From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Emanuel Berg via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: Closures in Emacs and their usage scenarios. Date: Tue, 12 Oct 2021 01:16:32 +0200 Message-ID: <87zgrfywxb.fsf@zoho.eu> References: <87r1ct3qzf.fsf@zoho.eu> <87mtngu48k.fsf@mbork.pl> Reply-To: Emanuel Berg Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="4388"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:IoCewtws5P1ncbwk62SLr17wT1o= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Oct 12 01:18:14 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 1ma4Yf-0000xG-Rb for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 12 Oct 2021 01:18:13 +0200 Original-Received: from localhost ([::1]:54092 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ma4Yd-0000Rn-Pr for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 11 Oct 2021 19:18:11 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:36446) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ma4XG-0000Rb-S6 for help-gnu-emacs@gnu.org; Mon, 11 Oct 2021 19:16:46 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]:51936) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ma4XE-00009w-5l for help-gnu-emacs@gnu.org; Mon, 11 Oct 2021 19:16:46 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1ma4XB-0009hn-5N for help-gnu-emacs@gnu.org; Tue, 12 Oct 2021 01:16:41 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: help-gnu-emacs@gnu.org Mail-Copies-To: never 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: -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 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:133728 Archived-At: Marcin Borkowski wrote: > Yet another use (which of course - technically - is again > a variant of the same thing) is generating a closure whose > behavior depends on the argument of the function that > defines it. Not following? > (defun negate (fun) > "Return a function returning the logical opposite of FUN." > (lambda (&rest args) > (not (apply fun args)))) Yes, I remember, no, I know you can do a lot with `lambda' (anonymous function I believe :)), I mean just the (let ((...) ...) (defun ... ) ... ) syntax Here are the 1 + a use cases I know of, where a -> 1. ;;; -*- lexical-binding: t -*- ;;; ;;; this file: ;;; http://user.it.uu.se/~embe8573/emacs-init/geh.el ;;; https://dataswamp.org/~incal/emacs-init/geh.el (require 'cl-lib) (let ((dope 1337)) (defun hope () (message "Hope is %d Dope" (cl-incf dope)) )) ;; (hope) (let ((forward #'forward-char)) (defun you-can-not-advance () (apply forward '(1))) (defun you-can-not-redo () (setq forward #'backward-char) )) ;; (you-can-not-advance) ;; (you-can-not-redo) -- underground experts united https://dataswamp.org/~incal