Dynamic wind & call/cc

gistfile1.rkt

#lang racket

(define k1 #f)
(define k2 #f)

(call-with-continuation-prompt
 (lambda ()
   ;; this dw will only run twice and not three for
   ;; the initial run, k1, and then k2
   (dynamic-wind
    (lambda () (displayln "pre1"))
    (lambda ()
      ;; create an application in continuation
      ((call/cc
        (lambda (k)
          (set! k1 k)
          (call/cc
           (lambda (k)
             (set! k2 k)
             ;; identity function for first run
             (lambda (x) x)))))
       ;; returned in first run
       ;; sent to k2 after invocation of k1
       (lambda (x) 5)))
    (lambda () (displayln "post1")))))

(call-with-continuation-prompt
 ;; invoke k1 and then invoke k2 
 (lambda () (k1 k2)))