> Aw, I should've used quotes or a separate line, the command is
>
> $ ghc-pkg check
>
> I meant: what does "ghc-pkg check" report.
>

Maybe we can try to break the problem down into smaller pieces.

Happstack is composed of multiple packages, and you could try them one
at a time to narrow things down a bit:

happstack-util
happstack-data
happstack-state
happstack-ixset
happstack-server
happstack

If you cabal install each one of the above in turn (and in order!) it
will mimic "cabal install happstack" fairly well.