1 implementation module yard
8 from Data.List import intersperse
9 from Text import instance Text String, class Text(concat)
13 import Control.Applicative
14 from Data.Func import $
17 instance toString Error where
18 toString (PositionalError l c e) =
19 concat [toString l,":",toString c,": ",e, "\n"]
20 toString (Error e) = concat ["-:-: ", e, "\n"]
22 runParser :: (Parser a b) [a] -> (Either Error b, [a])
23 runParser (Parser f) i = f i
25 instance + Error where
28 instance Functor (Parser a) where
31 instance Applicative (Parser a) where
32 pure a = Parser \i -> (Right a, i)
35 instance Monad (Parser a) where
36 bind p f = Parser \i -> case runParser p i of
37 (Right r, rest) = runParser (f r) rest
38 (Left e, _) = (Left e, i)
40 instance Alternative (Parser a) where
41 empty = Parser \i -> (Left $ Error "" , i)
42 (<|>) p1 p2 = Parser \i -> case runParser p1 i of
43 (Right r, rest) = (Right r, rest)
44 (Left e1, rest) = case runParser p2 i of
45 (Left e2, rest) = (Left $ e1+e2, i)
46 (Right r, rest) = (Right r, rest)
48 //Try the parser, if it fails decorate the error with Expected of the given String and position
49 (<?>) :: (Parser a b) Error -> Parser a b
50 (<?>) p e = Parser \i -> case runParser p i of
51 (Left e1, rest) = (Left $ e1 + e, rest)
52 (Right r, rest) = (Right r, rest)
58 top = Parser \i -> case i of
59 [] = (Left $ Error "", [])
60 [x:xs] = (Right x, xs)
63 peek = Parser \i -> case i of
64 [] = (Left $ Error "", [])
65 [x:xs] = (Right x, [x:xs])
67 //runs the left parser until the right parser succeeds. Returns the result of the left parser
68 //Note: if the right parser consumes input then this input is lost!
69 //If the left parser fails before the right parser succeeds the whole parser fails
70 (until) infix 2 :: (Parser a b) (Parser a c) -> Parser a [b]
71 (until) p guard = try $ until` p guard []
73 until` :: (Parser a b) (Parser a c) [b] -> Parser a [b]
74 until` p guard acc = Parser \i -> case runParser guard i of
75 (Right _, rest) = (Right acc, rest)
76 (Left _, _) = case runParser p i of
77 (Right r, rest) = runParser (until` p guard [r:acc]) rest
78 (Left e, _) = (Left e, i)
79 try :: (Parser a b) -> Parser a b
80 try p = Parser \i -> case runParser p i of
81 (Left e, _) = (Left e, i)
82 (Right r, rest) = (Right r, rest)
86 eof = Parser \i -> case i of
88 _ = (Left $ Error "", i)
90 satisfy :: (a -> Bool) -> Parser a a
91 satisfy f = top >>= \r -> if (f r) (return r) fail
93 check :: (a -> Bool) -> Parser a a
94 check f = peek >>= \r -> if (f r) (return r) fail
96 item :: a -> Parser a a | Eq a
97 item a = satisfy ((==)a)
99 list :: [a] -> Parser a [a] | Eq a
100 list as = mapM item as