Fixing "breaking packages"

[Simon Peyton-Jones]

|  I thought that "cabal install" should be viewed as installing an
|  instance of the requested package by recompiling the whole transitive
|  closure of dependencies from scratch, in a sort of NixOS-like way.
|  Given this view, Cabal's reuse of already compiled and installed
|  packages is purely an optimization that can prevent it from
|  recompiling some things if it is absolutely certain that doing so is
|  unnecessary. The problem then is just that Cabal is currently brokenly
|  unable to handle multiple instances of an installed package with the
|  same name and version. 

I believe that what you describe is precisely The Glorious Plan
http://hackage.haskell.org/trac/ghc/wiki/Commentary/GSoCMultipleInstances

It's just that no one has time to do it.  That's why I was raising it (again) to see if anyone has any bright ideas for un-gluing this particular log-jam.

Simon