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

app, if, int, iszero, iszero, lit, lit, succ, succ, t, term, term, test

The Scala gadts.scala source code

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]

object Test extends App {
  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)))))
}