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POClojure refs odd behaviour
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copied!<p>I feel like I'm missing something about the use of refs, something under the hood that isn't happening like I think it is. I'm making a thread-safe double linkedlist where the list is a hash containing refs to head and tail. A node of the list is represented by a hash containing previous, next and value. </p> <pre><code>(defn insert [list elem] (dosync (let [head @(:head list)] (if (nil? head) (do (ref-set (:head list) elem) (ref-set (:tail list) elem)) (do (ref-set (:head list) elem) (ref-set (:next elem) head);;fails! (ref-set (:prev head) elem))))));;fails! </code></pre> <p>This gives me a StackOverflow error. To be exact:</p> <p>StackOverflowError java.util.regex.Pattern$Curly.match </p> <p>It feels like I miss something in how refs work in Clojure, can anybody tell me what's wrong?</p> <hr> <p><strong>EDIT:</strong> Here is a link to the full "code". <a href="https://www.refheap.com/6544630b38b33b9d25d999829" rel="nofollow">https://www.refheap.com/6544630b38b33b9d25d999829</a> it fails on the last line, in the else clause of the insert function, when the head is not null anymore.</p> <pre><code>(def f (create-doubly-linked-list)) (def n (create-node 2)) (insert f n) (def m (create-node 3)) (insert (f m);;error! </code></pre> <p>Note that the error manifests when I try to <strong>access</strong> the list, or ie when I evaluate <strong>f</strong> in the repl, or when I execute the last line in the REPL.</p> <hr> <p><strong>UPDATE:</strong> Following code works, but accessing the list causes problems as well as printing it.</p> <pre><code>(def f (create-doubly-linked-list)) (def n (create-node 2)) (insert f n) (insert f (create-node 5)) (insert f (create-node 1)) (def m (create-node 3)) (insert f m) (is (= @(:value @(:tail f)) 2)) (is (= @(:value @(:head f)) 3)) </code></pre>

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