Roll your own IRC bot

Roll your own IRC bot in Haskell, with monads!

This tutorial is designed as a practical guide to writing real world code in Haskell, and hopes to intuitively motivate and introduce some of the advanced features of Haskell to the novice programmer. Our goal is to write a concise, robust and elegant IRC bot in Haskell.

Getting started

You'll need a reasonably recent version of GHC or Hugs. Our first step is to get on the network. So let's start by importing the Network package, and the standard IO library and defining a server to connect to.

import Network
import System.IO

server = "irc.freenode.org"
port   = 6667

main = do
    h <- connectTo server (PortNumber (fromIntegral port))
    hSetBuffering h NoBuffering
    t <- hGetContents h
    print t

The key here is the main function. This is the entry point to a Haskell program. We first connect to the server, then set the buffering on the socket off. Once we've got a socket, we can then just read and print any data we receive.

Put this code in the module 1.hs, and we can then run it. Use whichever system you like:

Using runhaskell:

   $ runhaskell 1.hs
   "NOTICE AUTH :*** Looking up your hostname...\r\nNOTICE AUTH :***
   Checking ident\r\nNOTICE AUTH :*** Found your hostname\r\n ...

Or we can just compile it to an executable with GHC:

   $ ghc --make 1.hs -o tutbot
   Chasing modules from: 1.hs
   Compiling Main             ( 1.hs, 1.o )
   Linking ...
   $ ./tutbot
   "NOTICE AUTH :*** Looking up your hostname...\r\nNOTICE AUTH :***
   Checking ident\r\nNOTICE AUTH :*** Found your hostname\r\n ...

Or using GHCi:

   $ ghci 1.hs
   *Main> main
   "NOTICE AUTH :*** Looking up your hostname...\r\nNOTICE AUTH :***
   Checking ident\r\nNOTICE AUTH :*** Found your hostname\r\n ...

Or in Hugs:

   $ runhugs 1.hs
   "NOTICE AUTH :*** Looking up your hostname...\r\nNOTICE AUTH :***
   Checking ident\r\nNOTICE AUTH :*** Found your hostname\r\n ...

Great! We're on the network.

Talking IRC

Now we're listening to the server, we better start sending some information back. Three details are important, the nick, the user name, and a channel to join. So let's send those.

import Network
import System.IO
import Text.Printf

server = "irc.freenode.org"
port   = 6667
chan   = "#tutbot-testing"
nick   = "tutbot"

main = do
    h <- connectTo server (PortNumber (fromIntegral port))
    hSetBuffering h NoBuffering
    write h "NICK" nick
    write h "USER" (nick++" 0 * :tutorial bot")
    write h "JOIN" chan
    listen h

write :: Handle -> String -> String -> IO ()
write h s t = do
    hPrintf h "%s %s\r\n" s t
    printf    "> %s %s\n" s t

listen h = forever $ do
    s <- hGetLine h
    putStrLn s
  where
    forever a = a >> forever a

Now, we've done quite a few things here. Firstly, we import Text.Printf, which will be useful. We also set up a channel name and bot nickname. The main function has been extended to send messages back to the IRC server, using a write function. Let's look at that a bit more closely:

write :: Handle -> String -> String -> IO ()
write h s t = do
    hPrintf h "%s %s\r\n" s t
    printf    "> %s %s\n" s t

We've given write an explicit type to help document it, and we'll use explicit types signatures from now on, as they're just good practice (though of course not required, as Haskell uses type inference to work out the types anyway).

The write function takes 3 arguments: a handle (our socket), and then two strings representing an IRC protocol action, and any arguments it takes. write then uses hPrintf<hask> to build an IRC message, and write it over the wire to the server. For debugging purposes we also print to standard output the message we send. Our second function, <hask>listen, is as follows:

listen :: Handle -> IO ()
listen h = forever $ do
    s <- hGetLine h
    putStrLn s
  where
    forever a = a >> forever a

This function takes a Handle argument, and sits in an infinite loop reading lines of text from the network, and printing them. We take advantage of two powerful features, lazy evaluation and higher order functions, to roll our own loop control structure, forever, as a normal function! forever<hask> takes a chunk of code as an argument, evaluates it, and recurses -- an infinite loop function. It is very common to roll our own control structures in Haskell this way, using higher order functions. No need to add new syntax to the language, when you can just write a normal function to implement whatever control flow you wish. Let's run this thing: <code> $ runhaskell 2.hs > NICK tutbot > USER tutbot 0 * :tutorial bot > JOIN #tutbot-testing NOTICE AUTH :*** Looking up your hostname... NOTICE AUTH :*** Found your hostname, welcome back NOTICE AUTH :*** Checking ident NOTICE AUTH :*** No identd (auth) response :orwell.freenode.net 001 tutbot :Welcome to the freenode IRC Network tutbot :orwell.freenode.net 002 tutbot :Your host is orwell.freenode.net ... :tutbot!n=tutbot@aa.bb.cc.dd JOIN :#tutbot-testing :orwell.freenode.net MODE #tutbot-testing +ns :orwell.freenode.net 353 tutbot @ #tutbot-testing :@tutbot :orwell.freenode.net 366 tutbot #tutbot-testing :End of /NAMES list. </code> And we're in business! From an irc client, we can watch the bot connect: <code> 15:02 -- tutbot [n=tutbot@aa.bb.cc.dd] has joined #tutbot-testing 15:02 dons> hello </code> And the bot logs to standard output: <code> :dons!i=dons@my.net PRIVMSG #tutbot-testing :hello </code> We can now implement some commands. == A simple interpreter == [[Category:Tutorials]]