1 (define (make-posn x y)
2   (local ((define x0 x)
3           (define y0 y)
4           (define (service-manager msg)
5             (cond
6               [(equal? msg 'x) x0]
7               [(equal? msg 'y) y0]
8               [(equal? msg 'set-x) (lambda (new-x) (set! x0 new-x))]
9               [(equal? msg 'set-y) (lambda (new-y) (set! y0 new-y))])))
10     service-manager))