From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: florian@fsavigny.de (Florian v. Savigny) Newsgroups: gmane.emacs.help Subject: Rationale behind conversion of a nil prefix arg to numeric 1 Date: Sun, 04 Sep 2016 14:23:35 +0200 Message-ID: <87y437c0qg.fsf@bertrandrussell.Speedport_W_723V_1_40_000> NNTP-Posting-Host: blaine.gmane.org Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1472991864 5479 195.159.176.226 (4 Sep 2016 12:24:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 4 Sep 2016 12:24:24 +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 14:24:13 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 1bgWT5-0008L7-Dj for geh-help-gnu-emacs@m.gmane.org; Sun, 04 Sep 2016 14:24:11 +0200 Original-Received: from localhost ([::1]:49784 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgWT2-00075Z-Vo for geh-help-gnu-emacs@m.gmane.org; Sun, 04 Sep 2016 08:24:09 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:51784) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgWSd-00075I-Lt for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 08:23:44 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bgWSZ-0003dR-Fq for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 08:23:42 -0400 Original-Received: from srv4.ns-domain-hosting.de ([178.63.89.203]:40753) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bgWSZ-0003d7-9G for help-gnu-emacs@gnu.org; Sun, 04 Sep 2016 08:23:39 -0400 X-No-Relay: not in my network Original-Received: from bertrandrussell.Speedport_W_723V_1_40_000 (p3E9EEF0C.dip0.t-ipconnect.de [62.158.239.12]) by srv4.ns-domain-hosting.de (Postfix) with ESMTPSA id C868A1863E0 for ; Sun, 4 Sep 2016 14:23:37 +0200 (CEST) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-Received-From: 178.63.89.203 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:111247 Archived-At: Hi there, I've written one or two functions whose invocation I modeled on Unix file permission bits (where a single digit is always unambiguously either 1, 2 and 4 or some sum of them; thus, possible values are 1, 2, 3 (1 + 2), 4, 5 (1 + 4), 6 (2 + 4) and 7 (1 + 2 + 4)) because I felt it was quite a nifty way of passing a command zero, one, two or three "flags" at once via an optional prefix argument. (Apart from the fact that it's quite easy to forget which number means which flag.) 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? Thanks for any enlightenment! Florian --=20 Florian von Savigny Melanchthonstr. 41 33615 Bielefeld