F# async simple example. Try it here: http://www.tryfsharp.org/create/vkobel/AsyncSimple.fsx

async.fs

open System.Threading

let workThenWait() = 
  async { 
    do! Async.Sleep(1000)
    printfn "work done"
  }

let demo() = 
  printfn "started"
  let work = workThenWait() |> Async.StartAsTask
  printfn "completed"
  work.Wait()
  
demo()