# File lib/highline.rb, line 208
  def ask( question, answer_type = String, &details ) # :yields: question
    @question ||= Question.new(question, answer_type, &details)
    
    return gather if @question.gather
  
    # readline() needs to handle it's own output, but readline only supports 
    # full line reading.  Therefore if @question.echo is anything but true, 
    # the prompt will not be issued. And we have to account for that now.
    say(@question) unless (@question.readline and @question.echo == true)
    begin
      @answer = @question.answer_or_default(get_response)
      unless @question.valid_answer?(@answer)
        explain_error(:not_valid)
        raise QuestionError
      end
      
      @answer = @question.convert(@answer)
      
      if @question.in_range?(@answer)
        if @question.confirm
          # need to add a layer of scope to ask a question inside a
          # question, without destroying instance data
          context_change = self.class.new(@input, @output, @wrap_at, @page_at)
          if @question.confirm == true
            confirm_question = "Are you sure?  "
          else
            # evaluate ERb under initial scope, so it will have
            # access to @question and @answer
            template  = ERB.new(@question.confirm, nil, "%")
            confirm_question = template.result(binding)
          end
          unless context_change.agree(confirm_question)
            explain_error(nil)
            raise QuestionError
          end
        end
        
        @answer
      else
        explain_error(:not_in_range)
        raise QuestionError
      end
    rescue QuestionError
      retry
    rescue ArgumentError, NameError => error
      raise if error.is_a?(NoMethodError)
      if error.message =~ /ambiguous/
        # the assumption here is that OptionParser::Completion#complete
        # (used for ambiguity resolution) throws exceptions containing 
        # the word 'ambiguous' whenever resolution fails
        explain_error(:ambiguous_completion)
      else
        explain_error(:invalid_type)
      end
      retry
    rescue Question::NoAutoCompleteMatch
      explain_error(:no_completion)
      retry
    ensure
      @question = nil    # Reset Question object.
    end
  end