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;; let-optionals* | |
(define (make-counters . args) | |
(let-optionals* args ((seed 0) | |
(step 1)) | |
(let ((x seed)) | |
(values (lambda () | |
(set! x (+ x step))) | |
(lambda () | |
(set! x (- x step))))))) | |
(use srfi-8) ; define-values | |
(define-values (inc dec) | |
(make-counters)) | |
(inc) | |
(dec) | |
(define-values (dec2 inc2) | |
(make-counters 100 -2)) | |
(inc2) | |
(dec2) | |
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