((call/cc
  (lambda (goto)
  (letrec ((start
  (lambda ()
  (print "start")
  (goto next)))
  (froz
  (lambda ()
  (print "froz")
  (goto last)))
  (next
  (lambda ()
  (print "next")
  (goto froz)))
  (last
  (lambda ()
  (print "last")
  (+ 3 4))))
  start))))