open System.Net

let rec Retry (f : unit -> 'T) (didSucceed : 'T -> bool) (timesMs : int list) =
   let rec retry times =
      match times with
      | [] ->
         f()
      | head::tail ->
         let result = f()
         if didSucceed result then
            result
         else
            async { do! Async.Sleep(head) } |> Async.RunSynchronously
            retry tail
   retry timesMs

let Demo1() =
   let rand = new System.Random()
   Retry (fun () -> rand.NextDouble()) (fun x -> x > 0.5) [1; 2; 4]

type DownloadResult = | Ok | NotOk

let Demo2() =
   use wc = new WebClient()
   Retry 
      (fun () -> 
         try
            printf "Downloading..."
            wc.DownloadFile("www.example.com", "file.txt")
            Ok
         with
         | _ -> NotOk)
      (fun result -> result = Ok)
      [1; 2; 4]