# File lib/proc_source.rb, line 13
  def get_lines(filename, start_line = 0)
    case filename
      # special "(irb)" descriptor?
      when "(irb)"
        IRB.conf[:MAIN_CONTEXT].io.line(start_line .. -1)
      # special "(eval...)" descriptor?
      when /^\(eval.+\)$/
        EVAL_LINES__[filename][start_line .. -1]
      # regular file
      else
        # Ruby already parsed this file? (see disclaimer above)
        if lines = SCRIPT_LINES__[filename]
          lines[(start_line - 1) .. -1]
        # If the file exists we're going to try reading it in
        elsif File.exist?(filename)
          begin
            File.readlines(filename)[(start_line - 1) .. -1]
          rescue
            nil
          end
        end
    end
  end