Control.Parallel.Strategies: definitions of rnf for most collections are poor

[bos]

These all perform a lot of consing, which seems rather undesirable. It would be very nice indeed if they could be rebaked in terms of strict left folds. Unfortunately, all of the collections in question seem only to expose non-strict left folds publicly.

instance (NFData k, NFData a) => NFData (Data.Map.Map k a) where
    rnf = rnf . Data.Map.toList

instance NFData a => NFData (Data.Set.Set a) where
    rnf = rnf . Data.Set.toList

instance NFData a => NFData (Data.Tree.Tree a) where
    rnf (Data.Tree.Node r f) = rnf r `seq` rnf f

instance NFData a => NFData (Data.IntMap.IntMap a) where
    rnf = rnf . Data.IntMap.toList

instance NFData Data.IntSet.IntSet where
    rnf = rnf . Data.IntSet.toList

[ross]

All but IntSet? are instances of Foldable, and so have Data.Foldable.foldl'.

[igloo]

I'm not sure exactly what changes you're proposing, if any, or if Ross's reply negates them, but please propose them using  http://www.haskell.org/haskellwiki/Library_submissions