+ try
+ let neighbs = UriTbl.find adjlist uri in
+ if Lazy.lazy_is_val neighbs.adjacency then
+ (* do not collapse already collapsed nodes *)
+ if Lazy.force neighbs.adjacency <> [] then
+ (* do not collapse nodes with no outgoing edges *)
+ UriTbl.replace adjlist uri { adjacency = lazy (f uri); shown = 0 }
+ with Not_found ->