From: Michael Heerdegen <michael_heerdegen@web.de>
To: help-gnu-emacs@gnu.org
Subject: Re: How does letf work?
Date: Thu, 30 Jan 2014 00:53:43 +0100 [thread overview]
Message-ID: <87mwie2vlk.fsf@web.de> (raw)
In-Reply-To: slrnlehfeo.6e2.joost.m.kremers@j.kremers4.news.arnhem.chello.nl
Joost Kremers <joost.m.kremers@gmail.com> writes:
> (letf (((cdr test-x) '(a b c d)))
> (cdr test-x))
>
> = > (KEY a b c d)
>
> Taking what you say at face value, one might expect that at the moment
> the value of (cdr test-x) is printed, it's already been changed back to
> the original value, so it should say (KEY 1 2 3 4), but it doesn't.
(cdr test-x) here references an object being a list equal to '(a b c d).
But after the letf has been left, that object is not anymore the cdr of
test-x, because its cdr has been restored. But that doesn't make the
return value "switch" to a different object.
The analogy with boxes is very helpful here.
Michael.
next prev parent reply other threads:[~2014-01-29 23:53 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-28 23:10 How does letf work? Florian Beck
2014-01-29 2:23 ` Michael Heerdegen
[not found] ` <mailman.13075.1390962244.10748.help-gnu-emacs@gnu.org>
2014-01-29 8:37 ` Joost Kremers
2014-01-29 9:14 ` Joost Kremers
2014-01-29 15:29 ` Florian Beck
2014-01-29 16:12 ` Nicolas Richard
2014-01-29 20:19 ` Florian Beck
2014-01-29 15:06 ` Nicolas Richard
2014-01-29 23:46 ` Michael Heerdegen
2014-01-29 23:53 ` Michael Heerdegen [this message]
[not found] <mailman.13065.1390951154.10748.help-gnu-emacs@gnu.org>
2014-01-29 0:35 ` Emanuel Berg
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