Make the Game a Service

Our Game module is currently just library code. It runs in the process that calls it, and that calling process must keep the game's state, passing it back with each call.

We're going to change this, making the Game into a server.

Rather than having new_game return a struct containing the state, it will now return a pid. That pid will be passed to make_move and tally in the same way the state was previously.

From the client's perspective, there is only one change to the API. Whereas make_move used to return { game, tally }, it will now return just the tally: the state is held internally in the process, and the pid never changes.

By the end of this process, you'll be able to do:

iex> game = Hangman.new_game
iex> tally = Hangman.make_move(game, "a")
iex> tally = Hangman.make_move(game, "s")

The tests and the human player code have been updated to use this slightly different API.

Remember to split your code into an implementation, server, and API. (The API part is lib/hangman.ex. You just need to change defdelegate into GenServer calls).

Also, I'm adding a new API function, new_word/1, which lets us force a particular word to be used.

It'll end up looking something like this:

defmodule Hangman do

  def new_game() do
    new_game(Dictionary.random_word)
  end

  def new_game(word) do
    { :ok, pid } = GenServer.start_link(Hangman.Server, word)
    pid
  end

  def make_move(pid, guess) do
    GenServer.call(pid, { :make_move, guess })
  end

  def tally(pid) do
    GenServer.call(pid, { :tally })
  end

end