monads.rkt

#lang racket/base
 
(require racket/control)
 
(struct monad (bind return) #:transparent)
 
(define-syntax-rule (with-monad ([val m]) body ...)
  (let* ([m-once m]
        [val
         (lambda (ma)
           (shift k
                  ((monad-bind m-once) ma k)))])
    (reset
     ((monad-return m-once)
      body ...))))
 
 
  (define list-m (monad (lambda (ma f) (apply append (map f ma))) list))
  (display (with-monad ((val list-m))
    (+ (val (list 1 2 3)) (val (list 4 5 6)))))