[Haskell-cafe] about GADTs on ghci

i have seen the documents in http://www.haskell.org/haskellwiki/Generalised_algebraic_datatype but i can not run the following code on ghci ex: data Term x where K :: Term (a -> b -> a) S :: Term ((a -> b -> c) -> (a -> b) -> a -> c) Const :: a -> Term a (:@) :: Term (a -> b) -> (Term a) -> Term b infixl 6 :@ could any tell me how to run the code? Thanks a lot