From: Florian Beck <abstraktion@t-online.de>
To: help-gnu-emacs@gnu.org
Subject: Re: Problem with position and find (cl)
Date: Fri, 20 Jun 2008 22:14:05 +0200 [thread overview]
Message-ID: <87hcbng8z6.fsf@sophokles.streitblatt.de> (raw)
In-Reply-To: 6c2gf4F3eltftU1@mid.individual.net
Marc Tfardy <m-t-o___CUT__IT@web.de> writes:
> Marc Tfardy schrieb:
>> I try with:
>> (member '(2) '((1) (2) (3) (4)))
`member' tests the components: ›2‹ ist always equal (in the sense of »eq«) to ›2‹
Compare:
(memq '(2) '((1) (2) (3) (4)))
(eq 2 2)
(eq '(2) '(2))
>>
>> and this gives a expectet results ((2) (3) (4)), but:
>> (find '(2) '((1) (2) (3) (4)))
>> or
>> (position '(2) '((1) (2) (3) (4)))
>>
>> returns nil. Why?
Because the first and the second »(2)« have the same components but are
*different* lists.
> But this works:
>
> (position '(2) '((1) (2) (3) (4)) :test (lambda (x y) (eq (car x) (car
> y))))
>
> Maybe position and find (and maybe some others functions)
> can not compare lists directly?
They can, but again, the elements are not identical. Compare:
(let* ((x '((1) (2) (3) (4)))
(y (cadr x))
(z '(2)))
(message "x: %s; y:%s" (position y x) (position z x)))
y ist the same object as the cadr of x, z is an entirely new object that
happens to have the same component.
>
> Marc
--
Florian Beck
next prev parent reply other threads:[~2008-06-20 20:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-20 18:30 Problem with position and find (cl) Marc Tfardy
2008-06-20 19:58 ` Marc Tfardy
2008-06-20 20:14 ` Florian Beck [this message]
2008-06-20 21:24 ` Thierry Volpiatto
[not found] ` <mailman.13619.1213996704.18990.help-gnu-emacs@gnu.org>
2008-06-20 23:14 ` Florian Beck
2008-06-21 2:04 ` Barry Margolin
2008-06-21 4:31 ` Florian Beck
2008-06-21 4:57 ` Thierry Volpiatto
2008-06-21 10:07 ` Marc Tfardy
2008-06-21 10:38 ` Marc Tfardy
2008-06-21 12:38 ` Thierry Volpiatto
2008-06-20 21:16 ` Thien-Thi Nguyen
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