From: "João Távora" <joaotavora@gmail.com>
To: Drew Adams <drew.adams@oracle.com>
Cc: 33998@debbugs.gnu.org, Deus Max <deusmax@gmx.com>
Subject: bug#33998: 27.0.50; cl-delete does not delete the first list element
Date: Tue, 08 Jan 2019 21:38:17 +0000 [thread overview]
Message-ID: <87muoaltiu.fsf@gmail.com> (raw)
In-Reply-To: <bc7ef6c0-2cc5-4b13-b40b-7f7368abd586@default> (Drew Adams's message of "Tue, 8 Jan 2019 11:07:03 -0800 (PST)")
Drew Adams <drew.adams@oracle.com> writes:
> It's not about implementation of `cl-delete'. It's
> not about the type of sequence you pass it. It's
> about a variable being something different from its
> value.
Drew, it is you who are missing something basic here:
(defun mistery (thing seq)
(let ((head (elt seq 0)))
(cl-delete thing seq)
(eq head (elt seq 0))))
Today, in Emacs this always returns t, for every THING and sequence SEQ
you can think of (in fact, for vectors, cl-delete delegates to cl-remove).
This is perfectly CL-compliant. But a future, different, also perfectly
CL-compliant, implementation of cl-delete, might very well make this
function return nil. In fact, if you port this code to SBCL or Allegro
CL by changing 'cl-delete' to 'cl:delete'
(mistery 1 (list 1 2 3 4)) ;; => t
(mistery 1 (vector 1 2 3 4)) ;; => nil
So again, for the nth time, it's a bad idea to rely on SEQ after calling
'cl-delete'.
João
next prev parent reply other threads:[~2019-01-08 21:38 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-06 13:30 bug#33998: 27.0.50; cl-delete does not delete the first list element Deus Max
2019-01-07 17:13 ` João Távora
2019-01-07 17:28 ` Drew Adams
2019-01-07 18:04 ` João Távora
2019-01-07 18:14 ` Drew Adams
2019-01-08 13:45 ` João Távora
2019-01-08 18:22 ` Drew Adams
2019-01-08 18:31 ` João Távora
2019-01-08 18:45 ` Drew Adams
2019-01-08 18:57 ` João Távora
2019-01-08 19:07 ` Drew Adams
2019-01-08 21:38 ` João Távora [this message]
2019-01-09 1:30 ` Drew Adams
2019-01-07 20:20 ` Deus Max
2019-01-07 20:27 ` Dmitry Gutov
2019-01-07 20:48 ` Deus Max
2019-01-07 21:06 ` João Távora
2019-01-07 22:46 ` Deus Max
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