class Operations {

	public callback ops(int $x, int $y, string $op){
		switch($op) {
			case 'ADD':
				return int() using ($x, $y) {
					return $x + $y;
				};
				break;
			case 'SUB':
				return int() using ($x, $y) {
					return $x - $y;
				};
				break;
			default:
				return string() {
					return 'Operation is not supported by class.';
				};
		}           
	}
}

class Program {

	public void main() {
		callback $fn;
		object $op =  new Operations();
		$fn = $op->ops(6, 7, 'ADD');
		print($fn() + "\n");
		$fn = $op->ops(6, 2, 'SUB');
		print($fn() + "\n");
		$fn = $op->ops(6, 7, 'MUL');
		print($fn() + "\n");
	}

}