From: "rgb" <rbielaws@i1.net>
Subject: Re: sharing list structure
Date: 24 Mar 2005 17:01:29 -0800 [thread overview]
Message-ID: <1111712489.491757.194480@g14g2000cwa.googlegroups.com> (raw)
In-Reply-To: <mailman.173.1111709565.28103.help-gnu-emacs@gnu.org>
Joe Corneli wrote:
> I'm not sure how to do the following:
>
> I have a list A, that grows, shrinks, and changes.
>
> I want to have a list B that includes list A within
> its list structure, along with other things, and that
> automatically keeps the "A" part of itself in synch
> with A.
>
There will certainly be some kid gloves involved because most of
the normal things you might want to do with A are destructive or
subversive to any pointer B might hold. The reason is, B is a
symbol in an obarray that points to a list element. That list
element might have a CDR which points to the same list element
that A points to but a change to A list can never cause the
pointer held by some element in list B to change. So any
operation involving setq A will very likely cause the
corresponding pointer in list B to point to an obsolete location.
> Is there a way to accomplish this? And if it can't be done with
> list structure alone, what other suggestions can you make?
I'm pretty sure this is not what you are looking for since
the position of the contents of B within list A is fixed.
(defmacro a+b () '`(,@A ,@B)) ;or any number of similar things
(setq A '(a b c d))
(setq B '(1 2 3 4))
(a+b)
=> (a b c d 1 2 3 4)
(setq a '(w x y z))
(setq b '(9 8 7 6))
(a+b)
=> (w x y z 9 8 7 6)
To be honest, I can't think of a way to do what it seems you
want in *any* language. But maybe I don't really understand.
next parent reply other threads:[~2005-03-25 1:01 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.173.1111709565.28103.help-gnu-emacs@gnu.org>
2005-03-25 1:01 ` rgb [this message]
2005-03-25 1:42 ` sharing list structure Joe Corneli
[not found] ` <mailman.182.1111716692.28103.help-gnu-emacs@gnu.org>
2005-03-25 5:44 ` rgb
2005-03-25 5:49 ` rgb
2005-03-25 6:08 ` Joe Corneli
2005-03-24 23:48 Joe Corneli
2005-03-25 0:17 ` Denis Bueno
2005-03-25 0:27 ` Joe Corneli
2005-03-25 0:35 ` Denis Bueno
[not found] ` <mailman.176.1111711460.28103.help-gnu-emacs@gnu.org>
2005-03-25 1:21 ` Thien-Thi Nguyen
2005-03-26 23:58 ` Stefan Monnier
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