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+;;; refill.el --- `auto-fill' by refilling paragraphs on changes
+
+;; Copyright (C) 2000 Free Software Foundation, Inc.
+
+;; Author: Dave Love <[email protected]>
+;; Keywords: wp
+
+;; This program 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 2 of the License, or
+;; (at your option) any later version.
+;;
+;; This program 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 this program; if not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; Provides a mode where paragraphs are refilled after changes in them
+;; (using `after-change-hooks').  This gives something akin to typical
+;; word processor-style filling.  We restrict refilling due to
+;; self-insertion to the characters which trigger auto-fill.
+
+;; It partly satisfies a todo item in enriched.el for some value of
+;; `without slowing down editing too much'.  It doesn't attempt to do
+;; anything (using `window-size-change-functions'?) about resizing
+;; windows -- who cares?
+
+;; This implementation is probably fragile and missing some special
+;; cases -- not extensively tested.  Yanking paragraph breaks, for
+;; instance, won't DTRT by refilling all the relevant paragraphs.
+
+;; You could do it a bit more efficiently (and robustly?) with just an
+;; auto-fill function, but that doesn't cope with changes other than
+;; through self-insertion.  (Using auto-fill and after-change
+;; functions together didn't seem winning.)  This could probably
+;; benefit from a less-general and faster `fill-paragraph-function',
+;; ideally as a primitive.
+
+;; The work is done in a local post-command hook but only if
+;; `refill-doit' has been set by the after-change function.  Using
+;; `post-command-hooks' ensures simply that refilling only happens
+;; once per command.
+
+;; [Per Abrahamsen's maniac.el does a similar thing, but operates from
+;; post-command-hook.  I don't understand the statement in it that
+;; after-change-hooks don't work for this purpose; perhaps there was
+;; some Emacs bug at the time.  ISTR maniac has problems with
+;; whitespace at the end of paragraphs.]
+
+;;; Code:
+
+(defun refill-fill-paragraph (arg)
+  "Like `fill-paragraph' but don't delete whitespace at paragraph end."
+  ;; Should probably use a text property indicating previously-filled
+  ;; stuff to avoid filling before the point of change.
+  (let ((before (point)))
+    (save-excursion
+      (forward-paragraph)
+      (skip-syntax-backward "-")
+      (let ((end (point))
+	    (beg (progn (backward-paragraph) (point))))
+	(goto-char before)
+	(save-restriction
+	  (if use-hard-newlines
+	      (fill-region beg end arg)
+	    (fill-region-as-paragraph beg end arg)))))))
+
+(defvar refill-doit nil
+  "Non-nil means that `refill-post-command-function' does its processing.
+Set by `refill-after-change-function' in `after-change-hooks' and
+unset by `refill-post-command-function' in `post-command-hooks'.  This
+ensures refilling is only done once per command that causes a change,
+regardless of the number of after-change calls from commands doing
+complex processing.")
+(make-variable-buffer-local 'refill-doit)
+
+(defun refill-after-change-function (beg end len)
+  "Function for `after-change-functions' which just sets `refill-doit'."
+  (unless undo-in-progress
+    (setq refill-doit t)))
+
+(defun refill-post-command-function ()
+  "Post-command function to do refilling (conditionally)."
+  (when refill-doit		; there was a change
+    ;; There's probably scope for more special cases here...
+    (cond
+     ((eq this-command 'self-insert-command)
+      ;; Respond to the same characters as auto-fill (other than
+      ;; newline, covered below).
+      (if (aref auto-fill-chars (char-before))
+	  (refill-fill-paragraph nil)))
+     ((or (eq this-command 'quoted-insert)
+	  (eq this-command 'fill-paragraph)
+	  (eq this-command 'fill-region))
+      nil)
+     ((or (eq this-command 'newline)
+	  (eq this-command 'newline-and-indent)
+	  (eq this-command 'open-line))
+      ;; Don't zap what was just inserted.
+      (save-excursion
+	(beginning-of-line)	 ; for newline-and-indent
+	(skip-chars-backward "\n")
+	(save-restriction
+	  (narrow-to-region (point-min) (point))
+	  (refill-fill-paragraph nil)))
+      (widen)
+      (save-excursion
+	(skip-chars-forward "\n")
+	(save-restriction
+	  (narrow-to-region (line-beginning-position) (point-max))
+	  (refill-fill-paragraph nil))))
+     (t (refill-fill-paragraph nil)))
+    (setq refill-doit nil)))
+
+(defvar refill-mode nil
+  "Non-nil if Refill mode is active.  Use `refill-mode' to toggle it.")
+(make-variable-buffer-local 'refill-mode)
+
+(defvar refill-mode-hook nil
+  "Normal hook run by function `refill-mode'.")
+
+(add-to-list 'minor-mode-alist '(refill-mode " Refill"))
+
+;;;###autoload
+(define-minor-mode refill-mode
+  "Toggle Refill minor mode.
+With prefix arg, turn Refill mode on iff arg is positive.
+
+When Refill mode is on, the current paragraph will be formatted when
+changes are made within it.  Self-inserting characters only cause
+refilling if they would cause auto-filling."
+  nil " Refill" nil
+  ;; This provides the test for recursive paragraph filling.
+  (make-local-variable 'fill-paragraph-function)
+  (if refill-mode
+      (progn (add-hook (make-local-hook 'after-change-functions)
+		       'refill-after-change-function nil t)
+	     (add-hook (make-local-hook 'post-command-hook)
+		       'refill-post-command-function nil t)
+	     (set (make-local-variable 'fill-paragraph-function)
+		  'refill-fill-paragraph)
+	     (auto-fill-mode 0))
+    (remove-hook 'after-change-functions 'refill-after-change-function t)
+    (remove-hook 'post-command-hook 'refill-post-command-function t)
+    (setq fill-paragraph-function nil)))
+
+(provide 'refill)
+
+;;; refill.el ends here