From: Teemu Likonen <tlikonen@iki.fi>
To: Xue Fuqiao <xfq.free@gmail.com>
Cc: help-gnu-emacs@gnu.org
Subject: Re: About Circular Objects
Date: Tue, 25 Dec 2012 16:52:27 +0200 [thread overview]
Message-ID: <87ip7q2nh0.fsf@mithlond.arda> (raw)
In-Reply-To: <20121225165249.e5822f6cc71fa88d959efcd0@gmail.com> (Xue Fuqiao's message of "Tue, 25 Dec 2012 16:52:49 +0800")
Xue Fuqiao [2012-12-25 16:52:49 +0800] wrote:
> I have a question about the #N# read syntax and #N= syntax. Look at
> this code:
>
> (progn
> (setq x '#1=(a #1#))
> (eq x (cdr x)))
>
> Why does this code return nil? Isn't the second element the list
> itself?
No. It's the CAR of the second cons cell that points to the list itself.
If you want the CDR of the first (and only) cons cell to point back to
the cons cell, you would use this:
(progn
(setq x '#1=(a . #1#)) ; Note the dotted list.
(eq x (cdr x)))
=> t
next prev parent reply other threads:[~2012-12-25 14:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-25 8:52 About Circular Objects Xue Fuqiao
2012-12-25 14:52 ` Teemu Likonen [this message]
[not found] <mailman.16090.1356446630.855.help-gnu-emacs@gnu.org>
2012-12-25 14:48 ` Lars Magne Ingebrigtsen
2012-12-25 14:51 ` Pascal J. Bourguignon
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