regret doing vs regret having done

[yun]

I know the difference in the meaning between “regret + gerund” and “regret + infinitive”

(A) regret + doing: feel sorry about what I did in the past.
(B) regret + to do: feel sorry about what I will do now.

However, I don’t exactly understand what difference exists in the below two sentences.
Could you please explain it to me?

(A) I regret not working harder.
(B) I regret not having worked harder.

 

[gabber]

The only real difference between them is that (A) is one word shorter, and therefore better. (Conservation of energy....)

 

[Raymott]

I know the difference in the meaning between “regret + gerund” and “regret + infinitive”

(A) regret + doing: feel sorry about what I did in the past.
(B) regret + to do: feel sorry about what I will do now.

However, I don’t exactly understand what difference exists in the below two sentences.
Could you please explain it to me?

(A) I regret not working harder.
(B) I regret not having worked harder.

B is strictly more correct if you are referring to the past.
I regret not having worked harder, because now I am poor, and my children did not receive an education.
You must use A for the present (and you can use it for the past):
I regret not working harder, because I can hardly afford my daily beer and cigarettes any more. (Present habitual)
Many people, Americans especially, would use A in place of B, as gabber has illustrated.