Snakes and Ladder - Elixir Game server

snakes_and_ladders.ex

defmodule GameServer do
  use GenServer

  def start do
    initial_state = {:players, [], :positions, Map.new, :snakes_and_ladders, [
      {:ladder, 5, 15}, {:ladder, 10, 22}, {:ladder, 25, 45}, {:snake, 35, 15}, {:snake, 65, 55}]}
    GenServer.start_link(__MODULE__, initial_state, name: __MODULE__)
  end

  def join(player), do: GenServer.cast(__MODULE__, {:join, player})

  def play, do: GenServer.call(__MODULE__, {:play})
  
  def display, do: GenServer.call(__MODULE__, {:display})

  def shutdown, do: GenServer.cast(__MODULE__, {:bye})
  
  def handle_cast({:join, player}, state) do
    {:players, players, :positions, positions, :snakes_and_ladders, snakes_and_ladders} = state
    {:noreply, {:players, [player | players], :positions, Map.put(positions, player, 1), :snakes_and_ladders, snakes_and_ladders}}
  end

  def handle_call({:play}, _from, state) do
    {:players, players, :positions, positions, :snakes_and_ladders, snakes_and_ladders} = state
    [current_player | others] = players
    dice_value = :random.uniform(6)
    new_position = next_position(positions[current_player] + dice_value, snakes_and_ladders)
    if new_position < 100 do
      new_positions = Map.put(positions, current_player, new_position)
      new_players = others ++ [current_player]
      {:reply, {current_player, new_position}, {:players, new_players, :positions, new_positions, :snakes_and_ladders, snakes_and_ladders}}
    else
      {:reply, {current_player, :winner}, state}
    end
  end

  def handle_call({:display}, _from, state) do
    {:players, _, :positions, positions, :snakes_and_ladders, _} = state
    {:reply, positions, state}
  end

  def handle_cast({:bye}, state), do: {:stop, :shutdown, state}

  defp next_position(pos, snakes_and_ladders) do
    handle_elem(Enum.filter(snakes_and_ladders, fn({_type, from, _to}) -> from == pos end), pos)
  end

  defp handle_elem([], pos), do: pos
  defp handle_elem([{:snake, _, to}], _), do: to
  defp handle_elem([{:ladder, _, to}], _), do: to
end

For playing game from iex:

c("snakes_and_ladders.ex")
GameServer.start
GameServer.join("a")
GameServer.join("b")
GameServer.join("c")
GameServer.play
GameServer.play
GameServer.play
GameServer.display
for i <- 1..50, do: GameServer.play
GameServer.display

@sathish316 Any particular reason you are using a tuple for the initial state and not a map?

%{players: [], positions: %{}, snakes_and_ladders: [ {:ladder, 5, 15}, {:ladder, 10, 22}, {:ladder, 25, 45}, {:snake, 35, 15}, {:snake, 65, 55}]}

@avinasha: No specific reason. I was following the convention of using {:ok , foo} tuples in elixir. Destructuring code could become a lot simpler if i use map.