不允许在wordpress插件中的另一个函数内调用函数？

Question

Im having dificulties to get this little plugin running.

function latest_price(){
global $wpdb;
$result = $wpdb->get_results("SELECT bid,ask FROM wp_ticker ORDER BY indate DESC limit 1");

$price = $result[0]->bid;
return $price;
}

 function outputprice(){
 $output = $this->latest_price();
echo $output;
}


add_shortcode ('getprice', 'outputprice');

when i try to run this shortcode on a wordpress page, the page doesnt load. when i turn on debugging i dont see any errors though? Is this kind of structuring allowed or should i use OOP and put the functions in a class?