428
+ − 1 \input texinfo @c -*-texinfo-*-
+ − 2 @setfilename ../info/cl.info
+ − 3 @settitle Common Lisp Extensions
+ − 4
+ − 5 @iftex
+ − 6 @finalout
+ − 7 @end iftex
+ − 8
+ − 9 @ifinfo
+ − 10 @dircategory XEmacs Editor
+ − 11 @direntry
1353
+ − 12 * Common Lisp: (cl). XEmacs Common Lisp emulation package.
428
+ − 13 @end direntry
+ − 14
1353
+ − 15 This file documents the XEmacs Common Lisp emulation package.
428
+ − 16
+ − 17 Copyright (C) 1993 Free Software Foundation, Inc.
+ − 18
+ − 19 Permission is granted to make and distribute verbatim copies of this
+ − 20 manual provided the copyright notice and this permission notice are
+ − 21 preserved on all copies.
+ − 22
+ − 23 @ignore
+ − 24 Permission is granted to process this file through TeX and print the
+ − 25 results, provided the printed document carries copying permission notice
+ − 26 identical to this one except for the removal of this paragraph (this
+ − 27 paragraph not being relevant to the printed manual).
+ − 28
+ − 29 @end ignore
+ − 30 Permission is granted to copy and distribute modified versions of this
+ − 31 manual under the conditions for verbatim copying, provided also that the
+ − 32 section entitled ``GNU General Public License'' is included exactly as
+ − 33 in the original, and provided that the entire resulting derived work is
+ − 34 distributed under the terms of a permission notice identical to this one.
+ − 35
+ − 36 Permission is granted to copy and distribute translations of this manual
+ − 37 into another language, under the above conditions for modified versions,
+ − 38 except that the section entitled ``GNU General Public License'' may be
+ − 39 included in a translation approved by the author instead of in the
+ − 40 original English.
+ − 41 @end ifinfo
+ − 42
+ − 43 @titlepage
+ − 44 @sp 6
+ − 45 @center @titlefont{Common Lisp Extensions}
+ − 46 @sp 4
+ − 47 @center For GNU Emacs Lisp
+ − 48 @sp 1
+ − 49 @center Version 2.02
+ − 50 @sp 5
+ − 51 @center Dave Gillespie
+ − 52 @center daveg@@synaptics.com
+ − 53 @page
+ − 54
+ − 55 @vskip 0pt plus 1filll
+ − 56 Copyright @copyright{} 1993 Free Software Foundation, Inc.
+ − 57
+ − 58 Permission is granted to make and distribute verbatim copies of
+ − 59 this manual provided the copyright notice and this permission notice
+ − 60 are preserved on all copies.
+ − 61
+ − 62 @ignore
+ − 63 Permission is granted to process this file through TeX and print the
+ − 64 results, provided the printed document carries copying permission notice
+ − 65 identical to this one except for the removal of this paragraph (this
+ − 66 paragraph not being relevant to the printed manual).
+ − 67
+ − 68 @end ignore
+ − 69 Permission is granted to copy and distribute modified versions of this
+ − 70 manual under the conditions for verbatim copying, provided also that the
+ − 71 section entitled ``GNU General Public License'' is included exactly as
+ − 72 in the original, and provided that the entire resulting derived work is
+ − 73 distributed under the terms of a permission notice identical to this one.
+ − 74
+ − 75 Permission is granted to copy and distribute translations of this manual
+ − 76 into another language, under the above conditions for modified versions,
+ − 77 except that the section entitled ``GNU General Public License'' may be
+ − 78 included in a translation approved by the author instead of in the
+ − 79 original English.
+ − 80 @end titlepage
+ − 81
+ − 82 @node Top, Overview,, (dir)
+ − 83 @chapter Common Lisp Extensions
+ − 84
+ − 85 @noindent
+ − 86 This document describes a set of Emacs Lisp facilities borrowed from
+ − 87 Common Lisp. All the facilities are described here in detail; for
+ − 88 more discussion and examples, Guy L. Steele's @cite{Common Lisp, the
+ − 89 Language}, second edition, is the definitive book on Common Lisp.
+ − 90 @iftex
+ − 91 Chapter numbers and most section numbers of this document parallel
+ − 92 those of Steele's book.
+ − 93 @end iftex
+ − 94 While this document does not assume any prior knowledge of Common
+ − 95 Lisp, it does assume a basic familiarity with Emacs Lisp.
+ − 96
+ − 97 @menu
+ − 98 * Overview:: Installation, usage, etc.
+ − 99 * Program Structure:: Arglists, `eval-when', `defalias'
+ − 100 * Predicates:: `typep', `eql', and `equalp'
+ − 101 * Control Structure:: `setf', `when', `do', `loop', etc.
+ − 102 * Macros:: Destructuring, `define-compiler-macro'
+ − 103 * Declarations:: `proclaim', `declare', etc.
+ − 104 * Symbols:: Property lists, `gensym'
+ − 105 * Numbers:: Predicates, functions, random numbers
+ − 106 * Sequences:: Mapping, functions, searching, sorting
+ − 107 * Lists:: `cadr', `sublis', `member*', `assoc*', etc.
+ − 108 * Hash Tables:: `make-hash-table', `gethash', etc.
+ − 109 * Structures:: `defstruct'
+ − 110 * Assertions:: `check-type', `assert', `ignore-errors'.
+ − 111
+ − 112 * Efficiency Concerns:: Hints and techniques
+ − 113 * Common Lisp Compatibility:: All known differences with Steele
+ − 114 * Old CL Compatibility:: All known differences with old cl.el
+ − 115 * Porting Common Lisp:: Hints for porting Common Lisp code
+ − 116
+ − 117 * Function Index::
+ − 118 * Variable Index::
+ − 119 @end menu
+ − 120
+ − 121 @node Overview, Program Structure, Top, Top
+ − 122 @ifinfo
+ − 123 @chapter Overview
+ − 124 @end ifinfo
+ − 125 @iftex
+ − 126 @section Overview
+ − 127 @end iftex
+ − 128
+ − 129 @noindent
+ − 130 Common Lisp is a huge language, and Common Lisp systems tend to be
+ − 131 massive and extremely complex. Emacs Lisp, by contrast, is rather
+ − 132 minimalist in the choice of Lisp features it offers the programmer.
+ − 133 As Emacs Lisp programmers have grown in number, and the applications
+ − 134 they write have grown more ambitious, it has become clear that Emacs
+ − 135 Lisp could benefit from many of the conveniences of Common Lisp.
+ − 136
+ − 137 The @dfn{CL} package adds a number of Common Lisp functions and
+ − 138 control structures to Emacs Lisp. While not a 100% complete
+ − 139 implementation of Common Lisp, @dfn{CL} adds enough functionality
+ − 140 to make Emacs Lisp programming significantly more convenient.
+ − 141
+ − 142 Some Common Lisp features have been omitted from this package
+ − 143 for various reasons:
+ − 144
+ − 145 @itemize @bullet
+ − 146 @item
+ − 147 Some features are too complex or bulky relative to their benefit
+ − 148 to Emacs Lisp programmers. CLOS and Common Lisp streams are fine
+ − 149 examples of this group.
+ − 150
+ − 151 @item
+ − 152 Other features cannot be implemented without modification to the
+ − 153 Emacs Lisp interpreter itself, such as multiple return values,
+ − 154 lexical scoping, case-insensitive symbols, and complex numbers.
+ − 155 The @dfn{CL} package generally makes no attempt to emulate these
+ − 156 features.
+ − 157
+ − 158 @item
+ − 159 Some features conflict with existing things in Emacs Lisp. For
+ − 160 example, Emacs' @code{assoc} function is incompatible with the
+ − 161 Common Lisp @code{assoc}. In such cases, this package usually
+ − 162 adds the suffix @samp{*} to the function name of the Common
+ − 163 Lisp version of the function (e.g., @code{assoc*}).
+ − 164 @end itemize
+ − 165
+ − 166 The package described here was written by Dave Gillespie,
+ − 167 @file{daveg@@synaptics.com}. It is a total rewrite of the original
+ − 168 1986 @file{cl.el} package by Cesar Quiroz. Most features of
+ − 169 the Quiroz package have been retained; any incompatibilities are
+ − 170 noted in the descriptions below. Care has been taken in this
+ − 171 version to ensure that each function is defined efficiently,
+ − 172 concisely, and with minimal impact on the rest of the Emacs
+ − 173 environment.
+ − 174
+ − 175 @menu
+ − 176 * Usage:: How to use the CL package
+ − 177 * Organization:: The package's five component files
+ − 178 * Installation:: Compiling and installing CL
+ − 179 * Naming Conventions:: Notes on CL function names
+ − 180 @end menu
+ − 181
+ − 182 @node Usage, Organization, Overview, Overview
+ − 183 @section Usage
+ − 184
+ − 185 @noindent
+ − 186 Lisp code that uses features from the @dfn{CL} package should
+ − 187 include at the beginning:
+ − 188
+ − 189 @example
+ − 190 (require 'cl)
+ − 191 @end example
+ − 192
+ − 193 @noindent
+ − 194 If you want to ensure that the new (Gillespie) version of @dfn{CL}
+ − 195 is the one that is present, add an additional @code{(require 'cl-19)}
+ − 196 call:
+ − 197
+ − 198 @example
+ − 199 (require 'cl)
+ − 200 (require 'cl-19)
+ − 201 @end example
+ − 202
+ − 203 @noindent
+ − 204 The second call will fail (with ``@file{cl-19.el} not found'') if
+ − 205 the old @file{cl.el} package was in use.
+ − 206
+ − 207 It is safe to arrange to load @dfn{CL} at all times, e.g.,
+ − 208 in your @file{.emacs} file. But it's a good idea, for portability,
+ − 209 to @code{(require 'cl)} in your code even if you do this.
+ − 210
+ − 211 @node Organization, Installation, Usage, Overview
+ − 212 @section Organization
+ − 213
+ − 214 @noindent
+ − 215 The Common Lisp package is organized into four files:
+ − 216
+ − 217 @table @file
+ − 218 @item cl.el
+ − 219 This is the ``main'' file, which contains basic functions
+ − 220 and information about the package. This file is relatively
+ − 221 compact---about 700 lines.
+ − 222
+ − 223 @item cl-extra.el
+ − 224 This file contains the larger, more complex or unusual functions.
+ − 225 It is kept separate so that packages which only want to use Common
+ − 226 Lisp fundamentals like the @code{cadr} function won't need to pay
+ − 227 the overhead of loading the more advanced functions.
+ − 228
+ − 229 @item cl-seq.el
+ − 230 This file contains most of the advanced functions for operating
+ − 231 on sequences or lists, such as @code{delete-if} and @code{assoc*}.
+ − 232
+ − 233 @item cl-macs.el
+ − 234 This file contains the features of the packages which are macros
+ − 235 instead of functions. Macros expand when the caller is compiled,
+ − 236 not when it is run, so the macros generally only need to be
+ − 237 present when the byte-compiler is running (or when the macros are
+ − 238 used in uncompiled code such as a @file{.emacs} file). Most of
+ − 239 the macros of this package are isolated in @file{cl-macs.el} so
+ − 240 that they won't take up memory unless you are compiling.
+ − 241 @end table
+ − 242
+ − 243 The file @file{cl.el} includes all necessary @code{autoload}
+ − 244 commands for the functions and macros in the other three files.
+ − 245 All you have to do is @code{(require 'cl)}, and @file{cl.el}
+ − 246 will take care of pulling in the other files when they are
+ − 247 needed.
+ − 248
+ − 249 There is another file, @file{cl-compat.el}, which defines some
+ − 250 routines from the older @file{cl.el} package that are no longer
+ − 251 present in the new package. This includes internal routines
+ − 252 like @code{setelt} and @code{zip-lists}, deprecated features
+ − 253 like @code{defkeyword}, and an emulation of the old-style
+ − 254 multiple-values feature. @xref{Old CL Compatibility}.
+ − 255
+ − 256 @node Installation, Naming Conventions, Organization, Overview
+ − 257 @section Installation
+ − 258
+ − 259 @noindent
+ − 260 Installation of the @dfn{CL} package is simple: Just put the
+ − 261 byte-compiled files @file{cl.elc}, @file{cl-extra.elc},
+ − 262 @file{cl-seq.elc}, @file{cl-macs.elc}, and @file{cl-compat.elc}
+ − 263 into a directory on your @code{load-path}.
+ − 264
+ − 265 There are no special requirements to compile this package:
+ − 266 The files do not have to be loaded before they are compiled,
+ − 267 nor do they need to be compiled in any particular order.
+ − 268
+ − 269 You may choose to put the files into your main @file{lisp/}
+ − 270 directory, replacing the original @file{cl.el} file there. Or,
+ − 271 you could put them into a directory that comes before @file{lisp/}
+ − 272 on your @code{load-path} so that the old @file{cl.el} is
+ − 273 effectively hidden.
+ − 274
+ − 275 Also, format the @file{cl.texinfo} file and put the resulting
+ − 276 Info files in the @file{info/} directory or another suitable place.
+ − 277
+ − 278 You may instead wish to leave this package's components all in
+ − 279 their own directory, and then add this directory to your
+ − 280 @code{load-path} and (Emacs 19 only) @code{Info-directory-list}.
+ − 281 Add the directory to the front of the list so the old @dfn{CL}
+ − 282 package and its documentation are hidden.
+ − 283
+ − 284 @node Naming Conventions, , Installation, Overview
+ − 285 @section Naming Conventions
+ − 286
+ − 287 @noindent
+ − 288 Except where noted, all functions defined by this package have the
+ − 289 same names and calling conventions as their Common Lisp counterparts.
+ − 290
+ − 291 Following is a complete list of functions whose names were changed
+ − 292 from Common Lisp, usually to avoid conflicts with Emacs. In each
+ − 293 case, a @samp{*} has been appended to the Common Lisp name to obtain
+ − 294 the Emacs name:
+ − 295
+ − 296 @example
+ − 297 defun* defsubst* defmacro* function*
440
+ − 298 member* assoc* rassoc* remove*
+ − 299 delete* mapcar* sort* floor*
+ − 300 ceiling* truncate* round* mod*
+ − 301 rem* random*
428
+ − 302 @end example
+ − 303
+ − 304 Internal function and variable names in the package are prefixed
+ − 305 by @code{cl-}. Here is a complete list of functions @emph{not}
+ − 306 prefixed by @code{cl-} which were not taken from Common Lisp:
+ − 307
+ − 308 @example
+ − 309 member delete remove remq
+ − 310 rassoc floatp-safe lexical-let lexical-let*
+ − 311 callf callf2 letf letf*
+ − 312 defsubst* defalias add-hook eval-when-compile
+ − 313 @end example
+ − 314
+ − 315 @noindent
+ − 316 (Most of these are Emacs 19 features provided to Emacs 18 users,
+ − 317 or introduced, like @code{remq}, for reasons of symmetry
+ − 318 with similar features.)
+ − 319
+ − 320 The following simple functions and macros are defined in @file{cl.el};
+ − 321 they do not cause other components like @file{cl-extra} to be loaded.
+ − 322
+ − 323 @example
+ − 324 eql floatp-safe abs endp
+ − 325 evenp oddp plusp minusp
+ − 326 last butlast nbutlast caar .. cddddr
+ − 327 list* ldiff rest first .. tenth
+ − 328 member [1] copy-list subst mapcar* [2]
+ − 329 adjoin [3] acons pairlis when
+ − 330 unless pop [4] push [4] pushnew [3,4]
+ − 331 incf [4] decf [4] proclaim declaim
+ − 332 add-hook
+ − 333 @end example
+ − 334
+ − 335 @noindent
+ − 336 [1] This is the Emacs 19-compatible function, not @code{member*}.
+ − 337
+ − 338 @noindent
+ − 339 [2] Only for one sequence argument or two list arguments.
+ − 340
+ − 341 @noindent
+ − 342 [3] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified,
+ − 343 and @code{:key} is not used.
+ − 344
+ − 345 @noindent
+ − 346 [4] Only when @var{place} is a plain variable name.
+ − 347
+ − 348 @iftex
+ − 349 @chapno=4
+ − 350 @end iftex
+ − 351
+ − 352 @node Program Structure, Predicates, Overview, Top
+ − 353 @chapter Program Structure
+ − 354
+ − 355 @noindent
+ − 356 This section describes features of the @dfn{CL} package which have to
+ − 357 do with programs as a whole: advanced argument lists for functions,
+ − 358 and the @code{eval-when} construct.
+ − 359
+ − 360 @menu
+ − 361 * Argument Lists:: `&key', `&aux', `defun*', `defmacro*'.
+ − 362 * Time of Evaluation:: The `eval-when' construct.
+ − 363 * Function Aliases:: The `defalias' function.
+ − 364 @end menu
+ − 365
+ − 366 @iftex
+ − 367 @secno=1
+ − 368 @end iftex
+ − 369
+ − 370 @node Argument Lists, Time of Evaluation, Program Structure, Program Structure
+ − 371 @section Argument Lists
+ − 372
+ − 373 @noindent
+ − 374 Emacs Lisp's notation for argument lists of functions is a subset of
+ − 375 the Common Lisp notation. As well as the familiar @code{&optional}
+ − 376 and @code{&rest} markers, Common Lisp allows you to specify default
+ − 377 values for optional arguments, and it provides the additional markers
+ − 378 @code{&key} and @code{&aux}.
+ − 379
+ − 380 Since argument parsing is built-in to Emacs, there is no way for
+ − 381 this package to implement Common Lisp argument lists seamlessly.
+ − 382 Instead, this package defines alternates for several Lisp forms
+ − 383 which you must use if you need Common Lisp argument lists.
+ − 384
+ − 385 @defspec defun* name arglist body...
+ − 386 This form is identical to the regular @code{defun} form, except
+ − 387 that @var{arglist} is allowed to be a full Common Lisp argument
+ − 388 list. Also, the function body is enclosed in an implicit block
+ − 389 called @var{name}; @pxref{Blocks and Exits}.
+ − 390 @end defspec
+ − 391
+ − 392 @defspec defsubst* name arglist body...
+ − 393 This is just like @code{defun*}, except that the function that
+ − 394 is defined is automatically proclaimed @code{inline}, i.e.,
+ − 395 calls to it may be expanded into in-line code by the byte compiler.
+ − 396 This is analogous to the @code{defsubst} form in Emacs 19;
+ − 397 @code{defsubst*} uses a different method (compiler macros) which
+ − 398 works in all version of Emacs, and also generates somewhat more
+ − 399 efficient inline expansions. In particular, @code{defsubst*}
+ − 400 arranges for the processing of keyword arguments, default values,
+ − 401 etc., to be done at compile-time whenever possible.
+ − 402 @end defspec
+ − 403
+ − 404 @defspec defmacro* name arglist body...
+ − 405 This is identical to the regular @code{defmacro} form,
+ − 406 except that @var{arglist} is allowed to be a full Common Lisp
+ − 407 argument list. The @code{&environment} keyword is supported as
+ − 408 described in Steele. The @code{&whole} keyword is supported only
+ − 409 within destructured lists (see below); top-level @code{&whole}
+ − 410 cannot be implemented with the current Emacs Lisp interpreter.
+ − 411 The macro expander body is enclosed in an implicit block called
+ − 412 @var{name}.
+ − 413 @end defspec
+ − 414
+ − 415 @defspec function* symbol-or-lambda
+ − 416 This is identical to the regular @code{function} form,
+ − 417 except that if the argument is a @code{lambda} form then that
+ − 418 form may use a full Common Lisp argument list.
+ − 419 @end defspec
+ − 420
+ − 421 Also, all forms (such as @code{defsetf} and @code{flet}) defined
+ − 422 in this package that include @var{arglist}s in their syntax allow
+ − 423 full Common Lisp argument lists.
+ − 424
+ − 425 Note that it is @emph{not} necessary to use @code{defun*} in
+ − 426 order to have access to most @dfn{CL} features in your function.
+ − 427 These features are always present; @code{defun*}'s only
+ − 428 difference from @code{defun} is its more flexible argument
+ − 429 lists and its implicit block.
+ − 430
+ − 431 The full form of a Common Lisp argument list is
+ − 432
+ − 433 @example
+ − 434 (@var{var}...
+ − 435 &optional (@var{var} @var{initform} @var{svar})...
+ − 436 &rest @var{var}
+ − 437 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})...
+ − 438 &aux (@var{var} @var{initform})...)
+ − 439 @end example
+ − 440
+ − 441 Each of the five argument list sections is optional. The @var{svar},
+ − 442 @var{initform}, and @var{keyword} parts are optional; if they are
+ − 443 omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.
+ − 444
+ − 445 The first section consists of zero or more @dfn{required} arguments.
+ − 446 These arguments must always be specified in a call to the function;
+ − 447 there is no difference between Emacs Lisp and Common Lisp as far as
+ − 448 required arguments are concerned.
+ − 449
+ − 450 The second section consists of @dfn{optional} arguments. These
+ − 451 arguments may be specified in the function call; if they are not,
+ − 452 @var{initform} specifies the default value used for the argument.
+ − 453 (No @var{initform} means to use @code{nil} as the default.) The
+ − 454 @var{initform} is evaluated with the bindings for the preceding
+ − 455 arguments already established; @code{(a &optional (b (1+ a)))}
+ − 456 matches one or two arguments, with the second argument defaulting
+ − 457 to one plus the first argument. If the @var{svar} is specified,
+ − 458 it is an auxiliary variable which is bound to @code{t} if the optional
+ − 459 argument was specified, or to @code{nil} if the argument was omitted.
+ − 460 If you don't use an @var{svar}, then there will be no way for your
+ − 461 function to tell whether it was called with no argument, or with
+ − 462 the default value passed explicitly as an argument.
+ − 463
+ − 464 The third section consists of a single @dfn{rest} argument. If
+ − 465 more arguments were passed to the function than are accounted for
+ − 466 by the required and optional arguments, those extra arguments are
+ − 467 collected into a list and bound to the ``rest'' argument variable.
+ − 468 Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
+ − 469 Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
+ − 470 macro contexts; this package accepts it all the time.
+ − 471
+ − 472 The fourth section consists of @dfn{keyword} arguments. These
+ − 473 are optional arguments which are specified by name rather than
+ − 474 positionally in the argument list. For example,
+ − 475
+ − 476 @example
+ − 477 (defun* foo (a &optional b &key c d (e 17)))
+ − 478 @end example
+ − 479
+ − 480 @noindent
+ − 481 defines a function which may be called with one, two, or more
+ − 482 arguments. The first two arguments are bound to @code{a} and
+ − 483 @code{b} in the usual way. The remaining arguments must be
+ − 484 pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
+ − 485 by the value to be bound to the corresponding argument variable.
+ − 486 (Symbols whose names begin with a colon are called @dfn{keywords},
+ − 487 and they are self-quoting in the same way as @code{nil} and
+ − 488 @code{t}.)
+ − 489
+ − 490 For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
+ − 491 arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword
+ − 492 appears more than once in the function call, the first occurrence
+ − 493 takes precedence over the later ones. Note that it is not possible
+ − 494 to specify keyword arguments without specifying the optional
+ − 495 argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
+ − 496 @code{b} to the keyword @code{:c}, then signal an error because
+ − 497 @code{2} is not a valid keyword.
+ − 498
+ − 499 If a @var{keyword} symbol is explicitly specified in the argument
+ − 500 list as shown in the above diagram, then that keyword will be
+ − 501 used instead of just the variable name prefixed with a colon.
+ − 502 You can specify a @var{keyword} symbol which does not begin with
+ − 503 a colon at all, but such symbols will not be self-quoting; you
+ − 504 will have to quote them explicitly with an apostrophe in the
+ − 505 function call.
+ − 506
+ − 507 Ordinarily it is an error to pass an unrecognized keyword to
+ − 508 a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask
+ − 509 Lisp to ignore unrecognized keywords, either by adding the
+ − 510 marker @code{&allow-other-keys} after the keyword section
+ − 511 of the argument list, or by specifying an @code{:allow-other-keys}
+ − 512 argument in the call whose value is non-@code{nil}. If the
+ − 513 function uses both @code{&rest} and @code{&key} at the same time,
+ − 514 the ``rest'' argument is bound to the keyword list as it appears
+ − 515 in the call. For example:
+ − 516
+ − 517 @smallexample
+ − 518 (defun* find-thing (thing &rest rest &key need &allow-other-keys)
+ − 519 (or (apply 'member* thing thing-list :allow-other-keys t rest)
+ − 520 (if need (error "Thing not found"))))
+ − 521 @end smallexample
+ − 522
+ − 523 @noindent
+ − 524 This function takes a @code{:need} keyword argument, but also
+ − 525 accepts other keyword arguments which are passed on to the
+ − 526 @code{member*} function. @code{allow-other-keys} is used to
+ − 527 keep both @code{find-thing} and @code{member*} from complaining
+ − 528 about each others' keywords in the arguments.
+ − 529
+ − 530 As a (significant) performance optimization, this package
+ − 531 implements the scan for keyword arguments by calling @code{memq}
+ − 532 to search for keywords in a ``rest'' argument. Technically
+ − 533 speaking, this is incorrect, since @code{memq} looks at the
+ − 534 odd-numbered values as well as the even-numbered keywords.
+ − 535 The net effect is that if you happen to pass a keyword symbol
+ − 536 as the @emph{value} of another keyword argument, where that
+ − 537 keyword symbol happens to equal the name of a valid keyword
+ − 538 argument of the same function, then the keyword parser will
+ − 539 become confused. This minor bug can only affect you if you
+ − 540 use keyword symbols as general-purpose data in your program;
+ − 541 this practice is strongly discouraged in Emacs Lisp.
+ − 542
+ − 543 The fifth section of the argument list consists of @dfn{auxiliary
+ − 544 variables}. These are not really arguments at all, but simply
+ − 545 variables which are bound to @code{nil} or to the specified
+ − 546 @var{initforms} during execution of the function. There is no
+ − 547 difference between the following two functions, except for a
+ − 548 matter of stylistic taste:
+ − 549
+ − 550 @example
+ − 551 (defun* foo (a b &aux (c (+ a b)) d)
+ − 552 @var{body})
+ − 553
+ − 554 (defun* foo (a b)
+ − 555 (let ((c (+ a b)) d)
+ − 556 @var{body}))
+ − 557 @end example
+ − 558
+ − 559 Argument lists support @dfn{destructuring}. In Common Lisp,
+ − 560 destructuring is only allowed with @code{defmacro}; this package
+ − 561 allows it with @code{defun*} and other argument lists as well.
+ − 562 In destructuring, any argument variable (@var{var} in the above
+ − 563 diagram) can be replaced by a list of variables, or more generally,
+ − 564 a recursive argument list. The corresponding argument value must
+ − 565 be a list whose elements match this recursive argument list.
+ − 566 For example:
+ − 567
+ − 568 @example
+ − 569 (defmacro* dolist ((var listform &optional resultform)
+ − 570 &rest body)
+ − 571 ...)
+ − 572 @end example
+ − 573
+ − 574 This says that the first argument of @code{dolist} must be a list
+ − 575 of two or three items; if there are other arguments as well as this
+ − 576 list, they are stored in @code{body}. All features allowed in
+ − 577 regular argument lists are allowed in these recursive argument lists.
+ − 578 In addition, the clause @samp{&whole @var{var}} is allowed at the
+ − 579 front of a recursive argument list. It binds @var{var} to the
+ − 580 whole list being matched; thus @code{(&whole all a b)} matches
+ − 581 a list of two things, with @code{a} bound to the first thing,
+ − 582 @code{b} bound to the second thing, and @code{all} bound to the
+ − 583 list itself. (Common Lisp allows @code{&whole} in top-level
+ − 584 @code{defmacro} argument lists as well, but Emacs Lisp does not
+ − 585 support this usage.)
+ − 586
+ − 587 One last feature of destructuring is that the argument list may be
+ − 588 dotted, so that the argument list @code{(a b . c)} is functionally
+ − 589 equivalent to @code{(a b &rest c)}.
+ − 590
+ − 591 If the optimization quality @code{safety} is set to 0
+ − 592 (@pxref{Declarations}), error checking for wrong number of
+ − 593 arguments and invalid keyword arguments is disabled. By default,
+ − 594 argument lists are rigorously checked.
+ − 595
+ − 596 @node Time of Evaluation, Function Aliases, Argument Lists, Program Structure
+ − 597 @section Time of Evaluation
+ − 598
+ − 599 @noindent
+ − 600 Normally, the byte-compiler does not actually execute the forms in
+ − 601 a file it compiles. For example, if a file contains @code{(setq foo t)},
+ − 602 the act of compiling it will not actually set @code{foo} to @code{t}.
+ − 603 This is true even if the @code{setq} was a top-level form (i.e., not
+ − 604 enclosed in a @code{defun} or other form). Sometimes, though, you
+ − 605 would like to have certain top-level forms evaluated at compile-time.
+ − 606 For example, the compiler effectively evaluates @code{defmacro} forms
+ − 607 at compile-time so that later parts of the file can refer to the
+ − 608 macros that are defined.
+ − 609
+ − 610 @defspec eval-when (situations...) forms...
+ − 611 This form controls when the body @var{forms} are evaluated.
+ − 612 The @var{situations} list may contain any set of the symbols
+ − 613 @code{compile}, @code{load}, and @code{eval} (or their long-winded
+ − 614 ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
+ − 615 and @code{:execute}).
+ − 616
+ − 617 The @code{eval-when} form is handled differently depending on
+ − 618 whether or not it is being compiled as a top-level form.
+ − 619 Specifically, it gets special treatment if it is being compiled
+ − 620 by a command such as @code{byte-compile-file} which compiles files
+ − 621 or buffers of code, and it appears either literally at the
+ − 622 top level of the file or inside a top-level @code{progn}.
+ − 623
+ − 624 For compiled top-level @code{eval-when}s, the body @var{forms} are
+ − 625 executed at compile-time if @code{compile} is in the @var{situations}
+ − 626 list, and the @var{forms} are written out to the file (to be executed
+ − 627 at load-time) if @code{load} is in the @var{situations} list.
+ − 628
+ − 629 For non-compiled-top-level forms, only the @code{eval} situation is
+ − 630 relevant. (This includes forms executed by the interpreter, forms
+ − 631 compiled with @code{byte-compile} rather than @code{byte-compile-file},
+ − 632 and non-top-level forms.) The @code{eval-when} acts like a
+ − 633 @code{progn} if @code{eval} is specified, and like @code{nil}
+ − 634 (ignoring the body @var{forms}) if not.
+ − 635
+ − 636 The rules become more subtle when @code{eval-when}s are nested;
+ − 637 consult Steele (second edition) for the gruesome details (and
+ − 638 some gruesome examples).
+ − 639
+ − 640 Some simple examples:
+ − 641
+ − 642 @example
+ − 643 ;; Top-level forms in foo.el:
+ − 644 (eval-when (compile) (setq foo1 'bar))
+ − 645 (eval-when (load) (setq foo2 'bar))
+ − 646 (eval-when (compile load) (setq foo3 'bar))
+ − 647 (eval-when (eval) (setq foo4 'bar))
+ − 648 (eval-when (eval compile) (setq foo5 'bar))
+ − 649 (eval-when (eval load) (setq foo6 'bar))
+ − 650 (eval-when (eval compile load) (setq foo7 'bar))
+ − 651 @end example
+ − 652
+ − 653 When @file{foo.el} is compiled, these variables will be set during
+ − 654 the compilation itself:
+ − 655
+ − 656 @example
+ − 657 foo1 foo3 foo5 foo7 ; `compile'
+ − 658 @end example
+ − 659
+ − 660 When @file{foo.elc} is loaded, these variables will be set:
+ − 661
+ − 662 @example
+ − 663 foo2 foo3 foo6 foo7 ; `load'
+ − 664 @end example
+ − 665
+ − 666 And if @file{foo.el} is loaded uncompiled, these variables will
+ − 667 be set:
+ − 668
+ − 669 @example
+ − 670 foo4 foo5 foo6 foo7 ; `eval'
+ − 671 @end example
+ − 672
+ − 673 If these seven @code{eval-when}s had been, say, inside a @code{defun},
+ − 674 then the first three would have been equivalent to @code{nil} and the
+ − 675 last four would have been equivalent to the corresponding @code{setq}s.
+ − 676
+ − 677 Note that @code{(eval-when (load eval) @dots{})} is equivalent
+ − 678 to @code{(progn @dots{})} in all contexts. The compiler treats
+ − 679 certain top-level forms, like @code{defmacro} (sort-of) and
+ − 680 @code{require}, as if they were wrapped in @code{(eval-when
+ − 681 (compile load eval) @dots{})}.
+ − 682 @end defspec
+ − 683
+ − 684 Emacs 19 includes two special forms related to @code{eval-when}.
+ − 685 One of these, @code{eval-when-compile}, is not quite equivalent to
+ − 686 any @code{eval-when} construct and is described below. This package
+ − 687 defines a version of @code{eval-when-compile} for the benefit of
+ − 688 Emacs 18 users.
+ − 689
+ − 690 The other form, @code{(eval-and-compile @dots{})}, is exactly
+ − 691 equivalent to @samp{(eval-when (compile load eval) @dots{})} and
+ − 692 so is not itself defined by this package.
+ − 693
+ − 694 @defspec eval-when-compile forms...
+ − 695 The @var{forms} are evaluated at compile-time; at execution time,
+ − 696 this form acts like a quoted constant of the resulting value. Used
+ − 697 at top-level, @code{eval-when-compile} is just like @samp{eval-when
+ − 698 (compile eval)}. In other contexts, @code{eval-when-compile}
+ − 699 allows code to be evaluated once at compile-time for efficiency
+ − 700 or other reasons.
+ − 701
+ − 702 This form is similar to the @samp{#.} syntax of true Common Lisp.
+ − 703 @end defspec
+ − 704
+ − 705 @defspec load-time-value form
+ − 706 The @var{form} is evaluated at load-time; at execution time,
+ − 707 this form acts like a quoted constant of the resulting value.
+ − 708
+ − 709 Early Common Lisp had a @samp{#,} syntax that was similar to
+ − 710 this, but ANSI Common Lisp replaced it with @code{load-time-value}
+ − 711 and gave it more well-defined semantics.
+ − 712
+ − 713 In a compiled file, @code{load-time-value} arranges for @var{form}
+ − 714 to be evaluated when the @file{.elc} file is loaded and then used
+ − 715 as if it were a quoted constant. In code compiled by
+ − 716 @code{byte-compile} rather than @code{byte-compile-file}, the
+ − 717 effect is identical to @code{eval-when-compile}. In uncompiled
+ − 718 code, both @code{eval-when-compile} and @code{load-time-value}
+ − 719 act exactly like @code{progn}.
+ − 720
+ − 721 @example
+ − 722 (defun report ()
+ − 723 (insert "This function was executed on: "
+ − 724 (current-time-string)
+ − 725 ", compiled on: "
+ − 726 (eval-when-compile (current-time-string))
+ − 727 ;; or '#.(current-time-string) in real Common Lisp
+ − 728 ", and loaded on: "
+ − 729 (load-time-value (current-time-string))))
+ − 730 @end example
+ − 731
+ − 732 @noindent
+ − 733 Byte-compiled, the above defun will result in the following code
+ − 734 (or its compiled equivalent, of course) in the @file{.elc} file:
+ − 735
+ − 736 @example
+ − 737 (setq --temp-- (current-time-string))
+ − 738 (defun report ()
+ − 739 (insert "This function was executed on: "
+ − 740 (current-time-string)
+ − 741 ", compiled on: "
+ − 742 '"Wed Jun 23 18:33:43 1993"
+ − 743 ", and loaded on: "
+ − 744 --temp--))
+ − 745 @end example
+ − 746 @end defspec
+ − 747
+ − 748 @node Function Aliases, , Time of Evaluation, Program Structure
+ − 749 @section Function Aliases
+ − 750
+ − 751 @noindent
+ − 752 This section describes a feature from GNU Emacs 19 which this
+ − 753 package makes available in other versions of Emacs.
+ − 754
+ − 755 @defun defalias symbol function
+ − 756 This function sets @var{symbol}'s function cell to @var{function}.
+ − 757 It is equivalent to @code{fset}, except that in GNU Emacs 19 it also
+ − 758 records the setting in @code{load-history} so that it can be undone
+ − 759 by a later @code{unload-feature}.
+ − 760
+ − 761 In other versions of Emacs, @code{defalias} is a synonym for
+ − 762 @code{fset}.
+ − 763 @end defun
+ − 764
+ − 765 @node Predicates, Control Structure, Program Structure, Top
+ − 766 @chapter Predicates
+ − 767
+ − 768 @noindent
+ − 769 This section describes functions for testing whether various
+ − 770 facts are true or false.
+ − 771
+ − 772 @menu
+ − 773 * Type Predicates:: `typep', `deftype', and `coerce'
+ − 774 * Equality Predicates:: `eql' and `equalp'
+ − 775 @end menu
+ − 776
+ − 777 @node Type Predicates, Equality Predicates, Predicates, Predicates
+ − 778 @section Type Predicates
+ − 779
+ − 780 @noindent
+ − 781 The @dfn{CL} package defines a version of the Common Lisp @code{typep}
+ − 782 predicate.
+ − 783
+ − 784 @defun typep object type
+ − 785 Check if @var{object} is of type @var{type}, where @var{type} is a
+ − 786 (quoted) type name of the sort used by Common Lisp. For example,
+ − 787 @code{(typep foo 'integer)} is equivalent to @code{(integerp foo)}.
+ − 788 @end defun
+ − 789
+ − 790 The @var{type} argument to the above function is either a symbol
+ − 791 or a list beginning with a symbol.
+ − 792
+ − 793 @itemize @bullet
+ − 794 @item
+ − 795 If the type name is a symbol, Emacs appends @samp{-p} to the
+ − 796 symbol name to form the name of a predicate function for testing
+ − 797 the type. (Built-in predicates whose names end in @samp{p} rather
+ − 798 than @samp{-p} are used when appropriate.)
+ − 799
+ − 800 @item
+ − 801 The type symbol @code{t} stands for the union of all types.
+ − 802 @code{(typep @var{object} t)} is always true. Likewise, the
+ − 803 type symbol @code{nil} stands for nothing at all, and
+ − 804 @code{(typep @var{object} nil)} is always false.
+ − 805
+ − 806 @item
+ − 807 The type symbol @code{null} represents the symbol @code{nil}.
+ − 808 Thus @code{(typep @var{object} 'null)} is equivalent to
+ − 809 @code{(null @var{object})}.
+ − 810
+ − 811 @item
+ − 812 The type symbol @code{real} is a synonym for @code{number}, and
+ − 813 @code{fixnum} is a synonym for @code{integer}.
+ − 814
+ − 815 @item
+ − 816 The type symbols @code{character} and @code{string-char} match
+ − 817 characters. In Emacs-19 and XEmacs-19, characters are the same thing as
+ − 818 integers in the range 0-255. In XEmacs-20, where characters are a
+ − 819 first-class data type, this checks for actual characters, and
+ − 820 @code{(typep @var{8bit-integer} 'character)} will return @code{nil}.
+ − 821
+ − 822 @item
+ − 823 The type symbol @code{float} uses the @code{floatp-safe} predicate
+ − 824 defined by this package rather than @code{floatp}, so it will work
+ − 825 correctly even in Emacs versions without floating-point support.
+ − 826
+ − 827 @item
+ − 828 The type list @code{(integer @var{low} @var{high})} represents all
+ − 829 integers between @var{low} and @var{high}, inclusive. Either bound
+ − 830 may be a list of a single integer to specify an exclusive limit,
+ − 831 or a @code{*} to specify no limit. The type @code{(integer * *)}
+ − 832 is thus equivalent to @code{integer}.
+ − 833
+ − 834 @item
+ − 835 Likewise, lists beginning with @code{float}, @code{real}, or
+ − 836 @code{number} represent numbers of that type falling in a particular
+ − 837 range.
+ − 838
+ − 839 @item
+ − 840 Lists beginning with @code{and}, @code{or}, and @code{not} form
+ − 841 combinations of types. For example, @code{(or integer (float 0 *))}
+ − 842 represents all objects that are integers or non-negative floats.
+ − 843
+ − 844 @item
+ − 845 Lists beginning with @code{member} or @code{member*} represent
+ − 846 objects @code{eql} to any of the following values. For example,
+ − 847 @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
+ − 848 and @code{(member nil)} is equivalent to @code{null}.
+ − 849
+ − 850 @item
+ − 851 Lists of the form @code{(satisfies @var{predicate})} represent
+ − 852 all objects for which @var{predicate} returns true when called
+ − 853 with that object as an argument.
+ − 854 @end itemize
+ − 855
+ − 856 The following function and macro (not technically predicates) are
+ − 857 related to @code{typep}.
+ − 858
+ − 859 @defun coerce object type
+ − 860 This function attempts to convert @var{object} to the specified
+ − 861 @var{type}. If @var{object} is already of that type as determined by
+ − 862 @code{typep}, it is simply returned. Otherwise, certain types of
+ − 863 conversions will be made: If @var{type} is any sequence type
+ − 864 (@code{string}, @code{list}, etc.) then @var{object} will be
+ − 865 converted to that type if possible. If @var{type} is
+ − 866 @code{character}, then strings of length one and symbols with
+ − 867 one-character names can be coerced. If @var{type} is @code{float},
+ − 868 then integers can be coerced in versions of Emacs that support
+ − 869 floats. In all other circumstances, @code{coerce} signals an
+ − 870 error.
+ − 871 @end defun
+ − 872
+ − 873 @defspec deftype name arglist forms...
+ − 874 This macro defines a new type called @var{name}. It is similar
+ − 875 to @code{defmacro} in many ways; when @var{name} is encountered
+ − 876 as a type name, the body @var{forms} are evaluated and should
+ − 877 return a type specifier that is equivalent to the type. The
+ − 878 @var{arglist} is a Common Lisp argument list of the sort accepted
+ − 879 by @code{defmacro*}. The type specifier @samp{(@var{name} @var{args}...)}
+ − 880 is expanded by calling the expander with those arguments; the type
+ − 881 symbol @samp{@var{name}} is expanded by calling the expander with
+ − 882 no arguments. The @var{arglist} is processed the same as for
+ − 883 @code{defmacro*} except that optional arguments without explicit
+ − 884 defaults use @code{*} instead of @code{nil} as the ``default''
+ − 885 default. Some examples:
+ − 886
+ − 887 @example
+ − 888 (deftype null () '(satisfies null)) ; predefined
+ − 889 (deftype list () '(or null cons)) ; predefined
+ − 890 (deftype unsigned-byte (&optional bits)
+ − 891 (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
+ − 892 (unsigned-byte 8) @equiv{} (integer 0 255)
+ − 893 (unsigned-byte) @equiv{} (integer 0 *)
+ − 894 unsigned-byte @equiv{} (integer 0 *)
+ − 895 @end example
+ − 896
+ − 897 @noindent
+ − 898 The last example shows how the Common Lisp @code{unsigned-byte}
+ − 899 type specifier could be implemented if desired; this package does
+ − 900 not implement @code{unsigned-byte} by default.
+ − 901 @end defspec
+ − 902
+ − 903 The @code{typecase} and @code{check-type} macros also use type
+ − 904 names. @xref{Conditionals}. @xref{Assertions}. The @code{map},
+ − 905 @code{concatenate}, and @code{merge} functions take type-name
+ − 906 arguments to specify the type of sequence to return. @xref{Sequences}.
+ − 907
+ − 908 @node Equality Predicates, , Type Predicates, Predicates
+ − 909 @section Equality Predicates
+ − 910
+ − 911 @noindent
+ − 912 This package defines two Common Lisp predicates, @code{eql} and
+ − 913 @code{equalp}.
+ − 914
+ − 915 @defun eql a b
+ − 916 This function is almost the same as @code{eq}, except that if @var{a}
+ − 917 and @var{b} are numbers of the same type, it compares them for numeric
+ − 918 equality (as if by @code{equal} instead of @code{eq}). This makes a
+ − 919 difference only for versions of Emacs that are compiled with
+ − 920 floating-point support, such as Emacs 19. Emacs floats are allocated
+ − 921 objects just like cons cells, which means that @code{(eq 3.0 3.0)}
+ − 922 will not necessarily be true---if the two @code{3.0}s were allocated
+ − 923 separately, the pointers will be different even though the numbers are
+ − 924 the same. But @code{(eql 3.0 3.0)} will always be true.
+ − 925
+ − 926 The types of the arguments must match, so @code{(eql 3 3.0)} is
+ − 927 still false.
+ − 928
+ − 929 Note that Emacs integers are ``direct'' rather than allocated, which
+ − 930 basically means @code{(eq 3 3)} will always be true. Thus @code{eq}
+ − 931 and @code{eql} behave differently only if floating-point numbers are
+ − 932 involved, and are indistinguishable on Emacs versions that don't
+ − 933 support floats.
+ − 934
+ − 935 There is a slight inconsistency with Common Lisp in the treatment of
+ − 936 positive and negative zeros. Some machines, notably those with IEEE
+ − 937 standard arithmetic, represent @code{+0} and @code{-0} as distinct
+ − 938 values. Normally this doesn't matter because the standard specifies
+ − 939 that @code{(= 0.0 -0.0)} should always be true, and this is indeed
+ − 940 what Emacs Lisp and Common Lisp do. But the Common Lisp standard
+ − 941 states that @code{(eql 0.0 -0.0)} and @code{(equal 0.0 -0.0)} should
+ − 942 be false on IEEE-like machines; Emacs Lisp does not do this, and in
+ − 943 fact the only known way to distinguish between the two zeros in Emacs
+ − 944 Lisp is to @code{format} them and check for a minus sign.
+ − 945 @end defun
+ − 946
+ − 947 @defun equalp a b
+ − 948 This function is a more flexible version of @code{equal}. In
+ − 949 particular, it compares strings and characters case-insensitively, and
+ − 950 it compares numbers without regard to type (so that @code{(equalp 3
+ − 951 3.0)} is true). Vectors and conses are compared recursively. All other
+ − 952 objects are compared as if by @code{equal}.
+ − 953
+ − 954 This function differs from Common Lisp @code{equalp} in several
+ − 955 respects. In keeping with the idea that strings are less
+ − 956 vector-like in Emacs Lisp, this package's @code{equalp} also will not
+ − 957 compare strings against vectors of integers.
+ − 958 @end defun
+ − 959
+ − 960 Also note that the Common Lisp functions @code{member} and @code{assoc}
+ − 961 use @code{eql} to compare elements, whereas Emacs Lisp follows the
+ − 962 MacLisp tradition and uses @code{equal} for these two functions.
+ − 963 In Emacs, use @code{member*} and @code{assoc*} to get functions
+ − 964 which use @code{eql} for comparisons.
+ − 965
+ − 966 @node Control Structure, Macros, Predicates, Top
+ − 967 @chapter Control Structure
+ − 968
+ − 969 @noindent
+ − 970 The features described in the following sections implement
+ − 971 various advanced control structures, including the powerful
+ − 972 @code{setf} facility and a number of looping and conditional
+ − 973 constructs.
+ − 974
+ − 975 @menu
+ − 976 * Assignment:: The `psetq' form
+ − 977 * Generalized Variables:: `setf', `incf', `push', etc.
+ − 978 * Variable Bindings:: `progv', `lexical-let', `flet', `macrolet'
+ − 979 * Conditionals:: `when', `unless', `case', `typecase'
+ − 980 * Blocks and Exits:: `block', `return', `return-from'
+ − 981 * Iteration:: `do', `dotimes', `dolist', `do-symbols'
+ − 982 * Loop Facility:: The Common Lisp `loop' macro
+ − 983 * Multiple Values:: `values', `multiple-value-bind', etc.
+ − 984 @end menu
+ − 985
+ − 986 @node Assignment, Generalized Variables, Control Structure, Control Structure
+ − 987 @section Assignment
+ − 988
+ − 989 @noindent
+ − 990 The @code{psetq} form is just like @code{setq}, except that multiple
+ − 991 assignments are done in parallel rather than sequentially.
+ − 992
+ − 993 @defspec psetq [symbol form]@dots{}
+ − 994 This special form (actually a macro) is used to assign to several
+ − 995 variables simultaneously. Given only one @var{symbol} and @var{form},
+ − 996 it has the same effect as @code{setq}. Given several @var{symbol}
+ − 997 and @var{form} pairs, it evaluates all the @var{form}s in advance
+ − 998 and then stores the corresponding variables afterwards.
+ − 999
+ − 1000 @example
+ − 1001 (setq x 2 y 3)
+ − 1002 (setq x (+ x y) y (* x y))
+ − 1003 x
+ − 1004 @result{} 5
+ − 1005 y ; @r{@code{y} was computed after @code{x} was set.}
+ − 1006 @result{} 15
+ − 1007 (setq x 2 y 3)
+ − 1008 (psetq x (+ x y) y (* x y))
+ − 1009 x
+ − 1010 @result{} 5
+ − 1011 y ; @r{@code{y} was computed before @code{x} was set.}
+ − 1012 @result{} 6
+ − 1013 @end example
+ − 1014
+ − 1015 The simplest use of @code{psetq} is @code{(psetq x y y x)}, which
+ − 1016 exchanges the values of two variables. (The @code{rotatef} form
+ − 1017 provides an even more convenient way to swap two variables;
+ − 1018 @pxref{Modify Macros}.)
+ − 1019
+ − 1020 @code{psetq} always returns @code{nil}.
+ − 1021 @end defspec
+ − 1022
+ − 1023 @node Generalized Variables, Variable Bindings, Assignment, Control Structure
+ − 1024 @section Generalized Variables
+ − 1025
+ − 1026 @noindent
+ − 1027 A ``generalized variable'' or ``place form'' is one of the many places
+ − 1028 in Lisp memory where values can be stored. The simplest place form is
+ − 1029 a regular Lisp variable. But the cars and cdrs of lists, elements
+ − 1030 of arrays, properties of symbols, and many other locations are also
+ − 1031 places where Lisp values are stored.
+ − 1032
+ − 1033 The @code{setf} form is like @code{setq}, except that it accepts
+ − 1034 arbitrary place forms on the left side rather than just
+ − 1035 symbols. For example, @code{(setf (car a) b)} sets the car of
+ − 1036 @code{a} to @code{b}, doing the same operation as @code{(setcar a b)}
+ − 1037 but without having to remember two separate functions for setting
+ − 1038 and accessing every type of place.
+ − 1039
+ − 1040 Generalized variables are analogous to ``lvalues'' in the C
+ − 1041 language, where @samp{x = a[i]} gets an element from an array
+ − 1042 and @samp{a[i] = x} stores an element using the same notation.
+ − 1043 Just as certain forms like @code{a[i]} can be lvalues in C, there
+ − 1044 is a set of forms that can be generalized variables in Lisp.
+ − 1045
+ − 1046 @menu
+ − 1047 * Basic Setf:: `setf' and place forms
+ − 1048 * Modify Macros:: `incf', `push', `rotatef', `letf', `callf', etc.
+ − 1049 * Customizing Setf:: `define-modify-macro', `defsetf', `define-setf-method'
+ − 1050 @end menu
+ − 1051
+ − 1052 @node Basic Setf, Modify Macros, Generalized Variables, Generalized Variables
+ − 1053 @subsection Basic Setf
+ − 1054
+ − 1055 @noindent
+ − 1056 The @code{setf} macro is the most basic way to operate on generalized
+ − 1057 variables.
+ − 1058
+ − 1059 @defspec setf [place form]@dots{}
+ − 1060 This macro evaluates @var{form} and stores it in @var{place}, which
+ − 1061 must be a valid generalized variable form. If there are several
+ − 1062 @var{place} and @var{form} pairs, the assignments are done sequentially
+ − 1063 just as with @code{setq}. @code{setf} returns the value of the last
+ − 1064 @var{form}.
+ − 1065
+ − 1066 The following Lisp forms will work as generalized variables, and
+ − 1067 so may legally appear in the @var{place} argument of @code{setf}:
+ − 1068
+ − 1069 @itemize @bullet
+ − 1070 @item
+ − 1071 A symbol naming a variable. In other words, @code{(setf x y)} is
+ − 1072 exactly equivalent to @code{(setq x y)}, and @code{setq} itself is
+ − 1073 strictly speaking redundant now that @code{setf} exists. Many
+ − 1074 programmers continue to prefer @code{setq} for setting simple
+ − 1075 variables, though, purely for stylistic or historical reasons.
446
+ − 1076 The form @code{(setf x y)} actually expands to @code{(setq x y)},
428
+ − 1077 so there is no performance penalty for using it in compiled code.
+ − 1078
+ − 1079 @item
+ − 1080 A call to any of the following Lisp functions:
+ − 1081
+ − 1082 @smallexample
+ − 1083 car cdr caar .. cddddr
+ − 1084 nth rest first .. tenth
+ − 1085 aref elt nthcdr
+ − 1086 symbol-function symbol-value symbol-plist
440
+ − 1087 get getf gethash
+ − 1088 subseq
428
+ − 1089 @end smallexample
+ − 1090
+ − 1091 @noindent
+ − 1092 Note that for @code{nthcdr} and @code{getf}, the list argument
+ − 1093 of the function must itself be a valid @var{place} form. For
+ − 1094 example, @code{(setf (nthcdr 0 foo) 7)} will set @code{foo} itself
+ − 1095 to 7. Note that @code{push} and @code{pop} on an @code{nthcdr}
+ − 1096 place can be used to insert or delete at any position in a list.
+ − 1097 The use of @code{nthcdr} as a @var{place} form is an extension
+ − 1098 to standard Common Lisp.
+ − 1099
+ − 1100 @item
+ − 1101 The following Emacs-specific functions are also @code{setf}-able.
+ − 1102 (Some of these are defined only in Emacs 19 or only in XEmacs.)
+ − 1103
+ − 1104 @smallexample
+ − 1105 buffer-file-name marker-position
+ − 1106 buffer-modified-p match-data
+ − 1107 buffer-name mouse-position
+ − 1108 buffer-string overlay-end
+ − 1109 buffer-substring overlay-get
+ − 1110 current-buffer overlay-start
+ − 1111 current-case-table point
+ − 1112 current-column point-marker
+ − 1113 current-global-map point-max
+ − 1114 current-input-mode point-min
+ − 1115 current-local-map process-buffer
+ − 1116 current-window-configuration process-filter
+ − 1117 default-file-modes process-sentinel
+ − 1118 default-value read-mouse-position
+ − 1119 documentation-property screen-height
+ − 1120 extent-data screen-menubar
+ − 1121 extent-end-position screen-width
+ − 1122 extent-start-position selected-window
+ − 1123 face-background selected-screen
+ − 1124 face-background-pixmap selected-frame
+ − 1125 face-font standard-case-table
+ − 1126 face-foreground syntax-table
+ − 1127 face-underline-p window-buffer
+ − 1128 file-modes window-dedicated-p
+ − 1129 frame-height window-display-table
+ − 1130 frame-parameters window-height
+ − 1131 frame-visible-p window-hscroll
+ − 1132 frame-width window-point
+ − 1133 get-register window-start
+ − 1134 getenv window-width
+ − 1135 global-key-binding x-get-cut-buffer
+ − 1136 keymap-parent x-get-cutbuffer
+ − 1137 local-key-binding x-get-secondary-selection
+ − 1138 mark x-get-selection
+ − 1139 mark-marker
+ − 1140 @end smallexample
+ − 1141
+ − 1142 Most of these have directly corresponding ``set'' functions, like
+ − 1143 @code{use-local-map} for @code{current-local-map}, or @code{goto-char}
+ − 1144 for @code{point}. A few, like @code{point-min}, expand to longer
+ − 1145 sequences of code when they are @code{setf}'d (@code{(narrow-to-region
+ − 1146 x (point-max))} in this case).
+ − 1147
+ − 1148 @item
+ − 1149 A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
+ − 1150 where @var{subplace} is itself a legal generalized variable whose
+ − 1151 current value is a string, and where the value stored is also a
+ − 1152 string. The new string is spliced into the specified part of the
+ − 1153 destination string. For example:
+ − 1154
+ − 1155 @example
+ − 1156 (setq a (list "hello" "world"))
+ − 1157 @result{} ("hello" "world")
+ − 1158 (cadr a)
+ − 1159 @result{} "world"
+ − 1160 (substring (cadr a) 2 4)
+ − 1161 @result{} "rl"
+ − 1162 (setf (substring (cadr a) 2 4) "o")
+ − 1163 @result{} "o"
+ − 1164 (cadr a)
+ − 1165 @result{} "wood"
+ − 1166 a
+ − 1167 @result{} ("hello" "wood")
+ − 1168 @end example
+ − 1169
+ − 1170 The generalized variable @code{buffer-substring}, listed above,
+ − 1171 also works in this way by replacing a portion of the current buffer.
+ − 1172
+ − 1173 @item
+ − 1174 A call of the form @code{(apply '@var{func} @dots{})} or
+ − 1175 @code{(apply (function @var{func}) @dots{})}, where @var{func}
+ − 1176 is a @code{setf}-able function whose store function is ``suitable''
+ − 1177 in the sense described in Steele's book; since none of the standard
+ − 1178 Emacs place functions are suitable in this sense, this feature is
+ − 1179 only interesting when used with places you define yourself with
+ − 1180 @code{define-setf-method} or the long form of @code{defsetf}.
+ − 1181
+ − 1182 @item
+ − 1183 A macro call, in which case the macro is expanded and @code{setf}
+ − 1184 is applied to the resulting form.
+ − 1185
+ − 1186 @item
+ − 1187 Any form for which a @code{defsetf} or @code{define-setf-method}
+ − 1188 has been made.
+ − 1189 @end itemize
+ − 1190
+ − 1191 Using any forms other than these in the @var{place} argument to
+ − 1192 @code{setf} will signal an error.
+ − 1193
+ − 1194 The @code{setf} macro takes care to evaluate all subforms in
+ − 1195 the proper left-to-right order; for example,
+ − 1196
+ − 1197 @example
+ − 1198 (setf (aref vec (incf i)) i)
+ − 1199 @end example
+ − 1200
+ − 1201 @noindent
+ − 1202 looks like it will evaluate @code{(incf i)} exactly once, before the
+ − 1203 following access to @code{i}; the @code{setf} expander will insert
+ − 1204 temporary variables as necessary to ensure that it does in fact work
+ − 1205 this way no matter what setf-method is defined for @code{aref}.
+ − 1206 (In this case, @code{aset} would be used and no such steps would
+ − 1207 be necessary since @code{aset} takes its arguments in a convenient
+ − 1208 order.)
+ − 1209
+ − 1210 However, if the @var{place} form is a macro which explicitly
+ − 1211 evaluates its arguments in an unusual order, this unusual order
+ − 1212 will be preserved. Adapting an example from Steele, given
+ − 1213
+ − 1214 @example
+ − 1215 (defmacro wrong-order (x y) (list 'aref y x))
+ − 1216 @end example
+ − 1217
+ − 1218 @noindent
+ − 1219 the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
+ − 1220 evaluate @var{b} first, then @var{a}, just as in an actual call
+ − 1221 to @code{wrong-order}.
+ − 1222 @end defspec
+ − 1223
+ − 1224 @node Modify Macros, Customizing Setf, Basic Setf, Generalized Variables
+ − 1225 @subsection Modify Macros
+ − 1226
+ − 1227 @noindent
+ − 1228 This package defines a number of other macros besides @code{setf}
+ − 1229 that operate on generalized variables. Many are interesting and
+ − 1230 useful even when the @var{place} is just a variable name.
+ − 1231
+ − 1232 @defspec psetf [place form]@dots{}
+ − 1233 This macro is to @code{setf} what @code{psetq} is to @code{setq}:
+ − 1234 When several @var{place}s and @var{form}s are involved, the
+ − 1235 assignments take place in parallel rather than sequentially.
+ − 1236 Specifically, all subforms are evaluated from left to right, then
+ − 1237 all the assignments are done (in an undefined order).
+ − 1238 @end defspec
+ − 1239
+ − 1240 @defspec incf place &optional x
+ − 1241 This macro increments the number stored in @var{place} by one, or
+ − 1242 by @var{x} if specified. The incremented value is returned. For
+ − 1243 example, @code{(incf i)} is equivalent to @code{(setq i (1+ i))}, and
+ − 1244 @code{(incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
+ − 1245
+ − 1246 Once again, care is taken to preserve the ``apparent'' order of
+ − 1247 evaluation. For example,
+ − 1248
+ − 1249 @example
+ − 1250 (incf (aref vec (incf i)))
+ − 1251 @end example
+ − 1252
+ − 1253 @noindent
+ − 1254 appears to increment @code{i} once, then increment the element of
+ − 1255 @code{vec} addressed by @code{i}; this is indeed exactly what it
+ − 1256 does, which means the above form is @emph{not} equivalent to the
+ − 1257 ``obvious'' expansion,
+ − 1258
+ − 1259 @example
+ − 1260 (setf (aref vec (incf i)) (1+ (aref vec (incf i)))) ; Wrong!
+ − 1261 @end example
+ − 1262
+ − 1263 @noindent
+ − 1264 but rather to something more like
+ − 1265
+ − 1266 @example
+ − 1267 (let ((temp (incf i)))
+ − 1268 (setf (aref vec temp) (1+ (aref vec temp))))
+ − 1269 @end example
+ − 1270
+ − 1271 @noindent
+ − 1272 Again, all of this is taken care of automatically by @code{incf} and
+ − 1273 the other generalized-variable macros.
+ − 1274
+ − 1275 As a more Emacs-specific example of @code{incf}, the expression
+ − 1276 @code{(incf (point) @var{n})} is essentially equivalent to
+ − 1277 @code{(forward-char @var{n})}.
+ − 1278 @end defspec
+ − 1279
+ − 1280 @defspec decf place &optional x
+ − 1281 This macro decrements the number stored in @var{place} by one, or
+ − 1282 by @var{x} if specified.
+ − 1283 @end defspec
+ − 1284
+ − 1285 @defspec pop place
+ − 1286 This macro removes and returns the first element of the list stored
+ − 1287 in @var{place}. It is analogous to @code{(prog1 (car @var{place})
+ − 1288 (setf @var{place} (cdr @var{place})))}, except that it takes care
+ − 1289 to evaluate all subforms only once.
+ − 1290 @end defspec
+ − 1291
+ − 1292 @defspec push x place
+ − 1293 This macro inserts @var{x} at the front of the list stored in
+ − 1294 @var{place}. It is analogous to @code{(setf @var{place} (cons
+ − 1295 @var{x} @var{place}))}, except for evaluation of the subforms.
+ − 1296 @end defspec
+ − 1297
+ − 1298 @defspec pushnew x place @t{&key :test :test-not :key}
+ − 1299 This macro inserts @var{x} at the front of the list stored in
+ − 1300 @var{place}, but only if @var{x} was not @code{eql} to any
+ − 1301 existing element of the list. The optional keyword arguments
+ − 1302 are interpreted in the same way as for @code{adjoin}.
+ − 1303 @xref{Lists as Sets}.
+ − 1304 @end defspec
+ − 1305
+ − 1306 @defspec shiftf place@dots{} newvalue
+ − 1307 This macro shifts the @var{place}s left by one, shifting in the
+ − 1308 value of @var{newvalue} (which may be any Lisp expression, not just
+ − 1309 a generalized variable), and returning the value shifted out of
+ − 1310 the first @var{place}. Thus, @code{(shiftf @var{a} @var{b} @var{c}
+ − 1311 @var{d})} is equivalent to
+ − 1312
+ − 1313 @example
+ − 1314 (prog1
+ − 1315 @var{a}
+ − 1316 (psetf @var{a} @var{b}
+ − 1317 @var{b} @var{c}
+ − 1318 @var{c} @var{d}))
+ − 1319 @end example
+ − 1320
+ − 1321 @noindent
+ − 1322 except that the subforms of @var{a}, @var{b}, and @var{c} are actually
+ − 1323 evaluated only once each and in the apparent order.
+ − 1324 @end defspec
+ − 1325
+ − 1326 @defspec rotatef place@dots{}
+ − 1327 This macro rotates the @var{place}s left by one in circular fashion.
+ − 1328 Thus, @code{(rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to
+ − 1329
+ − 1330 @example
+ − 1331 (psetf @var{a} @var{b}
+ − 1332 @var{b} @var{c}
+ − 1333 @var{c} @var{d}
+ − 1334 @var{d} @var{a})
+ − 1335 @end example
+ − 1336
+ − 1337 @noindent
+ − 1338 except for the evaluation of subforms. @code{rotatef} always
+ − 1339 returns @code{nil}. Note that @code{(rotatef @var{a} @var{b})}
+ − 1340 conveniently exchanges @var{a} and @var{b}.
+ − 1341 @end defspec
+ − 1342
+ − 1343 The following macros were invented for this package; they have no
+ − 1344 analogues in Common Lisp.
+ − 1345
+ − 1346 @defspec letf (bindings@dots{}) forms@dots{}
+ − 1347 This macro is analogous to @code{let}, but for generalized variables
+ − 1348 rather than just symbols. Each @var{binding} should be of the form
+ − 1349 @code{(@var{place} @var{value})}; the original contents of the
+ − 1350 @var{place}s are saved, the @var{value}s are stored in them, and
+ − 1351 then the body @var{form}s are executed. Afterwards, the @var{places}
+ − 1352 are set back to their original saved contents. This cleanup happens
+ − 1353 even if the @var{form}s exit irregularly due to a @code{throw} or an
+ − 1354 error.
+ − 1355
+ − 1356 For example,
+ − 1357
+ − 1358 @example
+ − 1359 (letf (((point) (point-min))
+ − 1360 (a 17))
+ − 1361 ...)
+ − 1362 @end example
+ − 1363
+ − 1364 @noindent
+ − 1365 moves ``point'' in the current buffer to the beginning of the buffer,
+ − 1366 and also binds @code{a} to 17 (as if by a normal @code{let}, since
+ − 1367 @code{a} is just a regular variable). After the body exits, @code{a}
+ − 1368 is set back to its original value and point is moved back to its
+ − 1369 original position.
+ − 1370
+ − 1371 Note that @code{letf} on @code{(point)} is not quite like a
+ − 1372 @code{save-excursion}, as the latter effectively saves a marker
+ − 1373 which tracks insertions and deletions in the buffer. Actually,
+ − 1374 a @code{letf} of @code{(point-marker)} is much closer to this
+ − 1375 behavior. (@code{point} and @code{point-marker} are equivalent
+ − 1376 as @code{setf} places; each will accept either an integer or a
+ − 1377 marker as the stored value.)
+ − 1378
+ − 1379 Since generalized variables look like lists, @code{let}'s shorthand
+ − 1380 of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
+ − 1381 be ambiguous in @code{letf} and is not allowed.
+ − 1382
+ − 1383 However, a @var{binding} specifier may be a one-element list
+ − 1384 @samp{(@var{place})}, which is similar to @samp{(@var{place}
+ − 1385 @var{place})}. In other words, the @var{place} is not disturbed
+ − 1386 on entry to the body, and the only effect of the @code{letf} is
+ − 1387 to restore the original value of @var{place} afterwards. (The
+ − 1388 redundant access-and-store suggested by the @code{(@var{place}
+ − 1389 @var{place})} example does not actually occur.)
+ − 1390
+ − 1391 In most cases, the @var{place} must have a well-defined value on
+ − 1392 entry to the @code{letf} form. The only exceptions are plain
+ − 1393 variables and calls to @code{symbol-value} and @code{symbol-function}.
+ − 1394 If the symbol is not bound on entry, it is simply made unbound by
+ − 1395 @code{makunbound} or @code{fmakunbound} on exit.
+ − 1396 @end defspec
+ − 1397
+ − 1398 @defspec letf* (bindings@dots{}) forms@dots{}
+ − 1399 This macro is to @code{letf} what @code{let*} is to @code{let}:
+ − 1400 It does the bindings in sequential rather than parallel order.
+ − 1401 @end defspec
+ − 1402
+ − 1403 @defspec callf @var{function} @var{place} @var{args}@dots{}
+ − 1404 This is the ``generic'' modify macro. It calls @var{function},
+ − 1405 which should be an unquoted function name, macro name, or lambda.
+ − 1406 It passes @var{place} and @var{args} as arguments, and assigns the
+ − 1407 result back to @var{place}. For example, @code{(incf @var{place}
+ − 1408 @var{n})} is the same as @code{(callf + @var{place} @var{n})}.
+ − 1409 Some more examples:
+ − 1410
+ − 1411 @example
+ − 1412 (callf abs my-number)
+ − 1413 (callf concat (buffer-name) "<" (int-to-string n) ">")
+ − 1414 (callf union happy-people (list joe bob) :test 'same-person)
+ − 1415 @end example
+ − 1416
+ − 1417 @xref{Customizing Setf}, for @code{define-modify-macro}, a way
+ − 1418 to create even more concise notations for modify macros. Note
+ − 1419 again that @code{callf} is an extension to standard Common Lisp.
+ − 1420 @end defspec
+ − 1421
+ − 1422 @defspec callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{}
+ − 1423 This macro is like @code{callf}, except that @var{place} is
+ − 1424 the @emph{second} argument of @var{function} rather than the
+ − 1425 first. For example, @code{(push @var{x} @var{place})} is
+ − 1426 equivalent to @code{(callf2 cons @var{x} @var{place})}.
+ − 1427 @end defspec
+ − 1428
+ − 1429 The @code{callf} and @code{callf2} macros serve as building
+ − 1430 blocks for other macros like @code{incf}, @code{pushnew}, and
+ − 1431 @code{define-modify-macro}. The @code{letf} and @code{letf*}
+ − 1432 macros are used in the processing of symbol macros;
+ − 1433 @pxref{Macro Bindings}.
+ − 1434
+ − 1435 @node Customizing Setf, , Modify Macros, Generalized Variables
+ − 1436 @subsection Customizing Setf
+ − 1437
+ − 1438 @noindent
+ − 1439 Common Lisp defines three macros, @code{define-modify-macro},
+ − 1440 @code{defsetf}, and @code{define-setf-method}, that allow the
+ − 1441 user to extend generalized variables in various ways.
+ − 1442
+ − 1443 @defspec define-modify-macro name arglist function [doc-string]
+ − 1444 This macro defines a ``read-modify-write'' macro similar to
+ − 1445 @code{incf} and @code{decf}. The macro @var{name} is defined
+ − 1446 to take a @var{place} argument followed by additional arguments
+ − 1447 described by @var{arglist}. The call
+ − 1448
+ − 1449 @example
+ − 1450 (@var{name} @var{place} @var{args}...)
+ − 1451 @end example
+ − 1452
+ − 1453 @noindent
+ − 1454 will be expanded to
+ − 1455
+ − 1456 @example
+ − 1457 (callf @var{func} @var{place} @var{args}...)
+ − 1458 @end example
+ − 1459
+ − 1460 @noindent
+ − 1461 which in turn is roughly equivalent to
+ − 1462
+ − 1463 @example
+ − 1464 (setf @var{place} (@var{func} @var{place} @var{args}...))
+ − 1465 @end example
+ − 1466
+ − 1467 For example:
+ − 1468
+ − 1469 @example
+ − 1470 (define-modify-macro incf (&optional (n 1)) +)
+ − 1471 (define-modify-macro concatf (&rest args) concat)
+ − 1472 @end example
+ − 1473
+ − 1474 Note that @code{&key} is not allowed in @var{arglist}, but
+ − 1475 @code{&rest} is sufficient to pass keywords on to the function.
+ − 1476
+ − 1477 Most of the modify macros defined by Common Lisp do not exactly
+ − 1478 follow the pattern of @code{define-modify-macro}. For example,
+ − 1479 @code{push} takes its arguments in the wrong order, and @code{pop}
+ − 1480 is completely irregular. You can define these macros ``by hand''
+ − 1481 using @code{get-setf-method}, or consult the source file
+ − 1482 @file{cl-macs.el} to see how to use the internal @code{setf}
+ − 1483 building blocks.
+ − 1484 @end defspec
+ − 1485
+ − 1486 @defspec defsetf access-fn update-fn
+ − 1487 This is the simpler of two @code{defsetf} forms. Where
+ − 1488 @var{access-fn} is the name of a function which accesses a place,
+ − 1489 this declares @var{update-fn} to be the corresponding store
+ − 1490 function. From now on,
+ − 1491
+ − 1492 @example
+ − 1493 (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value})
+ − 1494 @end example
+ − 1495
+ − 1496 @noindent
+ − 1497 will be expanded to
+ − 1498
+ − 1499 @example
+ − 1500 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value})
+ − 1501 @end example
+ − 1502
+ − 1503 @noindent
+ − 1504 The @var{update-fn} is required to be either a true function, or
+ − 1505 a macro which evaluates its arguments in a function-like way. Also,
+ − 1506 the @var{update-fn} is expected to return @var{value} as its result.
+ − 1507 Otherwise, the above expansion would not obey the rules for the way
+ − 1508 @code{setf} is supposed to behave.
+ − 1509
+ − 1510 As a special (non-Common-Lisp) extension, a third argument of @code{t}
+ − 1511 to @code{defsetf} says that the @code{update-fn}'s return value is
+ − 1512 not suitable, so that the above @code{setf} should be expanded to
+ − 1513 something more like
+ − 1514
+ − 1515 @example
+ − 1516 (let ((temp @var{value}))
+ − 1517 (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp)
+ − 1518 temp)
+ − 1519 @end example
+ − 1520
+ − 1521 Some examples of the use of @code{defsetf}, drawn from the standard
+ − 1522 suite of setf methods, are:
+ − 1523
+ − 1524 @example
+ − 1525 (defsetf car setcar)
+ − 1526 (defsetf symbol-value set)
+ − 1527 (defsetf buffer-name rename-buffer t)
+ − 1528 @end example
+ − 1529 @end defspec
+ − 1530
+ − 1531 @defspec defsetf access-fn arglist (store-var) forms@dots{}
+ − 1532 This is the second, more complex, form of @code{defsetf}. It is
+ − 1533 rather like @code{defmacro} except for the additional @var{store-var}
+ − 1534 argument. The @var{forms} should return a Lisp form which stores
+ − 1535 the value of @var{store-var} into the generalized variable formed
+ − 1536 by a call to @var{access-fn} with arguments described by @var{arglist}.
+ − 1537 The @var{forms} may begin with a string which documents the @code{setf}
+ − 1538 method (analogous to the doc string that appears at the front of a
+ − 1539 function).
+ − 1540
+ − 1541 For example, the simple form of @code{defsetf} is shorthand for
+ − 1542
+ − 1543 @example
+ − 1544 (defsetf @var{access-fn} (&rest args) (store)
+ − 1545 (append '(@var{update-fn}) args (list store)))
+ − 1546 @end example
+ − 1547
+ − 1548 The Lisp form that is returned can access the arguments from
+ − 1549 @var{arglist} and @var{store-var} in an unrestricted fashion;
+ − 1550 macros like @code{setf} and @code{incf} which invoke this
+ − 1551 setf-method will insert temporary variables as needed to make
+ − 1552 sure the apparent order of evaluation is preserved.
+ − 1553
+ − 1554 Another example drawn from the standard package:
+ − 1555
+ − 1556 @example
+ − 1557 (defsetf nth (n x) (store)
+ − 1558 (list 'setcar (list 'nthcdr n x) store))
+ − 1559 @end example
+ − 1560 @end defspec
+ − 1561
+ − 1562 @defspec define-setf-method access-fn arglist forms@dots{}
+ − 1563 This is the most general way to create new place forms. When
+ − 1564 a @code{setf} to @var{access-fn} with arguments described by
+ − 1565 @var{arglist} is expanded, the @var{forms} are evaluated and
+ − 1566 must return a list of five items:
+ − 1567
+ − 1568 @enumerate
+ − 1569 @item
+ − 1570 A list of @dfn{temporary variables}.
+ − 1571
+ − 1572 @item
+ − 1573 A list of @dfn{value forms} corresponding to the temporary variables
+ − 1574 above. The temporary variables will be bound to these value forms
+ − 1575 as the first step of any operation on the generalized variable.
+ − 1576
+ − 1577 @item
+ − 1578 A list of exactly one @dfn{store variable} (generally obtained
+ − 1579 from a call to @code{gensym}).
+ − 1580
+ − 1581 @item
+ − 1582 A Lisp form which stores the contents of the store variable into
+ − 1583 the generalized variable, assuming the temporaries have been
+ − 1584 bound as described above.
+ − 1585
+ − 1586 @item
+ − 1587 A Lisp form which accesses the contents of the generalized variable,
+ − 1588 assuming the temporaries have been bound.
+ − 1589 @end enumerate
+ − 1590
+ − 1591 This is exactly like the Common Lisp macro of the same name,
+ − 1592 except that the method returns a list of five values rather
+ − 1593 than the five values themselves, since Emacs Lisp does not
+ − 1594 support Common Lisp's notion of multiple return values.
+ − 1595
+ − 1596 Once again, the @var{forms} may begin with a documentation string.
+ − 1597
+ − 1598 A setf-method should be maximally conservative with regard to
+ − 1599 temporary variables. In the setf-methods generated by
+ − 1600 @code{defsetf}, the second return value is simply the list of
+ − 1601 arguments in the place form, and the first return value is a
+ − 1602 list of a corresponding number of temporary variables generated
+ − 1603 by @code{gensym}. Macros like @code{setf} and @code{incf} which
+ − 1604 use this setf-method will optimize away most temporaries that
+ − 1605 turn out to be unnecessary, so there is little reason for the
+ − 1606 setf-method itself to optimize.
+ − 1607 @end defspec
+ − 1608
+ − 1609 @defun get-setf-method place &optional env
+ − 1610 This function returns the setf-method for @var{place}, by
+ − 1611 invoking the definition previously recorded by @code{defsetf}
+ − 1612 or @code{define-setf-method}. The result is a list of five
+ − 1613 values as described above. You can use this function to build
+ − 1614 your own @code{incf}-like modify macros. (Actually, it is
+ − 1615 better to use the internal functions @code{cl-setf-do-modify}
+ − 1616 and @code{cl-setf-do-store}, which are a bit easier to use and
+ − 1617 which also do a number of optimizations; consult the source
+ − 1618 code for the @code{incf} function for a simple example.)
+ − 1619
+ − 1620 The argument @var{env} specifies the ``environment'' to be
+ − 1621 passed on to @code{macroexpand} if @code{get-setf-method} should
+ − 1622 need to expand a macro in @var{place}. It should come from
+ − 1623 an @code{&environment} argument to the macro or setf-method
+ − 1624 that called @code{get-setf-method}.
+ − 1625
+ − 1626 See also the source code for the setf-methods for @code{apply}
+ − 1627 and @code{substring}, each of which works by calling
+ − 1628 @code{get-setf-method} on a simpler case, then massaging
+ − 1629 the result in various ways.
+ − 1630 @end defun
+ − 1631
+ − 1632 Modern Common Lisp defines a second, independent way to specify
+ − 1633 the @code{setf} behavior of a function, namely ``@code{setf}
+ − 1634 functions'' whose names are lists @code{(setf @var{name})}
+ − 1635 rather than symbols. For example, @code{(defun (setf foo) @dots{})}
+ − 1636 defines the function that is used when @code{setf} is applied to
+ − 1637 @code{foo}. This package does not currently support @code{setf}
+ − 1638 functions. In particular, it is a compile-time error to use
+ − 1639 @code{setf} on a form which has not already been @code{defsetf}'d
+ − 1640 or otherwise declared; in newer Common Lisps, this would not be
+ − 1641 an error since the function @code{(setf @var{func})} might be
+ − 1642 defined later.
+ − 1643
+ − 1644 @iftex
+ − 1645 @secno=4
+ − 1646 @end iftex
+ − 1647
+ − 1648 @node Variable Bindings, Conditionals, Generalized Variables, Control Structure
+ − 1649 @section Variable Bindings
+ − 1650
+ − 1651 @noindent
+ − 1652 These Lisp forms make bindings to variables and function names,
+ − 1653 analogous to Lisp's built-in @code{let} form.
+ − 1654
+ − 1655 @xref{Modify Macros}, for the @code{letf} and @code{letf*} forms which
+ − 1656 are also related to variable bindings.
+ − 1657
+ − 1658 @menu
+ − 1659 * Dynamic Bindings:: The `progv' form
+ − 1660 * Lexical Bindings:: `lexical-let' and lexical closures
+ − 1661 * Function Bindings:: `flet' and `labels'
+ − 1662 * Macro Bindings:: `macrolet' and `symbol-macrolet'
+ − 1663 @end menu
+ − 1664
+ − 1665 @node Dynamic Bindings, Lexical Bindings, Variable Bindings, Variable Bindings
+ − 1666 @subsection Dynamic Bindings
+ − 1667
+ − 1668 @noindent
+ − 1669 The standard @code{let} form binds variables whose names are known
+ − 1670 at compile-time. The @code{progv} form provides an easy way to
+ − 1671 bind variables whose names are computed at run-time.
+ − 1672
+ − 1673 @defspec progv symbols values forms@dots{}
+ − 1674 This form establishes @code{let}-style variable bindings on a
+ − 1675 set of variables computed at run-time. The expressions
+ − 1676 @var{symbols} and @var{values} are evaluated, and must return lists
+ − 1677 of symbols and values, respectively. The symbols are bound to the
+ − 1678 corresponding values for the duration of the body @var{form}s.
+ − 1679 If @var{values} is shorter than @var{symbols}, the last few symbols
+ − 1680 are made unbound (as if by @code{makunbound}) inside the body.
+ − 1681 If @var{symbols} is shorter than @var{values}, the excess values
+ − 1682 are ignored.
+ − 1683 @end defspec
+ − 1684
+ − 1685 @node Lexical Bindings, Function Bindings, Dynamic Bindings, Variable Bindings
+ − 1686 @subsection Lexical Bindings
+ − 1687
+ − 1688 @noindent
+ − 1689 The @dfn{CL} package defines the following macro which
+ − 1690 more closely follows the Common Lisp @code{let} form:
+ − 1691
+ − 1692 @defspec lexical-let (bindings@dots{}) forms@dots{}
+ − 1693 This form is exactly like @code{let} except that the bindings it
+ − 1694 establishes are purely lexical. Lexical bindings are similar to
+ − 1695 local variables in a language like C: Only the code physically
+ − 1696 within the body of the @code{lexical-let} (after macro expansion)
+ − 1697 may refer to the bound variables.
+ − 1698
+ − 1699 @example
+ − 1700 (setq a 5)
+ − 1701 (defun foo (b) (+ a b))
+ − 1702 (let ((a 2)) (foo a))
+ − 1703 @result{} 4
+ − 1704 (lexical-let ((a 2)) (foo a))
+ − 1705 @result{} 7
+ − 1706 @end example
+ − 1707
+ − 1708 @noindent
+ − 1709 In this example, a regular @code{let} binding of @code{a} actually
+ − 1710 makes a temporary change to the global variable @code{a}, so @code{foo}
+ − 1711 is able to see the binding of @code{a} to 2. But @code{lexical-let}
+ − 1712 actually creates a distinct local variable @code{a} for use within its
+ − 1713 body, without any effect on the global variable of the same name.
+ − 1714
+ − 1715 The most important use of lexical bindings is to create @dfn{closures}.
+ − 1716 A closure is a function object that refers to an outside lexical
+ − 1717 variable. For example:
+ − 1718
+ − 1719 @example
+ − 1720 (defun make-adder (n)
+ − 1721 (lexical-let ((n n))
+ − 1722 (function (lambda (m) (+ n m)))))
+ − 1723 (setq add17 (make-adder 17))
+ − 1724 (funcall add17 4)
+ − 1725 @result{} 21
+ − 1726 @end example
+ − 1727
+ − 1728 @noindent
+ − 1729 The call @code{(make-adder 17)} returns a function object which adds
+ − 1730 17 to its argument. If @code{let} had been used instead of
+ − 1731 @code{lexical-let}, the function object would have referred to the
+ − 1732 global @code{n}, which would have been bound to 17 only during the
+ − 1733 call to @code{make-adder} itself.
+ − 1734
+ − 1735 @example
+ − 1736 (defun make-counter ()
+ − 1737 (lexical-let ((n 0))
+ − 1738 (function* (lambda (&optional (m 1)) (incf n m)))))
+ − 1739 (setq count-1 (make-counter))
+ − 1740 (funcall count-1 3)
+ − 1741 @result{} 3
+ − 1742 (funcall count-1 14)
+ − 1743 @result{} 17
+ − 1744 (setq count-2 (make-counter))
+ − 1745 (funcall count-2 5)
+ − 1746 @result{} 5
+ − 1747 (funcall count-1 2)
+ − 1748 @result{} 19
+ − 1749 (funcall count-2)
+ − 1750 @result{} 6
+ − 1751 @end example
+ − 1752
+ − 1753 @noindent
+ − 1754 Here we see that each call to @code{make-counter} creates a distinct
+ − 1755 local variable @code{n}, which serves as a private counter for the
+ − 1756 function object that is returned.
+ − 1757
+ − 1758 Closed-over lexical variables persist until the last reference to
+ − 1759 them goes away, just like all other Lisp objects. For example,
+ − 1760 @code{count-2} refers to a function object which refers to an
+ − 1761 instance of the variable @code{n}; this is the only reference
+ − 1762 to that variable, so after @code{(setq count-2 nil)} the garbage
+ − 1763 collector would be able to delete this instance of @code{n}.
+ − 1764 Of course, if a @code{lexical-let} does not actually create any
+ − 1765 closures, then the lexical variables are free as soon as the
+ − 1766 @code{lexical-let} returns.
+ − 1767
+ − 1768 Many closures are used only during the extent of the bindings they
+ − 1769 refer to; these are known as ``downward funargs'' in Lisp parlance.
+ − 1770 When a closure is used in this way, regular Emacs Lisp dynamic
+ − 1771 bindings suffice and will be more efficient than @code{lexical-let}
+ − 1772 closures:
+ − 1773
+ − 1774 @example
+ − 1775 (defun add-to-list (x list)
+ − 1776 (mapcar (function (lambda (y) (+ x y))) list))
+ − 1777 (add-to-list 7 '(1 2 5))
+ − 1778 @result{} (8 9 12)
+ − 1779 @end example
+ − 1780
+ − 1781 @noindent
+ − 1782 Since this lambda is only used while @code{x} is still bound,
+ − 1783 it is not necessary to make a true closure out of it.
+ − 1784
+ − 1785 You can use @code{defun} or @code{flet} inside a @code{lexical-let}
+ − 1786 to create a named closure. If several closures are created in the
+ − 1787 body of a single @code{lexical-let}, they all close over the same
+ − 1788 instance of the lexical variable.
+ − 1789
+ − 1790 The @code{lexical-let} form is an extension to Common Lisp. In
+ − 1791 true Common Lisp, all bindings are lexical unless declared otherwise.
+ − 1792 @end defspec
+ − 1793
+ − 1794 @defspec lexical-let* (bindings@dots{}) forms@dots{}
+ − 1795 This form is just like @code{lexical-let}, except that the bindings
+ − 1796 are made sequentially in the manner of @code{let*}.
+ − 1797 @end defspec
+ − 1798
+ − 1799 @node Function Bindings, Macro Bindings, Lexical Bindings, Variable Bindings
+ − 1800 @subsection Function Bindings
+ − 1801
+ − 1802 @noindent
+ − 1803 These forms make @code{let}-like bindings to functions instead
+ − 1804 of variables.
+ − 1805
+ − 1806 @defspec flet (bindings@dots{}) forms@dots{}
+ − 1807 This form establishes @code{let}-style bindings on the function
+ − 1808 cells of symbols rather than on the value cells. Each @var{binding}
+ − 1809 must be a list of the form @samp{(@var{name} @var{arglist}
+ − 1810 @var{forms}@dots{})}, which defines a function exactly as if
+ − 1811 it were a @code{defun*} form. The function @var{name} is defined
+ − 1812 accordingly for the duration of the body of the @code{flet}; then
+ − 1813 the old function definition, or lack thereof, is restored.
+ − 1814
+ − 1815 While @code{flet} in Common Lisp establishes a lexical binding of
+ − 1816 @var{name}, Emacs Lisp @code{flet} makes a dynamic binding. The
+ − 1817 result is that @code{flet} affects indirect calls to a function as
+ − 1818 well as calls directly inside the @code{flet} form itself.
+ − 1819
+ − 1820 You can use @code{flet} to disable or modify the behavior of a
+ − 1821 function in a temporary fashion. This will even work on Emacs
+ − 1822 primitives, although note that some calls to primitive functions
+ − 1823 internal to Emacs are made without going through the symbol's
+ − 1824 function cell, and so will not be affected by @code{flet}. For
+ − 1825 example,
+ − 1826
+ − 1827 @example
+ − 1828 (flet ((message (&rest args) (push args saved-msgs)))
+ − 1829 (do-something))
+ − 1830 @end example
+ − 1831
+ − 1832 This code attempts to replace the built-in function @code{message}
+ − 1833 with a function that simply saves the messages in a list rather
+ − 1834 than displaying them. The original definition of @code{message}
+ − 1835 will be restored after @code{do-something} exits. This code will
+ − 1836 work fine on messages generated by other Lisp code, but messages
+ − 1837 generated directly inside Emacs will not be caught since they make
+ − 1838 direct C-language calls to the message routines rather than going
+ − 1839 through the Lisp @code{message} function.
+ − 1840
+ − 1841 Functions defined by @code{flet} may use the full Common Lisp
+ − 1842 argument notation supported by @code{defun*}; also, the function
+ − 1843 body is enclosed in an implicit block as if by @code{defun*}.
+ − 1844 @xref{Program Structure}.
+ − 1845 @end defspec
+ − 1846
+ − 1847 @defspec labels (bindings@dots{}) forms@dots{}
+ − 1848 The @code{labels} form is a synonym for @code{flet}. (In Common
+ − 1849 Lisp, @code{labels} and @code{flet} differ in ways that depend on
+ − 1850 their lexical scoping; these distinctions vanish in dynamically
+ − 1851 scoped Emacs Lisp.)
+ − 1852 @end defspec
+ − 1853
+ − 1854 @node Macro Bindings, , Function Bindings, Variable Bindings
+ − 1855 @subsection Macro Bindings
+ − 1856
+ − 1857 @noindent
+ − 1858 These forms create local macros and ``symbol macros.''
+ − 1859
+ − 1860 @defspec macrolet (bindings@dots{}) forms@dots{}
+ − 1861 This form is analogous to @code{flet}, but for macros instead of
+ − 1862 functions. Each @var{binding} is a list of the same form as the
+ − 1863 arguments to @code{defmacro*} (i.e., a macro name, argument list,
+ − 1864 and macro-expander forms). The macro is defined accordingly for
+ − 1865 use within the body of the @code{macrolet}.
+ − 1866
+ − 1867 Because of the nature of macros, @code{macrolet} is lexically
+ − 1868 scoped even in Emacs Lisp: The @code{macrolet} binding will
+ − 1869 affect only calls that appear physically within the body
+ − 1870 @var{forms}, possibly after expansion of other macros in the
+ − 1871 body.
+ − 1872 @end defspec
+ − 1873
+ − 1874 @defspec symbol-macrolet (bindings@dots{}) forms@dots{}
+ − 1875 This form creates @dfn{symbol macros}, which are macros that look
+ − 1876 like variable references rather than function calls. Each
+ − 1877 @var{binding} is a list @samp{(@var{var} @var{expansion})};
+ − 1878 any reference to @var{var} within the body @var{forms} is
+ − 1879 replaced by @var{expansion}.
+ − 1880
+ − 1881 @example
+ − 1882 (setq bar '(5 . 9))
+ − 1883 (symbol-macrolet ((foo (car bar)))
+ − 1884 (incf foo))
+ − 1885 bar
+ − 1886 @result{} (6 . 9)
+ − 1887 @end example
+ − 1888
+ − 1889 A @code{setq} of a symbol macro is treated the same as a @code{setf}.
+ − 1890 I.e., @code{(setq foo 4)} in the above would be equivalent to
+ − 1891 @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
+ − 1892
+ − 1893 Likewise, a @code{let} or @code{let*} binding a symbol macro is
+ − 1894 treated like a @code{letf} or @code{letf*}. This differs from true
+ − 1895 Common Lisp, where the rules of lexical scoping cause a @code{let}
+ − 1896 binding to shadow a @code{symbol-macrolet} binding. In this package,
+ − 1897 only @code{lexical-let} and @code{lexical-let*} will shadow a symbol
+ − 1898 macro.
+ − 1899
+ − 1900 There is no analogue of @code{defmacro} for symbol macros; all symbol
+ − 1901 macros are local. A typical use of @code{symbol-macrolet} is in the
+ − 1902 expansion of another macro:
+ − 1903
+ − 1904 @example
+ − 1905 (defmacro* my-dolist ((x list) &rest body)
+ − 1906 (let ((var (gensym)))
+ − 1907 (list 'loop 'for var 'on list 'do
+ − 1908 (list* 'symbol-macrolet (list (list x (list 'car var)))
+ − 1909 body))))
+ − 1910
+ − 1911 (setq mylist '(1 2 3 4))
+ − 1912 (my-dolist (x mylist) (incf x))
+ − 1913 mylist
+ − 1914 @result{} (2 3 4 5)
+ − 1915 @end example
+ − 1916
+ − 1917 @noindent
+ − 1918 In this example, the @code{my-dolist} macro is similar to @code{dolist}
+ − 1919 (@pxref{Iteration}) except that the variable @code{x} becomes a true
+ − 1920 reference onto the elements of the list. The @code{my-dolist} call
+ − 1921 shown here expands to
+ − 1922
+ − 1923 @example
+ − 1924 (loop for G1234 on mylist do
+ − 1925 (symbol-macrolet ((x (car G1234)))
+ − 1926 (incf x)))
+ − 1927 @end example
+ − 1928
+ − 1929 @noindent
+ − 1930 which in turn expands to
+ − 1931
+ − 1932 @example
+ − 1933 (loop for G1234 on mylist do (incf (car G1234)))
+ − 1934 @end example
+ − 1935
+ − 1936 @xref{Loop Facility}, for a description of the @code{loop} macro.
+ − 1937 This package defines a nonstandard @code{in-ref} loop clause that
+ − 1938 works much like @code{my-dolist}.
+ − 1939 @end defspec
+ − 1940
+ − 1941 @node Conditionals, Blocks and Exits, Variable Bindings, Control Structure
+ − 1942 @section Conditionals
+ − 1943
+ − 1944 @noindent
+ − 1945 These conditional forms augment Emacs Lisp's simple @code{if},
+ − 1946 @code{and}, @code{or}, and @code{cond} forms.
+ − 1947
+ − 1948 @defspec when test forms@dots{}
+ − 1949 This is a variant of @code{if} where there are no ``else'' forms,
+ − 1950 and possibly several ``then'' forms. In particular,
+ − 1951
+ − 1952 @example
+ − 1953 (when @var{test} @var{a} @var{b} @var{c})
+ − 1954 @end example
+ − 1955
+ − 1956 @noindent
+ − 1957 is entirely equivalent to
+ − 1958
+ − 1959 @example
+ − 1960 (if @var{test} (progn @var{a} @var{b} @var{c}) nil)
+ − 1961 @end example
+ − 1962 @end defspec
+ − 1963
+ − 1964 @defspec unless test forms@dots{}
+ − 1965 This is a variant of @code{if} where there are no ``then'' forms,
+ − 1966 and possibly several ``else'' forms:
+ − 1967
+ − 1968 @example
+ − 1969 (unless @var{test} @var{a} @var{b} @var{c})
+ − 1970 @end example
+ − 1971
+ − 1972 @noindent
+ − 1973 is entirely equivalent to
+ − 1974
+ − 1975 @example
+ − 1976 (when (not @var{test}) @var{a} @var{b} @var{c})
+ − 1977 @end example
+ − 1978 @end defspec
+ − 1979
+ − 1980 @defspec case keyform clause@dots{}
+ − 1981 This macro evaluates @var{keyform}, then compares it with the key
+ − 1982 values listed in the various @var{clause}s. Whichever clause matches
+ − 1983 the key is executed; comparison is done by @code{eql}. If no clause
+ − 1984 matches, the @code{case} form returns @code{nil}. The clauses are
+ − 1985 of the form
+ − 1986
+ − 1987 @example
+ − 1988 (@var{keylist} @var{body-forms}@dots{})
+ − 1989 @end example
+ − 1990
+ − 1991 @noindent
+ − 1992 where @var{keylist} is a list of key values. If there is exactly
+ − 1993 one value, and it is not a cons cell or the symbol @code{nil} or
+ − 1994 @code{t}, then it can be used by itself as a @var{keylist} without
+ − 1995 being enclosed in a list. All key values in the @code{case} form
+ − 1996 must be distinct. The final clauses may use @code{t} in place of
+ − 1997 a @var{keylist} to indicate a default clause that should be taken
+ − 1998 if none of the other clauses match. (The symbol @code{otherwise}
+ − 1999 is also recognized in place of @code{t}. To make a clause that
+ − 2000 matches the actual symbol @code{t}, @code{nil}, or @code{otherwise},
+ − 2001 enclose the symbol in a list.)
+ − 2002
+ − 2003 For example, this expression reads a keystroke, then does one of
+ − 2004 four things depending on whether it is an @samp{a}, a @samp{b},
+ − 2005 a @key{RET} or @key{LFD}, or anything else.
+ − 2006
+ − 2007 @example
+ − 2008 (case (read-char)
+ − 2009 (?a (do-a-thing))
+ − 2010 (?b (do-b-thing))
+ − 2011 ((?\r ?\n) (do-ret-thing))
+ − 2012 (t (do-other-thing)))
+ − 2013 @end example
+ − 2014 @end defspec
+ − 2015
+ − 2016 @defspec ecase keyform clause@dots{}
+ − 2017 This macro is just like @code{case}, except that if the key does
+ − 2018 not match any of the clauses, an error is signalled rather than
+ − 2019 simply returning @code{nil}.
+ − 2020 @end defspec
+ − 2021
+ − 2022 @defspec typecase keyform clause@dots{}
+ − 2023 This macro is a version of @code{case} that checks for types
+ − 2024 rather than values. Each @var{clause} is of the form
+ − 2025 @samp{(@var{type} @var{body}...)}. @xref{Type Predicates},
+ − 2026 for a description of type specifiers. For example,
+ − 2027
+ − 2028 @example
+ − 2029 (typecase x
+ − 2030 (integer (munch-integer x))
+ − 2031 (float (munch-float x))
+ − 2032 (string (munch-integer (string-to-int x)))
+ − 2033 (t (munch-anything x)))
+ − 2034 @end example
+ − 2035
+ − 2036 The type specifier @code{t} matches any type of object; the word
+ − 2037 @code{otherwise} is also allowed. To make one clause match any of
+ − 2038 several types, use an @code{(or ...)} type specifier.
+ − 2039 @end defspec
+ − 2040
+ − 2041 @defspec etypecase keyform clause@dots{}
+ − 2042 This macro is just like @code{typecase}, except that if the key does
+ − 2043 not match any of the clauses, an error is signalled rather than
+ − 2044 simply returning @code{nil}.
+ − 2045 @end defspec
+ − 2046
+ − 2047 @node Blocks and Exits, Iteration, Conditionals, Control Structure
+ − 2048 @section Blocks and Exits
+ − 2049
+ − 2050 @noindent
+ − 2051 Common Lisp @dfn{blocks} provide a non-local exit mechanism very
+ − 2052 similar to @code{catch} and @code{throw}, but lexically rather than
+ − 2053 dynamically scoped. This package actually implements @code{block}
+ − 2054 in terms of @code{catch}; however, the lexical scoping allows the
+ − 2055 optimizing byte-compiler to omit the costly @code{catch} step if the
+ − 2056 body of the block does not actually @code{return-from} the block.
+ − 2057
+ − 2058 @defspec block name forms@dots{}
+ − 2059 The @var{forms} are evaluated as if by a @code{progn}. However,
+ − 2060 if any of the @var{forms} execute @code{(return-from @var{name})},
+ − 2061 they will jump out and return directly from the @code{block} form.
+ − 2062 The @code{block} returns the result of the last @var{form} unless
+ − 2063 a @code{return-from} occurs.
+ − 2064
+ − 2065 The @code{block}/@code{return-from} mechanism is quite similar to
+ − 2066 the @code{catch}/@code{throw} mechanism. The main differences are
+ − 2067 that block @var{name}s are unevaluated symbols, rather than forms
+ − 2068 (such as quoted symbols) which evaluate to a tag at run-time; and
+ − 2069 also that blocks are lexically scoped whereas @code{catch}/@code{throw}
+ − 2070 are dynamically scoped. This means that functions called from the
+ − 2071 body of a @code{catch} can also @code{throw} to the @code{catch},
+ − 2072 but the @code{return-from} referring to a block name must appear
+ − 2073 physically within the @var{forms} that make up the body of the block.
+ − 2074 They may not appear within other called functions, although they may
+ − 2075 appear within macro expansions or @code{lambda}s in the body. Block
+ − 2076 names and @code{catch} names form independent name-spaces.
+ − 2077
+ − 2078 In true Common Lisp, @code{defun} and @code{defmacro} surround
+ − 2079 the function or expander bodies with implicit blocks with the
+ − 2080 same name as the function or macro. This does not occur in Emacs
+ − 2081 Lisp, but this package provides @code{defun*} and @code{defmacro*}
+ − 2082 forms which do create the implicit block.
+ − 2083
+ − 2084 The Common Lisp looping constructs defined by this package,
+ − 2085 such as @code{loop} and @code{dolist}, also create implicit blocks
+ − 2086 just as in Common Lisp.
+ − 2087
+ − 2088 Because they are implemented in terms of Emacs Lisp @code{catch}
+ − 2089 and @code{throw}, blocks have the same overhead as actual
+ − 2090 @code{catch} constructs (roughly two function calls). However,
+ − 2091 Zawinski and Furuseth's optimizing byte compiler (standard in
+ − 2092 Emacs 19) will optimize away the @code{catch} if the block does
+ − 2093 not in fact contain any @code{return} or @code{return-from} calls
+ − 2094 that jump to it. This means that @code{do} loops and @code{defun*}
+ − 2095 functions which don't use @code{return} don't pay the overhead to
+ − 2096 support it.
+ − 2097 @end defspec
+ − 2098
+ − 2099 @defspec return-from name [result]
+ − 2100 This macro returns from the block named @var{name}, which must be
+ − 2101 an (unevaluated) symbol. If a @var{result} form is specified, it
+ − 2102 is evaluated to produce the result returned from the @code{block}.
+ − 2103 Otherwise, @code{nil} is returned.
+ − 2104 @end defspec
+ − 2105
+ − 2106 @defspec return [result]
+ − 2107 This macro is exactly like @code{(return-from nil @var{result})}.
+ − 2108 Common Lisp loops like @code{do} and @code{dolist} implicitly enclose
+ − 2109 themselves in @code{nil} blocks.
+ − 2110 @end defspec
+ − 2111
+ − 2112 @node Iteration, Loop Facility, Blocks and Exits, Control Structure
+ − 2113 @section Iteration
+ − 2114
+ − 2115 @noindent
+ − 2116 The macros described here provide more sophisticated, high-level
+ − 2117 looping constructs to complement Emacs Lisp's basic @code{while}
+ − 2118 loop.
+ − 2119
+ − 2120 @defspec loop forms@dots{}
+ − 2121 The @dfn{CL} package supports both the simple, old-style meaning of
+ − 2122 @code{loop} and the extremely powerful and flexible feature known as
+ − 2123 the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced
+ − 2124 facility is discussed in the following section; @pxref{Loop Facility}.
+ − 2125 The simple form of @code{loop} is described here.
+ − 2126
+ − 2127 If @code{loop} is followed by zero or more Lisp expressions,
+ − 2128 then @code{(loop @var{exprs}@dots{})} simply creates an infinite
+ − 2129 loop executing the expressions over and over. The loop is
+ − 2130 enclosed in an implicit @code{nil} block. Thus,
+ − 2131
+ − 2132 @example
+ − 2133 (loop (foo) (if (no-more) (return 72)) (bar))
+ − 2134 @end example
+ − 2135
+ − 2136 @noindent
+ − 2137 is exactly equivalent to
+ − 2138
+ − 2139 @example
+ − 2140 (block nil (while t (foo) (if (no-more) (return 72)) (bar)))
+ − 2141 @end example
+ − 2142
+ − 2143 If any of the expressions are plain symbols, the loop is instead
+ − 2144 interpreted as a Loop Macro specification as described later.
+ − 2145 (This is not a restriction in practice, since a plain symbol
+ − 2146 in the above notation would simply access and throw away the
+ − 2147 value of a variable.)
+ − 2148 @end defspec
+ − 2149
+ − 2150 @defspec do (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
+ − 2151 This macro creates a general iterative loop. Each @var{spec} is
+ − 2152 of the form
+ − 2153
+ − 2154 @example
+ − 2155 (@var{var} [@var{init} [@var{step}]])
+ − 2156 @end example
+ − 2157
+ − 2158 The loop works as follows: First, each @var{var} is bound to the
+ − 2159 associated @var{init} value as if by a @code{let} form. Then, in
+ − 2160 each iteration of the loop, the @var{end-test} is evaluated; if
+ − 2161 true, the loop is finished. Otherwise, the body @var{forms} are
+ − 2162 evaluated, then each @var{var} is set to the associated @var{step}
+ − 2163 expression (as if by a @code{psetq} form) and the next iteration
+ − 2164 begins. Once the @var{end-test} becomes true, the @var{result}
+ − 2165 forms are evaluated (with the @var{var}s still bound to their
+ − 2166 values) to produce the result returned by @code{do}.
+ − 2167
+ − 2168 The entire @code{do} loop is enclosed in an implicit @code{nil}
+ − 2169 block, so that you can use @code{(return)} to break out of the
+ − 2170 loop at any time.
+ − 2171
+ − 2172 If there are no @var{result} forms, the loop returns @code{nil}.
+ − 2173 If a given @var{var} has no @var{step} form, it is bound to its
+ − 2174 @var{init} value but not otherwise modified during the @code{do}
+ − 2175 loop (unless the code explicitly modifies it); this case is just
+ − 2176 a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})}
+ − 2177 around the loop. If @var{init} is also omitted it defaults to
+ − 2178 @code{nil}, and in this case a plain @samp{@var{var}} can be used
+ − 2179 in place of @samp{(@var{var})}, again following the analogy with
+ − 2180 @code{let}.
+ − 2181
+ − 2182 This example (from Steele) illustrates a loop which applies the
+ − 2183 function @code{f} to successive pairs of values from the lists
+ − 2184 @code{foo} and @code{bar}; it is equivalent to the call
+ − 2185 @code{(mapcar* 'f foo bar)}. Note that this loop has no body
+ − 2186 @var{forms} at all, performing all its work as side effects of
+ − 2187 the rest of the loop.
+ − 2188
+ − 2189 @example
+ − 2190 (do ((x foo (cdr x))
+ − 2191 (y bar (cdr y))
+ − 2192 (z nil (cons (f (car x) (car y)) z)))
+ − 2193 ((or (null x) (null y))
+ − 2194 (nreverse z)))
+ − 2195 @end example
+ − 2196 @end defspec
+ − 2197
+ − 2198 @defspec do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{}
+ − 2199 This is to @code{do} what @code{let*} is to @code{let}. In
+ − 2200 particular, the initial values are bound as if by @code{let*}
+ − 2201 rather than @code{let}, and the steps are assigned as if by
+ − 2202 @code{setq} rather than @code{psetq}.
+ − 2203
+ − 2204 Here is another way to write the above loop:
+ − 2205
+ − 2206 @example
+ − 2207 (do* ((xp foo (cdr xp))
+ − 2208 (yp bar (cdr yp))
+ − 2209 (x (car xp) (car xp))
+ − 2210 (y (car yp) (car yp))
+ − 2211 z)
+ − 2212 ((or (null xp) (null yp))
+ − 2213 (nreverse z))
+ − 2214 (push (f x y) z))
+ − 2215 @end example
+ − 2216 @end defspec
+ − 2217
+ − 2218 @defspec dolist (var list [result]) forms@dots{}
+ − 2219 This is a more specialized loop which iterates across the elements
+ − 2220 of a list. @var{list} should evaluate to a list; the body @var{forms}
+ − 2221 are executed with @var{var} bound to each element of the list in
+ − 2222 turn. Finally, the @var{result} form (or @code{nil}) is evaluated
+ − 2223 with @var{var} bound to @code{nil} to produce the result returned by
+ − 2224 the loop. The loop is surrounded by an implicit @code{nil} block.
+ − 2225 @end defspec
+ − 2226
+ − 2227 @defspec dotimes (var count [result]) forms@dots{}
+ − 2228 This is a more specialized loop which iterates a specified number
+ − 2229 of times. The body is executed with @var{var} bound to the integers
+ − 2230 from zero (inclusive) to @var{count} (exclusive), in turn. Then
+ − 2231 the @code{result} form is evaluated with @var{var} bound to the total
+ − 2232 number of iterations that were done (i.e., @code{(max 0 @var{count})})
+ − 2233 to get the return value for the loop form. The loop is surrounded
+ − 2234 by an implicit @code{nil} block.
+ − 2235 @end defspec
+ − 2236
+ − 2237 @defspec do-symbols (var [obarray [result]]) forms@dots{}
+ − 2238 This loop iterates over all interned symbols. If @var{obarray}
+ − 2239 is specified and is not @code{nil}, it loops over all symbols in
+ − 2240 that obarray. For each symbol, the body @var{forms} are evaluated
+ − 2241 with @var{var} bound to that symbol. The symbols are visited in
+ − 2242 an unspecified order. Afterward the @var{result} form, if any,
+ − 2243 is evaluated (with @var{var} bound to @code{nil}) to get the return
+ − 2244 value. The loop is surrounded by an implicit @code{nil} block.
+ − 2245 @end defspec
+ − 2246
+ − 2247 @defspec do-all-symbols (var [result]) forms@dots{}
+ − 2248 This is identical to @code{do-symbols} except that the @var{obarray}
+ − 2249 argument is omitted; it always iterates over the default obarray.
+ − 2250 @end defspec
+ − 2251
+ − 2252 @xref{Mapping over Sequences}, for some more functions for
+ − 2253 iterating over vectors or lists.
+ − 2254
+ − 2255 @node Loop Facility, Multiple Values, Iteration, Control Structure
+ − 2256 @section Loop Facility
+ − 2257
+ − 2258 @noindent
+ − 2259 A common complaint with Lisp's traditional looping constructs is
+ − 2260 that they are either too simple and limited, such as Common Lisp's
+ − 2261 @code{dotimes} or Emacs Lisp's @code{while}, or too unreadable and
+ − 2262 obscure, like Common Lisp's @code{do} loop.
+ − 2263
+ − 2264 To remedy this, recent versions of Common Lisp have added a new
+ − 2265 construct called the ``Loop Facility'' or ``@code{loop} macro,''
+ − 2266 with an easy-to-use but very powerful and expressive syntax.
+ − 2267
+ − 2268 @menu
+ − 2269 * Loop Basics:: `loop' macro, basic clause structure
+ − 2270 * Loop Examples:: Working examples of `loop' macro
+ − 2271 * For Clauses:: Clauses introduced by `for' or `as'
+ − 2272 * Iteration Clauses:: `repeat', `while', `thereis', etc.
+ − 2273 * Accumulation Clauses:: `collect', `sum', `maximize', etc.
+ − 2274 * Other Clauses:: `with', `if', `initially', `finally'
+ − 2275 @end menu
+ − 2276
+ − 2277 @node Loop Basics, Loop Examples, Loop Facility, Loop Facility
+ − 2278 @subsection Loop Basics
+ − 2279
+ − 2280 @noindent
+ − 2281 The @code{loop} macro essentially creates a mini-language within
+ − 2282 Lisp that is specially tailored for describing loops. While this
+ − 2283 language is a little strange-looking by the standards of regular Lisp,
+ − 2284 it turns out to be very easy to learn and well-suited to its purpose.
+ − 2285
+ − 2286 Since @code{loop} is a macro, all parsing of the loop language
+ − 2287 takes place at byte-compile time; compiled @code{loop}s are just
+ − 2288 as efficient as the equivalent @code{while} loops written longhand.
+ − 2289
+ − 2290 @defspec loop clauses@dots{}
+ − 2291 A loop construct consists of a series of @var{clause}s, each
+ − 2292 introduced by a symbol like @code{for} or @code{do}. Clauses
+ − 2293 are simply strung together in the argument list of @code{loop},
+ − 2294 with minimal extra parentheses. The various types of clauses
+ − 2295 specify initializations, such as the binding of temporary
+ − 2296 variables, actions to be taken in the loop, stepping actions,
+ − 2297 and final cleanup.
+ − 2298
+ − 2299 Common Lisp specifies a certain general order of clauses in a
+ − 2300 loop:
+ − 2301
+ − 2302 @example
+ − 2303 (loop @var{name-clause}
+ − 2304 @var{var-clauses}@dots{}
+ − 2305 @var{action-clauses}@dots{})
+ − 2306 @end example
+ − 2307
+ − 2308 The @var{name-clause} optionally gives a name to the implicit
+ − 2309 block that surrounds the loop. By default, the implicit block
+ − 2310 is named @code{nil}. The @var{var-clauses} specify what
+ − 2311 variables should be bound during the loop, and how they should
+ − 2312 be modified or iterated throughout the course of the loop. The
+ − 2313 @var{action-clauses} are things to be done during the loop, such
+ − 2314 as computing, collecting, and returning values.
+ − 2315
+ − 2316 The Emacs version of the @code{loop} macro is less restrictive about
+ − 2317 the order of clauses, but things will behave most predictably if
+ − 2318 you put the variable-binding clauses @code{with}, @code{for}, and
+ − 2319 @code{repeat} before the action clauses. As in Common Lisp,
+ − 2320 @code{initially} and @code{finally} clauses can go anywhere.
+ − 2321
+ − 2322 Loops generally return @code{nil} by default, but you can cause
+ − 2323 them to return a value by using an accumulation clause like
+ − 2324 @code{collect}, an end-test clause like @code{always}, or an
+ − 2325 explicit @code{return} clause to jump out of the implicit block.
+ − 2326 (Because the loop body is enclosed in an implicit block, you can
+ − 2327 also use regular Lisp @code{return} or @code{return-from} to
+ − 2328 break out of the loop.)
+ − 2329 @end defspec
+ − 2330
+ − 2331 The following sections give some examples of the Loop Macro in
+ − 2332 action, and describe the particular loop clauses in great detail.
+ − 2333 Consult the second edition of Steele's @dfn{Common Lisp, the Language},
+ − 2334 for additional discussion and examples of the @code{loop} macro.
+ − 2335
+ − 2336 @node Loop Examples, For Clauses, Loop Basics, Loop Facility
+ − 2337 @subsection Loop Examples
+ − 2338
+ − 2339 @noindent
+ − 2340 Before listing the full set of clauses that are allowed, let's
+ − 2341 look at a few example loops just to get a feel for the @code{loop}
+ − 2342 language.
+ − 2343
+ − 2344 @example
+ − 2345 (loop for buf in (buffer-list)
+ − 2346 collect (buffer-file-name buf))
+ − 2347 @end example
+ − 2348
+ − 2349 @noindent
+ − 2350 This loop iterates over all Emacs buffers, using the list
+ − 2351 returned by @code{buffer-list}. For each buffer @code{buf},
+ − 2352 it calls @code{buffer-file-name} and collects the results into
+ − 2353 a list, which is then returned from the @code{loop} construct.
+ − 2354 The result is a list of the file names of all the buffers in
+ − 2355 Emacs' memory. The words @code{for}, @code{in}, and @code{collect}
+ − 2356 are reserved words in the @code{loop} language.
+ − 2357
+ − 2358 @example
+ − 2359 (loop repeat 20 do (insert "Yowsa\n"))
+ − 2360 @end example
+ − 2361
+ − 2362 @noindent
+ − 2363 This loop inserts the phrase ``Yowsa'' twenty times in the
+ − 2364 current buffer.
+ − 2365
+ − 2366 @example
+ − 2367 (loop until (eobp) do (munch-line) (forward-line 1))
+ − 2368 @end example
+ − 2369
+ − 2370 @noindent
+ − 2371 This loop calls @code{munch-line} on every line until the end
+ − 2372 of the buffer. If point is already at the end of the buffer,
+ − 2373 the loop exits immediately.
+ − 2374
+ − 2375 @example
+ − 2376 (loop do (munch-line) until (eobp) do (forward-line 1))
+ − 2377 @end example
+ − 2378
+ − 2379 @noindent
+ − 2380 This loop is similar to the above one, except that @code{munch-line}
+ − 2381 is always called at least once.
+ − 2382
+ − 2383 @example
+ − 2384 (loop for x from 1 to 100
+ − 2385 for y = (* x x)
+ − 2386 until (>= y 729)
+ − 2387 finally return (list x (= y 729)))
+ − 2388 @end example
+ − 2389
+ − 2390 @noindent
+ − 2391 This more complicated loop searches for a number @code{x} whose
+ − 2392 square is 729. For safety's sake it only examines @code{x}
+ − 2393 values up to 100; dropping the phrase @samp{to 100} would
+ − 2394 cause the loop to count upwards with no limit. The second
+ − 2395 @code{for} clause defines @code{y} to be the square of @code{x}
+ − 2396 within the loop; the expression after the @code{=} sign is
+ − 2397 reevaluated each time through the loop. The @code{until}
+ − 2398 clause gives a condition for terminating the loop, and the
+ − 2399 @code{finally} clause says what to do when the loop finishes.
+ − 2400 (This particular example was written less concisely than it
+ − 2401 could have been, just for the sake of illustration.)
+ − 2402
+ − 2403 Note that even though this loop contains three clauses (two
+ − 2404 @code{for}s and an @code{until}) that would have been enough to
+ − 2405 define loops all by themselves, it still creates a single loop
+ − 2406 rather than some sort of triple-nested loop. You must explicitly
+ − 2407 nest your @code{loop} constructs if you want nested loops.
+ − 2408
+ − 2409 @node For Clauses, Iteration Clauses, Loop Examples, Loop Facility
+ − 2410 @subsection For Clauses
+ − 2411
+ − 2412 @noindent
+ − 2413 Most loops are governed by one or more @code{for} clauses.
+ − 2414 A @code{for} clause simultaneously describes variables to be
+ − 2415 bound, how those variables are to be stepped during the loop,
+ − 2416 and usually an end condition based on those variables.
+ − 2417
+ − 2418 The word @code{as} is a synonym for the word @code{for}. This
+ − 2419 word is followed by a variable name, then a word like @code{from}
+ − 2420 or @code{across} that describes the kind of iteration desired.
+ − 2421 In Common Lisp, the phrase @code{being the} sometimes precedes
+ − 2422 the type of iteration; in this package both @code{being} and
+ − 2423 @code{the} are optional. The word @code{each} is a synonym
+ − 2424 for @code{the}, and the word that follows it may be singular
+ − 2425 or plural: @samp{for x being the elements of y} or
+ − 2426 @samp{for x being each element of y}. Which form you use
+ − 2427 is purely a matter of style.
+ − 2428
+ − 2429 The variable is bound around the loop as if by @code{let}:
+ − 2430
+ − 2431 @example
+ − 2432 (setq i 'happy)
+ − 2433 (loop for i from 1 to 10 do (do-something-with i))
+ − 2434 i
+ − 2435 @result{} happy
+ − 2436 @end example
+ − 2437
+ − 2438 @table @code
+ − 2439 @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3}
+ − 2440 This type of @code{for} clause creates a counting loop. Each of
+ − 2441 the three sub-terms is optional, though there must be at least one
+ − 2442 term so that the clause is marked as a counting clause.
+ − 2443
+ − 2444 The three expressions are the starting value, the ending value, and
+ − 2445 the step value, respectively, of the variable. The loop counts
+ − 2446 upwards by default (@var{expr3} must be positive), from @var{expr1}
+ − 2447 to @var{expr2} inclusively. If you omit the @code{from} term, the
+ − 2448 loop counts from zero; if you omit the @code{to} term, the loop
+ − 2449 counts forever without stopping (unless stopped by some other
+ − 2450 loop clause, of course); if you omit the @code{by} term, the loop
+ − 2451 counts in steps of one.
+ − 2452
+ − 2453 You can replace the word @code{from} with @code{upfrom} or
+ − 2454 @code{downfrom} to indicate the direction of the loop. Likewise,
+ − 2455 you can replace @code{to} with @code{upto} or @code{downto}.
+ − 2456 For example, @samp{for x from 5 downto 1} executes five times
+ − 2457 with @code{x} taking on the integers from 5 down to 1 in turn.
+ − 2458 Also, you can replace @code{to} with @code{below} or @code{above},
+ − 2459 which are like @code{upto} and @code{downto} respectively except
+ − 2460 that they are exclusive rather than inclusive limits:
+ − 2461
+ − 2462 @example
+ − 2463 (loop for x to 10 collect x)
+ − 2464 @result{} (0 1 2 3 4 5 6 7 8 9 10)
+ − 2465 (loop for x below 10 collect x)
+ − 2466 @result{} (0 1 2 3 4 5 6 7 8 9)
+ − 2467 @end example
+ − 2468
+ − 2469 The @code{by} value is always positive, even for downward-counting
+ − 2470 loops. Some sort of @code{from} value is required for downward
+ − 2471 loops; @samp{for x downto 5} is not a legal loop clause all by
+ − 2472 itself.
+ − 2473
+ − 2474 @item for @var{var} in @var{list} by @var{function}
+ − 2475 This clause iterates @var{var} over all the elements of @var{list},
+ − 2476 in turn. If you specify the @code{by} term, then @var{function}
+ − 2477 is used to traverse the list instead of @code{cdr}; it must be a
+ − 2478 function taking one argument. For example:
+ − 2479
+ − 2480 @example
+ − 2481 (loop for x in '(1 2 3 4 5 6) collect (* x x))
+ − 2482 @result{} (1 4 9 16 25 36)
+ − 2483 (loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
+ − 2484 @result{} (1 9 25)
+ − 2485 @end example
+ − 2486
+ − 2487 @item for @var{var} on @var{list} by @var{function}
+ − 2488 This clause iterates @var{var} over all the cons cells of @var{list}.
+ − 2489
+ − 2490 @example
+ − 2491 (loop for x on '(1 2 3 4) collect x)
+ − 2492 @result{} ((1 2 3 4) (2 3 4) (3 4) (4))
+ − 2493 @end example
+ − 2494
+ − 2495 With @code{by}, there is no real reason that the @code{on} expression
+ − 2496 must be a list. For example:
+ − 2497
+ − 2498 @example
+ − 2499 (loop for x on first-animal by 'next-animal collect x)
+ − 2500 @end example
+ − 2501
+ − 2502 @noindent
+ − 2503 where @code{(next-animal x)} takes an ``animal'' @var{x} and returns
+ − 2504 the next in the (assumed) sequence of animals, or @code{nil} if
+ − 2505 @var{x} was the last animal in the sequence.
+ − 2506
+ − 2507 @item for @var{var} in-ref @var{list} by @var{function}
+ − 2508 This is like a regular @code{in} clause, but @var{var} becomes
+ − 2509 a @code{setf}-able ``reference'' onto the elements of the list
+ − 2510 rather than just a temporary variable. For example,
+ − 2511
+ − 2512 @example
+ − 2513 (loop for x in-ref my-list do (incf x))
+ − 2514 @end example
+ − 2515
+ − 2516 @noindent
+ − 2517 increments every element of @code{my-list} in place. This clause
+ − 2518 is an extension to standard Common Lisp.
+ − 2519
+ − 2520 @item for @var{var} across @var{array}
+ − 2521 This clause iterates @var{var} over all the elements of @var{array},
+ − 2522 which may be a vector or a string.
+ − 2523
+ − 2524 @example
+ − 2525 (loop for x across "aeiou"
+ − 2526 do (use-vowel (char-to-string x)))
+ − 2527 @end example
+ − 2528
+ − 2529 @item for @var{var} across-ref @var{array}
+ − 2530 This clause iterates over an array, with @var{var} a @code{setf}-able
+ − 2531 reference onto the elements; see @code{in-ref} above.
+ − 2532
+ − 2533 @item for @var{var} being the elements of @var{sequence}
+ − 2534 This clause iterates over the elements of @var{sequence}, which may
+ − 2535 be a list, vector, or string. Since the type must be determined
+ − 2536 at run-time, this is somewhat less efficient than @code{in} or
+ − 2537 @code{across}. The clause may be followed by the additional term
+ − 2538 @samp{using (index @var{var2})} to cause @var{var2} to be bound to
+ − 2539 the successive indices (starting at 0) of the elements.
+ − 2540
+ − 2541 This clause type is taken from older versions of the @code{loop} macro,
+ − 2542 and is not present in modern Common Lisp. The @samp{using (sequence ...)}
+ − 2543 term of the older macros is not supported.
+ − 2544
+ − 2545 @item for @var{var} being the elements of-ref @var{sequence}
+ − 2546 This clause iterates over a sequence, with @var{var} a @code{setf}-able
+ − 2547 reference onto the elements; see @code{in-ref} above.
+ − 2548
+ − 2549 @item for @var{var} being the symbols [of @var{obarray}]
+ − 2550 This clause iterates over symbols, either over all interned symbols
+ − 2551 or over all symbols in @var{obarray}. The loop is executed with
+ − 2552 @var{var} bound to each symbol in turn. The symbols are visited in
+ − 2553 an unspecified order.
+ − 2554
+ − 2555 As an example,
+ − 2556
+ − 2557 @example
+ − 2558 (loop for sym being the symbols
+ − 2559 when (fboundp sym)
+ − 2560 when (string-match "^map" (symbol-name sym))
+ − 2561 collect sym)
+ − 2562 @end example
+ − 2563
+ − 2564 @noindent
+ − 2565 returns a list of all the functions whose names begin with @samp{map}.
+ − 2566
+ − 2567 The Common Lisp words @code{external-symbols} and @code{present-symbols}
+ − 2568 are also recognized but are equivalent to @code{symbols} in Emacs Lisp.
+ − 2569
+ − 2570 Due to a minor implementation restriction, it will not work to have
+ − 2571 more than one @code{for} clause iterating over symbols, hash tables,
+ − 2572 keymaps, overlays, or intervals in a given @code{loop}. Fortunately,
+ − 2573 it would rarely if ever be useful to do so. It @emph{is} legal to mix
+ − 2574 one of these types of clauses with other clauses like @code{for ... to}
+ − 2575 or @code{while}.
+ − 2576
+ − 2577 @item for @var{var} being the hash-keys of @var{hash-table}
+ − 2578 This clause iterates over the entries in @var{hash-table}. For each
+ − 2579 hash table entry, @var{var} is bound to the entry's key. If you write
+ − 2580 @samp{the hash-values} instead, @var{var} is bound to the values
+ − 2581 of the entries. The clause may be followed by the additional
+ − 2582 term @samp{using (hash-values @var{var2})} (where @code{hash-values}
+ − 2583 is the opposite word of the word following @code{the}) to cause
+ − 2584 @var{var} and @var{var2} to be bound to the two parts of each
+ − 2585 hash table entry.
+ − 2586
+ − 2587 @item for @var{var} being the key-codes of @var{keymap}
+ − 2588 This clause iterates over the entries in @var{keymap}. In GNU Emacs 18
+ − 2589 and 19, keymaps are either alists or vectors, and key-codes are integers
+ − 2590 or symbols. In XEmacs, keymaps are a special new data type, and
+ − 2591 key-codes are symbols or lists of symbols. The iteration does not enter
+ − 2592 nested keymaps or inherited (parent) keymaps. You can use @samp{the
+ − 2593 key-bindings} to access the commands bound to the keys rather than the
+ − 2594 key codes, and you can add a @code{using} clause to access both the
+ − 2595 codes and the bindings together.
+ − 2596
+ − 2597 @item for @var{var} being the key-seqs of @var{keymap}
+ − 2598 This clause iterates over all key sequences defined by @var{keymap}
+ − 2599 and its nested keymaps, where @var{var} takes on values which are
+ − 2600 strings in Emacs 18 or vectors in Emacs 19. The strings or vectors
+ − 2601 are reused for each iteration, so you must copy them if you wish to keep
+ − 2602 them permanently. You can add a @samp{using (key-bindings ...)}
+ − 2603 clause to get the command bindings as well.
+ − 2604
+ − 2605 @item for @var{var} being the overlays [of @var{buffer}] @dots{}
+ − 2606 This clause iterates over the Emacs 19 ``overlays'' or XEmacs
+ − 2607 ``extents'' of a buffer (the clause @code{extents} is synonymous with
+ − 2608 @code{overlays}). Under Emacs 18, this clause iterates zero times. If
+ − 2609 the @code{of} term is omitted, the current buffer is used. This clause
+ − 2610 also accepts optional @samp{from @var{pos}} and @samp{to @var{pos}}
+ − 2611 terms, limiting the clause to overlays which overlap the specified
+ − 2612 region.
+ − 2613
+ − 2614 @item for @var{var} being the intervals [of @var{buffer}] @dots{}
+ − 2615 This clause iterates over all intervals of a buffer with constant
+ − 2616 text properties. The variable @var{var} will be bound to conses
+ − 2617 of start and end positions, where one start position is always equal
+ − 2618 to the previous end position. The clause allows @code{of},
+ − 2619 @code{from}, @code{to}, and @code{property} terms, where the latter
+ − 2620 term restricts the search to just the specified property. The
+ − 2621 @code{of} term may specify either a buffer or a string. This
+ − 2622 clause is useful only in GNU Emacs 19; in other versions, all
+ − 2623 buffers and strings consist of a single interval.
+ − 2624
+ − 2625 @item for @var{var} being the frames
+ − 2626 This clause iterates over all frames, i.e., X window system windows
+ − 2627 open on Emacs files. This clause works only under Emacs 19. The
+ − 2628 clause @code{screens} is a synonym for @code{frames}. The frames
+ − 2629 are visited in @code{next-frame} order starting from
+ − 2630 @code{selected-frame}.
+ − 2631
+ − 2632 @item for @var{var} being the windows [of @var{frame}]
+ − 2633 This clause iterates over the windows (in the Emacs sense) of
+ − 2634 the current frame, or of the specified @var{frame}. (In Emacs 18
+ − 2635 there is only ever one frame, and the @code{of} term is not
+ − 2636 allowed there.)
+ − 2637
+ − 2638 @item for @var{var} being the buffers
+ − 2639 This clause iterates over all buffers in Emacs. It is equivalent
+ − 2640 to @samp{for @var{var} in (buffer-list)}.
+ − 2641
+ − 2642 @item for @var{var} = @var{expr1} then @var{expr2}
+ − 2643 This clause does a general iteration. The first time through
+ − 2644 the loop, @var{var} will be bound to @var{expr1}. On the second
+ − 2645 and successive iterations it will be set by evaluating @var{expr2}
+ − 2646 (which may refer to the old value of @var{var}). For example,
+ − 2647 these two loops are effectively the same:
+ − 2648
+ − 2649 @example
+ − 2650 (loop for x on my-list by 'cddr do ...)
+ − 2651 (loop for x = my-list then (cddr x) while x do ...)
+ − 2652 @end example
+ − 2653
+ − 2654 Note that this type of @code{for} clause does not imply any sort
+ − 2655 of terminating condition; the above example combines it with a
+ − 2656 @code{while} clause to tell when to end the loop.
+ − 2657
+ − 2658 If you omit the @code{then} term, @var{expr1} is used both for
+ − 2659 the initial setting and for successive settings:
+ − 2660
+ − 2661 @example
+ − 2662 (loop for x = (random) when (> x 0) return x)
+ − 2663 @end example
+ − 2664
+ − 2665 @noindent
+ − 2666 This loop keeps taking random numbers from the @code{(random)}
+ − 2667 function until it gets a positive one, which it then returns.
+ − 2668 @end table
+ − 2669
+ − 2670 If you include several @code{for} clauses in a row, they are
+ − 2671 treated sequentially (as if by @code{let*} and @code{setq}).
+ − 2672 You can instead use the word @code{and} to link the clauses,
+ − 2673 in which case they are processed in parallel (as if by @code{let}
+ − 2674 and @code{psetq}).
+ − 2675
+ − 2676 @example
+ − 2677 (loop for x below 5 for y = nil then x collect (list x y))
+ − 2678 @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4))
+ − 2679 (loop for x below 5 and y = nil then x collect (list x y))
+ − 2680 @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3))
+ − 2681 @end example
+ − 2682
+ − 2683 @noindent
+ − 2684 In the first loop, @code{y} is set based on the value of @code{x}
+ − 2685 that was just set by the previous clause; in the second loop,
+ − 2686 @code{x} and @code{y} are set simultaneously so @code{y} is set
+ − 2687 based on the value of @code{x} left over from the previous time
+ − 2688 through the loop.
+ − 2689
+ − 2690 Another feature of the @code{loop} macro is @dfn{destructuring},
+ − 2691 similar in concept to the destructuring provided by @code{defmacro}.
+ − 2692 The @var{var} part of any @code{for} clause can be given as a list
+ − 2693 of variables instead of a single variable. The values produced
+ − 2694 during loop execution must be lists; the values in the lists are
+ − 2695 stored in the corresponding variables.
+ − 2696
+ − 2697 @example
+ − 2698 (loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y))
+ − 2699 @result{} (5 9 13)
+ − 2700 @end example
+ − 2701
+ − 2702 In loop destructuring, if there are more values than variables
+ − 2703 the trailing values are ignored, and if there are more variables
+ − 2704 than values the trailing variables get the value @code{nil}.
+ − 2705 If @code{nil} is used as a variable name, the corresponding
+ − 2706 values are ignored. Destructuring may be nested, and dotted
+ − 2707 lists of variables like @code{(x . y)} are allowed.
+ − 2708
+ − 2709 @node Iteration Clauses, Accumulation Clauses, For Clauses, Loop Facility
+ − 2710 @subsection Iteration Clauses
+ − 2711
+ − 2712 @noindent
+ − 2713 Aside from @code{for} clauses, there are several other loop clauses
+ − 2714 that control the way the loop operates. They might be used by
+ − 2715 themselves, or in conjunction with one or more @code{for} clauses.
+ − 2716
+ − 2717 @table @code
+ − 2718 @item repeat @var{integer}
+ − 2719 This clause simply counts up to the specified number using an
+ − 2720 internal temporary variable. The loops
+ − 2721
+ − 2722 @example
+ − 2723 (loop repeat n do ...)
+ − 2724 (loop for temp to n do ...)
+ − 2725 @end example
+ − 2726
+ − 2727 @noindent
+ − 2728 are identical except that the second one forces you to choose
+ − 2729 a name for a variable you aren't actually going to use.
+ − 2730
+ − 2731 @item while @var{condition}
+ − 2732 This clause stops the loop when the specified condition (any Lisp
+ − 2733 expression) becomes @code{nil}. For example, the following two
+ − 2734 loops are equivalent, except for the implicit @code{nil} block
+ − 2735 that surrounds the second one:
+ − 2736
+ − 2737 @example
+ − 2738 (while @var{cond} @var{forms}@dots{})
+ − 2739 (loop while @var{cond} do @var{forms}@dots{})
+ − 2740 @end example
+ − 2741
+ − 2742 @item until @var{condition}
+ − 2743 This clause stops the loop when the specified condition is true,
+ − 2744 i.e., non-@code{nil}.
+ − 2745
+ − 2746 @item always @var{condition}
+ − 2747 This clause stops the loop when the specified condition is @code{nil}.
+ − 2748 Unlike @code{while}, it stops the loop using @code{return nil} so that
+ − 2749 the @code{finally} clauses are not executed. If all the conditions
+ − 2750 were non-@code{nil}, the loop returns @code{t}:
+ − 2751
+ − 2752 @example
+ − 2753 (if (loop for size in size-list always (> size 10))
+ − 2754 (some-big-sizes)
+ − 2755 (no-big-sizes))
+ − 2756 @end example
+ − 2757
+ − 2758 @item never @var{condition}
+ − 2759 This clause is like @code{always}, except that the loop returns
+ − 2760 @code{t} if any conditions were false, or @code{nil} otherwise.
+ − 2761
+ − 2762 @item thereis @var{condition}
+ − 2763 This clause stops the loop when the specified form is non-@code{nil};
+ − 2764 in this case, it returns that non-@code{nil} value. If all the
+ − 2765 values were @code{nil}, the loop returns @code{nil}.
+ − 2766 @end table
+ − 2767
+ − 2768 @node Accumulation Clauses, Other Clauses, Iteration Clauses, Loop Facility
+ − 2769 @subsection Accumulation Clauses
+ − 2770
+ − 2771 @noindent
+ − 2772 These clauses cause the loop to accumulate information about the
+ − 2773 specified Lisp @var{form}. The accumulated result is returned
+ − 2774 from the loop unless overridden, say, by a @code{return} clause.
+ − 2775
+ − 2776 @table @code
+ − 2777 @item collect @var{form}
+ − 2778 This clause collects the values of @var{form} into a list. Several
+ − 2779 examples of @code{collect} appear elsewhere in this manual.
+ − 2780
+ − 2781 The word @code{collecting} is a synonym for @code{collect}, and
+ − 2782 likewise for the other accumulation clauses.
+ − 2783
+ − 2784 @item append @var{form}
+ − 2785 This clause collects lists of values into a result list using
+ − 2786 @code{append}.
+ − 2787
+ − 2788 @item nconc @var{form}
+ − 2789 This clause collects lists of values into a result list by
+ − 2790 destructively modifying the lists rather than copying them.
+ − 2791
+ − 2792 @item concat @var{form}
+ − 2793 This clause concatenates the values of the specified @var{form}
+ − 2794 into a string. (It and the following clause are extensions to
+ − 2795 standard Common Lisp.)
+ − 2796
+ − 2797 @item vconcat @var{form}
+ − 2798 This clause concatenates the values of the specified @var{form}
+ − 2799 into a vector.
+ − 2800
+ − 2801 @item count @var{form}
+ − 2802 This clause counts the number of times the specified @var{form}
+ − 2803 evaluates to a non-@code{nil} value.
+ − 2804
+ − 2805 @item sum @var{form}
+ − 2806 This clause accumulates the sum of the values of the specified
+ − 2807 @var{form}, which must evaluate to a number.
+ − 2808
+ − 2809 @item maximize @var{form}
+ − 2810 This clause accumulates the maximum value of the specified @var{form},
+ − 2811 which must evaluate to a number. The return value is undefined if
+ − 2812 @code{maximize} is executed zero times.
+ − 2813
+ − 2814 @item minimize @var{form}
+ − 2815 This clause accumulates the minimum value of the specified @var{form}.
+ − 2816 @end table
+ − 2817
+ − 2818 Accumulation clauses can be followed by @samp{into @var{var}} to
+ − 2819 cause the data to be collected into variable @var{var} (which is
+ − 2820 automatically @code{let}-bound during the loop) rather than an
+ − 2821 unnamed temporary variable. Also, @code{into} accumulations do
+ − 2822 not automatically imply a return value. The loop must use some
+ − 2823 explicit mechanism, such as @code{finally return}, to return
+ − 2824 the accumulated result.
+ − 2825
+ − 2826 It is legal for several accumulation clauses of the same type to
+ − 2827 accumulate into the same place. From Steele:
+ − 2828
+ − 2829 @example
+ − 2830 (loop for name in '(fred sue alice joe june)
+ − 2831 for kids in '((bob ken) () () (kris sunshine) ())
+ − 2832 collect name
+ − 2833 append kids)
+ − 2834 @result{} (fred bob ken sue alice joe kris sunshine june)
+ − 2835 @end example
+ − 2836
+ − 2837 @node Other Clauses, , Accumulation Clauses, Loop Facility
+ − 2838 @subsection Other Clauses
+ − 2839
+ − 2840 @noindent
+ − 2841 This section describes the remaining loop clauses.
+ − 2842
+ − 2843 @table @code
+ − 2844 @item with @var{var} = @var{value}
+ − 2845 This clause binds a variable to a value around the loop, but
+ − 2846 otherwise leaves the variable alone during the loop. The following
+ − 2847 loops are basically equivalent:
+ − 2848
+ − 2849 @example
+ − 2850 (loop with x = 17 do ...)
+ − 2851 (let ((x 17)) (loop do ...))
+ − 2852 (loop for x = 17 then x do ...)
+ − 2853 @end example
+ − 2854
+ − 2855 Naturally, the variable @var{var} might be used for some purpose
+ − 2856 in the rest of the loop. For example:
+ − 2857
+ − 2858 @example
+ − 2859 (loop for x in my-list with res = nil do (push x res)
+ − 2860 finally return res)
+ − 2861 @end example
+ − 2862
+ − 2863 This loop inserts the elements of @code{my-list} at the front of
+ − 2864 a new list being accumulated in @code{res}, then returns the
+ − 2865 list @code{res} at the end of the loop. The effect is similar
+ − 2866 to that of a @code{collect} clause, but the list gets reversed
+ − 2867 by virtue of the fact that elements are being pushed onto the
+ − 2868 front of @code{res} rather than the end.
+ − 2869
+ − 2870 If you omit the @code{=} term, the variable is initialized to
+ − 2871 @code{nil}. (Thus the @samp{= nil} in the above example is
+ − 2872 unnecessary.)
+ − 2873
+ − 2874 Bindings made by @code{with} are sequential by default, as if
+ − 2875 by @code{let*}. Just like @code{for} clauses, @code{with} clauses
+ − 2876 can be linked with @code{and} to cause the bindings to be made by
+ − 2877 @code{let} instead.
+ − 2878
+ − 2879 @item if @var{condition} @var{clause}
+ − 2880 This clause executes the following loop clause only if the specified
+ − 2881 condition is true. The following @var{clause} should be an accumulation,
+ − 2882 @code{do}, @code{return}, @code{if}, or @code{unless} clause.
+ − 2883 Several clauses may be linked by separating them with @code{and}.
+ − 2884 These clauses may be followed by @code{else} and a clause or clauses
+ − 2885 to execute if the condition was false. The whole construct may
+ − 2886 optionally be followed by the word @code{end} (which may be used to
+ − 2887 disambiguate an @code{else} or @code{and} in a nested @code{if}).
+ − 2888
+ − 2889 The actual non-@code{nil} value of the condition form is available
+ − 2890 by the name @code{it} in the ``then'' part. For example:
+ − 2891
+ − 2892 @example
+ − 2893 (setq funny-numbers '(6 13 -1))
+ − 2894 @result{} (6 13 -1)
+ − 2895 (loop for x below 10
+ − 2896 if (oddp x)
+ − 2897 collect x into odds
+ − 2898 and if (memq x funny-numbers) return (cdr it) end
+ − 2899 else
+ − 2900 collect x into evens
+ − 2901 finally return (vector odds evens))
+ − 2902 @result{} [(1 3 5 7 9) (0 2 4 6 8)]
+ − 2903 (setq funny-numbers '(6 7 13 -1))
+ − 2904 @result{} (6 7 13 -1)
+ − 2905 (loop <@r{same thing again}>)
+ − 2906 @result{} (13 -1)
+ − 2907 @end example
+ − 2908
+ − 2909 Note the use of @code{and} to put two clauses into the ``then''
+ − 2910 part, one of which is itself an @code{if} clause. Note also that
+ − 2911 @code{end}, while normally optional, was necessary here to make
+ − 2912 it clear that the @code{else} refers to the outermost @code{if}
+ − 2913 clause. In the first case, the loop returns a vector of lists
+ − 2914 of the odd and even values of @var{x}. In the second case, the
+ − 2915 odd number 7 is one of the @code{funny-numbers} so the loop
+ − 2916 returns early; the actual returned value is based on the result
+ − 2917 of the @code{memq} call.
+ − 2918
+ − 2919 @item when @var{condition} @var{clause}
+ − 2920 This clause is just a synonym for @code{if}.
+ − 2921
+ − 2922 @item unless @var{condition} @var{clause}
+ − 2923 The @code{unless} clause is just like @code{if} except that the
+ − 2924 sense of the condition is reversed.
+ − 2925
+ − 2926 @item named @var{name}
+ − 2927 This clause gives a name other than @code{nil} to the implicit
+ − 2928 block surrounding the loop. The @var{name} is the symbol to be
+ − 2929 used as the block name.
+ − 2930
+ − 2931 @item initially [do] @var{forms}...
+ − 2932 This keyword introduces one or more Lisp forms which will be
+ − 2933 executed before the loop itself begins (but after any variables
+ − 2934 requested by @code{for} or @code{with} have been bound to their
+ − 2935 initial values). @code{initially} clauses can appear anywhere;
+ − 2936 if there are several, they are executed in the order they appear
+ − 2937 in the loop. The keyword @code{do} is optional.
+ − 2938
+ − 2939 @item finally [do] @var{forms}...
+ − 2940 This introduces Lisp forms which will be executed after the loop
+ − 2941 finishes (say, on request of a @code{for} or @code{while}).
+ − 2942 @code{initially} and @code{finally} clauses may appear anywhere
+ − 2943 in the loop construct, but they are executed (in the specified
+ − 2944 order) at the beginning or end, respectively, of the loop.
+ − 2945
+ − 2946 @item finally return @var{form}
+ − 2947 This says that @var{form} should be executed after the loop
+ − 2948 is done to obtain a return value. (Without this, or some other
+ − 2949 clause like @code{collect} or @code{return}, the loop will simply
+ − 2950 return @code{nil}.) Variables bound by @code{for}, @code{with},
+ − 2951 or @code{into} will still contain their final values when @var{form}
+ − 2952 is executed.
+ − 2953
+ − 2954 @item do @var{forms}...
+ − 2955 The word @code{do} may be followed by any number of Lisp expressions
+ − 2956 which are executed as an implicit @code{progn} in the body of the
+ − 2957 loop. Many of the examples in this section illustrate the use of
+ − 2958 @code{do}.
+ − 2959
+ − 2960 @item return @var{form}
+ − 2961 This clause causes the loop to return immediately. The following
+ − 2962 Lisp form is evaluated to give the return value of the @code{loop}
+ − 2963 form. The @code{finally} clauses, if any, are not executed.
+ − 2964 Of course, @code{return} is generally used inside an @code{if} or
+ − 2965 @code{unless}, as its use in a top-level loop clause would mean
+ − 2966 the loop would never get to ``loop'' more than once.
+ − 2967
+ − 2968 The clause @samp{return @var{form}} is equivalent to
+ − 2969 @samp{do (return @var{form})} (or @code{return-from} if the loop
+ − 2970 was named). The @code{return} clause is implemented a bit more
+ − 2971 efficiently, though.
+ − 2972 @end table
+ − 2973
+ − 2974 While there is no high-level way to add user extensions to @code{loop}
+ − 2975 (comparable to @code{defsetf} for @code{setf}, say), this package
+ − 2976 does offer two properties called @code{cl-loop-handler} and
+ − 2977 @code{cl-loop-for-handler} which are functions to be called when
+ − 2978 a given symbol is encountered as a top-level loop clause or
+ − 2979 @code{for} clause, respectively. Consult the source code in
+ − 2980 file @file{cl-macs.el} for details.
+ − 2981
+ − 2982 This package's @code{loop} macro is compatible with that of Common
+ − 2983 Lisp, except that a few features are not implemented: @code{loop-finish}
+ − 2984 and data-type specifiers. Naturally, the @code{for} clauses which
+ − 2985 iterate over keymaps, overlays, intervals, frames, windows, and
+ − 2986 buffers are Emacs-specific extensions.
+ − 2987
+ − 2988 @node Multiple Values, , Loop Facility, Control Structure
+ − 2989 @section Multiple Values
+ − 2990
+ − 2991 @noindent
+ − 2992 Common Lisp functions can return zero or more results. Emacs Lisp
+ − 2993 functions, by contrast, always return exactly one result. This
+ − 2994 package makes no attempt to emulate Common Lisp multiple return
+ − 2995 values; Emacs versions of Common Lisp functions that return more
+ − 2996 than one value either return just the first value (as in
+ − 2997 @code{compiler-macroexpand}) or return a list of values (as in
+ − 2998 @code{get-setf-method}). This package @emph{does} define placeholders
+ − 2999 for the Common Lisp functions that work with multiple values, but
+ − 3000 in Emacs Lisp these functions simply operate on lists instead.
+ − 3001 The @code{values} form, for example, is a synonym for @code{list}
+ − 3002 in Emacs.
+ − 3003
+ − 3004 @defspec multiple-value-bind (var@dots{}) values-form forms@dots{}
+ − 3005 This form evaluates @var{values-form}, which must return a list of
+ − 3006 values. It then binds the @var{var}s to these respective values,
+ − 3007 as if by @code{let}, and then executes the body @var{forms}.
+ − 3008 If there are more @var{var}s than values, the extra @var{var}s
+ − 3009 are bound to @code{nil}. If there are fewer @var{var}s than
+ − 3010 values, the excess values are ignored.
+ − 3011 @end defspec
+ − 3012
+ − 3013 @defspec multiple-value-setq (var@dots{}) form
+ − 3014 This form evaluates @var{form}, which must return a list of values.
+ − 3015 It then sets the @var{var}s to these respective values, as if by
+ − 3016 @code{setq}. Extra @var{var}s or values are treated the same as
+ − 3017 in @code{multiple-value-bind}.
+ − 3018 @end defspec
+ − 3019
+ − 3020 The older Quiroz package attempted a more faithful (but still
+ − 3021 imperfect) emulation of Common Lisp multiple values. The old
+ − 3022 method ``usually'' simulated true multiple values quite well,
+ − 3023 but under certain circumstances would leave spurious return
+ − 3024 values in memory where a later, unrelated @code{multiple-value-bind}
+ − 3025 form would see them.
+ − 3026
+ − 3027 Since a perfect emulation is not feasible in Emacs Lisp, this
+ − 3028 package opts to keep it as simple and predictable as possible.
+ − 3029
+ − 3030 @node Macros, Declarations, Control Structure, Top
+ − 3031 @chapter Macros
+ − 3032
+ − 3033 @noindent
+ − 3034 This package implements the various Common Lisp features of
+ − 3035 @code{defmacro}, such as destructuring, @code{&environment},
+ − 3036 and @code{&body}. Top-level @code{&whole} is not implemented
+ − 3037 for @code{defmacro} due to technical difficulties.
+ − 3038 @xref{Argument Lists}.
+ − 3039
+ − 3040 Destructuring is made available to the user by way of the
+ − 3041 following macro:
+ − 3042
+ − 3043 @defspec destructuring-bind arglist expr forms@dots{}
+ − 3044 This macro expands to code which executes @var{forms}, with
+ − 3045 the variables in @var{arglist} bound to the list of values
+ − 3046 returned by @var{expr}. The @var{arglist} can include all
+ − 3047 the features allowed for @code{defmacro} argument lists,
+ − 3048 including destructuring. (The @code{&environment} keyword
+ − 3049 is not allowed.) The macro expansion will signal an error
+ − 3050 if @var{expr} returns a list of the wrong number of arguments
+ − 3051 or with incorrect keyword arguments.
+ − 3052 @end defspec
+ − 3053
+ − 3054 This package also includes the Common Lisp @code{define-compiler-macro}
+ − 3055 facility, which allows you to define compile-time expansions and
+ − 3056 optimizations for your functions.
+ − 3057
+ − 3058 @defspec define-compiler-macro name arglist forms@dots{}
+ − 3059 This form is similar to @code{defmacro}, except that it only expands
+ − 3060 calls to @var{name} at compile-time; calls processed by the Lisp
+ − 3061 interpreter are not expanded, nor are they expanded by the
+ − 3062 @code{macroexpand} function.
+ − 3063
+ − 3064 The argument list may begin with a @code{&whole} keyword and a
+ − 3065 variable. This variable is bound to the macro-call form itself,
+ − 3066 i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}.
+ − 3067 If the macro expander returns this form unchanged, then the
+ − 3068 compiler treats it as a normal function call. This allows
+ − 3069 compiler macros to work as optimizers for special cases of a
+ − 3070 function, leaving complicated cases alone.
+ − 3071
+ − 3072 For example, here is a simplified version of a definition that
+ − 3073 appears as a standard part of this package:
+ − 3074
+ − 3075 @example
+ − 3076 (define-compiler-macro member* (&whole form a list &rest keys)
+ − 3077 (if (and (null keys)
+ − 3078 (eq (car-safe a) 'quote)
+ − 3079 (not (floatp-safe (cadr a))))
+ − 3080 (list 'memq a list)
+ − 3081 form))
+ − 3082 @end example
+ − 3083
+ − 3084 @noindent
+ − 3085 This definition causes @code{(member* @var{a} @var{list})} to change
+ − 3086 to a call to the faster @code{memq} in the common case where @var{a}
+ − 3087 is a non-floating-point constant; if @var{a} is anything else, or
+ − 3088 if there are any keyword arguments in the call, then the original
+ − 3089 @code{member*} call is left intact. (The actual compiler macro
+ − 3090 for @code{member*} optimizes a number of other cases, including
+ − 3091 common @code{:test} predicates.)
+ − 3092 @end defspec
+ − 3093
+ − 3094 @defun compiler-macroexpand form
+ − 3095 This function is analogous to @code{macroexpand}, except that it
+ − 3096 expands compiler macros rather than regular macros. It returns
+ − 3097 @var{form} unchanged if it is not a call to a function for which
+ − 3098 a compiler macro has been defined, or if that compiler macro
+ − 3099 decided to punt by returning its @code{&whole} argument. Like
+ − 3100 @code{macroexpand}, it expands repeatedly until it reaches a form
+ − 3101 for which no further expansion is possible.
+ − 3102 @end defun
+ − 3103
+ − 3104 @xref{Macro Bindings}, for descriptions of the @code{macrolet}
+ − 3105 and @code{symbol-macrolet} forms for making ``local'' macro
+ − 3106 definitions.
+ − 3107
+ − 3108 @node Declarations, Symbols, Macros, Top
+ − 3109 @chapter Declarations
+ − 3110
+ − 3111 @noindent
+ − 3112 Common Lisp includes a complex and powerful ``declaration''
+ − 3113 mechanism that allows you to give the compiler special hints
+ − 3114 about the types of data that will be stored in particular variables,
+ − 3115 and about the ways those variables and functions will be used. This
+ − 3116 package defines versions of all the Common Lisp declaration forms:
+ − 3117 @code{declare}, @code{locally}, @code{proclaim}, @code{declaim},
+ − 3118 and @code{the}.
+ − 3119
+ − 3120 Most of the Common Lisp declarations are not currently useful in
+ − 3121 Emacs Lisp, as the byte-code system provides little opportunity
+ − 3122 to benefit from type information, and @code{special} declarations
+ − 3123 are redundant in a fully dynamically-scoped Lisp. A few
+ − 3124 declarations are meaningful when the optimizing Emacs 19 byte
+ − 3125 compiler is being used, however. Under the earlier non-optimizing
+ − 3126 compiler, these declarations will effectively be ignored.
+ − 3127
+ − 3128 @defun proclaim decl-spec
+ − 3129 This function records a ``global'' declaration specified by
+ − 3130 @var{decl-spec}. Since @code{proclaim} is a function, @var{decl-spec}
+ − 3131 is evaluated and thus should normally be quoted.
+ − 3132 @end defun
+ − 3133
+ − 3134 @defspec declaim decl-specs@dots{}
+ − 3135 This macro is like @code{proclaim}, except that it takes any number
+ − 3136 of @var{decl-spec} arguments, and the arguments are unevaluated and
+ − 3137 unquoted. The @code{declaim} macro also puts an @code{(eval-when
+ − 3138 (compile load eval) ...)} around the declarations so that they will
+ − 3139 be registered at compile-time as well as at run-time. (This is vital,
+ − 3140 since normally the declarations are meant to influence the way the
+ − 3141 compiler treats the rest of the file that contains the @code{declaim}
+ − 3142 form.)
+ − 3143 @end defspec
+ − 3144
+ − 3145 @defspec declare decl-specs@dots{}
+ − 3146 This macro is used to make declarations within functions and other
+ − 3147 code. Common Lisp allows declarations in various locations, generally
+ − 3148 at the beginning of any of the many ``implicit @code{progn}s''
+ − 3149 throughout Lisp syntax, such as function bodies, @code{let} bodies,
+ − 3150 etc. Currently the only declaration understood by @code{declare}
+ − 3151 is @code{special}.
+ − 3152 @end defspec
+ − 3153
+ − 3154 @defspec locally declarations@dots{} forms@dots{}
+ − 3155 In this package, @code{locally} is no different from @code{progn}.
+ − 3156 @end defspec
+ − 3157
+ − 3158 @defspec the type form
+ − 3159 Type information provided by @code{the} is ignored in this package;
+ − 3160 in other words, @code{(the @var{type} @var{form})} is equivalent
+ − 3161 to @var{form}. Future versions of the optimizing byte-compiler may
+ − 3162 make use of this information.
+ − 3163
+ − 3164 For example, @code{mapcar} can map over both lists and arrays. It is
+ − 3165 hard for the compiler to expand @code{mapcar} into an in-line loop
+ − 3166 unless it knows whether the sequence will be a list or an array ahead
+ − 3167 of time. With @code{(mapcar 'car (the vector foo))}, a future
+ − 3168 compiler would have enough information to expand the loop in-line.
+ − 3169 For now, Emacs Lisp will treat the above code as exactly equivalent
+ − 3170 to @code{(mapcar 'car foo)}.
+ − 3171 @end defspec
+ − 3172
+ − 3173 Each @var{decl-spec} in a @code{proclaim}, @code{declaim}, or
+ − 3174 @code{declare} should be a list beginning with a symbol that says
+ − 3175 what kind of declaration it is. This package currently understands
+ − 3176 @code{special}, @code{inline}, @code{notinline}, @code{optimize},
+ − 3177 and @code{warn} declarations. (The @code{warn} declaration is an
+ − 3178 extension of standard Common Lisp.) Other Common Lisp declarations,
+ − 3179 such as @code{type} and @code{ftype}, are silently ignored.
+ − 3180
+ − 3181 @table @code
+ − 3182 @item special
+ − 3183 Since all variables in Emacs Lisp are ``special'' (in the Common
+ − 3184 Lisp sense), @code{special} declarations are only advisory. They
+ − 3185 simply tell the optimizing byte compiler that the specified
+ − 3186 variables are intentionally being referred to without being
+ − 3187 bound in the body of the function. The compiler normally emits
+ − 3188 warnings for such references, since they could be typographical
+ − 3189 errors for references to local variables.
+ − 3190
+ − 3191 The declaration @code{(declare (special @var{var1} @var{var2}))} is
+ − 3192 equivalent to @code{(defvar @var{var1}) (defvar @var{var2})} in the
+ − 3193 optimizing compiler, or to nothing at all in older compilers (which
+ − 3194 do not warn for non-local references).
+ − 3195
+ − 3196 In top-level contexts, it is generally better to write
+ − 3197 @code{(defvar @var{var})} than @code{(declaim (special @var{var}))},
+ − 3198 since @code{defvar} makes your intentions clearer. But the older
+ − 3199 byte compilers can not handle @code{defvar}s appearing inside of
+ − 3200 functions, while @code{(declare (special @var{var}))} takes care
+ − 3201 to work correctly with all compilers.
+ − 3202
+ − 3203 @item inline
+ − 3204 The @code{inline} @var{decl-spec} lists one or more functions
+ − 3205 whose bodies should be expanded ``in-line'' into calling functions
+ − 3206 whenever the compiler is able to arrange for it. For example,
+ − 3207 the Common Lisp function @code{cadr} is declared @code{inline}
+ − 3208 by this package so that the form @code{(cadr @var{x})} will
+ − 3209 expand directly into @code{(car (cdr @var{x}))} when it is called
+ − 3210 in user functions, for a savings of one (relatively expensive)
+ − 3211 function call.
+ − 3212
+ − 3213 The following declarations are all equivalent. Note that the
+ − 3214 @code{defsubst} form is a convenient way to define a function
+ − 3215 and declare it inline all at once, but it is available only in
+ − 3216 Emacs 19.
+ − 3217
+ − 3218 @example
+ − 3219 (declaim (inline foo bar))
+ − 3220 (eval-when (compile load eval) (proclaim '(inline foo bar)))
442
+ − 3221 (proclaim-inline foo bar) ; XEmacs only
+ − 3222 (defsubst foo (...) ...) ; instead of defun; Emacs 19 only
428
+ − 3223 @end example
+ − 3224
+ − 3225 @strong{Please note:} This declaration remains in effect after the
+ − 3226 containing source file is done. It is correct to use it to
+ − 3227 request that a function you have defined should be inlined,
+ − 3228 but it is impolite to use it to request inlining of an external
+ − 3229 function.
+ − 3230
+ − 3231 In Common Lisp, it is possible to use @code{(declare (inline @dots{}))}
+ − 3232 before a particular call to a function to cause just that call to
+ − 3233 be inlined; the current byte compilers provide no way to implement
+ − 3234 this, so @code{(declare (inline @dots{}))} is currently ignored by
+ − 3235 this package.
+ − 3236
+ − 3237 @item notinline
+ − 3238 The @code{notinline} declaration lists functions which should
+ − 3239 not be inlined after all; it cancels a previous @code{inline}
+ − 3240 declaration.
+ − 3241
+ − 3242 @item optimize
+ − 3243 This declaration controls how much optimization is performed by
+ − 3244 the compiler. Naturally, it is ignored by the earlier non-optimizing
+ − 3245 compilers.
+ − 3246
+ − 3247 The word @code{optimize} is followed by any number of lists like
+ − 3248 @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several
+ − 3249 optimization ``qualities''; this package ignores all but @code{speed}
+ − 3250 and @code{safety}. The value of a quality should be an integer from
+ − 3251 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important.''
+ − 3252 The default level for both qualities is 1.
+ − 3253
+ − 3254 In this package, with the Emacs 19 optimizing compiler, the
+ − 3255 @code{speed} quality is tied to the @code{byte-compile-optimize}
+ − 3256 flag, which is set to @code{nil} for @code{(speed 0)} and to
+ − 3257 @code{t} for higher settings; and the @code{safety} quality is
+ − 3258 tied to the @code{byte-compile-delete-errors} flag, which is
+ − 3259 set to @code{t} for @code{(safety 3)} and to @code{nil} for all
+ − 3260 lower settings. (The latter flag controls whether the compiler
+ − 3261 is allowed to optimize out code whose only side-effect could
+ − 3262 be to signal an error, e.g., rewriting @code{(progn foo bar)} to
+ − 3263 @code{bar} when it is not known whether @code{foo} will be bound
+ − 3264 at run-time.)
+ − 3265
+ − 3266 Note that even compiling with @code{(safety 0)}, the Emacs
+ − 3267 byte-code system provides sufficient checking to prevent real
+ − 3268 harm from being done. For example, barring serious bugs in
+ − 3269 Emacs itself, Emacs will not crash with a segmentation fault
+ − 3270 just because of an error in a fully-optimized Lisp program.
+ − 3271
+ − 3272 The @code{optimize} declaration is normally used in a top-level
+ − 3273 @code{proclaim} or @code{declaim} in a file; Common Lisp allows
+ − 3274 it to be used with @code{declare} to set the level of optimization
+ − 3275 locally for a given form, but this will not work correctly with the
+ − 3276 current version of the optimizing compiler. (The @code{declare}
+ − 3277 will set the new optimization level, but that level will not
+ − 3278 automatically be unset after the enclosing form is done.)
+ − 3279
+ − 3280 @item warn
+ − 3281 This declaration controls what sorts of warnings are generated
+ − 3282 by the byte compiler. Again, only the optimizing compiler
+ − 3283 generates warnings. The word @code{warn} is followed by any
+ − 3284 number of ``warning qualities,'' similar in form to optimization
+ − 3285 qualities. The currently supported warning types are
+ − 3286 @code{redefine}, @code{callargs}, @code{unresolved}, and
+ − 3287 @code{free-vars}; in the current system, a value of 0 will
+ − 3288 disable these warnings and any higher value will enable them.
+ − 3289 See the documentation for the optimizing byte compiler for details.
+ − 3290 @end table
+ − 3291
+ − 3292 @node Symbols, Numbers, Declarations, Top
+ − 3293 @chapter Symbols
+ − 3294
+ − 3295 @noindent
+ − 3296 This package defines several symbol-related features that were
+ − 3297 missing from Emacs Lisp.
+ − 3298
+ − 3299 @menu
442
+ − 3300 * Property Lists:: `getf', `remf'
428
+ − 3301 * Creating Symbols:: `gensym', `gentemp'
+ − 3302 @end menu
+ − 3303
+ − 3304 @node Property Lists, Creating Symbols, Symbols, Symbols
+ − 3305 @section Property Lists
+ − 3306
+ − 3307 @noindent
+ − 3308 These functions augment the standard Emacs Lisp functions @code{get}
442
+ − 3309 and @code{put} for operating on properties attached to objects.
428
+ − 3310 There are also functions for working with property lists as
442
+ − 3311 first-class data structures not attached to particular objects.
428
+ − 3312
+ − 3313 @defun getf place property &optional default
+ − 3314 This function scans the list @var{place} as if it were a property
+ − 3315 list, i.e., a list of alternating property names and values. If
+ − 3316 an even-numbered element of @var{place} is found which is @code{eq}
+ − 3317 to @var{property}, the following odd-numbered element is returned.
+ − 3318 Otherwise, @var{default} is returned (or @code{nil} if no default
+ − 3319 is given).
+ − 3320
+ − 3321 In particular,
+ − 3322
+ − 3323 @example
+ − 3324 (get sym prop) @equiv{} (getf (symbol-plist sym) prop)
+ − 3325 @end example
+ − 3326
+ − 3327 It is legal to use @code{getf} as a @code{setf} place, in which case
+ − 3328 its @var{place} argument must itself be a legal @code{setf} place.
+ − 3329 The @var{default} argument, if any, is ignored in this context.
+ − 3330 The effect is to change (via @code{setcar}) the value cell in the
+ − 3331 list that corresponds to @var{property}, or to cons a new property-value
+ − 3332 pair onto the list if the property is not yet present.
+ − 3333
+ − 3334 @example
+ − 3335 (put sym prop val) @equiv{} (setf (getf (symbol-plist sym) prop) val)
+ − 3336 @end example
+ − 3337
440
+ − 3338 The @code{get} function is also @code{setf}-able. The fact that
+ − 3339 @code{default} is ignored can sometimes be useful:
428
+ − 3340
+ − 3341 @example
440
+ − 3342 (incf (get 'foo 'usage-count 0))
428
+ − 3343 @end example
+ − 3344
+ − 3345 Here, symbol @code{foo}'s @code{usage-count} property is incremented
+ − 3346 if it exists, or set to 1 (an incremented 0) otherwise.
+ − 3347
+ − 3348 When not used as a @code{setf} form, @code{getf} is just a regular
+ − 3349 function and its @var{place} argument can actually be any Lisp
+ − 3350 expression.
+ − 3351 @end defun
+ − 3352
+ − 3353 @defspec remf place property
+ − 3354 This macro removes the property-value pair for @var{property} from
+ − 3355 the property list stored at @var{place}, which is any @code{setf}-able
+ − 3356 place expression. It returns true if the property was found. Note
+ − 3357 that if @var{property} happens to be first on the list, this will
+ − 3358 effectively do a @code{(setf @var{place} (cddr @var{place}))},
+ − 3359 whereas if it occurs later, this simply uses @code{setcdr} to splice
+ − 3360 out the property and value cells.
+ − 3361 @end defspec
+ − 3362
+ − 3363 @iftex
+ − 3364 @secno=2
+ − 3365 @end iftex
+ − 3366
+ − 3367 @node Creating Symbols, , Property Lists, Symbols
+ − 3368 @section Creating Symbols
+ − 3369
+ − 3370 @noindent
+ − 3371 These functions create unique symbols, typically for use as
+ − 3372 temporary variables.
+ − 3373
+ − 3374 @defun gensym &optional x
+ − 3375 This function creates a new, uninterned symbol (using @code{make-symbol})
+ − 3376 with a unique name. (The name of an uninterned symbol is relevant
+ − 3377 only if the symbol is printed.) By default, the name is generated
+ − 3378 from an increasing sequence of numbers, @samp{G1000}, @samp{G1001},
+ − 3379 @samp{G1002}, etc. If the optional argument @var{x} is a string, that
+ − 3380 string is used as a prefix instead of @samp{G}. Uninterned symbols
+ − 3381 are used in macro expansions for temporary variables, to ensure that
+ − 3382 their names will not conflict with ``real'' variables in the user's
+ − 3383 code.
+ − 3384 @end defun
+ − 3385
+ − 3386 @defvar *gensym-counter*
+ − 3387 This variable holds the counter used to generate @code{gensym} names.
+ − 3388 It is incremented after each use by @code{gensym}. In Common Lisp
+ − 3389 this is initialized with 0, but this package initializes it with a
+ − 3390 random (time-dependent) value to avoid trouble when two files that
+ − 3391 each used @code{gensym} in their compilation are loaded together.
+ − 3392
+ − 3393 @strong{XEmacs note:} As of XEmacs 21.0, an uninterned symbol remains
+ − 3394 uninterned even after being dumped to bytecode. Older versions of Emacs
+ − 3395 didn't distinguish the printed representation of interned and uninterned
+ − 3396 symbols, so their names had to be treated more carefully.
+ − 3397 @end defvar
+ − 3398
+ − 3399 @defun gentemp &optional x
+ − 3400 This function is like @code{gensym}, except that it produces a new
+ − 3401 @emph{interned} symbol. If the symbol that is generated already
+ − 3402 exists, the function keeps incrementing the counter and trying
+ − 3403 again until a new symbol is generated.
+ − 3404 @end defun
+ − 3405
+ − 3406 The Quiroz @file{cl.el} package also defined a @code{defkeyword}
+ − 3407 form for creating self-quoting keyword symbols. This package
+ − 3408 automatically creates all keywords that are called for by
+ − 3409 @code{&key} argument specifiers, and discourages the use of
+ − 3410 keywords as data unrelated to keyword arguments, so the
+ − 3411 @code{defkeyword} form has been discontinued.
+ − 3412
+ − 3413 @iftex
+ − 3414 @chapno=11
+ − 3415 @end iftex
+ − 3416
+ − 3417 @node Numbers, Sequences, Symbols, Top
+ − 3418 @chapter Numbers
+ − 3419
+ − 3420 @noindent
+ − 3421 This section defines a few simple Common Lisp operations on numbers
+ − 3422 which were left out of Emacs Lisp.
+ − 3423
+ − 3424 @menu
+ − 3425 * Predicates on Numbers:: `plusp', `oddp', `floatp-safe', etc.
+ − 3426 * Numerical Functions:: `abs', `expt', `floor*', etc.
+ − 3427 * Random Numbers:: `random*', `make-random-state'
+ − 3428 * Implementation Parameters:: `most-positive-fixnum', `most-positive-float'
+ − 3429 @end menu
+ − 3430
+ − 3431 @iftex
+ − 3432 @secno=1
+ − 3433 @end iftex
+ − 3434
+ − 3435 @node Predicates on Numbers, Numerical Functions, Numbers, Numbers
+ − 3436 @section Predicates on Numbers
+ − 3437
+ − 3438 @noindent
+ − 3439 These functions return @code{t} if the specified condition is
+ − 3440 true of the numerical argument, or @code{nil} otherwise.
+ − 3441
+ − 3442 @defun plusp number
+ − 3443 This predicate tests whether @var{number} is positive. It is an
+ − 3444 error if the argument is not a number.
+ − 3445 @end defun
+ − 3446
+ − 3447 @defun minusp number
+ − 3448 This predicate tests whether @var{number} is negative. It is an
+ − 3449 error if the argument is not a number.
+ − 3450 @end defun
+ − 3451
+ − 3452 @defun oddp integer
+ − 3453 This predicate tests whether @var{integer} is odd. It is an
+ − 3454 error if the argument is not an integer.
+ − 3455 @end defun
+ − 3456
+ − 3457 @defun evenp integer
+ − 3458 This predicate tests whether @var{integer} is even. It is an
+ − 3459 error if the argument is not an integer.
+ − 3460 @end defun
+ − 3461
+ − 3462 @defun floatp-safe object
+ − 3463 This predicate tests whether @var{object} is a floating-point
+ − 3464 number. On systems that support floating-point, this is equivalent
+ − 3465 to @code{floatp}. On other systems, this always returns @code{nil}.
+ − 3466 @end defun
+ − 3467
+ − 3468 @iftex
+ − 3469 @secno=3
+ − 3470 @end iftex
+ − 3471
+ − 3472 @node Numerical Functions, Random Numbers, Predicates on Numbers, Numbers
+ − 3473 @section Numerical Functions
+ − 3474
+ − 3475 @noindent
+ − 3476 These functions perform various arithmetic operations on numbers.
+ − 3477
+ − 3478 @defun abs number
+ − 3479 This function returns the absolute value of @var{number}. (Newer
+ − 3480 versions of Emacs provide this as a built-in function; this package
+ − 3481 defines @code{abs} only for Emacs 18 versions which don't provide
+ − 3482 it as a primitive.)
+ − 3483 @end defun
+ − 3484
+ − 3485 @defun expt base power
+ − 3486 This function returns @var{base} raised to the power of @var{number}.
+ − 3487 (Newer versions of Emacs provide this as a built-in function; this
+ − 3488 package defines @code{expt} only for Emacs 18 versions which don't
+ − 3489 provide it as a primitive.)
+ − 3490 @end defun
+ − 3491
+ − 3492 @defun gcd &rest integers
+ − 3493 This function returns the Greatest Common Divisor of the arguments.
+ − 3494 For one argument, it returns the absolute value of that argument.
+ − 3495 For zero arguments, it returns zero.
+ − 3496 @end defun
+ − 3497
+ − 3498 @defun lcm &rest integers
+ − 3499 This function returns the Least Common Multiple of the arguments.
+ − 3500 For one argument, it returns the absolute value of that argument.
+ − 3501 For zero arguments, it returns one.
+ − 3502 @end defun
+ − 3503
+ − 3504 @defun isqrt integer
+ − 3505 This function computes the ``integer square root'' of its integer
+ − 3506 argument, i.e., the greatest integer less than or equal to the true
+ − 3507 square root of the argument.
+ − 3508 @end defun
+ − 3509
+ − 3510 @defun floor* number &optional divisor
+ − 3511 This function implements the Common Lisp @code{floor} function.
+ − 3512 It is called @code{floor*} to avoid name conflicts with the
+ − 3513 simpler @code{floor} function built-in to Emacs 19.
+ − 3514
+ − 3515 With one argument, @code{floor*} returns a list of two numbers:
+ − 3516 The argument rounded down (toward minus infinity) to an integer,
+ − 3517 and the ``remainder'' which would have to be added back to the
+ − 3518 first return value to yield the argument again. If the argument
+ − 3519 is an integer @var{x}, the result is always the list @code{(@var{x} 0)}.
+ − 3520 If the argument is an Emacs 19 floating-point number, the first
+ − 3521 result is a Lisp integer and the second is a Lisp float between
+ − 3522 0 (inclusive) and 1 (exclusive).
+ − 3523
+ − 3524 With two arguments, @code{floor*} divides @var{number} by
+ − 3525 @var{divisor}, and returns the floor of the quotient and the
+ − 3526 corresponding remainder as a list of two numbers. If
+ − 3527 @code{(floor* @var{x} @var{y})} returns @code{(@var{q} @var{r})},
+ − 3528 then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r}
+ − 3529 between 0 (inclusive) and @var{r} (exclusive). Also, note
+ − 3530 that @code{(floor* @var{x})} is exactly equivalent to
+ − 3531 @code{(floor* @var{x} 1)}.
+ − 3532
+ − 3533 This function is entirely compatible with Common Lisp's @code{floor}
+ − 3534 function, except that it returns the two results in a list since
+ − 3535 Emacs Lisp does not support multiple-valued functions.
+ − 3536 @end defun
+ − 3537
+ − 3538 @defun ceiling* number &optional divisor
+ − 3539 This function implements the Common Lisp @code{ceiling} function,
+ − 3540 which is analogous to @code{floor} except that it rounds the
+ − 3541 argument or quotient of the arguments up toward plus infinity.
+ − 3542 The remainder will be between 0 and minus @var{r}.
+ − 3543 @end defun
+ − 3544
+ − 3545 @defun truncate* number &optional divisor
+ − 3546 This function implements the Common Lisp @code{truncate} function,
+ − 3547 which is analogous to @code{floor} except that it rounds the
+ − 3548 argument or quotient of the arguments toward zero. Thus it is
+ − 3549 equivalent to @code{floor*} if the argument or quotient is
+ − 3550 positive, or to @code{ceiling*} otherwise. The remainder has
+ − 3551 the same sign as @var{number}.
+ − 3552 @end defun
+ − 3553
+ − 3554 @defun round* number &optional divisor
+ − 3555 This function implements the Common Lisp @code{round} function,
+ − 3556 which is analogous to @code{floor} except that it rounds the
+ − 3557 argument or quotient of the arguments to the nearest integer.
+ − 3558 In the case of a tie (the argument or quotient is exactly
+ − 3559 halfway between two integers), it rounds to the even integer.
+ − 3560 @end defun
+ − 3561
+ − 3562 @defun mod* number divisor
+ − 3563 This function returns the same value as the second return value
+ − 3564 of @code{floor}.
+ − 3565 @end defun
+ − 3566
+ − 3567 @defun rem* number divisor
+ − 3568 This function returns the same value as the second return value
+ − 3569 of @code{truncate}.
+ − 3570 @end defun
+ − 3571
+ − 3572 These definitions are compatible with those in the Quiroz
+ − 3573 @file{cl.el} package, except that this package appends @samp{*}
+ − 3574 to certain function names to avoid conflicts with existing
+ − 3575 Emacs 19 functions, and that the mechanism for returning
+ − 3576 multiple values is different.
+ − 3577
+ − 3578 @iftex
+ − 3579 @secno=8
+ − 3580 @end iftex
+ − 3581
+ − 3582 @node Random Numbers, Implementation Parameters, Numerical Functions, Numbers
+ − 3583 @section Random Numbers
+ − 3584
+ − 3585 @noindent
+ − 3586 This package also provides an implementation of the Common Lisp
+ − 3587 random number generator. It uses its own additive-congruential
+ − 3588 algorithm, which is much more likely to give statistically clean
+ − 3589 random numbers than the simple generators supplied by many
+ − 3590 operating systems.
+ − 3591
+ − 3592 @defun random* number &optional state
+ − 3593 This function returns a random nonnegative number less than
+ − 3594 @var{number}, and of the same type (either integer or floating-point).
+ − 3595 The @var{state} argument should be a @code{random-state} object
+ − 3596 which holds the state of the random number generator. The
+ − 3597 function modifies this state object as a side effect. If
+ − 3598 @var{state} is omitted, it defaults to the variable
+ − 3599 @code{*random-state*}, which contains a pre-initialized
+ − 3600 @code{random-state} object.
+ − 3601 @end defun
+ − 3602
+ − 3603 @defvar *random-state*
+ − 3604 This variable contains the system ``default'' @code{random-state}
+ − 3605 object, used for calls to @code{random*} that do not specify an
+ − 3606 alternative state object. Since any number of programs in the
+ − 3607 Emacs process may be accessing @code{*random-state*} in interleaved
+ − 3608 fashion, the sequence generated from this variable will be
+ − 3609 irreproducible for all intents and purposes.
+ − 3610 @end defvar
+ − 3611
+ − 3612 @defun make-random-state &optional state
+ − 3613 This function creates or copies a @code{random-state} object.
+ − 3614 If @var{state} is omitted or @code{nil}, it returns a new copy of
+ − 3615 @code{*random-state*}. This is a copy in the sense that future
+ − 3616 sequences of calls to @code{(random* @var{n})} and
+ − 3617 @code{(random* @var{n} @var{s})} (where @var{s} is the new
+ − 3618 random-state object) will return identical sequences of random
+ − 3619 numbers.
+ − 3620
+ − 3621 If @var{state} is a @code{random-state} object, this function
+ − 3622 returns a copy of that object. If @var{state} is @code{t}, this
+ − 3623 function returns a new @code{random-state} object seeded from the
+ − 3624 date and time. As an extension to Common Lisp, @var{state} may also
+ − 3625 be an integer in which case the new object is seeded from that
+ − 3626 integer; each different integer seed will result in a completely
+ − 3627 different sequence of random numbers.
+ − 3628
+ − 3629 It is legal to print a @code{random-state} object to a buffer or
+ − 3630 file and later read it back with @code{read}. If a program wishes
+ − 3631 to use a sequence of pseudo-random numbers which can be reproduced
+ − 3632 later for debugging, it can call @code{(make-random-state t)} to
+ − 3633 get a new sequence, then print this sequence to a file. When the
+ − 3634 program is later rerun, it can read the original run's random-state
+ − 3635 from the file.
+ − 3636 @end defun
+ − 3637
+ − 3638 @defun random-state-p object
+ − 3639 This predicate returns @code{t} if @var{object} is a
+ − 3640 @code{random-state} object, or @code{nil} otherwise.
+ − 3641 @end defun
+ − 3642
+ − 3643 @node Implementation Parameters, , Random Numbers, Numbers
+ − 3644 @section Implementation Parameters
+ − 3645
+ − 3646 @noindent
+ − 3647 This package defines several useful constants having to with numbers.
+ − 3648
+ − 3649 @defvar most-positive-fixnum
+ − 3650 This constant equals the largest value a Lisp integer can hold.
+ − 3651 It is typically @code{2^23-1} or @code{2^25-1}.
+ − 3652 @end defvar
+ − 3653
+ − 3654 @defvar most-negative-fixnum
+ − 3655 This constant equals the smallest (most negative) value a Lisp
+ − 3656 integer can hold.
+ − 3657 @end defvar
+ − 3658
+ − 3659 The following parameters have to do with floating-point numbers.
+ − 3660 This package determines their values by exercising the computer's
+ − 3661 floating-point arithmetic in various ways. Because this operation
+ − 3662 might be slow, the code for initializing them is kept in a separate
+ − 3663 function that must be called before the parameters can be used.
+ − 3664
+ − 3665 @defun cl-float-limits
+ − 3666 This function makes sure that the Common Lisp floating-point
+ − 3667 parameters like @code{most-positive-float} have been initialized.
+ − 3668 Until it is called, these parameters will be @code{nil}. If this
+ − 3669 version of Emacs does not support floats (e.g., most versions of
+ − 3670 Emacs 18), the parameters will remain @code{nil}. If the parameters
+ − 3671 have already been initialized, the function returns immediately.
+ − 3672
+ − 3673 The algorithm makes assumptions that will be valid for most modern
+ − 3674 machines, but will fail if the machine's arithmetic is extremely
+ − 3675 unusual, e.g., decimal.
+ − 3676 @end defun
+ − 3677
+ − 3678 Since true Common Lisp supports up to four different floating-point
+ − 3679 precisions, it has families of constants like
+ − 3680 @code{most-positive-single-float}, @code{most-positive-double-float},
+ − 3681 @code{most-positive-long-float}, and so on. Emacs has only one
+ − 3682 floating-point precision, so this package omits the precision word
+ − 3683 from the constants' names.
+ − 3684
+ − 3685 @defvar most-positive-float
+ − 3686 This constant equals the largest value a Lisp float can hold.
+ − 3687 For those systems whose arithmetic supports infinities, this is
+ − 3688 the largest @emph{finite} value. For IEEE machines, the value
+ − 3689 is approximately @code{1.79e+308}.
+ − 3690 @end defvar
+ − 3691
+ − 3692 @defvar most-negative-float
+ − 3693 This constant equals the most-negative value a Lisp float can hold.
+ − 3694 (It is assumed to be equal to @code{(- most-positive-float)}.)
+ − 3695 @end defvar
+ − 3696
+ − 3697 @defvar least-positive-float
+ − 3698 This constant equals the smallest Lisp float value greater than zero.
+ − 3699 For IEEE machines, it is about @code{4.94e-324} if denormals are
+ − 3700 supported or @code{2.22e-308} if not.
+ − 3701 @end defvar
+ − 3702
+ − 3703 @defvar least-positive-normalized-float
+ − 3704 This constant equals the smallest @emph{normalized} Lisp float greater
+ − 3705 than zero, i.e., the smallest value for which IEEE denormalization
+ − 3706 will not result in a loss of precision. For IEEE machines, this
+ − 3707 value is about @code{2.22e-308}. For machines that do not support
+ − 3708 the concept of denormalization and gradual underflow, this constant
+ − 3709 will always equal @code{least-positive-float}.
+ − 3710 @end defvar
+ − 3711
+ − 3712 @defvar least-negative-float
+ − 3713 This constant is the negative counterpart of @code{least-positive-float}.
+ − 3714 @end defvar
+ − 3715
+ − 3716 @defvar least-negative-normalized-float
+ − 3717 This constant is the negative counterpart of
+ − 3718 @code{least-positive-normalized-float}.
+ − 3719 @end defvar
+ − 3720
+ − 3721 @defvar float-epsilon
+ − 3722 This constant is the smallest positive Lisp float that can be added
+ − 3723 to 1.0 to produce a distinct value. Adding a smaller number to 1.0
+ − 3724 will yield 1.0 again due to roundoff. For IEEE machines, epsilon
+ − 3725 is about @code{2.22e-16}.
+ − 3726 @end defvar
+ − 3727
+ − 3728 @defvar float-negative-epsilon
+ − 3729 This is the smallest positive value that can be subtracted from
+ − 3730 1.0 to produce a distinct value. For IEEE machines, it is about
+ − 3731 @code{1.11e-16}.
+ − 3732 @end defvar
+ − 3733
+ − 3734 @iftex
+ − 3735 @chapno=13
+ − 3736 @end iftex
+ − 3737
+ − 3738 @node Sequences, Lists, Numbers, Top
+ − 3739 @chapter Sequences
+ − 3740
+ − 3741 @noindent
+ − 3742 Common Lisp defines a number of functions that operate on
+ − 3743 @dfn{sequences}, which are either lists, strings, or vectors.
+ − 3744 Emacs Lisp includes a few of these, notably @code{elt} and
+ − 3745 @code{length}; this package defines most of the rest.
+ − 3746
+ − 3747 @menu
+ − 3748 * Sequence Basics:: Arguments shared by all sequence functions
+ − 3749 * Mapping over Sequences:: `mapcar*', `mapcan', `map', `every', etc.
+ − 3750 * Sequence Functions:: `subseq', `remove*', `substitute', etc.
+ − 3751 * Searching Sequences:: `find', `position', `count', `search', etc.
+ − 3752 * Sorting Sequences:: `sort*', `stable-sort', `merge'
+ − 3753 @end menu
+ − 3754
+ − 3755 @node Sequence Basics, Mapping over Sequences, Sequences, Sequences
+ − 3756 @section Sequence Basics
+ − 3757
778
+ − 3758 @noindent Many of the sequence functions take keyword arguments;
+ − 3759 @pxref{Argument Lists}. All keyword arguments are optional and, if
+ − 3760 specified, may appear in any order.
428
+ − 3761
+ − 3762 The @code{:key} argument should be passed either @code{nil}, or a
+ − 3763 function of one argument. This key function is used as a filter
+ − 3764 through which the elements of the sequence are seen; for example,
+ − 3765 @code{(find x y :key 'car)} is similar to @code{(assoc* x y)}:
+ − 3766 It searches for an element of the list whose @code{car} equals
+ − 3767 @code{x}, rather than for an element which equals @code{x} itself.
+ − 3768 If @code{:key} is omitted or @code{nil}, the filter is effectively
+ − 3769 the identity function.
+ − 3770
+ − 3771 The @code{:test} and @code{:test-not} arguments should be either
+ − 3772 @code{nil}, or functions of two arguments. The test function is
+ − 3773 used to compare two sequence elements, or to compare a search value
+ − 3774 with sequence elements. (The two values are passed to the test
+ − 3775 function in the same order as the original sequence function
+ − 3776 arguments from which they are derived, or, if they both come from
+ − 3777 the same sequence, in the same order as they appear in that sequence.)
+ − 3778 The @code{:test} argument specifies a function which must return
+ − 3779 true (non-@code{nil}) to indicate a match; instead, you may use
+ − 3780 @code{:test-not} to give a function which returns @emph{false} to
+ − 3781 indicate a match. The default test function is @code{:test 'eql}.
+ − 3782
+ − 3783 Many functions which take @var{item} and @code{:test} or @code{:test-not}
+ − 3784 arguments also come in @code{-if} and @code{-if-not} varieties,
+ − 3785 where a @var{predicate} function is passed instead of @var{item},
+ − 3786 and sequence elements match if the predicate returns true on them
+ − 3787 (or false in the case of @code{-if-not}). For example:
+ − 3788
+ − 3789 @example
+ − 3790 (remove* 0 seq :test '=) @equiv{} (remove-if 'zerop seq)
+ − 3791 @end example
+ − 3792
+ − 3793 @noindent
+ − 3794 to remove all zeros from sequence @code{seq}.
+ − 3795
+ − 3796 Some operations can work on a subsequence of the argument sequence;
+ − 3797 these function take @code{:start} and @code{:end} arguments which
+ − 3798 default to zero and the length of the sequence, respectively.
+ − 3799 Only elements between @var{start} (inclusive) and @var{end}
+ − 3800 (exclusive) are affected by the operation. The @var{end} argument
+ − 3801 may be passed @code{nil} to signify the length of the sequence;
+ − 3802 otherwise, both @var{start} and @var{end} must be integers, with
+ − 3803 @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}.
+ − 3804 If the function takes two sequence arguments, the limits are
+ − 3805 defined by keywords @code{:start1} and @code{:end1} for the first,
+ − 3806 and @code{:start2} and @code{:end2} for the second.
+ − 3807
+ − 3808 A few functions accept a @code{:from-end} argument, which, if
+ − 3809 non-@code{nil}, causes the operation to go from right-to-left
+ − 3810 through the sequence instead of left-to-right, and a @code{:count}
+ − 3811 argument, which specifies an integer maximum number of elements
+ − 3812 to be removed or otherwise processed.
+ − 3813
+ − 3814 The sequence functions make no guarantees about the order in
+ − 3815 which the @code{:test}, @code{:test-not}, and @code{:key} functions
+ − 3816 are called on various elements. Therefore, it is a bad idea to depend
+ − 3817 on side effects of these functions. For example, @code{:from-end}
+ − 3818 may cause the sequence to be scanned actually in reverse, or it may
+ − 3819 be scanned forwards but computing a result ``as if'' it were scanned
+ − 3820 backwards. (Some functions, like @code{mapcar*} and @code{every},
+ − 3821 @emph{do} specify exactly the order in which the function is called
+ − 3822 so side effects are perfectly acceptable in those cases.)
+ − 3823
+ − 3824 Strings in GNU Emacs 19 may contain ``text properties'' as well
+ − 3825 as character data. Except as noted, it is undefined whether or
+ − 3826 not text properties are preserved by sequence functions. For
+ − 3827 example, @code{(remove* ?A @var{str})} may or may not preserve
+ − 3828 the properties of the characters copied from @var{str} into the
+ − 3829 result.
+ − 3830
+ − 3831 @node Mapping over Sequences, Sequence Functions, Sequence Basics, Sequences
+ − 3832 @section Mapping over Sequences
+ − 3833
+ − 3834 @noindent
+ − 3835 These functions ``map'' the function you specify over the elements
+ − 3836 of lists or arrays. They are all variations on the theme of the
+ − 3837 built-in function @code{mapcar}.
+ − 3838
+ − 3839 @defun mapcar* function seq &rest more-seqs
+ − 3840 This function calls @var{function} on successive parallel sets of
+ − 3841 elements from its argument sequences. Given a single @var{seq}
+ − 3842 argument it is equivalent to @code{mapcar}; given @var{n} sequences,
+ − 3843 it calls the function with the first elements of each of the sequences
+ − 3844 as the @var{n} arguments to yield the first element of the result
+ − 3845 list, then with the second elements, and so on. The mapping stops as
+ − 3846 soon as the shortest sequence runs out. The argument sequences may
+ − 3847 be any mixture of lists, strings, and vectors; the return sequence
+ − 3848 is always a list.
+ − 3849
+ − 3850 Common Lisp's @code{mapcar} accepts multiple arguments but works
+ − 3851 only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence
+ − 3852 argument. This package's @code{mapcar*} works as a compatible
+ − 3853 superset of both.
+ − 3854 @end defun
+ − 3855
+ − 3856 @defun map result-type function seq &rest more-seqs
+ − 3857 This function maps @var{function} over the argument sequences,
+ − 3858 just like @code{mapcar*}, but it returns a sequence of type
+ − 3859 @var{result-type} rather than a list. @var{result-type} must
+ − 3860 be one of the following symbols: @code{vector}, @code{string},
+ − 3861 @code{list} (in which case the effect is the same as for
+ − 3862 @code{mapcar*}), or @code{nil} (in which case the results are
+ − 3863 thrown away and @code{map} returns @code{nil}).
+ − 3864 @end defun
+ − 3865
+ − 3866 @defun maplist function list &rest more-lists
+ − 3867 This function calls @var{function} on each of its argument lists,
+ − 3868 then on the @code{cdr}s of those lists, and so on, until the
+ − 3869 shortest list runs out. The results are returned in the form
+ − 3870 of a list. Thus, @code{maplist} is like @code{mapcar*} except
+ − 3871 that it passes in the list pointers themselves rather than the
+ − 3872 @code{car}s of the advancing pointers.
+ − 3873 @end defun
+ − 3874
+ − 3875 @defun mapc function seq &rest more-seqs
+ − 3876 This function is like @code{mapcar*}, except that the values
+ − 3877 returned by @var{function} are ignored and thrown away rather
+ − 3878 than being collected into a list. The return value of @code{mapc}
+ − 3879 is @var{seq}, the first sequence.
+ − 3880 @end defun
+ − 3881
+ − 3882 @defun mapl function list &rest more-lists
+ − 3883 This function is like @code{maplist}, except that it throws away
+ − 3884 the values returned by @var{function}.
+ − 3885 @end defun
+ − 3886
+ − 3887 @defun mapcan function seq &rest more-seqs
+ − 3888 This function is like @code{mapcar*}, except that it concatenates
+ − 3889 the return values (which must be lists) using @code{nconc},
+ − 3890 rather than simply collecting them into a list.
+ − 3891 @end defun
+ − 3892
+ − 3893 @defun mapcon function list &rest more-lists
+ − 3894 This function is like @code{maplist}, except that it concatenates
+ − 3895 the return values using @code{nconc}.
+ − 3896 @end defun
+ − 3897
+ − 3898 @defun some predicate seq &rest more-seqs
+ − 3899 This function calls @var{predicate} on each element of @var{seq}
+ − 3900 in turn; if @var{predicate} returns a non-@code{nil} value,
+ − 3901 @code{some} returns that value, otherwise it returns @code{nil}.
+ − 3902 Given several sequence arguments, it steps through the sequences
+ − 3903 in parallel until the shortest one runs out, just as in
+ − 3904 @code{mapcar*}. You can rely on the left-to-right order in which
+ − 3905 the elements are visited, and on the fact that mapping stops
+ − 3906 immediately as soon as @var{predicate} returns non-@code{nil}.
+ − 3907 @end defun
+ − 3908
+ − 3909 @defun every predicate seq &rest more-seqs
+ − 3910 This function calls @var{predicate} on each element of the sequence(s)
+ − 3911 in turn; it returns @code{nil} as soon as @var{predicate} returns
+ − 3912 @code{nil} for any element, or @code{t} if the predicate was true
+ − 3913 for all elements.
+ − 3914 @end defun
+ − 3915
+ − 3916 @defun notany predicate seq &rest more-seqs
+ − 3917 This function calls @var{predicate} on each element of the sequence(s)
+ − 3918 in turn; it returns @code{nil} as soon as @var{predicate} returns
+ − 3919 a non-@code{nil} value for any element, or @code{t} if the predicate
+ − 3920 was @code{nil} for all elements.
+ − 3921 @end defun
+ − 3922
+ − 3923 @defun notevery predicate seq &rest more-seqs
+ − 3924 This function calls @var{predicate} on each element of the sequence(s)
+ − 3925 in turn; it returns a non-@code{nil} value as soon as @var{predicate}
+ − 3926 returns @code{nil} for any element, or @code{t} if the predicate was
+ − 3927 true for all elements.
+ − 3928 @end defun
+ − 3929
+ − 3930 @defun reduce function seq @t{&key :from-end :start :end :initial-value :key}
+ − 3931 This function combines the elements of @var{seq} using an associative
+ − 3932 binary operation. Suppose @var{function} is @code{*} and @var{seq} is
+ − 3933 the list @code{(2 3 4 5)}. The first two elements of the list are
+ − 3934 combined with @code{(* 2 3) = 6}; this is combined with the next
+ − 3935 element, @code{(* 6 4) = 24}, and that is combined with the final
+ − 3936 element: @code{(* 24 5) = 120}. Note that the @code{*} function happens
+ − 3937 to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as
+ − 3938 an explicit call to @code{reduce}.
+ − 3939
+ − 3940 If @code{:from-end} is true, the reduction is right-associative instead
+ − 3941 of left-associative:
+ − 3942
+ − 3943 @example
+ − 3944 (reduce '- '(1 2 3 4))
+ − 3945 @equiv{} (- (- (- 1 2) 3) 4) @result{} -8
+ − 3946 (reduce '- '(1 2 3 4) :from-end t)
+ − 3947 @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2
+ − 3948 @end example
+ − 3949
+ − 3950 If @code{:key} is specified, it is a function of one argument which
+ − 3951 is called on each of the sequence elements in turn.
+ − 3952
+ − 3953 If @code{:initial-value} is specified, it is effectively added to the
+ − 3954 front (or rear in the case of @code{:from-end}) of the sequence.
+ − 3955 The @code{:key} function is @emph{not} applied to the initial value.
+ − 3956
+ − 3957 If the sequence, including the initial value, has exactly one element
+ − 3958 then that element is returned without ever calling @var{function}.
+ − 3959 If the sequence is empty (and there is no initial value), then
+ − 3960 @var{function} is called with no arguments to obtain the return value.
+ − 3961 @end defun
+ − 3962
+ − 3963 All of these mapping operations can be expressed conveniently in
+ − 3964 terms of the @code{loop} macro. In compiled code, @code{loop} will
+ − 3965 be faster since it generates the loop as in-line code with no
+ − 3966 function calls.
+ − 3967
+ − 3968 @node Sequence Functions, Searching Sequences, Mapping over Sequences, Sequences
+ − 3969 @section Sequence Functions
+ − 3970
+ − 3971 @noindent
+ − 3972 This section describes a number of Common Lisp functions for
+ − 3973 operating on sequences.
+ − 3974
+ − 3975 @defun subseq sequence start &optional end
+ − 3976 This function returns a given subsequence of the argument
+ − 3977 @var{sequence}, which may be a list, string, or vector.
+ − 3978 The indices @var{start} and @var{end} must be in range, and
+ − 3979 @var{start} must be no greater than @var{end}. If @var{end}
+ − 3980 is omitted, it defaults to the length of the sequence. The
+ − 3981 return value is always a copy; it does not share structure
+ − 3982 with @var{sequence}.
+ − 3983
+ − 3984 As an extension to Common Lisp, @var{start} and/or @var{end}
+ − 3985 may be negative, in which case they represent a distance back
+ − 3986 from the end of the sequence. This is for compatibility with
+ − 3987 Emacs' @code{substring} function. Note that @code{subseq} is
+ − 3988 the @emph{only} sequence function that allows negative
+ − 3989 @var{start} and @var{end}.
+ − 3990
+ − 3991 You can use @code{setf} on a @code{subseq} form to replace a
+ − 3992 specified range of elements with elements from another sequence.
+ − 3993 The replacement is done as if by @code{replace}, described below.
+ − 3994 @end defun
+ − 3995
+ − 3996 @defun concatenate result-type &rest seqs
+ − 3997 This function concatenates the argument sequences together to
+ − 3998 form a result sequence of type @var{result-type}, one of the
+ − 3999 symbols @code{vector}, @code{string}, or @code{list}. The
+ − 4000 arguments are always copied, even in cases such as
+ − 4001 @code{(concatenate 'list '(1 2 3))} where the result is
+ − 4002 identical to an argument.
+ − 4003 @end defun
+ − 4004
+ − 4005 @defun fill seq item @t{&key :start :end}
+ − 4006 This function fills the elements of the sequence (or the specified
+ − 4007 part of the sequence) with the value @var{item}.
+ − 4008 @end defun
+ − 4009
+ − 4010 @defun replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2}
+ − 4011 This function copies part of @var{seq2} into part of @var{seq1}.
+ − 4012 The sequence @var{seq1} is not stretched or resized; the amount
+ − 4013 of data copied is simply the shorter of the source and destination
+ − 4014 (sub)sequences. The function returns @var{seq1}.
+ − 4015
+ − 4016 If @var{seq1} and @var{seq2} are @code{eq}, then the replacement
+ − 4017 will work correctly even if the regions indicated by the start
+ − 4018 and end arguments overlap. However, if @var{seq1} and @var{seq2}
+ − 4019 are lists which share storage but are not @code{eq}, and the
+ − 4020 start and end arguments specify overlapping regions, the effect
+ − 4021 is undefined.
+ − 4022 @end defun
+ − 4023
+ − 4024 @defun remove* item seq @t{&key :test :test-not :key :count :start :end :from-end}
+ − 4025 This returns a copy of @var{seq} with all elements matching
+ − 4026 @var{item} removed. The result may share storage with or be
+ − 4027 @code{eq} to @var{seq} in some circumstances, but the original
+ − 4028 @var{seq} will not be modified. The @code{:test}, @code{:test-not},
+ − 4029 and @code{:key} arguments define the matching test that is used;
+ − 4030 by default, elements @code{eql} to @var{item} are removed. The
+ − 4031 @code{:count} argument specifies the maximum number of matching
+ − 4032 elements that can be removed (only the leftmost @var{count} matches
+ − 4033 are removed). The @code{:start} and @code{:end} arguments specify
+ − 4034 a region in @var{seq} in which elements will be removed; elements
+ − 4035 outside that region are not matched or removed. The @code{:from-end}
+ − 4036 argument, if true, says that elements should be deleted from the
+ − 4037 end of the sequence rather than the beginning (this matters only
+ − 4038 if @var{count} was also specified).
+ − 4039 @end defun
+ − 4040
+ − 4041 @defun delete* item seq @t{&key :test :test-not :key :count :start :end :from-end}
+ − 4042 This deletes all elements of @var{seq} which match @var{item}.
+ − 4043 It is a destructive operation. Since Emacs Lisp does not support
+ − 4044 stretchable strings or vectors, this is the same as @code{remove*}
+ − 4045 for those sequence types. On lists, @code{remove*} will copy the
+ − 4046 list if necessary to preserve the original list, whereas
+ − 4047 @code{delete*} will splice out parts of the argument list.
+ − 4048 Compare @code{append} and @code{nconc}, which are analogous
+ − 4049 non-destructive and destructive list operations in Emacs Lisp.
+ − 4050 @end defun
+ − 4051
+ − 4052 @findex remove-if
+ − 4053 @findex remove-if-not
+ − 4054 @findex delete-if
+ − 4055 @findex delete-if-not
+ − 4056 The predicate-oriented functions @code{remove-if}, @code{remove-if-not},
+ − 4057 @code{delete-if}, and @code{delete-if-not} are defined similarly.
+ − 4058
+ − 4059 @defun delete item list
+ − 4060 This MacLisp-compatible function deletes from @var{list} all elements
+ − 4061 which are @code{equal} to @var{item}. The @code{delete} function is
+ − 4062 built-in to Emacs 19; this package defines it equivalently in Emacs 18.
+ − 4063 @end defun
+ − 4064
+ − 4065 @defun remove item list
+ − 4066 This function removes from @var{list} all elements which are
+ − 4067 @code{equal} to @var{item}. This package defines it for symmetry
+ − 4068 with @code{delete}, even though @code{remove} is not built-in to
+ − 4069 Emacs 19.
+ − 4070 @end defun
+ − 4071
+ − 4072 @defun remq item list
+ − 4073 This function removes from @var{list} all elements which are
+ − 4074 @code{eq} to @var{item}. This package defines it for symmetry
+ − 4075 with @code{delq}, even though @code{remq} is not built-in to
+ − 4076 Emacs 19.
+ − 4077 @end defun
+ − 4078
+ − 4079 @defun remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
+ − 4080 This function returns a copy of @var{seq} with duplicate elements
+ − 4081 removed. Specifically, if two elements from the sequence match
+ − 4082 according to the @code{:test}, @code{:test-not}, and @code{:key}
+ − 4083 arguments, only the rightmost one is retained. If @code{:from-end}
+ − 4084 is true, the leftmost one is retained instead. If @code{:start} or
+ − 4085 @code{:end} is specified, only elements within that subsequence are
+ − 4086 examined or removed.
+ − 4087 @end defun
+ − 4088
+ − 4089 @defun delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end}
+ − 4090 This function deletes duplicate elements from @var{seq}. It is
+ − 4091 a destructive version of @code{remove-duplicates}.
+ − 4092 @end defun
+ − 4093
+ − 4094 @defun substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
+ − 4095 This function returns a copy of @var{seq}, with all elements
+ − 4096 matching @var{old} replaced with @var{new}. The @code{:count},
+ − 4097 @code{:start}, @code{:end}, and @code{:from-end} arguments may be
+ − 4098 used to limit the number of substitutions made.
+ − 4099 @end defun
+ − 4100
+ − 4101 @defun nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end}
+ − 4102 This is a destructive version of @code{substitute}; it performs
+ − 4103 the substitution using @code{setcar} or @code{aset} rather than
+ − 4104 by returning a changed copy of the sequence.
+ − 4105 @end defun
+ − 4106
+ − 4107 @findex substitute-if
+ − 4108 @findex substitute-if-not
+ − 4109 @findex nsubstitute-if
+ − 4110 @findex nsubstitute-if-not
+ − 4111 The @code{substitute-if}, @code{substitute-if-not}, @code{nsubstitute-if},
+ − 4112 and @code{nsubstitute-if-not} functions are defined similarly. For
+ − 4113 these, a @var{predicate} is given in place of the @var{old} argument.
+ − 4114
+ − 4115 @node Searching Sequences, Sorting Sequences, Sequence Functions, Sequences
+ − 4116 @section Searching Sequences
+ − 4117
+ − 4118 @noindent
+ − 4119 These functions search for elements or subsequences in a sequence.
+ − 4120 (See also @code{member*} and @code{assoc*}; @pxref{Lists}.)
+ − 4121
+ − 4122 @defun find item seq @t{&key :test :test-not :key :start :end :from-end}
+ − 4123 This function searches @var{seq} for an element matching @var{item}.
+ − 4124 If it finds a match, it returns the matching element. Otherwise,
+ − 4125 it returns @code{nil}. It returns the leftmost match, unless
+ − 4126 @code{:from-end} is true, in which case it returns the rightmost
+ − 4127 match. The @code{:start} and @code{:end} arguments may be used to
+ − 4128 limit the range of elements that are searched.
+ − 4129 @end defun
+ − 4130
+ − 4131 @defun position item seq @t{&key :test :test-not :key :start :end :from-end}
+ − 4132 This function is like @code{find}, except that it returns the
+ − 4133 integer position in the sequence of the matching item rather than
+ − 4134 the item itself. The position is relative to the start of the
+ − 4135 sequence as a whole, even if @code{:start} is non-zero. The function
+ − 4136 returns @code{nil} if no matching element was found.
+ − 4137 @end defun
+ − 4138
+ − 4139 @defun count item seq @t{&key :test :test-not :key :start :end}
+ − 4140 This function returns the number of elements of @var{seq} which
+ − 4141 match @var{item}. The result is always a nonnegative integer.
+ − 4142 @end defun
+ − 4143
+ − 4144 @findex find-if
+ − 4145 @findex find-if-not
+ − 4146 @findex position-if
+ − 4147 @findex position-if-not
+ − 4148 @findex count-if
+ − 4149 @findex count-if-not
+ − 4150 The @code{find-if}, @code{find-if-not}, @code{position-if},
+ − 4151 @code{position-if-not}, @code{count-if}, and @code{count-if-not}
+ − 4152 functions are defined similarly.
+ − 4153
+ − 4154 @defun mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end}
+ − 4155 This function compares the specified parts of @var{seq1} and
+ − 4156 @var{seq2}. If they are the same length and the corresponding
+ − 4157 elements match (according to @code{:test}, @code{:test-not},
+ − 4158 and @code{:key}), the function returns @code{nil}. If there is
+ − 4159 a mismatch, the function returns the index (relative to @var{seq1})
+ − 4160 of the first mismatching element. This will be the leftmost pair of
+ − 4161 elements which do not match, or the position at which the shorter of
+ − 4162 the two otherwise-matching sequences runs out.
+ − 4163
+ − 4164 If @code{:from-end} is true, then the elements are compared from right
+ − 4165 to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}.
+ − 4166 If the sequences differ, then one plus the index of the rightmost
+ − 4167 difference (relative to @var{seq1}) is returned.
+ − 4168
+ − 4169 An interesting example is @code{(mismatch str1 str2 :key 'upcase)},
+ − 4170 which compares two strings case-insensitively.
+ − 4171 @end defun
+ − 4172
+ − 4173 @defun search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2}
+ − 4174 This function searches @var{seq2} for a subsequence that matches
+ − 4175 @var{seq1} (or part of it specified by @code{:start1} and
+ − 4176 @code{:end1}.) Only matches which fall entirely within the region
+ − 4177 defined by @code{:start2} and @code{:end2} will be considered.
+ − 4178 The return value is the index of the leftmost element of the
+ − 4179 leftmost match, relative to the start of @var{seq2}, or @code{nil}
+ − 4180 if no matches were found. If @code{:from-end} is true, the
+ − 4181 function finds the @emph{rightmost} matching subsequence.
+ − 4182 @end defun
+ − 4183
+ − 4184 @node Sorting Sequences, , Searching Sequences, Sequences
+ − 4185 @section Sorting Sequences
+ − 4186
+ − 4187 @defun sort* seq predicate @t{&key :key}
+ − 4188 This function sorts @var{seq} into increasing order as determined
+ − 4189 by using @var{predicate} to compare pairs of elements. @var{predicate}
+ − 4190 should return true (non-@code{nil}) if and only if its first argument
+ − 4191 is less than (not equal to) its second argument. For example,
+ − 4192 @code{<} and @code{string-lessp} are suitable predicate functions
+ − 4193 for sorting numbers and strings, respectively; @code{>} would sort
+ − 4194 numbers into decreasing rather than increasing order.
+ − 4195
+ − 4196 This function differs from Emacs' built-in @code{sort} in that it
+ − 4197 can operate on any type of sequence, not just lists. Also, it
+ − 4198 accepts a @code{:key} argument which is used to preprocess data
+ − 4199 fed to the @var{predicate} function. For example,
+ − 4200
+ − 4201 @example
+ − 4202 (setq data (sort data 'string-lessp :key 'downcase))
+ − 4203 @end example
+ − 4204
+ − 4205 @noindent
+ − 4206 sorts @var{data}, a sequence of strings, into increasing alphabetical
+ − 4207 order without regard to case. A @code{:key} function of @code{car}
+ − 4208 would be useful for sorting association lists.
+ − 4209
+ − 4210 The @code{sort*} function is destructive; it sorts lists by actually
+ − 4211 rearranging the @code{cdr} pointers in suitable fashion.
+ − 4212 @end defun
+ − 4213
+ − 4214 @defun stable-sort seq predicate @t{&key :key}
+ − 4215 This function sorts @var{seq} @dfn{stably}, meaning two elements
+ − 4216 which are equal in terms of @var{predicate} are guaranteed not to
+ − 4217 be rearranged out of their original order by the sort.
+ − 4218
+ − 4219 In practice, @code{sort*} and @code{stable-sort} are equivalent
+ − 4220 in Emacs Lisp because the underlying @code{sort} function is
+ − 4221 stable by default. However, this package reserves the right to
+ − 4222 use non-stable methods for @code{sort*} in the future.
+ − 4223 @end defun
+ − 4224
+ − 4225 @defun merge type seq1 seq2 predicate @t{&key :key}
+ − 4226 This function merges two sequences @var{seq1} and @var{seq2} by
+ − 4227 interleaving their elements. The result sequence, of type @var{type}
+ − 4228 (in the sense of @code{concatenate}), has length equal to the sum
+ − 4229 of the lengths of the two input sequences. The sequences may be
+ − 4230 modified destructively. Order of elements within @var{seq1} and
+ − 4231 @var{seq2} is preserved in the interleaving; elements of the two
+ − 4232 sequences are compared by @var{predicate} (in the sense of
+ − 4233 @code{sort}) and the lesser element goes first in the result.
+ − 4234 When elements are equal, those from @var{seq1} precede those from
+ − 4235 @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are
+ − 4236 both sorted according to @var{predicate}, then the result will be
+ − 4237 a merged sequence which is (stably) sorted according to
+ − 4238 @var{predicate}.
+ − 4239 @end defun
+ − 4240
+ − 4241 @node Lists, Hash Tables, Sequences, Top
+ − 4242 @chapter Lists
+ − 4243
+ − 4244 @noindent
+ − 4245 The functions described here operate on lists.
+ − 4246
+ − 4247 @menu
+ − 4248 * List Functions:: `caddr', `first', `last', `list*', etc.
+ − 4249 * Substitution of Expressions:: `subst', `sublis', etc.
+ − 4250 * Lists as Sets:: `member*', `adjoin', `union', etc.
+ − 4251 * Association Lists:: `assoc*', `rassoc*', `acons', `pairlis'
+ − 4252 @end menu
+ − 4253
+ − 4254 @node List Functions, Substitution of Expressions, Lists, Lists
+ − 4255 @section List Functions
+ − 4256
+ − 4257 @noindent
+ − 4258 This section describes a number of simple operations on lists,
+ − 4259 i.e., chains of cons cells.
+ − 4260
+ − 4261 @defun caddr x
+ − 4262 This function is equivalent to @code{(car (cdr (cdr @var{x})))}.
+ − 4263 Likewise, this package defines all 28 @code{c@var{xxx}r} functions
+ − 4264 where @var{xxx} is up to four @samp{a}s and/or @samp{d}s.
+ − 4265 All of these functions are @code{setf}-able, and calls to them
+ − 4266 are expanded inline by the byte-compiler for maximum efficiency.
+ − 4267 @end defun
+ − 4268
+ − 4269 @defun first x
+ − 4270 This function is a synonym for @code{(car @var{x})}. Likewise,
+ − 4271 the functions @code{second}, @code{third}, @dots{}, through
+ − 4272 @code{tenth} return the given element of the list @var{x}.
+ − 4273 @end defun
+ − 4274
+ − 4275 @defun rest x
+ − 4276 This function is a synonym for @code{(cdr @var{x})}.
+ − 4277 @end defun
+ − 4278
+ − 4279 @defun endp x
+ − 4280 Common Lisp defines this function to act like @code{null}, but
+ − 4281 signalling an error if @code{x} is neither a @code{nil} nor a
+ − 4282 cons cell. This package simply defines @code{endp} as a synonym
+ − 4283 for @code{null}.
+ − 4284 @end defun
+ − 4285
+ − 4286 @defun list-length x
+ − 4287 This function returns the length of list @var{x}, exactly like
+ − 4288 @code{(length @var{x})}, except that if @var{x} is a circular
+ − 4289 list (where the cdr-chain forms a loop rather than terminating
+ − 4290 with @code{nil}), this function returns @code{nil}. (The regular
+ − 4291 @code{length} function would get stuck if given a circular list.)
+ − 4292 @end defun
+ − 4293
+ − 4294 @defun last x &optional n
+ − 4295 This function returns the last cons, or the @var{n}th-to-last cons,
+ − 4296 of the list @var{x}. If @var{n} is omitted it defaults to 1.
+ − 4297 The ``last cons'' means the first cons cell of the list whose
+ − 4298 @code{cdr} is not another cons cell. (For normal lists, the
+ − 4299 @code{cdr} of the last cons will be @code{nil}.) This function
+ − 4300 returns @code{nil} if @var{x} is @code{nil} or shorter than
+ − 4301 @var{n}. Note that the last @emph{element} of the list is
+ − 4302 @code{(car (last @var{x}))}.
+ − 4303 @end defun
+ − 4304
+ − 4305 @defun butlast x &optional n
+ − 4306 This function returns the list @var{x} with the last element,
+ − 4307 or the last @var{n} elements, removed. If @var{n} is greater
+ − 4308 than zero it makes a copy of the list so as not to damage the
+ − 4309 original list. In general, @code{(append (butlast @var{x} @var{n})
+ − 4310 (last @var{x} @var{n}))} will return a list equal to @var{x}.
+ − 4311 @end defun
+ − 4312
+ − 4313 @defun nbutlast x &optional n
+ − 4314 This is a version of @code{butlast} that works by destructively
+ − 4315 modifying the @code{cdr} of the appropriate element, rather than
+ − 4316 making a copy of the list.
+ − 4317 @end defun
+ − 4318
+ − 4319 @defun list* arg &rest others
+ − 4320 This function constructs a list of its arguments. The final
+ − 4321 argument becomes the @code{cdr} of the last cell constructed.
+ − 4322 Thus, @code{(list* @var{a} @var{b} @var{c})} is equivalent to
+ − 4323 @code{(cons @var{a} (cons @var{b} @var{c}))}, and
+ − 4324 @code{(list* @var{a} @var{b} nil)} is equivalent to
+ − 4325 @code{(list @var{a} @var{b})}.
+ − 4326
+ − 4327 (Note that this function really is called @code{list*} in Common
+ − 4328 Lisp; it is not a name invented for this package like @code{member*}
+ − 4329 or @code{defun*}.)
+ − 4330 @end defun
+ − 4331
+ − 4332 @defun ldiff list sublist
+ − 4333 If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to
+ − 4334 one of the cons cells of @var{list}, then this function returns
+ − 4335 a copy of the part of @var{list} up to but not including
+ − 4336 @var{sublist}. For example, @code{(ldiff x (cddr x))} returns
+ − 4337 the first two elements of the list @code{x}. The result is a
+ − 4338 copy; the original @var{list} is not modified. If @var{sublist}
+ − 4339 is not a sublist of @var{list}, a copy of the entire @var{list}
+ − 4340 is returned.
+ − 4341 @end defun
+ − 4342
+ − 4343 @defun copy-list list
+ − 4344 This function returns a copy of the list @var{list}. It copies
+ − 4345 dotted lists like @code{(1 2 . 3)} correctly.
+ − 4346 @end defun
+ − 4347
+ − 4348 @defun copy-tree x &optional vecp
+ − 4349 This function returns a copy of the tree of cons cells @var{x}.
+ − 4350 Unlike @code{copy-sequence} (and its alias @code{copy-list}),
+ − 4351 which copies only along the @code{cdr} direction, this function
+ − 4352 copies (recursively) along both the @code{car} and the @code{cdr}
+ − 4353 directions. If @var{x} is not a cons cell, the function simply
+ − 4354 returns @var{x} unchanged. If the optional @var{vecp} argument
+ − 4355 is true, this function copies vectors (recursively) as well as
+ − 4356 cons cells.
+ − 4357 @end defun
+ − 4358
+ − 4359 @defun tree-equal x y @t{&key :test :test-not :key}
+ − 4360 This function compares two trees of cons cells. If @var{x} and
+ − 4361 @var{y} are both cons cells, their @code{car}s and @code{cdr}s are
+ − 4362 compared recursively. If neither @var{x} nor @var{y} is a cons
+ − 4363 cell, they are compared by @code{eql}, or according to the
+ − 4364 specified test. The @code{:key} function, if specified, is
+ − 4365 applied to the elements of both trees. @xref{Sequences}.
+ − 4366 @end defun
+ − 4367
+ − 4368 @iftex
+ − 4369 @secno=3
+ − 4370 @end iftex
+ − 4371
+ − 4372 @node Substitution of Expressions, Lists as Sets, List Functions, Lists
+ − 4373 @section Substitution of Expressions
+ − 4374
+ − 4375 @noindent
+ − 4376 These functions substitute elements throughout a tree of cons
+ − 4377 cells. (@xref{Sequence Functions}, for the @code{substitute}
+ − 4378 function, which works on just the top-level elements of a list.)
+ − 4379
+ − 4380 @defun subst new old tree @t{&key :test :test-not :key}
+ − 4381 This function substitutes occurrences of @var{old} with @var{new}
+ − 4382 in @var{tree}, a tree of cons cells. It returns a substituted
+ − 4383 tree, which will be a copy except that it may share storage with
+ − 4384 the argument @var{tree} in parts where no substitutions occurred.
+ − 4385 The original @var{tree} is not modified. This function recurses
+ − 4386 on, and compares against @var{old}, both @code{car}s and @code{cdr}s
+ − 4387 of the component cons cells. If @var{old} is itself a cons cell,
+ − 4388 then matching cells in the tree are substituted as usual without
+ − 4389 recursively substituting in that cell. Comparisons with @var{old}
+ − 4390 are done according to the specified test (@code{eql} by default).
+ − 4391 The @code{:key} function is applied to the elements of the tree
+ − 4392 but not to @var{old}.
+ − 4393 @end defun
+ − 4394
+ − 4395 @defun nsubst new old tree @t{&key :test :test-not :key}
+ − 4396 This function is like @code{subst}, except that it works by
+ − 4397 destructive modification (by @code{setcar} or @code{setcdr})
+ − 4398 rather than copying.
+ − 4399 @end defun
+ − 4400
+ − 4401 @findex subst-if
+ − 4402 @findex subst-if-not
+ − 4403 @findex nsubst-if
+ − 4404 @findex nsubst-if-not
+ − 4405 The @code{subst-if}, @code{subst-if-not}, @code{nsubst-if}, and
+ − 4406 @code{nsubst-if-not} functions are defined similarly.
+ − 4407
+ − 4408 @defun sublis alist tree @t{&key :test :test-not :key}
+ − 4409 This function is like @code{subst}, except that it takes an
+ − 4410 association list @var{alist} of @var{old}-@var{new} pairs.
+ − 4411 Each element of the tree (after applying the @code{:key}
+ − 4412 function, if any), is compared with the @code{car}s of
+ − 4413 @var{alist}; if it matches, it is replaced by the corresponding
+ − 4414 @code{cdr}.
+ − 4415 @end defun
+ − 4416
+ − 4417 @defun nsublis alist tree @t{&key :test :test-not :key}
+ − 4418 This is a destructive version of @code{sublis}.
+ − 4419 @end defun
+ − 4420
+ − 4421 @node Lists as Sets, Association Lists, Substitution of Expressions, Lists
+ − 4422 @section Lists as Sets
+ − 4423
+ − 4424 @noindent
+ − 4425 These functions perform operations on lists which represent sets
+ − 4426 of elements.
+ − 4427
+ − 4428 @defun member item list
+ − 4429 This MacLisp-compatible function searches @var{list} for an element
+ − 4430 which is @code{equal} to @var{item}. The @code{member} function is
+ − 4431 built-in to Emacs 19; this package defines it equivalently in Emacs 18.
+ − 4432 See the following function for a Common-Lisp compatible version.
+ − 4433 @end defun
+ − 4434
+ − 4435 @defun member* item list @t{&key :test :test-not :key}
+ − 4436 This function searches @var{list} for an element matching @var{item}.
+ − 4437 If a match is found, it returns the cons cell whose @code{car} was
+ − 4438 the matching element. Otherwise, it returns @code{nil}. Elements
+ − 4439 are compared by @code{eql} by default; you can use the @code{:test},
+ − 4440 @code{:test-not}, and @code{:key} arguments to modify this behavior.
+ − 4441 @xref{Sequences}.
+ − 4442
+ − 4443 Note that this function's name is suffixed by @samp{*} to avoid
+ − 4444 the incompatible @code{member} function defined in Emacs 19.
+ − 4445 (That function uses @code{equal} for comparisons; it is equivalent
+ − 4446 to @code{(member* @var{item} @var{list} :test 'equal)}.)
+ − 4447 @end defun
+ − 4448
+ − 4449 @findex member-if
+ − 4450 @findex member-if-not
+ − 4451 The @code{member-if} and @code{member-if-not} functions
+ − 4452 analogously search for elements which satisfy a given predicate.
+ − 4453
+ − 4454 @defun tailp sublist list
+ − 4455 This function returns @code{t} if @var{sublist} is a sublist of
+ − 4456 @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to
+ − 4457 any of its @code{cdr}s.
+ − 4458 @end defun
+ − 4459
+ − 4460 @defun adjoin item list @t{&key :test :test-not :key}
+ − 4461 This function conses @var{item} onto the front of @var{list},
+ − 4462 like @code{(cons @var{item} @var{list})}, but only if @var{item}
+ − 4463 is not already present on the list (as determined by @code{member*}).
+ − 4464 If a @code{:key} argument is specified, it is applied to
+ − 4465 @var{item} as well as to the elements of @var{list} during
+ − 4466 the search, on the reasoning that @var{item} is ``about'' to
+ − 4467 become part of the list.
+ − 4468 @end defun
+ − 4469
+ − 4470 @defun union list1 list2 @t{&key :test :test-not :key}
+ − 4471 This function combines two lists which represent sets of items,
+ − 4472 returning a list that represents the union of those two sets.
+ − 4473 The result list will contain all items which appear in @var{list1}
+ − 4474 or @var{list2}, and no others. If an item appears in both
+ − 4475 @var{list1} and @var{list2} it will be copied only once. If
+ − 4476 an item is duplicated in @var{list1} or @var{list2}, it is
+ − 4477 undefined whether or not that duplication will survive in the
+ − 4478 result list. The order of elements in the result list is also
+ − 4479 undefined.
+ − 4480 @end defun
+ − 4481
+ − 4482 @defun nunion list1 list2 @t{&key :test :test-not :key}
+ − 4483 This is a destructive version of @code{union}; rather than copying,
+ − 4484 it tries to reuse the storage of the argument lists if possible.
+ − 4485 @end defun
+ − 4486
+ − 4487 @defun intersection list1 list2 @t{&key :test :test-not :key}
+ − 4488 This function computes the intersection of the sets represented
+ − 4489 by @var{list1} and @var{list2}. It returns the list of items
+ − 4490 which appear in both @var{list1} and @var{list2}.
+ − 4491 @end defun
+ − 4492
+ − 4493 @defun nintersection list1 list2 @t{&key :test :test-not :key}
+ − 4494 This is a destructive version of @code{intersection}. It
+ − 4495 tries to reuse storage of @var{list1} rather than copying.
+ − 4496 It does @emph{not} reuse the storage of @var{list2}.
+ − 4497 @end defun
+ − 4498
+ − 4499 @defun set-difference list1 list2 @t{&key :test :test-not :key}
+ − 4500 This function computes the ``set difference'' of @var{list1}
+ − 4501 and @var{list2}, i.e., the set of elements that appear in
+ − 4502 @var{list1} but @emph{not} in @var{list2}.
+ − 4503 @end defun
+ − 4504
+ − 4505 @defun nset-difference list1 list2 @t{&key :test :test-not :key}
+ − 4506 This is a destructive @code{set-difference}, which will try
+ − 4507 to reuse @var{list1} if possible.
+ − 4508 @end defun
+ − 4509
+ − 4510 @defun set-exclusive-or list1 list2 @t{&key :test :test-not :key}
+ − 4511 This function computes the ``set exclusive or'' of @var{list1}
+ − 4512 and @var{list2}, i.e., the set of elements that appear in
+ − 4513 exactly one of @var{list1} and @var{list2}.
+ − 4514 @end defun
+ − 4515
+ − 4516 @defun nset-exclusive-or list1 list2 @t{&key :test :test-not :key}
+ − 4517 This is a destructive @code{set-exclusive-or}, which will try
+ − 4518 to reuse @var{list1} and @var{list2} if possible.
+ − 4519 @end defun
+ − 4520
+ − 4521 @defun subsetp list1 list2 @t{&key :test :test-not :key}
+ − 4522 This function checks whether @var{list1} represents a subset
+ − 4523 of @var{list2}, i.e., whether every element of @var{list1}
+ − 4524 also appears in @var{list2}.
+ − 4525 @end defun
+ − 4526
+ − 4527 @node Association Lists, , Lists as Sets, Lists
+ − 4528 @section Association Lists
+ − 4529
+ − 4530 @noindent
+ − 4531 An @dfn{association list} is a list representing a mapping from
+ − 4532 one set of values to another; any list whose elements are cons
+ − 4533 cells is an association list.
+ − 4534
+ − 4535 @defun assoc* item a-list @t{&key :test :test-not :key}
+ − 4536 This function searches the association list @var{a-list} for an
+ − 4537 element whose @code{car} matches (in the sense of @code{:test},
+ − 4538 @code{:test-not}, and @code{:key}, or by comparison with @code{eql})
+ − 4539 a given @var{item}. It returns the matching element, if any,
+ − 4540 otherwise @code{nil}. It ignores elements of @var{a-list} which
+ − 4541 are not cons cells. (This corresponds to the behavior of
+ − 4542 @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's
+ − 4543 @code{assoc} ignores @code{nil}s but considers any other non-cons
+ − 4544 elements of @var{a-list} to be an error.)
+ − 4545 @end defun
+ − 4546
+ − 4547 @defun rassoc* item a-list @t{&key :test :test-not :key}
+ − 4548 This function searches for an element whose @code{cdr} matches
+ − 4549 @var{item}. If @var{a-list} represents a mapping, this applies
+ − 4550 the inverse of the mapping to @var{item}.
+ − 4551 @end defun
+ − 4552
+ − 4553 @defun rassoc item a-list
+ − 4554 This function searches like @code{rassoc*} with a @code{:test}
+ − 4555 argument of @code{equal}. It is analogous to Emacs Lisp's
+ − 4556 standard @code{assoc} function, which derives from the MacLisp
+ − 4557 rather than the Common Lisp tradition.
+ − 4558 @end defun
+ − 4559
+ − 4560 @findex assoc-if
+ − 4561 @findex assoc-if-not
+ − 4562 @findex rassoc-if
+ − 4563 @findex rassoc-if-not
+ − 4564 The @code{assoc-if}, @code{assoc-if-not}, @code{rassoc-if},
+ − 4565 and @code{rassoc-if-not} functions are defined similarly.
+ − 4566
+ − 4567 Two simple functions for constructing association lists are:
+ − 4568
+ − 4569 @defun acons key value alist
+ − 4570 This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}.
+ − 4571 @end defun
+ − 4572
+ − 4573 @defun pairlis keys values &optional alist
+ − 4574 This is equivalent to @code{(nconc (mapcar* 'cons @var{keys} @var{values})
+ − 4575 @var{alist})}.
+ − 4576 @end defun
+ − 4577
+ − 4578 @node Hash Tables, Structures, Lists, Top
+ − 4579 @chapter Hash Tables
+ − 4580
+ − 4581 @noindent
+ − 4582 Hash tables are now implemented directly in the C code and documented in
446
+ − 4583 @ref{Hash Tables,,, lispref, XEmacs Lisp Reference Manual}.
428
+ − 4584
+ − 4585 @ignore
+ − 4586 A @dfn{hash table} is a data structure that maps ``keys'' onto
+ − 4587 ``values.'' Keys and values can be arbitrary Lisp data objects.
+ − 4588 Hash tables have the property that the time to search for a given
+ − 4589 key is roughly constant; simpler data structures like association
+ − 4590 lists take time proportional to the number of entries in the list.
+ − 4591
+ − 4592 @defun make-hash-table @t{&key :test :size}
+ − 4593 This function creates and returns a hash-table object whose
+ − 4594 function for comparing elements is @code{:test} (@code{eql}
+ − 4595 by default), and which is allocated to fit about @code{:size}
+ − 4596 elements. The @code{:size} argument is purely advisory; the
+ − 4597 table will stretch automatically if you store more elements in
+ − 4598 it. If @code{:size} is omitted, a reasonable default is used.
+ − 4599
+ − 4600 Common Lisp allows only @code{eq}, @code{eql}, @code{equal},
+ − 4601 and @code{equalp} as legal values for the @code{:test} argument.
+ − 4602 In this package, any reasonable predicate function will work,
+ − 4603 though if you use something else you should check the details of
+ − 4604 the hashing function described below to make sure it is suitable
+ − 4605 for your predicate.
+ − 4606
+ − 4607 Some versions of Emacs (like XEmacs) include a built-in hash
+ − 4608 table type; in these versions, @code{make-hash-table} with a test of
+ − 4609 @code{eq}, @code{eql}, or @code{equal} will use these built-in hash
+ − 4610 tables. In all other cases, it will return a hash-table object which
+ − 4611 takes the form of a list with an identifying ``tag'' symbol at the
+ − 4612 front. All of the hash table functions in this package can operate on
+ − 4613 both types of hash table; normally you will never know which type is
+ − 4614 being used.
+ − 4615
+ − 4616 This function accepts the additional Common Lisp keywords
+ − 4617 @code{:rehash-size} and @code{:rehash-threshold}, but it ignores
+ − 4618 their values.
+ − 4619 @end defun
+ − 4620
+ − 4621 @defun gethash key table &optional default
+ − 4622 This function looks up @var{key} in @var{table}. If @var{key}
+ − 4623 exists in the table, in the sense that it matches any of the existing
+ − 4624 keys according to the table's test function, then the associated value
+ − 4625 is returned. Otherwise, @var{default} (or @code{nil}) is returned.
+ − 4626
+ − 4627 To store new data in the hash table, use @code{setf} on a call to
+ − 4628 @code{gethash}. If @var{key} already exists in the table, the
+ − 4629 corresponding value is changed to the stored value. If @var{key}
+ − 4630 does not already exist, a new entry is added to the table and the
+ − 4631 table is reallocated to a larger size if necessary. The @var{default}
+ − 4632 argument is allowed but ignored in this case. The situation is
440
+ − 4633 exactly analogous to that of @code{get}; @pxref{Property Lists}.
428
+ − 4634 @end defun
+ − 4635
+ − 4636 @defun remhash key table
+ − 4637 This function removes the entry for @var{key} from @var{table}.
+ − 4638 If an entry was removed, it returns @code{t}. If @var{key} does
+ − 4639 not appear in the table, it does nothing and returns @code{nil}.
+ − 4640 @end defun
+ − 4641
+ − 4642 @defun clrhash table
+ − 4643 This function removes all the entries from @var{table}, leaving
+ − 4644 an empty hash table.
+ − 4645 @end defun
+ − 4646
+ − 4647 @defun maphash function table
+ − 4648 This function calls @var{function} for each entry in @var{table}.
+ − 4649 It passes two arguments to @var{function}, the key and the value
+ − 4650 of the given entry. The return value of @var{function} is ignored;
+ − 4651 @var{maphash} itself returns @code{nil}. @xref{Loop Facility}, for
+ − 4652 an alternate way of iterating over hash tables.
+ − 4653 @end defun
+ − 4654
+ − 4655 @defun hash-table-count table This function returns the number of
+ − 4656 entries in @var{table}. @strong{Warning:} The current implementation of
+ − 4657 XEmacs hash-tables does not decrement the stored @code{count}
+ − 4658 when @code{remhash} removes an entry. Therefore, the return value of
+ − 4659 this function is not dependable if you have used @code{remhash} on the
+ − 4660 table and the table's test is @code{eq}, @code{eql}, or @code{equal}.
+ − 4661 A slower, but reliable, way to count the entries is
+ − 4662 @code{(loop for x being the hash-keys of @var{table} count t)}.
+ − 4663 @end defun
+ − 4664
+ − 4665 @defun hash-table-p object This function returns @code{t} if
+ − 4666 @var{object} is a hash table, @code{nil} otherwise. It recognizes both
+ − 4667 types of hash tables (both XEmacs built-in tables and tables implemented
+ − 4668 with special lists.)
+ − 4669 @end defun
+ − 4670
+ − 4671 Sometimes when dealing with hash tables it is useful to know the
+ − 4672 exact ``hash function'' that is used. This package implements
+ − 4673 hash tables using Emacs Lisp ``obarrays,'' which are the same
+ − 4674 data structure that Emacs Lisp uses to keep track of symbols.
+ − 4675 Each hash table includes an embedded obarray. Key values given
+ − 4676 to @code{gethash} are converted by various means into strings,
+ − 4677 which are then looked up in the obarray using @code{intern} and
+ − 4678 @code{intern-soft}. The symbol, or ``bucket,'' corresponding to
+ − 4679 a given key string includes as its @code{symbol-value} an association
+ − 4680 list of all key-value pairs which hash to that string. Depending
+ − 4681 on the test function, it is possible for many entries to hash to
+ − 4682 the same bucket. For example, if the test is @code{eql}, then the
+ − 4683 symbol @code{foo} and two separately built strings @code{"foo"} will
+ − 4684 create three entries in the same bucket. Search time is linear
+ − 4685 within buckets, so hash tables will be most effective if you arrange
+ − 4686 not to store too many things that hash the same.
+ − 4687
+ − 4688 The following algorithm is used to convert Lisp objects to hash
+ − 4689 strings:
+ − 4690
+ − 4691 @itemize @bullet
+ − 4692 @item
+ − 4693 Strings are used directly as hash strings. (However, if the test
+ − 4694 function is @code{equalp}, strings are @code{downcase}d first.)
+ − 4695
+ − 4696 @item
+ − 4697 Symbols are hashed according to their @code{symbol-name}.
+ − 4698
+ − 4699 @item
+ − 4700 Integers are hashed into one of 16 buckets depending on their value
+ − 4701 modulo 16. Floating-point numbers are truncated to integers and
+ − 4702 hashed modulo 16.
+ − 4703
+ − 4704 @item
+ − 4705 Cons cells are hashed according to their @code{car}s; nonempty vectors
+ − 4706 are hashed according to their first element.
+ − 4707
+ − 4708 @item
+ − 4709 All other types of objects hash into a single bucket named @code{"*"}.
+ − 4710 @end itemize
+ − 4711
+ − 4712 @noindent
+ − 4713 Thus, for example, searching among many buffer objects in a hash table
+ − 4714 will devolve to a (still fairly fast) linear-time search through a
+ − 4715 single bucket, whereas searching for different symbols will be very
+ − 4716 fast since each symbol will, in general, hash into its own bucket.
+ − 4717
+ − 4718 The size of the obarray in a hash table is automatically adjusted
+ − 4719 as the number of elements increases.
+ − 4720
+ − 4721 As a special case, @code{make-hash-table} with a @code{:size} argument
+ − 4722 of 0 or 1 will create a hash-table object that uses a single association
+ − 4723 list rather than an obarray of many lists. For very small tables this
+ − 4724 structure will be more efficient since lookup does not require
+ − 4725 converting the key to a string or looking it up in an obarray.
+ − 4726 However, such tables are guaranteed to take time proportional to
+ − 4727 their size to do a search.
+ − 4728 @end ignore
+ − 4729
+ − 4730 @iftex
+ − 4731 @chapno=18
+ − 4732 @end iftex
+ − 4733
+ − 4734 @node Structures, Assertions, Hash Tables, Top
+ − 4735 @chapter Structures
+ − 4736
+ − 4737 @noindent
+ − 4738 The Common Lisp @dfn{structure} mechanism provides a general way
+ − 4739 to define data types similar to C's @code{struct} types. A
+ − 4740 structure is a Lisp object containing some number of @dfn{slots},
+ − 4741 each of which can hold any Lisp data object. Functions are
+ − 4742 provided for accessing and setting the slots, creating or copying
+ − 4743 structure objects, and recognizing objects of a particular structure
+ − 4744 type.
+ − 4745
+ − 4746 In true Common Lisp, each structure type is a new type distinct
+ − 4747 from all existing Lisp types. Since the underlying Emacs Lisp
+ − 4748 system provides no way to create new distinct types, this package
+ − 4749 implements structures as vectors (or lists upon request) with a
+ − 4750 special ``tag'' symbol to identify them.
+ − 4751
+ − 4752 @defspec defstruct name slots@dots{}
+ − 4753 The @code{defstruct} form defines a new structure type called
+ − 4754 @var{name}, with the specified @var{slots}. (The @var{slots}
+ − 4755 may begin with a string which documents the structure type.)
+ − 4756 In the simplest case, @var{name} and each of the @var{slots}
+ − 4757 are symbols. For example,
+ − 4758
+ − 4759 @example
+ − 4760 (defstruct person name age sex)
+ − 4761 @end example
+ − 4762
+ − 4763 @noindent
+ − 4764 defines a struct type called @code{person} which contains three
+ − 4765 slots. Given a @code{person} object @var{p}, you can access those
+ − 4766 slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})},
+ − 4767 and @code{(person-sex @var{p})}. You can also change these slots by
+ − 4768 using @code{setf} on any of these place forms:
+ − 4769
+ − 4770 @example
+ − 4771 (incf (person-age birthday-boy))
+ − 4772 @end example
+ − 4773
+ − 4774 You can create a new @code{person} by calling @code{make-person},
+ − 4775 which takes keyword arguments @code{:name}, @code{:age}, and
+ − 4776 @code{:sex} to specify the initial values of these slots in the
+ − 4777 new object. (Omitting any of these arguments leaves the corresponding
+ − 4778 slot ``undefined,'' according to the Common Lisp standard; in Emacs
+ − 4779 Lisp, such uninitialized slots are filled with @code{nil}.)
+ − 4780
+ − 4781 Given a @code{person}, @code{(copy-person @var{p})} makes a new
+ − 4782 object of the same type whose slots are @code{eq} to those of @var{p}.
+ − 4783
+ − 4784 Given any Lisp object @var{x}, @code{(person-p @var{x})} returns
+ − 4785 true if @var{x} looks like a @code{person}, false otherwise. (Again,
+ − 4786 in Common Lisp this predicate would be exact; in Emacs Lisp the
+ − 4787 best it can do is verify that @var{x} is a vector of the correct
+ − 4788 length which starts with the correct tag symbol.)
+ − 4789
+ − 4790 Accessors like @code{person-name} normally check their arguments
+ − 4791 (effectively using @code{person-p}) and signal an error if the
+ − 4792 argument is the wrong type. This check is affected by
+ − 4793 @code{(optimize (safety @dots{}))} declarations. Safety level 1,
+ − 4794 the default, uses a somewhat optimized check that will detect all
+ − 4795 incorrect arguments, but may use an uninformative error message
+ − 4796 (e.g., ``expected a vector'' instead of ``expected a @code{person}'').
+ − 4797 Safety level 0 omits all checks except as provided by the underlying
+ − 4798 @code{aref} call; safety levels 2 and 3 do rigorous checking that will
+ − 4799 always print a descriptive error message for incorrect inputs.
+ − 4800 @xref{Declarations}.
+ − 4801
+ − 4802 @example
+ − 4803 (setq dave (make-person :name "Dave" :sex 'male))
+ − 4804 @result{} [cl-struct-person "Dave" nil male]
+ − 4805 (setq other (copy-person dave))
+ − 4806 @result{} [cl-struct-person "Dave" nil male]
+ − 4807 (eq dave other)
+ − 4808 @result{} nil
+ − 4809 (eq (person-name dave) (person-name other))
+ − 4810 @result{} t
+ − 4811 (person-p dave)
+ − 4812 @result{} t
+ − 4813 (person-p [1 2 3 4])
+ − 4814 @result{} nil
+ − 4815 (person-p "Bogus")
+ − 4816 @result{} nil
+ − 4817 (person-p '[cl-struct-person counterfeit person object])
+ − 4818 @result{} t
+ − 4819 @end example
+ − 4820
+ − 4821 In general, @var{name} is either a name symbol or a list of a name
+ − 4822 symbol followed by any number of @dfn{struct options}; each @var{slot}
+ − 4823 is either a slot symbol or a list of the form @samp{(@var{slot-name}
+ − 4824 @var{default-value} @var{slot-options}@dots{})}. The @var{default-value}
+ − 4825 is a Lisp form which is evaluated any time an instance of the
+ − 4826 structure type is created without specifying that slot's value.
+ − 4827
+ − 4828 Common Lisp defines several slot options, but the only one
+ − 4829 implemented in this package is @code{:read-only}. A non-@code{nil}
+ − 4830 value for this option means the slot should not be @code{setf}-able;
+ − 4831 the slot's value is determined when the object is created and does
+ − 4832 not change afterward.
+ − 4833
+ − 4834 @example
+ − 4835 (defstruct person
+ − 4836 (name nil :read-only t)
+ − 4837 age
+ − 4838 (sex 'unknown))
+ − 4839 @end example
+ − 4840
+ − 4841 Any slot options other than @code{:read-only} are ignored.
+ − 4842
+ − 4843 For obscure historical reasons, structure options take a different
+ − 4844 form than slot options. A structure option is either a keyword
+ − 4845 symbol, or a list beginning with a keyword symbol possibly followed
+ − 4846 by arguments. (By contrast, slot options are key-value pairs not
+ − 4847 enclosed in lists.)
+ − 4848
+ − 4849 @example
+ − 4850 (defstruct (person (:constructor create-person)
+ − 4851 (:type list)
+ − 4852 :named)
+ − 4853 name age sex)
+ − 4854 @end example
+ − 4855
+ − 4856 The following structure options are recognized.
+ − 4857
+ − 4858 @table @code
+ − 4859 @iftex
+ − 4860 @itemmax=0 in
+ − 4861 @advance@leftskip-.5@tableindent
+ − 4862 @end iftex
+ − 4863 @item :conc-name
+ − 4864 The argument is a symbol whose print name is used as the prefix for
+ − 4865 the names of slot accessor functions. The default is the name of
+ − 4866 the struct type followed by a hyphen. The option @code{(:conc-name p-)}
+ − 4867 would change this prefix to @code{p-}. Specifying @code{nil} as an
+ − 4868 argument means no prefix, so that the slot names themselves are used
+ − 4869 to name the accessor functions.
+ − 4870
+ − 4871 @item :constructor
+ − 4872 In the simple case, this option takes one argument which is an
+ − 4873 alternate name to use for the constructor function. The default
+ − 4874 is @code{make-@var{name}}, e.g., @code{make-person}. The above
+ − 4875 example changes this to @code{create-person}. Specifying @code{nil}
+ − 4876 as an argument means that no standard constructor should be
+ − 4877 generated at all.
+ − 4878
+ − 4879 In the full form of this option, the constructor name is followed
+ − 4880 by an arbitrary argument list. @xref{Program Structure}, for a
+ − 4881 description of the format of Common Lisp argument lists. All
+ − 4882 options, such as @code{&rest} and @code{&key}, are supported.
+ − 4883 The argument names should match the slot names; each slot is
+ − 4884 initialized from the corresponding argument. Slots whose names
+ − 4885 do not appear in the argument list are initialized based on the
+ − 4886 @var{default-value} in their slot descriptor. Also, @code{&optional}
+ − 4887 and @code{&key} arguments which don't specify defaults take their
+ − 4888 defaults from the slot descriptor. It is legal to include arguments
+ − 4889 which don't correspond to slot names; these are useful if they are
+ − 4890 referred to in the defaults for optional, keyword, or @code{&aux}
+ − 4891 arguments which @emph{do} correspond to slots.
+ − 4892
+ − 4893 You can specify any number of full-format @code{:constructor}
+ − 4894 options on a structure. The default constructor is still generated
+ − 4895 as well unless you disable it with a simple-format @code{:constructor}
+ − 4896 option.
+ − 4897
+ − 4898 @example
+ − 4899 (defstruct
+ − 4900 (person
+ − 4901 (:constructor nil) ; no default constructor
+ − 4902 (:constructor new-person (name sex &optional (age 0)))
+ − 4903 (:constructor new-hound (&key (name "Rover")
+ − 4904 (dog-years 0)
+ − 4905 &aux (age (* 7 dog-years))
+ − 4906 (sex 'canine))))
+ − 4907 name age sex)
+ − 4908 @end example
+ − 4909
+ − 4910 The first constructor here takes its arguments positionally rather
+ − 4911 than by keyword. (In official Common Lisp terminology, constructors
+ − 4912 that work By Order of Arguments instead of by keyword are called
+ − 4913 ``BOA constructors.'' No, I'm not making this up.) For example,
+ − 4914 @code{(new-person "Jane" 'female)} generates a person whose slots
+ − 4915 are @code{"Jane"}, 0, and @code{female}, respectively.
+ − 4916
+ − 4917 The second constructor takes two keyword arguments, @code{:name},
+ − 4918 which initializes the @code{name} slot and defaults to @code{"Rover"},
+ − 4919 and @code{:dog-years}, which does not itself correspond to a slot
+ − 4920 but which is used to initialize the @code{age} slot. The @code{sex}
+ − 4921 slot is forced to the symbol @code{canine} with no syntax for
+ − 4922 overriding it.
+ − 4923
+ − 4924 @item :copier
+ − 4925 The argument is an alternate name for the copier function for
+ − 4926 this type. The default is @code{copy-@var{name}}. @code{nil}
+ − 4927 means not to generate a copier function. (In this implementation,
+ − 4928 all copier functions are simply synonyms for @code{copy-sequence}.)
+ − 4929
+ − 4930 @item :predicate
+ − 4931 The argument is an alternate name for the predicate which recognizes
+ − 4932 objects of this type. The default is @code{@var{name}-p}. @code{nil}
+ − 4933 means not to generate a predicate function. (If the @code{:type}
+ − 4934 option is used without the @code{:named} option, no predicate is
+ − 4935 ever generated.)
+ − 4936
+ − 4937 In true Common Lisp, @code{typep} is always able to recognize a
+ − 4938 structure object even if @code{:predicate} was used. In this
+ − 4939 package, @code{typep} simply looks for a function called
+ − 4940 @code{@var{typename}-p}, so it will work for structure types
+ − 4941 only if they used the default predicate name.
+ − 4942
+ − 4943 @item :include
+ − 4944 This option implements a very limited form of C++-style inheritance.
+ − 4945 The argument is the name of another structure type previously
+ − 4946 created with @code{defstruct}. The effect is to cause the new
+ − 4947 structure type to inherit all of the included structure's slots
+ − 4948 (plus, of course, any new slots described by this struct's slot
+ − 4949 descriptors). The new structure is considered a ``specialization''
+ − 4950 of the included one. In fact, the predicate and slot accessors
+ − 4951 for the included type will also accept objects of the new type.
+ − 4952
+ − 4953 If there are extra arguments to the @code{:include} option after
+ − 4954 the included-structure name, these options are treated as replacement
+ − 4955 slot descriptors for slots in the included structure, possibly with
+ − 4956 modified default values. Borrowing an example from Steele:
+ − 4957
+ − 4958 @example
+ − 4959 (defstruct person name (age 0) sex)
+ − 4960 @result{} person
+ − 4961 (defstruct (astronaut (:include person (age 45)))
+ − 4962 helmet-size
+ − 4963 (favorite-beverage 'tang))
+ − 4964 @result{} astronaut
+ − 4965
+ − 4966 (setq joe (make-person :name "Joe"))
+ − 4967 @result{} [cl-struct-person "Joe" 0 nil]
+ − 4968 (setq buzz (make-astronaut :name "Buzz"))
+ − 4969 @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang]
+ − 4970
+ − 4971 (list (person-p joe) (person-p buzz))
+ − 4972 @result{} (t t)
+ − 4973 (list (astronaut-p joe) (astronaut-p buzz))
+ − 4974 @result{} (nil t)
+ − 4975
+ − 4976 (person-name buzz)
+ − 4977 @result{} "Buzz"
+ − 4978 (astronaut-name joe)
+ − 4979 @result{} error: "astronaut-name accessing a non-astronaut"
+ − 4980 @end example
+ − 4981
+ − 4982 Thus, if @code{astronaut} is a specialization of @code{person},
+ − 4983 then every @code{astronaut} is also a @code{person} (but not the
+ − 4984 other way around). Every @code{astronaut} includes all the slots
+ − 4985 of a @code{person}, plus extra slots that are specific to
+ − 4986 astronauts. Operations that work on people (like @code{person-name})
+ − 4987 work on astronauts just like other people.
+ − 4988
+ − 4989 @item :print-function
+ − 4990 In full Common Lisp, this option allows you to specify a function
+ − 4991 which is called to print an instance of the structure type. The
+ − 4992 Emacs Lisp system offers no hooks into the Lisp printer which would
+ − 4993 allow for such a feature, so this package simply ignores
+ − 4994 @code{:print-function}.
+ − 4995
+ − 4996 @item :type
+ − 4997 The argument should be one of the symbols @code{vector} or @code{list}.
+ − 4998 This tells which underlying Lisp data type should be used to implement
+ − 4999 the new structure type. Vectors are used by default, but
+ − 5000 @code{(:type list)} will cause structure objects to be stored as
+ − 5001 lists instead.
+ − 5002
+ − 5003 The vector representation for structure objects has the advantage
+ − 5004 that all structure slots can be accessed quickly, although creating
+ − 5005 vectors is a bit slower in Emacs Lisp. Lists are easier to create,
+ − 5006 but take a relatively long time accessing the later slots.
+ − 5007
+ − 5008 @item :named
+ − 5009 This option, which takes no arguments, causes a characteristic ``tag''
+ − 5010 symbol to be stored at the front of the structure object. Using
+ − 5011 @code{:type} without also using @code{:named} will result in a
+ − 5012 structure type stored as plain vectors or lists with no identifying
+ − 5013 features.
+ − 5014
+ − 5015 The default, if you don't specify @code{:type} explicitly, is to
+ − 5016 use named vectors. Therefore, @code{:named} is only useful in
+ − 5017 conjunction with @code{:type}.
+ − 5018
+ − 5019 @example
+ − 5020 (defstruct (person1) name age sex)
+ − 5021 (defstruct (person2 (:type list) :named) name age sex)
+ − 5022 (defstruct (person3 (:type list)) name age sex)
+ − 5023
+ − 5024 (setq p1 (make-person1))
+ − 5025 @result{} [cl-struct-person1 nil nil nil]
+ − 5026 (setq p2 (make-person2))
+ − 5027 @result{} (person2 nil nil nil)
+ − 5028 (setq p3 (make-person3))
+ − 5029 @result{} (nil nil nil)
+ − 5030
+ − 5031 (person1-p p1)
+ − 5032 @result{} t
+ − 5033 (person2-p p2)
+ − 5034 @result{} t
+ − 5035 (person3-p p3)
+ − 5036 @result{} error: function person3-p undefined
+ − 5037 @end example
+ − 5038
+ − 5039 Since unnamed structures don't have tags, @code{defstruct} is not
+ − 5040 able to make a useful predicate for recognizing them. Also,
+ − 5041 accessors like @code{person3-name} will be generated but they
+ − 5042 will not be able to do any type checking. The @code{person3-name}
+ − 5043 function, for example, will simply be a synonym for @code{car} in
+ − 5044 this case. By contrast, @code{person2-name} is able to verify
+ − 5045 that its argument is indeed a @code{person2} object before
+ − 5046 proceeding.
+ − 5047
+ − 5048 @item :initial-offset
+ − 5049 The argument must be a nonnegative integer. It specifies a
+ − 5050 number of slots to be left ``empty'' at the front of the
+ − 5051 structure. If the structure is named, the tag appears at the
+ − 5052 specified position in the list or vector; otherwise, the first
+ − 5053 slot appears at that position. Earlier positions are filled
+ − 5054 with @code{nil} by the constructors and ignored otherwise. If
+ − 5055 the type @code{:include}s another type, then @code{:initial-offset}
+ − 5056 specifies a number of slots to be skipped between the last slot
+ − 5057 of the included type and the first new slot.
+ − 5058 @end table
+ − 5059 @end defspec
+ − 5060
+ − 5061 Except as noted, the @code{defstruct} facility of this package is
+ − 5062 entirely compatible with that of Common Lisp.
+ − 5063
+ − 5064 @iftex
+ − 5065 @chapno=23
+ − 5066 @end iftex
+ − 5067
+ − 5068 @node Assertions, Efficiency Concerns, Structures, Top
+ − 5069 @chapter Assertions and Errors
+ − 5070
+ − 5071 @noindent
+ − 5072 This section describes two macros that test @dfn{assertions}, i.e.,
+ − 5073 conditions which must be true if the program is operating correctly.
+ − 5074 Assertions never add to the behavior of a Lisp program; they simply
+ − 5075 make ``sanity checks'' to make sure everything is as it should be.
+ − 5076
+ − 5077 If the optimization property @code{speed} has been set to 3, and
+ − 5078 @code{safety} is less than 3, then the byte-compiler will optimize
+ − 5079 away the following assertions. Because assertions might be optimized
+ − 5080 away, it is a bad idea for them to include side-effects.
+ − 5081
+ − 5082 @defspec assert test-form [show-args string args@dots{}]
+ − 5083 This form verifies that @var{test-form} is true (i.e., evaluates to
+ − 5084 a non-@code{nil} value). If so, it returns @code{nil}. If the test
+ − 5085 is not satisfied, @code{assert} signals an error.
+ − 5086
+ − 5087 A default error message will be supplied which includes @var{test-form}.
+ − 5088 You can specify a different error message by including a @var{string}
+ − 5089 argument plus optional extra arguments. Those arguments are simply
+ − 5090 passed to @code{error} to signal the error.
+ − 5091
+ − 5092 If the optional second argument @var{show-args} is @code{t} instead
+ − 5093 of @code{nil}, then the error message (with or without @var{string})
+ − 5094 will also include all non-constant arguments of the top-level
+ − 5095 @var{form}. For example:
+ − 5096
+ − 5097 @example
+ − 5098 (assert (> x 10) t "x is too small: %d")
+ − 5099 @end example
+ − 5100
446
+ − 5101 This usage of @var{show-args} is a change to Common Lisp. In
428
+ − 5102 true Common Lisp, the second argument gives a list of @var{places}
+ − 5103 which can be @code{setf}'d by the user before continuing from the
446
+ − 5104 error.
428
+ − 5105 @end defspec
+ − 5106
446
+ − 5107 @defspec check-type place type &optional string
+ − 5108 This form verifies that @var{place} evaluates to a value of type
428
+ − 5109 @var{type}. If so, it returns @code{nil}. If not, @code{check-type}
446
+ − 5110 signals a continuable @code{wrong-type-argument} error. The default
+ − 5111 error message lists the erroneous value along with @var{type} and
+ − 5112 @var{place} themselves. If @var{string} is specified, it is included in
+ − 5113 the error message in place of @var{type}. For example:
428
+ − 5114
+ − 5115 @example
+ − 5116 (check-type x (integer 1 *) "a positive integer")
+ − 5117 @end example
+ − 5118
+ − 5119 @xref{Type Predicates}, for a description of the type specifiers
+ − 5120 that may be used for @var{type}.
+ − 5121
446
+ − 5122 Note that as in Common Lisp, the first argument to @code{check-type}
+ − 5123 should be a @var{place} suitable for use by @code{setf}, because
+ − 5124 @code{check-type} signals a continuable error that allows the user to
+ − 5125 modify @var{place}, most simply by returning a value from the debugger.
428
+ − 5126 @end defspec
+ − 5127
+ − 5128 The following error-related macro is also defined:
+ − 5129
+ − 5130 @defspec ignore-errors forms@dots{}
+ − 5131 This executes @var{forms} exactly like a @code{progn}, except that
+ − 5132 errors are ignored during the @var{forms}. More precisely, if
+ − 5133 an error is signalled then @code{ignore-errors} immediately
+ − 5134 aborts execution of the @var{forms} and returns @code{nil}.
+ − 5135 If the @var{forms} complete successfully, @code{ignore-errors}
+ − 5136 returns the result of the last @var{form}.
+ − 5137 @end defspec
+ − 5138
+ − 5139 @node Efficiency Concerns, Common Lisp Compatibility, Assertions, Top
+ − 5140 @appendix Efficiency Concerns
+ − 5141
+ − 5142 @appendixsec Macros
+ − 5143
+ − 5144 @noindent
+ − 5145 Many of the advanced features of this package, such as @code{defun*},
+ − 5146 @code{loop}, and @code{setf}, are implemented as Lisp macros. In
+ − 5147 byte-compiled code, these complex notations will be expanded into
+ − 5148 equivalent Lisp code which is simple and efficient. For example,
+ − 5149 the forms
+ − 5150
+ − 5151 @example
+ − 5152 (incf i n)
+ − 5153 (push x (car p))
+ − 5154 @end example
+ − 5155
+ − 5156 @noindent
+ − 5157 are expanded at compile-time to the Lisp forms
+ − 5158
+ − 5159 @example
+ − 5160 (setq i (+ i n))
+ − 5161 (setcar p (cons x (car p)))
+ − 5162 @end example
+ − 5163
+ − 5164 @noindent
+ − 5165 which are the most efficient ways of doing these respective operations
+ − 5166 in Lisp. Thus, there is no performance penalty for using the more
+ − 5167 readable @code{incf} and @code{push} forms in your compiled code.
+ − 5168
+ − 5169 @emph{Interpreted} code, on the other hand, must expand these macros
+ − 5170 every time they are executed. For this reason it is strongly
+ − 5171 recommended that code making heavy use of macros be compiled.
+ − 5172 (The features labelled ``Special Form'' instead of ``Function'' in
+ − 5173 this manual are macros.) A loop using @code{incf} a hundred times
+ − 5174 will execute considerably faster if compiled, and will also
+ − 5175 garbage-collect less because the macro expansion will not have
+ − 5176 to be generated, used, and thrown away a hundred times.
+ − 5177
+ − 5178 You can find out how a macro expands by using the
+ − 5179 @code{cl-prettyexpand} function.
+ − 5180
+ − 5181 @defun cl-prettyexpand form &optional full
+ − 5182 This function takes a single Lisp form as an argument and inserts
+ − 5183 a nicely formatted copy of it in the current buffer (which must be
+ − 5184 in Lisp mode so that indentation works properly). It also expands
+ − 5185 all Lisp macros which appear in the form. The easiest way to use
+ − 5186 this function is to go to the @code{*scratch*} buffer and type, say,
+ − 5187
+ − 5188 @example
+ − 5189 (cl-prettyexpand '(loop for x below 10 collect x))
+ − 5190 @end example
+ − 5191
+ − 5192 @noindent
+ − 5193 and type @kbd{C-x C-e} immediately after the closing parenthesis;
+ − 5194 the expansion
+ − 5195
+ − 5196 @example
+ − 5197 (block nil
+ − 5198 (let* ((x 0)
+ − 5199 (G1004 nil))
+ − 5200 (while (< x 10)
+ − 5201 (setq G1004 (cons x G1004))
+ − 5202 (setq x (+ x 1)))
+ − 5203 (nreverse G1004)))
+ − 5204 @end example
+ − 5205
+ − 5206 @noindent
+ − 5207 will be inserted into the buffer. (The @code{block} macro is
+ − 5208 expanded differently in the interpreter and compiler, so
+ − 5209 @code{cl-prettyexpand} just leaves it alone. The temporary
+ − 5210 variable @code{G1004} was created by @code{gensym}.)
+ − 5211
+ − 5212 If the optional argument @var{full} is true, then @emph{all}
+ − 5213 macros are expanded, including @code{block}, @code{eval-when},
+ − 5214 and compiler macros. Expansion is done as if @var{form} were
+ − 5215 a top-level form in a file being compiled. For example,
+ − 5216
+ − 5217 @example
+ − 5218 (cl-prettyexpand '(pushnew 'x list))
+ − 5219 @print{} (setq list (adjoin 'x list))
+ − 5220 (cl-prettyexpand '(pushnew 'x list) t)
+ − 5221 @print{} (setq list (if (memq 'x list) list (cons 'x list)))
+ − 5222 (cl-prettyexpand '(caddr (member* 'a list)) t)
+ − 5223 @print{} (car (cdr (cdr (memq 'a list))))
+ − 5224 @end example
+ − 5225
+ − 5226 Note that @code{adjoin}, @code{caddr}, and @code{member*} all
+ − 5227 have built-in compiler macros to optimize them in common cases.
+ − 5228 @end defun
+ − 5229
+ − 5230 @ifinfo
+ − 5231 @example
+ − 5232
+ − 5233 @end example
+ − 5234 @end ifinfo
+ − 5235 @appendixsec Error Checking
+ − 5236
+ − 5237 @noindent
+ − 5238 Common Lisp compliance has in general not been sacrificed for the
+ − 5239 sake of efficiency. A few exceptions have been made for cases
+ − 5240 where substantial gains were possible at the expense of marginal
+ − 5241 incompatibility. One example is the use of @code{memq} (which is
+ − 5242 treated very efficiently by the byte-compiler) to scan for keyword
+ − 5243 arguments; this can become confused in rare cases when keyword
+ − 5244 symbols are used as both keywords and data values at once. This
+ − 5245 is extremely unlikely to occur in practical code, and the use of
+ − 5246 @code{memq} allows functions with keyword arguments to be nearly
+ − 5247 as fast as functions that use @code{&optional} arguments.
+ − 5248
+ − 5249 The Common Lisp standard (as embodied in Steele's book) uses the
+ − 5250 phrase ``it is an error if'' to indicate a situation which is not
+ − 5251 supposed to arise in complying programs; implementations are strongly
+ − 5252 encouraged but not required to signal an error in these situations.
+ − 5253 This package sometimes omits such error checking in the interest of
+ − 5254 compactness and efficiency. For example, @code{do} variable
+ − 5255 specifiers are supposed to be lists of one, two, or three forms;
+ − 5256 extra forms are ignored by this package rather than signalling a
+ − 5257 syntax error. The @code{endp} function is simply a synonym for
+ − 5258 @code{null} in this package. Functions taking keyword arguments
+ − 5259 will accept an odd number of arguments, treating the trailing
+ − 5260 keyword as if it were followed by the value @code{nil}.
+ − 5261
+ − 5262 Argument lists (as processed by @code{defun*} and friends)
+ − 5263 @emph{are} checked rigorously except for the minor point just
+ − 5264 mentioned; in particular, keyword arguments are checked for
+ − 5265 validity, and @code{&allow-other-keys} and @code{:allow-other-keys}
+ − 5266 are fully implemented. Keyword validity checking is slightly
+ − 5267 time consuming (though not too bad in byte-compiled code);
+ − 5268 you can use @code{&allow-other-keys} to omit this check. Functions
+ − 5269 defined in this package such as @code{find} and @code{member*}
+ − 5270 do check their keyword arguments for validity.
+ − 5271
+ − 5272 @ifinfo
+ − 5273 @example
+ − 5274
+ − 5275 @end example
+ − 5276 @end ifinfo
+ − 5277 @appendixsec Optimizing Compiler
+ − 5278
+ − 5279 @noindent
+ − 5280 The byte-compiler that comes with Emacs 18 normally fails to expand
+ − 5281 macros that appear in top-level positions in the file (i.e., outside
+ − 5282 of @code{defun}s or other enclosing forms). This would have
+ − 5283 disastrous consequences to programs that used such top-level macros
+ − 5284 as @code{defun*}, @code{eval-when}, and @code{defstruct}. To
+ − 5285 work around this problem, the @dfn{CL} package patches the Emacs
+ − 5286 18 compiler to expand top-level macros. This patch will apply to
+ − 5287 your own macros, too, if they are used in a top-level context.
+ − 5288 The patch will not harm versions of the Emacs 18 compiler which
+ − 5289 have already had a similar patch applied, nor will it affect the
+ − 5290 optimizing Emacs 19 byte-compiler written by Jamie Zawinski and
+ − 5291 Hallvard Furuseth. The patch is applied to the byte compiler's
+ − 5292 code in Emacs' memory, @emph{not} to the @file{bytecomp.elc} file
+ − 5293 stored on disk.
+ − 5294
+ − 5295 The Emacs 19 compiler (for Emacs 18) is available from various
+ − 5296 Emacs Lisp archive sites such as @code{archive.cis.ohio-state.edu}.
+ − 5297 Its use is highly recommended; many of the Common Lisp macros emit
+ − 5298 code which can be improved by optimization. In particular,
+ − 5299 @code{block}s (whether explicit or implicit in constructs like
+ − 5300 @code{defun*} and @code{loop}) carry a fair run-time penalty; the
+ − 5301 optimizing compiler removes @code{block}s which are not actually
+ − 5302 referenced by @code{return} or @code{return-from} inside the block.
+ − 5303
+ − 5304 @node Common Lisp Compatibility, Old CL Compatibility, Efficiency Concerns, Top
+ − 5305 @appendix Common Lisp Compatibility
+ − 5306
+ − 5307 @noindent
+ − 5308 Following is a list of all known incompatibilities between this
+ − 5309 package and Common Lisp as documented in Steele (2nd edition).
+ − 5310
+ − 5311 Certain function names, such as @code{member}, @code{assoc}, and
+ − 5312 @code{floor}, were already taken by (incompatible) Emacs Lisp
+ − 5313 functions; this package appends @samp{*} to the names of its
+ − 5314 Common Lisp versions of these functions.
+ − 5315
+ − 5316 The word @code{defun*} is required instead of @code{defun} in order
+ − 5317 to use extended Common Lisp argument lists in a function. Likewise,
+ − 5318 @code{defmacro*} and @code{function*} are versions of those forms
+ − 5319 which understand full-featured argument lists. The @code{&whole}
+ − 5320 keyword does not work in @code{defmacro} argument lists (except
+ − 5321 inside recursive argument lists).
+ − 5322
+ − 5323 In order to allow an efficient implementation, keyword arguments use
+ − 5324 a slightly cheesy parser which may be confused if a keyword symbol
+ − 5325 is passed as the @emph{value} of another keyword argument.
+ − 5326 (Specifically, @code{(memq :@var{keyword} @var{rest-of-arguments})}
+ − 5327 is used to scan for @code{:@var{keyword}} among the supplied
+ − 5328 keyword arguments.)
+ − 5329
+ − 5330 The @code{eql} and @code{equal} predicates do not distinguish
+ − 5331 between IEEE floating-point plus and minus zero. The @code{equalp}
+ − 5332 predicate has several differences with Common Lisp; @pxref{Predicates}.
+ − 5333
+ − 5334 The @code{setf} mechanism is entirely compatible, except that
+ − 5335 setf-methods return a list of five values rather than five
+ − 5336 values directly. Also, the new ``@code{setf} function'' concept
+ − 5337 (typified by @code{(defun (setf foo) @dots{})}) is not implemented.
+ − 5338
+ − 5339 The @code{do-all-symbols} form is the same as @code{do-symbols}
+ − 5340 with no @var{obarray} argument. In Common Lisp, this form would
+ − 5341 iterate over all symbols in all packages. Since Emacs obarrays
+ − 5342 are not a first-class package mechanism, there is no way for
+ − 5343 @code{do-all-symbols} to locate any but the default obarray.
+ − 5344
+ − 5345 The @code{loop} macro is complete except that @code{loop-finish}
+ − 5346 and type specifiers are unimplemented.
+ − 5347
+ − 5348 The multiple-value return facility treats lists as multiple
+ − 5349 values, since Emacs Lisp cannot support multiple return values
+ − 5350 directly. The macros will be compatible with Common Lisp if
+ − 5351 @code{values} or @code{values-list} is always used to return to
+ − 5352 a @code{multiple-value-bind} or other multiple-value receiver;
+ − 5353 if @code{values} is used without @code{multiple-value-@dots{}}
+ − 5354 or vice-versa the effect will be different from Common Lisp.
+ − 5355
+ − 5356 Many Common Lisp declarations are ignored, and others match
+ − 5357 the Common Lisp standard in concept but not in detail. For
+ − 5358 example, local @code{special} declarations, which are purely
+ − 5359 advisory in Emacs Lisp, do not rigorously obey the scoping rules
+ − 5360 set down in Steele's book.
+ − 5361
+ − 5362 The variable @code{*gensym-counter*} starts out with a pseudo-random
+ − 5363 value rather than with zero. This is to cope with the fact that
+ − 5364 generated symbols become interned when they are written to and
+ − 5365 loaded back from a file.
+ − 5366
+ − 5367 The @code{defstruct} facility is compatible, except that structures
+ − 5368 are of type @code{:type vector :named} by default rather than some
+ − 5369 special, distinct type. Also, the @code{:type} slot option is ignored.
+ − 5370
+ − 5371 The second argument of @code{check-type} is treated differently.
+ − 5372
+ − 5373 @node Old CL Compatibility, Porting Common Lisp, Common Lisp Compatibility, Top
+ − 5374 @appendix Old CL Compatibility
+ − 5375
+ − 5376 @noindent
+ − 5377 Following is a list of all known incompatibilities between this package
+ − 5378 and the older Quiroz @file{cl.el} package.
+ − 5379
+ − 5380 This package's emulation of multiple return values in functions is
+ − 5381 incompatible with that of the older package. That package attempted
+ − 5382 to come as close as possible to true Common Lisp multiple return
+ − 5383 values; unfortunately, it could not be 100% reliable and so was prone
+ − 5384 to occasional surprises if used freely. This package uses a simpler
+ − 5385 method, namely replacing multiple values with lists of values, which
+ − 5386 is more predictable though more noticeably different from Common Lisp.
+ − 5387
+ − 5388 The @code{defkeyword} form and @code{keywordp} function are not
+ − 5389 implemented in this package.
+ − 5390
+ − 5391 The @code{member}, @code{floor}, @code{ceiling}, @code{truncate},
+ − 5392 @code{round}, @code{mod}, and @code{rem} functions are suffixed
+ − 5393 by @samp{*} in this package to avoid collision with existing
+ − 5394 functions in Emacs 18 or Emacs 19. The older package simply
+ − 5395 redefined these functions, overwriting the built-in meanings and
+ − 5396 causing serious portability problems with Emacs 19. (Some more
+ − 5397 recent versions of the Quiroz package changed the names to
+ − 5398 @code{cl-member}, etc.; this package defines the latter names as
+ − 5399 aliases for @code{member*}, etc.)
+ − 5400
+ − 5401 Certain functions in the old package which were buggy or inconsistent
+ − 5402 with the Common Lisp standard are incompatible with the conforming
+ − 5403 versions in this package. For example, @code{eql} and @code{member}
+ − 5404 were synonyms for @code{eq} and @code{memq} in that package, @code{setf}
+ − 5405 failed to preserve correct order of evaluation of its arguments, etc.
+ − 5406
+ − 5407 Finally, unlike the older package, this package is careful to
+ − 5408 prefix all of its internal names with @code{cl-}. Except for a
+ − 5409 few functions which are explicitly defined as additional features
+ − 5410 (such as @code{floatp-safe} and @code{letf}), this package does not
+ − 5411 export any non-@samp{cl-} symbols which are not also part of Common
+ − 5412 Lisp.
+ − 5413
+ − 5414 @ifinfo
+ − 5415 @example
+ − 5416
+ − 5417 @end example
+ − 5418 @end ifinfo
+ − 5419 @appendixsec The @code{cl-compat} package
+ − 5420
+ − 5421 @noindent
+ − 5422 The @dfn{CL} package includes emulations of some features of the
+ − 5423 old @file{cl.el}, in the form of a compatibility package
+ − 5424 @code{cl-compat}. To use it, put @code{(require 'cl-compat)} in
+ − 5425 your program.
+ − 5426
+ − 5427 The old package defined a number of internal routines without
+ − 5428 @code{cl-} prefixes or other annotations. Call to these routines
+ − 5429 may have crept into existing Lisp code. @code{cl-compat}
+ − 5430 provides emulations of the following internal routines:
+ − 5431 @code{pair-with-newsyms}, @code{zip-lists}, @code{unzip-lists},
+ − 5432 @code{reassemble-arglists}, @code{duplicate-symbols-p},
+ − 5433 @code{safe-idiv}.
+ − 5434
+ − 5435 Some @code{setf} forms translated into calls to internal
+ − 5436 functions that user code might call directly. The functions
+ − 5437 @code{setnth}, @code{setnthcdr}, and @code{setelt} fall in
+ − 5438 this category; they are defined by @code{cl-compat}, but the
+ − 5439 best fix is to change to use @code{setf} properly.
+ − 5440
+ − 5441 The @code{cl-compat} file defines the keyword functions
+ − 5442 @code{keywordp}, @code{keyword-of}, and @code{defkeyword},
+ − 5443 which are not defined by the new @dfn{CL} package because the
+ − 5444 use of keywords as data is discouraged.
+ − 5445
+ − 5446 The @code{build-klist} mechanism for parsing keyword arguments
+ − 5447 is emulated by @code{cl-compat}; the @code{with-keyword-args}
+ − 5448 macro is not, however, and in any case it's best to change to
+ − 5449 use the more natural keyword argument processing offered by
+ − 5450 @code{defun*}.
+ − 5451
+ − 5452 Multiple return values are treated differently by the two
+ − 5453 Common Lisp packages. The old package's method was more
+ − 5454 compatible with true Common Lisp, though it used heuristics
+ − 5455 that caused it to report spurious multiple return values in
+ − 5456 certain cases. The @code{cl-compat} package defines a set
+ − 5457 of multiple-value macros that are compatible with the old
+ − 5458 CL package; again, they are heuristic in nature, but they
+ − 5459 are guaranteed to work in any case where the old package's
+ − 5460 macros worked. To avoid name collision with the ``official''
+ − 5461 multiple-value facilities, the ones in @code{cl-compat} have
+ − 5462 capitalized names: @code{Values}, @code{Values-list},
+ − 5463 @code{Multiple-value-bind}, etc.
+ − 5464
+ − 5465 The functions @code{cl-floor}, @code{cl-ceiling}, @code{cl-truncate},
+ − 5466 and @code{cl-round} are defined by @code{cl-compat} to use the
+ − 5467 old-style multiple-value mechanism, just as they did in the old
+ − 5468 package. The newer @code{floor*} and friends return their two
+ − 5469 results in a list rather than as multiple values. Note that
+ − 5470 older versions of the old package used the unadorned names
+ − 5471 @code{floor}, @code{ceiling}, etc.; @code{cl-compat} cannot use
+ − 5472 these names because they conflict with Emacs 19 built-ins.
+ − 5473
+ − 5474 @node Porting Common Lisp, Function Index, Old CL Compatibility, Top
+ − 5475 @appendix Porting Common Lisp
+ − 5476
+ − 5477 @noindent
+ − 5478 This package is meant to be used as an extension to Emacs Lisp,
+ − 5479 not as an Emacs implementation of true Common Lisp. Some of the
+ − 5480 remaining differences between Emacs Lisp and Common Lisp make it
+ − 5481 difficult to port large Common Lisp applications to Emacs. For
+ − 5482 one, some of the features in this package are not fully compliant
+ − 5483 with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there
+ − 5484 are also quite a few features that this package does not provide
+ − 5485 at all. Here are some major omissions that you will want watch out
+ − 5486 for when bringing Common Lisp code into Emacs.
+ − 5487
+ − 5488 @itemize @bullet
+ − 5489 @item
+ − 5490 Case-insensitivity. Symbols in Common Lisp are case-insensitive
+ − 5491 by default. Some programs refer to a function or variable as
+ − 5492 @code{foo} in one place and @code{Foo} or @code{FOO} in another.
+ − 5493 Emacs Lisp will treat these as three distinct symbols.
+ − 5494
+ − 5495 Some Common Lisp code is written in all upper-case. While Emacs
+ − 5496 is happy to let the program's own functions and variables use
+ − 5497 this convention, calls to Lisp builtins like @code{if} and
+ − 5498 @code{defun} will have to be changed to lower-case.
+ − 5499
+ − 5500 @item
+ − 5501 Lexical scoping. In Common Lisp, function arguments and @code{let}
+ − 5502 bindings apply only to references physically within their bodies
+ − 5503 (or within macro expansions in their bodies). Emacs Lisp, by
+ − 5504 contrast, uses @dfn{dynamic scoping} wherein a binding to a
+ − 5505 variable is visible even inside functions called from the body.
+ − 5506
+ − 5507 Variables in Common Lisp can be made dynamically scoped by
+ − 5508 declaring them @code{special} or using @code{defvar}. In Emacs
+ − 5509 Lisp it is as if all variables were declared @code{special}.
+ − 5510
+ − 5511 Often you can use code that was written for lexical scoping
+ − 5512 even in a dynamically scoped Lisp, but not always. Here is
+ − 5513 an example of a Common Lisp code fragment that would fail in
+ − 5514 Emacs Lisp:
+ − 5515
+ − 5516 @example
+ − 5517 (defun map-odd-elements (func list)
+ − 5518 (loop for x in list
+ − 5519 for flag = t then (not flag)
+ − 5520 collect (if flag x (funcall func x))))
+ − 5521
+ − 5522 (defun add-odd-elements (list x)
+ − 5523 (map-odd-elements (function (lambda (a) (+ a x))) list))
+ − 5524 @end example
+ − 5525
+ − 5526 @noindent
+ − 5527 In Common Lisp, the two functions' usages of @code{x} are completely
+ − 5528 independent. In Emacs Lisp, the binding to @code{x} made by
+ − 5529 @code{add-odd-elements} will have been hidden by the binding
+ − 5530 in @code{map-odd-elements} by the time the @code{(+ a x)} function
+ − 5531 is called.
+ − 5532
+ − 5533 (This package avoids such problems in its own mapping functions
+ − 5534 by using names like @code{cl-x} instead of @code{x} internally;
+ − 5535 as long as you don't use the @code{cl-} prefix for your own
+ − 5536 variables no collision can occur.)
+ − 5537
+ − 5538 @xref{Lexical Bindings}, for a description of the @code{lexical-let}
+ − 5539 form which establishes a Common Lisp-style lexical binding, and some
+ − 5540 examples of how it differs from Emacs' regular @code{let}.
+ − 5541
+ − 5542 @item
+ − 5543 Common Lisp allows the shorthand @code{#'x} to stand for
+ − 5544 @code{(function x)}, just as @code{'x} stands for @code{(quote x)}.
+ − 5545 In Common Lisp, one traditionally uses @code{#'} notation when
+ − 5546 referring to the name of a function. In Emacs Lisp, it works
+ − 5547 just as well to use a regular quote:
+ − 5548
+ − 5549 @example
442
+ − 5550 (loop for x in y by #'cddr collect (mapcar #'plusp x)) ; Common Lisp
+ − 5551 (loop for x in y by 'cddr collect (mapcar 'plusp x)) ; Emacs Lisp
428
+ − 5552 @end example
+ − 5553
+ − 5554 When @code{#'} introduces a @code{lambda} form, it is best to
+ − 5555 write out @code{(function ...)} longhand in Emacs Lisp. You can
+ − 5556 use a regular quote, but then the byte-compiler won't know that
+ − 5557 the @code{lambda} expression is code that can be compiled.
+ − 5558
+ − 5559 @example
+ − 5560 (mapcar #'(lambda (x) (* x 2)) list) ; Common Lisp
+ − 5561 (mapcar (function (lambda (x) (* x 2))) list) ; Emacs Lisp
+ − 5562 @end example
+ − 5563
+ − 5564 XEmacs supports @code{#'} notation starting with version 19.8.
+ − 5565
+ − 5566 @item
+ − 5567 Reader macros. Common Lisp includes a second type of macro that
+ − 5568 works at the level of individual characters. For example, Common
+ − 5569 Lisp implements the quote notation by a reader macro called @code{'},
+ − 5570 whereas Emacs Lisp's parser just treats quote as a special case.
+ − 5571 Some Lisp packages use reader macros to create special syntaxes
+ − 5572 for themselves, which the Emacs parser is incapable of reading.
+ − 5573
+ − 5574 @item
+ − 5575 Other syntactic features. Common Lisp provides a number of
+ − 5576 notations beginning with @code{#} that the Emacs Lisp parser
+ − 5577 won't understand. For example, @samp{#| ... |#} is an
+ − 5578 alternate comment notation, and @samp{#+lucid (foo)} tells
+ − 5579 the parser to ignore the @code{(foo)} except in Lucid Common
+ − 5580 Lisp.
+ − 5581
+ − 5582 The number prefixes `#b', `#o', and `#x', however, are supported
+ − 5583 by the Emacs Lisp parser to represent numbers in binary, octal,
+ − 5584 and hexadecimal notation (or radix), just like in Common Lisp.
+ − 5585
+ − 5586 @item
+ − 5587 Packages. In Common Lisp, symbols are divided into @dfn{packages}.
+ − 5588 Symbols that are Lisp built-ins are typically stored in one package;
+ − 5589 symbols that are vendor extensions are put in another, and each
+ − 5590 application program would have a package for its own symbols.
+ − 5591 Certain symbols are ``exported'' by a package and others are
+ − 5592 internal; certain packages ``use'' or import the exported symbols
+ − 5593 of other packages. To access symbols that would not normally be
+ − 5594 visible due to this importing and exporting, Common Lisp provides
+ − 5595 a syntax like @code{package:symbol} or @code{package::symbol}.
+ − 5596
+ − 5597 Emacs Lisp has a single namespace for all interned symbols, and
+ − 5598 then uses a naming convention of putting a prefix like @code{cl-}
+ − 5599 in front of the name. Some Emacs packages adopt the Common Lisp-like
+ − 5600 convention of using @code{cl:} or @code{cl::} as the prefix.
+ − 5601 However, the Emacs parser does not understand colons and just
+ − 5602 treats them as part of the symbol name. Thus, while @code{mapcar}
+ − 5603 and @code{lisp:mapcar} may refer to the same symbol in Common
+ − 5604 Lisp, they are totally distinct in Emacs Lisp. Common Lisp
+ − 5605 programs which refer to a symbol by the full name sometimes
+ − 5606 and the short name other times will not port cleanly to Emacs.
+ − 5607
+ − 5608 Emacs Lisp does have a concept of ``obarrays,'' which are
+ − 5609 package-like collections of symbols, but this feature is not
+ − 5610 strong enough to be used as a true package mechanism.
+ − 5611
+ − 5612 @item
+ − 5613 Keywords. The notation @code{:test-not} in Common Lisp really
+ − 5614 is a shorthand for @code{keyword:test-not}; keywords are just
+ − 5615 symbols in a built-in @code{keyword} package with the special
+ − 5616 property that all its symbols are automatically self-evaluating.
+ − 5617 Common Lisp programs often use keywords liberally to avoid
+ − 5618 having to use quotes.
+ − 5619
+ − 5620 In Emacs Lisp a keyword is just a symbol whose name begins with
+ − 5621 a colon; since the Emacs parser does not treat them specially,
+ − 5622 they have to be explicitly made self-evaluating by a statement
+ − 5623 like @code{(setq :test-not ':test-not)}. This package arranges
+ − 5624 to execute such a statement whenever @code{defun*} or some
+ − 5625 other form sees a keyword being used as an argument. Common
+ − 5626 Lisp code that assumes that a symbol @code{:mumble} will be
+ − 5627 self-evaluating even though it was never introduced by a
+ − 5628 @code{defun*} will have to be fixed.
+ − 5629
+ − 5630 @item
+ − 5631 The @code{format} function is quite different between Common
+ − 5632 Lisp and Emacs Lisp. It takes an additional ``destination''
+ − 5633 argument before the format string. A destination of @code{nil}
+ − 5634 means to format to a string as in Emacs Lisp; a destination
+ − 5635 of @code{t} means to write to the terminal (similar to
+ − 5636 @code{message} in Emacs). Also, format control strings are
+ − 5637 utterly different; @code{~} is used instead of @code{%} to
+ − 5638 introduce format codes, and the set of available codes is
+ − 5639 much richer. There are no notations like @code{\n} for
+ − 5640 string literals; instead, @code{format} is used with the
+ − 5641 ``newline'' format code, @code{~%}. More advanced formatting
+ − 5642 codes provide such features as paragraph filling, case
+ − 5643 conversion, and even loops and conditionals.
+ − 5644
+ − 5645 While it would have been possible to implement most of Common
+ − 5646 Lisp @code{format} in this package (under the name @code{format*},
+ − 5647 of course), it was not deemed worthwhile. It would have required
+ − 5648 a huge amount of code to implement even a decent subset of
+ − 5649 @code{format*}, yet the functionality it would provide over
+ − 5650 Emacs Lisp's @code{format} would rarely be useful.
+ − 5651
+ − 5652 @item
+ − 5653 Vector constants use square brackets in Emacs Lisp, but
+ − 5654 @code{#(a b c)} notation in Common Lisp. To further complicate
+ − 5655 matters, Emacs 19 introduces its own @code{#(} notation for
+ − 5656 something entirely different---strings with properties.
+ − 5657
+ − 5658 @item
+ − 5659 Characters are distinct from integers in Common Lisp. The
+ − 5660 notation for character constants is also different: @code{#\A}
+ − 5661 instead of @code{?A}. Also, @code{string=} and @code{string-equal}
+ − 5662 are synonyms in Emacs Lisp whereas the latter is case-insensitive
+ − 5663 in Common Lisp.
+ − 5664
+ − 5665 @item
+ − 5666 Data types. Some Common Lisp data types do not exist in Emacs
+ − 5667 Lisp. Rational numbers and complex numbers are not present,
+ − 5668 nor are large integers (all integers are ``fixnums''). All
+ − 5669 arrays are one-dimensional. There are no readtables or pathnames;
+ − 5670 streams are a set of existing data types rather than a new data
+ − 5671 type of their own. Hash tables, random-states, structures, and
+ − 5672 packages (obarrays) are built from Lisp vectors or lists rather
+ − 5673 than being distinct types.
+ − 5674
+ − 5675 @item
+ − 5676 The Common Lisp Object System (CLOS) is not implemented,
+ − 5677 nor is the Common Lisp Condition System.
+ − 5678
+ − 5679 @item
+ − 5680 Common Lisp features that are completely redundant with Emacs
+ − 5681 Lisp features of a different name generally have not been
+ − 5682 implemented. For example, Common Lisp writes @code{defconstant}
+ − 5683 where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list}
+ − 5684 takes its arguments in different ways in the two Lisps but does
+ − 5685 exactly the same thing, so this package has not bothered to
+ − 5686 implement a Common Lisp-style @code{make-list}.
+ − 5687
+ − 5688 @item
+ − 5689 A few more notable Common Lisp features not included in this
+ − 5690 package: @code{compiler-let}, @code{tagbody}, @code{prog},
+ − 5691 @code{ldb/dpb}, @code{parse-integer}, @code{cerror}.
+ − 5692
+ − 5693 @item
+ − 5694 Recursion. While recursion works in Emacs Lisp just like it
+ − 5695 does in Common Lisp, various details of the Emacs Lisp system
+ − 5696 and compiler make recursion much less efficient than it is in
+ − 5697 most Lisps. Some schools of thought prefer to use recursion
+ − 5698 in Lisp over other techniques; they would sum a list of
+ − 5699 numbers using something like
+ − 5700
+ − 5701 @example
+ − 5702 (defun sum-list (list)
+ − 5703 (if list
+ − 5704 (+ (car list) (sum-list (cdr list)))
+ − 5705 0))
+ − 5706 @end example
+ − 5707
+ − 5708 @noindent
+ − 5709 where a more iteratively-minded programmer might write one of
+ − 5710 these forms:
+ − 5711
+ − 5712 @example
+ − 5713 (let ((total 0)) (dolist (x my-list) (incf total x)) total)
+ − 5714 (loop for x in my-list sum x)
+ − 5715 @end example
+ − 5716
+ − 5717 While this would be mainly a stylistic choice in most Common Lisps,
+ − 5718 in Emacs Lisp you should be aware that the iterative forms are
+ − 5719 much faster than recursion. Also, Lisp programmers will want to
+ − 5720 note that the current Emacs Lisp compiler does not optimize tail
+ − 5721 recursion.
+ − 5722 @end itemize
+ − 5723
+ − 5724 @node Function Index, Variable Index, Porting Common Lisp, Top
+ − 5725 @unnumbered Function Index
+ − 5726
+ − 5727 @printindex fn
+ − 5728
+ − 5729 @node Variable Index, , Function Index, Top
+ − 5730 @unnumbered Variable Index
+ − 5731
+ − 5732 @printindex vr
+ − 5733
+ − 5734 @contents
+ − 5735 @bye