open System.Threading.Task

type AsyncBuilder with
  member x.Bind(task : Task<'a>, f : 'a -> Async<'b>) =
    let task = task |> Async.AwaitTask
    async.Bind(task, f)


// Example
let work = async {
        use client = new System.Net.WebClient()
        let! bytes = client.DownloadDataTaskAsync(Uri("http://www.google.com"))  
        do! Task.Factory.StartNew<unit>(fun () -> File.WriteAllBytes(@"c:\temp\google.bin", bytes))

        do! Task.Run<unit>(fun () -> printfn "Bytes len %d" bytes.Length)

        return bytes } |> Async.RunSynchronously

printfn "first 5 Bytes %A" work.[0..4]