From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Code for cond* Date: Wed, 24 Jan 2024 10:55:37 -0500 Message-ID: References: <1AD5807F-91F7-4B92-BCB0-D0FEA904A75D@gmail.com> <8E0D0E7B-B733-4CB7-A34D-7FE80D3AB52D@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="9786"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: Stefan Kangas , emacs-devel@gnu.org To: JD Smith Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Wed Jan 24 16:57:36 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 1rSfd9-0002Ix-Qq for ged-emacs-devel@m.gmane-mx.org; Wed, 24 Jan 2024 16:57:36 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rSfcT-0006jp-DV; Wed, 24 Jan 2024 10:56:53 -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 1rSfcR-0006iC-OT for emacs-devel@gnu.org; Wed, 24 Jan 2024 10:56:51 -0500 Original-Received: from mailscanner.iro.umontreal.ca ([132.204.25.50]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rSfcP-0003Ng-6l for emacs-devel@gnu.org; Wed, 24 Jan 2024 10:56:51 -0500 Original-Received: from pmg3.iro.umontreal.ca (localhost [127.0.0.1]) by pmg3.iro.umontreal.ca (Proxmox) with ESMTP id 803D54445D9; Wed, 24 Jan 2024 10:56:47 -0500 (EST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=iro.umontreal.ca; s=mail; t=1706111806; bh=VEiTMiqSCIkNUvG9cAa5KWWNuGeY5C742Nb6ErKnCiU=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=b8jgOUdMPFvKn/iLag1xgFEXySMWjFUdgTha4aImogqEs8MtSpF2ZWz9Ksyau8kXh ZXv5EMu4NQKmdstKJSpRdMADrq4wAQIlS4LvzbfQIWvTQ3Yr6ekUUNez/RoFZeJ+DV 2o0V3vpUK/Rb7xGCRdFtT3oXbrp1KUePjpcv76CapzByjZjvwO5KhZwwE/Tsilf/uK 353tgRjk4BYZZ10IZjgT+IVmOKHCLLzWHaA5dh91cAYM0c55LF4UBl6r2I4F65wn0R xxQudblUrld5tFeiyIgzA4s6k9MscoAgMA91YD0VxFTERJtS0p3lnaLJwteqDzbcdF QO+ymy2g+Uocg== Original-Received: from mail01.iro.umontreal.ca (unknown [172.31.2.1]) by pmg3.iro.umontreal.ca (Proxmox) with ESMTP id 2E1A14400A1; Wed, 24 Jan 2024 10:56:46 -0500 (EST) Original-Received: from lechazo (lechon.iro.umontreal.ca [132.204.27.242]) by mail01.iro.umontreal.ca (Postfix) with ESMTPSA id 1F65312032C; Wed, 24 Jan 2024 10:56:46 -0500 (EST) In-Reply-To: <8E0D0E7B-B733-4CB7-A34D-7FE80D3AB52D@gmail.com> (JD Smith's message of "Wed, 24 Jan 2024 10:29:24 -0500") Received-SPF: pass client-ip=132.204.25.50; envelope-from=monnier@iro.umontreal.ca; helo=mailscanner.iro.umontreal.ca X-Spam_score_int: -42 X-Spam_score: -4.3 X-Spam_bar: ---- X-Spam_report: (-4.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=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:315318 Archived-At: > To explain this correctly, I=E2=80=99d need to understand where the mental > model breaks down. For example, I was surprised that this > forward/reverse symmetry was not maintained: > > (let ((list-var '(foo moo loo)) > (other 'boo)) > `(,@list-var . ,other)). ; -> (foo moo loo . boo) > > (pcase '(foo moo loo . boo) > (`(,@list-var . ,other) > (format "Got %S: %S" list-var other))). ; -> nil, expected =E2=80=9CGo= t (foo moo loo): boo" Note that (let ((list-var '(foo moo)) (other '(loo . boo))) `(,@list-var . ,other)) returns the same `(foo moo loo . boo)`, so there is not a unique way for a pattern like `(,@list-var . ,other) to match a given list. That's a large part of the reason why ,@ is not supported in Pcase's backward patterns. > I also noticed that "Backquote-Style Patterns: Backquote Patterns.=E2=80= =9D is > quite deep in the pcase doc structure, coming just after =E2=80=9CExtend= ing > =E2=80=98pcase=E2=80=99: Extending pcase. Define new kinds of patterns.= =E2=80=9D. Yet most > pcase examples I come across in the wild use backquote patterns. > I don=E2=80=99t know if that=E2=80=99s an intentional arrangement, or was= put in place > before people had experience with pcase and voted with their key-taps > for backquote style.=20 I think it's a mistake due to the docs being written by people too familiar with the implementation (where core Pcase does not include backquote patterns). I'd welcome a patch which corrects this, indeed. Stefan