regret to do 对要做的事遗憾。 (未做)
regret doing 对做过的事遗憾、后悔。 (已做)
I regret to have to do this, but I have no choice.
我很遗憾必须这样去做，我实在没有办法。（必须做的事情是将要做的）
I don't regret telling her what I thought.
我不为告诉她我的想法而后悔。（告诉已经做了）
We regret to inform you that your application has not been successful.
我们很遗憾地通知您，您的申请未通过。（将要通知）
I regret to inform you he died as a consequence of his injuries.
我很遗憾地通知你，他因伤势太重不治身亡。（将要通知）
We regret to inform you that you are being furloughedindefinitely
我们遗憾地通知您，您将要无限期地在家待岗。（将要通知）
He bitterly regretted ever having mentioned it.
他非常懊悔提起了那件事。（已经提起了）
He did not regret saying what he did but felt that he could have expressed it differently.
他并不后悔说了自己所做的事，但觉得本可以换一种方式表达。（说这个动作已经做了）
I don't regret stepping out of the security of marriage.
我并不后悔放弃了婚姻所带来的安全感。（放弃这个动作已经做了）
come to regret最终感到后悔
regret a decision为决定感到后悔
regret a loss为损失感到惋惜
express regret表达歉意
典型例题
---You were brave enough to raise objections at the meeting.
---Well, now I regret ___ that.
A. to do B. to be doing C. to have done D. having done
答案：D。regret having done sth. 对已发生的事感到遗憾。regret to do sth. 对将要做的事感到遗憾。本题为对已说的话感到后悔，因此选D。
小编最后送给大家一句共勉：
One single slip brings eternal regret, and looking back, yourwhole life has passed away.
一失足成千古恨，再回头已过百年身。