Factorial Promise

FactorialPromise.fs

let rec factorial (n : bigint) : Promise<bigint> =
    let pr = Promise<bigint> ()
    pr.Resolve n
    pr.Then (fun value ->
        if value = (bigint 0) then
            single (bigint 1)
        else
            factorial(n - (bigint 1)).Then (fun res -> single (n * res))
)

let pr = factorial (bigint 10000)
pr.Then (fun value ->
    printfn "Result = %A" value
) |> ignore