gistfile1.rb

# In Rails Controller
  def playlist
    @playlist = session[:playlist] = Playlist.new(current_user)
    render :layout => false
  end

# In RAILS view
xml.instruct! :xml, :version=>"1.0"
xml.playlist do
  if @playlist.currently_playing?
    xml.currently_playing do
      xml.song_in_list @playlist.current_song_in_playlist?
    end
  end
  
  xml.songs do
    @playlist.songs.each do |song|
      xml.song do
        xml.id song.id
        xml.title song.title
        xml.artist song.artist
        xml.path song.public_path
      end
    end
  end
end

# Would generate
<instruct...(whatever the XML stuff is for it>
<playlist>
  <currently_playing>
    <song_in_list>12</song_in_list>
  </currently_playing>
  
  <songs>
    <song>
      <id>32</id>
      <title>Some cool song</title>
      <artist>Foo Fighters</artist>
      <path>/path/to/cool_song.mp3</path>
    </song>
  </songs>
</playlist>