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
  23 ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  24 \f
  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 \f
  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
 107 The arguments to this command are as follow:
 108
 109 CHILD:     the name of the command for the derived mode.
 110 PARENT:    the name of the command for the parent mode (ie. text-mode).
 111 NAME:      a string which will appear in the status line (ie. \"Hypertext\")
 112 DOCSTRING: an optional documentation string--if you do not supply one,
 113            the function will attempt to invent something useful.
 114 BODY:      forms to execute just before running the
 115            hooks for the new mode.
 116
 117 Here 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
 121 You could then make new key bindings for `LaTeX-thesis-mode-map'
 122 without changing regular LaTeX mode.  In this example, BODY is empty,
 123 and DOCSTRING is generated by default.
 124
 125 On a more complicated level, the following command uses sgml-mode as
 126 the 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
 132 Note that if the documentation string had been left out, it would have
 133 been 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.
 175 A mode's class is the first ancestor which is NOT a derived mode.
 176 Use 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 \f
 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 \f
 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.
 210 Right now, if they don't already exist, set up a blank keymap, an
 211 empty syntax table, and an empty abbrev table -- these will be merged
 212 the 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 a syntax table which doesn't specify anything
 225                ;; for any char.  Valid data will be merged in by
 226                ;; derived-mode-merge-syntax-tables.
 227                (make-char-table 'syntax-table nil)
 228                (, (format "Syntax table for %s." mode)))))
 229     (put (derived-mode-syntax-table-name mode) 'derived-mode-unmerged t))
 230
 231   (if (boundp (derived-mode-abbrev-table-name mode))
 232       t
 233     (eval (` (defvar (, (derived-mode-abbrev-table-name mode))
 234                (progn (define-abbrev-table (derived-mode-abbrev-table-name mode) nil)
 235                       (make-abbrev-table))
 236                (, (format "Abbrev table for %s." mode)))))))
 237
 238 (defun derived-mode-make-docstring (parent child)
 239   "Construct a docstring for a new mode if none is provided."
 240
 241   (format "This major mode is a variant of `%s', created by `define-derived-mode'.
 242 It inherits all of the parent's attributes, but has its own keymap,
 243 abbrev table and syntax table:
 244
 245   `%s-map' and `%s-syntax-table'
 246
 247 which more-or-less shadow
 248
 249   `%s-map' and `%s-syntax-table'
 250
 251 \\{%s-map}" parent child child parent parent child))
 252
 253 \f
 254 ;; Utility functions for running a derived mode.
 255
 256 (defun derived-mode-set-keymap (mode)
 257   "Set the keymap of the new mode, maybe merging with the parent."
 258   (let* ((map-name (derived-mode-map-name mode))
 259          (new-map (eval map-name))
 260          (old-map (current-local-map)))
 261     (and old-map
 262          (get map-name 'derived-mode-unmerged)
 263          (derived-mode-merge-keymaps old-map new-map))
 264     (put map-name 'derived-mode-unmerged nil)
 265     (use-local-map new-map)))
 266
 267 (defun derived-mode-set-syntax-table (mode)
 268   "Set the syntax table of the new mode, maybe merging with the parent."
 269   (let* ((table-name (derived-mode-syntax-table-name mode))
 270          (old-table (syntax-table))
 271          (new-table (eval table-name)))
 272     (if (get table-name 'derived-mode-unmerged)
 273         (derived-mode-merge-syntax-tables old-table new-table))
 274     (put table-name 'derived-mode-unmerged nil)
 275     (set-syntax-table new-table)))
 276
 277 (defun derived-mode-set-abbrev-table (mode)
 278   "Set the abbrev table if it exists.
 279 Always merge its parent into it, since the merge is non-destructive."
 280   (let* ((table-name (derived-mode-abbrev-table-name mode))
 281          (old-table local-abbrev-table)
 282          (new-table (eval table-name)))
 283     (derived-mode-merge-abbrev-tables old-table new-table)
 284     (setq local-abbrev-table new-table)))
 285
 286 ;;;(defun derived-mode-run-setup-function (mode)
 287 ;;;  "Run the setup function if it exists."
 288
 289 ;;;  (let ((fname (derived-mode-setup-function-name mode)))
 290 ;;;    (if (fboundp fname)
 291 ;;;     (funcall fname))))
 292
 293 (defun derived-mode-run-hooks (mode)
 294   "Run the hooks if they exist."
 295
 296   (let ((hooks-name (derived-mode-hooks-name mode)))
 297     (if (boundp hooks-name)
 298         (run-hooks hooks-name))))
 299
 300 ;; Functions to merge maps and tables.
 301
 302 (defun derived-mode-merge-keymaps (old new)
 303   "Merge an old keymap into a new one.
 304 The old keymap is set to be the last cdr of the new one, so that there will
 305 be automatic inheritance."
 306   (let ((tail new))
 307     ;; Scan the NEW map for prefix keys.
 308     (while (consp tail)
 309       (and (consp (car tail))
 310            (let* ((key (vector (car (car tail))))
 311                   (subnew (lookup-key new key))
 312                   (subold (lookup-key old key)))
 313              ;; If KEY is a prefix key in both OLD and NEW, merge them.
 314              (and (keymapp subnew) (keymapp subold)
 315                   (derived-mode-merge-keymaps subold subnew))))
 316       (and (vectorp (car tail))
 317            ;; Search a vector of ASCII char bindings for prefix keys.
 318            (let ((i (1- (length (car tail)))))
 319              (while (>= i 0)
 320                (let* ((key (vector i))
 321                       (subnew (lookup-key new key))
 322                       (subold (lookup-key old key)))
 323                  ;; If KEY is a prefix key in both OLD and NEW, merge them.
 324                  (and (keymapp subnew) (keymapp subold)
 325                       (derived-mode-merge-keymaps subold subnew)))
 326                (setq i (1- i)))))
 327       (setq tail (cdr tail))))
 328   (setcdr (nthcdr (1- (length new)) new) old))
 329
 330 (defun derived-mode-merge-syntax-tables (old new)
 331   "Merge an old syntax table into a new one.
 332 Where the new table already has an entry, nothing is copied from the old one."
 333   (map-char-table
 334    (function (lambda (key value)
 335                (or (char-table-range new key)
 336                    (set-char-table-range new key value))))
 337    old))
 338
 339 ;; Merge an old abbrev table into a new one.
 340 ;; This function requires internal knowledge of how abbrev tables work,
 341 ;; presuming that they are obarrays with the abbrev as the symbol, the expansion
 342 ;; as the value of the symbol, and the hook as the function definition.
 343 (defun derived-mode-merge-abbrev-tables (old new)
 344   (if old
 345       (mapatoms
 346        (function
 347         (lambda (symbol)
 348           (or (intern-soft (symbol-name symbol) new)
 349               (define-abbrev new (symbol-name symbol)
 350                 (symbol-value symbol) (symbol-function symbol)))))
 351        old)))
 352
 353 (provide 'derived)
 354
 355 ;;; derived.el ends here