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From: booter@lll-crg.ARpA (Elaine Richards)
Newsgroups: net.ai,net.lang.prolog
Subject: HELP!!!!!
Message-ID: <1465@lll-crg.ARpA>
Date: Wed, 14-May-86 05:00:11 EDT
Article-I.D.: lll-crg.1465
Posted: Wed May 14 05:00:11 1986
Date-Received: Thu, 15-May-86 07:22:03 EDT
Organization: The Booban Renewal Department
Lines: 24
Xref: linus net.ai:3216 net.lang.prolog:662

I have been given this silly assignment to do in Prolog, a language which
is rapidly losing my favor. We are to do the folowing:

Define a Prolog predicate len(N,L) such that N is the length of list L.

Define a Prolog predicate nth(X,N,L) such that X is the Nth element of
list L.

I cannot seem to instantiate N past the value 0 on any of these.

My code looks like this:

len(N,[]) :- 0 !.
len(N,[_|Y] :- N! is N + 1,len(N1,L].

It gives me an error message indicating "_6543etc" or somesuch ghastly 
number/variable refuses to take the arithmetic operation.

The code for nth is similar and gives a similar error message.

Please send replies to {whateverthepathis}lll-crg!csuh!booter.

E
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