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Kotlin DSL: The Charming Parts

Freddie Wang & Shengyou Fan

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Who am I

  • Freddie Wang
  • Android engineer in SmartNews
  • ❤️ Kotlin ❤️

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Who am I

  • 范聖佑 (Shengyou Fan)
  • Developer Advocate in JetBrains
  • 用力推廣 Kotlin 中 ❤️

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Agenda

  • DSL at a glance
  • Kotlin syntax
  • Real world cases
  • Design your DSL
  • Q&A

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What’s DSL

Designed for a particular application domain, not for general-purpose

  • SQL
  • Regular Expression
  • Gradle

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External and Internal DSL

  • External: Independent syntax, need a parser to interpret the language
  • Internal: Written inside an existing host language.

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Why Kotlin DSL

  • Top level functions, Extension function, Lambda with receiver make writing DSL very easily
  • Built-in type-safe support
  • Syntax sugar Lambda outside of parenthesis and Infix notation makes Kotlin DSL structured and good readability.

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Kotlin Syntax

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Top level function

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Extension functions

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Lambda with receiver

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Infix notation

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Real world DSLs

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Real world cases

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Gradle Kotlin DSL

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Gradle syntax

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Kotlin Gradle DSL

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Kotlin DSL for HTML

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HTML DOM

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kotlinx.html

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Exposed SQL Framework

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Exposed SQL DSL

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Generated SQL

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Ktor Web Framework

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Ktor Routing DSL

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Write your own DSL

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Design a mini app

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Define the SimpleApp

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Design the syntax (1/3)

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Design the syntax (2/3)

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Design the syntax (3/3)

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Run the DSL

  1. Be part of the project
  2. Run it from external file
    • org.jetbrains.kotlin:kotlin-compiler-embeddable
    • ScriptEngine

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Live Demo - Using ScriptEngine

Check it on github - https://github.com/wangyung/kscript-dsl-example

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Q&A

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More cases