+;;; goto-last-change.el --- Move point through buffer-undo-list positions -*-coding: 'raw-text'; coding: iso-8859-1;-*-
+
+;; Copyright © 2003 Kevin Rodgers
+
+;; Author: Kevin Rodgers <ihs_4664@yahoo.com>
+;; Created: 17 Jun 2003
+;; Version: $Revision: 1.2 $
+;; Keywords: convenience
+;; RCS: $Id: goto-last-change.el,v 1.2 2003/07/30 17:43:47 kevinr Exp kevinr $
+
+;; Contributors:
+;; Attila Lendvai <attila.lendvai@gmail.com> (line distance and auto marks)
+
+;; 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:
+
+;; After installing goto-last-change.el in a `load-path' directory and
+;; compiling it with `M-x byte-compile-file', load it with
+;; (require 'goto-last-change)
+;; or autoload it with
+;; (autoload 'goto-last-change "goto-last-change"
+;; "Set point to the position of the last change." t)
+;;
+;; You may also want to bind a key to `M-x goto-last-change', e.g.
+;; (global-set-key "\C-x\C-\\" 'goto-last-change)
+
+;; goto-last-change.el was written in response to to the following:
+;;
+;; From: Dan Jacobson <jidanni@jidanni.org>
+;; Newsgroups: gnu.emacs.bug
+;; Subject: function to go to spot of last change
+;; Date: Sun, 15 Jun 2003 00:15:08 +0000 (UTC)
+;; Sender: news <news@main.gmane.org>
+;; Message-ID: <mailman.7910.1055637181.21513.bug-gnu-emacs@gnu.org>
+;; NNTP-Posting-Host: monty-python.gnu.org
+;;
+;;
+;; Why of course, a function to get the user to the spot of last changes
+;; in the current buffer(s?), that's what emacs must lack.
+;;
+;; How many times have you found yourself mosying [<-not in spell
+;; checker!?] thru a file when you wonder, where the heck was I just
+;; editing? Well, the best you can do is hit undo, ^F, and undo again,
+;; to get back. Hence the "burning need" for the additional function,
+;; which you might name the-jacobson-memorial-function, due to its brilliance.
+;; --
+;; http://jidanni.org/ Taiwan(04)25854780
+
+;;; Code:
+(provide 'goto-last-change)
+
+(or (fboundp 'last) ; Emacs 20
+ (require 'cl)) ; Emacs 19
+
+(defvar goto-last-change-undo nil
+ "The `buffer-undo-list' entry of the previous \\[goto-last-change] command.")
+(make-variable-buffer-local 'goto-last-change-undo)
+
+;;;###autoload
+(defun goto-last-change (&optional mark-point minimal-line-distance)
+ "Set point to the position of the last change.
+Consecutive calls set point to the position of the previous change.
+With a prefix arg (optional arg MARK-POINT non-nil), set mark so \
+\\[exchange-point-and-mark]
+will return point to the current position."
+ (interactive "P")
+ ;; (unless (buffer-modified-p)
+ ;; (error "Buffer not modified"))
+ (when (eq buffer-undo-list t)
+ (error "No undo information in this buffer"))
+ (when mark-point
+ (push-mark))
+ (unless minimal-line-distance
+ (setq minimal-line-distance 10))
+ (let ((position nil)
+ (undo-list (if (and (eq this-command last-command)
+ goto-last-change-undo)
+ (cdr (memq goto-last-change-undo buffer-undo-list))
+ buffer-undo-list))
+ undo)
+ (while (and undo-list
+ (or (not position)
+ (eql position (point))
+ (and minimal-line-distance
+ ;; The first invocation always goes to the last change, subsequent ones skip
+ ;; changes closer to (point) then minimal-line-distance.
+ (memq last-command '(goto-last-change
+ goto-last-change-with-auto-marks))
+ (< (count-lines (min position (point-max)) (point))
+ minimal-line-distance))))
+ (setq undo (car undo-list))
+ (cond ((and (consp undo) (integerp (car undo)) (integerp (cdr undo)))
+ ;; (BEG . END)
+ (setq position (cdr undo)))
+ ((and (consp undo) (stringp (car undo))) ; (TEXT . POSITION)
+ (setq position (abs (cdr undo))))
+ ((and (consp undo) (eq (car undo) t))) ; (t HIGH . LOW)
+ ((and (consp undo) (null (car undo)))
+ ;; (nil PROPERTY VALUE BEG . END)
+ (setq position (cdr (last undo))))
+ ((and (consp undo) (markerp (car undo)))) ; (MARKER . DISTANCE)
+ ((integerp undo)) ; POSITION
+ ((null undo)) ; nil
+ (t (error "Invalid undo entry: %s" undo)))
+ (setq undo-list (cdr undo-list)))
+ (cond (position
+ (setq goto-last-change-undo undo)
+ (goto-char (min position (point-max))))
+ ((and (eq this-command last-command)
+ goto-last-change-undo)
+ (setq goto-last-change-undo nil)
+ (error "No further undo information"))
+ (t
+ (setq goto-last-change-undo nil)
+ (error "Buffer not modified")))))
+
+(defun goto-last-change-with-auto-marks (&optional minimal-line-distance)
+ "Calls goto-last-change and sets the mark at only the first invocations
+in a sequence of invocations."
+ (interactive "P")
+ (goto-last-change (not (or (eq last-command 'goto-last-change-with-auto-marks)
+ (eq last-command t)))
+ minimal-line-distance))
+
+;; (global-set-key "\C-x\C-\\" 'goto-last-change)
+
+;;; goto-last-change.el ends here
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