MegaparsecRecoveryEOF.hs

{-# LANGUAGE GADTs #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TupleSections #-}
import           Control.Monad
import           Data.Text (Text)
import           Data.Void
import           Text.Megaparsec
import           Text.Megaparsec.Char
import qualified Text.Megaparsec.Char.Lexer as Lexer

type Parser = Parsec Void Text

sc :: Parser ()
sc = Lexer.space (void (takeWhile1P Nothing f)) lineComment empty
  where f x = x `elem` [' ', '\t']

scn :: Parser ()
scn = Lexer.space space1 lineComment empty

lineComment :: Parser ()
lineComment = Lexer.skipLineComment "#"

symbol :: Text -> Parser Text
symbol = Lexer.symbol sc

parseList :: Parser [Either (ParseError Char Void) Text]
parseList =
  many (withRecovery recover (Right <$> p)) <* eof
  where
    recover e =
      -- Changing this to skipManyTill anyChar (eof <|> void newline) will lead to an infinite loop since skipManyTill anyChar eof will always succeed.
      Left e <$ skipManyTill anyChar (void newline)
    p = do
      s <- try (symbol "foobar" <* notFollowedBy alphaNumChar)
      scn
      pure s

main :: IO ()
main = do
  -- This works fine
  parseTest parseList ("foobar2\nfoobar3\n")
  -- This will fail completely since we have nothing to sync up on.
  parseTest parseList ("foobar2\nfoobar3")