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Re: 'length' function for lists and cons cells?
From: |
Mark Skilbeck |
Subject: |
Re: 'length' function for lists and cons cells? |
Date: |
Fri, 22 Mar 2013 07:27:50 +0000 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
It just doesn't make sense to talk about the length of a dotted
_pair_, a cons-cell: it has a car and a cdr.
On Fri, Mar 22, 2013 at 03:38:11AM +0100, Thorsten Jolitz wrote:
> "Pascal J. Bourguignon" <pjb@informatimago.com> writes:
>
> > I don't understand what you want to do.
>
> well, avoid the errors I get when mapping alists with true lists and
> cons cells as elements with functions like 'lenght of 'cdr etc.
>
> > You can use length and dolist on alists and it will work perfectly:
> > (length '((a . 1) (b . 2) (c . 3)))
> > --> 3
>
> yes, but, when mapping the elements:
>
> ,------------------------------------------------------------
> | (length '(a . 1))
> |
> | Debugger entered--Lisp error: (wrong-type-argument listp 1)
> | length((a . 1))
> `------------------------------------------------------------
>
> > (dolist (entry '((a . 1) (b . 2) (c . 3)))
> > (destructuring-bind (key . value) entry
> > (insert (format "key = %S, value = %S\n" key value))))
> > key = a, value = 1
> > key = b, value = 2
> > key = c, value = 3
>
> I wasn't aware of destructuring-bind, thats cl stuff - had to look it up here:
> http://dto.github.com/notebook/require-cl.html#sec-6-6
>
> > If you want to count the cons cells, then why stop at the
> > dotted-lists? There are also circular lists. See how you can do it at:
> > https://gitorious.org/com-informatimago/com-informatimago/blobs/master/common-lisp/cesarum/list.lisp#line303
>
> ok, thanks for the hint.
>
- Re: 'length' function for lists and cons cells?, (continued)
- RE: 'length' function for lists and cons cells?, Drew Adams, 2013/03/21
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- Re: 'length' function for lists and cons cells?, Pascal J. Bourguignon, 2013/03/21
- Re: 'length' function for lists and cons cells?, Thorsten Jolitz, 2013/03/21
- Re: 'length' function for lists and cons cells?,
Mark Skilbeck <=
- Re: 'length' function for lists and cons cells?, Thorsten Jolitz, 2013/03/22
- Message not available
- Re: 'length' function for lists and cons cells?, Pascal J. Bourguignon, 2013/03/23
- RE: 'length' function for lists and cons cells?, Drew Adams, 2013/03/23
- Message not available
- Re: 'length' function for lists and cons cells?, Pascal J. Bourguignon, 2013/03/23
- RE: 'length' function for lists and cons cells?, Drew Adams, 2013/03/24
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