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prologsyntax-erroriso-prolog

Once in SICStus Prolog?

How can I use once in SICStus? In SWI Prolog, the following works:

test(X, Y, abc) :- once(X == 'true' ; Y == 'true').

but in SICStus Prolog, once seems to be unrecognized. What is the equivalent of once in SICStus? Thank you.

Solution

  • The answer is:

    test(X, Y, abc) :- once((X == 'true' ; Y == 'true')).

    The additional parenthesis did the trick.