[Haskell] Why functional programming matters
stephan.friedrichs at tu-bs.de
Wed Jan 23 15:43:22 EST 2008
Simon Peyton-Jones wrote:
> 2. War stories from real life. eg "In company X in 2004 they rewrote their application in Haskell/Caml with result Y". Again, for my purpose I can't tell very long stories; but your message can give a bit more detail than one might actually give in a presentation. The more concrete and specific, the better. E.g. what, exactly, about using a functional language made it a win for you?
We  implemented an ad-hoc chat system in Haskell in the SEP  at
The ad-hoc (there is no central server, every node has the same
behaviour) protocol  (not of our making) is rather complicated, as
each node on the network has to detect the neighbouring network topology
in order to route messages to their destination:
A <-> B <-> C
Besides, it has to handle netsplit and -merge situations: Two separate
networks might be connected by the spawning of a new node in between or
split by the disappearance of the latter.
There are public and private IRC-like channels, the latter is encrypted
by a symmetric cipher. Besides, there is an anonymous channel obscuring
a message's origin.
On top of that we built a nice gtk2hs GUI.
The project homepage is http://sep07.mroot.net/index.html. I regret it's
not in English :( - But the source code and documentation  are. You
can build the documentation from the snapshot .
The interesting thing about the project is, that it provides a nice
mixture of IO (network), purely functional protocol handling and
related data structures and a graphical user interface (GTK). Besides,
it was implemented by 3 other groups (two using Java, one using C++) as
well. Comparing the results, you see that the Haskell implementation is
not only more stable and provides more features, it also has about 70%
Let me know, if you're interested in details.
Hope this helps
 4 students: 2 experienced Haskell users and two newbies
 a practical course where a non-trivial software project has to be
planned, implemented and documented
 Complete repository available at:
Früher hieß es ja: Ich denke, also bin ich.
Heute weiß man: Es geht auch so.
- Dieter Nuhr
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