type user = { id : int; name : string }

let conn_str = "sqlite3:./data.db"

module type DB = Caqti_lwt.CONNECTION

let get_all_users_q = Caqti_request.Infix()

let pool = 
  let uri = Uri.of_string conn_str in
  match Caqti_lwt.connect_pool ~max_size:10 uri with
  | Ok pool -> pool
  | Error err -> failwith (Caqti_error.show err)

let get_users = 
  let get_users' (module C: Caqti_lwt.CONNECTION) =
    C.fold get_all_users_q

  let find_users =
   let open Lwt_result.Infix in
    fun (module Db : Caqti_lwt.CONNECTION) ->
      Db.collect_list find_users_request () >>| List.map make_user

  let () =
    let uri = Uri.of_string conn_str in
    match Lwt_main.run (Caqti_lwt.connect uri >>= find_users) with
    | Ok users ->
      List.iter (fun user -> Printf.printf "%d: %s\n" user.id user.name) users
    | Error err ->
      Format.eprintf "%a@." Caqti_error.pp err