我在使用镜头库访问Map数据类型时遇到一些问题。
data Card
= Ferme
| Boulangerie
data PlayerState = PlayerState {
_psCards :: Map Card Int,
} deriving (Show)
data GameState = GameState {
_gsPlayers :: [PlayerState]
} deriving (Show)
访问Map
时遇到问题
step :: (MonadState s m, HasGameState s, MonadIO m) => m ()
step = do
i <- use $ gsPlayers . ix 0 . psCards . ix Ferme
出现以下错误:
• Could not deduce (Monoid Int) arising from a use of ‘ix’
from the context: (MonadState s m, HasGameState s, MonadIO m)
bound by the type signature for:
step :: forall s (m :: * -> *).
(MonadState s m, HasGameState s, MonadIO m) =>
m ()
这是因为我在同一行中使用了带有不同参数的ix
吗?
https://stackoverflow.com/questions/55165769
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