ComputerCraft Maze Generator

--Creates a square maze with specified side length-
args = {...}
if #args < 1 then
  print("Usage: maze <size>")
  return
end
print("Place torches in slot 1 and fuel in slot 16, then press enter.")
read()
turtle.select(16)
size = tonumber(args[1])
maze = {}
for x = 1,size do
  maze[x] = {}
  for y = 1,size do
    maze[x][y] = false
  end
end
mx = 1 --X-coordinate
my = 1 --Y-coordinate
md = 1 --Direction
maze[1][1] = true
-------------------------
-------------------------
function isOpen(d)
  x = mx + dx(d)
  y = my + dy(d)
  if x < 1 or y < 1 or x > size or y > size then
    return false
  end
  m = maze[x][y]
  return not m
end
-------------------------
function dx(d)
  if d == 2 then
    return 1
  elseif d == 4 then
    return -1
  end
  return 0
end
-------------------------
function dy(d)
  if d == 1 then
    return 1
  elseif d == 3 then
    return -1
  end
  return 0
end
-------------------------
function face(d)
  if d > 4 then d = d - 4 end
  if math.abs(md - d) == 1 then
    if md > d then
      turnLeft()
    else
      turnRight()
    end
  elseif math.abs(md - d) == 2 then
    turnRight()
    turnRight()
  elseif math.abs(md - d) == 3 then
    if md > d then
      turnRight()
    else
      turnLeft()
    end
  end
  md = d
end
-------------------------
function turnLeft()
  md = md - 1
  if md == 0 then md = 4 end
  turtle.turnLeft()
end
function turnRight()
  md = md + 1
  if md == 5 then md = 1 end
  turtle.turnRight()
end
-------------------------
torches = 0
function carve(t)
  for i = 1,2 do
    if turtle.getFuelLevel() == 0 then
      if not turtle.refuel(1) then
        shell.run("reboot")
      end
    end
    while not turtle.forward() do
      turtle.dig()
    end
    if t then turtle.digDown() end
  end
  mx = mx + dx(md)
  my = my + dy(md)
  maze[mx][my] = true
  if t then
    torches = torches + 1
    if torches == 5 then
      turtle.select(1)
      torches = 0
      turtle.placeDown()
      turtle.select(16)
    end
  end
end
-------------------------
--Fisher-Yates shuffle---
function shuffle(t)
  local n = #t
  while n >= 2 do
    local k = math.random(n)
    t[n], t[k] = t[k], t[n]
    n = n - 1
  end
  return t
end
-------------------------
function main()
  local last = 0
  local dirs = {1,2,3,4}
  dirs = shuffle(dirs)
  last = md
  for k,v in ipairs(dirs) do
    if isOpen(v) then
      face(v)
      carve(true)
      main()
    end
  end
  face(last + 2)
  carve(false)
end
-------------------------
main()