From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Andreas Schwab Newsgroups: gmane.emacs.devel Subject: Re: Is this a bug in while-let or do I missunderstand it? Date: Sat, 09 Nov 2024 18:33:46 +0100 Message-ID: <87iksw5n2d.fsf@igel.home> References: <861pzkmk5v.fsf@gnu.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="30761"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: "Alfred M. Szmidt" , yuri.v.khan@gmail.com, arthur.miller@live.com, emacs-devel@gnu.org To: Eli Zaretskii Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sat Nov 09 18:35:14 2024 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1t9pMd-0007i7-Od for ged-emacs-devel@m.gmane-mx.org; Sat, 09 Nov 2024 18:35:11 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1t9pLc-0007iU-CB; Sat, 09 Nov 2024 12:34:08 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t9pLZ-0007hw-FK for emacs-devel@gnu.org; Sat, 09 Nov 2024 12:34:05 -0500 Original-Received: from mail-out.m-online.net ([212.18.0.9]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1t9pLX-0005vg-3P; Sat, 09 Nov 2024 12:34:05 -0500 Original-Received: from frontend01.mail.m-online.net (unknown [192.168.8.182]) by mail-out.m-online.net (Postfix) with ESMTP id 4Xm2wW1d75z1qsPs; Sat, 9 Nov 2024 18:33:47 +0100 (CET) Original-Received: from localhost (dynscan1.mnet-online.de [192.168.6.68]) by mail.m-online.net (Postfix) with ESMTP id 4Xm2wW0j2Xz1qqlS; Sat, 9 Nov 2024 18:33:47 +0100 (CET) X-Virus-Scanned: amavis at mnet-online.de Original-Received: from mail.mnet-online.de ([192.168.8.182]) by localhost (dynscan1.mail.m-online.net [192.168.6.68]) (amavis, port 10024) with ESMTP id T9C1-UlxRLtp; Sat, 9 Nov 2024 18:33:46 +0100 (CET) X-Auth-Info: BOpyEVGXYMw1le/ktyIC3FwXPo8mYncasrtnprG69sgMwga6SN51o53APENVODuP Original-Received: from igel.home (aftr-82-135-83-11.dynamic.mnet-online.de [82.135.83.11]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mail.mnet-online.de (Postfix) with ESMTPSA; Sat, 9 Nov 2024 18:33:46 +0100 (CET) Original-Received: by igel.home (Postfix, from userid 1000) id 136272C1ADF; Sat, 9 Nov 2024 18:33:46 +0100 (CET) In-Reply-To: <861pzkmk5v.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 09 Nov 2024 18:44:28 +0200") X-Yow: My EARS are GONE!! 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:325342 Archived-At: On Nov 09 2024, Eli Zaretskii wrote: >> It can be convenient to bind variables in conjunction with using a >> conditional. It's often the case that you compute a value, and then >> want to do something with that value if it's non-‘nil’. The >> straightforward way to do that is to just write, for instance: >> >> (let ((result1 (do-computation))) >> (when result1 >> (let ((result2 (do-more result1))) >> (when result2 >> (do-something result2))))) >> >> Since this is a very common pattern, Emacs provides a number of >> macros to make this easier and more readable. The above can be written >> the following way instead: >> >> ... following the various with various FOO-let forms, ending with >> while-let. > > The above description actually supports what Yuri was saying, not what > Arthur and you expect. The description only talks about when, where the condition is only evaluated once not matter what. If you replace when with while you have a very different situation. -- Andreas Schwab, schwab@linux-m68k.org GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1 "And now for something completely different."