DESIGNING A DSL IN KOTLIN

@NICOLAS_FRANKEL

ME, MYSELF AND I

2

Consultant

• Whatever the customer asks of me

Я изучаю русский язык

• Но мне очень трудно

@nicolas_frankel #kotlin #dsl #kaadin

HYBRIS, AN SAP COMPANY

3@nicolas_frankel #kotlin #dsl #kaadin

A DSL?

4

“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

GPL/DSL EXAMPLES

GPL DSL

XML • HTML• MathML

Java • Hamcrest• AssertJ• Fest Assert

Kotlin • Anko• Kaadin

5@nicolas_frankel #kotlin #dsl #kaadin

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

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");

7@nicolas_frankel #kotlin #dsl #kaadin

KOTLIN

8

“Statically typed programming languagefor the JVM, Android and the browser”

-- http://kotlinlang.org/

@nicolas_frankel #kotlin #dsl #kaadin

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

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

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

OUR GOAL FOR DSL

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“Looks” declarative...

But is code

@nicolas_frankel #kotlin #dsl #kaadin

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

WHICH FEATURE CAN WE LEVERAGE?

14

@nicolas_frankel #kotlin #dsl #kaadin

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!’

}

}

15

@nicolas_frankel #kotlin #dsl #kaadin

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

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

Q&A

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http://blog.frankel.ch/

@nicolas_frankel

http://frankel.in/

https://git.io/vHGER

@nicolas_frankel #kotlin #dsl #kaadin