\input texinfo @c -*-texinfo-*- @setfilename ../../info/cl.info @settitle Common Lisp Extensions @include docstyle.texi @include emacsver.texi @copying This file documents the GNU Emacs Common Lisp emulation package. Copyright @copyright{} 1993, 2001--2017 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, 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 the freedom to copy and modify this GNU manual.'' @end quotation @end copying @dircategory Emacs lisp libraries @direntry * CL: (cl). Partial Common Lisp support for Emacs Lisp. @end direntry @finalout @titlepage @sp 6 @center @titlefont{Common Lisp Extensions} @sp 4 @center For GNU Emacs Lisp @sp 1 @center as distributed with Emacs @value{EMACSVER} @sp 5 @center Dave Gillespie @center daveg@@synaptics.com @page @vskip 0pt plus 1filll @insertcopying @end titlepage @contents @ifnottex @node Top @top GNU Emacs Common Lisp Emulation @insertcopying @end ifnottex @menu * Overview:: Basics, usage, organization, naming conventions. * Program Structure:: Arglists, @code{cl-eval-when}. * Predicates:: Type predicates and equality predicates. * Control Structure:: Assignment, conditionals, blocks, looping. * Macros:: Destructuring, compiler macros. * Declarations:: @code{cl-proclaim}, @code{cl-declare}, etc. * Symbols:: Property lists, creating symbols. * Numbers:: Predicates, functions, random numbers. * Sequences:: Mapping, functions, searching, sorting. * Lists:: Functions, substitution, sets, associations. * Structures:: @code{cl-defstruct}. * Assertions:: Assertions and type checking. Appendices * Efficiency Concerns:: Hints and techniques. * Common Lisp Compatibility:: All known differences with Steele. * Porting Common Lisp:: Hints for porting Common Lisp code. * Obsolete Features:: Obsolete features. * GNU Free Documentation License:: The license for this documentation. Indexes * Function Index:: An entry for each documented function. * Variable Index:: An entry for each documented variable. * Concept Index:: An entry for each concept. @end menu @node Overview @chapter Overview @noindent This document describes a set of Emacs Lisp facilities borrowed from Common Lisp. All the facilities are described here in detail. While this document does not assume any prior knowledge of Common Lisp, it does assume a basic familiarity with Emacs Lisp. Common Lisp is a huge language, and Common Lisp systems tend to be massive and extremely complex. Emacs Lisp, by contrast, is rather minimalist in the choice of Lisp features it offers the programmer. As Emacs Lisp programmers have grown in number, and the applications they write have grown more ambitious, it has become clear that Emacs Lisp could benefit from many of the conveniences of Common Lisp. The @dfn{CL} package adds a number of Common Lisp functions and control structures to Emacs Lisp. While not a 100% complete implementation of Common Lisp, it adds enough functionality to make Emacs Lisp programming significantly more convenient. Some Common Lisp features have been omitted from this package for various reasons: @itemize @bullet @item Some features are too complex or bulky relative to their benefit to Emacs Lisp programmers. CLOS and Common Lisp streams are fine examples of this group. (The separate package EIEIO implements a subset of CLOS functionality. @xref{Top, , Introduction, eieio, EIEIO}.) @item Other features cannot be implemented without modification to the Emacs Lisp interpreter itself, such as multiple return values, case-insensitive symbols, and complex numbers. This package generally makes no attempt to emulate these features. @end itemize This package was originally written by Dave Gillespie, @file{daveg@@synaptics.com}, as a total rewrite of an earlier 1986 @file{cl.el} package by Cesar Quiroz. Care has been taken to ensure that each function is defined efficiently, concisely, and with minimal impact on the rest of the Emacs environment. Stefan Monnier added the file @file{cl-lib.el} and rationalized the namespace for Emacs 24.3. @menu * Usage:: How to use this package. * Organization:: The package's component files. * Naming Conventions:: Notes on function names. @end menu @node Usage @section Usage @noindent This package is distributed with Emacs, so there is no need to install any additional files in order to start using it. Lisp code that uses features from this package should simply include at the beginning: @example (require 'cl-lib) @end example @noindent You may wish to add such a statement to your init file, if you make frequent use of features from this package. Code that only uses macros from this package can enclose the above in @code{eval-when-compile}. Internally, this library is divided into several files, @pxref{Organization}. Your code should only ever load the main @file{cl-lib} file, which will load the others as needed. @node Organization @section Organization @noindent The Common Lisp package is organized into four main files: @table @file @item cl-lib.el This is the main file, which contains basic functions and information about the package. This file is relatively compact. @item cl-extra.el This file contains the larger, more complex or unusual functions. It is kept separate so that packages which only want to use Common Lisp fundamentals like the @code{cl-incf} function won't need to pay the overhead of loading the more advanced functions. @item cl-seq.el This file contains most of the advanced functions for operating on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}. @item cl-macs.el This file contains the features that are macros instead of functions. Macros expand when the caller is compiled, not when it is run, so the macros generally only need to be present when the byte-compiler is running (or when the macros are used in uncompiled code). Most of the macros of this package are isolated in @file{cl-macs.el} so that they won't take up memory unless you are compiling. @end table The file @file{cl-lib.el} includes all necessary @code{autoload} commands for the functions and macros in the other three files. All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el} will take care of pulling in the other files when they are needed. There is another file, @file{cl.el}, which was the main entry point to this package prior to Emacs 24.3. Nowadays, it is replaced by @file{cl-lib.el}. The two provide the same features (in most cases), but use different function names (in fact, @file{cl.el} mainly just defines aliases to the @file{cl-lib.el} definitions). Where @file{cl-lib.el} defines a function called, for example, @code{cl-incf}, @file{cl.el} uses the same name but without the @samp{cl-} prefix, e.g., @code{incf} in this example. There are a few exceptions to this. First, functions such as @code{cl-defun} where the unprefixed version was already used for a standard Emacs Lisp function. In such cases, the @file{cl.el} version adds a @samp{*} suffix, e.g., @code{defun*}. Second, there are some obsolete features that are only implemented in @file{cl.el}, not in @file{cl-lib.el}, because they are replaced by other standard Emacs Lisp features. Finally, in a very few cases the old @file{cl.el} versions do not behave in exactly the same way as the @file{cl-lib.el} versions. @xref{Obsolete Features}. @c There is also cl-mapc, which was called cl-mapc even before cl-lib.el. @c But not autoloaded, so maybe not much used? Since the old @file{cl.el} does not use a clean namespace, Emacs has a policy that packages distributed with Emacs must not load @code{cl} at run time. (It is ok for them to load @code{cl} at @emph{compile} time, with @code{eval-when-compile}, and use the macros it provides.) There is no such restriction on the use of @code{cl-lib}. New code should use @code{cl-lib} rather than @code{cl}. There is one more file, @file{cl-compat.el}, which defines some routines from the older Quiroz @file{cl.el} package that are not otherwise present in the new package. This file is obsolete and should not be used in new code. @node Naming Conventions @section Naming Conventions @noindent Except where noted, all functions defined by this package have the same calling conventions as their Common Lisp counterparts, and names that are those of Common Lisp plus a @samp{cl-} prefix. Internal function and variable names in the package are prefixed by @code{cl--}. Here is a complete list of functions prefixed by @code{cl-} that were @emph{not} taken from Common Lisp: @example cl-callf cl-callf2 cl-defsubst cl-letf cl-letf* @end example @c This is not uninteresting I suppose, but is of zero practical relevance @c to the user, and seems like a hostage to changing implementation details. The following simple functions and macros are defined in @file{cl-lib.el}; they do not cause other components like @file{cl-extra} to be loaded. @example cl-evenp cl-oddp cl-minusp cl-plusp cl-endp cl-subst cl-copy-list cl-list* cl-ldiff cl-rest cl-decf [1] cl-incf [1] cl-acons cl-adjoin [2] cl-pairlis cl-pushnew [1,2] cl-declaim cl-proclaim cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth cl-mapcar [3] @end example @noindent [1] Only when @var{place} is a plain variable name. @noindent [2] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified, and @code{:key} is not used. @noindent [3] Only for one sequence argument or two list arguments. @node Program Structure @chapter Program Structure @noindent This section describes features of this package that have to do with programs as a whole: advanced argument lists for functions, and the @code{cl-eval-when} construct. @menu * Argument Lists:: @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}. * Time of Evaluation:: The @code{cl-eval-when} construct. @end menu @node Argument Lists @section Argument Lists @cindex &key @cindex &aux @noindent Emacs Lisp's notation for argument lists of functions is a subset of the Common Lisp notation. As well as the familiar @code{&optional} and @code{&rest} markers, Common Lisp allows you to specify default values for optional arguments, and it provides the additional markers @code{&key} and @code{&aux}. Since argument parsing is built-in to Emacs, there is no way for this package to implement Common Lisp argument lists seamlessly. Instead, this package defines alternates for several Lisp forms which you must use if you need Common Lisp argument lists. @defmac cl-defun name arglist body@dots{} This form is identical to the regular @code{defun} form, except that @var{arglist} is allowed to be a full Common Lisp argument list. Also, the function body is enclosed in an implicit block called @var{name}; @pxref{Blocks and Exits}. @end defmac @defmac cl-iter-defun name arglist body@dots{} This form is identical to the regular @code{iter-defun} form, except that @var{arglist} is allowed to be a full Common Lisp argument list. Also, the function body is enclosed in an implicit block called @var{name}; @pxref{Blocks and Exits}. @end defmac @defmac cl-defsubst name arglist body@dots{} This is just like @code{cl-defun}, except that the function that is defined is automatically proclaimed @code{inline}, i.e., calls to it may be expanded into in-line code by the byte compiler. This is analogous to the @code{defsubst} form; @code{cl-defsubst} uses a different method (compiler macros) which works in all versions of Emacs, and also generates somewhat more @c For some examples, @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html efficient inline expansions. In particular, @code{cl-defsubst} arranges for the processing of keyword arguments, default values, etc., to be done at compile-time whenever possible. @end defmac @defmac cl-defmacro name arglist body@dots{} This is identical to the regular @code{defmacro} form, except that @var{arglist} is allowed to be a full Common Lisp argument list. The @code{&environment} keyword is supported as described in Steele's book @cite{Common Lisp, the Language}. The @code{&whole} keyword is supported only within destructured lists (see below); top-level @code{&whole} cannot be implemented with the current Emacs Lisp interpreter. The macro expander body is enclosed in an implicit block called @var{name}. @end defmac @defmac cl-function symbol-or-lambda This is identical to the regular @code{function} form, except that if the argument is a @code{lambda} form then that form may use a full Common Lisp argument list. @end defmac Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined in this package that include @var{arglist}s in their syntax allow full Common Lisp argument lists. Note that it is @emph{not} necessary to use @code{cl-defun} in order to have access to most CL features in your function. These features are always present; @code{cl-defun}'s only difference from @code{defun} is its more flexible argument lists and its implicit block. The full form of a Common Lisp argument list is @example (@var{var}@dots{} &optional (@var{var} @var{initform} @var{svar})@dots{} &rest @var{var} &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{} &aux (@var{var} @var{initform})@dots{}) @end example Each of the five argument list sections is optional. The @var{svar}, @var{initform}, and @var{keyword} parts are optional; if they are omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}. The first section consists of zero or more @dfn{required} arguments. These arguments must always be specified in a call to the function; there is no difference between Emacs Lisp and Common Lisp as far as required arguments are concerned. The second section consists of @dfn{optional} arguments. These arguments may be specified in the function call; if they are not, @var{initform} specifies the default value used for the argument. (No @var{initform} means to use @code{nil} as the default.) The @var{initform} is evaluated with the bindings for the preceding arguments already established; @code{(a &optional (b (1+ a)))} matches one or two arguments, with the second argument defaulting to one plus the first argument. If the @var{svar} is specified, it is an auxiliary variable which is bound to @code{t} if the optional argument was specified, or to @code{nil} if the argument was omitted. If you don't use an @var{svar}, then there will be no way for your function to tell whether it was called with no argument, or with the default value passed explicitly as an argument. The third section consists of a single @dfn{rest} argument. If more arguments were passed to the function than are accounted for by the required and optional arguments, those extra arguments are collected into a list and bound to the ``rest'' argument variable. Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp. Common Lisp accepts @code{&body} as a synonym for @code{&rest} in macro contexts; this package accepts it all the time. The fourth section consists of @dfn{keyword} arguments. These are optional arguments which are specified by name rather than positionally in the argument list. For example, @example (cl-defun foo (a &optional b &key c d (e 17))) @end example @noindent defines a function which may be called with one, two, or more arguments. The first two arguments are bound to @code{a} and @code{b} in the usual way. The remaining arguments must be pairs of the form @code{:c}, @code{:d}, or @code{:e} followed by the value to be bound to the corresponding argument variable. (Symbols whose names begin with a colon are called @dfn{keywords}, and they are self-quoting in the same way as @code{nil} and @code{t}.) For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword appears more than once in the function call, the first occurrence takes precedence over the later ones. Note that it is not possible to specify keyword arguments without specifying the optional argument @code{b} as well, since @code{(foo 1 :c 2)} would bind @code{b} to the keyword @code{:c}, then signal an error because @code{2} is not a valid keyword. You can also explicitly specify the keyword argument; it need not be simply the variable name prefixed with a colon. For example, @example (cl-defun bar (&key (a 1) ((baz b) 4))) @end example @noindent specifies a keyword @code{:a} that sets the variable @code{a} with default value 1, as well as a keyword @code{baz} that sets the variable @code{b} with default value 4. In this case, because @code{baz} is not self-quoting, you must quote it explicitly in the function call, like this: @example (bar :a 10 'baz 42) @end example Ordinarily, it is an error to pass an unrecognized keyword to a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask Lisp to ignore unrecognized keywords, either by adding the marker @code{&allow-other-keys} after the keyword section of the argument list, or by specifying an @code{:allow-other-keys} argument in the call whose value is non-@code{nil}. If the function uses both @code{&rest} and @code{&key} at the same time, the ``rest'' argument is bound to the keyword list as it appears in the call. For example: @example (cl-defun find-thing (thing &rest rest &key need &allow-other-keys) (or (apply 'cl-member thing thing-list :allow-other-keys t rest) (if need (error "Thing not found")))) @end example @noindent This function takes a @code{:need} keyword argument, but also accepts other keyword arguments which are passed on to the @code{cl-member} function. @code{allow-other-keys} is used to keep both @code{find-thing} and @code{cl-member} from complaining about each others' keywords in the arguments. The fifth section of the argument list consists of @dfn{auxiliary variables}. These are not really arguments at all, but simply variables which are bound to @code{nil} or to the specified @var{initforms} during execution of the function. There is no difference between the following two functions, except for a matter of stylistic taste: @example (cl-defun foo (a b &aux (c (+ a b)) d) @var{body}) (cl-defun foo (a b) (let ((c (+ a b)) d) @var{body})) @end example @cindex destructuring, in argument list Argument lists support @dfn{destructuring}. In Common Lisp, destructuring is only allowed with @code{defmacro}; this package allows it with @code{cl-defun} and other argument lists as well. In destructuring, any argument variable (@var{var} in the above example) can be replaced by a list of variables, or more generally, a recursive argument list. The corresponding argument value must be a list whose elements match this recursive argument list. For example: @example (cl-defmacro dolist ((var listform &optional resultform) &rest body) @dots{}) @end example This says that the first argument of @code{dolist} must be a list of two or three items; if there are other arguments as well as this list, they are stored in @code{body}. All features allowed in regular argument lists are allowed in these recursive argument lists. In addition, the clause @samp{&whole @var{var}} is allowed at the front of a recursive argument list. It binds @var{var} to the whole list being matched; thus @code{(&whole all a b)} matches a list of two things, with @code{a} bound to the first thing, @code{b} bound to the second thing, and @code{all} bound to the list itself. (Common Lisp allows @code{&whole} in top-level @code{defmacro} argument lists as well, but Emacs Lisp does not support this usage.) One last feature of destructuring is that the argument list may be dotted, so that the argument list @code{(a b . c)} is functionally equivalent to @code{(a b &rest c)}. If the optimization quality @code{safety} is set to 0 (@pxref{Declarations}), error checking for wrong number of arguments and invalid keyword arguments is disabled. By default, argument lists are rigorously checked. @node Time of Evaluation @section Time of Evaluation @noindent Normally, the byte-compiler does not actually execute the forms in a file it compiles. For example, if a file contains @code{(setq foo t)}, the act of compiling it will not actually set @code{foo} to @code{t}. This is true even if the @code{setq} was a top-level form (i.e., not enclosed in a @code{defun} or other form). Sometimes, though, you would like to have certain top-level forms evaluated at compile-time. For example, the compiler effectively evaluates @code{defmacro} forms at compile-time so that later parts of the file can refer to the macros that are defined. @defmac cl-eval-when (situations@dots{}) forms@dots{} This form controls when the body @var{forms} are evaluated. The @var{situations} list may contain any set of the symbols @code{compile}, @code{load}, and @code{eval} (or their long-winded ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel}, and @code{:execute}). The @code{cl-eval-when} form is handled differently depending on whether or not it is being compiled as a top-level form. Specifically, it gets special treatment if it is being compiled by a command such as @code{byte-compile-file} which compiles files or buffers of code, and it appears either literally at the top level of the file or inside a top-level @code{progn}. For compiled top-level @code{cl-eval-when}s, the body @var{forms} are executed at compile-time if @code{compile} is in the @var{situations} list, and the @var{forms} are written out to the file (to be executed at load-time) if @code{load} is in the @var{situations} list. For non-compiled-top-level forms, only the @code{eval} situation is relevant. (This includes forms executed by the interpreter, forms compiled with @code{byte-compile} rather than @code{byte-compile-file}, and non-top-level forms.) The @code{cl-eval-when} acts like a @code{progn} if @code{eval} is specified, and like @code{nil} (ignoring the body @var{forms}) if not. The rules become more subtle when @code{cl-eval-when}s are nested; consult Steele (second edition) for the gruesome details (and some gruesome examples). Some simple examples: @example ;; Top-level forms in foo.el: (cl-eval-when (compile) (setq foo1 'bar)) (cl-eval-when (load) (setq foo2 'bar)) (cl-eval-when (compile load) (setq foo3 'bar)) (cl-eval-when (eval) (setq foo4 'bar)) (cl-eval-when (eval compile) (setq foo5 'bar)) (cl-eval-when (eval load) (setq foo6 'bar)) (cl-eval-when (eval compile load) (setq foo7 'bar)) @end example When @file{foo.el} is compiled, these variables will be set during the compilation itself: @example foo1 foo3 foo5 foo7 ; 'compile' @end example When @file{foo.elc} is loaded, these variables will be set: @example foo2 foo3 foo6 foo7 ; 'load' @end example And if @file{foo.el} is loaded uncompiled, these variables will be set: @example foo4 foo5 foo6 foo7 ; 'eval' @end example If these seven @code{cl-eval-when}s had been, say, inside a @code{defun}, then the first three would have been equivalent to @code{nil} and the last four would have been equivalent to the corresponding @code{setq}s. Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent to @code{(progn @dots{})} in all contexts. The compiler treats certain top-level forms, like @code{defmacro} (sort-of) and @code{require}, as if they were wrapped in @code{(cl-eval-when (compile load eval) @dots{})}. @end defmac Emacs includes two special forms related to @code{cl-eval-when}. @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}. One of these, @code{eval-when-compile}, is not quite equivalent to any @code{cl-eval-when} construct and is described below. The other form, @code{(eval-and-compile @dots{})}, is exactly equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}. @defmac eval-when-compile forms@dots{} The @var{forms} are evaluated at compile-time; at execution time, this form acts like a quoted constant of the resulting value. Used at top-level, @code{eval-when-compile} is just like @samp{eval-when (compile eval)}. In other contexts, @code{eval-when-compile} allows code to be evaluated once at compile-time for efficiency or other reasons. This form is similar to the @samp{#.} syntax of true Common Lisp. @end defmac @defmac cl-load-time-value form The @var{form} is evaluated at load-time; at execution time, this form acts like a quoted constant of the resulting value. Early Common Lisp had a @samp{#,} syntax that was similar to this, but ANSI Common Lisp replaced it with @code{load-time-value} and gave it more well-defined semantics. In a compiled file, @code{cl-load-time-value} arranges for @var{form} to be evaluated when the @file{.elc} file is loaded and then used as if it were a quoted constant. In code compiled by @code{byte-compile} rather than @code{byte-compile-file}, the effect is identical to @code{eval-when-compile}. In uncompiled code, both @code{eval-when-compile} and @code{cl-load-time-value} act exactly like @code{progn}. @example (defun report () (insert "This function was executed on: " (current-time-string) ", compiled on: " (eval-when-compile (current-time-string)) ;; or '#.(current-time-string) in real Common Lisp ", and loaded on: " (cl-load-time-value (current-time-string)))) @end example @noindent Byte-compiled, the above defun will result in the following code (or its compiled equivalent, of course) in the @file{.elc} file: @example (setq --temp-- (current-time-string)) (defun report () (insert "This function was executed on: " (current-time-string) ", compiled on: " '"Wed Oct 31 16:32:28 2012" ", and loaded on: " --temp--)) @end example @end defmac @node Predicates @chapter Predicates @noindent This section describes functions for testing whether various facts are true or false. @menu * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}. * Equality Predicates:: @code{cl-equalp}. @end menu @node Type Predicates @section Type Predicates @defun cl-typep object type Check if @var{object} is of type @var{type}, where @var{type} is a (quoted) type name of the sort used by Common Lisp. For example, @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}. @end defun The @var{type} argument to the above function is either a symbol or a list beginning with a symbol. @itemize @bullet @item If the type name is a symbol, Emacs appends @samp{-p} to the symbol name to form the name of a predicate function for testing the type. (Built-in predicates whose names end in @samp{p} rather than @samp{-p} are used when appropriate.) @item The type symbol @code{t} stands for the union of all types. @code{(cl-typep @var{object} t)} is always true. Likewise, the type symbol @code{nil} stands for nothing at all, and @code{(cl-typep @var{object} nil)} is always false. @item The type symbol @code{null} represents the symbol @code{nil}. Thus @code{(cl-typep @var{object} 'null)} is equivalent to @code{(null @var{object})}. @item The type symbol @code{atom} represents all objects that are not cons cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to @code{(atom @var{object})}. @item The type symbol @code{real} is a synonym for @code{number}, and @code{fixnum} is a synonym for @code{integer}. @item The type symbols @code{character} and @code{string-char} match integers in the range from 0 to 255. @item The type list @code{(integer @var{low} @var{high})} represents all integers between @var{low} and @var{high}, inclusive. Either bound may be a list of a single integer to specify an exclusive limit, or a @code{*} to specify no limit. The type @code{(integer * *)} is thus equivalent to @code{integer}. @item Likewise, lists beginning with @code{float}, @code{real}, or @code{number} represent numbers of that type falling in a particular range. @item Lists beginning with @code{and}, @code{or}, and @code{not} form combinations of types. For example, @code{(or integer (float 0 *))} represents all objects that are integers or non-negative floats. @item Lists beginning with @code{member} or @code{cl-member} represent objects @code{eql} to any of the following values. For example, @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)}, and @code{(member nil)} is equivalent to @code{null}. @item Lists of the form @code{(satisfies @var{predicate})} represent all objects for which @var{predicate} returns true when called with that object as an argument. @end itemize The following function and macro (not technically predicates) are related to @code{cl-typep}. @defun cl-coerce object type This function attempts to convert @var{object} to the specified @var{type}. If @var{object} is already of that type as determined by @code{cl-typep}, it is simply returned. Otherwise, certain types of conversions will be made: If @var{type} is any sequence type (@code{string}, @code{list}, etc.)@: then @var{object} will be converted to that type if possible. If @var{type} is @code{character}, then strings of length one and symbols with one-character names can be coerced. If @var{type} is @code{float}, then integers can be coerced in versions of Emacs that support floats. In all other circumstances, @code{cl-coerce} signals an error. @end defun @defmac cl-deftype name arglist forms@dots{} This macro defines a new type called @var{name}. It is similar to @code{defmacro} in many ways; when @var{name} is encountered as a type name, the body @var{forms} are evaluated and should return a type specifier that is equivalent to the type. The @var{arglist} is a Common Lisp argument list of the sort accepted by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})} is expanded by calling the expander with those arguments; the type symbol @samp{@var{name}} is expanded by calling the expander with no arguments. The @var{arglist} is processed the same as for @code{cl-defmacro} except that optional arguments without explicit defaults use @code{*} instead of @code{nil} as the ``default'' default. Some examples: @example (cl-deftype null () '(satisfies null)) ; predefined (cl-deftype list () '(or null cons)) ; predefined (cl-deftype unsigned-byte (&optional bits) (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits))))) (unsigned-byte 8) @equiv{} (integer 0 255) (unsigned-byte) @equiv{} (integer 0 *) unsigned-byte @equiv{} (integer 0 *) @end example @noindent The last example shows how the Common Lisp @code{unsigned-byte} type specifier could be implemented if desired; this package does not implement @code{unsigned-byte} by default. @end defmac The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type} (@pxref{Assertions}) macros also use type names. The @code{cl-map}, @code{cl-concatenate}, and @code{cl-merge} functions take type-name arguments to specify the type of sequence to return. @xref{Sequences}. @node Equality Predicates @section Equality Predicates @noindent This package defines the Common Lisp predicate @code{cl-equalp}. @defun cl-equalp a b This function is a more flexible version of @code{equal}. In particular, it compares strings case-insensitively, and it compares numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is true). Vectors and conses are compared recursively. All other objects are compared as if by @code{equal}. This function differs from Common Lisp @code{equalp} in several respects. First, Common Lisp's @code{equalp} also compares @emph{characters} case-insensitively, which would be impractical in this package since Emacs does not distinguish between integers and characters. In keeping with the idea that strings are less vector-like in Emacs Lisp, this package's @code{cl-equalp} also will not compare strings against vectors of integers. @end defun Also note that the Common Lisp functions @code{member} and @code{assoc} use @code{eql} to compare elements, whereas Emacs Lisp follows the MacLisp tradition and uses @code{equal} for these two functions. The functions @code{cl-member} and @code{cl-assoc} use @code{eql}, as in Common Lisp. The standard Emacs Lisp functions @code{memq} and @code{assq} use @code{eq}, and the standard @code{memql} uses @code{eql}. @node Control Structure @chapter Control Structure @noindent The features described in the following sections implement various advanced control structures, including extensions to the standard @code{setf} facility, and a number of looping and conditional constructs. @menu * Assignment:: The @code{cl-psetq} form. * Generalized Variables:: Extensions to generalized variables. * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}. * Conditionals:: @code{cl-case}, @code{cl-typecase}. * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}. * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}. * Loop Facility:: The Common Lisp @code{loop} macro. * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc. @end menu @node Assignment @section Assignment @noindent The @code{cl-psetq} form is just like @code{setq}, except that multiple assignments are done in parallel rather than sequentially. @defmac cl-psetq [symbol form]@dots{} This special form (actually a macro) is used to assign to several variables simultaneously. Given only one @var{symbol} and @var{form}, it has the same effect as @code{setq}. Given several @var{symbol} and @var{form} pairs, it evaluates all the @var{form}s in advance and then stores the corresponding variables afterwards. @example (setq x 2 y 3) (setq x (+ x y) y (* x y)) x @result{} 5 y ; @r{@code{y} was computed after @code{x} was set.} @result{} 15 (setq x 2 y 3) (cl-psetq x (+ x y) y (* x y)) x @result{} 5 y ; @r{@code{y} was computed before @code{x} was set.} @result{} 6 @end example The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which exchanges the values of two variables. (The @code{cl-rotatef} form provides an even more convenient way to swap two variables; @pxref{Modify Macros}.) @code{cl-psetq} always returns @code{nil}. @end defmac @node Generalized Variables @section Generalized Variables @cindex generalized variable A @dfn{generalized variable} or @dfn{place form} is one of the many places in Lisp memory where values can be stored. The simplest place form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists, elements of arrays, properties of symbols, and many other locations are also places where Lisp values are stored. For basic information, @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}. This package provides several additional features related to generalized variables. @menu * Setf Extensions:: Additional @code{setf} places. * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc. @end menu @node Setf Extensions @subsection Setf Extensions Several standard (e.g., @code{car}) and Emacs-specific (e.g., @code{window-point}) Lisp functions are @code{setf}-able by default. This package defines @code{setf} handlers for several additional functions: @itemize @item Functions from this package: @example cl-rest cl-subseq cl-get cl-getf cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth @end example @noindent Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument of the function must itself be a valid @var{place} form. @item General Emacs Lisp functions: @example buffer-file-name getenv buffer-modified-p global-key-binding buffer-name local-key-binding buffer-string mark buffer-substring mark-marker current-buffer marker-position current-case-table mouse-position current-column point current-global-map point-marker current-input-mode point-max current-local-map point-min current-window-configuration read-mouse-position default-file-modes screen-height documentation-property screen-width face-background selected-window face-background-pixmap selected-screen face-font selected-frame face-foreground standard-case-table face-underline-p syntax-table file-modes visited-file-modtime frame-height window-height frame-parameters window-width frame-visible-p x-get-secondary-selection frame-width x-get-selection get-register @end example Most of these have directly corresponding ``set'' functions, like @code{use-local-map} for @code{current-local-map}, or @code{goto-char} for @code{point}. A few, like @code{point-min}, expand to longer sequences of code when they are used with @code{setf} (@code{(narrow-to-region x (point-max))} in this case). @item A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])}, where @var{subplace} is itself a valid generalized variable whose current value is a string, and where the value stored is also a string. The new string is spliced into the specified part of the destination string. For example: @example (setq a (list "hello" "world")) @result{} ("hello" "world") (cadr a) @result{} "world" (substring (cadr a) 2 4) @result{} "rl" (setf (substring (cadr a) 2 4) "o") @result{} "o" (cadr a) @result{} "wood" a @result{} ("hello" "wood") @end example The generalized variable @code{buffer-substring}, listed above, also works in this way by replacing a portion of the current buffer. @c FIXME? Also 'eq'? (see cl-lib.el) @c Currently commented out in cl.el. @ignore @item A call of the form @code{(apply '@var{func} @dots{})} or @code{(apply (function @var{func}) @dots{})}, where @var{func} is a @code{setf}-able function whose store function is ``suitable'' in the sense described in Steele's book; since none of the standard Emacs place functions are suitable in this sense, this feature is only interesting when used with places you define yourself with @code{define-setf-method} or the long form of @code{defsetf}. @xref{Obsolete Setf Customization}. @end ignore @c FIXME? Is this still true? @item A macro call, in which case the macro is expanded and @code{setf} is applied to the resulting form. @end itemize @c FIXME should this be in lispref? It seems self-evident. @c Contrast with the cl-incf example later on. @c Here it really only serves as a contrast to wrong-order. The @code{setf} macro takes care to evaluate all subforms in the proper left-to-right order; for example, @example (setf (aref vec (cl-incf i)) i) @end example @noindent looks like it will evaluate @code{(cl-incf i)} exactly once, before the following access to @code{i}; the @code{setf} expander will insert temporary variables as necessary to ensure that it does in fact work this way no matter what setf-method is defined for @code{aref}. (In this case, @code{aset} would be used and no such steps would be necessary since @code{aset} takes its arguments in a convenient order.) However, if the @var{place} form is a macro which explicitly evaluates its arguments in an unusual order, this unusual order will be preserved. Adapting an example from Steele, given @example (defmacro wrong-order (x y) (list 'aref y x)) @end example @noindent the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will evaluate @var{b} first, then @var{a}, just as in an actual call to @code{wrong-order}. @node Modify Macros @subsection Modify Macros @noindent This package defines a number of macros that operate on generalized variables. Many are interesting and useful even when the @var{place} is just a variable name. @defmac cl-psetf [place form]@dots{} This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}: When several @var{place}s and @var{form}s are involved, the assignments take place in parallel rather than sequentially. Specifically, all subforms are evaluated from left to right, then all the assignments are done (in an undefined order). @end defmac @defmac cl-incf place &optional x This macro increments the number stored in @var{place} by one, or by @var{x} if specified. The incremented value is returned. For example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}. As with @code{setf}, care is taken to preserve the ``apparent'' order of evaluation. For example, @example (cl-incf (aref vec (cl-incf i))) @end example @noindent appears to increment @code{i} once, then increment the element of @code{vec} addressed by @code{i}; this is indeed exactly what it does, which means the above form is @emph{not} equivalent to the ``obvious'' expansion, @example (setf (aref vec (cl-incf i)) (1+ (aref vec (cl-incf i)))) ; wrong! @end example @noindent but rather to something more like @example (let ((temp (cl-incf i))) (setf (aref vec temp) (1+ (aref vec temp)))) @end example @noindent Again, all of this is taken care of automatically by @code{cl-incf} and the other generalized-variable macros. As a more Emacs-specific example of @code{cl-incf}, the expression @code{(cl-incf (point) @var{n})} is essentially equivalent to @code{(forward-char @var{n})}. @end defmac @defmac cl-decf place &optional x This macro decrements the number stored in @var{place} by one, or by @var{x} if specified. @end defmac @defmac cl-pushnew x place @t{&key :test :test-not :key} This macro inserts @var{x} at the front of the list stored in @var{place}, but only if @var{x} was not @code{eql} to any existing element of the list. The optional keyword arguments are interpreted in the same way as for @code{cl-adjoin}. @xref{Lists as Sets}. @end defmac @defmac cl-shiftf place@dots{} newvalue This macro shifts the @var{place}s left by one, shifting in the value of @var{newvalue} (which may be any Lisp expression, not just a generalized variable), and returning the value shifted out of the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c} @var{d})} is equivalent to @example (prog1 @var{a} (cl-psetf @var{a} @var{b} @var{b} @var{c} @var{c} @var{d})) @end example @noindent except that the subforms of @var{a}, @var{b}, and @var{c} are actually evaluated only once each and in the apparent order. @end defmac @defmac cl-rotatef place@dots{} This macro rotates the @var{place}s left by one in circular fashion. Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to @example (cl-psetf @var{a} @var{b} @var{b} @var{c} @var{c} @var{d} @var{d} @var{a}) @end example @noindent except for the evaluation of subforms. @code{cl-rotatef} always returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})} conveniently exchanges @var{a} and @var{b}. @end defmac The following macros were invented for this package; they have no analogues in Common Lisp. @defmac cl-letf (bindings@dots{}) forms@dots{} This macro is analogous to @code{let}, but for generalized variables rather than just symbols. Each @var{binding} should be of the form @code{(@var{place} @var{value})}; the original contents of the @var{place}s are saved, the @var{value}s are stored in them, and then the body @var{form}s are executed. Afterwards, the @var{places} are set back to their original saved contents. This cleanup happens even if the @var{form}s exit irregularly due to a @code{throw} or an error. For example, @example (cl-letf (((point) (point-min)) (a 17)) @dots{}) @end example @noindent moves point in the current buffer to the beginning of the buffer, and also binds @code{a} to 17 (as if by a normal @code{let}, since @code{a} is just a regular variable). After the body exits, @code{a} is set back to its original value and point is moved back to its original position. Note that @code{cl-letf} on @code{(point)} is not quite like a @code{save-excursion}, as the latter effectively saves a marker which tracks insertions and deletions in the buffer. Actually, a @code{cl-letf} of @code{(point-marker)} is much closer to this behavior. (@code{point} and @code{point-marker} are equivalent as @code{setf} places; each will accept either an integer or a marker as the stored value.) Like in the case of @code{let}, the @var{value} forms are evaluated in the order they appear, but the order of bindings is unspecified. Therefore, avoid binding the same @var{place} more than once in a single @code{cl-letf} form. Since generalized variables look like lists, @code{let}'s shorthand of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would be ambiguous in @code{cl-letf} and is not allowed. However, a @var{binding} specifier may be a one-element list @samp{(@var{place})}, which is similar to @samp{(@var{place} @var{place})}. In other words, the @var{place} is not disturbed on entry to the body, and the only effect of the @code{cl-letf} is to restore the original value of @var{place} afterwards. @c I suspect this may no longer be true; either way it's @c implementation detail and so not essential to document. @ignore (The redundant access-and-store suggested by the @code{(@var{place} @var{place})} example does not actually occur.) @end ignore Note that in this case, and in fact almost every case, @var{place} must have a well-defined value outside the @code{cl-letf} body. There is essentially only one exception to this, which is @var{place} a plain variable with a specified @var{value} (such as @code{(a 17)} in the above example). @c See http://debbugs.gnu.org/12758 @c Some or all of this was true for cl.el, but not for cl-lib.el. @ignore The only exceptions are plain variables and calls to @code{symbol-value} and @code{symbol-function}. If the symbol is not bound on entry, it is simply made unbound by @code{makunbound} or @code{fmakunbound} on exit. @end ignore @end defmac @defmac cl-letf* (bindings@dots{}) forms@dots{} This macro is to @code{cl-letf} what @code{let*} is to @code{let}: It does the bindings in sequential rather than parallel order. @end defmac @defmac cl-callf @var{function} @var{place} @var{args}@dots{} This is the ``generic'' modify macro. It calls @var{function}, which should be an unquoted function name, macro name, or lambda. It passes @var{place} and @var{args} as arguments, and assigns the result back to @var{place}. For example, @code{(cl-incf @var{place} @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}. Some more examples: @example (cl-callf abs my-number) (cl-callf concat (buffer-name) "<" (number-to-string n) ">") (cl-callf cl-union happy-people (list joe bob) :test 'same-person) @end example Note again that @code{cl-callf} is an extension to standard Common Lisp. @end defmac @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{} This macro is like @code{cl-callf}, except that @var{place} is the @emph{second} argument of @var{function} rather than the first. For example, @code{(push @var{x} @var{place})} is equivalent to @code{(cl-callf2 cons @var{x} @var{place})}. @end defmac The @code{cl-callf} and @code{cl-callf2} macros serve as building blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}. The @code{cl-letf} and @code{cl-letf*} macros are used in the processing of symbol macros; @pxref{Macro Bindings}. @node Variable Bindings @section Variable Bindings @cindex variable binding @noindent These Lisp forms make bindings to variables and function names, analogous to Lisp's built-in @code{let} form. @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which are also related to variable bindings. @menu * Dynamic Bindings:: The @code{cl-progv} form. * Function Bindings:: @code{cl-flet} and @code{cl-labels}. * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}. @end menu @node Dynamic Bindings @subsection Dynamic Bindings @cindex dynamic binding @noindent The standard @code{let} form binds variables whose names are known at compile-time. The @code{cl-progv} form provides an easy way to bind variables whose names are computed at run-time. @defmac cl-progv symbols values forms@dots{} This form establishes @code{let}-style variable bindings on a set of variables computed at run-time. The expressions @var{symbols} and @var{values} are evaluated, and must return lists of symbols and values, respectively. The symbols are bound to the corresponding values for the duration of the body @var{form}s. If @var{values} is shorter than @var{symbols}, the last few symbols are bound to @code{nil}. If @var{symbols} is shorter than @var{values}, the excess values are ignored. @end defmac @node Function Bindings @subsection Function Bindings @cindex function binding @noindent These forms make @code{let}-like bindings to functions instead of variables. @defmac cl-flet (bindings@dots{}) forms@dots{} This form establishes @code{let}-style bindings on the function cells of symbols rather than on the value cells. Each @var{binding} must be a list of the form @samp{(@var{name} @var{arglist} @var{forms}@dots{})}, which defines a function exactly as if it were a @code{cl-defun} form. The function @var{name} is defined accordingly but only within the body of the @code{cl-flet}, hiding any external definition if applicable. The bindings are lexical in scope. This means that all references to the named functions must appear physically within the body of the @code{cl-flet} form. Functions defined by @code{cl-flet} may use the full Common Lisp argument notation supported by @code{cl-defun}; also, the function body is enclosed in an implicit block as if by @code{cl-defun}. @xref{Program Structure}. Note that the @file{cl.el} version of this macro behaves slightly differently. In particular, its binding is dynamic rather than lexical. @xref{Obsolete Macros}. @end defmac @defmac cl-labels (bindings@dots{}) forms@dots{} The @code{cl-labels} form is like @code{cl-flet}, except that the function bindings can be recursive. The scoping is lexical, but you can only capture functions in closures if @code{lexical-binding} is @code{t}. @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}. Lexical scoping means that all references to the named functions must appear physically within the body of the @code{cl-labels} form. References may appear both in the body @var{forms} of @code{cl-labels} itself, and in the bodies of the functions themselves. Thus, @code{cl-labels} can define local recursive functions, or mutually-recursive sets of functions. A ``reference'' to a function name is either a call to that function, or a use of its name quoted by @code{quote} or @code{function} to be passed on to, say, @code{mapcar}. Note that the @file{cl.el} version of this macro behaves slightly differently. @xref{Obsolete Macros}. @end defmac @node Macro Bindings @subsection Macro Bindings @cindex macro binding @noindent These forms create local macros and ``symbol macros''. @defmac cl-macrolet (bindings@dots{}) forms@dots{} This form is analogous to @code{cl-flet}, but for macros instead of functions. Each @var{binding} is a list of the same form as the arguments to @code{cl-defmacro} (i.e., a macro name, argument list, and macro-expander forms). The macro is defined accordingly for use within the body of the @code{cl-macrolet}. Because of the nature of macros, @code{cl-macrolet} is always lexically scoped. The @code{cl-macrolet} binding will affect only calls that appear physically within the body @var{forms}, possibly after expansion of other macros in the body. @end defmac @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{} This form creates @dfn{symbol macros}, which are macros that look like variable references rather than function calls. Each @var{binding} is a list @samp{(@var{var} @var{expansion})}; any reference to @var{var} within the body @var{forms} is replaced by @var{expansion}. @example (setq bar '(5 . 9)) (cl-symbol-macrolet ((foo (car bar))) (cl-incf foo)) bar @result{} (6 . 9) @end example A @code{setq} of a symbol macro is treated the same as a @code{setf}. I.e., @code{(setq foo 4)} in the above would be equivalent to @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}. Likewise, a @code{let} or @code{let*} binding a symbol macro is treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true Common Lisp, where the rules of lexical scoping cause a @code{let} binding to shadow a @code{symbol-macrolet} binding. In this package, such shadowing does not occur, even when @code{lexical-binding} is @c See http://debbugs.gnu.org/12119 @code{t}. (This behavior predates the addition of lexical binding to Emacs Lisp, and may change in future to respect @code{lexical-binding}.) At present in this package, only @code{lexical-let} and @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete Lexical Binding}. There is no analogue of @code{defmacro} for symbol macros; all symbol macros are local. A typical use of @code{cl-symbol-macrolet} is in the expansion of another macro: @example (cl-defmacro my-dolist ((x list) &rest body) (let ((var (cl-gensym))) (list 'cl-loop 'for var 'on list 'do (cl-list* 'cl-symbol-macrolet (list (list x (list 'car var))) body)))) (setq mylist '(1 2 3 4)) (my-dolist (x mylist) (cl-incf x)) mylist @result{} (2 3 4 5) @end example @noindent In this example, the @code{my-dolist} macro is similar to @code{dolist} (@pxref{Iteration}) except that the variable @code{x} becomes a true reference onto the elements of the list. The @code{my-dolist} call shown here expands to @example (cl-loop for G1234 on mylist do (cl-symbol-macrolet ((x (car G1234))) (cl-incf x))) @end example @noindent which in turn expands to @example (cl-loop for G1234 on mylist do (cl-incf (car G1234))) @end example @xref{Loop Facility}, for a description of the @code{cl-loop} macro. This package defines a nonstandard @code{in-ref} loop clause that works much like @code{my-dolist}. @end defmac @node Conditionals @section Conditionals @cindex conditionals @noindent These conditional forms augment Emacs Lisp's simple @code{if}, @code{and}, @code{or}, and @code{cond} forms. @defmac cl-case keyform clause@dots{} This macro evaluates @var{keyform}, then compares it with the key values listed in the various @var{clause}s. Whichever clause matches the key is executed; comparison is done by @code{eql}. If no clause matches, the @code{cl-case} form returns @code{nil}. The clauses are of the form @example (@var{keylist} @var{body-forms}@dots{}) @end example @noindent where @var{keylist} is a list of key values. If there is exactly one value, and it is not a cons cell or the symbol @code{nil} or @code{t}, then it can be used by itself as a @var{keylist} without being enclosed in a list. All key values in the @code{cl-case} form must be distinct. The final clauses may use @code{t} in place of a @var{keylist} to indicate a default clause that should be taken if none of the other clauses match. (The symbol @code{otherwise} is also recognized in place of @code{t}. To make a clause that matches the actual symbol @code{t}, @code{nil}, or @code{otherwise}, enclose the symbol in a list.) For example, this expression reads a keystroke, then does one of four things depending on whether it is an @samp{a}, a @samp{b}, a @key{RET} or @kbd{C-j}, or anything else. @example (cl-case (read-char) (?a (do-a-thing)) (?b (do-b-thing)) ((?\r ?\n) (do-ret-thing)) (t (do-other-thing))) @end example @end defmac @defmac cl-ecase keyform clause@dots{} This macro is just like @code{cl-case}, except that if the key does not match any of the clauses, an error is signaled rather than simply returning @code{nil}. @end defmac @defmac cl-typecase keyform clause@dots{} This macro is a version of @code{cl-case} that checks for types rather than values. Each @var{clause} is of the form @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates}, for a description of type specifiers. For example, @example (cl-typecase x (integer (munch-integer x)) (float (munch-float x)) (string (munch-integer (string-to-number x))) (t (munch-anything x))) @end example The type specifier @code{t} matches any type of object; the word @code{otherwise} is also allowed. To make one clause match any of several types, use an @code{(or @dots{})} type specifier. @end defmac @defmac cl-etypecase keyform clause@dots{} This macro is just like @code{cl-typecase}, except that if the key does not match any of the clauses, an error is signaled rather than simply returning @code{nil}. @end defmac @node Blocks and Exits @section Blocks and Exits @cindex block @cindex exit @noindent Common Lisp @dfn{blocks} provide a non-local exit mechanism very similar to @code{catch} and @code{throw}, with lexical scoping. This package actually implements @code{cl-block} in terms of @code{catch}; however, the lexical scoping allows the byte-compiler to omit the costly @code{catch} step if the body of the block does not actually @code{cl-return-from} the block. @defmac cl-block name forms@dots{} The @var{forms} are evaluated as if by a @code{progn}. However, if any of the @var{forms} execute @code{(cl-return-from @var{name})}, they will jump out and return directly from the @code{cl-block} form. The @code{cl-block} returns the result of the last @var{form} unless a @code{cl-return-from} occurs. The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to the @code{catch}/@code{throw} mechanism. The main differences are that block @var{name}s are unevaluated symbols, rather than forms (such as quoted symbols) that evaluate to a tag at run-time; and also that blocks are always lexically scoped. In a dynamically scoped @code{catch}, functions called from the @code{catch} body can also @code{throw} to the @code{catch}. This is not an option for @code{cl-block}, where the @code{cl-return-from} referring to a block name must appear physically within the @var{forms} that make up the body of the block. They may not appear within other called functions, although they may appear within macro expansions or @code{lambda}s in the body. Block names and @code{catch} names form independent name-spaces. In true Common Lisp, @code{defun} and @code{defmacro} surround the function or expander bodies with implicit blocks with the same name as the function or macro. This does not occur in Emacs Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro} forms, which do create the implicit block. The Common Lisp looping constructs defined by this package, such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks just as in Common Lisp. Because they are implemented in terms of Emacs Lisp's @code{catch} and @code{throw}, blocks have the same overhead as actual @code{catch} constructs (roughly two function calls). However, the byte compiler will optimize away the @code{catch} if the block does not in fact contain any @code{cl-return} or @code{cl-return-from} calls that jump to it. This means that @code{cl-do} loops and @code{cl-defun} functions that don't use @code{cl-return} don't pay the overhead to support it. @end defmac @defmac cl-return-from name [result] This macro returns from the block named @var{name}, which must be an (unevaluated) symbol. If a @var{result} form is specified, it is evaluated to produce the result returned from the @code{block}. Otherwise, @code{nil} is returned. @end defmac @defmac cl-return [result] This macro is exactly like @code{(cl-return-from nil @var{result})}. Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose themselves in @code{nil} blocks. @end defmac @c FIXME? Maybe this should be in a separate section? @defmac cl-tagbody &rest labels-or-statements This macro executes statements while allowing for control transfer to user-defined labels. Each element of @var{labels-or-statements} can be either a label (an integer or a symbol), or a cons-cell (a statement). This distinction is made before macroexpansion. Statements are executed in sequence, discarding any return value. Any statement can transfer control at any time to the statements that follow one of the labels with the special form @code{(go @var{label})}. Labels have lexical scope and dynamic extent. @end defmac @node Iteration @section Iteration @cindex iteration @noindent The macros described here provide more sophisticated, high-level looping constructs to complement Emacs Lisp's basic loop forms (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}). @defmac cl-loop forms@dots{} This package supports both the simple, old-style meaning of @code{loop} and the extremely powerful and flexible feature known as the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced facility is discussed in the following section; @pxref{Loop Facility}. The simple form of @code{loop} is described here. If @code{cl-loop} is followed by zero or more Lisp expressions, then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite loop executing the expressions over and over. The loop is enclosed in an implicit @code{nil} block. Thus, @example (cl-loop (foo) (if (no-more) (return 72)) (bar)) @end example @noindent is exactly equivalent to @example (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar))) @end example If any of the expressions are plain symbols, the loop is instead interpreted as a Loop Macro specification as described later. (This is not a restriction in practice, since a plain symbol in the above notation would simply access and throw away the value of a variable.) @end defmac @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{} This macro creates a general iterative loop. Each @var{spec} is of the form @example (@var{var} [@var{init} [@var{step}]]) @end example The loop works as follows: First, each @var{var} is bound to the associated @var{init} value as if by a @code{let} form. Then, in each iteration of the loop, the @var{end-test} is evaluated; if true, the loop is finished. Otherwise, the body @var{forms} are evaluated, then each @var{var} is set to the associated @var{step} expression (as if by a @code{cl-psetq} form) and the next iteration begins. Once the @var{end-test} becomes true, the @var{result} forms are evaluated (with the @var{var}s still bound to their values) to produce the result returned by @code{cl-do}. The entire @code{cl-do} loop is enclosed in an implicit @code{nil} block, so that you can use @code{(cl-return)} to break out of the loop at any time. If there are no @var{result} forms, the loop returns @code{nil}. If a given @var{var} has no @var{step} form, it is bound to its @var{init} value but not otherwise modified during the @code{cl-do} loop (unless the code explicitly modifies it); this case is just a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})} around the loop. If @var{init} is also omitted it defaults to @code{nil}, and in this case a plain @samp{@var{var}} can be used in place of @samp{(@var{var})}, again following the analogy with @code{let}. This example (from Steele) illustrates a loop that applies the function @code{f} to successive pairs of values from the lists @code{foo} and @code{bar}; it is equivalent to the call @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body @var{forms} at all, performing all its work as side effects of the rest of the loop. @example (cl-do ((x foo (cdr x)) (y bar (cdr y)) (z nil (cons (f (car x) (car y)) z))) ((or (null x) (null y)) (nreverse z))) @end example @end defmac @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{} This is to @code{cl-do} what @code{let*} is to @code{let}. In particular, the initial values are bound as if by @code{let*} rather than @code{let}, and the steps are assigned as if by @code{setq} rather than @code{cl-psetq}. Here is another way to write the above loop: @example (cl-do* ((xp foo (cdr xp)) (yp bar (cdr yp)) (x (car xp) (car xp)) (y (car yp) (car yp)) z) ((or (null xp) (null yp)) (nreverse z)) (push (f x y) z)) @end example @end defmac @defmac cl-dolist (var list [result]) forms@dots{} This is exactly like the standard Emacs Lisp macro @code{dolist}, but surrounds the loop with an implicit @code{nil} block. @end defmac @defmac cl-dotimes (var count [result]) forms@dots{} This is exactly like the standard Emacs Lisp macro @code{dotimes}, but surrounds the loop with an implicit @code{nil} block. The body is executed with @var{var} bound to the integers from zero (inclusive) to @var{count} (exclusive), in turn. Then @c FIXME lispref does not state this part explicitly, could move this there. the @code{result} form is evaluated with @var{var} bound to the total number of iterations that were done (i.e., @code{(max 0 @var{count})}) to get the return value for the loop form. @end defmac @defmac cl-do-symbols (var [obarray [result]]) forms@dots{} This loop iterates over all interned symbols. If @var{obarray} is specified and is not @code{nil}, it loops over all symbols in that obarray. For each symbol, the body @var{forms} are evaluated with @var{var} bound to that symbol. The symbols are visited in an unspecified order. Afterward the @var{result} form, if any, is evaluated (with @var{var} bound to @code{nil}) to get the return value. The loop is surrounded by an implicit @code{nil} block. @end defmac @defmac cl-do-all-symbols (var [result]) forms@dots{} This is identical to @code{cl-do-symbols} except that the @var{obarray} argument is omitted; it always iterates over the default obarray. @end defmac @xref{Mapping over Sequences}, for some more functions for iterating over vectors or lists. @node Loop Facility @section Loop Facility @cindex loop facility @noindent A common complaint with Lisp's traditional looping constructs was that they were either too simple and limited, such as @code{dotimes} or @code{while}, or too unreadable and obscure, like Common Lisp's @code{do} loop. To remedy this, Common Lisp added a construct called the ``Loop Facility'' or ``@code{loop} macro'', with an easy-to-use but very powerful and expressive syntax. @menu * Loop Basics:: The @code{cl-loop} macro, basic clause structure. * Loop Examples:: Working examples of the @code{cl-loop} macro. * For Clauses:: Clauses introduced by @code{for} or @code{as}. * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc. * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc. * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}. @end menu @node Loop Basics @subsection Loop Basics @noindent The @code{cl-loop} macro essentially creates a mini-language within Lisp that is specially tailored for describing loops. While this language is a little strange-looking by the standards of regular Lisp, it turns out to be very easy to learn and well-suited to its purpose. Since @code{cl-loop} is a macro, all parsing of the loop language takes place at byte-compile time; compiled @code{cl-loop}s are just as efficient as the equivalent @code{while} loops written longhand. @defmac cl-loop clauses@dots{} A loop construct consists of a series of @var{clause}s, each introduced by a symbol like @code{for} or @code{do}. Clauses are simply strung together in the argument list of @code{cl-loop}, with minimal extra parentheses. The various types of clauses specify initializations, such as the binding of temporary variables, actions to be taken in the loop, stepping actions, and final cleanup. Common Lisp specifies a certain general order of clauses in a loop: @example (loop @var{name-clause} @var{var-clauses}@dots{} @var{action-clauses}@dots{}) @end example The @var{name-clause} optionally gives a name to the implicit block that surrounds the loop. By default, the implicit block is named @code{nil}. The @var{var-clauses} specify what variables should be bound during the loop, and how they should be modified or iterated throughout the course of the loop. The @var{action-clauses} are things to be done during the loop, such as computing, collecting, and returning values. The Emacs version of the @code{cl-loop} macro is less restrictive about the order of clauses, but things will behave most predictably if you put the variable-binding clauses @code{with}, @code{for}, and @code{repeat} before the action clauses. As in Common Lisp, @code{initially} and @code{finally} clauses can go anywhere. Loops generally return @code{nil} by default, but you can cause them to return a value by using an accumulation clause like @code{collect}, an end-test clause like @code{always}, or an explicit @code{return} clause to jump out of the implicit block. (Because the loop body is enclosed in an implicit block, you can also use regular Lisp @code{cl-return} or @code{cl-return-from} to break out of the loop.) @end defmac The following sections give some examples of the loop macro in action, and describe the particular loop clauses in great detail. Consult the second edition of Steele for additional discussion and examples. @node Loop Examples @subsection Loop Examples @noindent Before listing the full set of clauses that are allowed, let's look at a few example loops just to get a feel for the @code{cl-loop} language. @example (cl-loop for buf in (buffer-list) collect (buffer-file-name buf)) @end example @noindent This loop iterates over all Emacs buffers, using the list returned by @code{buffer-list}. For each buffer @var{buf}, it calls @code{buffer-file-name} and collects the results into a list, which is then returned from the @code{cl-loop} construct. The result is a list of the file names of all the buffers in Emacs's memory. The words @code{for}, @code{in}, and @code{collect} are reserved words in the @code{cl-loop} language. @example (cl-loop repeat 20 do (insert "Yowsa\n")) @end example @noindent This loop inserts the phrase ``Yowsa'' twenty times in the current buffer. @example (cl-loop until (eobp) do (munch-line) (forward-line 1)) @end example @noindent This loop calls @code{munch-line} on every line until the end of the buffer. If point is already at the end of the buffer, the loop exits immediately. @example (cl-loop do (munch-line) until (eobp) do (forward-line 1)) @end example @noindent This loop is similar to the above one, except that @code{munch-line} is always called at least once. @example (cl-loop for x from 1 to 100 for y = (* x x) until (>= y 729) finally return (list x (= y 729))) @end example @noindent This more complicated loop searches for a number @code{x} whose square is 729. For safety's sake it only examines @code{x} values up to 100; dropping the phrase @samp{to 100} would cause the loop to count upwards with no limit. The second @code{for} clause defines @code{y} to be the square of @code{x} within the loop; the expression after the @code{=} sign is reevaluated each time through the loop. The @code{until} clause gives a condition for terminating the loop, and the @code{finally} clause says what to do when the loop finishes. (This particular example was written less concisely than it could have been, just for the sake of illustration.) Note that even though this loop contains three clauses (two @code{for}s and an @code{until}) that would have been enough to define loops all by themselves, it still creates a single loop rather than some sort of triple-nested loop. You must explicitly nest your @code{cl-loop} constructs if you want nested loops. @node For Clauses @subsection For Clauses @noindent Most loops are governed by one or more @code{for} clauses. A @code{for} clause simultaneously describes variables to be bound, how those variables are to be stepped during the loop, and usually an end condition based on those variables. The word @code{as} is a synonym for the word @code{for}. This word is followed by a variable name, then a word like @code{from} or @code{across} that describes the kind of iteration desired. In Common Lisp, the phrase @code{being the} sometimes precedes the type of iteration; in this package both @code{being} and @code{the} are optional. The word @code{each} is a synonym for @code{the}, and the word that follows it may be singular or plural: @samp{for x being the elements of y} or @samp{for x being each element of y}. Which form you use is purely a matter of style. The variable is bound around the loop as if by @code{let}: @example (setq i 'happy) (cl-loop for i from 1 to 10 do (do-something-with i)) i @result{} happy @end example @table @code @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3} This type of @code{for} clause creates a counting loop. Each of the three sub-terms is optional, though there must be at least one term so that the clause is marked as a counting clause. The three expressions are the starting value, the ending value, and the step value, respectively, of the variable. The loop counts upwards by default (@var{expr3} must be positive), from @var{expr1} to @var{expr2} inclusively. If you omit the @code{from} term, the loop counts from zero; if you omit the @code{to} term, the loop counts forever without stopping (unless stopped by some other loop clause, of course); if you omit the @code{by} term, the loop counts in steps of one. You can replace the word @code{from} with @code{upfrom} or @code{downfrom} to indicate the direction of the loop. Likewise, you can replace @code{to} with @code{upto} or @code{downto}. For example, @samp{for x from 5 downto 1} executes five times with @code{x} taking on the integers from 5 down to 1 in turn. Also, you can replace @code{to} with @code{below} or @code{above}, which are like @code{upto} and @code{downto} respectively except that they are exclusive rather than inclusive limits: @example (cl-loop for x to 10 collect x) @result{} (0 1 2 3 4 5 6 7 8 9 10) (cl-loop for x below 10 collect x) @result{} (0 1 2 3 4 5 6 7 8 9) @end example The @code{by} value is always positive, even for downward-counting loops. Some sort of @code{from} value is required for downward loops; @samp{for x downto 5} is not a valid loop clause all by itself. @item for @var{var} in @var{list} by @var{function} This clause iterates @var{var} over all the elements of @var{list}, in turn. If you specify the @code{by} term, then @var{function} is used to traverse the list instead of @code{cdr}; it must be a function taking one argument. For example: @example (cl-loop for x in '(1 2 3 4 5 6) collect (* x x)) @result{} (1 4 9 16 25 36) (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x)) @result{} (1 9 25) @end example @item for @var{var} on @var{list} by @var{function} This clause iterates @var{var} over all the cons cells of @var{list}. @example (cl-loop for x on '(1 2 3 4) collect x) @result{} ((1 2 3 4) (2 3 4) (3 4) (4)) @end example With @code{by}, there is no real reason that the @code{on} expression must be a list. For example: @example (cl-loop for x on first-animal by 'next-animal collect x) @end example @noindent where @code{(next-animal x)} takes an ``animal'' @var{x} and returns the next in the (assumed) sequence of animals, or @code{nil} if @var{x} was the last animal in the sequence. @item for @var{var} in-ref @var{list} by @var{function} This is like a regular @code{in} clause, but @var{var} becomes a @code{setf}-able ``reference'' onto the elements of the list rather than just a temporary variable. For example, @example (cl-loop for x in-ref my-list do (cl-incf x)) @end example @noindent increments every element of @code{my-list} in place. This clause is an extension to standard Common Lisp. @item for @var{var} across @var{array} This clause iterates @var{var} over all the elements of @var{array}, which may be a vector or a string. @example (cl-loop for x across "aeiou" do (use-vowel (char-to-string x))) @end example @item for @var{var} across-ref @var{array} This clause iterates over an array, with @var{var} a @code{setf}-able reference onto the elements; see @code{in-ref} above. @item for @var{var} being the elements of @var{sequence} This clause iterates over the elements of @var{sequence}, which may be a list, vector, or string. Since the type must be determined at run-time, this is somewhat less efficient than @code{in} or @code{across}. The clause may be followed by the additional term @samp{using (index @var{var2})} to cause @var{var2} to be bound to the successive indices (starting at 0) of the elements. This clause type is taken from older versions of the @code{loop} macro, and is not present in modern Common Lisp. The @samp{using (sequence @dots{})} term of the older macros is not supported. @item for @var{var} being the elements of-ref @var{sequence} This clause iterates over a sequence, with @var{var} a @code{setf}-able reference onto the elements; see @code{in-ref} above. @item for @var{var} being the matches of @var{regexp} This clause iterates over the matches for @var{regexp} in the current buffer. By default, @var{var} is bound to the full match. Optionally, @var{var} might be bound to a subpart of the match. It's also possible to restrict the loop to a given number of matches. For example, @example (cl-loop for x being the matches of "^(defun \\(\\S +\\)" using '(group 1 limit 10) collect x) @end example @noindent collects the next 10 function names after point. @item for @var{var} being the symbols [of @var{obarray}] This clause iterates over symbols, either over all interned symbols or over all symbols in @var{obarray}. The loop is executed with @var{var} bound to each symbol in turn. The symbols are visited in an unspecified order. As an example, @example (cl-loop for sym being the symbols when (fboundp sym) when (string-match "^map" (symbol-name sym)) collect sym) @end example @noindent returns a list of all the functions whose names begin with @samp{map}. The Common Lisp words @code{external-symbols} and @code{present-symbols} are also recognized but are equivalent to @code{symbols} in Emacs Lisp. Due to a minor implementation restriction, it will not work to have more than one @code{for} clause iterating over symbols, hash tables, keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately, it would rarely if ever be useful to do so. It @emph{is} valid to mix one of these types of clauses with other clauses like @code{for @dots{} to} or @code{while}. @item for @var{var} being the hash-keys of @var{hash-table} @itemx for @var{var} being the hash-values of @var{hash-table} This clause iterates over the entries in @var{hash-table} with @var{var} bound to each key, or value. A @samp{using} clause can bind a second variable to the opposite part. @example (cl-loop for k being the hash-keys of h using (hash-values v) do (message "key %S -> value %S" k v)) @end example @item for @var{var} being the key-codes of @var{keymap} @itemx for @var{var} being the key-bindings of @var{keymap} This clause iterates over the entries in @var{keymap}. The iteration does not enter nested keymaps but does enter inherited (parent) keymaps. A @code{using} clause can access both the codes and the bindings together. @example (cl-loop for c being the key-codes of (current-local-map) using (key-bindings b) do (message "key %S -> binding %S" c b)) @end example @item for @var{var} being the key-seqs of @var{keymap} This clause iterates over all key sequences defined by @var{keymap} and its nested keymaps, where @var{var} takes on values which are vectors. The strings or vectors are reused for each iteration, so you must copy them if you wish to keep them permanently. You can add a @samp{using (key-bindings @dots{})} clause to get the command bindings as well. @item for @var{var} being the overlays [of @var{buffer}] @dots{} This clause iterates over the ``overlays'' of a buffer (the clause @code{extents} is synonymous with @code{overlays}). If the @code{of} term is omitted, the current buffer is used. This clause also accepts optional @samp{from @var{pos}} and @samp{to @var{pos}} terms, limiting the clause to overlays which overlap the specified region. @item for @var{var} being the intervals [of @var{buffer}] @dots{} This clause iterates over all intervals of a buffer with constant text properties. The variable @var{var} will be bound to conses of start and end positions, where one start position is always equal to the previous end position. The clause allows @code{of}, @code{from}, @code{to}, and @code{property} terms, where the latter term restricts the search to just the specified property. The @code{of} term may specify either a buffer or a string. @item for @var{var} being the frames This clause iterates over all Emacs frames. The clause @code{screens} is a synonym for @code{frames}. The frames are visited in @code{next-frame} order starting from @code{selected-frame}. @item for @var{var} being the windows [of @var{frame}] This clause iterates over the windows (in the Emacs sense) of the current frame, or of the specified @var{frame}. It visits windows in @code{next-window} order starting from @code{selected-window} (or @code{frame-selected-window} if you specify @var{frame}). This clause treats the minibuffer window in the same way as @code{next-window} does. For greater flexibility, consider using @code{walk-windows} instead. @item for @var{var} being the buffers This clause iterates over all buffers in Emacs. It is equivalent to @samp{for @var{var} in (buffer-list)}. @item for @var{var} = @var{expr1} then @var{expr2} This clause does a general iteration. The first time through the loop, @var{var} will be bound to @var{expr1}. On the second and successive iterations it will be set by evaluating @var{expr2} (which may refer to the old value of @var{var}). For example, these two loops are effectively the same: @example (cl-loop for x on my-list by 'cddr do @dots{}) (cl-loop for x = my-list then (cddr x) while x do @dots{}) @end example Note that this type of @code{for} clause does not imply any sort of terminating condition; the above example combines it with a @code{while} clause to tell when to end the loop. If you omit the @code{then} term, @var{expr1} is used both for the initial setting and for successive settings: @example (cl-loop for x = (random) when (> x 0) return x) @end example @noindent This loop keeps taking random numbers from the @code{(random)} function until it gets a positive one, which it then returns. @end table If you include several @code{for} clauses in a row, they are treated sequentially (as if by @code{let*} and @code{setq}). You can instead use the word @code{and} to link the clauses, in which case they are processed in parallel (as if by @code{let} and @code{cl-psetq}). @example (cl-loop for x below 5 for y = nil then x collect (list x y)) @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4)) (cl-loop for x below 5 and y = nil then x collect (list x y)) @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3)) @end example @noindent In the first loop, @code{y} is set based on the value of @code{x} that was just set by the previous clause; in the second loop, @code{x} and @code{y} are set simultaneously so @code{y} is set based on the value of @code{x} left over from the previous time through the loop. @cindex destructuring, in cl-loop Another feature of the @code{cl-loop} macro is @emph{destructuring}, similar in concept to the destructuring provided by @code{defmacro} (@pxref{Argument Lists}). The @var{var} part of any @code{for} clause can be given as a list of variables instead of a single variable. The values produced during loop execution must be lists; the values in the lists are stored in the corresponding variables. @example (cl-loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y)) @result{} (5 9 13) @end example In loop destructuring, if there are more values than variables the trailing values are ignored, and if there are more variables than values the trailing variables get the value @code{nil}. If @code{nil} is used as a variable name, the corresponding values are ignored. Destructuring may be nested, and dotted lists of variables like @code{(x . y)} are allowed, so for example to process an alist @example (cl-loop for (key . value) in '((a . 1) (b . 2)) collect value) @result{} (1 2) @end example @node Iteration Clauses @subsection Iteration Clauses @noindent Aside from @code{for} clauses, there are several other loop clauses that control the way the loop operates. They might be used by themselves, or in conjunction with one or more @code{for} clauses. @table @code @item repeat @var{integer} This clause simply counts up to the specified number using an internal temporary variable. The loops @example (cl-loop repeat (1+ n) do @dots{}) (cl-loop for temp to n do @dots{}) @end example @noindent are identical except that the second one forces you to choose a name for a variable you aren't actually going to use. @item while @var{condition} This clause stops the loop when the specified condition (any Lisp expression) becomes @code{nil}. For example, the following two loops are equivalent, except for the implicit @code{nil} block that surrounds the second one: @example (while @var{cond} @var{forms}@dots{}) (cl-loop while @var{cond} do @var{forms}@dots{}) @end example @item until @var{condition} This clause stops the loop when the specified condition is true, i.e., non-@code{nil}. @item always @var{condition} This clause stops the loop when the specified condition is @code{nil}. Unlike @code{while}, it stops the loop using @code{return nil} so that the @code{finally} clauses are not executed. If all the conditions were non-@code{nil}, the loop returns @code{t}: @example (if (cl-loop for size in size-list always (> size 10)) (some-big-sizes) (no-big-sizes)) @end example @item never @var{condition} This clause is like @code{always}, except that the loop returns @code{t} if any conditions were false, or @code{nil} otherwise. @item thereis @var{condition} This clause stops the loop when the specified form is non-@code{nil}; in this case, it returns that non-@code{nil} value. If all the values were @code{nil}, the loop returns @code{nil}. @item iter-by @var{iterator} This clause iterates over the values from the specified form, an iterator object. See (@pxref{Generators,,,elisp,GNU Emacs Lisp Reference Manual}). @end table @node Accumulation Clauses @subsection Accumulation Clauses @noindent These clauses cause the loop to accumulate information about the specified Lisp @var{form}. The accumulated result is returned from the loop unless overridden, say, by a @code{return} clause. @table @code @item collect @var{form} This clause collects the values of @var{form} into a list. Several examples of @code{collect} appear elsewhere in this manual. The word @code{collecting} is a synonym for @code{collect}, and likewise for the other accumulation clauses. @item append @var{form} This clause collects lists of values into a result list using @code{append}. @item nconc @var{form} This clause collects lists of values into a result list by destructively modifying the lists rather than copying them. @item concat @var{form} This clause concatenates the values of the specified @var{form} into a string. (It and the following clause are extensions to standard Common Lisp.) @item vconcat @var{form} This clause concatenates the values of the specified @var{form} into a vector. @item count @var{form} This clause counts the number of times the specified @var{form} evaluates to a non-@code{nil} value. @item sum @var{form} This clause accumulates the sum of the values of the specified @var{form}, which must evaluate to a number. @item maximize @var{form} This clause accumulates the maximum value of the specified @var{form}, which must evaluate to a number. The return value is undefined if @code{maximize} is executed zero times. @item minimize @var{form} This clause accumulates the minimum value of the specified @var{form}. @end table Accumulation clauses can be followed by @samp{into @var{var}} to cause the data to be collected into variable @var{var} (which is automatically @code{let}-bound during the loop) rather than an unnamed temporary variable. Also, @code{into} accumulations do not automatically imply a return value. The loop must use some explicit mechanism, such as @code{finally return}, to return the accumulated result. It is valid for several accumulation clauses of the same type to accumulate into the same place. From Steele: @example (cl-loop for name in '(fred sue alice joe june) for kids in '((bob ken) () () (kris sunshine) ()) collect name append kids) @result{} (fred bob ken sue alice joe kris sunshine june) @end example @node Other Clauses @subsection Other Clauses @noindent This section describes the remaining loop clauses. @table @code @item with @var{var} = @var{value} This clause binds a variable to a value around the loop, but otherwise leaves the variable alone during the loop. The following loops are basically equivalent: @example (cl-loop with x = 17 do @dots{}) (let ((x 17)) (cl-loop do @dots{})) (cl-loop for x = 17 then x do @dots{}) @end example Naturally, the variable @var{var} might be used for some purpose in the rest of the loop. For example: @example (cl-loop for x in my-list with res = nil do (push x res) finally return res) @end example This loop inserts the elements of @code{my-list} at the front of a new list being accumulated in @code{res}, then returns the list @code{res} at the end of the loop. The effect is similar to that of a @code{collect} clause, but the list gets reversed by virtue of the fact that elements are being pushed onto the front of @code{res} rather than the end. If you omit the @code{=} term, the variable is initialized to @code{nil}. (Thus the @samp{= nil} in the above example is unnecessary.) Bindings made by @code{with} are sequential by default, as if by @code{let*}. Just like @code{for} clauses, @code{with} clauses can be linked with @code{and} to cause the bindings to be made by @code{let} instead. @item if @var{condition} @var{clause} This clause executes the following loop clause only if the specified condition is true. The following @var{clause} should be an accumulation, @code{do}, @code{return}, @code{if}, or @code{unless} clause. Several clauses may be linked by separating them with @code{and}. These clauses may be followed by @code{else} and a clause or clauses to execute if the condition was false. The whole construct may optionally be followed by the word @code{end} (which may be used to disambiguate an @code{else} or @code{and} in a nested @code{if}). The actual non-@code{nil} value of the condition form is available by the name @code{it} in the ``then'' part. For example: @example (setq funny-numbers '(6 13 -1)) @result{} (6 13 -1) (cl-loop for x below 10 if (cl-oddp x) collect x into odds and if (memq x funny-numbers) return (cdr it) end else collect x into evens finally return (vector odds evens)) @result{} [(1 3 5 7 9) (0 2 4 6 8)] (setq funny-numbers '(6 7 13 -1)) @result{} (6 7 13 -1) (cl-loop <@r{same thing again}>) @result{} (13 -1) @end example Note the use of @code{and} to put two clauses into the ``then'' part, one of which is itself an @code{if} clause. Note also that @code{end}, while normally optional, was necessary here to make it clear that the @code{else} refers to the outermost @code{if} clause. In the first case, the loop returns a vector of lists of the odd and even values of @var{x}. In the second case, the odd number 7 is one of the @code{funny-numbers} so the loop returns early; the actual returned value is based on the result of the @code{memq} call. @item when @var{condition} @var{clause} This clause is just a synonym for @code{if}. @item unless @var{condition} @var{clause} The @code{unless} clause is just like @code{if} except that the sense of the condition is reversed. @item named @var{name} This clause gives a name other than @code{nil} to the implicit block surrounding the loop. The @var{name} is the symbol to be used as the block name. @item initially [do] @var{forms}@dots{} This keyword introduces one or more Lisp forms which will be executed before the loop itself begins (but after any variables requested by @code{for} or @code{with} have been bound to their initial values). @code{initially} clauses can appear anywhere; if there are several, they are executed in the order they appear in the loop. The keyword @code{do} is optional. @item finally [do] @var{forms}@dots{} This introduces Lisp forms which will be executed after the loop finishes (say, on request of a @code{for} or @code{while}). @code{initially} and @code{finally} clauses may appear anywhere in the loop construct, but they are executed (in the specified order) at the beginning or end, respectively, of the loop. @item finally return @var{form} This says that @var{form} should be executed after the loop is done to obtain a return value. (Without this, or some other clause like @code{collect} or @code{return}, the loop will simply return @code{nil}.) Variables bound by @code{for}, @code{with}, or @code{into} will still contain their final values when @var{form} is executed. @item do @var{forms}@dots{} The word @code{do} may be followed by any number of Lisp expressions which are executed as an implicit @code{progn} in the body of the loop. Many of the examples in this section illustrate the use of @code{do}. @item return @var{form} This clause causes the loop to return immediately. The following Lisp form is evaluated to give the return value of the loop form. The @code{finally} clauses, if any, are not executed. Of course, @code{return} is generally used inside an @code{if} or @code{unless}, as its use in a top-level loop clause would mean the loop would never get to ``loop'' more than once. The clause @samp{return @var{form}} is equivalent to @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop was named). The @code{return} clause is implemented a bit more efficiently, though. @end table While there is no high-level way to add user extensions to @code{cl-loop}, this package does offer two properties called @code{cl-loop-handler} and @code{cl-loop-for-handler} which are functions to be called when a given symbol is encountered as a top-level loop clause or @code{for} clause, respectively. Consult the source code in file @file{cl-macs.el} for details. This package's @code{cl-loop} macro is compatible with that of Common Lisp, except that a few features are not implemented: @code{loop-finish} and data-type specifiers. Naturally, the @code{for} clauses that iterate over keymaps, overlays, intervals, frames, windows, and buffers are Emacs-specific extensions. @node Multiple Values @section Multiple Values @cindex multiple values @noindent Common Lisp functions can return zero or more results. Emacs Lisp functions, by contrast, always return exactly one result. This package makes no attempt to emulate Common Lisp multiple return values; Emacs versions of Common Lisp functions that return more than one value either return just the first value (as in @code{cl-compiler-macroexpand}) or return a list of values. This package @emph{does} define placeholders for the Common Lisp functions that work with multiple values, but in Emacs Lisp these functions simply operate on lists instead. The @code{cl-values} form, for example, is a synonym for @code{list} in Emacs. @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{} This form evaluates @var{values-form}, which must return a list of values. It then binds the @var{var}s to these respective values, as if by @code{let}, and then executes the body @var{forms}. If there are more @var{var}s than values, the extra @var{var}s are bound to @code{nil}. If there are fewer @var{var}s than values, the excess values are ignored. @end defmac @defmac cl-multiple-value-setq (var@dots{}) form This form evaluates @var{form}, which must return a list of values. It then sets the @var{var}s to these respective values, as if by @code{setq}. Extra @var{var}s or values are treated the same as in @code{cl-multiple-value-bind}. @end defmac Since a perfect emulation is not feasible in Emacs Lisp, this package opts to keep it as simple and predictable as possible. @node Macros @chapter Macros @noindent This package implements the various Common Lisp features of @code{defmacro}, such as destructuring, @code{&environment}, and @code{&body}. Top-level @code{&whole} is not implemented for @code{defmacro} due to technical difficulties. @xref{Argument Lists}. Destructuring is made available to the user by way of the following macro: @defmac cl-destructuring-bind arglist expr forms@dots{} This macro expands to code that executes @var{forms}, with the variables in @var{arglist} bound to the list of values returned by @var{expr}. The @var{arglist} can include all the features allowed for @code{cl-defmacro} argument lists, including destructuring. (The @code{&environment} keyword is not allowed.) The macro expansion will signal an error if @var{expr} returns a list of the wrong number of arguments or with incorrect keyword arguments. @end defmac @cindex compiler macros @cindex define compiler macros This package also includes the Common Lisp @code{define-compiler-macro} facility, which allows you to define compile-time expansions and optimizations for your functions. @defmac cl-define-compiler-macro name arglist forms@dots{} This form is similar to @code{defmacro}, except that it only expands calls to @var{name} at compile-time; calls processed by the Lisp interpreter are not expanded, nor are they expanded by the @code{macroexpand} function. The argument list may begin with a @code{&whole} keyword and a variable. This variable is bound to the macro-call form itself, i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}. If the macro expander returns this form unchanged, then the compiler treats it as a normal function call. This allows compiler macros to work as optimizers for special cases of a function, leaving complicated cases alone. For example, here is a simplified version of a definition that appears as a standard part of this package: @example (cl-define-compiler-macro cl-member (&whole form a list &rest keys) (if (and (null keys) (eq (car-safe a) 'quote) (not (floatp (cadr a)))) (list 'memq a list) form)) @end example @noindent This definition causes @code{(cl-member @var{a} @var{list})} to change to a call to the faster @code{memq} in the common case where @var{a} is a non-floating-point constant; if @var{a} is anything else, or if there are any keyword arguments in the call, then the original @code{cl-member} call is left intact. (The actual compiler macro for @code{cl-member} optimizes a number of other cases, including common @code{:test} predicates.) @end defmac @defun cl-compiler-macroexpand form This function is analogous to @code{macroexpand}, except that it expands compiler macros rather than regular macros. It returns @var{form} unchanged if it is not a call to a function for which a compiler macro has been defined, or if that compiler macro decided to punt by returning its @code{&whole} argument. Like @code{macroexpand}, it expands repeatedly until it reaches a form for which no further expansion is possible. @end defun @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet} and @code{cl-symbol-macrolet} forms for making ``local'' macro definitions. @node Declarations @chapter Declarations @noindent Common Lisp includes a complex and powerful ``declaration'' mechanism that allows you to give the compiler special hints about the types of data that will be stored in particular variables, and about the ways those variables and functions will be used. This package defines versions of all the Common Lisp declaration forms: @code{declare}, @code{locally}, @code{proclaim}, @code{declaim}, and @code{the}. Most of the Common Lisp declarations are not currently useful in Emacs Lisp. For example, the byte-code system provides little opportunity to benefit from type information. @ignore and @code{special} declarations are redundant in a fully dynamically-scoped Lisp. @end ignore A few declarations are meaningful when byte compiler optimizations are enabled, as they are by the default. Otherwise these declarations will effectively be ignored. @defun cl-proclaim decl-spec This function records a ``global'' declaration specified by @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec} is evaluated and thus should normally be quoted. @end defun @defmac cl-declaim decl-specs@dots{} This macro is like @code{cl-proclaim}, except that it takes any number of @var{decl-spec} arguments, and the arguments are unevaluated and unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when (compile load eval) @dots{})} around the declarations so that they will be registered at compile-time as well as at run-time. (This is vital, since normally the declarations are meant to influence the way the compiler treats the rest of the file that contains the @code{cl-declaim} form.) @end defmac @defmac cl-declare decl-specs@dots{} This macro is used to make declarations within functions and other code. Common Lisp allows declarations in various locations, generally at the beginning of any of the many ``implicit @code{progn}s'' throughout Lisp syntax, such as function bodies, @code{let} bodies, etc. Currently the only declaration understood by @code{cl-declare} is @code{special}. @end defmac @defmac cl-locally declarations@dots{} forms@dots{} In this package, @code{cl-locally} is no different from @code{progn}. @end defmac @defmac cl-the type form @code{cl-the} returns the value of @code{form}, first checking (if optimization settings permit) that it is of type @code{type}. Future byte-compiler optimizations may also make use of this information to improve runtime efficiency. For example, @code{mapcar} can map over both lists and arrays. It is hard for the compiler to expand @code{mapcar} into an in-line loop unless it knows whether the sequence will be a list or an array ahead of time. With @code{(mapcar 'car (cl-the vector foo))}, a future compiler would have enough information to expand the loop in-line. For now, Emacs Lisp will treat the above code as exactly equivalent to @code{(mapcar 'car foo)}. @end defmac Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or @code{cl-declare} should be a list beginning with a symbol that says what kind of declaration it is. This package currently understands @code{special}, @code{inline}, @code{notinline}, @code{optimize}, and @code{warn} declarations. (The @code{warn} declaration is an extension of standard Common Lisp.) Other Common Lisp declarations, such as @code{type} and @code{ftype}, are silently ignored. @table @code @item special @c FIXME ? Since all variables in Emacs Lisp are ``special'' (in the Common Lisp sense), @code{special} declarations are only advisory. They simply tell the byte compiler that the specified variables are intentionally being referred to without being bound in the body of the function. The compiler normally emits warnings for such references, since they could be typographical errors for references to local variables. The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}. In top-level contexts, it is generally better to write @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))}, since @code{defvar} makes your intentions clearer. @item inline The @code{inline} @var{decl-spec} lists one or more functions whose bodies should be expanded ``in-line'' into calling functions whenever the compiler is able to arrange for it. For example, the function @code{cl-acons} is declared @code{inline} by this package so that the form @code{(cl-acons @var{key} @var{value} @var{alist})} will expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})} when it is called in user functions, so as to save function calls. The following declarations are all equivalent. Note that the @code{defsubst} form is a convenient way to define a function and declare it inline all at once. @example (cl-declaim (inline foo bar)) (cl-eval-when (compile load eval) (cl-proclaim '(inline foo bar))) (defsubst foo (@dots{}) @dots{}) ; instead of defun @end example @strong{Please note:} this declaration remains in effect after the containing source file is done. It is correct to use it to request that a function you have defined should be inlined, but it is impolite to use it to request inlining of an external function. In Common Lisp, it is possible to use @code{(declare (inline @dots{}))} before a particular call to a function to cause just that call to be inlined; the current byte compilers provide no way to implement this, so @code{(cl-declare (inline @dots{}))} is currently ignored by this package. @item notinline The @code{notinline} declaration lists functions which should not be inlined after all; it cancels a previous @code{inline} declaration. @item optimize This declaration controls how much optimization is performed by the compiler. The word @code{optimize} is followed by any number of lists like @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several optimization ``qualities''; this package ignores all but @code{speed} and @code{safety}. The value of a quality should be an integer from 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''. The default level for both qualities is 1. In this package, the @code{speed} quality is tied to the @code{byte-optimize} flag, which is set to @code{nil} for @code{(speed 0)} and to @code{t} for higher settings; and the @code{safety} quality is tied to the @code{byte-compile-delete-errors} flag, which is set to @code{nil} for @code{(safety 3)} and to @code{t} for all lower settings. (The latter flag controls whether the compiler is allowed to optimize out code whose only side-effect could be to signal an error, e.g., rewriting @code{(progn foo bar)} to @code{bar} when it is not known whether @code{foo} will be bound at run-time.) Note that even compiling with @code{(safety 0)}, the Emacs byte-code system provides sufficient checking to prevent real harm from being done. For example, barring serious bugs in Emacs itself, Emacs will not crash with a segmentation fault just because of an error in a fully-optimized Lisp program. The @code{optimize} declaration is normally used in a top-level @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows it to be used with @code{declare} to set the level of optimization locally for a given form, but this will not work correctly with the current byte-compiler. (The @code{cl-declare} will set the new optimization level, but that level will not automatically be unset after the enclosing form is done.) @item warn This declaration controls what sorts of warnings are generated by the byte compiler. The word @code{warn} is followed by any number of ``warning qualities'', similar in form to optimization qualities. The currently supported warning types are @code{redefine}, @code{callargs}, @code{unresolved}, and @code{free-vars}; in the current system, a value of 0 will disable these warnings and any higher value will enable them. See the documentation of the variable @code{byte-compile-warnings} for more details. @end table @node Symbols @chapter Symbols @noindent This package defines several symbol-related features that were missing from Emacs Lisp. @menu * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}. * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}. @end menu @node Property Lists @section Property Lists @noindent These functions augment the standard Emacs Lisp functions @code{get} and @code{put} for operating on properties attached to symbols. There are also functions for working with property lists as first-class data structures not attached to particular symbols. @defun cl-get symbol property &optional default This function is like @code{get}, except that if the property is not found, the @var{default} argument provides the return value. (The Emacs Lisp @code{get} function always uses @code{nil} as the default; this package's @code{cl-get} is equivalent to Common Lisp's @code{get}.) The @code{cl-get} function is @code{setf}-able; when used in this fashion, the @var{default} argument is allowed but ignored. @end defun @defun cl-remprop symbol property This function removes the entry for @var{property} from the property list of @var{symbol}. It returns a true value if the property was indeed found and removed, or @code{nil} if there was no such property. (This function was probably omitted from Emacs originally because, since @code{get} did not allow a @var{default}, it was very difficult to distinguish between a missing property and a property whose value was @code{nil}; thus, setting a property to @code{nil} was close enough to @code{cl-remprop} for most purposes.) @end defun @defun cl-getf place property &optional default This function scans the list @var{place} as if it were a property list, i.e., a list of alternating property names and values. If an even-numbered element of @var{place} is found which is @code{eq} to @var{property}, the following odd-numbered element is returned. Otherwise, @var{default} is returned (or @code{nil} if no default is given). In particular, @example (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop) @end example It is valid to use @code{cl-getf} as a @code{setf} place, in which case its @var{place} argument must itself be a valid @code{setf} place. The @var{default} argument, if any, is ignored in this context. The effect is to change (via @code{setcar}) the value cell in the list that corresponds to @var{property}, or to cons a new property-value pair onto the list if the property is not yet present. @example (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val) @end example The @code{get} and @code{cl-get} functions are also @code{setf}-able. The fact that @code{default} is ignored can sometimes be useful: @example (cl-incf (cl-get 'foo 'usage-count 0)) @end example Here, symbol @code{foo}'s @code{usage-count} property is incremented if it exists, or set to 1 (an incremented 0) otherwise. When not used as a @code{setf} form, @code{cl-getf} is just a regular function and its @var{place} argument can actually be any Lisp expression. @end defun @defmac cl-remf place property This macro removes the property-value pair for @var{property} from the property list stored at @var{place}, which is any @code{setf}-able place expression. It returns true if the property was found. Note that if @var{property} happens to be first on the list, this will effectively do a @code{(setf @var{place} (cddr @var{place}))}, whereas if it occurs later, this simply uses @code{setcdr} to splice out the property and value cells. @end defmac @node Creating Symbols @section Creating Symbols @noindent These functions create unique symbols, typically for use as temporary variables. @defun cl-gensym &optional x This function creates a new, uninterned symbol (using @code{make-symbol}) with a unique name. (The name of an uninterned symbol is relevant only if the symbol is printed.) By default, the name is generated from an increasing sequence of numbers, @samp{G1000}, @samp{G1001}, @samp{G1002}, etc. If the optional argument @var{x} is a string, that string is used as a prefix instead of @samp{G}. Uninterned symbols are used in macro expansions for temporary variables, to ensure that their names will not conflict with ``real'' variables in the user's code. (Internally, the variable @code{cl--gensym-counter} holds the counter used to generate names. It is initialized with zero and incremented after each use.) @end defun @defun cl-gentemp &optional x This function is like @code{cl-gensym}, except that it produces a new @emph{interned} symbol. If the symbol that is generated already exists, the function keeps incrementing the counter and trying again until a new symbol is generated. @end defun This package automatically creates all keywords that are called for by @code{&key} argument specifiers, and discourages the use of keywords as data unrelated to keyword arguments, so the related function @code{defkeyword} (to create self-quoting keyword symbols) is not provided. @node Numbers @chapter Numbers @noindent This section defines a few simple Common Lisp operations on numbers that were left out of Emacs Lisp. @menu * Predicates on Numbers:: @code{cl-plusp}, @code{cl-oddp}, etc. * Numerical Functions:: @code{cl-floor}, @code{cl-ceiling}, etc. * Random Numbers:: @code{cl-random}, @code{cl-make-random-state}. * Implementation Parameters:: @code{cl-most-positive-float}, etc. @end menu @node Predicates on Numbers @section Predicates on Numbers @noindent These functions return @code{t} if the specified condition is true of the numerical argument, or @code{nil} otherwise. @defun cl-plusp number This predicate tests whether @var{number} is positive. It is an error if the argument is not a number. @end defun @defun cl-minusp number This predicate tests whether @var{number} is negative. It is an error if the argument is not a number. @end defun @defun cl-oddp integer This predicate tests whether @var{integer} is odd. It is an error if the argument is not an integer. @end defun @defun cl-evenp integer This predicate tests whether @var{integer} is even. It is an error if the argument is not an integer. @end defun @defun cl-digit-char-p char radix Test if @var{char} is a digit in the specified @var{radix} (default is 10). If it is, return the numerical value of digit @var{char} in @var{radix}. @end defun @node Numerical Functions @section Numerical Functions @noindent These functions perform various arithmetic operations on numbers. @defun cl-gcd &rest integers This function returns the Greatest Common Divisor of the arguments. For one argument, it returns the absolute value of that argument. For zero arguments, it returns zero. @end defun @defun cl-lcm &rest integers This function returns the Least Common Multiple of the arguments. For one argument, it returns the absolute value of that argument. For zero arguments, it returns one. @end defun @defun cl-isqrt integer This function computes the ``integer square root'' of its integer argument, i.e., the greatest integer less than or equal to the true square root of the argument. @end defun @defun cl-floor number &optional divisor With one argument, @code{cl-floor} returns a list of two numbers: The argument rounded down (toward minus infinity) to an integer, and the ``remainder'' which would have to be added back to the first return value to yield the argument again. If the argument is an integer @var{x}, the result is always the list @code{(@var{x} 0)}. If the argument is a floating-point number, the first result is a Lisp integer and the second is a Lisp float between 0 (inclusive) and 1 (exclusive). With two arguments, @code{cl-floor} divides @var{number} by @var{divisor}, and returns the floor of the quotient and the corresponding remainder as a list of two numbers. If @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})}, then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r} between 0 (inclusive) and @var{r} (exclusive). Also, note that @code{(cl-floor @var{x})} is exactly equivalent to @code{(cl-floor @var{x} 1)}. This function is entirely compatible with Common Lisp's @code{floor} function, except that it returns the two results in a list since Emacs Lisp does not support multiple-valued functions. @end defun @defun cl-ceiling number &optional divisor This function implements the Common Lisp @code{ceiling} function, which is analogous to @code{floor} except that it rounds the argument or quotient of the arguments up toward plus infinity. The remainder will be between 0 and minus @var{r}. @end defun @defun cl-truncate number &optional divisor This function implements the Common Lisp @code{truncate} function, which is analogous to @code{floor} except that it rounds the argument or quotient of the arguments toward zero. Thus it is equivalent to @code{cl-floor} if the argument or quotient is positive, or to @code{cl-ceiling} otherwise. The remainder has the same sign as @var{number}. @end defun @defun cl-round number &optional divisor This function implements the Common Lisp @code{round} function, which is analogous to @code{floor} except that it rounds the argument or quotient of the arguments to the nearest integer. In the case of a tie (the argument or quotient is exactly halfway between two integers), it rounds to the even integer. @end defun @defun cl-mod number divisor This function returns the same value as the second return value of @code{cl-floor}. @end defun @defun cl-rem number divisor This function returns the same value as the second return value of @code{cl-truncate}. @end defun @defun cl-parse-integer string &key start end radix junk-allowed This function implements the Common Lisp @code{parse-integer} function. It parses an integer in the specified @var{radix} from the substring of @var{string} between @var{start} and @var{end}. Any leading and trailing whitespace chars are ignored. The function signals an error if the substring between @var{start} and @var{end} cannot be parsed as an integer, unless @var{junk-allowed} is non-@code{nil}. @end defun @node Random Numbers @section Random Numbers @noindent This package also provides an implementation of the Common Lisp random number generator. It uses its own additive-congruential algorithm, which is much more likely to give statistically clean @c FIXME? Still true? random numbers than the simple generators supplied by many operating systems. @defun cl-random number &optional state This function returns a random nonnegative number less than @var{number}, and of the same type (either integer or floating-point). The @var{state} argument should be a @code{random-state} object that holds the state of the random number generator. The function modifies this state object as a side effect. If @var{state} is omitted, it defaults to the internal variable @code{cl--random-state}, which contains a pre-initialized default @code{random-state} object. (Since any number of programs in the Emacs process may be accessing @code{cl--random-state} in interleaved fashion, the sequence generated from this will be irreproducible for all intents and purposes.) @end defun @defun cl-make-random-state &optional state This function creates or copies a @code{random-state} object. If @var{state} is omitted or @code{nil}, it returns a new copy of @code{cl--random-state}. This is a copy in the sense that future sequences of calls to @code{(cl-random @var{n})} and @code{(cl-random @var{n} @var{s})} (where @var{s} is the new random-state object) will return identical sequences of random numbers. If @var{state} is a @code{random-state} object, this function returns a copy of that object. If @var{state} is @code{t}, this function returns a new @code{random-state} object seeded from the date and time. As an extension to Common Lisp, @var{state} may also be an integer in which case the new object is seeded from that integer; each different integer seed will result in a completely different sequence of random numbers. It is valid to print a @code{random-state} object to a buffer or file and later read it back with @code{read}. If a program wishes to use a sequence of pseudo-random numbers which can be reproduced later for debugging, it can call @code{(cl-make-random-state t)} to get a new sequence, then print this sequence to a file. When the program is later rerun, it can read the original run's random-state from the file. @end defun @defun cl-random-state-p object This predicate returns @code{t} if @var{object} is a @code{random-state} object, or @code{nil} otherwise. @end defun @node Implementation Parameters @section Implementation Parameters @noindent This package defines several useful constants having to do with floating-point numbers. It determines their values by exercising the computer's floating-point arithmetic in various ways. Because this operation might be slow, the code for initializing them is kept in a separate function that must be called before the parameters can be used. @defun cl-float-limits This function makes sure that the Common Lisp floating-point parameters like @code{cl-most-positive-float} have been initialized. Until it is called, these parameters will be @code{nil}. @c If this version of Emacs does not support floats, the parameters will @c remain @code{nil}. If the parameters have already been initialized, the function returns immediately. The algorithm makes assumptions that will be valid for almost all machines, but will fail if the machine's arithmetic is extremely unusual, e.g., decimal. @end defun Since true Common Lisp supports up to four different floating-point precisions, it has families of constants like @code{most-positive-single-float}, @code{most-positive-double-float}, @code{most-positive-long-float}, and so on. Emacs has only one floating-point precision, so this package omits the precision word from the constants' names. @defvar cl-most-positive-float This constant equals the largest value a Lisp float can hold. For those systems whose arithmetic supports infinities, this is the largest @emph{finite} value. For IEEE machines, the value is approximately @code{1.79e+308}. @end defvar @defvar cl-most-negative-float This constant equals the most negative value a Lisp float can hold. (It is assumed to be equal to @code{(- cl-most-positive-float)}.) @end defvar @defvar cl-least-positive-float This constant equals the smallest Lisp float value greater than zero. For IEEE machines, it is about @code{4.94e-324} if denormals are supported or @code{2.22e-308} if not. @end defvar @defvar cl-least-positive-normalized-float This constant equals the smallest @emph{normalized} Lisp float greater than zero, i.e., the smallest value for which IEEE denormalization will not result in a loss of precision. For IEEE machines, this value is about @code{2.22e-308}. For machines that do not support the concept of denormalization and gradual underflow, this constant will always equal @code{cl-least-positive-float}. @end defvar @defvar cl-least-negative-float This constant is the negative counterpart of @code{cl-least-positive-float}. @end defvar @defvar cl-least-negative-normalized-float This constant is the negative counterpart of @code{cl-least-positive-normalized-float}. @end defvar @defvar cl-float-epsilon This constant is the smallest positive Lisp float that can be added to 1.0 to produce a distinct value. Adding a smaller number to 1.0 will yield 1.0 again due to roundoff. For IEEE machines, epsilon is about @code{2.22e-16}. @end defvar @defvar cl-float-negative-epsilon This is the smallest positive value that can be subtracted from 1.0 to produce a distinct value. For IEEE machines, it is about @code{1.11e-16}. @end defvar @node Sequences @chapter Sequences @noindent Common Lisp defines a number of functions that operate on @dfn{sequences}, which are either lists, strings, or vectors. Emacs Lisp includes a few of these, notably @code{elt} and @code{length}; this package defines most of the rest. @menu * Sequence Basics:: Arguments shared by all sequence functions. * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc. * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc. * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc. * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}. @end menu @node Sequence Basics @section Sequence Basics @noindent Many of the sequence functions take keyword arguments; @pxref{Argument Lists}. All keyword arguments are optional and, if specified, may appear in any order. The @code{:key} argument should be passed either @code{nil}, or a function of one argument. This key function is used as a filter through which the elements of the sequence are seen; for example, @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}. It searches for an element of the list whose @sc{car} equals @code{x}, rather than for an element which equals @code{x} itself. If @code{:key} is omitted or @code{nil}, the filter is effectively the identity function. The @code{:test} and @code{:test-not} arguments should be either @code{nil}, or functions of two arguments. The test function is used to compare two sequence elements, or to compare a search value with sequence elements. (The two values are passed to the test function in the same order as the original sequence function arguments from which they are derived, or, if they both come from the same sequence, in the same order as they appear in that sequence.) The @code{:test} argument specifies a function which must return true (non-@code{nil}) to indicate a match; instead, you may use @code{:test-not} to give a function which returns @emph{false} to indicate a match. The default test function is @code{eql}. Many functions that take @var{item} and @code{:test} or @code{:test-not} arguments also come in @code{-if} and @code{-if-not} varieties, where a @var{predicate} function is passed instead of @var{item}, and sequence elements match if the predicate returns true on them (or false in the case of @code{-if-not}). For example: @example (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq) @end example @noindent to remove all zeros from sequence @code{seq}. Some operations can work on a subsequence of the argument sequence; these function take @code{:start} and @code{:end} arguments, which default to zero and the length of the sequence, respectively. Only elements between @var{start} (inclusive) and @var{end} (exclusive) are affected by the operation. The @var{end} argument may be passed @code{nil} to signify the length of the sequence; otherwise, both @var{start} and @var{end} must be integers, with @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}. If the function takes two sequence arguments, the limits are defined by keywords @code{:start1} and @code{:end1} for the first, and @code{:start2} and @code{:end2} for the second. A few functions accept a @code{:from-end} argument, which, if non-@code{nil}, causes the operation to go from right-to-left through the sequence instead of left-to-right, and a @code{:count} argument, which specifies an integer maximum number of elements to be removed or otherwise processed. The sequence functions make no guarantees about the order in which the @code{:test}, @code{:test-not}, and @code{:key} functions are called on various elements. Therefore, it is a bad idea to depend on side effects of these functions. For example, @code{:from-end} may cause the sequence to be scanned actually in reverse, or it may be scanned forwards but computing a result ``as if'' it were scanned backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every}, @emph{do} specify exactly the order in which the function is called so side effects are perfectly acceptable in those cases.) Strings may contain ``text properties'' as well as character data. Except as noted, it is undefined whether or not text properties are preserved by sequence functions. For example, @code{(cl-remove ?A @var{str})} may or may not preserve the properties of the characters copied from @var{str} into the result. @node Mapping over Sequences @section Mapping over Sequences @noindent These functions ``map'' the function you specify over the elements of lists or arrays. They are all variations on the theme of the built-in function @code{mapcar}. @defun cl-mapcar function seq &rest more-seqs This function calls @var{function} on successive parallel sets of elements from its argument sequences. Given a single @var{seq} argument it is equivalent to @code{mapcar}; given @var{n} sequences, it calls the function with the first elements of each of the sequences as the @var{n} arguments to yield the first element of the result list, then with the second elements, and so on. The mapping stops as soon as the shortest sequence runs out. The argument sequences may be any mixture of lists, strings, and vectors; the return sequence is always a list. Common Lisp's @code{mapcar} accepts multiple arguments but works only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence argument. This package's @code{cl-mapcar} works as a compatible superset of both. @end defun @defun cl-map result-type function seq &rest more-seqs This function maps @var{function} over the argument sequences, just like @code{cl-mapcar}, but it returns a sequence of type @var{result-type} rather than a list. @var{result-type} must be one of the following symbols: @code{vector}, @code{string}, @code{list} (in which case the effect is the same as for @code{cl-mapcar}), or @code{nil} (in which case the results are thrown away and @code{cl-map} returns @code{nil}). @end defun @defun cl-maplist function list &rest more-lists This function calls @var{function} on each of its argument lists, then on the @sc{cdr}s of those lists, and so on, until the shortest list runs out. The results are returned in the form of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except that it passes in the list pointers themselves rather than the @sc{car}s of the advancing pointers. @end defun @defun cl-mapc function seq &rest more-seqs This function is like @code{cl-mapcar}, except that the values returned by @var{function} are ignored and thrown away rather than being collected into a list. The return value of @code{cl-mapc} is @var{seq}, the first sequence. This function is more general than the Emacs primitive @code{mapc}. (Note that this function is called @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you might expect.) @c http://debbugs.gnu.org/6575 @end defun @defun cl-mapl function list &rest more-lists This function is like @code{cl-maplist}, except that it throws away the values returned by @var{function}. @end defun @defun cl-mapcan function seq &rest more-seqs This function is like @code{cl-mapcar}, except that it concatenates the return values (which must be lists) using @code{nconc}, rather than simply collecting them into a list. @end defun @defun cl-mapcon function list &rest more-lists This function is like @code{cl-maplist}, except that it concatenates the return values using @code{nconc}. @end defun @defun cl-some predicate seq &rest more-seqs This function calls @var{predicate} on each element of @var{seq} in turn; if @var{predicate} returns a non-@code{nil} value, @code{cl-some} returns that value, otherwise it returns @code{nil}. Given several sequence arguments, it steps through the sequences in parallel until the shortest one runs out, just as in @code{cl-mapcar}. You can rely on the left-to-right order in which the elements are visited, and on the fact that mapping stops immediately as soon as @var{predicate} returns non-@code{nil}. @end defun @defun cl-every predicate seq &rest more-seqs This function calls @var{predicate} on each element of the sequence(s) in turn; it returns @code{nil} as soon as @var{predicate} returns @code{nil} for any element, or @code{t} if the predicate was true for all elements. @end defun @defun cl-notany predicate seq &rest more-seqs This function calls @var{predicate} on each element of the sequence(s) in turn; it returns @code{nil} as soon as @var{predicate} returns a non-@code{nil} value for any element, or @code{t} if the predicate was @code{nil} for all elements. @end defun @defun cl-notevery predicate seq &rest more-seqs This function calls @var{predicate} on each element of the sequence(s) in turn; it returns a non-@code{nil} value as soon as @var{predicate} returns @code{nil} for any element, or @code{nil} if the predicate was true for all elements. @end defun @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key} This function combines the elements of @var{seq} using an associative binary operation. Suppose @var{function} is @code{*} and @var{seq} is the list @code{(2 3 4 5)}. The first two elements of the list are combined with @code{(* 2 3) = 6}; this is combined with the next element, @code{(* 6 4) = 24}, and that is combined with the final element: @code{(* 24 5) = 120}. Note that the @code{*} function happens to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as an explicit call to @code{cl-reduce}. If @code{:from-end} is true, the reduction is right-associative instead of left-associative: @example (cl-reduce '- '(1 2 3 4)) @equiv{} (- (- (- 1 2) 3) 4) @result{} -8 (cl-reduce '- '(1 2 3 4) :from-end t) @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2 @end example If @code{:key} is specified, it is a function of one argument, which is called on each of the sequence elements in turn. If @code{:initial-value} is specified, it is effectively added to the front (or rear in the case of @code{:from-end}) of the sequence. The @code{:key} function is @emph{not} applied to the initial value. If the sequence, including the initial value, has exactly one element then that element is returned without ever calling @var{function}. If the sequence is empty (and there is no initial value), then @var{function} is called with no arguments to obtain the return value. @end defun All of these mapping operations can be expressed conveniently in terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will be faster since it generates the loop as in-line code with no function calls. @node Sequence Functions @section Sequence Functions @noindent This section describes a number of Common Lisp functions for operating on sequences. @defun cl-subseq sequence start &optional end This function returns a given subsequence of the argument @var{sequence}, which may be a list, string, or vector. The indices @var{start} and @var{end} must be in range, and @var{start} must be no greater than @var{end}. If @var{end} is omitted, it defaults to the length of the sequence. The return value is always a copy; it does not share structure with @var{sequence}. As an extension to Common Lisp, @var{start} and/or @var{end} may be negative, in which case they represent a distance back from the end of the sequence. This is for compatibility with Emacs's @code{substring} function. Note that @code{cl-subseq} is the @emph{only} sequence function that allows negative @var{start} and @var{end}. You can use @code{setf} on a @code{cl-subseq} form to replace a specified range of elements with elements from another sequence. The replacement is done as if by @code{cl-replace}, described below. @end defun @defun cl-concatenate result-type &rest seqs This function concatenates the argument sequences together to form a result sequence of type @var{result-type}, one of the symbols @code{vector}, @code{string}, or @code{list}. The arguments are always copied, even in cases such as @code{(cl-concatenate 'list '(1 2 3))} where the result is identical to an argument. @end defun @defun cl-fill seq item @t{&key :start :end} This function fills the elements of the sequence (or the specified part of the sequence) with the value @var{item}. @end defun @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2} This function copies part of @var{seq2} into part of @var{seq1}. The sequence @var{seq1} is not stretched or resized; the amount of data copied is simply the shorter of the source and destination (sub)sequences. The function returns @var{seq1}. If @var{seq1} and @var{seq2} are @code{eq}, then the replacement will work correctly even if the regions indicated by the start and end arguments overlap. However, if @var{seq1} and @var{seq2} are lists that share storage but are not @code{eq}, and the start and end arguments specify overlapping regions, the effect is undefined. @end defun @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end} This returns a copy of @var{seq} with all elements matching @var{item} removed. The result may share storage with or be @code{eq} to @var{seq} in some circumstances, but the original @var{seq} will not be modified. The @code{:test}, @code{:test-not}, and @code{:key} arguments define the matching test that is used; by default, elements @code{eql} to @var{item} are removed. The @code{:count} argument specifies the maximum number of matching elements that can be removed (only the leftmost @var{count} matches are removed). The @code{:start} and @code{:end} arguments specify a region in @var{seq} in which elements will be removed; elements outside that region are not matched or removed. The @code{:from-end} argument, if true, says that elements should be deleted from the end of the sequence rather than the beginning (this matters only if @var{count} was also specified). @end defun @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end} This deletes all elements of @var{seq} that match @var{item}. It is a destructive operation. Since Emacs Lisp does not support stretchable strings or vectors, this is the same as @code{cl-remove} for those sequence types. On lists, @code{cl-remove} will copy the list if necessary to preserve the original list, whereas @code{cl-delete} will splice out parts of the argument list. Compare @code{append} and @code{nconc}, which are analogous non-destructive and destructive list operations in Emacs Lisp. @end defun @findex cl-remove-if @findex cl-remove-if-not @findex cl-delete-if @findex cl-delete-if-not The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not}, @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly. @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end} This function returns a copy of @var{seq} with duplicate elements removed. Specifically, if two elements from the sequence match according to the @code{:test}, @code{:test-not}, and @code{:key} arguments, only the rightmost one is retained. If @code{:from-end} is true, the leftmost one is retained instead. If @code{:start} or @code{:end} is specified, only elements within that subsequence are examined or removed. @end defun @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end} This function deletes duplicate elements from @var{seq}. It is a destructive version of @code{cl-remove-duplicates}. @end defun @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} This function returns a copy of @var{seq}, with all elements matching @var{old} replaced with @var{new}. The @code{:count}, @code{:start}, @code{:end}, and @code{:from-end} arguments may be used to limit the number of substitutions made. @end defun @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} This is a destructive version of @code{cl-substitute}; it performs the substitution using @code{setcar} or @code{aset} rather than by returning a changed copy of the sequence. @end defun @findex cl-substitute-if @findex cl-substitute-if-not @findex cl-nsubstitute-if @findex cl-nsubstitute-if-not The functions @code{cl-substitute-if}, @code{cl-substitute-if-not}, @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined similarly. For these, a @var{predicate} is given in place of the @var{old} argument. @node Searching Sequences @section Searching Sequences @noindent These functions search for elements or subsequences in a sequence. (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.) @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end} This function searches @var{seq} for an element matching @var{item}. If it finds a match, it returns the matching element. Otherwise, it returns @code{nil}. It returns the leftmost match, unless @code{:from-end} is true, in which case it returns the rightmost match. The @code{:start} and @code{:end} arguments may be used to limit the range of elements that are searched. @end defun @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end} This function is like @code{cl-find}, except that it returns the integer position in the sequence of the matching item rather than the item itself. The position is relative to the start of the sequence as a whole, even if @code{:start} is non-zero. The function returns @code{nil} if no matching element was found. @end defun @defun cl-count item seq @t{&key :test :test-not :key :start :end} This function returns the number of elements of @var{seq} which match @var{item}. The result is always a nonnegative integer. @end defun @findex cl-find-if @findex cl-find-if-not @findex cl-position-if @findex cl-position-if-not @findex cl-count-if @findex cl-count-if-not The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if}, @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not} functions are defined similarly. @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end} This function compares the specified parts of @var{seq1} and @var{seq2}. If they are the same length and the corresponding elements match (according to @code{:test}, @code{:test-not}, and @code{:key}), the function returns @code{nil}. If there is a mismatch, the function returns the index (relative to @var{seq1}) of the first mismatching element. This will be the leftmost pair of elements that do not match, or the position at which the shorter of the two otherwise-matching sequences runs out. If @code{:from-end} is true, then the elements are compared from right to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}. If the sequences differ, then one plus the index of the rightmost difference (relative to @var{seq1}) is returned. An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)}, which compares two strings case-insensitively. @end defun @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2} This function searches @var{seq2} for a subsequence that matches @var{seq1} (or part of it specified by @code{:start1} and @code{:end1}). Only matches that fall entirely within the region defined by @code{:start2} and @code{:end2} will be considered. The return value is the index of the leftmost element of the leftmost match, relative to the start of @var{seq2}, or @code{nil} if no matches were found. If @code{:from-end} is true, the function finds the @emph{rightmost} matching subsequence. @end defun @node Sorting Sequences @section Sorting Sequences @defun cl-sort seq predicate @t{&key :key} This function sorts @var{seq} into increasing order as determined by using @var{predicate} to compare pairs of elements. @var{predicate} should return true (non-@code{nil}) if and only if its first argument is less than (not equal to) its second argument. For example, @code{<} and @code{string-lessp} are suitable predicate functions for sorting numbers and strings, respectively; @code{>} would sort numbers into decreasing rather than increasing order. This function differs from Emacs's built-in @code{sort} in that it can operate on any type of sequence, not just lists. Also, it accepts a @code{:key} argument, which is used to preprocess data fed to the @var{predicate} function. For example, @example (setq data (cl-sort data 'string-lessp :key 'downcase)) @end example @noindent sorts @var{data}, a sequence of strings, into increasing alphabetical order without regard to case. A @code{:key} function of @code{car} would be useful for sorting association lists. It should only be a simple accessor though, since it's used heavily in the current implementation. The @code{cl-sort} function is destructive; it sorts lists by actually rearranging the @sc{cdr} pointers in suitable fashion. @end defun @defun cl-stable-sort seq predicate @t{&key :key} This function sorts @var{seq} @dfn{stably}, meaning two elements which are equal in terms of @var{predicate} are guaranteed not to be rearranged out of their original order by the sort. In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent in Emacs Lisp because the underlying @code{sort} function is stable by default. However, this package reserves the right to use non-stable methods for @code{cl-sort} in the future. @end defun @defun cl-merge type seq1 seq2 predicate @t{&key :key} This function merges two sequences @var{seq1} and @var{seq2} by interleaving their elements. The result sequence, of type @var{type} (in the sense of @code{cl-concatenate}), has length equal to the sum of the lengths of the two input sequences. The sequences may be modified destructively. Order of elements within @var{seq1} and @var{seq2} is preserved in the interleaving; elements of the two sequences are compared by @var{predicate} (in the sense of @code{sort}) and the lesser element goes first in the result. When elements are equal, those from @var{seq1} precede those from @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are both sorted according to @var{predicate}, then the result will be a merged sequence which is (stably) sorted according to @var{predicate}. @end defun @node Lists @chapter Lists @noindent The functions described here operate on lists. @menu * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc. * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc. * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc. * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc. @end menu @node List Functions @section List Functions @noindent This section describes a number of simple operations on lists, i.e., chains of cons cells. @defun cl-caddr x This function is equivalent to @code{(car (cdr (cdr @var{x})))}. Likewise, this package aliases all 24 @code{c@var{xxx}r} functions where @var{xxx} is up to four @samp{a}s and/or @samp{d}s. All of these functions are @code{setf}-able, and calls to them are expanded inline by the byte-compiler for maximum efficiency. @end defun @defun cl-first x This function is a synonym for @code{(car @var{x})}. Likewise, the functions @code{cl-second}, @code{cl-third}, @dots{}, through @code{cl-tenth} return the given element of the list @var{x}. @end defun @defun cl-rest x This function is a synonym for @code{(cdr @var{x})}. @end defun @defun cl-endp x This function acts like @code{null}, but signals an error if @code{x} is neither a @code{nil} nor a cons cell. @end defun @defun cl-list-length x This function returns the length of list @var{x}, exactly like @code{(length @var{x})}, except that if @var{x} is a circular list (where the @sc{cdr}-chain forms a loop rather than terminating with @code{nil}), this function returns @code{nil}. (The regular @code{length} function would get stuck if given a circular list. See also the @code{safe-length} function.) @end defun @defun cl-list* arg &rest others This function constructs a list of its arguments. The final argument becomes the @sc{cdr} of the last cell constructed. Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to @code{(cons @var{a} (cons @var{b} @var{c}))}, and @code{(cl-list* @var{a} @var{b} nil)} is equivalent to @code{(list @var{a} @var{b})}. @end defun @defun cl-ldiff list sublist If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to one of the cons cells of @var{list}, then this function returns a copy of the part of @var{list} up to but not including @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns the first two elements of the list @code{x}. The result is a copy; the original @var{list} is not modified. If @var{sublist} is not a sublist of @var{list}, a copy of the entire @var{list} is returned. @end defun @defun cl-copy-list list This function returns a copy of the list @var{list}. It copies dotted lists like @code{(1 2 . 3)} correctly. @end defun @defun cl-tree-equal x y @t{&key :test :test-not :key} This function compares two trees of cons cells. If @var{x} and @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are compared recursively. If neither @var{x} nor @var{y} is a cons cell, they are compared by @code{eql}, or according to the specified test. The @code{:key} function, if specified, is applied to the elements of both trees. @xref{Sequences}. @end defun @node Substitution of Expressions @section Substitution of Expressions @noindent These functions substitute elements throughout a tree of cons cells. (@xref{Sequence Functions}, for the @code{cl-substitute} function, which works on just the top-level elements of a list.) @defun cl-subst new old tree @t{&key :test :test-not :key} This function substitutes occurrences of @var{old} with @var{new} in @var{tree}, a tree of cons cells. It returns a substituted tree, which will be a copy except that it may share storage with the argument @var{tree} in parts where no substitutions occurred. The original @var{tree} is not modified. This function recurses on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s of the component cons cells. If @var{old} is itself a cons cell, then matching cells in the tree are substituted as usual without recursively substituting in that cell. Comparisons with @var{old} are done according to the specified test (@code{eql} by default). The @code{:key} function is applied to the elements of the tree but not to @var{old}. @end defun @defun cl-nsubst new old tree @t{&key :test :test-not :key} This function is like @code{cl-subst}, except that it works by destructive modification (by @code{setcar} or @code{setcdr}) rather than copying. @end defun @findex cl-subst-if @findex cl-subst-if-not @findex cl-nsubst-if @findex cl-nsubst-if-not The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and @code{cl-nsubst-if-not} functions are defined similarly. @defun cl-sublis alist tree @t{&key :test :test-not :key} This function is like @code{cl-subst}, except that it takes an association list @var{alist} of @var{old}-@var{new} pairs. Each element of the tree (after applying the @code{:key} function, if any), is compared with the @sc{car}s of @var{alist}; if it matches, it is replaced by the corresponding @sc{cdr}. @end defun @defun cl-nsublis alist tree @t{&key :test :test-not :key} This is a destructive version of @code{cl-sublis}. @end defun @node Lists as Sets @section Lists as Sets @noindent These functions perform operations on lists that represent sets of elements. @defun cl-member item list @t{&key :test :test-not :key} This function searches @var{list} for an element matching @var{item}. If a match is found, it returns the cons cell whose @sc{car} was the matching element. Otherwise, it returns @code{nil}. Elements are compared by @code{eql} by default; you can use the @code{:test}, @code{:test-not}, and @code{:key} arguments to modify this behavior. @xref{Sequences}. The standard Emacs lisp function @code{member} uses @code{equal} for comparisons; it is equivalent to @code{(cl-member @var{item} @var{list} :test 'equal)}. With no keyword arguments, @code{cl-member} is equivalent to @code{memq}. @end defun @findex cl-member-if @findex cl-member-if-not The @code{cl-member-if} and @code{cl-member-if-not} functions analogously search for elements that satisfy a given predicate. @defun cl-tailp sublist list This function returns @code{t} if @var{sublist} is a sublist of @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to any of its @sc{cdr}s. @end defun @defun cl-adjoin item list @t{&key :test :test-not :key} This function conses @var{item} onto the front of @var{list}, like @code{(cons @var{item} @var{list})}, but only if @var{item} is not already present on the list (as determined by @code{cl-member}). If a @code{:key} argument is specified, it is applied to @var{item} as well as to the elements of @var{list} during the search, on the reasoning that @var{item} is ``about'' to become part of the list. @end defun @defun cl-union list1 list2 @t{&key :test :test-not :key} This function combines two lists that represent sets of items, returning a list that represents the union of those two sets. The resulting list contains all items that appear in @var{list1} or @var{list2}, and no others. If an item appears in both @var{list1} and @var{list2} it is copied only once. If an item is duplicated in @var{list1} or @var{list2}, it is undefined whether or not that duplication will survive in the result list. The order of elements in the result list is also undefined. @end defun @defun cl-nunion list1 list2 @t{&key :test :test-not :key} This is a destructive version of @code{cl-union}; rather than copying, it tries to reuse the storage of the argument lists if possible. @end defun @defun cl-intersection list1 list2 @t{&key :test :test-not :key} This function computes the intersection of the sets represented by @var{list1} and @var{list2}. It returns the list of items that appear in both @var{list1} and @var{list2}. @end defun @defun cl-nintersection list1 list2 @t{&key :test :test-not :key} This is a destructive version of @code{cl-intersection}. It tries to reuse storage of @var{list1} rather than copying. It does @emph{not} reuse the storage of @var{list2}. @end defun @defun cl-set-difference list1 list2 @t{&key :test :test-not :key} This function computes the ``set difference'' of @var{list1} and @var{list2}, i.e., the set of elements that appear in @var{list1} but @emph{not} in @var{list2}. @end defun @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key} This is a destructive @code{cl-set-difference}, which will try to reuse @var{list1} if possible. @end defun @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key} This function computes the ``set exclusive or'' of @var{list1} and @var{list2}, i.e., the set of elements that appear in exactly one of @var{list1} and @var{list2}. @end defun @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key} This is a destructive @code{cl-set-exclusive-or}, which will try to reuse @var{list1} and @var{list2} if possible. @end defun @defun cl-subsetp list1 list2 @t{&key :test :test-not :key} This function checks whether @var{list1} represents a subset of @var{list2}, i.e., whether every element of @var{list1} also appears in @var{list2}. @end defun @node Association Lists @section Association Lists @noindent An @dfn{association list} is a list representing a mapping from one set of values to another; any list whose elements are cons cells is an association list. @defun cl-assoc item a-list @t{&key :test :test-not :key} This function searches the association list @var{a-list} for an element whose @sc{car} matches (in the sense of @code{:test}, @code{:test-not}, and @code{:key}, or by comparison with @code{eql}) a given @var{item}. It returns the matching element, if any, otherwise @code{nil}. It ignores elements of @var{a-list} that are not cons cells. (This corresponds to the behavior of @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's @code{assoc} ignores @code{nil}s but considers any other non-cons elements of @var{a-list} to be an error.) @end defun @defun cl-rassoc item a-list @t{&key :test :test-not :key} This function searches for an element whose @sc{cdr} matches @var{item}. If @var{a-list} represents a mapping, this applies the inverse of the mapping to @var{item}. @end defun @findex cl-assoc-if @findex cl-assoc-if-not @findex cl-rassoc-if @findex cl-rassoc-if-not The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if}, and @code{cl-rassoc-if-not} functions are defined similarly. Two simple functions for constructing association lists are: @defun cl-acons key value alist This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}. @end defun @defun cl-pairlis keys values &optional alist This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values}) @var{alist})}. @end defun @node Structures @chapter Structures @noindent The Common Lisp @dfn{structure} mechanism provides a general way to define data types similar to C's @code{struct} types. A structure is a Lisp object containing some number of @dfn{slots}, each of which can hold any Lisp data object. Functions are provided for accessing and setting the slots, creating or copying structure objects, and recognizing objects of a particular structure type. In true Common Lisp, each structure type is a new type distinct from all existing Lisp types. Since the underlying Emacs Lisp system provides no way to create new distinct types, this package implements structures as vectors (or lists upon request) with a special ``tag'' symbol to identify them. @defmac cl-defstruct name slots@dots{} The @code{cl-defstruct} form defines a new structure type called @var{name}, with the specified @var{slots}. (The @var{slots} may begin with a string which documents the structure type.) In the simplest case, @var{name} and each of the @var{slots} are symbols. For example, @example (cl-defstruct person name age sex) @end example @noindent defines a struct type called @code{person} that contains three slots. Given a @code{person} object @var{p}, you can access those slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})}, and @code{(person-sex @var{p})}. You can also change these slots by using @code{setf} on any of these place forms, for example: @example (cl-incf (person-age birthday-boy)) @end example You can create a new @code{person} by calling @code{make-person}, which takes keyword arguments @code{:name}, @code{:age}, and @code{:sex} to specify the initial values of these slots in the new object. (Omitting any of these arguments leaves the corresponding slot ``undefined'', according to the Common Lisp standard; in Emacs Lisp, such uninitialized slots are filled with @code{nil}.) Given a @code{person}, @code{(copy-person @var{p})} makes a new object of the same type whose slots are @code{eq} to those of @var{p}. Given any Lisp object @var{x}, @code{(person-p @var{x})} returns true if @var{x} is a @code{person}, and false otherwise. Accessors like @code{person-name} normally check their arguments (effectively using @code{person-p}) and signal an error if the argument is the wrong type. This check is affected by @code{(optimize (safety @dots{}))} declarations. Safety level 1, the default, uses a somewhat optimized check that will detect all incorrect arguments, but may use an uninformative error message (e.g., ``expected a vector'' instead of ``expected a @code{person}''). Safety level 0 omits all checks except as provided by the underlying @code{aref} call; safety levels 2 and 3 do rigorous checking that will always print a descriptive error message for incorrect inputs. @xref{Declarations}. @example (setq dave (make-person :name "Dave" :sex 'male)) @result{} [cl-struct-person "Dave" nil male] (setq other (copy-person dave)) @result{} [cl-struct-person "Dave" nil male] (eq dave other) @result{} nil (eq (person-name dave) (person-name other)) @result{} t (person-p dave) @result{} t (person-p [1 2 3 4]) @result{} nil (person-p "Bogus") @result{} nil (person-p '[cl-struct-person counterfeit person object]) @result{} t @end example In general, @var{name} is either a name symbol or a list of a name symbol followed by any number of @dfn{struct options}; each @var{slot} is either a slot symbol or a list of the form @samp{(@var{slot-name} @var{default-value} @var{slot-options}@dots{})}. The @var{default-value} is a Lisp form that is evaluated any time an instance of the structure type is created without specifying that slot's value. Common Lisp defines several slot options, but the only one implemented in this package is @code{:read-only}. A non-@code{nil} value for this option means the slot should not be @code{setf}-able; the slot's value is determined when the object is created and does not change afterward. @example (cl-defstruct person (name nil :read-only t) age (sex 'unknown)) @end example Any slot options other than @code{:read-only} are ignored. For obscure historical reasons, structure options take a different form than slot options. A structure option is either a keyword symbol, or a list beginning with a keyword symbol possibly followed by arguments. (By contrast, slot options are key-value pairs not enclosed in lists.) @example (cl-defstruct (person (:constructor create-person) (:type list) :named) name age sex) @end example The following structure options are recognized. @table @code @item :conc-name The argument is a symbol whose print name is used as the prefix for the names of slot accessor functions. The default is the name of the struct type followed by a hyphen. The option @code{(:conc-name p-)} would change this prefix to @code{p-}. Specifying @code{nil} as an argument means no prefix, so that the slot names themselves are used to name the accessor functions. @item :constructor In the simple case, this option takes one argument which is an alternate name to use for the constructor function. The default is @code{make-@var{name}}, e.g., @code{make-person}. The above example changes this to @code{create-person}. Specifying @code{nil} as an argument means that no standard constructor should be generated at all. In the full form of this option, the constructor name is followed by an arbitrary argument list. @xref{Program Structure}, for a description of the format of Common Lisp argument lists. All options, such as @code{&rest} and @code{&key}, are supported. The argument names should match the slot names; each slot is initialized from the corresponding argument. Slots whose names do not appear in the argument list are initialized based on the @var{default-value} in their slot descriptor. Also, @code{&optional} and @code{&key} arguments that don't specify defaults take their defaults from the slot descriptor. It is valid to include arguments that don't correspond to slot names; these are useful if they are referred to in the defaults for optional, keyword, or @code{&aux} arguments that @emph{do} correspond to slots. You can specify any number of full-format @code{:constructor} options on a structure. The default constructor is still generated as well unless you disable it with a simple-format @code{:constructor} option. @example (cl-defstruct (person (:constructor nil) ; no default constructor (:constructor new-person (name sex &optional (age 0))) (:constructor new-hound (&key (name "Rover") (dog-years 0) &aux (age (* 7 dog-years)) (sex 'canine)))) name age sex) @end example The first constructor here takes its arguments positionally rather than by keyword. (In official Common Lisp terminology, constructors that work By Order of Arguments instead of by keyword are called ``BOA constructors''. No, I'm not making this up.) For example, @code{(new-person "Jane" 'female)} generates a person whose slots are @code{"Jane"}, 0, and @code{female}, respectively. The second constructor takes two keyword arguments, @code{:name}, which initializes the @code{name} slot and defaults to @code{"Rover"}, and @code{:dog-years}, which does not itself correspond to a slot but which is used to initialize the @code{age} slot. The @code{sex} slot is forced to the symbol @code{canine} with no syntax for overriding it. @item :copier The argument is an alternate name for the copier function for this type. The default is @code{copy-@var{name}}. @code{nil} means not to generate a copier function. (In this implementation, all copier functions are simply synonyms for @code{copy-sequence}.) @item :predicate The argument is an alternate name for the predicate that recognizes objects of this type. The default is @code{@var{name}-p}. @code{nil} means not to generate a predicate function. (If the @code{:type} option is used without the @code{:named} option, no predicate is ever generated.) In true Common Lisp, @code{typep} is always able to recognize a structure object even if @code{:predicate} was used. In this package, @code{cl-typep} simply looks for a function called @code{@var{typename}-p}, so it will work for structure types only if they used the default predicate name. @item :include This option implements a very limited form of C++-style inheritance. The argument is the name of another structure type previously created with @code{cl-defstruct}. The effect is to cause the new structure type to inherit all of the included structure's slots (plus, of course, any new slots described by this struct's slot descriptors). The new structure is considered a ``specialization'' of the included one. In fact, the predicate and slot accessors for the included type will also accept objects of the new type. If there are extra arguments to the @code{:include} option after the included-structure name, these options are treated as replacement slot descriptors for slots in the included structure, possibly with modified default values. Borrowing an example from Steele: @example (cl-defstruct person name (age 0) sex) @result{} person (cl-defstruct (astronaut (:include person (age 45))) helmet-size (favorite-beverage 'tang)) @result{} astronaut (setq joe (make-person :name "Joe")) @result{} [cl-struct-person "Joe" 0 nil] (setq buzz (make-astronaut :name "Buzz")) @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang] (list (person-p joe) (person-p buzz)) @result{} (t t) (list (astronaut-p joe) (astronaut-p buzz)) @result{} (nil t) (person-name buzz) @result{} "Buzz" (astronaut-name joe) @result{} error: "astronaut-name accessing a non-astronaut" @end example Thus, if @code{astronaut} is a specialization of @code{person}, then every @code{astronaut} is also a @code{person} (but not the other way around). Every @code{astronaut} includes all the slots of a @code{person}, plus extra slots that are specific to astronauts. Operations that work on people (like @code{person-name}) work on astronauts just like other people. @item :print-function In full Common Lisp, this option allows you to specify a function that is called to print an instance of the structure type. The Emacs Lisp system offers no hooks into the Lisp printer which would allow for such a feature, so this package simply ignores @code{:print-function}. @item :type The argument should be one of the symbols @code{vector} or @code{list}. This tells which underlying Lisp data type should be used to implement the new structure type. Records are used by default, but @code{(:type vector)} will cause structure objects to be stored as vectors and @code{(:type list)} lists instead. The record and vector representations for structure objects have the advantage that all structure slots can be accessed quickly, although creating them are a bit slower in Emacs Lisp. Lists are easier to create, but take a relatively long time accessing the later slots. @item :named This option, which takes no arguments, causes a characteristic ``tag'' symbol to be stored at the front of the structure object. Using @code{:type} without also using @code{:named} will result in a structure type stored as plain vectors or lists with no identifying features. The default, if you don't specify @code{:type} explicitly, is to use records, which are always tagged. Therefore, @code{:named} is only useful in conjunction with @code{:type}. @example (cl-defstruct (person1) name age sex) (cl-defstruct (person2 (:type list) :named) name age sex) (cl-defstruct (person3 (:type list)) name age sex) (cl-defstruct (person4 (:type vector)) name age sex) (setq p1 (make-person1)) @result{} #s(person1 nil nil nil) (setq p2 (make-person2)) @result{} (person2 nil nil nil) (setq p3 (make-person3)) @result{} (nil nil nil) (setq p4 (make-person4)) @result{} [nil nil nil] (person1-p p1) @result{} t (person2-p p2) @result{} t (person3-p p3) @result{} error: function person3-p undefined @end example Since unnamed structures don't have tags, @code{cl-defstruct} is not able to make a useful predicate for recognizing them. Also, accessors like @code{person3-name} will be generated but they will not be able to do any type checking. The @code{person3-name} function, for example, will simply be a synonym for @code{car} in this case. By contrast, @code{person2-name} is able to verify that its argument is indeed a @code{person2} object before proceeding. @item :initial-offset The argument must be a nonnegative integer. It specifies a number of slots to be left ``empty'' at the front of the structure. If the structure is named, the tag appears at the specified position in the list or vector; otherwise, the first slot appears at that position. Earlier positions are filled with @code{nil} by the constructors and ignored otherwise. If the type @code{:include}s another type, then @code{:initial-offset} specifies a number of slots to be skipped between the last slot of the included type and the first new slot. @end table @end defmac Except as noted, the @code{cl-defstruct} facility of this package is entirely compatible with that of Common Lisp. The @code{cl-defstruct} package also provides a few structure introspection functions. @defun cl-struct-sequence-type struct-type This function returns the underlying data structure for @code{struct-type}, which is a symbol. It returns @code{record}, @code{vector} or @code{list}, or @code{nil} if @code{struct-type} is not actually a structure. @end defun @defun cl-struct-slot-info struct-type This function returns a list of slot descriptors for structure @code{struct-type}. Each entry in the list is @code{(name . opts)}, where @code{name} is the name of the slot and @code{opts} is the list of slot options given to @code{defstruct}. Dummy entries represent the slots used for the struct name and that are skipped to implement @code{:initial-offset}. @end defun @defun cl-struct-slot-offset struct-type slot-name Return the offset of slot @code{slot-name} in @code{struct-type}. The returned zero-based slot index is relative to the start of the structure data type and is adjusted for any structure name and :initial-offset slots. Signal error if struct @code{struct-type} does not contain @code{slot-name}. @end defun @defun cl-struct-slot-value struct-type slot-name inst Return the value of slot @code{slot-name} in @code{inst} of @code{struct-type}. @code{struct} and @code{slot-name} are symbols. @code{inst} is a structure instance. This routine is also a @code{setf} place. Can signal the same errors as @code{cl-struct-slot-offset}. @end defun @node Assertions @chapter Assertions and Errors @noindent This section describes two macros that test @dfn{assertions}, i.e., conditions which must be true if the program is operating correctly. Assertions never add to the behavior of a Lisp program; they simply make ``sanity checks'' to make sure everything is as it should be. If the optimization property @code{speed} has been set to 3, and @code{safety} is less than 3, then the byte-compiler will optimize away the following assertions. Because assertions might be optimized away, it is a bad idea for them to include side-effects. @defmac cl-assert test-form [show-args string args@dots{}] This form verifies that @var{test-form} is true (i.e., evaluates to a non-@code{nil} value). If so, it returns @code{nil}. If the test is not satisfied, @code{cl-assert} signals an error. A default error message will be supplied which includes @var{test-form}. You can specify a different error message by including a @var{string} argument plus optional extra arguments. Those arguments are simply passed to @code{error} to signal the error. If the optional second argument @var{show-args} is @code{t} instead of @code{nil}, then the error message (with or without @var{string}) will also include all non-constant arguments of the top-level @var{form}. For example: @example (cl-assert (> x 10) t "x is too small: %d") @end example This usage of @var{show-args} is an extension to Common Lisp. In true Common Lisp, the second argument gives a list of @var{places} which can be @code{setf}'d by the user before continuing from the error. Since Emacs Lisp does not support continuable errors, it makes no sense to specify @var{places}. @end defmac @defmac cl-check-type form type [string] This form verifies that @var{form} evaluates to a value of type @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type} signals a @code{wrong-type-argument} error. The default error message lists the erroneous value along with @var{type} and @var{form} themselves. If @var{string} is specified, it is included in the error message in place of @var{type}. For example: @example (cl-check-type x (integer 1 *) "a positive integer") @end example @xref{Type Predicates}, for a description of the type specifiers that may be used for @var{type}. Note that in Common Lisp, the first argument to @code{check-type} must be a @var{place} suitable for use by @code{setf}, because @code{check-type} signals a continuable error that allows the user to modify @var{place}. @end defmac @node Efficiency Concerns @appendix Efficiency Concerns @appendixsec Macros @noindent Many of the advanced features of this package, such as @code{cl-defun}, @code{cl-loop}, etc., are implemented as Lisp macros. In byte-compiled code, these complex notations will be expanded into equivalent Lisp code which is simple and efficient. For example, the form @example (cl-incf i n) @end example @noindent is expanded at compile-time to the Lisp form @example (setq i (+ i n)) @end example @noindent which is the most efficient ways of doing this operation in Lisp. Thus, there is no performance penalty for using the more readable @code{cl-incf} form in your compiled code. @emph{Interpreted} code, on the other hand, must expand these macros every time they are executed. For this reason it is strongly recommended that code making heavy use of macros be compiled. A loop using @code{cl-incf} a hundred times will execute considerably faster if compiled, and will also garbage-collect less because the macro expansion will not have to be generated, used, and thrown away a hundred times. You can find out how a macro expands by using the @code{cl-prettyexpand} function. @defun cl-prettyexpand form &optional full This function takes a single Lisp form as an argument and inserts a nicely formatted copy of it in the current buffer (which must be in Lisp mode so that indentation works properly). It also expands all Lisp macros that appear in the form. The easiest way to use this function is to go to the @file{*scratch*} buffer and type, say, @example (cl-prettyexpand '(cl-loop for x below 10 collect x)) @end example @noindent and type @kbd{C-x C-e} immediately after the closing parenthesis; an expansion similar to: @example (cl-block nil (let* ((x 0) (G1004 nil)) (while (< x 10) (setq G1004 (cons x G1004)) (setq x (+ x 1))) (nreverse G1004))) @end example @noindent will be inserted into the buffer. (The @code{cl-block} macro is expanded differently in the interpreter and compiler, so @code{cl-prettyexpand} just leaves it alone. The temporary variable @code{G1004} was created by @code{cl-gensym}.) If the optional argument @var{full} is true, then @emph{all} macros are expanded, including @code{cl-block}, @code{cl-eval-when}, and compiler macros. Expansion is done as if @var{form} were a top-level form in a file being compiled. @c FIXME none of these examples are still applicable. @ignore For example, @example (cl-prettyexpand '(cl-pushnew 'x list)) @print{} (setq list (cl-adjoin 'x list)) (cl-prettyexpand '(cl-pushnew 'x list) t) @print{} (setq list (if (memq 'x list) list (cons 'x list))) (cl-prettyexpand '(caddr (cl-member 'a list)) t) @print{} (car (cdr (cdr (memq 'a list)))) @end example @end ignore Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all have built-in compiler macros to optimize them in common cases. @end defun @appendixsec Error Checking @noindent Common Lisp compliance has in general not been sacrificed for the sake of efficiency. A few exceptions have been made for cases where substantial gains were possible at the expense of marginal incompatibility. The Common Lisp standard (as embodied in Steele's book) uses the phrase ``it is an error if'' to indicate a situation that is not supposed to arise in complying programs; implementations are strongly encouraged but not required to signal an error in these situations. This package sometimes omits such error checking in the interest of compactness and efficiency. For example, @code{cl-do} variable specifiers are supposed to be lists of one, two, or three forms; extra forms are ignored by this package rather than signaling a syntax error. Functions taking keyword arguments will accept an odd number of arguments, treating the trailing keyword as if it were followed by the value @code{nil}. Argument lists (as processed by @code{cl-defun} and friends) @emph{are} checked rigorously except for the minor point just mentioned; in particular, keyword arguments are checked for validity, and @code{&allow-other-keys} and @code{:allow-other-keys} are fully implemented. Keyword validity checking is slightly time consuming (though not too bad in byte-compiled code); you can use @code{&allow-other-keys} to omit this check. Functions defined in this package such as @code{cl-find} and @code{cl-member} do check their keyword arguments for validity. @appendixsec Compiler Optimizations @noindent Changing the value of @code{byte-optimize} from the default @code{t} is highly discouraged; many of the Common Lisp macros emit code that can be improved by optimization. In particular, @code{cl-block}s (whether explicit or implicit in constructs like @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the byte-compiler removes @code{cl-block}s that are not actually referenced by @code{cl-return} or @code{cl-return-from} inside the block. @node Common Lisp Compatibility @appendix Common Lisp Compatibility @noindent The following is a list of some of the most important incompatibilities between this package and Common Lisp as documented in Steele (2nd edition). The word @code{cl-defun} is required instead of @code{defun} in order to use extended Common Lisp argument lists in a function. Likewise, @code{cl-defmacro} and @code{cl-function} are versions of those forms which understand full-featured argument lists. The @code{&whole} keyword does not work in @code{cl-defmacro} argument lists (except inside recursive argument lists). The @code{equal} predicate does not distinguish between IEEE floating-point plus and minus zero. The @code{cl-equalp} predicate has several differences with Common Lisp; @pxref{Predicates}. The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols} with no @var{obarray} argument. In Common Lisp, this form would iterate over all symbols in all packages. Since Emacs obarrays are not a first-class package mechanism, there is no way for @code{cl-do-all-symbols} to locate any but the default obarray. The @code{cl-loop} macro is complete except that @code{loop-finish} and type specifiers are unimplemented. The multiple-value return facility treats lists as multiple values, since Emacs Lisp cannot support multiple return values directly. The macros will be compatible with Common Lisp if @code{cl-values} or @code{cl-values-list} is always used to return to a @code{cl-multiple-value-bind} or other multiple-value receiver; if @code{cl-values} is used without @code{cl-multiple-value-@dots{}} or vice-versa the effect will be different from Common Lisp. Many Common Lisp declarations are ignored, and others match the Common Lisp standard in concept but not in detail. For example, local @code{special} declarations, which are purely advisory in Emacs Lisp, do not rigorously obey the scoping rules set down in Steele's book. The variable @code{cl--gensym-counter} starts out with zero. The @code{cl-defstruct} facility is compatible, except that the @code{:type} slot option is ignored. The second argument of @code{cl-check-type} is treated differently. @node Porting Common Lisp @appendix Porting Common Lisp @noindent This package is meant to be used as an extension to Emacs Lisp, not as an Emacs implementation of true Common Lisp. Some of the remaining differences between Emacs Lisp and Common Lisp make it difficult to port large Common Lisp applications to Emacs. For one, some of the features in this package are not fully compliant with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there are also quite a few features that this package does not provide at all. Here are some major omissions that you will want to watch out for when bringing Common Lisp code into Emacs. @itemize @bullet @item Case-insensitivity. Symbols in Common Lisp are case-insensitive by default. Some programs refer to a function or variable as @code{foo} in one place and @code{Foo} or @code{FOO} in another. Emacs Lisp will treat these as three distinct symbols. Some Common Lisp code is written entirely in upper case. While Emacs is happy to let the program's own functions and variables use this convention, calls to Lisp builtins like @code{if} and @code{defun} will have to be changed to lower case. @item Lexical scoping. In Common Lisp, function arguments and @code{let} bindings apply only to references physically within their bodies (or within macro expansions in their bodies). Traditionally, Emacs Lisp uses @dfn{dynamic scoping} wherein a binding to a variable is visible even inside functions called from the body. @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}. Lexical binding is available since Emacs 24.1, so be sure to set @code{lexical-binding} to @code{t} if you need to emulate this aspect of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}. Here is an example of a Common Lisp code fragment that would fail in Emacs Lisp if @code{lexical-binding} were set to @code{nil}: @example (defun map-odd-elements (func list) (loop for x in list for flag = t then (not flag) collect (if flag x (funcall func x)))) (defun add-odd-elements (list x) (map-odd-elements (lambda (a) (+ a x)) list)) @end example @noindent With lexical binding, the two functions' usages of @code{x} are completely independent. With dynamic binding, the binding to @code{x} made by @code{add-odd-elements} will have been hidden by the binding in @code{map-odd-elements} by the time the @code{(+ a x)} function is called. Internally, this package uses lexical binding so that such problems do not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete @code{lexical-let} form that emulates a Common Lisp-style lexical binding when dynamic binding is in use. @item Reader macros. Common Lisp includes a second type of macro that works at the level of individual characters. For example, Common Lisp implements the quote notation by a reader macro called @code{'}, whereas Emacs Lisp's parser just treats quote as a special case. Some Lisp packages use reader macros to create special syntaxes for themselves, which the Emacs parser is incapable of reading. @item Other syntactic features. Common Lisp provides a number of notations beginning with @code{#} that the Emacs Lisp parser won't understand. For example, @samp{#| @dots{} |#} is an alternate comment notation, and @samp{#+lucid (foo)} tells the parser to ignore the @code{(foo)} except in Lucid Common Lisp. @item Packages. In Common Lisp, symbols are divided into @dfn{packages}. Symbols that are Lisp built-ins are typically stored in one package; symbols that are vendor extensions are put in another, and each application program would have a package for its own symbols. Certain symbols are ``exported'' by a package and others are internal; certain packages ``use'' or import the exported symbols of other packages. To access symbols that would not normally be visible due to this importing and exporting, Common Lisp provides a syntax like @code{package:symbol} or @code{package::symbol}. Emacs Lisp has a single namespace for all interned symbols, and then uses a naming convention of putting a prefix like @code{cl-} in front of the name. Some Emacs packages adopt the Common Lisp-like convention of using @code{cl:} or @code{cl::} as the prefix. However, the Emacs parser does not understand colons and just treats them as part of the symbol name. Thus, while @code{mapcar} and @code{lisp:mapcar} may refer to the same symbol in Common Lisp, they are totally distinct in Emacs Lisp. Common Lisp programs that refer to a symbol by the full name sometimes and the short name other times will not port cleanly to Emacs. Emacs Lisp does have a concept of ``obarrays'', which are package-like collections of symbols, but this feature is not strong enough to be used as a true package mechanism. @item The @code{format} function is quite different between Common Lisp and Emacs Lisp. It takes an additional ``destination'' argument before the format string. A destination of @code{nil} means to format to a string as in Emacs Lisp; a destination of @code{t} means to write to the terminal (similar to @code{message} in Emacs). Also, format control strings are utterly different; @code{~} is used instead of @code{%} to introduce format codes, and the set of available codes is much richer. There are no notations like @code{\n} for string literals; instead, @code{format} is used with the ``newline'' format code, @code{~%}. More advanced formatting codes provide such features as paragraph filling, case conversion, and even loops and conditionals. While it would have been possible to implement most of Common Lisp @code{format} in this package (under the name @code{cl-format}, of course), it was not deemed worthwhile. It would have required a huge amount of code to implement even a decent subset of @code{format}, yet the functionality it would provide over Emacs Lisp's @code{format} would rarely be useful. @item Vector constants use square brackets in Emacs Lisp, but @code{#(a b c)} notation in Common Lisp. To further complicate matters, Emacs has its own @code{#(} notation for something entirely different---strings with properties. @item Characters are distinct from integers in Common Lisp. The notation for character constants is also different: @code{#\A} in Common Lisp where Emacs Lisp uses @code{?A}. Also, @code{string=} and @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is case-insensitive in Common Lisp. @item Data types. Some Common Lisp data types do not exist in Emacs Lisp. Rational numbers and complex numbers are not present, nor are large integers (all integers are ``fixnums''). All arrays are one-dimensional. There are no readtables or pathnames; streams are a set of existing data types rather than a new data type of their own. Hash tables, random-states, and packages (obarrays) are built from Lisp vectors or lists rather than being distinct types. @item The Common Lisp Object System (CLOS) is not implemented, nor is the Common Lisp Condition System. However, the EIEIO package (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some CLOS functionality. @item Common Lisp features that are completely redundant with Emacs Lisp features of a different name generally have not been implemented. For example, Common Lisp writes @code{defconstant} where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list} takes its arguments in different ways in the two Lisps but does exactly the same thing, so this package has not bothered to implement a Common Lisp-style @code{make-list}. @item A few more notable Common Lisp features not included in this package: @code{compiler-let}, @code{prog}, @code{ldb/dpb}, @code{cerror}. @item Recursion. While recursion works in Emacs Lisp just like it does in Common Lisp, various details of the Emacs Lisp system and compiler make recursion much less efficient than it is in most Lisps. Some schools of thought prefer to use recursion in Lisp over other techniques; they would sum a list of numbers using something like @example (defun sum-list (list) (if list (+ (car list) (sum-list (cdr list))) 0)) @end example @noindent where a more iteratively-minded programmer might write one of these forms: @example (let ((total 0)) (dolist (x my-list) (incf total x)) total) (loop for x in my-list sum x) @end example While this would be mainly a stylistic choice in most Common Lisps, in Emacs Lisp you should be aware that the iterative forms are much faster than recursion. Also, Lisp programmers will want to note that the current Emacs Lisp compiler does not optimize tail recursion. @end itemize @node Obsolete Features @appendix Obsolete Features This section describes some features of the package that are obsolete and should not be used in new code. They are either only provided by the old @file{cl.el} entry point, not by the newer @file{cl-lib.el}; or where versions with a @samp{cl-} prefix do exist they do not behave in exactly the same way. @menu * Obsolete Lexical Binding:: An approximation of lexical binding. * Obsolete Macros:: Obsolete macros. * Obsolete Setf Customization:: Obsolete ways to customize setf. @end menu @node Obsolete Lexical Binding @appendixsec Obsolete Lexical Binding The following macros are extensions to Common Lisp, where all bindings are lexical unless declared otherwise. These features are likewise obsolete since the introduction of true lexical binding in Emacs 24.1. @defmac lexical-let (bindings@dots{}) forms@dots{} This form is exactly like @code{let} except that the bindings it establishes are purely lexical. @end defmac @c FIXME remove this and refer to elisp manual. @c Maybe merge some stuff from here to there? @noindent Lexical bindings are similar to local variables in a language like C: Only the code physically within the body of the @code{lexical-let} (after macro expansion) may refer to the bound variables. @example (setq a 5) (defun foo (b) (+ a b)) (let ((a 2)) (foo a)) @result{} 4 (lexical-let ((a 2)) (foo a)) @result{} 7 @end example @noindent In this example, a regular @code{let} binding of @code{a} actually makes a temporary change to the global variable @code{a}, so @code{foo} is able to see the binding of @code{a} to 2. But @code{lexical-let} actually creates a distinct local variable @code{a} for use within its body, without any effect on the global variable of the same name. The most important use of lexical bindings is to create @dfn{closures}. A closure is a function object that refers to an outside lexical variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}). For example: @example (defun make-adder (n) (lexical-let ((n n)) (function (lambda (m) (+ n m))))) (setq add17 (make-adder 17)) (funcall add17 4) @result{} 21 @end example @noindent The call @code{(make-adder 17)} returns a function object which adds 17 to its argument. If @code{let} had been used instead of @code{lexical-let}, the function object would have referred to the global @code{n}, which would have been bound to 17 only during the call to @code{make-adder} itself. @example (defun make-counter () (lexical-let ((n 0)) (cl-function (lambda (&optional (m 1)) (cl-incf n m))))) (setq count-1 (make-counter)) (funcall count-1 3) @result{} 3 (funcall count-1 14) @result{} 17 (setq count-2 (make-counter)) (funcall count-2 5) @result{} 5 (funcall count-1 2) @result{} 19 (funcall count-2) @result{} 6 @end example @noindent Here we see that each call to @code{make-counter} creates a distinct local variable @code{n}, which serves as a private counter for the function object that is returned. Closed-over lexical variables persist until the last reference to them goes away, just like all other Lisp objects. For example, @code{count-2} refers to a function object which refers to an instance of the variable @code{n}; this is the only reference to that variable, so after @code{(setq count-2 nil)} the garbage collector would be able to delete this instance of @code{n}. Of course, if a @code{lexical-let} does not actually create any closures, then the lexical variables are free as soon as the @code{lexical-let} returns. Many closures are used only during the extent of the bindings they refer to; these are known as ``downward funargs'' in Lisp parlance. When a closure is used in this way, regular Emacs Lisp dynamic bindings suffice and will be more efficient than @code{lexical-let} closures: @example (defun add-to-list (x list) (mapcar (lambda (y) (+ x y))) list) (add-to-list 7 '(1 2 5)) @result{} (8 9 12) @end example @noindent Since this lambda is only used while @code{x} is still bound, it is not necessary to make a true closure out of it. You can use @code{defun} or @code{flet} inside a @code{lexical-let} to create a named closure. If several closures are created in the body of a single @code{lexical-let}, they all close over the same instance of the lexical variable. @defmac lexical-let* (bindings@dots{}) forms@dots{} This form is just like @code{lexical-let}, except that the bindings are made sequentially in the manner of @code{let*}. @end defmac @node Obsolete Macros @appendixsec Obsolete Macros The following macros are obsolete, and are replaced by versions with a @samp{cl-} prefix that do not behave in exactly the same way. Consequently, the @file{cl.el} versions are not simply aliases to the @file{cl-lib.el} versions. @defmac flet (bindings@dots{}) forms@dots{} This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}), which behaves the same way as Common Lisp's @code{flet}. This @code{flet} takes the same arguments as @code{cl-flet}, but does not behave in precisely the same way. While @code{flet} in Common Lisp establishes a lexical function binding, this @code{flet} makes a dynamic binding (it dates from a time before Emacs had lexical binding). The result is that @code{flet} affects indirect calls to a function as well as calls directly inside the @code{flet} form itself. This will even work on Emacs primitives, although note that some calls to primitive functions internal to Emacs are made without going through the symbol's function cell, and so will not be affected by @code{flet}. For example, @example (flet ((message (&rest args) (push args saved-msgs))) (do-something)) @end example This code attempts to replace the built-in function @code{message} with a function that simply saves the messages in a list rather than displaying them. The original definition of @code{message} will be restored after @code{do-something} exits. This code will work fine on messages generated by other Lisp code, but messages generated directly inside Emacs will not be caught since they make direct C-language calls to the message routines rather than going through the Lisp @code{message} function. For those cases where the dynamic scoping of @code{flet} is desired, @code{cl-flet} is clearly not a substitute. The most direct replacement would be instead to use @code{cl-letf} to temporarily rebind @code{(symbol-function '@var{fun})}. But in most cases, a better substitute is to use advice, such as: @example (defvar my-fun-advice-enable nil) (add-advice '@var{fun} :around (lambda (orig &rest args) (if my-fun-advice-enable (do-something) (apply orig args)))) @end example so that you can then replace the @code{flet} with a simple dynamically scoped binding of @code{my-fun-advice-enable}. @c Bug#411. Note that many primitives (e.g., @code{+}) have special byte-compile handling. Attempts to redefine such functions using @code{flet}, @code{cl-letf}, or advice will fail when byte-compiled. @c Or cl-flet. @c In such cases, use @code{labels} instead. @end defmac @defmac labels (bindings@dots{}) forms@dots{} This macro is replaced by @code{cl-labels} (@pxref{Function Bindings}), which behaves the same way as Common Lisp's @code{labels}. This @code{labels} takes the same arguments as @code{cl-labels}, but does not behave in precisely the same way. This version of @code{labels} uses the obsolete @code{lexical-let} form (@pxref{Obsolete Lexical Binding}), rather than the true lexical binding that @code{cl-labels} uses. @end defmac @node Obsolete Setf Customization @appendixsec Obsolete Ways to Customize Setf Common Lisp defines three macros, @code{define-modify-macro}, @code{defsetf}, and @code{define-setf-method}, that allow the user to extend generalized variables in various ways. In Emacs, these are obsolete, replaced by various features of @file{gv.el} in Emacs 24.3. @xref{Adding Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}. @defmac define-modify-macro name arglist function [doc-string] This macro defines a ``read-modify-write'' macro similar to @code{cl-incf} and @code{cl-decf}. You can replace this macro with @code{gv-letplace}. The macro @var{name} is defined to take a @var{place} argument followed by additional arguments described by @var{arglist}. The call @example (@var{name} @var{place} @var{args}@dots{}) @end example @noindent will be expanded to @example (cl-callf @var{func} @var{place} @var{args}@dots{}) @end example @noindent which in turn is roughly equivalent to @example (setf @var{place} (@var{func} @var{place} @var{args}@dots{})) @end example For example: @example (define-modify-macro incf (&optional (n 1)) +) (define-modify-macro concatf (&rest args) concat) @end example Note that @code{&key} is not allowed in @var{arglist}, but @code{&rest} is sufficient to pass keywords on to the function. Most of the modify macros defined by Common Lisp do not exactly follow the pattern of @code{define-modify-macro}. For example, @code{push} takes its arguments in the wrong order, and @code{pop} is completely irregular. The above @code{incf} example could be written using @code{gv-letplace} as: @example (defmacro incf (place &optional n) (gv-letplace (getter setter) place (macroexp-let2 nil v (or n 1) (funcall setter `(+ ,v ,getter))))) @end example @ignore (defmacro concatf (place &rest args) (gv-letplace (getter setter) place (macroexp-let2 nil v (mapconcat 'identity args "") (funcall setter `(concat ,getter ,v))))) @end ignore @end defmac @defmac defsetf access-fn update-fn This is the simpler of two @code{defsetf} forms, and is replaced by @code{gv-define-simple-setter}. With @var{access-fn} the name of a function that accesses a place, this declares @var{update-fn} to be the corresponding store function. From now on, @example (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value}) @end example @noindent will be expanded to @example (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value}) @end example @noindent The @var{update-fn} is required to be either a true function, or a macro that evaluates its arguments in a function-like way. Also, the @var{update-fn} is expected to return @var{value} as its result. Otherwise, the above expansion would not obey the rules for the way @code{setf} is supposed to behave. As a special (non-Common-Lisp) extension, a third argument of @code{t} to @code{defsetf} says that the return value of @code{update-fn} is not suitable, so that the above @code{setf} should be expanded to something more like @example (let ((temp @var{value})) (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp) temp) @end example Some examples are: @example (defsetf car setcar) (defsetf buffer-name rename-buffer t) @end example These translate directly to @code{gv-define-simple-setter}: @example (gv-define-simple-setter car setcar) (gv-define-simple-setter buffer-name rename-buffer t) @end example @end defmac @defmac defsetf access-fn arglist (store-var) forms@dots{} This is the second, more complex, form of @code{defsetf}. It can be replaced by @code{gv-define-setter}. This form of @code{defsetf} is rather like @code{defmacro} except for the additional @var{store-var} argument. The @var{forms} should return a Lisp form that stores the value of @var{store-var} into the generalized variable formed by a call to @var{access-fn} with arguments described by @var{arglist}. The @var{forms} may begin with a string which documents the @code{setf} method (analogous to the doc string that appears at the front of a function). For example, the simple form of @code{defsetf} is shorthand for @example (defsetf @var{access-fn} (&rest args) (store) (append '(@var{update-fn}) args (list store))) @end example The Lisp form that is returned can access the arguments from @var{arglist} and @var{store-var} in an unrestricted fashion; macros like @code{cl-incf} that invoke this setf-method will insert temporary variables as needed to make sure the apparent order of evaluation is preserved. Another standard example: @example (defsetf nth (n x) (store) `(setcar (nthcdr ,n ,x) ,store)) @end example You could write this using @code{gv-define-setter} as: @example (gv-define-setter nth (store n x) `(setcar (nthcdr ,n ,x) ,store)) @end example @end defmac @defmac define-setf-method access-fn arglist forms@dots{} This is the most general way to create new place forms. You can replace this by @code{gv-define-setter} or @code{gv-define-expander}. When a @code{setf} to @var{access-fn} with arguments described by @var{arglist} is expanded, the @var{forms} are evaluated and must return a list of five items: @enumerate @item A list of @dfn{temporary variables}. @item A list of @dfn{value forms} corresponding to the temporary variables above. The temporary variables will be bound to these value forms as the first step of any operation on the generalized variable. @item A list of exactly one @dfn{store variable} (generally obtained from a call to @code{gensym}). @item A Lisp form that stores the contents of the store variable into the generalized variable, assuming the temporaries have been bound as described above. @item A Lisp form that accesses the contents of the generalized variable, assuming the temporaries have been bound. @end enumerate This is exactly like the Common Lisp macro of the same name, except that the method returns a list of five values rather than the five values themselves, since Emacs Lisp does not support Common Lisp's notion of multiple return values. (Note that the @code{setf} implementation provided by @file{gv.el} does not use this five item format. Its use here is only for backwards compatibility.) Once again, the @var{forms} may begin with a documentation string. A setf-method should be maximally conservative with regard to temporary variables. In the setf-methods generated by @code{defsetf}, the second return value is simply the list of arguments in the place form, and the first return value is a list of a corresponding number of temporary variables generated @c FIXME I don't think this is true anymore. by @code{cl-gensym}. Macros like @code{cl-incf} that use this setf-method will optimize away most temporaries that turn out to be unnecessary, so there is little reason for the setf-method itself to optimize. @end defmac @c Removed in Emacs 24.3, not possible to make a compatible replacement. @ignore @defun get-setf-method place &optional env This function returns the setf-method for @var{place}, by invoking the definition previously recorded by @code{defsetf} or @code{define-setf-method}. The result is a list of five values as described above. You can use this function to build your own @code{cl-incf}-like modify macros. The argument @var{env} specifies the ``environment'' to be passed on to @code{macroexpand} if @code{get-setf-method} should need to expand a macro in @var{place}. It should come from an @code{&environment} argument to the macro or setf-method that called @code{get-setf-method}. @end defun @end ignore @node GNU Free Documentation License @appendix GNU Free Documentation License @include doclicense.texi @node Function Index @unnumbered Function Index @printindex fn @node Variable Index @unnumbered Variable Index @printindex vr @node Concept Index @unnumbered Concept Index @printindex cp @bye