gistfile1.rb

  def file_tree files, sub = nil, &proc
    res = "<ul #{'class="subdir"' if sub }>"
    files.each do |file, value|
      subdir = (value.class == Hash) ? file_tree(value, 1) { |a, b| proc.call a, b } : nil
      res += proc.call file, subdir
    end
    res + '</ul>'
  end