Look on my works, ye Mighty, and despair!

In Part 1 we rendered an empty grid, but for a more interesting game we need to initialise the board with a random selection of dead & alive cells (known as the seed).

The Random package is a bit different in Elm; while it is possible to generate values one at a time, it’s more common to use a generator to produce a command:

init : (Model, Cmd Msg)
init =
    ([], Random.generate NewBoard (seedBoard))

seedBoard : Random.Generator Board
seedBoard =
    Random.list 5 seedRow

seedRow : Random.Generator Row
seedRow =
    Random.list 5 seedCell

seedCell : Random.Generator Cell
seedCell =
    Random.map (\b -> if b then Dead else Alive) Random.bool

We now initialise our grid as an empty list, and await the result of a command generating 5 rows of 5 cells, randomly Dead or Alive (coin flip).

Our update function needs to handle the message:

type Msg =
    NewBoard Board |
    Tick

update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
    case msg of
        Tick ->
            (model, Cmd.none)
        NewBoard board ->
            (board, Cmd.none)

If you run the code, you should see a 5×5 grid with approx half the squares alive (filled in black) and half the squares dead (filled white).

In the next part we will actually begin to play the game.