1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
abstract class M { def f: List[M] = Nil } object M1 extends M object M2 extends M { override def f = List(M1) } object M3 extends M { override def f = List(M1) override def f = List(M1) } object M4 extends M { override def f = List( M3, M2 ) }