[Haskell-cafe] non-hackage cabal repos? unpacking non-repo package tarballs?

[Claus Reinke]

I often find myself writing example code that I'd like
to distribute via cabal, but without further burdening
hackage with not generally useful packages.

1. The simplest approach would be if cabal could expose
its internal 'unpackPackage' as a command, so that

    author: cabal sdist
    user: cabal unpackPackage Example.tar.gz

would work (the point being that cabal handles .tar.gz,
which not all users have installed separately; distributing
the .tar.gz would be handled via the usual channels; and
after unpacking, cabal can build the source package).

Note that 'cabal unpack' does not seem helpful here, 
as it touches the package index instead of just looking 
at the tarball.

Could this be made possible, please? Or is it already?

2. Failing that, I remembered that cabal used to be designed
without a fixed package repo address, and a little digging
found options --remote-repo and --local-repo, as well as
the directory layout for package repositories:

http://hackage.haskell.org/trac/hackage/wiki/HackageDB

So this scenario seems possible, in principle:

    author: expose a package repo http://myrepo
    user: cabal --remote-repo=http://myrepo fetch Example

Is it possible to add a (temporary) repo location like this, 
especially for 'cabal fetch'/'cabal unpack'? I've managed 
to get 'cabal --local-repo=myrepo list Example' to work 
(needs uncompressed 00-index.tar), but not the remote
variant, and fetching from the local repo doesn't work,
either.

Are there any usage examples of these features?

Claus