simple-state-machine-1.kt

sealed class State(val previousState: State?) {
  class RequestReceived(val request: Int): State(null)
  class RequestValidated(val validationResult: Boolean, previousState: RequestReceived): State(previousState)
  class RequestProcessed(val response: Int, previousState: RequestValidated): State(previousState)
  class ResponseValidated(val validationResult: Boolean, previousState: RequestProcessed): State(previousState)
}