Halliday & Matthiessen (2014: 636-7):
In a yes/no question-answer sequence the answer may involve ellipsis of the whole clause, e.g.||| You mean || you were interested in him as a man in private life. ||| – ||| Yes, yes. [∅: I was interested in him as a man in private life.] |||
||| Have you been interviewed by Bedford yet? ||| – ||| No. [∅: I haven’t been interviewed by Bedford yet.] |||
||| ... and the value deal is three large pizzas delivered from $22.95. ||| Would you like to try that? – ||| Ah no thanks. [∅: I would not like to try that.] |||
The first clause in such a pair is not necessarily a question; it may have any speech function, e.g.||| I think || it is it must be very tough indeed. ||| – ||| Yes. [∅: It is very tough.] |||
||| You feel || it must be English. ||| – ||| Yes [∅: I feel it must be English]; || because I am English, || I feel || that I must study English literature || – that’s why. |||
||| I mean || that should mean [[ that an autobiography is your ideal]] . ||| – ||| Yes [∅: an autobiography is my ideal]; || but it also is a very good novel || I think. |||
Here yes and no serve as mood Adjuncts of polarity and the rest of the clause is elided.