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POClojure - reset! atom causing a stack overflow
 

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    <p>I am learning clojure and just playing with atoms and refs. Here is a simple tree implementation, but it is causing a stack overflow when executing the add-child method:</p> <pre><code>(ns mytree) (defprotocol PNode (add-child [this parent] "add 'this' node to the parent")) (defrecord Node [id parent name children] PNode (add-child [this p] (println "adding this to children of parent") (dosync (alter (:children p) conj this)) ;following causes a stack overflow -why? ; (println "reseting parent of this") ; (reset! parent p) )) (defn create-node [id name] (Node. id (atom nil) name (ref ()))) </code></pre> <p>Here is a sample session from REPL:</p> <pre><code>&gt;mytree&gt; (def root (create-node 1 "CEO")) &gt;#'mytree/root &gt;mytree&gt; (def child (create-node 2 "VP1")) &gt;#'mytree/child &gt;mytree&gt; (add-child child root) &gt;adding this to children of parent &gt;(#:mytree.Node{:id 2, :parent #&lt;Atom@4dffa9d: nil&gt;, :name "VP1", :children #&lt;Ref@cbe5beb: ()&gt;}) &gt;mytree&gt; root &gt;#:mytree.Node{:id 1, :parent #&lt;Atom@44896098: nil&gt;, :name "CEO", :children #&lt;Ref@2a75733a: &gt;(#:mytree.Node{:id 2, :parent #&lt;Atom@4dffa9d: nil&gt;, :name "VP1", :children #&lt;Ref@cbe5beb: ()&gt;})&gt;} &gt;mytree&gt; (def child2 (create-node 3 "VP2")) &gt;#'mytree/child2 resetting parent to child2 works &gt;mytree&gt; (reset! (:parent child) child2) &gt;#:mytree.Node{:id 3, :parent #&lt;Atom@43c32b82: nil&gt;, :name "VP2", :children #&lt;Ref@425d868f: ()&gt;} but resetting parent to root causes stack overflow - why?? &gt;mytree&gt; (reset! (:parent child) root) &gt;; Evaluation aborted. </code></pre> <p>As you can see above, reseting parent of child to child2 works, but resetting it to root causes a stack overflow. Can you help me understand why?</p>
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