label_tree.hs

data Tree a = Tree a [Tree a] deriving Show

label :: Tree a -> Tree (a, Int)
label t = label' 1 t

label' :: Int -> Tree a -> Tree (a, Int)
label' i (Tree x []) = Tree (x, i) []
label' i (Tree x ts) =
        let 
        processed = goThrough i ts
        Tree (y, label) list = last processed
        in
    Tree (x, label+1) processed


goThrough :: Int -> [Tree a] -> [Tree (a, Int)]
goThrough _ [] = []
goThrough i (t:ts) =
    let 
        Tree (val, label) list = label' i t
    in
    [Tree (val, label) list] ++ goThrough (label+1) ts