open SExpr
let get_url se_lst =
  match se_lst with
  | Expr [Atom ("url"); Atom (url)] -> Some (url)
  | _ -> None
let search_url se_lst =
  let rec aux se_lst =
    match se_lst with
    | [] -> None
    | hd::tl ->
        match get_url hd with
        | Some v -> Some v
        | None -> aux tl
  in
  aux se_lst
let match_se se =
  match se with
  | Expr (Atom ("gfx") :: se_lst) ->
      Printf.printf "one gfx found,\n";
      begin
        match search_url se_lst with
        | Some found ->
            Printf.printf " found-url: %s\n" found;
        | None ->
            Printf.printf " url-not-found\n";
      end
  | _ ->
      Printf.printf ".\n";
;;
let () =
  let filename = "./file.se" in
  let se_lst = SExpr.parse_file filename in
  let rec aux se_lst =
  match se_lst with
  | se::se_tl -> match_se se; aux se_tl
  | [] -> ()
  in
  aux se_lst