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From: Drew Adams <drew.adams@oracle.com>
To: Nicolas Petton <nicolas@petton.fr>,
	Stefan Monnier <monnier@iro.umontreal.ca>,
	Mark Oteiza <mvoteiza@udel.edu>
Cc: emacs-devel@gnu.org
Subject: RE: seq-some-p and nil
Date: Mon, 7 Sep 2015 01:06:51 -0700 (PDT)	[thread overview]
Message-ID: <674102d7-0e97-478a-af05-ca6d82c17c28@default> (raw)
In-Reply-To: <878u8i69ok.fsf@petton.fr>

> >> I also liked seq-some-p returning the matching element over cl-some
> >> returning the value returned by the predicate.
> >
> > But if the matched element is nil ...
> 
> If the function is not supposed to return non-nil if an element is
> matched but the element itself, then would it be ok? OTOH there would be
> again no way to differentiate between no element found and nil being
> found in the sequence.

1. That's too big a weakness.  It means that `seq-some' cannot
be used as a predicate.  (Again, lose the suffix `-p' if the
return value is important as something other than a Boolean.)

2. You can return both the sequence element and the value of the
predicate applied to it, as a cons: (ELEMENT . VALUE).

If the element is nil then the return value is (nil . VALUE).

That gives you both kinds of info, at the cost of a cons and
the trouble to dig out what you need from the cons.

3. If you never care about the VALUE, you could just return a
cons with the sequence element.  For nil the return value
would then be (nil).

#2 sounds reasonable.



  reply	other threads:[~2015-09-07  8:06 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-03 15:50 seq-some-p and nil Simen Heggestøyl
2015-09-03 16:42 ` Stefan Monnier
2015-09-03 17:19   ` Artur Malabarba
2015-09-03 17:35     ` John Mastro
2015-09-03 17:50       ` Drew Adams
2015-09-03 19:36         ` Nicolas Petton
2015-09-03 19:45       ` Nicolas Petton
2015-09-06  1:17         ` Mark Oteiza
2015-09-06 20:48           ` Nicolas Petton
2015-09-06 21:46           ` Stefan Monnier
2015-09-07  6:11             ` Nicolas Petton
2015-09-07  8:06               ` Drew Adams [this message]
2015-09-07 15:19                 ` Stefan Monnier
2015-09-07 15:23                   ` Mark Oteiza
2015-09-07 17:08                   ` Drew Adams
2015-09-07 20:44                   ` Nicolas Petton
2015-09-07 22:27                     ` Stefan Monnier
2015-09-08  7:09                       ` Nicolas Petton
2015-09-08 12:36                         ` Stefan Monnier
2015-09-08 13:07                           ` Nicolas Petton
2015-09-08 16:49                             ` Stefan Monnier
2015-09-08 17:01                               ` David Kastrup
2015-09-08 17:08                                 ` Drew Adams
2015-09-08 19:02                                   ` Nicolas Petton
2015-09-08 19:48                                     ` Drew Adams
2015-09-09  7:56                                       ` Nicolas Petton
2015-09-09 13:26                                         ` Drew Adams
2015-09-09 17:45                                           ` Stefan Monnier
2015-09-09 17:53                                             ` Drew Adams
2015-09-09 20:24                                               ` Stefan Monnier
2015-09-09 20:46                                                 ` Drew Adams
2015-09-09 21:44                                           ` Nicolas Petton
2015-09-08 18:43                                 ` Stefan Monnier
2015-09-08 19:03                                   ` David Kastrup
2015-09-08 18:59                               ` Nicolas Petton
2015-09-08 19:06                                 ` David Kastrup
2015-09-08 20:33                                 ` Stefan Monnier
2015-09-09  7:57                                   ` Nicolas Petton
2015-09-08 13:21                           ` Nicolas Petton
2015-09-08 13:37                             ` Mark Oteiza
2015-09-08 17:50                               ` Stefan Monnier
2015-09-09  2:19                                 ` Mark Oteiza
2015-09-09  4:28                                   ` Stephen J. Turnbull
2015-09-09  4:57                                     ` Mark Oteiza
2015-09-07 20:45                   ` Nicolas Petton
2015-09-03 19:40 ` Nicolas Petton
2015-09-10 17:46   ` Simen Heggestøyl
2015-09-10 22:12     ` Nicolas Petton
2015-09-22 17:17       ` Simen Heggestøyl
2015-09-23  8:38         ` Nicolas Petton
2015-09-23  8:44           ` David Kastrup
2015-09-23  8:48           ` Simen Heggestøyl
2015-09-23 10:57             ` Nicolas Petton
2015-09-28 19:17         ` Nicolas Petton

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