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This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for Emacs Version 19. Published by the Free Software Foundation, 675 Massachusetts Avenue, Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. File: elisp, Node: Copying, Next: Introduction, Prev: Top, Up: Top GNU GENERAL PUBLIC LICENSE ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, 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 Library 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. 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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 1. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under 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 another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you". Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. 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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 AN IDEA OF WHAT IT DOES. Copyright (C) 19YY 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., 675 Mass Ave, Cambridge, MA 02139, 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) 19YY 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 Library General Public License instead of this License. File: elisp, Node: Introduction, Next: Types of Lisp Object, Prev: Copying, Up: Top 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 describes Emacs Lisp, presuming 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 2.0. * Menu: * Caveats:: Flaws and a request for help. * Lisp History:: Emacs Lisp is descended from Maclisp. * Conventions:: How the manual is formatted. * Acknowledgements:: The authors, editors, and sponsors of this manual. File: elisp, Node: Caveats, Next: Lisp History, Prev: Introduction, Up: Introduction Caveats ======= This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few sections which are not included, 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 references to VMS and all information relating Sunview. (The Free Software Foundation expends no effort on support for Sunview, since we believe users should use the free X window system rather than proprietary window systems.) 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 which you are criticizing. Please mail comments and corrections to bug-lisp-manual@prep.ai.mit.edu --Bil Lewis, Dan LaLiberte, Richard Stallman File: elisp, Node: Lisp History, Next: Conventions, Prev: Caveats, Up: Introduction 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 superior for other purposes as well, such as writing editing commands. 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 1960's at MIT's Project MAC. Eventually the implementors of the descendents of Maclisp came together and developed a standard for Lisp systems, called Common Lisp. 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 of the 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. File: elisp, Node: Conventions, Next: Acknowledgements, Prev: Lisp History, Up: Introduction 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. * Menu: * Some Terms:: Explanation of terms we use in this manual. * nil and t:: How the symbols `nil' and `t' are used. * Evaluation Notation:: The format we use for examples of evaluation. * Printing Notation:: The format we use for examples that print output. * Error Messages:: The format we use for examples of errors. * Buffer Text Notation:: The format we use for buffer contents in examples. * Format of Descriptions:: Notation for describing functions, variables, etc. File: elisp, Node: Some Terms, Next: nil and t, Prev: Conventions, Up: Conventions Some Terms ---------- Throughout this manual, the phrases "the Lisp reader" and "the Lisp printer" are used to refer to those routines in Lisp that convert textual representations of Lisp objects into actual objects, and vice versa. *Note Printed Representation::, 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. Examples of Lisp code appear in this font or form: `(list 1 2 3)'. Names that represent arguments or metasyntactic variables appear in this font or form: FIRST-NUMBER. File: elisp, Node: nil and t, Next: Evaluation Notation, Prev: Some Terms, Up: Conventions `nil' and `t' ------------- In Lisp, the symbol `nil' is overloaded with three 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 use `()' when we wish to emphasize that it means the empty list, and we use `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 (not nil) ; Emphasize the truth value FALSE 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 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. *Note Accessing Variables::. File: elisp, Node: Evaluation Notation, Next: Printing Notation, Prev: nil and t, Up: Conventions Evaluation 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 actual 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 which produces identical results. The exact equivalence of two forms is indicated with `=='. (make-sparse-keymap) == (list 'keymap) File: elisp, Node: Printing Notation, Next: Error Messages, Prev: Evaluation Notation, Up: Conventions Printing Notation ----------------- Many of the examples in this manual print text when they are evaluated. If you execute the code from an example in a Lisp Interaction buffer (such as the buffer `*scratch*'), the printed text is inserted into the buffer. If the example is executed by other means (such as by evaluating the function `eval-region'), the text printed is usually displayed in the echo area. You should be aware that text displayed in the echo area is truncated to a single line. In examples that print text, the printed text is indicated with `-|', irrespective of how the form is executed. The value returned by evaluating the form (here `bar') follows on a separate line. (progn (print 'foo) (print 'bar)) -| foo -| bar => bar File: elisp, Node: Error Messages, Next: Buffer Text Notation, Prev: Printing Notation, Up: Conventions Error Messages -------------- Some examples cause errors to be signaled. In them, the error message (which always appears in the echo area) is shown on a line starting with `error-->'. Note that `error-->' itself does not appear in the echo area. (+ 23 'x) error--> Wrong type argument: integer-or-marker-p, x File: elisp, Node: Buffer Text Notation, Next: Format of Descriptions, Prev: Error Messages, Up: Conventions Buffer Text Notation -------------------- Some examples show modifications to text in a buffer, with "before" and "after" versions of the text. In such cases, the entire contents of the buffer in question are included between two lines of dashes containing the buffer name. In addition, the location of point is shown as `-!-'. (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 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 ---------- File: elisp, Node: Format of Descriptions, Prev: Buffer Text Notation, Up: Conventions Format of Descriptions ---------------------- 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. * Menu: * A Sample Function Description:: * A Sample Variable Description:: File: elisp, Node: A Sample Function Description, Next: A Sample Variable Description, Prev: Format of Descriptions, Up: Format of Descriptions A Sample Function Description ............................. In a function description, the name of the function being described appears first. It is followed on the same line by a list of parameters. The names used for the parameters are also used in the body of the description. The appearance of the keyword `&optional' in the parameter list indicates that the arguments for subsequent parameters may be omitted (omitted parameters default to `nil'). Do not write `&optional' when you call the function. The keyword `&rest' (which will always be followed by a single parameter) indicates that any number of arguments can follow. The value of the single following parameter will be a list of all these arguments. Do not write `&rest' when you call the function. Here is a description of an imaginary function `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 INTEGER2 is 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 parameter 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. Parameters named OBJECT may be of any type. (*Note Types of Lisp Object::, for a list of Emacs object types.) Parameters with other sorts of names (e.g., NEW-FILE) are discussed specifically in the description of the function. In some sections, features common to parameters of several functions are described at the beginning. *Note Lambda Expressions::, 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 parameters 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: - Special Form: count-loop (VAR [FROM TO [INC]]) BODY... This imaginary special form implements a loop that executes the BODY forms and then increments the variable VAR on each iteration. On the first iteration, the variable has the value FROM; on subsequent iterations, it is incremented by 1 (or by INC if that is given). The loop exits before executing BODY if 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, then VAR is bound to `nil' before the loop begins, and the loop exits if VAR is non-`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 are optional, but must both be present or both absent. If they are present, INC may optionally be specified as well. These arguments are grouped with the argument VAR into a list, to distinguish them from BODY, which includes all remaining elements of the form. File: elisp, Node: A Sample Variable Description, Prev: A Sample Function Description, Up: Format of Descriptions A Sample Variable Description ............................. A "variable" is a name that can hold a value. Although any variable can be set by the user, certain variables that exist specifically so that users can change them 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. - Variable: electric-future-map The value of this variable is a full keymap used by electric command future mode. The functions in this map will allow you to edit commands you have not yet thought about executing. User option descriptions have the same format, but `Variable' is replaced by `User Option'. File: elisp, Node: Acknowledgements, Prev: Conventions, Up: Introduction 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, David Boyes, Alan Carroll, David A. Duff, Beverly Erlebacher, David Eckelkamp, Eirik Fuller, Eric Hanchrow, George Hartzell, Nathan Hess, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, K. Richard Magill, Brian Marick, Roland McGrath, Skip Montanaro, John Gardiner Myers, Arnold D. Robbins, Raul Rockwell, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Jean White, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn. File: elisp, Node: Types of Lisp Object, Next: Numbers, Prev: Introduction, Up: Top Lisp Data Types *************** 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. 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", "subr", "byte-code function", and several special types, such as "buffer", that are related to editing. (*Note Editing Types::.) 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, it cannot be treated as a number because 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 remembers the type of any value you store in it. 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. * Menu: * Printed Representation:: How Lisp objects are represented as text. * Comments:: Comments and their formatting conventions. * Programming Types:: Types found in all Lisp systems. * Editing Types:: Types specific to Emacs. * Type Predicates:: Tests related to types. * Equality Predicates:: Tests of equality between any two objects. File: elisp, Node: Printed Representation, Next: Comments, Up: Types of Lisp Object Printed Representation and Read Syntax ====================================== The "printed representation" of an object is the format of the output generated by the Lisp printer (the function `print') for that object. The "read syntax" of an object is the format of the input accepted by the Lisp reader (the function `read') for that object. Most objects have more than one possible read syntax. Some types of object have no read syntax; except for these cases, the printed representation of an object is also a read syntax for it. 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. Every type has a printed representation. Some types have no read syntax, since it may not make sense to enter objects of these types directly in a Lisp program. For example, the buffer type does not have a read syntax. Objects of these types are printed in "hash notation": the characters `#<' followed by a descriptive string (typically the type name followed by the name of the object), and closed with a matching `>'. Hash notation cannot be read at all, so the Lisp reader signals the error `invalid-read-syntax' whenever a `#<' is encountered. (current-buffer) => #<buffer objects.texi> 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 (*note Evaluation::.). 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. *Note Input Functions::, for a description of `read', the basic function for reading objects. File: elisp, Node: Comments, Next: Programming Types, Prev: Printed Representation, Up: Types of Lisp Object Comments ======== 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 comment starts with a semicolon (`;') if it is not within a string or character constant, and continues to the end of line. Comments are discarded by the Lisp reader, and do not become part of the Lisp objects which represent the program within the Lisp system. *Note Comment Tips::, for conventions for formatting comments. File: elisp, Node: Programming Types, Next: Editing Types, Prev: Comments, Up: Types of Lisp Object 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 are provided in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp. * Menu: * Integer Type:: Numbers without fractional parts. * Floating Point Type:: Numbers with fractional parts and with a large range. * Character Type:: The representation of letters, numbers and control characters. * Sequence Type:: Both lists and arrays are classified as sequences. * List Type:: Lists gave Lisp its name (not to mention reputation). * Array Type:: Arrays include strings and vectors. * String Type:: An (efficient) array of characters. * Vector Type:: One-dimensional arrays. * Symbol Type:: A multi-use object that refers to a function, variable, property list, or itself. * Lisp Function Type:: A piece of executable code you can call from elsewhere. * Lisp Macro Type:: A method of expanding an expression into another expression, more fundamental but less pretty. * Primitive Function Type:: A function written in C, callable from Lisp. * Byte-Code Type:: A function written in Lisp, then compiled. * Autoload Type:: A type used for automatically loading seldom-used functions. File: elisp, Node: Integer Type, Next: Floating Point Type, Up: Programming Types Integer Type ------------ Integers are the only kind of number in GNU Emacs Lisp, version 18. The range of values for integers is -8388608 to 8388607 (24 bits; i.e., -2**23 to 2**23 - 1) on most machines, but is 25 or 26 bits on some systems. It is important to note that the Emacs Lisp arithmetic functions do not check for overflow. Thus `(1+ 8388607)' is -8388608 on 24-bit implementations. The read syntax for numbers is a sequence of (base ten) digits with an optional sign. The printed representation produced by the Lisp interpreter never has a leading `+'. -1 ; The integer -1. 1 ; The integer 1. +1 ; Also the integer 1. 16777217 ; Also the integer 1! ; (on a 24-bit or 25-bit implementation) *Note Numbers::, for more information. File: elisp, Node: Floating Point Type, Next: Character Type, Prev: Integer Type, Up: Programming Types Floating Point Type ------------------- Emacs version 19 supports floating point numbers, if compiled with the macro `LISP_FLOAT_TYPE' defined. The precise range of floating point numbers is machine-specific. 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. *Note Numbers::, for more information.