ther is a languare that supports what Ikalman does, it is scala. Here an
excerpt from the repl.
scala> val a = Left(123)
a: scala.util.Left[Int,Nothing] = Left(123)
scala> val b = Right("hallo")
b: scala.util.Right[Nothing,String] = Right(hallo)
scala> var c : Either[Int,String] = null
c: Either[Int,String] = null
scala> c = b
c: Either[Int,String] = Right(hallo)
scala> c = a
c: Either[Int,String] = Left(123)
scala>
Scala has the `Nothing` type and type covariance. Type covariance can only work
on reference types, and nim simply does not work that way.
