Translating Modula2 into D: variant records, pointer

[BLS]

Thanks Frits,
a lot of interesting stuff for a D newbie like me.
Frits van Bommel schrieb:

> * If you only ever set the union members right after constructing the 
> Node instance, you may also want to think about classes and inheritance 
> if you're OOP-inclined.

Indeed the snippet is part of a table driven (better data-structure) 
general parser. So I allways check Terminal first and then I set the 
union values.
It was anyway my next question : How to implement this the OOP way ?
  and ... Can opCall() help somehow ?
Thanks for beeing so patient with me. Bjoern