Monadic parsers

Parser.hs

{-# Language DeriveFunctor #-}

module Parser where

newtype Parser a = Parser { parse :: String -> [(a, String)] }
  deriving Functor

parserBind :: Parser a -> (a -> Parser b) -> Parser b
parserBind (Parser p) mf = Parser $ \s ->
  p s >>= (\(x,s) -> parse (mf x) s)

parserPure :: a -> Parser a
parserPure x = Parser $ \s -> [(x, s)]

instance Applicative Parser where
    pure = parserPure
    pf <*> p = pf `parserBind` \f ->
                 p `parserBind` \x ->
                    parserPure $ f x

instance Monad Parser where
    (>>=) = parserBind