Simple Tunnel

function Dig()
	if turtle.detect()==true then
		repeat
			turtle.dig()
		until turtle.detect() == false
	end
	if turtle.detectUp()==true then
		repeat
			turtle.digUp()
		until turtle.detectUp() == false
	end
	if turtle.detectDown()==true then
		repeat
			turtle.digDown()
		until turtle.detectDown() == false
	end
end

function forward()
        if turtle.detect() == true then
                repeat
                        turtle.dig()
                until turtle.detect() == false
        end
        if turtle.detect() == false then
                turtle.forward()
        end
end

i=0
repeat
	Dig() until Dig()==false
	if Dig() == false then
		turtle.turnLeft()
	end
	if Dig() == false then
		turtle.turnRight()
		turtle.turnRight()
	end
	if Dig() == false then
		turtle.turnLeft()
		forward()
		i=i+1
	end
until i==80
end
error()