Using Cabal for dependancies

[Neil Mitchell]

Hi,

The Yhc compiler depends on an increasingly large number of Cabal
packages - mtl and FilePath at the moment, but soon thats likely to
increase by at least 3. Cabal is not yet mature enough to compile Yhc,
and fitting in a compile of bits with Cabal will be quite hard because
of the existing complexity in Scons.

So what we'd really like to do is be able to call "cabal
check-its-installed FilePath", which would return an appropriate exit
code. If it wasn't installed then a darcs get, followed by a "cabal
install-it-please" would be very handy.

Does cabal-install provide the necessary bits for this? What is the
result of installing a package that is already installed? How long til
this kind of solution will be widely enough deployed that we can
actually use it? Does anyone else have any other suggestions?

Thanks

Neil