/**
  * Parse Sass code
  *
  * @param string Source
  * @param array Array of constants
  * @return string
  */
 public static function sass($source, array $constants = array())
 {
     if (!self::$instance instanceof SassParser) {
         self::$instance = new SassParser();
     }
     return self::$instance->setSource($source)->render();
 }