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    <p>I recommend the <a href="http://www.packtpub.com/clojure-high-performance-programming/book" rel="nofollow">Clojure High Performance Programming</a> book for addressing questions like yours.</p> <p>There are functions to unbox primitives (<code>byte</code>, <code>short</code>, <code>int</code>, <code>long</code>, <code>float</code>, <code>double</code>).</p> <p>Warn-on-reflection does not apply to numeric type reflection / failure to optimize numeric code. There is a lib to force warnings for numeric reflection - <a href="https://github.com/ztellman/primitive-math" rel="nofollow">primitive-math</a>.</p> <p>You can declare the types of function arguments and function return values <code>(defn ^Integer foo [^Integer x ^Integer y] (+ x y))</code>.</p> <p>Avoid apply if you want performance.</p> <p>Avoid varargs (a common reason to need apply) if you want performance. Varargs functions create garbage on every invocation (in order to construct the args map, which usually is not used outside the function body). <code>partial</code> always constructs a varargs function. Consider replacing the varargs (partial * x) with #(* x %), the latter can be optimized much more aggressively.</p> <p>There is a tradeoff with using primitive jvm single-type arrays (they are mutible and fixed in length, which can lead to more complex and brittle code), but they will perform better than the standard clojure sequential types, and are available if all else fails to get the performance you need.</p> <p>Also, use <a href="https://github.com/hugoduncan/criterium" rel="nofollow">criterium</a> to compare various implementations of your code, it has a bunch of tricks to help rule out the random things that affect execution time so you can see what really performs best in a tight loop.</p> <p>Also, regarding your representation of a point as [x y] - you can reduce the space and lookup overhead of the collection holding them with (defrecord point [x y]) (as long as you know they will remain two elements only, and you don't mind changing your code to ask for (:x point) or (:y point)). You could further optimize by making or using a simple two-number java class (with the tradeoff of losing immutibility).</p>
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    1. POCan this Clojure code be optimized?
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    1. CO"You can declare the types of function arguments and function return values" But can it ever be done so that the function can take/return primitives without boxing?
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    2. COif you use the referenced primitive-math lib as intended, it will help you ensure that the values stay unboxed. There are type declarations for unboxed types: `(defn ^long foo [^long x] ...)`. I now see that would have been a better example of typehinting a function.
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    3. CORegarding primitives: I found this, which helps, but is hard to find from clojure.org: http://dev.clojure.org/display/design/Documentation+for+1.3+Numerics
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