let ackermann M N =
    let rec acker (m, n, k) =
        match m,n with
            | 0, n -> k(n + 1)
            | m, 0 -> acker ((m - 1), 1, k)
            | m, n -> acker (m, (n - 1), (fun x -> acker ((m - 1), x, k)))
    acker (M, N, (fun x -> x))