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module Parser where | |
import Control.Applicative | |
import Control.Monad | |
------------------------------------------------------------------------------ | |
-- Definition | |
------------------------------------------------------------------------------ | |
newtype Parser s a = Parser { runParser :: s -> [(a, s)] } | |
------------------------------------------------------------------------------ | |
-- Instances | |
------------------------------------------------------------------------------ | |
instance Functor (Parser s) where | |
fmap f px = Parser $ \s -> do { (x, s') <- runParser px s | |
; return (f x, s') | |
} | |
instance Applicative (Parser s) where | |
pure x = Parser $ \s -> [(x, s)] | |
pf <*> px = Parser $ \s -> do { (f, s') <- runParser pf s | |
; (x, s'') <- runParser px s' | |
; return (f x, s'') | |
} | |
instance Monad (Parser s) where | |
px >>= fp = Parser $ \s -> do { (x, s') <- runParser px s | |
; runParser (fp x) s' | |
} | |
instance Alternative (Parser s) where | |
empty = Parser $ \_ -> [] | |
px <|> py = Parser $ \s -> case runParser px s of | |
[] -> runParser py s | |
res -> res | |
------------------------------------------------------------------------------ | |
-- Combinators | |
------------------------------------------------------------------------------ | |
choice :: [Parser s a] -> Parser s a | |
choice ps = foldr (<|>) empty ps | |
many1 :: Parser s a -> Parser s [a] | |
many1 p = (:) <$> p <*> many p | |
count :: Int -> Parser s a -> Parser s [a] | |
count n p = sequenceA (replicate n p) | |
option :: a -> Parser s a -> Parser s a | |
option x p = p <|> pure x | |
skipMany :: Parser s a -> Parser s () | |
skipMany p = void $ many p | |
skipMany1 :: Parser s a -> Parser s () | |
skipMany1 p = void $ many1 p | |
sepBy :: Parser s a -> Parser s sep -> Parser s [a] | |
sepBy px ps = sepBy1 px ps <|> pure [] | |
sepBy1 :: Parser s a -> Parser s sep -> Parser s [a] | |
sepBy1 px ps = (:) <$> px <*> many (ps *> px) | |
------------------------------------------------------------------------------ | |
-- Basic parsers | |
------------------------------------------------------------------------------ | |
top :: Parser [a] a | |
top = Parser $ \s -> case s of | |
(c:cs) -> [(c, cs)] | |
otherwise -> [] | |
satisfy :: (a -> Bool) -> Parser [a] a | |
satisfy p = top >>= \c -> if p c then | |
return c | |
else | |
empty | |
item :: Eq a => a -> Parser [a] a | |
item c = satisfy (== c) | |
oneOf :: Eq a => [a] -> Parser [a] a | |
oneOf xs = satisfy (`elem` xs) | |
string :: Eq a => [a] -> Parser [a] [a] | |
string cs = sequenceA (map item cs) | |
------------------------------------------------------------------------------ | |
-- Char parsers | |
------------------------------------------------------------------------------ | |
digit :: Parser [Char] Char | |
digit = oneOf ['0'..'9'] | |
integer :: Parser [Char] Integer | |
integer = read <$> many1 digit |
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