gistfile1.txt

type t = 
  | Pair of t * t
  | Number of int
  | Function of string (* or what? *)
  
let rec empty = Pair (empty, empty) (* make a looped value *)

let is_empty t = match t with
  | Pair (t1, t2) -> t == t1 && t == t2  (* using pointer equality *)
  | _ -> false