Conway's Game of Life in Ruby

life.rb

board = """
........................o...........
......................o.o...........
............oo......oo............oo
...........o...o....oo............oo
oo........o.....o...oo..............
oo........o...o.oo....o.o...........
..........o.....o.......o...........
...........o...o....................
............oo......................
"""

ALIVE = 'o'
DEAD = '.'

class Life
  def initialize board
    @board = board.scan(%r/^[.o]+$/m).map &:chars
  end

  def run
    puts "\e[H\e[2J"
    @board.each { |row| puts row.join }
    sleep 1
    @board = tick
    run
  end

  def tick
    y = -1
    @board.map do |row|
      x = -1
      y += 1
      row.map do |_|
        x += 1
        next_state x, y
      end
    end
  end

  def next_state x, y
    cell = @board[y][x]
    live_count = live_neighbors x, y
    alive = cell == ALIVE
    if alive
      case live_count
        when 2..3 then ALIVE
        else DEAD
      end
    else
      case live_count
        when 3 then ALIVE
        else DEAD
      end
    end
  end

  def live_neighbors x, y
    neighbors(x, y).count { |cell| cell == ALIVE }
  end

  def neighbors x, y
    coords = [[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]]
    coords.map { |x,y| @board[y][x] rescue DEAD }
  end
end

life = Life.new board
life.run