return values from function

I am using the is_tree function like shown on the wordpress conditional page. I think it used to work, but now somehow does not anymore.

I am calling the function like this and don’t get anything.
echo 'is_tree(18) is: '; echo is_tree( '18' );

But don’t get a true or a false, but just nothing. What could I be doing wrong? Could this be cause by something else?

Thanks a lot for help with this one. I don’t know too much about debugging php. I know the function gets called, but it just doesn’t seem to be returning anything.

Here is the actual function:

function is_tree( $pid ) {      // $pid = The ID of the page we're looking for pages underneath
    global $post;               // load details about this page

    if ( is_page($pid) )
        return true;            // we're at the page or at a sub page

    $anc = get_post_ancestors( $post->ID );
    foreach ( $anc as $ancestor ) {
        if( is_page() && $ancestor == $pid ) {
            return true;
        }
    }

    return false;  // we arn't at the page, and the page is not an ancestor
}