Ocaml: Lazy Lists

Question

How can I make a lazy list representing a sequence of doubling numbers? Example:

1 2 4 8 16 32

Answer 1

Using streams:

let f x = Stream.from (fun n -> Some (x * int_of_float (2.0 ** float_of_int n)))

or

let f x =
  let next = ref x in
    Stream.from (fun _ -> let y = !next in next := 2 * y ; Some y)

Using a custom lazy_list type:

type 'a lazy_list =
  | Nil
  | Cons of 'a * 'a lazy_list lazy_t
let rec f x = lazy (Cons (x, f (2*x)))

Answer 2

The great blog enfranchised mind has a great article on this topic:

http://enfranchisedmind.com/blog/posts/ocaml-lazy-lists-an-introduction/

You can also check out http://batteries.forge.ocamlcore.org/doc.preview%3Abatteries-beta1/html/api/Lazy%5Flist.html

which is the standard library for dealing with this.

This question is also very similar to this question:

What OCaml libraries are there for lazy list handling?