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.help Subject: Re: How to extract bindings from `pcase-let*`? Date: Tue, 16 Mar 2021 22:59:32 -0400 Message-ID: References: <319f8b2c-7ffc-9a26-0b7b-fe488036c77e@protonmail.com> <3217e2b9-1b58-1984-ba0a-4526e76cfb4d@protonmail.com> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="32134"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:djKCFVc9lIIt6FVAjBgLX6knd64= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Wed Mar 17 04:00:31 2021 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 1lMMQB-0008I6-33 for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 17 Mar 2021 04:00:31 +0100 Original-Received: from localhost ([::1]:58780 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lMMQA-0001yw-53 for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 16 Mar 2021 23:00:30 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:34254) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMMPR-0001yl-6u for help-gnu-emacs@gnu.org; Tue, 16 Mar 2021 22:59:45 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:41180) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lMMPP-0003oS-7r for help-gnu-emacs@gnu.org; Tue, 16 Mar 2021 22:59:44 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1lMMPL-0007Sy-GO for help-gnu-emacs@gnu.org; Wed, 17 Mar 2021 03:59:39 +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: -15 X-Spam_score: -1.6 X-Spam_bar: - X-Spam_report: (-1.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.25, 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: 2.1.23 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" Xref: news.gmane.io gmane.emacs.help:128427 Archived-At: > ;; => ((1 4) (3 6)) > (loopy (flag pcase) > (list elem '((1 (2 3)) (4 (5 6)))) > (collect `(,a (,_ ,b)) elem)) > > in which the `collect` expression expands into something like > > (setq a (append a (list some-value-from-elem))) > (setq b (append b (list some-other-value-from-elem))) > > where `some-value-from-elem` and `some-other-value-from-elem` are > determined by Pcase, Dash, or other destructuring systems. > > Do you think that this is doable using Pcase? You could do something like: (pcase--u `((,(pcase--match INCOMING (pcase--macroexpand PATTERN)) ,(lambda (vars) `(progn . ,(mapcar (lambda (v) `(push ,(cadr v) ,(car v))) vars)))))) where INCOMING is the incoming data (`elem` in your above example). As the `--` in there suggest, this is digging into pcase's internals. I think this code will work with Emacs-28 but the `cadr` would need to be replaced with `cdr` in earlier versions. Also, this does a `pcase` rather than a `pcase-let` so it will just silently do nothing if the pattern doesn't match. You can force the `pcase-let` semantics with something like: (pcase--u `((,(pcase--match INCOMING (pcase--macroexpand `(or ,PATTERN pcase--dontcare))) ,(lambda (vars) `(progn . ,(mapcar (lambda (v) `(push ,(cadr v) ,(car v))) vars)))))) See IELM session below. I suggest you `M-x report-emacs-bug` to request that this functionality be made accessible without having to rely on internals (and put me in the `X-Debbugs-Cc` when you do that). Stefan PS: I used `push` rather than your `setq+append+list` since it is algorithmically much better behaved (linear instead of quadratic complexity). ELISP> (pcase--u `((,(pcase--match 'elem (pcase--macroexpand '(or `(,a (,_ ,b)) pcase--dontcare))) ,(lambda (vars) `(progn . ,(mapcar (lambda (v) `(push ,(cadr v) ,(car v))) vars)))))) (progn (ignore (consp elem)) (let* ((x1507 (car-safe elem)) (x1508 (cdr-safe elem))) (progn (ignore (consp x1508)) (let* ((x1509 (car-safe x1508))) (progn (ignore (consp x1509)) (let* ((x1511 (cdr-safe x1509))) (progn (ignore (consp x1511)) (let* ((x1512 (car-safe x1511)) (x1513 (cdr-safe x1511))) (progn (ignore (null x1513)) (let* ((x1514 (cdr-safe x1508))) (progn (ignore (null x1514)) (progn (push x1512 b) (push x1507 a))))))))))))) ELISP>