From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Ihor Radchenko Newsgroups: gmane.emacs.devel Subject: Re: Instead of pcase Date: Mon, 25 Dec 2023 14:26:23 +0000 Message-ID: <878r5inysw.fsf@localhost> References: Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="28113"; mail-complaints-to="usenet@ciao.gmane.io" Cc: Adam Porter , emacs-devel@gnu.org To: rms@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Dec 25 15:24:06 2023 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 1rHlsE-00079O-Pi for ged-emacs-devel@m.gmane-mx.org; Mon, 25 Dec 2023 15:24:06 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rHlrS-0008BQ-Rp; Mon, 25 Dec 2023 09:23:18 -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 1rHlrR-0008B4-B5 for emacs-devel@gnu.org; Mon, 25 Dec 2023 09:23:17 -0500 Original-Received: from mout02.posteo.de ([185.67.36.66]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rHlrP-0004hU-36 for emacs-devel@gnu.org; Mon, 25 Dec 2023 09:23:17 -0500 Original-Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id D1236240101 for ; Mon, 25 Dec 2023 15:23:11 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1703514191; bh=iv4QLqo4XkB1Xqr2GrbTqjO/xnpaVGW46T3al1uHTSc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:From; b=EQL+gozZHP6ZpzKPYFhQZQWCX46aQ4lrCternl4rsbIPFpxdWT5cYJZgEOCUSwGXT ueRxaJeSVYU9lAqCPpV6iRKl+SgdBCidTm3TXZpc3NnSkd5ZdQ1CX0xq8xSJFyTdVz AQBOQxQLm6YLZoB4dSMmNewIUHEeT5CAnhSOr4ZokwZ3ABpuBiThUx91HaR52WRAG9 j1sXCcZxhLA+y2RPoRZcakQKYYj7adtGNjcUMhexocbgEIGJpvOa/Ew3r4Im6W5MSS zaKljwHg2Zzzuwc6exQMuQplL5q7SVrivAx01VmOPaTjE6wVDH+iTkWhzz3YZfdFnF LQEP+L2lspjrA== Original-Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4SzKrH11Hqz9rxG; Mon, 25 Dec 2023 15:23:10 +0100 (CET) In-Reply-To: Received-SPF: pass client-ip=185.67.36.66; envelope-from=yantar92@posteo.net; helo=mout02.posteo.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." 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:314208 Archived-At: Richard Stallman writes: > Constrained variable: (PRED VARIABLE) or, more generally, > (PRED VARIABLE OTHER-ARGS...) > ... > (symbolp sym) ; Match any symbol, bind `sym' to it. This one is clear, especially as ,(symbolp sym) - comma indicates that the form is special. > (> num-foos min-foos) ; Match any number greater than MIN-FOOS, > ; bind `num-foos' to it. But this is confusing - which symbol to bind and which one to eval is based purely on position in the ,(PRED ...) pattern. In such scenario, it is very easy to confuse that num-foos will be let-bound. It does not help that the whole thing looks like an ordinary function call. I'd suggest to provide a more clear indication about which symbol will be bound, so that it stands out compared to ordinary variables like min-foos. > Constrained variable constructs can be nested > > For example, > > (< (integerp num-foos) 1) ; Match any integer number > 1, > ; bind `num-foos' to it. This is also confusing. Looking at the above expression, I expect that we compare the return value of `integerp' with 1, but it is not the case - integerp returns nil or t. Again, it looks deceivingly similar to normal function call. > General constrained variable: (constrain VAR EXPRESSION) > > This general constrained variable pattern binds VAR to the > value being matched against, tentatively, then evaluates EXPRESSION. > If the result is true, the match succeeds and leaves VAR > bound to that value. > > For instance, > > (constrain x (and (> x 0) (< x 100))) > > succeeds if the value being matched aainst is in the open interval (0, 100), > and in that case it binds x to that value. This looks much better, as `constrain' is a special keyword that can be easily recognized and not confused with a function call. -- Ihor Radchenko // yantar92, Org mode contributor, Learn more about Org mode at . Support Org development at , or support my work at