A ComputerCraft program to dig a lit 3x3 tunnel

3x3_tunnel.lua

-- 3x3 Tunnel by dillmo --
--[[
      This program creates a 3x3 lit-up tunnel for as far as you want. To run
      this program, place your turtle on the bottom row of the middle column of
      your tunnel wall. Then, place torches in the turtle's first inventory
      slot and cobblestone is the second slot. Before running the program, be
      sure to configure the program to meet your needs.
--]]

-- Configuration --
local length = 61 -- The length of the tunnel

-- Function Definitions --
local function digVerticalLine()
  while turtle.detect() do
    turtle.dig()
  end
  turtle.forward()
  while turtle.detectUp() do
    turtle.digUp()
    os.sleep(0.5)
  end
  turtle.digDown()
end

local function turnAround()
  turtle.turnRight()
  turtle.turnRight()
end

local function checkForHoles()
  turtle.down()
  if not turtle.detectDown() then
    turtle.select(2)
    turtle.placeDown()
  end
  turtle.up()
end

local function digIntoWall()
  digVerticalLine()
  checkForHoles()
  turtle.turnLeft()
  digVerticalLine()
  checkForHoles()
  turnAround()
  turtle.forward()
  digVerticalLine()
  checkForHoles()
  turnAround()
  turtle.forward()
  turtle.turnRight()
end

-- Program --
turtle.up()
for i=0, length - 1 do
  digIntoWall()
  if i % 5 == 0 then
    turtle.select(1)
    turtle.placeDown()
  end
end