let main () : unit Deferred.t =
let card = {
suit = Spades;
rank = Ace;
} in
(* card -> string *)
let s = Marshal.to_string card [] in
print_endline s;
(* card -> string -> card *)
let card' = Marshal.from_string s 0 in
print_endline (Sexp.to_string (sexp_of_card card'));
return ()