Bank account example

prospect/examples/actor/bank-account.rkt

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+#lang prospect
+;; Hello-worldish "bank account" example.
+
+(require prospect/actor)
+
+(struct account (balance) #:prefab)
+(struct alter-balance-by (amount) #:prefab)
+
+(actor-body->spawn-action
+ (lambda ()
+   (actor (forever #:collect [(balance 0)]
+                   (assert (account balance))
+                   (on (message (alter-balance-by $amount))
+                       (+ balance amount))))
+
+   (actor (forever (on (asserted (account $balance))
+                       (printf "Balance changed to ~a\n" balance))))
+
+   (until (asserted (observe (alter-balance-by _))))
+   (send! (alter-balance-by +100))
+   (send! (alter-balance-by -30))
+   ))

prospect/examples/bank-account.rkt

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+#lang prospect
+;; Hello-worldish "bank account" example.
+
+(struct account (balance) #:prefab)
+(struct alter-balance-by (amount) #:prefab)
+
+(spawn (lambda (e balance)
+         (match e
+           [(message (alter-balance-by amount))
+            (define new-balance (+ balance amount))
+            (transition new-balance
+                        (patch-seq (retract (account balance))
+                                   (assert (account new-balance))))]
+           [_ #f]))
+       0
+       (patch-seq (sub (alter-balance-by ?))
+                  (assert (account 0))))
+
+(spawn (lambda (e s)
+         (match e
+           [(patch added removed)
+            (for [(balance (matcher-project/set/single added (compile-projection (account (?!)))))]
+              (printf "Balance changed to ~a\n" balance))
+            #f]
+           [_ #f]))
+       (void)
+       (sub (account ?)))
+
+(message (alter-balance-by +100))
+(message (alter-balance-by -30))