Добавил unless который противоположен if'у

klein.php

@@ -21,6 +21,7 @@ class Klein {
             ["{% for+:id , :id+in+:var %}", "foreach(#3s as #1s => #2s):"],
             ["{% endfor %}", "endforeach;"],
             ["{% if+:var %}", "if(isset(#1s) && #1s):"],
+            ["{% unless+:var %}", "if(!(isset(#1s) && #1s)):"],
             ["{% else %}", "else:"],
             ["{% endif %}", "endif;"],
             ["{{ :var }}", "echo #1s;"],
@@ -52,4 +53,4 @@ class Klein {
         eval(" ?>".$this->code."<?php ");
         return ob_get_clean();
     }
-}
+}