Need help with goto program

local tArgs = {...}
if #tArgs < 3 then
  write("Usage: ")
  write(shell.getRunningProgram())
  print(" <x> <y> <z>")
  return
end

local posX, posY, posZ = 0
dir = 0

function goUp()
  while not turtle.up() do
	goForward()
  end
  posY = posY + 1
end
function goDown()
  while not turtle.down() do
	goForward()
  end
  posY = posY - 1
end
function left()
  if dir < 0+1 then
	dir = 3
  else
	dir = dir - 1
  end
  turtle.turnLeft()
end
function right()
  if dir > 3-1 then
	dir = 0
  else
	dir = dir + 1
  end
  turtle.turnRight()
end
function goForward()
  while not turtle.forward() do
	goUp()
  end
  if dir == 0 then
	posZ = posZ + 1
  elseif dir == 1 then
	posX = posX + 1
  elseif dir == 2 then
	posZ = posZ - 1
  elseif dir == 3 then
	posX = posX - 1
  else
	error("Undefined direction.")
  end
end
function goBack()
  while not turtle.back() do
	goUp()
  end
  if dir == 0 then
	posZ = posZ - 1
  elseif dir == 1 then
	posX = posX - 1
  elseif dir == 2 then
	posZ = posZ + 1
  elseif dir == 3 then
	posX = posX + 1
  else
	error("Undefined direction.")
  end
end
function faceZ()
  if dir ~= 0 then
	if dir == 1 then
	  left()
	else
	  repeat
		right()
	  until dir == 0
	end
  end
end
function faceNZ()
  if dir ~= 2 then
	if dir == 3 then
	  left()
	else
	  repeat
		right()
	  until dir == 2
	end
  end
end
function faceX()
  if dir ~= 1 then
	if dir == 2 then
	  left()
	else
	  repeat
		right()
	  until dir == 1
	end
  end
end
function faceNX()
  if dir ~= 3 then
	if dir == 0 then
	  left()
	else
	  repeat
		right()
	  until dir == 3
	end
  end
end
function goto(x,y,z)
  print("Heading to x"..x..", y"..y..", z"..z.."!")
  repeat
	if x < posX then
	  faceNX()
	elseif x > posX then
	  faceX()
	end
	while x ~= posX do
	  goForward()
	end
	if z < posZ then
	  faceNZ()
	elseif z > posZ then
	  faceZ()
	end
	while z ~= posZ do
	  goForward()
	end
	while y < posY do
	  goDown()
	end
	while y > posY do
	  goUp()
	end
  until x == posX and y == posY and z == posZ
end
function dropOff()
  for i = 1, 16 do
	turtle.select(i)
	turtle.drop()
  end
  turtle.select(1)
end

local param1 = tonumber(tArgs[1])
local param2 = tonumber(tArgs[2])
local param3 = tonumber(tArgs[3])
goto(param1,param2,param3)
faceZ()

rednet.open("right")
local posX, posY, posZ = gps.locate(.5)
local curX, curY, curZ = posX, posY, posZ
rednet.close("right")
if not posX then
  print("Could not locate position!")
  return
end

function checkGPS()
  rednet.open("right")
  curX, curY, corZ = gps.locate(.5)
  rednet.close("right")
end

function checkDir()
  if curX ~= posX then
    if curX < posX then
      dir = 3
    elseif curX > posX then
      dir = 1
    end
  elseif curZ ~= posZ then
    if curZ < posZ then
      dir = 2
    elseif curZ > posZ then
      dir = 0
    end
  end
end

if not turtle.forward() then
  if not turtle.back() then
    turtle.turnRight()
    if not turtle.forward() then
      if not turtle.back() then
        turtle.turnLeft()
        print("No empty space found!")
        return
      else
        checkGPS()
        checkDir()
        while not turtle.forward() do
          if not turtle.dig() then
            turtle.attack()
          end
        end
        turtle.turnLeft()
      end
    else
      checkGPS()
      checkDir()
      for q = 1, 2 do
        turtle.turnRight()
      end
      while not turtle.forward() do
        if not turtle.dig() then
          turtle.attack()
        end
      end
      turtle.turnRight()
    end
  else
    checkGPS()
    checkDir()
    while not turtle.forward() do
      if not turtle.dig() then
        turtle.attack()
      end
    end
    turtle.turnLeft()
  end
else
  checkGPS()
  checkDir()
  for w = 1, 2 do
    turtle.turnRight()
  end
  while not turtle.forward() do
    if not turtle.dig() then
      turtle.attack()
    end
  end
  turtle.turnRight()
end