Use F# instead let async_copy (in:Stream) (out:Stream) = asnyc { let buf = Array.create 8192 let rec copy = async { return! match i

Use F# instead let async_copy (in:Stream) (out:Stream) = asnyc { let buf = Array.create 8192 let rec copy = async { return! match in.ReadAsync(0,buf.Length,buf) with | 0 -> () | x -> do! out.WriteAsnyc(0,x,buf); return! copy; } return! copy; } There's an async copy routine, not much more overhead than a sync copy. let sync_copy (in:Stream) (out:Stream) = let buf = Array.create 8192 let rec copy = match in.Read(0,buf.Length,buf) with | 0 -> () | x -> out.Write(0,x,buf); copy copy