OneLineParser.hs

module OneLineParser (parseOneLine) where

import System.Exit
import Text.Parsec hiding (Line, lookAhead, spaces)
import Text.Parsec.String
import Text.Parsec.Error
import qualified Text.Parsec as P

-- Parser utilities
-- | A nicer way to print an error message

printLineParserErrorMessage :: String -> ParseError -> IO a
printLineParserErrorMessage input err = do
    putStrLn (lineParserErrorMessage input err)
    exitFailure

lineParserErrorMessage :: String -> ParseError -> String
lineParserErrorMessage input err =
    "In " ++ sourceName pos ++ " column " ++ show (sourceColumn pos) ++ ":\n" ++
    input ++ "\n" ++
    replicate (sourceColumn pos - 1) ' ' ++ "↑" ++
    showErrorMessages "or" "unknown parse err" "expecting"
                      "unexpected" "end of input"
                      (errorMessages err)
  where pos = errorPos err

parseOneLine :: Parser a -> String -> String -> IO a
parseOneLine p name input =
    case P.parse p name input of
        Left e ->  printLineParserErrorMessage input e
        Right l -> return l