将 State 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

我有这些步骤：

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：

我如何获得 gamerTakesTwoCards 生成的牌组并将其传递给 dealerTakesTwoCards？
isBlackjack 可能会导致赢家，在这种情况下我需要停止并且 return 赢家。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
他们都抽了两张牌
如果没有 21 名获胜者
玩家继续抽牌直到 17
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去糖处理，只是弄清楚发生了什么：

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

无事可做。这就是重点。

无论isBlackjackreturn是None 或 Some。无论哪种方式，您都必须 return 一个 State[Deck, Player]。例如，您可以通过 Option 上的 fold 实现它，将 success-case 映射到 pure:

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

将 State monad 结果从程序中的一个步骤传递到另一个步骤 + 提前停止

Passing State monad result form one step to another in a program + stop early

monads

functional-programming

scala

for-comprehension

scala-cats