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.help Subject: Re: Question about let binding behavior Date: Thu, 10 Oct 2024 09:58:31 +0200 Message-ID: <87zfncie3c.fsf@neko.mail-host-address-is-not-set> References: <88c7526c-b7d9-46f8-8799-5825b97d20ba@protonmail.com> <8fc2872f-dded-4713-9937-61c3af974538@protonmail.com> <87bjztn17x.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="32003"; mail-complaints-to="usenet@ciao.gmane.io" To: Stefan Monnier , help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Thu Oct 10 09:59:24 2024 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 1syo4y-0008Dc-F7 for geh-help-gnu-emacs@m.gmane-mx.org; Thu, 10 Oct 2024 09:59:24 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1syo4S-00087Q-2I; Thu, 10 Oct 2024 03:58:52 -0400 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 1syo4N-00086x-Vp for help-gnu-emacs@gnu.org; Thu, 10 Oct 2024 03:58:49 -0400 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 1syo4H-0002w3-Ba for help-gnu-emacs@gnu.org; Thu, 10 Oct 2024 03:58:47 -0400 Original-Received: by logand.com (Postfix, from userid 1001) id 994E11A037A; Thu, 10 Oct 2024 09:58:37 +0200 (CEST) X-Mailer: emacs 29.4 (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, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 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-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:148147 Archived-At: On Wed 09 Oct 2024 at 19:39, Stefan Monnier via Users list for the GNU Emacs text editor wrote: >> or you can avoid the constant in the first place, for example with >> minimal change like this: >> >> (let ((baz `((quux . 0) (quuz . 0)))) > > Hmm... I think this makes no difference: ` does not guarantee it returns > a different object each time. > And indeed, if you try: > > (macroexpand '`((quux . 0) (quuz . 0))) > => > '((quux . 0) (quuz . 0)) ok, try (let ((baz `((quux . ,0) (quuz . ,0)))) (macroexpand '`((quux . ,0) (quuz . ,0))) => (list (cons 'quux 0) (cons 'quuz 0)) although sbcl does not get tricked and requires CL-USER> (macroexpand '`((quux . ,a) (quuz . ,b))) (LIST (LIST* 'QUUX A) (LIST* 'QUUZ B)) T (defun foo2 (bar &optional (a 0) (b 0)) (let ((baz `((quux . ,a) (quuz . ,b)))) (if (> 10 bar) (setf (cdr (assoc 'quux baz)) bar) (setf (cdr (assoc 'quuz baz)) bar)) baz)) (foo2 1) (foo2 100) in emacs-lisp: (defun foo2 (bar &optional a b) (let ((baz `((quux . ,(or a 0)) (quuz . ,(or b 0))))) (if (> 10 bar) (setcdr (assoc 'quux baz) bar) (setcdr (assoc 'quuz baz) bar)) baz)) (foo2 1) (foo2 100) although this also works in emacs-lisp (for now?): (defun foo3 (bar) (let* ((a 0) (b 0) (baz `((quux . ,a) (quuz . ,b)))) (if (> 10 bar) (setcdr (assoc 'quux baz) bar) (setcdr (assoc 'quuz baz) bar)) baz)) (foo3 1) (foo3 100)