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

martin martin.drautzburg at web.de
Sun Jul 10 09:55:31 UTC 2016

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

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