Fold for rose tree zippers

gistfile1.txt

tzFold :: (a -> TreePos Full b -> a) -> a -> TreePos Full b -> a
tzFold f acc t =
  foldSiblings $ foldChildren $ f acc t
  where
    foldChildren acc' =
      case firstChild t of
        Just c  -> tzFold f acc' c
        Nothing -> acc'
    foldSiblings acc' =
      case next t of
        Just s  -> tzFold f acc' s
        Nothing -> acc'