From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Philip Kaludercic Newsgroups: gmane.emacs.devel Subject: Re: recursion to iteration macro Date: Sat, 23 Mar 2024 07:12:25 +0000 Message-ID: <87le69e812.fsf@posteo.net> References: <871q813mgg.fsf@dataswamp.org> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="32464"; mail-complaints-to="usenet@ciao.gmane.io" To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sat Mar 23 08:13:09 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 1rnvYz-0008I8-Ir for ged-emacs-devel@m.gmane-mx.org; Sat, 23 Mar 2024 08:13:09 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rnvYQ-0006TZ-US; Sat, 23 Mar 2024 03:12:34 -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 1rnvYN-0006S0-Qi for emacs-devel@gnu.org; Sat, 23 Mar 2024 03:12:32 -0400 Original-Received: from mout01.posteo.de ([185.67.36.65]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rnvYL-0000Xs-Bm for emacs-devel@gnu.org; Sat, 23 Mar 2024 03:12:31 -0400 Original-Received: from submission (posteo.de [185.67.36.169]) by mout01.posteo.de (Postfix) with ESMTPS id 7CD66240027 for ; Sat, 23 Mar 2024 08:12:26 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1711177946; bh=nw5+0frc1DzQrhjAZPivSU6h1PgGlW6FvSxekR4fTjo=; h=From:To:Subject:OpenPGP:Date:Message-ID:MIME-Version:Content-Type: From; b=ry9R1s3ahjQi7RwMWIjGwfgUzHmh6zy9YwVvM6CSkZAHxW6s8sNfqDa/ANIuCLJ/2 b8Biw+ZMSwJQMjDs7nAxF3B2khDg+rH/ALsXBY9Vlp5AuF/rRQmAVWEdwENcq9PaEV vrB8gww5WkfVpb+WX2wKYk398VjLPseR/l1x5fM204A/3nI0otgxD2fEdaLxOk6zmO mIptwEMYbo2p1xPMhSqijqO1JiQIFMv/Vyo8DFpWpFO9n4okDRAp6oyrs8VCwwU4fW ydgBxXOW5X/EZ+xzMGxhEcIBlkVfmfTSuTiFBgYHLbjXEc2ndeANg9gmSutYhkztmU GcGNLJgyfu77g== Original-Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4V1r4B0Nmgz6txW for ; Sat, 23 Mar 2024 08:12:25 +0100 (CET) In-Reply-To: <871q813mgg.fsf@dataswamp.org> (Emanuel Berg's message of "Fri, 22 Mar 2024 23:56:15 +0100") OpenPGP: id=7126E1DE2F0CE35C770BED01F2C3CC513DB89F66; url="https://keys.openpgp.org/vks/v1/by-fingerprint/7126E1DE2F0CE35C770BED01F2C3CC513DB89F66"; preference=signencrypt Received-SPF: pass client-ip=185.67.36.65; envelope-from=philipk@posteo.net; helo=mout01.posteo.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, 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: 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:317243 Archived-At: Emanuel Berg writes: > Did anyone try to write a macro or by using some other method > to translate arbitrary use of recursion into functionally > equivalent code that is iteration only? > > I read [1] this is theoretically possible and that seems > reasonable as well, as with loops, local functions etc you > have everything you need to implement it. At least for tail-call recursion, named-let will turn recursive code into iterative code. But generally speaking, if you need to accumulate data on the stack, then it becomes a lot more difficult. > You can even have an expanding data structure, e.g. a list, to > implement a virtual stack, still all within the one function, > if you are fond of it. > > With execution all advantages should be with iteration but > sometimes recursion makes for compact, elegant code that can > also be more intuitive, more fun to write. > > Recursion is not so common, in part for this exact reason, but > if we had this, maybe we would see a little recursion > renaissance and proliferation? > > The best of both worlds anyone? You _will_ be assimilated! > > [1] https://en.wikipedia.org/wiki/Recursion_(computer_science) > https://stackoverflow.com/questions/931762/can-every-recursion-be-converted-into-iteration -- Philip Kaludercic on peregrine