尝试将元素添加到双向链表ocaml的前面

(* 定义双向链表节点类型 *)
type 'a node = {
  mutable value: 'a;
  mutable prev: 'a node option;
  mutable next: 'a node option;
}

(* 定义双向链表类型 *)
type 'a dllist = {
  mutable head: 'a node option;
  mutable tail: 'a node option;
}

(* 在双向链表的前面添加元素 *)
let add_front (dllist: 'a dllist) (value: 'a) : unit =
  let new_node = { value = value; prev = None; next = dllist.head } in
  match dllist.head with
  | Some node -> node.prev <- Some new_node
  | None -> dllist.tail <- Some new_node;
  dllist.head <- Some new_node

(* 使用双向链表 *)
let my_dllist = { head = None; tail = None }
add_front my_dllist 1
add_front my_dllist 2
add_front my_dllist 3

(* 打印双向链表中的元素 *)
let rec print_dllist (node: 'a node option) : unit =
  match node with
  | Some n ->
    print_endline (string_of_int n.value);
    print_dllist n.next
  | None -> ()

print_dllist my_dllist.head