Closures as Stateful Objects

closureobjs.rkt

#lang racket

(define (obj state msg)
  (match msg
    ['init (cons state (curry obj state))]
    ['get-x (cons state (curry obj state))]
    [(list 'set-x x) (cons x (curry obj x))]
    ['ping (cons "pong" (curry obj state))]))

(define-syntax-rule (send! obj msg)
  (let ([res (obj 'msg)])
    (set! obj (cdr res))
    (car res)))

(match-define (cons _ derp) (obj 5 'init))
(printf "~a\n" (send! derp get-x))
(printf "~a\n" (send! derp ping))
(printf "~a\n" (send! derp (set-x 10)))
(printf "~a\n" (send! derp get-x))