haskell检查用户输入错误

Question

我在haskell中编写应用程序,我想知道这是检查用户输入是否正常的最佳方法,例如,当我要求int时它是int,还是在请求格式良好的日期时它的日期？

感谢帮助

Answer 1

使用maybeRead.该函数是包含在Haskell库中的候选函数,但尚未实现.所以包括它的代码.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)


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

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