Bounded Existential types in Haskell

BoundedExistentials.hs

{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE ConstraintKinds #-}

module BoundedExistentials where

import GHC.Exts (Constraint)

class Constraint1 c where
  type Constr1 c a :: Constraint

data SerializableC

instance Constraint1 SerializableC where
  type Constr1 SerializableC a = (Read a, Show a)

data Any c k = forall s. c s => Any (k s)
data Any' c' k = forall s. Constr1 c' s => Any' (k s)

test :: Any' SerializableC []
test = Any' [1,2,3]