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