Fix pretty-printing precedence for equality constraints

diff --git a/compiler/types/TypeRep.lhs b/compiler/types/TypeRep.lhs
index c3bd746..5c29087 100644 (file)
--- a/compiler/types/TypeRep.lhs
+++ b/compiler/types/TypeRep.lhs
@@ -431,7 +431,13 @@ pprTypeApp tc tys = ppr_type_app TopPrec (getName tc) tys
 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