如何在Haskell中创建函数minimax？

Question

我一直在努力在Haskell中创建一个minimax函数，并且在SO上找不到任何好的替代品，因此我要问：

我想创建以下功能：

minimax :: Player -> Rose Board -> Rose Int

我想得到一个RoseTree of Integers，那些必须是1,0或-1（对于有转弯的玩家来说，移动可以是好的，中立的或坏的。

(root :> leaves)               -- constructor of a Rose
(board :> boards)              -- constructor of a Rose Board
(Int :> Ints)                  -- constructor of a Rose Int

我已经编写了函数hasWinner，minimal'和maximum'来简化：

hasWinner :: Board -> Maybe Player

minimum' :: [Int] -> Int
minimum' (x:xs) | x == -1 = -1
                | otherwise = minimum' xs

maximum' :: [Int] -> Int
maximum' (x:xs) | x == 1 = 1
                | otherwise = maximum' xs

此外，我认为我的基本情况如下：

minimax player (board :> []) = (0 :> [])

目前这就是我所在的地方：

minimax player (board :> boards)| maximum' [(isWinner player b (minimax' player)) | (b :> bs) <- boards] == 1 = _
                                | minimum' [(isWinner player b (minimax' player)) | (b :> bs) <- boards] == -1 = _
                                | otherwise = _
                 where   minimax' player     | player == P1 = P2
                                             | otherwise = P1
                         isWinner p1 board p2    | hasWinner board == Just p1 = 1
                                                 | hasWinner board == Just p2 = -1
                                                 | otherwise = 0

我似乎无法弄清楚当我找到一块既赢，丢失或没有后果的董事会时会发生什么。那么我如何使用正确的Rose Board再次调用minimax函数？

任何帮助是极大的赞赏！

拉蒙

Answer 1

我实际上发现了另一篇文章，讨论了我在这里遇到的同样问题：Haskell Recursive Minimax Tree

答案如下：

minimax :: Player -> Rose Board -> Rose Int
minimax p (r :> [])   | hasWinner r == Just P1 = 1    :> []
                      | hasWinner r == Just P2 = (-1) :> []
                      | otherwise              = 0    :> []
minimax P1 (r :> rs) = maximum (map root xs) :> xs
    where xs = map (minimax (nextPlayer P1)) rs

minimax P2 (r :> rs) = minimum (map root xs) :> xs
    where xs = map (minimax (nextPlayer P2)) rs

我希望至少这可以在将来帮助其他人。这个答案中使用的函数是：

root :: Rose a -> a
root (a :> bs) = a 

nextPlayer :: Player -> Player
nextPlayer P1 = P2
nextPlayer P2 = P1

hasWinner :: Board -> Maybe Player

minimum :: Ord a => [a] -> a
maximum :: Ord a => [a] -> a

干杯！