Instability of standard order

Request For Comments
2

I found compare/3 to be disappointingly illogical as a learner :grinning_face:

Exceptions are a last resort, for when there are no other reasonable actions… how about, for a point-in-time comparison:

compare_sound(C, X, Y) :-
    (   X \= Y
    ->  compare(S, X, Y),
        % Will be < or > sign
        C = comp(S)
    ;   X == Y
    ->  C = comp(=)
        % Insufficiently instantiated for sound comparison
    ;   C = insuf
    ).

Results:

?- compare_sound(C, A, A).
C = comp(=).

?- compare_sound(C, b(_), a(_)).
C = comp(>).

?- compare_sound(C, A, B).
C = insuf.

I think these results would be the least surprising for a learner.