Re: checking if a list is empty

From	Jussi Piitulainen <jpiitula@ling.helsinki.fi>
Newsgroups	comp.lang.python
Subject	Re: checking if a list is empty
Date	2011-05-08 18:59 +0300
Organization	University of Helsinki
Message-ID	<qotvcxlxjwv.fsf@ruuvi.it.helsinki.fi> (permalink)
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Steven D'Aprano writes:

> Lisp uses the empty list and the special atom NIL as false values,
> any other s-expression is true. Scheme is different: it defines a
> special false atom, and empty lists are considered true. In Ruby,

I'll inject a pedantic note: there is only one false value in both
Lisp (which now is mostly Common Lisp) and Scheme.

The empty list () and the symbol NIL in Lisp are one value, not two
values. The first Google hit (for me, just now) explains it the way I
understand it: <http://www.ida.liu.se/imported/cltl/clm/node9.html>.
(Common Lisp The Language, 2nd edition. Odd place to find that book.
It predates the formal standard, but then I think this particular
feature of the language is, indeed, as old as you say, and unlikely to
have changed.)

Scheme was the same. Then for a time it was not specified whether the
empty list was distinct from the false value or the symbol nil -
people disagreed and implementations were allowed to differ - until
the three were definitely separated.

Thread

Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-06 15:31 -0400
  Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-06 14:49 -0500
    Re: checking if a list is empty Adam Tauno Williams <awilliam@whitemice.org> - 2011-05-06 16:05 -0400
      Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-07 02:49 +0000
        Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 10:14 +0100
          Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 11:48 +0200
            Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 11:14 +0000
              Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 13:45 +0200
              Re: checking if a list is empty Laurent Claessens <moky.math@gmail.com> - 2011-05-11 13:45 +0200
          Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 13:36 +0000
            Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 15:00 +0100
              Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 00:46 +1000
              Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-11 08:53 -0700
              RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 13:50 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 19:15 +0100
                RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 14:59 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:08 +0100
                Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-11 12:17 -0700
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:13 +0100
                Re: checking if a list is empty Ian <hobson42@gmail.com> - 2011-05-11 22:02 +0100
                Re: checking if a list is empty Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-05-22 22:41 +0200
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 21:47 +0000
                Re: checking if a list is empty Steven Howe <howe.steven@gmail.com> - 2011-05-11 15:09 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 17:38 -0500
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 18:12 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-12 01:07 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 06:21 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 13:51 +1000
                Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-12 07:02 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-13 00:13 +1000
                Re: checking if a list is empty Ian <hobson42@gmail.com> - 2011-05-22 10:20 +0100
              Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-12 11:08 +1200
                Re: checking if a list is empty John J Lee <jjl@pobox.com> - 2011-05-21 15:46 +0100
                Re: checking if a list is empty Emile van Sebille <emile@fenx.com> - 2011-05-21 08:52 -0700
                Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-21 16:11 -0400
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-21 20:02 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-22 13:52 +1000
                Re: checking if a list is empty rusi <rustompmody@gmail.com> - 2011-05-21 21:32 -0700
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-22 15:16 +1000
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-22 01:02 +0000
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-22 12:56 +1000
    Re: checking if a list is empty Chris Rebert <clp2@rebertia.com> - 2011-05-06 13:46 -0700
    Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-07 10:51 +1000
    Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-07 08:28 +0000
      Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-07 22:50 -0500
        Re: checking if a list is empty Ethan Furman <ethan@stoneleaf.us> - 2011-05-07 21:57 -0700
          Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 11:47 +0100
            Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 13:45 +0000
              Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 15:34 +0100
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 16:26 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 19:05 +0100
                RE: checking if a list is empty "Prasad, Ramit" <ramit.prasad@jpmchase.com> - 2011-05-11 14:44 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 20:26 +0100
                Learning new languages (was: checking if a list is empty) Teemu Likonen <tlikonen@iki.fi> - 2011-05-12 06:37 +0300
                Re: checking if a list is empty Chris Torek <nospam@torek.net> - 2011-05-11 19:05 +0000
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-11 21:42 +0000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:23 +0100
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-11 10:31 -0600
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:46 +0100
            Re: checking if a list is empty "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-05-11 10:33 -0400
              Re: checking if a list is empty Redcat <redcat@catfolks.net> - 2011-05-11 15:31 +0000
              Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-11 18:44 +0100
              Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 16:24 -0500
                Re: checking if a list is empty alex23 <wuwei23@gmail.com> - 2011-05-11 20:31 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-11 22:53 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-12 06:13 +0000
                Re: checking if a list is empty "rurpy@yahoo.com" <rurpy@yahoo.com> - 2011-05-12 10:42 -0700
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 14:41 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-13 14:21 -0600
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 19:48 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-13 19:52 -0600
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-13 23:47 -0500
                Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-14 00:14 -0600
                Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-14 14:32 +1200
                Re: checking if a list is empty Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-14 14:26 +1200
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:13 +0100
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-12 16:46 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 08:28 +0100
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-12 17:37 +1000
                Re: checking if a list is empty "D'Arcy J.M. Cain" <darcy@druid.net> - 2011-05-12 01:49 -0400
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 07:21 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 22:16 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-12 13:43 +0100
                Re: checking if a list is empty Chris Angelico <rosuav@gmail.com> - 2011-05-12 23:20 +1000
                Re: checking if a list is empty Hans Georg Schaathun <hg@schaathun.net> - 2011-05-13 09:47 +0100
        Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-08 14:07 +0000
          Re: checking if a list is empty Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2011-05-08 18:59 +0300
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-08 18:41 -0400
          Re: checking if a list is empty Michael Torrie <torriem@gmail.com> - 2011-05-08 21:31 -0600
          Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-08 22:33 -0500
            Re: checking if a list is empty Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-08 22:34 -0600
              Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 16:58 -0500
                Re: checking if a list is empty Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-09 23:34 +0000
                Re: checking if a list is empty Ben Finney <ben+python@benfinney.id.au> - 2011-05-10 09:54 +1000
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 19:10 -0500
                Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-09 19:19 -0500
            Re: checking if a list is empty James Mills <prologic@shortcircuit.net.au> - 2011-05-09 14:46 +1000
          Re: checking if a list is empty harrismh777 <harrismh777@charter.net> - 2011-05-08 22:56 -0500
          Re: checking if a list is empty Terry Reedy <tjreedy@udel.edu> - 2011-05-09 17:30 -0400
          Re: checking if a list is empty Chris Torek <nospam@torek.net> - 2011-05-12 03:49 +0000

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