decl test_variants : Unit -> Unit
def test_variants = {
  var variant1 = | 'a' | 2 | "hello"
  var | val | err = f: x

  ; val -?> "something" // open variant as value in expr

  ; val -!> "nothing" // open variant as None in expr

  match variant1 with
    | 'a' -> "something"
    | 2 -> "nothing"
    | "hello" -> "nothing"
    | 11 -> "nothing"
}