Arie van Wingerden writes:
> Hi Christopher,
> 2018-05-11 15:31 GMT+02:00 Christopher Lemmer Webber <cweb...@dustycloud.org:
>> In comparison to Syndicate, Goblins is less a new language and more a
>> lightweight library for actors that interfaces nicely with "#lang
>> racket" type code
> For me personally Goblin would be the better choice I think.
If you do think that's the case (again, with the warning that it's
pre-alpha), I'd encourage you to look at the goblins/demos/ directory
for some examples. But here is the main API:
racket@> (require goblins)
;; Spawning an actor from a procedure
racket@> (define counting-actor
(let ([counter 0])
(set! counter (+ counter 1))
(format "I've been called ~a times" counter)))))
;; this sends a message, but we don't get a response...
;; "fire and forget"
racket@> (<- counting-actor)
;; this sends a message, but we do wait for a response...
;; "resume the continuation with a response"
racket@> (<<- counting-actor)
"I've been called 2 times"
;; Note that doing <<- outside an actor context will block the current
;; thread until a response comes in. Doing <<- within an actor will
;; stuff this into a queue we're "waiting on responses" from, but
;; the actor will robustly continue to respond to messages.
;; We can also spawn Racket's classes as actors fairly easily:
racket@> (define greeter%
(define/public (greet name)
(string-append "Hello, " name "!"))))
;; And we can send messages to their public methods
racket@> (<<- (spawn-new greeter%) 'greet "Bert")
;; Actors are shut down when all references to them are garbage
;; collected, so we don't need to worry about doing a one-off
;; spawn as we did above.
;; Subclassing of course works too.
racket@> (define groucher%
(init [annoyed-by "my back"])
(define am-annoyed-by annoyed-by)
(define/override (greet name)
(string-append "Grumble grumble... "
(super greet name)
am-annoyed-by " is irritating me..."))))
racket@> (<<- (spawn-new groucher%
[annoyed-by "your hair"])
"Grumble grumble... Hello, Grover!... your hair is irritating me..."
;; Here's a more complex example that demonstrates using our own address
;; with (self)
racket@> (let* ([narrator
(spawn-new (class object%
(define listeners '())
(define/public (subscribe address)
;; We don't care about the order of this
;; so fire and forget
(<- narrator "gossiper> Got a new subscriber!")
(set! listeners (cons address listeners)))
(define/public (spread-gossip msg)
(format "gossiper> Spreading juicy gossip:
(for ([listener listeners])
(<- listener 'receive-gossip msg)))))]
(define our-name name)
;; We're going to wait here because we don't want to return
;; until this completes
;; (self) is our own actor address and is bound dynamically
;; in a message handling context
(<<- gossiper 'subscribe (self)))
(define/public (receive-gossip msg)
(format "~a> Ooh, I just heard that ~a"
[sam (spawn-new listener% [name "sam"])]
[pat (spawn-new listener% [name "pat"])])
(<<- sam 'start-listening)
(<<- gossiper 'spread-gossip "Tim has great hair")
(<<- pat 'start-listening)
(<<- gossiper 'spread-gossip "Samantha has a nice car"))
gossiper> Got a new subscriber!
gossiper> Spreading juicy gossip: Tim has great hair
sam> Ooh, I just heard that Tim has great hair
gossiper> Got a new subscriber!
gossiper> Spreading juicy gossip: Samantha has a nice car
pat> Ooh, I just heard that Samantha has a nice car
racket@> sam> Ooh, I just heard that Samantha has a nice car
;; In fact you can see on that last one that since talking to the
;; gossiper is asynchronous with <-, it clobbered my racket prompt ;)
====== End tutorial ======
Hope that was interesting!
As you can see, it tries very hard to look a lot like racket code.
I used to have addresses even be callable as if
(address args ...) was implicitly the same as (<<- address args)
but since Goblins actors are "robust", I didn't want people to be
surprised that their actors may respond to other messages while waiting
for replies to their continuation with <<-.
But when I had it like that it didn't even look like message passing,
just normal procedure calls, which in a way was fun :)
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