MLStyle - are recursive ADTs possible

New to Julia
2

OK, I’m not sure why, but the solution is less, not more …

@data XX begin
    Nil
    Cons(hd, tl::XX)
end
function sum_list(lst)
    @match lst begin
        Nil => 0
        Cons(h, t) => h + sum_list(t)
    end
end
function printer(lst)
    @match lst begin
      Nil => println("[]")
      Cons(h, t) => begin
        print("$(h) . ")
        printer(t)
      end
    end
end
function make_test_1()
  return Cons(1, Cons(2, Cons(3, Nil)))
end
function make_test_2()
  return Cons("A", Cons("B", Cons("C", Nil)))
end
i = make_test_1()
s = make_test_2()
println("sum_list(i) = $(sum_list(i))")
#sum_list(i) = 6
printer(i)
#1 . 2 . 3 . []
printer(s)
#A . B . C . []