Conway's Game of Life in Ruby, aiming to be short but readable

game_of_life.rb

class String
  def reverse_color; "\033[7m#{self}\033[27m" end
end

class Cell
  attr_accessor :alive

  def initialize(neighbors)
    @neighbors = neighbors
    @alive = @fate = [false, true].sample
  end

  def breathe
    living = @neighbors.call.count(&:alive)
    @fate = false if living < 2 || living > 3
    @fate = true if living == 3
  end

  def existential
    @alive = @fate
  end
end

class World
  def initialize(size, speed, output = PutsGrid)
    @size, @speed, @output = size, speed, output
    generate
  end

  def live
    loop do
      tick
      sleep @speed
    end
  end

  def tick
    @output.out @grid.each { |y| y.each(&:breathe) }
  end

  def generate
    @grid = @size.times.map do |y|
      @size.times.map do |x|
        Cell.new(lambda do
          [-1, 1, 0].flat_map do |yp|
            [-1, 1, 0].map do |xp|
              @grid[(y + yp) % @size][(x + xp) % @size]
            end
          end[0...-1]
        end)
      end
    end
  end
end

class PutsGrid
  def self.out(grid)
    puts "\e[H\e[2J" # clear screen

    grid.each do |y|
      puts y.map{ |cell| cell.existential ? "  ".reverse_color : "  " }.join("")
    end
  end
end

size, speed = (ARGV[0] || 30).to_i, (ARGV[1] || 0.1).to_f
World.new(size, speed).live