X-Git-Url: http://git.hcoop.net/bpt/emacs.git/blobdiff_plain/baa573a3791927e88fad979ac8ffe34773fe7e93..c8875a656cfba42f646c4f7e25429e2c3b1588ce:/lispref/functions.texi

diff --git a/lispref/functions.texi b/lispref/functions.texi
index 035d231cf4..6cdcb6bce1 100644
--- a/lispref/functions.texi
+++ b/lispref/functions.texi
@@ -1,6 +1,7 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. 
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999
+@c   Free Software Foundation, Inc. 
 @c See the file elisp.texi for copying conditions.
 @setfilename ../info/functions
 @node Functions, Macros, Variables, Top
@@ -54,18 +55,18 @@ such as @code{car} or @code{append}.  These functions are also called
 @dfn{built-in} functions or @dfn{subrs}.  (Special forms are also
 considered primitives.)
 
-Usually the reason that a function is a primitives is because it is
-fundamental, because it provides a low-level interface to operating
-system services, or because it needs to run fast.  Primitives can be
-modified or added only by changing the C sources and recompiling the
-editor.  See @ref{Writing Emacs Primitives}.
+Usually the reason we implement a function as a primitive is either
+because it is fundamental, because it provides a low-level interface to
+operating system services, or because it needs to run fast.  Primitives
+can be modified or added only by changing the C sources and recompiling
+the editor.  See @ref{Writing Emacs Primitives}.
 
 @item lambda expression
 A @dfn{lambda expression} is a function written in Lisp.
 These are described in the following section.
-@ifinfo
+@ifnottex
 @xref{Lambda Expressions}.
-@end ifinfo
+@end ifnottex
 
 @item special form
 A @dfn{special form} is a primitive that is like a function but does not
@@ -110,6 +111,11 @@ A @dfn{byte-code function} is a function that has been compiled by the
 byte compiler.  @xref{Byte-Code Type}.
 @end table
 
+@defun functionp object
+This function returns @code{t} if @var{object} is any kind of function,
+or a special form or macro.
+@end defun
+
 @defun subrp object
 This function returns @code{t} if @var{object} is a built-in function
 (i.e., a Lisp primitive).
@@ -168,7 +174,7 @@ expression, but to be called as a function.
 @node Lambda Components
 @subsection Components of a Lambda Expression
 
-@ifinfo
+@ifnottex
 
   A function written in Lisp (a ``lambda expression'') is a list that
 looks like this:
@@ -179,7 +185,7 @@ looks like this:
   [@var{interactive-declaration}]
   @var{body-forms}@dots{})
 @end example
-@end ifinfo
+@end ifnottex
 
 @cindex lambda list
   The first element of a lambda expression is always the symbol
@@ -188,7 +194,7 @@ reason functions are defined to start with @code{lambda} is so that
 other lists, intended for other uses, will not accidentally be valid as
 functions.
 
-  The second element is a list of symbols--the argument variable names.
+  The second element is a list of symbols---the argument variable names.
 This is called the @dfn{lambda list}.  When a Lisp function is called,
 the argument values are matched up against the variables in the lambda
 list, which are given local bindings with the values provided.
@@ -267,7 +273,7 @@ that time, they were the only way to bind and initialize local
 variables.
 
 @node Argument List
-@subsection Advanced Features of Argument Lists
+@subsection Other Features of Argument Lists
 @kindex wrong-number-of-arguments
 @cindex argument binding
 @cindex binding arguments
@@ -326,7 +332,8 @@ This is what @code{substring} does; @code{nil} as the third argument to
 @quotation
 @b{Common Lisp note:} Common Lisp allows the function to specify what
 default value to use when an optional argument is omitted; Emacs Lisp
-always uses @code{nil}.
+always uses @code{nil}.  Emacs Lisp does not support ``supplied-p''
+variables that tell you whether an argument was explicitly passed.
 @end quotation
 
   For example, an argument list that looks like this:
@@ -379,7 +386,7 @@ facilities.  @xref{Documentation}, for how the @var{documentation-string} is
 accessed.
 
   It is a good idea to provide documentation strings for all the
-functions in your program, even those that are only called from within
+functions in your program, even those that are called only from within
 your program.  Documentation strings are like comments, except that they
 are easier to access.
 
@@ -412,7 +419,7 @@ as the return value and as the documentation.
   In most computer languages, every function has a name; the idea of a
 function without a name is nonsensical.  In Lisp, a function in the
 strictest sense has no name.  It is simply a list whose first element is
-@code{lambda}, or a primitive subr-object.
+@code{lambda}, a byte-code function object, or a primitive subr-object.
 
   However, a symbol can serve as the name of a function.  This happens
 when you put the function in the symbol's @dfn{function cell}
@@ -451,8 +458,13 @@ one symbol, this is just a matter of convenience.  It is easy to store
 it in several symbols using @code{fset}; then each of the symbols is
 equally well a name for the same function.
 
-  A symbol used as a function name may also be used as a variable;
-these two uses of a symbol are independent and do not conflict.
+  A symbol used as a function name may also be used as a variable; these
+two uses of a symbol are independent and do not conflict.  (Some Lisp
+dialects, such as Scheme, do not distinguish between a symbol's value
+and its function definition; a symbol's value as a variable is also its
+function definition.)  If you have not given a symbol a function
+definition, you cannot use it as a function; whether the symbol has a
+value as a variable makes no difference to this.
 
 @node Defining Functions
 @section Defining Functions
@@ -476,8 +488,8 @@ value.
 
 As described previously (@pxref{Lambda Expressions}),
 @var{argument-list} is a list of argument names and may include the
-keywords @code{&optional} and @code{&rest}.  Also, the first two forms
-in @var{body-forms} may be a documentation string and an interactive
+keywords @code{&optional} and @code{&rest}.  Also, the first two of the
+@var{body-forms} may be a documentation string and an interactive
 declaration.
 
 There is no conflict if the same symbol @var{name} is also used as a
@@ -566,11 +578,12 @@ function @code{concat} with arguments @code{"a"} and @code{"b"}.
 @xref{Evaluation}, for a description of evaluation.
 
   When you write a list as an expression in your program, the function
-name is part of the program.  This means that you choose which function
-to call, and how many arguments to give it, when you write the program.
-Usually that's just what you want.  Occasionally you need to decide at
-run time which function to call.  To do that, use the functions
-@code{funcall} and @code{apply}.
+name it calls is written in your program.  This means that you choose
+which function to call, and how many arguments to give it, when you
+write the program.  Usually that's just what you want.  Occasionally you
+need to compute at run time which function to call.  To do that, use the
+function @code{funcall}.  When you also need to determine at run time
+how many arguments to pass, use @code{apply}.
 
 @defun funcall function &rest arguments
 @code{funcall} calls @var{function} with @var{arguments}, and returns
@@ -610,15 +623,16 @@ above, it never knows them in the first place.
 @end group
 @end example
 
-Compare these example with the examples of @code{apply}.
+Compare these examples with the examples of @code{apply}.
 @end defun
 
 @defun apply function &rest arguments
 @code{apply} calls @var{function} with @var{arguments}, just like
 @code{funcall} but with one difference: the last of @var{arguments} is a
-list of arguments to give to @var{function}, rather than a single
-argument.  We also say that @code{apply} @dfn{spreads} this list so that
-each individual element becomes an argument.
+list of objects, which are passed to @var{function} as separate
+arguments, rather than a single list.  We say that @code{apply}
+@dfn{spreads} this list so that each individual element becomes an
+argument.
 
 @code{apply} returns the result of calling @var{function}.  As with
 @code{funcall}, @var{function} must either be a Lisp function or a
@@ -676,16 +690,24 @@ This function ignores any arguments and returns @code{nil}.
 @cindex mapping functions
 
   A @dfn{mapping function} applies a given function to each element of a
-list or other collection.  Emacs Lisp has three such functions;
+list or other collection.  Emacs Lisp has several such functions;
 @code{mapcar} and @code{mapconcat}, which scan a list, are described
-here.  For the third mapping function, @code{mapatoms}, see
-@ref{Creating Symbols}.
+here.  @xref{Creating Symbols}, for the function @code{mapatoms} which
+maps over the symbols in an obarray.  @xref{Hash Access}, for the
+function @code{maphash} which maps over key/value associations in a
+hash table.
+
+  These mapping functions do not allow char-tables because a char-table
+is a sparse array whose nominal range of indices is very large.  To map
+over a char-table in a way that deals properly with its sparse nature,
+use the function @code{map-char-table} (@pxref{Char-Tables}).
 
 @defun mapcar function sequence
 @code{mapcar} applies @var{function} to each element of @var{sequence}
 in turn, and returns a list of the results.
 
-The argument @var{sequence} may be a list, a vector, or a string.  The
+The argument @var{sequence} can be any kind of sequence except a
+char-table; that is, a list, a vector, a bool-vector, or a string.  The
 result is always a list.  The length of the result is the same as the
 length of @var{sequence}.
 
@@ -707,14 +729,14 @@ length of @var{sequence}.
 @end group
 
 @group
-(defun mapcar* (f &rest args)
+(defun mapcar* (function &rest args)
   "Apply FUNCTION to successive cars of all ARGS.
 Return the list of results."
   ;; @r{If no list is exhausted,}
   (if (not (memq 'nil args))              
-      ;; @r{apply function to @sc{CAR}s.}
-      (cons (apply f (mapcar 'car args))  
-            (apply 'mapcar* f             
+      ;; @r{apply function to @sc{car}s.}
+      (cons (apply function (mapcar 'car args))  
+            (apply 'mapcar* function             
                    ;; @r{Recurse for rest of elements.}
                    (mapcar 'cdr args)))))
 @end group
@@ -726,6 +748,13 @@ Return the list of results."
 @end smallexample
 @end defun
 
+@defun mapc function sequence
+@tindex mapc
+@code{mapc} is like @code{mapcar} except that @var{function} is used for
+side-effects only---the values it returns are ignored, not collected
+into a list.  @code{mapc} always returns @var{sequence}.
+@end defun
+
 @defun mapconcat function sequence separator
 @code{mapconcat} applies @var{function} to each element of
 @var{sequence}: the results, which must be strings, are concatenated.
@@ -734,7 +763,9 @@ Between each pair of result strings, @code{mapconcat} inserts the string
 other suitable punctuation.
 
 The argument @var{function} must be a function that can take one
-argument and return a string.
+argument and return a string.  The argument @var{sequence} can be any
+kind of sequence except a char-table; that is, a list, a vector, a
+bool-vector, or a string.
   
 @smallexample
 @group
@@ -793,56 +824,50 @@ is not the @emph{function definition} of @code{silly}.  We have not given
 @code{silly} any function definition, just a value as a variable.)
 
   Most of the time, anonymous functions are constants that appear in
-your program.  For example, you might want to pass one as an argument
-to the function @code{mapcar}, which applies any given function to each
-element of a list.  Here we pass an anonymous function that multiplies
-a number by two:
+your program.  For example, you might want to pass one as an argument to
+the function @code{mapcar}, which applies any given function to each
+element of a list.
+
+  Here we define a function @code{change-property} which 
+uses a function as its third argument:
 
 @example
 @group
-(defun double-each (list)
-  (mapcar '(lambda (x) (* 2 x)) list))
-@result{} double-each
+(defun change-property (symbol prop function)
+  (let ((value (get symbol prop)))
+    (put symbol prop (funcall function value))))
 @end group
+@end example
+
+@noindent
+Here we define a function that uses @code{change-property},
+passing it a function to double a number:
+
+@example
 @group
-(double-each '(2 11))
-@result{} (4 22)
+(defun double-property (symbol prop)
+  (change-property symbol prop '(lambda (x) (* 2 x))))
 @end group
 @end example
 
 @noindent
 In such cases, we usually use the special form @code{function} instead
-of simple quotation to quote the anonymous function.
-
-@defspec function function-object
-@cindex function quoting
-This special form returns @var{function-object} without evaluating it.
-In this, it is equivalent to @code{quote}.  However, it serves as a
-note to the Emacs Lisp compiler that @var{function-object} is intended
-to be used only as a function, and therefore can safely be compiled.
-Contrast this with @code{quote}, in @ref{Quoting}.
-@end defspec
-
-  Using @code{function} instead of @code{quote} makes a difference
-inside a function or macro that you are going to compile.  For example:
+of simple quotation to quote the anonymous function, like this:
 
 @example
 @group
-(defun double-each (list)
-  (mapcar (function (lambda (x) (* 2 x))) list))
-@result{} double-each
-@end group
-@group
-(double-each '(2 11))
-@result{} (4 22)
+(defun double-property (symbol prop)
+  (change-property symbol prop
+                   (function (lambda (x) (* 2 x)))))
 @end group
 @end example
 
-@noindent
-If this definition of @code{double-each} is compiled, the anonymous
-function is compiled as well.  By contrast, in the previous definition
-where ordinary @code{quote} is used, the argument passed to
-@code{mapcar} is the precise list shown:
+Using @code{function} instead of @code{quote} makes a difference if you
+compile the function @code{double-property}.  For example, if you
+compile the second definition of @code{double-property}, the anonymous
+function is compiled as well.  By contrast, if you compile the first
+definition which uses ordinary @code{quote}, the argument passed to
+@code{change-property} is the precise list shown:
 
 @example
 (lambda (x) (* x 2))
@@ -850,20 +875,43 @@ where ordinary @code{quote} is used, the argument passed to
 
 @noindent
 The Lisp compiler cannot assume this list is a function, even though it
-looks like one, since it does not know what @code{mapcar} does with the
-list.  Perhaps @code{mapcar} will check that the @sc{car} of the third
-element is the symbol @code{*}!  The advantage of @code{function} is
-that it tells the compiler to go ahead and compile the constant
-function.
+looks like one, since it does not know what @code{change-property} will
+do with the list.  Perhaps it will check whether the @sc{car} of the third
+element is the symbol @code{*}!  Using @code{function} tells the
+compiler it is safe to go ahead and compile the constant function.
 
   We sometimes write @code{function} instead of @code{quote} when
 quoting the name of a function, but this usage is just a sort of
-comment.
+comment:
 
 @example
 (function @var{symbol}) @equiv{} (quote @var{symbol}) @equiv{} '@var{symbol}
 @end example
 
+@cindex @samp{#'} syntax
+  The read syntax @code{#'} is a short-hand for using @code{function}.
+For example, 
+
+@example
+#'(lambda (x) (* x x))
+@end example
+
+@noindent
+is equivalent to
+
+@example
+(function (lambda (x) (* x x)))
+@end example
+
+@defspec function function-object
+@cindex function quoting
+This special form returns @var{function-object} without evaluating it.
+In this, it is equivalent to @code{quote}.  However, it serves as a
+note to the Emacs Lisp compiler that @var{function-object} is intended
+to be used only as a function, and therefore can safely be compiled.
+Contrast this with @code{quote}, in @ref{Quoting}.
+@end defspec
+
   See @code{documentation} in @ref{Accessing Documentation}, for a
 realistic example using @code{function} and an anonymous function.
 
@@ -931,12 +979,12 @@ is a legitimate function.
 @defun fmakunbound symbol
 This function makes @var{symbol}'s function cell void, so that a
 subsequent attempt to access this cell will cause a @code{void-function}
-error.  (See also @code{makunbound}, in @ref{Local Variables}.)
+error.  (See also @code{makunbound}, in @ref{Void Variables}.)
 
 @example
 @group
 (defun foo (x) x)
-     @result{} x
+     @result{} foo
 @end group
 @group
 (foo 1)
@@ -944,7 +992,7 @@ error.  (See also @code{makunbound}, in @ref{Local Variables}.)
 @end group
 @group
 (fmakunbound 'foo)
-     @result{} x
+     @result{} foo
 @end group
 @group
 (foo 1)
@@ -954,23 +1002,28 @@ error.  (See also @code{makunbound}, in @ref{Local Variables}.)
 @end defun
 
 @defun fset symbol definition
-This function stores @var{definition} in the function cell of @var{symbol}.
-The result is @var{definition}.  Normally @var{definition} should be a function
-or the name of a function, but this is not checked.
+This function stores @var{definition} in the function cell of
+@var{symbol}.  The result is @var{definition}.  Normally
+@var{definition} should be a function or the name of a function, but
+this is not checked.  The argument @var{symbol} is an ordinary evaluated
+argument.
 
 There are three normal uses of this function:
 
 @itemize @bullet
 @item
-Copying one symbol's function definition to another.  (In other words,
-making an alternate name for a function.)
+Copying one symbol's function definition to another---in other words,
+making an alternate name for a function.  (If you think of this as the
+definition of the new name, you should use @code{defalias} instead of
+@code{fset}; see @ref{Defining Functions}.)
 
 @item
 Giving a symbol a function definition that is not a list and therefore
 cannot be made with @code{defun}.  For example, you can use @code{fset}
 to give a symbol @code{s1} a function definition which is another symbol
 @code{s2}; then @code{s1} serves as an alias for whatever definition
-@code{s2} presently has.
+@code{s2} presently has.  (Once again use @code{defalias} instead of
+@code{fset} if you think of this as the definition of @code{s1}.)
 
 @item
 In constructs for defining or altering functions.  If @code{defun}
@@ -978,21 +1031,17 @@ were not a primitive, it could be written in Lisp (as a macro) using
 @code{fset}.
 @end itemize
 
-Here are examples of the first two uses:
+Here are examples of these uses:
 
 @example
 @group
-;; @r{Give @code{first} the same definition @code{car} has.}
-(fset 'first (symbol-function 'car))
-     @result{} #<subr car>
-@end group
-@group
-(first '(1 2 3))
-     @result{} 1
+;; @r{Save @code{foo}'s definition in @code{old-foo}.}
+(fset 'old-foo (symbol-function 'foo))
 @end group
 
 @group
 ;; @r{Make the symbol @code{car} the function definition of @code{xfirst}.}
+;; @r{(Most likely, @code{defalias} would be better than @code{fset} here.)}
 (fset 'xfirst 'car)
      @result{} car
 @end group
@@ -1014,10 +1063,14 @@ Here are examples of the first two uses:
 (fset 'kill-two-lines "\^u2\^k")
      @result{} "\^u2\^k"
 @end group
-@end example
 
-See also the related function @code{defalias}, in @ref{Defining
-Functions}.
+@group
+;; @r{Here is a function that alters other functions.}
+(defun copy-function-definition (new old)
+  "Define NEW with the same function definition as OLD."
+  (fset new (symbol-function old)))
+@end group
+@end example
 @end defun
 
   When writing a function that extends a previously defined function,
@@ -1042,7 +1095,8 @@ proper results.  The only way to avoid this problem is to make sure the
 file is loaded before moving aside the old definition of @code{foo}.
 
   But it is unmodular and unclean, in any case, for a Lisp file to
-redefine a function defined elsewhere.
+redefine a function defined elsewhere.  It is cleaner to use the advice
+facility (@pxref{Advising Functions}).
 
 @node Inline Functions
 @section Inline Functions
@@ -1067,15 +1121,14 @@ advantage of inline functions is greatest for small functions, you
 generally should not make large functions inline.
 
 It's possible to define a macro to expand into the same code that an
-inline function would execute.  But the macro would have a limitation:
-you can use it only explicitly---a macro cannot be called with
+inline function would execute.  (@xref{Macros}.)  But the macro would be
+limited to direct use in expressions---a macro cannot be called with
 @code{apply}, @code{mapcar} and so on.  Also, it takes some work to
-convert an ordinary function into a macro.  (@xref{Macros}.)  To convert
-it into an inline function is very easy; simply replace @code{defun}
-with @code{defsubst}.  Since each argument of an inline function is
-evaluated exactly once, you needn't worry about how many times the
-body uses the arguments, as you do for macros.  (@xref{Argument
-Evaluation}.)
+convert an ordinary function into a macro.  To convert it into an inline
+function is very easy; simply replace @code{defun} with @code{defsubst}.
+Since each argument of an inline function is evaluated exactly once, you
+needn't worry about how many times the body uses the arguments, as you
+do for macros.  (@xref{Argument Evaluation}.)
 
 Inline functions can be used and open-coded later on in the same file,
 following the definition, just like macros.
@@ -1111,6 +1164,9 @@ See @ref{Eval}.
 @item funcall
 See @ref{Calling Functions}.
 
+@item function
+See @ref{Anonymous Functions}.
+
 @item ignore
 See @ref{Calling Functions}.
 
@@ -1129,6 +1185,9 @@ See @ref{Creating Symbols}.
 @item mapcar
 See @ref{Mapping Functions}.
 
+@item map-char-table
+See @ref{Char-Tables}.
+
 @item mapconcat
 See @ref{Mapping Functions}.