example.erb

<div class="list">
  <ul>
    <% @items.each do |item| %>
      <li class="<%= item_classes_for_user(item, @current_user) %>">
        <%= image_tag "/icons/#{item.state}.png" %>
        <span class="name">
          <%= item.name %>
        </span>
      </li>
    <% end %>
  </ul>
</div>

example.haml

.list
  %ul
    - @items.each do |item|
      %li{ :class => item_classes_for_user(item, @current_user) }
        = image_tag "/icons/#{item.state}.png"
        %span.name= item.name

example.rb

# Erector
div :class => "list" do
  ul do
    @items.each do |item|
      li :class => item_classes_for_user(item, @current_user) do
        img :src => "/icons/#{item.state}.png"
        span item.name, :class => "name"
      end
    end
  end
end

example_helper.rb

def item_classes_for_user(item, user)
  classes = ["item", item.state]
  classes << "interesting" if item.interesting_to?(user)
  classes
end