From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Why is there no `until' in elisp? Date: Fri, 19 Oct 2018 11:34:01 -0400 Message-ID: References: <87murdu6to.fsf@portable.galex-713.eu> <87y3axjusi.fsf@portable.galex-713.eu> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1539963942 27174 195.159.176.226 (19 Oct 2018 15:45:42 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 19 Oct 2018 15:45:42 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Fri Oct 19 17:45:38 2018 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 1gDWxz-0006we-Jy for ged-emacs-devel@m.gmane.org; Fri, 19 Oct 2018 17:45:35 +0200 Original-Received: from localhost ([::1]:51171 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gDX05-0007vy-S2 for ged-emacs-devel@m.gmane.org; Fri, 19 Oct 2018 11:47:45 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:49651) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gDWzu-0007tV-Tu for emacs-devel@gnu.org; Fri, 19 Oct 2018 11:47:37 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gDWzr-0004H6-55 for emacs-devel@gnu.org; Fri, 19 Oct 2018 11:47:34 -0400 Original-Received: from [195.159.176.226] (port=44982 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gDWzp-00047W-8W for emacs-devel@gnu.org; Fri, 19 Oct 2018 11:47:29 -0400 Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1gDWxZ-0006Td-0C for emacs-devel@gnu.org; Fri, 19 Oct 2018 17:45:09 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 23 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:J0eZootpKwOdxrI4rOfSj9DqbQs= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 195.159.176.226 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:230497 Archived-At: > think `until' should refer to the version I gave because this is > probably the one which is going to be implemented naively by most > people, BTW, this is only true if those people have to implement it on top of the pre-existing `while`. Once you go down to implementing it as a sequence of byte-codes, then the `until` you proposed is no simpler than the one I proposed. So reversing your argument, if Elisp had my `until` and you wanted to define `while` would you define it to return nil or to return t? IOW would you define it as (defmacro while (test &rest body) `(until (not ,test) ,@body)) or (defmacro while (test &rest body) `(progn (until (not ,test) ,@body) nil)) ? Stefan