Luminate CMS: Assign classes .first & .last to first & last items in the list

fist-last-classes-list.html

<t:if test="length > 0">
  <ul><t:list>
   <t:set id="myClass" value="''" />
   <t:if test="index == 1"><t:set id="myClass" value="'first'" /></t:if>
   <t:if test="index == length"><t:set id="myClass" value="concat(myClass, ' last')" /></t:if>
   <t:set id="myClass" value="trim(myClass)" />
   <t:if test="!isNull(myClass)"><li class="${myClass}"></t:if>
   <t:else><li></t:else>
   <a href="${url}">${title}</a><p>${description}</p>
   </li>
  </t:list></ul>
</t:if>