bold-p, see set-face-font, see set-face-foreground, see set-face-inverse-video-p, see set-face-italic-p, see set-face-stipple, see set-face-underline-p, see set-file-modes, see set-file-times, see set-fontset-font, see set-frame-configuration, see set-frame-height, see set-frame-position, see set-frame-selected-window, see set-frame-size, see set-frame-width, see set-fringe-bitmap-face, see set-input-method, see set-input-mode, see set-keyboard-coding-system, see set-keymap-parent, see set-left-margin, see set-mark, see set-marker, see set-marker-insertion-type, see set-match-data, see set-minibuffer-window, see set-mouse-pixel-position, see set-mouse-position, see set-network-process-option, see set-process-buffer, see set-process-coding-system, see set-process-datagram-address, see set-process-filter, see set-process-filter-multibyte, see set-process-plist, see set-process-query-on-exit-flag, see set-process-sentinel, see set-register, see set-right-margin, see set-screen-height, see set-screen-width, see set-standard-case-table, see set-syntax-table, see set-terminal-coding-system, see set-text-properties, see set-time-zone-rule, see set-visited-file-modtime, see set-visited-file-name, see set-window-buffer, see set-window-configuration, see set-window-dedicated-p, see set-window-display-table, see set-window-fringes, see set-window-hscroll, see set-window-margins, see set-window-point, see set-window-redisplay-end-trigger, see set-window-scroll-bars, see set-window-start, see set-window-vscroll, see setcar, see setcdr, see setenv, see setplist, see setprv, see setq, see setq-default, see sets, see setting modes of files, see setting-constant, see severity level, see sexp motion, see shadowing of variables, see shallow binding, see shared structure, read syntax, see shell command arguments, see shell-command-history, see shell-command-to-string, see shell-quote-argument, see show-help-function, see shrink-window, see shrink-window-horizontally, see shrink-window-if-larger-than-buffer, see side effect, see signal, see signal-process, see signaling errors, see signals, see sigusr1 event, see sigusr2 event, see sin, see single-key-description, see sit-for, see site-init.el, see site-load.el, see site-run-file, see site-start.el, see size of frame, see size of window, see skip-chars-backward, see skip-chars-forward, see skip-syntax-backward, see skip-syntax-forward, see skipping characters, see skipping comments, see sleep-for, see small-temporary-file-directory, see Snarf-documentation, see sort, see sort-columns, see sort-fields, see sort-fold-case, see sort-lines, see sort-numeric-base, see sort-numeric-fields, see sort-pages, see sort-paragraphs, see sort-regexp-fields, see sort-subr, see sorting lists, see sorting text, see sound, see source breakpoints, see space (ASCII character), see spaces, pixel specification, see spaces, specified height or width, see sparse keymap, see SPC in minibuffer, see special, see special events, see special form descriptions, see special form evaluation, see special forms, see special forms for control structures, see special-display-buffer-names, see special-display-frame-alist, see special-display-function, see special-display-p, see special-display-popup-frame, see special-display-regexps, see special-event-map, see specify color, see speedups, see splicing (with backquote), see split-char, see split-height-threshold, see split-string, see split-string-default-separators, see split-window, see split-window-horizontally, see split-window-keep-point, see split-window-vertically, see splitting windows, see sqrt, see stable sort, see standard buffer-local variables, see standard colors for character terminals, see standard errors, see standard hooks, see standard keymaps, see standard regexps used in editing, see standard-case-table, see standard-category-table, see standard-display-table, see standard-input, see standard-output, see standard-syntax-table, see standard-translation-table-for-decode, see standard-translation-table-for-encode, see standards of coding style, see start-process, see start-process-shell-command, see startup of Emacs, see startup.el, see staticpro, protection from GC, see sticky text properties, see stop points, see stop-process, see stopping an infinite loop, see stopping on events, see store-match-data, see store-substring, see stream (for printing), see stream (for reading), see string, see string equality, see string in keymap, see string input stream, see string length, see string quote, see string search, see string to character, see string to number, see string to object, see string, number of bytes, see string, writing a doc string, see string-as-multibyte, see string-as-unibyte, see string-bytes, see string-chars-consed, see string-equal, see string-lessp, see string-make-multibyte, see string-make-unibyte, see string-match, see string-or-null-p, see string-to-char, see string-to-int, see string-to-multibyte, see string-to-number, see string-to-syntax, see string-width, see string<, see string=, see stringp, see strings, see strings with keyboard events, see strings, formatting them, see strings-consed, see subprocess, see subr, see subr-arity, see subrp, see subst-char-in-region, see substitute-command-keys, see substitute-in-file-name, see substitute-key-definition, see substituting keys in documentation, see substring, see substring-no-properties, see subtype of char-table, see suggestions, see super characters, see suppress-keymap, see suspend (cf. no-redraw-on-reenter), see suspend evaluation, see suspend-emacs, see suspend-hook, see suspend-resume-hook, see suspending Emacs, see switch-to-buffer, see switch-to-buffer-other-window, see switches on command line, see switching to a buffer, see sxhash, see symbol, see symbol components, see symbol constituent, see symbol equality, see symbol evaluation, see symbol function indirection, see symbol in keymap, see symbol name hashing, see symbol that evaluates to itself, see symbol with constant value, see symbol-file, see symbol-function, see symbol-name, see symbol-plist, see symbol-value, see symbolp, see symbols-consed, see synchronous subprocess, see syntactic font lock, see syntax class, see syntax descriptor, see syntax error (Edebug), see syntax flags, see syntax for characters, see syntax table, see syntax table example, see syntax table internals, see syntax tables in modes, see syntax-after, see syntax-begin-function, see syntax-class, see syntax-ppss, see syntax-ppss-flush-cache, see syntax-ppss-toplevel-pos, see syntax-table, see syntax-table (text property), see syntax-table-p, see system type and name, see system-configuration, see system-key-alist, see system-messages-locale, see system-name, see system-time-locale, see system-type, see t, see t input stream, see t output stream, see T tab (ASCII character), see tab deletion, see TAB in minibuffer, see tab-stop-list, see tab-to-tab-stop, see tab-width, see tabs stops for indentation, see tag on run time stack, see tag, customization keyword, see tan, see TCP, see temacs, see TEMP environment variable, see temp-buffer-setup-hook, see temp-buffer-show-function, see temp-buffer-show-hook, see temporary-file-directory, see TERM environment variable, see term-file-prefix, see term-setup-hook, see Termcap, see terminal frame, see terminal input, see terminal input modes, see terminal output, see terminal screen, see terminal-coding-system, see terminal-specific initialization, see termscript file, see terpri, see test-completion, see testcover-mark-all, see testcover-next-mark, see testcover-start, see testing types, see text, see text deletion, see text files and binary files, see text insertion, see text near point, see text parsing, see text properties, see text properties in files, see text properties in the mode line, see text representations, see text-char-description, see text-mode-abbrev-table, see text-mode-map, see text-mode-syntax-table, see text-properties-at, see text-property-any, see text-property-default-nonsticky, see text-property-not-all, see textual scrolling, see thing-at-point, see this-command, see this-command-keys, see this-command-keys-vector, see this-original-command, see three-step-help, see throw, see throw example, see tiled windows, see time-add, see time-less-p, see time-subtract, see time-to-day-in-year, see time-to-days, see timer, see timer-max-repeats, see timestamp of a mouse event, see timing programs, see tips for writing Lisp, see TMP environment variable, see TMPDIR environment variable, see toggle-read-only, see tool bar, see tool-bar-add-item, see tool-bar-add-item-from-menu, see tool-bar-border, see tool-bar-button-margin, see tool-bar-button-relief, see tool-bar-local-item-from-menu, see tool-bar-map, see tooltip, see top-level, see top-level form, see tq-close, see tq-create, see tq-enqueue, see trace buffer, see track-mouse, see trailing codes, see transaction queue, see transcendental functions, see transient-mark-mode, see translate-region, see translation tables, see translation-table-for-input, see transpose-regions, see triple-click events, see true, see true list, see truename (of file), see truncate, see truncate-lines, see truncate-partial-width-windows, see truncate-string-to-width, see truth value, see try-completion, see tty-color-alist, see tty-color-approximate, see tty-color-clear, see tty-color-define, see tty-color-translate, see tty-erase-char, see two's complement, see type, see type (button property), see type checking, see type checking internals, see type predicates, see type, defcustom keyword, see type-of, see U UDP, see umask, see unbalanced parentheses, see unbinding keys, see undefined, see undefined in keymap, see undefined key, see undo avoidance, see undo-ask-before-discard, see undo-boundary, see undo-in-progress, see undo-limit, see undo-outer-limit, see undo-strong-limit, see unexec, see unhandled-file-name-directory, see unibyte text, see unibyte-char-to-multibyte, see unicode character escape, see unintern, see uninterned symbol, see universal-argument, see unless, see unload-feature, see unload-feature-special-hooks, see unloading packages, see unloading packages, preparing for, see unlock-buffer, see unpacking, see unread-command-char, see unread-command-events, see unsafep, see unwind-protect, see unwinding, see up-list, see upcase, see upcase-initials, see upcase-region, see upcase-word, see update-directory-autoloads, see update-file-autoloads, see upper case, see upper case key sequence, see use-global-map, see use-hard-newlines, see use-local-map, see user identification, see user option, see user signals, see user-defined error, see user-full-name, see user-init-file, see user-login-name, see user-mail-address, see user-real-login-name, see user-real-uid, see user-uid, see user-variable-p, see user-variable-p example, see V value cell, see value of expression, see values, see variable, see variable aliases, see variable definition, see variable descriptions, see variable limit error, see variable with constant value, see variable, buffer-local, see variable-documentation, see variable-interactive, see variable-width spaces, see variant coding system, see vc-mode, see vc-prefix-map, see vconcat, see vector, see vector (type), see vector evaluation, see vector length, see vector-cells-consed, see vectorp, see verify-visited-file-modtime, see version number (in file name), see version, customization keyword, see version-control, see vertical fractional scrolling, see vertical tab, see vertical-line prefix key, see vertical-motion, see vertical-scroll-bar, see vertical-scroll-bar prefix key, see view part, model/view/controller, see view-file, see view-mode-map, see view-register, see visible frame, see visible-bell, see visible-frame-list, see visited file, see visited file mode, see visited-file-modtime, see visiting files, see void function, see void function cell, see void variable, see void-function, see void-text-area-pointer, see void-variable, see W waiting, see waiting for command key input, see waiting-for-user-input-p, see walk-windows, see warn, see warning type, see warning-fill-prefix, see warning-levels, see warning-minimum-level, see warning-minimum-log-level, see warning-prefix-function, see warning-series, see warning-suppress-log-types, see warning-suppress-types, see warning-type-format, see warnings, see wheel-down event, see wheel-up event, see when, see where-is-internal, see while, see while-no-input, see whitespace, see whitespace character, see wholenump, see widen, see widening, see window, see window (overlay property), see window configuration (Edebug), see window configurations, see window excursions, see window frame, see window header line, see window internals, see window layout in a frame, see window layout, all frames, see window manager, and frame parameters, see window ordering, cyclic, see window point, see window point internals, see window position, see window resizing, see window size, see window size, changing, see window splitting, see window start position, see window that satisfies a predicate, see window top line, see window tree, see window-at, see window-body-height, see window-buffer, see window-configuration-change-hook, see window-configuration-frame, see window-configuration-p, see window-current-scroll-bars, see window-dedicated-p, see window-display-table, see window-edges, see window-end, see window-frame, see window-fringes, see window-height, see window-hscroll, see window-inside-edges, see window-inside-pixel-edges, see window-line-height, see window-list, see window-live-p, see window-margins, see window-min-height, see window-min-width, see window-minibuffer-p, see window-pixel-edges, see window-point, see window-redisplay-end-trigger, see window-scroll-bars, see window-scroll-functions, see window-setup-hook, see window-size-change-functions, see window-size-fixed, see window-start, see window-system, see window-tree, see window-vscroll, see window-width, see windowp, see Windows file types, see windows, controlling precisely, see with-case-table, see with-current-buffer, see with-local-quit, see with-no-warnings, see with-output-to-string, see with-output-to-temp-buffer, see with-selected-window, see with-syntax-table, see with-temp-buffer, see with-temp-file, see with-temp-message, see with-timeout, see word constituent, see word-search-backward, see word-search-forward, see words-include-escapes, see write-abbrev-file, see write-char, see write-contents-functions, see write-file, see write-file-functions, see write-region, see write-region-annotate-functions, see writing a documentation string, see writing Emacs primitives, see writing to files, see wrong-number-of-arguments, see wrong-type-argument, see X X Window System, see x-alt-keysym, see x-bitmap-file-path, see x-close-connection, see x-color-defined-p, see x-color-values, see x-defined-colors, see x-display-color-p, see x-display-list, see x-dnd-known-types, see x-dnd-test-function, see x-dnd-types-alist, see x-family-fonts, see x-font-family-list, see x-get-cut-buffer, see x-get-resource, see x-get-selection, see x-hyper-keysym, see x-list-fonts, see x-meta-keysym, see x-open-connection, see x-parse-geometry, see x-pointer-shape, see x-popup-dialog, see x-popup-menu, see x-resource-class, see x-resource-name, see x-select-enable-clipboard, see x-sensitive-text-pointer-shape, see x-server-vendor, see x-server-version, see x-set-cut-buffer, see x-set-selection, see x-super-keysym, see X11 keysyms, see XBM, see XPM, see Y y-or-n-p, see y-or-n-p-with-timeout, see yank, see yank suppression, see yank-pop, see yank-undo-function, see yes-or-no questions, see yes-or-no-p, see Z zerop, see