It requires unix-compat to build. What does "cabal install
unix-compat" give you?

The same error. But...

If that's what's breaking you can try "cabal install
unix-compat-0.1.2.1" and then "cabal install happstack-util". Version
0.1.2.1 appears to be the most recent version of unix-compat that
doesn't specify version bounds on the unix package, which is what
you're having trouble with.

This worked, then "cabal install happstack" worked perfectly(!)

Can anyone point me to a tutorial which explains basics of cabal? I'm trying to navigate it, without understanding version bounds, or really anything related to how cabal handles versions of dependencies.

Thank you for the help!

Tom