Functional programming

Does anyone here have any experience with functional programming? I've been learning OCaml and Haskell recently, but there are things which are really painful to do with them (interactive programs).

Found a trivial game written in haskell which I bet took months to complete:
http://www24.brinkster.com/srineet/para/para.pdf

I like it though.

If you're wondering how interactive programs can be written in functional languages, you really should take a look at xmonad. It's a dwm-style tiling window manager in ~500 lines of Haskell. It had its first release after around a month of development, and at that point it already did things that dwm (written in C) didn't.