open System.Net

    open System

    open System.IO

    open Microsoft.FSharp.Control.CommonExtensions   

​

    // Fetch the contents of a URL asynchronously

    let fetchUrlAsync url =        

        async {   // "async" keyword and curly braces 

                  // creates an "async" object

            let req = WebRequest.Create(Uri(url)) 

            use! resp = req.AsyncGetResponse()    

                // use! is async assignment

            use stream = resp.GetResponseStream() 

                // "use" triggers automatic close()

                // on resource at end of scope

            use reader = new IO.StreamReader(stream) 

            let html = reader.ReadToEnd() 

            printfn "finished downloading %s" url 

            }

    let sites = ["http://www.bing.com";

                 "http://www.google.com";

                 "http://www.microsoft.com";

                 "http://www.amazon.com";

                 "http://www.yahoo.com"]

                  // do it

    sites 

    |> List.map fetchUrlAsync  // make a list of async tasks

    |> Async.Parallel          // set up the tasks to run in parallel

    |> Async.RunSynchronously  // start them off

​