NRBPerdijk

object EventSerializerRegistry extends JsonSerializerRegistry {
  override def serializers: immutable.Seq[JsonSerializer[_]] = Vector(
    JsonSerializer(Json.format[ActualItemPurchasedEvent])
  )

  private val addDefaultDiscount = JsPath.json.update((JsPath \ "item" \ "discount").json.put(JsNumber(0)))
  private val convertCustomerToClient =
    JsPath.json.update(
      //add the path client \ clientId to the json object, then copy the value of customerId into it
      (JsPath \ "client" \ "clientId").json.copyFrom((JsPath \ "customerId").json.pick)

NRBPerdijk

    <dependencies>
        <dependency>
            <groupId>org.graalvm.sdk</groupId>
            <artifactId>graal-sdk</artifactId>
            <version>1.0.0-rc14</version>
        </dependency>
    </dependencies>

NRBPerdijk

import org.graalvm.polyglot.{Context, Source}

object Main extends App {

  // We need to initialise a GraalContext that will do the mediation between the JVM languages and R
  val context: Context = Context.newBuilder("R").allowAllAccess(true).build()

  // Next, we need to create a Source, which needs to know what language it features and where to find the code.
  val source: Source = Source.newBuilder("R", Main.getClass.getResource("funHelloWorld.R")).build()

NRBPerdijk

printHelloWorld <- function() {
    # assigning a string to the variable
    helloWorld <- "Hello, World!"

    #printing the variable
    print(helloWorld)

    # here we concatenate the created variable with some extra information
    # R automatically returns the last statement, so we're done here!
    paste(helloWorld, "executed in R")

NRBPerdijk

# Some very impressive R stuff happens here. 
# (Well, we're pretending it does, anyway! It's really just a mock...)
# This function returns a data.frame containing a number of 
# weather forecasts that we need to bring back to the JVM
magicHappensHere <- function() {
    # Omitting mocking code here
    (...)
    
    # Like in Scala, the result of the last statement in an R function is its return.
    weatherForecasts

NRBPerdijk

generateWeatherForecasts <- function(pathToMagicFile) {

  # We're bringing the function contained in the file at the given location into scope
  source(paste(pathToMagicFile))

  # This returns a dataframe, a way for R to store large quantities of data
  # in an ordered manner (kind of like a Database Table...)
  weatherForecast <- magicHappensHere()

  # Like in Scala, the result of the last statement in an R function is its return.

NRBPerdijk

  // We need to initialise a GraalContext that will do the mediation between
  // the JVM languages and R
  val context: Context = Context.newBuilder("R").allowAllAccess(true).build()

  // Next, we need to create a Source which needs to know what language it features
  // and where to find the code.
  val sourceNoBindings: Source = 
    Source
      .newBuilder("R", Main.getClass.getResource("fun_NoBindingsWeatherForecasts.R"))
      .build()

NRBPerdijk

  // This function signature is a lot cleaner than the one that doesn't use bindings.
  // It is also completely Scala, meaning we do not have to do ANY parsing.
  val rMagicWithBindings: String => WeatherForecastList =
    context.eval(sourceWithBindings).as(classOf[String => WeatherForecastList])

NRBPerdijk

case class WeatherForecast(
  humidity: Percentage,
  windForecast: WindForecast,
  sunshine: Percentage,
  temperature: Temperature,
  chanceOfRain: ChanceOfRain
)
case class Temperature(degrees: Int, temperatureScale: String)
case class Percentage(percent: Double)
case class WindForecast(windSpeed: WindSpeed, direction: String)

NRBPerdijk

generateWeatherForecasts <- function(pathToMagicFile) {
  # We're bringing the function contained in the file at the given location into scope
  source(paste(pathToMagicFile))

  # This returns a dataframe, a way for R to store large quantities of data in an ordered
  # manner (kind of like a Database Table...)
  weatherForecast <- magicHappensHere()

  # We use the Scala Domain object provided through GraalVM bindings to get ourselves an
  # instance of the Scala wrapper containing a List of WeatherForecast