syndicate-2017/racket/syndicate/examples/bank-account.rkt

25 lines
887 B
Racket

#lang syndicate
;; Hello-worldish "bank account" example.
(struct account (balance) #:prefab)
(struct deposit (amount) #:prefab)
(define (manager e balance)
(match-event e
[(message (deposit amount))
(transition (+ balance amount) (patch-seq (retract (account balance))
(assert (account (+ balance amount)))))]))
(define (observer e _)
(when (patch? e) (for [(balance (project-assertions (patch-added e) (account (?!))))]
(printf "Balance changed to ~a\n" balance))))
(define (updater e _)
(when (patch/added? e)
(quit (list (message (deposit +100))
(message (deposit -30))))))
(spawn manager 0 (patch-seq (assert (observe (deposit ?))) (assert (account 0))))
(spawn observer (void) (assert (observe (account ?))))
(spawn updater (void) (assert (observe (observe (deposit ?)))))