Haskell的Monadic TicTacToe錯誤

Question

我開始在Haskell中實現TicTacToe：

import Control.Monad.State

data Player = X | O
data Field = Player | I deriving (Eq, Show, Read)

data GameField = G [[Field]]

type GameState = State GameField ()

initGame :: GameState
initGame = do
    put $ G [[I,I,I],[I,I,I],[I,I,I]]

action = do
    initGame

test = execState action $ G [[I,I,I],[I,I,I],[I,I,I]]

當我執行“測試”時，出現以下錯誤：

No instance for (Show GameField) arising from a use of `print'
Possible fix: add an instance declaration for (Show GameField)
In a stmt of an interactive GHCi command: print it

此問題的原因是什么，如何解決？

Answer 1

其實不是太含糊的消息。 如果沒有Show實例，請添加一個：

data GameField = G [[Field]] deriving (Show)

Answer 2

您只是忘了在您的GameField牌上添加“衍生節目”。這可以通過添加它來解決，就像這樣

import Control.Monad.State

data Player = X | O
data Field = Player | I deriving (Eq, Show, Read)

data GameField = G [[Field]]
  deriving Show

type GameState = State GameField ()

initGame :: GameState
initGame = do
    put $ G [[I,I,I],[I,I,I],[I,I,I]]

action = do
    initGame

test = execState action $ G [[I,I,I],[I,I,I],[I,I,I]]