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RE: 'length' function for lists and cons cells?
From: |
Drew Adams |
Subject: |
RE: 'length' function for lists and cons cells? |
Date: |
Thu, 21 Mar 2013 13:10:10 -0700 |
> which function could I use when I map an alist e.g. with dolist, that
> contains both types of associations as shown below: cons
> cells, or lists with 3 or more elements?
>
> 'length' doesn't work on cons cells:
>
> Debugger entered--Lisp error: (wrong-type-argument listp "c")
> length(("a" . "c"))
It's not clear to me what you're asking.
Are you looking for a "length" function that works for both true lists (but why
do you mention 3 or more elements?) and a cons whose last cdr is a non-nil atom?
If so then it is up to you to define what you want such a "length" to be/mean.
Perhaps what you want is something like this?
(defun thorsten-len (xs)
(cond ((null xs) 0)
((null (cdr xs)) 1)
((atom (cdr xs)) 2)
(t (1+ (thorsten-len (cdr xs))))))
(thorsten-len '(1 2 3 4 . 5)) => 5
(setq foo '((a . 1) (b 2) (c (3 3 3)) (d 4 4 4 . 4)))
(mapcar #'thorsten-len foo) => (2 2 2 5)
(setq bar ())
(dolist (ff foo) (push ff bar))
(reverse bar) => ((a . 1) (b 2) (c (3 3 3)) (d 4 4 4 . 4))
- 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, 2013/03/22
- 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