Ocaml: Lazy Lists

Question

How can I make a lazy list representing a sequence of doubling numbers? Example: ``` 1 2 4 8 16 32 ```

Accepted Answer

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)))
```

Solution