Write a function in OCaml:

cond_dup : 'a list -> ('a -> bool) -> 'a

list that takes in a list and preciate and duplicates all elements which satisfy the condition expressed in the predicate. For example, cond_dup [3;4;5] (fun x -> x mod 2 = 1) = [3;3;4;5;5].

let rec cond_dup l f =

(* YOUR CODE HERE *)

raise (Failure "Not implemented")

assert (cond_dup [3;4;5] (fun x -> x mod 2 = 1) = [3;3;4;5;5])