{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE RankNTypes #-}

type RelayHandler = forall i . Typeable i => (i -> SubscriptionId -> Event -> i)

data RelayPool = RelayPool [Relay] (Map SubscriptionId RelayHandler)

{-
    • Illegal polymorphic type:
        forall i. Typeable i => i -> SubscriptionId -> Event -> i
      GHC doesn't yet support impredicative polymorphism
    • In the expansion of type synonym ‘RelayHandler’
      In the definition of data constructor ‘RelayPool’
      In the data type declaration for ‘RelayPool’
-}