if blocks work with filtered variables

lib/liquid/context.rb

@@ -133,6 +133,9 @@ module Liquid
         :blank?
       when 'empty'
         :empty?
+      # filtered variables
+      when SpacelessFilter
+        filtered_variable(key)
       # Single quoted strings
       when /^'(.*)'$/
         $1.to_s
@@ -221,5 +224,9 @@ module Liquid
 
       object
     end
+    
+    def filtered_variable(markup)
+      Variable.new(markup).render(self)
+    end
   end
 end