/**
  * Accept method of the visitor design pattern. This method will be called
  * by a visitor during tree traversal.
  *
  * @param PHP_Depend_Code_ASTVisitorI $visitor The calling visitor instance.
  * @param mixed                       $data    Optional previous calculated data.
  *
  * @return mixed
  */
 public function accept(PHP_Depend_Code_ASTVisitorI $visitor, $data = null)
 {
     return $visitor->visitShiftLeftExpression($this, $data);
 }