How to design a Domain-Specific Language using features offered by the Kotlin language, using the Vaadin API as a example.

1. DESIGNING A DSL IN
KOTLIN
@NICOLAS_FRANKEL

2. ME, MYSELF AND I
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 By day
• Consultant
 By night
• Developer
• Blogger
• Book author
• Teacher/trainer
@nicolas_frankel #kotlin #dsl #kaadin

3. HYBRIS, AN SAP COMPANY
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@nicolas_frankel #kotlin #dsl #kaadin

4. A DSL?
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“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
@nicolas_frankel #kotlin #dsl #kaadin

5. GPL/DSL EXAMPLES
GPL DSL
XML • HTML
• MathML
Java • Hamcrest
• AssertJ
• Fest Assert
Kotlin • Anko
• Kaadin
• Bean DSL
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@nicolas_frankel #kotlin #dsl #kaadin

6. DESIGNING A DSL IN JAVA
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Method Sequencing
Method Chaining
Nested Method Calls
Lambdas
https://dzone.com/articles/building-a-dsl-in-java
@nicolas_frankel #kotlin #dsl #kaadin

7. ASSERTJ SAMPLE
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");
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@nicolas_frankel #kotlin #dsl #kaadin

8. KOTLIN
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“Statically typed programming language
for the JVM, Android and the browser”
-- http://kotlinlang.org/
@nicolas_frankel #kotlin #dsl #kaadin

9. A FEW FACTS
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Developed by JetBrains
• Soon co-managed by Google
Open Source
Compiles to
• JVM bytecode
• JavaScript
• (Native)
A "simpler Scala"
@nicolas_frankel #kotlin #dsl #kaadin

10. KOTLIN FEATURES
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Functional and object-oriented
Statically-typed
Null safe
No checked exceptions
Named & optional arguments
Lambdas
Extension functions
Java compatibility
(And more...)
@nicolas_frankel #kotlin #dsl #kaadin

11. SAMPLE: VAADIN UI
public class SampleUI extends UI {
@Override
protected void init(VaadinRequest req) {
setTheme("valo");
VerticalLayout layout = new VerticalLayout();
Label label =
new Label("<strong>Hello</strong>", HTML);
TextField field = new TextField("world!");
layout.addComponents(label, field);
layout.setMargin(true);
setContent(layout);
}
}
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@nicolas_frankel #kotlin #dsl #kaadin

12. OUR GOAL FOR DSL
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“Looks” declarative...
But is code
@nicolas_frankel #kotlin #dsl #kaadin

13. DECLARATIVE VAADIN UI
class KaadinSampler : UI() {
override fun init(req: VaadinRequest) {
theme = "valo"
verticalLayout(margin = true) {
html("<strong>Hello</strong>")
textField("world!")
}
}
}
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@nicolas_frankel #kotlin #dsl #kaadin

14. DEMO!
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@nicolas_frankel #kotlin #dsl #kaadin

15. WHY NOT GROOVY?
email {
from 'dsl-guru@mycompany.com’
to 'john.doe@waitaminute.com’
subject 'The pope has resigned!’
body {
p 'Really, the pope has resigned!’
}
}
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@nicolas_frankel #kotlin #dsl #kaadin

16. WHY NOT SCALA?
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
}
}
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@nicolas_frankel #kotlin #dsl #kaadin

17. TAKEAWAYS
1. 100% Java interoperability
2. Properties
3. Extension Functions
4. Named parameters
5. Default values
6. Lambdas with receiver
7. (Operator overloading)
8. (Infix)
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@nicolas_frankel #kotlin #dsl #kaadin

18. Q&A
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http://blog.frankel.ch/
@nicolas_frankel
http://frankel.in/
https://git.io/vd8d9
https://git.io/vHGER
@nicolas_frankel #kotlin #dsl #kaadin