My implementation of Conway's Game of Life

life.rb

# Run this:
# ruby < <(curl -s https://gist.githubusercontent.com/ambethia/1429621/raw/life.rb)

require 'curses'

class Life
  extend Curses

  CELL_CHAR = "*"

  def initialize(x, y)
    @columns = x
    @rows = y
    @cells = {}
  end

  def evolve
    @cells = {}.tap do |generation|
      @columns.times do |x|
        @rows.times do |y|
          generation[[x,y]] = true if will_live? x, y
        end
      end
    end
  end

  def will_live? *position
    neighbors = sum_of_neighbors(*position)
    if alive?(*position)
      neighbors == 2 || neighbors == 3
    else
      neighbors == 3
    end
  end

  def alive? *position
    @cells[position]
  end

  def seed! *coordinates
    coordinates.each do |position|
      @cells[position] = true
    end
  end

  private

  def sum_of_neighbors x, y
    neighbors = 0
    (-1..1).each do |u|
      (-1..1).each do |v|
        neighbors += 1 if alive?(x+u, y+v) && [u,v] != [0,0]
      end
    end
    neighbors
  end

  def self.evolve
    begin
      noecho
      init_screen
      curs_set 0
      stdscr

      life = new(cols, lines)

      # simple shape translated to the center
      simple_shape = [[0, 0], [0, -1], [1, 0], [1, 1], [-1, 0]]
      simple_shape.map! { |coords| [coords[0]+(cols/2), coords[1]+(lines/2)] }

      life.seed! *simple_shape

      loop do
        clear
        cols.times do |x|
          lines.times do |y|
            if life.alive? x, y
              setpos y, x
              addstr CELL_CHAR
            end
          end
        end
        refresh
        sleep(0.1)
        life.evolve
      end
    ensure
      close_screen
    end
  end
end

if ENV['TM_RUBY']
  require 'test/unit'

  class LifeTest < Test::Unit::TestCase

    def setup
      @life = Life.new(2,2)
    end

    def test_a_living_cell_should_not_survive_with_no_neighbors
      @life.seed! [0,0]
      assert !@life.will_live?(0,0)
    end

    def test_a_living_cell_should_not_survive_with_one_neighbor
      @life.seed! [0,0], [0,1]
      assert !@life.will_live?(0,0)
    end

    def test_a_living_cell_should_survive_with_two_neighbors
      @life.seed! [0,0], [0,1], [1,1]
      assert @life.will_live?(0,0)
    end

    def test_a_living_cell_should_survive_with_three_neighbors
      @life.seed! [0,0], [0,1], [1,1], [1,0]
      assert @life.will_live?(0,0)
    end

    def test_a_living_cell_should_not_survive_with_four_neighbors
      @life.seed! [0,0], [0,1], [1,1], [1,0], [1,-1]
      assert !@life.will_live?(0,0)
    end

    def test_a_dead_cell_should_live_with_three_neighbors
      @life.seed! [0,1], [1,1], [1,0]
      assert @life.will_live?(0,0)
    end

    def test_a_dead_cell_should_not_live_with_two_neighbors
      @life.seed! [0,1], [1,1]
      assert !@life.will_live?(0,0)
    end

    def test_a_dead_cell_should_not_live_with_four_neighbors
      @life.seed! [0,1], [1,1], [1,0], [1,-1]
      assert !@life.will_live?(0,0)
    end
  end
else
  Life.evolve
end