[Haskell-cafe] Parameterize constraints of existentially quantified types

Hi, I just found out that with the new ConstraintKinds extension we can parameterize the constraint of an existentially quantified type: {-# LANGUAGE KindSignatures, ConstraintKinds, ExistentialQuantification #-} import GHC.Exts data Some (c :: * -> Constraint) = forall a. c a => Some a This could be used to define SomeException for example: import Control.Exception (Exception) type SomeException = Some Exception Are there any other use cases? Bas