scala3-DTListExample.scala

scala> val list = 1 +: "two" +: DTNil
val list: DTNonEmptyList[1, Int, ? <: DTNonEmptyList[0, String, DTNil.type]] =
  DTNonEmptyList(1,DTNonEmptyList(two,DTNil))

scala> list.size
     | list.head
     | list.tail
val res0: Int = 2
val res1: Int = 1
val res2: list.T = DTNonEmptyList(two,DTNil)

scala> list.tail.size
     | list.tail.head
     | list.tail.tail
     | list.tail.tail.size
val res3: Int = 1
val res4: String = two
val res5: DTNil.type = DTNil
val res6: Int = 0

scala> list.tail.tail.head                // list.tail.tail is res5 == DTNil
     | list.tail.tail.tail
1 |list.tail.tail.head
  |^^^^^^^^^^^^^^^^^^^
  |value head is not a member of object DTNil
2 |list.tail.tail.tail
  |^^^^^^^^^^^^^^^^^^^
  |value tail is not a member of object DTNil

scala> DTNil.head
1 |DTNil.head
  |^^^^^^^^^^
  |value head is not a member of object DTNil

scala> DTNil.tail
1 |DTNil.tail
  |^^^^^^^^^^
  |value tail is not a member of object DTNil - did you mean DTNil.wait?

scala> DTNil.size
val res7: Int = 0