1;;; derived.el -- allow inheritance of major modes. 2;;; (formerly mode-clone.el) 3 4;; Copyright (C) 1993, 1994 Free Software Foundation, Inc. 5 6;; Author: David Megginson (dmeggins@aix1.uottawa.ca) 7;; Maintainer: FSF 8 9;; This file is part of GNU Emacs. 10 11;; GNU Emacs is free software; you can redistribute it and/or modify 12;; it under the terms of the GNU General Public License as published by 13;; the Free Software Foundation; either version 2, or (at your option) 14;; any later version. 15 16;; GNU Emacs is distributed in the hope that it will be useful, 17;; but WITHOUT ANY WARRANTY; without even the implied warranty of 18;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 19;; GNU General Public License for more details. 20 21;; You should have received a copy of the GNU General Public License 22;; along with GNU Emacs; see the file COPYING. If not, write to 23;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 24 25;;; Commentary: 26 27;; GNU Emacs is already, in a sense, object oriented -- each object 28;; (buffer) belongs to a class (major mode), and that class defines 29;; the relationship between messages (input events) and methods 30;; (commands) by means of a keymap. 31;; 32;; The only thing missing is a good scheme of inheritance. It is 33;; possible to simulate a single level of inheritance with generous 34;; use of hooks and a bit of work -- sgml-mode, for example, also runs 35;; the hooks for text-mode, and keymaps can inherit from other keymaps 36;; -- but generally, each major mode ends up reinventing the wheel. 37;; Ideally, someone should redesign all of Emacs's major modes to 38;; follow a more conventional object-oriented system: when defining a 39;; new major mode, the user should need only to name the existing mode 40;; it is most similar to, then list the (few) differences. 41;; 42;; In the mean time, this package offers most of the advantages of 43;; full inheritance with the existing major modes. The macro 44;; `define-derived-mode' allows the user to make a variant of an existing 45;; major mode, with its own keymap. The new mode will inherit the key 46;; bindings of its parent, and will, in fact, run its parent first 47;; every time it is called. For example, the commands 48;; 49;; (define-derived-mode hypertext-mode text-mode "Hypertext" 50;; "Major mode for hypertext.\n\n\\{hypertext-mode-map}" 51;; (setq case-fold-search nil)) 52;; 53;; (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link) 54;; 55;; will create a function `hypertext-mode' with its own (sparse) 56;; keymap `hypertext-mode-map.' The command M-x hypertext-mode will 57;; perform the following actions: 58;; 59;; - run the command (text-mode) to get its default setup 60;; - replace the current keymap with 'hypertext-mode-map,' which will 61;; inherit from 'text-mode-map'. 62;; - replace the current syntax table with 63;; 'hypertext-mode-syntax-table', which will borrow its defaults 64;; from the current text-mode-syntax-table. 65;; - replace the current abbrev table with 66;; 'hypertext-mode-abbrev-table', which will borrow its defaults 67;; from the current text-mode-abbrev table 68;; - change the mode line to read "Hypertext" 69;; - assign the value 'hypertext-mode' to the 'major-mode' variable 70;; - run the body of commands provided in the macro -- in this case, 71;; set the local variable `case-fold-search' to nil. 72;; - **run the command (hypertext-mode-setup), which is empty by 73;; default, but may be redefined by the user to contain special 74;; commands (ie. setting local variables like 'outline-regexp') 75;; **NOTE: do not use this option -- it will soon be obsolete. 76;; - run anything assigned to 'hypertext-mode-hooks' (obsolete, but 77;; supported for the sake of compatibility). 78;; 79;; The advantages of this system are threefold. First, text mode is 80;; untouched -- if you had added the new keystroke to `text-mode-map,' 81;; possibly using hooks, you would have added it to all text buffers 82;; -- here, it appears only in hypertext buffers, where it makes 83;; sense. Second, it is possible to build even further, and make 84;; a derived mode from a derived mode. The commands 85;; 86;; (define-derived-mode html-mode hypertext-mode "HTML") 87;; [various key definitions] 88;; 89;; will add a new major mode for HTML with very little fuss. 90;; 91;; Note also the function `derived-mode-class,' which returns the non-derived 92;; major mode which a derived mode is based on (ie. NOT necessarily the 93;; immediate parent). 94;; 95;; (derived-mode-class 'text-mode) ==> text-mode 96;; (derived-mode-class 'hypertext-mode) ==> text-mode 97;; (derived-mode-class 'html-mode) ==> text-mode 98 99;;; Code: 100 101;; PUBLIC: define a new major mode which inherits from an existing one. 102 103;;;###autoload 104(defmacro define-derived-mode (child parent name &optional docstring &rest body) 105 "Create a new mode as a variant of an existing mode. 106 107The arguments to this command are as follow: 108 109PARENT: the name of the command for the parent mode (ie. text-mode). 110CHILD: the name of the command for the derived mode. 111NAME: a string which will appear in the status line (ie. \"Hypertext\") 112DOCSTRING: an optional documentation string--if you do not supply one, 113 the function will attempt to invent something useful. 114BODY: forms to execute just before running the 115 hooks for the new mode. 116 117Here is how you could define LaTeX-Thesis mode as a variant of LaTeX mode: 118 119 (define-derived-mode LaTeX-thesis-mode LaTeX-mode \"LaTeX-Thesis\") 120 121You could then make new key bindings for `LaTeX-thesis-mode-map' 122without changing regular LaTeX mode. In this example, BODY is empty, 123and DOCSTRING is generated by default. 124 125On a more complicated level, the following command uses sgml-mode as 126the parent, and then sets the variable `case-fold-search' to nil: 127 128 (define-derived-mode article-mode sgml-mode \"Article\" 129 \"Major mode for editing technical articles.\" 130 (setq case-fold-search nil)) 131 132Note that if the documentation string had been left out, it would have 133been generated automatically, with a reference to the keymap." 134 135 ; Some trickiness, since what 136 ; appears to be the docstring 137 ; may really be the first 138 ; element of the body. 139 (if (and docstring (not (stringp docstring))) 140 (progn (setq body (cons docstring body)) 141 (setq docstring nil))) 142 (setq docstring (or docstring (derived-mode-make-docstring parent child))) 143 144 (` (progn 145 (derived-mode-init-mode-variables (quote (, child))) 146 (defun (, child) () 147 (, docstring) 148 (interactive) 149 ; Run the parent. 150 ((, parent)) 151 ; Identify special modes. 152 (if (get (quote (, parent)) 'special) 153 (put (quote (, child)) 'special t)) 154 ; Identify the child mode. 155 (setq major-mode (quote (, child))) 156 (setq mode-name (, name)) 157 ; Set up maps and tables. 158 (derived-mode-set-keymap (quote (, child))) 159 (derived-mode-set-syntax-table (quote (, child))) 160 (derived-mode-set-abbrev-table (quote (, child))) 161 ; Splice in the body (if any). 162 (,@ body) 163;;; ; Run the setup function, if 164;;; ; any -- this will soon be 165;;; ; obsolete. 166;;; (derived-mode-run-setup-function (quote (, child))) 167 ; Run the hooks, if any. 168 (derived-mode-run-hooks (quote (, child))))))) 169 170 171;; PUBLIC: find the ultimate class of a derived mode. 172 173(defun derived-mode-class (mode) 174 "Find the class of a major mode. 175A mode's class is the first ancestor which is NOT a derived mode. 176Use the `derived-mode-parent' property of the symbol to trace backwards." 177 (while (get mode 'derived-mode-parent) 178 (setq mode (get mode 'derived-mode-parent))) 179 mode) 180 181 182;; Inline functions to construct various names from a mode name. 183 184(defsubst derived-mode-setup-function-name (mode) 185 "Construct a setup-function name based on a mode name." 186 (intern (concat (symbol-name mode) "-setup"))) 187 188(defsubst derived-mode-hooks-name (mode) 189 "Construct a hooks name based on a mode name." 190 (intern (concat (symbol-name mode) "-hooks"))) 191 192(defsubst derived-mode-map-name (mode) 193 "Construct a map name based on a mode name." 194 (intern (concat (symbol-name mode) "-map"))) 195 196(defsubst derived-mode-syntax-table-name (mode) 197 "Construct a syntax-table name based on a mode name." 198 (intern (concat (symbol-name mode) "-syntax-table"))) 199 200(defsubst derived-mode-abbrev-table-name (mode) 201 "Construct an abbrev-table name based on a mode name." 202 (intern (concat (symbol-name mode) "-abbrev-table"))) 203 204 205;; Utility functions for defining a derived mode. 206 207;;;###autoload 208(defun derived-mode-init-mode-variables (mode) 209 "Initialise variables for a new mode. 210Right now, if they don't already exist, set up a blank keymap, an 211empty syntax table, and an empty abbrev table -- these will be merged 212the first time the mode is used." 213 214 (if (boundp (derived-mode-map-name mode)) 215 t 216 (eval (` (defvar (, (derived-mode-map-name mode)) 217 (make-sparse-keymap) 218 (, (format "Keymap for %s." mode))))) 219 (put (derived-mode-map-name mode) 'derived-mode-unmerged t)) 220 221 (if (boundp (derived-mode-syntax-table-name mode)) 222 t 223 (eval (` (defvar (, (derived-mode-syntax-table-name mode)) 224 (make-vector 256 nil) 225 (, (format "Syntax table for %s." mode))))) 226 (put (derived-mode-syntax-table-name mode) 'derived-mode-unmerged t)) 227 228 (if (boundp (derived-mode-abbrev-table-name mode)) 229 t 230 (eval (` (defvar (, (derived-mode-abbrev-table-name mode)) 231 (progn (define-abbrev-table (derived-mode-abbrev-table-name mode) nil) 232 (make-abbrev-table)) 233 (, (format "Abbrev table for %s." mode))))))) 234 235(defun derived-mode-make-docstring (parent child) 236 "Construct a docstring for a new mode if none is provided." 237 238 (format "This major mode is a variant of `%s', created by `define-derived-mode'. 239It inherits all of the parent's attributes, but has its own keymap, 240abbrev table and syntax table: 241 242 `%s-map' and `%s-syntax-table' 243 244which more-or-less shadow 245 246 `%s-map' and `%s-syntax-table' 247 248\\{%s-map}" parent child child parent parent child)) 249 250 251;; Utility functions for running a derived mode. 252 253(defun derived-mode-set-keymap (mode) 254 "Set the keymap of the new mode, maybe merging with the parent." 255 (let* ((map-name (derived-mode-map-name mode)) 256 (new-map (eval map-name)) 257 (old-map (current-local-map))) 258 (if (get map-name 'derived-mode-unmerged) 259 (derived-mode-merge-keymaps old-map new-map)) 260 (put map-name 'derived-mode-unmerged nil) 261 (use-local-map new-map))) 262 263(defun derived-mode-set-syntax-table (mode) 264 "Set the syntax table of the new mode, maybe merging with the parent." 265 (let* ((table-name (derived-mode-syntax-table-name mode)) 266 (old-table (syntax-table)) 267 (new-table (eval table-name))) 268 (if (get table-name 'derived-mode-unmerged) 269 (derived-mode-merge-syntax-tables old-table new-table)) 270 (put table-name 'derived-mode-unmerged nil) 271 (set-syntax-table new-table))) 272 273(defun derived-mode-set-abbrev-table (mode) 274 "Set the abbrev table if it exists. 275Always merge its parent into it, since the merge is non-destructive." 276 (let* ((table-name (derived-mode-abbrev-table-name mode)) 277 (old-table local-abbrev-table) 278 (new-table (eval table-name))) 279 (derived-mode-merge-abbrev-tables old-table new-table) 280 (setq local-abbrev-table new-table))) 281 282;;;(defun derived-mode-run-setup-function (mode) 283;;; "Run the setup function if it exists." 284 285;;; (let ((fname (derived-mode-setup-function-name mode))) 286;;; (if (fboundp fname) 287;;; (funcall fname)))) 288 289(defun derived-mode-run-hooks (mode) 290 "Run the hooks if they exist." 291 292 (let ((hooks-name (derived-mode-hooks-name mode))) 293 (if (boundp hooks-name) 294 (run-hooks hooks-name)))) 295 296;; Functions to merge maps and tables. 297 298(defun derived-mode-merge-keymaps (old new) 299 "Merge an old keymap into a new one. 300The old keymap is set to be the cdr of the new one, so that there will 301be automatic inheritance." 302 (setcdr (nthcdr (1- (length new)) new) old)) 303 304(defun derived-mode-merge-syntax-tables (old new) 305 "Merge an old syntax table into a new one. 306Where the new table already has an entry, nothing is copied from the old one." 307 (let ((idx 0) 308 (end (min (length new) (length old)))) 309 (while (< idx end) 310 (if (not (aref new idx)) 311 (aset new idx (aref old idx))) 312 (setq idx (1+ idx))))) 313 314(defun derived-mode-merge-abbrev-tables (old new) 315 "Merge an old abbrev table into a new one. 316This function requires internal knowledge of how abbrev tables work, 317presuming that they are obarrays with the abbrev as the symbol, the expansion 318as the value of the symbol, and the hook as the function definition. 319This could well break with some future version of Gnu Emacs." 320 (mapatoms 321 (function 322 (lambda (symbol) 323 (or (intern-soft (symbol-name symbol) new) 324 (define-abbrev new (symbol-name symbol) 325 (symbol-value symbol) (symbol-function symbol))))) 326 old)) 327 328(provide 'derived) 329 330;;; derived.el ends here 331