ListZipper duplicate

ListZipper.hs

-- duplicate $ ListZipper (2:.1:.Nil) 3 (4:.5:.Nil)
-- [[1] >2< [3,4,5],[] >1< [2,3,4,5]] >[2,1] >3< [4,5]< [[3,2,1] >4< [5],[4,3,2,1] >5< []]

-- data ListZipper a = ListZipper [a] a [a]
duplicate :: ListZipper a -> ListZipper (ListZipper a)
duplicate z@(ListZipper l i r) =
  let moveLeft (x :. xs) i rs = ListZipper xs x (i :. rs) :. moveLeft xs x (i :. rs)
      moveLeft Nil _ _ = Nil
      moveRight ls i (x :. xs) = ListZipper (i :. ls) x xs :. moveRight (i :. ls) x xs
      moveRight _ _ Nil = Nil
      l' = moveLeft l i r
      r' = moveRight l i r
   in ListZipper l' z r'