algorithm - 如何让这段Haskell代码更简洁？

Question

作为练习，我正在尝试用 Haskell 编写赌场游戏“ war ”的模拟。

http://en.wikipedia.org/wiki/Casino_war

这是一个非常简单的游戏，有一些规则。用我知道的任何一种命令式语言编写都是一个非常简单的问题，但是我正在努力用 Haskell 编写它。

我目前的代码:

 -- Simulation for the Casino War

import System.Random
import Data.Map

-------------------------------------------------------------------------------
-- stolen from the internet

fisherYatesStep :: RandomGen g => (Map Int a, g) -> (Int, a) -> (Map Int a, g)
fisherYatesStep (m, gen) (i, x) = ((insert j x . insert i (m ! j)) m, gen')
    where
        (j, gen') = randomR (0, i) gen

fisherYates :: RandomGen g => g -> [a] -> ([a], g)
fisherYates gen [] = ([], gen)
fisherYates gen l = toElems $ Prelude.foldl
        fisherYatesStep (initial (head l) gen) (numerate (tail l))
    where
        toElems (x, y) = (elems x, y)
        numerate = zip [1..]
        initial x gen = (singleton 0 x, gen)

-------------------------------------------------------------------------------

data State = Deal | Tie deriving Show

-- state: game state
-- # cards to deal
-- # cards to burn
-- cards on the table
-- indices for tied players
-- # players
-- players winning
-- dealer's winning
type GameState = (State, Int, Int, [Int], [Int], Int, [Int], Int)

gameRound :: GameState -> Int -> GameState
gameRound (Deal, toDeal, toBurn, inPlay, tied, numPlayers, pWins, dWins) card
    | toDeal > 0 =
        -- not enough card, deal a card
        (Deal, toDeal - 1, 0, card:inPlay, tied, numPlayers, pWins, dWins)
    | toDeal == 0 =
        -- enough cards in play now
        -- here should detemine whether or not there is any ties on the table,
        -- and go to the tie state
        let
            dealerCard = head inPlay
            p = zipWith (+) pWins $ (tail inPlay) >>=
                (\x -> if x < dealerCard then return (-1) else return 1)
            d = if dealerCard == (maximum inPlay) then dWins + 1 else dWins - 1
        in
            (Deal, numPlayers + 1, 0, [], tied, numPlayers, p, d)
gameRound (Tie, toDeal, toBurn, inPlay, tied, numPlayers, pWins, dWins) card
    -- i have no idea how to write the logic for the tie state AKA the "war" state
    | otherwise = (Tie, toDeal, toBurn, inPlay, tied, numPlayers, pWins, dWins)

-------------------------------------------------------------------------------

main = do
    rand <- newStdGen
    -- create the shuffled deck
    (deck, _) <- return $ fisherYates rand $ [2 .. 14] >>= (replicate 6)
    -- fold the state updating function over the deck
    putStrLn $ show $ Prelude.foldl gameRound
        (Deal, 7, 0, [], [], 6, [0 ..], 0) deck

-------------------------------------------------------------------------------

我理解为什么要创建随机数需要额外的工作，但我很确定我遗漏了一些基本的结构或概念。保留状态集合并在输入列表上运行分支逻辑应该不会这么尴尬。我什至想不出一个好的方法来为表中有关系的情况编写逻辑。

我不要求完整的解决方案。如果有人能指出我做错了什么，或者一些相关的好阅读 Material ，那就太好了。

提前致谢。

Answer 1

一种用于维护应用程序状态的有用设计模式是所谓的状态 monad。您可以找到描述和一些介绍性示例 here .此外，您可能需要考虑使用具有命名字段的数据类型而不是 GameState 的元组，例如:

data GameState = GameState { state :: State, 
                             toDeal :: Int
                           -- and so on
                           }

这将使使用 record syntax 访问/更新单个字段变得更加容易.