GND + my approach to `whiteSpace` don't get along.

[ekmett]

There is an issue with the notion of end users using GND to derive new instances.

The issue is if we put whiteSpace in TokenParser and expect users to override it, then if the user subclasses TokenParser, and uses GND to derive those instances, then any of those methods that call whiteSpace will call the one from the base type, due to the rules of GND!