Have you seen cabal2rpm? It's an external tool with a similar goal:
http://community.moertel.com/ss/space/Cabal2rpm/cabal2rpm.html
I hadn't seen it, no.
Can you outline any other differences between this command and cabal2rpm?
Cabal2rpm is much less sophisticated. The rpm command I wrote correctly calculates dependencies on other Haskell packages, and on system packages too. Also, cabal2rpm has clearly bitrotted from looking at the source, and would be unlikely to work now.
This seems like really cool work, but what do folks think about adding OS-specific items like this to Cabal.
I realise I get a bit less of a vote since I wrote this, but I think that cabal2rpm illustrates one aspect of the problem with keeping tools like this outside of Cabal: they break. Another aspect is that you have to be able to *find* the external tools. A Google search like "cabal rpm spec" does not yield cabal2rpm anywhere in the results.
My stance has been that we should keep such tools external to Cabal, layered on top of Cabal so as to not clutter Cabal too much, and to make Cabal's interface to the outside world as good as possible.
I certainly wouldn't mind there being a single command entry point for
building binary packages, e.g. bdist, with flags to control which kind
of binary package to build (RPM, deb, DMG, Innosetup, etc.). But I
really think it's a good thing for the language as a whole to make it as
easy as possible for people to provide binaries to their respective
OS/distro communities. This is a step towards that. I've written Mac
and Windows installers, too, so if the RPM stuff gets in, they're
natural targets.
You can see that the code I added has negligible effect on the core of
Cabal, so it doesn't add clutter.