| 1 | \input texinfo @c -*-texinfo-*- |
| 2 | @setfilename ../../info/cl |
| 3 | @settitle Common Lisp Extensions |
| 4 | @include emacsver.texi |
| 5 | |
| 6 | @copying |
| 7 | This file documents the GNU Emacs Common Lisp emulation package. |
| 8 | |
| 9 | Copyright @copyright{} 1993, 2001--2013 Free Software Foundation, Inc. |
| 10 | |
| 11 | @quotation |
| 12 | Permission is granted to copy, distribute and/or modify this document |
| 13 | under the terms of the GNU Free Documentation License, Version 1.3 or |
| 14 | any later version published by the Free Software Foundation; with no |
| 15 | Invariant Sections, with the Front-Cover texts being ``A GNU Manual'', |
| 16 | and with the Back-Cover Texts as in (a) below. A copy of the license |
| 17 | is included in the section entitled ``GNU Free Documentation License''. |
| 18 | |
| 19 | (a) The FSF's Back-Cover Text is: ``You have the freedom to copy and |
| 20 | modify this GNU manual.'' |
| 21 | @end quotation |
| 22 | @end copying |
| 23 | |
| 24 | @dircategory Emacs lisp libraries |
| 25 | @direntry |
| 26 | * CL: (cl). Partial Common Lisp support for Emacs Lisp. |
| 27 | @end direntry |
| 28 | |
| 29 | @finalout |
| 30 | |
| 31 | @titlepage |
| 32 | @sp 6 |
| 33 | @center @titlefont{Common Lisp Extensions} |
| 34 | @sp 4 |
| 35 | @center For GNU Emacs Lisp |
| 36 | @sp 1 |
| 37 | @center as distributed with Emacs @value{EMACSVER} |
| 38 | @sp 5 |
| 39 | @center Dave Gillespie |
| 40 | @center daveg@@synaptics.com |
| 41 | @page |
| 42 | @vskip 0pt plus 1filll |
| 43 | @insertcopying |
| 44 | @end titlepage |
| 45 | |
| 46 | @contents |
| 47 | |
| 48 | @ifnottex |
| 49 | @node Top |
| 50 | @top GNU Emacs Common Lisp Emulation |
| 51 | |
| 52 | @insertcopying |
| 53 | @end ifnottex |
| 54 | |
| 55 | @menu |
| 56 | * Overview:: Basics, usage, organization, naming conventions. |
| 57 | * Program Structure:: Arglists, @code{cl-eval-when}. |
| 58 | * Predicates:: Type predicates and equality predicates. |
| 59 | * Control Structure:: Assignment, conditionals, blocks, looping. |
| 60 | * Macros:: Destructuring, compiler macros. |
| 61 | * Declarations:: @code{cl-proclaim}, @code{cl-declare}, etc. |
| 62 | * Symbols:: Property lists, creating symbols. |
| 63 | * Numbers:: Predicates, functions, random numbers. |
| 64 | * Sequences:: Mapping, functions, searching, sorting. |
| 65 | * Lists:: Functions, substitution, sets, associations. |
| 66 | * Structures:: @code{cl-defstruct}. |
| 67 | * Assertions:: Assertions and type checking. |
| 68 | |
| 69 | Appendices |
| 70 | * Efficiency Concerns:: Hints and techniques. |
| 71 | * Common Lisp Compatibility:: All known differences with Steele. |
| 72 | * Porting Common Lisp:: Hints for porting Common Lisp code. |
| 73 | * Obsolete Features:: Obsolete features. |
| 74 | * GNU Free Documentation License:: The license for this documentation. |
| 75 | |
| 76 | Indexes |
| 77 | * Function Index:: An entry for each documented function. |
| 78 | * Variable Index:: An entry for each documented variable. |
| 79 | @end menu |
| 80 | |
| 81 | @node Overview |
| 82 | @chapter Overview |
| 83 | |
| 84 | @noindent |
| 85 | This document describes a set of Emacs Lisp facilities borrowed from |
| 86 | Common Lisp. All the facilities are described here in detail. While |
| 87 | this document does not assume any prior knowledge of Common Lisp, it |
| 88 | does assume a basic familiarity with Emacs Lisp. |
| 89 | |
| 90 | Common Lisp is a huge language, and Common Lisp systems tend to be |
| 91 | massive and extremely complex. Emacs Lisp, by contrast, is rather |
| 92 | minimalist in the choice of Lisp features it offers the programmer. |
| 93 | As Emacs Lisp programmers have grown in number, and the applications |
| 94 | they write have grown more ambitious, it has become clear that Emacs |
| 95 | Lisp could benefit from many of the conveniences of Common Lisp. |
| 96 | |
| 97 | The @dfn{CL} package adds a number of Common Lisp functions and |
| 98 | control structures to Emacs Lisp. While not a 100% complete |
| 99 | implementation of Common Lisp, it adds enough functionality |
| 100 | to make Emacs Lisp programming significantly more convenient. |
| 101 | |
| 102 | Some Common Lisp features have been omitted from this package |
| 103 | for various reasons: |
| 104 | |
| 105 | @itemize @bullet |
| 106 | @item |
| 107 | Some features are too complex or bulky relative to their benefit |
| 108 | to Emacs Lisp programmers. CLOS and Common Lisp streams are fine |
| 109 | examples of this group. (The separate package EIEIO implements |
| 110 | a subset of CLOS functionality. @xref{Top, , Introduction, eieio, EIEIO}.) |
| 111 | |
| 112 | @item |
| 113 | Other features cannot be implemented without modification to the |
| 114 | Emacs Lisp interpreter itself, such as multiple return values, |
| 115 | case-insensitive symbols, and complex numbers. |
| 116 | This package generally makes no attempt to emulate these features. |
| 117 | |
| 118 | @end itemize |
| 119 | |
| 120 | This package was originally written by Dave Gillespie, |
| 121 | @file{daveg@@synaptics.com}, as a total rewrite of an earlier 1986 |
| 122 | @file{cl.el} package by Cesar Quiroz. Care has been taken to ensure |
| 123 | that each function is defined efficiently, concisely, and with minimal |
| 124 | impact on the rest of the Emacs environment. Stefan Monnier added the |
| 125 | file @file{cl-lib.el} and rationalized the namespace for Emacs 24.3. |
| 126 | |
| 127 | @menu |
| 128 | * Usage:: How to use this package. |
| 129 | * Organization:: The package's component files. |
| 130 | * Naming Conventions:: Notes on function names. |
| 131 | @end menu |
| 132 | |
| 133 | @node Usage |
| 134 | @section Usage |
| 135 | |
| 136 | @noindent |
| 137 | This package is distributed with Emacs, so there is no need |
| 138 | to install any additional files in order to start using it. Lisp code |
| 139 | that uses features from this package should simply include at |
| 140 | the beginning: |
| 141 | |
| 142 | @example |
| 143 | (require 'cl-lib) |
| 144 | @end example |
| 145 | |
| 146 | @noindent |
| 147 | You may wish to add such a statement to your init file, if you |
| 148 | make frequent use of features from this package. |
| 149 | |
| 150 | @node Organization |
| 151 | @section Organization |
| 152 | |
| 153 | @noindent |
| 154 | The Common Lisp package is organized into four main files: |
| 155 | |
| 156 | @table @file |
| 157 | @item cl-lib.el |
| 158 | This is the main file, which contains basic functions |
| 159 | and information about the package. This file is relatively compact. |
| 160 | |
| 161 | @item cl-extra.el |
| 162 | This file contains the larger, more complex or unusual functions. |
| 163 | It is kept separate so that packages which only want to use Common |
| 164 | Lisp fundamentals like the @code{cl-incf} function won't need to pay |
| 165 | the overhead of loading the more advanced functions. |
| 166 | |
| 167 | @item cl-seq.el |
| 168 | This file contains most of the advanced functions for operating |
| 169 | on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}. |
| 170 | |
| 171 | @item cl-macs.el |
| 172 | This file contains the features that are macros instead of functions. |
| 173 | Macros expand when the caller is compiled, not when it is run, so the |
| 174 | macros generally only need to be present when the byte-compiler is |
| 175 | running (or when the macros are used in uncompiled code). Most of the |
| 176 | macros of this package are isolated in @file{cl-macs.el} so that they |
| 177 | won't take up memory unless you are compiling. |
| 178 | @end table |
| 179 | |
| 180 | The file @file{cl-lib.el} includes all necessary @code{autoload} |
| 181 | commands for the functions and macros in the other three files. |
| 182 | All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el} |
| 183 | will take care of pulling in the other files when they are |
| 184 | needed. |
| 185 | |
| 186 | There is another file, @file{cl.el}, which was the main entry point to |
| 187 | this package prior to Emacs 24.3. Nowadays, it is replaced by |
| 188 | @file{cl-lib.el}. The two provide the same features (in most cases), |
| 189 | but use different function names (in fact, @file{cl.el} mainly just |
| 190 | defines aliases to the @file{cl-lib.el} definitions). Where |
| 191 | @file{cl-lib.el} defines a function called, for example, |
| 192 | @code{cl-incf}, @file{cl.el} uses the same name but without the |
| 193 | @samp{cl-} prefix, e.g., @code{incf} in this example. There are a few |
| 194 | exceptions to this. First, functions such as @code{cl-defun} where |
| 195 | the unprefixed version was already used for a standard Emacs Lisp |
| 196 | function. In such cases, the @file{cl.el} version adds a @samp{*} |
| 197 | suffix, e.g., @code{defun*}. Second, there are some obsolete features |
| 198 | that are only implemented in @file{cl.el}, not in @file{cl-lib.el}, |
| 199 | because they are replaced by other standard Emacs Lisp features. |
| 200 | Finally, in a very few cases the old @file{cl.el} versions do not |
| 201 | behave in exactly the same way as the @file{cl-lib.el} versions. |
| 202 | @xref{Obsolete Features}. |
| 203 | @c There is also cl-mapc, which was called cl-mapc even before cl-lib.el. |
| 204 | @c But not autoloaded, so maybe not much used? |
| 205 | |
| 206 | Since the old @file{cl.el} does not use a clean namespace, Emacs has a |
| 207 | policy that packages distributed with Emacs must not load @code{cl} at |
| 208 | run time. (It is ok for them to load @code{cl} at @emph{compile} |
| 209 | time, with @code{eval-when-compile}, and use the macros it provides.) |
| 210 | There is no such restriction on the use of @code{cl-lib}. New code |
| 211 | should use @code{cl-lib} rather than @code{cl}. |
| 212 | |
| 213 | There is one more file, @file{cl-compat.el}, which defines some |
| 214 | routines from the older Quiroz @file{cl.el} package that are not otherwise |
| 215 | present in the new package. This file is obsolete and should not be |
| 216 | used in new code. |
| 217 | |
| 218 | @node Naming Conventions |
| 219 | @section Naming Conventions |
| 220 | |
| 221 | @noindent |
| 222 | Except where noted, all functions defined by this package have the |
| 223 | same calling conventions as their Common Lisp counterparts, and |
| 224 | names that are those of Common Lisp plus a @samp{cl-} prefix. |
| 225 | |
| 226 | Internal function and variable names in the package are prefixed |
| 227 | by @code{cl--}. Here is a complete list of functions prefixed by |
| 228 | @code{cl-} that were @emph{not} taken from Common Lisp: |
| 229 | |
| 230 | @example |
| 231 | cl-callf cl-callf2 cl-defsubst |
| 232 | cl-letf cl-letf* |
| 233 | @end example |
| 234 | |
| 235 | @c This is not uninteresting I suppose, but is of zero practical relevance |
| 236 | @c to the user, and seems like a hostage to changing implementation details. |
| 237 | The following simple functions and macros are defined in @file{cl-lib.el}; |
| 238 | they do not cause other components like @file{cl-extra} to be loaded. |
| 239 | |
| 240 | @example |
| 241 | cl-evenp cl-oddp cl-minusp |
| 242 | cl-plusp cl-endp cl-subst |
| 243 | cl-copy-list cl-list* cl-ldiff |
| 244 | cl-rest cl-decf [1] cl-incf [1] |
| 245 | cl-acons cl-adjoin [2] cl-pairlis |
| 246 | cl-pushnew [1,2] cl-declaim cl-proclaim |
| 247 | cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth |
| 248 | cl-mapcar [3] |
| 249 | @end example |
| 250 | |
| 251 | @noindent |
| 252 | [1] Only when @var{place} is a plain variable name. |
| 253 | |
| 254 | @noindent |
| 255 | [2] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified, |
| 256 | and @code{:key} is not used. |
| 257 | |
| 258 | @noindent |
| 259 | [3] Only for one sequence argument or two list arguments. |
| 260 | |
| 261 | @node Program Structure |
| 262 | @chapter Program Structure |
| 263 | |
| 264 | @noindent |
| 265 | This section describes features of this package that have to |
| 266 | do with programs as a whole: advanced argument lists for functions, |
| 267 | and the @code{cl-eval-when} construct. |
| 268 | |
| 269 | @menu |
| 270 | * Argument Lists:: @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}. |
| 271 | * Time of Evaluation:: The @code{cl-eval-when} construct. |
| 272 | @end menu |
| 273 | |
| 274 | @node Argument Lists |
| 275 | @section Argument Lists |
| 276 | |
| 277 | @noindent |
| 278 | Emacs Lisp's notation for argument lists of functions is a subset of |
| 279 | the Common Lisp notation. As well as the familiar @code{&optional} |
| 280 | and @code{&rest} markers, Common Lisp allows you to specify default |
| 281 | values for optional arguments, and it provides the additional markers |
| 282 | @code{&key} and @code{&aux}. |
| 283 | |
| 284 | Since argument parsing is built-in to Emacs, there is no way for |
| 285 | this package to implement Common Lisp argument lists seamlessly. |
| 286 | Instead, this package defines alternates for several Lisp forms |
| 287 | which you must use if you need Common Lisp argument lists. |
| 288 | |
| 289 | @defmac cl-defun name arglist body@dots{} |
| 290 | This form is identical to the regular @code{defun} form, except |
| 291 | that @var{arglist} is allowed to be a full Common Lisp argument |
| 292 | list. Also, the function body is enclosed in an implicit block |
| 293 | called @var{name}; @pxref{Blocks and Exits}. |
| 294 | @end defmac |
| 295 | |
| 296 | @defmac cl-defsubst name arglist body@dots{} |
| 297 | This is just like @code{cl-defun}, except that the function that |
| 298 | is defined is automatically proclaimed @code{inline}, i.e., |
| 299 | calls to it may be expanded into in-line code by the byte compiler. |
| 300 | This is analogous to the @code{defsubst} form; |
| 301 | @code{cl-defsubst} uses a different method (compiler macros) which |
| 302 | works in all versions of Emacs, and also generates somewhat more |
| 303 | @c For some examples, |
| 304 | @c see http://lists.gnu.org/archive/html/emacs-devel/2012-11/msg00009.html |
| 305 | efficient inline expansions. In particular, @code{cl-defsubst} |
| 306 | arranges for the processing of keyword arguments, default values, |
| 307 | etc., to be done at compile-time whenever possible. |
| 308 | @end defmac |
| 309 | |
| 310 | @defmac cl-defmacro name arglist body@dots{} |
| 311 | This is identical to the regular @code{defmacro} form, |
| 312 | except that @var{arglist} is allowed to be a full Common Lisp |
| 313 | argument list. The @code{&environment} keyword is supported as |
| 314 | described in Steele's book @cite{Common Lisp, the Language}. |
| 315 | The @code{&whole} keyword is supported only |
| 316 | within destructured lists (see below); top-level @code{&whole} |
| 317 | cannot be implemented with the current Emacs Lisp interpreter. |
| 318 | The macro expander body is enclosed in an implicit block called |
| 319 | @var{name}. |
| 320 | @end defmac |
| 321 | |
| 322 | @defmac cl-function symbol-or-lambda |
| 323 | This is identical to the regular @code{function} form, |
| 324 | except that if the argument is a @code{lambda} form then that |
| 325 | form may use a full Common Lisp argument list. |
| 326 | @end defmac |
| 327 | |
| 328 | Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined |
| 329 | in this package that include @var{arglist}s in their syntax allow |
| 330 | full Common Lisp argument lists. |
| 331 | |
| 332 | Note that it is @emph{not} necessary to use @code{cl-defun} in |
| 333 | order to have access to most CL features in your function. |
| 334 | These features are always present; @code{cl-defun}'s only |
| 335 | difference from @code{defun} is its more flexible argument |
| 336 | lists and its implicit block. |
| 337 | |
| 338 | The full form of a Common Lisp argument list is |
| 339 | |
| 340 | @example |
| 341 | (@var{var}@dots{} |
| 342 | &optional (@var{var} @var{initform} @var{svar})@dots{} |
| 343 | &rest @var{var} |
| 344 | &key ((@var{keyword} @var{var}) @var{initform} @var{svar})@dots{} |
| 345 | &aux (@var{var} @var{initform})@dots{}) |
| 346 | @end example |
| 347 | |
| 348 | Each of the five argument list sections is optional. The @var{svar}, |
| 349 | @var{initform}, and @var{keyword} parts are optional; if they are |
| 350 | omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}. |
| 351 | |
| 352 | The first section consists of zero or more @dfn{required} arguments. |
| 353 | These arguments must always be specified in a call to the function; |
| 354 | there is no difference between Emacs Lisp and Common Lisp as far as |
| 355 | required arguments are concerned. |
| 356 | |
| 357 | The second section consists of @dfn{optional} arguments. These |
| 358 | arguments may be specified in the function call; if they are not, |
| 359 | @var{initform} specifies the default value used for the argument. |
| 360 | (No @var{initform} means to use @code{nil} as the default.) The |
| 361 | @var{initform} is evaluated with the bindings for the preceding |
| 362 | arguments already established; @code{(a &optional (b (1+ a)))} |
| 363 | matches one or two arguments, with the second argument defaulting |
| 364 | to one plus the first argument. If the @var{svar} is specified, |
| 365 | it is an auxiliary variable which is bound to @code{t} if the optional |
| 366 | argument was specified, or to @code{nil} if the argument was omitted. |
| 367 | If you don't use an @var{svar}, then there will be no way for your |
| 368 | function to tell whether it was called with no argument, or with |
| 369 | the default value passed explicitly as an argument. |
| 370 | |
| 371 | The third section consists of a single @dfn{rest} argument. If |
| 372 | more arguments were passed to the function than are accounted for |
| 373 | by the required and optional arguments, those extra arguments are |
| 374 | collected into a list and bound to the ``rest'' argument variable. |
| 375 | Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp. |
| 376 | Common Lisp accepts @code{&body} as a synonym for @code{&rest} in |
| 377 | macro contexts; this package accepts it all the time. |
| 378 | |
| 379 | The fourth section consists of @dfn{keyword} arguments. These |
| 380 | are optional arguments which are specified by name rather than |
| 381 | positionally in the argument list. For example, |
| 382 | |
| 383 | @example |
| 384 | (cl-defun foo (a &optional b &key c d (e 17))) |
| 385 | @end example |
| 386 | |
| 387 | @noindent |
| 388 | defines a function which may be called with one, two, or more |
| 389 | arguments. The first two arguments are bound to @code{a} and |
| 390 | @code{b} in the usual way. The remaining arguments must be |
| 391 | pairs of the form @code{:c}, @code{:d}, or @code{:e} followed |
| 392 | by the value to be bound to the corresponding argument variable. |
| 393 | (Symbols whose names begin with a colon are called @dfn{keywords}, |
| 394 | and they are self-quoting in the same way as @code{nil} and |
| 395 | @code{t}.) |
| 396 | |
| 397 | For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five |
| 398 | arguments to 1, 2, 4, 3, and 17, respectively. If the same keyword |
| 399 | appears more than once in the function call, the first occurrence |
| 400 | takes precedence over the later ones. Note that it is not possible |
| 401 | to specify keyword arguments without specifying the optional |
| 402 | argument @code{b} as well, since @code{(foo 1 :c 2)} would bind |
| 403 | @code{b} to the keyword @code{:c}, then signal an error because |
| 404 | @code{2} is not a valid keyword. |
| 405 | |
| 406 | You can also explicitly specify the keyword argument; it need not be |
| 407 | simply the variable name prefixed with a colon. For example, |
| 408 | |
| 409 | @example |
| 410 | (cl-defun bar (&key (a 1) ((baz b) 4))) |
| 411 | @end example |
| 412 | |
| 413 | @noindent |
| 414 | |
| 415 | specifies a keyword @code{:a} that sets the variable @code{a} with |
| 416 | default value 1, as well as a keyword @code{baz} that sets the |
| 417 | variable @code{b} with default value 4. In this case, because |
| 418 | @code{baz} is not self-quoting, you must quote it explicitly in the |
| 419 | function call, like this: |
| 420 | |
| 421 | @example |
| 422 | (bar :a 10 'baz 42) |
| 423 | @end example |
| 424 | |
| 425 | Ordinarily, it is an error to pass an unrecognized keyword to |
| 426 | a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}. You can ask |
| 427 | Lisp to ignore unrecognized keywords, either by adding the |
| 428 | marker @code{&allow-other-keys} after the keyword section |
| 429 | of the argument list, or by specifying an @code{:allow-other-keys} |
| 430 | argument in the call whose value is non-@code{nil}. If the |
| 431 | function uses both @code{&rest} and @code{&key} at the same time, |
| 432 | the ``rest'' argument is bound to the keyword list as it appears |
| 433 | in the call. For example: |
| 434 | |
| 435 | @example |
| 436 | (cl-defun find-thing (thing &rest rest &key need &allow-other-keys) |
| 437 | (or (apply 'cl-member thing thing-list :allow-other-keys t rest) |
| 438 | (if need (error "Thing not found")))) |
| 439 | @end example |
| 440 | |
| 441 | @noindent |
| 442 | This function takes a @code{:need} keyword argument, but also |
| 443 | accepts other keyword arguments which are passed on to the |
| 444 | @code{cl-member} function. @code{allow-other-keys} is used to |
| 445 | keep both @code{find-thing} and @code{cl-member} from complaining |
| 446 | about each others' keywords in the arguments. |
| 447 | |
| 448 | The fifth section of the argument list consists of @dfn{auxiliary |
| 449 | variables}. These are not really arguments at all, but simply |
| 450 | variables which are bound to @code{nil} or to the specified |
| 451 | @var{initforms} during execution of the function. There is no |
| 452 | difference between the following two functions, except for a |
| 453 | matter of stylistic taste: |
| 454 | |
| 455 | @example |
| 456 | (cl-defun foo (a b &aux (c (+ a b)) d) |
| 457 | @var{body}) |
| 458 | |
| 459 | (cl-defun foo (a b) |
| 460 | (let ((c (+ a b)) d) |
| 461 | @var{body})) |
| 462 | @end example |
| 463 | |
| 464 | Argument lists support @dfn{destructuring}. In Common Lisp, |
| 465 | destructuring is only allowed with @code{defmacro}; this package |
| 466 | allows it with @code{cl-defun} and other argument lists as well. |
| 467 | In destructuring, any argument variable (@var{var} in the above |
| 468 | example) can be replaced by a list of variables, or more generally, |
| 469 | a recursive argument list. The corresponding argument value must |
| 470 | be a list whose elements match this recursive argument list. |
| 471 | For example: |
| 472 | |
| 473 | @example |
| 474 | (cl-defmacro dolist ((var listform &optional resultform) |
| 475 | &rest body) |
| 476 | @dots{}) |
| 477 | @end example |
| 478 | |
| 479 | This says that the first argument of @code{dolist} must be a list |
| 480 | of two or three items; if there are other arguments as well as this |
| 481 | list, they are stored in @code{body}. All features allowed in |
| 482 | regular argument lists are allowed in these recursive argument lists. |
| 483 | In addition, the clause @samp{&whole @var{var}} is allowed at the |
| 484 | front of a recursive argument list. It binds @var{var} to the |
| 485 | whole list being matched; thus @code{(&whole all a b)} matches |
| 486 | a list of two things, with @code{a} bound to the first thing, |
| 487 | @code{b} bound to the second thing, and @code{all} bound to the |
| 488 | list itself. (Common Lisp allows @code{&whole} in top-level |
| 489 | @code{defmacro} argument lists as well, but Emacs Lisp does not |
| 490 | support this usage.) |
| 491 | |
| 492 | One last feature of destructuring is that the argument list may be |
| 493 | dotted, so that the argument list @code{(a b . c)} is functionally |
| 494 | equivalent to @code{(a b &rest c)}. |
| 495 | |
| 496 | If the optimization quality @code{safety} is set to 0 |
| 497 | (@pxref{Declarations}), error checking for wrong number of |
| 498 | arguments and invalid keyword arguments is disabled. By default, |
| 499 | argument lists are rigorously checked. |
| 500 | |
| 501 | @node Time of Evaluation |
| 502 | @section Time of Evaluation |
| 503 | |
| 504 | @noindent |
| 505 | Normally, the byte-compiler does not actually execute the forms in |
| 506 | a file it compiles. For example, if a file contains @code{(setq foo t)}, |
| 507 | the act of compiling it will not actually set @code{foo} to @code{t}. |
| 508 | This is true even if the @code{setq} was a top-level form (i.e., not |
| 509 | enclosed in a @code{defun} or other form). Sometimes, though, you |
| 510 | would like to have certain top-level forms evaluated at compile-time. |
| 511 | For example, the compiler effectively evaluates @code{defmacro} forms |
| 512 | at compile-time so that later parts of the file can refer to the |
| 513 | macros that are defined. |
| 514 | |
| 515 | @defmac cl-eval-when (situations@dots{}) forms@dots{} |
| 516 | This form controls when the body @var{forms} are evaluated. |
| 517 | The @var{situations} list may contain any set of the symbols |
| 518 | @code{compile}, @code{load}, and @code{eval} (or their long-winded |
| 519 | ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel}, |
| 520 | and @code{:execute}). |
| 521 | |
| 522 | The @code{cl-eval-when} form is handled differently depending on |
| 523 | whether or not it is being compiled as a top-level form. |
| 524 | Specifically, it gets special treatment if it is being compiled |
| 525 | by a command such as @code{byte-compile-file} which compiles files |
| 526 | or buffers of code, and it appears either literally at the |
| 527 | top level of the file or inside a top-level @code{progn}. |
| 528 | |
| 529 | For compiled top-level @code{cl-eval-when}s, the body @var{forms} are |
| 530 | executed at compile-time if @code{compile} is in the @var{situations} |
| 531 | list, and the @var{forms} are written out to the file (to be executed |
| 532 | at load-time) if @code{load} is in the @var{situations} list. |
| 533 | |
| 534 | For non-compiled-top-level forms, only the @code{eval} situation is |
| 535 | relevant. (This includes forms executed by the interpreter, forms |
| 536 | compiled with @code{byte-compile} rather than @code{byte-compile-file}, |
| 537 | and non-top-level forms.) The @code{cl-eval-when} acts like a |
| 538 | @code{progn} if @code{eval} is specified, and like @code{nil} |
| 539 | (ignoring the body @var{forms}) if not. |
| 540 | |
| 541 | The rules become more subtle when @code{cl-eval-when}s are nested; |
| 542 | consult Steele (second edition) for the gruesome details (and |
| 543 | some gruesome examples). |
| 544 | |
| 545 | Some simple examples: |
| 546 | |
| 547 | @example |
| 548 | ;; Top-level forms in foo.el: |
| 549 | (cl-eval-when (compile) (setq foo1 'bar)) |
| 550 | (cl-eval-when (load) (setq foo2 'bar)) |
| 551 | (cl-eval-when (compile load) (setq foo3 'bar)) |
| 552 | (cl-eval-when (eval) (setq foo4 'bar)) |
| 553 | (cl-eval-when (eval compile) (setq foo5 'bar)) |
| 554 | (cl-eval-when (eval load) (setq foo6 'bar)) |
| 555 | (cl-eval-when (eval compile load) (setq foo7 'bar)) |
| 556 | @end example |
| 557 | |
| 558 | When @file{foo.el} is compiled, these variables will be set during |
| 559 | the compilation itself: |
| 560 | |
| 561 | @example |
| 562 | foo1 foo3 foo5 foo7 ; `compile' |
| 563 | @end example |
| 564 | |
| 565 | When @file{foo.elc} is loaded, these variables will be set: |
| 566 | |
| 567 | @example |
| 568 | foo2 foo3 foo6 foo7 ; `load' |
| 569 | @end example |
| 570 | |
| 571 | And if @file{foo.el} is loaded uncompiled, these variables will |
| 572 | be set: |
| 573 | |
| 574 | @example |
| 575 | foo4 foo5 foo6 foo7 ; `eval' |
| 576 | @end example |
| 577 | |
| 578 | If these seven @code{cl-eval-when}s had been, say, inside a @code{defun}, |
| 579 | then the first three would have been equivalent to @code{nil} and the |
| 580 | last four would have been equivalent to the corresponding @code{setq}s. |
| 581 | |
| 582 | Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent |
| 583 | to @code{(progn @dots{})} in all contexts. The compiler treats |
| 584 | certain top-level forms, like @code{defmacro} (sort-of) and |
| 585 | @code{require}, as if they were wrapped in @code{(cl-eval-when |
| 586 | (compile load eval) @dots{})}. |
| 587 | @end defmac |
| 588 | |
| 589 | Emacs includes two special forms related to @code{cl-eval-when}. |
| 590 | @xref{Eval During Compile,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 591 | One of these, @code{eval-when-compile}, is not quite equivalent to |
| 592 | any @code{cl-eval-when} construct and is described below. |
| 593 | |
| 594 | The other form, @code{(eval-and-compile @dots{})}, is exactly |
| 595 | equivalent to @samp{(cl-eval-when (compile load eval) @dots{})}. |
| 596 | |
| 597 | @defmac eval-when-compile forms@dots{} |
| 598 | The @var{forms} are evaluated at compile-time; at execution time, |
| 599 | this form acts like a quoted constant of the resulting value. Used |
| 600 | at top-level, @code{eval-when-compile} is just like @samp{eval-when |
| 601 | (compile eval)}. In other contexts, @code{eval-when-compile} |
| 602 | allows code to be evaluated once at compile-time for efficiency |
| 603 | or other reasons. |
| 604 | |
| 605 | This form is similar to the @samp{#.} syntax of true Common Lisp. |
| 606 | @end defmac |
| 607 | |
| 608 | @defmac cl-load-time-value form |
| 609 | The @var{form} is evaluated at load-time; at execution time, |
| 610 | this form acts like a quoted constant of the resulting value. |
| 611 | |
| 612 | Early Common Lisp had a @samp{#,} syntax that was similar to |
| 613 | this, but ANSI Common Lisp replaced it with @code{load-time-value} |
| 614 | and gave it more well-defined semantics. |
| 615 | |
| 616 | In a compiled file, @code{cl-load-time-value} arranges for @var{form} |
| 617 | to be evaluated when the @file{.elc} file is loaded and then used |
| 618 | as if it were a quoted constant. In code compiled by |
| 619 | @code{byte-compile} rather than @code{byte-compile-file}, the |
| 620 | effect is identical to @code{eval-when-compile}. In uncompiled |
| 621 | code, both @code{eval-when-compile} and @code{cl-load-time-value} |
| 622 | act exactly like @code{progn}. |
| 623 | |
| 624 | @example |
| 625 | (defun report () |
| 626 | (insert "This function was executed on: " |
| 627 | (current-time-string) |
| 628 | ", compiled on: " |
| 629 | (eval-when-compile (current-time-string)) |
| 630 | ;; or '#.(current-time-string) in real Common Lisp |
| 631 | ", and loaded on: " |
| 632 | (cl-load-time-value (current-time-string)))) |
| 633 | @end example |
| 634 | |
| 635 | @noindent |
| 636 | Byte-compiled, the above defun will result in the following code |
| 637 | (or its compiled equivalent, of course) in the @file{.elc} file: |
| 638 | |
| 639 | @example |
| 640 | (setq --temp-- (current-time-string)) |
| 641 | (defun report () |
| 642 | (insert "This function was executed on: " |
| 643 | (current-time-string) |
| 644 | ", compiled on: " |
| 645 | '"Wed Oct 31 16:32:28 2012" |
| 646 | ", and loaded on: " |
| 647 | --temp--)) |
| 648 | @end example |
| 649 | @end defmac |
| 650 | |
| 651 | @node Predicates |
| 652 | @chapter Predicates |
| 653 | |
| 654 | @noindent |
| 655 | This section describes functions for testing whether various |
| 656 | facts are true or false. |
| 657 | |
| 658 | @menu |
| 659 | * Type Predicates:: @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}. |
| 660 | * Equality Predicates:: @code{cl-equalp}. |
| 661 | @end menu |
| 662 | |
| 663 | @node Type Predicates |
| 664 | @section Type Predicates |
| 665 | |
| 666 | @defun cl-typep object type |
| 667 | Check if @var{object} is of type @var{type}, where @var{type} is a |
| 668 | (quoted) type name of the sort used by Common Lisp. For example, |
| 669 | @code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}. |
| 670 | @end defun |
| 671 | |
| 672 | The @var{type} argument to the above function is either a symbol |
| 673 | or a list beginning with a symbol. |
| 674 | |
| 675 | @itemize @bullet |
| 676 | @item |
| 677 | If the type name is a symbol, Emacs appends @samp{-p} to the |
| 678 | symbol name to form the name of a predicate function for testing |
| 679 | the type. (Built-in predicates whose names end in @samp{p} rather |
| 680 | than @samp{-p} are used when appropriate.) |
| 681 | |
| 682 | @item |
| 683 | The type symbol @code{t} stands for the union of all types. |
| 684 | @code{(cl-typep @var{object} t)} is always true. Likewise, the |
| 685 | type symbol @code{nil} stands for nothing at all, and |
| 686 | @code{(cl-typep @var{object} nil)} is always false. |
| 687 | |
| 688 | @item |
| 689 | The type symbol @code{null} represents the symbol @code{nil}. |
| 690 | Thus @code{(cl-typep @var{object} 'null)} is equivalent to |
| 691 | @code{(null @var{object})}. |
| 692 | |
| 693 | @item |
| 694 | The type symbol @code{atom} represents all objects that are not cons |
| 695 | cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to |
| 696 | @code{(atom @var{object})}. |
| 697 | |
| 698 | @item |
| 699 | The type symbol @code{real} is a synonym for @code{number}, and |
| 700 | @code{fixnum} is a synonym for @code{integer}. |
| 701 | |
| 702 | @item |
| 703 | The type symbols @code{character} and @code{string-char} match |
| 704 | integers in the range from 0 to 255. |
| 705 | |
| 706 | @c No longer relevant, so covered by first item above (float -> floatp). |
| 707 | @ignore |
| 708 | @item |
| 709 | The type symbol @code{float} uses the @code{cl-floatp-safe} predicate |
| 710 | defined by this package rather than @code{floatp}, so it will work |
| 711 | correctly even in Emacs versions without floating-point support. |
| 712 | @end ignore |
| 713 | |
| 714 | @item |
| 715 | The type list @code{(integer @var{low} @var{high})} represents all |
| 716 | integers between @var{low} and @var{high}, inclusive. Either bound |
| 717 | may be a list of a single integer to specify an exclusive limit, |
| 718 | or a @code{*} to specify no limit. The type @code{(integer * *)} |
| 719 | is thus equivalent to @code{integer}. |
| 720 | |
| 721 | @item |
| 722 | Likewise, lists beginning with @code{float}, @code{real}, or |
| 723 | @code{number} represent numbers of that type falling in a particular |
| 724 | range. |
| 725 | |
| 726 | @item |
| 727 | Lists beginning with @code{and}, @code{or}, and @code{not} form |
| 728 | combinations of types. For example, @code{(or integer (float 0 *))} |
| 729 | represents all objects that are integers or non-negative floats. |
| 730 | |
| 731 | @item |
| 732 | Lists beginning with @code{member} or @code{cl-member} represent |
| 733 | objects @code{eql} to any of the following values. For example, |
| 734 | @code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)}, |
| 735 | and @code{(member nil)} is equivalent to @code{null}. |
| 736 | |
| 737 | @item |
| 738 | Lists of the form @code{(satisfies @var{predicate})} represent |
| 739 | all objects for which @var{predicate} returns true when called |
| 740 | with that object as an argument. |
| 741 | @end itemize |
| 742 | |
| 743 | The following function and macro (not technically predicates) are |
| 744 | related to @code{cl-typep}. |
| 745 | |
| 746 | @defun cl-coerce object type |
| 747 | This function attempts to convert @var{object} to the specified |
| 748 | @var{type}. If @var{object} is already of that type as determined by |
| 749 | @code{cl-typep}, it is simply returned. Otherwise, certain types of |
| 750 | conversions will be made: If @var{type} is any sequence type |
| 751 | (@code{string}, @code{list}, etc.) then @var{object} will be |
| 752 | converted to that type if possible. If @var{type} is |
| 753 | @code{character}, then strings of length one and symbols with |
| 754 | one-character names can be coerced. If @var{type} is @code{float}, |
| 755 | then integers can be coerced in versions of Emacs that support |
| 756 | floats. In all other circumstances, @code{cl-coerce} signals an |
| 757 | error. |
| 758 | @end defun |
| 759 | |
| 760 | @defmac cl-deftype name arglist forms@dots{} |
| 761 | This macro defines a new type called @var{name}. It is similar |
| 762 | to @code{defmacro} in many ways; when @var{name} is encountered |
| 763 | as a type name, the body @var{forms} are evaluated and should |
| 764 | return a type specifier that is equivalent to the type. The |
| 765 | @var{arglist} is a Common Lisp argument list of the sort accepted |
| 766 | by @code{cl-defmacro}. The type specifier @samp{(@var{name} @var{args}@dots{})} |
| 767 | is expanded by calling the expander with those arguments; the type |
| 768 | symbol @samp{@var{name}} is expanded by calling the expander with |
| 769 | no arguments. The @var{arglist} is processed the same as for |
| 770 | @code{cl-defmacro} except that optional arguments without explicit |
| 771 | defaults use @code{*} instead of @code{nil} as the ``default'' |
| 772 | default. Some examples: |
| 773 | |
| 774 | @example |
| 775 | (cl-deftype null () '(satisfies null)) ; predefined |
| 776 | (cl-deftype list () '(or null cons)) ; predefined |
| 777 | (cl-deftype unsigned-byte (&optional bits) |
| 778 | (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits))))) |
| 779 | (unsigned-byte 8) @equiv{} (integer 0 255) |
| 780 | (unsigned-byte) @equiv{} (integer 0 *) |
| 781 | unsigned-byte @equiv{} (integer 0 *) |
| 782 | @end example |
| 783 | |
| 784 | @noindent |
| 785 | The last example shows how the Common Lisp @code{unsigned-byte} |
| 786 | type specifier could be implemented if desired; this package does |
| 787 | not implement @code{unsigned-byte} by default. |
| 788 | @end defmac |
| 789 | |
| 790 | The @code{cl-typecase} (@pxref{Conditionals}) and @code{cl-check-type} |
| 791 | (@pxref{Assertions}) macros also use type names. The @code{cl-map}, |
| 792 | @code{cl-concatenate}, and @code{cl-merge} functions take type-name |
| 793 | arguments to specify the type of sequence to return. @xref{Sequences}. |
| 794 | |
| 795 | @node Equality Predicates |
| 796 | @section Equality Predicates |
| 797 | |
| 798 | @noindent |
| 799 | This package defines the Common Lisp predicate @code{cl-equalp}. |
| 800 | |
| 801 | @defun cl-equalp a b |
| 802 | This function is a more flexible version of @code{equal}. In |
| 803 | particular, it compares strings case-insensitively, and it compares |
| 804 | numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is |
| 805 | true). Vectors and conses are compared recursively. All other |
| 806 | objects are compared as if by @code{equal}. |
| 807 | |
| 808 | This function differs from Common Lisp @code{equalp} in several |
| 809 | respects. First, Common Lisp's @code{equalp} also compares |
| 810 | @emph{characters} case-insensitively, which would be impractical |
| 811 | in this package since Emacs does not distinguish between integers |
| 812 | and characters. In keeping with the idea that strings are less |
| 813 | vector-like in Emacs Lisp, this package's @code{cl-equalp} also will |
| 814 | not compare strings against vectors of integers. |
| 815 | @end defun |
| 816 | |
| 817 | Also note that the Common Lisp functions @code{member} and @code{assoc} |
| 818 | use @code{eql} to compare elements, whereas Emacs Lisp follows the |
| 819 | MacLisp tradition and uses @code{equal} for these two functions. |
| 820 | In Emacs, use @code{memq} (or @code{cl-member}) and @code{assq} (or |
| 821 | @code{cl-assoc}) to get functions which use @code{eql} for comparisons. |
| 822 | |
| 823 | @node Control Structure |
| 824 | @chapter Control Structure |
| 825 | |
| 826 | @noindent |
| 827 | The features described in the following sections implement |
| 828 | various advanced control structures, including extensions to the |
| 829 | standard @code{setf} facility, and a number of looping and conditional |
| 830 | constructs. |
| 831 | |
| 832 | @menu |
| 833 | * Assignment:: The @code{cl-psetq} form. |
| 834 | * Generalized Variables:: Extensions to generalized variables. |
| 835 | * Variable Bindings:: @code{cl-progv}, @code{cl-flet}, @code{cl-macrolet}. |
| 836 | * Conditionals:: @code{cl-case}, @code{cl-typecase}. |
| 837 | * Blocks and Exits:: @code{cl-block}, @code{cl-return}, @code{cl-return-from}. |
| 838 | * Iteration:: @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}. |
| 839 | * Loop Facility:: The Common Lisp @code{loop} macro. |
| 840 | * Multiple Values:: @code{cl-values}, @code{cl-multiple-value-bind}, etc. |
| 841 | @end menu |
| 842 | |
| 843 | @node Assignment |
| 844 | @section Assignment |
| 845 | |
| 846 | @noindent |
| 847 | The @code{cl-psetq} form is just like @code{setq}, except that multiple |
| 848 | assignments are done in parallel rather than sequentially. |
| 849 | |
| 850 | @defmac cl-psetq [symbol form]@dots{} |
| 851 | This special form (actually a macro) is used to assign to several |
| 852 | variables simultaneously. Given only one @var{symbol} and @var{form}, |
| 853 | it has the same effect as @code{setq}. Given several @var{symbol} |
| 854 | and @var{form} pairs, it evaluates all the @var{form}s in advance |
| 855 | and then stores the corresponding variables afterwards. |
| 856 | |
| 857 | @example |
| 858 | (setq x 2 y 3) |
| 859 | (setq x (+ x y) y (* x y)) |
| 860 | x |
| 861 | @result{} 5 |
| 862 | y ; @r{@code{y} was computed after @code{x} was set.} |
| 863 | @result{} 15 |
| 864 | (setq x 2 y 3) |
| 865 | (cl-psetq x (+ x y) y (* x y)) |
| 866 | x |
| 867 | @result{} 5 |
| 868 | y ; @r{@code{y} was computed before @code{x} was set.} |
| 869 | @result{} 6 |
| 870 | @end example |
| 871 | |
| 872 | The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which |
| 873 | exchanges the values of two variables. (The @code{cl-rotatef} form |
| 874 | provides an even more convenient way to swap two variables; |
| 875 | @pxref{Modify Macros}.) |
| 876 | |
| 877 | @code{cl-psetq} always returns @code{nil}. |
| 878 | @end defmac |
| 879 | |
| 880 | @node Generalized Variables |
| 881 | @section Generalized Variables |
| 882 | |
| 883 | A @dfn{generalized variable} or @dfn{place form} is one of the many |
| 884 | places in Lisp memory where values can be stored. The simplest place |
| 885 | form is a regular Lisp variable. But the @sc{car}s and @sc{cdr}s of lists, |
| 886 | elements of arrays, properties of symbols, and many other locations |
| 887 | are also places where Lisp values are stored. For basic information, |
| 888 | @pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 889 | This package provides several additional features related to |
| 890 | generalized variables. |
| 891 | |
| 892 | @menu |
| 893 | * Setf Extensions:: Additional @code{setf} places. |
| 894 | * Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc. |
| 895 | @end menu |
| 896 | |
| 897 | @node Setf Extensions |
| 898 | @subsection Setf Extensions |
| 899 | |
| 900 | Several standard (e.g., @code{car}) and Emacs-specific |
| 901 | (e.g., @code{window-point}) Lisp functions are @code{setf}-able by default. |
| 902 | This package defines @code{setf} handlers for several additional functions: |
| 903 | |
| 904 | @itemize |
| 905 | @item |
| 906 | Functions from this package: |
| 907 | @example |
| 908 | cl-rest cl-subseq cl-get cl-getf |
| 909 | cl-caaar@dots{}cl-cddddr cl-first@dots{}cl-tenth |
| 910 | @end example |
| 911 | |
| 912 | @noindent |
| 913 | Note that for @code{cl-getf} (as for @code{nthcdr}), the list argument |
| 914 | of the function must itself be a valid @var{place} form. |
| 915 | |
| 916 | @item |
| 917 | General Emacs Lisp functions: |
| 918 | @example |
| 919 | buffer-file-name getenv |
| 920 | buffer-modified-p global-key-binding |
| 921 | buffer-name local-key-binding |
| 922 | buffer-string mark |
| 923 | buffer-substring mark-marker |
| 924 | current-buffer marker-position |
| 925 | current-case-table mouse-position |
| 926 | current-column point |
| 927 | current-global-map point-marker |
| 928 | current-input-mode point-max |
| 929 | current-local-map point-min |
| 930 | current-window-configuration read-mouse-position |
| 931 | default-file-modes screen-height |
| 932 | documentation-property screen-width |
| 933 | face-background selected-window |
| 934 | face-background-pixmap selected-screen |
| 935 | face-font selected-frame |
| 936 | face-foreground standard-case-table |
| 937 | face-underline-p syntax-table |
| 938 | file-modes visited-file-modtime |
| 939 | frame-height window-height |
| 940 | frame-parameters window-width |
| 941 | frame-visible-p x-get-secondary-selection |
| 942 | frame-width x-get-selection |
| 943 | get-register |
| 944 | @end example |
| 945 | |
| 946 | Most of these have directly corresponding ``set'' functions, like |
| 947 | @code{use-local-map} for @code{current-local-map}, or @code{goto-char} |
| 948 | for @code{point}. A few, like @code{point-min}, expand to longer |
| 949 | sequences of code when they are used with @code{setf} |
| 950 | (@code{(narrow-to-region x (point-max))} in this case). |
| 951 | |
| 952 | @item |
| 953 | A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])}, |
| 954 | where @var{subplace} is itself a valid generalized variable whose |
| 955 | current value is a string, and where the value stored is also a |
| 956 | string. The new string is spliced into the specified part of the |
| 957 | destination string. For example: |
| 958 | |
| 959 | @example |
| 960 | (setq a (list "hello" "world")) |
| 961 | @result{} ("hello" "world") |
| 962 | (cadr a) |
| 963 | @result{} "world" |
| 964 | (substring (cadr a) 2 4) |
| 965 | @result{} "rl" |
| 966 | (setf (substring (cadr a) 2 4) "o") |
| 967 | @result{} "o" |
| 968 | (cadr a) |
| 969 | @result{} "wood" |
| 970 | a |
| 971 | @result{} ("hello" "wood") |
| 972 | @end example |
| 973 | |
| 974 | The generalized variable @code{buffer-substring}, listed above, |
| 975 | also works in this way by replacing a portion of the current buffer. |
| 976 | |
| 977 | @c FIXME? Also `eq'? (see cl-lib.el) |
| 978 | |
| 979 | @c Currently commented out in cl.el. |
| 980 | @ignore |
| 981 | @item |
| 982 | A call of the form @code{(apply '@var{func} @dots{})} or |
| 983 | @code{(apply (function @var{func}) @dots{})}, where @var{func} |
| 984 | is a @code{setf}-able function whose store function is ``suitable'' |
| 985 | in the sense described in Steele's book; since none of the standard |
| 986 | Emacs place functions are suitable in this sense, this feature is |
| 987 | only interesting when used with places you define yourself with |
| 988 | @code{define-setf-method} or the long form of @code{defsetf}. |
| 989 | @xref{Obsolete Setf Customization}. |
| 990 | @end ignore |
| 991 | |
| 992 | @c FIXME? Is this still true? |
| 993 | @item |
| 994 | A macro call, in which case the macro is expanded and @code{setf} |
| 995 | is applied to the resulting form. |
| 996 | @end itemize |
| 997 | |
| 998 | @c FIXME should this be in lispref? It seems self-evident. |
| 999 | @c Contrast with the cl-incf example later on. |
| 1000 | @c Here it really only serves as a contrast to wrong-order. |
| 1001 | The @code{setf} macro takes care to evaluate all subforms in |
| 1002 | the proper left-to-right order; for example, |
| 1003 | |
| 1004 | @example |
| 1005 | (setf (aref vec (cl-incf i)) i) |
| 1006 | @end example |
| 1007 | |
| 1008 | @noindent |
| 1009 | looks like it will evaluate @code{(cl-incf i)} exactly once, before the |
| 1010 | following access to @code{i}; the @code{setf} expander will insert |
| 1011 | temporary variables as necessary to ensure that it does in fact work |
| 1012 | this way no matter what setf-method is defined for @code{aref}. |
| 1013 | (In this case, @code{aset} would be used and no such steps would |
| 1014 | be necessary since @code{aset} takes its arguments in a convenient |
| 1015 | order.) |
| 1016 | |
| 1017 | However, if the @var{place} form is a macro which explicitly |
| 1018 | evaluates its arguments in an unusual order, this unusual order |
| 1019 | will be preserved. Adapting an example from Steele, given |
| 1020 | |
| 1021 | @example |
| 1022 | (defmacro wrong-order (x y) (list 'aref y x)) |
| 1023 | @end example |
| 1024 | |
| 1025 | @noindent |
| 1026 | the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will |
| 1027 | evaluate @var{b} first, then @var{a}, just as in an actual call |
| 1028 | to @code{wrong-order}. |
| 1029 | |
| 1030 | @node Modify Macros |
| 1031 | @subsection Modify Macros |
| 1032 | |
| 1033 | @noindent |
| 1034 | This package defines a number of macros that operate on generalized |
| 1035 | variables. Many are interesting and useful even when the @var{place} |
| 1036 | is just a variable name. |
| 1037 | |
| 1038 | @defmac cl-psetf [place form]@dots{} |
| 1039 | This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}: |
| 1040 | When several @var{place}s and @var{form}s are involved, the |
| 1041 | assignments take place in parallel rather than sequentially. |
| 1042 | Specifically, all subforms are evaluated from left to right, then |
| 1043 | all the assignments are done (in an undefined order). |
| 1044 | @end defmac |
| 1045 | |
| 1046 | @defmac cl-incf place &optional x |
| 1047 | This macro increments the number stored in @var{place} by one, or |
| 1048 | by @var{x} if specified. The incremented value is returned. For |
| 1049 | example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and |
| 1050 | @code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}. |
| 1051 | |
| 1052 | As with @code{setf}, care is taken to preserve the ``apparent'' order |
| 1053 | of evaluation. For example, |
| 1054 | |
| 1055 | @example |
| 1056 | (cl-incf (aref vec (cl-incf i))) |
| 1057 | @end example |
| 1058 | |
| 1059 | @noindent |
| 1060 | appears to increment @code{i} once, then increment the element of |
| 1061 | @code{vec} addressed by @code{i}; this is indeed exactly what it |
| 1062 | does, which means the above form is @emph{not} equivalent to the |
| 1063 | ``obvious'' expansion, |
| 1064 | |
| 1065 | @example |
| 1066 | (setf (aref vec (cl-incf i)) |
| 1067 | (1+ (aref vec (cl-incf i)))) ; wrong! |
| 1068 | @end example |
| 1069 | |
| 1070 | @noindent |
| 1071 | but rather to something more like |
| 1072 | |
| 1073 | @example |
| 1074 | (let ((temp (cl-incf i))) |
| 1075 | (setf (aref vec temp) (1+ (aref vec temp)))) |
| 1076 | @end example |
| 1077 | |
| 1078 | @noindent |
| 1079 | Again, all of this is taken care of automatically by @code{cl-incf} and |
| 1080 | the other generalized-variable macros. |
| 1081 | |
| 1082 | As a more Emacs-specific example of @code{cl-incf}, the expression |
| 1083 | @code{(cl-incf (point) @var{n})} is essentially equivalent to |
| 1084 | @code{(forward-char @var{n})}. |
| 1085 | @end defmac |
| 1086 | |
| 1087 | @defmac cl-decf place &optional x |
| 1088 | This macro decrements the number stored in @var{place} by one, or |
| 1089 | by @var{x} if specified. |
| 1090 | @end defmac |
| 1091 | |
| 1092 | @defmac cl-pushnew x place @t{&key :test :test-not :key} |
| 1093 | This macro inserts @var{x} at the front of the list stored in |
| 1094 | @var{place}, but only if @var{x} was not @code{eql} to any |
| 1095 | existing element of the list. The optional keyword arguments |
| 1096 | are interpreted in the same way as for @code{cl-adjoin}. |
| 1097 | @xref{Lists as Sets}. |
| 1098 | @end defmac |
| 1099 | |
| 1100 | @defmac cl-shiftf place@dots{} newvalue |
| 1101 | This macro shifts the @var{place}s left by one, shifting in the |
| 1102 | value of @var{newvalue} (which may be any Lisp expression, not just |
| 1103 | a generalized variable), and returning the value shifted out of |
| 1104 | the first @var{place}. Thus, @code{(cl-shiftf @var{a} @var{b} @var{c} |
| 1105 | @var{d})} is equivalent to |
| 1106 | |
| 1107 | @example |
| 1108 | (prog1 |
| 1109 | @var{a} |
| 1110 | (cl-psetf @var{a} @var{b} |
| 1111 | @var{b} @var{c} |
| 1112 | @var{c} @var{d})) |
| 1113 | @end example |
| 1114 | |
| 1115 | @noindent |
| 1116 | except that the subforms of @var{a}, @var{b}, and @var{c} are actually |
| 1117 | evaluated only once each and in the apparent order. |
| 1118 | @end defmac |
| 1119 | |
| 1120 | @defmac cl-rotatef place@dots{} |
| 1121 | This macro rotates the @var{place}s left by one in circular fashion. |
| 1122 | Thus, @code{(cl-rotatef @var{a} @var{b} @var{c} @var{d})} is equivalent to |
| 1123 | |
| 1124 | @example |
| 1125 | (cl-psetf @var{a} @var{b} |
| 1126 | @var{b} @var{c} |
| 1127 | @var{c} @var{d} |
| 1128 | @var{d} @var{a}) |
| 1129 | @end example |
| 1130 | |
| 1131 | @noindent |
| 1132 | except for the evaluation of subforms. @code{cl-rotatef} always |
| 1133 | returns @code{nil}. Note that @code{(cl-rotatef @var{a} @var{b})} |
| 1134 | conveniently exchanges @var{a} and @var{b}. |
| 1135 | @end defmac |
| 1136 | |
| 1137 | The following macros were invented for this package; they have no |
| 1138 | analogues in Common Lisp. |
| 1139 | |
| 1140 | @defmac cl-letf (bindings@dots{}) forms@dots{} |
| 1141 | This macro is analogous to @code{let}, but for generalized variables |
| 1142 | rather than just symbols. Each @var{binding} should be of the form |
| 1143 | @code{(@var{place} @var{value})}; the original contents of the |
| 1144 | @var{place}s are saved, the @var{value}s are stored in them, and |
| 1145 | then the body @var{form}s are executed. Afterwards, the @var{places} |
| 1146 | are set back to their original saved contents. This cleanup happens |
| 1147 | even if the @var{form}s exit irregularly due to a @code{throw} or an |
| 1148 | error. |
| 1149 | |
| 1150 | For example, |
| 1151 | |
| 1152 | @example |
| 1153 | (cl-letf (((point) (point-min)) |
| 1154 | (a 17)) |
| 1155 | @dots{}) |
| 1156 | @end example |
| 1157 | |
| 1158 | @noindent |
| 1159 | moves point in the current buffer to the beginning of the buffer, |
| 1160 | and also binds @code{a} to 17 (as if by a normal @code{let}, since |
| 1161 | @code{a} is just a regular variable). After the body exits, @code{a} |
| 1162 | is set back to its original value and point is moved back to its |
| 1163 | original position. |
| 1164 | |
| 1165 | Note that @code{cl-letf} on @code{(point)} is not quite like a |
| 1166 | @code{save-excursion}, as the latter effectively saves a marker |
| 1167 | which tracks insertions and deletions in the buffer. Actually, |
| 1168 | a @code{cl-letf} of @code{(point-marker)} is much closer to this |
| 1169 | behavior. (@code{point} and @code{point-marker} are equivalent |
| 1170 | as @code{setf} places; each will accept either an integer or a |
| 1171 | marker as the stored value.) |
| 1172 | |
| 1173 | Since generalized variables look like lists, @code{let}'s shorthand |
| 1174 | of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would |
| 1175 | be ambiguous in @code{cl-letf} and is not allowed. |
| 1176 | |
| 1177 | However, a @var{binding} specifier may be a one-element list |
| 1178 | @samp{(@var{place})}, which is similar to @samp{(@var{place} |
| 1179 | @var{place})}. In other words, the @var{place} is not disturbed |
| 1180 | on entry to the body, and the only effect of the @code{cl-letf} is |
| 1181 | to restore the original value of @var{place} afterwards. |
| 1182 | @c I suspect this may no longer be true; either way it's |
| 1183 | @c implementation detail and so not essential to document. |
| 1184 | @ignore |
| 1185 | (The redundant access-and-store suggested by the @code{(@var{place} |
| 1186 | @var{place})} example does not actually occur.) |
| 1187 | @end ignore |
| 1188 | |
| 1189 | Note that in this case, and in fact almost every case, @var{place} |
| 1190 | must have a well-defined value outside the @code{cl-letf} body. |
| 1191 | There is essentially only one exception to this, which is @var{place} |
| 1192 | a plain variable with a specified @var{value} (such as @code{(a 17)} |
| 1193 | in the above example). |
| 1194 | @c See http://debbugs.gnu.org/12758 |
| 1195 | @c Some or all of this was true for cl.el, but not for cl-lib.el. |
| 1196 | @ignore |
| 1197 | The only exceptions are plain variables and calls to |
| 1198 | @code{symbol-value} and @code{symbol-function}. If the symbol is not |
| 1199 | bound on entry, it is simply made unbound by @code{makunbound} or |
| 1200 | @code{fmakunbound} on exit. |
| 1201 | @end ignore |
| 1202 | |
| 1203 | Note that the @file{cl.el} version of this macro behaves slightly |
| 1204 | differently. @xref{Obsolete Macros}. |
| 1205 | @end defmac |
| 1206 | |
| 1207 | @defmac cl-letf* (bindings@dots{}) forms@dots{} |
| 1208 | This macro is to @code{cl-letf} what @code{let*} is to @code{let}: |
| 1209 | It does the bindings in sequential rather than parallel order. |
| 1210 | @end defmac |
| 1211 | |
| 1212 | @defmac cl-callf @var{function} @var{place} @var{args}@dots{} |
| 1213 | This is the ``generic'' modify macro. It calls @var{function}, |
| 1214 | which should be an unquoted function name, macro name, or lambda. |
| 1215 | It passes @var{place} and @var{args} as arguments, and assigns the |
| 1216 | result back to @var{place}. For example, @code{(cl-incf @var{place} |
| 1217 | @var{n})} is the same as @code{(cl-callf + @var{place} @var{n})}. |
| 1218 | Some more examples: |
| 1219 | |
| 1220 | @example |
| 1221 | (cl-callf abs my-number) |
| 1222 | (cl-callf concat (buffer-name) "<" (number-to-string n) ">") |
| 1223 | (cl-callf cl-union happy-people (list joe bob) :test 'same-person) |
| 1224 | @end example |
| 1225 | |
| 1226 | Note again that @code{cl-callf} is an extension to standard Common Lisp. |
| 1227 | @end defmac |
| 1228 | |
| 1229 | @defmac cl-callf2 @var{function} @var{arg1} @var{place} @var{args}@dots{} |
| 1230 | This macro is like @code{cl-callf}, except that @var{place} is |
| 1231 | the @emph{second} argument of @var{function} rather than the |
| 1232 | first. For example, @code{(push @var{x} @var{place})} is |
| 1233 | equivalent to @code{(cl-callf2 cons @var{x} @var{place})}. |
| 1234 | @end defmac |
| 1235 | |
| 1236 | The @code{cl-callf} and @code{cl-callf2} macros serve as building |
| 1237 | blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}. |
| 1238 | The @code{cl-letf} and @code{cl-letf*} macros are used in the processing |
| 1239 | of symbol macros; @pxref{Macro Bindings}. |
| 1240 | |
| 1241 | |
| 1242 | @node Variable Bindings |
| 1243 | @section Variable Bindings |
| 1244 | |
| 1245 | @noindent |
| 1246 | These Lisp forms make bindings to variables and function names, |
| 1247 | analogous to Lisp's built-in @code{let} form. |
| 1248 | |
| 1249 | @xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which |
| 1250 | are also related to variable bindings. |
| 1251 | |
| 1252 | @menu |
| 1253 | * Dynamic Bindings:: The @code{cl-progv} form. |
| 1254 | * Function Bindings:: @code{cl-flet} and @code{cl-labels}. |
| 1255 | * Macro Bindings:: @code{cl-macrolet} and @code{cl-symbol-macrolet}. |
| 1256 | @end menu |
| 1257 | |
| 1258 | @node Dynamic Bindings |
| 1259 | @subsection Dynamic Bindings |
| 1260 | |
| 1261 | @noindent |
| 1262 | The standard @code{let} form binds variables whose names are known |
| 1263 | at compile-time. The @code{cl-progv} form provides an easy way to |
| 1264 | bind variables whose names are computed at run-time. |
| 1265 | |
| 1266 | @defmac cl-progv symbols values forms@dots{} |
| 1267 | This form establishes @code{let}-style variable bindings on a |
| 1268 | set of variables computed at run-time. The expressions |
| 1269 | @var{symbols} and @var{values} are evaluated, and must return lists |
| 1270 | of symbols and values, respectively. The symbols are bound to the |
| 1271 | corresponding values for the duration of the body @var{form}s. |
| 1272 | If @var{values} is shorter than @var{symbols}, the last few symbols |
| 1273 | are bound to @code{nil}. |
| 1274 | If @var{symbols} is shorter than @var{values}, the excess values |
| 1275 | are ignored. |
| 1276 | @end defmac |
| 1277 | |
| 1278 | @node Function Bindings |
| 1279 | @subsection Function Bindings |
| 1280 | |
| 1281 | @noindent |
| 1282 | These forms make @code{let}-like bindings to functions instead |
| 1283 | of variables. |
| 1284 | |
| 1285 | @defmac cl-flet (bindings@dots{}) forms@dots{} |
| 1286 | This form establishes @code{let}-style bindings on the function |
| 1287 | cells of symbols rather than on the value cells. Each @var{binding} |
| 1288 | must be a list of the form @samp{(@var{name} @var{arglist} |
| 1289 | @var{forms}@dots{})}, which defines a function exactly as if |
| 1290 | it were a @code{cl-defun} form. The function @var{name} is defined |
| 1291 | accordingly for the duration of the body of the @code{cl-flet}; then |
| 1292 | the old function definition, or lack thereof, is restored. |
| 1293 | |
| 1294 | You can use @code{cl-flet} to disable or modify the behavior of |
| 1295 | functions (including Emacs primitives) in a temporary, localized fashion. |
| 1296 | (Compare this with the idea of advising functions. |
| 1297 | @xref{Advising Functions,,,elisp,GNU Emacs Lisp Reference Manual}.) |
| 1298 | |
| 1299 | The bindings are lexical in scope. This means that all references to |
| 1300 | the named functions must appear physically within the body of the |
| 1301 | @code{cl-flet} form. |
| 1302 | |
| 1303 | Functions defined by @code{cl-flet} may use the full Common Lisp |
| 1304 | argument notation supported by @code{cl-defun}; also, the function |
| 1305 | body is enclosed in an implicit block as if by @code{cl-defun}. |
| 1306 | @xref{Program Structure}. |
| 1307 | |
| 1308 | Note that the @file{cl.el} version of this macro behaves slightly |
| 1309 | differently. In particular, its binding is dynamic rather than |
| 1310 | lexical. @xref{Obsolete Macros}. |
| 1311 | @end defmac |
| 1312 | |
| 1313 | @defmac cl-labels (bindings@dots{}) forms@dots{} |
| 1314 | The @code{cl-labels} form is like @code{cl-flet}, except that |
| 1315 | the function bindings can be recursive. The scoping is lexical, |
| 1316 | but you can only capture functions in closures if |
| 1317 | @code{lexical-binding} is @code{t}. |
| 1318 | @xref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}, and |
| 1319 | @ref{Using Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 1320 | |
| 1321 | Lexical scoping means that all references to the named |
| 1322 | functions must appear physically within the body of the |
| 1323 | @code{cl-labels} form. References may appear both in the body |
| 1324 | @var{forms} of @code{cl-labels} itself, and in the bodies of |
| 1325 | the functions themselves. Thus, @code{cl-labels} can define |
| 1326 | local recursive functions, or mutually-recursive sets of functions. |
| 1327 | |
| 1328 | A ``reference'' to a function name is either a call to that |
| 1329 | function, or a use of its name quoted by @code{quote} or |
| 1330 | @code{function} to be passed on to, say, @code{mapcar}. |
| 1331 | |
| 1332 | Note that the @file{cl.el} version of this macro behaves slightly |
| 1333 | differently. @xref{Obsolete Macros}. |
| 1334 | @end defmac |
| 1335 | |
| 1336 | @node Macro Bindings |
| 1337 | @subsection Macro Bindings |
| 1338 | |
| 1339 | @noindent |
| 1340 | These forms create local macros and ``symbol macros''. |
| 1341 | |
| 1342 | @defmac cl-macrolet (bindings@dots{}) forms@dots{} |
| 1343 | This form is analogous to @code{cl-flet}, but for macros instead of |
| 1344 | functions. Each @var{binding} is a list of the same form as the |
| 1345 | arguments to @code{cl-defmacro} (i.e., a macro name, argument list, |
| 1346 | and macro-expander forms). The macro is defined accordingly for |
| 1347 | use within the body of the @code{cl-macrolet}. |
| 1348 | |
| 1349 | Because of the nature of macros, @code{cl-macrolet} is always lexically |
| 1350 | scoped. The @code{cl-macrolet} binding will |
| 1351 | affect only calls that appear physically within the body |
| 1352 | @var{forms}, possibly after expansion of other macros in the |
| 1353 | body. |
| 1354 | @end defmac |
| 1355 | |
| 1356 | @defmac cl-symbol-macrolet (bindings@dots{}) forms@dots{} |
| 1357 | This form creates @dfn{symbol macros}, which are macros that look |
| 1358 | like variable references rather than function calls. Each |
| 1359 | @var{binding} is a list @samp{(@var{var} @var{expansion})}; |
| 1360 | any reference to @var{var} within the body @var{forms} is |
| 1361 | replaced by @var{expansion}. |
| 1362 | |
| 1363 | @example |
| 1364 | (setq bar '(5 . 9)) |
| 1365 | (cl-symbol-macrolet ((foo (car bar))) |
| 1366 | (cl-incf foo)) |
| 1367 | bar |
| 1368 | @result{} (6 . 9) |
| 1369 | @end example |
| 1370 | |
| 1371 | A @code{setq} of a symbol macro is treated the same as a @code{setf}. |
| 1372 | I.e., @code{(setq foo 4)} in the above would be equivalent to |
| 1373 | @code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}. |
| 1374 | |
| 1375 | Likewise, a @code{let} or @code{let*} binding a symbol macro is |
| 1376 | treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true |
| 1377 | Common Lisp, where the rules of lexical scoping cause a @code{let} |
| 1378 | binding to shadow a @code{symbol-macrolet} binding. In this package, |
| 1379 | such shadowing does not occur, even when @code{lexical-binding} is |
| 1380 | @c See http://debbugs.gnu.org/12119 |
| 1381 | @code{t}. (This behavior predates the addition of lexical binding to |
| 1382 | Emacs Lisp, and may change in future to respect @code{lexical-binding}.) |
| 1383 | At present in this package, only @code{lexical-let} and |
| 1384 | @code{lexical-let*} will shadow a symbol macro. @xref{Obsolete |
| 1385 | Lexical Binding}. |
| 1386 | |
| 1387 | There is no analogue of @code{defmacro} for symbol macros; all symbol |
| 1388 | macros are local. A typical use of @code{cl-symbol-macrolet} is in the |
| 1389 | expansion of another macro: |
| 1390 | |
| 1391 | @example |
| 1392 | (cl-defmacro my-dolist ((x list) &rest body) |
| 1393 | (let ((var (cl-gensym))) |
| 1394 | (list 'cl-loop 'for var 'on list 'do |
| 1395 | (cl-list* 'cl-symbol-macrolet |
| 1396 | (list (list x (list 'car var))) |
| 1397 | body)))) |
| 1398 | |
| 1399 | (setq mylist '(1 2 3 4)) |
| 1400 | (my-dolist (x mylist) (cl-incf x)) |
| 1401 | mylist |
| 1402 | @result{} (2 3 4 5) |
| 1403 | @end example |
| 1404 | |
| 1405 | @noindent |
| 1406 | In this example, the @code{my-dolist} macro is similar to @code{dolist} |
| 1407 | (@pxref{Iteration}) except that the variable @code{x} becomes a true |
| 1408 | reference onto the elements of the list. The @code{my-dolist} call |
| 1409 | shown here expands to |
| 1410 | |
| 1411 | @example |
| 1412 | (cl-loop for G1234 on mylist do |
| 1413 | (cl-symbol-macrolet ((x (car G1234))) |
| 1414 | (cl-incf x))) |
| 1415 | @end example |
| 1416 | |
| 1417 | @noindent |
| 1418 | which in turn expands to |
| 1419 | |
| 1420 | @example |
| 1421 | (cl-loop for G1234 on mylist do (cl-incf (car G1234))) |
| 1422 | @end example |
| 1423 | |
| 1424 | @xref{Loop Facility}, for a description of the @code{cl-loop} macro. |
| 1425 | This package defines a nonstandard @code{in-ref} loop clause that |
| 1426 | works much like @code{my-dolist}. |
| 1427 | @end defmac |
| 1428 | |
| 1429 | @node Conditionals |
| 1430 | @section Conditionals |
| 1431 | |
| 1432 | @noindent |
| 1433 | These conditional forms augment Emacs Lisp's simple @code{if}, |
| 1434 | @code{and}, @code{or}, and @code{cond} forms. |
| 1435 | |
| 1436 | @defmac cl-case keyform clause@dots{} |
| 1437 | This macro evaluates @var{keyform}, then compares it with the key |
| 1438 | values listed in the various @var{clause}s. Whichever clause matches |
| 1439 | the key is executed; comparison is done by @code{eql}. If no clause |
| 1440 | matches, the @code{cl-case} form returns @code{nil}. The clauses are |
| 1441 | of the form |
| 1442 | |
| 1443 | @example |
| 1444 | (@var{keylist} @var{body-forms}@dots{}) |
| 1445 | @end example |
| 1446 | |
| 1447 | @noindent |
| 1448 | where @var{keylist} is a list of key values. If there is exactly |
| 1449 | one value, and it is not a cons cell or the symbol @code{nil} or |
| 1450 | @code{t}, then it can be used by itself as a @var{keylist} without |
| 1451 | being enclosed in a list. All key values in the @code{cl-case} form |
| 1452 | must be distinct. The final clauses may use @code{t} in place of |
| 1453 | a @var{keylist} to indicate a default clause that should be taken |
| 1454 | if none of the other clauses match. (The symbol @code{otherwise} |
| 1455 | is also recognized in place of @code{t}. To make a clause that |
| 1456 | matches the actual symbol @code{t}, @code{nil}, or @code{otherwise}, |
| 1457 | enclose the symbol in a list.) |
| 1458 | |
| 1459 | For example, this expression reads a keystroke, then does one of |
| 1460 | four things depending on whether it is an @samp{a}, a @samp{b}, |
| 1461 | a @key{RET} or @kbd{C-j}, or anything else. |
| 1462 | |
| 1463 | @example |
| 1464 | (cl-case (read-char) |
| 1465 | (?a (do-a-thing)) |
| 1466 | (?b (do-b-thing)) |
| 1467 | ((?\r ?\n) (do-ret-thing)) |
| 1468 | (t (do-other-thing))) |
| 1469 | @end example |
| 1470 | @end defmac |
| 1471 | |
| 1472 | @defmac cl-ecase keyform clause@dots{} |
| 1473 | This macro is just like @code{cl-case}, except that if the key does |
| 1474 | not match any of the clauses, an error is signaled rather than |
| 1475 | simply returning @code{nil}. |
| 1476 | @end defmac |
| 1477 | |
| 1478 | @defmac cl-typecase keyform clause@dots{} |
| 1479 | This macro is a version of @code{cl-case} that checks for types |
| 1480 | rather than values. Each @var{clause} is of the form |
| 1481 | @samp{(@var{type} @var{body}@dots{})}. @xref{Type Predicates}, |
| 1482 | for a description of type specifiers. For example, |
| 1483 | |
| 1484 | @example |
| 1485 | (cl-typecase x |
| 1486 | (integer (munch-integer x)) |
| 1487 | (float (munch-float x)) |
| 1488 | (string (munch-integer (string-to-int x))) |
| 1489 | (t (munch-anything x))) |
| 1490 | @end example |
| 1491 | |
| 1492 | The type specifier @code{t} matches any type of object; the word |
| 1493 | @code{otherwise} is also allowed. To make one clause match any of |
| 1494 | several types, use an @code{(or @dots{})} type specifier. |
| 1495 | @end defmac |
| 1496 | |
| 1497 | @defmac cl-etypecase keyform clause@dots{} |
| 1498 | This macro is just like @code{cl-typecase}, except that if the key does |
| 1499 | not match any of the clauses, an error is signaled rather than |
| 1500 | simply returning @code{nil}. |
| 1501 | @end defmac |
| 1502 | |
| 1503 | @node Blocks and Exits |
| 1504 | @section Blocks and Exits |
| 1505 | |
| 1506 | @noindent |
| 1507 | Common Lisp @dfn{blocks} provide a non-local exit mechanism very |
| 1508 | similar to @code{catch} and @code{throw}, with lexical scoping. |
| 1509 | This package actually implements @code{cl-block} |
| 1510 | in terms of @code{catch}; however, the lexical scoping allows the |
| 1511 | byte-compiler to omit the costly @code{catch} step if the |
| 1512 | body of the block does not actually @code{cl-return-from} the block. |
| 1513 | |
| 1514 | @defmac cl-block name forms@dots{} |
| 1515 | The @var{forms} are evaluated as if by a @code{progn}. However, |
| 1516 | if any of the @var{forms} execute @code{(cl-return-from @var{name})}, |
| 1517 | they will jump out and return directly from the @code{cl-block} form. |
| 1518 | The @code{cl-block} returns the result of the last @var{form} unless |
| 1519 | a @code{cl-return-from} occurs. |
| 1520 | |
| 1521 | The @code{cl-block}/@code{cl-return-from} mechanism is quite similar to |
| 1522 | the @code{catch}/@code{throw} mechanism. The main differences are |
| 1523 | that block @var{name}s are unevaluated symbols, rather than forms |
| 1524 | (such as quoted symbols) that evaluate to a tag at run-time; and |
| 1525 | also that blocks are always lexically scoped. |
| 1526 | In a dynamically scoped @code{catch}, functions called from the |
| 1527 | @code{catch} body can also @code{throw} to the @code{catch}. This |
| 1528 | is not an option for @code{cl-block}, where |
| 1529 | the @code{cl-return-from} referring to a block name must appear |
| 1530 | physically within the @var{forms} that make up the body of the block. |
| 1531 | They may not appear within other called functions, although they may |
| 1532 | appear within macro expansions or @code{lambda}s in the body. Block |
| 1533 | names and @code{catch} names form independent name-spaces. |
| 1534 | |
| 1535 | In true Common Lisp, @code{defun} and @code{defmacro} surround |
| 1536 | the function or expander bodies with implicit blocks with the |
| 1537 | same name as the function or macro. This does not occur in Emacs |
| 1538 | Lisp, but this package provides @code{cl-defun} and @code{cl-defmacro} |
| 1539 | forms, which do create the implicit block. |
| 1540 | |
| 1541 | The Common Lisp looping constructs defined by this package, |
| 1542 | such as @code{cl-loop} and @code{cl-dolist}, also create implicit blocks |
| 1543 | just as in Common Lisp. |
| 1544 | |
| 1545 | Because they are implemented in terms of Emacs Lisp's @code{catch} |
| 1546 | and @code{throw}, blocks have the same overhead as actual |
| 1547 | @code{catch} constructs (roughly two function calls). However, |
| 1548 | the byte compiler will optimize away the @code{catch} |
| 1549 | if the block does |
| 1550 | not in fact contain any @code{cl-return} or @code{cl-return-from} calls |
| 1551 | that jump to it. This means that @code{cl-do} loops and @code{cl-defun} |
| 1552 | functions that don't use @code{cl-return} don't pay the overhead to |
| 1553 | support it. |
| 1554 | @end defmac |
| 1555 | |
| 1556 | @defmac cl-return-from name [result] |
| 1557 | This macro returns from the block named @var{name}, which must be |
| 1558 | an (unevaluated) symbol. If a @var{result} form is specified, it |
| 1559 | is evaluated to produce the result returned from the @code{block}. |
| 1560 | Otherwise, @code{nil} is returned. |
| 1561 | @end defmac |
| 1562 | |
| 1563 | @defmac cl-return [result] |
| 1564 | This macro is exactly like @code{(cl-return-from nil @var{result})}. |
| 1565 | Common Lisp loops like @code{cl-do} and @code{cl-dolist} implicitly enclose |
| 1566 | themselves in @code{nil} blocks. |
| 1567 | @end defmac |
| 1568 | |
| 1569 | @node Iteration |
| 1570 | @section Iteration |
| 1571 | |
| 1572 | @noindent |
| 1573 | The macros described here provide more sophisticated, high-level |
| 1574 | looping constructs to complement Emacs Lisp's basic loop forms |
| 1575 | (@pxref{Iteration,,,elisp,GNU Emacs Lisp Reference Manual}). |
| 1576 | |
| 1577 | @defmac cl-loop forms@dots{} |
| 1578 | This package supports both the simple, old-style meaning of |
| 1579 | @code{loop} and the extremely powerful and flexible feature known as |
| 1580 | the @dfn{Loop Facility} or @dfn{Loop Macro}. This more advanced |
| 1581 | facility is discussed in the following section; @pxref{Loop Facility}. |
| 1582 | The simple form of @code{loop} is described here. |
| 1583 | |
| 1584 | If @code{cl-loop} is followed by zero or more Lisp expressions, |
| 1585 | then @code{(cl-loop @var{exprs}@dots{})} simply creates an infinite |
| 1586 | loop executing the expressions over and over. The loop is |
| 1587 | enclosed in an implicit @code{nil} block. Thus, |
| 1588 | |
| 1589 | @example |
| 1590 | (cl-loop (foo) (if (no-more) (return 72)) (bar)) |
| 1591 | @end example |
| 1592 | |
| 1593 | @noindent |
| 1594 | is exactly equivalent to |
| 1595 | |
| 1596 | @example |
| 1597 | (cl-block nil (while t (foo) (if (no-more) (return 72)) (bar))) |
| 1598 | @end example |
| 1599 | |
| 1600 | If any of the expressions are plain symbols, the loop is instead |
| 1601 | interpreted as a Loop Macro specification as described later. |
| 1602 | (This is not a restriction in practice, since a plain symbol |
| 1603 | in the above notation would simply access and throw away the |
| 1604 | value of a variable.) |
| 1605 | @end defmac |
| 1606 | |
| 1607 | @defmac cl-do (spec@dots{}) (end-test [result@dots{}]) forms@dots{} |
| 1608 | This macro creates a general iterative loop. Each @var{spec} is |
| 1609 | of the form |
| 1610 | |
| 1611 | @example |
| 1612 | (@var{var} [@var{init} [@var{step}]]) |
| 1613 | @end example |
| 1614 | |
| 1615 | The loop works as follows: First, each @var{var} is bound to the |
| 1616 | associated @var{init} value as if by a @code{let} form. Then, in |
| 1617 | each iteration of the loop, the @var{end-test} is evaluated; if |
| 1618 | true, the loop is finished. Otherwise, the body @var{forms} are |
| 1619 | evaluated, then each @var{var} is set to the associated @var{step} |
| 1620 | expression (as if by a @code{cl-psetq} form) and the next iteration |
| 1621 | begins. Once the @var{end-test} becomes true, the @var{result} |
| 1622 | forms are evaluated (with the @var{var}s still bound to their |
| 1623 | values) to produce the result returned by @code{cl-do}. |
| 1624 | |
| 1625 | The entire @code{cl-do} loop is enclosed in an implicit @code{nil} |
| 1626 | block, so that you can use @code{(cl-return)} to break out of the |
| 1627 | loop at any time. |
| 1628 | |
| 1629 | If there are no @var{result} forms, the loop returns @code{nil}. |
| 1630 | If a given @var{var} has no @var{step} form, it is bound to its |
| 1631 | @var{init} value but not otherwise modified during the @code{cl-do} |
| 1632 | loop (unless the code explicitly modifies it); this case is just |
| 1633 | a shorthand for putting a @code{(let ((@var{var} @var{init})) @dots{})} |
| 1634 | around the loop. If @var{init} is also omitted it defaults to |
| 1635 | @code{nil}, and in this case a plain @samp{@var{var}} can be used |
| 1636 | in place of @samp{(@var{var})}, again following the analogy with |
| 1637 | @code{let}. |
| 1638 | |
| 1639 | This example (from Steele) illustrates a loop that applies the |
| 1640 | function @code{f} to successive pairs of values from the lists |
| 1641 | @code{foo} and @code{bar}; it is equivalent to the call |
| 1642 | @code{(cl-mapcar 'f foo bar)}. Note that this loop has no body |
| 1643 | @var{forms} at all, performing all its work as side effects of |
| 1644 | the rest of the loop. |
| 1645 | |
| 1646 | @example |
| 1647 | (cl-do ((x foo (cdr x)) |
| 1648 | (y bar (cdr y)) |
| 1649 | (z nil (cons (f (car x) (car y)) z))) |
| 1650 | ((or (null x) (null y)) |
| 1651 | (nreverse z))) |
| 1652 | @end example |
| 1653 | @end defmac |
| 1654 | |
| 1655 | @defmac cl-do* (spec@dots{}) (end-test [result@dots{}]) forms@dots{} |
| 1656 | This is to @code{cl-do} what @code{let*} is to @code{let}. In |
| 1657 | particular, the initial values are bound as if by @code{let*} |
| 1658 | rather than @code{let}, and the steps are assigned as if by |
| 1659 | @code{setq} rather than @code{cl-psetq}. |
| 1660 | |
| 1661 | Here is another way to write the above loop: |
| 1662 | |
| 1663 | @example |
| 1664 | (cl-do* ((xp foo (cdr xp)) |
| 1665 | (yp bar (cdr yp)) |
| 1666 | (x (car xp) (car xp)) |
| 1667 | (y (car yp) (car yp)) |
| 1668 | z) |
| 1669 | ((or (null xp) (null yp)) |
| 1670 | (nreverse z)) |
| 1671 | (push (f x y) z)) |
| 1672 | @end example |
| 1673 | @end defmac |
| 1674 | |
| 1675 | @defmac cl-dolist (var list [result]) forms@dots{} |
| 1676 | This is exactly like the standard Emacs Lisp macro @code{dolist}, |
| 1677 | but surrounds the loop with an implicit @code{nil} block. |
| 1678 | @end defmac |
| 1679 | |
| 1680 | @defmac cl-dotimes (var count [result]) forms@dots{} |
| 1681 | This is exactly like the standard Emacs Lisp macro @code{dotimes}, |
| 1682 | but surrounds the loop with an implicit @code{nil} block. |
| 1683 | The body is executed with @var{var} bound to the integers |
| 1684 | from zero (inclusive) to @var{count} (exclusive), in turn. Then |
| 1685 | @c FIXME lispref does not state this part explicitly, could move this there. |
| 1686 | the @code{result} form is evaluated with @var{var} bound to the total |
| 1687 | number of iterations that were done (i.e., @code{(max 0 @var{count})}) |
| 1688 | to get the return value for the loop form. |
| 1689 | @end defmac |
| 1690 | |
| 1691 | @defmac cl-do-symbols (var [obarray [result]]) forms@dots{} |
| 1692 | This loop iterates over all interned symbols. If @var{obarray} |
| 1693 | is specified and is not @code{nil}, it loops over all symbols in |
| 1694 | that obarray. For each symbol, the body @var{forms} are evaluated |
| 1695 | with @var{var} bound to that symbol. The symbols are visited in |
| 1696 | an unspecified order. Afterward the @var{result} form, if any, |
| 1697 | is evaluated (with @var{var} bound to @code{nil}) to get the return |
| 1698 | value. The loop is surrounded by an implicit @code{nil} block. |
| 1699 | @end defmac |
| 1700 | |
| 1701 | @defmac cl-do-all-symbols (var [result]) forms@dots{} |
| 1702 | This is identical to @code{cl-do-symbols} except that the @var{obarray} |
| 1703 | argument is omitted; it always iterates over the default obarray. |
| 1704 | @end defmac |
| 1705 | |
| 1706 | @xref{Mapping over Sequences}, for some more functions for |
| 1707 | iterating over vectors or lists. |
| 1708 | |
| 1709 | @node Loop Facility |
| 1710 | @section Loop Facility |
| 1711 | |
| 1712 | @noindent |
| 1713 | A common complaint with Lisp's traditional looping constructs was |
| 1714 | that they were either too simple and limited, such as @code{dotimes} |
| 1715 | or @code{while}, or too unreadable and obscure, like Common Lisp's |
| 1716 | @code{do} loop. |
| 1717 | |
| 1718 | To remedy this, Common Lisp added a construct called the ``Loop |
| 1719 | Facility'' or ``@code{loop} macro'', with an easy-to-use but very |
| 1720 | powerful and expressive syntax. |
| 1721 | |
| 1722 | @menu |
| 1723 | * Loop Basics:: The @code{cl-loop} macro, basic clause structure. |
| 1724 | * Loop Examples:: Working examples of the @code{cl-loop} macro. |
| 1725 | * For Clauses:: Clauses introduced by @code{for} or @code{as}. |
| 1726 | * Iteration Clauses:: @code{repeat}, @code{while}, @code{thereis}, etc. |
| 1727 | * Accumulation Clauses:: @code{collect}, @code{sum}, @code{maximize}, etc. |
| 1728 | * Other Clauses:: @code{with}, @code{if}, @code{initially}, @code{finally}. |
| 1729 | @end menu |
| 1730 | |
| 1731 | @node Loop Basics |
| 1732 | @subsection Loop Basics |
| 1733 | |
| 1734 | @noindent |
| 1735 | The @code{cl-loop} macro essentially creates a mini-language within |
| 1736 | Lisp that is specially tailored for describing loops. While this |
| 1737 | language is a little strange-looking by the standards of regular Lisp, |
| 1738 | it turns out to be very easy to learn and well-suited to its purpose. |
| 1739 | |
| 1740 | Since @code{cl-loop} is a macro, all parsing of the loop language |
| 1741 | takes place at byte-compile time; compiled @code{cl-loop}s are just |
| 1742 | as efficient as the equivalent @code{while} loops written longhand. |
| 1743 | |
| 1744 | @defmac cl-loop clauses@dots{} |
| 1745 | A loop construct consists of a series of @var{clause}s, each |
| 1746 | introduced by a symbol like @code{for} or @code{do}. Clauses |
| 1747 | are simply strung together in the argument list of @code{cl-loop}, |
| 1748 | with minimal extra parentheses. The various types of clauses |
| 1749 | specify initializations, such as the binding of temporary |
| 1750 | variables, actions to be taken in the loop, stepping actions, |
| 1751 | and final cleanup. |
| 1752 | |
| 1753 | Common Lisp specifies a certain general order of clauses in a |
| 1754 | loop: |
| 1755 | |
| 1756 | @example |
| 1757 | (loop @var{name-clause} |
| 1758 | @var{var-clauses}@dots{} |
| 1759 | @var{action-clauses}@dots{}) |
| 1760 | @end example |
| 1761 | |
| 1762 | The @var{name-clause} optionally gives a name to the implicit |
| 1763 | block that surrounds the loop. By default, the implicit block |
| 1764 | is named @code{nil}. The @var{var-clauses} specify what |
| 1765 | variables should be bound during the loop, and how they should |
| 1766 | be modified or iterated throughout the course of the loop. The |
| 1767 | @var{action-clauses} are things to be done during the loop, such |
| 1768 | as computing, collecting, and returning values. |
| 1769 | |
| 1770 | The Emacs version of the @code{cl-loop} macro is less restrictive about |
| 1771 | the order of clauses, but things will behave most predictably if |
| 1772 | you put the variable-binding clauses @code{with}, @code{for}, and |
| 1773 | @code{repeat} before the action clauses. As in Common Lisp, |
| 1774 | @code{initially} and @code{finally} clauses can go anywhere. |
| 1775 | |
| 1776 | Loops generally return @code{nil} by default, but you can cause |
| 1777 | them to return a value by using an accumulation clause like |
| 1778 | @code{collect}, an end-test clause like @code{always}, or an |
| 1779 | explicit @code{return} clause to jump out of the implicit block. |
| 1780 | (Because the loop body is enclosed in an implicit block, you can |
| 1781 | also use regular Lisp @code{cl-return} or @code{cl-return-from} to |
| 1782 | break out of the loop.) |
| 1783 | @end defmac |
| 1784 | |
| 1785 | The following sections give some examples of the loop macro in |
| 1786 | action, and describe the particular loop clauses in great detail. |
| 1787 | Consult the second edition of Steele for additional discussion |
| 1788 | and examples. |
| 1789 | |
| 1790 | @node Loop Examples |
| 1791 | @subsection Loop Examples |
| 1792 | |
| 1793 | @noindent |
| 1794 | Before listing the full set of clauses that are allowed, let's |
| 1795 | look at a few example loops just to get a feel for the @code{cl-loop} |
| 1796 | language. |
| 1797 | |
| 1798 | @example |
| 1799 | (cl-loop for buf in (buffer-list) |
| 1800 | collect (buffer-file-name buf)) |
| 1801 | @end example |
| 1802 | |
| 1803 | @noindent |
| 1804 | This loop iterates over all Emacs buffers, using the list |
| 1805 | returned by @code{buffer-list}. For each buffer @var{buf}, |
| 1806 | it calls @code{buffer-file-name} and collects the results into |
| 1807 | a list, which is then returned from the @code{cl-loop} construct. |
| 1808 | The result is a list of the file names of all the buffers in |
| 1809 | Emacs's memory. The words @code{for}, @code{in}, and @code{collect} |
| 1810 | are reserved words in the @code{cl-loop} language. |
| 1811 | |
| 1812 | @example |
| 1813 | (cl-loop repeat 20 do (insert "Yowsa\n")) |
| 1814 | @end example |
| 1815 | |
| 1816 | @noindent |
| 1817 | This loop inserts the phrase ``Yowsa'' twenty times in the |
| 1818 | current buffer. |
| 1819 | |
| 1820 | @example |
| 1821 | (cl-loop until (eobp) do (munch-line) (forward-line 1)) |
| 1822 | @end example |
| 1823 | |
| 1824 | @noindent |
| 1825 | This loop calls @code{munch-line} on every line until the end |
| 1826 | of the buffer. If point is already at the end of the buffer, |
| 1827 | the loop exits immediately. |
| 1828 | |
| 1829 | @example |
| 1830 | (cl-loop do (munch-line) until (eobp) do (forward-line 1)) |
| 1831 | @end example |
| 1832 | |
| 1833 | @noindent |
| 1834 | This loop is similar to the above one, except that @code{munch-line} |
| 1835 | is always called at least once. |
| 1836 | |
| 1837 | @example |
| 1838 | (cl-loop for x from 1 to 100 |
| 1839 | for y = (* x x) |
| 1840 | until (>= y 729) |
| 1841 | finally return (list x (= y 729))) |
| 1842 | @end example |
| 1843 | |
| 1844 | @noindent |
| 1845 | This more complicated loop searches for a number @code{x} whose |
| 1846 | square is 729. For safety's sake it only examines @code{x} |
| 1847 | values up to 100; dropping the phrase @samp{to 100} would |
| 1848 | cause the loop to count upwards with no limit. The second |
| 1849 | @code{for} clause defines @code{y} to be the square of @code{x} |
| 1850 | within the loop; the expression after the @code{=} sign is |
| 1851 | reevaluated each time through the loop. The @code{until} |
| 1852 | clause gives a condition for terminating the loop, and the |
| 1853 | @code{finally} clause says what to do when the loop finishes. |
| 1854 | (This particular example was written less concisely than it |
| 1855 | could have been, just for the sake of illustration.) |
| 1856 | |
| 1857 | Note that even though this loop contains three clauses (two |
| 1858 | @code{for}s and an @code{until}) that would have been enough to |
| 1859 | define loops all by themselves, it still creates a single loop |
| 1860 | rather than some sort of triple-nested loop. You must explicitly |
| 1861 | nest your @code{cl-loop} constructs if you want nested loops. |
| 1862 | |
| 1863 | @node For Clauses |
| 1864 | @subsection For Clauses |
| 1865 | |
| 1866 | @noindent |
| 1867 | Most loops are governed by one or more @code{for} clauses. |
| 1868 | A @code{for} clause simultaneously describes variables to be |
| 1869 | bound, how those variables are to be stepped during the loop, |
| 1870 | and usually an end condition based on those variables. |
| 1871 | |
| 1872 | The word @code{as} is a synonym for the word @code{for}. This |
| 1873 | word is followed by a variable name, then a word like @code{from} |
| 1874 | or @code{across} that describes the kind of iteration desired. |
| 1875 | In Common Lisp, the phrase @code{being the} sometimes precedes |
| 1876 | the type of iteration; in this package both @code{being} and |
| 1877 | @code{the} are optional. The word @code{each} is a synonym |
| 1878 | for @code{the}, and the word that follows it may be singular |
| 1879 | or plural: @samp{for x being the elements of y} or |
| 1880 | @samp{for x being each element of y}. Which form you use |
| 1881 | is purely a matter of style. |
| 1882 | |
| 1883 | The variable is bound around the loop as if by @code{let}: |
| 1884 | |
| 1885 | @example |
| 1886 | (setq i 'happy) |
| 1887 | (cl-loop for i from 1 to 10 do (do-something-with i)) |
| 1888 | i |
| 1889 | @result{} happy |
| 1890 | @end example |
| 1891 | |
| 1892 | @table @code |
| 1893 | @item for @var{var} from @var{expr1} to @var{expr2} by @var{expr3} |
| 1894 | This type of @code{for} clause creates a counting loop. Each of |
| 1895 | the three sub-terms is optional, though there must be at least one |
| 1896 | term so that the clause is marked as a counting clause. |
| 1897 | |
| 1898 | The three expressions are the starting value, the ending value, and |
| 1899 | the step value, respectively, of the variable. The loop counts |
| 1900 | upwards by default (@var{expr3} must be positive), from @var{expr1} |
| 1901 | to @var{expr2} inclusively. If you omit the @code{from} term, the |
| 1902 | loop counts from zero; if you omit the @code{to} term, the loop |
| 1903 | counts forever without stopping (unless stopped by some other |
| 1904 | loop clause, of course); if you omit the @code{by} term, the loop |
| 1905 | counts in steps of one. |
| 1906 | |
| 1907 | You can replace the word @code{from} with @code{upfrom} or |
| 1908 | @code{downfrom} to indicate the direction of the loop. Likewise, |
| 1909 | you can replace @code{to} with @code{upto} or @code{downto}. |
| 1910 | For example, @samp{for x from 5 downto 1} executes five times |
| 1911 | with @code{x} taking on the integers from 5 down to 1 in turn. |
| 1912 | Also, you can replace @code{to} with @code{below} or @code{above}, |
| 1913 | which are like @code{upto} and @code{downto} respectively except |
| 1914 | that they are exclusive rather than inclusive limits: |
| 1915 | |
| 1916 | @example |
| 1917 | (cl-loop for x to 10 collect x) |
| 1918 | @result{} (0 1 2 3 4 5 6 7 8 9 10) |
| 1919 | (cl-loop for x below 10 collect x) |
| 1920 | @result{} (0 1 2 3 4 5 6 7 8 9) |
| 1921 | @end example |
| 1922 | |
| 1923 | The @code{by} value is always positive, even for downward-counting |
| 1924 | loops. Some sort of @code{from} value is required for downward |
| 1925 | loops; @samp{for x downto 5} is not a valid loop clause all by |
| 1926 | itself. |
| 1927 | |
| 1928 | @item for @var{var} in @var{list} by @var{function} |
| 1929 | This clause iterates @var{var} over all the elements of @var{list}, |
| 1930 | in turn. If you specify the @code{by} term, then @var{function} |
| 1931 | is used to traverse the list instead of @code{cdr}; it must be a |
| 1932 | function taking one argument. For example: |
| 1933 | |
| 1934 | @example |
| 1935 | (cl-loop for x in '(1 2 3 4 5 6) collect (* x x)) |
| 1936 | @result{} (1 4 9 16 25 36) |
| 1937 | (cl-loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x)) |
| 1938 | @result{} (1 9 25) |
| 1939 | @end example |
| 1940 | |
| 1941 | @item for @var{var} on @var{list} by @var{function} |
| 1942 | This clause iterates @var{var} over all the cons cells of @var{list}. |
| 1943 | |
| 1944 | @example |
| 1945 | (cl-loop for x on '(1 2 3 4) collect x) |
| 1946 | @result{} ((1 2 3 4) (2 3 4) (3 4) (4)) |
| 1947 | @end example |
| 1948 | |
| 1949 | With @code{by}, there is no real reason that the @code{on} expression |
| 1950 | must be a list. For example: |
| 1951 | |
| 1952 | @example |
| 1953 | (cl-loop for x on first-animal by 'next-animal collect x) |
| 1954 | @end example |
| 1955 | |
| 1956 | @noindent |
| 1957 | where @code{(next-animal x)} takes an ``animal'' @var{x} and returns |
| 1958 | the next in the (assumed) sequence of animals, or @code{nil} if |
| 1959 | @var{x} was the last animal in the sequence. |
| 1960 | |
| 1961 | @item for @var{var} in-ref @var{list} by @var{function} |
| 1962 | This is like a regular @code{in} clause, but @var{var} becomes |
| 1963 | a @code{setf}-able ``reference'' onto the elements of the list |
| 1964 | rather than just a temporary variable. For example, |
| 1965 | |
| 1966 | @example |
| 1967 | (cl-loop for x in-ref my-list do (cl-incf x)) |
| 1968 | @end example |
| 1969 | |
| 1970 | @noindent |
| 1971 | increments every element of @code{my-list} in place. This clause |
| 1972 | is an extension to standard Common Lisp. |
| 1973 | |
| 1974 | @item for @var{var} across @var{array} |
| 1975 | This clause iterates @var{var} over all the elements of @var{array}, |
| 1976 | which may be a vector or a string. |
| 1977 | |
| 1978 | @example |
| 1979 | (cl-loop for x across "aeiou" |
| 1980 | do (use-vowel (char-to-string x))) |
| 1981 | @end example |
| 1982 | |
| 1983 | @item for @var{var} across-ref @var{array} |
| 1984 | This clause iterates over an array, with @var{var} a @code{setf}-able |
| 1985 | reference onto the elements; see @code{in-ref} above. |
| 1986 | |
| 1987 | @item for @var{var} being the elements of @var{sequence} |
| 1988 | This clause iterates over the elements of @var{sequence}, which may |
| 1989 | be a list, vector, or string. Since the type must be determined |
| 1990 | at run-time, this is somewhat less efficient than @code{in} or |
| 1991 | @code{across}. The clause may be followed by the additional term |
| 1992 | @samp{using (index @var{var2})} to cause @var{var2} to be bound to |
| 1993 | the successive indices (starting at 0) of the elements. |
| 1994 | |
| 1995 | This clause type is taken from older versions of the @code{loop} macro, |
| 1996 | and is not present in modern Common Lisp. The @samp{using (sequence @dots{})} |
| 1997 | term of the older macros is not supported. |
| 1998 | |
| 1999 | @item for @var{var} being the elements of-ref @var{sequence} |
| 2000 | This clause iterates over a sequence, with @var{var} a @code{setf}-able |
| 2001 | reference onto the elements; see @code{in-ref} above. |
| 2002 | |
| 2003 | @item for @var{var} being the symbols [of @var{obarray}] |
| 2004 | This clause iterates over symbols, either over all interned symbols |
| 2005 | or over all symbols in @var{obarray}. The loop is executed with |
| 2006 | @var{var} bound to each symbol in turn. The symbols are visited in |
| 2007 | an unspecified order. |
| 2008 | |
| 2009 | As an example, |
| 2010 | |
| 2011 | @example |
| 2012 | (cl-loop for sym being the symbols |
| 2013 | when (fboundp sym) |
| 2014 | when (string-match "^map" (symbol-name sym)) |
| 2015 | collect sym) |
| 2016 | @end example |
| 2017 | |
| 2018 | @noindent |
| 2019 | returns a list of all the functions whose names begin with @samp{map}. |
| 2020 | |
| 2021 | The Common Lisp words @code{external-symbols} and @code{present-symbols} |
| 2022 | are also recognized but are equivalent to @code{symbols} in Emacs Lisp. |
| 2023 | |
| 2024 | Due to a minor implementation restriction, it will not work to have |
| 2025 | more than one @code{for} clause iterating over symbols, hash tables, |
| 2026 | keymaps, overlays, or intervals in a given @code{cl-loop}. Fortunately, |
| 2027 | it would rarely if ever be useful to do so. It @emph{is} valid to mix |
| 2028 | one of these types of clauses with other clauses like @code{for @dots{} to} |
| 2029 | or @code{while}. |
| 2030 | |
| 2031 | @item for @var{var} being the hash-keys of @var{hash-table} |
| 2032 | @itemx for @var{var} being the hash-values of @var{hash-table} |
| 2033 | This clause iterates over the entries in @var{hash-table} with |
| 2034 | @var{var} bound to each key, or value. A @samp{using} clause can bind |
| 2035 | a second variable to the opposite part. |
| 2036 | |
| 2037 | @example |
| 2038 | (cl-loop for k being the hash-keys of h |
| 2039 | using (hash-values v) |
| 2040 | do |
| 2041 | (message "key %S -> value %S" k v)) |
| 2042 | @end example |
| 2043 | |
| 2044 | @item for @var{var} being the key-codes of @var{keymap} |
| 2045 | @itemx for @var{var} being the key-bindings of @var{keymap} |
| 2046 | This clause iterates over the entries in @var{keymap}. |
| 2047 | The iteration does not enter nested keymaps but does enter inherited |
| 2048 | (parent) keymaps. |
| 2049 | A @code{using} clause can access both the codes and the bindings |
| 2050 | together. |
| 2051 | |
| 2052 | @example |
| 2053 | (cl-loop for c being the key-codes of (current-local-map) |
| 2054 | using (key-bindings b) |
| 2055 | do |
| 2056 | (message "key %S -> binding %S" c b)) |
| 2057 | @end example |
| 2058 | |
| 2059 | |
| 2060 | @item for @var{var} being the key-seqs of @var{keymap} |
| 2061 | This clause iterates over all key sequences defined by @var{keymap} |
| 2062 | and its nested keymaps, where @var{var} takes on values which are |
| 2063 | vectors. The strings or vectors |
| 2064 | are reused for each iteration, so you must copy them if you wish to keep |
| 2065 | them permanently. You can add a @samp{using (key-bindings @dots{})} |
| 2066 | clause to get the command bindings as well. |
| 2067 | |
| 2068 | @item for @var{var} being the overlays [of @var{buffer}] @dots{} |
| 2069 | This clause iterates over the ``overlays'' of a buffer |
| 2070 | (the clause @code{extents} is synonymous |
| 2071 | with @code{overlays}). If the @code{of} term is omitted, the current |
| 2072 | buffer is used. |
| 2073 | This clause also accepts optional @samp{from @var{pos}} and |
| 2074 | @samp{to @var{pos}} terms, limiting the clause to overlays which |
| 2075 | overlap the specified region. |
| 2076 | |
| 2077 | @item for @var{var} being the intervals [of @var{buffer}] @dots{} |
| 2078 | This clause iterates over all intervals of a buffer with constant |
| 2079 | text properties. The variable @var{var} will be bound to conses |
| 2080 | of start and end positions, where one start position is always equal |
| 2081 | to the previous end position. The clause allows @code{of}, |
| 2082 | @code{from}, @code{to}, and @code{property} terms, where the latter |
| 2083 | term restricts the search to just the specified property. The |
| 2084 | @code{of} term may specify either a buffer or a string. |
| 2085 | |
| 2086 | @item for @var{var} being the frames |
| 2087 | This clause iterates over all Emacs frames. The clause @code{screens} is |
| 2088 | a synonym for @code{frames}. The frames are visited in |
| 2089 | @code{next-frame} order starting from @code{selected-frame}. |
| 2090 | |
| 2091 | @item for @var{var} being the windows [of @var{frame}] |
| 2092 | This clause iterates over the windows (in the Emacs sense) of |
| 2093 | the current frame, or of the specified @var{frame}. It visits windows |
| 2094 | in @code{next-window} order starting from @code{selected-window} |
| 2095 | (or @code{frame-selected-window} if you specify @var{frame}). |
| 2096 | This clause treats the minibuffer window in the same way as |
| 2097 | @code{next-window} does. For greater flexibility, consider using |
| 2098 | @code{walk-windows} instead. |
| 2099 | |
| 2100 | @item for @var{var} being the buffers |
| 2101 | This clause iterates over all buffers in Emacs. It is equivalent |
| 2102 | to @samp{for @var{var} in (buffer-list)}. |
| 2103 | |
| 2104 | @item for @var{var} = @var{expr1} then @var{expr2} |
| 2105 | This clause does a general iteration. The first time through |
| 2106 | the loop, @var{var} will be bound to @var{expr1}. On the second |
| 2107 | and successive iterations it will be set by evaluating @var{expr2} |
| 2108 | (which may refer to the old value of @var{var}). For example, |
| 2109 | these two loops are effectively the same: |
| 2110 | |
| 2111 | @example |
| 2112 | (cl-loop for x on my-list by 'cddr do @dots{}) |
| 2113 | (cl-loop for x = my-list then (cddr x) while x do @dots{}) |
| 2114 | @end example |
| 2115 | |
| 2116 | Note that this type of @code{for} clause does not imply any sort |
| 2117 | of terminating condition; the above example combines it with a |
| 2118 | @code{while} clause to tell when to end the loop. |
| 2119 | |
| 2120 | If you omit the @code{then} term, @var{expr1} is used both for |
| 2121 | the initial setting and for successive settings: |
| 2122 | |
| 2123 | @example |
| 2124 | (cl-loop for x = (random) when (> x 0) return x) |
| 2125 | @end example |
| 2126 | |
| 2127 | @noindent |
| 2128 | This loop keeps taking random numbers from the @code{(random)} |
| 2129 | function until it gets a positive one, which it then returns. |
| 2130 | @end table |
| 2131 | |
| 2132 | If you include several @code{for} clauses in a row, they are |
| 2133 | treated sequentially (as if by @code{let*} and @code{setq}). |
| 2134 | You can instead use the word @code{and} to link the clauses, |
| 2135 | in which case they are processed in parallel (as if by @code{let} |
| 2136 | and @code{cl-psetq}). |
| 2137 | |
| 2138 | @example |
| 2139 | (cl-loop for x below 5 for y = nil then x collect (list x y)) |
| 2140 | @result{} ((0 nil) (1 1) (2 2) (3 3) (4 4)) |
| 2141 | (cl-loop for x below 5 and y = nil then x collect (list x y)) |
| 2142 | @result{} ((0 nil) (1 0) (2 1) (3 2) (4 3)) |
| 2143 | @end example |
| 2144 | |
| 2145 | @noindent |
| 2146 | In the first loop, @code{y} is set based on the value of @code{x} |
| 2147 | that was just set by the previous clause; in the second loop, |
| 2148 | @code{x} and @code{y} are set simultaneously so @code{y} is set |
| 2149 | based on the value of @code{x} left over from the previous time |
| 2150 | through the loop. |
| 2151 | |
| 2152 | Another feature of the @code{cl-loop} macro is @emph{destructuring}, |
| 2153 | similar in concept to the destructuring provided by @code{defmacro} |
| 2154 | (@pxref{Argument Lists}). |
| 2155 | The @var{var} part of any @code{for} clause can be given as a list |
| 2156 | of variables instead of a single variable. The values produced |
| 2157 | during loop execution must be lists; the values in the lists are |
| 2158 | stored in the corresponding variables. |
| 2159 | |
| 2160 | @example |
| 2161 | (cl-loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y)) |
| 2162 | @result{} (5 9 13) |
| 2163 | @end example |
| 2164 | |
| 2165 | In loop destructuring, if there are more values than variables |
| 2166 | the trailing values are ignored, and if there are more variables |
| 2167 | than values the trailing variables get the value @code{nil}. |
| 2168 | If @code{nil} is used as a variable name, the corresponding |
| 2169 | values are ignored. Destructuring may be nested, and dotted |
| 2170 | lists of variables like @code{(x . y)} are allowed, so for example |
| 2171 | to process an alist |
| 2172 | |
| 2173 | @example |
| 2174 | (cl-loop for (key . value) in '((a . 1) (b . 2)) |
| 2175 | collect value) |
| 2176 | @result{} (1 2) |
| 2177 | @end example |
| 2178 | |
| 2179 | @node Iteration Clauses |
| 2180 | @subsection Iteration Clauses |
| 2181 | |
| 2182 | @noindent |
| 2183 | Aside from @code{for} clauses, there are several other loop clauses |
| 2184 | that control the way the loop operates. They might be used by |
| 2185 | themselves, or in conjunction with one or more @code{for} clauses. |
| 2186 | |
| 2187 | @table @code |
| 2188 | @item repeat @var{integer} |
| 2189 | This clause simply counts up to the specified number using an |
| 2190 | internal temporary variable. The loops |
| 2191 | |
| 2192 | @example |
| 2193 | (cl-loop repeat (1+ n) do @dots{}) |
| 2194 | (cl-loop for temp to n do @dots{}) |
| 2195 | @end example |
| 2196 | |
| 2197 | @noindent |
| 2198 | are identical except that the second one forces you to choose |
| 2199 | a name for a variable you aren't actually going to use. |
| 2200 | |
| 2201 | @item while @var{condition} |
| 2202 | This clause stops the loop when the specified condition (any Lisp |
| 2203 | expression) becomes @code{nil}. For example, the following two |
| 2204 | loops are equivalent, except for the implicit @code{nil} block |
| 2205 | that surrounds the second one: |
| 2206 | |
| 2207 | @example |
| 2208 | (while @var{cond} @var{forms}@dots{}) |
| 2209 | (cl-loop while @var{cond} do @var{forms}@dots{}) |
| 2210 | @end example |
| 2211 | |
| 2212 | @item until @var{condition} |
| 2213 | This clause stops the loop when the specified condition is true, |
| 2214 | i.e., non-@code{nil}. |
| 2215 | |
| 2216 | @item always @var{condition} |
| 2217 | This clause stops the loop when the specified condition is @code{nil}. |
| 2218 | Unlike @code{while}, it stops the loop using @code{return nil} so that |
| 2219 | the @code{finally} clauses are not executed. If all the conditions |
| 2220 | were non-@code{nil}, the loop returns @code{t}: |
| 2221 | |
| 2222 | @example |
| 2223 | (if (cl-loop for size in size-list always (> size 10)) |
| 2224 | (some-big-sizes) |
| 2225 | (no-big-sizes)) |
| 2226 | @end example |
| 2227 | |
| 2228 | @item never @var{condition} |
| 2229 | This clause is like @code{always}, except that the loop returns |
| 2230 | @code{t} if any conditions were false, or @code{nil} otherwise. |
| 2231 | |
| 2232 | @item thereis @var{condition} |
| 2233 | This clause stops the loop when the specified form is non-@code{nil}; |
| 2234 | in this case, it returns that non-@code{nil} value. If all the |
| 2235 | values were @code{nil}, the loop returns @code{nil}. |
| 2236 | @end table |
| 2237 | |
| 2238 | @node Accumulation Clauses |
| 2239 | @subsection Accumulation Clauses |
| 2240 | |
| 2241 | @noindent |
| 2242 | These clauses cause the loop to accumulate information about the |
| 2243 | specified Lisp @var{form}. The accumulated result is returned |
| 2244 | from the loop unless overridden, say, by a @code{return} clause. |
| 2245 | |
| 2246 | @table @code |
| 2247 | @item collect @var{form} |
| 2248 | This clause collects the values of @var{form} into a list. Several |
| 2249 | examples of @code{collect} appear elsewhere in this manual. |
| 2250 | |
| 2251 | The word @code{collecting} is a synonym for @code{collect}, and |
| 2252 | likewise for the other accumulation clauses. |
| 2253 | |
| 2254 | @item append @var{form} |
| 2255 | This clause collects lists of values into a result list using |
| 2256 | @code{append}. |
| 2257 | |
| 2258 | @item nconc @var{form} |
| 2259 | This clause collects lists of values into a result list by |
| 2260 | destructively modifying the lists rather than copying them. |
| 2261 | |
| 2262 | @item concat @var{form} |
| 2263 | This clause concatenates the values of the specified @var{form} |
| 2264 | into a string. (It and the following clause are extensions to |
| 2265 | standard Common Lisp.) |
| 2266 | |
| 2267 | @item vconcat @var{form} |
| 2268 | This clause concatenates the values of the specified @var{form} |
| 2269 | into a vector. |
| 2270 | |
| 2271 | @item count @var{form} |
| 2272 | This clause counts the number of times the specified @var{form} |
| 2273 | evaluates to a non-@code{nil} value. |
| 2274 | |
| 2275 | @item sum @var{form} |
| 2276 | This clause accumulates the sum of the values of the specified |
| 2277 | @var{form}, which must evaluate to a number. |
| 2278 | |
| 2279 | @item maximize @var{form} |
| 2280 | This clause accumulates the maximum value of the specified @var{form}, |
| 2281 | which must evaluate to a number. The return value is undefined if |
| 2282 | @code{maximize} is executed zero times. |
| 2283 | |
| 2284 | @item minimize @var{form} |
| 2285 | This clause accumulates the minimum value of the specified @var{form}. |
| 2286 | @end table |
| 2287 | |
| 2288 | Accumulation clauses can be followed by @samp{into @var{var}} to |
| 2289 | cause the data to be collected into variable @var{var} (which is |
| 2290 | automatically @code{let}-bound during the loop) rather than an |
| 2291 | unnamed temporary variable. Also, @code{into} accumulations do |
| 2292 | not automatically imply a return value. The loop must use some |
| 2293 | explicit mechanism, such as @code{finally return}, to return |
| 2294 | the accumulated result. |
| 2295 | |
| 2296 | It is valid for several accumulation clauses of the same type to |
| 2297 | accumulate into the same place. From Steele: |
| 2298 | |
| 2299 | @example |
| 2300 | (cl-loop for name in '(fred sue alice joe june) |
| 2301 | for kids in '((bob ken) () () (kris sunshine) ()) |
| 2302 | collect name |
| 2303 | append kids) |
| 2304 | @result{} (fred bob ken sue alice joe kris sunshine june) |
| 2305 | @end example |
| 2306 | |
| 2307 | @node Other Clauses |
| 2308 | @subsection Other Clauses |
| 2309 | |
| 2310 | @noindent |
| 2311 | This section describes the remaining loop clauses. |
| 2312 | |
| 2313 | @table @code |
| 2314 | @item with @var{var} = @var{value} |
| 2315 | This clause binds a variable to a value around the loop, but |
| 2316 | otherwise leaves the variable alone during the loop. The following |
| 2317 | loops are basically equivalent: |
| 2318 | |
| 2319 | @example |
| 2320 | (cl-loop with x = 17 do @dots{}) |
| 2321 | (let ((x 17)) (cl-loop do @dots{})) |
| 2322 | (cl-loop for x = 17 then x do @dots{}) |
| 2323 | @end example |
| 2324 | |
| 2325 | Naturally, the variable @var{var} might be used for some purpose |
| 2326 | in the rest of the loop. For example: |
| 2327 | |
| 2328 | @example |
| 2329 | (cl-loop for x in my-list with res = nil do (push x res) |
| 2330 | finally return res) |
| 2331 | @end example |
| 2332 | |
| 2333 | This loop inserts the elements of @code{my-list} at the front of |
| 2334 | a new list being accumulated in @code{res}, then returns the |
| 2335 | list @code{res} at the end of the loop. The effect is similar |
| 2336 | to that of a @code{collect} clause, but the list gets reversed |
| 2337 | by virtue of the fact that elements are being pushed onto the |
| 2338 | front of @code{res} rather than the end. |
| 2339 | |
| 2340 | If you omit the @code{=} term, the variable is initialized to |
| 2341 | @code{nil}. (Thus the @samp{= nil} in the above example is |
| 2342 | unnecessary.) |
| 2343 | |
| 2344 | Bindings made by @code{with} are sequential by default, as if |
| 2345 | by @code{let*}. Just like @code{for} clauses, @code{with} clauses |
| 2346 | can be linked with @code{and} to cause the bindings to be made by |
| 2347 | @code{let} instead. |
| 2348 | |
| 2349 | @item if @var{condition} @var{clause} |
| 2350 | This clause executes the following loop clause only if the specified |
| 2351 | condition is true. The following @var{clause} should be an accumulation, |
| 2352 | @code{do}, @code{return}, @code{if}, or @code{unless} clause. |
| 2353 | Several clauses may be linked by separating them with @code{and}. |
| 2354 | These clauses may be followed by @code{else} and a clause or clauses |
| 2355 | to execute if the condition was false. The whole construct may |
| 2356 | optionally be followed by the word @code{end} (which may be used to |
| 2357 | disambiguate an @code{else} or @code{and} in a nested @code{if}). |
| 2358 | |
| 2359 | The actual non-@code{nil} value of the condition form is available |
| 2360 | by the name @code{it} in the ``then'' part. For example: |
| 2361 | |
| 2362 | @example |
| 2363 | (setq funny-numbers '(6 13 -1)) |
| 2364 | @result{} (6 13 -1) |
| 2365 | (cl-loop for x below 10 |
| 2366 | if (cl-oddp x) |
| 2367 | collect x into odds |
| 2368 | and if (memq x funny-numbers) return (cdr it) end |
| 2369 | else |
| 2370 | collect x into evens |
| 2371 | finally return (vector odds evens)) |
| 2372 | @result{} [(1 3 5 7 9) (0 2 4 6 8)] |
| 2373 | (setq funny-numbers '(6 7 13 -1)) |
| 2374 | @result{} (6 7 13 -1) |
| 2375 | (cl-loop <@r{same thing again}>) |
| 2376 | @result{} (13 -1) |
| 2377 | @end example |
| 2378 | |
| 2379 | Note the use of @code{and} to put two clauses into the ``then'' |
| 2380 | part, one of which is itself an @code{if} clause. Note also that |
| 2381 | @code{end}, while normally optional, was necessary here to make |
| 2382 | it clear that the @code{else} refers to the outermost @code{if} |
| 2383 | clause. In the first case, the loop returns a vector of lists |
| 2384 | of the odd and even values of @var{x}. In the second case, the |
| 2385 | odd number 7 is one of the @code{funny-numbers} so the loop |
| 2386 | returns early; the actual returned value is based on the result |
| 2387 | of the @code{memq} call. |
| 2388 | |
| 2389 | @item when @var{condition} @var{clause} |
| 2390 | This clause is just a synonym for @code{if}. |
| 2391 | |
| 2392 | @item unless @var{condition} @var{clause} |
| 2393 | The @code{unless} clause is just like @code{if} except that the |
| 2394 | sense of the condition is reversed. |
| 2395 | |
| 2396 | @item named @var{name} |
| 2397 | This clause gives a name other than @code{nil} to the implicit |
| 2398 | block surrounding the loop. The @var{name} is the symbol to be |
| 2399 | used as the block name. |
| 2400 | |
| 2401 | @item initially [do] @var{forms}@dots{} |
| 2402 | This keyword introduces one or more Lisp forms which will be |
| 2403 | executed before the loop itself begins (but after any variables |
| 2404 | requested by @code{for} or @code{with} have been bound to their |
| 2405 | initial values). @code{initially} clauses can appear anywhere; |
| 2406 | if there are several, they are executed in the order they appear |
| 2407 | in the loop. The keyword @code{do} is optional. |
| 2408 | |
| 2409 | @item finally [do] @var{forms}@dots{} |
| 2410 | This introduces Lisp forms which will be executed after the loop |
| 2411 | finishes (say, on request of a @code{for} or @code{while}). |
| 2412 | @code{initially} and @code{finally} clauses may appear anywhere |
| 2413 | in the loop construct, but they are executed (in the specified |
| 2414 | order) at the beginning or end, respectively, of the loop. |
| 2415 | |
| 2416 | @item finally return @var{form} |
| 2417 | This says that @var{form} should be executed after the loop |
| 2418 | is done to obtain a return value. (Without this, or some other |
| 2419 | clause like @code{collect} or @code{return}, the loop will simply |
| 2420 | return @code{nil}.) Variables bound by @code{for}, @code{with}, |
| 2421 | or @code{into} will still contain their final values when @var{form} |
| 2422 | is executed. |
| 2423 | |
| 2424 | @item do @var{forms}@dots{} |
| 2425 | The word @code{do} may be followed by any number of Lisp expressions |
| 2426 | which are executed as an implicit @code{progn} in the body of the |
| 2427 | loop. Many of the examples in this section illustrate the use of |
| 2428 | @code{do}. |
| 2429 | |
| 2430 | @item return @var{form} |
| 2431 | This clause causes the loop to return immediately. The following |
| 2432 | Lisp form is evaluated to give the return value of the loop |
| 2433 | form. The @code{finally} clauses, if any, are not executed. |
| 2434 | Of course, @code{return} is generally used inside an @code{if} or |
| 2435 | @code{unless}, as its use in a top-level loop clause would mean |
| 2436 | the loop would never get to ``loop'' more than once. |
| 2437 | |
| 2438 | The clause @samp{return @var{form}} is equivalent to |
| 2439 | @samp{do (cl-return @var{form})} (or @code{cl-return-from} if the loop |
| 2440 | was named). The @code{return} clause is implemented a bit more |
| 2441 | efficiently, though. |
| 2442 | @end table |
| 2443 | |
| 2444 | While there is no high-level way to add user extensions to @code{cl-loop}, |
| 2445 | this package does offer two properties called @code{cl-loop-handler} |
| 2446 | and @code{cl-loop-for-handler} which are functions to be called when a |
| 2447 | given symbol is encountered as a top-level loop clause or @code{for} |
| 2448 | clause, respectively. Consult the source code in file |
| 2449 | @file{cl-macs.el} for details. |
| 2450 | |
| 2451 | This package's @code{cl-loop} macro is compatible with that of Common |
| 2452 | Lisp, except that a few features are not implemented: @code{loop-finish} |
| 2453 | and data-type specifiers. Naturally, the @code{for} clauses that |
| 2454 | iterate over keymaps, overlays, intervals, frames, windows, and |
| 2455 | buffers are Emacs-specific extensions. |
| 2456 | |
| 2457 | @node Multiple Values |
| 2458 | @section Multiple Values |
| 2459 | |
| 2460 | @noindent |
| 2461 | Common Lisp functions can return zero or more results. Emacs Lisp |
| 2462 | functions, by contrast, always return exactly one result. This |
| 2463 | package makes no attempt to emulate Common Lisp multiple return |
| 2464 | values; Emacs versions of Common Lisp functions that return more |
| 2465 | than one value either return just the first value (as in |
| 2466 | @code{cl-compiler-macroexpand}) or return a list of values. |
| 2467 | This package @emph{does} define placeholders |
| 2468 | for the Common Lisp functions that work with multiple values, but |
| 2469 | in Emacs Lisp these functions simply operate on lists instead. |
| 2470 | The @code{cl-values} form, for example, is a synonym for @code{list} |
| 2471 | in Emacs. |
| 2472 | |
| 2473 | @defmac cl-multiple-value-bind (var@dots{}) values-form forms@dots{} |
| 2474 | This form evaluates @var{values-form}, which must return a list of |
| 2475 | values. It then binds the @var{var}s to these respective values, |
| 2476 | as if by @code{let}, and then executes the body @var{forms}. |
| 2477 | If there are more @var{var}s than values, the extra @var{var}s |
| 2478 | are bound to @code{nil}. If there are fewer @var{var}s than |
| 2479 | values, the excess values are ignored. |
| 2480 | @end defmac |
| 2481 | |
| 2482 | @defmac cl-multiple-value-setq (var@dots{}) form |
| 2483 | This form evaluates @var{form}, which must return a list of values. |
| 2484 | It then sets the @var{var}s to these respective values, as if by |
| 2485 | @code{setq}. Extra @var{var}s or values are treated the same as |
| 2486 | in @code{cl-multiple-value-bind}. |
| 2487 | @end defmac |
| 2488 | |
| 2489 | Since a perfect emulation is not feasible in Emacs Lisp, this |
| 2490 | package opts to keep it as simple and predictable as possible. |
| 2491 | |
| 2492 | @node Macros |
| 2493 | @chapter Macros |
| 2494 | |
| 2495 | @noindent |
| 2496 | This package implements the various Common Lisp features of |
| 2497 | @code{defmacro}, such as destructuring, @code{&environment}, |
| 2498 | and @code{&body}. Top-level @code{&whole} is not implemented |
| 2499 | for @code{defmacro} due to technical difficulties. |
| 2500 | @xref{Argument Lists}. |
| 2501 | |
| 2502 | Destructuring is made available to the user by way of the |
| 2503 | following macro: |
| 2504 | |
| 2505 | @defmac cl-destructuring-bind arglist expr forms@dots{} |
| 2506 | This macro expands to code that executes @var{forms}, with |
| 2507 | the variables in @var{arglist} bound to the list of values |
| 2508 | returned by @var{expr}. The @var{arglist} can include all |
| 2509 | the features allowed for @code{cl-defmacro} argument lists, |
| 2510 | including destructuring. (The @code{&environment} keyword |
| 2511 | is not allowed.) The macro expansion will signal an error |
| 2512 | if @var{expr} returns a list of the wrong number of arguments |
| 2513 | or with incorrect keyword arguments. |
| 2514 | @end defmac |
| 2515 | |
| 2516 | This package also includes the Common Lisp @code{define-compiler-macro} |
| 2517 | facility, which allows you to define compile-time expansions and |
| 2518 | optimizations for your functions. |
| 2519 | |
| 2520 | @defmac cl-define-compiler-macro name arglist forms@dots{} |
| 2521 | This form is similar to @code{defmacro}, except that it only expands |
| 2522 | calls to @var{name} at compile-time; calls processed by the Lisp |
| 2523 | interpreter are not expanded, nor are they expanded by the |
| 2524 | @code{macroexpand} function. |
| 2525 | |
| 2526 | The argument list may begin with a @code{&whole} keyword and a |
| 2527 | variable. This variable is bound to the macro-call form itself, |
| 2528 | i.e., to a list of the form @samp{(@var{name} @var{args}@dots{})}. |
| 2529 | If the macro expander returns this form unchanged, then the |
| 2530 | compiler treats it as a normal function call. This allows |
| 2531 | compiler macros to work as optimizers for special cases of a |
| 2532 | function, leaving complicated cases alone. |
| 2533 | |
| 2534 | For example, here is a simplified version of a definition that |
| 2535 | appears as a standard part of this package: |
| 2536 | |
| 2537 | @example |
| 2538 | (cl-define-compiler-macro cl-member (&whole form a list &rest keys) |
| 2539 | (if (and (null keys) |
| 2540 | (eq (car-safe a) 'quote) |
| 2541 | (not (floatp (cadr a)))) |
| 2542 | (list 'memq a list) |
| 2543 | form)) |
| 2544 | @end example |
| 2545 | |
| 2546 | @noindent |
| 2547 | This definition causes @code{(cl-member @var{a} @var{list})} to change |
| 2548 | to a call to the faster @code{memq} in the common case where @var{a} |
| 2549 | is a non-floating-point constant; if @var{a} is anything else, or |
| 2550 | if there are any keyword arguments in the call, then the original |
| 2551 | @code{cl-member} call is left intact. (The actual compiler macro |
| 2552 | for @code{cl-member} optimizes a number of other cases, including |
| 2553 | common @code{:test} predicates.) |
| 2554 | @end defmac |
| 2555 | |
| 2556 | @defun cl-compiler-macroexpand form |
| 2557 | This function is analogous to @code{macroexpand}, except that it |
| 2558 | expands compiler macros rather than regular macros. It returns |
| 2559 | @var{form} unchanged if it is not a call to a function for which |
| 2560 | a compiler macro has been defined, or if that compiler macro |
| 2561 | decided to punt by returning its @code{&whole} argument. Like |
| 2562 | @code{macroexpand}, it expands repeatedly until it reaches a form |
| 2563 | for which no further expansion is possible. |
| 2564 | @end defun |
| 2565 | |
| 2566 | @xref{Macro Bindings}, for descriptions of the @code{cl-macrolet} |
| 2567 | and @code{cl-symbol-macrolet} forms for making ``local'' macro |
| 2568 | definitions. |
| 2569 | |
| 2570 | @node Declarations |
| 2571 | @chapter Declarations |
| 2572 | |
| 2573 | @noindent |
| 2574 | Common Lisp includes a complex and powerful ``declaration'' |
| 2575 | mechanism that allows you to give the compiler special hints |
| 2576 | about the types of data that will be stored in particular variables, |
| 2577 | and about the ways those variables and functions will be used. This |
| 2578 | package defines versions of all the Common Lisp declaration forms: |
| 2579 | @code{declare}, @code{locally}, @code{proclaim}, @code{declaim}, |
| 2580 | and @code{the}. |
| 2581 | |
| 2582 | Most of the Common Lisp declarations are not currently useful in Emacs |
| 2583 | Lisp. For example, the byte-code system provides little |
| 2584 | opportunity to benefit from type information. |
| 2585 | @ignore |
| 2586 | and @code{special} declarations are redundant in a fully |
| 2587 | dynamically-scoped Lisp. |
| 2588 | @end ignore |
| 2589 | A few declarations are meaningful when byte compiler optimizations |
| 2590 | are enabled, as they are by the default. Otherwise these |
| 2591 | declarations will effectively be ignored. |
| 2592 | |
| 2593 | @defun cl-proclaim decl-spec |
| 2594 | This function records a ``global'' declaration specified by |
| 2595 | @var{decl-spec}. Since @code{cl-proclaim} is a function, @var{decl-spec} |
| 2596 | is evaluated and thus should normally be quoted. |
| 2597 | @end defun |
| 2598 | |
| 2599 | @defmac cl-declaim decl-specs@dots{} |
| 2600 | This macro is like @code{cl-proclaim}, except that it takes any number |
| 2601 | of @var{decl-spec} arguments, and the arguments are unevaluated and |
| 2602 | unquoted. The @code{cl-declaim} macro also puts @code{(cl-eval-when |
| 2603 | (compile load eval) @dots{})} around the declarations so that they will |
| 2604 | be registered at compile-time as well as at run-time. (This is vital, |
| 2605 | since normally the declarations are meant to influence the way the |
| 2606 | compiler treats the rest of the file that contains the @code{cl-declaim} |
| 2607 | form.) |
| 2608 | @end defmac |
| 2609 | |
| 2610 | @defmac cl-declare decl-specs@dots{} |
| 2611 | This macro is used to make declarations within functions and other |
| 2612 | code. Common Lisp allows declarations in various locations, generally |
| 2613 | at the beginning of any of the many ``implicit @code{progn}s'' |
| 2614 | throughout Lisp syntax, such as function bodies, @code{let} bodies, |
| 2615 | etc. Currently the only declaration understood by @code{cl-declare} |
| 2616 | is @code{special}. |
| 2617 | @end defmac |
| 2618 | |
| 2619 | @defmac cl-locally declarations@dots{} forms@dots{} |
| 2620 | In this package, @code{cl-locally} is no different from @code{progn}. |
| 2621 | @end defmac |
| 2622 | |
| 2623 | @defmac cl-the type form |
| 2624 | Type information provided by @code{cl-the} is ignored in this package; |
| 2625 | in other words, @code{(cl-the @var{type} @var{form})} is equivalent to |
| 2626 | @var{form}. Future byte-compiler optimizations may make use of this |
| 2627 | information. |
| 2628 | |
| 2629 | For example, @code{mapcar} can map over both lists and arrays. It is |
| 2630 | hard for the compiler to expand @code{mapcar} into an in-line loop |
| 2631 | unless it knows whether the sequence will be a list or an array ahead |
| 2632 | of time. With @code{(mapcar 'car (cl-the vector foo))}, a future |
| 2633 | compiler would have enough information to expand the loop in-line. |
| 2634 | For now, Emacs Lisp will treat the above code as exactly equivalent |
| 2635 | to @code{(mapcar 'car foo)}. |
| 2636 | @end defmac |
| 2637 | |
| 2638 | Each @var{decl-spec} in a @code{cl-proclaim}, @code{cl-declaim}, or |
| 2639 | @code{cl-declare} should be a list beginning with a symbol that says |
| 2640 | what kind of declaration it is. This package currently understands |
| 2641 | @code{special}, @code{inline}, @code{notinline}, @code{optimize}, |
| 2642 | and @code{warn} declarations. (The @code{warn} declaration is an |
| 2643 | extension of standard Common Lisp.) Other Common Lisp declarations, |
| 2644 | such as @code{type} and @code{ftype}, are silently ignored. |
| 2645 | |
| 2646 | @table @code |
| 2647 | @item special |
| 2648 | @c FIXME ? |
| 2649 | Since all variables in Emacs Lisp are ``special'' (in the Common |
| 2650 | Lisp sense), @code{special} declarations are only advisory. They |
| 2651 | simply tell the byte compiler that the specified |
| 2652 | variables are intentionally being referred to without being |
| 2653 | bound in the body of the function. The compiler normally emits |
| 2654 | warnings for such references, since they could be typographical |
| 2655 | errors for references to local variables. |
| 2656 | |
| 2657 | The declaration @code{(cl-declare (special @var{var1} @var{var2}))} is |
| 2658 | equivalent to @code{(defvar @var{var1}) (defvar @var{var2})}. |
| 2659 | |
| 2660 | In top-level contexts, it is generally better to write |
| 2661 | @code{(defvar @var{var})} than @code{(cl-declaim (special @var{var}))}, |
| 2662 | since @code{defvar} makes your intentions clearer. |
| 2663 | |
| 2664 | @item inline |
| 2665 | The @code{inline} @var{decl-spec} lists one or more functions |
| 2666 | whose bodies should be expanded ``in-line'' into calling functions |
| 2667 | whenever the compiler is able to arrange for it. For example, |
| 2668 | the function @code{cl-acons} is declared @code{inline} |
| 2669 | by this package so that the form @code{(cl-acons @var{key} @var{value} |
| 2670 | @var{alist})} will |
| 2671 | expand directly into @code{(cons (cons @var{key} @var{value}) @var{alist})} |
| 2672 | when it is called in user functions, so as to save function calls. |
| 2673 | |
| 2674 | The following declarations are all equivalent. Note that the |
| 2675 | @code{defsubst} form is a convenient way to define a function |
| 2676 | and declare it inline all at once. |
| 2677 | |
| 2678 | @example |
| 2679 | (cl-declaim (inline foo bar)) |
| 2680 | (cl-eval-when (compile load eval) |
| 2681 | (cl-proclaim '(inline foo bar))) |
| 2682 | (defsubst foo (@dots{}) @dots{}) ; instead of defun |
| 2683 | @end example |
| 2684 | |
| 2685 | @strong{Please note:} this declaration remains in effect after the |
| 2686 | containing source file is done. It is correct to use it to |
| 2687 | request that a function you have defined should be inlined, |
| 2688 | but it is impolite to use it to request inlining of an external |
| 2689 | function. |
| 2690 | |
| 2691 | In Common Lisp, it is possible to use @code{(declare (inline @dots{}))} |
| 2692 | before a particular call to a function to cause just that call to |
| 2693 | be inlined; the current byte compilers provide no way to implement |
| 2694 | this, so @code{(cl-declare (inline @dots{}))} is currently ignored by |
| 2695 | this package. |
| 2696 | |
| 2697 | @item notinline |
| 2698 | The @code{notinline} declaration lists functions which should |
| 2699 | not be inlined after all; it cancels a previous @code{inline} |
| 2700 | declaration. |
| 2701 | |
| 2702 | @item optimize |
| 2703 | This declaration controls how much optimization is performed by |
| 2704 | the compiler. |
| 2705 | |
| 2706 | The word @code{optimize} is followed by any number of lists like |
| 2707 | @code{(speed 3)} or @code{(safety 2)}. Common Lisp defines several |
| 2708 | optimization ``qualities''; this package ignores all but @code{speed} |
| 2709 | and @code{safety}. The value of a quality should be an integer from |
| 2710 | 0 to 3, with 0 meaning ``unimportant'' and 3 meaning ``very important''. |
| 2711 | The default level for both qualities is 1. |
| 2712 | |
| 2713 | In this package, the @code{speed} quality is tied to the @code{byte-optimize} |
| 2714 | flag, which is set to @code{nil} for @code{(speed 0)} and to |
| 2715 | @code{t} for higher settings; and the @code{safety} quality is |
| 2716 | tied to the @code{byte-compile-delete-errors} flag, which is |
| 2717 | set to @code{nil} for @code{(safety 3)} and to @code{t} for all |
| 2718 | lower settings. (The latter flag controls whether the compiler |
| 2719 | is allowed to optimize out code whose only side-effect could |
| 2720 | be to signal an error, e.g., rewriting @code{(progn foo bar)} to |
| 2721 | @code{bar} when it is not known whether @code{foo} will be bound |
| 2722 | at run-time.) |
| 2723 | |
| 2724 | Note that even compiling with @code{(safety 0)}, the Emacs |
| 2725 | byte-code system provides sufficient checking to prevent real |
| 2726 | harm from being done. For example, barring serious bugs in |
| 2727 | Emacs itself, Emacs will not crash with a segmentation fault |
| 2728 | just because of an error in a fully-optimized Lisp program. |
| 2729 | |
| 2730 | The @code{optimize} declaration is normally used in a top-level |
| 2731 | @code{cl-proclaim} or @code{cl-declaim} in a file; Common Lisp allows |
| 2732 | it to be used with @code{declare} to set the level of optimization |
| 2733 | locally for a given form, but this will not work correctly with the |
| 2734 | current byte-compiler. (The @code{cl-declare} |
| 2735 | will set the new optimization level, but that level will not |
| 2736 | automatically be unset after the enclosing form is done.) |
| 2737 | |
| 2738 | @item warn |
| 2739 | This declaration controls what sorts of warnings are generated |
| 2740 | by the byte compiler. The word @code{warn} is followed by any |
| 2741 | number of ``warning qualities'', similar in form to optimization |
| 2742 | qualities. The currently supported warning types are |
| 2743 | @code{redefine}, @code{callargs}, @code{unresolved}, and |
| 2744 | @code{free-vars}; in the current system, a value of 0 will |
| 2745 | disable these warnings and any higher value will enable them. |
| 2746 | See the documentation of the variable @code{byte-compile-warnings} |
| 2747 | for more details. |
| 2748 | @end table |
| 2749 | |
| 2750 | @node Symbols |
| 2751 | @chapter Symbols |
| 2752 | |
| 2753 | @noindent |
| 2754 | This package defines several symbol-related features that were |
| 2755 | missing from Emacs Lisp. |
| 2756 | |
| 2757 | @menu |
| 2758 | * Property Lists:: @code{cl-get}, @code{cl-remprop}, @code{cl-getf}, @code{cl-remf}. |
| 2759 | * Creating Symbols:: @code{cl-gensym}, @code{cl-gentemp}. |
| 2760 | @end menu |
| 2761 | |
| 2762 | @node Property Lists |
| 2763 | @section Property Lists |
| 2764 | |
| 2765 | @noindent |
| 2766 | These functions augment the standard Emacs Lisp functions @code{get} |
| 2767 | and @code{put} for operating on properties attached to symbols. |
| 2768 | There are also functions for working with property lists as |
| 2769 | first-class data structures not attached to particular symbols. |
| 2770 | |
| 2771 | @defun cl-get symbol property &optional default |
| 2772 | This function is like @code{get}, except that if the property is |
| 2773 | not found, the @var{default} argument provides the return value. |
| 2774 | (The Emacs Lisp @code{get} function always uses @code{nil} as |
| 2775 | the default; this package's @code{cl-get} is equivalent to Common |
| 2776 | Lisp's @code{get}.) |
| 2777 | |
| 2778 | The @code{cl-get} function is @code{setf}-able; when used in this |
| 2779 | fashion, the @var{default} argument is allowed but ignored. |
| 2780 | @end defun |
| 2781 | |
| 2782 | @defun cl-remprop symbol property |
| 2783 | This function removes the entry for @var{property} from the property |
| 2784 | list of @var{symbol}. It returns a true value if the property was |
| 2785 | indeed found and removed, or @code{nil} if there was no such property. |
| 2786 | (This function was probably omitted from Emacs originally because, |
| 2787 | since @code{get} did not allow a @var{default}, it was very difficult |
| 2788 | to distinguish between a missing property and a property whose value |
| 2789 | was @code{nil}; thus, setting a property to @code{nil} was close |
| 2790 | enough to @code{cl-remprop} for most purposes.) |
| 2791 | @end defun |
| 2792 | |
| 2793 | @defun cl-getf place property &optional default |
| 2794 | This function scans the list @var{place} as if it were a property |
| 2795 | list, i.e., a list of alternating property names and values. If |
| 2796 | an even-numbered element of @var{place} is found which is @code{eq} |
| 2797 | to @var{property}, the following odd-numbered element is returned. |
| 2798 | Otherwise, @var{default} is returned (or @code{nil} if no default |
| 2799 | is given). |
| 2800 | |
| 2801 | In particular, |
| 2802 | |
| 2803 | @example |
| 2804 | (get sym prop) @equiv{} (cl-getf (symbol-plist sym) prop) |
| 2805 | @end example |
| 2806 | |
| 2807 | It is valid to use @code{cl-getf} as a @code{setf} place, in which case |
| 2808 | its @var{place} argument must itself be a valid @code{setf} place. |
| 2809 | The @var{default} argument, if any, is ignored in this context. |
| 2810 | The effect is to change (via @code{setcar}) the value cell in the |
| 2811 | list that corresponds to @var{property}, or to cons a new property-value |
| 2812 | pair onto the list if the property is not yet present. |
| 2813 | |
| 2814 | @example |
| 2815 | (put sym prop val) @equiv{} (setf (cl-getf (symbol-plist sym) prop) val) |
| 2816 | @end example |
| 2817 | |
| 2818 | The @code{get} and @code{cl-get} functions are also @code{setf}-able. |
| 2819 | The fact that @code{default} is ignored can sometimes be useful: |
| 2820 | |
| 2821 | @example |
| 2822 | (cl-incf (cl-get 'foo 'usage-count 0)) |
| 2823 | @end example |
| 2824 | |
| 2825 | Here, symbol @code{foo}'s @code{usage-count} property is incremented |
| 2826 | if it exists, or set to 1 (an incremented 0) otherwise. |
| 2827 | |
| 2828 | When not used as a @code{setf} form, @code{cl-getf} is just a regular |
| 2829 | function and its @var{place} argument can actually be any Lisp |
| 2830 | expression. |
| 2831 | @end defun |
| 2832 | |
| 2833 | @defmac cl-remf place property |
| 2834 | This macro removes the property-value pair for @var{property} from |
| 2835 | the property list stored at @var{place}, which is any @code{setf}-able |
| 2836 | place expression. It returns true if the property was found. Note |
| 2837 | that if @var{property} happens to be first on the list, this will |
| 2838 | effectively do a @code{(setf @var{place} (cddr @var{place}))}, |
| 2839 | whereas if it occurs later, this simply uses @code{setcdr} to splice |
| 2840 | out the property and value cells. |
| 2841 | @end defmac |
| 2842 | |
| 2843 | @node Creating Symbols |
| 2844 | @section Creating Symbols |
| 2845 | |
| 2846 | @noindent |
| 2847 | These functions create unique symbols, typically for use as |
| 2848 | temporary variables. |
| 2849 | |
| 2850 | @defun cl-gensym &optional x |
| 2851 | This function creates a new, uninterned symbol (using @code{make-symbol}) |
| 2852 | with a unique name. (The name of an uninterned symbol is relevant |
| 2853 | only if the symbol is printed.) By default, the name is generated |
| 2854 | from an increasing sequence of numbers, @samp{G1000}, @samp{G1001}, |
| 2855 | @samp{G1002}, etc. If the optional argument @var{x} is a string, that |
| 2856 | string is used as a prefix instead of @samp{G}. Uninterned symbols |
| 2857 | are used in macro expansions for temporary variables, to ensure that |
| 2858 | their names will not conflict with ``real'' variables in the user's |
| 2859 | code. |
| 2860 | |
| 2861 | (Internally, the variable @code{cl--gensym-counter} holds the counter |
| 2862 | used to generate names. It is incremented after each use. In Common |
| 2863 | Lisp this is initialized with 0, but this package initializes it with |
| 2864 | a random time-dependent value to avoid trouble when two files that |
| 2865 | each used @code{cl-gensym} in their compilation are loaded together. |
| 2866 | Uninterned symbols become interned when the compiler writes them out |
| 2867 | to a file and the Emacs loader loads them, so their names have to be |
| 2868 | treated a bit more carefully than in Common Lisp where uninterned |
| 2869 | symbols remain uninterned after loading.) |
| 2870 | @end defun |
| 2871 | |
| 2872 | @defun cl-gentemp &optional x |
| 2873 | This function is like @code{cl-gensym}, except that it produces a new |
| 2874 | @emph{interned} symbol. If the symbol that is generated already |
| 2875 | exists, the function keeps incrementing the counter and trying |
| 2876 | again until a new symbol is generated. |
| 2877 | @end defun |
| 2878 | |
| 2879 | This package automatically creates all keywords that are called for by |
| 2880 | @code{&key} argument specifiers, and discourages the use of keywords |
| 2881 | as data unrelated to keyword arguments, so the related function |
| 2882 | @code{defkeyword} (to create self-quoting keyword symbols) is not |
| 2883 | provided. |
| 2884 | |
| 2885 | @node Numbers |
| 2886 | @chapter Numbers |
| 2887 | |
| 2888 | @noindent |
| 2889 | This section defines a few simple Common Lisp operations on numbers |
| 2890 | that were left out of Emacs Lisp. |
| 2891 | |
| 2892 | @menu |
| 2893 | * Predicates on Numbers:: @code{cl-plusp}, @code{cl-oddp}, etc. |
| 2894 | * Numerical Functions:: @code{cl-floor}, @code{cl-ceiling}, etc. |
| 2895 | * Random Numbers:: @code{cl-random}, @code{cl-make-random-state}. |
| 2896 | * Implementation Parameters:: @code{cl-most-positive-float}, etc. |
| 2897 | @end menu |
| 2898 | |
| 2899 | @node Predicates on Numbers |
| 2900 | @section Predicates on Numbers |
| 2901 | |
| 2902 | @noindent |
| 2903 | These functions return @code{t} if the specified condition is |
| 2904 | true of the numerical argument, or @code{nil} otherwise. |
| 2905 | |
| 2906 | @defun cl-plusp number |
| 2907 | This predicate tests whether @var{number} is positive. It is an |
| 2908 | error if the argument is not a number. |
| 2909 | @end defun |
| 2910 | |
| 2911 | @defun cl-minusp number |
| 2912 | This predicate tests whether @var{number} is negative. It is an |
| 2913 | error if the argument is not a number. |
| 2914 | @end defun |
| 2915 | |
| 2916 | @defun cl-oddp integer |
| 2917 | This predicate tests whether @var{integer} is odd. It is an |
| 2918 | error if the argument is not an integer. |
| 2919 | @end defun |
| 2920 | |
| 2921 | @defun cl-evenp integer |
| 2922 | This predicate tests whether @var{integer} is even. It is an |
| 2923 | error if the argument is not an integer. |
| 2924 | @end defun |
| 2925 | |
| 2926 | @ignore |
| 2927 | @defun cl-floatp-safe object |
| 2928 | This predicate tests whether @var{object} is a floating-point |
| 2929 | number. On systems that support floating-point, this is equivalent |
| 2930 | to @code{floatp}. On other systems, this always returns @code{nil}. |
| 2931 | @end defun |
| 2932 | @end ignore |
| 2933 | |
| 2934 | @node Numerical Functions |
| 2935 | @section Numerical Functions |
| 2936 | |
| 2937 | @noindent |
| 2938 | These functions perform various arithmetic operations on numbers. |
| 2939 | |
| 2940 | @defun cl-gcd &rest integers |
| 2941 | This function returns the Greatest Common Divisor of the arguments. |
| 2942 | For one argument, it returns the absolute value of that argument. |
| 2943 | For zero arguments, it returns zero. |
| 2944 | @end defun |
| 2945 | |
| 2946 | @defun cl-lcm &rest integers |
| 2947 | This function returns the Least Common Multiple of the arguments. |
| 2948 | For one argument, it returns the absolute value of that argument. |
| 2949 | For zero arguments, it returns one. |
| 2950 | @end defun |
| 2951 | |
| 2952 | @defun cl-isqrt integer |
| 2953 | This function computes the ``integer square root'' of its integer |
| 2954 | argument, i.e., the greatest integer less than or equal to the true |
| 2955 | square root of the argument. |
| 2956 | @end defun |
| 2957 | |
| 2958 | @defun cl-floor number &optional divisor |
| 2959 | With one argument, @code{cl-floor} returns a list of two numbers: |
| 2960 | The argument rounded down (toward minus infinity) to an integer, |
| 2961 | and the ``remainder'' which would have to be added back to the |
| 2962 | first return value to yield the argument again. If the argument |
| 2963 | is an integer @var{x}, the result is always the list @code{(@var{x} 0)}. |
| 2964 | If the argument is a floating-point number, the first |
| 2965 | result is a Lisp integer and the second is a Lisp float between |
| 2966 | 0 (inclusive) and 1 (exclusive). |
| 2967 | |
| 2968 | With two arguments, @code{cl-floor} divides @var{number} by |
| 2969 | @var{divisor}, and returns the floor of the quotient and the |
| 2970 | corresponding remainder as a list of two numbers. If |
| 2971 | @code{(cl-floor @var{x} @var{y})} returns @code{(@var{q} @var{r})}, |
| 2972 | then @code{@var{q}*@var{y} + @var{r} = @var{x}}, with @var{r} |
| 2973 | between 0 (inclusive) and @var{r} (exclusive). Also, note |
| 2974 | that @code{(cl-floor @var{x})} is exactly equivalent to |
| 2975 | @code{(cl-floor @var{x} 1)}. |
| 2976 | |
| 2977 | This function is entirely compatible with Common Lisp's @code{floor} |
| 2978 | function, except that it returns the two results in a list since |
| 2979 | Emacs Lisp does not support multiple-valued functions. |
| 2980 | @end defun |
| 2981 | |
| 2982 | @defun cl-ceiling number &optional divisor |
| 2983 | This function implements the Common Lisp @code{ceiling} function, |
| 2984 | which is analogous to @code{floor} except that it rounds the |
| 2985 | argument or quotient of the arguments up toward plus infinity. |
| 2986 | The remainder will be between 0 and minus @var{r}. |
| 2987 | @end defun |
| 2988 | |
| 2989 | @defun cl-truncate number &optional divisor |
| 2990 | This function implements the Common Lisp @code{truncate} function, |
| 2991 | which is analogous to @code{floor} except that it rounds the |
| 2992 | argument or quotient of the arguments toward zero. Thus it is |
| 2993 | equivalent to @code{cl-floor} if the argument or quotient is |
| 2994 | positive, or to @code{cl-ceiling} otherwise. The remainder has |
| 2995 | the same sign as @var{number}. |
| 2996 | @end defun |
| 2997 | |
| 2998 | @defun cl-round number &optional divisor |
| 2999 | This function implements the Common Lisp @code{round} function, |
| 3000 | which is analogous to @code{floor} except that it rounds the |
| 3001 | argument or quotient of the arguments to the nearest integer. |
| 3002 | In the case of a tie (the argument or quotient is exactly |
| 3003 | halfway between two integers), it rounds to the even integer. |
| 3004 | @end defun |
| 3005 | |
| 3006 | @defun cl-mod number divisor |
| 3007 | This function returns the same value as the second return value |
| 3008 | of @code{cl-floor}. |
| 3009 | @end defun |
| 3010 | |
| 3011 | @defun cl-rem number divisor |
| 3012 | This function returns the same value as the second return value |
| 3013 | of @code{cl-truncate}. |
| 3014 | @end defun |
| 3015 | |
| 3016 | @node Random Numbers |
| 3017 | @section Random Numbers |
| 3018 | |
| 3019 | @noindent |
| 3020 | This package also provides an implementation of the Common Lisp |
| 3021 | random number generator. It uses its own additive-congruential |
| 3022 | algorithm, which is much more likely to give statistically clean |
| 3023 | @c FIXME? Still true? |
| 3024 | random numbers than the simple generators supplied by many |
| 3025 | operating systems. |
| 3026 | |
| 3027 | @defun cl-random number &optional state |
| 3028 | This function returns a random nonnegative number less than |
| 3029 | @var{number}, and of the same type (either integer or floating-point). |
| 3030 | The @var{state} argument should be a @code{random-state} object |
| 3031 | that holds the state of the random number generator. The |
| 3032 | function modifies this state object as a side effect. If |
| 3033 | @var{state} is omitted, it defaults to the internal variable |
| 3034 | @code{cl--random-state}, which contains a pre-initialized |
| 3035 | default @code{random-state} object. (Since any number of programs in |
| 3036 | the Emacs process may be accessing @code{cl--random-state} in |
| 3037 | interleaved fashion, the sequence generated from this will be |
| 3038 | irreproducible for all intents and purposes.) |
| 3039 | @end defun |
| 3040 | |
| 3041 | @defun cl-make-random-state &optional state |
| 3042 | This function creates or copies a @code{random-state} object. |
| 3043 | If @var{state} is omitted or @code{nil}, it returns a new copy of |
| 3044 | @code{cl--random-state}. This is a copy in the sense that future |
| 3045 | sequences of calls to @code{(cl-random @var{n})} and |
| 3046 | @code{(cl-random @var{n} @var{s})} (where @var{s} is the new |
| 3047 | random-state object) will return identical sequences of random |
| 3048 | numbers. |
| 3049 | |
| 3050 | If @var{state} is a @code{random-state} object, this function |
| 3051 | returns a copy of that object. If @var{state} is @code{t}, this |
| 3052 | function returns a new @code{random-state} object seeded from the |
| 3053 | date and time. As an extension to Common Lisp, @var{state} may also |
| 3054 | be an integer in which case the new object is seeded from that |
| 3055 | integer; each different integer seed will result in a completely |
| 3056 | different sequence of random numbers. |
| 3057 | |
| 3058 | It is valid to print a @code{random-state} object to a buffer or |
| 3059 | file and later read it back with @code{read}. If a program wishes |
| 3060 | to use a sequence of pseudo-random numbers which can be reproduced |
| 3061 | later for debugging, it can call @code{(cl-make-random-state t)} to |
| 3062 | get a new sequence, then print this sequence to a file. When the |
| 3063 | program is later rerun, it can read the original run's random-state |
| 3064 | from the file. |
| 3065 | @end defun |
| 3066 | |
| 3067 | @defun cl-random-state-p object |
| 3068 | This predicate returns @code{t} if @var{object} is a |
| 3069 | @code{random-state} object, or @code{nil} otherwise. |
| 3070 | @end defun |
| 3071 | |
| 3072 | @node Implementation Parameters |
| 3073 | @section Implementation Parameters |
| 3074 | |
| 3075 | @noindent |
| 3076 | This package defines several useful constants having to do with |
| 3077 | floating-point numbers. |
| 3078 | |
| 3079 | It determines their values by exercising the computer's |
| 3080 | floating-point arithmetic in various ways. Because this operation |
| 3081 | might be slow, the code for initializing them is kept in a separate |
| 3082 | function that must be called before the parameters can be used. |
| 3083 | |
| 3084 | @defun cl-float-limits |
| 3085 | This function makes sure that the Common Lisp floating-point parameters |
| 3086 | like @code{cl-most-positive-float} have been initialized. Until it is |
| 3087 | called, these parameters will be @code{nil}. |
| 3088 | @c If this version of Emacs does not support floats, the parameters will |
| 3089 | @c remain @code{nil}. |
| 3090 | If the parameters have already been initialized, the function returns |
| 3091 | immediately. |
| 3092 | |
| 3093 | The algorithm makes assumptions that will be valid for almost all |
| 3094 | machines, but will fail if the machine's arithmetic is extremely |
| 3095 | unusual, e.g., decimal. |
| 3096 | @end defun |
| 3097 | |
| 3098 | Since true Common Lisp supports up to four different floating-point |
| 3099 | precisions, it has families of constants like |
| 3100 | @code{most-positive-single-float}, @code{most-positive-double-float}, |
| 3101 | @code{most-positive-long-float}, and so on. Emacs has only one |
| 3102 | floating-point precision, so this package omits the precision word |
| 3103 | from the constants' names. |
| 3104 | |
| 3105 | @defvar cl-most-positive-float |
| 3106 | This constant equals the largest value a Lisp float can hold. |
| 3107 | For those systems whose arithmetic supports infinities, this is |
| 3108 | the largest @emph{finite} value. For IEEE machines, the value |
| 3109 | is approximately @code{1.79e+308}. |
| 3110 | @end defvar |
| 3111 | |
| 3112 | @defvar cl-most-negative-float |
| 3113 | This constant equals the most negative value a Lisp float can hold. |
| 3114 | (It is assumed to be equal to @code{(- cl-most-positive-float)}.) |
| 3115 | @end defvar |
| 3116 | |
| 3117 | @defvar cl-least-positive-float |
| 3118 | This constant equals the smallest Lisp float value greater than zero. |
| 3119 | For IEEE machines, it is about @code{4.94e-324} if denormals are |
| 3120 | supported or @code{2.22e-308} if not. |
| 3121 | @end defvar |
| 3122 | |
| 3123 | @defvar cl-least-positive-normalized-float |
| 3124 | This constant equals the smallest @emph{normalized} Lisp float greater |
| 3125 | than zero, i.e., the smallest value for which IEEE denormalization |
| 3126 | will not result in a loss of precision. For IEEE machines, this |
| 3127 | value is about @code{2.22e-308}. For machines that do not support |
| 3128 | the concept of denormalization and gradual underflow, this constant |
| 3129 | will always equal @code{cl-least-positive-float}. |
| 3130 | @end defvar |
| 3131 | |
| 3132 | @defvar cl-least-negative-float |
| 3133 | This constant is the negative counterpart of @code{cl-least-positive-float}. |
| 3134 | @end defvar |
| 3135 | |
| 3136 | @defvar cl-least-negative-normalized-float |
| 3137 | This constant is the negative counterpart of |
| 3138 | @code{cl-least-positive-normalized-float}. |
| 3139 | @end defvar |
| 3140 | |
| 3141 | @defvar cl-float-epsilon |
| 3142 | This constant is the smallest positive Lisp float that can be added |
| 3143 | to 1.0 to produce a distinct value. Adding a smaller number to 1.0 |
| 3144 | will yield 1.0 again due to roundoff. For IEEE machines, epsilon |
| 3145 | is about @code{2.22e-16}. |
| 3146 | @end defvar |
| 3147 | |
| 3148 | @defvar cl-float-negative-epsilon |
| 3149 | This is the smallest positive value that can be subtracted from |
| 3150 | 1.0 to produce a distinct value. For IEEE machines, it is about |
| 3151 | @code{1.11e-16}. |
| 3152 | @end defvar |
| 3153 | |
| 3154 | @node Sequences |
| 3155 | @chapter Sequences |
| 3156 | |
| 3157 | @noindent |
| 3158 | Common Lisp defines a number of functions that operate on |
| 3159 | @dfn{sequences}, which are either lists, strings, or vectors. |
| 3160 | Emacs Lisp includes a few of these, notably @code{elt} and |
| 3161 | @code{length}; this package defines most of the rest. |
| 3162 | |
| 3163 | @menu |
| 3164 | * Sequence Basics:: Arguments shared by all sequence functions. |
| 3165 | * Mapping over Sequences:: @code{cl-mapcar}, @code{cl-map}, @code{cl-maplist}, etc. |
| 3166 | * Sequence Functions:: @code{cl-subseq}, @code{cl-remove}, @code{cl-substitute}, etc. |
| 3167 | * Searching Sequences:: @code{cl-find}, @code{cl-count}, @code{cl-search}, etc. |
| 3168 | * Sorting Sequences:: @code{cl-sort}, @code{cl-stable-sort}, @code{cl-merge}. |
| 3169 | @end menu |
| 3170 | |
| 3171 | @node Sequence Basics |
| 3172 | @section Sequence Basics |
| 3173 | |
| 3174 | @noindent |
| 3175 | Many of the sequence functions take keyword arguments; @pxref{Argument |
| 3176 | Lists}. All keyword arguments are optional and, if specified, |
| 3177 | may appear in any order. |
| 3178 | |
| 3179 | The @code{:key} argument should be passed either @code{nil}, or a |
| 3180 | function of one argument. This key function is used as a filter |
| 3181 | through which the elements of the sequence are seen; for example, |
| 3182 | @code{(cl-find x y :key 'car)} is similar to @code{(cl-assoc x y)}. |
| 3183 | It searches for an element of the list whose @sc{car} equals |
| 3184 | @code{x}, rather than for an element which equals @code{x} itself. |
| 3185 | If @code{:key} is omitted or @code{nil}, the filter is effectively |
| 3186 | the identity function. |
| 3187 | |
| 3188 | The @code{:test} and @code{:test-not} arguments should be either |
| 3189 | @code{nil}, or functions of two arguments. The test function is |
| 3190 | used to compare two sequence elements, or to compare a search value |
| 3191 | with sequence elements. (The two values are passed to the test |
| 3192 | function in the same order as the original sequence function |
| 3193 | arguments from which they are derived, or, if they both come from |
| 3194 | the same sequence, in the same order as they appear in that sequence.) |
| 3195 | The @code{:test} argument specifies a function which must return |
| 3196 | true (non-@code{nil}) to indicate a match; instead, you may use |
| 3197 | @code{:test-not} to give a function which returns @emph{false} to |
| 3198 | indicate a match. The default test function is @code{eql}. |
| 3199 | |
| 3200 | Many functions that take @var{item} and @code{:test} or @code{:test-not} |
| 3201 | arguments also come in @code{-if} and @code{-if-not} varieties, |
| 3202 | where a @var{predicate} function is passed instead of @var{item}, |
| 3203 | and sequence elements match if the predicate returns true on them |
| 3204 | (or false in the case of @code{-if-not}). For example: |
| 3205 | |
| 3206 | @example |
| 3207 | (cl-remove 0 seq :test '=) @equiv{} (cl-remove-if 'zerop seq) |
| 3208 | @end example |
| 3209 | |
| 3210 | @noindent |
| 3211 | to remove all zeros from sequence @code{seq}. |
| 3212 | |
| 3213 | Some operations can work on a subsequence of the argument sequence; |
| 3214 | these function take @code{:start} and @code{:end} arguments, which |
| 3215 | default to zero and the length of the sequence, respectively. |
| 3216 | Only elements between @var{start} (inclusive) and @var{end} |
| 3217 | (exclusive) are affected by the operation. The @var{end} argument |
| 3218 | may be passed @code{nil} to signify the length of the sequence; |
| 3219 | otherwise, both @var{start} and @var{end} must be integers, with |
| 3220 | @code{0 <= @var{start} <= @var{end} <= (length @var{seq})}. |
| 3221 | If the function takes two sequence arguments, the limits are |
| 3222 | defined by keywords @code{:start1} and @code{:end1} for the first, |
| 3223 | and @code{:start2} and @code{:end2} for the second. |
| 3224 | |
| 3225 | A few functions accept a @code{:from-end} argument, which, if |
| 3226 | non-@code{nil}, causes the operation to go from right-to-left |
| 3227 | through the sequence instead of left-to-right, and a @code{:count} |
| 3228 | argument, which specifies an integer maximum number of elements |
| 3229 | to be removed or otherwise processed. |
| 3230 | |
| 3231 | The sequence functions make no guarantees about the order in |
| 3232 | which the @code{:test}, @code{:test-not}, and @code{:key} functions |
| 3233 | are called on various elements. Therefore, it is a bad idea to depend |
| 3234 | on side effects of these functions. For example, @code{:from-end} |
| 3235 | may cause the sequence to be scanned actually in reverse, or it may |
| 3236 | be scanned forwards but computing a result ``as if'' it were scanned |
| 3237 | backwards. (Some functions, like @code{cl-mapcar} and @code{cl-every}, |
| 3238 | @emph{do} specify exactly the order in which the function is called |
| 3239 | so side effects are perfectly acceptable in those cases.) |
| 3240 | |
| 3241 | Strings may contain ``text properties'' as well |
| 3242 | as character data. Except as noted, it is undefined whether or |
| 3243 | not text properties are preserved by sequence functions. For |
| 3244 | example, @code{(cl-remove ?A @var{str})} may or may not preserve |
| 3245 | the properties of the characters copied from @var{str} into the |
| 3246 | result. |
| 3247 | |
| 3248 | @node Mapping over Sequences |
| 3249 | @section Mapping over Sequences |
| 3250 | |
| 3251 | @noindent |
| 3252 | These functions ``map'' the function you specify over the elements |
| 3253 | of lists or arrays. They are all variations on the theme of the |
| 3254 | built-in function @code{mapcar}. |
| 3255 | |
| 3256 | @defun cl-mapcar function seq &rest more-seqs |
| 3257 | This function calls @var{function} on successive parallel sets of |
| 3258 | elements from its argument sequences. Given a single @var{seq} |
| 3259 | argument it is equivalent to @code{mapcar}; given @var{n} sequences, |
| 3260 | it calls the function with the first elements of each of the sequences |
| 3261 | as the @var{n} arguments to yield the first element of the result |
| 3262 | list, then with the second elements, and so on. The mapping stops as |
| 3263 | soon as the shortest sequence runs out. The argument sequences may |
| 3264 | be any mixture of lists, strings, and vectors; the return sequence |
| 3265 | is always a list. |
| 3266 | |
| 3267 | Common Lisp's @code{mapcar} accepts multiple arguments but works |
| 3268 | only on lists; Emacs Lisp's @code{mapcar} accepts a single sequence |
| 3269 | argument. This package's @code{cl-mapcar} works as a compatible |
| 3270 | superset of both. |
| 3271 | @end defun |
| 3272 | |
| 3273 | @defun cl-map result-type function seq &rest more-seqs |
| 3274 | This function maps @var{function} over the argument sequences, |
| 3275 | just like @code{cl-mapcar}, but it returns a sequence of type |
| 3276 | @var{result-type} rather than a list. @var{result-type} must |
| 3277 | be one of the following symbols: @code{vector}, @code{string}, |
| 3278 | @code{list} (in which case the effect is the same as for |
| 3279 | @code{cl-mapcar}), or @code{nil} (in which case the results are |
| 3280 | thrown away and @code{cl-map} returns @code{nil}). |
| 3281 | @end defun |
| 3282 | |
| 3283 | @defun cl-maplist function list &rest more-lists |
| 3284 | This function calls @var{function} on each of its argument lists, |
| 3285 | then on the @sc{cdr}s of those lists, and so on, until the |
| 3286 | shortest list runs out. The results are returned in the form |
| 3287 | of a list. Thus, @code{cl-maplist} is like @code{cl-mapcar} except |
| 3288 | that it passes in the list pointers themselves rather than the |
| 3289 | @sc{car}s of the advancing pointers. |
| 3290 | @end defun |
| 3291 | |
| 3292 | @defun cl-mapc function seq &rest more-seqs |
| 3293 | This function is like @code{cl-mapcar}, except that the values returned |
| 3294 | by @var{function} are ignored and thrown away rather than being |
| 3295 | collected into a list. The return value of @code{cl-mapc} is @var{seq}, |
| 3296 | the first sequence. This function is more general than the Emacs |
| 3297 | primitive @code{mapc}. (Note that this function is called |
| 3298 | @code{cl-mapc} even in @file{cl.el}, rather than @code{mapc*} as you |
| 3299 | might expect.) |
| 3300 | @c http://debbugs.gnu.org/6575 |
| 3301 | @end defun |
| 3302 | |
| 3303 | @defun cl-mapl function list &rest more-lists |
| 3304 | This function is like @code{cl-maplist}, except that it throws away |
| 3305 | the values returned by @var{function}. |
| 3306 | @end defun |
| 3307 | |
| 3308 | @defun cl-mapcan function seq &rest more-seqs |
| 3309 | This function is like @code{cl-mapcar}, except that it concatenates |
| 3310 | the return values (which must be lists) using @code{nconc}, |
| 3311 | rather than simply collecting them into a list. |
| 3312 | @end defun |
| 3313 | |
| 3314 | @defun cl-mapcon function list &rest more-lists |
| 3315 | This function is like @code{cl-maplist}, except that it concatenates |
| 3316 | the return values using @code{nconc}. |
| 3317 | @end defun |
| 3318 | |
| 3319 | @defun cl-some predicate seq &rest more-seqs |
| 3320 | This function calls @var{predicate} on each element of @var{seq} |
| 3321 | in turn; if @var{predicate} returns a non-@code{nil} value, |
| 3322 | @code{cl-some} returns that value, otherwise it returns @code{nil}. |
| 3323 | Given several sequence arguments, it steps through the sequences |
| 3324 | in parallel until the shortest one runs out, just as in |
| 3325 | @code{cl-mapcar}. You can rely on the left-to-right order in which |
| 3326 | the elements are visited, and on the fact that mapping stops |
| 3327 | immediately as soon as @var{predicate} returns non-@code{nil}. |
| 3328 | @end defun |
| 3329 | |
| 3330 | @defun cl-every predicate seq &rest more-seqs |
| 3331 | This function calls @var{predicate} on each element of the sequence(s) |
| 3332 | in turn; it returns @code{nil} as soon as @var{predicate} returns |
| 3333 | @code{nil} for any element, or @code{t} if the predicate was true |
| 3334 | for all elements. |
| 3335 | @end defun |
| 3336 | |
| 3337 | @defun cl-notany predicate seq &rest more-seqs |
| 3338 | This function calls @var{predicate} on each element of the sequence(s) |
| 3339 | in turn; it returns @code{nil} as soon as @var{predicate} returns |
| 3340 | a non-@code{nil} value for any element, or @code{t} if the predicate |
| 3341 | was @code{nil} for all elements. |
| 3342 | @end defun |
| 3343 | |
| 3344 | @defun cl-notevery predicate seq &rest more-seqs |
| 3345 | This function calls @var{predicate} on each element of the sequence(s) |
| 3346 | in turn; it returns a non-@code{nil} value as soon as @var{predicate} |
| 3347 | returns @code{nil} for any element, or @code{t} if the predicate was |
| 3348 | true for all elements. |
| 3349 | @end defun |
| 3350 | |
| 3351 | @defun cl-reduce function seq @t{&key :from-end :start :end :initial-value :key} |
| 3352 | This function combines the elements of @var{seq} using an associative |
| 3353 | binary operation. Suppose @var{function} is @code{*} and @var{seq} is |
| 3354 | the list @code{(2 3 4 5)}. The first two elements of the list are |
| 3355 | combined with @code{(* 2 3) = 6}; this is combined with the next |
| 3356 | element, @code{(* 6 4) = 24}, and that is combined with the final |
| 3357 | element: @code{(* 24 5) = 120}. Note that the @code{*} function happens |
| 3358 | to be self-reducing, so that @code{(* 2 3 4 5)} has the same effect as |
| 3359 | an explicit call to @code{cl-reduce}. |
| 3360 | |
| 3361 | If @code{:from-end} is true, the reduction is right-associative instead |
| 3362 | of left-associative: |
| 3363 | |
| 3364 | @example |
| 3365 | (cl-reduce '- '(1 2 3 4)) |
| 3366 | @equiv{} (- (- (- 1 2) 3) 4) @result{} -8 |
| 3367 | (cl-reduce '- '(1 2 3 4) :from-end t) |
| 3368 | @equiv{} (- 1 (- 2 (- 3 4))) @result{} -2 |
| 3369 | @end example |
| 3370 | |
| 3371 | If @code{:key} is specified, it is a function of one argument, which |
| 3372 | is called on each of the sequence elements in turn. |
| 3373 | |
| 3374 | If @code{:initial-value} is specified, it is effectively added to the |
| 3375 | front (or rear in the case of @code{:from-end}) of the sequence. |
| 3376 | The @code{:key} function is @emph{not} applied to the initial value. |
| 3377 | |
| 3378 | If the sequence, including the initial value, has exactly one element |
| 3379 | then that element is returned without ever calling @var{function}. |
| 3380 | If the sequence is empty (and there is no initial value), then |
| 3381 | @var{function} is called with no arguments to obtain the return value. |
| 3382 | @end defun |
| 3383 | |
| 3384 | All of these mapping operations can be expressed conveniently in |
| 3385 | terms of the @code{cl-loop} macro. In compiled code, @code{cl-loop} will |
| 3386 | be faster since it generates the loop as in-line code with no |
| 3387 | function calls. |
| 3388 | |
| 3389 | @node Sequence Functions |
| 3390 | @section Sequence Functions |
| 3391 | |
| 3392 | @noindent |
| 3393 | This section describes a number of Common Lisp functions for |
| 3394 | operating on sequences. |
| 3395 | |
| 3396 | @defun cl-subseq sequence start &optional end |
| 3397 | This function returns a given subsequence of the argument |
| 3398 | @var{sequence}, which may be a list, string, or vector. |
| 3399 | The indices @var{start} and @var{end} must be in range, and |
| 3400 | @var{start} must be no greater than @var{end}. If @var{end} |
| 3401 | is omitted, it defaults to the length of the sequence. The |
| 3402 | return value is always a copy; it does not share structure |
| 3403 | with @var{sequence}. |
| 3404 | |
| 3405 | As an extension to Common Lisp, @var{start} and/or @var{end} |
| 3406 | may be negative, in which case they represent a distance back |
| 3407 | from the end of the sequence. This is for compatibility with |
| 3408 | Emacs's @code{substring} function. Note that @code{cl-subseq} is |
| 3409 | the @emph{only} sequence function that allows negative |
| 3410 | @var{start} and @var{end}. |
| 3411 | |
| 3412 | You can use @code{setf} on a @code{cl-subseq} form to replace a |
| 3413 | specified range of elements with elements from another sequence. |
| 3414 | The replacement is done as if by @code{cl-replace}, described below. |
| 3415 | @end defun |
| 3416 | |
| 3417 | @defun cl-concatenate result-type &rest seqs |
| 3418 | This function concatenates the argument sequences together to |
| 3419 | form a result sequence of type @var{result-type}, one of the |
| 3420 | symbols @code{vector}, @code{string}, or @code{list}. The |
| 3421 | arguments are always copied, even in cases such as |
| 3422 | @code{(cl-concatenate 'list '(1 2 3))} where the result is |
| 3423 | identical to an argument. |
| 3424 | @end defun |
| 3425 | |
| 3426 | @defun cl-fill seq item @t{&key :start :end} |
| 3427 | This function fills the elements of the sequence (or the specified |
| 3428 | part of the sequence) with the value @var{item}. |
| 3429 | @end defun |
| 3430 | |
| 3431 | @defun cl-replace seq1 seq2 @t{&key :start1 :end1 :start2 :end2} |
| 3432 | This function copies part of @var{seq2} into part of @var{seq1}. |
| 3433 | The sequence @var{seq1} is not stretched or resized; the amount |
| 3434 | of data copied is simply the shorter of the source and destination |
| 3435 | (sub)sequences. The function returns @var{seq1}. |
| 3436 | |
| 3437 | If @var{seq1} and @var{seq2} are @code{eq}, then the replacement |
| 3438 | will work correctly even if the regions indicated by the start |
| 3439 | and end arguments overlap. However, if @var{seq1} and @var{seq2} |
| 3440 | are lists that share storage but are not @code{eq}, and the |
| 3441 | start and end arguments specify overlapping regions, the effect |
| 3442 | is undefined. |
| 3443 | @end defun |
| 3444 | |
| 3445 | @defun cl-remove item seq @t{&key :test :test-not :key :count :start :end :from-end} |
| 3446 | This returns a copy of @var{seq} with all elements matching |
| 3447 | @var{item} removed. The result may share storage with or be |
| 3448 | @code{eq} to @var{seq} in some circumstances, but the original |
| 3449 | @var{seq} will not be modified. The @code{:test}, @code{:test-not}, |
| 3450 | and @code{:key} arguments define the matching test that is used; |
| 3451 | by default, elements @code{eql} to @var{item} are removed. The |
| 3452 | @code{:count} argument specifies the maximum number of matching |
| 3453 | elements that can be removed (only the leftmost @var{count} matches |
| 3454 | are removed). The @code{:start} and @code{:end} arguments specify |
| 3455 | a region in @var{seq} in which elements will be removed; elements |
| 3456 | outside that region are not matched or removed. The @code{:from-end} |
| 3457 | argument, if true, says that elements should be deleted from the |
| 3458 | end of the sequence rather than the beginning (this matters only |
| 3459 | if @var{count} was also specified). |
| 3460 | @end defun |
| 3461 | |
| 3462 | @defun cl-delete item seq @t{&key :test :test-not :key :count :start :end :from-end} |
| 3463 | This deletes all elements of @var{seq} that match @var{item}. |
| 3464 | It is a destructive operation. Since Emacs Lisp does not support |
| 3465 | stretchable strings or vectors, this is the same as @code{cl-remove} |
| 3466 | for those sequence types. On lists, @code{cl-remove} will copy the |
| 3467 | list if necessary to preserve the original list, whereas |
| 3468 | @code{cl-delete} will splice out parts of the argument list. |
| 3469 | Compare @code{append} and @code{nconc}, which are analogous |
| 3470 | non-destructive and destructive list operations in Emacs Lisp. |
| 3471 | @end defun |
| 3472 | |
| 3473 | @findex cl-remove-if |
| 3474 | @findex cl-remove-if-not |
| 3475 | @findex cl-delete-if |
| 3476 | @findex cl-delete-if-not |
| 3477 | The predicate-oriented functions @code{cl-remove-if}, @code{cl-remove-if-not}, |
| 3478 | @code{cl-delete-if}, and @code{cl-delete-if-not} are defined similarly. |
| 3479 | |
| 3480 | @defun cl-remove-duplicates seq @t{&key :test :test-not :key :start :end :from-end} |
| 3481 | This function returns a copy of @var{seq} with duplicate elements |
| 3482 | removed. Specifically, if two elements from the sequence match |
| 3483 | according to the @code{:test}, @code{:test-not}, and @code{:key} |
| 3484 | arguments, only the rightmost one is retained. If @code{:from-end} |
| 3485 | is true, the leftmost one is retained instead. If @code{:start} or |
| 3486 | @code{:end} is specified, only elements within that subsequence are |
| 3487 | examined or removed. |
| 3488 | @end defun |
| 3489 | |
| 3490 | @defun cl-delete-duplicates seq @t{&key :test :test-not :key :start :end :from-end} |
| 3491 | This function deletes duplicate elements from @var{seq}. It is |
| 3492 | a destructive version of @code{cl-remove-duplicates}. |
| 3493 | @end defun |
| 3494 | |
| 3495 | @defun cl-substitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} |
| 3496 | This function returns a copy of @var{seq}, with all elements |
| 3497 | matching @var{old} replaced with @var{new}. The @code{:count}, |
| 3498 | @code{:start}, @code{:end}, and @code{:from-end} arguments may be |
| 3499 | used to limit the number of substitutions made. |
| 3500 | @end defun |
| 3501 | |
| 3502 | @defun cl-nsubstitute new old seq @t{&key :test :test-not :key :count :start :end :from-end} |
| 3503 | This is a destructive version of @code{cl-substitute}; it performs |
| 3504 | the substitution using @code{setcar} or @code{aset} rather than |
| 3505 | by returning a changed copy of the sequence. |
| 3506 | @end defun |
| 3507 | |
| 3508 | @findex cl-substitute-if |
| 3509 | @findex cl-substitute-if-not |
| 3510 | @findex cl-nsubstitute-if |
| 3511 | @findex cl-nsubstitute-if-not |
| 3512 | The functions @code{cl-substitute-if}, @code{cl-substitute-if-not}, |
| 3513 | @code{cl-nsubstitute-if}, and @code{cl-nsubstitute-if-not} are defined |
| 3514 | similarly. For these, a @var{predicate} is given in place of the |
| 3515 | @var{old} argument. |
| 3516 | |
| 3517 | @node Searching Sequences |
| 3518 | @section Searching Sequences |
| 3519 | |
| 3520 | @noindent |
| 3521 | These functions search for elements or subsequences in a sequence. |
| 3522 | (See also @code{cl-member} and @code{cl-assoc}; @pxref{Lists}.) |
| 3523 | |
| 3524 | @defun cl-find item seq @t{&key :test :test-not :key :start :end :from-end} |
| 3525 | This function searches @var{seq} for an element matching @var{item}. |
| 3526 | If it finds a match, it returns the matching element. Otherwise, |
| 3527 | it returns @code{nil}. It returns the leftmost match, unless |
| 3528 | @code{:from-end} is true, in which case it returns the rightmost |
| 3529 | match. The @code{:start} and @code{:end} arguments may be used to |
| 3530 | limit the range of elements that are searched. |
| 3531 | @end defun |
| 3532 | |
| 3533 | @defun cl-position item seq @t{&key :test :test-not :key :start :end :from-end} |
| 3534 | This function is like @code{cl-find}, except that it returns the |
| 3535 | integer position in the sequence of the matching item rather than |
| 3536 | the item itself. The position is relative to the start of the |
| 3537 | sequence as a whole, even if @code{:start} is non-zero. The function |
| 3538 | returns @code{nil} if no matching element was found. |
| 3539 | @end defun |
| 3540 | |
| 3541 | @defun cl-count item seq @t{&key :test :test-not :key :start :end} |
| 3542 | This function returns the number of elements of @var{seq} which |
| 3543 | match @var{item}. The result is always a nonnegative integer. |
| 3544 | @end defun |
| 3545 | |
| 3546 | @findex cl-find-if |
| 3547 | @findex cl-find-if-not |
| 3548 | @findex cl-position-if |
| 3549 | @findex cl-position-if-not |
| 3550 | @findex cl-count-if |
| 3551 | @findex cl-count-if-not |
| 3552 | The @code{cl-find-if}, @code{cl-find-if-not}, @code{cl-position-if}, |
| 3553 | @code{cl-position-if-not}, @code{cl-count-if}, and @code{cl-count-if-not} |
| 3554 | functions are defined similarly. |
| 3555 | |
| 3556 | @defun cl-mismatch seq1 seq2 @t{&key :test :test-not :key :start1 :end1 :start2 :end2 :from-end} |
| 3557 | This function compares the specified parts of @var{seq1} and |
| 3558 | @var{seq2}. If they are the same length and the corresponding |
| 3559 | elements match (according to @code{:test}, @code{:test-not}, |
| 3560 | and @code{:key}), the function returns @code{nil}. If there is |
| 3561 | a mismatch, the function returns the index (relative to @var{seq1}) |
| 3562 | of the first mismatching element. This will be the leftmost pair of |
| 3563 | elements that do not match, or the position at which the shorter of |
| 3564 | the two otherwise-matching sequences runs out. |
| 3565 | |
| 3566 | If @code{:from-end} is true, then the elements are compared from right |
| 3567 | to left starting at @code{(1- @var{end1})} and @code{(1- @var{end2})}. |
| 3568 | If the sequences differ, then one plus the index of the rightmost |
| 3569 | difference (relative to @var{seq1}) is returned. |
| 3570 | |
| 3571 | An interesting example is @code{(cl-mismatch str1 str2 :key 'upcase)}, |
| 3572 | which compares two strings case-insensitively. |
| 3573 | @end defun |
| 3574 | |
| 3575 | @defun cl-search seq1 seq2 @t{&key :test :test-not :key :from-end :start1 :end1 :start2 :end2} |
| 3576 | This function searches @var{seq2} for a subsequence that matches |
| 3577 | @var{seq1} (or part of it specified by @code{:start1} and |
| 3578 | @code{:end1}). Only matches that fall entirely within the region |
| 3579 | defined by @code{:start2} and @code{:end2} will be considered. |
| 3580 | The return value is the index of the leftmost element of the |
| 3581 | leftmost match, relative to the start of @var{seq2}, or @code{nil} |
| 3582 | if no matches were found. If @code{:from-end} is true, the |
| 3583 | function finds the @emph{rightmost} matching subsequence. |
| 3584 | @end defun |
| 3585 | |
| 3586 | @node Sorting Sequences |
| 3587 | @section Sorting Sequences |
| 3588 | |
| 3589 | @defun cl-sort seq predicate @t{&key :key} |
| 3590 | This function sorts @var{seq} into increasing order as determined |
| 3591 | by using @var{predicate} to compare pairs of elements. @var{predicate} |
| 3592 | should return true (non-@code{nil}) if and only if its first argument |
| 3593 | is less than (not equal to) its second argument. For example, |
| 3594 | @code{<} and @code{string-lessp} are suitable predicate functions |
| 3595 | for sorting numbers and strings, respectively; @code{>} would sort |
| 3596 | numbers into decreasing rather than increasing order. |
| 3597 | |
| 3598 | This function differs from Emacs's built-in @code{sort} in that it |
| 3599 | can operate on any type of sequence, not just lists. Also, it |
| 3600 | accepts a @code{:key} argument, which is used to preprocess data |
| 3601 | fed to the @var{predicate} function. For example, |
| 3602 | |
| 3603 | @example |
| 3604 | (setq data (cl-sort data 'string-lessp :key 'downcase)) |
| 3605 | @end example |
| 3606 | |
| 3607 | @noindent |
| 3608 | sorts @var{data}, a sequence of strings, into increasing alphabetical |
| 3609 | order without regard to case. A @code{:key} function of @code{car} |
| 3610 | would be useful for sorting association lists. It should only be a |
| 3611 | simple accessor though, since it's used heavily in the current |
| 3612 | implementation. |
| 3613 | |
| 3614 | The @code{cl-sort} function is destructive; it sorts lists by actually |
| 3615 | rearranging the @sc{cdr} pointers in suitable fashion. |
| 3616 | @end defun |
| 3617 | |
| 3618 | @defun cl-stable-sort seq predicate @t{&key :key} |
| 3619 | This function sorts @var{seq} @dfn{stably}, meaning two elements |
| 3620 | which are equal in terms of @var{predicate} are guaranteed not to |
| 3621 | be rearranged out of their original order by the sort. |
| 3622 | |
| 3623 | In practice, @code{cl-sort} and @code{cl-stable-sort} are equivalent |
| 3624 | in Emacs Lisp because the underlying @code{sort} function is |
| 3625 | stable by default. However, this package reserves the right to |
| 3626 | use non-stable methods for @code{cl-sort} in the future. |
| 3627 | @end defun |
| 3628 | |
| 3629 | @defun cl-merge type seq1 seq2 predicate @t{&key :key} |
| 3630 | This function merges two sequences @var{seq1} and @var{seq2} by |
| 3631 | interleaving their elements. The result sequence, of type @var{type} |
| 3632 | (in the sense of @code{cl-concatenate}), has length equal to the sum |
| 3633 | of the lengths of the two input sequences. The sequences may be |
| 3634 | modified destructively. Order of elements within @var{seq1} and |
| 3635 | @var{seq2} is preserved in the interleaving; elements of the two |
| 3636 | sequences are compared by @var{predicate} (in the sense of |
| 3637 | @code{sort}) and the lesser element goes first in the result. |
| 3638 | When elements are equal, those from @var{seq1} precede those from |
| 3639 | @var{seq2} in the result. Thus, if @var{seq1} and @var{seq2} are |
| 3640 | both sorted according to @var{predicate}, then the result will be |
| 3641 | a merged sequence which is (stably) sorted according to |
| 3642 | @var{predicate}. |
| 3643 | @end defun |
| 3644 | |
| 3645 | @node Lists |
| 3646 | @chapter Lists |
| 3647 | |
| 3648 | @noindent |
| 3649 | The functions described here operate on lists. |
| 3650 | |
| 3651 | @menu |
| 3652 | * List Functions:: @code{cl-caddr}, @code{cl-first}, @code{cl-list*}, etc. |
| 3653 | * Substitution of Expressions:: @code{cl-subst}, @code{cl-sublis}, etc. |
| 3654 | * Lists as Sets:: @code{cl-member}, @code{cl-adjoin}, @code{cl-union}, etc. |
| 3655 | * Association Lists:: @code{cl-assoc}, @code{cl-acons}, @code{cl-pairlis}, etc. |
| 3656 | @end menu |
| 3657 | |
| 3658 | @node List Functions |
| 3659 | @section List Functions |
| 3660 | |
| 3661 | @noindent |
| 3662 | This section describes a number of simple operations on lists, |
| 3663 | i.e., chains of cons cells. |
| 3664 | |
| 3665 | @defun cl-caddr x |
| 3666 | This function is equivalent to @code{(car (cdr (cdr @var{x})))}. |
| 3667 | Likewise, this package defines all 24 @code{c@var{xxx}r} functions |
| 3668 | where @var{xxx} is up to four @samp{a}s and/or @samp{d}s. |
| 3669 | All of these functions are @code{setf}-able, and calls to them |
| 3670 | are expanded inline by the byte-compiler for maximum efficiency. |
| 3671 | @end defun |
| 3672 | |
| 3673 | @defun cl-first x |
| 3674 | This function is a synonym for @code{(car @var{x})}. Likewise, |
| 3675 | the functions @code{cl-second}, @code{cl-third}, @dots{}, through |
| 3676 | @code{cl-tenth} return the given element of the list @var{x}. |
| 3677 | @end defun |
| 3678 | |
| 3679 | @defun cl-rest x |
| 3680 | This function is a synonym for @code{(cdr @var{x})}. |
| 3681 | @end defun |
| 3682 | |
| 3683 | @defun cl-endp x |
| 3684 | Common Lisp defines this function to act like @code{null}, but |
| 3685 | signaling an error if @code{x} is neither a @code{nil} nor a |
| 3686 | cons cell. This package simply defines @code{cl-endp} as a synonym |
| 3687 | for @code{null}. |
| 3688 | @end defun |
| 3689 | |
| 3690 | @defun cl-list-length x |
| 3691 | This function returns the length of list @var{x}, exactly like |
| 3692 | @code{(length @var{x})}, except that if @var{x} is a circular |
| 3693 | list (where the @sc{cdr}-chain forms a loop rather than terminating |
| 3694 | with @code{nil}), this function returns @code{nil}. (The regular |
| 3695 | @code{length} function would get stuck if given a circular list. |
| 3696 | See also the @code{safe-length} function.) |
| 3697 | @end defun |
| 3698 | |
| 3699 | @defun cl-list* arg &rest others |
| 3700 | This function constructs a list of its arguments. The final |
| 3701 | argument becomes the @sc{cdr} of the last cell constructed. |
| 3702 | Thus, @code{(cl-list* @var{a} @var{b} @var{c})} is equivalent to |
| 3703 | @code{(cons @var{a} (cons @var{b} @var{c}))}, and |
| 3704 | @code{(cl-list* @var{a} @var{b} nil)} is equivalent to |
| 3705 | @code{(list @var{a} @var{b})}. |
| 3706 | @end defun |
| 3707 | |
| 3708 | @defun cl-ldiff list sublist |
| 3709 | If @var{sublist} is a sublist of @var{list}, i.e., is @code{eq} to |
| 3710 | one of the cons cells of @var{list}, then this function returns |
| 3711 | a copy of the part of @var{list} up to but not including |
| 3712 | @var{sublist}. For example, @code{(cl-ldiff x (cddr x))} returns |
| 3713 | the first two elements of the list @code{x}. The result is a |
| 3714 | copy; the original @var{list} is not modified. If @var{sublist} |
| 3715 | is not a sublist of @var{list}, a copy of the entire @var{list} |
| 3716 | is returned. |
| 3717 | @end defun |
| 3718 | |
| 3719 | @defun cl-copy-list list |
| 3720 | This function returns a copy of the list @var{list}. It copies |
| 3721 | dotted lists like @code{(1 2 . 3)} correctly. |
| 3722 | @end defun |
| 3723 | |
| 3724 | @defun cl-tree-equal x y @t{&key :test :test-not :key} |
| 3725 | This function compares two trees of cons cells. If @var{x} and |
| 3726 | @var{y} are both cons cells, their @sc{car}s and @sc{cdr}s are |
| 3727 | compared recursively. If neither @var{x} nor @var{y} is a cons |
| 3728 | cell, they are compared by @code{eql}, or according to the |
| 3729 | specified test. The @code{:key} function, if specified, is |
| 3730 | applied to the elements of both trees. @xref{Sequences}. |
| 3731 | @end defun |
| 3732 | |
| 3733 | @node Substitution of Expressions |
| 3734 | @section Substitution of Expressions |
| 3735 | |
| 3736 | @noindent |
| 3737 | These functions substitute elements throughout a tree of cons |
| 3738 | cells. (@xref{Sequence Functions}, for the @code{cl-substitute} |
| 3739 | function, which works on just the top-level elements of a list.) |
| 3740 | |
| 3741 | @defun cl-subst new old tree @t{&key :test :test-not :key} |
| 3742 | This function substitutes occurrences of @var{old} with @var{new} |
| 3743 | in @var{tree}, a tree of cons cells. It returns a substituted |
| 3744 | tree, which will be a copy except that it may share storage with |
| 3745 | the argument @var{tree} in parts where no substitutions occurred. |
| 3746 | The original @var{tree} is not modified. This function recurses |
| 3747 | on, and compares against @var{old}, both @sc{car}s and @sc{cdr}s |
| 3748 | of the component cons cells. If @var{old} is itself a cons cell, |
| 3749 | then matching cells in the tree are substituted as usual without |
| 3750 | recursively substituting in that cell. Comparisons with @var{old} |
| 3751 | are done according to the specified test (@code{eql} by default). |
| 3752 | The @code{:key} function is applied to the elements of the tree |
| 3753 | but not to @var{old}. |
| 3754 | @end defun |
| 3755 | |
| 3756 | @defun cl-nsubst new old tree @t{&key :test :test-not :key} |
| 3757 | This function is like @code{cl-subst}, except that it works by |
| 3758 | destructive modification (by @code{setcar} or @code{setcdr}) |
| 3759 | rather than copying. |
| 3760 | @end defun |
| 3761 | |
| 3762 | @findex cl-subst-if |
| 3763 | @findex cl-subst-if-not |
| 3764 | @findex cl-nsubst-if |
| 3765 | @findex cl-nsubst-if-not |
| 3766 | The @code{cl-subst-if}, @code{cl-subst-if-not}, @code{cl-nsubst-if}, and |
| 3767 | @code{cl-nsubst-if-not} functions are defined similarly. |
| 3768 | |
| 3769 | @defun cl-sublis alist tree @t{&key :test :test-not :key} |
| 3770 | This function is like @code{cl-subst}, except that it takes an |
| 3771 | association list @var{alist} of @var{old}-@var{new} pairs. |
| 3772 | Each element of the tree (after applying the @code{:key} |
| 3773 | function, if any), is compared with the @sc{car}s of |
| 3774 | @var{alist}; if it matches, it is replaced by the corresponding |
| 3775 | @sc{cdr}. |
| 3776 | @end defun |
| 3777 | |
| 3778 | @defun cl-nsublis alist tree @t{&key :test :test-not :key} |
| 3779 | This is a destructive version of @code{cl-sublis}. |
| 3780 | @end defun |
| 3781 | |
| 3782 | @node Lists as Sets |
| 3783 | @section Lists as Sets |
| 3784 | |
| 3785 | @noindent |
| 3786 | These functions perform operations on lists that represent sets |
| 3787 | of elements. |
| 3788 | |
| 3789 | @defun cl-member item list @t{&key :test :test-not :key} |
| 3790 | This function searches @var{list} for an element matching @var{item}. |
| 3791 | If a match is found, it returns the cons cell whose @sc{car} was |
| 3792 | the matching element. Otherwise, it returns @code{nil}. Elements |
| 3793 | are compared by @code{eql} by default; you can use the @code{:test}, |
| 3794 | @code{:test-not}, and @code{:key} arguments to modify this behavior. |
| 3795 | @xref{Sequences}. |
| 3796 | |
| 3797 | The standard Emacs lisp function @code{member} uses @code{equal} for |
| 3798 | comparisons; it is equivalent to @code{(cl-member @var{item} @var{list} |
| 3799 | :test 'equal)}. With no keyword arguments, @code{cl-member} is |
| 3800 | equivalent to @code{memq}. |
| 3801 | @end defun |
| 3802 | |
| 3803 | @findex cl-member-if |
| 3804 | @findex cl-member-if-not |
| 3805 | The @code{cl-member-if} and @code{cl-member-if-not} functions |
| 3806 | analogously search for elements that satisfy a given predicate. |
| 3807 | |
| 3808 | @defun cl-tailp sublist list |
| 3809 | This function returns @code{t} if @var{sublist} is a sublist of |
| 3810 | @var{list}, i.e., if @var{sublist} is @code{eql} to @var{list} or to |
| 3811 | any of its @sc{cdr}s. |
| 3812 | @end defun |
| 3813 | |
| 3814 | @defun cl-adjoin item list @t{&key :test :test-not :key} |
| 3815 | This function conses @var{item} onto the front of @var{list}, |
| 3816 | like @code{(cons @var{item} @var{list})}, but only if @var{item} |
| 3817 | is not already present on the list (as determined by @code{cl-member}). |
| 3818 | If a @code{:key} argument is specified, it is applied to |
| 3819 | @var{item} as well as to the elements of @var{list} during |
| 3820 | the search, on the reasoning that @var{item} is ``about'' to |
| 3821 | become part of the list. |
| 3822 | @end defun |
| 3823 | |
| 3824 | @defun cl-union list1 list2 @t{&key :test :test-not :key} |
| 3825 | This function combines two lists that represent sets of items, |
| 3826 | returning a list that represents the union of those two sets. |
| 3827 | The resulting list contains all items that appear in @var{list1} |
| 3828 | or @var{list2}, and no others. If an item appears in both |
| 3829 | @var{list1} and @var{list2} it is copied only once. If |
| 3830 | an item is duplicated in @var{list1} or @var{list2}, it is |
| 3831 | undefined whether or not that duplication will survive in the |
| 3832 | result list. The order of elements in the result list is also |
| 3833 | undefined. |
| 3834 | @end defun |
| 3835 | |
| 3836 | @defun cl-nunion list1 list2 @t{&key :test :test-not :key} |
| 3837 | This is a destructive version of @code{cl-union}; rather than copying, |
| 3838 | it tries to reuse the storage of the argument lists if possible. |
| 3839 | @end defun |
| 3840 | |
| 3841 | @defun cl-intersection list1 list2 @t{&key :test :test-not :key} |
| 3842 | This function computes the intersection of the sets represented |
| 3843 | by @var{list1} and @var{list2}. It returns the list of items |
| 3844 | that appear in both @var{list1} and @var{list2}. |
| 3845 | @end defun |
| 3846 | |
| 3847 | @defun cl-nintersection list1 list2 @t{&key :test :test-not :key} |
| 3848 | This is a destructive version of @code{cl-intersection}. It |
| 3849 | tries to reuse storage of @var{list1} rather than copying. |
| 3850 | It does @emph{not} reuse the storage of @var{list2}. |
| 3851 | @end defun |
| 3852 | |
| 3853 | @defun cl-set-difference list1 list2 @t{&key :test :test-not :key} |
| 3854 | This function computes the ``set difference'' of @var{list1} |
| 3855 | and @var{list2}, i.e., the set of elements that appear in |
| 3856 | @var{list1} but @emph{not} in @var{list2}. |
| 3857 | @end defun |
| 3858 | |
| 3859 | @defun cl-nset-difference list1 list2 @t{&key :test :test-not :key} |
| 3860 | This is a destructive @code{cl-set-difference}, which will try |
| 3861 | to reuse @var{list1} if possible. |
| 3862 | @end defun |
| 3863 | |
| 3864 | @defun cl-set-exclusive-or list1 list2 @t{&key :test :test-not :key} |
| 3865 | This function computes the ``set exclusive or'' of @var{list1} |
| 3866 | and @var{list2}, i.e., the set of elements that appear in |
| 3867 | exactly one of @var{list1} and @var{list2}. |
| 3868 | @end defun |
| 3869 | |
| 3870 | @defun cl-nset-exclusive-or list1 list2 @t{&key :test :test-not :key} |
| 3871 | This is a destructive @code{cl-set-exclusive-or}, which will try |
| 3872 | to reuse @var{list1} and @var{list2} if possible. |
| 3873 | @end defun |
| 3874 | |
| 3875 | @defun cl-subsetp list1 list2 @t{&key :test :test-not :key} |
| 3876 | This function checks whether @var{list1} represents a subset |
| 3877 | of @var{list2}, i.e., whether every element of @var{list1} |
| 3878 | also appears in @var{list2}. |
| 3879 | @end defun |
| 3880 | |
| 3881 | @node Association Lists |
| 3882 | @section Association Lists |
| 3883 | |
| 3884 | @noindent |
| 3885 | An @dfn{association list} is a list representing a mapping from |
| 3886 | one set of values to another; any list whose elements are cons |
| 3887 | cells is an association list. |
| 3888 | |
| 3889 | @defun cl-assoc item a-list @t{&key :test :test-not :key} |
| 3890 | This function searches the association list @var{a-list} for an |
| 3891 | element whose @sc{car} matches (in the sense of @code{:test}, |
| 3892 | @code{:test-not}, and @code{:key}, or by comparison with @code{eql}) |
| 3893 | a given @var{item}. It returns the matching element, if any, |
| 3894 | otherwise @code{nil}. It ignores elements of @var{a-list} that |
| 3895 | are not cons cells. (This corresponds to the behavior of |
| 3896 | @code{assq} and @code{assoc} in Emacs Lisp; Common Lisp's |
| 3897 | @code{assoc} ignores @code{nil}s but considers any other non-cons |
| 3898 | elements of @var{a-list} to be an error.) |
| 3899 | @end defun |
| 3900 | |
| 3901 | @defun cl-rassoc item a-list @t{&key :test :test-not :key} |
| 3902 | This function searches for an element whose @sc{cdr} matches |
| 3903 | @var{item}. If @var{a-list} represents a mapping, this applies |
| 3904 | the inverse of the mapping to @var{item}. |
| 3905 | @end defun |
| 3906 | |
| 3907 | @findex cl-assoc-if |
| 3908 | @findex cl-assoc-if-not |
| 3909 | @findex cl-rassoc-if |
| 3910 | @findex cl-rassoc-if-not |
| 3911 | The @code{cl-assoc-if}, @code{cl-assoc-if-not}, @code{cl-rassoc-if}, |
| 3912 | and @code{cl-rassoc-if-not} functions are defined similarly. |
| 3913 | |
| 3914 | Two simple functions for constructing association lists are: |
| 3915 | |
| 3916 | @defun cl-acons key value alist |
| 3917 | This is equivalent to @code{(cons (cons @var{key} @var{value}) @var{alist})}. |
| 3918 | @end defun |
| 3919 | |
| 3920 | @defun cl-pairlis keys values &optional alist |
| 3921 | This is equivalent to @code{(nconc (cl-mapcar 'cons @var{keys} @var{values}) |
| 3922 | @var{alist})}. |
| 3923 | @end defun |
| 3924 | |
| 3925 | @node Structures |
| 3926 | @chapter Structures |
| 3927 | |
| 3928 | @noindent |
| 3929 | The Common Lisp @dfn{structure} mechanism provides a general way |
| 3930 | to define data types similar to C's @code{struct} types. A |
| 3931 | structure is a Lisp object containing some number of @dfn{slots}, |
| 3932 | each of which can hold any Lisp data object. Functions are |
| 3933 | provided for accessing and setting the slots, creating or copying |
| 3934 | structure objects, and recognizing objects of a particular structure |
| 3935 | type. |
| 3936 | |
| 3937 | In true Common Lisp, each structure type is a new type distinct |
| 3938 | from all existing Lisp types. Since the underlying Emacs Lisp |
| 3939 | system provides no way to create new distinct types, this package |
| 3940 | implements structures as vectors (or lists upon request) with a |
| 3941 | special ``tag'' symbol to identify them. |
| 3942 | |
| 3943 | @defmac cl-defstruct name slots@dots{} |
| 3944 | The @code{cl-defstruct} form defines a new structure type called |
| 3945 | @var{name}, with the specified @var{slots}. (The @var{slots} |
| 3946 | may begin with a string which documents the structure type.) |
| 3947 | In the simplest case, @var{name} and each of the @var{slots} |
| 3948 | are symbols. For example, |
| 3949 | |
| 3950 | @example |
| 3951 | (cl-defstruct person name age sex) |
| 3952 | @end example |
| 3953 | |
| 3954 | @noindent |
| 3955 | defines a struct type called @code{person} that contains three |
| 3956 | slots. Given a @code{person} object @var{p}, you can access those |
| 3957 | slots by calling @code{(person-name @var{p})}, @code{(person-age @var{p})}, |
| 3958 | and @code{(person-sex @var{p})}. You can also change these slots by |
| 3959 | using @code{setf} on any of these place forms, for example: |
| 3960 | |
| 3961 | @example |
| 3962 | (cl-incf (person-age birthday-boy)) |
| 3963 | @end example |
| 3964 | |
| 3965 | You can create a new @code{person} by calling @code{make-person}, |
| 3966 | which takes keyword arguments @code{:name}, @code{:age}, and |
| 3967 | @code{:sex} to specify the initial values of these slots in the |
| 3968 | new object. (Omitting any of these arguments leaves the corresponding |
| 3969 | slot ``undefined'', according to the Common Lisp standard; in Emacs |
| 3970 | Lisp, such uninitialized slots are filled with @code{nil}.) |
| 3971 | |
| 3972 | Given a @code{person}, @code{(copy-person @var{p})} makes a new |
| 3973 | object of the same type whose slots are @code{eq} to those of @var{p}. |
| 3974 | |
| 3975 | Given any Lisp object @var{x}, @code{(person-p @var{x})} returns |
| 3976 | true if @var{x} looks like a @code{person}, and false otherwise. (Again, |
| 3977 | in Common Lisp this predicate would be exact; in Emacs Lisp the |
| 3978 | best it can do is verify that @var{x} is a vector of the correct |
| 3979 | length that starts with the correct tag symbol.) |
| 3980 | |
| 3981 | Accessors like @code{person-name} normally check their arguments |
| 3982 | (effectively using @code{person-p}) and signal an error if the |
| 3983 | argument is the wrong type. This check is affected by |
| 3984 | @code{(optimize (safety @dots{}))} declarations. Safety level 1, |
| 3985 | the default, uses a somewhat optimized check that will detect all |
| 3986 | incorrect arguments, but may use an uninformative error message |
| 3987 | (e.g., ``expected a vector'' instead of ``expected a @code{person}''). |
| 3988 | Safety level 0 omits all checks except as provided by the underlying |
| 3989 | @code{aref} call; safety levels 2 and 3 do rigorous checking that will |
| 3990 | always print a descriptive error message for incorrect inputs. |
| 3991 | @xref{Declarations}. |
| 3992 | |
| 3993 | @example |
| 3994 | (setq dave (make-person :name "Dave" :sex 'male)) |
| 3995 | @result{} [cl-struct-person "Dave" nil male] |
| 3996 | (setq other (copy-person dave)) |
| 3997 | @result{} [cl-struct-person "Dave" nil male] |
| 3998 | (eq dave other) |
| 3999 | @result{} nil |
| 4000 | (eq (person-name dave) (person-name other)) |
| 4001 | @result{} t |
| 4002 | (person-p dave) |
| 4003 | @result{} t |
| 4004 | (person-p [1 2 3 4]) |
| 4005 | @result{} nil |
| 4006 | (person-p "Bogus") |
| 4007 | @result{} nil |
| 4008 | (person-p '[cl-struct-person counterfeit person object]) |
| 4009 | @result{} t |
| 4010 | @end example |
| 4011 | |
| 4012 | In general, @var{name} is either a name symbol or a list of a name |
| 4013 | symbol followed by any number of @dfn{struct options}; each @var{slot} |
| 4014 | is either a slot symbol or a list of the form @samp{(@var{slot-name} |
| 4015 | @var{default-value} @var{slot-options}@dots{})}. The @var{default-value} |
| 4016 | is a Lisp form that is evaluated any time an instance of the |
| 4017 | structure type is created without specifying that slot's value. |
| 4018 | |
| 4019 | Common Lisp defines several slot options, but the only one |
| 4020 | implemented in this package is @code{:read-only}. A non-@code{nil} |
| 4021 | value for this option means the slot should not be @code{setf}-able; |
| 4022 | the slot's value is determined when the object is created and does |
| 4023 | not change afterward. |
| 4024 | |
| 4025 | @example |
| 4026 | (cl-defstruct person |
| 4027 | (name nil :read-only t) |
| 4028 | age |
| 4029 | (sex 'unknown)) |
| 4030 | @end example |
| 4031 | |
| 4032 | Any slot options other than @code{:read-only} are ignored. |
| 4033 | |
| 4034 | For obscure historical reasons, structure options take a different |
| 4035 | form than slot options. A structure option is either a keyword |
| 4036 | symbol, or a list beginning with a keyword symbol possibly followed |
| 4037 | by arguments. (By contrast, slot options are key-value pairs not |
| 4038 | enclosed in lists.) |
| 4039 | |
| 4040 | @example |
| 4041 | (cl-defstruct (person (:constructor create-person) |
| 4042 | (:type list) |
| 4043 | :named) |
| 4044 | name age sex) |
| 4045 | @end example |
| 4046 | |
| 4047 | The following structure options are recognized. |
| 4048 | |
| 4049 | @table @code |
| 4050 | @item :conc-name |
| 4051 | The argument is a symbol whose print name is used as the prefix for |
| 4052 | the names of slot accessor functions. The default is the name of |
| 4053 | the struct type followed by a hyphen. The option @code{(:conc-name p-)} |
| 4054 | would change this prefix to @code{p-}. Specifying @code{nil} as an |
| 4055 | argument means no prefix, so that the slot names themselves are used |
| 4056 | to name the accessor functions. |
| 4057 | |
| 4058 | @item :constructor |
| 4059 | In the simple case, this option takes one argument which is an |
| 4060 | alternate name to use for the constructor function. The default |
| 4061 | is @code{make-@var{name}}, e.g., @code{make-person}. The above |
| 4062 | example changes this to @code{create-person}. Specifying @code{nil} |
| 4063 | as an argument means that no standard constructor should be |
| 4064 | generated at all. |
| 4065 | |
| 4066 | In the full form of this option, the constructor name is followed |
| 4067 | by an arbitrary argument list. @xref{Program Structure}, for a |
| 4068 | description of the format of Common Lisp argument lists. All |
| 4069 | options, such as @code{&rest} and @code{&key}, are supported. |
| 4070 | The argument names should match the slot names; each slot is |
| 4071 | initialized from the corresponding argument. Slots whose names |
| 4072 | do not appear in the argument list are initialized based on the |
| 4073 | @var{default-value} in their slot descriptor. Also, @code{&optional} |
| 4074 | and @code{&key} arguments that don't specify defaults take their |
| 4075 | defaults from the slot descriptor. It is valid to include arguments |
| 4076 | that don't correspond to slot names; these are useful if they are |
| 4077 | referred to in the defaults for optional, keyword, or @code{&aux} |
| 4078 | arguments that @emph{do} correspond to slots. |
| 4079 | |
| 4080 | You can specify any number of full-format @code{:constructor} |
| 4081 | options on a structure. The default constructor is still generated |
| 4082 | as well unless you disable it with a simple-format @code{:constructor} |
| 4083 | option. |
| 4084 | |
| 4085 | @example |
| 4086 | (cl-defstruct |
| 4087 | (person |
| 4088 | (:constructor nil) ; no default constructor |
| 4089 | (:constructor new-person |
| 4090 | (name sex &optional (age 0))) |
| 4091 | (:constructor new-hound (&key (name "Rover") |
| 4092 | (dog-years 0) |
| 4093 | &aux (age (* 7 dog-years)) |
| 4094 | (sex 'canine)))) |
| 4095 | name age sex) |
| 4096 | @end example |
| 4097 | |
| 4098 | The first constructor here takes its arguments positionally rather |
| 4099 | than by keyword. (In official Common Lisp terminology, constructors |
| 4100 | that work By Order of Arguments instead of by keyword are called |
| 4101 | ``BOA constructors''. No, I'm not making this up.) For example, |
| 4102 | @code{(new-person "Jane" 'female)} generates a person whose slots |
| 4103 | are @code{"Jane"}, 0, and @code{female}, respectively. |
| 4104 | |
| 4105 | The second constructor takes two keyword arguments, @code{:name}, |
| 4106 | which initializes the @code{name} slot and defaults to @code{"Rover"}, |
| 4107 | and @code{:dog-years}, which does not itself correspond to a slot |
| 4108 | but which is used to initialize the @code{age} slot. The @code{sex} |
| 4109 | slot is forced to the symbol @code{canine} with no syntax for |
| 4110 | overriding it. |
| 4111 | |
| 4112 | @item :copier |
| 4113 | The argument is an alternate name for the copier function for |
| 4114 | this type. The default is @code{copy-@var{name}}. @code{nil} |
| 4115 | means not to generate a copier function. (In this implementation, |
| 4116 | all copier functions are simply synonyms for @code{copy-sequence}.) |
| 4117 | |
| 4118 | @item :predicate |
| 4119 | The argument is an alternate name for the predicate that recognizes |
| 4120 | objects of this type. The default is @code{@var{name}-p}. @code{nil} |
| 4121 | means not to generate a predicate function. (If the @code{:type} |
| 4122 | option is used without the @code{:named} option, no predicate is |
| 4123 | ever generated.) |
| 4124 | |
| 4125 | In true Common Lisp, @code{typep} is always able to recognize a |
| 4126 | structure object even if @code{:predicate} was used. In this |
| 4127 | package, @code{cl-typep} simply looks for a function called |
| 4128 | @code{@var{typename}-p}, so it will work for structure types |
| 4129 | only if they used the default predicate name. |
| 4130 | |
| 4131 | @item :include |
| 4132 | This option implements a very limited form of C++-style inheritance. |
| 4133 | The argument is the name of another structure type previously |
| 4134 | created with @code{cl-defstruct}. The effect is to cause the new |
| 4135 | structure type to inherit all of the included structure's slots |
| 4136 | (plus, of course, any new slots described by this struct's slot |
| 4137 | descriptors). The new structure is considered a ``specialization'' |
| 4138 | of the included one. In fact, the predicate and slot accessors |
| 4139 | for the included type will also accept objects of the new type. |
| 4140 | |
| 4141 | If there are extra arguments to the @code{:include} option after |
| 4142 | the included-structure name, these options are treated as replacement |
| 4143 | slot descriptors for slots in the included structure, possibly with |
| 4144 | modified default values. Borrowing an example from Steele: |
| 4145 | |
| 4146 | @example |
| 4147 | (cl-defstruct person name (age 0) sex) |
| 4148 | @result{} person |
| 4149 | (cl-defstruct (astronaut (:include person (age 45))) |
| 4150 | helmet-size |
| 4151 | (favorite-beverage 'tang)) |
| 4152 | @result{} astronaut |
| 4153 | |
| 4154 | (setq joe (make-person :name "Joe")) |
| 4155 | @result{} [cl-struct-person "Joe" 0 nil] |
| 4156 | (setq buzz (make-astronaut :name "Buzz")) |
| 4157 | @result{} [cl-struct-astronaut "Buzz" 45 nil nil tang] |
| 4158 | |
| 4159 | (list (person-p joe) (person-p buzz)) |
| 4160 | @result{} (t t) |
| 4161 | (list (astronaut-p joe) (astronaut-p buzz)) |
| 4162 | @result{} (nil t) |
| 4163 | |
| 4164 | (person-name buzz) |
| 4165 | @result{} "Buzz" |
| 4166 | (astronaut-name joe) |
| 4167 | @result{} error: "astronaut-name accessing a non-astronaut" |
| 4168 | @end example |
| 4169 | |
| 4170 | Thus, if @code{astronaut} is a specialization of @code{person}, |
| 4171 | then every @code{astronaut} is also a @code{person} (but not the |
| 4172 | other way around). Every @code{astronaut} includes all the slots |
| 4173 | of a @code{person}, plus extra slots that are specific to |
| 4174 | astronauts. Operations that work on people (like @code{person-name}) |
| 4175 | work on astronauts just like other people. |
| 4176 | |
| 4177 | @item :print-function |
| 4178 | In full Common Lisp, this option allows you to specify a function |
| 4179 | that is called to print an instance of the structure type. The |
| 4180 | Emacs Lisp system offers no hooks into the Lisp printer which would |
| 4181 | allow for such a feature, so this package simply ignores |
| 4182 | @code{:print-function}. |
| 4183 | |
| 4184 | @item :type |
| 4185 | The argument should be one of the symbols @code{vector} or @code{list}. |
| 4186 | This tells which underlying Lisp data type should be used to implement |
| 4187 | the new structure type. Vectors are used by default, but |
| 4188 | @code{(:type list)} will cause structure objects to be stored as |
| 4189 | lists instead. |
| 4190 | |
| 4191 | The vector representation for structure objects has the advantage |
| 4192 | that all structure slots can be accessed quickly, although creating |
| 4193 | vectors is a bit slower in Emacs Lisp. Lists are easier to create, |
| 4194 | but take a relatively long time accessing the later slots. |
| 4195 | |
| 4196 | @item :named |
| 4197 | This option, which takes no arguments, causes a characteristic ``tag'' |
| 4198 | symbol to be stored at the front of the structure object. Using |
| 4199 | @code{:type} without also using @code{:named} will result in a |
| 4200 | structure type stored as plain vectors or lists with no identifying |
| 4201 | features. |
| 4202 | |
| 4203 | The default, if you don't specify @code{:type} explicitly, is to |
| 4204 | use named vectors. Therefore, @code{:named} is only useful in |
| 4205 | conjunction with @code{:type}. |
| 4206 | |
| 4207 | @example |
| 4208 | (cl-defstruct (person1) name age sex) |
| 4209 | (cl-defstruct (person2 (:type list) :named) name age sex) |
| 4210 | (cl-defstruct (person3 (:type list)) name age sex) |
| 4211 | |
| 4212 | (setq p1 (make-person1)) |
| 4213 | @result{} [cl-struct-person1 nil nil nil] |
| 4214 | (setq p2 (make-person2)) |
| 4215 | @result{} (person2 nil nil nil) |
| 4216 | (setq p3 (make-person3)) |
| 4217 | @result{} (nil nil nil) |
| 4218 | |
| 4219 | (person1-p p1) |
| 4220 | @result{} t |
| 4221 | (person2-p p2) |
| 4222 | @result{} t |
| 4223 | (person3-p p3) |
| 4224 | @result{} error: function person3-p undefined |
| 4225 | @end example |
| 4226 | |
| 4227 | Since unnamed structures don't have tags, @code{cl-defstruct} is not |
| 4228 | able to make a useful predicate for recognizing them. Also, |
| 4229 | accessors like @code{person3-name} will be generated but they |
| 4230 | will not be able to do any type checking. The @code{person3-name} |
| 4231 | function, for example, will simply be a synonym for @code{car} in |
| 4232 | this case. By contrast, @code{person2-name} is able to verify |
| 4233 | that its argument is indeed a @code{person2} object before |
| 4234 | proceeding. |
| 4235 | |
| 4236 | @item :initial-offset |
| 4237 | The argument must be a nonnegative integer. It specifies a |
| 4238 | number of slots to be left ``empty'' at the front of the |
| 4239 | structure. If the structure is named, the tag appears at the |
| 4240 | specified position in the list or vector; otherwise, the first |
| 4241 | slot appears at that position. Earlier positions are filled |
| 4242 | with @code{nil} by the constructors and ignored otherwise. If |
| 4243 | the type @code{:include}s another type, then @code{:initial-offset} |
| 4244 | specifies a number of slots to be skipped between the last slot |
| 4245 | of the included type and the first new slot. |
| 4246 | @end table |
| 4247 | @end defmac |
| 4248 | |
| 4249 | Except as noted, the @code{cl-defstruct} facility of this package is |
| 4250 | entirely compatible with that of Common Lisp. |
| 4251 | |
| 4252 | @node Assertions |
| 4253 | @chapter Assertions and Errors |
| 4254 | |
| 4255 | @noindent |
| 4256 | This section describes two macros that test @dfn{assertions}, i.e., |
| 4257 | conditions which must be true if the program is operating correctly. |
| 4258 | Assertions never add to the behavior of a Lisp program; they simply |
| 4259 | make ``sanity checks'' to make sure everything is as it should be. |
| 4260 | |
| 4261 | If the optimization property @code{speed} has been set to 3, and |
| 4262 | @code{safety} is less than 3, then the byte-compiler will optimize |
| 4263 | away the following assertions. Because assertions might be optimized |
| 4264 | away, it is a bad idea for them to include side-effects. |
| 4265 | |
| 4266 | @defmac cl-assert test-form [show-args string args@dots{}] |
| 4267 | This form verifies that @var{test-form} is true (i.e., evaluates to |
| 4268 | a non-@code{nil} value). If so, it returns @code{nil}. If the test |
| 4269 | is not satisfied, @code{cl-assert} signals an error. |
| 4270 | |
| 4271 | A default error message will be supplied which includes @var{test-form}. |
| 4272 | You can specify a different error message by including a @var{string} |
| 4273 | argument plus optional extra arguments. Those arguments are simply |
| 4274 | passed to @code{error} to signal the error. |
| 4275 | |
| 4276 | If the optional second argument @var{show-args} is @code{t} instead |
| 4277 | of @code{nil}, then the error message (with or without @var{string}) |
| 4278 | will also include all non-constant arguments of the top-level |
| 4279 | @var{form}. For example: |
| 4280 | |
| 4281 | @example |
| 4282 | (cl-assert (> x 10) t "x is too small: %d") |
| 4283 | @end example |
| 4284 | |
| 4285 | This usage of @var{show-args} is an extension to Common Lisp. In |
| 4286 | true Common Lisp, the second argument gives a list of @var{places} |
| 4287 | which can be @code{setf}'d by the user before continuing from the |
| 4288 | error. Since Emacs Lisp does not support continuable errors, it |
| 4289 | makes no sense to specify @var{places}. |
| 4290 | @end defmac |
| 4291 | |
| 4292 | @defmac cl-check-type form type [string] |
| 4293 | This form verifies that @var{form} evaluates to a value of type |
| 4294 | @var{type}. If so, it returns @code{nil}. If not, @code{cl-check-type} |
| 4295 | signals a @code{wrong-type-argument} error. The default error message |
| 4296 | lists the erroneous value along with @var{type} and @var{form} |
| 4297 | themselves. If @var{string} is specified, it is included in the |
| 4298 | error message in place of @var{type}. For example: |
| 4299 | |
| 4300 | @example |
| 4301 | (cl-check-type x (integer 1 *) "a positive integer") |
| 4302 | @end example |
| 4303 | |
| 4304 | @xref{Type Predicates}, for a description of the type specifiers |
| 4305 | that may be used for @var{type}. |
| 4306 | |
| 4307 | Note that in Common Lisp, the first argument to @code{check-type} |
| 4308 | must be a @var{place} suitable for use by @code{setf}, because |
| 4309 | @code{check-type} signals a continuable error that allows the |
| 4310 | user to modify @var{place}. |
| 4311 | @end defmac |
| 4312 | |
| 4313 | @node Efficiency Concerns |
| 4314 | @appendix Efficiency Concerns |
| 4315 | |
| 4316 | @appendixsec Macros |
| 4317 | |
| 4318 | @noindent |
| 4319 | Many of the advanced features of this package, such as @code{cl-defun}, |
| 4320 | @code{cl-loop}, etc., are implemented as Lisp macros. In |
| 4321 | byte-compiled code, these complex notations will be expanded into |
| 4322 | equivalent Lisp code which is simple and efficient. For example, |
| 4323 | the form |
| 4324 | |
| 4325 | @example |
| 4326 | (cl-incf i n) |
| 4327 | @end example |
| 4328 | |
| 4329 | @noindent |
| 4330 | is expanded at compile-time to the Lisp form |
| 4331 | |
| 4332 | @example |
| 4333 | (setq i (+ i n)) |
| 4334 | @end example |
| 4335 | |
| 4336 | @noindent |
| 4337 | which is the most efficient ways of doing this operation |
| 4338 | in Lisp. Thus, there is no performance penalty for using the more |
| 4339 | readable @code{cl-incf} form in your compiled code. |
| 4340 | |
| 4341 | @emph{Interpreted} code, on the other hand, must expand these macros |
| 4342 | every time they are executed. For this reason it is strongly |
| 4343 | recommended that code making heavy use of macros be compiled. |
| 4344 | A loop using @code{cl-incf} a hundred times will execute considerably |
| 4345 | faster if compiled, and will also garbage-collect less because the |
| 4346 | macro expansion will not have to be generated, used, and thrown away a |
| 4347 | hundred times. |
| 4348 | |
| 4349 | You can find out how a macro expands by using the |
| 4350 | @code{cl-prettyexpand} function. |
| 4351 | |
| 4352 | @defun cl-prettyexpand form &optional full |
| 4353 | This function takes a single Lisp form as an argument and inserts |
| 4354 | a nicely formatted copy of it in the current buffer (which must be |
| 4355 | in Lisp mode so that indentation works properly). It also expands |
| 4356 | all Lisp macros that appear in the form. The easiest way to use |
| 4357 | this function is to go to the @file{*scratch*} buffer and type, say, |
| 4358 | |
| 4359 | @example |
| 4360 | (cl-prettyexpand '(cl-loop for x below 10 collect x)) |
| 4361 | @end example |
| 4362 | |
| 4363 | @noindent |
| 4364 | and type @kbd{C-x C-e} immediately after the closing parenthesis; |
| 4365 | an expansion similar to: |
| 4366 | |
| 4367 | @example |
| 4368 | (cl-block nil |
| 4369 | (let* ((x 0) |
| 4370 | (G1004 nil)) |
| 4371 | (while (< x 10) |
| 4372 | (setq G1004 (cons x G1004)) |
| 4373 | (setq x (+ x 1))) |
| 4374 | (nreverse G1004))) |
| 4375 | @end example |
| 4376 | |
| 4377 | @noindent |
| 4378 | will be inserted into the buffer. (The @code{cl-block} macro is |
| 4379 | expanded differently in the interpreter and compiler, so |
| 4380 | @code{cl-prettyexpand} just leaves it alone. The temporary |
| 4381 | variable @code{G1004} was created by @code{cl-gensym}.) |
| 4382 | |
| 4383 | If the optional argument @var{full} is true, then @emph{all} |
| 4384 | macros are expanded, including @code{cl-block}, @code{cl-eval-when}, |
| 4385 | and compiler macros. Expansion is done as if @var{form} were |
| 4386 | a top-level form in a file being compiled. |
| 4387 | |
| 4388 | @c FIXME none of these examples are still applicable. |
| 4389 | @ignore |
| 4390 | For example, |
| 4391 | |
| 4392 | @example |
| 4393 | (cl-prettyexpand '(cl-pushnew 'x list)) |
| 4394 | @print{} (setq list (cl-adjoin 'x list)) |
| 4395 | (cl-prettyexpand '(cl-pushnew 'x list) t) |
| 4396 | @print{} (setq list (if (memq 'x list) list (cons 'x list))) |
| 4397 | (cl-prettyexpand '(caddr (cl-member 'a list)) t) |
| 4398 | @print{} (car (cdr (cdr (memq 'a list)))) |
| 4399 | @end example |
| 4400 | @end ignore |
| 4401 | |
| 4402 | Note that @code{cl-adjoin}, @code{cl-caddr}, and @code{cl-member} all |
| 4403 | have built-in compiler macros to optimize them in common cases. |
| 4404 | @end defun |
| 4405 | |
| 4406 | @appendixsec Error Checking |
| 4407 | |
| 4408 | @noindent |
| 4409 | Common Lisp compliance has in general not been sacrificed for the |
| 4410 | sake of efficiency. A few exceptions have been made for cases |
| 4411 | where substantial gains were possible at the expense of marginal |
| 4412 | incompatibility. |
| 4413 | |
| 4414 | The Common Lisp standard (as embodied in Steele's book) uses the |
| 4415 | phrase ``it is an error if'' to indicate a situation that is not |
| 4416 | supposed to arise in complying programs; implementations are strongly |
| 4417 | encouraged but not required to signal an error in these situations. |
| 4418 | This package sometimes omits such error checking in the interest of |
| 4419 | compactness and efficiency. For example, @code{cl-do} variable |
| 4420 | specifiers are supposed to be lists of one, two, or three forms; |
| 4421 | extra forms are ignored by this package rather than signaling a |
| 4422 | syntax error. The @code{cl-endp} function is simply a synonym for |
| 4423 | @code{null} in this package. Functions taking keyword arguments |
| 4424 | will accept an odd number of arguments, treating the trailing |
| 4425 | keyword as if it were followed by the value @code{nil}. |
| 4426 | |
| 4427 | Argument lists (as processed by @code{cl-defun} and friends) |
| 4428 | @emph{are} checked rigorously except for the minor point just |
| 4429 | mentioned; in particular, keyword arguments are checked for |
| 4430 | validity, and @code{&allow-other-keys} and @code{:allow-other-keys} |
| 4431 | are fully implemented. Keyword validity checking is slightly |
| 4432 | time consuming (though not too bad in byte-compiled code); |
| 4433 | you can use @code{&allow-other-keys} to omit this check. Functions |
| 4434 | defined in this package such as @code{cl-find} and @code{cl-member} |
| 4435 | do check their keyword arguments for validity. |
| 4436 | |
| 4437 | @appendixsec Compiler Optimizations |
| 4438 | |
| 4439 | @noindent |
| 4440 | Changing the value of @code{byte-optimize} from the default @code{t} |
| 4441 | is highly discouraged; many of the Common |
| 4442 | Lisp macros emit |
| 4443 | code that can be improved by optimization. In particular, |
| 4444 | @code{cl-block}s (whether explicit or implicit in constructs like |
| 4445 | @code{cl-defun} and @code{cl-loop}) carry a fair run-time penalty; the |
| 4446 | byte-compiler removes @code{cl-block}s that are not actually |
| 4447 | referenced by @code{cl-return} or @code{cl-return-from} inside the block. |
| 4448 | |
| 4449 | @node Common Lisp Compatibility |
| 4450 | @appendix Common Lisp Compatibility |
| 4451 | |
| 4452 | @noindent |
| 4453 | The following is a list of all known incompatibilities between this |
| 4454 | package and Common Lisp as documented in Steele (2nd edition). |
| 4455 | |
| 4456 | The word @code{cl-defun} is required instead of @code{defun} in order |
| 4457 | to use extended Common Lisp argument lists in a function. Likewise, |
| 4458 | @code{cl-defmacro} and @code{cl-function} are versions of those forms |
| 4459 | which understand full-featured argument lists. The @code{&whole} |
| 4460 | keyword does not work in @code{cl-defmacro} argument lists (except |
| 4461 | inside recursive argument lists). |
| 4462 | |
| 4463 | The @code{equal} predicate does not distinguish |
| 4464 | between IEEE floating-point plus and minus zero. The @code{cl-equalp} |
| 4465 | predicate has several differences with Common Lisp; @pxref{Predicates}. |
| 4466 | |
| 4467 | The @code{cl-do-all-symbols} form is the same as @code{cl-do-symbols} |
| 4468 | with no @var{obarray} argument. In Common Lisp, this form would |
| 4469 | iterate over all symbols in all packages. Since Emacs obarrays |
| 4470 | are not a first-class package mechanism, there is no way for |
| 4471 | @code{cl-do-all-symbols} to locate any but the default obarray. |
| 4472 | |
| 4473 | The @code{cl-loop} macro is complete except that @code{loop-finish} |
| 4474 | and type specifiers are unimplemented. |
| 4475 | |
| 4476 | The multiple-value return facility treats lists as multiple |
| 4477 | values, since Emacs Lisp cannot support multiple return values |
| 4478 | directly. The macros will be compatible with Common Lisp if |
| 4479 | @code{cl-values} or @code{cl-values-list} is always used to return to |
| 4480 | a @code{cl-multiple-value-bind} or other multiple-value receiver; |
| 4481 | if @code{cl-values} is used without @code{cl-multiple-value-@dots{}} |
| 4482 | or vice-versa the effect will be different from Common Lisp. |
| 4483 | |
| 4484 | Many Common Lisp declarations are ignored, and others match |
| 4485 | the Common Lisp standard in concept but not in detail. For |
| 4486 | example, local @code{special} declarations, which are purely |
| 4487 | advisory in Emacs Lisp, do not rigorously obey the scoping rules |
| 4488 | set down in Steele's book. |
| 4489 | |
| 4490 | The variable @code{cl--gensym-counter} starts out with a pseudo-random |
| 4491 | value rather than with zero. This is to cope with the fact that |
| 4492 | generated symbols become interned when they are written to and |
| 4493 | loaded back from a file. |
| 4494 | |
| 4495 | The @code{cl-defstruct} facility is compatible, except that structures |
| 4496 | are of type @code{:type vector :named} by default rather than some |
| 4497 | special, distinct type. Also, the @code{:type} slot option is ignored. |
| 4498 | |
| 4499 | The second argument of @code{cl-check-type} is treated differently. |
| 4500 | |
| 4501 | @node Porting Common Lisp |
| 4502 | @appendix Porting Common Lisp |
| 4503 | |
| 4504 | @noindent |
| 4505 | This package is meant to be used as an extension to Emacs Lisp, |
| 4506 | not as an Emacs implementation of true Common Lisp. Some of the |
| 4507 | remaining differences between Emacs Lisp and Common Lisp make it |
| 4508 | difficult to port large Common Lisp applications to Emacs. For |
| 4509 | one, some of the features in this package are not fully compliant |
| 4510 | with ANSI or Steele; @pxref{Common Lisp Compatibility}. But there |
| 4511 | are also quite a few features that this package does not provide |
| 4512 | at all. Here are some major omissions that you will want to watch out |
| 4513 | for when bringing Common Lisp code into Emacs. |
| 4514 | |
| 4515 | @itemize @bullet |
| 4516 | @item |
| 4517 | Case-insensitivity. Symbols in Common Lisp are case-insensitive |
| 4518 | by default. Some programs refer to a function or variable as |
| 4519 | @code{foo} in one place and @code{Foo} or @code{FOO} in another. |
| 4520 | Emacs Lisp will treat these as three distinct symbols. |
| 4521 | |
| 4522 | Some Common Lisp code is written entirely in upper case. While Emacs |
| 4523 | is happy to let the program's own functions and variables use |
| 4524 | this convention, calls to Lisp builtins like @code{if} and |
| 4525 | @code{defun} will have to be changed to lower case. |
| 4526 | |
| 4527 | @item |
| 4528 | Lexical scoping. In Common Lisp, function arguments and @code{let} |
| 4529 | bindings apply only to references physically within their bodies (or |
| 4530 | within macro expansions in their bodies). Traditionally, Emacs Lisp |
| 4531 | uses @dfn{dynamic scoping} wherein a binding to a variable is visible |
| 4532 | even inside functions called from the body. |
| 4533 | @xref{Dynamic Binding,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 4534 | Lexical binding is available since Emacs 24.1, so be sure to set |
| 4535 | @code{lexical-binding} to @code{t} if you need to emulate this aspect |
| 4536 | of Common Lisp. @xref{Lexical Binding,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 4537 | |
| 4538 | Here is an example of a Common Lisp code fragment that would fail in |
| 4539 | Emacs Lisp if @code{lexical-binding} were set to @code{nil}: |
| 4540 | |
| 4541 | @example |
| 4542 | (defun map-odd-elements (func list) |
| 4543 | (loop for x in list |
| 4544 | for flag = t then (not flag) |
| 4545 | collect (if flag x (funcall func x)))) |
| 4546 | |
| 4547 | (defun add-odd-elements (list x) |
| 4548 | (map-odd-elements (lambda (a) (+ a x)) list)) |
| 4549 | @end example |
| 4550 | |
| 4551 | @noindent |
| 4552 | With lexical binding, the two functions' usages of @code{x} are |
| 4553 | completely independent. With dynamic binding, the binding to @code{x} |
| 4554 | made by @code{add-odd-elements} will have been hidden by the binding |
| 4555 | in @code{map-odd-elements} by the time the @code{(+ a x)} function is |
| 4556 | called. |
| 4557 | |
| 4558 | Internally, this package uses lexical binding so that such problems do |
| 4559 | not occur. @xref{Obsolete Lexical Binding}, for a description of the obsolete |
| 4560 | @code{lexical-let} form that emulates a Common Lisp-style lexical |
| 4561 | binding when dynamic binding is in use. |
| 4562 | |
| 4563 | @item |
| 4564 | Reader macros. Common Lisp includes a second type of macro that |
| 4565 | works at the level of individual characters. For example, Common |
| 4566 | Lisp implements the quote notation by a reader macro called @code{'}, |
| 4567 | whereas Emacs Lisp's parser just treats quote as a special case. |
| 4568 | Some Lisp packages use reader macros to create special syntaxes |
| 4569 | for themselves, which the Emacs parser is incapable of reading. |
| 4570 | |
| 4571 | @item |
| 4572 | Other syntactic features. Common Lisp provides a number of |
| 4573 | notations beginning with @code{#} that the Emacs Lisp parser |
| 4574 | won't understand. For example, @samp{#| @dots{} |#} is an |
| 4575 | alternate comment notation, and @samp{#+lucid (foo)} tells |
| 4576 | the parser to ignore the @code{(foo)} except in Lucid Common |
| 4577 | Lisp. |
| 4578 | |
| 4579 | @item |
| 4580 | Packages. In Common Lisp, symbols are divided into @dfn{packages}. |
| 4581 | Symbols that are Lisp built-ins are typically stored in one package; |
| 4582 | symbols that are vendor extensions are put in another, and each |
| 4583 | application program would have a package for its own symbols. |
| 4584 | Certain symbols are ``exported'' by a package and others are |
| 4585 | internal; certain packages ``use'' or import the exported symbols |
| 4586 | of other packages. To access symbols that would not normally be |
| 4587 | visible due to this importing and exporting, Common Lisp provides |
| 4588 | a syntax like @code{package:symbol} or @code{package::symbol}. |
| 4589 | |
| 4590 | Emacs Lisp has a single namespace for all interned symbols, and |
| 4591 | then uses a naming convention of putting a prefix like @code{cl-} |
| 4592 | in front of the name. Some Emacs packages adopt the Common Lisp-like |
| 4593 | convention of using @code{cl:} or @code{cl::} as the prefix. |
| 4594 | However, the Emacs parser does not understand colons and just |
| 4595 | treats them as part of the symbol name. Thus, while @code{mapcar} |
| 4596 | and @code{lisp:mapcar} may refer to the same symbol in Common |
| 4597 | Lisp, they are totally distinct in Emacs Lisp. Common Lisp |
| 4598 | programs that refer to a symbol by the full name sometimes |
| 4599 | and the short name other times will not port cleanly to Emacs. |
| 4600 | |
| 4601 | Emacs Lisp does have a concept of ``obarrays'', which are |
| 4602 | package-like collections of symbols, but this feature is not |
| 4603 | strong enough to be used as a true package mechanism. |
| 4604 | |
| 4605 | @item |
| 4606 | The @code{format} function is quite different between Common |
| 4607 | Lisp and Emacs Lisp. It takes an additional ``destination'' |
| 4608 | argument before the format string. A destination of @code{nil} |
| 4609 | means to format to a string as in Emacs Lisp; a destination |
| 4610 | of @code{t} means to write to the terminal (similar to |
| 4611 | @code{message} in Emacs). Also, format control strings are |
| 4612 | utterly different; @code{~} is used instead of @code{%} to |
| 4613 | introduce format codes, and the set of available codes is |
| 4614 | much richer. There are no notations like @code{\n} for |
| 4615 | string literals; instead, @code{format} is used with the |
| 4616 | ``newline'' format code, @code{~%}. More advanced formatting |
| 4617 | codes provide such features as paragraph filling, case |
| 4618 | conversion, and even loops and conditionals. |
| 4619 | |
| 4620 | While it would have been possible to implement most of Common |
| 4621 | Lisp @code{format} in this package (under the name @code{cl-format}, |
| 4622 | of course), it was not deemed worthwhile. It would have required |
| 4623 | a huge amount of code to implement even a decent subset of |
| 4624 | @code{format}, yet the functionality it would provide over |
| 4625 | Emacs Lisp's @code{format} would rarely be useful. |
| 4626 | |
| 4627 | @item |
| 4628 | Vector constants use square brackets in Emacs Lisp, but |
| 4629 | @code{#(a b c)} notation in Common Lisp. To further complicate |
| 4630 | matters, Emacs has its own @code{#(} notation for |
| 4631 | something entirely different---strings with properties. |
| 4632 | |
| 4633 | @item |
| 4634 | Characters are distinct from integers in Common Lisp. The notation |
| 4635 | for character constants is also different: @code{#\A} in Common Lisp |
| 4636 | where Emacs Lisp uses @code{?A}. Also, @code{string=} and |
| 4637 | @code{string-equal} are synonyms in Emacs Lisp, whereas the latter is |
| 4638 | case-insensitive in Common Lisp. |
| 4639 | |
| 4640 | @item |
| 4641 | Data types. Some Common Lisp data types do not exist in Emacs |
| 4642 | Lisp. Rational numbers and complex numbers are not present, |
| 4643 | nor are large integers (all integers are ``fixnums''). All |
| 4644 | arrays are one-dimensional. There are no readtables or pathnames; |
| 4645 | streams are a set of existing data types rather than a new data |
| 4646 | type of their own. Hash tables, random-states, structures, and |
| 4647 | packages (obarrays) are built from Lisp vectors or lists rather |
| 4648 | than being distinct types. |
| 4649 | |
| 4650 | @item |
| 4651 | The Common Lisp Object System (CLOS) is not implemented, |
| 4652 | nor is the Common Lisp Condition System. However, the EIEIO package |
| 4653 | (@pxref{Top, , Introduction, eieio, EIEIO}) does implement some |
| 4654 | CLOS functionality. |
| 4655 | |
| 4656 | @item |
| 4657 | Common Lisp features that are completely redundant with Emacs |
| 4658 | Lisp features of a different name generally have not been |
| 4659 | implemented. For example, Common Lisp writes @code{defconstant} |
| 4660 | where Emacs Lisp uses @code{defconst}. Similarly, @code{make-list} |
| 4661 | takes its arguments in different ways in the two Lisps but does |
| 4662 | exactly the same thing, so this package has not bothered to |
| 4663 | implement a Common Lisp-style @code{make-list}. |
| 4664 | |
| 4665 | @item |
| 4666 | A few more notable Common Lisp features not included in this |
| 4667 | package: @code{compiler-let}, @code{tagbody}, @code{prog}, |
| 4668 | @code{ldb/dpb}, @code{parse-integer}, @code{cerror}. |
| 4669 | |
| 4670 | @item |
| 4671 | Recursion. While recursion works in Emacs Lisp just like it |
| 4672 | does in Common Lisp, various details of the Emacs Lisp system |
| 4673 | and compiler make recursion much less efficient than it is in |
| 4674 | most Lisps. Some schools of thought prefer to use recursion |
| 4675 | in Lisp over other techniques; they would sum a list of |
| 4676 | numbers using something like |
| 4677 | |
| 4678 | @example |
| 4679 | (defun sum-list (list) |
| 4680 | (if list |
| 4681 | (+ (car list) (sum-list (cdr list))) |
| 4682 | 0)) |
| 4683 | @end example |
| 4684 | |
| 4685 | @noindent |
| 4686 | where a more iteratively-minded programmer might write one of |
| 4687 | these forms: |
| 4688 | |
| 4689 | @example |
| 4690 | (let ((total 0)) (dolist (x my-list) (incf total x)) total) |
| 4691 | (loop for x in my-list sum x) |
| 4692 | @end example |
| 4693 | |
| 4694 | While this would be mainly a stylistic choice in most Common Lisps, |
| 4695 | in Emacs Lisp you should be aware that the iterative forms are |
| 4696 | much faster than recursion. Also, Lisp programmers will want to |
| 4697 | note that the current Emacs Lisp compiler does not optimize tail |
| 4698 | recursion. |
| 4699 | @end itemize |
| 4700 | |
| 4701 | @node Obsolete Features |
| 4702 | @appendix Obsolete Features |
| 4703 | |
| 4704 | This section describes some features of the package that are obsolete |
| 4705 | and should not be used in new code. They are either only provided by |
| 4706 | the old @file{cl.el} entry point, not by the newer @file{cl-lib.el}; |
| 4707 | or where versions with a @samp{cl-} prefix do exist they do not behave |
| 4708 | in exactly the same way. |
| 4709 | |
| 4710 | @menu |
| 4711 | * Obsolete Lexical Binding:: An approximation of lexical binding. |
| 4712 | * Obsolete Macros:: Obsolete macros. |
| 4713 | * Obsolete Setf Customization:: Obsolete ways to customize setf. |
| 4714 | @end menu |
| 4715 | |
| 4716 | @node Obsolete Lexical Binding |
| 4717 | @appendixsec Obsolete Lexical Binding |
| 4718 | |
| 4719 | The following macros are extensions to Common Lisp, where all bindings |
| 4720 | are lexical unless declared otherwise. These features are likewise |
| 4721 | obsolete since the introduction of true lexical binding in Emacs 24.1. |
| 4722 | |
| 4723 | @defmac lexical-let (bindings@dots{}) forms@dots{} |
| 4724 | This form is exactly like @code{let} except that the bindings it |
| 4725 | establishes are purely lexical. |
| 4726 | @end defmac |
| 4727 | |
| 4728 | @c FIXME remove this and refer to elisp manual. |
| 4729 | @c Maybe merge some stuff from here to there? |
| 4730 | @noindent |
| 4731 | Lexical bindings are similar to local variables in a language like C: |
| 4732 | Only the code physically within the body of the @code{lexical-let} |
| 4733 | (after macro expansion) may refer to the bound variables. |
| 4734 | |
| 4735 | @example |
| 4736 | (setq a 5) |
| 4737 | (defun foo (b) (+ a b)) |
| 4738 | (let ((a 2)) (foo a)) |
| 4739 | @result{} 4 |
| 4740 | (lexical-let ((a 2)) (foo a)) |
| 4741 | @result{} 7 |
| 4742 | @end example |
| 4743 | |
| 4744 | @noindent |
| 4745 | In this example, a regular @code{let} binding of @code{a} actually |
| 4746 | makes a temporary change to the global variable @code{a}, so @code{foo} |
| 4747 | is able to see the binding of @code{a} to 2. But @code{lexical-let} |
| 4748 | actually creates a distinct local variable @code{a} for use within its |
| 4749 | body, without any effect on the global variable of the same name. |
| 4750 | |
| 4751 | The most important use of lexical bindings is to create @dfn{closures}. |
| 4752 | A closure is a function object that refers to an outside lexical |
| 4753 | variable (@pxref{Closures,,,elisp,GNU Emacs Lisp Reference Manual}). |
| 4754 | For example: |
| 4755 | |
| 4756 | @example |
| 4757 | (defun make-adder (n) |
| 4758 | (lexical-let ((n n)) |
| 4759 | (function (lambda (m) (+ n m))))) |
| 4760 | (setq add17 (make-adder 17)) |
| 4761 | (funcall add17 4) |
| 4762 | @result{} 21 |
| 4763 | @end example |
| 4764 | |
| 4765 | @noindent |
| 4766 | The call @code{(make-adder 17)} returns a function object which adds |
| 4767 | 17 to its argument. If @code{let} had been used instead of |
| 4768 | @code{lexical-let}, the function object would have referred to the |
| 4769 | global @code{n}, which would have been bound to 17 only during the |
| 4770 | call to @code{make-adder} itself. |
| 4771 | |
| 4772 | @example |
| 4773 | (defun make-counter () |
| 4774 | (lexical-let ((n 0)) |
| 4775 | (cl-function (lambda (&optional (m 1)) (cl-incf n m))))) |
| 4776 | (setq count-1 (make-counter)) |
| 4777 | (funcall count-1 3) |
| 4778 | @result{} 3 |
| 4779 | (funcall count-1 14) |
| 4780 | @result{} 17 |
| 4781 | (setq count-2 (make-counter)) |
| 4782 | (funcall count-2 5) |
| 4783 | @result{} 5 |
| 4784 | (funcall count-1 2) |
| 4785 | @result{} 19 |
| 4786 | (funcall count-2) |
| 4787 | @result{} 6 |
| 4788 | @end example |
| 4789 | |
| 4790 | @noindent |
| 4791 | Here we see that each call to @code{make-counter} creates a distinct |
| 4792 | local variable @code{n}, which serves as a private counter for the |
| 4793 | function object that is returned. |
| 4794 | |
| 4795 | Closed-over lexical variables persist until the last reference to |
| 4796 | them goes away, just like all other Lisp objects. For example, |
| 4797 | @code{count-2} refers to a function object which refers to an |
| 4798 | instance of the variable @code{n}; this is the only reference |
| 4799 | to that variable, so after @code{(setq count-2 nil)} the garbage |
| 4800 | collector would be able to delete this instance of @code{n}. |
| 4801 | Of course, if a @code{lexical-let} does not actually create any |
| 4802 | closures, then the lexical variables are free as soon as the |
| 4803 | @code{lexical-let} returns. |
| 4804 | |
| 4805 | Many closures are used only during the extent of the bindings they |
| 4806 | refer to; these are known as ``downward funargs'' in Lisp parlance. |
| 4807 | When a closure is used in this way, regular Emacs Lisp dynamic |
| 4808 | bindings suffice and will be more efficient than @code{lexical-let} |
| 4809 | closures: |
| 4810 | |
| 4811 | @example |
| 4812 | (defun add-to-list (x list) |
| 4813 | (mapcar (lambda (y) (+ x y))) list) |
| 4814 | (add-to-list 7 '(1 2 5)) |
| 4815 | @result{} (8 9 12) |
| 4816 | @end example |
| 4817 | |
| 4818 | @noindent |
| 4819 | Since this lambda is only used while @code{x} is still bound, |
| 4820 | it is not necessary to make a true closure out of it. |
| 4821 | |
| 4822 | You can use @code{defun} or @code{flet} inside a @code{lexical-let} |
| 4823 | to create a named closure. If several closures are created in the |
| 4824 | body of a single @code{lexical-let}, they all close over the same |
| 4825 | instance of the lexical variable. |
| 4826 | |
| 4827 | @defmac lexical-let* (bindings@dots{}) forms@dots{} |
| 4828 | This form is just like @code{lexical-let}, except that the bindings |
| 4829 | are made sequentially in the manner of @code{let*}. |
| 4830 | @end defmac |
| 4831 | |
| 4832 | @node Obsolete Macros |
| 4833 | @appendixsec Obsolete Macros |
| 4834 | |
| 4835 | The following macros are obsolete, and are replaced by versions with |
| 4836 | a @samp{cl-} prefix that do not behave in exactly the same way. |
| 4837 | Consequently, the @file{cl.el} versions are not simply aliases to the |
| 4838 | @file{cl-lib.el} versions. |
| 4839 | |
| 4840 | @defmac flet (bindings@dots{}) forms@dots{} |
| 4841 | This macro is replaced by @code{cl-flet} (@pxref{Function Bindings}), |
| 4842 | which behaves the same way as Common Lisp's @code{flet}. |
| 4843 | This @code{flet} takes the same arguments as @code{cl-flet}, but does |
| 4844 | not behave in precisely the same way. |
| 4845 | |
| 4846 | While @code{flet} in Common Lisp establishes a lexical function |
| 4847 | binding, this @code{flet} makes a dynamic binding (it dates from a |
| 4848 | time before Emacs had lexical binding). The result is |
| 4849 | that @code{flet} affects indirect calls to a function as well as calls |
| 4850 | directly inside the @code{flet} form itself. |
| 4851 | |
| 4852 | This will even work on Emacs primitives, although note that some calls |
| 4853 | to primitive functions internal to Emacs are made without going |
| 4854 | through the symbol's function cell, and so will not be affected by |
| 4855 | @code{flet}. For example, |
| 4856 | |
| 4857 | @example |
| 4858 | (flet ((message (&rest args) (push args saved-msgs))) |
| 4859 | (do-something)) |
| 4860 | @end example |
| 4861 | |
| 4862 | This code attempts to replace the built-in function @code{message} |
| 4863 | with a function that simply saves the messages in a list rather |
| 4864 | than displaying them. The original definition of @code{message} |
| 4865 | will be restored after @code{do-something} exits. This code will |
| 4866 | work fine on messages generated by other Lisp code, but messages |
| 4867 | generated directly inside Emacs will not be caught since they make |
| 4868 | direct C-language calls to the message routines rather than going |
| 4869 | through the Lisp @code{message} function. |
| 4870 | |
| 4871 | @c Bug#411. |
| 4872 | Note that many primitives (e.g., @code{+}) have special byte-compile |
| 4873 | handling. Attempts to redefine such functions using @code{flet} will |
| 4874 | fail if byte-compiled. |
| 4875 | @c Or cl-flet. |
| 4876 | @c In such cases, use @code{labels} instead. |
| 4877 | @end defmac |
| 4878 | |
| 4879 | @defmac labels (bindings@dots{}) forms@dots{} |
| 4880 | This macro is replaced by @code{cl-labels} (@pxref{Function Bindings}), |
| 4881 | which behaves the same way as Common Lisp's @code{labels}. |
| 4882 | This @code{labels} takes the same arguments as @code{cl-labels}, but |
| 4883 | does not behave in precisely the same way. |
| 4884 | |
| 4885 | This version of @code{labels} uses the obsolete @code{lexical-let} |
| 4886 | form (@pxref{Obsolete Lexical Binding}), rather than the true |
| 4887 | lexical binding that @code{cl-labels} uses. |
| 4888 | @end defmac |
| 4889 | |
| 4890 | @defmac letf (bindings@dots{}) forms@dots{} |
| 4891 | This macro is almost exactly the same as @code{cl-letf}, which |
| 4892 | replaces it (@pxref{Modify Macros}). The only difference is in |
| 4893 | details that relate to some deprecated usage of @code{symbol-function} |
| 4894 | in place forms. |
| 4895 | @end defmac |
| 4896 | |
| 4897 | @node Obsolete Setf Customization |
| 4898 | @appendixsec Obsolete Ways to Customize Setf |
| 4899 | |
| 4900 | Common Lisp defines three macros, @code{define-modify-macro}, |
| 4901 | @code{defsetf}, and @code{define-setf-method}, that allow the |
| 4902 | user to extend generalized variables in various ways. |
| 4903 | In Emacs, these are obsolete, replaced by various features of |
| 4904 | @file{gv.el} in Emacs 24.3. |
| 4905 | @xref{Adding Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}. |
| 4906 | |
| 4907 | |
| 4908 | @defmac define-modify-macro name arglist function [doc-string] |
| 4909 | This macro defines a ``read-modify-write'' macro similar to |
| 4910 | @code{cl-incf} and @code{cl-decf}. You can replace this macro |
| 4911 | with @code{gv-letplace}. |
| 4912 | |
| 4913 | The macro @var{name} is defined to take a @var{place} argument |
| 4914 | followed by additional arguments described by @var{arglist}. The call |
| 4915 | |
| 4916 | @example |
| 4917 | (@var{name} @var{place} @var{args}@dots{}) |
| 4918 | @end example |
| 4919 | |
| 4920 | @noindent |
| 4921 | will be expanded to |
| 4922 | |
| 4923 | @example |
| 4924 | (cl-callf @var{func} @var{place} @var{args}@dots{}) |
| 4925 | @end example |
| 4926 | |
| 4927 | @noindent |
| 4928 | which in turn is roughly equivalent to |
| 4929 | |
| 4930 | @example |
| 4931 | (setf @var{place} (@var{func} @var{place} @var{args}@dots{})) |
| 4932 | @end example |
| 4933 | |
| 4934 | For example: |
| 4935 | |
| 4936 | @example |
| 4937 | (define-modify-macro incf (&optional (n 1)) +) |
| 4938 | (define-modify-macro concatf (&rest args) concat) |
| 4939 | @end example |
| 4940 | |
| 4941 | Note that @code{&key} is not allowed in @var{arglist}, but |
| 4942 | @code{&rest} is sufficient to pass keywords on to the function. |
| 4943 | |
| 4944 | Most of the modify macros defined by Common Lisp do not exactly |
| 4945 | follow the pattern of @code{define-modify-macro}. For example, |
| 4946 | @code{push} takes its arguments in the wrong order, and @code{pop} |
| 4947 | is completely irregular. |
| 4948 | |
| 4949 | The above @code{incf} example could be written using |
| 4950 | @code{gv-letplace} as: |
| 4951 | @example |
| 4952 | (defmacro incf (place &optional n) |
| 4953 | (gv-letplace (getter setter) place |
| 4954 | (macroexp-let2 nil v (or n 1) |
| 4955 | (funcall setter `(+ ,v ,getter))))) |
| 4956 | @end example |
| 4957 | @ignore |
| 4958 | (defmacro concatf (place &rest args) |
| 4959 | (gv-letplace (getter setter) place |
| 4960 | (macroexp-let2 nil v (mapconcat 'identity args "") |
| 4961 | (funcall setter `(concat ,getter ,v))))) |
| 4962 | @end ignore |
| 4963 | @end defmac |
| 4964 | |
| 4965 | @defmac defsetf access-fn update-fn |
| 4966 | This is the simpler of two @code{defsetf} forms, and is |
| 4967 | replaced by @code{gv-define-simple-setter}. |
| 4968 | |
| 4969 | With @var{access-fn} the name of a function that accesses a place, |
| 4970 | this declares @var{update-fn} to be the corresponding store function. |
| 4971 | From now on, |
| 4972 | |
| 4973 | @example |
| 4974 | (setf (@var{access-fn} @var{arg1} @var{arg2} @var{arg3}) @var{value}) |
| 4975 | @end example |
| 4976 | |
| 4977 | @noindent |
| 4978 | will be expanded to |
| 4979 | |
| 4980 | @example |
| 4981 | (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} @var{value}) |
| 4982 | @end example |
| 4983 | |
| 4984 | @noindent |
| 4985 | The @var{update-fn} is required to be either a true function, or |
| 4986 | a macro that evaluates its arguments in a function-like way. Also, |
| 4987 | the @var{update-fn} is expected to return @var{value} as its result. |
| 4988 | Otherwise, the above expansion would not obey the rules for the way |
| 4989 | @code{setf} is supposed to behave. |
| 4990 | |
| 4991 | As a special (non-Common-Lisp) extension, a third argument of @code{t} |
| 4992 | to @code{defsetf} says that the return value of @code{update-fn} is |
| 4993 | not suitable, so that the above @code{setf} should be expanded to |
| 4994 | something more like |
| 4995 | |
| 4996 | @example |
| 4997 | (let ((temp @var{value})) |
| 4998 | (@var{update-fn} @var{arg1} @var{arg2} @var{arg3} temp) |
| 4999 | temp) |
| 5000 | @end example |
| 5001 | |
| 5002 | Some examples are: |
| 5003 | |
| 5004 | @example |
| 5005 | (defsetf car setcar) |
| 5006 | (defsetf buffer-name rename-buffer t) |
| 5007 | @end example |
| 5008 | |
| 5009 | These translate directly to @code{gv-define-simple-setter}: |
| 5010 | |
| 5011 | @example |
| 5012 | (gv-define-simple-setter car setcar) |
| 5013 | (gv-define-simple-setter buffer-name rename-buffer t) |
| 5014 | @end example |
| 5015 | @end defmac |
| 5016 | |
| 5017 | @defmac defsetf access-fn arglist (store-var) forms@dots{} |
| 5018 | This is the second, more complex, form of @code{defsetf}. |
| 5019 | It can be replaced by @code{gv-define-setter}. |
| 5020 | |
| 5021 | This form of @code{defsetf} is rather like @code{defmacro} except for |
| 5022 | the additional @var{store-var} argument. The @var{forms} should |
| 5023 | return a Lisp form that stores the value of @var{store-var} into the |
| 5024 | generalized variable formed by a call to @var{access-fn} with |
| 5025 | arguments described by @var{arglist}. The @var{forms} may begin with |
| 5026 | a string which documents the @code{setf} method (analogous to the doc |
| 5027 | string that appears at the front of a function). |
| 5028 | |
| 5029 | For example, the simple form of @code{defsetf} is shorthand for |
| 5030 | |
| 5031 | @example |
| 5032 | (defsetf @var{access-fn} (&rest args) (store) |
| 5033 | (append '(@var{update-fn}) args (list store))) |
| 5034 | @end example |
| 5035 | |
| 5036 | The Lisp form that is returned can access the arguments from |
| 5037 | @var{arglist} and @var{store-var} in an unrestricted fashion; |
| 5038 | macros like @code{cl-incf} that invoke this |
| 5039 | setf-method will insert temporary variables as needed to make |
| 5040 | sure the apparent order of evaluation is preserved. |
| 5041 | |
| 5042 | Another standard example: |
| 5043 | |
| 5044 | @example |
| 5045 | (defsetf nth (n x) (store) |
| 5046 | `(setcar (nthcdr ,n ,x) ,store)) |
| 5047 | @end example |
| 5048 | |
| 5049 | You could write this using @code{gv-define-setter} as: |
| 5050 | |
| 5051 | @example |
| 5052 | (gv-define-setter nth (store n x) |
| 5053 | `(setcar (nthcdr ,n ,x) ,store)) |
| 5054 | @end example |
| 5055 | @end defmac |
| 5056 | |
| 5057 | @defmac define-setf-method access-fn arglist forms@dots{} |
| 5058 | This is the most general way to create new place forms. You can |
| 5059 | replace this by @code{gv-define-setter} or @code{gv-define-expander}. |
| 5060 | |
| 5061 | When a @code{setf} to @var{access-fn} with arguments described by |
| 5062 | @var{arglist} is expanded, the @var{forms} are evaluated and must |
| 5063 | return a list of five items: |
| 5064 | |
| 5065 | @enumerate |
| 5066 | @item |
| 5067 | A list of @dfn{temporary variables}. |
| 5068 | |
| 5069 | @item |
| 5070 | A list of @dfn{value forms} corresponding to the temporary variables |
| 5071 | above. The temporary variables will be bound to these value forms |
| 5072 | as the first step of any operation on the generalized variable. |
| 5073 | |
| 5074 | @item |
| 5075 | A list of exactly one @dfn{store variable} (generally obtained |
| 5076 | from a call to @code{gensym}). |
| 5077 | |
| 5078 | @item |
| 5079 | A Lisp form that stores the contents of the store variable into |
| 5080 | the generalized variable, assuming the temporaries have been |
| 5081 | bound as described above. |
| 5082 | |
| 5083 | @item |
| 5084 | A Lisp form that accesses the contents of the generalized variable, |
| 5085 | assuming the temporaries have been bound. |
| 5086 | @end enumerate |
| 5087 | |
| 5088 | This is exactly like the Common Lisp macro of the same name, |
| 5089 | except that the method returns a list of five values rather |
| 5090 | than the five values themselves, since Emacs Lisp does not |
| 5091 | support Common Lisp's notion of multiple return values. |
| 5092 | (Note that the @code{setf} implementation provided by @file{gv.el} |
| 5093 | does not use this five item format. Its use here is only for |
| 5094 | backwards compatibility.) |
| 5095 | |
| 5096 | Once again, the @var{forms} may begin with a documentation string. |
| 5097 | |
| 5098 | A setf-method should be maximally conservative with regard to |
| 5099 | temporary variables. In the setf-methods generated by |
| 5100 | @code{defsetf}, the second return value is simply the list of |
| 5101 | arguments in the place form, and the first return value is a |
| 5102 | list of a corresponding number of temporary variables generated |
| 5103 | @c FIXME I don't think this is true anymore. |
| 5104 | by @code{cl-gensym}. Macros like @code{cl-incf} that |
| 5105 | use this setf-method will optimize away most temporaries that |
| 5106 | turn out to be unnecessary, so there is little reason for the |
| 5107 | setf-method itself to optimize. |
| 5108 | @end defmac |
| 5109 | |
| 5110 | @c Removed in Emacs 24.3, not possible to make a compatible replacement. |
| 5111 | @ignore |
| 5112 | @defun get-setf-method place &optional env |
| 5113 | This function returns the setf-method for @var{place}, by |
| 5114 | invoking the definition previously recorded by @code{defsetf} |
| 5115 | or @code{define-setf-method}. The result is a list of five |
| 5116 | values as described above. You can use this function to build |
| 5117 | your own @code{cl-incf}-like modify macros. |
| 5118 | |
| 5119 | The argument @var{env} specifies the ``environment'' to be |
| 5120 | passed on to @code{macroexpand} if @code{get-setf-method} should |
| 5121 | need to expand a macro in @var{place}. It should come from |
| 5122 | an @code{&environment} argument to the macro or setf-method |
| 5123 | that called @code{get-setf-method}. |
| 5124 | @end defun |
| 5125 | @end ignore |
| 5126 | |
| 5127 | |
| 5128 | @node GNU Free Documentation License |
| 5129 | @appendix GNU Free Documentation License |
| 5130 | @include doclicense.texi |
| 5131 | |
| 5132 | @node Function Index |
| 5133 | @unnumbered Function Index |
| 5134 | |
| 5135 | @printindex fn |
| 5136 | |
| 5137 | @node Variable Index |
| 5138 | @unnumbered Variable Index |
| 5139 | |
| 5140 | @printindex vr |
| 5141 | |
| 5142 | @bye |