constructing simple pipelines in Scala

Playing a bit with constructing pipelines logically in Scala. A pipeline MUST start with a generator, folllowed by 0 to many transformers and MUST end with a serializer.

	trait PipelineComponent {
	def execute: Unit
	}
	trait Generator extends PipelineComponent {
	override def execute: Unit = print("Generator executing\n")
	}
	trait Transformer extends PipelineComponent {
	override def execute: Unit = print("Transformer executing\n")
	}
	trait Serializer extends PipelineComponent {
	override def execute: Unit = print("Serializer executing\n")
	}
	abstract class AbstractPipeline(pipelineComponents: List[PipelineComponent])
	case class EmptyPipeline extends AbstractPipeline(List()) {
	def add(generator: Generator): NonEmptyPipeline = new NonEmptyPipeline(List(generator))
	}
	case class NonEmptyPipeline(pipelineComponents: List[PipelineComponent]) extends AbstractPipeline(pipelineComponents) {
	def add(transformer: Transformer): NonEmptyPipeline = new NonEmptyPipeline(pipelineComponents :+ transformer)
	def add(serializer: Serializer): FinishedPipeline = new FinishedPipeline(pipelineComponents :+ serializer)
	}
	case class FinishedPipeline(pipelineComponents: List[PipelineComponent]) extends AbstractPipeline(pipelineComponents) {
	def execute(): Unit = pipelineComponents.foreach(_.execute)
	}
	/**
	object PipelineApp extends App {
	val generator = new Object with Generator
	val transformer1 = new Object with Transformer
	val transformer2 = new Object with Transformer
	val serializer = new Object with Serializer
	new EmptyPipeline().add(generator).add(transformer1).add(transformer2).add(serializer).execute
	}
	this will print:
	Generator executing
	Transformer executing
	Transformer executing
	Serializer executing
	**/

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