    def file_line_pointers
      file = line = nil
      c = self
      until file
        case c.irt_mode
        when :binding
          file = c.binding_file
          line = c.binding_line_no
        when :file
          file = c.irb_path
          line = c.last_line_no
        end
        c = c.parent_context
      end
      [file, line]
    end