(define (make-position x y)
  (define (get-x)
    x)

  (define (get-y)
    y)

  (define (set-x! new-value)
    (set! x new-value))

  (define (set-y! new-value)
    (set! y new-value))

  (define (position-dispatcher msg)
    (cond ((eq? msg 'get-x) get-x)
          ((eq? msg 'get-y) get-y)
          ((eq? msg 'set-x!) set-x!)
          ((eq? msg 'set-y!) set-y!)
          ))

  position-dispatcher)

(define p1 (make-position 10 20))
(define p2 (make-position 30 40))

(define (print x)
  (display x)
  (newline))

(print ((p1 'get-x)))
(print ((p1 'get-y)))
(print "---")

((p1 'set-x!) 5000)

(print ((p1 'get-x)))
(print ((p1 'get-y)))
(print "---")