[Nix-dev] GHC 7.4.1 and Haskell Platform (was: [Nix-commits] SVN commit: nix - r34059 - nixpkgs/trunk/pkgs/top-level)

[Peter Simons]

Hi Andres,

 >> The new versions of mtl and transformers break many important packages,
 >> such as monad-par, graphviz, pandoc, and all other packages that depend
 >> on any of those. This situation causes serious problems for me, because
 >> I depend on some of those packages for my daily work. IMHO, it is an
 >> overreaction to have all those builds fail, because some day in the
 >> future a new version of Haskell Platform *may* be released that *may*
 >> recommend the latest versions of 'transformers' and 'mtl'.
 >
 > You make it sound like I'm inventing things. Sure, it hasn't been
 > released yet, and there's been some discussion about these packages in
 > particular. Nevertheless, it's very likely that it happens, and it's
 > likely that it happens this month.

obviously, there are plans to release a new version of Haskell Platform. I
don't doubt that -- all I meant to emphasize is that this release hasn't
happened yet.

Generally speaking, there is a strong interest to conform to HP, because it
provides stability and predictability. We deviate from HP only when there is
a very compelling reason to do so.

Another interest of ours, however, is that we want to provide a usable
system, i.e. a package database that people can actually install and use.

Those two interests conflict. The upcoming HP standard is probably going to
mandate use of mtl 2.x and transformers 3.x -- so we have an interest in
using those packages in haskellPlatformArgs_future. On the other hand,
configuring GHC 7.4.1 to use those packages right now breaks a lot of other
packages, some of which are extremely popular, like monad-par, graphviz,
Pandoc, and everything else that depends on those. This gives us an
incentive *not* to update mtl and transformers right now.

Now, in order to decide whether we should update mtl today or not, we have
to weigh Haskell Platform conformance against usability.


 > I don't think we've ever made a decision to "support" 7.4.1 already. You
 > seem to see this differently.

Yes, exactly. I've been supporting GHC 7.4.1 for quite a while. I use it
myself, and I support it in the sense that I don't commit any updates
without testing first how they affect the 7.4.1 environment. I use monad-par
in several of my projects, and I also heavily depend on Pandoc. The mtl
update breaks those two packages, leaving me with a non-functional working
environment! That situation is very unpleasant for me.

Given the fact that the new HP standard hasn't been released yet, I feel
that having a usable system is more important than conformance. That
judgment is probably going to change once a new HP release has been made,
but until then I'd rather have a system that actually works.

Take care,
Peter