8sync: 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.¹ 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:

(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)))

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 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!

(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 '()))

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. It takes the hive as its first argument, the actor class as the second 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 "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.

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:

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).²

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:

… 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 we would really like to do is have our bot respond to individual "commands" like this:

Whee, that looks like fun! To implement it, we’re going to pull out Guile’s pattern matcher.

(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*"))))))

If you’re getting the sense that we could make this a bit less wordy, you’re right:

(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*"))))))

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?

Footnotes

(1)

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 a few decades ago.

(2)

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.

2.1 A silly little IRC bot

Footnotes

(1)

(2)