gistfile1.erb

<!--
 # ([].each {}).empty?
 # .each returns the enumerator
 # the block itself returns an array
-->

<% if @messages.each do |message| %>
  <%# code or partial to display the message %>
<% end.empty? %>
  You have no messages.
<% end %>

Thanks to @trooney for showing me this: http://stackoverflow.com/questions/1027871/rails-an-elegant-way-to-display-a-message-when-there-are-no-elements-in-databas/2977478#2977478