When I read about functor, in the sense used in that blogpost, I think that at least one such functor is built in to J so that it is somewhere between stilted and impossible to create examples that *don't* involve functor.
It seems that way to me because mapping is implied by the underlying relationship between nouns and verbs, a relationship that may best be called rank. The description of functor, with its scalar assumptions about values, makes things like shape a context of values that can be preserved. Thus, my sense is that functors permeate J to such a degree that it would make little sense to try to "implement" one to serve as an example. The most basic computations already involve it. If my interpretation can be criticized, I'd love to hear strong criticism. This is the sort of discussion that often comes up with people who come at programming from an ML perspective, so any mistakes I can avoid will help me as such conversations go on. -- Tracy ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
