cl.texi 200 KB
Newer Older
Glenn Morris's avatar
Glenn Morris committed
1
\input texinfo    @c -*-texinfo-*-
2
@setfilename ../../info/cl
Glenn Morris's avatar
Glenn Morris committed
3
@settitle Common Lisp Extensions
4
@include emacsver.texi
Glenn Morris's avatar
Glenn Morris committed
5 6 7 8

@copying
This file documents the GNU Emacs Common Lisp emulation package.

9
Copyright @copyright{} 1993, 2001-2012 Free Software Foundation, Inc.
Glenn Morris's avatar
Glenn Morris committed
10 11 12

@quotation
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
Glenn Morris's avatar
Glenn Morris committed
14
any later version published by the Free Software Foundation; with no
15 16 17
Invariant Sections, with the Front-Cover texts being ``A GNU Manual'',
and with the Back-Cover Texts as in (a) below.  A copy of the license
is included in the section entitled ``GNU Free Documentation License''.
Glenn Morris's avatar
Glenn Morris committed
18

19 20 21
(a) The FSF's Back-Cover Text is: ``You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.''
Glenn Morris's avatar
Glenn Morris committed
22 23 24
@end quotation
@end copying

25
@dircategory Emacs lisp libraries
Glenn Morris's avatar
Glenn Morris committed
26
@direntry
Glenn Morris's avatar
Glenn Morris committed
27
* CL: (cl).                     Partial Common Lisp support for Emacs Lisp.
Glenn Morris's avatar
Glenn Morris committed
28 29 30 31 32 33 34 35 36 37
@end direntry

@finalout

@titlepage
@sp 6
@center @titlefont{Common Lisp Extensions}
@sp 4
@center For GNU Emacs Lisp
@sp 1
38
@center as distributed with Emacs @value{EMACSVER}
Glenn Morris's avatar
Glenn Morris committed
39 40 41 42 43 44 45 46
@sp 5
@center Dave Gillespie
@center daveg@@synaptics.com
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

47 48 49
@contents

@ifnottex
50 51 52
@node Top
@top GNU Emacs Common Lisp Emulation

53 54 55
@insertcopying
@end ifnottex

Glenn Morris's avatar
Glenn Morris committed
56
@menu
57 58 59 60 61 62 63 64 65 66 67
* Overview::             Basics, usage, etc.
* Program Structure::    Arglists, @code{cl-eval-when}, @code{defalias}.
* Predicates::           @code{cl-typep} and @code{cl-equalp}.
* Control Structure::    @code{setf}, @code{cl-do}, @code{cl-loop}, etc.
* Macros::               Destructuring, @code{cl-define-compiler-macro}.
* Declarations::         @code{cl-proclaim}, @code{cl-declare}, etc.
* Symbols::              Property lists, @code{cl-gensym}.
* Numbers::              Predicates, functions, random numbers.
* Sequences::            Mapping, functions, searching, sorting.
* Lists::                @code{cl-caddr}, @code{cl-sublis}, @code{cl-member}, @code{cl-assoc}, etc.
* Structures::           @code{cl-defstruct}.
68
* Assertions::           @code{cl-check-type}, @code{cl-assert}.
69 70 71 72

* Efficiency Concerns::         Hints and techniques.
* Common Lisp Compatibility::   All known differences with Steele.
* Porting Common Lisp::         Hints for porting Common Lisp code.
Glenn Morris's avatar
Glenn Morris committed
73 74 75 76 77 78

* GNU Free Documentation License:: The license for this documentation.
* Function Index::
* Variable Index::
@end menu

79
@node Overview
Glenn Morris's avatar
Glenn Morris committed
80 81 82
@chapter Overview

@noindent
83 84 85 86 87
This document describes a set of Emacs Lisp facilities borrowed from
Common Lisp.  All the facilities are described here in detail.  While
this document does not assume any prior knowledge of Common Lisp, it
does assume a basic familiarity with Emacs Lisp.

Glenn Morris's avatar
Glenn Morris committed
88 89 90 91 92 93 94
Common Lisp is a huge language, and Common Lisp systems tend to be
massive and extremely complex.  Emacs Lisp, by contrast, is rather
minimalist in the choice of Lisp features it offers the programmer.
As Emacs Lisp programmers have grown in number, and the applications
they write have grown more ambitious, it has become clear that Emacs
Lisp could benefit from many of the conveniences of Common Lisp.

95
The @code{CL} package adds a number of Common Lisp functions and
Glenn Morris's avatar
Glenn Morris committed
96
control structures to Emacs Lisp.  While not a 100% complete
97
implementation of Common Lisp, @code{CL} adds enough functionality
Glenn Morris's avatar
Glenn Morris committed
98 99 100 101 102 103 104 105 106 107 108 109 110 111
to make Emacs Lisp programming significantly more convenient.

Some Common Lisp features have been omitted from this package
for various reasons:

@itemize @bullet
@item
Some features are too complex or bulky relative to their benefit
to Emacs Lisp programmers.  CLOS and Common Lisp streams are fine
examples of this group.

@item
Other features cannot be implemented without modification to the
Emacs Lisp interpreter itself, such as multiple return values,
112 113
case-insensitive symbols, and complex numbers.
The @code{CL} package generally makes no attempt to emulate these
Glenn Morris's avatar
Glenn Morris committed
114 115 116 117
features.

@end itemize

118 119
The package described here was originally written by Dave Gillespie,
@file{daveg@@synaptics.com}, as a total rewrite of an earlier
120 121 122 123 124
1986 @file{cl.el} package by Cesar Quiroz.  Care has been taken
to ensure that each function is defined efficiently, concisely, and
with minimal impact on the rest of the Emacs environment.  Stefan
Monnier added the file @file{cl-lib.el} and rationalized the namespace
for Emacs 24.3.
Glenn Morris's avatar
Glenn Morris committed
125 126

@menu
127 128 129
* Usage::                How to use the CL package.
* Organization::         The package's five component files.
* Naming Conventions::   Notes on CL function names.
Glenn Morris's avatar
Glenn Morris committed
130 131
@end menu

132
@node Usage
Glenn Morris's avatar
Glenn Morris committed
133 134 135
@section Usage

@noindent
136 137 138 139
The @code{CL} package is distributed with Emacs, so there is no need
to install any additional files in order to start using it.  Lisp code
that uses features from the @code{CL} package should simply include at
the beginning:
Glenn Morris's avatar
Glenn Morris committed
140 141

@example
142
(require 'cl-lib)
Glenn Morris's avatar
Glenn Morris committed
143 144 145
@end example

@noindent
146 147
You may wish to add such a statement to your init file, if you
make frequent use of CL features.
Glenn Morris's avatar
Glenn Morris committed
148

149
@node Organization
Glenn Morris's avatar
Glenn Morris committed
150 151 152
@section Organization

@noindent
153
The Common Lisp package is organized into four main files:
Glenn Morris's avatar
Glenn Morris committed
154 155

@table @file
156 157 158
@item cl-lib.el
This is the main file, which contains basic functions
and information about the package.  This file is relatively compact.
Glenn Morris's avatar
Glenn Morris committed
159 160 161 162

@item cl-extra.el
This file contains the larger, more complex or unusual functions.
It is kept separate so that packages which only want to use Common
163
Lisp fundamentals like the @code{cl-incf} function won't need to pay
Glenn Morris's avatar
Glenn Morris committed
164 165 166 167
the overhead of loading the more advanced functions.

@item cl-seq.el
This file contains most of the advanced functions for operating
168
on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}.
Glenn Morris's avatar
Glenn Morris committed
169 170

@item cl-macs.el
171 172 173 174 175 176
This file contains the features that are macros instead of functions.
Macros expand when the caller is compiled, not when it is run, so the
macros generally only need to be present when the byte-compiler is
running (or when the macros are used in uncompiled code).  Most of the
macros of this package are isolated in @file{cl-macs.el} so that they
won't take up memory unless you are compiling.
Glenn Morris's avatar
Glenn Morris committed
177 178
@end table

179
The file @file{cl-lib.el} includes all necessary @code{autoload}
Glenn Morris's avatar
Glenn Morris committed
180
commands for the functions and macros in the other three files.
181
All you have to do is @code{(require 'cl-lib)}, and @file{cl-lib.el}
Glenn Morris's avatar
Glenn Morris committed
182 183 184
will take care of pulling in the other files when they are
needed.

185 186 187 188 189 190 191 192 193 194 195 196 197
There is another file, @file{cl.el}, which was the main entry point
to the CL package prior to Emacs 24.3.  Nowadays, it is replaced
by @file{cl-lib.el}.  The two provide the same features, but use
different function names (in fact, @file{cl.el} just defines aliases
to the @file{cl-lib.el} definitions).  In particular, the old @file{cl.el}
does not use a clean namespace.  For this reason, Emacs has a policy
that packages distributed with Emacs must not load @code{cl} at run time.
(It is ok for them to load @code{cl} at @emph{compile} time, with
@code{eval-when-compile}, and use the macros it provides.)  There is
no such restriction on the use of @code{cl-lib}.  New code should use
@code{cl-lib} rather than @code{cl}.  @xref{Naming Conventions}.

There is one more file, @file{cl-compat.el}, which defines some
198 199 200
routines from the older Quiroz CL package that are not otherwise
present in the new package.  This file is obsolete and should not be
used in new code.
Glenn Morris's avatar
Glenn Morris committed
201

202
@node Naming Conventions
Glenn Morris's avatar
Glenn Morris committed
203 204 205 206
@section Naming Conventions

@noindent
Except where noted, all functions defined by this package have the
207 208
same calling conventions as their Common Lisp counterparts, and
names that are those of Common Lisp plus a @samp{cl-} prefix.
Glenn Morris's avatar
Glenn Morris committed
209 210

Internal function and variable names in the package are prefixed
211 212
by @code{cl--}.  Here is a complete list of functions prefixed by
@code{cl-} that were not taken from Common Lisp:
Glenn Morris's avatar
Glenn Morris committed
213

214
@c FIXME lexical-let lexical-let*
Glenn Morris's avatar
Glenn Morris committed
215
@example
216 217
cl-callf         cl-callf2        cl-defsubst
cl-floatp-safe   cl-letf          cl-letf*
Glenn Morris's avatar
Glenn Morris committed
218 219
@end example

220
The following simple functions and macros are defined in @file{cl-lib.el};
Glenn Morris's avatar
Glenn Morris committed
221 222 223
they do not cause other components like @file{cl-extra} to be loaded.

@example
224 225 226 227 228 229 230 231
cl-floatp-safe   cl-endp
cl-evenp         cl-oddp          cl-plusp         cl-minusp
cl-caaar .. cl-cddddr
cl-list*         cl-ldiff         cl-rest          cl-first .. cl-tenth
cl-copy-list     cl-subst         cl-mapcar [2]
cl-adjoin [3]    cl-acons         cl-pairlis
cl-pushnew [3,4] cl-incf [4]      cl-decf [4]
cl-proclaim      cl-declaim
Glenn Morris's avatar
Glenn Morris committed
232 233 234 235 236 237 238 239 240 241 242 243
@end example

@noindent
[2] Only for one sequence argument or two list arguments.

@noindent
[3] Only if @code{:test} is @code{eq}, @code{equal}, or unspecified,
and @code{:key} is not used.

@noindent
[4] Only when @var{place} is a plain variable name.

244
@node Program Structure
Glenn Morris's avatar
Glenn Morris committed
245 246 247
@chapter Program Structure

@noindent
248
This section describes features of the @code{CL} package that have to
Glenn Morris's avatar
Glenn Morris committed
249
do with programs as a whole: advanced argument lists for functions,
250
and the @code{cl-eval-when} construct.
Glenn Morris's avatar
Glenn Morris committed
251 252

@menu
253 254
* Argument Lists::       @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}.
* Time of Evaluation::   The @code{cl-eval-when} construct.
Glenn Morris's avatar
Glenn Morris committed
255 256 257 258 259 260
@end menu

@iftex
@secno=1
@end iftex

261
@node Argument Lists
Glenn Morris's avatar
Glenn Morris committed
262 263 264 265 266 267 268 269 270 271 272 273 274 275
@section Argument Lists

@noindent
Emacs Lisp's notation for argument lists of functions is a subset of
the Common Lisp notation.  As well as the familiar @code{&optional}
and @code{&rest} markers, Common Lisp allows you to specify default
values for optional arguments, and it provides the additional markers
@code{&key} and @code{&aux}.

Since argument parsing is built-in to Emacs, there is no way for
this package to implement Common Lisp argument lists seamlessly.
Instead, this package defines alternates for several Lisp forms
which you must use if you need Common Lisp argument lists.

276
@defspec cl-defun name arglist body...
Glenn Morris's avatar
Glenn Morris committed
277 278 279 280 281 282
This form is identical to the regular @code{defun} form, except
that @var{arglist} is allowed to be a full Common Lisp argument
list.  Also, the function body is enclosed in an implicit block
called @var{name}; @pxref{Blocks and Exits}.
@end defspec

283 284
@defspec cl-defsubst name arglist body...
This is just like @code{cl-defun}, except that the function that
Glenn Morris's avatar
Glenn Morris committed
285 286 287
is defined is automatically proclaimed @code{inline}, i.e.,
calls to it may be expanded into in-line code by the byte compiler.
This is analogous to the @code{defsubst} form;
288
@code{cl-defsubst} uses a different method (compiler macros) which
289
works in all versions of Emacs, and also generates somewhat more
290
efficient inline expansions.  In particular, @code{cl-defsubst}
Glenn Morris's avatar
Glenn Morris committed
291 292 293 294
arranges for the processing of keyword arguments, default values,
etc., to be done at compile-time whenever possible.
@end defspec

295
@defspec cl-defmacro name arglist body...
Glenn Morris's avatar
Glenn Morris committed
296 297 298 299 300 301 302 303 304 305
This is identical to the regular @code{defmacro} form,
except that @var{arglist} is allowed to be a full Common Lisp
argument list.  The @code{&environment} keyword is supported as
described in Steele.  The @code{&whole} keyword is supported only
within destructured lists (see below); top-level @code{&whole}
cannot be implemented with the current Emacs Lisp interpreter.
The macro expander body is enclosed in an implicit block called
@var{name}.
@end defspec

306
@defspec cl-function symbol-or-lambda
Glenn Morris's avatar
Glenn Morris committed
307 308 309 310 311
This is identical to the regular @code{function} form,
except that if the argument is a @code{lambda} form then that
form may use a full Common Lisp argument list.
@end defspec

312
Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
Glenn Morris's avatar
Glenn Morris committed
313 314 315
in this package that include @var{arglist}s in their syntax allow
full Common Lisp argument lists.

316 317 318
Note that it is @emph{not} necessary to use @code{cl-defun} in
order to have access to most @code{CL} features in your function.
These features are always present; @code{cl-defun}'s only
Glenn Morris's avatar
Glenn Morris committed
319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367
difference from @code{defun} is its more flexible argument
lists and its implicit block.

The full form of a Common Lisp argument list is

@example
(@var{var}...
 &optional (@var{var} @var{initform} @var{svar})...
 &rest @var{var}
 &key ((@var{keyword} @var{var}) @var{initform} @var{svar})...
 &aux (@var{var} @var{initform})...)
@end example

Each of the five argument list sections is optional.  The @var{svar},
@var{initform}, and @var{keyword} parts are optional; if they are
omitted, then @samp{(@var{var})} may be written simply @samp{@var{var}}.

The first section consists of zero or more @dfn{required} arguments.
These arguments must always be specified in a call to the function;
there is no difference between Emacs Lisp and Common Lisp as far as
required arguments are concerned.

The second section consists of @dfn{optional} arguments.  These
arguments may be specified in the function call; if they are not,
@var{initform} specifies the default value used for the argument.
(No @var{initform} means to use @code{nil} as the default.)  The
@var{initform} is evaluated with the bindings for the preceding
arguments already established; @code{(a &optional (b (1+ a)))}
matches one or two arguments, with the second argument defaulting
to one plus the first argument.  If the @var{svar} is specified,
it is an auxiliary variable which is bound to @code{t} if the optional
argument was specified, or to @code{nil} if the argument was omitted.
If you don't use an @var{svar}, then there will be no way for your
function to tell whether it was called with no argument, or with
the default value passed explicitly as an argument.

The third section consists of a single @dfn{rest} argument.  If
more arguments were passed to the function than are accounted for
by the required and optional arguments, those extra arguments are
collected into a list and bound to the ``rest'' argument variable.
Common Lisp's @code{&rest} is equivalent to that of Emacs Lisp.
Common Lisp accepts @code{&body} as a synonym for @code{&rest} in
macro contexts; this package accepts it all the time.

The fourth section consists of @dfn{keyword} arguments.  These
are optional arguments which are specified by name rather than
positionally in the argument list.  For example,

@example
368
(cl-defun foo (a &optional b &key c d (e 17)))
Glenn Morris's avatar
Glenn Morris committed
369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389
@end example

@noindent
defines a function which may be called with one, two, or more
arguments.  The first two arguments are bound to @code{a} and
@code{b} in the usual way.  The remaining arguments must be
pairs of the form @code{:c}, @code{:d}, or @code{:e} followed
by the value to be bound to the corresponding argument variable.
(Symbols whose names begin with a colon are called @dfn{keywords},
and they are self-quoting in the same way as @code{nil} and
@code{t}.)

For example, the call @code{(foo 1 2 :d 3 :c 4)} sets the five
arguments to 1, 2, 4, 3, and 17, respectively.  If the same keyword
appears more than once in the function call, the first occurrence
takes precedence over the later ones.  Note that it is not possible
to specify keyword arguments without specifying the optional
argument @code{b} as well, since @code{(foo 1 :c 2)} would bind
@code{b} to the keyword @code{:c}, then signal an error because
@code{2} is not a valid keyword.

390 391 392 393
You can also explicitly specify the keyword argument; it need not be
simply the variable name prefixed with a colon.  For example,

@example
394
(cl-defun bar (&key (a 1) ((baz b) 4)))
395 396 397 398 399 400 401 402 403 404 405 406 407 408 409
@end example

@noindent

specifies a keyword @code{:a} that sets the variable @code{a} with
default value 1, as well as a keyword @code{baz} that sets the
variable @code{b} with default value 4.  In this case, because
@code{baz} is not self-quoting, you must quote it explicitly in the
function call, like this:

@example
(bar :a 10 'baz 42)
@end example

Ordinarily, it is an error to pass an unrecognized keyword to
Glenn Morris's avatar
Glenn Morris committed
410 411 412 413 414 415 416 417 418 419
a function, e.g., @code{(foo 1 2 :c 3 :goober 4)}.  You can ask
Lisp to ignore unrecognized keywords, either by adding the
marker @code{&allow-other-keys} after the keyword section
of the argument list, or by specifying an @code{:allow-other-keys}
argument in the call whose value is non-@code{nil}.  If the
function uses both @code{&rest} and @code{&key} at the same time,
the ``rest'' argument is bound to the keyword list as it appears
in the call.  For example:

@smallexample
420 421
(cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
  (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
Glenn Morris's avatar
Glenn Morris committed
422 423 424 425 426 427
      (if need (error "Thing not found"))))
@end smallexample

@noindent
This function takes a @code{:need} keyword argument, but also
accepts other keyword arguments which are passed on to the
428 429
@code{cl-member} function.  @code{allow-other-keys} is used to
keep both @code{find-thing} and @code{cl-member} from complaining
Glenn Morris's avatar
Glenn Morris committed
430 431 432 433 434 435 436 437 438 439
about each others' keywords in the arguments.

The fifth section of the argument list consists of @dfn{auxiliary
variables}.  These are not really arguments at all, but simply
variables which are bound to @code{nil} or to the specified
@var{initforms} during execution of the function.  There is no
difference between the following two functions, except for a
matter of stylistic taste:

@example
440
(cl-defun foo (a b &aux (c (+ a b)) d)
Glenn Morris's avatar
Glenn Morris committed
441 442
  @var{body})

443
(cl-defun foo (a b)
Glenn Morris's avatar
Glenn Morris committed
444 445 446 447 448 449
  (let ((c (+ a b)) d)
    @var{body}))
@end example

Argument lists support @dfn{destructuring}.  In Common Lisp,
destructuring is only allowed with @code{defmacro}; this package
450
allows it with @code{cl-defun} and other argument lists as well.
Glenn Morris's avatar
Glenn Morris committed
451 452 453 454 455 456 457
In destructuring, any argument variable (@var{var} in the above
diagram) can be replaced by a list of variables, or more generally,
a recursive argument list.  The corresponding argument value must
be a list whose elements match this recursive argument list.
For example:

@example
458
(cl-defmacro dolist ((var listform &optional resultform)
Glenn Morris's avatar
Glenn Morris committed
459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484
                   &rest body)
  ...)
@end example

This says that the first argument of @code{dolist} must be a list
of two or three items; if there are other arguments as well as this
list, they are stored in @code{body}.  All features allowed in
regular argument lists are allowed in these recursive argument lists.
In addition, the clause @samp{&whole @var{var}} is allowed at the
front of a recursive argument list.  It binds @var{var} to the
whole list being matched; thus @code{(&whole all a b)} matches
a list of two things, with @code{a} bound to the first thing,
@code{b} bound to the second thing, and @code{all} bound to the
list itself.  (Common Lisp allows @code{&whole} in top-level
@code{defmacro} argument lists as well, but Emacs Lisp does not
support this usage.)

One last feature of destructuring is that the argument list may be
dotted, so that the argument list @code{(a b . c)} is functionally
equivalent to @code{(a b &rest c)}.

If the optimization quality @code{safety} is set to 0
(@pxref{Declarations}), error checking for wrong number of
arguments and invalid keyword arguments is disabled.  By default,
argument lists are rigorously checked.

485
@node Time of Evaluation
Glenn Morris's avatar
Glenn Morris committed
486 487 488 489 490 491 492 493 494 495 496 497 498
@section Time of Evaluation

@noindent
Normally, the byte-compiler does not actually execute the forms in
a file it compiles.  For example, if a file contains @code{(setq foo t)},
the act of compiling it will not actually set @code{foo} to @code{t}.
This is true even if the @code{setq} was a top-level form (i.e., not
enclosed in a @code{defun} or other form).  Sometimes, though, you
would like to have certain top-level forms evaluated at compile-time.
For example, the compiler effectively evaluates @code{defmacro} forms
at compile-time so that later parts of the file can refer to the
macros that are defined.

499
@defspec cl-eval-when (situations...) forms...
Glenn Morris's avatar
Glenn Morris committed
500 501 502 503 504 505
This form controls when the body @var{forms} are evaluated.
The @var{situations} list may contain any set of the symbols
@code{compile}, @code{load}, and @code{eval} (or their long-winded
ANSI equivalents, @code{:compile-toplevel}, @code{:load-toplevel},
and @code{:execute}).

506
The @code{cl-eval-when} form is handled differently depending on
Glenn Morris's avatar
Glenn Morris committed
507 508 509 510 511 512
whether or not it is being compiled as a top-level form.
Specifically, it gets special treatment if it is being compiled
by a command such as @code{byte-compile-file} which compiles files
or buffers of code, and it appears either literally at the
top level of the file or inside a top-level @code{progn}.

513
For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
Glenn Morris's avatar
Glenn Morris committed
514 515 516 517 518 519 520
executed at compile-time if @code{compile} is in the @var{situations}
list, and the @var{forms} are written out to the file (to be executed
at load-time) if @code{load} is in the @var{situations} list.

For non-compiled-top-level forms, only the @code{eval} situation is
relevant.  (This includes forms executed by the interpreter, forms
compiled with @code{byte-compile} rather than @code{byte-compile-file},
521
and non-top-level forms.)  The @code{cl-eval-when} acts like a
Glenn Morris's avatar
Glenn Morris committed
522 523 524
@code{progn} if @code{eval} is specified, and like @code{nil}
(ignoring the body @var{forms}) if not.

525
The rules become more subtle when @code{cl-eval-when}s are nested;
Glenn Morris's avatar
Glenn Morris committed
526 527 528 529 530 531 532
consult Steele (second edition) for the gruesome details (and
some gruesome examples).

Some simple examples:

@example
;; Top-level forms in foo.el:
533 534 535 536 537 538 539
(cl-eval-when (compile)           (setq foo1 'bar))
(cl-eval-when (load)              (setq foo2 'bar))
(cl-eval-when (compile load)      (setq foo3 'bar))
(cl-eval-when (eval)              (setq foo4 'bar))
(cl-eval-when (eval compile)      (setq foo5 'bar))
(cl-eval-when (eval load)         (setq foo6 'bar))
(cl-eval-when (eval compile load) (setq foo7 'bar))
Glenn Morris's avatar
Glenn Morris committed
540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561
@end example

When @file{foo.el} is compiled, these variables will be set during
the compilation itself:

@example
foo1  foo3  foo5  foo7      ; `compile'
@end example

When @file{foo.elc} is loaded, these variables will be set:

@example
foo2  foo3  foo6  foo7      ; `load'
@end example

And if @file{foo.el} is loaded uncompiled, these variables will
be set:

@example
foo4  foo5  foo6  foo7      ; `eval'
@end example

562
If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
Glenn Morris's avatar
Glenn Morris committed
563 564 565
then the first three would have been equivalent to @code{nil} and the
last four would have been equivalent to the corresponding @code{setq}s.

566
Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
Glenn Morris's avatar
Glenn Morris committed
567 568 569 570 571 572
to @code{(progn @dots{})} in all contexts.  The compiler treats
certain top-level forms, like @code{defmacro} (sort-of) and
@code{require}, as if they were wrapped in @code{(eval-when
(compile load eval) @dots{})}.
@end defspec

573
Emacs includes two special forms related to @code{cl-eval-when}.
Glenn Morris's avatar
Glenn Morris committed
574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591
One of these, @code{eval-when-compile}, is not quite equivalent to
any @code{eval-when} construct and is described below.

The other form, @code{(eval-and-compile @dots{})}, is exactly
equivalent to @samp{(eval-when (compile load eval) @dots{})} and
so is not itself defined by this package.

@defspec eval-when-compile forms...
The @var{forms} are evaluated at compile-time; at execution time,
this form acts like a quoted constant of the resulting value.  Used
at top-level, @code{eval-when-compile} is just like @samp{eval-when
(compile eval)}.  In other contexts, @code{eval-when-compile}
allows code to be evaluated once at compile-time for efficiency
or other reasons.

This form is similar to the @samp{#.} syntax of true Common Lisp.
@end defspec

592
@defspec cl-load-time-value form
Glenn Morris's avatar
Glenn Morris committed
593 594 595 596 597 598 599
The @var{form} is evaluated at load-time; at execution time,
this form acts like a quoted constant of the resulting value.

Early Common Lisp had a @samp{#,} syntax that was similar to
this, but ANSI Common Lisp replaced it with @code{load-time-value}
and gave it more well-defined semantics.

600
In a compiled file, @code{cl-load-time-value} arranges for @var{form}
Glenn Morris's avatar
Glenn Morris committed
601 602 603 604
to be evaluated when the @file{.elc} file is loaded and then used
as if it were a quoted constant.  In code compiled by
@code{byte-compile} rather than @code{byte-compile-file}, the
effect is identical to @code{eval-when-compile}.  In uncompiled
605
code, both @code{eval-when-compile} and @code{cl-load-time-value}
Glenn Morris's avatar
Glenn Morris committed
606 607 608 609 610 611 612 613 614 615
act exactly like @code{progn}.

@example
(defun report ()
  (insert "This function was executed on: "
          (current-time-string)
          ", compiled on: "
          (eval-when-compile (current-time-string))
          ;; or '#.(current-time-string) in real Common Lisp
          ", and loaded on: "
616
          (cl-load-time-value (current-time-string))))
Glenn Morris's avatar
Glenn Morris committed
617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634
@end example

@noindent
Byte-compiled, the above defun will result in the following code
(or its compiled equivalent, of course) in the @file{.elc} file:

@example
(setq --temp-- (current-time-string))
(defun report ()
  (insert "This function was executed on: "
          (current-time-string)
          ", compiled on: "
          '"Wed Jun 23 18:33:43 1993"
          ", and loaded on: "
          --temp--))
@end example
@end defspec

635
@node Predicates
Glenn Morris's avatar
Glenn Morris committed
636 637 638 639 640 641 642
@chapter Predicates

@noindent
This section describes functions for testing whether various
facts are true or false.

@menu
643 644
* Type Predicates::      @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
* Equality Predicates::  @code{cl-equalp}.
Glenn Morris's avatar
Glenn Morris committed
645 646
@end menu

647
@node Type Predicates
Glenn Morris's avatar
Glenn Morris committed
648 649 650
@section Type Predicates

@noindent
651
The @code{CL} package defines a version of the Common Lisp @code{typep}
Glenn Morris's avatar
Glenn Morris committed
652 653
predicate.

654
@defun cl-typep object type
Glenn Morris's avatar
Glenn Morris committed
655 656
Check if @var{object} is of type @var{type}, where @var{type} is a
(quoted) type name of the sort used by Common Lisp.  For example,
657
@code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
Glenn Morris's avatar
Glenn Morris committed
658 659 660 661 662 663 664 665 666 667 668 669 670 671
@end defun

The @var{type} argument to the above function is either a symbol
or a list beginning with a symbol.

@itemize @bullet
@item
If the type name is a symbol, Emacs appends @samp{-p} to the
symbol name to form the name of a predicate function for testing
the type.  (Built-in predicates whose names end in @samp{p} rather
than @samp{-p} are used when appropriate.)

@item
The type symbol @code{t} stands for the union of all types.
672
@code{(cl-typep @var{object} t)} is always true.  Likewise, the
Glenn Morris's avatar
Glenn Morris committed
673
type symbol @code{nil} stands for nothing at all, and
674
@code{(cl-typep @var{object} nil)} is always false.
Glenn Morris's avatar
Glenn Morris committed
675 676 677

@item
The type symbol @code{null} represents the symbol @code{nil}.
678
Thus @code{(cl-typep @var{object} 'null)} is equivalent to
Glenn Morris's avatar
Glenn Morris committed
679 680 681 682
@code{(null @var{object})}.

@item
The type symbol @code{atom} represents all objects that are not cons
683
cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
Glenn Morris's avatar
Glenn Morris committed
684 685 686 687 688 689 690 691 692 693 694
@code{(atom @var{object})}.

@item
The type symbol @code{real} is a synonym for @code{number}, and
@code{fixnum} is a synonym for @code{integer}.

@item
The type symbols @code{character} and @code{string-char} match
integers in the range from 0 to 255.

@item
695
The type symbol @code{float} uses the @code{cl-floatp-safe} predicate
Glenn Morris's avatar
Glenn Morris committed
696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716
defined by this package rather than @code{floatp}, so it will work
correctly even in Emacs versions without floating-point support.

@item
The type list @code{(integer @var{low} @var{high})} represents all
integers between @var{low} and @var{high}, inclusive.  Either bound
may be a list of a single integer to specify an exclusive limit,
or a @code{*} to specify no limit.  The type @code{(integer * *)}
is thus equivalent to @code{integer}.

@item
Likewise, lists beginning with @code{float}, @code{real}, or
@code{number} represent numbers of that type falling in a particular
range.

@item
Lists beginning with @code{and}, @code{or}, and @code{not} form
combinations of types.  For example, @code{(or integer (float 0 *))}
represents all objects that are integers or non-negative floats.

@item
717
Lists beginning with @code{member} or @code{cl-member} represent
Glenn Morris's avatar
Glenn Morris committed
718 719 720 721 722 723 724 725 726 727 728
objects @code{eql} to any of the following values.  For example,
@code{(member 1 2 3 4)} is equivalent to @code{(integer 1 4)},
and @code{(member nil)} is equivalent to @code{null}.

@item
Lists of the form @code{(satisfies @var{predicate})} represent
all objects for which @var{predicate} returns true when called
with that object as an argument.
@end itemize

The following function and macro (not technically predicates) are
729
related to @code{cl-typep}.
Glenn Morris's avatar
Glenn Morris committed
730

731
@defun cl-coerce object type
Glenn Morris's avatar
Glenn Morris committed
732 733 734 735 736 737 738 739 740
This function attempts to convert @var{object} to the specified
@var{type}.  If @var{object} is already of that type as determined by
@code{typep}, it is simply returned.  Otherwise, certain types of
conversions will be made:  If @var{type} is any sequence type
(@code{string}, @code{list}, etc.) then @var{object} will be
converted to that type if possible.  If @var{type} is
@code{character}, then strings of length one and symbols with
one-character names can be coerced.  If @var{type} is @code{float},
then integers can be coerced in versions of Emacs that support
741
floats.  In all other circumstances, @code{cl-coerce} signals an
Glenn Morris's avatar
Glenn Morris committed
742 743 744
error.
@end defun

745
@defspec cl-deftype name arglist forms...
Glenn Morris's avatar
Glenn Morris committed
746 747 748 749 750
This macro defines a new type called @var{name}.  It is similar
to @code{defmacro} in many ways; when @var{name} is encountered
as a type name, the body @var{forms} are evaluated and should
return a type specifier that is equivalent to the type.  The
@var{arglist} is a Common Lisp argument list of the sort accepted
751
by @code{cl-defmacro}.  The type specifier @samp{(@var{name} @var{args}...)}
Glenn Morris's avatar
Glenn Morris committed
752 753 754
is expanded by calling the expander with those arguments; the type
symbol @samp{@var{name}} is expanded by calling the expander with
no arguments.  The @var{arglist} is processed the same as for
755
@code{cl-defmacro} except that optional arguments without explicit
Glenn Morris's avatar
Glenn Morris committed
756 757 758 759
defaults use @code{*} instead of @code{nil} as the ``default''
default.  Some examples:

@example
760 761 762
(cl-deftype null () '(satisfies null))    ; predefined
(cl-deftype list () '(or null cons))      ; predefined
(cl-deftype unsigned-byte (&optional bits)
Glenn Morris's avatar
Glenn Morris committed
763 764 765 766 767 768 769 770 771 772 773 774
  (list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
(unsigned-byte 8)  @equiv{}  (integer 0 255)
(unsigned-byte)  @equiv{}  (integer 0 *)
unsigned-byte  @equiv{}  (integer 0 *)
@end example

@noindent
The last example shows how the Common Lisp @code{unsigned-byte}
type specifier could be implemented if desired; this package does
not implement @code{unsigned-byte} by default.
@end defspec

775 776 777
The @code{cl-typecase} and @code{cl-check-type} macros also use type
names.  @xref{Conditionals}.  @xref{Assertions}.  The @code{cl-map},
@code{cl-concatenate}, and @code{cl-merge} functions take type-name
Glenn Morris's avatar
Glenn Morris committed
778 779
arguments to specify the type of sequence to return.  @xref{Sequences}.

780
@node Equality Predicates
Glenn Morris's avatar
Glenn Morris committed
781 782 783
@section Equality Predicates

@noindent
784
This package defines the Common Lisp predicate @code{cl-equalp}.
Glenn Morris's avatar
Glenn Morris committed
785

786
@defun cl-equalp a b
Glenn Morris's avatar
Glenn Morris committed
787 788
This function is a more flexible version of @code{equal}.  In
particular, it compares strings case-insensitively, and it compares
789
numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
Glenn Morris's avatar
Glenn Morris committed
790 791 792 793 794 795 796 797
true).  Vectors and conses are compared recursively.  All other
objects are compared as if by @code{equal}.

This function differs from Common Lisp @code{equalp} in several
respects.  First, Common Lisp's @code{equalp} also compares
@emph{characters} case-insensitively, which would be impractical
in this package since Emacs does not distinguish between integers
and characters.  In keeping with the idea that strings are less
798
vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
Glenn Morris's avatar
Glenn Morris committed
799 800 801 802 803 804
not compare strings against vectors of integers.
@end defun

Also note that the Common Lisp functions @code{member} and @code{assoc}
use @code{eql} to compare elements, whereas Emacs Lisp follows the
MacLisp tradition and uses @code{equal} for these two functions.
805 806
In Emacs, use @code{memq} (or @code{cl-member}) and @code{assq} (or
@code{cl-assoc}) to get functions which use @code{eql} for comparisons.
Glenn Morris's avatar
Glenn Morris committed
807

808
@node Control Structure
Glenn Morris's avatar
Glenn Morris committed
809 810 811 812 813
@chapter Control Structure

@noindent
The features described in the following sections implement
various advanced control structures, including the powerful
814
@c FIXME setf is now in gv.el, not cl.
Glenn Morris's avatar
Glenn Morris committed
815 816 817
@code{setf} facility and a number of looping and conditional
constructs.

818 819 820
@c FIXME setf, push are standard now.
@c lexical-let is obsolete; flet is not cl-flet.
@c values is not cl-values.
Glenn Morris's avatar
Glenn Morris committed
821
@menu
822 823 824 825 826 827 828 829
* Assignment::             The @code{cl-psetq} form.
* Generalized Variables::  @code{setf}, @code{cl-incf}, @code{push}, etc.
* Variable Bindings::      @code{cl-progv}, @code{lexical-let}, @code{flet}, @code{cl-macrolet}.
* Conditionals::           @code{cl-case}, @code{cl-typecase}.
* Blocks and Exits::       @code{cl-block}, @code{cl-return}, @code{cl-return-from}.
* Iteration::              @code{cl-do}, @code{cl-dotimes}, @code{cl-dolist}, @code{cl-do-symbols}.
* Loop Facility::          The Common Lisp @code{cl-loop} macro.
* Multiple Values::        @code{values}, @code{cl-multiple-value-bind}, etc.
Glenn Morris's avatar
Glenn Morris committed
830 831
@end menu

832
@node Assignment
Glenn Morris's avatar
Glenn Morris committed
833 834 835
@section Assignment

@noindent
836
The @code{cl-psetq} form is just like @code{setq}, except that multiple
Glenn Morris's avatar
Glenn Morris committed
837 838
assignments are done in parallel rather than sequentially.

839
@defspec cl-psetq [symbol form]@dots{}
Glenn Morris's avatar
Glenn Morris committed
840 841 842 843 844 845 846 847 848 849 850 851 852 853
This special form (actually a macro) is used to assign to several
variables simultaneously.  Given only one @var{symbol} and @var{form},
it has the same effect as @code{setq}.  Given several @var{symbol}
and @var{form} pairs, it evaluates all the @var{form}s in advance
and then stores the corresponding variables afterwards.

@example
(setq x 2 y 3)
(setq x (+ x y)  y (* x y))
x
     @result{} 5
y                     ; @r{@code{y} was computed after @code{x} was set.}
     @result{} 15
(setq x 2 y 3)
854
(cl-psetq x (+ x y)  y (* x y))
Glenn Morris's avatar
Glenn Morris committed
855 856 857 858 859 860
x
     @result{} 5
y                     ; @r{@code{y} was computed before @code{x} was set.}
     @result{} 6
@end example

861 862
The simplest use of @code{cl-psetq} is @code{(cl-psetq x y y x)}, which
exchanges the values of two variables.  (The @code{cl-rotatef} form
Glenn Morris's avatar
Glenn Morris committed
863 864 865
provides an even more convenient way to swap two variables;
@pxref{Modify Macros}.)

866
@code{cl-psetq} always returns @code{nil}.
Glenn Morris's avatar
Glenn Morris committed
867 868
@end defspec

869
@c FIXME now in gv.el.
870
@node Generalized Variables
Glenn Morris's avatar
Glenn Morris committed
871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893
@section Generalized Variables

@noindent
A ``generalized variable'' or ``place form'' is one of the many places
in Lisp memory where values can be stored.  The simplest place form is
a regular Lisp variable.  But the cars and cdrs of lists, elements
of arrays, properties of symbols, and many other locations are also
places where Lisp values are stored.

The @code{setf} form is like @code{setq}, except that it accepts
arbitrary place forms on the left side rather than just
symbols.  For example, @code{(setf (car a) b)} sets the car of
@code{a} to @code{b}, doing the same operation as @code{(setcar a b)}
but without having to remember two separate functions for setting
and accessing every type of place.

Generalized variables are analogous to ``lvalues'' in the C
language, where @samp{x = a[i]} gets an element from an array
and @samp{a[i] = x} stores an element using the same notation.
Just as certain forms like @code{a[i]} can be lvalues in C, there
is a set of forms that can be generalized variables in Lisp.

@menu
894 895 896
* Basic Setf::         @code{setf} and place forms.
* Modify Macros::      @code{cl-incf}, @code{push}, @code{cl-rotatef}, @code{letf}, @code{cl-callf}, etc.
* Customizing Setf::   @code{define-modify-macro}, @code{defsetf}, @code{define-setf-method}.
Glenn Morris's avatar
Glenn Morris committed
897 898
@end menu

899
@node Basic Setf
Glenn Morris's avatar
Glenn Morris committed
900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980
@subsection Basic Setf

@noindent
The @code{setf} macro is the most basic way to operate on generalized
variables.

@defspec setf [place form]@dots{}
This macro evaluates @var{form} and stores it in @var{place}, which
must be a valid generalized variable form.  If there are several
@var{place} and @var{form} pairs, the assignments are done sequentially
just as with @code{setq}.  @code{setf} returns the value of the last
@var{form}.

The following Lisp forms will work as generalized variables, and
so may appear in the @var{place} argument of @code{setf}:

@itemize @bullet
@item
A symbol naming a variable.  In other words, @code{(setf x y)} is
exactly equivalent to @code{(setq x y)}, and @code{setq} itself is
strictly speaking redundant now that @code{setf} exists.  Many
programmers continue to prefer @code{setq} for setting simple
variables, though, purely for stylistic or historical reasons.
The macro @code{(setf x y)} actually expands to @code{(setq x y)},
so there is no performance penalty for using it in compiled code.

@item
A call to any of the following Lisp functions:

@smallexample
car                 cdr                 caar .. cddddr
nth                 rest                first .. tenth
aref                elt                 nthcdr
symbol-function     symbol-value        symbol-plist
get                 get*                getf
gethash             subseq
@end smallexample

@noindent
Note that for @code{nthcdr} and @code{getf}, the list argument
of the function must itself be a valid @var{place} form.  For
example, @code{(setf (nthcdr 0 foo) 7)} will set @code{foo} itself
to 7.  Note that @code{push} and @code{pop} on an @code{nthcdr}
place can be used to insert or delete at any position in a list.
The use of @code{nthcdr} as a @var{place} form is an extension
to standard Common Lisp.

@item
The following Emacs-specific functions are also @code{setf}-able.

@smallexample
buffer-file-name                  marker-position
buffer-modified-p                 match-data
buffer-name                       mouse-position
buffer-string                     overlay-end
buffer-substring                  overlay-get
current-buffer                    overlay-start
current-case-table                point
current-column                    point-marker
current-global-map                point-max
current-input-mode                point-min
current-local-map                 process-buffer
current-window-configuration      process-filter
default-file-modes                process-sentinel
default-value                     read-mouse-position
documentation-property            screen-height
extent-data                       screen-menubar
extent-end-position               screen-width
extent-start-position             selected-window
face-background                   selected-screen
face-background-pixmap            selected-frame
face-font                         standard-case-table
face-foreground                   syntax-table
face-underline-p                  window-buffer
file-modes                        window-dedicated-p
frame-height                      window-display-table
frame-parameters                  window-height
frame-visible-p                   window-hscroll
frame-width                       window-point
get-register                      window-start
getenv                            window-width
981 982 983 984
global-key-binding                x-get-secondary-selection
keymap-parent                     x-get-selection
local-key-binding                 
mark                              
Glenn Morris's avatar
Glenn Morris committed
985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043
mark-marker
@end smallexample

Most of these have directly corresponding ``set'' functions, like
@code{use-local-map} for @code{current-local-map}, or @code{goto-char}
for @code{point}.  A few, like @code{point-min}, expand to longer
sequences of code when they are @code{setf}'d (@code{(narrow-to-region
x (point-max))} in this case).

@item
A call of the form @code{(substring @var{subplace} @var{n} [@var{m}])},
where @var{subplace} is itself a valid generalized variable whose
current value is a string, and where the value stored is also a
string.  The new string is spliced into the specified part of the
destination string.  For example:

@example
(setq a (list "hello" "world"))
     @result{} ("hello" "world")
(cadr a)
     @result{} "world"
(substring (cadr a) 2 4)
     @result{} "rl"
(setf (substring (cadr a) 2 4) "o")
     @result{} "o"
(cadr a)
     @result{} "wood"
a
     @result{} ("hello" "wood")
@end example

The generalized variable @code{buffer-substring}, listed above,
also works in this way by replacing a portion of the current buffer.

@item
A call of the form @code{(apply '@var{func} @dots{})} or
@code{(apply (function @var{func}) @dots{})}, where @var{func}
is a @code{setf}-able function whose store function is ``suitable''
in the sense described in Steele's book; since none of the standard
Emacs place functions are suitable in this sense, this feature is
only interesting when used with places you define yourself with
@code{define-setf-method} or the long form of @code{defsetf}.

@item
A macro call, in which case the macro is expanded and @code{setf}
is applied to the resulting form.

@item
Any form for which a @code{defsetf} or @code{define-setf-method}
has been made.
@end itemize

Using any forms other than these in the @var{place} argument to
@code{setf} will signal an error.

The @code{setf} macro takes care to evaluate all subforms in
the proper left-to-right order; for example,

@example
1044
(setf (aref vec (cl-incf i)) i)
Glenn Morris's avatar
Glenn Morris committed
1045 1046 1047
@end example

@noindent
1048
looks like it will evaluate @code{(cl-incf i)} exactly once, before the
Glenn Morris's avatar
Glenn Morris committed
1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069
following access to @code{i}; the @code{setf} expander will insert
temporary variables as necessary to ensure that it does in fact work
this way no matter what setf-method is defined for @code{aref}.
(In this case, @code{aset} would be used and no such steps would
be necessary since @code{aset} takes its arguments in a convenient
order.)

However, if the @var{place} form is a macro which explicitly
evaluates its arguments in an unusual order, this unusual order
will be preserved.  Adapting an example from Steele, given

@example
(defmacro wrong-order (x y) (list 'aref y x))
@end example

@noindent
the form @code{(setf (wrong-order @var{a} @var{b}) 17)} will
evaluate @var{b} first, then @var{a}, just as in an actual call
to @code{wrong-order}.
@end defspec

1070
@node Modify Macros
Glenn Morris's avatar
Glenn Morris committed
1071 1072 1073 1074 1075 1076 1077
@subsection Modify Macros

@noindent
This package defines a number of other macros besides @code{setf}
that operate on generalized variables.  Many are interesting and
useful even when the @var{place} is just a variable name.

1078
@defspec cl-psetf [place form]@dots{}
1079
This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
Glenn Morris's avatar
Glenn Morris committed
1080 1081 1082 1083 1084 1085
When several @var{place}s and @var{form}s are involved, the
assignments take place in parallel rather than sequentially.
Specifically, all subforms are evaluated from left to right, then
all the assignments are done (in an undefined order).
@end defspec

1086
@defspec cl-incf place &optional x
Glenn Morris's avatar
Glenn Morris committed
1087 1088
This macro increments the number stored in @var{place} by one, or
by @var{x} if specified.  The incremented value is returned.  For
1089 1090
example, @code{(cl-incf i)} is equivalent to @code{(setq i (1+ i))}, and
@code{(cl-incf (car x) 2)} is equivalent to @code{(setcar x (+ (car x) 2))}.
Glenn Morris's avatar
Glenn Morris committed
1091 1092 1093 1094 1095

Once again, care is taken to preserve the ``apparent'' order of
evaluation.  For example,

@example
1096
(cl-incf (aref vec (cl-incf i)))
Glenn Morris's avatar
Glenn Morris committed
1097 1098 1099 1100 1101 1102 1103 1104 1105
@end example

@noindent
appears to increment @code{i} once, then increment the element of
@code{vec} addressed by @code{i}; this is indeed exactly what it
does, which means the above form is @emph{not} equivalent to the
``obvious'' expansion,

@example
1106
(setf (aref vec (cl-incf i)) (1+ (aref vec (cl-incf i))))   ; Wrong!
Glenn Morris's avatar
Glenn Morris committed
1107 1108 1109 1110 1111 1112
@end example

@noindent
but rather to something more like

@example
1113
(let ((temp (cl-incf i)))
Glenn Morris's avatar
Glenn Morris committed
1114 1115 1116 1117
  (setf (aref vec temp) (1+ (aref vec temp))))
@end example

@noindent
1118
Again, all of this is taken care of automatically by @code{cl-incf} and
Glenn Morris's avatar
Glenn Morris committed
1119 1120
the other generalized-variable macros.

1121 1122
As a more Emacs-specific example of @code{cl-incf}, the expression
@code{(cl-incf (point) @var{n})} is essentially equivalent to
Glenn Morris's avatar
Glenn Morris committed
1123 1124 1125
@code{(forward-char @var{n})}.
@end defspec

1126
@defspec cl-decf place &optional x
Glenn Morris's avatar
Glenn Morris committed
1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252
This macro decrements the number stored in @var{place} by one, or
by @var{x} if specified.
@end defspec

@defspec pop place
This macro removes and returns the first element of the list stored
in @var{place}.  It is analogous to @code{(prog1 (car @var{place})
(setf @var{place} (cdr @var{place})))}, except that it takes care
to evaluate all subforms only once.