implementation module yard

import StdTuple
import StdClass
import StdString
import StdList
import Data.Functor
import Data.Either
import Control.Monad
import Control.Applicative
from Data.Func import $

instance toString Error where
	toString ParseError = "General parse error"
	toString (LexError e) = "Lexer error: " +++ e

instance + Error where
    (+) (Expected as _) (Expected bs p) = Expected (as++bs) p
    (+) _ r                             = r

runParser :: (Parser a b) [a] -> (Either Error b, [a])
runParser (Parser f) i = f i

instance Functor (Parser a) where
    fmap f m = liftM f m

instance Applicative (Parser a) where
    pure a      = Parser \i -> (Right a, i)
    (<*>) sf p  = ap sf p

instance Monad (Parser a) where
    bind p f    = Parser \i -> case runParser p i of
        (Right r, rest) = runParser (f r) rest
        (Left e, rest)  = (Left e, rest)

instance Alternative (Parser a) where
    empty       = Parser \i -> (Left ParseError, i)
    (<|>) p1 p2 = Parser \i -> case runParser p1 i of
        (Right r, rest) = (Right r, rest)
        (Left e1, rest) = case runParser p2 i of
            (Right r, rest) = (Right r, rest)
            (Left e2, rest) = (Left (e1+e2), rest)

//Try the parser, if it fails decorate the error with Expected of the given String and position
(<?>) :: (Parser a b) (String, Int) -> Parser a b
(<?>) p (e,pos) = Parser \i -> case runParser p i of
    (Left e1, rest) = let error = (e1+(Expected [e] pos)) in (Left error, rest)
    (Right r, rest) = (Right r, rest)

fail :: Parser a b
fail = empty

top :: Parser a a
top = Parser \i -> case i of
    []      = (Left ParseError, [])
    [x:xs]  = (Right x, xs)

satisfy :: (a -> Bool) -> Parser a a
satisfy f = top >>= \r -> if (f r) (return r) fail

item :: a -> Parser a a | Eq a
item a  = satisfy ((==)a)

list :: [a] -> Parser a [a] | Eq a
list as = mapM item as