Untitled

let check predicate msg () =
  if not predicate then
    Some msg
  else
    None

let tryLogin() =
  let msgOpt =
    [
      $_POST['user_name'], "Empty Username"
      $_POST['user_password_new'], "EmptyPassword"
      ....
      ... , "You must provide valid e-mail address"
    ]
    |> List.map (fun (pred, msg) -> check (msg))
    |> List.<getFirstNotNone> (fun check -> check())

  match msgOpt with
  | Some msg -> msg
  | None ->
    <body>
    ""

let register() =
  if not <| empty($_POST) then
    $_SESSION["msg"] <- tryLogin()

  register_form()