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: How the backquote and the comma really work? Date: Thu, 25 Jun 2015 19:09:11 +0200 Message-ID: <87vbebg1fs.fsf@mbork.pl> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1435252190 14193 80.91.229.3 (25 Jun 2015 17:09:50 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 25 Jun 2015 17:09:50 +0000 (UTC) To: Help Gnu Emacs mailing list Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Jun 25 19:09:43 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 1Z8Aek-0006qJ-QR for geh-help-gnu-emacs@m.gmane.org; Thu, 25 Jun 2015 19:09:42 +0200 Original-Received: from localhost ([::1]:56727 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8Aek-0006ot-0V for geh-help-gnu-emacs@m.gmane.org; Thu, 25 Jun 2015 13:09:42 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:59483) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8AeV-0006mU-Jm for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 13:09:28 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z8AeQ-0006VO-L4 for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 13:09:27 -0400 Original-Received: from mail.mojserwer.eu ([2a01:5e00:2:52::8]:57148) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z8AeQ-0006UY-E0 for help-gnu-emacs@gnu.org; Thu, 25 Jun 2015 13:09:22 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by mail.mojserwer.eu (Postfix) with ESMTP id 1C54E6F2002 for ; Thu, 25 Jun 2015 19:09:20 +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 ITkZCEeGuvX7 for ; Thu, 25 Jun 2015 19:09:17 +0200 (CEST) Original-Received: from localhost (ipz217.internetdsl.tpnet.pl [79.190.154.217]) by mail.mojserwer.eu (Postfix) with ESMTPSA id 5485A4F607B for ; Thu, 25 Jun 2015 19:09:16 +0200 (CEST) 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:105159 Archived-At: Hi all, I decided that the time has come that I finally approach the scary backquote-comma duo. (While I understand it superficially, I=E2=80=99d l= ike to get it right and thoroughly this time.) So my question is whether my mental model (see below) is correct. So, I assume that when Emacs Lisp interpreter encounters a backquote, it looks at the expression after it. If it is anything but a list, it just works like the usual quote, and the backquoted expression evaluates to what was backquoted. 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? (I am aware that I didn=E2=80=99t t= ake into account the splicing operator, but it doesn=E2=80=99t introduce a lo= t of additional complexity) Of course, when writing it, I realized that my natural-language description is not extremely precise, so a bonus question is: can I find an Emacs Lisp metacircular evaluator (taking into account the quoting mechanisms) anywhere? And I know that I risk starting another thread lasting for dozens of messages;-) =E2=80=93 but I /do/ want to understand this stuff... In fac= t, in the spirit of another recent discussion, I want to write a simple code analyzer, finding one-legged =E2=80=98if=E2=80=99s and suggesting replaci= ng them with =E2=80=98when=E2=80=99s or =E2=80=98unless=E2=80=99es. This is trivial u= nless (pun intended) you want to take (back)quotes into consideration. Best regards, --=20 Marcin Borkowski This email was proudly sent http://mbork.pl from my Emacs.