Question

只是一个我无法解答的简单问题

我想将字符串解析为字符串或双字符串,其中空字符串或“n/a”被解析为无。例如:

data Value = S String | N (Maybe Double)

value::CharParser () Value
value = val <* spaces
    where val = N <$> v_number
           <|> S <$> v_string
           <|> N <$> v_nothing

以及领导和训练白色空间。

谢谢

编辑:

v_number :: CharParser () (Maybe Double)
v_number = do s <- getInput
          case readSigned readFloat s of
            [(n, s )] -> Just n <$ setInput s 
            _         -> empty

v_string :: CharParser () String
v_string = (many1 jchar)
    where jchar = char  \  *> (p_escape <|> p_unicode)
          <|> satisfy (`notElem` ""\")

我尝试了各种各样的事情......为了什么也无济于事......却一无所获。

Answer 1

也许像这样的东西吗?

value = do skipMany space
           choice $ map try [
            do string "n/a" <|> (eof >> return [])
               return $ N Nothing,
            do d <- many digit
               return $ N $ Just (read d)
            -- do ...       
                            ]

友情链接