;;; SPDX-License-Identifier: LGPL-3.0-or-later
;;; SPDX-FileCopyrightText: Copyright © 2010-2021 Tony Garnock-Jones <tonyg@leastfixedpoint.com>

#lang syndicate
;; Simple mutable box and count-to-infinity box client.

(message-struct set-box (new-value))
(assertion-struct box-state (value))

(module+ main
  (actor-system/dataspace (ds)
    (spawn #:name 'box
           (define-field current-value 0)
           (at ds
             (assert (box-state (current-value)))
             (when (message (set-box $new-value))
               (log-info "box: taking on new-value ~v" new-value)
               (current-value new-value)))
           (stop-when-true (= (current-value) 10)
             (log-info "box: terminating")))

    (spawn #:name 'client
           (at ds
             (stop-when (retracted (Observe (:pattern (set-box ,_)) _))
               (log-info "client: box has gone"))
             (when (asserted (box-state $v))
               (log-info "client: learned that box's value is now ~v" v)
               (send! ds (set-box (+ v 1))))
             (when (retracted (box-state _))
               (log-info "client: box state disappeared"))))))