Common mistake

mistake4.fs

async {
  let wc = new WebClient()
  let html = wc.DownloadString(uri)
  printfn "%s" html }

// To make code in F# async workflow actually asynchronous, 
// we need to use a primitive operation of type Async<'T> 
// (implemented usually in the F# library as an extension) and call it using let! or do!:

async {
  let wc = new WebClient()
  let! html = wc.AsyncDownloadString(uri) // Asynchronous call here!
  printfn "%s" html }