ludic/examples/events/scene_events.ludic

# scene_events.ludic — EV1 for scenes: a `public` scene promotes its on-enter /
# on-exit to public events scene_<S>_enter / scene_<S>_exit, extending the modding
# surface to the game's scene structure. A mod (native @On here, or foreign over
# the ABI) reacts as the game moves between scenes.
#
# Running it prints:  10 1 20 2 30 3
program SceneEvents {
  @On(scene_Menu_enter) handler Greet { print(1) }
  @On(scene_Menu_exit)  handler Bye   { print(2) }
  @On(scene_Game_enter) handler Begin { print(3) }

  scene Menu start public {
    on enter { print(10) }        # boot enters Menu: 10, then scene_Menu_enter -> 1
    on exit  { print(20) }        # become leaves Menu: 20, then scene_Menu_exit -> 2
    layer L { handler Go phase Update { become Game } }
  }

  scene Game public {
    on enter { print(30) }        # become enters Game: 30, then scene_Game_enter -> 3
    layer M { handler Stop phase Update { quit() } }
  }
}