enum Option<T> {
    None,
    Some T,
}

let from = fn x -> x << @(from (x+1))

let nats = from 0

let when = fn pred (x << xs) ->
  if !#pred x then
    Option::Some(from 0) << @(when pred !@xs)
  else 
    Option::None << @(when pred !@xs)

let switch = fn (x << xs) (e << es) -> 
  match e {
    Option::None => x << @(switch !@xs !@es),
    Option::Some (a << as) => a << @(switch !@as !@es)
  }

let loop_10 = switch nats (when #(fn x -> x % 10 == 0) nats)

let head = fn (hd << tl) -> hd

let print_loop_10 = print_int (head loop_10) << @print_loop_10

let chicken = 
  (match egg {
    x << egg => if x == 0 then true else false,
  }) << @chicken
and egg = 
  (match chicken {
      x << chicken => if x then 1 else 0,
    }) << @egg
with 0

let print_egg = print_int (head egg) << @print_egg