#lang syndicate

(struct echo-req (body) #:prefab)
(struct echo-resp (body) #:prefab)

(spawn (field [count 0])
       (on (message (echo-req $body))
           (send! (echo-resp body))
           (count (+ (count) 1))))

(spawn (on (message (echo-resp $body))
           (printf "Received: ~v\n" body)))

(spawn* (until (asserted (observe (echo-req _))))
        (until (asserted (observe (echo-resp _))))
        (send! (echo-req 0))
        (send! (echo-req 1))
        (send! (echo-req 2)))