解析 Haskell 中的元组 (String,Int)

Question

我需要解析 (String,Int) 类型，因为 userRatings 是为了正确读取 textFile，而我正在使用 Parsec。这是导入时的解析，我的 stringInt 元组函数有这个错误。

Expecting two more arguments to ‘Parsec (String, Int)’ Expected a type, but ‘Parsec (String, Int)’ has kind ‘* -> * -> *’ In the type signature for ‘stringIntTuple’: stringIntTuple :: Parsec (String, Int)

    import Control.Monad
    import Control.Applicative((<*))
    import Text.Parsec
        ( Parsec, ParseError, parse        -- Types and parser
        , between, noneOf, sepBy, many1    -- Combinators
        , char, spaces, digit, newline     -- Simple parsers
        )
    -- Types
    type Title = String
    type Director = String
    type Year = Int
    type UserRatings = (String,Int) 
    type Film = (Title, Director, Year , [UserRatings])
    type Period = (Year, Year)
    type Database = [Film]


    -- Parse a string to a string
    stringLit :: Parsec String u String
    stringLit = between (char '"') (char '"') $ many1 $ noneOf "\"\n"

    -- Parse a string to a list of strings
   listOfStrings :: Parsec String u [String]
   listOfStrings = stringLit `sepBy` (char ',' >> spaces)

   -- Parse a string to an int
   intLit :: Parsec String u Int
   intLit = fmap read $ many1 digit
   -- Or `read <$> many1 digit` with Control.Applicative
   stringIntTuple :: Parsec (String , Int)
   stringIntTuple = liftM2 (,) stringLit intLit

   film :: Parsec String u Film
   film = do

title <- stringLit
newline
director <- stringLit
newline
year <- intLit
newline
userRatings <- stringIntTuple
newline
return (title, director, year, userRatings)

Answer 1

错误消息基本上是说您没有提供足够的类型参数。如果您将元组解析器的签名与其他解析器的签名进行比较，您就会明白为什么：

stringLit :: Parsec String u String
listOfStrings :: Parsec String u [String]
stringIntTuple :: Parsec (String , Int)

在所有其他情况下，您提供三个类型参数，但对于 stringIntTuple，您只提供一个。

所以只需添加 String 和 u 作为前两个参数，就像您为其他参数所做的那样，它就会起作用。

解析 Haskell 中的元组 (String,Int)

Parsing a Tuple (String,Int) in Haskell

monads

parsing

haskell

tuples

parsec