I have made a Guile module which is capable of being used by the IRC bot bobot++. The code is available here:

http://zedstar.org/tarballs/sneektweet-0.1.tar.gz

The readme:

sneektweet 0.1:

Wraps some C/GLib code which posts to Twitter.

setup:

Edit configure.ac to set twitter account details.

from REPL:

john@thinkpad:~/workspace/sneektweet$ guile
guile> (use-modules (twitter sneektweet))
guile> (tweet "foobar")
guile> ** Message: posted update to Twitter

todo:

Add reading updates and posting back to IRC channel. 

bobot example code:

(use-modules (twitter sneektweet))

(define (sneektweet channel message)
  (if (> (string-length message) 140)
    (bot:say channel "Your message needs to be under 140 characters in length!")
    (tweet message)))

(bot:addcommand "tweet" sneektweet #t 2 0)