From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: =?utf-8?Q?=C3=93scar_Fuentes?= Newsgroups: gmane.emacs.help Subject: Re: (*) -> 1 Date: Wed, 18 Jan 2023 14:57:01 +0100 Message-ID: <87cz7c9c9e.fsf@telefonica.net> References: <87r0vuidjc.fsf@eder.anydns.info> <87y1q1kvdm.fsf@web.de> <87h6wpkrlq.fsf@web.de> <87zgahj7h3.fsf@web.de> 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="21023"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:Z8EN6ueStBpKO8sOAU+nmN5R22Q= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Wed Jan 18 14:57:44 2023 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 1pI8wi-0005K5-4U for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 18 Jan 2023 14:57:44 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pI8wK-0004om-4a; Wed, 18 Jan 2023 08:57:20 -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 1pI8wH-0004oS-U5 for help-gnu-emacs@gnu.org; Wed, 18 Jan 2023 08:57:17 -0500 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pI8wD-0005D2-MM for help-gnu-emacs@gnu.org; Wed, 18 Jan 2023 08:57:17 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1pI8wB-0004aB-OY for help-gnu-emacs@gnu.org; Wed, 18 Jan 2023 14:57:11 +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 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-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:142358 Archived-At: Jean Louis writes: > * Michael Heerdegen [2023-01-17 22:20]: >> The question of use is a valid one, we missed to answer it yet. It >> wasn't clear to me that this was part of what you are asking for. > > Yes, that one. > > Why authors decided to have (*) ➜ 1 which in case of me who could > delete some argument like from (* tonnes quantity) I could by mistake > delete "tonnes and quantity" and result of (*) would not be detected > because there is no error Throwing an error on this case is a reasonable possibility for the language designers, but instead they decided to extend * to zero and one arguments. Why? because it is convenient, because it makes possible to do things like (apply '* some-list) without caring about how many elements some-list has, which is handy when some-list comes from a place you don't control. As far as the extension of * is reasonable, it is nice to have, that's what the language designers thought. So what's the reasonable extension of * (the variadic function!) to zero arguments? Let's use some basic algebra: (apply '* (list a b)) == (apply '* (list 1 1 a b)) which is the same as: a * b == 1 * 1 * a * b remove b: a == 1 * 1 * a remove a: ? == 1 * 1 which the same as: (apply '* ()) == (apply '* (1 1)) or (*) == (* 1 1) So * applied to zero arguments shall be 1, because any other value would break the equality.