# File lib/rdoc/ri/paths.rb, line 50
  def self.each system, site, home, gems, *extra_dirs # :yields: directory, type
    extra_dirs.each do |dir|
      yield dir, :extra
    end

    yield SYSDIR,  :system if system
    yield SITEDIR, :site   if site
    yield HOMEDIR, :home   if home and HOMEDIR

    gemdirs.each do |dir|
      yield dir, :gem
    end if gems

    nil
  end