---

       # OBJECT introduce simple mutable structures
[hear] (define mutable-struct /
         ? lst /
         let ((data (map (? x / make-cell 0) (lst))))
          (? key /
           list-ref (data) (list-find (lst) (key) (? x 0))));

[hear] (define test-struct1 /
         mutable-struct /
         vector item1 item2 item3);

[hear] (set! (test-struct1 item1) 15);

[hear] (= (get! / test-struct1 item1) 15);