function left(vx, vy)
    return vy*-1, vx
end

function right(vx, vy)
    return vy, vx*-1
end

function turnLeft(vx, vy)
    turtle.turnLeft()
    return left()
end

function turnRight(vx, vy)
    turtle.turnRight()
    return right()
end

function currentSlotEmpty()
    return turtle.getItemCount(turtle.getSelectedSlot())==0
end

function reSelect()
    for i=1,16 do
        if turtle.getItemCount(i) > 0 then
            turtle.select(i)
            return
        end
    end
    -- exit the program early
    error()
end