From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: [External] : `let' vs `let*' Date: Tue, 15 Mar 2022 18:40:50 -0400 Message-ID: References: <87k0d03vaw.fsf@ericabrahamsen.net> <8735joc5of.fsf@web.de> <87r177rjzn.fsf@zoho.eu> <874k40iqmd.fsf_-_@zoho.eu> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="26912"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:kpDQmKKlcHSXLIaWdJ0QThOVmZQ= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Mar 15 23:41:24 2022 Return-path: Envelope-to: geh-help-gnu-emacs@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 1nUFr2-0006qu-AL for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 15 Mar 2022 23:41:24 +0100 Original-Received: from localhost ([::1]:47490 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nUFr1-0004Mg-5d for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 15 Mar 2022 18:41:23 -0400 Original-Received: from eggs.gnu.org ([209.51.188.92]:47610) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUFqc-0004MX-HW for help-gnu-emacs@gnu.org; Tue, 15 Mar 2022 18:40:58 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:38650) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUFqb-0001P5-3l for help-gnu-emacs@gnu.org; Tue, 15 Mar 2022 18:40:58 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1nUFqZ-0006O8-3b for help-gnu-emacs@gnu.org; Tue, 15 Mar 2022 23:40:55 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:136597 Archived-At: > (setq a 42) > (setq b 43) > (let ((a b) > (b a)) > (list a b)) > > => (43 42) While you can come up with such examples, they tend to always be contrived. In my experience, the benefit of `let` is only really seen in macros, where you can do: `(let ((x ,arg1) (y ,arg2) (f (lambda (,z) ,@body))) ...) without fear of capturing an `x` that might occur inside `arg2` or `body`. In hand-written code, having only `let*` and no `let` would make almost no difference. Stefan