ComputerCraft Quarry perimeter (middle)

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: " .. 8*size + 10)
  print(" ")
  turtle.select(16)
  while turtle.getFuelLevel() < (8*size + 10) do
    if turtle.refuel(1) == false then
      sleep(0.5)
    end
  end
end

function items()
  turtle.select(1)
  if turtle.getItemCount(1) < 12 then
    print("Place 12 blocks in the first slot.")
    while turtle.getItemCount(1) < 12 do
      sleep(1)
    end
  end
end

function node()
  turtle.digDown()
  turtle.placeDown()
  mark = mark+1
  print(mark .. "/12")
end

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

function edgeUp()
  turtle.turnLeft()
  go(up)
  turtle.digUp()
  go(up)
  turtle.digUp()
  turtle.dig()
  go(fwd)
  turtle.digUp()
  turtle.dig()
  go(fwd)
  turtle.digUp()
  turtle.turnLeft()
end

function edge()
  turtle.turnLeft()
  turtle.dig()
  go(fwd)
  turtle.digUp()
  turtle.turnLeft()
end

function edgeDown()
  turtle.turnLeft()
  turtle.dig()
  go(fwd)
  turtle.digUp()
  turtle.dig()
  go(fwd)
  turtle.digUp()
  turtle.digDown()
  go(down)
  turtle.digDown()
  go(down)
  turtle.turnLeft()
end

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

up = "up"
down = "down"
back = "back"
fwd = "fwd"
mark = 0

write("Quarry size: ")
size = read() + -1
while size < 2 or size > 63 do
  print("Invalid size! (Min = 3, Max = 64)")
  size = read() + -1
end

refuel()
items()

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

turtle.turnRight()
node()

line()
node()
edgeUp()
node()

line()
node()
turtle.turnRight()

line()
node()
edge()
node()

line()
node()
turtle.turnRight()

line()
node()
edgeDown()
node()

line()
node()
turtle.turnRight()

line()
node()
edge()
node()

line()

print("done!")