T11459.hs:9:20: error:
    • A newtype constructor cannot have existential type variables
      Parser :: forall a {k}.
                (forall (f :: k -> *) (r :: k).
                 Failure f r -> Success a f r -> f r)
                -> Parser a
    • In the definition of data constructor ‘Parser’
      In the newtype declaration for ‘Parser’