1 \input texinfo @c -*-texinfo-*-
2 @setfilename ../../info/cl
3 @settitle Common Lisp Extensions
7 This file documents the GNU Emacs Common Lisp emulation package.
9 Copyright @copyright{} 1993, 2001--2013 Free Software Foundation, Inc.
12 Permission is granted to copy, distribute and/or modify this document
13 under the terms of the GNU Free Documentation License, Version 1.3 or
14 any later version published by the Free Software Foundation; with no
15 Invariant Sections, with the Front-Cover texts being ``A GNU Manual'',
16 and with the Back-Cover Texts as in (a) below. A copy of the license
17 is included in the section entitled ``GNU Free Documentation License''.
19 (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
20 modify this GNU manual.''
24 @dircategory Emacs lisp libraries
26 * CL: (cl). Partial Common Lisp support for Emacs Lisp.
33 @center @titlefont{Common Lisp Extensions}
35 @center For GNU Emacs Lisp
37 @center as distributed with Emacs @value{EMACSVER}
39 @center Dave Gillespie
40 @center daveg@@synaptics.com
42 @vskip 0pt plus 1filll
50 @top GNU Emacs Common Lisp Emulation
56 * Overview:: Basics, usage, organization, naming conventions.
57 * Program Structure:: Arglists, @code{cl-eval-when}.
58 * Predicates:: Type predicates and equality predicates.
59 * Control Structure:: Assignment, conditionals, blocks, looping.
60 * Macros:: Destructuring, compiler macros.
61 * Declarations:: @code{cl-proclaim}, @code{cl-declare}, etc.
62 * Symbols:: Property lists, creating symbols.
63 * Numbers:: Predicates, functions, random numbers.
64 * Sequences:: Mapping, functions, searching, sorting.
65 * Lists:: Functions, substitution, sets, associations.
66 * Structures:: @code{cl-defstruct}.
67 * Assertions:: Assertions and type checking.
70 * Efficiency Concerns:: Hints and techniques.
71 * Common Lisp Compatibility:: All known differences with Steele.
72 * Porting Common Lisp:: Hints for porting Common Lisp code.
73 * Obsolete Features:: Obsolete features.
74 * GNU Free Documentation License:: The license for this documentation.
77 * Function Index:: An entry for each documented function.
78 * Variable Index:: An entry for each documented variable.
85 This document describes a set of Emacs Lisp facilities borrowed from
86 Common Lisp. All the facilities are described here in detail. While
87 this document does not assume any prior knowledge of Common Lisp, it
88 does assume a basic familiarity with Emacs Lisp.
90 Common Lisp is a huge language, and Common Lisp systems tend to be
91 massive and extremely complex. Emacs Lisp, by contrast, is rather
92 minimalist in the choice of Lisp features it offers the programmer.
93 As Emacs Lisp programmers have grown in number, and the applications
94 they write have grown more ambitious, it has become clear that Emacs
95 Lisp could benefit from many of the conveniences of Common Lisp.
97 The @dfn{CL} package adds a number of Common Lisp functions and
98 control structures to Emacs Lisp. While not a 100% complete
99 implementation of Common Lisp, it adds enough functionality
100 to make Emacs Lisp programming significantly more convenient.
102 Some Common Lisp features have been omitted from this package
107 Some features are too complex or bulky relative to their benefit
108 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine
109 examples of this group. (The separate package EIEIO implements
110 a subset of CLOS functionality. @xref{Top, , Introduction, eieio, EIEIO}.)
113 Other features cannot be implemented without modification to the
114 Emacs Lisp interpreter itself, such as multiple return values,
115 case-insensitive symbols, and complex numbers.
116 This package generally makes no attempt to emulate these features.
120 This package was originally written by Dave Gillespie,
121 @file{daveg@@synaptics.com}, as a total rewrite of an earlier 1986
122 @file{cl.el} package by Cesar Quiroz. Care has been taken to ensure
123 that each function is defined efficiently, concisely, and with minimal
124 impact on the rest of the Emacs environment. Stefan Monnier added the
125 file @file{cl-lib.el} and rationalized the namespace for Emacs 24.3.
128 * Usage:: How to use this package.
129 * Organization:: The package's component files.
130 * Naming Conventions:: Notes on function names.
137 This package is distributed with Emacs, so there is no need
138 to install any additional files in order to start using it. Lisp code
139 that uses features from this package should simply include at
147 You may wish to add such a statement to your init file, if you
148 make frequent use of features from this package.
151 @section Organization
154 The Common Lisp package is organized into four main files:
158 This is the main file, which contains basic functions
159 and information about the package. This file is relatively compact.
162 This file contains the larger, more complex or unusual functions.
163 It is kept separate so that packages which only want to use Common
164 Lisp fundamentals like the @code{cl-incf} function won't need to pay
165 the overhead of loading the more advanced functions.
168 This file contains most of the advanced functions for operating
169 on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}.
172 This file contains the features that are macros instead of functions.
173 Macros expand when the caller is compiled, not when it is run, so the
174 macros generally only need to be present when the byte-compiler is
175 running (or when the macros are used in uncompiled code). Most of the
176 macros of this package are isolated in @file{cl-macs.el} so that they
177 won't take up memory unless you are compiling.
180 The file @file{cl-lib.el} includes all necessary @code{autoload}
181 commands for the functions and macros in the other three files.
182 All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el}
183 will take care of pulling in the other files when they are
186 There is another file, @file{cl.el}, which was the main entry point to
187 this package prior to Emacs 24.3. Nowadays, it is replaced by
188 @file{cl-lib.el}. The two provide the same features (in most cases),
189 but use different function names (in fact, @file{cl.el} mainly just
190 defines aliases to the @file{cl-lib.el} definitions). Where
191 @file{cl-lib.el} defines a function called, for example,
192 @code{cl-incf}, @file{cl.el} uses the same name but without the
193 @samp{cl-} prefix, e.g., @code{incf} in this example. There are a few
194 exceptions to this. First, functions such as @code{cl-defun} where
195 the unprefixed version was already used for a standard Emacs Lisp
196 function. In such cases, the @file{cl.el} version adds a @samp{*}
197 suffix, e.g., @code{defun*}. Second, there are some obsolete features
198 that are only implemented in @file{cl.el}, not in @file{cl-lib.el},
199 because they are replaced by other standard Emacs Lisp features.
200 Finally, in a very few cases the old @file{cl.el} versions do not
201 behave in exactly the same way as the @file{cl-lib.el} versions.
202 @xref{Obsolete Features}.
203 @c There is also cl-mapc, which was called cl-mapc even before cl-lib.el.
204 @c But not autoloaded, so maybe not much used?
206 Since the old @file{cl.el} does not use a clean namespace, Emacs has a
207 policy that packages distributed with Emacs must not load @code{cl} at
208 run time. (It is ok for them to load @code{cl} at @emph{compile}
209 time, with @code{eval-when-compile}, and use the macros it provides.)
210 There is no such restriction on the use of @code{cl-lib}. New code
211 should use @code{cl-lib} rather than @code{cl}.
213 There is one more file, @file{cl-compat.el}, which defines some
214 routines from the older Quiroz @file{cl.el} package that are not otherwise
215 present in the new package. This file is obsolete and should not be
218 @node Naming Conventions
219 @section Naming Conventions
222 Except where noted, all functions defined by this package have the
223 same calling conventions as their Common Lisp counterparts, and
224 names that are those of Common Lisp plus a @samp{cl-} prefix.
226 Internal function and variable names in the package are prefixed
227 by @code{cl--}. Here is a complete list of functions prefixed by
228 @code{cl-} that were @emph{not} taken from Common Lisp:
231 cl-callf cl-callf2 cl-defsubst
235 @c This is not uninteresting I suppose, but is of zero practical relevance
236 @c to the user, and seems like a hostage to changing implementation details.
237 The following simple functions and macros are defined in @file{cl-lib.el};
238 they do not cause other components like @file{cl-extra} to be loaded.
241 cl-evenp cl-oddp cl-minusp
242 cl-plusp cl-endp cl-subst
243 cl-copy-list cl-list* cl-ldiff
244 cl-rest cl-decf [1] cl-incf [1]
245 cl-acons cl-adjoin [2] cl-pairlis
246 cl-pushnew [1,2] cl-declaim cl-proclaim
247 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
252 [1] Only when @var{place} is a plain variable name.
255 [2] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified,
256 and @code{:key} is not used.
259 [3] Only for one sequence argument or two list arguments.
261 @node Program Structure
262 @chapter Program Structure
265 This section describes features of this package that have to
266 do with programs as a whole: advanced argument lists for functions,
267 and the @code{cl-eval-when} construct.
270 * Argument Lists:: @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}.
271 * Time of Evaluation:: The @code{cl-eval-when} construct.
275 @section Argument Lists
280 Emacs Lisp's notation for argument lists of functions is a subset of
281 the Common Lisp notation. As well as the familiar @code{&optional}
282 and @code{&rest} markers, Common Lisp allows you to specify default
283 values for optional arguments, and it provides the additional markers
284 @code{&key} and @code{&aux}.
286 Since argument parsing is built-in to Emacs, there is no way for
287 this package to implement Common Lisp argument lists seamlessly.
288 Instead, this package defines alternates for several Lisp forms
289 which you must use if you need Common Lisp argument lists.
291 @defmac cl-defun name arglist body@dots{}
292 This form is identical to the regular @code{defun} form, except
293 that @var{arglist} is allowed to be a full Common Lisp argument
294 list. Also, the function body is enclosed in an implicit block
295 called @var{name}; @pxref{Blocks and Exits}.
298 @defmac cl-defsubst name arglist body@dots{}
299 This is just like @code{cl-defun}, except that the function that
300 is defined is automatically proclaimed @code{inline}, i.e.,
301 calls to it may be expanded into in-line code by the byte compiler.
302 This is analogous to the @code{defsubst} form;
303 @code{cl-defsubst} uses a different method (compiler macros) which
304 works in all versions of Emacs, and also generates somewhat more
305 @c For some examples,
306 @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html
307 efficient inline expansions. In particular, @code{cl-defsubst}
308 arranges for the processing of keyword arguments, default values,
309 etc., to be done at compile-time whenever possible.
312 @defmac cl-defmacro name arglist body@dots{}
313 This is identical to the regular @code{defmacro} form,
314 except that @var{arglist} is allowed to be a full Common Lisp
315 argument list. The @code{&environment} keyword is supported as
316 described in Steele's book @cite{Common Lisp, the Language}.
317 The @code{&whole} keyword is supported only
318 within destructured lists (see below); top-level @code{&whole}
319 cannot be implemented with the current Emacs Lisp interpreter.
320 The macro expander body is enclosed in an implicit block called
324 @defmac cl-function symbol-or-lambda
325 This is identical to the regular @code{function} form,
326 except that if the argument is a @code{lambda} form then that
327 form may use a full Common Lisp argument list.
330 Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
331 in this package that include @var{arglist}s in their syntax allow
332 full Common Lisp argument lists.
334 Note that it is @emph{not} necessary to use @code{cl-defun} in
335 order to have access to most CL features in your function.
336 These features are always present; @code{cl-defun}'s only
337 difference from @code{defun} is its more flexible argument
338 lists and its implicit block.
340 The full form of a Common Lisp argument list is
344 &optional (@var{var} @var{initform} @var{svar})@dots{}
346 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{}
347 &aux (@var{var} @var{initform})@dots{})
350 Each of the five argument list sections is optional. The @var{svar},
351 @var{initform}, and @var{keyword} parts are optional; if they are
352 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.
354 The first section consists of zero or more @dfn{required} arguments.
355 These arguments must always be specified in a call to the function;
356 there is no difference between Emacs Lisp and Common Lisp as far as
357 required arguments are concerned.
359 The second section consists of @dfn{optional} arguments. These
360 arguments may be specified in the function call; if they are not,
361 @var{initform} specifies the default value used for the argument.
362 (No @var{initform} means to use @code{nil} as the default.) The
363 @var{initform} is evaluated with the bindings for the preceding
364 arguments already established; @code{(a &optional (b (1+ a)))}
365 matches one or two arguments, with the second argument defaulting
366 to one plus the first argument. If the @var{svar} is specified,
367 it is an auxiliary variable which is bound to @code{t} if the optional
368 argument was specified, or to @code{nil} if the argument was omitted.
369 If you don't use an @var{svar}, then there will be no way for your
370 function to tell whether it was called with no argument, or with
371 the default value passed explicitly as an argument.
373 The third section consists of a single @dfn{rest} argument. If
374 more arguments were passed to the function than are accounted for
375 by the required and optional arguments, those extra arguments are
376 collected into a list and bound to the ``rest'' argument variable.
377 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
378 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
379 macro contexts; this package accepts it all the time.
381 The fourth section consists of @dfn{keyword} arguments. These
382 are optional arguments which are specified by name rather than
383 positionally in the argument list. For example,
386 (cl-defun foo (a &optional b &key c d (e 17)))
390 defines a function which may be called with one, two, or more
391 arguments. The first two arguments are bound to @code{a} and
392 @code{b} in the usual way. The remaining arguments must be
393 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
394 by the value to be bound to the corresponding argument variable.
395 (Symbols whose names begin with a colon are called @dfn{keywords},
396 and they are self-quoting in the same way as @code{nil} and
399 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
400 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword
401 appears more than once in the function call, the first occurrence
402 takes precedence over the later ones. Note that it is not possible
403 to specify keyword arguments without specifying the optional
404 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
405 @code{b} to the keyword @code{:c}, then signal an error because
406 @code{2} is not a valid keyword.
408 You can also explicitly specify the keyword argument; it need not be
409 simply the variable name prefixed with a colon. For example,
412 (cl-defun bar (&key (a 1) ((baz b) 4)))
417 specifies a keyword @code{:a} that sets the variable @code{a} with
418 default value 1, as well as a keyword @code{baz} that sets the
419 variable @code{b} with default value 4. In this case, because
420 @code{baz} is not self-quoting, you must quote it explicitly in the
421 function call, like this:
427 Ordinarily, it is an error to pass an unrecognized keyword to
428 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask
429 Lisp to ignore unrecognized keywords, either by adding the
430 marker @code{&allow-other-keys} after the keyword section
431 of the argument list, or by specifying an @code{:allow-other-keys}
432 argument in the call whose value is non-@code{nil}. If the
433 function uses both @code{&rest} and @code{&key} at the same time,
434 the ``rest'' argument is bound to the keyword list as it appears
435 in the call. For example:
438 (cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
439 (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
440 (if need (error "Thing not found"))))
444 This function takes a @code{:need} keyword argument, but also
445 accepts other keyword arguments which are passed on to the
446 @code{cl-member} function. @code{allow-other-keys} is used to
447 keep both @code{find-thing} and @code{cl-member} from complaining
448 about each others' keywords in the arguments.
450 The fifth section of the argument list consists of @dfn{auxiliary
451 variables}. These are not really arguments at all, but simply
452 variables which are bound to @code{nil} or to the specified
453 @var{initforms} during execution of the function. There is no
454 difference between the following two functions, except for a
455 matter of stylistic taste:
458 (cl-defun foo (a b &aux (c (+ a b)) d)
466 @cindex destructuring, in argument list
467 Argument lists support @dfn{destructuring}. In Common Lisp,
468 destructuring is only allowed with @code{defmacro}; this package
469 allows it with @code{cl-defun} and other argument lists as well.
470 In destructuring, any argument variable (@var{var} in the above
471 example) can be replaced by a list of variables, or more generally,
472 a recursive argument list. The corresponding argument value must
473 be a list whose elements match this recursive argument list.
477 (cl-defmacro dolist ((var listform &optional resultform)
482 This says that the first argument of @code{dolist} must be a list
483 of two or three items; if there are other arguments as well as this
484 list, they are stored in @code{body}. All features allowed in
485 regular argument lists are allowed in these recursive argument lists.
486 In addition, the clause @samp{&whole @var{var}} is allowed at the
487 front of a recursive argument list. It binds @var{var} to the
488 whole list being matched; thus @code{(&whole all a b)} matches
489 a list of two things, with @code{a} bound to the first thing,
490 @code{b} bound to the second thing, and @code{all} bound to the
491 list itself. (Common Lisp allows @code{&whole} in top-level
492 @code{defmacro} argument lists as well, but Emacs Lisp does not
495 One last feature of destructuring is that the argument list may be
496 dotted, so that the argument list @code{(a b . c)} is functionally
497 equivalent to @code{(a b &rest c)}.
499 If the optimization quality @code{safety} is set to 0
500 (@pxref{Declarations}), error checking for wrong number of
501 arguments and invalid keyword arguments is disabled. By default,
502 argument lists are rigorously checked.
504 @node Time of Evaluation
505 @section Time of Evaluation
508 Normally, the byte-compiler does not actually execute the forms in
509 a file it compiles. For example, if a file contains @code{(setq foo t)},
510 the act of compiling it will not actually set @code{foo} to @code{t}.
511 This is true even if the @code{setq} was a top-level form (i.e., not
512 enclosed in a @code{defun} or other form). Sometimes, though, you
513 would like to have certain top-level forms evaluated at compile-time.
514 For example, the compiler effectively evaluates @code{defmacro} forms
515 at compile-time so that later parts of the file can refer to the
516 macros that are defined.
518 @defmac cl-eval-when (situations@dots{}) forms@dots{}
519 This form controls when the body @var{forms} are evaluated.
520 The @var{situations} list may contain any set of the symbols
521 @code{compile}, @code{load}, and @code{eval} (or their long-winded
522 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
523 and @code{:execute}).
525 The @code{cl-eval-when} form is handled differently depending on
526 whether or not it is being compiled as a top-level form.
527 Specifically, it gets special treatment if it is being compiled
528 by a command such as @code{byte-compile-file} which compiles files
529 or buffers of code, and it appears either literally at the
530 top level of the file or inside a top-level @code{progn}.
532 For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
533 executed at compile-time if @code{compile} is in the @var{situations}
534 list, and the @var{forms} are written out to the file (to be executed
535 at load-time) if @code{load} is in the @var{situations} list.
537 For non-compiled-top-level forms, only the @code{eval} situation is
538 relevant. (This includes forms executed by the interpreter, forms
539 compiled with @code{byte-compile} rather than @code{byte-compile-file},
540 and non-top-level forms.) The @code{cl-eval-when} acts like a
541 @code{progn} if @code{eval} is specified, and like @code{nil}
542 (ignoring the body @var{forms}) if not.
544 The rules become more subtle when @code{cl-eval-when}s are nested;
545 consult Steele (second edition) for the gruesome details (and
546 some gruesome examples).
548 Some simple examples:
551 ;; Top-level forms in foo.el:
552 (cl-eval-when (compile) (setq foo1 'bar))
553 (cl-eval-when (load) (setq foo2 'bar))
554 (cl-eval-when (compile load) (setq foo3 'bar))
555 (cl-eval-when (eval) (setq foo4 'bar))
556 (cl-eval-when (eval compile) (setq foo5 'bar))
557 (cl-eval-when (eval load) (setq foo6 'bar))
558 (cl-eval-when (eval compile load) (setq foo7 'bar))
561 When @file{foo.el} is compiled, these variables will be set during
562 the compilation itself:
565 foo1 foo3 foo5 foo7 ; `compile'
568 When @file{foo.elc} is loaded, these variables will be set:
571 foo2 foo3 foo6 foo7 ; `load'
574 And if @file{foo.el} is loaded uncompiled, these variables will
578 foo4 foo5 foo6 foo7 ; `eval'
581 If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
582 then the first three would have been equivalent to @code{nil} and the
583 last four would have been equivalent to the corresponding @code{setq}s.
585 Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
586 to @code{(progn @dots{})} in all contexts. The compiler treats
587 certain top-level forms, like @code{defmacro} (sort-of) and
588 @code{require}, as if they were wrapped in @code{(cl-eval-when
589 (compile load eval) @dots{})}.
592 Emacs includes two special forms related to @code{cl-eval-when}.
593 @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}.
594 One of these, @code{eval-when-compile}, is not quite equivalent to
595 any @code{cl-eval-when} construct and is described below.
597 The other form, @code{(eval-and-compile @dots{})}, is exactly
598 equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}.
600 @defmac eval-when-compile forms@dots{}
601 The @var{forms} are evaluated at compile-time; at execution time,
602 this form acts like a quoted constant of the resulting value. Used
603 at top-level, @code{eval-when-compile} is just like @samp{eval-when
604 (compile eval)}. In other contexts, @code{eval-when-compile}
605 allows code to be evaluated once at compile-time for efficiency
608 This form is similar to the @samp{#.} syntax of true Common Lisp.
611 @defmac cl-load-time-value form
612 The @var{form} is evaluated at load-time; at execution time,
613 this form acts like a quoted constant of the resulting value.
615 Early Common Lisp had a @samp{#,} syntax that was similar to
616 this, but ANSI Common Lisp replaced it with @code{load-time-value}
617 and gave it more well-defined semantics.
619 In a compiled file, @code{cl-load-time-value} arranges for @var{form}
620 to be evaluated when the @file{.elc} file is loaded and then used
621 as if it were a quoted constant. In code compiled by
622 @code{byte-compile} rather than @code{byte-compile-file}, the
623 effect is identical to @code{eval-when-compile}. In uncompiled
624 code, both @code{eval-when-compile} and @code{cl-load-time-value}
625 act exactly like @code{progn}.
629 (insert "This function was executed on: "
630 (current-time-string)
632 (eval-when-compile (current-time-string))
633 ;; or '#.(current-time-string) in real Common Lisp
635 (cl-load-time-value (current-time-string))))
639 Byte-compiled, the above defun will result in the following code
640 (or its compiled equivalent, of course) in the @file{.elc} file:
643 (setq --temp-- (current-time-string))
645 (insert "This function was executed on: "
646 (current-time-string)
648 '"Wed Oct 31 16:32:28 2012"
658 This section describes functions for testing whether various
659 facts are true or false.
662 * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
663 * Equality Predicates:: @code{cl-equalp}.
666 @node Type Predicates
667 @section Type Predicates
669 @defun cl-typep object type
670 Check if @var{object} is of type @var{type}, where @var{type} is a
671 (quoted) type name of the sort used by Common Lisp. For example,
672 @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
675 The @var{type} argument to the above function is either a symbol
676 or a list beginning with a symbol.
680 If the type name is a symbol, Emacs appends @samp{-p} to the
681 symbol name to form the name of a predicate function for testing
682 the type. (Built-in predicates whose names end in @samp{p} rather
683 than @samp{-p} are used when appropriate.)
686 The type symbol @code{t} stands for the union of all types.
687 @code{(cl-typep @var{object} t)} is always true. Likewise, the
688 type symbol @code{nil} stands for nothing at all, and
689 @code{(cl-typep @var{object} nil)} is always false.
692 The type symbol @code{null} represents the symbol @code{nil}.
693 Thus @code{(cl-typep @var{object} 'null)} is equivalent to
694 @code{(null @var{object})}.
697 The type symbol @code{atom} represents all objects that are not cons
698 cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
699 @code{(atom @var{object})}.
702 The type symbol @code{real} is a synonym for @code{number}, and
703 @code{fixnum} is a synonym for @code{integer}.
706 The type symbols @code{character} and @code{string-char} match
707 integers in the range from 0 to 255.
710 The type list @code{(integer @var{low} @var{high})} represents all
711 integers between @var{low} and @var{high}, inclusive. Either bound
712 may be a list of a single integer to specify an exclusive limit,
713 or a @code{*} to specify no limit. The type @code{(integer * *)}
714 is thus equivalent to @code{integer}.
717 Likewise, lists beginning with @code{float}, @code{real}, or
718 @code{number} represent numbers of that type falling in a particular
722 Lists beginning with @code{and}, @code{or}, and @code{not} form
723 combinations of types. For example, @code{(or integer (float 0 *))}
724 represents all objects that are integers or non-negative floats.
727 Lists beginning with @code{member} or @code{cl-member} represent
728 objects @code{eql} to any of the following values. For example,
729 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
730 and @code{(member nil)} is equivalent to @code{null}.
733 Lists of the form @code{(satisfies @var{predicate})} represent
734 all objects for which @var{predicate} returns true when called
735 with that object as an argument.
738 The following function and macro (not technically predicates) are
739 related to @code{cl-typep}.
741 @defun cl-coerce object type
742 This function attempts to convert @var{object} to the specified
743 @var{type}. If @var{object} is already of that type as determined by
744 @code{cl-typep}, it is simply returned. Otherwise, certain types of
745 conversions will be made: If @var{type} is any sequence type
746 (@code{string}, @code{list}, etc.)@: then @var{object} will be
747 converted to that type if possible. If @var{type} is
748 @code{character}, then strings of length one and symbols with
749 one-character names can be coerced. If @var{type} is @code{float},
750 then integers can be coerced in versions of Emacs that support
751 floats. In all other circumstances, @code{cl-coerce} signals an
755 @defmac cl-deftype name arglist forms@dots{}
756 This macro defines a new type called @var{name}. It is similar
757 to @code{defmacro} in many ways; when @var{name} is encountered
758 as a type name, the body @var{forms} are evaluated and should
759 return a type specifier that is equivalent to the type. The
760 @var{arglist} is a Common Lisp argument list of the sort accepted
761 by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})}
762 is expanded by calling the expander with those arguments; the type
763 symbol @samp{@var{name}} is expanded by calling the expander with
764 no arguments. The @var{arglist} is processed the same as for
765 @code{cl-defmacro} except that optional arguments without explicit
766 defaults use @code{*} instead of @code{nil} as the ``default''
767 default. Some examples:
770 (cl-deftype null () '(satisfies null)) ; predefined
771 (cl-deftype list () '(or null cons)) ; predefined
772 (cl-deftype unsigned-byte (&optional bits)
773 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
774 (unsigned-byte 8) @equiv{} (integer 0 255)
775 (unsigned-byte) @equiv{} (integer 0 *)
776 unsigned-byte @equiv{} (integer 0 *)
780 The last example shows how the Common Lisp @code{unsigned-byte}
781 type specifier could be implemented if desired; this package does
782 not implement @code{unsigned-byte} by default.
785 The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type}
786 (@pxref{Assertions}) macros also use type names. The @code{cl-map},
787 @code{cl-concatenate}, and @code{cl-merge} functions take type-name
788 arguments to specify the type of sequence to return. @xref{Sequences}.
790 @node Equality Predicates
791 @section Equality Predicates
794 This package defines the Common Lisp predicate @code{cl-equalp}.
797 This function is a more flexible version of @code{equal}. In
798 particular, it compares strings case-insensitively, and it compares
799 numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
800 true). Vectors and conses are compared recursively. All other
801 objects are compared as if by @code{equal}.
803 This function differs from Common Lisp @code{equalp} in several
804 respects. First, Common Lisp's @code{equalp} also compares
805 @emph{characters} case-insensitively, which would be impractical
806 in this package since Emacs does not distinguish between integers
807 and characters. In keeping with the idea that strings are less
808 vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
809 not compare strings against vectors of integers.
812 Also note that the Common Lisp functions @code{member} and @code{assoc}
813 use @code{eql} to compare elements, whereas Emacs Lisp follows the
814 MacLisp tradition and uses @code{equal} for these two functions.
815 The functions @code{cl-member} and @code{cl-assoc} use @code{eql},
816 as in Common Lisp. The standard Emacs Lisp functions @code{memq} and
817 @code{assq} use @code{eq}, and the standard @code{memql} uses @code{eql}.
819 @node Control Structure
820 @chapter Control Structure
823 The features described in the following sections implement
824 various advanced control structures, including extensions to the
825 standard @code{setf} facility, and a number of looping and conditional
829 * Assignment:: The @code{cl-psetq} form.
830 * Generalized Variables:: Extensions to generalized variables.
831 * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}.
832 * Conditionals:: @code{cl-case}, @code{cl-typecase}.
833 * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}.
834 * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}.
835 * Loop Facility:: The Common Lisp @code{loop} macro.
836 * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc.
843 The @code{cl-psetq} form is just like @code{setq}, except that multiple
844 assignments are done in parallel rather than sequentially.
846 @defmac cl-psetq [symbol form]@dots{}
847 This special form (actually a macro) is used to assign to several
848 variables simultaneously. Given only one @var{symbol} and @var{form},
849 it has the same effect as @code{setq}. Given several @var{symbol}
850 and @var{form} pairs, it evaluates all the @var{form}s in advance
851 and then stores the corresponding variables afterwards.
855 (setq x (+ x y) y (* x y))
858 y ; @r{@code{y} was computed after @code{x} was set.}
861 (cl-psetq x (+ x y) y (* x y))
864 y ; @r{@code{y} was computed before @code{x} was set.}
868 The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which
869 exchanges the values of two variables. (The @code{cl-rotatef} form
870 provides an even more convenient way to swap two variables;
871 @pxref{Modify Macros}.)
873 @code{cl-psetq} always returns @code{nil}.
876 @node Generalized Variables
877 @section Generalized Variables
879 A @dfn{generalized variable} or @dfn{place form} is one of the many
880 places in Lisp memory where values can be stored. The simplest place
881 form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists,
882 elements of arrays, properties of symbols, and many other locations
883 are also places where Lisp values are stored. For basic information,
884 @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
885 This package provides several additional features related to
886 generalized variables.
889 * Setf Extensions:: Additional @code{setf} places.
890 * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc.
893 @node Setf Extensions
894 @subsection Setf Extensions
896 Several standard (e.g., @code{car}) and Emacs-specific
897 (e.g., @code{window-point}) Lisp functions are @code{setf}-able by default.
898 This package defines @code{setf} handlers for several additional functions:
902 Functions from this package:
904 cl-rest cl-subseq cl-get cl-getf
905 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
909 Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument
910 of the function must itself be a valid @var{place} form.
913 General Emacs Lisp functions:
915 buffer-file-name getenv
916 buffer-modified-p global-key-binding
917 buffer-name local-key-binding
919 buffer-substring mark-marker
920 current-buffer marker-position
921 current-case-table mouse-position
923 current-global-map point-marker
924 current-input-mode point-max
925 current-local-map point-min
926 current-window-configuration read-mouse-position
927 default-file-modes screen-height
928 documentation-property screen-width
929 face-background selected-window
930 face-background-pixmap selected-screen
931 face-font selected-frame
932 face-foreground standard-case-table
933 face-underline-p syntax-table
934 file-modes visited-file-modtime
935 frame-height window-height
936 frame-parameters window-width
937 frame-visible-p x-get-secondary-selection
938 frame-width x-get-selection
942 Most of these have directly corresponding ``set'' functions, like
943 @code{use-local-map} for @code{current-local-map}, or @code{goto-char}
944 for @code{point}. A few, like @code{point-min}, expand to longer
945 sequences of code when they are used with @code{setf}
946 (@code{(narrow-to-region x (point-max))} in this case).
949 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
950 where @var{subplace} is itself a valid generalized variable whose
951 current value is a string, and where the value stored is also a
952 string. The new string is spliced into the specified part of the
953 destination string. For example:
956 (setq a (list "hello" "world"))
957 @result{} ("hello" "world")
960 (substring (cadr a) 2 4)
962 (setf (substring (cadr a) 2 4) "o")
967 @result{} ("hello" "wood")
970 The generalized variable @code{buffer-substring}, listed above,
971 also works in this way by replacing a portion of the current buffer.
973 @c FIXME? Also `eq'? (see cl-lib.el)
975 @c Currently commented out in cl.el.
978 A call of the form @code{(apply '@var{func} @dots{})} or
979 @code{(apply (function @var{func}) @dots{})}, where @var{func}
980 is a @code{setf}-able function whose store function is ``suitable''
981 in the sense described in Steele's book; since none of the standard
982 Emacs place functions are suitable in this sense, this feature is
983 only interesting when used with places you define yourself with
984 @code{define-setf-method} or the long form of @code{defsetf}.
985 @xref{Obsolete Setf Customization}.
988 @c FIXME? Is this still true?
990 A macro call, in which case the macro is expanded and @code{setf}
991 is applied to the resulting form.
994 @c FIXME should this be in lispref? It seems self-evident.
995 @c Contrast with the cl-incf example later on.
996 @c Here it really only serves as a contrast to wrong-order.
997 The @code{setf} macro takes care to evaluate all subforms in
998 the proper left-to-right order; for example,
1001 (setf (aref vec (cl-incf i)) i)
1005 looks like it will evaluate @code{(cl-incf i)} exactly once, before the
1006 following access to @code{i}; the @code{setf} expander will insert
1007 temporary variables as necessary to ensure that it does in fact work
1008 this way no matter what setf-method is defined for @code{aref}.
1009 (In this case, @code{aset} would be used and no such steps would
1010 be necessary since @code{aset} takes its arguments in a convenient
1013 However, if the @var{place} form is a macro which explicitly
1014 evaluates its arguments in an unusual order, this unusual order
1015 will be preserved. Adapting an example from Steele, given
1018 (defmacro wrong-order (x y) (list 'aref y x))
1022 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
1023 evaluate @var{b} first, then @var{a}, just as in an actual call
1024 to @code{wrong-order}.
1027 @subsection Modify Macros
1030 This package defines a number of macros that operate on generalized
1031 variables. Many are interesting and useful even when the @var{place}
1032 is just a variable name.
1034 @defmac cl-psetf [place form]@dots{}
1035 This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
1036 When several @var{place}s and @var{form}s are involved, the
1037 assignments take place in parallel rather than sequentially.
1038 Specifically, all subforms are evaluated from left to right, then
1039 all the assignments are done (in an undefined order).
1042 @defmac cl-incf place &optional x
1043 This macro increments the number stored in @var{place} by one, or
1044 by @var{x} if specified. The incremented value is returned. For
1045 example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and
1046 @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
1048 As with @code{setf}, care is taken to preserve the ``apparent'' order
1049 of evaluation. For example,
1052 (cl-incf (aref vec (cl-incf i)))
1056 appears to increment @code{i} once, then increment the element of
1057 @code{vec} addressed by @code{i}; this is indeed exactly what it
1058 does, which means the above form is @emph{not} equivalent to the
1059 ``obvious'' expansion,
1062 (setf (aref vec (cl-incf i))
1063 (1+ (aref vec (cl-incf i)))) ; wrong!
1067 but rather to something more like
1070 (let ((temp (cl-incf i)))
1071 (setf (aref vec temp) (1+ (aref vec temp))))
1075 Again, all of this is taken care of automatically by @code{cl-incf} and
1076 the other generalized-variable macros.
1078 As a more Emacs-specific example of @code{cl-incf}, the expression
1079 @code{(cl-incf (point) @var{n})} is essentially equivalent to
1080 @code{(forward-char @var{n})}.
1083 @defmac cl-decf place &optional x
1084 This macro decrements the number stored in @var{place} by one, or
1085 by @var{x} if specified.
1088 @defmac cl-pushnew x place @t{&key :test :test-not :key}
1089 This macro inserts @var{x} at the front of the list stored in
1090 @var{place}, but only if @var{x} was not @code{eql} to any
1091 existing element of the list. The optional keyword arguments
1092 are interpreted in the same way as for @code{cl-adjoin}.
1093 @xref{Lists as Sets}.
1096 @defmac cl-shiftf place@dots{} newvalue
1097 This macro shifts the @var{place}s left by one, shifting in the
1098 value of @var{newvalue} (which may be any Lisp expression, not just
1099 a generalized variable), and returning the value shifted out of
1100 the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c}
1101 @var{d})} is equivalent to
1106 (cl-psetf @var{a} @var{b}
1112 except that the subforms of @var{a}, @var{b}, and @var{c} are actually
1113 evaluated only once each and in the apparent order.
1116 @defmac cl-rotatef place@dots{}
1117 This macro rotates the @var{place}s left by one in circular fashion.
1118 Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to
1121 (cl-psetf @var{a} @var{b}
1128 except for the evaluation of subforms. @code{cl-rotatef} always
1129 returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})}
1130 conveniently exchanges @var{a} and @var{b}.
1133 The following macros were invented for this package; they have no
1134 analogues in Common Lisp.
1136 @defmac cl-letf (bindings@dots{}) forms@dots{}
1137 This macro is analogous to @code{let}, but for generalized variables
1138 rather than just symbols. Each @var{binding} should be of the form
1139 @code{(@var{place} @var{value})}; the original contents of the
1140 @var{place}s are saved, the @var{value}s are stored in them, and
1141 then the body @var{form}s are executed. Afterwards, the @var{places}
1142 are set back to their original saved contents. This cleanup happens
1143 even if the @var{form}s exit irregularly due to a @code{throw} or an
1149 (cl-letf (((point) (point-min))
1155 moves point in the current buffer to the beginning of the buffer,
1156 and also binds @code{a} to 17 (as if by a normal @code{let}, since
1157 @code{a} is just a regular variable). After the body exits, @code{a}
1158 is set back to its original value and point is moved back to its
1161 Note that @code{cl-letf} on @code{(point)} is not quite like a
1162 @code{save-excursion}, as the latter effectively saves a marker
1163 which tracks insertions and deletions in the buffer. Actually,
1164 a @code{cl-letf} of @code{(point-marker)} is much closer to this
1165 behavior. (@code{point} and @code{point-marker} are equivalent
1166 as @code{setf} places; each will accept either an integer or a
1167 marker as the stored value.)
1169 Since generalized variables look like lists, @code{let}'s shorthand
1170 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
1171 be ambiguous in @code{cl-letf} and is not allowed.
1173 However, a @var{binding} specifier may be a one-element list
1174 @samp{(@var{place})}, which is similar to @samp{(@var{place}
1175 @var{place})}. In other words, the @var{place} is not disturbed
1176 on entry to the body, and the only effect of the @code{cl-letf} is
1177 to restore the original value of @var{place} afterwards.
1178 @c I suspect this may no longer be true; either way it's
1179 @c implementation detail and so not essential to document.
1181 (The redundant access-and-store suggested by the @code{(@var{place}
1182 @var{place})} example does not actually occur.)
1185 Note that in this case, and in fact almost every case, @var{place}
1186 must have a well-defined value outside the @code{cl-letf} body.
1187 There is essentially only one exception to this, which is @var{place}
1188 a plain variable with a specified @var{value} (such as @code{(a 17)}
1189 in the above example).
1190 @c See http://debbugs.gnu.org/12758
1191 @c Some or all of this was true for cl.el, but not for cl-lib.el.
1193 The only exceptions are plain variables and calls to
1194 @code{symbol-value} and @code{symbol-function}. If the symbol is not
1195 bound on entry, it is simply made unbound by @code{makunbound} or
1196 @code{fmakunbound} on exit.
1200 @defmac cl-letf* (bindings@dots{}) forms@dots{}
1201 This macro is to @code{cl-letf} what @code{let*} is to @code{let}:
1202 It does the bindings in sequential rather than parallel order.
1205 @defmac cl-callf @var{function} @var{place} @var{args}@dots{}
1206 This is the ``generic'' modify macro. It calls @var{function},
1207 which should be an unquoted function name, macro name, or lambda.
1208 It passes @var{place} and @var{args} as arguments, and assigns the
1209 result back to @var{place}. For example, @code{(cl-incf @var{place}
1210 @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}.
1214 (cl-callf abs my-number)
1215 (cl-callf concat (buffer-name) "<" (number-to-string n) ">")
1216 (cl-callf cl-union happy-people (list joe bob) :test 'same-person)
1219 Note again that @code{cl-callf} is an extension to standard Common Lisp.
1222 @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{}
1223 This macro is like @code{cl-callf}, except that @var{place} is
1224 the @emph{second} argument of @var{function} rather than the
1225 first. For example, @code{(push @var{x} @var{place})} is
1226 equivalent to @code{(cl-callf2 cons @var{x} @var{place})}.
1229 The @code{cl-callf} and @code{cl-callf2} macros serve as building
1230 blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}.
1231 The @code{cl-letf} and @code{cl-letf*} macros are used in the processing
1232 of symbol macros; @pxref{Macro Bindings}.
1235 @node Variable Bindings
1236 @section Variable Bindings
1239 These Lisp forms make bindings to variables and function names,
1240 analogous to Lisp's built-in @code{let} form.
1242 @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which
1243 are also related to variable bindings.
1246 * Dynamic Bindings:: The @code{cl-progv} form.
1247 * Function Bindings:: @code{cl-flet} and @code{cl-labels}.
1248 * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}.
1251 @node Dynamic Bindings
1252 @subsection Dynamic Bindings
1255 The standard @code{let} form binds variables whose names are known
1256 at compile-time. The @code{cl-progv} form provides an easy way to
1257 bind variables whose names are computed at run-time.
1259 @defmac cl-progv symbols values forms@dots{}
1260 This form establishes @code{let}-style variable bindings on a
1261 set of variables computed at run-time. The expressions
1262 @var{symbols} and @var{values} are evaluated, and must return lists
1263 of symbols and values, respectively. The symbols are bound to the
1264 corresponding values for the duration of the body @var{form}s.
1265 If @var{values} is shorter than @var{symbols}, the last few symbols
1266 are bound to @code{nil}.
1267 If @var{symbols} is shorter than @var{values}, the excess values
1271 @node Function Bindings
1272 @subsection Function Bindings
1275 These forms make @code{let}-like bindings to functions instead
1278 @defmac cl-flet (bindings@dots{}) forms@dots{}
1279 This form establishes @code{let}-style bindings on the function
1280 cells of symbols rather than on the value cells. Each @var{binding}
1281 must be a list of the form @samp{(@var{name} @var{arglist}
1282 @var{forms}@dots{})}, which defines a function exactly as if
1283 it were a @code{cl-defun} form. The function @var{name} is defined
1284 accordingly for the duration of the body of the @code{cl-flet}; then
1285 the old function definition, or lack thereof, is restored.
1287 You can use @code{cl-flet} to disable or modify the behavior of
1288 functions (including Emacs primitives) in a temporary, localized fashion.
1289 (Compare this with the idea of advising functions.
1290 @xref{Advising Functions,,,elisp,GNU Emacs Lisp Reference Manual}.)
1292 The bindings are lexical in scope. This means that all references to
1293 the named functions must appear physically within the body of the
1294 @code{cl-flet} form.
1296 Functions defined by @code{cl-flet} may use the full Common Lisp
1297 argument notation supported by @code{cl-defun}; also, the function
1298 body is enclosed in an implicit block as if by @code{cl-defun}.
1299 @xref{Program Structure}.
1301 Note that the @file{cl.el} version of this macro behaves slightly
1302 differently. In particular, its binding is dynamic rather than
1303 lexical. @xref{Obsolete Macros}.
1306 @defmac cl-labels (bindings@dots{}) forms@dots{}
1307 The @code{cl-labels} form is like @code{cl-flet}, except that
1308 the function bindings can be recursive. The scoping is lexical,
1309 but you can only capture functions in closures if
1310 @code{lexical-binding} is @code{t}.
1311 @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and
1312 @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
1314 Lexical scoping means that all references to the named
1315 functions must appear physically within the body of the
1316 @code{cl-labels} form. References may appear both in the body
1317 @var{forms} of @code{cl-labels} itself, and in the bodies of
1318 the functions themselves. Thus, @code{cl-labels} can define
1319 local recursive functions, or mutually-recursive sets of functions.
1321 A ``reference'' to a function name is either a call to that
1322 function, or a use of its name quoted by @code{quote} or
1323 @code{function} to be passed on to, say, @code{mapcar}.
1325 Note that the @file{cl.el} version of this macro behaves slightly
1326 differently. @xref{Obsolete Macros}.
1329 @node Macro Bindings
1330 @subsection Macro Bindings
1333 These forms create local macros and ``symbol macros''.
1335 @defmac cl-macrolet (bindings@dots{}) forms@dots{}
1336 This form is analogous to @code{cl-flet}, but for macros instead of
1337 functions. Each @var{binding} is a list of the same form as the
1338 arguments to @code{cl-defmacro} (i.e., a macro name, argument list,
1339 and macro-expander forms). The macro is defined accordingly for
1340 use within the body of the @code{cl-macrolet}.
1342 Because of the nature of macros, @code{cl-macrolet} is always lexically
1343 scoped. The @code{cl-macrolet} binding will
1344 affect only calls that appear physically within the body
1345 @var{forms}, possibly after expansion of other macros in the
1349 @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{}
1350 This form creates @dfn{symbol macros}, which are macros that look
1351 like variable references rather than function calls. Each
1352 @var{binding} is a list @samp{(@var{var} @var{expansion})};
1353 any reference to @var{var} within the body @var{forms} is
1354 replaced by @var{expansion}.
1358 (cl-symbol-macrolet ((foo (car bar)))
1364 A @code{setq} of a symbol macro is treated the same as a @code{setf}.
1365 I.e., @code{(setq foo 4)} in the above would be equivalent to
1366 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
1368 Likewise, a @code{let} or @code{let*} binding a symbol macro is
1369 treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true
1370 Common Lisp, where the rules of lexical scoping cause a @code{let}
1371 binding to shadow a @code{symbol-macrolet} binding. In this package,
1372 such shadowing does not occur, even when @code{lexical-binding} is
1373 @c See http://debbugs.gnu.org/12119
1374 @code{t}. (This behavior predates the addition of lexical binding to
1375 Emacs Lisp, and may change in future to respect @code{lexical-binding}.)
1376 At present in this package, only @code{lexical-let} and
1377 @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete
1380 There is no analogue of @code{defmacro} for symbol macros; all symbol
1381 macros are local. A typical use of @code{cl-symbol-macrolet} is in the
1382 expansion of another macro:
1385 (cl-defmacro my-dolist ((x list) &rest body)
1386 (let ((var (cl-gensym)))
1387 (list 'cl-loop 'for var 'on list 'do
1388 (cl-list* 'cl-symbol-macrolet
1389 (list (list x (list 'car var)))
1392 (setq mylist '(1 2 3 4))
1393 (my-dolist (x mylist) (cl-incf x))
1399 In this example, the @code{my-dolist} macro is similar to @code{dolist}
1400 (@pxref{Iteration}) except that the variable @code{x} becomes a true
1401 reference onto the elements of the list. The @code{my-dolist} call
1402 shown here expands to
1405 (cl-loop for G1234 on mylist do
1406 (cl-symbol-macrolet ((x (car G1234)))
1411 which in turn expands to
1414 (cl-loop for G1234 on mylist do (cl-incf (car G1234)))
1417 @xref{Loop Facility}, for a description of the @code{cl-loop} macro.
1418 This package defines a nonstandard @code{in-ref} loop clause that
1419 works much like @code{my-dolist}.
1423 @section Conditionals
1426 These conditional forms augment Emacs Lisp's simple @code{if},
1427 @code{and}, @code{or}, and @code{cond} forms.
1429 @defmac cl-case keyform clause@dots{}
1430 This macro evaluates @var{keyform}, then compares it with the key
1431 values listed in the various @var{clause}s. Whichever clause matches
1432 the key is executed; comparison is done by @code{eql}. If no clause
1433 matches, the @code{cl-case} form returns @code{nil}. The clauses are
1437 (@var{keylist} @var{body-forms}@dots{})
1441 where @var{keylist} is a list of key values. If there is exactly
1442 one value, and it is not a cons cell or the symbol @code{nil} or
1443 @code{t}, then it can be used by itself as a @var{keylist} without
1444 being enclosed in a list. All key values in the @code{cl-case} form
1445 must be distinct. The final clauses may use @code{t} in place of
1446 a @var{keylist} to indicate a default clause that should be taken
1447 if none of the other clauses match. (The symbol @code{otherwise}
1448 is also recognized in place of @code{t}. To make a clause that
1449 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise},
1450 enclose the symbol in a list.)
1452 For example, this expression reads a keystroke, then does one of
1453 four things depending on whether it is an @samp{a}, a @samp{b},
1454 a @key{RET} or @kbd{C-j}, or anything else.
1457 (cl-case (read-char)
1460 ((?\r ?\n) (do-ret-thing))
1461 (t (do-other-thing)))
1465 @defmac cl-ecase keyform clause@dots{}
1466 This macro is just like @code{cl-case}, except that if the key does
1467 not match any of the clauses, an error is signaled rather than
1468 simply returning @code{nil}.
1471 @defmac cl-typecase keyform clause@dots{}
1472 This macro is a version of @code{cl-case} that checks for types
1473 rather than values. Each @var{clause} is of the form
1474 @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates},
1475 for a description of type specifiers. For example,
1479 (integer (munch-integer x))
1480 (float (munch-float x))
1481 (string (munch-integer (string-to-int x)))
1482 (t (munch-anything x)))
1485 The type specifier @code{t} matches any type of object; the word
1486 @code{otherwise} is also allowed. To make one clause match any of
1487 several types, use an @code{(or @dots{})} type specifier.
1490 @defmac cl-etypecase keyform clause@dots{}
1491 This macro is just like @code{cl-typecase}, except that if the key does
1492 not match any of the clauses, an error is signaled rather than
1493 simply returning @code{nil}.
1496 @node Blocks and Exits
1497 @section Blocks and Exits
1501 Common Lisp @dfn{blocks} provide a non-local exit mechanism very
1502 similar to @code{catch} and @code{throw}, with lexical scoping.
1503 This package actually implements @code{cl-block}
1504 in terms of @code{catch}; however, the lexical scoping allows the
1505 byte-compiler to omit the costly @code{catch} step if the
1506 body of the block does not actually @code{cl-return-from} the block.
1508 @defmac cl-block name forms@dots{}
1509 The @var{forms} are evaluated as if by a @code{progn}. However,
1510 if any of the @var{forms} execute @code{(cl-return-from @var{name})},
1511 they will jump out and return directly from the @code{cl-block} form.
1512 The @code{cl-block} returns the result of the last @var{form} unless
1513 a @code{cl-return-from} occurs.
1515 The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to
1516 the @code{catch}/@code{throw} mechanism. The main differences are
1517 that block @var{name}s are unevaluated symbols, rather than forms
1518 (such as quoted symbols) that evaluate to a tag at run-time; and
1519 also that blocks are always lexically scoped.
1520 In a dynamically scoped @code{catch}, functions called from the
1521 @code{catch} body can also @code{throw} to the @code{catch}. This
1522 is not an option for @code{cl-block}, where
1523 the @code{cl-return-from} referring to a block name must appear
1524 physically within the @var{forms} that make up the body of the block.
1525 They may not appear within other called functions, although they may
1526 appear within macro expansions or @code{lambda}s in the body. Block
1527 names and @code{catch} names form independent name-spaces.
1529 In true Common Lisp, @code{defun} and @code{defmacro} surround
1530 the function or expander bodies with implicit blocks with the
1531 same name as the function or macro. This does not occur in Emacs
1532 Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro}
1533 forms, which do create the implicit block.
1535 The Common Lisp looping constructs defined by this package,
1536 such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks
1537 just as in Common Lisp.
1539 Because they are implemented in terms of Emacs Lisp's @code{catch}
1540 and @code{throw}, blocks have the same overhead as actual
1541 @code{catch} constructs (roughly two function calls). However,
1542 the byte compiler will optimize away the @code{catch}
1544 not in fact contain any @code{cl-return} or @code{cl-return-from} calls
1545 that jump to it. This means that @code{cl-do} loops and @code{cl-defun}
1546 functions that don't use @code{cl-return} don't pay the overhead to
1550 @defmac cl-return-from name [result]
1551 This macro returns from the block named @var{name}, which must be
1552 an (unevaluated) symbol. If a @var{result} form is specified, it
1553 is evaluated to produce the result returned from the @code{block}.
1554 Otherwise, @code{nil} is returned.
1557 @defmac cl-return [result]
1558 This macro is exactly like @code{(cl-return-from nil @var{result})}.
1559 Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose
1560 themselves in @code{nil} blocks.
1567 The macros described here provide more sophisticated, high-level
1568 looping constructs to complement Emacs Lisp's basic loop forms
1569 (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}).
1571 @defmac cl-loop forms@dots{}
1572 This package supports both the simple, old-style meaning of
1573 @code{loop} and the extremely powerful and flexible feature known as
1574 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced
1575 facility is discussed in the following section; @pxref{Loop Facility}.
1576 The simple form of @code{loop} is described here.
1578 If @code{cl-loop} is followed by zero or more Lisp expressions,
1579 then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite
1580 loop executing the expressions over and over. The loop is
1581 enclosed in an implicit @code{nil} block. Thus,
1584 (cl-loop (foo) (if (no-more) (return 72)) (bar))
1588 is exactly equivalent to
1591 (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar)))
1594 If any of the expressions are plain symbols, the loop is instead
1595 interpreted as a Loop Macro specification as described later.
1596 (This is not a restriction in practice, since a plain symbol
1597 in the above notation would simply access and throw away the
1598 value of a variable.)
1601 @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1602 This macro creates a general iterative loop. Each @var{spec} is
1606 (@var{var} [@var{init} [@var{step}]])
1609 The loop works as follows: First, each @var{var} is bound to the
1610 associated @var{init} value as if by a @code{let} form. Then, in
1611 each iteration of the loop, the @var{end-test} is evaluated; if
1612 true, the loop is finished. Otherwise, the body @var{forms} are
1613 evaluated, then each @var{var} is set to the associated @var{step}
1614 expression (as if by a @code{cl-psetq} form) and the next iteration
1615 begins. Once the @var{end-test} becomes true, the @var{result}
1616 forms are evaluated (with the @var{var}s still bound to their
1617 values) to produce the result returned by @code{cl-do}.
1619 The entire @code{cl-do} loop is enclosed in an implicit @code{nil}
1620 block, so that you can use @code{(cl-return)} to break out of the
1623 If there are no @var{result} forms, the loop returns @code{nil}.
1624 If a given @var{var} has no @var{step} form, it is bound to its
1625 @var{init} value but not otherwise modified during the @code{cl-do}
1626 loop (unless the code explicitly modifies it); this case is just
1627 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})}
1628 around the loop. If @var{init} is also omitted it defaults to
1629 @code{nil}, and in this case a plain @samp{@var{var}} can be used
1630 in place of @samp{(@var{var})}, again following the analogy with
1633 This example (from Steele) illustrates a loop that applies the
1634 function @code{f} to successive pairs of values from the lists
1635 @code{foo} and @code{bar}; it is equivalent to the call
1636 @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body
1637 @var{forms} at all, performing all its work as side effects of
1638 the rest of the loop.
1641 (cl-do ((x foo (cdr x))
1643 (z nil (cons (f (car x) (car y)) z)))
1644 ((or (null x) (null y))
1649 @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1650 This is to @code{cl-do} what @code{let*} is to @code{let}. In
1651 particular, the initial values are bound as if by @code{let*}
1652 rather than @code{let}, and the steps are assigned as if by
1653 @code{setq} rather than @code{cl-psetq}.
1655 Here is another way to write the above loop:
1658 (cl-do* ((xp foo (cdr xp))
1660 (x (car xp) (car xp))
1661 (y (car yp) (car yp))
1663 ((or (null xp) (null yp))
1669 @defmac cl-dolist (var list [result]) forms@dots{}
1670 This is exactly like the standard Emacs Lisp macro @code{dolist},
1671 but surrounds the loop with an implicit @code{nil} block.
1674 @defmac cl-dotimes (var count [result]) forms@dots{}
1675 This is exactly like the standard Emacs Lisp macro @code{dotimes},
1676 but surrounds the loop with an implicit @code{nil} block.
1677 The body is executed with @var{var} bound to the integers
1678 from zero (inclusive) to @var{count} (exclusive), in turn. Then
1679 @c FIXME lispref does not state this part explicitly, could move this there.
1680 the @code{result} form is evaluated with @var{var} bound to the total
1681 number of iterations that were done (i.e., @code{(max 0 @var{count})})
1682 to get the return value for the loop form.
1685 @defmac cl-do-symbols (var [obarray [result]]) forms@dots{}
1686 This loop iterates over all interned symbols. If @var{obarray}
1687 is specified and is not @code{nil}, it loops over all symbols in
1688 that obarray. For each symbol, the body @var{forms} are evaluated
1689 with @var{var} bound to that symbol. The symbols are visited in
1690 an unspecified order. Afterward the @var{result} form, if any,
1691 is evaluated (with @var{var} bound to @code{nil}) to get the return
1692 value. The loop is surrounded by an implicit @code{nil} block.
1695 @defmac cl-do-all-symbols (var [result]) forms@dots{}
1696 This is identical to @code{cl-do-symbols} except that the @var{obarray}
1697 argument is omitted; it always iterates over the default obarray.
1700 @xref{Mapping over Sequences}, for some more functions for
1701 iterating over vectors or lists.
1704 @section Loop Facility
1707 A common complaint with Lisp's traditional looping constructs was
1708 that they were either too simple and limited, such as @code{dotimes}
1709 or @code{while}, or too unreadable and obscure, like Common Lisp's
1712 To remedy this, Common Lisp added a construct called the ``Loop
1713 Facility'' or ``@code{loop} macro'', with an easy-to-use but very
1714 powerful and expressive syntax.
1717 * Loop Basics:: The @code{cl-loop} macro, basic clause structure.
1718 * Loop Examples:: Working examples of the @code{cl-loop} macro.
1719 * For Clauses:: Clauses introduced by @code{for} or @code{as}.
1720 * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc.
1721 * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc.
1722 * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}.
1726 @subsection Loop Basics
1729 The @code{cl-loop} macro essentially creates a mini-language within
1730 Lisp that is specially tailored for describing loops. While this
1731 language is a little strange-looking by the standards of regular Lisp,
1732 it turns out to be very easy to learn and well-suited to its purpose.
1734 Since @code{cl-loop} is a macro, all parsing of the loop language
1735 takes place at byte-compile time; compiled @code{cl-loop}s are just
1736 as efficient as the equivalent @code{while} loops written longhand.
1738 @defmac cl-loop clauses@dots{}
1739 A loop construct consists of a series of @var{clause}s, each
1740 introduced by a symbol like @code{for} or @code{do}. Clauses
1741 are simply strung together in the argument list of @code{cl-loop},
1742 with minimal extra parentheses. The various types of clauses
1743 specify initializations, such as the binding of temporary
1744 variables, actions to be taken in the loop, stepping actions,
1747 Common Lisp specifies a certain general order of clauses in a
1751 (loop @var{name-clause}
1752 @var{var-clauses}@dots{}
1753 @var{action-clauses}@dots{})
1756 The @var{name-clause} optionally gives a name to the implicit
1757 block that surrounds the loop. By default, the implicit block
1758 is named @code{nil}. The @var{var-clauses} specify what
1759 variables should be bound during the loop, and how they should
1760 be modified or iterated throughout the course of the loop. The
1761 @var{action-clauses} are things to be done during the loop, such
1762 as computing, collecting, and returning values.
1764 The Emacs version of the @code{cl-loop} macro is less restrictive about
1765 the order of clauses, but things will behave most predictably if
1766 you put the variable-binding clauses @code{with}, @code{for}, and
1767 @code{repeat} before the action clauses. As in Common Lisp,
1768 @code{initially} and @code{finally} clauses can go anywhere.
1770 Loops generally return @code{nil} by default, but you can cause
1771 them to return a value by using an accumulation clause like
1772 @code{collect}, an end-test clause like @code{always}, or an
1773 explicit @code{return} clause to jump out of the implicit block.
1774 (Because the loop body is enclosed in an implicit block, you can
1775 also use regular Lisp @code{cl-return} or @code{cl-return-from} to
1776 break out of the loop.)
1779 The following sections give some examples of the loop macro in
1780 action, and describe the particular loop clauses in great detail.
1781 Consult the second edition of Steele for additional discussion
1785 @subsection Loop Examples
1788 Before listing the full set of clauses that are allowed, let's
1789 look at a few example loops just to get a feel for the @code{cl-loop}
1793 (cl-loop for buf in (buffer-list)
1794 collect (buffer-file-name buf))
1798 This loop iterates over all Emacs buffers, using the list
1799 returned by @code{buffer-list}. For each buffer @var{buf},
1800 it calls @code{buffer-file-name} and collects the results into
1801 a list, which is then returned from the @code{cl-loop} construct.
1802 The result is a list of the file names of all the buffers in
1803 Emacs's memory. The words @code{for}, @code{in}, and @code{collect}
1804 are reserved words in the @code{cl-loop} language.
1807 (cl-loop repeat 20 do (insert "Yowsa\n"))
1811 This loop inserts the phrase ``Yowsa'' twenty times in the
1815 (cl-loop until (eobp) do (munch-line) (forward-line 1))
1819 This loop calls @code{munch-line} on every line until the end
1820 of the buffer. If point is already at the end of the buffer,
1821 the loop exits immediately.
1824 (cl-loop do (munch-line) until (eobp) do (forward-line 1))
1828 This loop is similar to the above one, except that @code{munch-line}
1829 is always called at least once.
1832 (cl-loop for x from 1 to 100
1835 finally return (list x (= y 729)))
1839 This more complicated loop searches for a number @code{x} whose
1840 square is 729. For safety's sake it only examines @code{x}
1841 values up to 100; dropping the phrase @samp{to 100} would
1842 cause the loop to count upwards with no limit. The second
1843 @code{for} clause defines @code{y} to be the square of @code{x}
1844 within the loop; the expression after the @code{=} sign is
1845 reevaluated each time through the loop. The @code{until}
1846 clause gives a condition for terminating the loop, and the
1847 @code{finally} clause says what to do when the loop finishes.
1848 (This particular example was written less concisely than it
1849 could have been, just for the sake of illustration.)
1851 Note that even though this loop contains three clauses (two
1852 @code{for}s and an @code{until}) that would have been enough to
1853 define loops all by themselves, it still creates a single loop
1854 rather than some sort of triple-nested loop. You must explicitly
1855 nest your @code{cl-loop} constructs if you want nested loops.
1858 @subsection For Clauses
1861 Most loops are governed by one or more @code{for} clauses.
1862 A @code{for} clause simultaneously describes variables to be
1863 bound, how those variables are to be stepped during the loop,
1864 and usually an end condition based on those variables.
1866 The word @code{as} is a synonym for the word @code{for}. This
1867 word is followed by a variable name, then a word like @code{from}
1868 or @code{across} that describes the kind of iteration desired.
1869 In Common Lisp, the phrase @code{being the} sometimes precedes
1870 the type of iteration; in this package both @code{being} and
1871 @code{the} are optional. The word @code{each} is a synonym
1872 for @code{the}, and the word that follows it may be singular
1873 or plural: @samp{for x being the elements of y} or
1874 @samp{for x being each element of y}. Which form you use
1875 is purely a matter of style.
1877 The variable is bound around the loop as if by @code{let}:
1881 (cl-loop for i from 1 to 10 do (do-something-with i))
1887 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3}
1888 This type of @code{for} clause creates a counting loop. Each of
1889 the three sub-terms is optional, though there must be at least one
1890 term so that the clause is marked as a counting clause.
1892 The three expressions are the starting value, the ending value, and
1893 the step value, respectively, of the variable. The loop counts
1894 upwards by default (@var{expr3} must be positive), from @var{expr1}
1895 to @var{expr2} inclusively. If you omit the @code{from} term, the
1896 loop counts from zero; if you omit the @code{to} term, the loop
1897 counts forever without stopping (unless stopped by some other
1898 loop clause, of course); if you omit the @code{by} term, the loop
1899 counts in steps of one.
1901 You can replace the word @code{from} with @code{upfrom} or
1902 @code{downfrom} to indicate the direction of the loop. Likewise,
1903 you can replace @code{to} with @code{upto} or @code{downto}.
1904 For example, @samp{for x from 5 downto 1} executes five times
1905 with @code{x} taking on the integers from 5 down to 1 in turn.
1906 Also, you can replace @code{to} with @code{below} or @code{above},
1907 which are like @code{upto} and @code{downto} respectively except
1908 that they are exclusive rather than inclusive limits:
1911 (cl-loop for x to 10 collect x)
1912 @result{} (0 1 2 3 4 5 6 7 8 9 10)
1913 (cl-loop for x below 10 collect x)
1914 @result{} (0 1 2 3 4 5 6 7 8 9)
1917 The @code{by} value is always positive, even for downward-counting
1918 loops. Some sort of @code{from} value is required for downward
1919 loops; @samp{for x downto 5} is not a valid loop clause all by
1922 @item for @var{var} in @var{list} by @var{function}
1923 This clause iterates @var{var} over all the elements of @var{list},
1924 in turn. If you specify the @code{by} term, then @var{function}
1925 is used to traverse the list instead of @code{cdr}; it must be a
1926 function taking one argument. For example:
1929 (cl-loop for x in '(1 2 3 4 5 6) collect (* x x))
1930 @result{} (1 4 9 16 25 36)
1931 (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
1935 @item for @var{var} on @var{list} by @var{function}
1936 This clause iterates @var{var} over all the cons cells of @var{list}.
1939 (cl-loop for x on '(1 2 3 4) collect x)
1940 @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
1943 With @code{by}, there is no real reason that the @code{on} expression
1944 must be a list. For example:
1947 (cl-loop for x on first-animal by 'next-animal collect x)
1951 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
1952 the next in the (assumed) sequence of animals, or @code{nil} if
1953 @var{x} was the last animal in the sequence.
1955 @item for @var{var} in-ref @var{list} by @var{function}
1956 This is like a regular @code{in} clause, but @var{var} becomes
1957 a @code{setf}-able ``reference'' onto the elements of the list
1958 rather than just a temporary variable. For example,
1961 (cl-loop for x in-ref my-list do (cl-incf x))
1965 increments every element of @code{my-list} in place. This clause
1966 is an extension to standard Common Lisp.
1968 @item for @var{var} across @var{array}
1969 This clause iterates @var{var} over all the elements of @var{array},
1970 which may be a vector or a string.
1973 (cl-loop for x across "aeiou"
1974 do (use-vowel (char-to-string x)))
1977 @item for @var{var} across-ref @var{array}
1978 This clause iterates over an array, with @var{var} a @code{setf}-able
1979 reference onto the elements; see @code{in-ref} above.
1981 @item for @var{var} being the elements of @var{sequence}
1982 This clause iterates over the elements of @var{sequence}, which may
1983 be a list, vector, or string. Since the type must be determined
1984 at run-time, this is somewhat less efficient than @code{in} or
1985 @code{across}. The clause may be followed by the additional term
1986 @samp{using (index @var{var2})} to cause @var{var2} to be bound to
1987 the successive indices (starting at 0) of the elements.
1989 This clause type is taken from older versions of the @code{loop} macro,
1990 and is not present in modern Common Lisp. The @samp{using (sequence @dots{})}
1991 term of the older macros is not supported.
1993 @item for @var{var} being the elements of-ref @var{sequence}
1994 This clause iterates over a sequence, with @var{var} a @code{setf}-able
1995 reference onto the elements; see @code{in-ref} above.
1997 @item for @var{var} being the symbols [of @var{obarray}]
1998 This clause iterates over symbols, either over all interned symbols
1999 or over all symbols in @var{obarray}. The loop is executed with
2000 @var{var} bound to each symbol in turn. The symbols are visited in
2001 an unspecified order.
2006 (cl-loop for sym being the symbols
2008 when (string-match "^map" (symbol-name sym))
2013 returns a list of all the functions whose names begin with @samp{map}.
2015 The Common Lisp words @code{external-symbols} and @code{present-symbols}
2016 are also recognized but are equivalent to @code{symbols} in Emacs Lisp.
2018 Due to a minor implementation restriction, it will not work to have
2019 more than one @code{for} clause iterating over symbols, hash tables,
2020 keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately,
2021 it would rarely if ever be useful to do so. It @emph{is} valid to mix
2022 one of these types of clauses with other clauses like @code{for @dots{} to}
2025 @item for @var{var} being the hash-keys of @var{hash-table}
2026 @itemx for @var{var} being the hash-values of @var{hash-table}
2027 This clause iterates over the entries in @var{hash-table} with
2028 @var{var} bound to each key, or value. A @samp{using} clause can bind
2029 a second variable to the opposite part.
2032 (cl-loop for k being the hash-keys of h
2033 using (hash-values v)
2035 (message "key %S -> value %S" k v))
2038 @item for @var{var} being the key-codes of @var{keymap}
2039 @itemx for @var{var} being the key-bindings of @var{keymap}
2040 This clause iterates over the entries in @var{keymap}.
2041 The iteration does not enter nested keymaps but does enter inherited
2043 A @code{using} clause can access both the codes and the bindings
2047 (cl-loop for c being the key-codes of (current-local-map)
2048 using (key-bindings b)
2050 (message "key %S -> binding %S" c b))
2054 @item for @var{var} being the key-seqs of @var{keymap}
2055 This clause iterates over all key sequences defined by @var{keymap}
2056 and its nested keymaps, where @var{var} takes on values which are
2057 vectors. The strings or vectors
2058 are reused for each iteration, so you must copy them if you wish to keep
2059 them permanently. You can add a @samp{using (key-bindings @dots{})}
2060 clause to get the command bindings as well.
2062 @item for @var{var} being the overlays [of @var{buffer}] @dots{}
2063 This clause iterates over the ``overlays'' of a buffer
2064 (the clause @code{extents} is synonymous
2065 with @code{overlays}). If the @code{of} term is omitted, the current
2067 This clause also accepts optional @samp{from @var{pos}} and
2068 @samp{to @var{pos}} terms, limiting the clause to overlays which
2069 overlap the specified region.
2071 @item for @var{var} being the intervals [of @var{buffer}] @dots{}
2072 This clause iterates over all intervals of a buffer with constant
2073 text properties. The variable @var{var} will be bound to conses
2074 of start and end positions, where one start position is always equal
2075 to the previous end position. The clause allows @code{of},
2076 @code{from}, @code{to}, and @code{property} terms, where the latter
2077 term restricts the search to just the specified property. The
2078 @code{of} term may specify either a buffer or a string.
2080 @item for @var{var} being the frames
2081 This clause iterates over all Emacs frames. The clause @code{screens} is
2082 a synonym for @code{frames}. The frames are visited in
2083 @code{next-frame} order starting from @code{selected-frame}.
2085 @item for @var{var} being the windows [of @var{frame}]
2086 This clause iterates over the windows (in the Emacs sense) of
2087 the current frame, or of the specified @var{frame}. It visits windows
2088 in @code{next-window} order starting from @code{selected-window}
2089 (or @code{frame-selected-window} if you specify @var{frame}).
2090 This clause treats the minibuffer window in the same way as
2091 @code{next-window} does. For greater flexibility, consider using
2092 @code{walk-windows} instead.
2094 @item for @var{var} being the buffers
2095 This clause iterates over all buffers in Emacs. It is equivalent
2096 to @samp{for @var{var} in (buffer-list)}.
2098 @item for @var{var} = @var{expr1} then @var{expr2}
2099 This clause does a general iteration. The first time through
2100 the loop, @var{var} will be bound to @var{expr1}. On the second
2101 and successive iterations it will be set by evaluating @var{expr2}
2102 (which may refer to the old value of @var{var}). For example,
2103 these two loops are effectively the same:
2106 (cl-loop for x on my-list by 'cddr do @dots{})
2107 (cl-loop for x = my-list then (cddr x) while x do @dots{})
2110 Note that this type of @code{for} clause does not imply any sort
2111 of terminating condition; the above example combines it with a
2112 @code{while} clause to tell when to end the loop.
2114 If you omit the @code{then} term, @var{expr1} is used both for
2115 the initial setting and for successive settings:
2118 (cl-loop for x = (random) when (> x 0) return x)
2122 This loop keeps taking random numbers from the @code{(random)}
2123 function until it gets a positive one, which it then returns.
2126 If you include several @code{for} clauses in a row, they are
2127 treated sequentially (as if by @code{let*} and @code{setq}).
2128 You can instead use the word @code{and} to link the clauses,
2129 in which case they are processed in parallel (as if by @code{let}
2130 and @code{cl-psetq}).
2133 (cl-loop for x below 5 for y = nil then x collect (list x y))
2134 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4))
2135 (cl-loop for x below 5 and y = nil then x collect (list x y))
2136 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3))
2140 In the first loop, @code{y} is set based on the value of @code{x}
2141 that was just set by the previous clause; in the second loop,
2142 @code{x} and @code{y} are set simultaneously so @code{y} is set
2143 based on the value of @code{x} left over from the previous time
2146 @cindex destructuring, in cl-loop
2147 Another feature of the @code{cl-loop} macro is @emph{destructuring},
2148 similar in concept to the destructuring provided by @code{defmacro}
2149 (@pxref{Argument Lists}).
2150 The @var{var} part of any @code{for} clause can be given as a list
2151 of variables instead of a single variable. The values produced
2152 during loop execution must be lists; the values in the lists are
2153 stored in the corresponding variables.
2156 (cl-loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y))
2160 In loop destructuring, if there are more values than variables
2161 the trailing values are ignored, and if there are more variables
2162 than values the trailing variables get the value @code{nil}.
2163 If @code{nil} is used as a variable name, the corresponding
2164 values are ignored. Destructuring may be nested, and dotted
2165 lists of variables like @code{(x . y)} are allowed, so for example
2169 (cl-loop for (key . value) in '((a . 1) (b . 2))
2174 @node Iteration Clauses
2175 @subsection Iteration Clauses
2178 Aside from @code{for} clauses, there are several other loop clauses
2179 that control the way the loop operates. They might be used by
2180 themselves, or in conjunction with one or more @code{for} clauses.
2183 @item repeat @var{integer}
2184 This clause simply counts up to the specified number using an
2185 internal temporary variable. The loops
2188 (cl-loop repeat (1+ n) do @dots{})
2189 (cl-loop for temp to n do @dots{})
2193 are identical except that the second one forces you to choose
2194 a name for a variable you aren't actually going to use.
2196 @item while @var{condition}
2197 This clause stops the loop when the specified condition (any Lisp
2198 expression) becomes @code{nil}. For example, the following two
2199 loops are equivalent, except for the implicit @code{nil} block
2200 that surrounds the second one:
2203 (while @var{cond} @var{forms}@dots{})
2204 (cl-loop while @var{cond} do @var{forms}@dots{})
2207 @item until @var{condition}
2208 This clause stops the loop when the specified condition is true,
2209 i.e., non-@code{nil}.
2211 @item always @var{condition}
2212 This clause stops the loop when the specified condition is @code{nil}.
2213 Unlike @code{while}, it stops the loop using @code{return nil} so that
2214 the @code{finally} clauses are not executed. If all the conditions
2215 were non-@code{nil}, the loop returns @code{t}:
2218 (if (cl-loop for size in size-list always (> size 10))
2223 @item never @var{condition}
2224 This clause is like @code{always}, except that the loop returns
2225 @code{t} if any conditions were false, or @code{nil} otherwise.
2227 @item thereis @var{condition}
2228 This clause stops the loop when the specified form is non-@code{nil};
2229 in this case, it returns that non-@code{nil} value. If all the
2230 values were @code{nil}, the loop returns @code{nil}.
2233 @node Accumulation Clauses
2234 @subsection Accumulation Clauses
2237 These clauses cause the loop to accumulate information about the
2238 specified Lisp @var{form}. The accumulated result is returned
2239 from the loop unless overridden, say, by a @code{return} clause.
2242 @item collect @var{form}
2243 This clause collects the values of @var{form} into a list. Several
2244 examples of @code{collect} appear elsewhere in this manual.
2246 The word @code{collecting} is a synonym for @code{collect}, and
2247 likewise for the other accumulation clauses.
2249 @item append @var{form}
2250 This clause collects lists of values into a result list using
2253 @item nconc @var{form}
2254 This clause collects lists of values into a result list by
2255 destructively modifying the lists rather than copying them.
2257 @item concat @var{form}
2258 This clause concatenates the values of the specified @var{form}
2259 into a string. (It and the following clause are extensions to
2260 standard Common Lisp.)
2262 @item vconcat @var{form}
2263 This clause concatenates the values of the specified @var{form}
2266 @item count @var{form}
2267 This clause counts the number of times the specified @var{form}
2268 evaluates to a non-@code{nil} value.
2270 @item sum @var{form}
2271 This clause accumulates the sum of the values of the specified
2272 @var{form}, which must evaluate to a number.
2274 @item maximize @var{form}
2275 This clause accumulates the maximum value of the specified @var{form},
2276 which must evaluate to a number. The return value is undefined if
2277 @code{maximize} is executed zero times.
2279 @item minimize @var{form}
2280 This clause accumulates the minimum value of the specified @var{form}.
2283 Accumulation clauses can be followed by @samp{into @var{var}} to
2284 cause the data to be collected into variable @var{var} (which is
2285 automatically @code{let}-bound during the loop) rather than an
2286 unnamed temporary variable. Also, @code{into} accumulations do
2287 not automatically imply a return value. The loop must use some
2288 explicit mechanism, such as @code{finally return}, to return
2289 the accumulated result.
2291 It is valid for several accumulation clauses of the same type to
2292 accumulate into the same place. From Steele:
2295 (cl-loop for name in '(fred sue alice joe june)
2296 for kids in '((bob ken) () () (kris sunshine) ())
2299 @result{} (fred bob ken sue alice joe kris sunshine june)
2303 @subsection Other Clauses
2306 This section describes the remaining loop clauses.
2309 @item with @var{var} = @var{value}
2310 This clause binds a variable to a value around the loop, but
2311 otherwise leaves the variable alone during the loop. The following
2312 loops are basically equivalent:
2315 (cl-loop with x = 17 do @dots{})
2316 (let ((x 17)) (cl-loop do @dots{}))
2317 (cl-loop for x = 17 then x do @dots{})
2320 Naturally, the variable @var{var} might be used for some purpose
2321 in the rest of the loop. For example:
2324 (cl-loop for x in my-list with res = nil do (push x res)
2328 This loop inserts the elements of @code{my-list} at the front of
2329 a new list being accumulated in @code{res}, then returns the
2330 list @code{res} at the end of the loop. The effect is similar
2331 to that of a @code{collect} clause, but the list gets reversed
2332 by virtue of the fact that elements are being pushed onto the
2333 front of @code{res} rather than the end.
2335 If you omit the @code{=} term, the variable is initialized to
2336 @code{nil}. (Thus the @samp{= nil} in the above example is
2339 Bindings made by @code{with} are sequential by default, as if
2340 by @code{let*}. Just like @code{for} clauses, @code{with} clauses
2341 can be linked with @code{and} to cause the bindings to be made by
2344 @item if @var{condition} @var{clause}
2345 This clause executes the following loop clause only if the specified
2346 condition is true. The following @var{clause} should be an accumulation,
2347 @code{do}, @code{return}, @code{if}, or @code{unless} clause.
2348 Several clauses may be linked by separating them with @code{and}.
2349 These clauses may be followed by @code{else} and a clause or clauses
2350 to execute if the condition was false. The whole construct may
2351 optionally be followed by the word @code{end} (which may be used to
2352 disambiguate an @code{else} or @code{and} in a nested @code{if}).
2354 The actual non-@code{nil} value of the condition form is available
2355 by the name @code{it} in the ``then'' part. For example:
2358 (setq funny-numbers '(6 13 -1))
2360 (cl-loop for x below 10
2363 and if (memq x funny-numbers) return (cdr it) end
2365 collect x into evens
2366 finally return (vector odds evens))
2367 @result{} [(1 3 5 7 9) (0 2 4 6 8)]
2368 (setq funny-numbers '(6 7 13 -1))
2369 @result{} (6 7 13 -1)
2370 (cl-loop <@r{same thing again}>)
2374 Note the use of @code{and} to put two clauses into the ``then''
2375 part, one of which is itself an @code{if} clause. Note also that
2376 @code{end}, while normally optional, was necessary here to make
2377 it clear that the @code{else} refers to the outermost @code{if}
2378 clause. In the first case, the loop returns a vector of lists
2379 of the odd and even values of @var{x}. In the second case, the
2380 odd number 7 is one of the @code{funny-numbers} so the loop
2381 returns early; the actual returned value is based on the result
2382 of the @code{memq} call.
2384 @item when @var{condition} @var{clause}
2385 This clause is just a synonym for @code{if}.
2387 @item unless @var{condition} @var{clause}
2388 The @code{unless} clause is just like @code{if} except that the
2389 sense of the condition is reversed.
2391 @item named @var{name}
2392 This clause gives a name other than @code{nil} to the implicit
2393 block surrounding the loop. The @var{name} is the symbol to be
2394 used as the block name.
2396 @item initially [do] @var{forms}@dots{}
2397 This keyword introduces one or more Lisp forms which will be
2398 executed before the loop itself begins (but after any variables
2399 requested by @code{for} or @code{with} have been bound to their
2400 initial values). @code{initially} clauses can appear anywhere;
2401 if there are several, they are executed in the order they appear
2402 in the loop. The keyword @code{do} is optional.
2404 @item finally [do] @var{forms}@dots{}
2405 This introduces Lisp forms which will be executed after the loop
2406 finishes (say, on request of a @code{for} or @code{while}).
2407 @code{initially} and @code{finally} clauses may appear anywhere
2408 in the loop construct, but they are executed (in the specified
2409 order) at the beginning or end, respectively, of the loop.
2411 @item finally return @var{form}
2412 This says that @var{form} should be executed after the loop
2413 is done to obtain a return value. (Without this, or some other
2414 clause like @code{collect} or @code{return}, the loop will simply
2415 return @code{nil}.) Variables bound by @code{for}, @code{with},
2416 or @code{into} will still contain their final values when @var{form}
2419 @item do @var{forms}@dots{}
2420 The word @code{do} may be followed by any number of Lisp expressions
2421 which are executed as an implicit @code{progn} in the body of the
2422 loop. Many of the examples in this section illustrate the use of
2425 @item return @var{form}
2426 This clause causes the loop to return immediately. The following
2427 Lisp form is evaluated to give the return value of the loop
2428 form. The @code{finally} clauses, if any, are not executed.
2429 Of course, @code{return} is generally used inside an @code{if} or
2430 @code{unless}, as its use in a top-level loop clause would mean
2431 the loop would never get to ``loop'' more than once.
2433 The clause @samp{return @var{form}} is equivalent to
2434 @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop
2435 was named). The @code{return} clause is implemented a bit more
2436 efficiently, though.
2439 While there is no high-level way to add user extensions to @code{cl-loop},
2440 this package does offer two properties called @code{cl-loop-handler}
2441 and @code{cl-loop-for-handler} which are functions to be called when a
2442 given symbol is encountered as a top-level loop clause or @code{for}
2443 clause, respectively. Consult the source code in file
2444 @file{cl-macs.el} for details.
2446 This package's @code{cl-loop} macro is compatible with that of Common
2447 Lisp, except that a few features are not implemented: @code{loop-finish}
2448 and data-type specifiers. Naturally, the @code{for} clauses that
2449 iterate over keymaps, overlays, intervals, frames, windows, and
2450 buffers are Emacs-specific extensions.
2452 @node Multiple Values
2453 @section Multiple Values
2456 Common Lisp functions can return zero or more results. Emacs Lisp
2457 functions, by contrast, always return exactly one result. This
2458 package makes no attempt to emulate Common Lisp multiple return
2459 values; Emacs versions of Common Lisp functions that return more
2460 than one value either return just the first value (as in
2461 @code{cl-compiler-macroexpand}) or return a list of values.
2462 This package @emph{does} define placeholders
2463 for the Common Lisp functions that work with multiple values, but
2464 in Emacs Lisp these functions simply operate on lists instead.
2465 The @code{cl-values} form, for example, is a synonym for @code{list}
2468 @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{}
2469 This form evaluates @var{values-form}, which must return a list of
2470 values. It then binds the @var{var}s to these respective values,
2471 as if by @code{let}, and then executes the body @var{forms}.
2472 If there are more @var{var}s than values, the extra @var{var}s
2473 are bound to @code{nil}. If there are fewer @var{var}s than
2474 values, the excess values are ignored.
2477 @defmac cl-multiple-value-setq (var@dots{}) form
2478 This form evaluates @var{form}, which must return a list of values.
2479 It then sets the @var{var}s to these respective values, as if by
2480 @code{setq}. Extra @var{var}s or values are treated the same as
2481 in @code{cl-multiple-value-bind}.
2484 Since a perfect emulation is not feasible in Emacs Lisp, this
2485 package opts to keep it as simple and predictable as possible.
2491 This package implements the various Common Lisp features of
2492 @code{defmacro}, such as destructuring, @code{&environment},
2493 and @code{&body}. Top-level @code{&whole} is not implemented
2494 for @code{defmacro} due to technical difficulties.
2495 @xref{Argument Lists}.
2497 Destructuring is made available to the user by way of the
2500 @defmac cl-destructuring-bind arglist expr forms@dots{}
2501 This macro expands to code that executes @var{forms}, with
2502 the variables in @var{arglist} bound to the list of values
2503 returned by @var{expr}. The @var{arglist} can include all
2504 the features allowed for @code{cl-defmacro} argument lists,
2505 including destructuring. (The @code{&environment} keyword
2506 is not allowed.) The macro expansion will signal an error
2507 if @var{expr} returns a list of the wrong number of arguments
2508 or with incorrect keyword arguments.
2511 @cindex compiler macros
2512 @cindex define compiler macros
2513 This package also includes the Common Lisp @code{define-compiler-macro}
2514 facility, which allows you to define compile-time expansions and
2515 optimizations for your functions.
2517 @defmac cl-define-compiler-macro name arglist forms@dots{}
2518 This form is similar to @code{defmacro}, except that it only expands
2519 calls to @var{name} at compile-time; calls processed by the Lisp
2520 interpreter are not expanded, nor are they expanded by the
2521 @code{macroexpand} function.
2523 The argument list may begin with a @code{&whole} keyword and a
2524 variable. This variable is bound to the macro-call form itself,
2525 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}.
2526 If the macro expander returns this form unchanged, then the
2527 compiler treats it as a normal function call. This allows
2528 compiler macros to work as optimizers for special cases of a
2529 function, leaving complicated cases alone.
2531 For example, here is a simplified version of a definition that
2532 appears as a standard part of this package:
2535 (cl-define-compiler-macro cl-member (&whole form a list &rest keys)
2536 (if (and (null keys)
2537 (eq (car-safe a) 'quote)
2538 (not (floatp (cadr a))))
2544 This definition causes @code{(cl-member @var{a} @var{list})} to change
2545 to a call to the faster @code{memq} in the common case where @var{a}
2546 is a non-floating-point constant; if @var{a} is anything else, or
2547 if there are any keyword arguments in the call, then the original
2548 @code{cl-member} call is left intact. (The actual compiler macro
2549 for @code{cl-member} optimizes a number of other cases, including
2550 common @code{:test} predicates.)
2553 @defun cl-compiler-macroexpand form
2554 This function is analogous to @code{macroexpand}, except that it
2555 expands compiler macros rather than regular macros. It returns
2556 @var{form} unchanged if it is not a call to a function for which
2557 a compiler macro has been defined, or if that compiler macro
2558 decided to punt by returning its @code{&whole} argument. Like
2559 @code{macroexpand}, it expands repeatedly until it reaches a form
2560 for which no further expansion is possible.
2563 @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet}
2564 and @code{cl-symbol-macrolet} forms for making ``local'' macro
2568 @chapter Declarations
2571 Common Lisp includes a complex and powerful ``declaration''
2572 mechanism that allows you to give the compiler special hints
2573 about the types of data that will be stored in particular variables,
2574 and about the ways those variables and functions will be used. This
2575 package defines versions of all the Common Lisp declaration forms:
2576 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim},
2579 Most of the Common Lisp declarations are not currently useful in Emacs
2580 Lisp. For example, the byte-code system provides little
2581 opportunity to benefit from type information.
2583 and @code{special} declarations are redundant in a fully
2584 dynamically-scoped Lisp.
2586 A few declarations are meaningful when byte compiler optimizations
2587 are enabled, as they are by the default. Otherwise these
2588 declarations will effectively be ignored.
2590 @defun cl-proclaim decl-spec
2591 This function records a ``global'' declaration specified by
2592 @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec}
2593 is evaluated and thus should normally be quoted.
2596 @defmac cl-declaim decl-specs@dots{}
2597 This macro is like @code{cl-proclaim}, except that it takes any number
2598 of @var{decl-spec} arguments, and the arguments are unevaluated and
2599 unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when
2600 (compile load eval) @dots{})} around the declarations so that they will
2601 be registered at compile-time as well as at run-time. (This is vital,
2602 since normally the declarations are meant to influence the way the
2603 compiler treats the rest of the file that contains the @code{cl-declaim}
2607 @defmac cl-declare decl-specs@dots{}
2608 This macro is used to make declarations within functions and other
2609 code. Common Lisp allows declarations in various locations, generally
2610 at the beginning of any of the many ``implicit @code{progn}s''
2611 throughout Lisp syntax, such as function bodies, @code{let} bodies,
2612 etc. Currently the only declaration understood by @code{cl-declare}
2616 @defmac cl-locally declarations@dots{} forms@dots{}
2617 In this package, @code{cl-locally} is no different from @code{progn}.
2620 @defmac cl-the type form
2621 Type information provided by @code{cl-the} is ignored in this package;
2622 in other words, @code{(cl-the @var{type} @var{form})} is equivalent to
2623 @var{form}. Future byte-compiler optimizations may make use of this
2626 For example, @code{mapcar} can map over both lists and arrays. It is
2627 hard for the compiler to expand @code{mapcar} into an in-line loop
2628 unless it knows whether the sequence will be a list or an array ahead
2629 of time. With @code{(mapcar 'car (cl-the vector foo))}, a future
2630 compiler would have enough information to expand the loop in-line.
2631 For now, Emacs Lisp will treat the above code as exactly equivalent
2632 to @code{(mapcar 'car foo)}.
2635 Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or
2636 @code{cl-declare} should be a list beginning with a symbol that says
2637 what kind of declaration it is. This package currently understands
2638 @code{special}, @code{inline}, @code{notinline}, @code{optimize},
2639 and @code{warn} declarations. (The @code{warn} declaration is an
2640 extension of standard Common Lisp.) Other Common Lisp declarations,
2641 such as @code{type} and @code{ftype}, are silently ignored.
2646 Since all variables in Emacs Lisp are ``special'' (in the Common
2647 Lisp sense), @code{special} declarations are only advisory. They
2648 simply tell the byte compiler that the specified
2649 variables are intentionally being referred to without being
2650 bound in the body of the function. The compiler normally emits
2651 warnings for such references, since they could be typographical
2652 errors for references to local variables.
2654 The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is
2655 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}.
2657 In top-level contexts, it is generally better to write
2658 @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))},
2659 since @code{defvar} makes your intentions clearer.
2662 The @code{inline} @var{decl-spec} lists one or more functions
2663 whose bodies should be expanded ``in-line'' into calling functions
2664 whenever the compiler is able to arrange for it. For example,
2665 the function @code{cl-acons} is declared @code{inline}
2666 by this package so that the form @code{(cl-acons @var{key} @var{value}
2668 expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})}
2669 when it is called in user functions, so as to save function calls.
2671 The following declarations are all equivalent. Note that the
2672 @code{defsubst} form is a convenient way to define a function
2673 and declare it inline all at once.
2676 (cl-declaim (inline foo bar))
2677 (cl-eval-when (compile load eval)
2678 (cl-proclaim '(inline foo bar)))
2679 (defsubst foo (@dots{}) @dots{}) ; instead of defun
2682 @strong{Please note:} this declaration remains in effect after the
2683 containing source file is done. It is correct to use it to
2684 request that a function you have defined should be inlined,
2685 but it is impolite to use it to request inlining of an external
2688 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))}
2689 before a particular call to a function to cause just that call to
2690 be inlined; the current byte compilers provide no way to implement
2691 this, so @code{(cl-declare (inline @dots{}))} is currently ignored by
2695 The @code{notinline} declaration lists functions which should
2696 not be inlined after all; it cancels a previous @code{inline}
2700 This declaration controls how much optimization is performed by
2703 The word @code{optimize} is followed by any number of lists like
2704 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several
2705 optimization ``qualities''; this package ignores all but @code{speed}
2706 and @code{safety}. The value of a quality should be an integer from
2707 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''.
2708 The default level for both qualities is 1.
2710 In this package, the @code{speed} quality is tied to the @code{byte-optimize}
2711 flag, which is set to @code{nil} for @code{(speed 0)} and to
2712 @code{t} for higher settings; and the @code{safety} quality is
2713 tied to the @code{byte-compile-delete-errors} flag, which is
2714 set to @code{nil} for @code{(safety 3)} and to @code{t} for all
2715 lower settings. (The latter flag controls whether the compiler
2716 is allowed to optimize out code whose only side-effect could
2717 be to signal an error, e.g., rewriting @code{(progn foo bar)} to
2718 @code{bar} when it is not known whether @code{foo} will be bound
2721 Note that even compiling with @code{(safety 0)}, the Emacs
2722 byte-code system provides sufficient checking to prevent real
2723 harm from being done. For example, barring serious bugs in
2724 Emacs itself, Emacs will not crash with a segmentation fault
2725 just because of an error in a fully-optimized Lisp program.
2727 The @code{optimize} declaration is normally used in a top-level
2728 @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows
2729 it to be used with @code{declare} to set the level of optimization
2730 locally for a given form, but this will not work correctly with the
2731 current byte-compiler. (The @code{cl-declare}
2732 will set the new optimization level, but that level will not
2733 automatically be unset after the enclosing form is done.)
2736 This declaration controls what sorts of warnings are generated
2737 by the byte compiler. The word @code{warn} is followed by any
2738 number of ``warning qualities'', similar in form to optimization
2739 qualities. The currently supported warning types are
2740 @code{redefine}, @code{callargs}, @code{unresolved}, and
2741 @code{free-vars}; in the current system, a value of 0 will
2742 disable these warnings and any higher value will enable them.
2743 See the documentation of the variable @code{byte-compile-warnings}
2751 This package defines several symbol-related features that were
2752 missing from Emacs Lisp.
2755 * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}.
2756 * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}.
2759 @node Property Lists
2760 @section Property Lists
2763 These functions augment the standard Emacs Lisp functions @code{get}
2764 and @code{put} for operating on properties attached to symbols.
2765 There are also functions for working with property lists as
2766 first-class data structures not attached to particular symbols.
2768 @defun cl-get symbol property &optional default
2769 This function is like @code{get}, except that if the property is
2770 not found, the @var{default} argument provides the return value.
2771 (The Emacs Lisp @code{get} function always uses @code{nil} as
2772 the default; this package's @code{cl-get} is equivalent to Common
2775 The @code{cl-get} function is @code{setf}-able; when used in this
2776 fashion, the @var{default} argument is allowed but ignored.
2779 @defun cl-remprop symbol property
2780 This function removes the entry for @var{property} from the property
2781 list of @var{symbol}. It returns a true value if the property was
2782 indeed found and removed, or @code{nil} if there was no such property.
2783 (This function was probably omitted from Emacs originally because,
2784 since @code{get} did not allow a @var{default}, it was very difficult
2785 to distinguish between a missing property and a property whose value
2786 was @code{nil}; thus, setting a property to @code{nil} was close
2787 enough to @code{cl-remprop} for most purposes.)
2790 @defun cl-getf place property &optional default
2791 This function scans the list @var{place} as if it were a property
2792 list, i.e., a list of alternating property names and values. If
2793 an even-numbered element of @var{place} is found which is @code{eq}
2794 to @var{property}, the following odd-numbered element is returned.
2795 Otherwise, @var{default} is returned (or @code{nil} if no default
2801 (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop)
2804 It is valid to use @code{cl-getf} as a @code{setf} place, in which case
2805 its @var{place} argument must itself be a valid @code{setf} place.
2806 The @var{default} argument, if any, is ignored in this context.
2807 The effect is to change (via @code{setcar}) the value cell in the
2808 list that corresponds to @var{property}, or to cons a new property-value
2809 pair onto the list if the property is not yet present.
2812 (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val)
2815 The @code{get} and @code{cl-get} functions are also @code{setf}-able.
2816 The fact that @code{default} is ignored can sometimes be useful:
2819 (cl-incf (cl-get 'foo 'usage-count 0))
2822 Here, symbol @code{foo}'s @code{usage-count} property is incremented
2823 if it exists, or set to 1 (an incremented 0) otherwise.
2825 When not used as a @code{setf} form, @code{cl-getf} is just a regular
2826 function and its @var{place} argument can actually be any Lisp
2830 @defmac cl-remf place property
2831 This macro removes the property-value pair for @var{property} from
2832 the property list stored at @var{place}, which is any @code{setf}-able
2833 place expression. It returns true if the property was found. Note
2834 that if @var{property} happens to be first on the list, this will
2835 effectively do a @code{(setf @var{place} (cddr @var{place}))},
2836 whereas if it occurs later, this simply uses @code{setcdr} to splice
2837 out the property and value cells.
2840 @node Creating Symbols
2841 @section Creating Symbols
2844 These functions create unique symbols, typically for use as
2845 temporary variables.
2847 @defun cl-gensym &optional x
2848 This function creates a new, uninterned symbol (using @code{make-symbol})
2849 with a unique name. (The name of an uninterned symbol is relevant
2850 only if the symbol is printed.) By default, the name is generated
2851 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001},
2852 @samp{G1002}, etc. If the optional argument @var{x} is a string, that
2853 string is used as a prefix instead of @samp{G}. Uninterned symbols
2854 are used in macro expansions for temporary variables, to ensure that
2855 their names will not conflict with ``real'' variables in the user's
2858 (Internally, the variable @code{cl--gensym-counter} holds the counter
2859 used to generate names. It is incremented after each use. In Common
2860 Lisp this is initialized with 0, but this package initializes it with
2861 a random time-dependent value to avoid trouble when two files that
2862 each used @code{cl-gensym} in their compilation are loaded together.
2863 Uninterned symbols become interned when the compiler writes them out
2864 to a file and the Emacs loader loads them, so their names have to be
2865 treated a bit more carefully than in Common Lisp where uninterned
2866 symbols remain uninterned after loading.)
2869 @defun cl-gentemp &optional x
2870 This function is like @code{cl-gensym}, except that it produces a new
2871 @emph{interned} symbol. If the symbol that is generated already
2872 exists, the function keeps incrementing the counter and trying
2873 again until a new symbol is generated.
2876 This package automatically creates all keywords that are called for by
2877 @code{&key} argument specifiers, and discourages the use of keywords
2878 as data unrelated to keyword arguments, so the related function
2879 @code{defkeyword} (to create self-quoting keyword symbols) is not
2886 This section defines a few simple Common Lisp operations on numbers
2887 that were left out of Emacs Lisp.
2890 * Predicates on Numbers:: @code{cl-plusp}, @code{cl-oddp}, etc.
2891 * Numerical Functions:: @code{cl-floor}, @code{cl-ceiling}, etc.
2892 * Random Numbers:: @code{cl-random}, @code{cl-make-random-state}.
2893 * Implementation Parameters:: @code{cl-most-positive-float}, etc.
2896 @node Predicates on Numbers
2897 @section Predicates on Numbers
2900 These functions return @code{t} if the specified condition is
2901 true of the numerical argument, or @code{nil} otherwise.
2903 @defun cl-plusp number
2904 This predicate tests whether @var{number} is positive. It is an
2905 error if the argument is not a number.
2908 @defun cl-minusp number
2909 This predicate tests whether @var{number} is negative. It is an
2910 error if the argument is not a number.
2913 @defun cl-oddp integer
2914 This predicate tests whether @var{integer} is odd. It is an
2915 error if the argument is not an integer.
2918 @defun cl-evenp integer
2919 This predicate tests whether @var{integer} is even. It is an
2920 error if the argument is not an integer.
2923 @node Numerical Functions
2924 @section Numerical Functions
2927 These functions perform various arithmetic operations on numbers.
2929 @defun cl-gcd &rest integers
2930 This function returns the Greatest Common Divisor of the arguments.
2931 For one argument, it returns the absolute value of that argument.
2932 For zero arguments, it returns zero.
2935 @defun cl-lcm &rest integers
2936 This function returns the Least Common Multiple of the arguments.
2937 For one argument, it returns the absolute value of that argument.
2938 For zero arguments, it returns one.
2941 @defun cl-isqrt integer
2942 This function computes the ``integer square root'' of its integer
2943 argument, i.e., the greatest integer less than or equal to the true
2944 square root of the argument.
2947 @defun cl-floor number &optional divisor
2948 With one argument, @code{cl-floor} returns a list of two numbers:
2949 The argument rounded down (toward minus infinity) to an integer,
2950 and the ``remainder'' which would have to be added back to the
2951 first return value to yield the argument again. If the argument
2952 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}.
2953 If the argument is a floating-point number, the first
2954 result is a Lisp integer and the second is a Lisp float between
2955 0 (inclusive) and 1 (exclusive).
2957 With two arguments, @code{cl-floor} divides @var{number} by
2958 @var{divisor}, and returns the floor of the quotient and the
2959 corresponding remainder as a list of two numbers. If
2960 @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})},
2961 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r}
2962 between 0 (inclusive) and @var{r} (exclusive). Also, note
2963 that @code{(cl-floor @var{x})} is exactly equivalent to
2964 @code{(cl-floor @var{x} 1)}.
2966 This function is entirely compatible with Common Lisp's @code{floor}
2967 function, except that it returns the two results in a list since
2968 Emacs Lisp does not support multiple-valued functions.
2971 @defun cl-ceiling number &optional divisor
2972 This function implements the Common Lisp @code{ceiling} function,
2973 which is analogous to @code{floor} except that it rounds the
2974 argument or quotient of the arguments up toward plus infinity.
2975 The remainder will be between 0 and minus @var{r}.
2978 @defun cl-truncate number &optional divisor
2979 This function implements the Common Lisp @code{truncate} function,
2980 which is analogous to @code{floor} except that it rounds the
2981 argument or quotient of the arguments toward zero. Thus it is
2982 equivalent to @code{cl-floor} if the argument or quotient is
2983 positive, or to @code{cl-ceiling} otherwise. The remainder has
2984 the same sign as @var{number}.
2987 @defun cl-round number &optional divisor
2988 This function implements the Common Lisp @code{round} function,
2989 which is analogous to @code{floor} except that it rounds the
2990 argument or quotient of the arguments to the nearest integer.
2991 In the case of a tie (the argument or quotient is exactly
2992 halfway between two integers), it rounds to the even integer.
2995 @defun cl-mod number divisor
2996 This function returns the same value as the second return value
3000 @defun cl-rem number divisor
3001 This function returns the same value as the second return value
3002 of @code{cl-truncate}.
3005 @node Random Numbers
3006 @section Random Numbers
3009 This package also provides an implementation of the Common Lisp
3010 random number generator. It uses its own additive-congruential
3011 algorithm, which is much more likely to give statistically clean
3012 @c FIXME? Still true?
3013 random numbers than the simple generators supplied by many
3016 @defun cl-random number &optional state
3017 This function returns a random nonnegative number less than
3018 @var{number}, and of the same type (either integer or floating-point).
3019 The @var{state} argument should be a @code{random-state} object
3020 that holds the state of the random number generator. The
3021 function modifies this state object as a side effect. If
3022 @var{state} is omitted, it defaults to the internal variable
3023 @code{cl--random-state}, which contains a pre-initialized
3024 default @code{random-state} object. (Since any number of programs in
3025 the Emacs process may be accessing @code{cl--random-state} in
3026 interleaved fashion, the sequence generated from this will be
3027 irreproducible for all intents and purposes.)
3030 @defun cl-make-random-state &optional state
3031 This function creates or copies a @code{random-state} object.
3032 If @var{state} is omitted or @code{nil}, it returns a new copy of
3033 @code{cl--random-state}. This is a copy in the sense that future
3034 sequences of calls to @code{(cl-random @var{n})} and
3035 @code{(cl-random @var{n} @var{s})} (where @var{s} is the new
3036 random-state object) will return identical sequences of random
3039 If @var{state} is a @code{random-state} object, this function
3040 returns a copy of that object. If @var{state} is @code{t}, this
3041 function returns a new @code{random-state} object seeded from the
3042 date and time. As an extension to Common Lisp, @var{state} may also
3043 be an integer in which case the new object is seeded from that
3044 integer; each different integer seed will result in a completely
3045 different sequence of random numbers.
3047 It is valid to print a @code{random-state} object to a buffer or
3048 file and later read it back with @code{read}. If a program wishes
3049 to use a sequence of pseudo-random numbers which can be reproduced
3050 later for debugging, it can call @code{(cl-make-random-state t)} to
3051 get a new sequence, then print this sequence to a file. When the
3052 program is later rerun, it can read the original run's random-state
3056 @defun cl-random-state-p object
3057 This predicate returns @code{t} if @var{object} is a
3058 @code{random-state} object, or @code{nil} otherwise.
3061 @node Implementation Parameters
3062 @section Implementation Parameters
3065 This package defines several useful constants having to do with
3066 floating-point numbers.
3068 It determines their values by exercising the computer's
3069 floating-point arithmetic in various ways. Because this operation
3070 might be slow, the code for initializing them is kept in a separate
3071 function that must be called before the parameters can be used.
3073 @defun cl-float-limits
3074 This function makes sure that the Common Lisp floating-point parameters
3075 like @code{cl-most-positive-float} have been initialized. Until it is
3076 called, these parameters will be @code{nil}.
3077 @c If this version of Emacs does not support floats, the parameters will
3078 @c remain @code{nil}.
3079 If the parameters have already been initialized, the function returns
3082 The algorithm makes assumptions that will be valid for almost all
3083 machines, but will fail if the machine's arithmetic is extremely
3084 unusual, e.g., decimal.
3087 Since true Common Lisp supports up to four different floating-point
3088 precisions, it has families of constants like
3089 @code{most-positive-single-float}, @code{most-positive-double-float},
3090 @code{most-positive-long-float}, and so on. Emacs has only one
3091 floating-point precision, so this package omits the precision word
3092 from the constants' names.
3094 @defvar cl-most-positive-float
3095 This constant equals the largest value a Lisp float can hold.
3096 For those systems whose arithmetic supports infinities, this is
3097 the largest @emph{finite} value. For IEEE machines, the value
3098 is approximately @code{1.79e+308}.
3101 @defvar cl-most-negative-float
3102 This constant equals the most negative value a Lisp float can hold.
3103 (It is assumed to be equal to @code{(- cl-most-positive-float)}.)
3106 @defvar cl-least-positive-float
3107 This constant equals the smallest Lisp float value greater than zero.
3108 For IEEE machines, it is about @code{4.94e-324} if denormals are
3109 supported or @code{2.22e-308} if not.
3112 @defvar cl-least-positive-normalized-float
3113 This constant equals the smallest @emph{normalized} Lisp float greater
3114 than zero, i.e., the smallest value for which IEEE denormalization
3115 will not result in a loss of precision. For IEEE machines, this
3116 value is about @code{2.22e-308}. For machines that do not support
3117 the concept of denormalization and gradual underflow, this constant
3118 will always equal @code{cl-least-positive-float}.
3121 @defvar cl-least-negative-float
3122 This constant is the negative counterpart of @code{cl-least-positive-float}.
3125 @defvar cl-least-negative-normalized-float
3126 This constant is the negative counterpart of
3127 @code{cl-least-positive-normalized-float}.
3130 @defvar cl-float-epsilon
3131 This constant is the smallest positive Lisp float that can be added
3132 to 1.0 to produce a distinct value. Adding a smaller number to 1.0
3133 will yield 1.0 again due to roundoff. For IEEE machines, epsilon
3134 is about @code{2.22e-16}.
3137 @defvar cl-float-negative-epsilon
3138 This is the smallest positive value that can be subtracted from
3139 1.0 to produce a distinct value. For IEEE machines, it is about
3147 Common Lisp defines a number of functions that operate on
3148 @dfn{sequences}, which are either lists, strings, or vectors.
3149 Emacs Lisp includes a few of these, notably @code{elt} and
3150 @code{length}; this package defines most of the rest.
3153 * Sequence Basics:: Arguments shared by all sequence functions.
3154 * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc.
3155 * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc.
3156 * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc.
3157 * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}.
3160 @node Sequence Basics
3161 @section Sequence Basics
3164 Many of the sequence functions take keyword arguments; @pxref{Argument
3165 Lists}. All keyword arguments are optional and, if specified,
3166 may appear in any order.
3168 The @code{:key} argument should be passed either @code{nil}, or a
3169 function of one argument. This key function is used as a filter
3170 through which the elements of the sequence are seen; for example,
3171 @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}.
3172 It searches for an element of the list whose @sc{car} equals
3173 @code{x}, rather than for an element which equals @code{x} itself.
3174 If @code{:key} is omitted or @code{nil}, the filter is effectively
3175 the identity function.
3177 The @code{:test} and @code{:test-not} arguments should be either
3178 @code{nil}, or functions of two arguments. The test function is
3179 used to compare two sequence elements, or to compare a search value
3180 with sequence elements. (The two values are passed to the test
3181 function in the same order as the original sequence function
3182 arguments from which they are derived, or, if they both come from
3183 the same sequence, in the same order as they appear in that sequence.)
3184 The @code{:test} argument specifies a function which must return
3185 true (non-@code{nil}) to indicate a match; instead, you may use
3186 @code{:test-not} to give a function which returns @emph{false} to
3187 indicate a match. The default test function is @code{eql}.
3189 Many functions that take @var{item} and @code{:test} or @code{:test-not}
3190 arguments also come in @code{-if} and @code{-if-not} varieties,
3191 where a @var{predicate} function is passed instead of @var{item},
3192 and sequence elements match if the predicate returns true on them
3193 (or false in the case of @code{-if-not}). For example:
3196 (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq)
3200 to remove all zeros from sequence @code{seq}.
3202 Some operations can work on a subsequence of the argument sequence;
3203 these function take @code{:start} and @code{:end} arguments, which
3204 default to zero and the length of the sequence, respectively.
3205 Only elements between @var{start} (inclusive) and @var{end}
3206 (exclusive) are affected by the operation. The @var{end} argument
3207 may be passed @code{nil} to signify the length of the sequence;
3208 otherwise, both @var{start} and @var{end} must be integers, with
3209 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}.
3210 If the function takes two sequence arguments, the limits are
3211 defined by keywords @code{:start1} and @code{:end1} for the first,
3212 and @code{:start2} and @code{:end2} for the second.
3214 A few functions accept a @code{:from-end} argument, which, if
3215 non-@code{nil}, causes the operation to go from right-to-left
3216 through the sequence instead of left-to-right, and a @code{:count}
3217 argument, which specifies an integer maximum number of elements
3218 to be removed or otherwise processed.
3220 The sequence functions make no guarantees about the order in
3221 which the @code{:test}, @code{:test-not}, and @code{:key} functions
3222 are called on various elements. Therefore, it is a bad idea to depend
3223 on side effects of these functions. For example, @code{:from-end}
3224 may cause the sequence to be scanned actually in reverse, or it may
3225 be scanned forwards but computing a result ``as if'' it were scanned
3226 backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every},
3227 @emph{do} specify exactly the order in which the function is called
3228 so side effects are perfectly acceptable in those cases.)
3230 Strings may contain ``text properties'' as well
3231 as character data. Except as noted, it is undefined whether or
3232 not text properties are preserved by sequence functions. For
3233 example, @code{(cl-remove ?A @var{str})} may or may not preserve
3234 the properties of the characters copied from @var{str} into the
3237 @node Mapping over Sequences
3238 @section Mapping over Sequences
3241 These functions ``map'' the function you specify over the elements
3242 of lists or arrays. They are all variations on the theme of the
3243 built-in function @code{mapcar}.
3245 @defun cl-mapcar function seq &rest more-seqs
3246 This function calls @var{function} on successive parallel sets of
3247 elements from its argument sequences. Given a single @var{seq}
3248 argument it is equivalent to @code{mapcar}; given @var{n} sequences,
3249 it calls the function with the first elements of each of the sequences
3250 as the @var{n} arguments to yield the first element of the result
3251 list, then with the second elements, and so on. The mapping stops as
3252 soon as the shortest sequence runs out. The argument sequences may
3253 be any mixture of lists, strings, and vectors; the return sequence
3256 Common Lisp's @code{mapcar} accepts multiple arguments but works
3257 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence
3258 argument. This package's @code{cl-mapcar} works as a compatible
3262 @defun cl-map result-type function seq &rest more-seqs
3263 This function maps @var{function} over the argument sequences,
3264 just like @code{cl-mapcar}, but it returns a sequence of type
3265 @var{result-type} rather than a list. @var{result-type} must
3266 be one of the following symbols: @code{vector}, @code{string},
3267 @code{list} (in which case the effect is the same as for
3268 @code{cl-mapcar}), or @code{nil} (in which case the results are
3269 thrown away and @code{cl-map} returns @code{nil}).
3272 @defun cl-maplist function list &rest more-lists
3273 This function calls @var{function} on each of its argument lists,
3274 then on the @sc{cdr}s of those lists, and so on, until the
3275 shortest list runs out. The results are returned in the form
3276 of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except
3277 that it passes in the list pointers themselves rather than the
3278 @sc{car}s of the advancing pointers.
3281 @defun cl-mapc function seq &rest more-seqs
3282 This function is like @code{cl-mapcar}, except that the values returned
3283 by @var{function} are ignored and thrown away rather than being
3284 collected into a list. The return value of @code{cl-mapc} is @var{seq},
3285 the first sequence. This function is more general than the Emacs
3286 primitive @code{mapc}. (Note that this function is called
3287 @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you
3289 @c http://debbugs.gnu.org/6575
3292 @defun cl-mapl function list &rest more-lists
3293 This function is like @code{cl-maplist}, except that it throws away
3294 the values returned by @var{function}.
3297 @defun cl-mapcan function seq &rest more-seqs
3298 This function is like @code{cl-mapcar}, except that it concatenates
3299 the return values (which must be lists) using @code{nconc},
3300 rather than simply collecting them into a list.
3303 @defun cl-mapcon function list &rest more-lists
3304 This function is like @code{cl-maplist}, except that it concatenates
3305 the return values using @code{nconc}.
3308 @defun cl-some predicate seq &rest more-seqs
3309 This function calls @var{predicate} on each element of @var{seq}
3310 in turn; if @var{predicate} returns a non-@code{nil} value,
3311 @code{cl-some} returns that value, otherwise it returns @code{nil}.
3312 Given several sequence arguments, it steps through the sequences
3313 in parallel until the shortest one runs out, just as in
3314 @code{cl-mapcar}. You can rely on the left-to-right order in which
3315 the elements are visited, and on the fact that mapping stops
3316 immediately as soon as @var{predicate} returns non-@code{nil}.
3319 @defun cl-every predicate seq &rest more-seqs
3320 This function calls @var{predicate} on each element of the sequence(s)
3321 in turn; it returns @code{nil} as soon as @var{predicate} returns
3322 @code{nil} for any element, or @code{t} if the predicate was true
3326 @defun cl-notany predicate seq &rest more-seqs
3327 This function calls @var{predicate} on each element of the sequence(s)
3328 in turn; it returns @code{nil} as soon as @var{predicate} returns
3329 a non-@code{nil} value for any element, or @code{t} if the predicate
3330 was @code{nil} for all elements.
3333 @defun cl-notevery predicate seq &rest more-seqs
3334 This function calls @var{predicate} on each element of the sequence(s)
3335 in turn; it returns a non-@code{nil} value as soon as @var{predicate}
3336 returns @code{nil} for any element, or @code{t} if the predicate was
3337 true for all elements.
3340 @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key}
3341 This function combines the elements of @var{seq} using an associative
3342 binary operation. Suppose @var{function} is @code{*} and @var{seq} is
3343 the list @code{(2 3 4 5)}. The first two elements of the list are
3344 combined with @code{(* 2 3) = 6}; this is combined with the next
3345 element, @code{(* 6 4) = 24}, and that is combined with the final
3346 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens
3347 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as
3348 an explicit call to @code{cl-reduce}.
3350 If @code{:from-end} is true, the reduction is right-associative instead
3351 of left-associative:
3354 (cl-reduce '- '(1 2 3 4))
3355 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8
3356 (cl-reduce '- '(1 2 3 4) :from-end t)
3357 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2
3360 If @code{:key} is specified, it is a function of one argument, which
3361 is called on each of the sequence elements in turn.
3363 If @code{:initial-value} is specified, it is effectively added to the
3364 front (or rear in the case of @code{:from-end}) of the sequence.
3365 The @code{:key} function is @emph{not} applied to the initial value.
3367 If the sequence, including the initial value, has exactly one element
3368 then that element is returned without ever calling @var{function}.
3369 If the sequence is empty (and there is no initial value), then
3370 @var{function} is called with no arguments to obtain the return value.
3373 All of these mapping operations can be expressed conveniently in
3374 terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will
3375 be faster since it generates the loop as in-line code with no
3378 @node Sequence Functions
3379 @section Sequence Functions
3382 This section describes a number of Common Lisp functions for
3383 operating on sequences.
3385 @defun cl-subseq sequence start &optional end
3386 This function returns a given subsequence of the argument
3387 @var{sequence}, which may be a list, string, or vector.
3388 The indices @var{start} and @var{end} must be in range, and
3389 @var{start} must be no greater than @var{end}. If @var{end}
3390 is omitted, it defaults to the length of the sequence. The
3391 return value is always a copy; it does not share structure
3392 with @var{sequence}.
3394 As an extension to Common Lisp, @var{start} and/or @var{end}
3395 may be negative, in which case they represent a distance back
3396 from the end of the sequence. This is for compatibility with
3397 Emacs's @code{substring} function. Note that @code{cl-subseq} is
3398 the @emph{only} sequence function that allows negative
3399 @var{start} and @var{end}.
3401 You can use @code{setf} on a @code{cl-subseq} form to replace a
3402 specified range of elements with elements from another sequence.
3403 The replacement is done as if by @code{cl-replace}, described below.
3406 @defun cl-concatenate result-type &rest seqs
3407 This function concatenates the argument sequences together to
3408 form a result sequence of type @var{result-type}, one of the
3409 symbols @code{vector}, @code{string}, or @code{list}. The
3410 arguments are always copied, even in cases such as
3411 @code{(cl-concatenate 'list '(1 2 3))} where the result is
3412 identical to an argument.
3415 @defun cl-fill seq item @t{&key :start :end}
3416 This function fills the elements of the sequence (or the specified
3417 part of the sequence) with the value @var{item}.
3420 @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2}
3421 This function copies part of @var{seq2} into part of @var{seq1}.
3422 The sequence @var{seq1} is not stretched or resized; the amount
3423 of data copied is simply the shorter of the source and destination
3424 (sub)sequences. The function returns @var{seq1}.
3426 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement
3427 will work correctly even if the regions indicated by the start
3428 and end arguments overlap. However, if @var{seq1} and @var{seq2}
3429 are lists that share storage but are not @code{eq}, and the
3430 start and end arguments specify overlapping regions, the effect
3434 @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end}
3435 This returns a copy of @var{seq} with all elements matching
3436 @var{item} removed. The result may share storage with or be
3437 @code{eq} to @var{seq} in some circumstances, but the original
3438 @var{seq} will not be modified. The @code{:test}, @code{:test-not},
3439 and @code{:key} arguments define the matching test that is used;
3440 by default, elements @code{eql} to @var{item} are removed. The
3441 @code{:count} argument specifies the maximum number of matching
3442 elements that can be removed (only the leftmost @var{count} matches
3443 are removed). The @code{:start} and @code{:end} arguments specify
3444 a region in @var{seq} in which elements will be removed; elements
3445 outside that region are not matched or removed. The @code{:from-end}
3446 argument, if true, says that elements should be deleted from the
3447 end of the sequence rather than the beginning (this matters only
3448 if @var{count} was also specified).
3451 @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end}
3452 This deletes all elements of @var{seq} that match @var{item}.
3453 It is a destructive operation. Since Emacs Lisp does not support
3454 stretchable strings or vectors, this is the same as @code{cl-remove}
3455 for those sequence types. On lists, @code{cl-remove} will copy the
3456 list if necessary to preserve the original list, whereas
3457 @code{cl-delete} will splice out parts of the argument list.
3458 Compare @code{append} and @code{nconc}, which are analogous
3459 non-destructive and destructive list operations in Emacs Lisp.
3462 @findex cl-remove-if
3463 @findex cl-remove-if-not
3464 @findex cl-delete-if
3465 @findex cl-delete-if-not
3466 The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not},
3467 @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly.
3469 @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3470 This function returns a copy of @var{seq} with duplicate elements
3471 removed. Specifically, if two elements from the sequence match
3472 according to the @code{:test}, @code{:test-not}, and @code{:key}
3473 arguments, only the rightmost one is retained. If @code{:from-end}
3474 is true, the leftmost one is retained instead. If @code{:start} or
3475 @code{:end} is specified, only elements within that subsequence are
3476 examined or removed.
3479 @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3480 This function deletes duplicate elements from @var{seq}. It is
3481 a destructive version of @code{cl-remove-duplicates}.
3484 @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3485 This function returns a copy of @var{seq}, with all elements
3486 matching @var{old} replaced with @var{new}. The @code{:count},
3487 @code{:start}, @code{:end}, and @code{:from-end} arguments may be
3488 used to limit the number of substitutions made.
3491 @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3492 This is a destructive version of @code{cl-substitute}; it performs
3493 the substitution using @code{setcar} or @code{aset} rather than
3494 by returning a changed copy of the sequence.
3497 @findex cl-substitute-if
3498 @findex cl-substitute-if-not
3499 @findex cl-nsubstitute-if
3500 @findex cl-nsubstitute-if-not
3501 The functions @code{cl-substitute-if}, @code{cl-substitute-if-not},
3502 @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined
3503 similarly. For these, a @var{predicate} is given in place of the
3506 @node Searching Sequences
3507 @section Searching Sequences
3510 These functions search for elements or subsequences in a sequence.
3511 (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.)
3513 @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end}
3514 This function searches @var{seq} for an element matching @var{item}.
3515 If it finds a match, it returns the matching element. Otherwise,
3516 it returns @code{nil}. It returns the leftmost match, unless
3517 @code{:from-end} is true, in which case it returns the rightmost
3518 match. The @code{:start} and @code{:end} arguments may be used to
3519 limit the range of elements that are searched.
3522 @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end}
3523 This function is like @code{cl-find}, except that it returns the
3524 integer position in the sequence of the matching item rather than
3525 the item itself. The position is relative to the start of the
3526 sequence as a whole, even if @code{:start} is non-zero. The function
3527 returns @code{nil} if no matching element was found.
3530 @defun cl-count item seq @t{&key :test :test-not :key :start :end}
3531 This function returns the number of elements of @var{seq} which
3532 match @var{item}. The result is always a nonnegative integer.
3536 @findex cl-find-if-not
3537 @findex cl-position-if
3538 @findex cl-position-if-not
3540 @findex cl-count-if-not
3541 The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if},
3542 @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not}
3543 functions are defined similarly.
3545 @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end}
3546 This function compares the specified parts of @var{seq1} and
3547 @var{seq2}. If they are the same length and the corresponding
3548 elements match (according to @code{:test}, @code{:test-not},
3549 and @code{:key}), the function returns @code{nil}. If there is
3550 a mismatch, the function returns the index (relative to @var{seq1})
3551 of the first mismatching element. This will be the leftmost pair of
3552 elements that do not match, or the position at which the shorter of
3553 the two otherwise-matching sequences runs out.
3555 If @code{:from-end} is true, then the elements are compared from right
3556 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}.
3557 If the sequences differ, then one plus the index of the rightmost
3558 difference (relative to @var{seq1}) is returned.
3560 An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)},
3561 which compares two strings case-insensitively.
3564 @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2}
3565 This function searches @var{seq2} for a subsequence that matches
3566 @var{seq1} (or part of it specified by @code{:start1} and
3567 @code{:end1}). Only matches that fall entirely within the region
3568 defined by @code{:start2} and @code{:end2} will be considered.
3569 The return value is the index of the leftmost element of the
3570 leftmost match, relative to the start of @var{seq2}, or @code{nil}
3571 if no matches were found. If @code{:from-end} is true, the
3572 function finds the @emph{rightmost} matching subsequence.
3575 @node Sorting Sequences
3576 @section Sorting Sequences
3578 @defun cl-sort seq predicate @t{&key :key}
3579 This function sorts @var{seq} into increasing order as determined
3580 by using @var{predicate} to compare pairs of elements. @var{predicate}
3581 should return true (non-@code{nil}) if and only if its first argument
3582 is less than (not equal to) its second argument. For example,
3583 @code{<} and @code{string-lessp} are suitable predicate functions
3584 for sorting numbers and strings, respectively; @code{>} would sort
3585 numbers into decreasing rather than increasing order.
3587 This function differs from Emacs's built-in @code{sort} in that it
3588 can operate on any type of sequence, not just lists. Also, it
3589 accepts a @code{:key} argument, which is used to preprocess data
3590 fed to the @var{predicate} function. For example,
3593 (setq data (cl-sort data 'string-lessp :key 'downcase))
3597 sorts @var{data}, a sequence of strings, into increasing alphabetical
3598 order without regard to case. A @code{:key} function of @code{car}
3599 would be useful for sorting association lists. It should only be a
3600 simple accessor though, since it's used heavily in the current
3603 The @code{cl-sort} function is destructive; it sorts lists by actually
3604 rearranging the @sc{cdr} pointers in suitable fashion.
3607 @defun cl-stable-sort seq predicate @t{&key :key}
3608 This function sorts @var{seq} @dfn{stably}, meaning two elements
3609 which are equal in terms of @var{predicate} are guaranteed not to
3610 be rearranged out of their original order by the sort.
3612 In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent
3613 in Emacs Lisp because the underlying @code{sort} function is
3614 stable by default. However, this package reserves the right to
3615 use non-stable methods for @code{cl-sort} in the future.
3618 @defun cl-merge type seq1 seq2 predicate @t{&key :key}
3619 This function merges two sequences @var{seq1} and @var{seq2} by
3620 interleaving their elements. The result sequence, of type @var{type}
3621 (in the sense of @code{cl-concatenate}), has length equal to the sum
3622 of the lengths of the two input sequences. The sequences may be
3623 modified destructively. Order of elements within @var{seq1} and
3624 @var{seq2} is preserved in the interleaving; elements of the two
3625 sequences are compared by @var{predicate} (in the sense of
3626 @code{sort}) and the lesser element goes first in the result.
3627 When elements are equal, those from @var{seq1} precede those from
3628 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are
3629 both sorted according to @var{predicate}, then the result will be
3630 a merged sequence which is (stably) sorted according to
3638 The functions described here operate on lists.
3641 * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc.
3642 * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc.
3643 * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc.
3644 * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc.
3647 @node List Functions
3648 @section List Functions
3651 This section describes a number of simple operations on lists,
3652 i.e., chains of cons cells.
3655 This function is equivalent to @code{(car (cdr (cdr @var{x})))}.
3656 Likewise, this package defines all 24 @code{c@var{xxx}r} functions
3657 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s.
3658 All of these functions are @code{setf}-able, and calls to them
3659 are expanded inline by the byte-compiler for maximum efficiency.
3663 This function is a synonym for @code{(car @var{x})}. Likewise,
3664 the functions @code{cl-second}, @code{cl-third}, @dots{}, through
3665 @code{cl-tenth} return the given element of the list @var{x}.
3669 This function is a synonym for @code{(cdr @var{x})}.
3673 Common Lisp defines this function to act like @code{null}, but
3674 signaling an error if @code{x} is neither a @code{nil} nor a
3675 cons cell. This package simply defines @code{cl-endp} as a synonym
3679 @defun cl-list-length x
3680 This function returns the length of list @var{x}, exactly like
3681 @code{(length @var{x})}, except that if @var{x} is a circular
3682 list (where the @sc{cdr}-chain forms a loop rather than terminating
3683 with @code{nil}), this function returns @code{nil}. (The regular
3684 @code{length} function would get stuck if given a circular list.
3685 See also the @code{safe-length} function.)
3688 @defun cl-list* arg &rest others
3689 This function constructs a list of its arguments. The final
3690 argument becomes the @sc{cdr} of the last cell constructed.
3691 Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to
3692 @code{(cons @var{a} (cons @var{b} @var{c}))}, and
3693 @code{(cl-list* @var{a} @var{b} nil)} is equivalent to
3694 @code{(list @var{a} @var{b})}.
3697 @defun cl-ldiff list sublist
3698 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to
3699 one of the cons cells of @var{list}, then this function returns
3700 a copy of the part of @var{list} up to but not including
3701 @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns
3702 the first two elements of the list @code{x}. The result is a
3703 copy; the original @var{list} is not modified. If @var{sublist}
3704 is not a sublist of @var{list}, a copy of the entire @var{list}
3708 @defun cl-copy-list list
3709 This function returns a copy of the list @var{list}. It copies
3710 dotted lists like @code{(1 2 . 3)} correctly.
3713 @defun cl-tree-equal x y @t{&key :test :test-not :key}
3714 This function compares two trees of cons cells. If @var{x} and
3715 @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are
3716 compared recursively. If neither @var{x} nor @var{y} is a cons
3717 cell, they are compared by @code{eql}, or according to the
3718 specified test. The @code{:key} function, if specified, is
3719 applied to the elements of both trees. @xref{Sequences}.
3722 @node Substitution of Expressions
3723 @section Substitution of Expressions
3726 These functions substitute elements throughout a tree of cons
3727 cells. (@xref{Sequence Functions}, for the @code{cl-substitute}
3728 function, which works on just the top-level elements of a list.)
3730 @defun cl-subst new old tree @t{&key :test :test-not :key}
3731 This function substitutes occurrences of @var{old} with @var{new}
3732 in @var{tree}, a tree of cons cells. It returns a substituted
3733 tree, which will be a copy except that it may share storage with
3734 the argument @var{tree} in parts where no substitutions occurred.
3735 The original @var{tree} is not modified. This function recurses
3736 on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s
3737 of the component cons cells. If @var{old} is itself a cons cell,
3738 then matching cells in the tree are substituted as usual without
3739 recursively substituting in that cell. Comparisons with @var{old}
3740 are done according to the specified test (@code{eql} by default).
3741 The @code{:key} function is applied to the elements of the tree
3742 but not to @var{old}.
3745 @defun cl-nsubst new old tree @t{&key :test :test-not :key}
3746 This function is like @code{cl-subst}, except that it works by
3747 destructive modification (by @code{setcar} or @code{setcdr})
3748 rather than copying.
3752 @findex cl-subst-if-not
3753 @findex cl-nsubst-if
3754 @findex cl-nsubst-if-not
3755 The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and
3756 @code{cl-nsubst-if-not} functions are defined similarly.
3758 @defun cl-sublis alist tree @t{&key :test :test-not :key}
3759 This function is like @code{cl-subst}, except that it takes an
3760 association list @var{alist} of @var{old}-@var{new} pairs.
3761 Each element of the tree (after applying the @code{:key}
3762 function, if any), is compared with the @sc{car}s of
3763 @var{alist}; if it matches, it is replaced by the corresponding
3767 @defun cl-nsublis alist tree @t{&key :test :test-not :key}
3768 This is a destructive version of @code{cl-sublis}.
3772 @section Lists as Sets
3775 These functions perform operations on lists that represent sets
3778 @defun cl-member item list @t{&key :test :test-not :key}
3779 This function searches @var{list} for an element matching @var{item}.
3780 If a match is found, it returns the cons cell whose @sc{car} was
3781 the matching element. Otherwise, it returns @code{nil}. Elements
3782 are compared by @code{eql} by default; you can use the @code{:test},
3783 @code{:test-not}, and @code{:key} arguments to modify this behavior.
3786 The standard Emacs lisp function @code{member} uses @code{equal} for
3787 comparisons; it is equivalent to @code{(cl-member @var{item} @var{list}
3788 :test 'equal)}. With no keyword arguments, @code{cl-member} is
3789 equivalent to @code{memq}.
3792 @findex cl-member-if
3793 @findex cl-member-if-not
3794 The @code{cl-member-if} and @code{cl-member-if-not} functions
3795 analogously search for elements that satisfy a given predicate.
3797 @defun cl-tailp sublist list
3798 This function returns @code{t} if @var{sublist} is a sublist of
3799 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to
3800 any of its @sc{cdr}s.
3803 @defun cl-adjoin item list @t{&key :test :test-not :key}
3804 This function conses @var{item} onto the front of @var{list},
3805 like @code{(cons @var{item} @var{list})}, but only if @var{item}
3806 is not already present on the list (as determined by @code{cl-member}).
3807 If a @code{:key} argument is specified, it is applied to
3808 @var{item} as well as to the elements of @var{list} during
3809 the search, on the reasoning that @var{item} is ``about'' to
3810 become part of the list.
3813 @defun cl-union list1 list2 @t{&key :test :test-not :key}
3814 This function combines two lists that represent sets of items,
3815 returning a list that represents the union of those two sets.
3816 The resulting list contains all items that appear in @var{list1}
3817 or @var{list2}, and no others. If an item appears in both
3818 @var{list1} and @var{list2} it is copied only once. If
3819 an item is duplicated in @var{list1} or @var{list2}, it is
3820 undefined whether or not that duplication will survive in the
3821 result list. The order of elements in the result list is also
3825 @defun cl-nunion list1 list2 @t{&key :test :test-not :key}
3826 This is a destructive version of @code{cl-union}; rather than copying,
3827 it tries to reuse the storage of the argument lists if possible.
3830 @defun cl-intersection list1 list2 @t{&key :test :test-not :key}
3831 This function computes the intersection of the sets represented
3832 by @var{list1} and @var{list2}. It returns the list of items
3833 that appear in both @var{list1} and @var{list2}.
3836 @defun cl-nintersection list1 list2 @t{&key :test :test-not :key}
3837 This is a destructive version of @code{cl-intersection}. It
3838 tries to reuse storage of @var{list1} rather than copying.
3839 It does @emph{not} reuse the storage of @var{list2}.
3842 @defun cl-set-difference list1 list2 @t{&key :test :test-not :key}
3843 This function computes the ``set difference'' of @var{list1}
3844 and @var{list2}, i.e., the set of elements that appear in
3845 @var{list1} but @emph{not} in @var{list2}.
3848 @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key}
3849 This is a destructive @code{cl-set-difference}, which will try
3850 to reuse @var{list1} if possible.
3853 @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key}
3854 This function computes the ``set exclusive or'' of @var{list1}
3855 and @var{list2}, i.e., the set of elements that appear in
3856 exactly one of @var{list1} and @var{list2}.
3859 @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key}
3860 This is a destructive @code{cl-set-exclusive-or}, which will try
3861 to reuse @var{list1} and @var{list2} if possible.
3864 @defun cl-subsetp list1 list2 @t{&key :test :test-not :key}
3865 This function checks whether @var{list1} represents a subset
3866 of @var{list2}, i.e., whether every element of @var{list1}
3867 also appears in @var{list2}.
3870 @node Association Lists
3871 @section Association Lists
3874 An @dfn{association list} is a list representing a mapping from
3875 one set of values to another; any list whose elements are cons
3876 cells is an association list.
3878 @defun cl-assoc item a-list @t{&key :test :test-not :key}
3879 This function searches the association list @var{a-list} for an
3880 element whose @sc{car} matches (in the sense of @code{:test},
3881 @code{:test-not}, and @code{:key}, or by comparison with @code{eql})
3882 a given @var{item}. It returns the matching element, if any,
3883 otherwise @code{nil}. It ignores elements of @var{a-list} that
3884 are not cons cells. (This corresponds to the behavior of
3885 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's
3886 @code{assoc} ignores @code{nil}s but considers any other non-cons
3887 elements of @var{a-list} to be an error.)
3890 @defun cl-rassoc item a-list @t{&key :test :test-not :key}
3891 This function searches for an element whose @sc{cdr} matches
3892 @var{item}. If @var{a-list} represents a mapping, this applies
3893 the inverse of the mapping to @var{item}.
3897 @findex cl-assoc-if-not
3898 @findex cl-rassoc-if
3899 @findex cl-rassoc-if-not
3900 The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if},
3901 and @code{cl-rassoc-if-not} functions are defined similarly.
3903 Two simple functions for constructing association lists are:
3905 @defun cl-acons key value alist
3906 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}.
3909 @defun cl-pairlis keys values &optional alist
3910 This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values})
3918 The Common Lisp @dfn{structure} mechanism provides a general way
3919 to define data types similar to C's @code{struct} types. A
3920 structure is a Lisp object containing some number of @dfn{slots},
3921 each of which can hold any Lisp data object. Functions are
3922 provided for accessing and setting the slots, creating or copying
3923 structure objects, and recognizing objects of a particular structure
3926 In true Common Lisp, each structure type is a new type distinct
3927 from all existing Lisp types. Since the underlying Emacs Lisp
3928 system provides no way to create new distinct types, this package
3929 implements structures as vectors (or lists upon request) with a
3930 special ``tag'' symbol to identify them.
3932 @defmac cl-defstruct name slots@dots{}
3933 The @code{cl-defstruct} form defines a new structure type called
3934 @var{name}, with the specified @var{slots}. (The @var{slots}
3935 may begin with a string which documents the structure type.)
3936 In the simplest case, @var{name} and each of the @var{slots}
3937 are symbols. For example,
3940 (cl-defstruct person name age sex)
3944 defines a struct type called @code{person} that contains three
3945 slots. Given a @code{person} object @var{p}, you can access those
3946 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})},
3947 and @code{(person-sex @var{p})}. You can also change these slots by
3948 using @code{setf} on any of these place forms, for example:
3951 (cl-incf (person-age birthday-boy))
3954 You can create a new @code{person} by calling @code{make-person},
3955 which takes keyword arguments @code{:name}, @code{:age}, and
3956 @code{:sex} to specify the initial values of these slots in the
3957 new object. (Omitting any of these arguments leaves the corresponding
3958 slot ``undefined'', according to the Common Lisp standard; in Emacs
3959 Lisp, such uninitialized slots are filled with @code{nil}.)
3961 Given a @code{person}, @code{(copy-person @var{p})} makes a new
3962 object of the same type whose slots are @code{eq} to those of @var{p}.
3964 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns
3965 true if @var{x} looks like a @code{person}, and false otherwise. (Again,
3966 in Common Lisp this predicate would be exact; in Emacs Lisp the
3967 best it can do is verify that @var{x} is a vector of the correct
3968 length that starts with the correct tag symbol.)
3970 Accessors like @code{person-name} normally check their arguments
3971 (effectively using @code{person-p}) and signal an error if the
3972 argument is the wrong type. This check is affected by
3973 @code{(optimize (safety @dots{}))} declarations. Safety level 1,
3974 the default, uses a somewhat optimized check that will detect all
3975 incorrect arguments, but may use an uninformative error message
3976 (e.g., ``expected a vector'' instead of ``expected a @code{person}'').
3977 Safety level 0 omits all checks except as provided by the underlying
3978 @code{aref} call; safety levels 2 and 3 do rigorous checking that will
3979 always print a descriptive error message for incorrect inputs.
3980 @xref{Declarations}.
3983 (setq dave (make-person :name "Dave" :sex 'male))
3984 @result{} [cl-struct-person "Dave" nil male]
3985 (setq other (copy-person dave))
3986 @result{} [cl-struct-person "Dave" nil male]
3989 (eq (person-name dave) (person-name other))
3993 (person-p [1 2 3 4])
3997 (person-p '[cl-struct-person counterfeit person object])
4001 In general, @var{name} is either a name symbol or a list of a name
4002 symbol followed by any number of @dfn{struct options}; each @var{slot}
4003 is either a slot symbol or a list of the form @samp{(@var{slot-name}
4004 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value}
4005 is a Lisp form that is evaluated any time an instance of the
4006 structure type is created without specifying that slot's value.
4008 Common Lisp defines several slot options, but the only one
4009 implemented in this package is @code{:read-only}. A non-@code{nil}
4010 value for this option means the slot should not be @code{setf}-able;
4011 the slot's value is determined when the object is created and does
4012 not change afterward.
4015 (cl-defstruct person
4016 (name nil :read-only t)
4021 Any slot options other than @code{:read-only} are ignored.
4023 For obscure historical reasons, structure options take a different
4024 form than slot options. A structure option is either a keyword
4025 symbol, or a list beginning with a keyword symbol possibly followed
4026 by arguments. (By contrast, slot options are key-value pairs not
4030 (cl-defstruct (person (:constructor create-person)
4036 The following structure options are recognized.
4040 The argument is a symbol whose print name is used as the prefix for
4041 the names of slot accessor functions. The default is the name of
4042 the struct type followed by a hyphen. The option @code{(:conc-name p-)}
4043 would change this prefix to @code{p-}. Specifying @code{nil} as an
4044 argument means no prefix, so that the slot names themselves are used
4045 to name the accessor functions.
4048 In the simple case, this option takes one argument which is an
4049 alternate name to use for the constructor function. The default
4050 is @code{make-@var{name}}, e.g., @code{make-person}. The above
4051 example changes this to @code{create-person}. Specifying @code{nil}
4052 as an argument means that no standard constructor should be
4055 In the full form of this option, the constructor name is followed
4056 by an arbitrary argument list. @xref{Program Structure}, for a
4057 description of the format of Common Lisp argument lists. All
4058 options, such as @code{&rest} and @code{&key}, are supported.
4059 The argument names should match the slot names; each slot is
4060 initialized from the corresponding argument. Slots whose names
4061 do not appear in the argument list are initialized based on the
4062 @var{default-value} in their slot descriptor. Also, @code{&optional}
4063 and @code{&key} arguments that don't specify defaults take their
4064 defaults from the slot descriptor. It is valid to include arguments
4065 that don't correspond to slot names; these are useful if they are
4066 referred to in the defaults for optional, keyword, or @code{&aux}
4067 arguments that @emph{do} correspond to slots.
4069 You can specify any number of full-format @code{:constructor}
4070 options on a structure. The default constructor is still generated
4071 as well unless you disable it with a simple-format @code{:constructor}
4077 (:constructor nil) ; no default constructor
4078 (:constructor new-person
4079 (name sex &optional (age 0)))
4080 (:constructor new-hound (&key (name "Rover")
4082 &aux (age (* 7 dog-years))
4087 The first constructor here takes its arguments positionally rather
4088 than by keyword. (In official Common Lisp terminology, constructors
4089 that work By Order of Arguments instead of by keyword are called
4090 ``BOA constructors''. No, I'm not making this up.) For example,
4091 @code{(new-person "Jane" 'female)} generates a person whose slots
4092 are @code{"Jane"}, 0, and @code{female}, respectively.
4094 The second constructor takes two keyword arguments, @code{:name},
4095 which initializes the @code{name} slot and defaults to @code{"Rover"},
4096 and @code{:dog-years}, which does not itself correspond to a slot
4097 but which is used to initialize the @code{age} slot. The @code{sex}
4098 slot is forced to the symbol @code{canine} with no syntax for
4102 The argument is an alternate name for the copier function for
4103 this type. The default is @code{copy-@var{name}}. @code{nil}
4104 means not to generate a copier function. (In this implementation,
4105 all copier functions are simply synonyms for @code{copy-sequence}.)
4108 The argument is an alternate name for the predicate that recognizes
4109 objects of this type. The default is @code{@var{name}-p}. @code{nil}
4110 means not to generate a predicate function. (If the @code{:type}
4111 option is used without the @code{:named} option, no predicate is
4114 In true Common Lisp, @code{typep} is always able to recognize a
4115 structure object even if @code{:predicate} was used. In this
4116 package, @code{cl-typep} simply looks for a function called
4117 @code{@var{typename}-p}, so it will work for structure types
4118 only if they used the default predicate name.
4121 This option implements a very limited form of C++-style inheritance.
4122 The argument is the name of another structure type previously
4123 created with @code{cl-defstruct}. The effect is to cause the new
4124 structure type to inherit all of the included structure's slots
4125 (plus, of course, any new slots described by this struct's slot
4126 descriptors). The new structure is considered a ``specialization''
4127 of the included one. In fact, the predicate and slot accessors
4128 for the included type will also accept objects of the new type.
4130 If there are extra arguments to the @code{:include} option after
4131 the included-structure name, these options are treated as replacement
4132 slot descriptors for slots in the included structure, possibly with
4133 modified default values. Borrowing an example from Steele:
4136 (cl-defstruct person name (age 0) sex)
4138 (cl-defstruct (astronaut (:include person (age 45)))
4140 (favorite-beverage 'tang))
4143 (setq joe (make-person :name "Joe"))
4144 @result{} [cl-struct-person "Joe" 0 nil]
4145 (setq buzz (make-astronaut :name "Buzz"))
4146 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang]
4148 (list (person-p joe) (person-p buzz))
4150 (list (astronaut-p joe) (astronaut-p buzz))
4155 (astronaut-name joe)
4156 @result{} error: "astronaut-name accessing a non-astronaut"
4159 Thus, if @code{astronaut} is a specialization of @code{person},
4160 then every @code{astronaut} is also a @code{person} (but not the
4161 other way around). Every @code{astronaut} includes all the slots
4162 of a @code{person}, plus extra slots that are specific to
4163 astronauts. Operations that work on people (like @code{person-name})
4164 work on astronauts just like other people.
4166 @item :print-function
4167 In full Common Lisp, this option allows you to specify a function
4168 that is called to print an instance of the structure type. The
4169 Emacs Lisp system offers no hooks into the Lisp printer which would
4170 allow for such a feature, so this package simply ignores
4171 @code{:print-function}.
4174 The argument should be one of the symbols @code{vector} or @code{list}.
4175 This tells which underlying Lisp data type should be used to implement
4176 the new structure type. Vectors are used by default, but
4177 @code{(:type list)} will cause structure objects to be stored as
4180 The vector representation for structure objects has the advantage
4181 that all structure slots can be accessed quickly, although creating
4182 vectors is a bit slower in Emacs Lisp. Lists are easier to create,
4183 but take a relatively long time accessing the later slots.
4186 This option, which takes no arguments, causes a characteristic ``tag''
4187 symbol to be stored at the front of the structure object. Using
4188 @code{:type} without also using @code{:named} will result in a
4189 structure type stored as plain vectors or lists with no identifying
4192 The default, if you don't specify @code{:type} explicitly, is to
4193 use named vectors. Therefore, @code{:named} is only useful in
4194 conjunction with @code{:type}.
4197 (cl-defstruct (person1) name age sex)
4198 (cl-defstruct (person2 (:type list) :named) name age sex)
4199 (cl-defstruct (person3 (:type list)) name age sex)
4201 (setq p1 (make-person1))
4202 @result{} [cl-struct-person1 nil nil nil]
4203 (setq p2 (make-person2))
4204 @result{} (person2 nil nil nil)
4205 (setq p3 (make-person3))
4206 @result{} (nil nil nil)
4213 @result{} error: function person3-p undefined
4216 Since unnamed structures don't have tags, @code{cl-defstruct} is not
4217 able to make a useful predicate for recognizing them. Also,
4218 accessors like @code{person3-name} will be generated but they
4219 will not be able to do any type checking. The @code{person3-name}
4220 function, for example, will simply be a synonym for @code{car} in
4221 this case. By contrast, @code{person2-name} is able to verify
4222 that its argument is indeed a @code{person2} object before
4225 @item :initial-offset
4226 The argument must be a nonnegative integer. It specifies a
4227 number of slots to be left ``empty'' at the front of the
4228 structure. If the structure is named, the tag appears at the
4229 specified position in the list or vector; otherwise, the first
4230 slot appears at that position. Earlier positions are filled
4231 with @code{nil} by the constructors and ignored otherwise. If
4232 the type @code{:include}s another type, then @code{:initial-offset}
4233 specifies a number of slots to be skipped between the last slot
4234 of the included type and the first new slot.
4238 Except as noted, the @code{cl-defstruct} facility of this package is
4239 entirely compatible with that of Common Lisp.
4242 @chapter Assertions and Errors
4245 This section describes two macros that test @dfn{assertions}, i.e.,
4246 conditions which must be true if the program is operating correctly.
4247 Assertions never add to the behavior of a Lisp program; they simply
4248 make ``sanity checks'' to make sure everything is as it should be.
4250 If the optimization property @code{speed} has been set to 3, and
4251 @code{safety} is less than 3, then the byte-compiler will optimize
4252 away the following assertions. Because assertions might be optimized
4253 away, it is a bad idea for them to include side-effects.
4255 @defmac cl-assert test-form [show-args string args@dots{}]
4256 This form verifies that @var{test-form} is true (i.e., evaluates to
4257 a non-@code{nil} value). If so, it returns @code{nil}. If the test
4258 is not satisfied, @code{cl-assert} signals an error.
4260 A default error message will be supplied which includes @var{test-form}.
4261 You can specify a different error message by including a @var{string}
4262 argument plus optional extra arguments. Those arguments are simply
4263 passed to @code{error} to signal the error.
4265 If the optional second argument @var{show-args} is @code{t} instead
4266 of @code{nil}, then the error message (with or without @var{string})
4267 will also include all non-constant arguments of the top-level
4268 @var{form}. For example:
4271 (cl-assert (> x 10) t "x is too small: %d")
4274 This usage of @var{show-args} is an extension to Common Lisp. In
4275 true Common Lisp, the second argument gives a list of @var{places}
4276 which can be @code{setf}'d by the user before continuing from the
4277 error. Since Emacs Lisp does not support continuable errors, it
4278 makes no sense to specify @var{places}.
4281 @defmac cl-check-type form type [string]
4282 This form verifies that @var{form} evaluates to a value of type
4283 @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type}
4284 signals a @code{wrong-type-argument} error. The default error message
4285 lists the erroneous value along with @var{type} and @var{form}
4286 themselves. If @var{string} is specified, it is included in the
4287 error message in place of @var{type}. For example:
4290 (cl-check-type x (integer 1 *) "a positive integer")
4293 @xref{Type Predicates}, for a description of the type specifiers
4294 that may be used for @var{type}.
4296 Note that in Common Lisp, the first argument to @code{check-type}
4297 must be a @var{place} suitable for use by @code{setf}, because
4298 @code{check-type} signals a continuable error that allows the
4299 user to modify @var{place}.
4302 @node Efficiency Concerns
4303 @appendix Efficiency Concerns
4308 Many of the advanced features of this package, such as @code{cl-defun},
4309 @code{cl-loop}, etc., are implemented as Lisp macros. In
4310 byte-compiled code, these complex notations will be expanded into
4311 equivalent Lisp code which is simple and efficient. For example,
4319 is expanded at compile-time to the Lisp form
4326 which is the most efficient ways of doing this operation
4327 in Lisp. Thus, there is no performance penalty for using the more
4328 readable @code{cl-incf} form in your compiled code.
4330 @emph{Interpreted} code, on the other hand, must expand these macros
4331 every time they are executed. For this reason it is strongly
4332 recommended that code making heavy use of macros be compiled.
4333 A loop using @code{cl-incf} a hundred times will execute considerably
4334 faster if compiled, and will also garbage-collect less because the
4335 macro expansion will not have to be generated, used, and thrown away a
4338 You can find out how a macro expands by using the
4339 @code{cl-prettyexpand} function.
4341 @defun cl-prettyexpand form &optional full
4342 This function takes a single Lisp form as an argument and inserts
4343 a nicely formatted copy of it in the current buffer (which must be
4344 in Lisp mode so that indentation works properly). It also expands
4345 all Lisp macros that appear in the form. The easiest way to use
4346 this function is to go to the @file{*scratch*} buffer and type, say,
4349 (cl-prettyexpand '(cl-loop for x below 10 collect x))
4353 and type @kbd{C-x C-e} immediately after the closing parenthesis;
4354 an expansion similar to:
4361 (setq G1004 (cons x G1004))
4367 will be inserted into the buffer. (The @code{cl-block} macro is
4368 expanded differently in the interpreter and compiler, so
4369 @code{cl-prettyexpand} just leaves it alone. The temporary
4370 variable @code{G1004} was created by @code{cl-gensym}.)
4372 If the optional argument @var{full} is true, then @emph{all}
4373 macros are expanded, including @code{cl-block}, @code{cl-eval-when},
4374 and compiler macros. Expansion is done as if @var{form} were
4375 a top-level form in a file being compiled.
4377 @c FIXME none of these examples are still applicable.
4382 (cl-prettyexpand '(cl-pushnew 'x list))
4383 @print{} (setq list (cl-adjoin 'x list))
4384 (cl-prettyexpand '(cl-pushnew 'x list) t)
4385 @print{} (setq list (if (memq 'x list) list (cons 'x list)))
4386 (cl-prettyexpand '(caddr (cl-member 'a list)) t)
4387 @print{} (car (cdr (cdr (memq 'a list))))
4391 Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all
4392 have built-in compiler macros to optimize them in common cases.
4395 @appendixsec Error Checking
4398 Common Lisp compliance has in general not been sacrificed for the
4399 sake of efficiency. A few exceptions have been made for cases
4400 where substantial gains were possible at the expense of marginal
4403 The Common Lisp standard (as embodied in Steele's book) uses the
4404 phrase ``it is an error if'' to indicate a situation that is not
4405 supposed to arise in complying programs; implementations are strongly
4406 encouraged but not required to signal an error in these situations.
4407 This package sometimes omits such error checking in the interest of
4408 compactness and efficiency. For example, @code{cl-do} variable
4409 specifiers are supposed to be lists of one, two, or three forms;
4410 extra forms are ignored by this package rather than signaling a
4411 syntax error. The @code{cl-endp} function is simply a synonym for
4412 @code{null} in this package. Functions taking keyword arguments
4413 will accept an odd number of arguments, treating the trailing
4414 keyword as if it were followed by the value @code{nil}.
4416 Argument lists (as processed by @code{cl-defun} and friends)
4417 @emph{are} checked rigorously except for the minor point just
4418 mentioned; in particular, keyword arguments are checked for
4419 validity, and @code{&allow-other-keys} and @code{:allow-other-keys}
4420 are fully implemented. Keyword validity checking is slightly
4421 time consuming (though not too bad in byte-compiled code);
4422 you can use @code{&allow-other-keys} to omit this check. Functions
4423 defined in this package such as @code{cl-find} and @code{cl-member}
4424 do check their keyword arguments for validity.
4426 @appendixsec Compiler Optimizations
4429 Changing the value of @code{byte-optimize} from the default @code{t}
4430 is highly discouraged; many of the Common
4432 code that can be improved by optimization. In particular,
4433 @code{cl-block}s (whether explicit or implicit in constructs like
4434 @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the
4435 byte-compiler removes @code{cl-block}s that are not actually
4436 referenced by @code{cl-return} or @code{cl-return-from} inside the block.
4438 @node Common Lisp Compatibility
4439 @appendix Common Lisp Compatibility
4442 The following is a list of all known incompatibilities between this
4443 package and Common Lisp as documented in Steele (2nd edition).
4445 The word @code{cl-defun} is required instead of @code{defun} in order
4446 to use extended Common Lisp argument lists in a function. Likewise,
4447 @code{cl-defmacro} and @code{cl-function} are versions of those forms
4448 which understand full-featured argument lists. The @code{&whole}
4449 keyword does not work in @code{cl-defmacro} argument lists (except
4450 inside recursive argument lists).
4452 The @code{equal} predicate does not distinguish
4453 between IEEE floating-point plus and minus zero. The @code{cl-equalp}
4454 predicate has several differences with Common Lisp; @pxref{Predicates}.
4456 The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols}
4457 with no @var{obarray} argument. In Common Lisp, this form would
4458 iterate over all symbols in all packages. Since Emacs obarrays
4459 are not a first-class package mechanism, there is no way for
4460 @code{cl-do-all-symbols} to locate any but the default obarray.
4462 The @code{cl-loop} macro is complete except that @code{loop-finish}
4463 and type specifiers are unimplemented.
4465 The multiple-value return facility treats lists as multiple
4466 values, since Emacs Lisp cannot support multiple return values
4467 directly. The macros will be compatible with Common Lisp if
4468 @code{cl-values} or @code{cl-values-list} is always used to return to
4469 a @code{cl-multiple-value-bind} or other multiple-value receiver;
4470 if @code{cl-values} is used without @code{cl-multiple-value-@dots{}}
4471 or vice-versa the effect will be different from Common Lisp.
4473 Many Common Lisp declarations are ignored, and others match
4474 the Common Lisp standard in concept but not in detail. For
4475 example, local @code{special} declarations, which are purely
4476 advisory in Emacs Lisp, do not rigorously obey the scoping rules
4477 set down in Steele's book.
4479 The variable @code{cl--gensym-counter} starts out with a pseudo-random
4480 value rather than with zero. This is to cope with the fact that
4481 generated symbols become interned when they are written to and
4482 loaded back from a file.
4484 The @code{cl-defstruct} facility is compatible, except that structures
4485 are of type @code{:type vector :named} by default rather than some
4486 special, distinct type. Also, the @code{:type} slot option is ignored.
4488 The second argument of @code{cl-check-type} is treated differently.
4490 @node Porting Common Lisp
4491 @appendix Porting Common Lisp
4494 This package is meant to be used as an extension to Emacs Lisp,
4495 not as an Emacs implementation of true Common Lisp. Some of the
4496 remaining differences between Emacs Lisp and Common Lisp make it
4497 difficult to port large Common Lisp applications to Emacs. For
4498 one, some of the features in this package are not fully compliant
4499 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there
4500 are also quite a few features that this package does not provide
4501 at all. Here are some major omissions that you will want to watch out
4502 for when bringing Common Lisp code into Emacs.
4506 Case-insensitivity. Symbols in Common Lisp are case-insensitive
4507 by default. Some programs refer to a function or variable as
4508 @code{foo} in one place and @code{Foo} or @code{FOO} in another.
4509 Emacs Lisp will treat these as three distinct symbols.
4511 Some Common Lisp code is written entirely in upper case. While Emacs
4512 is happy to let the program's own functions and variables use
4513 this convention, calls to Lisp builtins like @code{if} and
4514 @code{defun} will have to be changed to lower case.
4517 Lexical scoping. In Common Lisp, function arguments and @code{let}
4518 bindings apply only to references physically within their bodies (or
4519 within macro expansions in their bodies). Traditionally, Emacs Lisp
4520 uses @dfn{dynamic scoping} wherein a binding to a variable is visible
4521 even inside functions called from the body.
4522 @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4523 Lexical binding is available since Emacs 24.1, so be sure to set
4524 @code{lexical-binding} to @code{t} if you need to emulate this aspect
4525 of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4527 Here is an example of a Common Lisp code fragment that would fail in
4528 Emacs Lisp if @code{lexical-binding} were set to @code{nil}:
4531 (defun map-odd-elements (func list)
4533 for flag = t then (not flag)
4534 collect (if flag x (funcall func x))))
4536 (defun add-odd-elements (list x)
4537 (map-odd-elements (lambda (a) (+ a x)) list))
4541 With lexical binding, the two functions' usages of @code{x} are
4542 completely independent. With dynamic binding, the binding to @code{x}
4543 made by @code{add-odd-elements} will have been hidden by the binding
4544 in @code{map-odd-elements} by the time the @code{(+ a x)} function is
4547 Internally, this package uses lexical binding so that such problems do
4548 not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete
4549 @code{lexical-let} form that emulates a Common Lisp-style lexical
4550 binding when dynamic binding is in use.
4553 Reader macros. Common Lisp includes a second type of macro that
4554 works at the level of individual characters. For example, Common
4555 Lisp implements the quote notation by a reader macro called @code{'},
4556 whereas Emacs Lisp's parser just treats quote as a special case.
4557 Some Lisp packages use reader macros to create special syntaxes
4558 for themselves, which the Emacs parser is incapable of reading.
4561 Other syntactic features. Common Lisp provides a number of
4562 notations beginning with @code{#} that the Emacs Lisp parser
4563 won't understand. For example, @samp{#| @dots{} |#} is an
4564 alternate comment notation, and @samp{#+lucid (foo)} tells
4565 the parser to ignore the @code{(foo)} except in Lucid Common
4569 Packages. In Common Lisp, symbols are divided into @dfn{packages}.
4570 Symbols that are Lisp built-ins are typically stored in one package;
4571 symbols that are vendor extensions are put in another, and each
4572 application program would have a package for its own symbols.
4573 Certain symbols are ``exported'' by a package and others are
4574 internal; certain packages ``use'' or import the exported symbols
4575 of other packages. To access symbols that would not normally be
4576 visible due to this importing and exporting, Common Lisp provides
4577 a syntax like @code{package:symbol} or @code{package::symbol}.
4579 Emacs Lisp has a single namespace for all interned symbols, and
4580 then uses a naming convention of putting a prefix like @code{cl-}
4581 in front of the name. Some Emacs packages adopt the Common Lisp-like
4582 convention of using @code{cl:} or @code{cl::} as the prefix.
4583 However, the Emacs parser does not understand colons and just
4584 treats them as part of the symbol name. Thus, while @code{mapcar}
4585 and @code{lisp:mapcar} may refer to the same symbol in Common
4586 Lisp, they are totally distinct in Emacs Lisp. Common Lisp
4587 programs that refer to a symbol by the full name sometimes
4588 and the short name other times will not port cleanly to Emacs.
4590 Emacs Lisp does have a concept of ``obarrays'', which are
4591 package-like collections of symbols, but this feature is not
4592 strong enough to be used as a true package mechanism.
4595 The @code{format} function is quite different between Common
4596 Lisp and Emacs Lisp. It takes an additional ``destination''
4597 argument before the format string. A destination of @code{nil}
4598 means to format to a string as in Emacs Lisp; a destination
4599 of @code{t} means to write to the terminal (similar to
4600 @code{message} in Emacs). Also, format control strings are
4601 utterly different; @code{~} is used instead of @code{%} to
4602 introduce format codes, and the set of available codes is
4603 much richer. There are no notations like @code{\n} for
4604 string literals; instead, @code{format} is used with the
4605 ``newline'' format code, @code{~%}. More advanced formatting
4606 codes provide such features as paragraph filling, case
4607 conversion, and even loops and conditionals.
4609 While it would have been possible to implement most of Common
4610 Lisp @code{format} in this package (under the name @code{cl-format},
4611 of course), it was not deemed worthwhile. It would have required
4612 a huge amount of code to implement even a decent subset of
4613 @code{format}, yet the functionality it would provide over
4614 Emacs Lisp's @code{format} would rarely be useful.
4617 Vector constants use square brackets in Emacs Lisp, but
4618 @code{#(a b c)} notation in Common Lisp. To further complicate
4619 matters, Emacs has its own @code{#(} notation for
4620 something entirely different---strings with properties.
4623 Characters are distinct from integers in Common Lisp. The notation
4624 for character constants is also different: @code{#\A} in Common Lisp
4625 where Emacs Lisp uses @code{?A}. Also, @code{string=} and
4626 @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is
4627 case-insensitive in Common Lisp.
4630 Data types. Some Common Lisp data types do not exist in Emacs
4631 Lisp. Rational numbers and complex numbers are not present,
4632 nor are large integers (all integers are ``fixnums''). All
4633 arrays are one-dimensional. There are no readtables or pathnames;
4634 streams are a set of existing data types rather than a new data
4635 type of their own. Hash tables, random-states, structures, and
4636 packages (obarrays) are built from Lisp vectors or lists rather
4637 than being distinct types.
4640 The Common Lisp Object System (CLOS) is not implemented,
4641 nor is the Common Lisp Condition System. However, the EIEIO package
4642 (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some
4646 Common Lisp features that are completely redundant with Emacs
4647 Lisp features of a different name generally have not been
4648 implemented. For example, Common Lisp writes @code{defconstant}
4649 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list}
4650 takes its arguments in different ways in the two Lisps but does
4651 exactly the same thing, so this package has not bothered to
4652 implement a Common Lisp-style @code{make-list}.
4655 A few more notable Common Lisp features not included in this
4656 package: @code{compiler-let}, @code{tagbody}, @code{prog},
4657 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}.
4660 Recursion. While recursion works in Emacs Lisp just like it
4661 does in Common Lisp, various details of the Emacs Lisp system
4662 and compiler make recursion much less efficient than it is in
4663 most Lisps. Some schools of thought prefer to use recursion
4664 in Lisp over other techniques; they would sum a list of
4665 numbers using something like
4668 (defun sum-list (list)
4670 (+ (car list) (sum-list (cdr list)))
4675 where a more iteratively-minded programmer might write one of
4679 (let ((total 0)) (dolist (x my-list) (incf total x)) total)
4680 (loop for x in my-list sum x)
4683 While this would be mainly a stylistic choice in most Common Lisps,
4684 in Emacs Lisp you should be aware that the iterative forms are
4685 much faster than recursion. Also, Lisp programmers will want to
4686 note that the current Emacs Lisp compiler does not optimize tail
4690 @node Obsolete Features
4691 @appendix Obsolete Features
4693 This section describes some features of the package that are obsolete
4694 and should not be used in new code. They are either only provided by
4695 the old @file{cl.el} entry point, not by the newer @file{cl-lib.el};
4696 or where versions with a @samp{cl-} prefix do exist they do not behave
4697 in exactly the same way.
4700 * Obsolete Lexical Binding:: An approximation of lexical binding.
4701 * Obsolete Macros:: Obsolete macros.
4702 * Obsolete Setf Customization:: Obsolete ways to customize setf.
4705 @node Obsolete Lexical Binding
4706 @appendixsec Obsolete Lexical Binding
4708 The following macros are extensions to Common Lisp, where all bindings
4709 are lexical unless declared otherwise. These features are likewise
4710 obsolete since the introduction of true lexical binding in Emacs 24.1.
4712 @defmac lexical-let (bindings@dots{}) forms@dots{}
4713 This form is exactly like @code{let} except that the bindings it
4714 establishes are purely lexical.
4717 @c FIXME remove this and refer to elisp manual.
4718 @c Maybe merge some stuff from here to there?
4720 Lexical bindings are similar to local variables in a language like C:
4721 Only the code physically within the body of the @code{lexical-let}
4722 (after macro expansion) may refer to the bound variables.
4726 (defun foo (b) (+ a b))
4727 (let ((a 2)) (foo a))
4729 (lexical-let ((a 2)) (foo a))
4734 In this example, a regular @code{let} binding of @code{a} actually
4735 makes a temporary change to the global variable @code{a}, so @code{foo}
4736 is able to see the binding of @code{a} to 2. But @code{lexical-let}
4737 actually creates a distinct local variable @code{a} for use within its
4738 body, without any effect on the global variable of the same name.
4740 The most important use of lexical bindings is to create @dfn{closures}.
4741 A closure is a function object that refers to an outside lexical
4742 variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}).
4746 (defun make-adder (n)
4747 (lexical-let ((n n))
4748 (function (lambda (m) (+ n m)))))
4749 (setq add17 (make-adder 17))
4755 The call @code{(make-adder 17)} returns a function object which adds
4756 17 to its argument. If @code{let} had been used instead of
4757 @code{lexical-let}, the function object would have referred to the
4758 global @code{n}, which would have been bound to 17 only during the
4759 call to @code{make-adder} itself.
4762 (defun make-counter ()
4763 (lexical-let ((n 0))
4764 (cl-function (lambda (&optional (m 1)) (cl-incf n m)))))
4765 (setq count-1 (make-counter))
4768 (funcall count-1 14)
4770 (setq count-2 (make-counter))
4780 Here we see that each call to @code{make-counter} creates a distinct
4781 local variable @code{n}, which serves as a private counter for the
4782 function object that is returned.
4784 Closed-over lexical variables persist until the last reference to
4785 them goes away, just like all other Lisp objects. For example,
4786 @code{count-2} refers to a function object which refers to an
4787 instance of the variable @code{n}; this is the only reference
4788 to that variable, so after @code{(setq count-2 nil)} the garbage
4789 collector would be able to delete this instance of @code{n}.
4790 Of course, if a @code{lexical-let} does not actually create any
4791 closures, then the lexical variables are free as soon as the
4792 @code{lexical-let} returns.
4794 Many closures are used only during the extent of the bindings they
4795 refer to; these are known as ``downward funargs'' in Lisp parlance.
4796 When a closure is used in this way, regular Emacs Lisp dynamic
4797 bindings suffice and will be more efficient than @code{lexical-let}
4801 (defun add-to-list (x list)
4802 (mapcar (lambda (y) (+ x y))) list)
4803 (add-to-list 7 '(1 2 5))
4808 Since this lambda is only used while @code{x} is still bound,
4809 it is not necessary to make a true closure out of it.
4811 You can use @code{defun} or @code{flet} inside a @code{lexical-let}
4812 to create a named closure. If several closures are created in the
4813 body of a single @code{lexical-let}, they all close over the same
4814 instance of the lexical variable.
4816 @defmac lexical-let* (bindings@dots{}) forms@dots{}
4817 This form is just like @code{lexical-let}, except that the bindings
4818 are made sequentially in the manner of @code{let*}.
4821 @node Obsolete Macros
4822 @appendixsec Obsolete Macros
4824 The following macros are obsolete, and are replaced by versions with
4825 a @samp{cl-} prefix that do not behave in exactly the same way.
4826 Consequently, the @file{cl.el} versions are not simply aliases to the
4827 @file{cl-lib.el} versions.
4829 @defmac flet (bindings@dots{}) forms@dots{}
4830 This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}),
4831 which behaves the same way as Common Lisp's @code{flet}.
4832 This @code{flet} takes the same arguments as @code{cl-flet}, but does
4833 not behave in precisely the same way.
4835 While @code{flet} in Common Lisp establishes a lexical function
4836 binding, this @code{flet} makes a dynamic binding (it dates from a
4837 time before Emacs had lexical binding). The result is
4838 that @code{flet} affects indirect calls to a function as well as calls
4839 directly inside the @code{flet} form itself.
4841 This will even work on Emacs primitives, although note that some calls
4842 to primitive functions internal to Emacs are made without going
4843 through the symbol's function cell, and so will not be affected by
4844 @code{flet}. For example,
4847 (flet ((message (&rest args) (push args saved-msgs)))
4851 This code attempts to replace the built-in function @code{message}
4852 with a function that simply saves the messages in a list rather
4853 than displaying them. The original definition of @code{message}
4854 will be restored after @code{do-something} exits. This code will
4855 work fine on messages generated by other Lisp code, but messages
4856 generated directly inside Emacs will not be caught since they make
4857 direct C-language calls to the message routines rather than going
4858 through the Lisp @code{message} function.
4860 For those cases where the dynamic scoping of @code{flet} is desired,
4861 @code{cl-flet} is clearly not a substitute. The most direct replacement would
4862 be instead to use @code{cl-letf} to temporarily rebind @code{(symbol-function
4863 '@var{fun})}. But in most cases, a better substitute is to use an advice, such
4867 (defvar my-fun-advice-enable nil)
4868 (add-advice '@var{fun} :around
4869 (lambda (orig &rest args)
4870 (if my-fun-advice-enable (do-something)
4871 (apply orig args))))
4874 so that you can then replace the @code{flet} with a simple dynamically scoped
4875 binding of @code{my-fun-advice-enable}.
4878 Note that many primitives (e.g., @code{+}) have special byte-compile handling.
4879 Attempts to redefine such functions using @code{flet}, @code{cl-letf}, or an
4880 advice will fail when byte-compiled.
4882 @c In such cases, use @code{labels} instead.
4885 @defmac labels (bindings@dots{}) forms@dots{}
4886 This macro is replaced by @code{cl-labels} (@pxref{Function Bindings}),
4887 which behaves the same way as Common Lisp's @code{labels}.
4888 This @code{labels} takes the same arguments as @code{cl-labels}, but
4889 does not behave in precisely the same way.
4891 This version of @code{labels} uses the obsolete @code{lexical-let}
4892 form (@pxref{Obsolete Lexical Binding}), rather than the true
4893 lexical binding that @code{cl-labels} uses.
4896 @node Obsolete Setf Customization
4897 @appendixsec Obsolete Ways to Customize Setf
4899 Common Lisp defines three macros, @code{define-modify-macro},
4900 @code{defsetf}, and @code{define-setf-method}, that allow the
4901 user to extend generalized variables in various ways.
4902 In Emacs, these are obsolete, replaced by various features of
4903 @file{gv.el} in Emacs 24.3.
4904 @xref{Adding Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
4907 @defmac define-modify-macro name arglist function [doc-string]
4908 This macro defines a ``read-modify-write'' macro similar to
4909 @code{cl-incf} and @code{cl-decf}. You can replace this macro
4910 with @code{gv-letplace}.
4912 The macro @var{name} is defined to take a @var{place} argument
4913 followed by additional arguments described by @var{arglist}. The call
4916 (@var{name} @var{place} @var{args}@dots{})
4923 (cl-callf @var{func} @var{place} @var{args}@dots{})
4927 which in turn is roughly equivalent to
4930 (setf @var{place} (@var{func} @var{place} @var{args}@dots{}))
4936 (define-modify-macro incf (&optional (n 1)) +)
4937 (define-modify-macro concatf (&rest args) concat)
4940 Note that @code{&key} is not allowed in @var{arglist}, but
4941 @code{&rest} is sufficient to pass keywords on to the function.
4943 Most of the modify macros defined by Common Lisp do not exactly
4944 follow the pattern of @code{define-modify-macro}. For example,
4945 @code{push} takes its arguments in the wrong order, and @code{pop}
4946 is completely irregular.
4948 The above @code{incf} example could be written using
4949 @code{gv-letplace} as:
4951 (defmacro incf (place &optional n)
4952 (gv-letplace (getter setter) place
4953 (macroexp-let2 nil v (or n 1)
4954 (funcall setter `(+ ,v ,getter)))))
4957 (defmacro concatf (place &rest args)
4958 (gv-letplace (getter setter) place
4959 (macroexp-let2 nil v (mapconcat 'identity args "")
4960 (funcall setter `(concat ,getter ,v)))))
4964 @defmac defsetf access-fn update-fn
4965 This is the simpler of two @code{defsetf} forms, and is
4966 replaced by @code{gv-define-simple-setter}.
4968 With @var{access-fn} the name of a function that accesses a place,
4969 this declares @var{update-fn} to be the corresponding store function.
4973 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value})
4980 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value})
4984 The @var{update-fn} is required to be either a true function, or
4985 a macro that evaluates its arguments in a function-like way. Also,
4986 the @var{update-fn} is expected to return @var{value} as its result.
4987 Otherwise, the above expansion would not obey the rules for the way
4988 @code{setf} is supposed to behave.
4990 As a special (non-Common-Lisp) extension, a third argument of @code{t}
4991 to @code{defsetf} says that the return value of @code{update-fn} is
4992 not suitable, so that the above @code{setf} should be expanded to
4996 (let ((temp @var{value}))
4997 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp)
5004 (defsetf car setcar)
5005 (defsetf buffer-name rename-buffer t)
5008 These translate directly to @code{gv-define-simple-setter}:
5011 (gv-define-simple-setter car setcar)
5012 (gv-define-simple-setter buffer-name rename-buffer t)
5016 @defmac defsetf access-fn arglist (store-var) forms@dots{}
5017 This is the second, more complex, form of @code{defsetf}.
5018 It can be replaced by @code{gv-define-setter}.
5020 This form of @code{defsetf} is rather like @code{defmacro} except for
5021 the additional @var{store-var} argument. The @var{forms} should
5022 return a Lisp form that stores the value of @var{store-var} into the
5023 generalized variable formed by a call to @var{access-fn} with
5024 arguments described by @var{arglist}. The @var{forms} may begin with
5025 a string which documents the @code{setf} method (analogous to the doc
5026 string that appears at the front of a function).
5028 For example, the simple form of @code{defsetf} is shorthand for
5031 (defsetf @var{access-fn} (&rest args) (store)
5032 (append '(@var{update-fn}) args (list store)))
5035 The Lisp form that is returned can access the arguments from
5036 @var{arglist} and @var{store-var} in an unrestricted fashion;
5037 macros like @code{cl-incf} that invoke this
5038 setf-method will insert temporary variables as needed to make
5039 sure the apparent order of evaluation is preserved.
5041 Another standard example:
5044 (defsetf nth (n x) (store)
5045 `(setcar (nthcdr ,n ,x) ,store))
5048 You could write this using @code{gv-define-setter} as:
5051 (gv-define-setter nth (store n x)
5052 `(setcar (nthcdr ,n ,x) ,store))
5056 @defmac define-setf-method access-fn arglist forms@dots{}
5057 This is the most general way to create new place forms. You can
5058 replace this by @code{gv-define-setter} or @code{gv-define-expander}.
5060 When a @code{setf} to @var{access-fn} with arguments described by
5061 @var{arglist} is expanded, the @var{forms} are evaluated and must
5062 return a list of five items:
5066 A list of @dfn{temporary variables}.
5069 A list of @dfn{value forms} corresponding to the temporary variables
5070 above. The temporary variables will be bound to these value forms
5071 as the first step of any operation on the generalized variable.
5074 A list of exactly one @dfn{store variable} (generally obtained
5075 from a call to @code{gensym}).
5078 A Lisp form that stores the contents of the store variable into
5079 the generalized variable, assuming the temporaries have been
5080 bound as described above.
5083 A Lisp form that accesses the contents of the generalized variable,
5084 assuming the temporaries have been bound.
5087 This is exactly like the Common Lisp macro of the same name,
5088 except that the method returns a list of five values rather
5089 than the five values themselves, since Emacs Lisp does not
5090 support Common Lisp's notion of multiple return values.
5091 (Note that the @code{setf} implementation provided by @file{gv.el}
5092 does not use this five item format. Its use here is only for
5093 backwards compatibility.)
5095 Once again, the @var{forms} may begin with a documentation string.
5097 A setf-method should be maximally conservative with regard to
5098 temporary variables. In the setf-methods generated by
5099 @code{defsetf}, the second return value is simply the list of
5100 arguments in the place form, and the first return value is a
5101 list of a corresponding number of temporary variables generated
5102 @c FIXME I don't think this is true anymore.
5103 by @code{cl-gensym}. Macros like @code{cl-incf} that
5104 use this setf-method will optimize away most temporaries that
5105 turn out to be unnecessary, so there is little reason for the
5106 setf-method itself to optimize.
5109 @c Removed in Emacs 24.3, not possible to make a compatible replacement.
5111 @defun get-setf-method place &optional env
5112 This function returns the setf-method for @var{place}, by
5113 invoking the definition previously recorded by @code{defsetf}
5114 or @code{define-setf-method}. The result is a list of five
5115 values as described above. You can use this function to build
5116 your own @code{cl-incf}-like modify macros.
5118 The argument @var{env} specifies the ``environment'' to be
5119 passed on to @code{macroexpand} if @code{get-setf-method} should
5120 need to expand a macro in @var{place}. It should come from
5121 an @code{&environment} argument to the macro or setf-method
5122 that called @code{get-setf-method}.
5127 @node GNU Free Documentation License
5128 @appendix GNU Free Documentation License
5129 @include doclicense.texi
5131 @node Function Index
5132 @unnumbered Function Index
5136 @node Variable Index
5137 @unnumbered Variable Index