XML 変換のために多次元配列を効率的に反復する方法は?

$nodes = array(
    "parent node",
    "parent node",
    array(
        "child node",
        "child node",
        array(
            "grand child node",
            "grand child node"
        )
    )
);

<node>
    <node>parent node</node>
    <node>parent node</node>
    <node>
        <node>child node</node>
        <node>child node</node>
        <node>
            <node>grand child node</node>
            <node>grand child node</node>
        </node>
    </node>
</node>

class TranformArrayIterator extends RecursiveIteratorIterator
{
    ... // Implementation omitted for brevity
}

$iterator = new TranformArrayIterator(new RecursiveArrayIterator($nodes));

foreach($iterator as $val) {
    echo $val;
}

class TranformArrayIterator extends RecursiveIteratorIterator
{
    ... // Implementation omitted for brevity
}

$xmlWriter = new XmlWriter;
... // Configuration and initialization of XMLWriter omitted

$iterator = new TranformArrayIterator(
    $xmlWriter,
    new RecursiveArrayIterator($nodes)
);