Are circular references supported in clojure?
1. create two refs
user=> (def aref1 (ref {}))
#'user/aref1
user=> (def aref2 (ref {}))
#'user/aref2
user=> aref1
#<r...@98adae2: {}>
user=> aref2
#<r...@7b283052: {}>
2. alter ref1 to have a reference to ref2
user=> (dosync (ref-set aref1 {:a aref2}))
{:a #<r...@7b283052: {}>}
user=> aref1
#<r...@98adae2: {:a #<r...@7b283052: {}>}>
user=> aref2
#<r...@7b283052: {}>
3. alter ref2 to have a reference (pointer) to ref1
user=> (dosync (ref-set aref2 {:a aref1}))
{:a #<r...@98adae2: {:a #<r...@7b283052: {:a #<r...@98adae2: {:a
#<r...@7b283052: {:a #<r...@98adae2: {:a #<r...@7b283052: {:a
#<r...@98adae2: {:a #<r...@7b283052: {:a #<r...@98adae2: {:a
#<r...@7b283052: {:a #<r...@98adae2: {:a #<r...@7b283052: {:a
<SNIP...>
{:java.lang.StackOverflowError
<SNIP...>
4. So, I've got a stack overflow... What's the proper way to deal with
this? Are circular references like this not allowed?
5. I'm running into this b/c I'm trying to create two relationships for
the Dining Philosophers problem:
A Table references it's seated philosophers and chopsticks.
A Philosopher references the table they are seated at and the left and
right chopsticks on the table.
A Chopstick references either it's table or the Philosopher using it.
So, I have a mesh of references :-).
If you are interested, the code is at:
https://gist.github.com/757925
However, I'm still working on that code, and want to respond to Laurent
and Orion on a previous thread once I understand how to handle (or not
handle, perhaps) circular references.
-Todd
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