man : cl
File: cl, Node: Top, Next: Overview, Prev: (dir), Up: (dir)
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.
* Overview:: Installation, usage, etc.
* Program Structure:: Arglists, `eval-when', `defalias'
* Predicates:: `typep' and `equalp'
* Control Structure:: `setf', `do', `loop', etc.
* Macros:: Destructuring, `define-compiler-macro'
* Declarations:: `proclaim', `declare', etc.
* Symbols:: Property lists, `gensym'
* Numbers:: Predicates, functions, random numbers
* Sequences:: Mapping, functions, searching, sorting
* Lists:: `caddr', `sublis', `member*', `assoc*', etc.
* Structures:: `defstruct'
* Assertions:: `check-type', `assert', `ignore-errors'.
* Efficiency Concerns:: Hints and techniques
* Common Lisp Compatibility:: All known differences with Steele
* Old CL Compatibility:: All known differences with old cl.el
* Porting Common Lisp:: Hints for porting Common Lisp code
* GNU Free Documentation License:: The license for this documentation.
* Function Index::
* Variable Index::
File: cl, Node: Overview, Next: Program Structure, Prev: Top, Up: Top
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.
The "CL" package adds a number of Common Lisp functions and control
structures to Emacs Lisp. While not a 100% complete implementation of
Common Lisp, "CL" adds enough functionality to make Emacs Lisp
programming significantly more convenient.
*Please note:* the "CL" functions are not standard parts of the
Emacs Lisp name space, so it is legitimate for users to define them
with other, conflicting meanings. To avoid conflicting with those user
activities, we have a policy that packages installed in Emacs must not
load "CL" at run time. (It is ok for them to load "CL" at compile time
only, with `eval-when-compile', and use the macros it provides.) If
you are writing packages that you plan to distribute and invite
widespread use for, you might want to observe the same rule.
Some Common Lisp features have been omitted from this package for
* 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.
* Other features cannot be implemented without modification to the
Emacs Lisp interpreter itself, such as multiple return values,
lexical scoping, case-insensitive symbols, and complex numbers.
The "CL" package generally makes no attempt to emulate these
* Some features conflict with existing things in Emacs Lisp. For
example, Emacs' `assoc' function is incompatible with the Common
Lisp `assoc'. In such cases, this package usually adds the suffix
`*' to the function name of the Common Lisp version of the
function (e.g., `assoc*').
The package described here was written by Dave Gillespie,
`davegATsynaptics.com'. It is a total rewrite of the original 1986
`cl.el' package by Cesar Quiroz. Most features of the Quiroz package
have been retained; any incompatibilities are noted in the descriptions
below. Care has been taken in this version to ensure that each
function is defined efficiently, concisely, and with minimal impact on
the rest of the Emacs environment.
* Usage:: How to use the CL package
* Organization:: The package's five component files
* Installation:: Compiling and installing CL
* Naming Conventions:: Notes on CL function names
File: cl, Node: Usage, Next: Organization, Prev: Overview, Up: Overview
Lisp code that uses features from the "CL" package should include at
If you want to ensure that the new (Gillespie) version of "CL" is the
one that is present, add an additional `(require 'cl-19)' call:
The second call will fail (with "`cl-19.el' not found") if the old
`cl.el' package was in use.
It is safe to arrange to load "CL" at all times, e.g., in your
`.emacs' file. But it's a good idea, for portability, to `(require
'cl)' in your code even if you do this.
File: cl, Node: Organization, Next: Installation, Prev: Usage, Up: Overview
The Common Lisp package is organized into four files:
This is the "main" file, which contains basic functions and
information about the package. This file is relatively
compact--about 700 lines.
This file contains the larger, more complex or unusual functions.
It is kept separate so that packages which only want to use Common
Lisp fundamentals like the `cadr' function won't need to pay the
overhead of loading the more advanced functions.
This file contains most of the advanced functions for operating on
sequences or lists, such as `delete-if' and `assoc*'.
This file contains the features of the packages which 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 such as a `.emacs' file). Most of the
macros of this package are isolated in `cl-macs.el' so that they
won't take up memory unless you are compiling.
The file `cl.el' includes all necessary `autoload' commands for the
functions and macros in the other three files. All you have to do is
`(require 'cl)', and `cl.el' will take care of pulling in the other
files when they are needed.
There is another file, `cl-compat.el', which defines some routines
from the older `cl.el' package that are no longer present in the new
package. This includes internal routines like `setelt' and
`zip-lists', deprecated features like `defkeyword', and an emulation of
the old-style multiple-values feature. *Note Old CL Compatibility::.
File: cl, Node: Installation, Next: Naming Conventions, Prev: Organization, Up: Overview
Installation of the "CL" package is simple: Just put the byte-compiled
files `cl.elc', `cl-extra.elc', `cl-seq.elc', `cl-macs.elc', and
`cl-compat.elc' into a directory on your `load-path'.
There are no special requirements to compile this package: The files
do not have to be loaded before they are compiled, nor do they need to
be compiled in any particular order.
You may choose to put the files into your main `lisp/' directory,
replacing the original `cl.el' file there. Or, you could put them into
a directory that comes before `lisp/' on your `load-path' so that the
old `cl.el' is effectively hidden.
Also, format the `cl.texinfo' file and put the resulting Info files
in the `info/' directory or another suitable place.
You may instead wish to leave this package's components all in their
own directory, and then add this directory to your `load-path' and
`Info-directory-list'. Add the directory to the front of the list so
the old "CL" package and its documentation are hidden.
File: cl, Node: Naming Conventions, Prev: Installation, Up: Overview
2.4 Naming Conventions
Except where noted, all functions defined by this package have the same
names and calling conventions as their Common Lisp counterparts.
Following is a complete list of functions whose names were changed
from Common Lisp, usually to avoid conflicts with Emacs. In each case,
a `*' has been appended to the Common Lisp name to obtain the Emacs
defun* defsubst* defmacro* function*
member* assoc* rassoc* get*
remove* delete* mapcar* sort*
floor* ceiling* truncate* round*
mod* rem* random*
Internal function and variable names in the package are prefixed by
`cl-'. Here is a complete list of functions _not_ prefixed by `cl-'
which were not taken from Common Lisp:
floatp-safe lexical-let lexical-let*
callf callf2 letf letf*
The following simple functions and macros are defined in `cl.el';
they do not cause other components like `cl-extra' to be loaded.
evenp oddp plusp minusp
caaar .. cddddr
list* ldiff rest first .. tenth
copy-list subst mapcar* 
adjoin  acons pairlis pop 
push  pushnew [3,4] incf  decf 
 Only for one sequence argument or two list arguments.
 Only if `:test' is `eq', `equal', or unspecified, and `:key' is not
 Only when PLACE is a plain variable name.
File: cl, Node: Program Structure, Next: Predicates, Prev: Overview, Up: Top
3 Program Structure
This section describes features of the "CL" package which have to do
with programs as a whole: advanced argument lists for functions, and
the `eval-when' construct.
* Argument Lists:: `&key', `&aux', `defun*', `defmacro*'.
* Time of Evaluation:: The `eval-when' construct.
File: cl, Node: Argument Lists, Next: Time of Evaluation, Prev: Program Structure, Up: Program Structure
3.1 Argument Lists
Emacs Lisp's notation for argument lists of functions is a subset of
the Common Lisp notation. As well as the familiar `&optional' and
`&rest' markers, Common Lisp allows you to specify default values for
optional arguments, and it provides the additional markers `&key' and
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.
-- Special Form: defun* name arglist body...
This form is identical to the regular `defun' form, except that
ARGLIST is allowed to be a full Common Lisp argument list. Also,
the function body is enclosed in an implicit block called NAME;
*note Blocks and Exits::.
-- Special Form: defsubst* name arglist body...
This is just like `defun*', except that the function that is
defined is automatically proclaimed `inline', i.e., calls to it
may be expanded into in-line code by the byte compiler. This is
analogous to the `defsubst' form; `defsubst*' uses a different
method (compiler macros) which works in all version of Emacs, and
also generates somewhat more efficient inline expansions. In
particular, `defsubst*' arranges for the processing of keyword
arguments, default values, etc., to be done at compile-time
-- Special Form: defmacro* name arglist body...
This is identical to the regular `defmacro' form, except that
ARGLIST is allowed to be a full Common Lisp argument list. The
`&environment' keyword is supported as described in Steele. The
`&whole' keyword is supported only within destructured lists (see
below); top-level `&whole' cannot be implemented with the current
Emacs Lisp interpreter. The macro expander body is enclosed in an
implicit block called NAME.
-- Special Form: function* symbol-or-lambda
This is identical to the regular `function' form, except that if
the argument is a `lambda' form then that form may use a full
Common Lisp argument list.
Also, all forms (such as `defsetf' and `flet') defined in this
package that include ARGLISTs in their syntax allow full Common Lisp
Note that it is _not_ necessary to use `defun*' in order to have
access to most "CL" features in your function. These features are
always present; `defun*''s only difference from `defun' is its more
flexible argument lists and its implicit block.
The full form of a Common Lisp argument list is
&optional (VAR INITFORM SVAR)...
&key ((KEYWORD VAR) INITFORM SVAR)...
&aux (VAR INITFORM)...)
Each of the five argument list sections is optional. The SVAR,
INITFORM, and KEYWORD parts are optional; if they are omitted, then
`(VAR)' may be written simply `VAR'.
The first section consists of zero or more "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 "optional" arguments. These
arguments may be specified in the function call; if they are not,
INITFORM specifies the default value used for the argument. (No
INITFORM means to use `nil' as the default.) The INITFORM is evaluated
with the bindings for the preceding arguments already established; `(a
&optional (b (1+ a)))' matches one or two arguments, with the second
argument defaulting to one plus the first argument. If the SVAR is
specified, it is an auxiliary variable which is bound to `t' if the
optional argument was specified, or to `nil' if the argument was
omitted. If you don't use an 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 "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
`&rest' is equivalent to that of Emacs Lisp. Common Lisp accepts
`&body' as a synonym for `&rest' in macro contexts; this package
accepts it all the time.
The fourth section consists of "keyword" arguments. These are
optional arguments which are specified by name rather than positionally
in the argument list. For example,
(defun* foo (a &optional b &key c d (e 17)))
defines a function which may be called with one, two, or more
arguments. The first two arguments are bound to `a' and `b' in the
usual way. The remaining arguments must be pairs of the form `:c',
`:d', or `:e' followed by the value to be bound to the corresponding
argument variable. (Symbols whose names begin with a colon are called
"keywords", and they are self-quoting in the same way as `nil' and `t'.)
For example, the call `(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 `b' as well, since
`(foo 1 :c 2)' would bind `b' to the keyword `:c', then signal an error
because `2' is not a valid keyword.
If a KEYWORD symbol is explicitly specified in the argument list as
shown in the above diagram, then that keyword will be used instead of
just the variable name prefixed with a colon. You can specify a
KEYWORD symbol which does not begin with a colon at all, but such
symbols will not be self-quoting; you will have to quote them
explicitly with an apostrophe in the function call.
Ordinarily it is an error to pass an unrecognized keyword to a
function, e.g., `(foo 1 2 :c 3 :goober 4)'. You can ask Lisp to ignore
unrecognized keywords, either by adding the marker `&allow-other-keys'
after the keyword section of the argument list, or by specifying an
`:allow-other-keys' argument in the call whose value is non-`nil'. If
the function uses both `&rest' and `&key' at the same time, the "rest"
argument is bound to the keyword list as it appears in the call. For
(defun* find-thing (thing &rest rest &key need &allow-other-keys)
(or (apply 'member* thing thing-list :allow-other-keys t rest)
(if need (error "Thing not found"))))
This function takes a `:need' keyword argument, but also accepts other
keyword arguments which are passed on to the `member*' function.
`allow-other-keys' is used to keep both `find-thing' and `member*' from
complaining about each others' keywords in the arguments.
The fifth section of the argument list consists of "auxiliary
variables". These are not really arguments at all, but simply
variables which are bound to `nil' or to the specified INITFORMS during
execution of the function. There is no difference between the
following two functions, except for a matter of stylistic taste:
(defun* foo (a b &aux (c (+ a b)) d)
(defun* foo (a b)
(let ((c (+ a b)) d)
Argument lists support "destructuring". In Common Lisp,
destructuring is only allowed with `defmacro'; this package allows it
with `defun*' and other argument lists as well. In destructuring, any
argument variable (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:
(defmacro* dolist ((var listform &optional resultform)
This says that the first argument of `dolist' must be a list of two
or three items; if there are other arguments as well as this list, they
are stored in `body'. All features allowed in regular argument lists
are allowed in these recursive argument lists. In addition, the clause
`&whole VAR' is allowed at the front of a recursive argument list. It
binds VAR to the whole list being matched; thus `(&whole all a b)'
matches a list of two things, with `a' bound to the first thing, `b'
bound to the second thing, and `all' bound to the list itself. (Common
Lisp allows `&whole' in top-level `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 `(a b . c)' is functionally
equivalent to `(a b &rest c)'.
If the optimization quality `safety' is set to 0 (*note
Declarations::), error checking for wrong number of arguments and
invalid keyword arguments is disabled. By default, argument lists are
File: cl, Node: Time of Evaluation, Prev: Argument Lists, Up: Program Structure
3.2 Time of Evaluation
Normally, the byte-compiler does not actually execute the forms in a
file it compiles. For example, if a file contains `(setq foo t)', the
act of compiling it will not actually set `foo' to `t'. This is true
even if the `setq' was a top-level form (i.e., not enclosed in a
`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 `defmacro' forms at compile-time so that
later parts of the file can refer to the macros that are defined.
-- Special Form: eval-when (situations...) forms...
This form controls when the body FORMS are evaluated. The
SITUATIONS list may contain any set of the symbols `compile',
`load', and `eval' (or their long-winded ANSI equivalents,
`:compile-toplevel', `:load-toplevel', and `:execute').
The `eval-when' form is handled differently depending on 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 `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 `progn'.
For compiled top-level `eval-when's, the body FORMS are executed
at compile-time if `compile' is in the SITUATIONS list, and the
FORMS are written out to the file (to be executed at load-time) if
`load' is in the SITUATIONS list.
For non-compiled-top-level forms, only the `eval' situation is
relevant. (This includes forms executed by the interpreter, forms
compiled with `byte-compile' rather than `byte-compile-file', and
non-top-level forms.) The `eval-when' acts like a `progn' if
`eval' is specified, and like `nil' (ignoring the body FORMS) if
The rules become more subtle when `eval-when's are nested; consult
Steele (second edition) for the gruesome details (and some
Some simple examples:
;; Top-level forms in foo.el:
(eval-when (compile) (setq foo1 'bar))
(eval-when (load) (setq foo2 'bar))
(eval-when (compile load) (setq foo3 'bar))
(eval-when (eval) (setq foo4 'bar))
(eval-when (eval compile) (setq foo5 'bar))
(eval-when (eval load) (setq foo6 'bar))
(eval-when (eval compile load) (setq foo7 'bar))
When `foo.el' is compiled, these variables will be set during the
foo1 foo3 foo5 foo7 ; `compile'
When `foo.elc' is loaded, these variables will be set:
foo2 foo3 foo6 foo7 ; `load'
And if `foo.el' is loaded uncompiled, these variables will be set:
foo4 foo5 foo6 foo7 ; `eval'
If these seven `eval-when's had been, say, inside a `defun', then
the first three would have been equivalent to `nil' and the last
four would have been equivalent to the corresponding `setq's.
Note that `(eval-when (load eval) ...)' is equivalent to `(progn
...)' in all contexts. The compiler treats certain top-level
forms, like `defmacro' (sort-of) and `require', as if they were
wrapped in `(eval-when (compile load eval) ...)'.
Emacs includes two special forms related to `eval-when'. One of
these, `eval-when-compile', is not quite equivalent to any `eval-when'
construct and is described below.
The other form, `(eval-and-compile ...)', is exactly equivalent to
`(eval-when (compile load eval) ...)' and so is not itself defined by
-- Special Form: eval-when-compile forms...
The FORMS are evaluated at compile-time; at execution time, this
form acts like a quoted constant of the resulting value. Used at
top-level, `eval-when-compile' is just like `eval-when (compile
eval)'. In other contexts, `eval-when-compile' allows code to be
evaluated once at compile-time for efficiency or other reasons.
This form is similar to the `#.' syntax of true Common Lisp.
-- Special Form: load-time-value form
The 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 `#,' syntax that was similar to this, but
ANSI Common Lisp replaced it with `load-time-value' and gave it
more well-defined semantics.
In a compiled file, `load-time-value' arranges for FORM to be
evaluated when the `.elc' file is loaded and then used as if it
were a quoted constant. In code compiled by `byte-compile' rather
than `byte-compile-file', the effect is identical to
`eval-when-compile'. In uncompiled code, both `eval-when-compile'
and `load-time-value' act exactly like `progn'.
(defun report ()
(insert "This function was executed on: "
", compiled on: "
;; or '#.(current-time-string) in real Common Lisp
", and loaded on: "
Byte-compiled, the above defun will result in the following code
(or its compiled equivalent, of course) in the `.elc' file:
(setq --temp-- (current-time-string))
(defun report ()
(insert "This function was executed on: "
", compiled on: "
'"Wed Jun 23 18:33:43 1993"
", and loaded on: "
File: cl, Node: Predicates, Next: Control Structure, Prev: Program Structure, Up: Top
This section describes functions for testing whether various facts are
true or false.
* Type Predicates:: `typep', `deftype', and `coerce'
* Equality Predicates:: `equalp'
File: cl, Node: Type Predicates, Next: Equality Predicates, Prev: Predicates, Up: Predicates
4.1 Type Predicates
The "CL" package defines a version of the Common Lisp `typep' predicate.
-- Function: typep object type
Check if OBJECT is of type TYPE, where TYPE is a (quoted) type
name of the sort used by Common Lisp. For example, `(typep foo
'integer)' is equivalent to `(integerp foo)'.
The TYPE argument to the above function is either a symbol or a list
beginning with a symbol.
* If the type name is a symbol, Emacs appends `-p' to the symbol
name to form the name of a predicate function for testing the
type. (Built-in predicates whose names end in `p' rather than
`-p' are used when appropriate.)
* The type symbol `t' stands for the union of all types. `(typep
OBJECT t)' is always true. Likewise, the type symbol `nil' stands
for nothing at all, and `(typep OBJECT nil)' is always false.
* The type symbol `null' represents the symbol `nil'. Thus `(typep
OBJECT 'null)' is equivalent to `(null OBJECT)'.
* The type symbol `atom' represents all objects that are not cons
cells. Thus `(typep OBJECT 'atom)' is equivalent to `(atom
* The type symbol `real' is a synonym for `number', and `fixnum' is
a synonym for `integer'.
* The type symbols `character' and `string-char' match integers in
the range from 0 to 255.
* The type symbol `float' uses the `floatp-safe' predicate defined
by this package rather than `floatp', so it will work correctly
even in Emacs versions without floating-point support.
* The type list `(integer LOW HIGH)' represents all integers between
LOW and HIGH, inclusive. Either bound may be a list of a single
integer to specify an exclusive limit, or a `*' to specify no
limit. The type `(integer * *)' is thus equivalent to `integer'.
* Likewise, lists beginning with `float', `real', or `number'
represent numbers of that type falling in a particular range.
* Lists beginning with `and', `or', and `not' form combinations of
types. For example, `(or integer (float 0 *))' represents all
objects that are integers or non-negative floats.
* Lists beginning with `member' or `member*' represent objects `eql'
to any of the following values. For example, `(member 1 2 3 4)'
is equivalent to `(integer 1 4)', and `(member nil)' is equivalent
* Lists of the form `(satisfies PREDICATE)' represent all objects
for which PREDICATE returns true when called with that object as
The following function and macro (not technically predicates) are
related to `typep'.
-- Function: coerce object type
This function attempts to convert OBJECT to the specified TYPE.
If OBJECT is already of that type as determined by `typep', it is
simply returned. Otherwise, certain types of conversions will be
made: If TYPE is any sequence type (`string', `list', etc.) then
OBJECT will be converted to that type if possible. If TYPE is
`character', then strings of length one and symbols with
one-character names can be coerced. If TYPE is `float', then
integers can be coerced in versions of Emacs that support floats.
In all other circumstances, `coerce' signals an error.
-- Special Form: deftype name arglist forms...
This macro defines a new type called NAME. It is similar to
`defmacro' in many ways; when NAME is encountered as a type name,
the body FORMS are evaluated and should return a type specifier
that is equivalent to the type. The ARGLIST is a Common Lisp
argument list of the sort accepted by `defmacro*'. The type
specifier `(NAME ARGS...)' is expanded by calling the expander
with those arguments; the type symbol `NAME' is expanded by
calling the expander with no arguments. The ARGLIST is processed
the same as for `defmacro*' except that optional arguments without
explicit defaults use `*' instead of `nil' as the "default"
default. Some examples:
(deftype null () '(satisfies null)) ; predefined
(deftype list () '(or null cons)) ; predefined
(deftype unsigned-byte (&optional bits)
(list 'integer 0 (if (eq bits '*) bits (1- (lsh 1 bits)))))
(unsigned-byte 8) == (integer 0 255)
(unsigned-byte) == (integer 0 *)
unsigned-byte == (integer 0 *)
The last example shows how the Common Lisp `unsigned-byte' type
specifier could be implemented if desired; this package does not
implement `unsigned-byte' by default.
The `typecase' and `check-type' macros also use type names. *Note
Conditionals::. *Note Assertions::. The `map', `concatenate', and
`merge' functions take type-name arguments to specify the type of
sequence to return. *Note Sequences::.
File: cl, Node: Equality Predicates, Prev: Type Predicates, Up: Predicates
4.2 Equality Predicates
This package defines the Common Lisp predicate `equalp'.
-- Function: equalp a b
This function is a more flexible version of `equal'. In
particular, it compares strings case-insensitively, and it compares
numbers without regard to type (so that `(equalp 3 3.0)' is true).
Vectors and conses are compared recursively. All other objects
are compared as if by `equal'.
This function differs from Common Lisp `equalp' in several
respects. First, Common Lisp's `equalp' also compares
_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
vector-like in Emacs Lisp, this package's `equalp' also will not
compare strings against vectors of integers.
Also note that the Common Lisp functions `member' and `assoc' use
`eql' to compare elements, whereas Emacs Lisp follows the MacLisp
tradition and uses `equal' for these two functions. In Emacs, use
`member*' and `assoc*' to get functions which use `eql' for comparisons.
File: cl, Node: Control Structure, Next: Macros, Prev: Predicates, Up: Top
5 Control Structure
The features described in the following sections implement various
advanced control structures, including the powerful `setf' facility and
a number of looping and conditional constructs.
* Assignment:: The `psetq' form
* Generalized Variables:: `setf', `incf', `push', etc.
* Variable Bindings:: `progv', `lexical-let', `flet', `macrolet'
* Conditionals:: `case', `typecase'
* Blocks and Exits:: `block', `return', `return-from'
* Iteration:: `do', `dotimes', `dolist', `do-symbols'
* Loop Facility:: The Common Lisp `loop' macro
* Multiple Values:: `values', `multiple-value-bind', etc.
File: cl, Node: Assignment, Next: Generalized Variables, Prev: Control Structure, Up: Control Structure
The `psetq' form is just like `setq', except that multiple assignments
are done in parallel rather than sequentially.
-- Special Form: psetq [symbol form]...
This special form (actually a macro) is used to assign to several
variables simultaneously. Given only one SYMBOL and FORM, it has
the same effect as `setq'. Given several SYMBOL and FORM pairs,
it evaluates all the FORMs in advance and then stores the
corresponding variables afterwards.
(setq x 2 y 3)
(setq x (+ x y) y (* x y))
y ; `y' was computed after `x' was set.
(setq x 2 y 3)
(psetq x (+ x y) y (* x y))
y ; `y' was computed before `x' was set.
The simplest use of `psetq' is `(psetq x y y x)', which exchanges
the values of two variables. (The `rotatef' form provides an even
more convenient way to swap two variables; *note Modify Macros::.)
`psetq' always returns `nil'.
File: cl, Node: Generalized Variables, Next: Variable Bindings, Prev: Assignment, Up: Control Structure
5.2 Generalized Variables
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 `setf' form is like `setq', except that it accepts arbitrary
place forms on the left side rather than just symbols. For example,
`(setf (car a) b)' sets the car of `a' to `b', doing the same operation
as `(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 `x = a[i]' gets an element from an array and `a[i] = x' stores an
element using the same notation. Just as certain forms like `a[i]' can
be lvalues in C, there is a set of forms that can be generalized
variables in Lisp.
* Basic Setf:: `setf' and place forms
* Modify Macros:: `incf', `push', `rotatef', `letf', `callf', etc.
* Customizing Setf:: `define-modify-macro', `defsetf', `define-setf-method'
File: cl, Node: Basic Setf, Next: Modify Macros, Prev: Generalized Variables, Up: Generalized Variables
5.2.1 Basic Setf
The `setf' macro is the most basic way to operate on generalized
-- Special Form: setf [place form]...
This macro evaluates FORM and stores it in PLACE, which must be a
valid generalized variable form. If there are several PLACE and
FORM pairs, the assignments are done sequentially just as with
`setq'. `setf' returns the value of the last FORM.
The following Lisp forms will work as generalized variables, and
so may appear in the PLACE argument of `setf':
* A symbol naming a variable. In other words, `(setf x y)' is
exactly equivalent to `(setq x y)', and `setq' itself is
strictly speaking redundant now that `setf' exists. Many
programmers continue to prefer `setq' for setting simple
variables, though, purely for stylistic or historical reasons.
The macro `(setf x y)' actually expands to `(setq x y)', so
there is no performance penalty for using it in compiled code.
* A call to any of the following Lisp functions:
car cdr caar .. cddddr
nth rest first .. tenth
aref elt nthcdr
symbol-function symbol-value symbol-plist
get get* getf
Note that for `nthcdr' and `getf', the list argument of the
function must itself be a valid PLACE form. For example,
`(setf (nthcdr 0 foo) 7)' will set `foo' itself to 7. Note
that `push' and `pop' on an `nthcdr' place can be used to
insert or delete at any position in a list. The use of
`nthcdr' as a PLACE form is an extension to standard Common
* The following Emacs-specific functions are also `setf'-able.
Most of these have directly corresponding "set" functions,
like `use-local-map' for `current-local-map', or `goto-char'
for `point'. A few, like `point-min', expand to longer
sequences of code when they are `setf''d (`(narrow-to-region
x (point-max))' in this case).
* A call of the form `(substring SUBPLACE N [M])', where
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:
(setq a (list "hello" "world"))
=> ("hello" "world")
(substring (cadr a) 2 4)
(setf (substring (cadr a) 2 4) "o")
=> ("hello" "wood")
The generalized variable `buffer-substring', listed above,
also works in this way by replacing a portion of the current
* A call of the form `(apply 'FUNC ...)' or `(apply (function
FUNC) ...)', where FUNC is a `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
`define-setf-method' or the long form of `defsetf'.
* A macro call, in which case the macro is expanded and `setf'
is applied to the resulting form.
* Any form for which a `defsetf' or `define-setf-method' has
Using any forms other than these in the PLACE argument to `setf'
will signal an error.
The `setf' macro takes care to evaluate all subforms in the proper
left-to-right order; for example,
(setf (aref vec (incf i)) i)
looks like it will evaluate `(incf i)' exactly once, before the
following access to `i'; the `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 `aref'. (In this
case, `aset' would be used and no such steps would be necessary
since `aset' takes its arguments in a convenient order.)
However, if the 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
(defmacro wrong-order (x y) (list 'aref y x))
the form `(setf (wrong-order A B) 17)' will evaluate B first, then
A, just as in an actual call to `wrong-order'.
File: cl, Node: Modify Macros, Next: Customizing Setf, Prev: Basic Setf, Up: Generalized Variables
5.2.2 Modify Macros
This package defines a number of other macros besides `setf' that
operate on generalized variables. Many are interesting and useful even
when the PLACE is just a variable name.
-- Special Form: psetf [place form]...
This macro is to `setf' what `psetq' is to `setq': When several
PLACEs and FORMs 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).
-- Special Form: incf place &optional x
This macro increments the number stored in PLACE by one, or by X
if specified. The incremented value is returned. For example,
`(incf i)' is equivalent to `(setq i (1+ i))', and `(incf (car x)
2)' is equivalent to `(setcar x (+ (car x) 2))'.
Once again, care is taken to preserve the "apparent" order of
evaluation. For example,
(incf (aref vec (incf i)))
appears to increment `i' once, then increment the element of `vec'
addressed by `i'; this is indeed exactly what it does, which means
the above form is _not_ equivalent to the "obvious" expansion,
(setf (aref vec (incf i)) (1+ (aref vec (incf i)))) ; Wrong!
but rather to something more like
(let ((temp (incf i)))
(setf (aref vec temp) (1+ (aref vec temp))))
Again, all of this is taken care of automatically by `incf' and
the other generalized-variable macros.
As a more Emacs-specific example of `incf', the expression `(incf
(point) N)' is essentially equivalent to `(forward-char N)'.
-- Special Form: decf place &optional x
This macro decrements the number stored in PLACE by one, or by X
-- Special Form: pop place
This macro removes and returns the first element of the list stored
in PLACE. It is analogous to `(prog1 (car PLACE) (setf PLACE (cdr
PLACE)))', except that it takes care to evaluate all subforms only
-- Special Form: push x place
This macro inserts X at the front of the list stored in PLACE. It
is analogous to `(setf PLACE (cons X PLACE))', except for
evaluation of the subforms.
-- Special Form: pushnew x place &key :test :test-not :key
This macro inserts X at the front of the list stored in PLACE, but
only if X was not `eql' to any existing element of the list. The
optional keyword arguments are interpreted in the same way as for
`adjoin'. *Note Lists as Sets::.
-- Special Form: shiftf place... newvalue
This macro shifts the PLACEs left by one, shifting in the value of
NEWVALUE (which may be any Lisp expression, not just a generalized
variable), and returning the value shifted out of the first PLACE.
Thus, `(shiftf A B C D)' is equivalent to
(psetf A B
except that the subforms of A, B, and C are actually evaluated
only once each and in the apparent order.
-- Special Form: rotatef place...
This macro rotates the PLACEs left by one in circular fashion.
Thus, `(rotatef A B C D)' is equivalent to
(psetf A B
except for the evaluation of subforms. `rotatef' always returns
`nil'. Note that `(rotatef A B)' conveniently exchanges A and B.
The following macros were invented for this package; they have no
analogues in Common Lisp.
-- Special Form: letf (bindings...) forms...
This macro is analogous to `let', but for generalized variables
rather than just symbols. Each BINDING should be of the form
`(PLACE VALUE)'; the original contents of the PLACEs are saved,
the VALUEs are stored in them, and then the body FORMs are
executed. Afterwards, the PLACES are set back to their original
saved contents. This cleanup happens even if the FORMs exit
irregularly due to a `throw' or an error.
(letf (((point) (point-min))
moves "point" in the current buffer to the beginning of the buffer,
and also binds `a' to 17 (as if by a normal `let', since `a' is
just a regular variable). After the body exits, `a' is set back
to its original value and point is moved back to its original
Note that `letf' on `(point)' is not quite like a
`save-excursion', as the latter effectively saves a marker which
tracks insertions and deletions in the buffer. Actually, a `letf'
of `(point-marker)' is much closer to this behavior. (`point' and
`point-marker' are equivalent as `setf' places; each will accept
either an integer or a marker as the stored value.)
Since generalized variables look like lists, `let''s shorthand of
using `foo' for `(foo nil)' as a BINDING would be ambiguous in
`letf' and is not allowed.
However, a BINDING specifier may be a one-element list `(PLACE)',
which is similar to `(PLACE PLACE)'. In other words, the PLACE is
not disturbed on entry to the body, and the only effect of the
`letf' is to restore the original value of PLACE afterwards. (The
redundant access-and-store suggested by the `(PLACE PLACE)'
example does not actually occur.)
In most cases, the PLACE must have a well-defined value on entry
to the `letf' form. The only exceptions are plain variables and
calls to `symbol-value' and `symbol-function'. If the symbol is
not bound on entry, it is simply made unbound by `makunbound' or
`fmakunbound' on exit.
-- Special Form: letf* (bindings...) forms...
This macro is to `letf' what `let*' is to `let': It does the
bindings in sequential rather than parallel order.
-- Special Form: callf FUNCTION PLACE ARGS...
This is the "generic" modify macro. It calls FUNCTION, which
should be an unquoted function name, macro name, or lambda. It
passes PLACE and ARGS as arguments, and assigns the result back to
PLACE. For example, `(incf PLACE N)' is the same as `(callf +
PLACE N)'. Some more examples:
(callf abs my-number)
(callf concat (buffer-name) "<" (int-to-string n) ">")
(callf union happy-people (list joe bob) :test 'same-person)
*Note Customizing Setf::, for `define-modify-macro', a way to
create even more concise notations for modify macros. Note again
that `callf' is an extension to standard Common Lisp.
-- Special Form: callf2 FUNCTION ARG1 PLACE ARGS...
This macro is like `callf', except that PLACE is the _second_
argument of FUNCTION rather than the first. For example, `(push X
PLACE)' is equivalent to `(callf2 cons X PLACE)'.
The `callf' and `callf2' macros serve as building blocks for other
macros like `incf', `pushnew', and `define-modify-macro'. The `letf'
and `letf*' macros are used in the processing of symbol macros; *note
File: cl, Node: Customizing Setf, Prev: Modify Macros, Up: Generalized Variables
5.2.3 Customizing Setf
Common Lisp defines three macros, `define-modify-macro', `defsetf', and
`define-setf-method', that allow the user to extend generalized
variables in various ways.
-- Special Form: define-modify-macro name arglist function [doc-string]
This macro defines a "read-modify-write" macro similar to `incf'
and `decf'. The macro NAME is defined to take a PLACE argument
followed by additional arguments described by ARGLIST. The call
(NAME PLACE ARGS...)
will be expanded to
(callf FUNC PLACE ARGS...)
which in turn is roughly equivalent to
(setf PLACE (FUNC PLACE ARGS...))
(define-modify-macro incf (&optional (n 1)) +)
(define-modify-macro concatf (&rest args) concat)
Note that `&key' is not allowed in ARGLIST, but `&rest' is
sufficient to pass keywords on to the function.
Most of the modify macros defined by Common Lisp do not exactly
follow the pattern of `define-modify-macro'. For example, `push'
takes its arguments in the wrong order, and `pop' is completely
irregular. You can define these macros "by hand" using
`get-setf-method', or consult the source file `cl-macs.el' to see
how to use the internal `setf' building blocks.
-- Special Form: defsetf access-fn update-fn
This is the simpler of two `defsetf' forms. Where ACCESS-FN is
the name of a function which accesses a place, this declares
UPDATE-FN to be the corresponding store function. From now on,
(setf (ACCESS-FN ARG1 ARG2 ARG3) VALUE)
will be expanded to
(UPDATE-FN ARG1 ARG2 ARG3 VALUE)
The UPDATE-FN is required to be either a true function, or a macro
which evaluates its arguments in a function-like way. Also, the
UPDATE-FN is expected to return VALUE as its result. Otherwise,
the above expansion would not obey the rules for the way `setf' is
supposed to behave.
As a special (non-Common-Lisp) extension, a third argument of `t'
to `defsetf' says that the `update-fn''s return value is not
suitable, so that the above `setf' should be expanded to something
(let ((temp VALUE))
(UPDATE-FN ARG1 ARG2 ARG3 temp)
Some examples of the use of `defsetf', drawn from the standard
suite of setf methods, are:
(defsetf car setcar)
(defsetf symbol-value set)
(defsetf buffer-name rename-buffer t)
-- Special Form: defsetf access-fn arglist (store-var) forms...
This is the second, more complex, form of `defsetf'. It is rather
like `defmacro' except for the additional STORE-VAR argument. The
FORMS should return a Lisp form which stores the value of
STORE-VAR into the generalized variable formed by a call to
ACCESS-FN with arguments described by ARGLIST. The FORMS may
begin with a string which documents the `setf' method (analogous
to the doc string that appears at the front of a function).
For example, the simple form of `defsetf' is shorthand for
(defsetf ACCESS-FN (&rest args) (store)
(append '(UPDATE-FN) args (list store)))
The Lisp form that is returned can access the arguments from
ARGLIST and STORE-VAR in an unrestricted fashion; macros like
`setf' and `incf' which invoke this setf-method will insert
temporary variables as needed to make sure the apparent order of
evaluation is preserved.
Another example drawn from the standard package:
(defsetf nth (n x) (store)
(list 'setcar (list 'nthcdr n x) store))
-- Special Form: define-setf-method access-fn arglist forms...
This is the most general way to create new place forms. When a
`setf' to ACCESS-FN with arguments described by ARGLIST is
expanded, the FORMS are evaluated and must return a list of five
1. A list of "temporary variables".
2. A list of "value forms" corresponding to the temporary
variables above. The temporary variables will be bound to
these value forms as the first step of any operation on the
3. A list of exactly one "store variable" (generally obtained
from a call to `gensym').
4. A Lisp form which stores the contents of the store variable
into the generalized variable, assuming the temporaries have
been bound as described above.
5. A Lisp form which accesses the contents of the generalized
variable, assuming the temporaries have been bound.
This is exactly like the Common Lisp macro of the same name,
except that the method returns a list of five values rather than
the five values themselves, since Emacs Lisp does not support
Common Lisp's notion of multiple return values.
Once again, the FORMS may begin with a documentation string.
A setf-method should be maximally conservative with regard to
temporary variables. In the setf-methods generated by `defsetf',
the second return value is simply the list of arguments in the
place form, and the first return value is a list of a
corresponding number of temporary variables generated by `gensym'.
Macros like `setf' and `incf' which use this setf-method will
optimize away most temporaries that turn out to be unnecessary, so
there is little reason for the setf-method itself to optimize.
-- Function: get-setf-method place &optional env
This function returns the setf-method for PLACE, by invoking the
definition previously recorded by `defsetf' or
`define-setf-method'. The result is a list of five values as
described above. You can use this function to build your own
`incf'-like modify macros. (Actually, it is better to use the
internal functions `cl-setf-do-modify' and `cl-setf-do-store',
which are a bit easier to use and which also do a number of
optimizations; consult the source code for the `incf' function for
a simple example.)
The argument ENV specifies the "environment" to be passed on to
`macroexpand' if `get-setf-method' should need to expand a macro
in PLACE. It should come from an `&environment' argument to the
macro or setf-method that called `get-setf-method'.
See also the source code for the setf-methods for `apply' and
`substring', each of which works by calling `get-setf-method' on a
simpler case, then massaging the result in various ways.
Modern Common Lisp defines a second, independent way to specify the
`setf' behavior of a function, namely "`setf' functions" whose names
are lists `(setf NAME)' rather than symbols. For example, `(defun
(setf foo) ...)' defines the function that is used when `setf' is
applied to `foo'. This package does not currently support `setf'
functions. In particular, it is a compile-time error to use `setf' on
a form which has not already been `defsetf''d or otherwise declared; in
newer Common Lisps, this would not be an error since the function
`(setf FUNC)' might be defined later.
File: cl, Node: Variable Bindings, Next: Conditionals, Prev: Generalized Variables, Up: Control Structure
5.3 Variable Bindings
These Lisp forms make bindings to variables and function names,
analogous to Lisp's built-in `let' form.
*Note Modify Macros::, for the `letf' and `letf*' forms which are
also related to variable bindings.
* Dynamic Bindings:: The `progv' form
* Lexical Bindings:: `lexical-let' and lexical closures
* Function Bindings:: `flet' and `labels'
* Macro Bindings:: `macrolet' and `symbol-macrolet'
File: cl, Node: Dynamic Bindings, Next: Lexical Bindings, Prev: Variable Bindings, Up: Variable Bindings
5.3.1 Dynamic Bindings
The standard `let' form binds variables whose names are known at
compile-time. The `progv' form provides an easy way to bind variables
whose names are computed at run-time.
-- Special Form: progv symbols values forms...
This form establishes `let'-style variable bindings on a set of
variables computed at run-time. The expressions SYMBOLS and
VALUES are evaluated, and must return lists of symbols and values,
respectively. The symbols are bound to the corresponding values
for the duration of the body FORMs. If VALUES is shorter than
SYMBOLS, the last few symbols are made unbound (as if by
`makunbound') inside the body. If SYMBOLS is shorter than VALUES,
the excess values are ignored.
File: cl, Node: Lexical Bindings, Next: Function Bindings, Prev: Dynamic Bindings, Up: Variable Bindings
5.3.2 Lexical Bindings
The "CL" package defines the following macro which more closely follows
the Common Lisp `let' form:
-- Special Form: lexical-let (bindings...) forms...
This form is exactly like `let' except that the bindings it
establishes are purely lexical. Lexical bindings are similar to
local variables in a language like C: Only the code physically
within the body of the `lexical-let' (after macro expansion) may
refer to the bound variables.
(setq a 5)
(defun foo (b) (+ a b))
(let ((a 2)) (foo a))
(lexical-let ((a 2)) (foo a))
In this example, a regular `let' binding of `a' actually makes a
temporary change to the global variable `a', so `foo' is able to
see the binding of `a' to 2. But `lexical-let' actually creates a
distinct local variable `a' for use within its body, without any
effect on the global variable of the same name.
The most important use of lexical bindings is to create "closures".
A closure is a function object that refers to an outside lexical
variable. For example:
(defun make-adder (n)
(lexical-let ((n n))
(function (lambda (m) (+ n m)))))
(setq add17 (make-adder 17))
(funcall add17 4)
The call `(make-adder 17)' returns a function object which adds 17
to its argument. If `let' had been used instead of `lexical-let',
the function object would have referred to the global `n', which
would have been bound to 17 only during the call to `make-adder'
(defun make-counter ()
(lexical-let ((n 0))
(function* (lambda (&optional (m 1)) (incf n m)))))
(setq count-1 (make-counter))
(funcall count-1 3)
(funcall count-1 14)
(setq count-2 (make-counter))
(funcall count-2 5)
(funcall count-1 2)
Here we see that each call to `make-counter' creates a distinct
local variable `n', which serves as a private counter for the
function object that is returned.
Closed-over lexical variables persist until the last reference to
them goes away, just like all other Lisp objects. For example,
`count-2' refers to a function object which refers to an instance
of the variable `n'; this is the only reference to that variable,
so after `(setq count-2 nil)' the garbage collector would be able
to delete this instance of `n'. Of course, if a `lexical-let'
does not actually create any closures, then the lexical variables
are free as soon as the `lexical-let' returns.
Many closures are used only during the extent of the bindings they
refer to; these are known as "downward funargs" in Lisp parlance.
When a closure is used in this way, regular Emacs Lisp dynamic
bindings suffice and will be more efficient than `lexical-let'
(defun add-to-list (x list)
(mapcar (lambda (y) (+ x y))) list)
(add-to-list 7 '(1 2 5))
=> (8 9 12)
Since this lambda is only used while `x' is still bound, it is not
necessary to make a true closure out of it.
You can use `defun' or `flet' inside a `lexical-let' to create a
named closure. If several closures are created in the body of a
single `lexical-let', they all close over the same instance of the
The `lexical-let' form is an extension to Common Lisp. In true
Common Lisp, all bindings are lexical unless declared otherwise.
-- Special Form: lexical-let* (bindings...) forms...
This form is just like `lexical-let', except that the bindings are
made sequentially in the manner of `let*'.
File: cl, Node: Function Bindings, Next: Macro Bindings, Prev: Lexical Bindings, Up: Variable Bindings
5.3.3 Function Bindings
These forms make `let'-like bindings to functions instead of variables.
-- Special Form: flet (bindings...) forms...
This form establishes `let'-style bindings on the function cells
of symbols rather than on the value cells. Each BINDING must be a
list of the form `(NAME ARGLIST FORMS...)', which defines a
function exactly as if it were a `defun*' form. The function NAME
is defined accordingly for the duration of the body of the `flet';
then the old function definition, or lack thereof, is restored.
While `flet' in Common Lisp establishes a lexical binding of NAME,
Emacs Lisp `flet' makes a dynamic binding. The result is that
`flet' affects indirect calls to a function as well as calls
directly inside the `flet' form itself.
You can use `flet' to disable or modify the behavior of a function
in a temporary fashion. This will even work on Emacs primitives,
although note that some calls to primitive functions internal to
Emacs are made without going through the symbol's function cell,
and so will not be affected by `flet'. For example,
(flet ((message (&rest args) (push args saved-msgs)))
This code attempts to replace the built-in function `message' with
a function that simply saves the messages in a list rather than
displaying them. The original definition of `message' will be
restored after `do-something' exits. This code will work fine on
messages generated by other Lisp code, but messages generated
directly inside Emacs will not be caught since they make direct
C-language calls to the message routines rather than going through
the Lisp `message' function.
Functions defined by `flet' may use the full Common Lisp argument
notation supported by `defun*'; also, the function body is
enclosed in an implicit block as if by `defun*'. *Note Program
-- Special Form: labels (bindings...) forms...
The `labels' form is like `flet', except that it makes lexical
bindings of the function names rather than dynamic bindings. (In
true Common Lisp, both `flet' and `labels' make lexical bindings
of slightly different sorts; since Emacs Lisp is dynamically bound
by default, it seemed more appropriate for `flet' also to use
dynamic binding. The `labels' form, with its lexical binding, is
fully compatible with Common Lisp.)
Lexical scoping means that all references to the named functions
must appear physically within the body of the `labels' form.
References may appear both in the body FORMS of `labels' itself,
and in the bodies of the functions themselves. Thus, `labels' can
define local recursive functions, or mutually-recursive sets of
A "reference" to a function name is either a call to that
function, or a use of its name quoted by `quote' or `function' to
be passed on to, say, `mapcar'.
File: cl, Node: Macro Bindings, Prev: Function Bindings, Up: Variable Bindings
5.3.4 Macro Bindings
These forms create local macros and "symbol macros."
-- Special Form: macrolet (bindings...) forms...
This form is analogous to `flet', but for macros instead of
functions. Each BINDING is a list of the same form as the
arguments to `defmacro*' (i.e., a macro name, argument list, and
macro-expander forms). The macro is defined accordingly for use
within the body of the `macrolet'.
Because of the nature of macros, `macrolet' is lexically scoped
even in Emacs Lisp: The `macrolet' binding will affect only calls
that appear physically within the body FORMS, possibly after
expansion of other macros in the body.
-- Special Form: symbol-macrolet (bindings...) forms...
This form creates "symbol macros", which are macros that look like
variable references rather than function calls. Each BINDING is a
list `(VAR EXPANSION)'; any reference to VAR within the body FORMS
is replaced by EXPANSION.
(setq bar '(5 . 9))
(symbol-macrolet ((foo (car bar)))
=> (6 . 9)
A `setq' of a symbol macro is treated the same as a `setf'. I.e.,
`(setq foo 4)' in the above would be equivalent to `(setf foo 4)',
which in turn expands to `(setf (car bar) 4)'.
Likewise, a `let' or `let*' binding a symbol macro is treated like
a `letf' or `letf*'. This differs from true Common Lisp, where
the rules of lexical scoping cause a `let' binding to shadow a
`symbol-macrolet' binding. In this package, only `lexical-let'
and `lexical-let*' will shadow a symbol macro.
There is no analogue of `defmacro' for symbol macros; all symbol
macros are local. A typical use of `symbol-macrolet' is in the
expansion of another macro:
(defmacro* my-dolist ((x list) &rest body)
(let ((var (gensym)))
(list 'loop 'for var 'on list 'do
(list* 'symbol-macrolet (list (list x (list 'car var)))
(setq mylist '(1 2 3 4))
(my-dolist (x mylist) (incf x))
=> (2 3 4 5)
In this example, the `my-dolist' macro is similar to `dolist'
(*note Iteration::) except that the variable `x' becomes a true
reference onto the elements of the list. The `my-dolist' call
shown here expands to
(loop for G1234 on mylist do
(symbol-macrolet ((x (car G1234)))
which in turn expands to
(loop for G1234 on mylist do (incf (car G1234)))
*Note Loop Facility::, for a description of the `loop' macro.
This package defines a nonstandard `in-ref' loop clause that works
much like `my-dolist'.
File: cl, Node: Conditionals, Next: Blocks and Exits, Prev: Variable Bindings, Up: Control Structure
These conditional forms augment Emacs Lisp's simple `if', `and', `or',
and `cond' forms.
-- Special Form: case keyform clause...
This macro evaluates KEYFORM, then compares it with the key values
listed in the various CLAUSEs. Whichever clause matches the key
is executed; comparison is done by `eql'. If no clause matches,
the `case' form returns `nil'. The clauses are of the form
where KEYLIST is a list of key values. If there is exactly one
value, and it is not a cons cell or the symbol `nil' or `t', then
it can be used by itself as a KEYLIST without being enclosed in a
list. All key values in the `case' form must be distinct. The
final clauses may use `t' in place of a KEYLIST to indicate a
default clause that should be taken if none of the other clauses
match. (The symbol `otherwise' is also recognized in place of
`t'. To make a clause that matches the actual symbol `t', `nil',
or `otherwise', enclose the symbol in a list.)
For example, this expression reads a keystroke, then does one of
four things depending on whether it is an `a', a `b', a <RET> or
`C-j', or anything else.
((?\r ?\n) (do-ret-thing))
-- Special Form: ecase keyform clause...
This macro is just like `case', except that if the key does not
match any of the clauses, an error is signaled rather than simply
-- Special Form: typecase keyform clause...
This macro is a version of `case' that checks for types rather
than values. Each CLAUSE is of the form `(TYPE BODY...)'. *Note
Type Predicates::, for a description of type specifiers. For
(integer (munch-integer x))
(float (munch-float x))
(string (munch-integer (string-to-int x)))
(t (munch-anything x)))
The type specifier `t' matches any type of object; the word
`otherwise' is also allowed. To make one clause match any of
several types, use an `(or ...)' type specifier.
-- Special Form: etypecase keyform clause...
This macro is just like `typecase', except that if the key does
not match any of the clauses, an error is signaled rather than
simply returning `nil'.
File: cl, Node: Blocks and Exits, Next: Iteration, Prev: Conditionals, Up: Control Structure
5.5 Blocks and Exits
Common Lisp "blocks" provide a non-local exit mechanism very similar to
`catch' and `throw', but lexically rather than dynamically scoped.
This package actually implements `block' in terms of `catch'; however,
the lexical scoping allows the optimizing byte-compiler to omit the
costly `catch' step if the body of the block does not actually
`return-from' the block.
-- Special Form: block name forms...
The FORMS are evaluated as if by a `progn'. However, if any of
the FORMS execute `(return-from NAME)', they will jump out and
return directly from the `block' form. The `block' returns the
result of the last FORM unless a `return-from' occurs.
The `block'/`return-from' mechanism is quite similar to the
`catch'/`throw' mechanism. The main differences are that block
NAMEs are unevaluated symbols, rather than forms (such as quoted
symbols) which evaluate to a tag at run-time; and also that blocks
are lexically scoped whereas `catch'/`throw' are dynamically
scoped. This means that functions called from the body of a
`catch' can also `throw' to the `catch', but the `return-from'
referring to a block name must appear physically within the FORMS
that make up the body of the block. They may not appear within
other called functions, although they may appear within macro
expansions or `lambda's in the body. Block names and `catch'
names form independent name-spaces.
In true Common Lisp, `defun' and `defmacro' surround the function
or expander bodies with implicit blocks with the same name as the
function or macro. This does not occur in Emacs Lisp, but this
package provides `defun*' and `defmacro*' forms which do create
the implicit block.
The Common Lisp looping constructs defined by this package, such
as `loop' and `dolist', also create implicit blocks just as in
Because they are implemented in terms of Emacs Lisp `catch' and
`throw', blocks have the same overhead as actual `catch'
constructs (roughly two function calls). However, the optimizing
byte compiler will optimize away the `catch' if the block does not
in fact contain any `return' or `return-from' calls that jump to
it. This means that `do' loops and `defun*' functions which don't
use `return' don't pay the overhead to support it.
-- Special Form: return-from name [result]
This macro returns from the block named NAME, which must be an
(unevaluated) symbol. If a RESULT form is specified, it is
evaluated to produce the result returned from the `block'.
Otherwise, `nil' is returned.
-- Special Form: return [result]
This macro is exactly like `(return-from nil RESULT)'. Common
Lisp loops like `do' and `dolist' implicitly enclose themselves in
File: cl, Node: Iteration, Next: Loop Facility, Prev: Blocks and Exits, Up: Control Structure
The macros described here provide more sophisticated, high-level
looping constructs to complement Emacs Lisp's basic `while' loop.
-- Special Form: loop forms...
The "CL" package supports both the simple, old-style meaning of
`loop' and the extremely powerful and flexible feature known as
the "Loop Facility" or "Loop Macro". This more advanced facility
is discussed in the following section; *note Loop Facility::. The
simple form of `loop' is described here.
If `loop' is followed by zero or more Lisp expressions, then
`(loop EXPRS...)' simply creates an infinite loop executing the
expressions over and over. The loop is enclosed in an implicit
`nil' block. Thus,
(loop (foo) (if (no-more) (return 72)) (bar))
is exactly equivalent to
(block nil (while t (foo) (if (no-more) (return 72)) (bar)))
If any of the expressions are plain symbols, the loop is instead
interpreted as a Loop Macro specification as described later.
(This is not a restriction in practice, since a plain symbol in
the above notation would simply access and throw away the value of
-- Special Form: do (spec...) (end-test [result...]) forms...
This macro creates a general iterative loop. Each SPEC is of the
(VAR [INIT [STEP]])
The loop works as follows: First, each VAR is bound to the
associated INIT value as if by a `let' form. Then, in each
iteration of the loop, the END-TEST is evaluated; if true, the
loop is finished. Otherwise, the body FORMS are evaluated, then
each VAR is set to the associated STEP expression (as if by a
`psetq' form) and the next iteration begins. Once the END-TEST
becomes true, the RESULT forms are evaluated (with the VARs still
bound to their values) to produce the result returned by `do'.
The entire `do' loop is enclosed in an implicit `nil' block, so
that you can use `(return)' to break out of the loop at any time.
If there are no RESULT forms, the loop returns `nil'. If a given
VAR has no STEP form, it is bound to its INIT value but not
otherwise modified during the `do' loop (unless the code
explicitly modifies it); this case is just a shorthand for putting
a `(let ((VAR INIT)) ...)' around the loop. If INIT is also
omitted it defaults to `nil', and in this case a plain `VAR' can
be used in place of `(VAR)', again following the analogy with
This example (from Steele) illustrates a loop which applies the
function `f' to successive pairs of values from the lists `foo'
and `bar'; it is equivalent to the call `(mapcar* 'f foo bar)'.
Note that this loop has no body FORMS at all, performing all its
work as side effects of the rest of the loop.
(do ((x foo (cdr x))
(y bar (cdr y))
(z nil (cons (f (car x) (car y)) z)))
((or (null x) (null y))
-- Special Form: do* (spec...) (end-test [result...]) forms...
This is to `do' what `let*' is to `let'. In particular, the
initial values are bound as if by `let*' rather than `let', and
the steps are assigned as if by `setq' rather than `psetq'.
Here is another way to write the above loop:
(do* ((xp foo (cdr xp))
(yp bar (cdr yp))
(x (car xp) (car xp))
(y (car yp) (car yp))
((or (null xp) (null yp))
(push (f x y) z))
-- Special Form: dolist (var list [result]) forms...
This is a more specialized loop which iterates across the elements
of a list. LIST should evaluate to a list; the body FORMS are
executed with VAR bound to each element of the list in turn.
Finally, the RESULT form (or `nil') is evaluated with VAR bound to
`nil' to produce the result returned by the loop. Unlike with
Emacs's built in `dolist', the loop is surrounded by an implicit
-- Special Form: dotimes (var count [result]) forms...
This is a more specialized loop which iterates a specified number
of times. The body is executed with VAR bound to the integers
from zero (inclusive) to COUNT (exclusive), in turn. Then the
`result' form is evaluated with VAR bound to the total number of
iterations that were done (i.e., `(max 0 COUNT)') to get the
return value for the loop form. Unlike with Emacs's built in
`dolist', the loop is surrounded by an implicit `nil' block.
-- Special Form: do-symbols (var [obarray [result]]) forms...
This loop iterates over all interned symbols. If OBARRAY is
specified and is not `nil', it loops over all symbols in that
obarray. For each symbol, the body FORMS are evaluated with VAR
bound to that symbol. The symbols are visited in an unspecified
order. Afterward the RESULT form, if any, is evaluated (with VAR
bound to `nil') to get the return value. The loop is surrounded
by an implicit `nil' block.
-- Special Form: do-all-symbols (var [result]) forms...
This is identical to `do-symbols' except that the OBARRAY argument
is omitted; it always iterates over the default obarray.
*Note Mapping over Sequences::, for some more functions for
iterating over vectors or lists.
File: cl, Node: Loop Facility, Next: Multiple Values, Prev: Iteration, Up: Control Structure
5.7 Loop Facility
A common complaint with Lisp's traditional looping constructs is that
they are either too simple and limited, such as Common Lisp's `dotimes'
or Emacs Lisp's `while', or too unreadable and obscure, like Common
Lisp's `do' loop.
To remedy this, recent versions of Common Lisp have added a new
construct called the "Loop Facility" or "`loop' macro," with an
easy-to-use but very powerful and expressive syntax.
* Loop Basics:: `loop' macro, basic clause structure
* Loop Examples:: Working examples of `loop' macro
* For Clauses:: Clauses introduced by `for' or `as'
* Iteration Clauses:: `repeat', `while', `thereis', etc.
* Accumulation Clauses:: `collect', `sum', `maximize', etc.
* Other Clauses:: `with', `if', `initially', `finally'
File: cl, Node: Loop Basics, Next: Loop Examples, Prev: Loop Facility, Up: Loop Facility
5.7.1 Loop Basics
The `loop' macro essentially creates a mini-language within Lisp that
is specially tailored for describing loops. While this language is a
little strange-looking by the standards of regular Lisp, it turns out
to be very easy to learn and well-suited to its purpose.
Since `loop' is a macro, all parsing of the loop language takes
place at byte-compile time; compiled `loop's are just as efficient as
the equivalent `while' loops written longhand.
-- Special Form: loop clauses...
A loop construct consists of a series of CLAUSEs, each introduced
by a symbol like `for' or `do'. Clauses are simply strung
together in the argument list of `loop', with minimal extra
parentheses. The various types of clauses specify
initializations, such as the binding of temporary variables,
actions to be taken in the loop, stepping actions, and final
Common Lisp specifies a certain general order of clauses in a loop:
The NAME-CLAUSE optionally gives a name to the implicit block that
surrounds the loop. By default, the implicit block is named
`nil'. The VAR-CLAUSES specify what variables should be bound
during the loop, and how they should be modified or iterated
throughout the course of the loop. The ACTION-CLAUSES are things
to be done during the loop, such as computing, collecting, and
The Emacs version of the `loop' macro is less restrictive about
the order of clauses, but things will behave most predictably if
you put the variable-binding clauses `with', `for', and `repeat'
before the action clauses. As in Common Lisp, `initially' and
`finally' clauses can go anywhere.
Loops generally return `nil' by default, but you can cause them to
return a value by using an accumulation clause like `collect', an
end-test clause like `always', or an explicit `return' clause to
jump out of the implicit block. (Because the loop body is
enclosed in an implicit block, you can also use regular Lisp
`return' or `return-from' to break out of the loop.)
The following sections give some examples of the Loop Macro in
action, and describe the particular loop clauses in great detail.
Consult the second edition of Steele's "Common Lisp, the Language", for
additional discussion and examples of the `loop' macro.
File: cl, Node: Loop Examples, Next: For Clauses, Prev: Loop Basics, Up: Loop Facility
5.7.2 Loop Examples
Before listing the full set of clauses that are allowed, let's look at
a few example loops just to get a feel for the `loop' language.
(loop for buf in (buffer-list)
collect (buffer-file-name buf))
This loop iterates over all Emacs buffers, using the list returned by
`buffer-list'. For each buffer `buf', it calls `buffer-file-name' and
collects the results into a list, which is then returned from the
`loop' construct. The result is a list of the file names of all the
buffers in Emacs' memory. The words `for', `in', and `collect' are
reserved words in the `loop' language.
(loop repeat 20 do (insert "Yowsa\n"))
This loop inserts the phrase "Yowsa" twenty times in the current buffer.
(loop until (eobp) do (munch-line) (forward-line 1))
This loop calls `munch-line' on every line until the end of the buffer.
If point is already at the end of the buffer, the loop exits
(loop do (munch-line) until (eobp) do (forward-line 1))
This loop is similar to the above one, except that `munch-line' is
always called at least once.
(loop for x from 1 to 100
for y = (* x x)
until (>= y 729)
finally return (list x (= y 729)))
This more complicated loop searches for a number `x' whose square is
729. For safety's sake it only examines `x' values up to 100; dropping
the phrase `to 100' would cause the loop to count upwards with no
limit. The second `for' clause defines `y' to be the square of `x'
within the loop; the expression after the `=' sign is reevaluated each
time through the loop. The `until' clause gives a condition for
terminating the loop, and the `finally' clause says what to do when the
loop finishes. (This particular example was written less concisely
than it could have been, just for the sake of illustration.)
Note that even though this loop contains three clauses (two `for's
and an `until') that would have been enough to define loops all by
themselves, it still creates a single loop rather than some sort of
triple-nested loop. You must explicitly nest your `loop' constructs if
you want nested loops.
File: cl, Node: For Clauses, Next: Iteration Clauses, Prev: Loop Examples, Up: Loop Facility
5.7.3 For Clauses
Most loops are governed by one or more `for' clauses. A `for' clause
simultaneously describes variables to be bound, how those variables are
to be stepped during the loop, and usually an end condition based on
The word `as' is a synonym for the word `for'. This word is
followed by a variable name, then a word like `from' or `across' that
describes the kind of iteration desired. In Common Lisp, the phrase
`being the' sometimes precedes the type of iteration; in this package
both `being' and `the' are optional. The word `each' is a synonym for
`the', and the word that follows it may be singular or plural: `for x
being the elements of y' or `for x being each element of y'. Which
form you use is purely a matter of style.
The variable is bound around the loop as if by `let':
(setq i 'happy)
(loop for i from 1 to 10 do (do-something-with i))
`for VAR from EXPR1 to EXPR2 by EXPR3'
This type of `for' clause creates a counting loop. Each of the
three sub-terms is optional, though there must be at least one
term so that the clause is marked as a counting clause.
The three expressions are the starting value, the ending value, and
the step value, respectively, of the variable. The loop counts
upwards by default (EXPR3 must be positive), from EXPR1 to EXPR2
inclusively. If you omit the `from' term, the loop counts from
zero; if you omit the `to' term, the loop counts forever without
stopping (unless stopped by some other loop clause, of course); if
you omit the `by' term, the loop counts in steps of one.
You can replace the word `from' with `upfrom' or `downfrom' to
indicate the direction of the loop. Likewise, you can replace
`to' with `upto' or `downto'. For example, `for x from 5 downto
1' executes five times with `x' taking on the integers from 5 down
to 1 in turn. Also, you can replace `to' with `below' or `above',
which are like `upto' and `downto' respectively except that they
are exclusive rather than inclusive limits:
(loop for x to 10 collect x)
=> (0 1 2 3 4 5 6 7 8 9 10)
(loop for x below 10 collect x)
=> (0 1 2 3 4 5 6 7 8 9)
The `by' value is always positive, even for downward-counting
loops. Some sort of `from' value is required for downward loops;
`for x downto 5' is not a valid loop clause all by itself.
`for VAR in LIST by FUNCTION'
This clause iterates VAR over all the elements of LIST, in turn.
If you specify the `by' term, then FUNCTION is used to traverse
the list instead of `cdr'; it must be a function taking one
argument. For example:
(loop for x in '(1 2 3 4 5 6) collect (* x x))
=> (1 4 9 16 25 36)
(loop for x in '(1 2 3 4 5 6) by 'cddr collect (* x x))
=> (1 9 25)
`for VAR on LIST by FUNCTION'
This clause iterates VAR over all the cons cells of LIST.
(loop for x on '(1 2 3 4) collect x)
=> ((1 2 3 4) (2 3 4) (3 4) (4))
With `by', there is no real reason that the `on' expression must
be a list. For example:
(loop for x on first-animal by 'next-animal collect x)
where `(next-animal x)' takes an "animal" X and returns the next
in the (assumed) sequence of animals, or `nil' if X was the last
animal in the sequence.
`for VAR in-ref LIST by FUNCTION'
This is like a regular `in' clause, but VAR becomes a `setf'-able
"reference" onto the elements of the list rather than just a
temporary variable. For example,
(loop for x in-ref my-list do (incf x))
increments every element of `my-list' in place. This clause is an
extension to standard Common Lisp.
`for VAR across ARRAY'
This clause iterates VAR over all the elements of ARRAY, which may
be a vector or a string.
(loop for x across "aeiou"
do (use-vowel (char-to-string x)))
`for VAR across-ref ARRAY'
This clause iterates over an array, with VAR a `setf'-able
reference onto the elements; see `in-ref' above.
`for VAR being the elements of SEQUENCE'
This clause iterates over the elements of SEQUENCE, which may be a
list, vector, or string. Since the type must be determined at
run-time, this is somewhat less efficient than `in' or `across'.
The clause may be followed by the additional term `using (index
VAR2)' to cause VAR2 to be bound to the successive indices
(starting at 0) of the elements.
This clause type is taken from older versions of the `loop' macro,
and is not present in modern Common Lisp. The `using (sequence
...)' term of the older macros is not supported.
`for VAR being the elements of-ref SEQUENCE'
This clause iterates over a sequence, with VAR a `setf'-able
reference onto the elements; see `in-ref' above.
`for VAR being the symbols [of OBARRAY]'
This clause iterates over symbols, either over all interned symbols
or over all symbols in OBARRAY. The loop is executed with VAR
bound to each symbol in turn. The symbols are visited in an
As an example,
(loop for sym being the symbols
when (fboundp sym)
when (string-match "^map" (symbol-name sym))
returns a list of all the functions whose names begin with `map'.
The Common Lisp words `external-symbols' and `present-symbols' are
also recognized but are equivalent to `symbols' in Emacs Lisp.
Due to a minor implementation restriction, it will not work to have
more than one `for' clause iterating over symbols, hash tables,
keymaps, overlays, or intervals in a given `loop'. Fortunately,
it would rarely if ever be useful to do so. It _is_ valid to mix
one of these types of clauses with other clauses like `for ... to'
`for VAR being the hash-keys of HASH-TABLE'
This clause iterates over the entries in HASH-TABLE. For each
hash table entry, VAR is bound to the entry's key. If you write
`the hash-values' instead, VAR is bound to the values of the
entries. The clause may be followed by the additional term `using
(hash-values VAR2)' (where `hash-values' is the opposite word of
the word following `the') to cause VAR and VAR2 to be bound to the
two parts of each hash table entry.
`for VAR being the key-codes of KEYMAP'
This clause iterates over the entries in KEYMAP. The iteration
does not enter nested keymaps but does enter inherited (parent)
keymaps. You can use `the key-bindings' to access the commands
bound to the keys rather than the key codes, and you can add a
`using' clause to access both the codes and the bindings together.
`for VAR being the key-seqs of KEYMAP'
This clause iterates over all key sequences defined by KEYMAP and
its nested keymaps, where VAR takes on values which are vectors.
The strings or vectors are reused for each iteration, so you must
copy them if you wish to keep them permanently. You can add a
`using (key-bindings ...)' clause to get the command bindings as
`for VAR being the overlays [of BUFFER] ...'
This clause iterates over the "overlays" of a buffer (the clause
`extents' is synonymous with `overlays'). If the `of' term is
omitted, the current buffer is used. This clause also accepts
optional `from POS' and `to POS' terms, limiting the clause to
overlays which overlap the specified region.
`for VAR being the intervals [of BUFFER] ...'
This clause iterates over all intervals of a buffer with constant
text properties. The variable VAR will be bound to conses of
start and end positions, where one start position is always equal
to the previous end position. The clause allows `of', `from',
`to', and `property' terms, where the latter term restricts the
search to just the specified property. The `of' term may specify
either a buffer or a string.
`for VAR being the frames'
This clause iterates over all frames, i.e., X window system windows
open on Emacs files. The clause `screens' is a synonym for
`frames'. The frames are visited in `next-frame' order starting
`for VAR being the windows [of FRAME]'
This clause iterates over the windows (in the Emacs sense) of the
current frame, or of the specified FRAME.
`for VAR being the buffers'
This clause iterates over all buffers in Emacs. It is equivalent
to `for VAR in (buffer-list)'.
`for VAR = EXPR1 then EXPR2'
This clause does a general iteration. The first time through the
loop, VAR will be bound to EXPR1. On the second and successive
iterations it will be set by evaluating EXPR2 (which may refer to
the old value of VAR). For example, these two loops are
effectively the same:
(loop for x on my-list by 'cddr do ...)
(loop for x = my-list then (cddr x) while x do ...)
Note that this type of `for' clause does not imply any sort of
terminating condition; the above example combines it with a
`while' clause to tell when to end the loop.
If you omit the `then' term, EXPR1 is used both for the initial
setting and for successive settings:
(loop for x = (random) when (> x 0) return x)
This loop keeps taking random numbers from the `(random)' function
until it gets a positive one, which it then returns.
If you include several `for' clauses in a row, they are treated
sequentially (as if by `let*' and `setq'). You can instead use the
word `and' to link the clauses, in which case they are processed in
parallel (as if by `let' and `psetq').
(loop for x below 5 for y = nil then x collect (list x y))
=> ((0 nil) (1 1) (2 2) (3 3) (4 4))
(loop for x below 5 and y = nil then x collect (list x y))
=> ((0 nil) (1 0) (2 1) (3 2) (4 3))
In the first loop, `y' is set based on the value of `x' that was just
set by the previous clause; in the second loop, `x' and `y' are set
simultaneously so `y' is set based on the value of `x' left over from
the previous time through the loop.
Another feature of the `loop' macro is "destructuring", similar in
concept to the destructuring provided by `defmacro'. The VAR part of
any `for' clause can be given as a list of variables instead of a
single variable. The values produced during loop execution must be
lists; the values in the lists are stored in the corresponding
(loop for (x y) in '((2 3) (4 5) (6 7)) collect (+ x y))
=> (5 9 13)
In loop destructuring, if there are more values than variables the
trailing values are ignored, and if there are more variables than
values the trailing variables get the value `nil'. If `nil' is used as
a variable name, the corresponding values are ignored. Destructuring
may be nested, and dotted lists of variables like `(x . y)' are allowed.
File: cl, Node: Iteration Clauses, Next: Accumulation Clauses, Prev: For Clauses, Up: Loop Facility
5.7.4 Iteration Clauses
Aside from `for' clauses, there are several other loop clauses that
control the way the loop operates. They might be used by themselves,
or in conjunction with one or more `for' clauses.
This clause simply counts up to the specified number using an
internal temporary variable. The loops
(loop repeat n do ...)
(loop for temp to n do ...)
are identical except that the second one forces you to choose a
name for a variable you aren't actually going to use.
This clause stops the loop when the specified condition (any Lisp
expression) becomes `nil'. For example, the following two loops
are equivalent, except for the implicit `nil' block that surrounds
the second one:
(while COND FORMS...)
(loop while COND do FORMS...)
This clause stops the loop when the specified condition is true,
This clause stops the loop when the specified condition is `nil'.
Unlike `while', it stops the loop using `return nil' so that the
`finally' clauses are not executed. If all the conditions were
non-`nil', the loop returns `t':
(if (loop for size in size-list always (> size 10))
This clause is like `always', except that the loop returns `t' if
any conditions were false, or `nil' otherwise.
This clause stops the loop when the specified form is non-`nil';
in this case, it returns that non-`nil' value. If all the values
were `nil', the loop returns `nil'.
File: cl, Node: Accumulation Clauses, Next: Other Clauses, Prev: Iteration Clauses, Up: Loop Facility
5.7.5 Accumulation Clauses
These clauses cause the loop to accumulate information about the
specified Lisp FORM. The accumulated result is returned from the loop
unless overridden, say, by a `return' clause.
This clause collects the values of FORM into a list. Several
examples of `collect' appear elsewhere in this manual.
The word `collecting' is a synonym for `collect', and likewise for
the other accumulation clauses.
This clause collects lists of values into a result list using
This clause collects lists of values into a result list by
destructively modifying the lists rather than copying them.
This clause concatenates the values of the specified FORM into a
string. (It and the following clause are extensions to standard
This clause concatenates the values of the specified FORM into a
This clause counts the number of times the specified FORM
evaluates to a non-`nil' value.
This clause accumulates the sum of the values of the specified
FORM, which must evaluate to a number.
This clause accumulates the maximum value of the specified FORM,
which must evaluate to a number. The return value is undefined if
`maximize' is executed zero times.
This clause accumulates the minimum value of the specified FORM.
Accumulation clauses can be followed by `into VAR' to cause the data
to be collected into variable VAR (which is automatically `let'-bound
during the loop) rather than an unnamed temporary variable. Also,
`into' accumulations do not automatically imply a return value. The
loop must use some explicit mechanism, such as `finally return', to
return the accumulated result.
It is valid for several accumulation clauses of the same type to
accumulate into the same place. From Steele:
(loop for name in '(fred sue alice joe june)
for kids in '((bob ken) () () (kris sunshine) ())
=> (fred bob ken sue alice joe kris sunshine june)
File: cl, Node: Other Clauses, Prev: Accumulation Clauses, Up: Loop Facility
5.7.6 Other Clauses
This section describes the remaining loop clauses.
`with VAR = VALUE'
This clause binds a variable to a value around the loop, but
otherwise leaves the variable alone during the loop. The following
loops are basically equivalent:
(loop with x = 17 do ...)
(let ((x 17)) (loop do ...))
(loop for x = 17 then x do ...)
Naturally, the variable VAR might be used for some purpose in the
rest of the loop. For example:
(loop for x in my-list with res = nil do (push x res)
finally return res)
This loop inserts the elements of `my-list' at the front of a new
list being accumulated in `res', then returns the list `res' at
the end of the loop. The effect is similar to that of a `collect'
clause, but the list gets reversed by virtue of the fact that
elements are being pushed onto the front of `res' rather than the
If you omit the `=' term, the variable is initialized to `nil'.
(Thus the `= nil' in the above example is unnecessary.)
Bindings made by `with' are sequential by default, as if by
`let*'. Just like `for' clauses, `with' clauses can be linked
with `and' to cause the bindings to be made by `let' instead.
`if CONDITION CLAUSE'
This clause executes the following loop clause only if the
specified condition is true. The following CLAUSE should be an
accumulation, `do', `return', `if', or `unless' clause. Several
clauses may be linked by separating them with `and'. These
clauses may be followed by `else' and a clause or clauses to
execute if the condition was false. The whole construct may
optionally be followed by the word `end' (which may be used to
disambiguate an `else' or `and' in a nested `if').
The actual non-`nil' value of the condition form is available by
the name `it' in the "then" part. For example:
(setq funny-numbers '(6 13 -1))
=> (6 13 -1)
(loop for x below 10
if (oddp x)
collect x into odds
and if (memq x funny-numbers) return (cdr it) end
collect x into evens
finally return (vector odds evens))
=> [(1 3 5 7 9) (0 2 4 6 8)]
(setq funny-numbers '(6 7 13 -1))
=> (6 7 13 -1)
(loop <same thing again>)
=> (13 -1)
Note the use of `and' to put two clauses into the "then" part, one
of which is itself an `if' clause. Note also that `end', while
normally optional, was necessary here to make it clear that the
`else' refers to the outermost `if' clause. In the first case,
the loop returns a vector of lists of the odd and even values of
X. In the second case, the odd number 7 is one of the
`funny-numbers' so the loop returns early; the actual returned
value is based on the result of the `memq' call.
`when CONDITION CLAUSE'
This clause is just a synonym for `if'.
`unless CONDITION CLAUSE'
The `unless' clause is just like `if' except that the sense of the
condition is reversed.
This clause gives a name other than `nil' to the implicit block
surrounding the loop. The NAME is the symbol to be used as the
`initially [do] FORMS...'
This keyword introduces one or more Lisp forms which will be
executed before the loop itself begins (but after any variables
requested by `for' or `with' have been bound to their initial
values). `initially' clauses can appear anywhere; if there are
several, they are executed in the order they appear in the loop.
The keyword `do' is optional.
`finally [do] FORMS...'
This introduces Lisp forms which will be executed after the loop
finishes (say, on request of a `for' or `while'). `initially' and
`finally' clauses may appear anywhere in the loop construct, but
they are executed (in the specified order) at the beginning or
end, respectively, of the loop.
`finally return FORM'
This says that FORM should be executed after the loop is done to
obtain a return value. (Without this, or some other clause like
`collect' or `return', the loop will simply return `nil'.)
Variables bound by `for', `with', or `into' will still contain
their final values when FORM is executed.
The word `do' may be followed by any number of Lisp expressions
which are executed as an implicit `progn' in the body of the loop.
Many of the examples in this section illustrate the use of `do'.
This clause causes the loop to return immediately. The following
Lisp form is evaluated to give the return value of the `loop'
form. The `finally' clauses, if any, are not executed. Of
course, `return' is generally used inside an `if' or `unless', as
its use in a top-level loop clause would mean the loop would never
get to "loop" more than once.
The clause `return FORM' is equivalent to `do (return FORM)' (or
`return-from' if the loop was named). The `return' clause is
implemented a bit more efficiently, though.
While there is no high-level way to add user extensions to `loop'
(comparable to `defsetf' for `setf', say), this package does offer two
properties called `cl-loop-handler' and `cl-loop-for-handler' which are
functions to be called when a given symbol is encountered as a
top-level loop clause or `for' clause, respectively. Consult the
source code in file `cl-macs.el' for details.
This package's `loop' macro is compatible with that of Common Lisp,
except that a few features are not implemented: `loop-finish' and
data-type specifiers. Naturally, the `for' clauses which iterate over
keymaps, overlays, intervals, frames, windows, and buffers are
File: cl, Node: Multiple Values, Prev: Loop Facility, Up: Control Structure
5.8 Multiple Values
Common Lisp functions can return zero or more results. Emacs Lisp
functions, by contrast, always return exactly one result. This package
makes no attempt to emulate Common Lisp multiple return values; Emacs
versions of Common Lisp functions that return more than one value
either return just the first value (as in `compiler-macroexpand') or
return a list of values (as in `get-setf-method'). This package _does_
define placeholders for the Common Lisp functions that work with
multiple values, but in Emacs Lisp these functions simply operate on
lists instead. The `values' form, for example, is a synonym for `list'
-- Special Form: multiple-value-bind (var...) values-form forms...
This form evaluates VALUES-FORM, which must return a list of
values. It then binds the VARs to these respective values, as if
by `let', and then executes the body FORMS. If there are more
VARs than values, the extra VARs are bound to `nil'. If there are
fewer VARs than values, the excess values are ignored.
-- Special Form: multiple-value-setq (var...) form
This form evaluates FORM, which must return a list of values. It
then sets the VARs to these respective values, as if by `setq'.
Extra VARs or values are treated the same as in
The older Quiroz package attempted a more faithful (but still
imperfect) emulation of Common Lisp multiple values. The old method
"usually" simulated true multiple values quite well, but under certain
circumstances would leave spurious return values in memory where a
later, unrelated `multiple-value-bind' form would see them.
Since a perfect emulation is not feasible in Emacs Lisp, this
package opts to keep it as simple and predictable as possible.
File: cl, Node: Macros, Next: Declarations, Prev: Control Structure, Up: Top
This package implements the various Common Lisp features of `defmacro',
such as destructuring, `&environment', and `&body'. Top-level `&whole'
is not implemented for `defmacro' due to technical difficulties. *Note
Destructuring is made available to the user by way of the following
-- Special Form: destructuring-bind arglist expr forms...
This macro expands to code which executes FORMS, with the
variables in ARGLIST bound to the list of values returned by EXPR.
The ARGLIST can include all the features allowed for `defmacro'
argument lists, including destructuring. (The `&environment'
keyword is not allowed.) The macro expansion will signal an error
if EXPR returns a list of the wrong number of arguments or with
incorrect keyword arguments.
This package also includes the Common Lisp `define-compiler-macro'
facility, which allows you to define compile-time expansions and
optimizations for your functions.
-- Special Form: define-compiler-macro name arglist forms...
This form is similar to `defmacro', except that it only expands
calls to NAME at compile-time; calls processed by the Lisp
interpreter are not expanded, nor are they expanded by the
The argument list may begin with a `&whole' keyword and a
variable. This variable is bound to the macro-call form itself,
i.e., to a list of the form `(NAME ARGS...)'. If the macro
expander returns this form unchanged, then the compiler treats it
as a normal function call. This allows compiler macros to work as
optimizers for special cases of a function, leaving complicated
For example, here is a simplified version of a definition that
appears as a standard part of this package:
(define-compiler-macro member* (&whole form a list &rest keys)
(if (and (null keys)
(eq (car-safe a) 'quote)
(not (floatp-safe (cadr a))))
(list 'memq a list)
This definition causes `(member* A LIST)' to change to a call to
the faster `memq' in the common case where A is a
non-floating-point constant; if A is anything else, or if there
are any keyword arguments in the call, then the original `member*'
call is left intact. (The actual compiler macro for `member*'
optimizes a number of other cases, including common `:test'
-- Function: compiler-macroexpand form
This function is analogous to `macroexpand', except that it
expands compiler macros rather than regular macros. It returns
FORM unchanged if it is not a call to a function for which a
compiler macro has been defined, or if that compiler macro decided
to punt by returning its `&whole' argument. Like `macroexpand',
it expands repeatedly until it reaches a form for which no further
expansion is possible.
*Note Macro Bindings::, for descriptions of the `macrolet' and
`symbol-macrolet' forms for making "local" macro definitions.
File: cl, Node: Declarations, Next: Symbols, Prev: Macros, Up: Top
Common Lisp includes a complex and powerful "declaration" mechanism
that allows you to give the compiler special hints about the types of
data that will be stored in particular variables, and about the ways
those variables and functions will be used. This package defines
versions of all the Common Lisp declaration forms: `declare',
`locally', `proclaim', `declaim', and `the'.
Most of the Common Lisp declarations are not currently useful in
Emacs Lisp, as the byte-code system provides little opportunity to
benefit from type information, and `special' declarations are redundant
in a fully dynamically-scoped Lisp. A few declarations are meaningful
when the optimizing byte compiler is being used, however. Under the
earlier non-optimizing compiler, these declarations will effectively be
-- Function: proclaim decl-spec
This function records a "global" declaration specified by
DECL-SPEC. Since `proclaim' is a function, DECL-SPEC is evaluated
and thus should normally be quoted.
-- Special Form: declaim decl-specs...
This macro is like `proclaim', except that it takes any number of
DECL-SPEC arguments, and the arguments are unevaluated and
unquoted. The `declaim' macro also puts an `(eval-when (compile
load eval) ...)' around the declarations so that they will be
registered at compile-time as well as at run-time. (This is vital,
since normally the declarations are meant to influence the way the
compiler treats the rest of the file that contains the `declaim'
-- Special Form: declare decl-specs...
This macro is used to make declarations within functions and other
code. Common Lisp allows declarations in various locations,
generally at the beginning of any of the many "implicit `progn's"
throughout Lisp syntax, such as function bodies, `let' bodies,
etc. Currently the only declaration understood by `declare' is
-- Special Form: locally declarations... forms...
In this package, `locally' is no different from `progn'.
-- Special Form: the type form
Type information provided by `the' is ignored in this package; in
other words, `(the TYPE FORM)' is equivalent to FORM. Future
versions of the optimizing byte-compiler may make use of this
For example, `mapcar' can map over both lists and arrays. It is
hard for the compiler to expand `mapcar' into an in-line loop
unless it knows whether the sequence will be a list or an array
ahead of time. With `(mapcar 'car (the vector foo))', a future
compiler would have enough information to expand the loop in-line.
For now, Emacs Lisp will treat the above code as exactly equivalent
to `(mapcar 'car foo)'.
Each DECL-SPEC in a `proclaim', `declaim', or `declare' should be a
list beginning with a symbol that says what kind of declaration it is.
This package currently understands `special', `inline', `notinline',
`optimize', and `warn' declarations. (The `warn' declaration is an
extension of standard Common Lisp.) Other Common Lisp declarations,
such as `type' and `ftype', are silently ignored.
Since all variables in Emacs Lisp are "special" (in the Common
Lisp sense), `special' declarations are only advisory. They
simply tell the optimizing byte compiler that the specified
variables are intentionally being referred to without being bound
in the body of the function. The compiler normally emits warnings
for such references, since they could be typographical errors for
references to local variables.
The declaration `(declare (special VAR1 VAR2))' is equivalent to
`(defvar VAR1) (defvar VAR2)' in the optimizing compiler, or to
nothing at all in older compilers (which do not warn for non-local
In top-level contexts, it is generally better to write `(defvar
VAR)' than `(declaim (special VAR))', since `defvar' makes your
intentions clearer. But the older byte compilers can not handle
`defvar's appearing inside of functions, while `(declare (special
VAR))' takes care to work correctly with all compilers.
The `inline' DECL-SPEC lists one or more functions whose bodies
should be expanded "in-line" into calling functions whenever the
compiler is able to arrange for it. For example, the Common Lisp
function `cadr' is declared `inline' by this package so that the
form `(cadr X)' will expand directly into `(car (cdr X))' when it
is called in user functions, for a savings of one (relatively
expensive) function call.
The following declarations are all equivalent. Note that the
`defsubst' form is a convenient way to define a function and
declare it inline all at once.
(declaim (inline foo bar))
(eval-when (compile load eval) (proclaim '(inline foo bar)))
(defsubst foo (...) ...) ; instead of defun
*Please note:* this declaration remains in effect after the
containing source file is done. It is correct to use it to
request that a function you have defined should be inlined, but it
is impolite to use it to request inlining of an external function.
In Common Lisp, it is possible to use `(declare (inline ...))'
before a particular call to a function to cause just that call to
be inlined; the current byte compilers provide no way to implement
this, so `(declare (inline ...))' is currently ignored by this
The `notinline' declaration lists functions which should not be
inlined after all; it cancels a previous `inline' declaration.
This declaration controls how much optimization is performed by
the compiler. Naturally, it is ignored by the earlier
The word `optimize' is followed by any number of lists like
`(speed 3)' or `(safety 2)'. Common Lisp defines several
optimization "qualities"; this package ignores all but `speed' and
`safety'. The value of a quality should be an integer from 0 to
3, with 0 meaning "unimportant" and 3 meaning "very important."
The default level for both qualities is 1.
In this package, with the optimizing compiler, the `speed' quality
is tied to the `byte-compile-optimize' flag, which is set to `nil'
for `(speed 0)' and to `t' for higher settings; and the `safety'
quality is tied to the `byte-compile-delete-errors' flag, which is
set to `t' for `(safety 3)' and to `nil' for all lower settings.
(The latter flag controls whether the compiler is allowed to
optimize out code whose only side-effect could be to signal an
error, e.g., rewriting `(progn foo bar)' to `bar' when it is not
known whether `foo' will be bound at run-time.)
Note that even compiling with `(safety 0)', the Emacs byte-code
system provides sufficient checking to prevent real harm from
being done. For example, barring serious bugs in Emacs itself,
Emacs will not crash with a segmentation fault just because of an
error in a fully-optimized Lisp program.
The `optimize' declaration is normally used in a top-level
`proclaim' or `declaim' in a file; Common Lisp allows it to be
used with `declare' to set the level of optimization locally for a
given form, but this will not work correctly with the current
version of the optimizing compiler. (The `declare' will set the
new optimization level, but that level will not automatically be
unset after the enclosing form is done.)
This declaration controls what sorts of warnings are generated by
the byte compiler. Again, only the optimizing compiler generates
warnings. The word `warn' is followed by any number of "warning
qualities," similar in form to optimization qualities. The
currently supported warning types are `redefine', `callargs',
`unresolved', and `free-vars'; in the current system, a value of 0
will disable these warnings and any higher value will enable them.
See the documentation for the optimizing byte compiler for details.
File: cl, Node: Symbols, Next: Numbers, Prev: Declarations, Up: Top
This package defines several symbol-related features that were missing
from Emacs Lisp.
* Property Lists:: `get*', `remprop', `getf', `remf'
* Creating Symbols:: `gensym', `gentemp'
File: cl, Node: Property Lists, Next: Creating Symbols, Prev: Symbols, Up: Symbols
8.1 Property Lists
These functions augment the standard Emacs Lisp functions `get' and
`put' for operating on properties attached to symbols. There are also
functions for working with property lists as first-class data
structures not attached to particular symbols.
-- Function: get* symbol property &optional default
This function is like `get', except that if the property is not
found, the DEFAULT argument provides the return value. (The Emacs
Lisp `get' function always uses `nil' as the default; this
package's `get*' is equivalent to Common Lisp's `get'.)
The `get*' function is `setf'-able; when used in this fashion, the
DEFAULT argument is allowed but ignored.
-- Function: remprop symbol property
This function removes the entry for PROPERTY from the property
list of SYMBOL. It returns a true value if the property was
indeed found and removed, or `nil' if there was no such property.
(This function was probably omitted from Emacs originally because,
since `get' did not allow a DEFAULT, it was very difficult to
distinguish between a missing property and a property whose value
was `nil'; thus, setting a property to `nil' was close enough to
`remprop' for most purposes.)
-- Function: getf place property &optional default
This function scans the list PLACE as if it were a property list,
i.e., a list of alternating property names and values. If an
even-numbered element of PLACE is found which is `eq' to PROPERTY,
the following odd-numbered element is returned. Otherwise,
DEFAULT is returned (or `nil' if no default is given).
(get sym prop) == (getf (symbol-plist sym) prop)
It is valid to use `getf' as a `setf' place, in which case its
PLACE argument must itself be a valid `setf' place. The DEFAULT
argument, if any, is ignored in this context. The effect is to
change (via `setcar') the value cell in the list that corresponds
to PROPERTY, or to cons a new property-value pair onto the list if
the property is not yet present.
(put sym prop val) == (setf (getf (symbol-plist sym) prop) val)
The `get' and `get*' functions are also `setf'-able. The fact
that `default' is ignored can sometimes be useful:
(incf (get* 'foo 'usage-count 0))
Here, symbol `foo''s `usage-count' property is incremented if it
exists, or set to 1 (an incremented 0) otherwise.
When not used as a `setf' form, `getf' is just a regular function
and its PLACE argument can actually be any Lisp expression.
-- Special Form: remf place property
This macro removes the property-value pair for PROPERTY from the
property list stored at PLACE, which is any `setf'-able place
expression. It returns true if the property was found. Note that
if PROPERTY happens to be first on the list, this will effectively
do a `(setf PLACE (cddr PLACE))', whereas if it occurs later, this
simply uses `setcdr' to splice out the property and value cells.
File: cl, Node: Creating Symbols, Prev: Property Lists, Up: Symbols
8.2 Creating Symbols
These functions create unique symbols, typically for use as temporary
-- Function: gensym &optional x
This function creates a new, uninterned symbol (using
`make-symbol') with a unique name. (The name of an uninterned
symbol is relevant only if the symbol is printed.) By default,
the name is generated from an increasing sequence of numbers,
`G1000', `G1001', `G1002', etc. If the optional argument X is a
string, that string is used as a prefix instead of `G'.
Uninterned symbols are used in macro expansions for temporary
variables, to ensure that their names will not conflict with
"real" variables in the user's code.
-- Variable: *gensym-counter*
This variable holds the counter used to generate `gensym' names.
It is incremented after each use by `gensym'. In Common Lisp this
is initialized with 0, but this package initializes it with a
random (time-dependent) value to avoid trouble when two files that
each used `gensym' in their compilation are loaded together.
(Uninterned symbols become interned when the compiler writes them
out to a file and the Emacs loader loads them, so their names have
to be treated a bit more carefully than in Common Lisp where
uninterned symbols remain uninterned after loading.)
-- Function: gentemp &optional x
This function is like `gensym', except that it produces a new
_interned_ symbol. If the symbol that is generated already
exists, the function keeps incrementing the counter and trying
again until a new symbol is generated.
The Quiroz `cl.el' package also defined a `defkeyword' form for
creating self-quoting keyword symbols. This package automatically
creates all keywords that are called for by `&key' argument specifiers,
and discourages the use of keywords as data unrelated to keyword
arguments, so the `defkeyword' form has been discontinued.
File: cl, Node: Numbers, Next: Sequences, Prev: Symbols, Up: Top
This section defines a few simple Common Lisp operations on numbers
which were left out of Emacs Lisp.
* Predicates on Numbers:: `plusp', `oddp', `floatp-safe', etc.
* Numerical Functions:: `abs', `floor*', etc.
* Random Numbers:: `random*', `make-random-state'
* Implementation Parameters:: `most-positive-float'
File: cl, Node: Predicates on Numbers, Next: Numerical Functions, Prev: Numbers, Up: Numbers
9.1 Predicates on Numbers
These functions return `t' if the specified condition is true of the
numerical argument, or `nil' otherwise.
-- Function: plusp number
This predicate tests whether NUMBER is positive. It is an error
if the argument is not a number.
-- Function: minusp number
This predicate tests whether NUMBER is negative. It is an error
if the argument is not a number.
-- Function: oddp integer
This predicate tests whether INTEGER is odd. It is an error if
the argument is not an integer.
-- Function: evenp integer
This predicate tests whether INTEGER is even. It is an error if
the argument is not an integer.
-- Function: floatp-safe object
This predicate tests whether OBJECT is a floating-point number.
On systems that support floating-point, this is equivalent to
`floatp'. On other systems, this always returns `nil'.
File: cl, Node: Numerical Functions, Next: Random Numbers, Prev: Predicates on Numbers, Up: Numbers
9.2 Numerical Functions
These functions perform various arithmetic operations on numbers.
-- Function: gcd &rest integers
This function returns the Greatest Common Divisor of the arguments.
For one argument, it returns the absolute value of that argument.
For zero arguments, it returns zero.
-- Function: lcm &rest integers
This function returns the Least Common Multiple of the arguments.
For one argument, it returns the absolute value of that argument.
For zero arguments, it returns one.
-- Function: isqrt integer
This function computes the "integer square root" of its integer
argument, i.e., the greatest integer less than or equal to the true
square root of the argument.
-- Function: floor* number &optional divisor
This function implements the Common Lisp `floor' function. It is
called `floor*' to avoid name conflicts with the simpler `floor'
function built-in to Emacs.
With one argument, `floor*' returns a list of two numbers: The
argument rounded down (toward minus infinity) to an integer, and
the "remainder" which would have to be added back to the first
return value to yield the argument again. If the argument is an
integer X, the result is always the list `(X 0)'. If the argument
is a floating-point number, the first result is a Lisp integer and
the second is a Lisp float between 0 (inclusive) and 1 (exclusive).
With two arguments, `floor*' divides NUMBER by DIVISOR, and
returns the floor of the quotient and the corresponding remainder
as a list of two numbers. If `(floor* X Y)' returns `(Q R)', then
`Q*Y + R = X', with R between 0 (inclusive) and R (exclusive).
Also, note that `(floor* X)' is exactly equivalent to `(floor* X
This function is entirely compatible with Common Lisp's `floor'
function, except that it returns the two results in a list since
Emacs Lisp does not support multiple-valued functions.
-- Function: ceiling* number &optional divisor
This function implements the Common Lisp `ceiling' function, which
is analogous to `floor' except that it rounds the argument or
quotient of the arguments up toward plus infinity. The remainder
will be between 0 and minus R.
-- Function: truncate* number &optional divisor
This function implements the Common Lisp `truncate' function,
which is analogous to `floor' except that it rounds the argument
or quotient of the arguments toward zero. Thus it is equivalent
to `floor*' if the argument or quotient is positive, or to
`ceiling*' otherwise. The remainder has the same sign as NUMBER.
-- Function: round* number &optional divisor
This function implements the Common Lisp `round' function, which
is analogous to `floor' except that it rounds the argument or
quotient of the arguments to the nearest integer. In the case of
a tie (the argument or quotient is exactly halfway between two
integers), it rounds to the even integer.
-- Function: mod* number divisor
This function returns the same value as the second return value of
-- Function: rem* number divisor
This function returns the same value as the second return value of
These definitions are compatible with those in the Quiroz `cl.el'
package, except that this package appends `*' to certain function names
to avoid conflicts with existing Emacs functions, and that the
mechanism for returning multiple values is different.
File: cl, Node: Random Numbers, Next: Implementation Parameters, Prev: Numerical Functions, Up: Numbers
9.3 Random Numbers
This package also provides an implementation of the Common Lisp random
number generator. It uses its own additive-congruential algorithm,
which is much more likely to give statistically clean random numbers
than the simple generators supplied by many operating systems.
-- Function: random* number &optional state
This function returns a random nonnegative number less than
NUMBER, and of the same type (either integer or floating-point).
The STATE argument should be a `random-state' object which holds
the state of the random number generator. The function modifies
this state object as a side effect. If STATE is omitted, it
defaults to the variable `*random-state*', which contains a
pre-initialized `random-state' object.
-- Variable: *random-state*
This variable contains the system "default" `random-state' object,
used for calls to `random*' that do not specify an alternative
state object. Since any number of programs in the Emacs process
may be accessing `*random-state*' in interleaved fashion, the
sequence generated from this variable will be irreproducible for
all intents and purposes.
-- Function: make-random-state &optional state
This function creates or copies a `random-state' object. If STATE
is omitted or `nil', it returns a new copy of `*random-state*'.
This is a copy in the sense that future sequences of calls to
`(random* N)' and `(random* N S)' (where S is the new random-state
object) will return identical sequences of random numbers.
If STATE is a `random-state' object, this function returns a copy
of that object. If STATE is `t', this function returns a new
`random-state' object seeded from the date and time. As an
extension to Common Lisp, STATE may also be an integer in which
case the new object is seeded from that integer; each different
integer seed will result in a completely different sequence of
It is valid to print a `random-state' object to a buffer or file
and later read it back with `read'. If a program wishes to use a
sequence of pseudo-random numbers which can be reproduced later
for debugging, it can call `(make-random-state t)' to get a new
sequence, then print this sequence to a file. When the program is
later rerun, it can read the original run's random-state from the
-- Function: random-state-p object
This predicate returns `t' if OBJECT is a `random-state' object,
or `nil' otherwise.
File: cl, Node: Implementation Parameters, Prev: Random Numbers, Up: Numbers
9.4 Implementation Parameters
This package defines several useful constants having to with numbers.
The following parameters have to do with floating-point numbers.
This package determines their values by exercising the computer's
floating-point arithmetic in various ways. Because this operation
might be slow, the code for initializing them is kept in a separate
function that must be called before the parameters can be used.
-- Function: cl-float-limits
This function makes sure that the Common Lisp floating-point
parameters like `most-positive-float' have been initialized.
Until it is called, these parameters will be `nil'. If this
version of Emacs does not support floats, the parameters will
remain `nil'. If the parameters have already been initialized,
the function returns immediately.
The algorithm makes assumptions that will be valid for most modern
machines, but will fail if the machine's arithmetic is extremely
unusual, e.g., decimal.
Since true Common Lisp supports up to four different floating-point
precisions, it has families of constants like
`most-positive-long-float', and so on. Emacs has only one
floating-point precision, so this package omits the precision word from
the constants' names.
-- Variable: most-positive-float
This constant equals the largest value a Lisp float can hold. For
those systems whose arithmetic supports infinities, this is the
largest _finite_ value. For IEEE machines, the value is
-- Variable: most-negative-float
This constant equals the most-negative value a Lisp float can hold.
(It is assumed to be equal to `(- most-positive-float)'.)
-- Variable: least-positive-float
This constant equals the smallest Lisp float value greater than
zero. For IEEE machines, it is about `4.94e-324' if denormals are
supported or `2.22e-308' if not.
-- Variable: least-positive-normalized-float
This constant equals the smallest _normalized_ Lisp float greater
than zero, i.e., the smallest value for which IEEE denormalization
will not result in a loss of precision. For IEEE machines, this
value is about `2.22e-308'. For machines that do not support the
concept of denormalization and gradual underflow, this constant
will always equal `least-positive-float'.
-- Variable: least-negative-float
This constant is the negative counterpart of
-- Variable: least-negative-normalized-float
This constant is the negative counterpart of
-- Variable: float-epsilon
This constant is the smallest positive Lisp float that can be added
to 1.0 to produce a distinct value. Adding a smaller number to 1.0
will yield 1.0 again due to roundoff. For IEEE machines, epsilon
is about `2.22e-16'.
-- Variable: float-negative-epsilon
This is the smallest positive value that can be subtracted from
1.0 to produce a distinct value. For IEEE machines, it is about
File: cl, Node: Sequences, Next: Lists, Prev: Numbers, Up: Top
Common Lisp defines a number of functions that operate on "sequences",
which are either lists, strings, or vectors. Emacs Lisp includes a few
of these, notably `elt' and `length'; this package defines most of the
* Sequence Basics:: Arguments shared by all sequence functions
* Mapping over Sequences:: `mapcar*', `mapcan', `map', `every', etc.
* Sequence Functions:: `subseq', `remove*', `substitute', etc.
* Searching Sequences:: `find', `position', `count', `search', etc.
* Sorting Sequences:: `sort*', `stable-sort', `merge'
File: cl, Node: Sequence Basics, Next: Mapping over Sequences, Prev: Sequences, Up: Sequences
10.1 Sequence Basics
Many of the sequence functions take keyword arguments; *note Argument
Lists::. All keyword arguments are optional and, if specified, may
appear in any order.
The `:key' argument should be passed either `nil', or a function of
one argument. This key function is used as a filter through which the
elements of the sequence are seen; for example, `(find x y :key 'car)'
is similar to `(assoc* x y)': It searches for an element of the list
whose `car' equals `x', rather than for an element which equals `x'
itself. If `:key' is omitted or `nil', the filter is effectively the
The `:test' and `:test-not' arguments should be either `nil', or
functions of two arguments. The test function is used to compare two
sequence elements, or to compare a search value with sequence elements.
(The two values are passed to the test function in the same order as
the original sequence function arguments from which they are derived,
or, if they both come from the same sequence, in the same order as they
appear in that sequence.) The `:test' argument specifies a function
which must return true (non-`nil') to indicate a match; instead, you
may use `:test-not' to give a function which returns _false_ to
indicate a match. The default test function is `eql'.
Many functions which take ITEM and `:test' or `:test-not' arguments
also come in `-if' and `-if-not' varieties, where a PREDICATE function
is passed instead of ITEM, and sequence elements match if the predicate
returns true on them (or false in the case of `-if-not'). For example:
(remove* 0 seq :test '=) == (remove-if 'zerop seq)
to remove all zeros from sequence `seq'.
Some operations can work on a subsequence of the argument sequence;
these function take `:start' and `:end' arguments which default to zero
and the length of the sequence, respectively. Only elements between
START (inclusive) and END (exclusive) are affected by the operation.
The END argument may be passed `nil' to signify the length of the
sequence; otherwise, both START and END must be integers, with `0 <=
START <= END <= (length SEQ)'. If the function takes two sequence
arguments, the limits are defined by keywords `:start1' and `:end1' for
the first, and `:start2' and `:end2' for the second.
A few functions accept a `:from-end' argument, which, if non-`nil',
causes the operation to go from right-to-left through the sequence
instead of left-to-right, and a `:count' argument, which specifies an
integer maximum number of elements to be removed or otherwise processed.
The sequence functions make no guarantees about the order in which
the `:test', `:test-not', and `:key' functions are called on various
elements. Therefore, it is a bad idea to depend on side effects of
these functions. For example, `:from-end' may cause the sequence to be
scanned actually in reverse, or it may be scanned forwards but
computing a result "as if" it were scanned backwards. (Some functions,
like `mapcar*' and `every', _do_ specify exactly the order in which the
function is called so side effects are perfectly acceptable in those
Strings may contain "text properties" as well as character data.
Except as noted, it is undefined whether or not text properties are
preserved by sequence functions. For example, `(remove* ?A STR)' may
or may not preserve the properties of the characters copied from STR
into the result.
File: cl, Node: Mapping over Sequences, Next: Sequence Functions, Prev: Sequence Basics, Up: Sequences
10.2 Mapping over Sequences
These functions "map" the function you specify over the elements of
lists or arrays. They are all variations on the theme of the built-in
-- Function: mapcar* function seq &rest more-seqs
This function calls FUNCTION on successive parallel sets of
elements from its argument sequences. Given a single SEQ argument
it is equivalent to `mapcar'; given N sequences, it calls the
function with the first elements of each of the sequences as the N
arguments to yield the first element of the result list, then with
the second elements, and so on. The mapping stops as soon as the
shortest sequence runs out. The argument sequences may be any
mixture of lists, strings, and vectors; the return sequence is
always a list.
Common Lisp's `mapcar' accepts multiple arguments but works only
on lists; Emacs Lisp's `mapcar' accepts a single sequence
argument. This package's `mapcar*' works as a compatible superset
-- Function: map result-type function seq &rest more-seqs
This function maps FUNCTION over the argument sequences, just like
`mapcar*', but it returns a sequence of type RESULT-TYPE rather
than a list. RESULT-TYPE must be one of the following symbols:
`vector', `string', `list' (in which case the effect is the same
as for `mapcar*'), or `nil' (in which case the results are thrown
away and `map' returns `nil').
-- Function: maplist function list &rest more-lists
This function calls FUNCTION on each of its argument lists, then
on the `cdr's of those lists, and so on, until the shortest list
runs out. The results are returned in the form of a list. Thus,
`maplist' is like `mapcar*' except that it passes in the list
pointers themselves rather than the `car's of the advancing
-- Function: mapc function seq &rest more-seqs
This function is like `mapcar*', except that the values returned
by FUNCTION are ignored and thrown away rather than being
collected into a list. The return value of `mapc' is SEQ, the
first sequence. This function is more general than the Emacs
-- Function: mapl function list &rest more-lists
This function is like `maplist', except that it throws away the
values returned by FUNCTION.
-- Function: mapcan function seq &rest more-seqs
This function is like `mapcar*', except that it concatenates the
return values (which must be lists) using `nconc', rather than
simply collecting them into a list.
-- Function: mapcon function list &rest more-lists
This function is like `maplist', except that it concatenates the
return values using `nconc'.
-- Function: some predicate seq &rest more-seqs
This function calls PREDICATE on each element of SEQ in turn; if
PREDICATE returns a non-`nil' value, `some' returns that value,
otherwise it returns `nil'. Given several sequence arguments, it
steps through the sequences in parallel until the shortest one
runs out, just as in `mapcar*'. You can rely on the left-to-right
order in which the elements are visited, and on the fact that
mapping stops immediately as soon as PREDICATE returns non-`nil'.
-- Function: every predicate seq &rest more-seqs
This function calls PREDICATE on each element of the sequence(s)
in turn; it returns `nil' as soon as PREDICATE returns `nil' for
any element, or `t' if the predicate was true for all elements.
-- Function: notany predicate seq &rest more-seqs
This function calls PREDICATE on each element of the sequence(s)
in turn; it returns `nil' as soon as PREDICATE returns a non-`nil'
value for any element, or `t' if the predicate was `nil' for all
-- Function: notevery predicate seq &rest more-seqs
This function calls PREDICATE on each element of the sequence(s)
in turn; it returns a non-`nil' value as soon as PREDICATE returns
`nil' for any element, or `t' if the predicate was true for all
-- Function: reduce function seq &key :from-end :start :end
This function combines the elements of SEQ using an associative
binary operation. Suppose FUNCTION is `*' and SEQ is the list `(2
3 4 5)'. The first two elements of the list are combined with `(*
2 3) = 6'; this is combined with the next element, `(* 6 4) = 24',
and that is combined with the final element: `(* 24 5) = 120'.
Note that the `*' function happens to be self-reducing, so that
`(* 2 3 4 5)' has the same effect as an explicit call to `reduce'.
If `:from-end' is true, the reduction is right-associative instead
(reduce '- '(1 2 3 4))
== (- (- (- 1 2) 3) 4) => -8
(reduce '- '(1 2 3 4) :from-end t)
== (- 1 (- 2 (- 3 4))) => -2
If `:key' is specified, it is a function of one argument which is
called on each of the sequence elements in turn.
If `:initial-value' is specified, it is effectively added to the
front (or rear in the case of `:from-end') of the sequence. The
`:key' function is _not_ applied to the initial value.
If the sequence, including the initial value, has exactly one
element then that element is returned without ever calling
FUNCTION. If the sequence is empty (and there is no initial
value), then FUNCTION is called with no arguments to obtain the
All of these mapping operations can be expressed conveniently in
terms of the `loop' macro. In compiled code, `loop' will be faster
since it generates the loop as in-line code with no function calls.
File: cl, Node: Sequence Functions, Next: Searching Sequences, Prev: Mapping over Sequences, Up: Sequences
10.3 Sequence Functions
This section describes a number of Common Lisp functions for operating
-- Function: subseq sequence start &optional end
This function returns a given subsequence of the argument
SEQUENCE, which may be a list, string, or vector. The indices
START and END must be in range, and START must be no greater than
END. If END is omitted, it defaults to the length of the
sequence. The return value is always a copy; it does not share
structure with SEQUENCE.
As an extension to Common Lisp, START and/or END may be negative,
in which case they represent a distance back from the end of the
sequence. This is for compatibility with Emacs' `substring'
function. Note that `subseq' is the _only_ sequence function that
allows negative START and END.
You can use `setf' on a `subseq' form to replace a specified range
of elements with elements from another sequence. The replacement
is done as if by `replace', described below.
-- Function: concatenate result-type &rest seqs
This function concatenates the argument sequences together to form
a result sequence of type RESULT-TYPE, one of the symbols
`vector', `string', or `list'. The arguments are always copied,
even in cases such as `(concatenate 'list '(1 2 3))' where the
result is identical to an argument.
-- Function: fill seq item &key :start :end
This function fills the elements of the sequence (or the specified
part of the sequence) with the value ITEM.
-- Function: replace seq1 seq2 &key :start1 :end1 :start2 :end2
This function copies part of SEQ2 into part of SEQ1. The sequence
SEQ1 is not stretched or resized; the amount of data copied is
simply the shorter of the source and destination (sub)sequences.
The function returns SEQ1.
If SEQ1 and SEQ2 are `eq', then the replacement will work
correctly even if the regions indicated by the start and end
arguments overlap. However, if SEQ1 and SEQ2 are lists which
share storage but are not `eq', and the start and end arguments
specify overlapping regions, the effect is undefined.
-- Function: remove* item seq &key :test :test-not :key :count :start
This returns a copy of SEQ with all elements matching ITEM
removed. The result may share storage with or be `eq' to SEQ in
some circumstances, but the original SEQ will not be modified.
The `:test', `:test-not', and `:key' arguments define the matching
test that is used; by default, elements `eql' to ITEM are removed.
The `:count' argument specifies the maximum number of matching
elements that can be removed (only the leftmost COUNT matches are
removed). The `:start' and `:end' arguments specify a region in
SEQ in which elements will be removed; elements outside that
region are not matched or removed. The `:from-end' argument, if
true, says that elements should be deleted from the end of the
sequence rather than the beginning (this matters only if COUNT was
-- Function: delete* item seq &key :test :test-not :key :count :start
This deletes all elements of SEQ which match ITEM. It is a
destructive operation. Since Emacs Lisp does not support
stretchable strings or vectors, this is the same as `remove*' for
those sequence types. On lists, `remove*' will copy the list if
necessary to preserve the original list, whereas `delete*' will
splice out parts of the argument list. Compare `append' and
`nconc', which are analogous non-destructive and destructive list
operations in Emacs Lisp.
The predicate-oriented functions `remove-if', `remove-if-not',
`delete-if', and `delete-if-not' are defined similarly.
-- Function: remove-duplicates seq &key :test :test-not :key :start
This function returns a copy of SEQ with duplicate elements
removed. Specifically, if two elements from the sequence match
according to the `:test', `:test-not', and `:key' arguments, only
the rightmost one is retained. If `:from-end' is true, the
leftmost one is retained instead. If `:start' or `:end' is
specified, only elements within that subsequence are examined or
-- Function: delete-duplicates seq &key :test :test-not :key :start
This function deletes duplicate elements from SEQ. It is a
destructive version of `remove-duplicates'.
-- Function: substitute new old seq &key :test :test-not :key :count
:start :end :from-end
This function returns a copy of SEQ, with all elements matching
OLD replaced with NEW. The `:count', `:start', `:end', and
`:from-end' arguments may be used to limit the number of
-- Function: nsubstitute new old seq &key :test :test-not :key :count
:start :end :from-end
This is a destructive version of `substitute'; it performs the
substitution using `setcar' or `aset' rather than by returning a
changed copy of the sequence.
The `substitute-if', `substitute-if-not', `nsubstitute-if', and
`nsubstitute-if-not' functions are defined similarly. For these, a
PREDICATE is given in place of the OLD argument.
File: cl, Node: Searching Sequences, Next: Sorting Sequences, Prev: Sequence Functions, Up: Sequences
10.4 Searching Sequences
These functions search for elements or subsequences in a sequence.
(See also `member*' and `assoc*'; *note Lists::.)
-- Function: find item seq &key :test :test-not :key :start :end
This function searches SEQ for an element matching ITEM. If it
finds a match, it returns the matching element. Otherwise, it
returns `nil'. It returns the leftmost match, unless `:from-end'
is true, in which case it returns the rightmost match. The
`:start' and `:end' arguments may be used to limit the range of
elements that are searched.
-- Function: position item seq &key :test :test-not :key :start :end
This function is like `find', except that it returns the integer
position in the sequence of the matching item rather than the item
itself. The position is relative to the start of the sequence as
a whole, even if `:start' is non-zero. The function returns `nil'
if no matching element was found.
-- Function: count item seq &key :test :test-not :key :start :end
This function returns the number of elements of SEQ which match
ITEM. The result is always a nonnegative integer.
The `find-if', `find-if-not', `position-if', `position-if-not',
`count-if', and `count-if-not' functions are defined similarly.
-- Function: mismatch seq1 seq2 &key :test :test-not :key :start1
:end1 :start2 :end2 :from-end
This function compares the specified parts of SEQ1 and SEQ2. If
they are the same length and the corresponding elements match
(according to `:test', `:test-not', and `:key'), the function
returns `nil'. If there is a mismatch, the function returns the
index (relative to SEQ1) of the first mismatching element. This
will be the leftmost pair of elements which do not match, or the
position at which the shorter of the two otherwise-matching
sequences runs out.
If `:from-end' is true, then the elements are compared from right
to left starting at `(1- END1)' and `(1- END2)'. If the sequences
differ, then one plus the index of the rightmost difference
(relative to SEQ1) is returned.
An interesting example is `(mismatch str1 str2 :key 'upcase)',
which compares two strings case-insensitively.
-- Function: search seq1 seq2 &key :test :test-not :key :from-end
:start1 :end1 :start2 :end2
This function searches SEQ2 for a subsequence that matches SEQ1
(or part of it specified by `:start1' and `:end1'.) Only matches
which fall entirely within the region defined by `:start2' and
`:end2' will be considered. The return value is the index of the
leftmost element of the leftmost match, relative to the start of
SEQ2, or `nil' if no matches were found. If `:from-end' is true,
the function finds the _rightmost_ matching subsequence.
File: cl, Node: Sorting Sequences, Prev: Searching Sequences, Up: Sequences
10.5 Sorting Sequences
-- Function: sort* seq predicate &key :key
This function sorts SEQ into increasing order as determined by
using PREDICATE to compare pairs of elements. PREDICATE should
return true (non-`nil') if and only if its first argument is less
than (not equal to) its second argument. For example, `<' and
`string-lessp' are suitable predicate functions for sorting
numbers and strings, respectively; `>' would sort numbers into
decreasing rather than increasing order.
This function differs from Emacs' built-in `sort' in that it can
operate on any type of sequence, not just lists. Also, it accepts
a `:key' argument which is used to preprocess data fed to the
PREDICATE function. For example,
(setq data (sort* data 'string-lessp :key 'downcase))
sorts DATA, a sequence of strings, into increasing alphabetical
order without regard to case. A `:key' function of `car' would be
useful for sorting association lists. It should only be a simple
accessor though, it's used heavily in the current implementation.
The `sort*' function is destructive; it sorts lists by actually
rearranging the `cdr' pointers in suitable fashion.
-- Function: stable-sort seq predicate &key :key
This function sorts SEQ "stably", meaning two elements which are
equal in terms of PREDICATE are guaranteed not to be rearranged
out of their original order by the sort.
In practice, `sort*' and `stable-sort' are equivalent in Emacs
Lisp because the underlying `sort' function is stable by default.
However, this package reserves the right to use non-stable methods
for `sort*' in the future.
-- Function: merge type seq1 seq2 predicate &key :key
This function merges two sequences SEQ1 and SEQ2 by interleaving
their elements. The result sequence, of type TYPE (in the sense
of `concatenate'), has length equal to the sum of the lengths of
the two input sequences. The sequences may be modified
destructively. Order of elements within SEQ1 and SEQ2 is
preserved in the interleaving; elements of the two sequences are
compared by PREDICATE (in the sense of `sort') and the lesser
element goes first in the result. When elements are equal, those
from SEQ1 precede those from SEQ2 in the result. Thus, if SEQ1
and SEQ2 are both sorted according to PREDICATE, then the result
will be a merged sequence which is (stably) sorted according to
File: cl, Node: Lists, Next: Structures, Prev: Sequences, Up: Top
The functions described here operate on lists.
* List Functions:: `caddr', `first', `list*', etc.
* Substitution of Expressions:: `subst', `sublis', etc.
* Lists as Sets:: `member*', `adjoin', `union', etc.
* Association Lists:: `assoc*', `rassoc*', `acons', `pairlis'
File: cl, Node: List Functions, Next: Substitution of Expressions, Prev: Lists, Up: Lists
11.1 List Functions
This section describes a number of simple operations on lists, i.e.,
chains of cons cells.
-- Function: caddr x
This function is equivalent to `(car (cdr (cdr X)))'. Likewise,
this package defines all 28 `cXXXr' functions where XXX is up to
four `a's and/or `d's. All of these functions are `setf'-able,
and calls to them are expanded inline by the byte-compiler for
-- Function: first x
This function is a synonym for `(car X)'. Likewise, the functions
`second', `third', ..., through `tenth' return the given element
of the list X.
-- Function: rest x
This function is a synonym for `(cdr X)'.
-- Function: endp x
Common Lisp defines this function to act like `null', but
signaling an error if `x' is neither a `nil' nor a cons cell.
This package simply defines `endp' as a synonym for `null'.
-- Function: list-length x
This function returns the length of list X, exactly like `(length
X)', except that if X is a circular list (where the cdr-chain
forms a loop rather than terminating with `nil'), this function
returns `nil'. (The regular `length' function would get stuck if
given a circular list.)
-- Function: list* arg &rest others
This function constructs a list of its arguments. The final
argument becomes the `cdr' of the last cell constructed. Thus,
`(list* A B C)' is equivalent to `(cons A (cons B C))', and
`(list* A B nil)' is equivalent to `(list A B)'.
(Note that this function really is called `list*' in Common Lisp;
it is not a name invented for this package like `member*' or
-- Function: ldiff list sublist
If SUBLIST is a sublist of LIST, i.e., is `eq' to one of the cons
cells of LIST, then this function returns a copy of the part of
LIST up to but not including SUBLIST. For example, `(ldiff x
(cddr x))' returns the first two elements of the list `x'. The
result is a copy; the original LIST is not modified. If SUBLIST
is not a sublist of LIST, a copy of the entire LIST is returned.
-- Function: copy-list list
This function returns a copy of the list LIST. It copies dotted
lists like `(1 2 . 3)' correctly.
-- Function: copy-tree x &optional vecp
This function returns a copy of the tree of cons cells X. Unlike
`copy-sequence' (and its alias `copy-list'), which copies only
along the `cdr' direction, this function copies (recursively)
along both the `car' and the `cdr' directions. If X is not a cons
cell, the function simply returns X unchanged. If the optional
VECP argument is true, this function copies vectors (recursively)
as well as cons cells.
-- Function: tree-equal x y &key :test :test-not :key
This function compares two trees of cons cells. If X and Y are
both cons cells, their `car's and `cdr's are compared recursively.
If neither X nor Y is a cons cell, they are compared by `eql', or
according to the specified test. The `:key' function, if
specified, is applied to the elements of both trees. *Note
File: cl, Node: Substitution of Expressions, Next: Lists as Sets, Prev: List Functions, Up: Lists
11.2 Substitution of Expressions
These functions substitute elements throughout a tree of cons cells.
(*Note Sequence Functions::, for the `substitute' function, which works
on just the top-level elements of a list.)
-- Function: subst new old tree &key :test :test-not :key
This function substitutes occurrences of OLD with NEW in TREE, a
tree of cons cells. It returns a substituted tree, which will be
a copy except that it may share storage with the argument TREE in
parts where no substitutions occurred. The original TREE is not
modified. This function recurses on, and compares against OLD,
both `car's and `cdr's of the component cons cells. If OLD is
itself a cons cell, then matching cells in the tree are
substituted as usual without recursively substituting in that
cell. Comparisons with OLD are done according to the specified
test (`eql' by default). The `:key' function is applied to the
elements of the tree but not to OLD.
-- Function: nsubst new old tree &key :test :test-not :key
This function is like `subst', except that it works by destructive
modification (by `setcar' or `setcdr') rather than copying.
The `subst-if', `subst-if-not', `nsubst-if', and `nsubst-if-not'
functions are defined similarly.
-- Function: sublis alist tree &key :test :test-not :key
This function is like `subst', except that it takes an association
list ALIST of OLD-NEW pairs. Each element of the tree (after
applying the `:key' function, if any), is compared with the `car's
of ALIST; if it matches, it is replaced by the corresponding `cdr'.
-- Function: nsublis alist tree &key :test :test-not :key
This is a destructive version of `sublis'.
File: cl, Node: Lists as Sets, Next: Association Lists, Prev: Substitution of Expressions, Up: Lists
11.3 Lists as Sets
These functions perform operations on lists which represent sets of
-- Function: member* item list &key :test :test-not :key
This function searches LIST for an element matching ITEM. If a
match is found, it returns the cons cell whose `car' was the
matching element. Otherwise, it returns `nil'. Elements are
compared by `eql' by default; you can use the `:test',
`:test-not', and `:key' arguments to modify this behavior. *Note
Note that this function's name is suffixed by `*' to avoid the
incompatible `member' function defined in Emacs. (That function
uses `equal' for comparisons; it is equivalent to `(member* ITEM
LIST :test 'equal)'.)
The `member-if' and `member-if-not' functions analogously search for
elements which satisfy a given predicate.
-- Function: tailp sublist list
This function returns `t' if SUBLIST is a sublist of LIST, i.e.,
if SUBLIST is `eql' to LIST or to any of its `cdr's.
-- Function: adjoin item list &key :test :test-not :key
This function conses ITEM onto the front of LIST, like `(cons ITEM
LIST)', but only if ITEM is not already present on the list (as
determined by `member*'). If a `:key' argument is specified, it
is applied to ITEM as well as to the elements of LIST during the
search, on the reasoning that ITEM is "about" to become part of
-- Function: union list1 list2 &key :test :test-not :key
This function combines two lists which represent sets of items,
returning a list that represents the union of those two sets. The
result list will contain all items which appear in LIST1 or LIST2,
and no others. If an item appears in both LIST1 and LIST2 it will
be copied only once. If an item is duplicated in LIST1 or LIST2,
it is undefined whether or not that duplication will survive in the
result list. The order of elements in the result list is also
-- Function: nunion list1 list2 &key :test :test-not :key
This is a destructive version of `union'; rather than copying, it
tries to reuse the storage of the argument lists if possible.
-- Function: intersection list1 list2 &key :test :test-not :key
This function computes the intersection of the sets represented by
LIST1 and LIST2. It returns the list of items which appear in
both LIST1 and LIST2.
-- Function: nintersection list1 list2 &key :test :test-not :key
This is a destructive version of `intersection'. It tries to
reuse storage of LIST1 rather than copying. It does _not_ reuse
the storage of LIST2.
-- Function: set-difference list1 list2 &key :test :test-not :key
This function computes the "set difference" of LIST1 and LIST2,
i.e., the set of elements that appear in LIST1 but _not_ in LIST2.
-- Function: nset-difference list1 list2 &key :test :test-not :key
This is a destructive `set-difference', which will try to reuse
LIST1 if possible.
-- Function: set-exclusive-or list1 list2 &key :test :test-not :key
This function computes the "set exclusive or" of LIST1 and LIST2,
i.e., the set of elements that appear in exactly one of LIST1 and
-- Function: nset-exclusive-or list1 list2 &key :test :test-not :key
This is a destructive `set-exclusive-or', which will try to reuse
LIST1 and LIST2 if possible.
-- Function: subsetp list1 list2 &key :test :test-not :key
This function checks whether LIST1 represents a subset of LIST2,
i.e., whether every element of LIST1 also appears in LIST2.
File: cl, Node: Association Lists, Prev: Lists as Sets, Up: Lists
11.4 Association Lists
An "association list" is a list representing a mapping from one set of
values to another; any list whose elements are cons cells is an
-- Function: assoc* item a-list &key :test :test-not :key
This function searches the association list A-LIST for an element
whose `car' matches (in the sense of `:test', `:test-not', and
`:key', or by comparison with `eql') a given ITEM. It returns the
matching element, if any, otherwise `nil'. It ignores elements of
A-LIST which are not cons cells. (This corresponds to the
behavior of `assq' and `assoc' in Emacs Lisp; Common Lisp's
`assoc' ignores `nil's but considers any other non-cons elements
of A-LIST to be an error.)
-- Function: rassoc* item a-list &key :test :test-not :key
This function searches for an element whose `cdr' matches ITEM.
If A-LIST represents a mapping, this applies the inverse of the
mapping to ITEM.
The `assoc-if', `assoc-if-not', `rassoc-if', and `rassoc-if-not'
functions are defined similarly.
Two simple functions for constructing association lists are:
-- Function: acons key value alist
This is equivalent to `(cons (cons KEY VALUE) ALIST)'.
-- Function: pairlis keys values &optional alist
This is equivalent to `(nconc (mapcar* 'cons KEYS VALUES) ALIST)'.
File: cl, Node: Structures, Next: Assertions, Prev: Lists, Up: Top
The Common Lisp "structure" mechanism provides a general way to define
data types similar to C's `struct' types. A structure is a Lisp object
containing some number of "slots", each of which can hold any Lisp data
object. Functions are provided for accessing and setting the slots,
creating or copying structure objects, and recognizing objects of a
particular structure type.
In true Common Lisp, each structure type is a new type distinct from
all existing Lisp types. Since the underlying Emacs Lisp system
provides no way to create new distinct types, this package implements
structures as vectors (or lists upon request) with a special "tag"
symbol to identify them.
-- Special Form: defstruct name slots...
The `defstruct' form defines a new structure type called NAME,
with the specified SLOTS. (The SLOTS may begin with a string
which documents the structure type.) In the simplest case, NAME
and each of the SLOTS are symbols. For example,
(defstruct person name age sex)
defines a struct type called `person' which contains three slots.
Given a `person' object P, you can access those slots by calling
`(person-name P)', `(person-age P)', and `(person-sex P)'. You
can also change these slots by using `setf' on any of these place
(incf (person-age birthday-boy))
You can create a new `person' by calling `make-person', which
takes keyword arguments `:name', `:age', and `:sex' to specify the
initial values of these slots in the new object. (Omitting any of
these arguments leaves the corresponding slot "undefined,"
according to the Common Lisp standard; in Emacs Lisp, such
uninitialized slots are filled with `nil'.)
Given a `person', `(copy-person P)' makes a new object of the same
type whose slots are `eq' to those of P.
Given any Lisp object X, `(person-p X)' returns true if X looks
like a `person', false otherwise. (Again, in Common Lisp this
predicate would be exact; in Emacs Lisp the best it can do is
verify that X is a vector of the correct length which starts with
the correct tag symbol.)
Accessors like `person-name' normally check their arguments
(effectively using `person-p') and signal an error if the argument
is the wrong type. This check is affected by `(optimize (safety
...))' declarations. Safety level 1, the default, uses a somewhat
optimized check that will detect all incorrect arguments, but may
use an uninformative error message (e.g., "expected a vector"
instead of "expected a `person'"). Safety level 0 omits all
checks except as provided by the underlying `aref' call; safety
levels 2 and 3 do rigorous checking that will always print a
descriptive error message for incorrect inputs. *Note
(setq dave (make-person :name "Dave" :sex 'male))
=> [cl-struct-person "Dave" nil male]
(setq other (copy-person dave))
=> [cl-struct-person "Dave" nil male]
(eq dave other)
(eq (person-name dave) (person-name other))
(person-p [1 2 3 4])
(person-p '[cl-struct-person counterfeit person object])
In general, NAME is either a name symbol or a list of a name
symbol followed by any number of "struct options"; each SLOT is
either a slot symbol or a list of the form `(SLOT-NAME
DEFAULT-VALUE SLOT-OPTIONS...)'. The DEFAULT-VALUE is a Lisp form
which is evaluated any time an instance of the structure type is
created without specifying that slot's value.
Common Lisp defines several slot options, but the only one
implemented in this package is `:read-only'. A non-`nil' value
for this option means the slot should not be `setf'-able; the
slot's value is determined when the object is created and does not
(name nil :read-only t)
Any slot options other than `:read-only' are ignored.
For obscure historical reasons, structure options take a different
form than slot options. A structure option is either a keyword
symbol, or a list beginning with a keyword symbol possibly followed
by arguments. (By contrast, slot options are key-value pairs not
enclosed in lists.)
(defstruct (person (:constructor create-person)
name age sex)
The following structure options are recognized.
The argument is a symbol whose print name is used as the
prefix for the names of slot accessor functions. The default
is the name of the struct type followed by a hyphen. The
option `(:conc-name p-)' would change this prefix to `p-'.
Specifying `nil' as an argument means no prefix, so that the
slot names themselves are used to name the accessor functions.
In the simple case, this option takes one argument which is an
alternate name to use for the constructor function. The
default is `make-NAME', e.g., `make-person'. The above
example changes this to `create-person'. Specifying `nil' as
an argument means that no standard constructor should be
generated at all.
In the full form of this option, the constructor name is
followed by an arbitrary argument list. *Note Program
Structure::, for a description of the format of Common Lisp
argument lists. All options, such as `&rest' and `&key', are
supported. The argument names should match the slot names;
each slot is initialized from the corresponding argument.
Slots whose names do not appear in the argument list are
initialized based on the DEFAULT-VALUE in their slot
descriptor. Also, `&optional' and `&key' arguments which
don't specify defaults take their defaults from the slot
descriptor. It is valid to include arguments which don't
correspond to slot names; these are useful if they are
referred to in the defaults for optional, keyword, or `&aux'
arguments which _do_ correspond to slots.
You can specify any number of full-format `:constructor'
options on a structure. The default constructor is still
generated as well unless you disable it with a simple-format
(:constructor nil) ; no default constructor
(:constructor new-person (name sex &optional (age 0)))
(:constructor new-hound (&key (name "Rover")
&aux (age (* 7 dog-years))
name age sex)
The first constructor here takes its arguments positionally
rather than by keyword. (In official Common Lisp
terminology, constructors that work By Order of Arguments
instead of by keyword are called "BOA constructors." No, I'm
not making this up.) For example, `(new-person "Jane"
'female)' generates a person whose slots are `"Jane"', 0, and
The second constructor takes two keyword arguments, `:name',
which initializes the `name' slot and defaults to `"Rover"',
and `:dog-years', which does not itself correspond to a slot
but which is used to initialize the `age' slot. The `sex'
slot is forced to the symbol `canine' with no syntax for
The argument is an alternate name for the copier function for
this type. The default is `copy-NAME'. `nil' means not to
generate a copier function. (In this implementation, all
copier functions are simply synonyms for `copy-sequence'.)
The argument is an alternate name for the predicate which
recognizes objects of this type. The default is `NAME-p'.
`nil' means not to generate a predicate function. (If the
`:type' option is used without the `:named' option, no
predicate is ever generated.)
In true Common Lisp, `typep' is always able to recognize a
structure object even if `:predicate' was used. In this
package, `typep' simply looks for a function called
`TYPENAME-p', so it will work for structure types only if
they used the default predicate name.
This option implements a very limited form of C++-style
inheritance. The argument is the name of another structure
type previously created with `defstruct'. The effect is to
cause the new structure type to inherit all of the included
structure's slots (plus, of course, any new slots described
by this struct's slot descriptors). The new structure is
considered a "specialization" of the included one. In fact,
the predicate and slot accessors for the included type will
also accept objects of the new type.
If there are extra arguments to the `:include' option after
the included-structure name, these options are treated as
replacement slot descriptors for slots in the included
structure, possibly with modified default values. Borrowing
an example from Steele:
(defstruct person name (age 0) sex)
(defstruct (astronaut (:include person (age 45)))
(setq joe (make-person :name "Joe"))
=> [cl-struct-person "Joe" 0 nil]
(setq buzz (make-astronaut :name "Buzz"))
=> [cl-struct-astronaut "Buzz" 45 nil nil tang]
(list (person-p joe) (person-p buzz))
=> (t t)
(list (astronaut-p joe) (astronaut-p buzz))
=> (nil t)
=> error: "astronaut-name accessing a non-astronaut"
Thus, if `astronaut' is a specialization of `person', then
every `astronaut' is also a `person' (but not the other way
around). Every `astronaut' includes all the slots of a
`person', plus extra slots that are specific to astronauts.
Operations that work on people (like `person-name') work on
astronauts just like other people.
In full Common Lisp, this option allows you to specify a
function which is called to print an instance of the
structure type. The Emacs Lisp system offers no hooks into
the Lisp printer which would allow for such a feature, so
this package simply ignores `:print-function'.
The argument should be one of the symbols `vector' or `list'.
This tells which underlying Lisp data type should be used to
implement the new structure type. Vectors are used by
default, but `(:type list)' will cause structure objects to
be stored as lists instead.
The vector representation for structure objects has the
advantage that all structure slots can be accessed quickly,
although creating vectors is a bit slower in Emacs Lisp.
Lists are easier to create, but take a relatively long time
accessing the later slots.
This option, which takes no arguments, causes a
characteristic "tag" symbol to be stored at the front of the
structure object. Using `:type' without also using `:named'
will result in a structure type stored as plain vectors or
lists with no identifying features.
The default, if you don't specify `:type' explicitly, is to
use named vectors. Therefore, `:named' is only useful in
conjunction with `:type'.
(defstruct (person1) name age sex)
(defstruct (person2 (:type list) :named) name age sex)
(defstruct (person3 (:type list)) name age sex)
(setq p1 (make-person1))
=> [cl-struct-person1 nil nil nil]
(setq p2 (make-person2))
=> (person2 nil nil nil)
(setq p3 (make-person3))
=> (nil nil nil)
=> error: function person3-p undefined
Since unnamed structures don't have tags, `defstruct' is not
able to make a useful predicate for recognizing them. Also,
accessors like `person3-name' will be generated but they will
not be able to do any type checking. The `person3-name'
function, for example, will simply be a synonym for `car' in
this case. By contrast, `person2-name' is able to verify
that its argument is indeed a `person2' object before
The argument must be a nonnegative integer. It specifies a
number of slots to be left "empty" at the front of the
structure. If the structure is named, the tag appears at the
specified position in the list or vector; otherwise, the first
slot appears at that position. Earlier positions are filled
with `nil' by the constructors and ignored otherwise. If the
type `:include's another type, then `:initial-offset'
specifies a number of slots to be skipped between the last
slot of the included type and the first new slot.
Except as noted, the `defstruct' facility of this package is
entirely compatible with that of Common Lisp.
File: cl, Node: Assertions, Next: Efficiency Concerns, Prev: Structures, Up: Top
13 Assertions and Errors
This section describes two macros that test "assertions", i.e.,
conditions which must be true if the program is operating correctly.
Assertions never add to the behavior of a Lisp program; they simply
make "sanity checks" to make sure everything is as it should be.
If the optimization property `speed' has been set to 3, and `safety'
is less than 3, then the byte-compiler will optimize away the following
assertions. Because assertions might be optimized away, it is a bad
idea for them to include side-effects.
-- Special Form: assert test-form [show-args string args...]
This form verifies that TEST-FORM is true (i.e., evaluates to a
non-`nil' value). If so, it returns `nil'. If the test is not
satisfied, `assert' signals an error.
A default error message will be supplied which includes TEST-FORM.
You can specify a different error message by including a STRING
argument plus optional extra arguments. Those arguments are simply
passed to `error' to signal the error.
If the optional second argument SHOW-ARGS is `t' instead of `nil',
then the error message (with or without STRING) will also include
all non-constant arguments of the top-level FORM. For example:
(assert (> x 10) t "x is too small: %d")
This usage of SHOW-ARGS is an extension to Common Lisp. In true
Common Lisp, the second argument gives a list of PLACES which can
be `setf''d by the user before continuing from the error. Since
Emacs Lisp does not support continuable errors, it makes no sense
to specify PLACES.
-- Special Form: check-type form type [string]
This form verifies that FORM evaluates to a value of type TYPE.
If so, it returns `nil'. If not, `check-type' signals a
`wrong-type-argument' error. The default error message lists the
erroneous value along with TYPE and FORM themselves. If STRING is
specified, it is included in the error message in place of TYPE.
(check-type x (integer 1 *) "a positive integer")
*Note Type Predicates::, for a description of the type specifiers
that may be used for TYPE.
Note that in Common Lisp, the first argument to `check-type' must
be a PLACE suitable for use by `setf', because `check-type'
signals a continuable error that allows the user to modify PLACE.
The following error-related macro is also defined:
-- Special Form: ignore-errors forms...
This executes FORMS exactly like a `progn', except that errors are
ignored during the FORMS. More precisely, if an error is signaled
then `ignore-errors' immediately aborts execution of the FORMS and
returns `nil'. If the FORMS complete successfully, `ignore-errors'
returns the result of the last FORM.
File: cl, Node: Efficiency Concerns, Next: Common Lisp Compatibility, Prev: Assertions, Up: Top
Appendix A Efficiency Concerns
Many of the advanced features of this package, such as `defun*',
`loop', and `setf', are implemented as Lisp macros. In byte-compiled
code, these complex notations will be expanded into equivalent Lisp
code which is simple and efficient. For example, the forms
(incf i n)
(push x (car p))
are expanded at compile-time to the Lisp forms
(setq i (+ i n))
(setcar p (cons x (car p)))
which are the most efficient ways of doing these respective operations
in Lisp. Thus, there is no performance penalty for using the more
readable `incf' and `push' forms in your compiled code.
_Interpreted_ code, on the other hand, must expand these macros
every time they are executed. For this reason it is strongly
recommended that code making heavy use of macros be compiled. (The
features labeled "Special Form" instead of "Function" in this manual
are macros.) A loop using `incf' a hundred times will execute
considerably faster if compiled, and will also garbage-collect less
because the macro expansion will not have to be generated, used, and
thrown away a hundred times.
You can find out how a macro expands by using the `cl-prettyexpand'
-- Function: cl-prettyexpand form &optional full
This function takes a single Lisp form as an argument and inserts
a nicely formatted copy of it in the current buffer (which must be
in Lisp mode so that indentation works properly). It also expands
all Lisp macros which appear in the form. The easiest way to use
this function is to go to the `*scratch*' buffer and type, say,
(cl-prettyexpand '(loop for x below 10 collect x))
and type `C-x C-e' immediately after the closing parenthesis; the
(let* ((x 0)
(while (< x 10)
(setq G1004 (cons x G1004))
(setq x (+ x 1)))
will be inserted into the buffer. (The `block' macro is expanded
differently in the interpreter and compiler, so `cl-prettyexpand'
just leaves it alone. The temporary variable `G1004' was created
If the optional argument FULL is true, then _all_ macros are
expanded, including `block', `eval-when', and compiler macros.
Expansion is done as if FORM were a top-level form in a file being
compiled. For example,
(cl-prettyexpand '(pushnew 'x list))
-| (setq list (adjoin 'x list))
(cl-prettyexpand '(pushnew 'x list) t)
-| (setq list (if (memq 'x list) list (cons 'x list)))
(cl-prettyexpand '(caddr (member* 'a list)) t)
-| (car (cdr (cdr (memq 'a list))))
Note that `adjoin', `caddr', and `member*' all have built-in
compiler macros to optimize them in common cases.
A.2 Error Checking
Common Lisp compliance has in general not been sacrificed for the sake
of efficiency. A few exceptions have been made for cases where
substantial gains were possible at the expense of marginal
The Common Lisp standard (as embodied in Steele's book) uses the
phrase "it is an error if" to indicate a situation which is not
supposed to arise in complying programs; implementations are strongly
encouraged but not required to signal an error in these situations.
This package sometimes omits such error checking in the interest of
compactness and efficiency. For example, `do' variable specifiers are
supposed to be lists of one, two, or three forms; extra forms are
ignored by this package rather than signaling a syntax error. The
`endp' function is simply a synonym for `null' in this package.
Functions taking keyword arguments will accept an odd number of
arguments, treating the trailing keyword as if it were followed by the
Argument lists (as processed by `defun*' and friends) _are_ checked
rigorously except for the minor point just mentioned; in particular,
keyword arguments are checked for validity, and `&allow-other-keys' and
`:allow-other-keys' are fully implemented. Keyword validity checking
is slightly time consuming (though not too bad in byte-compiled code);
you can use `&allow-other-keys' to omit this check. Functions defined
in this package such as `find' and `member*' do check their keyword
arguments for validity.
A.3 Optimizing Compiler
Use of the optimizing Emacs compiler is highly recommended; many of the
Common Lisp macros emit code which can be improved by optimization. In
particular, `block's (whether explicit or implicit in constructs like
`defun*' and `loop') carry a fair run-time penalty; the optimizing
compiler removes `block's which are not actually referenced by `return'
or `return-from' inside the block.
File: cl, Node: Common Lisp Compatibility, Next: Old CL Compatibility, Prev: Efficiency Concerns, Up: Top
Appendix B Common Lisp Compatibility
Following is a list of all known incompatibilities between this package
and Common Lisp as documented in Steele (2nd edition).
Certain function names, such as `member', `assoc', and `floor', were
already taken by (incompatible) Emacs Lisp functions; this package
appends `*' to the names of its Common Lisp versions of these functions.
The word `defun*' is required instead of `defun' in order to use
extended Common Lisp argument lists in a function. Likewise,
`defmacro*' and `function*' are versions of those forms which
understand full-featured argument lists. The `&whole' keyword does not
work in `defmacro' argument lists (except inside recursive argument
The `equal' predicate does not distinguish between IEEE
floating-point plus and minus zero. The `equalp' predicate has several
differences with Common Lisp; *note Predicates::.
The `setf' mechanism is entirely compatible, except that
setf-methods return a list of five values rather than five values
directly. Also, the new "`setf' function" concept (typified by `(defun
(setf foo) ...)') is not implemented.
The `do-all-symbols' form is the same as `do-symbols' with no
OBARRAY argument. In Common Lisp, this form would iterate over all
symbols in all packages. Since Emacs obarrays are not a first-class
package mechanism, there is no way for `do-all-symbols' to locate any
but the default obarray.
The `loop' macro is complete except that `loop-finish' and type
specifiers are unimplemented.
The multiple-value return facility treats lists as multiple values,
since Emacs Lisp cannot support multiple return values directly. The
macros will be compatible with Common Lisp if `values' or `values-list'
is always used to return to a `multiple-value-bind' or other
multiple-value receiver; if `values' is used without
`multiple-value-...' or vice-versa the effect will be different from
Many Common Lisp declarations are ignored, and others match the
Common Lisp standard in concept but not in detail. For example, local
`special' declarations, which are purely advisory in Emacs Lisp, do not
rigorously obey the scoping rules set down in Steele's book.
The variable `*gensym-counter*' starts out with a pseudo-random
value rather than with zero. This is to cope with the fact that
generated symbols become interned when they are written to and loaded
back from a file.
The `defstruct' facility is compatible, except that structures are
of type `:type vector :named' by default rather than some special,
distinct type. Also, the `:type' slot option is ignored.
The second argument of `check-type' is treated differently.
File: cl, Node: Old CL Compatibility, Next: Porting Common Lisp, Prev: Common Lisp Compatibility, Up: Top
Appendix C Old CL Compatibility
Following is a list of all known incompatibilities between this package
and the older Quiroz `cl.el' package.
This package's emulation of multiple return values in functions is
incompatible with that of the older package. That package attempted to
come as close as possible to true Common Lisp multiple return values;
unfortunately, it could not be 100% reliable and so was prone to
occasional surprises if used freely. This package uses a simpler
method, namely replacing multiple values with lists of values, which is
more predictable though more noticeably different from Common Lisp.
The `defkeyword' form and `keywordp' function are not implemented in
The `member', `floor', `ceiling', `truncate', `round', `mod', and
`rem' functions are suffixed by `*' in this package to avoid collision
with existing functions in Emacs. The older package simply redefined
these functions, overwriting the built-in meanings and causing serious
portability problems. (Some more recent versions of the Quiroz package
changed the names to `cl-member', etc.; this package defines the latter
names as aliases for `member*', etc.)
Certain functions in the old package which were buggy or inconsistent
with the Common Lisp standard are incompatible with the conforming
versions in this package. For example, `eql' and `member' were
synonyms for `eq' and `memq' in that package, `setf' failed to preserve
correct order of evaluation of its arguments, etc.
Finally, unlike the older package, this package is careful to prefix
all of its internal names with `cl-'. Except for a few functions which
are explicitly defined as additional features (such as `floatp-safe'
and `letf'), this package does not export any non-`cl-' symbols which
are not also part of Common Lisp.
C.1 The `cl-compat' package
The "CL" package includes emulations of some features of the old
`cl.el', in the form of a compatibility package `cl-compat'. To use
it, put `(require 'cl-compat)' in your program.
The old package defined a number of internal routines without `cl-'
prefixes or other annotations. Call to these routines may have crept
into existing Lisp code. `cl-compat' provides emulations of the
following internal routines: `pair-with-newsyms', `zip-lists',
`unzip-lists', `reassemble-arglists', `duplicate-symbols-p',
Some `setf' forms translated into calls to internal functions that
user code might call directly. The functions `setnth', `setnthcdr',
and `setelt' fall in this category; they are defined by `cl-compat',
but the best fix is to change to use `setf' properly.
The `cl-compat' file defines the keyword functions `keywordp',
`keyword-of', and `defkeyword', which are not defined by the new "CL"
package because the use of keywords as data is discouraged.
The `build-klist' mechanism for parsing keyword arguments is
emulated by `cl-compat'; the `with-keyword-args' macro is not, however,
and in any case it's best to change to use the more natural keyword
argument processing offered by `defun*'.
Multiple return values are treated differently by the two Common
Lisp packages. The old package's method was more compatible with true
Common Lisp, though it used heuristics that caused it to report
spurious multiple return values in certain cases. The `cl-compat'
package defines a set of multiple-value macros that are compatible with
the old CL package; again, they are heuristic in nature, but they are
guaranteed to work in any case where the old package's macros worked.
To avoid name collision with the "official" multiple-value facilities,
the ones in `cl-compat' have capitalized names: `Values',
`Values-list', `Multiple-value-bind', etc.
The functions `cl-floor', `cl-ceiling', `cl-truncate', and
`cl-round' are defined by `cl-compat' to use the old-style
multiple-value mechanism, just as they did in the old package. The
newer `floor*' and friends return their two results in a list rather
than as multiple values. Note that older versions of the old package
used the unadorned names `floor', `ceiling', etc.; `cl-compat' cannot
use these names because they conflict with Emacs built-ins.
File: cl, Node: Porting Common Lisp, Next: GNU Free Documentation License, Prev: Old CL Compatibility, Up: Top
Appendix D Porting Common Lisp
This package is meant to be used as an extension to Emacs Lisp, not as
an Emacs implementation of true Common Lisp. Some of the remaining
differences between Emacs Lisp and Common Lisp make it difficult to
port large Common Lisp applications to Emacs. For one, some of the
features in this package are not fully compliant with ANSI or Steele;
*note Common Lisp Compatibility::. But there are also quite a few
features that this package does not provide at all. Here are some
major omissions that you will want to watch out for when bringing
Common Lisp code into Emacs.
* Case-insensitivity. Symbols in Common Lisp are case-insensitive
by default. Some programs refer to a function or variable as
`foo' in one place and `Foo' or `FOO' in another. Emacs Lisp will
treat these as three distinct symbols.
Some Common Lisp code is written entirely in upper case. While
Emacs is happy to let the program's own functions and variables use
this convention, calls to Lisp builtins like `if' and `defun' will
have to be changed to lower case.
* Lexical scoping. In Common Lisp, function arguments and `let'
bindings apply only to references physically within their bodies
(or within macro expansions in their bodies). Emacs Lisp, by
contrast, uses "dynamic scoping" wherein a binding to a variable
is visible even inside functions called from the body.
Variables in Common Lisp can be made dynamically scoped by
declaring them `special' or using `defvar'. In Emacs Lisp it is
as if all variables were declared `special'.
Often you can use code that was written for lexical scoping even
in a dynamically scoped Lisp, but not always. Here is an example
of a Common Lisp code fragment that would fail in Emacs Lisp:
(defun map-odd-elements (func list)
(loop for x in list
for flag = t then (not flag)
collect (if flag x (funcall func x))))
(defun add-odd-elements (list x)
(map-odd-elements (lambda (a) (+ a x))) list)
In Common Lisp, the two functions' usages of `x' are completely
independent. In Emacs Lisp, the binding to `x' made by
`add-odd-elements' will have been hidden by the binding in
`map-odd-elements' by the time the `(+ a x)' function is called.
(This package avoids such problems in its own mapping functions by
using names like `cl-x' instead of `x' internally; as long as you
don't use the `cl-' prefix for your own variables no collision can
*Note Lexical Bindings::, for a description of the `lexical-let'
form which establishes a Common Lisp-style lexical binding, and
some examples of how it differs from Emacs' regular `let'.
* Reader macros. Common Lisp includes a second type of macro that
works at the level of individual characters. For example, Common
Lisp implements the quote notation by a reader macro called `'',
whereas Emacs Lisp's parser just treats quote as a special case.
Some Lisp packages use reader macros to create special syntaxes
for themselves, which the Emacs parser is incapable of reading.
* Other syntactic features. Common Lisp provides a number of
notations beginning with `#' that the Emacs Lisp parser won't
understand. For example, `#| ... |#' is an alternate comment
notation, and `#+lucid (foo)' tells the parser to ignore the
`(foo)' except in Lucid Common Lisp.
* Packages. In Common Lisp, symbols are divided into "packages".
Symbols that are Lisp built-ins are typically stored in one
package; symbols that are vendor extensions are put in another,
and each application program would have a package for its own
symbols. Certain symbols are "exported" by a package and others
are internal; certain packages "use" or import the exported symbols
of other packages. To access symbols that would not normally be
visible due to this importing and exporting, Common Lisp provides
a syntax like `package:symbol' or `package::symbol'.
Emacs Lisp has a single namespace for all interned symbols, and
then uses a naming convention of putting a prefix like `cl-' in
front of the name. Some Emacs packages adopt the Common Lisp-like
convention of using `cl:' or `cl::' as the prefix. However, the
Emacs parser does not understand colons and just treats them as
part of the symbol name. Thus, while `mapcar' and `lisp:mapcar'
may refer to the same symbol in Common Lisp, they are totally
distinct in Emacs Lisp. Common Lisp programs which refer to a
symbol by the full name sometimes and the short name other times
will not port cleanly to Emacs.
Emacs Lisp does have a concept of "obarrays," which are
package-like collections of symbols, but this feature is not
strong enough to be used as a true package mechanism.
* The `format' function is quite different between Common Lisp and
Emacs Lisp. It takes an additional "destination" argument before
the format string. A destination of `nil' means to format to a
string as in Emacs Lisp; a destination of `t' means to write to
the terminal (similar to `message' in Emacs). Also, format
control strings are utterly different; `~' is used instead of `%'
to introduce format codes, and the set of available codes is much
richer. There are no notations like `\n' for string literals;
instead, `format' is used with the "newline" format code, `~%'.
More advanced formatting codes provide such features as paragraph
filling, case conversion, and even loops and conditionals.
While it would have been possible to implement most of Common Lisp
`format' in this package (under the name `format*', of course), it
was not deemed worthwhile. It would have required a huge amount
of code to implement even a decent subset of `format*', yet the
functionality it would provide over Emacs Lisp's `format' would
rarely be useful.
* Vector constants use square brackets in Emacs Lisp, but `#(a b c)'
notation in Common Lisp. To further complicate matters, Emacs has
its own `#(' notation for something entirely different--strings
* Characters are distinct from integers in Common Lisp. The notation
for character constants is also different: `#\A' in Common Lisp
where Emacs Lisp uses `?A'. Also, `string=' and `string-equal'
are synonyms in Emacs Lisp, whereas the latter is case-insensitive
in Common Lisp.
* Data types. Some Common Lisp data types do not exist in Emacs
Lisp. Rational numbers and complex numbers are not present, nor
are large integers (all integers are "fixnums"). All arrays are
one-dimensional. There are no readtables or pathnames; streams
are a set of existing data types rather than a new data type of
their own. Hash tables, random-states, structures, and packages
(obarrays) are built from Lisp vectors or lists rather than being
* The Common Lisp Object System (CLOS) is not implemented, nor is
the Common Lisp Condition System. However, the EIEIO package from
`ftp://ftp.ultranet.com/pub/zappo' does implement some CLOS
* Common Lisp features that are completely redundant with Emacs Lisp
features of a different name generally have not been implemented.
For example, Common Lisp writes `defconstant' where Emacs Lisp
uses `defconst'. Similarly, `make-list' takes its arguments in
different ways in the two Lisps but does exactly the same thing,
so this package has not bothered to implement a Common Lisp-style
* A few more notable Common Lisp features not included in this
package: `compiler-let', `tagbody', `prog', `ldb/dpb',
* Recursion. While recursion works in Emacs Lisp just like it does
in Common Lisp, various details of the Emacs Lisp system and
compiler make recursion much less efficient than it is in most
Lisps. Some schools of thought prefer to use recursion in Lisp
over other techniques; they would sum a list of numbers using
(defun sum-list (list)
(+ (car list) (sum-list (cdr list)))
where a more iteratively-minded programmer might write one of
(let ((total 0)) (dolist (x my-list) (incf total x)) total)
(loop for x in my-list sum x)
While this would be mainly a stylistic choice in most Common Lisps,
in Emacs Lisp you should be aware that the iterative forms are
much faster than recursion. Also, Lisp programmers will want to
note that the current Emacs Lisp compiler does not optimize tail
File: cl, Node: GNU Free Documentation License, Next: Function Index, Prev: Porting Common Lisp, Up: Top
Appendix E GNU Free Documentation License
Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
Everyone is permitted to copy and distribute verbatim copies
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This License is a kind of "copyleft," which means that derivative
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It complements the GNU General Public License, which is a copyleft
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We have designed this License in order to use it for manuals for
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We recommend this License principally for works whose purpose is
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Copyright (C) YEAR YOUR NAME.
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File: cl, Node: Function Index, Next: Variable Index, Prev: GNU Free Documentation License, Up: Top
* acons: Association Lists. (line 31)
* adjoin: Lists as Sets. (line 30)
* assert: Assertions. (line 17)
* assoc*: Association Lists. (line 11)
* assoc-if: Association Lists. (line 25)
* assoc-if-not: Association Lists. (line 25)
* block: Blocks and Exits. (line 14)
* caddr: List Functions. (line 10)
* callf: Modify Macros. (line 146)
* callf2: Modify Macros. (line 161)
* case: Conditionals. (line 10)
* ceiling*: Numerical Functions. (line 48)
* check-type: Assertions. (line 39)
* cl-float-limits: Implementation Parameters.
* cl-prettyexpand: Efficiency Concerns. (line 39)
* coerce: Type Predicates. (line 67)
* compiler-macroexpand: Macros. (line 60)
* concatenate: Sequence Functions. (line 28)
* copy-list: List Functions. (line 55)
* copy-tree: List Functions. (line 59)
* count: Searching Sequences. (line 27)
* count-if: Searching Sequences. (line 30)
* count-if-not: Searching Sequences. (line 30)
* decf: Modify Macros. (line 46)
* declaim: Declarations. (line 27)
* declare: Declarations. (line 37)
* define-compiler-macro: Macros. (line 28)
* define-modify-macro: Customizing Setf. (line 11)
* define-setf-method: Customizing Setf. (line 99)
* defmacro*: Argument Lists. (line 35)
* defsetf: Customizing Setf. (line 41)
* defstruct: Structures. (line 20)
* defsubst*: Argument Lists. (line 24)
* deftype: Type Predicates. (line 78)
* defun*: Argument Lists. (line 18)
* delete*: Sequence Functions. (line 68)
* delete-duplicates: Sequence Functions. (line 92)
* delete-if: Sequence Functions. (line 77)
* delete-if-not: Sequence Functions. (line 77)
* destructuring-bind: Macros. (line 15)
* do: Iteration. (line 34)
* do*: Iteration. (line 73)
* do-all-symbols: Iteration. (line 116)
* do-symbols: Iteration. (line 107)
* dolist: Iteration. (line 89)
* dotimes: Iteration. (line 98)
* ecase: Conditionals. (line 38)
* endp: List Functions. (line 25)
* equalp: Equality Predicates. (line 9)
* etypecase: Conditionals. (line 59)
* eval-when: Time of Evaluation. (line 16)
* eval-when-compile: Time of Evaluation. (line 86)
* evenp: Predicates on Numbers.
* every: Mapping over Sequences.
* fill: Sequence Functions. (line 35)
* find: Searching Sequences. (line 11)
* find-if: Searching Sequences. (line 30)
* find-if-not: Searching Sequences. (line 30)
* first: List Functions. (line 17)
* flet: Function Bindings. (line 9)
* floatp-safe: Predicates on Numbers.
* floor*: Numerical Functions. (line 24)
* function*: Argument Lists. (line 44)
* gcd: Numerical Functions. (line 9)
* gensym: Creating Symbols. (line 10)
* gentemp: Creating Symbols. (line 32)
* get*: Property Lists. (line 12)
* get-setf-method: Customizing Setf. (line 138)
* getf: Property Lists. (line 31)
* ignore-errors: Assertions. (line 58)
* incf: Modify Macros. (line 18)
* intersection: Lists as Sets. (line 52)
* isqrt: Numerical Functions. (line 19)
* labels: Function Bindings. (line 45)
* lcm: Numerical Functions. (line 14)
* ldiff: List Functions. (line 47)
* letf: Modify Macros. (line 97)
* letf*: Modify Macros. (line 142)
* lexical-let: Lexical Bindings. (line 10)
* lexical-let*: Lexical Bindings. (line 98)
* list*: List Functions. (line 37)
* list-length: List Functions. (line 30)
* load-time-value: Time of Evaluation. (line 95)
* locally: Declarations. (line 45)
* loop <1>: Loop Basics. (line 16)
* loop: Iteration. (line 10)
* macrolet: Macro Bindings. (line 9)
* make-random-state: Random Numbers. (line 29)
* map: Mapping over Sequences.
* mapc: Mapping over Sequences.
* mapcan: Mapping over Sequences.
* mapcar*: Mapping over Sequences.
* mapcon: Mapping over Sequences.
* mapl: Mapping over Sequences.
* maplist: Mapping over Sequences.
* member*: Lists as Sets. (line 10)
* member-if: Lists as Sets. (line 22)
* member-if-not: Lists as Sets. (line 22)
* merge: Sorting Sequences. (line 41)
* minusp: Predicates on Numbers.
* mismatch: Searching Sequences. (line 35)
* mod*: Numerical Functions. (line 68)
* multiple-value-bind: Multiple Values. (line 18)
* multiple-value-setq: Multiple Values. (line 25)
* nintersection: Lists as Sets. (line 57)
* notany: Mapping over Sequences.
* notevery: Mapping over Sequences.
* nset-difference: Lists as Sets. (line 66)
* nset-exclusive-or: Lists as Sets. (line 75)
* nsublis: Substitution of Expressions.
* nsubst: Substitution of Expressions.
* nsubst-if: Substitution of Expressions.
* nsubst-if-not: Substitution of Expressions.
* nsubstitute: Sequence Functions. (line 104)
* nsubstitute-if: Sequence Functions. (line 108)
* nsubstitute-if-not: Sequence Functions. (line 108)
* nunion: Lists as Sets. (line 48)
* oddp: Predicates on Numbers.
* pairlis: Association Lists. (line 34)
* plusp: Predicates on Numbers.
* pop: Modify Macros. (line 50)
* position: Searching Sequences. (line 20)
* position-if: Searching Sequences. (line 30)
* position-if-not: Searching Sequences. (line 30)
* proclaim: Declarations. (line 22)
* progv: Dynamic Bindings. (line 11)
* psetf: Modify Macros. (line 11)
* psetq: Assignment. (line 10)
* push: Modify Macros. (line 56)
* pushnew: Modify Macros. (line 61)
* random*: Random Numbers. (line 12)
* random-state-p: Random Numbers. (line 52)
* rassoc*: Association Lists. (line 21)
* rassoc-if: Association Lists. (line 25)
* rassoc-if-not: Association Lists. (line 25)
* reduce: Mapping over Sequences.
* rem*: Numerical Functions. (line 72)
* remf: Property Lists. (line 62)
* remove*: Sequence Functions. (line 52)
* remove-duplicates: Sequence Functions. (line 82)
* remove-if: Sequence Functions. (line 77)
* remove-if-not: Sequence Functions. (line 77)
* remprop: Property Lists. (line 21)
* replace: Sequence Functions. (line 39)
* rest: List Functions. (line 22)
* return: Blocks and Exits. (line 57)
* return-from: Blocks and Exits. (line 51)
* rotatef: Modify Macros. (line 82)
* round*: Numerical Functions. (line 61)
* search: Searching Sequences. (line 54)
* set-difference: Lists as Sets. (line 62)
* set-exclusive-or: Lists as Sets. (line 70)
* setf: Basic Setf. (line 10)
* shiftf: Modify Macros. (line 67)
* some: Mapping over Sequences.
* sort*: Sorting Sequences. (line 7)
* stable-sort: Sorting Sequences. (line 31)
* sublis: Substitution of Expressions.
* subseq: Sequence Functions. (line 10)
* subsetp: Lists as Sets. (line 79)
* subst: Substitution of Expressions.
* subst-if: Substitution of Expressions.
* subst-if-not: Substitution of Expressions.
* substitute: Sequence Functions. (line 97)
* substitute-if: Sequence Functions. (line 108)
* substitute-if-not: Sequence Functions. (line 108)
* symbol-macrolet: Macro Bindings. (line 21)
* tailp: Lists as Sets. (line 26)
* the: Declarations. (line 48)
* tree-equal: List Functions. (line 68)
* truncate*: Numerical Functions. (line 54)
* typecase: Conditionals. (line 43)
* typep: Type Predicates. (line 9)
* union: Lists as Sets. (line 38)
File: cl, Node: Variable Index, Prev: Function Index, Up: Top
* *gensym-counter*: Creating Symbols. (line 21)
* *random-state*: Random Numbers. (line 21)
* float-epsilon: Implementation Parameters.
* float-negative-epsilon: Implementation Parameters.
* least-negative-float: Implementation Parameters.
* least-negative-normalized-float: Implementation Parameters.
* least-positive-float: Implementation Parameters.
* least-positive-normalized-float: Implementation Parameters.
* most-negative-float: Implementation Parameters.
* most-positive-float: Implementation Parameters.