2006-03-29:  Removed superfluous thunking of "empty" values in polymorphic
             datastructures due to relaxed value restriction in new
             OCaml-releases.

2002-07-23:  Small beautification.

2001-06-05:  Made code more idiomatic.
             Implemented stubs in chapter 8.

1999-04-09:  Initial release.
