From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Tomas Hlavaty Newsgroups: gmane.emacs.devel Subject: Re: combining cond and let, to replace pcase. Date: Mon, 27 Nov 2023 18:07:58 +0100 Message-ID: <87zfyz15w1.fsf@neko.mail-host-address-is-not-set> References: <87v89t7y13.fsf@neko.mail-host-address-is-not-set> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="27734"; mail-complaints-to="usenet@ciao.gmane.io" Cc: emacs-devel@gnu.org To: rms@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Nov 27 18:09:03 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 1r7f6V-00070n-4n for ged-emacs-devel@m.gmane-mx.org; Mon, 27 Nov 2023 18:09:03 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1r7f5o-0007MS-9c; Mon, 27 Nov 2023 12:08:20 -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 1r7f5m-0007MG-AG for emacs-devel@gnu.org; Mon, 27 Nov 2023 12:08:18 -0500 Original-Received: from logand.com ([37.48.87.44]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1r7f5g-0004ZG-Vn; Mon, 27 Nov 2023 12:08:18 -0500 Original-Received: by logand.com (Postfix, from userid 1001) id 82EF719E77A; Mon, 27 Nov 2023 18:08:00 +0100 (CET) X-Mailer: emacs 28.2 (via feedmail 11-beta-1 I) In-Reply-To: Received-SPF: pass client-ip=37.48.87.44; envelope-from=tom@logand.com; helo=logand.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, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham 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:313288 Archived-At: On Sat 25 Nov 2023 at 22:14, Richard Stallman wrote: > > > ;; Same as a clause in `cond', > > > (CONDITION > > > do-this-if-CONDITION-then-exit...) > > > > > > ;; Variables to bind, as in let > > > (:bind (x foobar) y z (foo 5) a) > > > ;; Bindings continue in effect. > > > This seems nicer: > > > (if CONDITION > > do-this-if-CONDITION-then-exit... > > (let ((x foobar) y z (foo 5) a) > > ...)) > > That is what you can do now with `if' and `let', but many levels of > nexting get to be inconvenient and hard to read. That is one of the > practical conveniences of _using_ `pcase'. I think a replacement for > `pcase' should offer the same advantage. if you are after less nesting, cond or or can already do that: (cond ;; Same as a clause in `cond', (CONDITION do-this-if-CONDITION-then-exit...) ;; Variables to bind, as in let ((let ((x foobar) y z (foo 5) a) ;; Bindings continue in effect. ...)) ...) even better: (or ;; Same as a clause in `cond', (when CONDITION do-this-if-CONDITION-then-exit...) ;; Variables to bind, as in let (let ((x foobar) y z (foo 5) a) ;; Bindings continue in effect. ...) ...) no need for :bind which seems like superficial syntax that requires extra cond* macro definition with weird rules. > > It looks like everybody is trying to design a "do it all super-macro" > > If that refers to the approach of `pcase', in which there are dozens > of different features one must learn, then `cond*' represents turning > away from that approach. `cond*' has just four features, two of which > are modified from `cond'. > > That's why `cond*' will impose less burden of language complexity than > `pcase'. or, when, let are even simpler and the example with or is even more readable. I do not see what cond* brings. It seems that existing forms cover the control flow part well enough. What should be the focus is the destructuring part, like cl-destructuring-bind or your match, match-set, match-bind or the matching part of pcase. Btw there is even a kind of user-configurable version of the or macro, a kind of pluggable-or called run-hook-with-args-until-success which is like the or macro but with cases as functions in a list. This could allow for use-extensible variant, if the destructuring part was separate and reuseable.