let rec x = x;;
let rec f x = f x;;
f 0;;
let rec f x = if f = 0 then 0 else f x;;
let rec f x = if x = 0 then 0 else f x;;
f 0;;
f 2;;
List.hd (f 0 :: f 1 :: []);;
let rec from n = n :: (from (n + 1));;
from 5;;
let 'a llist = Nil | Cons of ('a * (unit -> 'a llist));;
type 'a llist = Nil | Cons of ('a * (unit -> 'a llist));;
let hd = function Nil -> failwith "nil" | Cons (x, _) -> x;;
let tl = function Nil -> failwith "nil" | Cons (_, t) -> t;;
let tl = function Nil -> failwith "nil" | Cons (_, t) -> t ();;
let rec to_list n xs = if n < 1 then [] else match xs with
  Nil -> []
| Cons (x, xs) -> x :: (to_list (n - 1) xs);;
let rec to_list n xs = if n < 1 then [] else match xs with
  Nil -> []
| Cons (x, xs) -> x :: (to_list (n - 1) (xs ()));;
to_list 5 (from 0);;
let rec from n = Cons (n, fun () -> from (n + 1));;
to_list 5 (from 0);;
to_list 500 (from 8);;
type 'a cell = Nil | Cons of 'a * 'a llist
 and 'a llist = unit -> 'a cell;;
let tl xs = match xs () with Nil -> failwith "nil" | Cons (_, xs) -> xs;;
let rec zipwith f xs ys = fun () -> match (xs (), ys ()) with
  (Cons (x, xs), Cons (y, ys)) -> Cons (f x y, zipwith f xs ys)
| _ -> Nil;;
let rec from n = fun () -> Cons (n, from (n + 1));;
zipwith (+) (from 0) (from 1);;
(zipwith (+) (from 0) (from 1)) ();;
tl (zipwith (+) (from 0) (from 1)) ;;
(tl (zipwith (+) (from 0) (from 1))) () ;;
let rec fibs = fun () -> Cons (0, fun () -> Cons (1, zipwith (+) fibs (tl fibs)));;
fibs ();;
tl fibs;;
(tl fibs) ();;
((tl (tl fibs)) ();;
((tl (tl fibs))) ();;
((tl (tl (tl fibs)))) ();;
(tl (tl (tl (tl fibs)))) ();;
(tl (tl (tl (tl (tl fibs))))) ();;
let rec to_list n xs = if n < 1 then [] else match xs () with Nil -> [] | Cons (x, t) -> x :: to_list (n-1) t;;
to_list 5 fibs;;
to_list 15 fibs;;
to_list 20 fibs;;
to_list 30 fibs;;
to_list 32 fibs;;
let e = lazy (print_string "bla");;
Lazy.force e;;
primes;;
to_list 1000 primes;;
List.rev (to_list 1000 primes);;
List.nth 1000 (to_list 1000 primes);;
List.nth (to_list 1000 primes) 1000;;
List.nth (to_list 1000 primes) 999;;