size = 10

function mine()
    turtle.dig()
    turtle.digUp()
    turtle.digDown()
    suc = turtle.forward()
    return suc
end

function walk (len)
    x = 0
    while x < len do
        if mine() then x = x + 1 end
    end
end

for i = 0,size do
    walk(size - i)
    turtle.turnRight()
    walk(size - i)
    turtle.turnRight()
end