hexPrefix :: Parser Integer
hexPrefix = do
    char '$'
    str <- many1 hexDigit
    return $ fst . head . readHex $ str
hexPrefix :: Parser Integer
hexPrefix = do
    char '$'
    str <- many1 hexDigit
    return $ fst . head . readHex $ str
hexPrefix = do
    char '$'
    str <- many1 hexDigit
    return $ fst . head . readHex $ str