[racket-dev] Typed Racket support for Ephemerons

BTW, I think there are a couple of typos in:

"15.2 Ephemerons
An ephemeron [Hayes97] is a generalization of a weak box (see Weak
Boxes). Instead of just containing one value, an e___m___phemeron
holds two values: one that is considered the value of the ephemeron
and another that is the ephemeron’s key. Like the value in a weak box,
the value in ___and___ ephemeron may be replaced by #f, but when the
key is no longer reachable (except possibly via weak references)
instead of when the value is no longer reachable."

Cheers
P.