Game of life in Elixir (take 1)

gol.exs

# Updated for 1.2.5

defmodule Life do
  def run(board) when is_binary(board) do
    board |> parse_board |> run
  end

  def run(board) do
    IO.write("\e[H\e[2J")
    Life.print_board board
    :timer.sleep 250
    unless board == next_board(board) do
      next_board(board) |> run
    end
  end

  def parse_board(board) do
    rows = List.flatten(Regex.scan(~r/^[.o]+$/m, board))
    Enum.map rows, &( String.graphemes(&1) )
  end

  def print_board(board) do
    Enum.each board, fn row ->
      IO.puts(Enum.join(row))
    end
  end

  def next_board(board) do
    board |> Enum.with_index |> Enum.map(fn {row, y} ->
      row |> Enum.with_index |> Enum.map(fn {_, x} ->
        next_state(board, x, y)
      end)
    end)
  end

  def next_state(board, x, y) do
    cell = cell_at(board, x, y)
    live_count = live_neighbors(board, x, y)
    next_state(cell, live_count)
  end

  def next_state("o", live_count) when live_count in 2..3, do: "o"

  def next_state("o", _), do: "."

  def next_state(".", live_count) when live_count === 3, do: "o"

  def next_state(".", _), do: "."

  def cell_at(_, x, y) when (x < 0 or y < 0), do:  "."

  def cell_at(board, x, y) do
    case Enum.at(board, y) do
      nil -> "."
      row -> Enum.at(row, x, ".")
    end
  end

  def live_neighbors(board, x, y) do
    Enum.count(neighbors(board, x, y), &( &1 === "o" ))
  end

  def neighbors(board, x, y) do
    coords = neighbor_coords(x, y)
    Enum.map coords, fn [x,y] -> cell_at(board, x,y) end
  end

  def neighbor_coords(x, y) do
    [[x-1, y-1], [x, y-1], [x+1, y-1],
     [x-1, y],             [x+1, y],
     [x-1, y+1], [x, y+1], [x+1, y+1]]
  end
end

board = """
.o......
..o.....
ooo.....
........
........
........
........
........
"""
Life.run(board)