[Haskell-cafe] What's wrong in my Data.Generic.Zipper code?

Hello all, I do not understand why this simple piece of code returns Nothing instead of [1,2,3]. Can anybody help? {-# LANGUAGE BangPatterns,NoMonomorphismRestriction, DeriveDataTypeable #-} import Data.Typeable import Data.Data import Data.Generics.Zipper ex_list1 :: [Int] ex_list1 = [1,2,3] t1 = toZipper ex_list1 -- *Main> getHole t1 -- Nothing