(The Buffer List): Fix xrefs.

[gnu-emacs] / lispref / variables.texi

diff --git a/lispref/variables.texi b/lispref/variables.texi
index 36cc2e47fe42975f9a9e3413f07f16c4bd431002..38fb929c16d14afaf1f4b791c0e645fbc17bc03f 100644 (file)
--- a/lispref/variables.texi
+++ b/lispref/variables.texi
@@ -1,6 +1,7 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Emacs Lisp Reference Manual.
 @c -*-texinfo-*-
 @c This is part of the GNU Emacs Lisp Reference Manual.

-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999,
+@c 2000, 2003, 2004

 @c   Free Software Foundation, Inc.
 @c See the file elisp.texi for copying conditions.
 @setfilename ../info/variables
 @c   Free Software Foundation, Inc.
 @c See the file elisp.texi for copying conditions.
 @setfilename ../info/variables


@@ -41,8 +42,10 @@ variable.
 * Buffer-Local Variables::  Variable values in effect only in one buffer.
 * Frame-Local Variables::   Variable values in effect only in one frame.
 * Future Local Variables::  New kinds of local values we might add some day.
 * Buffer-Local Variables::  Variable values in effect only in one buffer.
 * Frame-Local Variables::   Variable values in effect only in one frame.
 * Future Local Variables::  New kinds of local values we might add some day.

-* Variable Aliases::      Variables that are aliases for other variables.

 * File Local Variables::  Handling local variable lists in files.
 * File Local Variables::  Handling local variable lists in files.

+* Variable Aliases::      Variables that are aliases for other variables.
+* Variables with Restricted Values::  Non-constant variables whose value can
+                                        @emph{not} be an arbitrary Lisp object.

 @end menu
 
 @node Global Variables
 @end menu
 
 @node Global Variables


@@ -259,18 +262,20 @@ they are localized depending on ``where'' you are in Emacs, rather than
 localized in time.
 
 @defvar max-specpdl-size
 localized in time.
 
 @defvar max-specpdl-size

+@anchor{Definition of max-specpdl-size}

 @cindex variable limit error
 @cindex evaluation error
 @cindex infinite recursion
 This variable defines the limit on the total number of local variable
 @cindex variable limit error
 @cindex evaluation error
 @cindex infinite recursion
 This variable defines the limit on the total number of local variable

-bindings and @code{unwind-protect} cleanups (@pxref{Nonlocal Exits})
-that are allowed before signaling an error (with data @code{"Variable
-binding depth exceeds max-specpdl-size"}).
+bindings and @code{unwind-protect} cleanups (@pxref{Cleanups,,
+Cleaning Up from Nonlocal Exits}) that are allowed before signaling an
+error (with data @code{"Variable binding depth exceeds
+max-specpdl-size"}).

 
 This limit, with the associated error when it is exceeded, is one way
 that Lisp avoids infinite recursion on an ill-defined function.
 @code{max-lisp-eval-depth} provides another limit on depth of nesting.
 
 This limit, with the associated error when it is exceeded, is one way
 that Lisp avoids infinite recursion on an ill-defined function.
 @code{max-lisp-eval-depth} provides another limit on depth of nesting.

-@xref{Eval}.
+@xref{Definition of max-lisp-eval-depth,, Eval}.

 
 The default value is 600.  Entry to the Lisp debugger increases the
 value, if there is little room left, to make sure the debugger itself
 
 The default value is 600.  Entry to the Lisp debugger increases the
 value, if there is little room left, to make sure the debugger itself


@@ -564,7 +569,7 @@ though being declared using @code{defcustom}@footnote{They may also be
 declared equivalently in @file{cus-start.el}.} or by the first character
 of their @code{variable-documentation} property.  If the property exists
 and is a string, and its first character is @samp{*}, then the variable
 declared equivalently in @file{cus-start.el}.} or by the first character
 of their @code{variable-documentation} property.  If the property exists
 and is a string, and its first character is @samp{*}, then the variable

-is a user option.
+is a user option.  Aliases of user options are also user options.

 @end defun
 
 @kindex variable-interactive
 @end defun
 
 @kindex variable-interactive


@@ -898,6 +903,62 @@ foo                       ;; @r{@code{foo} was changed.}
     (setq @var{var} (cons @var{value} @var{var})))
 @end example
 
     (setq @var{var} (cons @var{value} @var{var})))
 @end example
 

+@defun add-to-ordered-list symbol element &optional order
+This function sets the variable @var{symbol} by inserting
+@var{element} into the old value, which must be a list, at the
+position specified by @var{order}.  If @var{element} is already a
+member of the list, its position in the list is adjusted according
+to @var{order}.  Membership is tested using @code{eq}.
+This function returns the resulting list, whether updated or not.
+
+The @var{order} is typically a number (integer or float), and the
+elements of the list are sorted in non-decreasing numerical order.
+
+@var{order} may also be omitted or @code{nil}.  Then the numeric order
+of @var{element} stays unchanged if it already has one; otherwise,
+@var{element} has no numeric order.  Elements without a numeric list
+order are placed at the end of the list, in no particular order.
+
+Any other value for @var{order} removes the numeric order of @var{element}
+if it already has one; otherwise, it is equivalent to @code{nil}.
+
+The argument @var{symbol} is not implicitly quoted;
+@code{add-to-ordered-list} is an ordinary function, like @code{set}
+and unlike @code{setq}.  Quote the argument yourself if that is what
+you want.
+
+The ordering information is stored in a hash table on @var{symbol}'s
+@code{list-order} property.
+@end defun
+
+Here's a scenario showing how to use @code{add-to-ordered-list}:
+
+@example
+(setq foo '())
+     @result{} nil
+
+(add-to-ordered-list 'foo 'a 1)     ;; @r{Add @code{a}.}
+     @result{} (a)
+
+(add-to-ordered-list 'foo 'c 3)     ;; @r{Add @code{c}.}
+     @result{} (a c)
+
+(add-to-ordered-list 'foo 'b 2)     ;; @r{Add @code{b}.}
+     @result{} (a b c)
+
+(add-to-ordered-list 'foo 'b 4)     ;; @r{Move @code{b}.}
+     @result{} (a c b)
+
+(add-to-ordered-list 'foo 'd)       ;; @r{Append @code{d}.}
+     @result{} (a c b d)
+
+(add-to-ordered-list 'foo 'e)       ;; @r{Add @code{e}}.
+     @result{} (a c b e d)
+
+foo                       ;; @r{@code{foo} was changed.}
+     @result{} (a c b e d)
+@end example
+

 @node Variable Scoping
 @section Scoping Rules for Variable Bindings
 
 @node Variable Scoping
 @section Scoping Rules for Variable Bindings
 


@@ -1331,6 +1392,12 @@ This returns @code{t} if @var{variable} is buffer-local in buffer
 @code{nil}.
 @end defun
 
 @code{nil}.
 @end defun
 

+@defun local-variable-if-set-p variable &optional buffer
+This returns @code{t} if @var{variable} will become buffer-local in
+buffer @var{buffer} (which defaults to the current buffer) if it is
+set there.
+@end defun
+

 @defun buffer-local-value variable buffer
 This function returns the buffer-local binding of @var{variable} (a
 symbol) in buffer @var{buffer}.  If @var{variable} does not have a
 @defun buffer-local-value variable buffer
 This function returns the buffer-local binding of @var{variable} (a
 symbol) in buffer @var{buffer}.  If @var{variable} does not have a


@@ -1418,8 +1485,11 @@ variables that major modes set should not be marked permanent.
 The function @code{kill-all-local-variables} runs this normal hook
 before it does anything else.  This gives major modes a way to arrange
 for something special to be done if the user switches to a different
 The function @code{kill-all-local-variables} runs this normal hook
 before it does anything else.  This gives major modes a way to arrange
 for something special to be done if the user switches to a different

-major mode.  For best results, make this variable buffer-local, so that
-it will disappear after doing its job and will not interfere with the
+major mode.  It is also useful for buffer-specific minor modes
+that should be forgotten if the user changes the major mode.
+
+For best results, make this variable buffer-local, so that it will
+disappear after doing its job and will not interfere with the

 subsequent major mode.  @xref{Hooks}.
 @end defvar
 
 subsequent major mode.  @xref{Hooks}.
 @end defvar
 


@@ -1674,6 +1744,92 @@ bindings offer a way to handle these situations more robustly.
   If sufficient application is found for either of these two kinds of
 local bindings, we will provide it in a subsequent Emacs version.
 
   If sufficient application is found for either of these two kinds of
 local bindings, we will provide it in a subsequent Emacs version.
 

+@node File Local Variables
+@section File Local Variables
+
+  This section describes the functions and variables that affect
+processing of file local variables.  @xref{File variables, ,
+Local Variables in Files, emacs, The GNU Emacs Manual}, for basic
+information about file local variables.
+
+@defopt enable-local-variables
+This variable controls whether to process file local variables.  A
+value of @code{t} means process them unconditionally; @code{nil} means
+ignore them; anything else means ask the user what to do for each
+file.  The default value is @code{t}.
+@end defopt
+
+@defun hack-local-variables &optional mode-only
+This function parses, and binds or evaluates as appropriate, any local
+variables specified by the contents of the current buffer.  The variable
+@code{enable-local-variables} has its effect here.  However, this
+function does not look for the @samp{mode:} local variable in the
+@w{@samp{-*-}} line.  @code{set-auto-mode} does that, also taking
+@code{enable-local-variables} into account (@pxref{Auto Major Mode}).
+
+If the optional argument @var{mode-only} is non-@code{nil}, then all
+this function does is return @code{t} if the @w{@samp{-*-}} line or
+the local variables list specifies a mode and @code{nil} otherwise.
+It does not set the mode nor any other file local variable.
+@end defun
+
+  If a file local variable could specify a function that would
+be called later, or an expression that would be executed later, simply
+visiting a file could take over your Emacs.  To prevent this, Emacs
+takes care not to allow to set such file local variables.
+
+  For one thing, any variable whose name ends in any of
+@samp{-command}, @samp{-frame-alist}, @samp{-function},
+@samp{-functions}, @samp{-hook}, @samp{-hooks}, @samp{-form},
+@samp{-forms}, @samp{-map}, @samp{-map-alist}, @samp{-mode-alist},
+@samp{-program}, or @samp{-predicate} cannot be given a file local
+value.  In general, you should use such a name whenever it is
+appropriate for the variable's meaning.  The variables
+@samp{font-lock-keywords}, @samp{font-lock-keywords} followed by a
+digit, and @samp{font-lock-syntactic-keywords} cannot be given file
+local values either.  These rules can be overridden by giving the
+variable's name a non-@code{nil} @code{safe-local-variable} property.
+If one gives it a @code{safe-local-variable} property of @code{t},
+then one can give the variable any file local value.  One can also
+give any symbol, including the above, a @code{safe-local-variable}
+property that is a function taking exactly one argument.  In that
+case, giving a variable with that name a file local value is only
+allowed if the function returns non-@code{nil} when called with that
+value as argument.
+
+  In addition, any variable whose name has a non-@code{nil}
+@code{risky-local-variable} property is also ignored.  So are all
+variables listed in @code{ignored-local-variables}:
+
+@defvar ignored-local-variables
+This variable holds a list of variables that should not be given local
+values by files.  Any value specified for one of these variables is
+ignored.
+@end defvar
+
+@defun risky-local-variable-p sym &optional val
+If @var{val} is non-@code{nil}, returns non-@code{nil} if giving
+@var{sym} a file local value of @var{val} would be risky, for any of
+the reasons stated above.  If @var{val} is @code{nil} or omitted, only
+returns @code{nil} if @var{sym} can be safely assigned any file local
+value whatsoever.
+@end defun
+
+  The @samp{Eval:} ``variable'' is also a potential loophole, so Emacs
+normally asks for confirmation before handling it.
+
+@defopt enable-local-eval
+This variable controls processing of @samp{Eval:} in @samp{-*-} lines
+or local variables
+lists in files being visited.  A value of @code{t} means process them
+unconditionally; @code{nil} means ignore them; anything else means ask
+the user what to do for each file.  The default value is @code{maybe}.
+@end defopt
+
+  Text properties are also potential loopholes, since their values
+could include functions to call.  So Emacs discards all text
+properties from string values specified for file local variables.
+

 @node Variable Aliases
 @section Variable Aliases
 
 @node Variable Aliases
 @section Variable Aliases
 


@@ -1685,25 +1841,59 @@ chosen, or because its meaning has partly changed---it can be useful
 to keep the old name as an @emph{alias} of the new one for
 compatibility.  You can do this with @code{defvaralias}.
 
 to keep the old name as an @emph{alias} of the new one for
 compatibility.  You can do this with @code{defvaralias}.
 

-@defun defvaralias alias-var base-var &optional docstring
-This function defines the symbol @var{alias-var} as a variable alias
-for symbol @var{base-var}. This means that retrieving the value of
-@var{alias-var} returns the value of @var{base-var}, and changing the
-value of @var{alias-var} changes the value of @var{base-var}.
+@defun defvaralias new-alias base-variable &optional docstring
+This function defines the symbol @var{new-alias} as a variable alias
+for symbol @var{base-variable}. This means that retrieving the value of
+@var{new-alias} returns the value of @var{base-variable}, and changing the
+value of @var{new-alias} changes the value of @var{base-variable}.

 
 If the @var{docstring} argument is non-@code{nil}, it specifies the
 
 If the @var{docstring} argument is non-@code{nil}, it specifies the

-documentation for @var{alias-var}; otherwise, the alias gets the same
-documentation as @var{base-var} has, if any, unless @var{base-var} is
-itself an alias, in which case @var{alias-var} gets the documentation
-of the variable at the end of the chain of aliases.
+documentation for @var{new-alias}; otherwise, the alias gets the same
+documentation as @var{base-variable} has, if any, unless
+@var{base-variable} is itself an alias, in which case @var{new-alias} gets
+the documentation of the variable at the end of the chain of aliases.
+
+This function returns @var{base-variable}.
+@end defun

 
 

-This function returns @var{base-var}.
+  Variable aliases are convenient for replacing an old name for a
+variable with a new name.  @code{make-obsolete-variable} declares that
+the old name is obsolete and therefore that it may be removed at some
+stage in the future.
+
+@defun make-obsolete-variable obsolete-name current-name &optional when
+This function makes the byte-compiler warn that the variable
+@var{obsolete-name} is obsolete.  If @var{current-name} is a symbol, it is
+the variable's new name; then the warning message says to use
+@var{current-name} instead of @var{obsolete-name}.  If @var{current-name}
+is a string, this is the message and there is no replacement variable.
+
+If provided, @var{when} should be a string indicating when the
+variable was first made obsolete---for example, a date or a release
+number.

 @end defun
 
 @end defun
 

+  You can make two variables synonyms and declare one obsolete at the
+same time using the macro @code{define-obsolete-variable-alias}.
+
+@defmac define-obsolete-variable-alias obsolete-name current-name &optional when docstring
+This macro marks the variable @var{obsolete-name} as obsolete and also
+makes it an alias for the variable @var{current-name}.  It is
+equivalent to the following:
+
+@example
+(defvaralias @var{obsolete-name} @var{current-name} @var{docstring})
+(make-obsolete-variable @var{obsolete-name} @var{current-name} @var{when})
+@end example
+@end defmac
+

 @defun indirect-variable variable
 This function returns the variable at the end of the chain of aliases
 of @var{variable}.  If @var{variable} is not a symbol, or if @var{variable} is
 not defined as an alias, the function returns @var{variable}.
 @defun indirect-variable variable
 This function returns the variable at the end of the chain of aliases
 of @var{variable}.  If @var{variable} is not a symbol, or if @var{variable} is
 not defined as an alias, the function returns @var{variable}.

+
+This function signals a @code{cyclic-variable-indirection} error if
+there is a loop in the chain of symbols.

 @end defun
 
 @example
 @end defun
 
 @example


@@ -1726,92 +1916,40 @@ foo
      @result{} 0
 @end example
 
      @result{} 0
 @end example
 

-@node File Local Variables
-@section File Local Variables
-
-  This section describes the functions and variables that affect
-processing of local variables lists in files. @xref{File variables, ,
-Local Variables in Files, emacs, The GNU Emacs Manual}, for basic
-information about file local variables.
-
-@defopt enable-local-variables
-This variable controls whether to process file local variables lists.  A
-value of @code{t} means process the local variables lists
-unconditionally; @code{nil} means ignore them; anything else means ask
-the user what to do for each file.  The default value is @code{t}.
-@end defopt
-
-@defun hack-local-variables &optional mode-only
-This function parses, and binds or evaluates as appropriate, any local
-variables specified by the contents of the current buffer.  The variable
-@code{enable-local-variables} has its effect here.  However, this
-function does not look for the @samp{mode:} local variable in the
-@w{@samp{-*-}} line.  @code{set-auto-mode} does that, also taking
-@code{enable-local-variables} into account.
+@node Variables with Restricted Values
+@section Variables with Restricted Values

 
 

-If the optional argument @var{mode-only} is non-@code{nil}, then all
-this function does is return @code{t} if the @w{@samp{-*-}} line
-specifies a mode and @code{nil} otherwise.  It does not set the mode
-nor any other file local variable.  It does not check whether a mode
-is specified in the local variables list at the end of the file.
-@end defun
+  Ordinary Lisp variables can be assigned any value that is a valid
+Lisp object.  However, certain Lisp variables are not defined in Lisp,
+but in C.  Most of these variables are defined in the C code using
+@code{DEFVAR_LISP}.  Like variables defined in Lisp, these can take on
+any value.  However, some variables are defined using
+@code{DEFVAR_INT} or @code{DEFVAR_BOOL}.  @xref{Defining Lisp
+variables in C,, Writing Emacs Primitives}, in particular the
+description of functions of the type @code{syms_of_@var{filename}},
+for a brief discussion of the C implementation.

 
 

-  If a file local variable list could specify a function that will
-be called later, or an expression that will be executed later, simply
-visiting a file could take over your Emacs.  To prevent this, Emacs
-takes care not to allow local variable lists to set such variables.
-
-  For one thing, any variable whose name ends in @samp{-command},
-@samp{-frame-alist}, @samp{-function}, @samp{-functions},
-@samp{-hook}, @samp{-hooks}, @samp{-form}, @samp{-forms}, @samp{-map},
-@samp{-map-alist}, @samp{-mode-alist}, @samp{-program}, or
-@samp{-predicate} cannot be set in a local variable list.  In general,
-you should use such a name whenever it is appropriate for the
-variable's meaning.  The variables @samp{font-lock-keywords},
-@samp{font-lock-keywords-[0-9]}, and
-@samp{font-lock-syntactic-keywords} cannot be set in a local variable
-list, either.  These rules can be overridden by giving the variable's
-name a non-@code{nil} @code{safe-local-variable} property.  If one
-gives it a @code{safe-local-variable} property of @code{t}, then one
-can give the variable any file local value.  One can also give any
-symbol, including the above, a @code{safe-local-variable} property
-that is a function taking exactly one argument.  In that case, giving
-a variable with that name a file local value is only allowed if the
-function returns non-@code{nil} when called with that value as
-argument.
+  Variables of type @code{DEFVAR_BOOL} can only take on the values
+@code{nil} or @code{t}.  Attempting to assign them any other value
+will set them to @code{t}:

 
 

-  In addition, any variable whose name has a non-@code{nil}
-@code{risky-local-variable} property is also ignored.  So are all
-variables listed in @code{ignored-local-variables}:
+@example
+(let ((display-hourglass 5))
+  display-hourglass)
+     @result{} t
+@end example

 
 

-@defvar ignored-local-variables
-This variable holds a list of variables that should not be
-set by a file's local variables list.  Any value specified
-for one of these variables is ignored.
+@defvar byte-boolean-vars
+This variable holds a list of all variables of type @code{DEFVAR_BOOL}.

 @end defvar
 
 @end defvar
 

-@defun risky-local-variable-p sym &optional val
-If @var{val} is non-@code{nil}, returns non-@code{nil} if giving
-@var{sym} a file local value of @var{val} would be risky, for any of
-the reasons stated above.  If @var{val} is @code{nil} or omitted, only
-returns @code{nil} if @var{sym} can be safely assigned any file local
-value whatsoever.
-@end defun
-
-  The @samp{Eval:} ``variable'' is also a potential loophole, so Emacs
-normally asks for confirmation before handling it.
-
-@defopt enable-local-eval
-This variable controls processing of @samp{Eval:} in local variables
-lists in files being visited.  A value of @code{t} means process them
-unconditionally; @code{nil} means ignore them; anything else means ask
-the user what to do for each file.  The default value is @code{maybe}.
-@end defopt
+  Variables of type @code{DEFVAR_INT} can only take on integer values.
+Attempting to assign them any other value will result in an error:

 
 

-  Text properties are also potential loopholes, since their values
-could include functions to call.  So Emacs discards all text
-properties from string values specified in a file's local variables
-list.
+@example
+(setq window-min-height 5.0)
+@error{} Wrong type argument: integerp, 5.0
+@end example

 
 @ignore
    arch-tag: 5ff62c44-2b51-47bb-99d4-fea5aeec5d3e
 
 @ignore
    arch-tag: 5ff62c44-2b51-47bb-99d4-fea5aeec5d3e