Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!mcvax!ukc!eagle.ukc.ac.uk!jrc
From: jrc@ukc.ac.uk (J.R.G.Cupitt)
Newsgroups: comp.lang.lisp
Subject: Re: permutations
Message-ID: <5671@eagle.ukc.ac.uk>
Date: 24 Oct 88 02:57:24 GMT
Article-I.D.: eagle.5671
References: <1131@amelia.nas.nasa.gov>
Reply-To: jrc@ukc.ac.uk (J.R.Cupitt)
Organization: Computing Lab, University of Kent at Canterbury, UK.
Lines: 22

In article <1131@amelia.nas.nasa.gov> raible@orville.nas.nasa.gov (Eric L. Raible) writes:
}(defun permutations (elements)
}  (if (null elements)
}      (list nil)
}      (mapcan
}       #'(lambda (element)
}	   (mapcar
}	    #'(lambda (permutation)
}		(cons element permutation))
}	    (permutations (remove element elements))))
}       elements)))
}
}Comments?  Alternatives?

Good grief! I almost collapsed when I saw this .. I realise that this is a
LISP group, but I can't resist posting the same algorithm in Miranda:

	perms :: [*] -> [[*]]
	perms x	= [[]], x = []
		= [ a:p | a <- x; p <- perms (x--[a]) ], otherwise

John Cupitt