getnext.rkt

;; Small example of pseudo-algebraic effects in Racket
#lang racket

(define handler-tag (make-continuation-prompt-tag 'handler))

;; Handler
(define ((handler x) k)
  (displayln (format "giving back value ~a" x))
  (call-with-continuation-prompt
   (lambda () (k x))
   handler-tag
   (handler (+ x 1))))

(call-with-continuation-prompt 
 (lambda ()
   (define (getnext)
     (call-with-composable-continuation
      (lambda (k)
        (abort-current-continuation handler-tag k))
      handler-tag))
   (let* ([x (+ 1 (getnext))]
          [y (+ 1 (getnext))])
     (+ 1 (getnext))))
 handler-tag
 (handler 0))