ask_yes_no (Gem::StreamUI)

    # File lib/rubygems/user_interaction.rb, line 168
      def ask_yes_no(question, default=nil)
        unless @ins.tty? then
          if default.nil? then
            raise Gem::OperationNotSupportedError,
                  "Not connected to a tty and no default specified"
          else
            return default
          end
        end

        qstr = case default
               when nil
                 'yn'
               when true
                 'Yn'
               else
                 'yN'
               end

        result = nil

        while result.nil?
          result = ask("#{question} [#{qstr}]")
          result = case result
          when /^[Yy].*/
            true
          when /^[Nn].*/
            false
          when /^$/
            default
          else
            nil
          end
        end

        return result
      end