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;;; derived.el --- allow inheritance of major modes
;; (formerly mode-clone.el)
;; Copyright (C) 1993-1994, 1999, 2001-2017 Free Software Foundation,
;; Inc.
;; Author: David Megginson (dmeggins@aix1.uottawa.ca)
;; Maintainer: emacs-devel@gnu.org
;; Keywords: extensions
;; Package: emacs
;; 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 3 of the License, 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. If not, see <https://www.gnu.org/licenses/>.
;;; 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:
;;; PRIVATE: defsubst must be defined before they are first used
(defsubst derived-mode-hook-name (mode)
"Construct a mode-hook name based on a MODE name."
(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.
The command `customize-mode' uses this.
:syntax-table TABLE
Use TABLE instead of the default (CHILD-syntax-table).
A nil value means to simply use the same syntax-table as the parent.
:abbrev-table TABLE
Use TABLE instead of the default (CHILD-abbrev-table).
A nil value means to simply use the same abbrev-table as the parent.
:after-hook FORM
A single lisp form which is evaluated after the mode hooks have been
run. It should not be quoted.
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.
The new mode runs the hook constructed by the function
`derived-mode-hook-name'.
See Info node `(elisp)Derived Modes' for more details."
(declare (debug (&define name symbolp sexp [&optional stringp]
[&rest keywordp sexp] def-body))
(doc-string 4)
;; Ask not what
;;(indent 3)
;; can do for you, ask what it can do to others. IOW, the
;; missing of indentation setting here is the indentation
;; setting and not an oversight.
)
(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)
(after-hook nil))
;; Process the keyword args.
(while (keywordp (car body))
(pcase (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))
(`:after-hook (setq after-hook (pop body)))
(_ (pop body))))
(setq docstring (derived-mode-make-docstring
parent child docstring syntax abbrev))
`(progn
(defvar ,hook nil)
(unless (get ',hook 'variable-documentation)
(put ',hook 'variable-documentation
,(format "Hook run after entering %s mode.
No problems result if this variable is not bound.
`add-hook' automatically binds it. (This is true for all hook variables.)"
name)))
(unless (boundp ',map)
(put ',map 'definition-name ',child))
(with-no-warnings (defvar ,map (make-sparse-keymap)))
(unless (get ',map 'variable-documentation)
(put ',map 'variable-documentation
(purecopy ,(format "Keymap for `%s'." child))))
,(if declare-syntax
`(progn
(defvar ,syntax)
(unless (boundp ',syntax)
(put ',syntax 'definition-name ',child)
(defvar ,syntax (make-syntax-table)))
(unless (get ',syntax 'variable-documentation)
(put ',syntax 'variable-documentation
(purecopy ,(format "Syntax table for `%s'." child))))))
,(if declare-abbrev
`(progn
(defvar ,abbrev)
(unless (boundp ',abbrev)
(put ',abbrev 'definition-name ',child)
(defvar ,abbrev
(progn (define-abbrev-table ',abbrev nil) ,abbrev)))
(unless (get ',abbrev 'variable-documentation)
(put ',abbrev 'variable-documentation
(purecopy ,(format "Abbrev table for `%s'." child))))))
(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)
;; It would probably be better to set the keymap's parent
;; at the toplevel rather than inside the mode function,
;; but this is not easy for at least the following reasons:
;; - the parent (and its keymap) may not yet be loaded.
;; - the parent's keymap name may be called something else
;; than <parent>-mode-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)))))
,(when declare-abbrev
`(unless (or (abbrev-table-get ,abbrev :parents)
;; This can happen if the major mode defines
;; the abbrev-table to be its parent's.
(eq ,abbrev local-abbrev-table))
(abbrev-table-put ,abbrev :parents
(list local-abbrev-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.
(run-mode-hooks ',hook)
,@(when after-hook
`((if delay-mode-hooks
(push ',after-hook delayed-after-hook-forms)
,after-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."
(declare (obsolete derived-mode-p "22.1"))
(while (get mode 'derived-mode-parent)
(setq mode (get mode 'derived-mode-parent)))
mode)
;;; 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)
;; FIXME filling.
(format "Major-mode.\nUses keymap `%s'%s%s." map
(if abbrev (format "%s abbrev table `%s'"
(if syntax "," " and") abbrev) "")
(if syntax (format " and syntax-table `%s'" syntax) ""))
(format "Major mode derived from `%s' by `define-derived-mode'.
It inherits all of the parent's attributes, but has its own keymap%s:
`%s'%s
which more-or-less shadow%s %s's corresponding table%s."
parent
(cond ((and abbrev syntax)
",\nabbrev table and syntax table")
(abbrev "\nand abbrev table")
(syntax "\nand syntax table")
(t ""))
map
(cond ((and abbrev syntax)
(format ", `%s' and `%s'" abbrev syntax))
((or abbrev syntax)
(format " and `%s'" (or abbrev syntax)))
(t ""))
(if (or abbrev syntax) "" "s")
parent
(if (or abbrev syntax) "s" "")))))
(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 (format "[`‘]%s['’]"
(regexp-quote
(symbol-name parent)))
docstring)
nil
(format "`%s' " parent))
"might have run,\nthis mode "))
(format "runs the hook `%s'" hook)
", as the final or penultimate 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)
"Initialize 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-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
|