Iterate function using unfold in OCaml

iterate.ml

(* The unfold function takes in 
a predicate (p) and 
a function (g) which takes an input (b). *)
let rec unfold p g b =
  if p b then [] else
    (match g b with (a, bprime) ->
       a :: unfold p g bprime)
;;

(* The iterate function takes in a function (f), 
and uses the unfold function with p and g passed. 
b is to be passed. *)

(* This function is equivalent to the Haskell iterate function. *)
let iterate f = unfold (fun x -> false) (fun x -> (x, (f x)));;

(* Giving unfold a predicate of x > 20 returns a list. *)
let iterate_p f = unfold (fun x -> (x > 20)) (fun x -> (x, (f x)));;

See the blog post.