scan

# File lib/rdoc/parser/ruby.rb, line 1655
  def scan
    reset

    catch :eof do
      begin
        parse_top_level_statements @top_level
      rescue StandardError => e
        bytes = ''

        20.times do @scanner.ungetc end
        count = 0
        60.times do |i|
          count = i
          byte = @scanner.getc
          break unless byte
          bytes << byte
        end
        count -= 20
        count.times do @scanner.ungetc end

        $stderr.puts #{self.class} failure around line #{@scanner.line_no} of#{@file_name}

        unless bytes.empty? then
          $stderr.puts
          $stderr.puts bytes.inspect
        end

        raise e
      end
    end

    @top_level
  end