The doc page http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/kind-polymorphism-and... that lists are now usable as types. So I'm trying to make a type level function to test if a type list contains a type. Unless I'm wrong, that calls to the use of a type family. {-# LANGUAGE DataKinds, TypeOperators, KindSignatures, TypeFamilies #-} data HBool = HTrue | HFalse -- Mandatory as Bool type is not currently promoted to a kind type family Member x (l :: [*]) :: HBool type instance Member x (x ': xs) = HTrue type instance Member x (y ': xs) = Member x xs type instance Member x (y ': '[]) = HFalse But the compiler complains about my instance conflicting. Is what I'm trying to do feasible? Second question: how can type level tuples (also mentioned in the doc page) be exploited? Aren't they redundant with type-level lists?