> In an implementation which boxes flonums, NaNs aren't a single value;

Yeah, and that's why we have eq? and eqv? NaNs, like other numbers, need
not be eq? but should be eqv? if they have the same bit pattern.

 > Closures and continuations are atomic

But "atomic" I don't mean "not a pair". I not quite sure how to define
it, but perhaps "something that can be finitely enumerated" gets close.
Perhaps "atomic" is not the best name for this property.

Anyway, this property is shared by chars, fixnums, flonums, null, EOF
objects. These (with the understandable exception of EOF) have standard
read syntax. By extension, the bignums and derivaties, while not finite,
also have a read syntax.

Anyway, NaNs clearly share this property, so I would suggest they have a
read syntax.

Regards,

Alan
--
Dr Alan Watson
Centro de Radioastronomía y Astrofísica
Universidad Astronómico Nacional de México