module EventDispatcher
  def init
    @listeners = {}
  end
  def on(event, &callback)
    @listeners[event] = [] if not @listeners[event]
    @listeners[event] << callback
    # do something
  end
  def register(event, method)
    @listeners[event] = [] if not @listeners[event]
    @listeners[event] << callback
  end
  def unregister(event, method)
    @listeners[event] = [] if not @listeners[event]
    @listeners[event] << callback
  end
end