addNewTodoEffect.kt

private val addNewTodoEffect = Transformer<State, Event, Event> { upstream ->
    upstream.ofEventType(Event.NewTodoEvent::class)
            .observeOn(Schedulers.io())
            .switchMap { (_, _, event) ->
                db.todoDao().add(
                        TodoEntity(
                                id = 0,
                                text = event.text,
                                completed = false
                        )
                )
                Observable.empty<Event>()
            }
}

Very good