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  1. PO
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    <p>If you accept a callback argument, you can just call it inside the <code>doseq</code>:</p> <pre><code>(defmulti scan [f table &amp; args] (mapv class args)) ; mapv returns vector (defmethod scan [String String] [f table start-key end-key] ; ^- java.lang classes are imported implicitly (let [scan ... scanner ...] ; no need for two separate lets (doseq [result scanner] ; call f here, e.g. (f result)))) </code></pre> <p>Here <code>f</code> will be called once per result. Its return value, as well as the result itself, will be discarded immediately. You can of course call <code>f</code> with some preprocessed version of <code>result</code>, e.g. <code>(f (foo result) (bar result))</code>.</p> <p>You could also return a sequence / vector of results to the client and let it do its own processing. If the sequence is lazy, you need to make sure that any resources backing it stay open for the duration of the processing (and presumably that they are closed later -- see <code>with-open</code>; the processing code would need to execute inside the <code>with-open</code> and be done with the processing when it returns).</p> <p>For example, to return a vector of preprocessed results to the client you could do</p> <pre><code>(defmethod scan ... (let [...] (mapv (fn preprocess-result [result] (result-&gt;map result)) scanner))) </code></pre> <p>The client can then do whatever it wants with them. Use <code>map</code> to return a lazy sequence instead. If the client then needs to open/close a resource, you could accept it as an argument to scan, so that the client could say</p> <pre><code>(with-open [r (some-resource)] ; or mapv, dorun+map, doall+for, ... (doseq [result (scan r ...)] (do-stuff-with result))) </code></pre>
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    1. POClojure and HBase: Iterate Lazily over a Scan
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    1. USMichał Marczyk
    1. USMichał Marczyk
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    1. COGot it thanks. Where I am at right now is returning a function that calls next on the result scanner until its exhausted `#(let [result (.next result-scanner)] (if (not= result nil) [(Bytes/toString (.getRow result)) (get-to-map result)] nil))` Next thing im working on understanding is then how to concisely call that function until it returns nil, then break out. `(let [cursor (hbase.table/scan table "k1" "r2")] ... )`
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      1. USDavid Williams
    2. CObtw. thanks for the java.lang.String -> String heads up
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      1. USDavid Williams
    3. COSure. I've edited the answer to add two examples of how to get preprocessed results to the client. Returning a collection -- often a lazy sequence -- to the client is much more usual in Clojure than using Java iterators or any workalikes. Another solution would be to return a reducer; you'd need to be on Clojure 1.5 for that, but then you could do your preprocessing with `r/map`, have the client do its own `r/map` (or whatever) and be free of any worries of intermediate allocations. The general feel of the code stays very similar.
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      1. USMichał Marczyk
 

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