scala> val pf1:PartialFunction[Int, String] = { case 3 => println("here in pf1"); "3"}
  val pf1: PartialFunction[Int,String] = <function1>
  
  scala> val pf2:PartialFunction[String, Unit] = { case "3" => println("here in pf2")}
  val pf2: PartialFunction[String,Unit] = <function1>
  
  scala> val chain = pf1 andThen pf2
  val chain: PartialFunction[Int,Unit] = <function1>
  
  scala> if(chain.isDefinedAt(3)) chain(3)
  here in pf1
  here in pf1
  here in pf2

  final class TransformHelper(func: StateFunction) {
    def using(andThen: PartialFunction[State, State]): StateFunction =
      func.andThen(andThen.orElse { case x => x })
  }

  final def transform(func: StateFunction): TransformHelper = new TransformHelper(func)

/**
   * Composes this partial function with another partial function that
   * gets applied to results of this partial function.
   *
   * Note that calling [[isDefinedAt]] on the resulting partial function may apply the first
   * partial function and execute its side effect. It is highly recommended to call [[applyOrElse]]
   * instead of [[isDefinedAt]] / [[apply]] for efficiency.
   *
   * @param  k  the transformation function
   * @tparam C  the result type of the transformation function.
   * @return a partial function with the domain of this partial function narrowed by
   *         other partial function, which maps arguments `x` to `k(this(x))`.
   */
  def andThen[C](k: PartialFunction[B, C]): PartialFunction[A, C] =
    new Combined[A, B, C](this, k)

  private[akka] def processEvent(event: Event, @unused source: AnyRef): Unit = {
    val stateFunc = stateFunctions(currentState.stateName)
    val nextState = if (stateFunc.isDefinedAt(event)) {
      stateFunc(event)
    } else {
      // handleEventDefault ensures that this is always defined
      handleEvent(event)
    }
    applyState(nextState)
  }

  private[akka] def processEvent(event: Event, @unused source: AnyRef): Unit = {
    val stateFunc = stateFunctions(currentState.stateName)
    val nextState = istateFunc.applyOrElse(event,  handleEvent)
    }
    applyState(nextState)
  }