LCOV - code coverage report
Current view: top level - lisp/emacs-lisp - derived.el (source / functions) Hit Total Coverage
Test: tramp-tests-after.info Lines: 113 185 61.1 %
Date: 2017-08-30 10:12:24 Functions: 6 17 35.3 %

          Line data    Source code
       1             : ;;; derived.el --- allow inheritance of major modes
       2             : ;; (formerly mode-clone.el)
       3             : 
       4             : ;; Copyright (C) 1993-1994, 1999, 2001-2017 Free Software Foundation,
       5             : ;; Inc.
       6             : 
       7             : ;; Author: David Megginson (dmeggins@aix1.uottawa.ca)
       8             : ;; Maintainer: emacs-devel@gnu.org
       9             : ;; Keywords: extensions
      10             : ;; Package: emacs
      11             : 
      12             : ;; This file is part of GNU Emacs.
      13             : 
      14             : ;; GNU Emacs is free software: you can redistribute it and/or modify
      15             : ;; it under the terms of the GNU General Public License as published by
      16             : ;; the Free Software Foundation, either version 3 of the License, or
      17             : ;; (at your option) any later version.
      18             : 
      19             : ;; GNU Emacs is distributed in the hope that it will be useful,
      20             : ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
      21             : ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      22             : ;; GNU General Public License for more details.
      23             : 
      24             : ;; You should have received a copy of the GNU General Public License
      25             : ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
      26             : 
      27             : ;;; Commentary:
      28             : 
      29             : ;; GNU Emacs is already, in a sense, object oriented -- each object
      30             : ;; (buffer) belongs to a class (major mode), and that class defines
      31             : ;; the relationship between messages (input events) and methods
      32             : ;; (commands) by means of a keymap.
      33             : ;;
      34             : ;; The only thing missing is a good scheme of inheritance.  It is
      35             : ;; possible to simulate a single level of inheritance with generous
      36             : ;; use of hooks and a bit of work -- sgml-mode, for example, also runs
      37             : ;; the hooks for text-mode, and keymaps can inherit from other keymaps
      38             : ;; -- but generally, each major mode ends up reinventing the wheel.
      39             : ;; Ideally, someone should redesign all of Emacs's major modes to
      40             : ;; follow a more conventional object-oriented system: when defining a
      41             : ;; new major mode, the user should need only to name the existing mode
      42             : ;; it is most similar to, then list the (few) differences.
      43             : ;;
      44             : ;; In the mean time, this package offers most of the advantages of
      45             : ;; full inheritance with the existing major modes.  The macro
      46             : ;; `define-derived-mode' allows the user to make a variant of an existing
      47             : ;; major mode, with its own keymap.  The new mode will inherit the key
      48             : ;; bindings of its parent, and will, in fact, run its parent first
      49             : ;; every time it is called.  For example, the commands
      50             : ;;
      51             : ;;  (define-derived-mode hypertext-mode text-mode "Hypertext"
      52             : ;;    "Major mode for hypertext.\n\n\\{hypertext-mode-map}"
      53             : ;;    (setq case-fold-search nil))
      54             : ;;
      55             : ;;  (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)
      56             : ;;
      57             : ;; will create a function `hypertext-mode' with its own (sparse)
      58             : ;; keymap `hypertext-mode-map.'  The command M-x hypertext-mode will
      59             : ;; perform the following actions:
      60             : ;;
      61             : ;; - run the command (text-mode) to get its default setup
      62             : ;; - replace the current keymap with 'hypertext-mode-map,' which will
      63             : ;;   inherit from 'text-mode-map'.
      64             : ;; - replace the current syntax table with
      65             : ;;   'hypertext-mode-syntax-table', which will borrow its defaults
      66             : ;;   from the current text-mode-syntax-table.
      67             : ;; - replace the current abbrev table with
      68             : ;;   'hypertext-mode-abbrev-table', which will borrow its defaults
      69             : ;;   from the current text-mode-abbrev table
      70             : ;; - change the mode line to read "Hypertext"
      71             : ;; - assign the value 'hypertext-mode' to the 'major-mode' variable
      72             : ;; - run the body of commands provided in the macro -- in this case,
      73             : ;;   set the local variable `case-fold-search' to nil.
      74             : ;;
      75             : ;; The advantages of this system are threefold.  First, text mode is
      76             : ;; untouched -- if you had added the new keystroke to `text-mode-map,'
      77             : ;; possibly using hooks, you would have added it to all text buffers
      78             : ;; -- here, it appears only in hypertext buffers, where it makes
      79             : ;; sense.  Second, it is possible to build even further, and make
      80             : ;; a derived mode from a derived mode.  The commands
      81             : ;;
      82             : ;;   (define-derived-mode html-mode hypertext-mode "HTML")
      83             : ;;   [various key definitions]
      84             : ;;
      85             : ;; will add a new major mode for HTML with very little fuss.
      86             : ;;
      87             : ;; Note also the function `derived-mode-p' which can tell if the current
      88             : ;; mode derives from another.  In a hypertext-mode, buffer, for example,
      89             : ;; (derived-mode-p 'text-mode) would return non-nil.  This should always
      90             : ;; be used in place of (eq major-mode 'text-mode).
      91             : 
      92             : ;;; Code:
      93             : 
      94             : ;;; PRIVATE: defsubst must be defined before they are first used
      95             : 
      96             : (defsubst derived-mode-hook-name (mode)
      97             :   "Construct a mode-hook name based on a MODE name."
      98          44 :   (intern (concat (symbol-name mode) "-hook")))
      99             : 
     100             : (defsubst derived-mode-map-name (mode)
     101             :   "Construct a map name based on a MODE name."
     102          44 :   (intern (concat (symbol-name mode) "-map")))
     103             : 
     104             : (defsubst derived-mode-syntax-table-name (mode)
     105             :   "Construct a syntax-table name based on a MODE name."
     106          22 :   (intern (concat (symbol-name mode) "-syntax-table")))
     107             : 
     108             : (defsubst derived-mode-abbrev-table-name (mode)
     109             :   "Construct an abbrev-table name based on a MODE name."
     110          22 :   (intern (concat (symbol-name mode) "-abbrev-table")))
     111             : 
     112             : ;; PUBLIC: define a new major mode which inherits from an existing one.
     113             : 
     114             : ;;;###autoload
     115             : (defmacro define-derived-mode (child parent name &optional docstring &rest body)
     116             :   "Create a new mode as a variant of an existing mode.
     117             : 
     118             : The arguments to this command are as follow:
     119             : 
     120             : CHILD:     the name of the command for the derived mode.
     121             : PARENT:    the name of the command for the parent mode (e.g. `text-mode')
     122             :            or nil if there is no parent.
     123             : NAME:      a string which will appear in the status line (e.g. \"Hypertext\")
     124             : DOCSTRING: an optional documentation string--if you do not supply one,
     125             :            the function will attempt to invent something useful.
     126             : BODY:      forms to execute just before running the
     127             :            hooks for the new mode.  Do not use `interactive' here.
     128             : 
     129             : BODY can start with a bunch of keyword arguments.  The following keyword
     130             :   arguments are currently understood:
     131             : :group GROUP
     132             :         Declare the customization group that corresponds to this mode.
     133             :         The command `customize-mode' uses this.
     134             : :syntax-table TABLE
     135             :         Use TABLE instead of the default (CHILD-syntax-table).
     136             :         A nil value means to simply use the same syntax-table as the parent.
     137             : :abbrev-table TABLE
     138             :         Use TABLE instead of the default (CHILD-abbrev-table).
     139             :         A nil value means to simply use the same abbrev-table as the parent.
     140             : :after-hook FORM
     141             :         A single lisp form which is evaluated after the mode hooks have been
     142             :         run.  It should not be quoted.
     143             : 
     144             : Here is how you could define LaTeX-Thesis mode as a variant of LaTeX mode:
     145             : 
     146             :   (define-derived-mode LaTeX-thesis-mode LaTeX-mode \"LaTeX-Thesis\")
     147             : 
     148             : You could then make new key bindings for `LaTeX-thesis-mode-map'
     149             : without changing regular LaTeX mode.  In this example, BODY is empty,
     150             : and DOCSTRING is generated by default.
     151             : 
     152             : On a more complicated level, the following command uses `sgml-mode' as
     153             : the parent, and then sets the variable `case-fold-search' to nil:
     154             : 
     155             :   (define-derived-mode article-mode sgml-mode \"Article\"
     156             :     \"Major mode for editing technical articles.\"
     157             :     (setq case-fold-search nil))
     158             : 
     159             : Note that if the documentation string had been left out, it would have
     160             : been generated automatically, with a reference to the keymap.
     161             : 
     162             : The new mode runs the hook constructed by the function
     163             : `derived-mode-hook-name'.
     164             : 
     165             : See Info node `(elisp)Derived Modes' for more details."
     166             :   (declare (debug (&define name symbolp sexp [&optional stringp]
     167             :                            [&rest keywordp sexp] def-body))
     168             :            (doc-string 4)
     169             :            ;; Ask not what
     170             :            ;;(indent 3)
     171             :            ;; can do for you, ask what it can do to others. IOW, the
     172             :            ;; missing of indentation setting here is the indentation
     173             :            ;; setting and not an oversight.
     174             :            )
     175             : 
     176          22 :   (when (and docstring (not (stringp docstring)))
     177             :     ;; Some trickiness, since what appears to be the docstring may really be
     178             :     ;; the first element of the body.
     179           6 :     (push docstring body)
     180          22 :     (setq docstring nil))
     181             : 
     182          22 :   (when (eq parent 'fundamental-mode) (setq parent nil))
     183             : 
     184          22 :   (let ((map (derived-mode-map-name child))
     185          22 :         (syntax (derived-mode-syntax-table-name child))
     186          22 :         (abbrev (derived-mode-abbrev-table-name child))
     187             :         (declare-abbrev t)
     188             :         (declare-syntax t)
     189          22 :         (hook (derived-mode-hook-name child))
     190             :         (group nil)
     191             :         (after-hook nil))
     192             : 
     193             :     ;; Process the keyword args.
     194          25 :     (while (keywordp (car body))
     195           6 :       (pcase (pop body)
     196           0 :         (`:group (setq group (pop body)))
     197           4 :         (`:abbrev-table (setq abbrev (pop body)) (setq declare-abbrev nil))
     198           2 :         (`:syntax-table (setq syntax (pop body)) (setq declare-syntax nil))
     199           0 :         (`:after-hook (setq after-hook (pop body)))
     200          22 :         (_ (pop body))))
     201             : 
     202          22 :     (setq docstring (derived-mode-make-docstring
     203          22 :                      parent child docstring syntax abbrev))
     204             : 
     205          22 :     `(progn
     206          22 :        (defvar ,hook nil
     207          22 :          ,(format "Hook run after entering %s mode.
     208             : No problems result if this variable is not bound.
     209             : `add-hook' automatically binds it.  (This is true for all hook variables.)"
     210          22 :                   name))
     211          22 :        (unless (boundp ',map)
     212          22 :          (put ',map 'definition-name ',child))
     213          22 :        (with-no-warnings (defvar ,map (make-sparse-keymap)))
     214          22 :        (unless (get ',map 'variable-documentation)
     215          22 :          (put ',map 'variable-documentation
     216          22 :               (purecopy ,(format "Keymap for `%s'." child))))
     217          22 :        ,(if declare-syntax
     218          21 :             `(progn
     219          21 :                (defvar ,syntax)
     220          21 :                (unless (boundp ',syntax)
     221          21 :                  (put ',syntax 'definition-name ',child)
     222          21 :                  (defvar ,syntax (make-syntax-table)))
     223          21 :                (unless (get ',syntax 'variable-documentation)
     224          21 :                  (put ',syntax 'variable-documentation
     225          22 :                       (purecopy ,(format "Syntax table for `%s'." child))))))
     226          22 :        ,(if declare-abbrev
     227          20 :             `(progn
     228          20 :                (defvar ,abbrev)
     229          20 :                (unless (boundp ',abbrev)
     230          20 :                  (put ',abbrev 'definition-name ',child)
     231          20 :                  (defvar ,abbrev
     232          20 :                    (progn (define-abbrev-table ',abbrev nil) ,abbrev)))
     233          20 :                (unless (get ',abbrev 'variable-documentation)
     234          20 :                  (put ',abbrev 'variable-documentation
     235          22 :                       (purecopy ,(format "Abbrev table for `%s'." child))))))
     236          22 :        (put ',child 'derived-mode-parent ',parent)
     237          22 :        ,(if group `(put ',child 'custom-mode-group ,group))
     238             : 
     239          22 :        (defun ,child ()
     240          22 :          ,docstring
     241             :          (interactive)
     242             :                                         ; Run the parent.
     243             :          (delay-mode-hooks
     244             : 
     245          22 :           (,(or parent 'kill-all-local-variables))
     246             :                                         ; Identify the child mode.
     247          22 :           (setq major-mode (quote ,child))
     248          22 :           (setq mode-name ,name)
     249             :                                         ; Identify special modes.
     250          22 :           ,(when parent
     251          13 :              `(progn
     252          13 :                 (if (get (quote ,parent) 'mode-class)
     253          13 :                     (put (quote ,child) 'mode-class
     254          13 :                          (get (quote ,parent) 'mode-class)))
     255             :                                         ; Set up maps and tables.
     256          13 :                 (unless (keymap-parent ,map)
     257             :                   ;; It would probably be better to set the keymap's parent
     258             :                   ;; at the toplevel rather than inside the mode function,
     259             :                   ;; but this is not easy for at least the following reasons:
     260             :                   ;; - the parent (and its keymap) may not yet be loaded.
     261             :                   ;; - the parent's keymap name may be called something else
     262             :                   ;;   than <parent>-mode-map.
     263          13 :                   (set-keymap-parent ,map (current-local-map)))
     264          13 :                 ,(when declare-syntax
     265          12 :                    `(let ((parent (char-table-parent ,syntax)))
     266             :                       (unless (and parent
     267             :                                    (not (eq parent (standard-syntax-table))))
     268          13 :                         (set-char-table-parent ,syntax (syntax-table)))))
     269          13 :                 ,(when declare-abbrev
     270          12 :                    `(unless (or (abbrev-table-get ,abbrev :parents)
     271             :                                 ;; This can happen if the major mode defines
     272             :                                 ;; the abbrev-table to be its parent's.
     273          12 :                                 (eq ,abbrev local-abbrev-table))
     274          12 :                       (abbrev-table-put ,abbrev :parents
     275          22 :                                         (list local-abbrev-table))))))
     276          22 :           (use-local-map ,map)
     277          22 :           ,(when syntax `(set-syntax-table ,syntax))
     278          22 :           ,(when abbrev `(setq local-abbrev-table ,abbrev))
     279             :                                         ; Splice in the body (if any).
     280          22 :           ,@body
     281             :           )
     282             :          ;; Run the hooks, if any.
     283          22 :          (run-mode-hooks ',hook)
     284          22 :          ,@(when after-hook
     285           0 :              `((if delay-mode-hooks
     286           0 :                    (push ',after-hook delayed-after-hook-forms)
     287          22 :                  ,after-hook)))))))
     288             : 
     289             : ;; PUBLIC: find the ultimate class of a derived mode.
     290             : 
     291             : (defun derived-mode-class (mode)
     292             :   "Find the class of a major MODE.
     293             : A mode's class is the first ancestor which is NOT a derived mode.
     294             : Use the `derived-mode-parent' property of the symbol to trace backwards.
     295             : Since major-modes might all derive from `fundamental-mode', this function
     296             : is not very useful."
     297             :   (declare (obsolete derived-mode-p "22.1"))
     298           0 :   (while (get mode 'derived-mode-parent)
     299           0 :     (setq mode (get mode 'derived-mode-parent)))
     300           0 :   mode)
     301             : 
     302             : 
     303             : ;;; PRIVATE
     304             : 
     305             : (defun derived-mode-make-docstring (parent child &optional
     306             :                                            docstring syntax abbrev)
     307             :   "Construct a docstring for a new mode if none is provided."
     308             : 
     309          22 :   (let ((map (derived-mode-map-name child))
     310          22 :         (hook (derived-mode-hook-name child)))
     311             : 
     312          22 :     (unless (stringp docstring)
     313             :       ;; Use a default docstring.
     314           3 :       (setq docstring
     315           3 :             (if (null parent)
     316             :                 ;; FIXME filling.
     317           1 :                 (format "Major-mode.\nUses keymap `%s'%s%s." map
     318           1 :                         (if abbrev (format "%s abbrev table `%s'"
     319           1 :                                            (if syntax "," " and") abbrev) "")
     320           1 :                         (if syntax (format " and syntax-table `%s'" syntax) ""))
     321           2 :               (format "Major mode derived from `%s' by `define-derived-mode'.
     322             : It inherits all of the parent's attributes, but has its own keymap%s:
     323             : 
     324             :   `%s'%s
     325             : 
     326             : which more-or-less shadow%s %s's corresponding table%s."
     327           2 :                       parent
     328           2 :                       (cond ((and abbrev syntax)
     329             :                              ",\nabbrev table and syntax table")
     330           0 :                             (abbrev "\nand abbrev table")
     331           0 :                             (syntax "\nand syntax table")
     332           2 :                             (t ""))
     333           2 :                       map
     334           2 :                       (cond ((and abbrev syntax)
     335           2 :                              (format ", `%s' and `%s'" abbrev syntax))
     336           0 :                             ((or abbrev syntax)
     337           0 :                              (format " and `%s'" (or abbrev syntax)))
     338           2 :                             (t ""))
     339           2 :                       (if (or abbrev syntax) "" "s")
     340           2 :                       parent
     341          22 :                       (if (or abbrev syntax) "s" "")))))
     342             : 
     343          22 :     (unless (string-match (regexp-quote (symbol-name hook)) docstring)
     344             :       ;; Make sure the docstring mentions the mode's hook.
     345          17 :       (setq docstring
     346          17 :             (concat docstring
     347          17 :                     (if (null parent)
     348             :                         "\n\nThis mode "
     349          10 :                       (concat
     350             :                        "\n\nIn addition to any hooks its parent mode "
     351          10 :                        (if (string-match (format "[`‘]%s['’]"
     352          10 :                                                  (regexp-quote
     353          10 :                                                   (symbol-name parent)))
     354          10 :                                          docstring)
     355             :                            nil
     356          10 :                          (format "`%s' " parent))
     357          17 :                        "might have run,\nthis mode "))
     358          17 :                     (format "runs the hook `%s'" hook)
     359          22 :                     ", as the final or penultimate step\nduring initialization.")))
     360             : 
     361          22 :     (unless (string-match "\\\\[{[]" docstring)
     362             :       ;; And don't forget to put the mode's keymap.
     363          22 :       (setq docstring (concat docstring "\n\n\\{" (symbol-name map) "}")))
     364             : 
     365          22 :     docstring))
     366             : 
     367             : 
     368             : ;;; OBSOLETE
     369             : ;; The functions below are only provided for backward compatibility with
     370             : ;; code byte-compiled with versions of derived.el prior to Emacs-21.
     371             : 
     372             : (defsubst derived-mode-setup-function-name (mode)
     373             :   "Construct a setup-function name based on a MODE name."
     374           0 :   (intern (concat (symbol-name mode) "-setup")))
     375             : 
     376             : 
     377             : ;; Utility functions for defining a derived mode.
     378             : 
     379             : ;;;###autoload
     380             : (defun derived-mode-init-mode-variables (mode)
     381             :   "Initialize variables for a new MODE.
     382             : Right now, if they don't already exist, set up a blank keymap, an
     383             : empty syntax table, and an empty abbrev table -- these will be merged
     384             : the first time the mode is used."
     385             : 
     386           0 :   (if (boundp (derived-mode-map-name mode))
     387             :       t
     388           0 :     (eval `(defvar ,(derived-mode-map-name mode)
     389             :                (make-sparse-keymap)
     390           0 :                ,(format "Keymap for %s." mode)))
     391           0 :     (put (derived-mode-map-name mode) 'derived-mode-unmerged t))
     392             : 
     393           0 :   (if (boundp (derived-mode-syntax-table-name mode))
     394             :       t
     395           0 :     (eval `(defvar ,(derived-mode-syntax-table-name mode)
     396             :              ;; Make a syntax table which doesn't specify anything
     397             :              ;; for any char.  Valid data will be merged in by
     398             :              ;; derived-mode-merge-syntax-tables.
     399             :              (make-char-table 'syntax-table nil)
     400           0 :              ,(format "Syntax table for %s." mode)))
     401           0 :     (put (derived-mode-syntax-table-name mode) 'derived-mode-unmerged t))
     402             : 
     403           0 :   (if (boundp (derived-mode-abbrev-table-name mode))
     404             :       t
     405           0 :     (eval `(defvar ,(derived-mode-abbrev-table-name mode)
     406             :              (progn
     407             :                (define-abbrev-table (derived-mode-abbrev-table-name mode) nil)
     408             :                (make-abbrev-table))
     409           0 :              ,(format "Abbrev table for %s." mode)))))
     410             : 
     411             : ;; Utility functions for running a derived mode.
     412             : 
     413             : (defun derived-mode-set-keymap (mode)
     414             :   "Set the keymap of the new MODE, maybe merging with the parent."
     415           0 :   (let* ((map-name (derived-mode-map-name mode))
     416           0 :          (new-map (eval map-name))
     417           0 :          (old-map (current-local-map)))
     418           0 :     (and old-map
     419           0 :          (get map-name 'derived-mode-unmerged)
     420           0 :          (derived-mode-merge-keymaps old-map new-map))
     421           0 :     (put map-name 'derived-mode-unmerged nil)
     422           0 :     (use-local-map new-map)))
     423             : 
     424             : (defun derived-mode-set-syntax-table (mode)
     425             :   "Set the syntax table of the new MODE, maybe merging with the parent."
     426           0 :   (let* ((table-name (derived-mode-syntax-table-name mode))
     427           0 :          (old-table (syntax-table))
     428           0 :          (new-table (eval table-name)))
     429           0 :     (if (get table-name 'derived-mode-unmerged)
     430           0 :         (derived-mode-merge-syntax-tables old-table new-table))
     431           0 :     (put table-name 'derived-mode-unmerged nil)
     432           0 :     (set-syntax-table new-table)))
     433             : 
     434             : (defun derived-mode-set-abbrev-table (mode)
     435             :   "Set the abbrev table for MODE if it exists.
     436             : Always merge its parent into it, since the merge is non-destructive."
     437           0 :   (let* ((table-name (derived-mode-abbrev-table-name mode))
     438           0 :          (old-table local-abbrev-table)
     439           0 :          (new-table (eval table-name)))
     440           0 :     (derived-mode-merge-abbrev-tables old-table new-table)
     441           0 :     (setq local-abbrev-table new-table)))
     442             : 
     443             : (defun derived-mode-run-hooks (mode)
     444             :    "Run the mode hook for MODE."
     445           0 :    (let ((hooks-name (derived-mode-hook-name mode)))
     446           0 :      (if (boundp hooks-name)
     447           0 :          (run-hooks hooks-name))))
     448             : 
     449             : ;; Functions to merge maps and tables.
     450             : 
     451             : (defun derived-mode-merge-keymaps (old new)
     452             :   "Merge an OLD keymap into a NEW one.
     453             : The old keymap is set to be the last cdr of the new one, so that there will
     454             : be automatic inheritance."
     455             :   ;; ?? Can this just use `set-keymap-parent'?
     456           0 :   (let ((tail new))
     457             :     ;; Scan the NEW map for prefix keys.
     458           0 :     (while (consp tail)
     459           0 :       (and (consp (car tail))
     460           0 :            (let* ((key (vector (car (car tail))))
     461           0 :                   (subnew (lookup-key new key))
     462           0 :                   (subold (lookup-key old key)))
     463             :              ;; If KEY is a prefix key in both OLD and NEW, merge them.
     464           0 :              (and (keymapp subnew) (keymapp subold)
     465           0 :                   (derived-mode-merge-keymaps subold subnew))))
     466           0 :       (and (vectorp (car tail))
     467             :            ;; Search a vector of ASCII char bindings for prefix keys.
     468           0 :            (let ((i (1- (length (car tail)))))
     469           0 :              (while (>= i 0)
     470           0 :                (let* ((key (vector i))
     471           0 :                       (subnew (lookup-key new key))
     472           0 :                       (subold (lookup-key old key)))
     473             :                  ;; If KEY is a prefix key in both OLD and NEW, merge them.
     474           0 :                  (and (keymapp subnew) (keymapp subold)
     475           0 :                       (derived-mode-merge-keymaps subold subnew)))
     476           0 :                (setq i (1- i)))))
     477           0 :       (setq tail (cdr tail))))
     478           0 :   (setcdr (nthcdr (1- (length new)) new) old))
     479             : 
     480             : (defun derived-mode-merge-syntax-tables (old new)
     481             :   "Merge an OLD syntax table into a NEW one.
     482             : Where the new table already has an entry, nothing is copied from the old one."
     483           0 :   (set-char-table-parent new old))
     484             : 
     485             : ;; Merge an old abbrev table into a new one.
     486             : ;; This function requires internal knowledge of how abbrev tables work,
     487             : ;; presuming that they are obarrays with the abbrev as the symbol, the expansion
     488             : ;; as the value of the symbol, and the hook as the function definition.
     489             : (defun derived-mode-merge-abbrev-tables (old new)
     490           0 :   (if old
     491           0 :       (mapatoms
     492             :        (lambda (symbol)
     493           0 :          (or (intern-soft (symbol-name symbol) new)
     494           0 :              (define-abbrev new (symbol-name symbol)
     495           0 :                (symbol-value symbol) (symbol-function symbol))))
     496           0 :        old)))
     497             : 
     498             : (provide 'derived)
     499             : 
     500             : ;;; derived.el ends here

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