ComputerCraft Quarry perimeter (single)

function go(dir)
  if dir=="fwd" then
    while turtle.forward() == false do
      turtle.dig()
      turtle.attack()
    end
  elseif dir=="up" then
    while turtle.up() == false do
      turtle.digUp()
      turtle.attackUp()
    end
  elseif dir=="down" then
    while turtle.down() == false do
      turtle.digDown()
      turtle.attackDown()
    end
  elseif dir=="back" then
    while turtle.back() == false do
      turtle.turnLeft()
      turtle.turnLeft()
      turtle.dig()
      turtle.attack()
      turtle.turnLeft()
      turtle.turnLeft()
    end
  end
end

function refuel()
  print("Fuel needed: " .. (3+comeback)*size)
  print(" ")
  turtle.select(16)
  while turtle.getFuelLevel() < ((3+comeback)*size) do
    if turtle.refuel(1) == false then
      sleep(0.5)
    end
  end
end

function items()
  turtle.select(1)
  if turtle.getItemCount(1) < 3 then
    print("Place 3 blocks in the first slot.")
    while turtle.getItemCount(1) < 3 do
      sleep(1)
    end
  end
end

function node()
  turtle.digDown()
  turtle.placeDown()
end

function line()
  for i=1, size do
    turtle.digUp()
    turtle.dig()
    go(fwd)
  end
  turtle.digUp()
end

function turnBack()
  turtle.turnLeft()
  turtle.turnLeft()
end

-------------------------------------------------------

up = "up"
down = "down"
back = "back"
fwd = "fwd"

write("Quarry size: ")
size = read() + -1
while size < 2 or size > 63 do
  print("Invalid size! (Min = 3, Max = 64)")
  size = read() + -1
end
write("Return back? (1=Yes, 0=No): ")
comeback = read() + 0
if comeback ~= 1 then
  comeback = 0
end

refuel()
items()

--------------------------------------------------------

node()
line()
node()
turnBack()
line()
turtle.turnLeft()
line()
node()
if comeback == 1 then
  turnBack()
  line()
end

print("done!")