From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Eric Abrahamsen Newsgroups: gmane.emacs.help Subject: Re: Question about parse-time-string and date-to-time Date: Wed, 29 Mar 2017 16:12:04 -0700 Message-ID: <87bmsj8ypn.fsf@ericabrahamsen.net> References: <87shlv23xt.fsf@ericabrahamsen.net> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1490829196 2717 195.159.176.226 (29 Mar 2017 23:13:16 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 29 Mar 2017 23:13:16 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Thu Mar 30 01:13:11 2017 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 1ctMm0-0008BD-M8 for geh-help-gnu-emacs@m.gmane.org; Thu, 30 Mar 2017 01:13:04 +0200 Original-Received: from localhost ([::1]:33003 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ctMm6-0000W7-DH for geh-help-gnu-emacs@m.gmane.org; Wed, 29 Mar 2017 19:13:10 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:33794) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ctMla-0000Vk-7o for help-gnu-emacs@gnu.org; Wed, 29 Mar 2017 19:12:39 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ctMlX-0005jj-32 for help-gnu-emacs@gnu.org; Wed, 29 Mar 2017 19:12:38 -0400 Original-Received: from [195.159.176.226] (port=39202 helo=blaine.gmane.org) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1ctMlW-0005j2-Sm for help-gnu-emacs@gnu.org; Wed, 29 Mar 2017 19:12:35 -0400 Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1ctMlN-0004XZ-9P for help-gnu-emacs@gnu.org; Thu, 30 Mar 2017 01:12:25 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 57 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:+MiUTfojWMHz74ram6HMkNWECGU= X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 195.159.176.226 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:112667 Archived-At: John Mastro writes: > Eric Abrahamsen wrote: >> A conundrum: >> >> parse-time-string accepts a string representing a date, and parses it >> into a list of time elements, with nil for the unknowns. >> >> date-to-time calls parse-time-string and passes the result straight to >> encode-time, to produce a time value. >> >> encode-time accepts series of time elements, and raises an error if any >> of them are nil. >> >> I might be missing something, but I don't see how date-to-time could >> ever work. Wouldn't it always have to replace the nils with zeros before >> passing the result to encode time? > > It looks like, if the first call to `encode-time' signals an error, it > re-tries using the result of calling `timezone-make-date-arpa-standard' > on the original DATE argument: > > (defun date-to-time (date) > (condition-case err > (apply 'encode-time (parse-time-string date)) > (error > ;; ... > (apply 'encode-time > (parse-time-string > (timezone-make-date-arpa-standard date))) > ;; ... > ))) > > I was not familiar with `timezone-make-date-arpa-standard', and am not > familiar with "arpanet standard date" as a concept. It seems to > guarantee that some valid date string will be returned, but not > necessarily the one I would have guessed when time information is > missing: > > (timezone-make-date-arpa-standard "2017-03-29 3:05:00") > ;=> "28 Mar 2017 20:05:00 -0700" > (timezone-make-date-arpa-standard "2017-03-29") > ;=> "31 Dec 1999 16:00:00 -0800" > (timezone-make-date-arpa-standard "3/29/2016") > ;=> "31 Dec 1999 16:00:00 -0800" > > And sure enough: > > (equal (date-to-time "2017-03-29") > (date-to-time "31 Dec 1999 16:00:00 -0800")) > ;=> t > > So it seems like it returns an arbitrary date if time elements are > missing? That's what I've found. If parse-time-string returns any nil values, then you get 31 Dec, 1999. I'd rather get an error!