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| author | Vin Shelton <acs@xemacs.org> |
|---|---|
| date | Sun, 08 Jan 2012 22:29:06 -0500 |
| parents | bd80d9103fc8 |
| children |
| 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 * Porting Common Lisp:: Hints for porting Common Lisp code | |
| 115 | |
| 116 * Function Index:: | |
| 117 * Variable Index:: | |
| 118 @end menu | |
| 119 | |
| 120 @node Overview, Program Structure, Top, Top | |
| 121 @ifinfo | |
| 122 @chapter Overview | |
| 123 @end ifinfo | |
| 124 @iftex | |
| 125 @section Overview | |
| 126 @end iftex | |
| 127 | |
| 128 @noindent | |
| 129 Common Lisp is a huge language, and Common Lisp systems tend to be | |
| 130 massive and extremely complex. Emacs Lisp, by contrast, is rather | |
| 131 minimalist in the choice of Lisp features it offers the programmer. | |
| 132 As Emacs Lisp programmers have grown in number, and the applications | |
| 133 they write have grown more ambitious, it has become clear that Emacs | |
| 134 Lisp could benefit from many of the conveniences of Common Lisp. | |
| 135 | |
| 136 The @dfn{CL} package adds a number of Common Lisp functions and | |
| 137 control structures to Emacs Lisp. While not a 100% complete | |
| 138 implementation of Common Lisp, @dfn{CL} adds enough functionality | |
| 139 to make Emacs Lisp programming significantly more convenient. | |
| 140 | |
| 141 Some Common Lisp features have been omitted from this package | |
| 142 for various reasons: | |
| 143 | |
| 144 @itemize @bullet | |
| 145 @item | |
| 146 Some features are too complex or bulky relative to their benefit | |
| 147 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine | |
| 148 examples of this group. | |
| 149 | |
| 150 @item | |
| 151 Other features cannot be implemented without modification to the | |
| 152 Emacs Lisp interpreter itself, such as multiple return values, | |
| 153 lexical scoping, case-insensitive symbols, and complex numbers. | |
| 154 The @dfn{CL} package generally makes no attempt to emulate these | |
| 155 features. | |
| 156 | |
| 157 @item | |
| 158 Some features conflict with existing things in Emacs Lisp. For | |
| 159 example, Emacs' @code{assoc} function is incompatible with the | |
| 160 Common Lisp @code{assoc}. In such cases, this package usually | |
| 161 adds the suffix @samp{*} to the function name of the Common | |
| 162 Lisp version of the function (e.g., @code{assoc*}). | |
| 163 @end itemize | |
| 164 | |
| 165 The package described here was written by Dave Gillespie, | |
| 166 @file{daveg@@synaptics.com}. It is a total rewrite of the original | |
| 167 1986 @file{cl.el} package by Cesar Quiroz. Most features of | |
| 168 the Quiroz package have been retained; any incompatibilities are | |
| 169 noted in the descriptions below. Care has been taken in this | |
| 170 version to ensure that each function is defined efficiently, | |
| 171 concisely, and with minimal impact on the rest of the Emacs | |
| 172 environment. | |
| 173 | |
| 174 @menu | |
| 175 * Usage:: How to use the CL package | |
| 176 * Organization:: The package's five component files | |
| 177 * Installation:: Compiling and installing CL | |
| 178 * Naming Conventions:: Notes on CL function names | |
| 179 @end menu | |
| 180 | |
| 181 @node Usage, Organization, Overview, Overview | |
| 182 @section Usage | |
| 183 | |
| 184 @noindent | |
| 185 Lisp code that uses features from the @dfn{CL} package should | |
| 186 include at the beginning: | |
| 187 | |
| 188 @example | |
| 189 (require 'cl) | |
| 190 @end example | |
| 191 | |
| 192 It is safe to arrange to load @dfn{CL} at all times, e.g., | |
| 193 in your @file{.emacs} file. But it's a good idea, for portability, | |
| 194 to @code{(require 'cl)} in your code even if you do this. | |
| 195 | |
| 196 @node Organization, Installation, Usage, Overview | |
| 197 @section Organization | |
| 198 | |
| 199 @noindent | |
| 200 The Common Lisp package is organized into four files: | |
| 201 | |
| 202 @table @file | |
| 203 @item cl.el | |
| 204 This is the ``main'' file, which contains basic functions | |
| 205 and information about the package. This file is relatively | |
| 206 compact---about 700 lines. | |
| 207 | |
| 208 @item cl-extra.el | |
| 209 This file contains the larger, more complex or unusual functions. | |
| 210 It is kept separate so that packages which only want to use Common | |
| 211 Lisp fundamentals like the @code{cadr} function won't need to pay | |
| 212 the overhead of loading the more advanced functions. | |
| 213 | |
| 214 @item cl-seq.el | |
| 215 This file contains most of the advanced functions for operating | |
| 216 on sequences or lists, such as @code{delete-if} and @code{assoc*}. | |
| 217 | |
| 218 @item cl-macs.el | |
| 219 This file contains the features of the packages which are macros | |
| 220 instead of functions. Macros expand when the caller is compiled, | |
| 221 not when it is run, so the macros generally only need to be | |
| 222 present when the byte-compiler is running (or when the macros are | |
| 223 used in uncompiled code such as a @file{.emacs} file). Most of | |
| 224 the macros of this package are isolated in @file{cl-macs.el} so | |
| 225 that they won't take up memory unless you are compiling. | |
| 226 @end table | |
| 227 | |
| 228 The file @file{cl.el} includes all necessary @code{autoload} | |
| 229 commands for the functions and macros in the other three files. | |
| 230 All you have to do is @code{(require 'cl)}, and @file{cl.el} | |
| 231 will take care of pulling in the other files when they are | |
| 232 needed. | |
| 233 | |
| 234 @node Installation, Naming Conventions, Organization, Overview | |
| 235 @section Installation | |
| 236 | |
| 237 @noindent | |
| 238 Installation of the @dfn{CL} package is simple: Just put the | |
| 239 byte-compiled files @file{cl.elc}, @file{cl-extra.elc}, | |
| 240 @file{cl-seq.elc}, @file{cl-macs.elc}, and @file{cl-compat.elc} | |
| 241 into a directory on your @code{load-path}. | |
| 242 | |
| 243 There are no special requirements to compile this package: | |
| 244 The files do not have to be loaded before they are compiled, | |
| 245 nor do they need to be compiled in any particular order. | |
| 246 | |
| 247 You may choose to put the files into your main @file{lisp/} | |
| 248 directory, replacing the original @file{cl.el} file there. Or, | |
| 249 you could put them into a directory that comes before @file{lisp/} | |
| 250 on your @code{load-path} so that the old @file{cl.el} is | |
| 251 effectively hidden. | |
| 252 | |
| 253 Also, format the @file{cl.texinfo} file and put the resulting | |
| 254 Info files in the @file{info/} directory or another suitable place. | |
| 255 | |
| 256 You may instead wish to leave this package's components all in | |
| 257 their own directory, and then add this directory to your | |
| 258 @code{load-path} and (Emacs 19 only) @code{Info-directory-list}. | |
| 259 Add the directory to the front of the list so the old @dfn{CL} | |
| 260 package and its documentation are hidden. | |
| 261 | |
| 262 @node Naming Conventions, , Installation, Overview | |
| 263 @section Naming Conventions | |
| 264 | |
| 265 @noindent | |
| 266 Except where noted, all functions defined by this package have the | |
| 267 same names and calling conventions as their Common Lisp counterparts. | |
| 268 | |
| 269 Following is a complete list of functions whose names were changed | |
| 270 from Common Lisp, usually to avoid conflicts with Emacs. In each | |
| 271 case, a @samp{*} has been appended to the Common Lisp name to obtain | |
| 272 the Emacs name: | |
| 273 | |
| 274 @example | |
| 275 defun* defsubst* defmacro* function* | |
| 440 | 276 member* assoc* rassoc* remove* |
| 277 delete* mapcar* sort* floor* | |
| 278 ceiling* truncate* round* mod* | |
| 279 rem* random* | |
| 428 | 280 @end example |
| 281 | |
| 282 Internal function and variable names in the package are prefixed | |
| 283 by @code{cl-}. Here is a complete list of functions @emph{not} | |
| 284 prefixed by @code{cl-} which were not taken from Common Lisp: | |
| 285 | |
| 286 @example | |
| 287 member delete remove remq | |
| 288 rassoc floatp-safe lexical-let lexical-let* | |
| 289 callf callf2 letf letf* | |
| 290 defsubst* defalias add-hook eval-when-compile | |
| 291 @end example | |
| 292 | |
| 293 @noindent | |
| 294 (Most of these are Emacs 19 features provided to Emacs 18 users, | |
| 295 or introduced, like @code{remq}, for reasons of symmetry | |
| 296 with similar features.) | |
| 297 | |
| 298 The following simple functions and macros are defined in @file{cl.el}; | |
| 299 they do not cause other components like @file{cl-extra} to be loaded. | |
| 300 | |
| 301 @example | |
| 302 eql floatp-safe abs endp | |
| 303 evenp oddp plusp minusp | |
| 304 last butlast nbutlast caar .. cddddr | |
| 305 list* ldiff rest first .. tenth | |
| 306 member [1] copy-list subst mapcar* [2] | |
| 307 adjoin [3] acons pairlis when | |
| 308 unless pop [4] push [4] pushnew [3,4] | |
| 309 incf [4] decf [4] proclaim declaim | |
| 310 add-hook | |
| 311 @end example | |
| 312 | |
| 313 @noindent | |
| 314 [1] This is the Emacs 19-compatible function, not @code{member*}. | |
| 315 | |
| 316 @noindent | |
| 317 [2] Only for one sequence argument or two list arguments. | |
| 318 | |
| 319 @noindent | |
| 320 [3] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified, | |
| 321 and @code{:key} is not used. | |
| 322 | |
| 323 @noindent | |
| 324 [4] Only when @var{place} is a plain variable name. | |
| 325 | |
| 326 @iftex | |
| 327 @chapno=4 | |
| 328 @end iftex | |
| 329 | |
| 330 @node Program Structure, Predicates, Overview, Top | |
| 331 @chapter Program Structure | |
| 332 | |
| 333 @noindent | |
| 334 This section describes features of the @dfn{CL} package which have to | |
| 335 do with programs as a whole: advanced argument lists for functions, | |
| 336 and the @code{eval-when} construct. | |
| 337 | |
| 338 @menu | |
| 339 * Argument Lists:: `&key', `&aux', `defun*', `defmacro*'. | |
| 340 * Time of Evaluation:: The `eval-when' construct. | |
| 341 * Function Aliases:: The `defalias' function. | |
| 342 @end menu | |
| 343 | |
| 344 @iftex | |
| 345 @secno=1 | |
| 346 @end iftex | |
| 347 | |
| 348 @node Argument Lists, Time of Evaluation, Program Structure, Program Structure | |
| 349 @section Argument Lists | |
| 350 | |
| 351 @noindent | |
| 352 Emacs Lisp's notation for argument lists of functions is a subset of | |
| 353 the Common Lisp notation. As well as the familiar @code{&optional} | |
| 354 and @code{&rest} markers, Common Lisp allows you to specify default | |
| 355 values for optional arguments, and it provides the additional markers | |
| 356 @code{&key} and @code{&aux}. | |
| 357 | |
| 358 Since argument parsing is built-in to Emacs, there is no way for | |
| 359 this package to implement Common Lisp argument lists seamlessly. | |
| 360 Instead, this package defines alternates for several Lisp forms | |
| 361 which you must use if you need Common Lisp argument lists. | |
| 362 | |
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363 @defmac defun* name arglist body... |
| 428 | 364 This form is identical to the regular @code{defun} form, except |
| 365 that @var{arglist} is allowed to be a full Common Lisp argument | |
| 366 list. Also, the function body is enclosed in an implicit block | |
| 367 called @var{name}; @pxref{Blocks and Exits}. | |
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368 @end defmac |
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369 |
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370 @defmac defsubst* name arglist body... |
| 428 | 371 This is just like @code{defun*}, except that the function that |
| 372 is defined is automatically proclaimed @code{inline}, i.e., | |
| 373 calls to it may be expanded into in-line code by the byte compiler. | |
| 374 This is analogous to the @code{defsubst} form in Emacs 19; | |
| 375 @code{defsubst*} uses a different method (compiler macros) which | |
| 376 works in all version of Emacs, and also generates somewhat more | |
| 377 efficient inline expansions. In particular, @code{defsubst*} | |
| 378 arranges for the processing of keyword arguments, default values, | |
| 379 etc., to be done at compile-time whenever possible. | |
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380 @end defmac |
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381 |
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382 @defmac defmacro* name arglist body... |
| 428 | 383 This is identical to the regular @code{defmacro} form, |
| 384 except that @var{arglist} is allowed to be a full Common Lisp | |
| 385 argument list. The @code{&environment} keyword is supported as | |
| 386 described in Steele. The @code{&whole} keyword is supported only | |
| 387 within destructured lists (see below); top-level @code{&whole} | |
| 388 cannot be implemented with the current Emacs Lisp interpreter. | |
| 389 The macro expander body is enclosed in an implicit block called | |
| 390 @var{name}. | |
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391 @end defmac |
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392 |
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393 @defmac function* symbol-or-lambda |
| 428 | 394 This is identical to the regular @code{function} form, |
| 395 except that if the argument is a @code{lambda} form then that | |
| 396 form may use a full Common Lisp argument list. | |
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397 @end defmac |
| 428 | 398 |
| 399 Also, all forms (such as @code{defsetf} and @code{flet}) defined | |
| 400 in this package that include @var{arglist}s in their syntax allow | |
| 401 full Common Lisp argument lists. | |
| 402 | |
| 403 Note that it is @emph{not} necessary to use @code{defun*} in | |
| 404 order to have access to most @dfn{CL} features in your function. | |
| 405 These features are always present; @code{defun*}'s only | |
| 406 difference from @code{defun} is its more flexible argument | |
| 407 lists and its implicit block. | |
| 408 | |
| 409 The full form of a Common Lisp argument list is | |
| 410 | |
| 411 @example | |
| 412 (@var{var}... | |
| 413 &optional (@var{var} @var{initform} @var{svar})... | |
| 414 &rest @var{var} | |
| 415 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})... | |
| 416 &aux (@var{var} @var{initform})...) | |
| 417 @end example | |
| 418 | |
| 419 Each of the five argument list sections is optional. The @var{svar}, | |
| 420 @var{initform}, and @var{keyword} parts are optional; if they are | |
| 421 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}. | |
| 422 | |
| 423 The first section consists of zero or more @dfn{required} arguments. | |
| 424 These arguments must always be specified in a call to the function; | |
| 425 there is no difference between Emacs Lisp and Common Lisp as far as | |
| 426 required arguments are concerned. | |
| 427 | |
| 428 The second section consists of @dfn{optional} arguments. These | |
| 429 arguments may be specified in the function call; if they are not, | |
| 430 @var{initform} specifies the default value used for the argument. | |
| 431 (No @var{initform} means to use @code{nil} as the default.) The | |
| 432 @var{initform} is evaluated with the bindings for the preceding | |
| 433 arguments already established; @code{(a &optional (b (1+ a)))} | |
| 434 matches one or two arguments, with the second argument defaulting | |
| 435 to one plus the first argument. If the @var{svar} is specified, | |
| 436 it is an auxiliary variable which is bound to @code{t} if the optional | |
| 437 argument was specified, or to @code{nil} if the argument was omitted. | |
| 438 If you don't use an @var{svar}, then there will be no way for your | |
| 439 function to tell whether it was called with no argument, or with | |
| 440 the default value passed explicitly as an argument. | |
| 441 | |
| 442 The third section consists of a single @dfn{rest} argument. If | |
| 443 more arguments were passed to the function than are accounted for | |
| 444 by the required and optional arguments, those extra arguments are | |
| 445 collected into a list and bound to the ``rest'' argument variable. | |
| 446 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp. | |
| 447 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in | |
| 448 macro contexts; this package accepts it all the time. | |
| 449 | |
| 450 The fourth section consists of @dfn{keyword} arguments. These | |
| 451 are optional arguments which are specified by name rather than | |
| 452 positionally in the argument list. For example, | |
| 453 | |
| 454 @example | |
| 455 (defun* foo (a &optional b &key c d (e 17))) | |
| 456 @end example | |
| 457 | |
| 458 @noindent | |
| 459 defines a function which may be called with one, two, or more | |
| 460 arguments. The first two arguments are bound to @code{a} and | |
| 461 @code{b} in the usual way. The remaining arguments must be | |
| 462 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed | |
| 463 by the value to be bound to the corresponding argument variable. | |
| 464 (Symbols whose names begin with a colon are called @dfn{keywords}, | |
| 465 and they are self-quoting in the same way as @code{nil} and | |
| 466 @code{t}.) | |
| 467 | |
| 468 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five | |
| 469 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword | |
| 470 appears more than once in the function call, the first occurrence | |
| 471 takes precedence over the later ones. Note that it is not possible | |
| 472 to specify keyword arguments without specifying the optional | |
| 473 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind | |
| 474 @code{b} to the keyword @code{:c}, then signal an error because | |
| 475 @code{2} is not a valid keyword. | |
| 476 | |
| 477 If a @var{keyword} symbol is explicitly specified in the argument | |
| 478 list as shown in the above diagram, then that keyword will be | |
| 479 used instead of just the variable name prefixed with a colon. | |
| 480 You can specify a @var{keyword} symbol which does not begin with | |
| 481 a colon at all, but such symbols will not be self-quoting; you | |
| 482 will have to quote them explicitly with an apostrophe in the | |
| 483 function call. | |
| 484 | |
| 485 Ordinarily it is an error to pass an unrecognized keyword to | |
| 486 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask | |
| 487 Lisp to ignore unrecognized keywords, either by adding the | |
| 488 marker @code{&allow-other-keys} after the keyword section | |
| 489 of the argument list, or by specifying an @code{:allow-other-keys} | |
| 490 argument in the call whose value is non-@code{nil}. If the | |
| 491 function uses both @code{&rest} and @code{&key} at the same time, | |
| 492 the ``rest'' argument is bound to the keyword list as it appears | |
| 493 in the call. For example: | |
| 494 | |
| 495 @smallexample | |
| 496 (defun* find-thing (thing &rest rest &key need &allow-other-keys) | |
| 497 (or (apply 'member* thing thing-list :allow-other-keys t rest) | |
| 498 (if need (error "Thing not found")))) | |
| 499 @end smallexample | |
| 500 | |
| 501 @noindent | |
| 502 This function takes a @code{:need} keyword argument, but also | |
| 503 accepts other keyword arguments which are passed on to the | |
| 504 @code{member*} function. @code{allow-other-keys} is used to | |
| 505 keep both @code{find-thing} and @code{member*} from complaining | |
| 506 about each others' keywords in the arguments. | |
| 507 | |
| 508 As a (significant) performance optimization, this package | |
| 509 implements the scan for keyword arguments by calling @code{memq} | |
| 510 to search for keywords in a ``rest'' argument. Technically | |
| 511 speaking, this is incorrect, since @code{memq} looks at the | |
| 512 odd-numbered values as well as the even-numbered keywords. | |
| 513 The net effect is that if you happen to pass a keyword symbol | |
| 514 as the @emph{value} of another keyword argument, where that | |
| 515 keyword symbol happens to equal the name of a valid keyword | |
| 516 argument of the same function, then the keyword parser will | |
| 517 become confused. This minor bug can only affect you if you | |
| 518 use keyword symbols as general-purpose data in your program; | |
| 519 this practice is strongly discouraged in Emacs Lisp. | |
| 520 | |
| 521 The fifth section of the argument list consists of @dfn{auxiliary | |
| 522 variables}. These are not really arguments at all, but simply | |
| 523 variables which are bound to @code{nil} or to the specified | |
| 524 @var{initforms} during execution of the function. There is no | |
| 525 difference between the following two functions, except for a | |
| 526 matter of stylistic taste: | |
| 527 | |
| 528 @example | |
| 529 (defun* foo (a b &aux (c (+ a b)) d) | |
| 530 @var{body}) | |
| 531 | |
| 532 (defun* foo (a b) | |
| 533 (let ((c (+ a b)) d) | |
| 534 @var{body})) | |
| 535 @end example | |
| 536 | |
| 537 Argument lists support @dfn{destructuring}. In Common Lisp, | |
| 538 destructuring is only allowed with @code{defmacro}; this package | |
| 539 allows it with @code{defun*} and other argument lists as well. | |
| 540 In destructuring, any argument variable (@var{var} in the above | |
| 541 diagram) can be replaced by a list of variables, or more generally, | |
| 542 a recursive argument list. The corresponding argument value must | |
| 543 be a list whose elements match this recursive argument list. | |
| 544 For example: | |
| 545 | |
| 546 @example | |
| 547 (defmacro* dolist ((var listform &optional resultform) | |
| 548 &rest body) | |
| 549 ...) | |
| 550 @end example | |
| 551 | |
| 552 This says that the first argument of @code{dolist} must be a list | |
| 553 of two or three items; if there are other arguments as well as this | |
| 554 list, they are stored in @code{body}. All features allowed in | |
| 555 regular argument lists are allowed in these recursive argument lists. | |
| 556 In addition, the clause @samp{&whole @var{var}} is allowed at the | |
| 557 front of a recursive argument list. It binds @var{var} to the | |
| 558 whole list being matched; thus @code{(&whole all a b)} matches | |
| 559 a list of two things, with @code{a} bound to the first thing, | |
| 560 @code{b} bound to the second thing, and @code{all} bound to the | |
| 561 list itself. (Common Lisp allows @code{&whole} in top-level | |
| 562 @code{defmacro} argument lists as well, but Emacs Lisp does not | |
| 563 support this usage.) | |
| 564 | |
| 565 One last feature of destructuring is that the argument list may be | |
| 566 dotted, so that the argument list @code{(a b . c)} is functionally | |
| 567 equivalent to @code{(a b &rest c)}. | |
| 568 | |
| 569 If the optimization quality @code{safety} is set to 0 | |
| 570 (@pxref{Declarations}), error checking for wrong number of | |
| 571 arguments and invalid keyword arguments is disabled. By default, | |
| 572 argument lists are rigorously checked. | |
| 573 | |
| 574 @node Time of Evaluation, Function Aliases, Argument Lists, Program Structure | |
| 575 @section Time of Evaluation | |
| 576 | |
| 577 @noindent | |
| 578 Normally, the byte-compiler does not actually execute the forms in | |
| 579 a file it compiles. For example, if a file contains @code{(setq foo t)}, | |
| 580 the act of compiling it will not actually set @code{foo} to @code{t}. | |
| 581 This is true even if the @code{setq} was a top-level form (i.e., not | |
| 582 enclosed in a @code{defun} or other form). Sometimes, though, you | |
| 583 would like to have certain top-level forms evaluated at compile-time. | |
| 584 For example, the compiler effectively evaluates @code{defmacro} forms | |
| 585 at compile-time so that later parts of the file can refer to the | |
| 586 macros that are defined. | |
| 587 | |
|
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588 @defmac eval-when (situations...) forms... |
| 428 | 589 This form controls when the body @var{forms} are evaluated. |
| 590 The @var{situations} list may contain any set of the symbols | |
| 591 @code{compile}, @code{load}, and @code{eval} (or their long-winded | |
| 592 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel}, | |
| 593 and @code{:execute}). | |
| 594 | |
| 595 The @code{eval-when} form is handled differently depending on | |
| 596 whether or not it is being compiled as a top-level form. | |
| 597 Specifically, it gets special treatment if it is being compiled | |
| 598 by a command such as @code{byte-compile-file} which compiles files | |
| 599 or buffers of code, and it appears either literally at the | |
| 600 top level of the file or inside a top-level @code{progn}. | |
| 601 | |
| 602 For compiled top-level @code{eval-when}s, the body @var{forms} are | |
| 603 executed at compile-time if @code{compile} is in the @var{situations} | |
| 604 list, and the @var{forms} are written out to the file (to be executed | |
| 605 at load-time) if @code{load} is in the @var{situations} list. | |
| 606 | |
| 607 For non-compiled-top-level forms, only the @code{eval} situation is | |
| 608 relevant. (This includes forms executed by the interpreter, forms | |
| 609 compiled with @code{byte-compile} rather than @code{byte-compile-file}, | |
| 610 and non-top-level forms.) The @code{eval-when} acts like a | |
| 611 @code{progn} if @code{eval} is specified, and like @code{nil} | |
| 612 (ignoring the body @var{forms}) if not. | |
| 613 | |
| 614 The rules become more subtle when @code{eval-when}s are nested; | |
| 615 consult Steele (second edition) for the gruesome details (and | |
| 616 some gruesome examples). | |
| 617 | |
| 618 Some simple examples: | |
| 619 | |
| 620 @example | |
| 621 ;; Top-level forms in foo.el: | |
| 622 (eval-when (compile) (setq foo1 'bar)) | |
| 623 (eval-when (load) (setq foo2 'bar)) | |
| 624 (eval-when (compile load) (setq foo3 'bar)) | |
| 625 (eval-when (eval) (setq foo4 'bar)) | |
| 626 (eval-when (eval compile) (setq foo5 'bar)) | |
| 627 (eval-when (eval load) (setq foo6 'bar)) | |
| 628 (eval-when (eval compile load) (setq foo7 'bar)) | |
| 629 @end example | |
| 630 | |
| 631 When @file{foo.el} is compiled, these variables will be set during | |
| 632 the compilation itself: | |
| 633 | |
| 634 @example | |
| 635 foo1 foo3 foo5 foo7 ; `compile' | |
| 636 @end example | |
| 637 | |
| 638 When @file{foo.elc} is loaded, these variables will be set: | |
| 639 | |
| 640 @example | |
| 641 foo2 foo3 foo6 foo7 ; `load' | |
| 642 @end example | |
| 643 | |
| 644 And if @file{foo.el} is loaded uncompiled, these variables will | |
| 645 be set: | |
| 646 | |
| 647 @example | |
| 648 foo4 foo5 foo6 foo7 ; `eval' | |
| 649 @end example | |
| 650 | |
| 651 If these seven @code{eval-when}s had been, say, inside a @code{defun}, | |
| 652 then the first three would have been equivalent to @code{nil} and the | |
| 653 last four would have been equivalent to the corresponding @code{setq}s. | |
| 654 | |
| 655 Note that @code{(eval-when (load eval) @dots{})} is equivalent | |
| 656 to @code{(progn @dots{})} in all contexts. The compiler treats | |
| 657 certain top-level forms, like @code{defmacro} (sort-of) and | |
| 658 @code{require}, as if they were wrapped in @code{(eval-when | |
| 659 (compile load eval) @dots{})}. | |
|
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660 @end defmac |
| 428 | 661 |
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662 Emacs 19 includes two special operators related to @code{eval-when}. |
| 428 | 663 One of these, @code{eval-when-compile}, is not quite equivalent to |
| 664 any @code{eval-when} construct and is described below. This package | |
| 665 defines a version of @code{eval-when-compile} for the benefit of | |
| 666 Emacs 18 users. | |
| 667 | |
| 668 The other form, @code{(eval-and-compile @dots{})}, is exactly | |
| 669 equivalent to @samp{(eval-when (compile load eval) @dots{})} and | |
| 670 so is not itself defined by this package. | |
| 671 | |
|
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672 @defmac eval-when-compile forms... |
| 428 | 673 The @var{forms} are evaluated at compile-time; at execution time, |
| 674 this form acts like a quoted constant of the resulting value. Used | |
| 675 at top-level, @code{eval-when-compile} is just like @samp{eval-when | |
| 676 (compile eval)}. In other contexts, @code{eval-when-compile} | |
| 677 allows code to be evaluated once at compile-time for efficiency | |
| 678 or other reasons. | |
| 679 | |
| 680 This form is similar to the @samp{#.} syntax of true Common Lisp. | |
|
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681 @end defmac |
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682 |
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683 @defmac load-time-value form |
| 428 | 684 The @var{form} is evaluated at load-time; at execution time, |
| 685 this form acts like a quoted constant of the resulting value. | |
| 686 | |
| 687 Early Common Lisp had a @samp{#,} syntax that was similar to | |
| 688 this, but ANSI Common Lisp replaced it with @code{load-time-value} | |
| 689 and gave it more well-defined semantics. | |
| 690 | |
| 691 In a compiled file, @code{load-time-value} arranges for @var{form} | |
| 692 to be evaluated when the @file{.elc} file is loaded and then used | |
| 693 as if it were a quoted constant. In code compiled by | |
| 694 @code{byte-compile} rather than @code{byte-compile-file}, the | |
| 695 effect is identical to @code{eval-when-compile}. In uncompiled | |
| 696 code, both @code{eval-when-compile} and @code{load-time-value} | |
| 697 act exactly like @code{progn}. | |
| 698 | |
| 699 @example | |
| 700 (defun report () | |
| 701 (insert "This function was executed on: " | |
| 702 (current-time-string) | |
| 703 ", compiled on: " | |
| 704 (eval-when-compile (current-time-string)) | |
| 705 ;; or '#.(current-time-string) in real Common Lisp | |
| 706 ", and loaded on: " | |
| 707 (load-time-value (current-time-string)))) | |
| 708 @end example | |
| 709 | |
| 710 @noindent | |
| 711 Byte-compiled, the above defun will result in the following code | |
| 712 (or its compiled equivalent, of course) in the @file{.elc} file: | |
| 713 | |
| 714 @example | |
| 715 (setq --temp-- (current-time-string)) | |
| 716 (defun report () | |
| 717 (insert "This function was executed on: " | |
| 718 (current-time-string) | |
| 719 ", compiled on: " | |
| 720 '"Wed Jun 23 18:33:43 1993" | |
| 721 ", and loaded on: " | |
| 722 --temp--)) | |
| 723 @end example | |
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724 @end defmac |
| 428 | 725 |
| 726 @node Function Aliases, , Time of Evaluation, Program Structure | |
| 727 @section Function Aliases | |
| 728 | |
| 729 @noindent | |
| 730 This section describes a feature from GNU Emacs 19 which this | |
| 731 package makes available in other versions of Emacs. | |
| 732 | |
| 733 @defun defalias symbol function | |
| 734 This function sets @var{symbol}'s function cell to @var{function}. | |
| 735 It is equivalent to @code{fset}, except that in GNU Emacs 19 it also | |
| 736 records the setting in @code{load-history} so that it can be undone | |
| 737 by a later @code{unload-feature}. | |
| 738 | |
| 739 In other versions of Emacs, @code{defalias} is a synonym for | |
| 740 @code{fset}. | |
| 741 @end defun | |
| 742 | |
| 743 @node Predicates, Control Structure, Program Structure, Top | |
| 744 @chapter Predicates | |
| 745 | |
| 746 @noindent | |
| 747 This section describes functions for testing whether various | |
| 748 facts are true or false. | |
| 749 | |
| 750 @menu | |
| 751 * Type Predicates:: `typep', `deftype', and `coerce' | |
| 752 * Equality Predicates:: `eql' and `equalp' | |
| 753 @end menu | |
| 754 | |
| 755 @node Type Predicates, Equality Predicates, Predicates, Predicates | |
| 756 @section Type Predicates | |
| 757 | |
| 758 @noindent | |
| 759 The @dfn{CL} package defines a version of the Common Lisp @code{typep} | |
| 760 predicate. | |
| 761 | |
| 762 @defun typep object type | |
| 763 Check if @var{object} is of type @var{type}, where @var{type} is a | |
| 764 (quoted) type name of the sort used by Common Lisp. For example, | |
| 765 @code{(typep foo 'integer)} is equivalent to @code{(integerp foo)}. | |
| 766 @end defun | |
| 767 | |
| 768 The @var{type} argument to the above function is either a symbol | |
| 769 or a list beginning with a symbol. | |
| 770 | |
| 771 @itemize @bullet | |
| 772 @item | |
| 773 If the type name is a symbol, Emacs appends @samp{-p} to the | |
| 774 symbol name to form the name of a predicate function for testing | |
| 775 the type. (Built-in predicates whose names end in @samp{p} rather | |
| 776 than @samp{-p} are used when appropriate.) | |
| 777 | |
| 778 @item | |
| 779 The type symbol @code{t} stands for the union of all types. | |
| 780 @code{(typep @var{object} t)} is always true. Likewise, the | |
| 781 type symbol @code{nil} stands for nothing at all, and | |
| 782 @code{(typep @var{object} nil)} is always false. | |
| 783 | |
| 784 @item | |
| 785 The type symbol @code{null} represents the symbol @code{nil}. | |
| 786 Thus @code{(typep @var{object} 'null)} is equivalent to | |
| 787 @code{(null @var{object})}. | |
| 788 | |
| 789 @item | |
| 790 The type symbol @code{real} is a synonym for @code{number}, and | |
| 791 @code{fixnum} is a synonym for @code{integer}. | |
| 792 | |
| 793 @item | |
| 794 The type symbols @code{character} and @code{string-char} match | |
| 795 characters. In Emacs-19 and XEmacs-19, characters are the same thing as | |
| 796 integers in the range 0-255. In XEmacs-20, where characters are a | |
| 797 first-class data type, this checks for actual characters, and | |
| 798 @code{(typep @var{8bit-integer} 'character)} will return @code{nil}. | |
| 799 | |
| 800 @item | |
| 801 The type symbol @code{float} uses the @code{floatp-safe} predicate | |
| 802 defined by this package rather than @code{floatp}, so it will work | |
| 803 correctly even in Emacs versions without floating-point support. | |
| 804 | |
| 805 @item | |
| 806 The type list @code{(integer @var{low} @var{high})} represents all | |
| 807 integers between @var{low} and @var{high}, inclusive. Either bound | |
| 808 may be a list of a single integer to specify an exclusive limit, | |
| 809 or a @code{*} to specify no limit. The type @code{(integer * *)} | |
| 810 is thus equivalent to @code{integer}. | |
| 811 | |
| 812 @item | |
| 813 Likewise, lists beginning with @code{float}, @code{real}, or | |
| 814 @code{number} represent numbers of that type falling in a particular | |
| 815 range. | |
| 816 | |
| 817 @item | |
| 818 Lists beginning with @code{and}, @code{or}, and @code{not} form | |
| 819 combinations of types. For example, @code{(or integer (float 0 *))} | |
| 820 represents all objects that are integers or non-negative floats. | |
| 821 | |
| 822 @item | |
| 823 Lists beginning with @code{member} or @code{member*} represent | |
| 824 objects @code{eql} to any of the following values. For example, | |
| 825 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)}, | |
| 826 and @code{(member nil)} is equivalent to @code{null}. | |
| 827 | |
| 828 @item | |
| 829 Lists of the form @code{(satisfies @var{predicate})} represent | |
| 830 all objects for which @var{predicate} returns true when called | |
| 831 with that object as an argument. | |
| 832 @end itemize | |
| 833 | |
| 834 The following function and macro (not technically predicates) are | |
| 835 related to @code{typep}. | |
| 836 | |
| 837 @defun coerce object type | |
| 838 This function attempts to convert @var{object} to the specified | |
| 839 @var{type}. If @var{object} is already of that type as determined by | |
| 840 @code{typep}, it is simply returned. Otherwise, certain types of | |
| 841 conversions will be made: If @var{type} is any sequence type | |
| 842 (@code{string}, @code{list}, etc.) then @var{object} will be | |
| 843 converted to that type if possible. If @var{type} is | |
| 844 @code{character}, then strings of length one and symbols with | |
| 845 one-character names can be coerced. If @var{type} is @code{float}, | |
| 846 then integers can be coerced in versions of Emacs that support | |
| 847 floats. In all other circumstances, @code{coerce} signals an | |
| 848 error. | |
| 849 @end defun | |
| 850 | |
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851 @defmac deftype name arglist forms... |
| 428 | 852 This macro defines a new type called @var{name}. It is similar |
| 853 to @code{defmacro} in many ways; when @var{name} is encountered | |
| 854 as a type name, the body @var{forms} are evaluated and should | |
| 855 return a type specifier that is equivalent to the type. The | |
| 856 @var{arglist} is a Common Lisp argument list of the sort accepted | |
| 857 by @code{defmacro*}. The type specifier @samp{(@var{name} @var{args}...)} | |
| 858 is expanded by calling the expander with those arguments; the type | |
| 859 symbol @samp{@var{name}} is expanded by calling the expander with | |
| 860 no arguments. The @var{arglist} is processed the same as for | |
| 861 @code{defmacro*} except that optional arguments without explicit | |
| 862 defaults use @code{*} instead of @code{nil} as the ``default'' | |
| 863 default. Some examples: | |
| 864 | |
| 865 @example | |
| 866 (deftype null () '(satisfies null)) ; predefined | |
| 867 (deftype list () '(or null cons)) ; predefined | |
| 868 (deftype unsigned-byte (&optional bits) | |
| 869 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits))))) | |
| 870 (unsigned-byte 8) @equiv{} (integer 0 255) | |
| 871 (unsigned-byte) @equiv{} (integer 0 *) | |
| 872 unsigned-byte @equiv{} (integer 0 *) | |
| 873 @end example | |
| 874 | |
| 875 @noindent | |
| 876 The last example shows how the Common Lisp @code{unsigned-byte} | |
| 877 type specifier could be implemented if desired; this package does | |
| 878 not implement @code{unsigned-byte} by default. | |
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879 @end defmac |
| 428 | 880 |
| 881 The @code{typecase} and @code{check-type} macros also use type | |
| 882 names. @xref{Conditionals}. @xref{Assertions}. The @code{map}, | |
| 883 @code{concatenate}, and @code{merge} functions take type-name | |
| 884 arguments to specify the type of sequence to return. @xref{Sequences}. | |
| 885 | |
| 886 @node Equality Predicates, , Type Predicates, Predicates | |
| 887 @section Equality Predicates | |
| 888 | |
| 889 @noindent | |
| 890 This package defines two Common Lisp predicates, @code{eql} and | |
| 891 @code{equalp}. | |
| 892 | |
| 893 @defun eql a b | |
| 894 This function is almost the same as @code{eq}, except that if @var{a} | |
| 895 and @var{b} are numbers of the same type, it compares them for numeric | |
| 896 equality (as if by @code{equal} instead of @code{eq}). This makes a | |
| 897 difference only for versions of Emacs that are compiled with | |
| 898 floating-point support, such as Emacs 19. Emacs floats are allocated | |
| 899 objects just like cons cells, which means that @code{(eq 3.0 3.0)} | |
| 900 will not necessarily be true---if the two @code{3.0}s were allocated | |
| 901 separately, the pointers will be different even though the numbers are | |
| 902 the same. But @code{(eql 3.0 3.0)} will always be true. | |
| 903 | |
| 904 The types of the arguments must match, so @code{(eql 3 3.0)} is | |
| 905 still false. | |
| 906 | |
| 907 Note that Emacs integers are ``direct'' rather than allocated, which | |
| 908 basically means @code{(eq 3 3)} will always be true. Thus @code{eq} | |
| 909 and @code{eql} behave differently only if floating-point numbers are | |
| 910 involved, and are indistinguishable on Emacs versions that don't | |
| 911 support floats. | |
| 912 | |
| 913 There is a slight inconsistency with Common Lisp in the treatment of | |
| 914 positive and negative zeros. Some machines, notably those with IEEE | |
| 915 standard arithmetic, represent @code{+0} and @code{-0} as distinct | |
| 916 values. Normally this doesn't matter because the standard specifies | |
| 917 that @code{(= 0.0 -0.0)} should always be true, and this is indeed | |
| 918 what Emacs Lisp and Common Lisp do. But the Common Lisp standard | |
| 919 states that @code{(eql 0.0 -0.0)} and @code{(equal 0.0 -0.0)} should | |
| 920 be false on IEEE-like machines; Emacs Lisp does not do this, and in | |
| 921 fact the only known way to distinguish between the two zeros in Emacs | |
| 922 Lisp is to @code{format} them and check for a minus sign. | |
| 923 @end defun | |
| 924 | |
| 925 @defun equalp a b | |
| 926 This function is a more flexible version of @code{equal}. In | |
| 927 particular, it compares strings and characters case-insensitively, and | |
| 928 it compares numbers without regard to type (so that @code{(equalp 3 | |
| 929 3.0)} is true). Vectors and conses are compared recursively. All other | |
| 930 objects are compared as if by @code{equal}. | |
| 931 | |
| 932 This function differs from Common Lisp @code{equalp} in several | |
| 933 respects. In keeping with the idea that strings are less | |
| 934 vector-like in Emacs Lisp, this package's @code{equalp} also will not | |
| 935 compare strings against vectors of integers. | |
| 936 @end defun | |
| 937 | |
| 938 Also note that the Common Lisp functions @code{member} and @code{assoc} | |
| 939 use @code{eql} to compare elements, whereas Emacs Lisp follows the | |
| 940 MacLisp tradition and uses @code{equal} for these two functions. | |
| 941 In Emacs, use @code{member*} and @code{assoc*} to get functions | |
| 942 which use @code{eql} for comparisons. | |
| 943 | |
| 944 @node Control Structure, Macros, Predicates, Top | |
| 945 @chapter Control Structure | |
| 946 | |
| 947 @noindent | |
| 948 The features described in the following sections implement | |
| 949 various advanced control structures, including the powerful | |
| 950 @code{setf} facility and a number of looping and conditional | |
| 951 constructs. | |
| 952 | |
| 953 @menu | |
| 954 * Assignment:: The `psetq' form | |
| 955 * Generalized Variables:: `setf', `incf', `push', etc. | |
| 956 * Variable Bindings:: `progv', `lexical-let', `flet', `macrolet' | |
| 957 * Conditionals:: `when', `unless', `case', `typecase' | |
| 958 * Blocks and Exits:: `block', `return', `return-from' | |
| 959 * Iteration:: `do', `dotimes', `dolist', `do-symbols' | |
| 960 * Loop Facility:: The Common Lisp `loop' macro | |
| 961 * Multiple Values:: `values', `multiple-value-bind', etc. | |
| 962 @end menu | |
| 963 | |
| 964 @node Assignment, Generalized Variables, Control Structure, Control Structure | |
| 965 @section Assignment | |
| 966 | |
| 967 @noindent | |
| 968 The @code{psetq} form is just like @code{setq}, except that multiple | |
| 969 assignments are done in parallel rather than sequentially. | |
| 970 | |
|
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971 @defmac psetq [symbol form]@dots{} |
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972 This macro is used to assign to several |
| 428 | 973 variables simultaneously. Given only one @var{symbol} and @var{form}, |
| 974 it has the same effect as @code{setq}. Given several @var{symbol} | |
| 975 and @var{form} pairs, it evaluates all the @var{form}s in advance | |
| 976 and then stores the corresponding variables afterwards. | |
| 977 | |
| 978 @example | |
| 979 (setq x 2 y 3) | |
| 980 (setq x (+ x y) y (* x y)) | |
| 981 x | |
| 982 @result{} 5 | |
| 983 y ; @r{@code{y} was computed after @code{x} was set.} | |
| 984 @result{} 15 | |
| 985 (setq x 2 y 3) | |
| 986 (psetq x (+ x y) y (* x y)) | |
| 987 x | |
| 988 @result{} 5 | |
| 989 y ; @r{@code{y} was computed before @code{x} was set.} | |
| 990 @result{} 6 | |
| 991 @end example | |
| 992 | |
| 993 The simplest use of @code{psetq} is @code{(psetq x y y x)}, which | |
| 994 exchanges the values of two variables. (The @code{rotatef} form | |
| 995 provides an even more convenient way to swap two variables; | |
| 996 @pxref{Modify Macros}.) | |
| 997 | |
| 998 @code{psetq} always returns @code{nil}. | |
|
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999 @end defmac |
| 428 | 1000 |
| 1001 @node Generalized Variables, Variable Bindings, Assignment, Control Structure | |
| 1002 @section Generalized Variables | |
| 1003 | |
| 1004 @noindent | |
| 1005 A ``generalized variable'' or ``place form'' is one of the many places | |
| 1006 in Lisp memory where values can be stored. The simplest place form is | |
| 1007 a regular Lisp variable. But the cars and cdrs of lists, elements | |
| 1008 of arrays, properties of symbols, and many other locations are also | |
| 1009 places where Lisp values are stored. | |
| 1010 | |
| 1011 The @code{setf} form is like @code{setq}, except that it accepts | |
| 1012 arbitrary place forms on the left side rather than just | |
| 1013 symbols. For example, @code{(setf (car a) b)} sets the car of | |
| 1014 @code{a} to @code{b}, doing the same operation as @code{(setcar a b)} | |
| 1015 but without having to remember two separate functions for setting | |
| 1016 and accessing every type of place. | |
| 1017 | |
| 1018 Generalized variables are analogous to ``lvalues'' in the C | |
| 1019 language, where @samp{x = a[i]} gets an element from an array | |
| 1020 and @samp{a[i] = x} stores an element using the same notation. | |
| 1021 Just as certain forms like @code{a[i]} can be lvalues in C, there | |
| 1022 is a set of forms that can be generalized variables in Lisp. | |
| 1023 | |
| 1024 @menu | |
| 1025 * Basic Setf:: `setf' and place forms | |
| 1026 * Modify Macros:: `incf', `push', `rotatef', `letf', `callf', etc. | |
| 1027 * Customizing Setf:: `define-modify-macro', `defsetf', `define-setf-method' | |
| 1028 @end menu | |
| 1029 | |
| 1030 @node Basic Setf, Modify Macros, Generalized Variables, Generalized Variables | |
| 1031 @subsection Basic Setf | |
| 1032 | |
| 1033 @noindent | |
| 1034 The @code{setf} macro is the most basic way to operate on generalized | |
| 1035 variables. | |
| 1036 | |
|
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1037 @defmac setf [place form]@dots{} |
| 428 | 1038 This macro evaluates @var{form} and stores it in @var{place}, which |
| 1039 must be a valid generalized variable form. If there are several | |
| 1040 @var{place} and @var{form} pairs, the assignments are done sequentially | |
| 1041 just as with @code{setq}. @code{setf} returns the value of the last | |
| 1042 @var{form}. | |
| 1043 | |
| 1044 The following Lisp forms will work as generalized variables, and | |
| 1045 so may legally appear in the @var{place} argument of @code{setf}: | |
| 1046 | |
| 1047 @itemize @bullet | |
| 1048 @item | |
| 1049 A symbol naming a variable. In other words, @code{(setf x y)} is | |
| 1050 exactly equivalent to @code{(setq x y)}, and @code{setq} itself is | |
| 1051 strictly speaking redundant now that @code{setf} exists. Many | |
| 1052 programmers continue to prefer @code{setq} for setting simple | |
| 1053 variables, though, purely for stylistic or historical reasons. | |
| 446 | 1054 The form @code{(setf x y)} actually expands to @code{(setq x y)}, |
| 428 | 1055 so there is no performance penalty for using it in compiled code. |
| 1056 | |
| 1057 @item | |
| 1058 A call to any of the following Lisp functions: | |
| 1059 | |
| 1060 @smallexample | |
| 1061 car cdr caar .. cddddr | |
| 1062 nth rest first .. tenth | |
| 1063 aref elt nthcdr | |
| 1064 symbol-function symbol-value symbol-plist | |
| 440 | 1065 get getf gethash |
| 1066 subseq | |
| 428 | 1067 @end smallexample |
| 1068 | |
| 1069 @noindent | |
| 1070 Note that for @code{nthcdr} and @code{getf}, the list argument | |
| 1071 of the function must itself be a valid @var{place} form. For | |
| 1072 example, @code{(setf (nthcdr 0 foo) 7)} will set @code{foo} itself | |
| 1073 to 7. Note that @code{push} and @code{pop} on an @code{nthcdr} | |
| 1074 place can be used to insert or delete at any position in a list. | |
| 1075 The use of @code{nthcdr} as a @var{place} form is an extension | |
| 1076 to standard Common Lisp. | |
| 1077 | |
| 1078 @item | |
| 1079 The following Emacs-specific functions are also @code{setf}-able. | |
| 1080 (Some of these are defined only in Emacs 19 or only in XEmacs.) | |
| 1081 | |
| 1082 @smallexample | |
| 1083 buffer-file-name marker-position | |
| 1084 buffer-modified-p match-data | |
| 1085 buffer-name mouse-position | |
| 1086 buffer-string overlay-end | |
| 1087 buffer-substring overlay-get | |
| 1088 current-buffer overlay-start | |
| 1089 current-case-table point | |
| 1090 current-column point-marker | |
| 1091 current-global-map point-max | |
| 1092 current-input-mode point-min | |
| 1093 current-local-map process-buffer | |
| 1094 current-window-configuration process-filter | |
| 1095 default-file-modes process-sentinel | |
| 1096 default-value read-mouse-position | |
| 1097 documentation-property screen-height | |
| 1098 extent-data screen-menubar | |
| 1099 extent-end-position screen-width | |
| 1100 extent-start-position selected-window | |
| 1101 face-background selected-screen | |
| 1102 face-background-pixmap selected-frame | |
| 1103 face-font standard-case-table | |
| 1104 face-foreground syntax-table | |
| 1105 face-underline-p window-buffer | |
| 1106 file-modes window-dedicated-p | |
| 1107 frame-height window-display-table | |
| 1108 frame-parameters window-height | |
| 1109 frame-visible-p window-hscroll | |
| 1110 frame-width window-point | |
| 1111 get-register window-start | |
| 1112 getenv window-width | |
| 1113 global-key-binding x-get-cut-buffer | |
| 1114 keymap-parent x-get-cutbuffer | |
| 1115 local-key-binding x-get-secondary-selection | |
| 1116 mark x-get-selection | |
| 1117 mark-marker | |
| 1118 @end smallexample | |
| 1119 | |
| 1120 Most of these have directly corresponding ``set'' functions, like | |
| 1121 @code{use-local-map} for @code{current-local-map}, or @code{goto-char} | |
| 1122 for @code{point}. A few, like @code{point-min}, expand to longer | |
| 1123 sequences of code when they are @code{setf}'d (@code{(narrow-to-region | |
| 1124 x (point-max))} in this case). | |
| 1125 | |
| 1126 @item | |
| 1127 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])}, | |
| 1128 where @var{subplace} is itself a legal generalized variable whose | |
| 1129 current value is a string, and where the value stored is also a | |
| 1130 string. The new string is spliced into the specified part of the | |
| 1131 destination string. For example: | |
| 1132 | |
| 1133 @example | |
| 1134 (setq a (list "hello" "world")) | |
| 1135 @result{} ("hello" "world") | |
| 1136 (cadr a) | |
| 1137 @result{} "world" | |
| 1138 (substring (cadr a) 2 4) | |
| 1139 @result{} "rl" | |
| 1140 (setf (substring (cadr a) 2 4) "o") | |
| 1141 @result{} "o" | |
| 1142 (cadr a) | |
| 1143 @result{} "wood" | |
| 1144 a | |
| 1145 @result{} ("hello" "wood") | |
| 1146 @end example | |
| 1147 | |
| 1148 The generalized variable @code{buffer-substring}, listed above, | |
| 1149 also works in this way by replacing a portion of the current buffer. | |
| 1150 | |
| 1151 @item | |
| 1152 A call of the form @code{(apply '@var{func} @dots{})} or | |
| 1153 @code{(apply (function @var{func}) @dots{})}, where @var{func} | |
| 1154 is a @code{setf}-able function whose store function is ``suitable'' | |
| 1155 in the sense described in Steele's book; since none of the standard | |
| 1156 Emacs place functions are suitable in this sense, this feature is | |
| 1157 only interesting when used with places you define yourself with | |
| 1158 @code{define-setf-method} or the long form of @code{defsetf}. | |
| 1159 | |
| 1160 @item | |
| 1161 A macro call, in which case the macro is expanded and @code{setf} | |
| 1162 is applied to the resulting form. | |
| 1163 | |
| 1164 @item | |
| 1165 Any form for which a @code{defsetf} or @code{define-setf-method} | |
| 1166 has been made. | |
| 1167 @end itemize | |
| 1168 | |
| 1169 Using any forms other than these in the @var{place} argument to | |
| 1170 @code{setf} will signal an error. | |
| 1171 | |
| 1172 The @code{setf} macro takes care to evaluate all subforms in | |
| 1173 the proper left-to-right order; for example, | |
| 1174 | |
| 1175 @example | |
| 1176 (setf (aref vec (incf i)) i) | |
| 1177 @end example | |
| 1178 | |
| 1179 @noindent | |
| 1180 looks like it will evaluate @code{(incf i)} exactly once, before the | |
| 1181 following access to @code{i}; the @code{setf} expander will insert | |
| 1182 temporary variables as necessary to ensure that it does in fact work | |
| 1183 this way no matter what setf-method is defined for @code{aref}. | |
| 1184 (In this case, @code{aset} would be used and no such steps would | |
| 1185 be necessary since @code{aset} takes its arguments in a convenient | |
| 1186 order.) | |
| 1187 | |
| 1188 However, if the @var{place} form is a macro which explicitly | |
| 1189 evaluates its arguments in an unusual order, this unusual order | |
| 1190 will be preserved. Adapting an example from Steele, given | |
| 1191 | |
| 1192 @example | |
| 1193 (defmacro wrong-order (x y) (list 'aref y x)) | |
| 1194 @end example | |
| 1195 | |
| 1196 @noindent | |
| 1197 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will | |
| 1198 evaluate @var{b} first, then @var{a}, just as in an actual call | |
| 1199 to @code{wrong-order}. | |
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1200 @end defmac |
| 428 | 1201 |
| 1202 @node Modify Macros, Customizing Setf, Basic Setf, Generalized Variables | |
| 1203 @subsection Modify Macros | |
| 1204 | |
| 1205 @noindent | |
| 1206 This package defines a number of other macros besides @code{setf} | |
| 1207 that operate on generalized variables. Many are interesting and | |
| 1208 useful even when the @var{place} is just a variable name. | |
| 1209 | |
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1210 @defmac psetf [place form]@dots{} |
| 428 | 1211 This macro is to @code{setf} what @code{psetq} is to @code{setq}: |
| 1212 When several @var{place}s and @var{form}s are involved, the | |
| 1213 assignments take place in parallel rather than sequentially. | |
| 1214 Specifically, all subforms are evaluated from left to right, then | |
| 1215 all the assignments are done (in an undefined order). | |
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1216 @end defmac |
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1217 |
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1218 @defmac incf place &optional x |
| 428 | 1219 This macro increments the number stored in @var{place} by one, or |
| 1220 by @var{x} if specified. The incremented value is returned. For | |
| 1221 example, @code{(incf i)} is equivalent to @code{(setq i (1+ i))}, and | |
| 1222 @code{(incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}. | |
| 1223 | |
| 1224 Once again, care is taken to preserve the ``apparent'' order of | |
| 1225 evaluation. For example, | |
| 1226 | |
| 1227 @example | |
| 1228 (incf (aref vec (incf i))) | |
| 1229 @end example | |
| 1230 | |
| 1231 @noindent | |
| 1232 appears to increment @code{i} once, then increment the element of | |
| 1233 @code{vec} addressed by @code{i}; this is indeed exactly what it | |
| 1234 does, which means the above form is @emph{not} equivalent to the | |
| 1235 ``obvious'' expansion, | |
| 1236 | |
| 1237 @example | |
| 1238 (setf (aref vec (incf i)) (1+ (aref vec (incf i)))) ; Wrong! | |
| 1239 @end example | |
| 1240 | |
| 1241 @noindent | |
| 1242 but rather to something more like | |
| 1243 | |
| 1244 @example | |
| 1245 (let ((temp (incf i))) | |
| 1246 (setf (aref vec temp) (1+ (aref vec temp)))) | |
| 1247 @end example | |
| 1248 | |
| 1249 @noindent | |
| 1250 Again, all of this is taken care of automatically by @code{incf} and | |
| 1251 the other generalized-variable macros. | |
| 1252 | |
| 1253 As a more Emacs-specific example of @code{incf}, the expression | |
| 1254 @code{(incf (point) @var{n})} is essentially equivalent to | |
| 1255 @code{(forward-char @var{n})}. | |
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1256 @end defmac |
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1257 |
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1258 @defmac decf place &optional x |
| 428 | 1259 This macro decrements the number stored in @var{place} by one, or |
| 1260 by @var{x} if specified. | |
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1261 @end defmac |
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1262 |
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1263 @defmac pop place |
| 428 | 1264 This macro removes and returns the first element of the list stored |
| 1265 in @var{place}. It is analogous to @code{(prog1 (car @var{place}) | |
| 1266 (setf @var{place} (cdr @var{place})))}, except that it takes care | |
| 1267 to evaluate all subforms only once. | |
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1268 @end defmac |
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1269 |
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1270 @defmac push x place |
| 428 | 1271 This macro inserts @var{x} at the front of the list stored in |
| 1272 @var{place}. It is analogous to @code{(setf @var{place} (cons | |
| 1273 @var{x} @var{place}))}, except for evaluation of the subforms. | |
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1274 @end defmac |
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1275 |
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1276 @defmac pushnew x place @t{&key :test :test-not :key} |
| 428 | 1277 This macro inserts @var{x} at the front of the list stored in |
| 1278 @var{place}, but only if @var{x} was not @code{eql} to any | |
| 1279 existing element of the list. The optional keyword arguments | |
| 1280 are interpreted in the same way as for @code{adjoin}. | |
| 1281 @xref{Lists as Sets}. | |
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1282 @end defmac |
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1283 |
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1284 @defmac shiftf place@dots{} newvalue |
| 428 | 1285 This macro shifts the @var{place}s left by one, shifting in the |
| 1286 value of @var{newvalue} (which may be any Lisp expression, not just | |
| 1287 a generalized variable), and returning the value shifted out of | |
| 1288 the first @var{place}. Thus, @code{(shiftf @var{a} @var{b} @var{c} | |
| 1289 @var{d})} is equivalent to | |
| 1290 | |
| 1291 @example | |
| 1292 (prog1 | |
| 1293 @var{a} | |
| 1294 (psetf @var{a} @var{b} | |
| 1295 @var{b} @var{c} | |
| 1296 @var{c} @var{d})) | |
| 1297 @end example | |
| 1298 | |
| 1299 @noindent | |
| 1300 except that the subforms of @var{a}, @var{b}, and @var{c} are actually | |
| 1301 evaluated only once each and in the apparent order. | |
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1302 @end defmac |
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1303 |
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1304 @defmac rotatef place@dots{} |
| 428 | 1305 This macro rotates the @var{place}s left by one in circular fashion. |
| 1306 Thus, @code{(rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to | |
| 1307 | |
| 1308 @example | |
| 1309 (psetf @var{a} @var{b} | |
| 1310 @var{b} @var{c} | |
| 1311 @var{c} @var{d} | |
| 1312 @var{d} @var{a}) | |
| 1313 @end example | |
| 1314 | |
| 1315 @noindent | |
| 1316 except for the evaluation of subforms. @code{rotatef} always | |
| 1317 returns @code{nil}. Note that @code{(rotatef @var{a} @var{b})} | |
| 1318 conveniently exchanges @var{a} and @var{b}. | |
|
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1319 @end defmac |
| 428 | 1320 |
| 1321 The following macros were invented for this package; they have no | |
| 1322 analogues in Common Lisp. | |
| 1323 | |
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1324 @defmac letf (bindings@dots{}) forms@dots{} |
| 428 | 1325 This macro is analogous to @code{let}, but for generalized variables |
| 1326 rather than just symbols. Each @var{binding} should be of the form | |
| 1327 @code{(@var{place} @var{value})}; the original contents of the | |
| 1328 @var{place}s are saved, the @var{value}s are stored in them, and | |
| 1329 then the body @var{form}s are executed. Afterwards, the @var{places} | |
| 1330 are set back to their original saved contents. This cleanup happens | |
| 1331 even if the @var{form}s exit irregularly due to a @code{throw} or an | |
| 1332 error. | |
| 1333 | |
| 1334 For example, | |
| 1335 | |
| 1336 @example | |
| 1337 (letf (((point) (point-min)) | |
| 1338 (a 17)) | |
| 1339 ...) | |
| 1340 @end example | |
| 1341 | |
| 1342 @noindent | |
| 1343 moves ``point'' in the current buffer to the beginning of the buffer, | |
| 1344 and also binds @code{a} to 17 (as if by a normal @code{let}, since | |
| 1345 @code{a} is just a regular variable). After the body exits, @code{a} | |
| 1346 is set back to its original value and point is moved back to its | |
| 1347 original position. | |
| 1348 | |
| 1349 Note that @code{letf} on @code{(point)} is not quite like a | |
| 1350 @code{save-excursion}, as the latter effectively saves a marker | |
| 1351 which tracks insertions and deletions in the buffer. Actually, | |
| 1352 a @code{letf} of @code{(point-marker)} is much closer to this | |
| 1353 behavior. (@code{point} and @code{point-marker} are equivalent | |
| 1354 as @code{setf} places; each will accept either an integer or a | |
| 1355 marker as the stored value.) | |
| 1356 | |
| 1357 Since generalized variables look like lists, @code{let}'s shorthand | |
| 1358 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would | |
| 1359 be ambiguous in @code{letf} and is not allowed. | |
| 1360 | |
| 1361 However, a @var{binding} specifier may be a one-element list | |
| 1362 @samp{(@var{place})}, which is similar to @samp{(@var{place} | |
| 1363 @var{place})}. In other words, the @var{place} is not disturbed | |
| 1364 on entry to the body, and the only effect of the @code{letf} is | |
| 1365 to restore the original value of @var{place} afterwards. (The | |
| 1366 redundant access-and-store suggested by the @code{(@var{place} | |
| 1367 @var{place})} example does not actually occur.) | |
| 1368 | |
| 1369 In most cases, the @var{place} must have a well-defined value on | |
| 1370 entry to the @code{letf} form. The only exceptions are plain | |
| 1371 variables and calls to @code{symbol-value} and @code{symbol-function}. | |
| 1372 If the symbol is not bound on entry, it is simply made unbound by | |
| 1373 @code{makunbound} or @code{fmakunbound} on exit. | |
|
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1374 @end defmac |
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1375 |
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1376 @defmac letf* (bindings@dots{}) forms@dots{} |
| 428 | 1377 This macro is to @code{letf} what @code{let*} is to @code{let}: |
| 1378 It does the bindings in sequential rather than parallel order. | |
|
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1379 @end defmac |
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1380 |
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1381 @defmac callf @var{function} @var{place} @var{args}@dots{} |
| 428 | 1382 This is the ``generic'' modify macro. It calls @var{function}, |
| 1383 which should be an unquoted function name, macro name, or lambda. | |
| 1384 It passes @var{place} and @var{args} as arguments, and assigns the | |
| 1385 result back to @var{place}. For example, @code{(incf @var{place} | |
| 1386 @var{n})} is the same as @code{(callf + @var{place} @var{n})}. | |
| 1387 Some more examples: | |
| 1388 | |
| 1389 @example | |
| 1390 (callf abs my-number) | |
| 1391 (callf concat (buffer-name) "<" (int-to-string n) ">") | |
| 1392 (callf union happy-people (list joe bob) :test 'same-person) | |
| 1393 @end example | |
| 1394 | |
| 1395 @xref{Customizing Setf}, for @code{define-modify-macro}, a way | |
| 1396 to create even more concise notations for modify macros. Note | |
| 1397 again that @code{callf} is an extension to standard Common Lisp. | |
|
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1398 @end defmac |
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1399 |
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1400 @defmac callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{} |
| 428 | 1401 This macro is like @code{callf}, except that @var{place} is |
| 1402 the @emph{second} argument of @var{function} rather than the | |
| 1403 first. For example, @code{(push @var{x} @var{place})} is | |
| 1404 equivalent to @code{(callf2 cons @var{x} @var{place})}. | |
|
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1405 @end defmac |
| 428 | 1406 |
| 1407 The @code{callf} and @code{callf2} macros serve as building | |
| 1408 blocks for other macros like @code{incf}, @code{pushnew}, and | |
| 1409 @code{define-modify-macro}. The @code{letf} and @code{letf*} | |
| 1410 macros are used in the processing of symbol macros; | |
| 1411 @pxref{Macro Bindings}. | |
| 1412 | |
| 1413 @node Customizing Setf, , Modify Macros, Generalized Variables | |
| 1414 @subsection Customizing Setf | |
| 1415 | |
| 1416 @noindent | |
| 1417 Common Lisp defines three macros, @code{define-modify-macro}, | |
| 1418 @code{defsetf}, and @code{define-setf-method}, that allow the | |
| 1419 user to extend generalized variables in various ways. | |
| 1420 | |
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1421 @defmac define-modify-macro name arglist function [doc-string] |
| 428 | 1422 This macro defines a ``read-modify-write'' macro similar to |
| 1423 @code{incf} and @code{decf}. The macro @var{name} is defined | |
| 1424 to take a @var{place} argument followed by additional arguments | |
| 1425 described by @var{arglist}. The call | |
| 1426 | |
| 1427 @example | |
| 1428 (@var{name} @var{place} @var{args}...) | |
| 1429 @end example | |
| 1430 | |
| 1431 @noindent | |
| 1432 will be expanded to | |
| 1433 | |
| 1434 @example | |
| 1435 (callf @var{func} @var{place} @var{args}...) | |
| 1436 @end example | |
| 1437 | |
| 1438 @noindent | |
| 1439 which in turn is roughly equivalent to | |
| 1440 | |
| 1441 @example | |
| 1442 (setf @var{place} (@var{func} @var{place} @var{args}...)) | |
| 1443 @end example | |
| 1444 | |
| 1445 For example: | |
| 1446 | |
| 1447 @example | |
| 1448 (define-modify-macro incf (&optional (n 1)) +) | |
| 1449 (define-modify-macro concatf (&rest args) concat) | |
| 1450 @end example | |
| 1451 | |
| 1452 Note that @code{&key} is not allowed in @var{arglist}, but | |
| 1453 @code{&rest} is sufficient to pass keywords on to the function. | |
| 1454 | |
| 1455 Most of the modify macros defined by Common Lisp do not exactly | |
| 1456 follow the pattern of @code{define-modify-macro}. For example, | |
| 1457 @code{push} takes its arguments in the wrong order, and @code{pop} | |
| 1458 is completely irregular. You can define these macros ``by hand'' | |
| 1459 using @code{get-setf-method}, or consult the source file | |
| 1460 @file{cl-macs.el} to see how to use the internal @code{setf} | |
| 1461 building blocks. | |
|
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1462 @end defmac |
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1463 |
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1464 @defmac defsetf access-fn update-fn |
| 428 | 1465 This is the simpler of two @code{defsetf} forms. Where |
| 1466 @var{access-fn} is the name of a function which accesses a place, | |
| 1467 this declares @var{update-fn} to be the corresponding store | |
| 1468 function. From now on, | |
| 1469 | |
| 1470 @example | |
| 1471 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value}) | |
| 1472 @end example | |
| 1473 | |
| 1474 @noindent | |
| 1475 will be expanded to | |
| 1476 | |
| 1477 @example | |
| 1478 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value}) | |
| 1479 @end example | |
| 1480 | |
| 1481 @noindent | |
| 1482 The @var{update-fn} is required to be either a true function, or | |
| 1483 a macro which evaluates its arguments in a function-like way. Also, | |
| 1484 the @var{update-fn} is expected to return @var{value} as its result. | |
| 1485 Otherwise, the above expansion would not obey the rules for the way | |
| 1486 @code{setf} is supposed to behave. | |
| 1487 | |
| 1488 As a special (non-Common-Lisp) extension, a third argument of @code{t} | |
| 1489 to @code{defsetf} says that the @code{update-fn}'s return value is | |
| 1490 not suitable, so that the above @code{setf} should be expanded to | |
| 1491 something more like | |
| 1492 | |
| 1493 @example | |
| 1494 (let ((temp @var{value})) | |
| 1495 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp) | |
| 1496 temp) | |
| 1497 @end example | |
| 1498 | |
| 1499 Some examples of the use of @code{defsetf}, drawn from the standard | |
| 1500 suite of setf methods, are: | |
| 1501 | |
| 1502 @example | |
| 1503 (defsetf car setcar) | |
| 1504 (defsetf symbol-value set) | |
| 1505 (defsetf buffer-name rename-buffer t) | |
| 1506 @end example | |
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1507 @end defmac |
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1508 |
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1509 @defmac defsetf access-fn arglist (store-var) forms@dots{} |
| 428 | 1510 This is the second, more complex, form of @code{defsetf}. It is |
| 1511 rather like @code{defmacro} except for the additional @var{store-var} | |
| 1512 argument. The @var{forms} should return a Lisp form which stores | |
| 1513 the value of @var{store-var} into the generalized variable formed | |
| 1514 by a call to @var{access-fn} with arguments described by @var{arglist}. | |
| 1515 The @var{forms} may begin with a string which documents the @code{setf} | |
| 1516 method (analogous to the doc string that appears at the front of a | |
| 1517 function). | |
| 1518 | |
| 1519 For example, the simple form of @code{defsetf} is shorthand for | |
| 1520 | |
| 1521 @example | |
| 1522 (defsetf @var{access-fn} (&rest args) (store) | |
| 1523 (append '(@var{update-fn}) args (list store))) | |
| 1524 @end example | |
| 1525 | |
| 1526 The Lisp form that is returned can access the arguments from | |
| 1527 @var{arglist} and @var{store-var} in an unrestricted fashion; | |
| 1528 macros like @code{setf} and @code{incf} which invoke this | |
| 1529 setf-method will insert temporary variables as needed to make | |
| 1530 sure the apparent order of evaluation is preserved. | |
| 1531 | |
| 1532 Another example drawn from the standard package: | |
| 1533 | |
| 1534 @example | |
| 1535 (defsetf nth (n x) (store) | |
| 1536 (list 'setcar (list 'nthcdr n x) store)) | |
| 1537 @end example | |
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1538 @end defmac |
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1539 |
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1540 @defmac define-setf-method access-fn arglist forms@dots{} |
| 428 | 1541 This is the most general way to create new place forms. When |
| 1542 a @code{setf} to @var{access-fn} with arguments described by | |
| 1543 @var{arglist} is expanded, the @var{forms} are evaluated and | |
| 1544 must return a list of five items: | |
| 1545 | |
| 1546 @enumerate | |
| 1547 @item | |
| 1548 A list of @dfn{temporary variables}. | |
| 1549 | |
| 1550 @item | |
| 1551 A list of @dfn{value forms} corresponding to the temporary variables | |
| 1552 above. The temporary variables will be bound to these value forms | |
| 1553 as the first step of any operation on the generalized variable. | |
| 1554 | |
| 1555 @item | |
| 1556 A list of exactly one @dfn{store variable} (generally obtained | |
| 1557 from a call to @code{gensym}). | |
| 1558 | |
| 1559 @item | |
| 1560 A Lisp form which stores the contents of the store variable into | |
| 1561 the generalized variable, assuming the temporaries have been | |
| 1562 bound as described above. | |
| 1563 | |
| 1564 @item | |
| 1565 A Lisp form which accesses the contents of the generalized variable, | |
| 1566 assuming the temporaries have been bound. | |
| 1567 @end enumerate | |
| 1568 | |
| 1569 This is exactly like the Common Lisp macro of the same name, | |
| 1570 except that the method returns a list of five values rather | |
| 1571 than the five values themselves, since Emacs Lisp does not | |
| 1572 support Common Lisp's notion of multiple return values. | |
| 1573 | |
| 1574 Once again, the @var{forms} may begin with a documentation string. | |
| 1575 | |
| 1576 A setf-method should be maximally conservative with regard to | |
| 1577 temporary variables. In the setf-methods generated by | |
| 1578 @code{defsetf}, the second return value is simply the list of | |
| 1579 arguments in the place form, and the first return value is a | |
| 1580 list of a corresponding number of temporary variables generated | |
| 1581 by @code{gensym}. Macros like @code{setf} and @code{incf} which | |
| 1582 use this setf-method will optimize away most temporaries that | |
| 1583 turn out to be unnecessary, so there is little reason for the | |
| 1584 setf-method itself to optimize. | |
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1585 @end defmac |
| 428 | 1586 |
| 1587 @defun get-setf-method place &optional env | |
| 1588 This function returns the setf-method for @var{place}, by | |
| 1589 invoking the definition previously recorded by @code{defsetf} | |
| 1590 or @code{define-setf-method}. The result is a list of five | |
| 1591 values as described above. You can use this function to build | |
| 1592 your own @code{incf}-like modify macros. (Actually, it is | |
| 1593 better to use the internal functions @code{cl-setf-do-modify} | |
| 1594 and @code{cl-setf-do-store}, which are a bit easier to use and | |
| 1595 which also do a number of optimizations; consult the source | |
| 1596 code for the @code{incf} function for a simple example.) | |
| 1597 | |
| 1598 The argument @var{env} specifies the ``environment'' to be | |
| 1599 passed on to @code{macroexpand} if @code{get-setf-method} should | |
| 1600 need to expand a macro in @var{place}. It should come from | |
| 1601 an @code{&environment} argument to the macro or setf-method | |
| 1602 that called @code{get-setf-method}. | |
| 1603 | |
| 1604 See also the source code for the setf-methods for @code{apply} | |
| 1605 and @code{substring}, each of which works by calling | |
| 1606 @code{get-setf-method} on a simpler case, then massaging | |
| 1607 the result in various ways. | |
| 1608 @end defun | |
| 1609 | |
| 1610 Modern Common Lisp defines a second, independent way to specify | |
| 1611 the @code{setf} behavior of a function, namely ``@code{setf} | |
| 1612 functions'' whose names are lists @code{(setf @var{name})} | |
| 1613 rather than symbols. For example, @code{(defun (setf foo) @dots{})} | |
| 1614 defines the function that is used when @code{setf} is applied to | |
| 1615 @code{foo}. This package does not currently support @code{setf} | |
| 1616 functions. In particular, it is a compile-time error to use | |
| 1617 @code{setf} on a form which has not already been @code{defsetf}'d | |
| 1618 or otherwise declared; in newer Common Lisps, this would not be | |
| 1619 an error since the function @code{(setf @var{func})} might be | |
| 1620 defined later. | |
| 1621 | |
| 1622 @iftex | |
| 1623 @secno=4 | |
| 1624 @end iftex | |
| 1625 | |
| 1626 @node Variable Bindings, Conditionals, Generalized Variables, Control Structure | |
| 1627 @section Variable Bindings | |
| 1628 | |
| 1629 @noindent | |
| 1630 These Lisp forms make bindings to variables and function names, | |
| 1631 analogous to Lisp's built-in @code{let} form. | |
| 1632 | |
| 1633 @xref{Modify Macros}, for the @code{letf} and @code{letf*} forms which | |
| 1634 are also related to variable bindings. | |
| 1635 | |
| 1636 @menu | |
| 1637 * Dynamic Bindings:: The `progv' form | |
| 1638 * Lexical Bindings:: `lexical-let' and lexical closures | |
| 1639 * Function Bindings:: `flet' and `labels' | |
| 1640 * Macro Bindings:: `macrolet' and `symbol-macrolet' | |
| 1641 @end menu | |
| 1642 | |
| 1643 @node Dynamic Bindings, Lexical Bindings, Variable Bindings, Variable Bindings | |
| 1644 @subsection Dynamic Bindings | |
| 1645 | |
| 1646 @noindent | |
| 1647 The standard @code{let} form binds variables whose names are known | |
| 1648 at compile-time. The @code{progv} form provides an easy way to | |
| 1649 bind variables whose names are computed at run-time. | |
| 1650 | |
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1651 @defmac progv symbols values forms@dots{} |
| 428 | 1652 This form establishes @code{let}-style variable bindings on a |
| 1653 set of variables computed at run-time. The expressions | |
| 1654 @var{symbols} and @var{values} are evaluated, and must return lists | |
| 1655 of symbols and values, respectively. The symbols are bound to the | |
| 1656 corresponding values for the duration of the body @var{form}s. | |
| 1657 If @var{values} is shorter than @var{symbols}, the last few symbols | |
| 1658 are made unbound (as if by @code{makunbound}) inside the body. | |
| 1659 If @var{symbols} is shorter than @var{values}, the excess values | |
| 1660 are ignored. | |
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1661 @end defmac |
| 428 | 1662 |
| 1663 @node Lexical Bindings, Function Bindings, Dynamic Bindings, Variable Bindings | |
| 1664 @subsection Lexical Bindings | |
| 1665 | |
| 1666 @noindent | |
| 1667 The @dfn{CL} package defines the following macro which | |
| 1668 more closely follows the Common Lisp @code{let} form: | |
| 1669 | |
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1670 @defmac lexical-let (bindings@dots{}) forms@dots{} |
| 428 | 1671 This form is exactly like @code{let} except that the bindings it |
| 1672 establishes are purely lexical. Lexical bindings are similar to | |
| 1673 local variables in a language like C: Only the code physically | |
| 1674 within the body of the @code{lexical-let} (after macro expansion) | |
| 1675 may refer to the bound variables. | |
| 1676 | |
| 1677 @example | |
| 1678 (setq a 5) | |
| 1679 (defun foo (b) (+ a b)) | |
| 1680 (let ((a 2)) (foo a)) | |
| 1681 @result{} 4 | |
| 1682 (lexical-let ((a 2)) (foo a)) | |
| 1683 @result{} 7 | |
| 1684 @end example | |
| 1685 | |
| 1686 @noindent | |
| 1687 In this example, a regular @code{let} binding of @code{a} actually | |
| 1688 makes a temporary change to the global variable @code{a}, so @code{foo} | |
| 1689 is able to see the binding of @code{a} to 2. But @code{lexical-let} | |
| 1690 actually creates a distinct local variable @code{a} for use within its | |
| 1691 body, without any effect on the global variable of the same name. | |
| 1692 | |
| 1693 The most important use of lexical bindings is to create @dfn{closures}. | |
| 1694 A closure is a function object that refers to an outside lexical | |
| 1695 variable. For example: | |
| 1696 | |
| 1697 @example | |
| 1698 (defun make-adder (n) | |
| 1699 (lexical-let ((n n)) | |
| 1700 (function (lambda (m) (+ n m))))) | |
| 1701 (setq add17 (make-adder 17)) | |
| 1702 (funcall add17 4) | |
| 1703 @result{} 21 | |
| 1704 @end example | |
| 1705 | |
| 1706 @noindent | |
| 1707 The call @code{(make-adder 17)} returns a function object which adds | |
| 1708 17 to its argument. If @code{let} had been used instead of | |
| 1709 @code{lexical-let}, the function object would have referred to the | |
| 1710 global @code{n}, which would have been bound to 17 only during the | |
| 1711 call to @code{make-adder} itself. | |
| 1712 | |
| 1713 @example | |
| 1714 (defun make-counter () | |
| 1715 (lexical-let ((n 0)) | |
| 1716 (function* (lambda (&optional (m 1)) (incf n m))))) | |
| 1717 (setq count-1 (make-counter)) | |
| 1718 (funcall count-1 3) | |
| 1719 @result{} 3 | |
| 1720 (funcall count-1 14) | |
| 1721 @result{} 17 | |
| 1722 (setq count-2 (make-counter)) | |
| 1723 (funcall count-2 5) | |
| 1724 @result{} 5 | |
| 1725 (funcall count-1 2) | |
| 1726 @result{} 19 | |
| 1727 (funcall count-2) | |
| 1728 @result{} 6 | |
| 1729 @end example | |
| 1730 | |
| 1731 @noindent | |
| 1732 Here we see that each call to @code{make-counter} creates a distinct | |
| 1733 local variable @code{n}, which serves as a private counter for the | |
| 1734 function object that is returned. | |
| 1735 | |
| 1736 Closed-over lexical variables persist until the last reference to | |
| 1737 them goes away, just like all other Lisp objects. For example, | |
| 1738 @code{count-2} refers to a function object which refers to an | |
| 1739 instance of the variable @code{n}; this is the only reference | |
| 1740 to that variable, so after @code{(setq count-2 nil)} the garbage | |
| 1741 collector would be able to delete this instance of @code{n}. | |
| 1742 Of course, if a @code{lexical-let} does not actually create any | |
| 1743 closures, then the lexical variables are free as soon as the | |
| 1744 @code{lexical-let} returns. | |
| 1745 | |
| 1746 Many closures are used only during the extent of the bindings they | |
| 1747 refer to; these are known as ``downward funargs'' in Lisp parlance. | |
| 1748 When a closure is used in this way, regular Emacs Lisp dynamic | |
| 1749 bindings suffice and will be more efficient than @code{lexical-let} | |
| 1750 closures: | |
| 1751 | |
| 1752 @example | |
| 1753 (defun add-to-list (x list) | |
| 1754 (mapcar (function (lambda (y) (+ x y))) list)) | |
| 1755 (add-to-list 7 '(1 2 5)) | |
| 1756 @result{} (8 9 12) | |
| 1757 @end example | |
| 1758 | |
| 1759 @noindent | |
| 1760 Since this lambda is only used while @code{x} is still bound, | |
| 1761 it is not necessary to make a true closure out of it. | |
| 1762 | |
| 1763 You can use @code{defun} or @code{flet} inside a @code{lexical-let} | |
| 1764 to create a named closure. If several closures are created in the | |
| 1765 body of a single @code{lexical-let}, they all close over the same | |
| 1766 instance of the lexical variable. | |
| 1767 | |
| 1768 The @code{lexical-let} form is an extension to Common Lisp. In | |
| 1769 true Common Lisp, all bindings are lexical unless declared otherwise. | |
|
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1770 @end defmac |
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1771 |
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1772 @defmac lexical-let* (bindings@dots{}) forms@dots{} |
| 428 | 1773 This form is just like @code{lexical-let}, except that the bindings |
| 1774 are made sequentially in the manner of @code{let*}. | |
|
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1775 @end defmac |
| 428 | 1776 |
| 1777 @node Function Bindings, Macro Bindings, Lexical Bindings, Variable Bindings | |
| 1778 @subsection Function Bindings | |
| 1779 | |
| 1780 @noindent | |
|
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1781 These forms make @code{let}-like bindings to functions instead of |
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1782 variables. Normally you should use @code{labels}, it is less expensive in |
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1783 compiled code and avoids the problems of dynamic scope. |
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1784 |
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1785 @defmac labels (bindings@dots{}) forms@dots{} |
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1786 This form establishes @code{lexical-let}-style bindings on the function cells |
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1787 of symbols rather than on their value cells. Each @var{binding} must be a |
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1788 list of the form @samp{(@var{name} @var{arglist} @var{forms}@dots{})}, which |
|
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1789 defines a function exactly as if it were a @code{defun*} form. The function |
|
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Improve the implementation, documentation of #'labels, #'flet.
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1790 @var{name} is available within @var{forms}, within the body of @var{name}, and |
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1791 within the body of any other functions in @var{bindings}. This allows the |
|
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1792 establishment of recursive and mutually-referential functions. |
|
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1793 |
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1794 These functions are not available by name at run-time to code textually |
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1795 outside of the @code{labels} form, though they may be passed to other code by |
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1796 value. Since @code{labels} makes lexical rather than dynamic bindings, |
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1797 bindings of functions like @code{+} and @code{list} that have byte codes will |
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1798 succeed---that is, calls to such functions within @var{form} will reflect the |
|
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1799 bindings within the @code{labels} form, something not true of @code{flet}, |
|
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1800 which see. |
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1801 |
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1802 Within @var{forms}, to access a bound function as a callable object, quote its |
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1803 name using @var{#'name}, as in the following example. |
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1804 |
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1805 @example |
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1806 (labels ((1+ (number) |
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1807 "Return 1.0 added to NUMBER" |
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1808 (+ number 1.0))) |
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1809 (map 'vector #'1+ '(10 9 8 7 6 5 4 3 2 1))) |
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1810 @result{} [11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0] |
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1811 @end example |
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1812 |
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1813 Functions defined by @code{labels} may use the full Common Lisp argument |
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1814 notation supported by @code{defun*}; also, the function body is enclosed in an |
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1815 implicit block as if by @code{defun*}. @xref{Program Structure}. |
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1816 @end defmac |
| 428 | 1817 |
|
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1818 @defmac flet (bindings@dots{}) forms@dots{} |
|
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1819 This form establishes @code{let}-style bindings on the function cells of |
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1820 symbols rather than on the value cells. In contravention of Common Lisp, |
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1821 Emacs Lisp @code{flet} establishes dynamic bindings (available at runtime) |
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1822 rather than lexical (available at compile time, but outside of @var{forms}, |
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1823 not at runtime). The result is that @code{flet} affects indirect calls to a |
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1824 function as well as calls directly inside the @code{flet} form itself. |
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1825 |
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1826 You can use @code{flet} to disable or modify the behavior of a function in a |
|
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1827 temporary fashion. This will even work on XEmacs primitives, although note |
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1828 that some calls to primitive functions internal to XEmacs are made without |
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1829 going through the symbol's function cell, and so will not be affected by |
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1830 @code{flet}. For example, |
| 428 | 1831 |
| 1832 @example | |
| 1833 (flet ((message (&rest args) (push args saved-msgs))) | |
| 1834 (do-something)) | |
| 1835 @end example | |
| 1836 | |
|
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1837 This code attempts to replace the built-in function @code{message} with a |
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1838 function that simply saves the messages in a list rather than displaying them. |
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1839 The original definition of @code{message} will be restored after |
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1840 @code{do-something} exits. This code will work fine on messages generated by |
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1841 other Lisp code, but messages generated directly inside XEmacs will not be |
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1842 caught since they make direct C-language calls to the message routines rather |
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1843 than going through the Lisp @code{message} function. |
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1844 |
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1845 This is equally true for functions with associated byte codes, since they are |
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1846 also not accessed through the Lisp function slot. The byte compiler will |
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1847 warn in both these cases. |
|
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1848 @end defmac |
| 428 | 1849 |
| 1850 @node Macro Bindings, , Function Bindings, Variable Bindings | |
| 1851 @subsection Macro Bindings | |
| 1852 | |
| 1853 @noindent | |
| 1854 These forms create local macros and ``symbol macros.'' | |
| 1855 | |
|
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1856 @defmac macrolet (bindings@dots{}) forms@dots{} |
| 428 | 1857 This form is analogous to @code{flet}, but for macros instead of |
| 1858 functions. Each @var{binding} is a list of the same form as the | |
| 1859 arguments to @code{defmacro*} (i.e., a macro name, argument list, | |
| 1860 and macro-expander forms). The macro is defined accordingly for | |
| 1861 use within the body of the @code{macrolet}. | |
| 1862 | |
| 1863 Because of the nature of macros, @code{macrolet} is lexically | |
| 1864 scoped even in Emacs Lisp: The @code{macrolet} binding will | |
| 1865 affect only calls that appear physically within the body | |
| 1866 @var{forms}, possibly after expansion of other macros in the | |
| 1867 body. | |
|
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1868 @end defmac |
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1869 |
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1870 @defmac symbol-macrolet (bindings@dots{}) forms@dots{} |
| 428 | 1871 This form creates @dfn{symbol macros}, which are macros that look |
| 1872 like variable references rather than function calls. Each | |
| 1873 @var{binding} is a list @samp{(@var{var} @var{expansion})}; | |
| 1874 any reference to @var{var} within the body @var{forms} is | |
| 1875 replaced by @var{expansion}. | |
| 1876 | |
| 1877 @example | |
| 1878 (setq bar '(5 . 9)) | |
| 1879 (symbol-macrolet ((foo (car bar))) | |
| 1880 (incf foo)) | |
| 1881 bar | |
| 1882 @result{} (6 . 9) | |
| 1883 @end example | |
| 1884 | |
| 1885 A @code{setq} of a symbol macro is treated the same as a @code{setf}. | |
| 1886 I.e., @code{(setq foo 4)} in the above would be equivalent to | |
| 1887 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}. | |
| 1888 | |
| 1889 Likewise, a @code{let} or @code{let*} binding a symbol macro is | |
| 1890 treated like a @code{letf} or @code{letf*}. This differs from true | |
| 1891 Common Lisp, where the rules of lexical scoping cause a @code{let} | |
| 1892 binding to shadow a @code{symbol-macrolet} binding. In this package, | |
| 1893 only @code{lexical-let} and @code{lexical-let*} will shadow a symbol | |
| 1894 macro. | |
| 1895 | |
| 1896 There is no analogue of @code{defmacro} for symbol macros; all symbol | |
| 1897 macros are local. A typical use of @code{symbol-macrolet} is in the | |
| 1898 expansion of another macro: | |
| 1899 | |
| 1900 @example | |
| 1901 (defmacro* my-dolist ((x list) &rest body) | |
| 1902 (let ((var (gensym))) | |
| 1903 (list 'loop 'for var 'on list 'do | |
| 1904 (list* 'symbol-macrolet (list (list x (list 'car var))) | |
| 1905 body)))) | |
| 1906 | |
| 1907 (setq mylist '(1 2 3 4)) | |
| 1908 (my-dolist (x mylist) (incf x)) | |
| 1909 mylist | |
| 1910 @result{} (2 3 4 5) | |
| 1911 @end example | |
| 1912 | |
| 1913 @noindent | |
| 1914 In this example, the @code{my-dolist} macro is similar to @code{dolist} | |
| 1915 (@pxref{Iteration}) except that the variable @code{x} becomes a true | |
| 1916 reference onto the elements of the list. The @code{my-dolist} call | |
| 1917 shown here expands to | |
| 1918 | |
| 1919 @example | |
| 1920 (loop for G1234 on mylist do | |
| 1921 (symbol-macrolet ((x (car G1234))) | |
| 1922 (incf x))) | |
| 1923 @end example | |
| 1924 | |
| 1925 @noindent | |
| 1926 which in turn expands to | |
| 1927 | |
| 1928 @example | |
| 1929 (loop for G1234 on mylist do (incf (car G1234))) | |
| 1930 @end example | |
| 1931 | |
| 1932 @xref{Loop Facility}, for a description of the @code{loop} macro. | |
| 1933 This package defines a nonstandard @code{in-ref} loop clause that | |
| 1934 works much like @code{my-dolist}. | |
|
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1935 @end defmac |
| 428 | 1936 |
| 1937 @node Conditionals, Blocks and Exits, Variable Bindings, Control Structure | |
| 1938 @section Conditionals | |
| 1939 | |
| 1940 @noindent | |
| 1941 These conditional forms augment Emacs Lisp's simple @code{if}, | |
| 1942 @code{and}, @code{or}, and @code{cond} forms. | |
| 1943 | |
|
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1944 @defmac when test forms@dots{} |
| 428 | 1945 This is a variant of @code{if} where there are no ``else'' forms, |
| 1946 and possibly several ``then'' forms. In particular, | |
| 1947 | |
| 1948 @example | |
| 1949 (when @var{test} @var{a} @var{b} @var{c}) | |
| 1950 @end example | |
| 1951 | |
| 1952 @noindent | |
| 1953 is entirely equivalent to | |
| 1954 | |
| 1955 @example | |
| 1956 (if @var{test} (progn @var{a} @var{b} @var{c}) nil) | |
| 1957 @end example | |
|
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1958 @end defmac |
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1959 |
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1960 @defmac unless test forms@dots{} |
| 428 | 1961 This is a variant of @code{if} where there are no ``then'' forms, |
| 1962 and possibly several ``else'' forms: | |
| 1963 | |
| 1964 @example | |
| 1965 (unless @var{test} @var{a} @var{b} @var{c}) | |
| 1966 @end example | |
| 1967 | |
| 1968 @noindent | |
| 1969 is entirely equivalent to | |
| 1970 | |
| 1971 @example | |
| 1972 (when (not @var{test}) @var{a} @var{b} @var{c}) | |
| 1973 @end example | |
|
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1974 @end defmac |
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1975 |
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1976 @defmac case keyform clause@dots{} |
| 428 | 1977 This macro evaluates @var{keyform}, then compares it with the key |
| 1978 values listed in the various @var{clause}s. Whichever clause matches | |
| 1979 the key is executed; comparison is done by @code{eql}. If no clause | |
| 1980 matches, the @code{case} form returns @code{nil}. The clauses are | |
| 1981 of the form | |
| 1982 | |
| 1983 @example | |
| 1984 (@var{keylist} @var{body-forms}@dots{}) | |
| 1985 @end example | |
| 1986 | |
| 1987 @noindent | |
| 1988 where @var{keylist} is a list of key values. If there is exactly | |
| 1989 one value, and it is not a cons cell or the symbol @code{nil} or | |
| 1990 @code{t}, then it can be used by itself as a @var{keylist} without | |
| 1991 being enclosed in a list. All key values in the @code{case} form | |
| 1992 must be distinct. The final clauses may use @code{t} in place of | |
| 1993 a @var{keylist} to indicate a default clause that should be taken | |
| 1994 if none of the other clauses match. (The symbol @code{otherwise} | |
| 1995 is also recognized in place of @code{t}. To make a clause that | |
| 1996 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise}, | |
| 1997 enclose the symbol in a list.) | |
| 1998 | |
| 1999 For example, this expression reads a keystroke, then does one of | |
| 2000 four things depending on whether it is an @samp{a}, a @samp{b}, | |
| 2001 a @key{RET} or @key{LFD}, or anything else. | |
| 2002 | |
| 2003 @example | |
| 2004 (case (read-char) | |
| 2005 (?a (do-a-thing)) | |
| 2006 (?b (do-b-thing)) | |
| 2007 ((?\r ?\n) (do-ret-thing)) | |
| 2008 (t (do-other-thing))) | |
| 2009 @end example | |
|
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2010 @end defmac |
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2011 |
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2012 @defmac ecase keyform clause@dots{} |
| 428 | 2013 This macro is just like @code{case}, except that if the key does |
| 2014 not match any of the clauses, an error is signalled rather than | |
| 2015 simply returning @code{nil}. | |
|
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2016 @end defmac |
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2017 |
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2018 @defmac typecase keyform clause@dots{} |
| 428 | 2019 This macro is a version of @code{case} that checks for types |
| 2020 rather than values. Each @var{clause} is of the form | |
| 2021 @samp{(@var{type} @var{body}...)}. @xref{Type Predicates}, | |
| 2022 for a description of type specifiers. For example, | |
| 2023 | |
| 2024 @example | |
| 2025 (typecase x | |
| 2026 (integer (munch-integer x)) | |
| 2027 (float (munch-float x)) | |
| 2028 (string (munch-integer (string-to-int x))) | |
| 2029 (t (munch-anything x))) | |
| 2030 @end example | |
| 2031 | |
| 2032 The type specifier @code{t} matches any type of object; the word | |
| 2033 @code{otherwise} is also allowed. To make one clause match any of | |
| 2034 several types, use an @code{(or ...)} type specifier. | |
|
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2035 @end defmac |
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2036 |
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2037 @defmac etypecase keyform clause@dots{} |
| 428 | 2038 This macro is just like @code{typecase}, except that if the key does |
| 2039 not match any of the clauses, an error is signalled rather than | |
| 2040 simply returning @code{nil}. | |
|
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2041 @end defmac |
| 428 | 2042 |
| 2043 @node Blocks and Exits, Iteration, Conditionals, Control Structure | |
| 2044 @section Blocks and Exits | |
| 2045 | |
| 2046 @noindent | |
| 2047 Common Lisp @dfn{blocks} provide a non-local exit mechanism very | |
| 2048 similar to @code{catch} and @code{throw}, but lexically rather than | |
| 2049 dynamically scoped. This package actually implements @code{block} | |
| 2050 in terms of @code{catch}; however, the lexical scoping allows the | |
| 2051 optimizing byte-compiler to omit the costly @code{catch} step if the | |
| 2052 body of the block does not actually @code{return-from} the block. | |
| 2053 | |
|
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2054 @defmac block name forms@dots{} |
| 428 | 2055 The @var{forms} are evaluated as if by a @code{progn}. However, |
| 2056 if any of the @var{forms} execute @code{(return-from @var{name})}, | |
| 2057 they will jump out and return directly from the @code{block} form. | |
| 2058 The @code{block} returns the result of the last @var{form} unless | |
| 2059 a @code{return-from} occurs. | |
| 2060 | |
| 2061 The @code{block}/@code{return-from} mechanism is quite similar to | |
| 2062 the @code{catch}/@code{throw} mechanism. The main differences are | |
| 2063 that block @var{name}s are unevaluated symbols, rather than forms | |
| 2064 (such as quoted symbols) which evaluate to a tag at run-time; and | |
| 2065 also that blocks are lexically scoped whereas @code{catch}/@code{throw} | |
| 2066 are dynamically scoped. This means that functions called from the | |
| 2067 body of a @code{catch} can also @code{throw} to the @code{catch}, | |
| 2068 but the @code{return-from} referring to a block name must appear | |
| 2069 physically within the @var{forms} that make up the body of the block. | |
| 2070 They may not appear within other called functions, although they may | |
| 2071 appear within macro expansions or @code{lambda}s in the body. Block | |
| 2072 names and @code{catch} names form independent name-spaces. | |
| 2073 | |
| 2074 In true Common Lisp, @code{defun} and @code{defmacro} surround | |
| 2075 the function or expander bodies with implicit blocks with the | |
| 2076 same name as the function or macro. This does not occur in Emacs | |
| 2077 Lisp, but this package provides @code{defun*} and @code{defmacro*} | |
| 2078 forms which do create the implicit block. | |
| 2079 | |
| 2080 The Common Lisp looping constructs defined by this package, | |
| 2081 such as @code{loop} and @code{dolist}, also create implicit blocks | |
| 2082 just as in Common Lisp. | |
| 2083 | |
| 2084 Because they are implemented in terms of Emacs Lisp @code{catch} | |
| 2085 and @code{throw}, blocks have the same overhead as actual | |
| 2086 @code{catch} constructs (roughly two function calls). However, | |
| 2087 Zawinski and Furuseth's optimizing byte compiler (standard in | |
| 2088 Emacs 19) will optimize away the @code{catch} if the block does | |
| 2089 not in fact contain any @code{return} or @code{return-from} calls | |
| 2090 that jump to it. This means that @code{do} loops and @code{defun*} | |
| 2091 functions which don't use @code{return} don't pay the overhead to | |
| 2092 support it. | |
|
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2093 @end defmac |
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2094 |
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2095 @defmac return-from name [result] |
| 428 | 2096 This macro returns from the block named @var{name}, which must be |
| 2097 an (unevaluated) symbol. If a @var{result} form is specified, it | |
| 2098 is evaluated to produce the result returned from the @code{block}. | |
| 2099 Otherwise, @code{nil} is returned. | |
|
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2100 @end defmac |
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2101 |
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2102 @defmac return [result] |
| 428 | 2103 This macro is exactly like @code{(return-from nil @var{result})}. |
| 2104 Common Lisp loops like @code{do} and @code{dolist} implicitly enclose | |
| 2105 themselves in @code{nil} blocks. | |
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2106 @end defmac |
| 428 | 2107 |
| 2108 @node Iteration, Loop Facility, Blocks and Exits, Control Structure | |
| 2109 @section Iteration | |
| 2110 | |
| 2111 @noindent | |
| 2112 The macros described here provide more sophisticated, high-level | |
| 2113 looping constructs to complement Emacs Lisp's basic @code{while} | |
| 2114 loop. | |
| 2115 | |
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2116 @defmac loop forms@dots{} |
| 428 | 2117 The @dfn{CL} package supports both the simple, old-style meaning of |
| 2118 @code{loop} and the extremely powerful and flexible feature known as | |
| 2119 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced | |
| 2120 facility is discussed in the following section; @pxref{Loop Facility}. | |
| 2121 The simple form of @code{loop} is described here. | |
| 2122 | |
| 2123 If @code{loop} is followed by zero or more Lisp expressions, | |
| 2124 then @code{(loop @var{exprs}@dots{})} simply creates an infinite | |
| 2125 loop executing the expressions over and over. The loop is | |
| 2126 enclosed in an implicit @code{nil} block. Thus, | |
| 2127 | |
| 2128 @example | |
| 2129 (loop (foo) (if (no-more) (return 72)) (bar)) | |
| 2130 @end example | |
| 2131 | |
| 2132 @noindent | |
| 2133 is exactly equivalent to | |
| 2134 | |
| 2135 @example | |
| 2136 (block nil (while t (foo) (if (no-more) (return 72)) (bar))) | |
| 2137 @end example | |
| 2138 | |
| 2139 If any of the expressions are plain symbols, the loop is instead | |
| 2140 interpreted as a Loop Macro specification as described later. | |
| 2141 (This is not a restriction in practice, since a plain symbol | |
| 2142 in the above notation would simply access and throw away the | |
| 2143 value of a variable.) | |
|
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2144 @end defmac |
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2145 |
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2146 @defmac do (spec@dots{}) (end-test [result@dots{}]) forms@dots{} |
| 428 | 2147 This macro creates a general iterative loop. Each @var{spec} is |
| 2148 of the form | |
| 2149 | |
| 2150 @example | |
| 2151 (@var{var} [@var{init} [@var{step}]]) | |
| 2152 @end example | |
| 2153 | |
| 2154 The loop works as follows: First, each @var{var} is bound to the | |
| 2155 associated @var{init} value as if by a @code{let} form. Then, in | |
| 2156 each iteration of the loop, the @var{end-test} is evaluated; if | |
| 2157 true, the loop is finished. Otherwise, the body @var{forms} are | |
| 2158 evaluated, then each @var{var} is set to the associated @var{step} | |
| 2159 expression (as if by a @code{psetq} form) and the next iteration | |
| 2160 begins. Once the @var{end-test} becomes true, the @var{result} | |
| 2161 forms are evaluated (with the @var{var}s still bound to their | |
| 2162 values) to produce the result returned by @code{do}. | |
| 2163 | |
| 2164 The entire @code{do} loop is enclosed in an implicit @code{nil} | |
| 2165 block, so that you can use @code{(return)} to break out of the | |
| 2166 loop at any time. | |
| 2167 | |
| 2168 If there are no @var{result} forms, the loop returns @code{nil}. | |
| 2169 If a given @var{var} has no @var{step} form, it is bound to its | |
| 2170 @var{init} value but not otherwise modified during the @code{do} | |
| 2171 loop (unless the code explicitly modifies it); this case is just | |
| 2172 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})} | |
| 2173 around the loop. If @var{init} is also omitted it defaults to | |
| 2174 @code{nil}, and in this case a plain @samp{@var{var}} can be used | |
| 2175 in place of @samp{(@var{var})}, again following the analogy with | |
| 2176 @code{let}. | |
| 2177 | |
| 2178 This example (from Steele) illustrates a loop which applies the | |
| 2179 function @code{f} to successive pairs of values from the lists | |
| 2180 @code{foo} and @code{bar}; it is equivalent to the call | |
| 2181 @code{(mapcar* 'f foo bar)}. Note that this loop has no body | |
| 2182 @var{forms} at all, performing all its work as side effects of | |
| 2183 the rest of the loop. | |
| 2184 | |
| 2185 @example | |
| 2186 (do ((x foo (cdr x)) | |
| 2187 (y bar (cdr y)) | |
| 2188 (z nil (cons (f (car x) (car y)) z))) | |
| 2189 ((or (null x) (null y)) | |
| 2190 (nreverse z))) | |
| 2191 @end example | |
|
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2192 @end defmac |
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2193 |
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2194 @defmac do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{} |
| 428 | 2195 This is to @code{do} what @code{let*} is to @code{let}. In |
| 2196 particular, the initial values are bound as if by @code{let*} | |
| 2197 rather than @code{let}, and the steps are assigned as if by | |
| 2198 @code{setq} rather than @code{psetq}. | |
| 2199 | |
| 2200 Here is another way to write the above loop: | |
| 2201 | |
| 2202 @example | |
| 2203 (do* ((xp foo (cdr xp)) | |
| 2204 (yp bar (cdr yp)) | |
| 2205 (x (car xp) (car xp)) | |
| 2206 (y (car yp) (car yp)) | |
| 2207 z) | |
| 2208 ((or (null xp) (null yp)) | |
| 2209 (nreverse z)) | |
| 2210 (push (f x y) z)) | |
| 2211 @end example | |
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2212 @end defmac |
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2213 |
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2214 @defmac dolist (var list [result]) forms@dots{} |
| 428 | 2215 This is a more specialized loop which iterates across the elements |
| 2216 of a list. @var{list} should evaluate to a list; the body @var{forms} | |
| 2217 are executed with @var{var} bound to each element of the list in | |
| 2218 turn. Finally, the @var{result} form (or @code{nil}) is evaluated | |
| 2219 with @var{var} bound to @code{nil} to produce the result returned by | |
| 2220 the loop. The loop is surrounded by an implicit @code{nil} block. | |
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2221 @end defmac |
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2222 |
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2223 @defmac dotimes (var count [result]) forms@dots{} |
| 428 | 2224 This is a more specialized loop which iterates a specified number |
| 2225 of times. The body is executed with @var{var} bound to the integers | |
| 2226 from zero (inclusive) to @var{count} (exclusive), in turn. Then | |
| 2227 the @code{result} form is evaluated with @var{var} bound to the total | |
| 2228 number of iterations that were done (i.e., @code{(max 0 @var{count})}) | |
| 2229 to get the return value for the loop form. The loop is surrounded | |
| 2230 by an implicit @code{nil} block. | |
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2231 @end defmac |
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2232 |
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2233 @defmac do-symbols (var [obarray [result]]) forms@dots{} |
| 428 | 2234 This loop iterates over all interned symbols. If @var{obarray} |
| 2235 is specified and is not @code{nil}, it loops over all symbols in | |
| 2236 that obarray. For each symbol, the body @var{forms} are evaluated | |
| 2237 with @var{var} bound to that symbol. The symbols are visited in | |
| 2238 an unspecified order. Afterward the @var{result} form, if any, | |
| 2239 is evaluated (with @var{var} bound to @code{nil}) to get the return | |
| 2240 value. The loop is surrounded by an implicit @code{nil} block. | |
|
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2241 @end defmac |
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2242 |
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2243 @defmac do-all-symbols (var [result]) forms@dots{} |
| 428 | 2244 This is identical to @code{do-symbols} except that the @var{obarray} |
| 2245 argument is omitted; it always iterates over the default obarray. | |
|
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2246 @end defmac |
| 428 | 2247 |
| 2248 @xref{Mapping over Sequences}, for some more functions for | |
| 2249 iterating over vectors or lists. | |
| 2250 | |
| 2251 @node Loop Facility, Multiple Values, Iteration, Control Structure | |
| 2252 @section Loop Facility | |
| 2253 | |
| 2254 @noindent | |
| 2255 A common complaint with Lisp's traditional looping constructs is | |
| 2256 that they are either too simple and limited, such as Common Lisp's | |
| 2257 @code{dotimes} or Emacs Lisp's @code{while}, or too unreadable and | |
| 2258 obscure, like Common Lisp's @code{do} loop. | |
| 2259 | |
| 2260 To remedy this, recent versions of Common Lisp have added a new | |
| 2261 construct called the ``Loop Facility'' or ``@code{loop} macro,'' | |
| 2262 with an easy-to-use but very powerful and expressive syntax. | |
| 2263 | |
| 2264 @menu | |
| 2265 * Loop Basics:: `loop' macro, basic clause structure | |
| 2266 * Loop Examples:: Working examples of `loop' macro | |
| 2267 * For Clauses:: Clauses introduced by `for' or `as' | |
| 2268 * Iteration Clauses:: `repeat', `while', `thereis', etc. | |
| 2269 * Accumulation Clauses:: `collect', `sum', `maximize', etc. | |
| 2270 * Other Clauses:: `with', `if', `initially', `finally' | |
| 2271 @end menu | |
| 2272 | |
| 2273 @node Loop Basics, Loop Examples, Loop Facility, Loop Facility | |
| 2274 @subsection Loop Basics | |
| 2275 | |
| 2276 @noindent | |
| 2277 The @code{loop} macro essentially creates a mini-language within | |
| 2278 Lisp that is specially tailored for describing loops. While this | |
| 2279 language is a little strange-looking by the standards of regular Lisp, | |
| 2280 it turns out to be very easy to learn and well-suited to its purpose. | |
| 2281 | |
| 2282 Since @code{loop} is a macro, all parsing of the loop language | |
| 2283 takes place at byte-compile time; compiled @code{loop}s are just | |
| 2284 as efficient as the equivalent @code{while} loops written longhand. | |
| 2285 | |
|
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Aidan Kehoe <kehoea@parhasard.net>
parents:
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|
2286 @defmac loop clauses@dots{} |
| 428 | 2287 A loop construct consists of a series of @var{clause}s, each |
| 2288 introduced by a symbol like @code{for} or @code{do}. Clauses | |
| 2289 are simply strung together in the argument list of @code{loop}, | |
| 2290 with minimal extra parentheses. The various types of clauses | |
| 2291 specify initializations, such as the binding of temporary | |
| 2292 variables, actions to be taken in the loop, stepping actions, | |
| 2293 and final cleanup. | |
| 2294 | |
| 2295 Common Lisp specifies a certain general order of clauses in a | |
| 2296 loop: | |
| 2297 | |
| 2298 @example | |
| 2299 (loop @var{name-clause} | |
| 2300 @var{var-clauses}@dots{} | |
| 2301 @var{action-clauses}@dots{}) | |
| 2302 @end example | |
| 2303 | |
| 2304 The @var{name-clause} optionally gives a name to the implicit | |
| 2305 block that surrounds the loop. By default, the implicit block | |
| 2306 is named @code{nil}. The @var{var-clauses} specify what | |
| 2307 variables should be bound during the loop, and how they should | |
| 2308 be modified or iterated throughout the course of the loop. The | |
| 2309 @var{action-clauses} are things to be done during the loop, such | |
| 2310 as computing, collecting, and returning values. | |
| 2311 | |
| 2312 The Emacs version of the @code{loop} macro is less restrictive about | |
| 2313 the order of clauses, but things will behave most predictably if | |
| 2314 you put the variable-binding clauses @code{with}, @code{for}, and | |
| 2315 @code{repeat} before the action clauses. As in Common Lisp, | |
| 2316 @code{initially} and @code{finally} clauses can go anywhere. | |
| 2317 | |
| 2318 Loops generally return @code{nil} by default, but you can cause | |
| 2319 them to return a value by using an accumulation clause like | |
| 2320 @code{collect}, an end-test clause like @code{always}, or an | |
| 2321 explicit @code{return} clause to jump out of the implicit block. | |
| 2322 (Because the loop body is enclosed in an implicit block, you can | |
| 2323 also use regular Lisp @code{return} or @code{return-from} to | |
| 2324 break out of the loop.) | |
|
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Aidan Kehoe <kehoea@parhasard.net>
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|
2325 @end defmac |
| 428 | 2326 |
| 2327 The following sections give some examples of the Loop Macro in | |
| 2328 action, and describe the particular loop clauses in great detail. | |
| 2329 Consult the second edition of Steele's @dfn{Common Lisp, the Language}, | |
| 2330 for additional discussion and examples of the @code{loop} macro. | |
| 2331 | |
| 2332 @node Loop Examples, For Clauses, Loop Basics, Loop Facility | |
| 2333 @subsection Loop Examples | |
| 2334 | |
| 2335 @noindent | |
| 2336 Before listing the full set of clauses that are allowed, let's | |
| 2337 look at a few example loops just to get a feel for the @code{loop} | |
| 2338 language. | |
| 2339 | |
| 2340 @example | |
| 2341 (loop for buf in (buffer-list) | |
| 2342 collect (buffer-file-name buf)) | |
| 2343 @end example | |
| 2344 | |
| 2345 @noindent | |
| 2346 This loop iterates over all Emacs buffers, using the list | |
| 2347 returned by @code{buffer-list}. For each buffer @code{buf}, | |
| 2348 it calls @code{buffer-file-name} and collects the results into | |
| 2349 a list, which is then returned from the @code{loop} construct. | |
| 2350 The result is a list of the file names of all the buffers in | |
| 2351 Emacs' memory. The words @code{for}, @code{in}, and @code{collect} | |
| 2352 are reserved words in the @code{loop} language. | |
| 2353 | |
| 2354 @example | |
| 2355 (loop repeat 20 do (insert "Yowsa\n")) | |
| 2356 @end example | |
| 2357 | |
| 2358 @noindent | |
| 2359 This loop inserts the phrase ``Yowsa'' twenty times in the | |
| 2360 current buffer. | |
| 2361 | |
| 2362 @example | |
| 2363 (loop until (eobp) do (munch-line) (forward-line 1)) | |
| 2364 @end example | |
| 2365 | |
| 2366 @noindent | |
| 2367 This loop calls @code{munch-line} on every line until the end | |
| 2368 of the buffer. If point is already at the end of the buffer, | |
| 2369 the loop exits immediately. | |
| 2370 | |
| 2371 @example | |
| 2372 (loop do (munch-line) until (eobp) do (forward-line 1)) | |
| 2373 @end example | |
| 2374 | |
| 2375 @noindent | |
| 2376 This loop is similar to the above one, except that @code{munch-line} | |
| 2377 is always called at least once. | |
| 2378 | |
| 2379 @example | |
| 2380 (loop for x from 1 to 100 | |
| 2381 for y = (* x x) | |
| 2382 until (>= y 729) | |
| 2383 finally return (list x (= y 729))) | |
| 2384 @end example | |
| 2385 | |
| 2386 @noindent | |
| 2387 This more complicated loop searches for a number @code{x} whose | |
| 2388 square is 729. For safety's sake it only examines @code{x} | |
| 2389 values up to 100; dropping the phrase @samp{to 100} would | |
| 2390 cause the loop to count upwards with no limit. The second | |
| 2391 @code{for} clause defines @code{y} to be the square of @code{x} | |
| 2392 within the loop; the expression after the @code{=} sign is | |
| 2393 reevaluated each time through the loop. The @code{until} | |
| 2394 clause gives a condition for terminating the loop, and the | |
| 2395 @code{finally} clause says what to do when the loop finishes. | |
| 2396 (This particular example was written less concisely than it | |
| 2397 could have been, just for the sake of illustration.) | |
| 2398 | |
| 2399 Note that even though this loop contains three clauses (two | |
| 2400 @code{for}s and an @code{until}) that would have been enough to | |
| 2401 define loops all by themselves, it still creates a single loop | |
| 2402 rather than some sort of triple-nested loop. You must explicitly | |
| 2403 nest your @code{loop} constructs if you want nested loops. | |
| 2404 | |
| 2405 @node For Clauses, Iteration Clauses, Loop Examples, Loop Facility | |
| 2406 @subsection For Clauses | |
| 2407 | |
| 2408 @noindent | |
| 2409 Most loops are governed by one or more @code{for} clauses. | |
| 2410 A @code{for} clause simultaneously describes variables to be | |
| 2411 bound, how those variables are to be stepped during the loop, | |
| 2412 and usually an end condition based on those variables. | |
| 2413 | |
| 2414 The word @code{as} is a synonym for the word @code{for}. This | |
| 2415 word is followed by a variable name, then a word like @code{from} | |
| 2416 or @code{across} that describes the kind of iteration desired. | |
| 2417 In Common Lisp, the phrase @code{being the} sometimes precedes | |
| 2418 the type of iteration; in this package both @code{being} and | |
| 2419 @code{the} are optional. The word @code{each} is a synonym | |
| 2420 for @code{the}, and the word that follows it may be singular | |
| 2421 or plural: @samp{for x being the elements of y} or | |
| 2422 @samp{for x being each element of y}. Which form you use | |
| 2423 is purely a matter of style. | |
| 2424 | |
| 2425 The variable is bound around the loop as if by @code{let}: | |
| 2426 | |
| 2427 @example | |
| 2428 (setq i 'happy) | |
| 2429 (loop for i from 1 to 10 do (do-something-with i)) | |
| 2430 i | |
| 2431 @result{} happy | |
| 2432 @end example | |
| 2433 | |
| 2434 @table @code | |
| 2435 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3} | |
| 2436 This type of @code{for} clause creates a counting loop. Each of | |
| 2437 the three sub-terms is optional, though there must be at least one | |
| 2438 term so that the clause is marked as a counting clause. | |
| 2439 | |
| 2440 The three expressions are the starting value, the ending value, and | |
| 2441 the step value, respectively, of the variable. The loop counts | |
| 2442 upwards by default (@var{expr3} must be positive), from @var{expr1} | |
| 2443 to @var{expr2} inclusively. If you omit the @code{from} term, the | |
| 2444 loop counts from zero; if you omit the @code{to} term, the loop | |
| 2445 counts forever without stopping (unless stopped by some other | |
| 2446 loop clause, of course); if you omit the @code{by} term, the loop | |
| 2447 counts in steps of one. | |
| 2448 | |
| 2449 You can replace the word @code{from} with @code{upfrom} or | |
| 2450 @code{downfrom} to indicate the direction of the loop. Likewise, | |
| 2451 you can replace @code{to} with @code{upto} or @code{downto}. | |
| 2452 For example, @samp{for x from 5 downto 1} executes five times | |
| 2453 with @code{x} taking on the integers from 5 down to 1 in turn. | |
| 2454 Also, you can replace @code{to} with @code{below} or @code{above}, | |
| 2455 which are like @code{upto} and @code{downto} respectively except | |
| 2456 that they are exclusive rather than inclusive limits: | |
| 2457 | |
| 2458 @example | |
| 2459 (loop for x to 10 collect x) | |
| 2460 @result{} (0 1 2 3 4 5 6 7 8 9 10) | |
| 2461 (loop for x below 10 collect x) | |
| 2462 @result{} (0 1 2 3 4 5 6 7 8 9) | |
| 2463 @end example | |
| 2464 | |
| 2465 The @code{by} value is always positive, even for downward-counting | |
| 2466 loops. Some sort of @code{from} value is required for downward | |
| 2467 loops; @samp{for x downto 5} is not a legal loop clause all by | |
| 2468 itself. | |
| 2469 | |
| 2470 @item for @var{var} in @var{list} by @var{function} | |
| 2471 This clause iterates @var{var} over all the elements of @var{list}, | |
| 2472 in turn. If you specify the @code{by} term, then @var{function} | |
| 2473 is used to traverse the list instead of @code{cdr}; it must be a | |
| 2474 function taking one argument. For example: | |
| 2475 | |
| 2476 @example | |
| 2477 (loop for x in '(1 2 3 4 5 6) collect (* x x)) | |
| 2478 @result{} (1 4 9 16 25 36) | |
| 2479 (loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x)) | |
| 2480 @result{} (1 9 25) | |
| 2481 @end example | |
| 2482 | |
| 2483 @item for @var{var} on @var{list} by @var{function} | |
| 2484 This clause iterates @var{var} over all the cons cells of @var{list}. | |
| 2485 | |
| 2486 @example | |
| 2487 (loop for x on '(1 2 3 4) collect x) | |
| 2488 @result{} ((1 2 3 4) (2 3 4) (3 4) (4)) | |
| 2489 @end example | |
| 2490 | |
| 2491 With @code{by}, there is no real reason that the @code{on} expression | |
| 2492 must be a list. For example: | |
| 2493 | |
| 2494 @example | |
| 2495 (loop for x on first-animal by 'next-animal collect x) | |
| 2496 @end example | |
| 2497 | |
| 2498 @noindent | |
| 2499 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns | |
| 2500 the next in the (assumed) sequence of animals, or @code{nil} if | |
| 2501 @var{x} was the last animal in the sequence. | |
| 2502 | |
| 2503 @item for @var{var} in-ref @var{list} by @var{function} | |
| 2504 This is like a regular @code{in} clause, but @var{var} becomes | |
| 2505 a @code{setf}-able ``reference'' onto the elements of the list | |
| 2506 rather than just a temporary variable. For example, | |
| 2507 | |
| 2508 @example | |
| 2509 (loop for x in-ref my-list do (incf x)) | |
| 2510 @end example | |
| 2511 | |
| 2512 @noindent | |
| 2513 increments every element of @code{my-list} in place. This clause | |
| 2514 is an extension to standard Common Lisp. | |
| 2515 | |
| 2516 @item for @var{var} across @var{array} | |
| 2517 This clause iterates @var{var} over all the elements of @var{array}, | |
| 2518 which may be a vector or a string. | |
| 2519 | |
| 2520 @example | |
| 2521 (loop for x across "aeiou" | |
| 2522 do (use-vowel (char-to-string x))) | |
| 2523 @end example | |
| 2524 | |
| 2525 @item for @var{var} across-ref @var{array} | |
| 2526 This clause iterates over an array, with @var{var} a @code{setf}-able | |
| 2527 reference onto the elements; see @code{in-ref} above. | |
| 2528 | |
| 2529 @item for @var{var} being the elements of @var{sequence} | |
| 2530 This clause iterates over the elements of @var{sequence}, which may | |
| 2531 be a list, vector, or string. Since the type must be determined | |
| 2532 at run-time, this is somewhat less efficient than @code{in} or | |
| 2533 @code{across}. The clause may be followed by the additional term | |
| 2534 @samp{using (index @var{var2})} to cause @var{var2} to be bound to | |
| 2535 the successive indices (starting at 0) of the elements. | |
| 2536 | |
| 2537 This clause type is taken from older versions of the @code{loop} macro, | |
| 2538 and is not present in modern Common Lisp. The @samp{using (sequence ...)} | |
| 2539 term of the older macros is not supported. | |
| 2540 | |
| 2541 @item for @var{var} being the elements of-ref @var{sequence} | |
| 2542 This clause iterates over a sequence, with @var{var} a @code{setf}-able | |
| 2543 reference onto the elements; see @code{in-ref} above. | |
| 2544 | |
| 2545 @item for @var{var} being the symbols [of @var{obarray}] | |
| 2546 This clause iterates over symbols, either over all interned symbols | |
| 2547 or over all symbols in @var{obarray}. The loop is executed with | |
| 2548 @var{var} bound to each symbol in turn. The symbols are visited in | |
| 2549 an unspecified order. | |
| 2550 | |
| 2551 As an example, | |
| 2552 | |
| 2553 @example | |
| 2554 (loop for sym being the symbols | |
| 2555 when (fboundp sym) | |
| 2556 when (string-match "^map" (symbol-name sym)) | |
| 2557 collect sym) | |
| 2558 @end example | |
| 2559 | |
| 2560 @noindent | |
| 2561 returns a list of all the functions whose names begin with @samp{map}. | |
| 2562 | |
| 2563 The Common Lisp words @code{external-symbols} and @code{present-symbols} | |
| 2564 are also recognized but are equivalent to @code{symbols} in Emacs Lisp. | |
| 2565 | |
| 2566 Due to a minor implementation restriction, it will not work to have | |
| 2567 more than one @code{for} clause iterating over symbols, hash tables, | |
| 2568 keymaps, overlays, or intervals in a given @code{loop}. Fortunately, | |
| 2569 it would rarely if ever be useful to do so. It @emph{is} legal to mix | |
| 2570 one of these types of clauses with other clauses like @code{for ... to} | |
| 2571 or @code{while}. | |
| 2572 | |
| 2573 @item for @var{var} being the hash-keys of @var{hash-table} | |
| 2574 This clause iterates over the entries in @var{hash-table}. For each | |
| 2575 hash table entry, @var{var} is bound to the entry's key. If you write | |
| 2576 @samp{the hash-values} instead, @var{var} is bound to the values | |
| 2577 of the entries. The clause may be followed by the additional | |
| 2578 term @samp{using (hash-values @var{var2})} (where @code{hash-values} | |
| 2579 is the opposite word of the word following @code{the}) to cause | |
| 2580 @var{var} and @var{var2} to be bound to the two parts of each | |
| 2581 hash table entry. | |
| 2582 | |
| 2583 @item for @var{var} being the key-codes of @var{keymap} | |
| 2584 This clause iterates over the entries in @var{keymap}. In GNU Emacs 18 | |
| 2585 and 19, keymaps are either alists or vectors, and key-codes are integers | |
| 2586 or symbols. In XEmacs, keymaps are a special new data type, and | |
| 2587 key-codes are symbols or lists of symbols. The iteration does not enter | |
| 2588 nested keymaps or inherited (parent) keymaps. You can use @samp{the | |
| 2589 key-bindings} to access the commands bound to the keys rather than the | |
| 2590 key codes, and you can add a @code{using} clause to access both the | |
| 2591 codes and the bindings together. | |
| 2592 | |
| 2593 @item for @var{var} being the key-seqs of @var{keymap} | |
| 2594 This clause iterates over all key sequences defined by @var{keymap} | |
| 2595 and its nested keymaps, where @var{var} takes on values which are | |
| 2596 strings in Emacs 18 or vectors in Emacs 19. The strings or vectors | |
| 2597 are reused for each iteration, so you must copy them if you wish to keep | |
| 2598 them permanently. You can add a @samp{using (key-bindings ...)} | |
| 2599 clause to get the command bindings as well. | |
| 2600 | |
| 2601 @item for @var{var} being the overlays [of @var{buffer}] @dots{} | |
| 2602 This clause iterates over the Emacs 19 ``overlays'' or XEmacs | |
| 2603 ``extents'' of a buffer (the clause @code{extents} is synonymous with | |
| 2604 @code{overlays}). Under Emacs 18, this clause iterates zero times. If | |
| 2605 the @code{of} term is omitted, the current buffer is used. This clause | |
| 2606 also accepts optional @samp{from @var{pos}} and @samp{to @var{pos}} | |
| 2607 terms, limiting the clause to overlays which overlap the specified | |
| 2608 region. | |
| 2609 | |
| 2610 @item for @var{var} being the intervals [of @var{buffer}] @dots{} | |
| 2611 This clause iterates over all intervals of a buffer with constant | |
| 2612 text properties. The variable @var{var} will be bound to conses | |
| 2613 of start and end positions, where one start position is always equal | |
| 2614 to the previous end position. The clause allows @code{of}, | |
| 2615 @code{from}, @code{to}, and @code{property} terms, where the latter | |
| 2616 term restricts the search to just the specified property. The | |
| 2617 @code{of} term may specify either a buffer or a string. This | |
| 2618 clause is useful only in GNU Emacs 19; in other versions, all | |
| 2619 buffers and strings consist of a single interval. | |
| 2620 | |
| 2621 @item for @var{var} being the frames | |
| 2622 This clause iterates over all frames, i.e., X window system windows | |
| 2623 open on Emacs files. This clause works only under Emacs 19. The | |
| 2624 clause @code{screens} is a synonym for @code{frames}. The frames | |
| 2625 are visited in @code{next-frame} order starting from | |
| 2626 @code{selected-frame}. | |
| 2627 | |
| 2628 @item for @var{var} being the windows [of @var{frame}] | |
| 2629 This clause iterates over the windows (in the Emacs sense) of | |
| 2630 the current frame, or of the specified @var{frame}. (In Emacs 18 | |
| 2631 there is only ever one frame, and the @code{of} term is not | |
| 2632 allowed there.) | |
| 2633 | |
| 2634 @item for @var{var} being the buffers | |
| 2635 This clause iterates over all buffers in Emacs. It is equivalent | |
| 2636 to @samp{for @var{var} in (buffer-list)}. | |
| 2637 | |
| 2638 @item for @var{var} = @var{expr1} then @var{expr2} | |
| 2639 This clause does a general iteration. The first time through | |
| 2640 the loop, @var{var} will be bound to @var{expr1}. On the second | |
| 2641 and successive iterations it will be set by evaluating @var{expr2} | |
| 2642 (which may refer to the old value of @var{var}). For example, | |
| 2643 these two loops are effectively the same: | |
| 2644 | |
| 2645 @example | |
| 2646 (loop for x on my-list by 'cddr do ...) | |
| 2647 (loop for x = my-list then (cddr x) while x do ...) | |
| 2648 @end example | |
| 2649 | |
| 2650 Note that this type of @code{for} clause does not imply any sort | |
| 2651 of terminating condition; the above example combines it with a | |
| 2652 @code{while} clause to tell when to end the loop. | |
| 2653 | |
| 2654 If you omit the @code{then} term, @var{expr1} is used both for | |
| 2655 the initial setting and for successive settings: | |
| 2656 | |
| 2657 @example | |
| 2658 (loop for x = (random) when (> x 0) return x) | |
| 2659 @end example | |
| 2660 | |
| 2661 @noindent | |
| 2662 This loop keeps taking random numbers from the @code{(random)} | |
| 2663 function until it gets a positive one, which it then returns. | |
| 2664 @end table | |
| 2665 | |
| 2666 If you include several @code{for} clauses in a row, they are | |
| 2667 treated sequentially (as if by @code{let*} and @code{setq}). | |
| 2668 You can instead use the word @code{and} to link the clauses, | |
| 2669 in which case they are processed in parallel (as if by @code{let} | |
| 2670 and @code{psetq}). | |
| 2671 | |
| 2672 @example | |
| 2673 (loop for x below 5 for y = nil then x collect (list x y)) | |
| 2674 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4)) | |
| 2675 (loop for x below 5 and y = nil then x collect (list x y)) | |
| 2676 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3)) | |
| 2677 @end example | |
| 2678 | |
| 2679 @noindent | |
| 2680 In the first loop, @code{y} is set based on the value of @code{x} | |
| 2681 that was just set by the previous clause; in the second loop, | |
| 2682 @code{x} and @code{y} are set simultaneously so @code{y} is set | |
| 2683 based on the value of @code{x} left over from the previous time | |
| 2684 through the loop. | |
| 2685 | |
| 2686 Another feature of the @code{loop} macro is @dfn{destructuring}, | |
| 2687 similar in concept to the destructuring provided by @code{defmacro}. | |
| 2688 The @var{var} part of any @code{for} clause can be given as a list | |
| 2689 of variables instead of a single variable. The values produced | |
| 2690 during loop execution must be lists; the values in the lists are | |
| 2691 stored in the corresponding variables. | |
| 2692 | |
| 2693 @example | |
| 2694 (loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y)) | |
| 2695 @result{} (5 9 13) | |
| 2696 @end example | |
| 2697 | |
| 2698 In loop destructuring, if there are more values than variables | |
| 2699 the trailing values are ignored, and if there are more variables | |
| 2700 than values the trailing variables get the value @code{nil}. | |
| 2701 If @code{nil} is used as a variable name, the corresponding | |
| 2702 values are ignored. Destructuring may be nested, and dotted | |
| 2703 lists of variables like @code{(x . y)} are allowed. | |
| 2704 | |
| 2705 @node Iteration Clauses, Accumulation Clauses, For Clauses, Loop Facility | |
| 2706 @subsection Iteration Clauses | |
| 2707 | |
| 2708 @noindent | |
| 2709 Aside from @code{for} clauses, there are several other loop clauses | |
| 2710 that control the way the loop operates. They might be used by | |
| 2711 themselves, or in conjunction with one or more @code{for} clauses. | |
| 2712 | |
| 2713 @table @code | |
| 2714 @item repeat @var{integer} | |
| 2715 This clause simply counts up to the specified number using an | |
| 2716 internal temporary variable. The loops | |
| 2717 | |
| 2718 @example | |
| 2719 (loop repeat n do ...) | |
| 2720 (loop for temp to n do ...) | |
| 2721 @end example | |
| 2722 | |
| 2723 @noindent | |
| 2724 are identical except that the second one forces you to choose | |
| 2725 a name for a variable you aren't actually going to use. | |
| 2726 | |
| 2727 @item while @var{condition} | |
| 2728 This clause stops the loop when the specified condition (any Lisp | |
| 2729 expression) becomes @code{nil}. For example, the following two | |
| 2730 loops are equivalent, except for the implicit @code{nil} block | |
| 2731 that surrounds the second one: | |
| 2732 | |
| 2733 @example | |
| 2734 (while @var{cond} @var{forms}@dots{}) | |
| 2735 (loop while @var{cond} do @var{forms}@dots{}) | |
| 2736 @end example | |
| 2737 | |
| 2738 @item until @var{condition} | |
| 2739 This clause stops the loop when the specified condition is true, | |
| 2740 i.e., non-@code{nil}. | |
| 2741 | |
| 2742 @item always @var{condition} | |
| 2743 This clause stops the loop when the specified condition is @code{nil}. | |
| 2744 Unlike @code{while}, it stops the loop using @code{return nil} so that | |
| 2745 the @code{finally} clauses are not executed. If all the conditions | |
| 2746 were non-@code{nil}, the loop returns @code{t}: | |
| 2747 | |
| 2748 @example | |
| 2749 (if (loop for size in size-list always (> size 10)) | |
| 2750 (some-big-sizes) | |
| 2751 (no-big-sizes)) | |
| 2752 @end example | |
| 2753 | |
| 2754 @item never @var{condition} | |
| 2755 This clause is like @code{always}, except that the loop returns | |
| 2756 @code{t} if any conditions were false, or @code{nil} otherwise. | |
| 2757 | |
| 2758 @item thereis @var{condition} | |
| 2759 This clause stops the loop when the specified form is non-@code{nil}; | |
| 2760 in this case, it returns that non-@code{nil} value. If all the | |
| 2761 values were @code{nil}, the loop returns @code{nil}. | |
| 2762 @end table | |
| 2763 | |
| 2764 @node Accumulation Clauses, Other Clauses, Iteration Clauses, Loop Facility | |
| 2765 @subsection Accumulation Clauses | |
| 2766 | |
| 2767 @noindent | |
| 2768 These clauses cause the loop to accumulate information about the | |
| 2769 specified Lisp @var{form}. The accumulated result is returned | |
| 2770 from the loop unless overridden, say, by a @code{return} clause. | |
| 2771 | |
| 2772 @table @code | |
| 2773 @item collect @var{form} | |
| 2774 This clause collects the values of @var{form} into a list. Several | |
| 2775 examples of @code{collect} appear elsewhere in this manual. | |
| 2776 | |
| 2777 The word @code{collecting} is a synonym for @code{collect}, and | |
| 2778 likewise for the other accumulation clauses. | |
| 2779 | |
| 2780 @item append @var{form} | |
| 2781 This clause collects lists of values into a result list using | |
| 2782 @code{append}. | |
| 2783 | |
| 2784 @item nconc @var{form} | |
| 2785 This clause collects lists of values into a result list by | |
| 2786 destructively modifying the lists rather than copying them. | |
| 2787 | |
| 2788 @item concat @var{form} | |
| 2789 This clause concatenates the values of the specified @var{form} | |
| 2790 into a string. (It and the following clause are extensions to | |
| 2791 standard Common Lisp.) | |
| 2792 | |
| 2793 @item vconcat @var{form} | |
| 2794 This clause concatenates the values of the specified @var{form} | |
| 2795 into a vector. | |
| 2796 | |
| 2797 @item count @var{form} | |
| 2798 This clause counts the number of times the specified @var{form} | |
| 2799 evaluates to a non-@code{nil} value. | |
| 2800 | |
| 2801 @item sum @var{form} | |
| 2802 This clause accumulates the sum of the values of the specified | |
| 2803 @var{form}, which must evaluate to a number. | |
| 2804 | |
| 2805 @item maximize @var{form} | |
| 2806 This clause accumulates the maximum value of the specified @var{form}, | |
| 2807 which must evaluate to a number. The return value is undefined if | |
| 2808 @code{maximize} is executed zero times. | |
| 2809 | |
| 2810 @item minimize @var{form} | |
| 2811 This clause accumulates the minimum value of the specified @var{form}. | |
| 2812 @end table | |
| 2813 | |
| 2814 Accumulation clauses can be followed by @samp{into @var{var}} to | |
| 2815 cause the data to be collected into variable @var{var} (which is | |
| 2816 automatically @code{let}-bound during the loop) rather than an | |
| 2817 unnamed temporary variable. Also, @code{into} accumulations do | |
| 2818 not automatically imply a return value. The loop must use some | |
| 2819 explicit mechanism, such as @code{finally return}, to return | |
| 2820 the accumulated result. | |
| 2821 | |
| 2822 It is legal for several accumulation clauses of the same type to | |
| 2823 accumulate into the same place. From Steele: | |
| 2824 | |
| 2825 @example | |
| 2826 (loop for name in '(fred sue alice joe june) | |
| 2827 for kids in '((bob ken) () () (kris sunshine) ()) | |
| 2828 collect name | |
| 2829 append kids) | |
| 2830 @result{} (fred bob ken sue alice joe kris sunshine june) | |
| 2831 @end example | |
| 2832 | |
| 2833 @node Other Clauses, , Accumulation Clauses, Loop Facility | |
| 2834 @subsection Other Clauses | |
| 2835 | |
| 2836 @noindent | |
| 2837 This section describes the remaining loop clauses. | |
| 2838 | |
| 2839 @table @code | |
| 2840 @item with @var{var} = @var{value} | |
| 2841 This clause binds a variable to a value around the loop, but | |
| 2842 otherwise leaves the variable alone during the loop. The following | |
| 2843 loops are basically equivalent: | |
| 2844 | |
| 2845 @example | |
| 2846 (loop with x = 17 do ...) | |
| 2847 (let ((x 17)) (loop do ...)) | |
| 2848 (loop for x = 17 then x do ...) | |
| 2849 @end example | |
| 2850 | |
| 2851 Naturally, the variable @var{var} might be used for some purpose | |
| 2852 in the rest of the loop. For example: | |
| 2853 | |
| 2854 @example | |
| 2855 (loop for x in my-list with res = nil do (push x res) | |
| 2856 finally return res) | |
| 2857 @end example | |
| 2858 | |
| 2859 This loop inserts the elements of @code{my-list} at the front of | |
| 2860 a new list being accumulated in @code{res}, then returns the | |
| 2861 list @code{res} at the end of the loop. The effect is similar | |
| 2862 to that of a @code{collect} clause, but the list gets reversed | |
| 2863 by virtue of the fact that elements are being pushed onto the | |
| 2864 front of @code{res} rather than the end. | |
| 2865 | |
| 2866 If you omit the @code{=} term, the variable is initialized to | |
| 2867 @code{nil}. (Thus the @samp{= nil} in the above example is | |
| 2868 unnecessary.) | |
| 2869 | |
| 2870 Bindings made by @code{with} are sequential by default, as if | |
| 2871 by @code{let*}. Just like @code{for} clauses, @code{with} clauses | |
| 2872 can be linked with @code{and} to cause the bindings to be made by | |
| 2873 @code{let} instead. | |
| 2874 | |
| 2875 @item if @var{condition} @var{clause} | |
| 2876 This clause executes the following loop clause only if the specified | |
| 2877 condition is true. The following @var{clause} should be an accumulation, | |
| 2878 @code{do}, @code{return}, @code{if}, or @code{unless} clause. | |
| 2879 Several clauses may be linked by separating them with @code{and}. | |
| 2880 These clauses may be followed by @code{else} and a clause or clauses | |
| 2881 to execute if the condition was false. The whole construct may | |
| 2882 optionally be followed by the word @code{end} (which may be used to | |
| 2883 disambiguate an @code{else} or @code{and} in a nested @code{if}). | |
| 2884 | |
| 2885 The actual non-@code{nil} value of the condition form is available | |
| 2886 by the name @code{it} in the ``then'' part. For example: | |
| 2887 | |
| 2888 @example | |
| 2889 (setq funny-numbers '(6 13 -1)) | |
| 2890 @result{} (6 13 -1) | |
| 2891 (loop for x below 10 | |
| 2892 if (oddp x) | |
| 2893 collect x into odds | |
| 2894 and if (memq x funny-numbers) return (cdr it) end | |
| 2895 else | |
| 2896 collect x into evens | |
| 2897 finally return (vector odds evens)) | |
| 2898 @result{} [(1 3 5 7 9) (0 2 4 6 8)] | |
| 2899 (setq funny-numbers '(6 7 13 -1)) | |
| 2900 @result{} (6 7 13 -1) | |
| 2901 (loop <@r{same thing again}>) | |
| 2902 @result{} (13 -1) | |
| 2903 @end example | |
| 2904 | |
| 2905 Note the use of @code{and} to put two clauses into the ``then'' | |
| 2906 part, one of which is itself an @code{if} clause. Note also that | |
| 2907 @code{end}, while normally optional, was necessary here to make | |
| 2908 it clear that the @code{else} refers to the outermost @code{if} | |
| 2909 clause. In the first case, the loop returns a vector of lists | |
| 2910 of the odd and even values of @var{x}. In the second case, the | |
| 2911 odd number 7 is one of the @code{funny-numbers} so the loop | |
| 2912 returns early; the actual returned value is based on the result | |
| 2913 of the @code{memq} call. | |
| 2914 | |
| 2915 @item when @var{condition} @var{clause} | |
| 2916 This clause is just a synonym for @code{if}. | |
| 2917 | |
| 2918 @item unless @var{condition} @var{clause} | |
| 2919 The @code{unless} clause is just like @code{if} except that the | |
| 2920 sense of the condition is reversed. | |
| 2921 | |
| 2922 @item named @var{name} | |
| 2923 This clause gives a name other than @code{nil} to the implicit | |
| 2924 block surrounding the loop. The @var{name} is the symbol to be | |
| 2925 used as the block name. | |
| 2926 | |
| 2927 @item initially [do] @var{forms}... | |
| 2928 This keyword introduces one or more Lisp forms which will be | |
| 2929 executed before the loop itself begins (but after any variables | |
| 2930 requested by @code{for} or @code{with} have been bound to their | |
| 2931 initial values). @code{initially} clauses can appear anywhere; | |
| 2932 if there are several, they are executed in the order they appear | |
| 2933 in the loop. The keyword @code{do} is optional. | |
| 2934 | |
| 2935 @item finally [do] @var{forms}... | |
| 2936 This introduces Lisp forms which will be executed after the loop | |
| 2937 finishes (say, on request of a @code{for} or @code{while}). | |
| 2938 @code{initially} and @code{finally} clauses may appear anywhere | |
| 2939 in the loop construct, but they are executed (in the specified | |
| 2940 order) at the beginning or end, respectively, of the loop. | |
| 2941 | |
| 2942 @item finally return @var{form} | |
| 2943 This says that @var{form} should be executed after the loop | |
| 2944 is done to obtain a return value. (Without this, or some other | |
| 2945 clause like @code{collect} or @code{return}, the loop will simply | |
| 2946 return @code{nil}.) Variables bound by @code{for}, @code{with}, | |
| 2947 or @code{into} will still contain their final values when @var{form} | |
| 2948 is executed. | |
| 2949 | |
| 2950 @item do @var{forms}... | |
| 2951 The word @code{do} may be followed by any number of Lisp expressions | |
| 2952 which are executed as an implicit @code{progn} in the body of the | |
| 2953 loop. Many of the examples in this section illustrate the use of | |
| 2954 @code{do}. | |
| 2955 | |
| 2956 @item return @var{form} | |
| 2957 This clause causes the loop to return immediately. The following | |
| 2958 Lisp form is evaluated to give the return value of the @code{loop} | |
| 2959 form. The @code{finally} clauses, if any, are not executed. | |
| 2960 Of course, @code{return} is generally used inside an @code{if} or | |
| 2961 @code{unless}, as its use in a top-level loop clause would mean | |
| 2962 the loop would never get to ``loop'' more than once. | |
| 2963 | |
| 2964 The clause @samp{return @var{form}} is equivalent to | |
| 2965 @samp{do (return @var{form})} (or @code{return-from} if the loop | |
| 2966 was named). The @code{return} clause is implemented a bit more | |
| 2967 efficiently, though. | |
| 2968 @end table | |
| 2969 | |
| 2970 While there is no high-level way to add user extensions to @code{loop} | |
| 2971 (comparable to @code{defsetf} for @code{setf}, say), this package | |
| 2972 does offer two properties called @code{cl-loop-handler} and | |
| 2973 @code{cl-loop-for-handler} which are functions to be called when | |
| 2974 a given symbol is encountered as a top-level loop clause or | |
| 2975 @code{for} clause, respectively. Consult the source code in | |
| 2976 file @file{cl-macs.el} for details. | |
| 2977 | |
| 2978 This package's @code{loop} macro is compatible with that of Common | |
| 2979 Lisp, except that a few features are not implemented: @code{loop-finish} | |
| 2980 and data-type specifiers. Naturally, the @code{for} clauses which | |
| 2981 iterate over keymaps, overlays, intervals, frames, windows, and | |
| 2982 buffers are Emacs-specific extensions. | |
| 2983 | |
| 2984 @node Multiple Values, , Loop Facility, Control Structure | |
| 2985 @section Multiple Values | |
| 2986 | |
|
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2987 This functionality has been moved to core XEmacs, and is documented in |
|
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2988 the XEmacs Lisp reference, @pxref{(lispref.info)Multiple values}. |
| 428 | 2989 |
| 2990 @node Macros, Declarations, Control Structure, Top | |
| 2991 @chapter Macros | |
| 2992 | |
| 2993 @noindent | |
| 2994 This package implements the various Common Lisp features of | |
| 2995 @code{defmacro}, such as destructuring, @code{&environment}, | |
| 2996 and @code{&body}. Top-level @code{&whole} is not implemented | |
| 2997 for @code{defmacro} due to technical difficulties. | |
| 2998 @xref{Argument Lists}. | |
| 2999 | |
| 3000 Destructuring is made available to the user by way of the | |
| 3001 following macro: | |
| 3002 | |
|
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3003 @defmac destructuring-bind arglist expr forms@dots{} |
| 428 | 3004 This macro expands to code which executes @var{forms}, with |
| 3005 the variables in @var{arglist} bound to the list of values | |
| 3006 returned by @var{expr}. The @var{arglist} can include all | |
| 3007 the features allowed for @code{defmacro} argument lists, | |
| 3008 including destructuring. (The @code{&environment} keyword | |
| 3009 is not allowed.) The macro expansion will signal an error | |
| 3010 if @var{expr} returns a list of the wrong number of arguments | |
| 3011 or with incorrect keyword arguments. | |
|
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3012 @end defmac |
| 428 | 3013 |
| 3014 This package also includes the Common Lisp @code{define-compiler-macro} | |
| 3015 facility, which allows you to define compile-time expansions and | |
| 3016 optimizations for your functions. | |
| 3017 | |
|
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3018 @defmac define-compiler-macro name arglist forms@dots{} |
| 428 | 3019 This form is similar to @code{defmacro}, except that it only expands |
| 3020 calls to @var{name} at compile-time; calls processed by the Lisp | |
| 3021 interpreter are not expanded, nor are they expanded by the | |
| 3022 @code{macroexpand} function. | |
| 3023 | |
| 3024 The argument list may begin with a @code{&whole} keyword and a | |
| 3025 variable. This variable is bound to the macro-call form itself, | |
| 3026 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}. | |
| 3027 If the macro expander returns this form unchanged, then the | |
| 3028 compiler treats it as a normal function call. This allows | |
| 3029 compiler macros to work as optimizers for special cases of a | |
| 3030 function, leaving complicated cases alone. | |
| 3031 | |
| 3032 For example, here is a simplified version of a definition that | |
| 3033 appears as a standard part of this package: | |
| 3034 | |
| 3035 @example | |
| 3036 (define-compiler-macro member* (&whole form a list &rest keys) | |
| 3037 (if (and (null keys) | |
| 3038 (eq (car-safe a) 'quote) | |
| 3039 (not (floatp-safe (cadr a)))) | |
| 3040 (list 'memq a list) | |
| 3041 form)) | |
| 3042 @end example | |
| 3043 | |
| 3044 @noindent | |
| 3045 This definition causes @code{(member* @var{a} @var{list})} to change | |
| 3046 to a call to the faster @code{memq} in the common case where @var{a} | |
| 3047 is a non-floating-point constant; if @var{a} is anything else, or | |
| 3048 if there are any keyword arguments in the call, then the original | |
| 3049 @code{member*} call is left intact. (The actual compiler macro | |
| 3050 for @code{member*} optimizes a number of other cases, including | |
| 3051 common @code{:test} predicates.) | |
|
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|
3052 @end defmac |
| 428 | 3053 |
| 3054 @defun compiler-macroexpand form | |
| 3055 This function is analogous to @code{macroexpand}, except that it | |
| 3056 expands compiler macros rather than regular macros. It returns | |
| 3057 @var{form} unchanged if it is not a call to a function for which | |
| 3058 a compiler macro has been defined, or if that compiler macro | |
| 3059 decided to punt by returning its @code{&whole} argument. Like | |
| 3060 @code{macroexpand}, it expands repeatedly until it reaches a form | |
| 3061 for which no further expansion is possible. | |
| 3062 @end defun | |
| 3063 | |
| 3064 @xref{Macro Bindings}, for descriptions of the @code{macrolet} | |
| 3065 and @code{symbol-macrolet} forms for making ``local'' macro | |
| 3066 definitions. | |
| 3067 | |
| 3068 @node Declarations, Symbols, Macros, Top | |
| 3069 @chapter Declarations | |
| 3070 | |
| 3071 @noindent | |
| 3072 Common Lisp includes a complex and powerful ``declaration'' | |
| 3073 mechanism that allows you to give the compiler special hints | |
| 3074 about the types of data that will be stored in particular variables, | |
| 3075 and about the ways those variables and functions will be used. This | |
| 3076 package defines versions of all the Common Lisp declaration forms: | |
| 3077 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim}, | |
| 3078 and @code{the}. | |
| 3079 | |
| 3080 Most of the Common Lisp declarations are not currently useful in | |
| 3081 Emacs Lisp, as the byte-code system provides little opportunity | |
| 3082 to benefit from type information, and @code{special} declarations | |
| 3083 are redundant in a fully dynamically-scoped Lisp. A few | |
| 3084 declarations are meaningful when the optimizing Emacs 19 byte | |
| 3085 compiler is being used, however. Under the earlier non-optimizing | |
| 3086 compiler, these declarations will effectively be ignored. | |
| 3087 | |
| 3088 @defun proclaim decl-spec | |
| 3089 This function records a ``global'' declaration specified by | |
| 3090 @var{decl-spec}. Since @code{proclaim} is a function, @var{decl-spec} | |
| 3091 is evaluated and thus should normally be quoted. | |
| 3092 @end defun | |
| 3093 | |
|
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|
3094 @defmac declaim decl-specs@dots{} |
| 428 | 3095 This macro is like @code{proclaim}, except that it takes any number |
| 3096 of @var{decl-spec} arguments, and the arguments are unevaluated and | |
| 3097 unquoted. The @code{declaim} macro also puts an @code{(eval-when | |
| 3098 (compile load eval) ...)} around the declarations so that they will | |
| 3099 be registered at compile-time as well as at run-time. (This is vital, | |
| 3100 since normally the declarations are meant to influence the way the | |
| 3101 compiler treats the rest of the file that contains the @code{declaim} | |
| 3102 form.) | |
|
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|
3103 @end defmac |
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|
3104 |
|
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|
3105 @defmac declare decl-specs@dots{} |
| 428 | 3106 This macro is used to make declarations within functions and other |
| 3107 code. Common Lisp allows declarations in various locations, generally | |
| 3108 at the beginning of any of the many ``implicit @code{progn}s'' | |
| 3109 throughout Lisp syntax, such as function bodies, @code{let} bodies, | |
| 3110 etc. Currently the only declaration understood by @code{declare} | |
| 3111 is @code{special}. | |
|
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3112 @end defmac |
|
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|
3113 |
|
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|
3114 @defmac locally declarations@dots{} forms@dots{} |
| 428 | 3115 In this package, @code{locally} is no different from @code{progn}. |
|
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|
3116 @end defmac |
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|
3117 |
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|
3118 @defmac the type form |
| 428 | 3119 Type information provided by @code{the} is ignored in this package; |
| 3120 in other words, @code{(the @var{type} @var{form})} is equivalent | |
| 3121 to @var{form}. Future versions of the optimizing byte-compiler may | |
| 3122 make use of this information. | |
| 3123 | |
| 3124 For example, @code{mapcar} can map over both lists and arrays. It is | |
| 3125 hard for the compiler to expand @code{mapcar} into an in-line loop | |
| 3126 unless it knows whether the sequence will be a list or an array ahead | |
| 3127 of time. With @code{(mapcar 'car (the vector foo))}, a future | |
| 3128 compiler would have enough information to expand the loop in-line. | |
| 3129 For now, Emacs Lisp will treat the above code as exactly equivalent | |
| 3130 to @code{(mapcar 'car foo)}. | |
|
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|
3131 @end defmac |
| 428 | 3132 |
| 3133 Each @var{decl-spec} in a @code{proclaim}, @code{declaim}, or | |
| 3134 @code{declare} should be a list beginning with a symbol that says | |
| 3135 what kind of declaration it is. This package currently understands | |
| 3136 @code{special}, @code{inline}, @code{notinline}, @code{optimize}, | |
| 3137 and @code{warn} declarations. (The @code{warn} declaration is an | |
| 3138 extension of standard Common Lisp.) Other Common Lisp declarations, | |
| 3139 such as @code{type} and @code{ftype}, are silently ignored. | |
| 3140 | |
| 3141 @table @code | |
| 3142 @item special | |
| 3143 Since all variables in Emacs Lisp are ``special'' (in the Common | |
| 3144 Lisp sense), @code{special} declarations are only advisory. They | |
| 3145 simply tell the optimizing byte compiler that the specified | |
| 3146 variables are intentionally being referred to without being | |
| 3147 bound in the body of the function. The compiler normally emits | |
| 3148 warnings for such references, since they could be typographical | |
| 3149 errors for references to local variables. | |
| 3150 | |
| 3151 The declaration @code{(declare (special @var{var1} @var{var2}))} is | |
| 3152 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})} in the | |
| 3153 optimizing compiler, or to nothing at all in older compilers (which | |
| 3154 do not warn for non-local references). | |
| 3155 | |
| 3156 In top-level contexts, it is generally better to write | |
| 3157 @code{(defvar @var{var})} than @code{(declaim (special @var{var}))}, | |
| 3158 since @code{defvar} makes your intentions clearer. But the older | |
| 3159 byte compilers can not handle @code{defvar}s appearing inside of | |
| 3160 functions, while @code{(declare (special @var{var}))} takes care | |
| 3161 to work correctly with all compilers. | |
| 3162 | |
| 3163 @item inline | |
| 3164 The @code{inline} @var{decl-spec} lists one or more functions | |
| 3165 whose bodies should be expanded ``in-line'' into calling functions | |
| 3166 whenever the compiler is able to arrange for it. For example, | |
| 3167 the Common Lisp function @code{cadr} is declared @code{inline} | |
| 3168 by this package so that the form @code{(cadr @var{x})} will | |
| 3169 expand directly into @code{(car (cdr @var{x}))} when it is called | |
| 3170 in user functions, for a savings of one (relatively expensive) | |
| 3171 function call. | |
| 3172 | |
| 3173 The following declarations are all equivalent. Note that the | |
| 3174 @code{defsubst} form is a convenient way to define a function | |
| 3175 and declare it inline all at once, but it is available only in | |
| 3176 Emacs 19. | |
| 3177 | |
| 3178 @example | |
| 3179 (declaim (inline foo bar)) | |
| 3180 (eval-when (compile load eval) (proclaim '(inline foo bar))) | |
| 442 | 3181 (proclaim-inline foo bar) ; XEmacs only |
| 3182 (defsubst foo (...) ...) ; instead of defun; Emacs 19 only | |
| 428 | 3183 @end example |
| 3184 | |
| 3185 @strong{Please note:} This declaration remains in effect after the | |
| 3186 containing source file is done. It is correct to use it to | |
| 3187 request that a function you have defined should be inlined, | |
| 3188 but it is impolite to use it to request inlining of an external | |
| 3189 function. | |
| 3190 | |
| 3191 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))} | |
| 3192 before a particular call to a function to cause just that call to | |
| 3193 be inlined; the current byte compilers provide no way to implement | |
| 3194 this, so @code{(declare (inline @dots{}))} is currently ignored by | |
| 3195 this package. | |
| 3196 | |
| 3197 @item notinline | |
| 3198 The @code{notinline} declaration lists functions which should | |
| 3199 not be inlined after all; it cancels a previous @code{inline} | |
| 3200 declaration. | |
| 3201 | |
| 3202 @item optimize | |
| 3203 This declaration controls how much optimization is performed by | |
| 3204 the compiler. Naturally, it is ignored by the earlier non-optimizing | |
| 3205 compilers. | |
| 3206 | |
| 3207 The word @code{optimize} is followed by any number of lists like | |
| 3208 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several | |
| 3209 optimization ``qualities''; this package ignores all but @code{speed} | |
| 3210 and @code{safety}. The value of a quality should be an integer from | |
| 3211 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important.'' | |
| 3212 The default level for both qualities is 1. | |
| 3213 | |
| 3214 In this package, with the Emacs 19 optimizing compiler, the | |
| 3215 @code{speed} quality is tied to the @code{byte-compile-optimize} | |
| 3216 flag, which is set to @code{nil} for @code{(speed 0)} and to | |
| 3217 @code{t} for higher settings; and the @code{safety} quality is | |
| 3218 tied to the @code{byte-compile-delete-errors} flag, which is | |
| 3219 set to @code{t} for @code{(safety 3)} and to @code{nil} for all | |
| 3220 lower settings. (The latter flag controls whether the compiler | |
| 3221 is allowed to optimize out code whose only side-effect could | |
| 3222 be to signal an error, e.g., rewriting @code{(progn foo bar)} to | |
| 3223 @code{bar} when it is not known whether @code{foo} will be bound | |
| 3224 at run-time.) | |
| 3225 | |
| 3226 Note that even compiling with @code{(safety 0)}, the Emacs | |
| 3227 byte-code system provides sufficient checking to prevent real | |
| 3228 harm from being done. For example, barring serious bugs in | |
| 3229 Emacs itself, Emacs will not crash with a segmentation fault | |
| 3230 just because of an error in a fully-optimized Lisp program. | |
| 3231 | |
| 3232 The @code{optimize} declaration is normally used in a top-level | |
| 3233 @code{proclaim} or @code{declaim} in a file; Common Lisp allows | |
| 3234 it to be used with @code{declare} to set the level of optimization | |
| 3235 locally for a given form, but this will not work correctly with the | |
| 3236 current version of the optimizing compiler. (The @code{declare} | |
| 3237 will set the new optimization level, but that level will not | |
| 3238 automatically be unset after the enclosing form is done.) | |
| 3239 | |
| 3240 @item warn | |
| 3241 This declaration controls what sorts of warnings are generated | |
| 3242 by the byte compiler. Again, only the optimizing compiler | |
| 3243 generates warnings. The word @code{warn} is followed by any | |
| 3244 number of ``warning qualities,'' similar in form to optimization | |
| 3245 qualities. The currently supported warning types are | |
| 3246 @code{redefine}, @code{callargs}, @code{unresolved}, and | |
| 3247 @code{free-vars}; in the current system, a value of 0 will | |
| 3248 disable these warnings and any higher value will enable them. | |
| 3249 See the documentation for the optimizing byte compiler for details. | |
| 3250 @end table | |
| 3251 | |
| 3252 @node Symbols, Numbers, Declarations, Top | |
| 3253 @chapter Symbols | |
| 3254 | |
| 3255 @noindent | |
| 3256 This package defines several symbol-related features that were | |
| 3257 missing from Emacs Lisp. | |
| 3258 | |
| 3259 @menu | |
| 442 | 3260 * Property Lists:: `getf', `remf' |
| 428 | 3261 * Creating Symbols:: `gensym', `gentemp' |
| 3262 @end menu | |
| 3263 | |
| 3264 @node Property Lists, Creating Symbols, Symbols, Symbols | |
| 3265 @section Property Lists | |
| 3266 | |
| 3267 @noindent | |
| 3268 These functions augment the standard Emacs Lisp functions @code{get} | |
| 442 | 3269 and @code{put} for operating on properties attached to objects. |
| 428 | 3270 There are also functions for working with property lists as |
| 442 | 3271 first-class data structures not attached to particular objects. |
| 428 | 3272 |
| 3273 @defun getf place property &optional default | |
| 3274 This function scans the list @var{place} as if it were a property | |
| 3275 list, i.e., a list of alternating property names and values. If | |
| 3276 an even-numbered element of @var{place} is found which is @code{eq} | |
| 3277 to @var{property}, the following odd-numbered element is returned. | |
| 3278 Otherwise, @var{default} is returned (or @code{nil} if no default | |
| 3279 is given). | |
| 3280 | |
| 3281 In particular, | |
| 3282 | |
| 3283 @example | |
| 3284 (get sym prop) @equiv{} (getf (symbol-plist sym) prop) | |
| 3285 @end example | |
| 3286 | |
| 3287 It is legal to use @code{getf} as a @code{setf} place, in which case | |
| 3288 its @var{place} argument must itself be a legal @code{setf} place. | |
| 3289 The @var{default} argument, if any, is ignored in this context. | |
| 3290 The effect is to change (via @code{setcar}) the value cell in the | |
| 3291 list that corresponds to @var{property}, or to cons a new property-value | |
| 3292 pair onto the list if the property is not yet present. | |
| 3293 | |
| 3294 @example | |
| 3295 (put sym prop val) @equiv{} (setf (getf (symbol-plist sym) prop) val) | |
| 3296 @end example | |
| 3297 | |
| 440 | 3298 The @code{get} function is also @code{setf}-able. The fact that |
| 3299 @code{default} is ignored can sometimes be useful: | |
| 428 | 3300 |
| 3301 @example | |
| 440 | 3302 (incf (get 'foo 'usage-count 0)) |
| 428 | 3303 @end example |
| 3304 | |
| 3305 Here, symbol @code{foo}'s @code{usage-count} property is incremented | |
| 3306 if it exists, or set to 1 (an incremented 0) otherwise. | |
| 3307 | |
| 3308 When not used as a @code{setf} form, @code{getf} is just a regular | |
| 3309 function and its @var{place} argument can actually be any Lisp | |
| 3310 expression. | |
| 3311 @end defun | |
| 3312 | |
|
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|
3313 @defmac remf place property |
| 428 | 3314 This macro removes the property-value pair for @var{property} from |
| 3315 the property list stored at @var{place}, which is any @code{setf}-able | |
| 3316 place expression. It returns true if the property was found. Note | |
| 3317 that if @var{property} happens to be first on the list, this will | |
| 3318 effectively do a @code{(setf @var{place} (cddr @var{place}))}, | |
| 3319 whereas if it occurs later, this simply uses @code{setcdr} to splice | |
| 3320 out the property and value cells. | |
|
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|
3321 @end defmac |
| 428 | 3322 |
| 3323 @iftex | |
| 3324 @secno=2 | |
| 3325 @end iftex | |
| 3326 | |
| 3327 @node Creating Symbols, , Property Lists, Symbols | |
| 3328 @section Creating Symbols | |
| 3329 | |
| 3330 @noindent | |
| 3331 These functions create unique symbols, typically for use as | |
| 3332 temporary variables. | |
| 3333 | |
| 3334 @defun gensym &optional x | |
| 3335 This function creates a new, uninterned symbol (using @code{make-symbol}) | |
| 3336 with a unique name. (The name of an uninterned symbol is relevant | |
| 3337 only if the symbol is printed.) By default, the name is generated | |
| 3338 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001}, | |
| 3339 @samp{G1002}, etc. If the optional argument @var{x} is a string, that | |
| 3340 string is used as a prefix instead of @samp{G}. Uninterned symbols | |
| 3341 are used in macro expansions for temporary variables, to ensure that | |
| 3342 their names will not conflict with ``real'' variables in the user's | |
| 3343 code. | |
| 3344 @end defun | |
| 3345 | |
| 3346 @defvar *gensym-counter* | |
| 3347 This variable holds the counter used to generate @code{gensym} names. | |
| 3348 It is incremented after each use by @code{gensym}. In Common Lisp | |
| 3349 this is initialized with 0, but this package initializes it with a | |
| 3350 random (time-dependent) value to avoid trouble when two files that | |
| 3351 each used @code{gensym} in their compilation are loaded together. | |
| 3352 | |
| 3353 @strong{XEmacs note:} As of XEmacs 21.0, an uninterned symbol remains | |
| 3354 uninterned even after being dumped to bytecode. Older versions of Emacs | |
| 3355 didn't distinguish the printed representation of interned and uninterned | |
| 3356 symbols, so their names had to be treated more carefully. | |
| 3357 @end defvar | |
| 3358 | |
| 3359 @defun gentemp &optional x | |
| 3360 This function is like @code{gensym}, except that it produces a new | |
| 3361 @emph{interned} symbol. If the symbol that is generated already | |
| 3362 exists, the function keeps incrementing the counter and trying | |
| 3363 again until a new symbol is generated. | |
| 3364 @end defun | |
| 3365 | |
| 3366 The Quiroz @file{cl.el} package also defined a @code{defkeyword} | |
| 3367 form for creating self-quoting keyword symbols. This package | |
| 3368 automatically creates all keywords that are called for by | |
| 3369 @code{&key} argument specifiers, and discourages the use of | |
| 3370 keywords as data unrelated to keyword arguments, so the | |
| 3371 @code{defkeyword} form has been discontinued. | |
| 3372 | |
| 3373 @iftex | |
| 3374 @chapno=11 | |
| 3375 @end iftex | |
| 3376 | |
| 3377 @node Numbers, Sequences, Symbols, Top | |
| 3378 @chapter Numbers | |
| 3379 | |
| 3380 @noindent | |
| 3381 This section defines a few simple Common Lisp operations on numbers | |
| 3382 which were left out of Emacs Lisp. | |
| 3383 | |
| 3384 @menu | |
| 3385 * Predicates on Numbers:: `plusp', `oddp', `floatp-safe', etc. | |
| 3386 * Numerical Functions:: `abs', `expt', `floor*', etc. | |
| 3387 * Random Numbers:: `random*', `make-random-state' | |
| 3388 * Implementation Parameters:: `most-positive-fixnum', `most-positive-float' | |
| 3389 @end menu | |
| 3390 | |
| 3391 @iftex | |
| 3392 @secno=1 | |
| 3393 @end iftex | |
| 3394 | |
| 3395 @node Predicates on Numbers, Numerical Functions, Numbers, Numbers | |
| 3396 @section Predicates on Numbers | |
| 3397 | |
| 3398 @noindent | |
| 3399 These functions return @code{t} if the specified condition is | |
| 3400 true of the numerical argument, or @code{nil} otherwise. | |
| 3401 | |
| 3402 @defun plusp number | |
| 3403 This predicate tests whether @var{number} is positive. It is an | |
| 3404 error if the argument is not a number. | |
| 3405 @end defun | |
| 3406 | |
| 3407 @defun minusp number | |
| 3408 This predicate tests whether @var{number} is negative. It is an | |
| 3409 error if the argument is not a number. | |
| 3410 @end defun | |
| 3411 | |
| 3412 @defun oddp integer | |
| 3413 This predicate tests whether @var{integer} is odd. It is an | |
| 3414 error if the argument is not an integer. | |
| 3415 @end defun | |
| 3416 | |
| 3417 @defun evenp integer | |
| 3418 This predicate tests whether @var{integer} is even. It is an | |
| 3419 error if the argument is not an integer. | |
| 3420 @end defun | |
| 3421 | |
| 3422 @defun floatp-safe object | |
| 3423 This predicate tests whether @var{object} is a floating-point | |
| 3424 number. On systems that support floating-point, this is equivalent | |
| 3425 to @code{floatp}. On other systems, this always returns @code{nil}. | |
| 3426 @end defun | |
| 3427 | |
| 3428 @iftex | |
| 3429 @secno=3 | |
| 3430 @end iftex | |
| 3431 | |
| 3432 @node Numerical Functions, Random Numbers, Predicates on Numbers, Numbers | |
| 3433 @section Numerical Functions | |
| 3434 | |
| 3435 @noindent | |
| 3436 These functions perform various arithmetic operations on numbers. | |
| 3437 | |
| 3438 @defun abs number | |
| 3439 This function returns the absolute value of @var{number}. (Newer | |
| 3440 versions of Emacs provide this as a built-in function; this package | |
| 3441 defines @code{abs} only for Emacs 18 versions which don't provide | |
| 3442 it as a primitive.) | |
| 3443 @end defun | |
| 3444 | |
| 3445 @defun expt base power | |
| 3446 This function returns @var{base} raised to the power of @var{number}. | |
| 3447 (Newer versions of Emacs provide this as a built-in function; this | |
| 3448 package defines @code{expt} only for Emacs 18 versions which don't | |
| 3449 provide it as a primitive.) | |
| 3450 @end defun | |
| 3451 | |
| 3452 @defun gcd &rest integers | |
| 3453 This function returns the Greatest Common Divisor of the arguments. | |
| 3454 For one argument, it returns the absolute value of that argument. | |
| 3455 For zero arguments, it returns zero. | |
| 3456 @end defun | |
| 3457 | |
| 3458 @defun lcm &rest integers | |
| 3459 This function returns the Least Common Multiple of the arguments. | |
| 3460 For one argument, it returns the absolute value of that argument. | |
| 3461 For zero arguments, it returns one. | |
| 3462 @end defun | |
| 3463 | |
| 3464 @defun isqrt integer | |
| 3465 This function computes the ``integer square root'' of its integer | |
| 3466 argument, i.e., the greatest integer less than or equal to the true | |
| 3467 square root of the argument. | |
| 3468 @end defun | |
| 3469 | |
| 3470 @defun mod* number divisor | |
| 3471 This function returns the same value as the second return value | |
| 3472 of @code{floor}. | |
| 3473 @end defun | |
| 3474 | |
| 3475 @defun rem* number divisor | |
| 3476 This function returns the same value as the second return value | |
| 3477 of @code{truncate}. | |
| 3478 @end defun | |
| 3479 | |
|
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3480 @noindent |
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|
3481 The following functions are identical to their built-in counterparts, |
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|
3482 without the trailing @code{*} in their names, but they return lists |
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|
3483 instead of multiple values. @pxref{(lispref.info)Rounding Operations} |
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|
3484 |
|
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|
3485 @defun floor* number &optional divisor |
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3486 @end defun |
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|
3487 |
|
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|
3488 @defun ceiling* number &optional divisor |
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|
3489 @end defun |
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|
3490 |
|
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|
3491 @defun truncate* number &optional divisor |
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3492 @end defun |
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|
3493 |
|
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|
3494 @defun round* number &optional divisor |
|
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3495 @end defun |
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|
3496 |
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|
3497 All the above definitions are compatible with those in the Quiroz |
| 428 | 3498 @file{cl.el} package, except that this package appends @samp{*} |
| 3499 to certain function names to avoid conflicts with existing | |
| 3500 Emacs 19 functions, and that the mechanism for returning | |
| 3501 multiple values is different. | |
| 3502 | |
| 3503 @iftex | |
| 3504 @secno=8 | |
| 3505 @end iftex | |
| 3506 | |
| 3507 @node Random Numbers, Implementation Parameters, Numerical Functions, Numbers | |
| 3508 @section Random Numbers | |
| 3509 | |
| 3510 @noindent | |
| 3511 This package also provides an implementation of the Common Lisp | |
| 3512 random number generator. It uses its own additive-congruential | |
| 3513 algorithm, which is much more likely to give statistically clean | |
| 3514 random numbers than the simple generators supplied by many | |
| 3515 operating systems. | |
| 3516 | |
| 3517 @defun random* number &optional state | |
| 3518 This function returns a random nonnegative number less than | |
| 3519 @var{number}, and of the same type (either integer or floating-point). | |
| 3520 The @var{state} argument should be a @code{random-state} object | |
| 3521 which holds the state of the random number generator. The | |
| 3522 function modifies this state object as a side effect. If | |
| 3523 @var{state} is omitted, it defaults to the variable | |
| 3524 @code{*random-state*}, which contains a pre-initialized | |
| 3525 @code{random-state} object. | |
| 3526 @end defun | |
| 3527 | |
| 3528 @defvar *random-state* | |
| 3529 This variable contains the system ``default'' @code{random-state} | |
| 3530 object, used for calls to @code{random*} that do not specify an | |
| 3531 alternative state object. Since any number of programs in the | |
| 3532 Emacs process may be accessing @code{*random-state*} in interleaved | |
| 3533 fashion, the sequence generated from this variable will be | |
| 3534 irreproducible for all intents and purposes. | |
| 3535 @end defvar | |
| 3536 | |
| 3537 @defun make-random-state &optional state | |
| 3538 This function creates or copies a @code{random-state} object. | |
| 3539 If @var{state} is omitted or @code{nil}, it returns a new copy of | |
| 3540 @code{*random-state*}. This is a copy in the sense that future | |
| 3541 sequences of calls to @code{(random* @var{n})} and | |
| 3542 @code{(random* @var{n} @var{s})} (where @var{s} is the new | |
| 3543 random-state object) will return identical sequences of random | |
| 3544 numbers. | |
| 3545 | |
| 3546 If @var{state} is a @code{random-state} object, this function | |
| 3547 returns a copy of that object. If @var{state} is @code{t}, this | |
| 3548 function returns a new @code{random-state} object seeded from the | |
| 3549 date and time. As an extension to Common Lisp, @var{state} may also | |
| 3550 be an integer in which case the new object is seeded from that | |
| 3551 integer; each different integer seed will result in a completely | |
| 3552 different sequence of random numbers. | |
| 3553 | |
| 3554 It is legal to print a @code{random-state} object to a buffer or | |
| 3555 file and later read it back with @code{read}. If a program wishes | |
| 3556 to use a sequence of pseudo-random numbers which can be reproduced | |
| 3557 later for debugging, it can call @code{(make-random-state t)} to | |
| 3558 get a new sequence, then print this sequence to a file. When the | |
| 3559 program is later rerun, it can read the original run's random-state | |
| 3560 from the file. | |
| 3561 @end defun | |
| 3562 | |
| 3563 @defun random-state-p object | |
| 3564 This predicate returns @code{t} if @var{object} is a | |
| 3565 @code{random-state} object, or @code{nil} otherwise. | |
| 3566 @end defun | |
| 3567 | |
| 3568 @node Implementation Parameters, , Random Numbers, Numbers | |
| 3569 @section Implementation Parameters | |
| 3570 | |
| 3571 @noindent | |
| 3572 This package defines several useful constants having to with numbers. | |
| 3573 | |
| 3574 @defvar most-positive-fixnum | |
| 3575 This constant equals the largest value a Lisp integer can hold. | |
| 3576 It is typically @code{2^23-1} or @code{2^25-1}. | |
| 3577 @end defvar | |
| 3578 | |
| 3579 @defvar most-negative-fixnum | |
| 3580 This constant equals the smallest (most negative) value a Lisp | |
| 3581 integer can hold. | |
| 3582 @end defvar | |
| 3583 | |
| 3584 The following parameters have to do with floating-point numbers. | |
| 3585 This package determines their values by exercising the computer's | |
| 3586 floating-point arithmetic in various ways. Because this operation | |
| 3587 might be slow, the code for initializing them is kept in a separate | |
| 3588 function that must be called before the parameters can be used. | |
| 3589 | |
| 3590 @defun cl-float-limits | |
| 3591 This function makes sure that the Common Lisp floating-point | |
| 3592 parameters like @code{most-positive-float} have been initialized. | |
| 3593 Until it is called, these parameters will be @code{nil}. If this | |
| 3594 version of Emacs does not support floats (e.g., most versions of | |
| 3595 Emacs 18), the parameters will remain @code{nil}. If the parameters | |
| 3596 have already been initialized, the function returns immediately. | |
| 3597 | |
| 3598 The algorithm makes assumptions that will be valid for most modern | |
| 3599 machines, but will fail if the machine's arithmetic is extremely | |
| 3600 unusual, e.g., decimal. | |
| 3601 @end defun | |
| 3602 | |
| 3603 Since true Common Lisp supports up to four different floating-point | |
| 3604 precisions, it has families of constants like | |
| 3605 @code{most-positive-single-float}, @code{most-positive-double-float}, | |
| 3606 @code{most-positive-long-float}, and so on. Emacs has only one | |
| 3607 floating-point precision, so this package omits the precision word | |
| 3608 from the constants' names. | |
| 3609 | |
| 3610 @defvar most-positive-float | |
| 3611 This constant equals the largest value a Lisp float can hold. | |
| 3612 For those systems whose arithmetic supports infinities, this is | |
| 3613 the largest @emph{finite} value. For IEEE machines, the value | |
| 3614 is approximately @code{1.79e+308}. | |
| 3615 @end defvar | |
| 3616 | |
| 3617 @defvar most-negative-float | |
| 3618 This constant equals the most-negative value a Lisp float can hold. | |
| 3619 (It is assumed to be equal to @code{(- most-positive-float)}.) | |
| 3620 @end defvar | |
| 3621 | |
| 3622 @defvar least-positive-float | |
| 3623 This constant equals the smallest Lisp float value greater than zero. | |
| 3624 For IEEE machines, it is about @code{4.94e-324} if denormals are | |
| 3625 supported or @code{2.22e-308} if not. | |
| 3626 @end defvar | |
| 3627 | |
| 3628 @defvar least-positive-normalized-float | |
| 3629 This constant equals the smallest @emph{normalized} Lisp float greater | |
| 3630 than zero, i.e., the smallest value for which IEEE denormalization | |
| 3631 will not result in a loss of precision. For IEEE machines, this | |
| 3632 value is about @code{2.22e-308}. For machines that do not support | |
| 3633 the concept of denormalization and gradual underflow, this constant | |
| 3634 will always equal @code{least-positive-float}. | |
| 3635 @end defvar | |
| 3636 | |
| 3637 @defvar least-negative-float | |
| 3638 This constant is the negative counterpart of @code{least-positive-float}. | |
| 3639 @end defvar | |
| 3640 | |
| 3641 @defvar least-negative-normalized-float | |
| 3642 This constant is the negative counterpart of | |
| 3643 @code{least-positive-normalized-float}. | |
| 3644 @end defvar | |
| 3645 | |
| 3646 @defvar float-epsilon | |
| 3647 This constant is the smallest positive Lisp float that can be added | |
| 3648 to 1.0 to produce a distinct value. Adding a smaller number to 1.0 | |
| 3649 will yield 1.0 again due to roundoff. For IEEE machines, epsilon | |
| 3650 is about @code{2.22e-16}. | |
| 3651 @end defvar | |
| 3652 | |
| 3653 @defvar float-negative-epsilon | |
| 3654 This is the smallest positive value that can be subtracted from | |
| 3655 1.0 to produce a distinct value. For IEEE machines, it is about | |
| 3656 @code{1.11e-16}. | |
| 3657 @end defvar | |
| 3658 | |
| 3659 @iftex | |
| 3660 @chapno=13 | |
| 3661 @end iftex | |
| 3662 | |
| 3663 @node Sequences, Lists, Numbers, Top | |
| 3664 @chapter Sequences | |
| 3665 | |
| 3666 @noindent | |
| 3667 Common Lisp defines a number of functions that operate on | |
| 3668 @dfn{sequences}, which are either lists, strings, or vectors. | |
| 3669 Emacs Lisp includes a few of these, notably @code{elt} and | |
| 3670 @code{length}; this package defines most of the rest. | |
| 3671 | |
| 3672 @menu | |
| 3673 * Sequence Basics:: Arguments shared by all sequence functions | |
| 3674 * Mapping over Sequences:: `mapcar*', `mapcan', `map', `every', etc. | |
| 3675 * Sequence Functions:: `subseq', `remove*', `substitute', etc. | |
| 3676 * Searching Sequences:: `find', `position', `count', `search', etc. | |
| 3677 * Sorting Sequences:: `sort*', `stable-sort', `merge' | |
| 3678 @end menu | |
| 3679 | |
| 3680 @node Sequence Basics, Mapping over Sequences, Sequences, Sequences | |
| 3681 @section Sequence Basics | |
| 3682 | |
| 778 | 3683 @noindent Many of the sequence functions take keyword arguments; |
| 3684 @pxref{Argument Lists}. All keyword arguments are optional and, if | |
| 3685 specified, may appear in any order. | |
| 428 | 3686 |
| 3687 The @code{:key} argument should be passed either @code{nil}, or a | |
| 3688 function of one argument. This key function is used as a filter | |
| 3689 through which the elements of the sequence are seen; for example, | |
| 3690 @code{(find x y :key 'car)} is similar to @code{(assoc* x y)}: | |
| 3691 It searches for an element of the list whose @code{car} equals | |
| 3692 @code{x}, rather than for an element which equals @code{x} itself. | |
| 3693 If @code{:key} is omitted or @code{nil}, the filter is effectively | |
| 3694 the identity function. | |
| 3695 | |
| 3696 The @code{:test} and @code{:test-not} arguments should be either | |
| 3697 @code{nil}, or functions of two arguments. The test function is | |
| 3698 used to compare two sequence elements, or to compare a search value | |
| 3699 with sequence elements. (The two values are passed to the test | |
| 3700 function in the same order as the original sequence function | |
| 3701 arguments from which they are derived, or, if they both come from | |
| 3702 the same sequence, in the same order as they appear in that sequence.) | |
| 3703 The @code{:test} argument specifies a function which must return | |
| 3704 true (non-@code{nil}) to indicate a match; instead, you may use | |
| 3705 @code{:test-not} to give a function which returns @emph{false} to | |
| 3706 indicate a match. The default test function is @code{:test 'eql}. | |
| 3707 | |
| 3708 Many functions which take @var{item} and @code{:test} or @code{:test-not} | |
| 3709 arguments also come in @code{-if} and @code{-if-not} varieties, | |
| 3710 where a @var{predicate} function is passed instead of @var{item}, | |
| 3711 and sequence elements match if the predicate returns true on them | |
| 3712 (or false in the case of @code{-if-not}). For example: | |
| 3713 | |
| 3714 @example | |
| 3715 (remove* 0 seq :test '=) @equiv{} (remove-if 'zerop seq) | |
| 3716 @end example | |
| 3717 | |
| 3718 @noindent | |
| 3719 to remove all zeros from sequence @code{seq}. | |
| 3720 | |
| 3721 Some operations can work on a subsequence of the argument sequence; | |
| 3722 these function take @code{:start} and @code{:end} arguments which | |
| 3723 default to zero and the length of the sequence, respectively. | |
| 3724 Only elements between @var{start} (inclusive) and @var{end} | |
| 3725 (exclusive) are affected by the operation. The @var{end} argument | |
| 3726 may be passed @code{nil} to signify the length of the sequence; | |
| 3727 otherwise, both @var{start} and @var{end} must be integers, with | |
| 3728 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}. | |
| 3729 If the function takes two sequence arguments, the limits are | |
| 3730 defined by keywords @code{:start1} and @code{:end1} for the first, | |
| 3731 and @code{:start2} and @code{:end2} for the second. | |
| 3732 | |
| 3733 A few functions accept a @code{:from-end} argument, which, if | |
| 3734 non-@code{nil}, causes the operation to go from right-to-left | |
| 3735 through the sequence instead of left-to-right, and a @code{:count} | |
| 3736 argument, which specifies an integer maximum number of elements | |
| 3737 to be removed or otherwise processed. | |
| 3738 | |
| 3739 The sequence functions make no guarantees about the order in | |
| 3740 which the @code{:test}, @code{:test-not}, and @code{:key} functions | |
| 3741 are called on various elements. Therefore, it is a bad idea to depend | |
| 3742 on side effects of these functions. For example, @code{:from-end} | |
| 3743 may cause the sequence to be scanned actually in reverse, or it may | |
| 3744 be scanned forwards but computing a result ``as if'' it were scanned | |
| 3745 backwards. (Some functions, like @code{mapcar*} and @code{every}, | |
| 3746 @emph{do} specify exactly the order in which the function is called | |
| 3747 so side effects are perfectly acceptable in those cases.) | |
| 3748 | |
| 3749 Strings in GNU Emacs 19 may contain ``text properties'' as well | |
| 3750 as character data. Except as noted, it is undefined whether or | |
| 3751 not text properties are preserved by sequence functions. For | |
| 3752 example, @code{(remove* ?A @var{str})} may or may not preserve | |
| 3753 the properties of the characters copied from @var{str} into the | |
| 3754 result. | |
| 3755 | |
| 3756 @node Mapping over Sequences, Sequence Functions, Sequence Basics, Sequences | |
| 3757 @section Mapping over Sequences | |
| 3758 | |
| 3759 @noindent | |
| 3760 These functions ``map'' the function you specify over the elements | |
| 3761 of lists or arrays. They are all variations on the theme of the | |
| 3762 built-in function @code{mapcar}. | |
| 3763 | |
| 3764 @defun mapcar* function seq &rest more-seqs | |
| 3765 This function calls @var{function} on successive parallel sets of | |
| 3766 elements from its argument sequences. Given a single @var{seq} | |
| 3767 argument it is equivalent to @code{mapcar}; given @var{n} sequences, | |
| 3768 it calls the function with the first elements of each of the sequences | |
| 3769 as the @var{n} arguments to yield the first element of the result | |
| 3770 list, then with the second elements, and so on. The mapping stops as | |
| 3771 soon as the shortest sequence runs out. The argument sequences may | |
| 3772 be any mixture of lists, strings, and vectors; the return sequence | |
| 3773 is always a list. | |
| 3774 | |
| 3775 Common Lisp's @code{mapcar} accepts multiple arguments but works | |
| 3776 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence | |
| 3777 argument. This package's @code{mapcar*} works as a compatible | |
| 3778 superset of both. | |
| 3779 @end defun | |
| 3780 | |
| 3781 @defun map result-type function seq &rest more-seqs | |
| 3782 This function maps @var{function} over the argument sequences, | |
| 3783 just like @code{mapcar*}, but it returns a sequence of type | |
| 3784 @var{result-type} rather than a list. @var{result-type} must | |
| 3785 be one of the following symbols: @code{vector}, @code{string}, | |
| 3786 @code{list} (in which case the effect is the same as for | |
| 3787 @code{mapcar*}), or @code{nil} (in which case the results are | |
| 3788 thrown away and @code{map} returns @code{nil}). | |
| 3789 @end defun | |
| 3790 | |
| 3791 @defun maplist function list &rest more-lists | |
| 3792 This function calls @var{function} on each of its argument lists, | |
| 3793 then on the @code{cdr}s of those lists, and so on, until the | |
| 3794 shortest list runs out. The results are returned in the form | |
| 3795 of a list. Thus, @code{maplist} is like @code{mapcar*} except | |
| 3796 that it passes in the list pointers themselves rather than the | |
| 3797 @code{car}s of the advancing pointers. | |
| 3798 @end defun | |
| 3799 | |
| 3800 @defun mapc function seq &rest more-seqs | |
| 3801 This function is like @code{mapcar*}, except that the values | |
| 3802 returned by @var{function} are ignored and thrown away rather | |
| 3803 than being collected into a list. The return value of @code{mapc} | |
| 3804 is @var{seq}, the first sequence. | |
| 3805 @end defun | |
| 3806 | |
| 3807 @defun mapl function list &rest more-lists | |
| 3808 This function is like @code{maplist}, except that it throws away | |
| 3809 the values returned by @var{function}. | |
| 3810 @end defun | |
| 3811 | |
| 3812 @defun mapcan function seq &rest more-seqs | |
| 3813 This function is like @code{mapcar*}, except that it concatenates | |
| 3814 the return values (which must be lists) using @code{nconc}, | |
| 3815 rather than simply collecting them into a list. | |
| 3816 @end defun | |
| 3817 | |
| 3818 @defun mapcon function list &rest more-lists | |
| 3819 This function is like @code{maplist}, except that it concatenates | |
| 3820 the return values using @code{nconc}. | |
| 3821 @end defun | |
| 3822 | |
| 3823 @defun some predicate seq &rest more-seqs | |
| 3824 This function calls @var{predicate} on each element of @var{seq} | |
| 3825 in turn; if @var{predicate} returns a non-@code{nil} value, | |
| 3826 @code{some} returns that value, otherwise it returns @code{nil}. | |
| 3827 Given several sequence arguments, it steps through the sequences | |
| 3828 in parallel until the shortest one runs out, just as in | |
| 3829 @code{mapcar*}. You can rely on the left-to-right order in which | |
| 3830 the elements are visited, and on the fact that mapping stops | |
| 3831 immediately as soon as @var{predicate} returns non-@code{nil}. | |
| 3832 @end defun | |
| 3833 | |
| 3834 @defun every predicate seq &rest more-seqs | |
| 3835 This function calls @var{predicate} on each element of the sequence(s) | |
| 3836 in turn; it returns @code{nil} as soon as @var{predicate} returns | |
| 3837 @code{nil} for any element, or @code{t} if the predicate was true | |
| 3838 for all elements. | |
| 3839 @end defun | |
| 3840 | |
| 3841 @defun notany predicate seq &rest more-seqs | |
| 3842 This function calls @var{predicate} on each element of the sequence(s) | |
| 3843 in turn; it returns @code{nil} as soon as @var{predicate} returns | |
| 3844 a non-@code{nil} value for any element, or @code{t} if the predicate | |
| 3845 was @code{nil} for all elements. | |
| 3846 @end defun | |
| 3847 | |
| 3848 @defun notevery predicate seq &rest more-seqs | |
| 3849 This function calls @var{predicate} on each element of the sequence(s) | |
| 3850 in turn; it returns a non-@code{nil} value as soon as @var{predicate} | |
| 3851 returns @code{nil} for any element, or @code{t} if the predicate was | |
| 3852 true for all elements. | |
| 3853 @end defun | |
| 3854 | |
| 3855 @defun reduce function seq @t{&key :from-end :start :end :initial-value :key} | |
| 3856 This function combines the elements of @var{seq} using an associative | |
| 3857 binary operation. Suppose @var{function} is @code{*} and @var{seq} is | |
| 3858 the list @code{(2 3 4 5)}. The first two elements of the list are | |
| 3859 combined with @code{(* 2 3) = 6}; this is combined with the next | |
| 3860 element, @code{(* 6 4) = 24}, and that is combined with the final | |
| 3861 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens | |
| 3862 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as | |
| 3863 an explicit call to @code{reduce}. | |
| 3864 | |
| 3865 If @code{:from-end} is true, the reduction is right-associative instead | |
| 3866 of left-associative: | |
| 3867 | |
| 3868 @example | |
| 3869 (reduce '- '(1 2 3 4)) | |
| 3870 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8 | |
| 3871 (reduce '- '(1 2 3 4) :from-end t) | |
| 3872 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2 | |
| 3873 @end example | |
| 3874 | |
| 3875 If @code{:key} is specified, it is a function of one argument which | |
| 3876 is called on each of the sequence elements in turn. | |
| 3877 | |
| 3878 If @code{:initial-value} is specified, it is effectively added to the | |
| 3879 front (or rear in the case of @code{:from-end}) of the sequence. | |
| 3880 The @code{:key} function is @emph{not} applied to the initial value. | |
| 3881 | |
| 3882 If the sequence, including the initial value, has exactly one element | |
| 3883 then that element is returned without ever calling @var{function}. | |
| 3884 If the sequence is empty (and there is no initial value), then | |
| 3885 @var{function} is called with no arguments to obtain the return value. | |
| 3886 @end defun | |
| 3887 | |
| 3888 All of these mapping operations can be expressed conveniently in | |
| 3889 terms of the @code{loop} macro. In compiled code, @code{loop} will | |
| 3890 be faster since it generates the loop as in-line code with no | |
| 3891 function calls. | |
| 3892 | |
| 3893 @node Sequence Functions, Searching Sequences, Mapping over Sequences, Sequences | |
| 3894 @section Sequence Functions | |
| 3895 | |
| 3896 @noindent | |
| 3897 This section describes a number of Common Lisp functions for | |
| 3898 operating on sequences. | |
| 3899 | |
| 3900 @defun subseq sequence start &optional end | |
| 3901 This function returns a given subsequence of the argument | |
| 3902 @var{sequence}, which may be a list, string, or vector. | |
| 3903 The indices @var{start} and @var{end} must be in range, and | |
| 3904 @var{start} must be no greater than @var{end}. If @var{end} | |
| 3905 is omitted, it defaults to the length of the sequence. The | |
| 3906 return value is always a copy; it does not share structure | |
| 3907 with @var{sequence}. | |
| 3908 | |
| 3909 As an extension to Common Lisp, @var{start} and/or @var{end} | |
| 3910 may be negative, in which case they represent a distance back | |
| 3911 from the end of the sequence. This is for compatibility with | |
| 3912 Emacs' @code{substring} function. Note that @code{subseq} is | |
| 3913 the @emph{only} sequence function that allows negative | |
| 3914 @var{start} and @var{end}. | |
| 3915 | |
| 3916 You can use @code{setf} on a @code{subseq} form to replace a | |
| 3917 specified range of elements with elements from another sequence. | |
| 3918 The replacement is done as if by @code{replace}, described below. | |
| 3919 @end defun | |
| 3920 | |
| 3921 @defun concatenate result-type &rest seqs | |
| 3922 This function concatenates the argument sequences together to | |
| 3923 form a result sequence of type @var{result-type}, one of the | |
| 3924 symbols @code{vector}, @code{string}, or @code{list}. The | |
| 3925 arguments are always copied, even in cases such as | |
| 3926 @code{(concatenate 'list '(1 2 3))} where the result is | |
| 3927 identical to an argument. | |
| 3928 @end defun | |
| 3929 | |
| 3930 @defun fill seq item @t{&key :start :end} | |
| 3931 This function fills the elements of the sequence (or the specified | |
| 3932 part of the sequence) with the value @var{item}. | |
| 3933 @end defun | |
| 3934 | |
| 3935 @defun replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2} | |
| 3936 This function copies part of @var{seq2} into part of @var{seq1}. | |
| 3937 The sequence @var{seq1} is not stretched or resized; the amount | |
| 3938 of data copied is simply the shorter of the source and destination | |
| 3939 (sub)sequences. The function returns @var{seq1}. | |
| 3940 | |
| 3941 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement | |
| 3942 will work correctly even if the regions indicated by the start | |
| 3943 and end arguments overlap. However, if @var{seq1} and @var{seq2} | |
| 3944 are lists which share storage but are not @code{eq}, and the | |
| 3945 start and end arguments specify overlapping regions, the effect | |
| 3946 is undefined. | |
| 3947 @end defun | |
| 3948 | |
| 3949 @defun remove* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 3950 This returns a copy of @var{seq} with all elements matching | |
| 3951 @var{item} removed. The result may share storage with or be | |
| 3952 @code{eq} to @var{seq} in some circumstances, but the original | |
| 3953 @var{seq} will not be modified. The @code{:test}, @code{:test-not}, | |
| 3954 and @code{:key} arguments define the matching test that is used; | |
| 3955 by default, elements @code{eql} to @var{item} are removed. The | |
| 3956 @code{:count} argument specifies the maximum number of matching | |
| 3957 elements that can be removed (only the leftmost @var{count} matches | |
| 3958 are removed). The @code{:start} and @code{:end} arguments specify | |
| 3959 a region in @var{seq} in which elements will be removed; elements | |
| 3960 outside that region are not matched or removed. The @code{:from-end} | |
| 3961 argument, if true, says that elements should be deleted from the | |
| 3962 end of the sequence rather than the beginning (this matters only | |
| 3963 if @var{count} was also specified). | |
| 3964 @end defun | |
| 3965 | |
| 3966 @defun delete* item seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 3967 This deletes all elements of @var{seq} which match @var{item}. | |
| 3968 It is a destructive operation. Since Emacs Lisp does not support | |
| 3969 stretchable strings or vectors, this is the same as @code{remove*} | |
| 3970 for those sequence types. On lists, @code{remove*} will copy the | |
| 3971 list if necessary to preserve the original list, whereas | |
| 3972 @code{delete*} will splice out parts of the argument list. | |
| 3973 Compare @code{append} and @code{nconc}, which are analogous | |
| 3974 non-destructive and destructive list operations in Emacs Lisp. | |
| 3975 @end defun | |
| 3976 | |
| 3977 @findex remove-if | |
| 3978 @findex remove-if-not | |
| 3979 @findex delete-if | |
| 3980 @findex delete-if-not | |
| 3981 The predicate-oriented functions @code{remove-if}, @code{remove-if-not}, | |
| 3982 @code{delete-if}, and @code{delete-if-not} are defined similarly. | |
| 3983 | |
| 3984 @defun delete item list | |
| 3985 This MacLisp-compatible function deletes from @var{list} all elements | |
| 3986 which are @code{equal} to @var{item}. The @code{delete} function is | |
| 3987 built-in to Emacs 19; this package defines it equivalently in Emacs 18. | |
| 3988 @end defun | |
| 3989 | |
| 3990 @defun remove item list | |
| 3991 This function removes from @var{list} all elements which are | |
| 3992 @code{equal} to @var{item}. This package defines it for symmetry | |
| 3993 with @code{delete}, even though @code{remove} is not built-in to | |
| 3994 Emacs 19. | |
| 3995 @end defun | |
| 3996 | |
| 3997 @defun remq item list | |
| 3998 This function removes from @var{list} all elements which are | |
| 3999 @code{eq} to @var{item}. This package defines it for symmetry | |
| 4000 with @code{delq}, even though @code{remq} is not built-in to | |
| 4001 Emacs 19. | |
| 4002 @end defun | |
| 4003 | |
| 4004 @defun remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4005 This function returns a copy of @var{seq} with duplicate elements | |
| 4006 removed. Specifically, if two elements from the sequence match | |
| 4007 according to the @code{:test}, @code{:test-not}, and @code{:key} | |
| 4008 arguments, only the rightmost one is retained. If @code{:from-end} | |
| 4009 is true, the leftmost one is retained instead. If @code{:start} or | |
| 4010 @code{:end} is specified, only elements within that subsequence are | |
| 4011 examined or removed. | |
| 4012 @end defun | |
| 4013 | |
| 4014 @defun delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4015 This function deletes duplicate elements from @var{seq}. It is | |
| 4016 a destructive version of @code{remove-duplicates}. | |
| 4017 @end defun | |
| 4018 | |
| 4019 @defun substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4020 This function returns a copy of @var{seq}, with all elements | |
| 4021 matching @var{old} replaced with @var{new}. The @code{:count}, | |
| 4022 @code{:start}, @code{:end}, and @code{:from-end} arguments may be | |
| 4023 used to limit the number of substitutions made. | |
| 4024 @end defun | |
| 4025 | |
| 4026 @defun nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} | |
| 4027 This is a destructive version of @code{substitute}; it performs | |
| 4028 the substitution using @code{setcar} or @code{aset} rather than | |
| 4029 by returning a changed copy of the sequence. | |
| 4030 @end defun | |
| 4031 | |
| 4032 @findex substitute-if | |
| 4033 @findex substitute-if-not | |
| 4034 @findex nsubstitute-if | |
| 4035 @findex nsubstitute-if-not | |
| 4036 The @code{substitute-if}, @code{substitute-if-not}, @code{nsubstitute-if}, | |
| 4037 and @code{nsubstitute-if-not} functions are defined similarly. For | |
| 4038 these, a @var{predicate} is given in place of the @var{old} argument. | |
| 4039 | |
| 4040 @node Searching Sequences, Sorting Sequences, Sequence Functions, Sequences | |
| 4041 @section Searching Sequences | |
| 4042 | |
| 4043 @noindent | |
| 4044 These functions search for elements or subsequences in a sequence. | |
| 4045 (See also @code{member*} and @code{assoc*}; @pxref{Lists}.) | |
| 4046 | |
| 4047 @defun find item seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4048 This function searches @var{seq} for an element matching @var{item}. | |
| 4049 If it finds a match, it returns the matching element. Otherwise, | |
| 4050 it returns @code{nil}. It returns the leftmost match, unless | |
| 4051 @code{:from-end} is true, in which case it returns the rightmost | |
| 4052 match. The @code{:start} and @code{:end} arguments may be used to | |
| 4053 limit the range of elements that are searched. | |
| 4054 @end defun | |
| 4055 | |
| 4056 @defun position item seq @t{&key :test :test-not :key :start :end :from-end} | |
| 4057 This function is like @code{find}, except that it returns the | |
| 4058 integer position in the sequence of the matching item rather than | |
| 4059 the item itself. The position is relative to the start of the | |
| 4060 sequence as a whole, even if @code{:start} is non-zero. The function | |
| 4061 returns @code{nil} if no matching element was found. | |
| 4062 @end defun | |
| 4063 | |
| 4064 @defun count item seq @t{&key :test :test-not :key :start :end} | |
| 4065 This function returns the number of elements of @var{seq} which | |
| 4066 match @var{item}. The result is always a nonnegative integer. | |
| 4067 @end defun | |
| 4068 | |
| 4069 @findex find-if | |
| 4070 @findex find-if-not | |
| 4071 @findex position-if | |
| 4072 @findex position-if-not | |
| 4073 @findex count-if | |
| 4074 @findex count-if-not | |
| 4075 The @code{find-if}, @code{find-if-not}, @code{position-if}, | |
| 4076 @code{position-if-not}, @code{count-if}, and @code{count-if-not} | |
| 4077 functions are defined similarly. | |
| 4078 | |
| 4079 @defun mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end} | |
| 4080 This function compares the specified parts of @var{seq1} and | |
| 4081 @var{seq2}. If they are the same length and the corresponding | |
| 4082 elements match (according to @code{:test}, @code{:test-not}, | |
| 4083 and @code{:key}), the function returns @code{nil}. If there is | |
| 4084 a mismatch, the function returns the index (relative to @var{seq1}) | |
| 4085 of the first mismatching element. This will be the leftmost pair of | |
| 4086 elements which do not match, or the position at which the shorter of | |
| 4087 the two otherwise-matching sequences runs out. | |
| 4088 | |
| 4089 If @code{:from-end} is true, then the elements are compared from right | |
| 4090 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}. | |
| 4091 If the sequences differ, then one plus the index of the rightmost | |
| 4092 difference (relative to @var{seq1}) is returned. | |
| 4093 | |
| 4094 An interesting example is @code{(mismatch str1 str2 :key 'upcase)}, | |
| 4095 which compares two strings case-insensitively. | |
| 4096 @end defun | |
| 4097 | |
| 4098 @defun search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2} | |
| 4099 This function searches @var{seq2} for a subsequence that matches | |
| 4100 @var{seq1} (or part of it specified by @code{:start1} and | |
| 4101 @code{:end1}.) Only matches which fall entirely within the region | |
| 4102 defined by @code{:start2} and @code{:end2} will be considered. | |
| 4103 The return value is the index of the leftmost element of the | |
| 4104 leftmost match, relative to the start of @var{seq2}, or @code{nil} | |
| 4105 if no matches were found. If @code{:from-end} is true, the | |
| 4106 function finds the @emph{rightmost} matching subsequence. | |
| 4107 @end defun | |
| 4108 | |
| 4109 @node Sorting Sequences, , Searching Sequences, Sequences | |
| 4110 @section Sorting Sequences | |
| 4111 | |
| 4112 @defun sort* seq predicate @t{&key :key} | |
| 4113 This function sorts @var{seq} into increasing order as determined | |
| 4114 by using @var{predicate} to compare pairs of elements. @var{predicate} | |
| 4115 should return true (non-@code{nil}) if and only if its first argument | |
| 4116 is less than (not equal to) its second argument. For example, | |
| 4117 @code{<} and @code{string-lessp} are suitable predicate functions | |
| 4118 for sorting numbers and strings, respectively; @code{>} would sort | |
| 4119 numbers into decreasing rather than increasing order. | |
| 4120 | |
| 4121 This function differs from Emacs' built-in @code{sort} in that it | |
| 4122 can operate on any type of sequence, not just lists. Also, it | |
| 4123 accepts a @code{:key} argument which is used to preprocess data | |
| 4124 fed to the @var{predicate} function. For example, | |
| 4125 | |
| 4126 @example | |
| 4127 (setq data (sort data 'string-lessp :key 'downcase)) | |
| 4128 @end example | |
| 4129 | |
| 4130 @noindent | |
| 4131 sorts @var{data}, a sequence of strings, into increasing alphabetical | |
| 4132 order without regard to case. A @code{:key} function of @code{car} | |
| 4133 would be useful for sorting association lists. | |
| 4134 | |
| 4135 The @code{sort*} function is destructive; it sorts lists by actually | |
| 4136 rearranging the @code{cdr} pointers in suitable fashion. | |
| 4137 @end defun | |
| 4138 | |
| 4139 @defun stable-sort seq predicate @t{&key :key} | |
| 4140 This function sorts @var{seq} @dfn{stably}, meaning two elements | |
| 4141 which are equal in terms of @var{predicate} are guaranteed not to | |
| 4142 be rearranged out of their original order by the sort. | |
| 4143 | |
| 4144 In practice, @code{sort*} and @code{stable-sort} are equivalent | |
| 4145 in Emacs Lisp because the underlying @code{sort} function is | |
| 4146 stable by default. However, this package reserves the right to | |
| 4147 use non-stable methods for @code{sort*} in the future. | |
| 4148 @end defun | |
| 4149 | |
| 4150 @defun merge type seq1 seq2 predicate @t{&key :key} | |
| 4151 This function merges two sequences @var{seq1} and @var{seq2} by | |
| 4152 interleaving their elements. The result sequence, of type @var{type} | |
| 4153 (in the sense of @code{concatenate}), has length equal to the sum | |
| 4154 of the lengths of the two input sequences. The sequences may be | |
| 4155 modified destructively. Order of elements within @var{seq1} and | |
| 4156 @var{seq2} is preserved in the interleaving; elements of the two | |
| 4157 sequences are compared by @var{predicate} (in the sense of | |
| 4158 @code{sort}) and the lesser element goes first in the result. | |
| 4159 When elements are equal, those from @var{seq1} precede those from | |
| 4160 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are | |
| 4161 both sorted according to @var{predicate}, then the result will be | |
| 4162 a merged sequence which is (stably) sorted according to | |
| 4163 @var{predicate}. | |
| 4164 @end defun | |
| 4165 | |
| 4166 @node Lists, Hash Tables, Sequences, Top | |
| 4167 @chapter Lists | |
| 4168 | |
| 4169 @noindent | |
| 4170 The functions described here operate on lists. | |
| 4171 | |
| 4172 @menu | |
| 4173 * List Functions:: `caddr', `first', `last', `list*', etc. | |
| 4174 * Substitution of Expressions:: `subst', `sublis', etc. | |
| 4175 * Lists as Sets:: `member*', `adjoin', `union', etc. | |
| 4176 * Association Lists:: `assoc*', `rassoc*', `acons', `pairlis' | |
| 4177 @end menu | |
| 4178 | |
| 4179 @node List Functions, Substitution of Expressions, Lists, Lists | |
| 4180 @section List Functions | |
| 4181 | |
| 4182 @noindent | |
| 4183 This section describes a number of simple operations on lists, | |
| 4184 i.e., chains of cons cells. | |
| 4185 | |
| 4186 @defun caddr x | |
| 4187 This function is equivalent to @code{(car (cdr (cdr @var{x})))}. | |
| 4188 Likewise, this package defines all 28 @code{c@var{xxx}r} functions | |
| 4189 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s. | |
| 4190 All of these functions are @code{setf}-able, and calls to them | |
| 4191 are expanded inline by the byte-compiler for maximum efficiency. | |
| 4192 @end defun | |
| 4193 | |
| 4194 @defun first x | |
| 4195 This function is a synonym for @code{(car @var{x})}. Likewise, | |
| 4196 the functions @code{second}, @code{third}, @dots{}, through | |
| 4197 @code{tenth} return the given element of the list @var{x}. | |
| 4198 @end defun | |
| 4199 | |
| 4200 @defun rest x | |
| 4201 This function is a synonym for @code{(cdr @var{x})}. | |
| 4202 @end defun | |
| 4203 | |
| 4204 @defun endp x | |
| 4205 Common Lisp defines this function to act like @code{null}, but | |
| 4206 signalling an error if @code{x} is neither a @code{nil} nor a | |
| 4207 cons cell. This package simply defines @code{endp} as a synonym | |
| 4208 for @code{null}. | |
| 4209 @end defun | |
| 4210 | |
| 4211 @defun list-length x | |
| 4212 This function returns the length of list @var{x}, exactly like | |
| 4213 @code{(length @var{x})}, except that if @var{x} is a circular | |
| 4214 list (where the cdr-chain forms a loop rather than terminating | |
| 4215 with @code{nil}), this function returns @code{nil}. (The regular | |
| 4216 @code{length} function would get stuck if given a circular list.) | |
| 4217 @end defun | |
| 4218 | |
| 4219 @defun last x &optional n | |
| 4220 This function returns the last cons, or the @var{n}th-to-last cons, | |
| 4221 of the list @var{x}. If @var{n} is omitted it defaults to 1. | |
| 4222 The ``last cons'' means the first cons cell of the list whose | |
| 4223 @code{cdr} is not another cons cell. (For normal lists, the | |
| 4224 @code{cdr} of the last cons will be @code{nil}.) This function | |
| 4225 returns @code{nil} if @var{x} is @code{nil} or shorter than | |
| 4226 @var{n}. Note that the last @emph{element} of the list is | |
| 4227 @code{(car (last @var{x}))}. | |
| 4228 @end defun | |
| 4229 | |
| 4230 @defun butlast x &optional n | |
| 4231 This function returns the list @var{x} with the last element, | |
| 4232 or the last @var{n} elements, removed. If @var{n} is greater | |
| 4233 than zero it makes a copy of the list so as not to damage the | |
| 4234 original list. In general, @code{(append (butlast @var{x} @var{n}) | |
| 4235 (last @var{x} @var{n}))} will return a list equal to @var{x}. | |
| 4236 @end defun | |
| 4237 | |
| 4238 @defun nbutlast x &optional n | |
| 4239 This is a version of @code{butlast} that works by destructively | |
| 4240 modifying the @code{cdr} of the appropriate element, rather than | |
| 4241 making a copy of the list. | |
| 4242 @end defun | |
| 4243 | |
| 4244 @defun list* arg &rest others | |
| 4245 This function constructs a list of its arguments. The final | |
| 4246 argument becomes the @code{cdr} of the last cell constructed. | |
| 4247 Thus, @code{(list* @var{a} @var{b} @var{c})} is equivalent to | |
| 4248 @code{(cons @var{a} (cons @var{b} @var{c}))}, and | |
| 4249 @code{(list* @var{a} @var{b} nil)} is equivalent to | |
| 4250 @code{(list @var{a} @var{b})}. | |
| 4251 | |
| 4252 (Note that this function really is called @code{list*} in Common | |
| 4253 Lisp; it is not a name invented for this package like @code{member*} | |
| 4254 or @code{defun*}.) | |
| 4255 @end defun | |
| 4256 | |
| 4257 @defun ldiff list sublist | |
| 4258 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to | |
| 4259 one of the cons cells of @var{list}, then this function returns | |
| 4260 a copy of the part of @var{list} up to but not including | |
| 4261 @var{sublist}. For example, @code{(ldiff x (cddr x))} returns | |
| 4262 the first two elements of the list @code{x}. The result is a | |
| 4263 copy; the original @var{list} is not modified. If @var{sublist} | |
| 4264 is not a sublist of @var{list}, a copy of the entire @var{list} | |
| 4265 is returned. | |
| 4266 @end defun | |
| 4267 | |
| 4268 @defun copy-list list | |
| 4269 This function returns a copy of the list @var{list}. It copies | |
| 4270 dotted lists like @code{(1 2 . 3)} correctly. | |
| 4271 @end defun | |
| 4272 | |
| 4273 @defun copy-tree x &optional vecp | |
| 4274 This function returns a copy of the tree of cons cells @var{x}. | |
| 4275 Unlike @code{copy-sequence} (and its alias @code{copy-list}), | |
| 4276 which copies only along the @code{cdr} direction, this function | |
| 4277 copies (recursively) along both the @code{car} and the @code{cdr} | |
| 4278 directions. If @var{x} is not a cons cell, the function simply | |
| 4279 returns @var{x} unchanged. If the optional @var{vecp} argument | |
| 4280 is true, this function copies vectors (recursively) as well as | |
| 4281 cons cells. | |
| 4282 @end defun | |
| 4283 | |
| 4284 @defun tree-equal x y @t{&key :test :test-not :key} | |
| 4285 This function compares two trees of cons cells. If @var{x} and | |
| 4286 @var{y} are both cons cells, their @code{car}s and @code{cdr}s are | |
| 4287 compared recursively. If neither @var{x} nor @var{y} is a cons | |
| 4288 cell, they are compared by @code{eql}, or according to the | |
| 4289 specified test. The @code{:key} function, if specified, is | |
| 4290 applied to the elements of both trees. @xref{Sequences}. | |
| 4291 @end defun | |
| 4292 | |
| 4293 @iftex | |
| 4294 @secno=3 | |
| 4295 @end iftex | |
| 4296 | |
| 4297 @node Substitution of Expressions, Lists as Sets, List Functions, Lists | |
| 4298 @section Substitution of Expressions | |
| 4299 | |
| 4300 @noindent | |
| 4301 These functions substitute elements throughout a tree of cons | |
| 4302 cells. (@xref{Sequence Functions}, for the @code{substitute} | |
| 4303 function, which works on just the top-level elements of a list.) | |
| 4304 | |
| 4305 @defun subst new old tree @t{&key :test :test-not :key} | |
| 4306 This function substitutes occurrences of @var{old} with @var{new} | |
| 4307 in @var{tree}, a tree of cons cells. It returns a substituted | |
| 4308 tree, which will be a copy except that it may share storage with | |
| 4309 the argument @var{tree} in parts where no substitutions occurred. | |
| 4310 The original @var{tree} is not modified. This function recurses | |
| 4311 on, and compares against @var{old}, both @code{car}s and @code{cdr}s | |
| 4312 of the component cons cells. If @var{old} is itself a cons cell, | |
| 4313 then matching cells in the tree are substituted as usual without | |
| 4314 recursively substituting in that cell. Comparisons with @var{old} | |
| 4315 are done according to the specified test (@code{eql} by default). | |
| 4316 The @code{:key} function is applied to the elements of the tree | |
| 4317 but not to @var{old}. | |
| 4318 @end defun | |
| 4319 | |
| 4320 @defun nsubst new old tree @t{&key :test :test-not :key} | |
| 4321 This function is like @code{subst}, except that it works by | |
| 4322 destructive modification (by @code{setcar} or @code{setcdr}) | |
| 4323 rather than copying. | |
| 4324 @end defun | |
| 4325 | |
| 4326 @findex subst-if | |
| 4327 @findex subst-if-not | |
| 4328 @findex nsubst-if | |
| 4329 @findex nsubst-if-not | |
| 4330 The @code{subst-if}, @code{subst-if-not}, @code{nsubst-if}, and | |
| 4331 @code{nsubst-if-not} functions are defined similarly. | |
| 4332 | |
| 4333 @defun sublis alist tree @t{&key :test :test-not :key} | |
| 4334 This function is like @code{subst}, except that it takes an | |
| 4335 association list @var{alist} of @var{old}-@var{new} pairs. | |
| 4336 Each element of the tree (after applying the @code{:key} | |
| 4337 function, if any), is compared with the @code{car}s of | |
| 4338 @var{alist}; if it matches, it is replaced by the corresponding | |
| 4339 @code{cdr}. | |
| 4340 @end defun | |
| 4341 | |
| 4342 @defun nsublis alist tree @t{&key :test :test-not :key} | |
| 4343 This is a destructive version of @code{sublis}. | |
| 4344 @end defun | |
| 4345 | |
| 4346 @node Lists as Sets, Association Lists, Substitution of Expressions, Lists | |
| 4347 @section Lists as Sets | |
| 4348 | |
| 4349 @noindent | |
| 4350 These functions perform operations on lists which represent sets | |
| 4351 of elements. | |
| 4352 | |
| 4353 @defun member item list | |
| 4354 This MacLisp-compatible function searches @var{list} for an element | |
| 4355 which is @code{equal} to @var{item}. The @code{member} function is | |
| 4356 built-in to Emacs 19; this package defines it equivalently in Emacs 18. | |
| 4357 See the following function for a Common-Lisp compatible version. | |
| 4358 @end defun | |
| 4359 | |
| 4360 @defun member* item list @t{&key :test :test-not :key} | |
| 4361 This function searches @var{list} for an element matching @var{item}. | |
| 4362 If a match is found, it returns the cons cell whose @code{car} was | |
| 4363 the matching element. Otherwise, it returns @code{nil}. Elements | |
| 4364 are compared by @code{eql} by default; you can use the @code{:test}, | |
| 4365 @code{:test-not}, and @code{:key} arguments to modify this behavior. | |
| 4366 @xref{Sequences}. | |
| 4367 | |
| 4368 Note that this function's name is suffixed by @samp{*} to avoid | |
| 4369 the incompatible @code{member} function defined in Emacs 19. | |
| 4370 (That function uses @code{equal} for comparisons; it is equivalent | |
| 4371 to @code{(member* @var{item} @var{list} :test 'equal)}.) | |
| 4372 @end defun | |
| 4373 | |
| 4374 @findex member-if | |
| 4375 @findex member-if-not | |
| 4376 The @code{member-if} and @code{member-if-not} functions | |
| 4377 analogously search for elements which satisfy a given predicate. | |
| 4378 | |
| 4379 @defun tailp sublist list | |
| 4380 This function returns @code{t} if @var{sublist} is a sublist of | |
| 4381 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to | |
| 4382 any of its @code{cdr}s. | |
| 4383 @end defun | |
| 4384 | |
| 4385 @defun adjoin item list @t{&key :test :test-not :key} | |
| 4386 This function conses @var{item} onto the front of @var{list}, | |
| 4387 like @code{(cons @var{item} @var{list})}, but only if @var{item} | |
| 4388 is not already present on the list (as determined by @code{member*}). | |
| 4389 If a @code{:key} argument is specified, it is applied to | |
| 4390 @var{item} as well as to the elements of @var{list} during | |
| 4391 the search, on the reasoning that @var{item} is ``about'' to | |
| 4392 become part of the list. | |
| 4393 @end defun | |
| 4394 | |
| 4395 @defun union list1 list2 @t{&key :test :test-not :key} | |
| 4396 This function combines two lists which represent sets of items, | |
| 4397 returning a list that represents the union of those two sets. | |
| 4398 The result list will contain all items which appear in @var{list1} | |
| 4399 or @var{list2}, and no others. If an item appears in both | |
| 4400 @var{list1} and @var{list2} it will be copied only once. If | |
| 4401 an item is duplicated in @var{list1} or @var{list2}, it is | |
| 4402 undefined whether or not that duplication will survive in the | |
| 4403 result list. The order of elements in the result list is also | |
| 4404 undefined. | |
| 4405 @end defun | |
| 4406 | |
| 4407 @defun nunion list1 list2 @t{&key :test :test-not :key} | |
| 4408 This is a destructive version of @code{union}; rather than copying, | |
| 4409 it tries to reuse the storage of the argument lists if possible. | |
| 4410 @end defun | |
| 4411 | |
| 4412 @defun intersection list1 list2 @t{&key :test :test-not :key} | |
| 4413 This function computes the intersection of the sets represented | |
| 4414 by @var{list1} and @var{list2}. It returns the list of items | |
| 4415 which appear in both @var{list1} and @var{list2}. | |
| 4416 @end defun | |
| 4417 | |
| 4418 @defun nintersection list1 list2 @t{&key :test :test-not :key} | |
| 4419 This is a destructive version of @code{intersection}. It | |
| 4420 tries to reuse storage of @var{list1} rather than copying. | |
| 4421 It does @emph{not} reuse the storage of @var{list2}. | |
| 4422 @end defun | |
| 4423 | |
| 4424 @defun set-difference list1 list2 @t{&key :test :test-not :key} | |
| 4425 This function computes the ``set difference'' of @var{list1} | |
| 4426 and @var{list2}, i.e., the set of elements that appear in | |
| 4427 @var{list1} but @emph{not} in @var{list2}. | |
| 4428 @end defun | |
| 4429 | |
| 4430 @defun nset-difference list1 list2 @t{&key :test :test-not :key} | |
| 4431 This is a destructive @code{set-difference}, which will try | |
| 4432 to reuse @var{list1} if possible. | |
| 4433 @end defun | |
| 4434 | |
| 4435 @defun set-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
| 4436 This function computes the ``set exclusive or'' of @var{list1} | |
| 4437 and @var{list2}, i.e., the set of elements that appear in | |
| 4438 exactly one of @var{list1} and @var{list2}. | |
| 4439 @end defun | |
| 4440 | |
| 4441 @defun nset-exclusive-or list1 list2 @t{&key :test :test-not :key} | |
| 4442 This is a destructive @code{set-exclusive-or}, which will try | |
| 4443 to reuse @var{list1} and @var{list2} if possible. | |
| 4444 @end defun | |
| 4445 | |
| 4446 @defun subsetp list1 list2 @t{&key :test :test-not :key} | |
| 4447 This function checks whether @var{list1} represents a subset | |
| 4448 of @var{list2}, i.e., whether every element of @var{list1} | |
| 4449 also appears in @var{list2}. | |
| 4450 @end defun | |
| 4451 | |
| 4452 @node Association Lists, , Lists as Sets, Lists | |
| 4453 @section Association Lists | |
| 4454 | |
| 4455 @noindent | |
| 4456 An @dfn{association list} is a list representing a mapping from | |
| 4457 one set of values to another; any list whose elements are cons | |
| 4458 cells is an association list. | |
| 4459 | |
| 4460 @defun assoc* item a-list @t{&key :test :test-not :key} | |
| 4461 This function searches the association list @var{a-list} for an | |
| 4462 element whose @code{car} matches (in the sense of @code{:test}, | |
| 4463 @code{:test-not}, and @code{:key}, or by comparison with @code{eql}) | |
| 4464 a given @var{item}. It returns the matching element, if any, | |
| 4465 otherwise @code{nil}. It ignores elements of @var{a-list} which | |
| 4466 are not cons cells. (This corresponds to the behavior of | |
| 4467 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's | |
| 4468 @code{assoc} ignores @code{nil}s but considers any other non-cons | |
| 4469 elements of @var{a-list} to be an error.) | |
| 4470 @end defun | |
| 4471 | |
| 4472 @defun rassoc* item a-list @t{&key :test :test-not :key} | |
| 4473 This function searches for an element whose @code{cdr} matches | |
| 4474 @var{item}. If @var{a-list} represents a mapping, this applies | |
| 4475 the inverse of the mapping to @var{item}. | |
| 4476 @end defun | |
| 4477 | |
| 4478 @defun rassoc item a-list | |
| 4479 This function searches like @code{rassoc*} with a @code{:test} | |
| 4480 argument of @code{equal}. It is analogous to Emacs Lisp's | |
| 4481 standard @code{assoc} function, which derives from the MacLisp | |
| 4482 rather than the Common Lisp tradition. | |
| 4483 @end defun | |
| 4484 | |
| 4485 @findex assoc-if | |
| 4486 @findex assoc-if-not | |
| 4487 @findex rassoc-if | |
| 4488 @findex rassoc-if-not | |
| 4489 The @code{assoc-if}, @code{assoc-if-not}, @code{rassoc-if}, | |
| 4490 and @code{rassoc-if-not} functions are defined similarly. | |
| 4491 | |
| 4492 Two simple functions for constructing association lists are: | |
| 4493 | |
| 4494 @defun acons key value alist | |
| 4495 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}. | |
| 4496 @end defun | |
| 4497 | |
| 4498 @defun pairlis keys values &optional alist | |
| 4499 This is equivalent to @code{(nconc (mapcar* 'cons @var{keys} @var{values}) | |
| 4500 @var{alist})}. | |
| 4501 @end defun | |
| 4502 | |
| 4503 @node Hash Tables, Structures, Lists, Top | |
| 4504 @chapter Hash Tables | |
| 4505 | |
| 4506 @noindent | |
| 4507 Hash tables are now implemented directly in the C code and documented in | |
| 446 | 4508 @ref{Hash Tables,,, lispref, XEmacs Lisp Reference Manual}. |
| 428 | 4509 |
| 4510 @ignore | |
| 4511 A @dfn{hash table} is a data structure that maps ``keys'' onto | |
| 4512 ``values.'' Keys and values can be arbitrary Lisp data objects. | |
| 4513 Hash tables have the property that the time to search for a given | |
| 4514 key is roughly constant; simpler data structures like association | |
| 4515 lists take time proportional to the number of entries in the list. | |
| 4516 | |
| 4517 @defun make-hash-table @t{&key :test :size} | |
| 4518 This function creates and returns a hash-table object whose | |
| 4519 function for comparing elements is @code{:test} (@code{eql} | |
| 4520 by default), and which is allocated to fit about @code{:size} | |
| 4521 elements. The @code{:size} argument is purely advisory; the | |
| 4522 table will stretch automatically if you store more elements in | |
| 4523 it. If @code{:size} is omitted, a reasonable default is used. | |
| 4524 | |
| 4525 Common Lisp allows only @code{eq}, @code{eql}, @code{equal}, | |
| 4526 and @code{equalp} as legal values for the @code{:test} argument. | |
| 4527 In this package, any reasonable predicate function will work, | |
| 4528 though if you use something else you should check the details of | |
| 4529 the hashing function described below to make sure it is suitable | |
| 4530 for your predicate. | |
| 4531 | |
| 4532 Some versions of Emacs (like XEmacs) include a built-in hash | |
| 4533 table type; in these versions, @code{make-hash-table} with a test of | |
| 4534 @code{eq}, @code{eql}, or @code{equal} will use these built-in hash | |
| 4535 tables. In all other cases, it will return a hash-table object which | |
| 4536 takes the form of a list with an identifying ``tag'' symbol at the | |
| 4537 front. All of the hash table functions in this package can operate on | |
| 4538 both types of hash table; normally you will never know which type is | |
| 4539 being used. | |
| 4540 | |
| 4541 This function accepts the additional Common Lisp keywords | |
| 4542 @code{:rehash-size} and @code{:rehash-threshold}, but it ignores | |
| 4543 their values. | |
| 4544 @end defun | |
| 4545 | |
| 4546 @defun gethash key table &optional default | |
| 4547 This function looks up @var{key} in @var{table}. If @var{key} | |
| 4548 exists in the table, in the sense that it matches any of the existing | |
| 4549 keys according to the table's test function, then the associated value | |
| 4550 is returned. Otherwise, @var{default} (or @code{nil}) is returned. | |
| 4551 | |
| 4552 To store new data in the hash table, use @code{setf} on a call to | |
| 4553 @code{gethash}. If @var{key} already exists in the table, the | |
| 4554 corresponding value is changed to the stored value. If @var{key} | |
| 4555 does not already exist, a new entry is added to the table and the | |
| 4556 table is reallocated to a larger size if necessary. The @var{default} | |
| 4557 argument is allowed but ignored in this case. The situation is | |
| 440 | 4558 exactly analogous to that of @code{get}; @pxref{Property Lists}. |
| 428 | 4559 @end defun |
| 4560 | |
| 4561 @defun remhash key table | |
| 4562 This function removes the entry for @var{key} from @var{table}. | |
| 4563 If an entry was removed, it returns @code{t}. If @var{key} does | |
| 4564 not appear in the table, it does nothing and returns @code{nil}. | |
| 4565 @end defun | |
| 4566 | |
| 4567 @defun clrhash table | |
| 4568 This function removes all the entries from @var{table}, leaving | |
| 4569 an empty hash table. | |
| 4570 @end defun | |
| 4571 | |
| 4572 @defun maphash function table | |
| 4573 This function calls @var{function} for each entry in @var{table}. | |
| 4574 It passes two arguments to @var{function}, the key and the value | |
| 4575 of the given entry. The return value of @var{function} is ignored; | |
| 4576 @var{maphash} itself returns @code{nil}. @xref{Loop Facility}, for | |
| 4577 an alternate way of iterating over hash tables. | |
| 4578 @end defun | |
| 4579 | |
| 4580 @defun hash-table-count table This function returns the number of | |
| 4581 entries in @var{table}. @strong{Warning:} The current implementation of | |
| 4582 XEmacs hash-tables does not decrement the stored @code{count} | |
| 4583 when @code{remhash} removes an entry. Therefore, the return value of | |
| 4584 this function is not dependable if you have used @code{remhash} on the | |
| 4585 table and the table's test is @code{eq}, @code{eql}, or @code{equal}. | |
| 4586 A slower, but reliable, way to count the entries is | |
| 4587 @code{(loop for x being the hash-keys of @var{table} count t)}. | |
| 4588 @end defun | |
| 4589 | |
| 4590 @defun hash-table-p object This function returns @code{t} if | |
| 4591 @var{object} is a hash table, @code{nil} otherwise. It recognizes both | |
| 4592 types of hash tables (both XEmacs built-in tables and tables implemented | |
| 4593 with special lists.) | |
| 4594 @end defun | |
| 4595 | |
| 4596 Sometimes when dealing with hash tables it is useful to know the | |
| 4597 exact ``hash function'' that is used. This package implements | |
| 4598 hash tables using Emacs Lisp ``obarrays,'' which are the same | |
| 4599 data structure that Emacs Lisp uses to keep track of symbols. | |
| 4600 Each hash table includes an embedded obarray. Key values given | |
| 4601 to @code{gethash} are converted by various means into strings, | |
| 4602 which are then looked up in the obarray using @code{intern} and | |
| 4603 @code{intern-soft}. The symbol, or ``bucket,'' corresponding to | |
| 4604 a given key string includes as its @code{symbol-value} an association | |
| 4605 list of all key-value pairs which hash to that string. Depending | |
| 4606 on the test function, it is possible for many entries to hash to | |
| 4607 the same bucket. For example, if the test is @code{eql}, then the | |
| 4608 symbol @code{foo} and two separately built strings @code{"foo"} will | |
| 4609 create three entries in the same bucket. Search time is linear | |
| 4610 within buckets, so hash tables will be most effective if you arrange | |
| 4611 not to store too many things that hash the same. | |
| 4612 | |
| 4613 The following algorithm is used to convert Lisp objects to hash | |
| 4614 strings: | |
| 4615 | |
| 4616 @itemize @bullet | |
| 4617 @item | |
| 4618 Strings are used directly as hash strings. (However, if the test | |
| 4619 function is @code{equalp}, strings are @code{downcase}d first.) | |
| 4620 | |
| 4621 @item | |
| 4622 Symbols are hashed according to their @code{symbol-name}. | |
| 4623 | |
| 4624 @item | |
| 4625 Integers are hashed into one of 16 buckets depending on their value | |
| 4626 modulo 16. Floating-point numbers are truncated to integers and | |
| 4627 hashed modulo 16. | |
| 4628 | |
| 4629 @item | |
| 4630 Cons cells are hashed according to their @code{car}s; nonempty vectors | |
| 4631 are hashed according to their first element. | |
| 4632 | |
| 4633 @item | |
| 4634 All other types of objects hash into a single bucket named @code{"*"}. | |
| 4635 @end itemize | |
| 4636 | |
| 4637 @noindent | |
| 4638 Thus, for example, searching among many buffer objects in a hash table | |
| 4639 will devolve to a (still fairly fast) linear-time search through a | |
| 4640 single bucket, whereas searching for different symbols will be very | |
| 4641 fast since each symbol will, in general, hash into its own bucket. | |
| 4642 | |
| 4643 The size of the obarray in a hash table is automatically adjusted | |
| 4644 as the number of elements increases. | |
| 4645 | |
| 4646 As a special case, @code{make-hash-table} with a @code{:size} argument | |
| 4647 of 0 or 1 will create a hash-table object that uses a single association | |
| 4648 list rather than an obarray of many lists. For very small tables this | |
| 4649 structure will be more efficient since lookup does not require | |
| 4650 converting the key to a string or looking it up in an obarray. | |
| 4651 However, such tables are guaranteed to take time proportional to | |
| 4652 their size to do a search. | |
| 4653 @end ignore | |
| 4654 | |
| 4655 @iftex | |
| 4656 @chapno=18 | |
| 4657 @end iftex | |
| 4658 | |
| 4659 @node Structures, Assertions, Hash Tables, Top | |
| 4660 @chapter Structures | |
| 4661 | |
| 4662 @noindent | |
| 4663 The Common Lisp @dfn{structure} mechanism provides a general way | |
| 4664 to define data types similar to C's @code{struct} types. A | |
| 4665 structure is a Lisp object containing some number of @dfn{slots}, | |
| 4666 each of which can hold any Lisp data object. Functions are | |
| 4667 provided for accessing and setting the slots, creating or copying | |
| 4668 structure objects, and recognizing objects of a particular structure | |
| 4669 type. | |
| 4670 | |
| 4671 In true Common Lisp, each structure type is a new type distinct | |
| 4672 from all existing Lisp types. Since the underlying Emacs Lisp | |
| 4673 system provides no way to create new distinct types, this package | |
| 4674 implements structures as vectors (or lists upon request) with a | |
| 4675 special ``tag'' symbol to identify them. | |
| 4676 | |
|
5547
a46c5c8d6564
Avoid calling various macros "special operators" in the manuals.
Aidan Kehoe <kehoea@parhasard.net>
parents:
5361
diff
changeset
|
4677 @defmac defstruct name slots@dots{} |
| 428 | 4678 The @code{defstruct} form defines a new structure type called |
| 4679 @var{name}, with the specified @var{slots}. (The @var{slots} | |
| 4680 may begin with a string which documents the structure type.) | |
| 4681 In the simplest case, @var{name} and each of the @var{slots} | |
| 4682 are symbols. For example, | |
| 4683 | |
| 4684 @example | |
| 4685 (defstruct person name age sex) | |
| 4686 @end example | |
| 4687 | |
| 4688 @noindent | |
| 4689 defines a struct type called @code{person} which contains three | |
| 4690 slots. Given a @code{person} object @var{p}, you can access those | |
| 4691 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})}, | |
| 4692 and @code{(person-sex @var{p})}. You can also change these slots by | |
| 4693 using @code{setf} on any of these place forms: | |
| 4694 | |
| 4695 @example | |
| 4696 (incf (person-age birthday-boy)) | |
| 4697 @end example | |
| 4698 | |
| 4699 You can create a new @code{person} by calling @code{make-person}, | |
| 4700 which takes keyword arguments @code{:name}, @code{:age}, and | |
| 4701 @code{:sex} to specify the initial values of these slots in the | |
| 4702 new object. (Omitting any of these arguments leaves the corresponding | |
| 4703 slot ``undefined,'' according to the Common Lisp standard; in Emacs | |
| 4704 Lisp, such uninitialized slots are filled with @code{nil}.) | |
| 4705 | |
| 4706 Given a @code{person}, @code{(copy-person @var{p})} makes a new | |
| 4707 object of the same type whose slots are @code{eq} to those of @var{p}. | |
| 4708 | |
| 4709 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns | |
| 4710 true if @var{x} looks like a @code{person}, false otherwise. (Again, | |
| 4711 in Common Lisp this predicate would be exact; in Emacs Lisp the | |
| 4712 best it can do is verify that @var{x} is a vector of the correct | |
| 4713 length which starts with the correct tag symbol.) | |
| 4714 | |
| 4715 Accessors like @code{person-name} normally check their arguments | |
| 4716 (effectively using @code{person-p}) and signal an error if the | |
| 4717 argument is the wrong type. This check is affected by | |
| 4718 @code{(optimize (safety @dots{}))} declarations. Safety level 1, | |
| 4719 the default, uses a somewhat optimized check that will detect all | |
| 4720 incorrect arguments, but may use an uninformative error message | |
| 4721 (e.g., ``expected a vector'' instead of ``expected a @code{person}''). | |
| 4722 Safety level 0 omits all checks except as provided by the underlying | |
| 4723 @code{aref} call; safety levels 2 and 3 do rigorous checking that will | |
| 4724 always print a descriptive error message for incorrect inputs. | |
| 4725 @xref{Declarations}. | |
| 4726 | |
| 4727 @example | |
| 4728 (setq dave (make-person :name "Dave" :sex 'male)) | |
| 4729 @result{} [cl-struct-person "Dave" nil male] | |
| 4730 (setq other (copy-person dave)) | |
| 4731 @result{} [cl-struct-person "Dave" nil male] | |
| 4732 (eq dave other) | |
| 4733 @result{} nil | |
| 4734 (eq (person-name dave) (person-name other)) | |
| 4735 @result{} t | |
| 4736 (person-p dave) | |
| 4737 @result{} t | |
| 4738 (person-p [1 2 3 4]) | |
| 4739 @result{} nil | |
| 4740 (person-p "Bogus") | |
| 4741 @result{} nil | |
| 4742 (person-p '[cl-struct-person counterfeit person object]) | |
| 4743 @result{} t | |
| 4744 @end example | |
| 4745 | |
| 4746 In general, @var{name} is either a name symbol or a list of a name | |
| 4747 symbol followed by any number of @dfn{struct options}; each @var{slot} | |
| 4748 is either a slot symbol or a list of the form @samp{(@var{slot-name} | |
| 4749 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value} | |
| 4750 is a Lisp form which is evaluated any time an instance of the | |
| 4751 structure type is created without specifying that slot's value. | |
| 4752 | |
| 4753 Common Lisp defines several slot options, but the only one | |
| 4754 implemented in this package is @code{:read-only}. A non-@code{nil} | |
| 4755 value for this option means the slot should not be @code{setf}-able; | |
| 4756 the slot's value is determined when the object is created and does | |
| 4757 not change afterward. | |
| 4758 | |
| 4759 @example | |
| 4760 (defstruct person | |
| 4761 (name nil :read-only t) | |
| 4762 age | |
| 4763 (sex 'unknown)) | |
| 4764 @end example | |
| 4765 | |
| 4766 Any slot options other than @code{:read-only} are ignored. | |
| 4767 | |
| 4768 For obscure historical reasons, structure options take a different | |
| 4769 form than slot options. A structure option is either a keyword | |
| 4770 symbol, or a list beginning with a keyword symbol possibly followed | |
| 4771 by arguments. (By contrast, slot options are key-value pairs not | |
| 4772 enclosed in lists.) | |
| 4773 | |
| 4774 @example | |
| 4775 (defstruct (person (:constructor create-person) | |
| 4776 (:type list) | |
| 4777 :named) | |
| 4778 name age sex) | |
| 4779 @end example | |
| 4780 | |
| 4781 The following structure options are recognized. | |
| 4782 | |
| 4783 @table @code | |
| 4784 @iftex | |
| 4785 @itemmax=0 in | |
| 4786 @advance@leftskip-.5@tableindent | |
| 4787 @end iftex | |
| 4788 @item :conc-name | |
| 4789 The argument is a symbol whose print name is used as the prefix for | |
| 4790 the names of slot accessor functions. The default is the name of | |
| 4791 the struct type followed by a hyphen. The option @code{(:conc-name p-)} | |
| 4792 would change this prefix to @code{p-}. Specifying @code{nil} as an | |
| 4793 argument means no prefix, so that the slot names themselves are used | |
| 4794 to name the accessor functions. | |
| 4795 | |
| 4796 @item :constructor | |
| 4797 In the simple case, this option takes one argument which is an | |
| 4798 alternate name to use for the constructor function. The default | |
| 4799 is @code{make-@var{name}}, e.g., @code{make-person}. The above | |
| 4800 example changes this to @code{create-person}. Specifying @code{nil} | |
| 4801 as an argument means that no standard constructor should be | |
| 4802 generated at all. | |
| 4803 | |
| 4804 In the full form of this option, the constructor name is followed | |
| 4805 by an arbitrary argument list. @xref{Program Structure}, for a | |
| 4806 description of the format of Common Lisp argument lists. All | |
| 4807 options, such as @code{&rest} and @code{&key}, are supported. | |
| 4808 The argument names should match the slot names; each slot is | |
| 4809 initialized from the corresponding argument. Slots whose names | |
| 4810 do not appear in the argument list are initialized based on the | |
| 4811 @var{default-value} in their slot descriptor. Also, @code{&optional} | |
| 4812 and @code{&key} arguments which don't specify defaults take their | |
| 4813 defaults from the slot descriptor. It is legal to include arguments | |
| 4814 which don't correspond to slot names; these are useful if they are | |
| 4815 referred to in the defaults for optional, keyword, or @code{&aux} | |
| 4816 arguments which @emph{do} correspond to slots. | |
| 4817 | |
| 4818 You can specify any number of full-format @code{:constructor} | |
| 4819 options on a structure. The default constructor is still generated | |
| 4820 as well unless you disable it with a simple-format @code{:constructor} | |
| 4821 option. | |
| 4822 | |
| 4823 @example | |
| 4824 (defstruct | |
| 4825 (person | |
| 4826 (:constructor nil) ; no default constructor | |
| 4827 (:constructor new-person (name sex &optional (age 0))) | |
| 4828 (:constructor new-hound (&key (name "Rover") | |
| 4829 (dog-years 0) | |
| 4830 &aux (age (* 7 dog-years)) | |
| 4831 (sex 'canine)))) | |
| 4832 name age sex) | |
| 4833 @end example | |
| 4834 | |
| 4835 The first constructor here takes its arguments positionally rather | |
| 4836 than by keyword. (In official Common Lisp terminology, constructors | |
| 4837 that work By Order of Arguments instead of by keyword are called | |
| 4838 ``BOA constructors.'' No, I'm not making this up.) For example, | |
| 4839 @code{(new-person "Jane" 'female)} generates a person whose slots | |
| 4840 are @code{"Jane"}, 0, and @code{female}, respectively. | |
| 4841 | |
| 4842 The second constructor takes two keyword arguments, @code{:name}, | |
| 4843 which initializes the @code{name} slot and defaults to @code{"Rover"}, | |
| 4844 and @code{:dog-years}, which does not itself correspond to a slot | |
| 4845 but which is used to initialize the @code{age} slot. The @code{sex} | |
| 4846 slot is forced to the symbol @code{canine} with no syntax for | |
| 4847 overriding it. | |
| 4848 | |
| 4849 @item :copier | |
| 4850 The argument is an alternate name for the copier function for | |
| 4851 this type. The default is @code{copy-@var{name}}. @code{nil} | |
| 4852 means not to generate a copier function. (In this implementation, | |
| 4853 all copier functions are simply synonyms for @code{copy-sequence}.) | |
| 4854 | |
| 4855 @item :predicate | |
| 4856 The argument is an alternate name for the predicate which recognizes | |
| 4857 objects of this type. The default is @code{@var{name}-p}. @code{nil} | |
| 4858 means not to generate a predicate function. (If the @code{:type} | |
| 4859 option is used without the @code{:named} option, no predicate is | |
| 4860 ever generated.) | |
| 4861 | |
| 4862 In true Common Lisp, @code{typep} is always able to recognize a | |
| 4863 structure object even if @code{:predicate} was used. In this | |
| 4864 package, @code{typep} simply looks for a function called | |
| 4865 @code{@var{typename}-p}, so it will work for structure types | |
| 4866 only if they used the default predicate name. | |
| 4867 | |
| 4868 @item :include | |
| 4869 This option implements a very limited form of C++-style inheritance. | |
| 4870 The argument is the name of another structure type previously | |
| 4871 created with @code{defstruct}. The effect is to cause the new | |
| 4872 structure type to inherit all of the included structure's slots | |
| 4873 (plus, of course, any new slots described by this struct's slot | |
| 4874 descriptors). The new structure is considered a ``specialization'' | |
| 4875 of the included one. In fact, the predicate and slot accessors | |
| 4876 for the included type will also accept objects of the new type. | |
| 4877 | |
| 4878 If there are extra arguments to the @code{:include} option after | |
| 4879 the included-structure name, these options are treated as replacement | |
| 4880 slot descriptors for slots in the included structure, possibly with | |
| 4881 modified default values. Borrowing an example from Steele: | |
| 4882 | |
| 4883 @example | |
| 4884 (defstruct person name (age 0) sex) | |
| 4885 @result{} person | |
| 4886 (defstruct (astronaut (:include person (age 45))) | |
| 4887 helmet-size | |
| 4888 (favorite-beverage 'tang)) | |
| 4889 @result{} astronaut | |
| 4890 | |
| 4891 (setq joe (make-person :name "Joe")) | |
| 4892 @result{} [cl-struct-person "Joe" 0 nil] | |
| 4893 (setq buzz (make-astronaut :name "Buzz")) | |
| 4894 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang] | |
| 4895 | |
| 4896 (list (person-p joe) (person-p buzz)) | |
| 4897 @result{} (t t) | |
| 4898 (list (astronaut-p joe) (astronaut-p buzz)) | |
| 4899 @result{} (nil t) | |
| 4900 | |
| 4901 (person-name buzz) | |
| 4902 @result{} "Buzz" | |
| 4903 (astronaut-name joe) | |
| 4904 @result{} error: "astronaut-name accessing a non-astronaut" | |
| 4905 @end example | |
| 4906 | |
| 4907 Thus, if @code{astronaut} is a specialization of @code{person}, | |
| 4908 then every @code{astronaut} is also a @code{person} (but not the | |
| 4909 other way around). Every @code{astronaut} includes all the slots | |
| 4910 of a @code{person}, plus extra slots that are specific to | |
| 4911 astronauts. Operations that work on people (like @code{person-name}) | |
| 4912 work on astronauts just like other people. | |
| 4913 | |
| 4914 @item :print-function | |
| 4915 In full Common Lisp, this option allows you to specify a function | |
| 4916 which is called to print an instance of the structure type. The | |
| 4917 Emacs Lisp system offers no hooks into the Lisp printer which would | |
| 4918 allow for such a feature, so this package simply ignores | |
| 4919 @code{:print-function}. | |
| 4920 | |
| 4921 @item :type | |
| 4922 The argument should be one of the symbols @code{vector} or @code{list}. | |
| 4923 This tells which underlying Lisp data type should be used to implement | |
| 4924 the new structure type. Vectors are used by default, but | |
| 4925 @code{(:type list)} will cause structure objects to be stored as | |
| 4926 lists instead. | |
| 4927 | |
| 4928 The vector representation for structure objects has the advantage | |
| 4929 that all structure slots can be accessed quickly, although creating | |
| 4930 vectors is a bit slower in Emacs Lisp. Lists are easier to create, | |
| 4931 but take a relatively long time accessing the later slots. | |
| 4932 | |
| 4933 @item :named | |
| 4934 This option, which takes no arguments, causes a characteristic ``tag'' | |
| 4935 symbol to be stored at the front of the structure object. Using | |
| 4936 @code{:type} without also using @code{:named} will result in a | |
| 4937 structure type stored as plain vectors or lists with no identifying | |
| 4938 features. | |
| 4939 | |
| 4940 The default, if you don't specify @code{:type} explicitly, is to | |
| 4941 use named vectors. Therefore, @code{:named} is only useful in | |
| 4942 conjunction with @code{:type}. | |
| 4943 | |
| 4944 @example | |
| 4945 (defstruct (person1) name age sex) | |
| 4946 (defstruct (person2 (:type list) :named) name age sex) | |
| 4947 (defstruct (person3 (:type list)) name age sex) | |
| 4948 | |
| 4949 (setq p1 (make-person1)) | |
| 4950 @result{} [cl-struct-person1 nil nil nil] | |
| 4951 (setq p2 (make-person2)) | |
| 4952 @result{} (person2 nil nil nil) | |
| 4953 (setq p3 (make-person3)) | |
| 4954 @result{} (nil nil nil) | |
| 4955 | |
| 4956 (person1-p p1) | |
| 4957 @result{} t | |
| 4958 (person2-p p2) | |
| 4959 @result{} t | |
| 4960 (person3-p p3) | |
| 4961 @result{} error: function person3-p undefined | |
| 4962 @end example | |
| 4963 | |
| 4964 Since unnamed structures don't have tags, @code{defstruct} is not | |
| 4965 able to make a useful predicate for recognizing them. Also, | |
| 4966 accessors like @code{person3-name} will be generated but they | |
| 4967 will not be able to do any type checking. The @code{person3-name} | |
| 4968 function, for example, will simply be a synonym for @code{car} in | |
| 4969 this case. By contrast, @code{person2-name} is able to verify | |
| 4970 that its argument is indeed a @code{person2} object before | |
| 4971 proceeding. | |
| 4972 | |
| 4973 @item :initial-offset | |
| 4974 The argument must be a nonnegative integer. It specifies a | |
| 4975 number of slots to be left ``empty'' at the front of the | |
| 4976 structure. If the structure is named, the tag appears at the | |
| 4977 specified position in the list or vector; otherwise, the first | |
| 4978 slot appears at that position. Earlier positions are filled | |
| 4979 with @code{nil} by the constructors and ignored otherwise. If | |
| 4980 the type @code{:include}s another type, then @code{:initial-offset} | |
| 4981 specifies a number of slots to be skipped between the last slot | |
| 4982 of the included type and the first new slot. | |
| 4983 @end table | |
|
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4984 @end defmac |
| 428 | 4985 |
| 4986 Except as noted, the @code{defstruct} facility of this package is | |
| 4987 entirely compatible with that of Common Lisp. | |
| 4988 | |
| 4989 @iftex | |
| 4990 @chapno=23 | |
| 4991 @end iftex | |
| 4992 | |
| 4993 @node Assertions, Efficiency Concerns, Structures, Top | |
| 4994 @chapter Assertions and Errors | |
| 4995 | |
| 4996 @noindent | |
| 4997 This section describes two macros that test @dfn{assertions}, i.e., | |
| 4998 conditions which must be true if the program is operating correctly. | |
| 4999 Assertions never add to the behavior of a Lisp program; they simply | |
| 5000 make ``sanity checks'' to make sure everything is as it should be. | |
| 5001 | |
| 5002 If the optimization property @code{speed} has been set to 3, and | |
| 5003 @code{safety} is less than 3, then the byte-compiler will optimize | |
| 5004 away the following assertions. Because assertions might be optimized | |
| 5005 away, it is a bad idea for them to include side-effects. | |
| 5006 | |
|
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|
5007 @defmac assert test-form [show-args string args@dots{}] |
| 428 | 5008 This form verifies that @var{test-form} is true (i.e., evaluates to |
| 5009 a non-@code{nil} value). If so, it returns @code{nil}. If the test | |
| 5010 is not satisfied, @code{assert} signals an error. | |
| 5011 | |
| 5012 A default error message will be supplied which includes @var{test-form}. | |
| 5013 You can specify a different error message by including a @var{string} | |
| 5014 argument plus optional extra arguments. Those arguments are simply | |
| 5015 passed to @code{error} to signal the error. | |
| 5016 | |
| 5017 If the optional second argument @var{show-args} is @code{t} instead | |
| 5018 of @code{nil}, then the error message (with or without @var{string}) | |
| 5019 will also include all non-constant arguments of the top-level | |
| 5020 @var{form}. For example: | |
| 5021 | |
| 5022 @example | |
| 5023 (assert (> x 10) t "x is too small: %d") | |
| 5024 @end example | |
| 5025 | |
| 446 | 5026 This usage of @var{show-args} is a change to Common Lisp. In |
| 428 | 5027 true Common Lisp, the second argument gives a list of @var{places} |
| 5028 which can be @code{setf}'d by the user before continuing from the | |
| 446 | 5029 error. |
|
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|
5030 @end defmac |
|
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|
5031 |
|
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|
5032 @defmac check-type place type &optional string |
| 446 | 5033 This form verifies that @var{place} evaluates to a value of type |
| 428 | 5034 @var{type}. If so, it returns @code{nil}. If not, @code{check-type} |
| 446 | 5035 signals a continuable @code{wrong-type-argument} error. The default |
| 5036 error message lists the erroneous value along with @var{type} and | |
| 5037 @var{place} themselves. If @var{string} is specified, it is included in | |
| 5038 the error message in place of @var{type}. For example: | |
| 428 | 5039 |
| 5040 @example | |
| 5041 (check-type x (integer 1 *) "a positive integer") | |
| 5042 @end example | |
| 5043 | |
| 5044 @xref{Type Predicates}, for a description of the type specifiers | |
| 5045 that may be used for @var{type}. | |
| 5046 | |
| 446 | 5047 Note that as in Common Lisp, the first argument to @code{check-type} |
| 5048 should be a @var{place} suitable for use by @code{setf}, because | |
| 5049 @code{check-type} signals a continuable error that allows the user to | |
| 5050 modify @var{place}, most simply by returning a value from the debugger. | |
|
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|
5051 @end defmac |
| 428 | 5052 |
| 5053 The following error-related macro is also defined: | |
| 5054 | |
|
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|
5055 @defmac ignore-errors forms@dots{} |
| 428 | 5056 This executes @var{forms} exactly like a @code{progn}, except that |
| 5057 errors are ignored during the @var{forms}. More precisely, if | |
| 5058 an error is signalled then @code{ignore-errors} immediately | |
| 5059 aborts execution of the @var{forms} and returns @code{nil}. | |
| 5060 If the @var{forms} complete successfully, @code{ignore-errors} | |
| 5061 returns the result of the last @var{form}. | |
|
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|
5062 @end defmac |
| 428 | 5063 |
| 5064 @node Efficiency Concerns, Common Lisp Compatibility, Assertions, Top | |
| 5065 @appendix Efficiency Concerns | |
| 5066 | |
| 5067 @appendixsec Macros | |
| 5068 | |
| 5069 @noindent | |
| 5070 Many of the advanced features of this package, such as @code{defun*}, | |
| 5071 @code{loop}, and @code{setf}, are implemented as Lisp macros. In | |
| 5072 byte-compiled code, these complex notations will be expanded into | |
| 5073 equivalent Lisp code which is simple and efficient. For example, | |
| 5074 the forms | |
| 5075 | |
| 5076 @example | |
| 5077 (incf i n) | |
| 5078 (push x (car p)) | |
| 5079 @end example | |
| 5080 | |
| 5081 @noindent | |
| 5082 are expanded at compile-time to the Lisp forms | |
| 5083 | |
| 5084 @example | |
| 5085 (setq i (+ i n)) | |
| 5086 (setcar p (cons x (car p))) | |
| 5087 @end example | |
| 5088 | |
| 5089 @noindent | |
| 5090 which are the most efficient ways of doing these respective operations | |
| 5091 in Lisp. Thus, there is no performance penalty for using the more | |
| 5092 readable @code{incf} and @code{push} forms in your compiled code. | |
| 5093 | |
| 5094 @emph{Interpreted} code, on the other hand, must expand these macros | |
| 5095 every time they are executed. For this reason it is strongly | |
| 5096 recommended that code making heavy use of macros be compiled. | |
| 5097 (The features labelled ``Special Form'' instead of ``Function'' in | |
| 5098 this manual are macros.) A loop using @code{incf} a hundred times | |
| 5099 will execute considerably faster if compiled, and will also | |
| 5100 garbage-collect less because the macro expansion will not have | |
| 5101 to be generated, used, and thrown away a hundred times. | |
| 5102 | |
| 5103 You can find out how a macro expands by using the | |
| 5104 @code{cl-prettyexpand} function. | |
| 5105 | |
| 5106 @defun cl-prettyexpand form &optional full | |
| 5107 This function takes a single Lisp form as an argument and inserts | |
| 5108 a nicely formatted copy of it in the current buffer (which must be | |
| 5109 in Lisp mode so that indentation works properly). It also expands | |
| 5110 all Lisp macros which appear in the form. The easiest way to use | |
| 5111 this function is to go to the @code{*scratch*} buffer and type, say, | |
| 5112 | |
| 5113 @example | |
| 5114 (cl-prettyexpand '(loop for x below 10 collect x)) | |
| 5115 @end example | |
| 5116 | |
| 5117 @noindent | |
| 5118 and type @kbd{C-x C-e} immediately after the closing parenthesis; | |
| 5119 the expansion | |
| 5120 | |
| 5121 @example | |
| 5122 (block nil | |
| 5123 (let* ((x 0) | |
| 5124 (G1004 nil)) | |
| 5125 (while (< x 10) | |
| 5126 (setq G1004 (cons x G1004)) | |
| 5127 (setq x (+ x 1))) | |
| 5128 (nreverse G1004))) | |
| 5129 @end example | |
| 5130 | |
| 5131 @noindent | |
| 5132 will be inserted into the buffer. (The @code{block} macro is | |
| 5133 expanded differently in the interpreter and compiler, so | |
| 5134 @code{cl-prettyexpand} just leaves it alone. The temporary | |
| 5135 variable @code{G1004} was created by @code{gensym}.) | |
| 5136 | |
| 5137 If the optional argument @var{full} is true, then @emph{all} | |
| 5138 macros are expanded, including @code{block}, @code{eval-when}, | |
| 5139 and compiler macros. Expansion is done as if @var{form} were | |
| 5140 a top-level form in a file being compiled. For example, | |
| 5141 | |
| 5142 @example | |
| 5143 (cl-prettyexpand '(pushnew 'x list)) | |
| 5144 @print{} (setq list (adjoin 'x list)) | |
| 5145 (cl-prettyexpand '(pushnew 'x list) t) | |
| 5146 @print{} (setq list (if (memq 'x list) list (cons 'x list))) | |
| 5147 (cl-prettyexpand '(caddr (member* 'a list)) t) | |
| 5148 @print{} (car (cdr (cdr (memq 'a list)))) | |
| 5149 @end example | |
| 5150 | |
| 5151 Note that @code{adjoin}, @code{caddr}, and @code{member*} all | |
| 5152 have built-in compiler macros to optimize them in common cases. | |
| 5153 @end defun | |
| 5154 | |
| 5155 @ifinfo | |
| 5156 @example | |
| 5157 | |
| 5158 @end example | |
| 5159 @end ifinfo | |
| 5160 @appendixsec Error Checking | |
| 5161 | |
| 5162 @noindent | |
| 5163 Common Lisp compliance has in general not been sacrificed for the | |
| 5164 sake of efficiency. A few exceptions have been made for cases | |
| 5165 where substantial gains were possible at the expense of marginal | |
| 5166 incompatibility. One example is the use of @code{memq} (which is | |
| 5167 treated very efficiently by the byte-compiler) to scan for keyword | |
| 5168 arguments; this can become confused in rare cases when keyword | |
| 5169 symbols are used as both keywords and data values at once. This | |
| 5170 is extremely unlikely to occur in practical code, and the use of | |
| 5171 @code{memq} allows functions with keyword arguments to be nearly | |
| 5172 as fast as functions that use @code{&optional} arguments. | |
| 5173 | |
| 5174 The Common Lisp standard (as embodied in Steele's book) uses the | |
| 5175 phrase ``it is an error if'' to indicate a situation which is not | |
| 5176 supposed to arise in complying programs; implementations are strongly | |
| 5177 encouraged but not required to signal an error in these situations. | |
| 5178 This package sometimes omits such error checking in the interest of | |
| 5179 compactness and efficiency. For example, @code{do} variable | |
| 5180 specifiers are supposed to be lists of one, two, or three forms; | |
| 5181 extra forms are ignored by this package rather than signalling a | |
| 5182 syntax error. The @code{endp} function is simply a synonym for | |
| 5183 @code{null} in this package. Functions taking keyword arguments | |
| 5184 will accept an odd number of arguments, treating the trailing | |
| 5185 keyword as if it were followed by the value @code{nil}. | |
| 5186 | |
| 5187 Argument lists (as processed by @code{defun*} and friends) | |
| 5188 @emph{are} checked rigorously except for the minor point just | |
| 5189 mentioned; in particular, keyword arguments are checked for | |
| 5190 validity, and @code{&allow-other-keys} and @code{:allow-other-keys} | |
| 5191 are fully implemented. Keyword validity checking is slightly | |
| 5192 time consuming (though not too bad in byte-compiled code); | |
| 5193 you can use @code{&allow-other-keys} to omit this check. Functions | |
| 5194 defined in this package such as @code{find} and @code{member*} | |
| 5195 do check their keyword arguments for validity. | |
| 5196 | |
| 5197 @ifinfo | |
| 5198 @example | |
| 5199 | |
| 5200 @end example | |
| 5201 @end ifinfo | |
| 5202 @appendixsec Optimizing Compiler | |
| 5203 | |
| 5204 @noindent | |
| 5205 The byte-compiler that comes with Emacs 18 normally fails to expand | |
| 5206 macros that appear in top-level positions in the file (i.e., outside | |
| 5207 of @code{defun}s or other enclosing forms). This would have | |
| 5208 disastrous consequences to programs that used such top-level macros | |
| 5209 as @code{defun*}, @code{eval-when}, and @code{defstruct}. To | |
| 5210 work around this problem, the @dfn{CL} package patches the Emacs | |
| 5211 18 compiler to expand top-level macros. This patch will apply to | |
| 5212 your own macros, too, if they are used in a top-level context. | |
| 5213 The patch will not harm versions of the Emacs 18 compiler which | |
| 5214 have already had a similar patch applied, nor will it affect the | |
| 5215 optimizing Emacs 19 byte-compiler written by Jamie Zawinski and | |
| 5216 Hallvard Furuseth. The patch is applied to the byte compiler's | |
| 5217 code in Emacs' memory, @emph{not} to the @file{bytecomp.elc} file | |
| 5218 stored on disk. | |
| 5219 | |
| 5220 The Emacs 19 compiler (for Emacs 18) is available from various | |
| 5221 Emacs Lisp archive sites such as @code{archive.cis.ohio-state.edu}. | |
| 5222 Its use is highly recommended; many of the Common Lisp macros emit | |
| 5223 code which can be improved by optimization. In particular, | |
| 5224 @code{block}s (whether explicit or implicit in constructs like | |
| 5225 @code{defun*} and @code{loop}) carry a fair run-time penalty; the | |
| 5226 optimizing compiler removes @code{block}s which are not actually | |
| 5227 referenced by @code{return} or @code{return-from} inside the block. | |
| 5228 | |
|
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5229 @node Common Lisp Compatibility, Porting Common Lisp, Efficiency Concerns, Top |
| 428 | 5230 @appendix Common Lisp Compatibility |
| 5231 | |
| 5232 @noindent | |
| 5233 Following is a list of all known incompatibilities between this | |
| 5234 package and Common Lisp as documented in Steele (2nd edition). | |
| 5235 | |
| 5236 Certain function names, such as @code{member}, @code{assoc}, and | |
| 5237 @code{floor}, were already taken by (incompatible) Emacs Lisp | |
| 5238 functions; this package appends @samp{*} to the names of its | |
| 5239 Common Lisp versions of these functions. | |
| 5240 | |
| 5241 The word @code{defun*} is required instead of @code{defun} in order | |
| 5242 to use extended Common Lisp argument lists in a function. Likewise, | |
| 5243 @code{defmacro*} and @code{function*} are versions of those forms | |
| 5244 which understand full-featured argument lists. The @code{&whole} | |
| 5245 keyword does not work in @code{defmacro} argument lists (except | |
| 5246 inside recursive argument lists). | |
| 5247 | |
| 5248 In order to allow an efficient implementation, keyword arguments use | |
| 5249 a slightly cheesy parser which may be confused if a keyword symbol | |
| 5250 is passed as the @emph{value} of another keyword argument. | |
| 5251 (Specifically, @code{(memq :@var{keyword} @var{rest-of-arguments})} | |
| 5252 is used to scan for @code{:@var{keyword}} among the supplied | |
| 5253 keyword arguments.) | |
| 5254 | |
| 5255 The @code{eql} and @code{equal} predicates do not distinguish | |
| 5256 between IEEE floating-point plus and minus zero. The @code{equalp} | |
| 5257 predicate has several differences with Common Lisp; @pxref{Predicates}. | |
| 5258 | |
| 5259 The @code{setf} mechanism is entirely compatible, except that | |
| 5260 setf-methods return a list of five values rather than five | |
| 5261 values directly. Also, the new ``@code{setf} function'' concept | |
| 5262 (typified by @code{(defun (setf foo) @dots{})}) is not implemented. | |
| 5263 | |
| 5264 The @code{do-all-symbols} form is the same as @code{do-symbols} | |
| 5265 with no @var{obarray} argument. In Common Lisp, this form would | |
| 5266 iterate over all symbols in all packages. Since Emacs obarrays | |
| 5267 are not a first-class package mechanism, there is no way for | |
| 5268 @code{do-all-symbols} to locate any but the default obarray. | |
| 5269 | |
| 5270 The @code{loop} macro is complete except that @code{loop-finish} | |
| 5271 and type specifiers are unimplemented. | |
| 5272 | |
| 5273 Many Common Lisp declarations are ignored, and others match | |
| 5274 the Common Lisp standard in concept but not in detail. For | |
| 5275 example, local @code{special} declarations, which are purely | |
| 5276 advisory in Emacs Lisp, do not rigorously obey the scoping rules | |
| 5277 set down in Steele's book. | |
| 5278 | |
| 5279 The variable @code{*gensym-counter*} starts out with a pseudo-random | |
| 5280 value rather than with zero. This is to cope with the fact that | |
| 5281 generated symbols become interned when they are written to and | |
| 5282 loaded back from a file. | |
| 5283 | |
| 5284 The @code{defstruct} facility is compatible, except that structures | |
| 5285 are of type @code{:type vector :named} by default rather than some | |
| 5286 special, distinct type. Also, the @code{:type} slot option is ignored. | |
| 5287 | |
| 5288 The second argument of @code{check-type} is treated differently. | |
| 5289 | |
|
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changeset
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5290 @node Porting Common Lisp, Function Index, Common Lisp Compatibility, Top |
| 428 | 5291 @appendix Porting Common Lisp |
| 5292 | |
| 5293 @noindent | |
| 5294 This package is meant to be used as an extension to Emacs Lisp, | |
| 5295 not as an Emacs implementation of true Common Lisp. Some of the | |
| 5296 remaining differences between Emacs Lisp and Common Lisp make it | |
| 5297 difficult to port large Common Lisp applications to Emacs. For | |
| 5298 one, some of the features in this package are not fully compliant | |
| 5299 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there | |
| 5300 are also quite a few features that this package does not provide | |
| 5301 at all. Here are some major omissions that you will want watch out | |
| 5302 for when bringing Common Lisp code into Emacs. | |
| 5303 | |
| 5304 @itemize @bullet | |
| 5305 @item | |
| 5306 Case-insensitivity. Symbols in Common Lisp are case-insensitive | |
| 5307 by default. Some programs refer to a function or variable as | |
| 5308 @code{foo} in one place and @code{Foo} or @code{FOO} in another. | |
| 5309 Emacs Lisp will treat these as three distinct symbols. | |
| 5310 | |
| 5311 Some Common Lisp code is written in all upper-case. While Emacs | |
| 5312 is happy to let the program's own functions and variables use | |
| 5313 this convention, calls to Lisp builtins like @code{if} and | |
| 5314 @code{defun} will have to be changed to lower-case. | |
| 5315 | |
| 5316 @item | |
| 5317 Lexical scoping. In Common Lisp, function arguments and @code{let} | |
| 5318 bindings apply only to references physically within their bodies | |
| 5319 (or within macro expansions in their bodies). Emacs Lisp, by | |
| 5320 contrast, uses @dfn{dynamic scoping} wherein a binding to a | |
| 5321 variable is visible even inside functions called from the body. | |
| 5322 | |
| 5323 Variables in Common Lisp can be made dynamically scoped by | |
| 5324 declaring them @code{special} or using @code{defvar}. In Emacs | |
| 5325 Lisp it is as if all variables were declared @code{special}. | |
| 5326 | |
| 5327 Often you can use code that was written for lexical scoping | |
| 5328 even in a dynamically scoped Lisp, but not always. Here is | |
| 5329 an example of a Common Lisp code fragment that would fail in | |
| 5330 Emacs Lisp: | |
| 5331 | |
| 5332 @example | |
| 5333 (defun map-odd-elements (func list) | |
| 5334 (loop for x in list | |
| 5335 for flag = t then (not flag) | |
| 5336 collect (if flag x (funcall func x)))) | |
| 5337 | |
| 5338 (defun add-odd-elements (list x) | |
| 5339 (map-odd-elements (function (lambda (a) (+ a x))) list)) | |
| 5340 @end example | |
| 5341 | |
| 5342 @noindent | |
| 5343 In Common Lisp, the two functions' usages of @code{x} are completely | |
| 5344 independent. In Emacs Lisp, the binding to @code{x} made by | |
| 5345 @code{add-odd-elements} will have been hidden by the binding | |
| 5346 in @code{map-odd-elements} by the time the @code{(+ a x)} function | |
| 5347 is called. | |
| 5348 | |
| 5349 (This package avoids such problems in its own mapping functions | |
| 5350 by using names like @code{cl-x} instead of @code{x} internally; | |
| 5351 as long as you don't use the @code{cl-} prefix for your own | |
| 5352 variables no collision can occur.) | |
| 5353 | |
| 5354 @xref{Lexical Bindings}, for a description of the @code{lexical-let} | |
| 5355 form which establishes a Common Lisp-style lexical binding, and some | |
| 5356 examples of how it differs from Emacs' regular @code{let}. | |
| 5357 | |
| 5358 @item | |
| 5359 Common Lisp allows the shorthand @code{#'x} to stand for | |
| 5360 @code{(function x)}, just as @code{'x} stands for @code{(quote x)}. | |
| 5361 In Common Lisp, one traditionally uses @code{#'} notation when | |
| 5362 referring to the name of a function. In Emacs Lisp, it works | |
| 5363 just as well to use a regular quote: | |
| 5364 | |
| 5365 @example | |
| 442 | 5366 (loop for x in y by #'cddr collect (mapcar #'plusp x)) ; Common Lisp |
| 5367 (loop for x in y by 'cddr collect (mapcar 'plusp x)) ; Emacs Lisp | |
| 428 | 5368 @end example |
| 5369 | |
| 5370 When @code{#'} introduces a @code{lambda} form, it is best to | |
| 5371 write out @code{(function ...)} longhand in Emacs Lisp. You can | |
| 5372 use a regular quote, but then the byte-compiler won't know that | |
| 5373 the @code{lambda} expression is code that can be compiled. | |
| 5374 | |
| 5375 @example | |
| 5376 (mapcar #'(lambda (x) (* x 2)) list) ; Common Lisp | |
| 5377 (mapcar (function (lambda (x) (* x 2))) list) ; Emacs Lisp | |
| 5378 @end example | |
| 5379 | |
| 5380 XEmacs supports @code{#'} notation starting with version 19.8. | |
| 5381 | |
| 5382 @item | |
| 5383 Reader macros. Common Lisp includes a second type of macro that | |
| 5384 works at the level of individual characters. For example, Common | |
| 5385 Lisp implements the quote notation by a reader macro called @code{'}, | |
| 5386 whereas Emacs Lisp's parser just treats quote as a special case. | |
| 5387 Some Lisp packages use reader macros to create special syntaxes | |
| 5388 for themselves, which the Emacs parser is incapable of reading. | |
| 5389 | |
| 5390 @item | |
| 5391 Other syntactic features. Common Lisp provides a number of | |
| 5392 notations beginning with @code{#} that the Emacs Lisp parser | |
| 5393 won't understand. For example, @samp{#| ... |#} is an | |
| 5394 alternate comment notation, and @samp{#+lucid (foo)} tells | |
| 5395 the parser to ignore the @code{(foo)} except in Lucid Common | |
| 5396 Lisp. | |
| 5397 | |
| 5398 The number prefixes `#b', `#o', and `#x', however, are supported | |
| 5399 by the Emacs Lisp parser to represent numbers in binary, octal, | |
| 5400 and hexadecimal notation (or radix), just like in Common Lisp. | |
| 5401 | |
| 5402 @item | |
| 5403 Packages. In Common Lisp, symbols are divided into @dfn{packages}. | |
| 5404 Symbols that are Lisp built-ins are typically stored in one package; | |
| 5405 symbols that are vendor extensions are put in another, and each | |
| 5406 application program would have a package for its own symbols. | |
| 5407 Certain symbols are ``exported'' by a package and others are | |
| 5408 internal; certain packages ``use'' or import the exported symbols | |
| 5409 of other packages. To access symbols that would not normally be | |
| 5410 visible due to this importing and exporting, Common Lisp provides | |
| 5411 a syntax like @code{package:symbol} or @code{package::symbol}. | |
| 5412 | |
| 5413 Emacs Lisp has a single namespace for all interned symbols, and | |
| 5414 then uses a naming convention of putting a prefix like @code{cl-} | |
| 5415 in front of the name. Some Emacs packages adopt the Common Lisp-like | |
| 5416 convention of using @code{cl:} or @code{cl::} as the prefix. | |
| 5417 However, the Emacs parser does not understand colons and just | |
| 5418 treats them as part of the symbol name. Thus, while @code{mapcar} | |
| 5419 and @code{lisp:mapcar} may refer to the same symbol in Common | |
| 5420 Lisp, they are totally distinct in Emacs Lisp. Common Lisp | |
| 5421 programs which refer to a symbol by the full name sometimes | |
| 5422 and the short name other times will not port cleanly to Emacs. | |
| 5423 | |
| 5424 Emacs Lisp does have a concept of ``obarrays,'' which are | |
| 5425 package-like collections of symbols, but this feature is not | |
| 5426 strong enough to be used as a true package mechanism. | |
| 5427 | |
| 5428 @item | |
| 5429 Keywords. The notation @code{:test-not} in Common Lisp really | |
| 5430 is a shorthand for @code{keyword:test-not}; keywords are just | |
| 5431 symbols in a built-in @code{keyword} package with the special | |
| 5432 property that all its symbols are automatically self-evaluating. | |
| 5433 Common Lisp programs often use keywords liberally to avoid | |
| 5434 having to use quotes. | |
| 5435 | |
| 5436 In Emacs Lisp a keyword is just a symbol whose name begins with | |
| 5437 a colon; since the Emacs parser does not treat them specially, | |
| 5438 they have to be explicitly made self-evaluating by a statement | |
| 5439 like @code{(setq :test-not ':test-not)}. This package arranges | |
| 5440 to execute such a statement whenever @code{defun*} or some | |
| 5441 other form sees a keyword being used as an argument. Common | |
| 5442 Lisp code that assumes that a symbol @code{:mumble} will be | |
| 5443 self-evaluating even though it was never introduced by a | |
| 5444 @code{defun*} will have to be fixed. | |
| 5445 | |
| 5446 @item | |
| 5447 The @code{format} function is quite different between Common | |
| 5448 Lisp and Emacs Lisp. It takes an additional ``destination'' | |
| 5449 argument before the format string. A destination of @code{nil} | |
| 5450 means to format to a string as in Emacs Lisp; a destination | |
| 5451 of @code{t} means to write to the terminal (similar to | |
| 5452 @code{message} in Emacs). Also, format control strings are | |
| 5453 utterly different; @code{~} is used instead of @code{%} to | |
| 5454 introduce format codes, and the set of available codes is | |
| 5455 much richer. There are no notations like @code{\n} for | |
| 5456 string literals; instead, @code{format} is used with the | |
| 5457 ``newline'' format code, @code{~%}. More advanced formatting | |
| 5458 codes provide such features as paragraph filling, case | |
| 5459 conversion, and even loops and conditionals. | |
| 5460 | |
| 5461 While it would have been possible to implement most of Common | |
| 5462 Lisp @code{format} in this package (under the name @code{format*}, | |
| 5463 of course), it was not deemed worthwhile. It would have required | |
| 5464 a huge amount of code to implement even a decent subset of | |
| 5465 @code{format*}, yet the functionality it would provide over | |
| 5466 Emacs Lisp's @code{format} would rarely be useful. | |
| 5467 | |
| 5468 @item | |
| 5469 Vector constants use square brackets in Emacs Lisp, but | |
| 5470 @code{#(a b c)} notation in Common Lisp. To further complicate | |
| 5471 matters, Emacs 19 introduces its own @code{#(} notation for | |
| 5472 something entirely different---strings with properties. | |
| 5473 | |
| 5474 @item | |
| 5475 Characters are distinct from integers in Common Lisp. The | |
| 5476 notation for character constants is also different: @code{#\A} | |
| 5477 instead of @code{?A}. Also, @code{string=} and @code{string-equal} | |
| 5478 are synonyms in Emacs Lisp whereas the latter is case-insensitive | |
| 5479 in Common Lisp. | |
| 5480 | |
| 5481 @item | |
| 5482 Data types. Some Common Lisp data types do not exist in Emacs | |
| 5483 Lisp. Rational numbers and complex numbers are not present, | |
| 5484 nor are large integers (all integers are ``fixnums''). All | |
| 5485 arrays are one-dimensional. There are no readtables or pathnames; | |
| 5486 streams are a set of existing data types rather than a new data | |
| 5487 type of their own. Hash tables, random-states, structures, and | |
| 5488 packages (obarrays) are built from Lisp vectors or lists rather | |
| 5489 than being distinct types. | |
| 5490 | |
| 5491 @item | |
| 5492 The Common Lisp Object System (CLOS) is not implemented, | |
| 5493 nor is the Common Lisp Condition System. | |
| 5494 | |
| 5495 @item | |
| 5496 Common Lisp features that are completely redundant with Emacs | |
| 5497 Lisp features of a different name generally have not been | |
| 5498 implemented. For example, Common Lisp writes @code{defconstant} | |
| 5499 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list} | |
| 5500 takes its arguments in different ways in the two Lisps but does | |
| 5501 exactly the same thing, so this package has not bothered to | |
| 5502 implement a Common Lisp-style @code{make-list}. | |
| 5503 | |
| 5504 @item | |
| 5505 A few more notable Common Lisp features not included in this | |
| 5506 package: @code{compiler-let}, @code{tagbody}, @code{prog}, | |
| 5507 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}. | |
| 5508 | |
| 5509 @item | |
| 5510 Recursion. While recursion works in Emacs Lisp just like it | |
| 5511 does in Common Lisp, various details of the Emacs Lisp system | |
| 5512 and compiler make recursion much less efficient than it is in | |
| 5513 most Lisps. Some schools of thought prefer to use recursion | |
| 5514 in Lisp over other techniques; they would sum a list of | |
| 5515 numbers using something like | |
| 5516 | |
| 5517 @example | |
| 5518 (defun sum-list (list) | |
| 5519 (if list | |
| 5520 (+ (car list) (sum-list (cdr list))) | |
| 5521 0)) | |
| 5522 @end example | |
| 5523 | |
| 5524 @noindent | |
| 5525 where a more iteratively-minded programmer might write one of | |
| 5526 these forms: | |
| 5527 | |
| 5528 @example | |
| 5529 (let ((total 0)) (dolist (x my-list) (incf total x)) total) | |
| 5530 (loop for x in my-list sum x) | |
| 5531 @end example | |
| 5532 | |
| 5533 While this would be mainly a stylistic choice in most Common Lisps, | |
| 5534 in Emacs Lisp you should be aware that the iterative forms are | |
| 5535 much faster than recursion. Also, Lisp programmers will want to | |
| 5536 note that the current Emacs Lisp compiler does not optimize tail | |
| 5537 recursion. | |
| 5538 @end itemize | |
| 5539 | |
| 5540 @node Function Index, Variable Index, Porting Common Lisp, Top | |
| 5541 @unnumbered Function Index | |
| 5542 | |
| 5543 @printindex fn | |
| 5544 | |
| 5545 @node Variable Index, , Function Index, Top | |
| 5546 @unnumbered Variable Index | |
| 5547 | |
| 5548 @printindex vr | |
| 5549 | |
| 5550 @contents | |
| 5551 @bye |