public function compile($AST)
{
// depth-first traversal and rendering of Abstract Syntax Tree (AST)
$evaluator_str = XpresionNode::DFT($AST, array(__NAMESPACE__ . '\\Xpresion', 'render'), true);
return array($evaluator_str, XpresionUtils::evaluator_factory($evaluator_str, $this->Fn, $this->_cache));
}
