Ch24_Backtracking.hs

{-# LANGUAGE OverloadedStrings #-}

module BT where

import Control.Applicative
import qualified Data.Attoparsec.ByteString as A
import Data.Attoparsec.ByteString (parseOnly)
import Data.ByteString (ByteString)
import Text.Trifecta hiding (parseTest)
import Text.Parsec (Parsec, parseTest)

trifP
  :: Show a
  => Parser a -> String -> IO ()
trifP p i = print $ parseString p mempty i

parsecP
  :: Show a
  => Parsec String () a -> String -> IO ()
parsecP = parseTest

attoP
  :: Show a
  => A.Parser a -> ByteString -> IO ()
attoP p i = print $ parseOnly p i


nobackParse
  :: (Monad f, CharParsing f)
  => f Char
nobackParse = (char '1' >> char '2') <|> char '3'

tryParse
  :: (Monad f, CharParsing f)
  => f Char
tryParse = try (char '1' >> char '2') <|> char '3'

main :: IO ()
main = do
  -- trifecta
  trifP nobackParse "13"
  trifP tryParse "13"
  -- parsec
  parsecP nobackParse "13"
  parsecP tryParse "13"
  -- attoparsec
  attoP nobackParse "13"
  attoP tryParse "13"