confusion about the rule taught and example

Question

If the rule is ne...pas +passe compose +depuis longtemps means not  in a long time, surely Martin n'est pas arrive depuis longtemps would translate as Martin hasn't been here in a long time, not Martin hasn't been here long?

Answer

Martin n'est pas arrivé depuis longtemps -- (literally:) "Martin hasn't arrived for long," which means that he hasn't been here for long.

Answer

I agree with Jane, it's quite confusing. According to the lesson, the present tense is translated as "not long", but the passé composé should be translated as "not in a long time". So it should mean "Martin hasn't arrived in a long time", but it seems to be following the rule for the present tense instead.

When arriver means "to happen", I think you do get the expected meaning according to the rules:

"ça n'est pas arrivé depuis longtemps" = "that hasn't happened in a long time"

If I had to guess at an explanation for this, I'd say that the rules in the lesson should be considered just as rules of thumb. When you have a negative sentence it could either be negating the verb (= it didn't happen) or the "longtemps" (= not long). You have to work out which it is from the context.

Answer

Agreed. It is confusing and not entirely logical. French, in one word. ;)

Answer

I think the issue is to think not about the translation but  what is being described.