• simonpj's avatar
    [project @ 2004-08-18 09:33:03 by simonpj] · 370765b2
    simonpj authored
    		Fix a fundep bug
    Big thank-you to Martin Sulzmann for finding this functional dependency bug.
    The new defn of FunDeps.Equation is:
    	type Equation = (TyVarSet, [(Type, Type)])
    Before it was (TyVarSet, Type, Type), so each pair of types was separately
    quantified (wrong).
    It's important that we have a *list* of pairs of types.  Consider
     	class C a b c | a -> b c where ...
    	instance C Int x x where ...
    Then, given the constraint (C Int Bool v) we should improve v to Bool,
    via the equation ({x}, [(Bool,x), (v,x)])
    This would not happen if the class had looked like
    	class C a b c | a -> b, a -> c
    Test in typecheck/should_compile/tc180