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+;;; derived.el --- allow inheritance of major modes
+;;; (formerly mode-clone.el)
+
+;; Copyright (C) 1993, 1994, 1999, 2003 Free Software Foundation, Inc.
+
+;; Author: David Megginson (dmeggins@aix1.uottawa.ca)
+;; Maintainer: FSF
+;; Keywords: extensions
+
+;; 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.
+;;
+;; 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-p' which can tell if the current
+;; mode derives from another.  In a hypertext-mode, buffer, for example,
+;; (derived-mode-p 'text-mode) would return non-nil.  This should always
+;; be used in place of (eq major-mode 'text-mode).
+
+;;; Code:
+
+(eval-when-compile (require 'cl))
+
+;;; PRIVATE: defsubst must be defined before they are first used
+
+(defsubst derived-mode-hook-name (mode)
+  "Construct the mode hook name based on mode name MODE."
+  (intern (concat (symbol-name mode) "-hook")))
+
+(defsubst derived-mode-map-name (mode)
+  "Construct a map name based on a MODE name."
+  (intern (concat (symbol-name mode) "-map")))
+
+(defsubst derived-mode-syntax-table-name (mode)
+  "Construct a syntax-table name based on a MODE name."
+  (intern (concat (symbol-name mode) "-syntax-table")))
+
+(defsubst derived-mode-abbrev-table-name (mode)
+  "Construct an abbrev-table name based on a MODE name."
+  (intern (concat (symbol-name mode) "-abbrev-table")))
+
+;; 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 (e.g. `text-mode')
+           or nil if there is no parent.
+NAME:      a string which will appear in the status line (e.g. \"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.  Do not use `interactive' here.
+
+BODY can start with a bunch of keyword arguments.  The following keyword
+  arguments are currently understood:
+:group GROUP
+	Declare the customization group that corresponds to this mode.
+:syntax-table TABLE
+	Use TABLE instead of the default.
+	A nil value means to simply use the same syntax-table as the parent.
+:abbrev-table TABLE
+	Use TABLE instead of the default.
+	A nil value means to simply use the same abbrev-table as the parent.
+
+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."
+  (declare (debug (&define name symbolp sexp [&optional stringp]
+			   [&rest keywordp sexp] def-body)))
+
+  (when (and docstring (not (stringp docstring)))
+    ;; Some trickiness, since what appears to be the docstring may really be
+    ;; the first element of the body.
+    (push docstring body)
+    (setq docstring nil))
+
+  (when (eq parent 'fundamental-mode) (setq parent nil))
+
+  (let ((map (derived-mode-map-name child))
+	(syntax (derived-mode-syntax-table-name child))
+	(abbrev (derived-mode-abbrev-table-name child))
+	(declare-abbrev t)
+	(declare-syntax t)
+	(hook (derived-mode-hook-name child))
+	(group nil))
+
+    ;; Process the keyword args.
+    (while (keywordp (car body))
+      (case (pop body)
+	(:group (setq group (pop body)))
+	(:abbrev-table (setq abbrev (pop body)) (setq declare-abbrev nil))
+	(:syntax-table (setq syntax (pop body)) (setq declare-syntax nil))
+	(t (pop body))))
+
+    (setq docstring (derived-mode-make-docstring
+		     parent child docstring syntax abbrev))
+
+    `(progn
+       (defvar ,map (make-sparse-keymap))
+       ,(if declare-syntax
+	    `(defvar ,syntax (make-syntax-table)))
+       ,(if declare-abbrev
+	    `(defvar ,abbrev
+	       (progn (define-abbrev-table ',abbrev nil) ,abbrev)))
+       (put ',child 'derived-mode-parent ',parent)
+       ,(if group `(put ',child 'custom-mode-group ,group))
+
+       (defun ,child ()
+	 ,docstring
+	 (interactive)
+					; Run the parent.
+	 (delay-mode-hooks
+
+	  (,(or parent 'kill-all-local-variables))
+					; Identify the child mode.
+	  (setq major-mode (quote ,child))
+	  (setq mode-name ,name)
+					; Identify special modes.
+	  ,(when parent
+	     `(progn
+		(if (get (quote ,parent) 'mode-class)
+		    (put (quote ,child) 'mode-class
+			 (get (quote ,parent) 'mode-class)))
+					; Set up maps and tables.
+		(unless (keymap-parent ,map)
+		  (set-keymap-parent ,map (current-local-map)))
+		,(when declare-syntax
+		   `(let ((parent (char-table-parent ,syntax)))
+		      (unless (and parent
+				   (not (eq parent (standard-syntax-table))))
+			(set-char-table-parent ,syntax (syntax-table)))))))
+
+	  (use-local-map ,map)
+	  ,(when syntax `(set-syntax-table ,syntax))
+	  ,(when abbrev `(setq local-abbrev-table ,abbrev))
+					; Splice in the body (if any).
+	  ,@body
+	  )
+	 ;; Run the hooks, if any.
+	 ;; Make the generated code work in older Emacs versions
+	 ;; that do not yet have run-mode-hooks.
+	 (if (fboundp 'run-mode-hooks)
+	     (run-mode-hooks ',hook)
+	   (run-hooks ',hook))))))
+
+;; 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.
+Since major-modes might all derive from `fundamental-mode', this function
+is not very useful."
+  (while (get mode 'derived-mode-parent)
+    (setq mode (get mode 'derived-mode-parent)))
+  mode)
+(make-obsolete 'derived-mode-class 'derived-mode-p "21.4")
+
+
+;;; PRIVATE
+
+(defun derived-mode-make-docstring (parent child &optional
+					   docstring syntax abbrev)
+  "Construct a docstring for a new mode if none is provided."
+
+  (let ((map (derived-mode-map-name child))
+	(hook (derived-mode-hook-name child)))
+
+    (unless (stringp docstring)
+      ;; Use a default docstring.
+      (setq docstring
+	    (if (null parent)
+		(format "Major-mode.
+Uses keymap `%s', abbrev table `%s' and syntax-table `%s'." map abbrev syntax)
+	      (format "Major mode derived from `%s' by `define-derived-mode'.
+It inherits all of the parent's attributes, but has its own keymap,
+abbrev table and syntax table:
+
+  `%s', `%s' and `%s'
+
+which more-or-less shadow %s's corresponding tables."
+		      parent map abbrev syntax parent))))
+
+    (unless (string-match (regexp-quote (symbol-name hook)) docstring)
+      ;; Make sure the docstring mentions the mode's hook.
+      (setq docstring
+	    (concat docstring
+		    (if (null parent)
+			"\n\nThis mode "
+		      (concat
+		       "\n\nIn addition to any hooks its parent mode "
+		       (if (string-match (regexp-quote (format "`%s'" parent))
+					 docstring) nil
+			 (format "`%s' " parent))
+		       "might have run,\nthis mode "))
+		    (format "runs the hook `%s'" hook)
+		    ", as the final step\nduring initialization.")))
+
+    (unless (string-match "\\\\[{[]" docstring)
+      ;; And don't forget to put the mode's keymap.
+      (setq docstring (concat docstring "\n\n\\{" (symbol-name map) "}")))
+
+    docstring))
+
+
+;;; OBSOLETE
+;; The functions below are only provided for backward compatibility with
+;; code byte-compiled with versions of derived.el prior to Emacs-21.
+
+(defsubst derived-mode-setup-function-name (mode)
+  "Construct a setup-function name based on a MODE name."
+  (intern (concat (symbol-name mode) "-setup")))
+
+
+;; Utility functions for defining a derived mode.
+
+;;;###autoload
+(defun derived-mode-init-mode-variables (mode)
+  "Initialise variables for a new MODE.
+Right now, if they don't already exist, set up a blank keymap, an
+empty syntax table, and an empty abbrev table -- these will be merged
+the first time the mode is used."
+
+  (if (boundp (derived-mode-map-name mode))
+      t
+    (eval `(defvar ,(derived-mode-map-name mode)
+	       (make-sparse-keymap)
+	       ,(format "Keymap for %s." mode)))
+    (put (derived-mode-map-name mode) 'derived-mode-unmerged t))
+
+  (if (boundp (derived-mode-syntax-table-name mode))
+      t
+    (eval `(defvar ,(derived-mode-syntax-table-name mode)
+	     ;; Make a syntax table which doesn't specify anything
+	     ;; for any char.  Valid data will be merged in by
+	     ;; derived-mode-merge-syntax-tables.
+	     (make-char-table 'syntax-table nil)
+	     ,(format "Syntax table for %s." mode)))
+    (put (derived-mode-syntax-table-name mode) 'derived-mode-unmerged t))
+
+  (if (boundp (derived-mode-abbrev-table-name mode))
+      t
+    (eval `(defvar ,(derived-mode-abbrev-table-name mode)
+	     (progn
+	       (define-abbrev-table (derived-mode-abbrev-table-name mode) nil)
+	       (make-abbrev-table))
+	     ,(format "Abbrev table for %s." mode)))))
+
+;; Utility functions for running a derived mode.
+
+(defun derived-mode-set-keymap (mode)
+  "Set the keymap of the new MODE, maybe merging with the parent."
+  (let* ((map-name (derived-mode-map-name mode))
+	 (new-map (eval map-name))
+	 (old-map (current-local-map)))
+    (and old-map
+	 (get map-name 'derived-mode-unmerged)
+	 (derived-mode-merge-keymaps old-map new-map))
+    (put map-name 'derived-mode-unmerged nil)
+    (use-local-map new-map)))
+
+(defun derived-mode-set-syntax-table (mode)
+  "Set the syntax table of the new MODE, maybe merging with the parent."
+  (let* ((table-name (derived-mode-syntax-table-name mode))
+	 (old-table (syntax-table))
+	 (new-table (eval table-name)))
+    (if (get table-name 'derived-mode-unmerged)
+	(derived-mode-merge-syntax-tables old-table new-table))
+    (put table-name 'derived-mode-unmerged nil)
+    (set-syntax-table new-table)))
+
+(defun derived-mode-set-abbrev-table (mode)
+  "Set the abbrev table for MODE if it exists.
+Always merge its parent into it, since the merge is non-destructive."
+  (let* ((table-name (derived-mode-abbrev-table-name mode))
+	 (old-table local-abbrev-table)
+	 (new-table (eval table-name)))
+    (derived-mode-merge-abbrev-tables old-table new-table)
+    (setq local-abbrev-table new-table)))
+
+;;;(defun derived-mode-run-setup-function (mode)
+;;;  "Run the setup function if it exists."
+
+;;;  (let ((fname (derived-mode-setup-function-name mode)))
+;;;    (if (fboundp fname)
+;;;	(funcall fname))))
+
+(defun derived-mode-run-hooks (mode)
+  "Run the mode hook for MODE."
+  (let ((hooks-name (derived-mode-hook-name mode)))
+    (if (boundp hooks-name)
+	(run-hooks hooks-name))))
+
+;; Functions to merge maps and tables.
+
+(defun derived-mode-merge-keymaps (old new)
+  "Merge an OLD keymap into a NEW one.
+The old keymap is set to be the last cdr of the new one, so that there will
+be automatic inheritance."
+  ;; ?? Can this just use `set-keymap-parent'?
+  (let ((tail new))
+    ;; Scan the NEW map for prefix keys.
+    (while (consp tail)
+      (and (consp (car tail))
+	   (let* ((key (vector (car (car tail))))
+		  (subnew (lookup-key new key))
+		  (subold (lookup-key old key)))
+	     ;; If KEY is a prefix key in both OLD and NEW, merge them.
+	     (and (keymapp subnew) (keymapp subold)
+		  (derived-mode-merge-keymaps subold subnew))))
+      (and (vectorp (car tail))
+	   ;; Search a vector of ASCII char bindings for prefix keys.
+	   (let ((i (1- (length (car tail)))))
+	     (while (>= i 0)
+	       (let* ((key (vector i))
+		      (subnew (lookup-key new key))
+		      (subold (lookup-key old key)))
+		 ;; If KEY is a prefix key in both OLD and NEW, merge them.
+		 (and (keymapp subnew) (keymapp subold)
+		      (derived-mode-merge-keymaps subold subnew)))
+	       (setq i (1- i)))))
+      (setq tail (cdr tail))))
+  (setcdr (nthcdr (1- (length new)) new) old))
+
+(defun derived-mode-merge-syntax-tables (old new)
+  "Merge an OLD syntax table into a NEW one.
+Where the new table already has an entry, nothing is copied from the old one."
+  (set-char-table-parent new old))
+
+;; Merge an old abbrev table into a new one.
+;; This function requires internal knowledge of how abbrev tables work,
+;; presuming that they are obarrays with the abbrev as the symbol, the expansion
+;; as the value of the symbol, and the hook as the function definition.
+(defun derived-mode-merge-abbrev-tables (old new)
+  (if old
+      (mapatoms
+       (lambda (symbol)
+	 (or (intern-soft (symbol-name symbol) new)
+	     (define-abbrev new (symbol-name symbol)
+	       (symbol-value symbol) (symbol-function symbol))))
+       old)))
+
+(provide 'derived)
+
+;;; derived.el ends here