1 \input texinfo @c -*-texinfo-*-
2 @setfilename ../../info/cl.info
3 @settitle Common Lisp Extensions
8 This file documents the GNU Emacs Common Lisp emulation package.
10 Copyright @copyright{} 1993, 2001--2016 Free Software Foundation, Inc.
13 Permission is granted to copy, distribute and/or modify this document
14 under the terms of the GNU Free Documentation License, Version 1.3 or
15 any later version published by the Free Software Foundation; with no
16 Invariant Sections, with the Front-Cover Texts being ``A GNU Manual'',
17 and with the Back-Cover Texts as in (a) below. A copy of the license
18 is included in the section entitled ``GNU Free Documentation License''.
20 (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
21 modify this GNU manual.''
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. (The separate package EIEIO implements
111 a subset of CLOS functionality. @xref{Top, , Introduction, eieio, EIEIO}.)
114 Other features cannot be implemented without modification to the
115 Emacs Lisp interpreter itself, such as multiple return values,
116 case-insensitive symbols, and complex numbers.
117 This package generally makes no attempt to emulate these features.
121 This package was originally written by Dave Gillespie,
122 @file{daveg@@synaptics.com}, as a total rewrite of an earlier 1986
123 @file{cl.el} package by Cesar Quiroz. Care has been taken to ensure
124 that each function is defined efficiently, concisely, and with minimal
125 impact on the rest of the Emacs environment. Stefan Monnier added the
126 file @file{cl-lib.el} and rationalized the namespace for Emacs 24.3.
129 * Usage:: How to use this package.
130 * Organization:: The package's component files.
131 * Naming Conventions:: Notes on function names.
138 This package is distributed with Emacs, so there is no need
139 to install any additional files in order to start using it. Lisp code
140 that uses features from this package should simply include at
148 You may wish to add such a statement to your init file, if you
149 make frequent use of features from this package.
151 Code that only uses macros from this package can enclose the above in
152 @code{eval-when-compile}. Internally, this library is divided into
153 several files, @pxref{Organization}. Your code should only ever load
154 the main @file{cl-lib} file, which will load the others as needed.
157 @section Organization
160 The Common Lisp package is organized into four main files:
164 This is the main file, which contains basic functions
165 and information about the package. This file is relatively compact.
168 This file contains the larger, more complex or unusual functions.
169 It is kept separate so that packages which only want to use Common
170 Lisp fundamentals like the @code{cl-incf} function won't need to pay
171 the overhead of loading the more advanced functions.
174 This file contains most of the advanced functions for operating
175 on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}.
178 This file contains the features that are macros instead of functions.
179 Macros expand when the caller is compiled, not when it is run, so the
180 macros generally only need to be present when the byte-compiler is
181 running (or when the macros are used in uncompiled code). Most of the
182 macros of this package are isolated in @file{cl-macs.el} so that they
183 won't take up memory unless you are compiling.
186 The file @file{cl-lib.el} includes all necessary @code{autoload}
187 commands for the functions and macros in the other three files.
188 All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el}
189 will take care of pulling in the other files when they are
192 There is another file, @file{cl.el}, which was the main entry point to
193 this package prior to Emacs 24.3. Nowadays, it is replaced by
194 @file{cl-lib.el}. The two provide the same features (in most cases),
195 but use different function names (in fact, @file{cl.el} mainly just
196 defines aliases to the @file{cl-lib.el} definitions). Where
197 @file{cl-lib.el} defines a function called, for example,
198 @code{cl-incf}, @file{cl.el} uses the same name but without the
199 @samp{cl-} prefix, e.g., @code{incf} in this example. There are a few
200 exceptions to this. First, functions such as @code{cl-defun} where
201 the unprefixed version was already used for a standard Emacs Lisp
202 function. In such cases, the @file{cl.el} version adds a @samp{*}
203 suffix, e.g., @code{defun*}. Second, there are some obsolete features
204 that are only implemented in @file{cl.el}, not in @file{cl-lib.el},
205 because they are replaced by other standard Emacs Lisp features.
206 Finally, in a very few cases the old @file{cl.el} versions do not
207 behave in exactly the same way as the @file{cl-lib.el} versions.
208 @xref{Obsolete Features}.
209 @c There is also cl-mapc, which was called cl-mapc even before cl-lib.el.
210 @c But not autoloaded, so maybe not much used?
212 Since the old @file{cl.el} does not use a clean namespace, Emacs has a
213 policy that packages distributed with Emacs must not load @code{cl} at
214 run time. (It is ok for them to load @code{cl} at @emph{compile}
215 time, with @code{eval-when-compile}, and use the macros it provides.)
216 There is no such restriction on the use of @code{cl-lib}. New code
217 should use @code{cl-lib} rather than @code{cl}.
219 There is one more file, @file{cl-compat.el}, which defines some
220 routines from the older Quiroz @file{cl.el} package that are not otherwise
221 present in the new package. This file is obsolete and should not be
224 @node Naming Conventions
225 @section Naming Conventions
228 Except where noted, all functions defined by this package have the
229 same calling conventions as their Common Lisp counterparts, and
230 names that are those of Common Lisp plus a @samp{cl-} prefix.
232 Internal function and variable names in the package are prefixed
233 by @code{cl--}. Here is a complete list of functions prefixed by
234 @code{cl-} that were @emph{not} taken from Common Lisp:
237 cl-callf cl-callf2 cl-defsubst
241 @c This is not uninteresting I suppose, but is of zero practical relevance
242 @c to the user, and seems like a hostage to changing implementation details.
243 The following simple functions and macros are defined in @file{cl-lib.el};
244 they do not cause other components like @file{cl-extra} to be loaded.
247 cl-evenp cl-oddp cl-minusp
248 cl-plusp cl-endp cl-subst
249 cl-copy-list cl-list* cl-ldiff
250 cl-rest cl-decf [1] cl-incf [1]
251 cl-acons cl-adjoin [2] cl-pairlis
252 cl-pushnew [1,2] cl-declaim cl-proclaim
253 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
258 [1] Only when @var{place} is a plain variable name.
261 [2] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified,
262 and @code{:key} is not used.
265 [3] Only for one sequence argument or two list arguments.
267 @node Program Structure
268 @chapter Program Structure
271 This section describes features of this package that have to
272 do with programs as a whole: advanced argument lists for functions,
273 and the @code{cl-eval-when} construct.
276 * Argument Lists:: @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}.
277 * Time of Evaluation:: The @code{cl-eval-when} construct.
281 @section Argument Lists
286 Emacs Lisp's notation for argument lists of functions is a subset of
287 the Common Lisp notation. As well as the familiar @code{&optional}
288 and @code{&rest} markers, Common Lisp allows you to specify default
289 values for optional arguments, and it provides the additional markers
290 @code{&key} and @code{&aux}.
292 Since argument parsing is built-in to Emacs, there is no way for
293 this package to implement Common Lisp argument lists seamlessly.
294 Instead, this package defines alternates for several Lisp forms
295 which you must use if you need Common Lisp argument lists.
297 @defmac cl-defun name arglist body@dots{}
298 This form is identical to the regular @code{defun} form, except
299 that @var{arglist} is allowed to be a full Common Lisp argument
300 list. Also, the function body is enclosed in an implicit block
301 called @var{name}; @pxref{Blocks and Exits}.
304 @defmac cl-iter-defun name arglist body@dots{}
305 This form is identical to the regular @code{iter-defun} form, except
306 that @var{arglist} is allowed to be a full Common Lisp argument
307 list. Also, the function body is enclosed in an implicit block
308 called @var{name}; @pxref{Blocks and Exits}.
311 @defmac cl-defsubst name arglist body@dots{}
312 This is just like @code{cl-defun}, except that the function that
313 is defined is automatically proclaimed @code{inline}, i.e.,
314 calls to it may be expanded into in-line code by the byte compiler.
315 This is analogous to the @code{defsubst} form;
316 @code{cl-defsubst} uses a different method (compiler macros) which
317 works in all versions of Emacs, and also generates somewhat more
318 @c For some examples,
319 @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html
320 efficient inline expansions. In particular, @code{cl-defsubst}
321 arranges for the processing of keyword arguments, default values,
322 etc., to be done at compile-time whenever possible.
325 @defmac cl-defmacro name arglist body@dots{}
326 This is identical to the regular @code{defmacro} form,
327 except that @var{arglist} is allowed to be a full Common Lisp
328 argument list. The @code{&environment} keyword is supported as
329 described in Steele's book @cite{Common Lisp, the Language}.
330 The @code{&whole} keyword is supported only
331 within destructured lists (see below); top-level @code{&whole}
332 cannot be implemented with the current Emacs Lisp interpreter.
333 The macro expander body is enclosed in an implicit block called
337 @defmac cl-function symbol-or-lambda
338 This is identical to the regular @code{function} form,
339 except that if the argument is a @code{lambda} form then that
340 form may use a full Common Lisp argument list.
343 Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
344 in this package that include @var{arglist}s in their syntax allow
345 full Common Lisp argument lists.
347 Note that it is @emph{not} necessary to use @code{cl-defun} in
348 order to have access to most CL features in your function.
349 These features are always present; @code{cl-defun}'s only
350 difference from @code{defun} is its more flexible argument
351 lists and its implicit block.
353 The full form of a Common Lisp argument list is
357 &optional (@var{var} @var{initform} @var{svar})@dots{}
359 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{}
360 &aux (@var{var} @var{initform})@dots{})
363 Each of the five argument list sections is optional. The @var{svar},
364 @var{initform}, and @var{keyword} parts are optional; if they are
365 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.
367 The first section consists of zero or more @dfn{required} arguments.
368 These arguments must always be specified in a call to the function;
369 there is no difference between Emacs Lisp and Common Lisp as far as
370 required arguments are concerned.
372 The second section consists of @dfn{optional} arguments. These
373 arguments may be specified in the function call; if they are not,
374 @var{initform} specifies the default value used for the argument.
375 (No @var{initform} means to use @code{nil} as the default.) The
376 @var{initform} is evaluated with the bindings for the preceding
377 arguments already established; @code{(a &optional (b (1+ a)))}
378 matches one or two arguments, with the second argument defaulting
379 to one plus the first argument. If the @var{svar} is specified,
380 it is an auxiliary variable which is bound to @code{t} if the optional
381 argument was specified, or to @code{nil} if the argument was omitted.
382 If you don't use an @var{svar}, then there will be no way for your
383 function to tell whether it was called with no argument, or with
384 the default value passed explicitly as an argument.
386 The third section consists of a single @dfn{rest} argument. If
387 more arguments were passed to the function than are accounted for
388 by the required and optional arguments, those extra arguments are
389 collected into a list and bound to the ``rest'' argument variable.
390 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
391 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
392 macro contexts; this package accepts it all the time.
394 The fourth section consists of @dfn{keyword} arguments. These
395 are optional arguments which are specified by name rather than
396 positionally in the argument list. For example,
399 (cl-defun foo (a &optional b &key c d (e 17)))
403 defines a function which may be called with one, two, or more
404 arguments. The first two arguments are bound to @code{a} and
405 @code{b} in the usual way. The remaining arguments must be
406 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
407 by the value to be bound to the corresponding argument variable.
408 (Symbols whose names begin with a colon are called @dfn{keywords},
409 and they are self-quoting in the same way as @code{nil} and
412 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
413 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword
414 appears more than once in the function call, the first occurrence
415 takes precedence over the later ones. Note that it is not possible
416 to specify keyword arguments without specifying the optional
417 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
418 @code{b} to the keyword @code{:c}, then signal an error because
419 @code{2} is not a valid keyword.
421 You can also explicitly specify the keyword argument; it need not be
422 simply the variable name prefixed with a colon. For example,
425 (cl-defun bar (&key (a 1) ((baz b) 4)))
430 specifies a keyword @code{:a} that sets the variable @code{a} with
431 default value 1, as well as a keyword @code{baz} that sets the
432 variable @code{b} with default value 4. In this case, because
433 @code{baz} is not self-quoting, you must quote it explicitly in the
434 function call, like this:
440 Ordinarily, it is an error to pass an unrecognized keyword to
441 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask
442 Lisp to ignore unrecognized keywords, either by adding the
443 marker @code{&allow-other-keys} after the keyword section
444 of the argument list, or by specifying an @code{:allow-other-keys}
445 argument in the call whose value is non-@code{nil}. If the
446 function uses both @code{&rest} and @code{&key} at the same time,
447 the ``rest'' argument is bound to the keyword list as it appears
448 in the call. For example:
451 (cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
452 (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
453 (if need (error "Thing not found"))))
457 This function takes a @code{:need} keyword argument, but also
458 accepts other keyword arguments which are passed on to the
459 @code{cl-member} function. @code{allow-other-keys} is used to
460 keep both @code{find-thing} and @code{cl-member} from complaining
461 about each others' keywords in the arguments.
463 The fifth section of the argument list consists of @dfn{auxiliary
464 variables}. These are not really arguments at all, but simply
465 variables which are bound to @code{nil} or to the specified
466 @var{initforms} during execution of the function. There is no
467 difference between the following two functions, except for a
468 matter of stylistic taste:
471 (cl-defun foo (a b &aux (c (+ a b)) d)
479 @cindex destructuring, in argument list
480 Argument lists support @dfn{destructuring}. In Common Lisp,
481 destructuring is only allowed with @code{defmacro}; this package
482 allows it with @code{cl-defun} and other argument lists as well.
483 In destructuring, any argument variable (@var{var} in the above
484 example) can be replaced by a list of variables, or more generally,
485 a recursive argument list. The corresponding argument value must
486 be a list whose elements match this recursive argument list.
490 (cl-defmacro dolist ((var listform &optional resultform)
495 This says that the first argument of @code{dolist} must be a list
496 of two or three items; if there are other arguments as well as this
497 list, they are stored in @code{body}. All features allowed in
498 regular argument lists are allowed in these recursive argument lists.
499 In addition, the clause @samp{&whole @var{var}} is allowed at the
500 front of a recursive argument list. It binds @var{var} to the
501 whole list being matched; thus @code{(&whole all a b)} matches
502 a list of two things, with @code{a} bound to the first thing,
503 @code{b} bound to the second thing, and @code{all} bound to the
504 list itself. (Common Lisp allows @code{&whole} in top-level
505 @code{defmacro} argument lists as well, but Emacs Lisp does not
508 One last feature of destructuring is that the argument list may be
509 dotted, so that the argument list @code{(a b . c)} is functionally
510 equivalent to @code{(a b &rest c)}.
512 If the optimization quality @code{safety} is set to 0
513 (@pxref{Declarations}), error checking for wrong number of
514 arguments and invalid keyword arguments is disabled. By default,
515 argument lists are rigorously checked.
517 @node Time of Evaluation
518 @section Time of Evaluation
521 Normally, the byte-compiler does not actually execute the forms in
522 a file it compiles. For example, if a file contains @code{(setq foo t)},
523 the act of compiling it will not actually set @code{foo} to @code{t}.
524 This is true even if the @code{setq} was a top-level form (i.e., not
525 enclosed in a @code{defun} or other form). Sometimes, though, you
526 would like to have certain top-level forms evaluated at compile-time.
527 For example, the compiler effectively evaluates @code{defmacro} forms
528 at compile-time so that later parts of the file can refer to the
529 macros that are defined.
531 @defmac cl-eval-when (situations@dots{}) forms@dots{}
532 This form controls when the body @var{forms} are evaluated.
533 The @var{situations} list may contain any set of the symbols
534 @code{compile}, @code{load}, and @code{eval} (or their long-winded
535 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
536 and @code{:execute}).
538 The @code{cl-eval-when} form is handled differently depending on
539 whether or not it is being compiled as a top-level form.
540 Specifically, it gets special treatment if it is being compiled
541 by a command such as @code{byte-compile-file} which compiles files
542 or buffers of code, and it appears either literally at the
543 top level of the file or inside a top-level @code{progn}.
545 For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
546 executed at compile-time if @code{compile} is in the @var{situations}
547 list, and the @var{forms} are written out to the file (to be executed
548 at load-time) if @code{load} is in the @var{situations} list.
550 For non-compiled-top-level forms, only the @code{eval} situation is
551 relevant. (This includes forms executed by the interpreter, forms
552 compiled with @code{byte-compile} rather than @code{byte-compile-file},
553 and non-top-level forms.) The @code{cl-eval-when} acts like a
554 @code{progn} if @code{eval} is specified, and like @code{nil}
555 (ignoring the body @var{forms}) if not.
557 The rules become more subtle when @code{cl-eval-when}s are nested;
558 consult Steele (second edition) for the gruesome details (and
559 some gruesome examples).
561 Some simple examples:
564 ;; Top-level forms in foo.el:
565 (cl-eval-when (compile) (setq foo1 'bar))
566 (cl-eval-when (load) (setq foo2 'bar))
567 (cl-eval-when (compile load) (setq foo3 'bar))
568 (cl-eval-when (eval) (setq foo4 'bar))
569 (cl-eval-when (eval compile) (setq foo5 'bar))
570 (cl-eval-when (eval load) (setq foo6 'bar))
571 (cl-eval-when (eval compile load) (setq foo7 'bar))
574 When @file{foo.el} is compiled, these variables will be set during
575 the compilation itself:
578 foo1 foo3 foo5 foo7 ; 'compile'
581 When @file{foo.elc} is loaded, these variables will be set:
584 foo2 foo3 foo6 foo7 ; 'load'
587 And if @file{foo.el} is loaded uncompiled, these variables will
591 foo4 foo5 foo6 foo7 ; 'eval'
594 If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
595 then the first three would have been equivalent to @code{nil} and the
596 last four would have been equivalent to the corresponding @code{setq}s.
598 Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
599 to @code{(progn @dots{})} in all contexts. The compiler treats
600 certain top-level forms, like @code{defmacro} (sort-of) and
601 @code{require}, as if they were wrapped in @code{(cl-eval-when
602 (compile load eval) @dots{})}.
605 Emacs includes two special forms related to @code{cl-eval-when}.
606 @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}.
607 One of these, @code{eval-when-compile}, is not quite equivalent to
608 any @code{cl-eval-when} construct and is described below.
610 The other form, @code{(eval-and-compile @dots{})}, is exactly
611 equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}.
613 @defmac eval-when-compile forms@dots{}
614 The @var{forms} are evaluated at compile-time; at execution time,
615 this form acts like a quoted constant of the resulting value. Used
616 at top-level, @code{eval-when-compile} is just like @samp{eval-when
617 (compile eval)}. In other contexts, @code{eval-when-compile}
618 allows code to be evaluated once at compile-time for efficiency
621 This form is similar to the @samp{#.} syntax of true Common Lisp.
624 @defmac cl-load-time-value form
625 The @var{form} is evaluated at load-time; at execution time,
626 this form acts like a quoted constant of the resulting value.
628 Early Common Lisp had a @samp{#,} syntax that was similar to
629 this, but ANSI Common Lisp replaced it with @code{load-time-value}
630 and gave it more well-defined semantics.
632 In a compiled file, @code{cl-load-time-value} arranges for @var{form}
633 to be evaluated when the @file{.elc} file is loaded and then used
634 as if it were a quoted constant. In code compiled by
635 @code{byte-compile} rather than @code{byte-compile-file}, the
636 effect is identical to @code{eval-when-compile}. In uncompiled
637 code, both @code{eval-when-compile} and @code{cl-load-time-value}
638 act exactly like @code{progn}.
642 (insert "This function was executed on: "
643 (current-time-string)
645 (eval-when-compile (current-time-string))
646 ;; or '#.(current-time-string) in real Common Lisp
648 (cl-load-time-value (current-time-string))))
652 Byte-compiled, the above defun will result in the following code
653 (or its compiled equivalent, of course) in the @file{.elc} file:
656 (setq --temp-- (current-time-string))
658 (insert "This function was executed on: "
659 (current-time-string)
661 '"Wed Oct 31 16:32:28 2012"
671 This section describes functions for testing whether various
672 facts are true or false.
675 * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
676 * Equality Predicates:: @code{cl-equalp}.
679 @node Type Predicates
680 @section Type Predicates
682 @defun cl-typep object type
683 Check if @var{object} is of type @var{type}, where @var{type} is a
684 (quoted) type name of the sort used by Common Lisp. For example,
685 @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
688 The @var{type} argument to the above function is either a symbol
689 or a list beginning with a symbol.
693 If the type name is a symbol, Emacs appends @samp{-p} to the
694 symbol name to form the name of a predicate function for testing
695 the type. (Built-in predicates whose names end in @samp{p} rather
696 than @samp{-p} are used when appropriate.)
699 The type symbol @code{t} stands for the union of all types.
700 @code{(cl-typep @var{object} t)} is always true. Likewise, the
701 type symbol @code{nil} stands for nothing at all, and
702 @code{(cl-typep @var{object} nil)} is always false.
705 The type symbol @code{null} represents the symbol @code{nil}.
706 Thus @code{(cl-typep @var{object} 'null)} is equivalent to
707 @code{(null @var{object})}.
710 The type symbol @code{atom} represents all objects that are not cons
711 cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
712 @code{(atom @var{object})}.
715 The type symbol @code{real} is a synonym for @code{number}, and
716 @code{fixnum} is a synonym for @code{integer}.
719 The type symbols @code{character} and @code{string-char} match
720 integers in the range from 0 to 255.
723 The type list @code{(integer @var{low} @var{high})} represents all
724 integers between @var{low} and @var{high}, inclusive. Either bound
725 may be a list of a single integer to specify an exclusive limit,
726 or a @code{*} to specify no limit. The type @code{(integer * *)}
727 is thus equivalent to @code{integer}.
730 Likewise, lists beginning with @code{float}, @code{real}, or
731 @code{number} represent numbers of that type falling in a particular
735 Lists beginning with @code{and}, @code{or}, and @code{not} form
736 combinations of types. For example, @code{(or integer (float 0 *))}
737 represents all objects that are integers or non-negative floats.
740 Lists beginning with @code{member} or @code{cl-member} represent
741 objects @code{eql} to any of the following values. For example,
742 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
743 and @code{(member nil)} is equivalent to @code{null}.
746 Lists of the form @code{(satisfies @var{predicate})} represent
747 all objects for which @var{predicate} returns true when called
748 with that object as an argument.
751 The following function and macro (not technically predicates) are
752 related to @code{cl-typep}.
754 @defun cl-coerce object type
755 This function attempts to convert @var{object} to the specified
756 @var{type}. If @var{object} is already of that type as determined by
757 @code{cl-typep}, it is simply returned. Otherwise, certain types of
758 conversions will be made: If @var{type} is any sequence type
759 (@code{string}, @code{list}, etc.)@: then @var{object} will be
760 converted to that type if possible. If @var{type} is
761 @code{character}, then strings of length one and symbols with
762 one-character names can be coerced. If @var{type} is @code{float},
763 then integers can be coerced in versions of Emacs that support
764 floats. In all other circumstances, @code{cl-coerce} signals an
768 @defmac cl-deftype name arglist forms@dots{}
769 This macro defines a new type called @var{name}. It is similar
770 to @code{defmacro} in many ways; when @var{name} is encountered
771 as a type name, the body @var{forms} are evaluated and should
772 return a type specifier that is equivalent to the type. The
773 @var{arglist} is a Common Lisp argument list of the sort accepted
774 by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})}
775 is expanded by calling the expander with those arguments; the type
776 symbol @samp{@var{name}} is expanded by calling the expander with
777 no arguments. The @var{arglist} is processed the same as for
778 @code{cl-defmacro} except that optional arguments without explicit
779 defaults use @code{*} instead of @code{nil} as the ``default''
780 default. Some examples:
783 (cl-deftype null () '(satisfies null)) ; predefined
784 (cl-deftype list () '(or null cons)) ; predefined
785 (cl-deftype unsigned-byte (&optional bits)
786 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
787 (unsigned-byte 8) @equiv{} (integer 0 255)
788 (unsigned-byte) @equiv{} (integer 0 *)
789 unsigned-byte @equiv{} (integer 0 *)
793 The last example shows how the Common Lisp @code{unsigned-byte}
794 type specifier could be implemented if desired; this package does
795 not implement @code{unsigned-byte} by default.
798 The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type}
799 (@pxref{Assertions}) macros also use type names. The @code{cl-map},
800 @code{cl-concatenate}, and @code{cl-merge} functions take type-name
801 arguments to specify the type of sequence to return. @xref{Sequences}.
803 @node Equality Predicates
804 @section Equality Predicates
807 This package defines the Common Lisp predicate @code{cl-equalp}.
810 This function is a more flexible version of @code{equal}. In
811 particular, it compares strings case-insensitively, and it compares
812 numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
813 true). Vectors and conses are compared recursively. All other
814 objects are compared as if by @code{equal}.
816 This function differs from Common Lisp @code{equalp} in several
817 respects. First, Common Lisp's @code{equalp} also compares
818 @emph{characters} case-insensitively, which would be impractical
819 in this package since Emacs does not distinguish between integers
820 and characters. In keeping with the idea that strings are less
821 vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
822 not compare strings against vectors of integers.
825 Also note that the Common Lisp functions @code{member} and @code{assoc}
826 use @code{eql} to compare elements, whereas Emacs Lisp follows the
827 MacLisp tradition and uses @code{equal} for these two functions.
828 The functions @code{cl-member} and @code{cl-assoc} use @code{eql},
829 as in Common Lisp. The standard Emacs Lisp functions @code{memq} and
830 @code{assq} use @code{eq}, and the standard @code{memql} uses @code{eql}.
832 @node Control Structure
833 @chapter Control Structure
836 The features described in the following sections implement
837 various advanced control structures, including extensions to the
838 standard @code{setf} facility, and a number of looping and conditional
842 * Assignment:: The @code{cl-psetq} form.
843 * Generalized Variables:: Extensions to generalized variables.
844 * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}.
845 * Conditionals:: @code{cl-case}, @code{cl-typecase}.
846 * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}.
847 * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}.
848 * Loop Facility:: The Common Lisp @code{loop} macro.
849 * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc.
856 The @code{cl-psetq} form is just like @code{setq}, except that multiple
857 assignments are done in parallel rather than sequentially.
859 @defmac cl-psetq [symbol form]@dots{}
860 This special form (actually a macro) is used to assign to several
861 variables simultaneously. Given only one @var{symbol} and @var{form},
862 it has the same effect as @code{setq}. Given several @var{symbol}
863 and @var{form} pairs, it evaluates all the @var{form}s in advance
864 and then stores the corresponding variables afterwards.
868 (setq x (+ x y) y (* x y))
871 y ; @r{@code{y} was computed after @code{x} was set.}
874 (cl-psetq x (+ x y) y (* x y))
877 y ; @r{@code{y} was computed before @code{x} was set.}
881 The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which
882 exchanges the values of two variables. (The @code{cl-rotatef} form
883 provides an even more convenient way to swap two variables;
884 @pxref{Modify Macros}.)
886 @code{cl-psetq} always returns @code{nil}.
889 @node Generalized Variables
890 @section Generalized Variables
892 A @dfn{generalized variable} or @dfn{place form} is one of the many
893 places in Lisp memory where values can be stored. The simplest place
894 form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists,
895 elements of arrays, properties of symbols, and many other locations
896 are also places where Lisp values are stored. For basic information,
897 @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
898 This package provides several additional features related to
899 generalized variables.
902 * Setf Extensions:: Additional @code{setf} places.
903 * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc.
906 @node Setf Extensions
907 @subsection Setf Extensions
909 Several standard (e.g., @code{car}) and Emacs-specific
910 (e.g., @code{window-point}) Lisp functions are @code{setf}-able by default.
911 This package defines @code{setf} handlers for several additional functions:
915 Functions from this package:
917 cl-rest cl-subseq cl-get cl-getf
918 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
922 Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument
923 of the function must itself be a valid @var{place} form.
926 General Emacs Lisp functions:
928 buffer-file-name getenv
929 buffer-modified-p global-key-binding
930 buffer-name local-key-binding
932 buffer-substring mark-marker
933 current-buffer marker-position
934 current-case-table mouse-position
936 current-global-map point-marker
937 current-input-mode point-max
938 current-local-map point-min
939 current-window-configuration read-mouse-position
940 default-file-modes screen-height
941 documentation-property screen-width
942 face-background selected-window
943 face-background-pixmap selected-screen
944 face-font selected-frame
945 face-foreground standard-case-table
946 face-underline-p syntax-table
947 file-modes visited-file-modtime
948 frame-height window-height
949 frame-parameters window-width
950 frame-visible-p x-get-secondary-selection
951 frame-width x-get-selection
955 Most of these have directly corresponding ``set'' functions, like
956 @code{use-local-map} for @code{current-local-map}, or @code{goto-char}
957 for @code{point}. A few, like @code{point-min}, expand to longer
958 sequences of code when they are used with @code{setf}
959 (@code{(narrow-to-region x (point-max))} in this case).
962 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
963 where @var{subplace} is itself a valid generalized variable whose
964 current value is a string, and where the value stored is also a
965 string. The new string is spliced into the specified part of the
966 destination string. For example:
969 (setq a (list "hello" "world"))
970 @result{} ("hello" "world")
973 (substring (cadr a) 2 4)
975 (setf (substring (cadr a) 2 4) "o")
980 @result{} ("hello" "wood")
983 The generalized variable @code{buffer-substring}, listed above,
984 also works in this way by replacing a portion of the current buffer.
986 @c FIXME? Also 'eq'? (see cl-lib.el)
988 @c Currently commented out in cl.el.
991 A call of the form @code{(apply '@var{func} @dots{})} or
992 @code{(apply (function @var{func}) @dots{})}, where @var{func}
993 is a @code{setf}-able function whose store function is ``suitable''
994 in the sense described in Steele's book; since none of the standard
995 Emacs place functions are suitable in this sense, this feature is
996 only interesting when used with places you define yourself with
997 @code{define-setf-method} or the long form of @code{defsetf}.
998 @xref{Obsolete Setf Customization}.
1001 @c FIXME? Is this still true?
1003 A macro call, in which case the macro is expanded and @code{setf}
1004 is applied to the resulting form.
1007 @c FIXME should this be in lispref? It seems self-evident.
1008 @c Contrast with the cl-incf example later on.
1009 @c Here it really only serves as a contrast to wrong-order.
1010 The @code{setf} macro takes care to evaluate all subforms in
1011 the proper left-to-right order; for example,
1014 (setf (aref vec (cl-incf i)) i)
1018 looks like it will evaluate @code{(cl-incf i)} exactly once, before the
1019 following access to @code{i}; the @code{setf} expander will insert
1020 temporary variables as necessary to ensure that it does in fact work
1021 this way no matter what setf-method is defined for @code{aref}.
1022 (In this case, @code{aset} would be used and no such steps would
1023 be necessary since @code{aset} takes its arguments in a convenient
1026 However, if the @var{place} form is a macro which explicitly
1027 evaluates its arguments in an unusual order, this unusual order
1028 will be preserved. Adapting an example from Steele, given
1031 (defmacro wrong-order (x y) (list 'aref y x))
1035 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
1036 evaluate @var{b} first, then @var{a}, just as in an actual call
1037 to @code{wrong-order}.
1040 @subsection Modify Macros
1043 This package defines a number of macros that operate on generalized
1044 variables. Many are interesting and useful even when the @var{place}
1045 is just a variable name.
1047 @defmac cl-psetf [place form]@dots{}
1048 This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
1049 When several @var{place}s and @var{form}s are involved, the
1050 assignments take place in parallel rather than sequentially.
1051 Specifically, all subforms are evaluated from left to right, then
1052 all the assignments are done (in an undefined order).
1055 @defmac cl-incf place &optional x
1056 This macro increments the number stored in @var{place} by one, or
1057 by @var{x} if specified. The incremented value is returned. For
1058 example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and
1059 @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
1061 As with @code{setf}, care is taken to preserve the ``apparent'' order
1062 of evaluation. For example,
1065 (cl-incf (aref vec (cl-incf i)))
1069 appears to increment @code{i} once, then increment the element of
1070 @code{vec} addressed by @code{i}; this is indeed exactly what it
1071 does, which means the above form is @emph{not} equivalent to the
1072 ``obvious'' expansion,
1075 (setf (aref vec (cl-incf i))
1076 (1+ (aref vec (cl-incf i)))) ; wrong!
1080 but rather to something more like
1083 (let ((temp (cl-incf i)))
1084 (setf (aref vec temp) (1+ (aref vec temp))))
1088 Again, all of this is taken care of automatically by @code{cl-incf} and
1089 the other generalized-variable macros.
1091 As a more Emacs-specific example of @code{cl-incf}, the expression
1092 @code{(cl-incf (point) @var{n})} is essentially equivalent to
1093 @code{(forward-char @var{n})}.
1096 @defmac cl-decf place &optional x
1097 This macro decrements the number stored in @var{place} by one, or
1098 by @var{x} if specified.
1101 @defmac cl-pushnew x place @t{&key :test :test-not :key}
1102 This macro inserts @var{x} at the front of the list stored in
1103 @var{place}, but only if @var{x} was not @code{eql} to any
1104 existing element of the list. The optional keyword arguments
1105 are interpreted in the same way as for @code{cl-adjoin}.
1106 @xref{Lists as Sets}.
1109 @defmac cl-shiftf place@dots{} newvalue
1110 This macro shifts the @var{place}s left by one, shifting in the
1111 value of @var{newvalue} (which may be any Lisp expression, not just
1112 a generalized variable), and returning the value shifted out of
1113 the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c}
1114 @var{d})} is equivalent to
1119 (cl-psetf @var{a} @var{b}
1125 except that the subforms of @var{a}, @var{b}, and @var{c} are actually
1126 evaluated only once each and in the apparent order.
1129 @defmac cl-rotatef place@dots{}
1130 This macro rotates the @var{place}s left by one in circular fashion.
1131 Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to
1134 (cl-psetf @var{a} @var{b}
1141 except for the evaluation of subforms. @code{cl-rotatef} always
1142 returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})}
1143 conveniently exchanges @var{a} and @var{b}.
1146 The following macros were invented for this package; they have no
1147 analogues in Common Lisp.
1149 @defmac cl-letf (bindings@dots{}) forms@dots{}
1150 This macro is analogous to @code{let}, but for generalized variables
1151 rather than just symbols. Each @var{binding} should be of the form
1152 @code{(@var{place} @var{value})}; the original contents of the
1153 @var{place}s are saved, the @var{value}s are stored in them, and
1154 then the body @var{form}s are executed. Afterwards, the @var{places}
1155 are set back to their original saved contents. This cleanup happens
1156 even if the @var{form}s exit irregularly due to a @code{throw} or an
1162 (cl-letf (((point) (point-min))
1168 moves point in the current buffer to the beginning of the buffer,
1169 and also binds @code{a} to 17 (as if by a normal @code{let}, since
1170 @code{a} is just a regular variable). After the body exits, @code{a}
1171 is set back to its original value and point is moved back to its
1174 Note that @code{cl-letf} on @code{(point)} is not quite like a
1175 @code{save-excursion}, as the latter effectively saves a marker
1176 which tracks insertions and deletions in the buffer. Actually,
1177 a @code{cl-letf} of @code{(point-marker)} is much closer to this
1178 behavior. (@code{point} and @code{point-marker} are equivalent
1179 as @code{setf} places; each will accept either an integer or a
1180 marker as the stored value.)
1182 Since generalized variables look like lists, @code{let}'s shorthand
1183 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
1184 be ambiguous in @code{cl-letf} and is not allowed.
1186 However, a @var{binding} specifier may be a one-element list
1187 @samp{(@var{place})}, which is similar to @samp{(@var{place}
1188 @var{place})}. In other words, the @var{place} is not disturbed
1189 on entry to the body, and the only effect of the @code{cl-letf} is
1190 to restore the original value of @var{place} afterwards.
1191 @c I suspect this may no longer be true; either way it's
1192 @c implementation detail and so not essential to document.
1194 (The redundant access-and-store suggested by the @code{(@var{place}
1195 @var{place})} example does not actually occur.)
1198 Note that in this case, and in fact almost every case, @var{place}
1199 must have a well-defined value outside the @code{cl-letf} body.
1200 There is essentially only one exception to this, which is @var{place}
1201 a plain variable with a specified @var{value} (such as @code{(a 17)}
1202 in the above example).
1203 @c See http://debbugs.gnu.org/12758
1204 @c Some or all of this was true for cl.el, but not for cl-lib.el.
1206 The only exceptions are plain variables and calls to
1207 @code{symbol-value} and @code{symbol-function}. If the symbol is not
1208 bound on entry, it is simply made unbound by @code{makunbound} or
1209 @code{fmakunbound} on exit.
1213 @defmac cl-letf* (bindings@dots{}) forms@dots{}
1214 This macro is to @code{cl-letf} what @code{let*} is to @code{let}:
1215 It does the bindings in sequential rather than parallel order.
1218 @defmac cl-callf @var{function} @var{place} @var{args}@dots{}
1219 This is the ``generic'' modify macro. It calls @var{function},
1220 which should be an unquoted function name, macro name, or lambda.
1221 It passes @var{place} and @var{args} as arguments, and assigns the
1222 result back to @var{place}. For example, @code{(cl-incf @var{place}
1223 @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}.
1227 (cl-callf abs my-number)
1228 (cl-callf concat (buffer-name) "<" (number-to-string n) ">")
1229 (cl-callf cl-union happy-people (list joe bob) :test 'same-person)
1232 Note again that @code{cl-callf} is an extension to standard Common Lisp.
1235 @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{}
1236 This macro is like @code{cl-callf}, except that @var{place} is
1237 the @emph{second} argument of @var{function} rather than the
1238 first. For example, @code{(push @var{x} @var{place})} is
1239 equivalent to @code{(cl-callf2 cons @var{x} @var{place})}.
1242 The @code{cl-callf} and @code{cl-callf2} macros serve as building
1243 blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}.
1244 The @code{cl-letf} and @code{cl-letf*} macros are used in the processing
1245 of symbol macros; @pxref{Macro Bindings}.
1248 @node Variable Bindings
1249 @section Variable Bindings
1252 These Lisp forms make bindings to variables and function names,
1253 analogous to Lisp's built-in @code{let} form.
1255 @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which
1256 are also related to variable bindings.
1259 * Dynamic Bindings:: The @code{cl-progv} form.
1260 * Function Bindings:: @code{cl-flet} and @code{cl-labels}.
1261 * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}.
1264 @node Dynamic Bindings
1265 @subsection Dynamic Bindings
1268 The standard @code{let} form binds variables whose names are known
1269 at compile-time. The @code{cl-progv} form provides an easy way to
1270 bind variables whose names are computed at run-time.
1272 @defmac cl-progv symbols values forms@dots{}
1273 This form establishes @code{let}-style variable bindings on a
1274 set of variables computed at run-time. The expressions
1275 @var{symbols} and @var{values} are evaluated, and must return lists
1276 of symbols and values, respectively. The symbols are bound to the
1277 corresponding values for the duration of the body @var{form}s.
1278 If @var{values} is shorter than @var{symbols}, the last few symbols
1279 are bound to @code{nil}.
1280 If @var{symbols} is shorter than @var{values}, the excess values
1284 @node Function Bindings
1285 @subsection Function Bindings
1288 These forms make @code{let}-like bindings to functions instead
1291 @defmac cl-flet (bindings@dots{}) forms@dots{}
1292 This form establishes @code{let}-style bindings on the function
1293 cells of symbols rather than on the value cells. Each @var{binding}
1294 must be a list of the form @samp{(@var{name} @var{arglist}
1295 @var{forms}@dots{})}, which defines a function exactly as if
1296 it were a @code{cl-defun} form. The function @var{name} is defined
1297 accordingly but only within the body of the @code{cl-flet}, hiding any external
1298 definition if applicable.
1300 The bindings are lexical in scope. This means that all references to
1301 the named functions must appear physically within the body of the
1302 @code{cl-flet} form.
1304 Functions defined by @code{cl-flet} may use the full Common Lisp
1305 argument notation supported by @code{cl-defun}; also, the function
1306 body is enclosed in an implicit block as if by @code{cl-defun}.
1307 @xref{Program Structure}.
1309 Note that the @file{cl.el} version of this macro behaves slightly
1310 differently. In particular, its binding is dynamic rather than
1311 lexical. @xref{Obsolete Macros}.
1314 @defmac cl-labels (bindings@dots{}) forms@dots{}
1315 The @code{cl-labels} form is like @code{cl-flet}, except that
1316 the function bindings can be recursive. The scoping is lexical,
1317 but you can only capture functions in closures if
1318 @code{lexical-binding} is @code{t}.
1319 @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and
1320 @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
1322 Lexical scoping means that all references to the named
1323 functions must appear physically within the body of the
1324 @code{cl-labels} form. References may appear both in the body
1325 @var{forms} of @code{cl-labels} itself, and in the bodies of
1326 the functions themselves. Thus, @code{cl-labels} can define
1327 local recursive functions, or mutually-recursive sets of functions.
1329 A ``reference'' to a function name is either a call to that
1330 function, or a use of its name quoted by @code{quote} or
1331 @code{function} to be passed on to, say, @code{mapcar}.
1333 Note that the @file{cl.el} version of this macro behaves slightly
1334 differently. @xref{Obsolete Macros}.
1337 @node Macro Bindings
1338 @subsection Macro Bindings
1341 These forms create local macros and ``symbol macros''.
1343 @defmac cl-macrolet (bindings@dots{}) forms@dots{}
1344 This form is analogous to @code{cl-flet}, but for macros instead of
1345 functions. Each @var{binding} is a list of the same form as the
1346 arguments to @code{cl-defmacro} (i.e., a macro name, argument list,
1347 and macro-expander forms). The macro is defined accordingly for
1348 use within the body of the @code{cl-macrolet}.
1350 Because of the nature of macros, @code{cl-macrolet} is always lexically
1351 scoped. The @code{cl-macrolet} binding will
1352 affect only calls that appear physically within the body
1353 @var{forms}, possibly after expansion of other macros in the
1357 @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{}
1358 This form creates @dfn{symbol macros}, which are macros that look
1359 like variable references rather than function calls. Each
1360 @var{binding} is a list @samp{(@var{var} @var{expansion})};
1361 any reference to @var{var} within the body @var{forms} is
1362 replaced by @var{expansion}.
1366 (cl-symbol-macrolet ((foo (car bar)))
1372 A @code{setq} of a symbol macro is treated the same as a @code{setf}.
1373 I.e., @code{(setq foo 4)} in the above would be equivalent to
1374 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
1376 Likewise, a @code{let} or @code{let*} binding a symbol macro is
1377 treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true
1378 Common Lisp, where the rules of lexical scoping cause a @code{let}
1379 binding to shadow a @code{symbol-macrolet} binding. In this package,
1380 such shadowing does not occur, even when @code{lexical-binding} is
1381 @c See http://debbugs.gnu.org/12119
1382 @code{t}. (This behavior predates the addition of lexical binding to
1383 Emacs Lisp, and may change in future to respect @code{lexical-binding}.)
1384 At present in this package, only @code{lexical-let} and
1385 @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete
1388 There is no analogue of @code{defmacro} for symbol macros; all symbol
1389 macros are local. A typical use of @code{cl-symbol-macrolet} is in the
1390 expansion of another macro:
1393 (cl-defmacro my-dolist ((x list) &rest body)
1394 (let ((var (cl-gensym)))
1395 (list 'cl-loop 'for var 'on list 'do
1396 (cl-list* 'cl-symbol-macrolet
1397 (list (list x (list 'car var)))
1400 (setq mylist '(1 2 3 4))
1401 (my-dolist (x mylist) (cl-incf x))
1407 In this example, the @code{my-dolist} macro is similar to @code{dolist}
1408 (@pxref{Iteration}) except that the variable @code{x} becomes a true
1409 reference onto the elements of the list. The @code{my-dolist} call
1410 shown here expands to
1413 (cl-loop for G1234 on mylist do
1414 (cl-symbol-macrolet ((x (car G1234)))
1419 which in turn expands to
1422 (cl-loop for G1234 on mylist do (cl-incf (car G1234)))
1425 @xref{Loop Facility}, for a description of the @code{cl-loop} macro.
1426 This package defines a nonstandard @code{in-ref} loop clause that
1427 works much like @code{my-dolist}.
1431 @section Conditionals
1434 These conditional forms augment Emacs Lisp's simple @code{if},
1435 @code{and}, @code{or}, and @code{cond} forms.
1437 @defmac cl-case keyform clause@dots{}
1438 This macro evaluates @var{keyform}, then compares it with the key
1439 values listed in the various @var{clause}s. Whichever clause matches
1440 the key is executed; comparison is done by @code{eql}. If no clause
1441 matches, the @code{cl-case} form returns @code{nil}. The clauses are
1445 (@var{keylist} @var{body-forms}@dots{})
1449 where @var{keylist} is a list of key values. If there is exactly
1450 one value, and it is not a cons cell or the symbol @code{nil} or
1451 @code{t}, then it can be used by itself as a @var{keylist} without
1452 being enclosed in a list. All key values in the @code{cl-case} form
1453 must be distinct. The final clauses may use @code{t} in place of
1454 a @var{keylist} to indicate a default clause that should be taken
1455 if none of the other clauses match. (The symbol @code{otherwise}
1456 is also recognized in place of @code{t}. To make a clause that
1457 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise},
1458 enclose the symbol in a list.)
1460 For example, this expression reads a keystroke, then does one of
1461 four things depending on whether it is an @samp{a}, a @samp{b},
1462 a @key{RET} or @kbd{C-j}, or anything else.
1465 (cl-case (read-char)
1468 ((?\r ?\n) (do-ret-thing))
1469 (t (do-other-thing)))
1473 @defmac cl-ecase keyform clause@dots{}
1474 This macro is just like @code{cl-case}, except that if the key does
1475 not match any of the clauses, an error is signaled rather than
1476 simply returning @code{nil}.
1479 @defmac cl-typecase keyform clause@dots{}
1480 This macro is a version of @code{cl-case} that checks for types
1481 rather than values. Each @var{clause} is of the form
1482 @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates},
1483 for a description of type specifiers. For example,
1487 (integer (munch-integer x))
1488 (float (munch-float x))
1489 (string (munch-integer (string-to-int x)))
1490 (t (munch-anything x)))
1493 The type specifier @code{t} matches any type of object; the word
1494 @code{otherwise} is also allowed. To make one clause match any of
1495 several types, use an @code{(or @dots{})} type specifier.
1498 @defmac cl-etypecase keyform clause@dots{}
1499 This macro is just like @code{cl-typecase}, except that if the key does
1500 not match any of the clauses, an error is signaled rather than
1501 simply returning @code{nil}.
1504 @node Blocks and Exits
1505 @section Blocks and Exits
1509 Common Lisp @dfn{blocks} provide a non-local exit mechanism very
1510 similar to @code{catch} and @code{throw}, with lexical scoping.
1511 This package actually implements @code{cl-block}
1512 in terms of @code{catch}; however, the lexical scoping allows the
1513 byte-compiler to omit the costly @code{catch} step if the
1514 body of the block does not actually @code{cl-return-from} the block.
1516 @defmac cl-block name forms@dots{}
1517 The @var{forms} are evaluated as if by a @code{progn}. However,
1518 if any of the @var{forms} execute @code{(cl-return-from @var{name})},
1519 they will jump out and return directly from the @code{cl-block} form.
1520 The @code{cl-block} returns the result of the last @var{form} unless
1521 a @code{cl-return-from} occurs.
1523 The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to
1524 the @code{catch}/@code{throw} mechanism. The main differences are
1525 that block @var{name}s are unevaluated symbols, rather than forms
1526 (such as quoted symbols) that evaluate to a tag at run-time; and
1527 also that blocks are always lexically scoped.
1528 In a dynamically scoped @code{catch}, functions called from the
1529 @code{catch} body can also @code{throw} to the @code{catch}. This
1530 is not an option for @code{cl-block}, where
1531 the @code{cl-return-from} referring to a block name must appear
1532 physically within the @var{forms} that make up the body of the block.
1533 They may not appear within other called functions, although they may
1534 appear within macro expansions or @code{lambda}s in the body. Block
1535 names and @code{catch} names form independent name-spaces.
1537 In true Common Lisp, @code{defun} and @code{defmacro} surround
1538 the function or expander bodies with implicit blocks with the
1539 same name as the function or macro. This does not occur in Emacs
1540 Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro}
1541 forms, which do create the implicit block.
1543 The Common Lisp looping constructs defined by this package,
1544 such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks
1545 just as in Common Lisp.
1547 Because they are implemented in terms of Emacs Lisp's @code{catch}
1548 and @code{throw}, blocks have the same overhead as actual
1549 @code{catch} constructs (roughly two function calls). However,
1550 the byte compiler will optimize away the @code{catch}
1552 not in fact contain any @code{cl-return} or @code{cl-return-from} calls
1553 that jump to it. This means that @code{cl-do} loops and @code{cl-defun}
1554 functions that don't use @code{cl-return} don't pay the overhead to
1558 @defmac cl-return-from name [result]
1559 This macro returns from the block named @var{name}, which must be
1560 an (unevaluated) symbol. If a @var{result} form is specified, it
1561 is evaluated to produce the result returned from the @code{block}.
1562 Otherwise, @code{nil} is returned.
1565 @defmac cl-return [result]
1566 This macro is exactly like @code{(cl-return-from nil @var{result})}.
1567 Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose
1568 themselves in @code{nil} blocks.
1571 @c FIXME? Maybe this should be in a separate section?
1572 @defmac cl-tagbody &rest labels-or-statements
1573 This macro executes statements while allowing for control transfer to
1574 user-defined labels. Each element of @var{labels-or-statements} can
1575 be either a label (an integer or a symbol), or a cons-cell
1576 (a statement). This distinction is made before macroexpansion.
1577 Statements are executed in sequence, discarding any return value.
1578 Any statement can transfer control at any time to the statements that follow
1579 one of the labels with the special form @code{(go @var{label})}.
1580 Labels have lexical scope and dynamic extent.
1588 The macros described here provide more sophisticated, high-level
1589 looping constructs to complement Emacs Lisp's basic loop forms
1590 (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}).
1592 @defmac cl-loop forms@dots{}
1593 This package supports both the simple, old-style meaning of
1594 @code{loop} and the extremely powerful and flexible feature known as
1595 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced
1596 facility is discussed in the following section; @pxref{Loop Facility}.
1597 The simple form of @code{loop} is described here.
1599 If @code{cl-loop} is followed by zero or more Lisp expressions,
1600 then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite
1601 loop executing the expressions over and over. The loop is
1602 enclosed in an implicit @code{nil} block. Thus,
1605 (cl-loop (foo) (if (no-more) (return 72)) (bar))
1609 is exactly equivalent to
1612 (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar)))
1615 If any of the expressions are plain symbols, the loop is instead
1616 interpreted as a Loop Macro specification as described later.
1617 (This is not a restriction in practice, since a plain symbol
1618 in the above notation would simply access and throw away the
1619 value of a variable.)
1622 @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1623 This macro creates a general iterative loop. Each @var{spec} is
1627 (@var{var} [@var{init} [@var{step}]])
1630 The loop works as follows: First, each @var{var} is bound to the
1631 associated @var{init} value as if by a @code{let} form. Then, in
1632 each iteration of the loop, the @var{end-test} is evaluated; if
1633 true, the loop is finished. Otherwise, the body @var{forms} are
1634 evaluated, then each @var{var} is set to the associated @var{step}
1635 expression (as if by a @code{cl-psetq} form) and the next iteration
1636 begins. Once the @var{end-test} becomes true, the @var{result}
1637 forms are evaluated (with the @var{var}s still bound to their
1638 values) to produce the result returned by @code{cl-do}.
1640 The entire @code{cl-do} loop is enclosed in an implicit @code{nil}
1641 block, so that you can use @code{(cl-return)} to break out of the
1644 If there are no @var{result} forms, the loop returns @code{nil}.
1645 If a given @var{var} has no @var{step} form, it is bound to its
1646 @var{init} value but not otherwise modified during the @code{cl-do}
1647 loop (unless the code explicitly modifies it); this case is just
1648 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})}
1649 around the loop. If @var{init} is also omitted it defaults to
1650 @code{nil}, and in this case a plain @samp{@var{var}} can be used
1651 in place of @samp{(@var{var})}, again following the analogy with
1654 This example (from Steele) illustrates a loop that applies the
1655 function @code{f} to successive pairs of values from the lists
1656 @code{foo} and @code{bar}; it is equivalent to the call
1657 @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body
1658 @var{forms} at all, performing all its work as side effects of
1659 the rest of the loop.
1662 (cl-do ((x foo (cdr x))
1664 (z nil (cons (f (car x) (car y)) z)))
1665 ((or (null x) (null y))
1670 @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1671 This is to @code{cl-do} what @code{let*} is to @code{let}. In
1672 particular, the initial values are bound as if by @code{let*}
1673 rather than @code{let}, and the steps are assigned as if by
1674 @code{setq} rather than @code{cl-psetq}.
1676 Here is another way to write the above loop:
1679 (cl-do* ((xp foo (cdr xp))
1681 (x (car xp) (car xp))
1682 (y (car yp) (car yp))
1684 ((or (null xp) (null yp))
1690 @defmac cl-dolist (var list [result]) forms@dots{}
1691 This is exactly like the standard Emacs Lisp macro @code{dolist},
1692 but surrounds the loop with an implicit @code{nil} block.
1695 @defmac cl-dotimes (var count [result]) forms@dots{}
1696 This is exactly like the standard Emacs Lisp macro @code{dotimes},
1697 but surrounds the loop with an implicit @code{nil} block.
1698 The body is executed with @var{var} bound to the integers
1699 from zero (inclusive) to @var{count} (exclusive), in turn. Then
1700 @c FIXME lispref does not state this part explicitly, could move this there.
1701 the @code{result} form is evaluated with @var{var} bound to the total
1702 number of iterations that were done (i.e., @code{(max 0 @var{count})})
1703 to get the return value for the loop form.
1706 @defmac cl-do-symbols (var [obarray [result]]) forms@dots{}
1707 This loop iterates over all interned symbols. If @var{obarray}
1708 is specified and is not @code{nil}, it loops over all symbols in
1709 that obarray. For each symbol, the body @var{forms} are evaluated
1710 with @var{var} bound to that symbol. The symbols are visited in
1711 an unspecified order. Afterward the @var{result} form, if any,
1712 is evaluated (with @var{var} bound to @code{nil}) to get the return
1713 value. The loop is surrounded by an implicit @code{nil} block.
1716 @defmac cl-do-all-symbols (var [result]) forms@dots{}
1717 This is identical to @code{cl-do-symbols} except that the @var{obarray}
1718 argument is omitted; it always iterates over the default obarray.
1721 @xref{Mapping over Sequences}, for some more functions for
1722 iterating over vectors or lists.
1725 @section Loop Facility
1728 A common complaint with Lisp's traditional looping constructs was
1729 that they were either too simple and limited, such as @code{dotimes}
1730 or @code{while}, or too unreadable and obscure, like Common Lisp's
1733 To remedy this, Common Lisp added a construct called the ``Loop
1734 Facility'' or ``@code{loop} macro'', with an easy-to-use but very
1735 powerful and expressive syntax.
1738 * Loop Basics:: The @code{cl-loop} macro, basic clause structure.
1739 * Loop Examples:: Working examples of the @code{cl-loop} macro.
1740 * For Clauses:: Clauses introduced by @code{for} or @code{as}.
1741 * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc.
1742 * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc.
1743 * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}.
1747 @subsection Loop Basics
1750 The @code{cl-loop} macro essentially creates a mini-language within
1751 Lisp that is specially tailored for describing loops. While this
1752 language is a little strange-looking by the standards of regular Lisp,
1753 it turns out to be very easy to learn and well-suited to its purpose.
1755 Since @code{cl-loop} is a macro, all parsing of the loop language
1756 takes place at byte-compile time; compiled @code{cl-loop}s are just
1757 as efficient as the equivalent @code{while} loops written longhand.
1759 @defmac cl-loop clauses@dots{}
1760 A loop construct consists of a series of @var{clause}s, each
1761 introduced by a symbol like @code{for} or @code{do}. Clauses
1762 are simply strung together in the argument list of @code{cl-loop},
1763 with minimal extra parentheses. The various types of clauses
1764 specify initializations, such as the binding of temporary
1765 variables, actions to be taken in the loop, stepping actions,
1768 Common Lisp specifies a certain general order of clauses in a
1772 (loop @var{name-clause}
1773 @var{var-clauses}@dots{}
1774 @var{action-clauses}@dots{})
1777 The @var{name-clause} optionally gives a name to the implicit
1778 block that surrounds the loop. By default, the implicit block
1779 is named @code{nil}. The @var{var-clauses} specify what
1780 variables should be bound during the loop, and how they should
1781 be modified or iterated throughout the course of the loop. The
1782 @var{action-clauses} are things to be done during the loop, such
1783 as computing, collecting, and returning values.
1785 The Emacs version of the @code{cl-loop} macro is less restrictive about
1786 the order of clauses, but things will behave most predictably if
1787 you put the variable-binding clauses @code{with}, @code{for}, and
1788 @code{repeat} before the action clauses. As in Common Lisp,
1789 @code{initially} and @code{finally} clauses can go anywhere.
1791 Loops generally return @code{nil} by default, but you can cause
1792 them to return a value by using an accumulation clause like
1793 @code{collect}, an end-test clause like @code{always}, or an
1794 explicit @code{return} clause to jump out of the implicit block.
1795 (Because the loop body is enclosed in an implicit block, you can
1796 also use regular Lisp @code{cl-return} or @code{cl-return-from} to
1797 break out of the loop.)
1800 The following sections give some examples of the loop macro in
1801 action, and describe the particular loop clauses in great detail.
1802 Consult the second edition of Steele for additional discussion
1806 @subsection Loop Examples
1809 Before listing the full set of clauses that are allowed, let's
1810 look at a few example loops just to get a feel for the @code{cl-loop}
1814 (cl-loop for buf in (buffer-list)
1815 collect (buffer-file-name buf))
1819 This loop iterates over all Emacs buffers, using the list
1820 returned by @code{buffer-list}. For each buffer @var{buf},
1821 it calls @code{buffer-file-name} and collects the results into
1822 a list, which is then returned from the @code{cl-loop} construct.
1823 The result is a list of the file names of all the buffers in
1824 Emacs's memory. The words @code{for}, @code{in}, and @code{collect}
1825 are reserved words in the @code{cl-loop} language.
1828 (cl-loop repeat 20 do (insert "Yowsa\n"))
1832 This loop inserts the phrase ``Yowsa'' twenty times in the
1836 (cl-loop until (eobp) do (munch-line) (forward-line 1))
1840 This loop calls @code{munch-line} on every line until the end
1841 of the buffer. If point is already at the end of the buffer,
1842 the loop exits immediately.
1845 (cl-loop do (munch-line) until (eobp) do (forward-line 1))
1849 This loop is similar to the above one, except that @code{munch-line}
1850 is always called at least once.
1853 (cl-loop for x from 1 to 100
1856 finally return (list x (= y 729)))
1860 This more complicated loop searches for a number @code{x} whose
1861 square is 729. For safety's sake it only examines @code{x}
1862 values up to 100; dropping the phrase @samp{to 100} would
1863 cause the loop to count upwards with no limit. The second
1864 @code{for} clause defines @code{y} to be the square of @code{x}
1865 within the loop; the expression after the @code{=} sign is
1866 reevaluated each time through the loop. The @code{until}
1867 clause gives a condition for terminating the loop, and the
1868 @code{finally} clause says what to do when the loop finishes.
1869 (This particular example was written less concisely than it
1870 could have been, just for the sake of illustration.)
1872 Note that even though this loop contains three clauses (two
1873 @code{for}s and an @code{until}) that would have been enough to
1874 define loops all by themselves, it still creates a single loop
1875 rather than some sort of triple-nested loop. You must explicitly
1876 nest your @code{cl-loop} constructs if you want nested loops.
1879 @subsection For Clauses
1882 Most loops are governed by one or more @code{for} clauses.
1883 A @code{for} clause simultaneously describes variables to be
1884 bound, how those variables are to be stepped during the loop,
1885 and usually an end condition based on those variables.
1887 The word @code{as} is a synonym for the word @code{for}. This
1888 word is followed by a variable name, then a word like @code{from}
1889 or @code{across} that describes the kind of iteration desired.
1890 In Common Lisp, the phrase @code{being the} sometimes precedes
1891 the type of iteration; in this package both @code{being} and
1892 @code{the} are optional. The word @code{each} is a synonym
1893 for @code{the}, and the word that follows it may be singular
1894 or plural: @samp{for x being the elements of y} or
1895 @samp{for x being each element of y}. Which form you use
1896 is purely a matter of style.
1898 The variable is bound around the loop as if by @code{let}:
1902 (cl-loop for i from 1 to 10 do (do-something-with i))
1908 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3}
1909 This type of @code{for} clause creates a counting loop. Each of
1910 the three sub-terms is optional, though there must be at least one
1911 term so that the clause is marked as a counting clause.
1913 The three expressions are the starting value, the ending value, and
1914 the step value, respectively, of the variable. The loop counts
1915 upwards by default (@var{expr3} must be positive), from @var{expr1}
1916 to @var{expr2} inclusively. If you omit the @code{from} term, the
1917 loop counts from zero; if you omit the @code{to} term, the loop
1918 counts forever without stopping (unless stopped by some other
1919 loop clause, of course); if you omit the @code{by} term, the loop
1920 counts in steps of one.
1922 You can replace the word @code{from} with @code{upfrom} or
1923 @code{downfrom} to indicate the direction of the loop. Likewise,
1924 you can replace @code{to} with @code{upto} or @code{downto}.
1925 For example, @samp{for x from 5 downto 1} executes five times
1926 with @code{x} taking on the integers from 5 down to 1 in turn.
1927 Also, you can replace @code{to} with @code{below} or @code{above},
1928 which are like @code{upto} and @code{downto} respectively except
1929 that they are exclusive rather than inclusive limits:
1932 (cl-loop for x to 10 collect x)
1933 @result{} (0 1 2 3 4 5 6 7 8 9 10)
1934 (cl-loop for x below 10 collect x)
1935 @result{} (0 1 2 3 4 5 6 7 8 9)
1938 The @code{by} value is always positive, even for downward-counting
1939 loops. Some sort of @code{from} value is required for downward
1940 loops; @samp{for x downto 5} is not a valid loop clause all by
1943 @item for @var{var} in @var{list} by @var{function}
1944 This clause iterates @var{var} over all the elements of @var{list},
1945 in turn. If you specify the @code{by} term, then @var{function}
1946 is used to traverse the list instead of @code{cdr}; it must be a
1947 function taking one argument. For example:
1950 (cl-loop for x in '(1 2 3 4 5 6) collect (* x x))
1951 @result{} (1 4 9 16 25 36)
1952 (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
1956 @item for @var{var} on @var{list} by @var{function}
1957 This clause iterates @var{var} over all the cons cells of @var{list}.
1960 (cl-loop for x on '(1 2 3 4) collect x)
1961 @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
1964 With @code{by}, there is no real reason that the @code{on} expression
1965 must be a list. For example:
1968 (cl-loop for x on first-animal by 'next-animal collect x)
1972 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
1973 the next in the (assumed) sequence of animals, or @code{nil} if
1974 @var{x} was the last animal in the sequence.
1976 @item for @var{var} in-ref @var{list} by @var{function}
1977 This is like a regular @code{in} clause, but @var{var} becomes
1978 a @code{setf}-able ``reference'' onto the elements of the list
1979 rather than just a temporary variable. For example,
1982 (cl-loop for x in-ref my-list do (cl-incf x))
1986 increments every element of @code{my-list} in place. This clause
1987 is an extension to standard Common Lisp.
1989 @item for @var{var} across @var{array}
1990 This clause iterates @var{var} over all the elements of @var{array},
1991 which may be a vector or a string.
1994 (cl-loop for x across "aeiou"
1995 do (use-vowel (char-to-string x)))
1998 @item for @var{var} across-ref @var{array}
1999 This clause iterates over an array, with @var{var} a @code{setf}-able
2000 reference onto the elements; see @code{in-ref} above.
2002 @item for @var{var} being the elements of @var{sequence}
2003 This clause iterates over the elements of @var{sequence}, which may
2004 be a list, vector, or string. Since the type must be determined
2005 at run-time, this is somewhat less efficient than @code{in} or
2006 @code{across}. The clause may be followed by the additional term
2007 @samp{using (index @var{var2})} to cause @var{var2} to be bound to
2008 the successive indices (starting at 0) of the elements.
2010 This clause type is taken from older versions of the @code{loop} macro,
2011 and is not present in modern Common Lisp. The @samp{using (sequence @dots{})}
2012 term of the older macros is not supported.
2014 @item for @var{var} being the elements of-ref @var{sequence}
2015 This clause iterates over a sequence, with @var{var} a @code{setf}-able
2016 reference onto the elements; see @code{in-ref} above.
2018 @item for @var{var} being the symbols [of @var{obarray}]
2019 This clause iterates over symbols, either over all interned symbols
2020 or over all symbols in @var{obarray}. The loop is executed with
2021 @var{var} bound to each symbol in turn. The symbols are visited in
2022 an unspecified order.
2027 (cl-loop for sym being the symbols
2029 when (string-match "^map" (symbol-name sym))
2034 returns a list of all the functions whose names begin with @samp{map}.
2036 The Common Lisp words @code{external-symbols} and @code{present-symbols}
2037 are also recognized but are equivalent to @code{symbols} in Emacs Lisp.
2039 Due to a minor implementation restriction, it will not work to have
2040 more than one @code{for} clause iterating over symbols, hash tables,
2041 keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately,
2042 it would rarely if ever be useful to do so. It @emph{is} valid to mix
2043 one of these types of clauses with other clauses like @code{for @dots{} to}
2046 @item for @var{var} being the hash-keys of @var{hash-table}
2047 @itemx for @var{var} being the hash-values of @var{hash-table}
2048 This clause iterates over the entries in @var{hash-table} with
2049 @var{var} bound to each key, or value. A @samp{using} clause can bind
2050 a second variable to the opposite part.
2053 (cl-loop for k being the hash-keys of h
2054 using (hash-values v)
2056 (message "key %S -> value %S" k v))
2059 @item for @var{var} being the key-codes of @var{keymap}
2060 @itemx for @var{var} being the key-bindings of @var{keymap}
2061 This clause iterates over the entries in @var{keymap}.
2062 The iteration does not enter nested keymaps but does enter inherited
2064 A @code{using} clause can access both the codes and the bindings
2068 (cl-loop for c being the key-codes of (current-local-map)
2069 using (key-bindings b)
2071 (message "key %S -> binding %S" c b))
2075 @item for @var{var} being the key-seqs of @var{keymap}
2076 This clause iterates over all key sequences defined by @var{keymap}
2077 and its nested keymaps, where @var{var} takes on values which are
2078 vectors. The strings or vectors
2079 are reused for each iteration, so you must copy them if you wish to keep
2080 them permanently. You can add a @samp{using (key-bindings @dots{})}
2081 clause to get the command bindings as well.
2083 @item for @var{var} being the overlays [of @var{buffer}] @dots{}
2084 This clause iterates over the ``overlays'' of a buffer
2085 (the clause @code{extents} is synonymous
2086 with @code{overlays}). If the @code{of} term is omitted, the current
2088 This clause also accepts optional @samp{from @var{pos}} and
2089 @samp{to @var{pos}} terms, limiting the clause to overlays which
2090 overlap the specified region.
2092 @item for @var{var} being the intervals [of @var{buffer}] @dots{}
2093 This clause iterates over all intervals of a buffer with constant
2094 text properties. The variable @var{var} will be bound to conses
2095 of start and end positions, where one start position is always equal
2096 to the previous end position. The clause allows @code{of},
2097 @code{from}, @code{to}, and @code{property} terms, where the latter
2098 term restricts the search to just the specified property. The
2099 @code{of} term may specify either a buffer or a string.
2101 @item for @var{var} being the frames
2102 This clause iterates over all Emacs frames. The clause @code{screens} is
2103 a synonym for @code{frames}. The frames are visited in
2104 @code{next-frame} order starting from @code{selected-frame}.
2106 @item for @var{var} being the windows [of @var{frame}]
2107 This clause iterates over the windows (in the Emacs sense) of
2108 the current frame, or of the specified @var{frame}. It visits windows
2109 in @code{next-window} order starting from @code{selected-window}
2110 (or @code{frame-selected-window} if you specify @var{frame}).
2111 This clause treats the minibuffer window in the same way as
2112 @code{next-window} does. For greater flexibility, consider using
2113 @code{walk-windows} instead.
2115 @item for @var{var} being the buffers
2116 This clause iterates over all buffers in Emacs. It is equivalent
2117 to @samp{for @var{var} in (buffer-list)}.
2119 @item for @var{var} = @var{expr1} then @var{expr2}
2120 This clause does a general iteration. The first time through
2121 the loop, @var{var} will be bound to @var{expr1}. On the second
2122 and successive iterations it will be set by evaluating @var{expr2}
2123 (which may refer to the old value of @var{var}). For example,
2124 these two loops are effectively the same:
2127 (cl-loop for x on my-list by 'cddr do @dots{})
2128 (cl-loop for x = my-list then (cddr x) while x do @dots{})
2131 Note that this type of @code{for} clause does not imply any sort
2132 of terminating condition; the above example combines it with a
2133 @code{while} clause to tell when to end the loop.
2135 If you omit the @code{then} term, @var{expr1} is used both for
2136 the initial setting and for successive settings:
2139 (cl-loop for x = (random) when (> x 0) return x)
2143 This loop keeps taking random numbers from the @code{(random)}
2144 function until it gets a positive one, which it then returns.
2147 If you include several @code{for} clauses in a row, they are
2148 treated sequentially (as if by @code{let*} and @code{setq}).
2149 You can instead use the word @code{and} to link the clauses,
2150 in which case they are processed in parallel (as if by @code{let}
2151 and @code{cl-psetq}).
2154 (cl-loop for x below 5 for y = nil then x collect (list x y))
2155 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4))
2156 (cl-loop for x below 5 and y = nil then x collect (list x y))
2157 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3))
2161 In the first loop, @code{y} is set based on the value of @code{x}
2162 that was just set by the previous clause; in the second loop,
2163 @code{x} and @code{y} are set simultaneously so @code{y} is set
2164 based on the value of @code{x} left over from the previous time
2167 @cindex destructuring, in cl-loop
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}.
2253 @item iter-by @var{iterator}
2254 This clause iterates over the values from the specified form, an
2255 iterator object. See (@pxref{Generators,,,elisp,GNU Emacs Lisp
2259 @node Accumulation Clauses
2260 @subsection Accumulation Clauses
2263 These clauses cause the loop to accumulate information about the
2264 specified Lisp @var{form}. The accumulated result is returned
2265 from the loop unless overridden, say, by a @code{return} clause.
2268 @item collect @var{form}
2269 This clause collects the values of @var{form} into a list. Several
2270 examples of @code{collect} appear elsewhere in this manual.
2272 The word @code{collecting} is a synonym for @code{collect}, and
2273 likewise for the other accumulation clauses.
2275 @item append @var{form}
2276 This clause collects lists of values into a result list using
2279 @item nconc @var{form}
2280 This clause collects lists of values into a result list by
2281 destructively modifying the lists rather than copying them.
2283 @item concat @var{form}
2284 This clause concatenates the values of the specified @var{form}
2285 into a string. (It and the following clause are extensions to
2286 standard Common Lisp.)
2288 @item vconcat @var{form}
2289 This clause concatenates the values of the specified @var{form}
2292 @item count @var{form}
2293 This clause counts the number of times the specified @var{form}
2294 evaluates to a non-@code{nil} value.
2296 @item sum @var{form}
2297 This clause accumulates the sum of the values of the specified
2298 @var{form}, which must evaluate to a number.
2300 @item maximize @var{form}
2301 This clause accumulates the maximum value of the specified @var{form},
2302 which must evaluate to a number. The return value is undefined if
2303 @code{maximize} is executed zero times.
2305 @item minimize @var{form}
2306 This clause accumulates the minimum value of the specified @var{form}.
2309 Accumulation clauses can be followed by @samp{into @var{var}} to
2310 cause the data to be collected into variable @var{var} (which is
2311 automatically @code{let}-bound during the loop) rather than an
2312 unnamed temporary variable. Also, @code{into} accumulations do
2313 not automatically imply a return value. The loop must use some
2314 explicit mechanism, such as @code{finally return}, to return
2315 the accumulated result.
2317 It is valid for several accumulation clauses of the same type to
2318 accumulate into the same place. From Steele:
2321 (cl-loop for name in '(fred sue alice joe june)
2322 for kids in '((bob ken) () () (kris sunshine) ())
2325 @result{} (fred bob ken sue alice joe kris sunshine june)
2329 @subsection Other Clauses
2332 This section describes the remaining loop clauses.
2335 @item with @var{var} = @var{value}
2336 This clause binds a variable to a value around the loop, but
2337 otherwise leaves the variable alone during the loop. The following
2338 loops are basically equivalent:
2341 (cl-loop with x = 17 do @dots{})
2342 (let ((x 17)) (cl-loop do @dots{}))
2343 (cl-loop for x = 17 then x do @dots{})
2346 Naturally, the variable @var{var} might be used for some purpose
2347 in the rest of the loop. For example:
2350 (cl-loop for x in my-list with res = nil do (push x res)
2354 This loop inserts the elements of @code{my-list} at the front of
2355 a new list being accumulated in @code{res}, then returns the
2356 list @code{res} at the end of the loop. The effect is similar
2357 to that of a @code{collect} clause, but the list gets reversed
2358 by virtue of the fact that elements are being pushed onto the
2359 front of @code{res} rather than the end.
2361 If you omit the @code{=} term, the variable is initialized to
2362 @code{nil}. (Thus the @samp{= nil} in the above example is
2365 Bindings made by @code{with} are sequential by default, as if
2366 by @code{let*}. Just like @code{for} clauses, @code{with} clauses
2367 can be linked with @code{and} to cause the bindings to be made by
2370 @item if @var{condition} @var{clause}
2371 This clause executes the following loop clause only if the specified
2372 condition is true. The following @var{clause} should be an accumulation,
2373 @code{do}, @code{return}, @code{if}, or @code{unless} clause.
2374 Several clauses may be linked by separating them with @code{and}.
2375 These clauses may be followed by @code{else} and a clause or clauses
2376 to execute if the condition was false. The whole construct may
2377 optionally be followed by the word @code{end} (which may be used to
2378 disambiguate an @code{else} or @code{and} in a nested @code{if}).
2380 The actual non-@code{nil} value of the condition form is available
2381 by the name @code{it} in the ``then'' part. For example:
2384 (setq funny-numbers '(6 13 -1))
2386 (cl-loop for x below 10
2389 and if (memq x funny-numbers) return (cdr it) end
2391 collect x into evens
2392 finally return (vector odds evens))
2393 @result{} [(1 3 5 7 9) (0 2 4 6 8)]
2394 (setq funny-numbers '(6 7 13 -1))
2395 @result{} (6 7 13 -1)
2396 (cl-loop <@r{same thing again}>)
2400 Note the use of @code{and} to put two clauses into the ``then''
2401 part, one of which is itself an @code{if} clause. Note also that
2402 @code{end}, while normally optional, was necessary here to make
2403 it clear that the @code{else} refers to the outermost @code{if}
2404 clause. In the first case, the loop returns a vector of lists
2405 of the odd and even values of @var{x}. In the second case, the
2406 odd number 7 is one of the @code{funny-numbers} so the loop
2407 returns early; the actual returned value is based on the result
2408 of the @code{memq} call.
2410 @item when @var{condition} @var{clause}
2411 This clause is just a synonym for @code{if}.
2413 @item unless @var{condition} @var{clause}
2414 The @code{unless} clause is just like @code{if} except that the
2415 sense of the condition is reversed.
2417 @item named @var{name}
2418 This clause gives a name other than @code{nil} to the implicit
2419 block surrounding the loop. The @var{name} is the symbol to be
2420 used as the block name.
2422 @item initially [do] @var{forms}@dots{}
2423 This keyword introduces one or more Lisp forms which will be
2424 executed before the loop itself begins (but after any variables
2425 requested by @code{for} or @code{with} have been bound to their
2426 initial values). @code{initially} clauses can appear anywhere;
2427 if there are several, they are executed in the order they appear
2428 in the loop. The keyword @code{do} is optional.
2430 @item finally [do] @var{forms}@dots{}
2431 This introduces Lisp forms which will be executed after the loop
2432 finishes (say, on request of a @code{for} or @code{while}).
2433 @code{initially} and @code{finally} clauses may appear anywhere
2434 in the loop construct, but they are executed (in the specified
2435 order) at the beginning or end, respectively, of the loop.
2437 @item finally return @var{form}
2438 This says that @var{form} should be executed after the loop
2439 is done to obtain a return value. (Without this, or some other
2440 clause like @code{collect} or @code{return}, the loop will simply
2441 return @code{nil}.) Variables bound by @code{for}, @code{with},
2442 or @code{into} will still contain their final values when @var{form}
2445 @item do @var{forms}@dots{}
2446 The word @code{do} may be followed by any number of Lisp expressions
2447 which are executed as an implicit @code{progn} in the body of the
2448 loop. Many of the examples in this section illustrate the use of
2451 @item return @var{form}
2452 This clause causes the loop to return immediately. The following
2453 Lisp form is evaluated to give the return value of the loop
2454 form. The @code{finally} clauses, if any, are not executed.
2455 Of course, @code{return} is generally used inside an @code{if} or
2456 @code{unless}, as its use in a top-level loop clause would mean
2457 the loop would never get to ``loop'' more than once.
2459 The clause @samp{return @var{form}} is equivalent to
2460 @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop
2461 was named). The @code{return} clause is implemented a bit more
2462 efficiently, though.
2465 While there is no high-level way to add user extensions to @code{cl-loop},
2466 this package does offer two properties called @code{cl-loop-handler}
2467 and @code{cl-loop-for-handler} which are functions to be called when a
2468 given symbol is encountered as a top-level loop clause or @code{for}
2469 clause, respectively. Consult the source code in file
2470 @file{cl-macs.el} for details.
2472 This package's @code{cl-loop} macro is compatible with that of Common
2473 Lisp, except that a few features are not implemented: @code{loop-finish}
2474 and data-type specifiers. Naturally, the @code{for} clauses that
2475 iterate over keymaps, overlays, intervals, frames, windows, and
2476 buffers are Emacs-specific extensions.
2478 @node Multiple Values
2479 @section Multiple Values
2482 Common Lisp functions can return zero or more results. Emacs Lisp
2483 functions, by contrast, always return exactly one result. This
2484 package makes no attempt to emulate Common Lisp multiple return
2485 values; Emacs versions of Common Lisp functions that return more
2486 than one value either return just the first value (as in
2487 @code{cl-compiler-macroexpand}) or return a list of values.
2488 This package @emph{does} define placeholders
2489 for the Common Lisp functions that work with multiple values, but
2490 in Emacs Lisp these functions simply operate on lists instead.
2491 The @code{cl-values} form, for example, is a synonym for @code{list}
2494 @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{}
2495 This form evaluates @var{values-form}, which must return a list of
2496 values. It then binds the @var{var}s to these respective values,
2497 as if by @code{let}, and then executes the body @var{forms}.
2498 If there are more @var{var}s than values, the extra @var{var}s
2499 are bound to @code{nil}. If there are fewer @var{var}s than
2500 values, the excess values are ignored.
2503 @defmac cl-multiple-value-setq (var@dots{}) form
2504 This form evaluates @var{form}, which must return a list of values.
2505 It then sets the @var{var}s to these respective values, as if by
2506 @code{setq}. Extra @var{var}s or values are treated the same as
2507 in @code{cl-multiple-value-bind}.
2510 Since a perfect emulation is not feasible in Emacs Lisp, this
2511 package opts to keep it as simple and predictable as possible.
2517 This package implements the various Common Lisp features of
2518 @code{defmacro}, such as destructuring, @code{&environment},
2519 and @code{&body}. Top-level @code{&whole} is not implemented
2520 for @code{defmacro} due to technical difficulties.
2521 @xref{Argument Lists}.
2523 Destructuring is made available to the user by way of the
2526 @defmac cl-destructuring-bind arglist expr forms@dots{}
2527 This macro expands to code that executes @var{forms}, with
2528 the variables in @var{arglist} bound to the list of values
2529 returned by @var{expr}. The @var{arglist} can include all
2530 the features allowed for @code{cl-defmacro} argument lists,
2531 including destructuring. (The @code{&environment} keyword
2532 is not allowed.) The macro expansion will signal an error
2533 if @var{expr} returns a list of the wrong number of arguments
2534 or with incorrect keyword arguments.
2537 @cindex compiler macros
2538 @cindex define compiler macros
2539 This package also includes the Common Lisp @code{define-compiler-macro}
2540 facility, which allows you to define compile-time expansions and
2541 optimizations for your functions.
2543 @defmac cl-define-compiler-macro name arglist forms@dots{}
2544 This form is similar to @code{defmacro}, except that it only expands
2545 calls to @var{name} at compile-time; calls processed by the Lisp
2546 interpreter are not expanded, nor are they expanded by the
2547 @code{macroexpand} function.
2549 The argument list may begin with a @code{&whole} keyword and a
2550 variable. This variable is bound to the macro-call form itself,
2551 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}.
2552 If the macro expander returns this form unchanged, then the
2553 compiler treats it as a normal function call. This allows
2554 compiler macros to work as optimizers for special cases of a
2555 function, leaving complicated cases alone.
2557 For example, here is a simplified version of a definition that
2558 appears as a standard part of this package:
2561 (cl-define-compiler-macro cl-member (&whole form a list &rest keys)
2562 (if (and (null keys)
2563 (eq (car-safe a) 'quote)
2564 (not (floatp (cadr a))))
2570 This definition causes @code{(cl-member @var{a} @var{list})} to change
2571 to a call to the faster @code{memq} in the common case where @var{a}
2572 is a non-floating-point constant; if @var{a} is anything else, or
2573 if there are any keyword arguments in the call, then the original
2574 @code{cl-member} call is left intact. (The actual compiler macro
2575 for @code{cl-member} optimizes a number of other cases, including
2576 common @code{:test} predicates.)
2579 @defun cl-compiler-macroexpand form
2580 This function is analogous to @code{macroexpand}, except that it
2581 expands compiler macros rather than regular macros. It returns
2582 @var{form} unchanged if it is not a call to a function for which
2583 a compiler macro has been defined, or if that compiler macro
2584 decided to punt by returning its @code{&whole} argument. Like
2585 @code{macroexpand}, it expands repeatedly until it reaches a form
2586 for which no further expansion is possible.
2589 @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet}
2590 and @code{cl-symbol-macrolet} forms for making ``local'' macro
2594 @chapter Declarations
2597 Common Lisp includes a complex and powerful ``declaration''
2598 mechanism that allows you to give the compiler special hints
2599 about the types of data that will be stored in particular variables,
2600 and about the ways those variables and functions will be used. This
2601 package defines versions of all the Common Lisp declaration forms:
2602 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim},
2605 Most of the Common Lisp declarations are not currently useful in Emacs
2606 Lisp. For example, the byte-code system provides little
2607 opportunity to benefit from type information.
2609 and @code{special} declarations are redundant in a fully
2610 dynamically-scoped Lisp.
2612 A few declarations are meaningful when byte compiler optimizations
2613 are enabled, as they are by the default. Otherwise these
2614 declarations will effectively be ignored.
2616 @defun cl-proclaim decl-spec
2617 This function records a ``global'' declaration specified by
2618 @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec}
2619 is evaluated and thus should normally be quoted.
2622 @defmac cl-declaim decl-specs@dots{}
2623 This macro is like @code{cl-proclaim}, except that it takes any number
2624 of @var{decl-spec} arguments, and the arguments are unevaluated and
2625 unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when
2626 (compile load eval) @dots{})} around the declarations so that they will
2627 be registered at compile-time as well as at run-time. (This is vital,
2628 since normally the declarations are meant to influence the way the
2629 compiler treats the rest of the file that contains the @code{cl-declaim}
2633 @defmac cl-declare decl-specs@dots{}
2634 This macro is used to make declarations within functions and other
2635 code. Common Lisp allows declarations in various locations, generally
2636 at the beginning of any of the many ``implicit @code{progn}s''
2637 throughout Lisp syntax, such as function bodies, @code{let} bodies,
2638 etc. Currently the only declaration understood by @code{cl-declare}
2642 @defmac cl-locally declarations@dots{} forms@dots{}
2643 In this package, @code{cl-locally} is no different from @code{progn}.
2646 @defmac cl-the type form
2647 @code{cl-the} returns the value of @code{form}, first checking (if
2648 optimization settings permit) that it is of type @code{type}. Future
2649 byte-compiler optimizations may also make use of this information to
2650 improve runtime efficiency.
2652 For example, @code{mapcar} can map over both lists and arrays. It is
2653 hard for the compiler to expand @code{mapcar} into an in-line loop
2654 unless it knows whether the sequence will be a list or an array ahead
2655 of time. With @code{(mapcar 'car (cl-the vector foo))}, a future
2656 compiler would have enough information to expand the loop in-line.
2657 For now, Emacs Lisp will treat the above code as exactly equivalent
2658 to @code{(mapcar 'car foo)}.
2661 Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or
2662 @code{cl-declare} should be a list beginning with a symbol that says
2663 what kind of declaration it is. This package currently understands
2664 @code{special}, @code{inline}, @code{notinline}, @code{optimize},
2665 and @code{warn} declarations. (The @code{warn} declaration is an
2666 extension of standard Common Lisp.) Other Common Lisp declarations,
2667 such as @code{type} and @code{ftype}, are silently ignored.
2672 Since all variables in Emacs Lisp are ``special'' (in the Common
2673 Lisp sense), @code{special} declarations are only advisory. They
2674 simply tell the byte compiler that the specified
2675 variables are intentionally being referred to without being
2676 bound in the body of the function. The compiler normally emits
2677 warnings for such references, since they could be typographical
2678 errors for references to local variables.
2680 The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is
2681 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}.
2683 In top-level contexts, it is generally better to write
2684 @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))},
2685 since @code{defvar} makes your intentions clearer.
2688 The @code{inline} @var{decl-spec} lists one or more functions
2689 whose bodies should be expanded ``in-line'' into calling functions
2690 whenever the compiler is able to arrange for it. For example,
2691 the function @code{cl-acons} is declared @code{inline}
2692 by this package so that the form @code{(cl-acons @var{key} @var{value}
2694 expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})}
2695 when it is called in user functions, so as to save function calls.
2697 The following declarations are all equivalent. Note that the
2698 @code{defsubst} form is a convenient way to define a function
2699 and declare it inline all at once.
2702 (cl-declaim (inline foo bar))
2703 (cl-eval-when (compile load eval)
2704 (cl-proclaim '(inline foo bar)))
2705 (defsubst foo (@dots{}) @dots{}) ; instead of defun
2708 @strong{Please note:} this declaration remains in effect after the
2709 containing source file is done. It is correct to use it to
2710 request that a function you have defined should be inlined,
2711 but it is impolite to use it to request inlining of an external
2714 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))}
2715 before a particular call to a function to cause just that call to
2716 be inlined; the current byte compilers provide no way to implement
2717 this, so @code{(cl-declare (inline @dots{}))} is currently ignored by
2721 The @code{notinline} declaration lists functions which should
2722 not be inlined after all; it cancels a previous @code{inline}
2726 This declaration controls how much optimization is performed by
2729 The word @code{optimize} is followed by any number of lists like
2730 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several
2731 optimization ``qualities''; this package ignores all but @code{speed}
2732 and @code{safety}. The value of a quality should be an integer from
2733 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''.
2734 The default level for both qualities is 1.
2736 In this package, the @code{speed} quality is tied to the @code{byte-optimize}
2737 flag, which is set to @code{nil} for @code{(speed 0)} and to
2738 @code{t} for higher settings; and the @code{safety} quality is
2739 tied to the @code{byte-compile-delete-errors} flag, which is
2740 set to @code{nil} for @code{(safety 3)} and to @code{t} for all
2741 lower settings. (The latter flag controls whether the compiler
2742 is allowed to optimize out code whose only side-effect could
2743 be to signal an error, e.g., rewriting @code{(progn foo bar)} to
2744 @code{bar} when it is not known whether @code{foo} will be bound
2747 Note that even compiling with @code{(safety 0)}, the Emacs
2748 byte-code system provides sufficient checking to prevent real
2749 harm from being done. For example, barring serious bugs in
2750 Emacs itself, Emacs will not crash with a segmentation fault
2751 just because of an error in a fully-optimized Lisp program.
2753 The @code{optimize} declaration is normally used in a top-level
2754 @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows
2755 it to be used with @code{declare} to set the level of optimization
2756 locally for a given form, but this will not work correctly with the
2757 current byte-compiler. (The @code{cl-declare}
2758 will set the new optimization level, but that level will not
2759 automatically be unset after the enclosing form is done.)
2762 This declaration controls what sorts of warnings are generated
2763 by the byte compiler. The word @code{warn} is followed by any
2764 number of ``warning qualities'', similar in form to optimization
2765 qualities. The currently supported warning types are
2766 @code{redefine}, @code{callargs}, @code{unresolved}, and
2767 @code{free-vars}; in the current system, a value of 0 will
2768 disable these warnings and any higher value will enable them.
2769 See the documentation of the variable @code{byte-compile-warnings}
2777 This package defines several symbol-related features that were
2778 missing from Emacs Lisp.
2781 * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}.
2782 * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}.
2785 @node Property Lists
2786 @section Property Lists
2789 These functions augment the standard Emacs Lisp functions @code{get}
2790 and @code{put} for operating on properties attached to symbols.
2791 There are also functions for working with property lists as
2792 first-class data structures not attached to particular symbols.
2794 @defun cl-get symbol property &optional default
2795 This function is like @code{get}, except that if the property is
2796 not found, the @var{default} argument provides the return value.
2797 (The Emacs Lisp @code{get} function always uses @code{nil} as
2798 the default; this package's @code{cl-get} is equivalent to Common
2801 The @code{cl-get} function is @code{setf}-able; when used in this
2802 fashion, the @var{default} argument is allowed but ignored.
2805 @defun cl-remprop symbol property
2806 This function removes the entry for @var{property} from the property
2807 list of @var{symbol}. It returns a true value if the property was
2808 indeed found and removed, or @code{nil} if there was no such property.
2809 (This function was probably omitted from Emacs originally because,
2810 since @code{get} did not allow a @var{default}, it was very difficult
2811 to distinguish between a missing property and a property whose value
2812 was @code{nil}; thus, setting a property to @code{nil} was close
2813 enough to @code{cl-remprop} for most purposes.)
2816 @defun cl-getf place property &optional default
2817 This function scans the list @var{place} as if it were a property
2818 list, i.e., a list of alternating property names and values. If
2819 an even-numbered element of @var{place} is found which is @code{eq}
2820 to @var{property}, the following odd-numbered element is returned.
2821 Otherwise, @var{default} is returned (or @code{nil} if no default
2827 (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop)
2830 It is valid to use @code{cl-getf} as a @code{setf} place, in which case
2831 its @var{place} argument must itself be a valid @code{setf} place.
2832 The @var{default} argument, if any, is ignored in this context.
2833 The effect is to change (via @code{setcar}) the value cell in the
2834 list that corresponds to @var{property}, or to cons a new property-value
2835 pair onto the list if the property is not yet present.
2838 (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val)
2841 The @code{get} and @code{cl-get} functions are also @code{setf}-able.
2842 The fact that @code{default} is ignored can sometimes be useful:
2845 (cl-incf (cl-get 'foo 'usage-count 0))
2848 Here, symbol @code{foo}'s @code{usage-count} property is incremented
2849 if it exists, or set to 1 (an incremented 0) otherwise.
2851 When not used as a @code{setf} form, @code{cl-getf} is just a regular
2852 function and its @var{place} argument can actually be any Lisp
2856 @defmac cl-remf place property
2857 This macro removes the property-value pair for @var{property} from
2858 the property list stored at @var{place}, which is any @code{setf}-able
2859 place expression. It returns true if the property was found. Note
2860 that if @var{property} happens to be first on the list, this will
2861 effectively do a @code{(setf @var{place} (cddr @var{place}))},
2862 whereas if it occurs later, this simply uses @code{setcdr} to splice
2863 out the property and value cells.
2866 @node Creating Symbols
2867 @section Creating Symbols
2870 These functions create unique symbols, typically for use as
2871 temporary variables.
2873 @defun cl-gensym &optional x
2874 This function creates a new, uninterned symbol (using @code{make-symbol})
2875 with a unique name. (The name of an uninterned symbol is relevant
2876 only if the symbol is printed.) By default, the name is generated
2877 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001},
2878 @samp{G1002}, etc. If the optional argument @var{x} is a string, that
2879 string is used as a prefix instead of @samp{G}. Uninterned symbols
2880 are used in macro expansions for temporary variables, to ensure that
2881 their names will not conflict with ``real'' variables in the user's
2884 (Internally, the variable @code{cl--gensym-counter} holds the counter
2885 used to generate names. It is initialized with zero and incremented
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.
2943 @defun cl-digit-char-p char radix
2944 Test if @var{char} is a digit in the specified @var{radix} (default is
2945 10). If it is, return the numerical value of digit @var{char} in
2949 @node Numerical Functions
2950 @section Numerical Functions
2953 These functions perform various arithmetic operations on numbers.
2955 @defun cl-gcd &rest integers
2956 This function returns the Greatest Common Divisor of the arguments.
2957 For one argument, it returns the absolute value of that argument.
2958 For zero arguments, it returns zero.
2961 @defun cl-lcm &rest integers
2962 This function returns the Least Common Multiple of the arguments.
2963 For one argument, it returns the absolute value of that argument.
2964 For zero arguments, it returns one.
2967 @defun cl-isqrt integer
2968 This function computes the ``integer square root'' of its integer
2969 argument, i.e., the greatest integer less than or equal to the true
2970 square root of the argument.
2973 @defun cl-floor number &optional divisor
2974 With one argument, @code{cl-floor} returns a list of two numbers:
2975 The argument rounded down (toward minus infinity) to an integer,
2976 and the ``remainder'' which would have to be added back to the
2977 first return value to yield the argument again. If the argument
2978 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}.
2979 If the argument is a floating-point number, the first
2980 result is a Lisp integer and the second is a Lisp float between
2981 0 (inclusive) and 1 (exclusive).
2983 With two arguments, @code{cl-floor} divides @var{number} by
2984 @var{divisor}, and returns the floor of the quotient and the
2985 corresponding remainder as a list of two numbers. If
2986 @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})},
2987 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r}
2988 between 0 (inclusive) and @var{r} (exclusive). Also, note
2989 that @code{(cl-floor @var{x})} is exactly equivalent to
2990 @code{(cl-floor @var{x} 1)}.
2992 This function is entirely compatible with Common Lisp's @code{floor}
2993 function, except that it returns the two results in a list since
2994 Emacs Lisp does not support multiple-valued functions.
2997 @defun cl-ceiling number &optional divisor
2998 This function implements the Common Lisp @code{ceiling} function,
2999 which is analogous to @code{floor} except that it rounds the
3000 argument or quotient of the arguments up toward plus infinity.
3001 The remainder will be between 0 and minus @var{r}.
3004 @defun cl-truncate number &optional divisor
3005 This function implements the Common Lisp @code{truncate} function,
3006 which is analogous to @code{floor} except that it rounds the
3007 argument or quotient of the arguments toward zero. Thus it is
3008 equivalent to @code{cl-floor} if the argument or quotient is
3009 positive, or to @code{cl-ceiling} otherwise. The remainder has
3010 the same sign as @var{number}.
3013 @defun cl-round number &optional divisor
3014 This function implements the Common Lisp @code{round} function,
3015 which is analogous to @code{floor} except that it rounds the
3016 argument or quotient of the arguments to the nearest integer.
3017 In the case of a tie (the argument or quotient is exactly
3018 halfway between two integers), it rounds to the even integer.
3021 @defun cl-mod number divisor
3022 This function returns the same value as the second return value
3026 @defun cl-rem number divisor
3027 This function returns the same value as the second return value
3028 of @code{cl-truncate}.
3031 @defun cl-parse-integer string &key start end radix junk-allowed
3032 This function implements the Common Lisp @code{parse-integer}
3033 function. It parses an integer in the specified @var{radix} from the
3034 substring of @var{string} between @var{start} and @var{end}. Any
3035 leading and trailing whitespace chars are ignored. The function
3036 signals an error if the substring between @var{start} and @var{end}
3037 cannot be parsed as an integer, unless @var{junk-allowed} is
3041 @node Random Numbers
3042 @section Random Numbers
3045 This package also provides an implementation of the Common Lisp
3046 random number generator. It uses its own additive-congruential
3047 algorithm, which is much more likely to give statistically clean
3048 @c FIXME? Still true?
3049 random numbers than the simple generators supplied by many
3052 @defun cl-random number &optional state
3053 This function returns a random nonnegative number less than
3054 @var{number}, and of the same type (either integer or floating-point).
3055 The @var{state} argument should be a @code{random-state} object
3056 that holds the state of the random number generator. The
3057 function modifies this state object as a side effect. If
3058 @var{state} is omitted, it defaults to the internal variable
3059 @code{cl--random-state}, which contains a pre-initialized
3060 default @code{random-state} object. (Since any number of programs in
3061 the Emacs process may be accessing @code{cl--random-state} in
3062 interleaved fashion, the sequence generated from this will be
3063 irreproducible for all intents and purposes.)
3066 @defun cl-make-random-state &optional state
3067 This function creates or copies a @code{random-state} object.
3068 If @var{state} is omitted or @code{nil}, it returns a new copy of
3069 @code{cl--random-state}. This is a copy in the sense that future
3070 sequences of calls to @code{(cl-random @var{n})} and
3071 @code{(cl-random @var{n} @var{s})} (where @var{s} is the new
3072 random-state object) will return identical sequences of random
3075 If @var{state} is a @code{random-state} object, this function
3076 returns a copy of that object. If @var{state} is @code{t}, this
3077 function returns a new @code{random-state} object seeded from the
3078 date and time. As an extension to Common Lisp, @var{state} may also
3079 be an integer in which case the new object is seeded from that
3080 integer; each different integer seed will result in a completely
3081 different sequence of random numbers.
3083 It is valid to print a @code{random-state} object to a buffer or
3084 file and later read it back with @code{read}. If a program wishes
3085 to use a sequence of pseudo-random numbers which can be reproduced
3086 later for debugging, it can call @code{(cl-make-random-state t)} to
3087 get a new sequence, then print this sequence to a file. When the
3088 program is later rerun, it can read the original run's random-state
3092 @defun cl-random-state-p object
3093 This predicate returns @code{t} if @var{object} is a
3094 @code{random-state} object, or @code{nil} otherwise.
3097 @node Implementation Parameters
3098 @section Implementation Parameters
3101 This package defines several useful constants having to do with
3102 floating-point numbers.
3104 It determines their values by exercising the computer's
3105 floating-point arithmetic in various ways. Because this operation
3106 might be slow, the code for initializing them is kept in a separate
3107 function that must be called before the parameters can be used.
3109 @defun cl-float-limits
3110 This function makes sure that the Common Lisp floating-point parameters
3111 like @code{cl-most-positive-float} have been initialized. Until it is
3112 called, these parameters will be @code{nil}.
3113 @c If this version of Emacs does not support floats, the parameters will
3114 @c remain @code{nil}.
3115 If the parameters have already been initialized, the function returns
3118 The algorithm makes assumptions that will be valid for almost all
3119 machines, but will fail if the machine's arithmetic is extremely
3120 unusual, e.g., decimal.
3123 Since true Common Lisp supports up to four different floating-point
3124 precisions, it has families of constants like
3125 @code{most-positive-single-float}, @code{most-positive-double-float},
3126 @code{most-positive-long-float}, and so on. Emacs has only one
3127 floating-point precision, so this package omits the precision word
3128 from the constants' names.
3130 @defvar cl-most-positive-float
3131 This constant equals the largest value a Lisp float can hold.
3132 For those systems whose arithmetic supports infinities, this is
3133 the largest @emph{finite} value. For IEEE machines, the value
3134 is approximately @code{1.79e+308}.
3137 @defvar cl-most-negative-float
3138 This constant equals the most negative value a Lisp float can hold.
3139 (It is assumed to be equal to @code{(- cl-most-positive-float)}.)
3142 @defvar cl-least-positive-float
3143 This constant equals the smallest Lisp float value greater than zero.
3144 For IEEE machines, it is about @code{4.94e-324} if denormals are
3145 supported or @code{2.22e-308} if not.
3148 @defvar cl-least-positive-normalized-float
3149 This constant equals the smallest @emph{normalized} Lisp float greater
3150 than zero, i.e., the smallest value for which IEEE denormalization
3151 will not result in a loss of precision. For IEEE machines, this
3152 value is about @code{2.22e-308}. For machines that do not support
3153 the concept of denormalization and gradual underflow, this constant
3154 will always equal @code{cl-least-positive-float}.
3157 @defvar cl-least-negative-float
3158 This constant is the negative counterpart of @code{cl-least-positive-float}.
3161 @defvar cl-least-negative-normalized-float
3162 This constant is the negative counterpart of
3163 @code{cl-least-positive-normalized-float}.
3166 @defvar cl-float-epsilon
3167 This constant is the smallest positive Lisp float that can be added
3168 to 1.0 to produce a distinct value. Adding a smaller number to 1.0
3169 will yield 1.0 again due to roundoff. For IEEE machines, epsilon
3170 is about @code{2.22e-16}.
3173 @defvar cl-float-negative-epsilon
3174 This is the smallest positive value that can be subtracted from
3175 1.0 to produce a distinct value. For IEEE machines, it is about
3183 Common Lisp defines a number of functions that operate on
3184 @dfn{sequences}, which are either lists, strings, or vectors.
3185 Emacs Lisp includes a few of these, notably @code{elt} and
3186 @code{length}; this package defines most of the rest.
3189 * Sequence Basics:: Arguments shared by all sequence functions.
3190 * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc.
3191 * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc.
3192 * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc.
3193 * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}.
3196 @node Sequence Basics
3197 @section Sequence Basics
3200 Many of the sequence functions take keyword arguments; @pxref{Argument
3201 Lists}. All keyword arguments are optional and, if specified,
3202 may appear in any order.
3204 The @code{:key} argument should be passed either @code{nil}, or a
3205 function of one argument. This key function is used as a filter
3206 through which the elements of the sequence are seen; for example,
3207 @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}.
3208 It searches for an element of the list whose @sc{car} equals
3209 @code{x}, rather than for an element which equals @code{x} itself.
3210 If @code{:key} is omitted or @code{nil}, the filter is effectively
3211 the identity function.
3213 The @code{:test} and @code{:test-not} arguments should be either
3214 @code{nil}, or functions of two arguments. The test function is
3215 used to compare two sequence elements, or to compare a search value
3216 with sequence elements. (The two values are passed to the test
3217 function in the same order as the original sequence function
3218 arguments from which they are derived, or, if they both come from
3219 the same sequence, in the same order as they appear in that sequence.)
3220 The @code{:test} argument specifies a function which must return
3221 true (non-@code{nil}) to indicate a match; instead, you may use
3222 @code{:test-not} to give a function which returns @emph{false} to
3223 indicate a match. The default test function is @code{eql}.
3225 Many functions that take @var{item} and @code{:test} or @code{:test-not}
3226 arguments also come in @code{-if} and @code{-if-not} varieties,
3227 where a @var{predicate} function is passed instead of @var{item},
3228 and sequence elements match if the predicate returns true on them
3229 (or false in the case of @code{-if-not}). For example:
3232 (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq)
3236 to remove all zeros from sequence @code{seq}.
3238 Some operations can work on a subsequence of the argument sequence;
3239 these function take @code{:start} and @code{:end} arguments, which
3240 default to zero and the length of the sequence, respectively.
3241 Only elements between @var{start} (inclusive) and @var{end}
3242 (exclusive) are affected by the operation. The @var{end} argument
3243 may be passed @code{nil} to signify the length of the sequence;
3244 otherwise, both @var{start} and @var{end} must be integers, with
3245 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}.
3246 If the function takes two sequence arguments, the limits are
3247 defined by keywords @code{:start1} and @code{:end1} for the first,
3248 and @code{:start2} and @code{:end2} for the second.
3250 A few functions accept a @code{:from-end} argument, which, if
3251 non-@code{nil}, causes the operation to go from right-to-left
3252 through the sequence instead of left-to-right, and a @code{:count}
3253 argument, which specifies an integer maximum number of elements
3254 to be removed or otherwise processed.
3256 The sequence functions make no guarantees about the order in
3257 which the @code{:test}, @code{:test-not}, and @code{:key} functions
3258 are called on various elements. Therefore, it is a bad idea to depend
3259 on side effects of these functions. For example, @code{:from-end}
3260 may cause the sequence to be scanned actually in reverse, or it may
3261 be scanned forwards but computing a result ``as if'' it were scanned
3262 backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every},
3263 @emph{do} specify exactly the order in which the function is called
3264 so side effects are perfectly acceptable in those cases.)
3266 Strings may contain ``text properties'' as well
3267 as character data. Except as noted, it is undefined whether or
3268 not text properties are preserved by sequence functions. For
3269 example, @code{(cl-remove ?A @var{str})} may or may not preserve
3270 the properties of the characters copied from @var{str} into the
3273 @node Mapping over Sequences
3274 @section Mapping over Sequences
3277 These functions ``map'' the function you specify over the elements
3278 of lists or arrays. They are all variations on the theme of the
3279 built-in function @code{mapcar}.
3281 @defun cl-mapcar function seq &rest more-seqs
3282 This function calls @var{function} on successive parallel sets of
3283 elements from its argument sequences. Given a single @var{seq}
3284 argument it is equivalent to @code{mapcar}; given @var{n} sequences,
3285 it calls the function with the first elements of each of the sequences
3286 as the @var{n} arguments to yield the first element of the result
3287 list, then with the second elements, and so on. The mapping stops as
3288 soon as the shortest sequence runs out. The argument sequences may
3289 be any mixture of lists, strings, and vectors; the return sequence
3292 Common Lisp's @code{mapcar} accepts multiple arguments but works
3293 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence
3294 argument. This package's @code{cl-mapcar} works as a compatible
3298 @defun cl-map result-type function seq &rest more-seqs
3299 This function maps @var{function} over the argument sequences,
3300 just like @code{cl-mapcar}, but it returns a sequence of type
3301 @var{result-type} rather than a list. @var{result-type} must
3302 be one of the following symbols: @code{vector}, @code{string},
3303 @code{list} (in which case the effect is the same as for
3304 @code{cl-mapcar}), or @code{nil} (in which case the results are
3305 thrown away and @code{cl-map} returns @code{nil}).
3308 @defun cl-maplist function list &rest more-lists
3309 This function calls @var{function} on each of its argument lists,
3310 then on the @sc{cdr}s of those lists, and so on, until the
3311 shortest list runs out. The results are returned in the form
3312 of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except
3313 that it passes in the list pointers themselves rather than the
3314 @sc{car}s of the advancing pointers.
3317 @defun cl-mapc function seq &rest more-seqs
3318 This function is like @code{cl-mapcar}, except that the values returned
3319 by @var{function} are ignored and thrown away rather than being
3320 collected into a list. The return value of @code{cl-mapc} is @var{seq},
3321 the first sequence. This function is more general than the Emacs
3322 primitive @code{mapc}. (Note that this function is called
3323 @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you
3325 @c http://debbugs.gnu.org/6575
3328 @defun cl-mapl function list &rest more-lists
3329 This function is like @code{cl-maplist}, except that it throws away
3330 the values returned by @var{function}.
3333 @defun cl-mapcan function seq &rest more-seqs
3334 This function is like @code{cl-mapcar}, except that it concatenates
3335 the return values (which must be lists) using @code{nconc},
3336 rather than simply collecting them into a list.
3339 @defun cl-mapcon function list &rest more-lists
3340 This function is like @code{cl-maplist}, except that it concatenates
3341 the return values using @code{nconc}.
3344 @defun cl-some predicate seq &rest more-seqs
3345 This function calls @var{predicate} on each element of @var{seq}
3346 in turn; if @var{predicate} returns a non-@code{nil} value,
3347 @code{cl-some} returns that value, otherwise it returns @code{nil}.
3348 Given several sequence arguments, it steps through the sequences
3349 in parallel until the shortest one runs out, just as in
3350 @code{cl-mapcar}. You can rely on the left-to-right order in which
3351 the elements are visited, and on the fact that mapping stops
3352 immediately as soon as @var{predicate} returns non-@code{nil}.
3355 @defun cl-every predicate seq &rest more-seqs
3356 This function calls @var{predicate} on each element of the sequence(s)
3357 in turn; it returns @code{nil} as soon as @var{predicate} returns
3358 @code{nil} for any element, or @code{t} if the predicate was true
3362 @defun cl-notany predicate seq &rest more-seqs
3363 This function calls @var{predicate} on each element of the sequence(s)
3364 in turn; it returns @code{nil} as soon as @var{predicate} returns
3365 a non-@code{nil} value for any element, or @code{t} if the predicate
3366 was @code{nil} for all elements.
3369 @defun cl-notevery predicate seq &rest more-seqs
3370 This function calls @var{predicate} on each element of the sequence(s)
3371 in turn; it returns a non-@code{nil} value as soon as @var{predicate}
3372 returns @code{nil} for any element, or @code{nil} if the predicate was
3373 true for all elements.
3376 @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key}
3377 This function combines the elements of @var{seq} using an associative
3378 binary operation. Suppose @var{function} is @code{*} and @var{seq} is
3379 the list @code{(2 3 4 5)}. The first two elements of the list are
3380 combined with @code{(* 2 3) = 6}; this is combined with the next
3381 element, @code{(* 6 4) = 24}, and that is combined with the final
3382 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens
3383 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as
3384 an explicit call to @code{cl-reduce}.
3386 If @code{:from-end} is true, the reduction is right-associative instead
3387 of left-associative:
3390 (cl-reduce '- '(1 2 3 4))
3391 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8
3392 (cl-reduce '- '(1 2 3 4) :from-end t)
3393 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2
3396 If @code{:key} is specified, it is a function of one argument, which
3397 is called on each of the sequence elements in turn.
3399 If @code{:initial-value} is specified, it is effectively added to the
3400 front (or rear in the case of @code{:from-end}) of the sequence.
3401 The @code{:key} function is @emph{not} applied to the initial value.
3403 If the sequence, including the initial value, has exactly one element
3404 then that element is returned without ever calling @var{function}.
3405 If the sequence is empty (and there is no initial value), then
3406 @var{function} is called with no arguments to obtain the return value.
3409 All of these mapping operations can be expressed conveniently in
3410 terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will
3411 be faster since it generates the loop as in-line code with no
3414 @node Sequence Functions
3415 @section Sequence Functions
3418 This section describes a number of Common Lisp functions for
3419 operating on sequences.
3421 @defun cl-subseq sequence start &optional end
3422 This function returns a given subsequence of the argument
3423 @var{sequence}, which may be a list, string, or vector.
3424 The indices @var{start} and @var{end} must be in range, and
3425 @var{start} must be no greater than @var{end}. If @var{end}
3426 is omitted, it defaults to the length of the sequence. The
3427 return value is always a copy; it does not share structure
3428 with @var{sequence}.
3430 As an extension to Common Lisp, @var{start} and/or @var{end}
3431 may be negative, in which case they represent a distance back
3432 from the end of the sequence. This is for compatibility with
3433 Emacs's @code{substring} function. Note that @code{cl-subseq} is
3434 the @emph{only} sequence function that allows negative
3435 @var{start} and @var{end}.
3437 You can use @code{setf} on a @code{cl-subseq} form to replace a
3438 specified range of elements with elements from another sequence.
3439 The replacement is done as if by @code{cl-replace}, described below.
3442 @defun cl-concatenate result-type &rest seqs
3443 This function concatenates the argument sequences together to
3444 form a result sequence of type @var{result-type}, one of the
3445 symbols @code{vector}, @code{string}, or @code{list}. The
3446 arguments are always copied, even in cases such as
3447 @code{(cl-concatenate 'list '(1 2 3))} where the result is
3448 identical to an argument.
3451 @defun cl-fill seq item @t{&key :start :end}
3452 This function fills the elements of the sequence (or the specified
3453 part of the sequence) with the value @var{item}.
3456 @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2}
3457 This function copies part of @var{seq2} into part of @var{seq1}.
3458 The sequence @var{seq1} is not stretched or resized; the amount
3459 of data copied is simply the shorter of the source and destination
3460 (sub)sequences. The function returns @var{seq1}.
3462 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement
3463 will work correctly even if the regions indicated by the start
3464 and end arguments overlap. However, if @var{seq1} and @var{seq2}
3465 are lists that share storage but are not @code{eq}, and the
3466 start and end arguments specify overlapping regions, the effect
3470 @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end}
3471 This returns a copy of @var{seq} with all elements matching
3472 @var{item} removed. The result may share storage with or be
3473 @code{eq} to @var{seq} in some circumstances, but the original
3474 @var{seq} will not be modified. The @code{:test}, @code{:test-not},
3475 and @code{:key} arguments define the matching test that is used;
3476 by default, elements @code{eql} to @var{item} are removed. The
3477 @code{:count} argument specifies the maximum number of matching
3478 elements that can be removed (only the leftmost @var{count} matches
3479 are removed). The @code{:start} and @code{:end} arguments specify
3480 a region in @var{seq} in which elements will be removed; elements
3481 outside that region are not matched or removed. The @code{:from-end}
3482 argument, if true, says that elements should be deleted from the
3483 end of the sequence rather than the beginning (this matters only
3484 if @var{count} was also specified).
3487 @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end}
3488 This deletes all elements of @var{seq} that match @var{item}.
3489 It is a destructive operation. Since Emacs Lisp does not support
3490 stretchable strings or vectors, this is the same as @code{cl-remove}
3491 for those sequence types. On lists, @code{cl-remove} will copy the
3492 list if necessary to preserve the original list, whereas
3493 @code{cl-delete} will splice out parts of the argument list.
3494 Compare @code{append} and @code{nconc}, which are analogous
3495 non-destructive and destructive list operations in Emacs Lisp.
3498 @findex cl-remove-if
3499 @findex cl-remove-if-not
3500 @findex cl-delete-if
3501 @findex cl-delete-if-not
3502 The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not},
3503 @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly.
3505 @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3506 This function returns a copy of @var{seq} with duplicate elements
3507 removed. Specifically, if two elements from the sequence match
3508 according to the @code{:test}, @code{:test-not}, and @code{:key}
3509 arguments, only the rightmost one is retained. If @code{:from-end}
3510 is true, the leftmost one is retained instead. If @code{:start} or
3511 @code{:end} is specified, only elements within that subsequence are
3512 examined or removed.
3515 @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3516 This function deletes duplicate elements from @var{seq}. It is
3517 a destructive version of @code{cl-remove-duplicates}.
3520 @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3521 This function returns a copy of @var{seq}, with all elements
3522 matching @var{old} replaced with @var{new}. The @code{:count},
3523 @code{:start}, @code{:end}, and @code{:from-end} arguments may be
3524 used to limit the number of substitutions made.
3527 @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3528 This is a destructive version of @code{cl-substitute}; it performs
3529 the substitution using @code{setcar} or @code{aset} rather than
3530 by returning a changed copy of the sequence.
3533 @findex cl-substitute-if
3534 @findex cl-substitute-if-not
3535 @findex cl-nsubstitute-if
3536 @findex cl-nsubstitute-if-not
3537 The functions @code{cl-substitute-if}, @code{cl-substitute-if-not},
3538 @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined
3539 similarly. For these, a @var{predicate} is given in place of the
3542 @node Searching Sequences
3543 @section Searching Sequences
3546 These functions search for elements or subsequences in a sequence.
3547 (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.)
3549 @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end}
3550 This function searches @var{seq} for an element matching @var{item}.
3551 If it finds a match, it returns the matching element. Otherwise,
3552 it returns @code{nil}. It returns the leftmost match, unless
3553 @code{:from-end} is true, in which case it returns the rightmost
3554 match. The @code{:start} and @code{:end} arguments may be used to
3555 limit the range of elements that are searched.
3558 @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end}
3559 This function is like @code{cl-find}, except that it returns the
3560 integer position in the sequence of the matching item rather than
3561 the item itself. The position is relative to the start of the
3562 sequence as a whole, even if @code{:start} is non-zero. The function
3563 returns @code{nil} if no matching element was found.
3566 @defun cl-count item seq @t{&key :test :test-not :key :start :end}
3567 This function returns the number of elements of @var{seq} which
3568 match @var{item}. The result is always a nonnegative integer.
3572 @findex cl-find-if-not
3573 @findex cl-position-if
3574 @findex cl-position-if-not
3576 @findex cl-count-if-not
3577 The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if},
3578 @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not}
3579 functions are defined similarly.
3581 @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end}
3582 This function compares the specified parts of @var{seq1} and
3583 @var{seq2}. If they are the same length and the corresponding
3584 elements match (according to @code{:test}, @code{:test-not},
3585 and @code{:key}), the function returns @code{nil}. If there is
3586 a mismatch, the function returns the index (relative to @var{seq1})
3587 of the first mismatching element. This will be the leftmost pair of
3588 elements that do not match, or the position at which the shorter of
3589 the two otherwise-matching sequences runs out.
3591 If @code{:from-end} is true, then the elements are compared from right
3592 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}.
3593 If the sequences differ, then one plus the index of the rightmost
3594 difference (relative to @var{seq1}) is returned.
3596 An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)},
3597 which compares two strings case-insensitively.
3600 @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2}
3601 This function searches @var{seq2} for a subsequence that matches
3602 @var{seq1} (or part of it specified by @code{:start1} and
3603 @code{:end1}). Only matches that fall entirely within the region
3604 defined by @code{:start2} and @code{:end2} will be considered.
3605 The return value is the index of the leftmost element of the
3606 leftmost match, relative to the start of @var{seq2}, or @code{nil}
3607 if no matches were found. If @code{:from-end} is true, the
3608 function finds the @emph{rightmost} matching subsequence.
3611 @node Sorting Sequences
3612 @section Sorting Sequences
3614 @defun cl-sort seq predicate @t{&key :key}
3615 This function sorts @var{seq} into increasing order as determined
3616 by using @var{predicate} to compare pairs of elements. @var{predicate}
3617 should return true (non-@code{nil}) if and only if its first argument
3618 is less than (not equal to) its second argument. For example,
3619 @code{<} and @code{string-lessp} are suitable predicate functions
3620 for sorting numbers and strings, respectively; @code{>} would sort
3621 numbers into decreasing rather than increasing order.
3623 This function differs from Emacs's built-in @code{sort} in that it
3624 can operate on any type of sequence, not just lists. Also, it
3625 accepts a @code{:key} argument, which is used to preprocess data
3626 fed to the @var{predicate} function. For example,
3629 (setq data (cl-sort data 'string-lessp :key 'downcase))
3633 sorts @var{data}, a sequence of strings, into increasing alphabetical
3634 order without regard to case. A @code{:key} function of @code{car}
3635 would be useful for sorting association lists. It should only be a
3636 simple accessor though, since it's used heavily in the current
3639 The @code{cl-sort} function is destructive; it sorts lists by actually
3640 rearranging the @sc{cdr} pointers in suitable fashion.
3643 @defun cl-stable-sort seq predicate @t{&key :key}
3644 This function sorts @var{seq} @dfn{stably}, meaning two elements
3645 which are equal in terms of @var{predicate} are guaranteed not to
3646 be rearranged out of their original order by the sort.
3648 In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent
3649 in Emacs Lisp because the underlying @code{sort} function is
3650 stable by default. However, this package reserves the right to
3651 use non-stable methods for @code{cl-sort} in the future.
3654 @defun cl-merge type seq1 seq2 predicate @t{&key :key}
3655 This function merges two sequences @var{seq1} and @var{seq2} by
3656 interleaving their elements. The result sequence, of type @var{type}
3657 (in the sense of @code{cl-concatenate}), has length equal to the sum
3658 of the lengths of the two input sequences. The sequences may be
3659 modified destructively. Order of elements within @var{seq1} and
3660 @var{seq2} is preserved in the interleaving; elements of the two
3661 sequences are compared by @var{predicate} (in the sense of
3662 @code{sort}) and the lesser element goes first in the result.
3663 When elements are equal, those from @var{seq1} precede those from
3664 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are
3665 both sorted according to @var{predicate}, then the result will be
3666 a merged sequence which is (stably) sorted according to
3674 The functions described here operate on lists.
3677 * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc.
3678 * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc.
3679 * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc.
3680 * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc.
3683 @node List Functions
3684 @section List Functions
3687 This section describes a number of simple operations on lists,
3688 i.e., chains of cons cells.
3691 This function is equivalent to @code{(car (cdr (cdr @var{x})))}.
3692 Likewise, this package defines all 24 @code{c@var{xxx}r} functions
3693 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s.
3694 All of these functions are @code{setf}-able, and calls to them
3695 are expanded inline by the byte-compiler for maximum efficiency.
3699 This function is a synonym for @code{(car @var{x})}. Likewise,
3700 the functions @code{cl-second}, @code{cl-third}, @dots{}, through
3701 @code{cl-tenth} return the given element of the list @var{x}.
3705 This function is a synonym for @code{(cdr @var{x})}.
3709 This function acts like @code{null}, but signals an error if @code{x}
3710 is neither a @code{nil} nor a cons cell.
3713 @defun cl-list-length x
3714 This function returns the length of list @var{x}, exactly like
3715 @code{(length @var{x})}, except that if @var{x} is a circular
3716 list (where the @sc{cdr}-chain forms a loop rather than terminating
3717 with @code{nil}), this function returns @code{nil}. (The regular
3718 @code{length} function would get stuck if given a circular list.
3719 See also the @code{safe-length} function.)
3722 @defun cl-list* arg &rest others
3723 This function constructs a list of its arguments. The final
3724 argument becomes the @sc{cdr} of the last cell constructed.
3725 Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to
3726 @code{(cons @var{a} (cons @var{b} @var{c}))}, and
3727 @code{(cl-list* @var{a} @var{b} nil)} is equivalent to
3728 @code{(list @var{a} @var{b})}.
3731 @defun cl-ldiff list sublist
3732 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to
3733 one of the cons cells of @var{list}, then this function returns
3734 a copy of the part of @var{list} up to but not including
3735 @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns
3736 the first two elements of the list @code{x}. The result is a
3737 copy; the original @var{list} is not modified. If @var{sublist}
3738 is not a sublist of @var{list}, a copy of the entire @var{list}
3742 @defun cl-copy-list list
3743 This function returns a copy of the list @var{list}. It copies
3744 dotted lists like @code{(1 2 . 3)} correctly.
3747 @defun cl-tree-equal x y @t{&key :test :test-not :key}
3748 This function compares two trees of cons cells. If @var{x} and
3749 @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are
3750 compared recursively. If neither @var{x} nor @var{y} is a cons
3751 cell, they are compared by @code{eql}, or according to the
3752 specified test. The @code{:key} function, if specified, is
3753 applied to the elements of both trees. @xref{Sequences}.
3756 @node Substitution of Expressions
3757 @section Substitution of Expressions
3760 These functions substitute elements throughout a tree of cons
3761 cells. (@xref{Sequence Functions}, for the @code{cl-substitute}
3762 function, which works on just the top-level elements of a list.)
3764 @defun cl-subst new old tree @t{&key :test :test-not :key}
3765 This function substitutes occurrences of @var{old} with @var{new}
3766 in @var{tree}, a tree of cons cells. It returns a substituted
3767 tree, which will be a copy except that it may share storage with
3768 the argument @var{tree} in parts where no substitutions occurred.
3769 The original @var{tree} is not modified. This function recurses
3770 on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s
3771 of the component cons cells. If @var{old} is itself a cons cell,
3772 then matching cells in the tree are substituted as usual without
3773 recursively substituting in that cell. Comparisons with @var{old}
3774 are done according to the specified test (@code{eql} by default).
3775 The @code{:key} function is applied to the elements of the tree
3776 but not to @var{old}.
3779 @defun cl-nsubst new old tree @t{&key :test :test-not :key}
3780 This function is like @code{cl-subst}, except that it works by
3781 destructive modification (by @code{setcar} or @code{setcdr})
3782 rather than copying.
3786 @findex cl-subst-if-not
3787 @findex cl-nsubst-if
3788 @findex cl-nsubst-if-not
3789 The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and
3790 @code{cl-nsubst-if-not} functions are defined similarly.
3792 @defun cl-sublis alist tree @t{&key :test :test-not :key}
3793 This function is like @code{cl-subst}, except that it takes an
3794 association list @var{alist} of @var{old}-@var{new} pairs.
3795 Each element of the tree (after applying the @code{:key}
3796 function, if any), is compared with the @sc{car}s of
3797 @var{alist}; if it matches, it is replaced by the corresponding
3801 @defun cl-nsublis alist tree @t{&key :test :test-not :key}
3802 This is a destructive version of @code{cl-sublis}.
3806 @section Lists as Sets
3809 These functions perform operations on lists that represent sets
3812 @defun cl-member item list @t{&key :test :test-not :key}
3813 This function searches @var{list} for an element matching @var{item}.
3814 If a match is found, it returns the cons cell whose @sc{car} was
3815 the matching element. Otherwise, it returns @code{nil}. Elements
3816 are compared by @code{eql} by default; you can use the @code{:test},
3817 @code{:test-not}, and @code{:key} arguments to modify this behavior.
3820 The standard Emacs lisp function @code{member} uses @code{equal} for
3821 comparisons; it is equivalent to @code{(cl-member @var{item} @var{list}
3822 :test 'equal)}. With no keyword arguments, @code{cl-member} is
3823 equivalent to @code{memq}.
3826 @findex cl-member-if
3827 @findex cl-member-if-not
3828 The @code{cl-member-if} and @code{cl-member-if-not} functions
3829 analogously search for elements that satisfy a given predicate.
3831 @defun cl-tailp sublist list
3832 This function returns @code{t} if @var{sublist} is a sublist of
3833 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to
3834 any of its @sc{cdr}s.
3837 @defun cl-adjoin item list @t{&key :test :test-not :key}
3838 This function conses @var{item} onto the front of @var{list},
3839 like @code{(cons @var{item} @var{list})}, but only if @var{item}
3840 is not already present on the list (as determined by @code{cl-member}).
3841 If a @code{:key} argument is specified, it is applied to
3842 @var{item} as well as to the elements of @var{list} during
3843 the search, on the reasoning that @var{item} is ``about'' to
3844 become part of the list.
3847 @defun cl-union list1 list2 @t{&key :test :test-not :key}
3848 This function combines two lists that represent sets of items,
3849 returning a list that represents the union of those two sets.
3850 The resulting list contains all items that appear in @var{list1}
3851 or @var{list2}, and no others. If an item appears in both
3852 @var{list1} and @var{list2} it is copied only once. If
3853 an item is duplicated in @var{list1} or @var{list2}, it is
3854 undefined whether or not that duplication will survive in the
3855 result list. The order of elements in the result list is also
3859 @defun cl-nunion list1 list2 @t{&key :test :test-not :key}
3860 This is a destructive version of @code{cl-union}; rather than copying,
3861 it tries to reuse the storage of the argument lists if possible.
3864 @defun cl-intersection list1 list2 @t{&key :test :test-not :key}
3865 This function computes the intersection of the sets represented
3866 by @var{list1} and @var{list2}. It returns the list of items
3867 that appear in both @var{list1} and @var{list2}.
3870 @defun cl-nintersection list1 list2 @t{&key :test :test-not :key}
3871 This is a destructive version of @code{cl-intersection}. It
3872 tries to reuse storage of @var{list1} rather than copying.
3873 It does @emph{not} reuse the storage of @var{list2}.
3876 @defun cl-set-difference list1 list2 @t{&key :test :test-not :key}
3877 This function computes the ``set difference'' of @var{list1}
3878 and @var{list2}, i.e., the set of elements that appear in
3879 @var{list1} but @emph{not} in @var{list2}.
3882 @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key}
3883 This is a destructive @code{cl-set-difference}, which will try
3884 to reuse @var{list1} if possible.
3887 @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key}
3888 This function computes the ``set exclusive or'' of @var{list1}
3889 and @var{list2}, i.e., the set of elements that appear in
3890 exactly one of @var{list1} and @var{list2}.
3893 @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key}
3894 This is a destructive @code{cl-set-exclusive-or}, which will try
3895 to reuse @var{list1} and @var{list2} if possible.
3898 @defun cl-subsetp list1 list2 @t{&key :test :test-not :key}
3899 This function checks whether @var{list1} represents a subset
3900 of @var{list2}, i.e., whether every element of @var{list1}
3901 also appears in @var{list2}.
3904 @node Association Lists
3905 @section Association Lists
3908 An @dfn{association list} is a list representing a mapping from
3909 one set of values to another; any list whose elements are cons
3910 cells is an association list.
3912 @defun cl-assoc item a-list @t{&key :test :test-not :key}
3913 This function searches the association list @var{a-list} for an
3914 element whose @sc{car} matches (in the sense of @code{:test},
3915 @code{:test-not}, and @code{:key}, or by comparison with @code{eql})
3916 a given @var{item}. It returns the matching element, if any,
3917 otherwise @code{nil}. It ignores elements of @var{a-list} that
3918 are not cons cells. (This corresponds to the behavior of
3919 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's
3920 @code{assoc} ignores @code{nil}s but considers any other non-cons
3921 elements of @var{a-list} to be an error.)
3924 @defun cl-rassoc item a-list @t{&key :test :test-not :key}
3925 This function searches for an element whose @sc{cdr} matches
3926 @var{item}. If @var{a-list} represents a mapping, this applies
3927 the inverse of the mapping to @var{item}.
3931 @findex cl-assoc-if-not
3932 @findex cl-rassoc-if
3933 @findex cl-rassoc-if-not
3934 The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if},
3935 and @code{cl-rassoc-if-not} functions are defined similarly.
3937 Two simple functions for constructing association lists are:
3939 @defun cl-acons key value alist
3940 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}.
3943 @defun cl-pairlis keys values &optional alist
3944 This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values})
3952 The Common Lisp @dfn{structure} mechanism provides a general way
3953 to define data types similar to C's @code{struct} types. A
3954 structure is a Lisp object containing some number of @dfn{slots},
3955 each of which can hold any Lisp data object. Functions are
3956 provided for accessing and setting the slots, creating or copying
3957 structure objects, and recognizing objects of a particular structure
3960 In true Common Lisp, each structure type is a new type distinct
3961 from all existing Lisp types. Since the underlying Emacs Lisp
3962 system provides no way to create new distinct types, this package
3963 implements structures as vectors (or lists upon request) with a
3964 special ``tag'' symbol to identify them.
3966 @defmac cl-defstruct name slots@dots{}
3967 The @code{cl-defstruct} form defines a new structure type called
3968 @var{name}, with the specified @var{slots}. (The @var{slots}
3969 may begin with a string which documents the structure type.)
3970 In the simplest case, @var{name} and each of the @var{slots}
3971 are symbols. For example,
3974 (cl-defstruct person name age sex)
3978 defines a struct type called @code{person} that contains three
3979 slots. Given a @code{person} object @var{p}, you can access those
3980 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})},
3981 and @code{(person-sex @var{p})}. You can also change these slots by
3982 using @code{setf} on any of these place forms, for example:
3985 (cl-incf (person-age birthday-boy))
3988 You can create a new @code{person} by calling @code{make-person},
3989 which takes keyword arguments @code{:name}, @code{:age}, and
3990 @code{:sex} to specify the initial values of these slots in the
3991 new object. (Omitting any of these arguments leaves the corresponding
3992 slot ``undefined'', according to the Common Lisp standard; in Emacs
3993 Lisp, such uninitialized slots are filled with @code{nil}.)
3995 Given a @code{person}, @code{(copy-person @var{p})} makes a new
3996 object of the same type whose slots are @code{eq} to those of @var{p}.
3998 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns
3999 true if @var{x} looks like a @code{person}, and false otherwise. (Again,
4000 in Common Lisp this predicate would be exact; in Emacs Lisp the
4001 best it can do is verify that @var{x} is a vector of the correct
4002 length that starts with the correct tag symbol.)
4004 Accessors like @code{person-name} normally check their arguments
4005 (effectively using @code{person-p}) and signal an error if the
4006 argument is the wrong type. This check is affected by
4007 @code{(optimize (safety @dots{}))} declarations. Safety level 1,
4008 the default, uses a somewhat optimized check that will detect all
4009 incorrect arguments, but may use an uninformative error message
4010 (e.g., ``expected a vector'' instead of ``expected a @code{person}'').
4011 Safety level 0 omits all checks except as provided by the underlying
4012 @code{aref} call; safety levels 2 and 3 do rigorous checking that will
4013 always print a descriptive error message for incorrect inputs.
4014 @xref{Declarations}.
4017 (setq dave (make-person :name "Dave" :sex 'male))
4018 @result{} [cl-struct-person "Dave" nil male]
4019 (setq other (copy-person dave))
4020 @result{} [cl-struct-person "Dave" nil male]
4023 (eq (person-name dave) (person-name other))
4027 (person-p [1 2 3 4])
4031 (person-p '[cl-struct-person counterfeit person object])
4035 In general, @var{name} is either a name symbol or a list of a name
4036 symbol followed by any number of @dfn{struct options}; each @var{slot}
4037 is either a slot symbol or a list of the form @samp{(@var{slot-name}
4038 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value}
4039 is a Lisp form that is evaluated any time an instance of the
4040 structure type is created without specifying that slot's value.
4042 Common Lisp defines several slot options, but the only one
4043 implemented in this package is @code{:read-only}. A non-@code{nil}
4044 value for this option means the slot should not be @code{setf}-able;
4045 the slot's value is determined when the object is created and does
4046 not change afterward.
4049 (cl-defstruct person
4050 (name nil :read-only t)
4055 Any slot options other than @code{:read-only} are ignored.
4057 For obscure historical reasons, structure options take a different
4058 form than slot options. A structure option is either a keyword
4059 symbol, or a list beginning with a keyword symbol possibly followed
4060 by arguments. (By contrast, slot options are key-value pairs not
4064 (cl-defstruct (person (:constructor create-person)
4070 The following structure options are recognized.
4074 The argument is a symbol whose print name is used as the prefix for
4075 the names of slot accessor functions. The default is the name of
4076 the struct type followed by a hyphen. The option @code{(:conc-name p-)}
4077 would change this prefix to @code{p-}. Specifying @code{nil} as an
4078 argument means no prefix, so that the slot names themselves are used
4079 to name the accessor functions.
4082 In the simple case, this option takes one argument which is an
4083 alternate name to use for the constructor function. The default
4084 is @code{make-@var{name}}, e.g., @code{make-person}. The above
4085 example changes this to @code{create-person}. Specifying @code{nil}
4086 as an argument means that no standard constructor should be
4089 In the full form of this option, the constructor name is followed
4090 by an arbitrary argument list. @xref{Program Structure}, for a
4091 description of the format of Common Lisp argument lists. All
4092 options, such as @code{&rest} and @code{&key}, are supported.
4093 The argument names should match the slot names; each slot is
4094 initialized from the corresponding argument. Slots whose names
4095 do not appear in the argument list are initialized based on the
4096 @var{default-value} in their slot descriptor. Also, @code{&optional}
4097 and @code{&key} arguments that don't specify defaults take their
4098 defaults from the slot descriptor. It is valid to include arguments
4099 that don't correspond to slot names; these are useful if they are
4100 referred to in the defaults for optional, keyword, or @code{&aux}
4101 arguments that @emph{do} correspond to slots.
4103 You can specify any number of full-format @code{:constructor}
4104 options on a structure. The default constructor is still generated
4105 as well unless you disable it with a simple-format @code{:constructor}
4111 (:constructor nil) ; no default constructor
4112 (:constructor new-person
4113 (name sex &optional (age 0)))
4114 (:constructor new-hound (&key (name "Rover")
4116 &aux (age (* 7 dog-years))
4121 The first constructor here takes its arguments positionally rather
4122 than by keyword. (In official Common Lisp terminology, constructors
4123 that work By Order of Arguments instead of by keyword are called
4124 ``BOA constructors''. No, I'm not making this up.) For example,
4125 @code{(new-person "Jane" 'female)} generates a person whose slots
4126 are @code{"Jane"}, 0, and @code{female}, respectively.
4128 The second constructor takes two keyword arguments, @code{:name},
4129 which initializes the @code{name} slot and defaults to @code{"Rover"},
4130 and @code{:dog-years}, which does not itself correspond to a slot
4131 but which is used to initialize the @code{age} slot. The @code{sex}
4132 slot is forced to the symbol @code{canine} with no syntax for
4136 The argument is an alternate name for the copier function for
4137 this type. The default is @code{copy-@var{name}}. @code{nil}
4138 means not to generate a copier function. (In this implementation,
4139 all copier functions are simply synonyms for @code{copy-sequence}.)
4142 The argument is an alternate name for the predicate that recognizes
4143 objects of this type. The default is @code{@var{name}-p}. @code{nil}
4144 means not to generate a predicate function. (If the @code{:type}
4145 option is used without the @code{:named} option, no predicate is
4148 In true Common Lisp, @code{typep} is always able to recognize a
4149 structure object even if @code{:predicate} was used. In this
4150 package, @code{cl-typep} simply looks for a function called
4151 @code{@var{typename}-p}, so it will work for structure types
4152 only if they used the default predicate name.
4155 This option implements a very limited form of C++-style inheritance.
4156 The argument is the name of another structure type previously
4157 created with @code{cl-defstruct}. The effect is to cause the new
4158 structure type to inherit all of the included structure's slots
4159 (plus, of course, any new slots described by this struct's slot
4160 descriptors). The new structure is considered a ``specialization''
4161 of the included one. In fact, the predicate and slot accessors
4162 for the included type will also accept objects of the new type.
4164 If there are extra arguments to the @code{:include} option after
4165 the included-structure name, these options are treated as replacement
4166 slot descriptors for slots in the included structure, possibly with
4167 modified default values. Borrowing an example from Steele:
4170 (cl-defstruct person name (age 0) sex)
4172 (cl-defstruct (astronaut (:include person (age 45)))
4174 (favorite-beverage 'tang))
4177 (setq joe (make-person :name "Joe"))
4178 @result{} [cl-struct-person "Joe" 0 nil]
4179 (setq buzz (make-astronaut :name "Buzz"))
4180 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang]
4182 (list (person-p joe) (person-p buzz))
4184 (list (astronaut-p joe) (astronaut-p buzz))
4189 (astronaut-name joe)
4190 @result{} error: "astronaut-name accessing a non-astronaut"
4193 Thus, if @code{astronaut} is a specialization of @code{person},
4194 then every @code{astronaut} is also a @code{person} (but not the
4195 other way around). Every @code{astronaut} includes all the slots
4196 of a @code{person}, plus extra slots that are specific to
4197 astronauts. Operations that work on people (like @code{person-name})
4198 work on astronauts just like other people.
4200 @item :print-function
4201 In full Common Lisp, this option allows you to specify a function
4202 that is called to print an instance of the structure type. The
4203 Emacs Lisp system offers no hooks into the Lisp printer which would
4204 allow for such a feature, so this package simply ignores
4205 @code{:print-function}.
4208 The argument should be one of the symbols @code{vector} or @code{list}.
4209 This tells which underlying Lisp data type should be used to implement
4210 the new structure type. Vectors are used by default, but
4211 @code{(:type list)} will cause structure objects to be stored as
4214 The vector representation for structure objects has the advantage
4215 that all structure slots can be accessed quickly, although creating
4216 vectors is a bit slower in Emacs Lisp. Lists are easier to create,
4217 but take a relatively long time accessing the later slots.
4220 This option, which takes no arguments, causes a characteristic ``tag''
4221 symbol to be stored at the front of the structure object. Using
4222 @code{:type} without also using @code{:named} will result in a
4223 structure type stored as plain vectors or lists with no identifying
4226 The default, if you don't specify @code{:type} explicitly, is to
4227 use named vectors. Therefore, @code{:named} is only useful in
4228 conjunction with @code{:type}.
4231 (cl-defstruct (person1) name age sex)
4232 (cl-defstruct (person2 (:type list) :named) name age sex)
4233 (cl-defstruct (person3 (:type list)) name age sex)
4235 (setq p1 (make-person1))
4236 @result{} [cl-struct-person1 nil nil nil]
4237 (setq p2 (make-person2))
4238 @result{} (person2 nil nil nil)
4239 (setq p3 (make-person3))
4240 @result{} (nil nil nil)
4247 @result{} error: function person3-p undefined
4250 Since unnamed structures don't have tags, @code{cl-defstruct} is not
4251 able to make a useful predicate for recognizing them. Also,
4252 accessors like @code{person3-name} will be generated but they
4253 will not be able to do any type checking. The @code{person3-name}
4254 function, for example, will simply be a synonym for @code{car} in
4255 this case. By contrast, @code{person2-name} is able to verify
4256 that its argument is indeed a @code{person2} object before
4259 @item :initial-offset
4260 The argument must be a nonnegative integer. It specifies a
4261 number of slots to be left ``empty'' at the front of the
4262 structure. If the structure is named, the tag appears at the
4263 specified position in the list or vector; otherwise, the first
4264 slot appears at that position. Earlier positions are filled
4265 with @code{nil} by the constructors and ignored otherwise. If
4266 the type @code{:include}s another type, then @code{:initial-offset}
4267 specifies a number of slots to be skipped between the last slot
4268 of the included type and the first new slot.
4272 Except as noted, the @code{cl-defstruct} facility of this package is
4273 entirely compatible with that of Common Lisp.
4275 The @code{cl-defstruct} package also provides a few structure
4276 introspection functions.
4278 @defun cl-struct-sequence-type struct-type
4279 This function returns the underlying data structure for
4280 @code{struct-type}, which is a symbol. It returns @code{vector} or
4281 @code{list}, or @code{nil} if @code{struct-type} is not actually a
4285 @defun cl-struct-slot-info struct-type
4286 This function returns a list of slot descriptors for structure
4287 @code{struct-type}. Each entry in the list is @code{(name . opts)},
4288 where @code{name} is the name of the slot and @code{opts} is the list
4289 of slot options given to @code{defstruct}. Dummy entries represent
4290 the slots used for the struct name and that are skipped to implement
4291 @code{:initial-offset}.
4294 @defun cl-struct-slot-offset struct-type slot-name
4295 Return the offset of slot @code{slot-name} in @code{struct-type}. The
4296 returned zero-based slot index is relative to the start of the
4297 structure data type and is adjusted for any structure name and
4298 :initial-offset slots. Signal error if struct @code{struct-type} does
4299 not contain @code{slot-name}.
4302 @defun cl-struct-slot-value struct-type slot-name inst
4303 Return the value of slot @code{slot-name} in @code{inst} of
4304 @code{struct-type}. @code{struct} and @code{slot-name} are symbols.
4305 @code{inst} is a structure instance. This routine is also a
4306 @code{setf} place. Can signal the same errors as @code{cl-struct-slot-offset}.
4310 @chapter Assertions and Errors
4313 This section describes two macros that test @dfn{assertions}, i.e.,
4314 conditions which must be true if the program is operating correctly.
4315 Assertions never add to the behavior of a Lisp program; they simply
4316 make ``sanity checks'' to make sure everything is as it should be.
4318 If the optimization property @code{speed} has been set to 3, and
4319 @code{safety} is less than 3, then the byte-compiler will optimize
4320 away the following assertions. Because assertions might be optimized
4321 away, it is a bad idea for them to include side-effects.
4323 @defmac cl-assert test-form [show-args string args@dots{}]
4324 This form verifies that @var{test-form} is true (i.e., evaluates to
4325 a non-@code{nil} value). If so, it returns @code{nil}. If the test
4326 is not satisfied, @code{cl-assert} signals an error.
4328 A default error message will be supplied which includes @var{test-form}.
4329 You can specify a different error message by including a @var{string}
4330 argument plus optional extra arguments. Those arguments are simply
4331 passed to @code{error} to signal the error.
4333 If the optional second argument @var{show-args} is @code{t} instead
4334 of @code{nil}, then the error message (with or without @var{string})
4335 will also include all non-constant arguments of the top-level
4336 @var{form}. For example:
4339 (cl-assert (> x 10) t "x is too small: %d")
4342 This usage of @var{show-args} is an extension to Common Lisp. In
4343 true Common Lisp, the second argument gives a list of @var{places}
4344 which can be @code{setf}'d by the user before continuing from the
4345 error. Since Emacs Lisp does not support continuable errors, it
4346 makes no sense to specify @var{places}.
4349 @defmac cl-check-type form type [string]
4350 This form verifies that @var{form} evaluates to a value of type
4351 @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type}
4352 signals a @code{wrong-type-argument} error. The default error message
4353 lists the erroneous value along with @var{type} and @var{form}
4354 themselves. If @var{string} is specified, it is included in the
4355 error message in place of @var{type}. For example:
4358 (cl-check-type x (integer 1 *) "a positive integer")
4361 @xref{Type Predicates}, for a description of the type specifiers
4362 that may be used for @var{type}.
4364 Note that in Common Lisp, the first argument to @code{check-type}
4365 must be a @var{place} suitable for use by @code{setf}, because
4366 @code{check-type} signals a continuable error that allows the
4367 user to modify @var{place}.
4370 @node Efficiency Concerns
4371 @appendix Efficiency Concerns
4376 Many of the advanced features of this package, such as @code{cl-defun},
4377 @code{cl-loop}, etc., are implemented as Lisp macros. In
4378 byte-compiled code, these complex notations will be expanded into
4379 equivalent Lisp code which is simple and efficient. For example,
4387 is expanded at compile-time to the Lisp form
4394 which is the most efficient ways of doing this operation
4395 in Lisp. Thus, there is no performance penalty for using the more
4396 readable @code{cl-incf} form in your compiled code.
4398 @emph{Interpreted} code, on the other hand, must expand these macros
4399 every time they are executed. For this reason it is strongly
4400 recommended that code making heavy use of macros be compiled.
4401 A loop using @code{cl-incf} a hundred times will execute considerably
4402 faster if compiled, and will also garbage-collect less because the
4403 macro expansion will not have to be generated, used, and thrown away a
4406 You can find out how a macro expands by using the
4407 @code{cl-prettyexpand} function.
4409 @defun cl-prettyexpand form &optional full
4410 This function takes a single Lisp form as an argument and inserts
4411 a nicely formatted copy of it in the current buffer (which must be
4412 in Lisp mode so that indentation works properly). It also expands
4413 all Lisp macros that appear in the form. The easiest way to use
4414 this function is to go to the @file{*scratch*} buffer and type, say,
4417 (cl-prettyexpand '(cl-loop for x below 10 collect x))
4421 and type @kbd{C-x C-e} immediately after the closing parenthesis;
4422 an expansion similar to:
4429 (setq G1004 (cons x G1004))
4435 will be inserted into the buffer. (The @code{cl-block} macro is
4436 expanded differently in the interpreter and compiler, so
4437 @code{cl-prettyexpand} just leaves it alone. The temporary
4438 variable @code{G1004} was created by @code{cl-gensym}.)
4440 If the optional argument @var{full} is true, then @emph{all}
4441 macros are expanded, including @code{cl-block}, @code{cl-eval-when},
4442 and compiler macros. Expansion is done as if @var{form} were
4443 a top-level form in a file being compiled.
4445 @c FIXME none of these examples are still applicable.
4450 (cl-prettyexpand '(cl-pushnew 'x list))
4451 @print{} (setq list (cl-adjoin 'x list))
4452 (cl-prettyexpand '(cl-pushnew 'x list) t)
4453 @print{} (setq list (if (memq 'x list) list (cons 'x list)))
4454 (cl-prettyexpand '(caddr (cl-member 'a list)) t)
4455 @print{} (car (cdr (cdr (memq 'a list))))
4459 Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all
4460 have built-in compiler macros to optimize them in common cases.
4463 @appendixsec Error Checking
4466 Common Lisp compliance has in general not been sacrificed for the
4467 sake of efficiency. A few exceptions have been made for cases
4468 where substantial gains were possible at the expense of marginal
4471 The Common Lisp standard (as embodied in Steele's book) uses the
4472 phrase ``it is an error if'' to indicate a situation that is not
4473 supposed to arise in complying programs; implementations are strongly
4474 encouraged but not required to signal an error in these situations.
4475 This package sometimes omits such error checking in the interest of
4476 compactness and efficiency. For example, @code{cl-do} variable
4477 specifiers are supposed to be lists of one, two, or three forms; extra
4478 forms are ignored by this package rather than signaling a syntax
4479 error. Functions taking keyword arguments will accept an odd number
4480 of arguments, treating the trailing keyword as if it were followed by
4481 the value @code{nil}.
4483 Argument lists (as processed by @code{cl-defun} and friends)
4484 @emph{are} checked rigorously except for the minor point just
4485 mentioned; in particular, keyword arguments are checked for
4486 validity, and @code{&allow-other-keys} and @code{:allow-other-keys}
4487 are fully implemented. Keyword validity checking is slightly
4488 time consuming (though not too bad in byte-compiled code);
4489 you can use @code{&allow-other-keys} to omit this check. Functions
4490 defined in this package such as @code{cl-find} and @code{cl-member}
4491 do check their keyword arguments for validity.
4493 @appendixsec Compiler Optimizations
4496 Changing the value of @code{byte-optimize} from the default @code{t}
4497 is highly discouraged; many of the Common
4499 code that can be improved by optimization. In particular,
4500 @code{cl-block}s (whether explicit or implicit in constructs like
4501 @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the
4502 byte-compiler removes @code{cl-block}s that are not actually
4503 referenced by @code{cl-return} or @code{cl-return-from} inside the block.
4505 @node Common Lisp Compatibility
4506 @appendix Common Lisp Compatibility
4509 The following is a list of some of the most important
4510 incompatibilities between this package and Common Lisp as documented
4511 in Steele (2nd edition).
4513 The word @code{cl-defun} is required instead of @code{defun} in order
4514 to use extended Common Lisp argument lists in a function. Likewise,
4515 @code{cl-defmacro} and @code{cl-function} are versions of those forms
4516 which understand full-featured argument lists. The @code{&whole}
4517 keyword does not work in @code{cl-defmacro} argument lists (except
4518 inside recursive argument lists).
4520 The @code{equal} predicate does not distinguish
4521 between IEEE floating-point plus and minus zero. The @code{cl-equalp}
4522 predicate has several differences with Common Lisp; @pxref{Predicates}.
4524 The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols}
4525 with no @var{obarray} argument. In Common Lisp, this form would
4526 iterate over all symbols in all packages. Since Emacs obarrays
4527 are not a first-class package mechanism, there is no way for
4528 @code{cl-do-all-symbols} to locate any but the default obarray.
4530 The @code{cl-loop} macro is complete except that @code{loop-finish}
4531 and type specifiers are unimplemented.
4533 The multiple-value return facility treats lists as multiple
4534 values, since Emacs Lisp cannot support multiple return values
4535 directly. The macros will be compatible with Common Lisp if
4536 @code{cl-values} or @code{cl-values-list} is always used to return to
4537 a @code{cl-multiple-value-bind} or other multiple-value receiver;
4538 if @code{cl-values} is used without @code{cl-multiple-value-@dots{}}
4539 or vice-versa the effect will be different from Common Lisp.
4541 Many Common Lisp declarations are ignored, and others match
4542 the Common Lisp standard in concept but not in detail. For
4543 example, local @code{special} declarations, which are purely
4544 advisory in Emacs Lisp, do not rigorously obey the scoping rules
4545 set down in Steele's book.
4547 The variable @code{cl--gensym-counter} starts out with zero.
4549 The @code{cl-defstruct} facility is compatible, except that structures
4550 are of type @code{:type vector :named} by default rather than some
4551 special, distinct type. Also, the @code{:type} slot option is ignored.
4553 The second argument of @code{cl-check-type} is treated differently.
4555 @node Porting Common Lisp
4556 @appendix Porting Common Lisp
4559 This package is meant to be used as an extension to Emacs Lisp,
4560 not as an Emacs implementation of true Common Lisp. Some of the
4561 remaining differences between Emacs Lisp and Common Lisp make it
4562 difficult to port large Common Lisp applications to Emacs. For
4563 one, some of the features in this package are not fully compliant
4564 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there
4565 are also quite a few features that this package does not provide
4566 at all. Here are some major omissions that you will want to watch out
4567 for when bringing Common Lisp code into Emacs.
4571 Case-insensitivity. Symbols in Common Lisp are case-insensitive
4572 by default. Some programs refer to a function or variable as
4573 @code{foo} in one place and @code{Foo} or @code{FOO} in another.
4574 Emacs Lisp will treat these as three distinct symbols.
4576 Some Common Lisp code is written entirely in upper case. While Emacs
4577 is happy to let the program's own functions and variables use
4578 this convention, calls to Lisp builtins like @code{if} and
4579 @code{defun} will have to be changed to lower case.
4582 Lexical scoping. In Common Lisp, function arguments and @code{let}
4583 bindings apply only to references physically within their bodies (or
4584 within macro expansions in their bodies). Traditionally, Emacs Lisp
4585 uses @dfn{dynamic scoping} wherein a binding to a variable is visible
4586 even inside functions called from the body.
4587 @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4588 Lexical binding is available since Emacs 24.1, so be sure to set
4589 @code{lexical-binding} to @code{t} if you need to emulate this aspect
4590 of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4592 Here is an example of a Common Lisp code fragment that would fail in
4593 Emacs Lisp if @code{lexical-binding} were set to @code{nil}:
4596 (defun map-odd-elements (func list)
4598 for flag = t then (not flag)
4599 collect (if flag x (funcall func x))))
4601 (defun add-odd-elements (list x)
4602 (map-odd-elements (lambda (a) (+ a x)) list))
4606 With lexical binding, the two functions' usages of @code{x} are
4607 completely independent. With dynamic binding, the binding to @code{x}
4608 made by @code{add-odd-elements} will have been hidden by the binding
4609 in @code{map-odd-elements} by the time the @code{(+ a x)} function is
4612 Internally, this package uses lexical binding so that such problems do
4613 not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete
4614 @code{lexical-let} form that emulates a Common Lisp-style lexical
4615 binding when dynamic binding is in use.
4618 Reader macros. Common Lisp includes a second type of macro that
4619 works at the level of individual characters. For example, Common
4620 Lisp implements the quote notation by a reader macro called @code{'},
4621 whereas Emacs Lisp's parser just treats quote as a special case.
4622 Some Lisp packages use reader macros to create special syntaxes
4623 for themselves, which the Emacs parser is incapable of reading.
4626 Other syntactic features. Common Lisp provides a number of
4627 notations beginning with @code{#} that the Emacs Lisp parser
4628 won't understand. For example, @samp{#| @dots{} |#} is an
4629 alternate comment notation, and @samp{#+lucid (foo)} tells
4630 the parser to ignore the @code{(foo)} except in Lucid Common
4634 Packages. In Common Lisp, symbols are divided into @dfn{packages}.
4635 Symbols that are Lisp built-ins are typically stored in one package;
4636 symbols that are vendor extensions are put in another, and each
4637 application program would have a package for its own symbols.
4638 Certain symbols are ``exported'' by a package and others are
4639 internal; certain packages ``use'' or import the exported symbols
4640 of other packages. To access symbols that would not normally be
4641 visible due to this importing and exporting, Common Lisp provides
4642 a syntax like @code{package:symbol} or @code{package::symbol}.
4644 Emacs Lisp has a single namespace for all interned symbols, and
4645 then uses a naming convention of putting a prefix like @code{cl-}
4646 in front of the name. Some Emacs packages adopt the Common Lisp-like
4647 convention of using @code{cl:} or @code{cl::} as the prefix.
4648 However, the Emacs parser does not understand colons and just
4649 treats them as part of the symbol name. Thus, while @code{mapcar}
4650 and @code{lisp:mapcar} may refer to the same symbol in Common
4651 Lisp, they are totally distinct in Emacs Lisp. Common Lisp
4652 programs that refer to a symbol by the full name sometimes
4653 and the short name other times will not port cleanly to Emacs.
4655 Emacs Lisp does have a concept of ``obarrays'', which are
4656 package-like collections of symbols, but this feature is not
4657 strong enough to be used as a true package mechanism.
4660 The @code{format} function is quite different between Common
4661 Lisp and Emacs Lisp. It takes an additional ``destination''
4662 argument before the format string. A destination of @code{nil}
4663 means to format to a string as in Emacs Lisp; a destination
4664 of @code{t} means to write to the terminal (similar to
4665 @code{message} in Emacs). Also, format control strings are
4666 utterly different; @code{~} is used instead of @code{%} to
4667 introduce format codes, and the set of available codes is
4668 much richer. There are no notations like @code{\n} for
4669 string literals; instead, @code{format} is used with the
4670 ``newline'' format code, @code{~%}. More advanced formatting
4671 codes provide such features as paragraph filling, case
4672 conversion, and even loops and conditionals.
4674 While it would have been possible to implement most of Common
4675 Lisp @code{format} in this package (under the name @code{cl-format},
4676 of course), it was not deemed worthwhile. It would have required
4677 a huge amount of code to implement even a decent subset of
4678 @code{format}, yet the functionality it would provide over
4679 Emacs Lisp's @code{format} would rarely be useful.
4682 Vector constants use square brackets in Emacs Lisp, but
4683 @code{#(a b c)} notation in Common Lisp. To further complicate
4684 matters, Emacs has its own @code{#(} notation for
4685 something entirely different---strings with properties.
4688 Characters are distinct from integers in Common Lisp. The notation
4689 for character constants is also different: @code{#\A} in Common Lisp
4690 where Emacs Lisp uses @code{?A}. Also, @code{string=} and
4691 @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is
4692 case-insensitive in Common Lisp.
4695 Data types. Some Common Lisp data types do not exist in Emacs
4696 Lisp. Rational numbers and complex numbers are not present,
4697 nor are large integers (all integers are ``fixnums''). All
4698 arrays are one-dimensional. There are no readtables or pathnames;
4699 streams are a set of existing data types rather than a new data
4700 type of their own. Hash tables, random-states, structures, and
4701 packages (obarrays) are built from Lisp vectors or lists rather
4702 than being distinct types.
4705 The Common Lisp Object System (CLOS) is not implemented,
4706 nor is the Common Lisp Condition System. However, the EIEIO package
4707 (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some
4711 Common Lisp features that are completely redundant with Emacs
4712 Lisp features of a different name generally have not been
4713 implemented. For example, Common Lisp writes @code{defconstant}
4714 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list}
4715 takes its arguments in different ways in the two Lisps but does
4716 exactly the same thing, so this package has not bothered to
4717 implement a Common Lisp-style @code{make-list}.
4720 A few more notable Common Lisp features not included in this package:
4721 @code{compiler-let}, @code{prog}, @code{ldb/dpb}, @code{cerror}.
4724 Recursion. While recursion works in Emacs Lisp just like it
4725 does in Common Lisp, various details of the Emacs Lisp system
4726 and compiler make recursion much less efficient than it is in
4727 most Lisps. Some schools of thought prefer to use recursion
4728 in Lisp over other techniques; they would sum a list of
4729 numbers using something like
4732 (defun sum-list (list)
4734 (+ (car list) (sum-list (cdr list)))
4739 where a more iteratively-minded programmer might write one of
4743 (let ((total 0)) (dolist (x my-list) (incf total x)) total)
4744 (loop for x in my-list sum x)
4747 While this would be mainly a stylistic choice in most Common Lisps,
4748 in Emacs Lisp you should be aware that the iterative forms are
4749 much faster than recursion. Also, Lisp programmers will want to
4750 note that the current Emacs Lisp compiler does not optimize tail
4754 @node Obsolete Features
4755 @appendix Obsolete Features
4757 This section describes some features of the package that are obsolete
4758 and should not be used in new code. They are either only provided by
4759 the old @file{cl.el} entry point, not by the newer @file{cl-lib.el};
4760 or where versions with a @samp{cl-} prefix do exist they do not behave
4761 in exactly the same way.
4764 * Obsolete Lexical Binding:: An approximation of lexical binding.
4765 * Obsolete Macros:: Obsolete macros.
4766 * Obsolete Setf Customization:: Obsolete ways to customize setf.
4769 @node Obsolete Lexical Binding
4770 @appendixsec Obsolete Lexical Binding
4772 The following macros are extensions to Common Lisp, where all bindings
4773 are lexical unless declared otherwise. These features are likewise
4774 obsolete since the introduction of true lexical binding in Emacs 24.1.
4776 @defmac lexical-let (bindings@dots{}) forms@dots{}
4777 This form is exactly like @code{let} except that the bindings it
4778 establishes are purely lexical.
4781 @c FIXME remove this and refer to elisp manual.
4782 @c Maybe merge some stuff from here to there?
4784 Lexical bindings are similar to local variables in a language like C:
4785 Only the code physically within the body of the @code{lexical-let}
4786 (after macro expansion) may refer to the bound variables.
4790 (defun foo (b) (+ a b))
4791 (let ((a 2)) (foo a))
4793 (lexical-let ((a 2)) (foo a))
4798 In this example, a regular @code{let} binding of @code{a} actually
4799 makes a temporary change to the global variable @code{a}, so @code{foo}
4800 is able to see the binding of @code{a} to 2. But @code{lexical-let}
4801 actually creates a distinct local variable @code{a} for use within its
4802 body, without any effect on the global variable of the same name.
4804 The most important use of lexical bindings is to create @dfn{closures}.
4805 A closure is a function object that refers to an outside lexical
4806 variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}).
4810 (defun make-adder (n)
4811 (lexical-let ((n n))
4812 (function (lambda (m) (+ n m)))))
4813 (setq add17 (make-adder 17))
4819 The call @code{(make-adder 17)} returns a function object which adds
4820 17 to its argument. If @code{let} had been used instead of
4821 @code{lexical-let}, the function object would have referred to the
4822 global @code{n}, which would have been bound to 17 only during the
4823 call to @code{make-adder} itself.
4826 (defun make-counter ()
4827 (lexical-let ((n 0))
4828 (cl-function (lambda (&optional (m 1)) (cl-incf n m)))))
4829 (setq count-1 (make-counter))
4832 (funcall count-1 14)
4834 (setq count-2 (make-counter))
4844 Here we see that each call to @code{make-counter} creates a distinct
4845 local variable @code{n}, which serves as a private counter for the
4846 function object that is returned.
4848 Closed-over lexical variables persist until the last reference to
4849 them goes away, just like all other Lisp objects. For example,
4850 @code{count-2} refers to a function object which refers to an
4851 instance of the variable @code{n}; this is the only reference
4852 to that variable, so after @code{(setq count-2 nil)} the garbage
4853 collector would be able to delete this instance of @code{n}.
4854 Of course, if a @code{lexical-let} does not actually create any
4855 closures, then the lexical variables are free as soon as the
4856 @code{lexical-let} returns.
4858 Many closures are used only during the extent of the bindings they
4859 refer to; these are known as ``downward funargs'' in Lisp parlance.
4860 When a closure is used in this way, regular Emacs Lisp dynamic
4861 bindings suffice and will be more efficient than @code{lexical-let}
4865 (defun add-to-list (x list)
4866 (mapcar (lambda (y) (+ x y))) list)
4867 (add-to-list 7 '(1 2 5))
4872 Since this lambda is only used while @code{x} is still bound,
4873 it is not necessary to make a true closure out of it.
4875 You can use @code{defun} or @code{flet} inside a @code{lexical-let}
4876 to create a named closure. If several closures are created in the
4877 body of a single @code{lexical-let}, they all close over the same
4878 instance of the lexical variable.
4880 @defmac lexical-let* (bindings@dots{}) forms@dots{}
4881 This form is just like @code{lexical-let}, except that the bindings
4882 are made sequentially in the manner of @code{let*}.
4885 @node Obsolete Macros
4886 @appendixsec Obsolete Macros
4888 The following macros are obsolete, and are replaced by versions with
4889 a @samp{cl-} prefix that do not behave in exactly the same way.
4890 Consequently, the @file{cl.el} versions are not simply aliases to the
4891 @file{cl-lib.el} versions.
4893 @defmac flet (bindings@dots{}) forms@dots{}
4894 This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}),
4895 which behaves the same way as Common Lisp's @code{flet}.
4896 This @code{flet} takes the same arguments as @code{cl-flet}, but does
4897 not behave in precisely the same way.
4899 While @code{flet} in Common Lisp establishes a lexical function
4900 binding, this @code{flet} makes a dynamic binding (it dates from a
4901 time before Emacs had lexical binding). The result is
4902 that @code{flet} affects indirect calls to a function as well as calls
4903 directly inside the @code{flet} form itself.
4905 This will even work on Emacs primitives, although note that some calls
4906 to primitive functions internal to Emacs are made without going
4907 through the symbol's function cell, and so will not be affected by
4908 @code{flet}. For example,
4911 (flet ((message (&rest args) (push args saved-msgs)))
4915 This code attempts to replace the built-in function @code{message}
4916 with a function that simply saves the messages in a list rather
4917 than displaying them. The original definition of @code{message}
4918 will be restored after @code{do-something} exits. This code will
4919 work fine on messages generated by other Lisp code, but messages
4920 generated directly inside Emacs will not be caught since they make
4921 direct C-language calls to the message routines rather than going
4922 through the Lisp @code{message} function.
4924 For those cases where the dynamic scoping of @code{flet} is desired,
4925 @code{cl-flet} is clearly not a substitute. The most direct replacement would
4926 be instead to use @code{cl-letf} to temporarily rebind @code{(symbol-function
4927 '@var{fun})}. But in most cases, a better substitute is to use advice, such
4931 (defvar my-fun-advice-enable nil)
4932 (add-advice '@var{fun} :around
4933 (lambda (orig &rest args)
4934 (if my-fun-advice-enable (do-something)
4935 (apply orig args))))
4938 so that you can then replace the @code{flet} with a simple dynamically scoped
4939 binding of @code{my-fun-advice-enable}.
4942 Note that many primitives (e.g., @code{+}) have special byte-compile handling.
4943 Attempts to redefine such functions using @code{flet}, @code{cl-letf}, or
4944 advice will fail when byte-compiled.
4946 @c In such cases, use @code{labels} instead.
4949 @defmac labels (bindings@dots{}) forms@dots{}
4950 This macro is replaced by @code{cl-labels} (@pxref{Function Bindings}),
4951 which behaves the same way as Common Lisp's @code{labels}.
4952 This @code{labels} takes the same arguments as @code{cl-labels}, but
4953 does not behave in precisely the same way.
4955 This version of @code{labels} uses the obsolete @code{lexical-let}
4956 form (@pxref{Obsolete Lexical Binding}), rather than the true
4957 lexical binding that @code{cl-labels} uses.
4960 @node Obsolete Setf Customization
4961 @appendixsec Obsolete Ways to Customize Setf
4963 Common Lisp defines three macros, @code{define-modify-macro},
4964 @code{defsetf}, and @code{define-setf-method}, that allow the
4965 user to extend generalized variables in various ways.
4966 In Emacs, these are obsolete, replaced by various features of
4967 @file{gv.el} in Emacs 24.3.
4968 @xref{Adding Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
4971 @defmac define-modify-macro name arglist function [doc-string]
4972 This macro defines a ``read-modify-write'' macro similar to
4973 @code{cl-incf} and @code{cl-decf}. You can replace this macro
4974 with @code{gv-letplace}.
4976 The macro @var{name} is defined to take a @var{place} argument
4977 followed by additional arguments described by @var{arglist}. The call
4980 (@var{name} @var{place} @var{args}@dots{})
4987 (cl-callf @var{func} @var{place} @var{args}@dots{})
4991 which in turn is roughly equivalent to
4994 (setf @var{place} (@var{func} @var{place} @var{args}@dots{}))
5000 (define-modify-macro incf (&optional (n 1)) +)
5001 (define-modify-macro concatf (&rest args) concat)
5004 Note that @code{&key} is not allowed in @var{arglist}, but
5005 @code{&rest} is sufficient to pass keywords on to the function.
5007 Most of the modify macros defined by Common Lisp do not exactly
5008 follow the pattern of @code{define-modify-macro}. For example,
5009 @code{push} takes its arguments in the wrong order, and @code{pop}
5010 is completely irregular.
5012 The above @code{incf} example could be written using
5013 @code{gv-letplace} as:
5015 (defmacro incf (place &optional n)
5016 (gv-letplace (getter setter) place
5017 (macroexp-let2 nil v (or n 1)
5018 (funcall setter `(+ ,v ,getter)))))
5021 (defmacro concatf (place &rest args)
5022 (gv-letplace (getter setter) place
5023 (macroexp-let2 nil v (mapconcat 'identity args "")
5024 (funcall setter `(concat ,getter ,v)))))
5028 @defmac defsetf access-fn update-fn
5029 This is the simpler of two @code{defsetf} forms, and is
5030 replaced by @code{gv-define-simple-setter}.
5032 With @var{access-fn} the name of a function that accesses a place,
5033 this declares @var{update-fn} to be the corresponding store function.
5037 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value})
5044 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value})
5048 The @var{update-fn} is required to be either a true function, or
5049 a macro that evaluates its arguments in a function-like way. Also,
5050 the @var{update-fn} is expected to return @var{value} as its result.
5051 Otherwise, the above expansion would not obey the rules for the way
5052 @code{setf} is supposed to behave.
5054 As a special (non-Common-Lisp) extension, a third argument of @code{t}
5055 to @code{defsetf} says that the return value of @code{update-fn} is
5056 not suitable, so that the above @code{setf} should be expanded to
5060 (let ((temp @var{value}))
5061 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp)
5068 (defsetf car setcar)
5069 (defsetf buffer-name rename-buffer t)
5072 These translate directly to @code{gv-define-simple-setter}:
5075 (gv-define-simple-setter car setcar)
5076 (gv-define-simple-setter buffer-name rename-buffer t)
5080 @defmac defsetf access-fn arglist (store-var) forms@dots{}
5081 This is the second, more complex, form of @code{defsetf}.
5082 It can be replaced by @code{gv-define-setter}.
5084 This form of @code{defsetf} is rather like @code{defmacro} except for
5085 the additional @var{store-var} argument. The @var{forms} should
5086 return a Lisp form that stores the value of @var{store-var} into the
5087 generalized variable formed by a call to @var{access-fn} with
5088 arguments described by @var{arglist}. The @var{forms} may begin with
5089 a string which documents the @code{setf} method (analogous to the doc
5090 string that appears at the front of a function).
5092 For example, the simple form of @code{defsetf} is shorthand for
5095 (defsetf @var{access-fn} (&rest args) (store)
5096 (append '(@var{update-fn}) args (list store)))
5099 The Lisp form that is returned can access the arguments from
5100 @var{arglist} and @var{store-var} in an unrestricted fashion;
5101 macros like @code{cl-incf} that invoke this
5102 setf-method will insert temporary variables as needed to make
5103 sure the apparent order of evaluation is preserved.
5105 Another standard example:
5108 (defsetf nth (n x) (store)
5109 `(setcar (nthcdr ,n ,x) ,store))
5112 You could write this using @code{gv-define-setter} as:
5115 (gv-define-setter nth (store n x)
5116 `(setcar (nthcdr ,n ,x) ,store))
5120 @defmac define-setf-method access-fn arglist forms@dots{}
5121 This is the most general way to create new place forms. You can
5122 replace this by @code{gv-define-setter} or @code{gv-define-expander}.
5124 When a @code{setf} to @var{access-fn} with arguments described by
5125 @var{arglist} is expanded, the @var{forms} are evaluated and must
5126 return a list of five items:
5130 A list of @dfn{temporary variables}.
5133 A list of @dfn{value forms} corresponding to the temporary variables
5134 above. The temporary variables will be bound to these value forms
5135 as the first step of any operation on the generalized variable.
5138 A list of exactly one @dfn{store variable} (generally obtained
5139 from a call to @code{gensym}).
5142 A Lisp form that stores the contents of the store variable into
5143 the generalized variable, assuming the temporaries have been
5144 bound as described above.
5147 A Lisp form that accesses the contents of the generalized variable,
5148 assuming the temporaries have been bound.
5151 This is exactly like the Common Lisp macro of the same name,
5152 except that the method returns a list of five values rather
5153 than the five values themselves, since Emacs Lisp does not
5154 support Common Lisp's notion of multiple return values.
5155 (Note that the @code{setf} implementation provided by @file{gv.el}
5156 does not use this five item format. Its use here is only for
5157 backwards compatibility.)
5159 Once again, the @var{forms} may begin with a documentation string.
5161 A setf-method should be maximally conservative with regard to
5162 temporary variables. In the setf-methods generated by
5163 @code{defsetf}, the second return value is simply the list of
5164 arguments in the place form, and the first return value is a
5165 list of a corresponding number of temporary variables generated
5166 @c FIXME I don't think this is true anymore.
5167 by @code{cl-gensym}. Macros like @code{cl-incf} that
5168 use this setf-method will optimize away most temporaries that
5169 turn out to be unnecessary, so there is little reason for the
5170 setf-method itself to optimize.
5173 @c Removed in Emacs 24.3, not possible to make a compatible replacement.
5175 @defun get-setf-method place &optional env
5176 This function returns the setf-method for @var{place}, by
5177 invoking the definition previously recorded by @code{defsetf}
5178 or @code{define-setf-method}. The result is a list of five
5179 values as described above. You can use this function to build
5180 your own @code{cl-incf}-like modify macros.
5182 The argument @var{env} specifies the ``environment'' to be
5183 passed on to @code{macroexpand} if @code{get-setf-method} should
5184 need to expand a macro in @var{place}. It should come from
5185 an @code{&environment} argument to the macro or setf-method
5186 that called @code{get-setf-method}.
5191 @node GNU Free Documentation License
5192 @appendix GNU Free Documentation License
5193 @include doclicense.texi
5195 @node Function Index
5196 @unnumbered Function Index
5200 @node Variable Index
5201 @unnumbered Variable Index