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, 2001-2012 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. Buying copies from the FSF supports it in
21 developing GNU and promoting software freedom.''
25 @dircategory Emacs lisp libraries
27 * CL: (cl). Partial Common Lisp support for Emacs Lisp.
34 @center @titlefont{Common Lisp Extensions}
36 @center For GNU Emacs Lisp
38 @center as distributed with Emacs @value{EMACSVER}
40 @center Dave Gillespie
41 @center daveg@@synaptics.com
43 @vskip 0pt plus 1filll
51 @top GNU Emacs Common Lisp Emulation
57 * Overview:: Basics, usage, organization, naming conventions.
58 * Program Structure:: Arglists, @code{cl-eval-when}.
59 * Predicates:: Type predicates and equality predicates.
60 * Control Structure:: Assignment, conditionals, blocks, looping.
61 * Macros:: Destructuring, compiler macros.
62 * Declarations:: @code{cl-proclaim}, @code{cl-declare}, etc.
63 * Symbols:: Property lists, creating symbols.
64 * Numbers:: Predicates, functions, random numbers.
65 * Sequences:: Mapping, functions, searching, sorting.
66 * Lists:: Functions, substitution, sets, associations.
67 * Structures:: @code{cl-defstruct}.
68 * Assertions:: Assertions and type checking.
71 * Efficiency Concerns:: Hints and techniques.
72 * Common Lisp Compatibility:: All known differences with Steele.
73 * Porting Common Lisp:: Hints for porting Common Lisp code.
74 * Obsolete Features:: Obsolete features.
75 * GNU Free Documentation License:: The license for this documentation.
78 * Function Index:: An entry for each documented function.
79 * Variable Index:: An entry for each documented variable.
86 This document describes a set of Emacs Lisp facilities borrowed from
87 Common Lisp. All the facilities are described here in detail. While
88 this document does not assume any prior knowledge of Common Lisp, it
89 does assume a basic familiarity with Emacs Lisp.
91 Common Lisp is a huge language, and Common Lisp systems tend to be
92 massive and extremely complex. Emacs Lisp, by contrast, is rather
93 minimalist in the choice of Lisp features it offers the programmer.
94 As Emacs Lisp programmers have grown in number, and the applications
95 they write have grown more ambitious, it has become clear that Emacs
96 Lisp could benefit from many of the conveniences of Common Lisp.
98 The @dfn{CL} package adds a number of Common Lisp functions and
99 control structures to Emacs Lisp. While not a 100% complete
100 implementation of Common Lisp, it adds enough functionality
101 to make Emacs Lisp programming significantly more convenient.
103 Some Common Lisp features have been omitted from this package
108 Some features are too complex or bulky relative to their benefit
109 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine
110 examples of this group.
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
278 Emacs Lisp's notation for argument lists of functions is a subset of
279 the Common Lisp notation. As well as the familiar @code{&optional}
280 and @code{&rest} markers, Common Lisp allows you to specify default
281 values for optional arguments, and it provides the additional markers
282 @code{&key} and @code{&aux}.
284 Since argument parsing is built-in to Emacs, there is no way for
285 this package to implement Common Lisp argument lists seamlessly.
286 Instead, this package defines alternates for several Lisp forms
287 which you must use if you need Common Lisp argument lists.
289 @defmac cl-defun name arglist body@dots{}
290 This form is identical to the regular @code{defun} form, except
291 that @var{arglist} is allowed to be a full Common Lisp argument
292 list. Also, the function body is enclosed in an implicit block
293 called @var{name}; @pxref{Blocks and Exits}.
296 @defmac cl-defsubst name arglist body@dots{}
297 This is just like @code{cl-defun}, except that the function that
298 is defined is automatically proclaimed @code{inline}, i.e.,
299 calls to it may be expanded into in-line code by the byte compiler.
300 This is analogous to the @code{defsubst} form;
301 @code{cl-defsubst} uses a different method (compiler macros) which
302 works in all versions of Emacs, and also generates somewhat more
303 @c For some examples,
304 @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html
305 efficient inline expansions. In particular, @code{cl-defsubst}
306 arranges for the processing of keyword arguments, default values,
307 etc., to be done at compile-time whenever possible.
310 @defmac cl-defmacro name arglist body@dots{}
311 This is identical to the regular @code{defmacro} form,
312 except that @var{arglist} is allowed to be a full Common Lisp
313 argument list. The @code{&environment} keyword is supported as
314 described in Steele's book @cite{Common Lisp, the Language}.
315 The @code{&whole} keyword is supported only
316 within destructured lists (see below); top-level @code{&whole}
317 cannot be implemented with the current Emacs Lisp interpreter.
318 The macro expander body is enclosed in an implicit block called
322 @defmac cl-function symbol-or-lambda
323 This is identical to the regular @code{function} form,
324 except that if the argument is a @code{lambda} form then that
325 form may use a full Common Lisp argument list.
328 Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
329 in this package that include @var{arglist}s in their syntax allow
330 full Common Lisp argument lists.
332 Note that it is @emph{not} necessary to use @code{cl-defun} in
333 order to have access to most CL features in your function.
334 These features are always present; @code{cl-defun}'s only
335 difference from @code{defun} is its more flexible argument
336 lists and its implicit block.
338 The full form of a Common Lisp argument list is
342 &optional (@var{var} @var{initform} @var{svar})@dots{}
344 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{}
345 &aux (@var{var} @var{initform})@dots{})
348 Each of the five argument list sections is optional. The @var{svar},
349 @var{initform}, and @var{keyword} parts are optional; if they are
350 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.
352 The first section consists of zero or more @dfn{required} arguments.
353 These arguments must always be specified in a call to the function;
354 there is no difference between Emacs Lisp and Common Lisp as far as
355 required arguments are concerned.
357 The second section consists of @dfn{optional} arguments. These
358 arguments may be specified in the function call; if they are not,
359 @var{initform} specifies the default value used for the argument.
360 (No @var{initform} means to use @code{nil} as the default.) The
361 @var{initform} is evaluated with the bindings for the preceding
362 arguments already established; @code{(a &optional (b (1+ a)))}
363 matches one or two arguments, with the second argument defaulting
364 to one plus the first argument. If the @var{svar} is specified,
365 it is an auxiliary variable which is bound to @code{t} if the optional
366 argument was specified, or to @code{nil} if the argument was omitted.
367 If you don't use an @var{svar}, then there will be no way for your
368 function to tell whether it was called with no argument, or with
369 the default value passed explicitly as an argument.
371 The third section consists of a single @dfn{rest} argument. If
372 more arguments were passed to the function than are accounted for
373 by the required and optional arguments, those extra arguments are
374 collected into a list and bound to the ``rest'' argument variable.
375 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
376 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
377 macro contexts; this package accepts it all the time.
379 The fourth section consists of @dfn{keyword} arguments. These
380 are optional arguments which are specified by name rather than
381 positionally in the argument list. For example,
384 (cl-defun foo (a &optional b &key c d (e 17)))
388 defines a function which may be called with one, two, or more
389 arguments. The first two arguments are bound to @code{a} and
390 @code{b} in the usual way. The remaining arguments must be
391 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
392 by the value to be bound to the corresponding argument variable.
393 (Symbols whose names begin with a colon are called @dfn{keywords},
394 and they are self-quoting in the same way as @code{nil} and
397 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
398 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword
399 appears more than once in the function call, the first occurrence
400 takes precedence over the later ones. Note that it is not possible
401 to specify keyword arguments without specifying the optional
402 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
403 @code{b} to the keyword @code{:c}, then signal an error because
404 @code{2} is not a valid keyword.
406 You can also explicitly specify the keyword argument; it need not be
407 simply the variable name prefixed with a colon. For example,
410 (cl-defun bar (&key (a 1) ((baz b) 4)))
415 specifies a keyword @code{:a} that sets the variable @code{a} with
416 default value 1, as well as a keyword @code{baz} that sets the
417 variable @code{b} with default value 4. In this case, because
418 @code{baz} is not self-quoting, you must quote it explicitly in the
419 function call, like this:
425 Ordinarily, it is an error to pass an unrecognized keyword to
426 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask
427 Lisp to ignore unrecognized keywords, either by adding the
428 marker @code{&allow-other-keys} after the keyword section
429 of the argument list, or by specifying an @code{:allow-other-keys}
430 argument in the call whose value is non-@code{nil}. If the
431 function uses both @code{&rest} and @code{&key} at the same time,
432 the ``rest'' argument is bound to the keyword list as it appears
433 in the call. For example:
436 (cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
437 (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
438 (if need (error "Thing not found"))))
442 This function takes a @code{:need} keyword argument, but also
443 accepts other keyword arguments which are passed on to the
444 @code{cl-member} function. @code{allow-other-keys} is used to
445 keep both @code{find-thing} and @code{cl-member} from complaining
446 about each others' keywords in the arguments.
448 The fifth section of the argument list consists of @dfn{auxiliary
449 variables}. These are not really arguments at all, but simply
450 variables which are bound to @code{nil} or to the specified
451 @var{initforms} during execution of the function. There is no
452 difference between the following two functions, except for a
453 matter of stylistic taste:
456 (cl-defun foo (a b &aux (c (+ a b)) d)
464 Argument lists support @dfn{destructuring}. In Common Lisp,
465 destructuring is only allowed with @code{defmacro}; this package
466 allows it with @code{cl-defun} and other argument lists as well.
467 In destructuring, any argument variable (@var{var} in the above
468 example) can be replaced by a list of variables, or more generally,
469 a recursive argument list. The corresponding argument value must
470 be a list whose elements match this recursive argument list.
474 (cl-defmacro dolist ((var listform &optional resultform)
479 This says that the first argument of @code{dolist} must be a list
480 of two or three items; if there are other arguments as well as this
481 list, they are stored in @code{body}. All features allowed in
482 regular argument lists are allowed in these recursive argument lists.
483 In addition, the clause @samp{&whole @var{var}} is allowed at the
484 front of a recursive argument list. It binds @var{var} to the
485 whole list being matched; thus @code{(&whole all a b)} matches
486 a list of two things, with @code{a} bound to the first thing,
487 @code{b} bound to the second thing, and @code{all} bound to the
488 list itself. (Common Lisp allows @code{&whole} in top-level
489 @code{defmacro} argument lists as well, but Emacs Lisp does not
492 One last feature of destructuring is that the argument list may be
493 dotted, so that the argument list @code{(a b . c)} is functionally
494 equivalent to @code{(a b &rest c)}.
496 If the optimization quality @code{safety} is set to 0
497 (@pxref{Declarations}), error checking for wrong number of
498 arguments and invalid keyword arguments is disabled. By default,
499 argument lists are rigorously checked.
501 @node Time of Evaluation
502 @section Time of Evaluation
505 Normally, the byte-compiler does not actually execute the forms in
506 a file it compiles. For example, if a file contains @code{(setq foo t)},
507 the act of compiling it will not actually set @code{foo} to @code{t}.
508 This is true even if the @code{setq} was a top-level form (i.e., not
509 enclosed in a @code{defun} or other form). Sometimes, though, you
510 would like to have certain top-level forms evaluated at compile-time.
511 For example, the compiler effectively evaluates @code{defmacro} forms
512 at compile-time so that later parts of the file can refer to the
513 macros that are defined.
515 @defmac cl-eval-when (situations@dots{}) forms@dots{}
516 This form controls when the body @var{forms} are evaluated.
517 The @var{situations} list may contain any set of the symbols
518 @code{compile}, @code{load}, and @code{eval} (or their long-winded
519 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
520 and @code{:execute}).
522 The @code{cl-eval-when} form is handled differently depending on
523 whether or not it is being compiled as a top-level form.
524 Specifically, it gets special treatment if it is being compiled
525 by a command such as @code{byte-compile-file} which compiles files
526 or buffers of code, and it appears either literally at the
527 top level of the file or inside a top-level @code{progn}.
529 For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
530 executed at compile-time if @code{compile} is in the @var{situations}
531 list, and the @var{forms} are written out to the file (to be executed
532 at load-time) if @code{load} is in the @var{situations} list.
534 For non-compiled-top-level forms, only the @code{eval} situation is
535 relevant. (This includes forms executed by the interpreter, forms
536 compiled with @code{byte-compile} rather than @code{byte-compile-file},
537 and non-top-level forms.) The @code{cl-eval-when} acts like a
538 @code{progn} if @code{eval} is specified, and like @code{nil}
539 (ignoring the body @var{forms}) if not.
541 The rules become more subtle when @code{cl-eval-when}s are nested;
542 consult Steele (second edition) for the gruesome details (and
543 some gruesome examples).
545 Some simple examples:
548 ;; Top-level forms in foo.el:
549 (cl-eval-when (compile) (setq foo1 'bar))
550 (cl-eval-when (load) (setq foo2 'bar))
551 (cl-eval-when (compile load) (setq foo3 'bar))
552 (cl-eval-when (eval) (setq foo4 'bar))
553 (cl-eval-when (eval compile) (setq foo5 'bar))
554 (cl-eval-when (eval load) (setq foo6 'bar))
555 (cl-eval-when (eval compile load) (setq foo7 'bar))
558 When @file{foo.el} is compiled, these variables will be set during
559 the compilation itself:
562 foo1 foo3 foo5 foo7 ; `compile'
565 When @file{foo.elc} is loaded, these variables will be set:
568 foo2 foo3 foo6 foo7 ; `load'
571 And if @file{foo.el} is loaded uncompiled, these variables will
575 foo4 foo5 foo6 foo7 ; `eval'
578 If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
579 then the first three would have been equivalent to @code{nil} and the
580 last four would have been equivalent to the corresponding @code{setq}s.
582 Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
583 to @code{(progn @dots{})} in all contexts. The compiler treats
584 certain top-level forms, like @code{defmacro} (sort-of) and
585 @code{require}, as if they were wrapped in @code{(cl-eval-when
586 (compile load eval) @dots{})}.
589 Emacs includes two special forms related to @code{cl-eval-when}.
590 @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}.
591 One of these, @code{eval-when-compile}, is not quite equivalent to
592 any @code{cl-eval-when} construct and is described below.
594 The other form, @code{(eval-and-compile @dots{})}, is exactly
595 equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}.
597 @defmac eval-when-compile forms@dots{}
598 The @var{forms} are evaluated at compile-time; at execution time,
599 this form acts like a quoted constant of the resulting value. Used
600 at top-level, @code{eval-when-compile} is just like @samp{eval-when
601 (compile eval)}. In other contexts, @code{eval-when-compile}
602 allows code to be evaluated once at compile-time for efficiency
605 This form is similar to the @samp{#.} syntax of true Common Lisp.
608 @defmac cl-load-time-value form
609 The @var{form} is evaluated at load-time; at execution time,
610 this form acts like a quoted constant of the resulting value.
612 Early Common Lisp had a @samp{#,} syntax that was similar to
613 this, but ANSI Common Lisp replaced it with @code{load-time-value}
614 and gave it more well-defined semantics.
616 In a compiled file, @code{cl-load-time-value} arranges for @var{form}
617 to be evaluated when the @file{.elc} file is loaded and then used
618 as if it were a quoted constant. In code compiled by
619 @code{byte-compile} rather than @code{byte-compile-file}, the
620 effect is identical to @code{eval-when-compile}. In uncompiled
621 code, both @code{eval-when-compile} and @code{cl-load-time-value}
622 act exactly like @code{progn}.
626 (insert "This function was executed on: "
627 (current-time-string)
629 (eval-when-compile (current-time-string))
630 ;; or '#.(current-time-string) in real Common Lisp
632 (cl-load-time-value (current-time-string))))
636 Byte-compiled, the above defun will result in the following code
637 (or its compiled equivalent, of course) in the @file{.elc} file:
640 (setq --temp-- (current-time-string))
642 (insert "This function was executed on: "
643 (current-time-string)
645 '"Wed Oct 31 16:32:28 2012"
655 This section describes functions for testing whether various
656 facts are true or false.
659 * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
660 * Equality Predicates:: @code{cl-equalp}.
663 @node Type Predicates
664 @section Type Predicates
666 @defun cl-typep object type
667 Check if @var{object} is of type @var{type}, where @var{type} is a
668 (quoted) type name of the sort used by Common Lisp. For example,
669 @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
672 The @var{type} argument to the above function is either a symbol
673 or a list beginning with a symbol.
677 If the type name is a symbol, Emacs appends @samp{-p} to the
678 symbol name to form the name of a predicate function for testing
679 the type. (Built-in predicates whose names end in @samp{p} rather
680 than @samp{-p} are used when appropriate.)
683 The type symbol @code{t} stands for the union of all types.
684 @code{(cl-typep @var{object} t)} is always true. Likewise, the
685 type symbol @code{nil} stands for nothing at all, and
686 @code{(cl-typep @var{object} nil)} is always false.
689 The type symbol @code{null} represents the symbol @code{nil}.
690 Thus @code{(cl-typep @var{object} 'null)} is equivalent to
691 @code{(null @var{object})}.
694 The type symbol @code{atom} represents all objects that are not cons
695 cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
696 @code{(atom @var{object})}.
699 The type symbol @code{real} is a synonym for @code{number}, and
700 @code{fixnum} is a synonym for @code{integer}.
703 The type symbols @code{character} and @code{string-char} match
704 integers in the range from 0 to 255.
706 @c No longer relevant, so covered by first item above (float -> floatp).
709 The type symbol @code{float} uses the @code{cl-floatp-safe} predicate
710 defined by this package rather than @code{floatp}, so it will work
711 correctly even in Emacs versions without floating-point support.
715 The type list @code{(integer @var{low} @var{high})} represents all
716 integers between @var{low} and @var{high}, inclusive. Either bound
717 may be a list of a single integer to specify an exclusive limit,
718 or a @code{*} to specify no limit. The type @code{(integer * *)}
719 is thus equivalent to @code{integer}.
722 Likewise, lists beginning with @code{float}, @code{real}, or
723 @code{number} represent numbers of that type falling in a particular
727 Lists beginning with @code{and}, @code{or}, and @code{not} form
728 combinations of types. For example, @code{(or integer (float 0 *))}
729 represents all objects that are integers or non-negative floats.
732 Lists beginning with @code{member} or @code{cl-member} represent
733 objects @code{eql} to any of the following values. For example,
734 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
735 and @code{(member nil)} is equivalent to @code{null}.
738 Lists of the form @code{(satisfies @var{predicate})} represent
739 all objects for which @var{predicate} returns true when called
740 with that object as an argument.
743 The following function and macro (not technically predicates) are
744 related to @code{cl-typep}.
746 @defun cl-coerce object type
747 This function attempts to convert @var{object} to the specified
748 @var{type}. If @var{object} is already of that type as determined by
749 @code{cl-typep}, it is simply returned. Otherwise, certain types of
750 conversions will be made: If @var{type} is any sequence type
751 (@code{string}, @code{list}, etc.) then @var{object} will be
752 converted to that type if possible. If @var{type} is
753 @code{character}, then strings of length one and symbols with
754 one-character names can be coerced. If @var{type} is @code{float},
755 then integers can be coerced in versions of Emacs that support
756 floats. In all other circumstances, @code{cl-coerce} signals an
760 @defmac cl-deftype name arglist forms@dots{}
761 This macro defines a new type called @var{name}. It is similar
762 to @code{defmacro} in many ways; when @var{name} is encountered
763 as a type name, the body @var{forms} are evaluated and should
764 return a type specifier that is equivalent to the type. The
765 @var{arglist} is a Common Lisp argument list of the sort accepted
766 by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})}
767 is expanded by calling the expander with those arguments; the type
768 symbol @samp{@var{name}} is expanded by calling the expander with
769 no arguments. The @var{arglist} is processed the same as for
770 @code{cl-defmacro} except that optional arguments without explicit
771 defaults use @code{*} instead of @code{nil} as the ``default''
772 default. Some examples:
775 (cl-deftype null () '(satisfies null)) ; predefined
776 (cl-deftype list () '(or null cons)) ; predefined
777 (cl-deftype unsigned-byte (&optional bits)
778 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
779 (unsigned-byte 8) @equiv{} (integer 0 255)
780 (unsigned-byte) @equiv{} (integer 0 *)
781 unsigned-byte @equiv{} (integer 0 *)
785 The last example shows how the Common Lisp @code{unsigned-byte}
786 type specifier could be implemented if desired; this package does
787 not implement @code{unsigned-byte} by default.
790 The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type}
791 (@pxref{Assertions}) macros also use type names. The @code{cl-map},
792 @code{cl-concatenate}, and @code{cl-merge} functions take type-name
793 arguments to specify the type of sequence to return. @xref{Sequences}.
795 @node Equality Predicates
796 @section Equality Predicates
799 This package defines the Common Lisp predicate @code{cl-equalp}.
802 This function is a more flexible version of @code{equal}. In
803 particular, it compares strings case-insensitively, and it compares
804 numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
805 true). Vectors and conses are compared recursively. All other
806 objects are compared as if by @code{equal}.
808 This function differs from Common Lisp @code{equalp} in several
809 respects. First, Common Lisp's @code{equalp} also compares
810 @emph{characters} case-insensitively, which would be impractical
811 in this package since Emacs does not distinguish between integers
812 and characters. In keeping with the idea that strings are less
813 vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
814 not compare strings against vectors of integers.
817 Also note that the Common Lisp functions @code{member} and @code{assoc}
818 use @code{eql} to compare elements, whereas Emacs Lisp follows the
819 MacLisp tradition and uses @code{equal} for these two functions.
820 In Emacs, use @code{memq} (or @code{cl-member}) and @code{assq} (or
821 @code{cl-assoc}) to get functions which use @code{eql} for comparisons.
823 @node Control Structure
824 @chapter Control Structure
827 The features described in the following sections implement
828 various advanced control structures, including extensions to the
829 standard @code{setf} facility, and a number of looping and conditional
833 * Assignment:: The @code{cl-psetq} form.
834 * Generalized Variables:: Extensions to generalized variables.
835 * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}.
836 * Conditionals:: @code{cl-case}, @code{cl-typecase}.
837 * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}.
838 * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}.
839 * Loop Facility:: The Common Lisp @code{loop} macro.
840 * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc.
847 The @code{cl-psetq} form is just like @code{setq}, except that multiple
848 assignments are done in parallel rather than sequentially.
850 @defmac cl-psetq [symbol form]@dots{}
851 This special form (actually a macro) is used to assign to several
852 variables simultaneously. Given only one @var{symbol} and @var{form},
853 it has the same effect as @code{setq}. Given several @var{symbol}
854 and @var{form} pairs, it evaluates all the @var{form}s in advance
855 and then stores the corresponding variables afterwards.
859 (setq x (+ x y) y (* x y))
862 y ; @r{@code{y} was computed after @code{x} was set.}
865 (cl-psetq x (+ x y) y (* x y))
868 y ; @r{@code{y} was computed before @code{x} was set.}
872 The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which
873 exchanges the values of two variables. (The @code{cl-rotatef} form
874 provides an even more convenient way to swap two variables;
875 @pxref{Modify Macros}.)
877 @code{cl-psetq} always returns @code{nil}.
880 @node Generalized Variables
881 @section Generalized Variables
883 A @dfn{generalized variable} or @dfn{place form} is one of the many
884 places in Lisp memory where values can be stored. The simplest place
885 form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists,
886 elements of arrays, properties of symbols, and many other locations
887 are also places where Lisp values are stored. For basic information,
888 @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
889 This package provides several additional features related to
890 generalized variables.
893 * Setf Extensions:: Additional @code{setf} places.
894 * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc.
897 @node Setf Extensions
898 @subsection Setf Extensions
900 Several standard (e.g.@: @code{car}) and Emacs-specific
901 (e.g.@: @code{window-point}) Lisp functions are @code{setf}-able by default.
902 This package defines @code{setf} handlers for several additional functions:
906 Functions from this package:
908 cl-rest cl-subseq cl-get cl-getf
909 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
913 Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument
914 of the function must itself be a valid @var{place} form.
917 General Emacs Lisp functions:
919 buffer-file-name getenv
920 buffer-modified-p global-key-binding
921 buffer-name local-key-binding
923 buffer-substring mark-marker
924 current-buffer marker-position
925 current-case-table mouse-position
927 current-global-map point-marker
928 current-input-mode point-max
929 current-local-map point-min
930 current-window-configuration read-mouse-position
931 default-file-modes screen-height
932 documentation-property screen-width
933 face-background selected-window
934 face-background-pixmap selected-screen
935 face-font selected-frame
936 face-foreground standard-case-table
937 face-underline-p syntax-table
938 file-modes visited-file-modtime
939 frame-height window-height
940 frame-parameters window-width
941 frame-visible-p x-get-secondary-selection
942 frame-width x-get-selection
946 Most of these have directly corresponding ``set'' functions, like
947 @code{use-local-map} for @code{current-local-map}, or @code{goto-char}
948 for @code{point}. A few, like @code{point-min}, expand to longer
949 sequences of code when they are used with @code{setf}
950 (@code{(narrow-to-region x (point-max))} in this case).
953 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
954 where @var{subplace} is itself a valid generalized variable whose
955 current value is a string, and where the value stored is also a
956 string. The new string is spliced into the specified part of the
957 destination string. For example:
960 (setq a (list "hello" "world"))
961 @result{} ("hello" "world")
964 (substring (cadr a) 2 4)
966 (setf (substring (cadr a) 2 4) "o")
971 @result{} ("hello" "wood")
974 The generalized variable @code{buffer-substring}, listed above,
975 also works in this way by replacing a portion of the current buffer.
977 @c FIXME? Also `eq'? (see cl-lib.el)
979 @c Currently commented out in cl.el.
982 A call of the form @code{(apply '@var{func} @dots{})} or
983 @code{(apply (function @var{func}) @dots{})}, where @var{func}
984 is a @code{setf}-able function whose store function is ``suitable''
985 in the sense described in Steele's book; since none of the standard
986 Emacs place functions are suitable in this sense, this feature is
987 only interesting when used with places you define yourself with
988 @code{define-setf-method} or the long form of @code{defsetf}.
989 @xref{Obsolete Setf Customization}.
993 A macro call, in which case the macro is expanded and @code{setf}
994 is applied to the resulting form.
997 Any form for which a @code{defsetf} or @code{define-setf-method}
998 has been made. @xref{Obsolete Setf Customization}.
1001 @c FIXME should this be in lispref? It seems self-evident.
1002 @c Contrast with the cl-incf example later on.
1003 @c Here it really only serves as a contrast to wrong-order.
1004 The @code{setf} macro takes care to evaluate all subforms in
1005 the proper left-to-right order; for example,
1008 (setf (aref vec (cl-incf i)) i)
1012 looks like it will evaluate @code{(cl-incf i)} exactly once, before the
1013 following access to @code{i}; the @code{setf} expander will insert
1014 temporary variables as necessary to ensure that it does in fact work
1015 this way no matter what setf-method is defined for @code{aref}.
1016 (In this case, @code{aset} would be used and no such steps would
1017 be necessary since @code{aset} takes its arguments in a convenient
1020 However, if the @var{place} form is a macro which explicitly
1021 evaluates its arguments in an unusual order, this unusual order
1022 will be preserved. Adapting an example from Steele, given
1025 (defmacro wrong-order (x y) (list 'aref y x))
1029 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
1030 evaluate @var{b} first, then @var{a}, just as in an actual call
1031 to @code{wrong-order}.
1034 @subsection Modify Macros
1037 This package defines a number of macros that operate on generalized
1038 variables. Many are interesting and useful even when the @var{place}
1039 is just a variable name.
1041 @defmac cl-psetf [place form]@dots{}
1042 This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
1043 When several @var{place}s and @var{form}s are involved, the
1044 assignments take place in parallel rather than sequentially.
1045 Specifically, all subforms are evaluated from left to right, then
1046 all the assignments are done (in an undefined order).
1049 @defmac cl-incf place &optional x
1050 This macro increments the number stored in @var{place} by one, or
1051 by @var{x} if specified. The incremented value is returned. For
1052 example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and
1053 @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
1055 As with @code{setf}, care is taken to preserve the ``apparent'' order
1056 of evaluation. For example,
1059 (cl-incf (aref vec (cl-incf i)))
1063 appears to increment @code{i} once, then increment the element of
1064 @code{vec} addressed by @code{i}; this is indeed exactly what it
1065 does, which means the above form is @emph{not} equivalent to the
1066 ``obvious'' expansion,
1069 (setf (aref vec (cl-incf i))
1070 (1+ (aref vec (cl-incf i)))) ; wrong!
1074 but rather to something more like
1077 (let ((temp (cl-incf i)))
1078 (setf (aref vec temp) (1+ (aref vec temp))))
1082 Again, all of this is taken care of automatically by @code{cl-incf} and
1083 the other generalized-variable macros.
1085 As a more Emacs-specific example of @code{cl-incf}, the expression
1086 @code{(cl-incf (point) @var{n})} is essentially equivalent to
1087 @code{(forward-char @var{n})}.
1090 @defmac cl-decf place &optional x
1091 This macro decrements the number stored in @var{place} by one, or
1092 by @var{x} if specified.
1095 @defmac cl-pushnew x place @t{&key :test :test-not :key}
1096 This macro inserts @var{x} at the front of the list stored in
1097 @var{place}, but only if @var{x} was not @code{eql} to any
1098 existing element of the list. The optional keyword arguments
1099 are interpreted in the same way as for @code{cl-adjoin}.
1100 @xref{Lists as Sets}.
1103 @defmac cl-shiftf place@dots{} newvalue
1104 This macro shifts the @var{place}s left by one, shifting in the
1105 value of @var{newvalue} (which may be any Lisp expression, not just
1106 a generalized variable), and returning the value shifted out of
1107 the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c}
1108 @var{d})} is equivalent to
1113 (cl-psetf @var{a} @var{b}
1119 except that the subforms of @var{a}, @var{b}, and @var{c} are actually
1120 evaluated only once each and in the apparent order.
1123 @defmac cl-rotatef place@dots{}
1124 This macro rotates the @var{place}s left by one in circular fashion.
1125 Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to
1128 (cl-psetf @var{a} @var{b}
1135 except for the evaluation of subforms. @code{cl-rotatef} always
1136 returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})}
1137 conveniently exchanges @var{a} and @var{b}.
1140 The following macros were invented for this package; they have no
1141 analogues in Common Lisp.
1143 @defmac cl-letf (bindings@dots{}) forms@dots{}
1144 This macro is analogous to @code{let}, but for generalized variables
1145 rather than just symbols. Each @var{binding} should be of the form
1146 @code{(@var{place} @var{value})}; the original contents of the
1147 @var{place}s are saved, the @var{value}s are stored in them, and
1148 then the body @var{form}s are executed. Afterwards, the @var{places}
1149 are set back to their original saved contents. This cleanup happens
1150 even if the @var{form}s exit irregularly due to a @code{throw} or an
1156 (cl-letf (((point) (point-min))
1162 moves point in the current buffer to the beginning of the buffer,
1163 and also binds @code{a} to 17 (as if by a normal @code{let}, since
1164 @code{a} is just a regular variable). After the body exits, @code{a}
1165 is set back to its original value and point is moved back to its
1168 Note that @code{cl-letf} on @code{(point)} is not quite like a
1169 @code{save-excursion}, as the latter effectively saves a marker
1170 which tracks insertions and deletions in the buffer. Actually,
1171 a @code{cl-letf} of @code{(point-marker)} is much closer to this
1172 behavior. (@code{point} and @code{point-marker} are equivalent
1173 as @code{setf} places; each will accept either an integer or a
1174 marker as the stored value.)
1176 Since generalized variables look like lists, @code{let}'s shorthand
1177 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
1178 be ambiguous in @code{cl-letf} and is not allowed.
1180 However, a @var{binding} specifier may be a one-element list
1181 @samp{(@var{place})}, which is similar to @samp{(@var{place}
1182 @var{place})}. In other words, the @var{place} is not disturbed
1183 on entry to the body, and the only effect of the @code{cl-letf} is
1184 to restore the original value of @var{place} afterwards.
1185 @c I suspect this may no longer be true; either way it's
1186 @c implementation detail and so not essential to document.
1188 (The redundant access-and-store suggested by the @code{(@var{place}
1189 @var{place})} example does not actually occur.)
1192 Note that in this case, and in fact almost every case, @var{place}
1193 must have a well-defined value outside the @code{cl-letf} body.
1194 There is essentially only one exception to this, which is @var{place}
1195 a plain variable with a specified @var{value} (such as @code{(a 17)}
1196 in the above example).
1197 @c See http://debbugs.gnu.org/12758
1198 @c Some or all of this was true for cl.el, but not for cl-lib.el.
1200 The only exceptions are plain variables and calls to
1201 @code{symbol-value} and @code{symbol-function}. If the symbol is not
1202 bound on entry, it is simply made unbound by @code{makunbound} or
1203 @code{fmakunbound} on exit.
1206 Note that the @file{cl.el} version of this macro behaves slightly
1207 differently. @xref{Obsolete Macros}.
1210 @defmac cl-letf* (bindings@dots{}) forms@dots{}
1211 This macro is to @code{cl-letf} what @code{let*} is to @code{let}:
1212 It does the bindings in sequential rather than parallel order.
1215 @defmac cl-callf @var{function} @var{place} @var{args}@dots{}
1216 This is the ``generic'' modify macro. It calls @var{function},
1217 which should be an unquoted function name, macro name, or lambda.
1218 It passes @var{place} and @var{args} as arguments, and assigns the
1219 result back to @var{place}. For example, @code{(cl-incf @var{place}
1220 @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}.
1224 (cl-callf abs my-number)
1225 (cl-callf concat (buffer-name) "<" (number-to-string n) ">")
1226 (cl-callf cl-union happy-people (list joe bob) :test 'same-person)
1229 Note again that @code{cl-callf} is an extension to standard Common Lisp.
1232 @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{}
1233 This macro is like @code{cl-callf}, except that @var{place} is
1234 the @emph{second} argument of @var{function} rather than the
1235 first. For example, @code{(push @var{x} @var{place})} is
1236 equivalent to @code{(cl-callf2 cons @var{x} @var{place})}.
1239 The @code{cl-callf} and @code{cl-callf2} macros serve as building
1240 blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}.
1241 The @code{cl-letf} and @code{cl-letf*} macros are used in the processing
1242 of symbol macros; @pxref{Macro Bindings}.
1245 @node Variable Bindings
1246 @section Variable Bindings
1249 These Lisp forms make bindings to variables and function names,
1250 analogous to Lisp's built-in @code{let} form.
1252 @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which
1253 are also related to variable bindings.
1256 * Dynamic Bindings:: The @code{cl-progv} form.
1257 * Function Bindings:: @code{cl-flet} and @code{cl-labels}.
1258 * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}.
1261 @node Dynamic Bindings
1262 @subsection Dynamic Bindings
1265 The standard @code{let} form binds variables whose names are known
1266 at compile-time. The @code{cl-progv} form provides an easy way to
1267 bind variables whose names are computed at run-time.
1269 @defmac cl-progv symbols values forms@dots{}
1270 This form establishes @code{let}-style variable bindings on a
1271 set of variables computed at run-time. The expressions
1272 @var{symbols} and @var{values} are evaluated, and must return lists
1273 of symbols and values, respectively. The symbols are bound to the
1274 corresponding values for the duration of the body @var{form}s.
1275 If @var{values} is shorter than @var{symbols}, the last few symbols
1276 are bound to @code{nil}.
1277 If @var{symbols} is shorter than @var{values}, the excess values
1281 @node Function Bindings
1282 @subsection Function Bindings
1285 These forms make @code{let}-like bindings to functions instead
1288 @defmac cl-flet (bindings@dots{}) forms@dots{}
1289 This form establishes @code{let}-style bindings on the function
1290 cells of symbols rather than on the value cells. Each @var{binding}
1291 must be a list of the form @samp{(@var{name} @var{arglist}
1292 @var{forms}@dots{})}, which defines a function exactly as if
1293 it were a @code{cl-defun} form. The function @var{name} is defined
1294 accordingly for the duration of the body of the @code{cl-flet}; then
1295 the old function definition, or lack thereof, is restored.
1297 You can use @code{cl-flet} to disable or modify the behavior of a
1298 function in a temporary fashion. (Compare this with the idea
1299 of advising functions.
1300 @xref{Advising Functions,,,elisp,GNU Emacs Lisp Reference Manual}.)
1301 This will even work on Emacs primitives, although note that some calls
1302 to primitive functions internal to Emacs are made without going
1303 through the symbol's function cell, and so will not be affected by
1304 @code{cl-flet}. For example,
1307 (cl-flet ((message (&rest args) (push args saved-msgs)))
1311 This code attempts to replace the built-in function @code{message}
1312 with a function that simply saves the messages in a list rather
1313 than displaying them. The original definition of @code{message}
1314 will be restored after @code{do-something} exits. This code will
1315 work fine on messages generated by other Lisp code, but messages
1316 generated directly inside Emacs will not be caught since they make
1317 direct C-language calls to the message routines rather than going
1318 through the Lisp @code{message} function.
1320 Functions defined by @code{cl-flet} may use the full Common Lisp
1321 argument notation supported by @code{cl-defun}; also, the function
1322 body is enclosed in an implicit block as if by @code{cl-defun}.
1323 @xref{Program Structure}.
1325 Note that the @file{cl.el} version of this macro behaves slightly
1326 differently. @xref{Obsolete Macros}.
1329 @defmac cl-labels (bindings@dots{}) forms@dots{}
1330 The @code{cl-labels} form is like @code{cl-flet}, except that
1331 the function bindings can be recursive. The scoping is lexical,
1332 but you can only capture functions in closures if
1333 @code{lexical-binding} is @code{t}.
1334 @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and
1335 @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
1337 Lexical scoping means that all references to the named
1338 functions must appear physically within the body of the
1339 @code{cl-labels} form. References may appear both in the body
1340 @var{forms} of @code{cl-labels} itself, and in the bodies of
1341 the functions themselves. Thus, @code{cl-labels} can define
1342 local recursive functions, or mutually-recursive sets of functions.
1344 A ``reference'' to a function name is either a call to that
1345 function, or a use of its name quoted by @code{quote} or
1346 @code{function} to be passed on to, say, @code{mapcar}.
1348 Note that the @file{cl.el} version of this macro behaves slightly
1349 differently. @xref{Obsolete Macros}.
1352 @node Macro Bindings
1353 @subsection Macro Bindings
1356 These forms create local macros and ``symbol macros''.
1358 @defmac cl-macrolet (bindings@dots{}) forms@dots{}
1359 This form is analogous to @code{cl-flet}, but for macros instead of
1360 functions. Each @var{binding} is a list of the same form as the
1361 arguments to @code{cl-defmacro} (i.e., a macro name, argument list,
1362 and macro-expander forms). The macro is defined accordingly for
1363 use within the body of the @code{cl-macrolet}.
1365 Because of the nature of macros, @code{cl-macrolet} is always lexically
1366 scoped. The @code{cl-macrolet} binding will
1367 affect only calls that appear physically within the body
1368 @var{forms}, possibly after expansion of other macros in the
1372 @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{}
1373 This form creates @dfn{symbol macros}, which are macros that look
1374 like variable references rather than function calls. Each
1375 @var{binding} is a list @samp{(@var{var} @var{expansion})};
1376 any reference to @var{var} within the body @var{forms} is
1377 replaced by @var{expansion}.
1381 (cl-symbol-macrolet ((foo (car bar)))
1387 A @code{setq} of a symbol macro is treated the same as a @code{setf}.
1388 I.e., @code{(setq foo 4)} in the above would be equivalent to
1389 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
1391 Likewise, a @code{let} or @code{let*} binding a symbol macro is
1392 treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true
1393 Common Lisp, where the rules of lexical scoping cause a @code{let}
1394 binding to shadow a @code{symbol-macrolet} binding. In this package,
1395 such shadowing does not occur, even when @code{lexical-binding} is
1396 @c See http://debbugs.gnu.org/12119
1397 @code{t}. (This behavior predates the addition of lexical binding to
1398 Emacs Lisp, and may change in future to respect @code{lexical-binding}.)
1399 At present in this package, only @code{lexical-let} and
1400 @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete
1403 There is no analogue of @code{defmacro} for symbol macros; all symbol
1404 macros are local. A typical use of @code{cl-symbol-macrolet} is in the
1405 expansion of another macro:
1408 (cl-defmacro my-dolist ((x list) &rest body)
1409 (let ((var (cl-gensym)))
1410 (list 'cl-loop 'for var 'on list 'do
1411 (cl-list* 'cl-symbol-macrolet
1412 (list (list x (list 'car var)))
1415 (setq mylist '(1 2 3 4))
1416 (my-dolist (x mylist) (cl-incf x))
1422 In this example, the @code{my-dolist} macro is similar to @code{dolist}
1423 (@pxref{Iteration}) except that the variable @code{x} becomes a true
1424 reference onto the elements of the list. The @code{my-dolist} call
1425 shown here expands to
1428 (cl-loop for G1234 on mylist do
1429 (cl-symbol-macrolet ((x (car G1234)))
1434 which in turn expands to
1437 (cl-loop for G1234 on mylist do (cl-incf (car G1234)))
1440 @xref{Loop Facility}, for a description of the @code{cl-loop} macro.
1441 This package defines a nonstandard @code{in-ref} loop clause that
1442 works much like @code{my-dolist}.
1446 @section Conditionals
1449 These conditional forms augment Emacs Lisp's simple @code{if},
1450 @code{and}, @code{or}, and @code{cond} forms.
1452 @defmac cl-case keyform clause@dots{}
1453 This macro evaluates @var{keyform}, then compares it with the key
1454 values listed in the various @var{clause}s. Whichever clause matches
1455 the key is executed; comparison is done by @code{eql}. If no clause
1456 matches, the @code{cl-case} form returns @code{nil}. The clauses are
1460 (@var{keylist} @var{body-forms}@dots{})
1464 where @var{keylist} is a list of key values. If there is exactly
1465 one value, and it is not a cons cell or the symbol @code{nil} or
1466 @code{t}, then it can be used by itself as a @var{keylist} without
1467 being enclosed in a list. All key values in the @code{cl-case} form
1468 must be distinct. The final clauses may use @code{t} in place of
1469 a @var{keylist} to indicate a default clause that should be taken
1470 if none of the other clauses match. (The symbol @code{otherwise}
1471 is also recognized in place of @code{t}. To make a clause that
1472 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise},
1473 enclose the symbol in a list.)
1475 For example, this expression reads a keystroke, then does one of
1476 four things depending on whether it is an @samp{a}, a @samp{b},
1477 a @key{RET} or @kbd{C-j}, or anything else.
1480 (cl-case (read-char)
1483 ((?\r ?\n) (do-ret-thing))
1484 (t (do-other-thing)))
1488 @defmac cl-ecase keyform clause@dots{}
1489 This macro is just like @code{cl-case}, except that if the key does
1490 not match any of the clauses, an error is signaled rather than
1491 simply returning @code{nil}.
1494 @defmac cl-typecase keyform clause@dots{}
1495 This macro is a version of @code{cl-case} that checks for types
1496 rather than values. Each @var{clause} is of the form
1497 @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates},
1498 for a description of type specifiers. For example,
1502 (integer (munch-integer x))
1503 (float (munch-float x))
1504 (string (munch-integer (string-to-int x)))
1505 (t (munch-anything x)))
1508 The type specifier @code{t} matches any type of object; the word
1509 @code{otherwise} is also allowed. To make one clause match any of
1510 several types, use an @code{(or @dots{})} type specifier.
1513 @defmac cl-etypecase keyform clause@dots{}
1514 This macro is just like @code{cl-typecase}, except that if the key does
1515 not match any of the clauses, an error is signaled rather than
1516 simply returning @code{nil}.
1519 @node Blocks and Exits
1520 @section Blocks and Exits
1523 Common Lisp @dfn{blocks} provide a non-local exit mechanism very
1524 similar to @code{catch} and @code{throw}, with lexical scoping.
1525 This package actually implements @code{cl-block}
1526 in terms of @code{catch}; however, the lexical scoping allows the
1527 byte-compiler to omit the costly @code{catch} step if the
1528 body of the block does not actually @code{cl-return-from} the block.
1530 @defmac cl-block name forms@dots{}
1531 The @var{forms} are evaluated as if by a @code{progn}. However,
1532 if any of the @var{forms} execute @code{(cl-return-from @var{name})},
1533 they will jump out and return directly from the @code{cl-block} form.
1534 The @code{cl-block} returns the result of the last @var{form} unless
1535 a @code{cl-return-from} occurs.
1537 The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to
1538 the @code{catch}/@code{throw} mechanism. The main differences are
1539 that block @var{name}s are unevaluated symbols, rather than forms
1540 (such as quoted symbols) that evaluate to a tag at run-time; and
1541 also that blocks are always lexically scoped.
1542 In a dynamically scoped @code{catch}, functions called from the
1543 @code{catch} body can also @code{throw} to the @code{catch}. This
1544 is not an option for @code{cl-block}, where
1545 the @code{cl-return-from} referring to a block name must appear
1546 physically within the @var{forms} that make up the body of the block.
1547 They may not appear within other called functions, although they may
1548 appear within macro expansions or @code{lambda}s in the body. Block
1549 names and @code{catch} names form independent name-spaces.
1551 In true Common Lisp, @code{defun} and @code{defmacro} surround
1552 the function or expander bodies with implicit blocks with the
1553 same name as the function or macro. This does not occur in Emacs
1554 Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro}
1555 forms, which do create the implicit block.
1557 The Common Lisp looping constructs defined by this package,
1558 such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks
1559 just as in Common Lisp.
1561 Because they are implemented in terms of Emacs Lisp's @code{catch}
1562 and @code{throw}, blocks have the same overhead as actual
1563 @code{catch} constructs (roughly two function calls). However,
1564 the byte compiler will optimize away the @code{catch}
1566 not in fact contain any @code{cl-return} or @code{cl-return-from} calls
1567 that jump to it. This means that @code{cl-do} loops and @code{cl-defun}
1568 functions that don't use @code{cl-return} don't pay the overhead to
1572 @defmac cl-return-from name [result]
1573 This macro returns from the block named @var{name}, which must be
1574 an (unevaluated) symbol. If a @var{result} form is specified, it
1575 is evaluated to produce the result returned from the @code{block}.
1576 Otherwise, @code{nil} is returned.
1579 @defmac cl-return [result]
1580 This macro is exactly like @code{(cl-return-from nil @var{result})}.
1581 Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose
1582 themselves in @code{nil} blocks.
1589 The macros described here provide more sophisticated, high-level
1590 looping constructs to complement Emacs Lisp's basic loop forms
1591 (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}).
1593 @defmac cl-loop forms@dots{}
1594 This package supports both the simple, old-style meaning of
1595 @code{loop} and the extremely powerful and flexible feature known as
1596 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced
1597 facility is discussed in the following section; @pxref{Loop Facility}.
1598 The simple form of @code{loop} is described here.
1600 If @code{cl-loop} is followed by zero or more Lisp expressions,
1601 then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite
1602 loop executing the expressions over and over. The loop is
1603 enclosed in an implicit @code{nil} block. Thus,
1606 (cl-loop (foo) (if (no-more) (return 72)) (bar))
1610 is exactly equivalent to
1613 (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar)))
1616 If any of the expressions are plain symbols, the loop is instead
1617 interpreted as a Loop Macro specification as described later.
1618 (This is not a restriction in practice, since a plain symbol
1619 in the above notation would simply access and throw away the
1620 value of a variable.)
1623 @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1624 This macro creates a general iterative loop. Each @var{spec} is
1628 (@var{var} [@var{init} [@var{step}]])
1631 The loop works as follows: First, each @var{var} is bound to the
1632 associated @var{init} value as if by a @code{let} form. Then, in
1633 each iteration of the loop, the @var{end-test} is evaluated; if
1634 true, the loop is finished. Otherwise, the body @var{forms} are
1635 evaluated, then each @var{var} is set to the associated @var{step}
1636 expression (as if by a @code{cl-psetq} form) and the next iteration
1637 begins. Once the @var{end-test} becomes true, the @var{result}
1638 forms are evaluated (with the @var{var}s still bound to their
1639 values) to produce the result returned by @code{cl-do}.
1641 The entire @code{cl-do} loop is enclosed in an implicit @code{nil}
1642 block, so that you can use @code{(cl-return)} to break out of the
1645 If there are no @var{result} forms, the loop returns @code{nil}.
1646 If a given @var{var} has no @var{step} form, it is bound to its
1647 @var{init} value but not otherwise modified during the @code{cl-do}
1648 loop (unless the code explicitly modifies it); this case is just
1649 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})}
1650 around the loop. If @var{init} is also omitted it defaults to
1651 @code{nil}, and in this case a plain @samp{@var{var}} can be used
1652 in place of @samp{(@var{var})}, again following the analogy with
1655 This example (from Steele) illustrates a loop that applies the
1656 function @code{f} to successive pairs of values from the lists
1657 @code{foo} and @code{bar}; it is equivalent to the call
1658 @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body
1659 @var{forms} at all, performing all its work as side effects of
1660 the rest of the loop.
1663 (cl-do ((x foo (cdr x))
1665 (z nil (cons (f (car x) (car y)) z)))
1666 ((or (null x) (null y))
1671 @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1672 This is to @code{cl-do} what @code{let*} is to @code{let}. In
1673 particular, the initial values are bound as if by @code{let*}
1674 rather than @code{let}, and the steps are assigned as if by
1675 @code{setq} rather than @code{cl-psetq}.
1677 Here is another way to write the above loop:
1680 (cl-do* ((xp foo (cdr xp))
1682 (x (car xp) (car xp))
1683 (y (car yp) (car yp))
1685 ((or (null xp) (null yp))
1691 @defmac cl-dolist (var list [result]) forms@dots{}
1692 This is exactly like the standard Emacs Lisp macro @code{dolist},
1693 but surrounds the loop with an implicit @code{nil} block.
1696 @defmac cl-dotimes (var count [result]) forms@dots{}
1697 This is exactly like the standard Emacs Lisp macro @code{dotimes},
1698 but surrounds the loop with an implicit @code{nil} block.
1699 The body is executed with @var{var} bound to the integers
1700 from zero (inclusive) to @var{count} (exclusive), in turn. Then
1701 @c FIXME lispref does not state this part explicitly, could move this there.
1702 the @code{result} form is evaluated with @var{var} bound to the total
1703 number of iterations that were done (i.e., @code{(max 0 @var{count})})
1704 to get the return value for the loop form.
1707 @defmac cl-do-symbols (var [obarray [result]]) forms@dots{}
1708 This loop iterates over all interned symbols. If @var{obarray}
1709 is specified and is not @code{nil}, it loops over all symbols in
1710 that obarray. For each symbol, the body @var{forms} are evaluated
1711 with @var{var} bound to that symbol. The symbols are visited in
1712 an unspecified order. Afterward the @var{result} form, if any,
1713 is evaluated (with @var{var} bound to @code{nil}) to get the return
1714 value. The loop is surrounded by an implicit @code{nil} block.
1717 @defmac cl-do-all-symbols (var [result]) forms@dots{}
1718 This is identical to @code{cl-do-symbols} except that the @var{obarray}
1719 argument is omitted; it always iterates over the default obarray.
1722 @xref{Mapping over Sequences}, for some more functions for
1723 iterating over vectors or lists.
1726 @section Loop Facility
1729 A common complaint with Lisp's traditional looping constructs was
1730 that they were either too simple and limited, such as @code{dotimes}
1731 or @code{while}, or too unreadable and obscure, like Common Lisp's
1734 To remedy this, Common Lisp added a construct called the ``Loop
1735 Facility'' or ``@code{loop} macro'', with an easy-to-use but very
1736 powerful and expressive syntax.
1739 * Loop Basics:: The @code{cl-loop} macro, basic clause structure.
1740 * Loop Examples:: Working examples of the @code{cl-loop} macro.
1741 * For Clauses:: Clauses introduced by @code{for} or @code{as}.
1742 * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc.
1743 * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc.
1744 * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}.
1748 @subsection Loop Basics
1751 The @code{cl-loop} macro essentially creates a mini-language within
1752 Lisp that is specially tailored for describing loops. While this
1753 language is a little strange-looking by the standards of regular Lisp,
1754 it turns out to be very easy to learn and well-suited to its purpose.
1756 Since @code{cl-loop} is a macro, all parsing of the loop language
1757 takes place at byte-compile time; compiled @code{cl-loop}s are just
1758 as efficient as the equivalent @code{while} loops written longhand.
1760 @defmac cl-loop clauses@dots{}
1761 A loop construct consists of a series of @var{clause}s, each
1762 introduced by a symbol like @code{for} or @code{do}. Clauses
1763 are simply strung together in the argument list of @code{cl-loop},
1764 with minimal extra parentheses. The various types of clauses
1765 specify initializations, such as the binding of temporary
1766 variables, actions to be taken in the loop, stepping actions,
1769 Common Lisp specifies a certain general order of clauses in a
1773 (loop @var{name-clause}
1774 @var{var-clauses}@dots{}
1775 @var{action-clauses}@dots{})
1778 The @var{name-clause} optionally gives a name to the implicit
1779 block that surrounds the loop. By default, the implicit block
1780 is named @code{nil}. The @var{var-clauses} specify what
1781 variables should be bound during the loop, and how they should
1782 be modified or iterated throughout the course of the loop. The
1783 @var{action-clauses} are things to be done during the loop, such
1784 as computing, collecting, and returning values.
1786 The Emacs version of the @code{cl-loop} macro is less restrictive about
1787 the order of clauses, but things will behave most predictably if
1788 you put the variable-binding clauses @code{with}, @code{for}, and
1789 @code{repeat} before the action clauses. As in Common Lisp,
1790 @code{initially} and @code{finally} clauses can go anywhere.
1792 Loops generally return @code{nil} by default, but you can cause
1793 them to return a value by using an accumulation clause like
1794 @code{collect}, an end-test clause like @code{always}, or an
1795 explicit @code{return} clause to jump out of the implicit block.
1796 (Because the loop body is enclosed in an implicit block, you can
1797 also use regular Lisp @code{cl-return} or @code{cl-return-from} to
1798 break out of the loop.)
1801 The following sections give some examples of the loop macro in
1802 action, and describe the particular loop clauses in great detail.
1803 Consult the second edition of Steele for additional discussion
1807 @subsection Loop Examples
1810 Before listing the full set of clauses that are allowed, let's
1811 look at a few example loops just to get a feel for the @code{cl-loop}
1815 (cl-loop for buf in (buffer-list)
1816 collect (buffer-file-name buf))
1820 This loop iterates over all Emacs buffers, using the list
1821 returned by @code{buffer-list}. For each buffer @var{buf},
1822 it calls @code{buffer-file-name} and collects the results into
1823 a list, which is then returned from the @code{cl-loop} construct.
1824 The result is a list of the file names of all the buffers in
1825 Emacs's memory. The words @code{for}, @code{in}, and @code{collect}
1826 are reserved words in the @code{cl-loop} language.
1829 (cl-loop repeat 20 do (insert "Yowsa\n"))
1833 This loop inserts the phrase ``Yowsa'' twenty times in the
1837 (cl-loop until (eobp) do (munch-line) (forward-line 1))
1841 This loop calls @code{munch-line} on every line until the end
1842 of the buffer. If point is already at the end of the buffer,
1843 the loop exits immediately.
1846 (cl-loop do (munch-line) until (eobp) do (forward-line 1))
1850 This loop is similar to the above one, except that @code{munch-line}
1851 is always called at least once.
1854 (cl-loop for x from 1 to 100
1857 finally return (list x (= y 729)))
1861 This more complicated loop searches for a number @code{x} whose
1862 square is 729. For safety's sake it only examines @code{x}
1863 values up to 100; dropping the phrase @samp{to 100} would
1864 cause the loop to count upwards with no limit. The second
1865 @code{for} clause defines @code{y} to be the square of @code{x}
1866 within the loop; the expression after the @code{=} sign is
1867 reevaluated each time through the loop. The @code{until}
1868 clause gives a condition for terminating the loop, and the
1869 @code{finally} clause says what to do when the loop finishes.
1870 (This particular example was written less concisely than it
1871 could have been, just for the sake of illustration.)
1873 Note that even though this loop contains three clauses (two
1874 @code{for}s and an @code{until}) that would have been enough to
1875 define loops all by themselves, it still creates a single loop
1876 rather than some sort of triple-nested loop. You must explicitly
1877 nest your @code{cl-loop} constructs if you want nested loops.
1880 @subsection For Clauses
1883 Most loops are governed by one or more @code{for} clauses.
1884 A @code{for} clause simultaneously describes variables to be
1885 bound, how those variables are to be stepped during the loop,
1886 and usually an end condition based on those variables.
1888 The word @code{as} is a synonym for the word @code{for}. This
1889 word is followed by a variable name, then a word like @code{from}
1890 or @code{across} that describes the kind of iteration desired.
1891 In Common Lisp, the phrase @code{being the} sometimes precedes
1892 the type of iteration; in this package both @code{being} and
1893 @code{the} are optional. The word @code{each} is a synonym
1894 for @code{the}, and the word that follows it may be singular
1895 or plural: @samp{for x being the elements of y} or
1896 @samp{for x being each element of y}. Which form you use
1897 is purely a matter of style.
1899 The variable is bound around the loop as if by @code{let}:
1903 (cl-loop for i from 1 to 10 do (do-something-with i))
1909 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3}
1910 This type of @code{for} clause creates a counting loop. Each of
1911 the three sub-terms is optional, though there must be at least one
1912 term so that the clause is marked as a counting clause.
1914 The three expressions are the starting value, the ending value, and
1915 the step value, respectively, of the variable. The loop counts
1916 upwards by default (@var{expr3} must be positive), from @var{expr1}
1917 to @var{expr2} inclusively. If you omit the @code{from} term, the
1918 loop counts from zero; if you omit the @code{to} term, the loop
1919 counts forever without stopping (unless stopped by some other
1920 loop clause, of course); if you omit the @code{by} term, the loop
1921 counts in steps of one.
1923 You can replace the word @code{from} with @code{upfrom} or
1924 @code{downfrom} to indicate the direction of the loop. Likewise,
1925 you can replace @code{to} with @code{upto} or @code{downto}.
1926 For example, @samp{for x from 5 downto 1} executes five times
1927 with @code{x} taking on the integers from 5 down to 1 in turn.
1928 Also, you can replace @code{to} with @code{below} or @code{above},
1929 which are like @code{upto} and @code{downto} respectively except
1930 that they are exclusive rather than inclusive limits:
1933 (cl-loop for x to 10 collect x)
1934 @result{} (0 1 2 3 4 5 6 7 8 9 10)
1935 (cl-loop for x below 10 collect x)
1936 @result{} (0 1 2 3 4 5 6 7 8 9)
1939 The @code{by} value is always positive, even for downward-counting
1940 loops. Some sort of @code{from} value is required for downward
1941 loops; @samp{for x downto 5} is not a valid loop clause all by
1944 @item for @var{var} in @var{list} by @var{function}
1945 This clause iterates @var{var} over all the elements of @var{list},
1946 in turn. If you specify the @code{by} term, then @var{function}
1947 is used to traverse the list instead of @code{cdr}; it must be a
1948 function taking one argument. For example:
1951 (cl-loop for x in '(1 2 3 4 5 6) collect (* x x))
1952 @result{} (1 4 9 16 25 36)
1953 (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
1957 @item for @var{var} on @var{list} by @var{function}
1958 This clause iterates @var{var} over all the cons cells of @var{list}.
1961 (cl-loop for x on '(1 2 3 4) collect x)
1962 @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
1965 With @code{by}, there is no real reason that the @code{on} expression
1966 must be a list. For example:
1969 (cl-loop for x on first-animal by 'next-animal collect x)
1973 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
1974 the next in the (assumed) sequence of animals, or @code{nil} if
1975 @var{x} was the last animal in the sequence.
1977 @item for @var{var} in-ref @var{list} by @var{function}
1978 This is like a regular @code{in} clause, but @var{var} becomes
1979 a @code{setf}-able ``reference'' onto the elements of the list
1980 rather than just a temporary variable. For example,
1983 (cl-loop for x in-ref my-list do (cl-incf x))
1987 increments every element of @code{my-list} in place. This clause
1988 is an extension to standard Common Lisp.
1990 @item for @var{var} across @var{array}
1991 This clause iterates @var{var} over all the elements of @var{array},
1992 which may be a vector or a string.
1995 (cl-loop for x across "aeiou"
1996 do (use-vowel (char-to-string x)))
1999 @item for @var{var} across-ref @var{array}
2000 This clause iterates over an array, with @var{var} a @code{setf}-able
2001 reference onto the elements; see @code{in-ref} above.
2003 @item for @var{var} being the elements of @var{sequence}
2004 This clause iterates over the elements of @var{sequence}, which may
2005 be a list, vector, or string. Since the type must be determined
2006 at run-time, this is somewhat less efficient than @code{in} or
2007 @code{across}. The clause may be followed by the additional term
2008 @samp{using (index @var{var2})} to cause @var{var2} to be bound to
2009 the successive indices (starting at 0) of the elements.
2011 This clause type is taken from older versions of the @code{loop} macro,
2012 and is not present in modern Common Lisp. The @samp{using (sequence @dots{})}
2013 term of the older macros is not supported.
2015 @item for @var{var} being the elements of-ref @var{sequence}
2016 This clause iterates over a sequence, with @var{var} a @code{setf}-able
2017 reference onto the elements; see @code{in-ref} above.
2019 @item for @var{var} being the symbols [of @var{obarray}]
2020 This clause iterates over symbols, either over all interned symbols
2021 or over all symbols in @var{obarray}. The loop is executed with
2022 @var{var} bound to each symbol in turn. The symbols are visited in
2023 an unspecified order.
2028 (cl-loop for sym being the symbols
2030 when (string-match "^map" (symbol-name sym))
2035 returns a list of all the functions whose names begin with @samp{map}.
2037 The Common Lisp words @code{external-symbols} and @code{present-symbols}
2038 are also recognized but are equivalent to @code{symbols} in Emacs Lisp.
2040 Due to a minor implementation restriction, it will not work to have
2041 more than one @code{for} clause iterating over symbols, hash tables,
2042 keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately,
2043 it would rarely if ever be useful to do so. It @emph{is} valid to mix
2044 one of these types of clauses with other clauses like @code{for @dots{} to}
2047 @item for @var{var} being the hash-keys of @var{hash-table}
2048 @itemx for @var{var} being the hash-values of @var{hash-table}
2049 This clause iterates over the entries in @var{hash-table} with
2050 @var{var} bound to each key, or value. A @samp{using} clause can bind
2051 a second variable to the opposite part.
2054 (cl-loop for k being the hash-keys of h
2055 using (hash-values v)
2057 (message "key %S -> value %S" k v))
2060 @item for @var{var} being the key-codes of @var{keymap}
2061 @itemx for @var{var} being the key-bindings of @var{keymap}
2062 This clause iterates over the entries in @var{keymap}.
2063 The iteration does not enter nested keymaps but does enter inherited
2065 A @code{using} clause can access both the codes and the bindings
2069 (cl-loop for c being the key-codes of (current-local-map)
2070 using (key-bindings b)
2072 (message "key %S -> binding %S" c b))
2076 @item for @var{var} being the key-seqs of @var{keymap}
2077 This clause iterates over all key sequences defined by @var{keymap}
2078 and its nested keymaps, where @var{var} takes on values which are
2079 vectors. The strings or vectors
2080 are reused for each iteration, so you must copy them if you wish to keep
2081 them permanently. You can add a @samp{using (key-bindings @dots{})}
2082 clause to get the command bindings as well.
2084 @item for @var{var} being the overlays [of @var{buffer}] @dots{}
2085 This clause iterates over the ``overlays'' of a buffer
2086 (the clause @code{extents} is synonymous
2087 with @code{overlays}). If the @code{of} term is omitted, the current
2089 This clause also accepts optional @samp{from @var{pos}} and
2090 @samp{to @var{pos}} terms, limiting the clause to overlays which
2091 overlap the specified region.
2093 @item for @var{var} being the intervals [of @var{buffer}] @dots{}
2094 This clause iterates over all intervals of a buffer with constant
2095 text properties. The variable @var{var} will be bound to conses
2096 of start and end positions, where one start position is always equal
2097 to the previous end position. The clause allows @code{of},
2098 @code{from}, @code{to}, and @code{property} terms, where the latter
2099 term restricts the search to just the specified property. The
2100 @code{of} term may specify either a buffer or a string.
2102 @item for @var{var} being the frames
2103 This clause iterates over all Emacs frames. The clause @code{screens} is
2104 a synonym for @code{frames}. The frames are visited in
2105 @code{next-frame} order starting from @code{selected-frame}.
2107 @item for @var{var} being the windows [of @var{frame}]
2108 This clause iterates over the windows (in the Emacs sense) of
2109 the current frame, or of the specified @var{frame}. It visits windows
2110 in @code{next-window} order starting from @code{selected-window}
2111 (or @code{frame-selected-window} if you specify @var{frame}).
2112 This clause treats the minibuffer window in the same way as
2113 @code{next-window} does. For greater flexibility, consider using
2114 @code{walk-windows} instead.
2116 @item for @var{var} being the buffers
2117 This clause iterates over all buffers in Emacs. It is equivalent
2118 to @samp{for @var{var} in (buffer-list)}.
2120 @item for @var{var} = @var{expr1} then @var{expr2}
2121 This clause does a general iteration. The first time through
2122 the loop, @var{var} will be bound to @var{expr1}. On the second
2123 and successive iterations it will be set by evaluating @var{expr2}
2124 (which may refer to the old value of @var{var}). For example,
2125 these two loops are effectively the same:
2128 (cl-loop for x on my-list by 'cddr do @dots{})
2129 (cl-loop for x = my-list then (cddr x) while x do @dots{})
2132 Note that this type of @code{for} clause does not imply any sort
2133 of terminating condition; the above example combines it with a
2134 @code{while} clause to tell when to end the loop.
2136 If you omit the @code{then} term, @var{expr1} is used both for
2137 the initial setting and for successive settings:
2140 (cl-loop for x = (random) when (> x 0) return x)
2144 This loop keeps taking random numbers from the @code{(random)}
2145 function until it gets a positive one, which it then returns.
2148 If you include several @code{for} clauses in a row, they are
2149 treated sequentially (as if by @code{let*} and @code{setq}).
2150 You can instead use the word @code{and} to link the clauses,
2151 in which case they are processed in parallel (as if by @code{let}
2152 and @code{cl-psetq}).
2155 (cl-loop for x below 5 for y = nil then x collect (list x y))
2156 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4))
2157 (cl-loop for x below 5 and y = nil then x collect (list x y))
2158 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3))
2162 In the first loop, @code{y} is set based on the value of @code{x}
2163 that was just set by the previous clause; in the second loop,
2164 @code{x} and @code{y} are set simultaneously so @code{y} is set
2165 based on the value of @code{x} left over from the previous time
2168 Another feature of the @code{cl-loop} macro is @emph{destructuring},
2169 similar in concept to the destructuring provided by @code{defmacro}
2170 (@pxref{Argument Lists}).
2171 The @var{var} part of any @code{for} clause can be given as a list
2172 of variables instead of a single variable. The values produced
2173 during loop execution must be lists; the values in the lists are
2174 stored in the corresponding variables.
2177 (cl-loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y))
2181 In loop destructuring, if there are more values than variables
2182 the trailing values are ignored, and if there are more variables
2183 than values the trailing variables get the value @code{nil}.
2184 If @code{nil} is used as a variable name, the corresponding
2185 values are ignored. Destructuring may be nested, and dotted
2186 lists of variables like @code{(x . y)} are allowed, so for example
2190 (cl-loop for (key . value) in '((a . 1) (b . 2))
2195 @node Iteration Clauses
2196 @subsection Iteration Clauses
2199 Aside from @code{for} clauses, there are several other loop clauses
2200 that control the way the loop operates. They might be used by
2201 themselves, or in conjunction with one or more @code{for} clauses.
2204 @item repeat @var{integer}
2205 This clause simply counts up to the specified number using an
2206 internal temporary variable. The loops
2209 (cl-loop repeat (1+ n) do @dots{})
2210 (cl-loop for temp to n do @dots{})
2214 are identical except that the second one forces you to choose
2215 a name for a variable you aren't actually going to use.
2217 @item while @var{condition}
2218 This clause stops the loop when the specified condition (any Lisp
2219 expression) becomes @code{nil}. For example, the following two
2220 loops are equivalent, except for the implicit @code{nil} block
2221 that surrounds the second one:
2224 (while @var{cond} @var{forms}@dots{})
2225 (cl-loop while @var{cond} do @var{forms}@dots{})
2228 @item until @var{condition}
2229 This clause stops the loop when the specified condition is true,
2230 i.e., non-@code{nil}.
2232 @item always @var{condition}
2233 This clause stops the loop when the specified condition is @code{nil}.
2234 Unlike @code{while}, it stops the loop using @code{return nil} so that
2235 the @code{finally} clauses are not executed. If all the conditions
2236 were non-@code{nil}, the loop returns @code{t}:
2239 (if (cl-loop for size in size-list always (> size 10))
2244 @item never @var{condition}
2245 This clause is like @code{always}, except that the loop returns
2246 @code{t} if any conditions were false, or @code{nil} otherwise.
2248 @item thereis @var{condition}
2249 This clause stops the loop when the specified form is non-@code{nil};
2250 in this case, it returns that non-@code{nil} value. If all the
2251 values were @code{nil}, the loop returns @code{nil}.
2254 @node Accumulation Clauses
2255 @subsection Accumulation Clauses
2258 These clauses cause the loop to accumulate information about the
2259 specified Lisp @var{form}. The accumulated result is returned
2260 from the loop unless overridden, say, by a @code{return} clause.
2263 @item collect @var{form}
2264 This clause collects the values of @var{form} into a list. Several
2265 examples of @code{collect} appear elsewhere in this manual.
2267 The word @code{collecting} is a synonym for @code{collect}, and
2268 likewise for the other accumulation clauses.
2270 @item append @var{form}
2271 This clause collects lists of values into a result list using
2274 @item nconc @var{form}
2275 This clause collects lists of values into a result list by
2276 destructively modifying the lists rather than copying them.
2278 @item concat @var{form}
2279 This clause concatenates the values of the specified @var{form}
2280 into a string. (It and the following clause are extensions to
2281 standard Common Lisp.)
2283 @item vconcat @var{form}
2284 This clause concatenates the values of the specified @var{form}
2287 @item count @var{form}
2288 This clause counts the number of times the specified @var{form}
2289 evaluates to a non-@code{nil} value.
2291 @item sum @var{form}
2292 This clause accumulates the sum of the values of the specified
2293 @var{form}, which must evaluate to a number.
2295 @item maximize @var{form}
2296 This clause accumulates the maximum value of the specified @var{form},
2297 which must evaluate to a number. The return value is undefined if
2298 @code{maximize} is executed zero times.
2300 @item minimize @var{form}
2301 This clause accumulates the minimum value of the specified @var{form}.
2304 Accumulation clauses can be followed by @samp{into @var{var}} to
2305 cause the data to be collected into variable @var{var} (which is
2306 automatically @code{let}-bound during the loop) rather than an
2307 unnamed temporary variable. Also, @code{into} accumulations do
2308 not automatically imply a return value. The loop must use some
2309 explicit mechanism, such as @code{finally return}, to return
2310 the accumulated result.
2312 It is valid for several accumulation clauses of the same type to
2313 accumulate into the same place. From Steele:
2316 (cl-loop for name in '(fred sue alice joe june)
2317 for kids in '((bob ken) () () (kris sunshine) ())
2320 @result{} (fred bob ken sue alice joe kris sunshine june)
2324 @subsection Other Clauses
2327 This section describes the remaining loop clauses.
2330 @item with @var{var} = @var{value}
2331 This clause binds a variable to a value around the loop, but
2332 otherwise leaves the variable alone during the loop. The following
2333 loops are basically equivalent:
2336 (cl-loop with x = 17 do @dots{})
2337 (let ((x 17)) (cl-loop do @dots{}))
2338 (cl-loop for x = 17 then x do @dots{})
2341 Naturally, the variable @var{var} might be used for some purpose
2342 in the rest of the loop. For example:
2345 (cl-loop for x in my-list with res = nil do (push x res)
2349 This loop inserts the elements of @code{my-list} at the front of
2350 a new list being accumulated in @code{res}, then returns the
2351 list @code{res} at the end of the loop. The effect is similar
2352 to that of a @code{collect} clause, but the list gets reversed
2353 by virtue of the fact that elements are being pushed onto the
2354 front of @code{res} rather than the end.
2356 If you omit the @code{=} term, the variable is initialized to
2357 @code{nil}. (Thus the @samp{= nil} in the above example is
2360 Bindings made by @code{with} are sequential by default, as if
2361 by @code{let*}. Just like @code{for} clauses, @code{with} clauses
2362 can be linked with @code{and} to cause the bindings to be made by
2365 @item if @var{condition} @var{clause}
2366 This clause executes the following loop clause only if the specified
2367 condition is true. The following @var{clause} should be an accumulation,
2368 @code{do}, @code{return}, @code{if}, or @code{unless} clause.
2369 Several clauses may be linked by separating them with @code{and}.
2370 These clauses may be followed by @code{else} and a clause or clauses
2371 to execute if the condition was false. The whole construct may
2372 optionally be followed by the word @code{end} (which may be used to
2373 disambiguate an @code{else} or @code{and} in a nested @code{if}).
2375 The actual non-@code{nil} value of the condition form is available
2376 by the name @code{it} in the ``then'' part. For example:
2379 (setq funny-numbers '(6 13 -1))
2381 (cl-loop for x below 10
2384 and if (memq x funny-numbers) return (cdr it) end
2386 collect x into evens
2387 finally return (vector odds evens))
2388 @result{} [(1 3 5 7 9) (0 2 4 6 8)]
2389 (setq funny-numbers '(6 7 13 -1))
2390 @result{} (6 7 13 -1)
2391 (cl-loop <@r{same thing again}>)
2395 Note the use of @code{and} to put two clauses into the ``then''
2396 part, one of which is itself an @code{if} clause. Note also that
2397 @code{end}, while normally optional, was necessary here to make
2398 it clear that the @code{else} refers to the outermost @code{if}
2399 clause. In the first case, the loop returns a vector of lists
2400 of the odd and even values of @var{x}. In the second case, the
2401 odd number 7 is one of the @code{funny-numbers} so the loop
2402 returns early; the actual returned value is based on the result
2403 of the @code{memq} call.
2405 @item when @var{condition} @var{clause}
2406 This clause is just a synonym for @code{if}.
2408 @item unless @var{condition} @var{clause}
2409 The @code{unless} clause is just like @code{if} except that the
2410 sense of the condition is reversed.
2412 @item named @var{name}
2413 This clause gives a name other than @code{nil} to the implicit
2414 block surrounding the loop. The @var{name} is the symbol to be
2415 used as the block name.
2417 @item initially [do] @var{forms}@dots{}
2418 This keyword introduces one or more Lisp forms which will be
2419 executed before the loop itself begins (but after any variables
2420 requested by @code{for} or @code{with} have been bound to their
2421 initial values). @code{initially} clauses can appear anywhere;
2422 if there are several, they are executed in the order they appear
2423 in the loop. The keyword @code{do} is optional.
2425 @item finally [do] @var{forms}@dots{}
2426 This introduces Lisp forms which will be executed after the loop
2427 finishes (say, on request of a @code{for} or @code{while}).
2428 @code{initially} and @code{finally} clauses may appear anywhere
2429 in the loop construct, but they are executed (in the specified
2430 order) at the beginning or end, respectively, of the loop.
2432 @item finally return @var{form}
2433 This says that @var{form} should be executed after the loop
2434 is done to obtain a return value. (Without this, or some other
2435 clause like @code{collect} or @code{return}, the loop will simply
2436 return @code{nil}.) Variables bound by @code{for}, @code{with},
2437 or @code{into} will still contain their final values when @var{form}
2440 @item do @var{forms}@dots{}
2441 The word @code{do} may be followed by any number of Lisp expressions
2442 which are executed as an implicit @code{progn} in the body of the
2443 loop. Many of the examples in this section illustrate the use of
2446 @item return @var{form}
2447 This clause causes the loop to return immediately. The following
2448 Lisp form is evaluated to give the return value of the loop
2449 form. The @code{finally} clauses, if any, are not executed.
2450 Of course, @code{return} is generally used inside an @code{if} or
2451 @code{unless}, as its use in a top-level loop clause would mean
2452 the loop would never get to ``loop'' more than once.
2454 The clause @samp{return @var{form}} is equivalent to
2455 @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop
2456 was named). The @code{return} clause is implemented a bit more
2457 efficiently, though.
2460 While there is no high-level way to add user extensions to @code{cl-loop},
2461 this package does offer two properties called @code{cl-loop-handler}
2462 and @code{cl-loop-for-handler} which are functions to be called when a
2463 given symbol is encountered as a top-level loop clause or @code{for}
2464 clause, respectively. Consult the source code in file
2465 @file{cl-macs.el} for details.
2467 This package's @code{cl-loop} macro is compatible with that of Common
2468 Lisp, except that a few features are not implemented: @code{loop-finish}
2469 and data-type specifiers. Naturally, the @code{for} clauses that
2470 iterate over keymaps, overlays, intervals, frames, windows, and
2471 buffers are Emacs-specific extensions.
2473 @node Multiple Values
2474 @section Multiple Values
2477 Common Lisp functions can return zero or more results. Emacs Lisp
2478 functions, by contrast, always return exactly one result. This
2479 package makes no attempt to emulate Common Lisp multiple return
2480 values; Emacs versions of Common Lisp functions that return more
2481 than one value either return just the first value (as in
2482 @code{cl-compiler-macroexpand}) or return a list of values.
2483 This package @emph{does} define placeholders
2484 for the Common Lisp functions that work with multiple values, but
2485 in Emacs Lisp these functions simply operate on lists instead.
2486 The @code{cl-values} form, for example, is a synonym for @code{list}
2489 @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{}
2490 This form evaluates @var{values-form}, which must return a list of
2491 values. It then binds the @var{var}s to these respective values,
2492 as if by @code{let}, and then executes the body @var{forms}.
2493 If there are more @var{var}s than values, the extra @var{var}s
2494 are bound to @code{nil}. If there are fewer @var{var}s than
2495 values, the excess values are ignored.
2498 @defmac cl-multiple-value-setq (var@dots{}) form
2499 This form evaluates @var{form}, which must return a list of values.
2500 It then sets the @var{var}s to these respective values, as if by
2501 @code{setq}. Extra @var{var}s or values are treated the same as
2502 in @code{cl-multiple-value-bind}.
2505 Since a perfect emulation is not feasible in Emacs Lisp, this
2506 package opts to keep it as simple and predictable as possible.
2512 This package implements the various Common Lisp features of
2513 @code{defmacro}, such as destructuring, @code{&environment},
2514 and @code{&body}. Top-level @code{&whole} is not implemented
2515 for @code{defmacro} due to technical difficulties.
2516 @xref{Argument Lists}.
2518 Destructuring is made available to the user by way of the
2521 @defmac cl-destructuring-bind arglist expr forms@dots{}
2522 This macro expands to code that executes @var{forms}, with
2523 the variables in @var{arglist} bound to the list of values
2524 returned by @var{expr}. The @var{arglist} can include all
2525 the features allowed for @code{cl-defmacro} argument lists,
2526 including destructuring. (The @code{&environment} keyword
2527 is not allowed.) The macro expansion will signal an error
2528 if @var{expr} returns a list of the wrong number of arguments
2529 or with incorrect keyword arguments.
2532 This package also includes the Common Lisp @code{define-compiler-macro}
2533 facility, which allows you to define compile-time expansions and
2534 optimizations for your functions.
2536 @defmac cl-define-compiler-macro name arglist forms@dots{}
2537 This form is similar to @code{defmacro}, except that it only expands
2538 calls to @var{name} at compile-time; calls processed by the Lisp
2539 interpreter are not expanded, nor are they expanded by the
2540 @code{macroexpand} function.
2542 The argument list may begin with a @code{&whole} keyword and a
2543 variable. This variable is bound to the macro-call form itself,
2544 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}.
2545 If the macro expander returns this form unchanged, then the
2546 compiler treats it as a normal function call. This allows
2547 compiler macros to work as optimizers for special cases of a
2548 function, leaving complicated cases alone.
2550 For example, here is a simplified version of a definition that
2551 appears as a standard part of this package:
2554 (cl-define-compiler-macro cl-member (&whole form a list &rest keys)
2555 (if (and (null keys)
2556 (eq (car-safe a) 'quote)
2557 (not (floatp (cadr a))))
2563 This definition causes @code{(cl-member @var{a} @var{list})} to change
2564 to a call to the faster @code{memq} in the common case where @var{a}
2565 is a non-floating-point constant; if @var{a} is anything else, or
2566 if there are any keyword arguments in the call, then the original
2567 @code{cl-member} call is left intact. (The actual compiler macro
2568 for @code{cl-member} optimizes a number of other cases, including
2569 common @code{:test} predicates.)
2572 @defun cl-compiler-macroexpand form
2573 This function is analogous to @code{macroexpand}, except that it
2574 expands compiler macros rather than regular macros. It returns
2575 @var{form} unchanged if it is not a call to a function for which
2576 a compiler macro has been defined, or if that compiler macro
2577 decided to punt by returning its @code{&whole} argument. Like
2578 @code{macroexpand}, it expands repeatedly until it reaches a form
2579 for which no further expansion is possible.
2582 @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet}
2583 and @code{cl-symbol-macrolet} forms for making ``local'' macro
2587 @chapter Declarations
2590 Common Lisp includes a complex and powerful ``declaration''
2591 mechanism that allows you to give the compiler special hints
2592 about the types of data that will be stored in particular variables,
2593 and about the ways those variables and functions will be used. This
2594 package defines versions of all the Common Lisp declaration forms:
2595 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim},
2598 Most of the Common Lisp declarations are not currently useful in Emacs
2599 Lisp. For example, the byte-code system provides little
2600 opportunity to benefit from type information.
2602 and @code{special} declarations are redundant in a fully
2603 dynamically-scoped Lisp.
2605 A few declarations are meaningful when byte compiler optimizations
2606 are enabled, as they are by the default. Otherwise these
2607 declarations will effectively be ignored.
2609 @defun cl-proclaim decl-spec
2610 This function records a ``global'' declaration specified by
2611 @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec}
2612 is evaluated and thus should normally be quoted.
2615 @defmac cl-declaim decl-specs@dots{}
2616 This macro is like @code{cl-proclaim}, except that it takes any number
2617 of @var{decl-spec} arguments, and the arguments are unevaluated and
2618 unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when
2619 (compile load eval) @dots{})} around the declarations so that they will
2620 be registered at compile-time as well as at run-time. (This is vital,
2621 since normally the declarations are meant to influence the way the
2622 compiler treats the rest of the file that contains the @code{cl-declaim}
2626 @defmac cl-declare decl-specs@dots{}
2627 This macro is used to make declarations within functions and other
2628 code. Common Lisp allows declarations in various locations, generally
2629 at the beginning of any of the many ``implicit @code{progn}s''
2630 throughout Lisp syntax, such as function bodies, @code{let} bodies,
2631 etc. Currently the only declaration understood by @code{cl-declare}
2635 @defmac cl-locally declarations@dots{} forms@dots{}
2636 In this package, @code{cl-locally} is no different from @code{progn}.
2639 @defmac cl-the type form
2640 Type information provided by @code{cl-the} is ignored in this package;
2641 in other words, @code{(cl-the @var{type} @var{form})} is equivalent to
2642 @var{form}. Future byte-compiler optimizations may make use of this
2645 For example, @code{mapcar} can map over both lists and arrays. It is
2646 hard for the compiler to expand @code{mapcar} into an in-line loop
2647 unless it knows whether the sequence will be a list or an array ahead
2648 of time. With @code{(mapcar 'car (cl-the vector foo))}, a future
2649 compiler would have enough information to expand the loop in-line.
2650 For now, Emacs Lisp will treat the above code as exactly equivalent
2651 to @code{(mapcar 'car foo)}.
2654 Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or
2655 @code{cl-declare} should be a list beginning with a symbol that says
2656 what kind of declaration it is. This package currently understands
2657 @code{special}, @code{inline}, @code{notinline}, @code{optimize},
2658 and @code{warn} declarations. (The @code{warn} declaration is an
2659 extension of standard Common Lisp.) Other Common Lisp declarations,
2660 such as @code{type} and @code{ftype}, are silently ignored.
2665 Since all variables in Emacs Lisp are ``special'' (in the Common
2666 Lisp sense), @code{special} declarations are only advisory. They
2667 simply tell the byte compiler that the specified
2668 variables are intentionally being referred to without being
2669 bound in the body of the function. The compiler normally emits
2670 warnings for such references, since they could be typographical
2671 errors for references to local variables.
2673 The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is
2674 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}.
2676 In top-level contexts, it is generally better to write
2677 @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))},
2678 since @code{defvar} makes your intentions clearer.
2681 The @code{inline} @var{decl-spec} lists one or more functions
2682 whose bodies should be expanded ``in-line'' into calling functions
2683 whenever the compiler is able to arrange for it. For example,
2684 the function @code{cl-acons} is declared @code{inline}
2685 by this package so that the form @code{(cl-acons @var{key} @var{value}
2687 expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})}
2688 when it is called in user functions, so as to save function calls.
2690 The following declarations are all equivalent. Note that the
2691 @code{defsubst} form is a convenient way to define a function
2692 and declare it inline all at once.
2695 (cl-declaim (inline foo bar))
2696 (cl-eval-when (compile load eval)
2697 (cl-proclaim '(inline foo bar)))
2698 (defsubst foo (@dots{}) @dots{}) ; instead of defun
2701 @strong{Please note:} this declaration remains in effect after the
2702 containing source file is done. It is correct to use it to
2703 request that a function you have defined should be inlined,
2704 but it is impolite to use it to request inlining of an external
2707 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))}
2708 before a particular call to a function to cause just that call to
2709 be inlined; the current byte compilers provide no way to implement
2710 this, so @code{(cl-declare (inline @dots{}))} is currently ignored by
2714 The @code{notinline} declaration lists functions which should
2715 not be inlined after all; it cancels a previous @code{inline}
2719 This declaration controls how much optimization is performed by
2722 The word @code{optimize} is followed by any number of lists like
2723 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several
2724 optimization ``qualities''; this package ignores all but @code{speed}
2725 and @code{safety}. The value of a quality should be an integer from
2726 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''.
2727 The default level for both qualities is 1.
2729 In this package, the @code{speed} quality is tied to the @code{byte-optimize}
2730 flag, which is set to @code{nil} for @code{(speed 0)} and to
2731 @code{t} for higher settings; and the @code{safety} quality is
2732 tied to the @code{byte-compile-delete-errors} flag, which is
2733 set to @code{nil} for @code{(safety 3)} and to @code{t} for all
2734 lower settings. (The latter flag controls whether the compiler
2735 is allowed to optimize out code whose only side-effect could
2736 be to signal an error, e.g., rewriting @code{(progn foo bar)} to
2737 @code{bar} when it is not known whether @code{foo} will be bound
2740 Note that even compiling with @code{(safety 0)}, the Emacs
2741 byte-code system provides sufficient checking to prevent real
2742 harm from being done. For example, barring serious bugs in
2743 Emacs itself, Emacs will not crash with a segmentation fault
2744 just because of an error in a fully-optimized Lisp program.
2746 The @code{optimize} declaration is normally used in a top-level
2747 @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows
2748 it to be used with @code{declare} to set the level of optimization
2749 locally for a given form, but this will not work correctly with the
2750 current byte-compiler. (The @code{cl-declare}
2751 will set the new optimization level, but that level will not
2752 automatically be unset after the enclosing form is done.)
2755 This declaration controls what sorts of warnings are generated
2756 by the byte compiler. The word @code{warn} is followed by any
2757 number of ``warning qualities'', similar in form to optimization
2758 qualities. The currently supported warning types are
2759 @code{redefine}, @code{callargs}, @code{unresolved}, and
2760 @code{free-vars}; in the current system, a value of 0 will
2761 disable these warnings and any higher value will enable them.
2762 See the documentation of the variable @code{byte-compile-warnings}
2770 This package defines several symbol-related features that were
2771 missing from Emacs Lisp.
2774 * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}.
2775 * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}.
2778 @node Property Lists
2779 @section Property Lists
2782 These functions augment the standard Emacs Lisp functions @code{get}
2783 and @code{put} for operating on properties attached to symbols.
2784 There are also functions for working with property lists as
2785 first-class data structures not attached to particular symbols.
2787 @defun cl-get symbol property &optional default
2788 This function is like @code{get}, except that if the property is
2789 not found, the @var{default} argument provides the return value.
2790 (The Emacs Lisp @code{get} function always uses @code{nil} as
2791 the default; this package's @code{cl-get} is equivalent to Common
2794 The @code{cl-get} function is @code{setf}-able; when used in this
2795 fashion, the @var{default} argument is allowed but ignored.
2798 @defun cl-remprop symbol property
2799 This function removes the entry for @var{property} from the property
2800 list of @var{symbol}. It returns a true value if the property was
2801 indeed found and removed, or @code{nil} if there was no such property.
2802 (This function was probably omitted from Emacs originally because,
2803 since @code{get} did not allow a @var{default}, it was very difficult
2804 to distinguish between a missing property and a property whose value
2805 was @code{nil}; thus, setting a property to @code{nil} was close
2806 enough to @code{cl-remprop} for most purposes.)
2809 @defun cl-getf place property &optional default
2810 This function scans the list @var{place} as if it were a property
2811 list, i.e., a list of alternating property names and values. If
2812 an even-numbered element of @var{place} is found which is @code{eq}
2813 to @var{property}, the following odd-numbered element is returned.
2814 Otherwise, @var{default} is returned (or @code{nil} if no default
2820 (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop)
2823 It is valid to use @code{cl-getf} as a @code{setf} place, in which case
2824 its @var{place} argument must itself be a valid @code{setf} place.
2825 The @var{default} argument, if any, is ignored in this context.
2826 The effect is to change (via @code{setcar}) the value cell in the
2827 list that corresponds to @var{property}, or to cons a new property-value
2828 pair onto the list if the property is not yet present.
2831 (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val)
2834 The @code{get} and @code{cl-get} functions are also @code{setf}-able.
2835 The fact that @code{default} is ignored can sometimes be useful:
2838 (cl-incf (cl-get 'foo 'usage-count 0))
2841 Here, symbol @code{foo}'s @code{usage-count} property is incremented
2842 if it exists, or set to 1 (an incremented 0) otherwise.
2844 When not used as a @code{setf} form, @code{cl-getf} is just a regular
2845 function and its @var{place} argument can actually be any Lisp
2849 @defmac cl-remf place property
2850 This macro removes the property-value pair for @var{property} from
2851 the property list stored at @var{place}, which is any @code{setf}-able
2852 place expression. It returns true if the property was found. Note
2853 that if @var{property} happens to be first on the list, this will
2854 effectively do a @code{(setf @var{place} (cddr @var{place}))},
2855 whereas if it occurs later, this simply uses @code{setcdr} to splice
2856 out the property and value cells.
2859 @node Creating Symbols
2860 @section Creating Symbols
2863 These functions create unique symbols, typically for use as
2864 temporary variables.
2866 @defun cl-gensym &optional x
2867 This function creates a new, uninterned symbol (using @code{make-symbol})
2868 with a unique name. (The name of an uninterned symbol is relevant
2869 only if the symbol is printed.) By default, the name is generated
2870 @c FIXME no longer true?
2871 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001},
2872 @samp{G1002}, etc. If the optional argument @var{x} is a string, that
2873 string is used as a prefix instead of @samp{G}. Uninterned symbols
2874 are used in macro expansions for temporary variables, to ensure that
2875 their names will not conflict with ``real'' variables in the user's
2878 (Internally, the variable @code{cl--gensym-counter} holds the counter
2879 used to generate names. It is incremented after each use. In Common
2880 Lisp this is initialized with 0, but this package initializes it with
2881 a random time-dependent value to avoid trouble when two files that
2882 each used @code{cl-gensym} in their compilation are loaded together.
2883 Uninterned symbols become interned when the compiler writes them out
2884 to a file and the Emacs loader loads them, so their names have to be
2885 treated a bit more carefully than in Common Lisp where uninterned
2886 symbols remain uninterned after loading.)
2889 @defun cl-gentemp &optional x
2890 This function is like @code{cl-gensym}, except that it produces a new
2891 @emph{interned} symbol. If the symbol that is generated already
2892 exists, the function keeps incrementing the counter and trying
2893 again until a new symbol is generated.
2896 This package automatically creates all keywords that are called for by
2897 @code{&key} argument specifiers, and discourages the use of keywords
2898 as data unrelated to keyword arguments, so the related function
2899 @code{defkeyword} (to create self-quoting keyword symbols) is not
2906 This section defines a few simple Common Lisp operations on numbers
2907 that were left out of Emacs Lisp.
2910 * Predicates on Numbers:: @code{cl-plusp}, @code{cl-oddp}, etc.
2911 * Numerical Functions:: @code{cl-floor}, @code{cl-ceiling}, etc.
2912 * Random Numbers:: @code{cl-random}, @code{cl-make-random-state}.
2913 * Implementation Parameters:: @code{cl-most-positive-float}, etc.
2916 @node Predicates on Numbers
2917 @section Predicates on Numbers
2920 These functions return @code{t} if the specified condition is
2921 true of the numerical argument, or @code{nil} otherwise.
2923 @defun cl-plusp number
2924 This predicate tests whether @var{number} is positive. It is an
2925 error if the argument is not a number.
2928 @defun cl-minusp number
2929 This predicate tests whether @var{number} is negative. It is an
2930 error if the argument is not a number.
2933 @defun cl-oddp integer
2934 This predicate tests whether @var{integer} is odd. It is an
2935 error if the argument is not an integer.
2938 @defun cl-evenp integer
2939 This predicate tests whether @var{integer} is even. It is an
2940 error if the argument is not an integer.
2944 @defun cl-floatp-safe object
2945 This predicate tests whether @var{object} is a floating-point
2946 number. On systems that support floating-point, this is equivalent
2947 to @code{floatp}. On other systems, this always returns @code{nil}.
2951 @node Numerical Functions
2952 @section Numerical Functions
2955 These functions perform various arithmetic operations on numbers.
2957 @defun cl-gcd &rest integers
2958 This function returns the Greatest Common Divisor of the arguments.
2959 For one argument, it returns the absolute value of that argument.
2960 For zero arguments, it returns zero.
2963 @defun cl-lcm &rest integers
2964 This function returns the Least Common Multiple of the arguments.
2965 For one argument, it returns the absolute value of that argument.
2966 For zero arguments, it returns one.
2969 @defun cl-isqrt integer
2970 This function computes the ``integer square root'' of its integer
2971 argument, i.e., the greatest integer less than or equal to the true
2972 square root of the argument.
2975 @defun cl-floor number &optional divisor
2976 With one argument, @code{cl-floor} returns a list of two numbers:
2977 The argument rounded down (toward minus infinity) to an integer,
2978 and the ``remainder'' which would have to be added back to the
2979 first return value to yield the argument again. If the argument
2980 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}.
2981 If the argument is a floating-point number, the first
2982 result is a Lisp integer and the second is a Lisp float between
2983 0 (inclusive) and 1 (exclusive).
2985 With two arguments, @code{cl-floor} divides @var{number} by
2986 @var{divisor}, and returns the floor of the quotient and the
2987 corresponding remainder as a list of two numbers. If
2988 @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})},
2989 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r}
2990 between 0 (inclusive) and @var{r} (exclusive). Also, note
2991 that @code{(cl-floor @var{x})} is exactly equivalent to
2992 @code{(cl-floor @var{x} 1)}.
2994 This function is entirely compatible with Common Lisp's @code{floor}
2995 function, except that it returns the two results in a list since
2996 Emacs Lisp does not support multiple-valued functions.
2999 @defun cl-ceiling number &optional divisor
3000 This function implements the Common Lisp @code{ceiling} function,
3001 which is analogous to @code{floor} except that it rounds the
3002 argument or quotient of the arguments up toward plus infinity.
3003 The remainder will be between 0 and minus @var{r}.
3006 @defun cl-truncate number &optional divisor
3007 This function implements the Common Lisp @code{truncate} function,
3008 which is analogous to @code{floor} except that it rounds the
3009 argument or quotient of the arguments toward zero. Thus it is
3010 equivalent to @code{cl-floor} if the argument or quotient is
3011 positive, or to @code{cl-ceiling} otherwise. The remainder has
3012 the same sign as @var{number}.
3015 @defun cl-round number &optional divisor
3016 This function implements the Common Lisp @code{round} function,
3017 which is analogous to @code{floor} except that it rounds the
3018 argument or quotient of the arguments to the nearest integer.
3019 In the case of a tie (the argument or quotient is exactly
3020 halfway between two integers), it rounds to the even integer.
3023 @defun cl-mod number divisor
3024 This function returns the same value as the second return value
3028 @defun cl-rem number divisor
3029 This function returns the same value as the second return value
3030 of @code{cl-truncate}.
3033 @node Random Numbers
3034 @section Random Numbers
3037 This package also provides an implementation of the Common Lisp
3038 random number generator. It uses its own additive-congruential
3039 algorithm, which is much more likely to give statistically clean
3040 @c FIXME? Still true?
3041 random numbers than the simple generators supplied by many
3044 @defun cl-random number &optional state
3045 This function returns a random nonnegative number less than
3046 @var{number}, and of the same type (either integer or floating-point).
3047 The @var{state} argument should be a @code{random-state} object
3048 that holds the state of the random number generator. The
3049 function modifies this state object as a side effect. If
3050 @var{state} is omitted, it defaults to the internal variable
3051 @code{cl--random-state}, which contains a pre-initialized
3052 default @code{random-state} object. (Since any number of programs in
3053 the Emacs process may be accessing @code{cl--random-state} in
3054 interleaved fashion, the sequence generated from this will be
3055 irreproducible for all intents and purposes.)
3058 @defun cl-make-random-state &optional state
3059 This function creates or copies a @code{random-state} object.
3060 If @var{state} is omitted or @code{nil}, it returns a new copy of
3061 @code{cl--random-state}. This is a copy in the sense that future
3062 sequences of calls to @code{(cl-random @var{n})} and
3063 @code{(cl-random @var{n} @var{s})} (where @var{s} is the new
3064 random-state object) will return identical sequences of random
3067 If @var{state} is a @code{random-state} object, this function
3068 returns a copy of that object. If @var{state} is @code{t}, this
3069 function returns a new @code{random-state} object seeded from the
3070 date and time. As an extension to Common Lisp, @var{state} may also
3071 be an integer in which case the new object is seeded from that
3072 integer; each different integer seed will result in a completely
3073 different sequence of random numbers.
3075 It is valid to print a @code{random-state} object to a buffer or
3076 file and later read it back with @code{read}. If a program wishes
3077 to use a sequence of pseudo-random numbers which can be reproduced
3078 later for debugging, it can call @code{(cl-make-random-state t)} to
3079 get a new sequence, then print this sequence to a file. When the
3080 program is later rerun, it can read the original run's random-state
3084 @defun cl-random-state-p object
3085 This predicate returns @code{t} if @var{object} is a
3086 @code{random-state} object, or @code{nil} otherwise.
3089 @node Implementation Parameters
3090 @section Implementation Parameters
3093 This package defines several useful constants having to do with
3094 floating-point numbers.
3096 It determines their values by exercising the computer's
3097 floating-point arithmetic in various ways. Because this operation
3098 might be slow, the code for initializing them is kept in a separate
3099 function that must be called before the parameters can be used.
3101 @defun cl-float-limits
3102 This function makes sure that the Common Lisp floating-point parameters
3103 like @code{cl-most-positive-float} have been initialized. Until it is
3104 called, these parameters will be @code{nil}.
3105 @c If this version of Emacs does not support floats, the parameters will
3106 @c remain @code{nil}.
3107 If the parameters have already been initialized, the function returns
3110 The algorithm makes assumptions that will be valid for almost all
3111 machines, but will fail if the machine's arithmetic is extremely
3112 unusual, e.g., decimal.
3115 Since true Common Lisp supports up to four different floating-point
3116 precisions, it has families of constants like
3117 @code{most-positive-single-float}, @code{most-positive-double-float},
3118 @code{most-positive-long-float}, and so on. Emacs has only one
3119 floating-point precision, so this package omits the precision word
3120 from the constants' names.
3122 @defvar cl-most-positive-float
3123 This constant equals the largest value a Lisp float can hold.
3124 For those systems whose arithmetic supports infinities, this is
3125 the largest @emph{finite} value. For IEEE machines, the value
3126 is approximately @code{1.79e+308}.
3129 @defvar cl-most-negative-float
3130 This constant equals the most negative value a Lisp float can hold.
3131 (It is assumed to be equal to @code{(- cl-most-positive-float)}.)
3134 @defvar cl-least-positive-float
3135 This constant equals the smallest Lisp float value greater than zero.
3136 For IEEE machines, it is about @code{4.94e-324} if denormals are
3137 supported or @code{2.22e-308} if not.
3140 @defvar cl-least-positive-normalized-float
3141 This constant equals the smallest @emph{normalized} Lisp float greater
3142 than zero, i.e., the smallest value for which IEEE denormalization
3143 will not result in a loss of precision. For IEEE machines, this
3144 value is about @code{2.22e-308}. For machines that do not support
3145 the concept of denormalization and gradual underflow, this constant
3146 will always equal @code{cl-least-positive-float}.
3149 @defvar cl-least-negative-float
3150 This constant is the negative counterpart of @code{cl-least-positive-float}.
3153 @defvar cl-least-negative-normalized-float
3154 This constant is the negative counterpart of
3155 @code{cl-least-positive-normalized-float}.
3158 @defvar cl-float-epsilon
3159 This constant is the smallest positive Lisp float that can be added
3160 to 1.0 to produce a distinct value. Adding a smaller number to 1.0
3161 will yield 1.0 again due to roundoff. For IEEE machines, epsilon
3162 is about @code{2.22e-16}.
3165 @defvar cl-float-negative-epsilon
3166 This is the smallest positive value that can be subtracted from
3167 1.0 to produce a distinct value. For IEEE machines, it is about
3175 Common Lisp defines a number of functions that operate on
3176 @dfn{sequences}, which are either lists, strings, or vectors.
3177 Emacs Lisp includes a few of these, notably @code{elt} and
3178 @code{length}; this package defines most of the rest.
3181 * Sequence Basics:: Arguments shared by all sequence functions.
3182 * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc.
3183 * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc.
3184 * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc.
3185 * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}.
3188 @node Sequence Basics
3189 @section Sequence Basics
3192 Many of the sequence functions take keyword arguments; @pxref{Argument
3193 Lists}. All keyword arguments are optional and, if specified,
3194 may appear in any order.
3196 The @code{:key} argument should be passed either @code{nil}, or a
3197 function of one argument. This key function is used as a filter
3198 through which the elements of the sequence are seen; for example,
3199 @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}.
3200 It searches for an element of the list whose @sc{car} equals
3201 @code{x}, rather than for an element which equals @code{x} itself.
3202 If @code{:key} is omitted or @code{nil}, the filter is effectively
3203 the identity function.
3205 The @code{:test} and @code{:test-not} arguments should be either
3206 @code{nil}, or functions of two arguments. The test function is
3207 used to compare two sequence elements, or to compare a search value
3208 with sequence elements. (The two values are passed to the test
3209 function in the same order as the original sequence function
3210 arguments from which they are derived, or, if they both come from
3211 the same sequence, in the same order as they appear in that sequence.)
3212 The @code{:test} argument specifies a function which must return
3213 true (non-@code{nil}) to indicate a match; instead, you may use
3214 @code{:test-not} to give a function which returns @emph{false} to
3215 indicate a match. The default test function is @code{eql}.
3217 Many functions that take @var{item} and @code{:test} or @code{:test-not}
3218 arguments also come in @code{-if} and @code{-if-not} varieties,
3219 where a @var{predicate} function is passed instead of @var{item},
3220 and sequence elements match if the predicate returns true on them
3221 (or false in the case of @code{-if-not}). For example:
3224 (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq)
3228 to remove all zeros from sequence @code{seq}.
3230 Some operations can work on a subsequence of the argument sequence;
3231 these function take @code{:start} and @code{:end} arguments, which
3232 default to zero and the length of the sequence, respectively.
3233 Only elements between @var{start} (inclusive) and @var{end}
3234 (exclusive) are affected by the operation. The @var{end} argument
3235 may be passed @code{nil} to signify the length of the sequence;
3236 otherwise, both @var{start} and @var{end} must be integers, with
3237 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}.
3238 If the function takes two sequence arguments, the limits are
3239 defined by keywords @code{:start1} and @code{:end1} for the first,
3240 and @code{:start2} and @code{:end2} for the second.
3242 A few functions accept a @code{:from-end} argument, which, if
3243 non-@code{nil}, causes the operation to go from right-to-left
3244 through the sequence instead of left-to-right, and a @code{:count}
3245 argument, which specifies an integer maximum number of elements
3246 to be removed or otherwise processed.
3248 The sequence functions make no guarantees about the order in
3249 which the @code{:test}, @code{:test-not}, and @code{:key} functions
3250 are called on various elements. Therefore, it is a bad idea to depend
3251 on side effects of these functions. For example, @code{:from-end}
3252 may cause the sequence to be scanned actually in reverse, or it may
3253 be scanned forwards but computing a result ``as if'' it were scanned
3254 backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every},
3255 @emph{do} specify exactly the order in which the function is called
3256 so side effects are perfectly acceptable in those cases.)
3258 Strings may contain ``text properties'' as well
3259 as character data. Except as noted, it is undefined whether or
3260 not text properties are preserved by sequence functions. For
3261 example, @code{(cl-remove ?A @var{str})} may or may not preserve
3262 the properties of the characters copied from @var{str} into the
3265 @node Mapping over Sequences
3266 @section Mapping over Sequences
3269 These functions ``map'' the function you specify over the elements
3270 of lists or arrays. They are all variations on the theme of the
3271 built-in function @code{mapcar}.
3273 @defun cl-mapcar function seq &rest more-seqs
3274 This function calls @var{function} on successive parallel sets of
3275 elements from its argument sequences. Given a single @var{seq}
3276 argument it is equivalent to @code{mapcar}; given @var{n} sequences,
3277 it calls the function with the first elements of each of the sequences
3278 as the @var{n} arguments to yield the first element of the result
3279 list, then with the second elements, and so on. The mapping stops as
3280 soon as the shortest sequence runs out. The argument sequences may
3281 be any mixture of lists, strings, and vectors; the return sequence
3284 Common Lisp's @code{mapcar} accepts multiple arguments but works
3285 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence
3286 argument. This package's @code{cl-mapcar} works as a compatible
3290 @defun cl-map result-type function seq &rest more-seqs
3291 This function maps @var{function} over the argument sequences,
3292 just like @code{cl-mapcar}, but it returns a sequence of type
3293 @var{result-type} rather than a list. @var{result-type} must
3294 be one of the following symbols: @code{vector}, @code{string},
3295 @code{list} (in which case the effect is the same as for
3296 @code{cl-mapcar}), or @code{nil} (in which case the results are
3297 thrown away and @code{cl-map} returns @code{nil}).
3300 @defun cl-maplist function list &rest more-lists
3301 This function calls @var{function} on each of its argument lists,
3302 then on the @sc{cdr}s of those lists, and so on, until the
3303 shortest list runs out. The results are returned in the form
3304 of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except
3305 that it passes in the list pointers themselves rather than the
3306 @sc{car}s of the advancing pointers.
3309 @defun cl-mapc function seq &rest more-seqs
3310 This function is like @code{cl-mapcar}, except that the values returned
3311 by @var{function} are ignored and thrown away rather than being
3312 collected into a list. The return value of @code{cl-mapc} is @var{seq},
3313 the first sequence. This function is more general than the Emacs
3314 primitive @code{mapc}. (Note that this function is called
3315 @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you
3317 @c http://debbugs.gnu.org/6575
3320 @defun cl-mapl function list &rest more-lists
3321 This function is like @code{cl-maplist}, except that it throws away
3322 the values returned by @var{function}.
3325 @defun cl-mapcan function seq &rest more-seqs
3326 This function is like @code{cl-mapcar}, except that it concatenates
3327 the return values (which must be lists) using @code{nconc},
3328 rather than simply collecting them into a list.
3331 @defun cl-mapcon function list &rest more-lists
3332 This function is like @code{cl-maplist}, except that it concatenates
3333 the return values using @code{nconc}.
3336 @defun cl-some predicate seq &rest more-seqs
3337 This function calls @var{predicate} on each element of @var{seq}
3338 in turn; if @var{predicate} returns a non-@code{nil} value,
3339 @code{cl-some} returns that value, otherwise it returns @code{nil}.
3340 Given several sequence arguments, it steps through the sequences
3341 in parallel until the shortest one runs out, just as in
3342 @code{cl-mapcar}. You can rely on the left-to-right order in which
3343 the elements are visited, and on the fact that mapping stops
3344 immediately as soon as @var{predicate} returns non-@code{nil}.
3347 @defun cl-every predicate seq &rest more-seqs
3348 This function calls @var{predicate} on each element of the sequence(s)
3349 in turn; it returns @code{nil} as soon as @var{predicate} returns
3350 @code{nil} for any element, or @code{t} if the predicate was true
3354 @defun cl-notany predicate seq &rest more-seqs
3355 This function calls @var{predicate} on each element of the sequence(s)
3356 in turn; it returns @code{nil} as soon as @var{predicate} returns
3357 a non-@code{nil} value for any element, or @code{t} if the predicate
3358 was @code{nil} for all elements.
3361 @defun cl-notevery predicate seq &rest more-seqs
3362 This function calls @var{predicate} on each element of the sequence(s)
3363 in turn; it returns a non-@code{nil} value as soon as @var{predicate}
3364 returns @code{nil} for any element, or @code{t} if the predicate was
3365 true for all elements.
3368 @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key}
3369 This function combines the elements of @var{seq} using an associative
3370 binary operation. Suppose @var{function} is @code{*} and @var{seq} is
3371 the list @code{(2 3 4 5)}. The first two elements of the list are
3372 combined with @code{(* 2 3) = 6}; this is combined with the next
3373 element, @code{(* 6 4) = 24}, and that is combined with the final
3374 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens
3375 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as
3376 an explicit call to @code{cl-reduce}.
3378 If @code{:from-end} is true, the reduction is right-associative instead
3379 of left-associative:
3382 (cl-reduce '- '(1 2 3 4))
3383 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8
3384 (cl-reduce '- '(1 2 3 4) :from-end t)
3385 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2
3388 If @code{:key} is specified, it is a function of one argument, which
3389 is called on each of the sequence elements in turn.
3391 If @code{:initial-value} is specified, it is effectively added to the
3392 front (or rear in the case of @code{:from-end}) of the sequence.
3393 The @code{:key} function is @emph{not} applied to the initial value.
3395 If the sequence, including the initial value, has exactly one element
3396 then that element is returned without ever calling @var{function}.
3397 If the sequence is empty (and there is no initial value), then
3398 @var{function} is called with no arguments to obtain the return value.
3401 All of these mapping operations can be expressed conveniently in
3402 terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will
3403 be faster since it generates the loop as in-line code with no
3406 @node Sequence Functions
3407 @section Sequence Functions
3410 This section describes a number of Common Lisp functions for
3411 operating on sequences.
3413 @defun cl-subseq sequence start &optional end
3414 This function returns a given subsequence of the argument
3415 @var{sequence}, which may be a list, string, or vector.
3416 The indices @var{start} and @var{end} must be in range, and
3417 @var{start} must be no greater than @var{end}. If @var{end}
3418 is omitted, it defaults to the length of the sequence. The
3419 return value is always a copy; it does not share structure
3420 with @var{sequence}.
3422 As an extension to Common Lisp, @var{start} and/or @var{end}
3423 may be negative, in which case they represent a distance back
3424 from the end of the sequence. This is for compatibility with
3425 Emacs's @code{substring} function. Note that @code{cl-subseq} is
3426 the @emph{only} sequence function that allows negative
3427 @var{start} and @var{end}.
3429 You can use @code{setf} on a @code{cl-subseq} form to replace a
3430 specified range of elements with elements from another sequence.
3431 The replacement is done as if by @code{cl-replace}, described below.
3434 @defun cl-concatenate result-type &rest seqs
3435 This function concatenates the argument sequences together to
3436 form a result sequence of type @var{result-type}, one of the
3437 symbols @code{vector}, @code{string}, or @code{list}. The
3438 arguments are always copied, even in cases such as
3439 @code{(cl-concatenate 'list '(1 2 3))} where the result is
3440 identical to an argument.
3443 @defun cl-fill seq item @t{&key :start :end}
3444 This function fills the elements of the sequence (or the specified
3445 part of the sequence) with the value @var{item}.
3448 @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2}
3449 This function copies part of @var{seq2} into part of @var{seq1}.
3450 The sequence @var{seq1} is not stretched or resized; the amount
3451 of data copied is simply the shorter of the source and destination
3452 (sub)sequences. The function returns @var{seq1}.
3454 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement
3455 will work correctly even if the regions indicated by the start
3456 and end arguments overlap. However, if @var{seq1} and @var{seq2}
3457 are lists that share storage but are not @code{eq}, and the
3458 start and end arguments specify overlapping regions, the effect
3462 @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end}
3463 This returns a copy of @var{seq} with all elements matching
3464 @var{item} removed. The result may share storage with or be
3465 @code{eq} to @var{seq} in some circumstances, but the original
3466 @var{seq} will not be modified. The @code{:test}, @code{:test-not},
3467 and @code{:key} arguments define the matching test that is used;
3468 by default, elements @code{eql} to @var{item} are removed. The
3469 @code{:count} argument specifies the maximum number of matching
3470 elements that can be removed (only the leftmost @var{count} matches
3471 are removed). The @code{:start} and @code{:end} arguments specify
3472 a region in @var{seq} in which elements will be removed; elements
3473 outside that region are not matched or removed. The @code{:from-end}
3474 argument, if true, says that elements should be deleted from the
3475 end of the sequence rather than the beginning (this matters only
3476 if @var{count} was also specified).
3479 @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end}
3480 This deletes all elements of @var{seq} that match @var{item}.
3481 It is a destructive operation. Since Emacs Lisp does not support
3482 stretchable strings or vectors, this is the same as @code{cl-remove}
3483 for those sequence types. On lists, @code{cl-remove} will copy the
3484 list if necessary to preserve the original list, whereas
3485 @code{cl-delete} will splice out parts of the argument list.
3486 Compare @code{append} and @code{nconc}, which are analogous
3487 non-destructive and destructive list operations in Emacs Lisp.
3490 @findex cl-remove-if
3491 @findex cl-remove-if-not
3492 @findex cl-delete-if
3493 @findex cl-delete-if-not
3494 The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not},
3495 @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly.
3497 @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3498 This function returns a copy of @var{seq} with duplicate elements
3499 removed. Specifically, if two elements from the sequence match
3500 according to the @code{:test}, @code{:test-not}, and @code{:key}
3501 arguments, only the rightmost one is retained. If @code{:from-end}
3502 is true, the leftmost one is retained instead. If @code{:start} or
3503 @code{:end} is specified, only elements within that subsequence are
3504 examined or removed.
3507 @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3508 This function deletes duplicate elements from @var{seq}. It is
3509 a destructive version of @code{cl-remove-duplicates}.
3512 @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3513 This function returns a copy of @var{seq}, with all elements
3514 matching @var{old} replaced with @var{new}. The @code{:count},
3515 @code{:start}, @code{:end}, and @code{:from-end} arguments may be
3516 used to limit the number of substitutions made.
3519 @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3520 This is a destructive version of @code{cl-substitute}; it performs
3521 the substitution using @code{setcar} or @code{aset} rather than
3522 by returning a changed copy of the sequence.
3525 @findex cl-substitute-if
3526 @findex cl-substitute-if-not
3527 @findex cl-nsubstitute-if
3528 @findex cl-nsubstitute-if-not
3529 The functions @code{cl-substitute-if}, @code{cl-substitute-if-not},
3530 @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined
3531 similarly. For these, a @var{predicate} is given in place of the
3534 @node Searching Sequences
3535 @section Searching Sequences
3538 These functions search for elements or subsequences in a sequence.
3539 (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.)
3541 @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end}
3542 This function searches @var{seq} for an element matching @var{item}.
3543 If it finds a match, it returns the matching element. Otherwise,
3544 it returns @code{nil}. It returns the leftmost match, unless
3545 @code{:from-end} is true, in which case it returns the rightmost
3546 match. The @code{:start} and @code{:end} arguments may be used to
3547 limit the range of elements that are searched.
3550 @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end}
3551 This function is like @code{cl-find}, except that it returns the
3552 integer position in the sequence of the matching item rather than
3553 the item itself. The position is relative to the start of the
3554 sequence as a whole, even if @code{:start} is non-zero. The function
3555 returns @code{nil} if no matching element was found.
3558 @defun cl-count item seq @t{&key :test :test-not :key :start :end}
3559 This function returns the number of elements of @var{seq} which
3560 match @var{item}. The result is always a nonnegative integer.
3564 @findex cl-find-if-not
3565 @findex cl-position-if
3566 @findex cl-position-if-not
3568 @findex cl-count-if-not
3569 The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if},
3570 @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not}
3571 functions are defined similarly.
3573 @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end}
3574 This function compares the specified parts of @var{seq1} and
3575 @var{seq2}. If they are the same length and the corresponding
3576 elements match (according to @code{:test}, @code{:test-not},
3577 and @code{:key}), the function returns @code{nil}. If there is
3578 a mismatch, the function returns the index (relative to @var{seq1})
3579 of the first mismatching element. This will be the leftmost pair of
3580 elements that do not match, or the position at which the shorter of
3581 the two otherwise-matching sequences runs out.
3583 If @code{:from-end} is true, then the elements are compared from right
3584 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}.
3585 If the sequences differ, then one plus the index of the rightmost
3586 difference (relative to @var{seq1}) is returned.
3588 An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)},
3589 which compares two strings case-insensitively.
3592 @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2}
3593 This function searches @var{seq2} for a subsequence that matches
3594 @var{seq1} (or part of it specified by @code{:start1} and
3595 @code{:end1}). Only matches that fall entirely within the region
3596 defined by @code{:start2} and @code{:end2} will be considered.
3597 The return value is the index of the leftmost element of the
3598 leftmost match, relative to the start of @var{seq2}, or @code{nil}
3599 if no matches were found. If @code{:from-end} is true, the
3600 function finds the @emph{rightmost} matching subsequence.
3603 @node Sorting Sequences
3604 @section Sorting Sequences
3606 @defun cl-sort seq predicate @t{&key :key}
3607 This function sorts @var{seq} into increasing order as determined
3608 by using @var{predicate} to compare pairs of elements. @var{predicate}
3609 should return true (non-@code{nil}) if and only if its first argument
3610 is less than (not equal to) its second argument. For example,
3611 @code{<} and @code{string-lessp} are suitable predicate functions
3612 for sorting numbers and strings, respectively; @code{>} would sort
3613 numbers into decreasing rather than increasing order.
3615 This function differs from Emacs's built-in @code{sort} in that it
3616 can operate on any type of sequence, not just lists. Also, it
3617 accepts a @code{:key} argument, which is used to preprocess data
3618 fed to the @var{predicate} function. For example,
3621 (setq data (cl-sort data 'string-lessp :key 'downcase))
3625 sorts @var{data}, a sequence of strings, into increasing alphabetical
3626 order without regard to case. A @code{:key} function of @code{car}
3627 would be useful for sorting association lists. It should only be a
3628 simple accessor though, since it's used heavily in the current
3631 The @code{cl-sort} function is destructive; it sorts lists by actually
3632 rearranging the @sc{cdr} pointers in suitable fashion.
3635 @defun cl-stable-sort seq predicate @t{&key :key}
3636 This function sorts @var{seq} @dfn{stably}, meaning two elements
3637 which are equal in terms of @var{predicate} are guaranteed not to
3638 be rearranged out of their original order by the sort.
3640 In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent
3641 in Emacs Lisp because the underlying @code{sort} function is
3642 stable by default. However, this package reserves the right to
3643 use non-stable methods for @code{cl-sort} in the future.
3646 @defun cl-merge type seq1 seq2 predicate @t{&key :key}
3647 This function merges two sequences @var{seq1} and @var{seq2} by
3648 interleaving their elements. The result sequence, of type @var{type}
3649 (in the sense of @code{cl-concatenate}), has length equal to the sum
3650 of the lengths of the two input sequences. The sequences may be
3651 modified destructively. Order of elements within @var{seq1} and
3652 @var{seq2} is preserved in the interleaving; elements of the two
3653 sequences are compared by @var{predicate} (in the sense of
3654 @code{sort}) and the lesser element goes first in the result.
3655 When elements are equal, those from @var{seq1} precede those from
3656 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are
3657 both sorted according to @var{predicate}, then the result will be
3658 a merged sequence which is (stably) sorted according to
3666 The functions described here operate on lists.
3669 * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc.
3670 * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc.
3671 * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc.
3672 * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc.
3675 @node List Functions
3676 @section List Functions
3679 This section describes a number of simple operations on lists,
3680 i.e., chains of cons cells.
3683 This function is equivalent to @code{(car (cdr (cdr @var{x})))}.
3684 Likewise, this package defines all 24 @code{c@var{xxx}r} functions
3685 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s.
3686 All of these functions are @code{setf}-able, and calls to them
3687 are expanded inline by the byte-compiler for maximum efficiency.
3691 This function is a synonym for @code{(car @var{x})}. Likewise,
3692 the functions @code{cl-second}, @code{cl-third}, @dots{}, through
3693 @code{cl-tenth} return the given element of the list @var{x}.
3697 This function is a synonym for @code{(cdr @var{x})}.
3701 Common Lisp defines this function to act like @code{null}, but
3702 signaling an error if @code{x} is neither a @code{nil} nor a
3703 cons cell. This package simply defines @code{cl-endp} as a synonym
3707 @defun cl-list-length x
3708 This function returns the length of list @var{x}, exactly like
3709 @code{(length @var{x})}, except that if @var{x} is a circular
3710 list (where the @sc{cdr}-chain forms a loop rather than terminating
3711 with @code{nil}), this function returns @code{nil}. (The regular
3712 @code{length} function would get stuck if given a circular list.
3713 See also the @code{safe-length} function.)
3716 @defun cl-list* arg &rest others
3717 This function constructs a list of its arguments. The final
3718 argument becomes the @sc{cdr} of the last cell constructed.
3719 Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to
3720 @code{(cons @var{a} (cons @var{b} @var{c}))}, and
3721 @code{(cl-list* @var{a} @var{b} nil)} is equivalent to
3722 @code{(list @var{a} @var{b})}.
3725 @defun cl-ldiff list sublist
3726 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to
3727 one of the cons cells of @var{list}, then this function returns
3728 a copy of the part of @var{list} up to but not including
3729 @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns
3730 the first two elements of the list @code{x}. The result is a
3731 copy; the original @var{list} is not modified. If @var{sublist}
3732 is not a sublist of @var{list}, a copy of the entire @var{list}
3736 @defun cl-copy-list list
3737 This function returns a copy of the list @var{list}. It copies
3738 dotted lists like @code{(1 2 . 3)} correctly.
3741 @defun cl-tree-equal x y @t{&key :test :test-not :key}
3742 This function compares two trees of cons cells. If @var{x} and
3743 @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are
3744 compared recursively. If neither @var{x} nor @var{y} is a cons
3745 cell, they are compared by @code{eql}, or according to the
3746 specified test. The @code{:key} function, if specified, is
3747 applied to the elements of both trees. @xref{Sequences}.
3750 @node Substitution of Expressions
3751 @section Substitution of Expressions
3754 These functions substitute elements throughout a tree of cons
3755 cells. (@xref{Sequence Functions}, for the @code{cl-substitute}
3756 function, which works on just the top-level elements of a list.)
3758 @defun cl-subst new old tree @t{&key :test :test-not :key}
3759 This function substitutes occurrences of @var{old} with @var{new}
3760 in @var{tree}, a tree of cons cells. It returns a substituted
3761 tree, which will be a copy except that it may share storage with
3762 the argument @var{tree} in parts where no substitutions occurred.
3763 The original @var{tree} is not modified. This function recurses
3764 on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s
3765 of the component cons cells. If @var{old} is itself a cons cell,
3766 then matching cells in the tree are substituted as usual without
3767 recursively substituting in that cell. Comparisons with @var{old}
3768 are done according to the specified test (@code{eql} by default).
3769 The @code{:key} function is applied to the elements of the tree
3770 but not to @var{old}.
3773 @defun cl-nsubst new old tree @t{&key :test :test-not :key}
3774 This function is like @code{cl-subst}, except that it works by
3775 destructive modification (by @code{setcar} or @code{setcdr})
3776 rather than copying.
3780 @findex cl-subst-if-not
3781 @findex cl-nsubst-if
3782 @findex cl-nsubst-if-not
3783 The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and
3784 @code{cl-nsubst-if-not} functions are defined similarly.
3786 @defun cl-sublis alist tree @t{&key :test :test-not :key}
3787 This function is like @code{cl-subst}, except that it takes an
3788 association list @var{alist} of @var{old}-@var{new} pairs.
3789 Each element of the tree (after applying the @code{:key}
3790 function, if any), is compared with the @sc{car}s of
3791 @var{alist}; if it matches, it is replaced by the corresponding
3795 @defun cl-nsublis alist tree @t{&key :test :test-not :key}
3796 This is a destructive version of @code{cl-sublis}.
3800 @section Lists as Sets
3803 These functions perform operations on lists that represent sets
3806 @defun cl-member item list @t{&key :test :test-not :key}
3807 This function searches @var{list} for an element matching @var{item}.
3808 If a match is found, it returns the cons cell whose @sc{car} was
3809 the matching element. Otherwise, it returns @code{nil}. Elements
3810 are compared by @code{eql} by default; you can use the @code{:test},
3811 @code{:test-not}, and @code{:key} arguments to modify this behavior.
3814 The standard Emacs lisp function @code{member} uses @code{equal} for
3815 comparisons; it is equivalent to @code{(cl-member @var{item} @var{list}
3816 :test 'equal)}. With no keyword arguments, @code{cl-member} is
3817 equivalent to @code{memq}.
3820 @findex cl-member-if
3821 @findex cl-member-if-not
3822 The @code{cl-member-if} and @code{cl-member-if-not} functions
3823 analogously search for elements that satisfy a given predicate.
3825 @defun cl-tailp sublist list
3826 This function returns @code{t} if @var{sublist} is a sublist of
3827 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to
3828 any of its @sc{cdr}s.
3831 @defun cl-adjoin item list @t{&key :test :test-not :key}
3832 This function conses @var{item} onto the front of @var{list},
3833 like @code{(cons @var{item} @var{list})}, but only if @var{item}
3834 is not already present on the list (as determined by @code{cl-member}).
3835 If a @code{:key} argument is specified, it is applied to
3836 @var{item} as well as to the elements of @var{list} during
3837 the search, on the reasoning that @var{item} is ``about'' to
3838 become part of the list.
3841 @defun cl-union list1 list2 @t{&key :test :test-not :key}
3842 This function combines two lists that represent sets of items,
3843 returning a list that represents the union of those two sets.
3844 The resulting list contains all items that appear in @var{list1}
3845 or @var{list2}, and no others. If an item appears in both
3846 @var{list1} and @var{list2} it is copied only once. If
3847 an item is duplicated in @var{list1} or @var{list2}, it is
3848 undefined whether or not that duplication will survive in the
3849 result list. The order of elements in the result list is also
3853 @defun cl-nunion list1 list2 @t{&key :test :test-not :key}
3854 This is a destructive version of @code{cl-union}; rather than copying,
3855 it tries to reuse the storage of the argument lists if possible.
3858 @defun cl-intersection list1 list2 @t{&key :test :test-not :key}
3859 This function computes the intersection of the sets represented
3860 by @var{list1} and @var{list2}. It returns the list of items
3861 that appear in both @var{list1} and @var{list2}.
3864 @defun cl-nintersection list1 list2 @t{&key :test :test-not :key}
3865 This is a destructive version of @code{cl-intersection}. It
3866 tries to reuse storage of @var{list1} rather than copying.
3867 It does @emph{not} reuse the storage of @var{list2}.
3870 @defun cl-set-difference list1 list2 @t{&key :test :test-not :key}
3871 This function computes the ``set difference'' of @var{list1}
3872 and @var{list2}, i.e., the set of elements that appear in
3873 @var{list1} but @emph{not} in @var{list2}.
3876 @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key}
3877 This is a destructive @code{cl-set-difference}, which will try
3878 to reuse @var{list1} if possible.
3881 @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key}
3882 This function computes the ``set exclusive or'' of @var{list1}
3883 and @var{list2}, i.e., the set of elements that appear in
3884 exactly one of @var{list1} and @var{list2}.
3887 @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key}
3888 This is a destructive @code{cl-set-exclusive-or}, which will try
3889 to reuse @var{list1} and @var{list2} if possible.
3892 @defun cl-subsetp list1 list2 @t{&key :test :test-not :key}
3893 This function checks whether @var{list1} represents a subset
3894 of @var{list2}, i.e., whether every element of @var{list1}
3895 also appears in @var{list2}.
3898 @node Association Lists
3899 @section Association Lists
3902 An @dfn{association list} is a list representing a mapping from
3903 one set of values to another; any list whose elements are cons
3904 cells is an association list.
3906 @defun cl-assoc item a-list @t{&key :test :test-not :key}
3907 This function searches the association list @var{a-list} for an
3908 element whose @sc{car} matches (in the sense of @code{:test},
3909 @code{:test-not}, and @code{:key}, or by comparison with @code{eql})
3910 a given @var{item}. It returns the matching element, if any,
3911 otherwise @code{nil}. It ignores elements of @var{a-list} that
3912 are not cons cells. (This corresponds to the behavior of
3913 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's
3914 @code{assoc} ignores @code{nil}s but considers any other non-cons
3915 elements of @var{a-list} to be an error.)
3918 @defun cl-rassoc item a-list @t{&key :test :test-not :key}
3919 This function searches for an element whose @sc{cdr} matches
3920 @var{item}. If @var{a-list} represents a mapping, this applies
3921 the inverse of the mapping to @var{item}.
3925 @findex cl-assoc-if-not
3926 @findex cl-rassoc-if
3927 @findex cl-rassoc-if-not
3928 The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if},
3929 and @code{cl-rassoc-if-not} functions are defined similarly.
3931 Two simple functions for constructing association lists are:
3933 @defun cl-acons key value alist
3934 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}.
3937 @defun cl-pairlis keys values &optional alist
3938 This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values})
3946 The Common Lisp @dfn{structure} mechanism provides a general way
3947 to define data types similar to C's @code{struct} types. A
3948 structure is a Lisp object containing some number of @dfn{slots},
3949 each of which can hold any Lisp data object. Functions are
3950 provided for accessing and setting the slots, creating or copying
3951 structure objects, and recognizing objects of a particular structure
3954 In true Common Lisp, each structure type is a new type distinct
3955 from all existing Lisp types. Since the underlying Emacs Lisp
3956 system provides no way to create new distinct types, this package
3957 implements structures as vectors (or lists upon request) with a
3958 special ``tag'' symbol to identify them.
3960 @defmac cl-defstruct name slots@dots{}
3961 The @code{cl-defstruct} form defines a new structure type called
3962 @var{name}, with the specified @var{slots}. (The @var{slots}
3963 may begin with a string which documents the structure type.)
3964 In the simplest case, @var{name} and each of the @var{slots}
3965 are symbols. For example,
3968 (cl-defstruct person name age sex)
3972 defines a struct type called @code{person} that contains three
3973 slots. Given a @code{person} object @var{p}, you can access those
3974 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})},
3975 and @code{(person-sex @var{p})}. You can also change these slots by
3976 using @code{setf} on any of these place forms, for example:
3979 (cl-incf (person-age birthday-boy))
3982 You can create a new @code{person} by calling @code{make-person},
3983 which takes keyword arguments @code{:name}, @code{:age}, and
3984 @code{:sex} to specify the initial values of these slots in the
3985 new object. (Omitting any of these arguments leaves the corresponding
3986 slot ``undefined'', according to the Common Lisp standard; in Emacs
3987 Lisp, such uninitialized slots are filled with @code{nil}.)
3989 Given a @code{person}, @code{(copy-person @var{p})} makes a new
3990 object of the same type whose slots are @code{eq} to those of @var{p}.
3992 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns
3993 true if @var{x} looks like a @code{person}, and false otherwise. (Again,
3994 in Common Lisp this predicate would be exact; in Emacs Lisp the
3995 best it can do is verify that @var{x} is a vector of the correct
3996 length that starts with the correct tag symbol.)
3998 Accessors like @code{person-name} normally check their arguments
3999 (effectively using @code{person-p}) and signal an error if the
4000 argument is the wrong type. This check is affected by
4001 @code{(optimize (safety @dots{}))} declarations. Safety level 1,
4002 the default, uses a somewhat optimized check that will detect all
4003 incorrect arguments, but may use an uninformative error message
4004 (e.g., ``expected a vector'' instead of ``expected a @code{person}'').
4005 Safety level 0 omits all checks except as provided by the underlying
4006 @code{aref} call; safety levels 2 and 3 do rigorous checking that will
4007 always print a descriptive error message for incorrect inputs.
4008 @xref{Declarations}.
4011 (setq dave (make-person :name "Dave" :sex 'male))
4012 @result{} [cl-struct-person "Dave" nil male]
4013 (setq other (copy-person dave))
4014 @result{} [cl-struct-person "Dave" nil male]
4017 (eq (person-name dave) (person-name other))
4021 (person-p [1 2 3 4])
4025 (person-p '[cl-struct-person counterfeit person object])
4029 In general, @var{name} is either a name symbol or a list of a name
4030 symbol followed by any number of @dfn{struct options}; each @var{slot}
4031 is either a slot symbol or a list of the form @samp{(@var{slot-name}
4032 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value}
4033 is a Lisp form that is evaluated any time an instance of the
4034 structure type is created without specifying that slot's value.
4036 Common Lisp defines several slot options, but the only one
4037 implemented in this package is @code{:read-only}. A non-@code{nil}
4038 value for this option means the slot should not be @code{setf}-able;
4039 the slot's value is determined when the object is created and does
4040 not change afterward.
4043 (cl-defstruct person
4044 (name nil :read-only t)
4049 Any slot options other than @code{:read-only} are ignored.
4051 For obscure historical reasons, structure options take a different
4052 form than slot options. A structure option is either a keyword
4053 symbol, or a list beginning with a keyword symbol possibly followed
4054 by arguments. (By contrast, slot options are key-value pairs not
4058 (cl-defstruct (person (:constructor create-person)
4064 The following structure options are recognized.
4068 The argument is a symbol whose print name is used as the prefix for
4069 the names of slot accessor functions. The default is the name of
4070 the struct type followed by a hyphen. The option @code{(:conc-name p-)}
4071 would change this prefix to @code{p-}. Specifying @code{nil} as an
4072 argument means no prefix, so that the slot names themselves are used
4073 to name the accessor functions.
4076 In the simple case, this option takes one argument which is an
4077 alternate name to use for the constructor function. The default
4078 is @code{make-@var{name}}, e.g., @code{make-person}. The above
4079 example changes this to @code{create-person}. Specifying @code{nil}
4080 as an argument means that no standard constructor should be
4083 In the full form of this option, the constructor name is followed
4084 by an arbitrary argument list. @xref{Program Structure}, for a
4085 description of the format of Common Lisp argument lists. All
4086 options, such as @code{&rest} and @code{&key}, are supported.
4087 The argument names should match the slot names; each slot is
4088 initialized from the corresponding argument. Slots whose names
4089 do not appear in the argument list are initialized based on the
4090 @var{default-value} in their slot descriptor. Also, @code{&optional}
4091 and @code{&key} arguments that don't specify defaults take their
4092 defaults from the slot descriptor. It is valid to include arguments
4093 that don't correspond to slot names; these are useful if they are
4094 referred to in the defaults for optional, keyword, or @code{&aux}
4095 arguments that @emph{do} correspond to slots.
4097 You can specify any number of full-format @code{:constructor}
4098 options on a structure. The default constructor is still generated
4099 as well unless you disable it with a simple-format @code{:constructor}
4105 (:constructor nil) ; no default constructor
4106 (:constructor new-person
4107 (name sex &optional (age 0)))
4108 (:constructor new-hound (&key (name "Rover")
4110 &aux (age (* 7 dog-years))
4115 The first constructor here takes its arguments positionally rather
4116 than by keyword. (In official Common Lisp terminology, constructors
4117 that work By Order of Arguments instead of by keyword are called
4118 ``BOA constructors''. No, I'm not making this up.) For example,
4119 @code{(new-person "Jane" 'female)} generates a person whose slots
4120 are @code{"Jane"}, 0, and @code{female}, respectively.
4122 The second constructor takes two keyword arguments, @code{:name},
4123 which initializes the @code{name} slot and defaults to @code{"Rover"},
4124 and @code{:dog-years}, which does not itself correspond to a slot
4125 but which is used to initialize the @code{age} slot. The @code{sex}
4126 slot is forced to the symbol @code{canine} with no syntax for
4130 The argument is an alternate name for the copier function for
4131 this type. The default is @code{copy-@var{name}}. @code{nil}
4132 means not to generate a copier function. (In this implementation,
4133 all copier functions are simply synonyms for @code{copy-sequence}.)
4136 The argument is an alternate name for the predicate that recognizes
4137 objects of this type. The default is @code{@var{name}-p}. @code{nil}
4138 means not to generate a predicate function. (If the @code{:type}
4139 option is used without the @code{:named} option, no predicate is
4142 In true Common Lisp, @code{typep} is always able to recognize a
4143 structure object even if @code{:predicate} was used. In this
4144 package, @code{cl-typep} simply looks for a function called
4145 @code{@var{typename}-p}, so it will work for structure types
4146 only if they used the default predicate name.
4149 This option implements a very limited form of C++-style inheritance.
4150 The argument is the name of another structure type previously
4151 created with @code{cl-defstruct}. The effect is to cause the new
4152 structure type to inherit all of the included structure's slots
4153 (plus, of course, any new slots described by this struct's slot
4154 descriptors). The new structure is considered a ``specialization''
4155 of the included one. In fact, the predicate and slot accessors
4156 for the included type will also accept objects of the new type.
4158 If there are extra arguments to the @code{:include} option after
4159 the included-structure name, these options are treated as replacement
4160 slot descriptors for slots in the included structure, possibly with
4161 modified default values. Borrowing an example from Steele:
4164 (cl-defstruct person name (age 0) sex)
4166 (cl-defstruct (astronaut (:include person (age 45)))
4168 (favorite-beverage 'tang))
4171 (setq joe (make-person :name "Joe"))
4172 @result{} [cl-struct-person "Joe" 0 nil]
4173 (setq buzz (make-astronaut :name "Buzz"))
4174 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang]
4176 (list (person-p joe) (person-p buzz))
4178 (list (astronaut-p joe) (astronaut-p buzz))
4183 (astronaut-name joe)
4184 @result{} error: "astronaut-name accessing a non-astronaut"
4187 Thus, if @code{astronaut} is a specialization of @code{person},
4188 then every @code{astronaut} is also a @code{person} (but not the
4189 other way around). Every @code{astronaut} includes all the slots
4190 of a @code{person}, plus extra slots that are specific to
4191 astronauts. Operations that work on people (like @code{person-name})
4192 work on astronauts just like other people.
4194 @item :print-function
4195 In full Common Lisp, this option allows you to specify a function
4196 that is called to print an instance of the structure type. The
4197 Emacs Lisp system offers no hooks into the Lisp printer which would
4198 allow for such a feature, so this package simply ignores
4199 @code{:print-function}.
4202 The argument should be one of the symbols @code{vector} or @code{list}.
4203 This tells which underlying Lisp data type should be used to implement
4204 the new structure type. Vectors are used by default, but
4205 @code{(:type list)} will cause structure objects to be stored as
4208 The vector representation for structure objects has the advantage
4209 that all structure slots can be accessed quickly, although creating
4210 vectors is a bit slower in Emacs Lisp. Lists are easier to create,
4211 but take a relatively long time accessing the later slots.
4214 This option, which takes no arguments, causes a characteristic ``tag''
4215 symbol to be stored at the front of the structure object. Using
4216 @code{:type} without also using @code{:named} will result in a
4217 structure type stored as plain vectors or lists with no identifying
4220 The default, if you don't specify @code{:type} explicitly, is to
4221 use named vectors. Therefore, @code{:named} is only useful in
4222 conjunction with @code{:type}.
4225 (cl-defstruct (person1) name age sex)
4226 (cl-defstruct (person2 (:type list) :named) name age sex)
4227 (cl-defstruct (person3 (:type list)) name age sex)
4229 (setq p1 (make-person1))
4230 @result{} [cl-struct-person1 nil nil nil]
4231 (setq p2 (make-person2))
4232 @result{} (person2 nil nil nil)
4233 (setq p3 (make-person3))
4234 @result{} (nil nil nil)
4241 @result{} error: function person3-p undefined
4244 Since unnamed structures don't have tags, @code{cl-defstruct} is not
4245 able to make a useful predicate for recognizing them. Also,
4246 accessors like @code{person3-name} will be generated but they
4247 will not be able to do any type checking. The @code{person3-name}
4248 function, for example, will simply be a synonym for @code{car} in
4249 this case. By contrast, @code{person2-name} is able to verify
4250 that its argument is indeed a @code{person2} object before
4253 @item :initial-offset
4254 The argument must be a nonnegative integer. It specifies a
4255 number of slots to be left ``empty'' at the front of the
4256 structure. If the structure is named, the tag appears at the
4257 specified position in the list or vector; otherwise, the first
4258 slot appears at that position. Earlier positions are filled
4259 with @code{nil} by the constructors and ignored otherwise. If
4260 the type @code{:include}s another type, then @code{:initial-offset}
4261 specifies a number of slots to be skipped between the last slot
4262 of the included type and the first new slot.
4266 Except as noted, the @code{cl-defstruct} facility of this package is
4267 entirely compatible with that of Common Lisp.
4270 @chapter Assertions and Errors
4273 This section describes two macros that test @dfn{assertions}, i.e.,
4274 conditions which must be true if the program is operating correctly.
4275 Assertions never add to the behavior of a Lisp program; they simply
4276 make ``sanity checks'' to make sure everything is as it should be.
4278 If the optimization property @code{speed} has been set to 3, and
4279 @code{safety} is less than 3, then the byte-compiler will optimize
4280 away the following assertions. Because assertions might be optimized
4281 away, it is a bad idea for them to include side-effects.
4283 @defmac cl-assert test-form [show-args string args@dots{}]
4284 This form verifies that @var{test-form} is true (i.e., evaluates to
4285 a non-@code{nil} value). If so, it returns @code{nil}. If the test
4286 is not satisfied, @code{cl-assert} signals an error.
4288 A default error message will be supplied which includes @var{test-form}.
4289 You can specify a different error message by including a @var{string}
4290 argument plus optional extra arguments. Those arguments are simply
4291 passed to @code{error} to signal the error.
4293 If the optional second argument @var{show-args} is @code{t} instead
4294 of @code{nil}, then the error message (with or without @var{string})
4295 will also include all non-constant arguments of the top-level
4296 @var{form}. For example:
4299 (cl-assert (> x 10) t "x is too small: %d")
4302 This usage of @var{show-args} is an extension to Common Lisp. In
4303 true Common Lisp, the second argument gives a list of @var{places}
4304 which can be @code{setf}'d by the user before continuing from the
4305 error. Since Emacs Lisp does not support continuable errors, it
4306 makes no sense to specify @var{places}.
4309 @defmac cl-check-type form type [string]
4310 This form verifies that @var{form} evaluates to a value of type
4311 @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type}
4312 signals a @code{wrong-type-argument} error. The default error message
4313 lists the erroneous value along with @var{type} and @var{form}
4314 themselves. If @var{string} is specified, it is included in the
4315 error message in place of @var{type}. For example:
4318 (cl-check-type x (integer 1 *) "a positive integer")
4321 @xref{Type Predicates}, for a description of the type specifiers
4322 that may be used for @var{type}.
4324 Note that in Common Lisp, the first argument to @code{check-type}
4325 must be a @var{place} suitable for use by @code{setf}, because
4326 @code{check-type} signals a continuable error that allows the
4327 user to modify @var{place}.
4330 @node Efficiency Concerns
4331 @appendix Efficiency Concerns
4336 Many of the advanced features of this package, such as @code{cl-defun},
4337 @code{cl-loop}, etc., are implemented as Lisp macros. In
4338 byte-compiled code, these complex notations will be expanded into
4339 equivalent Lisp code which is simple and efficient. For example,
4347 is expanded at compile-time to the Lisp form
4354 which is the most efficient ways of doing this operation
4355 in Lisp. Thus, there is no performance penalty for using the more
4356 readable @code{cl-incf} form in your compiled code.
4358 @emph{Interpreted} code, on the other hand, must expand these macros
4359 every time they are executed. For this reason it is strongly
4360 recommended that code making heavy use of macros be compiled.
4361 A loop using @code{cl-incf} a hundred times will execute considerably
4362 faster if compiled, and will also garbage-collect less because the
4363 macro expansion will not have to be generated, used, and thrown away a
4366 You can find out how a macro expands by using the
4367 @code{cl-prettyexpand} function.
4369 @defun cl-prettyexpand form &optional full
4370 This function takes a single Lisp form as an argument and inserts
4371 a nicely formatted copy of it in the current buffer (which must be
4372 in Lisp mode so that indentation works properly). It also expands
4373 all Lisp macros that appear in the form. The easiest way to use
4374 this function is to go to the @file{*scratch*} buffer and type, say,
4377 (cl-prettyexpand '(cl-loop for x below 10 collect x))
4381 and type @kbd{C-x C-e} immediately after the closing parenthesis;
4382 an expansion similar to:
4389 (setq G1004 (cons x G1004))
4395 will be inserted into the buffer. (The @code{cl-block} macro is
4396 expanded differently in the interpreter and compiler, so
4397 @code{cl-prettyexpand} just leaves it alone. The temporary
4398 variable @code{G1004} was created by @code{cl-gensym}.)
4400 If the optional argument @var{full} is true, then @emph{all}
4401 macros are expanded, including @code{cl-block}, @code{cl-eval-when},
4402 and compiler macros. Expansion is done as if @var{form} were
4403 a top-level form in a file being compiled.
4405 @c FIXME none of these examples are still applicable.
4410 (cl-prettyexpand '(cl-pushnew 'x list))
4411 @print{} (setq list (cl-adjoin 'x list))
4412 (cl-prettyexpand '(cl-pushnew 'x list) t)
4413 @print{} (setq list (if (memq 'x list) list (cons 'x list)))
4414 (cl-prettyexpand '(caddr (cl-member 'a list)) t)
4415 @print{} (car (cdr (cdr (memq 'a list))))
4419 Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all
4420 have built-in compiler macros to optimize them in common cases.
4423 @appendixsec Error Checking
4426 Common Lisp compliance has in general not been sacrificed for the
4427 sake of efficiency. A few exceptions have been made for cases
4428 where substantial gains were possible at the expense of marginal
4431 The Common Lisp standard (as embodied in Steele's book) uses the
4432 phrase ``it is an error if'' to indicate a situation that is not
4433 supposed to arise in complying programs; implementations are strongly
4434 encouraged but not required to signal an error in these situations.
4435 This package sometimes omits such error checking in the interest of
4436 compactness and efficiency. For example, @code{cl-do} variable
4437 specifiers are supposed to be lists of one, two, or three forms;
4438 extra forms are ignored by this package rather than signaling a
4439 syntax error. The @code{cl-endp} function is simply a synonym for
4440 @code{null} in this package. Functions taking keyword arguments
4441 will accept an odd number of arguments, treating the trailing
4442 keyword as if it were followed by the value @code{nil}.
4444 Argument lists (as processed by @code{cl-defun} and friends)
4445 @emph{are} checked rigorously except for the minor point just
4446 mentioned; in particular, keyword arguments are checked for
4447 validity, and @code{&allow-other-keys} and @code{:allow-other-keys}
4448 are fully implemented. Keyword validity checking is slightly
4449 time consuming (though not too bad in byte-compiled code);
4450 you can use @code{&allow-other-keys} to omit this check. Functions
4451 defined in this package such as @code{cl-find} and @code{cl-member}
4452 do check their keyword arguments for validity.
4454 @appendixsec Compiler Optimizations
4457 Changing the value of @code{byte-optimize} from the default @code{t}
4458 is highly discouraged; many of the Common
4460 code that can be improved by optimization. In particular,
4461 @code{cl-block}s (whether explicit or implicit in constructs like
4462 @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the
4463 byte-compiler removes @code{cl-block}s that are not actually
4464 referenced by @code{cl-return} or @code{cl-return-from} inside the block.
4466 @node Common Lisp Compatibility
4467 @appendix Common Lisp Compatibility
4470 The following is a list of all known incompatibilities between this
4471 package and Common Lisp as documented in Steele (2nd edition).
4473 The word @code{cl-defun} is required instead of @code{defun} in order
4474 to use extended Common Lisp argument lists in a function. Likewise,
4475 @code{cl-defmacro} and @code{cl-function} are versions of those forms
4476 which understand full-featured argument lists. The @code{&whole}
4477 keyword does not work in @code{cl-defmacro} argument lists (except
4478 inside recursive argument lists).
4480 The @code{equal} predicate does not distinguish
4481 between IEEE floating-point plus and minus zero. The @code{cl-equalp}
4482 predicate has several differences with Common Lisp; @pxref{Predicates}.
4484 @c FIXME consider moving to lispref
4486 The @code{setf} mechanism is entirely compatible, except that
4487 setf-methods return a list of five values rather than five
4488 values directly. Also, the new ``@code{setf} function'' concept
4489 (typified by @code{(defun (setf foo) @dots{})}) is not implemented.
4492 The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols}
4493 with no @var{obarray} argument. In Common Lisp, this form would
4494 iterate over all symbols in all packages. Since Emacs obarrays
4495 are not a first-class package mechanism, there is no way for
4496 @code{cl-do-all-symbols} to locate any but the default obarray.
4498 The @code{cl-loop} macro is complete except that @code{loop-finish}
4499 and type specifiers are unimplemented.
4501 The multiple-value return facility treats lists as multiple
4502 values, since Emacs Lisp cannot support multiple return values
4503 directly. The macros will be compatible with Common Lisp if
4504 @code{cl-values} or @code{cl-values-list} is always used to return to
4505 a @code{cl-multiple-value-bind} or other multiple-value receiver;
4506 if @code{cl-values} is used without @code{cl-multiple-value-@dots{}}
4507 or vice-versa the effect will be different from Common Lisp.
4509 Many Common Lisp declarations are ignored, and others match
4510 the Common Lisp standard in concept but not in detail. For
4511 example, local @code{special} declarations, which are purely
4512 advisory in Emacs Lisp, do not rigorously obey the scoping rules
4513 set down in Steele's book.
4515 The variable @code{cl--gensym-counter} starts out with a pseudo-random
4516 value rather than with zero. This is to cope with the fact that
4517 generated symbols become interned when they are written to and
4518 loaded back from a file.
4520 The @code{cl-defstruct} facility is compatible, except that structures
4521 are of type @code{:type vector :named} by default rather than some
4522 special, distinct type. Also, the @code{:type} slot option is ignored.
4524 The second argument of @code{cl-check-type} is treated differently.
4526 @node Porting Common Lisp
4527 @appendix Porting Common Lisp
4530 This package is meant to be used as an extension to Emacs Lisp,
4531 not as an Emacs implementation of true Common Lisp. Some of the
4532 remaining differences between Emacs Lisp and Common Lisp make it
4533 difficult to port large Common Lisp applications to Emacs. For
4534 one, some of the features in this package are not fully compliant
4535 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there
4536 are also quite a few features that this package does not provide
4537 at all. Here are some major omissions that you will want to watch out
4538 for when bringing Common Lisp code into Emacs.
4542 Case-insensitivity. Symbols in Common Lisp are case-insensitive
4543 by default. Some programs refer to a function or variable as
4544 @code{foo} in one place and @code{Foo} or @code{FOO} in another.
4545 Emacs Lisp will treat these as three distinct symbols.
4547 Some Common Lisp code is written entirely in upper case. While Emacs
4548 is happy to let the program's own functions and variables use
4549 this convention, calls to Lisp builtins like @code{if} and
4550 @code{defun} will have to be changed to lower case.
4553 Lexical scoping. In Common Lisp, function arguments and @code{let}
4554 bindings apply only to references physically within their bodies (or
4555 within macro expansions in their bodies). Traditionally, Emacs Lisp
4556 uses @dfn{dynamic scoping} wherein a binding to a variable is visible
4557 even inside functions called from the body.
4558 @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4559 Lexical binding is available since Emacs 24.1, so be sure to set
4560 @code{lexical-binding} to @code{t} if you need to emulate this aspect
4561 of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4563 Here is an example of a Common Lisp code fragment that would fail in
4564 Emacs Lisp if @code{lexical-binding} were set to @code{nil}:
4567 (defun map-odd-elements (func list)
4569 for flag = t then (not flag)
4570 collect (if flag x (funcall func x))))
4572 (defun add-odd-elements (list x)
4573 (map-odd-elements (lambda (a) (+ a x)) list))
4577 With lexical binding, the two functions' usages of @code{x} are
4578 completely independent. With dynamic binding, the binding to @code{x}
4579 made by @code{add-odd-elements} will have been hidden by the binding
4580 in @code{map-odd-elements} by the time the @code{(+ a x)} function is
4583 Internally, this package uses lexical binding so that such problems do
4584 not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete
4585 @code{lexical-let} form that emulates a Common Lisp-style lexical
4586 binding when dynamic binding is in use.
4589 Reader macros. Common Lisp includes a second type of macro that
4590 works at the level of individual characters. For example, Common
4591 Lisp implements the quote notation by a reader macro called @code{'},
4592 whereas Emacs Lisp's parser just treats quote as a special case.
4593 Some Lisp packages use reader macros to create special syntaxes
4594 for themselves, which the Emacs parser is incapable of reading.
4597 Other syntactic features. Common Lisp provides a number of
4598 notations beginning with @code{#} that the Emacs Lisp parser
4599 won't understand. For example, @samp{#| @dots{} |#} is an
4600 alternate comment notation, and @samp{#+lucid (foo)} tells
4601 the parser to ignore the @code{(foo)} except in Lucid Common
4605 Packages. In Common Lisp, symbols are divided into @dfn{packages}.
4606 Symbols that are Lisp built-ins are typically stored in one package;
4607 symbols that are vendor extensions are put in another, and each
4608 application program would have a package for its own symbols.
4609 Certain symbols are ``exported'' by a package and others are
4610 internal; certain packages ``use'' or import the exported symbols
4611 of other packages. To access symbols that would not normally be
4612 visible due to this importing and exporting, Common Lisp provides
4613 a syntax like @code{package:symbol} or @code{package::symbol}.
4615 Emacs Lisp has a single namespace for all interned symbols, and
4616 then uses a naming convention of putting a prefix like @code{cl-}
4617 in front of the name. Some Emacs packages adopt the Common Lisp-like
4618 convention of using @code{cl:} or @code{cl::} as the prefix.
4619 However, the Emacs parser does not understand colons and just
4620 treats them as part of the symbol name. Thus, while @code{mapcar}
4621 and @code{lisp:mapcar} may refer to the same symbol in Common
4622 Lisp, they are totally distinct in Emacs Lisp. Common Lisp
4623 programs that refer to a symbol by the full name sometimes
4624 and the short name other times will not port cleanly to Emacs.
4626 Emacs Lisp does have a concept of ``obarrays'', which are
4627 package-like collections of symbols, but this feature is not
4628 strong enough to be used as a true package mechanism.
4631 The @code{format} function is quite different between Common
4632 Lisp and Emacs Lisp. It takes an additional ``destination''
4633 argument before the format string. A destination of @code{nil}
4634 means to format to a string as in Emacs Lisp; a destination
4635 of @code{t} means to write to the terminal (similar to
4636 @code{message} in Emacs). Also, format control strings are
4637 utterly different; @code{~} is used instead of @code{%} to
4638 introduce format codes, and the set of available codes is
4639 much richer. There are no notations like @code{\n} for
4640 string literals; instead, @code{format} is used with the
4641 ``newline'' format code, @code{~%}. More advanced formatting
4642 codes provide such features as paragraph filling, case
4643 conversion, and even loops and conditionals.
4645 While it would have been possible to implement most of Common
4646 Lisp @code{format} in this package (under the name @code{cl-format},
4647 of course), it was not deemed worthwhile. It would have required
4648 a huge amount of code to implement even a decent subset of
4649 @code{format}, yet the functionality it would provide over
4650 Emacs Lisp's @code{format} would rarely be useful.
4653 Vector constants use square brackets in Emacs Lisp, but
4654 @code{#(a b c)} notation in Common Lisp. To further complicate
4655 matters, Emacs has its own @code{#(} notation for
4656 something entirely different---strings with properties.
4659 Characters are distinct from integers in Common Lisp. The notation
4660 for character constants is also different: @code{#\A} in Common Lisp
4661 where Emacs Lisp uses @code{?A}. Also, @code{string=} and
4662 @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is
4663 case-insensitive in Common Lisp.
4666 Data types. Some Common Lisp data types do not exist in Emacs
4667 Lisp. Rational numbers and complex numbers are not present,
4668 nor are large integers (all integers are ``fixnums''). All
4669 arrays are one-dimensional. There are no readtables or pathnames;
4670 streams are a set of existing data types rather than a new data
4671 type of their own. Hash tables, random-states, structures, and
4672 packages (obarrays) are built from Lisp vectors or lists rather
4673 than being distinct types.
4676 The Common Lisp Object System (CLOS) is not implemented,
4677 nor is the Common Lisp Condition System. However, the EIEIO package
4678 (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some
4682 Common Lisp features that are completely redundant with Emacs
4683 Lisp features of a different name generally have not been
4684 implemented. For example, Common Lisp writes @code{defconstant}
4685 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list}
4686 takes its arguments in different ways in the two Lisps but does
4687 exactly the same thing, so this package has not bothered to
4688 implement a Common Lisp-style @code{make-list}.
4691 A few more notable Common Lisp features not included in this
4692 package: @code{compiler-let}, @code{tagbody}, @code{prog},
4693 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}.
4696 Recursion. While recursion works in Emacs Lisp just like it
4697 does in Common Lisp, various details of the Emacs Lisp system
4698 and compiler make recursion much less efficient than it is in
4699 most Lisps. Some schools of thought prefer to use recursion
4700 in Lisp over other techniques; they would sum a list of
4701 numbers using something like
4704 (defun sum-list (list)
4706 (+ (car list) (sum-list (cdr list)))
4711 where a more iteratively-minded programmer might write one of
4715 (let ((total 0)) (dolist (x my-list) (incf total x)) total)
4716 (loop for x in my-list sum x)
4719 While this would be mainly a stylistic choice in most Common Lisps,
4720 in Emacs Lisp you should be aware that the iterative forms are
4721 much faster than recursion. Also, Lisp programmers will want to
4722 note that the current Emacs Lisp compiler does not optimize tail
4726 @node Obsolete Features
4727 @appendix Obsolete Features
4729 This section describes some features of the package that are obsolete
4730 and should not be used in new code. They are either only provided by
4731 the old @file{cl.el} entry point, not by the newer @file{cl-lib.el};
4732 or where versions with a @samp{cl-} prefix do exist they do not behave
4733 in exactly the same way.
4736 * Obsolete Lexical Binding:: An approximation of lexical binding.
4737 * Obsolete Macros:: Obsolete macros.
4738 * Obsolete Setf Customization:: Obsolete ways to customize setf.
4741 @node Obsolete Lexical Binding
4742 @appendixsec Obsolete Lexical Binding
4744 The following macros are extensions to Common Lisp, where all bindings
4745 are lexical unless declared otherwise. These features are likewise
4746 obsolete since the introduction of true lexical binding in Emacs 24.1.
4748 @defmac lexical-let (bindings@dots{}) forms@dots{}
4749 This form is exactly like @code{let} except that the bindings it
4750 establishes are purely lexical.
4753 @c FIXME remove this and refer to elisp manual.
4754 @c Maybe merge some stuff from here to there?
4756 Lexical bindings are similar to local variables in a language like C:
4757 Only the code physically within the body of the @code{lexical-let}
4758 (after macro expansion) may refer to the bound variables.
4762 (defun foo (b) (+ a b))
4763 (let ((a 2)) (foo a))
4765 (lexical-let ((a 2)) (foo a))
4770 In this example, a regular @code{let} binding of @code{a} actually
4771 makes a temporary change to the global variable @code{a}, so @code{foo}
4772 is able to see the binding of @code{a} to 2. But @code{lexical-let}
4773 actually creates a distinct local variable @code{a} for use within its
4774 body, without any effect on the global variable of the same name.
4776 The most important use of lexical bindings is to create @dfn{closures}.
4777 A closure is a function object that refers to an outside lexical
4778 variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}).
4782 (defun make-adder (n)
4783 (lexical-let ((n n))
4784 (function (lambda (m) (+ n m)))))
4785 (setq add17 (make-adder 17))
4791 The call @code{(make-adder 17)} returns a function object which adds
4792 17 to its argument. If @code{let} had been used instead of
4793 @code{lexical-let}, the function object would have referred to the
4794 global @code{n}, which would have been bound to 17 only during the
4795 call to @code{make-adder} itself.
4798 (defun make-counter ()
4799 (lexical-let ((n 0))
4800 (cl-function (lambda (&optional (m 1)) (cl-incf n m)))))
4801 (setq count-1 (make-counter))
4804 (funcall count-1 14)
4806 (setq count-2 (make-counter))
4816 Here we see that each call to @code{make-counter} creates a distinct
4817 local variable @code{n}, which serves as a private counter for the
4818 function object that is returned.
4820 Closed-over lexical variables persist until the last reference to
4821 them goes away, just like all other Lisp objects. For example,
4822 @code{count-2} refers to a function object which refers to an
4823 instance of the variable @code{n}; this is the only reference
4824 to that variable, so after @code{(setq count-2 nil)} the garbage
4825 collector would be able to delete this instance of @code{n}.
4826 Of course, if a @code{lexical-let} does not actually create any
4827 closures, then the lexical variables are free as soon as the
4828 @code{lexical-let} returns.
4830 Many closures are used only during the extent of the bindings they
4831 refer to; these are known as ``downward funargs'' in Lisp parlance.
4832 When a closure is used in this way, regular Emacs Lisp dynamic
4833 bindings suffice and will be more efficient than @code{lexical-let}
4837 (defun add-to-list (x list)
4838 (mapcar (lambda (y) (+ x y))) list)
4839 (add-to-list 7 '(1 2 5))
4844 Since this lambda is only used while @code{x} is still bound,
4845 it is not necessary to make a true closure out of it.
4847 You can use @code{defun} or @code{flet} inside a @code{lexical-let}
4848 to create a named closure. If several closures are created in the
4849 body of a single @code{lexical-let}, they all close over the same
4850 instance of the lexical variable.
4852 @defmac lexical-let* (bindings@dots{}) forms@dots{}
4853 This form is just like @code{lexical-let}, except that the bindings
4854 are made sequentially in the manner of @code{let*}.
4857 @node Obsolete Macros
4858 @appendixsec Obsolete Macros
4860 The following macros are obsolete, and are replaced by versions with
4861 a @samp{cl-} prefix that do not behave in exactly the same way.
4862 Consequently, the @file{cl.el} versions are not simply aliases to the
4863 @file{cl-lib.el} versions.
4865 @defmac flet (bindings@dots{}) forms@dots{}
4866 This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}),
4867 which behaves the same way as Common Lisp's @code{flet}.
4868 This @code{flet} takes the same arguments as @code{cl-flet}, but does
4869 not behave in precisely the same way.
4871 While @code{flet} in Common Lisp establishes a lexical function
4872 binding, this @code{flet} makes a dynamic binding (it dates from a
4873 time before Emacs had lexical binding). The result is
4874 that @code{flet} affects indirect calls to a function as well as calls
4875 directly inside the @code{flet} form itself.
4878 Note that many primitives (e.g.@: @code{+}) have special byte-compile
4879 handling. Attempts to redefine such functions using @code{flet} will
4880 fail if 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 @defmac letf (bindings@dots{}) forms@dots{}
4897 This macro is almost exactly the same as @code{cl-letf}, which
4898 replaces it (@pxref{Modify Macros}). The only difference is in
4899 details that relate to some deprecated usage of @code{symbol-function}
4903 @node Obsolete Setf Customization
4904 @appendixsec Obsolete Ways to Customize Setf
4906 Common Lisp defines three macros, @code{define-modify-macro},
4907 @code{defsetf}, and @code{define-setf-method}, that allow the
4908 user to extend generalized variables in various ways.
4909 In Emacs, these are obsolete, replaced by various features of
4910 @file{gv.el} in Emacs 24.3. Many of the implementation
4911 details in the following are out-of-date.
4912 @c FIXME this whole section needs updating.
4914 @defmac define-modify-macro name arglist function [doc-string]
4915 This macro defines a ``read-modify-write'' macro similar to
4916 @code{cl-incf} and @code{cl-decf}. The macro @var{name} is defined
4917 to take a @var{place} argument followed by additional arguments
4918 described by @var{arglist}. The call
4921 (@var{name} @var{place} @var{args}@dots{})
4928 (cl-callf @var{func} @var{place} @var{args}@dots{})
4932 which in turn is roughly equivalent to
4935 (setf @var{place} (@var{func} @var{place} @var{args}@dots{}))
4941 (define-modify-macro cl-incf (&optional (n 1)) +)
4942 (define-modify-macro cl-concatf (&rest args) concat)
4945 Note that @code{&key} is not allowed in @var{arglist}, but
4946 @code{&rest} is sufficient to pass keywords on to the function.
4948 Most of the modify macros defined by Common Lisp do not exactly
4949 follow the pattern of @code{define-modify-macro}. For example,
4950 @code{push} takes its arguments in the wrong order, and @code{pop}
4951 is completely irregular. You can define these macros ``by hand''
4952 using @code{get-setf-method}, or consult the source
4953 to see how to use the internal @code{setf} building blocks.
4956 @defmac defsetf access-fn update-fn
4957 This is the simpler of two @code{defsetf} forms. Where
4958 @var{access-fn} is the name of a function which accesses a place,
4959 this declares @var{update-fn} to be the corresponding store
4960 function. From now on,
4963 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value})
4970 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value})
4974 The @var{update-fn} is required to be either a true function, or
4975 a macro which evaluates its arguments in a function-like way. Also,
4976 the @var{update-fn} is expected to return @var{value} as its result.
4977 Otherwise, the above expansion would not obey the rules for the way
4978 @code{setf} is supposed to behave.
4980 As a special (non-Common-Lisp) extension, a third argument of @code{t}
4981 to @code{defsetf} says that the return value of @code{update-fn} is
4982 not suitable, so that the above @code{setf} should be expanded to
4986 (let ((temp @var{value}))
4987 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp)
4991 Some examples of the use of @code{defsetf}, drawn from the standard
4992 suite of setf methods, are:
4995 (defsetf car setcar)
4996 (defsetf symbol-value set)
4997 (defsetf buffer-name rename-buffer t)
5001 @defmac defsetf access-fn arglist (store-var) forms@dots{}
5002 This is the second, more complex, form of @code{defsetf}. It is
5003 rather like @code{defmacro} except for the additional @var{store-var}
5004 argument. The @var{forms} should return a Lisp form that stores
5005 the value of @var{store-var} into the generalized variable formed
5006 by a call to @var{access-fn} with arguments described by @var{arglist}.
5007 The @var{forms} may begin with a string which documents the @code{setf}
5008 method (analogous to the doc string that appears at the front of a
5011 For example, the simple form of @code{defsetf} is shorthand for
5014 (defsetf @var{access-fn} (&rest args) (store)
5015 (append '(@var{update-fn}) args (list store)))
5018 The Lisp form that is returned can access the arguments from
5019 @var{arglist} and @var{store-var} in an unrestricted fashion;
5020 macros like @code{cl-incf} that invoke this
5021 setf-method will insert temporary variables as needed to make
5022 sure the apparent order of evaluation is preserved.
5024 Another example drawn from the standard package:
5027 (defsetf nth (n x) (store)
5028 (list 'setcar (list 'nthcdr n x) store))
5032 @defmac define-setf-method access-fn arglist forms@dots{}
5033 This is the most general way to create new place forms. When
5034 a @code{setf} to @var{access-fn} with arguments described by
5035 @var{arglist} is expanded, the @var{forms} are evaluated and
5036 must return a list of five items:
5037 @c FIXME Is this still true?
5041 A list of @dfn{temporary variables}.
5044 A list of @dfn{value forms} corresponding to the temporary variables
5045 above. The temporary variables will be bound to these value forms
5046 as the first step of any operation on the generalized variable.
5049 A list of exactly one @dfn{store variable} (generally obtained
5050 from a call to @code{gensym}).
5053 A Lisp form that stores the contents of the store variable into
5054 the generalized variable, assuming the temporaries have been
5055 bound as described above.
5058 A Lisp form that accesses the contents of the generalized variable,
5059 assuming the temporaries have been bound.
5062 This is exactly like the Common Lisp macro of the same name,
5063 except that the method returns a list of five values rather
5064 than the five values themselves, since Emacs Lisp does not
5065 support Common Lisp's notion of multiple return values.
5067 Once again, the @var{forms} may begin with a documentation string.
5069 A setf-method should be maximally conservative with regard to
5070 temporary variables. In the setf-methods generated by
5071 @code{defsetf}, the second return value is simply the list of
5072 arguments in the place form, and the first return value is a
5073 list of a corresponding number of temporary variables generated
5074 @c FIXME I don't think this is true anymore.
5075 by @code{cl-gensym}. Macros like @code{cl-incf} that
5076 use this setf-method will optimize away most temporaries that
5077 turn out to be unnecessary, so there is little reason for the
5078 setf-method itself to optimize.
5081 @defun get-setf-method place &optional env
5082 This function returns the setf-method for @var{place}, by
5083 invoking the definition previously recorded by @code{defsetf}
5084 or @code{define-setf-method}. The result is a list of five
5085 values as described above. You can use this function to build
5086 your own @code{cl-incf}-like modify macros.
5087 @c These no longer exist.
5089 (Actually, it is better to use the internal functions
5090 @code{cl-setf-do-modify} and @code{cl-setf-do-store}, which are a bit
5091 easier to use and which also do a number of optimizations; consult the
5092 source code for the @code{cl-incf} function for a simple example.)
5095 The argument @var{env} specifies the ``environment'' to be
5096 passed on to @code{macroexpand} if @code{get-setf-method} should
5097 need to expand a macro in @var{place}. It should come from
5098 an @code{&environment} argument to the macro or setf-method
5099 that called @code{get-setf-method}.
5101 @c FIXME No longer true.
5102 See also the source code for the setf-method for
5103 @c Also @code{apply}, but that is commented out.
5104 @code{substring}, which works by calling @code{get-setf-method} on a
5105 simpler case, then massaging the result.
5108 @c FIXME does not belong here any more, maybe in lispref?
5109 Modern Common Lisp defines a second, independent way to specify
5110 the @code{setf} behavior of a function, namely ``@code{setf}
5111 functions'' whose names are lists @code{(setf @var{name})}
5112 rather than symbols. For example, @code{(defun (setf foo) @dots{})}
5113 defines the function that is used when @code{setf} is applied to
5114 @code{foo}. This package does not currently support @code{setf}
5115 functions. In particular, it is a compile-time error to use
5116 @code{setf} on a form which has not already been @code{defsetf}'d
5117 or otherwise declared; in newer Common Lisps, this would not be
5118 an error since the function @code{(setf @var{func})} might be
5122 @node GNU Free Documentation License
5123 @appendix GNU Free Documentation License
5124 @include doclicense.texi
5126 @node Function Index
5127 @unnumbered Function Index
5131 @node Variable Index
5132 @unnumbered Variable Index