pprPred :: PredType -> SDoc
pprPred (ClassP cls tys) = pprClassPred cls tys
pprPred (IParam ip ty) = ppr ip <> dcolon <> pprType ty
-pprPred (EqPred ty1 ty2) = sep [ppr ty1, nest 2 (ptext (sLit "~")), ppr ty2]
+pprPred (EqPred ty1 ty2) = sep [ ppr_type FunPrec ty1
+ , nest 2 (ptext (sLit "~"))
+ , ppr_type FunPrec ty2]
+ -- Precedence looks like (->) so that we get
+ -- Maybe a ~ Bool
+ -- (a->a) ~ Bool
+ -- Note parens on the latter!
pprClassPred :: Class -> [Type] -> SDoc
pprClassPred clas tys = ppr_type_app TopPrec (getName clas) tys