On Tue, Aug 29, 2006 at 03:05:39PM +0200, Stephane Bortzmeyer wrote:
Parsec provides "count n p" to run the parser p exactly n times. I'm looking for a combinator "countBetween m n p" which will run the parser between m and n times. It does not exist in Parsec.
Much to my surprise, it seems quite difficult to write it myself and, until now, I failed (the best result I had was with the "option" combinator, which unfortunately requires a dummy value, returned when the parser fails).
How about this? countBetween m n p = do xs <- count m p ys <- count (n - m) $ option Nothing $ do y <- p return (Just y) return (xs ++ catMaybes ys) Assuming n >= m.
Does anyone has a solution? Preferrably one I can understand, which means not yet with liftM :-)
No liftM, as requested :-) Best regards Tomasz