+
+
+
+// Clean adaption of Yard, a parsec like parser combinator
+:: Parser a = Parser ([Char] -> (LexerOutput a, [Char]))
+
+runParser :: (Parser a) [Char] -> (LexerOutput a, [Char])
+runParser (Parser p) s = p s
+
+instance Functor Parser where
+ fmap f s = liftM f s
+
+instance Applicative Parser where
+ pure a = Parser $ \s -> (Right a, s)
+ (<*>) sf s = ap sf s
+
+instance Monad Parser where
+ bind p f = Parser $ \s -> let (out, rest) = runParser p s in case out of
+ Left e = (Left e, rest)
+ Right t = runParser (f t) rest
+
+//gives us some, many and optional
+instance Alternative Parser where
+ empty = zero
+ (<|>) p1 p2 = parserAlternative p1 p2
+parserAlternative p1 p2 = Parser $ \s -> let (out, rest) = runParser p1 s in case out of
+ Left e = runParser p2 s
+ Right t = (Right t, rest)
+
+//parser that fails with error
+fail :: String -> Parser a
+fail e = Parser $ \s -> (Left e, s)
+
+//parser that always fails
+zero :: Parser a
+zero = fail "Zero parser"
+
+//matches exactly one Char
+item :: Parser Char
+item = Parser $ \s -> case s of
+ [] = (Left "Unexpected empty input", s)
+ [x:xs] = (Right x, xs)
+
+//matches any char which satisfies f
+satisfy :: (Char -> Bool) -> Parser Char
+satisfy f = item >>= (\r -> if (f r) (return r) zero)
+
+//tries a parser, if it fails returns a default value
+optionalDef :: a (Parser a) -> Parser a
+optionalDef def p = parserAlternative p (return def)
+
+//matched given char
+char :: Char -> Parser Char
+char c = satisfy (\i -> c==i) //I hate that we can't do: satisfy (==c)
+
+alpha :: Parser Char
+alpha = satisfy isAlpha
+
+digit :: Parser Char
+digit = satisfy isDigit
+
+//matches a given String
+string :: [Char] -> Parser [Char]
+string s = mapM_ char s >>| return s
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