comment_form_partial_reducer.kt

fun reduce(event: TextChangedEvent): (CommentFormData) -> CommentFormData {
  // implementation
  return { state -> 
    // Let's check comment validity
    val isValid = event.enteredText.length > 5
    // Update the current state with the changes
    return state.copy(comment = event.enteredText, isCommentValid = isValid)
  }
}

fun reduce(event: Lce<Comment>): (CommentFormData) -> CommentFormData {
  // Update the submit request
  return { state -> state.copy(submitRequest = event) }
}

 fun formState(
    textChangedEvents: Observable<TextChangedEvent>,
    submitEvents: Observable<SubmitCommentEvent>
  ) : Observable<CommentFormData> {
   val textChangedReducer: Observable<(CommentFormData) -> CommentFormData> = textChangedEvents.map { textEvent -> reduce(textEvent) }
   
    // Explicitly declaring the type, for clarity sake
    val requestStateReducer: Observable<(CommentFormData) -> CommentFormData> = submitEvents
      .switchMap { event -> commentRepo.submit(event.comment) }
      .map { lceEvent -> reduce(lceEvent) }
    
    // We now have a clear common type (which happens to be a lambda)
    val reducers: Observable<(CommentFormData) -> CommentFormData> = Observable.merge(textChangedReducer, requestStateReducer)
    
    // And to finish this
    return reducers.scan(initialState) { reducer, state -> reducer.invoke(state) } 
  }