From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: phillip.lord@russet.org.uk (Phillip Lord) Newsgroups: gmane.emacs.devel Subject: Re: The poor state of documentation of pcase like things. Date: Sat, 19 Dec 2015 19:23:44 +0000 Message-ID: <87mvt6nsxr.fsf@russet.org.uk> References: <20151216202605.GA3752@acm.fritz.box> <87mvt859cw.fsf@russet.org.uk> <87poy2tqrc.fsf@web.de> 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 1450553061 18070 80.91.229.3 (19 Dec 2015 19:24:21 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 19 Dec 2015 19:24:21 +0000 (UTC) Cc: emacs-devel@gnu.org To: Michael Heerdegen Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Sat Dec 19 20:24:15 2015 Return-path: Envelope-to: ged-emacs-devel@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 1aAN70-0007hQ-Sn for ged-emacs-devel@m.gmane.org; Sat, 19 Dec 2015 20:24:15 +0100 Original-Received: from localhost ([::1]:38368 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aAN70-0002nM-9I for ged-emacs-devel@m.gmane.org; Sat, 19 Dec 2015 14:24:14 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:52381) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aAN6h-0002l7-Hs for emacs-devel@gnu.org; Sat, 19 Dec 2015 14:23:56 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aAN6e-0004cS-9l for emacs-devel@gnu.org; Sat, 19 Dec 2015 14:23:55 -0500 Original-Received: from cheviot22.ncl.ac.uk ([128.240.234.22]:41036) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aAN6e-0004c7-40 for emacs-devel@gnu.org; Sat, 19 Dec 2015 14:23:52 -0500 Original-Received: from smtpauth-vm.ncl.ac.uk ([10.8.233.129] helo=smtpauth.ncl.ac.uk) by cheviot22.ncl.ac.uk with esmtp (Exim 4.63) (envelope-from ) id 1aAN6X-0007gy-G1; Sat, 19 Dec 2015 19:23:46 +0000 Original-Received: from cpc6-benw10-2-0-cust45.gate.cable.virginm.net ([92.238.179.46] helo=localhost) by smtpauth.ncl.ac.uk with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.63) (envelope-from ) id 1aAN6X-0002Vi-O6; Sat, 19 Dec 2015 19:23:45 +0000 In-Reply-To: <87poy2tqrc.fsf@web.de> (Michael Heerdegen's message of "Sat, 19 Dec 2015 16:14:15 +0100") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 128.240.234.22 X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.14 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.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:196519 Archived-At: Michael Heerdegen writes: > phillip.lord@russet.org.uk (Phillip Lord) writes: > >> (pcase '(3 1 2) >> (`(_ 1 2) >> (message "Matched a list of anything followed by (2 3)"))) >> >> prints nothing. >> >> while this... >> >> (pcase '(3 1 2) >> (`(,_ 1 2) >> (message "Matched a list of anything followed by (2 3)"))) >> >> prints the message (which should be "followed by (2 3)"). >> >> I am a bit surprised to find that _ needs , in these examples, and I >> think that it's a bug. > > I think it's intentional, and it fits the documentation. Not convinced. The documentation says.... =E2=80=98(pred numberp)=E2=80=99 is a pattern that simply checks that =E2= =80=98exp=E2=80=99 is a number, and =E2=80=98_=E2=80=99 is the catch-all pattern that matches anything. for example, which made me assume that "_" matches anything. > We think of elements in a backquoted list to be all quoted unless > explicitly unquoted. It makes no sense that '_ matches any expression. > It matches only the symbol _, and that can be useful, too. To be it seems unintuitive, to be honest. It took me a while to work this out; John made the same mistake, it seems. Phil