Promise with Scheduler

ScheduledPromise.fs

type Promise<'a> () =
    let mutable result : Result<'a, exn> option = None
    let catchCbs = List<Callback<exn>> ()
    let thenCbs = List<Callback<'a>> ()

    member this.Resolve (value: 'a) =
        result <- Some <| Ok value

        for cb in thenCbs do
            scheduler.Post  (fun () -> cb value)

    member this.Reject (error : exn) =
        result <- Some <| Error error

        for cb in catchCbs do
            scheduler.Post (fun () -> cb error)

    member this.Then<'a> (cb : Callback<'a>) : Promise<'a> =
        thenCbs.Add cb

        // Replay existing result if any
        result
        |> Option.map (Result.map (fun value -> scheduler.Post (fun () -> cb value)))
        |> ignore
        this

    // Subscribe OnError
    member this.Catch (cb: Callback<exn>) =
        catchCbs.Add cb

        // Replay existing error if any
        result
        |> Option.map (Result.mapError (fun error -> scheduler.Post (fun () -> cb error)))
        |> ignore
        this