From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Marcin Borkowski Newsgroups: gmane.emacs.help Subject: Re: How the backquote and the comma really work? Date: Thu, 25 Jun 2015 20:06:46 +0200 Message-ID: <87si9ffys0.fsf@mbork.pl> References: <87vbebg1fs.fsf@mbork.pl> <87r3ozy9pf.fsf@web.de> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1435255638 7741 80.91.229.3 (25 Jun 2015 18:07:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 25 Jun 2015 18:07:18 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Jun 25 20:07:11 2015 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Z8BYM-0004vJ-BM for geh-help-gnu-emacs@m.gmane.org; Thu, 25 Jun 2015 20:07:10 +0200 Original-Received: from localhost ([::1]:56934 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8BYL-0007JB-OU for geh-help-gnu-emacs@m.gmane.org; Thu, 25 Jun 2015 14:07:09 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:51146) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8BYA-0007J3-Ky for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 14:06:59 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z8BY6-0001DM-Hq for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 14:06:58 -0400 Original-Received: from mail.mojserwer.eu ([2a01:5e00:2:52::8]:51880) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8BY6-0001D1-9S for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 14:06:54 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by mail.mojserwer.eu (Postfix) with ESMTP id A11D36F2002 for ; Thu, 25 Jun 2015 20:06:53 +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 XVxZZGryEMyJ for ; Thu, 25 Jun 2015 20:06:51 +0200 (CEST) Original-Received: from localhost (ipz217.internetdsl.tpnet.pl [79.190.154.217]) by mail.mojserwer.eu (Postfix) with ESMTPSA id 59A224F607B for ; Thu, 25 Jun 2015 20:06:51 +0200 (CEST) In-reply-to: <87r3ozy9pf.fsf@web.de> X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-Received-From: 2a01:5e00:2:52::8 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 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.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:105163 Archived-At: On 2015-06-25, at 19:33, Michael Heerdegen wrote: > Marcin Borkowski writes: > >> So, I assume that when Emacs Lisp interpreter encounters a backquote > > It's even less mystical: backquote is just a normal macro: > > C-h f ` RET Thanks. OTOH, backquote.el has more than 200 lines of code, and it is a bit complicated (I would guess that it might contain some optimizations/error checking/whatever). Seeing a simplistic (though working in typical/correct cases) version might be rather illuminating, no? > It's also a reader macro so that you can write > > `thing > > as an abbreviation of of > > (` thing) > > but that's just a detail. Interesting. Where is that defined? >> If it is a list, its element are read and scanned. If any part of the >> list (probably a nested one) begins with a comma, the whole thing after >> the comma (be it a symbol, a list or whatever) is evaluated as usual, >> and the result is put into the resulting list. >> >> Whew. Is that (more or less) right? > > Seems to be a reasonable mental model. Of course, the elements have > already been read by the reader. Whether these are evaluated or not > depends on whether the macro finds the `backquote-unquote-symbol' in > front of them, so to say. > >> so a bonus question is: can I find an Emacs Lisp metacircular >> evaluator (taking into account the quoting mechanisms) anywhere? > > You don't need a meta thing, since backquote is completely implemented > in Elisp, just read the source code ;-) See above: it is pretty much complicated compared to entry-level stuff in SICP. (Though I guess that I will just put my shoulder to the wheel and study the code. That might lead to more questions;-).) > Regards, > > Michael. Thanks a lot, -- Marcin Borkowski http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski Faculty of Mathematics and Computer Science Adam Mickiewicz University