http://rosettacode.org/wiki/Forest_fire#Lua

LuaForestFire.lua

--The values used to represent trees, fires, and empty space.
local TREE = 'T'
local BURNING = '#'
local EMPTY = ' '

--Returns a table with gettors and settors for 2D coordinates.
--This implementation uses a single underlying 1-dimensional
--array table. It could also be changed to use a 2-dimensional
--table of row/column tables, or a table with serialized coordinates.
local function array2d(w,h)
  local function coords(x,y)
    return y * w + x
  end

  local array = {}
  local methods = {}

  function methods.get(x, y)
    return array[coords(x, y)]
  end

  function methods.set(x, y, val)
    array[coords(x, y)] = val
  end

  function methods.tostring()
    local rows={}
    for i=1,#h do
      rows[i]=table.concat(array,'',coords(0,i),coords(w,i))
    end
  end

  return access
end

local function makeforest (width, height, init_tree_prob, f_prob, p_prob)
  local forest = array2d(width, height)

  --add additional methods to the array
end