nat.ml

(* nats = 0 :: List.map (fun x -> x+1) nats *)

type 'a lazylist =
  | Nil
  | Cons of 'a * (unit -> 'a lazylist)

let rec take n l =
  match (n,l) with
  | 0,_ -> []
  | _,Nil -> []
  | _,Cons (x,l) -> x :: take (n-1) (l ())

let rec map f = function
  | Nil -> Nil
  | Cons (x,l) -> Cons (f x, fun () -> map f (l ()))

let rec nats = Cons (1, fun () -> map succ nats)