My Datalog stuff has a lot of circularities, and I chose the "map of keys" approach. It has worked pretty well for me.
On Thu, Feb 12, 2009 at 3:24 PM, Jason Wolfe <jawo...@berkeley.edu> wrote: > > I think there are two basic ways to do this. One is to use one of the > mutable Clojure types mentioned above (or any mutable Java type) to > make an actually circular structure, as you describe. For instance, > you could accomplish (almost) what you want if :parent is an atom. > > The other way is to give up on true circularity, and use an auxiliary > map. For instance, suppose that each node also had a unique :name, > and :parent and :children gave the *names* of the parent and > children. Then, you maintain a separate map from names to nodes. > When you want the actual parent or children of a node, you directly > look up the names of these nodes, and then translate these to nodes > using the auxiliary map. Of course, you can easily wrap this behavior > in some auxiliary functions. The main downside of this approach is > that you have to pass the auxiliary map around everywhere (you can't > stuff it into the nodes, since this would again require mutability). > A middle-ground would be to use a Java (mutable) HashMap for this > purpose, which could be stored inside each node. > > Cheers, > Jason > > > > On Feb 12, 12:32 am, timc <timgcl...@gmail.com> wrote: > > I'm new to Clojure so this may be a stupid question. > > > > I want to make a tree out of these things: > > > > (defstruct treeNode :parent :children :data) > > > > so that every node knows which node is its parent and which nodes are > > its children. > > > > But, given that these things are immutable, I am baffled as to how the > > tree may be constructed - in particular how it's possible to make > > immutable things that 'point at' each other. > > > > Any guidance on this would be greatly appreciated. > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
