[jerf]

That would get into the stuff at the bottom, when you simulate other data structures within your data structure. A non-cyclic data structure can simulate cyclicness with IDs on nodes and things that store links... it's generally how you do it in Haskell, in fact, since while saying "it can't" do true graphs is perhaps a smidge overstrong it is certainly not practical to try to modify knot-tied structures. (I've seen the question "How would I do a graph?" repeatedly on /r/haskell, and "use IDs in a map" is generally what comes back.) But you're putting a layer on top of your store.

(By the by... you know you can trust me, because... semantic. Semantic.)