[plt-scheme] equal? operator

Matthew Flatt writes:
 > The only problems with an equality-test property are the same as in
 > Java: fitting the equality function into a single-dispatch system, and
 > supporting a hash-function property whose value must be consistent with
 > the equality property value. (Are there other issues?)

There's the issue of whether `equal?' is allowed/expected to raise an
error if the arguments are different types (like `char=?') or whether
it should return false.  But maybe that decision is up to the
programmer and MzScheme should be agnostic.

--dougo at place.org