hash tables and GC

[gz@spt.entity.com (Gail Zacharias)]

I think you might have misunderstood.  These things are a new data type, which
doesn't replace any existing lisp data type.  You can't get one without
explicitly asking for it, which you presumably only do if you want the special
behavior it provides.  Given that, there's no problem with mapping over them.
In fact doing so is necessary in the primary application we have for them
(keeping track of marks in the editor).  The issue about presenting them as
hash tables is simply a question of whether they should be viewed as providing
a mapping between pairs of objects like hash tables do, or simply storing
a set of objects like lists do.