Sprache als Werkzeug: DSLs mit Kotlin (JAX 2020)
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The document discusses Domain-Specific Languages (DSLs) in Kotlin, explaining their definitions and types, including external and internal DSLs. It highlights various advantages of using DSLs, such as clearer scoping and improved expressiveness, and provides examples of building blocks for creating DSLs in Kotlin. Additionally, it features practical applications of DSLs, including a Gherkin test DSL for structuring executable specifications.
Sprache als Werkzeug: DSLs mit Kotlin (JAX 2020)
- 1. 1 Sprache als Werkzeug DSLs mit Kotlin @toddquackenbush on Unsplash @maverick_1601 Frank Scheffler
- 3. 3 Domain Specific Languages: Definition “DSLs are small languages, focused on a particular aspect of a software system. You can't build a whole program with a DSL, but you often use multiple DSLs in a system mainly written in a general purpose language.” - Martin Fowler with Rebecca Parsons https://images-eu.ssl-images-amazon.com/images/I/51qFZ0yIUsL.jpg
- 4. 4 Domain Specific Languages: Definition “DSLs come in two main forms: external and internal. An external DSL is a language that's parsed independently of the host general purpose language: good examples include regular expressions and CSS.” - Martin Fowler with Rebecca Parsons https://images-eu.ssl-images-amazon.com/images/I/51qFZ0yIUsL.jpg
- 5. 5 Domain Specific Languages: Definition “Internal DSLs are a particular form of API in a host general purpose language, often referred to as a fluent interface. The way mocking libraries, such as JMock, define expectations for tests are good examples of this.” - Martin Fowler with Rebecca Parsons https://images-eu.ssl-images-amazon.com/images/I/51qFZ0yIUsL.jpg
- 6. 6 Kotlin Internal DSL Selection Gradle Kotlin DSL https://github.com/gradle/kotlin-dsl Beans/Router/MockMvc DSL https://github.com/spring-projects/spring-framework Kotlin Test https://github.com/kotlintest/kotlintest Kuery SQL in Kotlin https://www.kotlinresources.com/library/kuery/ Spring Fu Microframework https://github.com/spring-projects/spring-fu GeoJSON Builder DSL https://github.com/dxfrontiers/kotlin-geojson-dsl
- 7. 7 1. Predictable Domain logic is expressed declaratively, while execution is controlled by the DSL. 2. Safer Restricted dialect and clearer scoping reduces unsafe operations. 3. More expressive Domain code clearly expresses what should be done. Domain specific errors are easier to understand. 4. Portable Domain logic execution can be ported to new platforms, if necessary. 5. Easier to understand Domain experts are able to learn the DSL in less time. DSL Advantages
- 8. 8 Building Blocks for DSLs in Kotlin 1/2 Simplified Lambda Syntax Extension Functions
- 9. 9 Building Blocks for DSLs in Kotlin 2/2 Lambdas with Receiver Operator Overloading
- 10. 10 A Gherkin Test DSL “Gherkin uses a set of special keywords to give structure and meaning to executable specifications.” - Cucumber GIVEN state before behavior is applied WHEN specifies the behavior part THEN defines changes or expected outcome
- 11. 11 The Calculator: Classical Verification
- 12. 12 The Calculator: Gherkin-Style Verification “given”-Lambda yields the test subject “when”-Lambda receives test subject and returns test execution result “then”-Lambda receives an assertion object wrapping the test result
- 13. 13 Gherkin DSL: Capturing the “test setup”
- 14. 14 Gherkin DSL: Capturing the “execution result”
- 15. 15 Gherkin DSL: Triggering test and verification
- 16. 16 Gherkin DSL: Extensibility optional assertion chaining repeated/parallel test execution repeated/clean test subject creation
- 18. 18 Using Infix Extension Functions
- 19. 19 Scoping Infix Extension Functions
- 21. 21 Almost unlimited possibilities ... Some homework for you!
- 22. 22 Kotlin DSL Building Blocks 1. Capturing declarations/logic using Lambdas 2. Providing Declarative Context using Lambdas with Receiver 3. Providing scoped (extension) functions 4. Improving Readability using infix notation 5. (Operator overloading)
- 23. 23 What’s the next DSL you’ll be designing? Sprache als Werkzeug DSLs mit Kotlin https://github.com/dxfrontiers/kotlin-gherkin-dsl/tree/kkon https://www.heise.de/developer/artikel/Sprache-als-Werkzeug-DSLs-mit-Kotlin-bauen-4599797.html https://blog.digitalfrontiers.de @maverick_1601 https://github.com/maverick1601 https://bit.ly/2EDAagi Frank Scheffler