🚀 go-pugleaf

btoben@crappie.usd.edu (B. Toben) writes:


>Hi - 
Hi back to you
>I know precious little about prolog, but I have an assignment due in prolog
>to solve a problem.  I've gone to the instructor about it, but she doesn't
>seem too concerned, so I was hoping for a little help.  The problem is that
>when I have a clause like

>			drives(mike,X) :- X <> "camaro".

>I get an error if I state a goal like     drives(mike,Z)    because 
>Turbo Prolog says it has nothing to compare against "camaro".  I understand
^^^^^^^^^^^^^ Include standard statements about Turbo Prolog not being prolog
>why I get the error, but my question is, is there a way around it, using that
>general logic?

I don't know about Turbo Prolog but in normal prolog you would say:
drives(mike,X) :- '\+'(X = 'camaro').
	or
drives(mike,camaro) :- !,fail.
drives(mike,_).

Which would give no answers to you question. A better solution would be:

drives(mike,X) :- car(X), X <> "camaro". /* if this is correct syntax */

This would ensure that mike is driving cars and X is instantiated before
the test. Your query would result in listing all the cars except camaro
upon backtracking.
(ofcourse the predicate car/1 must be declared!)

Arjen