You say it's NOT Present Continuous. So it is "be + going + to + future"? Right?
I did
not say it is not present continuous. I said that it is not helpful to refer to it in this way.
Swan does indeed say that it is 'really' a present progressive form. Having said that, he refers to it as '
be going + infinitive' or 'the
going-to structure'. Quirk et al treat
be going to as a semi-auxiliary.
Verona suggests that grammar books and reality are sometimes two different things. I don't think this is the case here. I suspect that most grammarians would agree that it
is present continuous/progressive in form. However, as the structure is used effectively as a whole as a method of expressing futurity, contrasting with other ways of expressing futurity (including the present continuous of most verbs), it seems unhelpful to insist that it is a present progressive.
Although some writers say that it is not possible, many people use 'going to go'; there are 9538 citations in the Corpus of Contemporary American.
Thus we can have:
1. I go to France next week.
2. I am going to France next week.
3. I am going to go to France next week.
4. I will go to France next week.
5. I'll be going to France next week.
It is useful to label #2 as 'the present progressive (of
go) to express futurity', and #3 as the
[BE]+going+to' future (of
go).