lighter

success = false
triedTimes = 1
turn = 1
slot = 1
turtle.select (slot)
while triedTimes < 5 do
  t, b=turtle.inspectBlock ()
  if t and b.name=="minecraft:stone" then
    turtle.digDown ()
    turtle.placeDown ()
  else
    if turn == 1 then
      doTurnRight ()
    else
      doTurnLeft ()
  end
  repeat
    moveForward ()
    t, b=turtle.inspectDown()
    success = t and (b.name=="minecraft:stone")
    if not success then
      triedTimes = triedTimes + 1
    end
  until success or triedTimes == 5
  if turtle.getItemCount (slot) == 1 then
    turtle.select (slot = slot + 1)
  end
end

function turnRight ()
  turtle.turnRight ()
  moveForward ()
  turtle.turnRight ()
  turn = 2
end

function turnLeft ()
  turtle.turnLeft ()
  moveForward ()
  turtle.turnLeft()
  turn = 1
end

function moveForward ()
  turtle.forward ()
  turtle.forward ()
  turtle.forward ()
end