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1 | \input texinfo @c -*-texinfo-*- |
2 | @setfilename ../info/cl | |
3 | @settitle Common Lisp Extensions | |
4 | ||
5 | @dircategory Editors | |
6 | @direntry | |
7 | * CL: (cl). Partial Common Lisp support for Emacs Lisp. | |
8 | @end direntry | |
9 | ||
10 | @iftex | |
11 | @finalout | |
12 | @end iftex | |
13 | ||
14 | @ifinfo | |
15 | This file documents the GNU Emacs Common Lisp emulation package. | |
16 | ||
17 | Copyright (C) 1993 Free Software Foundation, Inc. | |
18 | ||
19 | Permission is granted to make and distribute verbatim copies of this | |
20 | manual provided the copyright notice and this permission notice are | |
21 | preserved on all copies. | |
22 | ||
23 | @ignore | |
24 | Permission is granted to process this file through TeX and print the | |
25 | results, provided the printed document carries copying permission notice | |
26 | identical to this one except for the removal of this paragraph (this | |
27 | paragraph not being relevant to the printed manual). | |
28 | ||
29 | @end ignore | |
30 | Permission is granted to copy and distribute modified versions of this | |
31 | manual under the conditions for verbatim copying, provided also that the | |
32 | section entitled ``GNU General Public License'' is included exactly as | |
33 | in the original, and provided that the entire resulting derived work is | |
34 | distributed under the terms of a permission notice identical to this one. | |
35 | ||
36 | Permission is granted to copy and distribute translations of this manual | |
37 | into another language, under the above conditions for modified versions, | |
38 | except that the section entitled ``GNU General Public License'' may be | |
39 | included in a translation approved by the author instead of in the | |
40 | original English. | |
41 | @end ifinfo | |
42 | ||
43 | @titlepage | |
44 | @sp 6 | |
45 | @center @titlefont{Common Lisp Extensions} | |
46 | @sp 4 | |
47 | @center For GNU Emacs Lisp | |
48 | @sp 1 | |
49 | @center Version 2.02 | |
50 | @sp 5 | |
51 | @center Dave Gillespie | |
52 | @center daveg@@synaptics.com | |
53 | @page | |
54 | ||
55 | @vskip 0pt plus 1filll | |
56 | Copyright @copyright{} 1993 Free Software Foundation, Inc. | |
57 | ||
58 | Permission is granted to make and distribute verbatim copies of | |
59 | this manual provided the copyright notice and this permission notice | |
60 | are preserved on all copies. | |
61 | ||
62 | @ignore | |
63 | Permission is granted to process this file through TeX and print the | |
64 | results, provided the printed document carries copying permission notice | |
65 | identical to this one except for the removal of this paragraph (this | |
66 | paragraph not being relevant to the printed manual). | |
67 | ||
68 | @end ignore | |
69 | Permission is granted to copy and distribute modified versions of this | |
70 | manual under the conditions for verbatim copying, provided also that the | |
71 | section entitled ``GNU General Public License'' is included exactly as | |
72 | in the original, and provided that the entire resulting derived work is | |
73 | distributed under the terms of a permission notice identical to this one. | |
74 | ||
75 | Permission is granted to copy and distribute translations of this manual | |
76 | into another language, under the above conditions for modified versions, | |
77 | except that the section entitled ``GNU General Public License'' may be | |
78 | included in a translation approved by the author instead of in the | |
79 | original English. | |
80 | @end titlepage | |
81 | ||
82 | @node Top, Overview,, (dir) | |
83 | @chapter Common Lisp Extensions | |
84 | ||
85 | @noindent | |
86 | This document describes a set of Emacs Lisp facilities borrowed from | |
87 | Common Lisp. All the facilities are described here in detail. While | |
88 | this document does not assume any prior knowledge of Common Lisp, it | |
89 | does assume a basic familiarity with Emacs Lisp. | |
90 | ||
91 | @menu | |
92 | * Overview:: Installation, usage, etc. | |
93 | * Program Structure:: Arglists, `eval-when', `defalias' | |
94 | * Predicates:: `typep', `eql', and `equalp' | |
95 | * Control Structure:: `setf', `do', `loop', etc. | |
96 | * Macros:: Destructuring, `define-compiler-macro' | |
97 | * Declarations:: `proclaim', `declare', etc. | |
98 | * Symbols:: Property lists, `gensym' | |
99 | * Numbers:: Predicates, functions, random numbers | |
100 | * Sequences:: Mapping, functions, searching, sorting | |
101 | * Lists:: `cadr', `sublis', `member*', `assoc*', etc. | |
102 | * Hash Tables:: `make-hash-table', `gethash', etc. | |
103 | * Structures:: `defstruct' | |
104 | * Assertions:: `check-type', `assert', `ignore-errors'. | |
105 | ||
106 | * Efficiency Concerns:: Hints and techniques | |
107 | * Common Lisp Compatibility:: All known differences with Steele | |
108 | * Old CL Compatibility:: All known differences with old cl.el | |
109 | * Porting Common Lisp:: Hints for porting Common Lisp code | |
110 | ||
111 | * Function Index:: | |
112 | * Variable Index:: | |
113 | @end menu | |
114 | ||
115 | @node Overview, Program Structure, Top, Top | |
116 | @ifinfo | |
117 | @chapter Overview | |
118 | @end ifinfo | |
119 | @iftex | |
120 | @section Overview | |
121 | @end iftex | |
122 | ||
123 | @noindent | |
124 | Common Lisp is a huge language, and Common Lisp systems tend to be | |
125 | massive and extremely complex. Emacs Lisp, by contrast, is rather | |
126 | minimalist in the choice of Lisp features it offers the programmer. | |
127 | As Emacs Lisp programmers have grown in number, and the applications | |
128 | they write have grown more ambitious, it has become clear that Emacs | |
129 | Lisp could benefit from many of the conveniences of Common Lisp. | |
130 | ||
131 | The @dfn{CL} package adds a number of Common Lisp functions and | |
132 | control structures to Emacs Lisp. While not a 100% complete | |
133 | implementation of Common Lisp, @dfn{CL} adds enough functionality | |
134 | to make Emacs Lisp programming significantly more convenient. | |
135 | ||
136 | Some Common Lisp features have been omitted from this package | |
137 | for various reasons: | |
138 | ||
139 | @itemize @bullet | |
140 | @item | |
141 | Some features are too complex or bulky relative to their benefit | |
142 | to Emacs Lisp programmers. CLOS and Common Lisp streams are fine | |
143 | examples of this group. | |
144 | ||
145 | @item | |
146 | Other features cannot be implemented without modification to the | |
147 | Emacs Lisp interpreter itself, such as multiple return values, | |
148 | lexical scoping, case-insensitive symbols, and complex numbers. | |
149 | The @dfn{CL} package generally makes no attempt to emulate these | |
150 | features. | |
151 | ||
152 | @item | |
153 | Some features conflict with existing things in Emacs Lisp. For | |
154 | example, Emacs' @code{assoc} function is incompatible with the | |
155 | Common Lisp @code{assoc}. In such cases, this package usually | |
156 | adds the suffix @samp{*} to the function name of the Common | |
157 | Lisp version of the function (e.g., @code{assoc*}). | |
158 | @end itemize | |
159 | ||
160 | The package described here was written by Dave Gillespie, | |
161 | @file{daveg@@synaptics.com}. It is a total rewrite of the original | |
162 | 1986 @file{cl.el} package by Cesar Quiroz. Most features of the | |
163 | the Quiroz package have been retained; any incompatibilities are | |
164 | noted in the descriptions below. Care has been taken in this | |
165 | version to ensure that each function is defined efficiently, | |
166 | concisely, and with minimal impact on the rest of the Emacs | |
167 | environment. | |
168 | ||
169 | @menu | |
170 | * Usage:: How to use the CL package | |
171 | * Organization:: The package's five component files | |
172 | * Installation:: Compiling and installing CL | |
173 | * Naming Conventions:: Notes on CL function names | |
174 | @end menu | |
175 | ||
176 | @node Usage, Organization, Overview, Overview | |
177 | @section Usage | |
178 | ||
179 | @noindent | |
180 | Lisp code that uses features from the @dfn{CL} package should | |
181 | include at the beginning: | |
182 | ||
183 | @example | |
184 | (require 'cl) | |
185 | @end example | |
186 | ||
187 | @noindent | |
188 | If you want to ensure that the new (Gillespie) version of @dfn{CL} | |
189 | is the one that is present, add an additional @code{(require 'cl-19)} | |
190 | call: | |
191 | ||
192 | @example | |
193 | (require 'cl) | |
194 | (require 'cl-19) | |
195 | @end example | |
196 | ||
197 | @noindent | |
198 | The second call will fail (with ``@file{cl-19.el} not found'') if | |
199 | the old @file{cl.el} package was in use. | |
200 | ||
201 | It is safe to arrange to load @dfn{CL} at all times, e.g., | |
202 | in your @file{.emacs} file. But it's a good idea, for portability, | |
203 | to @code{(require 'cl)} in your code even if you do this. | |
204 | ||
205 | @node Organization, Installation, Usage, Overview | |
206 | @section Organization | |
207 | ||
208 | @noindent | |
209 | The Common Lisp package is organized into four files: | |
210 | ||
211 | @table @file | |
212 | @item cl.el | |
213 | This is the ``main'' file, which contains basic functions | |
214 | and information about the package. This file is relatively | |
215 | compact---about 700 lines. | |
216 | ||
217 | @item cl-extra.el | |
218 | This file contains the larger, more complex or unusual functions. | |
219 | It is kept separate so that packages which only want to use Common | |
220 | Lisp fundamentals like the @code{cadr} function won't need to pay | |
221 | the overhead of loading the more advanced functions. | |
222 | ||
223 | @item cl-seq.el | |
224 | This file contains most of the advanced functions for operating | |
225 | on sequences or lists, such as @code{delete-if} and @code{assoc*}. | |
226 | ||
227 | @item cl-macs.el | |
228 | This file contains the features of the packages which are macros | |
229 | instead of functions. Macros expand when the caller is compiled, | |
230 | not when it is run, so the macros generally only need to be | |
231 | present when the byte-compiler is running (or when the macros are | |
232 | used in uncompiled code such as a @file{.emacs} file). Most of | |
233 | the macros of this package are isolated in @file{cl-macs.el} so | |
234 | that they won't take up memory unless you are compiling. | |
235 | @end table | |
236 | ||
237 | The file @file{cl.el} includes all necessary @code{autoload} | |
238 | commands for the functions and macros in the other three files. | |
239 | All you have to do is @code{(require 'cl)}, and @file{cl.el} | |
240 | will take care of pulling in the other files when they are | |
241 | needed. | |
242 | ||
243 | There is another file, @file{cl-compat.el}, which defines some | |
244 | routines from the older @file{cl.el} package that are no longer | |
245 | present in the new package. This includes internal routines | |
246 | like @code{setelt} and @code{zip-lists}, deprecated features | |
247 | like @code{defkeyword}, and an emulation of the old-style | |
248 | multiple-values feature. @xref{Old CL Compatibility}. | |
249 | ||
250 | @node Installation, Naming Conventions, Organization, Overview | |
251 | @section Installation | |
252 | ||
253 | @noindent | |
254 | Installation of the @dfn{CL} package is simple: Just put the | |
255 | byte-compiled files @file{cl.elc}, @file{cl-extra.elc}, | |
256 | @file{cl-seq.elc}, @file{cl-macs.elc}, and @file{cl-compat.elc} | |
257 | into a directory on your @code{load-path}. | |
258 | ||
259 | There are no special requirements to compile this package: | |
260 | The files do not have to be loaded before they are compiled, | |
261 | nor do they need to be compiled in any particular order. | |
262 | ||
263 | You may choose to put the files into your main @file{lisp/} | |
264 | directory, replacing the original @file{cl.el} file there. Or, | |
265 | you could put them into a directory that comes before @file{lisp/} | |
266 | on your @code{load-path} so that the old @file{cl.el} is | |
267 | effectively hidden. | |
268 | ||
269 | Also, format the @file{cl.texinfo} file and put the resulting | |
270 | Info files in the @file{info/} directory or another suitable place. | |
271 | ||
272 | You may instead wish to leave this package's components all in | |
273 | their own directory, and then add this directory to your | |
274 | @code{load-path} and (Emacs 19 only) @code{Info-directory-list}. | |
275 | Add the directory to the front of the list so the old @dfn{CL} | |
276 | package and its documentation are hidden. | |
277 | ||
278 | @node Naming Conventions, , Installation, Overview | |
279 | @section Naming Conventions | |
280 | ||
281 | @noindent | |
282 | Except where noted, all functions defined by this package have the | |
283 | same names and calling conventions as their Common Lisp counterparts. | |
284 | ||
285 | Following is a complete list of functions whose names were changed | |
286 | from Common Lisp, usually to avoid conflicts with Emacs. In each | |
287 | case, a @samp{*} has been appended to the Common Lisp name to obtain | |
288 | the Emacs name: | |
289 | ||
290 | @example | |
291 | defun* defsubst* defmacro* function* | |
292 | member* assoc* rassoc* get* | |
293 | remove* delete* mapcar* sort* | |
294 | floor* ceiling* truncate* round* | |
295 | mod* rem* random* last* | |
296 | @end example | |
297 | ||
298 | Internal function and variable names in the package are prefixed | |
299 | by @code{cl-}. Here is a complete list of functions @emph{not} | |
300 | prefixed by @code{cl-} which were not taken from Common Lisp: | |
301 | ||
302 | @example | |
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303 | member remove remq |
304 | floatp-safe lexical-let lexical-let* | |
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305 | callf callf2 letf letf* |
306 | defsubst* defalias add-hook eval-when-compile | |
307 | @end example | |
308 | ||
309 | @noindent | |
310 | (Most of these are Emacs 19 features provided to Emacs 18 users, | |
311 | or introduced, like @code{remq}, for reasons of symmetry | |
312 | with similar features.) | |
313 | ||
314 | The following simple functions and macros are defined in @file{cl.el}; | |
315 | they do not cause other components like @file{cl-extra} to be loaded. | |
316 | ||
317 | @example | |
ed4d9494 | 318 | eql floatp-safe endp |
6bf7aab6 | 319 | evenp oddp plusp minusp |
ed4d9494 | 320 | butlast nbutlast caaar .. cddddr |
6bf7aab6 | 321 | list* ldiff rest first .. tenth |
ed4d9494 | 322 | copy-list subst mapcar* [2] |
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323 | adjoin [3] acons pairlis pop [4] |
324 | push [4] pushnew [3,4] incf [4] decf [4] | |
325 | proclaim declaim | |
326 | @end example | |
327 | ||
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328 | @noindent |
329 | [2] Only for one sequence argument or two list arguments. | |
330 | ||
331 | @noindent | |
332 | [3] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified, | |
333 | and @code{:key} is not used. | |
334 | ||
335 | @noindent | |
336 | [4] Only when @var{place} is a plain variable name. | |
337 | ||
338 | @iftex | |
339 | @chapno=4 | |
340 | @end iftex | |
341 | ||
342 | @node Program Structure, Predicates, Overview, Top | |
343 | @chapter Program Structure | |
344 | ||
345 | @noindent | |
346 | This section describes features of the @dfn{CL} package which have to | |
347 | do with programs as a whole: advanced argument lists for functions, | |
348 | and the @code{eval-when} construct. | |
349 | ||
350 | @menu | |
351 | * Argument Lists:: `&key', `&aux', `defun*', `defmacro*'. | |
352 | * Time of Evaluation:: The `eval-when' construct. | |
353 | * Function Aliases:: The `defalias' function. | |
354 | @end menu | |
355 | ||
356 | @iftex | |
357 | @secno=1 | |
358 | @end iftex | |
359 | ||
360 | @node Argument Lists, Time of Evaluation, Program Structure, Program Structure | |
361 | @section Argument Lists | |
362 | ||
363 | @noindent | |
364 | Emacs Lisp's notation for argument lists of functions is a subset of | |
365 | the Common Lisp notation. As well as the familiar @code{&optional} | |
366 | and @code{&rest} markers, Common Lisp allows you to specify default | |
367 | values for optional arguments, and it provides the additional markers | |
368 | @code{&key} and @code{&aux}. | |
369 | ||
370 | Since argument parsing is built-in to Emacs, there is no way for | |
371 | this package to implement Common Lisp argument lists seamlessly. | |
372 | Instead, this package defines alternates for several Lisp forms | |
373 | which you must use if you need Common Lisp argument lists. | |
374 | ||
375 | @defspec defun* name arglist body... | |
376 | This form is identical to the regular @code{defun} form, except | |
377 | that @var{arglist} is allowed to be a full Common Lisp argument | |
378 | list. Also, the function body is enclosed in an implicit block | |
379 | called @var{name}; @pxref{Blocks and Exits}. | |
380 | @end defspec | |
381 | ||
382 | @defspec defsubst* name arglist body... | |
383 | This is just like @code{defun*}, except that the function that | |
384 | is defined is automatically proclaimed @code{inline}, i.e., | |
385 | calls to it may be expanded into in-line code by the byte compiler. | |
386 | This is analogous to the @code{defsubst} form in Emacs 19; | |
387 | @code{defsubst*} uses a different method (compiler macros) which | |
388 | works in all version of Emacs, and also generates somewhat more | |
389 | efficient inline expansions. In particular, @code{defsubst*} | |
390 | arranges for the processing of keyword arguments, default values, | |
391 | etc., to be done at compile-time whenever possible. | |
392 | @end defspec | |
393 | ||
394 | @defspec defmacro* name arglist body... | |
395 | This is identical to the regular @code{defmacro} form, | |
396 | except that @var{arglist} is allowed to be a full Common Lisp | |
397 | argument list. The @code{&environment} keyword is supported as | |
398 | described in Steele. The @code{&whole} keyword is supported only | |
399 | within destructured lists (see below); top-level @code{&whole} | |
400 | cannot be implemented with the current Emacs Lisp interpreter. | |
401 | The macro expander body is enclosed in an implicit block called | |
402 | @var{name}. | |
403 | @end defspec | |
404 | ||
405 | @defspec function* symbol-or-lambda | |
406 | This is identical to the regular @code{function} form, | |
407 | except that if the argument is a @code{lambda} form then that | |
408 | form may use a full Common Lisp argument list. | |
409 | @end defspec | |
410 | ||
411 | Also, all forms (such as @code{defsetf} and @code{flet}) defined | |
412 | in this package that include @var{arglist}s in their syntax allow | |
413 | full Common Lisp argument lists. | |
414 | ||
415 | Note that it is @emph{not} necessary to use @code{defun*} in | |
416 | order to have access to most @dfn{CL} features in your function. | |
417 | These features are always present; @code{defun*}'s only | |
418 | difference from @code{defun} is its more flexible argument | |
419 | lists and its implicit block. | |
420 | ||
421 | The full form of a Common Lisp argument list is | |
422 | ||
423 | @example | |
424 | (@var{var}... | |
425 | &optional (@var{var} @var{initform} @var{svar})... | |
426 | &rest @var{var} | |
427 | &key ((@var{keyword} @var{var}) @var{initform} @var{svar})... | |
428 | &aux (@var{var} @var{initform})...) | |
429 | @end example | |
430 | ||
431 | Each of the five argument list sections is optional. The @var{svar}, | |
432 | @var{initform}, and @var{keyword} parts are optional; if they are | |
433 | omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}. | |
434 | ||
435 | The first section consists of zero or more @dfn{required} arguments. | |
436 | These arguments must always be specified in a call to the function; | |
437 | there is no difference between Emacs Lisp and Common Lisp as far as | |
438 | required arguments are concerned. | |
439 | ||
440 | The second section consists of @dfn{optional} arguments. These | |
441 | arguments may be specified in the function call; if they are not, | |
442 | @var{initform} specifies the default value used for the argument. | |
443 | (No @var{initform} means to use @code{nil} as the default.) The | |
444 | @var{initform} is evaluated with the bindings for the preceding | |
445 | arguments already established; @code{(a &optional (b (1+ a)))} | |
446 | matches one or two arguments, with the second argument defaulting | |
447 | to one plus the first argument. If the @var{svar} is specified, | |
448 | it is an auxiliary variable which is bound to @code{t} if the optional | |
449 | argument was specified, or to @code{nil} if the argument was omitted. | |
450 | If you don't use an @var{svar}, then there will be no way for your | |
451 | function to tell whether it was called with no argument, or with | |
452 | the default value passed explicitly as an argument. | |
453 | ||
454 | The third section consists of a single @dfn{rest} argument. If | |
455 | more arguments were passed to the function than are accounted for | |
456 | by the required and optional arguments, those extra arguments are | |
457 | collected into a list and bound to the ``rest'' argument variable. | |
458 | Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp. | |
459 | Common Lisp accepts @code{&body} as a synonym for @code{&rest} in | |
460 | macro contexts; this package accepts it all the time. | |
461 | ||
462 | The fourth section consists of @dfn{keyword} arguments. These | |
463 | are optional arguments which are specified by name rather than | |
464 | positionally in the argument list. For example, | |
465 | ||
466 | @example | |
467 | (defun* foo (a &optional b &key c d (e 17))) | |
468 | @end example | |
469 | ||
470 | @noindent | |
471 | defines a function which may be called with one, two, or more | |
472 | arguments. The first two arguments are bound to @code{a} and | |
473 | @code{b} in the usual way. The remaining arguments must be | |
474 | pairs of the form @code{:c}, @code{:d}, or @code{:e} followed | |
475 | by the value to be bound to the corresponding argument variable. | |
476 | (Symbols whose names begin with a colon are called @dfn{keywords}, | |
477 | and they are self-quoting in the same way as @code{nil} and | |
478 | @code{t}.) | |
479 | ||
480 | For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five | |
481 | arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword | |
482 | appears more than once in the function call, the first occurrence | |
483 | takes precedence over the later ones. Note that it is not possible | |
484 | to specify keyword arguments without specifying the optional | |
485 | argument @code{b} as well, since @code{(foo 1 :c 2)} would bind | |
486 | @code{b} to the keyword @code{:c}, then signal an error because | |
487 | @code{2} is not a valid keyword. | |
488 | ||
489 | If a @var{keyword} symbol is explicitly specified in the argument | |
490 | list as shown in the above diagram, then that keyword will be | |
491 | used instead of just the variable name prefixed with a colon. | |
492 | You can specify a @var{keyword} symbol which does not begin with | |
493 | a colon at all, but such symbols will not be self-quoting; you | |
494 | will have to quote them explicitly with an apostrophe in the | |
495 | function call. | |
496 | ||
497 | Ordinarily it is an error to pass an unrecognized keyword to | |
498 | a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask | |
499 | Lisp to ignore unrecognized keywords, either by adding the | |
500 | marker @code{&allow-other-keys} after the keyword section | |
501 | of the argument list, or by specifying an @code{:allow-other-keys} | |
502 | argument in the call whose value is non-@code{nil}. If the | |
503 | function uses both @code{&rest} and @code{&key} at the same time, | |
504 | the ``rest'' argument is bound to the keyword list as it appears | |
505 | in the call. For example: | |
506 | ||
507 | @smallexample | |
508 | (defun* find-thing (thing &rest rest &key need &allow-other-keys) | |
509 | (or (apply 'member* thing thing-list :allow-other-keys t rest) | |
510 | (if need (error "Thing not found")))) | |
511 | @end smallexample | |
512 | ||
513 | @noindent | |
514 | This function takes a @code{:need} keyword argument, but also | |
515 | accepts other keyword arguments which are passed on to the | |
516 | @code{member*} function. @code{allow-other-keys} is used to | |
517 | keep both @code{find-thing} and @code{member*} from complaining | |
518 | about each others' keywords in the arguments. | |
519 | ||
520 | As a (significant) performance optimization, this package | |
521 | implements the scan for keyword arguments by calling @code{memq} | |
522 | to search for keywords in a ``rest'' argument. Technically | |
523 | speaking, this is incorrect, since @code{memq} looks at the | |
524 | odd-numbered values as well as the even-numbered keywords. | |
525 | The net effect is that if you happen to pass a keyword symbol | |
526 | as the @emph{value} of another keyword argument, where that | |
527 | keyword symbol happens to equal the name of a valid keyword | |
528 | argument of the same function, then the keyword parser will | |
529 | become confused. This minor bug can only affect you if you | |
530 | use keyword symbols as general-purpose data in your program; | |
531 | this practice is strongly discouraged in Emacs Lisp. | |
532 | ||
533 | The fifth section of the argument list consists of @dfn{auxiliary | |
534 | variables}. These are not really arguments at all, but simply | |
535 | variables which are bound to @code{nil} or to the specified | |
536 | @var{initforms} during execution of the function. There is no | |
537 | difference between the following two functions, except for a | |
538 | matter of stylistic taste: | |
539 | ||
540 | @example | |
541 | (defun* foo (a b &aux (c (+ a b)) d) | |
542 | @var{body}) | |
543 | ||
544 | (defun* foo (a b) | |
545 | (let ((c (+ a b)) d) | |
546 | @var{body})) | |
547 | @end example | |
548 | ||
549 | Argument lists support @dfn{destructuring}. In Common Lisp, | |
550 | destructuring is only allowed with @code{defmacro}; this package | |
551 | allows it with @code{defun*} and other argument lists as well. | |
552 | In destructuring, any argument variable (@var{var} in the above | |
553 | diagram) can be replaced by a list of variables, or more generally, | |
554 | a recursive argument list. The corresponding argument value must | |
555 | be a list whose elements match this recursive argument list. | |
556 | For example: | |
557 | ||
558 | @example | |
559 | (defmacro* dolist ((var listform &optional resultform) | |
560 | &rest body) | |
561 | ...) | |
562 | @end example | |
563 | ||
564 | This says that the first argument of @code{dolist} must be a list | |
565 | of two or three items; if there are other arguments as well as this | |
566 | list, they are stored in @code{body}. All features allowed in | |
567 | regular argument lists are allowed in these recursive argument lists. | |
568 | In addition, the clause @samp{&whole @var{var}} is allowed at the | |
569 | front of a recursive argument list. It binds @var{var} to the | |
570 | whole list being matched; thus @code{(&whole all a b)} matches | |
571 | a list of two things, with @code{a} bound to the first thing, | |
572 | @code{b} bound to the second thing, and @code{all} bound to the | |
573 | list itself. (Common Lisp allows @code{&whole} in top-level | |
574 | @code{defmacro} argument lists as well, but Emacs Lisp does not | |
575 | support this usage.) | |
576 | ||
577 | One last feature of destructuring is that the argument list may be | |
578 | dotted, so that the argument list @code{(a b . c)} is functionally | |
579 | equivalent to @code{(a b &rest c)}. | |
580 | ||
581 | If the optimization quality @code{safety} is set to 0 | |
582 | (@pxref{Declarations}), error checking for wrong number of | |
583 | arguments and invalid keyword arguments is disabled. By default, | |
584 | argument lists are rigorously checked. | |
585 | ||
586 | @node Time of Evaluation, Function Aliases, Argument Lists, Program Structure | |
587 | @section Time of Evaluation | |
588 | ||
589 | @noindent | |
590 | Normally, the byte-compiler does not actually execute the forms in | |
591 | a file it compiles. For example, if a file contains @code{(setq foo t)}, | |
592 | the act of compiling it will not actually set @code{foo} to @code{t}. | |
593 | This is true even if the @code{setq} was a top-level form (i.e., not | |
594 | enclosed in a @code{defun} or other form). Sometimes, though, you | |
595 | would like to have certain top-level forms evaluated at compile-time. | |
596 | For example, the compiler effectively evaluates @code{defmacro} forms | |
597 | at compile-time so that later parts of the file can refer to the | |
598 | macros that are defined. | |
599 | ||
600 | @defspec eval-when (situations...) forms... | |
601 | This form controls when the body @var{forms} are evaluated. | |
602 | The @var{situations} list may contain any set of the symbols | |
603 | @code{compile}, @code{load}, and @code{eval} (or their long-winded | |
604 | ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel}, | |
605 | and @code{:execute}). | |
606 | ||
607 | The @code{eval-when} form is handled differently depending on | |
608 | whether or not it is being compiled as a top-level form. | |
609 | Specifically, it gets special treatment if it is being compiled | |
610 | by a command such as @code{byte-compile-file} which compiles files | |
611 | or buffers of code, and it appears either literally at the | |
612 | top level of the file or inside a top-level @code{progn}. | |
613 | ||
614 | For compiled top-level @code{eval-when}s, the body @var{forms} are | |
615 | executed at compile-time if @code{compile} is in the @var{situations} | |
616 | list, and the @var{forms} are written out to the file (to be executed | |
617 | at load-time) if @code{load} is in the @var{situations} list. | |
618 | ||
619 | For non-compiled-top-level forms, only the @code{eval} situation is | |
620 | relevant. (This includes forms executed by the interpreter, forms | |
621 | compiled with @code{byte-compile} rather than @code{byte-compile-file}, | |
622 | and non-top-level forms.) The @code{eval-when} acts like a | |
623 | @code{progn} if @code{eval} is specified, and like @code{nil} | |
624 | (ignoring the body @var{forms}) if not. | |
625 | ||
626 | The rules become more subtle when @code{eval-when}s are nested; | |
627 | consult Steele (second edition) for the gruesome details (and | |
628 | some gruesome examples). | |
629 | ||
630 | Some simple examples: | |
631 | ||
632 | @example | |
633 | ;; Top-level forms in foo.el: | |
634 | (eval-when (compile) (setq foo1 'bar)) | |
635 | (eval-when (load) (setq foo2 'bar)) | |
636 | (eval-when (compile load) (setq foo3 'bar)) | |
637 | (eval-when (eval) (setq foo4 'bar)) | |
638 | (eval-when (eval compile) (setq foo5 'bar)) | |
639 | (eval-when (eval load) (setq foo6 'bar)) | |
640 | (eval-when (eval compile load) (setq foo7 'bar)) | |
641 | @end example | |
642 | ||
643 | When @file{foo.el} is compiled, these variables will be set during | |
644 | the compilation itself: | |
645 | ||
646 | @example | |
647 | foo1 foo3 foo5 foo7 ; `compile' | |
648 | @end example | |
649 | ||
650 | When @file{foo.elc} is loaded, these variables will be set: | |
651 | ||
652 | @example | |
653 | foo2 foo3 foo6 foo7 ; `load' | |
654 | @end example | |
655 | ||
656 | And if @file{foo.el} is loaded uncompiled, these variables will | |
657 | be set: | |
658 | ||
659 | @example | |
660 | foo4 foo5 foo6 foo7 ; `eval' | |
661 | @end example | |
662 | ||
663 | If these seven @code{eval-when}s had been, say, inside a @code{defun}, | |
664 | then the first three would have been equivalent to @code{nil} and the | |
665 | last four would have been equivalent to the corresponding @code{setq}s. | |
666 | ||
667 | Note that @code{(eval-when (load eval) @dots{})} is equivalent | |
668 | to @code{(progn @dots{})} in all contexts. The compiler treats | |
669 | certain top-level forms, like @code{defmacro} (sort-of) and | |
670 | @code{require}, as if they were wrapped in @code{(eval-when | |
671 | (compile load eval) @dots{})}. | |
672 | @end defspec | |
673 | ||
674 | Emacs 19 includes two special forms related to @code{eval-when}. | |
675 | One of these, @code{eval-when-compile}, is not quite equivalent to | |
ed4d9494 | 676 | any @code{eval-when} construct and is described below. |
6bf7aab6 DL |
677 | |
678 | The other form, @code{(eval-and-compile @dots{})}, is exactly | |
679 | equivalent to @samp{(eval-when (compile load eval) @dots{})} and | |
680 | so is not itself defined by this package. | |
681 | ||
682 | @defspec eval-when-compile forms... | |
683 | The @var{forms} are evaluated at compile-time; at execution time, | |
684 | this form acts like a quoted constant of the resulting value. Used | |
685 | at top-level, @code{eval-when-compile} is just like @samp{eval-when | |
686 | (compile eval)}. In other contexts, @code{eval-when-compile} | |
687 | allows code to be evaluated once at compile-time for efficiency | |
688 | or other reasons. | |
689 | ||
690 | This form is similar to the @samp{#.} syntax of true Common Lisp. | |
691 | @end defspec | |
692 | ||
693 | @defspec load-time-value form | |
694 | The @var{form} is evaluated at load-time; at execution time, | |
695 | this form acts like a quoted constant of the resulting value. | |
696 | ||
697 | Early Common Lisp had a @samp{#,} syntax that was similar to | |
698 | this, but ANSI Common Lisp replaced it with @code{load-time-value} | |
699 | and gave it more well-defined semantics. | |
700 | ||
701 | In a compiled file, @code{load-time-value} arranges for @var{form} | |
702 | to be evaluated when the @file{.elc} file is loaded and then used | |
703 | as if it were a quoted constant. In code compiled by | |
704 | @code{byte-compile} rather than @code{byte-compile-file}, the | |
705 | effect is identical to @code{eval-when-compile}. In uncompiled | |
706 | code, both @code{eval-when-compile} and @code{load-time-value} | |
707 | act exactly like @code{progn}. | |
708 | ||
709 | @example | |
710 | (defun report () | |
711 | (insert "This function was executed on: " | |
712 | (current-time-string) | |
713 | ", compiled on: " | |
714 | (eval-when-compile (current-time-string)) | |
715 | ;; or '#.(current-time-string) in real Common Lisp | |
716 | ", and loaded on: " | |
717 | (load-time-value (current-time-string)))) | |
718 | @end example | |
719 | ||
720 | @noindent | |
721 | Byte-compiled, the above defun will result in the following code | |
722 | (or its compiled equivalent, of course) in the @file{.elc} file: | |
723 | ||
724 | @example | |
725 | (setq --temp-- (current-time-string)) | |
726 | (defun report () | |
727 | (insert "This function was executed on: " | |
728 | (current-time-string) | |
729 | ", compiled on: " | |
730 | '"Wed Jun 23 18:33:43 1993" | |
731 | ", and loaded on: " | |
732 | --temp--)) | |
733 | @end example | |
734 | @end defspec | |
735 | ||
736 | @node Function Aliases, , Time of Evaluation, Program Structure | |
737 | @section Function Aliases | |
738 | ||
739 | @noindent | |
740 | This section describes a feature from GNU Emacs 19 which this | |
741 | package makes available in other versions of Emacs. | |
742 | ||
743 | @defun defalias symbol function | |
744 | This function sets @var{symbol}'s function cell to @var{function}. | |
745 | It is equivalent to @code{fset}, except that in GNU Emacs 19 it also | |
746 | records the setting in @code{load-history} so that it can be undone | |
747 | by a later @code{unload-feature}. | |
748 | ||
749 | In other versions of Emacs, @code{defalias} is a synonym for | |
750 | @code{fset}. | |
751 | @end defun | |
752 | ||
753 | @node Predicates, Control Structure, Program Structure, Top | |
754 | @chapter Predicates | |
755 | ||
756 | @noindent | |
757 | This section describes functions for testing whether various | |
758 | facts are true or false. | |
759 | ||
760 | @menu | |
761 | * Type Predicates:: `typep', `deftype', and `coerce' | |
762 | * Equality Predicates:: `eql' and `equalp' | |
763 | @end menu | |
764 | ||
765 | @node Type Predicates, Equality Predicates, Predicates, Predicates | |
766 | @section Type Predicates | |
767 | ||
768 | @noindent | |
769 | The @dfn{CL} package defines a version of the Common Lisp @code{typep} | |
770 | predicate. | |
771 | ||
772 | @defun typep object type | |
773 | Check if @var{object} is of type @var{type}, where @var{type} is a | |
774 | (quoted) type name of the sort used by Common Lisp. For example, | |
775 | @code{(typep foo 'integer)} is equivalent to @code{(integerp foo)}. | |
776 | @end defun | |
777 | ||
778 | The @var{type} argument to the above function is either a symbol | |
779 | or a list beginning with a symbol. | |
780 | ||
781 | @itemize @bullet | |
782 | @item | |
783 | If the type name is a symbol, Emacs appends @samp{-p} to the | |
784 | symbol name to form the name of a predicate function for testing | |
785 | the type. (Built-in predicates whose names end in @samp{p} rather | |
786 | than @samp{-p} are used when appropriate.) | |
787 | ||
788 | @item | |
789 | The type symbol @code{t} stands for the union of all types. | |
790 | @code{(typep @var{object} t)} is always true. Likewise, the | |
791 | type symbol @code{nil} stands for nothing at all, and | |
792 | @code{(typep @var{object} nil)} is always false. | |
793 | ||
794 | @item | |
795 | The type symbol @code{null} represents the symbol @code{nil}. | |
796 | Thus @code{(typep @var{object} 'null)} is equivalent to | |
797 | @code{(null @var{object})}. | |
798 | ||
799 | @item | |
800 | The type symbol @code{real} is a synonym for @code{number}, and | |
801 | @code{fixnum} is a synonym for @code{integer}. | |
802 | ||
803 | @item | |
804 | The type symbols @code{character} and @code{string-char} match | |
805 | integers in the range from 0 to 255. | |
806 | ||
807 | @item | |
808 | The type symbol @code{float} uses the @code{floatp-safe} predicate | |
809 | defined by this package rather than @code{floatp}, so it will work | |
810 | correctly even in Emacs versions without floating-point support. | |
811 | ||
812 | @item | |
813 | The type list @code{(integer @var{low} @var{high})} represents all | |
814 | integers between @var{low} and @var{high}, inclusive. Either bound | |
815 | may be a list of a single integer to specify an exclusive limit, | |
816 | or a @code{*} to specify no limit. The type @code{(integer * *)} | |
817 | is thus equivalent to @code{integer}. | |
818 | ||
819 | @item | |
820 | Likewise, lists beginning with @code{float}, @code{real}, or | |
821 | @code{number} represent numbers of that type falling in a particular | |
822 | range. | |
823 | ||
824 | @item | |
825 | Lists beginning with @code{and}, @code{or}, and @code{not} form | |
826 | combinations of types. For example, @code{(or integer (float 0 *))} | |
827 | represents all objects that are integers or non-negative floats. | |
828 | ||
829 | @item | |
830 | Lists beginning with @code{member} or @code{member*} represent | |
831 | objects @code{eql} to any of the following values. For example, | |
832 | @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)}, | |
833 | and @code{(member nil)} is equivalent to @code{null}. | |
834 | ||
835 | @item | |
836 | Lists of the form @code{(satisfies @var{predicate})} represent | |
837 | all objects for which @var{predicate} returns true when called | |
838 | with that object as an argument. | |
839 | @end itemize | |
840 | ||
841 | The following function and macro (not technically predicates) are | |
842 | related to @code{typep}. | |
843 | ||
844 | @defun coerce object type | |
845 | This function attempts to convert @var{object} to the specified | |
846 | @var{type}. If @var{object} is already of that type as determined by | |
847 | @code{typep}, it is simply returned. Otherwise, certain types of | |
848 | conversions will be made: If @var{type} is any sequence type | |
849 | (@code{string}, @code{list}, etc.) then @var{object} will be | |
850 | converted to that type if possible. If @var{type} is | |
851 | @code{character}, then strings of length one and symbols with | |
852 | one-character names can be coerced. If @var{type} is @code{float}, | |
853 | then integers can be coerced in versions of Emacs that support | |
854 | floats. In all other circumstances, @code{coerce} signals an | |
855 | error. | |
856 | @end defun | |
857 | ||
858 | @defspec deftype name arglist forms... | |
859 | This macro defines a new type called @var{name}. It is similar | |
860 | to @code{defmacro} in many ways; when @var{name} is encountered | |
861 | as a type name, the body @var{forms} are evaluated and should | |
862 | return a type specifier that is equivalent to the type. The | |
863 | @var{arglist} is a Common Lisp argument list of the sort accepted | |
864 | by @code{defmacro*}. The type specifier @samp{(@var{name} @var{args}...)} | |
865 | is expanded by calling the expander with those arguments; the type | |
866 | symbol @samp{@var{name}} is expanded by calling the expander with | |
867 | no arguments. The @var{arglist} is processed the same as for | |
868 | @code{defmacro*} except that optional arguments without explicit | |
869 | defaults use @code{*} instead of @code{nil} as the ``default'' | |
870 | default. Some examples: | |
871 | ||
872 | @example | |
873 | (deftype null () '(satisfies null)) ; predefined | |
874 | (deftype list () '(or null cons)) ; predefined | |
875 | (deftype unsigned-byte (&optional bits) | |
876 | (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits))))) | |
877 | (unsigned-byte 8) @equiv{} (integer 0 255) | |
878 | (unsigned-byte) @equiv{} (integer 0 *) | |
879 | unsigned-byte @equiv{} (integer 0 *) | |
880 | @end example | |
881 | ||
882 | @noindent | |
883 | The last example shows how the Common Lisp @code{unsigned-byte} | |
884 | type specifier could be implemented if desired; this package does | |
885 | not implement @code{unsigned-byte} by default. | |
886 | @end defspec | |
887 | ||
888 | The @code{typecase} and @code{check-type} macros also use type | |
889 | names. @xref{Conditionals}. @xref{Assertions}. The @code{map}, | |
890 | @code{concatenate}, and @code{merge} functions take type-name | |
891 | arguments to specify the type of sequence to return. @xref{Sequences}. | |
892 | ||
893 | @node Equality Predicates, , Type Predicates, Predicates | |
894 | @section Equality Predicates | |
895 | ||
896 | @noindent | |
897 | This package defines two Common Lisp predicates, @code{eql} and | |
898 | @code{equalp}. | |
899 | ||
900 | @defun eql a b | |
901 | This function is almost the same as @code{eq}, except that if @var{a} | |
902 | and @var{b} are numbers of the same type, it compares them for numeric | |
903 | equality (as if by @code{equal} instead of @code{eq}). This makes a | |
904 | difference only for versions of Emacs that are compiled with | |
905 | floating-point support, such as Emacs 19. Emacs floats are allocated | |
906 | objects just like cons cells, which means that @code{(eq 3.0 3.0)} | |
907 | will not necessarily be true---if the two @code{3.0}s were allocated | |
908 | separately, the pointers will be different even though the numbers are | |
909 | the same. But @code{(eql 3.0 3.0)} will always be true. | |
910 | ||
911 | The types of the arguments must match, so @code{(eql 3 3.0)} is | |
912 | still false. | |
913 | ||
914 | Note that Emacs integers are ``direct'' rather than allocated, which | |
915 | basically means @code{(eq 3 3)} will always be true. Thus @code{eq} | |
916 | and @code{eql} behave differently only if floating-point numbers are | |
917 | involved, and are indistinguishable on Emacs versions that don't | |
918 | support floats. | |
919 | ||
920 | There is a slight inconsistency with Common Lisp in the treatment of | |
921 | positive and negative zeros. Some machines, notably those with IEEE | |
922 | standard arithmetic, represent @code{+0} and @code{-0} as distinct | |
923 | values. Normally this doesn't matter because the standard specifies | |
924 | that @code{(= 0.0 -0.0)} should always be true, and this is indeed | |
925 | what Emacs Lisp and Common Lisp do. But the Common Lisp standard | |
926 | states that @code{(eql 0.0 -0.0)} and @code{(equal 0.0 -0.0)} should | |
927 | be false on IEEE-like machines; Emacs Lisp does not do this, and in | |
928 | fact the only known way to distinguish between the two zeros in Emacs | |
929 | Lisp is to @code{format} them and check for a minus sign. | |
930 | @end defun | |
931 | ||
932 | @defun equalp a b | |
933 | This function is a more flexible version of @code{equal}. In | |
934 | particular, it compares strings case-insensitively, and it compares | |
935 | numbers without regard to type (so that @code{(equalp 3 3.0)} is | |
936 | true). Vectors and conses are compared recursively. All other | |
937 | objects are compared as if by @code{equal}. | |
938 | ||
939 | This function differs from Common Lisp @code{equalp} in several | |
940 | respects. First, Common Lisp's @code{equalp} also compares | |
941 | @emph{characters} case-insensitively, which would be impractical | |
942 | in this package since Emacs does not distinguish between integers | |
943 | and characters. In keeping with the idea that strings are less | |
944 | vector-like in Emacs Lisp, this package's @code{equalp} also will | |
945 | not compare strings against vectors of integers. Finally, Common | |
946 | Lisp's @code{equalp} compares hash tables without regard to | |
947 | ordering, whereas this package simply compares hash tables in | |
948 | terms of their underlying structure (which means vectors for Lucid | |
949 | Emacs 19 hash tables, or lists for other hash tables). | |
950 | @end defun | |
951 | ||
952 | Also note that the Common Lisp functions @code{member} and @code{assoc} | |
953 | use @code{eql} to compare elements, whereas Emacs Lisp follows the | |
954 | MacLisp tradition and uses @code{equal} for these two functions. | |
955 | In Emacs, use @code{member*} and @code{assoc*} to get functions | |
956 | which use @code{eql} for comparisons. | |
957 | ||
958 | @node Control Structure, Macros, Predicates, Top | |
959 | @chapter Control Structure | |
960 | ||
961 | @noindent | |
962 | The features described in the following sections implement | |
963 | various advanced control structures, including the powerful | |
964 | @code{setf} facility and a number of looping and conditional | |
965 | constructs. | |
966 | ||
967 | @menu | |
968 | * Assignment:: The `psetq' form | |
969 | * Generalized Variables:: `setf', `incf', `push', etc. | |
970 | * Variable Bindings:: `progv', `lexical-let', `flet', `macrolet' | |
971 | * Conditionals:: `case', `typecase' | |
972 | * Blocks and Exits:: `block', `return', `return-from' | |
2995b042 | 973 | * Iteration:: `do', `dotimes', `dolist', `do-symbols' |
6bf7aab6 DL |
974 | * Loop Facility:: The Common Lisp `loop' macro |
975 | * Multiple Values:: `values', `multiple-value-bind', etc. | |
976 | @end menu | |
977 | ||
978 | @node Assignment, Generalized Variables, Control Structure, Control Structure | |
979 | @section Assignment | |
980 | ||
981 | @noindent | |
982 | The @code{psetq} form is just like @code{setq}, except that multiple | |
983 | assignments are done in parallel rather than sequentially. | |
984 | ||
985 | @defspec psetq [symbol form]@dots{} | |
986 | This special form (actually a macro) is used to assign to several | |
987 | variables simultaneously. Given only one @var{symbol} and @var{form}, | |
988 | it has the same effect as @code{setq}. Given several @var{symbol} | |
989 | and @var{form} pairs, it evaluates all the @var{form}s in advance | |
990 | and then stores the corresponding variables afterwards. | |
991 | ||
992 | @example | |
993 | (setq x 2 y 3) | |
994 | (setq x (+ x y) y (* x y)) | |
995 | x | |
996 | @result{} 5 | |
997 | y ; @r{@code{y} was computed after @code{x} was set.} | |
998 | @result{} 15 | |
999 | (setq x 2 y 3) | |
1000 | (psetq x (+ x y) y (* x y)) | |
1001 | x | |
1002 | @result{} 5 | |
1003 | y ; @r{@code{y} was computed before @code{x} was set.} | |
1004 | @result{} 6 | |
1005 | @end example | |
1006 | ||
1007 | The simplest use of @code{psetq} is @code{(psetq x y y x)}, which | |
1008 | exchanges the values of two variables. (The @code{rotatef} form | |
1009 | provides an even more convenient way to swap two variables; | |
1010 | @pxref{Modify Macros}.) | |
1011 | ||
1012 | @code{psetq} always returns @code{nil}. | |
1013 | @end defspec | |
1014 | ||
1015 | @node Generalized Variables, Variable Bindings, Assignment, Control Structure | |
1016 | @section Generalized Variables | |
1017 | ||
1018 | @noindent | |
1019 | A ``generalized variable'' or ``place form'' is one of the many places | |
1020 | in Lisp memory where values can be stored. The simplest place form is | |
1021 | a regular Lisp variable. But the cars and cdrs of lists, elements | |
1022 | of arrays, properties of symbols, and many other locations are also | |
1023 | places where Lisp values are stored. | |
1024 | ||
1025 | The @code{setf} form is like @code{setq}, except that it accepts | |
1026 | arbitrary place forms on the left side rather than just | |
1027 | symbols. For example, @code{(setf (car a) b)} sets the car of | |
1028 | @code{a} to @code{b}, doing the same operation as @code{(setcar a b)} | |
1029 | but without having to remember two separate functions for setting | |
1030 | and accessing every type of place. | |
1031 | ||
1032 | Generalized variables are analogous to ``lvalues'' in the C | |
1033 | language, where @samp{x = a[i]} gets an element from an array | |
1034 | and @samp{a[i] = x} stores an element using the same notation. | |
1035 | Just as certain forms like @code{a[i]} can be lvalues in C, there | |
1036 | is a set of forms that can be generalized variables in Lisp. | |
1037 | ||
1038 | @menu | |
1039 | * Basic Setf:: `setf' and place forms | |
1040 | * Modify Macros:: `incf', `push', `rotatef', `letf', `callf', etc. | |
1041 | * Customizing Setf:: `define-modify-macro', `defsetf', `define-setf-method' | |
1042 | @end menu | |
1043 | ||
1044 | @node Basic Setf, Modify Macros, Generalized Variables, Generalized Variables | |
1045 | @subsection Basic Setf | |
1046 | ||
1047 | @noindent | |
1048 | The @code{setf} macro is the most basic way to operate on generalized | |
1049 | variables. | |
1050 | ||
1051 | @defspec setf [place form]@dots{} | |
1052 | This macro evaluates @var{form} and stores it in @var{place}, which | |
1053 | must be a valid generalized variable form. If there are several | |
1054 | @var{place} and @var{form} pairs, the assignments are done sequentially | |
1055 | just as with @code{setq}. @code{setf} returns the value of the last | |
1056 | @var{form}. | |
1057 | ||
1058 | The following Lisp forms will work as generalized variables, and | |
1059 | so may legally appear in the @var{place} argument of @code{setf}: | |
1060 | ||
1061 | @itemize @bullet | |
1062 | @item | |
1063 | A symbol naming a variable. In other words, @code{(setf x y)} is | |
1064 | exactly equivalent to @code{(setq x y)}, and @code{setq} itself is | |
1065 | strictly speaking redundant now that @code{setf} exists. Many | |
1066 | programmers continue to prefer @code{setq} for setting simple | |
1067 | variables, though, purely for stylistic or historical reasons. | |
1068 | The macro @code{(setf x y)} actually expands to @code{(setq x y)}, | |
1069 | so there is no performance penalty for using it in compiled code. | |
1070 | ||
1071 | @item | |
1072 | A call to any of the following Lisp functions: | |
1073 | ||
1074 | @smallexample | |
1075 | car cdr caar .. cddddr | |
1076 | nth rest first .. tenth | |
1077 | aref elt nthcdr | |
1078 | symbol-function symbol-value symbol-plist | |
1079 | get get* getf | |
1080 | gethash subseq | |
1081 | @end smallexample | |
1082 | ||
1083 | @noindent | |
1084 | Note that for @code{nthcdr} and @code{getf}, the list argument | |
1085 | of the function must itself be a valid @var{place} form. For | |
1086 | example, @code{(setf (nthcdr 0 foo) 7)} will set @code{foo} itself | |
1087 | to 7. Note that @code{push} and @code{pop} on an @code{nthcdr} | |
1088 | place can be used to insert or delete at any position in a list. | |
1089 | The use of @code{nthcdr} as a @var{place} form is an extension | |
1090 | to standard Common Lisp. | |
1091 | ||
1092 | @item | |
1093 | The following Emacs-specific functions are also @code{setf}-able. | |
1094 | (Some of these are defined only in Emacs 19 or only in Lucid Emacs.) | |
1095 | ||
1096 | @smallexample | |
1097 | buffer-file-name marker-position | |
1098 | buffer-modified-p match-data | |
1099 | buffer-name mouse-position | |
1100 | buffer-string overlay-end | |
1101 | buffer-substring overlay-get | |
1102 | current-buffer overlay-start | |
1103 | current-case-table point | |
1104 | current-column point-marker | |
1105 | current-global-map point-max | |
1106 | current-input-mode point-min | |
1107 | current-local-map process-buffer | |
1108 | current-window-configuration process-filter | |
1109 | default-file-modes process-sentinel | |
1110 | default-value read-mouse-position | |
1111 | documentation-property screen-height | |
1112 | extent-data screen-menubar | |
1113 | extent-end-position screen-width | |
1114 | extent-start-position selected-window | |
1115 | face-background selected-screen | |
1116 | face-background-pixmap selected-frame | |
1117 | face-font standard-case-table | |
1118 | face-foreground syntax-table | |
1119 | face-underline-p window-buffer | |
1120 | file-modes window-dedicated-p | |
1121 | frame-height window-display-table | |
1122 | frame-parameters window-height | |
1123 | frame-visible-p window-hscroll | |
1124 | frame-width window-point | |
1125 | get-register window-start | |
1126 | getenv window-width | |
1127 | global-key-binding x-get-cut-buffer | |
1128 | keymap-parent x-get-cutbuffer | |
1129 | local-key-binding x-get-secondary-selection | |
1130 | mark x-get-selection | |
1131 | mark-marker | |
1132 | @end smallexample | |
1133 | ||
1134 | Most of these have directly corresponding ``set'' functions, like | |
1135 | @code{use-local-map} for @code{current-local-map}, or @code{goto-char} | |
1136 | for @code{point}. A few, like @code{point-min}, expand to longer | |
1137 | sequences of code when they are @code{setf}'d (@code{(narrow-to-region | |
1138 | x (point-max))} in this case). | |
1139 | ||
1140 | @item | |
1141 | A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])}, | |
1142 | where @var{subplace} is itself a legal generalized variable whose | |
1143 | current value is a string, and where the value stored is also a | |
1144 | string. The new string is spliced into the specified part of the | |
1145 | destination string. For example: | |
1146 | ||
1147 | @example | |
1148 | (setq a (list "hello" "world")) | |
1149 | @result{} ("hello" "world") | |
1150 | (cadr a) | |
1151 | @result{} "world" | |
1152 | (substring (cadr a) 2 4) | |
1153 | @result{} "rl" | |
1154 | (setf (substring (cadr a) 2 4) "o") | |
1155 | @result{} "o" | |
1156 | (cadr a) | |
1157 | @result{} "wood" | |
1158 | a | |
1159 | @result{} ("hello" "wood") | |
1160 | @end example | |
1161 | ||
1162 | The generalized variable @code{buffer-substring}, listed above, | |
1163 | also works in this way by replacing a portion of the current buffer. | |
1164 | ||
1165 | @item | |
1166 | A call of the form @code{(apply '@var{func} @dots{})} or | |
1167 | @code{(apply (function @var{func}) @dots{})}, where @var{func} | |
1168 | is a @code{setf}-able function whose store function is ``suitable'' | |
1169 | in the sense described in Steele's book; since none of the standard | |
1170 | Emacs place functions are suitable in this sense, this feature is | |
1171 | only interesting when used with places you define yourself with | |
1172 | @code{define-setf-method} or the long form of @code{defsetf}. | |
1173 | ||
1174 | @item | |
1175 | A macro call, in which case the macro is expanded and @code{setf} | |
1176 | is applied to the resulting form. | |
1177 | ||
1178 | @item | |
1179 | Any form for which a @code{defsetf} or @code{define-setf-method} | |
1180 | has been made. | |
1181 | @end itemize | |
1182 | ||
1183 | Using any forms other than these in the @var{place} argument to | |
1184 | @code{setf} will signal an error. | |
1185 | ||
1186 | The @code{setf} macro takes care to evaluate all subforms in | |
1187 | the proper left-to-right order; for example, | |
1188 | ||
1189 | @example | |
1190 | (setf (aref vec (incf i)) i) | |
1191 | @end example | |
1192 | ||
1193 | @noindent | |
1194 | looks like it will evaluate @code{(incf i)} exactly once, before the | |
1195 | following access to @code{i}; the @code{setf} expander will insert | |
1196 | temporary variables as necessary to ensure that it does in fact work | |
1197 | this way no matter what setf-method is defined for @code{aref}. | |
1198 | (In this case, @code{aset} would be used and no such steps would | |
1199 | be necessary since @code{aset} takes its arguments in a convenient | |
1200 | order.) | |
1201 | ||
1202 | However, if the @var{place} form is a macro which explicitly | |
1203 | evaluates its arguments in an unusual order, this unusual order | |
1204 | will be preserved. Adapting an example from Steele, given | |
1205 | ||
1206 | @example | |
1207 | (defmacro wrong-order (x y) (list 'aref y x)) | |
1208 | @end example | |
1209 | ||
1210 | @noindent | |
1211 | the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will | |
1212 | evaluate @var{b} first, then @var{a}, just as in an actual call | |
1213 | to @code{wrong-order}. | |
1214 | @end defspec | |
1215 | ||
1216 | @node Modify Macros, Customizing Setf, Basic Setf, Generalized Variables | |
1217 | @subsection Modify Macros | |
1218 | ||
1219 | @noindent | |
1220 | This package defines a number of other macros besides @code{setf} | |
1221 | that operate on generalized variables. Many are interesting and | |
1222 | useful even when the @var{place} is just a variable name. | |
1223 | ||
1224 | @defspec psetf [place form]@dots{} | |
1225 | This macro is to @code{setf} what @code{psetq} is to @code{setq}: | |
1226 | When several @var{place}s and @var{form}s are involved, the | |
1227 | assignments take place in parallel rather than sequentially. | |
1228 | Specifically, all subforms are evaluated from left to right, then | |
1229 | all the assignments are done (in an undefined order). | |
1230 | @end defspec | |
1231 | ||
1232 | @defspec incf place &optional x | |
1233 | This macro increments the number stored in @var{place} by one, or | |
1234 | by @var{x} if specified. The incremented value is returned. For | |
1235 | example, @code{(incf i)} is equivalent to @code{(setq i (1+ i))}, and | |
1236 | @code{(incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}. | |
1237 | ||
1238 | Once again, care is taken to preserve the ``apparent'' order of | |
1239 | evaluation. For example, | |
1240 | ||
1241 | @example | |
1242 | (incf (aref vec (incf i))) | |
1243 | @end example | |
1244 | ||
1245 | @noindent | |
1246 | appears to increment @code{i} once, then increment the element of | |
1247 | @code{vec} addressed by @code{i}; this is indeed exactly what it | |
1248 | does, which means the above form is @emph{not} equivalent to the | |
1249 | ``obvious'' expansion, | |
1250 | ||
1251 | @example | |
1252 | (setf (aref vec (incf i)) (1+ (aref vec (incf i)))) ; Wrong! | |
1253 | @end example | |
1254 | ||
1255 | @noindent | |
1256 | but rather to something more like | |
1257 | ||
1258 | @example | |
1259 | (let ((temp (incf i))) | |
1260 | (setf (aref vec temp) (1+ (aref vec temp)))) | |
1261 | @end example | |
1262 | ||
1263 | @noindent | |
1264 | Again, all of this is taken care of automatically by @code{incf} and | |
1265 | the other generalized-variable macros. | |
1266 | ||
1267 | As a more Emacs-specific example of @code{incf}, the expression | |
1268 | @code{(incf (point) @var{n})} is essentially equivalent to | |
1269 | @code{(forward-char @var{n})}. | |
1270 | @end defspec | |
1271 | ||
1272 | @defspec decf place &optional x | |
1273 | This macro decrements the number stored in @var{place} by one, or | |
1274 | by @var{x} if specified. | |
1275 | @end defspec | |
1276 | ||
1277 | @defspec pop place | |
1278 | This macro removes and returns the first element of the list stored | |
1279 | in @var{place}. It is analogous to @code{(prog1 (car @var{place}) | |
1280 | (setf @var{place} (cdr @var{place})))}, except that it takes care | |
1281 | to evaluate all subforms only once. | |
1282 | @end defspec | |
1283 | ||
1284 | @defspec push x place | |
1285 | This macro inserts @var{x} at the front of the list stored in | |
1286 | @var{place}. It is analogous to @code{(setf @var{place} (cons | |
1287 | @var{x} @var{place}))}, except for evaluation of the subforms. | |
1288 | @end defspec | |
1289 | ||
1290 | @defspec pushnew x place @t{&key :test :test-not :key} | |
1291 | This macro inserts @var{x} at the front of the list stored in | |
1292 | @var{place}, but only if @var{x} was not @code{eql} to any | |
1293 | existing element of the list. The optional keyword arguments | |
1294 | are interpreted in the same way as for @code{adjoin}. | |
1295 | @xref{Lists as Sets}. | |
1296 | @end defspec | |
1297 | ||
1298 | @defspec shiftf place@dots{} newvalue | |
1299 | This macro shifts the @var{place}s left by one, shifting in the | |
1300 | value of @var{newvalue} (which may be any Lisp expression, not just | |
1301 | a generalized variable), and returning the value shifted out of | |
1302 | the first @var{place}. Thus, @code{(shiftf @var{a} @var{b} @var{c} | |
1303 | @var{d})} is equivalent to | |
1304 | ||
1305 | @example | |
1306 | (prog1 | |
1307 | @var{a} | |
1308 | (psetf @var{a} @var{b} | |
1309 | @var{b} @var{c} | |
1310 | @var{c} @var{d})) | |
1311 | @end example | |
1312 | ||
1313 | @noindent | |
1314 | except that the subforms of @var{a}, @var{b}, and @var{c} are actually | |
1315 | evaluated only once each and in the apparent order. | |
1316 | @end defspec | |
1317 | ||
1318 | @defspec rotatef place@dots{} | |
1319 | This macro rotates the @var{place}s left by one in circular fashion. | |
1320 | Thus, @code{(rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to | |
1321 | ||
1322 | @example | |
1323 | (psetf @var{a} @var{b} | |
1324 | @var{b} @var{c} | |
1325 | @var{c} @var{d} | |
1326 | @var{d} @var{a}) | |
1327 | @end example | |
1328 | ||
1329 | @noindent | |
1330 | except for the evaluation of subforms. @code{rotatef} always | |
1331 | returns @code{nil}. Note that @code{(rotatef @var{a} @var{b})} | |
1332 | conveniently exchanges @var{a} and @var{b}. | |
1333 | @end defspec | |
1334 | ||
1335 | The following macros were invented for this package; they have no | |
1336 | analogues in Common Lisp. | |
1337 | ||
1338 | @defspec letf (bindings@dots{}) forms@dots{} | |
1339 | This macro is analogous to @code{let}, but for generalized variables | |
1340 | rather than just symbols. Each @var{binding} should be of the form | |
1341 | @code{(@var{place} @var{value})}; the original contents of the | |
1342 | @var{place}s are saved, the @var{value}s are stored in them, and | |
1343 | then the body @var{form}s are executed. Afterwards, the @var{places} | |
1344 | are set back to their original saved contents. This cleanup happens | |
1345 | even if the @var{form}s exit irregularly due to a @code{throw} or an | |
1346 | error. | |
1347 | ||
1348 | For example, | |
1349 | ||
1350 | @example | |
1351 | (letf (((point) (point-min)) | |
1352 | (a 17)) | |
1353 | ...) | |
1354 | @end example | |
1355 | ||
1356 | @noindent | |
1357 | moves ``point'' in the current buffer to the beginning of the buffer, | |
1358 | and also binds @code{a} to 17 (as if by a normal @code{let}, since | |
1359 | @code{a} is just a regular variable). After the body exits, @code{a} | |
1360 | is set back to its original value and point is moved back to its | |
1361 | original position. | |
1362 | ||
1363 | Note that @code{letf} on @code{(point)} is not quite like a | |
1364 | @code{save-excursion}, as the latter effectively saves a marker | |
1365 | which tracks insertions and deletions in the buffer. Actually, | |
1366 | a @code{letf} of @code{(point-marker)} is much closer to this | |
1367 | behavior. (@code{point} and @code{point-marker} are equivalent | |
1368 | as @code{setf} places; each will accept either an integer or a | |
1369 | marker as the stored value.) | |
1370 | ||
1371 | Since generalized variables look like lists, @code{let}'s shorthand | |
1372 | of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would | |
1373 | be ambiguous in @code{letf} and is not allowed. | |
1374 | ||
1375 | However, a @var{binding} specifier may be a one-element list | |
1376 | @samp{(@var{place})}, which is similar to @samp{(@var{place} | |
1377 | @var{place})}. In other words, the @var{place} is not disturbed | |
1378 | on entry to the body, and the only effect of the @code{letf} is | |
1379 | to restore the original value of @var{place} afterwards. (The | |
1380 | redundant access-and-store suggested by the @code{(@var{place} | |
1381 | @var{place})} example does not actually occur.) | |
1382 | ||
1383 | In most cases, the @var{place} must have a well-defined value on | |
1384 | entry to the @code{letf} form. The only exceptions are plain | |
1385 | variables and calls to @code{symbol-value} and @code{symbol-function}. | |
1386 | If the symbol is not bound on entry, it is simply made unbound by | |
1387 | @code{makunbound} or @code{fmakunbound} on exit. | |
1388 | @end defspec | |
1389 | ||
1390 | @defspec letf* (bindings@dots{}) forms@dots{} | |
1391 | This macro is to @code{letf} what @code{let*} is to @code{let}: | |
1392 | It does the bindings in sequential rather than parallel order. | |
1393 | @end defspec | |
1394 | ||
1395 | @defspec callf @var{function} @var{place} @var{args}@dots{} | |
1396 | This is the ``generic'' modify macro. It calls @var{function}, | |
1397 | which should be an unquoted function name, macro name, or lambda. | |
1398 | It passes @var{place} and @var{args} as arguments, and assigns the | |
1399 | result back to @var{place}. For example, @code{(incf @var{place} | |
1400 | @var{n})} is the same as @code{(callf + @var{place} @var{n})}. | |
1401 | Some more examples: | |
1402 | ||
1403 | @example | |
1404 | (callf abs my-number) | |
1405 | (callf concat (buffer-name) "<" (int-to-string n) ">") | |
1406 | (callf union happy-people (list joe bob) :test 'same-person) | |
1407 | @end example | |
1408 | ||
1409 | @xref{Customizing Setf}, for @code{define-modify-macro}, a way | |
1410 | to create even more concise notations for modify macros. Note | |
1411 | again that @code{callf} is an extension to standard Common Lisp. | |
1412 | @end defspec | |
1413 | ||
1414 | @defspec callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{} | |
1415 | This macro is like @code{callf}, except that @var{place} is | |
1416 | the @emph{second} argument of @var{function} rather than the | |
1417 | first. For example, @code{(push @var{x} @var{place})} is | |
1418 | equivalent to @code{(callf2 cons @var{x} @var{place})}. | |
1419 | @end defspec | |
1420 | ||
1421 | The @code{callf} and @code{callf2} macros serve as building | |
1422 | blocks for other macros like @code{incf}, @code{pushnew}, and | |
1423 | @code{define-modify-macro}. The @code{letf} and @code{letf*} | |
1424 | macros are used in the processing of symbol macros; | |
1425 | @pxref{Macro Bindings}. | |
1426 | ||
1427 | @node Customizing Setf, , Modify Macros, Generalized Variables | |
1428 | @subsection Customizing Setf | |
1429 | ||
1430 | @noindent | |
1431 | Common Lisp defines three macros, @code{define-modify-macro}, | |
1432 | @code{defsetf}, and @code{define-setf-method}, that allow the | |
1433 | user to extend generalized variables in various ways. | |
1434 | ||
1435 | @defspec define-modify-macro name arglist function [doc-string] | |
1436 | This macro defines a ``read-modify-write'' macro similar to | |
1437 | @code{incf} and @code{decf}. The macro @var{name} is defined | |
1438 | to take a @var{place} argument followed by additional arguments | |
1439 | described by @var{arglist}. The call | |
1440 | ||
1441 | @example | |
1442 | (@var{name} @var{place} @var{args}...) | |
1443 | @end example | |
1444 | ||
1445 | @noindent | |
1446 | will be expanded to | |
1447 | ||
1448 | @example | |
1449 | (callf @var{func} @var{place} @var{args}...) | |
1450 | @end example | |
1451 | ||
1452 | @noindent | |
1453 | which in turn is roughly equivalent to | |
1454 | ||
1455 | @example | |
1456 | (setf @var{place} (@var{func} @var{place} @var{args}...)) | |
1457 | @end example | |
1458 | ||
1459 | For example: | |
1460 | ||
1461 | @example | |
1462 | (define-modify-macro incf (&optional (n 1)) +) | |
1463 | (define-modify-macro concatf (&rest args) concat) | |
1464 | @end example | |
1465 | ||
1466 | Note that @code{&key} is not allowed in @var{arglist}, but | |
1467 | @code{&rest} is sufficient to pass keywords on to the function. | |
1468 | ||
1469 | Most of the modify macros defined by Common Lisp do not exactly | |
1470 | follow the pattern of @code{define-modify-macro}. For example, | |
1471 | @code{push} takes its arguments in the wrong order, and @code{pop} | |
1472 | is completely irregular. You can define these macros ``by hand'' | |
1473 | using @code{get-setf-method}, or consult the source file | |
1474 | @file{cl-macs.el} to see how to use the internal @code{setf} | |
1475 | building blocks. | |
1476 | @end defspec | |
1477 | ||
1478 | @defspec defsetf access-fn update-fn | |
1479 | This is the simpler of two @code{defsetf} forms. Where | |
1480 | @var{access-fn} is the name of a function which accesses a place, | |
1481 | this declares @var{update-fn} to be the corresponding store | |
1482 | function. From now on, | |
1483 | ||
1484 | @example | |
1485 | (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value}) | |
1486 | @end example | |
1487 | ||
1488 | @noindent | |
1489 | will be expanded to | |
1490 | ||
1491 | @example | |
1492 | (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value}) | |
1493 | @end example | |
1494 | ||
1495 | @noindent | |
1496 | The @var{update-fn} is required to be either a true function, or | |
1497 | a macro which evaluates its arguments in a function-like way. Also, | |
1498 | the @var{update-fn} is expected to return @var{value} as its result. | |
1499 | Otherwise, the above expansion would not obey the rules for the way | |
1500 | @code{setf} is supposed to behave. | |
1501 | ||
1502 | As a special (non-Common-Lisp) extension, a third argument of @code{t} | |
1503 | to @code{defsetf} says that the @code{update-fn}'s return value is | |
1504 | not suitable, so that the above @code{setf} should be expanded to | |
1505 | something more like | |
1506 | ||
1507 | @example | |
1508 | (let ((temp @var{value})) | |
1509 | (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp) | |
1510 | temp) | |
1511 | @end example | |
1512 | ||
1513 | Some examples of the use of @code{defsetf}, drawn from the standard | |
1514 | suite of setf methods, are: | |
1515 | ||
1516 | @example | |
1517 | (defsetf car setcar) | |
1518 | (defsetf symbol-value set) | |
1519 | (defsetf buffer-name rename-buffer t) | |
1520 | @end example | |
1521 | @end defspec | |
1522 | ||
1523 | @defspec defsetf access-fn arglist (store-var) forms@dots{} | |
1524 | This is the second, more complex, form of @code{defsetf}. It is | |
1525 | rather like @code{defmacro} except for the additional @var{store-var} | |
1526 | argument. The @var{forms} should return a Lisp form which stores | |
1527 | the value of @var{store-var} into the generalized variable formed | |
1528 | by a call to @var{access-fn} with arguments described by @var{arglist}. | |
1529 | The @var{forms} may begin with a string which documents the @code{setf} | |
1530 | method (analogous to the doc string that appears at the front of a | |
1531 | function). | |
1532 | ||
1533 | For example, the simple form of @code{defsetf} is shorthand for | |
1534 | ||
1535 | @example | |
1536 | (defsetf @var{access-fn} (&rest args) (store) | |
1537 | (append '(@var{update-fn}) args (list store))) | |
1538 | @end example | |
1539 | ||
1540 | The Lisp form that is returned can access the arguments from | |
1541 | @var{arglist} and @var{store-var} in an unrestricted fashion; | |
1542 | macros like @code{setf} and @code{incf} which invoke this | |
1543 | setf-method will insert temporary variables as needed to make | |
1544 | sure the apparent order of evaluation is preserved. | |
1545 | ||
1546 | Another example drawn from the standard package: | |
1547 | ||
1548 | @example | |
1549 | (defsetf nth (n x) (store) | |
1550 | (list 'setcar (list 'nthcdr n x) store)) | |
1551 | @end example | |
1552 | @end defspec | |
1553 | ||
1554 | @defspec define-setf-method access-fn arglist forms@dots{} | |
1555 | This is the most general way to create new place forms. When | |
1556 | a @code{setf} to @var{access-fn} with arguments described by | |
1557 | @var{arglist} is expanded, the @var{forms} are evaluated and | |
1558 | must return a list of five items: | |
1559 | ||
1560 | @enumerate | |
1561 | @item | |
1562 | A list of @dfn{temporary variables}. | |
1563 | ||
1564 | @item | |
1565 | A list of @dfn{value forms} corresponding to the temporary variables | |
1566 | above. The temporary variables will be bound to these value forms | |
1567 | as the first step of any operation on the generalized variable. | |
1568 | ||
1569 | @item | |
1570 | A list of exactly one @dfn{store variable} (generally obtained | |
1571 | from a call to @code{gensym}). | |
1572 | ||
1573 | @item | |
1574 | A Lisp form which stores the contents of the store variable into | |
1575 | the generalized variable, assuming the temporaries have been | |
1576 | bound as described above. | |
1577 | ||
1578 | @item | |
1579 | A Lisp form which accesses the contents of the generalized variable, | |
1580 | assuming the temporaries have been bound. | |
1581 | @end enumerate | |
1582 | ||
1583 | This is exactly like the Common Lisp macro of the same name, | |
1584 | except that the method returns a list of five values rather | |
1585 | than the five values themselves, since Emacs Lisp does not | |
1586 | support Common Lisp's notion of multiple return values. | |
1587 | ||
1588 | Once again, the @var{forms} may begin with a documentation string. | |
1589 | ||
1590 | A setf-method should be maximally conservative with regard to | |
1591 | temporary variables. In the setf-methods generated by | |
1592 | @code{defsetf}, the second return value is simply the list of | |
1593 | arguments in the place form, and the first return value is a | |
1594 | list of a corresponding number of temporary variables generated | |
1595 | by @code{gensym}. Macros like @code{setf} and @code{incf} which | |
1596 | use this setf-method will optimize away most temporaries that | |
1597 | turn out to be unnecessary, so there is little reason for the | |
1598 | setf-method itself to optimize. | |
1599 | @end defspec | |
1600 | ||
1601 | @defun get-setf-method place &optional env | |
1602 | This function returns the setf-method for @var{place}, by | |
1603 | invoking the definition previously recorded by @code{defsetf} | |
1604 | or @code{define-setf-method}. The result is a list of five | |
1605 | values as described above. You can use this function to build | |
1606 | your own @code{incf}-like modify macros. (Actually, it is | |
1607 | better to use the internal functions @code{cl-setf-do-modify} | |
1608 | and @code{cl-setf-do-store}, which are a bit easier to use and | |
1609 | which also do a number of optimizations; consult the source | |
1610 | code for the @code{incf} function for a simple example.) | |
1611 | ||
1612 | The argument @var{env} specifies the ``environment'' to be | |
1613 | passed on to @code{macroexpand} if @code{get-setf-method} should | |
1614 | need to expand a macro in @var{place}. It should come from | |
1615 | an @code{&environment} argument to the macro or setf-method | |
1616 | that called @code{get-setf-method}. | |
1617 | ||
1618 | See also the source code for the setf-methods for @code{apply} | |
1619 | and @code{substring}, each of which works by calling | |
1620 | @code{get-setf-method} on a simpler case, then massaging | |
1621 | the result in various ways. | |
1622 | @end defun | |
1623 | ||
1624 | Modern Common Lisp defines a second, independent way to specify | |
1625 | the @code{setf} behavior of a function, namely ``@code{setf} | |
1626 | functions'' whose names are lists @code{(setf @var{name})} | |
1627 | rather than symbols. For example, @code{(defun (setf foo) @dots{})} | |
1628 | defines the function that is used when @code{setf} is applied to | |
1629 | @code{foo}. This package does not currently support @code{setf} | |
1630 | functions. In particular, it is a compile-time error to use | |
1631 | @code{setf} on a form which has not already been @code{defsetf}'d | |
1632 | or otherwise declared; in newer Common Lisps, this would not be | |
1633 | an error since the function @code{(setf @var{func})} might be | |
1634 | defined later. | |
1635 | ||
1636 | @iftex | |
1637 | @secno=4 | |
1638 | @end iftex | |
1639 | ||
1640 | @node Variable Bindings, Conditionals, Generalized Variables, Control Structure | |
1641 | @section Variable Bindings | |
1642 | ||
1643 | @noindent | |
1644 | These Lisp forms make bindings to variables and function names, | |
1645 | analogous to Lisp's built-in @code{let} form. | |
1646 | ||
1647 | @xref{Modify Macros}, for the @code{letf} and @code{letf*} forms which | |
1648 | are also related to variable bindings. | |
1649 | ||
1650 | @menu | |
1651 | * Dynamic Bindings:: The `progv' form | |
1652 | * Lexical Bindings:: `lexical-let' and lexical closures | |
1653 | * Function Bindings:: `flet' and `labels' | |
1654 | * Macro Bindings:: `macrolet' and `symbol-macrolet' | |
1655 | @end menu | |
1656 | ||
1657 | @node Dynamic Bindings, Lexical Bindings, Variable Bindings, Variable Bindings | |
1658 | @subsection Dynamic Bindings | |
1659 | ||
1660 | @noindent | |
1661 | The standard @code{let} form binds variables whose names are known | |
1662 | at compile-time. The @code{progv} form provides an easy way to | |
1663 | bind variables whose names are computed at run-time. | |
1664 | ||
1665 | @defspec progv symbols values forms@dots{} | |
1666 | This form establishes @code{let}-style variable bindings on a | |
1667 | set of variables computed at run-time. The expressions | |
1668 | @var{symbols} and @var{values} are evaluated, and must return lists | |
1669 | of symbols and values, respectively. The symbols are bound to the | |
1670 | corresponding values for the duration of the body @var{form}s. | |
1671 | If @var{values} is shorter than @var{symbols}, the last few symbols | |
1672 | are made unbound (as if by @code{makunbound}) inside the body. | |
1673 | If @var{symbols} is shorter than @var{values}, the excess values | |
1674 | are ignored. | |
1675 | @end defspec | |
1676 | ||
1677 | @node Lexical Bindings, Function Bindings, Dynamic Bindings, Variable Bindings | |
1678 | @subsection Lexical Bindings | |
1679 | ||
1680 | @noindent | |
1681 | The @dfn{CL} package defines the following macro which | |
1682 | more closely follows the Common Lisp @code{let} form: | |
1683 | ||
1684 | @defspec lexical-let (bindings@dots{}) forms@dots{} | |
1685 | This form is exactly like @code{let} except that the bindings it | |
1686 | establishes are purely lexical. Lexical bindings are similar to | |
1687 | local variables in a language like C: Only the code physically | |
1688 | within the body of the @code{lexical-let} (after macro expansion) | |
1689 | may refer to the bound variables. | |
1690 | ||
1691 | @example | |
1692 | (setq a 5) | |
1693 | (defun foo (b) (+ a b)) | |
1694 | (let ((a 2)) (foo a)) | |
1695 | @result{} 4 | |
1696 | (lexical-let ((a 2)) (foo a)) | |
1697 | @result{} 7 | |
1698 | @end example | |
1699 | ||
1700 | @noindent | |
1701 | In this example, a regular @code{let} binding of @code{a} actually | |
1702 | makes a temporary change to the global variable @code{a}, so @code{foo} | |
1703 | is able to see the binding of @code{a} to 2. But @code{lexical-let} | |
1704 | actually creates a distinct local variable @code{a} for use within its | |
1705 | body, without any effect on the global variable of the same name. | |
1706 | ||
1707 | The most important use of lexical bindings is to create @dfn{closures}. | |
1708 | A closure is a function object that refers to an outside lexical | |
1709 | variable. For example: | |
1710 | ||
1711 | @example | |
1712 | (defun make-adder (n) | |
1713 | (lexical-let ((n n)) | |
1714 | (function (lambda (m) (+ n m))))) | |
1715 | (setq add17 (make-adder 17)) | |
1716 | (funcall add17 4) | |
1717 | @result{} 21 | |
1718 | @end example | |
1719 | ||
1720 | @noindent | |
1721 | The call @code{(make-adder 17)} returns a function object which adds | |
1722 | 17 to its argument. If @code{let} had been used instead of | |
1723 | @code{lexical-let}, the function object would have referred to the | |
1724 | global @code{n}, which would have been bound to 17 only during the | |
1725 | call to @code{make-adder} itself. | |
1726 | ||
1727 | @example | |
1728 | (defun make-counter () | |
1729 | (lexical-let ((n 0)) | |
1730 | (function* (lambda (&optional (m 1)) (incf n m))))) | |
1731 | (setq count-1 (make-counter)) | |
1732 | (funcall count-1 3) | |
1733 | @result{} 3 | |
1734 | (funcall count-1 14) | |
1735 | @result{} 17 | |
1736 | (setq count-2 (make-counter)) | |
1737 | (funcall count-2 5) | |
1738 | @result{} 5 | |
1739 | (funcall count-1 2) | |
1740 | @result{} 19 | |
1741 | (funcall count-2) | |
1742 | @result{} 6 | |
1743 | @end example | |
1744 | ||
1745 | @noindent | |
1746 | Here we see that each call to @code{make-counter} creates a distinct | |
1747 | local variable @code{n}, which serves as a private counter for the | |
1748 | function object that is returned. | |
1749 | ||
1750 | Closed-over lexical variables persist until the last reference to | |
1751 | them goes away, just like all other Lisp objects. For example, | |
1752 | @code{count-2} refers to a function object which refers to an | |
1753 | instance of the variable @code{n}; this is the only reference | |
1754 | to that variable, so after @code{(setq count-2 nil)} the garbage | |
1755 | collector would be able to delete this instance of @code{n}. | |
1756 | Of course, if a @code{lexical-let} does not actually create any | |
1757 | closures, then the lexical variables are free as soon as the | |
1758 | @code{lexical-let} returns. | |
1759 | ||
1760 | Many closures are used only during the extent of the bindings they | |
1761 | refer to; these are known as ``downward funargs'' in Lisp parlance. | |
1762 | When a closure is used in this way, regular Emacs Lisp dynamic | |
1763 | bindings suffice and will be more efficient than @code{lexical-let} | |
1764 | closures: | |
1765 | ||
1766 | @example | |
1767 | (defun add-to-list (x list) | |
1768 | (mapcar (function (lambda (y) (+ x y))) list)) | |
1769 | (add-to-list 7 '(1 2 5)) | |
1770 | @result{} (8 9 12) | |
1771 | @end example | |
1772 | ||
1773 | @noindent | |
1774 | Since this lambda is only used while @code{x} is still bound, | |
1775 | it is not necessary to make a true closure out of it. | |
1776 | ||
1777 | You can use @code{defun} or @code{flet} inside a @code{lexical-let} | |
1778 | to create a named closure. If several closures are created in the | |
1779 | body of a single @code{lexical-let}, they all close over the same | |
1780 | instance of the lexical variable. | |
1781 | ||
1782 | The @code{lexical-let} form is an extension to Common Lisp. In | |
1783 | true Common Lisp, all bindings are lexical unless declared otherwise. | |
1784 | @end defspec | |
1785 | ||
1786 | @defspec lexical-let* (bindings@dots{}) forms@dots{} | |
1787 | This form is just like @code{lexical-let}, except that the bindings | |
1788 | are made sequentially in the manner of @code{let*}. | |
1789 | @end defspec | |
1790 | ||
1791 | @node Function Bindings, Macro Bindings, Lexical Bindings, Variable Bindings | |
1792 | @subsection Function Bindings | |
1793 | ||
1794 | @noindent | |
1795 | These forms make @code{let}-like bindings to functions instead | |
1796 | of variables. | |
1797 | ||
1798 | @defspec flet (bindings@dots{}) forms@dots{} | |
1799 | This form establishes @code{let}-style bindings on the function | |
1800 | cells of symbols rather than on the value cells. Each @var{binding} | |
1801 | must be a list of the form @samp{(@var{name} @var{arglist} | |
1802 | @var{forms}@dots{})}, which defines a function exactly as if | |
1803 | it were a @code{defun*} form. The function @var{name} is defined | |
1804 | accordingly for the duration of the body of the @code{flet}; then | |
1805 | the old function definition, or lack thereof, is restored. | |
1806 | ||
1807 | While @code{flet} in Common Lisp establishes a lexical binding of | |
1808 | @var{name}, Emacs Lisp @code{flet} makes a dynamic binding. The | |
1809 | result is that @code{flet} affects indirect calls to a function as | |
1810 | well as calls directly inside the @code{flet} form itself. | |
1811 | ||
1812 | You can use @code{flet} to disable or modify the behavior of a | |
1813 | function in a temporary fashion. This will even work on Emacs | |
1814 | primitives, although note that some calls to primitive functions | |
1815 | internal to Emacs are made without going through the symbol's | |
1816 | function cell, and so will not be affected by @code{flet}. For | |
1817 | example, | |
1818 | ||
1819 | @example | |
1820 | (flet ((message (&rest args) (push args saved-msgs))) | |
1821 | (do-something)) | |
1822 | @end example | |
1823 | ||
1824 | This code attempts to replace the built-in function @code{message} | |
1825 | with a function that simply saves the messages in a list rather | |
1826 | than displaying them. The original definition of @code{message} | |
1827 | will be restored after @code{do-something} exits. This code will | |
1828 | work fine on messages generated by other Lisp code, but messages | |
1829 | generated directly inside Emacs will not be caught since they make | |
1830 | direct C-language calls to the message routines rather than going | |
1831 | through the Lisp @code{message} function. | |
1832 | ||
1833 | Functions defined by @code{flet} may use the full Common Lisp | |
1834 | argument notation supported by @code{defun*}; also, the function | |
1835 | body is enclosed in an implicit block as if by @code{defun*}. | |
1836 | @xref{Program Structure}. | |
1837 | @end defspec | |
1838 | ||
1839 | @defspec labels (bindings@dots{}) forms@dots{} | |
1840 | The @code{labels} form is like @code{flet}, except that it | |
1841 | makes lexical bindings of the function names rather than | |
1842 | dynamic bindings. (In true Common Lisp, both @code{flet} and | |
1843 | @code{labels} make lexical bindings of slightly different sorts; | |
1844 | since Emacs Lisp is dynamically bound by default, it seemed | |
1845 | more appropriate for @code{flet} also to use dynamic binding. | |
1846 | The @code{labels} form, with its lexical binding, is fully | |
1847 | compatible with Common Lisp.) | |
1848 | ||
1849 | Lexical scoping means that all references to the named | |
1850 | functions must appear physically within the body of the | |
1851 | @code{labels} form. References may appear both in the body | |
1852 | @var{forms} of @code{labels} itself, and in the bodies of | |
1853 | the functions themselves. Thus, @code{labels} can define | |
1854 | local recursive functions, or mutually-recursive sets of | |
1855 | functions. | |
1856 | ||
1857 | A ``reference'' to a function name is either a call to that | |
1858 | function, or a use of its name quoted by @code{quote} or | |
1859 | @code{function} to be passed on to, say, @code{mapcar}. | |
1860 | @end defspec | |
1861 | ||
1862 | @node Macro Bindings, , Function Bindings, Variable Bindings | |
1863 | @subsection Macro Bindings | |
1864 | ||
1865 | @noindent | |
1866 | These forms create local macros and ``symbol macros.'' | |
1867 | ||
1868 | @defspec macrolet (bindings@dots{}) forms@dots{} | |
1869 | This form is analogous to @code{flet}, but for macros instead of | |
1870 | functions. Each @var{binding} is a list of the same form as the | |
1871 | arguments to @code{defmacro*} (i.e., a macro name, argument list, | |
1872 | and macro-expander forms). The macro is defined accordingly for | |
1873 | use within the body of the @code{macrolet}. | |
1874 | ||
1875 | Because of the nature of macros, @code{macrolet} is lexically | |
1876 | scoped even in Emacs Lisp: The @code{macrolet} binding will | |
1877 | affect only calls that appear physically within the body | |
1878 | @var{forms}, possibly after expansion of other macros in the | |
1879 | body. | |
1880 | @end defspec | |
1881 | ||
1882 | @defspec symbol-macrolet (bindings@dots{}) forms@dots{} | |
1883 | This form creates @dfn{symbol macros}, which are macros that look | |
1884 | like variable references rather than function calls. Each | |
1885 | @var{binding} is a list @samp{(@var{var} @var{expansion})}; | |
1886 | any reference to @var{var} within the body @var{forms} is | |
1887 | replaced by @var{expansion}. | |
1888 | ||
1889 | @example | |
1890 | (setq bar '(5 . 9)) | |
1891 | (symbol-macrolet ((foo (car bar))) | |
1892 | (incf foo)) | |
1893 | bar | |
1894 | @result{} (6 . 9) | |
1895 | @end example | |
1896 | ||
1897 | A @code{setq} of a symbol macro is treated the same as a @code{setf}. | |
1898 | I.e., @code{(setq foo 4)} in the above would be equivalent to | |
1899 | @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}. | |
1900 | ||
1901 | Likewise, a @code{let} or @code{let*} binding a symbol macro is | |
1902 | treated like a @code{letf} or @code{letf*}. This differs from true | |
1903 | Common Lisp, where the rules of lexical scoping cause a @code{let} | |
1904 | binding to shadow a @code{symbol-macrolet} binding. In this package, | |
1905 | only @code{lexical-let} and @code{lexical-let*} will shadow a symbol | |
1906 | macro. | |
1907 | ||
1908 | There is no analogue of @code{defmacro} for symbol macros; all symbol | |
1909 | macros are local. A typical use of @code{symbol-macrolet} is in the | |
1910 | expansion of another macro: | |
1911 | ||
1912 | @example | |
1913 | (defmacro* my-dolist ((x list) &rest body) | |
1914 | (let ((var (gensym))) | |
1915 | (list 'loop 'for var 'on list 'do | |
1916 | (list* 'symbol-macrolet (list (list x (list 'car var))) | |
1917 | body)))) | |
1918 | ||
1919 | (setq mylist '(1 2 3 4)) | |
1920 | (my-dolist (x mylist) (incf x)) | |
1921 | mylist | |
1922 | @result{} (2 3 4 5) | |
1923 | @end example | |
1924 | ||
1925 | @noindent | |
1926 | In this example, the @code{my-dolist} macro is similar to @code{dolist} | |
2995b042 | 1927 | (@pxref{Iteration}) except that the variable @code{x} becomes a true |
6bf7aab6 DL |
1928 | reference onto the elements of the list. The @code{my-dolist} call |
1929 | shown here expands to | |
1930 | ||
1931 | @example | |
1932 | (loop for G1234 on mylist do | |
1933 | (symbol-macrolet ((x (car G1234))) | |
1934 | (incf x))) | |
1935 | @end example | |
1936 | ||
1937 | @noindent | |
1938 | which in turn expands to | |
1939 | ||
1940 | @example | |
1941 | (loop for G1234 on mylist do (incf (car G1234))) | |
1942 | @end example | |
1943 | ||
1944 | @xref{Loop Facility}, for a description of the @code{loop} macro. | |
1945 | This package defines a nonstandard @code{in-ref} loop clause that | |
1946 | works much like @code{my-dolist}. | |
1947 | @end defspec | |
1948 | ||
1949 | @node Conditionals, Blocks and Exits, Variable Bindings, Control Structure | |
1950 | @section Conditionals | |
1951 | ||
1952 | @noindent | |
1953 | These conditional forms augment Emacs Lisp's simple @code{if}, | |
1954 | @code{and}, @code{or}, and @code{cond} forms. | |
1955 | ||
1956 | @defspec case keyform clause@dots{} | |
1957 | This macro evaluates @var{keyform}, then compares it with the key | |
1958 | values listed in the various @var{clause}s. Whichever clause matches | |
1959 | the key is executed; comparison is done by @code{eql}. If no clause | |
1960 | matches, the @code{case} form returns @code{nil}. The clauses are | |
1961 | of the form | |
1962 | ||
1963 | @example | |
1964 | (@var{keylist} @var{body-forms}@dots{}) | |
1965 | @end example | |
1966 | ||
1967 | @noindent | |
1968 | where @var{keylist} is a list of key values. If there is exactly | |
1969 | one value, and it is not a cons cell or the symbol @code{nil} or | |
1970 | @code{t}, then it can be used by itself as a @var{keylist} without | |
1971 | being enclosed in a list. All key values in the @code{case} form | |
1972 | must be distinct. The final clauses may use @code{t} in place of | |
1973 | a @var{keylist} to indicate a default clause that should be taken | |
1974 | if none of the other clauses match. (The symbol @code{otherwise} | |
1975 | is also recognized in place of @code{t}. To make a clause that | |
1976 | matches the actual symbol @code{t}, @code{nil}, or @code{otherwise}, | |
1977 | enclose the symbol in a list.) | |
1978 | ||
1979 | For example, this expression reads a keystroke, then does one of | |
1980 | four things depending on whether it is an @samp{a}, a @samp{b}, | |
1981 | a @key{RET} or @kbd{C-j}, or anything else. | |
1982 | ||
1983 | @example | |
1984 | (case (read-char) | |
1985 | (?a (do-a-thing)) | |
1986 | (?b (do-b-thing)) | |
1987 | ((?\r ?\n) (do-ret-thing)) | |
1988 | (t (do-other-thing))) | |
1989 | @end example | |
1990 | @end defspec | |
1991 | ||
1992 | @defspec ecase keyform clause@dots{} | |
1993 | This macro is just like @code{case}, except that if the key does | |
1994 | not match any of the clauses, an error is signaled rather than | |
1995 | simply returning @code{nil}. | |
1996 | @end defspec | |
1997 | ||
1998 | @defspec typecase keyform clause@dots{} | |
1999 | This macro is a version of @code{case} that checks for types | |
2000 | rather than values. Each @var{clause} is of the form | |
2001 | @samp{(@var{type} @var{body}...)}. @xref{Type Predicates}, | |
2002 | for a description of type specifiers. For example, | |
2003 | ||
2004 | @example | |
2005 | (typecase x | |
2006 | (integer (munch-integer x)) | |
2007 | (float (munch-float x)) | |
2008 | (string (munch-integer (string-to-int x))) | |
2009 | (t (munch-anything x))) | |
2010 | @end example | |
2011 | ||
2012 | The type specifier @code{t} matches any type of object; the word | |
2013 | @code{otherwise} is also allowed. To make one clause match any of | |
2014 | several types, use an @code{(or ...)} type specifier. | |
2015 | @end defspec | |
2016 | ||
2017 | @defspec etypecase keyform clause@dots{} | |
2018 | This macro is just like @code{typecase}, except that if the key does | |
2019 | not match any of the clauses, an error is signaled rather than | |
2020 | simply returning @code{nil}. | |
2021 | @end defspec | |
2022 | ||
2023 | @node Blocks and Exits, Iteration, Conditionals, Control Structure | |
2024 | @section Blocks and Exits | |
2025 | ||
2026 | @noindent | |
2027 | Common Lisp @dfn{blocks} provide a non-local exit mechanism very | |
2028 | similar to @code{catch} and @code{throw}, but lexically rather than | |
2029 | dynamically scoped. This package actually implements @code{block} | |
2030 | in terms of @code{catch}; however, the lexical scoping allows the | |
2031 | optimizing byte-compiler to omit the costly @code{catch} step if the | |
2032 | body of the block does not actually @code{return-from} the block. | |
2033 | ||
2034 | @defspec block name forms@dots{} | |
2035 | The @var{forms} are evaluated as if by a @code{progn}. However, | |
2036 | if any of the @var{forms} execute @code{(return-from @var{name})}, | |
2037 | they will jump out and return directly from the @code{block} form. | |
2038 | The @code{block} returns the result of the last @var{form} unless | |
2039 | a @code{return-from} occurs. | |
2040 | ||
2041 | The @code{block}/@code{return-from} mechanism is quite similar to | |
2042 | the @code{catch}/@code{throw} mechanism. The main differences are | |
2043 | that block @var{name}s are unevaluated symbols, rather than forms | |
2044 | (such as quoted symbols) which evaluate to a tag at run-time; and | |
2045 | also that blocks are lexically scoped whereas @code{catch}/@code{throw} | |
2046 | are dynamically scoped. This means that functions called from the | |
2047 | body of a @code{catch} can also @code{throw} to the @code{catch}, | |
2048 | but the @code{return-from} referring to a block name must appear | |
2049 | physically within the @var{forms} that make up the body of the block. | |
2050 | They may not appear within other called functions, although they may | |
2051 | appear within macro expansions or @code{lambda}s in the body. Block | |
2052 | names and @code{catch} names form independent name-spaces. | |
2053 | ||
2054 | In true Common Lisp, @code{defun} and @code{defmacro} surround | |
2055 | the function or expander bodies with implicit blocks with the | |
2056 | same name as the function or macro. This does not occur in Emacs | |
2057 | Lisp, but this package provides @code{defun*} and @code{defmacro*} | |
2058 | forms which do create the implicit block. | |
2059 | ||
2060 | The Common Lisp looping constructs defined by this package, | |
2995b042 | 2061 | such as @code{loop} and @code{dolist}, also create implicit blocks |
6bf7aab6 DL |
2062 | just as in Common Lisp. |
2063 | ||
2064 | Because they are implemented in terms of Emacs Lisp @code{catch} | |
2065 | and @code{throw}, blocks have the same overhead as actual | |
2066 | @code{catch} constructs (roughly two function calls). However, | |
2067 | Zawinski and Furuseth's optimizing byte compiler (standard in | |
2068 | Emacs 19) will optimize away the @code{catch} if the block does | |
2069 | not in fact contain any @code{return} or @code{return-from} calls | |
2070 | that jump to it. This means that @code{do} loops and @code{defun*} | |
2071 | functions which don't use @code{return} don't pay the overhead to | |
2072 | support it. | |
2073 | @end defspec | |
2074 | ||
2075 | @defspec return-from name [result] | |
2076 | This macro returns from the block named @var{name}, which must be | |
2077 | an (unevaluated) symbol. If a @var{result} form is specified, it | |
2078 | is evaluated to produce the result returned from the @code{block}. | |
2079 | Otherwise, @code{nil} is returned. | |
2080 | @end defspec | |
2081 | ||
2082 | @defspec return [result] | |
2083 | This macro is exactly like @code{(return-from nil @var{result})}. | |
2995b042 | 2084 | Common Lisp loops like @code{do} and @code{dolist} implicitly enclose |
6bf7aab6 DL |
2085 | themselves in @code{nil} blocks. |
2086 | @end defspec | |
2087 | ||
2088 | @node Iteration, Loop Facility, Blocks and Exits, Control Structure | |
2089 | @section Iteration | |
2090 | ||
2091 | @noindent | |
2092 | The macros described here provide more sophisticated, high-level | |
2093 | looping constructs to complement Emacs Lisp's basic @code{while} | |
2094 | loop. | |
2095 | ||
2096 | @defspec loop forms@dots{} | |
2097 | The @dfn{CL} package supports both the simple, old-style meaning of | |
2098 | @code{loop} and the extremely powerful and flexible feature known as | |
2099 | the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced | |
2100 | facility is discussed in the following section; @pxref{Loop Facility}. | |
2101 | The simple form of @code{loop} is described here. | |
2102 | ||
2103 | If @code{loop} is followed by zero or more Lisp expressions, | |
2104 | then @code{(loop @var{exprs}@dots{})} simply creates an infinite | |
2105 | loop executing the expressions over and over. The loop is | |
2106 | enclosed in an implicit @code{nil} block. Thus, | |
2107 | ||
2108 | @example | |
2109 | (loop (foo) (if (no-more) (return 72)) (bar)) | |
2110 | @end example | |
2111 | ||
2112 | @noindent | |
2113 | is exactly equivalent to | |
2114 | ||
2115 | @example | |
2116 | (block nil (while t (foo) (if (no-more) (return 72)) (bar))) | |
2117 | @end example | |
2118 | ||
2119 | If any of the expressions are plain symbols, the loop is instead | |
2120 | interpreted as a Loop Macro specification as described later. | |
2121 | (This is not a restriction in practice, since a plain symbol | |
2122 | in the above notation would simply access and throw away the | |
2123 | value of a variable.) | |
2124 | @end defspec | |
2125 | ||
2126 | @defspec do (spec@dots{}) (end-test [result@dots{}]) forms@dots{} | |
2127 | This macro creates a general iterative loop. Each @var{spec} is | |
2128 | of the form | |
2129 | ||
2130 | @example | |
2131 | (@var{var} [@var{init} [@var{step}]]) | |
2132 | @end example | |
2133 | ||
2134 | The loop works as follows: First, each @var{var} is bound to the | |
2135 | associated @var{init} value as if by a @code{let} form. Then, in | |
2136 | each iteration of the loop, the @var{end-test} is evaluated; if | |
2137 | true, the loop is finished. Otherwise, the body @var{forms} are | |
2138 | evaluated, then each @var{var} is set to the associated @var{step} | |
2139 | expression (as if by a @code{psetq} form) and the next iteration | |
2140 | begins. Once the @var{end-test} becomes true, the @var{result} | |
2141 | forms are evaluated (with the @var{var}s still bound to their | |
2142 | values) to produce the result returned by @code{do}. | |
2143 | ||
2144 | The entire @code{do} loop is enclosed in an implicit @code{nil} | |
2145 | block, so that you can use @code{(return)} to break out of the | |
2146 | loop at any time. | |
2147 | ||
2148 | If there are no @var{result} forms, the loop returns @code{nil}. | |
2149 | If a given @var{var} has no @var{step} form, it is bound to its | |
2150 | @var{init} value but not otherwise modified during the @code{do} | |
2151 | loop (unless the code explicitly modifies it); this case is just | |
2152 | a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})} | |
2153 | around the loop. If @var{init} is also omitted it defaults to | |
2154 | @code{nil}, and in this case a plain @samp{@var{var}} can be used | |
2155 | in place of @samp{(@var{var})}, again following the analogy with | |
2156 | @code{let}. | |
2157 | ||
2158 | This example (from Steele) illustrates a loop which applies the | |
2159 | function @code{f} to successive pairs of values from the lists | |
2160 | @code{foo} and @code{bar}; it is equivalent to the call | |
2161 | @code{(mapcar* 'f foo bar)}. Note that this loop has no body | |
2162 | @var{forms} at all, performing all its work as side effects of | |
2163 | the rest of the loop. | |
2164 | ||
2165 | @example | |
2166 | (do ((x foo (cdr x)) | |
2167 | (y bar (cdr y)) | |
2168 | (z nil (cons (f (car x) (car y)) z))) | |
2169 | ((or (null x) (null y)) | |
2170 | (nreverse z))) | |
2171 | @end example | |
2172 | @end defspec | |
2173 | ||
2174 | @defspec do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{} | |
2175 | This is to @code{do} what @code{let*} is to @code{let}. In | |
2176 | particular, the initial values are bound as if by @code{let*} | |
2177 | rather than @code{let}, and the steps are assigned as if by | |
2178 | @code{setq} rather than @code{psetq}. | |
2179 | ||
2180 | Here is another way to write the above loop: | |
2181 | ||
2182 | @example | |
2183 | (do* ((xp foo (cdr xp)) | |
2184 | (yp bar (cdr yp)) | |
2185 | (x (car xp) (car xp)) | |
2186 | (y (car yp) (car yp)) | |
2187 | z) | |
2188 | ((or (null xp) (null yp)) | |
2189 | (nreverse z)) | |
2190 | (push (f x y) z)) | |
2191 | @end example | |
2192 | @end defspec | |
2193 | ||
2995b042 DL |
2194 | @defspec dolist (var list [result]) forms@dots{} |
2195 | This is a more specialized loop which iterates across the elements | |
2196 | of a list. @var{list} should evaluate to a list; the body @var{forms} | |
2197 | are executed with @var{var} bound to each element of the list in | |
2198 | turn. Finally, the @var{result} form (or @code{nil}) is evaluated | |
2199 | with @var{var} bound to @code{nil} to produce the result returned by | |
2200 | the loop. Unlike with Emacs's built in @code{dolist}, the loop is | |
2201 | surrounded by an implicit @code{nil} block. | |
2202 | @end defspec | |
2203 | ||
2204 | @defspec dotimes (var count [result]) forms@dots{} | |
2205 | This is a more specialized loop which iterates a specified number | |
2206 | of times. The body is executed with @var{var} bound to the integers | |
2207 | from zero (inclusive) to @var{count} (exclusive), in turn. Then | |
2208 | the @code{result} form is evaluated with @var{var} bound to the total | |
2209 | number of iterations that were done (i.e., @code{(max 0 @var{count})}) | |
2210 | to get the return value for the loop form. Unlike with Emacs's built in | |
2211 | @code{dolist}, the loop is surrounded by an implicit @code{nil} block. | |
2212 | @end defspec | |
2213 | ||
6bf7aab6 DL |
2214 | @defspec do-symbols (var [obarray [result]]) forms@dots{} |
2215 | This loop iterates over all interned symbols. If @var{obarray} | |
2216 | is specified and is not @code{nil}, it loops over all symbols in | |
2217 | that obarray. For each symbol, the body @var{forms} are evaluated | |
2218 | with @var{var} bound to that symbol. The symbols are visited in | |
2219 | an unspecified order. Afterward the @var{result} form, if any, | |
2220 | is evaluated (with @var{var} bound to @code{nil}) to get the return | |
2221 | value. The loop is surrounded by an implicit @code{nil} block. | |
2222 | @end defspec | |
2223 | ||
2224 | @defspec do-all-symbols (var [result]) forms@dots{} | |
2225 | This is identical to @code{do-symbols} except that the @var{obarray} | |
2226 | argument is omitted; it always iterates over the default obarray. | |
2227 | @end defspec | |
2228 | ||
2229 | @xref{Mapping over Sequences}, for some more functions for | |
2230 | iterating over vectors or lists. | |
2231 | ||
2232 | @node Loop Facility, Multiple Values, Iteration, Control Structure | |
2233 | @section Loop Facility | |
2234 | ||
2235 | @noindent | |
2236 | A common complaint with Lisp's traditional looping constructs is | |
2237 | that they are either too simple and limited, such as Common Lisp's | |
2238 | @code{dotimes} or Emacs Lisp's @code{while}, or too unreadable and | |
2239 | obscure, like Common Lisp's @code{do} loop. | |
2240 | ||
2241 | To remedy this, recent versions of Common Lisp have added a new | |
2242 | construct called the ``Loop Facility'' or ``@code{loop} macro,'' | |
2243 | with an easy-to-use but very powerful and expressive syntax. | |
2244 | ||
2245 | @menu | |
2246 | * Loop Basics:: `loop' macro, basic clause structure | |
2247 | * Loop Examples:: Working examples of `loop' macro | |
2248 | * For Clauses:: Clauses introduced by `for' or `as' | |
2249 | * Iteration Clauses:: `repeat', `while', `thereis', etc. | |
2250 | * Accumulation Clauses:: `collect', `sum', `maximize', etc. | |
2251 | * Other Clauses:: `with', `if', `initially', `finally' | |
2252 | @end menu | |
2253 | ||
2254 | @node Loop Basics, Loop Examples, Loop Facility, Loop Facility | |
2255 | @subsection Loop Basics | |
2256 | ||
2257 | @noindent | |
2258 | The @code{loop} macro essentially creates a mini-language within | |
2259 | Lisp that is specially tailored for describing loops. While this | |
2260 | language is a little strange-looking by the standards of regular Lisp, | |
2261 | it turns out to be very easy to learn and well-suited to its purpose. | |
2262 | ||
2263 | Since @code{loop} is a macro, all parsing of the loop language | |
2264 | takes place at byte-compile time; compiled @code{loop}s are just | |
2265 | as efficient as the equivalent @code{while} loops written longhand. | |
2266 | ||
2267 | @defspec loop clauses@dots{} | |
2268 | A loop construct consists of a series of @var{clause}s, each | |
2269 | introduced by a symbol like @code{for} or @code{do}. Clauses | |
2270 | are simply strung together in the argument list of @code{loop}, | |
2271 | with minimal extra parentheses. The various types of clauses | |
2272 | specify initializations, such as the binding of temporary | |
2273 | variables, actions to be taken in the loop, stepping actions, | |
2274 | and final cleanup. | |
2275 | ||
2276 | Common Lisp specifies a certain general order of clauses in a | |
2277 | loop: | |
2278 | ||
2279 | @example | |
2280 | (loop @var{name-clause} | |
2281 | @var{var-clauses}@dots{} | |
2282 | @var{action-clauses}@dots{}) | |
2283 | @end example | |
2284 | ||
2285 | The @var{name-clause} optionally gives a name to the implicit | |
2286 | block that surrounds the loop. By default, the implicit block | |
2287 | is named @code{nil}. The @var{var-clauses} specify what | |
2288 | variables should be bound during the loop, and how they should | |
2289 | be modified or iterated throughout the course of the loop. The | |
2290 | @var{action-clauses} are things to be done during the loop, such | |
2291 | as computing, collecting, and returning values. | |
2292 | ||
2293 | The Emacs version of the @code{loop} macro is less restrictive about | |
2294 | the order of clauses, but things will behave most predictably if | |
2295 | you put the variable-binding clauses @code{with}, @code{for}, and | |
2296 | @code{repeat} before the action clauses. As in Common Lisp, | |
2297 | @code{initially} and @code{finally} clauses can go anywhere. | |
2298 | ||
2299 | Loops generally return @code{nil} by default, but you can cause | |
2300 | them to return a value by using an accumulation clause like | |
2301 | @code{collect}, an end-test clause like @code{always}, or an | |
2302 | explicit @code{return} clause to jump out of the implicit block. | |
2303 | (Because the loop body is enclosed in an implicit block, you can | |
2304 | also use regular Lisp @code{return} or @code{return-from} to | |
2305 | break out of the loop.) | |
2306 | @end defspec | |
2307 | ||
2308 | The following sections give some examples of the Loop Macro in | |
2309 | action, and describe the particular loop clauses in great detail. | |
2310 | Consult the second edition of Steele's @dfn{Common Lisp, the Language}, | |
2311 | for additional discussion and examples of the @code{loop} macro. | |
2312 | ||
2313 | @node Loop Examples, For Clauses, Loop Basics, Loop Facility | |
2314 | @subsection Loop Examples | |
2315 | ||
2316 | @noindent | |
2317 | Before listing the full set of clauses that are allowed, let's | |
2318 | look at a few example loops just to get a feel for the @code{loop} | |
2319 | language. | |
2320 | ||
2321 | @example | |
2322 | (loop for buf in (buffer-list) | |
2323 | collect (buffer-file-name buf)) | |
2324 | @end example | |
2325 | ||
2326 | @noindent | |
2327 | This loop iterates over all Emacs buffers, using the list | |
2328 | returned by @code{buffer-list}. For each buffer @code{buf}, | |
2329 | it calls @code{buffer-file-name} and collects the results into | |
2330 | a list, which is then returned from the @code{loop} construct. | |
2331 | The result is a list of the file names of all the buffers in | |
2332 | Emacs' memory. The words @code{for}, @code{in}, and @code{collect} | |
2333 | are reserved words in the @code{loop} language. | |
2334 | ||
2335 | @example | |
2336 | (loop repeat 20 do (insert "Yowsa\n")) | |
2337 | @end example | |
2338 | ||
2339 | @noindent | |
2340 | This loop inserts the phrase ``Yowsa'' twenty times in the | |
2341 | current buffer. | |
2342 | ||
2343 | @example | |
2344 | (loop until (eobp) do (munch-line) (forward-line 1)) | |
2345 | @end example | |
2346 | ||
2347 | @noindent | |
2348 | This loop calls @code{munch-line} on every line until the end | |
2349 | of the buffer. If point is already at the end of the buffer, | |
2350 | the loop exits immediately. | |
2351 | ||
2352 | @example | |
2353 | (loop do (munch-line) until (eobp) do (forward-line 1)) | |
2354 | @end example | |
2355 | ||
2356 | @noindent | |
2357 | This loop is similar to the above one, except that @code{munch-line} | |
2358 | is always called at least once. | |
2359 | ||
2360 | @example | |
2361 | (loop for x from 1 to 100 | |
2362 | for y = (* x x) | |
2363 | until (>= y 729) | |
2364 | finally return (list x (= y 729))) | |
2365 | @end example | |
2366 | ||
2367 | @noindent | |
2368 | This more complicated loop searches for a number @code{x} whose | |
2369 | square is 729. For safety's sake it only examines @code{x} | |
2370 | values up to 100; dropping the phrase @samp{to 100} would | |
2371 | cause the loop to count upwards with no limit. The second | |
2372 | @code{for} clause defines @code{y} to be the square of @code{x} | |
2373 | within the loop; the expression after the @code{=} sign is | |
2374 | reevaluated each time through the loop. The @code{until} | |
2375 | clause gives a condition for terminating the loop, and the | |
2376 | @code{finally} clause says what to do when the loop finishes. | |
2377 | (This particular example was written less concisely than it | |
2378 | could have been, just for the sake of illustration.) | |
2379 | ||
2380 | Note that even though this loop contains three clauses (two | |
2381 | @code{for}s and an @code{until}) that would have been enough to | |
2382 | define loops all by themselves, it still creates a single loop | |
2383 | rather than some sort of triple-nested loop. You must explicitly | |
2384 | nest your @code{loop} constructs if you want nested loops. | |
2385 | ||
2386 | @node For Clauses, Iteration Clauses, Loop Examples, Loop Facility | |
2387 | @subsection For Clauses | |
2388 | ||
2389 | @noindent | |
2390 | Most loops are governed by one or more @code{for} clauses. | |
2391 | A @code{for} clause simultaneously describes variables to be | |
2392 | bound, how those variables are to be stepped during the loop, | |
2393 | and usually an end condition based on those variables. | |
2394 | ||
2395 | The word @code{as} is a synonym for the word @code{for}. This | |
2396 | word is followed by a variable name, then a word like @code{from} | |
2397 | or @code{across} that describes the kind of iteration desired. | |
2398 | In Common Lisp, the phrase @code{being the} sometimes precedes | |
2399 | the type of iteration; in this package both @code{being} and | |
2400 | @code{the} are optional. The word @code{each} is a synonym | |
2401 | for @code{the}, and the word that follows it may be singular | |
2402 | or plural: @samp{for x being the elements of y} or | |
2403 | @samp{for x being each element of y}. Which form you use | |
2404 | is purely a matter of style. | |
2405 | ||
2406 | The variable is bound around the loop as if by @code{let}: | |
2407 | ||
2408 | @example | |
2409 | (setq i 'happy) | |
2410 | (loop for i from 1 to 10 do (do-something-with i)) | |
2411 | i | |
2412 | @result{} happy | |
2413 | @end example | |
2414 | ||
2415 | @table @code | |
2416 | @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3} | |
2417 | This type of @code{for} clause creates a counting loop. Each of | |
2418 | the three sub-terms is optional, though there must be at least one | |
2419 | term so that the clause is marked as a counting clause. | |
2420 | ||
2421 | The three expressions are the starting value, the ending value, and | |
2422 | the step value, respectively, of the variable. The loop counts | |
2423 | upwards by default (@var{expr3} must be positive), from @var{expr1} | |
2424 | to @var{expr2} inclusively. If you omit the @code{from} term, the | |
2425 | loop counts from zero; if you omit the @code{to} term, the loop | |
2426 | counts forever without stopping (unless stopped by some other | |
2427 | loop clause, of course); if you omit the @code{by} term, the loop | |
2428 | counts in steps of one. | |
2429 | ||
2430 | You can replace the word @code{from} with @code{upfrom} or | |
2431 | @code{downfrom} to indicate the direction of the loop. Likewise, | |
2432 | you can replace @code{to} with @code{upto} or @code{downto}. | |
2433 | For example, @samp{for x from 5 downto 1} executes five times | |
2434 | with @code{x} taking on the integers from 5 down to 1 in turn. | |
2435 | Also, you can replace @code{to} with @code{below} or @code{above}, | |
2436 | which are like @code{upto} and @code{downto} respectively except | |
2437 | that they are exclusive rather than inclusive limits: | |
2438 | ||
2439 | @example | |
2440 | (loop for x to 10 collect x) | |
2441 | @result{} (0 1 2 3 4 5 6 7 8 9 10) | |
2442 | (loop for x below 10 collect x) | |
2443 | @result{} (0 1 2 3 4 5 6 7 8 9) | |
2444 | @end example | |
2445 | ||
2446 | The @code{by} value is always positive, even for downward-counting | |
2447 | loops. Some sort of @code{from} value is required for downward | |
2448 | loops; @samp{for x downto 5} is not a legal loop clause all by | |
2449 | itself. | |
2450 | ||
2451 | @item for @var{var} in @var{list} by @var{function} | |
2452 | This clause iterates @var{var} over all the elements of @var{list}, | |
2453 | in turn. If you specify the @code{by} term, then @var{function} | |
2454 | is used to traverse the list instead of @code{cdr}; it must be a | |
2455 | function taking one argument. For example: | |
2456 | ||
2457 | @example | |
2458 | (loop for x in '(1 2 3 4 5 6) collect (* x x)) | |
2459 | @result{} (1 4 9 16 25 36) | |
2460 | (loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x)) | |
2461 | @result{} (1 9 25) | |
2462 | @end example | |
2463 | ||
2464 | @item for @var{var} on @var{list} by @var{function} | |
2465 | This clause iterates @var{var} over all the cons cells of @var{list}. | |
2466 | ||
2467 | @example | |
2468 | (loop for x on '(1 2 3 4) collect x) | |
2469 | @result{} ((1 2 3 4) (2 3 4) (3 4) (4)) | |
2470 | @end example | |
2471 | ||
2472 | With @code{by}, there is no real reason that the @code{on} expression | |
2473 | must be a list. For example: | |
2474 | ||
2475 | @example | |
2476 | (loop for x on first-animal by 'next-animal collect x) | |
2477 | @end example | |
2478 | ||
2479 | @noindent | |
2480 | where @code{(next-animal x)} takes an ``animal'' @var{x} and returns | |
2481 | the next in the (assumed) sequence of animals, or @code{nil} if | |
2482 | @var{x} was the last animal in the sequence. | |
2483 | ||
2484 | @item for @var{var} in-ref @var{list} by @var{function} | |
2485 | This is like a regular @code{in} clause, but @var{var} becomes | |
2486 | a @code{setf}-able ``reference'' onto the elements of the list | |
2487 | rather than just a temporary variable. For example, | |
2488 | ||
2489 | @example | |
2490 | (loop for x in-ref my-list do (incf x)) | |
2491 | @end example | |
2492 | ||
2493 | @noindent | |
2494 | increments every element of @code{my-list} in place. This clause | |
2495 | is an extension to standard Common Lisp. | |
2496 | ||
2497 | @item for @var{var} across @var{array} | |
2498 | This clause iterates @var{var} over all the elements of @var{array}, | |
2499 | which may be a vector or a string. | |
2500 | ||
2501 | @example | |
2502 | (loop for x across "aeiou" | |
2503 | do (use-vowel (char-to-string x))) | |
2504 | @end example | |
2505 | ||
2506 | @item for @var{var} across-ref @var{array} | |
2507 | This clause iterates over an array, with @var{var} a @code{setf}-able | |
2508 | reference onto the elements; see @code{in-ref} above. | |
2509 | ||
2510 | @item for @var{var} being the elements of @var{sequence} | |
2511 | This clause iterates over the elements of @var{sequence}, which may | |
2512 | be a list, vector, or string. Since the type must be determined | |
2513 | at run-time, this is somewhat less efficient than @code{in} or | |
2514 | @code{across}. The clause may be followed by the additional term | |
2515 | @samp{using (index @var{var2})} to cause @var{var2} to be bound to | |
2516 | the successive indices (starting at 0) of the elements. | |
2517 | ||
2518 | This clause type is taken from older versions of the @code{loop} macro, | |
2519 | and is not present in modern Common Lisp. The @samp{using (sequence ...)} | |
2520 | term of the older macros is not supported. | |
2521 | ||
2522 | @item for @var{var} being the elements of-ref @var{sequence} | |
2523 | This clause iterates over a sequence, with @var{var} a @code{setf}-able | |
2524 | reference onto the elements; see @code{in-ref} above. | |
2525 | ||
2526 | @item for @var{var} being the symbols [of @var{obarray}] | |
2527 | This clause iterates over symbols, either over all interned symbols | |
2528 | or over all symbols in @var{obarray}. The loop is executed with | |
2529 | @var{var} bound to each symbol in turn. The symbols are visited in | |
2530 | an unspecified order. | |
2531 | ||
2532 | As an example, | |
2533 | ||
2534 | @example | |
2535 | (loop for sym being the symbols | |
2536 | when (fboundp sym) | |
2537 | when (string-match "^map" (symbol-name sym)) | |
2538 | collect sym) | |
2539 | @end example | |
2540 | ||
2541 | @noindent | |
2542 | returns a list of all the functions whose names begin with @samp{map}. | |
2543 | ||
2544 | The Common Lisp words @code{external-symbols} and @code{present-symbols} | |
2545 | are also recognized but are equivalent to @code{symbols} in Emacs Lisp. | |
2546 | ||
2547 | Due to a minor implementation restriction, it will not work to have | |
2548 | more than one @code{for} clause iterating over symbols, hash tables, | |
2549 | keymaps, overlays, or intervals in a given @code{loop}. Fortunately, | |
2550 | it would rarely if ever be useful to do so. It @emph{is} legal to mix | |
2551 | one of these types of clauses with other clauses like @code{for ... to} | |
2552 | or @code{while}. | |
2553 | ||
2554 | @item for @var{var} being the hash-keys of @var{hash-table} | |
2555 | This clause iterates over the entries in @var{hash-table}. For each | |
2556 | hash table entry, @var{var} is bound to the entry's key. If you write | |
2557 | @samp{the hash-values} instead, @var{var} is bound to the values | |
2558 | of the entries. The clause may be followed by the additional | |
2559 | term @samp{using (hash-values @var{var2})} (where @code{hash-values} | |
2560 | is the opposite word of the word following @code{the}) to cause | |
2561 | @var{var} and @var{var2} to be bound to the two parts of each | |
2562 | hash table entry. | |
2563 | ||
2564 | @item for @var{var} being the key-codes of @var{keymap} | |
2565 | This clause iterates over the entries in @var{keymap}. In GNU Emacs | |
2566 | 18 and 19, keymaps are either alists or vectors, and key-codes are | |
2567 | integers or symbols. In Lucid Emacs 19, keymaps are a special new | |
2568 | data type, and key-codes are symbols or lists of symbols. The | |
2569 | iteration does not enter nested keymaps or inherited (parent) keymaps. | |
2570 | You can use @samp{the key-bindings} to access the commands bound to | |
2571 | the keys rather than the key codes, and you can add a @code{using} | |
2572 | clause to access both the codes and the bindings together. | |
2573 | ||
2574 | @item for @var{var} being the key-seqs of @var{keymap} | |
2575 | This clause iterates over all key sequences defined by @var{keymap} | |
2576 | and its nested keymaps, where @var{var} takes on values which are | |
ed4d9494 | 2577 | vectors. The strings or vectors |
6bf7aab6 DL |
2578 | are reused for each iteration, so you must copy them if you wish to keep |
2579 | them permanently. You can add a @samp{using (key-bindings ...)} | |
2580 | clause to get the command bindings as well. | |
2581 | ||
2582 | @item for @var{var} being the overlays [of @var{buffer}] @dots{} | |
2583 | This clause iterates over the Emacs 19 ``overlays'' or Lucid | |
2584 | Emacs ``extents'' of a buffer (the clause @code{extents} is synonymous | |
ed4d9494 DL |
2585 | with @code{overlays}). If the @code{of} term is omitted, the current |
2586 | buffer is used. | |
6bf7aab6 DL |
2587 | This clause also accepts optional @samp{from @var{pos}} and |
2588 | @samp{to @var{pos}} terms, limiting the clause to overlays which | |
2589 | overlap the specified region. | |
2590 | ||
2591 | @item for @var{var} being the intervals [of @var{buffer}] @dots{} | |
2592 | This clause iterates over all intervals of a buffer with constant | |
2593 | text properties. The variable @var{var} will be bound to conses | |
2594 | of start and end positions, where one start position is always equal | |
2595 | to the previous end position. The clause allows @code{of}, | |
2596 | @code{from}, @code{to}, and @code{property} terms, where the latter | |
2597 | term restricts the search to just the specified property. The | |
2598 | @code{of} term may specify either a buffer or a string. This | |
2599 | clause is useful only in GNU Emacs 19; in other versions, all | |
2600 | buffers and strings consist of a single interval. | |
2601 | ||
2602 | @item for @var{var} being the frames | |
2603 | This clause iterates over all frames, i.e., X window system windows | |
2604 | open on Emacs files. This clause works only under Emacs 19. The | |
2605 | clause @code{screens} is a synonym for @code{frames}. The frames | |
2606 | are visited in @code{next-frame} order starting from | |
2607 | @code{selected-frame}. | |
2608 | ||
2609 | @item for @var{var} being the windows [of @var{frame}] | |
2610 | This clause iterates over the windows (in the Emacs sense) of | |
ed4d9494 | 2611 | the current frame, or of the specified @var{frame}. |
6bf7aab6 DL |
2612 | |
2613 | @item for @var{var} being the buffers | |
2614 | This clause iterates over all buffers in Emacs. It is equivalent | |
2615 | to @samp{for @var{var} in (buffer-list)}. | |
2616 | ||
2617 | @item for @var{var} = @var{expr1} then @var{expr2} | |
2618 | This clause does a general iteration. The first time through | |
2619 | the loop, @var{var} will be bound to @var{expr1}. On the second | |
2620 | and successive iterations it will be set by evaluating @var{expr2} | |
2621 | (which may refer to the old value of @var{var}). For example, | |
2622 | these two loops are effectively the same: | |
2623 | ||
2624 | @example | |
2625 | (loop for x on my-list by 'cddr do ...) | |
2626 | (loop for x = my-list then (cddr x) while x do ...) | |
2627 | @end example | |
2628 | ||
2629 | Note that this type of @code{for} clause does not imply any sort | |
2630 | of terminating condition; the above example combines it with a | |
2631 | @code{while} clause to tell when to end the loop. | |
2632 | ||
2633 | If you omit the @code{then} term, @var{expr1} is used both for | |
2634 | the initial setting and for successive settings: | |
2635 | ||
2636 | @example | |
2637 | (loop for x = (random) when (> x 0) return x) | |
2638 | @end example | |
2639 | ||
2640 | @noindent | |
2641 | This loop keeps taking random numbers from the @code{(random)} | |
2642 | function until it gets a positive one, which it then returns. | |
2643 | @end table | |
2644 | ||
2645 | If you include several @code{for} clauses in a row, they are | |
2646 | treated sequentially (as if by @code{let*} and @code{setq}). | |
2647 | You can instead use the word @code{and} to link the clauses, | |
2648 | in which case they are processed in parallel (as if by @code{let} | |
2649 | and @code{psetq}). | |
2650 | ||
2651 | @example | |
2652 | (loop for x below 5 for y = nil then x collect (list x y)) | |
2653 | @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4)) | |
2654 | (loop for x below 5 and y = nil then x collect (list x y)) | |
2655 | @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3)) | |
2656 | @end example | |
2657 | ||
2658 | @noindent | |
2659 | In the first loop, @code{y} is set based on the value of @code{x} | |
2660 | that was just set by the previous clause; in the second loop, | |
2661 | @code{x} and @code{y} are set simultaneously so @code{y} is set | |
2662 | based on the value of @code{x} left over from the previous time | |
2663 | through the loop. | |
2664 | ||
2665 | Another feature of the @code{loop} macro is @dfn{destructuring}, | |
2666 | similar in concept to the destructuring provided by @code{defmacro}. | |
2667 | The @var{var} part of any @code{for} clause can be given as a list | |
2668 | of variables instead of a single variable. The values produced | |
2669 | during loop execution must be lists; the values in the lists are | |
2670 | stored in the corresponding variables. | |
2671 | ||
2672 | @example | |
2673 | (loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y)) | |
2674 | @result{} (5 9 13) | |
2675 | @end example | |
2676 | ||
2677 | In loop destructuring, if there are more values than variables | |
2678 | the trailing values are ignored, and if there are more variables | |
2679 | than values the trailing variables get the value @code{nil}. | |
2680 | If @code{nil} is used as a variable name, the corresponding | |
2681 | values are ignored. Destructuring may be nested, and dotted | |
2682 | lists of variables like @code{(x . y)} are allowed. | |
2683 | ||
2684 | @node Iteration Clauses, Accumulation Clauses, For Clauses, Loop Facility | |
2685 | @subsection Iteration Clauses | |
2686 | ||
2687 | @noindent | |
2688 | Aside from @code{for} clauses, there are several other loop clauses | |
2689 | that control the way the loop operates. They might be used by | |
2690 | themselves, or in conjunction with one or more @code{for} clauses. | |
2691 | ||
2692 | @table @code | |
2693 | @item repeat @var{integer} | |
2694 | This clause simply counts up to the specified number using an | |
2695 | internal temporary variable. The loops | |
2696 | ||
2697 | @example | |
2698 | (loop repeat n do ...) | |
2699 | (loop for temp to n do ...) | |
2700 | @end example | |
2701 | ||
2702 | @noindent | |
2703 | are identical except that the second one forces you to choose | |
2704 | a name for a variable you aren't actually going to use. | |
2705 | ||
2706 | @item while @var{condition} | |
2707 | This clause stops the loop when the specified condition (any Lisp | |
2708 | expression) becomes @code{nil}. For example, the following two | |
2709 | loops are equivalent, except for the implicit @code{nil} block | |
2710 | that surrounds the second one: | |
2711 | ||
2712 | @example | |
2713 | (while @var{cond} @var{forms}@dots{}) | |
2714 | (loop while @var{cond} do @var{forms}@dots{}) | |
2715 | @end example | |
2716 | ||
2717 | @item until @var{condition} | |
2718 | This clause stops the loop when the specified condition is true, | |
2719 | i.e., non-@code{nil}. | |
2720 | ||
2721 | @item always @var{condition} | |
2722 | This clause stops the loop when the specified condition is @code{nil}. | |
2723 | Unlike @code{while}, it stops the loop using @code{return nil} so that | |
2724 | the @code{finally} clauses are not executed. If all the conditions | |
2725 | were non-@code{nil}, the loop returns @code{t}: | |
2726 | ||
2727 | @example | |
2728 | (if (loop for size in size-list always (> size 10)) | |
2729 | (some-big-sizes) | |
2730 | (no-big-sizes)) | |
2731 | @end example | |
2732 | ||
2733 | @item never @var{condition} | |
2734 | This clause is like @code{always}, except that the loop returns | |
2735 | @code{t} if any conditions were false, or @code{nil} otherwise. | |
2736 | ||
2737 | @item thereis @var{condition} | |
2738 | This clause stops the loop when the specified form is non-@code{nil}; | |
2739 | in this case, it returns that non-@code{nil} value. If all the | |
2740 | values were @code{nil}, the loop returns @code{nil}. | |
2741 | @end table | |
2742 | ||
2743 | @node Accumulation Clauses, Other Clauses, Iteration Clauses, Loop Facility | |
2744 | @subsection Accumulation Clauses | |
2745 | ||
2746 | @noindent | |
2747 | These clauses cause the loop to accumulate information about the | |
2748 | specified Lisp @var{form}. The accumulated result is returned | |
2749 | from the loop unless overridden, say, by a @code{return} clause. | |
2750 | ||
2751 | @table @code | |
2752 | @item collect @var{form} | |
2753 | This clause collects the values of @var{form} into a list. Several | |
2754 | examples of @code{collect} appear elsewhere in this manual. | |
2755 | ||
2756 | The word @code{collecting} is a synonym for @code{collect}, and | |
2757 | likewise for the other accumulation clauses. | |
2758 | ||
2759 | @item append @var{form} | |
2760 | This clause collects lists of values into a result list using | |
2761 | @code{append}. | |
2762 | ||
2763 | @item nconc @var{form} | |
2764 | This clause collects lists of values into a result list by | |
2765 | destructively modifying the lists rather than copying them. | |
2766 | ||
2767 | @item concat @var{form} | |
2768 | This clause concatenates the values of the specified @var{form} | |
2769 | into a string. (It and the following clause are extensions to | |
2770 | standard Common Lisp.) | |
2771 | ||
2772 | @item vconcat @var{form} | |
2773 | This clause concatenates the values of the specified @var{form} | |
2774 | into a vector. | |
2775 | ||
2776 | @item count @var{form} | |
2777 | This clause counts the number of times the specified @var{form} | |
2778 | evaluates to a non-@code{nil} value. | |
2779 | ||
2780 | @item sum @var{form} | |
2781 | This clause accumulates the sum of the values of the specified | |
2782 | @var{form}, which must evaluate to a number. | |
2783 | ||
2784 | @item maximize @var{form} | |
2785 | This clause accumulates the maximum value of the specified @var{form}, | |
2786 | which must evaluate to a number. The return value is undefined if | |
2787 | @code{maximize} is executed zero times. | |
2788 | ||
2789 | @item minimize @var{form} | |
2790 | This clause accumulates the minimum value of the specified @var{form}. | |
2791 | @end table | |
2792 | ||
2793 | Accumulation clauses can be followed by @samp{into @var{var}} to | |
2794 | cause the data to be collected into variable @var{var} (which is | |
2795 | automatically @code{let}-bound during the loop) rather than an | |
2796 | unnamed temporary variable. Also, @code{into} accumulations do | |
2797 | not automatically imply a return value. The loop must use some | |
2798 | explicit mechanism, such as @code{finally return}, to return | |
2799 | the accumulated result. | |
2800 | ||
2801 | It is legal for several accumulation clauses of the same type to | |
2802 | accumulate into the same place. From Steele: | |
2803 | ||
2804 | @example | |
2805 | (loop for name in '(fred sue alice joe june) | |
2806 | for kids in '((bob ken) () () (kris sunshine) ()) | |
2807 | collect name | |
2808 | append kids) | |
2809 | @result{} (fred bob ken sue alice joe kris sunshine june) | |
2810 | @end example | |
2811 | ||
2812 | @node Other Clauses, , Accumulation Clauses, Loop Facility | |
2813 | @subsection Other Clauses | |
2814 | ||
2815 | @noindent | |
2816 | This section describes the remaining loop clauses. | |
2817 | ||
2818 | @table @code | |
2819 | @item with @var{var} = @var{value} | |
2820 | This clause binds a variable to a value around the loop, but | |
2821 | otherwise leaves the variable alone during the loop. The following | |
2822 | loops are basically equivalent: | |
2823 | ||
2824 | @example | |
2825 | (loop with x = 17 do ...) | |
2826 | (let ((x 17)) (loop do ...)) | |
2827 | (loop for x = 17 then x do ...) | |
2828 | @end example | |
2829 | ||
2830 | Naturally, the variable @var{var} might be used for some purpose | |
2831 | in the rest of the loop. For example: | |
2832 | ||
2833 | @example | |
2834 | (loop for x in my-list with res = nil do (push x res) | |
2835 | finally return res) | |
2836 | @end example | |
2837 | ||
2838 | This loop inserts the elements of @code{my-list} at the front of | |
2839 | a new list being accumulated in @code{res}, then returns the | |
2840 | list @code{res} at the end of the loop. The effect is similar | |
2841 | to that of a @code{collect} clause, but the list gets reversed | |
2842 | by virtue of the fact that elements are being pushed onto the | |
2843 | front of @code{res} rather than the end. | |
2844 | ||
2845 | If you omit the @code{=} term, the variable is initialized to | |
2846 | @code{nil}. (Thus the @samp{= nil} in the above example is | |
2847 | unnecessary.) | |
2848 | ||
2849 | Bindings made by @code{with} are sequential by default, as if | |
2850 | by @code{let*}. Just like @code{for} clauses, @code{with} clauses | |
2851 | can be linked with @code{and} to cause the bindings to be made by | |
2852 | @code{let} instead. | |
2853 | ||
2854 | @item if @var{condition} @var{clause} | |
2855 | This clause executes the following loop clause only if the specified | |
2856 | condition is true. The following @var{clause} should be an accumulation, | |
2857 | @code{do}, @code{return}, @code{if}, or @code{unless} clause. | |
2858 | Several clauses may be linked by separating them with @code{and}. | |
2859 | These clauses may be followed by @code{else} and a clause or clauses | |
2860 | to execute if the condition was false. The whole construct may | |
2861 | optionally be followed by the word @code{end} (which may be used to | |
2862 | disambiguate an @code{else} or @code{and} in a nested @code{if}). | |
2863 | ||
2864 | The actual non-@code{nil} value of the condition form is available | |
2865 | by the name @code{it} in the ``then'' part. For example: | |
2866 | ||
2867 | @example | |
2868 | (setq funny-numbers '(6 13 -1)) | |
2869 | @result{} (6 13 -1) | |
2870 | (loop for x below 10 | |
2871 | if (oddp x) | |
2872 | collect x into odds | |
2873 | and if (memq x funny-numbers) return (cdr it) end | |
2874 | else | |
2875 | collect x into evens | |
2876 | finally return (vector odds evens)) | |
2877 | @result{} [(1 3 5 7 9) (0 2 4 6 8)] | |
2878 | (setq funny-numbers '(6 7 13 -1)) | |
2879 | @result{} (6 7 13 -1) | |
2880 | (loop <@r{same thing again}>) | |
2881 | @result{} (13 -1) | |
2882 | @end example | |
2883 | ||
2884 | Note the use of @code{and} to put two clauses into the ``then'' | |
2885 | part, one of which is itself an @code{if} clause. Note also that | |
2886 | @code{end}, while normally optional, was necessary here to make | |
2887 | it clear that the @code{else} refers to the outermost @code{if} | |
2888 | clause. In the first case, the loop returns a vector of lists | |
2889 | of the odd and even values of @var{x}. In the second case, the | |
2890 | odd number 7 is one of the @code{funny-numbers} so the loop | |
2891 | returns early; the actual returned value is based on the result | |
2892 | of the @code{memq} call. | |
2893 | ||
2894 | @item when @var{condition} @var{clause} | |
2895 | This clause is just a synonym for @code{if}. | |
2896 | ||
2897 | @item unless @var{condition} @var{clause} | |
2898 | The @code{unless} clause is just like @code{if} except that the | |
2899 | sense of the condition is reversed. | |
2900 | ||
2901 | @item named @var{name} | |
2902 | This clause gives a name other than @code{nil} to the implicit | |
2903 | block surrounding the loop. The @var{name} is the symbol to be | |
2904 | used as the block name. | |
2905 | ||
2906 | @item initially [do] @var{forms}... | |
2907 | This keyword introduces one or more Lisp forms which will be | |
2908 | executed before the loop itself begins (but after any variables | |
2909 | requested by @code{for} or @code{with} have been bound to their | |
2910 | initial values). @code{initially} clauses can appear anywhere; | |
2911 | if there are several, they are executed in the order they appear | |
2912 | in the loop. The keyword @code{do} is optional. | |
2913 | ||
2914 | @item finally [do] @var{forms}... | |
2915 | This introduces Lisp forms which will be executed after the loop | |
2916 | finishes (say, on request of a @code{for} or @code{while}). | |
2917 | @code{initially} and @code{finally} clauses may appear anywhere | |
2918 | in the loop construct, but they are executed (in the specified | |
2919 | order) at the beginning or end, respectively, of the loop. | |
2920 | ||
2921 | @item finally return @var{form} | |
2922 | This says that @var{form} should be executed after the loop | |
2923 | is done to obtain a return value. (Without this, or some other | |
2924 | clause like @code{collect} or @code{return}, the loop will simply | |
2925 | return @code{nil}.) Variables bound by @code{for}, @code{with}, | |
2926 | or @code{into} will still contain their final values when @var{form} | |
2927 | is executed. | |
2928 | ||
2929 | @item do @var{forms}... | |
2930 | The word @code{do} may be followed by any number of Lisp expressions | |
2931 | which are executed as an implicit @code{progn} in the body of the | |
2932 | loop. Many of the examples in this section illustrate the use of | |
2933 | @code{do}. | |
2934 | ||
2935 | @item return @var{form} | |
2936 | This clause causes the loop to return immediately. The following | |
2937 | Lisp form is evaluated to give the return value of the @code{loop} | |
2938 | form. The @code{finally} clauses, if any, are not executed. | |
2939 | Of course, @code{return} is generally used inside an @code{if} or | |
2940 | @code{unless}, as its use in a top-level loop clause would mean | |
2941 | the loop would never get to ``loop'' more than once. | |
2942 | ||
2943 | The clause @samp{return @var{form}} is equivalent to | |
2944 | @samp{do (return @var{form})} (or @code{return-from} if the loop | |
2945 | was named). The @code{return} clause is implemented a bit more | |
2946 | efficiently, though. | |
2947 | @end table | |
2948 | ||
2949 | While there is no high-level way to add user extensions to @code{loop} | |
2950 | (comparable to @code{defsetf} for @code{setf}, say), this package | |
2951 | does offer two properties called @code{cl-loop-handler} and | |
2952 | @code{cl-loop-for-handler} which are functions to be called when | |
2953 | a given symbol is encountered as a top-level loop clause or | |
2954 | @code{for} clause, respectively. Consult the source code in | |
2955 | file @file{cl-macs.el} for details. | |
2956 | ||
2957 | This package's @code{loop} macro is compatible with that of Common | |
2958 | Lisp, except that a few features are not implemented: @code{loop-finish} | |
2959 | and data-type specifiers. Naturally, the @code{for} clauses which | |
2960 | iterate over keymaps, overlays, intervals, frames, windows, and | |
2961 | buffers are Emacs-specific extensions. | |
2962 | ||
2963 | @node Multiple Values, , Loop Facility, Control Structure | |
2964 | @section Multiple Values | |
2965 | ||
2966 | @noindent | |
2967 | Common Lisp functions can return zero or more results. Emacs Lisp | |
2968 | functions, by contrast, always return exactly one result. This | |
2969 | package makes no attempt to emulate Common Lisp multiple return | |
2970 | values; Emacs versions of Common Lisp functions that return more | |
2971 | than one value either return just the first value (as in | |
2972 | @code{compiler-macroexpand}) or return a list of values (as in | |
2973 | @code{get-setf-method}). This package @emph{does} define placeholders | |
2974 | for the Common Lisp functions that work with multiple values, but | |
2975 | in Emacs Lisp these functions simply operate on lists instead. | |
2976 | The @code{values} form, for example, is a synonym for @code{list} | |
2977 | in Emacs. | |
2978 | ||
2979 | @defspec multiple-value-bind (var@dots{}) values-form forms@dots{} | |
2980 | This form evaluates @var{values-form}, which must return a list of | |
2981 | values. It then binds the @var{var}s to these respective values, | |
2982 | as if by @code{let}, and then executes the body @var{forms}. | |
2983 | If there are more @var{var}s than values, the extra @var{var}s | |
2984 | are bound to @code{nil}. If there are fewer @var{var}s than | |
2985 | values, the excess values are ignored. | |
2986 | @end defspec | |
2987 | ||
2988 | @defspec multiple-value-setq (var@dots{}) form | |
2989 | This form evaluates @var{form}, which must return a list of values. | |
2990 | It then sets the @var{var}s to these respective values, as if by | |
2991 | @code{setq}. Extra @var{var}s or values are treated the same as | |
2992 | in @code{multiple-value-bind}. | |
2993 | @end defspec | |
2994 | ||
2995 | The older Quiroz package attempted a more faithful (but still | |
2996 | imperfect) emulation of Common Lisp multiple values. The old | |
2997 | method ``usually'' simulated true multiple values quite well, | |
2998 | but under certain circumstances would leave spurious return | |
2999 | values in memory where a later, unrelated @code{multiple-value-bind} | |
3000 | form would see them. | |
3001 | ||
3002 | Since a perfect emulation is not feasible in Emacs Lisp, this | |
3003 | package opts to keep it as simple and predictable as possible. | |
3004 | ||
3005 | @node Macros, Declarations, Control Structure, Top | |
3006 | @chapter Macros | |
3007 | ||
3008 | @noindent | |
3009 | This package implements the various Common Lisp features of | |
3010 | @code{defmacro}, such as destructuring, @code{&environment}, | |
3011 | and @code{&body}. Top-level @code{&whole} is not implemented | |
3012 | for @code{defmacro} due to technical difficulties. | |
3013 | @xref{Argument Lists}. | |
3014 | ||
3015 | Destructuring is made available to the user by way of the | |
3016 | following macro: | |
3017 | ||
3018 | @defspec destructuring-bind arglist expr forms@dots{} | |
3019 | This macro expands to code which executes @var{forms}, with | |
3020 | the variables in @var{arglist} bound to the list of values | |
3021 | returned by @var{expr}. The @var{arglist} can include all | |
3022 | the features allowed for @code{defmacro} argument lists, | |
3023 | including destructuring. (The @code{&environment} keyword | |
3024 | is not allowed.) The macro expansion will signal an error | |
3025 | if @var{expr} returns a list of the wrong number of arguments | |
3026 | or with incorrect keyword arguments. | |
3027 | @end defspec | |
3028 | ||
3029 | This package also includes the Common Lisp @code{define-compiler-macro} | |
3030 | facility, which allows you to define compile-time expansions and | |
3031 | optimizations for your functions. | |
3032 | ||
3033 | @defspec define-compiler-macro name arglist forms@dots{} | |
3034 | This form is similar to @code{defmacro}, except that it only expands | |
3035 | calls to @var{name} at compile-time; calls processed by the Lisp | |
3036 | interpreter are not expanded, nor are they expanded by the | |
3037 | @code{macroexpand} function. | |
3038 | ||
3039 | The argument list may begin with a @code{&whole} keyword and a | |
3040 | variable. This variable is bound to the macro-call form itself, | |
3041 | i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}. | |
3042 | If the macro expander returns this form unchanged, then the | |
3043 | compiler treats it as a normal function call. This allows | |
3044 | compiler macros to work as optimizers for special cases of a | |
3045 | function, leaving complicated cases alone. | |
3046 | ||
3047 | For example, here is a simplified version of a definition that | |
3048 | appears as a standard part of this package: | |
3049 | ||
3050 | @example | |
3051 | (define-compiler-macro member* (&whole form a list &rest keys) | |
3052 | (if (and (null keys) | |
3053 | (eq (car-safe a) 'quote) | |
3054 | (not (floatp-safe (cadr a)))) | |
3055 | (list 'memq a list) | |
3056 | form)) | |
3057 | @end example | |
3058 | ||
3059 | @noindent | |
3060 | This definition causes @code{(member* @var{a} @var{list})} to change | |
3061 | to a call to the faster @code{memq} in the common case where @var{a} | |
3062 | is a non-floating-point constant; if @var{a} is anything else, or | |
3063 | if there are any keyword arguments in the call, then the original | |
3064 | @code{member*} call is left intact. (The actual compiler macro | |
3065 | for @code{member*} optimizes a number of other cases, including | |
3066 | common @code{:test} predicates.) | |
3067 | @end defspec | |
3068 | ||
3069 | @defun compiler-macroexpand form | |
3070 | This function is analogous to @code{macroexpand}, except that it | |
3071 | expands compiler macros rather than regular macros. It returns | |
3072 | @var{form} unchanged if it is not a call to a function for which | |
3073 | a compiler macro has been defined, or if that compiler macro | |
3074 | decided to punt by returning its @code{&whole} argument. Like | |
3075 | @code{macroexpand}, it expands repeatedly until it reaches a form | |
3076 | for which no further expansion is possible. | |
3077 | @end defun | |
3078 | ||
3079 | @xref{Macro Bindings}, for descriptions of the @code{macrolet} | |
3080 | and @code{symbol-macrolet} forms for making ``local'' macro | |
3081 | definitions. | |
3082 | ||
3083 | @node Declarations, Symbols, Macros, Top | |
3084 | @chapter Declarations | |
3085 | ||
3086 | @noindent | |
3087 | Common Lisp includes a complex and powerful ``declaration'' | |
3088 | mechanism that allows you to give the compiler special hints | |
3089 | about the types of data that will be stored in particular variables, | |
3090 | and about the ways those variables and functions will be used. This | |
3091 | package defines versions of all the Common Lisp declaration forms: | |
3092 | @code{declare}, @code{locally}, @code{proclaim}, @code{declaim}, | |
3093 | and @code{the}. | |
3094 | ||
3095 | Most of the Common Lisp declarations are not currently useful in | |
3096 | Emacs Lisp, as the byte-code system provides little opportunity | |
3097 | to benefit from type information, and @code{special} declarations | |
3098 | are redundant in a fully dynamically-scoped Lisp. A few | |
3099 | declarations are meaningful when the optimizing Emacs 19 byte | |
3100 | compiler is being used, however. Under the earlier non-optimizing | |
3101 | compiler, these declarations will effectively be ignored. | |
3102 | ||
3103 | @defun proclaim decl-spec | |
3104 | This function records a ``global'' declaration specified by | |
3105 | @var{decl-spec}. Since @code{proclaim} is a function, @var{decl-spec} | |
3106 | is evaluated and thus should normally be quoted. | |
3107 | @end defun | |
3108 | ||
3109 | @defspec declaim decl-specs@dots{} | |
3110 | This macro is like @code{proclaim}, except that it takes any number | |
3111 | of @var{decl-spec} arguments, and the arguments are unevaluated and | |
3112 | unquoted. The @code{declaim} macro also puts an @code{(eval-when | |
3113 | (compile load eval) ...)} around the declarations so that they will | |
3114 | be registered at compile-time as well as at run-time. (This is vital, | |
3115 | since normally the declarations are meant to influence the way the | |
3116 | compiler treats the rest of the file that contains the @code{declaim} | |
3117 | form.) | |
3118 | @end defspec | |
3119 | ||
3120 | @defspec declare decl-specs@dots{} | |
3121 | This macro is used to make declarations within functions and other | |
3122 | code. Common Lisp allows declarations in various locations, generally | |
3123 | at the beginning of any of the many ``implicit @code{progn}s'' | |
3124 | throughout Lisp syntax, such as function bodies, @code{let} bodies, | |
3125 | etc. Currently the only declaration understood by @code{declare} | |
3126 | is @code{special}. | |
3127 | @end defspec | |
3128 | ||
3129 | @defspec locally declarations@dots{} forms@dots{} | |
3130 | In this package, @code{locally} is no different from @code{progn}. | |
3131 | @end defspec | |
3132 | ||
3133 | @defspec the type form | |
3134 | Type information provided by @code{the} is ignored in this package; | |
3135 | in other words, @code{(the @var{type} @var{form})} is equivalent | |
3136 | to @var{form}. Future versions of the optimizing byte-compiler may | |
3137 | make use of this information. | |
3138 | ||
3139 | For example, @code{mapcar} can map over both lists and arrays. It is | |
3140 | hard for the compiler to expand @code{mapcar} into an in-line loop | |
3141 | unless it knows whether the sequence will be a list or an array ahead | |
3142 | of time. With @code{(mapcar 'car (the vector foo))}, a future | |
3143 | compiler would have enough information to expand the loop in-line. | |
3144 | For now, Emacs Lisp will treat the above code as exactly equivalent | |
3145 | to @code{(mapcar 'car foo)}. | |
3146 | @end defspec | |
3147 | ||
3148 | Each @var{decl-spec} in a @code{proclaim}, @code{declaim}, or | |
3149 | @code{declare} should be a list beginning with a symbol that says | |
3150 | what kind of declaration it is. This package currently understands | |
3151 | @code{special}, @code{inline}, @code{notinline}, @code{optimize}, | |
3152 | and @code{warn} declarations. (The @code{warn} declaration is an | |
3153 | extension of standard Common Lisp.) Other Common Lisp declarations, | |
3154 | such as @code{type} and @code{ftype}, are silently ignored. | |
3155 | ||
3156 | @table @code | |
3157 | @item special | |
3158 | Since all variables in Emacs Lisp are ``special'' (in the Common | |
3159 | Lisp sense), @code{special} declarations are only advisory. They | |
3160 | simply tell the optimizing byte compiler that the specified | |
3161 | variables are intentionally being referred to without being | |
3162 | bound in the body of the function. The compiler normally emits | |
3163 | warnings for such references, since they could be typographical | |
3164 | errors for references to local variables. | |
3165 | ||
3166 | The declaration @code{(declare (special @var{var1} @var{var2}))} is | |
3167 | equivalent to @code{(defvar @var{var1}) (defvar @var{var2})} in the | |
3168 | optimizing compiler, or to nothing at all in older compilers (which | |
3169 | do not warn for non-local references). | |
3170 | ||
3171 | In top-level contexts, it is generally better to write | |
3172 | @code{(defvar @var{var})} than @code{(declaim (special @var{var}))}, | |
3173 | since @code{defvar} makes your intentions clearer. But the older | |
3174 | byte compilers can not handle @code{defvar}s appearing inside of | |
3175 | functions, while @code{(declare (special @var{var}))} takes care | |
3176 | to work correctly with all compilers. | |
3177 | ||
3178 | @item inline | |
3179 | The @code{inline} @var{decl-spec} lists one or more functions | |
3180 | whose bodies should be expanded ``in-line'' into calling functions | |
3181 | whenever the compiler is able to arrange for it. For example, | |
3182 | the Common Lisp function @code{cadr} is declared @code{inline} | |
3183 | by this package so that the form @code{(cadr @var{x})} will | |
3184 | expand directly into @code{(car (cdr @var{x}))} when it is called | |
3185 | in user functions, for a savings of one (relatively expensive) | |
3186 | function call. | |
3187 | ||
3188 | The following declarations are all equivalent. Note that the | |
3189 | @code{defsubst} form is a convenient way to define a function | |
3190 | and declare it inline all at once, but it is available only in | |
3191 | Emacs 19. | |
3192 | ||
3193 | @example | |
3194 | (declaim (inline foo bar)) | |
3195 | (eval-when (compile load eval) (proclaim '(inline foo bar))) | |
3196 | (proclaim-inline foo bar) ; Lucid Emacs only | |
3197 | (defsubst foo (...) ...) ; instead of defun; Emacs 19 only | |
3198 | @end example | |
3199 | ||
3200 | @strong{Note:} This declaration remains in effect after the | |
3201 | containing source file is done. It is correct to use it to | |
3202 | request that a function you have defined should be inlined, | |
3203 | but it is impolite to use it to request inlining of an external | |
3204 | function. | |
3205 | ||
3206 | In Common Lisp, it is possible to use @code{(declare (inline @dots{}))} | |
3207 | before a particular call to a function to cause just that call to | |
3208 | be inlined; the current byte compilers provide no way to implement | |
3209 | this, so @code{(declare (inline @dots{}))} is currently ignored by | |
3210 | this package. | |
3211 | ||
3212 | @item notinline | |
3213 | The @code{notinline} declaration lists functions which should | |
3214 | not be inlined after all; it cancels a previous @code{inline} | |
3215 | declaration. | |
3216 | ||
3217 | @item optimize | |
3218 | This declaration controls how much optimization is performed by | |
3219 | the compiler. Naturally, it is ignored by the earlier non-optimizing | |
3220 | compilers. | |
3221 | ||
3222 | The word @code{optimize} is followed by any number of lists like | |
3223 | @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several | |
3224 | optimization ``qualities''; this package ignores all but @code{speed} | |
3225 | and @code{safety}. The value of a quality should be an integer from | |
3226 | 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important.'' | |
3227 | The default level for both qualities is 1. | |
3228 | ||
3229 | In this package, with the Emacs 19 optimizing compiler, the | |
3230 | @code{speed} quality is tied to the @code{byte-compile-optimize} | |
3231 | flag, which is set to @code{nil} for @code{(speed 0)} and to | |
3232 | @code{t} for higher settings; and the @code{safety} quality is | |
3233 | tied to the @code{byte-compile-delete-errors} flag, which is | |
3234 | set to @code{t} for @code{(safety 3)} and to @code{nil} for all | |
3235 | lower settings. (The latter flag controls whether the compiler | |
3236 | is allowed to optimize out code whose only side-effect could | |
3237 | be to signal an error, e.g., rewriting @code{(progn foo bar)} to | |
3238 | @code{bar} when it is not known whether @code{foo} will be bound | |
3239 | at run-time.) | |
3240 | ||
3241 | Note that even compiling with @code{(safety 0)}, the Emacs | |
3242 | byte-code system provides sufficient checking to prevent real | |
3243 | harm from being done. For example, barring serious bugs in | |
3244 | Emacs itself, Emacs will not crash with a segmentation fault | |
3245 | just because of an error in a fully-optimized Lisp program. | |
3246 | ||
3247 | The @code{optimize} declaration is normally used in a top-level | |
3248 | @code{proclaim} or @code{declaim} in a file; Common Lisp allows | |
3249 | it to be used with @code{declare} to set the level of optimization | |
3250 | locally for a given form, but this will not work correctly with the | |
3251 | current version of the optimizing compiler. (The @code{declare} | |
3252 | will set the new optimization level, but that level will not | |
3253 | automatically be unset after the enclosing form is done.) | |
3254 | ||
3255 | @item warn | |
3256 | This declaration controls what sorts of warnings are generated | |
3257 | by the byte compiler. Again, only the optimizing compiler | |
3258 | generates warnings. The word @code{warn} is followed by any | |
3259 | number of ``warning qualities,'' similar in form to optimization | |
3260 | qualities. The currently supported warning types are | |
3261 | @code{redefine}, @code{callargs}, @code{unresolved}, and | |
3262 | @code{free-vars}; in the current system, a value of 0 will | |
3263 | disable these warnings and any higher value will enable them. | |
3264 | See the documentation for the optimizing byte compiler for details. | |
3265 | @end table | |
3266 | ||
3267 | @node Symbols, Numbers, Declarations, Top | |
3268 | @chapter Symbols | |
3269 | ||
3270 | @noindent | |
3271 | This package defines several symbol-related features that were | |
3272 | missing from Emacs Lisp. | |
3273 | ||
3274 | @menu | |
3275 | * Property Lists:: `get*', `remprop', `getf', `remf' | |
3276 | * Creating Symbols:: `gensym', `gentemp' | |
3277 | @end menu | |
3278 | ||
3279 | @node Property Lists, Creating Symbols, Symbols, Symbols | |
3280 | @section Property Lists | |
3281 | ||
3282 | @noindent | |
3283 | These functions augment the standard Emacs Lisp functions @code{get} | |
3284 | and @code{put} for operating on properties attached to symbols. | |
3285 | There are also functions for working with property lists as | |
3286 | first-class data structures not attached to particular symbols. | |
3287 | ||
3288 | @defun get* symbol property &optional default | |
3289 | This function is like @code{get}, except that if the property is | |
3290 | not found, the @var{default} argument provides the return value. | |
3291 | (The Emacs Lisp @code{get} function always uses @code{nil} as | |
3292 | the default; this package's @code{get*} is equivalent to Common | |
3293 | Lisp's @code{get}.) | |
3294 | ||
3295 | The @code{get*} function is @code{setf}-able; when used in this | |
3296 | fashion, the @var{default} argument is allowed but ignored. | |
3297 | @end defun | |
3298 | ||
3299 | @defun remprop symbol property | |
3300 | This function removes the entry for @var{property} from the property | |
3301 | list of @var{symbol}. It returns a true value if the property was | |
3302 | indeed found and removed, or @code{nil} if there was no such property. | |
3303 | (This function was probably omitted from Emacs originally because, | |
3304 | since @code{get} did not allow a @var{default}, it was very difficult | |
3305 | to distinguish between a missing property and a property whose value | |
3306 | was @code{nil}; thus, setting a property to @code{nil} was close | |
3307 | enough to @code{remprop} for most purposes.) | |
3308 | @end defun | |
3309 | ||
3310 | @defun getf place property &optional default | |
3311 | This function scans the list @var{place} as if it were a property | |
3312 | list, i.e., a list of alternating property names and values. If | |
3313 | an even-numbered element of @var{place} is found which is @code{eq} | |
3314 | to @var{property}, the following odd-numbered element is returned. | |
3315 | Otherwise, @var{default} is returned (or @code{nil} if no default | |
3316 | is given). | |
3317 | ||
3318 | In particular, | |
3319 | ||
3320 | @example | |
3321 | (get sym prop) @equiv{} (getf (symbol-plist sym) prop) | |
3322 | @end example | |
3323 | ||
3324 | It is legal to use @code{getf} as a @code{setf} place, in which case | |
3325 | its @var{place} argument must itself be a legal @code{setf} place. | |
3326 | The @var{default} argument, if any, is ignored in this context. | |
3327 | The effect is to change (via @code{setcar}) the value cell in the | |
3328 | list that corresponds to @var{property}, or to cons a new property-value | |
3329 | pair onto the list if the property is not yet present. | |
3330 | ||
3331 | @example | |
3332 | (put sym prop val) @equiv{} (setf (getf (symbol-plist sym) prop) val) | |
3333 | @end example | |
3334 | ||
3335 | The @code{get} and @code{get*} functions are also @code{setf}-able. | |
3336 | The fact that @code{default} is ignored can sometimes be useful: | |
3337 | ||
3338 | @example | |
3339 | (incf (get* 'foo 'usage-count 0)) | |
3340 | @end example | |
3341 | ||
3342 | Here, symbol @code{foo}'s @code{usage-count} property is incremented | |
3343 | if it exists, or set to 1 (an incremented 0) otherwise. | |
3344 | ||
3345 | When not used as a @code{setf} form, @code{getf} is just a regular | |
3346 | function and its @var{place} argument can actually be any Lisp | |
3347 | expression. | |
3348 | @end defun | |
3349 | ||
3350 | @defspec remf place property | |
3351 | This macro removes the property-value pair for @var{property} from | |
3352 | the property list stored at @var{place}, which is any @code{setf}-able | |
3353 | place expression. It returns true if the property was found. Note | |
3354 | that if @var{property} happens to be first on the list, this will | |
3355 | effectively do a @code{(setf @var{place} (cddr @var{place}))}, | |
3356 | whereas if it occurs later, this simply uses @code{setcdr} to splice | |
3357 | out the property and value cells. | |
3358 | @end defspec | |
3359 | ||
3360 | @iftex | |
3361 | @secno=2 | |
3362 | @end iftex | |
3363 | ||
3364 | @node Creating Symbols, , Property Lists, Symbols | |
3365 | @section Creating Symbols | |
3366 | ||
3367 | @noindent | |
3368 | These functions create unique symbols, typically for use as | |
3369 | temporary variables. | |
3370 | ||
3371 | @defun gensym &optional x | |
3372 | This function creates a new, uninterned symbol (using @code{make-symbol}) | |
3373 | with a unique name. (The name of an uninterned symbol is relevant | |
3374 | only if the symbol is printed.) By default, the name is generated | |
3375 | from an increasing sequence of numbers, @samp{G1000}, @samp{G1001}, | |
3376 | @samp{G1002}, etc. If the optional argument @var{x} is a string, that | |
3377 | string is used as a prefix instead of @samp{G}. Uninterned symbols | |
3378 | are used in macro expansions for temporary variables, to ensure that | |
3379 | their names will not conflict with ``real'' variables in the user's | |
3380 | code. | |
3381 | @end defun | |
3382 | ||
3383 | @defvar *gensym-counter* | |
3384 | This variable holds the counter used to generate @code{gensym} names. | |
3385 | It is incremented after each use by @code{gensym}. In Common Lisp | |
3386 | this is initialized with 0, but this package initializes it with a | |
3387 | random (time-dependent) value to avoid trouble when two files that | |
3388 | each used @code{gensym} in their compilation are loaded together. | |
3389 | (Uninterned symbols become interned when the compiler writes them | |
3390 | out to a file and the Emacs loader loads them, so their names have to | |
3391 | be treated a bit more carefully than in Common Lisp where uninterned | |
3392 | symbols remain uninterned after loading.) | |
3393 | @end defvar | |
3394 | ||
3395 | @defun gentemp &optional x | |
3396 | This function is like @code{gensym}, except that it produces a new | |
3397 | @emph{interned} symbol. If the symbol that is generated already | |
3398 | exists, the function keeps incrementing the counter and trying | |
3399 | again until a new symbol is generated. | |
3400 | @end defun | |
3401 | ||
3402 | The Quiroz @file{cl.el} package also defined a @code{defkeyword} | |
3403 | form for creating self-quoting keyword symbols. This package | |
3404 | automatically creates all keywords that are called for by | |
3405 | @code{&key} argument specifiers, and discourages the use of | |
3406 | keywords as data unrelated to keyword arguments, so the | |
3407 | @code{defkeyword} form has been discontinued. | |
3408 | ||
3409 | @iftex | |
3410 | @chapno=11 | |
3411 | @end iftex | |
3412 | ||
3413 | @node Numbers, Sequences, Symbols, Top | |
3414 | @chapter Numbers | |
3415 | ||
3416 | @noindent | |
3417 | This section defines a few simple Common Lisp operations on numbers | |
3418 | which were left out of Emacs Lisp. | |
3419 | ||
3420 | @menu | |
3421 | * Predicates on Numbers:: `plusp', `oddp', `floatp-safe', etc. | |
76162e12 | 3422 | * Numerical Functions:: `abs', `floor*', etc. |
6bf7aab6 DL |
3423 | * Random Numbers:: `random*', `make-random-state' |
3424 | * Implementation Parameters:: `most-positive-fixnum', `most-positive-float' | |
3425 | @end menu | |
3426 | ||
3427 | @iftex | |
3428 | @secno=1 | |
3429 | @end iftex | |
3430 | ||
3431 | @node Predicates on Numbers, Numerical Functions, Numbers, Numbers | |
3432 | @section Predicates on Numbers | |
3433 | ||
3434 | @noindent | |
3435 | These functions return @code{t} if the specified condition is | |
3436 | true of the numerical argument, or @code{nil} otherwise. | |
3437 | ||
3438 | @defun plusp number | |
3439 | This predicate tests whether @var{number} is positive. It is an | |
3440 | error if the argument is not a number. | |
3441 | @end defun | |
3442 | ||
3443 | @defun minusp number | |
3444 | This predicate tests whether @var{number} is negative. It is an | |
3445 | error if the argument is not a number. | |
3446 | @end defun | |
3447 | ||
3448 | @defun oddp integer | |
3449 | This predicate tests whether @var{integer} is odd. It is an | |
3450 | error if the argument is not an integer. | |
3451 | @end defun | |
3452 | ||
3453 | @defun evenp integer | |
3454 | This predicate tests whether @var{integer} is even. It is an | |
3455 | error if the argument is not an integer. | |
3456 | @end defun | |
3457 | ||
3458 | @defun floatp-safe object | |
3459 | This predicate tests whether @var{object} is a floating-point | |
3460 | number. On systems that support floating-point, this is equivalent | |
3461 | to @code{floatp}. On other systems, this always returns @code{nil}. | |
3462 | @end defun | |
3463 | ||
3464 | @iftex | |
3465 | @secno=3 | |
3466 | @end iftex | |
3467 | ||
3468 | @node Numerical Functions, Random Numbers, Predicates on Numbers, Numbers | |
3469 | @section Numerical Functions | |
3470 | ||
3471 | @noindent | |
3472 | These functions perform various arithmetic operations on numbers. | |
3473 | ||
6bf7aab6 DL |
3474 | @defun gcd &rest integers |
3475 | This function returns the Greatest Common Divisor of the arguments. | |
3476 | For one argument, it returns the absolute value of that argument. | |
3477 | For zero arguments, it returns zero. | |
3478 | @end defun | |
3479 | ||
3480 | @defun lcm &rest integers | |
3481 | This function returns the Least Common Multiple of the arguments. | |
3482 | For one argument, it returns the absolute value of that argument. | |
3483 | For zero arguments, it returns one. | |
3484 | @end defun | |
3485 | ||
3486 | @defun isqrt integer | |
3487 | This function computes the ``integer square root'' of its integer | |
3488 | argument, i.e., the greatest integer less than or equal to the true | |
3489 | square root of the argument. | |
3490 | @end defun | |
3491 | ||
3492 | @defun floor* number &optional divisor | |
3493 | This function implements the Common Lisp @code{floor} function. | |
3494 | It is called @code{floor*} to avoid name conflicts with the | |
3495 | simpler @code{floor} function built-in to Emacs 19. | |
3496 | ||
3497 | With one argument, @code{floor*} returns a list of two numbers: | |
3498 | The argument rounded down (toward minus infinity) to an integer, | |
3499 | and the ``remainder'' which would have to be added back to the | |
3500 | first return value to yield the argument again. If the argument | |
3501 | is an integer @var{x}, the result is always the list @code{(@var{x} 0)}. | |
3502 | If the argument is an Emacs 19 floating-point number, the first | |
3503 | result is a Lisp integer and the second is a Lisp float between | |
3504 | 0 (inclusive) and 1 (exclusive). | |
3505 | ||
3506 | With two arguments, @code{floor*} divides @var{number} by | |
3507 | @var{divisor}, and returns the floor of the quotient and the | |
3508 | corresponding remainder as a list of two numbers. If | |
3509 | @code{(floor* @var{x} @var{y})} returns @code{(@var{q} @var{r})}, | |
3510 | then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r} | |
3511 | between 0 (inclusive) and @var{r} (exclusive). Also, note | |
3512 | that @code{(floor* @var{x})} is exactly equivalent to | |
3513 | @code{(floor* @var{x} 1)}. | |
3514 | ||
3515 | This function is entirely compatible with Common Lisp's @code{floor} | |
3516 | function, except that it returns the two results in a list since | |
3517 | Emacs Lisp does not support multiple-valued functions. | |
3518 | @end defun | |
3519 | ||
3520 | @defun ceiling* number &optional divisor | |
3521 | This function implements the Common Lisp @code{ceiling} function, | |
3522 | which is analogous to @code{floor} except that it rounds the | |
3523 | argument or quotient of the arguments up toward plus infinity. | |
3524 | The remainder will be between 0 and minus @var{r}. | |
3525 | @end defun | |
3526 | ||
3527 | @defun truncate* number &optional divisor | |
3528 | This function implements the Common Lisp @code{truncate} function, | |
3529 | which is analogous to @code{floor} except that it rounds the | |
3530 | argument or quotient of the arguments toward zero. Thus it is | |
3531 | equivalent to @code{floor*} if the argument or quotient is | |
3532 | positive, or to @code{ceiling*} otherwise. The remainder has | |
3533 | the same sign as @var{number}. | |
3534 | @end defun | |
3535 | ||
3536 | @defun round* number &optional divisor | |
3537 | This function implements the Common Lisp @code{round} function, | |
3538 | which is analogous to @code{floor} except that it rounds the | |
3539 | argument or quotient of the arguments to the nearest integer. | |
3540 | In the case of a tie (the argument or quotient is exactly | |
3541 | halfway between two integers), it rounds to the even integer. | |
3542 | @end defun | |
3543 | ||
3544 | @defun mod* number divisor | |
3545 | This function returns the same value as the second return value | |
3546 | of @code{floor}. | |
3547 | @end defun | |
3548 | ||
3549 | @defun rem* number divisor | |
3550 | This function returns the same value as the second return value | |
3551 | of @code{truncate}. | |
3552 | @end defun | |
3553 | ||
3554 | These definitions are compatible with those in the Quiroz | |
3555 | @file{cl.el} package, except that this package appends @samp{*} | |
3556 | to certain function names to avoid conflicts with existing | |
3557 | Emacs 19 functions, and that the mechanism for returning | |
3558 | multiple values is different. | |
3559 | ||
3560 | @iftex | |
3561 | @secno=8 | |
3562 | @end iftex | |
3563 | ||
3564 | @node Random Numbers, Implementation Parameters, Numerical Functions, Numbers | |
3565 | @section Random Numbers | |
3566 | ||
3567 | @noindent | |
3568 | This package also provides an implementation of the Common Lisp | |
3569 | random number generator. It uses its own additive-congruential | |
3570 | algorithm, which is much more likely to give statistically clean | |
3571 | random numbers than the simple generators supplied by many | |
3572 | operating systems. | |
3573 | ||
3574 | @defun random* number &optional state | |
3575 | This function returns a random nonnegative number less than | |
3576 | @var{number}, and of the same type (either integer or floating-point). | |
3577 | The @var{state} argument should be a @code{random-state} object | |
3578 | which holds the state of the random number generator. The | |
3579 | function modifies this state object as a side effect. If | |
3580 | @var{state} is omitted, it defaults to the variable | |
3581 | @code{*random-state*}, which contains a pre-initialized | |
3582 | @code{random-state} object. | |
3583 | @end defun | |
3584 | ||
3585 | @defvar *random-state* | |
3586 | This variable contains the system ``default'' @code{random-state} | |
3587 | object, used for calls to @code{random*} that do not specify an | |
3588 | alternative state object. Since any number of programs in the | |
3589 | Emacs process may be accessing @code{*random-state*} in interleaved | |
3590 | fashion, the sequence generated from this variable will be | |
3591 | irreproducible for all intents and purposes. | |
3592 | @end defvar | |
3593 | ||
3594 | @defun make-random-state &optional state | |
3595 | This function creates or copies a @code{random-state} object. | |
3596 | If @var{state} is omitted or @code{nil}, it returns a new copy of | |
3597 | @code{*random-state*}. This is a copy in the sense that future | |
3598 | sequences of calls to @code{(random* @var{n})} and | |
3599 | @code{(random* @var{n} @var{s})} (where @var{s} is the new | |
3600 | random-state object) will return identical sequences of random | |
3601 | numbers. | |
3602 | ||
3603 | If @var{state} is a @code{random-state} object, this function | |
3604 | returns a copy of that object. If @var{state} is @code{t}, this | |
3605 | function returns a new @code{random-state} object seeded from the | |
3606 | date and time. As an extension to Common Lisp, @var{state} may also | |
3607 | be an integer in which case the new object is seeded from that | |
3608 | integer; each different integer seed will result in a completely | |
3609 | different sequence of random numbers. | |
3610 | ||
3611 | It is legal to print a @code{random-state} object to a buffer or | |
3612 | file and later read it back with @code{read}. If a program wishes | |
3613 | to use a sequence of pseudo-random numbers which can be reproduced | |
3614 | later for debugging, it can call @code{(make-random-state t)} to | |
3615 | get a new sequence, then print this sequence to a file. When the | |
3616 | program is later rerun, it can read the original run's random-state | |
3617 | from the file. | |
3618 | @end defun | |
3619 | ||
3620 | @defun random-state-p object | |
3621 | This predicate returns @code{t} if @var{object} is a | |
3622 | @code{random-state} object, or @code{nil} otherwise. | |
3623 | @end defun | |
3624 | ||
3625 | @node Implementation Parameters, , Random Numbers, Numbers | |
3626 | @section Implementation Parameters | |
3627 | ||
3628 | @noindent | |
3629 | This package defines several useful constants having to with numbers. | |
3630 | ||
3631 | @defvar most-positive-fixnum | |
3632 | This constant equals the largest value a Lisp integer can hold. | |
3633 | It is typically @code{2^23-1} or @code{2^25-1}. | |
3634 | @end defvar | |
3635 | ||
3636 | @defvar most-negative-fixnum | |
3637 | This constant equals the smallest (most negative) value a Lisp | |
3638 | integer can hold. | |
3639 | @end defvar | |
3640 | ||
3641 | The following parameters have to do with floating-point numbers. | |
3642 | This package determines their values by exercising the computer's | |
3643 | floating-point arithmetic in various ways. Because this operation | |
3644 | might be slow, the code for initializing them is kept in a separate | |
3645 | function that must be called before the parameters can be used. | |
3646 | ||
3647 | @defun cl-float-limits | |
3648 | This function makes sure that the Common Lisp floating-point | |
3649 | parameters like @code{most-positive-float} have been initialized. | |
3650 | Until it is called, these parameters will be @code{nil}. If this | |
3651 | version of Emacs does not support floats (e.g., most versions of | |
3652 | Emacs 18), the parameters will remain @code{nil}. If the parameters | |
3653 | have already been initialized, the function returns immediately. | |
3654 | ||
3655 | The algorithm makes assumptions that will be valid for most modern | |
3656 | machines, but will fail if the machine's arithmetic is extremely | |
3657 | unusual, e.g., decimal. | |
3658 | @end defun | |
3659 | ||
3660 | Since true Common Lisp supports up to four different floating-point | |
3661 | precisions, it has families of constants like | |
3662 | @code{most-positive-single-float}, @code{most-positive-double-float}, | |
3663 | @code{most-positive-long-float}, and so on. Emacs has only one | |
3664 | floating-point precision, so this package omits the precision word | |
3665 | from the constants' names. | |
3666 | ||
3667 | @defvar most-positive-float | |
3668 | This constant equals the largest value a Lisp float can hold. | |
3669 | For those systems whose arithmetic supports infinities, this is | |
3670 | the largest @emph{finite} value. For IEEE machines, the value | |
3671 | is approximately @code{1.79e+308}. | |
3672 | @end defvar | |
3673 | ||
3674 | @defvar most-negative-float | |
3675 | This constant equals the most-negative value a Lisp float can hold. | |
3676 | (It is assumed to be equal to @code{(- most-positive-float)}.) | |
3677 | @end defvar | |
3678 | ||
3679 | @defvar least-positive-float | |
3680 | This constant equals the smallest Lisp float value greater than zero. | |
3681 | For IEEE machines, it is about @code{4.94e-324} if denormals are | |
3682 | supported or @code{2.22e-308} if not. | |
3683 | @end defvar | |
3684 | ||
3685 | @defvar least-positive-normalized-float | |
3686 | This constant equals the smallest @emph{normalized} Lisp float greater | |
3687 | than zero, i.e., the smallest value for which IEEE denormalization | |
3688 | will not result in a loss of precision. For IEEE machines, this | |
3689 | value is about @code{2.22e-308}. For machines that do not support | |
3690 | the concept of denormalization and gradual underflow, this constant | |
3691 | will always equal @code{least-positive-float}. | |
3692 | @end defvar | |
3693 | ||
3694 | @defvar least-negative-float | |
3695 | This constant is the negative counterpart of @code{least-positive-float}. | |
3696 | @end defvar | |
3697 | ||
3698 | @defvar least-negative-normalized-float | |
3699 | This constant is the negative counterpart of | |
3700 | @code{least-positive-normalized-float}. | |
3701 | @end defvar | |
3702 | ||
3703 | @defvar float-epsilon | |
3704 | This constant is the smallest positive Lisp float that can be added | |
3705 | to 1.0 to produce a distinct value. Adding a smaller number to 1.0 | |
3706 | will yield 1.0 again due to roundoff. For IEEE machines, epsilon | |
3707 | is about @code{2.22e-16}. | |
3708 | @end defvar | |
3709 | ||
3710 | @defvar float-negative-epsilon | |
3711 | This is the smallest positive value that can be subtracted from | |
3712 | 1.0 to produce a distinct value. For IEEE machines, it is about | |
3713 | @code{1.11e-16}. | |
3714 | @end defvar | |
3715 | ||
3716 | @iftex | |
3717 | @chapno=13 | |
3718 | @end iftex | |
3719 | ||
3720 | @node Sequences, Lists, Numbers, Top | |
3721 | @chapter Sequences | |
3722 | ||
3723 | @noindent | |
3724 | Common Lisp defines a number of functions that operate on | |
3725 | @dfn{sequences}, which are either lists, strings, or vectors. | |
3726 | Emacs Lisp includes a few of these, notably @code{elt} and | |
3727 | @code{length}; this package defines most of the rest. | |
3728 | ||
3729 | @menu | |
3730 | * Sequence Basics:: Arguments shared by all sequence functions | |
3731 | * Mapping over Sequences:: `mapcar*', `mapcan', `map', `every', etc. | |
3732 | * Sequence Functions:: `subseq', `remove*', `substitute', etc. | |
3733 | * Searching Sequences:: `find', `position', `count', `search', etc. | |
3734 | * Sorting Sequences:: `sort*', `stable-sort', `merge' | |
3735 | @end menu | |
3736 | ||
3737 | @node Sequence Basics, Mapping over Sequences, Sequences, Sequences | |
3738 | @section Sequence Basics | |
3739 | ||
3740 | @noindent | |
3741 | Many of the sequence functions take keyword arguments; @pxref{Argument | |
3742 | Lists}. All keyword arguments are optional and, if specified, | |
3743 | may appear in any order. | |
3744 | ||
3745 | The @code{:key} argument should be passed either @code{nil}, or a | |
3746 | function of one argument. This key function is used as a filter | |
3747 | through which the elements of the sequence are seen; for example, | |
3748 | @code{(find x y :key 'car)} is similar to @code{(assoc* x y)}: | |
3749 | It searches for an element of the list whose @code{car} equals | |
3750 | @code{x}, rather than for an element which equals @code{x} itself. | |
3751 | If @code{:key} is omitted or @code{nil}, the filter is effectively | |
3752 | the identity function. | |
3753 | ||
3754 | The @code{:test} and @code{:test-not} arguments should be either | |
3755 | @code{nil}, or functions of two arguments. The test function is | |
3756 | used to compare two sequence elements, or to compare a search value | |
3757 | with sequence elements. (The two values are passed to the test | |
3758 | function in the same order as the original sequence function | |
3759 | arguments from which they are derived, or, if they both come from | |
3760 | the same sequence, in the same order as they appear in that sequence.) | |
3761 | The @code{:test} argument specifies a function which must return | |
3762 | true (non-@code{nil}) to indicate a match; instead, you may use | |
3763 | @code{:test-not} to give a function which returns @emph{false} to | |
3764 | indicate a match. The default test function is @code{:test 'eql}. | |
3765 | ||
3766 | Many functions which take @var{item} and @code{:test} or @code{:test-not} | |
3767 | arguments also come in @code{-if} and @code{-if-not} varieties, | |
3768 | where a @var{predicate} function is passed instead of @var{item}, | |
3769 | and sequence elements match if the predicate returns true on them | |
3770 | (or false in the case of @code{-if-not}). For example: | |
3771 | ||
3772 | @example | |
3773 | (remove* 0 seq :test '=) @equiv{} (remove-if 'zerop seq) | |
3774 | @end example | |
3775 | ||
3776 | @noindent | |
3777 | to remove all zeros from sequence @code{seq}. | |
3778 | ||
3779 | Some operations can work on a subsequence of the argument sequence; | |
3780 | these function take @code{:start} and @code{:end} arguments which | |
3781 | default to zero and the length of the sequence, respectively. | |
3782 | Only elements between @var{start} (inclusive) and @var{end} | |
3783 | (exclusive) are affected by the operation. The @var{end} argument | |
3784 | may be passed @code{nil} to signify the length of the sequence; | |
3785 | otherwise, both @var{start} and @var{end} must be integers, with | |
3786 | @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}. | |
3787 | If the function takes two sequence arguments, the limits are | |
3788 | defined by keywords @code{:start1} and @code{:end1} for the first, | |
3789 | and @code{:start2} and @code{:end2} for the second. | |
3790 | ||
3791 | A few functions accept a @code{:from-end} argument, which, if | |
3792 | non-@code{nil}, causes the operation to go from right-to-left | |
3793 | through the sequence instead of left-to-right, and a @code{:count} | |
3794 | argument, which specifies an integer maximum number of elements | |
3795 | to be removed or otherwise processed. | |
3796 | ||
3797 | The sequence functions make no guarantees about the order in | |
3798 | which the @code{:test}, @code{:test-not}, and @code{:key} functions | |
3799 | are called on various elements. Therefore, it is a bad idea to depend | |
3800 | on side effects of these functions. For example, @code{:from-end} | |
3801 | may cause the sequence to be scanned actually in reverse, or it may | |
3802 | be scanned forwards but computing a result ``as if'' it were scanned | |
3803 | backwards. (Some functions, like @code{mapcar*} and @code{every}, | |
3804 | @emph{do} specify exactly the order in which the function is called | |
3805 | so side effects are perfectly acceptable in those cases.) | |
3806 | ||
3807 | Strings in GNU Emacs 19 may contain ``text properties'' as well | |
3808 | as character data. Except as noted, it is undefined whether or | |
3809 | not text properties are preserved by sequence functions. For | |
3810 | example, @code{(remove* ?A @var{str})} may or may not preserve | |
3811 | the properties of the characters copied from @var{str} into the | |
3812 | result. | |
3813 | ||
3814 | @node Mapping over Sequences, Sequence Functions, Sequence Basics, Sequences | |
3815 | @section Mapping over Sequences | |
3816 | ||
3817 | @noindent | |
3818 | These functions ``map'' the function you specify over the elements | |
3819 | of lists or arrays. They are all variations on the theme of the | |
3820 | built-in function @code{mapcar}. | |
3821 | ||
3822 | @defun mapcar* function seq &rest more-seqs | |
3823 | This function calls @var{function} on successive parallel sets of | |
3824 | elements from its argument sequences. Given a single @var{seq} | |
3825 | argument it is equivalent to @code{mapcar}; given @var{n} sequences, | |
3826 | it calls the function with the first elements of each of the sequences | |
3827 | as the @var{n} arguments to yield the first element of the result | |
3828 | list, then with the second elements, and so on. The mapping stops as | |
3829 | soon as the shortest sequence runs out. The argument sequences may | |
3830 | be any mixture of lists, strings, and vectors; the return sequence | |
3831 | is always a list. | |
3832 | ||
3833 | Common Lisp's @code{mapcar} accepts multiple arguments but works | |
3834 | only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence | |
3835 | argument. This package's @code{mapcar*} works as a compatible | |
3836 | superset of both. | |
3837 | @end defun | |
3838 | ||
3839 | @defun map result-type function seq &rest more-seqs | |
3840 | This function maps @var{function} over the argument sequences, | |
3841 | just like @code{mapcar*}, but it returns a sequence of type | |
3842 | @var{result-type} rather than a list. @var{result-type} must | |
3843 | be one of the following symbols: @code{vector}, @code{string}, | |
3844 | @code{list} (in which case the effect is the same as for | |
3845 | @code{mapcar*}), or @code{nil} (in which case the results are | |
3846 | thrown away and @code{map} returns @code{nil}). | |
3847 | @end defun | |
3848 | ||
3849 | @defun maplist function list &rest more-lists | |
3850 | This function calls @var{function} on each of its argument lists, | |
3851 | then on the @code{cdr}s of those lists, and so on, until the | |
3852 | shortest list runs out. The results are returned in the form | |
3853 | of a list. Thus, @code{maplist} is like @code{mapcar*} except | |
3854 | that it passes in the list pointers themselves rather than the | |
3855 | @code{car}s of the advancing pointers. | |
3856 | @end defun | |
3857 | ||
3858 | @defun mapc function seq &rest more-seqs | |
3859 | This function is like @code{mapcar*}, except that the values | |
3860 | returned by @var{function} are ignored and thrown away rather | |
3861 | than being collected into a list. The return value of @code{mapc} | |
3862 | is @var{seq}, the first sequence. | |
3863 | @end defun | |
3864 | ||
3865 | @defun mapl function list &rest more-lists | |
3866 | This function is like @code{maplist}, except that it throws away | |
3867 | the values returned by @var{function}. | |
3868 | @end defun | |
3869 | ||
3870 | @defun mapcan function seq &rest more-seqs | |
3871 | This function is like @code{mapcar*}, except that it concatenates | |
3872 | the return values (which must be lists) using @code{nconc}, | |
3873 | rather than simply collecting them into a list. | |
3874 | @end defun | |
3875 | ||
3876 | @defun mapcon function list &rest more-lists | |
3877 | This function is like @code{maplist}, except that it concatenates | |
3878 | the return values using @code{nconc}. | |
3879 | @end defun | |
3880 | ||
3881 | @defun some predicate seq &rest more-seqs | |
3882 | This function calls @var{predicate} on each element of @var{seq} | |
3883 | in turn; if @var{predicate} returns a non-@code{nil} value, | |
3884 | @code{some} returns that value, otherwise it returns @code{nil}. | |
3885 | Given several sequence arguments, it steps through the sequences | |
3886 | in parallel until the shortest one runs out, just as in | |
3887 | @code{mapcar*}. You can rely on the left-to-right order in which | |
3888 | the elements are visited, and on the fact that mapping stops | |
3889 | immediately as soon as @var{predicate} returns non-@code{nil}. | |
3890 | @end defun | |
3891 | ||
3892 | @defun every predicate seq &rest more-seqs | |
3893 | This function calls @var{predicate} on each element of the sequence(s) | |
3894 | in turn; it returns @code{nil} as soon as @var{predicate} returns | |
3895 | @code{nil} for any element, or @code{t} if the predicate was true | |
3896 | for all elements. | |
3897 | @end defun | |
3898 | ||
3899 | @defun notany predicate seq &rest more-seqs | |
3900 | This function calls @var{predicate} on each element of the sequence(s) | |
3901 | in turn; it returns @code{nil} as soon as @var{predicate} returns | |
3902 | a non-@code{nil} value for any element, or @code{t} if the predicate | |
3903 | was @code{nil} for all elements. | |
3904 | @end defun | |
3905 | ||
3906 | @defun notevery predicate seq &rest more-seqs | |
3907 | This function calls @var{predicate} on each element of the sequence(s) | |
3908 | in turn; it returns a non-@code{nil} value as soon as @var{predicate} | |
3909 | returns @code{nil} for any element, or @code{t} if the predicate was | |
3910 | true for all elements. | |
3911 | @end defun | |
3912 | ||
3913 | @defun reduce function seq @t{&key :from-end :start :end :initial-value :key} | |
3914 | This function combines the elements of @var{seq} using an associative | |
3915 | binary operation. Suppose @var{function} is @code{*} and @var{seq} is | |
3916 | the list @code{(2 3 4 5)}. The first two elements of the list are | |
3917 | combined with @code{(* 2 3) = 6}; this is combined with the next | |
3918 | element, @code{(* 6 4) = 24}, and that is combined with the final | |
3919 | element: @code{(* 24 5) = 120}. Note that the @code{*} function happens | |
3920 | to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as | |
3921 | an explicit call to @code{reduce}. | |
3922 | ||
3923 | If @code{:from-end} is true, the reduction is right-associative instead | |
3924 | of left-associative: | |
3925 | ||
3926 | @example | |
3927 | (reduce '- '(1 2 3 4)) | |
3928 | @equiv{} (- (- (- 1 2) 3) 4) @result{} -8 | |
3929 | (reduce '- '(1 2 3 4) :from-end t) | |
3930 | @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2 | |
3931 | @end example | |
3932 | ||
3933 | If @code{:key} is specified, it is a function of one argument which | |
3934 | is called on each of the sequence elements in turn. | |
3935 | ||
3936 | If @code{:initial-value} is specified, it is effectively added to the | |
3937 | front (or rear in the case of @code{:from-end}) of the sequence. | |
3938 | The @code{:key} function is @emph{not} applied to the initial value. | |
3939 | ||
3940 | If the sequence, including the initial value, has exactly one element | |
3941 | then that element is returned without ever calling @var{function}. | |
3942 | If the sequence is empty (and there is no initial value), then | |
3943 | @var{function} is called with no arguments to obtain the return value. | |
3944 | @end defun | |
3945 | ||
3946 | All of these mapping operations can be expressed conveniently in | |
3947 | terms of the @code{loop} macro. In compiled code, @code{loop} will | |
3948 | be faster since it generates the loop as in-line code with no | |
3949 | function calls. | |
3950 | ||
3951 | @node Sequence Functions, Searching Sequences, Mapping over Sequences, Sequences | |
3952 | @section Sequence Functions | |
3953 | ||
3954 | @noindent | |
3955 | This section describes a number of Common Lisp functions for | |
3956 | operating on sequences. | |
3957 | ||
3958 | @defun subseq sequence start &optional end | |
3959 | This function returns a given subsequence of the argument | |
3960 | @var{sequence}, which may be a list, string, or vector. | |
3961 | The indices @var{start} and @var{end} must be in range, and | |
3962 | @var{start} must be no greater than @var{end}. If @var{end} | |
3963 | is omitted, it defaults to the length of the sequence. The | |
3964 | return value is always a copy; it does not share structure | |
3965 | with @var{sequence}. | |
3966 | ||
3967 | As an extension to Common Lisp, @var{start} and/or @var{end} | |
3968 | may be negative, in which case they represent a distance back | |
3969 | from the end of the sequence. This is for compatibility with | |
3970 | Emacs' @code{substring} function. Note that @code{subseq} is | |
3971 | the @emph{only} sequence function that allows negative | |
3972 | @var{start} and @var{end}. | |
3973 | ||
3974 | You can use @code{setf} on a @code{subseq} form to replace a | |
3975 | specified range of elements with elements from another sequence. | |
3976 | The replacement is done as if by @code{replace}, described below. | |
3977 | @end defun | |
3978 | ||
3979 | @defun concatenate result-type &rest seqs | |
3980 | This function concatenates the argument sequences together to | |
3981 | form a result sequence of type @var{result-type}, one of the | |
3982 | symbols @code{vector}, @code{string}, or @code{list}. The | |
3983 | arguments are always copied, even in cases such as | |
3984 | @code{(concatenate 'list '(1 2 3))} where the result is | |
3985 | identical to an argument. | |
3986 | @end defun | |
3987 | ||
3988 | @defun fill seq item @t{&key :start :end} | |
3989 | This function fills the elements of the sequence (or the specified | |
3990 | part of the sequence) with the value @var{item}. | |
3991 | @end defun | |
3992 | ||
3993 | @defun replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2} | |
3994 | This function copies part of @var{seq2} into part of @var{seq1}. | |
3995 | The sequence @var{seq1} is not stretched or resized; the amount | |
3996 | of data copied is simply the shorter of the source and destination | |
3997 | (sub)sequences. The function returns @var{seq1}. | |
3998 | ||
3999 | If @var{seq1} and @var{seq2} are @code{eq}, then the replacement | |
4000 | will work correctly even if the regions indicated by the start | |
4001 | and end arguments overlap. However, if @var{seq1} and @var{seq2} | |
4002 | are lists which share storage but are not @code{eq}, and the | |
4003 | start and end arguments specify overlapping regions, the effect | |
4004 | is undefined. | |
4005 | @end defun | |
4006 | ||
4007 | @defun remove* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
4008 | This returns a copy of @var{seq} with all elements matching | |
4009 | @var{item} removed. The result may share storage with or be | |
4010 | @code{eq} to @var{seq} in some circumstances, but the original | |
4011 | @var{seq} will not be modified. The @code{:test}, @code{:test-not}, | |
4012 | and @code{:key} arguments define the matching test that is used; | |
4013 | by default, elements @code{eql} to @var{item} are removed. The | |
4014 | @code{:count} argument specifies the maximum number of matching | |
4015 | elements that can be removed (only the leftmost @var{count} matches | |
4016 | are removed). The @code{:start} and @code{:end} arguments specify | |
4017 | a region in @var{seq} in which elements will be removed; elements | |
4018 | outside that region are not matched or removed. The @code{:from-end} | |
4019 | argument, if true, says that elements should be deleted from the | |
4020 | end of the sequence rather than the beginning (this matters only | |
4021 | if @var{count} was also specified). | |
4022 | @end defun | |
4023 | ||
4024 | @defun delete* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
4025 | This deletes all elements of @var{seq} which match @var{item}. | |
4026 | It is a destructive operation. Since Emacs Lisp does not support | |
4027 | stretchable strings or vectors, this is the same as @code{remove*} | |
4028 | for those sequence types. On lists, @code{remove*} will copy the | |
4029 | list if necessary to preserve the original list, whereas | |
4030 | @code{delete*} will splice out parts of the argument list. | |
4031 | Compare @code{append} and @code{nconc}, which are analogous | |
4032 | non-destructive and destructive list operations in Emacs Lisp. | |
4033 | @end defun | |
4034 | ||
4035 | @findex remove-if | |
4036 | @findex remove-if-not | |
4037 | @findex delete-if | |
4038 | @findex delete-if-not | |
4039 | The predicate-oriented functions @code{remove-if}, @code{remove-if-not}, | |
4040 | @code{delete-if}, and @code{delete-if-not} are defined similarly. | |
4041 | ||
6bf7aab6 DL |
4042 | @defun remove item list |
4043 | This function removes from @var{list} all elements which are | |
4044 | @code{equal} to @var{item}. This package defines it for symmetry | |
4045 | with @code{delete}, even though @code{remove} is not built-in to | |
4046 | Emacs 19. | |
4047 | @end defun | |
4048 | ||
4049 | @defun remq item list | |
4050 | This function removes from @var{list} all elements which are | |
4051 | @code{eq} to @var{item}. This package defines it for symmetry | |
4052 | with @code{delq}, even though @code{remq} is not built-in to | |
4053 | Emacs 19. | |
4054 | @end defun | |
4055 | ||
4056 | @defun remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
4057 | This function returns a copy of @var{seq} with duplicate elements | |
4058 | removed. Specifically, if two elements from the sequence match | |
4059 | according to the @code{:test}, @code{:test-not}, and @code{:key} | |
4060 | arguments, only the rightmost one is retained. If @code{:from-end} | |
4061 | is true, the leftmost one is retained instead. If @code{:start} or | |
4062 | @code{:end} is specified, only elements within that subsequence are | |
4063 | examined or removed. | |
4064 | @end defun | |
4065 | ||
4066 | @defun delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
4067 | This function deletes duplicate elements from @var{seq}. It is | |
4068 | a destructive version of @code{remove-duplicates}. | |
4069 | @end defun | |
4070 | ||
4071 | @defun substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
4072 | This function returns a copy of @var{seq}, with all elements | |
4073 | matching @var{old} replaced with @var{new}. The @code{:count}, | |
4074 | @code{:start}, @code{:end}, and @code{:from-end} arguments may be | |
4075 | used to limit the number of substitutions made. | |
4076 | @end defun | |
4077 | ||
4078 | @defun nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
4079 | This is a destructive version of @code{substitute}; it performs | |
4080 | the substitution using @code{setcar} or @code{aset} rather than | |
4081 | by returning a changed copy of the sequence. | |
4082 | @end defun | |
4083 | ||
4084 | @findex substitute-if | |
4085 | @findex substitute-if-not | |
4086 | @findex nsubstitute-if | |
4087 | @findex nsubstitute-if-not | |
4088 | The @code{substitute-if}, @code{substitute-if-not}, @code{nsubstitute-if}, | |
4089 | and @code{nsubstitute-if-not} functions are defined similarly. For | |
4090 | these, a @var{predicate} is given in place of the @var{old} argument. | |
4091 | ||
4092 | @node Searching Sequences, Sorting Sequences, Sequence Functions, Sequences | |
4093 | @section Searching Sequences | |
4094 | ||
4095 | @noindent | |
4096 | These functions search for elements or subsequences in a sequence. | |
4097 | (See also @code{member*} and @code{assoc*}; @pxref{Lists}.) | |
4098 | ||
4099 | @defun find item seq @t{&key :test :test-not :key :start :end :from-end} | |
4100 | This function searches @var{seq} for an element matching @var{item}. | |
4101 | If it finds a match, it returns the matching element. Otherwise, | |
4102 | it returns @code{nil}. It returns the leftmost match, unless | |
4103 | @code{:from-end} is true, in which case it returns the rightmost | |
4104 | match. The @code{:start} and @code{:end} arguments may be used to | |
4105 | limit the range of elements that are searched. | |
4106 | @end defun | |
4107 | ||
4108 | @defun position item seq @t{&key :test :test-not :key :start :end :from-end} | |
4109 | This function is like @code{find}, except that it returns the | |
4110 | integer position in the sequence of the matching item rather than | |
4111 | the item itself. The position is relative to the start of the | |
4112 | sequence as a whole, even if @code{:start} is non-zero. The function | |
4113 | returns @code{nil} if no matching element was found. | |
4114 | @end defun | |
4115 | ||
4116 | @defun count item seq @t{&key :test :test-not :key :start :end} | |
4117 | This function returns the number of elements of @var{seq} which | |
4118 | match @var{item}. The result is always a nonnegative integer. | |
4119 | @end defun | |
4120 | ||
4121 | @findex find-if | |
4122 | @findex find-if-not | |
4123 | @findex position-if | |
4124 | @findex position-if-not | |
4125 | @findex count-if | |
4126 | @findex count-if-not | |
4127 | The @code{find-if}, @code{find-if-not}, @code{position-if}, | |
4128 | @code{position-if-not}, @code{count-if}, and @code{count-if-not} | |
4129 | functions are defined similarly. | |
4130 | ||
4131 | @defun mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end} | |
4132 | This function compares the specified parts of @var{seq1} and | |
4133 | @var{seq2}. If they are the same length and the corresponding | |
4134 | elements match (according to @code{:test}, @code{:test-not}, | |
4135 | and @code{:key}), the function returns @code{nil}. If there is | |
4136 | a mismatch, the function returns the index (relative to @var{seq1}) | |
4137 | of the first mismatching element. This will be the leftmost pair of | |
4138 | elements which do not match, or the position at which the shorter of | |
4139 | the two otherwise-matching sequences runs out. | |
4140 | ||
4141 | If @code{:from-end} is true, then the elements are compared from right | |
4142 | to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}. | |
4143 | If the sequences differ, then one plus the index of the rightmost | |
4144 | difference (relative to @var{seq1}) is returned. | |
4145 | ||
4146 | An interesting example is @code{(mismatch str1 str2 :key 'upcase)}, | |
4147 | which compares two strings case-insensitively. | |
4148 | @end defun | |
4149 | ||
4150 | @defun search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2} | |
4151 | This function searches @var{seq2} for a subsequence that matches | |
4152 | @var{seq1} (or part of it specified by @code{:start1} and | |
4153 | @code{:end1}.) Only matches which fall entirely within the region | |
4154 | defined by @code{:start2} and @code{:end2} will be considered. | |
4155 | The return value is the index of the leftmost element of the | |
4156 | leftmost match, relative to the start of @var{seq2}, or @code{nil} | |
4157 | if no matches were found. If @code{:from-end} is true, the | |
4158 | function finds the @emph{rightmost} matching subsequence. | |
4159 | @end defun | |
4160 | ||
4161 | @node Sorting Sequences, , Searching Sequences, Sequences | |
4162 | @section Sorting Sequences | |
4163 | ||
4164 | @defun sort* seq predicate @t{&key :key} | |
4165 | This function sorts @var{seq} into increasing order as determined | |
4166 | by using @var{predicate} to compare pairs of elements. @var{predicate} | |
4167 | should return true (non-@code{nil}) if and only if its first argument | |
4168 | is less than (not equal to) its second argument. For example, | |
4169 | @code{<} and @code{string-lessp} are suitable predicate functions | |
4170 | for sorting numbers and strings, respectively; @code{>} would sort | |
4171 | numbers into decreasing rather than increasing order. | |
4172 | ||
4173 | This function differs from Emacs' built-in @code{sort} in that it | |
4174 | can operate on any type of sequence, not just lists. Also, it | |
4175 | accepts a @code{:key} argument which is used to preprocess data | |
4176 | fed to the @var{predicate} function. For example, | |
4177 | ||
4178 | @example | |
4179 | (setq data (sort data 'string-lessp :key 'downcase)) | |
4180 | @end example | |
4181 | ||
4182 | @noindent | |
4183 | sorts @var{data}, a sequence of strings, into increasing alphabetical | |
4184 | order without regard to case. A @code{:key} function of @code{car} | |
4185 | would be useful for sorting association lists. | |
4186 | ||
4187 | The @code{sort*} function is destructive; it sorts lists by actually | |
4188 | rearranging the @code{cdr} pointers in suitable fashion. | |
4189 | @end defun | |
4190 | ||
4191 | @defun stable-sort seq predicate @t{&key :key} | |
4192 | This function sorts @var{seq} @dfn{stably}, meaning two elements | |
4193 | which are equal in terms of @var{predicate} are guaranteed not to | |
4194 | be rearranged out of their original order by the sort. | |
4195 | ||
4196 | In practice, @code{sort*} and @code{stable-sort} are equivalent | |
4197 | in Emacs Lisp because the underlying @code{sort} function is | |
4198 | stable by default. However, this package reserves the right to | |
4199 | use non-stable methods for @code{sort*} in the future. | |
4200 | @end defun | |
4201 | ||
4202 | @defun merge type seq1 seq2 predicate @t{&key :key} | |
4203 | This function merges two sequences @var{seq1} and @var{seq2} by | |
4204 | interleaving their elements. The result sequence, of type @var{type} | |
4205 | (in the sense of @code{concatenate}), has length equal to the sum | |
4206 | of the lengths of the two input sequences. The sequences may be | |
4207 | modified destructively. Order of elements within @var{seq1} and | |
4208 | @var{seq2} is preserved in the interleaving; elements of the two | |
4209 | sequences are compared by @var{predicate} (in the sense of | |
4210 | @code{sort}) and the lesser element goes first in the result. | |
4211 | When elements are equal, those from @var{seq1} precede those from | |
4212 | @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are | |
4213 | both sorted according to @var{predicate}, then the result will be | |
4214 | a merged sequence which is (stably) sorted according to | |
4215 | @var{predicate}. | |
4216 | @end defun | |
4217 | ||
4218 | @node Lists, Hash Tables, Sequences, Top | |
4219 | @chapter Lists | |
4220 | ||
4221 | @noindent | |
4222 | The functions described here operate on lists. | |
4223 | ||
4224 | @menu | |
4225 | * List Functions:: `caddr', `first', `last*', `list*', etc. | |
4226 | * Substitution of Expressions:: `subst', `sublis', etc. | |
4227 | * Lists as Sets:: `member*', `adjoin', `union', etc. | |
4228 | * Association Lists:: `assoc*', `rassoc*', `acons', `pairlis' | |
4229 | @end menu | |
4230 | ||
4231 | @node List Functions, Substitution of Expressions, Lists, Lists | |
4232 | @section List Functions | |
4233 | ||
4234 | @noindent | |
4235 | This section describes a number of simple operations on lists, | |
4236 | i.e., chains of cons cells. | |
4237 | ||
4238 | @defun caddr x | |
4239 | This function is equivalent to @code{(car (cdr (cdr @var{x})))}. | |
4240 | Likewise, this package defines all 28 @code{c@var{xxx}r} functions | |
4241 | where @var{xxx} is up to four @samp{a}s and/or @samp{d}s. | |
4242 | All of these functions are @code{setf}-able, and calls to them | |
4243 | are expanded inline by the byte-compiler for maximum efficiency. | |
4244 | @end defun | |
4245 | ||
4246 | @defun first x | |
4247 | This function is a synonym for @code{(car @var{x})}. Likewise, | |
4248 | the functions @code{second}, @code{third}, @dots{}, through | |
4249 | @code{tenth} return the given element of the list @var{x}. | |
4250 | @end defun | |
4251 | ||
4252 | @defun rest x | |
4253 | This function is a synonym for @code{(cdr @var{x})}. | |
4254 | @end defun | |
4255 | ||
4256 | @defun endp x | |
4257 | Common Lisp defines this function to act like @code{null}, but | |
4258 | signaling an error if @code{x} is neither a @code{nil} nor a | |
4259 | cons cell. This package simply defines @code{endp} as a synonym | |
4260 | for @code{null}. | |
4261 | @end defun | |
4262 | ||
4263 | @defun list-length x | |
4264 | This function returns the length of list @var{x}, exactly like | |
4265 | @code{(length @var{x})}, except that if @var{x} is a circular | |
4266 | list (where the cdr-chain forms a loop rather than terminating | |
4267 | with @code{nil}), this function returns @code{nil}. (The regular | |
4268 | @code{length} function would get stuck if given a circular list.) | |
4269 | @end defun | |
4270 | ||
4271 | @defun last* x &optional n | |
4272 | This function returns the last cons, or the @var{n}th-to-last cons, | |
4273 | of the list @var{x}. If @var{n} is omitted it defaults to 1. | |
4274 | The ``last cons'' means the first cons cell of the list whose | |
4275 | @code{cdr} is not another cons cell. (For normal lists, the | |
4276 | @code{cdr} of the last cons will be @code{nil}.) This function | |
4277 | returns @code{nil} if @var{x} is @code{nil} or shorter than | |
4278 | @var{n}. Note that the last @emph{element} of the list is | |
4279 | @code{(car (last @var{x}))}. | |
4280 | ||
4281 | The Emacs function @code{last} does the same thing | |
4282 | except that it does not handle the optional argument @var{n}. | |
4283 | @end defun | |
4284 | ||
4285 | @defun butlast x &optional n | |
4286 | This function returns the list @var{x} with the last element, | |
4287 | or the last @var{n} elements, removed. If @var{n} is greater | |
4288 | than zero it makes a copy of the list so as not to damage the | |
4289 | original list. In general, @code{(append (butlast @var{x} @var{n}) | |
4290 | (last @var{x} @var{n}))} will return a list equal to @var{x}. | |
4291 | @end defun | |
4292 | ||
4293 | @defun nbutlast x &optional n | |
4294 | This is a version of @code{butlast} that works by destructively | |
4295 | modifying the @code{cdr} of the appropriate element, rather than | |
4296 | making a copy of the list. | |
4297 | @end defun | |
4298 | ||
4299 | @defun list* arg &rest others | |
4300 | This function constructs a list of its arguments. The final | |
4301 | argument becomes the @code{cdr} of the last cell constructed. | |
4302 | Thus, @code{(list* @var{a} @var{b} @var{c})} is equivalent to | |
4303 | @code{(cons @var{a} (cons @var{b} @var{c}))}, and | |
4304 | @code{(list* @var{a} @var{b} nil)} is equivalent to | |
4305 | @code{(list @var{a} @var{b})}. | |
4306 | ||
4307 | (Note that this function really is called @code{list*} in Common | |
4308 | Lisp; it is not a name invented for this package like @code{member*} | |
4309 | or @code{defun*}.) | |
4310 | @end defun | |
4311 | ||
4312 | @defun ldiff list sublist | |
4313 | If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to | |
4314 | one of the cons cells of @var{list}, then this function returns | |
4315 | a copy of the part of @var{list} up to but not including | |
4316 | @var{sublist}. For example, @code{(ldiff x (cddr x))} returns | |
4317 | the first two elements of the list @code{x}. The result is a | |
4318 | copy; the original @var{list} is not modified. If @var{sublist} | |
4319 | is not a sublist of @var{list}, a copy of the entire @var{list} | |
4320 | is returned. | |
4321 | @end defun | |
4322 | ||
4323 | @defun copy-list list | |
4324 | This function returns a copy of the list @var{list}. It copies | |
4325 | dotted lists like @code{(1 2 . 3)} correctly. | |
4326 | @end defun | |
4327 | ||
4328 | @defun copy-tree x &optional vecp | |
4329 | This function returns a copy of the tree of cons cells @var{x}. | |
4330 | Unlike @code{copy-sequence} (and its alias @code{copy-list}), | |
4331 | which copies only along the @code{cdr} direction, this function | |
4332 | copies (recursively) along both the @code{car} and the @code{cdr} | |
4333 | directions. If @var{x} is not a cons cell, the function simply | |
4334 | returns @var{x} unchanged. If the optional @var{vecp} argument | |
4335 | is true, this function copies vectors (recursively) as well as | |
4336 | cons cells. | |
4337 | @end defun | |
4338 | ||
4339 | @defun tree-equal x y @t{&key :test :test-not :key} | |
4340 | This function compares two trees of cons cells. If @var{x} and | |
4341 | @var{y} are both cons cells, their @code{car}s and @code{cdr}s are | |
4342 | compared recursively. If neither @var{x} nor @var{y} is a cons | |
4343 | cell, they are compared by @code{eql}, or according to the | |
4344 | specified test. The @code{:key} function, if specified, is | |
4345 | applied to the elements of both trees. @xref{Sequences}. | |
4346 | @end defun | |
4347 | ||
4348 | @iftex | |
4349 | @secno=3 | |
4350 | @end iftex | |
4351 | ||
4352 | @node Substitution of Expressions, Lists as Sets, List Functions, Lists | |
4353 | @section Substitution of Expressions | |
4354 | ||
4355 | @noindent | |
4356 | These functions substitute elements throughout a tree of cons | |
4357 | cells. (@xref{Sequence Functions}, for the @code{substitute} | |
4358 | function, which works on just the top-level elements of a list.) | |
4359 | ||
4360 | @defun subst new old tree @t{&key :test :test-not :key} | |
4361 | This function substitutes occurrences of @var{old} with @var{new} | |
4362 | in @var{tree}, a tree of cons cells. It returns a substituted | |
4363 | tree, which will be a copy except that it may share storage with | |
4364 | the argument @var{tree} in parts where no substitutions occurred. | |
4365 | The original @var{tree} is not modified. This function recurses | |
4366 | on, and compares against @var{old}, both @code{car}s and @code{cdr}s | |
4367 | of the component cons cells. If @var{old} is itself a cons cell, | |
4368 | then matching cells in the tree are substituted as usual without | |
4369 | recursively substituting in that cell. Comparisons with @var{old} | |
4370 | are done according to the specified test (@code{eql} by default). | |
4371 | The @code{:key} function is applied to the elements of the tree | |
4372 | but not to @var{old}. | |
4373 | @end defun | |
4374 | ||
4375 | @defun nsubst new old tree @t{&key :test :test-not :key} | |
4376 | This function is like @code{subst}, except that it works by | |
4377 | destructive modification (by @code{setcar} or @code{setcdr}) | |
4378 | rather than copying. | |
4379 | @end defun | |
4380 | ||
4381 | @findex subst-if | |
4382 | @findex subst-if-not | |
4383 | @findex nsubst-if | |
4384 | @findex nsubst-if-not | |
4385 | The @code{subst-if}, @code{subst-if-not}, @code{nsubst-if}, and | |
4386 | @code{nsubst-if-not} functions are defined similarly. | |
4387 | ||
4388 | @defun sublis alist tree @t{&key :test :test-not :key} | |
4389 | This function is like @code{subst}, except that it takes an | |
4390 | association list @var{alist} of @var{old}-@var{new} pairs. | |
4391 | Each element of the tree (after applying the @code{:key} | |
4392 | function, if any), is compared with the @code{car}s of | |
4393 | @var{alist}; if it matches, it is replaced by the corresponding | |
4394 | @code{cdr}. | |
4395 | @end defun | |
4396 | ||
4397 | @defun nsublis alist tree @t{&key :test :test-not :key} | |
4398 | This is a destructive version of @code{sublis}. | |
4399 | @end defun | |
4400 | ||
4401 | @node Lists as Sets, Association Lists, Substitution of Expressions, Lists | |
4402 | @section Lists as Sets | |
4403 | ||
4404 | @noindent | |
4405 | These functions perform operations on lists which represent sets | |
4406 | of elements. | |
4407 | ||
6bf7aab6 DL |
4408 | @defun member* item list @t{&key :test :test-not :key} |
4409 | This function searches @var{list} for an element matching @var{item}. | |
4410 | If a match is found, it returns the cons cell whose @code{car} was | |
4411 | the matching element. Otherwise, it returns @code{nil}. Elements | |
4412 | are compared by @code{eql} by default; you can use the @code{:test}, | |
4413 | @code{:test-not}, and @code{:key} arguments to modify this behavior. | |
4414 | @xref{Sequences}. | |
4415 | ||
4416 | Note that this function's name is suffixed by @samp{*} to avoid | |
4417 | the incompatible @code{member} function defined in Emacs 19. | |
4418 | (That function uses @code{equal} for comparisons; it is equivalent | |
4419 | to @code{(member* @var{item} @var{list} :test 'equal)}.) | |
4420 | @end defun | |
4421 | ||
4422 | @findex member-if | |
4423 | @findex member-if-not | |
4424 | The @code{member-if} and @code{member-if-not} functions | |
4425 | analogously search for elements which satisfy a given predicate. | |
4426 | ||
4427 | @defun tailp sublist list | |
4428 | This function returns @code{t} if @var{sublist} is a sublist of | |
4429 | @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to | |
4430 | any of its @code{cdr}s. | |
4431 | @end defun | |
4432 | ||
4433 | @defun adjoin item list @t{&key :test :test-not :key} | |
4434 | This function conses @var{item} onto the front of @var{list}, | |
4435 | like @code{(cons @var{item} @var{list})}, but only if @var{item} | |
4436 | is not already present on the list (as determined by @code{member*}). | |
4437 | If a @code{:key} argument is specified, it is applied to | |
4438 | @var{item} as well as to the elements of @var{list} during | |
4439 | the search, on the reasoning that @var{item} is ``about'' to | |
4440 | become part of the list. | |
4441 | @end defun | |
4442 | ||
4443 | @defun union list1 list2 @t{&key :test :test-not :key} | |
4444 | This function combines two lists which represent sets of items, | |
4445 | returning a list that represents the union of those two sets. | |
4446 | The result list will contain all items which appear in @var{list1} | |
4447 | or @var{list2}, and no others. If an item appears in both | |
4448 | @var{list1} and @var{list2} it will be copied only once. If | |
4449 | an item is duplicated in @var{list1} or @var{list2}, it is | |
4450 | undefined whether or not that duplication will survive in the | |
4451 | result list. The order of elements in the result list is also | |
4452 | undefined. | |
4453 | @end defun | |
4454 | ||
4455 | @defun nunion list1 list2 @t{&key :test :test-not :key} | |
4456 | This is a destructive version of @code{union}; rather than copying, | |
4457 | it tries to reuse the storage of the argument lists if possible. | |
4458 | @end defun | |
4459 | ||
4460 | @defun intersection list1 list2 @t{&key :test :test-not :key} | |
4461 | This function computes the intersection of the sets represented | |
4462 | by @var{list1} and @var{list2}. It returns the list of items | |
4463 | which appear in both @var{list1} and @var{list2}. | |
4464 | @end defun | |
4465 | ||
4466 | @defun nintersection list1 list2 @t{&key :test :test-not :key} | |
4467 | This is a destructive version of @code{intersection}. It | |
4468 | tries to reuse storage of @var{list1} rather than copying. | |
4469 | It does @emph{not} reuse the storage of @var{list2}. | |
4470 | @end defun | |
4471 | ||
4472 | @defun set-difference list1 list2 @t{&key :test :test-not :key} | |
4473 | This function computes the ``set difference'' of @var{list1} | |
4474 | and @var{list2}, i.e., the set of elements that appear in | |
4475 | @var{list1} but @emph{not} in @var{list2}. | |
4476 | @end defun | |
4477 | ||
4478 | @defun nset-difference list1 list2 @t{&key :test :test-not :key} | |
4479 | This is a destructive @code{set-difference}, which will try | |
4480 | to reuse @var{list1} if possible. | |
4481 | @end defun | |
4482 | ||
4483 | @defun set-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
4484 | This function computes the ``set exclusive or'' of @var{list1} | |
4485 | and @var{list2}, i.e., the set of elements that appear in | |
4486 | exactly one of @var{list1} and @var{list2}. | |
4487 | @end defun | |
4488 | ||
4489 | @defun nset-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
4490 | This is a destructive @code{set-exclusive-or}, which will try | |
4491 | to reuse @var{list1} and @var{list2} if possible. | |
4492 | @end defun | |
4493 | ||
4494 | @defun subsetp list1 list2 @t{&key :test :test-not :key} | |
4495 | This function checks whether @var{list1} represents a subset | |
4496 | of @var{list2}, i.e., whether every element of @var{list1} | |
4497 | also appears in @var{list2}. | |
4498 | @end defun | |
4499 | ||
4500 | @node Association Lists, , Lists as Sets, Lists | |
4501 | @section Association Lists | |
4502 | ||
4503 | @noindent | |
4504 | An @dfn{association list} is a list representing a mapping from | |
4505 | one set of values to another; any list whose elements are cons | |
4506 | cells is an association list. | |
4507 | ||
4508 | @defun assoc* item a-list @t{&key :test :test-not :key} | |
4509 | This function searches the association list @var{a-list} for an | |
4510 | element whose @code{car} matches (in the sense of @code{:test}, | |
4511 | @code{:test-not}, and @code{:key}, or by comparison with @code{eql}) | |
4512 | a given @var{item}. It returns the matching element, if any, | |
4513 | otherwise @code{nil}. It ignores elements of @var{a-list} which | |
4514 | are not cons cells. (This corresponds to the behavior of | |
4515 | @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's | |
4516 | @code{assoc} ignores @code{nil}s but considers any other non-cons | |
4517 | elements of @var{a-list} to be an error.) | |
4518 | @end defun | |
4519 | ||
4520 | @defun rassoc* item a-list @t{&key :test :test-not :key} | |
4521 | This function searches for an element whose @code{cdr} matches | |
4522 | @var{item}. If @var{a-list} represents a mapping, this applies | |
4523 | the inverse of the mapping to @var{item}. | |
4524 | @end defun | |
4525 | ||
6bf7aab6 DL |
4526 | @findex assoc-if |
4527 | @findex assoc-if-not | |
4528 | @findex rassoc-if | |
4529 | @findex rassoc-if-not | |
4530 | The @code{assoc-if}, @code{assoc-if-not}, @code{rassoc-if}, | |
4531 | and @code{rassoc-if-not} functions are defined similarly. | |
4532 | ||
4533 | Two simple functions for constructing association lists are: | |
4534 | ||
4535 | @defun acons key value alist | |
4536 | This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}. | |
4537 | @end defun | |
4538 | ||
4539 | @defun pairlis keys values &optional alist | |
4540 | This is equivalent to @code{(nconc (mapcar* 'cons @var{keys} @var{values}) | |
4541 | @var{alist})}. | |
4542 | @end defun | |
4543 | ||
4544 | @node Hash Tables, Structures, Lists, Top | |
4545 | @chapter Hash Tables | |
4546 | ||
4547 | @noindent | |
4548 | A @dfn{hash table} is a data structure that maps ``keys'' onto | |
4549 | ``values.'' Keys and values can be arbitrary Lisp data objects. | |
4550 | Hash tables have the property that the time to search for a given | |
4551 | key is roughly constant; simpler data structures like association | |
4552 | lists take time proportional to the number of entries in the list. | |
4553 | ||
4554 | @defun make-hash-table @t{&key :test :size} | |
4555 | This function creates and returns a hash-table object whose | |
4556 | function for comparing elements is @code{:test} (@code{eql} | |
4557 | by default), and which is allocated to fit about @code{:size} | |
4558 | elements. The @code{:size} argument is purely advisory; the | |
4559 | table will stretch automatically if you store more elements in | |
4560 | it. If @code{:size} is omitted, a reasonable default is used. | |
4561 | ||
4562 | Common Lisp allows only @code{eq}, @code{eql}, @code{equal}, | |
4563 | and @code{equalp} as legal values for the @code{:test} argument. | |
4564 | In this package, any reasonable predicate function will work, | |
4565 | though if you use something else you should check the details of | |
4566 | the hashing function described below to make sure it is suitable | |
4567 | for your predicate. | |
4568 | ||
4569 | Some versions of Emacs (like Lucid Emacs 19) include a built-in | |
4570 | hash table type; in these versions, @code{make-hash-table} with | |
4571 | a test of @code{eq} will use these built-in hash tables. In all | |
4572 | other cases, it will return a hash-table object which takes the | |
4573 | form of a list with an identifying ``tag'' symbol at the front. | |
4574 | All of the hash table functions in this package can operate on | |
4575 | both types of hash table; normally you will never know which | |
4576 | type is being used. | |
4577 | ||
4578 | This function accepts the additional Common Lisp keywords | |
4579 | @code{:rehash-size} and @code{:rehash-threshold}, but it ignores | |
4580 | their values. | |
4581 | @end defun | |
4582 | ||
4583 | @defun gethash key table &optional default | |
4584 | This function looks up @var{key} in @var{table}. If @var{key} | |
4585 | exists in the table, in the sense that it matches any of the existing | |
4586 | keys according to the table's test function, then the associated value | |
4587 | is returned. Otherwise, @var{default} (or @code{nil}) is returned. | |
4588 | ||
4589 | To store new data in the hash table, use @code{setf} on a call to | |
4590 | @code{gethash}. If @var{key} already exists in the table, the | |
4591 | corresponding value is changed to the stored value. If @var{key} | |
4592 | does not already exist, a new entry is added to the table and the | |
4593 | table is reallocated to a larger size if necessary. The @var{default} | |
4594 | argument is allowed but ignored in this case. The situation is | |
4595 | exactly analogous to that of @code{get*}; @pxref{Property Lists}. | |
4596 | @end defun | |
4597 | ||
4598 | @defun remhash key table | |
4599 | This function removes the entry for @var{key} from @var{table}. | |
4600 | If an entry was removed, it returns @code{t}. If @var{key} does | |
4601 | not appear in the table, it does nothing and returns @code{nil}. | |
4602 | @end defun | |
4603 | ||
4604 | @defun clrhash table | |
4605 | This function removes all the entries from @var{table}, leaving | |
4606 | an empty hash table. | |
4607 | @end defun | |
4608 | ||
4609 | @defun maphash function table | |
4610 | This function calls @var{function} for each entry in @var{table}. | |
4611 | It passes two arguments to @var{function}, the key and the value | |
4612 | of the given entry. The return value of @var{function} is ignored; | |
4613 | @var{maphash} itself returns @code{nil}. @xref{Loop Facility}, for | |
4614 | an alternate way of iterating over hash tables. | |
4615 | @end defun | |
4616 | ||
4617 | @defun hash-table-count table | |
4618 | This function returns the number of entries in @var{table}. | |
4619 | @strong{Warning:} The current implementation of Lucid Emacs 19 | |
4620 | hash-tables does not decrement the stored @code{count} when | |
4621 | @code{remhash} removes an entry. Therefore, the return value of | |
4622 | this function is not dependable if you have used @code{remhash} | |
4623 | on the table and the table's test is @code{eq}. A slower, but | |
4624 | reliable, way to count the entries is @code{(loop for x being the | |
4625 | hash-keys of @var{table} count t)}. | |
4626 | @end defun | |
4627 | ||
4628 | @defun hash-table-p object | |
4629 | This function returns @code{t} if @var{object} is a hash table, | |
4630 | @code{nil} otherwise. It recognizes both types of hash tables | |
4631 | (both Lucid Emacs built-in tables and tables implemented with | |
4632 | special lists.) | |
4633 | @end defun | |
4634 | ||
4635 | Sometimes when dealing with hash tables it is useful to know the | |
4636 | exact ``hash function'' that is used. This package implements | |
4637 | hash tables using Emacs Lisp ``obarrays,'' which are the same | |
4638 | data structure that Emacs Lisp uses to keep track of symbols. | |
4639 | Each hash table includes an embedded obarray. Key values given | |
4640 | to @code{gethash} are converted by various means into strings, | |
4641 | which are then looked up in the obarray using @code{intern} and | |
4642 | @code{intern-soft}. The symbol, or ``bucket,'' corresponding to | |
4643 | a given key string includes as its @code{symbol-value} an association | |
4644 | list of all key-value pairs which hash to that string. Depending | |
4645 | on the test function, it is possible for many entries to hash to | |
4646 | the same bucket. For example, if the test is @code{eql}, then the | |
4647 | symbol @code{foo} and two separately built strings @code{"foo"} will | |
4648 | create three entries in the same bucket. Search time is linear | |
4649 | within buckets, so hash tables will be most effective if you arrange | |
4650 | not to store too many things that hash the same. | |
4651 | ||
4652 | The following algorithm is used to convert Lisp objects to hash | |
4653 | strings: | |
4654 | ||
4655 | @itemize @bullet | |
4656 | @item | |
4657 | Strings are used directly as hash strings. (However, if the test | |
4658 | function is @code{equalp}, strings are @code{downcase}d first.) | |
4659 | ||
4660 | @item | |
4661 | Symbols are hashed according to their @code{symbol-name}. | |
4662 | ||
4663 | @item | |
4664 | Integers are hashed into one of 16 buckets depending on their value | |
4665 | modulo 16. Floating-point numbers are truncated to integers and | |
4666 | hashed modulo 16. | |
4667 | ||
4668 | @item | |
4669 | Cons cells are hashed according to their @code{car}s; nonempty vectors | |
4670 | are hashed according to their first element. | |
4671 | ||
4672 | @item | |
4673 | All other types of objects hash into a single bucket named @code{"*"}. | |
4674 | @end itemize | |
4675 | ||
4676 | @noindent | |
4677 | Thus, for example, searching among many buffer objects in a hash table | |
4678 | will devolve to a (still fairly fast) linear-time search through a | |
4679 | single bucket, whereas searching for different symbols will be very | |
4680 | fast since each symbol will, in general, hash into its own bucket. | |
4681 | ||
4682 | The size of the obarray in a hash table is automatically adjusted | |
4683 | as the number of elements increases. | |
4684 | ||
4685 | As a special case, @code{make-hash-table} with a @code{:size} argument | |
4686 | of 0 or 1 will create a hash-table object that uses a single association | |
4687 | list rather than an obarray of many lists. For very small tables this | |
4688 | structure will be more efficient since lookup does not require | |
4689 | converting the key to a string or looking it up in an obarray. | |
4690 | However, such tables are guaranteed to take time proportional to | |
4691 | their size to do a search. | |
4692 | ||
4693 | @iftex | |
4694 | @chapno=18 | |
4695 | @end iftex | |
4696 | ||
4697 | @node Structures, Assertions, Hash Tables, Top | |
4698 | @chapter Structures | |
4699 | ||
4700 | @noindent | |
4701 | The Common Lisp @dfn{structure} mechanism provides a general way | |
4702 | to define data types similar to C's @code{struct} types. A | |
4703 | structure is a Lisp object containing some number of @dfn{slots}, | |
4704 | each of which can hold any Lisp data object. Functions are | |
4705 | provided for accessing and setting the slots, creating or copying | |
4706 | structure objects, and recognizing objects of a particular structure | |
4707 | type. | |
4708 | ||
4709 | In true Common Lisp, each structure type is a new type distinct | |
4710 | from all existing Lisp types. Since the underlying Emacs Lisp | |
4711 | system provides no way to create new distinct types, this package | |
4712 | implements structures as vectors (or lists upon request) with a | |
4713 | special ``tag'' symbol to identify them. | |
4714 | ||
4715 | @defspec defstruct name slots@dots{} | |
4716 | The @code{defstruct} form defines a new structure type called | |
4717 | @var{name}, with the specified @var{slots}. (The @var{slots} | |
4718 | may begin with a string which documents the structure type.) | |
4719 | In the simplest case, @var{name} and each of the @var{slots} | |
4720 | are symbols. For example, | |
4721 | ||
4722 | @example | |
4723 | (defstruct person name age sex) | |
4724 | @end example | |
4725 | ||
4726 | @noindent | |
4727 | defines a struct type called @code{person} which contains three | |
4728 | slots. Given a @code{person} object @var{p}, you can access those | |
4729 | slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})}, | |
4730 | and @code{(person-sex @var{p})}. You can also change these slots by | |
4731 | using @code{setf} on any of these place forms: | |
4732 | ||
4733 | @example | |
4734 | (incf (person-age birthday-boy)) | |
4735 | @end example | |
4736 | ||
4737 | You can create a new @code{person} by calling @code{make-person}, | |
4738 | which takes keyword arguments @code{:name}, @code{:age}, and | |
4739 | @code{:sex} to specify the initial values of these slots in the | |
4740 | new object. (Omitting any of these arguments leaves the corresponding | |
4741 | slot ``undefined,'' according to the Common Lisp standard; in Emacs | |
4742 | Lisp, such uninitialized slots are filled with @code{nil}.) | |
4743 | ||
4744 | Given a @code{person}, @code{(copy-person @var{p})} makes a new | |
4745 | object of the same type whose slots are @code{eq} to those of @var{p}. | |
4746 | ||
4747 | Given any Lisp object @var{x}, @code{(person-p @var{x})} returns | |
4748 | true if @var{x} looks like a @code{person}, false otherwise. (Again, | |
4749 | in Common Lisp this predicate would be exact; in Emacs Lisp the | |
4750 | best it can do is verify that @var{x} is a vector of the correct | |
4751 | length which starts with the correct tag symbol.) | |
4752 | ||
4753 | Accessors like @code{person-name} normally check their arguments | |
4754 | (effectively using @code{person-p}) and signal an error if the | |
4755 | argument is the wrong type. This check is affected by | |
4756 | @code{(optimize (safety @dots{}))} declarations. Safety level 1, | |
4757 | the default, uses a somewhat optimized check that will detect all | |
4758 | incorrect arguments, but may use an uninformative error message | |
4759 | (e.g., ``expected a vector'' instead of ``expected a @code{person}''). | |
4760 | Safety level 0 omits all checks except as provided by the underlying | |
4761 | @code{aref} call; safety levels 2 and 3 do rigorous checking that will | |
4762 | always print a descriptive error message for incorrect inputs. | |
4763 | @xref{Declarations}. | |
4764 | ||
4765 | @example | |
4766 | (setq dave (make-person :name "Dave" :sex 'male)) | |
4767 | @result{} [cl-struct-person "Dave" nil male] | |
4768 | (setq other (copy-person dave)) | |
4769 | @result{} [cl-struct-person "Dave" nil male] | |
4770 | (eq dave other) | |
4771 | @result{} nil | |
4772 | (eq (person-name dave) (person-name other)) | |
4773 | @result{} t | |
4774 | (person-p dave) | |
4775 | @result{} t | |
4776 | (person-p [1 2 3 4]) | |
4777 | @result{} nil | |
4778 | (person-p "Bogus") | |
4779 | @result{} nil | |
4780 | (person-p '[cl-struct-person counterfeit person object]) | |
4781 | @result{} t | |
4782 | @end example | |
4783 | ||
4784 | In general, @var{name} is either a name symbol or a list of a name | |
4785 | symbol followed by any number of @dfn{struct options}; each @var{slot} | |
4786 | is either a slot symbol or a list of the form @samp{(@var{slot-name} | |
4787 | @var{default-value} @var{slot-options}@dots{})}. The @var{default-value} | |
4788 | is a Lisp form which is evaluated any time an instance of the | |
4789 | structure type is created without specifying that slot's value. | |
4790 | ||
4791 | Common Lisp defines several slot options, but the only one | |
4792 | implemented in this package is @code{:read-only}. A non-@code{nil} | |
4793 | value for this option means the slot should not be @code{setf}-able; | |
4794 | the slot's value is determined when the object is created and does | |
4795 | not change afterward. | |
4796 | ||
4797 | @example | |
4798 | (defstruct person | |
4799 | (name nil :read-only t) | |
4800 | age | |
4801 | (sex 'unknown)) | |
4802 | @end example | |
4803 | ||
4804 | Any slot options other than @code{:read-only} are ignored. | |
4805 | ||
4806 | For obscure historical reasons, structure options take a different | |
4807 | form than slot options. A structure option is either a keyword | |
4808 | symbol, or a list beginning with a keyword symbol possibly followed | |
4809 | by arguments. (By contrast, slot options are key-value pairs not | |
4810 | enclosed in lists.) | |
4811 | ||
4812 | @example | |
4813 | (defstruct (person (:constructor create-person) | |
4814 | (:type list) | |
4815 | :named) | |
4816 | name age sex) | |
4817 | @end example | |
4818 | ||
4819 | The following structure options are recognized. | |
4820 | ||
4821 | @table @code | |
4822 | @iftex | |
4823 | @itemmax=0 in | |
4824 | @advance@leftskip-.5@tableindent | |
4825 | @end iftex | |
4826 | @item :conc-name | |
4827 | The argument is a symbol whose print name is used as the prefix for | |
4828 | the names of slot accessor functions. The default is the name of | |
4829 | the struct type followed by a hyphen. The option @code{(:conc-name p-)} | |
4830 | would change this prefix to @code{p-}. Specifying @code{nil} as an | |
4831 | argument means no prefix, so that the slot names themselves are used | |
4832 | to name the accessor functions. | |
4833 | ||
4834 | @item :constructor | |
4835 | In the simple case, this option takes one argument which is an | |
4836 | alternate name to use for the constructor function. The default | |
4837 | is @code{make-@var{name}}, e.g., @code{make-person}. The above | |
4838 | example changes this to @code{create-person}. Specifying @code{nil} | |
4839 | as an argument means that no standard constructor should be | |
4840 | generated at all. | |
4841 | ||
4842 | In the full form of this option, the constructor name is followed | |
4843 | by an arbitrary argument list. @xref{Program Structure}, for a | |
4844 | description of the format of Common Lisp argument lists. All | |
4845 | options, such as @code{&rest} and @code{&key}, are supported. | |
4846 | The argument names should match the slot names; each slot is | |
4847 | initialized from the corresponding argument. Slots whose names | |
4848 | do not appear in the argument list are initialized based on the | |
4849 | @var{default-value} in their slot descriptor. Also, @code{&optional} | |
4850 | and @code{&key} arguments which don't specify defaults take their | |
4851 | defaults from the slot descriptor. It is legal to include arguments | |
4852 | which don't correspond to slot names; these are useful if they are | |
4853 | referred to in the defaults for optional, keyword, or @code{&aux} | |
4854 | arguments which @emph{do} correspond to slots. | |
4855 | ||
4856 | You can specify any number of full-format @code{:constructor} | |
4857 | options on a structure. The default constructor is still generated | |
4858 | as well unless you disable it with a simple-format @code{:constructor} | |
4859 | option. | |
4860 | ||
4861 | @example | |
4862 | (defstruct | |
4863 | (person | |
4864 | (:constructor nil) ; no default constructor | |
4865 | (:constructor new-person (name sex &optional (age 0))) | |
4866 | (:constructor new-hound (&key (name "Rover") | |
4867 | (dog-years 0) | |
4868 | &aux (age (* 7 dog-years)) | |
4869 | (sex 'canine)))) | |
4870 | name age sex) | |
4871 | @end example | |
4872 | ||
4873 | The first constructor here takes its arguments positionally rather | |
4874 | than by keyword. (In official Common Lisp terminology, constructors | |
4875 | that work By Order of Arguments instead of by keyword are called | |
4876 | ``BOA constructors.'' No, I'm not making this up.) For example, | |
4877 | @code{(new-person "Jane" 'female)} generates a person whose slots | |
4878 | are @code{"Jane"}, 0, and @code{female}, respectively. | |
4879 | ||
4880 | The second constructor takes two keyword arguments, @code{:name}, | |
4881 | which initializes the @code{name} slot and defaults to @code{"Rover"}, | |
4882 | and @code{:dog-years}, which does not itself correspond to a slot | |
4883 | but which is used to initialize the @code{age} slot. The @code{sex} | |
4884 | slot is forced to the symbol @code{canine} with no syntax for | |
4885 | overriding it. | |
4886 | ||
4887 | @item :copier | |
4888 | The argument is an alternate name for the copier function for | |
4889 | this type. The default is @code{copy-@var{name}}. @code{nil} | |
4890 | means not to generate a copier function. (In this implementation, | |
4891 | all copier functions are simply synonyms for @code{copy-sequence}.) | |
4892 | ||
4893 | @item :predicate | |
4894 | The argument is an alternate name for the predicate which recognizes | |
4895 | objects of this type. The default is @code{@var{name}-p}. @code{nil} | |
4896 | means not to generate a predicate function. (If the @code{:type} | |
4897 | option is used without the @code{:named} option, no predicate is | |
4898 | ever generated.) | |
4899 | ||
4900 | In true Common Lisp, @code{typep} is always able to recognize a | |
4901 | structure object even if @code{:predicate} was used. In this | |
4902 | package, @code{typep} simply looks for a function called | |
4903 | @code{@var{typename}-p}, so it will work for structure types | |
4904 | only if they used the default predicate name. | |
4905 | ||
4906 | @item :include | |
4907 | This option implements a very limited form of C++-style inheritance. | |
4908 | The argument is the name of another structure type previously | |
4909 | created with @code{defstruct}. The effect is to cause the new | |
4910 | structure type to inherit all of the included structure's slots | |
4911 | (plus, of course, any new slots described by this struct's slot | |
4912 | descriptors). The new structure is considered a ``specialization'' | |
4913 | of the included one. In fact, the predicate and slot accessors | |
4914 | for the included type will also accept objects of the new type. | |
4915 | ||
4916 | If there are extra arguments to the @code{:include} option after | |
4917 | the included-structure name, these options are treated as replacement | |
4918 | slot descriptors for slots in the included structure, possibly with | |
4919 | modified default values. Borrowing an example from Steele: | |
4920 | ||
4921 | @example | |
4922 | (defstruct person name (age 0) sex) | |
4923 | @result{} person | |
4924 | (defstruct (astronaut (:include person (age 45))) | |
4925 | helmet-size | |
4926 | (favorite-beverage 'tang)) | |
4927 | @result{} astronaut | |
4928 | ||
4929 | (setq joe (make-person :name "Joe")) | |
4930 | @result{} [cl-struct-person "Joe" 0 nil] | |
4931 | (setq buzz (make-astronaut :name "Buzz")) | |
4932 | @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang] | |
4933 | ||
4934 | (list (person-p joe) (person-p buzz)) | |
4935 | @result{} (t t) | |
4936 | (list (astronaut-p joe) (astronaut-p buzz)) | |
4937 | @result{} (nil t) | |
4938 | ||
4939 | (person-name buzz) | |
4940 | @result{} "Buzz" | |
4941 | (astronaut-name joe) | |
4942 | @result{} error: "astronaut-name accessing a non-astronaut" | |
4943 | @end example | |
4944 | ||
4945 | Thus, if @code{astronaut} is a specialization of @code{person}, | |
4946 | then every @code{astronaut} is also a @code{person} (but not the | |
4947 | other way around). Every @code{astronaut} includes all the slots | |
4948 | of a @code{person}, plus extra slots that are specific to | |
4949 | astronauts. Operations that work on people (like @code{person-name}) | |
4950 | work on astronauts just like other people. | |
4951 | ||
4952 | @item :print-function | |
4953 | In full Common Lisp, this option allows you to specify a function | |
4954 | which is called to print an instance of the structure type. The | |
4955 | Emacs Lisp system offers no hooks into the Lisp printer which would | |
4956 | allow for such a feature, so this package simply ignores | |
4957 | @code{:print-function}. | |
4958 | ||
4959 | @item :type | |
4960 | The argument should be one of the symbols @code{vector} or @code{list}. | |
4961 | This tells which underlying Lisp data type should be used to implement | |
4962 | the new structure type. Vectors are used by default, but | |
4963 | @code{(:type list)} will cause structure objects to be stored as | |
4964 | lists instead. | |
4965 | ||
4966 | The vector representation for structure objects has the advantage | |
4967 | that all structure slots can be accessed quickly, although creating | |
4968 | vectors is a bit slower in Emacs Lisp. Lists are easier to create, | |
4969 | but take a relatively long time accessing the later slots. | |
4970 | ||
4971 | @item :named | |
4972 | This option, which takes no arguments, causes a characteristic ``tag'' | |
4973 | symbol to be stored at the front of the structure object. Using | |
4974 | @code{:type} without also using @code{:named} will result in a | |
4975 | structure type stored as plain vectors or lists with no identifying | |
4976 | features. | |
4977 | ||
4978 | The default, if you don't specify @code{:type} explicitly, is to | |
4979 | use named vectors. Therefore, @code{:named} is only useful in | |
4980 | conjunction with @code{:type}. | |
4981 | ||
4982 | @example | |
4983 | (defstruct (person1) name age sex) | |
4984 | (defstruct (person2 (:type list) :named) name age sex) | |
4985 | (defstruct (person3 (:type list)) name age sex) | |
4986 | ||
4987 | (setq p1 (make-person1)) | |
4988 | @result{} [cl-struct-person1 nil nil nil] | |
4989 | (setq p2 (make-person2)) | |
4990 | @result{} (person2 nil nil nil) | |
4991 | (setq p3 (make-person3)) | |
4992 | @result{} (nil nil nil) | |
4993 | ||
4994 | (person1-p p1) | |
4995 | @result{} t | |
4996 | (person2-p p2) | |
4997 | @result{} t | |
4998 | (person3-p p3) | |
4999 | @result{} error: function person3-p undefined | |
5000 | @end example | |
5001 | ||
5002 | Since unnamed structures don't have tags, @code{defstruct} is not | |
5003 | able to make a useful predicate for recognizing them. Also, | |
5004 | accessors like @code{person3-name} will be generated but they | |
5005 | will not be able to do any type checking. The @code{person3-name} | |
5006 | function, for example, will simply be a synonym for @code{car} in | |
5007 | this case. By contrast, @code{person2-name} is able to verify | |
5008 | that its argument is indeed a @code{person2} object before | |
5009 | proceeding. | |
5010 | ||
5011 | @item :initial-offset | |
5012 | The argument must be a nonnegative integer. It specifies a | |
5013 | number of slots to be left ``empty'' at the front of the | |
5014 | structure. If the structure is named, the tag appears at the | |
5015 | specified position in the list or vector; otherwise, the first | |
5016 | slot appears at that position. Earlier positions are filled | |
5017 | with @code{nil} by the constructors and ignored otherwise. If | |
5018 | the type @code{:include}s another type, then @code{:initial-offset} | |
5019 | specifies a number of slots to be skipped between the last slot | |
5020 | of the included type and the first new slot. | |
5021 | @end table | |
5022 | @end defspec | |
5023 | ||
5024 | Except as noted, the @code{defstruct} facility of this package is | |
5025 | entirely compatible with that of Common Lisp. | |
5026 | ||
5027 | @iftex | |
5028 | @chapno=23 | |
5029 | @end iftex | |
5030 | ||
5031 | @node Assertions, Efficiency Concerns, Structures, Top | |
5032 | @chapter Assertions and Errors | |
5033 | ||
5034 | @noindent | |
5035 | This section describes two macros that test @dfn{assertions}, i.e., | |
5036 | conditions which must be true if the program is operating correctly. | |
5037 | Assertions never add to the behavior of a Lisp program; they simply | |
5038 | make ``sanity checks'' to make sure everything is as it should be. | |
5039 | ||
5040 | If the optimization property @code{speed} has been set to 3, and | |
5041 | @code{safety} is less than 3, then the byte-compiler will optimize | |
5042 | away the following assertions. Because assertions might be optimized | |
5043 | away, it is a bad idea for them to include side-effects. | |
5044 | ||
5045 | @defspec assert test-form [show-args string args@dots{}] | |
5046 | This form verifies that @var{test-form} is true (i.e., evaluates to | |
5047 | a non-@code{nil} value). If so, it returns @code{nil}. If the test | |
5048 | is not satisfied, @code{assert} signals an error. | |
5049 | ||
5050 | A default error message will be supplied which includes @var{test-form}. | |
5051 | You can specify a different error message by including a @var{string} | |
5052 | argument plus optional extra arguments. Those arguments are simply | |
5053 | passed to @code{error} to signal the error. | |
5054 | ||
5055 | If the optional second argument @var{show-args} is @code{t} instead | |
5056 | of @code{nil}, then the error message (with or without @var{string}) | |
5057 | will also include all non-constant arguments of the top-level | |
5058 | @var{form}. For example: | |
5059 | ||
5060 | @example | |
5061 | (assert (> x 10) t "x is too small: %d") | |
5062 | @end example | |
5063 | ||
5064 | This usage of @var{show-args} is an extension to Common Lisp. In | |
5065 | true Common Lisp, the second argument gives a list of @var{places} | |
5066 | which can be @code{setf}'d by the user before continuing from the | |
5067 | error. Since Emacs Lisp does not support continuable errors, it | |
5068 | makes no sense to specify @var{places}. | |
5069 | @end defspec | |
5070 | ||
5071 | @defspec check-type form type [string] | |
5072 | This form verifies that @var{form} evaluates to a value of type | |
5073 | @var{type}. If so, it returns @code{nil}. If not, @code{check-type} | |
5074 | signals a @code{wrong-type-argument} error. The default error message | |
5075 | lists the erroneous value along with @var{type} and @var{form} | |
5076 | themselves. If @var{string} is specified, it is included in the | |
5077 | error message in place of @var{type}. For example: | |
5078 | ||
5079 | @example | |
5080 | (check-type x (integer 1 *) "a positive integer") | |
5081 | @end example | |
5082 | ||
5083 | @xref{Type Predicates}, for a description of the type specifiers | |
5084 | that may be used for @var{type}. | |
5085 | ||
5086 | Note that in Common Lisp, the first argument to @code{check-type} | |
5087 | must be a @var{place} suitable for use by @code{setf}, because | |
5088 | @code{check-type} signals a continuable error that allows the | |
5089 | user to modify @var{place}. | |
5090 | @end defspec | |
5091 | ||
5092 | The following error-related macro is also defined: | |
5093 | ||
5094 | @defspec ignore-errors forms@dots{} | |
5095 | This executes @var{forms} exactly like a @code{progn}, except that | |
5096 | errors are ignored during the @var{forms}. More precisely, if | |
5097 | an error is signaled then @code{ignore-errors} immediately | |
5098 | aborts execution of the @var{forms} and returns @code{nil}. | |
5099 | If the @var{forms} complete successfully, @code{ignore-errors} | |
5100 | returns the result of the last @var{form}. | |
5101 | @end defspec | |
5102 | ||
5103 | @node Efficiency Concerns, Common Lisp Compatibility, Assertions, Top | |
5104 | @appendix Efficiency Concerns | |
5105 | ||
5106 | @appendixsec Macros | |
5107 | ||
5108 | @noindent | |
5109 | Many of the advanced features of this package, such as @code{defun*}, | |
5110 | @code{loop}, and @code{setf}, are implemented as Lisp macros. In | |
5111 | byte-compiled code, these complex notations will be expanded into | |
5112 | equivalent Lisp code which is simple and efficient. For example, | |
5113 | the forms | |
5114 | ||
5115 | @example | |
5116 | (incf i n) | |
5117 | (push x (car p)) | |
5118 | @end example | |
5119 | ||
5120 | @noindent | |
5121 | are expanded at compile-time to the Lisp forms | |
5122 | ||
5123 | @example | |
5124 | (setq i (+ i n)) | |
5125 | (setcar p (cons x (car p))) | |
5126 | @end example | |
5127 | ||
5128 | @noindent | |
5129 | which are the most efficient ways of doing these respective operations | |
5130 | in Lisp. Thus, there is no performance penalty for using the more | |
5131 | readable @code{incf} and @code{push} forms in your compiled code. | |
5132 | ||
5133 | @emph{Interpreted} code, on the other hand, must expand these macros | |
5134 | every time they are executed. For this reason it is strongly | |
5135 | recommended that code making heavy use of macros be compiled. | |
5136 | (The features labeled ``Special Form'' instead of ``Function'' in | |
5137 | this manual are macros.) A loop using @code{incf} a hundred times | |
5138 | will execute considerably faster if compiled, and will also | |
5139 | garbage-collect less because the macro expansion will not have | |
5140 | to be generated, used, and thrown away a hundred times. | |
5141 | ||
5142 | You can find out how a macro expands by using the | |
5143 | @code{cl-prettyexpand} function. | |
5144 | ||
5145 | @defun cl-prettyexpand form &optional full | |
5146 | This function takes a single Lisp form as an argument and inserts | |
5147 | a nicely formatted copy of it in the current buffer (which must be | |
5148 | in Lisp mode so that indentation works properly). It also expands | |
5149 | all Lisp macros which appear in the form. The easiest way to use | |
5150 | this function is to go to the @code{*scratch*} buffer and type, say, | |
5151 | ||
5152 | @example | |
5153 | (cl-prettyexpand '(loop for x below 10 collect x)) | |
5154 | @end example | |
5155 | ||
5156 | @noindent | |
5157 | and type @kbd{C-x C-e} immediately after the closing parenthesis; | |
5158 | the expansion | |
5159 | ||
5160 | @example | |
5161 | (block nil | |
5162 | (let* ((x 0) | |
5163 | (G1004 nil)) | |
5164 | (while (< x 10) | |
5165 | (setq G1004 (cons x G1004)) | |
5166 | (setq x (+ x 1))) | |
5167 | (nreverse G1004))) | |
5168 | @end example | |
5169 | ||
5170 | @noindent | |
5171 | will be inserted into the buffer. (The @code{block} macro is | |
5172 | expanded differently in the interpreter and compiler, so | |
5173 | @code{cl-prettyexpand} just leaves it alone. The temporary | |
5174 | variable @code{G1004} was created by @code{gensym}.) | |
5175 | ||
5176 | If the optional argument @var{full} is true, then @emph{all} | |
5177 | macros are expanded, including @code{block}, @code{eval-when}, | |
5178 | and compiler macros. Expansion is done as if @var{form} were | |
5179 | a top-level form in a file being compiled. For example, | |
5180 | ||
5181 | @example | |
5182 | (cl-prettyexpand '(pushnew 'x list)) | |
5183 | @print{} (setq list (adjoin 'x list)) | |
5184 | (cl-prettyexpand '(pushnew 'x list) t) | |
5185 | @print{} (setq list (if (memq 'x list) list (cons 'x list))) | |
5186 | (cl-prettyexpand '(caddr (member* 'a list)) t) | |
5187 | @print{} (car (cdr (cdr (memq 'a list)))) | |
5188 | @end example | |
5189 | ||
5190 | Note that @code{adjoin}, @code{caddr}, and @code{member*} all | |
5191 | have built-in compiler macros to optimize them in common cases. | |
5192 | @end defun | |
5193 | ||
5194 | @ifinfo | |
5195 | @example | |
5196 | ||
5197 | @end example | |
5198 | @end ifinfo | |
5199 | @appendixsec Error Checking | |
5200 | ||
5201 | @noindent | |
5202 | Common Lisp compliance has in general not been sacrificed for the | |
5203 | sake of efficiency. A few exceptions have been made for cases | |
5204 | where substantial gains were possible at the expense of marginal | |
5205 | incompatibility. One example is the use of @code{memq} (which is | |
5206 | treated very efficiently by the byte-compiler) to scan for keyword | |
5207 | arguments; this can become confused in rare cases when keyword | |
5208 | symbols are used as both keywords and data values at once. This | |
5209 | is extremely unlikely to occur in practical code, and the use of | |
5210 | @code{memq} allows functions with keyword arguments to be nearly | |
5211 | as fast as functions that use @code{&optional} arguments. | |
5212 | ||
5213 | The Common Lisp standard (as embodied in Steele's book) uses the | |
5214 | phrase ``it is an error if'' to indicate a situation which is not | |
5215 | supposed to arise in complying programs; implementations are strongly | |
5216 | encouraged but not required to signal an error in these situations. | |
5217 | This package sometimes omits such error checking in the interest of | |
5218 | compactness and efficiency. For example, @code{do} variable | |
5219 | specifiers are supposed to be lists of one, two, or three forms; | |
5220 | extra forms are ignored by this package rather than signaling a | |
5221 | syntax error. The @code{endp} function is simply a synonym for | |
5222 | @code{null} in this package. Functions taking keyword arguments | |
5223 | will accept an odd number of arguments, treating the trailing | |
5224 | keyword as if it were followed by the value @code{nil}. | |
5225 | ||
5226 | Argument lists (as processed by @code{defun*} and friends) | |
5227 | @emph{are} checked rigorously except for the minor point just | |
5228 | mentioned; in particular, keyword arguments are checked for | |
5229 | validity, and @code{&allow-other-keys} and @code{:allow-other-keys} | |
5230 | are fully implemented. Keyword validity checking is slightly | |
5231 | time consuming (though not too bad in byte-compiled code); | |
5232 | you can use @code{&allow-other-keys} to omit this check. Functions | |
5233 | defined in this package such as @code{find} and @code{member*} | |
5234 | do check their keyword arguments for validity. | |
5235 | ||
5236 | @ifinfo | |
5237 | @example | |
5238 | ||
5239 | @end example | |
5240 | @end ifinfo | |
5241 | @appendixsec Optimizing Compiler | |
5242 | ||
5243 | @noindent | |
5244 | The byte-compiler that comes with Emacs 18 normally fails to expand | |
5245 | macros that appear in top-level positions in the file (i.e., outside | |
5246 | of @code{defun}s or other enclosing forms). This would have | |
5247 | disastrous consequences to programs that used such top-level macros | |
5248 | as @code{defun*}, @code{eval-when}, and @code{defstruct}. To | |
5249 | work around this problem, the @dfn{CL} package patches the Emacs | |
5250 | 18 compiler to expand top-level macros. This patch will apply to | |
5251 | your own macros, too, if they are used in a top-level context. | |
5252 | The patch will not harm versions of the Emacs 18 compiler which | |
5253 | have already had a similar patch applied, nor will it affect the | |
5254 | optimizing Emacs 19 byte-compiler written by Jamie Zawinski and | |
5255 | Hallvard Furuseth. The patch is applied to the byte compiler's | |
5256 | code in Emacs' memory, @emph{not} to the @file{bytecomp.elc} file | |
5257 | stored on disk. | |
5258 | ||
ed4d9494 DL |
5259 | Use of the Emacs 19 compiler is highly recommended; many of the Common |
5260 | Lisp macros emit | |
6bf7aab6 DL |
5261 | code which can be improved by optimization. In particular, |
5262 | @code{block}s (whether explicit or implicit in constructs like | |
5263 | @code{defun*} and @code{loop}) carry a fair run-time penalty; the | |
5264 | optimizing compiler removes @code{block}s which are not actually | |
5265 | referenced by @code{return} or @code{return-from} inside the block. | |
5266 | ||
5267 | @node Common Lisp Compatibility, Old CL Compatibility, Efficiency Concerns, Top | |
5268 | @appendix Common Lisp Compatibility | |
5269 | ||
5270 | @noindent | |
5271 | Following is a list of all known incompatibilities between this | |
5272 | package and Common Lisp as documented in Steele (2nd edition). | |
5273 | ||
5274 | Certain function names, such as @code{member}, @code{assoc}, and | |
5275 | @code{floor}, were already taken by (incompatible) Emacs Lisp | |
5276 | functions; this package appends @samp{*} to the names of its | |
5277 | Common Lisp versions of these functions. | |
5278 | ||
5279 | The word @code{defun*} is required instead of @code{defun} in order | |
5280 | to use extended Common Lisp argument lists in a function. Likewise, | |
5281 | @code{defmacro*} and @code{function*} are versions of those forms | |
5282 | which understand full-featured argument lists. The @code{&whole} | |
5283 | keyword does not work in @code{defmacro} argument lists (except | |
5284 | inside recursive argument lists). | |
5285 | ||
5286 | In order to allow an efficient implementation, keyword arguments use | |
5287 | a slightly cheesy parser which may be confused if a keyword symbol | |
5288 | is passed as the @emph{value} of another keyword argument. | |
5289 | (Specifically, @code{(memq :@var{keyword} @var{rest-of-arguments})} | |
5290 | is used to scan for @code{:@var{keyword}} among the supplied | |
5291 | keyword arguments.) | |
5292 | ||
5293 | The @code{eql} and @code{equal} predicates do not distinguish | |
5294 | between IEEE floating-point plus and minus zero. The @code{equalp} | |
5295 | predicate has several differences with Common Lisp; @pxref{Predicates}. | |
5296 | ||
5297 | The @code{setf} mechanism is entirely compatible, except that | |
5298 | setf-methods return a list of five values rather than five | |
5299 | values directly. Also, the new ``@code{setf} function'' concept | |
5300 | (typified by @code{(defun (setf foo) @dots{})}) is not implemented. | |
5301 | ||
5302 | The @code{do-all-symbols} form is the same as @code{do-symbols} | |
5303 | with no @var{obarray} argument. In Common Lisp, this form would | |
5304 | iterate over all symbols in all packages. Since Emacs obarrays | |
5305 | are not a first-class package mechanism, there is no way for | |
5306 | @code{do-all-symbols} to locate any but the default obarray. | |
5307 | ||
5308 | The @code{loop} macro is complete except that @code{loop-finish} | |
5309 | and type specifiers are unimplemented. | |
5310 | ||
5311 | The multiple-value return facility treats lists as multiple | |
5312 | values, since Emacs Lisp cannot support multiple return values | |
5313 | directly. The macros will be compatible with Common Lisp if | |
5314 | @code{values} or @code{values-list} is always used to return to | |
5315 | a @code{multiple-value-bind} or other multiple-value receiver; | |
5316 | if @code{values} is used without @code{multiple-value-@dots{}} | |
5317 | or vice-versa the effect will be different from Common Lisp. | |
5318 | ||
5319 | Many Common Lisp declarations are ignored, and others match | |
5320 | the Common Lisp standard in concept but not in detail. For | |
5321 | example, local @code{special} declarations, which are purely | |
5322 | advisory in Emacs Lisp, do not rigorously obey the scoping rules | |
5323 | set down in Steele's book. | |
5324 | ||
5325 | The variable @code{*gensym-counter*} starts out with a pseudo-random | |
5326 | value rather than with zero. This is to cope with the fact that | |
5327 | generated symbols become interned when they are written to and | |
5328 | loaded back from a file. | |
5329 | ||
5330 | The @code{defstruct} facility is compatible, except that structures | |
5331 | are of type @code{:type vector :named} by default rather than some | |
5332 | special, distinct type. Also, the @code{:type} slot option is ignored. | |
5333 | ||
5334 | The second argument of @code{check-type} is treated differently. | |
5335 | ||
5336 | @node Old CL Compatibility, Porting Common Lisp, Common Lisp Compatibility, Top | |
5337 | @appendix Old CL Compatibility | |
5338 | ||
5339 | @noindent | |
5340 | Following is a list of all known incompatibilities between this package | |
5341 | and the older Quiroz @file{cl.el} package. | |
5342 | ||
5343 | This package's emulation of multiple return values in functions is | |
5344 | incompatible with that of the older package. That package attempted | |
5345 | to come as close as possible to true Common Lisp multiple return | |
5346 | values; unfortunately, it could not be 100% reliable and so was prone | |
5347 | to occasional surprises if used freely. This package uses a simpler | |
5348 | method, namely replacing multiple values with lists of values, which | |
5349 | is more predictable though more noticeably different from Common Lisp. | |
5350 | ||
5351 | The @code{defkeyword} form and @code{keywordp} function are not | |
5352 | implemented in this package. | |
5353 | ||
5354 | The @code{member}, @code{floor}, @code{ceiling}, @code{truncate}, | |
5355 | @code{round}, @code{mod}, and @code{rem} functions are suffixed | |
5356 | by @samp{*} in this package to avoid collision with existing | |
ed4d9494 | 5357 | functions in Emacs. The older package simply |
6bf7aab6 DL |
5358 | redefined these functions, overwriting the built-in meanings and |
5359 | causing serious portability problems with Emacs 19. (Some more | |
5360 | recent versions of the Quiroz package changed the names to | |
5361 | @code{cl-member}, etc.; this package defines the latter names as | |
5362 | aliases for @code{member*}, etc.) | |
5363 | ||
5364 | Certain functions in the old package which were buggy or inconsistent | |
5365 | with the Common Lisp standard are incompatible with the conforming | |
5366 | versions in this package. For example, @code{eql} and @code{member} | |
5367 | were synonyms for @code{eq} and @code{memq} in that package, @code{setf} | |
5368 | failed to preserve correct order of evaluation of its arguments, etc. | |
5369 | ||
5370 | Finally, unlike the older package, this package is careful to | |
5371 | prefix all of its internal names with @code{cl-}. Except for a | |
5372 | few functions which are explicitly defined as additional features | |
5373 | (such as @code{floatp-safe} and @code{letf}), this package does not | |
5374 | export any non-@samp{cl-} symbols which are not also part of Common | |
5375 | Lisp. | |
5376 | ||
5377 | @ifinfo | |
5378 | @example | |
5379 | ||
5380 | @end example | |
5381 | @end ifinfo | |
5382 | @appendixsec The @code{cl-compat} package | |
5383 | ||
5384 | @noindent | |
5385 | The @dfn{CL} package includes emulations of some features of the | |
5386 | old @file{cl.el}, in the form of a compatibility package | |
5387 | @code{cl-compat}. To use it, put @code{(require 'cl-compat)} in | |
5388 | your program. | |
5389 | ||
5390 | The old package defined a number of internal routines without | |
5391 | @code{cl-} prefixes or other annotations. Call to these routines | |
5392 | may have crept into existing Lisp code. @code{cl-compat} | |
5393 | provides emulations of the following internal routines: | |
5394 | @code{pair-with-newsyms}, @code{zip-lists}, @code{unzip-lists}, | |
5395 | @code{reassemble-arglists}, @code{duplicate-symbols-p}, | |
5396 | @code{safe-idiv}. | |
5397 | ||
5398 | Some @code{setf} forms translated into calls to internal | |
5399 | functions that user code might call directly. The functions | |
5400 | @code{setnth}, @code{setnthcdr}, and @code{setelt} fall in | |
5401 | this category; they are defined by @code{cl-compat}, but the | |
5402 | best fix is to change to use @code{setf} properly. | |
5403 | ||
5404 | The @code{cl-compat} file defines the keyword functions | |
5405 | @code{keywordp}, @code{keyword-of}, and @code{defkeyword}, | |
5406 | which are not defined by the new @dfn{CL} package because the | |
5407 | use of keywords as data is discouraged. | |
5408 | ||
5409 | The @code{build-klist} mechanism for parsing keyword arguments | |
5410 | is emulated by @code{cl-compat}; the @code{with-keyword-args} | |
5411 | macro is not, however, and in any case it's best to change to | |
5412 | use the more natural keyword argument processing offered by | |
5413 | @code{defun*}. | |
5414 | ||
5415 | Multiple return values are treated differently by the two | |
5416 | Common Lisp packages. The old package's method was more | |
5417 | compatible with true Common Lisp, though it used heuristics | |
5418 | that caused it to report spurious multiple return values in | |
5419 | certain cases. The @code{cl-compat} package defines a set | |
5420 | of multiple-value macros that are compatible with the old | |
5421 | CL package; again, they are heuristic in nature, but they | |
5422 | are guaranteed to work in any case where the old package's | |
5423 | macros worked. To avoid name collision with the ``official'' | |
5424 | multiple-value facilities, the ones in @code{cl-compat} have | |
5425 | capitalized names: @code{Values}, @code{Values-list}, | |
5426 | @code{Multiple-value-bind}, etc. | |
5427 | ||
5428 | The functions @code{cl-floor}, @code{cl-ceiling}, @code{cl-truncate}, | |
5429 | and @code{cl-round} are defined by @code{cl-compat} to use the | |
5430 | old-style multiple-value mechanism, just as they did in the old | |
5431 | package. The newer @code{floor*} and friends return their two | |
5432 | results in a list rather than as multiple values. Note that | |
5433 | older versions of the old package used the unadorned names | |
5434 | @code{floor}, @code{ceiling}, etc.; @code{cl-compat} cannot use | |
5435 | these names because they conflict with Emacs 19 built-ins. | |
5436 | ||
5437 | @node Porting Common Lisp, Function Index, Old CL Compatibility, Top | |
5438 | @appendix Porting Common Lisp | |
5439 | ||
5440 | @noindent | |
5441 | This package is meant to be used as an extension to Emacs Lisp, | |
5442 | not as an Emacs implementation of true Common Lisp. Some of the | |
5443 | remaining differences between Emacs Lisp and Common Lisp make it | |
5444 | difficult to port large Common Lisp applications to Emacs. For | |
5445 | one, some of the features in this package are not fully compliant | |
5446 | with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there | |
5447 | are also quite a few features that this package does not provide | |
5448 | at all. Here are some major omissions that you will want watch out | |
5449 | for when bringing Common Lisp code into Emacs. | |
5450 | ||
5451 | @itemize @bullet | |
5452 | @item | |
5453 | Case-insensitivity. Symbols in Common Lisp are case-insensitive | |
5454 | by default. Some programs refer to a function or variable as | |
5455 | @code{foo} in one place and @code{Foo} or @code{FOO} in another. | |
5456 | Emacs Lisp will treat these as three distinct symbols. | |
5457 | ||
5458 | Some Common Lisp code is written entirely in upper case. While Emacs | |
5459 | is happy to let the program's own functions and variables use | |
5460 | this convention, calls to Lisp builtins like @code{if} and | |
5461 | @code{defun} will have to be changed to lower case. | |
5462 | ||
5463 | @item | |
5464 | Lexical scoping. In Common Lisp, function arguments and @code{let} | |
5465 | bindings apply only to references physically within their bodies | |
5466 | (or within macro expansions in their bodies). Emacs Lisp, by | |
5467 | contrast, uses @dfn{dynamic scoping} wherein a binding to a | |
5468 | variable is visible even inside functions called from the body. | |
5469 | ||
5470 | Variables in Common Lisp can be made dynamically scoped by | |
5471 | declaring them @code{special} or using @code{defvar}. In Emacs | |
5472 | Lisp it is as if all variables were declared @code{special}. | |
5473 | ||
5474 | Often you can use code that was written for lexical scoping | |
5475 | even in a dynamically scoped Lisp, but not always. Here is | |
5476 | an example of a Common Lisp code fragment that would fail in | |
5477 | Emacs Lisp: | |
5478 | ||
5479 | @example | |
5480 | (defun map-odd-elements (func list) | |
5481 | (loop for x in list | |
5482 | for flag = t then (not flag) | |
5483 | collect (if flag x (funcall func x)))) | |
5484 | ||
5485 | (defun add-odd-elements (list x) | |
5486 | (map-odd-elements (function (lambda (a) (+ a x))) list)) | |
5487 | @end example | |
5488 | ||
5489 | @noindent | |
5490 | In Common Lisp, the two functions' usages of @code{x} are completely | |
5491 | independent. In Emacs Lisp, the binding to @code{x} made by | |
5492 | @code{add-odd-elements} will have been hidden by the binding | |
5493 | in @code{map-odd-elements} by the time the @code{(+ a x)} function | |
5494 | is called. | |
5495 | ||
5496 | (This package avoids such problems in its own mapping functions | |
5497 | by using names like @code{cl-x} instead of @code{x} internally; | |
5498 | as long as you don't use the @code{cl-} prefix for your own | |
5499 | variables no collision can occur.) | |
5500 | ||
5501 | @xref{Lexical Bindings}, for a description of the @code{lexical-let} | |
5502 | form which establishes a Common Lisp-style lexical binding, and some | |
5503 | examples of how it differs from Emacs' regular @code{let}. | |
5504 | ||
5505 | @item | |
5506 | Reader macros. Common Lisp includes a second type of macro that | |
5507 | works at the level of individual characters. For example, Common | |
5508 | Lisp implements the quote notation by a reader macro called @code{'}, | |
5509 | whereas Emacs Lisp's parser just treats quote as a special case. | |
5510 | Some Lisp packages use reader macros to create special syntaxes | |
5511 | for themselves, which the Emacs parser is incapable of reading. | |
5512 | ||
5513 | The lack of reader macros, incidentally, is the reason behind | |
5514 | Emacs Lisp's unusual backquote syntax. Since backquotes are | |
5515 | implemented as a Lisp package and not built-in to the Emacs | |
5516 | parser, they are forced to use a regular macro named @code{`} | |
5517 | which is used with the standard function/macro call notation. | |
5518 | ||
5519 | @item | |
5520 | Other syntactic features. Common Lisp provides a number of | |
5521 | notations beginning with @code{#} that the Emacs Lisp parser | |
5522 | won't understand. For example, @samp{#| ... |#} is an | |
5523 | alternate comment notation, and @samp{#+lucid (foo)} tells | |
5524 | the parser to ignore the @code{(foo)} except in Lucid Common | |
5525 | Lisp. | |
5526 | ||
5527 | @item | |
5528 | Packages. In Common Lisp, symbols are divided into @dfn{packages}. | |
5529 | Symbols that are Lisp built-ins are typically stored in one package; | |
5530 | symbols that are vendor extensions are put in another, and each | |
5531 | application program would have a package for its own symbols. | |
5532 | Certain symbols are ``exported'' by a package and others are | |
5533 | internal; certain packages ``use'' or import the exported symbols | |
5534 | of other packages. To access symbols that would not normally be | |
5535 | visible due to this importing and exporting, Common Lisp provides | |
5536 | a syntax like @code{package:symbol} or @code{package::symbol}. | |
5537 | ||
5538 | Emacs Lisp has a single namespace for all interned symbols, and | |
5539 | then uses a naming convention of putting a prefix like @code{cl-} | |
5540 | in front of the name. Some Emacs packages adopt the Common Lisp-like | |
5541 | convention of using @code{cl:} or @code{cl::} as the prefix. | |
5542 | However, the Emacs parser does not understand colons and just | |
5543 | treats them as part of the symbol name. Thus, while @code{mapcar} | |
5544 | and @code{lisp:mapcar} may refer to the same symbol in Common | |
5545 | Lisp, they are totally distinct in Emacs Lisp. Common Lisp | |
5546 | programs which refer to a symbol by the full name sometimes | |
5547 | and the short name other times will not port cleanly to Emacs. | |
5548 | ||
5549 | Emacs Lisp does have a concept of ``obarrays,'' which are | |
5550 | package-like collections of symbols, but this feature is not | |
5551 | strong enough to be used as a true package mechanism. | |
5552 | ||
5553 | @item | |
5554 | The @code{format} function is quite different between Common | |
5555 | Lisp and Emacs Lisp. It takes an additional ``destination'' | |
5556 | argument before the format string. A destination of @code{nil} | |
5557 | means to format to a string as in Emacs Lisp; a destination | |
5558 | of @code{t} means to write to the terminal (similar to | |
5559 | @code{message} in Emacs). Also, format control strings are | |
5560 | utterly different; @code{~} is used instead of @code{%} to | |
5561 | introduce format codes, and the set of available codes is | |
5562 | much richer. There are no notations like @code{\n} for | |
5563 | string literals; instead, @code{format} is used with the | |
5564 | ``newline'' format code, @code{~%}. More advanced formatting | |
5565 | codes provide such features as paragraph filling, case | |
5566 | conversion, and even loops and conditionals. | |
5567 | ||
5568 | While it would have been possible to implement most of Common | |
5569 | Lisp @code{format} in this package (under the name @code{format*}, | |
5570 | of course), it was not deemed worthwhile. It would have required | |
5571 | a huge amount of code to implement even a decent subset of | |
5572 | @code{format*}, yet the functionality it would provide over | |
5573 | Emacs Lisp's @code{format} would rarely be useful. | |
5574 | ||
5575 | @item | |
5576 | Vector constants use square brackets in Emacs Lisp, but | |
5577 | @code{#(a b c)} notation in Common Lisp. To further complicate | |
5578 | matters, Emacs 19 introduces its own @code{#(} notation for | |
5579 | something entirely different---strings with properties. | |
5580 | ||
5581 | @item | |
5582 | Characters are distinct from integers in Common Lisp. The | |
5583 | notation for character constants is also different: @code{#\A} | |
5584 | instead of @code{?A}. Also, @code{string=} and @code{string-equal} | |
5585 | are synonyms in Emacs Lisp whereas the latter is case-insensitive | |
5586 | in Common Lisp. | |
5587 | ||
5588 | @item | |
5589 | Data types. Some Common Lisp data types do not exist in Emacs | |
5590 | Lisp. Rational numbers and complex numbers are not present, | |
5591 | nor are large integers (all integers are ``fixnums''). All | |
5592 | arrays are one-dimensional. There are no readtables or pathnames; | |
5593 | streams are a set of existing data types rather than a new data | |
5594 | type of their own. Hash tables, random-states, structures, and | |
5595 | packages (obarrays) are built from Lisp vectors or lists rather | |
5596 | than being distinct types. | |
5597 | ||
5598 | @item | |
5599 | The Common Lisp Object System (CLOS) is not implemented, | |
5600 | nor is the Common Lisp Condition System. However, the EIEIO package | |
5601 | from @uref{ftp://ftp.ultranet.com/pub/zappo} does implement some | |
5602 | CLOS functionality. | |
5603 | ||
5604 | @item | |
5605 | Common Lisp features that are completely redundant with Emacs | |
5606 | Lisp features of a different name generally have not been | |
5607 | implemented. For example, Common Lisp writes @code{defconstant} | |
5608 | where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list} | |
5609 | takes its arguments in different ways in the two Lisps but does | |
5610 | exactly the same thing, so this package has not bothered to | |
5611 | implement a Common Lisp-style @code{make-list}. | |
5612 | ||
5613 | @item | |
5614 | A few more notable Common Lisp features not included in this | |
5615 | package: @code{compiler-let}, @code{tagbody}, @code{prog}, | |
5616 | @code{ldb/dpb}, @code{parse-integer}, @code{cerror}. | |
5617 | ||
5618 | @item | |
5619 | Recursion. While recursion works in Emacs Lisp just like it | |
5620 | does in Common Lisp, various details of the Emacs Lisp system | |
5621 | and compiler make recursion much less efficient than it is in | |
5622 | most Lisps. Some schools of thought prefer to use recursion | |
5623 | in Lisp over other techniques; they would sum a list of | |
5624 | numbers using something like | |
5625 | ||
5626 | @example | |
5627 | (defun sum-list (list) | |
5628 | (if list | |
5629 | (+ (car list) (sum-list (cdr list))) | |
5630 | 0)) | |
5631 | @end example | |
5632 | ||
5633 | @noindent | |
5634 | where a more iteratively-minded programmer might write one of | |
5635 | these forms: | |
5636 | ||
5637 | @example | |
5638 | (let ((total 0)) (dolist (x my-list) (incf total x)) total) | |
5639 | (loop for x in my-list sum x) | |
5640 | @end example | |
5641 | ||
5642 | While this would be mainly a stylistic choice in most Common Lisps, | |
5643 | in Emacs Lisp you should be aware that the iterative forms are | |
5644 | much faster than recursion. Also, Lisp programmers will want to | |
5645 | note that the current Emacs Lisp compiler does not optimize tail | |
5646 | recursion. | |
5647 | @end itemize | |
5648 | ||
5649 | @node Function Index, Variable Index, Porting Common Lisp, Top | |
5650 | @unnumbered Function Index | |
5651 | ||
5652 | @printindex fn | |
5653 | ||
5654 | @node Variable Index, , Function Index, Top | |
5655 | @unnumbered Variable Index | |
5656 | ||
5657 | @printindex vr | |
5658 | ||
5659 | @contents | |
5660 | @bye |