In a local copy of Parsec.Prim I've added: mapState :: (st1 -> st2) -> State tok st1 -> State tok st2 mapState f (State i p u) = State i p $ f u mapOkReply :: (st1 -> st2) -> Reply tok st1 a -> Reply tok st2 a mapOkReply _ (Error a) = Error a mapOkReply f (Ok a s e) = Ok a (mapState f s) e mapConsumed :: (a -> b) -> Consumed a -> Consumed b mapConsumed f (Consumed a) = Consumed $ f a mapConsumed f (Empty a) = Empty $ f a mapParse :: (st2 -> st1) -> (st1 -> st2) -> GenParser tok st1 a -> GenParser tok st2 a mapParse f g (Parser p) = Parser (mapConsumed (mapOkReply g) . p . mapState f) parseWithState :: GenParser tok inter a -> inter -> GenParser tok st a parseWithState p inter = do st <- getState mapParse (const inter) (const st) p I've only exported mapParse and parseWithState. HTH Christian John Knottenbelt wrote:
Hi
I was wondering if it was possible to write a function that allows changing the state type of the Parser monad from Parsec.
The full parser type is: GenParser p s a, where p is the token type, s is the state type and a is the return type of the monad. However, I mostly use CharParser s a which is a synonym for GenParser Char s a.
What I would like is a function that allows me to combine CharParsers with differing state types. Something like:
runParser' :: CharParser t a -> t -> CharParser s (t,a)
So that I can use parsers written to work with different state types together on the same input stream.
Does anybody know if this is possible, or how one might do it with Parsec?
Thanks
John _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users