From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Emanuel Berg Newsgroups: gmane.emacs.devel Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Date: Sun, 03 Sep 2023 02:18:03 +0200 Message-ID: <87bkekp0sk.fsf@dataswamp.org> References: <87zg2bosf3.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="35140"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: emacs-devel@gnu.org Cancel-Lock: sha1:w6HGFWcXZ6uS7umItwHo7fQwLZs= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sun Sep 03 06:35:20 2023 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 1qcepU-0008up-A5 for ged-emacs-devel@m.gmane-mx.org; Sun, 03 Sep 2023 06:35:20 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qcenV-00049H-Vp; Sun, 03 Sep 2023 00:33:18 -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 1qcaoj-0004jQ-1J for emacs-devel@gnu.org; Sat, 02 Sep 2023 20:18:17 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qcaof-0001gz-6D for emacs-devel@gnu.org; Sat, 02 Sep 2023 20:18:16 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1qcaoc-0006MI-Tq for emacs-devel@gnu.org; Sun, 03 Sep 2023 02:18:10 +0200 X-Injected-Via-Gmane: http://gmane.org/ Mail-Followup-To: emacs-devel@gnu.org Mail-Copies-To: never Received-SPF: pass client-ip=116.202.254.214; envelope-from=ged-emacs-devel@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-Mailman-Approved-At: Sun, 03 Sep 2023 00:32:49 -0400 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:309926 Archived-At: Stefan Monnier via "Emacs development discussions." wrote: >>>> In C, we have the very useful conditional compilation >>>> directives introduced by #if or #ifdef, etc., which end >>>> at #end. >>> >>> Those are directives to the C preprocessor and some people >>> say it is a sign of weakness such a thing is even >>> necessary to begin with. >>> >>> Let's see if they are right! >>> >>> What problem do you have? If we can solve it in Elisp, we >>> cannot say those people saying that are wrong. >> >> FWIW, Common Lisp has reader macros to solve the problem: >> http://clhs.lisp.se/Body/24_aba.htm > > I don't see why reader macros would be needed here. > Reader macros are useful to introduce funny new shorthands > or to avoid *reading* a chunk of code (e.g. because it uses > some unsupported funny syntax) but in the present case we > can read both branches of the `if` just fine, we just want > to throw away one of the two before we macro-expand it. In general, Lisp macros seem much more powerful and versatile than the C preprocessor, and they are part of the language as well. But let's say preprocessor directives are part of the C language as well then even tho it doesn't feel like it, really. The question is then, is there anything you can do with the C preprocessor which you _cannot_ do in Lisp - with or without macros? -- underground experts united https://dataswamp.org/~incal