scan

# File lib/rdoc/parser/ruby.rb, line 1476
  def scan
    reset

    catch :eof do
      catch :enddoc 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
    end

    @top_level
  end