unexpected symbol, attempt to index ? (a nil value)

function mineForward1()
  while(turtle.forward()==false) do
	turtle.dig()
	sleep(0.3)
  end
  return true
end
function mineForward(n)
  local i = 0
  while(i<n) do
	mineForward1()
	i = i + 1
  end
  return true
end
function mineUp1()
  while(turtle.up()==false) do
	turtle.digUp()
	sleep(0.3)
  end
  return true
end
function mineUp(n)
  local i = 0
  while(i<n) do
	mineUp1()
	i = i + 1
  end
  return true
end
function mineDown1()
  while(turtle.down()==false) do
	turtle.digDown()
	sleep(0.3)
  end
  return true
end
function mineDown(n)
  local i = 0
  while(i<n) do
	mineDown1()
	i = i + 1
  end
  return true
end
function backUp(n)
  local i = 0
  while(i<n) do
	while(turtle.back()==false) do
	  sleep(0.1)
	end
	i = i + 1
  end
  return true
end
function turnAround()
  turtle.turnLeft()
  turtle.turnLeft()
  return true
end
function place(n)
  turtle.select(n)
  turtle.place()
  return true
end
function digRoomLayer(width, PT)
  for i=1, width-2 do
	mineForward(i)
	turtle.turnLeft()
	mineForward(i)
	turtle.turnLeft()
  end
  for i=1, 3 do
	mineForward((n-1)/2+1)
	if PT then
	  turnAround()
	  place(1)
	  turnAround()
	end
	mineForward((n-1)/2)-1)
	turtle.turnLeft()
  end
  mineForward(2)
  turtle.turnRight()
  backUp(1)
  if PT then
	place(1)
  end
  backUp((n-1)/2-1)
  return true
end
function digRoom(width, height)
  digRoomLayer(width, true)
  for i=1, height-1 do
	mineDown(1)
	digRoomLayer(width, false)
  end
  return true
end