Hi! I want to test whether a sequence of the characters 'A' and 'B' can represent a sequence of the symbols x and y where x may be represented by one or more 'A's and y may be represented by one or more 'A's or one or more 'B's. In code, I would like to see the following: λ> "AABB" `represents` [x, y] True λ> "AA" `represents` [x, y] True But with my current implementation using attoparsec only the first example works as expected: import Control.Applicative import Data.Attoparsec.ByteString.Char8 import Data.ByteString import Data.Either import Data.Foldable import Data.Word type Symbol = Parser [Word8] x :: Symbol x = many1 (char8 'A') y :: Symbol y = many1 (char8 'A') <|> many1 (char8 'B') represents :: ByteString -> [Symbol] -> Bool bs `represents` symbols = isRight $ parseOnly ((sequenceA_ symbols) *> endOfInput) bs It seems that in "AA" `represents` [x, y] x consumes all the 'A's, leaving none for y. Is it possible to solve this with attoparsec or are there other parsing libraries that I could use instead? Cheers, Simon