From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Marcin Borkowski Newsgroups: gmane.emacs.help Subject: Re: How to create a higher order function? Date: Fri, 24 Sep 2021 11:00:37 +0200 Message-ID: <87fstufive.fsf@mbork.pl> References: <87k0jawotx.fsf@mbork.pl> <87bl4m6uds.fsf@t14.reltub.ca> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="11773"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: mu4e 1.1.0; emacs 28.0.50 Cc: Help Gnu Emacs mailing list To: Leo Butler Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Fri Sep 24 11:01:32 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 1mTh5H-0002uB-C1 for geh-help-gnu-emacs@m.gmane-mx.org; Fri, 24 Sep 2021 11:01:31 +0200 Original-Received: from localhost ([::1]:50098 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mTh5F-00060V-QD for geh-help-gnu-emacs@m.gmane-mx.org; Fri, 24 Sep 2021 05:01:29 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:35220) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mTh4d-0005zB-Be for help-gnu-emacs@gnu.org; Fri, 24 Sep 2021 05:00:51 -0400 Original-Received: from mail.mojserwer.eu ([195.110.48.8]:34440) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mTh4Y-0006wt-DM for help-gnu-emacs@gnu.org; Fri, 24 Sep 2021 05:00:50 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by mail.mojserwer.eu (Postfix) with ESMTP id E3E78E6DB1; Fri, 24 Sep 2021 11:00:44 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at mail.mojserwer.eu Original-Received: from mail.mojserwer.eu ([127.0.0.1]) by localhost (mail.mojserwer.eu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9ZZAGh3hWuWq; Fri, 24 Sep 2021 11:00:38 +0200 (CEST) Original-Received: from localhost (178235147106.dynamic-3-poz-k-0-1-0.vectranet.pl [178.235.147.106]) by mail.mojserwer.eu (Postfix) with ESMTPSA id E2A5FE6208; Fri, 24 Sep 2021 11:00:37 +0200 (CEST) In-reply-to: <87bl4m6uds.fsf@t14.reltub.ca> Received-SPF: pass client-ip=195.110.48.8; envelope-from=mbork@mbork.pl; helo=mail.mojserwer.eu X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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: 2.1.23 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:133210 Archived-At: On 2021-09-21, at 13:27, Leo Butler wrote: > Marcin Borkowski writes: > >> Hi all, >> >> assume that I want a function which "inverts" the meaning of a given >> predicate. Something that would turn `<' into `>=' etc. >> >> So, here's a better (at least: working) version (B): >> >> ;;; -*- lexical-binding: nil; -*- >> (defun negate (fun) >> "Return a function returning the logical opposite of FUN." >> `(lambda (&rest args) >> (not (apply ,(symbol-function fun) args)))) > > I think negate would need to be a defmacro in this case, not a defun. Maybe. I'm not really convinced. > This construction, as it is, would return a list, not a lambda function. > > `(foo ,X bar) is equivalent to (list 'foo X 'bar). > >> >> >> It seems to work fine, even if it's a bit complicated. >> >> Of course, the more obvious way to do it is to use the first definition >> under lexical scope (C): >> >> ;;; -*- lexical-binding: t; -*- >> (defun negate (fun) >> "Try to return a function returning the logical opposite of FUN." >> (lambda (&rest args) >> (not (apply fun args)))) > > Obviously C is better. > > Q: I see you use mu4e. How do you get the code highlighted? (in my Gnus, > the background is distinctive blue). ??? I don't do anything in particular apart from using a pretty old version of mu/mu4e. And code is not highlighted in my emails. Best, -- Marcin Borkowski http://mbork.pl