gerund / to-infinitive

They regret not inviting Ann to go to the cinema with them as Ann is very angry now.

你已解釋,
‘regret + gerund = 後悔做過某事 (事情已發生)
regret + to-infinitive = 對將要做的事情感到遺憾”

我只有少少補充

Ann is very angry now.
Ann 為什麼生氣? 因為她是無被邀請去看電影, 可能感覺上被人”飛” 或者被人忽略 (ignore), 覺得他們當她”無到”. 看電影已發生了, 不是將要做的事情.

其他的例子:
Ann does not regret leaving her boyfriend as she has just found out that he has been unfaithful to her.
離開男朋友這事已發生, 知道男朋友"拈花惹草" 是剛剛知道

Ann does not regret ditching her boyfriend as she has just found out that he has been a womanizer for years.

Note:
ditched her boyfriend = 把她的男朋友甩了
womanizer = 沉溺於女色的人；玩弄女性者

We regret to inform you [=we are sorry to tell you] that we have offered the job to someone else.

inform you 不是以前 inform you, 已發生的 action, 實際上現在通知你


2014-12-24 07:12:55 補充：
regret doing something = to feel sorry about something you have done and wish you had not done it

regret to say/inform/tell = to feel sorry to let you know ( ~ used when you are giving someone bad news)

2014-12-24 07:45:26 補充：
分別是一個是已發生或動作已完成, 對做了的事感到遺憾

另一個還未發生,將要做或跟住會做, 未做之先, 感到遺憾