A Kotlin DSL to code business process

Process modeling pre-requisite

Pre-requisite: BPMN in 2 minutes!

BPMN Process definition

Application based on business processes

Studio to design processes

Pros of using the full platform

As a developer…​

Another approach

What is a DSL?

Domain specific language

External DSLs

Internal DSLs

We already uses DSLs

def "should return user given its id and tenant id"() {
    given:
    def expectedUser = aUser(new User(id: 1))
    when:
    def user = repository.findById(1).get()
    then:
    user == expectedUser
}

We already uses DSLs

plugins {
    `kotlin-dsl`
}
repositories {
    jcenter()
}
dependencies {
    compile("commons-httpclient:commons-httpclient:3.1")
}

Kotlin DSL

Kotlin lang

Kotlin makes writing DSL easy

html {
    head {
        title {+"Some title"}
    }
    body {
        h1 {+"Some title"}
        p  {+"Some text"}
        a(href = "http://kotlinlang.org") {+"Kotlin"}
    }
}

A DSL for processes from scratsh

The process

Function literals with receiver

fun html(init: HTML.() -> Unit): HTML {
    val html = HTML()  // create the receiver object
    html.init()        // pass the receiver object to the lambda
    return html
}

@DslMarker

@DslMarker
annotation class ProcessDSLMarker

html {
    head {
        head {} // should be forbidden
    }
    // ...
}

The general rule:
- an implicit receiver may *belong to a DSL @X*
    if marked with a corresponding DSL marker annotation
- two implicit receivers of the same DSL
    are not accessible in the same scope
- the closest one wins
- other available receivers are resolved as usual,
     but if the resulting resolved call binds to such a receiver,
     it's a compilation error

Expression body

fun sum(a: Int, b: Int) = a + b

fun data(init: DataContainer.() -> Unit) {
    DataContainer(builder).init()
}

fun data(init: DataContainer.() -> Unit) = DataContainer(builder).init()

Default arguments

// Bad
fun foo() = foo("a")
fun foo(a: String) { ... }

// Good
fun foo(a: String = "a") { ... }

automaticTask("name"){
}

automaticTask("name")

Infix functions

infix fun Int.shl(x: Int): Int { ... }

// calling the function using the infix notation
1 shl 2

// is the same as
1.shl(2)

text("type").describedAs("type of the loan")

text("type") describedAs "type of the loan"

Extension function

fun MutableList<Int>.swap(index1: Int, index2: Int) {
    val tmp = this[index1] // 'this' corresponds to the list
    this[index1] = this[index2]
    this[index2] = tmp
}

actor("requester") mappedToUser "john"

"requester" mappedToUser "john"

Property with getter

val isEmpty: Boolean
    get() = this.size == 0

text("type") describedAs "type of the loan"

text named "type" describedAs "type of the loan"

"Dynamic DSL"

Why using a DSL?

Validation

Discovery

Speak the language of your domain

Feedbacks on writing a DSL

process {
    data {
        text named "myData"
    }
}