Quantified Constraints with a Multi-Param Type Class

quantified_mptc.hs

{-# language QuantifiedConstraints #-}
{-# language MultiParamTypeClasses #-}
{-# language UndecidableInstances #-}

module QuantifiedMptc where

import Data.Functor.Identity
import Data.Char

class Bar x where
  bar :: x -> Int

class Foo s a where
  foo :: s -> a -> Bool

instance (forall s. Foo s a, Show a) => Bar (Identity a) where
  bar (Identity x) = fromEnum (foo True x)

I just wanted to confirm that this compiled before I attempted to apply in to a real problem.