From: Marcin Borkowski <mbork@mbork.pl>
To: Help Gnu Emacs mailing list <help-gnu-emacs@gnu.org>
Subject: Why is booleanp defined this way?
Date: Fri, 17 Apr 2015 22:34:45 +0200 [thread overview]
Message-ID: <87siby7au6.fsf@mbork.pl> (raw)
Hi all,
this is what I found in subr.el:
,----
| (defun booleanp (object)
| "Return t if OBJECT is one of the two canonical boolean values: t or nil.
| Otherwise, return nil."
| (and (memq object '(nil t)) t))
`----
Seemingly, it doesn't make much sense: what is the purpose of saying
(and (whatever) t)
instead of just
(whatever)
for a predicate? Of course, this "normalizes" any "truthy" value to
"t", but is it really needed for anything (except perhaps being
elegant)?
Best,
--
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University
next reply other threads:[~2015-04-17 20:34 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-17 20:34 Marcin Borkowski [this message]
2015-04-17 20:49 ` Why is booleanp defined this way? Jorge A. Alfaro-Murillo
[not found] ` <mailman.962.1429303822.904.help-gnu-emacs@gnu.org>
2015-04-17 23:06 ` Emanuel Berg
2015-04-18 0:41 ` Pascal J. Bourguignon
2015-04-18 1:06 ` Emanuel Berg
2015-04-18 1:23 ` Pascal J. Bourguignon
2015-04-18 7:44 ` Marcin Borkowski
2015-04-18 8:37 ` Stefan Nobis
2015-04-19 23:15 ` Emanuel Berg
2015-04-18 2:37 ` Drew Adams
2015-04-18 6:13 ` Tassilo Horn
[not found] <mailman.946.1429302909.904.help-gnu-emacs@gnu.org>
2015-04-17 20:55 ` Pascal J. Bourguignon
2015-04-17 23:20 ` Barry Margolin
2015-04-17 23:30 ` Emanuel Berg
2015-04-18 0:43 ` Pascal J. Bourguignon
2015-04-18 3:13 ` Barry Margolin
2015-04-18 3:12 ` Barry Margolin
2015-04-18 2:01 ` Rusi
2015-04-18 2:23 ` Emanuel Berg
2015-04-18 2:33 ` Rusi
2015-04-18 2:55 ` Emanuel Berg
2015-04-18 3:11 ` Barry Margolin
2015-04-18 3:35 ` Rusi
2015-04-18 4:56 ` Barry Margolin
2015-04-19 23:08 ` Emanuel Berg
2015-04-19 23:00 ` Emanuel Berg
2015-04-18 21:24 ` Emanuel Berg
2015-04-18 7:52 ` Marcin Borkowski
[not found] ` <mailman.997.1429343558.904.help-gnu-emacs@gnu.org>
2015-04-18 12:43 ` Rusi
2015-04-18 4:09 ` Pascal J. Bourguignon
2015-04-18 5:00 ` Rusi
2015-04-18 3:50 ` Pascal J. Bourguignon
2015-04-18 5:03 ` Stefan Monnier
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