0.1 Introduction

Most graphical user interface toolkits provide a number of standard user interface controls (sometimes known as ‘widgets’ or ‘gadgets’). Historically, Emacs didn’t support anything like this, except for its incredible powerful text “widget”. However, since XEmacs 21.4, XEmacs has supported “native” widgets (GUI controls implemented as Lisp APIs in C for the MS Windows, Motif, Athena, and GTK toolkits) and libglade (GUI controls with an XML API for the GTK toolkit). On the other hand, Emacs does provide the necessary primitives to implement many other widgets within a text buffer, and of course this is the only way to implement self-contained controls in a text terminal. The widget package simplifies this task.

Examples of some basic widgets include:

link

Areas of text with an associated action. Intended for hypertext links embedded in text.

push-button

Like link, but intended for stand-alone buttons.

editable-field

An editable text field. It can be either variable or fixed length.

menu-choice

Allows the user to choose one of multiple options from a menu, each option is itself a widget. Only the selected option will be visible in the buffer.

radio-button-choice

Allows the user to choose one of multiple options by activating radio buttons. The options are implemented as widgets. All options will be visible in the buffer.

item

A simple constant widget intended to be used in the menu-choice and radio-button-choice widgets.

choice-item

A button item only intended for use in choices. When invoked, the user will be asked to select another option from the choice widget.

toggle

A simple ‘on’/‘off’ switch.

checkbox

A checkbox (‘[ ]’/‘[X]’).

editable-list

Create an editable list. The user can insert or delete items in the list. Each list item is itself a widget.

Now, of what possible use can support for widgets be in a text editor? I’m glad you asked. The answer is that widgets are useful for implementing forms. A form in Emacs is a buffer where the user is supposed to fill out a number of fields, each of which has a specific meaning. The user is not supposed to change or delete any of the text between the fields. Examples of forms in Emacs are the ‘forms’ package (of course), the customize buffers, the mail and news compose modes, and the HTML form support in the ‘w3’ browser.

The advantages for a programmer of using the widget package to implement forms are:

1. More complex fields than just editable text are supported.
2. You can give the users immediate feedback if they enter invalid data in a text field, and sometimes prevent entering invalid data.
3. You can have fixed sized fields, thus allowing multiple fields to be lined up in columns.
4. It is simple to query or set the value of a field.
5. Editing happens in a normal buffer, not in the mini-buffer.
6. Packages using the library get a uniform look-and-feel, making them easier for the user to learn.
7. As support for embedded graphics improve, the widget library will be extended to use the GUI features. This means that your code using the widget library will also use the new graphic features automatically.
8. A widget specification is implemented as a class, and new subclasses can be derived from any class, by restricting or extending the behavior.

In order to minimize the code that is loaded by users who does not create any widgets, the code has been split in two files:

‘widget.el’

This declares the user variables, defines the function define-widget, and autoloads the function widget-create.

‘wid-edit.el’

Everything else is here. Do not load it explicitly, as it will be autoloaded when needed.

In order to minimize the code that is loaded by users who does not create any widgets, the code has been split in two files:

‘widget.el’

This will declare the user variables, define the function widget-define, and autoload the function widget-create.

‘wid-edit.el’

Everything else is here, there is no reason to load it explicitly, as it will be autoloaded when needed.

0.2 User Interface

A form consists of read only text for documentation and some fields, where each field contains two parts, a tag and a value. The tags are used to identify the fields, so the documentation can refer to the ‘foo field’, meaning the field tagged with ‘Foo’. Here is an example form:

Here is some documentation.

Name: My Name     Choose: This option
Address:  Some Place
In some City
Some country.

See also _other work_ for more information.

Numbers: count to three below
[INS] [DEL] One
[INS] [DEL] Eh, two?
[INS] [DEL] Five!
[INS]

Select multiple:

[X] This
[ ] That
[X] Thus

Select one:

(*) One
( ) Another One.
( ) A Final One.

[Apply Form] [Reset Form]

The top level widgets in this example are tagged ‘Name’, ‘Choose’, ‘Address’, ‘_other work_’, ‘Numbers’, ‘Select multiple’, ‘Select one’, ‘[Apply Form]’, and ‘[Reset Form]’. There are basically two things the user can do within a form, namely editing the editable text fields and activating the buttons.

0.2.1 Editable Text Fields

In the example, the value for the ‘Name’ is most likely displayed in an editable text field, and so are values for each of the members of the ‘Numbers’ list. All the normal Emacs editing operations are available for editing these fields. The only restriction is that each change you make must be contained within a single editable text field. For example, capitalizing all text from the middle of one field to the middle of another field is prohibited.

Editable text fields are created by the editable-field widget.

Warning: In an editable-field widget, the editable field must not be adjacent to another widget—that won’t work. You must put some text in between. Either make this text part of the editable-field widget itself, or insert it with widget-insert.

The :format keyword is useful for generating the necessary text; for instance, if you give it a value of "Name: %v ", the ‘Name: ’ part will provide the necessary separating text before the field and the trailing space will provide the separating text after the field. If you don’t include the :size keyword, the field will extend to the end of the line, and the terminating newline will provide separation after.

Warning: In an editable-field widget, the ‘%v’ escape must be preceded by some other text in the :format string (if specified).

The editing text fields are highlighted with the widget-field-face face, making them easy to find.

Face: widget-field-face

Face used for other editing fields.

0.2.2 Buttons

Some portions of the buffer have an associated action, which can be invoked by a standard key or mouse command. These portions are called buttons. The default commands for activating a button are:

<RET>

Command: widget-button-press pos &optional event

Invoke the button at pos, defaulting to point. If point is not located on a button, invoke the binding in widget-global-map (by default the global map).

Mouse-2

Command: widget-button-click event

Invoke the button at the location of the mouse pointer. If the mouse pointer is located in an editable text field, invoke the binding in widget-global-map (by default the global map).

There are several different kind of buttons, all of which are present in the example:

The Option Field Tags

When you invoke one of these buttons, you will be asked to choose between a number of different options. This is how you edit an option field. Option fields are created by the menu-choice widget. In the example, ‘Choose’ is an option field tag.

The ‘[INS]’ and ‘[DEL]’ buttons

Activating these will insert or delete elements from an editable list. The list is created by the editable-list widget.

Embedded Buttons

The ‘_other work_’ is an example of an embedded button. Embedded buttons are not associated with any fields, but can serve any purpose, such as implementing hypertext references. They are usually created by the link widget.

The ‘[ ]’ and ‘[X]’ buttons

Activating one of these will convert it to the other. This is useful for implementing multiple-choice fields. You can create them with the checkbox widget.

The ‘( )’ and ‘(*)’ buttons

Only one radio button in a radio-button-choice widget can be selected at any time. When you invoke one of the unselected radio buttons, it will be selected and the previous selected radio button will become unselected.

The ‘[Apply Form]’ and ‘[Reset Form]’ buttons

These are explicit buttons made with the push-button widget. The main difference from the link widget is that the buttons will be displayed as GUI buttons when possible.

To make them easier to locate, buttons are emphasized in the buffer.

Face: widget-button-face

Face used for buttons.

User Option: widget-mouse-face

Face used for highlighting a button when the mouse pointer moves across it.

0.2.3 Navigation

You can use all the normal Emacs commands to move around in a form buffer, plus you will have these additional commands:

<TAB>

Command: widget-forward &optional count

Move point count buttons or editing fields forward.

M-<TAB>

S-<TAB>

Command: widget-backward &optional count

Move point count buttons or editing fields backward.

0.3 Programming Example

Here is the code to implement the user interface example (see section User Interface).

(require 'widget)

(eval-when-compile
  (require 'wid-edit))

(defvar widget-example-repeat)

(defun widget-example ()
  "Create the widgets from the Widget manual."
  (interactive)
  (kill-buffer (get-buffer-create "*Widget Example*"))
  (switch-to-buffer (get-buffer-create "*Widget Example*"))
  (kill-all-local-variables)
  (make-local-variable 'widget-example-repeat)
  (widget-insert "Here is some documentation.\n\n")
  (widget-create 'editable-field
		 :size 13
		 :format "Name: %v " ; Text after the field!
		 "My Name")
  (widget-create 'menu-choice
		 :tag "Choose"
		 :value "This"
		 :help-echo "Choose me, please!"
		 :notify (lambda (widget &rest ignore)
			   (message "%s is a good choice!"
				    (widget-value widget)))
		 '(item :tag "This option" :value "This")
		 '(choice-item "That option")
		 '(editable-field :menu-tag "No option" "Thus option"))
  (widget-create 'editable-field
		 :format "Address: %v"
		 "Some Place\nIn some City\nSome country.")
  (widget-insert "\nSee also ")
  (widget-create 'link
		 :notify (lambda (&rest ignore)
			   (widget-value-set widget-example-repeat
					     '("En" "To" "Tre"))
			   (widget-setup))
		 "other work")
  (widget-insert
    " for more information.\n\nNumbers: count to three below\n")
  (setq widget-example-repeat
        (widget-create 'editable-list
                       :entry-format "%i %d %v"
                       :notify (lambda (widget &rest ignore)
                                 (let ((old (widget-get widget
                                                        ':example-length))
                                       (new (length (widget-value widget))))
                                   (unless (eq old new)
                                     (widget-put widget ':example-length new)
                                     (message "You can count to %d." new))))
                       :value '("One" "Eh, two?" "Five!")
                       '(editable-field :value "three")))
  (widget-insert "\n\nSelect multiple:\n\n")
  (widget-create 'checkbox t)
  (widget-insert " This\n")
  (widget-create 'checkbox nil)
  (widget-insert " That\n")
  (widget-create 'checkbox
                 :notify (lambda (&rest ignore) (message "Tickle"))
                 t)
  (widget-insert " Thus\n\nSelect one:\n\n")
  (widget-create 'radio-button-choice
                 :value "One"
                 :notify (lambda (widget &rest ignore)
                           (message "You selected %s"
                                    (widget-value widget)))
                 '(item "One") '(item "Another One.") '(item "A Final One."))
  (widget-insert "\n")
  (widget-create 'push-button
		 :notify (lambda (&rest ignore)
			   (if (= (length (widget-value widget-example-repeat))
				  3)
			       (message "Congratulation!")
			     (error "Three was the count!")))
		 "Apply Form")
  (widget-insert " ")
  (widget-create 'push-button
                 :notify (lambda (&rest ignore)
                           (widget-example))
                 "Reset Form")
  (widget-insert "\n")
  (use-local-map widget-keymap)
  (widget-setup))

0.4 Setting Up the Buffer

Widgets are created with widget-create, which returns a widget object. This object can be queried and manipulated by other widget functions, until it is deleted with widget-delete. After the widgets have been created, widget-setup must be called to enable them.

Function: widget-create type [ keyword argument ]…

Create and return a widget of type type. The syntax for the type argument is described in Basic Types.

The keyword arguments can be used to overwrite the keyword arguments that are part of type.

Function: widget-delete widget

Delete widget and remove it from the buffer.

Function: widget-setup

Set up a buffer to support widgets.

This should be called after creating all the widgets and before allowing the user to edit them.

If you want to insert text outside the widgets in the form, the recommended way to do that is with widget-insert.

Function: widget-insert

Insert the arguments, either strings or characters, at point. The inserted text will be read-only.

There is a standard widget keymap which you might find useful.

Const: widget-keymap

A keymap with the global keymap as its parent.
<TAB> and C-<TAB> are bound to widget-forward and widget-backward, respectively. <RET> and Mouse-2 are bound to widget-button-press and widget-button-click.

Variable: widget-global-map

Keymap used by widget-button-press and widget-button-click when not on a button. By default this is global-map.

0.5 Basic Types

This is the general syntax of a type specification:

name ::= (name [keyword argument]... args)
     |   name

where name is a widget name, keyword is the name of a property, argument is the value of the property, and args are interpreted in a widget specific way.

The following keyword arguments apply to all widgets:

:value

The initial value for widgets of this type.

:format

This string will be inserted in the buffer when you create a widget. The following ‘%’ escapes are available:

‘%[’

‘%]’

The text inside will be marked as a button.

By default, the text will be shown in widget-button-face, and surrounded by brackets.

User Option: widget-button-prefix

String to prefix buttons.

User Option: widget-button-suffix

String to suffix buttons.

‘%{’

‘%}’

The text inside will be displayed in the face specified by :sample-face.

‘%v’

This will be replaced with the buffer representation of the widget’s value. What this is depends on the widget type.

Warning: In an editable-field widget, the ‘%v’ escape must be preceded by some other text in the format string (if specified).

‘%d’

Insert the string specified by :doc here.

‘%h’

Like ‘%d’, with the following modifications: If the documentation string is more than one line, it will add a button which will toggle between showing only the first line, and showing the full text. Furthermore, if there is no :doc property in the widget, it will instead examine the :documentation-property property. If it is a lambda expression, it will be called with the widget’s value as an argument, and the result will be used as the documentation text.

‘%t’

Insert the string specified by :tag here, or the princ representation of the value if there is no tag.

‘%%’

Insert a literal ‘%’.

:button-face

Face used to highlight text inside %[ %] in the format.

:button-prefix

:button-suffix

Text around %[ %] in the format.

These can be

nil

No text is inserted.

a string

The string is inserted literally.

a symbol

The value of the symbol is expanded according to this table.

:doc

The string inserted by the ‘%d’ or ‘%h’ escape in the format string.

:tag

The string inserted by the ‘%t’ escape in the format string.

:tag-glyph

Name of image to use instead of the string specified by :tag on Emacsen that supports it.

:help-echo

Specifies how to display a message whenever you move to the widget with either widget-forward or widget-backward or move the mouse over it (using the standard help-echo mechanism). The argument is either a string to display, a function of one argument, the widget, which should return a string to display, or a form that evaluates to such a string.

:follow-link

Specifies how to interpret a <mouse-1> click on the widget. See (elisp)Clickable Text section ‘Defining Clickable Text’ in the Emacs Lisp Reference Manual.

:indent

An integer indicating the absolute number of spaces to indent children of this widget.

:offset

An integer indicating how many extra spaces to add to the widget’s grandchildren compared to this widget.

:extra-offset

An integer indicating how many extra spaces to add to the widget’s children compared to this widget.

:notify

A function called each time the widget or a nested widget is changed. The function is called with two or three arguments. The first argument is the widget itself, the second argument is the widget that was changed, and the third argument is the event leading to the change, if any. In editable fields, this includes all insertions, deletions, etc. To watch only for “final” actions, redefine the :action callback.

:menu-tag

Tag used in the menu when the widget is used as an option in a menu-choice widget.

:menu-tag-get

Function used for finding the tag when the widget is used as an option in a menu-choice widget. By default, the tag used will be either the :menu-tag or :tag property if present, or the princ representation of the :value property if not.

:match

Should be a function called with two arguments, the widget and a value, and returning non-nil if the widget can represent the specified value.

:validate

A function which takes a widget as an argument, and returns nil if the widget’s current value is valid for the widget. Otherwise it should return the widget containing the invalid data, and set that widget’s :error property to a string explaining the error.

The following predefined function can be used:

Function: widget-children-validate widget

All the :children of widget must be valid.

:tab-order

Specify the order in which widgets are traversed with widget-forward or widget-backward. This is only partially implemented.

1. Widgets with tabbing order -1 are ignored.
2. (Unimplemented) When on a widget with tabbing order n, go to the next widget in the buffer with tabbing order n+1 or nil, whichever comes first.
3. When on a widget with no tabbing order specified, go to the next widget in the buffer with a positive tabbing order, or nil

:parent

The parent of a nested widget (e.g. a menu-choice item or an element of an editable-list widget).

:sibling-args

This keyword is only used for members of a radio-button-choice or checklist. The value should be a list of extra keyword arguments, which will be used when creating the radio-button or checkbox associated with this item.

User Option: widget-glyph-directory

Directory where glyphs are found. Widget will look here for a file with the same name as specified for the image, with either a ‘.xpm’ (if supported) or ‘.xbm’ extension.

User Option: widget-glyph-enable

If non-nil, allow glyphs to appear on displays where they are supported.

0.5.1 The link Widget

Syntax:

type ::= (link [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer.

By default the link will be shown in brackets.

User Option: widget-link-prefix

String to prefix links.

User Option: widget-link-suffix

String to suffix links.

0.5.2 The url-link Widget

Syntax:

type ::= (url-link [keyword argument]...  url)

When this link is invoked, the WWW browser specified by browse-url-browser-function will be called with url.

0.5.3 The info-link Widget

Syntax:

type ::= (info-link [keyword argument]...  address)

When this link is invoked, the built-in Info reader is started on address.

0.5.4 The push-button Widget

Syntax:

type ::= (push-button [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer.

By default the tag will be shown in brackets.

User Option: widget-push-button-prefix

String to prefix push buttons.

User Option: widget-push-button-suffix

String to suffix push buttons.

0.5.5 The editable-field Widget

Syntax:

type ::= (editable-field [keyword argument]... [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the field. This widget will match all string values.

The following extra properties are recognized:

:size

The minimum width of the editable field.
By default the field will reach to the end of the line. If the content is too large, the displayed representation will expand to contain it. The content is not truncated to size.

:value-face

Face used for highlighting the editable field. Default is widget-field-face, see User Interface.

:secret

Character used to display the value. You can set this to e.g. ?* if the field contains a password or other secret information. By default, this is nil, and the value is not secret.

:valid-regexp

By default the :validate function will match the content of the field with the value of this attribute. The default value is "" which matches everything.

:keymap

Keymap used in the editable field. The default value is widget-field-keymap, which allows you to use all the normal editing commands, even if the buffer’s major mode suppresses some of them. Pressing <RET> invokes the function specified by :action.

0.5.6 The text Widget

This is just like editable-field, but intended for multiline text fields. The default :keymap is widget-text-keymap, which does not rebind the <RET> key.

0.5.7 The menu-choice Widget

Syntax:

type ::= (menu-choice [keyword argument]... type ... )

The type argument represents each possible choice. The widget’s value will be that of the chosen type argument. This widget will match any value matching at least one of the specified type arguments.

:void

Widget type used as a fallback when the value does not match any of the specified type arguments.

:case-fold

Set this to nil if you don’t want to ignore case when prompting for a choice through the minibuffer.

:children

A list whose CAR is the widget representing the currently chosen type in the buffer.

:choice

The current chosen type.

:args

The list of types.

0.5.8 The radio-button-choice Widget

Syntax:

type ::= (radio-button-choice [keyword argument]...  type ... )

The component types specify the choices, with one radio button for each. The widget’s value will be that of the chosen type argument. This widget matches any value that matches at least one of the specified type arguments.

The following extra properties are recognized.

:entry-format

This string will be inserted for each entry in the list. The following ‘%’ escapes are available:

‘%v’

Replace with the buffer representation of the type widget.

‘%b’

Replace with the radio button.

‘%%’

Insert a literal ‘%’.

:button-args

A list of keywords to pass to the radio buttons. Useful for setting e.g. the ‘:help-echo’ for each button.

:buttons

The widgets representing the radio buttons.

:children

The widgets representing each type.

:choice

The current chosen type

:args

The list of types.

You can add extra radio button items to a radio-button-choice widget after it has been created with the function widget-radio-add-item.

Function: widget-radio-add-item widget type

Add to radio-button-choice widget widget a new radio button item of type type.

Please note that such items added after the radio-button-choice widget has been created will not be properly destructed when you call widget-delete.

0.5.9 The item Widget

Syntax:

item ::= (item [keyword argument]... value)

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer. This widget will only match the specified value.

0.5.10 The choice-item Widget

Syntax:

item ::= (choice-item [keyword argument]... value)

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer as a button. Activating the button of a choice-item is equivalent to activating the parent widget. This widget will only match the specified value.

0.5.11 The toggle Widget

Syntax:

type ::= (toggle [keyword argument]...)

The widget has two possible states, ‘on’ and ‘off’, which correspond to a t or nil value, respectively.

The following extra properties are recognized:

:on

A string representing the ‘on’ state. By default the string ‘on’.

:off

A string representing the ‘off’ state. By default the string ‘off’.

:on-glyph

Name of a glyph to be used instead of the ‘:on’ text string, on emacsen that supports this.

:off-glyph

Name of a glyph to be used instead of the ‘:off’ text string, on emacsen that supports this.

0.5.12 The checkbox Widget

This widget has two possible states, ‘selected’ and ‘unselected’, which corresponds to a t or nil value.

Syntax:

type ::= (checkbox [keyword argument]...)

0.5.13 The checklist Widget

Syntax:

type ::= (checklist [keyword argument]...  type ... )

The type arguments represent each checklist item. The widget’s value will be a list containing the values of all checked type arguments. The checklist widget will match a list whose elements all match at least one of the specified type arguments.

The following extra properties are recognized:

:entry-format

This string will be inserted for each entry in the list. The following ‘%’ escapes are available:

‘%v’

Replaced with the buffer representation of the type widget.

‘%b’

Replace with the checkbox.

‘%%’

Insert a literal ‘%’.

:greedy

Usually a checklist will only match if the items are in the exact sequence given in the specification. By setting :greedy to non-nil, it will allow the items to appear in any sequence. However, if you extract the value they will be in the sequence given in the checklist, i.e. the original sequence is forgotten.

:button-args

A list of keywords to pass to the checkboxes. Useful for setting e.g. the ‘:help-echo’ for each checkbox.

:buttons

The widgets representing the checkboxes.

:children

The widgets representing each type.

:args

The list of types.

0.5.14 The editable-list Widget

Syntax:

type ::= (editable-list [keyword argument]... type)

The value is a list, where each member represents one widget of type type.

The following extra properties are recognized:

:entry-format

This string will be inserted for each entry in the list. The following ‘%’ escapes are available:

‘%v’

This will be replaced with the buffer representation of the type widget.

‘%i’

Insert the [INS] button.

‘%d’

Insert the [DEL] button.

‘%%’

Insert a literal ‘%’.

:insert-button-args

A list of keyword arguments to pass to the insert buttons.

:delete-button-args

A list of keyword arguments to pass to the delete buttons.

:append-button-args

A list of keyword arguments to pass to the trailing insert button.

:buttons

The widgets representing the insert and delete buttons.

:children

The widgets representing the elements of the list.

:args

List whose CAR is the type of the list elements.

0.5.15 The group Widget

This widget simply groups other widgets together.

Syntax:

type ::= (group [keyword argument]... type...)

The value is a list, with one member for each type.

0.6 Sexp Types

A number of widgets for editing s-expressions (Lisp types), sexp for short, are also available. These basically fall in several categories described in this section.

0.6.1 The Constant Widgets

The const widget can contain any Lisp expression, but the user is prohibited from editing it, which is mainly useful as a component of one of the composite widgets.

The syntax for the const widget is:

type ::= (const [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property and can be any s-expression.

Widget: const

This will display any valid s-expression in an immutable part of the buffer.

There are two variations of the const widget, namely variable-item and function-item. These should contain a symbol with a variable or function binding. The major difference from the const widget is that they will allow the user to see the variable or function documentation for the symbol.

Widget: variable-item

An immutable symbol that is bound as a variable.

Widget: function-item

An immutable symbol that is bound as a function.

0.6.2 Generic Sexp Widget

The sexp widget can contain any Lisp expression, and allows the user to edit it inline in the buffer.

The syntax for the sexp widget is:

type ::= (sexp [keyword argument]...  [ value ])

Widget: sexp

This will allow you to edit any valid s-expression in an editable buffer field.

The sexp widget takes the same keyword arguments as the editable-field widget. See section The editable-field Widget.

0.6.3 Atomic Sexp Widgets

The atoms are s-expressions that do not consist of other s-expressions. For example, a string, a file name, or a symbol are atoms, while a list is a composite type. You can edit the value of an atom with the following widgets.

The syntax for all the atoms are:

type ::= (construct [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property and must be an expression of the same type as the widget. That is, the string widget can only be initialized with a string.

All the atom widgets take the same keyword arguments as the editable-field widget. See section The editable-field Widget.

Widget: string

Allows you to edit a string in an editable field.

Widget: regexp

Allows you to edit a regular expression in an editable field.

Widget: character

Allows you to enter a character in an editable field.

Widget: file

Allows you to edit a file name in an editable field.

Keywords:

:must-match

If this is set to non-nil, only existing file names will be allowed in the minibuffer.

Widget: directory

Allows you to edit a directory name in an editable field. Similar to the file widget.

Widget: symbol

Allows you to edit a Lisp symbol in an editable field.

Widget: function

Allows you to edit a lambda expression, or a function name with completion.

Widget: variable

Allows you to edit a variable name, with completion.

Widget: integer

Allows you to edit an integer in an editable field.

Widget: number

Allows you to edit a number in an editable field.

Widget: boolean

Allows you to edit a boolean. In Lisp this means a variable which is either nil meaning false, or non-nil meaning true.

0.6.4 Composite Sexp Widgets

The syntax for the composite widget construct is:

type ::= (construct [keyword argument]...  component...)

where each component must be a widget type. Each component widget will be displayed in the buffer, and will be editable by the user.

Widget: cons

The value of a cons widget must be a cons-cell whose CAR and CDR have two specified types. It uses this syntax:

type ::= (cons [keyword argument]... car-type cdr-type)

Widget: choice

The value matched by a choice widget must have one of a fixed set of types. The widget’s syntax is as follows:

type ::= (choice [keyword argument]... type ... )

The value of a choice widget can be anything that matches any of the types.

Widget: list

The value of a list widget must be a list whose element types match the specified component types:

type ::= (list [keyword argument]... component-type...)

Thus, (list string number) matches lists of two elements, the first being a string and the second being a number.

Widget: vector

The vector widget is like the list widget but matches vectors instead of lists. Thus, (vector string number) matches vectors of two elements, the first being a string and the second being a number.

The above suffice for specifying fixed size lists and vectors. To get variable length lists and vectors, you can use a choice, set, or repeat widget together with the :inline keyword. If any component of a composite widget has the :inline keyword set, its value must be a list which will then be spliced into the composite. For example, to specify a list whose first element must be a file name, and whose remaining elements should either be the symbol t or two strings (file names), you can use the following widget specification:

(list file
      (choice (const t)
              (list :inline t
                    :value ("foo" "bar")
                    string string)))

The value of a widget of this type will either have the form (file t) or (file string string).

This concept of :inline may be hard to understand. It was certainly hard to implement, so instead of confusing you more by trying to explain it here, I’ll just suggest you meditate over it for a while.

Widget: set

Specifies a type whose values are the lists whose elements all belong to a given set. The order of elements of the list is not significant. Here’s the syntax:

type ::= (set [keyword argument]... permitted-element ... )

Use const to specify each permitted element, like this: (set (const a) (const b)).

Widget: repeat

Specifies a list of any number of elements that fit a certain type.

type ::= (repeat [keyword argument]... type)

0.7 Properties

You can examine or set the value of a widget by using the widget object that was returned by widget-create.

Function: widget-value widget

Return the current value contained in widget. It is an error to call this function on an uninitialized widget.

Function: widget-value-set widget value

Set the value contained in widget to value. It is an error to call this function with an invalid value.

Important: You must call widget-setup after modifying the value of a widget before the user is allowed to edit the widget again. It is enough to call widget-setup once if you modify multiple widgets. This is currently only necessary if the widget contains an editing field, but may be necessary for other widgets in the future.

If your application needs to associate some information with the widget objects, for example a reference to the item being edited, it can be done with widget-put and widget-get. The property names must begin with a ‘:’.

Function: widget-put widget property value

In widget set property to value. property should be a symbol, while value can be anything.

Function: widget-get widget property

In widget return the value for property. property should be a symbol, the value is what was last set by widget-put for property.

Function: widget-member widget property

Non-nil if widget has a value (even nil) for property property.

Occasionally it can be useful to know which kind of widget you have, i.e. the name of the widget type you gave when the widget was created.

Function: widget-type widget

Return the name of widget, a symbol.

Widgets can be in two states: active, which means they are modifiable by the user, or inactive, which means they cannot be modified by the user. You can query or set the state with the following code:

;; Examine if widget is active or not.
(if (widget-apply widget :active)
    (message "Widget is active.")
  (message "Widget is inactive.")

;; Make widget inactive.
(widget-apply widget :deactivate)

;; Make widget active.
(widget-apply widget :activate)

A widget is inactive if it, or any of its ancestors (found by following the :parent link), have been deactivated. To make sure a widget is really active, you must therefore activate both it and all its ancestors.

(while widget
  (widget-apply widget :activate)
  (setq widget (widget-get widget :parent)))

You can check if a widget has been made inactive by examining the value of the :inactive keyword. If this is non-nil, the widget itself has been deactivated. This is different from using the :active keyword, in that the latter tells you if the widget or any of its ancestors have been deactivated. Do not attempt to set the :inactive keyword directly. Use the :activate :deactivate keywords instead.

0.8 Defining New Widgets

You can define specialized widgets with define-widget. It allows you to create a shorthand for more complex widgets, including specifying component widgets and new default values for the keyword arguments.

Function: define-widget name class doc &rest args

Define a new widget type named name from class.

name and class should both be symbols, class should be one of the existing widget types.

The third argument doc is a documentation string for the widget.

After the new widget has been defined the following two calls will create identical widgets:

• (widget-create name)

• (apply widget-create class args)

Using define-widget just stores the definition of the widget type in the widget-type property of name, which is what widget-create uses.

If you only want to specify defaults for keywords with no complex conversions, you can use identity as your :convert-widget function.

The following additional keyword arguments are useful when defining new widgets:

:convert-widget

Method to convert type-specific components of a widget type before instantiating a widget of that type. Not normally called from user code, it is invoked by widget-convert. Typical operations include converting types of child widgets to widget instances and converting values from external format (i.e., as expected by the calling code) to internal format (which is often different for the convenience of widget manipulation). It takes a widget type as an argument, and returns the converted widget type. When a widget is created, the value of this property is called for the widget type, then for all the widget’s parent types, most derived first. (The property is reevaluated for each parent type.)

The following predefined functions can be used here:

Function: widget-types-convert-widget widget

Convert each member of :args in widget from a widget type to a widget.

Function: widget-value-convert-widget widget

Initialize :value from (car :args) in widget, and reset :args.

:copy

Function to deep copy a widget type. It takes a shallow copy of the widget type as an argument (made by copy-sequence), and returns a deep copy. The purpose of this is to avoid having different instances of combined widgets share nested attributes. Any member of the widget which might be changed in place (rather than replaced) should be copied by this method. (widget-copy uses copy-sequence to ensure that the top-level list is a copy.) This particularly applies to child widgets.

The following predefined functions can be used here:

Function: widget-types-copy widget

Copy :args as widget types in widget.

:value-to-internal

Function to convert the value to the internal format. The function takes two arguments, a widget and an external value. It returns the internal value. The function is called on the present :value when the widget is created, and on any value set later with widget-value-set.

:value-to-external

Function to convert the value to the external format. The function takes two arguments, a widget and an internal value, and returns the external value. The function is called on the present :value when the widget is created, and on any value set later with widget-value-set.

:create

Function to create a widget from scratch. The function takes one argument, a widget, and inserts it in the buffer. Not normally called from user code. Instead, call widget-create or related functions, which take a type argument, (usually) convert it to a widget, call the :create function to insert it in the buffer, and then return the (possibly converted) widget.

The default, widget-default-create, is invariably appropriate. (None of the standard widgets specify :create.)

:delete

Function to delete a widget. The function takes one argument, a widget, and should remove all traces of the widget from the buffer.

The default value is:

Function: widget-default-delete widget

Remove widget from the buffer. Delete all :children and :buttons in widget.

In most cases you should not change this value, but instead use :value-delete to make any additional cleanup.

:value-create

Function to expand the ‘%v’ escape in the format string. It will be called with the widget as its argument and should insert a representation of the widget’s value in the buffer.

Nested widgets should be listed in :children or :buttons to make sure they are automatically deleted.

:value-delete

Should remove the representation of the widget’s value from the buffer. It will be called with the widget as its argument. It doesn’t have to remove the text, but it should release markers and delete nested widgets if these are not listed in :children or :buttons.

:value-get

Function to extract the value of a widget, as it is displayed in the buffer.

The following predefined function can be used here:

Function: widget-value-value-get widget

Return the :value property of widget.

:format-handler

Function to handle unknown ‘%’ escapes in the format string. It will be called with the widget and the character that follows the ‘%’ as arguments. You can set this to allow your widget to handle non-standard escapes.

You should end up calling widget-default-format-handler to handle unknown escape sequences. It will handle the ‘%h’ and any future escape sequences as well as give an error for unknown escapes.

:action

Function to handle user initiated events. By default, :notify the parent. Actions normally do not include mere edits, but refer to things like invoking buttons or hitting enter in an editable field. To watch for any change, redefine the :notify callback.

The following predefined function can be used here:

Function: widget-parent-action widget &optional event

Tell :parent of widget to handle the :action.
Optional event is the event that triggered the action.

:prompt-value

Function to prompt for a value in the minibuffer. The function should take four arguments, widget, prompt, value, and unbound and should return a value for widget entered by the user. prompt is the prompt to use. value is the default value to use, unless unbound is non-nil, in which case there is no default value. The function should read the value using the method most natural for this widget and does not have to check whether it matches.

If you want to define a new widget from scratch, use the default widget as its base.

Widget: default

Widget used as a base for other widgets.

It provides most of the functionality that is referred to as “by default” in this text.

In implementing complex hierarchical widgets (e.g., using the ‘group’ widget), the following functions may be useful. The syntax for the type arguments to these functions is described in Basic Types.

Function: widget-create-child-and-convert parent type &rest args

As a child of parent, create a widget with type type and value value. type is copied, and the :widget-convert method is applied to the optional keyword arguments from args.

Function: widget-create-child parent type

As a child of parent, create a widget with type type. type is copied, but no conversion method is applied.

Function: widget-create-child-value parent type value

As a child of parent, create a widget with type type and value value. type is copied, but no conversion method is applied.

Function: widget-convert type &rest args

Convert type to a widget without inserting it in the buffer. The optional args are additional keyword arguments.

The widget’s :args property is set from the longest tail of args whose ‘cdr’ is not a keyword, or if that is null, from the longest tail of type’s :args property whose cdr is not a keyword. Keyword arguments from args are set, and the :value property (if any) is converted from external to internal format.

widget-convert is typically not called from user code; rather it is called implicitly through the ‘widget-create*’ functions.

0.9 Widget Browser

There is a separate package to browse widgets. This is intended to help programmers who want to examine the content of a widget. The browser shows the value of each keyword, but uses links for certain keywords such as ‘:parent’, which avoids printing cyclic structures.

Command: widget-browse widget

Create a widget browser for widget. When called interactively, prompt for widget.

Command: widget-browse-other-window widget

Create a widget browser for widget and show it in another window. When called interactively, prompt for widget.

Command: widget-browse-at pos

Create a widget browser for the widget at pos. When called interactively, use the position of point.

0.10 Widget Minor Mode

There is a minor mode for manipulating widgets in major modes that don’t provide any support for widgets themselves. This is mostly intended to be useful for programmers doing experiments.

Command: widget-minor-mode

Toggle minor mode for traversing widgets. With arg, turn widget mode on if and only if arg is positive.

Variable: widget-minor-mode-keymap

Keymap used in widget-minor-mode.

0.11 Utilities.

Function: widget-prompt-value widget prompt [ value unbound ]

Prompt for a value matching widget, using prompt.
The current value is assumed to be value, unless unbound is non-nil.

Function: widget-get-sibling widget

Get the item which widget is assumed to toggle.
This is only meaningful for radio buttons or checkboxes in a list.

0.12 Wishlist

• It should be possible to add or remove items from a list with C-k and C-o (suggested by RMS).
• The ‘[INS]’ and ‘[DEL]’ buttons should be replaced by a single dash (‘-’). The dash should be a button that, when invoked, asks whether you want to add or delete an item (RMS wanted to git rid of the ugly buttons, the dash is my idea).
• The menu-choice tag should be prettier, something like the abbreviated menus in Open Look.
• Finish :tab-order.
• Make indentation work with glyphs and proportional fonts.
• Add commands to show overview of object and class hierarchies to the browser.
• Find a way to disable mouse highlight for inactive widgets.
• Find a way to make glyphs look inactive.
• Add property-list widget.
• Add association-list widget.
• Add key-binding widget.
• Add widget widget for editing widget specifications.
• Find clean way to implement variable length list. See TeX-printer-list for an explanation.
• C-h in widget-prompt-value should give type specific help.
• Add a mailto widget.
• C-e e in a fixed size field should go to the end of the text in the field, not the end of the field itself.
• Use an overlay instead of markers to delimit the widget. Create accessors for the end points.
• Clicking on documentation links should call describe-function or widget-browse-other-window and friends directly, instead of going through apropos. If more than one function is valid for the symbol, it should pop up a menu.

0.13 Internals

This (very brief!) section provides a few notes on the internal structure and implementation of Emacs widgets. Avoid relying on this information. (We intend to improve it, but this will take some time.) To the extent that it actually describes APIs, the information will be moved to appropriate sections of the manual in due course.

0.13.1 The Widget and Type Structures

Widgets and types are currently both implemented as lists.

A symbol may be defined as a type name using define-widget. See section Defining New Widgets. A type is a list whose car is a previously defined type name, nil, or (recursively) a type. The car is the class or parent type of the type, and properties which are not specified in the new type will be inherited from ancestors. Probably the only type without a class should be the default type. The cdr of a type is a plist whose keys are widget property keywords.

A type or type name may also be referred to as an unconverted widget.

A converted widget or widget instance is a list whose car is a type name or a type, and whose cdr is a property list. Furthermore, all children of the converted widget must be converted. Finally, in the process of appropriate parts of the list structure are copied to ensure that changes in values of one instance do not affect another’s.

This document was generated by Aidan Kehoe on December 27, 2016 using texi2html 1.82.