I need to parse fixed length fields with attoparsec but im now struggling with the compiler.
Im still a newbie, the code below is the closest solution I have:
> {-# LANGUAGE OverloadedStrings #-}
> import Control.Applicative
> import Data.Text as T
> import Data.Attoparsec.Combinator
> import Data.Attoparsec.Text hiding (take)
> import Data.Char
> import Prelude hiding (take)
>
> type City = Text
> type Ready = Bool
> data CityReady = CR City Ready deriving Show
>
> input = T.unlines ["#London 1",
> "#Seoul 0",
> "#Tokyo 0",
> "#New York 1"]
>
> parseCityReady = many $ CR <$> cityParser <*> readyParser <* endOfLine
>
> cityParser = char '#' *>
> takeTill isSpace <*
> skipWhile isHorizontalSpace
>
>
> readyParser = char '1' *> pure True <|> char '0' *> pure False
>
> main =
> case parseOnly parseCityReady input of
> Left err -> print err
> Right xs -> mapM_ print xs
>
This is all great but it is only returning Cities without spaces.
CR "London" True
CR "Seoul" False
CR "Tokyo" False
I have tried using applicative to take 20 characters for the City text string
> cityParser = char '#' *>
> take 20
and even do syntax
> cityParser = do char '#'
> city <- take 20
> return city
but both approaches fail to compile with this error:
Couldn't match expected type `attoparsec-0.10.4.0:Data.Attoparsec.Internal.Types.Parser
Text b0'
with actual type `Text -> Text'
In the return type of a call of `take'
Probable cause: `take' is applied to too few arguments
In the second argument of `(*>)', namely `take 20'
In the expression: char '#' *> take 20
What is causing the ghc to ask for Text -> Text
when the take
has a type of Int -> Text -> Text
?
How do I solve it in both applicative and do-syntax?