From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: Why is there no `until' in elisp? Date: Wed, 17 Oct 2018 10:50:34 -0700 Organization: UCLA Computer Science Department Message-ID: <86294998-2c96-a1be-6a83-2e34b7fa6046@cs.ucla.edu> References: <87murdu6to.fsf@portable.galex-713.eu> <87lg6xgc58.fsf@portable.galex-713.eu> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1539798577 28230 195.159.176.226 (17 Oct 2018 17:49:37 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 17 Oct 2018 17:49:37 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 Cc: Stefan Monnier , Emacs developers To: Yuri Khan , galex-713@galex-713.eu Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Wed Oct 17 19:49:33 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 1gCpwq-0007Fa-VT for ged-emacs-devel@m.gmane.org; Wed, 17 Oct 2018 19:49:33 +0200 Original-Received: from localhost ([::1]:38441 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gCpyx-0002cK-A0 for ged-emacs-devel@m.gmane.org; Wed, 17 Oct 2018 13:51:43 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:37096) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gCpy6-0002c9-70 for emacs-devel@gnu.org; Wed, 17 Oct 2018 13:50:50 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gCpxz-00079y-JW for emacs-devel@gnu.org; Wed, 17 Oct 2018 13:50:50 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:52922) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gCpxx-00075g-Lv for emacs-devel@gnu.org; Wed, 17 Oct 2018 13:50:43 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id B2663161737; Wed, 17 Oct 2018 10:50:35 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id frbBkPlE3Swo; Wed, 17 Oct 2018 10:50:35 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id F1C59161747; Wed, 17 Oct 2018 10:50:34 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id w3tmvdSFavbT; Wed, 17 Oct 2018 10:50:34 -0700 (PDT) Original-Received: from Penguin.CS.UCLA.EDU (Penguin.CS.UCLA.EDU [131.179.64.200]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id D6E9D161737; Wed, 17 Oct 2018 10:50:34 -0700 (PDT) Openpgp: preference=signencrypt Autocrypt: addr=eggert@cs.ucla.edu; prefer-encrypt=mutual; keydata= xsFNBEyAcmQBEADAAyH2xoTu7ppG5D3a8FMZEon74dCvc4+q1XA2J2tBy2pwaTqfhpxxdGA9 Jj50UJ3PD4bSUEgN8tLZ0san47l5XTAFLi2456ciSl5m8sKaHlGdt9XmAAtmXqeZVIYX/UFS 96fDzf4xhEmm/y7LbYEPQdUdxu47xA5KhTYp5bltF3WYDz1Ygd7gx07Auwp7iw7eNvnoDTAl KAl8KYDZzbDNCQGEbpY3efZIvPdeI+FWQN4W+kghy+P6au6PrIIhYraeua7XDdb2LS1en3Ss mE3QjqfRqI/A2ue8JMwsvXe/WK38Ezs6x74iTaqI3AFH6ilAhDqpMnd/msSESNFt76DiO1ZK QMr9amVPknjfPmJISqdhgB1DlEdw34sROf6V8mZw0xfqT6PKE46LcFefzs0kbg4GORf8vjG2 Sf1tk5eU8MBiyN/bZ03bKNjNYMpODDQQwuP84kYLkX2wBxxMAhBxwbDVZudzxDZJ1C2VXujC OJVxq2kljBM9ETYuUGqd75AW2LXrLw6+MuIsHFAYAgRr7+KcwDgBAfwhPBYX34nSSiHlmLC+ KaHLeCLF5ZI2vKm3HEeCTtlOg7xZEONgwzL+fdKo+D6SoC8RRxJKs8a3sVfI4t6CnrQzvJbB n6gxdgCu5i29J1QCYrCYvql2UyFPAK+do99/1jOXT4m2836j1wARAQABzSBQYXVsIEVnZ2Vy dCA8ZWdnZXJ0QGNzLnVjbGEuZWR1PsLBfgQTAQIAKAUCTIByZAIbAwUJEswDAAYLCQgHAwIG FQgCCQoLBBYCAwECH In-Reply-To: Content-Language: en-US X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 131.179.128.68 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:230459 Archived-At: On 10/17/18 2:46 AM, Yuri Khan wrote: > + Pascal has =E2=80=98repeat=E2=80=99/=E2=80=98until=E2=80=99 (a termin= ation post-condition loop), and > it was my first association for the name =E2=80=98until=E2=80=99. Pascal did it right, for a reason I haven't seen mentioned in this=20 thread. The natural tendency when reading a conditional is to assume=20 that the condition will be true in the code that immediately follows the=20 text of the condition. This works for (if C S) and (while C S), and it=20 also works for Pascal's 'repeat S1 until C; S2' where C is true just=20 before S2 is executed. It does not work for the confusing C syntax 'do=20 S1 while (C); S2' where C is false just before S2 is executed. It also=20 does not work for the proposed Elisp syntax (until C S), where C would=20 be false just before S is executed. Because of this elementary=20 psychological principle, the Elisp syntax for the proposed loop=20 construct should *not* be (until C S).