From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eli Zaretskii Newsgroups: gmane.emacs.help Subject: Re: Rationale behind conversion of a nil prefix arg to numeric 1 Date: Sun, 04 Sep 2016 17:23:23 +0300 Message-ID: <83oa43d9r8.fsf@gnu.org> References: <87y437c0qg.fsf@bertrandrussell.Speedport_W_723V_1_40_000> NNTP-Posting-Host: blaine.gmane.org X-Trace: blaine.gmane.org 1472999039 28626 195.159.176.226 (4 Sep 2016 14:23:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 4 Sep 2016 14:23:59 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Sep 04 16:23:53 2016 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bgYKp-0006EZ-PI for geh-help-gnu-emacs@m.gmane.org; Sun, 04 Sep 2016 16:23:47 +0200 Original-Received: from localhost ([::1]:50051 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgYKn-0002lc-H3 for geh-help-gnu-emacs@m.gmane.org; Sun, 04 Sep 2016 10:23:45 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:41102) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgYKO-0002lD-SF for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 10:23:21 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bgYKL-00064o-JG for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 10:23:20 -0400 Original-Received: from fencepost.gnu.org ([2001:4830:134:3::e]:54154) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgYKL-00064Z-Fw for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 10:23:17 -0400 Original-Received: from 84.94.185.246.cable.012.net.il ([84.94.185.246]:1800 helo=home-c4e4a596f7) by fencepost.gnu.org with esmtpsa (TLS1.2:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1bgYKJ-0006X9-Lv for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 10:23:16 -0400 In-reply-to: <87y437c0qg.fsf@bertrandrussell.Speedport_W_723V_1_40_000> (florian@fsavigny.de) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 2001:4830:134:3::e X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.21 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" Xref: news.gmane.org gmane.emacs.help:111248 Archived-At: > Date: Sun, 04 Sep 2016 14:23:35 +0200 > From: florian@fsavigny.de (Florian v. Savigny) > > Naively, I used the numeric conversion of the prefix arg, i.e. > > (interactive "p") > > which passes the prefix arg converted to a number. However, if I call > the function with no prefix argument, which is, expectedly, nil in raw > form, it converts this to the number 1. (This is what > `prefix-numeric-value' does, as explained in the docstring.) > > While I understand that this is how it is done, I am quite puzzled > about the logic behind this. It would seem intuitive to me to convert > nil to either the number 0 or, again, nil, but never to the number > 1. And practically, converting nil to 1 has the consequence that > calling the command with no prefix arg: > > M-x command > > is exactly the same as calling it with a prefix arg of 1: > > C-u 1 M-x command > > because the prefix arg converted to a number is 1 in both cases, which > reduces the number of possibilities of calling the command by one. > > I can circumvent this (and get the behaviour that I would expect) by > writing the function with > > (if current-prefix-arg (prefix-numeric-value current-prefix-arg)) > > in an explicit interactive list, but I am still wondering about the > rationale of representing nil as the number one. Does this make sense, > or is it useful, in some way? Yes. Most commands use the argument as a repeat count, so having it default to one makes perfect sense.