digger

function forward() turtle.forward() end
function up() turtle.up() end
function down() turtle.down() end
function left() turtle.turnLeft() end
function right() turtle.turnRight() end

function left2()
 for
  m = 1, 2, 1 do
  left()
 end
end

function right2()
 for
  m = 1, 2, 1 do
  right()
 end
end

function digDown()
 while (true) do
  if
   turtle.detectDown() == true then
   turtle.digDown(left)
  else
   break
  end
 end
end

function dig()
 while (true) do
  if
   turtle.detect() == true then
   turtle.dig(left)
  else
   break
  end
 end
end

function digUp()
 while (true) do
  if
   turtle.detectUp() == true then
   turtle.digUp(left)
  else
   break
  end
 end
end

function detectDown()
 if
  turtle.detectDown() == false then
  turtle.select(1)
  turtle.placeDown()
 end
end

function detect()
 if
  turtle.detect() == false then
  turtle.select(1)
  turtle.place()
 end
end

function detectUp()
 if
  turtle.detectUp() == false then
  turtle.select(1)
  turtle.placeUp()
 end
end

-- left side of 3x3 tunnel
dig()
 forward()
 left()
detectDown()
detect()
digUp()
 up()
detect()
digUp()
 up()
detect()
detectUp()
right2()

-- top side of 3x3 tunnel
dig()
 forward()
detectUp()
digDown()
dig()
 forward()
detectUp()
detect()

-- right side of 3x3 tunnel
digDown()
 down()
detect()
digDown()
 down()
detect()
detectDown()
left2()

-- bottom side of 3x3 tunnel
dig()
 forward()
detectDown()
 forward()
right()