36.1. How It Works

One of the many useful properties of objects is that each object provides a contained scope for functions and data. Inheritance allows you to use this scope separately from where it's defined. A DSL can use this facility by defining DSL functions on a base class, and then allowing developers to write DSL programs in subclasses. The base class can also define fields to hold any parsing data that's required.

Using a base class like this is an obvious place for an Expression Builder. Clients then write DSL programs in a subclass of the Expression Builder. Using inheritance allows them to add other DSL functions in the subclass, or even override base functions in the DSL object if they need to.