[racket] Tricky Continuations Problem

Hello everyone,

I am not that good with continuations, and am having trouble accomplishing
what I want - which is quite trick. A little help and wisdom would be
greatly appreciated.

(define-special-computation-block
  (let ((i 0))
    ... computation block 1 ...
    (yield) ;;suspend computation
    (set! i 1)
    ... computation block 2 ...
    (yield) ;;suspend computation
    (set! i 2)
    ... computation block 3 ...
    (yield) ;;suspend computation
    (set! i 3)))

The above code defines a piece of computation that can be suspended and
resumed, and I got that part of it working properly using call/cc. However
the computation also carries some state: the i variable. I would like to
"save" the state of the computation after computation block 1, such that I
can resume it from there over and over with i still equal to 0. Is this
possible using portable R6RS scheme?

Thanks very much for your help!
  -Patrick
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