[racket] Places, Channels as Events. Labeling Places.

You want handle-evt

On Thu, Dec 13, 2012 at 3:27 PM, Ray Racine <ray.racine at gmail.com> wrote:
> Using a Place or a Place-Channel as a sync event returns the value of a
> place-channel-get and not the Place itself.
>
> Most events return the actual `thing' which one sync'd on.  This is not true
> with places and channels, one gets the message itself.

I don't think it's true of "most" events. Other channels and some
ports do the same thing.

>
> The conundrum is identification of which Place / Place-Channel actually
> fired.  Places themselves have no real mechanism supporting GUID labeling or
> even simple naming/labeling.   There is no (place-name my-place) or ability
> to assign an identifier upon creation.  There is documented support for
> Place and Place-Channel equality.  So one can work around all this at the
> app code level, i.e. implement their own labeling system for Places.
>
> However assuming a roll your own labeling system there is still the
> anonymity of a place / place-channel when used as a sync event issue.
>
> (let ((msg (sync pl-1 pl-2 pl-3))))
>    ;; no idea from which place msg came from, unless explicitly recorded in
> the msg itself.
>    ;; e.g. (Msg-sender msg) -> my home brewed Place-GUID
>
> Compare and contrast with ports used as an event.  A port used as a sync
> event results in the port itself upon which one can do whatever this
> knowledge.  For example, I might opt *not* to read the port as this time,
> even unilaterally close it without reading.
>
> Consider the following parallel, asynchronous request/response idiom.
>
> Given N request msgs and P places, issue one request message per ready
> place. (Ready in the sense it is not processing a request.)
>
> I want something like
>
> (let loop ((msgs ...))
>   ...
>   (let ((ready-place (sync p1 p2 p3)))
>         (process-response (place-channel-get ready-place))
>         (process-request ready-place (car msgs))
>         (loop (cdr msgs))

(let loop ((msgs ...))
 (apply sync (map (lambda (ready-place)
                     (handle-evt ready-place
                        (lambda (response)
                          (p-r response) (p-rq ready-p (car ..)) (loop ...)
   ) ..... )

Jay


> How would one approach something like this given `sync' not returning the
> ready place but the received msg from some anonymous place which was ready.
>
>
>
> Thanks,
>
> Ray
>
>
>
>
>
>
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--
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://faculty.cs.byu.edu/~jay

"The glory of God is Intelligence" - D&C 93