Criterion format converter

import Control.Applicative
import qualified Data.ByteString.Char8 as BS
import Data.Attoparsec.Char8
import qualified Data.Attoparsec.Char8 as Parsec (takeWhile)
import Data.List
import Data.Maybe
import Text.Printf

type Word = BS.ByteString
data Criterion = Criterion Word [(Maybe Criterion, Word)]
    deriving Show

convert :: Criterion -> String
convert (Criterion word pairs) = case catMaybes criterions of
    [] -> outWords
    cr -> printf "(&%s(|%s))" outWords (concatMap (printf "(%s)" . convert :: Criterion -> String) cr)
    where (criterions, words) = unzip pairs
          outWords = printf "(%s %s)" (BS.unpack word) (BS.unpack $ BS.unwords words)

criterion = Criterion <$> Parsec.takeWhile (notInClass " ]") <*> many pair

pair = do
    space
    crit <- optional (char '[' *> criterion <* char ']' <* space)
    word <- char '"' *> Parsec.takeWhile (/= '"') <* char '"'
    return (crit, word)

main = BS.getLine >>= putStrLn . either id convert . parseOnly criterion