1 \input texinfo @c -*-texinfo-*-
2 @setfilename ../../info/cl
3 @settitle Common Lisp Extensions
7 This file documents the GNU Emacs Common Lisp emulation package.
9 Copyright @copyright{} 1993, 2001--2013 Free Software Foundation, Inc.
12 Permission is granted to copy, distribute and/or modify this document
13 under the terms of the GNU Free Documentation License, Version 1.3 or
14 any later version published by the Free Software Foundation; with no
15 Invariant Sections, with the Front-Cover texts being ``A GNU Manual'',
16 and with the Back-Cover Texts as in (a) below. A copy of the license
17 is included in the section entitled ``GNU Free Documentation License''.
19 (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
20 modify this GNU manual.''
24 @dircategory Emacs lisp libraries
26 * CL: (cl). Partial Common Lisp support for Emacs Lisp.
33 @center @titlefont{Common Lisp Extensions}
35 @center For GNU Emacs Lisp
37 @center as distributed with Emacs @value{EMACSVER}
39 @center Dave Gillespie
40 @center daveg@@synaptics.com
42 @vskip 0pt plus 1filll
50 @top GNU Emacs Common Lisp Emulation
56 * Overview:: Basics, usage, organization, naming conventions.
57 * Program Structure:: Arglists, @code{cl-eval-when}.
58 * Predicates:: Type predicates and equality predicates.
59 * Control Structure:: Assignment, conditionals, blocks, looping.
60 * Macros:: Destructuring, compiler macros.
61 * Declarations:: @code{cl-proclaim}, @code{cl-declare}, etc.
62 * Symbols:: Property lists, creating symbols.
63 * Numbers:: Predicates, functions, random numbers.
64 * Sequences:: Mapping, functions, searching, sorting.
65 * Lists:: Functions, substitution, sets, associations.
66 * Structures:: @code{cl-defstruct}.
67 * Assertions:: Assertions and type checking.
70 * Efficiency Concerns:: Hints and techniques.
71 * Common Lisp Compatibility:: All known differences with Steele.
72 * Porting Common Lisp:: Hints for porting Common Lisp code.
73 * Obsolete Features:: Obsolete features.
74 * GNU Free Documentation License:: The license for this documentation.
77 * Function Index:: An entry for each documented function.
78 * Variable Index:: An entry for each documented variable.
85 This document describes a set of Emacs Lisp facilities borrowed from
86 Common Lisp. All the facilities are described here in detail. While
87 this document does not assume any prior knowledge of Common Lisp, it
88 does assume a basic familiarity with Emacs Lisp.
90 Common Lisp is a huge language, and Common Lisp systems tend to be
91 massive and extremely complex. Emacs Lisp, by contrast, is rather
92 minimalist in the choice of Lisp features it offers the programmer.
93 As Emacs Lisp programmers have grown in number, and the applications
94 they write have grown more ambitious, it has become clear that Emacs
95 Lisp could benefit from many of the conveniences of Common Lisp.
97 The @dfn{CL} package adds a number of Common Lisp functions and
98 control structures to Emacs Lisp. While not a 100% complete
99 implementation of Common Lisp, it adds enough functionality
100 to make Emacs Lisp programming significantly more convenient.
102 Some Common Lisp features have been omitted from this package
107 Some features are too complex or bulky relative to their benefit
108 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine
109 examples of this group. (The separate package EIEIO implements
110 a subset of CLOS functionality. @xref{Top, , Introduction, eieio, EIEIO}.)
113 Other features cannot be implemented without modification to the
114 Emacs Lisp interpreter itself, such as multiple return values,
115 case-insensitive symbols, and complex numbers.
116 This package generally makes no attempt to emulate these features.
120 This package was originally written by Dave Gillespie,
121 @file{daveg@@synaptics.com}, as a total rewrite of an earlier 1986
122 @file{cl.el} package by Cesar Quiroz. Care has been taken to ensure
123 that each function is defined efficiently, concisely, and with minimal
124 impact on the rest of the Emacs environment. Stefan Monnier added the
125 file @file{cl-lib.el} and rationalized the namespace for Emacs 24.3.
128 * Usage:: How to use this package.
129 * Organization:: The package's component files.
130 * Naming Conventions:: Notes on function names.
137 This package is distributed with Emacs, so there is no need
138 to install any additional files in order to start using it. Lisp code
139 that uses features from this package should simply include at
147 You may wish to add such a statement to your init file, if you
148 make frequent use of features from this package.
151 @section Organization
154 The Common Lisp package is organized into four main files:
158 This is the main file, which contains basic functions
159 and information about the package. This file is relatively compact.
162 This file contains the larger, more complex or unusual functions.
163 It is kept separate so that packages which only want to use Common
164 Lisp fundamentals like the @code{cl-incf} function won't need to pay
165 the overhead of loading the more advanced functions.
168 This file contains most of the advanced functions for operating
169 on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}.
172 This file contains the features that are macros instead of functions.
173 Macros expand when the caller is compiled, not when it is run, so the
174 macros generally only need to be present when the byte-compiler is
175 running (or when the macros are used in uncompiled code). Most of the
176 macros of this package are isolated in @file{cl-macs.el} so that they
177 won't take up memory unless you are compiling.
180 The file @file{cl-lib.el} includes all necessary @code{autoload}
181 commands for the functions and macros in the other three files.
182 All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el}
183 will take care of pulling in the other files when they are
186 There is another file, @file{cl.el}, which was the main entry point to
187 this package prior to Emacs 24.3. Nowadays, it is replaced by
188 @file{cl-lib.el}. The two provide the same features (in most cases),
189 but use different function names (in fact, @file{cl.el} mainly just
190 defines aliases to the @file{cl-lib.el} definitions). Where
191 @file{cl-lib.el} defines a function called, for example,
192 @code{cl-incf}, @file{cl.el} uses the same name but without the
193 @samp{cl-} prefix, e.g., @code{incf} in this example. There are a few
194 exceptions to this. First, functions such as @code{cl-defun} where
195 the unprefixed version was already used for a standard Emacs Lisp
196 function. In such cases, the @file{cl.el} version adds a @samp{*}
197 suffix, e.g., @code{defun*}. Second, there are some obsolete features
198 that are only implemented in @file{cl.el}, not in @file{cl-lib.el},
199 because they are replaced by other standard Emacs Lisp features.
200 Finally, in a very few cases the old @file{cl.el} versions do not
201 behave in exactly the same way as the @file{cl-lib.el} versions.
202 @xref{Obsolete Features}.
203 @c There is also cl-mapc, which was called cl-mapc even before cl-lib.el.
204 @c But not autoloaded, so maybe not much used?
206 Since the old @file{cl.el} does not use a clean namespace, Emacs has a
207 policy that packages distributed with Emacs must not load @code{cl} at
208 run time. (It is ok for them to load @code{cl} at @emph{compile}
209 time, with @code{eval-when-compile}, and use the macros it provides.)
210 There is no such restriction on the use of @code{cl-lib}. New code
211 should use @code{cl-lib} rather than @code{cl}.
213 There is one more file, @file{cl-compat.el}, which defines some
214 routines from the older Quiroz @file{cl.el} package that are not otherwise
215 present in the new package. This file is obsolete and should not be
218 @node Naming Conventions
219 @section Naming Conventions
222 Except where noted, all functions defined by this package have the
223 same calling conventions as their Common Lisp counterparts, and
224 names that are those of Common Lisp plus a @samp{cl-} prefix.
226 Internal function and variable names in the package are prefixed
227 by @code{cl--}. Here is a complete list of functions prefixed by
228 @code{cl-} that were @emph{not} taken from Common Lisp:
231 cl-callf cl-callf2 cl-defsubst
235 @c This is not uninteresting I suppose, but is of zero practical relevance
236 @c to the user, and seems like a hostage to changing implementation details.
237 The following simple functions and macros are defined in @file{cl-lib.el};
238 they do not cause other components like @file{cl-extra} to be loaded.
241 cl-evenp cl-oddp cl-minusp
242 cl-plusp cl-endp cl-subst
243 cl-copy-list cl-list* cl-ldiff
244 cl-rest cl-decf [1] cl-incf [1]
245 cl-acons cl-adjoin [2] cl-pairlis
246 cl-pushnew [1,2] cl-declaim cl-proclaim
247 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
252 [1] Only when @var{place} is a plain variable name.
255 [2] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified,
256 and @code{:key} is not used.
259 [3] Only for one sequence argument or two list arguments.
261 @node Program Structure
262 @chapter Program Structure
265 This section describes features of this package that have to
266 do with programs as a whole: advanced argument lists for functions,
267 and the @code{cl-eval-when} construct.
270 * Argument Lists:: @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}.
271 * Time of Evaluation:: The @code{cl-eval-when} construct.
275 @section Argument Lists
278 Emacs Lisp's notation for argument lists of functions is a subset of
279 the Common Lisp notation. As well as the familiar @code{&optional}
280 and @code{&rest} markers, Common Lisp allows you to specify default
281 values for optional arguments, and it provides the additional markers
282 @code{&key} and @code{&aux}.
284 Since argument parsing is built-in to Emacs, there is no way for
285 this package to implement Common Lisp argument lists seamlessly.
286 Instead, this package defines alternates for several Lisp forms
287 which you must use if you need Common Lisp argument lists.
289 @defmac cl-defun name arglist body@dots{}
290 This form is identical to the regular @code{defun} form, except
291 that @var{arglist} is allowed to be a full Common Lisp argument
292 list. Also, the function body is enclosed in an implicit block
293 called @var{name}; @pxref{Blocks and Exits}.
296 @defmac cl-defsubst name arglist body@dots{}
297 This is just like @code{cl-defun}, except that the function that
298 is defined is automatically proclaimed @code{inline}, i.e.,
299 calls to it may be expanded into in-line code by the byte compiler.
300 This is analogous to the @code{defsubst} form;
301 @code{cl-defsubst} uses a different method (compiler macros) which
302 works in all versions of Emacs, and also generates somewhat more
303 @c For some examples,
304 @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html
305 efficient inline expansions. In particular, @code{cl-defsubst}
306 arranges for the processing of keyword arguments, default values,
307 etc., to be done at compile-time whenever possible.
310 @defmac cl-defmacro name arglist body@dots{}
311 This is identical to the regular @code{defmacro} form,
312 except that @var{arglist} is allowed to be a full Common Lisp
313 argument list. The @code{&environment} keyword is supported as
314 described in Steele's book @cite{Common Lisp, the Language}.
315 The @code{&whole} keyword is supported only
316 within destructured lists (see below); top-level @code{&whole}
317 cannot be implemented with the current Emacs Lisp interpreter.
318 The macro expander body is enclosed in an implicit block called
322 @defmac cl-function symbol-or-lambda
323 This is identical to the regular @code{function} form,
324 except that if the argument is a @code{lambda} form then that
325 form may use a full Common Lisp argument list.
328 Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
329 in this package that include @var{arglist}s in their syntax allow
330 full Common Lisp argument lists.
332 Note that it is @emph{not} necessary to use @code{cl-defun} in
333 order to have access to most CL features in your function.
334 These features are always present; @code{cl-defun}'s only
335 difference from @code{defun} is its more flexible argument
336 lists and its implicit block.
338 The full form of a Common Lisp argument list is
342 &optional (@var{var} @var{initform} @var{svar})@dots{}
344 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{}
345 &aux (@var{var} @var{initform})@dots{})
348 Each of the five argument list sections is optional. The @var{svar},
349 @var{initform}, and @var{keyword} parts are optional; if they are
350 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.
352 The first section consists of zero or more @dfn{required} arguments.
353 These arguments must always be specified in a call to the function;
354 there is no difference between Emacs Lisp and Common Lisp as far as
355 required arguments are concerned.
357 The second section consists of @dfn{optional} arguments. These
358 arguments may be specified in the function call; if they are not,
359 @var{initform} specifies the default value used for the argument.
360 (No @var{initform} means to use @code{nil} as the default.) The
361 @var{initform} is evaluated with the bindings for the preceding
362 arguments already established; @code{(a &optional (b (1+ a)))}
363 matches one or two arguments, with the second argument defaulting
364 to one plus the first argument. If the @var{svar} is specified,
365 it is an auxiliary variable which is bound to @code{t} if the optional
366 argument was specified, or to @code{nil} if the argument was omitted.
367 If you don't use an @var{svar}, then there will be no way for your
368 function to tell whether it was called with no argument, or with
369 the default value passed explicitly as an argument.
371 The third section consists of a single @dfn{rest} argument. If
372 more arguments were passed to the function than are accounted for
373 by the required and optional arguments, those extra arguments are
374 collected into a list and bound to the ``rest'' argument variable.
375 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
376 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
377 macro contexts; this package accepts it all the time.
379 The fourth section consists of @dfn{keyword} arguments. These
380 are optional arguments which are specified by name rather than
381 positionally in the argument list. For example,
384 (cl-defun foo (a &optional b &key c d (e 17)))
388 defines a function which may be called with one, two, or more
389 arguments. The first two arguments are bound to @code{a} and
390 @code{b} in the usual way. The remaining arguments must be
391 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
392 by the value to be bound to the corresponding argument variable.
393 (Symbols whose names begin with a colon are called @dfn{keywords},
394 and they are self-quoting in the same way as @code{nil} and
397 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
398 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword
399 appears more than once in the function call, the first occurrence
400 takes precedence over the later ones. Note that it is not possible
401 to specify keyword arguments without specifying the optional
402 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
403 @code{b} to the keyword @code{:c}, then signal an error because
404 @code{2} is not a valid keyword.
406 You can also explicitly specify the keyword argument; it need not be
407 simply the variable name prefixed with a colon. For example,
410 (cl-defun bar (&key (a 1) ((baz b) 4)))
415 specifies a keyword @code{:a} that sets the variable @code{a} with
416 default value 1, as well as a keyword @code{baz} that sets the
417 variable @code{b} with default value 4. In this case, because
418 @code{baz} is not self-quoting, you must quote it explicitly in the
419 function call, like this:
425 Ordinarily, it is an error to pass an unrecognized keyword to
426 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask
427 Lisp to ignore unrecognized keywords, either by adding the
428 marker @code{&allow-other-keys} after the keyword section
429 of the argument list, or by specifying an @code{:allow-other-keys}
430 argument in the call whose value is non-@code{nil}. If the
431 function uses both @code{&rest} and @code{&key} at the same time,
432 the ``rest'' argument is bound to the keyword list as it appears
433 in the call. For example:
436 (cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
437 (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
438 (if need (error "Thing not found"))))
442 This function takes a @code{:need} keyword argument, but also
443 accepts other keyword arguments which are passed on to the
444 @code{cl-member} function. @code{allow-other-keys} is used to
445 keep both @code{find-thing} and @code{cl-member} from complaining
446 about each others' keywords in the arguments.
448 The fifth section of the argument list consists of @dfn{auxiliary
449 variables}. These are not really arguments at all, but simply
450 variables which are bound to @code{nil} or to the specified
451 @var{initforms} during execution of the function. There is no
452 difference between the following two functions, except for a
453 matter of stylistic taste:
456 (cl-defun foo (a b &aux (c (+ a b)) d)
464 Argument lists support @dfn{destructuring}. In Common Lisp,
465 destructuring is only allowed with @code{defmacro}; this package
466 allows it with @code{cl-defun} and other argument lists as well.
467 In destructuring, any argument variable (@var{var} in the above
468 example) can be replaced by a list of variables, or more generally,
469 a recursive argument list. The corresponding argument value must
470 be a list whose elements match this recursive argument list.
474 (cl-defmacro dolist ((var listform &optional resultform)
479 This says that the first argument of @code{dolist} must be a list
480 of two or three items; if there are other arguments as well as this
481 list, they are stored in @code{body}. All features allowed in
482 regular argument lists are allowed in these recursive argument lists.
483 In addition, the clause @samp{&whole @var{var}} is allowed at the
484 front of a recursive argument list. It binds @var{var} to the
485 whole list being matched; thus @code{(&whole all a b)} matches
486 a list of two things, with @code{a} bound to the first thing,
487 @code{b} bound to the second thing, and @code{all} bound to the
488 list itself. (Common Lisp allows @code{&whole} in top-level
489 @code{defmacro} argument lists as well, but Emacs Lisp does not
492 One last feature of destructuring is that the argument list may be
493 dotted, so that the argument list @code{(a b . c)} is functionally
494 equivalent to @code{(a b &rest c)}.
496 If the optimization quality @code{safety} is set to 0
497 (@pxref{Declarations}), error checking for wrong number of
498 arguments and invalid keyword arguments is disabled. By default,
499 argument lists are rigorously checked.
501 @node Time of Evaluation
502 @section Time of Evaluation
505 Normally, the byte-compiler does not actually execute the forms in
506 a file it compiles. For example, if a file contains @code{(setq foo t)},
507 the act of compiling it will not actually set @code{foo} to @code{t}.
508 This is true even if the @code{setq} was a top-level form (i.e., not
509 enclosed in a @code{defun} or other form). Sometimes, though, you
510 would like to have certain top-level forms evaluated at compile-time.
511 For example, the compiler effectively evaluates @code{defmacro} forms
512 at compile-time so that later parts of the file can refer to the
513 macros that are defined.
515 @defmac cl-eval-when (situations@dots{}) forms@dots{}
516 This form controls when the body @var{forms} are evaluated.
517 The @var{situations} list may contain any set of the symbols
518 @code{compile}, @code{load}, and @code{eval} (or their long-winded
519 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
520 and @code{:execute}).
522 The @code{cl-eval-when} form is handled differently depending on
523 whether or not it is being compiled as a top-level form.
524 Specifically, it gets special treatment if it is being compiled
525 by a command such as @code{byte-compile-file} which compiles files
526 or buffers of code, and it appears either literally at the
527 top level of the file or inside a top-level @code{progn}.
529 For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
530 executed at compile-time if @code{compile} is in the @var{situations}
531 list, and the @var{forms} are written out to the file (to be executed
532 at load-time) if @code{load} is in the @var{situations} list.
534 For non-compiled-top-level forms, only the @code{eval} situation is
535 relevant. (This includes forms executed by the interpreter, forms
536 compiled with @code{byte-compile} rather than @code{byte-compile-file},
537 and non-top-level forms.) The @code{cl-eval-when} acts like a
538 @code{progn} if @code{eval} is specified, and like @code{nil}
539 (ignoring the body @var{forms}) if not.
541 The rules become more subtle when @code{cl-eval-when}s are nested;
542 consult Steele (second edition) for the gruesome details (and
543 some gruesome examples).
545 Some simple examples:
548 ;; Top-level forms in foo.el:
549 (cl-eval-when (compile) (setq foo1 'bar))
550 (cl-eval-when (load) (setq foo2 'bar))
551 (cl-eval-when (compile load) (setq foo3 'bar))
552 (cl-eval-when (eval) (setq foo4 'bar))
553 (cl-eval-when (eval compile) (setq foo5 'bar))
554 (cl-eval-when (eval load) (setq foo6 'bar))
555 (cl-eval-when (eval compile load) (setq foo7 'bar))
558 When @file{foo.el} is compiled, these variables will be set during
559 the compilation itself:
562 foo1 foo3 foo5 foo7 ; `compile'
565 When @file{foo.elc} is loaded, these variables will be set:
568 foo2 foo3 foo6 foo7 ; `load'
571 And if @file{foo.el} is loaded uncompiled, these variables will
575 foo4 foo5 foo6 foo7 ; `eval'
578 If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
579 then the first three would have been equivalent to @code{nil} and the
580 last four would have been equivalent to the corresponding @code{setq}s.
582 Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
583 to @code{(progn @dots{})} in all contexts. The compiler treats
584 certain top-level forms, like @code{defmacro} (sort-of) and
585 @code{require}, as if they were wrapped in @code{(cl-eval-when
586 (compile load eval) @dots{})}.
589 Emacs includes two special forms related to @code{cl-eval-when}.
590 @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}.
591 One of these, @code{eval-when-compile}, is not quite equivalent to
592 any @code{cl-eval-when} construct and is described below.
594 The other form, @code{(eval-and-compile @dots{})}, is exactly
595 equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}.
597 @defmac eval-when-compile forms@dots{}
598 The @var{forms} are evaluated at compile-time; at execution time,
599 this form acts like a quoted constant of the resulting value. Used
600 at top-level, @code{eval-when-compile} is just like @samp{eval-when
601 (compile eval)}. In other contexts, @code{eval-when-compile}
602 allows code to be evaluated once at compile-time for efficiency
605 This form is similar to the @samp{#.} syntax of true Common Lisp.
608 @defmac cl-load-time-value form
609 The @var{form} is evaluated at load-time; at execution time,
610 this form acts like a quoted constant of the resulting value.
612 Early Common Lisp had a @samp{#,} syntax that was similar to
613 this, but ANSI Common Lisp replaced it with @code{load-time-value}
614 and gave it more well-defined semantics.
616 In a compiled file, @code{cl-load-time-value} arranges for @var{form}
617 to be evaluated when the @file{.elc} file is loaded and then used
618 as if it were a quoted constant. In code compiled by
619 @code{byte-compile} rather than @code{byte-compile-file}, the
620 effect is identical to @code{eval-when-compile}. In uncompiled
621 code, both @code{eval-when-compile} and @code{cl-load-time-value}
622 act exactly like @code{progn}.
626 (insert "This function was executed on: "
627 (current-time-string)
629 (eval-when-compile (current-time-string))
630 ;; or '#.(current-time-string) in real Common Lisp
632 (cl-load-time-value (current-time-string))))
636 Byte-compiled, the above defun will result in the following code
637 (or its compiled equivalent, of course) in the @file{.elc} file:
640 (setq --temp-- (current-time-string))
642 (insert "This function was executed on: "
643 (current-time-string)
645 '"Wed Oct 31 16:32:28 2012"
655 This section describes functions for testing whether various
656 facts are true or false.
659 * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
660 * Equality Predicates:: @code{cl-equalp}.
663 @node Type Predicates
664 @section Type Predicates
666 @defun cl-typep object type
667 Check if @var{object} is of type @var{type}, where @var{type} is a
668 (quoted) type name of the sort used by Common Lisp. For example,
669 @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
672 The @var{type} argument to the above function is either a symbol
673 or a list beginning with a symbol.
677 If the type name is a symbol, Emacs appends @samp{-p} to the
678 symbol name to form the name of a predicate function for testing
679 the type. (Built-in predicates whose names end in @samp{p} rather
680 than @samp{-p} are used when appropriate.)
683 The type symbol @code{t} stands for the union of all types.
684 @code{(cl-typep @var{object} t)} is always true. Likewise, the
685 type symbol @code{nil} stands for nothing at all, and
686 @code{(cl-typep @var{object} nil)} is always false.
689 The type symbol @code{null} represents the symbol @code{nil}.
690 Thus @code{(cl-typep @var{object} 'null)} is equivalent to
691 @code{(null @var{object})}.
694 The type symbol @code{atom} represents all objects that are not cons
695 cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
696 @code{(atom @var{object})}.
699 The type symbol @code{real} is a synonym for @code{number}, and
700 @code{fixnum} is a synonym for @code{integer}.
703 The type symbols @code{character} and @code{string-char} match
704 integers in the range from 0 to 255.
706 @c No longer relevant, so covered by first item above (float -> floatp).
709 The type symbol @code{float} uses the @code{cl-floatp-safe} predicate
710 defined by this package rather than @code{floatp}, so it will work
711 correctly even in Emacs versions without floating-point support.
715 The type list @code{(integer @var{low} @var{high})} represents all
716 integers between @var{low} and @var{high}, inclusive. Either bound
717 may be a list of a single integer to specify an exclusive limit,
718 or a @code{*} to specify no limit. The type @code{(integer * *)}
719 is thus equivalent to @code{integer}.
722 Likewise, lists beginning with @code{float}, @code{real}, or
723 @code{number} represent numbers of that type falling in a particular
727 Lists beginning with @code{and}, @code{or}, and @code{not} form
728 combinations of types. For example, @code{(or integer (float 0 *))}
729 represents all objects that are integers or non-negative floats.
732 Lists beginning with @code{member} or @code{cl-member} represent
733 objects @code{eql} to any of the following values. For example,
734 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
735 and @code{(member nil)} is equivalent to @code{null}.
738 Lists of the form @code{(satisfies @var{predicate})} represent
739 all objects for which @var{predicate} returns true when called
740 with that object as an argument.
743 The following function and macro (not technically predicates) are
744 related to @code{cl-typep}.
746 @defun cl-coerce object type
747 This function attempts to convert @var{object} to the specified
748 @var{type}. If @var{object} is already of that type as determined by
749 @code{cl-typep}, it is simply returned. Otherwise, certain types of
750 conversions will be made: If @var{type} is any sequence type
751 (@code{string}, @code{list}, etc.) then @var{object} will be
752 converted to that type if possible. If @var{type} is
753 @code{character}, then strings of length one and symbols with
754 one-character names can be coerced. If @var{type} is @code{float},
755 then integers can be coerced in versions of Emacs that support
756 floats. In all other circumstances, @code{cl-coerce} signals an
760 @defmac cl-deftype name arglist forms@dots{}
761 This macro defines a new type called @var{name}. It is similar
762 to @code{defmacro} in many ways; when @var{name} is encountered
763 as a type name, the body @var{forms} are evaluated and should
764 return a type specifier that is equivalent to the type. The
765 @var{arglist} is a Common Lisp argument list of the sort accepted
766 by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})}
767 is expanded by calling the expander with those arguments; the type
768 symbol @samp{@var{name}} is expanded by calling the expander with
769 no arguments. The @var{arglist} is processed the same as for
770 @code{cl-defmacro} except that optional arguments without explicit
771 defaults use @code{*} instead of @code{nil} as the ``default''
772 default. Some examples:
775 (cl-deftype null () '(satisfies null)) ; predefined
776 (cl-deftype list () '(or null cons)) ; predefined
777 (cl-deftype unsigned-byte (&optional bits)
778 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
779 (unsigned-byte 8) @equiv{} (integer 0 255)
780 (unsigned-byte) @equiv{} (integer 0 *)
781 unsigned-byte @equiv{} (integer 0 *)
785 The last example shows how the Common Lisp @code{unsigned-byte}
786 type specifier could be implemented if desired; this package does
787 not implement @code{unsigned-byte} by default.
790 The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type}
791 (@pxref{Assertions}) macros also use type names. The @code{cl-map},
792 @code{cl-concatenate}, and @code{cl-merge} functions take type-name
793 arguments to specify the type of sequence to return. @xref{Sequences}.
795 @node Equality Predicates
796 @section Equality Predicates
799 This package defines the Common Lisp predicate @code{cl-equalp}.
802 This function is a more flexible version of @code{equal}. In
803 particular, it compares strings case-insensitively, and it compares
804 numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
805 true). Vectors and conses are compared recursively. All other
806 objects are compared as if by @code{equal}.
808 This function differs from Common Lisp @code{equalp} in several
809 respects. First, Common Lisp's @code{equalp} also compares
810 @emph{characters} case-insensitively, which would be impractical
811 in this package since Emacs does not distinguish between integers
812 and characters. In keeping with the idea that strings are less
813 vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
814 not compare strings against vectors of integers.
817 Also note that the Common Lisp functions @code{member} and @code{assoc}
818 use @code{eql} to compare elements, whereas Emacs Lisp follows the
819 MacLisp tradition and uses @code{equal} for these two functions.
820 In Emacs, use @code{memq} (or @code{cl-member}) and @code{assq} (or
821 @code{cl-assoc}) to get functions which use @code{eql} for comparisons.
823 @node Control Structure
824 @chapter Control Structure
827 The features described in the following sections implement
828 various advanced control structures, including extensions to the
829 standard @code{setf} facility, and a number of looping and conditional
833 * Assignment:: The @code{cl-psetq} form.
834 * Generalized Variables:: Extensions to generalized variables.
835 * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}.
836 * Conditionals:: @code{cl-case}, @code{cl-typecase}.
837 * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}.
838 * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}.
839 * Loop Facility:: The Common Lisp @code{loop} macro.
840 * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc.
847 The @code{cl-psetq} form is just like @code{setq}, except that multiple
848 assignments are done in parallel rather than sequentially.
850 @defmac cl-psetq [symbol form]@dots{}
851 This special form (actually a macro) is used to assign to several
852 variables simultaneously. Given only one @var{symbol} and @var{form},
853 it has the same effect as @code{setq}. Given several @var{symbol}
854 and @var{form} pairs, it evaluates all the @var{form}s in advance
855 and then stores the corresponding variables afterwards.
859 (setq x (+ x y) y (* x y))
862 y ; @r{@code{y} was computed after @code{x} was set.}
865 (cl-psetq x (+ x y) y (* x y))
868 y ; @r{@code{y} was computed before @code{x} was set.}
872 The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which
873 exchanges the values of two variables. (The @code{cl-rotatef} form
874 provides an even more convenient way to swap two variables;
875 @pxref{Modify Macros}.)
877 @code{cl-psetq} always returns @code{nil}.
880 @node Generalized Variables
881 @section Generalized Variables
883 A @dfn{generalized variable} or @dfn{place form} is one of the many
884 places in Lisp memory where values can be stored. The simplest place
885 form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists,
886 elements of arrays, properties of symbols, and many other locations
887 are also places where Lisp values are stored. For basic information,
888 @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
889 This package provides several additional features related to
890 generalized variables.
893 * Setf Extensions:: Additional @code{setf} places.
894 * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc.
897 @node Setf Extensions
898 @subsection Setf Extensions
900 Several standard (e.g., @code{car}) and Emacs-specific
901 (e.g., @code{window-point}) Lisp functions are @code{setf}-able by default.
902 This package defines @code{setf} handlers for several additional functions:
906 Functions from this package:
908 cl-rest cl-subseq cl-get cl-getf
909 cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth
913 Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument
914 of the function must itself be a valid @var{place} form.
917 General Emacs Lisp functions:
919 buffer-file-name getenv
920 buffer-modified-p global-key-binding
921 buffer-name local-key-binding
923 buffer-substring mark-marker
924 current-buffer marker-position
925 current-case-table mouse-position
927 current-global-map point-marker
928 current-input-mode point-max
929 current-local-map point-min
930 current-window-configuration read-mouse-position
931 default-file-modes screen-height
932 documentation-property screen-width
933 face-background selected-window
934 face-background-pixmap selected-screen
935 face-font selected-frame
936 face-foreground standard-case-table
937 face-underline-p syntax-table
938 file-modes visited-file-modtime
939 frame-height window-height
940 frame-parameters window-width
941 frame-visible-p x-get-secondary-selection
942 frame-width x-get-selection
946 Most of these have directly corresponding ``set'' functions, like
947 @code{use-local-map} for @code{current-local-map}, or @code{goto-char}
948 for @code{point}. A few, like @code{point-min}, expand to longer
949 sequences of code when they are used with @code{setf}
950 (@code{(narrow-to-region x (point-max))} in this case).
953 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
954 where @var{subplace} is itself a valid generalized variable whose
955 current value is a string, and where the value stored is also a
956 string. The new string is spliced into the specified part of the
957 destination string. For example:
960 (setq a (list "hello" "world"))
961 @result{} ("hello" "world")
964 (substring (cadr a) 2 4)
966 (setf (substring (cadr a) 2 4) "o")
971 @result{} ("hello" "wood")
974 The generalized variable @code{buffer-substring}, listed above,
975 also works in this way by replacing a portion of the current buffer.
977 @c FIXME? Also `eq'? (see cl-lib.el)
979 @c Currently commented out in cl.el.
982 A call of the form @code{(apply '@var{func} @dots{})} or
983 @code{(apply (function @var{func}) @dots{})}, where @var{func}
984 is a @code{setf}-able function whose store function is ``suitable''
985 in the sense described in Steele's book; since none of the standard
986 Emacs place functions are suitable in this sense, this feature is
987 only interesting when used with places you define yourself with
988 @code{define-setf-method} or the long form of @code{defsetf}.
989 @xref{Obsolete Setf Customization}.
992 @c FIXME? Is this still true?
994 A macro call, in which case the macro is expanded and @code{setf}
995 is applied to the resulting form.
998 @c FIXME should this be in lispref? It seems self-evident.
999 @c Contrast with the cl-incf example later on.
1000 @c Here it really only serves as a contrast to wrong-order.
1001 The @code{setf} macro takes care to evaluate all subforms in
1002 the proper left-to-right order; for example,
1005 (setf (aref vec (cl-incf i)) i)
1009 looks like it will evaluate @code{(cl-incf i)} exactly once, before the
1010 following access to @code{i}; the @code{setf} expander will insert
1011 temporary variables as necessary to ensure that it does in fact work
1012 this way no matter what setf-method is defined for @code{aref}.
1013 (In this case, @code{aset} would be used and no such steps would
1014 be necessary since @code{aset} takes its arguments in a convenient
1017 However, if the @var{place} form is a macro which explicitly
1018 evaluates its arguments in an unusual order, this unusual order
1019 will be preserved. Adapting an example from Steele, given
1022 (defmacro wrong-order (x y) (list 'aref y x))
1026 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
1027 evaluate @var{b} first, then @var{a}, just as in an actual call
1028 to @code{wrong-order}.
1031 @subsection Modify Macros
1034 This package defines a number of macros that operate on generalized
1035 variables. Many are interesting and useful even when the @var{place}
1036 is just a variable name.
1038 @defmac cl-psetf [place form]@dots{}
1039 This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
1040 When several @var{place}s and @var{form}s are involved, the
1041 assignments take place in parallel rather than sequentially.
1042 Specifically, all subforms are evaluated from left to right, then
1043 all the assignments are done (in an undefined order).
1046 @defmac cl-incf place &optional x
1047 This macro increments the number stored in @var{place} by one, or
1048 by @var{x} if specified. The incremented value is returned. For
1049 example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and
1050 @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
1052 As with @code{setf}, care is taken to preserve the ``apparent'' order
1053 of evaluation. For example,
1056 (cl-incf (aref vec (cl-incf i)))
1060 appears to increment @code{i} once, then increment the element of
1061 @code{vec} addressed by @code{i}; this is indeed exactly what it
1062 does, which means the above form is @emph{not} equivalent to the
1063 ``obvious'' expansion,
1066 (setf (aref vec (cl-incf i))
1067 (1+ (aref vec (cl-incf i)))) ; wrong!
1071 but rather to something more like
1074 (let ((temp (cl-incf i)))
1075 (setf (aref vec temp) (1+ (aref vec temp))))
1079 Again, all of this is taken care of automatically by @code{cl-incf} and
1080 the other generalized-variable macros.
1082 As a more Emacs-specific example of @code{cl-incf}, the expression
1083 @code{(cl-incf (point) @var{n})} is essentially equivalent to
1084 @code{(forward-char @var{n})}.
1087 @defmac cl-decf place &optional x
1088 This macro decrements the number stored in @var{place} by one, or
1089 by @var{x} if specified.
1092 @defmac cl-pushnew x place @t{&key :test :test-not :key}
1093 This macro inserts @var{x} at the front of the list stored in
1094 @var{place}, but only if @var{x} was not @code{eql} to any
1095 existing element of the list. The optional keyword arguments
1096 are interpreted in the same way as for @code{cl-adjoin}.
1097 @xref{Lists as Sets}.
1100 @defmac cl-shiftf place@dots{} newvalue
1101 This macro shifts the @var{place}s left by one, shifting in the
1102 value of @var{newvalue} (which may be any Lisp expression, not just
1103 a generalized variable), and returning the value shifted out of
1104 the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c}
1105 @var{d})} is equivalent to
1110 (cl-psetf @var{a} @var{b}
1116 except that the subforms of @var{a}, @var{b}, and @var{c} are actually
1117 evaluated only once each and in the apparent order.
1120 @defmac cl-rotatef place@dots{}
1121 This macro rotates the @var{place}s left by one in circular fashion.
1122 Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to
1125 (cl-psetf @var{a} @var{b}
1132 except for the evaluation of subforms. @code{cl-rotatef} always
1133 returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})}
1134 conveniently exchanges @var{a} and @var{b}.
1137 The following macros were invented for this package; they have no
1138 analogues in Common Lisp.
1140 @defmac cl-letf (bindings@dots{}) forms@dots{}
1141 This macro is analogous to @code{let}, but for generalized variables
1142 rather than just symbols. Each @var{binding} should be of the form
1143 @code{(@var{place} @var{value})}; the original contents of the
1144 @var{place}s are saved, the @var{value}s are stored in them, and
1145 then the body @var{form}s are executed. Afterwards, the @var{places}
1146 are set back to their original saved contents. This cleanup happens
1147 even if the @var{form}s exit irregularly due to a @code{throw} or an
1153 (cl-letf (((point) (point-min))
1159 moves point in the current buffer to the beginning of the buffer,
1160 and also binds @code{a} to 17 (as if by a normal @code{let}, since
1161 @code{a} is just a regular variable). After the body exits, @code{a}
1162 is set back to its original value and point is moved back to its
1165 Note that @code{cl-letf} on @code{(point)} is not quite like a
1166 @code{save-excursion}, as the latter effectively saves a marker
1167 which tracks insertions and deletions in the buffer. Actually,
1168 a @code{cl-letf} of @code{(point-marker)} is much closer to this
1169 behavior. (@code{point} and @code{point-marker} are equivalent
1170 as @code{setf} places; each will accept either an integer or a
1171 marker as the stored value.)
1173 Since generalized variables look like lists, @code{let}'s shorthand
1174 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
1175 be ambiguous in @code{cl-letf} and is not allowed.
1177 However, a @var{binding} specifier may be a one-element list
1178 @samp{(@var{place})}, which is similar to @samp{(@var{place}
1179 @var{place})}. In other words, the @var{place} is not disturbed
1180 on entry to the body, and the only effect of the @code{cl-letf} is
1181 to restore the original value of @var{place} afterwards.
1182 @c I suspect this may no longer be true; either way it's
1183 @c implementation detail and so not essential to document.
1185 (The redundant access-and-store suggested by the @code{(@var{place}
1186 @var{place})} example does not actually occur.)
1189 Note that in this case, and in fact almost every case, @var{place}
1190 must have a well-defined value outside the @code{cl-letf} body.
1191 There is essentially only one exception to this, which is @var{place}
1192 a plain variable with a specified @var{value} (such as @code{(a 17)}
1193 in the above example).
1194 @c See http://debbugs.gnu.org/12758
1195 @c Some or all of this was true for cl.el, but not for cl-lib.el.
1197 The only exceptions are plain variables and calls to
1198 @code{symbol-value} and @code{symbol-function}. If the symbol is not
1199 bound on entry, it is simply made unbound by @code{makunbound} or
1200 @code{fmakunbound} on exit.
1204 @defmac cl-letf* (bindings@dots{}) forms@dots{}
1205 This macro is to @code{cl-letf} what @code{let*} is to @code{let}:
1206 It does the bindings in sequential rather than parallel order.
1209 @defmac cl-callf @var{function} @var{place} @var{args}@dots{}
1210 This is the ``generic'' modify macro. It calls @var{function},
1211 which should be an unquoted function name, macro name, or lambda.
1212 It passes @var{place} and @var{args} as arguments, and assigns the
1213 result back to @var{place}. For example, @code{(cl-incf @var{place}
1214 @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}.
1218 (cl-callf abs my-number)
1219 (cl-callf concat (buffer-name) "<" (number-to-string n) ">")
1220 (cl-callf cl-union happy-people (list joe bob) :test 'same-person)
1223 Note again that @code{cl-callf} is an extension to standard Common Lisp.
1226 @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{}
1227 This macro is like @code{cl-callf}, except that @var{place} is
1228 the @emph{second} argument of @var{function} rather than the
1229 first. For example, @code{(push @var{x} @var{place})} is
1230 equivalent to @code{(cl-callf2 cons @var{x} @var{place})}.
1233 The @code{cl-callf} and @code{cl-callf2} macros serve as building
1234 blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}.
1235 The @code{cl-letf} and @code{cl-letf*} macros are used in the processing
1236 of symbol macros; @pxref{Macro Bindings}.
1239 @node Variable Bindings
1240 @section Variable Bindings
1243 These Lisp forms make bindings to variables and function names,
1244 analogous to Lisp's built-in @code{let} form.
1246 @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which
1247 are also related to variable bindings.
1250 * Dynamic Bindings:: The @code{cl-progv} form.
1251 * Function Bindings:: @code{cl-flet} and @code{cl-labels}.
1252 * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}.
1255 @node Dynamic Bindings
1256 @subsection Dynamic Bindings
1259 The standard @code{let} form binds variables whose names are known
1260 at compile-time. The @code{cl-progv} form provides an easy way to
1261 bind variables whose names are computed at run-time.
1263 @defmac cl-progv symbols values forms@dots{}
1264 This form establishes @code{let}-style variable bindings on a
1265 set of variables computed at run-time. The expressions
1266 @var{symbols} and @var{values} are evaluated, and must return lists
1267 of symbols and values, respectively. The symbols are bound to the
1268 corresponding values for the duration of the body @var{form}s.
1269 If @var{values} is shorter than @var{symbols}, the last few symbols
1270 are bound to @code{nil}.
1271 If @var{symbols} is shorter than @var{values}, the excess values
1275 @node Function Bindings
1276 @subsection Function Bindings
1279 These forms make @code{let}-like bindings to functions instead
1282 @defmac cl-flet (bindings@dots{}) forms@dots{}
1283 This form establishes @code{let}-style bindings on the function
1284 cells of symbols rather than on the value cells. Each @var{binding}
1285 must be a list of the form @samp{(@var{name} @var{arglist}
1286 @var{forms}@dots{})}, which defines a function exactly as if
1287 it were a @code{cl-defun} form. The function @var{name} is defined
1288 accordingly for the duration of the body of the @code{cl-flet}; then
1289 the old function definition, or lack thereof, is restored.
1291 You can use @code{cl-flet} to disable or modify the behavior of
1292 functions (including Emacs primitives) in a temporary, localized fashion.
1293 (Compare this with the idea of advising functions.
1294 @xref{Advising Functions,,,elisp,GNU Emacs Lisp Reference Manual}.)
1296 The bindings are lexical in scope. This means that all references to
1297 the named functions must appear physically within the body of the
1298 @code{cl-flet} form.
1300 Functions defined by @code{cl-flet} may use the full Common Lisp
1301 argument notation supported by @code{cl-defun}; also, the function
1302 body is enclosed in an implicit block as if by @code{cl-defun}.
1303 @xref{Program Structure}.
1305 Note that the @file{cl.el} version of this macro behaves slightly
1306 differently. In particular, its binding is dynamic rather than
1307 lexical. @xref{Obsolete Macros}.
1310 @defmac cl-labels (bindings@dots{}) forms@dots{}
1311 The @code{cl-labels} form is like @code{cl-flet}, except that
1312 the function bindings can be recursive. The scoping is lexical,
1313 but you can only capture functions in closures if
1314 @code{lexical-binding} is @code{t}.
1315 @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and
1316 @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
1318 Lexical scoping means that all references to the named
1319 functions must appear physically within the body of the
1320 @code{cl-labels} form. References may appear both in the body
1321 @var{forms} of @code{cl-labels} itself, and in the bodies of
1322 the functions themselves. Thus, @code{cl-labels} can define
1323 local recursive functions, or mutually-recursive sets of functions.
1325 A ``reference'' to a function name is either a call to that
1326 function, or a use of its name quoted by @code{quote} or
1327 @code{function} to be passed on to, say, @code{mapcar}.
1329 Note that the @file{cl.el} version of this macro behaves slightly
1330 differently. @xref{Obsolete Macros}.
1333 @node Macro Bindings
1334 @subsection Macro Bindings
1337 These forms create local macros and ``symbol macros''.
1339 @defmac cl-macrolet (bindings@dots{}) forms@dots{}
1340 This form is analogous to @code{cl-flet}, but for macros instead of
1341 functions. Each @var{binding} is a list of the same form as the
1342 arguments to @code{cl-defmacro} (i.e., a macro name, argument list,
1343 and macro-expander forms). The macro is defined accordingly for
1344 use within the body of the @code{cl-macrolet}.
1346 Because of the nature of macros, @code{cl-macrolet} is always lexically
1347 scoped. The @code{cl-macrolet} binding will
1348 affect only calls that appear physically within the body
1349 @var{forms}, possibly after expansion of other macros in the
1353 @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{}
1354 This form creates @dfn{symbol macros}, which are macros that look
1355 like variable references rather than function calls. Each
1356 @var{binding} is a list @samp{(@var{var} @var{expansion})};
1357 any reference to @var{var} within the body @var{forms} is
1358 replaced by @var{expansion}.
1362 (cl-symbol-macrolet ((foo (car bar)))
1368 A @code{setq} of a symbol macro is treated the same as a @code{setf}.
1369 I.e., @code{(setq foo 4)} in the above would be equivalent to
1370 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
1372 Likewise, a @code{let} or @code{let*} binding a symbol macro is
1373 treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true
1374 Common Lisp, where the rules of lexical scoping cause a @code{let}
1375 binding to shadow a @code{symbol-macrolet} binding. In this package,
1376 such shadowing does not occur, even when @code{lexical-binding} is
1377 @c See http://debbugs.gnu.org/12119
1378 @code{t}. (This behavior predates the addition of lexical binding to
1379 Emacs Lisp, and may change in future to respect @code{lexical-binding}.)
1380 At present in this package, only @code{lexical-let} and
1381 @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete
1384 There is no analogue of @code{defmacro} for symbol macros; all symbol
1385 macros are local. A typical use of @code{cl-symbol-macrolet} is in the
1386 expansion of another macro:
1389 (cl-defmacro my-dolist ((x list) &rest body)
1390 (let ((var (cl-gensym)))
1391 (list 'cl-loop 'for var 'on list 'do
1392 (cl-list* 'cl-symbol-macrolet
1393 (list (list x (list 'car var)))
1396 (setq mylist '(1 2 3 4))
1397 (my-dolist (x mylist) (cl-incf x))
1403 In this example, the @code{my-dolist} macro is similar to @code{dolist}
1404 (@pxref{Iteration}) except that the variable @code{x} becomes a true
1405 reference onto the elements of the list. The @code{my-dolist} call
1406 shown here expands to
1409 (cl-loop for G1234 on mylist do
1410 (cl-symbol-macrolet ((x (car G1234)))
1415 which in turn expands to
1418 (cl-loop for G1234 on mylist do (cl-incf (car G1234)))
1421 @xref{Loop Facility}, for a description of the @code{cl-loop} macro.
1422 This package defines a nonstandard @code{in-ref} loop clause that
1423 works much like @code{my-dolist}.
1427 @section Conditionals
1430 These conditional forms augment Emacs Lisp's simple @code{if},
1431 @code{and}, @code{or}, and @code{cond} forms.
1433 @defmac cl-case keyform clause@dots{}
1434 This macro evaluates @var{keyform}, then compares it with the key
1435 values listed in the various @var{clause}s. Whichever clause matches
1436 the key is executed; comparison is done by @code{eql}. If no clause
1437 matches, the @code{cl-case} form returns @code{nil}. The clauses are
1441 (@var{keylist} @var{body-forms}@dots{})
1445 where @var{keylist} is a list of key values. If there is exactly
1446 one value, and it is not a cons cell or the symbol @code{nil} or
1447 @code{t}, then it can be used by itself as a @var{keylist} without
1448 being enclosed in a list. All key values in the @code{cl-case} form
1449 must be distinct. The final clauses may use @code{t} in place of
1450 a @var{keylist} to indicate a default clause that should be taken
1451 if none of the other clauses match. (The symbol @code{otherwise}
1452 is also recognized in place of @code{t}. To make a clause that
1453 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise},
1454 enclose the symbol in a list.)
1456 For example, this expression reads a keystroke, then does one of
1457 four things depending on whether it is an @samp{a}, a @samp{b},
1458 a @key{RET} or @kbd{C-j}, or anything else.
1461 (cl-case (read-char)
1464 ((?\r ?\n) (do-ret-thing))
1465 (t (do-other-thing)))
1469 @defmac cl-ecase keyform clause@dots{}
1470 This macro is just like @code{cl-case}, except that if the key does
1471 not match any of the clauses, an error is signaled rather than
1472 simply returning @code{nil}.
1475 @defmac cl-typecase keyform clause@dots{}
1476 This macro is a version of @code{cl-case} that checks for types
1477 rather than values. Each @var{clause} is of the form
1478 @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates},
1479 for a description of type specifiers. For example,
1483 (integer (munch-integer x))
1484 (float (munch-float x))
1485 (string (munch-integer (string-to-int x)))
1486 (t (munch-anything x)))
1489 The type specifier @code{t} matches any type of object; the word
1490 @code{otherwise} is also allowed. To make one clause match any of
1491 several types, use an @code{(or @dots{})} type specifier.
1494 @defmac cl-etypecase keyform clause@dots{}
1495 This macro is just like @code{cl-typecase}, except that if the key does
1496 not match any of the clauses, an error is signaled rather than
1497 simply returning @code{nil}.
1500 @node Blocks and Exits
1501 @section Blocks and Exits
1504 Common Lisp @dfn{blocks} provide a non-local exit mechanism very
1505 similar to @code{catch} and @code{throw}, with lexical scoping.
1506 This package actually implements @code{cl-block}
1507 in terms of @code{catch}; however, the lexical scoping allows the
1508 byte-compiler to omit the costly @code{catch} step if the
1509 body of the block does not actually @code{cl-return-from} the block.
1511 @defmac cl-block name forms@dots{}
1512 The @var{forms} are evaluated as if by a @code{progn}. However,
1513 if any of the @var{forms} execute @code{(cl-return-from @var{name})},
1514 they will jump out and return directly from the @code{cl-block} form.
1515 The @code{cl-block} returns the result of the last @var{form} unless
1516 a @code{cl-return-from} occurs.
1518 The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to
1519 the @code{catch}/@code{throw} mechanism. The main differences are
1520 that block @var{name}s are unevaluated symbols, rather than forms
1521 (such as quoted symbols) that evaluate to a tag at run-time; and
1522 also that blocks are always lexically scoped.
1523 In a dynamically scoped @code{catch}, functions called from the
1524 @code{catch} body can also @code{throw} to the @code{catch}. This
1525 is not an option for @code{cl-block}, where
1526 the @code{cl-return-from} referring to a block name must appear
1527 physically within the @var{forms} that make up the body of the block.
1528 They may not appear within other called functions, although they may
1529 appear within macro expansions or @code{lambda}s in the body. Block
1530 names and @code{catch} names form independent name-spaces.
1532 In true Common Lisp, @code{defun} and @code{defmacro} surround
1533 the function or expander bodies with implicit blocks with the
1534 same name as the function or macro. This does not occur in Emacs
1535 Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro}
1536 forms, which do create the implicit block.
1538 The Common Lisp looping constructs defined by this package,
1539 such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks
1540 just as in Common Lisp.
1542 Because they are implemented in terms of Emacs Lisp's @code{catch}
1543 and @code{throw}, blocks have the same overhead as actual
1544 @code{catch} constructs (roughly two function calls). However,
1545 the byte compiler will optimize away the @code{catch}
1547 not in fact contain any @code{cl-return} or @code{cl-return-from} calls
1548 that jump to it. This means that @code{cl-do} loops and @code{cl-defun}
1549 functions that don't use @code{cl-return} don't pay the overhead to
1553 @defmac cl-return-from name [result]
1554 This macro returns from the block named @var{name}, which must be
1555 an (unevaluated) symbol. If a @var{result} form is specified, it
1556 is evaluated to produce the result returned from the @code{block}.
1557 Otherwise, @code{nil} is returned.
1560 @defmac cl-return [result]
1561 This macro is exactly like @code{(cl-return-from nil @var{result})}.
1562 Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose
1563 themselves in @code{nil} blocks.
1570 The macros described here provide more sophisticated, high-level
1571 looping constructs to complement Emacs Lisp's basic loop forms
1572 (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}).
1574 @defmac cl-loop forms@dots{}
1575 This package supports both the simple, old-style meaning of
1576 @code{loop} and the extremely powerful and flexible feature known as
1577 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced
1578 facility is discussed in the following section; @pxref{Loop Facility}.
1579 The simple form of @code{loop} is described here.
1581 If @code{cl-loop} is followed by zero or more Lisp expressions,
1582 then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite
1583 loop executing the expressions over and over. The loop is
1584 enclosed in an implicit @code{nil} block. Thus,
1587 (cl-loop (foo) (if (no-more) (return 72)) (bar))
1591 is exactly equivalent to
1594 (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar)))
1597 If any of the expressions are plain symbols, the loop is instead
1598 interpreted as a Loop Macro specification as described later.
1599 (This is not a restriction in practice, since a plain symbol
1600 in the above notation would simply access and throw away the
1601 value of a variable.)
1604 @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1605 This macro creates a general iterative loop. Each @var{spec} is
1609 (@var{var} [@var{init} [@var{step}]])
1612 The loop works as follows: First, each @var{var} is bound to the
1613 associated @var{init} value as if by a @code{let} form. Then, in
1614 each iteration of the loop, the @var{end-test} is evaluated; if
1615 true, the loop is finished. Otherwise, the body @var{forms} are
1616 evaluated, then each @var{var} is set to the associated @var{step}
1617 expression (as if by a @code{cl-psetq} form) and the next iteration
1618 begins. Once the @var{end-test} becomes true, the @var{result}
1619 forms are evaluated (with the @var{var}s still bound to their
1620 values) to produce the result returned by @code{cl-do}.
1622 The entire @code{cl-do} loop is enclosed in an implicit @code{nil}
1623 block, so that you can use @code{(cl-return)} to break out of the
1626 If there are no @var{result} forms, the loop returns @code{nil}.
1627 If a given @var{var} has no @var{step} form, it is bound to its
1628 @var{init} value but not otherwise modified during the @code{cl-do}
1629 loop (unless the code explicitly modifies it); this case is just
1630 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})}
1631 around the loop. If @var{init} is also omitted it defaults to
1632 @code{nil}, and in this case a plain @samp{@var{var}} can be used
1633 in place of @samp{(@var{var})}, again following the analogy with
1636 This example (from Steele) illustrates a loop that applies the
1637 function @code{f} to successive pairs of values from the lists
1638 @code{foo} and @code{bar}; it is equivalent to the call
1639 @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body
1640 @var{forms} at all, performing all its work as side effects of
1641 the rest of the loop.
1644 (cl-do ((x foo (cdr x))
1646 (z nil (cons (f (car x) (car y)) z)))
1647 ((or (null x) (null y))
1652 @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
1653 This is to @code{cl-do} what @code{let*} is to @code{let}. In
1654 particular, the initial values are bound as if by @code{let*}
1655 rather than @code{let}, and the steps are assigned as if by
1656 @code{setq} rather than @code{cl-psetq}.
1658 Here is another way to write the above loop:
1661 (cl-do* ((xp foo (cdr xp))
1663 (x (car xp) (car xp))
1664 (y (car yp) (car yp))
1666 ((or (null xp) (null yp))
1672 @defmac cl-dolist (var list [result]) forms@dots{}
1673 This is exactly like the standard Emacs Lisp macro @code{dolist},
1674 but surrounds the loop with an implicit @code{nil} block.
1677 @defmac cl-dotimes (var count [result]) forms@dots{}
1678 This is exactly like the standard Emacs Lisp macro @code{dotimes},
1679 but surrounds the loop with an implicit @code{nil} block.
1680 The body is executed with @var{var} bound to the integers
1681 from zero (inclusive) to @var{count} (exclusive), in turn. Then
1682 @c FIXME lispref does not state this part explicitly, could move this there.
1683 the @code{result} form is evaluated with @var{var} bound to the total
1684 number of iterations that were done (i.e., @code{(max 0 @var{count})})
1685 to get the return value for the loop form.
1688 @defmac cl-do-symbols (var [obarray [result]]) forms@dots{}
1689 This loop iterates over all interned symbols. If @var{obarray}
1690 is specified and is not @code{nil}, it loops over all symbols in
1691 that obarray. For each symbol, the body @var{forms} are evaluated
1692 with @var{var} bound to that symbol. The symbols are visited in
1693 an unspecified order. Afterward the @var{result} form, if any,
1694 is evaluated (with @var{var} bound to @code{nil}) to get the return
1695 value. The loop is surrounded by an implicit @code{nil} block.
1698 @defmac cl-do-all-symbols (var [result]) forms@dots{}
1699 This is identical to @code{cl-do-symbols} except that the @var{obarray}
1700 argument is omitted; it always iterates over the default obarray.
1703 @xref{Mapping over Sequences}, for some more functions for
1704 iterating over vectors or lists.
1707 @section Loop Facility
1710 A common complaint with Lisp's traditional looping constructs was
1711 that they were either too simple and limited, such as @code{dotimes}
1712 or @code{while}, or too unreadable and obscure, like Common Lisp's
1715 To remedy this, Common Lisp added a construct called the ``Loop
1716 Facility'' or ``@code{loop} macro'', with an easy-to-use but very
1717 powerful and expressive syntax.
1720 * Loop Basics:: The @code{cl-loop} macro, basic clause structure.
1721 * Loop Examples:: Working examples of the @code{cl-loop} macro.
1722 * For Clauses:: Clauses introduced by @code{for} or @code{as}.
1723 * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc.
1724 * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc.
1725 * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}.
1729 @subsection Loop Basics
1732 The @code{cl-loop} macro essentially creates a mini-language within
1733 Lisp that is specially tailored for describing loops. While this
1734 language is a little strange-looking by the standards of regular Lisp,
1735 it turns out to be very easy to learn and well-suited to its purpose.
1737 Since @code{cl-loop} is a macro, all parsing of the loop language
1738 takes place at byte-compile time; compiled @code{cl-loop}s are just
1739 as efficient as the equivalent @code{while} loops written longhand.
1741 @defmac cl-loop clauses@dots{}
1742 A loop construct consists of a series of @var{clause}s, each
1743 introduced by a symbol like @code{for} or @code{do}. Clauses
1744 are simply strung together in the argument list of @code{cl-loop},
1745 with minimal extra parentheses. The various types of clauses
1746 specify initializations, such as the binding of temporary
1747 variables, actions to be taken in the loop, stepping actions,
1750 Common Lisp specifies a certain general order of clauses in a
1754 (loop @var{name-clause}
1755 @var{var-clauses}@dots{}
1756 @var{action-clauses}@dots{})
1759 The @var{name-clause} optionally gives a name to the implicit
1760 block that surrounds the loop. By default, the implicit block
1761 is named @code{nil}. The @var{var-clauses} specify what
1762 variables should be bound during the loop, and how they should
1763 be modified or iterated throughout the course of the loop. The
1764 @var{action-clauses} are things to be done during the loop, such
1765 as computing, collecting, and returning values.
1767 The Emacs version of the @code{cl-loop} macro is less restrictive about
1768 the order of clauses, but things will behave most predictably if
1769 you put the variable-binding clauses @code{with}, @code{for}, and
1770 @code{repeat} before the action clauses. As in Common Lisp,
1771 @code{initially} and @code{finally} clauses can go anywhere.
1773 Loops generally return @code{nil} by default, but you can cause
1774 them to return a value by using an accumulation clause like
1775 @code{collect}, an end-test clause like @code{always}, or an
1776 explicit @code{return} clause to jump out of the implicit block.
1777 (Because the loop body is enclosed in an implicit block, you can
1778 also use regular Lisp @code{cl-return} or @code{cl-return-from} to
1779 break out of the loop.)
1782 The following sections give some examples of the loop macro in
1783 action, and describe the particular loop clauses in great detail.
1784 Consult the second edition of Steele for additional discussion
1788 @subsection Loop Examples
1791 Before listing the full set of clauses that are allowed, let's
1792 look at a few example loops just to get a feel for the @code{cl-loop}
1796 (cl-loop for buf in (buffer-list)
1797 collect (buffer-file-name buf))
1801 This loop iterates over all Emacs buffers, using the list
1802 returned by @code{buffer-list}. For each buffer @var{buf},
1803 it calls @code{buffer-file-name} and collects the results into
1804 a list, which is then returned from the @code{cl-loop} construct.
1805 The result is a list of the file names of all the buffers in
1806 Emacs's memory. The words @code{for}, @code{in}, and @code{collect}
1807 are reserved words in the @code{cl-loop} language.
1810 (cl-loop repeat 20 do (insert "Yowsa\n"))
1814 This loop inserts the phrase ``Yowsa'' twenty times in the
1818 (cl-loop until (eobp) do (munch-line) (forward-line 1))
1822 This loop calls @code{munch-line} on every line until the end
1823 of the buffer. If point is already at the end of the buffer,
1824 the loop exits immediately.
1827 (cl-loop do (munch-line) until (eobp) do (forward-line 1))
1831 This loop is similar to the above one, except that @code{munch-line}
1832 is always called at least once.
1835 (cl-loop for x from 1 to 100
1838 finally return (list x (= y 729)))
1842 This more complicated loop searches for a number @code{x} whose
1843 square is 729. For safety's sake it only examines @code{x}
1844 values up to 100; dropping the phrase @samp{to 100} would
1845 cause the loop to count upwards with no limit. The second
1846 @code{for} clause defines @code{y} to be the square of @code{x}
1847 within the loop; the expression after the @code{=} sign is
1848 reevaluated each time through the loop. The @code{until}
1849 clause gives a condition for terminating the loop, and the
1850 @code{finally} clause says what to do when the loop finishes.
1851 (This particular example was written less concisely than it
1852 could have been, just for the sake of illustration.)
1854 Note that even though this loop contains three clauses (two
1855 @code{for}s and an @code{until}) that would have been enough to
1856 define loops all by themselves, it still creates a single loop
1857 rather than some sort of triple-nested loop. You must explicitly
1858 nest your @code{cl-loop} constructs if you want nested loops.
1861 @subsection For Clauses
1864 Most loops are governed by one or more @code{for} clauses.
1865 A @code{for} clause simultaneously describes variables to be
1866 bound, how those variables are to be stepped during the loop,
1867 and usually an end condition based on those variables.
1869 The word @code{as} is a synonym for the word @code{for}. This
1870 word is followed by a variable name, then a word like @code{from}
1871 or @code{across} that describes the kind of iteration desired.
1872 In Common Lisp, the phrase @code{being the} sometimes precedes
1873 the type of iteration; in this package both @code{being} and
1874 @code{the} are optional. The word @code{each} is a synonym
1875 for @code{the}, and the word that follows it may be singular
1876 or plural: @samp{for x being the elements of y} or
1877 @samp{for x being each element of y}. Which form you use
1878 is purely a matter of style.
1880 The variable is bound around the loop as if by @code{let}:
1884 (cl-loop for i from 1 to 10 do (do-something-with i))
1890 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3}
1891 This type of @code{for} clause creates a counting loop. Each of
1892 the three sub-terms is optional, though there must be at least one
1893 term so that the clause is marked as a counting clause.
1895 The three expressions are the starting value, the ending value, and
1896 the step value, respectively, of the variable. The loop counts
1897 upwards by default (@var{expr3} must be positive), from @var{expr1}
1898 to @var{expr2} inclusively. If you omit the @code{from} term, the
1899 loop counts from zero; if you omit the @code{to} term, the loop
1900 counts forever without stopping (unless stopped by some other
1901 loop clause, of course); if you omit the @code{by} term, the loop
1902 counts in steps of one.
1904 You can replace the word @code{from} with @code{upfrom} or
1905 @code{downfrom} to indicate the direction of the loop. Likewise,
1906 you can replace @code{to} with @code{upto} or @code{downto}.
1907 For example, @samp{for x from 5 downto 1} executes five times
1908 with @code{x} taking on the integers from 5 down to 1 in turn.
1909 Also, you can replace @code{to} with @code{below} or @code{above},
1910 which are like @code{upto} and @code{downto} respectively except
1911 that they are exclusive rather than inclusive limits:
1914 (cl-loop for x to 10 collect x)
1915 @result{} (0 1 2 3 4 5 6 7 8 9 10)
1916 (cl-loop for x below 10 collect x)
1917 @result{} (0 1 2 3 4 5 6 7 8 9)
1920 The @code{by} value is always positive, even for downward-counting
1921 loops. Some sort of @code{from} value is required for downward
1922 loops; @samp{for x downto 5} is not a valid loop clause all by
1925 @item for @var{var} in @var{list} by @var{function}
1926 This clause iterates @var{var} over all the elements of @var{list},
1927 in turn. If you specify the @code{by} term, then @var{function}
1928 is used to traverse the list instead of @code{cdr}; it must be a
1929 function taking one argument. For example:
1932 (cl-loop for x in '(1 2 3 4 5 6) collect (* x x))
1933 @result{} (1 4 9 16 25 36)
1934 (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
1938 @item for @var{var} on @var{list} by @var{function}
1939 This clause iterates @var{var} over all the cons cells of @var{list}.
1942 (cl-loop for x on '(1 2 3 4) collect x)
1943 @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
1946 With @code{by}, there is no real reason that the @code{on} expression
1947 must be a list. For example:
1950 (cl-loop for x on first-animal by 'next-animal collect x)
1954 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
1955 the next in the (assumed) sequence of animals, or @code{nil} if
1956 @var{x} was the last animal in the sequence.
1958 @item for @var{var} in-ref @var{list} by @var{function}
1959 This is like a regular @code{in} clause, but @var{var} becomes
1960 a @code{setf}-able ``reference'' onto the elements of the list
1961 rather than just a temporary variable. For example,
1964 (cl-loop for x in-ref my-list do (cl-incf x))
1968 increments every element of @code{my-list} in place. This clause
1969 is an extension to standard Common Lisp.
1971 @item for @var{var} across @var{array}
1972 This clause iterates @var{var} over all the elements of @var{array},
1973 which may be a vector or a string.
1976 (cl-loop for x across "aeiou"
1977 do (use-vowel (char-to-string x)))
1980 @item for @var{var} across-ref @var{array}
1981 This clause iterates over an array, with @var{var} a @code{setf}-able
1982 reference onto the elements; see @code{in-ref} above.
1984 @item for @var{var} being the elements of @var{sequence}
1985 This clause iterates over the elements of @var{sequence}, which may
1986 be a list, vector, or string. Since the type must be determined
1987 at run-time, this is somewhat less efficient than @code{in} or
1988 @code{across}. The clause may be followed by the additional term
1989 @samp{using (index @var{var2})} to cause @var{var2} to be bound to
1990 the successive indices (starting at 0) of the elements.
1992 This clause type is taken from older versions of the @code{loop} macro,
1993 and is not present in modern Common Lisp. The @samp{using (sequence @dots{})}
1994 term of the older macros is not supported.
1996 @item for @var{var} being the elements of-ref @var{sequence}
1997 This clause iterates over a sequence, with @var{var} a @code{setf}-able
1998 reference onto the elements; see @code{in-ref} above.
2000 @item for @var{var} being the symbols [of @var{obarray}]
2001 This clause iterates over symbols, either over all interned symbols
2002 or over all symbols in @var{obarray}. The loop is executed with
2003 @var{var} bound to each symbol in turn. The symbols are visited in
2004 an unspecified order.
2009 (cl-loop for sym being the symbols
2011 when (string-match "^map" (symbol-name sym))
2016 returns a list of all the functions whose names begin with @samp{map}.
2018 The Common Lisp words @code{external-symbols} and @code{present-symbols}
2019 are also recognized but are equivalent to @code{symbols} in Emacs Lisp.
2021 Due to a minor implementation restriction, it will not work to have
2022 more than one @code{for} clause iterating over symbols, hash tables,
2023 keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately,
2024 it would rarely if ever be useful to do so. It @emph{is} valid to mix
2025 one of these types of clauses with other clauses like @code{for @dots{} to}
2028 @item for @var{var} being the hash-keys of @var{hash-table}
2029 @itemx for @var{var} being the hash-values of @var{hash-table}
2030 This clause iterates over the entries in @var{hash-table} with
2031 @var{var} bound to each key, or value. A @samp{using} clause can bind
2032 a second variable to the opposite part.
2035 (cl-loop for k being the hash-keys of h
2036 using (hash-values v)
2038 (message "key %S -> value %S" k v))
2041 @item for @var{var} being the key-codes of @var{keymap}
2042 @itemx for @var{var} being the key-bindings of @var{keymap}
2043 This clause iterates over the entries in @var{keymap}.
2044 The iteration does not enter nested keymaps but does enter inherited
2046 A @code{using} clause can access both the codes and the bindings
2050 (cl-loop for c being the key-codes of (current-local-map)
2051 using (key-bindings b)
2053 (message "key %S -> binding %S" c b))
2057 @item for @var{var} being the key-seqs of @var{keymap}
2058 This clause iterates over all key sequences defined by @var{keymap}
2059 and its nested keymaps, where @var{var} takes on values which are
2060 vectors. The strings or vectors
2061 are reused for each iteration, so you must copy them if you wish to keep
2062 them permanently. You can add a @samp{using (key-bindings @dots{})}
2063 clause to get the command bindings as well.
2065 @item for @var{var} being the overlays [of @var{buffer}] @dots{}
2066 This clause iterates over the ``overlays'' of a buffer
2067 (the clause @code{extents} is synonymous
2068 with @code{overlays}). If the @code{of} term is omitted, the current
2070 This clause also accepts optional @samp{from @var{pos}} and
2071 @samp{to @var{pos}} terms, limiting the clause to overlays which
2072 overlap the specified region.
2074 @item for @var{var} being the intervals [of @var{buffer}] @dots{}
2075 This clause iterates over all intervals of a buffer with constant
2076 text properties. The variable @var{var} will be bound to conses
2077 of start and end positions, where one start position is always equal
2078 to the previous end position. The clause allows @code{of},
2079 @code{from}, @code{to}, and @code{property} terms, where the latter
2080 term restricts the search to just the specified property. The
2081 @code{of} term may specify either a buffer or a string.
2083 @item for @var{var} being the frames
2084 This clause iterates over all Emacs frames. The clause @code{screens} is
2085 a synonym for @code{frames}. The frames are visited in
2086 @code{next-frame} order starting from @code{selected-frame}.
2088 @item for @var{var} being the windows [of @var{frame}]
2089 This clause iterates over the windows (in the Emacs sense) of
2090 the current frame, or of the specified @var{frame}. It visits windows
2091 in @code{next-window} order starting from @code{selected-window}
2092 (or @code{frame-selected-window} if you specify @var{frame}).
2093 This clause treats the minibuffer window in the same way as
2094 @code{next-window} does. For greater flexibility, consider using
2095 @code{walk-windows} instead.
2097 @item for @var{var} being the buffers
2098 This clause iterates over all buffers in Emacs. It is equivalent
2099 to @samp{for @var{var} in (buffer-list)}.
2101 @item for @var{var} = @var{expr1} then @var{expr2}
2102 This clause does a general iteration. The first time through
2103 the loop, @var{var} will be bound to @var{expr1}. On the second
2104 and successive iterations it will be set by evaluating @var{expr2}
2105 (which may refer to the old value of @var{var}). For example,
2106 these two loops are effectively the same:
2109 (cl-loop for x on my-list by 'cddr do @dots{})
2110 (cl-loop for x = my-list then (cddr x) while x do @dots{})
2113 Note that this type of @code{for} clause does not imply any sort
2114 of terminating condition; the above example combines it with a
2115 @code{while} clause to tell when to end the loop.
2117 If you omit the @code{then} term, @var{expr1} is used both for
2118 the initial setting and for successive settings:
2121 (cl-loop for x = (random) when (> x 0) return x)
2125 This loop keeps taking random numbers from the @code{(random)}
2126 function until it gets a positive one, which it then returns.
2129 If you include several @code{for} clauses in a row, they are
2130 treated sequentially (as if by @code{let*} and @code{setq}).
2131 You can instead use the word @code{and} to link the clauses,
2132 in which case they are processed in parallel (as if by @code{let}
2133 and @code{cl-psetq}).
2136 (cl-loop for x below 5 for y = nil then x collect (list x y))
2137 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4))
2138 (cl-loop for x below 5 and y = nil then x collect (list x y))
2139 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3))
2143 In the first loop, @code{y} is set based on the value of @code{x}
2144 that was just set by the previous clause; in the second loop,
2145 @code{x} and @code{y} are set simultaneously so @code{y} is set
2146 based on the value of @code{x} left over from the previous time
2149 Another feature of the @code{cl-loop} macro is @emph{destructuring},
2150 similar in concept to the destructuring provided by @code{defmacro}
2151 (@pxref{Argument Lists}).
2152 The @var{var} part of any @code{for} clause can be given as a list
2153 of variables instead of a single variable. The values produced
2154 during loop execution must be lists; the values in the lists are
2155 stored in the corresponding variables.
2158 (cl-loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y))
2162 In loop destructuring, if there are more values than variables
2163 the trailing values are ignored, and if there are more variables
2164 than values the trailing variables get the value @code{nil}.
2165 If @code{nil} is used as a variable name, the corresponding
2166 values are ignored. Destructuring may be nested, and dotted
2167 lists of variables like @code{(x . y)} are allowed, so for example
2171 (cl-loop for (key . value) in '((a . 1) (b . 2))
2176 @node Iteration Clauses
2177 @subsection Iteration Clauses
2180 Aside from @code{for} clauses, there are several other loop clauses
2181 that control the way the loop operates. They might be used by
2182 themselves, or in conjunction with one or more @code{for} clauses.
2185 @item repeat @var{integer}
2186 This clause simply counts up to the specified number using an
2187 internal temporary variable. The loops
2190 (cl-loop repeat (1+ n) do @dots{})
2191 (cl-loop for temp to n do @dots{})
2195 are identical except that the second one forces you to choose
2196 a name for a variable you aren't actually going to use.
2198 @item while @var{condition}
2199 This clause stops the loop when the specified condition (any Lisp
2200 expression) becomes @code{nil}. For example, the following two
2201 loops are equivalent, except for the implicit @code{nil} block
2202 that surrounds the second one:
2205 (while @var{cond} @var{forms}@dots{})
2206 (cl-loop while @var{cond} do @var{forms}@dots{})
2209 @item until @var{condition}
2210 This clause stops the loop when the specified condition is true,
2211 i.e., non-@code{nil}.
2213 @item always @var{condition}
2214 This clause stops the loop when the specified condition is @code{nil}.
2215 Unlike @code{while}, it stops the loop using @code{return nil} so that
2216 the @code{finally} clauses are not executed. If all the conditions
2217 were non-@code{nil}, the loop returns @code{t}:
2220 (if (cl-loop for size in size-list always (> size 10))
2225 @item never @var{condition}
2226 This clause is like @code{always}, except that the loop returns
2227 @code{t} if any conditions were false, or @code{nil} otherwise.
2229 @item thereis @var{condition}
2230 This clause stops the loop when the specified form is non-@code{nil};
2231 in this case, it returns that non-@code{nil} value. If all the
2232 values were @code{nil}, the loop returns @code{nil}.
2235 @node Accumulation Clauses
2236 @subsection Accumulation Clauses
2239 These clauses cause the loop to accumulate information about the
2240 specified Lisp @var{form}. The accumulated result is returned
2241 from the loop unless overridden, say, by a @code{return} clause.
2244 @item collect @var{form}
2245 This clause collects the values of @var{form} into a list. Several
2246 examples of @code{collect} appear elsewhere in this manual.
2248 The word @code{collecting} is a synonym for @code{collect}, and
2249 likewise for the other accumulation clauses.
2251 @item append @var{form}
2252 This clause collects lists of values into a result list using
2255 @item nconc @var{form}
2256 This clause collects lists of values into a result list by
2257 destructively modifying the lists rather than copying them.
2259 @item concat @var{form}
2260 This clause concatenates the values of the specified @var{form}
2261 into a string. (It and the following clause are extensions to
2262 standard Common Lisp.)
2264 @item vconcat @var{form}
2265 This clause concatenates the values of the specified @var{form}
2268 @item count @var{form}
2269 This clause counts the number of times the specified @var{form}
2270 evaluates to a non-@code{nil} value.
2272 @item sum @var{form}
2273 This clause accumulates the sum of the values of the specified
2274 @var{form}, which must evaluate to a number.
2276 @item maximize @var{form}
2277 This clause accumulates the maximum value of the specified @var{form},
2278 which must evaluate to a number. The return value is undefined if
2279 @code{maximize} is executed zero times.
2281 @item minimize @var{form}
2282 This clause accumulates the minimum value of the specified @var{form}.
2285 Accumulation clauses can be followed by @samp{into @var{var}} to
2286 cause the data to be collected into variable @var{var} (which is
2287 automatically @code{let}-bound during the loop) rather than an
2288 unnamed temporary variable. Also, @code{into} accumulations do
2289 not automatically imply a return value. The loop must use some
2290 explicit mechanism, such as @code{finally return}, to return
2291 the accumulated result.
2293 It is valid for several accumulation clauses of the same type to
2294 accumulate into the same place. From Steele:
2297 (cl-loop for name in '(fred sue alice joe june)
2298 for kids in '((bob ken) () () (kris sunshine) ())
2301 @result{} (fred bob ken sue alice joe kris sunshine june)
2305 @subsection Other Clauses
2308 This section describes the remaining loop clauses.
2311 @item with @var{var} = @var{value}
2312 This clause binds a variable to a value around the loop, but
2313 otherwise leaves the variable alone during the loop. The following
2314 loops are basically equivalent:
2317 (cl-loop with x = 17 do @dots{})
2318 (let ((x 17)) (cl-loop do @dots{}))
2319 (cl-loop for x = 17 then x do @dots{})
2322 Naturally, the variable @var{var} might be used for some purpose
2323 in the rest of the loop. For example:
2326 (cl-loop for x in my-list with res = nil do (push x res)
2330 This loop inserts the elements of @code{my-list} at the front of
2331 a new list being accumulated in @code{res}, then returns the
2332 list @code{res} at the end of the loop. The effect is similar
2333 to that of a @code{collect} clause, but the list gets reversed
2334 by virtue of the fact that elements are being pushed onto the
2335 front of @code{res} rather than the end.
2337 If you omit the @code{=} term, the variable is initialized to
2338 @code{nil}. (Thus the @samp{= nil} in the above example is
2341 Bindings made by @code{with} are sequential by default, as if
2342 by @code{let*}. Just like @code{for} clauses, @code{with} clauses
2343 can be linked with @code{and} to cause the bindings to be made by
2346 @item if @var{condition} @var{clause}
2347 This clause executes the following loop clause only if the specified
2348 condition is true. The following @var{clause} should be an accumulation,
2349 @code{do}, @code{return}, @code{if}, or @code{unless} clause.
2350 Several clauses may be linked by separating them with @code{and}.
2351 These clauses may be followed by @code{else} and a clause or clauses
2352 to execute if the condition was false. The whole construct may
2353 optionally be followed by the word @code{end} (which may be used to
2354 disambiguate an @code{else} or @code{and} in a nested @code{if}).
2356 The actual non-@code{nil} value of the condition form is available
2357 by the name @code{it} in the ``then'' part. For example:
2360 (setq funny-numbers '(6 13 -1))
2362 (cl-loop for x below 10
2365 and if (memq x funny-numbers) return (cdr it) end
2367 collect x into evens
2368 finally return (vector odds evens))
2369 @result{} [(1 3 5 7 9) (0 2 4 6 8)]
2370 (setq funny-numbers '(6 7 13 -1))
2371 @result{} (6 7 13 -1)
2372 (cl-loop <@r{same thing again}>)
2376 Note the use of @code{and} to put two clauses into the ``then''
2377 part, one of which is itself an @code{if} clause. Note also that
2378 @code{end}, while normally optional, was necessary here to make
2379 it clear that the @code{else} refers to the outermost @code{if}
2380 clause. In the first case, the loop returns a vector of lists
2381 of the odd and even values of @var{x}. In the second case, the
2382 odd number 7 is one of the @code{funny-numbers} so the loop
2383 returns early; the actual returned value is based on the result
2384 of the @code{memq} call.
2386 @item when @var{condition} @var{clause}
2387 This clause is just a synonym for @code{if}.
2389 @item unless @var{condition} @var{clause}
2390 The @code{unless} clause is just like @code{if} except that the
2391 sense of the condition is reversed.
2393 @item named @var{name}
2394 This clause gives a name other than @code{nil} to the implicit
2395 block surrounding the loop. The @var{name} is the symbol to be
2396 used as the block name.
2398 @item initially [do] @var{forms}@dots{}
2399 This keyword introduces one or more Lisp forms which will be
2400 executed before the loop itself begins (but after any variables
2401 requested by @code{for} or @code{with} have been bound to their
2402 initial values). @code{initially} clauses can appear anywhere;
2403 if there are several, they are executed in the order they appear
2404 in the loop. The keyword @code{do} is optional.
2406 @item finally [do] @var{forms}@dots{}
2407 This introduces Lisp forms which will be executed after the loop
2408 finishes (say, on request of a @code{for} or @code{while}).
2409 @code{initially} and @code{finally} clauses may appear anywhere
2410 in the loop construct, but they are executed (in the specified
2411 order) at the beginning or end, respectively, of the loop.
2413 @item finally return @var{form}
2414 This says that @var{form} should be executed after the loop
2415 is done to obtain a return value. (Without this, or some other
2416 clause like @code{collect} or @code{return}, the loop will simply
2417 return @code{nil}.) Variables bound by @code{for}, @code{with},
2418 or @code{into} will still contain their final values when @var{form}
2421 @item do @var{forms}@dots{}
2422 The word @code{do} may be followed by any number of Lisp expressions
2423 which are executed as an implicit @code{progn} in the body of the
2424 loop. Many of the examples in this section illustrate the use of
2427 @item return @var{form}
2428 This clause causes the loop to return immediately. The following
2429 Lisp form is evaluated to give the return value of the loop
2430 form. The @code{finally} clauses, if any, are not executed.
2431 Of course, @code{return} is generally used inside an @code{if} or
2432 @code{unless}, as its use in a top-level loop clause would mean
2433 the loop would never get to ``loop'' more than once.
2435 The clause @samp{return @var{form}} is equivalent to
2436 @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop
2437 was named). The @code{return} clause is implemented a bit more
2438 efficiently, though.
2441 While there is no high-level way to add user extensions to @code{cl-loop},
2442 this package does offer two properties called @code{cl-loop-handler}
2443 and @code{cl-loop-for-handler} which are functions to be called when a
2444 given symbol is encountered as a top-level loop clause or @code{for}
2445 clause, respectively. Consult the source code in file
2446 @file{cl-macs.el} for details.
2448 This package's @code{cl-loop} macro is compatible with that of Common
2449 Lisp, except that a few features are not implemented: @code{loop-finish}
2450 and data-type specifiers. Naturally, the @code{for} clauses that
2451 iterate over keymaps, overlays, intervals, frames, windows, and
2452 buffers are Emacs-specific extensions.
2454 @node Multiple Values
2455 @section Multiple Values
2458 Common Lisp functions can return zero or more results. Emacs Lisp
2459 functions, by contrast, always return exactly one result. This
2460 package makes no attempt to emulate Common Lisp multiple return
2461 values; Emacs versions of Common Lisp functions that return more
2462 than one value either return just the first value (as in
2463 @code{cl-compiler-macroexpand}) or return a list of values.
2464 This package @emph{does} define placeholders
2465 for the Common Lisp functions that work with multiple values, but
2466 in Emacs Lisp these functions simply operate on lists instead.
2467 The @code{cl-values} form, for example, is a synonym for @code{list}
2470 @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{}
2471 This form evaluates @var{values-form}, which must return a list of
2472 values. It then binds the @var{var}s to these respective values,
2473 as if by @code{let}, and then executes the body @var{forms}.
2474 If there are more @var{var}s than values, the extra @var{var}s
2475 are bound to @code{nil}. If there are fewer @var{var}s than
2476 values, the excess values are ignored.
2479 @defmac cl-multiple-value-setq (var@dots{}) form
2480 This form evaluates @var{form}, which must return a list of values.
2481 It then sets the @var{var}s to these respective values, as if by
2482 @code{setq}. Extra @var{var}s or values are treated the same as
2483 in @code{cl-multiple-value-bind}.
2486 Since a perfect emulation is not feasible in Emacs Lisp, this
2487 package opts to keep it as simple and predictable as possible.
2493 This package implements the various Common Lisp features of
2494 @code{defmacro}, such as destructuring, @code{&environment},
2495 and @code{&body}. Top-level @code{&whole} is not implemented
2496 for @code{defmacro} due to technical difficulties.
2497 @xref{Argument Lists}.
2499 Destructuring is made available to the user by way of the
2502 @defmac cl-destructuring-bind arglist expr forms@dots{}
2503 This macro expands to code that executes @var{forms}, with
2504 the variables in @var{arglist} bound to the list of values
2505 returned by @var{expr}. The @var{arglist} can include all
2506 the features allowed for @code{cl-defmacro} argument lists,
2507 including destructuring. (The @code{&environment} keyword
2508 is not allowed.) The macro expansion will signal an error
2509 if @var{expr} returns a list of the wrong number of arguments
2510 or with incorrect keyword arguments.
2513 This package also includes the Common Lisp @code{define-compiler-macro}
2514 facility, which allows you to define compile-time expansions and
2515 optimizations for your functions.
2517 @defmac cl-define-compiler-macro name arglist forms@dots{}
2518 This form is similar to @code{defmacro}, except that it only expands
2519 calls to @var{name} at compile-time; calls processed by the Lisp
2520 interpreter are not expanded, nor are they expanded by the
2521 @code{macroexpand} function.
2523 The argument list may begin with a @code{&whole} keyword and a
2524 variable. This variable is bound to the macro-call form itself,
2525 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}.
2526 If the macro expander returns this form unchanged, then the
2527 compiler treats it as a normal function call. This allows
2528 compiler macros to work as optimizers for special cases of a
2529 function, leaving complicated cases alone.
2531 For example, here is a simplified version of a definition that
2532 appears as a standard part of this package:
2535 (cl-define-compiler-macro cl-member (&whole form a list &rest keys)
2536 (if (and (null keys)
2537 (eq (car-safe a) 'quote)
2538 (not (floatp (cadr a))))
2544 This definition causes @code{(cl-member @var{a} @var{list})} to change
2545 to a call to the faster @code{memq} in the common case where @var{a}
2546 is a non-floating-point constant; if @var{a} is anything else, or
2547 if there are any keyword arguments in the call, then the original
2548 @code{cl-member} call is left intact. (The actual compiler macro
2549 for @code{cl-member} optimizes a number of other cases, including
2550 common @code{:test} predicates.)
2553 @defun cl-compiler-macroexpand form
2554 This function is analogous to @code{macroexpand}, except that it
2555 expands compiler macros rather than regular macros. It returns
2556 @var{form} unchanged if it is not a call to a function for which
2557 a compiler macro has been defined, or if that compiler macro
2558 decided to punt by returning its @code{&whole} argument. Like
2559 @code{macroexpand}, it expands repeatedly until it reaches a form
2560 for which no further expansion is possible.
2563 @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet}
2564 and @code{cl-symbol-macrolet} forms for making ``local'' macro
2568 @chapter Declarations
2571 Common Lisp includes a complex and powerful ``declaration''
2572 mechanism that allows you to give the compiler special hints
2573 about the types of data that will be stored in particular variables,
2574 and about the ways those variables and functions will be used. This
2575 package defines versions of all the Common Lisp declaration forms:
2576 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim},
2579 Most of the Common Lisp declarations are not currently useful in Emacs
2580 Lisp. For example, the byte-code system provides little
2581 opportunity to benefit from type information.
2583 and @code{special} declarations are redundant in a fully
2584 dynamically-scoped Lisp.
2586 A few declarations are meaningful when byte compiler optimizations
2587 are enabled, as they are by the default. Otherwise these
2588 declarations will effectively be ignored.
2590 @defun cl-proclaim decl-spec
2591 This function records a ``global'' declaration specified by
2592 @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec}
2593 is evaluated and thus should normally be quoted.
2596 @defmac cl-declaim decl-specs@dots{}
2597 This macro is like @code{cl-proclaim}, except that it takes any number
2598 of @var{decl-spec} arguments, and the arguments are unevaluated and
2599 unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when
2600 (compile load eval) @dots{})} around the declarations so that they will
2601 be registered at compile-time as well as at run-time. (This is vital,
2602 since normally the declarations are meant to influence the way the
2603 compiler treats the rest of the file that contains the @code{cl-declaim}
2607 @defmac cl-declare decl-specs@dots{}
2608 This macro is used to make declarations within functions and other
2609 code. Common Lisp allows declarations in various locations, generally
2610 at the beginning of any of the many ``implicit @code{progn}s''
2611 throughout Lisp syntax, such as function bodies, @code{let} bodies,
2612 etc. Currently the only declaration understood by @code{cl-declare}
2616 @defmac cl-locally declarations@dots{} forms@dots{}
2617 In this package, @code{cl-locally} is no different from @code{progn}.
2620 @defmac cl-the type form
2621 Type information provided by @code{cl-the} is ignored in this package;
2622 in other words, @code{(cl-the @var{type} @var{form})} is equivalent to
2623 @var{form}. Future byte-compiler optimizations may make use of this
2626 For example, @code{mapcar} can map over both lists and arrays. It is
2627 hard for the compiler to expand @code{mapcar} into an in-line loop
2628 unless it knows whether the sequence will be a list or an array ahead
2629 of time. With @code{(mapcar 'car (cl-the vector foo))}, a future
2630 compiler would have enough information to expand the loop in-line.
2631 For now, Emacs Lisp will treat the above code as exactly equivalent
2632 to @code{(mapcar 'car foo)}.
2635 Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or
2636 @code{cl-declare} should be a list beginning with a symbol that says
2637 what kind of declaration it is. This package currently understands
2638 @code{special}, @code{inline}, @code{notinline}, @code{optimize},
2639 and @code{warn} declarations. (The @code{warn} declaration is an
2640 extension of standard Common Lisp.) Other Common Lisp declarations,
2641 such as @code{type} and @code{ftype}, are silently ignored.
2646 Since all variables in Emacs Lisp are ``special'' (in the Common
2647 Lisp sense), @code{special} declarations are only advisory. They
2648 simply tell the byte compiler that the specified
2649 variables are intentionally being referred to without being
2650 bound in the body of the function. The compiler normally emits
2651 warnings for such references, since they could be typographical
2652 errors for references to local variables.
2654 The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is
2655 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}.
2657 In top-level contexts, it is generally better to write
2658 @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))},
2659 since @code{defvar} makes your intentions clearer.
2662 The @code{inline} @var{decl-spec} lists one or more functions
2663 whose bodies should be expanded ``in-line'' into calling functions
2664 whenever the compiler is able to arrange for it. For example,
2665 the function @code{cl-acons} is declared @code{inline}
2666 by this package so that the form @code{(cl-acons @var{key} @var{value}
2668 expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})}
2669 when it is called in user functions, so as to save function calls.
2671 The following declarations are all equivalent. Note that the
2672 @code{defsubst} form is a convenient way to define a function
2673 and declare it inline all at once.
2676 (cl-declaim (inline foo bar))
2677 (cl-eval-when (compile load eval)
2678 (cl-proclaim '(inline foo bar)))
2679 (defsubst foo (@dots{}) @dots{}) ; instead of defun
2682 @strong{Please note:} this declaration remains in effect after the
2683 containing source file is done. It is correct to use it to
2684 request that a function you have defined should be inlined,
2685 but it is impolite to use it to request inlining of an external
2688 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))}
2689 before a particular call to a function to cause just that call to
2690 be inlined; the current byte compilers provide no way to implement
2691 this, so @code{(cl-declare (inline @dots{}))} is currently ignored by
2695 The @code{notinline} declaration lists functions which should
2696 not be inlined after all; it cancels a previous @code{inline}
2700 This declaration controls how much optimization is performed by
2703 The word @code{optimize} is followed by any number of lists like
2704 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several
2705 optimization ``qualities''; this package ignores all but @code{speed}
2706 and @code{safety}. The value of a quality should be an integer from
2707 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''.
2708 The default level for both qualities is 1.
2710 In this package, the @code{speed} quality is tied to the @code{byte-optimize}
2711 flag, which is set to @code{nil} for @code{(speed 0)} and to
2712 @code{t} for higher settings; and the @code{safety} quality is
2713 tied to the @code{byte-compile-delete-errors} flag, which is
2714 set to @code{nil} for @code{(safety 3)} and to @code{t} for all
2715 lower settings. (The latter flag controls whether the compiler
2716 is allowed to optimize out code whose only side-effect could
2717 be to signal an error, e.g., rewriting @code{(progn foo bar)} to
2718 @code{bar} when it is not known whether @code{foo} will be bound
2721 Note that even compiling with @code{(safety 0)}, the Emacs
2722 byte-code system provides sufficient checking to prevent real
2723 harm from being done. For example, barring serious bugs in
2724 Emacs itself, Emacs will not crash with a segmentation fault
2725 just because of an error in a fully-optimized Lisp program.
2727 The @code{optimize} declaration is normally used in a top-level
2728 @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows
2729 it to be used with @code{declare} to set the level of optimization
2730 locally for a given form, but this will not work correctly with the
2731 current byte-compiler. (The @code{cl-declare}
2732 will set the new optimization level, but that level will not
2733 automatically be unset after the enclosing form is done.)
2736 This declaration controls what sorts of warnings are generated
2737 by the byte compiler. The word @code{warn} is followed by any
2738 number of ``warning qualities'', similar in form to optimization
2739 qualities. The currently supported warning types are
2740 @code{redefine}, @code{callargs}, @code{unresolved}, and
2741 @code{free-vars}; in the current system, a value of 0 will
2742 disable these warnings and any higher value will enable them.
2743 See the documentation of the variable @code{byte-compile-warnings}
2751 This package defines several symbol-related features that were
2752 missing from Emacs Lisp.
2755 * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}.
2756 * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}.
2759 @node Property Lists
2760 @section Property Lists
2763 These functions augment the standard Emacs Lisp functions @code{get}
2764 and @code{put} for operating on properties attached to symbols.
2765 There are also functions for working with property lists as
2766 first-class data structures not attached to particular symbols.
2768 @defun cl-get symbol property &optional default
2769 This function is like @code{get}, except that if the property is
2770 not found, the @var{default} argument provides the return value.
2771 (The Emacs Lisp @code{get} function always uses @code{nil} as
2772 the default; this package's @code{cl-get} is equivalent to Common
2775 The @code{cl-get} function is @code{setf}-able; when used in this
2776 fashion, the @var{default} argument is allowed but ignored.
2779 @defun cl-remprop symbol property
2780 This function removes the entry for @var{property} from the property
2781 list of @var{symbol}. It returns a true value if the property was
2782 indeed found and removed, or @code{nil} if there was no such property.
2783 (This function was probably omitted from Emacs originally because,
2784 since @code{get} did not allow a @var{default}, it was very difficult
2785 to distinguish between a missing property and a property whose value
2786 was @code{nil}; thus, setting a property to @code{nil} was close
2787 enough to @code{cl-remprop} for most purposes.)
2790 @defun cl-getf place property &optional default
2791 This function scans the list @var{place} as if it were a property
2792 list, i.e., a list of alternating property names and values. If
2793 an even-numbered element of @var{place} is found which is @code{eq}
2794 to @var{property}, the following odd-numbered element is returned.
2795 Otherwise, @var{default} is returned (or @code{nil} if no default
2801 (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop)
2804 It is valid to use @code{cl-getf} as a @code{setf} place, in which case
2805 its @var{place} argument must itself be a valid @code{setf} place.
2806 The @var{default} argument, if any, is ignored in this context.
2807 The effect is to change (via @code{setcar}) the value cell in the
2808 list that corresponds to @var{property}, or to cons a new property-value
2809 pair onto the list if the property is not yet present.
2812 (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val)
2815 The @code{get} and @code{cl-get} functions are also @code{setf}-able.
2816 The fact that @code{default} is ignored can sometimes be useful:
2819 (cl-incf (cl-get 'foo 'usage-count 0))
2822 Here, symbol @code{foo}'s @code{usage-count} property is incremented
2823 if it exists, or set to 1 (an incremented 0) otherwise.
2825 When not used as a @code{setf} form, @code{cl-getf} is just a regular
2826 function and its @var{place} argument can actually be any Lisp
2830 @defmac cl-remf place property
2831 This macro removes the property-value pair for @var{property} from
2832 the property list stored at @var{place}, which is any @code{setf}-able
2833 place expression. It returns true if the property was found. Note
2834 that if @var{property} happens to be first on the list, this will
2835 effectively do a @code{(setf @var{place} (cddr @var{place}))},
2836 whereas if it occurs later, this simply uses @code{setcdr} to splice
2837 out the property and value cells.
2840 @node Creating Symbols
2841 @section Creating Symbols
2844 These functions create unique symbols, typically for use as
2845 temporary variables.
2847 @defun cl-gensym &optional x
2848 This function creates a new, uninterned symbol (using @code{make-symbol})
2849 with a unique name. (The name of an uninterned symbol is relevant
2850 only if the symbol is printed.) By default, the name is generated
2851 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001},
2852 @samp{G1002}, etc. If the optional argument @var{x} is a string, that
2853 string is used as a prefix instead of @samp{G}. Uninterned symbols
2854 are used in macro expansions for temporary variables, to ensure that
2855 their names will not conflict with ``real'' variables in the user's
2858 (Internally, the variable @code{cl--gensym-counter} holds the counter
2859 used to generate names. It is incremented after each use. In Common
2860 Lisp this is initialized with 0, but this package initializes it with
2861 a random time-dependent value to avoid trouble when two files that
2862 each used @code{cl-gensym} in their compilation are loaded together.
2863 Uninterned symbols become interned when the compiler writes them out
2864 to a file and the Emacs loader loads them, so their names have to be
2865 treated a bit more carefully than in Common Lisp where uninterned
2866 symbols remain uninterned after loading.)
2869 @defun cl-gentemp &optional x
2870 This function is like @code{cl-gensym}, except that it produces a new
2871 @emph{interned} symbol. If the symbol that is generated already
2872 exists, the function keeps incrementing the counter and trying
2873 again until a new symbol is generated.
2876 This package automatically creates all keywords that are called for by
2877 @code{&key} argument specifiers, and discourages the use of keywords
2878 as data unrelated to keyword arguments, so the related function
2879 @code{defkeyword} (to create self-quoting keyword symbols) is not
2886 This section defines a few simple Common Lisp operations on numbers
2887 that were left out of Emacs Lisp.
2890 * Predicates on Numbers:: @code{cl-plusp}, @code{cl-oddp}, etc.
2891 * Numerical Functions:: @code{cl-floor}, @code{cl-ceiling}, etc.
2892 * Random Numbers:: @code{cl-random}, @code{cl-make-random-state}.
2893 * Implementation Parameters:: @code{cl-most-positive-float}, etc.
2896 @node Predicates on Numbers
2897 @section Predicates on Numbers
2900 These functions return @code{t} if the specified condition is
2901 true of the numerical argument, or @code{nil} otherwise.
2903 @defun cl-plusp number
2904 This predicate tests whether @var{number} is positive. It is an
2905 error if the argument is not a number.
2908 @defun cl-minusp number
2909 This predicate tests whether @var{number} is negative. It is an
2910 error if the argument is not a number.
2913 @defun cl-oddp integer
2914 This predicate tests whether @var{integer} is odd. It is an
2915 error if the argument is not an integer.
2918 @defun cl-evenp integer
2919 This predicate tests whether @var{integer} is even. It is an
2920 error if the argument is not an integer.
2924 @defun cl-floatp-safe object
2925 This predicate tests whether @var{object} is a floating-point
2926 number. On systems that support floating-point, this is equivalent
2927 to @code{floatp}. On other systems, this always returns @code{nil}.
2931 @node Numerical Functions
2932 @section Numerical Functions
2935 These functions perform various arithmetic operations on numbers.
2937 @defun cl-gcd &rest integers
2938 This function returns the Greatest Common Divisor of the arguments.
2939 For one argument, it returns the absolute value of that argument.
2940 For zero arguments, it returns zero.
2943 @defun cl-lcm &rest integers
2944 This function returns the Least Common Multiple of the arguments.
2945 For one argument, it returns the absolute value of that argument.
2946 For zero arguments, it returns one.
2949 @defun cl-isqrt integer
2950 This function computes the ``integer square root'' of its integer
2951 argument, i.e., the greatest integer less than or equal to the true
2952 square root of the argument.
2955 @defun cl-floor number &optional divisor
2956 With one argument, @code{cl-floor} returns a list of two numbers:
2957 The argument rounded down (toward minus infinity) to an integer,
2958 and the ``remainder'' which would have to be added back to the
2959 first return value to yield the argument again. If the argument
2960 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}.
2961 If the argument is a floating-point number, the first
2962 result is a Lisp integer and the second is a Lisp float between
2963 0 (inclusive) and 1 (exclusive).
2965 With two arguments, @code{cl-floor} divides @var{number} by
2966 @var{divisor}, and returns the floor of the quotient and the
2967 corresponding remainder as a list of two numbers. If
2968 @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})},
2969 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r}
2970 between 0 (inclusive) and @var{r} (exclusive). Also, note
2971 that @code{(cl-floor @var{x})} is exactly equivalent to
2972 @code{(cl-floor @var{x} 1)}.
2974 This function is entirely compatible with Common Lisp's @code{floor}
2975 function, except that it returns the two results in a list since
2976 Emacs Lisp does not support multiple-valued functions.
2979 @defun cl-ceiling number &optional divisor
2980 This function implements the Common Lisp @code{ceiling} function,
2981 which is analogous to @code{floor} except that it rounds the
2982 argument or quotient of the arguments up toward plus infinity.
2983 The remainder will be between 0 and minus @var{r}.
2986 @defun cl-truncate number &optional divisor
2987 This function implements the Common Lisp @code{truncate} function,
2988 which is analogous to @code{floor} except that it rounds the
2989 argument or quotient of the arguments toward zero. Thus it is
2990 equivalent to @code{cl-floor} if the argument or quotient is
2991 positive, or to @code{cl-ceiling} otherwise. The remainder has
2992 the same sign as @var{number}.
2995 @defun cl-round number &optional divisor
2996 This function implements the Common Lisp @code{round} function,
2997 which is analogous to @code{floor} except that it rounds the
2998 argument or quotient of the arguments to the nearest integer.
2999 In the case of a tie (the argument or quotient is exactly
3000 halfway between two integers), it rounds to the even integer.
3003 @defun cl-mod number divisor
3004 This function returns the same value as the second return value
3008 @defun cl-rem number divisor
3009 This function returns the same value as the second return value
3010 of @code{cl-truncate}.
3013 @node Random Numbers
3014 @section Random Numbers
3017 This package also provides an implementation of the Common Lisp
3018 random number generator. It uses its own additive-congruential
3019 algorithm, which is much more likely to give statistically clean
3020 @c FIXME? Still true?
3021 random numbers than the simple generators supplied by many
3024 @defun cl-random number &optional state
3025 This function returns a random nonnegative number less than
3026 @var{number}, and of the same type (either integer or floating-point).
3027 The @var{state} argument should be a @code{random-state} object
3028 that holds the state of the random number generator. The
3029 function modifies this state object as a side effect. If
3030 @var{state} is omitted, it defaults to the internal variable
3031 @code{cl--random-state}, which contains a pre-initialized
3032 default @code{random-state} object. (Since any number of programs in
3033 the Emacs process may be accessing @code{cl--random-state} in
3034 interleaved fashion, the sequence generated from this will be
3035 irreproducible for all intents and purposes.)
3038 @defun cl-make-random-state &optional state
3039 This function creates or copies a @code{random-state} object.
3040 If @var{state} is omitted or @code{nil}, it returns a new copy of
3041 @code{cl--random-state}. This is a copy in the sense that future
3042 sequences of calls to @code{(cl-random @var{n})} and
3043 @code{(cl-random @var{n} @var{s})} (where @var{s} is the new
3044 random-state object) will return identical sequences of random
3047 If @var{state} is a @code{random-state} object, this function
3048 returns a copy of that object. If @var{state} is @code{t}, this
3049 function returns a new @code{random-state} object seeded from the
3050 date and time. As an extension to Common Lisp, @var{state} may also
3051 be an integer in which case the new object is seeded from that
3052 integer; each different integer seed will result in a completely
3053 different sequence of random numbers.
3055 It is valid to print a @code{random-state} object to a buffer or
3056 file and later read it back with @code{read}. If a program wishes
3057 to use a sequence of pseudo-random numbers which can be reproduced
3058 later for debugging, it can call @code{(cl-make-random-state t)} to
3059 get a new sequence, then print this sequence to a file. When the
3060 program is later rerun, it can read the original run's random-state
3064 @defun cl-random-state-p object
3065 This predicate returns @code{t} if @var{object} is a
3066 @code{random-state} object, or @code{nil} otherwise.
3069 @node Implementation Parameters
3070 @section Implementation Parameters
3073 This package defines several useful constants having to do with
3074 floating-point numbers.
3076 It determines their values by exercising the computer's
3077 floating-point arithmetic in various ways. Because this operation
3078 might be slow, the code for initializing them is kept in a separate
3079 function that must be called before the parameters can be used.
3081 @defun cl-float-limits
3082 This function makes sure that the Common Lisp floating-point parameters
3083 like @code{cl-most-positive-float} have been initialized. Until it is
3084 called, these parameters will be @code{nil}.
3085 @c If this version of Emacs does not support floats, the parameters will
3086 @c remain @code{nil}.
3087 If the parameters have already been initialized, the function returns
3090 The algorithm makes assumptions that will be valid for almost all
3091 machines, but will fail if the machine's arithmetic is extremely
3092 unusual, e.g., decimal.
3095 Since true Common Lisp supports up to four different floating-point
3096 precisions, it has families of constants like
3097 @code{most-positive-single-float}, @code{most-positive-double-float},
3098 @code{most-positive-long-float}, and so on. Emacs has only one
3099 floating-point precision, so this package omits the precision word
3100 from the constants' names.
3102 @defvar cl-most-positive-float
3103 This constant equals the largest value a Lisp float can hold.
3104 For those systems whose arithmetic supports infinities, this is
3105 the largest @emph{finite} value. For IEEE machines, the value
3106 is approximately @code{1.79e+308}.
3109 @defvar cl-most-negative-float
3110 This constant equals the most negative value a Lisp float can hold.
3111 (It is assumed to be equal to @code{(- cl-most-positive-float)}.)
3114 @defvar cl-least-positive-float
3115 This constant equals the smallest Lisp float value greater than zero.
3116 For IEEE machines, it is about @code{4.94e-324} if denormals are
3117 supported or @code{2.22e-308} if not.
3120 @defvar cl-least-positive-normalized-float
3121 This constant equals the smallest @emph{normalized} Lisp float greater
3122 than zero, i.e., the smallest value for which IEEE denormalization
3123 will not result in a loss of precision. For IEEE machines, this
3124 value is about @code{2.22e-308}. For machines that do not support
3125 the concept of denormalization and gradual underflow, this constant
3126 will always equal @code{cl-least-positive-float}.
3129 @defvar cl-least-negative-float
3130 This constant is the negative counterpart of @code{cl-least-positive-float}.
3133 @defvar cl-least-negative-normalized-float
3134 This constant is the negative counterpart of
3135 @code{cl-least-positive-normalized-float}.
3138 @defvar cl-float-epsilon
3139 This constant is the smallest positive Lisp float that can be added
3140 to 1.0 to produce a distinct value. Adding a smaller number to 1.0
3141 will yield 1.0 again due to roundoff. For IEEE machines, epsilon
3142 is about @code{2.22e-16}.
3145 @defvar cl-float-negative-epsilon
3146 This is the smallest positive value that can be subtracted from
3147 1.0 to produce a distinct value. For IEEE machines, it is about
3155 Common Lisp defines a number of functions that operate on
3156 @dfn{sequences}, which are either lists, strings, or vectors.
3157 Emacs Lisp includes a few of these, notably @code{elt} and
3158 @code{length}; this package defines most of the rest.
3161 * Sequence Basics:: Arguments shared by all sequence functions.
3162 * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc.
3163 * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc.
3164 * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc.
3165 * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}.
3168 @node Sequence Basics
3169 @section Sequence Basics
3172 Many of the sequence functions take keyword arguments; @pxref{Argument
3173 Lists}. All keyword arguments are optional and, if specified,
3174 may appear in any order.
3176 The @code{:key} argument should be passed either @code{nil}, or a
3177 function of one argument. This key function is used as a filter
3178 through which the elements of the sequence are seen; for example,
3179 @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}.
3180 It searches for an element of the list whose @sc{car} equals
3181 @code{x}, rather than for an element which equals @code{x} itself.
3182 If @code{:key} is omitted or @code{nil}, the filter is effectively
3183 the identity function.
3185 The @code{:test} and @code{:test-not} arguments should be either
3186 @code{nil}, or functions of two arguments. The test function is
3187 used to compare two sequence elements, or to compare a search value
3188 with sequence elements. (The two values are passed to the test
3189 function in the same order as the original sequence function
3190 arguments from which they are derived, or, if they both come from
3191 the same sequence, in the same order as they appear in that sequence.)
3192 The @code{:test} argument specifies a function which must return
3193 true (non-@code{nil}) to indicate a match; instead, you may use
3194 @code{:test-not} to give a function which returns @emph{false} to
3195 indicate a match. The default test function is @code{eql}.
3197 Many functions that take @var{item} and @code{:test} or @code{:test-not}
3198 arguments also come in @code{-if} and @code{-if-not} varieties,
3199 where a @var{predicate} function is passed instead of @var{item},
3200 and sequence elements match if the predicate returns true on them
3201 (or false in the case of @code{-if-not}). For example:
3204 (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq)
3208 to remove all zeros from sequence @code{seq}.
3210 Some operations can work on a subsequence of the argument sequence;
3211 these function take @code{:start} and @code{:end} arguments, which
3212 default to zero and the length of the sequence, respectively.
3213 Only elements between @var{start} (inclusive) and @var{end}
3214 (exclusive) are affected by the operation. The @var{end} argument
3215 may be passed @code{nil} to signify the length of the sequence;
3216 otherwise, both @var{start} and @var{end} must be integers, with
3217 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}.
3218 If the function takes two sequence arguments, the limits are
3219 defined by keywords @code{:start1} and @code{:end1} for the first,
3220 and @code{:start2} and @code{:end2} for the second.
3222 A few functions accept a @code{:from-end} argument, which, if
3223 non-@code{nil}, causes the operation to go from right-to-left
3224 through the sequence instead of left-to-right, and a @code{:count}
3225 argument, which specifies an integer maximum number of elements
3226 to be removed or otherwise processed.
3228 The sequence functions make no guarantees about the order in
3229 which the @code{:test}, @code{:test-not}, and @code{:key} functions
3230 are called on various elements. Therefore, it is a bad idea to depend
3231 on side effects of these functions. For example, @code{:from-end}
3232 may cause the sequence to be scanned actually in reverse, or it may
3233 be scanned forwards but computing a result ``as if'' it were scanned
3234 backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every},
3235 @emph{do} specify exactly the order in which the function is called
3236 so side effects are perfectly acceptable in those cases.)
3238 Strings may contain ``text properties'' as well
3239 as character data. Except as noted, it is undefined whether or
3240 not text properties are preserved by sequence functions. For
3241 example, @code{(cl-remove ?A @var{str})} may or may not preserve
3242 the properties of the characters copied from @var{str} into the
3245 @node Mapping over Sequences
3246 @section Mapping over Sequences
3249 These functions ``map'' the function you specify over the elements
3250 of lists or arrays. They are all variations on the theme of the
3251 built-in function @code{mapcar}.
3253 @defun cl-mapcar function seq &rest more-seqs
3254 This function calls @var{function} on successive parallel sets of
3255 elements from its argument sequences. Given a single @var{seq}
3256 argument it is equivalent to @code{mapcar}; given @var{n} sequences,
3257 it calls the function with the first elements of each of the sequences
3258 as the @var{n} arguments to yield the first element of the result
3259 list, then with the second elements, and so on. The mapping stops as
3260 soon as the shortest sequence runs out. The argument sequences may
3261 be any mixture of lists, strings, and vectors; the return sequence
3264 Common Lisp's @code{mapcar} accepts multiple arguments but works
3265 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence
3266 argument. This package's @code{cl-mapcar} works as a compatible
3270 @defun cl-map result-type function seq &rest more-seqs
3271 This function maps @var{function} over the argument sequences,
3272 just like @code{cl-mapcar}, but it returns a sequence of type
3273 @var{result-type} rather than a list. @var{result-type} must
3274 be one of the following symbols: @code{vector}, @code{string},
3275 @code{list} (in which case the effect is the same as for
3276 @code{cl-mapcar}), or @code{nil} (in which case the results are
3277 thrown away and @code{cl-map} returns @code{nil}).
3280 @defun cl-maplist function list &rest more-lists
3281 This function calls @var{function} on each of its argument lists,
3282 then on the @sc{cdr}s of those lists, and so on, until the
3283 shortest list runs out. The results are returned in the form
3284 of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except
3285 that it passes in the list pointers themselves rather than the
3286 @sc{car}s of the advancing pointers.
3289 @defun cl-mapc function seq &rest more-seqs
3290 This function is like @code{cl-mapcar}, except that the values returned
3291 by @var{function} are ignored and thrown away rather than being
3292 collected into a list. The return value of @code{cl-mapc} is @var{seq},
3293 the first sequence. This function is more general than the Emacs
3294 primitive @code{mapc}. (Note that this function is called
3295 @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you
3297 @c http://debbugs.gnu.org/6575
3300 @defun cl-mapl function list &rest more-lists
3301 This function is like @code{cl-maplist}, except that it throws away
3302 the values returned by @var{function}.
3305 @defun cl-mapcan function seq &rest more-seqs
3306 This function is like @code{cl-mapcar}, except that it concatenates
3307 the return values (which must be lists) using @code{nconc},
3308 rather than simply collecting them into a list.
3311 @defun cl-mapcon function list &rest more-lists
3312 This function is like @code{cl-maplist}, except that it concatenates
3313 the return values using @code{nconc}.
3316 @defun cl-some predicate seq &rest more-seqs
3317 This function calls @var{predicate} on each element of @var{seq}
3318 in turn; if @var{predicate} returns a non-@code{nil} value,
3319 @code{cl-some} returns that value, otherwise it returns @code{nil}.
3320 Given several sequence arguments, it steps through the sequences
3321 in parallel until the shortest one runs out, just as in
3322 @code{cl-mapcar}. You can rely on the left-to-right order in which
3323 the elements are visited, and on the fact that mapping stops
3324 immediately as soon as @var{predicate} returns non-@code{nil}.
3327 @defun cl-every predicate seq &rest more-seqs
3328 This function calls @var{predicate} on each element of the sequence(s)
3329 in turn; it returns @code{nil} as soon as @var{predicate} returns
3330 @code{nil} for any element, or @code{t} if the predicate was true
3334 @defun cl-notany predicate seq &rest more-seqs
3335 This function calls @var{predicate} on each element of the sequence(s)
3336 in turn; it returns @code{nil} as soon as @var{predicate} returns
3337 a non-@code{nil} value for any element, or @code{t} if the predicate
3338 was @code{nil} for all elements.
3341 @defun cl-notevery predicate seq &rest more-seqs
3342 This function calls @var{predicate} on each element of the sequence(s)
3343 in turn; it returns a non-@code{nil} value as soon as @var{predicate}
3344 returns @code{nil} for any element, or @code{t} if the predicate was
3345 true for all elements.
3348 @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key}
3349 This function combines the elements of @var{seq} using an associative
3350 binary operation. Suppose @var{function} is @code{*} and @var{seq} is
3351 the list @code{(2 3 4 5)}. The first two elements of the list are
3352 combined with @code{(* 2 3) = 6}; this is combined with the next
3353 element, @code{(* 6 4) = 24}, and that is combined with the final
3354 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens
3355 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as
3356 an explicit call to @code{cl-reduce}.
3358 If @code{:from-end} is true, the reduction is right-associative instead
3359 of left-associative:
3362 (cl-reduce '- '(1 2 3 4))
3363 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8
3364 (cl-reduce '- '(1 2 3 4) :from-end t)
3365 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2
3368 If @code{:key} is specified, it is a function of one argument, which
3369 is called on each of the sequence elements in turn.
3371 If @code{:initial-value} is specified, it is effectively added to the
3372 front (or rear in the case of @code{:from-end}) of the sequence.
3373 The @code{:key} function is @emph{not} applied to the initial value.
3375 If the sequence, including the initial value, has exactly one element
3376 then that element is returned without ever calling @var{function}.
3377 If the sequence is empty (and there is no initial value), then
3378 @var{function} is called with no arguments to obtain the return value.
3381 All of these mapping operations can be expressed conveniently in
3382 terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will
3383 be faster since it generates the loop as in-line code with no
3386 @node Sequence Functions
3387 @section Sequence Functions
3390 This section describes a number of Common Lisp functions for
3391 operating on sequences.
3393 @defun cl-subseq sequence start &optional end
3394 This function returns a given subsequence of the argument
3395 @var{sequence}, which may be a list, string, or vector.
3396 The indices @var{start} and @var{end} must be in range, and
3397 @var{start} must be no greater than @var{end}. If @var{end}
3398 is omitted, it defaults to the length of the sequence. The
3399 return value is always a copy; it does not share structure
3400 with @var{sequence}.
3402 As an extension to Common Lisp, @var{start} and/or @var{end}
3403 may be negative, in which case they represent a distance back
3404 from the end of the sequence. This is for compatibility with
3405 Emacs's @code{substring} function. Note that @code{cl-subseq} is
3406 the @emph{only} sequence function that allows negative
3407 @var{start} and @var{end}.
3409 You can use @code{setf} on a @code{cl-subseq} form to replace a
3410 specified range of elements with elements from another sequence.
3411 The replacement is done as if by @code{cl-replace}, described below.
3414 @defun cl-concatenate result-type &rest seqs
3415 This function concatenates the argument sequences together to
3416 form a result sequence of type @var{result-type}, one of the
3417 symbols @code{vector}, @code{string}, or @code{list}. The
3418 arguments are always copied, even in cases such as
3419 @code{(cl-concatenate 'list '(1 2 3))} where the result is
3420 identical to an argument.
3423 @defun cl-fill seq item @t{&key :start :end}
3424 This function fills the elements of the sequence (or the specified
3425 part of the sequence) with the value @var{item}.
3428 @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2}
3429 This function copies part of @var{seq2} into part of @var{seq1}.
3430 The sequence @var{seq1} is not stretched or resized; the amount
3431 of data copied is simply the shorter of the source and destination
3432 (sub)sequences. The function returns @var{seq1}.
3434 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement
3435 will work correctly even if the regions indicated by the start
3436 and end arguments overlap. However, if @var{seq1} and @var{seq2}
3437 are lists that share storage but are not @code{eq}, and the
3438 start and end arguments specify overlapping regions, the effect
3442 @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end}
3443 This returns a copy of @var{seq} with all elements matching
3444 @var{item} removed. The result may share storage with or be
3445 @code{eq} to @var{seq} in some circumstances, but the original
3446 @var{seq} will not be modified. The @code{:test}, @code{:test-not},
3447 and @code{:key} arguments define the matching test that is used;
3448 by default, elements @code{eql} to @var{item} are removed. The
3449 @code{:count} argument specifies the maximum number of matching
3450 elements that can be removed (only the leftmost @var{count} matches
3451 are removed). The @code{:start} and @code{:end} arguments specify
3452 a region in @var{seq} in which elements will be removed; elements
3453 outside that region are not matched or removed. The @code{:from-end}
3454 argument, if true, says that elements should be deleted from the
3455 end of the sequence rather than the beginning (this matters only
3456 if @var{count} was also specified).
3459 @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end}
3460 This deletes all elements of @var{seq} that match @var{item}.
3461 It is a destructive operation. Since Emacs Lisp does not support
3462 stretchable strings or vectors, this is the same as @code{cl-remove}
3463 for those sequence types. On lists, @code{cl-remove} will copy the
3464 list if necessary to preserve the original list, whereas
3465 @code{cl-delete} will splice out parts of the argument list.
3466 Compare @code{append} and @code{nconc}, which are analogous
3467 non-destructive and destructive list operations in Emacs Lisp.
3470 @findex cl-remove-if
3471 @findex cl-remove-if-not
3472 @findex cl-delete-if
3473 @findex cl-delete-if-not
3474 The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not},
3475 @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly.
3477 @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3478 This function returns a copy of @var{seq} with duplicate elements
3479 removed. Specifically, if two elements from the sequence match
3480 according to the @code{:test}, @code{:test-not}, and @code{:key}
3481 arguments, only the rightmost one is retained. If @code{:from-end}
3482 is true, the leftmost one is retained instead. If @code{:start} or
3483 @code{:end} is specified, only elements within that subsequence are
3484 examined or removed.
3487 @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
3488 This function deletes duplicate elements from @var{seq}. It is
3489 a destructive version of @code{cl-remove-duplicates}.
3492 @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3493 This function returns a copy of @var{seq}, with all elements
3494 matching @var{old} replaced with @var{new}. The @code{:count},
3495 @code{:start}, @code{:end}, and @code{:from-end} arguments may be
3496 used to limit the number of substitutions made.
3499 @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
3500 This is a destructive version of @code{cl-substitute}; it performs
3501 the substitution using @code{setcar} or @code{aset} rather than
3502 by returning a changed copy of the sequence.
3505 @findex cl-substitute-if
3506 @findex cl-substitute-if-not
3507 @findex cl-nsubstitute-if
3508 @findex cl-nsubstitute-if-not
3509 The functions @code{cl-substitute-if}, @code{cl-substitute-if-not},
3510 @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined
3511 similarly. For these, a @var{predicate} is given in place of the
3514 @node Searching Sequences
3515 @section Searching Sequences
3518 These functions search for elements or subsequences in a sequence.
3519 (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.)
3521 @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end}
3522 This function searches @var{seq} for an element matching @var{item}.
3523 If it finds a match, it returns the matching element. Otherwise,
3524 it returns @code{nil}. It returns the leftmost match, unless
3525 @code{:from-end} is true, in which case it returns the rightmost
3526 match. The @code{:start} and @code{:end} arguments may be used to
3527 limit the range of elements that are searched.
3530 @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end}
3531 This function is like @code{cl-find}, except that it returns the
3532 integer position in the sequence of the matching item rather than
3533 the item itself. The position is relative to the start of the
3534 sequence as a whole, even if @code{:start} is non-zero. The function
3535 returns @code{nil} if no matching element was found.
3538 @defun cl-count item seq @t{&key :test :test-not :key :start :end}
3539 This function returns the number of elements of @var{seq} which
3540 match @var{item}. The result is always a nonnegative integer.
3544 @findex cl-find-if-not
3545 @findex cl-position-if
3546 @findex cl-position-if-not
3548 @findex cl-count-if-not
3549 The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if},
3550 @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not}
3551 functions are defined similarly.
3553 @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end}
3554 This function compares the specified parts of @var{seq1} and
3555 @var{seq2}. If they are the same length and the corresponding
3556 elements match (according to @code{:test}, @code{:test-not},
3557 and @code{:key}), the function returns @code{nil}. If there is
3558 a mismatch, the function returns the index (relative to @var{seq1})
3559 of the first mismatching element. This will be the leftmost pair of
3560 elements that do not match, or the position at which the shorter of
3561 the two otherwise-matching sequences runs out.
3563 If @code{:from-end} is true, then the elements are compared from right
3564 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}.
3565 If the sequences differ, then one plus the index of the rightmost
3566 difference (relative to @var{seq1}) is returned.
3568 An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)},
3569 which compares two strings case-insensitively.
3572 @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2}
3573 This function searches @var{seq2} for a subsequence that matches
3574 @var{seq1} (or part of it specified by @code{:start1} and
3575 @code{:end1}). Only matches that fall entirely within the region
3576 defined by @code{:start2} and @code{:end2} will be considered.
3577 The return value is the index of the leftmost element of the
3578 leftmost match, relative to the start of @var{seq2}, or @code{nil}
3579 if no matches were found. If @code{:from-end} is true, the
3580 function finds the @emph{rightmost} matching subsequence.
3583 @node Sorting Sequences
3584 @section Sorting Sequences
3586 @defun cl-sort seq predicate @t{&key :key}
3587 This function sorts @var{seq} into increasing order as determined
3588 by using @var{predicate} to compare pairs of elements. @var{predicate}
3589 should return true (non-@code{nil}) if and only if its first argument
3590 is less than (not equal to) its second argument. For example,
3591 @code{<} and @code{string-lessp} are suitable predicate functions
3592 for sorting numbers and strings, respectively; @code{>} would sort
3593 numbers into decreasing rather than increasing order.
3595 This function differs from Emacs's built-in @code{sort} in that it
3596 can operate on any type of sequence, not just lists. Also, it
3597 accepts a @code{:key} argument, which is used to preprocess data
3598 fed to the @var{predicate} function. For example,
3601 (setq data (cl-sort data 'string-lessp :key 'downcase))
3605 sorts @var{data}, a sequence of strings, into increasing alphabetical
3606 order without regard to case. A @code{:key} function of @code{car}
3607 would be useful for sorting association lists. It should only be a
3608 simple accessor though, since it's used heavily in the current
3611 The @code{cl-sort} function is destructive; it sorts lists by actually
3612 rearranging the @sc{cdr} pointers in suitable fashion.
3615 @defun cl-stable-sort seq predicate @t{&key :key}
3616 This function sorts @var{seq} @dfn{stably}, meaning two elements
3617 which are equal in terms of @var{predicate} are guaranteed not to
3618 be rearranged out of their original order by the sort.
3620 In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent
3621 in Emacs Lisp because the underlying @code{sort} function is
3622 stable by default. However, this package reserves the right to
3623 use non-stable methods for @code{cl-sort} in the future.
3626 @defun cl-merge type seq1 seq2 predicate @t{&key :key}
3627 This function merges two sequences @var{seq1} and @var{seq2} by
3628 interleaving their elements. The result sequence, of type @var{type}
3629 (in the sense of @code{cl-concatenate}), has length equal to the sum
3630 of the lengths of the two input sequences. The sequences may be
3631 modified destructively. Order of elements within @var{seq1} and
3632 @var{seq2} is preserved in the interleaving; elements of the two
3633 sequences are compared by @var{predicate} (in the sense of
3634 @code{sort}) and the lesser element goes first in the result.
3635 When elements are equal, those from @var{seq1} precede those from
3636 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are
3637 both sorted according to @var{predicate}, then the result will be
3638 a merged sequence which is (stably) sorted according to
3646 The functions described here operate on lists.
3649 * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc.
3650 * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc.
3651 * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc.
3652 * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc.
3655 @node List Functions
3656 @section List Functions
3659 This section describes a number of simple operations on lists,
3660 i.e., chains of cons cells.
3663 This function is equivalent to @code{(car (cdr (cdr @var{x})))}.
3664 Likewise, this package defines all 24 @code{c@var{xxx}r} functions
3665 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s.
3666 All of these functions are @code{setf}-able, and calls to them
3667 are expanded inline by the byte-compiler for maximum efficiency.
3671 This function is a synonym for @code{(car @var{x})}. Likewise,
3672 the functions @code{cl-second}, @code{cl-third}, @dots{}, through
3673 @code{cl-tenth} return the given element of the list @var{x}.
3677 This function is a synonym for @code{(cdr @var{x})}.
3681 Common Lisp defines this function to act like @code{null}, but
3682 signaling an error if @code{x} is neither a @code{nil} nor a
3683 cons cell. This package simply defines @code{cl-endp} as a synonym
3687 @defun cl-list-length x
3688 This function returns the length of list @var{x}, exactly like
3689 @code{(length @var{x})}, except that if @var{x} is a circular
3690 list (where the @sc{cdr}-chain forms a loop rather than terminating
3691 with @code{nil}), this function returns @code{nil}. (The regular
3692 @code{length} function would get stuck if given a circular list.
3693 See also the @code{safe-length} function.)
3696 @defun cl-list* arg &rest others
3697 This function constructs a list of its arguments. The final
3698 argument becomes the @sc{cdr} of the last cell constructed.
3699 Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to
3700 @code{(cons @var{a} (cons @var{b} @var{c}))}, and
3701 @code{(cl-list* @var{a} @var{b} nil)} is equivalent to
3702 @code{(list @var{a} @var{b})}.
3705 @defun cl-ldiff list sublist
3706 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to
3707 one of the cons cells of @var{list}, then this function returns
3708 a copy of the part of @var{list} up to but not including
3709 @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns
3710 the first two elements of the list @code{x}. The result is a
3711 copy; the original @var{list} is not modified. If @var{sublist}
3712 is not a sublist of @var{list}, a copy of the entire @var{list}
3716 @defun cl-copy-list list
3717 This function returns a copy of the list @var{list}. It copies
3718 dotted lists like @code{(1 2 . 3)} correctly.
3721 @defun cl-tree-equal x y @t{&key :test :test-not :key}
3722 This function compares two trees of cons cells. If @var{x} and
3723 @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are
3724 compared recursively. If neither @var{x} nor @var{y} is a cons
3725 cell, they are compared by @code{eql}, or according to the
3726 specified test. The @code{:key} function, if specified, is
3727 applied to the elements of both trees. @xref{Sequences}.
3730 @node Substitution of Expressions
3731 @section Substitution of Expressions
3734 These functions substitute elements throughout a tree of cons
3735 cells. (@xref{Sequence Functions}, for the @code{cl-substitute}
3736 function, which works on just the top-level elements of a list.)
3738 @defun cl-subst new old tree @t{&key :test :test-not :key}
3739 This function substitutes occurrences of @var{old} with @var{new}
3740 in @var{tree}, a tree of cons cells. It returns a substituted
3741 tree, which will be a copy except that it may share storage with
3742 the argument @var{tree} in parts where no substitutions occurred.
3743 The original @var{tree} is not modified. This function recurses
3744 on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s
3745 of the component cons cells. If @var{old} is itself a cons cell,
3746 then matching cells in the tree are substituted as usual without
3747 recursively substituting in that cell. Comparisons with @var{old}
3748 are done according to the specified test (@code{eql} by default).
3749 The @code{:key} function is applied to the elements of the tree
3750 but not to @var{old}.
3753 @defun cl-nsubst new old tree @t{&key :test :test-not :key}
3754 This function is like @code{cl-subst}, except that it works by
3755 destructive modification (by @code{setcar} or @code{setcdr})
3756 rather than copying.
3760 @findex cl-subst-if-not
3761 @findex cl-nsubst-if
3762 @findex cl-nsubst-if-not
3763 The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and
3764 @code{cl-nsubst-if-not} functions are defined similarly.
3766 @defun cl-sublis alist tree @t{&key :test :test-not :key}
3767 This function is like @code{cl-subst}, except that it takes an
3768 association list @var{alist} of @var{old}-@var{new} pairs.
3769 Each element of the tree (after applying the @code{:key}
3770 function, if any), is compared with the @sc{car}s of
3771 @var{alist}; if it matches, it is replaced by the corresponding
3775 @defun cl-nsublis alist tree @t{&key :test :test-not :key}
3776 This is a destructive version of @code{cl-sublis}.
3780 @section Lists as Sets
3783 These functions perform operations on lists that represent sets
3786 @defun cl-member item list @t{&key :test :test-not :key}
3787 This function searches @var{list} for an element matching @var{item}.
3788 If a match is found, it returns the cons cell whose @sc{car} was
3789 the matching element. Otherwise, it returns @code{nil}. Elements
3790 are compared by @code{eql} by default; you can use the @code{:test},
3791 @code{:test-not}, and @code{:key} arguments to modify this behavior.
3794 The standard Emacs lisp function @code{member} uses @code{equal} for
3795 comparisons; it is equivalent to @code{(cl-member @var{item} @var{list}
3796 :test 'equal)}. With no keyword arguments, @code{cl-member} is
3797 equivalent to @code{memq}.
3800 @findex cl-member-if
3801 @findex cl-member-if-not
3802 The @code{cl-member-if} and @code{cl-member-if-not} functions
3803 analogously search for elements that satisfy a given predicate.
3805 @defun cl-tailp sublist list
3806 This function returns @code{t} if @var{sublist} is a sublist of
3807 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to
3808 any of its @sc{cdr}s.
3811 @defun cl-adjoin item list @t{&key :test :test-not :key}
3812 This function conses @var{item} onto the front of @var{list},
3813 like @code{(cons @var{item} @var{list})}, but only if @var{item}
3814 is not already present on the list (as determined by @code{cl-member}).
3815 If a @code{:key} argument is specified, it is applied to
3816 @var{item} as well as to the elements of @var{list} during
3817 the search, on the reasoning that @var{item} is ``about'' to
3818 become part of the list.
3821 @defun cl-union list1 list2 @t{&key :test :test-not :key}
3822 This function combines two lists that represent sets of items,
3823 returning a list that represents the union of those two sets.
3824 The resulting list contains all items that appear in @var{list1}
3825 or @var{list2}, and no others. If an item appears in both
3826 @var{list1} and @var{list2} it is copied only once. If
3827 an item is duplicated in @var{list1} or @var{list2}, it is
3828 undefined whether or not that duplication will survive in the
3829 result list. The order of elements in the result list is also
3833 @defun cl-nunion list1 list2 @t{&key :test :test-not :key}
3834 This is a destructive version of @code{cl-union}; rather than copying,
3835 it tries to reuse the storage of the argument lists if possible.
3838 @defun cl-intersection list1 list2 @t{&key :test :test-not :key}
3839 This function computes the intersection of the sets represented
3840 by @var{list1} and @var{list2}. It returns the list of items
3841 that appear in both @var{list1} and @var{list2}.
3844 @defun cl-nintersection list1 list2 @t{&key :test :test-not :key}
3845 This is a destructive version of @code{cl-intersection}. It
3846 tries to reuse storage of @var{list1} rather than copying.
3847 It does @emph{not} reuse the storage of @var{list2}.
3850 @defun cl-set-difference list1 list2 @t{&key :test :test-not :key}
3851 This function computes the ``set difference'' of @var{list1}
3852 and @var{list2}, i.e., the set of elements that appear in
3853 @var{list1} but @emph{not} in @var{list2}.
3856 @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key}
3857 This is a destructive @code{cl-set-difference}, which will try
3858 to reuse @var{list1} if possible.
3861 @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key}
3862 This function computes the ``set exclusive or'' of @var{list1}
3863 and @var{list2}, i.e., the set of elements that appear in
3864 exactly one of @var{list1} and @var{list2}.
3867 @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key}
3868 This is a destructive @code{cl-set-exclusive-or}, which will try
3869 to reuse @var{list1} and @var{list2} if possible.
3872 @defun cl-subsetp list1 list2 @t{&key :test :test-not :key}
3873 This function checks whether @var{list1} represents a subset
3874 of @var{list2}, i.e., whether every element of @var{list1}
3875 also appears in @var{list2}.
3878 @node Association Lists
3879 @section Association Lists
3882 An @dfn{association list} is a list representing a mapping from
3883 one set of values to another; any list whose elements are cons
3884 cells is an association list.
3886 @defun cl-assoc item a-list @t{&key :test :test-not :key}
3887 This function searches the association list @var{a-list} for an
3888 element whose @sc{car} matches (in the sense of @code{:test},
3889 @code{:test-not}, and @code{:key}, or by comparison with @code{eql})
3890 a given @var{item}. It returns the matching element, if any,
3891 otherwise @code{nil}. It ignores elements of @var{a-list} that
3892 are not cons cells. (This corresponds to the behavior of
3893 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's
3894 @code{assoc} ignores @code{nil}s but considers any other non-cons
3895 elements of @var{a-list} to be an error.)
3898 @defun cl-rassoc item a-list @t{&key :test :test-not :key}
3899 This function searches for an element whose @sc{cdr} matches
3900 @var{item}. If @var{a-list} represents a mapping, this applies
3901 the inverse of the mapping to @var{item}.
3905 @findex cl-assoc-if-not
3906 @findex cl-rassoc-if
3907 @findex cl-rassoc-if-not
3908 The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if},
3909 and @code{cl-rassoc-if-not} functions are defined similarly.
3911 Two simple functions for constructing association lists are:
3913 @defun cl-acons key value alist
3914 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}.
3917 @defun cl-pairlis keys values &optional alist
3918 This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values})
3926 The Common Lisp @dfn{structure} mechanism provides a general way
3927 to define data types similar to C's @code{struct} types. A
3928 structure is a Lisp object containing some number of @dfn{slots},
3929 each of which can hold any Lisp data object. Functions are
3930 provided for accessing and setting the slots, creating or copying
3931 structure objects, and recognizing objects of a particular structure
3934 In true Common Lisp, each structure type is a new type distinct
3935 from all existing Lisp types. Since the underlying Emacs Lisp
3936 system provides no way to create new distinct types, this package
3937 implements structures as vectors (or lists upon request) with a
3938 special ``tag'' symbol to identify them.
3940 @defmac cl-defstruct name slots@dots{}
3941 The @code{cl-defstruct} form defines a new structure type called
3942 @var{name}, with the specified @var{slots}. (The @var{slots}
3943 may begin with a string which documents the structure type.)
3944 In the simplest case, @var{name} and each of the @var{slots}
3945 are symbols. For example,
3948 (cl-defstruct person name age sex)
3952 defines a struct type called @code{person} that contains three
3953 slots. Given a @code{person} object @var{p}, you can access those
3954 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})},
3955 and @code{(person-sex @var{p})}. You can also change these slots by
3956 using @code{setf} on any of these place forms, for example:
3959 (cl-incf (person-age birthday-boy))
3962 You can create a new @code{person} by calling @code{make-person},
3963 which takes keyword arguments @code{:name}, @code{:age}, and
3964 @code{:sex} to specify the initial values of these slots in the
3965 new object. (Omitting any of these arguments leaves the corresponding
3966 slot ``undefined'', according to the Common Lisp standard; in Emacs
3967 Lisp, such uninitialized slots are filled with @code{nil}.)
3969 Given a @code{person}, @code{(copy-person @var{p})} makes a new
3970 object of the same type whose slots are @code{eq} to those of @var{p}.
3972 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns
3973 true if @var{x} looks like a @code{person}, and false otherwise. (Again,
3974 in Common Lisp this predicate would be exact; in Emacs Lisp the
3975 best it can do is verify that @var{x} is a vector of the correct
3976 length that starts with the correct tag symbol.)
3978 Accessors like @code{person-name} normally check their arguments
3979 (effectively using @code{person-p}) and signal an error if the
3980 argument is the wrong type. This check is affected by
3981 @code{(optimize (safety @dots{}))} declarations. Safety level 1,
3982 the default, uses a somewhat optimized check that will detect all
3983 incorrect arguments, but may use an uninformative error message
3984 (e.g., ``expected a vector'' instead of ``expected a @code{person}'').
3985 Safety level 0 omits all checks except as provided by the underlying
3986 @code{aref} call; safety levels 2 and 3 do rigorous checking that will
3987 always print a descriptive error message for incorrect inputs.
3988 @xref{Declarations}.
3991 (setq dave (make-person :name "Dave" :sex 'male))
3992 @result{} [cl-struct-person "Dave" nil male]
3993 (setq other (copy-person dave))
3994 @result{} [cl-struct-person "Dave" nil male]
3997 (eq (person-name dave) (person-name other))
4001 (person-p [1 2 3 4])
4005 (person-p '[cl-struct-person counterfeit person object])
4009 In general, @var{name} is either a name symbol or a list of a name
4010 symbol followed by any number of @dfn{struct options}; each @var{slot}
4011 is either a slot symbol or a list of the form @samp{(@var{slot-name}
4012 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value}
4013 is a Lisp form that is evaluated any time an instance of the
4014 structure type is created without specifying that slot's value.
4016 Common Lisp defines several slot options, but the only one
4017 implemented in this package is @code{:read-only}. A non-@code{nil}
4018 value for this option means the slot should not be @code{setf}-able;
4019 the slot's value is determined when the object is created and does
4020 not change afterward.
4023 (cl-defstruct person
4024 (name nil :read-only t)
4029 Any slot options other than @code{:read-only} are ignored.
4031 For obscure historical reasons, structure options take a different
4032 form than slot options. A structure option is either a keyword
4033 symbol, or a list beginning with a keyword symbol possibly followed
4034 by arguments. (By contrast, slot options are key-value pairs not
4038 (cl-defstruct (person (:constructor create-person)
4044 The following structure options are recognized.
4048 The argument is a symbol whose print name is used as the prefix for
4049 the names of slot accessor functions. The default is the name of
4050 the struct type followed by a hyphen. The option @code{(:conc-name p-)}
4051 would change this prefix to @code{p-}. Specifying @code{nil} as an
4052 argument means no prefix, so that the slot names themselves are used
4053 to name the accessor functions.
4056 In the simple case, this option takes one argument which is an
4057 alternate name to use for the constructor function. The default
4058 is @code{make-@var{name}}, e.g., @code{make-person}. The above
4059 example changes this to @code{create-person}. Specifying @code{nil}
4060 as an argument means that no standard constructor should be
4063 In the full form of this option, the constructor name is followed
4064 by an arbitrary argument list. @xref{Program Structure}, for a
4065 description of the format of Common Lisp argument lists. All
4066 options, such as @code{&rest} and @code{&key}, are supported.
4067 The argument names should match the slot names; each slot is
4068 initialized from the corresponding argument. Slots whose names
4069 do not appear in the argument list are initialized based on the
4070 @var{default-value} in their slot descriptor. Also, @code{&optional}
4071 and @code{&key} arguments that don't specify defaults take their
4072 defaults from the slot descriptor. It is valid to include arguments
4073 that don't correspond to slot names; these are useful if they are
4074 referred to in the defaults for optional, keyword, or @code{&aux}
4075 arguments that @emph{do} correspond to slots.
4077 You can specify any number of full-format @code{:constructor}
4078 options on a structure. The default constructor is still generated
4079 as well unless you disable it with a simple-format @code{:constructor}
4085 (:constructor nil) ; no default constructor
4086 (:constructor new-person
4087 (name sex &optional (age 0)))
4088 (:constructor new-hound (&key (name "Rover")
4090 &aux (age (* 7 dog-years))
4095 The first constructor here takes its arguments positionally rather
4096 than by keyword. (In official Common Lisp terminology, constructors
4097 that work By Order of Arguments instead of by keyword are called
4098 ``BOA constructors''. No, I'm not making this up.) For example,
4099 @code{(new-person "Jane" 'female)} generates a person whose slots
4100 are @code{"Jane"}, 0, and @code{female}, respectively.
4102 The second constructor takes two keyword arguments, @code{:name},
4103 which initializes the @code{name} slot and defaults to @code{"Rover"},
4104 and @code{:dog-years}, which does not itself correspond to a slot
4105 but which is used to initialize the @code{age} slot. The @code{sex}
4106 slot is forced to the symbol @code{canine} with no syntax for
4110 The argument is an alternate name for the copier function for
4111 this type. The default is @code{copy-@var{name}}. @code{nil}
4112 means not to generate a copier function. (In this implementation,
4113 all copier functions are simply synonyms for @code{copy-sequence}.)
4116 The argument is an alternate name for the predicate that recognizes
4117 objects of this type. The default is @code{@var{name}-p}. @code{nil}
4118 means not to generate a predicate function. (If the @code{:type}
4119 option is used without the @code{:named} option, no predicate is
4122 In true Common Lisp, @code{typep} is always able to recognize a
4123 structure object even if @code{:predicate} was used. In this
4124 package, @code{cl-typep} simply looks for a function called
4125 @code{@var{typename}-p}, so it will work for structure types
4126 only if they used the default predicate name.
4129 This option implements a very limited form of C++-style inheritance.
4130 The argument is the name of another structure type previously
4131 created with @code{cl-defstruct}. The effect is to cause the new
4132 structure type to inherit all of the included structure's slots
4133 (plus, of course, any new slots described by this struct's slot
4134 descriptors). The new structure is considered a ``specialization''
4135 of the included one. In fact, the predicate and slot accessors
4136 for the included type will also accept objects of the new type.
4138 If there are extra arguments to the @code{:include} option after
4139 the included-structure name, these options are treated as replacement
4140 slot descriptors for slots in the included structure, possibly with
4141 modified default values. Borrowing an example from Steele:
4144 (cl-defstruct person name (age 0) sex)
4146 (cl-defstruct (astronaut (:include person (age 45)))
4148 (favorite-beverage 'tang))
4151 (setq joe (make-person :name "Joe"))
4152 @result{} [cl-struct-person "Joe" 0 nil]
4153 (setq buzz (make-astronaut :name "Buzz"))
4154 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang]
4156 (list (person-p joe) (person-p buzz))
4158 (list (astronaut-p joe) (astronaut-p buzz))
4163 (astronaut-name joe)
4164 @result{} error: "astronaut-name accessing a non-astronaut"
4167 Thus, if @code{astronaut} is a specialization of @code{person},
4168 then every @code{astronaut} is also a @code{person} (but not the
4169 other way around). Every @code{astronaut} includes all the slots
4170 of a @code{person}, plus extra slots that are specific to
4171 astronauts. Operations that work on people (like @code{person-name})
4172 work on astronauts just like other people.
4174 @item :print-function
4175 In full Common Lisp, this option allows you to specify a function
4176 that is called to print an instance of the structure type. The
4177 Emacs Lisp system offers no hooks into the Lisp printer which would
4178 allow for such a feature, so this package simply ignores
4179 @code{:print-function}.
4182 The argument should be one of the symbols @code{vector} or @code{list}.
4183 This tells which underlying Lisp data type should be used to implement
4184 the new structure type. Vectors are used by default, but
4185 @code{(:type list)} will cause structure objects to be stored as
4188 The vector representation for structure objects has the advantage
4189 that all structure slots can be accessed quickly, although creating
4190 vectors is a bit slower in Emacs Lisp. Lists are easier to create,
4191 but take a relatively long time accessing the later slots.
4194 This option, which takes no arguments, causes a characteristic ``tag''
4195 symbol to be stored at the front of the structure object. Using
4196 @code{:type} without also using @code{:named} will result in a
4197 structure type stored as plain vectors or lists with no identifying
4200 The default, if you don't specify @code{:type} explicitly, is to
4201 use named vectors. Therefore, @code{:named} is only useful in
4202 conjunction with @code{:type}.
4205 (cl-defstruct (person1) name age sex)
4206 (cl-defstruct (person2 (:type list) :named) name age sex)
4207 (cl-defstruct (person3 (:type list)) name age sex)
4209 (setq p1 (make-person1))
4210 @result{} [cl-struct-person1 nil nil nil]
4211 (setq p2 (make-person2))
4212 @result{} (person2 nil nil nil)
4213 (setq p3 (make-person3))
4214 @result{} (nil nil nil)
4221 @result{} error: function person3-p undefined
4224 Since unnamed structures don't have tags, @code{cl-defstruct} is not
4225 able to make a useful predicate for recognizing them. Also,
4226 accessors like @code{person3-name} will be generated but they
4227 will not be able to do any type checking. The @code{person3-name}
4228 function, for example, will simply be a synonym for @code{car} in
4229 this case. By contrast, @code{person2-name} is able to verify
4230 that its argument is indeed a @code{person2} object before
4233 @item :initial-offset
4234 The argument must be a nonnegative integer. It specifies a
4235 number of slots to be left ``empty'' at the front of the
4236 structure. If the structure is named, the tag appears at the
4237 specified position in the list or vector; otherwise, the first
4238 slot appears at that position. Earlier positions are filled
4239 with @code{nil} by the constructors and ignored otherwise. If
4240 the type @code{:include}s another type, then @code{:initial-offset}
4241 specifies a number of slots to be skipped between the last slot
4242 of the included type and the first new slot.
4246 Except as noted, the @code{cl-defstruct} facility of this package is
4247 entirely compatible with that of Common Lisp.
4250 @chapter Assertions and Errors
4253 This section describes two macros that test @dfn{assertions}, i.e.,
4254 conditions which must be true if the program is operating correctly.
4255 Assertions never add to the behavior of a Lisp program; they simply
4256 make ``sanity checks'' to make sure everything is as it should be.
4258 If the optimization property @code{speed} has been set to 3, and
4259 @code{safety} is less than 3, then the byte-compiler will optimize
4260 away the following assertions. Because assertions might be optimized
4261 away, it is a bad idea for them to include side-effects.
4263 @defmac cl-assert test-form [show-args string args@dots{}]
4264 This form verifies that @var{test-form} is true (i.e., evaluates to
4265 a non-@code{nil} value). If so, it returns @code{nil}. If the test
4266 is not satisfied, @code{cl-assert} signals an error.
4268 A default error message will be supplied which includes @var{test-form}.
4269 You can specify a different error message by including a @var{string}
4270 argument plus optional extra arguments. Those arguments are simply
4271 passed to @code{error} to signal the error.
4273 If the optional second argument @var{show-args} is @code{t} instead
4274 of @code{nil}, then the error message (with or without @var{string})
4275 will also include all non-constant arguments of the top-level
4276 @var{form}. For example:
4279 (cl-assert (> x 10) t "x is too small: %d")
4282 This usage of @var{show-args} is an extension to Common Lisp. In
4283 true Common Lisp, the second argument gives a list of @var{places}
4284 which can be @code{setf}'d by the user before continuing from the
4285 error. Since Emacs Lisp does not support continuable errors, it
4286 makes no sense to specify @var{places}.
4289 @defmac cl-check-type form type [string]
4290 This form verifies that @var{form} evaluates to a value of type
4291 @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type}
4292 signals a @code{wrong-type-argument} error. The default error message
4293 lists the erroneous value along with @var{type} and @var{form}
4294 themselves. If @var{string} is specified, it is included in the
4295 error message in place of @var{type}. For example:
4298 (cl-check-type x (integer 1 *) "a positive integer")
4301 @xref{Type Predicates}, for a description of the type specifiers
4302 that may be used for @var{type}.
4304 Note that in Common Lisp, the first argument to @code{check-type}
4305 must be a @var{place} suitable for use by @code{setf}, because
4306 @code{check-type} signals a continuable error that allows the
4307 user to modify @var{place}.
4310 @node Efficiency Concerns
4311 @appendix Efficiency Concerns
4316 Many of the advanced features of this package, such as @code{cl-defun},
4317 @code{cl-loop}, etc., are implemented as Lisp macros. In
4318 byte-compiled code, these complex notations will be expanded into
4319 equivalent Lisp code which is simple and efficient. For example,
4327 is expanded at compile-time to the Lisp form
4334 which is the most efficient ways of doing this operation
4335 in Lisp. Thus, there is no performance penalty for using the more
4336 readable @code{cl-incf} form in your compiled code.
4338 @emph{Interpreted} code, on the other hand, must expand these macros
4339 every time they are executed. For this reason it is strongly
4340 recommended that code making heavy use of macros be compiled.
4341 A loop using @code{cl-incf} a hundred times will execute considerably
4342 faster if compiled, and will also garbage-collect less because the
4343 macro expansion will not have to be generated, used, and thrown away a
4346 You can find out how a macro expands by using the
4347 @code{cl-prettyexpand} function.
4349 @defun cl-prettyexpand form &optional full
4350 This function takes a single Lisp form as an argument and inserts
4351 a nicely formatted copy of it in the current buffer (which must be
4352 in Lisp mode so that indentation works properly). It also expands
4353 all Lisp macros that appear in the form. The easiest way to use
4354 this function is to go to the @file{*scratch*} buffer and type, say,
4357 (cl-prettyexpand '(cl-loop for x below 10 collect x))
4361 and type @kbd{C-x C-e} immediately after the closing parenthesis;
4362 an expansion similar to:
4369 (setq G1004 (cons x G1004))
4375 will be inserted into the buffer. (The @code{cl-block} macro is
4376 expanded differently in the interpreter and compiler, so
4377 @code{cl-prettyexpand} just leaves it alone. The temporary
4378 variable @code{G1004} was created by @code{cl-gensym}.)
4380 If the optional argument @var{full} is true, then @emph{all}
4381 macros are expanded, including @code{cl-block}, @code{cl-eval-when},
4382 and compiler macros. Expansion is done as if @var{form} were
4383 a top-level form in a file being compiled.
4385 @c FIXME none of these examples are still applicable.
4390 (cl-prettyexpand '(cl-pushnew 'x list))
4391 @print{} (setq list (cl-adjoin 'x list))
4392 (cl-prettyexpand '(cl-pushnew 'x list) t)
4393 @print{} (setq list (if (memq 'x list) list (cons 'x list)))
4394 (cl-prettyexpand '(caddr (cl-member 'a list)) t)
4395 @print{} (car (cdr (cdr (memq 'a list))))
4399 Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all
4400 have built-in compiler macros to optimize them in common cases.
4403 @appendixsec Error Checking
4406 Common Lisp compliance has in general not been sacrificed for the
4407 sake of efficiency. A few exceptions have been made for cases
4408 where substantial gains were possible at the expense of marginal
4411 The Common Lisp standard (as embodied in Steele's book) uses the
4412 phrase ``it is an error if'' to indicate a situation that is not
4413 supposed to arise in complying programs; implementations are strongly
4414 encouraged but not required to signal an error in these situations.
4415 This package sometimes omits such error checking in the interest of
4416 compactness and efficiency. For example, @code{cl-do} variable
4417 specifiers are supposed to be lists of one, two, or three forms;
4418 extra forms are ignored by this package rather than signaling a
4419 syntax error. The @code{cl-endp} function is simply a synonym for
4420 @code{null} in this package. Functions taking keyword arguments
4421 will accept an odd number of arguments, treating the trailing
4422 keyword as if it were followed by the value @code{nil}.
4424 Argument lists (as processed by @code{cl-defun} and friends)
4425 @emph{are} checked rigorously except for the minor point just
4426 mentioned; in particular, keyword arguments are checked for
4427 validity, and @code{&allow-other-keys} and @code{:allow-other-keys}
4428 are fully implemented. Keyword validity checking is slightly
4429 time consuming (though not too bad in byte-compiled code);
4430 you can use @code{&allow-other-keys} to omit this check. Functions
4431 defined in this package such as @code{cl-find} and @code{cl-member}
4432 do check their keyword arguments for validity.
4434 @appendixsec Compiler Optimizations
4437 Changing the value of @code{byte-optimize} from the default @code{t}
4438 is highly discouraged; many of the Common
4440 code that can be improved by optimization. In particular,
4441 @code{cl-block}s (whether explicit or implicit in constructs like
4442 @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the
4443 byte-compiler removes @code{cl-block}s that are not actually
4444 referenced by @code{cl-return} or @code{cl-return-from} inside the block.
4446 @node Common Lisp Compatibility
4447 @appendix Common Lisp Compatibility
4450 The following is a list of all known incompatibilities between this
4451 package and Common Lisp as documented in Steele (2nd edition).
4453 The word @code{cl-defun} is required instead of @code{defun} in order
4454 to use extended Common Lisp argument lists in a function. Likewise,
4455 @code{cl-defmacro} and @code{cl-function} are versions of those forms
4456 which understand full-featured argument lists. The @code{&whole}
4457 keyword does not work in @code{cl-defmacro} argument lists (except
4458 inside recursive argument lists).
4460 The @code{equal} predicate does not distinguish
4461 between IEEE floating-point plus and minus zero. The @code{cl-equalp}
4462 predicate has several differences with Common Lisp; @pxref{Predicates}.
4464 The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols}
4465 with no @var{obarray} argument. In Common Lisp, this form would
4466 iterate over all symbols in all packages. Since Emacs obarrays
4467 are not a first-class package mechanism, there is no way for
4468 @code{cl-do-all-symbols} to locate any but the default obarray.
4470 The @code{cl-loop} macro is complete except that @code{loop-finish}
4471 and type specifiers are unimplemented.
4473 The multiple-value return facility treats lists as multiple
4474 values, since Emacs Lisp cannot support multiple return values
4475 directly. The macros will be compatible with Common Lisp if
4476 @code{cl-values} or @code{cl-values-list} is always used to return to
4477 a @code{cl-multiple-value-bind} or other multiple-value receiver;
4478 if @code{cl-values} is used without @code{cl-multiple-value-@dots{}}
4479 or vice-versa the effect will be different from Common Lisp.
4481 Many Common Lisp declarations are ignored, and others match
4482 the Common Lisp standard in concept but not in detail. For
4483 example, local @code{special} declarations, which are purely
4484 advisory in Emacs Lisp, do not rigorously obey the scoping rules
4485 set down in Steele's book.
4487 The variable @code{cl--gensym-counter} starts out with a pseudo-random
4488 value rather than with zero. This is to cope with the fact that
4489 generated symbols become interned when they are written to and
4490 loaded back from a file.
4492 The @code{cl-defstruct} facility is compatible, except that structures
4493 are of type @code{:type vector :named} by default rather than some
4494 special, distinct type. Also, the @code{:type} slot option is ignored.
4496 The second argument of @code{cl-check-type} is treated differently.
4498 @node Porting Common Lisp
4499 @appendix Porting Common Lisp
4502 This package is meant to be used as an extension to Emacs Lisp,
4503 not as an Emacs implementation of true Common Lisp. Some of the
4504 remaining differences between Emacs Lisp and Common Lisp make it
4505 difficult to port large Common Lisp applications to Emacs. For
4506 one, some of the features in this package are not fully compliant
4507 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there
4508 are also quite a few features that this package does not provide
4509 at all. Here are some major omissions that you will want to watch out
4510 for when bringing Common Lisp code into Emacs.
4514 Case-insensitivity. Symbols in Common Lisp are case-insensitive
4515 by default. Some programs refer to a function or variable as
4516 @code{foo} in one place and @code{Foo} or @code{FOO} in another.
4517 Emacs Lisp will treat these as three distinct symbols.
4519 Some Common Lisp code is written entirely in upper case. While Emacs
4520 is happy to let the program's own functions and variables use
4521 this convention, calls to Lisp builtins like @code{if} and
4522 @code{defun} will have to be changed to lower case.
4525 Lexical scoping. In Common Lisp, function arguments and @code{let}
4526 bindings apply only to references physically within their bodies (or
4527 within macro expansions in their bodies). Traditionally, Emacs Lisp
4528 uses @dfn{dynamic scoping} wherein a binding to a variable is visible
4529 even inside functions called from the body.
4530 @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4531 Lexical binding is available since Emacs 24.1, so be sure to set
4532 @code{lexical-binding} to @code{t} if you need to emulate this aspect
4533 of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}.
4535 Here is an example of a Common Lisp code fragment that would fail in
4536 Emacs Lisp if @code{lexical-binding} were set to @code{nil}:
4539 (defun map-odd-elements (func list)
4541 for flag = t then (not flag)
4542 collect (if flag x (funcall func x))))
4544 (defun add-odd-elements (list x)
4545 (map-odd-elements (lambda (a) (+ a x)) list))
4549 With lexical binding, the two functions' usages of @code{x} are
4550 completely independent. With dynamic binding, the binding to @code{x}
4551 made by @code{add-odd-elements} will have been hidden by the binding
4552 in @code{map-odd-elements} by the time the @code{(+ a x)} function is
4555 Internally, this package uses lexical binding so that such problems do
4556 not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete
4557 @code{lexical-let} form that emulates a Common Lisp-style lexical
4558 binding when dynamic binding is in use.
4561 Reader macros. Common Lisp includes a second type of macro that
4562 works at the level of individual characters. For example, Common
4563 Lisp implements the quote notation by a reader macro called @code{'},
4564 whereas Emacs Lisp's parser just treats quote as a special case.
4565 Some Lisp packages use reader macros to create special syntaxes
4566 for themselves, which the Emacs parser is incapable of reading.
4569 Other syntactic features. Common Lisp provides a number of
4570 notations beginning with @code{#} that the Emacs Lisp parser
4571 won't understand. For example, @samp{#| @dots{} |#} is an
4572 alternate comment notation, and @samp{#+lucid (foo)} tells
4573 the parser to ignore the @code{(foo)} except in Lucid Common
4577 Packages. In Common Lisp, symbols are divided into @dfn{packages}.
4578 Symbols that are Lisp built-ins are typically stored in one package;
4579 symbols that are vendor extensions are put in another, and each
4580 application program would have a package for its own symbols.
4581 Certain symbols are ``exported'' by a package and others are
4582 internal; certain packages ``use'' or import the exported symbols
4583 of other packages. To access symbols that would not normally be
4584 visible due to this importing and exporting, Common Lisp provides
4585 a syntax like @code{package:symbol} or @code{package::symbol}.
4587 Emacs Lisp has a single namespace for all interned symbols, and
4588 then uses a naming convention of putting a prefix like @code{cl-}
4589 in front of the name. Some Emacs packages adopt the Common Lisp-like
4590 convention of using @code{cl:} or @code{cl::} as the prefix.
4591 However, the Emacs parser does not understand colons and just
4592 treats them as part of the symbol name. Thus, while @code{mapcar}
4593 and @code{lisp:mapcar} may refer to the same symbol in Common
4594 Lisp, they are totally distinct in Emacs Lisp. Common Lisp
4595 programs that refer to a symbol by the full name sometimes
4596 and the short name other times will not port cleanly to Emacs.
4598 Emacs Lisp does have a concept of ``obarrays'', which are
4599 package-like collections of symbols, but this feature is not
4600 strong enough to be used as a true package mechanism.
4603 The @code{format} function is quite different between Common
4604 Lisp and Emacs Lisp. It takes an additional ``destination''
4605 argument before the format string. A destination of @code{nil}
4606 means to format to a string as in Emacs Lisp; a destination
4607 of @code{t} means to write to the terminal (similar to
4608 @code{message} in Emacs). Also, format control strings are
4609 utterly different; @code{~} is used instead of @code{%} to
4610 introduce format codes, and the set of available codes is
4611 much richer. There are no notations like @code{\n} for
4612 string literals; instead, @code{format} is used with the
4613 ``newline'' format code, @code{~%}. More advanced formatting
4614 codes provide such features as paragraph filling, case
4615 conversion, and even loops and conditionals.
4617 While it would have been possible to implement most of Common
4618 Lisp @code{format} in this package (under the name @code{cl-format},
4619 of course), it was not deemed worthwhile. It would have required
4620 a huge amount of code to implement even a decent subset of
4621 @code{format}, yet the functionality it would provide over
4622 Emacs Lisp's @code{format} would rarely be useful.
4625 Vector constants use square brackets in Emacs Lisp, but
4626 @code{#(a b c)} notation in Common Lisp. To further complicate
4627 matters, Emacs has its own @code{#(} notation for
4628 something entirely different---strings with properties.
4631 Characters are distinct from integers in Common Lisp. The notation
4632 for character constants is also different: @code{#\A} in Common Lisp
4633 where Emacs Lisp uses @code{?A}. Also, @code{string=} and
4634 @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is
4635 case-insensitive in Common Lisp.
4638 Data types. Some Common Lisp data types do not exist in Emacs
4639 Lisp. Rational numbers and complex numbers are not present,
4640 nor are large integers (all integers are ``fixnums''). All
4641 arrays are one-dimensional. There are no readtables or pathnames;
4642 streams are a set of existing data types rather than a new data
4643 type of their own. Hash tables, random-states, structures, and
4644 packages (obarrays) are built from Lisp vectors or lists rather
4645 than being distinct types.
4648 The Common Lisp Object System (CLOS) is not implemented,
4649 nor is the Common Lisp Condition System. However, the EIEIO package
4650 (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some
4654 Common Lisp features that are completely redundant with Emacs
4655 Lisp features of a different name generally have not been
4656 implemented. For example, Common Lisp writes @code{defconstant}
4657 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list}
4658 takes its arguments in different ways in the two Lisps but does
4659 exactly the same thing, so this package has not bothered to
4660 implement a Common Lisp-style @code{make-list}.
4663 A few more notable Common Lisp features not included in this
4664 package: @code{compiler-let}, @code{tagbody}, @code{prog},
4665 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}.
4668 Recursion. While recursion works in Emacs Lisp just like it
4669 does in Common Lisp, various details of the Emacs Lisp system
4670 and compiler make recursion much less efficient than it is in
4671 most Lisps. Some schools of thought prefer to use recursion
4672 in Lisp over other techniques; they would sum a list of
4673 numbers using something like
4676 (defun sum-list (list)
4678 (+ (car list) (sum-list (cdr list)))
4683 where a more iteratively-minded programmer might write one of
4687 (let ((total 0)) (dolist (x my-list) (incf total x)) total)
4688 (loop for x in my-list sum x)
4691 While this would be mainly a stylistic choice in most Common Lisps,
4692 in Emacs Lisp you should be aware that the iterative forms are
4693 much faster than recursion. Also, Lisp programmers will want to
4694 note that the current Emacs Lisp compiler does not optimize tail
4698 @node Obsolete Features
4699 @appendix Obsolete Features
4701 This section describes some features of the package that are obsolete
4702 and should not be used in new code. They are either only provided by
4703 the old @file{cl.el} entry point, not by the newer @file{cl-lib.el};
4704 or where versions with a @samp{cl-} prefix do exist they do not behave
4705 in exactly the same way.
4708 * Obsolete Lexical Binding:: An approximation of lexical binding.
4709 * Obsolete Macros:: Obsolete macros.
4710 * Obsolete Setf Customization:: Obsolete ways to customize setf.
4713 @node Obsolete Lexical Binding
4714 @appendixsec Obsolete Lexical Binding
4716 The following macros are extensions to Common Lisp, where all bindings
4717 are lexical unless declared otherwise. These features are likewise
4718 obsolete since the introduction of true lexical binding in Emacs 24.1.
4720 @defmac lexical-let (bindings@dots{}) forms@dots{}
4721 This form is exactly like @code{let} except that the bindings it
4722 establishes are purely lexical.
4725 @c FIXME remove this and refer to elisp manual.
4726 @c Maybe merge some stuff from here to there?
4728 Lexical bindings are similar to local variables in a language like C:
4729 Only the code physically within the body of the @code{lexical-let}
4730 (after macro expansion) may refer to the bound variables.
4734 (defun foo (b) (+ a b))
4735 (let ((a 2)) (foo a))
4737 (lexical-let ((a 2)) (foo a))
4742 In this example, a regular @code{let} binding of @code{a} actually
4743 makes a temporary change to the global variable @code{a}, so @code{foo}
4744 is able to see the binding of @code{a} to 2. But @code{lexical-let}
4745 actually creates a distinct local variable @code{a} for use within its
4746 body, without any effect on the global variable of the same name.
4748 The most important use of lexical bindings is to create @dfn{closures}.
4749 A closure is a function object that refers to an outside lexical
4750 variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}).
4754 (defun make-adder (n)
4755 (lexical-let ((n n))
4756 (function (lambda (m) (+ n m)))))
4757 (setq add17 (make-adder 17))
4763 The call @code{(make-adder 17)} returns a function object which adds
4764 17 to its argument. If @code{let} had been used instead of
4765 @code{lexical-let}, the function object would have referred to the
4766 global @code{n}, which would have been bound to 17 only during the
4767 call to @code{make-adder} itself.
4770 (defun make-counter ()
4771 (lexical-let ((n 0))
4772 (cl-function (lambda (&optional (m 1)) (cl-incf n m)))))
4773 (setq count-1 (make-counter))
4776 (funcall count-1 14)
4778 (setq count-2 (make-counter))
4788 Here we see that each call to @code{make-counter} creates a distinct
4789 local variable @code{n}, which serves as a private counter for the
4790 function object that is returned.
4792 Closed-over lexical variables persist until the last reference to
4793 them goes away, just like all other Lisp objects. For example,
4794 @code{count-2} refers to a function object which refers to an
4795 instance of the variable @code{n}; this is the only reference
4796 to that variable, so after @code{(setq count-2 nil)} the garbage
4797 collector would be able to delete this instance of @code{n}.
4798 Of course, if a @code{lexical-let} does not actually create any
4799 closures, then the lexical variables are free as soon as the
4800 @code{lexical-let} returns.
4802 Many closures are used only during the extent of the bindings they
4803 refer to; these are known as ``downward funargs'' in Lisp parlance.
4804 When a closure is used in this way, regular Emacs Lisp dynamic
4805 bindings suffice and will be more efficient than @code{lexical-let}
4809 (defun add-to-list (x list)
4810 (mapcar (lambda (y) (+ x y))) list)
4811 (add-to-list 7 '(1 2 5))
4816 Since this lambda is only used while @code{x} is still bound,
4817 it is not necessary to make a true closure out of it.
4819 You can use @code{defun} or @code{flet} inside a @code{lexical-let}
4820 to create a named closure. If several closures are created in the
4821 body of a single @code{lexical-let}, they all close over the same
4822 instance of the lexical variable.
4824 @defmac lexical-let* (bindings@dots{}) forms@dots{}
4825 This form is just like @code{lexical-let}, except that the bindings
4826 are made sequentially in the manner of @code{let*}.
4829 @node Obsolete Macros
4830 @appendixsec Obsolete Macros
4832 The following macros are obsolete, and are replaced by versions with
4833 a @samp{cl-} prefix that do not behave in exactly the same way.
4834 Consequently, the @file{cl.el} versions are not simply aliases to the
4835 @file{cl-lib.el} versions.
4837 @defmac flet (bindings@dots{}) forms@dots{}
4838 This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}),
4839 which behaves the same way as Common Lisp's @code{flet}.
4840 This @code{flet} takes the same arguments as @code{cl-flet}, but does
4841 not behave in precisely the same way.
4843 While @code{flet} in Common Lisp establishes a lexical function
4844 binding, this @code{flet} makes a dynamic binding (it dates from a
4845 time before Emacs had lexical binding). The result is
4846 that @code{flet} affects indirect calls to a function as well as calls
4847 directly inside the @code{flet} form itself.
4849 This will even work on Emacs primitives, although note that some calls
4850 to primitive functions internal to Emacs are made without going
4851 through the symbol's function cell, and so will not be affected by
4852 @code{flet}. For example,
4855 (flet ((message (&rest args) (push args saved-msgs)))
4859 This code attempts to replace the built-in function @code{message}
4860 with a function that simply saves the messages in a list rather
4861 than displaying them. The original definition of @code{message}
4862 will be restored after @code{do-something} exits. This code will
4863 work fine on messages generated by other Lisp code, but messages
4864 generated directly inside Emacs will not be caught since they make
4865 direct C-language calls to the message routines rather than going
4866 through the Lisp @code{message} function.
4869 Note that many primitives (e.g., @code{+}) have special byte-compile
4870 handling. Attempts to redefine such functions using @code{flet} will
4871 fail if byte-compiled.
4873 @c In such cases, use @code{labels} instead.
4876 @defmac labels (bindings@dots{}) forms@dots{}
4877 This macro is replaced by @code{cl-labels} (@pxref{Function Bindings}),
4878 which behaves the same way as Common Lisp's @code{labels}.
4879 This @code{labels} takes the same arguments as @code{cl-labels}, but
4880 does not behave in precisely the same way.
4882 This version of @code{labels} uses the obsolete @code{lexical-let}
4883 form (@pxref{Obsolete Lexical Binding}), rather than the true
4884 lexical binding that @code{cl-labels} uses.
4887 @node Obsolete Setf Customization
4888 @appendixsec Obsolete Ways to Customize Setf
4890 Common Lisp defines three macros, @code{define-modify-macro},
4891 @code{defsetf}, and @code{define-setf-method}, that allow the
4892 user to extend generalized variables in various ways.
4893 In Emacs, these are obsolete, replaced by various features of
4894 @file{gv.el} in Emacs 24.3.
4895 @xref{Adding Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
4898 @defmac define-modify-macro name arglist function [doc-string]
4899 This macro defines a ``read-modify-write'' macro similar to
4900 @code{cl-incf} and @code{cl-decf}. You can replace this macro
4901 with @code{gv-letplace}.
4903 The macro @var{name} is defined to take a @var{place} argument
4904 followed by additional arguments described by @var{arglist}. The call
4907 (@var{name} @var{place} @var{args}@dots{})
4914 (cl-callf @var{func} @var{place} @var{args}@dots{})
4918 which in turn is roughly equivalent to
4921 (setf @var{place} (@var{func} @var{place} @var{args}@dots{}))
4927 (define-modify-macro incf (&optional (n 1)) +)
4928 (define-modify-macro concatf (&rest args) concat)
4931 Note that @code{&key} is not allowed in @var{arglist}, but
4932 @code{&rest} is sufficient to pass keywords on to the function.
4934 Most of the modify macros defined by Common Lisp do not exactly
4935 follow the pattern of @code{define-modify-macro}. For example,
4936 @code{push} takes its arguments in the wrong order, and @code{pop}
4937 is completely irregular.
4939 The above @code{incf} example could be written using
4940 @code{gv-letplace} as:
4942 (defmacro incf (place &optional n)
4943 (gv-letplace (getter setter) place
4944 (macroexp-let2 nil v (or n 1)
4945 (funcall setter `(+ ,v ,getter)))))
4948 (defmacro concatf (place &rest args)
4949 (gv-letplace (getter setter) place
4950 (macroexp-let2 nil v (mapconcat 'identity args "")
4951 (funcall setter `(concat ,getter ,v)))))
4955 @defmac defsetf access-fn update-fn
4956 This is the simpler of two @code{defsetf} forms, and is
4957 replaced by @code{gv-define-simple-setter}.
4959 With @var{access-fn} the name of a function that accesses a place,
4960 this declares @var{update-fn} to be the corresponding store function.
4964 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value})
4971 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value})
4975 The @var{update-fn} is required to be either a true function, or
4976 a macro that evaluates its arguments in a function-like way. Also,
4977 the @var{update-fn} is expected to return @var{value} as its result.
4978 Otherwise, the above expansion would not obey the rules for the way
4979 @code{setf} is supposed to behave.
4981 As a special (non-Common-Lisp) extension, a third argument of @code{t}
4982 to @code{defsetf} says that the return value of @code{update-fn} is
4983 not suitable, so that the above @code{setf} should be expanded to
4987 (let ((temp @var{value}))
4988 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp)
4995 (defsetf car setcar)
4996 (defsetf buffer-name rename-buffer t)
4999 These translate directly to @code{gv-define-simple-setter}:
5002 (gv-define-simple-setter car setcar)
5003 (gv-define-simple-setter buffer-name rename-buffer t)
5007 @defmac defsetf access-fn arglist (store-var) forms@dots{}
5008 This is the second, more complex, form of @code{defsetf}.
5009 It can be replaced by @code{gv-define-setter}.
5011 This form of @code{defsetf} is rather like @code{defmacro} except for
5012 the additional @var{store-var} argument. The @var{forms} should
5013 return a Lisp form that stores the value of @var{store-var} into the
5014 generalized variable formed by a call to @var{access-fn} with
5015 arguments described by @var{arglist}. The @var{forms} may begin with
5016 a string which documents the @code{setf} method (analogous to the doc
5017 string that appears at the front of a function).
5019 For example, the simple form of @code{defsetf} is shorthand for
5022 (defsetf @var{access-fn} (&rest args) (store)
5023 (append '(@var{update-fn}) args (list store)))
5026 The Lisp form that is returned can access the arguments from
5027 @var{arglist} and @var{store-var} in an unrestricted fashion;
5028 macros like @code{cl-incf} that invoke this
5029 setf-method will insert temporary variables as needed to make
5030 sure the apparent order of evaluation is preserved.
5032 Another standard example:
5035 (defsetf nth (n x) (store)
5036 `(setcar (nthcdr ,n ,x) ,store))
5039 You could write this using @code{gv-define-setter} as:
5042 (gv-define-setter nth (store n x)
5043 `(setcar (nthcdr ,n ,x) ,store))
5047 @defmac define-setf-method access-fn arglist forms@dots{}
5048 This is the most general way to create new place forms. You can
5049 replace this by @code{gv-define-setter} or @code{gv-define-expander}.
5051 When a @code{setf} to @var{access-fn} with arguments described by
5052 @var{arglist} is expanded, the @var{forms} are evaluated and must
5053 return a list of five items:
5057 A list of @dfn{temporary variables}.
5060 A list of @dfn{value forms} corresponding to the temporary variables
5061 above. The temporary variables will be bound to these value forms
5062 as the first step of any operation on the generalized variable.
5065 A list of exactly one @dfn{store variable} (generally obtained
5066 from a call to @code{gensym}).
5069 A Lisp form that stores the contents of the store variable into
5070 the generalized variable, assuming the temporaries have been
5071 bound as described above.
5074 A Lisp form that accesses the contents of the generalized variable,
5075 assuming the temporaries have been bound.
5078 This is exactly like the Common Lisp macro of the same name,
5079 except that the method returns a list of five values rather
5080 than the five values themselves, since Emacs Lisp does not
5081 support Common Lisp's notion of multiple return values.
5082 (Note that the @code{setf} implementation provided by @file{gv.el}
5083 does not use this five item format. Its use here is only for
5084 backwards compatibility.)
5086 Once again, the @var{forms} may begin with a documentation string.
5088 A setf-method should be maximally conservative with regard to
5089 temporary variables. In the setf-methods generated by
5090 @code{defsetf}, the second return value is simply the list of
5091 arguments in the place form, and the first return value is a
5092 list of a corresponding number of temporary variables generated
5093 @c FIXME I don't think this is true anymore.
5094 by @code{cl-gensym}. Macros like @code{cl-incf} that
5095 use this setf-method will optimize away most temporaries that
5096 turn out to be unnecessary, so there is little reason for the
5097 setf-method itself to optimize.
5100 @c Removed in Emacs 24.3, not possible to make a compatible replacement.
5102 @defun get-setf-method place &optional env
5103 This function returns the setf-method for @var{place}, by
5104 invoking the definition previously recorded by @code{defsetf}
5105 or @code{define-setf-method}. The result is a list of five
5106 values as described above. You can use this function to build
5107 your own @code{cl-incf}-like modify macros.
5109 The argument @var{env} specifies the ``environment'' to be
5110 passed on to @code{macroexpand} if @code{get-setf-method} should
5111 need to expand a macro in @var{place}. It should come from
5112 an @code{&environment} argument to the macro or setf-method
5113 that called @code{get-setf-method}.
5118 @node GNU Free Documentation License
5119 @appendix GNU Free Documentation License
5120 @include doclicense.texi
5122 @node Function Index
5123 @unnumbered Function Index
5127 @node Variable Index
5128 @unnumbered Variable Index