# Permission is granted to copy, distribute and/or modify this document # under the terms of the GNU Free Documentation License, Version 1.3 # or any later version published by the Free Software Foundation; # with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. # A copy of the license is included in the section entitled ``GNU # Free Documentation License''. # # A copy of the license is also available from the Free Software # Foundation Web site at http://www.gnu.org/licenses/fdl.html # # Altenately, this document is also available under the Lesser General # Public License, version 3 or later, as published by the Free Software # Foundation. # # A copy of the license is also available from the Free Software # Foundation Web site at http://www.gnu.org/licenses/lgpl.html * Preface Welcome to 8sync's documentation! 8sync is an asynchronous programming environment for GNU Guile. (Get it? 8sync? Async??? Quiet your groans, it's a great name!) 8sync has some nice properties: - 8sync uses the actor model as its fundamental concurrency synchronization mechanism. Since the actor model is a "shared nothing" asynchronous environment, you don't need to worry about deadlocks or other tricky problems common to other asynchronous models. Actors are modular units of code and state which communicate by sending messages to each other. - If you've done enough asynchronous programming, you're probably familiar with the dreaded term "callback hell". Getting around callback hell usually involves a tradeoff of other, still rather difficult to wrap your brain around programming patterns. 8sync uses some clever tricks involving "delimited continuations" under the hood to make the code you write look familiar and straightforward. When you need to send a request to another actor and get some information back from it without blocking, there's no need to write a separate procedure... 8sync's scheduler will suspend your procedure and wake it back up when a response is ready. - Even nonblocking I/O code is straightforward to write. Thanks to the "suspendable ports" code introduced in Guile 2.2, writing asynchronous, nonblocking networked code looks mostly like writing the same synchronous code. 8sync's scheduler handles suspending and resuming networked code that would otherwise block. - 8sync aims to be "batteries included". Useful subsystems for IRC bots, HTTP servers, and so on are included out of the box. - 8sync prioritizes live hacking. If using an editor like Emacs with a nice mode like Geiser, an 8sync-using developer can change and fine-tune the behavior of code /while it runs/. This makes both debugging and development much more natural, allowing the right designs to evolve under your fingertips. A productive hacker is a happy hacker, after all! In the future, 8sync will also provide the ability to spawn and communicate with actors on different threads, processes, and machines, with most code running the same as if actors were running in the same execution environment. But as a caution, 8sync is still very young. The API is stabilizing, but not yet stable, and it is not yet well "battle-tested". Hacker beware! But, consider this as much an opportunity as a warning. 8sync is in a state where there is much room for feedback and contributions. Your help wanted! And now, into the wild, beautiful frontier. Onward! * Tutorial ** Intro to the tutorial IRC! Internet Relay Chat! The classic chat protocol of the Internet. And it turns out, one of the best places to learn about networked programming. In the 1990s I remember stumbling into some funky IRC chat rooms and being astounded that people there had what they called "bots" hanging around. From then until now, I've always enjoyed encountering bots whose range of functionality has spanned from saying absurd things, to taking messages when their "owners" were offline, to reporting the weather, to logging meetings for participants. And it turns out, IRC bots are a great way to cut your teeth on networked programming; since IRC is a fairly simple line-delineated protocol, it's a great way to learn to interact with sockets. (My first IRC bot helped my team pick a place to go to lunch, previously a source of significant dispute!) At the time of writing, venture capital awash startups are trying to turn chatbots into "big business"... a strange (and perhaps absurd) thing given chat bots being a fairly mundane novelty amongst hackers and teenagers everywhere in the 1990s. We ourselves are going to explore chat bots as a basis for getting our feet wet in 8sync. We'll start from a minimalist example using an irc bot with most of the work done for us, then move on to constructing our own actors as "game pieces" which interface with our bot, then experiment with just how easy it is to add new networked layers by tacking on a high score to our game, and as a finale we'll dive into writing our own little irc bot framework "from scratch" on top of the 8sync actor model. Alright, let's get started. This should be a lot of fun! ** A silly little IRC bot First of all, we're going to need to import some modules. Put this at the top of your file: #+BEGIN_SRC scheme (use-modules (8sync) ; 8sync's agenda and actors (8sync systems irc) ; the irc bot subsystem (oop goops) ; 8sync's actors use GOOPS (ice-9 format) ; basic string formatting (ice-9 match)) ; pattern matching #+END_SRC Now we need to add our bot. Initially, it won't do much. #+BEGIN_SRC scheme (define-class ()) (define-method (handle-line (irc-bot ) speaker channel line emote?) (if emote? (format #t "~a emoted ~s in channel ~a\n" speaker line channel) (format #t "~a said ~s in channel ~a\n" speaker line channel))) #+END_SRC We've just defined our own IRC bot! This is an 8sync actor. (8sync uses GOOPS to define actors.) We extended the handle-line generic method, so this is the code that will be called whenever the IRC bot "hears" anything. For now the code is pretty basic: it just outputs whatever it "hears" from a user in a channel to the current output port. Pretty boring! But it should help us make sure we have things working when we kick things off. Speaking of, even though we've defined our actor, it's not running yet. Time to fix that! #+BEGIN_SRC scheme (define* (run-bot #:key (username "examplebot") (server "irc.freenode.net") (channels '("##botchat"))) (define hive (make-hive)) (define irc-bot (hive-create-actor* hive "irc-bot" #:username username #:server server #:channels channels)) (run-hive hive (list (bootstrap-message hive irc-bot 'init)))) #+END_SRC Actors are connected to something called a "hive", which is a special kind of actor that runs all the other actors. Actors can spawn other actors, but before we start the hive we use this special "hive-create-actor*" method. It takes the hive as its first argument, the actor class as the second argument, a decorative "cookie" as the third argument (this is optional, but it helps with debugging... you can skip it by setting it to #f if you prefer), and the rest are initialization arguments to the actor. hive-create-actor* passes back not the actor itself (we don't get access to that usually) but the *id* of the actor. (More on this later.) Finally we run the hive with run-hive and pass it a list of "bootstrapped" messages. Normally actors send messages to each other (and sometimes themselves), but we need to send a message or messages to start things or else nothing is going to happen. We can run it like: #+BEGIN_SRC scheme (run-bot #:username "some-bot-username") ; be creative! #+END_SRC Assuming all the tubes on the internet are properly connected, you should be able to join the "##botchat" channel on irc.freenode.net and see your bot join as well. Now, as you probably guessed, you can't really /do/ much yet. If you talk to the bot, it'll send messages to the terminal informing you as such, but it's hardly a chat bot if it's not chatting yet. So let's do the most boring (and annoying) thing possible. Let's get it to echo whatever we say back to us. Change handle-line to this: #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) (<- irc-bot (actor-id irc-bot) 'send-line channel (format #f "Bawwwwk! ~a says: ~a" speaker line))) #+END_SRC This will do exactly what it looks like: repeat back whatever anyone says like an obnoxious parrot. Give it a try, but don't keep it running for too long... this bot is so annoying it's likely to get banned from whatever channel you put it in. This method handler does have the advantage of being simple though. It introduces a new concept simply... sending a message! Whenever you see "<-", you can think of that as saying "send this message". The arguments to "<-" are as follows: the actor sending the message, the id of the actor the message is being sent to, the "action" we want to invoke (a symbol), and the rest are arguments to the "action handler" which is in this case send-line (with itself takes two arguments: the channel our bot should send a message to, and the line we want it to spit out to the channel). (Footnote: 8sync's name for sending a message, "<-", comes from older, early lisp object oriented systems which were, as it turned out, inspired by the actor model! Eventually message passing was dropped in favor of something called "generic functions" or "generic methods" (you may observe we made use of such a thing in extending handle-line). Many lispers believe that there is no need for message passing with generic methods and some advanced functional techniques, but in a concurrent environment message passing becomes useful again, especially when the communicating objects / actors are not in the same address space.) Normally in the actor model, we don't have direct references to an actor, only an identifier. This is for two reasons: to quasi-enforce the "shared nothing" environment (actors absolutely control their own resources, and "all you can do is send a message" to request that they modify them) and because... well, you don't even know where that actor is! Actors can be anything, and anywhere. It's possible in 8sync to have an actor on a remote hive, which means the actor could be on a remote process or even remote machine, and in most cases message passing will look exactly the same. (There are some exceptions; it's possible for two actors on the same hive to "hand off" some special types of data that can't be serialized across processes or the network, eg a socket or a closure, perhaps even one with mutable state. This must be done with care, and the actors should be careful both to ensure that they are both local and that the actor handing things off no longer accesses that value to preserve the actor model. But this is an advanced topic, and we are getting ahead of ourselves.) We have to supply the id of the receiving actor, and usually we'd have only the identifier. But since in this case, since the actor we're sending this to is ourselves, we have to pass in our identifier, since the Hive won't deliver to anything other than an address. Astute readers may observe, since this is a case where we are just referencing our own object, couldn't we just call "sending a line" as a method of our own object without all the message passing? Indeed, we do have such a method, so we /could/ rewrite handle-line like so: #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) (irc-bot-send-line irc-bot channel (format #f "Bawwwwk! ~a says: ~a" speaker line))) #+END_SRC ... but we want to get you comfortable and familiar with message passing, and we'll be making use of this same message passing shortly so that /other/ actors may participate in communicating with IRC through our IRC bot. Anyway, our current message handler is simply too annoying. What would be much more interesting is if we could recognize when an actor could repeat messages /only/ when someone is speaking to it directly. Luckily this is an easy adjustment to make. #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) (define my-name (irc-bot-username irc-bot)) (define (looks-like-me? str) (or (equal? str my-name) (equal? str (string-concatenate (list my-name ":"))))) (when (looks-like-me?) (<- irc-bot (actor-id irc-bot) 'send-line channel (format #f "Bawwwwk! ~a says: ~a" speaker line)))) #+END_SRC This is relatively straightforward, but it isn't very interesting. What we would really like to do is have our bot respond to individual "commands" like this: #+BEGIN_SRC text examplebot: hi! Oh hi foo-user! examplebot: botsnack Yippie! *does a dance!* examplebot: echo I'm a very silly bot I'm a very silly bot #+END_SRC Whee, that looks like fun! To implement it, we're going to pull out Guile's pattern matcher. #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) (define my-name (irc-bot-username irc-bot)) (define (looks-like-me? str) (or (equal? str my-name) (equal? str (string-concatenate (list my-name ":"))))) (match (string-split line #\space) (((? looks-like-me? _) action action-args ...) (match action ;; The classic botsnack! ("botsnack" (<- irc-bot (actor-id irc-bot) 'send-line channel "Yippie! *does a dance!*")) ;; Return greeting ((or "hello" "hello!" "hello." "greetings" "greetings." "greetings!" "hei" "hei." "hei!" "hi" "hi!") (<- irc-bot (actor-id irc-bot) 'send-line channel (format #f "Oh hi ~a!" speaker))) ("echo" (<- irc-bot (actor-id irc-bot) 'send-line channel (string-join action-args " "))) ;; ---> Add yours here <--- ;; Default (_ (<- irc-bot (actor-id irc-bot) 'send-line channel "*stupid puppy look*")))))) #+END_SRC Parsing the pattern matcher syntax is left as an exercise for the reader. If you're getting the sense that we could make this a bit less wordy, you're right: #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) (define my-name (irc-bot-username irc-bot)) (define (looks-like-me? str) (or (equal? str my-name) (equal? str (string-concatenate (list my-name ":"))))) (define (respond respond-line) (<- irc-bot (actor-id irc-bot) 'send-line channel respond-line)) (match (string-split line #\space) (((? looks-like-me? _) action action-args ...) (match action ;; The classic botsnack! ("botsnack" (respond "Yippie! *does a dance!*")) ;; Return greeting ((or "hello" "hello!" "hello." "greetings" "greetings." "greetings!" "hei" "hei." "hei!" "hi" "hi." "hi!") (respond (format #f "Oh hi ~a!" speaker))) ("echo" (respond (string-join action-args " "))) ;; ---> Add yours here <--- ;; Default (_ (respond "*stupid puppy look*")))))) #+END_SRC Okay, that looks pretty good! Now we have enough information to build an IRC bot that can do a lot of things. Take some time to experiment with extending the bot a bit before moving on to the next section! What cool commands can you add? ** An intermission: about live hacking This section is optional, but highly recommended. It requires that you're a user of GNU Emacs. If you aren't, don't worry... you can forge ahead and come back in case you ever do become an Emacs user. (If you're more familiar with Vi/Vim style editing, I hear good things about Spacemacs...) So you may have noticed while updating the last section that the start/stop cycle of hacking isn't really ideal. You might either edit a file in your editor, then run it, or type the whole program into the REPL, but then you'll have to spend extra time copying it to a file. Wouldn't it be nice if it were possible to both write code in a file and try it as you go? And wouldn't it be even better if you could live edit a program while it's running? Luckily, there's a great Emacs mode called Geiser which makes editing and hacking and experimenting all happen in harmony. And even better, 8sync is optimized for this experience. 8sync provides easy drop-in "cooperative REPL" support, and most code can be simply redefined on the fly in 8sync through Geiser and actors will immediately update their behavior, so you can test and tweak things as you go. Okay, enough talking. Let's add it! Redefine run-bot like so: #+BEGIN_SRC scheme (define* (run-bot #:key (username "examplebot") (server "irc.freenode.net") (channels '("##botchat")) (repl-path "/tmp/8sync-repl")) (define hive (make-hive)) (define irc-bot (hive-create-actor* hive "irc-bot" #:username username #:server server #:channels channels)) (define repl-manager (hive-create-actor* hive "repl" #:path repl-path)) (run-hive hive (list (bootstrap-message hive irc-bot 'init) (bootstrap-message hive repl-manager 'init)))) #+END_SRC If we put a call to run-bot at the bottom of our file we can call it, and the repl-manager will start something we can connect to automatically. Horray! Now when we run this it'll start up a REPL with a unix domain socket at the repl-path. We can connect to it in emacs like so: : M-x geiser-connect-local guile /tmp/8sync-repl Okay, so what does this get us? Well, we can now live edit our program. Let's change how our bot behaves a bit. Let's change handle-line and tweak how the bot responds to a botsnack. Change this part: #+BEGIN_SRC scheme ;; From this: ("botsnack" (respond "Yippie! *does a dance!*")) ;; To this: ("botsnack" (respond "Yippie! *catches botsnack in midair!*")) #+END_SRC Okay, now let's evaluate the change of the definition. You can hit "C-M-x" anywhere in the definition to re-evaluate. (You can also position your cursor at the end of the definition and press "C-x C-e", but I've come to like "C-M-x" better because I can evaluate as soon as I'm done writing.) Now, on IRC, ask your bot for a botsnack. The bot should give the new message... with no need to stop and start the program! Let's fix a bug live. Our current program works great if you talk to your bot in the same IRC channel, but what if you try to talk to them over private message? #+BEGIN_SRC text IRC> /query examplebot examplebot: hi! #+END_SRC Hm, we aren't seeing any response on IRC! Huh? What's going on? It's time to do some debugging. There are plenty of debugging tools in Guile, but sometimes the simplest is the nicest, and the simplest debugging route around is good old fashioned print debugging. It turns out Guile has an under-advertised feature which makes print debugging really easy called "pk", pronounced "peek". What pk accepts a list of arguments, prints out the whole thing, but returns the last argument. This makes wrapping bits of our code pretty easy to see what's going on. So let's peek into our program with pk. Edit the respond section to see what channel it's really sending things to: #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) ;; [... snip ...] (define (respond respond-line) (<- irc-bot (actor-id irc-bot) 'send-line (pk 'channel channel) respond-line)) ;; [... snip ...] ) #+END_SRC Re-evaluate. Now let's ping our bot in both the channel and over PM. #+BEGIN_SRC text ;;; (channel "##botchat") ;;; (channel "sinkbot") #+END_SRC Oh okay, this makes sense. When we're talking in a normal multi-user channel, the channel we see the message coming from is the same one we send to. But over PM, the channel is a username, and in this case the username we're sending our line of text to is ourselves. That isn't what we want. Let's edit our code so that if we see that the channel we're sending to looks like our own username that we respond back to the sender. (We can remove the pk now that we know what's going on.) #+BEGIN_SRC scheme (define-method (handle-line (irc-bot ) speaker channel line emote?) ;; [... snip ...] (define (respond respond-line) (<- irc-bot (actor-id irc-bot) 'send-line (if (looks-like-me? channel) speaker ; PM session channel) ; normal IRC channel respond-line)) ;; [... snip ...] ) #+END_SRC Re-evaluate and test. #+BEGIN_SRC text IRC> /query examplebot examplebot: hi! Oh hi foo-user! #+END_SRC Horray! ** Writing our own actors and sending messages between them Let's write the most basic, boring actor possible. How about an actor that start sleeping, and keeps sleeping? #+BEGIN_SRC scheme (use-modules (oop goops) (8sync)) (define-class () (actions #:allocation #:each-subclass #:init-value (build-actions (loop sleeper-loop)))) (define (sleeper-loop actor message) (while (actor-am-i-alive? actor) (display "Zzzzzzzz....\n") ;; Sleep for one second (8sleep 1))) (let* ((hive (make-hive)) (sleeper (hive-create-actor hive ))) (run-hive hive (list (bootstrap-message hive sleeper 'loop)))) #+END_SRC We see some particular things in this example. One thing is that our actor has an actions slot. This is used to look up what the "action handler" for a message is. We have to set the #:allocation to either #:each-subclass or #:class. (#:class should be fine, except there is [[https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25211][a bug in Guile]] which keeps us from using it for now.) In our sleeper-loop we also see a call to "8sleep". "8sleep" is like Guile's "sleep" method, except it is non-blocking and will always yield to the scheduler. Our while loop also checks "actor-am-i-alive?" to see whether or not it is still registered. In general, if you keep a loop in your actor that regularly yields to the scheduler, you should check this. (An alternate way to handle it would be to not use a while loop at all but simply send a message to ourselves with "<-" to call the sleeper-loop handler again. If the actor was dead, the message simply would not be delivered and thus the loop would stop.) This actor is pretty lazy though. Time to get back to work! #+BEGIN_SRC scheme (use-modules (8sync) (oop goops)) (define-class () (direct-report #:init-keyword #:direct-report #:getter manager-direct-report) (actions #:allocation #:each-subclass #:init-value (build-actions (assign-task manager-assign-task)))) (define (manager-assign-task manager message difficulty) "Delegate a task to our direct report" (display "manager> Work on this task for me!\n") (<- manager (manager-direct-report manager) 'work-on-this difficulty)) #+END_SRC Here we're constructing a very simple manager actor. This manager keeps track of a direct report and tells them to start working on a task... simple delegation. Nothing here is really new, but note that our friend "<-" (which means "send message") is back. There's one difference this time... the first time we saw "<-" was in the handle-line procedure of the irc-bot, and in that case we explicitly pulled the actor-id after the actor we were sending the message to (ourselves), which we aren't doing here. But that was an unusual case, because the actor was ourself. In this case, and in general, actors don't have direct references to other actors; instead, all they have is access to identifiers which reference other actors. #+BEGIN_SRC scheme (define-class () (task-left #:init-keyword #:task-left #:accessor worker-task-left) (actions #:allocation #:each-subclass #:init-value (build-actions (work-on-this worker-work-on-this)))) (define (worker-work-on-this worker message difficulty) "" (set! (worker-task-left worker) difficulty) (display "worker> Whatever you say, boss!\n") (while (and (actor-am-i-alive? worker) (> (worker-task-left worker) 0)) (display "worker> *huff puff*\n") (set! (worker-task-left worker) (- (worker-task-left worker) 1)) (8sync (/ 1 3))) (display "worker> Looks like I'm done! Can I go home yet?\n")) #+END_SRC The worker also contains familiar code, but we now see that we can call 8sync with non-integer real numbers. Looks like there's nothing left to do but run it: #+BEGIN_SRC scheme (let* ((hive (make-hive)) (worker (hive-create-actor hive )) (manager (hive-create-actor hive #:direct-report worker))) (run-hive hive (list (bootstrap-message hive manager 'assign-task 5)))) #+END_SRC #+BEGIN_SRC text manager> Work on this task for me! worker> Whatever you say, boss! worker> *huff puff* worker> *huff puff* worker> *huff puff* worker> *huff puff* worker> *huff puff* worker> Looks like I'm done! Can I go home yet? #+END_SRC "<-" pays no attention to what happens with the messages it has sent off. This is useful in many cases... we can blast off many messages and continue along without holding anything back. But sometimes we want to make sure that something completes before we do something else, or we want to send a message and get some sort of information back. Luckily 8sync comes with an answer to that with "<-wait", which will suspend the caller until the callee gives some sort of response, but which does not block the rest of the program from running. Let's try applying that to our own code by turning our manager into a micromanager. #+END_SRC #+BEGIN_SRC scheme ;;; Update this method (define (manager-assign-task manager message difficulty) "Delegate a task to our direct report" (display "manager> Work on this task for me!\n") (<- manager (manager-direct-report manager) 'work-on-this difficulty) ;; call the micromanagement loop (manager-micromanage-loop manager)) ;;; And add the following ;;; (... Note: do not model actual employee management off this) (define (manager-micromanage-loop manager) "Pester direct report until they're done with their task." (display "manager> Are you done yet???\n") (let ((still-working (msg-val (<-wait manager (manager-direct-report manager) 'done-yet?)))) (if still-working (begin (display "manager> Harumph!\n") (8sleep 1) (when (actor-am-i-alive? manager) (manager-micromanage-loop manager))) (begin (display "manager> Oh! I guess you can go home then.\n") (<- manager (manager-direct-report manager) 'go-home))))) #+END_SRC We've appended a micromanagement loop here... but what's going on? "<-wait", as it sounds, waits for a reply, and returns a reply message. In this case there's a value in the body of the message we want, so we pull it out with msg-val. (It's possible for a remote actor to return multiple values, in which case we'd want to use msg-receive, but that's a bit more complicated.) Of course, we need to update our worker accordingly as well. #+BEGIN_SRC scheme ;;; Update the worker to add the following new actions: (define-class () (task-left #:init-keyword #:task-left #:accessor worker-task-left) (actions #:allocation #:each-subclass #:init-value (build-actions (work-on-this worker-work-on-this) ;; Add these: (done-yet? worker-done-yet?) (go-home worker-go-home)))) ;;; New procedures: (define (worker-done-yet? worker message) "Reply with whether or not we're done yet." (<-reply worker message (= (worker-task-left worker) 0))) (define (worker-go-home worker message) "It's off of work for us!" (display "worker> Whew! Free at last.") (self-destruct worker)) #+END_SRC "<-reply" is what actually returns the information to the actor waiting on the reply. It takes as an argument the actor sending the message, the message it is in reply to, and the rest of the arguments are the "body" of the message. (If an actor handles a message that is being "waited on" but does not explicitly reply to it, an auto-reply with an empty body will be triggered so that the waiting actor is not left waiting around.) The last thing to note is the call to "self-destruct". This does what you might expect: it removes the actor from the hive. No new messages will be sent to it. Ka-poof! ** Writing our own from scratch * API reference * Systems reference ** IRC ** Web / HTTP ** COMMENT Websockets