labltkではなくてlablgtk2を使ってみる

let hello () =
  print_endline "Hello World";
  flush stdout

let delete_event ev =
  print_endline "Delete event occurred";
  flush stdout;
  true

let destroy () = GMain.Main.quit ()

let main () =
  let window = GWindow.window ~border_width:10 () in
  window#event#connect#delete ~callback:delete_event;
  window#connect#destroy ~callback:destroy;
  let button = GButton.button ~label:"Hello World" ~packing:window#add () in
  button#connect#clicked ~callback:hello;
  button#connect#clicked ~callback:window#destroy;
  window#show ();
  GMain.Main.main ()

let _ = main ()