Add support for vectors/arrays

[edsko]

Boxed vectors are already supported, but adding support for the other flavours is a bit trickier:

• Storable and Primitive vectors have a Storable constraint on the element type, and we have no Storable instance for Void. We could define an oprhan, but even then I'm not sure that casting an empty Vector a to Vector Void is safe. Needs a bit of thought.
• Unboxed is a data family; not necessarily a problem, just requires a lot of cases.

[edsko]

We can't actually infer anything for Storable; see

recover-rtti/src/Debug/RecoverRTTI/Wrappers.hs

Line 86 in 6ce3119

-- | Storable vector ("Data.Vector.Storable")

[edsko]

Same goes for primitive vectors.

[edsko]

As it turns out, we can in principle do better for unboxed arrays; I figured out the technical details of how to deal with the data family in 76c70e1 . However, unfortunately it turns out all of the instances of the Vector type family are all newtype instances, not data instances, and so aren't visible on the heap at all :-( This means that all we see are the underlying primitive vectors, for which we can basically do no classification.

[edsko]

This means that vector is now dealt with; remains to deal with array, which is at least partly based around GHC.Arr. Once we have support for array I think all primitive types are accounted for.

[edsko]

Opened haskell/vector#391 to ask about #2 (comment) .

[edsko]

WIP PR at #22 .