Auto: Building a Declarative Chatbot with Implicit Serialization

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Today we’re going to continue along with the All About Auto introduction series and look at building a declarative chatbot using the denotational components from the auto library that is modular and has implicit serialization. Most importantly, we’ll look at the “design process”, and principles of architecture that you can apply to your own projects.

This post assumes some concepts from the tutorial, or at least my last post or the README. If some of these ideas seem completely new, than looking through the tutorial or the docs might refresh your mind…feel free to also leave a comment, stop by #haskell-auto on freenode where I go by jle`, or tweet me

All of the code in this tutorial can be downloaded and run using runghc (with the appropriate dependencies installed). Feel free to play along!

Overall Layout

auto is a library that at the highest level gives you a stream transformer on streams of values. Transform a stream of input values to a stream of output values. So when we approach a chat bot, we have to think — what are the inputs, and what are the outputs?

The choice should be pretty straightforward – our input stream is a stream of input messages from the irc server, and our output stream is a stream of messages to send to the server. In haskell we like types, so let’s make some types.

-- first, our imports
-- source:

import Control.Auto
import Control.Auto.Blip
import Control.Auto.Collection  (mux)
import Control.Auto.Run         (runOnChanM)
import Control.Auto.Serialize   (serializing')
import Control.Auto.Switch      (resetOn)
import Control.Concurrent       (Chan, newChan, writeChan, forkIO, threadDelay)
import Control.Monad            (void, forever)
import Control.Monad.IO.Class
import Data.Foldable            (forM_)
import Data.Map                 (Map)
import Data.Serialize
import Data.Text hiding         (words, unwords, map)
import Data.Text.Encoding
import Data.Text.Encoding.Error
import Data.Time
import Network.SimpleIRC
import Prelude hiding           ((.), id)   -- we use (.) and id from `Control.Category`
import qualified Data.Map       as M
-- source:

type Nick    = String
type Channel = String
type Message = String

data InMessage = InMessage { _inMessageNick   :: Nick
                           , _inMessageBody   :: Message
                           , _inMessageSource :: Channel
                           , _inMessageTime   :: UTCTime
                           } deriving Show

newtype OutMessages = OutMessages (Map Channel [Message]) deriving Show

instance Monoid OutMessages where
    mempty  = OutMessages M.empty
    mappend (OutMessages m1) (OutMessages m2)
            = OutMessages (M.unionWith (++) m1 m2)

We make some type aliases to make things a bit clearer. Our inputs are going to be a data type/“struct” with a nick, a body, a source, and a time. Our outputs are going to be a Data.Map.Map from containers associating channels with messages to send. I’m just adding here a Monoid instance in case we want to combine OutMessages maps.

The type for a chat bot over a monad m would then be:

-- source:

type ChatBot m = Auto m InMessage OutMessages

A ChatBot takes a stream of InMessages and returns a stream of OutMessagess…and might have effects in m as it does so.

Note that we get a free instance of Monoid on ChatBot m:

mappend :: ChatBot m -> ChatBot m -> ChatBot m

That takes two ChatBots and creates a new ChatBot that forks the input stream (sends all InMessages) to both of the original ones, and mappends the results. So the new ChatBot will send message to both original ones and return a “combined” OutMessages.

However, not all modules really have to “care” about the room of the outputs…they might just always reply directly to the room they received the message on. So it’ll help us to also make another sort of Auto:

-- source:

type RoomBot m = Auto m InMessage (Blip [Message])

A RoomBot doesn’t care where its messages go…it just replies to the same room it got its input from. It outputs a blip stream of message lists; when it doesn’t want to send messages out, it doesn’t emit. When it does, it does emit, with the list of messages.

(Remember, a blip stream is just like a normal stream of values, except it only actually has a value every once in a while, when it “emits”. A Blip Bool is a stream that sometimes, occasionally emits with a Bool. We work with them using combinators and Autos from Control.Auto.Blip)


We can write a quick helper function to convert a RoomBot into a full-on ChatBot, so we can merge them together with mappend/(<>):

-- source:

perRoom :: Monad m => RoomBot m -> ChatBot m
perRoom rb = proc inp@(InMessage _ _ src _) -> do
    messages <- fromBlips [] . rb -< inp
    id -< OutMessages $ M.singleton src messages

(This example uses proc notation; see this proc notation primer for a quick run-down of the relevant aspects)

We say that messages is just the output of rb fed with the input, except it “collapses” the blip stream into a normal stream by substituting in [] whenever the stream doesn’t emit. So messages is [] when rb doesn’t emit (it doesn’t want to send anything), and messages is [message1, message2 ...], with the emitted contents, when it does.

The “output” will be a singleton map with the source of the input and the messages to send to that source.

So now if we have a RoomBot m, we can convert it up into a ChatBot m, and combine it/merge it with other ChatBot ms.

The whole deal

We have enough now then to imagine our entire program architecture:

  • Write a bunch of separate modules, as ChatBot ms or RoomBot ms, which ever one is more convenient. The beauty is that we can merge them all together in the end with our promoter.
  • Combine all of our modules with mconcat — that is, something like chatBot = mconcat [module1, module2, module3, module 4]. And that’s it, that’s our entire chat bot!
  • Having an overall chatBot :: ChatBot m, we can use something like runOnChan from Control.Auto.Run to have it exist on a concurrent thread and watch a channel for input, and perform an action on output.
  • Find an out-of-the-box irc library that can trigger adding something to a concurrent queue when it receives a message, and where you can send messages to rooms.

And…that’s it. Program logic in our ChatBot ms, and handling the “view”/input with our backend.

Free Serialization

Remember that auto gives us the ability to serialize and resume our Autos for free…so we can at any time save the state of our chat bot to disk, and resume it when we re-load. We don’t have to worry about manually gathering our state between each Auto and writing serialization code.

There’s a “convenience combinator” called serializing' in Control.Auto.Serialize (it’s one of many different ones that can do something like this; check out the module to see other ways of varying disciplined-ness!). It’ll take any Auto and turn it into an Auto that “self-serializes” — when you begin running it, it automatically loads its previous state if it exists, and as you run it, it automatically maintains an updated “resume state” on disk.

serializing' :: MonadIO m => FilePath -> ChatBot m -> ChatBot m

Note that serializing' fp :: MonadIO m => ChatBot m -> ChatBot m. It looks a lot like an “identity-ish” sort of function, right? That’s because it is meant to behave like id…the returned ChatBot behaves identical to the previous one…except it splices in the serializing action in-between. (We are in MonadIO now, because the Auto has to access IO in order to serialize itself between steps).

So, instead of

chatBot :: Monad m => ChatBot m
chatBot = mconcat [module1, module2, module3]

We can do:

chatBot :: MonadIO m => ChatBot m
chatBot = serializing' "state.dat" $ mconcat [module1, module2, module3]

And now our chatBot will automatically resume itself on program startup, and keep its state backed up on disk at state.dat. We get this for free, without doing anything extra in the composition of our modules.

Note that in practice, with a bot you are actively developing, this might not be the best idea. serializing' analyzes your Autos to determine a serialization and reloading strategy, and applies that to do its job. However, if you, for example, add a new module to your chat bot…the serialization strategy will change, and your new bot won’t be able to resume old save files.

One solution at this point is just to serialize individual modules that you do not see yourself changing…or even just serializing parts of the modules you don’t see yourself changing. Then you can change each portion separately and not worry about migration issues.

chatBot :: MonadIO m => ChatBot m
chatBot = mconcat [ serializing' "m1.dat" module1
                  , module2
                  , serializing' "m3.dat" module3

We’re not all-or-nothing now here, either! So, module1 gets serialized and auto-resumed from m1.dat, module2 is not serialized at all, and module3 now gets serialized and auto-resumed from m3.dat.

IRC Backend (the ugly part)

Before we get started on our actual modules, let’s just write out the backend/interface between our ChatBot and irc to get it out of the way. This will vary based on what library you use; I’m going to use the simpleirc-0.3.0, but feel free to use any interface/library you want.

-- source:

withIrcConf :: IrcConfig -> ChatBot IO -> IO ()
withIrcConf ircconf chatbot = do

    -- chan to receive `InMessage`s
    inputChan <- newChan :: IO (Chan InMessage)

    -- configuring IRC
    let events   = cEvents ircconf ++ [ Privmsg (onMessage inputChan) ]
        ircconf' = ircconf { cEvents = events }

    -- connect; simplified for demonstration purposes
    Right server <- connect ircconf' True True

    -- run `chatbot` on `inputChan`
    void . forkIO . void $
        runOnChanM id (processOutput server) inputChan chatbot

    -- what to do when `chatBot` outputs
    processOutput :: MIrc -> OutMessages -> IO Bool
    processOutput server (OutMessages outs) = do
      print outs
      _ <- flip M.traverseWithKey outs $ \channel messages -> do
        let channel' = encodeUtf8 . pack $ channel
        forM_ messages $ \message -> do
          let message' = encodeUtf8 . pack $ message
          sendMsg server channel' message'
      return True       -- "yes, continue on"

    -- what to do when you get a new message
    onMessage :: Chan InMessage -> EventFunc
    onMessage inputChan = \_ message -> do
      case (mNick message, mOrigin message) of
        (Just nick, Just src) -> do
          time <- getCurrentTime
          writeChan inputChan $ InMessage (unpack (decodeUtf8 nick))
                                          (unpack (decodeUtf8 (mMsg message)))
                                          (unpack (decodeUtf8 src))

channels :: [Channel]
channels = ["#testchan1", "#testchan2"]

conf :: IrcConfig
conf = (mkDefaultConfig "myserver" "mynick") { cChannels = channels }

main :: IO ()
main = do
    withIrcConf conf chatBot
    forever (threadDelay 1000000000)

That should be it…don’t worry if you don’t understand all of it, most of it is just implementation details from simpleirc. The overall loop is runOnChanM waits on a separate thread for inputChan…when it gets input, it runs it through ChatBot and sends the outputs through simpleirc’s interface. Meanwhile, onMessage is triggered whenever simpleirc receives a message, where it prepares an InMessage and drops it off at inputChan.

runOnChanM :: Monad m
           => (forall c. m c -> IO c)   -- convert `m` to `IO`
           -> (b -> IO Bool)            -- handle output
           -> Chan a                    -- chan to await input on
           -> Auto m a b                -- `Auto` to run
           -> IO (Auto m a b)

runOnChanM runs any Auto m a b, as long as there’s a way to convert it to Auto IO a b (we can use a ChatBot IO, so we just put id there). You give it a “handler” b -> IO Bool that it run whenever it outputs; if the handler returns False, then the whole thing stops. You give it the Chan a to await for input as on, and it takes care of the rest. It blocks until the handler returns False, where it’ll return the “updated” Auto m a b with updated state after running through all of those inputs.

Phew. With that out of the way, let’s get right on to the fun part — building our chat bot modules.

The Modules


What’s a common module? Well, we can write a module that keeps track of the last time any user was “seen” (sent a message), and then respond when there is a query.

There are two components here…the part that keeps track of the last seen time, and the part that responds to queries.

Keeping track of our last seen time sounds like a job that takes in a stream of (Nick, UTCTime) pairs and outputs a stream of Map Nick UTCTime, where we could look up the last seen time for a nick by looking up the nick in the map.

Logically, this is pretty straightforward, and anything other than accum (which is like foldl') would really be a bit overkill; every input would just update the output map.

trackSeens :: Monad m => Auto m (Nick, UTCTime) (Map Nick UTCTime)
trackSeens = accum (\mp (nick, time) -> M.insert nick time mp) M.empty

accum takes the same thing that foldl takes:

foldl ::            (b -> a -> b) -> b -> [a] -> b
accum :: Monad m => (b -> a -> b) -> b -> Auto m a b

So it basically “folds up” the entire history of inputs, with a starting value. Every time an input comes, the output is the new folded history of inputs. You can sort of think of it as it applying the function to any incoming values to an internal accumulator and updating it at every step.

By the way, because trackSeens is self-serializing, we need a Serialize instance for UTCTime…just for the sake of demonstration, let’s make one now. Let’s also write a Serialize instance for Day (which represents a date) too, while we’re at it.

-- source:

instance Serialize UTCTime where
    get = read <$> get      -- haha don't do this in real life.
    put = put . show

instance Serialize Day where
    get = ModifiedJulianDay <$> get
    put = put . toModifiedJulianDay

The next component is just to respond to requests. We want to do something on some “triggering” input. Every once in a while, some input will come that will “trigger” some special response. This is a sign that we can use blip streams.

queryBlips :: Auto m Message (Blip Nick)
queryBlips = emitJusts (getRequest . words)
    getRequest ("@seen":nick:_) = Just nick
    getRequest _                = Nothing

queryBlips takes an input stream of strings and turns it into an output blip stream that emits with a Nick whenever the input stream contains a request in the form of "@seen [nick]".

With these simple blocks, we can build our seenBot:

-- seenBot :: Monad m => Auto m InMessage (Blip [Message])
-- source:

seenBot :: Monad m => RoomBot m
seenBot = proc (InMessage nick msg _ time) -> do
    seens  <- trackSeens -< (nick, time)

    queryB <- queryBlips -< msg

    let respond :: Nick -> [Message]
        respond qry = case M.lookup qry seens of
                        Just t  -> [qry ++ " last seen at " ++ show t ++ "."]
                        Nothing -> ["No record of " ++ qry ++ "."]

    id -< respond <$> queryB
    trackSeens :: Monad m => Auto m (Nick, UTCTime) (Map Nick UTCTime)
    trackSeens = accum (\mp (nick, time) -> M.insert nick time mp) M.empty
    queryBlips :: Auto m Message (Blip Nick)
    queryBlips = emitJusts (getRequest . words)
        getRequest ("@seen":nick:_) = Just nick
        getRequest _                = Nothing

Here we define respond as a function that takes a Nick and returns the output [Message]. We could have also defined it outside as a helper function respond :: Map Nick UTCTime -> Nick -> [Message]…but seens is already in scope, so we might as well just do it there.

For our output, we use the Functor instance of blip streams. respond <$> queryB is a blip stream that emits whenever queryB emits (so, whenever there is a query input), but replaces the emitted value with the result of the function on the value. So whenever queryB emits, this whole thing emits with respond applied to whatever Nick was emitted — in this case, our [Message].

Short, sweet, simple. In fact, trackSeens and queryBlips are small enough that their definition could really have been inlined. Breaking them down just allowed us to look at them individually for this tutorial.

So that’s it for that; also, if we wanted seenBot to serialize and persist across sessions, all we have to do is use:

serializing' "seenbot.dat" seenBot :: MonadIO m => RoomBot m

Neat, right?

If we forsee ourselves adding more features to seenBot, we can future-proof our seenBot for now by only serializing trackSeens, meaning replacing that line with:

    seens <- serializing' "seen.dat" trackSeens -< (nick, time)

Remember, serializing' fp acts as a sort of “identity”, so you can drop it in anywhere and you’d expect it to behave the same.


Another common bot is a “reputation bot”, which allows users to increment or decrement another user’s reputation scores, and look up a user’s total score.

Again there are two components — keeping track of the scores of all of the users, and responding to requests.

This time though, our “score updates” only happen every once in a while, triggered by certain words in the message. Again, this pattern calls for a blip stream:

updateBlips :: Auto m (Nick, Message) (Blip (Nick, Int))
updateBlips = emitJusts getUpdateCommand
    -- updater is the person triggering the update blip
    getUpdateCommand (updater, msg) =
      case words msg of
        "@addRep":nick:_ | nick /= updater -> Just (nick, 1)
        "@subRep":nick:_                   -> Just (nick, -1)
        _                                  -> Nothing

updateBlips takes in a stream of (Nick, Message), with the person who is sending the message and their message, and outputs a blip stream that and emits with a (Nick, Int) whenever the message is a command. The emitted (Nick, Int) has the person to adjust, and the amount to adjust by. Note that we ignore commands where the person is trying to increase their own reputation because that’s just lame.

We probably want to keep track of the scores as a Map Nick Int, so we can do that with something like accum again. However, accum takes a stream of normal values, but we have a blip stream, so we can use scanB instead. scanB is pretty much the same thing, but it collapses a blip stream into a value stream by holding the “current result” of the fold.1

trackReps :: Monad m => Auto m (Blip (Nick, Int)) (Map Nick Int)
trackReps = scanB (\mp (nick, change) -> M.insertWith (+) nick change mp) M.empty

And finally, the “response” portion — we want to be able to respond to commands and look up the result. We basically had this identical pattern for seenBot:

queryBlips :: Auto m Message (Blip Nick)
queryBlips = emitJusts (getRequest . words)
    getRequest ("@rep":nick:_) = Just nick
    getRequest _                = Nothing

And…now we can wrap it all together with a nice proc block:

-- repBot :: Monad m => Auto m InMessage (Blip [Message])
-- source:

repBot :: Monad m => RoomBot m
repBot = proc (InMessage nick msg _ _) -> do
    updateB <- updateBlips -< (nick, msg)

    reps    <- trackReps   -< updateB

    queryB  <- queryBlips  -< msg

    let lookupRep :: Nick -> [Message]
        lookupRep nick = [nick ++ " has a reputation of " ++ show rep ++ "."]
            rep = M.findWithDefault 0 nick reps

    id -< lookupRep <$> queryB
    updateBlips :: Auto m (Nick, Message) (Blip (Nick, Int))
    updateBlips = emitJusts getUpdateCommand
        -- updater is the person triggering the update blip
        getUpdateCommand (updater, msg) =
          case words msg of
            "@addRep":nick:_ | nick /= updater -> Just (nick, 1)
            "@subRep":nick:_                   -> Just (nick, -1)
            _                                  -> Nothing
    trackReps :: Monad m => Auto m (Blip (Nick, Int)) (Map Nick Int)
    trackReps = scanB (\mp (nick, change) -> M.insertWith (+) nick change mp) M.empty
    queryBlips :: Auto m Message (Blip Nick)
    queryBlips = emitJusts (getRequest . words)
        getRequest ("@rep":nick:_) = Just nick
        getRequest _                = Nothing

Again note that we take advantage of the Functor instance of blip streams to create a new blip stream (lookupRep <$> queryB) that emits whenever queryB emits, but replaces the value with lookupRep applied to whatever Nick was in the query blip. We also take advantage that reps is in scope and define lookupRep right there in the block.


Let’s just go over one more module…and I think you’ll be able to use your imagination to think of and implement your own from here.

Let’s make an “announceBot”, that listens for “announcement” messages from anyone (even in private messages) and broadcasts them to all of the channels in the provided list. It rate-limits the announcements, though, so that a user is only limited to three announcements per day.

We can start with our typical “blip stream that emits on a certain command” to start off everything:

announceBlips :: Monad m => Auto m (Nick, Message) (Blip [Message])
announceBlips = emitJusts getAnnounces
    getAnnounces (nick, msg) =
      case words msg of
        "@ann":ann -> Just [nick ++ " says \"" ++ unwords ann ++ "\"."]
        _          -> Nothing

announceBlips takes in a nick-message pair and emits an announcement [Message] whenever the incoming message is an announcement command.

Next, we’d like to keep track of how many times a user has made an announcement today. This is pretty much just scanB again like with repBot:

trackAnns :: Monad m => Auto m (Blip Nick) (Map Nick Int)
trackAnns = scanB (\mp nick -> M.insertWith (+) nick 1 mp) M.empty

However, we’d like to be able to “reset” this map whenever a new day arrives. For that, we can use resetOn from Control.Auto.Switch, which takes an Auto and gives it a “reset channel” input blip stream, that resets the whole thing whenever the blip stream emits:

resetOn :: Monad m => Auto m a b -> Auto m (a        , Blip c) b
resetOn trackAnns :: Monad m =>     Auto m (Blip Nick, Blip c) (Map Nick Int)

(It doesn’t care about the actual value emitted, so we can leave it as a type variable c conceptually.)

Now the only thing we need is a blip stream that emits whenever there is a new day. For that, we can use onChange from Control.Auto.Blip:

newDayBlips :: Monad m => Auto m Day (Blip Day)
newDayBlips = onChange

newDayBlips takes in a stream of Days (from Data.Time) that we get from the InMessage and outputs a blip stream that emits whenever the day changes. It emits with the new Day…but we don’t really care about the emitted value, we’re just using it to trigger resetOn trackAnns.

Finally, let’s wrap it all together!

Remember, announceBot is a full on ChatBot m, and not a RoomBot m anymore, so it has to say where it wants to send its messages.

-- announceBot :: Monad m => [Channel] -> Auto m InMessage OutMessages
-- source:

announceBot :: Monad m => [Channel] -> ChatBot m
announceBot chans = proc (InMessage nick msg src time) -> do
    announceB <- announceBlips     -< (nick, msg)

    newDayB   <- newDayBlips       -< utctDay time

    annCounts <- resetOn trackAnns -< (nick <$ announceB, newDayB)

    let hasFlooded  = M.findWithDefault 0 nick annCounts > 3

        targetChans :: [Channel]
        targetChans | hasFlooded = [src]
                    | otherwise  = chans

        outB        :: Blip [Message]
        outB        | hasFlooded = [nick ++ ": No flooding!"] <$ announceB
                    | otherwise  = announceB

        outMsgsB    :: Blip OutMessages
        outMsgsB    = (\out -> OutMessages (M.fromList (map (,out) targetChans)))
                  <$> outB

    fromBlips mempty -< outMsgsB
    announceBlips :: Monad m => Auto m (Nick, Message) (Blip [Message])
    announceBlips = emitJusts getAnnounces
        getAnnounces (nick, msg) =
          case words msg of
            "@ann":ann -> Just [nick ++ " says \"" ++ unwords ann ++ "\"."]
            _          -> Nothing
    newDayBlips :: Monad m => Auto m Day (Blip Day)
    newDayBlips = onChange
    trackAnns :: Monad m => Auto m (Blip Nick) (Map Nick Int)
    trackAnns = scanB (\mp nick -> M.insertWith (+) nick 1 mp) M.empty

Only slightly more involved, but still pretty readable, right? We find out if things have flooded, and our target channels will be just the original source if true (a message as a reprimand); otherwise, all the channels in chans. If they have flooded, then our outB (blip stream of [Message] to send to each room) will just be ["No flooding!"] if yes, or the actual announcement otherwise.

Finally, our Blip OutMessages will be the OutMessage formed by associating all of the channels in targetChans with the message in outB…emitting whenever outB emits.

Note here that we use (<$) from the Functor instance of blip streams. x <$ fooB is a new blip stream that emits whenever fooB emits…but instead replaces the emitted value. So for 4 <$ fooB, if fooB emits with "hello", 4 <$ fooB emits with 4. “Emit at the same time, but pry out the value and put in your own.”

Finally we use fromBlips, which we met before in the definition of perRoom: the output is the OutMessage in outMsgsB whenever outMsgsB does emit…or it’s mempty (the empty map) when it doesn’t.

Wrapping it all up

We have three nice modules now. Now let’s wrap it all together.

-- source:

chatBot :: MonadIO m => ChatBot m
chatBot = serializing' "chatbot.dat"
        . mconcat $ [ perRoom seenBot
                    , perRoom repBot
                    , announceBot channels

Or, to future-proof, in case we foresee adding new modules:

-- source:

chatBot' :: MonadIO m => ChatBot m
chatBot' = mconcat [ perRoom . serializing' "seens.dat" $ seenBot
                   , perRoom . serializing' "reps.dat"  $ repBot
                   ,           serializing' "anns.dat"  $ announceBot channels

And…that’s it!

Feel free to download and run this all yourself using runghc! (provided you have the appropriate libraries installed)


This is a quick diversion! It’s slightly more advanced, so don’t worry if you don’t understand it immediately.

Note that the perRoom upgrade has the same RoomBot m watch all of the channels and send any replies back to the channel that it just received from. Every channel is really interacting with the same RoomBot instance, with one shared state. So perRoom repBot keeps track of reputations between rooms — asking for someone’s reputation in one room will be the same as asking for it in another room.

Another way we could “upgrade” a RoomBot is to give each channel its own little copy, with separate state. We can do this using mux:

-- source:

isolatedRooms :: Monad m => RoomBot m -> ChatBot m
isolatedRooms rb = proc inp@(InMessage _ _ src _) -> do
    messages <- fromBlips [] . mux (const rb) -< (src, inp)
    id -< OutMessages $ M.singleton src messages

mux is an “Auto multiplexer”:

mux :: (k -> Auto m a b) -> Auto m (k, a) b

mux f associates a separate/different Auto, with its own isolated state, with every key k. It takes in a stream of key-input pairs (k, a) and feeds the a into the Auto it has associated with that key k. The function f is what Auto initialize if the k has not yet been seen before.

So we feed it a (Channel, InMessage), and it feeds in that InMessage to the RoomBot m associated with that Channel…and the output is the Blip [Message] blip stream that the RoomBot at that Channel popped out.

Our “auto initialization function” is const rb, because no matter what channel we’re in, we always want to initialize with the same rb.

So, for example, if we had isolatedRooms repBot, if a message came from channel #foo saying "@rep john", only the repBot associated with #foo would get the message, and only that repBot’s output will be displayed. If here is not yet a repBot instance associated with #foo, then a new one will be created by calling const repBot on "#foo"…initializing a new repBot that only knows about #foo messages.

So now every channel has its own repBot, and maintains its own independent reputation database.


Hopefully, going over this project, you’re starting to see some common and powerful idioms and tools. I hope that a clear picture of how to approach and finish a program with the auto library looks…and how beneficial the platform and what it offers is to streamlining the development process.

Also, hopefully the “declarative” nature of everything is apparent. Especially for proc blocks…everything just “looks like” a graph of relationships. This quantity is related to this quantity in this way, this quantity is related to that in that way, etc. It looks like you’re just specifying a graph of relationships, which is really what the core of auto is all about. We assemble complex relationships by putting together small, simple relationships.

Another interesting thing is that we never really explicitly managed any sort of state or state type. All of our Autos handled their state on their own. We didn’t need to make a giant massive aggregate bulky “global state” type…and we can add new “aspects” of state (new modules) without ever having to change any data type. The state all manages itself!

And yeah, we didn’t just implement “easy” modules/components…these are actual working components that you might see in real bots, and not just toy ones.

Where can we go from here? Well, you might actually want to maybe write “subscription” Autos that are updated every minute or so:

type ChronBot m = Auto m UTCTime OutMessages

You feed them inputs every minute with the time, and it’s allowed to react with the time and output an OutMessages. You can use this bot to implement things like rss feed watchers/subscribers, for instance.

So, instead of using an input channel waiting for InMessage, you might wait for Either InMessage UTCTime…and drop in Left im whenever you get a message, and Right time from a thread that just waits a minute and repeatedly throws in times.

We can do this with minimal extra work by using the (|||) combinator from Control.Arrow:

(|||) :: Auto m a c -> Auto m b c -> Auto m (Either a         b      ) c
(|||) :: ChatBot m  -> ChronBot m -> Auto m (Either InMessage UTCTime) OutMessages

And…you get it all for free! No extra work. Now both the ChatBot and the ChronBot will wait on the input stream, and the Lefts will be fed to the ChatBot and the Rights will be fed to the ChronBot.

Anyway, this post is long enough. Have fun exploring auto on your own; expect more tutorials soon as I continue the All About Auto series, too. I’m always happy to hear about any project you might be working on! You can find me on twitter as mstk. If you have any questions or comments/suggestions, feel free to leave a comment down below or drop by freenode’s #haskell-auto or #haskell-game, where I go by jle`! And, as always, happy Haskelling!

  1. scanB f x0 :: Auto m (Blip a) b, but there’s also accumB f x0 :: Auto m a (Blip a) (Blip b), which emits whenever the input emits only.↩︎

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