I'm a big believer in Clojure / Rich Hickey's principles regarding the separation of Identity and State (http://www.infoq.com/presentations/ Are-We-There-Yet-Rich-Hickey) and how this is generally a good idea.
However I've recently been running into what seems to be a slight conceptual challenge with this model - I'm creating a simulation system where there is a "world" that contains within it (among other things) a number of "actors". Basically the actors are some form of "nested identity" within the world. I'd like to be able to think about the world as a single value. So the entire "state of the world" could be considered as an identity with a current value that is immutable and stored in a single ref. (as an aside, making the world a persistent data structure is actually particularly useful for things like efficiently recording a sequence of world states, simulation of alternate histories etc.). At the same time however, the "actors" within the world also have their own identity. This is where it starts to get tricky. There seem to be several options on how to handle of this, but none of them seem very pretty...... a) separate out the actor identities but keep the value of the actors within the world state - seems to work, but you now have to keep multiple identities in sync - if the state of an actor changes, you have to update *both* the world state and the state of the specific actor. And now the entire state of the world isn't contained within the world identity so you can't easily do snapshots etc. b) Don't use Clojure managed references for actor identity - instead give each actor some form of ID and look up this ID within the world state whenever the actor is referred to. Again this seems to work, but you now you don't get the benefits of Clojure's references, you have a second class form of "identity" and need to wrap everything in a lot of functions to handle all the ID lookups etc. c) Put actor identities inside the world state - nasty! now the world state is mutable........ Am I missing something? Is there an easy way to handle this? Or is this genuinely a complex problem with the Clojure identity/state model? Any thoughts 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 Note that posts from new members are moderated - please be patient with your first post. 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
