Scala example source code file (gadts.scala)

This example Scala source code file (gadts.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

application, if, int, iszero, iszero, lit, lit, succ, succ, t, term, term

The Scala gadts.scala source code

package examples

object gadts extends Application {

  abstract class Term[T]
  case class Lit(x: Int) extends Term[Int]
  case class Succ(t: Term[Int]) extends Term[Int]
  case class IsZero(t: Term[Int]) extends Term[Boolean]
  case class If[T](c: Term[Boolean],
                   t1: Term[T],
                   t2: Term[T]) extends Term[T]

  def eval[T](t: Term[T]): T = t match {
    case Lit(n)        => n
    case Succ(u)       => eval(u) + 1
    case IsZero(u)     => eval(u) == 0
    case If(c, u1, u2) => eval(if (eval(c)) u1 else u2)
  }
  println(
    eval(If(IsZero(Lit(1)), Lit(41), Succ(Lit(41)))))
}