view_state_effect.kt

private val viewStateEffect = Transformer<State, Event, Event.ViewStateEvent> { upstream ->
    upstream.distinctUntilChanged { old, new -> old.second == new.second }
            .map { (_, state, _) ->
                val viewState = state.todos.map {
			 TodoViewData(it.id, it.text, it.completed) 
			}
                     .sortedBy { it.completed }
                Event.ViewStateEvent(viewState)
            }
}