function not executing

hello I am turning a PHP into a function to be executed on a page template, the code when itself is run through directly from the template file works but when I create a function in code snippets and call it on the page template it breaks
this is the code

function getPrevNext(){
$pagelist = get_pages("child_of=".$post->post_parent."&parent=".$post->post_parent."&sort_column=menu_order&sort_order=asc");
	$pages = array();
	foreach ($pagelist as $page) {
	   $pages[] += $page->ID;
	}

$current = array_search($post->ID, $pages);
	$prevID = $pages[$current-1];
	$nextID = $pages[$current+1];
	
	echo '<div class="navigation">';
	
	if (!empty($prevID)) {
		echo '<div class="alignleft">';
		echo '<a href="';
		echo get_permalink($prevID);
		echo '"';
		echo 'title="';
		echo get_the_title($prevID); 
		echo'">Previous</a>';
		echo "</div>";
	}
	if (!empty($nextID)) {
		echo '<div class="alignright">';
		echo '<a href="';
		echo get_permalink($nextID);
		echo '"';
		echo 'title="';
		echo get_the_title($nextID); 
		echo'">Next</a>';
		echo "</div>";		
	}
}