/in/foo.cc: In function 'Result Match(std::__cxx11::string&)':
/in/foo.cc:16:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < s.length(); i++)
                     ~~^~~~~~~~~~~~
/in/foo.cc:20:12: warning: suggest explicit braces to avoid ambiguous 'else' [-Wparentheses]
         if (s[i] == ')')
            ^