Initial stab at implementation (largely cribbed from js-marketplace)
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#lang racket/base
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(require racket/match)
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(require racket/list)
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(require "pattern.rkt")
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(require "functional-queue.rkt")
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(require (only-in web-server/private/util exn->string))
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(provide (struct-out route)
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(struct-out routing-update)
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(struct-out message)
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(struct-out quit)
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(struct-out process)
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(struct-out transition)
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sub
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pub
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spawn
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send
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feedback
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spawn-world
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transition-bind
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sequence-transitions)
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(struct route (subscription? pattern meta-level level) #:prefab)
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;; Events
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(struct routing-update (routes) #:prefab)
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(struct message (body meta-level feedback?) #:prefab)
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;; Actions (in addition to Events)
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;; (spawn is just process)
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(struct quit () #:prefab)
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;; Actors and Configurations
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(struct process (routes behavior state) #:transparent)
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(struct world (next-pid event-queue process-table downward-routes process-actions) #:transparent)
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;; Behavior : maybe event * state -> transition
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(struct transition (state actions) #:transparent)
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(define (drop-route r)
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(match-define (route s? p ml l) r)
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(and (positive? ml) (route s? p (- ml 1) l)))
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(define (lift-route r)
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(match-define (route s? p ml l) r)
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(route s? p (+ ml 1) l))
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(define (sub p #:meta-level [ml 0] #:level [l 0]) (route #t p ml l))
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(define (pub p #:meta-level [ml 0] #:level [l 0]) (route #t p ml l))
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(define (spawn behavior state [initial-routes '()]) (process initial-routes behavior state))
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(define (send body #:meta-level [ml 0]) (message body ml #f))
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(define (feedback body #:meta-level [ml 0]) (message body ml #t))
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(define (drop-routes rs) (filter-map drop-route rs))
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(define (lift-routes rs) (map lift-routes rs))
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(define (intersect-routes rs1 rs2)
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(let loop1 ((rs1 rs1)
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(acc '()))
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(match rs1
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['() (reverse acc)]
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[(cons r1 rs1)
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(let loop2 ((rs2 rs2)
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(acc acc))
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(match rs2
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['() (loop1 rs1 acc)]
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[(cons r2 rs2)
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(if (and (equal? (route-subscription? r1) (not (route-subscription? r2)))
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(= (route-meta-level r1) (route-meta-level r2))
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(< (route-level r1) (route-level r2)))
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(intersect (route-pattern r1) (route-pattern r2)
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(lambda (rr) (loop2 rs2 (cons rr acc)))
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(lambda () (loop2 rs2 acc)))
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(loop2 rs2 acc))]))])))
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(define (filter-event e rs)
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(match e
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[(routing-update e-rs)
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(routing-update (intersect-routes e-rs rs))]
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[(message body meta-level feedback?)
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(let loop ((rs rs))
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(match rs
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['() #f]
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[(cons r rs)
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(and (= meta-level (route-meta-level r))
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(equal? feedback? (not (route-subscription? r)))
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(intersect body (route-pattern r)
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(lambda (dummy) e)
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(lambda () (loop rs))))]))]))
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(define (spawn-world boot-actions)
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(spawn world-handle-event
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(enqueue-actions (world 0
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(make-queue)
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(hash)
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'()
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(make-queue))
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-1
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boot-actions)))
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(define (enqueue-actions w pid actions)
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(struct-copy world w
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[process-actions (queue-append-list (world-process-actions w)
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(map (lambda (a) (cons pid a)) (flatten actions)))]))
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(define (quiescent? w)
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(and (queue-empty? (world-event-queue w))
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(queue-empty? (world-process-actions w))))
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(define (deliver e pid p)
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(with-handlers ([(lambda (exn) #t)
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(lambda (exn)
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(log-error "Process ~a died with exception:\n~a" pid (exn->string exn))
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(transition (process-state p) (list (quit))))])
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((process-behavior p) e (process-state p))))
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(define (apply-transition pid t w)
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(match-define (transition new-state new-actions) t)
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(let* ((w (transform-process pid w (lambda (p) (struct-copy process p [state new-state])))))
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(enqueue-actions w pid new-actions)))
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(define (step-children w)
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(let-values (((w step-taken?)
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(for/fold ([w w] [step-taken? #f]) (((pid p) (in-hash (world-process-table w))))
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(define t (deliver #f pid p))
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(if t
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(values (apply-transition pid t w) #t)
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(values w step-taken?)))))
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(and step-taken? (transition w '()))))
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(define (transition-bind k t0)
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(match-define (transition state0 actions0) t0)
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(match-define (transition state1 actions1) (k state0))
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(transition state1 (cons actions0 actions1)))
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(define (sequence-transitions t0 . steps)
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(foldl transition-bind t0 steps))
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(define (perform-actions w)
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(for/fold ([t (transition (struct-copy world w [process-actions (make-queue)]) '())])
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((entry (in-list (queue->list (world-process-actions w)))))
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(match-define (cons pid a) entry)
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(transition-bind (perform-action pid a) t)))
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(define (dispatch-events w)
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(transition (for/fold ([w (struct-copy world w [event-queue (make-queue)])])
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((e (in-list (queue->list (world-event-queue w)))))
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(dispatch-event e w))
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'()))
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(define (transform-process pid w f)
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(define p (hash-ref (world-process-table w) pid))
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(if p
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(struct-copy world w [process-table (hash-set (world-process-table w) pid (f p))])
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w))
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(define (enqueue-event e w)
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(struct-copy world w [event-queue (enqueue (world-event-queue w) e)]))
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(define ((perform-action pid a) w)
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(match a
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[(? process? new-p)
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(let* ((new-pid (world-next-pid w))
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(w (struct-copy world w [next-pid (+ new-pid 1)]))
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(w (struct-copy world w [process-table
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(hash-set (world-process-table w) new-pid new-p)])))
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(issue-routing-update w))]
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[(quit)
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(let* ((w (struct-copy world w [process-table (hash-remove (world-process-table w) pid)])))
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(issue-routing-update w))]
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[(routing-update routes)
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(let* ((w (transform-process pid w (lambda (p) (struct-copy process p [routes routes])))))
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(issue-routing-update w))]
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[(message body meta-level feedback?)
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(if (zero? meta-level)
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(transition (enqueue-event a w) '())
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(transition w (message body (- meta-level 1) feedback?)))]))
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(define (aggregate-routes base w)
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(apply append base (for/list ((p (in-hash-values (world-process-table w)))) (process-routes p))))
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(define (issue-local-routing-update w)
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(enqueue-event (routing-update (aggregate-routes (world-downward-routes w) w)) w))
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(define (issue-routing-update w)
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(transition (issue-local-routing-update w)
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(routing-update (drop-routes (aggregate-routes '() w)))))
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(define (dispatch-event e w)
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(for/fold ([w w]) (((pid p) (in-hash (world-process-table w))))
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(define e1 (filter-event e (process-routes p)))
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(if e1
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(apply-transition pid (deliver e1 pid p) w)
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w)))
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(define (world-handle-event e w)
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(if (or e (not (quiescent? w)))
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(sequence-transitions (transition (inject-event e w) '())
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dispatch-events
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perform-actions
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(lambda (w) (or (step-children w) (transition w '()))))
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(step-children w)))
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(define (inject-event e w)
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(match e
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[(routing-update routes)
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(issue-local-routing-update (struct-copy world w [downward-routes (lift-routes routes)]))]
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[(message body meta-level feedback?)
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(enqueue-event (message body (+ meta-level 1) feedback?) w)]))
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