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


-- | Assuming that 0 won't occur
-- Find maximum value in a tree
maxOfTree :: Tree Int -> Int
maxOfTree Empty        = 0
maxOfTree (Node l x r) = max x (max (maxOfTree l) (maxOfTree r))

-- | Replace all elements in a tree with a value
replaceElems :: Tree Int -> Int -> Tree Int
replaceElems Empty        x = Empty
replaceElems (Node l _ r) x = Node (replaceElems l x) x (replaceElems r x)

-- | Replace all elements in a tree with its maximum value
maxT :: Tree Int -> Tree Int
maxT t = replaceElems t (maxOfTree t)


sampleTree = Node (Node Empty 2 Empty) 3 (Node Empty 4 Empty)
rv = maxT sampleTree
-- Node (Node Empty 4 Empty) 4 (Node Empty 4 Empty)