Proposal: Make `NFData` a fundamental/primitive type-class (by making `deepseq` a GHC-boot package)

[Paterson, Ross]

Simon Marlow writes:
> That's what we have right now, the problem is that deepseq can't define
> a good instance for NFData Map, because it can't see enough of the
> internals of Map.

Couldn't the strict foldl do it?