{-# LANGUAGE UnicodeSyntax #-}
module Tuple where





data Tree a = Leaf | Node (Tree a) a (Tree a) deriving Show

labelTree ∷ Tree a → Tree Int
labelTree t = fst $ labelTreeW t 0

labelTreeW ∷ Tree a → Int → (Tree Int, Int)
labelTreeW Leaf counter = (Leaf, counter)
labelTreeW (Node l _ r) counter = let
		(l', counterL) = labelTreeW l counter
		counterN       = counterL + 1
		(r', counterR) = labelTreeW r counterN
	in (Node l' counterN r', counterR)