(define-syntax let/cc
  (syntax-rules ()
    ((_ ?var ?body)
     (call-with-current-continuation (lambda (?var) ?body)))))

(define resume #f)

(define (error) (/ 1 0))

(define (makecoroutine body)
  (let ((lcs #f))
    (letrec ((newcoroutine
	      (lambda (value)
		(lcs value)))
	     (localresume
	      (lambda (cont value)
		(let ((received-value
		       (let/cc localcont
			  (begin (set! lcs localcont)
				 (cont value)))))
		  (set! resume localresume)
		  received-value
		  ))))
      (let/cc exit
	 (begin (body (localresume exit newcoroutine))
		(error))))))

(define (example)
  (let/cc returncont
     (let ((co1 #f)
	   (co2 #f))
       (set! co1
	     (makecoroutine
	      (lambda (initval1)
		(write "1 ")
		(write initval1)
		(set! initval1 (resume co2 (+ initval1 1)))
		(write "1 ")
		(write initval1)
		(set! initval1 (resume co2 (+ initval1 1)))
		(returncont initval1)
		)))
       (set! co2
	     (makecoroutine
	      (lambda (initval2)
		(write "2 ")
		(write initval2)
		(set! initval2 (resume co1 (+ initval2 1)))
		(write "2 ")
		(resume co1 (+ initval2 1))
		)))
       (co1 33)
       )))