let exists_key key dict =
  match dict_find key dict with
    None -> false
  | _ -> true

(* Exercice 5 *)
(* 6. *)
let rec dict_adds couples dict =
  match couples with
    [] -> dict
  | (k, v)::tl -> dict_adds tl (dict_add k v dict)

(* Exercice 6 *)
(* 7. *)
let make_dict couples = dict_adds couples dict_empty

(* Exercice 7 *)
(* 8. *)
let find_word word dict =
  match dict_find word dict with
    None -> "?" ^ word ^ "?"
  | Some w -> w

(* Exercice 8 *)
(* 9. *)
let translate words dict = List.map (fun w -> find_word w dict) words