data Tree x = Leaf x
            | Node x [Tree x]
 
dfs tree limit
    | limit == 0 = []
    | otherwise  =
        case tree of
            Leaf x          -> [x]
            Node x children -> x : traverse children (limit - 1)
 
traverse children limit
    | limit == 0 = []
    | otherwise  =
        case children of
            []       -> []
            x : rest ->
                result ++ traverse rest (limit - length result)
                where result = dfs x limit
 
example_tree =
    Node 0 [
        Node 1 [Leaf 2, Leaf 3],
        Node 4 [Node 5 [Leaf 6]],
        Leaf 7
    ]
 
main = do
    print $ map (\limit -> dfs example_tree limit) [1..8]

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