Control.Parallel.Strategies contains many NFData instances for types defined in base, but not all. I propose adding NFData instances for all types in base where it makes sense. The specific issue I had was with Data.Version. I wanted to 'rnf' some type which contained a Version, but it had no instance for NFData. The only solution is to add an instance in your own code, where it doesn't really belong. Therefor I checked the base package for other other types which also lacked an NFData instance. I would like some feedback on the instances for STRef and IORef. Does it make sense to have them? I used a trick to force their evaluation since their constructors are not exported. Discussion deadline: October 7 Ticket: http://hackage.haskell.org/trac/ghc/ticket/3537 Regards, Roel van Dijk