File: gadts.scala

package info (click to toggle)
scala 2.7.7.dfsg-4
  • links: PTS, VCS
  • area: main
  • in suites: squeeze
  • size: 75,804 kB
  • ctags: 1,852
  • sloc: java: 7,762; xml: 6,608; sh: 1,723; cs: 158; makefile: 9; ansic: 6
file content (17 lines) | stat: -rw-r--r-- 582 bytes parent folder | download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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 Application {
  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)))))
}