From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Jean Louis Newsgroups: gmane.emacs.help Subject: Re: Does pcase need progn in if condition Date: Sat, 22 May 2021 12:09:28 +0300 Message-ID: References: <87k0nr9yb5.fsf@zoho.eu> 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="30497"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/2.0.6 (2021-03-06) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Sat May 22 11:13:50 2021 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 1lkNhd-0007j5-QC for geh-help-gnu-emacs@m.gmane-mx.org; Sat, 22 May 2021 11:13:49 +0200 Original-Received: from localhost ([::1]:59420 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lkNhc-0000M1-SI for geh-help-gnu-emacs@m.gmane-mx.org; Sat, 22 May 2021 05:13:48 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:46664) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lkNgo-0000Ld-Mj for help-gnu-emacs@gnu.org; Sat, 22 May 2021 05:12:58 -0400 Original-Received: from stw1.rcdrun.com ([217.170.207.13]:33295) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lkNgm-0005pP-Bc for help-gnu-emacs@gnu.org; Sat, 22 May 2021 05:12:58 -0400 Original-Received: from localhost ([::ffff:154.224.42.9]) (AUTH: PLAIN admin, TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by stw1.rcdrun.com with ESMTPSA id 00000000000ADF16.0000000060A8CB15.00002BE1; Sat, 22 May 2021 02:12:52 -0700 Mail-Followup-To: help-gnu-emacs@gnu.org Content-Disposition: inline In-Reply-To: <87k0nr9yb5.fsf@zoho.eu> Received-SPF: pass client-ip=217.170.207.13; envelope-from=bugs@gnu.support; helo=stw1.rcdrun.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 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:130049 Archived-At: * Emanuel Berg via Users list for the GNU Emacs text editor [2021-05-22 07:40]: > sometimes one can put useful things there, e.g. `let', and > avoid using progn for this reason > > Yeah, progn is imbecile, almost. only, for some reason, prog1 > is cool, and prog2 is weird. > > (if t 1 2 3 4) ; 1 `progn` returns the the last value: (progn '(do-something) '(do-more) emacs-build-number) ⇒ 1 and is better looking then `let` when empty: (let () (message "hello") '(do-more) emacs-build-number) ⇒ 1 `prog1' is very handy as it will not return the last value but the value from 1st form: Example is when you wish to return a value and after that informa a user like here below: (cond ((= a 1) (do-something)) (t (prog1 nil (message "Query shall be longer...")))) After returning `report' it will message user about it. Maybe you wish to return the status of a function and continue informing user? (defun function () "Return REPORT" (prog1 report (message report))) And `prog2' is more than this, it will return the value from 2nd form, not third or first. (prog2 (do-this-but-not-keep-return-value) (do-this-and-keep-and-return-value) (do-more-something-but-return-value-is-from-above)) -- Jean Take action in Free Software Foundation campaigns: https://www.fsf.org/campaigns Sign an open letter in support of Richard M. Stallman https://stallmansupport.org/