import StdTuple
import StdClass
import StdString
+import StdList
import Data.Functor
import Data.Either
import Control.Monad
toString ParseError = "General parse error"
toString (LexError e) = "Lexer error: " +++ e
+instance + Error where
+ (+) (Expected as) (Expected bs) = Expected (as++bs)
+ (+) _ r = r
+
runParser :: (Parser a b) [a] -> (Either Error b, [a])
runParser (Parser f) i = f i
empty = Parser \i -> (Left ParseError, i)
(<|>) p1 p2 = Parser \i -> case runParser p1 i of
(Right r, rest) = (Right r, rest)
- (Left _, rest) = runParser p2 i
+ (Left e1, rest) = case runParser p2 i of
+ (Right r, rest) = (Right r, rest)
+ (Left e2, rest) = (Left (e1+e2), rest)
+
+<?> :: (Parser a b) String -> Parser a b
+<?> p e = Parser \i -> case runParser p i of
+ (Left e1, rest) = (Left (e1+(Expected [e])), rest)
+ (Right r, rest) = (Right r, rest)
fail :: Parser a b
fail = empty