Minecraft turtle program to make tubes

tube.lua

-- Build a tube, a safe passage for someone to move (as through the Nether)
-- Usage: "tube N", where N is the number of squares forward to build the tube

-- Fuel goes in slot 16
-- Torches in slot 15
-- Building materials in 1-14

-- Utility function: refuel, move forward, dig out if necessary
function go(dig)
  -- refuel
  if turtle.getFuelLevel() < 5 then
    turtle.select(16)
    turtle.refuel(1)
  end
  -- dig forward if necessary
  while (dig and turtle.detect()) do
    turtle.dig()
    sleep(0.5)
  end
  -- move forward
  local moveSucceeded = turtle.forward()
  -- dig up if necessary
  while (dig and turtle.detectUp()) do
    turtle.digUp()
   sleep(0.5)
  end
  return moveSucceeded
end

-- Drop a torch
function torch()
  turtle.select(15)
  turtle.turnRight()
  turtle.turnRight()
  turtle.place()
  turtle.turnLeft()
  turtle.turnLeft()
end

-- select a slot that has some stone in it
function selectStone()
  local slot
  for i=1,14 do
    turtle.select(i)
    if turtle.getItemCount(i) > 0 then
      slot = i
      break
    end
  end
  return turtle.getItemCount(slot) > 0
end

-- Place stones to left and right of turtle
function placeLeftRight()
  selectStone()
  turtle.turnLeft()
  turtle.place()
  selectStone()
  turtle.turnRight()
  turtle.turnRight()
  turtle.place()
  turtle.turnLeft()
end

-- Place a ring of stones around the tube where the turtle is
function place()
  -- Place bottom part
  selectStone()
  turtle.placeDown()
  placeLeftRight()

  -- Place top part
  turtle.up()
  selectStone()
  turtle.placeUp()
  placeLeftRight()
  turtle.down()
end

-- Parse command line
args={...}
maxZ=tonumber(args[1])

-- Move forward, digging and building the tube
for z=0,maxZ-1 do
  go(true)
  place()
end

-- Turn around and come home
turtle.turnRight()
turtle.turnRight()

torchIndex = 0
for z=0,maxZ-1 do
  go(false)
  torchIndex = torchIndex + 1
  if (torchIndex % 15) == 1 then
    torch()
  end
end

turtle.turnRight()
turtle.turnRight()