Adding UNION/MAP -- Feedback and tips pls!

[Russell Brennan]

> Aside:  There IS actually a very simple way to port DEC UNION code;
> simply change them to structures (i.e. derived types).  That wastes
> memory but, compared to the machines on which they were used, modern
> ones have near-infinite memory.  I can't think of a circumstance under
> which working DEC UNION code would fail with that trick.
Of course if you have the ability to change *all* the code in use then
there are several ways to replace union.  On the other hand, if you
need to maintain a consistent API (always a good thing) or simply
cannot change some pieces of code, then you are out of luck.  As is
often the case, what is practical is not always what is best.