lisp/derived.el

   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 the
  23 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  24 ;; Boston, MA 02111-1307, USA.
  25 \f
  26 ;;; Commentary:
  27
  28 ;; GNU Emacs is already, in a sense, object oriented -- each object
  29 ;; (buffer) belongs to a class (major mode), and that class defines
  30 ;; the relationship between messages (input events) and methods
  31 ;; (commands) by means of a keymap.
  32 ;;
  33 ;; The only thing missing is a good scheme of inheritance.  It is
  34 ;; possible to simulate a single level of inheritance with generous
  35 ;; use of hooks and a bit of work -- sgml-mode, for example, also runs
  36 ;; the hooks for text-mode, and keymaps can inherit from other keymaps
  37 ;; -- but generally, each major mode ends up reinventing the wheel.
  38 ;; Ideally, someone should redesign all of Emacs's major modes to
  39 ;; follow a more conventional object-oriented system: when defining a
  40 ;; new major mode, the user should need only to name the existing mode
  41 ;; it is most similar to, then list the (few) differences.
  42 ;;
  43 ;; In the mean time, this package offers most of the advantages of
  44 ;; full inheritance with the existing major modes.  The macro
  45 ;; `define-derived-mode' allows the user to make a variant of an existing
  46 ;; major mode, with its own keymap.  The new mode will inherit the key
  47 ;; bindings of its parent, and will, in fact, run its parent first
  48 ;; every time it is called.  For example, the commands
  49 ;;
  50 ;;  (define-derived-mode hypertext-mode text-mode "Hypertext"
  51 ;;    "Major mode for hypertext.\n\n\\{hypertext-mode-map}"
  52 ;;    (setq case-fold-search nil))
  53 ;;
  54 ;;  (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)
  55 ;;
  56 ;; will create a function `hypertext-mode' with its own (sparse)
  57 ;; keymap `hypertext-mode-map.'  The command M-x hypertext-mode will
  58 ;; perform the following actions:
  59 ;;
  60 ;; - run the command (text-mode) to get its default setup
  61 ;; - replace the current keymap with 'hypertext-mode-map,' which will
  62 ;;   inherit from 'text-mode-map'.
  63 ;; - replace the current syntax table with
  64 ;;   'hypertext-mode-syntax-table', which will borrow its defaults
  65 ;;   from the current text-mode-syntax-table.
  66 ;; - replace the current abbrev table with
  67 ;;   'hypertext-mode-abbrev-table', which will borrow its defaults
  68 ;;   from the current text-mode-abbrev table
  69 ;; - change the mode line to read "Hypertext"
  70 ;; - assign the value 'hypertext-mode' to the 'major-mode' variable
  71 ;; - run the body of commands provided in the macro -- in this case,
  72 ;;   set the local variable `case-fold-search' to nil.
  73 ;; - **run the command (hypertext-mode-setup), which is empty by
  74 ;;   default, but may be redefined by the user to contain special
  75 ;;   commands (ie. setting local variables like 'outline-regexp')
  76 ;;   **NOTE: do not use this option -- it will soon be obsolete.
  77 ;; - run anything assigned to 'hypertext-mode-hooks' (obsolete, but
  78 ;;   supported for the sake of compatibility).
  79 ;;
  80 ;; The advantages of this system are threefold.  First, text mode is
  81 ;; untouched -- if you had added the new keystroke to `text-mode-map,'
  82 ;; possibly using hooks, you would have added it to all text buffers
  83 ;; -- here, it appears only in hypertext buffers, where it makes
  84 ;; sense.  Second, it is possible to build even further, and make
  85 ;; a derived mode from a derived mode.  The commands
  86 ;;
  87 ;;   (define-derived-mode html-mode hypertext-mode "HTML")
  88 ;;   [various key definitions]
  89 ;;
  90 ;; will add a new major mode for HTML with very little fuss.
  91 ;;
  92 ;; Note also the function `derived-mode-class,' which returns the non-derived
  93 ;; major mode which a derived mode is based on (ie. NOT necessarily the
  94 ;; immediate parent).
  95 ;;
  96 ;; (derived-mode-class 'text-mode) ==> text-mode
  97 ;; (derived-mode-class 'hypertext-mode) ==> text-mode
  98 ;; (derived-mode-class 'html-mode) ==> text-mode
  99 \f
 100 ;;; Code:
 101
 102 ;; PUBLIC: define a new major mode which inherits from an existing one.
 103
 104 ;;;###autoload
 105 (defmacro define-derived-mode (child parent name &optional docstring &rest body)
 106   "Create a new mode as a variant of an existing mode.
 107
 108 The arguments to this command are as follow:
 109
 110 CHILD:     the name of the command for the derived mode.
 111 PARENT:    the name of the command for the parent mode (ie. text-mode).
 112 NAME:      a string which will appear in the status line (ie. \"Hypertext\")
 113 DOCSTRING: an optional documentation string--if you do not supply one,
 114            the function will attempt to invent something useful.
 115 BODY:      forms to execute just before running the
 116            hooks for the new mode.
 117
 118 Here is how you could define LaTeX-Thesis mode as a variant of LaTeX mode:
 119
 120   (define-derived-mode LaTeX-thesis-mode LaTeX-mode \"LaTeX-Thesis\")
 121
 122 You could then make new key bindings for `LaTeX-thesis-mode-map'
 123 without changing regular LaTeX mode.  In this example, BODY is empty,
 124 and DOCSTRING is generated by default.
 125
 126 On a more complicated level, the following command uses sgml-mode as
 127 the parent, and then sets the variable `case-fold-search' to nil:
 128
 129   (define-derived-mode article-mode sgml-mode \"Article\"
 130     \"Major mode for editing technical articles.\"
 131     (setq case-fold-search nil))
 132
 133 Note that if the documentation string had been left out, it would have
 134 been generated automatically, with a reference to the keymap."
 135
 136                                         ; Some trickiness, since what
 137                                         ; appears to be the docstring
 138                                         ; may really be the first
 139                                         ; element of the body.
 140   (if (and docstring (not (stringp docstring)))
 141       (progn (setq body (cons docstring body))
 142              (setq docstring nil)))
 143   (setq docstring (or docstring (derived-mode-make-docstring parent child)))
 144
 145   (` (progn
 146        (derived-mode-init-mode-variables (quote (, child)))
 147        (defun (, child) ()
 148          (, docstring)
 149          (interactive)
 150                                         ; Run the parent.
 151          ((, parent))
 152                                         ; Identify special modes.
 153          (if (get (quote (, parent)) 'special)
 154              (put (quote (, child)) 'special t))
 155                                         ; Identify the child mode.
 156          (setq major-mode (quote (, child)))
 157          (setq mode-name (, name))
 158                                         ; Set up maps and tables.
 159          (derived-mode-set-keymap (quote (, child)))
 160          (derived-mode-set-syntax-table (quote (, child)))
 161          (derived-mode-set-abbrev-table (quote (, child)))
 162                                         ; Splice in the body (if any).
 163          (,@ body)
 164 ;;;                                     ; Run the setup function, if
 165 ;;;                                     ; any -- this will soon be
 166 ;;;                                     ; obsolete.
 167 ;;;      (derived-mode-run-setup-function (quote (, child)))
 168                                         ; Run the hooks, if any.
 169          (derived-mode-run-hooks (quote (, child)))))))
 170
 171
 172 ;; PUBLIC: find the ultimate class of a derived mode.
 173
 174 (defun derived-mode-class (mode)
 175   "Find the class of a major mode.
 176 A mode's class is the first ancestor which is NOT a derived mode.
 177 Use the `derived-mode-parent' property of the symbol to trace backwards."
 178   (while (get mode 'derived-mode-parent)
 179     (setq mode (get mode 'derived-mode-parent)))
 180   mode)
 181
 182 \f
 183 ;; Inline functions to construct various names from a mode name.
 184
 185 (defsubst derived-mode-setup-function-name (mode)
 186   "Construct a setup-function name based on a mode name."
 187   (intern (concat (symbol-name mode) "-setup")))
 188
 189 (defsubst derived-mode-hooks-name (mode)
 190   "Construct a hooks name based on a mode name."
 191   (intern (concat (symbol-name mode) "-hooks")))
 192
 193 (defsubst derived-mode-map-name (mode)
 194   "Construct a map name based on a mode name."
 195   (intern (concat (symbol-name mode) "-map")))
 196
 197 (defsubst derived-mode-syntax-table-name (mode)
 198   "Construct a syntax-table name based on a mode name."
 199   (intern (concat (symbol-name mode) "-syntax-table")))
 200
 201 (defsubst derived-mode-abbrev-table-name (mode)
 202   "Construct an abbrev-table name based on a mode name."
 203   (intern (concat (symbol-name mode) "-abbrev-table")))
 204
 205 \f
 206 ;; Utility functions for defining a derived mode.
 207
 208 ;;;###autoload
 209 (defun derived-mode-init-mode-variables (mode)
 210   "Initialise variables for a new mode.
 211 Right now, if they don't already exist, set up a blank keymap, an
 212 empty syntax table, and an empty abbrev table -- these will be merged
 213 the first time the mode is used."
 214
 215   (if (boundp (derived-mode-map-name mode))
 216       t
 217     (eval (` (defvar (, (derived-mode-map-name mode))
 218                (make-sparse-keymap)
 219                (, (format "Keymap for %s." mode)))))
 220     (put (derived-mode-map-name mode) 'derived-mode-unmerged t))
 221
 222   (if (boundp (derived-mode-syntax-table-name mode))
 223       t
 224     (eval (` (defvar (, (derived-mode-syntax-table-name mode))
 225                ;; Make a syntax table which doesn't specify anything
 226                ;; for any char.  Valid data will be merged in by
 227                ;; derived-mode-merge-syntax-tables.
 228                (make-char-table 'syntax-table nil)
 229                (, (format "Syntax table for %s." mode)))))
 230     (put (derived-mode-syntax-table-name mode) 'derived-mode-unmerged t))
 231
 232   (if (boundp (derived-mode-abbrev-table-name mode))
 233       t
 234     (eval (` (defvar (, (derived-mode-abbrev-table-name mode))
 235                (progn (define-abbrev-table (derived-mode-abbrev-table-name mode) nil)
 236                       (make-abbrev-table))
 237                (, (format "Abbrev table for %s." mode)))))))
 238
 239 (defun derived-mode-make-docstring (parent child)
 240   "Construct a docstring for a new mode if none is provided."
 241
 242   (format "This major mode is a variant of `%s', created by `define-derived-mode'.
 243 It inherits all of the parent's attributes, but has its own keymap,
 244 abbrev table and syntax table:
 245
 246   `%s-map' and `%s-syntax-table'
 247
 248 which more-or-less shadow
 249
 250   `%s-map' and `%s-syntax-table'
 251
 252 \\{%s-map}" parent child child parent parent child))
 253
 254 \f
 255 ;; Utility functions for running a derived mode.
 256
 257 (defun derived-mode-set-keymap (mode)
 258   "Set the keymap of the new mode, maybe merging with the parent."
 259   (let* ((map-name (derived-mode-map-name mode))
 260          (new-map (eval map-name))
 261          (old-map (current-local-map)))
 262     (and old-map
 263          (get map-name 'derived-mode-unmerged)
 264          (derived-mode-merge-keymaps old-map new-map))
 265     (put map-name 'derived-mode-unmerged nil)
 266     (use-local-map new-map)))
 267
 268 (defun derived-mode-set-syntax-table (mode)
 269   "Set the syntax table of the new mode, maybe merging with the parent."
 270   (let* ((table-name (derived-mode-syntax-table-name mode))
 271          (old-table (syntax-table))
 272          (new-table (eval table-name)))
 273     (if (get table-name 'derived-mode-unmerged)
 274         (derived-mode-merge-syntax-tables old-table new-table))
 275     (put table-name 'derived-mode-unmerged nil)
 276     (set-syntax-table new-table)))
 277
 278 (defun derived-mode-set-abbrev-table (mode)
 279   "Set the abbrev table if it exists.
 280 Always merge its parent into it, since the merge is non-destructive."
 281   (let* ((table-name (derived-mode-abbrev-table-name mode))
 282          (old-table local-abbrev-table)
 283          (new-table (eval table-name)))
 284     (derived-mode-merge-abbrev-tables old-table new-table)
 285     (setq local-abbrev-table new-table)))
 286
 287 ;;;(defun derived-mode-run-setup-function (mode)
 288 ;;;  "Run the setup function if it exists."
 289
 290 ;;;  (let ((fname (derived-mode-setup-function-name mode)))
 291 ;;;    (if (fboundp fname)
 292 ;;;     (funcall fname))))
 293
 294 (defun derived-mode-run-hooks (mode)
 295   "Run the hooks if they exist."
 296
 297   (let ((hooks-name (derived-mode-hooks-name mode)))
 298     (if (boundp hooks-name)
 299         (run-hooks hooks-name))))
 300
 301 ;; Functions to merge maps and tables.
 302
 303 (defun derived-mode-merge-keymaps (old new)
 304   "Merge an old keymap into a new one.
 305 The old keymap is set to be the last cdr of the new one, so that there will
 306 be automatic inheritance."
 307   (let ((tail new))
 308     ;; Scan the NEW map for prefix keys.
 309     (while (consp tail)
 310       (and (consp (car tail))
 311            (let* ((key (vector (car (car tail))))
 312                   (subnew (lookup-key new key))
 313                   (subold (lookup-key old key)))
 314              ;; If KEY is a prefix key in both OLD and NEW, merge them.
 315              (and (keymapp subnew) (keymapp subold)
 316                   (derived-mode-merge-keymaps subold subnew))))
 317       (and (vectorp (car tail))
 318            ;; Search a vector of ASCII char bindings for prefix keys.
 319            (let ((i (1- (length (car tail)))))
 320              (while (>= i 0)
 321                (let* ((key (vector i))
 322                       (subnew (lookup-key new key))
 323                       (subold (lookup-key old key)))
 324                  ;; If KEY is a prefix key in both OLD and NEW, merge them.
 325                  (and (keymapp subnew) (keymapp subold)
 326                       (derived-mode-merge-keymaps subold subnew)))
 327                (setq i (1- i)))))
 328       (setq tail (cdr tail))))
 329   (setcdr (nthcdr (1- (length new)) new) old))
 330
 331 (defun derived-mode-merge-syntax-tables (old new)
 332   "Merge an old syntax table into a new one.
 333 Where the new table already has an entry, nothing is copied from the old one."
 334   (set-char-table-parent new old))
 335
 336 ;; Merge an old abbrev table into a new one.
 337 ;; This function requires internal knowledge of how abbrev tables work,
 338 ;; presuming that they are obarrays with the abbrev as the symbol, the expansion
 339 ;; as the value of the symbol, and the hook as the function definition.
 340 (defun derived-mode-merge-abbrev-tables (old new)
 341   (if old
 342       (mapatoms
 343        (function
 344         (lambda (symbol)
 345           (or (intern-soft (symbol-name symbol) new)
 346               (define-abbrev new (symbol-name symbol)
 347                 (symbol-value symbol) (symbol-function symbol)))))
 348        old)))
 349
 350 (provide 'derived)
 351
 352 ;;; derived.el ends here