从列表中读取整数

Question

我在 Haskell 中遇到以下问题：

我想解析这样的列表： ["1", "2", "3"] 变成 Maybe [Int]。我能做的是，使用Text.Read 中的readMaybe，通过以下方式获得[Maybe Int] int：

parseList :: [String] -> [Maybe Int]
parseList l = map readMaybe l :: [Maybe Int]

我可以这样做：

parseListMaybe :: [String] -> Maybe [Int]
parseListMaybe l = if (any isNothing parsed) then Nothing
                   else (Just $ catMaybes parsed)
                   where parsed = parseList l

但这在我看来并不是解决这个问题的最优雅和最精确的方法。我会很感激这方面的一些提示

Answer 1

使用来自Control.Monad的sequence：

\> import Control.Monad (sequence)
\> import Text.Read (readMaybe)
\> sequence (readMaybe <$> ["1", "2", "3"]) :: Maybe [Int]
Just [1,2,3]
\> sequence (readMaybe <$> ["1", "xyz", "3"]) :: Maybe [Int]
Nothing