Conways Game of Life in CoffeeScript

game_of_life.coffee

#
# Utility methods: Uses Underscore.js
#

flatten_nested_array = (array) -> _.flatten(array, true) # flattens to one level of nesting
includes = (target, coll) -> _.any(coll, (item) -> _.isEqual(item, target)) # allows for searching for arrays
frequencies = (coll) -> _.countBy(coll, _.identity) # return a map of how many times each element appears in a given list

# Javascript only supports strings as keys for associative arrays. This converts a "1,1" into [1,1]
key_to_array = (string) ->
  splitted = string.split(',')
  [parseInt(splitted[0]), parseInt(splitted[1])]

#
# Conway's Game of Life
#

neighbours_of = ([x, y]) ->
  [[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]]
  
neighbour_frequencies = (world) ->
  all_neighbours_of_live_cells = (neighbours_of(cell) for cell in world)
  frequencies(flatten_nested_array(all_neighbours_of_live_cells))

survives = (num_of_neighbours, alive) ->
  return yes if alive and (num_of_neighbours == 2 or num_of_neighbours == 3)
  return yes if not alive and num_of_neighbours == 3
  no

is_alive = (cell, world) ->
  includes(key_to_array(cell), world)

evolve = (world) ->
  (key_to_array(cell) for cell, count of neighbour_frequencies(world) when survives(count, is_alive(cell, world)))

game_loop = (world, times_to_evolve, listener) ->
  for [1..times_to_evolve]
    world = evolve(world)
    listener(world)

# world is a set of live cells
world = [[0, 1], [1, 1], [2, 1]]

game_loop(world, 5, (new_world) ->
  console.log (cell.toString() for cell in new_world))

# prints
# ["1,2", "1,1", "1,0"]
# ["0,1", "1,1", "2,1"]
# ["1,2", "1,1", "1,0"]
# ["0,1", "1,1", "2,1"]
# ["1,2", "1,1", "1,0"]

gol.html

<script src="http://code.jquery.com/jquery-1.8.2.min.js"></script>
<script src="http://underscorejs.org/underscore-min.js"></script>
<script src="game_of_life.js"></script>

Hey @joejag, what's going on in line 32?

if candidate_cell of frequencies_found

I've never seen of used like that and can't get my head around it.

Ah, is it checking if the object has the key candidate_cell?

Hey, 'of' checks to see if it's a key in the hash

I have to imagine there's a better way to do the frequencies method.

Why not just

for candidate_cell in all_neighbouring_cells frequencies_found[candidate_cell] ||= 0 frequencies_found[candidate_cell]++

^ except with not broken indentation ;)

Very nice. I've changed the frequencies method accordingly!

I've reshaped frequencies into a utility function, which makes it clearer