class

# This is articles/article.rhtml
<h2><%= @article.title %></h2>

<p>
  <%= @article.body %>
</p>

<% if @article.has_comments? %>
  <ul>
    <%= render :partial => 'comment', :collection => comment.children %>
  </ul>
<% end %>

# This is articles/_comment.rhtml
<li>
  <%= comment.title %>

  <p>
    <%= comment.body %>
  </p>
  
  <% if comment.has_children? %>
    <ul>
    <%= render :partial => 'comment', :collection => comment.children %>
    </ul>
  <% end %>
  
</li>