To help myself learn Racket, I ported a simple JavaScript ircbot module I wrote for Node.js to Racket. The Racket version is built atop the Racket irc package, so the low-level code is handled by that. My module simply provides some utility functions to make it easier to implement IRC bots.

My code is as follows. I know it's rather long and probably fairly unreadable, and for that I apologize. I'm not looking for anything extremely specific, but I would like to know if I'm violating any major conventions of the language in any obvious ways.

#lang racket

(provide ircbot-connect

;; ---------------------------------------------------------------------------------------------------

(require (for-syntax racket/syntax))

(require racket/async-channel)
(require irc)
(require srfi/13)

(struct ircbot-connection (server nick username realname channels triggers pmtrigger
                                  action-handlers chat-handlers trigger-handlers message-handlers
                                  self-handlers self-action-handlers join-handlers part-handlers
                                  quit-handlers nick-handlers

(define (ircbot-connect #:server [server "localhost"]
                        #:port [port 6667]
                        #:nick [nick "racketircbot"]
                        #:username [username "racketircbot"]
                        #:realname [realname "racketircbot"]
                        #:channels [channels (list)]
                        #:triggers [triggers (list)]
                        #:pmtrigger [pmtrigger #f])
  (define-values (connection ready-event)
    (irc-connect server port nick username realname))
  (sync ready-event)
  (for ([channel channels])
    (irc-join-channel connection channel))
  (ircbot-connection server nick username realname channels triggers pmtrigger
                     (box '()) (box '()) (box '()) (box '()) (box '())
                     (box '()) (box '()) (box '()) (box '()) (box '())

(define (ircbot-say connection message [channels (ircbot-connection-channels connection)])
  (when (not (list? channels))
    (set! channels (list channels)))
  (define action #f)
  (when (equal? (string-contains message "/me ") 0)
    (set! action #t)
    (set! message (substring message 4)))
  (for ([channel channels])
    (if action
        (irc-send-command (ircbot-connection-connection connection)
                          channel (format ":\u0001ACTION ~a\u0001" message))
        (irc-send-message (ircbot-connection-connection connection) channel message))))

;; ---------------------------------------------------------------------------------------------------

(define-syntax (define-ircbot-listener stx)
  (syntax-case stx ()
    [(define-ircbot-listener name)
     #`(define (#,(format-id #'name #:source #'name
                             (syntax-e #'name)) connection callback)
         (set-box! (#,(format-id #'name #:source #'name
                                 (syntax-e #'name)) connection)
                   (append (unbox (#,(format-id #'name #:source #'name
                                                (syntax-e #'name)) connection))
                           (list callback))))]))

(define-ircbot-listener action)
(define-ircbot-listener chat)
(define-ircbot-listener trigger)
(define-ircbot-listener message)
(define-ircbot-listener self)
(define-ircbot-listener self-action)
(define-ircbot-listener join)
(define-ircbot-listener part)
(define-ircbot-listener quit)
(define-ircbot-listener nick)

;; ---------------------------------------------------------------------------------------------------

(define (channel? str)
  (equal? (string-ref str 0) #\#))

(define (respond connection sender recipient response)
  (irc-send-message (ircbot-connection-connection connection)
                    (if (channel? recipient) recipient sender)
  (when (channel? recipient)
    (map (λ (el) (el (hash "text" response))) (unbox (ircbot-connection-self-handlers connection)))))

(define (ircbot-listen connection)
  (let loop ()
    (define message (async-channel-get
                     (irc-connection-incoming (ircbot-connection-connection connection))))
    (match message
      [(irc-message prefix "PRIVMSG" params _)
       (define prefix-match (regexp-match #rx"^[^!]+" prefix))
       (when prefix-match
         (define sender (first prefix-match))
         (define recipient (first params))
         (define message (second params))
         (define action-match (regexp-match #rx"^\u0001ACTION ([^\u0001]*)\u0001" message))
         (define (callback text cb)
           (cb (hash "sender" sender
                     "recipient" recipient
                     "message"  text
                     "type" (if action-match "action" "chat")
                     "private"  (not (channel? recipient)))
               (λ (response) (respond connection sender recipient response))))
            (set! message (second action-match))
            ; call all message handlers
            (map (curry callback message)
                 (unbox (ircbot-connection-message-handlers connection)))
            ; call all action handlers
            (map (curry callback message)
                 (unbox (ircbot-connection-action-handlers connection)))
            ; call all message handlers
            (map (curry callback message)
                 (unbox (ircbot-connection-message-handlers connection)))
            ; call all action handlers
            (map (curry callback message)
                 (unbox (ircbot-connection-chat-handlers connection)))
            ; call trigger handlers if necessary
            (define triggered #f)
            (define args (string-split message))
            (define trigger (first args))
            (define reconstructed (string-join (rest args)))
            (when (member trigger (ircbot-connection-triggers connection))
              (set! triggered #t)
              (map (curry callback reconstructed)
                   (unbox (ircbot-connection-trigger-handlers connection))))
            ; call trigger handlers on pm if enabled
            (when (and
                   (not triggered)
                   (ircbot-connection-pmtrigger connection)
                   (not (channel? recipient)))
              (set! triggered #t)
              (map (curry callback message)
                   (unbox (ircbot-connection-trigger-handlers connection))))
      [(irc-message prefix "JOIN" params _)
       (define prefix-match (regexp-match #rx"^[^!]+" prefix))
       (when prefix-match
         (for ([callback (unbox (ircbot-connection-join-handlers connection))])
           (callback (hash "channel" (first params)
                           "nick" (first prefix-match)))))]
      [(irc-message prefix "PART" params _)
       (define prefix-match (regexp-match #rx"^[^!]+" prefix))
       (when prefix-match
         (for ([callback (unbox (ircbot-connection-part-handlers connection))])
           (callback (hash "channel" (first params)
                           "nick" (first prefix-match)
                           "reason" (second params)))))]
      [(irc-message prefix "QUIT" params _)
       (define prefix-match (regexp-match #rx"^[^!]+" prefix))
       (when prefix-match
         (for ([callback (unbox (ircbot-connection-quit-handlers connection))])
           (callback (hash "nick" (first prefix-match)
                           "reason" (first params)))))]
      [(irc-message prefix "NICK" params _)
       (define prefix-match (regexp-match #rx"^[^!]+" prefix))
       (when prefix-match
         (for ([callback (unbox (ircbot-connection-nick-handlers connection))])
           (callback (hash "oldnick" (first prefix-match)
                           "newnick" (first params)))))]
      [_ (void)])

In case this makes it more clear, here is an extremely simple bot implemented using the above module.

#lang racket

(require "irc-bot.rkt")

(define connection (ircbot-connect #:nick "racketbot"
                                   #:username "racketbot"
                                   #:realname "RacketBot 9000"
                                   #:channels (list "#racket")
                                   #:triggers (list "!rb")
                                   #:pmtrigger #t))

; log chats
(ircbot-listen-chat connection
                    (λ (data respond)
                      (printf "<~a> ~a~n"
                              (hash-ref data "sender")
                              (hash-ref data "message"))))
; log actions
(ircbot-listen-action connection
                      (λ (data respond)
                        (printf "* ~a ~a~n"
                                (hash-ref data "sender")
                                (hash-ref data "message"))))

; respond to simple commands
(ircbot-listen-trigger connection
                       (λ (data respond)
                         (define args (string-split (hash-ref data "message")))
                         (match args
                           [(list "hello")
                            (respond (format "Hello, ~a!" (hash-ref data "sender")))]
                           [(list "random" n)
                            (respond (number->string (random (string->number n))))]
                           [_ (void)]

(ircbot-listen connection)

The bot prints standard chat messages and CTCP actions to stdout, and it responds to the !rb hello and !rb random <n> commands.

  • \$\begingroup\$ I might be misunderstanding, but: Do you really need to use boxes? Racket structs can be mutable (all fields, or just specific fields, as you wish, using #:mutable). So you could e.g. directly (set!-irc-connection-XXX-handlers x (some-mod (irc-connection-XXX-handlers x))), as opposed to (set-box! (irc-connection-XXX-handlers x) (some-mod (unbox (irc-connection-XXX-handlers x)))). \$\endgroup\$ Sep 22, 2014 at 20:04
  • \$\begingroup\$ @GregHendershott You're quite right, I didn't realize #:mutable existed when I wrote this. \$\endgroup\$ Sep 22, 2014 at 22:51

1 Answer 1


Here are my comments after a brief reading:

  • First, if you intend to make this library fit for general use, add documentation in comments for the provided functions. See the Racket style guide for examples
  • Also, if you intend to make this a more general library, don't include default arguments (e.g. for ircbot-connect) unless they make sense for all users. Most users will connect to port 6667, but most users will not want to use the nick "racketircbot"
  • I agree with Greg Hendershott, I don't you don't need boxes in your struct - just use the #:mutable keyword
  • Break your code up into shorter functions where the logic is complex (e.g. the PRIVMSG handling should be a separate function). This is a good practice for all languages, not just Racket.
  • The use of curry seems awkward, but I haven't read the code in-depth enough to figure out if it's needed or not
  • Allowing the channels argument to ircbot-say be either a list or a single channel strikes me as strange - document this at the very least, but consider changing it to just take a list.
  • Your code is quite imperative in places, while Racket favors a more functional style. When you find yourself using set!, try to find a way to use just define instead, and only define each variable once.

I rewrote ircbot-say in a more functional form (although it's still not perfect):

(define (ircbot-say connection message [channels (ircbot-connection-channels connection)])
  (define channel-list (if (list? channels) channels (list channels)))
  (cond ([(string-contains message "/me ")
          (for ([channel channels])
            (irc-send-command (ircbot-connection-connection connection)
                              channel (format ":\u0001ACTION ~a\u0001" (substring message 4))))]
          (for ([channel channels])
            (irc-send-message (ircbot-connection-connection connection) channel message))])))

Otherwise, though, I think your code looks Racket-y. The match branches in ircbot-listen are exactly the kind of thing I envisioned when I wrote the irc package.

  • 5
    \$\begingroup\$ P.S. I'm happy to take any feedback you have about the irc package itself. I published it just as a starting point for a more full-fledged library, and I'd love to know what other functionality you think should be included, or bugs you've found. \$\endgroup\$ Sep 22, 2014 at 20:57
  • 3
    \$\begingroup\$ Welcome to Code Review, I know nothing about this language but I will spread the link to it so you might get some votes! \$\endgroup\$ Sep 22, 2014 at 21:01
  • \$\begingroup\$ Thanks much for this! I certainly agree with everything you've outlined. As for the irc package itself, it seems to work well, and I haven't encountered any bugs. The only thing I'd like to see would be some built-in support for CTCP messages, mostly to be able to more easily handle the extremely common ACTION command. Otherwise, though, I can't think of anything off the top of my head. Support for modes and formatting colors/styles would be nice, but probably wouldn't be particularly practical, anyway. \$\endgroup\$ Sep 22, 2014 at 22:57

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