Why is Nil required at the end of a list built using the cons operator

Question

I\'m learning Scala at the moment (Programming Scala, 2nd Edition, Odersky).

When building a list using the cons operator we have to write:

val l = 1         


        

Answer 1

Actually, you can make it work yourself:

scala> implicit class Listable[A](val value: A) {
     |   def ::[B >: A](other: B): List[B] = other :: value :: Nil
     | }
defined class Listable

scala> val xs = 1 :: 2 :: 3 :: 4
xs: List[Int] = List(1, 2, 3, 4)

scala> val ys = "A" :: "B" :: "C"
ys: List[String] = List(A, B, C)

scala>