X-Git-Url: https://git.hcoop.net/bpt/emacs.git/blobdiff_plain/257210319f10abebbfd7c12784cf3a8e112c3562..ab422c4d6899b1442cb6954c1829c1fb656b006c:/doc/lispref/symbols.texi diff --git a/doc/lispref/symbols.texi b/doc/lispref/symbols.texi index d7497ab6f3..3e6c8266ef 100644 --- a/doc/lispref/symbols.texi +++ b/doc/lispref/symbols.texi @@ -1,6 +1,7 @@ @c -*-texinfo-*- @c This is part of the GNU Emacs Lisp Reference Manual. -@c Copyright (C) 1990-1995, 1998-1999, 2001-2012 Free Software Foundation, Inc. +@c Copyright (C) 1990-1995, 1998-1999, 2001-2013 Free Software +@c Foundation, Inc. @c See the file elisp.texi for copying conditions. @node Symbols @chapter Symbols @@ -13,8 +14,8 @@ as variables and as function names; see @ref{Variables}, and @ref{Functions}. For the precise read syntax for symbols, see @ref{Symbol Type}. - You can test whether an arbitrary Lisp object is a symbol -with @code{symbolp}: + You can test whether an arbitrary Lisp object is a symbol with +@code{symbolp}: @defun symbolp object This function returns @code{t} if @var{object} is a symbol, @code{nil} @@ -26,7 +27,7 @@ otherwise. and property lists. * Definitions:: A definition says how a symbol will be used. * Creating Symbols:: How symbols are kept unique. -* Property Lists:: Each symbol has a property list +* Symbol Properties:: Each symbol has a property list for recording miscellaneous information. @end menu @@ -91,7 +92,7 @@ the contents of a symbol's function cell, use the function The property list cell normally should hold a correctly formatted property list. To get a symbol's property list, use the function -@code{symbol-plist}. @xref{Property Lists}. +@code{symbol-plist}. @xref{Symbol Properties}. The function cell or the value cell may be @dfn{void}, which means that the cell does not reference any object. (This is not the same @@ -153,8 +154,8 @@ that cell can hold only one Lisp object at any given time. @xref{Macros}. As previously noted, Emacs Lisp allows the same symbol to be defined -both as a variable (e.g.@: with @code{defvar}) and as a function or -macro (e.g.@: with @code{defun}). Such definitions do not conflict. +both as a variable (e.g., with @code{defvar}) and as a function or +macro (e.g., with @code{defun}). Such definitions do not conflict. These definition also act as guides for programming tools. For example, the @kbd{C-h f} and @kbd{C-h v} commands create help buffers @@ -376,109 +377,34 @@ If @code{unintern} does delete a symbol, it returns @code{t}. Otherwise it returns @code{nil}. @end defun -@node Property Lists -@section Property Lists -@cindex property list -@cindex plist +@node Symbol Properties +@section Symbol Properties +@cindex symbol property - A @dfn{property list} (@dfn{plist} for short) is a list of paired -elements. Each of the pairs associates a property name (usually a -symbol) with a property or value. + A symbol may possess any number of @dfn{symbol properties}, which +can be used to record miscellaneous information about the symbol. For +example, when a symbol has a @code{risky-local-variable} property with +a non-@code{nil} value, that means the variable which the symbol names +is a risky file-local variable (@pxref{File Local Variables}). - Every symbol has a cell that stores a property list (@pxref{Symbol -Components}). This property list is used to record information about -the symbol, such as its variable documentation and the name of the -file where it was defined. - - Property lists can also be used in other contexts. For instance, -you can assign property lists to character positions in a string or -buffer. @xref{Text Properties}. - - The property names and values in a property list can be any Lisp -objects, but the names are usually symbols. Property list functions -compare the property names using @code{eq}. Here is an example of a -property list, found on the symbol @code{progn} when the compiler is -loaded: - -@example -(lisp-indent-function 0 byte-compile byte-compile-progn) -@end example - -@noindent -Here @code{lisp-indent-function} and @code{byte-compile} are property -names, and the other two elements are the corresponding values. + Each symbol's properties and property values are stored in the +symbol's property list cell (@pxref{Symbol Components}), in the form +of a property list (@pxref{Property Lists}). @menu -* Plists and Alists:: Comparison of the advantages of property - lists and association lists. -* Symbol Plists:: Functions to access symbols' property lists. -* Other Plists:: Accessing property lists stored elsewhere. +* Symbol Plists:: Accessing symbol properties. +* Standard Properties:: Standard meanings of symbol properties. @end menu -@node Plists and Alists -@subsection Property Lists and Association Lists -@cindex plist vs. alist -@cindex alist vs. plist - -@cindex property lists vs association lists - Association lists (@pxref{Association Lists}) are very similar to -property lists. In contrast to association lists, the order of the -pairs in the property list is not significant since the property names -must be distinct. - - Property lists are better than association lists for attaching -information to various Lisp function names or variables. If your -program keeps all such information in one association list, it will -typically need to search that entire list each time it checks for an -association for a particular Lisp function name or variable, which -could be slow. By contrast, if you keep the same information in the -property lists of the function names or variables themselves, each -search will scan only the length of one property list, which is -usually short. This is why the documentation for a variable is -recorded in a property named @code{variable-documentation}. The byte -compiler likewise uses properties to record those functions needing -special treatment. - - However, association lists have their own advantages. Depending on -your application, it may be faster to add an association to the front of -an association list than to update a property. All properties for a -symbol are stored in the same property list, so there is a possibility -of a conflict between different uses of a property name. (For this -reason, it is a good idea to choose property names that are probably -unique, such as by beginning the property name with the program's usual -name-prefix for variables and functions.) An association list may be -used like a stack where associations are pushed on the front of the list -and later discarded; this is not possible with a property list. - @node Symbol Plists -@subsection Property List Functions for Symbols - -@defun symbol-plist symbol -This function returns the property list of @var{symbol}. -@end defun - -@defun setplist symbol plist -This function sets @var{symbol}'s property list to @var{plist}. -Normally, @var{plist} should be a well-formed property list, but this is -not enforced. The return value is @var{plist}. +@subsection Accessing Symbol Properties -@example -(setplist 'foo '(a 1 b (2 3) c nil)) - @result{} (a 1 b (2 3) c nil) -(symbol-plist 'foo) - @result{} (a 1 b (2 3) c nil) -@end example - -For symbols in special obarrays, which are not used for ordinary -purposes, it may make sense to use the property list cell in a -nonstandard fashion; in fact, the abbrev mechanism does so -(@pxref{Abbrevs}). -@end defun + The following functions can be used to access symbol properties. @defun get symbol property -This function finds the value of the property named @var{property} in -@var{symbol}'s property list. If there is no such property, @code{nil} -is returned. Thus, there is no distinction between a value of +This function returns the value of the property named @var{property} +in @var{symbol}'s property list. If there is no such property, it +returns @code{nil}. Thus, there is no distinction between a value of @code{nil} and the absence of the property. The name @var{property} is compared with the existing property names @@ -504,69 +430,141 @@ The @code{put} function returns @var{value}. @end example @end defun -@node Other Plists -@subsection Property Lists Outside Symbols - - These functions are useful for manipulating property lists -not stored in symbols: - -@defun plist-get plist property -This returns the value of the @var{property} property stored in the -property list @var{plist}. It accepts a malformed @var{plist} -argument. If @var{property} is not found in the @var{plist}, it -returns @code{nil}. For example, - -@example -(plist-get '(foo 4) 'foo) - @result{} 4 -(plist-get '(foo 4 bad) 'foo) - @result{} 4 -(plist-get '(foo 4 bad) 'bad) - @result{} nil -(plist-get '(foo 4 bad) 'bar) - @result{} nil -@end example +@defun symbol-plist symbol +This function returns the property list of @var{symbol}. @end defun -@defun plist-put plist property value -This stores @var{value} as the value of the @var{property} property in -the property list @var{plist}. It may modify @var{plist} destructively, -or it may construct a new list structure without altering the old. The -function returns the modified property list, so you can store that back -in the place where you got @var{plist}. For example, +@defun setplist symbol plist +This function sets @var{symbol}'s property list to @var{plist}. +Normally, @var{plist} should be a well-formed property list, but this is +not enforced. The return value is @var{plist}. @example -(setq my-plist '(bar t foo 4)) - @result{} (bar t foo 4) -(setq my-plist (plist-put my-plist 'foo 69)) - @result{} (bar t foo 69) -(setq my-plist (plist-put my-plist 'quux '(a))) - @result{} (bar t foo 69 quux (a)) +(setplist 'foo '(a 1 b (2 3) c nil)) + @result{} (a 1 b (2 3) c nil) +(symbol-plist 'foo) + @result{} (a 1 b (2 3) c nil) @end example -@end defun - You could define @code{put} in terms of @code{plist-put} as follows: +For symbols in special obarrays, which are not used for ordinary +purposes, it may make sense to use the property list cell in a +nonstandard fashion; in fact, the abbrev mechanism does so +(@pxref{Abbrevs}). + +You could define @code{put} in terms of @code{setplist} and +@code{plist-put}, as follows: @example (defun put (symbol prop value) (setplist symbol (plist-put (symbol-plist symbol) prop value))) @end example - -@defun lax-plist-get plist property -Like @code{plist-get} except that it compares properties -using @code{equal} instead of @code{eq}. @end defun -@defun lax-plist-put plist property value -Like @code{plist-put} except that it compares properties -using @code{equal} instead of @code{eq}. +@defun function-get symbol property +This function is identical to @code{get}, except that if @var{symbol} +is the name of a function alias, it looks in the property list of the +symbol naming the actual function. @xref{Defining Functions}. @end defun -@defun plist-member plist property -This returns non-@code{nil} if @var{plist} contains the given -@var{property}. Unlike @code{plist-get}, this allows you to distinguish -between a missing property and a property with the value @code{nil}. -The value is actually the tail of @var{plist} whose @code{car} is -@var{property}. -@end defun +@node Standard Properties +@subsection Standard Symbol Properties + + Here, we list the symbol properties which are used for special +purposes in Emacs. In the following table, whenever we say ``the +named function'', that means the function whose name is the relevant +symbol; similarly for ``the named variable'' etc. + +@table @code +@item :advertised-binding +This property value specifies the preferred key binding, when showing +documentation, for the named function. @xref{Keys in Documentation}. + +@item char-table-extra-slots +The value, if non-@code{nil}, specifies the number of extra slots in +the named char-table type. @xref{Char-Tables}. + +@item customized-face +@itemx face-defface-spec +@itemx saved-face +@itemx theme-face +These properties are used to record a face's standard, saved, +customized, and themed face specs. Do not set them directly; they are +managed by @code{defface} and related functions. @xref{Defining +Faces}. + +@item customized-value +@itemx saved-value +@itemx standard-value +@itemx theme-value +These properties are used to record a customizable variable's standard +value, saved value, customized-but-unsaved value, and themed values. +Do not set them directly; they are managed by @code{defcustom} and +related functions. @xref{Variable Definitions}. + +@item disabled +If the value is non-@code{nil}, the named function is disabled as a +command. @xref{Disabling Commands}. + +@item face-documentation +The value stores the documentation string of the named face. This is +set automatically by @code{defface}. @xref{Defining Faces}. + +@item history-length +The value, if non-@code{nil}, specifies the maximum minibuffer history +length for the named history list variable. @xref{Minibuffer +History}. + +@item interactive-form +The value is an interactive form for the named function. Normally, +you should not set this directly; use the @code{interactive} special +form instead. @xref{Interactive Call}. + +@item menu-enable +The value is an expression for determining whether the named menu item +should be enabled in menus. @xref{Simple Menu Items}. + +@item mode-class +If the value is @code{special}, the named major mode is ``special''. +@xref{Major Mode Conventions}. + +@item permanent-local +If the value is non-@code{nil}, the named variable is a buffer-local +variable whose value should not be reset when changing major modes. +@xref{Creating Buffer-Local}. + +@item permanent-local-hook +If the value is non-@code{nil}, the named function should not be +deleted from the local value of a hook variable when changing major +modes. @xref{Setting Hooks}. + +@item pure +This property is used internally to mark certain named functions for +byte compiler optimization. Do not set it. + +@item risky-local-variable +If the value is non-@code{nil}, the named variable is considered risky +as a file-local variable. @xref{File Local Variables}. + +@item safe-function +If the value is non-@code{nil}, the named function is considered +generally safe for evaluation. @xref{Function Safety}. + +@item safe-local-eval-function +If the value is non-@code{nil}, the named function is safe to call in +file-local evaluation forms. @xref{File Local Variables}. + +@item safe-local-variable +The value specifies a function for determining safe file-local values +for the named variable. @xref{File Local Variables}. + +@item side-effect-free +A non-@code{nil} value indicates that the named function is free of +side-effects, for determining function safety (@pxref{Function +Safety}) as well as for byte compiler optimizations. Do not set it. + +@item variable-documentation +If non-@code{nil}, this specifies the named vaariable's documentation +string. This is set automatically by @code{defvar} and related +functions. @xref{Defining Faces}. +@end table