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derived.el
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Lisp/Scheme
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1996-05-27
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;;; derived.el --- allow inheritance of major modes.
;;; (formerly mode-clone.el)
;; Copyright (C) 1993, 1994 Free Software Foundation, Inc.
;; Author: David Megginson (dmeggins@aix1.uottawa.ca)
;; Maintainer: FSF
;; This file is part of GNU Emacs.
;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING. If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.
;;; Commentary:
;; GNU Emacs is already, in a sense, object oriented -- each object
;; (buffer) belongs to a class (major mode), and that class defines
;; the relationship between messages (input events) and methods
;; (commands) by means of a keymap.
;;
;; The only thing missing is a good scheme of inheritance. It is
;; possible to simulate a single level of inheritance with generous
;; use of hooks and a bit of work -- sgml-mode, for example, also runs
;; the hooks for text-mode, and keymaps can inherit from other keymaps
;; -- but generally, each major mode ends up reinventing the wheel.
;; Ideally, someone should redesign all of Emacs's major modes to
;; follow a more conventional object-oriented system: when defining a
;; new major mode, the user should need only to name the existing mode
;; it is most similar to, then list the (few) differences.
;;
;; In the mean time, this package offers most of the advantages of
;; full inheritance with the existing major modes. The macro
;; `define-derived-mode' allows the user to make a variant of an existing
;; major mode, with its own keymap. The new mode will inherit the key
;; bindings of its parent, and will, in fact, run its parent first
;; every time it is called. For example, the commands
;;
;; (define-derived-mode hypertext-mode text-mode "Hypertext"
;; "Major mode for hypertext.\n\n\\{hypertext-mode-map}"
;; (setq case-fold-search nil))
;;
;; (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)
;;
;; will create a function `hypertext-mode' with its own (sparse)
;; keymap `hypertext-mode-map.' The command M-x hypertext-mode will
;; perform the following actions:
;;
;; - run the command (text-mode) to get its default setup
;; - replace the current keymap with 'hypertext-mode-map,' which will
;; inherit from 'text-mode-map'.
;; - replace the current syntax table with
;; 'hypertext-mode-syntax-table', which will borrow its defaults
;; from the current text-mode-syntax-table.
;; - replace the current abbrev table with
;; 'hypertext-mode-abbrev-table', which will borrow its defaults
;; from the current text-mode-abbrev table
;; - change the mode line to read "Hypertext"
;; - assign the value 'hypertext-mode' to the 'major-mode' variable
;; - run the body of commands provided in the macro -- in this case,
;; set the local variable `case-fold-search' to nil.
;; - **run the command (hypertext-mode-setup), which is empty by
;; default, but may be redefined by the user to contain special
;; commands (ie. setting local variables like 'outline-regexp')
;; **NOTE: do not use this option -- it will soon be obsolete.
;; - run anything assigned to 'hypertext-mode-hooks' (obsolete, but
;; supported for the sake of compatibility).
;;
;; The advantages of this system are threefold. First, text mode is
;; untouched -- if you had added the new keystroke to `text-mode-map,'
;; possibly using hooks, you would have added it to all text buffers
;; -- here, it appears only in hypertext buffers, where it makes
;; sense. Second, it is possible to build even further, and make
;; a derived mode from a derived mode. The commands
;;
;; (define-derived-mode html-mode hypertext-mode "HTML")
;; [various key definitions]
;;
;; will add a new major mode for HTML with very little fuss.
;;
;; Note also the function `derived-mode-class,' which returns the non-derived
;; major mode which a derived mode is based on (ie. NOT necessarily the
;; immediate parent).
;;
;; (derived-mode-class 'text-mode) ==> text-mode
;; (derived-mode-class 'hypertext-mode) ==> text-mode
;; (derived-mode-class 'html-mode) ==> text-mode
;;; Code:
;; PUBLIC: define a new major mode which inherits from an existing one.
;;;###autoload
(defmacro define-derived-mode (child parent name &optional docstring &rest body)
"Create a new mode as a variant of an existing mode.
The arguments to this command are as follow:
CHILD: the name of the command for the derived mode.
PARENT: the name of the command for the parent mode (ie. text-mode).
NAME: a string which will appear in the status line (ie. \"Hypertext\")
DOCSTRING: an optional documentation string--if you do not supply one,
the function will attempt to invent something useful.
BODY: forms to execute just before running the
hooks for the new mode.
Here is how you could define LaTeX-Thesis mode as a variant of LaTeX mode:
(define-derived-mode LaTeX-thesis-mode LaTeX-mode \"LaTeX-Thesis\")
You could then make new key bindings for `LaTeX-thesis-mode-map'
without changing regular LaTeX mode. In this example, BODY is empty,
and DOCSTRING is generated by default.
On a more complicated level, the following command uses sgml-mode as
the parent, and then sets the variable `case-fold-search' to nil:
(define-derived-mode article-mode sgml-mode \"Article\"
\"Major mode for editing technical articles.\"
(setq case-fold-search nil))
Note that if the documentation string had been left out, it would have
been generated automatically, with a reference to the keymap."
; Some trickiness, since what
; appears to be the docstring
; may really be the first
; element of the body.
(if (and docstring (not (stringp docstring)))
(progn (setq body (cons docstring body))
(setq docstring nil)))
(setq docstring (or docstring (derived-mode-make-docstring parent child)))
(` (progn
(derived-mode-init-mode-variables (quote (, child)))
(defun (, child) ()
(, docstring)
(interactive)
; Run the parent.
((, parent))
; Identify special modes.
(if (get (quote (, parent)) 'special)
(put (quote (, child)) 'special t))
; Identify the child mode.
(setq major-mode (quote (, child)))
(setq mode-name (, name))
; Set up maps and tables.
(derived-mode-set-keymap (quote (, child)))
(derived-mode-set-syntax-table (quote (, child)))
(derived-mode-set-abbrev-table (quote (, child)))
; Splice in the body (if any).
(,@ body)
;;; ; Run the setup function, if
;;; ; any -- this will soon be
;;; ; obsolete.
;;; (derived-mode-run-setup-function (quote (, child)))
; Run the hooks, if any.
(derived-mode-run-hooks (quote (, child)))))))
;; PUBLIC: find the ultimate class of a derived mode.
(defun derived-mode-class (mode)
"Find the class of a major mode.
A mode's class is the first ancestor which is NOT a derived mode.
Use the `derived-mode-parent' property of the symbol to trace backwards."
(while (get mode 'derived-mode-parent)
(setq mode (get mode 'derived-mode-parent)))
mode)
;; Inline functions to construct various names from a mode name.
(defsubst derived-mode-setup-function-name (mode)
"Construct a setup-function name based on a mode name."
(intern (concat (symbol-name mode) "-setup")))
(defsubst derived-mode-hooks-name (mode)
"Construct a hooks name based on a mode name."
(intern (concat (symbol-name mode) "-hooks")))
(defsubst derived-mode-map-name (mode)
"