haskell 模拟 : define func in datatype with class-constraint

Question

有这个功能

httpLBS :: MonadIO m => Request -> m (Response ByteString) 

在 Network.HTTP.Simple 模块 ( doc ) 中，我想将其与我的 Ctx 数据一起传递(以便稍后在集成测试中进行模拟) -对象

data Ctx =
    Ctx {
        token :: String,
        httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
    } deriving (Show)

但是我收到了这个错误:

Prelude> :l Context.hs
[1 of 1] Compiling Context          ( Context.hs, interpreted )

Context.hs:19:32: error: Not in scope: type variable ‘m’
   |
19 |         httpLBSFunc :: MonadIO m => Request -> m (Response B.ByteString)
   |                                ^

Context.hs:19:48: error: Not in scope: type variable ‘m’
   |
19 |         httpLBSFunc :: MonadIO m => Request -> m (Response B.ByteString)
   |                                                ^
Failed, no modules loaded.

如何在我的 Ctx 数据类型中正确定义此方法？？

Answer 1

我不知道用实际的 Monad IO 替换约束 MonadIO 有什么缺点，但对我来说这足以让它运行:

data Ctx =
    Ctx {
        token :: String,
        httpLBSFunc :: Request -> IO (Response ByteString)
    } deriving (Show)

我什至不知道它们之间的确切区别