local x, y, z = 15, 6, 30
local left = true;

while (y > 0) do
    y=y-1;

    while (x > 0) do
        for _ = 1, z-1 do
            turtle.dig();
            turtle.forward();
        end; x=x-1;

        if (x > 0) then
            local func = (left and turtle.turnLeft) or turtle.turnRight;

            func();
            turtle.dig();
            turtle.forward();
            func();

            for _ = 1, z-1 do
                turtle.dig();
                turtle.forward();
            end; x=x-1;

            if (x > 0) then
                local func = (left and turtle.turnRight) or turtle.turnLeft;

                func();
                turtle.dig();
                turtle.forward();
                func();
            end
        end
    end;

    if (y > 0) then
        turtle.digUp();
        turtle.up();
    end
end