README.md

Domain Specific Languages (DSLs)

Convened by Diomidis and Richard.

Methods you can use to work with DSLs with Java include the following.

Use default methods in interfaces to provide to the DSL client an instance of the DSLs runtime and environment.
Use the self type trick
Generate code at compile time, e.g. through Java annotation processing
Implement the DSL in Groovy, Scala, or Kotlin.
Implement a fluent API.
- Microsoft apparently uses this approach to auto-generate (via another DSL) the Azure interfaces for diverse programming languages.
- jOOQ does this for database queries.
Use an IDE's metaprogramming framework based on EMF or use Xtext.

DSLs can be easily implemented in Goovy and used from Java.
As an example consider the Goovy DSL that is used for constructing Jenkins job pipelines.
A DSL implemented in Groovy provides Eclipse editing support.
The marginal cost of including Groovy as a dependency in a Java project may be zero, because many Java projects already use Spock for testing.
The project's host (the main entry point) has to be Groovy, which may be a problem if the Java project is based on a framework with its own entry point.
It is better to start with a dynamic implementation of the DSL, and once things get stable, implement it in a static manner to get a more usable and safe implementation.
When designing an internal DSL you need to carefully balance how much general purpose language functionality you expose to make the DSL usable and flexible, versus how much you take away to avoid giving your users rope to hang themselves.