优化非尾递归函数

Question

I have this function whose essential operations are outlined as follows:

function render($index) {
    foreach($things[$index] as $key => $data) {
        echo '<div>';
        /* irrelevant operations */
        if(isset($data['id'])) {
            echo '<div class="wrap">';
            render($things[$data['id']]);
            echo '</div>';
        }
        echo '</div>';
    }
}

I can not for the life of me figure out how to optimize this function; I fear that PHP implode if the call stack gets too big.

Is there any way to optimize this function?

Answer 1

This code is untested, but from the top of my head, the iterative function should look something like this:

function render($index){
    $stack = array();
    array_push($index);

    $pre = '';
    $post = '';

    while(!empty($stack)){
        $idx = array_pop($stack);

        foreach($things[$idx] as $key => $value){
            $pre .= '<1>';
            $spost = '';

            if(isset($data['id'])){
                $pre .= '<2 class="wrap">';
                $spost .= '</2>';

                $stack[] = $things[$data['id']];
            }

            $spost .= '</1>';
            $post .= $spost;
        }
    }

    return $pre . $post;
}