haskell 检查用户输入错误

Question

我正在用haskell编写应用程序，我想知道这是检查用户输入是否正确的最佳方法，例如当我要求int时它是int还是当要求格式正确的日期时它是日期？

感谢帮助

Answer 1

使用maybeRead。该函数是一个候选函数包含在 Haskell 库中，但它还没有出现在然而。因此请包含它的代码。这是一个完整的解决方案:

import Data.Time
import Data.Maybe (listToMaybe)
import System.IO (hSetBuffering, BufferMode(NoBuffering), stdout)<p></p>

<p>main = do
  hSetBuffering stdout NoBuffering
  putStr "Enter an Int: "
  maybeInt <- fmap maybeRead getLine :: IO (Maybe Int)
  maybe (putStrLn "That's not an Int!")
        (putStrLn . ("The Int is " ++) . show)
        maybeInt
  putStr "Enter a date: "
  maybeDate <- fmap maybeRead getLine :: IO (Maybe Day)
  maybe (putStrLn "That's not a date!")
        (putStrLn . ("The date is " ++) . show)
        maybeDate</p>

<p>maybeRead :: Read a => String -> Maybe a
maybeRead = fmap fst . listToMaybe . filter (null . snd) . reads
</p>