title: Clojure closure efficiency?
body: <p>Quite often, I swap! an atom value using an anonymous function that uses one or more external values in calculating the new value.  There are two ways to do this, one with what I understand is a closure and one not, and my question is which is the better / more efficient way to do it?</p>
  
  <p>Here's a simple made-up example -- adding a variable numeric value to an atom -- showing both approaches:</p>
  
  <pre><code>(def my-atom (atom 0))
  
  (defn add-val-with-closure [n]
    (swap! my-atom 
           (fn [curr-val] 
             ;; we pull 'n' from outside the scope of the function
             ;; asking the compiler to do some magic to make this work
             (+ curr-val n)) ))
  
  (defn add-val-no-closure [n]
    (swap! my-atom 
           (fn [curr-val val-to-add] 
             ;; we bring 'n' into the scope of the function as the second function parameter
             ;; so no closure is needed
             (+ curr-val val-to-add))
           n))
  </code></pre>
  
  <p>This is a made-up example, and of course, you wouldn't actually write this code to solve this specific problem, because:</p>
  
  <pre><code>(swap! my-atom + n)
  </code></pre>
  
  <p>does the same thing without any need for an additional function.</p>
  
  <p>But in more complicated cases you do need a function, and then the question arises.  For me, the two ways of solving the problem are of about equal complexity from a coding perspective.  If that's the case, which should I prefer?  My working assumption is that the non-closure method is the better one (because it's simpler for the compiler to implement).</p>
  
  <p>There's a third way to solve the problem, which is not to use an anonymous function.  If you use a separate named function, then you can't use a closure and the question doesn't arise.  But inlining an anonymous function often makes for more readable code, and I'd like to leave that pattern in my toolkit.</p>
  
  <p>Thanks!</p>
  
  <p><strong>edit in response to A. Webb's answer below</strong> (this was too long to put into a comment):</p>
  
  <p>My use of the word "efficiency" in the question was misleading.  Better words might have been "elegance" or "simplicity."  </p>
  
  <p>One of the things that I like about Clojure is that while you can write code to execute any particular algorithm faster in other languages, if you write idiomatic Clojure code it's going to be decently fast, and it's going to be simple, elegant, and maintainable.  As the problems you're trying to solve get more complex, the simplicity, elegance and maintainability get more and more important.  IMO, Clojure is the most "efficient" tool in this sense for solving a whole range of complex problems.  </p>
  
  <p>My question was really -- given that there are two ways that I can solve this problem, what's the more idiomatic and Clojure-esque way of doing it?  For me when I ask that question, how 'fast' the two approaches are is one consideration.  It's not the most important one, but I still think it's a legitimate consideration if this is a common pattern and the different approaches are a wash from other perspectives.  I take A. Webb's answer below to be, "Whoa!  Pull back from the weeds!  The compiler will handle either approach just fine, and the relative efficiency of each approach is anyway unknowable without getting deeper into the weeds of target platforms and the like. So take your hint from the name of the language and when it makes sense to do so, use closures."</p>
  
  <p><strong>closing edit on April 10, 2014</strong></p>
  
  <p>I'm going to mark A. Webb's answer as accepted, although I'm really accepting A. Webb's answer and omiel's answer -- unfortunately I can't accept them both, and adding my own answer that rolls them up seems just a bit gratuitous.</p>
  
  <p>One of the many things that I love about Clojure is the community of people who work together on it.  Learning a computer language doesn't just mean learning code syntax -- more fundamentally it means learning patterns of thinking about and understanding problems. Clojure, and Lisp behind it, has an incredibly powerful set of such patterns.  For example, homoiconicity ("code as data") means that you can dynamically generate code at compile time using macros, or destructuring allows you to concisely and readably unpack complex data structures.  None of the patterns are unique to Clojure, but Clojure brings them all together in ways that make solving problems a joy.  And the only way to learn those patterns is from people who know and use them already.  When I first picked Clojure more than a year ago, one of the reasons that I picked it over Scala and other contenders was the reputation of the Clojure community for being helpful and constructive. And I haven't been disappointed -- this exchange around my question, like so many others on StackOverflow and elsewhere, shows how willing the community is to help a newcomer like me -- thank you!</p>