Rose trees, continuation-passing style

RoseTreeCps.fs

type ContinuationMonad() =
    member __.Bind(m, f) = fun c -> m (fun a -> f a c)
    member __.Return(x) = fun k -> k x

let cont = ContinuationMonad()

let rec reduce fs =
    cont {
        match fs with
        | [] -> return []
        | head :: tail ->
            let! result = head
            let! results = reduce tail
            return result :: results
    }

type 'a Tree = Node of 'a * 'a Tree list

let leaf a = Node (a, [])

let rec findMax (Node (i, chld)) =
    cont {
        let! maxVals = chld |> List.map findMax |> reduce
        return List.max (i :: maxVals)
    }

[<EntryPoint>]
let main argv =
    let t = Node (1, [ leaf 2; leaf 3 ])
    findMax t (printfn "%A")   // will be 3
    0