data BinTree a = Node a (BinTree a) (BinTree a)
               | Empty
               deriving (Eq, Show)

treeFold :: (a -> b -> b -> b) -> b -> BinTree a -> b
treeFold n e (Node v l r) = n v (treeFold n e l)
                                (treeFold n e r)
treeFold n e Empty        = e

tree01 :: BinTree Int
tree01 = Node 2 (Node 3 (Node 5 Empty Empty) Empty)
                (Node 4 (Node 1 Empty Empty) (Node 1 Empty Empty))

tree02 :: BinTree String
tree02 = Node "C" (Node "A" Empty (Node "B" Empty Empty))
                  (Node "E" (Node "D" Empty Empty) Empty)

tree03 :: BinTree (Int,Int)
tree03 = Node (3,3) (Node (2,1) Empty Empty) (Node (1,1) Empty Empty)

tree04 :: BinTree a
tree04 = Empty

tree05 :: BinTree Bool
tree05 = Node False (Node False Empty (Node True Empty Empty))
                    (Node False Empty Empty)

tree06 :: BinTree (Int, Int -> Bool)
tree06 = Node (0,even)
              (Node (1,odd) (Node (2,(== 1)) Empty Empty) Empty)
              (Node (3,(< 5)) Empty
                              (Node (4,((== 0) . mod 12)) Empty Empty))