Haskell “readMay”和“readMay”有什么区别？

两个函数

readMay

和

readMaybe

具有相同的签名

reada=>String->Maybe a

---

他们之间有什么区别吗？如果是，它们是什么？这两个功能中哪一个应该是首选的？

没有区别。以下是

readMay

的定义：

-- | This function provides a more precise error message than 'readEither' from 'base'.
readEitherSafe :: Read a => String -> Either String a
readEitherSafe s = case [x | (x,t) <- reads s, ("","") <- lex t] of
        [x] -> Right x
        []  -> Left $ "no parse on " ++ prefix
        _   -> Left $ "ambiguous parse on " ++ prefix
    where
        maxLength = 15
        prefix = '\"' : a ++ if length s <= maxLength then b ++ "\"" else "...\""
            where (a,b) = splitAt (maxLength - 3) s

readMay :: Read a => String -> Maybe a
readMay = eitherToMaybe . readEitherSafe

它们在中间错误消息中有所不同（

readEitherSafe

显示输入），但结果相同

---

---

readMay

from

Safe

早于

readMay

from

Text.Read

。除非您的

基础
版本低于4.6.0.0，否则请使用
文本中的
readMaybe
。阅读
，因为它不需要另一个软件包。
我是否确认一个在
安全
中，另一个在
文本中。阅读
模块？是的，您是正确的
-- | Parse a string using the 'Read' instance.
-- Succeeds if there is exactly one valid result.
-- A 'Left' value indicates a parse error.
--
-- @since 4.6.0.0
readEither :: Read a => String -> Either String a
readEither s =
  case [ x | (x,"") <- readPrec_to_S read' minPrec s ] of
    [x] -> Right x
    []  -> Left "Prelude.read: no parse"
    _   -> Left "Prelude.read: ambiguous parse"
 where
  read' =
    do x <- readPrec
       lift P.skipSpaces
       return x

-- | Parse a string using the 'Read' instance.
-- Succeeds if there is exactly one valid result.
--
-- @since 4.6.0.0
readMaybe :: Read a => String -> Maybe a
readMaybe s = case readEither s of
                Left _  -> Nothing
                Right a -> Just a