functional game of life — from http://beyondscheme.com/2016/distributed-game-of-life-in-elixir#comment-2721697256

game_of_life.ex

def calc_next_grid(grid) do
  Enum.reduce(alive_plus_neighbors(grid), MapSet.new, fn({x, y}, grid2) ->
    is_alive = MapSet.member?(grid, {x, y})
    num_neighbors = count_neighbors(grid, {x, y})

    if should_live?(is_alive, num_neighbors) do
      MapSet.put(grid2, {x, y})
    else
      grid2
    end
  end)
end

defp alive_plus_neighbors(grid) do
  offsets = [{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 0}, {0, 1}, {1, -1}, {1, 0}, {1, 1}]

  Enum.reduce(grid, MapSet.new, fn({x, y}, grid2) ->
    Enum.reduce(offsets, grid2, fn({x_off, y_off}, grid3) ->
      MapSet.put(grid3, {x + x_off, y + y_off})
    end)
  end)
end

defp should_live?(is_alive, num_neighbors) do
  (num_neighbors == 2 && is_alive) || (num_neighbors == 3)
end

defp count_neighbors(grid, {x, y}) do
  offsets = [{-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1}]

  Enum.reduce(offsets, 0, fn({x_off, y_off}, acc) ->
    acc + if MapSet.member?(grid, {x + x_off, y + y_off}), do: 1, else: 0
  end)
end