#lang syndicate
;; Test case for a bug relating to use of parameters to accumulate
;; actions across react/suspend when an intermediate parameterization
;; for current-dataflow-subject-id has taken place.
;;
;; Expected output:
;;     flag: 'clear
;;     flag: 'set
;;     - '(saw ping)
;;
;; Previously expected output:
;;     flag: 'clear
;;     - 'first
;;     flag: 'set
;;     - '(saw ping)
;;
;; Buggy output:
;;     flag: 'clear
;;     - 'first
;;     flag: 'clear

(struct x (v) #:prefab)

(spawn (on (message (x 'ping))
           (send! (x 'pong))))

(spawn (field [flag 'clear])
       (begin/dataflow
         (printf "flag: ~v\n" (flag)))

       (field [spec #f])
       (begin/dataflow
         (when (spec)
           (let-event [(asserted (observe (x (spec))))]
                      (send! (x (list 'saw (spec))))
                      (flag 'set))))

       (on-start (send! (x 'first)))
       (on (message (x 'first))
           (spec 'ping)))

(spawn (on (message (x $v))
           (printf "- ~v\n" v)))