rror condition, then in some
    sense you expect it to happen, or the check is wasted code.</p>

    <p>A more appropriate question to ask is: ``do we want stack
    unwinding here?'' Because actually handling an exception is likely
    to be significantly slower than executing mainline code, you
    should also ask: ``Can I afford stack unwinding here?'' For
    example, a desktop application performing a long computation might
    periodically check to see whether the user had pressed a cancel
    button