In this chapter, we covered the Interpreter design pattern. The Interpreter pattern is used to offer a programming-like framework to advanced users and domain experts, but without exposing the complexities of a programming language. This is achieved by implementing a DSL.

A DSL is a computer language that has limited expressiveness and targets a specific domain. There are two categories of DSLs: internal DSLs and external DSLs. While internal DSLs are built on top of a host programming language and rely on it, external DSLs are implemented from scratch and do not depend on an existing programming language. Interpreter is related only to internal DSLs.

Musical notation is an example of a non-software DSL. The musician acts as the Interpreter that uses the notation to produce music. From a software perspective, many Python template engines make use of Internal DSLs. PyT is a high-performance Python DSL to generate (X)HTML. We also saw how the Mesa library of Chromium uses the Interpreter...