haversine formula for MySQL in PHP

haversine.php

<?php

function haversine($lat1, $long1, $lat2, $long2)
{
	return "(3959 * acos(cos(radians($lat1)) * cos(radians($lat2)) * cos(radians($long2) - radians($long1)) + sin(radians($lat1)) * sin(radians($lat2))))";
}