[lec04] Scala 3 migration

src/main/scala/laziness/LazyList.scala

 package laziness
 
-sealed trait LazyList[+A]:
+enum LazyList[+A]:
+  case Empty
+  case Cons(h: () => A, t: () => LazyList[A])
+
   // uncomment to be able to use cons(h, t) and empty directly
   // imports methods from the companion object
   //import LazyList._
@@ -28,8 +31,6 @@ sealed trait LazyList[+A]:
     case Cons(x, xs) => f(x(), xs().foldRight(z)(f))
     case Empty => z
 
-case object Empty extends LazyList[Nothing]
-case class Cons[+A](h: () => A, t: () => LazyList[A]) extends LazyList[A]
 
 object LazyList: // companion object