Async CE with and! parallelism

AsyncAndBang.fsx

type Parallel() =
    member this.Bind (a, f) = async.Bind
    member this.Bind2 (a, b, f) = async {
        let! [|x; y|] = Async.Parallel [a; b]
        return! f (x, y)
    }
    member this.Bind3 (a, b, c, f) = async {
        let! [|x; y; z|] = Async.Parallel [a; b; c]
        return! f (x, y, z)
    }
    member this.Return value = async.Return value
    member this.ReturnFrom value = async.ReturnFrom value
    member this.Delay f = async.Delay f
let parallel = Parallel()

let sleepAndReturn s x = async {
    do! Async.Sleep (s*1000)
    return x }

let a =
    parallel {
        let scale = 1
        let! x = sleepAndReturn scale 1
        and! y = sleepAndReturn scale 2
        and! z = sleepAndReturn scale 3
        return x + y + z }
#time
a |> Async.RunSynchronously

> a |> Async.RunSynchronously;;
Real: 00:00:01.001, CPU: 00:00:00.046, GC gen0: 0, gen1: 0, gen2: 0
val it: int = 6