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1 ;;; redo.el -- Redo/undo system for XEmacs
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2
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3 ;; Copyright (C) 1985, 1986, 1987, 1993-1995 Free Software Foundation, Inc.
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4 ;; Copyright (C) 1995 Tinker Systems and INS Engineering Corp.
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5 ;; Copyright (C) 1997 Kyle E. Jones
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6
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7 ;; Author: Kyle E. Jones, February 1997
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8 ;; Keywords: lisp, extensions
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9
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10 ;; This file is part of XEmacs.
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11
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12 ;; XEmacs is free software; you can redistribute it and/or modify it
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13 ;; under the terms of the GNU General Public License as published by
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14 ;; the Free Software Foundation; either version 2, or (at your option)
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15 ;; any later version.
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16
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17 ;; XEmacs is distributed in the hope that it will be useful, but
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18 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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20 ;; General Public License for more details.
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21
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22 ;; You should have received a copy of the GNU General Public License
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23 ;; along with XEmacs; see the file COPYING. If not, write to the Free
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24 ;; Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
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25 ;; 02111-1307, USA.
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26
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27 ;;; Synched up with: Not in FSF.
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28
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29 ;;; Commentary:
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30
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31 ;; Derived partly from lisp/prim/simple.el in XEmacs.
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32
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33 ;; Emacs' normal undo system allows you to undo an arbitrary
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34 ;; number of buffer changes. These undos are recorded as ordinary
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35 ;; buffer changes themselves. So when you break the chain of
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36 ;; undos by issuing some other command, you can then undo all
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37 ;; the undos. The chain of recorded buffer modifications
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38 ;; therefore grows without bound, truncated only at garbage
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39 ;; collection time.
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40 ;;
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41 ;; The redo/undo system is different in two ways:
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42 ;; 1. The undo/redo command chain is only broken by a buffer
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43 ;; modification. You can move around the buffer or switch
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44 ;; buffers and still come back and do more undos or redos.
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45 ;; 2. The `redo' command rescinds the most recent undo without
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46 ;; recording the change as a _new_ buffer change. It
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47 ;; completely reverses the effect of the undo, which
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48 ;; includes making the chain of buffer modification records
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49 ;; shorter by one, to counteract the effect of the undo
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50 ;; command making the record list longer by one.
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51 ;;
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52 ;; Installation:
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53 ;;
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54 ;; Save this file as redo.el, byte compile it and put the
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55 ;; resulting redo.elc file in a directory that is listed in
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56 ;; load-path.
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57 ;;
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58 ;; In your .emacs file, add
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59 ;; (require 'redo)
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60 ;; and the system will be enabled.
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61
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62 ;;; Code:
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63
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64 (provide 'redo)
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65
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66 (defvar redo-version "1.01"
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67 "Version number for the Redo package.")
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68
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69 (defvar last-buffer-undo-list nil
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70 "The head of buffer-undo-list at the last time an undo or redo was done.")
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71 (make-variable-buffer-local 'last-buffer-undo-list)
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72
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73 (make-variable-buffer-local 'pending-undo-list)
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74
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75 (defun redo (&optional count)
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76 "Redo the the most recent undo.
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77 Prefix arg COUNT means redo the COUNT most recent undos.
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78 If you have modified the buffer since the last redo or undo,
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79 then you cannot redo any undos before then."
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80 (interactive "*p")
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81 (if (eq buffer-undo-list t)
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82 (error "No undo information in this buffer"))
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83 (if (eq last-buffer-undo-list nil)
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84 (error "No undos to redo"))
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85 (or (eq last-buffer-undo-list buffer-undo-list)
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86 (and (null (car-safe buffer-undo-list))
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87 (eq last-buffer-undo-list (cdr-safe buffer-undo-list)))
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88 (error "Buffer modified since last undo/redo, cannot redo"))
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89 (and (or (eq buffer-undo-list pending-undo-list)
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90 (eq (cdr buffer-undo-list) pending-undo-list))
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91 (error "No further undos to redo in this buffer"))
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92 (or (eq (selected-window) (minibuffer-window))
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93 (message "Redo..."))
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94 (let ((modified (buffer-modified-p))
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95 (recent-save (recent-auto-save-p))
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96 (old-undo-list buffer-undo-list)
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97 (p (cdr buffer-undo-list))
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98 (records-between 0))
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99 ;; count the number of undo records between the head of the
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100 ;; undo chain and the pointer to the next change. Note that
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101 ;; by `record' we mean clumps of change records, not the
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102 ;; boundary records. The number of records will always be a
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103 ;; multiple of 2, because an undo moves the pending pointer
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104 ;; forward one record and prepend a record to the head of the
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105 ;; chain. Thus the separation always increases by two. WHen
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106 ;; we decrease it we will decrease it by a multiple of 2
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107 ;; also.
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108 (while p
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109 (cond ((eq p pending-undo-list)
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110 (setq p nil))
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111 ((null (car p))
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112 (setq records-between (1+ records-between))
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113 (setq p (cdr p)))
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114 (t
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115 (setq p (cdr p)))))
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116 ;; we're off by one if pending pointer is nil, because there
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117 ;; was no boundary record in front of it to count.
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118 (and (null pending-undo-list)
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119 (setq records-between (1+ records-between)))
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120 ;; don't allow the user to redo more undos than exist.
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121 ;; only half the records between the list head and the pending
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122 ;; pointer are undos that are a part of this command chain.
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123 (setq count (min (/ records-between 2) count)
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124 p (primitive-undo (1+ count) buffer-undo-list))
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125 (if (eq p old-undo-list)
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126 nil ;; nothing happened
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127 ;; set buffer-undo-list to the new undo list. if has been
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128 ;; shortened by `count' records.
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129 (setq buffer-undo-list p)
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130 ;; primitive-undo returns a list without a leading undo
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131 ;; boundary. add one.
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132 (undo-boundary)
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133 ;; now move the pending pointer backward in the undo list
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134 ;; to reflect the redo. sure would be nice if this list
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135 ;; were doubly linked, but no... so we have to run down the
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136 ;; list from the head and stop at the right place.
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137 (let ((n (- records-between count)))
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138 (setq p (cdr old-undo-list))
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139 (while (and p (> n 0))
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140 (if (null (car p))
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141 (setq n (1- n)))
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142 (setq p (cdr p)))
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143 (setq pending-undo-list p)))
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144 (and modified (not (buffer-modified-p))
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145 (delete-auto-save-file-if-necessary recent-save))
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146 (or (eq (selected-window) (minibuffer-window))
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147 (message "Redo!"))
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148 (setq last-buffer-undo-list buffer-undo-list)))
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149
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150 (defun undo (&optional arg)
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151 "Undo some previous changes.
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152 Repeat this command to undo more changes.
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153 A numeric argument serves as a repeat count."
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154 (interactive "*p")
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155 (let ((modified (buffer-modified-p))
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156 (recent-save (recent-auto-save-p)))
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157 (or (eq (selected-window) (minibuffer-window))
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158 (message "Undo..."))
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159 (or (eq last-buffer-undo-list buffer-undo-list)
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160 (and (null (car-safe buffer-undo-list))
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161 (eq last-buffer-undo-list (cdr-safe buffer-undo-list)))
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162 (progn (undo-start)
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163 (undo-more 1)))
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164 (undo-more (or arg 1))
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165 ;; Don't specify a position in the undo record for the undo command.
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166 ;; Instead, undoing this should move point to where the change is.
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167 ;;
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168 ;;;; The old code for this was mad! It deleted all set-point
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169 ;;;; references to the position from the whole undo list,
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170 ;;;; instead of just the cells from the beginning to the next
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171 ;;;; undo boundary. This does what I think the other code
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172 ;;;; meant to do.
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173 (let ((list buffer-undo-list)
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174 (prev nil))
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175 (while (and list (not (null (car list))))
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176 (if (integerp (car list))
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177 (if prev
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178 (setcdr prev (cdr list))
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179 ;; impossible now, but maybe not in the future
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180 (setq buffer-undo-list (cdr list))))
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181 (setq prev list
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182 list (cdr list))))
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183 (and modified (not (buffer-modified-p))
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184 (delete-auto-save-file-if-necessary recent-save)))
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185 (or (eq (selected-window) (minibuffer-window))
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186 (message "Undo!"))
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187 (setq last-buffer-undo-list buffer-undo-list))
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188
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189 ;;; redo.el ends here
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