public function createChildExpression()
{
$expression = new Expression();
$this->_nested_expressions[] = $expression;
$expression->setParent($this);
return $expression;
}
public function getToExpressionLevel(Expression $expression, $level = 0)
{
if ($level == 0) {
return $expression;
}
if ($level < 0) {
throw new \Exception("no");
}
return $this->getToExpressionLevel($expression->getLastChild(), --$level);
}
