# 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
+#
+# 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 http://www.gnu.org/licenses/lgpl.html
#+BEGIN_SRC scheme
(define-class <my-irc-bot> (<irc-bot>))
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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)
(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 =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!
(channels '("##botchat")))
(define hive (make-hive))
(define irc-bot
- (bootstrap-actor* hive <my-irc-bot> "irc-bot"
- #:username username
- #:server server
- #:channels channels))
+ (bootstrap-actor hive <my-irc-bot>
+ #:username username
+ #:server server
+ #:channels channels))
(run-hive hive '()))
#+END_SRC
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 "bootstrap-actor*" method.
+this special =bootstrap-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. bootstrap-actor* passes back not the actor itself (we don't
+argument, and the rest are initialization arguments to the
+actor.
+=bootstrap-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
Change handle-line to this:
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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_SRC
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.)
+the line we want it to spit out to the channel).[fn:send-message-provenance]
Normally in the actor model, we don't have direct references to
an actor, only an identifier.
like so:
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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_SRC
To implement it, we're going to pull out Guile's pattern matcher.
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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)
you're right:
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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)
thing given chat bots being a fairly mundane novelty amongst hackers
and teenagers everywhere a few decades ago.
+[fn:send-message-provenance]
+ 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.
+
** Writing our own actors
Let's write the most basic, boring actor possible.
(define (sleeper-loop actor message)
(while (actor-alive? actor)
(display "Zzzzzzzz....\n")
- ;; Sleep for one second
+ ;; Sleep for one second
(8sleep (sleeper-sleep-secs actor))))
(let* ((hive (make-hive))
#+END_SRC
We see some particular things in this example.
-One thing is that our <sleeper> actor has an actions slot.
+One thing is that our =<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 #: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.)
+We have to set the #:allocation to either =#:each-subclass= or
+=#:class=.[fn:class-bug]
The only action handler we've added is for =*init*=, which is called
implicitly when the actor first starts up.
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.
+to the scheduler, you should check this.[fn:actor-alive-deprecated-soon]
(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.
worker> Whew! Free at last.
#+END_SRC
+[fn:class-bug]
+ #: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.
+
+[fn:actor-alive-deprecated-soon]
+ Or rather, for now you should call =actor-alive?= if your code
+ is looping like this.
+ In the future, after an actor dies, its coroutines will
+ automatically be "canceled".
+
** Writing our own network-enabled actor
So, you want to write a networked actor!
(define-actor <telcmd> (<actor>)
((*init* telcmd-init)
(*cleanup* telcmd-cleanup)
- (new-client telcmd-new-client))
+ (new-client telcmd-new-client)
+ (handle-line telcmd-handle-line))
(socket #:accessor telcmd-socket
#:init-value #f))
#+END_SRC
(cond ((eof-object? line)
(close client))
(else
- (telcmd-handle-line telcmd client
- (string-trim-right line #\return))
+ (<- (actor-id telcmd) 'handle-line
+ client (string-trim-right line #\return))
(when (actor-alive? telcmd)
(loop)))))))
- (define (telcmd-handle-line telcmd client line)
+ (define (telcmd-handle-line telcmd message client line)
(match (string-split line #\space)
(("") #f) ; ignore empty lines
(("time" _ ...)
The actual method called whenever we have a "line" of input is pretty
straightforward... in fact it looks an awful lot like the IRC bot
handle-line procedure we used earlier.
-No surprises there!
+No surprises there![fn:why-send-a-message-to-handle-line]
Now let's run it:
finishes handling one message.
Our loop couldn't look quite like this though!
-** An intermission: about live hacking
+[fn:why-send-a-message-to-handle-line]
+ 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 /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.
+
+** An intermission on live hacking
This section is optional, but highly recommended.
It requires that you're a user of GNU Emacs.
(repl-path "/tmp/8sync-repl"))
(define hive (make-hive))
(define irc-bot
- (bootstrap-actor* hive <my-irc-bot> "irc-bot"
- #:username username
- #:server server
- #:channels channels))
+ (bootstrap-actor hive <my-irc-bot>
+ #:username username
+ #:server server
+ #:channels channels))
(define repl-manager
- (bootstrap-actor* hive <repl-manager> "repl"
- #:path repl-path))
+ (bootstrap-actor hive <repl-manager>
+ #:path repl-path))
(run-hive hive '()))
#+END_SRC
things to:
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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)
(We can remove the pk now that we know what's going on.)
#+BEGIN_SRC scheme
- (define-method (handle-line (irc-bot <my-irc-bot>) speaker channel
- line emote?)
+ (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
actual theory!
8sync is based on the [[https://en.wikipedia.org/wiki/Actor_model][actor model]] whereas fibers follows
[[http://usingcsp.com/][Communicating Sequential Processes (CSP)]], which is a form of
-[[https://en.wikipedia.org/wiki/Process_calculus][process calculi]].
+[[https://en.wikipedia.org/wiki/Process_calculus][process calculi]].
And it turns out, the
[[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
projects / 8sync.git / blobdiff