How to achieve code folding effects in Emacs?

Question

Whats the best way to achieve something like code folding, or the type of cycling that org-mode uses. What would be the best solution in elisp to create this type of behavi

Answer 1

I believe that your comparison of your "project" to folding is not quite good, because folding is about changing the appearance while keeping the buffer contents intact (the text). Your project would involve showing extra text while keeping the buffer contents intact, AFAIU. So. it's not implementable as a composition of text-insertion and folding (then, the buffer contents would be changed).

But perhaps, it's indeed possible with the same mechanism as folding is done with -- "overlays"... Consider the "before-string" and "after-string" overlay properties; perhaps, you could put your function definitions into these strings belonging to a zero-length overlay at the point. Look at outline-flag-region function to see how overlays are used in the outline mode.