structure Shell =
struct
  open CML

  datatype msg = KEY of int * int * int * int

  fun keyCallback mailbox (key, scancode, action, mode) =
    (print "hello\n";
    Mailbox.send  (mailbox, (KEY (key, scancode, action, mode))))

  fun callbackListener mailbox =
  let
    val _ =
      case Mailbox.recv mailbox of
         KEY (key, scancode, action, mode) =>
           print (String.concat
             [ "key: "
             , Int.toString key
             , " scancode: "
             , Int.toString scancode
             , " action: "
             , Int.toString action
             , " mode: "
             , Int.toString mode
             , "\n"
             ])
  in
    callbackListener mailbox
  end

  fun loop (window) =
    if not (Glfw.windowShouldClose window) then
      let
        val _ = Gles3.clearColor (0.1, 0.1, 0.1, 0.1)
        val _ = Gles3.clear ()

        val _ = Glfw.pollEvents ()
        val _ = Glfw.swapBuffers window
      in
        loop (window)
      end
    else
      Glfw.terminate ()

  fun main () =
    let
      (* Set up GLFW. *)
      val _ = Glfw.init ()
      val _ = Glfw.windowHint (Glfw.CONTEXT_VERSION_MAJOR (), 3)
      val _ = Glfw.windowHint (Glfw.DEPRECATED (), Glfw.FALSE ())
      val _ = Glfw.windowHint (Glfw.SAMPLES (), 4)
      val window = Glfw.createWindow (500, 500, "MLton - box x box")
      val _ = Glfw.makeContextCurrent window
      val _ = Gles3.loadGlad ()

      val inputMailbox = Mailbox.mailbox ()
      (* Set callback sender *)
      val _ = CML.spawn (fn () =>
        let
          val kbCallback = keyCallback inputMailbox
          val _ = Key.export kbCallback
          val _ = Key.setCallback window
        in
          ()
        end)
      (* Set callback listener *)
      val _ = CML.spawn (fn () => callbackListener inputMailbox)
    in
      loop (window)
    end
end

val _ = RunCML.doit (Shell.main, NONE)