basic_reducer_rxjava_example.kt

fun dataStream(
  textChangedEvents: Flowable<TextChangedEvent>,
  submitCommentEvents: Flowable<SubmitCommentEvent>
): Flowable<CommentFormData> {
  // We need to start with something
  val initialFormState = CommentFormData(comment = "", isCommentValid = false, submitRequest = null)
  // RxJava scan operator takes initial state and a reduce function
  // This operator manages the state for us, where it will keep track 
  // of the latest state and provide it for next incoming event 
  return textChangedEvents.scan(initialFormState) { event, currentState ->                                              
     reduce(event, currentState)
  }
}