@settitle 8sync
@c %**end of header
@copying
-Copyright @copyright{} 2015 Christopher Allan Webber @email{cwebber@dustycloud.org}
+Copyright @copyright{} 2015 Christopher Allan Webber @email{cwebber@@dustycloud.org}
@end copying
@quotation
A copy of the license is also available from the Free Software
Foundation Web site at @url{http://www.gnu.org/licenses/fdl.html}.
-Altenately, this document is also available under the Lesser General
+Alternately, 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 @url{http://www.gnu.org/licenses/lgpl.html}.
-
@end quotation
@titlepage
-@title 8sync 0.1
-@subtitle Using 8sync, an asynchronous event loop for Guile
+@title 8sync
+@subtitle 8sync, asynchronous actors for Guile
@author Christopher Allan Webber
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage
-@end ifnottex
-
@c Output the table of the contents at the beginning.
@contents
@ifnottex
-@node Top
+@node Top, Preface, (dir), (dir)
@top 8sync
@insertcopying
@c Generate the nodes for this menu with `C-c C-u C-m'.
+@c Update all node entries with `C-c C-u C-n'.
+@c Insert new nodes with `C-c C-c n'.
+
@menu
-* Introduction:: About 8sync
+* Preface::
+* Tutorial::
+* API reference::
+* Systems reference::
+* Addendum::
* Copying This Manual::
-* Index:: Complete index.
+* Index::
@end menu
-@c Update all node entries with `C-c C-u C-n'.
-@c Insert new nodes with `C-c C-c n'.
+\f
+
+@node Preface
+@chapter 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:
+
+@itemize
+@item
+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.
+@item
+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@dots{} 8sync's scheduler will suspend
+your procedure and wake it back up when a response is ready.
+@item
+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.
+@item
+8sync aims to be "batteries included".
+Useful subsystems for IRC bots, HTTP servers, and so on are
+included out of the box.
+@item
+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 @emph{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!
+@end itemize
+
+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!
+
+@node Tutorial
+@chapter Tutorial
+
+@menu
+* A silly little IRC bot::
+* Writing our own actors::
+* Writing our own network-enabled actor::
+* An intermission on live hacking::
+@end menu
+
+\f
+
+@node A silly little IRC bot
+@section A silly little IRC bot
+
+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.@footnote{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"@dots{} a strange (and perhaps absurd)
+thing given chat bots being a fairly mundane novelty amongst hackers
+and teenagers everywhere a few decades ago.}
+We ourselves are going to explore chat bots as a basis for getting our
+feet wet in 8sync.
+
+First of all, we're going to need to import some modules. Put this at
+the top of your file:
+
+@example
+(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 example
+
+Now we need to add our bot. Initially, it won't do much.
+
+@example
+(define-class <my-irc-bot> (<irc-bot>))
+
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ 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 example
+
+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.
+This method is itself an action handler, hence the second argument
+for @verb{~message~}, which we can ignore for now.
+Pleasantly, the message's argument body is passed in as the rest of
+the arguments.
+
+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!
+
+@example
+(define* (run-bot #:key (username "examplebot")
+ (server "irc.freenode.net")
+ (channels '("##botchat")))
+ (define hive (make-hive))
+ (define irc-bot
+ (bootstrap-actor hive <my-irc-bot>
+ #:username username
+ #:server server
+ #:channels channels))
+ (run-hive hive '()))
+@end example
+
+Actors are connected to something called a "hive", which is a
+special kind of actor that runs and manages all the other actors.
+Actors can spawn other actors, but before we start the hive we use
+this special @verb{~bootstrap-actor~} method.
+It takes the hive as its first argument, the actor class as the second
+argument, and the rest are initialization arguments to the
+actor.
+@verb{~bootstrap-actor~} passes back not the actor itself (we don't
+get access to that usually) but the @strong{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:
+
+@example
+(run-bot #:username "some-bot-name") ; be creative!
+@end example
+
+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 @emph{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:
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ speaker channel line emote?)
+ (<- (actor-id irc-bot) 'send-line channel
+ (format #f "Bawwwwk! ~a says: ~a" speaker line)))
+@end example
+
+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@dots{} 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@dots{} 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@dots{} 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 @emph{could} rewrite handle-line
+like so:
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ speaker channel line emote?)
+ (irc-bot-send-line irc-bot channel
+ (format #f "Bawwwwk! ~a says: ~a" speaker line)))
+@end example
+
+@dots{} 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 @emph{other} actors may participate in communicating with IRC
+through our IRC bot.
+
+Anyway, our current message handler is simply too annoying.
+What we would really like to do is have our bot respond to individual
+"commands" like this:
+
+@example
+<foo-user> examplebot: hi!
+<examplebot> Oh hi foo-user!
+<foo-user> examplebot: botsnack
+<examplebot> Yippie! *does a dance!*
+<foo-user> examplebot: echo I'm a very silly bot
+<examplebot> I'm a very silly bot
+@end example
+
+Whee, that looks like fun!
+To implement it, we're going to pull out Guile's pattern matcher.
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ 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"
+ (<- (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!")
+ (<- (actor-id irc-bot) 'send-line channel
+ (format #f "Oh hi ~a!" speaker)))
+ ("echo"
+ (<- (actor-id irc-bot) 'send-line channel
+ (string-join action-args " ")))
+
+ ;; ---> Add yours here <---
+
+ ;; Default
+ (_
+ (<- (actor-id irc-bot) 'send-line channel
+ "*stupid puppy look*"))))))
+@end example
+
+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:
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ 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)
+ (<- (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 example
+
+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?
+
+\f
+@node Writing our own actors
+@section Writing our own actors
+
+Let's write the most basic, boring actor possible.
+How about an actor that start sleeping, and keeps sleeping?
+
+@example
+(use-modules (oop goops)
+ (8sync))
+
+(define-class <sleeper> (<actor>)
+ (actions #:allocation #:each-subclass
+ #:init-value (build-actions
+ (*init* sleeper-loop))))
+
+(define (sleeper-loop actor message)
+ (while (actor-alive? actor)
+ (display "Zzzzzzzz....\n")
+ ;; Sleep for one second
+ (8sleep (sleeper-sleep-secs actor))))
+
+(let* ((hive (make-hive))
+ (sleeper (bootstrap-actor hive <sleeper>)))
+ (run-hive hive '()))
+@end example
+
+We see some particular things in this example.
+One thing is that our @verb{~<sleeper>~} 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 @verb{~#:each-subclass~} or
+@verb{~#:class~}.@footnote{#:class should be fine, except there is @uref{https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25211,a bug in Guile} which keeps
+us from using it for now.}
+
+The only action handler we've added is for @verb{~*init*~}, which is called
+implicitly when the actor first starts up.
+(This will be true whether we bootstrap the actor before the hive
+starts or create it during the hive's execution.)
+
+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-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.@footnote{Or rather, for now you should call @verb{~actor-alive?~} if your code
+is looping like this.
+In the future, after an actor dies, its coroutines will
+automatically be "canceled".}
+(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.)
+
+It turns out we could have written the class for the actor much more
+simply:
+
+@example
+;; You could do this instead of the define-class above.
+(define-actor <sleeper> (<actor>)
+ ((*init* sleeper-loop)))
+@end example
+
+This is sugar, and expands into exactly the same thing as the
+define-class above.
+The third argument is an argument list, the same as what's passed
+into build-actions.
+Everything after that is a slot.
+So for example, if we had added an optional slot to specify
+how many seconds to sleep, we could have done it like so:
+
+@example
+(define-actor <sleeper> (<actor>)
+ ((*init* sleeper-loop))
+ (sleep-secs #:init-value 1
+ #:getter sleeper-sleep-secs))
+@end example
+
+This actor is pretty lazy though.
+Time to get back to work!
+Let's build a worker / manager type system.
+
+@example
+(use-modules (8sync)
+ (oop goops))
+
+(define-actor <manager> (<actor>)
+ ((assign-task manager-assign-task))
+ (direct-report #:init-keyword #:direct-report
+ #:getter manager-direct-report))
+
+(define (manager-assign-task manager message difficulty)
+ "Delegate a task to our direct report"
+ (display "manager> Work on this task for me!\n")
+ (<- (manager-direct-report manager)
+ 'work-on-this difficulty))
+@end example
+
+This manager keeps track of a direct report and tells them to start
+working on a task@dots{} simple delegation.
+Nothing here is really new, but note that our friend "<-" (which means
+"send message") is back.
+There's one difference this time@dots{} 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.
+
+@example
+(define-actor <worker> (<actor>)
+ ((work-on-this worker-work-on-this))
+ (task-left #:init-keyword #:task-left
+ #:accessor worker-task-left))
+
+(define (worker-work-on-this worker message difficulty)
+ "Work on one task until done."
+ (set! (worker-task-left worker) difficulty)
+ (display "worker> Whatever you say, boss!\n")
+ (while (and (actor-alive? worker)
+ (> (worker-task-left worker) 0))
+ (display "worker> *huff puff*\n")
+ (set! (worker-task-left worker)
+ (- (worker-task-left worker) 1))
+ (8sleep (/ 1 3))))
+@end example
+
+The worker also contains familiar code, but we now see that we can
+call 8sleep with non-integer real numbers.
+
+Looks like there's nothing left to do but run it.
+
+@example
+(let* ((hive (make-hive))
+ (worker (bootstrap-actor hive <worker>))
+ (manager (bootstrap-actor hive <manager>
+ #:direct-report worker)))
+ (run-hive hive (list (bootstrap-message hive manager 'assign-task 5))))
+@end example
+
+Unlike the @verb{~<sleeper>~}, our @verb{~<manager>~} doesn't have an implicit
+@verb{~*init*~} method, so we've bootstrapped the calling @verb{~assign-task~} action.
+
+@example
+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*
+@end example
+
+"<-" pays no attention to what happens with the messages it has sent
+off.
+This is useful in many cases@dots{} 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.
+
+@example
+;;; 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-direct-report manager)
+ 'work-on-this difficulty)
+
+ ;; Wait a moment, then call the micromanagement loop
+ (8sleep (/ 1 2))
+ (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 ((worker-is-done
+ (mbody-val (<-wait (manager-direct-report manager)
+ 'done-yet?))))
+ (if worker-is-done
+ (begin (display "manager> Oh! I guess you can go home then.\n")
+ (<- (manager-direct-report manager) 'go-home))
+ (begin (display "manager> Harumph!\n")
+ (8sleep (/ 1 2))
+ (when (actor-alive? manager)
+ (manager-micromanage-loop manager))))))
+@end example
+
+We've appended a micromanagement loop here@dots{} 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 mbody-val.
+(It's possible for a remote actor to return multiple values, in which
+case we'd want to use mbody-receive, but that's a bit more
+complicated.)
+
+Of course, we need to update our worker accordingly as well.
+
+@example
+;;; Update the worker to add the following new actions:
+(define-actor <worker> (<actor>)
+ ((work-on-this worker-work-on-this)
+ ;; Add these:
+ (done-yet? worker-done-yet?)
+ (go-home worker-go-home))
+ (task-left #:init-keyword #:task-left
+ #:accessor worker-task-left))
+
+;;; New procedures:
+(define (worker-done-yet? worker message)
+ "Reply with whether or not we're done yet."
+ (let ((am-i-done? (= (worker-task-left worker) 0)))
+ (if am-i-done?
+ (display "worker> Yes, I finished up!\n")
+ (display "worker> No... I'm still working on it...\n"))
+ (<-reply message am-i-done?)))
+
+(define (worker-go-home worker message)
+ "It's off of work for us!"
+ (display "worker> Whew! Free at last.\n")
+ (self-destruct worker))
+@end example
+
+(As you've probably guessed, you wouldn't normally call @verb{~display~}
+everywhere as we are in this program@dots{} that's just to make the
+examples more illustrative.)
+
+"<-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!
-@node Introduction
-@chapter Introduction
+Running it is the same as before:
-8sync 8sync 8sync!
+@example
+(let* ((hive (make-hive))
+ (worker (bootstrap-actor hive <worker>))
+ (manager (bootstrap-actor hive <manager>
+ #:direct-report worker)))
+ (run-hive hive (list (bootstrap-message hive manager 'assign-task 5))))
+@end example
+But the output is a bit different:
+
+@example
+manager> Work on this task for me!
+worker> Whatever you say, boss!
+worker> *huff puff*
+worker> *huff puff*
+manager> Are you done yet???
+worker> No... I'm still working on it...
+manager> Harumph!
+worker> *huff puff*
+manager> Are you done yet???
+worker> *huff puff*
+worker> No... I'm still working on it...
+manager> Harumph!
+worker> *huff puff*
+manager> Are you done yet???
+worker> Yes, I finished up!
+manager> Oh! I guess you can go home then.
+worker> Whew! Free at last.
+@end example
+
+\f
+@node Writing our own network-enabled actor
+@section Writing our own network-enabled actor
+
+So, you want to write a networked actor!
+Well, luckily that's pretty easy, especially with all you know so far.
+
+@example
+(use-modules (oop goops)
+ (8sync)
+ (ice-9 rdelim) ; line delineated i/o
+ (ice-9 match)) ; pattern matching
+
+(define-actor <telcmd> (<actor>)
+ ((*init* telcmd-init)
+ (*cleanup* telcmd-cleanup)
+ (new-client telcmd-new-client)
+ (handle-line telcmd-handle-line))
+ (socket #:accessor telcmd-socket
+ #:init-value #f))
+@end example
+
+Nothing surprising about the actor definition, though we do see that
+it has a slot for a socket.
+Unsurprisingly, that will be set up in the @verb{~*init*~} handler.
+
+@example
+(define (set-port-nonblocking! port)
+ (let ((flags (fcntl port F_GETFL)))
+ (fcntl port F_SETFL (logior O_NONBLOCK flags))))
+
+(define (setup-socket)
+ ;; our socket
+ (define s
+ (socket PF_INET SOCK_STREAM 0))
+ ;; reuse port even if busy
+ (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
+ ;; connect to port 8889 on localhost
+ (bind s AF_INET INADDR_LOOPBACK 8889)
+ ;; make it nonblocking and start listening
+ (set-port-nonblocking! s)
+ (listen s 5)
+ s)
+
+(define (telcmd-init telcmd message)
+ (set! (telcmd-socket telcmd) (setup-socket))
+ (display "Connect like: telnet localhost 8889\n")
+ (while (actor-alive? telcmd)
+ (let ((client-connection (accept (telcmd-socket telcmd))))
+ (<- (actor-id telcmd) 'new-client client-connection))))
+
+(define (telcmd-cleanup telcmd message)
+ (display "Closing socket!\n")
+ (when (telcmd-socket telcmd)
+ (close (telcmd-socket telcmd))))
+@end example
+
+That @verb{~setup-socket~} code looks pretty hard to read!
+But that's pretty standard code for setting up a socket.
+One special thing is done though@dots{} the call to
+@verb{~set-port-nonblocking!~} sets flags on the socket port so that,
+you guessed it, will be a nonblocking port.
+
+This is put to immediate use in the telcmd-init method.
+This code looks suspiciously like it @emph{should} block@dots{} after
+all, it just keeps looping forever.
+But since 8sync is using Guile's suspendable ports code feature,
+so every time this loop hits the @verb{~accept~} call, if that call
+@emph{would have} blocked, instead this whole procedure suspends
+to the scheduler@dots{} automatically!@dots{} allowing other code to run.
+
+So, as soon as we do accept a connection, we send a message to
+ourselves with the @verb{~new-client~} action.
+But wait!
+Aren't actors only supposed to handle one message at a time?
+If the telcmd-init loop just keeps on looping and looping,
+when will the @verb{~new-client~} message ever be handled?
+8sync actors only receive one message at a time, but by default if an
+actor's message handler suspends to the agenda for some reason (such
+as to send a message or on handling I/O), that actor may continue to
+accept other messages, but always in the same thread.@footnote{This is customizable: an actor can be set up to queue messages so
+that absolutely no messages are handled until the actor completely
+finishes handling one message.
+Our loop couldn't look quite like this though!}
+
+We also see that we've established a @verb{~*cleanup*~} handler.
+This is run any time either the actor dies, either through self
+destructing, because the hive completes its work, or because
+a signal was sent to interrupt or terminate our program.
+In our case, we politely close the socket when @verb{~<telcmd>~} dies.
+
+@example
+(define (telcmd-new-client telcmd message client-connection)
+ (define client (car client-connection))
+ (set-port-nonblocking! client)
+ (let loop ()
+ (let ((line (read-line client)))
+ (cond ((eof-object? line)
+ (close client))
+ (else
+ (<- (actor-id telcmd) 'handle-line
+ client (string-trim-right line #\return))
+ (when (actor-alive? telcmd)
+ (loop)))))))
+
+(define (telcmd-handle-line telcmd message client line)
+ (match (string-split line #\space)
+ (("") #f) ; ignore empty lines
+ (("time" _ ...)
+ (display
+ (strftime "The time is: %c\n" (localtime (current-time)))
+ client))
+ (("echo" rest ...)
+ (format client "~a\n" (string-join rest " ")))
+ ;; default
+ (_ (display "Sorry, I don't know that command.\n" client))))
+@end example
+
+Okay, we have a client, so we handle it!
+And once again@dots{} we see this goes off on a loop of its own!
+(Also once again, we have to do the @verb{~set-port-nonblocking!~} song and
+dance.)
+This loop also automatically suspends when it would otherwise block@dots{}
+as long as read-line has information to process, it'll keep going, but
+if it would have blocked waiting for input, then it would suspend the
+agenda.@footnote{If there's a lot of data coming in and you don't want your I/O loop
+to become too "greedy", take a look at @verb{~setvbuf~}.}
+
+The actual method called whenever we have a "line" of input is pretty
+straightforward@dots{} in fact it looks an awful lot like the IRC bot
+handle-line procedure we used earlier.
+No surprises there!@footnote{Well, there may be one surprise to a careful observer.
+Why are we sending a message to ourselves?
+Couldn't we have just dropped the argument of "message" to
+telcmd-handle-line and just called it like any other procedure?
+Indeed, we @emph{could} do that, but sending a message to ourself has
+an added advantage: if we accidentally "break" the
+telcmd-handle-line procedure in some way (say we add a fun new
+command we're playing with it), raising an exception won't break
+and disconnect the client's main loop, it'll just break the
+message handler for that one line, and our telcmd will happily
+chug along accepting another command from the user while we try
+to figure out what happened to the last one.}
+
+Now let's run it:
+
+@example
+(let* ((hive (make-hive))
+ (telcmd (bootstrap-actor hive <telcmd>)))
+ (run-hive hive '()))
+@end example
+
+Open up another terminal@dots{} you can connect via telnet:
+
+@example
+$ telnet localhost 8889
+Trying 127.0.0.1...
+Connected to localhost.
+Escape character is '^]'.
+time
+The time is: Thu Jan 5 03:20:17 2017
+echo this is an echo
+this is an echo
+shmmmmmmorp
+Sorry, I don't know that command.
+@end example
+
+Horray, it works!
+Type @verb{~Ctrl+] Ctrl+d~} to exit telnet.
+
+Not so bad!
+There's more that could be optimized, but we'll consider that to be
+advanced topics of discussion.
+
+So that's a pretty solid intro to how 8sync works!
+Now that you've gone through this introduction, we hope you'll have fun
+writing and hooking together your own actors.
+Since actors are so modular, it's easy to have a program that has
+multiple subystems working together.
+You could build a worker queue system that displayed a web interface
+and spat out notifications about when tasks finish to IRC, and making
+all those actors talk to each other should be a piece of cake.
+The sky's the limit!
+
+Happy hacking!
+
+\f
+@node An intermission on live hacking
+@section An intermission on 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@dots{} 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@dots{})
+
+Remember all the way back when we were working on the IRC bot?
+So you may have noticed while updating that 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:
+
+@example
+(define* (run-bot #:key (username "examplebot")
+ (server "irc.freenode.net")
+ (channels '("##botchat"))
+ (repl-path "/tmp/8sync-repl"))
+ (define hive (make-hive))
+ (define irc-bot
+ (bootstrap-actor hive <my-irc-bot>
+ #:username username
+ #:server server
+ #:channels channels))
+ (define repl-manager
+ (bootstrap-actor hive <repl-manager>
+ #:path repl-path))
+
+ (run-hive hive '()))
+@end example
+
+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:
+
+@example
+M-x geiser-connect-local <RET> guile <RET> /tmp/8sync-repl <RET>
+
+@end example
+
+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:
+
+@example
+;; From this:
+("botsnack"
+ (respond "Yippie! *does a dance!*"))
+
+;; To this:
+("botsnack"
+ (respond "Yippie! *catches botsnack in midair!*"))
+@end example
+
+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@dots{} 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?
+
+@example
+IRC> /query examplebot
+<foo-user> examplebot: hi!
+@end example
+
+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:
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ speaker channel line emote?)
+ ;; [... snip ...]
+ (define (respond respond-line)
+ (<- (actor-id irc-bot) 'send-line (pk 'channel channel)
+ respond-line))
+ ;; [... snip ...]
+ )
+@end example
+
+Re-evaluate.
+Now let's ping our bot in both the channel and over PM.
+
+@example
+;;; (channel "##botchat")
+
+;;; (channel "sinkbot")
+@end example
+
+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.)
+
+@example
+(define-method (handle-line (irc-bot <my-irc-bot>) message
+ speaker channel line emote?)
+ ;; [... snip ...]
+ (define (respond respond-line)
+ (<- (actor-id irc-bot) 'send-line
+ (if (looks-like-me? channel)
+ speaker ; PM session
+ channel) ; normal IRC channel
+ respond-line))
+ ;; [... snip ...]
+ )
+@end example
+
+Re-evaluate and test.
+
+@example
+IRC> /query examplebot
+<foo-user> examplebot: hi!
+<examplebot> Oh hi foo-user!
+@end example
+
+Horray!
+
+\f
+@node API reference
+@chapter API reference
+
+\f
+@node Systems reference
+@chapter Systems reference
+
+@menu
+* IRC::
+* Web / HTTP::
+@end menu
+
+\f
+@node IRC
+@section IRC
+
+\f
+@node Web / HTTP
+@section Web / HTTP
+
+\f
+@node Addendum
+@chapter Addendum
+
+@menu
+* Recommended emacs additions::
+* 8sync and Fibers::
+* 8sync's license and general comments on copyleft::
+* Acknowledgements::
+@end menu
+
+\f
+@node Recommended emacs additions
+@section Recommended emacs additions
+
+In order for @verb{~mbody-receive~} to indent properly, put this in your
+.emacs:
+
+@lisp
+(put 'mbody-receive 'scheme-indent-function 2)
+@end lisp
+
+@node 8sync and Fibers
+@section 8sync and Fibers
+
+One other major library for asynchronous communication in Guile-land
+is @uref{https://github.com/wingo/fibers/,Fibers}.
+There's a lot of overlap:
+
+@itemize
+@item
+Both use Guile's suspendable-ports facility
+@item
+Both communicate between asynchronous processes using message passing;
+you don't have to squint hard to see the relationship between Fibers'
+channels and 8sync's actor inboxes.
+@end itemize
+
+However, there are clearly differences too.
+There's a one to one relationship between 8sync actors and an actor inbox,
+whereas each Fibers fiber may read from multiple channels, for example.
+
+Luckily, it turns out there's a clear relationship, based on real,
+actual theory!
+8sync is based on the @uref{https://en.wikipedia.org/wiki/Actor_model,actor model} whereas fibers follows
+@uref{http://usingcsp.com/,Communicating Sequential Processes (CSP)}, which is a form of
+@uref{https://en.wikipedia.org/wiki/Process_calculus,process calculi}.
+And it turns out, the
+@uref{https://en.wikipedia.org/wiki/Actor_model_and_process_calculi,relationship between the actor model and process calculi} is well documented,
+and even more precisely, the
+@uref{https://en.wikipedia.org/wiki/Communicating_sequential_processes#Comparison_with_the_Actor_Model,relationship between CSP and the actor model} is well understood too.
+
+So, 8sync and Fibers do take somewhat different approaches, but both
+have a solid theoretical backing@dots{} and their theories are well
+understood in terms of each other.
+Good news for theory nerds!
+
+(Since the actors and CSP are @uref{https://en.wikipedia.org/wiki/Dual_%28mathematics%29,dual}, maybe eventually 8sync will be
+implemented on top of Fibers@dots{} that remains to be seen!)
+
+\f
+@node 8sync's license and general comments on copyleft
+@section 8sync's license and general comments on copyleft
+
+8sync is released under the GNU LGPL (Lesser General Public License),
+version 3 or later, as published by the Free Software Foundation.
+The short version of this is that if you distribute a modifications to
+8sync, whether alone or in some larger combination, must release the
+corresponding source code.
+A program which uses this library, if distributed without source code,
+must also allow relinking with a modified version of this library.
+In general, it is best to contribute them back to 8sync under the same terms;
+we'd appreciate any enhancements or fixes to be contributed upstream to
+8sync itself.
+(This is an intentional oversimplification for brevity, please read the LGPL
+for the precise terms.)
+
+This usage of the LGPL helps us ensure that 8sync and derivatives of
+8sync as a library will remain free.
+Though it is not a requirement, we request you use 8sync to build free
+software rather than use it to contribute to the growing world of
+proprietary software.
+
+The choice of the LGPL for 8sync was a strategic one.
+This is not a general recommendation to use the LGPL instead of the GPL
+for all libraries.
+In general, we encourage stronger copyleft.
+(For more thinking on this position, see
+@uref{https://www.gnu.org/licenses/why-not-lgpl.html,
+ Why you shouldn't use the Lesser GPL for your next library}.)
+
+Although 8sync provides some unique features, its main functionality
+is as an asynchronous programming environment, and there are many
+other asynchronous programming environments out there such as Node.js
+for Javascript and Asyncio for Python (there are others as well).
+It is popular in some of these communities to hold anti-copyleft positions,
+which is unfortunate, and many community members seem to be adopting
+these positions because other developers they look up to are holding
+them.
+If you have come from one of these communities and are exploring 8sync, we
+hope reading this will help you reconsider your position.
+
+In particular, if you are building a library or application that uses
+8sync in some useful way, consider releasing your program under the GNU
+GPL or GNU AGPL!
+In a world where more and more software is locked down, where software is used
+to restrict users, we could use every chance we can get to provide
+protections so that software which is free remains free, and encourages even
+more software freedom to be built upon it.
+
+So to answer the question, ``Can I build a proprietary program on top of
+8sync?'' our response is
+``Yes, but please don't.
+Choose to release your software under a freedom-respecting license.
+And help us turn the tide towards greater software freedom...
+consider a strong copyleft license!''
+
+@node Acknowledgements
+@section Acknowledgements
+
+8sync has a number of inspirations:
+
+@itemize @bullet
+@item
+@uref{https://docs.python.org/3.5/library/asyncio.html, asyncio}
+for Python provides a nice asynchronous programming environment, and
+makes great use of generator-style coroutines.
+It's a bit more difficult to work with than 8sync (or so thinks the author)
+because you have to ``line up'' the coroutines.
+
+@item
+@uref{http://dthompson.us/pages/software/sly.html, Sly}
+by David Thompson is an awesome functional reactive game programming
+library for Guile.
+If you want to write graphical games, Sly is almost certainly a better choice
+than 8sync.
+Thanks to David for being very patient in explaining tough concepts;
+experience on hacking Sly greatly informed 8sync's development.
+(Check out Sly, it rocks!)
+
+@item
+Reading @uref{https://mitpress.mit.edu/sicp/, SICP}, particularly
+@uref{https://mitpress.mit.edu/sicp/full-text/book/book-Z-H-19.html#%_chap_3,
+ Chapter 3's writings on concurrent systems},
+greatly informed 8sync's design.
+
+@item
+Finally, @uref{http://xudd.readthedocs.io/en/latest/, XUDD}
+was an earlier ``research project'' that preceeded 8sync.
+It attempted to bring an actor model system to Python.
+However, the author eventually grew frustrated with some of Python's
+limitations, fell in love with Guile, and well... now we have 8sync.
+Much of 8sync's actor model design came from experiments in developing
+XUDD.
+
+@end itemize
+
+The motivation to build 8sync came out of
+@uref{https://lists.gnu.org/archive/html/guile-devel/2015-10/msg00015.html,
+ a conversation}
+at the FSF 30th party between Mark Weaver, David Thompson, Andrew
+Engelbrecht, and Christopher Allan Webber over how to build
+an asynchronous event loop for Guile and just what would be needed.
+
+A little over a month after that, hacking on 8sync began!
+
+\f
@node Copying This Manual
@appendix Copying This Manual
+This manual is licensed under the GNU Free Documentation License, with
+no invariant sections. At your option, it is also available under the
+GNU Lesser General Public License, as published by the Free Software
+Foundation, version 3 or any later version.
+
+\f
+
@menu
* GNU Free Documentation License:: License for copying this manual.
@end menu
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