Section 32 Want more of a challenge? View in iconic form (experimental)

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       # OBJECT introduce method handler wrappers
[hear] (define add-method /
         lambda (object name method)
          (hash-add
            (object)
            (name)
            (? dummy /
             method /
             object)));

[hear] (define call / ? x / x 0);

[hear] (define test-struct2 /
         mutable-struct /
         vector x y);

[hear] (set! (test-struct2 x) 10);

[hear] (set! (test-struct2 y) 20);

[hear] (= (get! / test-struct2 x) 10);

[hear] (= (get! / test-struct2 y) 20);

[hear] (define test-struct3 /
         add-method
          (test-struct2)
          sum
          (? self /
           + (get! / self x) (get! / self y)));

[hear] (= (get! / test-struct3 x) 10);

[hear] (= (get! / test-struct3 y) 20);

[hear] (= (call / test-struct3 sum) 30);

[hear] (set! (test-struct3 y) 10);

[hear] (= (call / test-struct3 sum) 20);

[hear] (set! (test-struct2 y) 5);

[hear] (= (call / test-struct3 sum) 15);