@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1997, 1998, 1999, 2000, 2002 Free Software Foundation, Inc.
+@c Copyright (C) 1997, 1998, 1999, 2000, 2002, 2003 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/customize
@node Customization, Loading, Macros, Top
@menu
* Common Keywords::
-* Group Definitions::
-* Variable Definitions::
+* Group Definitions::
+* Variable Definitions::
* Customization Types::
@end menu
in the customization buffer with the Info node name.
@item (url-link @var{url})
-Link to a web page; @var{url} is a string which specifies the @sc{url}.
+Link to a web page; @var{url} is a string which specifies the @acronym{URL}.
The link appears in the customization buffer as @var{url}.
@item (emacs-commentary-link @var{library})
@var{default} because they are not expanded when editing the value,
causing list values to appear to have the wrong structure.
+If you specify the @code{:set} option, to make the variable take other
+special actions when set through the customization buffer, the
+variable's documentation string should tell the user specifically how
+to do the same job in hand-written Lisp code.
+
When you evaluate a @code{defcustom} form with @kbd{C-M-x} in Emacs Lisp
mode (@code{eval-defun}), a special feature of @code{eval-defun}
arranges to set the variable unconditionally, without testing whether
@item :get @var{getfunction}
Specify @var{getfunction} as the way to extract the value of this
option. The function @var{getfunction} should take one argument, a
-symbol, and should return the ``current value'' for that symbol (which
-need not be the symbol's Lisp value). The default is
-@code{default-value}.
+symbol, and should return whatever customize should use as the
+``current value'' for that symbol (which need not be the symbol's Lisp
+value). The default is @code{default-value}.
+
+You have to really understand the workings of Custom to use
+@code{:get} correctly. It is meant for values that are treated in
+Custom as variables but are not actually stored in Lisp variables. It
+is almost surely a mistake to specify @code{getfunction} for a value
+that really is stored in a Lisp variable.
@item :initialize @var{function}
@var{function} should be a function used to initialize the variable when
@table @code
@item custom-initialize-set
Use the variable's @code{:set} function to initialize the variable, but
-do not reinitialize it if it is already non-void. This is the default
-@code{:initialize} function.
+do not reinitialize it if it is already non-void.
@item custom-initialize-default
Like @code{custom-initialize-set}, but use the function
customizing the variable will do so.
@item custom-initialize-reset
-Always use the @code{:set} function to initialize the variable. If the
-variable is already non-void, reset it by calling the @code{:set}
+Always use the @code{:set} function to initialize the variable. If
+the variable is already non-void, reset it by calling the @code{:set}
function using the current value (returned by the @code{:get} method).
+This is the default @code{:initialize} function.
@item custom-initialize-changed
Use the @code{:set} function to initialize the variable, if it is
customization buffer for editing.
You specify the customization type in @code{defcustom} with the
-@code{:type} keyword. The argument of @code{:type} is evaluated; since
-types that vary at run time are rarely useful, normally you use a quoted
-constant. For example:
+@code{:type} keyword. The argument of @code{:type} is evaluated, but
+only once when the @code{defcustom} is executed, so it isn't useful
+for the value to vary. Normally we use a quoted constant. For
+example:
@example
(defcustom diff-command "diff"
* Composite Types::
* Splicing into Lists::
* Type Keywords::
+* Defining New Types::
@end menu
All customization types are implemented as widgets; see @ref{Top, ,
-Introduction, widget, The Emacs Widget Library} for details.
+Introduction, widget, The Emacs Widget Library}, for details.
@node Simple Types
@subsection Simple Types
in the customization buffer.
@item number
-The value must be a number, and is represented textually in the
-customization buffer.
+The value must be a number (floating point or integer), and is
+represented textually in the customization buffer.
+
+@item float
+The value must be a floating point number, and is represented
+textually in the customization buffer.
@item string
The value must be a string, and the customization buffer shows just the
@end smallexample
@noindent
-instead of
+instead of
@smallexample
(defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3))
key, using variations of this trick:
@smallexample
-(defcustom person-data '(("brian" 50 t)
+(defcustom person-data '(("brian" 50 t)
("dorith" 55 nil)
("ken" 52 t))
"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG)."
:type '(alist :value-type (group age boolean)))
-(defcustom pets '(("brian")
+(defcustom pets '(("brian")
("dorith" "dog" "guppy")
("ken" "cat"))
"Alist of people's pets.
@item color
The value must be a valid color name, and you can do completion with
-@kbd{M-@key{TAB}}. A sample is provided,
+@kbd{M-@key{TAB}}. A sample is provided.
@end table
@node Composite Types
a @code{const}, you should specify a valid default for that alternative
using the @code{:value} keyword. @xref{Type Keywords}.
+If some values are covered by more than one of the alternatives,
+customize will choose the first alternative that the value fits. This
+means you should always list the most specific types first, and the
+most general last. Here's an example of proper usage:
+
+@example
+(choice (const :tag "Off" nil) symbol (sexp :tag "Other"))
+@end example
+
+@noindent
+This way, the special value @code{nil} is not treated like other
+symbols, and symbols are not treated like other Lisp expressions.
+
@item (radio @var{element-types}@dots{})
This is similar to @code{choice}, except that the choices are displayed
using `radio buttons' rather than a menu. This has the advantage of
keyword.
@item %%
-Display a literal @samp{%}.
+Display a literal @samp{%}.
@end table
@item :action @var{action}
@code{widget-backward}, it will display the string @var{motion-doc} in
the echo area. In addition, @var{motion-doc} is used as the mouse
@code{help-echo} string and may actually be a function or form evaluated
-to yield a help string as for @code{help-echo} text properties.
+to yield a help string. If it is a function, it is called with one
+argument, the widget.
@c @xref{Text help-echo}.
@item :match @var{function}
@item
Widgets with tabbing order @code{-1} are ignored.
-@item
+@item
(Unimplemented) When on a widget with tabbing order @var{n}, go to the
next widget in the buffer with tabbing order @var{n+1} or @code{nil},
whichever comes first.
@code{checkbox} associated with this item.
@end ignore
@end table
+
+@node Defining New Types
+@subsection Defining New Types
+
+In the previous sections we have described how to construct elaborate
+type specifications for @code{defcustom}. In some cases you may want to
+give such a type specification a name. The obvious case is when you are
+using the same type for many user options, rather than repeat the
+specification for each option, you can give the type specification a
+name once, and use that name each @code{defcustom}. The other case is
+when a user option accept a recursive datastructure. To make it
+possible for a datatype to refer to itself, it needs to have a name.
+
+Since custom types are implemented as widgets, the way to define a new
+customize type is to define a new widget. We are not going to describe
+the widget interface here in details, see @ref{Top, , Introduction,
+widget, The Emacs Widget Library}, for that. Instead we are going to
+demonstrate the minimal functionality needed for defining new customize
+types by a simple example.
+
+@example
+(define-widget 'binary-tree-of-string 'lazy
+ "A binary tree made of cons-cells and strings."
+ :offset 4
+ :tag "Node"
+ :type '(choice (string :tag "Leaf" :value "")
+ (cons :tag "Interior"
+ :value ("" . "")
+ binary-tree-of-string
+ binary-tree-of-string)))
+
+(defcustom foo-bar ""
+ "Sample variable holding a binary tree of strings."
+ :type 'binary-tree-of-string)
+@end example
+
+The function to define a new widget is name @code{define-widget}. The
+first argument is the symbol we want to make a new widget type. The
+second argument is a symbol representing an existing widget, the new
+widget is going to be defined in terms of difference from the existing
+widget. For the purpose of defining new customization types, the
+@code{lazy} widget is perfect, because it accept a @code{:type} keyword
+argument with the same syntax as the keyword argument to
+@code{defcustom} with the same name. The third argument is a
+documentation string for the new widget. You will be able to see that
+string with the @kbd{M-x widget-browse @key{ret} binary-tree-of-string
+@key{ret}} command.
+
+After these mandatory arguments follows the keyword arguments. The most
+important is @code{:type}, which describes the datatype we want to match
+with this widget. Here a @code{binary-tree-of-string} is described as
+being either a string, or a cons-cell whose car and cdr are themselves
+both @code{binary-tree-of-string}. Note the reference to the widget
+type we are currently in the process of defining. The @code{:tag}
+attribute is a string to name the widget in the user interface, and the
+@code{:offset} argument are there to ensure that child nodes are
+indented four spaces relatively to the parent node, making the tree
+structure apparent in the customization buffer.
+
+The @code{defcustom} shows how the new widget can be used as an ordinary
+customization type.
+
+If you wonder about the name @code{lazy}, know that the other composite
+widgets convert their inferior widgets to internal form when the widget
+is instantiated in a buffer. This conversion is recursive, so the
+inferior widgets will convert @emph{their} inferior widgets. If the
+datastructure is itself recursive, this conversion will go on forever,
+or at least until Emacs run out of stack space. The @code{lazy} widget
+stop this recursion, it will only convert its @code{:type} argument when
+needed.
+
+@ignore
+ arch-tag: d1b8fad3-f48c-4ce4-a402-f73b5ef19bd2
+@end ignore
HCoop / bpt / emacs.git / blobdiff