Presentation - DSLs in Kotlin by Niranjan Ratnakar

Presentation slides for SD Kotlin's July 2018 meeting

Transcript

1. Domain Specific Languages (DSLs) in Kotlin Niranjan Ratnakar
2. Outline • What are DSLs? • Why should we use DSLs? • Kotlin features to enable DSLs • Walk through of type safe HTML builder
3. What are DSLs? • [Wikipedia definition] • A domain-specific language (DSL) is a computer language specialized to a particular application domain. • This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains.
4. What are DSLs? • A DSL is like an electric drill: it is a powerful tool with a wide variety of uses, but a specific context, namely, putting holes in things. • A GPL is a complete workbench, with a variety of tools intended for performing a variety of tasks.
5. Another example of DSLs • Recently, companies are working on AI processors • AI can be done by CPUs and GPUs • Why do we need custom AI processors? – Power efficiency – Speed
6. Examples • Regular expressions • SQL • Android layouts (?) – Implemented traditionally in XML – Inflated by Android framework at runtime
7. Why use DSLs? • Code looks closer to domain description. It is at a higher level of abstraction. • Lesser cognitive load for domain experts to write and maintain code. • The compiler (if applicable) can provide assistance while writing code. – We will see this in the type safe builder example
8. Why use DSL? (Advanced) • We wont go into much details on this topic. • Interpreter design pattern – Write a program description using a restricted set of primitives – Interpret the program separately • Multiple interpretations for a single program • Example, evaluate an expression tree or print it
9. Kotlin support for DSLs • Write DSLs with Kotlin as the host language • Programs look closer to the domain • Can use language constructs – for, if, ... • Example, Anko for android layouts – Better looking layout – Easier data binding
10. Anko
11. Kotlin features to enable DSLs • Extension functions – http://kotlinlang.org/docs/reference/extensions.html • Lambda with receivers – http://kotlinlang.org/docs/reference/lambdas.html • Passing a lambda to the last parameter – https://kotlinlang.org/docs/reference/lambdas.html
16. Type safe HTML builders • http://kotlinlang.org/docs/reference/type-safe- builders.html • https://try.kotlinlang.org/#/Examples/Longer %20examples/HTML%20Builder/HTML %20Builder.kt •
17. Walkthrough • Specify the HTML document as a DSL – (Work with a subset of HTML tags) – Can have tags that depend on command line arguments • Covert the HTML document to a string • Use StringBuilder for efficiency • Lets go to code!