[Haskell-beginners] Cabal-install of local package

[Stefan Höck]

Dear list

Like many other I seem to be struggling with some of the concepts of
cabal and cabal-install. For the records: I use cabal-install 1.20.0.3
and ghc 7.8.3 on arch linux.

For starters, I implemented my own idea of an improved prelude, called
the package efa-prelude and the module it exports Efa.Prelude. I then
built the package and installed it using `cabal install --user`.
This worked and a folder for the library was created at
"$HOME/.cabal/lib/x86_64-linux-ghc-7.8.3/efa-prelude-0.1.0".
I also registered the library using `cabal register --user` and
now cabal prints some information about the package when I type
`cabal info efa-prelude`. I am also able to import Efa.Prelude into
ghci.

However, when I now try to use this library in another local project
using a sandbox this time, I can build the project but
when I try to install it into the sandbox I get the following error
message:

    Resolving dependencies...
    cabal: Could not resolve dependencies:
    trying: test-0.1.0 (user goal)
    next goal: efa-prelude (dependency of test-0.1.0)
    Dependency tree exhaustively searched.

I just tried and the install works if I do it outside of a sandbox.
Obviously I am missing something crucial here. Could somebody please point me
in the right direction what is needed to make my own packages available
in a sanboxed install?

Thanks for your time

Stefan