--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lisp/gnus/gnus-undo.el	Mon Aug 13 09:13:56 2007 +0200
@@ -0,0 +1,168 @@
+;;; gnus-undo.el --- minor mode for undoing in Gnus
+;; Copyright (C) 1996,97 Free Software Foundation, Inc.
+
+;; Author: Lars Magne Ingebrigtsen <larsi@ifi.uio.no>
+;; Keywords: news
+
+;; 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 2, 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; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; This package allows arbitrary undoing in Gnus buffers.  As all the
+;; Gnus buffers aren't very text-oriented (what is in the buffers is
+;; just some random representation of the actual data), normal Emacs
+;; undoing doesn't work at all for Gnus.
+;;
+;; This package works by letting Gnus register functions for reversing
+;; actions, and then calling these functions when the user pushes the
+;; `undo' key.  As with normal `undo', there it is possible to set
+;; undo boundaries and so on.
+;;
+;; Internally, the undo sequence is represented by the
+;; `gnus-undo-actions' list, where each element is a list of functions
+;; to be called, in sequence, to undo some action.  (An "action" is a
+;; collection of functions.)
+;;
+;; For instance, a function for killing a group will call
+;; `gnus-undo-register' with a function that un-kills the group.  This
+;; package will put that function into an action.
+
+;;; Code:
+
+(require 'gnus-util)
+(require 'gnus)
+
+(defvar gnus-undo-mode nil
+  "Minor mode for undoing in Gnus buffers.")
+
+(defvar gnus-undo-mode-hook nil
+  "Hook called in all `gnus-undo-mode' buffers.")
+
+;;; Internal variables.
+
+(defvar gnus-undo-actions nil)
+(defvar gnus-undo-boundary t)
+(defvar gnus-undo-last nil)
+(defvar gnus-undo-boundary-inhibit nil)
+
+;;; Minor mode definition.
+
+(defvar gnus-undo-mode-map nil)
+
+(unless gnus-undo-mode-map
+  (setq gnus-undo-mode-map (make-sparse-keymap))
+
+  (gnus-define-keys gnus-undo-mode-map
+   "\M-\C-_" gnus-undo))
+
+(defun gnus-undo-make-menu-bar ()
+  (when nil
+  (define-key-after (current-local-map) [menu-bar file gnus-undo]
+    (cons "Undo" 'gnus-undo-actions)
+    [menu-bar file whatever])))
+
+(defun gnus-undo-mode (&optional arg)
+  "Minor mode for providing `undo' in Gnus buffers.
+
+\\{gnus-undo-mode-map}"
+  (interactive "P")
+  (set (make-local-variable 'gnus-undo-mode)
+       (if (null arg) (not gnus-undo-mode)
+	 (> (prefix-numeric-value arg) 0)))
+  (set (make-local-variable 'gnus-undo-actions) nil)
+  (set (make-local-variable 'gnus-undo-boundary) t)
+  (when gnus-undo-mode
+    ;; Set up the menu.
+    (when (gnus-visual-p 'undo-menu 'menu)
+      (gnus-undo-make-menu-bar))
+    ;; Don't display anything in the mode line -- too annoying.
+    ;;(unless (assq 'gnus-undo-mode minor-mode-alist)
+    ;;  (push '(gnus-undo-mode " Undo") minor-mode-alist))
+    (unless (assq 'gnus-undo-mode minor-mode-map-alist)
+      (push (cons 'gnus-undo-mode gnus-undo-mode-map)
+	    minor-mode-map-alist))
+    (make-local-hook 'post-command-hook)
+    (gnus-add-hook 'post-command-hook 'gnus-undo-boundary nil t)
+    (add-hook 'gnus-summary-exit-hook 'gnus-undo-boundary)
+    (run-hooks 'gnus-undo-mode-hook)))
+
+;;; Interface functions.
+
+(defun gnus-disable-undo (&optional buffer)
+  "Disable undoing in the current buffer."
+  (interactive)
+  (save-excursion
+    (when buffer
+      (set-buffer buffer))
+    (gnus-undo-mode -1)))
+
+(defun gnus-undo-boundary ()
+  "Set Gnus undo boundary."
+  (if gnus-undo-boundary-inhibit
+      (setq gnus-undo-boundary-inhibit nil)
+    (setq gnus-undo-boundary t)))
+
+(defun gnus-undo-register (form)
+  "Register FORMS as something to be performed to undo a change.
+FORMS may use backtick quote syntax."
+  (when gnus-undo-mode
+    (gnus-undo-register-1
+     `(lambda ()
+	,form))))
+
+(put 'gnus-undo-register 'lisp-indent-function 0)
+(put 'gnus-undo-register 'edebug-form-spec '(body))
+
+(defun gnus-undo-register-1 (function)
+  "Register FUNCTION as something to be performed to undo a change."
+  (when gnus-undo-mode
+    (cond
+     ;; We are on a boundary, so we create a new action.
+     (gnus-undo-boundary
+      (push (list function) gnus-undo-actions)
+      (setq gnus-undo-boundary nil))
+     ;; Prepend the function to an old action.
+     (gnus-undo-actions
+      (setcar gnus-undo-actions (cons function (car gnus-undo-actions))))
+     ;; Initialize list.
+     (t
+      (setq gnus-undo-actions (list (list function)))))
+    (setq gnus-undo-boundary-inhibit t)))
+
+(defun gnus-undo (n)
+  "Undo some previous changes in Gnus buffers.
+Repeat this command to undo more changes.
+A numeric argument serves as a repeat count."
+  (interactive "p")
+  (unless gnus-undo-mode
+    (error "Undoing is not enabled in this buffer"))
+  (message "%s" last-command)
+  (when (or (not (eq last-command 'gnus-undo))
+	    (not gnus-undo-last))
+    (setq gnus-undo-last gnus-undo-actions))
+  (let ((action (pop gnus-undo-last)))
+    (unless action
+      (error "Nothing further to undo"))
+    (setq gnus-undo-actions (delq action gnus-undo-actions))
+    (setq gnus-undo-boundary t)
+    (while action
+      (funcall (pop action)))))
+
+(provide 'gnus-undo)
+
+;;; gnus-undo.el ends here