treelabel.hs

data Tree a = Node a | Bend a (Tree a) | Branch a (Tree a) (Tree a) deriving Show


label :: Tree a -> Tree Int
label = undefined

labelfrom :: Int -> Tree a -> (Tree Int, Int)
labelfrom i (Node a) = (Node (i+1), i+1)
labelfrom i (Bend a t) = (Bend (j+1) lt, j+1)
    where
      (lt, j) = labelfrom i t
labelfrom i (Branch a t1 t2) = (Branch (j2+1) lt1 lt2, j2+1)
    where
      (lt1, j1) = labelfrom i t1
      (lt2, j2) = labelfrom j1 t2