From: kai.grossjohann@gmx.net (Kai Großjohann)
Subject: Re: LISP: Very Very Basic Question.
Date: Wed, 09 Apr 2003 15:59:49 +0200 [thread overview]
Message-ID: <84u1d793fu.fsf@lucy.is.informatik.uni-duisburg.de> (raw)
In-Reply-To: mailman.4322.1049863665.21513.help-gnu-emacs@gnu.org
Gurucharan <gurucharan.murudeshwar@wipro.com> writes:
> Can anyone explain the way in which the LISP "list"
>
> is implemented internally ?
The basic data structure is a cons cell. It is a pair consisting of
a car and a cdr. The car and the cdr can be numbers or strings etc,
or pointers to cons cells.
For example, (1 . 2) is a cons cell where the car is 1 and the cdr is
2.
You can build binary trees from cons cells:
( (1 . 2) . (3 . 4) )
This corresponds to the following tree:
*
/ \
* *
/ \ / \
1 2 3 4
There is a special value nil which means "empty", other languages use
the term "null".
A list is a degenerated binary tree, where the cars contain the list
elements, and the cdr points to the rest of the list. And nil means
the empty list. So (1 . nil) is a one-element list, and (1 . (2 .
nil)) is a two-element list, and (1 . (2 . (3 . nil))) is a
three-element list. The three-element list as a tree:
*
/ \
1 *
/ \
2 *
/ \
3 nil
--
A preposition is not a good thing to end a sentence with.
next prev parent reply other threads:[~2003-04-09 13:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-07 20:27 List Seperator Artist
2003-04-07 20:52 ` Johan Bockgård
2003-04-09 4:22 ` Artist
2003-04-09 4:53 ` LISP: Very Very Basic Question Gurucharan
[not found] ` <mailman.4322.1049863665.21513.help-gnu-emacs@gnu.org>
2003-04-09 13:50 ` lawrence mitchell
2003-04-09 13:59 ` Kai Großjohann [this message]
2003-04-09 15:04 ` List Seperator Johan Bockgård
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