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copied!<p>I would not use <code>ref-set</code> but <code>alter</code> because you don't reset the state to a completely new value, but update it to a new value which is obtained from the old one.</p> <pre><code>(defn block-scanner [trigger-string] (let [curr (ref trigger-string) trig trigger-string] (fn [data] (doseq [c data] (when (seq @curr) (dosync (alter curr #(if (-> % first (= c)) (rest %) trig))))) (empty? @curr)))) </code></pre> <p>Then it is not necessary to use refs since you don't have to coordinate changes. Here an atom is a better fit, since it can be changed without all the STM ceremony.</p> <pre><code>(defn block-scanner [trigger-string] (let [curr (atom trigger-string) trig trigger-string] (fn [data] (doseq [c data] (when (seq @curr) (swap! curr #(if (-> % first (= c)) (rest %) trig)))) (empty? @curr)))) </code></pre> <p>Next I would get rid of the imperative style.</p> <ul> <li>it does more than it should: it traverses all data - even if we found a match already. We should stop early.</li> <li>it is not thread-safe, since we access the atom multiple times - it might change in between. So we must touch the atom only once. <em>(Although this is probably not interesting in this case, but it's good to make it a habit.)</em></li> <li>it's ugly. We can do all the work functionally and just save the state, when we come to a result.</li> </ul> <pre><code>(defn block-scanner [trigger-string] (let [state (atom trigger-string) advance (fn [trigger d] (when trigger (condp = d (first trigger) (next trigger) ; This is maybe a bug in the book. The book code ; matches "foojihad", but not "jijihad". (first trigger-string) (next trigger-string) trigger-string))) update (fn [trigger data] (if-let [data (seq data)] (when-let [trigger (advance trigger (first data))] (recur trigger (rest data))) trigger))] (fn [data] (nil? (swap! state update data))))) </code></pre>

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