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\input texinfo    @c -*-texinfo-*-
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@setfilename ../../info/cl
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@settitle Common Lisp Extensions
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@include emacsver.texi
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@copying
This file documents the GNU Emacs Common Lisp emulation package.

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Copyright @copyright{} 1993, 2001-2012 Free Software Foundation, Inc.
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@quotation
Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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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''.
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(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.''
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@end quotation
@end copying

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@dircategory Emacs lisp libraries
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@direntry
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* CL: (cl).                     Partial Common Lisp support for Emacs Lisp.
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@end direntry

@finalout

@titlepage
@sp 6
@center @titlefont{Common Lisp Extensions}
@sp 4
@center For GNU Emacs Lisp
@sp 1
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@center as distributed with Emacs @value{EMACSVER}
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@sp 5
@center Dave Gillespie
@center daveg@@synaptics.com
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

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@contents

@ifnottex
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@node Top
@top GNU Emacs Common Lisp Emulation

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@insertcopying
@end ifnottex

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@menu
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* Overview::             Basics, usage, etc.
* Program Structure::    Arglists, @code{cl-eval-when}, @code{defalias}.
* Predicates::           @code{cl-typep} and @code{cl-equalp}.
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* Control Structure::    @code{cl-do}, @code{cl-loop}, etc.
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* 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}.
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* Assertions::           @code{cl-check-type}, @code{cl-assert}.
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* Efficiency Concerns::         Hints and techniques.
* Common Lisp Compatibility::   All known differences with Steele.
* Porting Common Lisp::         Hints for porting Common Lisp code.
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* Obsolete Features::           Obsolete features.
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* GNU Free Documentation License:: The license for this documentation.
* Function Index::
* Variable Index::
@end menu

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@node Overview
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@chapter Overview

@noindent
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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.

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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.

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The @code{CL} package adds a number of Common Lisp functions and
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control structures to Emacs Lisp.  While not a 100% complete
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implementation of Common Lisp, @code{CL} adds enough functionality
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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,
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case-insensitive symbols, and complex numbers.
The @code{CL} package generally makes no attempt to emulate these
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features.

@end itemize

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This package was originally written by Dave Gillespie,
@file{daveg@@synaptics.com}, as a total rewrite of an earlier 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.
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@menu
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* Usage::                How to use the CL package.
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* Organization::         The package's component files.
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* Naming Conventions::   Notes on CL function names.
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@end menu

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@node Usage
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@section Usage

@noindent
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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:
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@example
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(require 'cl-lib)
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@end example

@noindent
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You may wish to add such a statement to your init file, if you
make frequent use of CL features.
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@node Organization
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@section Organization

@noindent
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The Common Lisp package is organized into four main files:
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@table @file
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@item cl-lib.el
This is the main file, which contains basic functions
and information about the package.  This file is relatively compact.
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@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
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Lisp fundamentals like the @code{cl-incf} function won't need to pay
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the overhead of loading the more advanced functions.

@item cl-seq.el
This file contains most of the advanced functions for operating
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on sequences or lists, such as @code{cl-delete-if} and @code{cl-assoc}.
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@item cl-macs.el
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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.
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@end table

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

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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 (in most cases),
but use different function names (in fact, @file{cl.el} mainly just
defines aliases to the @file{cl-lib.el} definitions).  Where
@file{cl-lib.el} defines a function called, for example,
@code{cl-incf}, @file{cl.el} uses the same name but without the
@samp{cl-} prefix, e.g. @code{incf} in this example.  There are a few
exceptions to this.  First, functions such as @code{cl-defun} where
the unprefixed version was already used for a standard Emacs Lisp
function.  In such cases, the @file{cl.el} version adds a @samp{*}
suffix, e.g. @code{defun*}.  Second, there are some obsolete features
that are only implemented in @file{cl.el}, not in @file{cl-lib.el},
because they are replaced by other standard Emacs Lisp features.
Finally, in a very few cases the old @file{cl.el} versions do not
behave in exactly the same way as the @file{cl-lib.el} versions.
@xref{Obsolete Features}.

Since the old @file{cl.el} does not use a clean namespace, 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}.
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There is one more file, @file{cl-compat.el}, which defines some
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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.
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@node Naming Conventions
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@section Naming Conventions

@noindent
Except where noted, all functions defined by this package have the
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same calling conventions as their Common Lisp counterparts, and
names that are those of Common Lisp plus a @samp{cl-} prefix.
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Internal function and variable names in the package are prefixed
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by @code{cl--}.  Here is a complete list of functions prefixed by
@code{cl-} that were not taken from Common Lisp:
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@example
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cl-callf         cl-callf2        cl-defsubst
cl-floatp-safe   cl-letf          cl-letf*
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@end example

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The following simple functions and macros are defined in @file{cl-lib.el};
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they do not cause other components like @file{cl-extra} to be loaded.

@example
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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
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@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.

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@node Program Structure
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@chapter Program Structure

@noindent
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This section describes features of the @code{CL} package that have to
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do with programs as a whole: advanced argument lists for functions,
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and the @code{cl-eval-when} construct.
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@menu
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* Argument Lists::       @code{&key}, @code{&aux}, @code{cl-defun}, @code{cl-defmacro}.
* Time of Evaluation::   The @code{cl-eval-when} construct.
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@end menu

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@node Argument Lists
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@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.

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@defmac cl-defun name arglist body...
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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}.
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@end defmac
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@defmac cl-defsubst name arglist body...
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This is just like @code{cl-defun}, except that the function that
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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;
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@code{cl-defsubst} uses a different method (compiler macros) which
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works in all versions of Emacs, and also generates somewhat more
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efficient inline expansions.  In particular, @code{cl-defsubst}
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arranges for the processing of keyword arguments, default values,
etc., to be done at compile-time whenever possible.
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@end defmac
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@defmac cl-defmacro name arglist body...
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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}.
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@end defmac
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@defmac cl-function symbol-or-lambda
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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.
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@end defmac
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Also, all forms (such as @code{cl-flet} and @code{cl-labels}) defined
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in this package that include @var{arglist}s in their syntax allow
full Common Lisp argument lists.

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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
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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
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(cl-defun foo (a &optional b &key c d (e 17)))
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@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.

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

@example
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(cl-defun bar (&key (a 1) ((baz b) 4)))
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@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
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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
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(cl-defun find-thing (thing &rest rest &key need &allow-other-keys)
  (or (apply 'cl-member thing thing-list :allow-other-keys t rest)
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      (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
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@code{cl-member} function.  @code{allow-other-keys} is used to
keep both @code{find-thing} and @code{cl-member} from complaining
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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
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(cl-defun foo (a b &aux (c (+ a b)) d)
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  @var{body})

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(cl-defun foo (a b)
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  (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
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allows it with @code{cl-defun} and other argument lists as well.
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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
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(cl-defmacro dolist ((var listform &optional resultform)
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                   &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.

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@node Time of Evaluation
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@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.

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@defmac cl-eval-when (situations...) forms...
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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}).

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The @code{cl-eval-when} form is handled differently depending on
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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}.

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For compiled top-level @code{cl-eval-when}s, the body @var{forms} are
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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},
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and non-top-level forms.)  The @code{cl-eval-when} acts like a
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@code{progn} if @code{eval} is specified, and like @code{nil}
(ignoring the body @var{forms}) if not.

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The rules become more subtle when @code{cl-eval-when}s are nested;
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consult Steele (second edition) for the gruesome details (and
some gruesome examples).

Some simple examples:

@example
;; Top-level forms in foo.el:
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(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))
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@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

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If these seven @code{cl-eval-when}s had been, say, inside a @code{defun},
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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.

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Note that @code{(cl-eval-when (load eval) @dots{})} is equivalent
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to @code{(progn @dots{})} in all contexts.  The compiler treats
certain top-level forms, like @code{defmacro} (sort-of) and
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@code{require}, as if they were wrapped in @code{(cl-eval-when
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(compile load eval) @dots{})}.
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@end defmac
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Emacs includes two special forms related to @code{cl-eval-when}.
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One of these, @code{eval-when-compile}, is not quite equivalent to
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any @code{cl-eval-when} construct and is described below.
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The other form, @code{(eval-and-compile @dots{})}, is exactly
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equivalent to @samp{(cl-eval-when (compile load eval) @dots{})} and
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so is not itself defined by this package.

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@defmac eval-when-compile forms...
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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.
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@end defmac
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@defmac cl-load-time-value form
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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.

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In a compiled file, @code{cl-load-time-value} arranges for @var{form}
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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
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code, both @code{eval-when-compile} and @code{cl-load-time-value}
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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: "
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          (cl-load-time-value (current-time-string))))
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@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
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@end defmac
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@node Predicates
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@chapter Predicates

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

@menu
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* Type Predicates::      @code{cl-typep}, @code{cl-deftype}, and @code{cl-coerce}.
* Equality Predicates::  @code{cl-equalp}.
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@end menu

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@node Type Predicates
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@section Type Predicates

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@defun cl-typep object type
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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,
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@code{(cl-typep foo 'integer)} is equivalent to @code{(integerp foo)}.
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@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.
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@code{(cl-typep @var{object} t)} is always true.  Likewise, the
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type symbol @code{nil} stands for nothing at all, and
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@code{(cl-typep @var{object} nil)} is always false.
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@item
The type symbol @code{null} represents the symbol @code{nil}.
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Thus @code{(cl-typep @var{object} 'null)} is equivalent to
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@code{(null @var{object})}.

@item
The type symbol @code{atom} represents all objects that are not cons
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cells. Thus @code{(cl-typep @var{object} 'atom)} is equivalent to
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@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
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The type symbol @code{float} uses the @code{cl-floatp-safe} predicate
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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
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Lists beginning with @code{member} or @code{cl-member} represent
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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
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related to @code{cl-typep}.
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@defun cl-coerce object type
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This function attempts to convert @var{object} to the specified
@var{type}.  If @var{object} is already of that type as determined by
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@code{cl-typep}, it is simply returned.  Otherwise, certain types of
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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
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floats.  In all other circumstances, @code{cl-coerce} signals an
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error.
@end defun

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@defmac cl-deftype name arglist forms...
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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
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by @code{cl-defmacro}.  The type specifier @samp{(@var{name} @var{args}...)}
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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
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@code{cl-defmacro} except that optional arguments without explicit
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defaults use @code{*} instead of @code{nil} as the ``default''
default.  Some examples:

@example
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(cl-deftype null () '(satisfies null))    ; predefined
(cl-deftype list () '(or null cons))      ; predefined
(cl-deftype unsigned-byte (&optional bits)
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  (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.
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@end defmac
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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
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arguments to specify the type of sequence to return.  @xref{Sequences}.

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@node Equality Predicates
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@section Equality Predicates

@noindent
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This package defines the Common Lisp predicate @code{cl-equalp}.
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@defun cl-equalp a b
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This function is a more flexible version of @code{equal}.  In
particular, it compares strings case-insensitively, and it compares
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numbers without regard to type (so that @code{(cl-equalp 3 3.0)} is
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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
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vector-like in Emacs Lisp, this package's @code{cl-equalp} also will
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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.
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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.
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@node Control Structure
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@chapter Control Structure

@noindent
The features described in the following sections implement
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various advanced control structures, including extensions to the
standard @code{setf} facility, and a number of looping and conditional
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constructs.

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@c FIXME
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@c flet is not cl-flet.
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@menu
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* Assignment::             The @code{cl-psetq} form.
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* Generalized Variables::  Extensions to generalized variables.
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* Variable Bindings::      @code{cl-progv}, @code{flet}, @code{cl-macrolet}.
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* 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.
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* Multiple Values::        @code{cl-values}, @code{cl-multiple-value-bind}, etc.
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@end menu

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@node Assignment
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@section Assignment

@noindent
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The @code{cl-psetq} form is just like @code{setq}, except that multiple
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assignments are done in parallel rather than sequentially.

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@defmac cl-psetq [symbol form]@dots{}
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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)
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(cl-psetq x (+ x y)  y (* x y))
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x
     @result{} 5
y                     ; @r{@code{y} was computed before @code{x} was set.}
     @result{} 6
@end example

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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
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provides an even more convenient way to swap two variables;
@pxref{Modify Macros}.)

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@code{cl-psetq} always returns @code{nil}.
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@end defmac
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@node Generalized Variables
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@section Generalized Variables

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A @dfn{generalized variable} or @dfn{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.  For basic information,
@pxref{Generalized Variables,,,elisp,GNU Emacs Lisp Reference Manual}.
This package provides several additional features related to
generalized variables.
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@menu
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* Setf Extensions::    Additional @code{setf} places.
* Modify Macros::      @code{cl-incf}, @code{cl-rotatef}, @code{letf}, @code{cl-callf}, etc.
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* Customizing Setf::   @code{define-modify-macro}, @code{defsetf}, @code{define-setf-method}.
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@end menu

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@node Setf Extensions
@subsection Setf Extensions
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Several standard (e.g. @code{car}) and Emacs-specific
(e.g. @code{window-point}) Lisp functions are @code{setf}-able by default.
This package defines @code{setf} handlers for several additional functions:
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@itemize
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@item
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Functions from @code{CL} itself:
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@smallexample
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cl-caaar .. cl-cddddr         cl-first .. cl-tenth
cl-rest     cl-get            cl-getf     cl-subseq
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@end smallexample

@item
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General Emacs Lisp functions:
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@smallexample
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buffer-file-name                   getenv
buffer-modified-p                  global-key-binding
buffer-name                        local-key-binding
buffer-string                      mark
buffer-substring                   mark-marker
current-buffer                     marker-position
current-case-table                 mouse-position
current-column                     point
current-global-map                 point-marker
current-input-mode                 point-max
current-local-map                  point-min
current-window-configuration       read-mouse-position
default-file-modes                 screen-height
documentation-property             screen-width
face-background                    selected-window
face-background-pixmap             selected-screen
face-font                          selected-frame
face-foreground                    standard-case-table
face-underline-p                   syntax-table
file-modes                         visited-file-modtime
frame-height                       window-height
frame-parameters                   window-width
frame-visible-p                    x-get-secondary-selection
frame-width                        x-get-selection
get-register
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@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
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sequences of code when they are used with @code{setf}
(@code{(narrow-to-region x (point-max))} in this case).
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@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.

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@c FIXME? Also `eq'? (see cl-lib.el)

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@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

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@c FIXME should this be in lispref?  It seems self-evident.
@c Contrast with the cl-incf example later on.
@c Here it really only serves as a constrast to wrong-order.
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The @code{setf} macro takes care to evaluate all subforms in
the proper left-to-right order; for example,

@example
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(setf (aref vec (cl-incf i)) i)
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@end example

@noindent
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looks like it will evaluate @code{(cl-incf i)} exactly once, before the
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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}.

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@node Modify Macros
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@subsection Modify Macros

@noindent
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This package defines a number of macros that operate on generalized
variables.  Many are interesting and useful even when the @var{place}
is just a variable name.
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@defmac cl-psetf [place form]@dots{}
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This macro is to @code{setf} what @code{cl-psetq} is to @code{setq}:
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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).
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@end defmac
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@defmac cl-incf place &optional x
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This macro increments the number stored in @var{place} by one, or
by @var{x} if specified.  The incremented value is returned.  For
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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))}.
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As with @code{setf}, care is taken to preserve the ``apparent'' order
of evaluation.  For example,
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@example
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(cl-incf (aref vec (cl-incf i)))
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@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
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(setf (aref vec (cl-incf i))
      (1+ (aref vec (cl-incf i))))   ; wrong!
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