ask_yes_no (Gem::StreamUI)

    # File lib/rubygems/user_interaction.rb, line 115
        def ask_yes_no(question, default=nil)
          if not @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