parse

# File lib/optparse.rb, line 705
      def parse(arg, argv, &error)
        if !(val = arg) and (argv.empty? or /\A-/ =~ (val = argv[0]))
          return nil, block, nil
        end
        opt = (val = parse_arg(val, &error))[1]
        val = conv_arg(*val)
        if opt and !arg
          argv.shift
        else
          val[0] = nil
        end
        val
      end