I already had GHC installed so I could build darcs but I needed a few additional packages to install HAppS. Most of these I obtained via apt-get but I had to manually install the following two:
Once they were installed compiling and building HAppS is done using the Cabal based setup file:
runhaskell Setup.hs configure runhaskell Setup.hs build sudo runhaskell Setup.hs install
Once that's out of the way I tried out the 'hello' example. This is located in the 'examples' subdirectory of 'HAppS' and needs to be built and run:
This starts up an application server listening on port 8000. Where to go from there in terms of building apps I'm not sure as there doesn't seem to be much 'how to' style documentation. Digging through the source and examples looks to be the next thing to try.