[Rd] How do I reliably and efficiently hash a function?

[Konrad Rudolph]

@Jeroen, here’s what I’m solving with my hacking the parent
environment chain: I’m essentially re-implementing `base::attach` —
except that I’m attaching objects *locally* in the function instead of
globally. I don’t think this can be done in any way except by
modifying the parent environment chain. Incidentally, package
namespaces do largely the same thing. The difference is that they only
need to do it *once* (when loaded), and subsequent function calls do
not modify this chain.