redukt-v1.kt

fun <S, E> createStore(
    initial: S,
    eventsSource: Observable<E>,
    reducer: (S, E) -> S,
    transformer: ObservableTransformer<in Triple<S, S, E>, out E>
): Observable<S> {
  val state = behaviorSubjectDefault(initial)
  val events = behaviorSubject<E>()
  eventsSource.subscribe(events::onNext)
  events.withLatestFrom(state) { ev, oldState ->
    val newState = reducer(oldState, ev)
    state.onNext(newState)
    Triple(oldState, newState, ev)
  }
      .compose(transformer)
      .subscribe(events)

  return state
}