let () =
  (* Create an empty map *)
  let m = Hashtbl.create 10 in
  (* Set key/value pairs *)
  Hashtbl.add m "k1" 7;
  Hashtbl.add m "k2" 13;

  (* Printing a map will show all of its key/value pairs *)
  let print_map m =
    Hashtbl.iter (fun k v -> Printf.printf "%s: %d\n" k v) m
  in
  Printf.printf "map:\n";
  print_map m;

  (* Get a value for a key *)
  let v1 = Hashtbl.find_opt m "k1" in
  Printf.printf "v1: %s\n" (match v1 with Some v -> string_of_int v | None -> "None");

  (* If the key doesn't exist, None is returned *)
  let v3 = Hashtbl.find_opt m "k3" in
  Printf.printf "v3: %s\n" (match v3 with Some v -> string_of_int v | None -> "None");

  (* The length of a map (number of key/value pairs) *)
  Printf.printf "len: %d\n" (Hashtbl.length m);

  (* Remove a key/value pair from a map *)
  Hashtbl.remove m "k2";
  Printf.printf "map (after deletion):\n";
  print_map m;

  (* To clear all key/value pairs from a map *)
  Hashtbl.reset m;
  Printf.printf "map (after clear):\n";
  print_map m;

  (* Check if a key is present in the map *)
  Hashtbl.add m "k2" 13;
  let prs = Hashtbl.find_opt m "k2" in
  Printf.printf "prs: %b\n" (match prs with Some _ -> true | None -> false);

  (* Declare and initialize a new map *)
  let n = Hashtbl.create 10 in
  Hashtbl.add n "foo" 1;
  Hashtbl.add n "bar" 2;
  Printf.printf "map (new map):\n";
  print_map n;

  (* Check equality of two maps *)
  let n2 = Hashtbl.create 10 in
  Hashtbl.add n2 "foo" 1;
  Hashtbl.add n2 "bar" 2;
  if Hashtbl.equal (=) n n2 then
    Printf.printf "n == n2\n"
  else
    Printf.printf "n != n2\n"