This is a set of instructions for a very bare-bones, Cabalized, and sandboxed build.
$ mkdir happstack01 && cd happstack01/
$ cabal init .
$ <CR><CR><CR><CR><CR><CR><CR><CR><CR> 1 <CR><CR><CR>
$ mkdir src
$ touch src/Main.hs
$ vi happstack-01.cabal
In happstack01.cabal
...
library
exposed-modules:
Main
build-depends: base >=4.6 && <4.7
, happstack-server
hs-source-dirs: src
default-language: Haskell2010
Then
$ cabal sandbox init
$ cabal install --only-dependencies
$ vi src/Main.hs
In src/Main.hs
import Happstack.Server
main :: IO ()
main = simpleHTTP nullConf $ return "Hello sandbox!"
Get some coffee while the sandbox builds.
$ cabal repl
> main
After this I usually add an executable
entry to the Cabal file and begin to build the server from that.