# games-of-life

is a Mathematical solution to any Game of Life variation

Demo | Installation | Idea | Example | See also | License

## Demo

I created this hexagonal *Game of Life* demo to show that this package generalize
the *Game of Life* in any of its variations.
Click the image below to try it!

## Installation

With npm do

```
npm install games-of-life
```

You could also use a CDN adding this to your HTML page

```
<script src="https://unpkg.com/games-of-life/dist/games-of-life.min.js"></script>
```

## Idea

On the 30th of May 2015, I have participated in a Coderetreat at Milan XPUG.

We have had so much fun coding implementations of the Game of Life.

As a mathematician, I think it is a very interesting problem. I couldn’t resist to generalize it and try to solve it in any of its variations.

Let’s start with some abstractions.

A function *getNeighboursOf*, which returns the set of cells adjacent to a given cell, defines the shape of *Game of Life* universe.

Infact, since

```
getNeighboursOf(cell1) = getNeightboursOf(cell2) ⇒ cell1 = cell2
```

it can be said that the set of neighbours of a cell is dual to the cell itself, hence the definition of the *getNeighboursOf* function is equivalent to the definition of the space of a *Game of Life* universe. Note that it defines the concept of **nearness**.

In other words,

if you define a

getNeighboursfunction you also shape the space of aGame of Lifeuniverse

On the other hand, let be given the definition of an *isAlive* function, which returns `true`

if the given cell is alive, `false`

otherwise.
It can be easily extended to an *areAlive* function which, given a list of cells, returns a list of booleans; following a similar identification we used for the *getNeighboursOf* function, an *isAlive* function describes the state of a *Game of Life* universe at a given moment.

The considerations above allow to implement an **abstract** *Game of Life* in a functional way, in any of its variations, for example:

- finite grid
- infinite grid
- 2-dimensional, 3-dimensional, n-dimensional
- square, triangular, hexagonal tiles
- cylinder, torus, moebius strip, boy surface

Take a look to createWorld.js for the implementation’s details.

The world has a *transition rule* which defaults to the classicTransitionRule.js.

## Example

A simple example is the infinite grid with two dimensional coordinates.

Define a *getNeighboursOf* which returns the neighbours of a given cell.

```
function getNeighboursOf (cell) {
var x = cell[0]
var y = cell[1]
var neighbours = []
for (var j = y - 1; j <= y + 1; j++) {
for (var i = x - 1; i <= x + 1; i++) {
if ((i === x) && (j === y)) {
continue
}
neighbours.push([i, j])
}
}
return neighbours
}
// Alias the adjacency function with a more meaningful name,
// to improve semantic in the example code below.
var infiniteGrid2d = getNeighboursOf
```

Create a *Game of Life* world, and get the *evolve* function

```
var gamesOfLife = require('games-of-life')
var createWorld = gamesOfLife.createWorld
var transitionRule = gamesOfLife.classicTransitionRule.bind(null, 2, 3, 3)
var world = createWorld(infiniteGrid2d)
var evolve = world(transitionRule)
```

The empty grid is represented by a function that always returns false, so

```
function emptyGrid () {
return false
}
evolve(emptyGrid) // will always return false
```

Try with a single cell at the origin

```
function singleCellAtTheOrigin (cell) {
return ((cell[0] === 0) && (cell[1] === 0))
}
evolve(singleCellAtTheOrigin) // will always return false too, cause the cell dies
```

Ok, a more interesting example is the blinker

```
function horyzontalBlinker (cell) {
var x = cell[0]
var y = cell[1]
if (y !== 0) {
return false
}
if ((x >= -1) && (x <= 1)) {
return true
}
return false
}
function verticalBlinker (cell) {
var x = cell[0]
var y = cell[1]
if (x !== 0) {
return false
}
if ((y >= -1) && (y <= 1)) {
return true
}
return false
}
```

You may check that the *verticalBlinker* evolves in the *horyzontalBlinker* and vice versa

```
for (var i = -1; i < 1; i++) {
for (var j = -1; j < 1; j++) {
console.log(evolve(verticalBlinker)(i, j) === horyzontalBlinker(i, j)) // true
}
}
```

## See also

External links: