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I am trying to build a simple greatest common divisor (cmmdc) in prolog and, for the following code, I get a fail on newY = X mod Y. Can anyone help me out?

% cmmdc(X: intreg, Y: intreg, Ret: intreg)
% (i, i, o), (i, i, i)

cmmdc(X, 0, X):- !.
cmmdc(X, Y, Ret):-
    newY = X mod Y,
    cmmdc(Y, newY, Ret).
TessellatingHeckler
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Radu Andrei Vaida
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1 Answers1

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newY starts with a lowercase letter, so it is an atom instead of a varaible.

= is unification, not arithmetic.

The atom newY is not the same as the term mod(X,Y) so unification fails.

Use NewY is X mod Y instead.

TessellatingHeckler
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