Kotlin is one of those “new” JVM languages that are currently rocking the boat. Although it’s made a great impact on Android, it’s equally good on the server side. As Domain-Specific Languages are constrained by the language they run on, Kotlin frees developers from Java fluent builders to propose something better. Using the Vaadin web framework as an example, I’ll demo how one could design its own DSL with Kotlin.

1. @nicolas_frankel
Writing a Domain-
Specific Language in
Kotlin

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

3. @nicolas_frankel
Hazelcast
HAZELCAST IMDG is an operational,
in-memory, distributed computing
platform that manages data using
in-memory storage, and performs
parallel execution for breakthrough
application speed and scale.
HAZELCAST JET is the ultra fast,
application embeddable, 3rd
generation stream processing
engine for low latency batch
and stream processing.

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 • SVG
• 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
• “Looks” declarative...
• But is code
Our goal for DSL

9. @nicolas_frankel
Let’s use Kotlin!

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. (Reified generics)
9. (Infix)
Takeaways

14. @nicolas_frankel
• https://blog.frankel.ch/
• @nicolas_frankel
• https://bit.ly/kotlindsl
• https://bit.ly/kaadin-site
Thanks a lot!