87 lines
3.2 KiB

;;; SPDX-License-Identifier: LGPL-3.0-or-later
;;; SPDX-FileCopyrightText: Copyright © 2010-2021 Tony Garnock-Jones <>
#lang syndicate
;; Santa Claus Problem
(require/activate syndicate/drivers/timer)
(require racket/list)
(require racket/set)
(assertion-struct elf-has-a-problem (id))
(assertion-struct reindeer-has-returned (id))
(assertion-struct problem-resolved (id))
(assertion-struct deliver-toys ())
(define N-ELVES 10)
(define ELF-GROUP-SIZE 3)
(define N-REINDEER 9)
(define (elf)
(define elf-self (gensym 'elf))
(spawn* #:name elf-self
(let work-industriously ()
(sleep (/ (random 1000) 1000.0))
(react (assert (elf-has-a-problem elf-self))
(stop-when (asserted (problem-resolved elf-self))
(define (reindeer)
(define reindeer-self (gensym 'reindeer))
(spawn* #:name reindeer-self
(let holiday ()
(sleep (/ (random 9000) 1000.0))
(react (assert (reindeer-has-returned reindeer-self))
(stop-when (asserted (deliver-toys))
(react (stop-when (retracted (deliver-toys))
(spawn* #:name 'santa
(define (wait-for-work)
(react (define/query-set stuck-elves (elf-has-a-problem $id) id)
(define/query-set returned-reindeer (reindeer-has-returned $id) id)
(stop-when-true (= (set-count (returned-reindeer)) N-REINDEER)
(stop-when-true (>= (set-count (stuck-elves)) ELF-GROUP-SIZE)
(talk-to-elves (take (set->list (stuck-elves)) ELF-GROUP-SIZE)))))
(define (harness-reindeer)
(react (assert (deliver-toys))
(stop-when (retracted (reindeer-has-returned _))
(define (talk-to-elves elves)
(match elves
['() (wait-for-work)]
[(cons elf remainder)
(react (assert (problem-resolved elf))
(stop-when (retracted (elf-has-a-problem elf))
(talk-to-elves remainder)))]))
(for [(i N-ELVES)] (elf))
(for [(i N-REINDEER)] (reindeer))
(spawn #:name 'narrator
(during (elf-has-a-problem $id)
(on-start (printf "~a has a problem!\n" id))
(on-stop (printf "~a's problem is resolved. ~a returns to work.\n" id id)))
(on (asserted (reindeer-has-returned $id))
(printf "~a has returned from holiday and is ready to deliver toys!\n" id))
(on (retracted (reindeer-has-returned $id))
(printf "~a delivers toys with the other reindeer.\n" id)
(react (stop-when (retracted (deliver-toys))
(printf "~a has been dismissed by Santa, and goes back on holiday.\n" id))))
(on (asserted (deliver-toys))
(printf "Santa does the delivery run!\n"))
(on (asserted (problem-resolved $id))
(printf "Santa resolves the problem of ~a.\n" id)))