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'. As
long as those changes have such profound negative effects on our packages, those
upgrades should be deferred. This approach seems consistent with the way we've
handled these matters things in the past, too. For example, we happily break
conformance with older versions of HP, when those changes are beneficial for
users. In other words, we have usually valued usability over strict conformance
before, and IMHO that is a sensible policy.
I agree that it's nice to test what kind of trouble these upgrades cause, but I
don't believe that 'trunk' is the right place to perform those tests. The breakage
these changes cause affect users who rely on Nixpkgs to provide a stable working
environment.
svn path=/nixpkgs/trunk/; revision=34059
767db7397c