anchor.diff:      ;
   
   facet_param returns [String facet, JSONObject param]
  -    :   LPAR column_name COMMA STRING_LITERAL COMMA facet_param_type COMMA (val=value | valList=value_list) RPAR
  +    :   LPAR column_name COMMA STRING_LITERAL COMMA facet_param_type COMMA (val=value | valList=non_variable_value_list) RPAR
           {
               $facet = $column_name.text; // XXX Check error here?
               try {
  
positive.code:         }
      ;
  
  value_list returns [Object json]
  @init {
      JSONArray jsonArray = new JSONArray();
  }
  
negative.code:         )* RPAR
          {
              $json = jsonArray;
          }
      ;
  
  
  value_list returns [Object json]
      :   non_variable_value_list
          {
              $json = $non_variable_value_list.json;
          }
      |   VARIABLE
          {
  