如何提及不同的模块

Question

我不知道如何同时导入两个不同的模块。以下代码

import qualified Data.Map as Map 
import Data.List

phoneBookToList :: (Ord k) => [(k,String)] -> Map.Map k String
phoneBookToList xs = Map.fromListWith (\n1 n2 -> n1 ++ ", " ++ n2) xs

phoneBookFromWithList :: (Ord k) => [(k,a)] -> Map k [a]
phoneBookFromWithList = Map.fromListWith (++)  $ map (\(k,a) -> (k,[a]))

抛出此错误

Not in scope: type constructor or class `Map'
Perhaps you meant `Map.Map' (imported from Data.Map)
Failed, modules loaded: none.

map (\(k,a) -> (k,[a]))我试图从默认的Prelude模块中使用它。我试过Data.List.map (\(k,a) -> (k,[a]))，但仍然出错。它虽然是一个GHCi命令。提前致谢

Answer 1

您要导入Data.Map限定为Map，但尝试在没有资格的情况下参考Map数据类型。

您需要将Map k [a]的类型签名中的phoneBookFromWithList更改为Map.Map k [a]才能正确引用Map数据类型。