HandleCommand.scala

def handleCommand(command: GameCommand): Either[GameRulesViolation, Game] = command match {
  case StartGame(players) => this match {
    case ug: UninitializedGame => ug.start(players)
    case _ => GameAlreadyStartedViolation
  }
  case RollDice(player) => this match {
    case rg: RunningGame => rg.roll(player)
    case _ => GameNotRunningViolation
  }
}