tmap

tmap :: ( a -> b ) -> ( Tree a -> Tree b )
tmap f t = case t of
    Leaf -> Leaf
    Node {} -> 
        Node { key   = f (key t)
             , left  = tmap f (left t)
             , right = tmap f (right t)
             }

Aufgabe: probieren Sie tmap odd ( make [4,1,6,3] )