How do you make snippets work properly in YAMS

<?php
$pageid = $modx->documentObject['id'];
$table = "ch_site_content";
$tableVars = "ch_site_tmplvar_contentvalues";

echo'<div id="navigation">
    <ul>
	';

$sql = "Select * from $table where parent = 0 and published = 1 and deleted != 1 and hidemenu = 0 order by menuindex asc";
$result = $modx->db->query($sql); 
while($row = $modx->db->getRow( $result ) )
{
	if($row['id'] == $pageid)
		echo'<li class="navigationselected"><a href="[~'.$row['id'].'~]">'.$row['pagetitle'].'</a></li>';
	else
		echo'<li><a href="[~'.$row['id'].'~]">'.$row['pagetitle'].'</a></li>';
}
    echo'</ul>
</div>
';
?>