38 lines
856 B
Haskell
38 lines
856 B
Haskell
module Parser where
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import Data.Char
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import Control.Arrow
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import Control.Applicative
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import Control.Monad
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newtype Parser a = Parser { parse :: String -> [(a,String)] }
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instance Functor Parser where
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fmap f (Parser a) = Parser $ \s -> first f <$> a s
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instance Applicative Parser where
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pure x = Parser $ \s -> pure (x,s)
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(Parser pab) <*> (Parser pa) = Parser $ \s -> do
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(ab, s1) <- pab s
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(a, s2) <- pa s1
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pure (ab a, s2)
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instance Monad Parser where
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return = pure
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(Parser a) >>= f = Parser $ \s -> (\(x,s1) -> parse (f x) s1) =<< a s
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instance Alternative Parser where
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empty = Parser $ \s -> []
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(Parser p) <|> (Parser q) = Parser $ \s -> p s <|> q s
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token :: Parser Char
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token = Parser $ \s -> case s of
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(x:xs) -> [(x,xs)]
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_ -> []
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satisfy :: (Char -> Bool) -> Parser Char
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satisfy p = do
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x <- token
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guard (p x)
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pure x
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