From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Alan Mackenzie Newsgroups: gmane.emacs.devel Subject: Re: Unbalanced change hooks (part 2) Date: Mon, 1 Aug 2016 20:52:23 +0000 Message-ID: <20160801205223.GD15055@acm.fritz.box> References: <20160731121642.GB2205@acm.fritz.box> <83a8gxq288.fsf@gnu.org> <20160731172804.GD2205@acm.fritz.box> <834m75ptij.fsf@gnu.org> <20160731212635.GF2205@acm.fritz.box> <83shuoocwp.fsf@gnu.org> <20160801165323.GB15055@acm.fritz.box> <20160801171552.GC15055@acm.fritz.box> <838twgnuso.fsf@gnu.org> NNTP-Posting-Host: blaine Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1470084808 26866 195.159.176.226 (1 Aug 2016 20:53:28 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 1 Aug 2016 20:53:28 +0000 (UTC) User-Agent: Mutt/1.5.24 (2015-08-30) Cc: ofv@wanadoo.es, rcopley@gmail.com, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Mon Aug 01 22:53:24 2016 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bUKDD-0006jq-Dk for ged-emacs-devel@m.gmane.org; Mon, 01 Aug 2016 22:53:23 +0200 Original-Received: from localhost ([::1]:52788 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bUKDA-00058P-1o for ged-emacs-devel@m.gmane.org; Mon, 01 Aug 2016 16:53:20 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:40917) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bUKCy-00054p-AC for emacs-devel@gnu.org; Mon, 01 Aug 2016 16:53:09 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bUKCu-0007O8-BF for emacs-devel@gnu.org; Mon, 01 Aug 2016 16:53:08 -0400 Original-Received: from mail.muc.de ([193.149.48.3]:53997) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bUKCu-0007Nm-0w for emacs-devel@gnu.org; Mon, 01 Aug 2016 16:53:04 -0400 Original-Received: (qmail 30265 invoked by uid 3782); 1 Aug 2016 20:53:02 -0000 Original-Received: from acm.muc.de (p548C70EF.dip0.t-ipconnect.de [84.140.112.239]) by colin.muc.de (tmda-ofmipd) with ESMTP; Mon, 01 Aug 2016 22:53:01 +0200 Original-Received: (qmail 16096 invoked by uid 1000); 1 Aug 2016 20:52:23 -0000 Content-Disposition: inline In-Reply-To: <838twgnuso.fsf@gnu.org> X-Delivery-Agent: TMDA/1.1.12 (Macallan) X-Primary-Address: acm@muc.de X-detected-operating-system: by eggs.gnu.org: FreeBSD 9.x X-Received-From: 193.149.48.3 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:206329 Archived-At: Hello, Eli. On Mon, Aug 01, 2016 at 10:39:03PM +0300, Eli Zaretskii wrote: > > Date: Mon, 1 Aug 2016 17:15:52 +0000 > > Cc: ofv@wanadoo.es, rcopley@gmail.com, emacs-devel@gnu.org > > From: Alan Mackenzie > > How about the following idea: we create a special purpose undo list > > separate from the existing one. Every change is recorded on this list, > > regardless of whether or not main undo is disabled. After each > > invocation of after-change-functions the list is emptied. > > (defmacro with-change-undone (&rest forms) ...) > > An after-change-function can invoke the macro `with-change-undone' which > > would undo the changes, execute the &rest forms, then redo the changes. > > Surely this would satisfy both of us, no? > Sounds gross, but if this is the only way to solve this problem, and > you can live with it, so can I. > I do suggest to wait with conclusions for a while, perhaps a better > idea will come up. Slightly less gross, perhaps: (i) Abandon the use of before-change-functions. (ii) Enable undo in pre-command-hook, if necessary. (iii) At each after-change-functions call: a - Analyze buffer-undo-list down as far as (or pos (next-nil)), and revert the insertion or deletion which as been made, taking particular care over coalesced multiple insertions/deletions. b - (setq pos (current-position-in-undo-list)) c - Perform what used to be before-change actions. d - restore the insertion/deletion. e - Perform the normal after-change functions. (iv) Disable undo in post-command-hook, if appropriate. This is less gross in that it uses the standard undo list rather than creating a new special purpose one. It would also be usable in existing Emacsen. But I still say it would be preferable to have a function `old-string' callable from after-change-functions rather than having to mess around with the undo list in (ii), (iii)a, and (iv). -- Alan Mackenzie (Nuremberg, Germany).