scala - 将状态单子(monad)结果从程序中的一个步骤传递到另一个步骤+提前停止

Question

我有以下步骤:

trait BlackjackSteps {
    def gamerTakesTwoCards(gamerName:String): State[Deck, Gamer]
    def dealerTakesTwoCards: State[Deck, Dealer]
    def isBlackjack(gamer: Gamer, dealer: Dealer): Option[Player]
    def gamerDrawsCards(gamer: Gamer): State[Deck, Gamer]
    def dealerDrawsCards(dealer: Dealer, gamer: Gamer): State[Deck, Dealer]
    def determineWinner(gamer: Gamer, dealer: Dealer): Player

    def program(gamerName:String): State[Deck, Player] = for {
      gamer <- gamerTakesTwoCards(gamerName)
      dealer <- dealerTakesTwoCards
      //winner = isBlackjack(gamer, dealer)
      gamerFinal <- gamerDrawsCards(gamer)
      dealerFinal <- dealerDrawsCards(dealer, gamerFinal)
      winnerFinal = determineWinner(gamerFinal, dealerFinal)
    } yield  winnerFinal
  }

两个问题:

• 如何获取由 gamerTakesTwoCards 生成的牌组并将其传递给 DealerTakesTwoCards？

• isBlackjack 可能会导致获胜者，在这种情况下我需要停止并返回获胜者。我怎样才能改变上面的代码来做到这一点？

游戏:

• 玩家和荷官玩游戏
• 他们都抓了两张牌
• 如果没有 21 名获胜者
• 玩家一直抓牌直到 17 点
• 得分不超过 21 分的最高玩家获胜!

完整代码在这里:https://bitbucket.org/jameskingconsulting/blackjack-scala/src/master/

编辑:

我已经对理解进行了脱糖处理，只是为了弄清楚发生了什么:

def program(gamerName:String): State[Deck, Player] =
      gamerTakesTwoCards(gamerName).flatMap( gamer =>
        dealerTakesTwoCards.flatMap(dealer =>
          isBlackjack(gamer, dealer).fold(

            gamerDrawsCards(gamer).flatMap( gamerFinal =>
              dealerDrawsCards(dealer, gamerFinal).map( dealerFinal =>
                determineWinner(gamerFinal, dealerFinal)
              )
            )

          )(State.pure[Deck, Player])
        ))

Answer 1

1. 无事可做。这就是重点。

2. 无论isBlackjack返回的是None还是Some，在这两种情况下都必须返回获胜者。无论哪种方式，您都必须返回一个State[Deck, Player]。例如，您可以通过 Option 上的 fold 来实现它，通过 pure 映射成功案例:

   def program(gamerName:String): State[Deck, Player] = for {
     gamer <- gamerTakesTwoCards(gamerName)
     dealer <- dealerTakesTwoCards
     winner <- isBlackjack(gamer, dealer).fold(for {
       gamerFinal <- gamerDrawsCards(gamer)
       dealerFinal <- dealerDrawsCards(dealer, gamerFinal)
       winnerFinal = determineWinner(gamerFinal, dealerFinal)
     } yield winnerFinal)(State.pure[Deck, Player])
   } yield winner