Game of life presents a network with cells that die, survive or born, depending on their neighbours. Each cell has a maximum of 8 neighbours.

Think of the network as a grid of squares, each square beeing a cell.

The way the cells live follows next rules:

• if a cell has less than 2 neighbours it dies
• if a cell has more than 3 neighbours it dies
• if a cell has 3 neighbours cell they generate 1

See Conway's Game of Life, and also the rules summary.

The implemenation was inspired by episode #13 from Ruby Tapas: Singleton Object (see http://devblog.avdi.org/2012/10/22/rubytapas-episode-13-singleton-objects/).

It starts with a random network, then applies the above rules.

As the network may end in cycling states (a network that does not change anymore or the same states come over and over), the implementation uses a history of last states to detect such cases and restart a new random network.

The output is a simple Text UI (terminal output) using the curses library.

As it only runs on Unix-like systems, I created a basic implementation of the curses library for jRuby using the Java/Swing GUI layer, so that it can run on all systems. The curses support is limited to make the game run and is not 'curses' compatible. The library is available as a gem on https://github.com/jeanlazarou/jruby_curses.

Run the application with:

ruby game_of_life.rb

With jRuby:

jruby --1.9 -Ilib game_of_life.rb

The implementation contains a class named NetBuilder that helps creating networks (see the test in tests.rb).

The builder expects a block like:

net = NetBuilder.build {
   head '  0 1 2 3 4 5 6 7 8 9'
   line '0 . . . . . . . . . .'
   line '1 . . . . . . . . . .'
   line '2 . . . . . . . . . .'
   line '3 . . # # . . . . . .'
   line '4 . . . . . . # . . .'
   line '5 . . . . . # . . . .'
   line '6 . . . . # . . . . .'
   line '7 . . . . . . . . . .'
   line '8 . . . . . . . . . .'
   line '9 . . . . . . . . . #'
}

Here is the usage message of the script:

Usage: game_of_life.rb [options]

Where options include:
    -w, --width w                    Width for the board width (defaults to 20)
    -h, --height h                   Height for the board height (defaults to 20)
    -r, --rate sec                   Next generation rate (in seconds, can be a float)
                                     (defaults to 2)
    -n, --no-cycle-detection         Disable cycle detection and network restart
                                     (defaults to 'enabled')
    -s, --shape file                 A file containing a network shape as startup network
                                     Using the network builder.
    -?, --help                       Show this message

A you can see the script can start with predefined shapes (see samples in the shapes directory) using the shape option.

See conwaylife site for other shapes (I created the ones available after their list).

• Unfortunately, both MRI 1.9.2 and 1.9.3 did not include 'curses' after installing them with rvm, I managed to make it work by copying the curses.so file from 1.9.1 to lib/ruby/1.9.1/i686-linux.
• As of Ruby 2.1 the curses library is not part of the standard library anymore, and is available as a Ruby gem (https://github.com/ruby/curses).
• The curses gem also works fine with the Rubinius implementation of Ruby.

- Jean Lazarou