f :: Eq a => a -> a
rather than
f :: (Eq a) => a -> a
forall_part = ptext (sLit "forall") <+> interppSP tvs <> dot
pprHsContext :: (OutputableBndr name) => HsContext name -> SDoc
forall_part = ptext (sLit "forall") <+> interppSP tvs <> dot
pprHsContext :: (OutputableBndr name) => HsContext name -> SDoc
-pprHsContext [] = empty
-pprHsContext cxt = ppr_hs_context cxt <+> ptext (sLit "=>")
+pprHsContext [] = empty
+pprHsContext [L _ pred]
+ | noParenHsPred pred = ppr pred <+> ptext (sLit "=>")
+pprHsContext cxt = ppr_hs_context cxt <+> ptext (sLit "=>")
+
+noParenHsPred :: HsPred name -> Bool
+-- c.f. TypeRep.noParenPred
+noParenHsPred (HsClassP {}) = True
+noParenHsPred (HsEqualP {}) = True
+noParenHsPred (HsIParam {}) = False
ppr_hs_context :: (OutputableBndr name) => HsContext name -> SDoc
ppr_hs_context [] = empty
ppr_hs_context :: (OutputableBndr name) => HsContext name -> SDoc
ppr_hs_context [] = empty
pprTheta theta = parens (sep (punctuate comma (map pprPred theta)))
pprThetaArrow :: ThetaType -> SDoc
pprTheta theta = parens (sep (punctuate comma (map pprPred theta)))
pprThetaArrow :: ThetaType -> SDoc
-pprThetaArrow theta
- | null theta = empty
- | otherwise = parens (sep (punctuate comma (map pprPred theta))) <+> ptext (sLit "=>")
+pprThetaArrow [] = empty
+pprThetaArrow [pred]
+ | noParenPred pred = pprPred pred <+> ptext (sLit "=>")
+pprThetaArrow preds = parens (sep (punctuate comma (map pprPred preds))) <+> ptext (sLit "=>")
+
+noParenPred :: PredType -> Bool
+-- A predicate that can appear without parens before a "=>"
+-- C a => a -> a
+-- a~b => a -> b
+-- But (?x::Int) => Int -> Int
+noParenPred (ClassP {}) = True
+noParenPred (EqPred {}) = True
+noParenPred (IParam {}) = False
------------------
instance Outputable Type where
------------------
instance Outputable Type where