blob: 88e1ff9fdbfed9459137fe9ac35ff9ad47b2b6d3 (
plain) (
tree)
|
|
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)
}
Console.println(
eval(If(IsZero(Lit(1)), Lit(41), Succ(Lit(41)))))
}
|