It's Scala. They show the definitions of the "When" and "And" in the post: case class And(contract1: Contract, contract2: Contract) extends Contract case c

It's Scala. They show the definitions of the "When" and "And" in the post: case class And(contract1: Contract, contract2: Contract) extends Contract case class When(date: LocalDate, contract: Contract) extends Contract It's basically a DSL on top of Scala.