heads-up: Haskell updates

[Ricardo Wurmus]

Hi Guix,

I’ve just pushed a very large number of updates to Haskell packages and
switched to GHC 8 as the default.

I have built almost all of these updated packages and some packages that
depend on them, including r-rmarkdown, hisat, darcs, xmonad, and r-rcas.

One notable exception is idris — I could not make it build at all.
Neither the current version, nor any of the following versions up to
1.2.0.  Help in this area is appreciated.

Some notes:

* updating Haskell packages automatically is dangerous as not all
  packages work well together.  When updating I often had to take a few
  steps back to reduce the version number.  On Hackage I picked the LTS
  version where available.

* this is based on my previous work from October 2016.  Only few
  packages had been updated since then, so most of my changes still
  applied.  When it wasn’t necessary I didn’t bother updating my
  updates.  This means that a second pass could be useful to update
  packages that are below their LTS versions.

  In general I think we really need someone who feels responsible for
  *all* the Haskell packages.  It’s not okay to keep most of them at old
  versions for over a year.

* many problems are caused by the fact that GHC includes a bunch of
  packages that really shouldn’t be overridden by packages.  Examples
  are ghc-directory, ghc-binary, ghc-bytestring, etc.  Since we still
  have packages where these inputs are used, there can be conflicts down
  the line, which are hard to fix.

* I liberally added the “--allow-newer” configure flag to packages that
  have strict version constraints.  In most cases that was to allow for
  a later version of QuickCheck.

* If you find that anything is broken now that worked before, please
  coordinate updates and fixes on address@hidden

I hope this big blob of changes won’t inconvenience you too much.

--
Ricardo

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