The Interpreter pattern

Often, we need to create a domain-specific language (DSL). A DSL is a computer language of limited expressiveness targeting a particular domain. DSLs are used for different things, such as combat simulation, billing, visualization, configuration, and communication protocols. DSLs are divided into internal DSLs and external DSLs.

Internal DSLs are built on top of a host programming language. An example of an internal DSL is a language that solves linear equations using Python. The advantages of using an internal DSL are that we don’t have to worry about creating, compiling, and parsing grammar because these are already taken care of by the host language. The disadvantage is that we are constrained by the features of the host language. It is very challenging to create an expressive, concise, and fluent internal DSL if the host language does not have these features.

External DSLs do not depend on host languages. The creator of the DSL can decide all...