instance Data a => Data (Bag a) where
gfoldl k z b = z listToBag `k` bagToList b -- traverse abstract type abstractly
toConstr _ = abstractConstr $ "Bag("++show (typeOf (undefined::a))++")"
instance Data a => Data (Bag a) where
gfoldl k z b = z listToBag `k` bagToList b -- traverse abstract type abstractly
toConstr _ = abstractConstr $ "Bag("++show (typeOf (undefined::a))++")"