type 'a t = UTF8.Buffer.buffer -> unit
type 'a obs = UTF8.Buffer.buffer -> unit

let str s buffer =
  UTF8.Buffer.add_string buffer s

let num n buffer =
  if DataType.Num.is_integer n then
    DataType.Num.to_int n
      |> string_of_int
      |> UTF8.from_utf8string
      |> UTF8.Buffer.add_string buffer
  else
    let f = DataType.Num.to_float n
    and to_b = UTF8.Format.formatter_of_buffer buffer in
    ignore @@ UTF8.Format.fprintf to_b "%.2f" f;
    Format.pp_print_flush to_b ()

let date n buffer =
  let y, m, d = DataType.Date.date_from_julian_day n in
  UTF8.Printf.bprintf buffer "%d/%d/%d" y m d

let bool b buffer =
  UTF8.Printf.bprintf buffer "%B" b

let observe elem buffer = elem buffer