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 "Emacs development discussions." Newsgroups: gmane.emacs.devel Subject: Re: pcase bindings in patterns with complicated logic Date: Tue, 23 Jan 2024 14:59:54 -0500 Message-ID: References: <87il3xt38w.fsf@localhost> <875xzwjta2.fsf@posteo.net> <878r4rsyyt.fsf@localhost> <87r0ijj48v.fsf@posteo.net> <871qajsx5z.fsf@localhost> <87le8riyvp.fsf@posteo.net> <87r0ihl8lr.fsf@localhost> <87zfx2943z.fsf@localhost> <87sf2s5fx4.fsf@localhost> <87edeag4r1.fsf@localhost> 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="14654"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: Stefan Monnier To: emacs-devel@gnu.org Cancel-Lock: sha1:Q242ugbaKZP4SKFDwre3tYmqlVQ= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Tue Jan 23 21:01:05 2024 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 1rSMxE-0003Zb-Tz for ged-emacs-devel@m.gmane-mx.org; Tue, 23 Jan 2024 21:01:04 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rSMwN-0004j5-HO; Tue, 23 Jan 2024 15:00:11 -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 1rSMwL-0004is-VB for emacs-devel@gnu.org; Tue, 23 Jan 2024 15:00:09 -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 1rSMwK-00008L-4i for emacs-devel@gnu.org; Tue, 23 Jan 2024 15:00:09 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1rSMwG-0002GV-Dv for emacs-devel@gnu.org; Tue, 23 Jan 2024 21:00:04 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=ged-emacs-devel@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, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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:315275 Archived-At: > The `app` pattern is mostly for internal use when defining other > patterns. It's key to the implementation of patterns like backquote so > it's very important, but you'll rarely see it "out and about" in > a `pcase` or `pcase-let` statement. BTW, if you want help to understand the general design of Pcase, a good read is that of the design of `match` for Racket: Extensible Pattern Matching in an Extensible Language Sam Tobin-Hochstadt, 2010 https://arxiv.org/abs/1106.2578 I didn't know about that `match` construct when I started Pcase (and now that I actually pay attention to the publication date I realize that maybe it's not because I missed it in my searches but because it came out around the same time), but when I found it, I "realigned" Pcase to be more like Racket's `match`. The implementation is not quite the same because sadly our ELisp implementation doesn't handle (tail) calls quite as efficiently as Racket, but there's a large overlap when it comes to the exposed functionality. Stefan