An Internal Domain-Specific Language (DSL) is a domain-specific language that is embedded within a host programming language. Unlike an external DSL, which has its own separate syntax and tools, an internal DSL leverages the existing syntax and features of the host language to create a specialized language that’s tailored to a particular domain or problem space.
Here are some characteristics of an internal DSL:
- Host Language Integration: An internal DSL takes advantage of the syntax, libraries, and constructs of the host programming language. This means that developers can use familiar programming constructs while also incorporating domain-specific abstractions.
- Natural Expression: Since the internal DSL uses the syntax of the host language, the code written in the DSL tends to look and feel like idiomatic code in that language. This makes it easier for developers to learn and use the DSL.
- Code Reuse: Developers can seamlessly combine code written in the internal DSL with regular code written in the host language, allowing for efficient reuse of existing libraries and components.
- Abstraction and Convenience: Internal DSLs can provide domain-specific abstractions that make complex operations easier to express and understand. This can improve the readability and maintainability of code.
- Simplified Integration: An internal DSL doesn’t require separate parsing and tooling, as it directly uses the capabilities of the host language. This can simplify the development process and reduce the overhead associated with creating an external DSL.
- Limited Flexibility: Internal DSLs are limited by the capabilities and constraints of the host language. While they offer domain-specific abstractions, they may not be as powerful or expressive as an external DSL designed from the ground up.
- Less Learning Curve: Developers who are already familiar with the host language can quickly adopt and start using an internal DSL without the need to learn a new syntax.
Examples of internal DSLs include jQuery for manipulating HTML and CSS using JavaScript, ActiveRecord in Ruby on Rails for database querying and manipulation, and LINQ (Language-Integrated Query) in C# for querying data collections using a declarative syntax. These internal DSLs allow developers to work with domain-specific concepts using the syntax and features of the underlying host language.