23.2.5 Defining Derived Modes

It's often useful to define a new major mode in terms of an existing one. An easy way to do this is to use define-derived-mode.

Macro: define-derived-mode variant parent name docstring keyword-args… body…

This construct defines variant as a major mode command, using name as the string form of the mode name. variant and parent should be unquoted symbols.

The new command variant is defined to call the function parent, then override certain aspects of that parent mode:

• The new mode has its own sparse keymap, named variant-map. define-derived-mode makes the parent mode's keymap the parent of the new map, unless variant-map is already set and already has a parent.
• The new mode has its own syntax table, kept in the variable variant-syntax-table, unless you override this using the :syntax-table keyword (see below). define-derived-mode makes the parent mode's syntax-table the parent of variant-syntax-table, unless the latter is already set and already has a parent different from the standard syntax table.
• The new mode has its own abbrev table, kept in the variable variant-abbrev-table, unless you override this using the :abbrev-table keyword (see below).
• The new mode has its own mode hook, variant-hook. It runs this hook, after running the hooks of its ancestor modes, with run-mode-hooks, as the last thing it does. Voir la section Mode Hooks.

In addition, you can specify how to override other aspects of parent with body. The command variant evaluates the forms in body after setting up all its usual overrides, just before running the mode hooks.

You can also specify nil for parent. This gives the new mode no parent. Then define-derived-mode behaves as described above, but, of course, omits all actions connected with parent.

The argument docstring specifies the documentation string for the new mode. define-derived-mode adds some general information about the mode's hook, followed by the mode's keymap, at the end of this docstring. If you omit docstring, define-derived-mode generates a documentation string.

The keyword-args are pairs of keywords and values. The values are evaluated. The following keywords are currently supported:

:syntax-table

You can use this to explicitly specify a syntax table for the new mode. If you specify a nil value, the new mode uses the same syntax table as parent, or the standard syntax table if parent is nil. (Note that this does not follow the convention used for non-keyword arguments that a nil value is equivalent with not specifying the argument.)

:abbrev-table

You can use this to explicitly specify an abbrev table for the new mode. If you specify a nil value, the new mode uses the same abbrev table as parent, or fundamental-mode-abbrev-table if parent is nil. (Again, a nil value is not equivalent to not specifying this keyword.)

:group

If this is specified, the value should be the customization group for this mode. (Not all major modes have one.) Only the (still experimental and unadvertised) command customize-mode currently uses this. define-derived-mode does not automatically define the specified customization group.

Here is a hypothetical example:

(define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)

Do not write an interactive spec in the definition; define-derived-mode does that automatically.

Ce document a été généré par Eric Reinbold le 13 Octobre 2007 en utilisant texi2html 1.78.