For the client javascript is obligatory. For the server you have a choice, yesod is written in haskell. Might be that javascript is not the best language there, no? ;-) The original developer of node.js:
Node.js Interview: 4 Questions with Creator Ryan Dahl
" Why did you originally choose javascript for node?
Dahl: Originally I didn't. I had several failed private projects doing
the same on C, Lua, and Haskell. Haskell is pretty ideal but I'm not
smart enough to hack the GHC."
http://bostinno.streetwise.co/2011/01/31/node-js-interview-4-questions-with-creator-ryan-dahl/
As a sidenote the interesting thoughts of EDW on learning java vs
haskell: http://chrisdone.com/posts/dijkstra-haskell-java
Rants on node (doubtless not the only):
http://notes.ericjiang.com/posts/751
https://news.ycombinator.com/item?id=4495101
--
Kind regards,
Stefan Houtzager
Houtzager ICT consultancy & development
www.linkedin.com/in/stefanhoutzager