Input IO monad

InputIOMonad.kt

object Input { 
  ...
  private fun handle(programState: ProgramState, input: String): ProgramState = either {
    ...
    val newState =
      when (currentState) {
        is InProgress -> {
          val move =
            Move.parse(input)
              .mapLeft(errorToCurrentState)
              .bind()
          currentState.make(move).mapLeft(errorToCurrentState).bind()
        }
        else -> currentState
      }
    newState
  }
}