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annotate man/cl.texi @ 4709:db7068430402
Add explicit GPL v2 or later notices to Bill Perry's code, where such notices
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| author | Jerry James <james@xemacs.org> |
|---|---|
| date | Mon, 05 Oct 2009 11:08:59 -0600 |
| parents | 8f1ee2d15784 |
| children | 755ae5b97edb |
| rev | line source |
|---|---|
| 428 | 1 \input texinfo @c -*-texinfo-*- |
| 2 @setfilename ../info/cl.info | |
| 3 @settitle Common Lisp Extensions | |
| 4 | |
| 5 @iftex | |
| 6 @finalout | |
| 7 @end iftex | |
| 8 | |
| 9 @ifinfo | |
| 10 @dircategory XEmacs Editor | |
| 11 @direntry | |
| 1353 | 12 * Common Lisp: (cl). XEmacs Common Lisp emulation package. |
| 428 | 13 @end direntry |
| 14 | |
| 1353 | 15 This file documents the XEmacs Common Lisp emulation package. |
| 428 | 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; for | |
| 88 more discussion and examples, Guy L. Steele's @cite{Common Lisp, the | |
| 89 Language}, second edition, is the definitive book on Common Lisp. | |
| 90 @iftex | |
| 91 Chapter numbers and most section numbers of this document parallel | |
| 92 those of Steele's book. | |
| 93 @end iftex | |
| 94 While this document does not assume any prior knowledge of Common | |
| 95 Lisp, it does assume a basic familiarity with Emacs Lisp. | |
| 96 | |
| 97 @menu | |
| 98 * Overview:: Installation, usage, etc. | |
| 99 * Program Structure:: Arglists, `eval-when', `defalias' | |
| 100 * Predicates:: `typep', `eql', and `equalp' | |
| 101 * Control Structure:: `setf', `when', `do', `loop', etc. | |
| 102 * Macros:: Destructuring, `define-compiler-macro' | |
| 103 * Declarations:: `proclaim', `declare', etc. | |
| 104 * Symbols:: Property lists, `gensym' | |
| 105 * Numbers:: Predicates, functions, random numbers | |
| 106 * Sequences:: Mapping, functions, searching, sorting | |
| 107 * Lists:: `cadr', `sublis', `member*', `assoc*', etc. | |
| 108 * Hash Tables:: `make-hash-table', `gethash', etc. | |
| 109 * Structures:: `defstruct' | |
| 110 * Assertions:: `check-type', `assert', `ignore-errors'. | |
| 111 | |
| 112 * Efficiency Concerns:: Hints and techniques | |
| 113 * Common Lisp Compatibility:: All known differences with Steele | |
| 114 * Old CL Compatibility:: All known differences with old cl.el | |
| 115 * Porting Common Lisp:: Hints for porting Common Lisp code | |
| 116 | |
| 117 * Function Index:: | |
| 118 * Variable Index:: | |
| 119 @end menu | |
| 120 | |
| 121 @node Overview, Program Structure, Top, Top | |
| 122 @ifinfo | |
| 123 @chapter Overview | |
| 124 @end ifinfo | |
| 125 @iftex | |
| 126 @section Overview | |
| 127 @end iftex | |
| 128 | |
| 129 @noindent | |
| 130 Common Lisp is a huge language, and Common Lisp systems tend to be | |
| 131 massive and extremely complex. Emacs Lisp, by contrast, is rather | |
| 132 minimalist in the choice of Lisp features it offers the programmer. | |
| 133 As Emacs Lisp programmers have grown in number, and the applications | |
| 134 they write have grown more ambitious, it has become clear that Emacs | |
| 135 Lisp could benefit from many of the conveniences of Common Lisp. | |
| 136 | |
| 137 The @dfn{CL} package adds a number of Common Lisp functions and | |
| 138 control structures to Emacs Lisp. While not a 100% complete | |
| 139 implementation of Common Lisp, @dfn{CL} adds enough functionality | |
| 140 to make Emacs Lisp programming significantly more convenient. | |
| 141 | |
| 142 Some Common Lisp features have been omitted from this package | |
| 143 for various reasons: | |
| 144 | |
| 145 @itemize @bullet | |
| 146 @item | |
| 147 Some features are too complex or bulky relative to their benefit | |
| 148 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine | |
| 149 examples of this group. | |
| 150 | |
| 151 @item | |
| 152 Other features cannot be implemented without modification to the | |
| 153 Emacs Lisp interpreter itself, such as multiple return values, | |
| 154 lexical scoping, case-insensitive symbols, and complex numbers. | |
| 155 The @dfn{CL} package generally makes no attempt to emulate these | |
| 156 features. | |
| 157 | |
| 158 @item | |
| 159 Some features conflict with existing things in Emacs Lisp. For | |
| 160 example, Emacs' @code{assoc} function is incompatible with the | |
| 161 Common Lisp @code{assoc}. In such cases, this package usually | |
| 162 adds the suffix @samp{*} to the function name of the Common | |
| 163 Lisp version of the function (e.g., @code{assoc*}). | |
| 164 @end itemize | |
| 165 | |
| 166 The package described here was written by Dave Gillespie, | |
| 167 @file{daveg@@synaptics.com}. It is a total rewrite of the original | |
| 168 1986 @file{cl.el} package by Cesar Quiroz. Most features of | |
| 169 the Quiroz package have been retained; any incompatibilities are | |
| 170 noted in the descriptions below. Care has been taken in this | |
| 171 version to ensure that each function is defined efficiently, | |
| 172 concisely, and with minimal impact on the rest of the Emacs | |
| 173 environment. | |
| 174 | |
| 175 @menu | |
| 176 * Usage:: How to use the CL package | |
| 177 * Organization:: The package's five component files | |
| 178 * Installation:: Compiling and installing CL | |
| 179 * Naming Conventions:: Notes on CL function names | |
| 180 @end menu | |
| 181 | |
| 182 @node Usage, Organization, Overview, Overview | |
| 183 @section Usage | |
| 184 | |
| 185 @noindent | |
| 186 Lisp code that uses features from the @dfn{CL} package should | |
| 187 include at the beginning: | |
| 188 | |
| 189 @example | |
| 190 (require 'cl) | |
| 191 @end example | |
| 192 | |
| 193 @noindent | |
| 194 If you want to ensure that the new (Gillespie) version of @dfn{CL} | |
| 195 is the one that is present, add an additional @code{(require 'cl-19)} | |
| 196 call: | |
| 197 | |
| 198 @example | |
| 199 (require 'cl) | |
| 200 (require 'cl-19) | |
| 201 @end example | |
| 202 | |
| 203 @noindent | |
| 204 The second call will fail (with ``@file{cl-19.el} not found'') if | |
| 205 the old @file{cl.el} package was in use. | |
| 206 | |
| 207 It is safe to arrange to load @dfn{CL} at all times, e.g., | |
| 208 in your @file{.emacs} file. But it's a good idea, for portability, | |
| 209 to @code{(require 'cl)} in your code even if you do this. | |
| 210 | |
| 211 @node Organization, Installation, Usage, Overview | |
| 212 @section Organization | |
| 213 | |
| 214 @noindent | |
| 215 The Common Lisp package is organized into four files: | |
| 216 | |
| 217 @table @file | |
| 218 @item cl.el | |
| 219 This is the ``main'' file, which contains basic functions | |
| 220 and information about the package. This file is relatively | |
| 221 compact---about 700 lines. | |
| 222 | |
| 223 @item cl-extra.el | |
| 224 This file contains the larger, more complex or unusual functions. | |
| 225 It is kept separate so that packages which only want to use Common | |
| 226 Lisp fundamentals like the @code{cadr} function won't need to pay | |
| 227 the overhead of loading the more advanced functions. | |
| 228 | |
| 229 @item cl-seq.el | |
| 230 This file contains most of the advanced functions for operating | |
| 231 on sequences or lists, such as @code{delete-if} and @code{assoc*}. | |
| 232 | |
| 233 @item cl-macs.el | |
| 234 This file contains the features of the packages which are macros | |
| 235 instead of functions. Macros expand when the caller is compiled, | |
| 236 not when it is run, so the macros generally only need to be | |
| 237 present when the byte-compiler is running (or when the macros are | |
| 238 used in uncompiled code such as a @file{.emacs} file). Most of | |
| 239 the macros of this package are isolated in @file{cl-macs.el} so | |
| 240 that they won't take up memory unless you are compiling. | |
| 241 @end table | |
| 242 | |
| 243 The file @file{cl.el} includes all necessary @code{autoload} | |
| 244 commands for the functions and macros in the other three files. | |
| 245 All you have to do is @code{(require 'cl)}, and @file{cl.el} | |
| 246 will take care of pulling in the other files when they are | |
| 247 needed. | |
| 248 | |
| 249 There is another file, @file{cl-compat.el}, which defines some | |
| 250 routines from the older @file{cl.el} package that are no longer | |
| 251 present in the new package. This includes internal routines | |
|
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252 like @code{setelt} and @code{zip-lists}, and deprecated features |
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253 like @code{defkeyword}. @xref{Old CL Compatibility}. |
| 428 | 254 |
| 255 @node Installation, Naming Conventions, Organization, Overview | |
| 256 @section Installation | |
| 257 | |
| 258 @noindent | |
| 259 Installation of the @dfn{CL} package is simple: Just put the | |
| 260 byte-compiled files @file{cl.elc}, @file{cl-extra.elc}, | |
| 261 @file{cl-seq.elc}, @file{cl-macs.elc}, and @file{cl-compat.elc} | |
| 262 into a directory on your @code{load-path}. | |
| 263 | |
| 264 There are no special requirements to compile this package: | |
| 265 The files do not have to be loaded before they are compiled, | |
| 266 nor do they need to be compiled in any particular order. | |
| 267 | |
| 268 You may choose to put the files into your main @file{lisp/} | |
| 269 directory, replacing the original @file{cl.el} file there. Or, | |
| 270 you could put them into a directory that comes before @file{lisp/} | |
| 271 on your @code{load-path} so that the old @file{cl.el} is | |
| 272 effectively hidden. | |
| 273 | |
| 274 Also, format the @file{cl.texinfo} file and put the resulting | |
| 275 Info files in the @file{info/} directory or another suitable place. | |
| 276 | |
| 277 You may instead wish to leave this package's components all in | |
| 278 their own directory, and then add this directory to your | |
| 279 @code{load-path} and (Emacs 19 only) @code{Info-directory-list}. | |
| 280 Add the directory to the front of the list so the old @dfn{CL} | |
| 281 package and its documentation are hidden. | |
| 282 | |
| 283 @node Naming Conventions, , Installation, Overview | |
| 284 @section Naming Conventions | |
| 285 | |
| 286 @noindent | |
| 287 Except where noted, all functions defined by this package have the | |
| 288 same names and calling conventions as their Common Lisp counterparts. | |
| 289 | |
| 290 Following is a complete list of functions whose names were changed | |
| 291 from Common Lisp, usually to avoid conflicts with Emacs. In each | |
| 292 case, a @samp{*} has been appended to the Common Lisp name to obtain | |
| 293 the Emacs name: | |
| 294 | |
| 295 @example | |
| 296 defun* defsubst* defmacro* function* | |
| 440 | 297 member* assoc* rassoc* remove* |
| 298 delete* mapcar* sort* floor* | |
| 299 ceiling* truncate* round* mod* | |
| 300 rem* random* | |
| 428 | 301 @end example |
| 302 | |
| 303 Internal function and variable names in the package are prefixed | |
| 304 by @code{cl-}. Here is a complete list of functions @emph{not} | |
| 305 prefixed by @code{cl-} which were not taken from Common Lisp: | |
| 306 | |
| 307 @example | |
| 308 member delete remove remq | |
| 309 rassoc floatp-safe lexical-let lexical-let* | |
| 310 callf callf2 letf letf* | |
| 311 defsubst* defalias add-hook eval-when-compile | |
| 312 @end example | |
| 313 | |
| 314 @noindent | |
| 315 (Most of these are Emacs 19 features provided to Emacs 18 users, | |
| 316 or introduced, like @code{remq}, for reasons of symmetry | |
| 317 with similar features.) | |
| 318 | |
| 319 The following simple functions and macros are defined in @file{cl.el}; | |
| 320 they do not cause other components like @file{cl-extra} to be loaded. | |
| 321 | |
| 322 @example | |
| 323 eql floatp-safe abs endp | |
| 324 evenp oddp plusp minusp | |
| 325 last butlast nbutlast caar .. cddddr | |
| 326 list* ldiff rest first .. tenth | |
| 327 member [1] copy-list subst mapcar* [2] | |
| 328 adjoin [3] acons pairlis when | |
| 329 unless pop [4] push [4] pushnew [3,4] | |
| 330 incf [4] decf [4] proclaim declaim | |
| 331 add-hook | |
| 332 @end example | |
| 333 | |
| 334 @noindent | |
| 335 [1] This is the Emacs 19-compatible function, not @code{member*}. | |
| 336 | |
| 337 @noindent | |
| 338 [2] Only for one sequence argument or two list arguments. | |
| 339 | |
| 340 @noindent | |
| 341 [3] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified, | |
| 342 and @code{:key} is not used. | |
| 343 | |
| 344 @noindent | |
| 345 [4] Only when @var{place} is a plain variable name. | |
| 346 | |
| 347 @iftex | |
| 348 @chapno=4 | |
| 349 @end iftex | |
| 350 | |
| 351 @node Program Structure, Predicates, Overview, Top | |
| 352 @chapter Program Structure | |
| 353 | |
| 354 @noindent | |
| 355 This section describes features of the @dfn{CL} package which have to | |
| 356 do with programs as a whole: advanced argument lists for functions, | |
| 357 and the @code{eval-when} construct. | |
| 358 | |
| 359 @menu | |
| 360 * Argument Lists:: `&key', `&aux', `defun*', `defmacro*'. | |
| 361 * Time of Evaluation:: The `eval-when' construct. | |
| 362 * Function Aliases:: The `defalias' function. | |
| 363 @end menu | |
| 364 | |
| 365 @iftex | |
| 366 @secno=1 | |
| 367 @end iftex | |
| 368 | |
| 369 @node Argument Lists, Time of Evaluation, Program Structure, Program Structure | |
| 370 @section Argument Lists | |
| 371 | |
| 372 @noindent | |
| 373 Emacs Lisp's notation for argument lists of functions is a subset of | |
| 374 the Common Lisp notation. As well as the familiar @code{&optional} | |
| 375 and @code{&rest} markers, Common Lisp allows you to specify default | |
| 376 values for optional arguments, and it provides the additional markers | |
| 377 @code{&key} and @code{&aux}. | |
| 378 | |
| 379 Since argument parsing is built-in to Emacs, there is no way for | |
| 380 this package to implement Common Lisp argument lists seamlessly. | |
| 381 Instead, this package defines alternates for several Lisp forms | |
| 382 which you must use if you need Common Lisp argument lists. | |
| 383 | |
| 384 @defspec defun* name arglist body... | |
| 385 This form is identical to the regular @code{defun} form, except | |
| 386 that @var{arglist} is allowed to be a full Common Lisp argument | |
| 387 list. Also, the function body is enclosed in an implicit block | |
| 388 called @var{name}; @pxref{Blocks and Exits}. | |
| 389 @end defspec | |
| 390 | |
| 391 @defspec defsubst* name arglist body... | |
| 392 This is just like @code{defun*}, except that the function that | |
| 393 is defined is automatically proclaimed @code{inline}, i.e., | |
| 394 calls to it may be expanded into in-line code by the byte compiler. | |
| 395 This is analogous to the @code{defsubst} form in Emacs 19; | |
| 396 @code{defsubst*} uses a different method (compiler macros) which | |
| 397 works in all version of Emacs, and also generates somewhat more | |
| 398 efficient inline expansions. In particular, @code{defsubst*} | |
| 399 arranges for the processing of keyword arguments, default values, | |
| 400 etc., to be done at compile-time whenever possible. | |
| 401 @end defspec | |
| 402 | |
| 403 @defspec defmacro* name arglist body... | |
| 404 This is identical to the regular @code{defmacro} form, | |
| 405 except that @var{arglist} is allowed to be a full Common Lisp | |
| 406 argument list. The @code{&environment} keyword is supported as | |
| 407 described in Steele. The @code{&whole} keyword is supported only | |
| 408 within destructured lists (see below); top-level @code{&whole} | |
| 409 cannot be implemented with the current Emacs Lisp interpreter. | |
| 410 The macro expander body is enclosed in an implicit block called | |
| 411 @var{name}. | |
| 412 @end defspec | |
| 413 | |
| 414 @defspec function* symbol-or-lambda | |
| 415 This is identical to the regular @code{function} form, | |
| 416 except that if the argument is a @code{lambda} form then that | |
| 417 form may use a full Common Lisp argument list. | |
| 418 @end defspec | |
| 419 | |
| 420 Also, all forms (such as @code{defsetf} and @code{flet}) defined | |
| 421 in this package that include @var{arglist}s in their syntax allow | |
| 422 full Common Lisp argument lists. | |
| 423 | |
| 424 Note that it is @emph{not} necessary to use @code{defun*} in | |
| 425 order to have access to most @dfn{CL} features in your function. | |
| 426 These features are always present; @code{defun*}'s only | |
| 427 difference from @code{defun} is its more flexible argument | |
| 428 lists and its implicit block. | |
| 429 | |
| 430 The full form of a Common Lisp argument list is | |
| 431 | |
| 432 @example | |
| 433 (@var{var}... | |
| 434 &optional (@var{var} @var{initform} @var{svar})... | |
| 435 &rest @var{var} | |
| 436 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})... | |
| 437 &aux (@var{var} @var{initform})...) | |
| 438 @end example | |
| 439 | |
| 440 Each of the five argument list sections is optional. The @var{svar}, | |
| 441 @var{initform}, and @var{keyword} parts are optional; if they are | |
| 442 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}. | |
| 443 | |
| 444 The first section consists of zero or more @dfn{required} arguments. | |
| 445 These arguments must always be specified in a call to the function; | |
| 446 there is no difference between Emacs Lisp and Common Lisp as far as | |
| 447 required arguments are concerned. | |
| 448 | |
| 449 The second section consists of @dfn{optional} arguments. These | |
| 450 arguments may be specified in the function call; if they are not, | |
| 451 @var{initform} specifies the default value used for the argument. | |
| 452 (No @var{initform} means to use @code{nil} as the default.) The | |
| 453 @var{initform} is evaluated with the bindings for the preceding | |
| 454 arguments already established; @code{(a &optional (b (1+ a)))} | |
| 455 matches one or two arguments, with the second argument defaulting | |
| 456 to one plus the first argument. If the @var{svar} is specified, | |
| 457 it is an auxiliary variable which is bound to @code{t} if the optional | |
| 458 argument was specified, or to @code{nil} if the argument was omitted. | |
| 459 If you don't use an @var{svar}, then there will be no way for your | |
| 460 function to tell whether it was called with no argument, or with | |
| 461 the default value passed explicitly as an argument. | |
| 462 | |
| 463 The third section consists of a single @dfn{rest} argument. If | |
| 464 more arguments were passed to the function than are accounted for | |
| 465 by the required and optional arguments, those extra arguments are | |
| 466 collected into a list and bound to the ``rest'' argument variable. | |
| 467 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp. | |
| 468 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in | |
| 469 macro contexts; this package accepts it all the time. | |
| 470 | |
| 471 The fourth section consists of @dfn{keyword} arguments. These | |
| 472 are optional arguments which are specified by name rather than | |
| 473 positionally in the argument list. For example, | |
| 474 | |
| 475 @example | |
| 476 (defun* foo (a &optional b &key c d (e 17))) | |
| 477 @end example | |
| 478 | |
| 479 @noindent | |
| 480 defines a function which may be called with one, two, or more | |
| 481 arguments. The first two arguments are bound to @code{a} and | |
| 482 @code{b} in the usual way. The remaining arguments must be | |
| 483 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed | |
| 484 by the value to be bound to the corresponding argument variable. | |
| 485 (Symbols whose names begin with a colon are called @dfn{keywords}, | |
| 486 and they are self-quoting in the same way as @code{nil} and | |
| 487 @code{t}.) | |
| 488 | |
| 489 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five | |
| 490 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword | |
| 491 appears more than once in the function call, the first occurrence | |
| 492 takes precedence over the later ones. Note that it is not possible | |
| 493 to specify keyword arguments without specifying the optional | |
| 494 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind | |
| 495 @code{b} to the keyword @code{:c}, then signal an error because | |
| 496 @code{2} is not a valid keyword. | |
| 497 | |
| 498 If a @var{keyword} symbol is explicitly specified in the argument | |
| 499 list as shown in the above diagram, then that keyword will be | |
| 500 used instead of just the variable name prefixed with a colon. | |
| 501 You can specify a @var{keyword} symbol which does not begin with | |
| 502 a colon at all, but such symbols will not be self-quoting; you | |
| 503 will have to quote them explicitly with an apostrophe in the | |
| 504 function call. | |
| 505 | |
| 506 Ordinarily it is an error to pass an unrecognized keyword to | |
| 507 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask | |
| 508 Lisp to ignore unrecognized keywords, either by adding the | |
| 509 marker @code{&allow-other-keys} after the keyword section | |
| 510 of the argument list, or by specifying an @code{:allow-other-keys} | |
| 511 argument in the call whose value is non-@code{nil}. If the | |
| 512 function uses both @code{&rest} and @code{&key} at the same time, | |
| 513 the ``rest'' argument is bound to the keyword list as it appears | |
| 514 in the call. For example: | |
| 515 | |
| 516 @smallexample | |
| 517 (defun* find-thing (thing &rest rest &key need &allow-other-keys) | |
| 518 (or (apply 'member* thing thing-list :allow-other-keys t rest) | |
| 519 (if need (error "Thing not found")))) | |
| 520 @end smallexample | |
| 521 | |
| 522 @noindent | |
| 523 This function takes a @code{:need} keyword argument, but also | |
| 524 accepts other keyword arguments which are passed on to the | |
| 525 @code{member*} function. @code{allow-other-keys} is used to | |
| 526 keep both @code{find-thing} and @code{member*} from complaining | |
| 527 about each others' keywords in the arguments. | |
| 528 | |
| 529 As a (significant) performance optimization, this package | |
| 530 implements the scan for keyword arguments by calling @code{memq} | |
| 531 to search for keywords in a ``rest'' argument. Technically | |
| 532 speaking, this is incorrect, since @code{memq} looks at the | |
| 533 odd-numbered values as well as the even-numbered keywords. | |
| 534 The net effect is that if you happen to pass a keyword symbol | |
| 535 as the @emph{value} of another keyword argument, where that | |
| 536 keyword symbol happens to equal the name of a valid keyword | |
| 537 argument of the same function, then the keyword parser will | |
| 538 become confused. This minor bug can only affect you if you | |
| 539 use keyword symbols as general-purpose data in your program; | |
| 540 this practice is strongly discouraged in Emacs Lisp. | |
| 541 | |
| 542 The fifth section of the argument list consists of @dfn{auxiliary | |
| 543 variables}. These are not really arguments at all, but simply | |
| 544 variables which are bound to @code{nil} or to the specified | |
| 545 @var{initforms} during execution of the function. There is no | |
| 546 difference between the following two functions, except for a | |
| 547 matter of stylistic taste: | |
| 548 | |
| 549 @example | |
| 550 (defun* foo (a b &aux (c (+ a b)) d) | |
| 551 @var{body}) | |
| 552 | |
| 553 (defun* foo (a b) | |
| 554 (let ((c (+ a b)) d) | |
| 555 @var{body})) | |
| 556 @end example | |
| 557 | |
| 558 Argument lists support @dfn{destructuring}. In Common Lisp, | |
| 559 destructuring is only allowed with @code{defmacro}; this package | |
| 560 allows it with @code{defun*} and other argument lists as well. | |
| 561 In destructuring, any argument variable (@var{var} in the above | |
| 562 diagram) can be replaced by a list of variables, or more generally, | |
| 563 a recursive argument list. The corresponding argument value must | |
| 564 be a list whose elements match this recursive argument list. | |
| 565 For example: | |
| 566 | |
| 567 @example | |
| 568 (defmacro* dolist ((var listform &optional resultform) | |
| 569 &rest body) | |
| 570 ...) | |
| 571 @end example | |
| 572 | |
| 573 This says that the first argument of @code{dolist} must be a list | |
| 574 of two or three items; if there are other arguments as well as this | |
| 575 list, they are stored in @code{body}. All features allowed in | |
| 576 regular argument lists are allowed in these recursive argument lists. | |
| 577 In addition, the clause @samp{&whole @var{var}} is allowed at the | |
| 578 front of a recursive argument list. It binds @var{var} to the | |
| 579 whole list being matched; thus @code{(&whole all a b)} matches | |
| 580 a list of two things, with @code{a} bound to the first thing, | |
| 581 @code{b} bound to the second thing, and @code{all} bound to the | |
| 582 list itself. (Common Lisp allows @code{&whole} in top-level | |
| 583 @code{defmacro} argument lists as well, but Emacs Lisp does not | |
| 584 support this usage.) | |
| 585 | |
| 586 One last feature of destructuring is that the argument list may be | |
| 587 dotted, so that the argument list @code{(a b . c)} is functionally | |
| 588 equivalent to @code{(a b &rest c)}. | |
| 589 | |
| 590 If the optimization quality @code{safety} is set to 0 | |
| 591 (@pxref{Declarations}), error checking for wrong number of | |
| 592 arguments and invalid keyword arguments is disabled. By default, | |
| 593 argument lists are rigorously checked. | |
| 594 | |
| 595 @node Time of Evaluation, Function Aliases, Argument Lists, Program Structure | |
| 596 @section Time of Evaluation | |
| 597 | |
| 598 @noindent | |
| 599 Normally, the byte-compiler does not actually execute the forms in | |
| 600 a file it compiles. For example, if a file contains @code{(setq foo t)}, | |
| 601 the act of compiling it will not actually set @code{foo} to @code{t}. | |
| 602 This is true even if the @code{setq} was a top-level form (i.e., not | |
| 603 enclosed in a @code{defun} or other form). Sometimes, though, you | |
| 604 would like to have certain top-level forms evaluated at compile-time. | |
| 605 For example, the compiler effectively evaluates @code{defmacro} forms | |
| 606 at compile-time so that later parts of the file can refer to the | |
| 607 macros that are defined. | |
| 608 | |
| 609 @defspec eval-when (situations...) forms... | |
| 610 This form controls when the body @var{forms} are evaluated. | |
| 611 The @var{situations} list may contain any set of the symbols | |
| 612 @code{compile}, @code{load}, and @code{eval} (or their long-winded | |
| 613 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel}, | |
| 614 and @code{:execute}). | |
| 615 | |
| 616 The @code{eval-when} form is handled differently depending on | |
| 617 whether or not it is being compiled as a top-level form. | |
| 618 Specifically, it gets special treatment if it is being compiled | |
| 619 by a command such as @code{byte-compile-file} which compiles files | |
| 620 or buffers of code, and it appears either literally at the | |
| 621 top level of the file or inside a top-level @code{progn}. | |
| 622 | |
| 623 For compiled top-level @code{eval-when}s, the body @var{forms} are | |
| 624 executed at compile-time if @code{compile} is in the @var{situations} | |
| 625 list, and the @var{forms} are written out to the file (to be executed | |
| 626 at load-time) if @code{load} is in the @var{situations} list. | |
| 627 | |
| 628 For non-compiled-top-level forms, only the @code{eval} situation is | |
| 629 relevant. (This includes forms executed by the interpreter, forms | |
| 630 compiled with @code{byte-compile} rather than @code{byte-compile-file}, | |
| 631 and non-top-level forms.) The @code{eval-when} acts like a | |
| 632 @code{progn} if @code{eval} is specified, and like @code{nil} | |
| 633 (ignoring the body @var{forms}) if not. | |
| 634 | |
| 635 The rules become more subtle when @code{eval-when}s are nested; | |
| 636 consult Steele (second edition) for the gruesome details (and | |
| 637 some gruesome examples). | |
| 638 | |
| 639 Some simple examples: | |
| 640 | |
| 641 @example | |
| 642 ;; Top-level forms in foo.el: | |
| 643 (eval-when (compile) (setq foo1 'bar)) | |
| 644 (eval-when (load) (setq foo2 'bar)) | |
| 645 (eval-when (compile load) (setq foo3 'bar)) | |
| 646 (eval-when (eval) (setq foo4 'bar)) | |
| 647 (eval-when (eval compile) (setq foo5 'bar)) | |
| 648 (eval-when (eval load) (setq foo6 'bar)) | |
| 649 (eval-when (eval compile load) (setq foo7 'bar)) | |
| 650 @end example | |
| 651 | |
| 652 When @file{foo.el} is compiled, these variables will be set during | |
| 653 the compilation itself: | |
| 654 | |
| 655 @example | |
| 656 foo1 foo3 foo5 foo7 ; `compile' | |
| 657 @end example | |
| 658 | |
| 659 When @file{foo.elc} is loaded, these variables will be set: | |
| 660 | |
| 661 @example | |
| 662 foo2 foo3 foo6 foo7 ; `load' | |
| 663 @end example | |
| 664 | |
| 665 And if @file{foo.el} is loaded uncompiled, these variables will | |
| 666 be set: | |
| 667 | |
| 668 @example | |
| 669 foo4 foo5 foo6 foo7 ; `eval' | |
| 670 @end example | |
| 671 | |
| 672 If these seven @code{eval-when}s had been, say, inside a @code{defun}, | |
| 673 then the first three would have been equivalent to @code{nil} and the | |
| 674 last four would have been equivalent to the corresponding @code{setq}s. | |
| 675 | |
| 676 Note that @code{(eval-when (load eval) @dots{})} is equivalent | |
| 677 to @code{(progn @dots{})} in all contexts. The compiler treats | |
| 678 certain top-level forms, like @code{defmacro} (sort-of) and | |
| 679 @code{require}, as if they were wrapped in @code{(eval-when | |
| 680 (compile load eval) @dots{})}. | |
| 681 @end defspec | |
| 682 | |
| 683 Emacs 19 includes two special forms related to @code{eval-when}. | |
| 684 One of these, @code{eval-when-compile}, is not quite equivalent to | |
| 685 any @code{eval-when} construct and is described below. This package | |
| 686 defines a version of @code{eval-when-compile} for the benefit of | |
| 687 Emacs 18 users. | |
| 688 | |
| 689 The other form, @code{(eval-and-compile @dots{})}, is exactly | |
| 690 equivalent to @samp{(eval-when (compile load eval) @dots{})} and | |
| 691 so is not itself defined by this package. | |
| 692 | |
| 693 @defspec eval-when-compile forms... | |
| 694 The @var{forms} are evaluated at compile-time; at execution time, | |
| 695 this form acts like a quoted constant of the resulting value. Used | |
| 696 at top-level, @code{eval-when-compile} is just like @samp{eval-when | |
| 697 (compile eval)}. In other contexts, @code{eval-when-compile} | |
| 698 allows code to be evaluated once at compile-time for efficiency | |
| 699 or other reasons. | |
| 700 | |
| 701 This form is similar to the @samp{#.} syntax of true Common Lisp. | |
| 702 @end defspec | |
| 703 | |
| 704 @defspec load-time-value form | |
| 705 The @var{form} is evaluated at load-time; at execution time, | |
| 706 this form acts like a quoted constant of the resulting value. | |
| 707 | |
| 708 Early Common Lisp had a @samp{#,} syntax that was similar to | |
| 709 this, but ANSI Common Lisp replaced it with @code{load-time-value} | |
| 710 and gave it more well-defined semantics. | |
| 711 | |
| 712 In a compiled file, @code{load-time-value} arranges for @var{form} | |
| 713 to be evaluated when the @file{.elc} file is loaded and then used | |
| 714 as if it were a quoted constant. In code compiled by | |
| 715 @code{byte-compile} rather than @code{byte-compile-file}, the | |
| 716 effect is identical to @code{eval-when-compile}. In uncompiled | |
| 717 code, both @code{eval-when-compile} and @code{load-time-value} | |
| 718 act exactly like @code{progn}. | |
| 719 | |
| 720 @example | |
| 721 (defun report () | |
| 722 (insert "This function was executed on: " | |
| 723 (current-time-string) | |
| 724 ", compiled on: " | |
| 725 (eval-when-compile (current-time-string)) | |
| 726 ;; or '#.(current-time-string) in real Common Lisp | |
| 727 ", and loaded on: " | |
| 728 (load-time-value (current-time-string)))) | |
| 729 @end example | |
| 730 | |
| 731 @noindent | |
| 732 Byte-compiled, the above defun will result in the following code | |
| 733 (or its compiled equivalent, of course) in the @file{.elc} file: | |
| 734 | |
| 735 @example | |
| 736 (setq --temp-- (current-time-string)) | |
| 737 (defun report () | |
| 738 (insert "This function was executed on: " | |
| 739 (current-time-string) | |
| 740 ", compiled on: " | |
| 741 '"Wed Jun 23 18:33:43 1993" | |
| 742 ", and loaded on: " | |
| 743 --temp--)) | |
| 744 @end example | |
| 745 @end defspec | |
| 746 | |
| 747 @node Function Aliases, , Time of Evaluation, Program Structure | |
| 748 @section Function Aliases | |
| 749 | |
| 750 @noindent | |
| 751 This section describes a feature from GNU Emacs 19 which this | |
| 752 package makes available in other versions of Emacs. | |
| 753 | |
| 754 @defun defalias symbol function | |
| 755 This function sets @var{symbol}'s function cell to @var{function}. | |
| 756 It is equivalent to @code{fset}, except that in GNU Emacs 19 it also | |
| 757 records the setting in @code{load-history} so that it can be undone | |
| 758 by a later @code{unload-feature}. | |
| 759 | |
| 760 In other versions of Emacs, @code{defalias} is a synonym for | |
| 761 @code{fset}. | |
| 762 @end defun | |
| 763 | |
| 764 @node Predicates, Control Structure, Program Structure, Top | |
| 765 @chapter Predicates | |
| 766 | |
| 767 @noindent | |
| 768 This section describes functions for testing whether various | |
| 769 facts are true or false. | |
| 770 | |
| 771 @menu | |
| 772 * Type Predicates:: `typep', `deftype', and `coerce' | |
| 773 * Equality Predicates:: `eql' and `equalp' | |
| 774 @end menu | |
| 775 | |
| 776 @node Type Predicates, Equality Predicates, Predicates, Predicates | |
| 777 @section Type Predicates | |
| 778 | |
| 779 @noindent | |
| 780 The @dfn{CL} package defines a version of the Common Lisp @code{typep} | |
| 781 predicate. | |
| 782 | |
| 783 @defun typep object type | |
| 784 Check if @var{object} is of type @var{type}, where @var{type} is a | |
| 785 (quoted) type name of the sort used by Common Lisp. For example, | |
| 786 @code{(typep foo 'integer)} is equivalent to @code{(integerp foo)}. | |
| 787 @end defun | |
| 788 | |
| 789 The @var{type} argument to the above function is either a symbol | |
| 790 or a list beginning with a symbol. | |
| 791 | |
| 792 @itemize @bullet | |
| 793 @item | |
| 794 If the type name is a symbol, Emacs appends @samp{-p} to the | |
| 795 symbol name to form the name of a predicate function for testing | |
| 796 the type. (Built-in predicates whose names end in @samp{p} rather | |
| 797 than @samp{-p} are used when appropriate.) | |
| 798 | |
| 799 @item | |
| 800 The type symbol @code{t} stands for the union of all types. | |
| 801 @code{(typep @var{object} t)} is always true. Likewise, the | |
| 802 type symbol @code{nil} stands for nothing at all, and | |
| 803 @code{(typep @var{object} nil)} is always false. | |
| 804 | |
| 805 @item | |
| 806 The type symbol @code{null} represents the symbol @code{nil}. | |
| 807 Thus @code{(typep @var{object} 'null)} is equivalent to | |
| 808 @code{(null @var{object})}. | |
| 809 | |
| 810 @item | |
| 811 The type symbol @code{real} is a synonym for @code{number}, and | |
| 812 @code{fixnum} is a synonym for @code{integer}. | |
| 813 | |
| 814 @item | |
| 815 The type symbols @code{character} and @code{string-char} match | |
| 816 characters. In Emacs-19 and XEmacs-19, characters are the same thing as | |
| 817 integers in the range 0-255. In XEmacs-20, where characters are a | |
| 818 first-class data type, this checks for actual characters, and | |
| 819 @code{(typep @var{8bit-integer} 'character)} will return @code{nil}. | |
| 820 | |
| 821 @item | |
| 822 The type symbol @code{float} uses the @code{floatp-safe} predicate | |
| 823 defined by this package rather than @code{floatp}, so it will work | |
| 824 correctly even in Emacs versions without floating-point support. | |
| 825 | |
| 826 @item | |
| 827 The type list @code{(integer @var{low} @var{high})} represents all | |
| 828 integers between @var{low} and @var{high}, inclusive. Either bound | |
| 829 may be a list of a single integer to specify an exclusive limit, | |
| 830 or a @code{*} to specify no limit. The type @code{(integer * *)} | |
| 831 is thus equivalent to @code{integer}. | |
| 832 | |
| 833 @item | |
| 834 Likewise, lists beginning with @code{float}, @code{real}, or | |
| 835 @code{number} represent numbers of that type falling in a particular | |
| 836 range. | |
| 837 | |
| 838 @item | |
| 839 Lists beginning with @code{and}, @code{or}, and @code{not} form | |
| 840 combinations of types. For example, @code{(or integer (float 0 *))} | |
| 841 represents all objects that are integers or non-negative floats. | |
| 842 | |
| 843 @item | |
| 844 Lists beginning with @code{member} or @code{member*} represent | |
| 845 objects @code{eql} to any of the following values. For example, | |
| 846 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)}, | |
| 847 and @code{(member nil)} is equivalent to @code{null}. | |
| 848 | |
| 849 @item | |
| 850 Lists of the form @code{(satisfies @var{predicate})} represent | |
| 851 all objects for which @var{predicate} returns true when called | |
| 852 with that object as an argument. | |
| 853 @end itemize | |
| 854 | |
| 855 The following function and macro (not technically predicates) are | |
| 856 related to @code{typep}. | |
| 857 | |
| 858 @defun coerce object type | |
| 859 This function attempts to convert @var{object} to the specified | |
| 860 @var{type}. If @var{object} is already of that type as determined by | |
| 861 @code{typep}, it is simply returned. Otherwise, certain types of | |
| 862 conversions will be made: If @var{type} is any sequence type | |
| 863 (@code{string}, @code{list}, etc.) then @var{object} will be | |
| 864 converted to that type if possible. If @var{type} is | |
| 865 @code{character}, then strings of length one and symbols with | |
| 866 one-character names can be coerced. If @var{type} is @code{float}, | |
| 867 then integers can be coerced in versions of Emacs that support | |
| 868 floats. In all other circumstances, @code{coerce} signals an | |
| 869 error. | |
| 870 @end defun | |
| 871 | |
| 872 @defspec deftype name arglist forms... | |
| 873 This macro defines a new type called @var{name}. It is similar | |
| 874 to @code{defmacro} in many ways; when @var{name} is encountered | |
| 875 as a type name, the body @var{forms} are evaluated and should | |
| 876 return a type specifier that is equivalent to the type. The | |
| 877 @var{arglist} is a Common Lisp argument list of the sort accepted | |
| 878 by @code{defmacro*}. The type specifier @samp{(@var{name} @var{args}...)} | |
| 879 is expanded by calling the expander with those arguments; the type | |
| 880 symbol @samp{@var{name}} is expanded by calling the expander with | |
| 881 no arguments. The @var{arglist} is processed the same as for | |
| 882 @code{defmacro*} except that optional arguments without explicit | |
| 883 defaults use @code{*} instead of @code{nil} as the ``default'' | |
| 884 default. Some examples: | |
| 885 | |
| 886 @example | |
| 887 (deftype null () '(satisfies null)) ; predefined | |
| 888 (deftype list () '(or null cons)) ; predefined | |
| 889 (deftype unsigned-byte (&optional bits) | |
| 890 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits))))) | |
| 891 (unsigned-byte 8) @equiv{} (integer 0 255) | |
| 892 (unsigned-byte) @equiv{} (integer 0 *) | |
| 893 unsigned-byte @equiv{} (integer 0 *) | |
| 894 @end example | |
| 895 | |
| 896 @noindent | |
| 897 The last example shows how the Common Lisp @code{unsigned-byte} | |
| 898 type specifier could be implemented if desired; this package does | |
| 899 not implement @code{unsigned-byte} by default. | |
| 900 @end defspec | |
| 901 | |
| 902 The @code{typecase} and @code{check-type} macros also use type | |
| 903 names. @xref{Conditionals}. @xref{Assertions}. The @code{map}, | |
| 904 @code{concatenate}, and @code{merge} functions take type-name | |
| 905 arguments to specify the type of sequence to return. @xref{Sequences}. | |
| 906 | |
| 907 @node Equality Predicates, , Type Predicates, Predicates | |
| 908 @section Equality Predicates | |
| 909 | |
| 910 @noindent | |
| 911 This package defines two Common Lisp predicates, @code{eql} and | |
| 912 @code{equalp}. | |
| 913 | |
| 914 @defun eql a b | |
| 915 This function is almost the same as @code{eq}, except that if @var{a} | |
| 916 and @var{b} are numbers of the same type, it compares them for numeric | |
| 917 equality (as if by @code{equal} instead of @code{eq}). This makes a | |
| 918 difference only for versions of Emacs that are compiled with | |
| 919 floating-point support, such as Emacs 19. Emacs floats are allocated | |
| 920 objects just like cons cells, which means that @code{(eq 3.0 3.0)} | |
| 921 will not necessarily be true---if the two @code{3.0}s were allocated | |
| 922 separately, the pointers will be different even though the numbers are | |
| 923 the same. But @code{(eql 3.0 3.0)} will always be true. | |
| 924 | |
| 925 The types of the arguments must match, so @code{(eql 3 3.0)} is | |
| 926 still false. | |
| 927 | |
| 928 Note that Emacs integers are ``direct'' rather than allocated, which | |
| 929 basically means @code{(eq 3 3)} will always be true. Thus @code{eq} | |
| 930 and @code{eql} behave differently only if floating-point numbers are | |
| 931 involved, and are indistinguishable on Emacs versions that don't | |
| 932 support floats. | |
| 933 | |
| 934 There is a slight inconsistency with Common Lisp in the treatment of | |
| 935 positive and negative zeros. Some machines, notably those with IEEE | |
| 936 standard arithmetic, represent @code{+0} and @code{-0} as distinct | |
| 937 values. Normally this doesn't matter because the standard specifies | |
| 938 that @code{(= 0.0 -0.0)} should always be true, and this is indeed | |
| 939 what Emacs Lisp and Common Lisp do. But the Common Lisp standard | |
| 940 states that @code{(eql 0.0 -0.0)} and @code{(equal 0.0 -0.0)} should | |
| 941 be false on IEEE-like machines; Emacs Lisp does not do this, and in | |
| 942 fact the only known way to distinguish between the two zeros in Emacs | |
| 943 Lisp is to @code{format} them and check for a minus sign. | |
| 944 @end defun | |
| 945 | |
| 946 @defun equalp a b | |
| 947 This function is a more flexible version of @code{equal}. In | |
| 948 particular, it compares strings and characters case-insensitively, and | |
| 949 it compares numbers without regard to type (so that @code{(equalp 3 | |
| 950 3.0)} is true). Vectors and conses are compared recursively. All other | |
| 951 objects are compared as if by @code{equal}. | |
| 952 | |
| 953 This function differs from Common Lisp @code{equalp} in several | |
| 954 respects. In keeping with the idea that strings are less | |
| 955 vector-like in Emacs Lisp, this package's @code{equalp} also will not | |
| 956 compare strings against vectors of integers. | |
| 957 @end defun | |
| 958 | |
| 959 Also note that the Common Lisp functions @code{member} and @code{assoc} | |
| 960 use @code{eql} to compare elements, whereas Emacs Lisp follows the | |
| 961 MacLisp tradition and uses @code{equal} for these two functions. | |
| 962 In Emacs, use @code{member*} and @code{assoc*} to get functions | |
| 963 which use @code{eql} for comparisons. | |
| 964 | |
| 965 @node Control Structure, Macros, Predicates, Top | |
| 966 @chapter Control Structure | |
| 967 | |
| 968 @noindent | |
| 969 The features described in the following sections implement | |
| 970 various advanced control structures, including the powerful | |
| 971 @code{setf} facility and a number of looping and conditional | |
| 972 constructs. | |
| 973 | |
| 974 @menu | |
| 975 * Assignment:: The `psetq' form | |
| 976 * Generalized Variables:: `setf', `incf', `push', etc. | |
| 977 * Variable Bindings:: `progv', `lexical-let', `flet', `macrolet' | |
| 978 * Conditionals:: `when', `unless', `case', `typecase' | |
| 979 * Blocks and Exits:: `block', `return', `return-from' | |
| 980 * Iteration:: `do', `dotimes', `dolist', `do-symbols' | |
| 981 * Loop Facility:: The Common Lisp `loop' macro | |
| 982 * Multiple Values:: `values', `multiple-value-bind', etc. | |
| 983 @end menu | |
| 984 | |
| 985 @node Assignment, Generalized Variables, Control Structure, Control Structure | |
| 986 @section Assignment | |
| 987 | |
| 988 @noindent | |
| 989 The @code{psetq} form is just like @code{setq}, except that multiple | |
| 990 assignments are done in parallel rather than sequentially. | |
| 991 | |
| 992 @defspec psetq [symbol form]@dots{} | |
| 993 This special form (actually a macro) is used to assign to several | |
| 994 variables simultaneously. Given only one @var{symbol} and @var{form}, | |
| 995 it has the same effect as @code{setq}. Given several @var{symbol} | |
| 996 and @var{form} pairs, it evaluates all the @var{form}s in advance | |
| 997 and then stores the corresponding variables afterwards. | |
| 998 | |
| 999 @example | |
| 1000 (setq x 2 y 3) | |
| 1001 (setq x (+ x y) y (* x y)) | |
| 1002 x | |
| 1003 @result{} 5 | |
| 1004 y ; @r{@code{y} was computed after @code{x} was set.} | |
| 1005 @result{} 15 | |
| 1006 (setq x 2 y 3) | |
| 1007 (psetq x (+ x y) y (* x y)) | |
| 1008 x | |
| 1009 @result{} 5 | |
| 1010 y ; @r{@code{y} was computed before @code{x} was set.} | |
| 1011 @result{} 6 | |
| 1012 @end example | |
| 1013 | |
| 1014 The simplest use of @code{psetq} is @code{(psetq x y y x)}, which | |
| 1015 exchanges the values of two variables. (The @code{rotatef} form | |
| 1016 provides an even more convenient way to swap two variables; | |
| 1017 @pxref{Modify Macros}.) | |
| 1018 | |
| 1019 @code{psetq} always returns @code{nil}. | |
| 1020 @end defspec | |
| 1021 | |
| 1022 @node Generalized Variables, Variable Bindings, Assignment, Control Structure | |
| 1023 @section Generalized Variables | |
| 1024 | |
| 1025 @noindent | |
| 1026 A ``generalized variable'' or ``place form'' is one of the many places | |
| 1027 in Lisp memory where values can be stored. The simplest place form is | |
| 1028 a regular Lisp variable. But the cars and cdrs of lists, elements | |
| 1029 of arrays, properties of symbols, and many other locations are also | |
| 1030 places where Lisp values are stored. | |
| 1031 | |
| 1032 The @code{setf} form is like @code{setq}, except that it accepts | |
| 1033 arbitrary place forms on the left side rather than just | |
| 1034 symbols. For example, @code{(setf (car a) b)} sets the car of | |
| 1035 @code{a} to @code{b}, doing the same operation as @code{(setcar a b)} | |
| 1036 but without having to remember two separate functions for setting | |
| 1037 and accessing every type of place. | |
| 1038 | |
| 1039 Generalized variables are analogous to ``lvalues'' in the C | |
| 1040 language, where @samp{x = a[i]} gets an element from an array | |
| 1041 and @samp{a[i] = x} stores an element using the same notation. | |
| 1042 Just as certain forms like @code{a[i]} can be lvalues in C, there | |
| 1043 is a set of forms that can be generalized variables in Lisp. | |
| 1044 | |
| 1045 @menu | |
| 1046 * Basic Setf:: `setf' and place forms | |
| 1047 * Modify Macros:: `incf', `push', `rotatef', `letf', `callf', etc. | |
| 1048 * Customizing Setf:: `define-modify-macro', `defsetf', `define-setf-method' | |
| 1049 @end menu | |
| 1050 | |
| 1051 @node Basic Setf, Modify Macros, Generalized Variables, Generalized Variables | |
| 1052 @subsection Basic Setf | |
| 1053 | |
| 1054 @noindent | |
| 1055 The @code{setf} macro is the most basic way to operate on generalized | |
| 1056 variables. | |
| 1057 | |
| 1058 @defspec setf [place form]@dots{} | |
| 1059 This macro evaluates @var{form} and stores it in @var{place}, which | |
| 1060 must be a valid generalized variable form. If there are several | |
| 1061 @var{place} and @var{form} pairs, the assignments are done sequentially | |
| 1062 just as with @code{setq}. @code{setf} returns the value of the last | |
| 1063 @var{form}. | |
| 1064 | |
| 1065 The following Lisp forms will work as generalized variables, and | |
| 1066 so may legally appear in the @var{place} argument of @code{setf}: | |
| 1067 | |
| 1068 @itemize @bullet | |
| 1069 @item | |
| 1070 A symbol naming a variable. In other words, @code{(setf x y)} is | |
| 1071 exactly equivalent to @code{(setq x y)}, and @code{setq} itself is | |
| 1072 strictly speaking redundant now that @code{setf} exists. Many | |
| 1073 programmers continue to prefer @code{setq} for setting simple | |
| 1074 variables, though, purely for stylistic or historical reasons. | |
| 446 | 1075 The form @code{(setf x y)} actually expands to @code{(setq x y)}, |
| 428 | 1076 so there is no performance penalty for using it in compiled code. |
| 1077 | |
| 1078 @item | |
| 1079 A call to any of the following Lisp functions: | |
| 1080 | |
| 1081 @smallexample | |
| 1082 car cdr caar .. cddddr | |
| 1083 nth rest first .. tenth | |
| 1084 aref elt nthcdr | |
| 1085 symbol-function symbol-value symbol-plist | |
| 440 | 1086 get getf gethash |
| 1087 subseq | |
| 428 | 1088 @end smallexample |
| 1089 | |
| 1090 @noindent | |
| 1091 Note that for @code{nthcdr} and @code{getf}, the list argument | |
| 1092 of the function must itself be a valid @var{place} form. For | |
| 1093 example, @code{(setf (nthcdr 0 foo) 7)} will set @code{foo} itself | |
| 1094 to 7. Note that @code{push} and @code{pop} on an @code{nthcdr} | |
| 1095 place can be used to insert or delete at any position in a list. | |
| 1096 The use of @code{nthcdr} as a @var{place} form is an extension | |
| 1097 to standard Common Lisp. | |
| 1098 | |
| 1099 @item | |
| 1100 The following Emacs-specific functions are also @code{setf}-able. | |
| 1101 (Some of these are defined only in Emacs 19 or only in XEmacs.) | |
| 1102 | |
| 1103 @smallexample | |
| 1104 buffer-file-name marker-position | |
| 1105 buffer-modified-p match-data | |
| 1106 buffer-name mouse-position | |
| 1107 buffer-string overlay-end | |
| 1108 buffer-substring overlay-get | |
| 1109 current-buffer overlay-start | |
| 1110 current-case-table point | |
| 1111 current-column point-marker | |
| 1112 current-global-map point-max | |
| 1113 current-input-mode point-min | |
| 1114 current-local-map process-buffer | |
| 1115 current-window-configuration process-filter | |
| 1116 default-file-modes process-sentinel | |
| 1117 default-value read-mouse-position | |
| 1118 documentation-property screen-height | |
| 1119 extent-data screen-menubar | |
| 1120 extent-end-position screen-width | |
| 1121 extent-start-position selected-window | |
| 1122 face-background selected-screen | |
| 1123 face-background-pixmap selected-frame | |
| 1124 face-font standard-case-table | |
| 1125 face-foreground syntax-table | |
| 1126 face-underline-p window-buffer | |
| 1127 file-modes window-dedicated-p | |
| 1128 frame-height window-display-table | |
| 1129 frame-parameters window-height | |
| 1130 frame-visible-p window-hscroll | |
| 1131 frame-width window-point | |
| 1132 get-register window-start | |
| 1133 getenv window-width | |
| 1134 global-key-binding x-get-cut-buffer | |
| 1135 keymap-parent x-get-cutbuffer | |
| 1136 local-key-binding x-get-secondary-selection | |
| 1137 mark x-get-selection | |
| 1138 mark-marker | |
| 1139 @end smallexample | |
| 1140 | |
| 1141 Most of these have directly corresponding ``set'' functions, like | |
| 1142 @code{use-local-map} for @code{current-local-map}, or @code{goto-char} | |
| 1143 for @code{point}. A few, like @code{point-min}, expand to longer | |
| 1144 sequences of code when they are @code{setf}'d (@code{(narrow-to-region | |
| 1145 x (point-max))} in this case). | |
| 1146 | |
| 1147 @item | |
| 1148 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])}, | |
| 1149 where @var{subplace} is itself a legal generalized variable whose | |
| 1150 current value is a string, and where the value stored is also a | |
| 1151 string. The new string is spliced into the specified part of the | |
| 1152 destination string. For example: | |
| 1153 | |
| 1154 @example | |
| 1155 (setq a (list "hello" "world")) | |
| 1156 @result{} ("hello" "world") | |
| 1157 (cadr a) | |
| 1158 @result{} "world" | |
| 1159 (substring (cadr a) 2 4) | |
| 1160 @result{} "rl" | |
| 1161 (setf (substring (cadr a) 2 4) "o") | |
| 1162 @result{} "o" | |
| 1163 (cadr a) | |
| 1164 @result{} "wood" | |
| 1165 a | |
| 1166 @result{} ("hello" "wood") | |
| 1167 @end example | |
| 1168 | |
| 1169 The generalized variable @code{buffer-substring}, listed above, | |
| 1170 also works in this way by replacing a portion of the current buffer. | |
| 1171 | |
| 1172 @item | |
| 1173 A call of the form @code{(apply '@var{func} @dots{})} or | |
| 1174 @code{(apply (function @var{func}) @dots{})}, where @var{func} | |
| 1175 is a @code{setf}-able function whose store function is ``suitable'' | |
| 1176 in the sense described in Steele's book; since none of the standard | |
| 1177 Emacs place functions are suitable in this sense, this feature is | |
| 1178 only interesting when used with places you define yourself with | |
| 1179 @code{define-setf-method} or the long form of @code{defsetf}. | |
| 1180 | |
| 1181 @item | |
| 1182 A macro call, in which case the macro is expanded and @code{setf} | |
| 1183 is applied to the resulting form. | |
| 1184 | |
| 1185 @item | |
| 1186 Any form for which a @code{defsetf} or @code{define-setf-method} | |
| 1187 has been made. | |
| 1188 @end itemize | |
| 1189 | |
| 1190 Using any forms other than these in the @var{place} argument to | |
| 1191 @code{setf} will signal an error. | |
| 1192 | |
| 1193 The @code{setf} macro takes care to evaluate all subforms in | |
| 1194 the proper left-to-right order; for example, | |
| 1195 | |
| 1196 @example | |
| 1197 (setf (aref vec (incf i)) i) | |
| 1198 @end example | |
| 1199 | |
| 1200 @noindent | |
| 1201 looks like it will evaluate @code{(incf i)} exactly once, before the | |
| 1202 following access to @code{i}; the @code{setf} expander will insert | |
| 1203 temporary variables as necessary to ensure that it does in fact work | |
| 1204 this way no matter what setf-method is defined for @code{aref}. | |
| 1205 (In this case, @code{aset} would be used and no such steps would | |
| 1206 be necessary since @code{aset} takes its arguments in a convenient | |
| 1207 order.) | |
| 1208 | |
| 1209 However, if the @var{place} form is a macro which explicitly | |
| 1210 evaluates its arguments in an unusual order, this unusual order | |
| 1211 will be preserved. Adapting an example from Steele, given | |
| 1212 | |
| 1213 @example | |
| 1214 (defmacro wrong-order (x y) (list 'aref y x)) | |
| 1215 @end example | |
| 1216 | |
| 1217 @noindent | |
| 1218 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will | |
| 1219 evaluate @var{b} first, then @var{a}, just as in an actual call | |
| 1220 to @code{wrong-order}. | |
| 1221 @end defspec | |
| 1222 | |
| 1223 @node Modify Macros, Customizing Setf, Basic Setf, Generalized Variables | |
| 1224 @subsection Modify Macros | |
| 1225 | |
| 1226 @noindent | |
| 1227 This package defines a number of other macros besides @code{setf} | |
| 1228 that operate on generalized variables. Many are interesting and | |
| 1229 useful even when the @var{place} is just a variable name. | |
| 1230 | |
| 1231 @defspec psetf [place form]@dots{} | |
| 1232 This macro is to @code{setf} what @code{psetq} is to @code{setq}: | |
| 1233 When several @var{place}s and @var{form}s are involved, the | |
| 1234 assignments take place in parallel rather than sequentially. | |
| 1235 Specifically, all subforms are evaluated from left to right, then | |
| 1236 all the assignments are done (in an undefined order). | |
| 1237 @end defspec | |
| 1238 | |
| 1239 @defspec incf place &optional x | |
| 1240 This macro increments the number stored in @var{place} by one, or | |
| 1241 by @var{x} if specified. The incremented value is returned. For | |
| 1242 example, @code{(incf i)} is equivalent to @code{(setq i (1+ i))}, and | |
| 1243 @code{(incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}. | |
| 1244 | |
| 1245 Once again, care is taken to preserve the ``apparent'' order of | |
| 1246 evaluation. For example, | |
| 1247 | |
| 1248 @example | |
| 1249 (incf (aref vec (incf i))) | |
| 1250 @end example | |
| 1251 | |
| 1252 @noindent | |
| 1253 appears to increment @code{i} once, then increment the element of | |
| 1254 @code{vec} addressed by @code{i}; this is indeed exactly what it | |
| 1255 does, which means the above form is @emph{not} equivalent to the | |
| 1256 ``obvious'' expansion, | |
| 1257 | |
| 1258 @example | |
| 1259 (setf (aref vec (incf i)) (1+ (aref vec (incf i)))) ; Wrong! | |
| 1260 @end example | |
| 1261 | |
| 1262 @noindent | |
| 1263 but rather to something more like | |
| 1264 | |
| 1265 @example | |
| 1266 (let ((temp (incf i))) | |
| 1267 (setf (aref vec temp) (1+ (aref vec temp)))) | |
| 1268 @end example | |
| 1269 | |
| 1270 @noindent | |
| 1271 Again, all of this is taken care of automatically by @code{incf} and | |
| 1272 the other generalized-variable macros. | |
| 1273 | |
| 1274 As a more Emacs-specific example of @code{incf}, the expression | |
| 1275 @code{(incf (point) @var{n})} is essentially equivalent to | |
| 1276 @code{(forward-char @var{n})}. | |
| 1277 @end defspec | |
| 1278 | |
| 1279 @defspec decf place &optional x | |
| 1280 This macro decrements the number stored in @var{place} by one, or | |
| 1281 by @var{x} if specified. | |
| 1282 @end defspec | |
| 1283 | |
| 1284 @defspec pop place | |
| 1285 This macro removes and returns the first element of the list stored | |
| 1286 in @var{place}. It is analogous to @code{(prog1 (car @var{place}) | |
| 1287 (setf @var{place} (cdr @var{place})))}, except that it takes care | |
| 1288 to evaluate all subforms only once. | |
| 1289 @end defspec | |
| 1290 | |
| 1291 @defspec push x place | |
| 1292 This macro inserts @var{x} at the front of the list stored in | |
| 1293 @var{place}. It is analogous to @code{(setf @var{place} (cons | |
| 1294 @var{x} @var{place}))}, except for evaluation of the subforms. | |
| 1295 @end defspec | |
| 1296 | |
| 1297 @defspec pushnew x place @t{&key :test :test-not :key} | |
| 1298 This macro inserts @var{x} at the front of the list stored in | |
| 1299 @var{place}, but only if @var{x} was not @code{eql} to any | |
| 1300 existing element of the list. The optional keyword arguments | |
| 1301 are interpreted in the same way as for @code{adjoin}. | |
| 1302 @xref{Lists as Sets}. | |
| 1303 @end defspec | |
| 1304 | |
| 1305 @defspec shiftf place@dots{} newvalue | |
| 1306 This macro shifts the @var{place}s left by one, shifting in the | |
| 1307 value of @var{newvalue} (which may be any Lisp expression, not just | |
| 1308 a generalized variable), and returning the value shifted out of | |
| 1309 the first @var{place}. Thus, @code{(shiftf @var{a} @var{b} @var{c} | |
| 1310 @var{d})} is equivalent to | |
| 1311 | |
| 1312 @example | |
| 1313 (prog1 | |
| 1314 @var{a} | |
| 1315 (psetf @var{a} @var{b} | |
| 1316 @var{b} @var{c} | |
| 1317 @var{c} @var{d})) | |
| 1318 @end example | |
| 1319 | |
| 1320 @noindent | |
| 1321 except that the subforms of @var{a}, @var{b}, and @var{c} are actually | |
| 1322 evaluated only once each and in the apparent order. | |
| 1323 @end defspec | |
| 1324 | |
| 1325 @defspec rotatef place@dots{} | |
| 1326 This macro rotates the @var{place}s left by one in circular fashion. | |
| 1327 Thus, @code{(rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to | |
| 1328 | |
| 1329 @example | |
| 1330 (psetf @var{a} @var{b} | |
| 1331 @var{b} @var{c} | |
| 1332 @var{c} @var{d} | |
| 1333 @var{d} @var{a}) | |
| 1334 @end example | |
| 1335 | |
| 1336 @noindent | |
| 1337 except for the evaluation of subforms. @code{rotatef} always | |
| 1338 returns @code{nil}. Note that @code{(rotatef @var{a} @var{b})} | |
| 1339 conveniently exchanges @var{a} and @var{b}. | |
| 1340 @end defspec | |
| 1341 | |
| 1342 The following macros were invented for this package; they have no | |
| 1343 analogues in Common Lisp. | |
| 1344 | |
| 1345 @defspec letf (bindings@dots{}) forms@dots{} | |
| 1346 This macro is analogous to @code{let}, but for generalized variables | |
| 1347 rather than just symbols. Each @var{binding} should be of the form | |
| 1348 @code{(@var{place} @var{value})}; the original contents of the | |
| 1349 @var{place}s are saved, the @var{value}s are stored in them, and | |
| 1350 then the body @var{form}s are executed. Afterwards, the @var{places} | |
| 1351 are set back to their original saved contents. This cleanup happens | |
| 1352 even if the @var{form}s exit irregularly due to a @code{throw} or an | |
| 1353 error. | |
| 1354 | |
| 1355 For example, | |
| 1356 | |
| 1357 @example | |
| 1358 (letf (((point) (point-min)) | |
| 1359 (a 17)) | |
| 1360 ...) | |
| 1361 @end example | |
| 1362 | |
| 1363 @noindent | |
| 1364 moves ``point'' in the current buffer to the beginning of the buffer, | |
| 1365 and also binds @code{a} to 17 (as if by a normal @code{let}, since | |
| 1366 @code{a} is just a regular variable). After the body exits, @code{a} | |
| 1367 is set back to its original value and point is moved back to its | |
| 1368 original position. | |
| 1369 | |
| 1370 Note that @code{letf} on @code{(point)} is not quite like a | |
| 1371 @code{save-excursion}, as the latter effectively saves a marker | |
| 1372 which tracks insertions and deletions in the buffer. Actually, | |
| 1373 a @code{letf} of @code{(point-marker)} is much closer to this | |
| 1374 behavior. (@code{point} and @code{point-marker} are equivalent | |
| 1375 as @code{setf} places; each will accept either an integer or a | |
| 1376 marker as the stored value.) | |
| 1377 | |
| 1378 Since generalized variables look like lists, @code{let}'s shorthand | |
| 1379 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would | |
| 1380 be ambiguous in @code{letf} and is not allowed. | |
| 1381 | |
| 1382 However, a @var{binding} specifier may be a one-element list | |
| 1383 @samp{(@var{place})}, which is similar to @samp{(@var{place} | |
| 1384 @var{place})}. In other words, the @var{place} is not disturbed | |
| 1385 on entry to the body, and the only effect of the @code{letf} is | |
| 1386 to restore the original value of @var{place} afterwards. (The | |
| 1387 redundant access-and-store suggested by the @code{(@var{place} | |
| 1388 @var{place})} example does not actually occur.) | |
| 1389 | |
| 1390 In most cases, the @var{place} must have a well-defined value on | |
| 1391 entry to the @code{letf} form. The only exceptions are plain | |
| 1392 variables and calls to @code{symbol-value} and @code{symbol-function}. | |
| 1393 If the symbol is not bound on entry, it is simply made unbound by | |
| 1394 @code{makunbound} or @code{fmakunbound} on exit. | |
| 1395 @end defspec | |
| 1396 | |
| 1397 @defspec letf* (bindings@dots{}) forms@dots{} | |
| 1398 This macro is to @code{letf} what @code{let*} is to @code{let}: | |
| 1399 It does the bindings in sequential rather than parallel order. | |
| 1400 @end defspec | |
| 1401 | |
| 1402 @defspec callf @var{function} @var{place} @var{args}@dots{} | |
| 1403 This is the ``generic'' modify macro. It calls @var{function}, | |
| 1404 which should be an unquoted function name, macro name, or lambda. | |
| 1405 It passes @var{place} and @var{args} as arguments, and assigns the | |
| 1406 result back to @var{place}. For example, @code{(incf @var{place} | |
| 1407 @var{n})} is the same as @code{(callf + @var{place} @var{n})}. | |
| 1408 Some more examples: | |
| 1409 | |
| 1410 @example | |
| 1411 (callf abs my-number) | |
| 1412 (callf concat (buffer-name) "<" (int-to-string n) ">") | |
| 1413 (callf union happy-people (list joe bob) :test 'same-person) | |
| 1414 @end example | |
| 1415 | |
| 1416 @xref{Customizing Setf}, for @code{define-modify-macro}, a way | |
| 1417 to create even more concise notations for modify macros. Note | |
| 1418 again that @code{callf} is an extension to standard Common Lisp. | |
| 1419 @end defspec | |
| 1420 | |
| 1421 @defspec callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{} | |
| 1422 This macro is like @code{callf}, except that @var{place} is | |
| 1423 the @emph{second} argument of @var{function} rather than the | |
| 1424 first. For example, @code{(push @var{x} @var{place})} is | |
| 1425 equivalent to @code{(callf2 cons @var{x} @var{place})}. | |
| 1426 @end defspec | |
| 1427 | |
| 1428 The @code{callf} and @code{callf2} macros serve as building | |
| 1429 blocks for other macros like @code{incf}, @code{pushnew}, and | |
| 1430 @code{define-modify-macro}. The @code{letf} and @code{letf*} | |
| 1431 macros are used in the processing of symbol macros; | |
| 1432 @pxref{Macro Bindings}. | |
| 1433 | |
| 1434 @node Customizing Setf, , Modify Macros, Generalized Variables | |
| 1435 @subsection Customizing Setf | |
| 1436 | |
| 1437 @noindent | |
| 1438 Common Lisp defines three macros, @code{define-modify-macro}, | |
| 1439 @code{defsetf}, and @code{define-setf-method}, that allow the | |
| 1440 user to extend generalized variables in various ways. | |
| 1441 | |
| 1442 @defspec define-modify-macro name arglist function [doc-string] | |
| 1443 This macro defines a ``read-modify-write'' macro similar to | |
| 1444 @code{incf} and @code{decf}. The macro @var{name} is defined | |
| 1445 to take a @var{place} argument followed by additional arguments | |
| 1446 described by @var{arglist}. The call | |
| 1447 | |
| 1448 @example | |
| 1449 (@var{name} @var{place} @var{args}...) | |
| 1450 @end example | |
| 1451 | |
| 1452 @noindent | |
| 1453 will be expanded to | |
| 1454 | |
| 1455 @example | |
| 1456 (callf @var{func} @var{place} @var{args}...) | |
| 1457 @end example | |
| 1458 | |
| 1459 @noindent | |
| 1460 which in turn is roughly equivalent to | |
| 1461 | |
| 1462 @example | |
| 1463 (setf @var{place} (@var{func} @var{place} @var{args}...)) | |
| 1464 @end example | |
| 1465 | |
| 1466 For example: | |
| 1467 | |
| 1468 @example | |
| 1469 (define-modify-macro incf (&optional (n 1)) +) | |
| 1470 (define-modify-macro concatf (&rest args) concat) | |
| 1471 @end example | |
| 1472 | |
| 1473 Note that @code{&key} is not allowed in @var{arglist}, but | |
| 1474 @code{&rest} is sufficient to pass keywords on to the function. | |
| 1475 | |
| 1476 Most of the modify macros defined by Common Lisp do not exactly | |
| 1477 follow the pattern of @code{define-modify-macro}. For example, | |
| 1478 @code{push} takes its arguments in the wrong order, and @code{pop} | |
| 1479 is completely irregular. You can define these macros ``by hand'' | |
| 1480 using @code{get-setf-method}, or consult the source file | |
| 1481 @file{cl-macs.el} to see how to use the internal @code{setf} | |
| 1482 building blocks. | |
| 1483 @end defspec | |
| 1484 | |
| 1485 @defspec defsetf access-fn update-fn | |
| 1486 This is the simpler of two @code{defsetf} forms. Where | |
| 1487 @var{access-fn} is the name of a function which accesses a place, | |
| 1488 this declares @var{update-fn} to be the corresponding store | |
| 1489 function. From now on, | |
| 1490 | |
| 1491 @example | |
| 1492 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value}) | |
| 1493 @end example | |
| 1494 | |
| 1495 @noindent | |
| 1496 will be expanded to | |
| 1497 | |
| 1498 @example | |
| 1499 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value}) | |
| 1500 @end example | |
| 1501 | |
| 1502 @noindent | |
| 1503 The @var{update-fn} is required to be either a true function, or | |
| 1504 a macro which evaluates its arguments in a function-like way. Also, | |
| 1505 the @var{update-fn} is expected to return @var{value} as its result. | |
| 1506 Otherwise, the above expansion would not obey the rules for the way | |
| 1507 @code{setf} is supposed to behave. | |
| 1508 | |
| 1509 As a special (non-Common-Lisp) extension, a third argument of @code{t} | |
| 1510 to @code{defsetf} says that the @code{update-fn}'s return value is | |
| 1511 not suitable, so that the above @code{setf} should be expanded to | |
| 1512 something more like | |
| 1513 | |
| 1514 @example | |
| 1515 (let ((temp @var{value})) | |
| 1516 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp) | |
| 1517 temp) | |
| 1518 @end example | |
| 1519 | |
| 1520 Some examples of the use of @code{defsetf}, drawn from the standard | |
| 1521 suite of setf methods, are: | |
| 1522 | |
| 1523 @example | |
| 1524 (defsetf car setcar) | |
| 1525 (defsetf symbol-value set) | |
| 1526 (defsetf buffer-name rename-buffer t) | |
| 1527 @end example | |
| 1528 @end defspec | |
| 1529 | |
| 1530 @defspec defsetf access-fn arglist (store-var) forms@dots{} | |
| 1531 This is the second, more complex, form of @code{defsetf}. It is | |
| 1532 rather like @code{defmacro} except for the additional @var{store-var} | |
| 1533 argument. The @var{forms} should return a Lisp form which stores | |
| 1534 the value of @var{store-var} into the generalized variable formed | |
| 1535 by a call to @var{access-fn} with arguments described by @var{arglist}. | |
| 1536 The @var{forms} may begin with a string which documents the @code{setf} | |
| 1537 method (analogous to the doc string that appears at the front of a | |
| 1538 function). | |
| 1539 | |
| 1540 For example, the simple form of @code{defsetf} is shorthand for | |
| 1541 | |
| 1542 @example | |
| 1543 (defsetf @var{access-fn} (&rest args) (store) | |
| 1544 (append '(@var{update-fn}) args (list store))) | |
| 1545 @end example | |
| 1546 | |
| 1547 The Lisp form that is returned can access the arguments from | |
| 1548 @var{arglist} and @var{store-var} in an unrestricted fashion; | |
| 1549 macros like @code{setf} and @code{incf} which invoke this | |
| 1550 setf-method will insert temporary variables as needed to make | |
| 1551 sure the apparent order of evaluation is preserved. | |
| 1552 | |
| 1553 Another example drawn from the standard package: | |
| 1554 | |
| 1555 @example | |
| 1556 (defsetf nth (n x) (store) | |
| 1557 (list 'setcar (list 'nthcdr n x) store)) | |
| 1558 @end example | |
| 1559 @end defspec | |
| 1560 | |
| 1561 @defspec define-setf-method access-fn arglist forms@dots{} | |
| 1562 This is the most general way to create new place forms. When | |
| 1563 a @code{setf} to @var{access-fn} with arguments described by | |
| 1564 @var{arglist} is expanded, the @var{forms} are evaluated and | |
| 1565 must return a list of five items: | |
| 1566 | |
| 1567 @enumerate | |
| 1568 @item | |
| 1569 A list of @dfn{temporary variables}. | |
| 1570 | |
| 1571 @item | |
| 1572 A list of @dfn{value forms} corresponding to the temporary variables | |
| 1573 above. The temporary variables will be bound to these value forms | |
| 1574 as the first step of any operation on the generalized variable. | |
| 1575 | |
| 1576 @item | |
| 1577 A list of exactly one @dfn{store variable} (generally obtained | |
| 1578 from a call to @code{gensym}). | |
| 1579 | |
| 1580 @item | |
| 1581 A Lisp form which stores the contents of the store variable into | |
| 1582 the generalized variable, assuming the temporaries have been | |
| 1583 bound as described above. | |
| 1584 | |
| 1585 @item | |
| 1586 A Lisp form which accesses the contents of the generalized variable, | |
| 1587 assuming the temporaries have been bound. | |
| 1588 @end enumerate | |
| 1589 | |
| 1590 This is exactly like the Common Lisp macro of the same name, | |
| 1591 except that the method returns a list of five values rather | |
| 1592 than the five values themselves, since Emacs Lisp does not | |
| 1593 support Common Lisp's notion of multiple return values. | |
| 1594 | |
| 1595 Once again, the @var{forms} may begin with a documentation string. | |
| 1596 | |
| 1597 A setf-method should be maximally conservative with regard to | |
| 1598 temporary variables. In the setf-methods generated by | |
| 1599 @code{defsetf}, the second return value is simply the list of | |
| 1600 arguments in the place form, and the first return value is a | |
| 1601 list of a corresponding number of temporary variables generated | |
| 1602 by @code{gensym}. Macros like @code{setf} and @code{incf} which | |
| 1603 use this setf-method will optimize away most temporaries that | |
| 1604 turn out to be unnecessary, so there is little reason for the | |
| 1605 setf-method itself to optimize. | |
| 1606 @end defspec | |
| 1607 | |
| 1608 @defun get-setf-method place &optional env | |
| 1609 This function returns the setf-method for @var{place}, by | |
| 1610 invoking the definition previously recorded by @code{defsetf} | |
| 1611 or @code{define-setf-method}. The result is a list of five | |
| 1612 values as described above. You can use this function to build | |
| 1613 your own @code{incf}-like modify macros. (Actually, it is | |
| 1614 better to use the internal functions @code{cl-setf-do-modify} | |
| 1615 and @code{cl-setf-do-store}, which are a bit easier to use and | |
| 1616 which also do a number of optimizations; consult the source | |
| 1617 code for the @code{incf} function for a simple example.) | |
| 1618 | |
| 1619 The argument @var{env} specifies the ``environment'' to be | |
| 1620 passed on to @code{macroexpand} if @code{get-setf-method} should | |
| 1621 need to expand a macro in @var{place}. It should come from | |
| 1622 an @code{&environment} argument to the macro or setf-method | |
| 1623 that called @code{get-setf-method}. | |
| 1624 | |
| 1625 See also the source code for the setf-methods for @code{apply} | |
| 1626 and @code{substring}, each of which works by calling | |
| 1627 @code{get-setf-method} on a simpler case, then massaging | |
| 1628 the result in various ways. | |
| 1629 @end defun | |
| 1630 | |
| 1631 Modern Common Lisp defines a second, independent way to specify | |
| 1632 the @code{setf} behavior of a function, namely ``@code{setf} | |
| 1633 functions'' whose names are lists @code{(setf @var{name})} | |
| 1634 rather than symbols. For example, @code{(defun (setf foo) @dots{})} | |
| 1635 defines the function that is used when @code{setf} is applied to | |
| 1636 @code{foo}. This package does not currently support @code{setf} | |
| 1637 functions. In particular, it is a compile-time error to use | |
| 1638 @code{setf} on a form which has not already been @code{defsetf}'d | |
| 1639 or otherwise declared; in newer Common Lisps, this would not be | |
| 1640 an error since the function @code{(setf @var{func})} might be | |
| 1641 defined later. | |
| 1642 | |
| 1643 @iftex | |
| 1644 @secno=4 | |
| 1645 @end iftex | |
| 1646 | |
| 1647 @node Variable Bindings, Conditionals, Generalized Variables, Control Structure | |
| 1648 @section Variable Bindings | |
| 1649 | |
| 1650 @noindent | |
| 1651 These Lisp forms make bindings to variables and function names, | |
| 1652 analogous to Lisp's built-in @code{let} form. | |
| 1653 | |
| 1654 @xref{Modify Macros}, for the @code{letf} and @code{letf*} forms which | |
| 1655 are also related to variable bindings. | |
| 1656 | |
| 1657 @menu | |
| 1658 * Dynamic Bindings:: The `progv' form | |
| 1659 * Lexical Bindings:: `lexical-let' and lexical closures | |
| 1660 * Function Bindings:: `flet' and `labels' | |
| 1661 * Macro Bindings:: `macrolet' and `symbol-macrolet' | |
| 1662 @end menu | |
| 1663 | |
| 1664 @node Dynamic Bindings, Lexical Bindings, Variable Bindings, Variable Bindings | |
| 1665 @subsection Dynamic Bindings | |
| 1666 | |
| 1667 @noindent | |
| 1668 The standard @code{let} form binds variables whose names are known | |
| 1669 at compile-time. The @code{progv} form provides an easy way to | |
| 1670 bind variables whose names are computed at run-time. | |
| 1671 | |
| 1672 @defspec progv symbols values forms@dots{} | |
| 1673 This form establishes @code{let}-style variable bindings on a | |
| 1674 set of variables computed at run-time. The expressions | |
| 1675 @var{symbols} and @var{values} are evaluated, and must return lists | |
| 1676 of symbols and values, respectively. The symbols are bound to the | |
| 1677 corresponding values for the duration of the body @var{form}s. | |
| 1678 If @var{values} is shorter than @var{symbols}, the last few symbols | |
| 1679 are made unbound (as if by @code{makunbound}) inside the body. | |
| 1680 If @var{symbols} is shorter than @var{values}, the excess values | |
| 1681 are ignored. | |
| 1682 @end defspec | |
| 1683 | |
| 1684 @node Lexical Bindings, Function Bindings, Dynamic Bindings, Variable Bindings | |
| 1685 @subsection Lexical Bindings | |
| 1686 | |
| 1687 @noindent | |
| 1688 The @dfn{CL} package defines the following macro which | |
| 1689 more closely follows the Common Lisp @code{let} form: | |
| 1690 | |
| 1691 @defspec lexical-let (bindings@dots{}) forms@dots{} | |
| 1692 This form is exactly like @code{let} except that the bindings it | |
| 1693 establishes are purely lexical. Lexical bindings are similar to | |
| 1694 local variables in a language like C: Only the code physically | |
| 1695 within the body of the @code{lexical-let} (after macro expansion) | |
| 1696 may refer to the bound variables. | |
| 1697 | |
| 1698 @example | |
| 1699 (setq a 5) | |
| 1700 (defun foo (b) (+ a b)) | |
| 1701 (let ((a 2)) (foo a)) | |
| 1702 @result{} 4 | |
| 1703 (lexical-let ((a 2)) (foo a)) | |
| 1704 @result{} 7 | |
| 1705 @end example | |
| 1706 | |
| 1707 @noindent | |
| 1708 In this example, a regular @code{let} binding of @code{a} actually | |
| 1709 makes a temporary change to the global variable @code{a}, so @code{foo} | |
| 1710 is able to see the binding of @code{a} to 2. But @code{lexical-let} | |
| 1711 actually creates a distinct local variable @code{a} for use within its | |
| 1712 body, without any effect on the global variable of the same name. | |
| 1713 | |
| 1714 The most important use of lexical bindings is to create @dfn{closures}. | |
| 1715 A closure is a function object that refers to an outside lexical | |
| 1716 variable. For example: | |
| 1717 | |
| 1718 @example | |
| 1719 (defun make-adder (n) | |
| 1720 (lexical-let ((n n)) | |
| 1721 (function (lambda (m) (+ n m))))) | |
| 1722 (setq add17 (make-adder 17)) | |
| 1723 (funcall add17 4) | |
| 1724 @result{} 21 | |
| 1725 @end example | |
| 1726 | |
| 1727 @noindent | |
| 1728 The call @code{(make-adder 17)} returns a function object which adds | |
| 1729 17 to its argument. If @code{let} had been used instead of | |
| 1730 @code{lexical-let}, the function object would have referred to the | |
| 1731 global @code{n}, which would have been bound to 17 only during the | |
| 1732 call to @code{make-adder} itself. | |
| 1733 | |
| 1734 @example | |
| 1735 (defun make-counter () | |
| 1736 (lexical-let ((n 0)) | |
| 1737 (function* (lambda (&optional (m 1)) (incf n m))))) | |
| 1738 (setq count-1 (make-counter)) | |
| 1739 (funcall count-1 3) | |
| 1740 @result{} 3 | |
| 1741 (funcall count-1 14) | |
| 1742 @result{} 17 | |
| 1743 (setq count-2 (make-counter)) | |
| 1744 (funcall count-2 5) | |
| 1745 @result{} 5 | |
| 1746 (funcall count-1 2) | |
| 1747 @result{} 19 | |
| 1748 (funcall count-2) | |
| 1749 @result{} 6 | |
| 1750 @end example | |
| 1751 | |
| 1752 @noindent | |
| 1753 Here we see that each call to @code{make-counter} creates a distinct | |
| 1754 local variable @code{n}, which serves as a private counter for the | |
| 1755 function object that is returned. | |
| 1756 | |
| 1757 Closed-over lexical variables persist until the last reference to | |
| 1758 them goes away, just like all other Lisp objects. For example, | |
| 1759 @code{count-2} refers to a function object which refers to an | |
| 1760 instance of the variable @code{n}; this is the only reference | |
| 1761 to that variable, so after @code{(setq count-2 nil)} the garbage | |
| 1762 collector would be able to delete this instance of @code{n}. | |
| 1763 Of course, if a @code{lexical-let} does not actually create any | |
| 1764 closures, then the lexical variables are free as soon as the | |
| 1765 @code{lexical-let} returns. | |
| 1766 | |
| 1767 Many closures are used only during the extent of the bindings they | |
| 1768 refer to; these are known as ``downward funargs'' in Lisp parlance. | |
| 1769 When a closure is used in this way, regular Emacs Lisp dynamic | |
| 1770 bindings suffice and will be more efficient than @code{lexical-let} | |
| 1771 closures: | |
| 1772 | |
| 1773 @example | |
| 1774 (defun add-to-list (x list) | |
| 1775 (mapcar (function (lambda (y) (+ x y))) list)) | |
| 1776 (add-to-list 7 '(1 2 5)) | |
| 1777 @result{} (8 9 12) | |
| 1778 @end example | |
| 1779 | |
| 1780 @noindent | |
| 1781 Since this lambda is only used while @code{x} is still bound, | |
| 1782 it is not necessary to make a true closure out of it. | |
| 1783 | |
| 1784 You can use @code{defun} or @code{flet} inside a @code{lexical-let} | |
| 1785 to create a named closure. If several closures are created in the | |
| 1786 body of a single @code{lexical-let}, they all close over the same | |
| 1787 instance of the lexical variable. | |
| 1788 | |
| 1789 The @code{lexical-let} form is an extension to Common Lisp. In | |
| 1790 true Common Lisp, all bindings are lexical unless declared otherwise. | |
| 1791 @end defspec | |
| 1792 | |
| 1793 @defspec lexical-let* (bindings@dots{}) forms@dots{} | |
| 1794 This form is just like @code{lexical-let}, except that the bindings | |
| 1795 are made sequentially in the manner of @code{let*}. | |
| 1796 @end defspec | |
| 1797 | |
| 1798 @node Function Bindings, Macro Bindings, Lexical Bindings, Variable Bindings | |
| 1799 @subsection Function Bindings | |
| 1800 | |
| 1801 @noindent | |
| 1802 These forms make @code{let}-like bindings to functions instead | |
| 1803 of variables. | |
| 1804 | |
| 1805 @defspec flet (bindings@dots{}) forms@dots{} | |
| 1806 This form establishes @code{let}-style bindings on the function | |
| 1807 cells of symbols rather than on the value cells. Each @var{binding} | |
| 1808 must be a list of the form @samp{(@var{name} @var{arglist} | |
| 1809 @var{forms}@dots{})}, which defines a function exactly as if | |
| 1810 it were a @code{defun*} form. The function @var{name} is defined | |
| 1811 accordingly for the duration of the body of the @code{flet}; then | |
| 1812 the old function definition, or lack thereof, is restored. | |
| 1813 | |
| 1814 While @code{flet} in Common Lisp establishes a lexical binding of | |
| 1815 @var{name}, Emacs Lisp @code{flet} makes a dynamic binding. The | |
| 1816 result is that @code{flet} affects indirect calls to a function as | |
| 1817 well as calls directly inside the @code{flet} form itself. | |
| 1818 | |
| 1819 You can use @code{flet} to disable or modify the behavior of a | |
| 1820 function in a temporary fashion. This will even work on Emacs | |
| 1821 primitives, although note that some calls to primitive functions | |
| 1822 internal to Emacs are made without going through the symbol's | |
| 1823 function cell, and so will not be affected by @code{flet}. For | |
| 1824 example, | |
| 1825 | |
| 1826 @example | |
| 1827 (flet ((message (&rest args) (push args saved-msgs))) | |
| 1828 (do-something)) | |
| 1829 @end example | |
| 1830 | |
| 1831 This code attempts to replace the built-in function @code{message} | |
| 1832 with a function that simply saves the messages in a list rather | |
| 1833 than displaying them. The original definition of @code{message} | |
| 1834 will be restored after @code{do-something} exits. This code will | |
| 1835 work fine on messages generated by other Lisp code, but messages | |
| 1836 generated directly inside Emacs will not be caught since they make | |
| 1837 direct C-language calls to the message routines rather than going | |
| 1838 through the Lisp @code{message} function. | |
| 1839 | |
| 1840 Functions defined by @code{flet} may use the full Common Lisp | |
| 1841 argument notation supported by @code{defun*}; also, the function | |
| 1842 body is enclosed in an implicit block as if by @code{defun*}. | |
| 1843 @xref{Program Structure}. | |
| 1844 @end defspec | |
| 1845 | |
| 1846 @defspec labels (bindings@dots{}) forms@dots{} | |
| 1847 The @code{labels} form is a synonym for @code{flet}. (In Common | |
| 1848 Lisp, @code{labels} and @code{flet} differ in ways that depend on | |
| 1849 their lexical scoping; these distinctions vanish in dynamically | |
| 1850 scoped Emacs Lisp.) | |
| 1851 @end defspec | |
| 1852 | |
| 1853 @node Macro Bindings, , Function Bindings, Variable Bindings | |
| 1854 @subsection Macro Bindings | |
| 1855 | |
| 1856 @noindent | |
| 1857 These forms create local macros and ``symbol macros.'' | |
| 1858 | |
| 1859 @defspec macrolet (bindings@dots{}) forms@dots{} | |
| 1860 This form is analogous to @code{flet}, but for macros instead of | |
| 1861 functions. Each @var{binding} is a list of the same form as the | |
| 1862 arguments to @code{defmacro*} (i.e., a macro name, argument list, | |
| 1863 and macro-expander forms). The macro is defined accordingly for | |
| 1864 use within the body of the @code{macrolet}. | |
| 1865 | |
| 1866 Because of the nature of macros, @code{macrolet} is lexically | |
| 1867 scoped even in Emacs Lisp: The @code{macrolet} binding will | |
| 1868 affect only calls that appear physically within the body | |
| 1869 @var{forms}, possibly after expansion of other macros in the | |
| 1870 body. | |
| 1871 @end defspec | |
| 1872 | |
| 1873 @defspec symbol-macrolet (bindings@dots{}) forms@dots{} | |
| 1874 This form creates @dfn{symbol macros}, which are macros that look | |
| 1875 like variable references rather than function calls. Each | |
| 1876 @var{binding} is a list @samp{(@var{var} @var{expansion})}; | |
| 1877 any reference to @var{var} within the body @var{forms} is | |
| 1878 replaced by @var{expansion}. | |
| 1879 | |
| 1880 @example | |
| 1881 (setq bar '(5 . 9)) | |
| 1882 (symbol-macrolet ((foo (car bar))) | |
| 1883 (incf foo)) | |
| 1884 bar | |
| 1885 @result{} (6 . 9) | |
| 1886 @end example | |
| 1887 | |
| 1888 A @code{setq} of a symbol macro is treated the same as a @code{setf}. | |
| 1889 I.e., @code{(setq foo 4)} in the above would be equivalent to | |
| 1890 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}. | |
| 1891 | |
| 1892 Likewise, a @code{let} or @code{let*} binding a symbol macro is | |
| 1893 treated like a @code{letf} or @code{letf*}. This differs from true | |
| 1894 Common Lisp, where the rules of lexical scoping cause a @code{let} | |
| 1895 binding to shadow a @code{symbol-macrolet} binding. In this package, | |
| 1896 only @code{lexical-let} and @code{lexical-let*} will shadow a symbol | |
| 1897 macro. | |
| 1898 | |
| 1899 There is no analogue of @code{defmacro} for symbol macros; all symbol | |
| 1900 macros are local. A typical use of @code{symbol-macrolet} is in the | |
| 1901 expansion of another macro: | |
| 1902 | |
| 1903 @example | |
| 1904 (defmacro* my-dolist ((x list) &rest body) | |
| 1905 (let ((var (gensym))) | |
| 1906 (list 'loop 'for var 'on list 'do | |
| 1907 (list* 'symbol-macrolet (list (list x (list 'car var))) | |
| 1908 body)))) | |
| 1909 | |
| 1910 (setq mylist '(1 2 3 4)) | |
| 1911 (my-dolist (x mylist) (incf x)) | |
| 1912 mylist | |
| 1913 @result{} (2 3 4 5) | |
| 1914 @end example | |
| 1915 | |
| 1916 @noindent | |
| 1917 In this example, the @code{my-dolist} macro is similar to @code{dolist} | |
| 1918 (@pxref{Iteration}) except that the variable @code{x} becomes a true | |
| 1919 reference onto the elements of the list. The @code{my-dolist} call | |
| 1920 shown here expands to | |
| 1921 | |
| 1922 @example | |
| 1923 (loop for G1234 on mylist do | |
| 1924 (symbol-macrolet ((x (car G1234))) | |
| 1925 (incf x))) | |
| 1926 @end example | |
| 1927 | |
| 1928 @noindent | |
| 1929 which in turn expands to | |
| 1930 | |
| 1931 @example | |
| 1932 (loop for G1234 on mylist do (incf (car G1234))) | |
| 1933 @end example | |
| 1934 | |
| 1935 @xref{Loop Facility}, for a description of the @code{loop} macro. | |
| 1936 This package defines a nonstandard @code{in-ref} loop clause that | |
| 1937 works much like @code{my-dolist}. | |
| 1938 @end defspec | |
| 1939 | |
| 1940 @node Conditionals, Blocks and Exits, Variable Bindings, Control Structure | |
| 1941 @section Conditionals | |
| 1942 | |
| 1943 @noindent | |
| 1944 These conditional forms augment Emacs Lisp's simple @code{if}, | |
| 1945 @code{and}, @code{or}, and @code{cond} forms. | |
| 1946 | |
| 1947 @defspec when test forms@dots{} | |
| 1948 This is a variant of @code{if} where there are no ``else'' forms, | |
| 1949 and possibly several ``then'' forms. In particular, | |
| 1950 | |
| 1951 @example | |
| 1952 (when @var{test} @var{a} @var{b} @var{c}) | |
| 1953 @end example | |
| 1954 | |
| 1955 @noindent | |
| 1956 is entirely equivalent to | |
| 1957 | |
| 1958 @example | |
| 1959 (if @var{test} (progn @var{a} @var{b} @var{c}) nil) | |
| 1960 @end example | |
| 1961 @end defspec | |
| 1962 | |
| 1963 @defspec unless test forms@dots{} | |
| 1964 This is a variant of @code{if} where there are no ``then'' forms, | |
| 1965 and possibly several ``else'' forms: | |
| 1966 | |
| 1967 @example | |
| 1968 (unless @var{test} @var{a} @var{b} @var{c}) | |
| 1969 @end example | |
| 1970 | |
| 1971 @noindent | |
| 1972 is entirely equivalent to | |
| 1973 | |
| 1974 @example | |
| 1975 (when (not @var{test}) @var{a} @var{b} @var{c}) | |
| 1976 @end example | |
| 1977 @end defspec | |
| 1978 | |
| 1979 @defspec case keyform clause@dots{} | |
| 1980 This macro evaluates @var{keyform}, then compares it with the key | |
| 1981 values listed in the various @var{clause}s. Whichever clause matches | |
| 1982 the key is executed; comparison is done by @code{eql}. If no clause | |
| 1983 matches, the @code{case} form returns @code{nil}. The clauses are | |
| 1984 of the form | |
| 1985 | |
| 1986 @example | |
| 1987 (@var{keylist} @var{body-forms}@dots{}) | |
| 1988 @end example | |
| 1989 | |
| 1990 @noindent | |
| 1991 where @var{keylist} is a list of key values. If there is exactly | |
| 1992 one value, and it is not a cons cell or the symbol @code{nil} or | |
| 1993 @code{t}, then it can be used by itself as a @var{keylist} without | |
| 1994 being enclosed in a list. All key values in the @code{case} form | |
| 1995 must be distinct. The final clauses may use @code{t} in place of | |
| 1996 a @var{keylist} to indicate a default clause that should be taken | |
| 1997 if none of the other clauses match. (The symbol @code{otherwise} | |
| 1998 is also recognized in place of @code{t}. To make a clause that | |
| 1999 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise}, | |
| 2000 enclose the symbol in a list.) | |
| 2001 | |
| 2002 For example, this expression reads a keystroke, then does one of | |
| 2003 four things depending on whether it is an @samp{a}, a @samp{b}, | |
| 2004 a @key{RET} or @key{LFD}, or anything else. | |
| 2005 | |
| 2006 @example | |
| 2007 (case (read-char) | |
| 2008 (?a (do-a-thing)) | |
| 2009 (?b (do-b-thing)) | |
| 2010 ((?\r ?\n) (do-ret-thing)) | |
| 2011 (t (do-other-thing))) | |
| 2012 @end example | |
| 2013 @end defspec | |
| 2014 | |
| 2015 @defspec ecase keyform clause@dots{} | |
| 2016 This macro is just like @code{case}, except that if the key does | |
| 2017 not match any of the clauses, an error is signalled rather than | |
| 2018 simply returning @code{nil}. | |
| 2019 @end defspec | |
| 2020 | |
| 2021 @defspec typecase keyform clause@dots{} | |
| 2022 This macro is a version of @code{case} that checks for types | |
| 2023 rather than values. Each @var{clause} is of the form | |
| 2024 @samp{(@var{type} @var{body}...)}. @xref{Type Predicates}, | |
| 2025 for a description of type specifiers. For example, | |
| 2026 | |
| 2027 @example | |
| 2028 (typecase x | |
| 2029 (integer (munch-integer x)) | |
| 2030 (float (munch-float x)) | |
| 2031 (string (munch-integer (string-to-int x))) | |
| 2032 (t (munch-anything x))) | |
| 2033 @end example | |
| 2034 | |
| 2035 The type specifier @code{t} matches any type of object; the word | |
| 2036 @code{otherwise} is also allowed. To make one clause match any of | |
| 2037 several types, use an @code{(or ...)} type specifier. | |
| 2038 @end defspec | |
| 2039 | |
| 2040 @defspec etypecase keyform clause@dots{} | |
| 2041 This macro is just like @code{typecase}, except that if the key does | |
| 2042 not match any of the clauses, an error is signalled rather than | |
| 2043 simply returning @code{nil}. | |
| 2044 @end defspec | |
| 2045 | |
| 2046 @node Blocks and Exits, Iteration, Conditionals, Control Structure | |
| 2047 @section Blocks and Exits | |
| 2048 | |
| 2049 @noindent | |
| 2050 Common Lisp @dfn{blocks} provide a non-local exit mechanism very | |
| 2051 similar to @code{catch} and @code{throw}, but lexically rather than | |
| 2052 dynamically scoped. This package actually implements @code{block} | |
| 2053 in terms of @code{catch}; however, the lexical scoping allows the | |
| 2054 optimizing byte-compiler to omit the costly @code{catch} step if the | |
| 2055 body of the block does not actually @code{return-from} the block. | |
| 2056 | |
| 2057 @defspec block name forms@dots{} | |
| 2058 The @var{forms} are evaluated as if by a @code{progn}. However, | |
| 2059 if any of the @var{forms} execute @code{(return-from @var{name})}, | |
| 2060 they will jump out and return directly from the @code{block} form. | |
| 2061 The @code{block} returns the result of the last @var{form} unless | |
| 2062 a @code{return-from} occurs. | |
| 2063 | |
| 2064 The @code{block}/@code{return-from} mechanism is quite similar to | |
| 2065 the @code{catch}/@code{throw} mechanism. The main differences are | |
| 2066 that block @var{name}s are unevaluated symbols, rather than forms | |
| 2067 (such as quoted symbols) which evaluate to a tag at run-time; and | |
| 2068 also that blocks are lexically scoped whereas @code{catch}/@code{throw} | |
| 2069 are dynamically scoped. This means that functions called from the | |
| 2070 body of a @code{catch} can also @code{throw} to the @code{catch}, | |
| 2071 but the @code{return-from} referring to a block name must appear | |
| 2072 physically within the @var{forms} that make up the body of the block. | |
| 2073 They may not appear within other called functions, although they may | |
| 2074 appear within macro expansions or @code{lambda}s in the body. Block | |
| 2075 names and @code{catch} names form independent name-spaces. | |
| 2076 | |
| 2077 In true Common Lisp, @code{defun} and @code{defmacro} surround | |
| 2078 the function or expander bodies with implicit blocks with the | |
| 2079 same name as the function or macro. This does not occur in Emacs | |
| 2080 Lisp, but this package provides @code{defun*} and @code{defmacro*} | |
| 2081 forms which do create the implicit block. | |
| 2082 | |
| 2083 The Common Lisp looping constructs defined by this package, | |
| 2084 such as @code{loop} and @code{dolist}, also create implicit blocks | |
| 2085 just as in Common Lisp. | |
| 2086 | |
| 2087 Because they are implemented in terms of Emacs Lisp @code{catch} | |
| 2088 and @code{throw}, blocks have the same overhead as actual | |
| 2089 @code{catch} constructs (roughly two function calls). However, | |
| 2090 Zawinski and Furuseth's optimizing byte compiler (standard in | |
| 2091 Emacs 19) will optimize away the @code{catch} if the block does | |
| 2092 not in fact contain any @code{return} or @code{return-from} calls | |
| 2093 that jump to it. This means that @code{do} loops and @code{defun*} | |
| 2094 functions which don't use @code{return} don't pay the overhead to | |
| 2095 support it. | |
| 2096 @end defspec | |
| 2097 | |
| 2098 @defspec return-from name [result] | |
| 2099 This macro returns from the block named @var{name}, which must be | |
| 2100 an (unevaluated) symbol. If a @var{result} form is specified, it | |
| 2101 is evaluated to produce the result returned from the @code{block}. | |
| 2102 Otherwise, @code{nil} is returned. | |
| 2103 @end defspec | |
| 2104 | |
| 2105 @defspec return [result] | |
| 2106 This macro is exactly like @code{(return-from nil @var{result})}. | |
| 2107 Common Lisp loops like @code{do} and @code{dolist} implicitly enclose | |
| 2108 themselves in @code{nil} blocks. | |
| 2109 @end defspec | |
| 2110 | |
| 2111 @node Iteration, Loop Facility, Blocks and Exits, Control Structure | |
| 2112 @section Iteration | |
| 2113 | |
| 2114 @noindent | |
| 2115 The macros described here provide more sophisticated, high-level | |
| 2116 looping constructs to complement Emacs Lisp's basic @code{while} | |
| 2117 loop. | |
| 2118 | |
| 2119 @defspec loop forms@dots{} | |
| 2120 The @dfn{CL} package supports both the simple, old-style meaning of | |
| 2121 @code{loop} and the extremely powerful and flexible feature known as | |
| 2122 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced | |
| 2123 facility is discussed in the following section; @pxref{Loop Facility}. | |
| 2124 The simple form of @code{loop} is described here. | |
| 2125 | |
| 2126 If @code{loop} is followed by zero or more Lisp expressions, | |
| 2127 then @code{(loop @var{exprs}@dots{})} simply creates an infinite | |
| 2128 loop executing the expressions over and over. The loop is | |
| 2129 enclosed in an implicit @code{nil} block. Thus, | |
| 2130 | |
| 2131 @example | |
| 2132 (loop (foo) (if (no-more) (return 72)) (bar)) | |
| 2133 @end example | |
| 2134 | |
| 2135 @noindent | |
| 2136 is exactly equivalent to | |
| 2137 | |
| 2138 @example | |
| 2139 (block nil (while t (foo) (if (no-more) (return 72)) (bar))) | |
| 2140 @end example | |
| 2141 | |
| 2142 If any of the expressions are plain symbols, the loop is instead | |
| 2143 interpreted as a Loop Macro specification as described later. | |
| 2144 (This is not a restriction in practice, since a plain symbol | |
| 2145 in the above notation would simply access and throw away the | |
| 2146 value of a variable.) | |
| 2147 @end defspec | |
| 2148 | |
| 2149 @defspec do (spec@dots{}) (end-test [result@dots{}]) forms@dots{} | |
| 2150 This macro creates a general iterative loop. Each @var{spec} is | |
| 2151 of the form | |
| 2152 | |
| 2153 @example | |
| 2154 (@var{var} [@var{init} [@var{step}]]) | |
| 2155 @end example | |
| 2156 | |
| 2157 The loop works as follows: First, each @var{var} is bound to the | |
| 2158 associated @var{init} value as if by a @code{let} form. Then, in | |
| 2159 each iteration of the loop, the @var{end-test} is evaluated; if | |
| 2160 true, the loop is finished. Otherwise, the body @var{forms} are | |
| 2161 evaluated, then each @var{var} is set to the associated @var{step} | |
| 2162 expression (as if by a @code{psetq} form) and the next iteration | |
| 2163 begins. Once the @var{end-test} becomes true, the @var{result} | |
| 2164 forms are evaluated (with the @var{var}s still bound to their | |
| 2165 values) to produce the result returned by @code{do}. | |
| 2166 | |
| 2167 The entire @code{do} loop is enclosed in an implicit @code{nil} | |
| 2168 block, so that you can use @code{(return)} to break out of the | |
| 2169 loop at any time. | |
| 2170 | |
| 2171 If there are no @var{result} forms, the loop returns @code{nil}. | |
| 2172 If a given @var{var} has no @var{step} form, it is bound to its | |
| 2173 @var{init} value but not otherwise modified during the @code{do} | |
| 2174 loop (unless the code explicitly modifies it); this case is just | |
| 2175 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})} | |
| 2176 around the loop. If @var{init} is also omitted it defaults to | |
| 2177 @code{nil}, and in this case a plain @samp{@var{var}} can be used | |
| 2178 in place of @samp{(@var{var})}, again following the analogy with | |
| 2179 @code{let}. | |
| 2180 | |
| 2181 This example (from Steele) illustrates a loop which applies the | |
| 2182 function @code{f} to successive pairs of values from the lists | |
| 2183 @code{foo} and @code{bar}; it is equivalent to the call | |
| 2184 @code{(mapcar* 'f foo bar)}. Note that this loop has no body | |
| 2185 @var{forms} at all, performing all its work as side effects of | |
| 2186 the rest of the loop. | |
| 2187 | |
| 2188 @example | |
| 2189 (do ((x foo (cdr x)) | |
| 2190 (y bar (cdr y)) | |
| 2191 (z nil (cons (f (car x) (car y)) z))) | |
| 2192 ((or (null x) (null y)) | |
| 2193 (nreverse z))) | |
| 2194 @end example | |
| 2195 @end defspec | |
| 2196 | |
| 2197 @defspec do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{} | |
| 2198 This is to @code{do} what @code{let*} is to @code{let}. In | |
| 2199 particular, the initial values are bound as if by @code{let*} | |
| 2200 rather than @code{let}, and the steps are assigned as if by | |
| 2201 @code{setq} rather than @code{psetq}. | |
| 2202 | |
| 2203 Here is another way to write the above loop: | |
| 2204 | |
| 2205 @example | |
| 2206 (do* ((xp foo (cdr xp)) | |
| 2207 (yp bar (cdr yp)) | |
| 2208 (x (car xp) (car xp)) | |
| 2209 (y (car yp) (car yp)) | |
| 2210 z) | |
| 2211 ((or (null xp) (null yp)) | |
| 2212 (nreverse z)) | |
| 2213 (push (f x y) z)) | |
| 2214 @end example | |
| 2215 @end defspec | |
| 2216 | |
| 2217 @defspec dolist (var list [result]) forms@dots{} | |
| 2218 This is a more specialized loop which iterates across the elements | |
| 2219 of a list. @var{list} should evaluate to a list; the body @var{forms} | |
| 2220 are executed with @var{var} bound to each element of the list in | |
| 2221 turn. Finally, the @var{result} form (or @code{nil}) is evaluated | |
| 2222 with @var{var} bound to @code{nil} to produce the result returned by | |
| 2223 the loop. The loop is surrounded by an implicit @code{nil} block. | |
| 2224 @end defspec | |
| 2225 | |
| 2226 @defspec dotimes (var count [result]) forms@dots{} | |
| 2227 This is a more specialized loop which iterates a specified number | |
| 2228 of times. The body is executed with @var{var} bound to the integers | |
| 2229 from zero (inclusive) to @var{count} (exclusive), in turn. Then | |
| 2230 the @code{result} form is evaluated with @var{var} bound to the total | |
| 2231 number of iterations that were done (i.e., @code{(max 0 @var{count})}) | |
| 2232 to get the return value for the loop form. The loop is surrounded | |
| 2233 by an implicit @code{nil} block. | |
| 2234 @end defspec | |
| 2235 | |
| 2236 @defspec do-symbols (var [obarray [result]]) forms@dots{} | |
| 2237 This loop iterates over all interned symbols. If @var{obarray} | |
| 2238 is specified and is not @code{nil}, it loops over all symbols in | |
| 2239 that obarray. For each symbol, the body @var{forms} are evaluated | |
| 2240 with @var{var} bound to that symbol. The symbols are visited in | |
| 2241 an unspecified order. Afterward the @var{result} form, if any, | |
| 2242 is evaluated (with @var{var} bound to @code{nil}) to get the return | |
| 2243 value. The loop is surrounded by an implicit @code{nil} block. | |
| 2244 @end defspec | |
| 2245 | |
| 2246 @defspec do-all-symbols (var [result]) forms@dots{} | |
| 2247 This is identical to @code{do-symbols} except that the @var{obarray} | |
| 2248 argument is omitted; it always iterates over the default obarray. | |
| 2249 @end defspec | |
| 2250 | |
| 2251 @xref{Mapping over Sequences}, for some more functions for | |
| 2252 iterating over vectors or lists. | |
| 2253 | |
| 2254 @node Loop Facility, Multiple Values, Iteration, Control Structure | |
| 2255 @section Loop Facility | |
| 2256 | |
| 2257 @noindent | |
| 2258 A common complaint with Lisp's traditional looping constructs is | |
| 2259 that they are either too simple and limited, such as Common Lisp's | |
| 2260 @code{dotimes} or Emacs Lisp's @code{while}, or too unreadable and | |
| 2261 obscure, like Common Lisp's @code{do} loop. | |
| 2262 | |
| 2263 To remedy this, recent versions of Common Lisp have added a new | |
| 2264 construct called the ``Loop Facility'' or ``@code{loop} macro,'' | |
| 2265 with an easy-to-use but very powerful and expressive syntax. | |
| 2266 | |
| 2267 @menu | |
| 2268 * Loop Basics:: `loop' macro, basic clause structure | |
| 2269 * Loop Examples:: Working examples of `loop' macro | |
| 2270 * For Clauses:: Clauses introduced by `for' or `as' | |
| 2271 * Iteration Clauses:: `repeat', `while', `thereis', etc. | |
| 2272 * Accumulation Clauses:: `collect', `sum', `maximize', etc. | |
| 2273 * Other Clauses:: `with', `if', `initially', `finally' | |
| 2274 @end menu | |
| 2275 | |
| 2276 @node Loop Basics, Loop Examples, Loop Facility, Loop Facility | |
| 2277 @subsection Loop Basics | |
| 2278 | |
| 2279 @noindent | |
| 2280 The @code{loop} macro essentially creates a mini-language within | |
| 2281 Lisp that is specially tailored for describing loops. While this | |
| 2282 language is a little strange-looking by the standards of regular Lisp, | |
| 2283 it turns out to be very easy to learn and well-suited to its purpose. | |
| 2284 | |
| 2285 Since @code{loop} is a macro, all parsing of the loop language | |
| 2286 takes place at byte-compile time; compiled @code{loop}s are just | |
| 2287 as efficient as the equivalent @code{while} loops written longhand. | |
| 2288 | |
| 2289 @defspec loop clauses@dots{} | |
| 2290 A loop construct consists of a series of @var{clause}s, each | |
| 2291 introduced by a symbol like @code{for} or @code{do}. Clauses | |
| 2292 are simply strung together in the argument list of @code{loop}, | |
| 2293 with minimal extra parentheses. The various types of clauses | |
| 2294 specify initializations, such as the binding of temporary | |
| 2295 variables, actions to be taken in the loop, stepping actions, | |
| 2296 and final cleanup. | |
| 2297 | |
| 2298 Common Lisp specifies a certain general order of clauses in a | |
| 2299 loop: | |
| 2300 | |
| 2301 @example | |
| 2302 (loop @var{name-clause} | |
| 2303 @var{var-clauses}@dots{} | |
| 2304 @var{action-clauses}@dots{}) | |
| 2305 @end example | |
| 2306 | |
| 2307 The @var{name-clause} optionally gives a name to the implicit | |
| 2308 block that surrounds the loop. By default, the implicit block | |
| 2309 is named @code{nil}. The @var{var-clauses} specify what | |
| 2310 variables should be bound during the loop, and how they should | |
| 2311 be modified or iterated throughout the course of the loop. The | |
| 2312 @var{action-clauses} are things to be done during the loop, such | |
| 2313 as computing, collecting, and returning values. | |
| 2314 | |
| 2315 The Emacs version of the @code{loop} macro is less restrictive about | |
| 2316 the order of clauses, but things will behave most predictably if | |
| 2317 you put the variable-binding clauses @code{with}, @code{for}, and | |
| 2318 @code{repeat} before the action clauses. As in Common Lisp, | |
| 2319 @code{initially} and @code{finally} clauses can go anywhere. | |
| 2320 | |
| 2321 Loops generally return @code{nil} by default, but you can cause | |
| 2322 them to return a value by using an accumulation clause like | |
| 2323 @code{collect}, an end-test clause like @code{always}, or an | |
| 2324 explicit @code{return} clause to jump out of the implicit block. | |
| 2325 (Because the loop body is enclosed in an implicit block, you can | |
| 2326 also use regular Lisp @code{return} or @code{return-from} to | |
| 2327 break out of the loop.) | |
| 2328 @end defspec | |
| 2329 | |
| 2330 The following sections give some examples of the Loop Macro in | |
| 2331 action, and describe the particular loop clauses in great detail. | |
| 2332 Consult the second edition of Steele's @dfn{Common Lisp, the Language}, | |
| 2333 for additional discussion and examples of the @code{loop} macro. | |
| 2334 | |
| 2335 @node Loop Examples, For Clauses, Loop Basics, Loop Facility | |
| 2336 @subsection Loop Examples | |
| 2337 | |
| 2338 @noindent | |
| 2339 Before listing the full set of clauses that are allowed, let's | |
| 2340 look at a few example loops just to get a feel for the @code{loop} | |
| 2341 language. | |
| 2342 | |
| 2343 @example | |
| 2344 (loop for buf in (buffer-list) | |
| 2345 collect (buffer-file-name buf)) | |
| 2346 @end example | |
| 2347 | |
| 2348 @noindent | |
| 2349 This loop iterates over all Emacs buffers, using the list | |
| 2350 returned by @code{buffer-list}. For each buffer @code{buf}, | |
| 2351 it calls @code{buffer-file-name} and collects the results into | |
| 2352 a list, which is then returned from the @code{loop} construct. | |
| 2353 The result is a list of the file names of all the buffers in | |
| 2354 Emacs' memory. The words @code{for}, @code{in}, and @code{collect} | |
| 2355 are reserved words in the @code{loop} language. | |
| 2356 | |
| 2357 @example | |
| 2358 (loop repeat 20 do (insert "Yowsa\n")) | |
| 2359 @end example | |
| 2360 | |
| 2361 @noindent | |
| 2362 This loop inserts the phrase ``Yowsa'' twenty times in the | |
| 2363 current buffer. | |
| 2364 | |
| 2365 @example | |
| 2366 (loop until (eobp) do (munch-line) (forward-line 1)) | |
| 2367 @end example | |
| 2368 | |
| 2369 @noindent | |
| 2370 This loop calls @code{munch-line} on every line until the end | |
| 2371 of the buffer. If point is already at the end of the buffer, | |
| 2372 the loop exits immediately. | |
| 2373 | |
| 2374 @example | |
| 2375 (loop do (munch-line) until (eobp) do (forward-line 1)) | |
| 2376 @end example | |
| 2377 | |
| 2378 @noindent | |
| 2379 This loop is similar to the above one, except that @code{munch-line} | |
| 2380 is always called at least once. | |
| 2381 | |
| 2382 @example | |
| 2383 (loop for x from 1 to 100 | |
| 2384 for y = (* x x) | |
| 2385 until (>= y 729) | |
| 2386 finally return (list x (= y 729))) | |
| 2387 @end example | |
| 2388 | |
| 2389 @noindent | |
| 2390 This more complicated loop searches for a number @code{x} whose | |
| 2391 square is 729. For safety's sake it only examines @code{x} | |
| 2392 values up to 100; dropping the phrase @samp{to 100} would | |
| 2393 cause the loop to count upwards with no limit. The second | |
| 2394 @code{for} clause defines @code{y} to be the square of @code{x} | |
| 2395 within the loop; the expression after the @code{=} sign is | |
| 2396 reevaluated each time through the loop. The @code{until} | |
| 2397 clause gives a condition for terminating the loop, and the | |
| 2398 @code{finally} clause says what to do when the loop finishes. | |
| 2399 (This particular example was written less concisely than it | |
| 2400 could have been, just for the sake of illustration.) | |
| 2401 | |
| 2402 Note that even though this loop contains three clauses (two | |
| 2403 @code{for}s and an @code{until}) that would have been enough to | |
| 2404 define loops all by themselves, it still creates a single loop | |
| 2405 rather than some sort of triple-nested loop. You must explicitly | |
| 2406 nest your @code{loop} constructs if you want nested loops. | |
| 2407 | |
| 2408 @node For Clauses, Iteration Clauses, Loop Examples, Loop Facility | |
| 2409 @subsection For Clauses | |
| 2410 | |
| 2411 @noindent | |
| 2412 Most loops are governed by one or more @code{for} clauses. | |
| 2413 A @code{for} clause simultaneously describes variables to be | |
| 2414 bound, how those variables are to be stepped during the loop, | |
| 2415 and usually an end condition based on those variables. | |
| 2416 | |
| 2417 The word @code{as} is a synonym for the word @code{for}. This | |
| 2418 word is followed by a variable name, then a word like @code{from} | |
| 2419 or @code{across} that describes the kind of iteration desired. | |
| 2420 In Common Lisp, the phrase @code{being the} sometimes precedes | |
| 2421 the type of iteration; in this package both @code{being} and | |
| 2422 @code{the} are optional. The word @code{each} is a synonym | |
| 2423 for @code{the}, and the word that follows it may be singular | |
| 2424 or plural: @samp{for x being the elements of y} or | |
| 2425 @samp{for x being each element of y}. Which form you use | |
| 2426 is purely a matter of style. | |
| 2427 | |
| 2428 The variable is bound around the loop as if by @code{let}: | |
| 2429 | |
| 2430 @example | |
| 2431 (setq i 'happy) | |
| 2432 (loop for i from 1 to 10 do (do-something-with i)) | |
| 2433 i | |
| 2434 @result{} happy | |
| 2435 @end example | |
| 2436 | |
| 2437 @table @code | |
| 2438 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3} | |
| 2439 This type of @code{for} clause creates a counting loop. Each of | |
| 2440 the three sub-terms is optional, though there must be at least one | |
| 2441 term so that the clause is marked as a counting clause. | |
| 2442 | |
| 2443 The three expressions are the starting value, the ending value, and | |
| 2444 the step value, respectively, of the variable. The loop counts | |
| 2445 upwards by default (@var{expr3} must be positive), from @var{expr1} | |
| 2446 to @var{expr2} inclusively. If you omit the @code{from} term, the | |
| 2447 loop counts from zero; if you omit the @code{to} term, the loop | |
| 2448 counts forever without stopping (unless stopped by some other | |
| 2449 loop clause, of course); if you omit the @code{by} term, the loop | |
| 2450 counts in steps of one. | |
| 2451 | |
| 2452 You can replace the word @code{from} with @code{upfrom} or | |
| 2453 @code{downfrom} to indicate the direction of the loop. Likewise, | |
| 2454 you can replace @code{to} with @code{upto} or @code{downto}. | |
| 2455 For example, @samp{for x from 5 downto 1} executes five times | |
| 2456 with @code{x} taking on the integers from 5 down to 1 in turn. | |
| 2457 Also, you can replace @code{to} with @code{below} or @code{above}, | |
| 2458 which are like @code{upto} and @code{downto} respectively except | |
| 2459 that they are exclusive rather than inclusive limits: | |
| 2460 | |
| 2461 @example | |
| 2462 (loop for x to 10 collect x) | |
| 2463 @result{} (0 1 2 3 4 5 6 7 8 9 10) | |
| 2464 (loop for x below 10 collect x) | |
| 2465 @result{} (0 1 2 3 4 5 6 7 8 9) | |
| 2466 @end example | |
| 2467 | |
| 2468 The @code{by} value is always positive, even for downward-counting | |
| 2469 loops. Some sort of @code{from} value is required for downward | |
| 2470 loops; @samp{for x downto 5} is not a legal loop clause all by | |
| 2471 itself. | |
| 2472 | |
| 2473 @item for @var{var} in @var{list} by @var{function} | |
| 2474 This clause iterates @var{var} over all the elements of @var{list}, | |
| 2475 in turn. If you specify the @code{by} term, then @var{function} | |
| 2476 is used to traverse the list instead of @code{cdr}; it must be a | |
| 2477 function taking one argument. For example: | |
| 2478 | |
| 2479 @example | |
| 2480 (loop for x in '(1 2 3 4 5 6) collect (* x x)) | |
| 2481 @result{} (1 4 9 16 25 36) | |
| 2482 (loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x)) | |
| 2483 @result{} (1 9 25) | |
| 2484 @end example | |
| 2485 | |
| 2486 @item for @var{var} on @var{list} by @var{function} | |
| 2487 This clause iterates @var{var} over all the cons cells of @var{list}. | |
| 2488 | |
| 2489 @example | |
| 2490 (loop for x on '(1 2 3 4) collect x) | |
| 2491 @result{} ((1 2 3 4) (2 3 4) (3 4) (4)) | |
| 2492 @end example | |
| 2493 | |
| 2494 With @code{by}, there is no real reason that the @code{on} expression | |
| 2495 must be a list. For example: | |
| 2496 | |
| 2497 @example | |
| 2498 (loop for x on first-animal by 'next-animal collect x) | |
| 2499 @end example | |
| 2500 | |
| 2501 @noindent | |
| 2502 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns | |
| 2503 the next in the (assumed) sequence of animals, or @code{nil} if | |
| 2504 @var{x} was the last animal in the sequence. | |
| 2505 | |
| 2506 @item for @var{var} in-ref @var{list} by @var{function} | |
| 2507 This is like a regular @code{in} clause, but @var{var} becomes | |
| 2508 a @code{setf}-able ``reference'' onto the elements of the list | |
| 2509 rather than just a temporary variable. For example, | |
| 2510 | |
| 2511 @example | |
| 2512 (loop for x in-ref my-list do (incf x)) | |
| 2513 @end example | |
| 2514 | |
| 2515 @noindent | |
| 2516 increments every element of @code{my-list} in place. This clause | |
| 2517 is an extension to standard Common Lisp. | |
| 2518 | |
| 2519 @item for @var{var} across @var{array} | |
| 2520 This clause iterates @var{var} over all the elements of @var{array}, | |
| 2521 which may be a vector or a string. | |
| 2522 | |
| 2523 @example | |
| 2524 (loop for x across "aeiou" | |
| 2525 do (use-vowel (char-to-string x))) | |
| 2526 @end example | |
| 2527 | |
| 2528 @item for @var{var} across-ref @var{array} | |
| 2529 This clause iterates over an array, with @var{var} a @code{setf}-able | |
| 2530 reference onto the elements; see @code{in-ref} above. | |
| 2531 | |
| 2532 @item for @var{var} being the elements of @var{sequence} | |
| 2533 This clause iterates over the elements of @var{sequence}, which may | |
| 2534 be a list, vector, or string. Since the type must be determined | |
| 2535 at run-time, this is somewhat less efficient than @code{in} or | |
| 2536 @code{across}. The clause may be followed by the additional term | |
| 2537 @samp{using (index @var{var2})} to cause @var{var2} to be bound to | |
| 2538 the successive indices (starting at 0) of the elements. | |
| 2539 | |
| 2540 This clause type is taken from older versions of the @code{loop} macro, | |
| 2541 and is not present in modern Common Lisp. The @samp{using (sequence ...)} | |
| 2542 term of the older macros is not supported. | |
| 2543 | |
| 2544 @item for @var{var} being the elements of-ref @var{sequence} | |
| 2545 This clause iterates over a sequence, with @var{var} a @code{setf}-able | |
| 2546 reference onto the elements; see @code{in-ref} above. | |
| 2547 | |
| 2548 @item for @var{var} being the symbols [of @var{obarray}] | |
| 2549 This clause iterates over symbols, either over all interned symbols | |
| 2550 or over all symbols in @var{obarray}. The loop is executed with | |
| 2551 @var{var} bound to each symbol in turn. The symbols are visited in | |
| 2552 an unspecified order. | |
| 2553 | |
| 2554 As an example, | |
| 2555 | |
| 2556 @example | |
| 2557 (loop for sym being the symbols | |
| 2558 when (fboundp sym) | |
| 2559 when (string-match "^map" (symbol-name sym)) | |
| 2560 collect sym) | |
| 2561 @end example | |
| 2562 | |
| 2563 @noindent | |
| 2564 returns a list of all the functions whose names begin with @samp{map}. | |
| 2565 | |
| 2566 The Common Lisp words @code{external-symbols} and @code{present-symbols} | |
| 2567 are also recognized but are equivalent to @code{symbols} in Emacs Lisp. | |
| 2568 | |
| 2569 Due to a minor implementation restriction, it will not work to have | |
| 2570 more than one @code{for} clause iterating over symbols, hash tables, | |
| 2571 keymaps, overlays, or intervals in a given @code{loop}. Fortunately, | |
| 2572 it would rarely if ever be useful to do so. It @emph{is} legal to mix | |
| 2573 one of these types of clauses with other clauses like @code{for ... to} | |
| 2574 or @code{while}. | |
| 2575 | |
| 2576 @item for @var{var} being the hash-keys of @var{hash-table} | |
| 2577 This clause iterates over the entries in @var{hash-table}. For each | |
| 2578 hash table entry, @var{var} is bound to the entry's key. If you write | |
| 2579 @samp{the hash-values} instead, @var{var} is bound to the values | |
| 2580 of the entries. The clause may be followed by the additional | |
| 2581 term @samp{using (hash-values @var{var2})} (where @code{hash-values} | |
| 2582 is the opposite word of the word following @code{the}) to cause | |
| 2583 @var{var} and @var{var2} to be bound to the two parts of each | |
| 2584 hash table entry. | |
| 2585 | |
| 2586 @item for @var{var} being the key-codes of @var{keymap} | |
| 2587 This clause iterates over the entries in @var{keymap}. In GNU Emacs 18 | |
| 2588 and 19, keymaps are either alists or vectors, and key-codes are integers | |
| 2589 or symbols. In XEmacs, keymaps are a special new data type, and | |
| 2590 key-codes are symbols or lists of symbols. The iteration does not enter | |
| 2591 nested keymaps or inherited (parent) keymaps. You can use @samp{the | |
| 2592 key-bindings} to access the commands bound to the keys rather than the | |
| 2593 key codes, and you can add a @code{using} clause to access both the | |
| 2594 codes and the bindings together. | |
| 2595 | |
| 2596 @item for @var{var} being the key-seqs of @var{keymap} | |
| 2597 This clause iterates over all key sequences defined by @var{keymap} | |
| 2598 and its nested keymaps, where @var{var} takes on values which are | |
| 2599 strings in Emacs 18 or vectors in Emacs 19. The strings or vectors | |
| 2600 are reused for each iteration, so you must copy them if you wish to keep | |
| 2601 them permanently. You can add a @samp{using (key-bindings ...)} | |
| 2602 clause to get the command bindings as well. | |
| 2603 | |
| 2604 @item for @var{var} being the overlays [of @var{buffer}] @dots{} | |
| 2605 This clause iterates over the Emacs 19 ``overlays'' or XEmacs | |
| 2606 ``extents'' of a buffer (the clause @code{extents} is synonymous with | |
| 2607 @code{overlays}). Under Emacs 18, this clause iterates zero times. If | |
| 2608 the @code{of} term is omitted, the current buffer is used. This clause | |
| 2609 also accepts optional @samp{from @var{pos}} and @samp{to @var{pos}} | |
| 2610 terms, limiting the clause to overlays which overlap the specified | |
| 2611 region. | |
| 2612 | |
| 2613 @item for @var{var} being the intervals [of @var{buffer}] @dots{} | |
| 2614 This clause iterates over all intervals of a buffer with constant | |
| 2615 text properties. The variable @var{var} will be bound to conses | |
| 2616 of start and end positions, where one start position is always equal | |
| 2617 to the previous end position. The clause allows @code{of}, | |
| 2618 @code{from}, @code{to}, and @code{property} terms, where the latter | |
| 2619 term restricts the search to just the specified property. The | |
| 2620 @code{of} term may specify either a buffer or a string. This | |
| 2621 clause is useful only in GNU Emacs 19; in other versions, all | |
| 2622 buffers and strings consist of a single interval. | |
| 2623 | |
| 2624 @item for @var{var} being the frames | |
| 2625 This clause iterates over all frames, i.e., X window system windows | |
| 2626 open on Emacs files. This clause works only under Emacs 19. The | |
| 2627 clause @code{screens} is a synonym for @code{frames}. The frames | |
| 2628 are visited in @code{next-frame} order starting from | |
| 2629 @code{selected-frame}. | |
| 2630 | |
| 2631 @item for @var{var} being the windows [of @var{frame}] | |
| 2632 This clause iterates over the windows (in the Emacs sense) of | |
| 2633 the current frame, or of the specified @var{frame}. (In Emacs 18 | |
| 2634 there is only ever one frame, and the @code{of} term is not | |
| 2635 allowed there.) | |
| 2636 | |
| 2637 @item for @var{var} being the buffers | |
| 2638 This clause iterates over all buffers in Emacs. It is equivalent | |
| 2639 to @samp{for @var{var} in (buffer-list)}. | |
| 2640 | |
| 2641 @item for @var{var} = @var{expr1} then @var{expr2} | |
| 2642 This clause does a general iteration. The first time through | |
| 2643 the loop, @var{var} will be bound to @var{expr1}. On the second | |
| 2644 and successive iterations it will be set by evaluating @var{expr2} | |
| 2645 (which may refer to the old value of @var{var}). For example, | |
| 2646 these two loops are effectively the same: | |
| 2647 | |
| 2648 @example | |
| 2649 (loop for x on my-list by 'cddr do ...) | |
| 2650 (loop for x = my-list then (cddr x) while x do ...) | |
| 2651 @end example | |
| 2652 | |
| 2653 Note that this type of @code{for} clause does not imply any sort | |
| 2654 of terminating condition; the above example combines it with a | |
| 2655 @code{while} clause to tell when to end the loop. | |
| 2656 | |
| 2657 If you omit the @code{then} term, @var{expr1} is used both for | |
| 2658 the initial setting and for successive settings: | |
| 2659 | |
| 2660 @example | |
| 2661 (loop for x = (random) when (> x 0) return x) | |
| 2662 @end example | |
| 2663 | |
| 2664 @noindent | |
| 2665 This loop keeps taking random numbers from the @code{(random)} | |
| 2666 function until it gets a positive one, which it then returns. | |
| 2667 @end table | |
| 2668 | |
| 2669 If you include several @code{for} clauses in a row, they are | |
| 2670 treated sequentially (as if by @code{let*} and @code{setq}). | |
| 2671 You can instead use the word @code{and} to link the clauses, | |
| 2672 in which case they are processed in parallel (as if by @code{let} | |
| 2673 and @code{psetq}). | |
| 2674 | |
| 2675 @example | |
| 2676 (loop for x below 5 for y = nil then x collect (list x y)) | |
| 2677 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4)) | |
| 2678 (loop for x below 5 and y = nil then x collect (list x y)) | |
| 2679 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3)) | |
| 2680 @end example | |
| 2681 | |
| 2682 @noindent | |
| 2683 In the first loop, @code{y} is set based on the value of @code{x} | |
| 2684 that was just set by the previous clause; in the second loop, | |
| 2685 @code{x} and @code{y} are set simultaneously so @code{y} is set | |
| 2686 based on the value of @code{x} left over from the previous time | |
| 2687 through the loop. | |
| 2688 | |
| 2689 Another feature of the @code{loop} macro is @dfn{destructuring}, | |
| 2690 similar in concept to the destructuring provided by @code{defmacro}. | |
| 2691 The @var{var} part of any @code{for} clause can be given as a list | |
| 2692 of variables instead of a single variable. The values produced | |
| 2693 during loop execution must be lists; the values in the lists are | |
| 2694 stored in the corresponding variables. | |
| 2695 | |
| 2696 @example | |
| 2697 (loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y)) | |
| 2698 @result{} (5 9 13) | |
| 2699 @end example | |
| 2700 | |
| 2701 In loop destructuring, if there are more values than variables | |
| 2702 the trailing values are ignored, and if there are more variables | |
| 2703 than values the trailing variables get the value @code{nil}. | |
| 2704 If @code{nil} is used as a variable name, the corresponding | |
| 2705 values are ignored. Destructuring may be nested, and dotted | |
| 2706 lists of variables like @code{(x . y)} are allowed. | |
| 2707 | |
| 2708 @node Iteration Clauses, Accumulation Clauses, For Clauses, Loop Facility | |
| 2709 @subsection Iteration Clauses | |
| 2710 | |
| 2711 @noindent | |
| 2712 Aside from @code{for} clauses, there are several other loop clauses | |
| 2713 that control the way the loop operates. They might be used by | |
| 2714 themselves, or in conjunction with one or more @code{for} clauses. | |
| 2715 | |
| 2716 @table @code | |
| 2717 @item repeat @var{integer} | |
| 2718 This clause simply counts up to the specified number using an | |
| 2719 internal temporary variable. The loops | |
| 2720 | |
| 2721 @example | |
| 2722 (loop repeat n do ...) | |
| 2723 (loop for temp to n do ...) | |
| 2724 @end example | |
| 2725 | |
| 2726 @noindent | |
| 2727 are identical except that the second one forces you to choose | |
| 2728 a name for a variable you aren't actually going to use. | |
| 2729 | |
| 2730 @item while @var{condition} | |
| 2731 This clause stops the loop when the specified condition (any Lisp | |
| 2732 expression) becomes @code{nil}. For example, the following two | |
| 2733 loops are equivalent, except for the implicit @code{nil} block | |
| 2734 that surrounds the second one: | |
| 2735 | |
| 2736 @example | |
| 2737 (while @var{cond} @var{forms}@dots{}) | |
| 2738 (loop while @var{cond} do @var{forms}@dots{}) | |
| 2739 @end example | |
| 2740 | |
| 2741 @item until @var{condition} | |
| 2742 This clause stops the loop when the specified condition is true, | |
| 2743 i.e., non-@code{nil}. | |
| 2744 | |
| 2745 @item always @var{condition} | |
| 2746 This clause stops the loop when the specified condition is @code{nil}. | |
| 2747 Unlike @code{while}, it stops the loop using @code{return nil} so that | |
| 2748 the @code{finally} clauses are not executed. If all the conditions | |
| 2749 were non-@code{nil}, the loop returns @code{t}: | |
| 2750 | |
| 2751 @example | |
| 2752 (if (loop for size in size-list always (> size 10)) | |
| 2753 (some-big-sizes) | |
| 2754 (no-big-sizes)) | |
| 2755 @end example | |
| 2756 | |
| 2757 @item never @var{condition} | |
| 2758 This clause is like @code{always}, except that the loop returns | |
| 2759 @code{t} if any conditions were false, or @code{nil} otherwise. | |
| 2760 | |
| 2761 @item thereis @var{condition} | |
| 2762 This clause stops the loop when the specified form is non-@code{nil}; | |
| 2763 in this case, it returns that non-@code{nil} value. If all the | |
| 2764 values were @code{nil}, the loop returns @code{nil}. | |
| 2765 @end table | |
| 2766 | |
| 2767 @node Accumulation Clauses, Other Clauses, Iteration Clauses, Loop Facility | |
| 2768 @subsection Accumulation Clauses | |
| 2769 | |
| 2770 @noindent | |
| 2771 These clauses cause the loop to accumulate information about the | |
| 2772 specified Lisp @var{form}. The accumulated result is returned | |
| 2773 from the loop unless overridden, say, by a @code{return} clause. | |
| 2774 | |
| 2775 @table @code | |
| 2776 @item collect @var{form} | |
| 2777 This clause collects the values of @var{form} into a list. Several | |
| 2778 examples of @code{collect} appear elsewhere in this manual. | |
| 2779 | |
| 2780 The word @code{collecting} is a synonym for @code{collect}, and | |
| 2781 likewise for the other accumulation clauses. | |
| 2782 | |
| 2783 @item append @var{form} | |
| 2784 This clause collects lists of values into a result list using | |
| 2785 @code{append}. | |
| 2786 | |
| 2787 @item nconc @var{form} | |
| 2788 This clause collects lists of values into a result list by | |
| 2789 destructively modifying the lists rather than copying them. | |
| 2790 | |
| 2791 @item concat @var{form} | |
| 2792 This clause concatenates the values of the specified @var{form} | |
| 2793 into a string. (It and the following clause are extensions to | |
| 2794 standard Common Lisp.) | |
| 2795 | |
| 2796 @item vconcat @var{form} | |
| 2797 This clause concatenates the values of the specified @var{form} | |
| 2798 into a vector. | |
| 2799 | |
| 2800 @item count @var{form} | |
| 2801 This clause counts the number of times the specified @var{form} | |
| 2802 evaluates to a non-@code{nil} value. | |
| 2803 | |
| 2804 @item sum @var{form} | |
| 2805 This clause accumulates the sum of the values of the specified | |
| 2806 @var{form}, which must evaluate to a number. | |
| 2807 | |
| 2808 @item maximize @var{form} | |
| 2809 This clause accumulates the maximum value of the specified @var{form}, | |
| 2810 which must evaluate to a number. The return value is undefined if | |
| 2811 @code{maximize} is executed zero times. | |
| 2812 | |
| 2813 @item minimize @var{form} | |
| 2814 This clause accumulates the minimum value of the specified @var{form}. | |
| 2815 @end table | |
| 2816 | |
| 2817 Accumulation clauses can be followed by @samp{into @var{var}} to | |
| 2818 cause the data to be collected into variable @var{var} (which is | |
| 2819 automatically @code{let}-bound during the loop) rather than an | |
| 2820 unnamed temporary variable. Also, @code{into} accumulations do | |
| 2821 not automatically imply a return value. The loop must use some | |
| 2822 explicit mechanism, such as @code{finally return}, to return | |
| 2823 the accumulated result. | |
| 2824 | |
| 2825 It is legal for several accumulation clauses of the same type to | |
| 2826 accumulate into the same place. From Steele: | |
| 2827 | |
| 2828 @example | |
| 2829 (loop for name in '(fred sue alice joe june) | |
| 2830 for kids in '((bob ken) () () (kris sunshine) ()) | |
| 2831 collect name | |
| 2832 append kids) | |
| 2833 @result{} (fred bob ken sue alice joe kris sunshine june) | |
| 2834 @end example | |
| 2835 | |
| 2836 @node Other Clauses, , Accumulation Clauses, Loop Facility | |
| 2837 @subsection Other Clauses | |
| 2838 | |
| 2839 @noindent | |
| 2840 This section describes the remaining loop clauses. | |
| 2841 | |
| 2842 @table @code | |
| 2843 @item with @var{var} = @var{value} | |
| 2844 This clause binds a variable to a value around the loop, but | |
| 2845 otherwise leaves the variable alone during the loop. The following | |
| 2846 loops are basically equivalent: | |
| 2847 | |
| 2848 @example | |
| 2849 (loop with x = 17 do ...) | |
| 2850 (let ((x 17)) (loop do ...)) | |
| 2851 (loop for x = 17 then x do ...) | |
| 2852 @end example | |
| 2853 | |
| 2854 Naturally, the variable @var{var} might be used for some purpose | |
| 2855 in the rest of the loop. For example: | |
| 2856 | |
| 2857 @example | |
| 2858 (loop for x in my-list with res = nil do (push x res) | |
| 2859 finally return res) | |
| 2860 @end example | |
| 2861 | |
| 2862 This loop inserts the elements of @code{my-list} at the front of | |
| 2863 a new list being accumulated in @code{res}, then returns the | |
| 2864 list @code{res} at the end of the loop. The effect is similar | |
| 2865 to that of a @code{collect} clause, but the list gets reversed | |
| 2866 by virtue of the fact that elements are being pushed onto the | |
| 2867 front of @code{res} rather than the end. | |
| 2868 | |
| 2869 If you omit the @code{=} term, the variable is initialized to | |
| 2870 @code{nil}. (Thus the @samp{= nil} in the above example is | |
| 2871 unnecessary.) | |
| 2872 | |
| 2873 Bindings made by @code{with} are sequential by default, as if | |
| 2874 by @code{let*}. Just like @code{for} clauses, @code{with} clauses | |
| 2875 can be linked with @code{and} to cause the bindings to be made by | |
| 2876 @code{let} instead. | |
| 2877 | |
| 2878 @item if @var{condition} @var{clause} | |
| 2879 This clause executes the following loop clause only if the specified | |
| 2880 condition is true. The following @var{clause} should be an accumulation, | |
| 2881 @code{do}, @code{return}, @code{if}, or @code{unless} clause. | |
| 2882 Several clauses may be linked by separating them with @code{and}. | |
| 2883 These clauses may be followed by @code{else} and a clause or clauses | |
| 2884 to execute if the condition was false. The whole construct may | |
| 2885 optionally be followed by the word @code{end} (which may be used to | |
| 2886 disambiguate an @code{else} or @code{and} in a nested @code{if}). | |
| 2887 | |
| 2888 The actual non-@code{nil} value of the condition form is available | |
| 2889 by the name @code{it} in the ``then'' part. For example: | |
| 2890 | |
| 2891 @example | |
| 2892 (setq funny-numbers '(6 13 -1)) | |
| 2893 @result{} (6 13 -1) | |
| 2894 (loop for x below 10 | |
| 2895 if (oddp x) | |
| 2896 collect x into odds | |
| 2897 and if (memq x funny-numbers) return (cdr it) end | |
| 2898 else | |
| 2899 collect x into evens | |
| 2900 finally return (vector odds evens)) | |
| 2901 @result{} [(1 3 5 7 9) (0 2 4 6 8)] | |
| 2902 (setq funny-numbers '(6 7 13 -1)) | |
| 2903 @result{} (6 7 13 -1) | |
| 2904 (loop <@r{same thing again}>) | |
| 2905 @result{} (13 -1) | |
| 2906 @end example | |
| 2907 | |
| 2908 Note the use of @code{and} to put two clauses into the ``then'' | |
| 2909 part, one of which is itself an @code{if} clause. Note also that | |
| 2910 @code{end}, while normally optional, was necessary here to make | |
| 2911 it clear that the @code{else} refers to the outermost @code{if} | |
| 2912 clause. In the first case, the loop returns a vector of lists | |
| 2913 of the odd and even values of @var{x}. In the second case, the | |
| 2914 odd number 7 is one of the @code{funny-numbers} so the loop | |
| 2915 returns early; the actual returned value is based on the result | |
| 2916 of the @code{memq} call. | |
| 2917 | |
| 2918 @item when @var{condition} @var{clause} | |
| 2919 This clause is just a synonym for @code{if}. | |
| 2920 | |
| 2921 @item unless @var{condition} @var{clause} | |
| 2922 The @code{unless} clause is just like @code{if} except that the | |
| 2923 sense of the condition is reversed. | |
| 2924 | |
| 2925 @item named @var{name} | |
| 2926 This clause gives a name other than @code{nil} to the implicit | |
| 2927 block surrounding the loop. The @var{name} is the symbol to be | |
| 2928 used as the block name. | |
| 2929 | |
| 2930 @item initially [do] @var{forms}... | |
| 2931 This keyword introduces one or more Lisp forms which will be | |
| 2932 executed before the loop itself begins (but after any variables | |
| 2933 requested by @code{for} or @code{with} have been bound to their | |
| 2934 initial values). @code{initially} clauses can appear anywhere; | |
| 2935 if there are several, they are executed in the order they appear | |
| 2936 in the loop. The keyword @code{do} is optional. | |
| 2937 | |
| 2938 @item finally [do] @var{forms}... | |
| 2939 This introduces Lisp forms which will be executed after the loop | |
| 2940 finishes (say, on request of a @code{for} or @code{while}). | |
| 2941 @code{initially} and @code{finally} clauses may appear anywhere | |
| 2942 in the loop construct, but they are executed (in the specified | |
| 2943 order) at the beginning or end, respectively, of the loop. | |
| 2944 | |
| 2945 @item finally return @var{form} | |
| 2946 This says that @var{form} should be executed after the loop | |
| 2947 is done to obtain a return value. (Without this, or some other | |
| 2948 clause like @code{collect} or @code{return}, the loop will simply | |
| 2949 return @code{nil}.) Variables bound by @code{for}, @code{with}, | |
| 2950 or @code{into} will still contain their final values when @var{form} | |
| 2951 is executed. | |
| 2952 | |
| 2953 @item do @var{forms}... | |
| 2954 The word @code{do} may be followed by any number of Lisp expressions | |
| 2955 which are executed as an implicit @code{progn} in the body of the | |
| 2956 loop. Many of the examples in this section illustrate the use of | |
| 2957 @code{do}. | |
| 2958 | |
| 2959 @item return @var{form} | |
| 2960 This clause causes the loop to return immediately. The following | |
| 2961 Lisp form is evaluated to give the return value of the @code{loop} | |
| 2962 form. The @code{finally} clauses, if any, are not executed. | |
| 2963 Of course, @code{return} is generally used inside an @code{if} or | |
| 2964 @code{unless}, as its use in a top-level loop clause would mean | |
| 2965 the loop would never get to ``loop'' more than once. | |
| 2966 | |
| 2967 The clause @samp{return @var{form}} is equivalent to | |
| 2968 @samp{do (return @var{form})} (or @code{return-from} if the loop | |
| 2969 was named). The @code{return} clause is implemented a bit more | |
| 2970 efficiently, though. | |
| 2971 @end table | |
| 2972 | |
| 2973 While there is no high-level way to add user extensions to @code{loop} | |
| 2974 (comparable to @code{defsetf} for @code{setf}, say), this package | |
| 2975 does offer two properties called @code{cl-loop-handler} and | |
| 2976 @code{cl-loop-for-handler} which are functions to be called when | |
| 2977 a given symbol is encountered as a top-level loop clause or | |
| 2978 @code{for} clause, respectively. Consult the source code in | |
| 2979 file @file{cl-macs.el} for details. | |
| 2980 | |
| 2981 This package's @code{loop} macro is compatible with that of Common | |
| 2982 Lisp, except that a few features are not implemented: @code{loop-finish} | |
| 2983 and data-type specifiers. Naturally, the @code{for} clauses which | |
| 2984 iterate over keymaps, overlays, intervals, frames, windows, and | |
| 2985 buffers are Emacs-specific extensions. | |
| 2986 | |
| 2987 @node Multiple Values, , Loop Facility, Control Structure | |
| 2988 @section Multiple Values | |
| 2989 | |
| 2990 @noindent | |
| 2991 Common Lisp functions can return zero or more results. Emacs Lisp | |
| 2992 functions, by contrast, always return exactly one result. This | |
| 2993 package makes no attempt to emulate Common Lisp multiple return | |
| 2994 values; Emacs versions of Common Lisp functions that return more | |
| 2995 than one value either return just the first value (as in | |
| 2996 @code{compiler-macroexpand}) or return a list of values (as in | |
| 2997 @code{get-setf-method}). This package @emph{does} define placeholders | |
| 2998 for the Common Lisp functions that work with multiple values, but | |
| 2999 in Emacs Lisp these functions simply operate on lists instead. | |
| 3000 The @code{values} form, for example, is a synonym for @code{list} | |
| 3001 in Emacs. | |
| 3002 | |
| 3003 @defspec multiple-value-bind (var@dots{}) values-form forms@dots{} | |
| 3004 This form evaluates @var{values-form}, which must return a list of | |
| 3005 values. It then binds the @var{var}s to these respective values, | |
| 3006 as if by @code{let}, and then executes the body @var{forms}. | |
| 3007 If there are more @var{var}s than values, the extra @var{var}s | |
| 3008 are bound to @code{nil}. If there are fewer @var{var}s than | |
| 3009 values, the excess values are ignored. | |
| 3010 @end defspec | |
| 3011 | |
| 3012 @defspec multiple-value-setq (var@dots{}) form | |
| 3013 This form evaluates @var{form}, which must return a list of values. | |
| 3014 It then sets the @var{var}s to these respective values, as if by | |
| 3015 @code{setq}. Extra @var{var}s or values are treated the same as | |
| 3016 in @code{multiple-value-bind}. | |
| 3017 @end defspec | |
| 3018 | |
| 3019 The older Quiroz package attempted a more faithful (but still | |
| 3020 imperfect) emulation of Common Lisp multiple values. The old | |
| 3021 method ``usually'' simulated true multiple values quite well, | |
| 3022 but under certain circumstances would leave spurious return | |
| 3023 values in memory where a later, unrelated @code{multiple-value-bind} | |
| 3024 form would see them. | |
| 3025 | |
| 3026 Since a perfect emulation is not feasible in Emacs Lisp, this | |
| 3027 package opts to keep it as simple and predictable as possible. | |
| 3028 | |
| 3029 @node Macros, Declarations, Control Structure, Top | |
| 3030 @chapter Macros | |
| 3031 | |
| 3032 @noindent | |
| 3033 This package implements the various Common Lisp features of | |
| 3034 @code{defmacro}, such as destructuring, @code{&environment}, | |
| 3035 and @code{&body}. Top-level @code{&whole} is not implemented | |
| 3036 for @code{defmacro} due to technical difficulties. | |
| 3037 @xref{Argument Lists}. | |
| 3038 | |
| 3039 Destructuring is made available to the user by way of the | |
| 3040 following macro: | |
| 3041 | |
| 3042 @defspec destructuring-bind arglist expr forms@dots{} | |
| 3043 This macro expands to code which executes @var{forms}, with | |
| 3044 the variables in @var{arglist} bound to the list of values | |
| 3045 returned by @var{expr}. The @var{arglist} can include all | |
| 3046 the features allowed for @code{defmacro} argument lists, | |
| 3047 including destructuring. (The @code{&environment} keyword | |
| 3048 is not allowed.) The macro expansion will signal an error | |
| 3049 if @var{expr} returns a list of the wrong number of arguments | |
| 3050 or with incorrect keyword arguments. | |
| 3051 @end defspec | |
| 3052 | |
| 3053 This package also includes the Common Lisp @code{define-compiler-macro} | |
| 3054 facility, which allows you to define compile-time expansions and | |
| 3055 optimizations for your functions. | |
| 3056 | |
| 3057 @defspec define-compiler-macro name arglist forms@dots{} | |
| 3058 This form is similar to @code{defmacro}, except that it only expands | |
| 3059 calls to @var{name} at compile-time; calls processed by the Lisp | |
| 3060 interpreter are not expanded, nor are they expanded by the | |
| 3061 @code{macroexpand} function. | |
| 3062 | |
| 3063 The argument list may begin with a @code{&whole} keyword and a | |
| 3064 variable. This variable is bound to the macro-call form itself, | |
| 3065 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}. | |
| 3066 If the macro expander returns this form unchanged, then the | |
| 3067 compiler treats it as a normal function call. This allows | |
| 3068 compiler macros to work as optimizers for special cases of a | |
| 3069 function, leaving complicated cases alone. | |
| 3070 | |
| 3071 For example, here is a simplified version of a definition that | |
| 3072 appears as a standard part of this package: | |
| 3073 | |
| 3074 @example | |
| 3075 (define-compiler-macro member* (&whole form a list &rest keys) | |
| 3076 (if (and (null keys) | |
| 3077 (eq (car-safe a) 'quote) | |
| 3078 (not (floatp-safe (cadr a)))) | |
| 3079 (list 'memq a list) | |
| 3080 form)) | |
| 3081 @end example | |
| 3082 | |
| 3083 @noindent | |
| 3084 This definition causes @code{(member* @var{a} @var{list})} to change | |
| 3085 to a call to the faster @code{memq} in the common case where @var{a} | |
| 3086 is a non-floating-point constant; if @var{a} is anything else, or | |
| 3087 if there are any keyword arguments in the call, then the original | |
| 3088 @code{member*} call is left intact. (The actual compiler macro | |
| 3089 for @code{member*} optimizes a number of other cases, including | |
| 3090 common @code{:test} predicates.) | |
| 3091 @end defspec | |
| 3092 | |
| 3093 @defun compiler-macroexpand form | |
| 3094 This function is analogous to @code{macroexpand}, except that it | |
| 3095 expands compiler macros rather than regular macros. It returns | |
| 3096 @var{form} unchanged if it is not a call to a function for which | |
| 3097 a compiler macro has been defined, or if that compiler macro | |
| 3098 decided to punt by returning its @code{&whole} argument. Like | |
| 3099 @code{macroexpand}, it expands repeatedly until it reaches a form | |
| 3100 for which no further expansion is possible. | |
| 3101 @end defun | |
| 3102 | |
| 3103 @xref{Macro Bindings}, for descriptions of the @code{macrolet} | |
| 3104 and @code{symbol-macrolet} forms for making ``local'' macro | |
| 3105 definitions. | |
| 3106 | |
| 3107 @node Declarations, Symbols, Macros, Top | |
| 3108 @chapter Declarations | |
| 3109 | |
| 3110 @noindent | |
| 3111 Common Lisp includes a complex and powerful ``declaration'' | |
| 3112 mechanism that allows you to give the compiler special hints | |
| 3113 about the types of data that will be stored in particular variables, | |
| 3114 and about the ways those variables and functions will be used. This | |
| 3115 package defines versions of all the Common Lisp declaration forms: | |
| 3116 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim}, | |
| 3117 and @code{the}. | |
| 3118 | |
| 3119 Most of the Common Lisp declarations are not currently useful in | |
| 3120 Emacs Lisp, as the byte-code system provides little opportunity | |
| 3121 to benefit from type information, and @code{special} declarations | |
| 3122 are redundant in a fully dynamically-scoped Lisp. A few | |
| 3123 declarations are meaningful when the optimizing Emacs 19 byte | |
| 3124 compiler is being used, however. Under the earlier non-optimizing | |
| 3125 compiler, these declarations will effectively be ignored. | |
| 3126 | |
| 3127 @defun proclaim decl-spec | |
| 3128 This function records a ``global'' declaration specified by | |
| 3129 @var{decl-spec}. Since @code{proclaim} is a function, @var{decl-spec} | |
| 3130 is evaluated and thus should normally be quoted. | |
| 3131 @end defun | |
| 3132 | |
| 3133 @defspec declaim decl-specs@dots{} | |
| 3134 This macro is like @code{proclaim}, except that it takes any number | |
| 3135 of @var{decl-spec} arguments, and the arguments are unevaluated and | |
| 3136 unquoted. The @code{declaim} macro also puts an @code{(eval-when | |
| 3137 (compile load eval) ...)} around the declarations so that they will | |
| 3138 be registered at compile-time as well as at run-time. (This is vital, | |
| 3139 since normally the declarations are meant to influence the way the | |
| 3140 compiler treats the rest of the file that contains the @code{declaim} | |
| 3141 form.) | |
| 3142 @end defspec | |
| 3143 | |
| 3144 @defspec declare decl-specs@dots{} | |
| 3145 This macro is used to make declarations within functions and other | |
| 3146 code. Common Lisp allows declarations in various locations, generally | |
| 3147 at the beginning of any of the many ``implicit @code{progn}s'' | |
| 3148 throughout Lisp syntax, such as function bodies, @code{let} bodies, | |
| 3149 etc. Currently the only declaration understood by @code{declare} | |
| 3150 is @code{special}. | |
| 3151 @end defspec | |
| 3152 | |
| 3153 @defspec locally declarations@dots{} forms@dots{} | |
| 3154 In this package, @code{locally} is no different from @code{progn}. | |
| 3155 @end defspec | |
| 3156 | |
| 3157 @defspec the type form | |
| 3158 Type information provided by @code{the} is ignored in this package; | |
| 3159 in other words, @code{(the @var{type} @var{form})} is equivalent | |
| 3160 to @var{form}. Future versions of the optimizing byte-compiler may | |
| 3161 make use of this information. | |
| 3162 | |
| 3163 For example, @code{mapcar} can map over both lists and arrays. It is | |
| 3164 hard for the compiler to expand @code{mapcar} into an in-line loop | |
| 3165 unless it knows whether the sequence will be a list or an array ahead | |
| 3166 of time. With @code{(mapcar 'car (the vector foo))}, a future | |
| 3167 compiler would have enough information to expand the loop in-line. | |
| 3168 For now, Emacs Lisp will treat the above code as exactly equivalent | |
| 3169 to @code{(mapcar 'car foo)}. | |
| 3170 @end defspec | |
| 3171 | |
| 3172 Each @var{decl-spec} in a @code{proclaim}, @code{declaim}, or | |
| 3173 @code{declare} should be a list beginning with a symbol that says | |
| 3174 what kind of declaration it is. This package currently understands | |
| 3175 @code{special}, @code{inline}, @code{notinline}, @code{optimize}, | |
| 3176 and @code{warn} declarations. (The @code{warn} declaration is an | |
| 3177 extension of standard Common Lisp.) Other Common Lisp declarations, | |
| 3178 such as @code{type} and @code{ftype}, are silently ignored. | |
| 3179 | |
| 3180 @table @code | |
| 3181 @item special | |
| 3182 Since all variables in Emacs Lisp are ``special'' (in the Common | |
| 3183 Lisp sense), @code{special} declarations are only advisory. They | |
| 3184 simply tell the optimizing byte compiler that the specified | |
| 3185 variables are intentionally being referred to without being | |
| 3186 bound in the body of the function. The compiler normally emits | |
| 3187 warnings for such references, since they could be typographical | |
| 3188 errors for references to local variables. | |
| 3189 | |
| 3190 The declaration @code{(declare (special @var{var1} @var{var2}))} is | |
| 3191 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})} in the | |
| 3192 optimizing compiler, or to nothing at all in older compilers (which | |
| 3193 do not warn for non-local references). | |
| 3194 | |
| 3195 In top-level contexts, it is generally better to write | |
| 3196 @code{(defvar @var{var})} than @code{(declaim (special @var{var}))}, | |
| 3197 since @code{defvar} makes your intentions clearer. But the older | |
| 3198 byte compilers can not handle @code{defvar}s appearing inside of | |
| 3199 functions, while @code{(declare (special @var{var}))} takes care | |
| 3200 to work correctly with all compilers. | |
| 3201 | |
| 3202 @item inline | |
| 3203 The @code{inline} @var{decl-spec} lists one or more functions | |
| 3204 whose bodies should be expanded ``in-line'' into calling functions | |
| 3205 whenever the compiler is able to arrange for it. For example, | |
| 3206 the Common Lisp function @code{cadr} is declared @code{inline} | |
| 3207 by this package so that the form @code{(cadr @var{x})} will | |
| 3208 expand directly into @code{(car (cdr @var{x}))} when it is called | |
| 3209 in user functions, for a savings of one (relatively expensive) | |
| 3210 function call. | |
| 3211 | |
| 3212 The following declarations are all equivalent. Note that the | |
| 3213 @code{defsubst} form is a convenient way to define a function | |
| 3214 and declare it inline all at once, but it is available only in | |
| 3215 Emacs 19. | |
| 3216 | |
| 3217 @example | |
| 3218 (declaim (inline foo bar)) | |
| 3219 (eval-when (compile load eval) (proclaim '(inline foo bar))) | |
| 442 | 3220 (proclaim-inline foo bar) ; XEmacs only |
| 3221 (defsubst foo (...) ...) ; instead of defun; Emacs 19 only | |
| 428 | 3222 @end example |
| 3223 | |
| 3224 @strong{Please note:} This declaration remains in effect after the | |
| 3225 containing source file is done. It is correct to use it to | |
| 3226 request that a function you have defined should be inlined, | |
| 3227 but it is impolite to use it to request inlining of an external | |
| 3228 function. | |
| 3229 | |
| 3230 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))} | |
| 3231 before a particular call to a function to cause just that call to | |
| 3232 be inlined; the current byte compilers provide no way to implement | |
| 3233 this, so @code{(declare (inline @dots{}))} is currently ignored by | |
| 3234 this package. | |
| 3235 | |
| 3236 @item notinline | |
| 3237 The @code{notinline} declaration lists functions which should | |
| 3238 not be inlined after all; it cancels a previous @code{inline} | |
| 3239 declaration. | |
| 3240 | |
| 3241 @item optimize | |
| 3242 This declaration controls how much optimization is performed by | |
| 3243 the compiler. Naturally, it is ignored by the earlier non-optimizing | |
| 3244 compilers. | |
| 3245 | |
| 3246 The word @code{optimize} is followed by any number of lists like | |
| 3247 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several | |
| 3248 optimization ``qualities''; this package ignores all but @code{speed} | |
| 3249 and @code{safety}. The value of a quality should be an integer from | |
| 3250 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important.'' | |
| 3251 The default level for both qualities is 1. | |
| 3252 | |
| 3253 In this package, with the Emacs 19 optimizing compiler, the | |
| 3254 @code{speed} quality is tied to the @code{byte-compile-optimize} | |
| 3255 flag, which is set to @code{nil} for @code{(speed 0)} and to | |
| 3256 @code{t} for higher settings; and the @code{safety} quality is | |
| 3257 tied to the @code{byte-compile-delete-errors} flag, which is | |
| 3258 set to @code{t} for @code{(safety 3)} and to @code{nil} for all | |
| 3259 lower settings. (The latter flag controls whether the compiler | |
| 3260 is allowed to optimize out code whose only side-effect could | |
| 3261 be to signal an error, e.g., rewriting @code{(progn foo bar)} to | |
| 3262 @code{bar} when it is not known whether @code{foo} will be bound | |
| 3263 at run-time.) | |
| 3264 | |
| 3265 Note that even compiling with @code{(safety 0)}, the Emacs | |
| 3266 byte-code system provides sufficient checking to prevent real | |
| 3267 harm from being done. For example, barring serious bugs in | |
| 3268 Emacs itself, Emacs will not crash with a segmentation fault | |
| 3269 just because of an error in a fully-optimized Lisp program. | |
| 3270 | |
| 3271 The @code{optimize} declaration is normally used in a top-level | |
| 3272 @code{proclaim} or @code{declaim} in a file; Common Lisp allows | |
| 3273 it to be used with @code{declare} to set the level of optimization | |
| 3274 locally for a given form, but this will not work correctly with the | |
| 3275 current version of the optimizing compiler. (The @code{declare} | |
| 3276 will set the new optimization level, but that level will not | |
| 3277 automatically be unset after the enclosing form is done.) | |
| 3278 | |
| 3279 @item warn | |
| 3280 This declaration controls what sorts of warnings are generated | |
| 3281 by the byte compiler. Again, only the optimizing compiler | |
| 3282 generates warnings. The word @code{warn} is followed by any | |
| 3283 number of ``warning qualities,'' similar in form to optimization | |
| 3284 qualities. The currently supported warning types are | |
| 3285 @code{redefine}, @code{callargs}, @code{unresolved}, and | |
| 3286 @code{free-vars}; in the current system, a value of 0 will | |
| 3287 disable these warnings and any higher value will enable them. | |
| 3288 See the documentation for the optimizing byte compiler for details. | |
| 3289 @end table | |
| 3290 | |
| 3291 @node Symbols, Numbers, Declarations, Top | |
| 3292 @chapter Symbols | |
| 3293 | |
| 3294 @noindent | |
| 3295 This package defines several symbol-related features that were | |
| 3296 missing from Emacs Lisp. | |
| 3297 | |
| 3298 @menu | |
| 442 | 3299 * Property Lists:: `getf', `remf' |
| 428 | 3300 * Creating Symbols:: `gensym', `gentemp' |
| 3301 @end menu | |
| 3302 | |
| 3303 @node Property Lists, Creating Symbols, Symbols, Symbols | |
| 3304 @section Property Lists | |
| 3305 | |
| 3306 @noindent | |
| 3307 These functions augment the standard Emacs Lisp functions @code{get} | |
| 442 | 3308 and @code{put} for operating on properties attached to objects. |
| 428 | 3309 There are also functions for working with property lists as |
| 442 | 3310 first-class data structures not attached to particular objects. |
| 428 | 3311 |
| 3312 @defun getf place property &optional default | |
| 3313 This function scans the list @var{place} as if it were a property | |
| 3314 list, i.e., a list of alternating property names and values. If | |
| 3315 an even-numbered element of @var{place} is found which is @code{eq} | |
| 3316 to @var{property}, the following odd-numbered element is returned. | |
| 3317 Otherwise, @var{default} is returned (or @code{nil} if no default | |
| 3318 is given). | |
| 3319 | |
| 3320 In particular, | |
| 3321 | |
| 3322 @example | |
| 3323 (get sym prop) @equiv{} (getf (symbol-plist sym) prop) | |
| 3324 @end example | |
| 3325 | |
| 3326 It is legal to use @code{getf} as a @code{setf} place, in which case | |
| 3327 its @var{place} argument must itself be a legal @code{setf} place. | |
| 3328 The @var{default} argument, if any, is ignored in this context. | |
| 3329 The effect is to change (via @code{setcar}) the value cell in the | |
| 3330 list that corresponds to @var{property}, or to cons a new property-value | |
| 3331 pair onto the list if the property is not yet present. | |
| 3332 | |
| 3333 @example | |
| 3334 (put sym prop val) @equiv{} (setf (getf (symbol-plist sym) prop) val) | |
| 3335 @end example | |
| 3336 | |
| 440 | 3337 The @code{get} function is also @code{setf}-able. The fact that |
| 3338 @code{default} is ignored can sometimes be useful: | |
| 428 | 3339 |
| 3340 @example | |
| 440 | 3341 (incf (get 'foo 'usage-count 0)) |
| 428 | 3342 @end example |
| 3343 | |
| 3344 Here, symbol @code{foo}'s @code{usage-count} property is incremented | |
| 3345 if it exists, or set to 1 (an incremented 0) otherwise. | |
| 3346 | |
| 3347 When not used as a @code{setf} form, @code{getf} is just a regular | |
| 3348 function and its @var{place} argument can actually be any Lisp | |
| 3349 expression. | |
| 3350 @end defun | |
| 3351 | |
| 3352 @defspec remf place property | |
| 3353 This macro removes the property-value pair for @var{property} from | |
| 3354 the property list stored at @var{place}, which is any @code{setf}-able | |
| 3355 place expression. It returns true if the property was found. Note | |
| 3356 that if @var{property} happens to be first on the list, this will | |
| 3357 effectively do a @code{(setf @var{place} (cddr @var{place}))}, | |
| 3358 whereas if it occurs later, this simply uses @code{setcdr} to splice | |
| 3359 out the property and value cells. | |
| 3360 @end defspec | |
| 3361 | |
| 3362 @iftex | |
| 3363 @secno=2 | |
| 3364 @end iftex | |
| 3365 | |
| 3366 @node Creating Symbols, , Property Lists, Symbols | |
| 3367 @section Creating Symbols | |
| 3368 | |
| 3369 @noindent | |
| 3370 These functions create unique symbols, typically for use as | |
| 3371 temporary variables. | |
| 3372 | |
| 3373 @defun gensym &optional x | |
| 3374 This function creates a new, uninterned symbol (using @code{make-symbol}) | |
| 3375 with a unique name. (The name of an uninterned symbol is relevant | |
| 3376 only if the symbol is printed.) By default, the name is generated | |
| 3377 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001}, | |
| 3378 @samp{G1002}, etc. If the optional argument @var{x} is a string, that | |
| 3379 string is used as a prefix instead of @samp{G}. Uninterned symbols | |
| 3380 are used in macro expansions for temporary variables, to ensure that | |
| 3381 their names will not conflict with ``real'' variables in the user's | |
| 3382 code. | |
| 3383 @end defun | |
| 3384 | |
| 3385 @defvar *gensym-counter* | |
| 3386 This variable holds the counter used to generate @code{gensym} names. | |
| 3387 It is incremented after each use by @code{gensym}. In Common Lisp | |
| 3388 this is initialized with 0, but this package initializes it with a | |
| 3389 random (time-dependent) value to avoid trouble when two files that | |
| 3390 each used @code{gensym} in their compilation are loaded together. | |
| 3391 | |
| 3392 @strong{XEmacs note:} As of XEmacs 21.0, an uninterned symbol remains | |
| 3393 uninterned even after being dumped to bytecode. Older versions of Emacs | |
| 3394 didn't distinguish the printed representation of interned and uninterned | |
| 3395 symbols, so their names had to be treated more carefully. | |
| 3396 @end defvar | |
| 3397 | |
| 3398 @defun gentemp &optional x | |
| 3399 This function is like @code{gensym}, except that it produces a new | |
| 3400 @emph{interned} symbol. If the symbol that is generated already | |
| 3401 exists, the function keeps incrementing the counter and trying | |
| 3402 again until a new symbol is generated. | |
| 3403 @end defun | |
| 3404 | |
| 3405 The Quiroz @file{cl.el} package also defined a @code{defkeyword} | |
| 3406 form for creating self-quoting keyword symbols. This package | |
| 3407 automatically creates all keywords that are called for by | |
| 3408 @code{&key} argument specifiers, and discourages the use of | |
| 3409 keywords as data unrelated to keyword arguments, so the | |
| 3410 @code{defkeyword} form has been discontinued. | |
| 3411 | |
| 3412 @iftex | |
| 3413 @chapno=11 | |
| 3414 @end iftex | |
| 3415 | |
| 3416 @node Numbers, Sequences, Symbols, Top | |
| 3417 @chapter Numbers | |
| 3418 | |
| 3419 @noindent | |
| 3420 This section defines a few simple Common Lisp operations on numbers | |
| 3421 which were left out of Emacs Lisp. | |
| 3422 | |
| 3423 @menu | |
| 3424 * Predicates on Numbers:: `plusp', `oddp', `floatp-safe', etc. | |
| 3425 * Numerical Functions:: `abs', `expt', `floor*', etc. | |
| 3426 * Random Numbers:: `random*', `make-random-state' | |
| 3427 * Implementation Parameters:: `most-positive-fixnum', `most-positive-float' | |
| 3428 @end menu | |
| 3429 | |
| 3430 @iftex | |
| 3431 @secno=1 | |
| 3432 @end iftex | |
| 3433 | |
| 3434 @node Predicates on Numbers, Numerical Functions, Numbers, Numbers | |
| 3435 @section Predicates on Numbers | |
| 3436 | |
| 3437 @noindent | |
| 3438 These functions return @code{t} if the specified condition is | |
| 3439 true of the numerical argument, or @code{nil} otherwise. | |
| 3440 | |
| 3441 @defun plusp number | |
| 3442 This predicate tests whether @var{number} is positive. It is an | |
| 3443 error if the argument is not a number. | |
| 3444 @end defun | |
| 3445 | |
| 3446 @defun minusp number | |
| 3447 This predicate tests whether @var{number} is negative. It is an | |
| 3448 error if the argument is not a number. | |
| 3449 @end defun | |
| 3450 | |
| 3451 @defun oddp integer | |
| 3452 This predicate tests whether @var{integer} is odd. It is an | |
| 3453 error if the argument is not an integer. | |
| 3454 @end defun | |
| 3455 | |
| 3456 @defun evenp integer | |
| 3457 This predicate tests whether @var{integer} is even. It is an | |
| 3458 error if the argument is not an integer. | |
| 3459 @end defun | |
| 3460 | |
| 3461 @defun floatp-safe object | |
| 3462 This predicate tests whether @var{object} is a floating-point | |
| 3463 number. On systems that support floating-point, this is equivalent | |
| 3464 to @code{floatp}. On other systems, this always returns @code{nil}. | |
| 3465 @end defun | |
| 3466 | |
| 3467 @iftex | |
| 3468 @secno=3 | |
| 3469 @end iftex | |
| 3470 | |
| 3471 @node Numerical Functions, Random Numbers, Predicates on Numbers, Numbers | |
| 3472 @section Numerical Functions | |
| 3473 | |
| 3474 @noindent | |
| 3475 These functions perform various arithmetic operations on numbers. | |
| 3476 | |
| 3477 @defun abs number | |
| 3478 This function returns the absolute value of @var{number}. (Newer | |
| 3479 versions of Emacs provide this as a built-in function; this package | |
| 3480 defines @code{abs} only for Emacs 18 versions which don't provide | |
| 3481 it as a primitive.) | |
| 3482 @end defun | |
| 3483 | |
| 3484 @defun expt base power | |
| 3485 This function returns @var{base} raised to the power of @var{number}. | |
| 3486 (Newer versions of Emacs provide this as a built-in function; this | |
| 3487 package defines @code{expt} only for Emacs 18 versions which don't | |
| 3488 provide it as a primitive.) | |
| 3489 @end defun | |
| 3490 | |
| 3491 @defun gcd &rest integers | |
| 3492 This function returns the Greatest Common Divisor of the arguments. | |
| 3493 For one argument, it returns the absolute value of that argument. | |
| 3494 For zero arguments, it returns zero. | |
| 3495 @end defun | |
| 3496 | |
| 3497 @defun lcm &rest integers | |
| 3498 This function returns the Least Common Multiple of the arguments. | |
| 3499 For one argument, it returns the absolute value of that argument. | |
| 3500 For zero arguments, it returns one. | |
| 3501 @end defun | |
| 3502 | |
| 3503 @defun isqrt integer | |
| 3504 This function computes the ``integer square root'' of its integer | |
| 3505 argument, i.e., the greatest integer less than or equal to the true | |
| 3506 square root of the argument. | |
| 3507 @end defun | |
| 3508 | |
| 3509 @defun floor* number &optional divisor | |
| 3510 This function implements the Common Lisp @code{floor} function. | |
| 3511 It is called @code{floor*} to avoid name conflicts with the | |
| 3512 simpler @code{floor} function built-in to Emacs 19. | |
| 3513 | |
| 3514 With one argument, @code{floor*} returns a list of two numbers: | |
| 3515 The argument rounded down (toward minus infinity) to an integer, | |
| 3516 and the ``remainder'' which would have to be added back to the | |
| 3517 first return value to yield the argument again. If the argument | |
| 3518 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}. | |
| 3519 If the argument is an Emacs 19 floating-point number, the first | |
| 3520 result is a Lisp integer and the second is a Lisp float between | |
| 3521 0 (inclusive) and 1 (exclusive). | |
| 3522 | |
| 3523 With two arguments, @code{floor*} divides @var{number} by | |
| 3524 @var{divisor}, and returns the floor of the quotient and the | |
| 3525 corresponding remainder as a list of two numbers. If | |
| 3526 @code{(floor* @var{x} @var{y})} returns @code{(@var{q} @var{r})}, | |
| 3527 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r} | |
| 3528 between 0 (inclusive) and @var{r} (exclusive). Also, note | |
| 3529 that @code{(floor* @var{x})} is exactly equivalent to | |
| 3530 @code{(floor* @var{x} 1)}. | |
| 3531 | |
| 3532 This function is entirely compatible with Common Lisp's @code{floor} | |
| 3533 function, except that it returns the two results in a list since | |
| 3534 Emacs Lisp does not support multiple-valued functions. | |
| 3535 @end defun | |
| 3536 | |
| 3537 @defun ceiling* number &optional divisor | |
| 3538 This function implements the Common Lisp @code{ceiling} function, | |
| 3539 which is analogous to @code{floor} except that it rounds the | |
| 3540 argument or quotient of the arguments up toward plus infinity. | |
| 3541 The remainder will be between 0 and minus @var{r}. | |
| 3542 @end defun | |
| 3543 | |
| 3544 @defun truncate* number &optional divisor | |
| 3545 This function implements the Common Lisp @code{truncate} function, | |
| 3546 which is analogous to @code{floor} except that it rounds the | |
| 3547 argument or quotient of the arguments toward zero. Thus it is | |
| 3548 equivalent to @code{floor*} if the argument or quotient is | |
| 3549 positive, or to @code{ceiling*} otherwise. The remainder has | |
| 3550 the same sign as @var{number}. | |
| 3551 @end defun | |
| 3552 | |
| 3553 @defun round* number &optional divisor | |
| 3554 This function implements the Common Lisp @code{round} function, | |
| 3555 which is analogous to @code{floor} except that it rounds the | |
| 3556 argument or quotient of the arguments to the nearest integer. | |
| 3557 In the case of a tie (the argument or quotient is exactly | |
| 3558 halfway between two integers), it rounds to the even integer. | |
| 3559 @end defun | |
| 3560 | |
| 3561 @defun mod* number divisor | |
| 3562 This function returns the same value as the second return value | |
| 3563 of @code{floor}. | |
| 3564 @end defun | |
| 3565 | |
| 3566 @defun rem* number divisor | |
| 3567 This function returns the same value as the second return value | |
| 3568 of @code{truncate}. | |
| 3569 @end defun | |
| 3570 | |
| 3571 These definitions are compatible with those in the Quiroz | |
| 3572 @file{cl.el} package, except that this package appends @samp{*} | |
| 3573 to certain function names to avoid conflicts with existing | |
| 3574 Emacs 19 functions, and that the mechanism for returning | |
| 3575 multiple values is different. | |
| 3576 | |
| 3577 @iftex | |
| 3578 @secno=8 | |
| 3579 @end iftex | |
| 3580 | |
| 3581 @node Random Numbers, Implementation Parameters, Numerical Functions, Numbers | |
| 3582 @section Random Numbers | |
| 3583 | |
| 3584 @noindent | |
| 3585 This package also provides an implementation of the Common Lisp | |
| 3586 random number generator. It uses its own additive-congruential | |
| 3587 algorithm, which is much more likely to give statistically clean | |
| 3588 random numbers than the simple generators supplied by many | |
| 3589 operating systems. | |
| 3590 | |
| 3591 @defun random* number &optional state | |
| 3592 This function returns a random nonnegative number less than | |
| 3593 @var{number}, and of the same type (either integer or floating-point). | |
| 3594 The @var{state} argument should be a @code{random-state} object | |
| 3595 which holds the state of the random number generator. The | |
| 3596 function modifies this state object as a side effect. If | |
| 3597 @var{state} is omitted, it defaults to the variable | |
| 3598 @code{*random-state*}, which contains a pre-initialized | |
| 3599 @code{random-state} object. | |
| 3600 @end defun | |
| 3601 | |
| 3602 @defvar *random-state* | |
| 3603 This variable contains the system ``default'' @code{random-state} | |
| 3604 object, used for calls to @code{random*} that do not specify an | |
| 3605 alternative state object. Since any number of programs in the | |
| 3606 Emacs process may be accessing @code{*random-state*} in interleaved | |
| 3607 fashion, the sequence generated from this variable will be | |
| 3608 irreproducible for all intents and purposes. | |
| 3609 @end defvar | |
| 3610 | |
| 3611 @defun make-random-state &optional state | |
| 3612 This function creates or copies a @code{random-state} object. | |
| 3613 If @var{state} is omitted or @code{nil}, it returns a new copy of | |
| 3614 @code{*random-state*}. This is a copy in the sense that future | |
| 3615 sequences of calls to @code{(random* @var{n})} and | |
| 3616 @code{(random* @var{n} @var{s})} (where @var{s} is the new | |
| 3617 random-state object) will return identical sequences of random | |
| 3618 numbers. | |
| 3619 | |
| 3620 If @var{state} is a @code{random-state} object, this function | |
| 3621 returns a copy of that object. If @var{state} is @code{t}, this | |
| 3622 function returns a new @code{random-state} object seeded from the | |
| 3623 date and time. As an extension to Common Lisp, @var{state} may also | |
| 3624 be an integer in which case the new object is seeded from that | |
| 3625 integer; each different integer seed will result in a completely | |
| 3626 different sequence of random numbers. | |
| 3627 | |
| 3628 It is legal to print a @code{random-state} object to a buffer or | |
| 3629 file and later read it back with @code{read}. If a program wishes | |
| 3630 to use a sequence of pseudo-random numbers which can be reproduced | |
| 3631 later for debugging, it can call @code{(make-random-state t)} to | |
| 3632 get a new sequence, then print this sequence to a file. When the | |
| 3633 program is later rerun, it can read the original run's random-state | |
| 3634 from the file. | |
| 3635 @end defun | |
| 3636 | |
| 3637 @defun random-state-p object | |
| 3638 This predicate returns @code{t} if @var{object} is a | |
| 3639 @code{random-state} object, or @code{nil} otherwise. | |
| 3640 @end defun | |
| 3641 | |
| 3642 @node Implementation Parameters, , Random Numbers, Numbers | |
| 3643 @section Implementation Parameters | |
| 3644 | |
| 3645 @noindent | |
| 3646 This package defines several useful constants having to with numbers. | |
| 3647 | |
| 3648 @defvar most-positive-fixnum | |
| 3649 This constant equals the largest value a Lisp integer can hold. | |
| 3650 It is typically @code{2^23-1} or @code{2^25-1}. | |
| 3651 @end defvar | |
| 3652 | |
| 3653 @defvar most-negative-fixnum | |
| 3654 This constant equals the smallest (most negative) value a Lisp | |
| 3655 integer can hold. | |
| 3656 @end defvar | |
| 3657 | |
| 3658 The following parameters have to do with floating-point numbers. | |
| 3659 This package determines their values by exercising the computer's | |
| 3660 floating-point arithmetic in various ways. Because this operation | |
| 3661 might be slow, the code for initializing them is kept in a separate | |
| 3662 function that must be called before the parameters can be used. | |
| 3663 | |
| 3664 @defun cl-float-limits | |
| 3665 This function makes sure that the Common Lisp floating-point | |
| 3666 parameters like @code{most-positive-float} have been initialized. | |
| 3667 Until it is called, these parameters will be @code{nil}. If this | |
| 3668 version of Emacs does not support floats (e.g., most versions of | |
| 3669 Emacs 18), the parameters will remain @code{nil}. If the parameters | |
| 3670 have already been initialized, the function returns immediately. | |
| 3671 | |
| 3672 The algorithm makes assumptions that will be valid for most modern | |
| 3673 machines, but will fail if the machine's arithmetic is extremely | |
| 3674 unusual, e.g., decimal. | |
| 3675 @end defun | |
| 3676 | |
| 3677 Since true Common Lisp supports up to four different floating-point | |
| 3678 precisions, it has families of constants like | |
| 3679 @code{most-positive-single-float}, @code{most-positive-double-float}, | |
| 3680 @code{most-positive-long-float}, and so on. Emacs has only one | |
| 3681 floating-point precision, so this package omits the precision word | |
| 3682 from the constants' names. | |
| 3683 | |
| 3684 @defvar most-positive-float | |
| 3685 This constant equals the largest value a Lisp float can hold. | |
| 3686 For those systems whose arithmetic supports infinities, this is | |
| 3687 the largest @emph{finite} value. For IEEE machines, the value | |
| 3688 is approximately @code{1.79e+308}. | |
| 3689 @end defvar | |
| 3690 | |
| 3691 @defvar most-negative-float | |
| 3692 This constant equals the most-negative value a Lisp float can hold. | |
| 3693 (It is assumed to be equal to @code{(- most-positive-float)}.) | |
| 3694 @end defvar | |
| 3695 | |
| 3696 @defvar least-positive-float | |
| 3697 This constant equals the smallest Lisp float value greater than zero. | |
| 3698 For IEEE machines, it is about @code{4.94e-324} if denormals are | |
| 3699 supported or @code{2.22e-308} if not. | |
| 3700 @end defvar | |
| 3701 | |
| 3702 @defvar least-positive-normalized-float | |
| 3703 This constant equals the smallest @emph{normalized} Lisp float greater | |
| 3704 than zero, i.e., the smallest value for which IEEE denormalization | |
| 3705 will not result in a loss of precision. For IEEE machines, this | |
| 3706 value is about @code{2.22e-308}. For machines that do not support | |
| 3707 the concept of denormalization and gradual underflow, this constant | |
| 3708 will always equal @code{least-positive-float}. | |
| 3709 @end defvar | |
| 3710 | |
| 3711 @defvar least-negative-float | |
| 3712 This constant is the negative counterpart of @code{least-positive-float}. | |
| 3713 @end defvar | |
| 3714 | |
| 3715 @defvar least-negative-normalized-float | |
| 3716 This constant is the negative counterpart of | |
| 3717 @code{least-positive-normalized-float}. | |
| 3718 @end defvar | |
| 3719 | |
| 3720 @defvar float-epsilon | |
| 3721 This constant is the smallest positive Lisp float that can be added | |
| 3722 to 1.0 to produce a distinct value. Adding a smaller number to 1.0 | |
| 3723 will yield 1.0 again due to roundoff. For IEEE machines, epsilon | |
| 3724 is about @code{2.22e-16}. | |
| 3725 @end defvar | |
| 3726 | |
| 3727 @defvar float-negative-epsilon | |
| 3728 This is the smallest positive value that can be subtracted from | |
| 3729 1.0 to produce a distinct value. For IEEE machines, it is about | |
| 3730 @code{1.11e-16}. | |
| 3731 @end defvar | |
| 3732 | |
| 3733 @iftex | |
| 3734 @chapno=13 | |
| 3735 @end iftex | |
| 3736 | |
| 3737 @node Sequences, Lists, Numbers, Top | |
| 3738 @chapter Sequences | |
| 3739 | |
| 3740 @noindent | |
| 3741 Common Lisp defines a number of functions that operate on | |
| 3742 @dfn{sequences}, which are either lists, strings, or vectors. | |
| 3743 Emacs Lisp includes a few of these, notably @code{elt} and | |
| 3744 @code{length}; this package defines most of the rest. | |
| 3745 | |
| 3746 @menu | |
| 3747 * Sequence Basics:: Arguments shared by all sequence functions | |
| 3748 * Mapping over Sequences:: `mapcar*', `mapcan', `map', `every', etc. | |
| 3749 * Sequence Functions:: `subseq', `remove*', `substitute', etc. | |
| 3750 * Searching Sequences:: `find', `position', `count', `search', etc. | |
| 3751 * Sorting Sequences:: `sort*', `stable-sort', `merge' | |
| 3752 @end menu | |
| 3753 | |
| 3754 @node Sequence Basics, Mapping over Sequences, Sequences, Sequences | |
| 3755 @section Sequence Basics | |
| 3756 | |
| 778 | 3757 @noindent Many of the sequence functions take keyword arguments; |
| 3758 @pxref{Argument Lists}. All keyword arguments are optional and, if | |
| 3759 specified, may appear in any order. | |
| 428 | 3760 |
| 3761 The @code{:key} argument should be passed either @code{nil}, or a | |
| 3762 function of one argument. This key function is used as a filter | |
| 3763 through which the elements of the sequence are seen; for example, | |
| 3764 @code{(find x y :key 'car)} is similar to @code{(assoc* x y)}: | |
| 3765 It searches for an element of the list whose @code{car} equals | |
| 3766 @code{x}, rather than for an element which equals @code{x} itself. | |
| 3767 If @code{:key} is omitted or @code{nil}, the filter is effectively | |
| 3768 the identity function. | |
| 3769 | |
| 3770 The @code{:test} and @code{:test-not} arguments should be either | |
| 3771 @code{nil}, or functions of two arguments. The test function is | |
| 3772 used to compare two sequence elements, or to compare a search value | |
| 3773 with sequence elements. (The two values are passed to the test | |
| 3774 function in the same order as the original sequence function | |
| 3775 arguments from which they are derived, or, if they both come from | |
| 3776 the same sequence, in the same order as they appear in that sequence.) | |
| 3777 The @code{:test} argument specifies a function which must return | |
| 3778 true (non-@code{nil}) to indicate a match; instead, you may use | |
| 3779 @code{:test-not} to give a function which returns @emph{false} to | |
| 3780 indicate a match. The default test function is @code{:test 'eql}. | |
| 3781 | |
| 3782 Many functions which take @var{item} and @code{:test} or @code{:test-not} | |
| 3783 arguments also come in @code{-if} and @code{-if-not} varieties, | |
| 3784 where a @var{predicate} function is passed instead of @var{item}, | |
| 3785 and sequence elements match if the predicate returns true on them | |
| 3786 (or false in the case of @code{-if-not}). For example: | |
| 3787 | |
| 3788 @example | |
| 3789 (remove* 0 seq :test '=) @equiv{} (remove-if 'zerop seq) | |
| 3790 @end example | |
| 3791 | |
| 3792 @noindent | |
| 3793 to remove all zeros from sequence @code{seq}. | |
| 3794 | |
| 3795 Some operations can work on a subsequence of the argument sequence; | |
| 3796 these function take @code{:start} and @code{:end} arguments which | |
| 3797 default to zero and the length of the sequence, respectively. | |
| 3798 Only elements between @var{start} (inclusive) and @var{end} | |
| 3799 (exclusive) are affected by the operation. The @var{end} argument | |
| 3800 may be passed @code{nil} to signify the length of the sequence; | |
| 3801 otherwise, both @var{start} and @var{end} must be integers, with | |
| 3802 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}. | |
| 3803 If the function takes two sequence arguments, the limits are | |
| 3804 defined by keywords @code{:start1} and @code{:end1} for the first, | |
| 3805 and @code{:start2} and @code{:end2} for the second. | |
| 3806 | |
| 3807 A few functions accept a @code{:from-end} argument, which, if | |
| 3808 non-@code{nil}, causes the operation to go from right-to-left | |
| 3809 through the sequence instead of left-to-right, and a @code{:count} | |
| 3810 argument, which specifies an integer maximum number of elements | |
| 3811 to be removed or otherwise processed. | |
| 3812 | |
| 3813 The sequence functions make no guarantees about the order in | |
| 3814 which the @code{:test}, @code{:test-not}, and @code{:key} functions | |
| 3815 are called on various elements. Therefore, it is a bad idea to depend | |
| 3816 on side effects of these functions. For example, @code{:from-end} | |
| 3817 may cause the sequence to be scanned actually in reverse, or it may | |
| 3818 be scanned forwards but computing a result ``as if'' it were scanned | |
| 3819 backwards. (Some functions, like @code{mapcar*} and @code{every}, | |
| 3820 @emph{do} specify exactly the order in which the function is called | |
| 3821 so side effects are perfectly acceptable in those cases.) | |
| 3822 | |
| 3823 Strings in GNU Emacs 19 may contain ``text properties'' as well | |
| 3824 as character data. Except as noted, it is undefined whether or | |
| 3825 not text properties are preserved by sequence functions. For | |
| 3826 example, @code{(remove* ?A @var{str})} may or may not preserve | |
| 3827 the properties of the characters copied from @var{str} into the | |
| 3828 result. | |
| 3829 | |
| 3830 @node Mapping over Sequences, Sequence Functions, Sequence Basics, Sequences | |
| 3831 @section Mapping over Sequences | |
| 3832 | |
| 3833 @noindent | |
| 3834 These functions ``map'' the function you specify over the elements | |
| 3835 of lists or arrays. They are all variations on the theme of the | |
| 3836 built-in function @code{mapcar}. | |
| 3837 | |
| 3838 @defun mapcar* function seq &rest more-seqs | |
| 3839 This function calls @var{function} on successive parallel sets of | |
| 3840 elements from its argument sequences. Given a single @var{seq} | |
| 3841 argument it is equivalent to @code{mapcar}; given @var{n} sequences, | |
| 3842 it calls the function with the first elements of each of the sequences | |
| 3843 as the @var{n} arguments to yield the first element of the result | |
| 3844 list, then with the second elements, and so on. The mapping stops as | |
| 3845 soon as the shortest sequence runs out. The argument sequences may | |
| 3846 be any mixture of lists, strings, and vectors; the return sequence | |
| 3847 is always a list. | |
| 3848 | |
| 3849 Common Lisp's @code{mapcar} accepts multiple arguments but works | |
| 3850 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence | |
| 3851 argument. This package's @code{mapcar*} works as a compatible | |
| 3852 superset of both. | |
| 3853 @end defun | |
| 3854 | |
| 3855 @defun map result-type function seq &rest more-seqs | |
| 3856 This function maps @var{function} over the argument sequences, | |
| 3857 just like @code{mapcar*}, but it returns a sequence of type | |
| 3858 @var{result-type} rather than a list. @var{result-type} must | |
| 3859 be one of the following symbols: @code{vector}, @code{string}, | |
| 3860 @code{list} (in which case the effect is the same as for | |
| 3861 @code{mapcar*}), or @code{nil} (in which case the results are | |
| 3862 thrown away and @code{map} returns @code{nil}). | |
| 3863 @end defun | |
| 3864 | |
| 3865 @defun maplist function list &rest more-lists | |
| 3866 This function calls @var{function} on each of its argument lists, | |
| 3867 then on the @code{cdr}s of those lists, and so on, until the | |
| 3868 shortest list runs out. The results are returned in the form | |
| 3869 of a list. Thus, @code{maplist} is like @code{mapcar*} except | |
| 3870 that it passes in the list pointers themselves rather than the | |
| 3871 @code{car}s of the advancing pointers. | |
| 3872 @end defun | |
| 3873 | |
| 3874 @defun mapc function seq &rest more-seqs | |
| 3875 This function is like @code{mapcar*}, except that the values | |
| 3876 returned by @var{function} are ignored and thrown away rather | |
| 3877 than being collected into a list. The return value of @code{mapc} | |
| 3878 is @var{seq}, the first sequence. | |
| 3879 @end defun | |
| 3880 | |
| 3881 @defun mapl function list &rest more-lists | |
| 3882 This function is like @code{maplist}, except that it throws away | |
| 3883 the values returned by @var{function}. | |
| 3884 @end defun | |
| 3885 | |
| 3886 @defun mapcan function seq &rest more-seqs | |
| 3887 This function is like @code{mapcar*}, except that it concatenates | |
| 3888 the return values (which must be lists) using @code{nconc}, | |
| 3889 rather than simply collecting them into a list. | |
| 3890 @end defun | |
| 3891 | |
| 3892 @defun mapcon function list &rest more-lists | |
| 3893 This function is like @code{maplist}, except that it concatenates | |
| 3894 the return values using @code{nconc}. | |
| 3895 @end defun | |
| 3896 | |
| 3897 @defun some predicate seq &rest more-seqs | |
| 3898 This function calls @var{predicate} on each element of @var{seq} | |
| 3899 in turn; if @var{predicate} returns a non-@code{nil} value, | |
| 3900 @code{some} returns that value, otherwise it returns @code{nil}. | |
| 3901 Given several sequence arguments, it steps through the sequences | |
| 3902 in parallel until the shortest one runs out, just as in | |
| 3903 @code{mapcar*}. You can rely on the left-to-right order in which | |
| 3904 the elements are visited, and on the fact that mapping stops | |
| 3905 immediately as soon as @var{predicate} returns non-@code{nil}. | |
| 3906 @end defun | |
| 3907 | |
| 3908 @defun every predicate seq &rest more-seqs | |
| 3909 This function calls @var{predicate} on each element of the sequence(s) | |
| 3910 in turn; it returns @code{nil} as soon as @var{predicate} returns | |
| 3911 @code{nil} for any element, or @code{t} if the predicate was true | |
| 3912 for all elements. | |
| 3913 @end defun | |
| 3914 | |
| 3915 @defun notany predicate seq &rest more-seqs | |
| 3916 This function calls @var{predicate} on each element of the sequence(s) | |
| 3917 in turn; it returns @code{nil} as soon as @var{predicate} returns | |
| 3918 a non-@code{nil} value for any element, or @code{t} if the predicate | |
| 3919 was @code{nil} for all elements. | |
| 3920 @end defun | |
| 3921 | |
| 3922 @defun notevery predicate seq &rest more-seqs | |
| 3923 This function calls @var{predicate} on each element of the sequence(s) | |
| 3924 in turn; it returns a non-@code{nil} value as soon as @var{predicate} | |
| 3925 returns @code{nil} for any element, or @code{t} if the predicate was | |
| 3926 true for all elements. | |
| 3927 @end defun | |
| 3928 | |
| 3929 @defun reduce function seq @t{&key :from-end :start :end :initial-value :key} | |
| 3930 This function combines the elements of @var{seq} using an associative | |
| 3931 binary operation. Suppose @var{function} is @code{*} and @var{seq} is | |
| 3932 the list @code{(2 3 4 5)}. The first two elements of the list are | |
| 3933 combined with @code{(* 2 3) = 6}; this is combined with the next | |
| 3934 element, @code{(* 6 4) = 24}, and that is combined with the final | |
| 3935 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens | |
| 3936 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as | |
| 3937 an explicit call to @code{reduce}. | |
| 3938 | |
| 3939 If @code{:from-end} is true, the reduction is right-associative instead | |
| 3940 of left-associative: | |
| 3941 | |
| 3942 @example | |
| 3943 (reduce '- '(1 2 3 4)) | |
| 3944 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8 | |
| 3945 (reduce '- '(1 2 3 4) :from-end t) | |
| 3946 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2 | |
| 3947 @end example | |
| 3948 | |
| 3949 If @code{:key} is specified, it is a function of one argument which | |
| 3950 is called on each of the sequence elements in turn. | |
| 3951 | |
| 3952 If @code{:initial-value} is specified, it is effectively added to the | |
| 3953 front (or rear in the case of @code{:from-end}) of the sequence. | |
| 3954 The @code{:key} function is @emph{not} applied to the initial value. | |
| 3955 | |
| 3956 If the sequence, including the initial value, has exactly one element | |
| 3957 then that element is returned without ever calling @var{function}. | |
| 3958 If the sequence is empty (and there is no initial value), then | |
| 3959 @var{function} is called with no arguments to obtain the return value. | |
| 3960 @end defun | |
| 3961 | |
| 3962 All of these mapping operations can be expressed conveniently in | |
| 3963 terms of the @code{loop} macro. In compiled code, @code{loop} will | |
| 3964 be faster since it generates the loop as in-line code with no | |
| 3965 function calls. | |
| 3966 | |
| 3967 @node Sequence Functions, Searching Sequences, Mapping over Sequences, Sequences | |
| 3968 @section Sequence Functions | |
| 3969 | |
| 3970 @noindent | |
| 3971 This section describes a number of Common Lisp functions for | |
| 3972 operating on sequences. | |
| 3973 | |
| 3974 @defun subseq sequence start &optional end | |
| 3975 This function returns a given subsequence of the argument | |
| 3976 @var{sequence}, which may be a list, string, or vector. | |
| 3977 The indices @var{start} and @var{end} must be in range, and | |
| 3978 @var{start} must be no greater than @var{end}. If @var{end} | |
| 3979 is omitted, it defaults to the length of the sequence. The | |
| 3980 return value is always a copy; it does not share structure | |
| 3981 with @var{sequence}. | |
| 3982 | |
| 3983 As an extension to Common Lisp, @var{start} and/or @var{end} | |
| 3984 may be negative, in which case they represent a distance back | |
| 3985 from the end of the sequence. This is for compatibility with | |
| 3986 Emacs' @code{substring} function. Note that @code{subseq} is | |
| 3987 the @emph{only} sequence function that allows negative | |
| 3988 @var{start} and @var{end}. | |
| 3989 | |
| 3990 You can use @code{setf} on a @code{subseq} form to replace a | |
| 3991 specified range of elements with elements from another sequence. | |
| 3992 The replacement is done as if by @code{replace}, described below. | |
| 3993 @end defun | |
| 3994 | |
| 3995 @defun concatenate result-type &rest seqs | |
| 3996 This function concatenates the argument sequences together to | |
| 3997 form a result sequence of type @var{result-type}, one of the | |
| 3998 symbols @code{vector}, @code{string}, or @code{list}. The | |
| 3999 arguments are always copied, even in cases such as | |
| 4000 @code{(concatenate 'list '(1 2 3))} where the result is | |
| 4001 identical to an argument. | |
| 4002 @end defun | |
| 4003 | |
| 4004 @defun fill seq item @t{&key :start :end} | |
| 4005 This function fills the elements of the sequence (or the specified | |
| 4006 part of the sequence) with the value @var{item}. | |
| 4007 @end defun | |
| 4008 | |
| 4009 @defun replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2} | |
| 4010 This function copies part of @var{seq2} into part of @var{seq1}. | |
| 4011 The sequence @var{seq1} is not stretched or resized; the amount | |
| 4012 of data copied is simply the shorter of the source and destination | |
| 4013 (sub)sequences. The function returns @var{seq1}. | |
| 4014 | |
| 4015 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement | |
| 4016 will work correctly even if the regions indicated by the start | |
| 4017 and end arguments overlap. However, if @var{seq1} and @var{seq2} | |
| 4018 are lists which share storage but are not @code{eq}, and the | |
| 4019 start and end arguments specify overlapping regions, the effect | |
| 4020 is undefined. | |
| 4021 @end defun | |
| 4022 | |
| 4023 @defun remove* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4024 This returns a copy of @var{seq} with all elements matching | |
| 4025 @var{item} removed. The result may share storage with or be | |
| 4026 @code{eq} to @var{seq} in some circumstances, but the original | |
| 4027 @var{seq} will not be modified. The @code{:test}, @code{:test-not}, | |
| 4028 and @code{:key} arguments define the matching test that is used; | |
| 4029 by default, elements @code{eql} to @var{item} are removed. The | |
| 4030 @code{:count} argument specifies the maximum number of matching | |
| 4031 elements that can be removed (only the leftmost @var{count} matches | |
| 4032 are removed). The @code{:start} and @code{:end} arguments specify | |
| 4033 a region in @var{seq} in which elements will be removed; elements | |
| 4034 outside that region are not matched or removed. The @code{:from-end} | |
| 4035 argument, if true, says that elements should be deleted from the | |
| 4036 end of the sequence rather than the beginning (this matters only | |
| 4037 if @var{count} was also specified). | |
| 4038 @end defun | |
| 4039 | |
| 4040 @defun delete* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4041 This deletes all elements of @var{seq} which match @var{item}. | |
| 4042 It is a destructive operation. Since Emacs Lisp does not support | |
| 4043 stretchable strings or vectors, this is the same as @code{remove*} | |
| 4044 for those sequence types. On lists, @code{remove*} will copy the | |
| 4045 list if necessary to preserve the original list, whereas | |
| 4046 @code{delete*} will splice out parts of the argument list. | |
| 4047 Compare @code{append} and @code{nconc}, which are analogous | |
| 4048 non-destructive and destructive list operations in Emacs Lisp. | |
| 4049 @end defun | |
| 4050 | |
| 4051 @findex remove-if | |
| 4052 @findex remove-if-not | |
| 4053 @findex delete-if | |
| 4054 @findex delete-if-not | |
| 4055 The predicate-oriented functions @code{remove-if}, @code{remove-if-not}, | |
| 4056 @code{delete-if}, and @code{delete-if-not} are defined similarly. | |
| 4057 | |
| 4058 @defun delete item list | |
| 4059 This MacLisp-compatible function deletes from @var{list} all elements | |
| 4060 which are @code{equal} to @var{item}. The @code{delete} function is | |
| 4061 built-in to Emacs 19; this package defines it equivalently in Emacs 18. | |
| 4062 @end defun | |
| 4063 | |
| 4064 @defun remove item list | |
| 4065 This function removes from @var{list} all elements which are | |
| 4066 @code{equal} to @var{item}. This package defines it for symmetry | |
| 4067 with @code{delete}, even though @code{remove} is not built-in to | |
| 4068 Emacs 19. | |
| 4069 @end defun | |
| 4070 | |
| 4071 @defun remq item list | |
| 4072 This function removes from @var{list} all elements which are | |
| 4073 @code{eq} to @var{item}. This package defines it for symmetry | |
| 4074 with @code{delq}, even though @code{remq} is not built-in to | |
| 4075 Emacs 19. | |
| 4076 @end defun | |
| 4077 | |
| 4078 @defun remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4079 This function returns a copy of @var{seq} with duplicate elements | |
| 4080 removed. Specifically, if two elements from the sequence match | |
| 4081 according to the @code{:test}, @code{:test-not}, and @code{:key} | |
| 4082 arguments, only the rightmost one is retained. If @code{:from-end} | |
| 4083 is true, the leftmost one is retained instead. If @code{:start} or | |
| 4084 @code{:end} is specified, only elements within that subsequence are | |
| 4085 examined or removed. | |
| 4086 @end defun | |
| 4087 | |
| 4088 @defun delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4089 This function deletes duplicate elements from @var{seq}. It is | |
| 4090 a destructive version of @code{remove-duplicates}. | |
| 4091 @end defun | |
| 4092 | |
| 4093 @defun substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4094 This function returns a copy of @var{seq}, with all elements | |
| 4095 matching @var{old} replaced with @var{new}. The @code{:count}, | |
| 4096 @code{:start}, @code{:end}, and @code{:from-end} arguments may be | |
| 4097 used to limit the number of substitutions made. | |
| 4098 @end defun | |
| 4099 | |
| 4100 @defun nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4101 This is a destructive version of @code{substitute}; it performs | |
| 4102 the substitution using @code{setcar} or @code{aset} rather than | |
| 4103 by returning a changed copy of the sequence. | |
| 4104 @end defun | |
| 4105 | |
| 4106 @findex substitute-if | |
| 4107 @findex substitute-if-not | |
| 4108 @findex nsubstitute-if | |
| 4109 @findex nsubstitute-if-not | |
| 4110 The @code{substitute-if}, @code{substitute-if-not}, @code{nsubstitute-if}, | |
| 4111 and @code{nsubstitute-if-not} functions are defined similarly. For | |
| 4112 these, a @var{predicate} is given in place of the @var{old} argument. | |
| 4113 | |
| 4114 @node Searching Sequences, Sorting Sequences, Sequence Functions, Sequences | |
| 4115 @section Searching Sequences | |
| 4116 | |
| 4117 @noindent | |
| 4118 These functions search for elements or subsequences in a sequence. | |
| 4119 (See also @code{member*} and @code{assoc*}; @pxref{Lists}.) | |
| 4120 | |
| 4121 @defun find item seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4122 This function searches @var{seq} for an element matching @var{item}. | |
| 4123 If it finds a match, it returns the matching element. Otherwise, | |
| 4124 it returns @code{nil}. It returns the leftmost match, unless | |
| 4125 @code{:from-end} is true, in which case it returns the rightmost | |
| 4126 match. The @code{:start} and @code{:end} arguments may be used to | |
| 4127 limit the range of elements that are searched. | |
| 4128 @end defun | |
| 4129 | |
| 4130 @defun position item seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4131 This function is like @code{find}, except that it returns the | |
| 4132 integer position in the sequence of the matching item rather than | |
| 4133 the item itself. The position is relative to the start of the | |
| 4134 sequence as a whole, even if @code{:start} is non-zero. The function | |
| 4135 returns @code{nil} if no matching element was found. | |
| 4136 @end defun | |
| 4137 | |
| 4138 @defun count item seq @t{&key :test :test-not :key :start :end} | |
| 4139 This function returns the number of elements of @var{seq} which | |
| 4140 match @var{item}. The result is always a nonnegative integer. | |
| 4141 @end defun | |
| 4142 | |
| 4143 @findex find-if | |
| 4144 @findex find-if-not | |
| 4145 @findex position-if | |
| 4146 @findex position-if-not | |
| 4147 @findex count-if | |
| 4148 @findex count-if-not | |
| 4149 The @code{find-if}, @code{find-if-not}, @code{position-if}, | |
| 4150 @code{position-if-not}, @code{count-if}, and @code{count-if-not} | |
| 4151 functions are defined similarly. | |
| 4152 | |
| 4153 @defun mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end} | |
| 4154 This function compares the specified parts of @var{seq1} and | |
| 4155 @var{seq2}. If they are the same length and the corresponding | |
| 4156 elements match (according to @code{:test}, @code{:test-not}, | |
| 4157 and @code{:key}), the function returns @code{nil}. If there is | |
| 4158 a mismatch, the function returns the index (relative to @var{seq1}) | |
| 4159 of the first mismatching element. This will be the leftmost pair of | |
| 4160 elements which do not match, or the position at which the shorter of | |
| 4161 the two otherwise-matching sequences runs out. | |
| 4162 | |
| 4163 If @code{:from-end} is true, then the elements are compared from right | |
| 4164 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}. | |
| 4165 If the sequences differ, then one plus the index of the rightmost | |
| 4166 difference (relative to @var{seq1}) is returned. | |
| 4167 | |
| 4168 An interesting example is @code{(mismatch str1 str2 :key 'upcase)}, | |
| 4169 which compares two strings case-insensitively. | |
| 4170 @end defun | |
| 4171 | |
| 4172 @defun search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2} | |
| 4173 This function searches @var{seq2} for a subsequence that matches | |
| 4174 @var{seq1} (or part of it specified by @code{:start1} and | |
| 4175 @code{:end1}.) Only matches which fall entirely within the region | |
| 4176 defined by @code{:start2} and @code{:end2} will be considered. | |
| 4177 The return value is the index of the leftmost element of the | |
| 4178 leftmost match, relative to the start of @var{seq2}, or @code{nil} | |
| 4179 if no matches were found. If @code{:from-end} is true, the | |
| 4180 function finds the @emph{rightmost} matching subsequence. | |
| 4181 @end defun | |
| 4182 | |
| 4183 @node Sorting Sequences, , Searching Sequences, Sequences | |
| 4184 @section Sorting Sequences | |
| 4185 | |
| 4186 @defun sort* seq predicate @t{&key :key} | |
| 4187 This function sorts @var{seq} into increasing order as determined | |
| 4188 by using @var{predicate} to compare pairs of elements. @var{predicate} | |
| 4189 should return true (non-@code{nil}) if and only if its first argument | |
| 4190 is less than (not equal to) its second argument. For example, | |
| 4191 @code{<} and @code{string-lessp} are suitable predicate functions | |
| 4192 for sorting numbers and strings, respectively; @code{>} would sort | |
| 4193 numbers into decreasing rather than increasing order. | |
| 4194 | |
| 4195 This function differs from Emacs' built-in @code{sort} in that it | |
| 4196 can operate on any type of sequence, not just lists. Also, it | |
| 4197 accepts a @code{:key} argument which is used to preprocess data | |
| 4198 fed to the @var{predicate} function. For example, | |
| 4199 | |
| 4200 @example | |
| 4201 (setq data (sort data 'string-lessp :key 'downcase)) | |
| 4202 @end example | |
| 4203 | |
| 4204 @noindent | |
| 4205 sorts @var{data}, a sequence of strings, into increasing alphabetical | |
| 4206 order without regard to case. A @code{:key} function of @code{car} | |
| 4207 would be useful for sorting association lists. | |
| 4208 | |
| 4209 The @code{sort*} function is destructive; it sorts lists by actually | |
| 4210 rearranging the @code{cdr} pointers in suitable fashion. | |
| 4211 @end defun | |
| 4212 | |
| 4213 @defun stable-sort seq predicate @t{&key :key} | |
| 4214 This function sorts @var{seq} @dfn{stably}, meaning two elements | |
| 4215 which are equal in terms of @var{predicate} are guaranteed not to | |
| 4216 be rearranged out of their original order by the sort. | |
| 4217 | |
| 4218 In practice, @code{sort*} and @code{stable-sort} are equivalent | |
| 4219 in Emacs Lisp because the underlying @code{sort} function is | |
| 4220 stable by default. However, this package reserves the right to | |
| 4221 use non-stable methods for @code{sort*} in the future. | |
| 4222 @end defun | |
| 4223 | |
| 4224 @defun merge type seq1 seq2 predicate @t{&key :key} | |
| 4225 This function merges two sequences @var{seq1} and @var{seq2} by | |
| 4226 interleaving their elements. The result sequence, of type @var{type} | |
| 4227 (in the sense of @code{concatenate}), has length equal to the sum | |
| 4228 of the lengths of the two input sequences. The sequences may be | |
| 4229 modified destructively. Order of elements within @var{seq1} and | |
| 4230 @var{seq2} is preserved in the interleaving; elements of the two | |
| 4231 sequences are compared by @var{predicate} (in the sense of | |
| 4232 @code{sort}) and the lesser element goes first in the result. | |
| 4233 When elements are equal, those from @var{seq1} precede those from | |
| 4234 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are | |
| 4235 both sorted according to @var{predicate}, then the result will be | |
| 4236 a merged sequence which is (stably) sorted according to | |
| 4237 @var{predicate}. | |
| 4238 @end defun | |
| 4239 | |
| 4240 @node Lists, Hash Tables, Sequences, Top | |
| 4241 @chapter Lists | |
| 4242 | |
| 4243 @noindent | |
| 4244 The functions described here operate on lists. | |
| 4245 | |
| 4246 @menu | |
| 4247 * List Functions:: `caddr', `first', `last', `list*', etc. | |
| 4248 * Substitution of Expressions:: `subst', `sublis', etc. | |
| 4249 * Lists as Sets:: `member*', `adjoin', `union', etc. | |
| 4250 * Association Lists:: `assoc*', `rassoc*', `acons', `pairlis' | |
| 4251 @end menu | |
| 4252 | |
| 4253 @node List Functions, Substitution of Expressions, Lists, Lists | |
| 4254 @section List Functions | |
| 4255 | |
| 4256 @noindent | |
| 4257 This section describes a number of simple operations on lists, | |
| 4258 i.e., chains of cons cells. | |
| 4259 | |
| 4260 @defun caddr x | |
| 4261 This function is equivalent to @code{(car (cdr (cdr @var{x})))}. | |
| 4262 Likewise, this package defines all 28 @code{c@var{xxx}r} functions | |
| 4263 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s. | |
| 4264 All of these functions are @code{setf}-able, and calls to them | |
| 4265 are expanded inline by the byte-compiler for maximum efficiency. | |
| 4266 @end defun | |
| 4267 | |
| 4268 @defun first x | |
| 4269 This function is a synonym for @code{(car @var{x})}. Likewise, | |
| 4270 the functions @code{second}, @code{third}, @dots{}, through | |
| 4271 @code{tenth} return the given element of the list @var{x}. | |
| 4272 @end defun | |
| 4273 | |
| 4274 @defun rest x | |
| 4275 This function is a synonym for @code{(cdr @var{x})}. | |
| 4276 @end defun | |
| 4277 | |
| 4278 @defun endp x | |
| 4279 Common Lisp defines this function to act like @code{null}, but | |
| 4280 signalling an error if @code{x} is neither a @code{nil} nor a | |
| 4281 cons cell. This package simply defines @code{endp} as a synonym | |
| 4282 for @code{null}. | |
| 4283 @end defun | |
| 4284 | |
| 4285 @defun list-length x | |
| 4286 This function returns the length of list @var{x}, exactly like | |
| 4287 @code{(length @var{x})}, except that if @var{x} is a circular | |
| 4288 list (where the cdr-chain forms a loop rather than terminating | |
| 4289 with @code{nil}), this function returns @code{nil}. (The regular | |
| 4290 @code{length} function would get stuck if given a circular list.) | |
| 4291 @end defun | |
| 4292 | |
| 4293 @defun last x &optional n | |
| 4294 This function returns the last cons, or the @var{n}th-to-last cons, | |
| 4295 of the list @var{x}. If @var{n} is omitted it defaults to 1. | |
| 4296 The ``last cons'' means the first cons cell of the list whose | |
| 4297 @code{cdr} is not another cons cell. (For normal lists, the | |
| 4298 @code{cdr} of the last cons will be @code{nil}.) This function | |
| 4299 returns @code{nil} if @var{x} is @code{nil} or shorter than | |
| 4300 @var{n}. Note that the last @emph{element} of the list is | |
| 4301 @code{(car (last @var{x}))}. | |
| 4302 @end defun | |
| 4303 | |
| 4304 @defun butlast x &optional n | |
| 4305 This function returns the list @var{x} with the last element, | |
| 4306 or the last @var{n} elements, removed. If @var{n} is greater | |
| 4307 than zero it makes a copy of the list so as not to damage the | |
| 4308 original list. In general, @code{(append (butlast @var{x} @var{n}) | |
| 4309 (last @var{x} @var{n}))} will return a list equal to @var{x}. | |
| 4310 @end defun | |
| 4311 | |
| 4312 @defun nbutlast x &optional n | |
| 4313 This is a version of @code{butlast} that works by destructively | |
| 4314 modifying the @code{cdr} of the appropriate element, rather than | |
| 4315 making a copy of the list. | |
| 4316 @end defun | |
| 4317 | |
| 4318 @defun list* arg &rest others | |
| 4319 This function constructs a list of its arguments. The final | |
| 4320 argument becomes the @code{cdr} of the last cell constructed. | |
| 4321 Thus, @code{(list* @var{a} @var{b} @var{c})} is equivalent to | |
| 4322 @code{(cons @var{a} (cons @var{b} @var{c}))}, and | |
| 4323 @code{(list* @var{a} @var{b} nil)} is equivalent to | |
| 4324 @code{(list @var{a} @var{b})}. | |
| 4325 | |
| 4326 (Note that this function really is called @code{list*} in Common | |
| 4327 Lisp; it is not a name invented for this package like @code{member*} | |
| 4328 or @code{defun*}.) | |
| 4329 @end defun | |
| 4330 | |
| 4331 @defun ldiff list sublist | |
| 4332 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to | |
| 4333 one of the cons cells of @var{list}, then this function returns | |
| 4334 a copy of the part of @var{list} up to but not including | |
| 4335 @var{sublist}. For example, @code{(ldiff x (cddr x))} returns | |
| 4336 the first two elements of the list @code{x}. The result is a | |
| 4337 copy; the original @var{list} is not modified. If @var{sublist} | |
| 4338 is not a sublist of @var{list}, a copy of the entire @var{list} | |
| 4339 is returned. | |
| 4340 @end defun | |
| 4341 | |
| 4342 @defun copy-list list | |
| 4343 This function returns a copy of the list @var{list}. It copies | |
| 4344 dotted lists like @code{(1 2 . 3)} correctly. | |
| 4345 @end defun | |
| 4346 | |
| 4347 @defun copy-tree x &optional vecp | |
| 4348 This function returns a copy of the tree of cons cells @var{x}. | |
| 4349 Unlike @code{copy-sequence} (and its alias @code{copy-list}), | |
| 4350 which copies only along the @code{cdr} direction, this function | |
| 4351 copies (recursively) along both the @code{car} and the @code{cdr} | |
| 4352 directions. If @var{x} is not a cons cell, the function simply | |
| 4353 returns @var{x} unchanged. If the optional @var{vecp} argument | |
| 4354 is true, this function copies vectors (recursively) as well as | |
| 4355 cons cells. | |
| 4356 @end defun | |
| 4357 | |
| 4358 @defun tree-equal x y @t{&key :test :test-not :key} | |
| 4359 This function compares two trees of cons cells. If @var{x} and | |
| 4360 @var{y} are both cons cells, their @code{car}s and @code{cdr}s are | |
| 4361 compared recursively. If neither @var{x} nor @var{y} is a cons | |
| 4362 cell, they are compared by @code{eql}, or according to the | |
| 4363 specified test. The @code{:key} function, if specified, is | |
| 4364 applied to the elements of both trees. @xref{Sequences}. | |
| 4365 @end defun | |
| 4366 | |
| 4367 @iftex | |
| 4368 @secno=3 | |
| 4369 @end iftex | |
| 4370 | |
| 4371 @node Substitution of Expressions, Lists as Sets, List Functions, Lists | |
| 4372 @section Substitution of Expressions | |
| 4373 | |
| 4374 @noindent | |
| 4375 These functions substitute elements throughout a tree of cons | |
| 4376 cells. (@xref{Sequence Functions}, for the @code{substitute} | |
| 4377 function, which works on just the top-level elements of a list.) | |
| 4378 | |
| 4379 @defun subst new old tree @t{&key :test :test-not :key} | |
| 4380 This function substitutes occurrences of @var{old} with @var{new} | |
| 4381 in @var{tree}, a tree of cons cells. It returns a substituted | |
| 4382 tree, which will be a copy except that it may share storage with | |
| 4383 the argument @var{tree} in parts where no substitutions occurred. | |
| 4384 The original @var{tree} is not modified. This function recurses | |
| 4385 on, and compares against @var{old}, both @code{car}s and @code{cdr}s | |
| 4386 of the component cons cells. If @var{old} is itself a cons cell, | |
| 4387 then matching cells in the tree are substituted as usual without | |
| 4388 recursively substituting in that cell. Comparisons with @var{old} | |
| 4389 are done according to the specified test (@code{eql} by default). | |
| 4390 The @code{:key} function is applied to the elements of the tree | |
| 4391 but not to @var{old}. | |
| 4392 @end defun | |
| 4393 | |
| 4394 @defun nsubst new old tree @t{&key :test :test-not :key} | |
| 4395 This function is like @code{subst}, except that it works by | |
| 4396 destructive modification (by @code{setcar} or @code{setcdr}) | |
| 4397 rather than copying. | |
| 4398 @end defun | |
| 4399 | |
| 4400 @findex subst-if | |
| 4401 @findex subst-if-not | |
| 4402 @findex nsubst-if | |
| 4403 @findex nsubst-if-not | |
| 4404 The @code{subst-if}, @code{subst-if-not}, @code{nsubst-if}, and | |
| 4405 @code{nsubst-if-not} functions are defined similarly. | |
| 4406 | |
| 4407 @defun sublis alist tree @t{&key :test :test-not :key} | |
| 4408 This function is like @code{subst}, except that it takes an | |
| 4409 association list @var{alist} of @var{old}-@var{new} pairs. | |
| 4410 Each element of the tree (after applying the @code{:key} | |
| 4411 function, if any), is compared with the @code{car}s of | |
| 4412 @var{alist}; if it matches, it is replaced by the corresponding | |
| 4413 @code{cdr}. | |
| 4414 @end defun | |
| 4415 | |
| 4416 @defun nsublis alist tree @t{&key :test :test-not :key} | |
| 4417 This is a destructive version of @code{sublis}. | |
| 4418 @end defun | |
| 4419 | |
| 4420 @node Lists as Sets, Association Lists, Substitution of Expressions, Lists | |
| 4421 @section Lists as Sets | |
| 4422 | |
| 4423 @noindent | |
| 4424 These functions perform operations on lists which represent sets | |
| 4425 of elements. | |
| 4426 | |
| 4427 @defun member item list | |
| 4428 This MacLisp-compatible function searches @var{list} for an element | |
| 4429 which is @code{equal} to @var{item}. The @code{member} function is | |
| 4430 built-in to Emacs 19; this package defines it equivalently in Emacs 18. | |
| 4431 See the following function for a Common-Lisp compatible version. | |
| 4432 @end defun | |
| 4433 | |
| 4434 @defun member* item list @t{&key :test :test-not :key} | |
| 4435 This function searches @var{list} for an element matching @var{item}. | |
| 4436 If a match is found, it returns the cons cell whose @code{car} was | |
| 4437 the matching element. Otherwise, it returns @code{nil}. Elements | |
| 4438 are compared by @code{eql} by default; you can use the @code{:test}, | |
| 4439 @code{:test-not}, and @code{:key} arguments to modify this behavior. | |
| 4440 @xref{Sequences}. | |
| 4441 | |
| 4442 Note that this function's name is suffixed by @samp{*} to avoid | |
| 4443 the incompatible @code{member} function defined in Emacs 19. | |
| 4444 (That function uses @code{equal} for comparisons; it is equivalent | |
| 4445 to @code{(member* @var{item} @var{list} :test 'equal)}.) | |
| 4446 @end defun | |
| 4447 | |
| 4448 @findex member-if | |
| 4449 @findex member-if-not | |
| 4450 The @code{member-if} and @code{member-if-not} functions | |
| 4451 analogously search for elements which satisfy a given predicate. | |
| 4452 | |
| 4453 @defun tailp sublist list | |
| 4454 This function returns @code{t} if @var{sublist} is a sublist of | |
| 4455 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to | |
| 4456 any of its @code{cdr}s. | |
| 4457 @end defun | |
| 4458 | |
| 4459 @defun adjoin item list @t{&key :test :test-not :key} | |
| 4460 This function conses @var{item} onto the front of @var{list}, | |
| 4461 like @code{(cons @var{item} @var{list})}, but only if @var{item} | |
| 4462 is not already present on the list (as determined by @code{member*}). | |
| 4463 If a @code{:key} argument is specified, it is applied to | |
| 4464 @var{item} as well as to the elements of @var{list} during | |
| 4465 the search, on the reasoning that @var{item} is ``about'' to | |
| 4466 become part of the list. | |
| 4467 @end defun | |
| 4468 | |
| 4469 @defun union list1 list2 @t{&key :test :test-not :key} | |
| 4470 This function combines two lists which represent sets of items, | |
| 4471 returning a list that represents the union of those two sets. | |
| 4472 The result list will contain all items which appear in @var{list1} | |
| 4473 or @var{list2}, and no others. If an item appears in both | |
| 4474 @var{list1} and @var{list2} it will be copied only once. If | |
| 4475 an item is duplicated in @var{list1} or @var{list2}, it is | |
| 4476 undefined whether or not that duplication will survive in the | |
| 4477 result list. The order of elements in the result list is also | |
| 4478 undefined. | |
| 4479 @end defun | |
| 4480 | |
| 4481 @defun nunion list1 list2 @t{&key :test :test-not :key} | |
| 4482 This is a destructive version of @code{union}; rather than copying, | |
| 4483 it tries to reuse the storage of the argument lists if possible. | |
| 4484 @end defun | |
| 4485 | |
| 4486 @defun intersection list1 list2 @t{&key :test :test-not :key} | |
| 4487 This function computes the intersection of the sets represented | |
| 4488 by @var{list1} and @var{list2}. It returns the list of items | |
| 4489 which appear in both @var{list1} and @var{list2}. | |
| 4490 @end defun | |
| 4491 | |
| 4492 @defun nintersection list1 list2 @t{&key :test :test-not :key} | |
| 4493 This is a destructive version of @code{intersection}. It | |
| 4494 tries to reuse storage of @var{list1} rather than copying. | |
| 4495 It does @emph{not} reuse the storage of @var{list2}. | |
| 4496 @end defun | |
| 4497 | |
| 4498 @defun set-difference list1 list2 @t{&key :test :test-not :key} | |
| 4499 This function computes the ``set difference'' of @var{list1} | |
| 4500 and @var{list2}, i.e., the set of elements that appear in | |
| 4501 @var{list1} but @emph{not} in @var{list2}. | |
| 4502 @end defun | |
| 4503 | |
| 4504 @defun nset-difference list1 list2 @t{&key :test :test-not :key} | |
| 4505 This is a destructive @code{set-difference}, which will try | |
| 4506 to reuse @var{list1} if possible. | |
| 4507 @end defun | |
| 4508 | |
| 4509 @defun set-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
| 4510 This function computes the ``set exclusive or'' of @var{list1} | |
| 4511 and @var{list2}, i.e., the set of elements that appear in | |
| 4512 exactly one of @var{list1} and @var{list2}. | |
| 4513 @end defun | |
| 4514 | |
| 4515 @defun nset-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
| 4516 This is a destructive @code{set-exclusive-or}, which will try | |
| 4517 to reuse @var{list1} and @var{list2} if possible. | |
| 4518 @end defun | |
| 4519 | |
| 4520 @defun subsetp list1 list2 @t{&key :test :test-not :key} | |
| 4521 This function checks whether @var{list1} represents a subset | |
| 4522 of @var{list2}, i.e., whether every element of @var{list1} | |
| 4523 also appears in @var{list2}. | |
| 4524 @end defun | |
| 4525 | |
| 4526 @node Association Lists, , Lists as Sets, Lists | |
| 4527 @section Association Lists | |
| 4528 | |
| 4529 @noindent | |
| 4530 An @dfn{association list} is a list representing a mapping from | |
| 4531 one set of values to another; any list whose elements are cons | |
| 4532 cells is an association list. | |
| 4533 | |
| 4534 @defun assoc* item a-list @t{&key :test :test-not :key} | |
| 4535 This function searches the association list @var{a-list} for an | |
| 4536 element whose @code{car} matches (in the sense of @code{:test}, | |
| 4537 @code{:test-not}, and @code{:key}, or by comparison with @code{eql}) | |
| 4538 a given @var{item}. It returns the matching element, if any, | |
| 4539 otherwise @code{nil}. It ignores elements of @var{a-list} which | |
| 4540 are not cons cells. (This corresponds to the behavior of | |
| 4541 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's | |
| 4542 @code{assoc} ignores @code{nil}s but considers any other non-cons | |
| 4543 elements of @var{a-list} to be an error.) | |
| 4544 @end defun | |
| 4545 | |
| 4546 @defun rassoc* item a-list @t{&key :test :test-not :key} | |
| 4547 This function searches for an element whose @code{cdr} matches | |
| 4548 @var{item}. If @var{a-list} represents a mapping, this applies | |
| 4549 the inverse of the mapping to @var{item}. | |
| 4550 @end defun | |
| 4551 | |
| 4552 @defun rassoc item a-list | |
| 4553 This function searches like @code{rassoc*} with a @code{:test} | |
| 4554 argument of @code{equal}. It is analogous to Emacs Lisp's | |
| 4555 standard @code{assoc} function, which derives from the MacLisp | |
| 4556 rather than the Common Lisp tradition. | |
| 4557 @end defun | |
| 4558 | |
| 4559 @findex assoc-if | |
| 4560 @findex assoc-if-not | |
| 4561 @findex rassoc-if | |
| 4562 @findex rassoc-if-not | |
| 4563 The @code{assoc-if}, @code{assoc-if-not}, @code{rassoc-if}, | |
| 4564 and @code{rassoc-if-not} functions are defined similarly. | |
| 4565 | |
| 4566 Two simple functions for constructing association lists are: | |
| 4567 | |
| 4568 @defun acons key value alist | |
| 4569 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}. | |
| 4570 @end defun | |
| 4571 | |
| 4572 @defun pairlis keys values &optional alist | |
| 4573 This is equivalent to @code{(nconc (mapcar* 'cons @var{keys} @var{values}) | |
| 4574 @var{alist})}. | |
| 4575 @end defun | |
| 4576 | |
| 4577 @node Hash Tables, Structures, Lists, Top | |
| 4578 @chapter Hash Tables | |
| 4579 | |
| 4580 @noindent | |
| 4581 Hash tables are now implemented directly in the C code and documented in | |
| 446 | 4582 @ref{Hash Tables,,, lispref, XEmacs Lisp Reference Manual}. |
| 428 | 4583 |
| 4584 @ignore | |
| 4585 A @dfn{hash table} is a data structure that maps ``keys'' onto | |
| 4586 ``values.'' Keys and values can be arbitrary Lisp data objects. | |
| 4587 Hash tables have the property that the time to search for a given | |
| 4588 key is roughly constant; simpler data structures like association | |
| 4589 lists take time proportional to the number of entries in the list. | |
| 4590 | |
| 4591 @defun make-hash-table @t{&key :test :size} | |
| 4592 This function creates and returns a hash-table object whose | |
| 4593 function for comparing elements is @code{:test} (@code{eql} | |
| 4594 by default), and which is allocated to fit about @code{:size} | |
| 4595 elements. The @code{:size} argument is purely advisory; the | |
| 4596 table will stretch automatically if you store more elements in | |
| 4597 it. If @code{:size} is omitted, a reasonable default is used. | |
| 4598 | |
| 4599 Common Lisp allows only @code{eq}, @code{eql}, @code{equal}, | |
| 4600 and @code{equalp} as legal values for the @code{:test} argument. | |
| 4601 In this package, any reasonable predicate function will work, | |
| 4602 though if you use something else you should check the details of | |
| 4603 the hashing function described below to make sure it is suitable | |
| 4604 for your predicate. | |
| 4605 | |
| 4606 Some versions of Emacs (like XEmacs) include a built-in hash | |
| 4607 table type; in these versions, @code{make-hash-table} with a test of | |
| 4608 @code{eq}, @code{eql}, or @code{equal} will use these built-in hash | |
| 4609 tables. In all other cases, it will return a hash-table object which | |
| 4610 takes the form of a list with an identifying ``tag'' symbol at the | |
| 4611 front. All of the hash table functions in this package can operate on | |
| 4612 both types of hash table; normally you will never know which type is | |
| 4613 being used. | |
| 4614 | |
| 4615 This function accepts the additional Common Lisp keywords | |
| 4616 @code{:rehash-size} and @code{:rehash-threshold}, but it ignores | |
| 4617 their values. | |
| 4618 @end defun | |
| 4619 | |
| 4620 @defun gethash key table &optional default | |
| 4621 This function looks up @var{key} in @var{table}. If @var{key} | |
| 4622 exists in the table, in the sense that it matches any of the existing | |
| 4623 keys according to the table's test function, then the associated value | |
| 4624 is returned. Otherwise, @var{default} (or @code{nil}) is returned. | |
| 4625 | |
| 4626 To store new data in the hash table, use @code{setf} on a call to | |
| 4627 @code{gethash}. If @var{key} already exists in the table, the | |
| 4628 corresponding value is changed to the stored value. If @var{key} | |
| 4629 does not already exist, a new entry is added to the table and the | |
| 4630 table is reallocated to a larger size if necessary. The @var{default} | |
| 4631 argument is allowed but ignored in this case. The situation is | |
| 440 | 4632 exactly analogous to that of @code{get}; @pxref{Property Lists}. |
| 428 | 4633 @end defun |
| 4634 | |
| 4635 @defun remhash key table | |
| 4636 This function removes the entry for @var{key} from @var{table}. | |
| 4637 If an entry was removed, it returns @code{t}. If @var{key} does | |
| 4638 not appear in the table, it does nothing and returns @code{nil}. | |
| 4639 @end defun | |
| 4640 | |
| 4641 @defun clrhash table | |
| 4642 This function removes all the entries from @var{table}, leaving | |
| 4643 an empty hash table. | |
| 4644 @end defun | |
| 4645 | |
| 4646 @defun maphash function table | |
| 4647 This function calls @var{function} for each entry in @var{table}. | |
| 4648 It passes two arguments to @var{function}, the key and the value | |
| 4649 of the given entry. The return value of @var{function} is ignored; | |
| 4650 @var{maphash} itself returns @code{nil}. @xref{Loop Facility}, for | |
| 4651 an alternate way of iterating over hash tables. | |
| 4652 @end defun | |
| 4653 | |
| 4654 @defun hash-table-count table This function returns the number of | |
| 4655 entries in @var{table}. @strong{Warning:} The current implementation of | |
| 4656 XEmacs hash-tables does not decrement the stored @code{count} | |
| 4657 when @code{remhash} removes an entry. Therefore, the return value of | |
| 4658 this function is not dependable if you have used @code{remhash} on the | |
| 4659 table and the table's test is @code{eq}, @code{eql}, or @code{equal}. | |
| 4660 A slower, but reliable, way to count the entries is | |
| 4661 @code{(loop for x being the hash-keys of @var{table} count t)}. | |
| 4662 @end defun | |
| 4663 | |
| 4664 @defun hash-table-p object This function returns @code{t} if | |
| 4665 @var{object} is a hash table, @code{nil} otherwise. It recognizes both | |
| 4666 types of hash tables (both XEmacs built-in tables and tables implemented | |
| 4667 with special lists.) | |
| 4668 @end defun | |
| 4669 | |
| 4670 Sometimes when dealing with hash tables it is useful to know the | |
| 4671 exact ``hash function'' that is used. This package implements | |
| 4672 hash tables using Emacs Lisp ``obarrays,'' which are the same | |
| 4673 data structure that Emacs Lisp uses to keep track of symbols. | |
| 4674 Each hash table includes an embedded obarray. Key values given | |
| 4675 to @code{gethash} are converted by various means into strings, | |
| 4676 which are then looked up in the obarray using @code{intern} and | |
| 4677 @code{intern-soft}. The symbol, or ``bucket,'' corresponding to | |
| 4678 a given key string includes as its @code{symbol-value} an association | |
| 4679 list of all key-value pairs which hash to that string. Depending | |
| 4680 on the test function, it is possible for many entries to hash to | |
| 4681 the same bucket. For example, if the test is @code{eql}, then the | |
| 4682 symbol @code{foo} and two separately built strings @code{"foo"} will | |
| 4683 create three entries in the same bucket. Search time is linear | |
| 4684 within buckets, so hash tables will be most effective if you arrange | |
| 4685 not to store too many things that hash the same. | |
| 4686 | |
| 4687 The following algorithm is used to convert Lisp objects to hash | |
| 4688 strings: | |
| 4689 | |
| 4690 @itemize @bullet | |
| 4691 @item | |
| 4692 Strings are used directly as hash strings. (However, if the test | |
| 4693 function is @code{equalp}, strings are @code{downcase}d first.) | |
| 4694 | |
| 4695 @item | |
| 4696 Symbols are hashed according to their @code{symbol-name}. | |
| 4697 | |
| 4698 @item | |
| 4699 Integers are hashed into one of 16 buckets depending on their value | |
| 4700 modulo 16. Floating-point numbers are truncated to integers and | |
| 4701 hashed modulo 16. | |
| 4702 | |
| 4703 @item | |
| 4704 Cons cells are hashed according to their @code{car}s; nonempty vectors | |
| 4705 are hashed according to their first element. | |
| 4706 | |
| 4707 @item | |
| 4708 All other types of objects hash into a single bucket named @code{"*"}. | |
| 4709 @end itemize | |
| 4710 | |
| 4711 @noindent | |
| 4712 Thus, for example, searching among many buffer objects in a hash table | |
| 4713 will devolve to a (still fairly fast) linear-time search through a | |
| 4714 single bucket, whereas searching for different symbols will be very | |
| 4715 fast since each symbol will, in general, hash into its own bucket. | |
| 4716 | |
| 4717 The size of the obarray in a hash table is automatically adjusted | |
| 4718 as the number of elements increases. | |
| 4719 | |
| 4720 As a special case, @code{make-hash-table} with a @code{:size} argument | |
| 4721 of 0 or 1 will create a hash-table object that uses a single association | |
| 4722 list rather than an obarray of many lists. For very small tables this | |
| 4723 structure will be more efficient since lookup does not require | |
| 4724 converting the key to a string or looking it up in an obarray. | |
| 4725 However, such tables are guaranteed to take time proportional to | |
| 4726 their size to do a search. | |
| 4727 @end ignore | |
| 4728 | |
| 4729 @iftex | |
| 4730 @chapno=18 | |
| 4731 @end iftex | |
| 4732 | |
| 4733 @node Structures, Assertions, Hash Tables, Top | |
| 4734 @chapter Structures | |
| 4735 | |
| 4736 @noindent | |
| 4737 The Common Lisp @dfn{structure} mechanism provides a general way | |
| 4738 to define data types similar to C's @code{struct} types. A | |
| 4739 structure is a Lisp object containing some number of @dfn{slots}, | |
| 4740 each of which can hold any Lisp data object. Functions are | |
| 4741 provided for accessing and setting the slots, creating or copying | |
| 4742 structure objects, and recognizing objects of a particular structure | |
| 4743 type. | |
| 4744 | |
| 4745 In true Common Lisp, each structure type is a new type distinct | |
| 4746 from all existing Lisp types. Since the underlying Emacs Lisp | |
| 4747 system provides no way to create new distinct types, this package | |
| 4748 implements structures as vectors (or lists upon request) with a | |
| 4749 special ``tag'' symbol to identify them. | |
| 4750 | |
| 4751 @defspec defstruct name slots@dots{} | |
| 4752 The @code{defstruct} form defines a new structure type called | |
| 4753 @var{name}, with the specified @var{slots}. (The @var{slots} | |
| 4754 may begin with a string which documents the structure type.) | |
| 4755 In the simplest case, @var{name} and each of the @var{slots} | |
| 4756 are symbols. For example, | |
| 4757 | |
| 4758 @example | |
| 4759 (defstruct person name age sex) | |
| 4760 @end example | |
| 4761 | |
| 4762 @noindent | |
| 4763 defines a struct type called @code{person} which contains three | |
| 4764 slots. Given a @code{person} object @var{p}, you can access those | |
| 4765 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})}, | |
| 4766 and @code{(person-sex @var{p})}. You can also change these slots by | |
| 4767 using @code{setf} on any of these place forms: | |
| 4768 | |
| 4769 @example | |
| 4770 (incf (person-age birthday-boy)) | |
| 4771 @end example | |
| 4772 | |
| 4773 You can create a new @code{person} by calling @code{make-person}, | |
| 4774 which takes keyword arguments @code{:name}, @code{:age}, and | |
| 4775 @code{:sex} to specify the initial values of these slots in the | |
| 4776 new object. (Omitting any of these arguments leaves the corresponding | |
| 4777 slot ``undefined,'' according to the Common Lisp standard; in Emacs | |
| 4778 Lisp, such uninitialized slots are filled with @code{nil}.) | |
| 4779 | |
| 4780 Given a @code{person}, @code{(copy-person @var{p})} makes a new | |
| 4781 object of the same type whose slots are @code{eq} to those of @var{p}. | |
| 4782 | |
| 4783 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns | |
| 4784 true if @var{x} looks like a @code{person}, false otherwise. (Again, | |
| 4785 in Common Lisp this predicate would be exact; in Emacs Lisp the | |
| 4786 best it can do is verify that @var{x} is a vector of the correct | |
| 4787 length which starts with the correct tag symbol.) | |
| 4788 | |
| 4789 Accessors like @code{person-name} normally check their arguments | |
| 4790 (effectively using @code{person-p}) and signal an error if the | |
| 4791 argument is the wrong type. This check is affected by | |
| 4792 @code{(optimize (safety @dots{}))} declarations. Safety level 1, | |
| 4793 the default, uses a somewhat optimized check that will detect all | |
| 4794 incorrect arguments, but may use an uninformative error message | |
| 4795 (e.g., ``expected a vector'' instead of ``expected a @code{person}''). | |
| 4796 Safety level 0 omits all checks except as provided by the underlying | |
| 4797 @code{aref} call; safety levels 2 and 3 do rigorous checking that will | |
| 4798 always print a descriptive error message for incorrect inputs. | |
| 4799 @xref{Declarations}. | |
| 4800 | |
| 4801 @example | |
| 4802 (setq dave (make-person :name "Dave" :sex 'male)) | |
| 4803 @result{} [cl-struct-person "Dave" nil male] | |
| 4804 (setq other (copy-person dave)) | |
| 4805 @result{} [cl-struct-person "Dave" nil male] | |
| 4806 (eq dave other) | |
| 4807 @result{} nil | |
| 4808 (eq (person-name dave) (person-name other)) | |
| 4809 @result{} t | |
| 4810 (person-p dave) | |
| 4811 @result{} t | |
| 4812 (person-p [1 2 3 4]) | |
| 4813 @result{} nil | |
| 4814 (person-p "Bogus") | |
| 4815 @result{} nil | |
| 4816 (person-p '[cl-struct-person counterfeit person object]) | |
| 4817 @result{} t | |
| 4818 @end example | |
| 4819 | |
| 4820 In general, @var{name} is either a name symbol or a list of a name | |
| 4821 symbol followed by any number of @dfn{struct options}; each @var{slot} | |
| 4822 is either a slot symbol or a list of the form @samp{(@var{slot-name} | |
| 4823 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value} | |
| 4824 is a Lisp form which is evaluated any time an instance of the | |
| 4825 structure type is created without specifying that slot's value. | |
| 4826 | |
| 4827 Common Lisp defines several slot options, but the only one | |
| 4828 implemented in this package is @code{:read-only}. A non-@code{nil} | |
| 4829 value for this option means the slot should not be @code{setf}-able; | |
| 4830 the slot's value is determined when the object is created and does | |
| 4831 not change afterward. | |
| 4832 | |
| 4833 @example | |
| 4834 (defstruct person | |
| 4835 (name nil :read-only t) | |
| 4836 age | |
| 4837 (sex 'unknown)) | |
| 4838 @end example | |
| 4839 | |
| 4840 Any slot options other than @code{:read-only} are ignored. | |
| 4841 | |
| 4842 For obscure historical reasons, structure options take a different | |
| 4843 form than slot options. A structure option is either a keyword | |
| 4844 symbol, or a list beginning with a keyword symbol possibly followed | |
| 4845 by arguments. (By contrast, slot options are key-value pairs not | |
| 4846 enclosed in lists.) | |
| 4847 | |
| 4848 @example | |
| 4849 (defstruct (person (:constructor create-person) | |
| 4850 (:type list) | |
| 4851 :named) | |
| 4852 name age sex) | |
| 4853 @end example | |
| 4854 | |
| 4855 The following structure options are recognized. | |
| 4856 | |
| 4857 @table @code | |
| 4858 @iftex | |
| 4859 @itemmax=0 in | |
| 4860 @advance@leftskip-.5@tableindent | |
| 4861 @end iftex | |
| 4862 @item :conc-name | |
| 4863 The argument is a symbol whose print name is used as the prefix for | |
| 4864 the names of slot accessor functions. The default is the name of | |
| 4865 the struct type followed by a hyphen. The option @code{(:conc-name p-)} | |
| 4866 would change this prefix to @code{p-}. Specifying @code{nil} as an | |
| 4867 argument means no prefix, so that the slot names themselves are used | |
| 4868 to name the accessor functions. | |
| 4869 | |
| 4870 @item :constructor | |
| 4871 In the simple case, this option takes one argument which is an | |
| 4872 alternate name to use for the constructor function. The default | |
| 4873 is @code{make-@var{name}}, e.g., @code{make-person}. The above | |
| 4874 example changes this to @code{create-person}. Specifying @code{nil} | |
| 4875 as an argument means that no standard constructor should be | |
| 4876 generated at all. | |
| 4877 | |
| 4878 In the full form of this option, the constructor name is followed | |
| 4879 by an arbitrary argument list. @xref{Program Structure}, for a | |
| 4880 description of the format of Common Lisp argument lists. All | |
| 4881 options, such as @code{&rest} and @code{&key}, are supported. | |
| 4882 The argument names should match the slot names; each slot is | |
| 4883 initialized from the corresponding argument. Slots whose names | |
| 4884 do not appear in the argument list are initialized based on the | |
| 4885 @var{default-value} in their slot descriptor. Also, @code{&optional} | |
| 4886 and @code{&key} arguments which don't specify defaults take their | |
| 4887 defaults from the slot descriptor. It is legal to include arguments | |
| 4888 which don't correspond to slot names; these are useful if they are | |
| 4889 referred to in the defaults for optional, keyword, or @code{&aux} | |
| 4890 arguments which @emph{do} correspond to slots. | |
| 4891 | |
| 4892 You can specify any number of full-format @code{:constructor} | |
| 4893 options on a structure. The default constructor is still generated | |
| 4894 as well unless you disable it with a simple-format @code{:constructor} | |
| 4895 option. | |
| 4896 | |
| 4897 @example | |
| 4898 (defstruct | |
| 4899 (person | |
| 4900 (:constructor nil) ; no default constructor | |
| 4901 (:constructor new-person (name sex &optional (age 0))) | |
| 4902 (:constructor new-hound (&key (name "Rover") | |
| 4903 (dog-years 0) | |
| 4904 &aux (age (* 7 dog-years)) | |
| 4905 (sex 'canine)))) | |
| 4906 name age sex) | |
| 4907 @end example | |
| 4908 | |
| 4909 The first constructor here takes its arguments positionally rather | |
| 4910 than by keyword. (In official Common Lisp terminology, constructors | |
| 4911 that work By Order of Arguments instead of by keyword are called | |
| 4912 ``BOA constructors.'' No, I'm not making this up.) For example, | |
| 4913 @code{(new-person "Jane" 'female)} generates a person whose slots | |
| 4914 are @code{"Jane"}, 0, and @code{female}, respectively. | |
| 4915 | |
| 4916 The second constructor takes two keyword arguments, @code{:name}, | |
| 4917 which initializes the @code{name} slot and defaults to @code{"Rover"}, | |
| 4918 and @code{:dog-years}, which does not itself correspond to a slot | |
| 4919 but which is used to initialize the @code{age} slot. The @code{sex} | |
| 4920 slot is forced to the symbol @code{canine} with no syntax for | |
| 4921 overriding it. | |
| 4922 | |
| 4923 @item :copier | |
| 4924 The argument is an alternate name for the copier function for | |
| 4925 this type. The default is @code{copy-@var{name}}. @code{nil} | |
| 4926 means not to generate a copier function. (In this implementation, | |
| 4927 all copier functions are simply synonyms for @code{copy-sequence}.) | |
| 4928 | |
| 4929 @item :predicate | |
| 4930 The argument is an alternate name for the predicate which recognizes | |
| 4931 objects of this type. The default is @code{@var{name}-p}. @code{nil} | |
| 4932 means not to generate a predicate function. (If the @code{:type} | |
| 4933 option is used without the @code{:named} option, no predicate is | |
| 4934 ever generated.) | |
| 4935 | |
| 4936 In true Common Lisp, @code{typep} is always able to recognize a | |
| 4937 structure object even if @code{:predicate} was used. In this | |
| 4938 package, @code{typep} simply looks for a function called | |
| 4939 @code{@var{typename}-p}, so it will work for structure types | |
| 4940 only if they used the default predicate name. | |
| 4941 | |
| 4942 @item :include | |
| 4943 This option implements a very limited form of C++-style inheritance. | |
| 4944 The argument is the name of another structure type previously | |
| 4945 created with @code{defstruct}. The effect is to cause the new | |
| 4946 structure type to inherit all of the included structure's slots | |
| 4947 (plus, of course, any new slots described by this struct's slot | |
| 4948 descriptors). The new structure is considered a ``specialization'' | |
| 4949 of the included one. In fact, the predicate and slot accessors | |
| 4950 for the included type will also accept objects of the new type. | |
| 4951 | |
| 4952 If there are extra arguments to the @code{:include} option after | |
| 4953 the included-structure name, these options are treated as replacement | |
| 4954 slot descriptors for slots in the included structure, possibly with | |
| 4955 modified default values. Borrowing an example from Steele: | |
| 4956 | |
| 4957 @example | |
| 4958 (defstruct person name (age 0) sex) | |
| 4959 @result{} person | |
| 4960 (defstruct (astronaut (:include person (age 45))) | |
| 4961 helmet-size | |
| 4962 (favorite-beverage 'tang)) | |
| 4963 @result{} astronaut | |
| 4964 | |
| 4965 (setq joe (make-person :name "Joe")) | |
| 4966 @result{} [cl-struct-person "Joe" 0 nil] | |
| 4967 (setq buzz (make-astronaut :name "Buzz")) | |
| 4968 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang] | |
| 4969 | |
| 4970 (list (person-p joe) (person-p buzz)) | |
| 4971 @result{} (t t) | |
| 4972 (list (astronaut-p joe) (astronaut-p buzz)) | |
| 4973 @result{} (nil t) | |
| 4974 | |
| 4975 (person-name buzz) | |
| 4976 @result{} "Buzz" | |
| 4977 (astronaut-name joe) | |
| 4978 @result{} error: "astronaut-name accessing a non-astronaut" | |
| 4979 @end example | |
| 4980 | |
| 4981 Thus, if @code{astronaut} is a specialization of @code{person}, | |
| 4982 then every @code{astronaut} is also a @code{person} (but not the | |
| 4983 other way around). Every @code{astronaut} includes all the slots | |
| 4984 of a @code{person}, plus extra slots that are specific to | |
| 4985 astronauts. Operations that work on people (like @code{person-name}) | |
| 4986 work on astronauts just like other people. | |
| 4987 | |
| 4988 @item :print-function | |
| 4989 In full Common Lisp, this option allows you to specify a function | |
| 4990 which is called to print an instance of the structure type. The | |
| 4991 Emacs Lisp system offers no hooks into the Lisp printer which would | |
| 4992 allow for such a feature, so this package simply ignores | |
| 4993 @code{:print-function}. | |
| 4994 | |
| 4995 @item :type | |
| 4996 The argument should be one of the symbols @code{vector} or @code{list}. | |
| 4997 This tells which underlying Lisp data type should be used to implement | |
| 4998 the new structure type. Vectors are used by default, but | |
| 4999 @code{(:type list)} will cause structure objects to be stored as | |
| 5000 lists instead. | |
| 5001 | |
| 5002 The vector representation for structure objects has the advantage | |
| 5003 that all structure slots can be accessed quickly, although creating | |
| 5004 vectors is a bit slower in Emacs Lisp. Lists are easier to create, | |
| 5005 but take a relatively long time accessing the later slots. | |
| 5006 | |
| 5007 @item :named | |
| 5008 This option, which takes no arguments, causes a characteristic ``tag'' | |
| 5009 symbol to be stored at the front of the structure object. Using | |
| 5010 @code{:type} without also using @code{:named} will result in a | |
| 5011 structure type stored as plain vectors or lists with no identifying | |
| 5012 features. | |
| 5013 | |
| 5014 The default, if you don't specify @code{:type} explicitly, is to | |
| 5015 use named vectors. Therefore, @code{:named} is only useful in | |
| 5016 conjunction with @code{:type}. | |
| 5017 | |
| 5018 @example | |
| 5019 (defstruct (person1) name age sex) | |
| 5020 (defstruct (person2 (:type list) :named) name age sex) | |
| 5021 (defstruct (person3 (:type list)) name age sex) | |
| 5022 | |
| 5023 (setq p1 (make-person1)) | |
| 5024 @result{} [cl-struct-person1 nil nil nil] | |
| 5025 (setq p2 (make-person2)) | |
| 5026 @result{} (person2 nil nil nil) | |
| 5027 (setq p3 (make-person3)) | |
| 5028 @result{} (nil nil nil) | |
| 5029 | |
| 5030 (person1-p p1) | |
| 5031 @result{} t | |
| 5032 (person2-p p2) | |
| 5033 @result{} t | |
| 5034 (person3-p p3) | |
| 5035 @result{} error: function person3-p undefined | |
| 5036 @end example | |
| 5037 | |
| 5038 Since unnamed structures don't have tags, @code{defstruct} is not | |
| 5039 able to make a useful predicate for recognizing them. Also, | |
| 5040 accessors like @code{person3-name} will be generated but they | |
| 5041 will not be able to do any type checking. The @code{person3-name} | |
| 5042 function, for example, will simply be a synonym for @code{car} in | |
| 5043 this case. By contrast, @code{person2-name} is able to verify | |
| 5044 that its argument is indeed a @code{person2} object before | |
| 5045 proceeding. | |
| 5046 | |
| 5047 @item :initial-offset | |
| 5048 The argument must be a nonnegative integer. It specifies a | |
| 5049 number of slots to be left ``empty'' at the front of the | |
| 5050 structure. If the structure is named, the tag appears at the | |
| 5051 specified position in the list or vector; otherwise, the first | |
| 5052 slot appears at that position. Earlier positions are filled | |
| 5053 with @code{nil} by the constructors and ignored otherwise. If | |
| 5054 the type @code{:include}s another type, then @code{:initial-offset} | |
| 5055 specifies a number of slots to be skipped between the last slot | |
| 5056 of the included type and the first new slot. | |
| 5057 @end table | |
| 5058 @end defspec | |
| 5059 | |
| 5060 Except as noted, the @code{defstruct} facility of this package is | |
| 5061 entirely compatible with that of Common Lisp. | |
| 5062 | |
| 5063 @iftex | |
| 5064 @chapno=23 | |
| 5065 @end iftex | |
| 5066 | |
| 5067 @node Assertions, Efficiency Concerns, Structures, Top | |
| 5068 @chapter Assertions and Errors | |
| 5069 | |
| 5070 @noindent | |
| 5071 This section describes two macros that test @dfn{assertions}, i.e., | |
| 5072 conditions which must be true if the program is operating correctly. | |
| 5073 Assertions never add to the behavior of a Lisp program; they simply | |
| 5074 make ``sanity checks'' to make sure everything is as it should be. | |
| 5075 | |
| 5076 If the optimization property @code{speed} has been set to 3, and | |
| 5077 @code{safety} is less than 3, then the byte-compiler will optimize | |
| 5078 away the following assertions. Because assertions might be optimized | |
| 5079 away, it is a bad idea for them to include side-effects. | |
| 5080 | |
| 5081 @defspec assert test-form [show-args string args@dots{}] | |
| 5082 This form verifies that @var{test-form} is true (i.e., evaluates to | |
| 5083 a non-@code{nil} value). If so, it returns @code{nil}. If the test | |
| 5084 is not satisfied, @code{assert} signals an error. | |
| 5085 | |
| 5086 A default error message will be supplied which includes @var{test-form}. | |
| 5087 You can specify a different error message by including a @var{string} | |
| 5088 argument plus optional extra arguments. Those arguments are simply | |
| 5089 passed to @code{error} to signal the error. | |
| 5090 | |
| 5091 If the optional second argument @var{show-args} is @code{t} instead | |
| 5092 of @code{nil}, then the error message (with or without @var{string}) | |
| 5093 will also include all non-constant arguments of the top-level | |
| 5094 @var{form}. For example: | |
| 5095 | |
| 5096 @example | |
| 5097 (assert (> x 10) t "x is too small: %d") | |
| 5098 @end example | |
| 5099 | |
| 446 | 5100 This usage of @var{show-args} is a change to Common Lisp. In |
| 428 | 5101 true Common Lisp, the second argument gives a list of @var{places} |
| 5102 which can be @code{setf}'d by the user before continuing from the | |
| 446 | 5103 error. |
| 428 | 5104 @end defspec |
| 5105 | |
| 446 | 5106 @defspec check-type place type &optional string |
| 5107 This form verifies that @var{place} evaluates to a value of type | |
| 428 | 5108 @var{type}. If so, it returns @code{nil}. If not, @code{check-type} |
| 446 | 5109 signals a continuable @code{wrong-type-argument} error. The default |
| 5110 error message lists the erroneous value along with @var{type} and | |
| 5111 @var{place} themselves. If @var{string} is specified, it is included in | |
| 5112 the error message in place of @var{type}. For example: | |
| 428 | 5113 |
| 5114 @example | |
| 5115 (check-type x (integer 1 *) "a positive integer") | |
| 5116 @end example | |
| 5117 | |
| 5118 @xref{Type Predicates}, for a description of the type specifiers | |
| 5119 that may be used for @var{type}. | |
| 5120 | |
| 446 | 5121 Note that as in Common Lisp, the first argument to @code{check-type} |
| 5122 should be a @var{place} suitable for use by @code{setf}, because | |
| 5123 @code{check-type} signals a continuable error that allows the user to | |
| 5124 modify @var{place}, most simply by returning a value from the debugger. | |
| 428 | 5125 @end defspec |
| 5126 | |
| 5127 The following error-related macro is also defined: | |
| 5128 | |
| 5129 @defspec ignore-errors forms@dots{} | |
| 5130 This executes @var{forms} exactly like a @code{progn}, except that | |
| 5131 errors are ignored during the @var{forms}. More precisely, if | |
| 5132 an error is signalled then @code{ignore-errors} immediately | |
| 5133 aborts execution of the @var{forms} and returns @code{nil}. | |
| 5134 If the @var{forms} complete successfully, @code{ignore-errors} | |
| 5135 returns the result of the last @var{form}. | |
| 5136 @end defspec | |
| 5137 | |
| 5138 @node Efficiency Concerns, Common Lisp Compatibility, Assertions, Top | |
| 5139 @appendix Efficiency Concerns | |
| 5140 | |
| 5141 @appendixsec Macros | |
| 5142 | |
| 5143 @noindent | |
| 5144 Many of the advanced features of this package, such as @code{defun*}, | |
| 5145 @code{loop}, and @code{setf}, are implemented as Lisp macros. In | |
| 5146 byte-compiled code, these complex notations will be expanded into | |
| 5147 equivalent Lisp code which is simple and efficient. For example, | |
| 5148 the forms | |
| 5149 | |
| 5150 @example | |
| 5151 (incf i n) | |
| 5152 (push x (car p)) | |
| 5153 @end example | |
| 5154 | |
| 5155 @noindent | |
| 5156 are expanded at compile-time to the Lisp forms | |
| 5157 | |
| 5158 @example | |
| 5159 (setq i (+ i n)) | |
| 5160 (setcar p (cons x (car p))) | |
| 5161 @end example | |
| 5162 | |
| 5163 @noindent | |
| 5164 which are the most efficient ways of doing these respective operations | |
| 5165 in Lisp. Thus, there is no performance penalty for using the more | |
| 5166 readable @code{incf} and @code{push} forms in your compiled code. | |
| 5167 | |
| 5168 @emph{Interpreted} code, on the other hand, must expand these macros | |
| 5169 every time they are executed. For this reason it is strongly | |
| 5170 recommended that code making heavy use of macros be compiled. | |
| 5171 (The features labelled ``Special Form'' instead of ``Function'' in | |
| 5172 this manual are macros.) A loop using @code{incf} a hundred times | |
| 5173 will execute considerably faster if compiled, and will also | |
| 5174 garbage-collect less because the macro expansion will not have | |
| 5175 to be generated, used, and thrown away a hundred times. | |
| 5176 | |
| 5177 You can find out how a macro expands by using the | |
| 5178 @code{cl-prettyexpand} function. | |
| 5179 | |
| 5180 @defun cl-prettyexpand form &optional full | |
| 5181 This function takes a single Lisp form as an argument and inserts | |
| 5182 a nicely formatted copy of it in the current buffer (which must be | |
| 5183 in Lisp mode so that indentation works properly). It also expands | |
| 5184 all Lisp macros which appear in the form. The easiest way to use | |
| 5185 this function is to go to the @code{*scratch*} buffer and type, say, | |
| 5186 | |
| 5187 @example | |
| 5188 (cl-prettyexpand '(loop for x below 10 collect x)) | |
| 5189 @end example | |
| 5190 | |
| 5191 @noindent | |
| 5192 and type @kbd{C-x C-e} immediately after the closing parenthesis; | |
| 5193 the expansion | |
| 5194 | |
| 5195 @example | |
| 5196 (block nil | |
| 5197 (let* ((x 0) | |
| 5198 (G1004 nil)) | |
| 5199 (while (< x 10) | |
| 5200 (setq G1004 (cons x G1004)) | |
| 5201 (setq x (+ x 1))) | |
| 5202 (nreverse G1004))) | |
| 5203 @end example | |
| 5204 | |
| 5205 @noindent | |
| 5206 will be inserted into the buffer. (The @code{block} macro is | |
| 5207 expanded differently in the interpreter and compiler, so | |
| 5208 @code{cl-prettyexpand} just leaves it alone. The temporary | |
| 5209 variable @code{G1004} was created by @code{gensym}.) | |
| 5210 | |
| 5211 If the optional argument @var{full} is true, then @emph{all} | |
| 5212 macros are expanded, including @code{block}, @code{eval-when}, | |
| 5213 and compiler macros. Expansion is done as if @var{form} were | |
| 5214 a top-level form in a file being compiled. For example, | |
| 5215 | |
| 5216 @example | |
| 5217 (cl-prettyexpand '(pushnew 'x list)) | |
| 5218 @print{} (setq list (adjoin 'x list)) | |
| 5219 (cl-prettyexpand '(pushnew 'x list) t) | |
| 5220 @print{} (setq list (if (memq 'x list) list (cons 'x list))) | |
| 5221 (cl-prettyexpand '(caddr (member* 'a list)) t) | |
| 5222 @print{} (car (cdr (cdr (memq 'a list)))) | |
| 5223 @end example | |
| 5224 | |
| 5225 Note that @code{adjoin}, @code{caddr}, and @code{member*} all | |
| 5226 have built-in compiler macros to optimize them in common cases. | |
| 5227 @end defun | |
| 5228 | |
| 5229 @ifinfo | |
| 5230 @example | |
| 5231 | |
| 5232 @end example | |
| 5233 @end ifinfo | |
| 5234 @appendixsec Error Checking | |
| 5235 | |
| 5236 @noindent | |
| 5237 Common Lisp compliance has in general not been sacrificed for the | |
| 5238 sake of efficiency. A few exceptions have been made for cases | |
| 5239 where substantial gains were possible at the expense of marginal | |
| 5240 incompatibility. One example is the use of @code{memq} (which is | |
| 5241 treated very efficiently by the byte-compiler) to scan for keyword | |
| 5242 arguments; this can become confused in rare cases when keyword | |
| 5243 symbols are used as both keywords and data values at once. This | |
| 5244 is extremely unlikely to occur in practical code, and the use of | |
| 5245 @code{memq} allows functions with keyword arguments to be nearly | |
| 5246 as fast as functions that use @code{&optional} arguments. | |
| 5247 | |
| 5248 The Common Lisp standard (as embodied in Steele's book) uses the | |
| 5249 phrase ``it is an error if'' to indicate a situation which is not | |
| 5250 supposed to arise in complying programs; implementations are strongly | |
| 5251 encouraged but not required to signal an error in these situations. | |
| 5252 This package sometimes omits such error checking in the interest of | |
| 5253 compactness and efficiency. For example, @code{do} variable | |
| 5254 specifiers are supposed to be lists of one, two, or three forms; | |
| 5255 extra forms are ignored by this package rather than signalling a | |
| 5256 syntax error. The @code{endp} function is simply a synonym for | |
| 5257 @code{null} in this package. Functions taking keyword arguments | |
| 5258 will accept an odd number of arguments, treating the trailing | |
| 5259 keyword as if it were followed by the value @code{nil}. | |
| 5260 | |
| 5261 Argument lists (as processed by @code{defun*} and friends) | |
| 5262 @emph{are} checked rigorously except for the minor point just | |
| 5263 mentioned; in particular, keyword arguments are checked for | |
| 5264 validity, and @code{&allow-other-keys} and @code{:allow-other-keys} | |
| 5265 are fully implemented. Keyword validity checking is slightly | |
| 5266 time consuming (though not too bad in byte-compiled code); | |
| 5267 you can use @code{&allow-other-keys} to omit this check. Functions | |
| 5268 defined in this package such as @code{find} and @code{member*} | |
| 5269 do check their keyword arguments for validity. | |
| 5270 | |
| 5271 @ifinfo | |
| 5272 @example | |
| 5273 | |
| 5274 @end example | |
| 5275 @end ifinfo | |
| 5276 @appendixsec Optimizing Compiler | |
| 5277 | |
| 5278 @noindent | |
| 5279 The byte-compiler that comes with Emacs 18 normally fails to expand | |
| 5280 macros that appear in top-level positions in the file (i.e., outside | |
| 5281 of @code{defun}s or other enclosing forms). This would have | |
| 5282 disastrous consequences to programs that used such top-level macros | |
| 5283 as @code{defun*}, @code{eval-when}, and @code{defstruct}. To | |
| 5284 work around this problem, the @dfn{CL} package patches the Emacs | |
| 5285 18 compiler to expand top-level macros. This patch will apply to | |
| 5286 your own macros, too, if they are used in a top-level context. | |
| 5287 The patch will not harm versions of the Emacs 18 compiler which | |
| 5288 have already had a similar patch applied, nor will it affect the | |
| 5289 optimizing Emacs 19 byte-compiler written by Jamie Zawinski and | |
| 5290 Hallvard Furuseth. The patch is applied to the byte compiler's | |
| 5291 code in Emacs' memory, @emph{not} to the @file{bytecomp.elc} file | |
| 5292 stored on disk. | |
| 5293 | |
| 5294 The Emacs 19 compiler (for Emacs 18) is available from various | |
| 5295 Emacs Lisp archive sites such as @code{archive.cis.ohio-state.edu}. | |
| 5296 Its use is highly recommended; many of the Common Lisp macros emit | |
| 5297 code which can be improved by optimization. In particular, | |
| 5298 @code{block}s (whether explicit or implicit in constructs like | |
| 5299 @code{defun*} and @code{loop}) carry a fair run-time penalty; the | |
| 5300 optimizing compiler removes @code{block}s which are not actually | |
| 5301 referenced by @code{return} or @code{return-from} inside the block. | |
| 5302 | |
| 5303 @node Common Lisp Compatibility, Old CL Compatibility, Efficiency Concerns, Top | |
| 5304 @appendix Common Lisp Compatibility | |
| 5305 | |
| 5306 @noindent | |
| 5307 Following is a list of all known incompatibilities between this | |
| 5308 package and Common Lisp as documented in Steele (2nd edition). | |
| 5309 | |
| 5310 Certain function names, such as @code{member}, @code{assoc}, and | |
| 5311 @code{floor}, were already taken by (incompatible) Emacs Lisp | |
| 5312 functions; this package appends @samp{*} to the names of its | |
| 5313 Common Lisp versions of these functions. | |
| 5314 | |
| 5315 The word @code{defun*} is required instead of @code{defun} in order | |
| 5316 to use extended Common Lisp argument lists in a function. Likewise, | |
| 5317 @code{defmacro*} and @code{function*} are versions of those forms | |
| 5318 which understand full-featured argument lists. The @code{&whole} | |
| 5319 keyword does not work in @code{defmacro} argument lists (except | |
| 5320 inside recursive argument lists). | |
| 5321 | |
| 5322 In order to allow an efficient implementation, keyword arguments use | |
| 5323 a slightly cheesy parser which may be confused if a keyword symbol | |
| 5324 is passed as the @emph{value} of another keyword argument. | |
| 5325 (Specifically, @code{(memq :@var{keyword} @var{rest-of-arguments})} | |
| 5326 is used to scan for @code{:@var{keyword}} among the supplied | |
| 5327 keyword arguments.) | |
| 5328 | |
| 5329 The @code{eql} and @code{equal} predicates do not distinguish | |
| 5330 between IEEE floating-point plus and minus zero. The @code{equalp} | |
| 5331 predicate has several differences with Common Lisp; @pxref{Predicates}. | |
| 5332 | |
| 5333 The @code{setf} mechanism is entirely compatible, except that | |
| 5334 setf-methods return a list of five values rather than five | |
| 5335 values directly. Also, the new ``@code{setf} function'' concept | |
| 5336 (typified by @code{(defun (setf foo) @dots{})}) is not implemented. | |
| 5337 | |
| 5338 The @code{do-all-symbols} form is the same as @code{do-symbols} | |
| 5339 with no @var{obarray} argument. In Common Lisp, this form would | |
| 5340 iterate over all symbols in all packages. Since Emacs obarrays | |
| 5341 are not a first-class package mechanism, there is no way for | |
| 5342 @code{do-all-symbols} to locate any but the default obarray. | |
| 5343 | |
| 5344 The @code{loop} macro is complete except that @code{loop-finish} | |
| 5345 and type specifiers are unimplemented. | |
| 5346 | |
| 5347 Many Common Lisp declarations are ignored, and others match | |
| 5348 the Common Lisp standard in concept but not in detail. For | |
| 5349 example, local @code{special} declarations, which are purely | |
| 5350 advisory in Emacs Lisp, do not rigorously obey the scoping rules | |
| 5351 set down in Steele's book. | |
| 5352 | |
| 5353 The variable @code{*gensym-counter*} starts out with a pseudo-random | |
| 5354 value rather than with zero. This is to cope with the fact that | |
| 5355 generated symbols become interned when they are written to and | |
| 5356 loaded back from a file. | |
| 5357 | |
| 5358 The @code{defstruct} facility is compatible, except that structures | |
| 5359 are of type @code{:type vector :named} by default rather than some | |
| 5360 special, distinct type. Also, the @code{:type} slot option is ignored. | |
| 5361 | |
| 5362 The second argument of @code{check-type} is treated differently. | |
| 5363 | |
| 5364 @node Old CL Compatibility, Porting Common Lisp, Common Lisp Compatibility, Top | |
| 5365 @appendix Old CL Compatibility | |
| 5366 | |
| 5367 @noindent | |
| 5368 Following is a list of all known incompatibilities between this package | |
| 5369 and the older Quiroz @file{cl.el} package. | |
| 5370 | |
| 5371 The @code{defkeyword} form and @code{keywordp} function are not | |
| 5372 implemented in this package. | |
| 5373 | |
| 5374 The @code{member}, @code{floor}, @code{ceiling}, @code{truncate}, | |
| 5375 @code{round}, @code{mod}, and @code{rem} functions are suffixed | |
| 5376 by @samp{*} in this package to avoid collision with existing | |
| 5377 functions in Emacs 18 or Emacs 19. The older package simply | |
| 5378 redefined these functions, overwriting the built-in meanings and | |
| 5379 causing serious portability problems with Emacs 19. (Some more | |
| 5380 recent versions of the Quiroz package changed the names to | |
| 5381 @code{cl-member}, etc.; this package defines the latter names as | |
| 5382 aliases for @code{member*}, etc.) | |
| 5383 | |
| 5384 Certain functions in the old package which were buggy or inconsistent | |
| 5385 with the Common Lisp standard are incompatible with the conforming | |
| 5386 versions in this package. For example, @code{eql} and @code{member} | |
| 5387 were synonyms for @code{eq} and @code{memq} in that package, @code{setf} | |
| 5388 failed to preserve correct order of evaluation of its arguments, etc. | |
| 5389 | |
| 5390 Finally, unlike the older package, this package is careful to | |
| 5391 prefix all of its internal names with @code{cl-}. Except for a | |
| 5392 few functions which are explicitly defined as additional features | |
| 5393 (such as @code{floatp-safe} and @code{letf}), this package does not | |
| 5394 export any non-@samp{cl-} symbols which are not also part of Common | |
| 5395 Lisp. | |
| 5396 | |
| 5397 @ifinfo | |
| 5398 @example | |
| 5399 | |
| 5400 @end example | |
| 5401 @end ifinfo | |
| 5402 @appendixsec The @code{cl-compat} package | |
| 5403 | |
| 5404 @noindent | |
| 5405 The @dfn{CL} package includes emulations of some features of the | |
| 5406 old @file{cl.el}, in the form of a compatibility package | |
| 5407 @code{cl-compat}. To use it, put @code{(require 'cl-compat)} in | |
| 5408 your program. | |
| 5409 | |
| 5410 The old package defined a number of internal routines without | |
| 5411 @code{cl-} prefixes or other annotations. Call to these routines | |
| 5412 may have crept into existing Lisp code. @code{cl-compat} | |
| 5413 provides emulations of the following internal routines: | |
| 5414 @code{pair-with-newsyms}, @code{zip-lists}, @code{unzip-lists}, | |
| 5415 @code{reassemble-arglists}, @code{duplicate-symbols-p}, | |
| 5416 @code{safe-idiv}. | |
| 5417 | |
| 5418 Some @code{setf} forms translated into calls to internal | |
| 5419 functions that user code might call directly. The functions | |
| 5420 @code{setnth}, @code{setnthcdr}, and @code{setelt} fall in | |
| 5421 this category; they are defined by @code{cl-compat}, but the | |
| 5422 best fix is to change to use @code{setf} properly. | |
| 5423 | |
| 5424 The @code{cl-compat} file defines the keyword functions | |
| 5425 @code{keywordp}, @code{keyword-of}, and @code{defkeyword}, | |
| 5426 which are not defined by the new @dfn{CL} package because the | |
| 5427 use of keywords as data is discouraged. | |
| 5428 | |
| 5429 The @code{build-klist} mechanism for parsing keyword arguments | |
| 5430 is emulated by @code{cl-compat}; the @code{with-keyword-args} | |
| 5431 macro is not, however, and in any case it's best to change to | |
| 5432 use the more natural keyword argument processing offered by | |
| 5433 @code{defun*}. | |
| 5434 | |
| 5435 The functions @code{cl-floor}, @code{cl-ceiling}, @code{cl-truncate}, | |
| 5436 and @code{cl-round} are defined by @code{cl-compat} to use the | |
| 5437 old-style multiple-value mechanism, just as they did in the old | |
| 5438 package. The newer @code{floor*} and friends return their two | |
| 5439 results in a list rather than as multiple values. Note that | |
| 5440 older versions of the old package used the unadorned names | |
| 5441 @code{floor}, @code{ceiling}, etc.; @code{cl-compat} cannot use | |
| 5442 these names because they conflict with Emacs 19 built-ins. | |
| 5443 | |
| 5444 @node Porting Common Lisp, Function Index, Old CL Compatibility, Top | |
| 5445 @appendix Porting Common Lisp | |
| 5446 | |
| 5447 @noindent | |
| 5448 This package is meant to be used as an extension to Emacs Lisp, | |
| 5449 not as an Emacs implementation of true Common Lisp. Some of the | |
| 5450 remaining differences between Emacs Lisp and Common Lisp make it | |
| 5451 difficult to port large Common Lisp applications to Emacs. For | |
| 5452 one, some of the features in this package are not fully compliant | |
| 5453 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there | |
| 5454 are also quite a few features that this package does not provide | |
| 5455 at all. Here are some major omissions that you will want watch out | |
| 5456 for when bringing Common Lisp code into Emacs. | |
| 5457 | |
| 5458 @itemize @bullet | |
| 5459 @item | |
| 5460 Case-insensitivity. Symbols in Common Lisp are case-insensitive | |
| 5461 by default. Some programs refer to a function or variable as | |
| 5462 @code{foo} in one place and @code{Foo} or @code{FOO} in another. | |
| 5463 Emacs Lisp will treat these as three distinct symbols. | |
| 5464 | |
| 5465 Some Common Lisp code is written in all upper-case. While Emacs | |
| 5466 is happy to let the program's own functions and variables use | |
| 5467 this convention, calls to Lisp builtins like @code{if} and | |
| 5468 @code{defun} will have to be changed to lower-case. | |
| 5469 | |
| 5470 @item | |
| 5471 Lexical scoping. In Common Lisp, function arguments and @code{let} | |
| 5472 bindings apply only to references physically within their bodies | |
| 5473 (or within macro expansions in their bodies). Emacs Lisp, by | |
| 5474 contrast, uses @dfn{dynamic scoping} wherein a binding to a | |
| 5475 variable is visible even inside functions called from the body. | |
| 5476 | |
| 5477 Variables in Common Lisp can be made dynamically scoped by | |
| 5478 declaring them @code{special} or using @code{defvar}. In Emacs | |
| 5479 Lisp it is as if all variables were declared @code{special}. | |
| 5480 | |
| 5481 Often you can use code that was written for lexical scoping | |
| 5482 even in a dynamically scoped Lisp, but not always. Here is | |
| 5483 an example of a Common Lisp code fragment that would fail in | |
| 5484 Emacs Lisp: | |
| 5485 | |
| 5486 @example | |
| 5487 (defun map-odd-elements (func list) | |
| 5488 (loop for x in list | |
| 5489 for flag = t then (not flag) | |
| 5490 collect (if flag x (funcall func x)))) | |
| 5491 | |
| 5492 (defun add-odd-elements (list x) | |
| 5493 (map-odd-elements (function (lambda (a) (+ a x))) list)) | |
| 5494 @end example | |
| 5495 | |
| 5496 @noindent | |
| 5497 In Common Lisp, the two functions' usages of @code{x} are completely | |
| 5498 independent. In Emacs Lisp, the binding to @code{x} made by | |
| 5499 @code{add-odd-elements} will have been hidden by the binding | |
| 5500 in @code{map-odd-elements} by the time the @code{(+ a x)} function | |
| 5501 is called. | |
| 5502 | |
| 5503 (This package avoids such problems in its own mapping functions | |
| 5504 by using names like @code{cl-x} instead of @code{x} internally; | |
| 5505 as long as you don't use the @code{cl-} prefix for your own | |
| 5506 variables no collision can occur.) | |
| 5507 | |
| 5508 @xref{Lexical Bindings}, for a description of the @code{lexical-let} | |
| 5509 form which establishes a Common Lisp-style lexical binding, and some | |
| 5510 examples of how it differs from Emacs' regular @code{let}. | |
| 5511 | |
| 5512 @item | |
| 5513 Common Lisp allows the shorthand @code{#'x} to stand for | |
| 5514 @code{(function x)}, just as @code{'x} stands for @code{(quote x)}. | |
| 5515 In Common Lisp, one traditionally uses @code{#'} notation when | |
| 5516 referring to the name of a function. In Emacs Lisp, it works | |
| 5517 just as well to use a regular quote: | |
| 5518 | |
| 5519 @example | |
| 442 | 5520 (loop for x in y by #'cddr collect (mapcar #'plusp x)) ; Common Lisp |
| 5521 (loop for x in y by 'cddr collect (mapcar 'plusp x)) ; Emacs Lisp | |
| 428 | 5522 @end example |
| 5523 | |
| 5524 When @code{#'} introduces a @code{lambda} form, it is best to | |
| 5525 write out @code{(function ...)} longhand in Emacs Lisp. You can | |
| 5526 use a regular quote, but then the byte-compiler won't know that | |
| 5527 the @code{lambda} expression is code that can be compiled. | |
| 5528 | |
| 5529 @example | |
| 5530 (mapcar #'(lambda (x) (* x 2)) list) ; Common Lisp | |
| 5531 (mapcar (function (lambda (x) (* x 2))) list) ; Emacs Lisp | |
| 5532 @end example | |
| 5533 | |
| 5534 XEmacs supports @code{#'} notation starting with version 19.8. | |
| 5535 | |
| 5536 @item | |
| 5537 Reader macros. Common Lisp includes a second type of macro that | |
| 5538 works at the level of individual characters. For example, Common | |
| 5539 Lisp implements the quote notation by a reader macro called @code{'}, | |
| 5540 whereas Emacs Lisp's parser just treats quote as a special case. | |
| 5541 Some Lisp packages use reader macros to create special syntaxes | |
| 5542 for themselves, which the Emacs parser is incapable of reading. | |
| 5543 | |
| 5544 @item | |
| 5545 Other syntactic features. Common Lisp provides a number of | |
| 5546 notations beginning with @code{#} that the Emacs Lisp parser | |
| 5547 won't understand. For example, @samp{#| ... |#} is an | |
| 5548 alternate comment notation, and @samp{#+lucid (foo)} tells | |
| 5549 the parser to ignore the @code{(foo)} except in Lucid Common | |
| 5550 Lisp. | |
| 5551 | |
| 5552 The number prefixes `#b', `#o', and `#x', however, are supported | |
| 5553 by the Emacs Lisp parser to represent numbers in binary, octal, | |
| 5554 and hexadecimal notation (or radix), just like in Common Lisp. | |
| 5555 | |
| 5556 @item | |
| 5557 Packages. In Common Lisp, symbols are divided into @dfn{packages}. | |
| 5558 Symbols that are Lisp built-ins are typically stored in one package; | |
| 5559 symbols that are vendor extensions are put in another, and each | |
| 5560 application program would have a package for its own symbols. | |
| 5561 Certain symbols are ``exported'' by a package and others are | |
| 5562 internal; certain packages ``use'' or import the exported symbols | |
| 5563 of other packages. To access symbols that would not normally be | |
| 5564 visible due to this importing and exporting, Common Lisp provides | |
| 5565 a syntax like @code{package:symbol} or @code{package::symbol}. | |
| 5566 | |
| 5567 Emacs Lisp has a single namespace for all interned symbols, and | |
| 5568 then uses a naming convention of putting a prefix like @code{cl-} | |
| 5569 in front of the name. Some Emacs packages adopt the Common Lisp-like | |
| 5570 convention of using @code{cl:} or @code{cl::} as the prefix. | |
| 5571 However, the Emacs parser does not understand colons and just | |
| 5572 treats them as part of the symbol name. Thus, while @code{mapcar} | |
| 5573 and @code{lisp:mapcar} may refer to the same symbol in Common | |
| 5574 Lisp, they are totally distinct in Emacs Lisp. Common Lisp | |
| 5575 programs which refer to a symbol by the full name sometimes | |
| 5576 and the short name other times will not port cleanly to Emacs. | |
| 5577 | |
| 5578 Emacs Lisp does have a concept of ``obarrays,'' which are | |
| 5579 package-like collections of symbols, but this feature is not | |
| 5580 strong enough to be used as a true package mechanism. | |
| 5581 | |
| 5582 @item | |
| 5583 Keywords. The notation @code{:test-not} in Common Lisp really | |
| 5584 is a shorthand for @code{keyword:test-not}; keywords are just | |
| 5585 symbols in a built-in @code{keyword} package with the special | |
| 5586 property that all its symbols are automatically self-evaluating. | |
| 5587 Common Lisp programs often use keywords liberally to avoid | |
| 5588 having to use quotes. | |
| 5589 | |
| 5590 In Emacs Lisp a keyword is just a symbol whose name begins with | |
| 5591 a colon; since the Emacs parser does not treat them specially, | |
| 5592 they have to be explicitly made self-evaluating by a statement | |
| 5593 like @code{(setq :test-not ':test-not)}. This package arranges | |
| 5594 to execute such a statement whenever @code{defun*} or some | |
| 5595 other form sees a keyword being used as an argument. Common | |
| 5596 Lisp code that assumes that a symbol @code{:mumble} will be | |
| 5597 self-evaluating even though it was never introduced by a | |
| 5598 @code{defun*} will have to be fixed. | |
| 5599 | |
| 5600 @item | |
| 5601 The @code{format} function is quite different between Common | |
| 5602 Lisp and Emacs Lisp. It takes an additional ``destination'' | |
| 5603 argument before the format string. A destination of @code{nil} | |
| 5604 means to format to a string as in Emacs Lisp; a destination | |
| 5605 of @code{t} means to write to the terminal (similar to | |
| 5606 @code{message} in Emacs). Also, format control strings are | |
| 5607 utterly different; @code{~} is used instead of @code{%} to | |
| 5608 introduce format codes, and the set of available codes is | |
| 5609 much richer. There are no notations like @code{\n} for | |
| 5610 string literals; instead, @code{format} is used with the | |
| 5611 ``newline'' format code, @code{~%}. More advanced formatting | |
| 5612 codes provide such features as paragraph filling, case | |
| 5613 conversion, and even loops and conditionals. | |
| 5614 | |
| 5615 While it would have been possible to implement most of Common | |
| 5616 Lisp @code{format} in this package (under the name @code{format*}, | |
| 5617 of course), it was not deemed worthwhile. It would have required | |
| 5618 a huge amount of code to implement even a decent subset of | |
| 5619 @code{format*}, yet the functionality it would provide over | |
| 5620 Emacs Lisp's @code{format} would rarely be useful. | |
| 5621 | |
| 5622 @item | |
| 5623 Vector constants use square brackets in Emacs Lisp, but | |
| 5624 @code{#(a b c)} notation in Common Lisp. To further complicate | |
| 5625 matters, Emacs 19 introduces its own @code{#(} notation for | |
| 5626 something entirely different---strings with properties. | |
| 5627 | |
| 5628 @item | |
| 5629 Characters are distinct from integers in Common Lisp. The | |
| 5630 notation for character constants is also different: @code{#\A} | |
| 5631 instead of @code{?A}. Also, @code{string=} and @code{string-equal} | |
| 5632 are synonyms in Emacs Lisp whereas the latter is case-insensitive | |
| 5633 in Common Lisp. | |
| 5634 | |
| 5635 @item | |
| 5636 Data types. Some Common Lisp data types do not exist in Emacs | |
| 5637 Lisp. Rational numbers and complex numbers are not present, | |
| 5638 nor are large integers (all integers are ``fixnums''). All | |
| 5639 arrays are one-dimensional. There are no readtables or pathnames; | |
| 5640 streams are a set of existing data types rather than a new data | |
| 5641 type of their own. Hash tables, random-states, structures, and | |
| 5642 packages (obarrays) are built from Lisp vectors or lists rather | |
| 5643 than being distinct types. | |
| 5644 | |
| 5645 @item | |
| 5646 The Common Lisp Object System (CLOS) is not implemented, | |
| 5647 nor is the Common Lisp Condition System. | |
| 5648 | |
| 5649 @item | |
| 5650 Common Lisp features that are completely redundant with Emacs | |
| 5651 Lisp features of a different name generally have not been | |
| 5652 implemented. For example, Common Lisp writes @code{defconstant} | |
| 5653 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list} | |
| 5654 takes its arguments in different ways in the two Lisps but does | |
| 5655 exactly the same thing, so this package has not bothered to | |
| 5656 implement a Common Lisp-style @code{make-list}. | |
| 5657 | |
| 5658 @item | |
| 5659 A few more notable Common Lisp features not included in this | |
| 5660 package: @code{compiler-let}, @code{tagbody}, @code{prog}, | |
| 5661 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}. | |
| 5662 | |
| 5663 @item | |
| 5664 Recursion. While recursion works in Emacs Lisp just like it | |
| 5665 does in Common Lisp, various details of the Emacs Lisp system | |
| 5666 and compiler make recursion much less efficient than it is in | |
| 5667 most Lisps. Some schools of thought prefer to use recursion | |
| 5668 in Lisp over other techniques; they would sum a list of | |
| 5669 numbers using something like | |
| 5670 | |
| 5671 @example | |
| 5672 (defun sum-list (list) | |
| 5673 (if list | |
| 5674 (+ (car list) (sum-list (cdr list))) | |
| 5675 0)) | |
| 5676 @end example | |
| 5677 | |
| 5678 @noindent | |
| 5679 where a more iteratively-minded programmer might write one of | |
| 5680 these forms: | |
| 5681 | |
| 5682 @example | |
| 5683 (let ((total 0)) (dolist (x my-list) (incf total x)) total) | |
| 5684 (loop for x in my-list sum x) | |
| 5685 @end example | |
| 5686 | |
| 5687 While this would be mainly a stylistic choice in most Common Lisps, | |
| 5688 in Emacs Lisp you should be aware that the iterative forms are | |
| 5689 much faster than recursion. Also, Lisp programmers will want to | |
| 5690 note that the current Emacs Lisp compiler does not optimize tail | |
| 5691 recursion. | |
| 5692 @end itemize | |
| 5693 | |
| 5694 @node Function Index, Variable Index, Porting Common Lisp, Top | |
| 5695 @unnumbered Function Index | |
| 5696 | |
| 5697 @printindex fn | |
| 5698 | |
| 5699 @node Variable Index, , Function Index, Top | |
| 5700 @unnumbered Variable Index | |
| 5701 | |
| 5702 @printindex vr | |
| 5703 | |
| 5704 @contents | |
| 5705 @bye |