@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999,
-@c 2000, 2003, 2004
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1998, 1999, 2000,
+@c 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/variables
@node Variables, Functions, Control Structures, Top
* 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.
+* 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 Constant Variables
@section Variables that Never Change
-@vindex nil
-@vindex t
@kindex setting-constant
@cindex keyword symbol
+@cindex variable with constant value
+@cindex constant variables
+@cindex symbol that evaluates to itself
+@cindex symbol with constant value
In Emacs Lisp, certain symbols normally evaluate to themselves. These
include @code{nil} and @code{t}, as well as any symbol whose name starts
@end example
@defun keywordp object
-@tindex keywordp
function returns @code{t} if @var{object} is a symbol whose name
starts with @samp{:}, interned in the standard obarray, and returns
@code{nil} otherwise.
@code{max-lisp-eval-depth} provides another limit on depth of nesting.
@xref{Definition of max-lisp-eval-depth,, Eval}.
-The default value is 600. Entry to the Lisp debugger increases the
+The default value is 1000. Entry to the Lisp debugger increases the
value, if there is little room left, to make sure the debugger itself
has room to execute.
@end defvar
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
@item @dots{}-command
The value is a whole shell command.
-@item @samp{}-switches
+@item @dots{}-switches
The value specifies options for a command.
@end table
@end group
@group
-;; @r{Here the value of @code{abracadabra},}
+;; @r{Here, the value of @code{abracadabra},}
;; @r{which is @code{foo},}
;; @r{is the symbol whose value is examined.}
(let ((abracadabra 'foo))
@end quotation
@end defun
- One other function for setting a variable is designed to add
-an element to a list if it is not already present in the list.
-
-@defun add-to-list symbol element &optional append
-This function sets the variable @var{symbol} by consing @var{element}
-onto the old value, if @var{element} is not already a member of that
-value. It returns the resulting list, whether updated or not. The
-value of @var{symbol} had better be a list already before the call.
-Membership is tested using @code{equal}.
-
-Normally, if @var{element} is added, it is added to the front of
-@var{symbol}, but if the optional argument @var{append} is
-non-@code{nil}, it is added at the end.
-
-The argument @var{symbol} is not implicitly quoted; @code{add-to-list}
-is an ordinary function, like @code{set} and unlike @code{setq}. Quote
-the argument yourself if that is what you want.
-@end defun
-
-Here's a scenario showing how to use @code{add-to-list}:
-
-@example
-(setq foo '(a b))
- @result{} (a b)
-
-(add-to-list 'foo 'c) ;; @r{Add @code{c}.}
- @result{} (c a b)
-
-(add-to-list 'foo 'b) ;; @r{No effect.}
- @result{} (c a b)
-
-foo ;; @r{@code{foo} was changed.}
- @result{} (c a b)
-@end example
-
- An equivalent expression for @code{(add-to-list '@var{var}
-@var{value})} is this:
-
-@example
-(or (member @var{value} @var{var})
- (setq @var{var} (cons @var{value} @var{var})))
-@end example
-
@node Variable Scoping
@section Scoping Rules for Variable Bindings
@end example
@cindex closures not available
- Some Lisp dialects have ``closures'', objects that are like functions
+ Some Lisp dialects have ``closures,'' objects that are like functions
but record additional variable bindings. Emacs Lisp does not have
closures.
@node Buffer-Local Variables
@section Buffer-Local Variables
-@cindex variables, buffer-local
+@cindex variable, buffer-local
@cindex buffer-local variables
Global and local variable bindings are found in most programming
@defun kill-all-local-variables
This function eliminates all the buffer-local variable bindings of the
-current buffer except for variables marked as ``permanent''. As a
+current buffer except for variables marked as ``permanent.'' As a
result, the buffer will see the default values of most variables.
This function also resets certain other information pertaining to the
@node Frame-Local Variables
@section Frame-Local Variables
+@cindex frame-local variables
Just as variables can have buffer-local bindings, they can also have
frame-local bindings. These bindings belong to one frame, and are in
If the variable is terminal-local, this function signals an error,
because such variables cannot have frame-local bindings as well.
@xref{Multiple Displays}. A few variables that are implemented
-specially in Emacs can be (and usually are) buffer-local, but can never
-be frame-local.
+specially in Emacs can be buffer-local, but can never be frame-local.
This command returns @var{variable}.
@end deffn
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
+@cindex file local variables
+
+ A file can specify local variable values; Emacs uses these to create
+buffer-local bindings for those variables in the buffer visiting that
+file. @xref{File variables, , Local Variables in Files, emacs, The
+GNU Emacs Manual}, for basic information about file local variables.
+This section describes the functions and variables that affect
+processing of file local variables.
+
+@defopt enable-local-variables
+This variable controls whether to process file local variables.
+The possible values are:
+
+@table @asis
+@item @code{t} (the default)
+Set the safe variables, and query (once) about any unsafe variables.
+@item @code{:safe}
+Set only the safe variables and do not query.
+@item @code{:all}
+Set all the variables and do not query.
+@item @code{nil}
+Don't set any variables.
+@item anything else
+Query (once) about all the variables.
+@end table
+@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. Emacs takes several
+measures to prevent this.
+
+@cindex safe local variable
+ You can specify safe values for a variable with a
+@code{safe-local-variable} property. The property has to be
+a function of one argument; any value is safe if the function
+returns non-@code{nil} given that value. Many commonly encountered
+file variables standardly have @code{safe-local-variable} properties,
+including @code{fill-column}, @code{fill-prefix}, and
+@code{indent-tabs-mode}. For boolean-valued variables that are safe,
+use @code{booleanp} as the property value. Lambda expressions should
+be quoted so that @code{describe-variable} can display the predicate.
+
+@defopt safe-local-variable-values
+This variable provides another way to mark some variable values as
+safe. It is a list of cons cells @code{(@var{var} . @var{val})},
+where @var{var} is a variable name and @var{val} is a value which is
+safe for that variable.
+
+When Emacs asks the user whether or not to obey a set of file local
+variable specifications, the user can choose to mark them as safe.
+Doing so adds those variable/value pairs to
+@code{safe-local-variable-values}, and saves it to the user's custom
+file.
+@end defopt
+
+@defun safe-local-variable-p sym val
+This function returns non-@code{nil} if it is safe to give @var{sym}
+the value @var{val}, based on the above criteria.
+@end defun
+
+@c @cindex risky local variable Duplicates risky-local-variable
+ Some variables are considered @dfn{risky}. A 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} is considered risky. The
+variables @samp{font-lock-keywords}, @samp{font-lock-keywords}
+followed by a digit, and @samp{font-lock-syntactic-keywords} are also
+considered risky. Finally, any variable whose name has a
+non-@code{nil} @code{risky-local-variable} property is considered
+risky.
+
+@defun risky-local-variable-p sym
+This function returns non-@code{nil} if @var{sym} is a risky variable,
+based on the above criteria.
+@end defun
+
+ If a variable is risky, it will not be entered automatically into
+@code{safe-local-variable-values} as described above. Therefore,
+Emacs will always query before setting a risky variable, unless the
+user explicitly allows the setting by customizing
+@code{safe-local-variable-values} directly.
+
+@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
+completely ignored.
+@end defvar
+
+ 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
+
+@defopt safe-local-eval-forms
+This variable holds a list of expressions that are safe to
+evaluate when found in the @samp{Eval:} ``variable'' in a file
+local variables list.
+@end defopt
+
+ If the expression is a function call and the function has a
+@code{safe-local-eval-function} property, the property value
+determines whether the expression is safe to evaluate. The property
+value can be a predicate to call to test the expression, a list of
+such predicates (it's safe if any predicate succeeds), or @code{t}
+(always safe provided the arguments are constant).
+
+ 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
+@cindex variable aliases
It is sometimes useful to make two variables synonyms, so that both
variables always have the same value, and changing either one also
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}. The two aliased variable names always share the
+same value and the same bindings.
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-var}.
+This function returns @var{base-variable}.
@end defun
-Variable aliases are convenient for replacing an old name for a
+ 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.
-@defmac make-obsolete-variable variable new &optional when
-This macro makes the byte-compiler warn that the variable
-@var{variable} is obsolete. If @var{new} is a symbol, it is the
-variable's new name; then the warning message says to use @var{new}
-instead of @var{variable}. If @var{new} is a string, this is the
-message and there is no replacement variable.
+@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 defmac
+@end defun
-You can make two variables synonyms and declare one obsolete at the
+ 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 variable new &optional when docstring
-This macro marks the variable @var{variable} as obsolete and also
-makes it an alias for the variable @var{new}.
+@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:
-If provided, @var{when} should be a string indicating when
-@var{variable} was first made obsolete. The optional argument
-@var{docstring} specifies the documentation string for @var{variable}.
-If @var{docstring} is omitted or nil, @var{variable} uses the
-documentation string of @var{new} unless it already has one of its
-own.
+@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
@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.
-
-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
-
- If a file local variable list 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 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.
-
- 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
-set by a file's local variables list. 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 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 in a file's local variables
-list.
-
@node Variables with Restricted Values
@section Variables with Restricted Values