1 只有regret to do,而没有regret to have done.你一定被误导了.
2 有regret having done 和regret doing 它们在meaning上没有difference,
3 regret to do 与regret doing在意义上有很大区别.
I regret telling / having told her the truth====I wish I hadn't told her the truth.(我后悔告诉了她真相)
I regret to say we can't let you in====I am sorry to say we can't let you in.（非常不好意思地说我们不能让你进去）regret to say的意思是：可能会冒犯或得罪你,但还是必须要说,