Snake

• Why Snake?
• It's Snake!
• Easy, but requires:
• Arrays
• Loops
• UI
• Input

Elm

• Haskell in a browser
• Compiles to JavaScript
• Pure functional code...
• ...embedded in the real world
• Fast responsive UIs
• "Functional Reactive Programming"
• Helpful compiler, time-machine debugger

No guesswork

No guesswork

Haskell

Or, "The Price You Pay"

type alias Snake =
    {
          dir  : Direction
        , body : List Point
    }

Haskell

Or, "The Price You Pay"

grow_snake : List Point -> List Point
grow_snake body = body ++ repeat 5 ( Point 0 0 )

Haskell

eat_apple : Model -> Model
eat_apple model =
    case List.head model.snake.body of
        Nothing -> model  -- Snake is empty - won't happen
        Just h  ->
            if h == model.apple
               then
                   let ( apple_pos, seed ) =
                       new_apple_position model.random_seed world_size
                   in
                   {
                       model |
                           snake       <- grow_snake model.snake,
                           apple       <- apple_pos,
                           random_seed <- seed
                   }
               else model

Haskell

view : Signal.Address Action -> Model -> Html

HTML

Make a DOM in code

view address model =
    div
        [ class "main_div" ]
        [ text "Hello" ]

<div class="main_div">Hello<div>

HTML

Including clever code

game_trs : Model -> List Html
game_trs model =
    List.map
        ( game_tr model )
        [1..model.size.height]

Signals

type Action = Tick Time | KeyPress KeyCode

update : Action -> Model -> ( Model, Effects Action )
update action model =
  case action of
    Tick now ->
      ( frame model now, Effects.tick Tick )

    KeyPress key ->
      ( process_key model key, Effects.none )

Signals

view : Signal.Address Action -> Model -> Html
view address model =
    div
        [ onKeyDown address KeyPress ]
        [ game_table model ]

More info