(interpret
 '(define (generalized-fold knull1? kar1 kdr1 glist1 kons2 knil2)
    (define (lp glist1 glist2)
      (if (knull1? glist1) glist2
          (lp (kdr1 glist1) (kons2 (kar1 glist1) glist2))))
    (lp glist1 knil2)))

(interpret '(define next! #f))
(interpret '(define terminate! #f))
(interpret '(define %escape #f))
(interpret '(call/cc (lambda (k) (set! %escape k))))

(interpret
 '(define (continued-fraction x)
    (define terminate? #f)
    (define p0 1) (define p1 0) (define q0 0) (define q1 1)
    (set! terminate! (lambda () (set! terminate? #t) (next!)))

    (generalized-fold
     (lambda (_) terminate?)
     (lambda (x)
       (define x0 (inexact->exact (floor x)))
       (call/cc (lambda (k2)
                  (define p2 (+ (* x0 p1) p0)) (define q2 (+ (* x0 q1) q0))
                  (set! p0 p1) (set! q0 q1) (set! p1 p2) (set! q1 q2)
                  (set! next! k2)
                  (%escape (string->symbol {[q1]/[p1]})))) ; JScheme's quasi-string
       x0)
     (lambda (x) (/ 1 (- x (floor x))))
     x cons '())))