This document discusses domain-specific languages (DSLs) and outlines how to design a DSL using Kotlin. It provides examples of DSLs in various languages like XML, Java with libraries like Hamcrest and AssertJ, and Kotlin with libraries like Anko and Ktor. It discusses features of Kotlin that are useful for building DSLs like properties, extension functions, named parameters and default values. The document concludes by thanking the audience.

1. @nicolas_frankel
A demo based intro
Kotlin Domain-Specific
Language

2. @nicolas_frankel
• Developer, team lead, architect,
whatever it takes
• Recent Developer Advocate
• Kotlin fanboy
Me, myself and I

3. @nicolas_frankel
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4. @nicolas_frankel
“A Domain-Specific Language is
a computer language specialized to
a particular application domain.
This is in contrast to a General-
Purpose Language, which is broadly
applicable across domains.”
--Wikipedia
Domain-Specific Language?

5. @nicolas_frankel
GPL/DSL examples
GPL DSL
XML • HTML
• MathML
Java • Hamcrest
• AssertJ
• Fest Assert
Kotlin • Anko
• Kaadin

6. @nicolas_frankel
• Method Sequencing
• Method Chaining
• Nested Method Calls
• Lambdas
Designing a DSL on Java

7. @nicolas_frankel
assertThat(frodo.getName())
.startsWith("Fro")
.endsWith("do")
.isEqualToIgnoringCase("frodo");
assertThat(fellowshipOfTheRing)
.filteredOn(c ->
c.getName().contains("o"))
.containsOnly(aragorn, frodo, legolas)
.extracting(c -> c.getRace().getName())
.contains("Hobbit", "Elf", "Man");
AssertJ example

8. @nicolas_frankel
Kotlin
“Statically typed programming
language
for the JVM, Android and the
browser”
-- http://kotlinlang.org/

9. @nicolas_frankel
• “Looks” declarative...
• But is code
Our goal for DSL

10. @nicolas_frankel

11. @nicolas_frankel
Why not Groovy?
email {
from 'dsl-guru@mycompany.com'
to 'john.doe@waitaminute.com'
subject 'The president has resigned!'
body {
p 'Really, the president did resign!'
}
}

12. @nicolas_frankel
object SquareRoot extends Baysick {
def main(args:Array[String]) = {
10 PRINT "Enter a number"
20 INPUT 'n
30 PRINT "Square root of " % "'n is " % SQRT('n)
40 END RUN
}
}
Why not Scala?

13. @nicolas_frankel
1. 100% Java interoperability
2. Properties
3. Extension Functions
4. Named parameters
5. Default values
6. Lambdas with receiver
7. (Operator overloading)
8. (Infix)
Takeaways

14. @nicolas_frankel
• https://blog.frankel.ch/
• @nicolas_frankel
• https://git.io/vd8d9
Thanks a lot!