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    <p>Based on Michaels imperative Java solution, this is a idiomatic (lazy sequences) Clojure solution:</p> <pre><code>(ns stackoverflow (:import (java.nio.charset Charset CharsetEncoder))) (defn all-letters [charset] (let [encoder (. (Charset/forName charset) newEncoder)] (letfn [(valid-char? [c] (and (.canEncode encoder (char c)) (Character/isLetter c))) (all-letters-lazy [c] (when (&lt;= c (int Character/MAX_VALUE)) (if (valid-char? c) (lazy-seq (cons (char c) (all-letters-lazy (inc c)))) (recur (inc c)))))] (all-letters-lazy 0)))) </code></pre> <p><strong>Update:</strong> Thanks cgrand for this preferable high-level solution:</p> <pre><code>(defn letters [charset-name] (let [ce (-&gt; charset-name java.nio.charset.Charset/forName .newEncoder)] (-&gt;&gt; (range 0 (int Character/MAX_VALUE)) (map char) (filter #(and (.canEncode ce %) (Character/isLetter %)))))) </code></pre> <p>But the performace comparison between my first approach</p> <pre><code>user&gt; (time (doall (stackoverflow/all-letters "ascii"))) "Elapsed time: 33.333336 msecs" (\A \B \C \D \E \F \G \H \I \J \K \L \M \N \O \P \Q \R \S \T \U \V \W \X \Y \Z \\ a \b \c \d \e \f \g \h \i \j \k \l \m \n \o \p \q \r \s \t \u \v \w \x \y \z) </code></pre> <p>and your solution </p> <pre><code>user&gt; (time (doall (stackoverflow/letters "ascii"))) "Elapsed time: 666.666654 msecs" (\A \B \C \D \E \F \G \H \I \J \K \L \M \N \O \P \Q \R \S \T \U \V \W \X \Y \Z \\ a \b \c \d \e \f \g \h \i \j \k \l \m \n \o \p \q \r \s \t \u \v \w \x \y \z) </code></pre> <p>is quite interesting. </p>
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    1. POHow do I get the set of all letters in Java/Clojure?
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    1. USJürgen Hötzel
    1. USJürgen Hötzel
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    1. COIdiomatic lazy seq fns scarcely use lazy-seq: lazy-seq is low-level. The core of your code is better written as: (->> (range 0 (int Character/MAX_VALUE)) (map char) (filter #(and (.canEncode ce %) (Character/isLetter %))) see http://gist.github.com/357407. Another thing: . and .. are somewaht legacy so don't use them.
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    2. COThanks! Why is "." and ".." considered legacy? Any resources?
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    3. CO-> is a better .. since you mix fn and methods (in .method notation), so .. has no interest except saving you a dot per method call (and making less easy to spot them when you go type-hinting). And (.method obj) is more lispy by putting the method in function position. Similarly prefer Foo. to (new Foo). Give the sugarized forms (.foo, Foo. and Foo/BAR) a try and you'll see they are much nicer to use (and allow for easier factorization later on).
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