[Small-cl-src] RE: a Clisp problem (Xie Wen Sheng)

5 Dec 2005

      Hi, All:

I got a solution from comp.lang.lisp:

Pascal Bourguignon:
(DEFUN COMBINE (ARGS)
  "
RETURN:  (elt args 0) x (elt args 1) x ... x (elt args (1- (length args)))
         = the set of tuples built taking one item in order from each list
           in args.
EXAMPLE: (COMBINE '((WWW FTP) (EXA) (COM ORG)))
           --> ((WWW EXA COM) (WWW EXA ORG) (FTP EXA COM) (FTP EXA ORG))
"
  (COND
   ((NULL ARGS) '(NIL))
   ((NULL (CAR ARGS)) (COMBINE (CDR ARGS)))
   ((CONSP (CAR ARGS))
    (MAPCAN (LAMBDA (ITEM) (COMBINE (cons ITEM (CDR ARGS))))
            (CAR ARGS)))
   (T
    (MAPCAN (LAMBDA (REST) (LIST (CONS (CAR ARGS) REST)))
            (COMBINE (CDR ARGS)))))) 

Tron3k:
(defun combine (lst)
    (if (endp lst)
        (list '())
        (loop with crest = (combine (rest lst))
              for item in (first lst)
              nconc (loop for items in crest
                          collect (cons item items))))) 

Thank you all.

XIE Wensheng

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Today's Topics:

   1. a Clisp problem (Xie Wen Sheng)

----------------------------------------------------------------------

Message: 1
Date: Mon, 28 Nov 2005 16:22:54 +0800
From: "Xie Wen Sheng" <wen-sheng.xie@thomson.net>
Subject: [Small-cl-src] a Clisp problem
To: <small-cl-src@hexapodia.net>
Message-ID:
	<CE1F1B158B2B1C4080BA3F114B158B5B019013@szntsmail01.ap.thmulti.com>
Content-Type: text/plain;	charset="iso-8859-1"

Hi ,All

I'm new to lisp, using GNU Clisp.

I have a problem when I do some Lisp programming training.

For example, for the list (a (b1 b2) c (d1 d2) (e1 e2 e3) f), I need a function to return all the possible combinations like:
((a b1 c d1 e1 f)
(a b1 c d1 e2 f)
(a b1 c d1 e3 f)
(a b1 c d2 e1 f)
(a b1 c d2 e2 f)
(a b1 c d2 e3 f)
(a b2 c d1 e1 f)
(a b2 c d1 e2 f)
(a b2 c d1 e3 f)
(a b2 c d2 e1 f)
(a b2 c d2 e2 f)
(a b2 c d2 e3 f))

My tries trended to be unsuccessful. Is it too easy to ask this here? If so, where is the forum for people like me?

best regards,

XIE Wensheng

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