相关疑难解决方法(0)

有没有办法对monad中存储的值执行一个案例,而不必将名称绑定到它？

即而不是这样做:

c <- getChar
case c of
  ...

有没有办法做到这一点:

mcase getChar of
  ...

或者,如果case语句可以部分应用,那将是很好的:

case of
  ...

会不情愿地:

\a -> case a of
  ...

所以你可以这样做:

getChar >>= case of
              ...

我有一个yaml文件:

base123:
  key1: "key1"
  key2: "key2"
  key3: "key3"

和代码,它被允许从中读取所有3个值:

read123 :: IO (String, String, String)
read123 = do
  rawConfig <- Y.decodeFile "config.yml" :: IO (Maybe Y.Value)
  case rawConfig of
    Just res1 ->
      case res1 of
        Object res2 ->
          case (LHashMap.lookup "base123" res2) of
            Just (Object res3) -> 
              case (LHashMap.lookup "key1" res3) of
                Just (String key1) -> 
                  case (LHashMap.lookup "key2" res3) of
                    Just (String key2) -> 
                      case (LHashMap.lookup "key3" res3) of
                        Just (String key3) -> return (key1, key2, key3)
        _ -> …