Chapter 20. Domain-Specific Languages in Scala

A domain-specific language (DSL) is a programming language that mimics the terms, idioms, and expressions used among experts in the targeted domain. Code written in a DSL reads like structured prose for the domain. Ideally, a domain expert with little experience in programming can read, understand, and validate this code, if not also write code in the DSL.

We will just scratch the surface of this large topic and Scala’s support for it. For more in-depth coverage, see the DSL references in Appendix A.

Well-crafted DSLs offer several benefits:


A DSL hides implementation details and exposes only those abstractions relevant to the domain.


Because implementation details are encapsulated, a DSL optimizes the effort required to write or modify code for application features.


A DSL helps developers understand the domain and domain experts to verify that the implementation meets the requirements.

However, DSLs also have several drawbacks:

DSLs are difficult to create

Although writing a DSL is “cool,” the effort shouldn’t be underestimated. First, the implementation techniques can be nontrivial (see the following example). Second, good DSLs are harder to design than traditional APIs. The latter tend to follow language idioms for API design, where uniformity is important and easy to follow. In contrast, because each DSL is a unique language, we are free to create idioms that reflect the unique ...

Get Programming Scala, 2nd Edition now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.