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From: vinson@linc.cis.upenn.edu (Jack Vinson)
Newsgroups: comp.lang.lisp
Subject: messing with lists
Message-ID: <43991@netnews.upenn.edu>
Date: 31 May 91 21:23:24 GMT
Sender: news@netnews.upenn.edu
Reply-To: vinson@linc.cis.upenn.edu (Jack Vinson)
Organization: University of Pennsylvania
Lines: 36
Nntp-Posting-Host: linc.cis.upenn.edu


Hi Folks, again, (can you tell I'm doing a lot of hacking?)

I will try to describe my problem by example:

Start with
(setq my-list '((a b c d e f)))

Find out how many sets of data I will be playing with and end up with
my list looking like (for five sets of data)
((a b c d e f) (a b c d e f) (a b c d e f) (a b c d e f) (a b c d e f))

I wanted to set up a separate function to do this because there are a couple
different lists to which this applies.

I tried using this 
(defun fill-list (n form)
  (do ((i 1 (1+ i)))
      ((= i n) form)
      (setf form (append (list (car form)) form))))

(setf my-list (fill-list 5 my-list))

Which appears to work until I try setf on various elements in the sublists.  I
guess fill-list retains pointers, cuz when I (setf (nth 3 (car my-list)) 'x)
all of the d's get changed rather than just the one in the first sublist.


Does this make any sense.  I don't know at the start how many copies of the
list I will want, otherwise I would just make the initial setq of the correct
size.

Thanks for help on previous questions and this one and those to come....


Jack Vinson				vinson@linc.cis.upenn.edu