How does this handle the situation where I want both package A and package B installed, but they each want a different version of package C?
How would your distro handle it if those packages were written in C?
I'd say the C-leaning factions of the open-source community have largely accepted the convention that ABI/API changes that cause incompatibilities are accompanied by bumps in the major version number. There are, of course, exceptions, but my feeling is they are rare, generally well-publicized, and quickly fixed. To be honest, I don't even know if hackage authors tend to follow this convention because...
With Haskell it seems worse because everything has conservative dependencies in a *.cabal file and Cabal will refuse to build the thing unless they're met.
... Haskell seems worse to me in that if package foo is updated, every other package depending on foo (recursely) must then be rebuilt, even if they didn't change and even if the interface presented by foo didn't change. C programs do not suffer similarly and my limited experience with ``cabal hell'' would have been a non-event if this recompilation process wasn't necessary. I don't know what technical issues necessitate it and I don't know whether the conventions required to make it feasible are already in place, which is partially what I'm trying to learn here. =) Additionally, it seems that the hackage ecosystem is far more intertwined than that of third-party Python packages (I have no experience with Ruby). That is, many things in hackage depend on other things in hackage whereas far more Python packages depend only on the libraries included in the base install. This is not a knock against Haskell by any means; it is, in fact, a testament to the powerful abstractions it supplies and enables. It does, however, weaken the ``other languages have this problem, too'' argument. Perhaps the solution is a more rigorous effort to keep the Haskell Platform up to date, especially with well-regarded ``building block'' libraries (eg, lens), and possibly even on a fixed schedule. Then hackage authors can be encouraged to make their stuff compatible with particular releases of the Haskell Platform and ``normal'' users would only need to worry about upgrades whenever the Platform is updated. But then we're really edging out on the slippery slope to Haskell becoming a distro unto itself. pete