open Core.Std


let () =
  let module Users = Set.Make(String) in
  let ic = Unix.open_process_in "ps aux" in
  let lines = In_channel.input_lines ic in
  let names_list = List.map lines ~f:(fun line ->
				      let split_list = String.split line ~on:' ' in
				      List.hd_exn split_list) in
  let users = Users.of_list names_list in
  let peeps = List.fold_right (Users.to_list users) ~f:(fun new_name old_string ->
							new_name ^ ":" ^ old_string)
			      ~init:"" in
  print_endline @@ "User Accounts on this machine: \n" ^ peeps;
  ignore @@ Unix.close_process_in ic;