local turn = "left"

function turn()

  if turn == "left" then

    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
    turtle.forward()

    turn = "right"
  else

    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
    turtle.forward()

   turn = "left"
    end

end

function main()


 while turtle.detectDown() do

  turtle.digDown()
  turtle.forward()

  end

  turn()
  main()

end



main()