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19 行
310 B

  1. (define (make-counter) (let ((var 0)) (lambda () (mutate var (+ 1 var)) var)))
  2. (define counter1 (make-counter))
  3. (assert (= (counter1) 1))
  4. (define counter2 (make-counter))
  5. (assert (= (counter2) 1))
  6. (assert (= (counter2) 2))
  7. (assert (= (counter1) 2))
  8. (assert (= (counter1) 3))
  9. (assert (= (counter2) 3))