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: Function that changes value of a variable Date: Sat, 20 Aug 2022 22:40:15 -0400 Message-ID: References: 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="333"; 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:QvqePVaZTEe/oi2K57AulPH9MOo= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Sun Aug 21 04:41:30 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 1oPau2-000AWt-Ar for geh-help-gnu-emacs@m.gmane-mx.org; Sun, 21 Aug 2022 04:41:30 +0200 Original-Received: from localhost ([::1]:40072 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oPau0-0007qO-1b for geh-help-gnu-emacs@m.gmane-mx.org; Sat, 20 Aug 2022 22:41:28 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:38852) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oPatF-0007q0-7N for help-gnu-emacs@gnu.org; Sat, 20 Aug 2022 22:40:41 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:43890) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oPat9-0005R2-8H for help-gnu-emacs@gnu.org; Sat, 20 Aug 2022 22:40:40 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1oPasx-0009Mq-QN for help-gnu-emacs@gnu.org; Sun, 21 Aug 2022 04:40:23 +0200 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: -15 X-Spam_score: -1.6 X-Spam_bar: - X-Spam_report: (-1.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_TEMPERROR=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:138955 Archived-At: > I am trying to change the value a a variable with the following function, > but is not working as intended. > > (defun constrain (var min-n max-n) "Ensure that value of var is between > MIN-N and MAX-N inclusive by constraining." (cond ((< var min-n) (setq > var min-n)) ((> var max-n) (setq var max-n)) ((eq var t) (setq var > 1)) ((eq var nil) (setq var 0)))) [ Written this way, it's rather illegible. It was probably manged by your MUA because it wasn't labeled as "code" or "preformatted text" or somesuch. ] > Have done the following test, but the value stays 21. Of course, because the call only passes the value of the variable, not the variable itself [ and according your your comment in https://emacs.stackexchange.com/questions/73192, you know that already. ] Variables aren't first class objects, so you need to use a reference to the variable: (defun my-constrain (varef ...) ... (setf (gv-deref varref) ...) ...) You can then pass a reference to your variable with something like: (my-constrain (gv-ref pingu) ...) Of course a simpler solution is to do something else, such as: (setq pingu (my-constrain pingu ...)) so `my-constrain` doesn't need to set any variable any more and can be a pure function instead. Stefan