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

[martin]

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