Hangman—The OTP iteration

It's time to take our Hangman game up a notch.

This assignment takes Hangman and turns it into a supervised set of OTP servers.

We'll be taking two modules, Game and Dictionary, and making servers of each.

These modules will be part of a supervision tree. The constraints of this supervision are simple:

If the Game exits normally, do nothing. If it crashes, restart it (and just it).

If the Dictionary exits for any reason, kill any game, and restart both the Dictionary and the Game.

(Hint: you'll need two supervisors.)

I need you to add a single paragraph comment to the top of lib/hangman.ex explaining why you have chosen the supervision structure that you use.

Details for 5345 and 7345 Students

Convert the current dictionary module to a GenServer inline (that is, the dictionary code and the GenServer api and callbacks will all be in the dictionary module).

You'll register the dictionary server under the name :dictionary.

Convert the game to a GenServer using the outside style (so you'll write a separate GameServer module that calls functions in the existing game.ex file. Give the GameServer a name.

You'll need to add top-level supervision to lib/hangman.ex, and you'll need to add a second subsupervisor in lib/hangman/....

Update your mix.exs to start the servers automatically (by referencing the top-level supervisor).

You'll play the game using

status = Hangman.GameServer.make_move(guess)

Where status is one of :won, :lost, :good_guess, or :bad_guess.

The other API calls are

length       = Hangman.GameServer.word_length
letters_used = Hangman.GameServer.letters_used_so_far
turns_left   = Hangman.GameServer.turns_left
word         = Hangman.GameServer.word_as_string(reveal = true|false)

These behave just like the API in assignment 2.

A Starting Point

To make my life easier, this project already has a version of the assignment 2 hangman game. You job is to turn game.ex and dictionary.ex into GenServers, and to add the appropriate supervision tree and support modules.

Tests

You can use mix test to test your code. Right now, all but one of the tests fail, because they are written for the OTP version of the app. As you start to add functionality, more and more will pass.

Grading

A total of 100 marks are available:

50 for a working program (one that passes the tests included here and any others I may run while grading)

10 for a good description of the supervision strategy you use, justifying why it meets the requirements above

20 for elegant code

10 for good-looking code

10 for the rest :)

Copying code from other students will be penalized.

8k Students

You will do the same as above, but with one small twist.

You will implement the game servers so that you can run an arbitrary number of them in parallel. To do this, the game server supervisor will need to use the simple_one_for_one strategy, and create worker processes when requested.

The game supervisor will have a function new_game that starts a new GameServer child process and returns its pid. That child is a GenServer.

You play the game using the GameServer interface. In your case, you'll need to keep the original first parameter to each call, as you'll need to pass the pid in.

The game process should terminate normally when the game is either won or lost. It won't need to be restarted.

So, a sample iex session might be:

iex> g1 = Hangman.GameSupervisor.new_game
iex> Hangman.GameServer.make_move(g1, "e")
iex> Hangman.GameServer.word_as_string(g1)
"_ _ _ e _ e"
iex> g2 = Hangman.GameSupervisor.new_game
iex> Hangman.GameServer.make_move(g1, "e")
iex> Hangman.GameServer.word_as_string(g2)
"e _ _ _ _ _"
iex> Hangman.GameServer.word_as_string(g1)
"_ _ _ e _ e"

You'll need to update the tests accordingly.