-- This comparison is used exclusively (I think) for the
-- finite map built in TcSimplify
cmpPredX env (ClassP c1 tys1) (ClassP c2 tys2) = (c1 `compare` c2) `thenCmp` cmpTypesX env tys1 tys2
-cmpPredX env (IParam _ _) (ClassP _ _) = LT
-cmpPredX env (ClassP _ _) (IParam _ _) = GT
cmpPredX env (EqPred ty1 ty2) (EqPred ty1' ty2') = (cmpTypeX env ty1 ty1') `thenCmp` (cmpTypeX env ty2 ty2')
+
+-- Constructor order: IParam < ClassP < EqPred
+cmpPredX env (IParam {}) _ = LT
+cmpPredX env (ClassP {}) (IParam {}) = GT
+cmpPredX env (ClassP {}) (EqPred {}) = LT
+cmpPredX env (EqPred {}) _ = GT
\end{code}
PredTypes are used as a FM key in TcSimplify,