SubBuilder.scala

trait AbstractCreatureBuilder {
  
  var bodyParts = List.empty[String]

  def creatureType: String
  
  def addBodyPart(name: String): AbstractCreatureBuilder
  
  override def toString = {
    "A " + creatureType + " with " + bodyParts.mkString(", ")
  }
}

class HumanCreatureBuilder extends AbstractCreatureBuilder {
  
  override def creatureType = "human"
    
  override def addBodyPart(name: String): HumanCreatureBuilder = {
    bodyParts ::= "human " + name
    this
  }
  
  def addSelfAwareness: HumanCreatureBuilder = {
    addBodyPart("self awareness")
  }
  
}

class AnimalCreatureBuilder extends AbstractCreatureBuilder {
  
  override def creatureType = "animal"

  override def addBodyPart(name: String): AnimalCreatureBuilder = {
    bodyParts ::= "animal " + name
    this
  }

  def addClaws: AnimalCreatureBuilder = {
    addBodyPart("claws")
  }
  
}

object SubBuilder {
  def main(args : Array[String]) : Unit = {
    println((new HumanCreatureBuilder).addBodyPart("eyes").addBodyPart("nose").addBodyPart("mouth").addSelfAwareness)
    println((new AnimalCreatureBuilder).addBodyPart("eyes").addBodyPart("beak").addBodyPart("wings").addClaws)
  }
}