F# Continuation Monad (Tail Recursive Factorial)

// Continuation Monad in F#

type ContinuationMonad() =

    // ma -> (a -> mb) -> mb

    member this.Bind (m, f) = fun c -> m (fun a -> f a c)

    // a -> ma

    member this.Return x = fun k -> k x

    // ma -> ma

    member this.ReturnFrom m = m

let cont = ContinuationMonad()

let fac n =

    let rec loop n =

      cont {

              match n with

              | n when n = 0I -> return 1I

              | _ -> let! x = fun f -> f n

                     let! y = loop (n - 1I)

                     return x * y

           }

    loop n (fun x -> x)

printf "%A" (fac 100000I)