#lang racket

(define R1-c (lambda (arg) (display "Error R1-c not defined yet") ))
(define R2-c (lambda (arg) (display "Error R2-c not defined yet") ))

(define R1 
  (lambda ()
    (call/cc 
     (lambda (break) 
       (let ((i 5))
         ; capture our continuation, but bail out of further execution
         (call/cc (lambda (k) (set! R1-c k) (break "R1-c defined")))
         ;
         ; The next time the-continuation is called, we start here.
         (display "R1 - I am back ")
         ; we are mutating the state inside the continuation, so we get
         ; a new result everytime we invoke the continuation
         (set! i (- i 1))
         (display i) (newline)
         (if (> i 0) (R2-c 0) i)
         ) 
       )
     )
    ))

(define R2 
  (lambda ()
    (call/cc 
     (lambda (break) 
       (let ((i 5))
         ; capture our continuation, but bail out of further execution
         (call/cc (lambda (k) (set! R2-c k) (break "R2-c defined")))
         ;
         ; The next time the-continuation is called, we start here.
         (display "R2 - I am back ")
         ; we are mutating the state inside the continuation, so we get
         ; a new result everytime we invoke the continuation
         (set! i (+ i 1))
         (display i) (newline)
         (R1-c 0)
         i)
       ) 
     )
    )
  )

; to start things off we need to
(R1)
(R2)
(R1-c) ; or (R2-c) if you want R2 to go first