Do you mean a web app idea/example itself or the Hiawatha configuration to run a Haskell app (which I think could be done with either FastCGI or a reverse proxy)?
As an aside, I read some of
Learn You a Haskell for Great Good! [learnyouahaskell.com] and started to work on a simple utility to pull down an ad server list and export to a Bind zones file the other week. I'm a novice programmer anyway, so trying functional programming in Haskell is proving... interesting.