(define (cycle-lists xs ys)
  (define (get-stream-by-array xs)
      (letrec ([f (lambda (x)
                (if (= x (- (length xs) 1))
                    (cons (list-ref xs x) (lambda () (f 0)))
                    (cons (list-ref xs x) (lambda () (f (+ x 1))))))])
    (lambda () (f 0))))

  (define (cycle-streams s1 s2)
    (lambda () (cons (cons (car (s1)) (car (s2))) (cycle-streams (cdr (s1)) (cdr (s2))))))

  (cycle-streams (get-stream-by-array xs) (get-stream-by-array ys)))