Land isn't traditionally considered capital. The buckets are normally land, labor, and capital. The closest thing we broadly see to someone whose function is holding capital is someone who owns stock in the stock market. It is likely that most programmers own stock. If I were a betting man, I expect that programmers have more impact on capital than farmers do. But we still have to split hairs over what "main" means.
One interpretation, which is what I suspect most would go to, is where one's income is primarily derived from owning stock. So, in other words, old, retired people. But I don't think anyone here was thinking about the retired. The discussion was about people actively producing food and software.
Another possible interpretation is about impact. If those stocks didn't exist, a lot of the capital wouldn't have been able to be created, and thus there wouldn't have been jobs to go with it; meaning that owning the capital makes it one's main function as without it one wouldn't have a job to go to. But I can already hear you furiously typing how that isn't a satisfactory take. I'd agree.
Maybe it's about attention? Someone who actively watches over to their capital would be seen as it being their main function, while someone who leaves their capital ownership up to a financial advisor so they don't have to think about it wouldn't. But then we're back to the computer. Most programmers watch over that capital, if nothing else. That doesn't really work either.
The only remaining interpretation I can come up, given the connotations often associated with landlord, is a group of people not like by another group of people. But that doesn't have anything to do with capital at all, so... Consider me stumped on what this has to do with the discussion (if we are to ignore the explicit sarcasm involved).