code: func (e *EBus) On(event string, fn EvHandler) {
  	log.Debugf("registering event `%s`", event)
  	topic, ok := e.eventList[event]
  
  	if !ok {
  		topic = list.List{}
  	}
  
  	topic.PushBack(fn)
  	e.eventList[event] = topic
  }
docs: // Registering listener for provided event.