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    <p>As for how this works: </p> <p>Each term of the fibonacci series is obviously the result of adding the previous two terms. That's what map is doing here, map applies + to each element in each sequence until one of the sequences runs out (which they won't in this case, of course). So the result is a sequence of numbers that result from adding one term in the sequence to the next term in the sequence. Then you need lazy-cat to give it a starting point and make sure the function only returns what it's asked for.</p> <p>The problem with this implementation is that fib-seq is holding onto the whole sequence for as long as the fib-seq is defined, so it will eventually run you out of memory.</p> <p>Stuart Halloway's book spends some time on dissecting different implementations of this function, I think the most interesting one is below (it's Christophe Grande's):</p> <pre><code>(defn fibo [] (map first (iterate (fn [[a b]] [b (+ a b)]) [0 1]))) </code></pre> <p>Unlike the posted implementation previously read elements of the sequence have nothing holding onto them so this one can keep running without generating an OutOfMemoryError. </p> <p>How to get thinking in these terms is a harder question. So far for me it's a matter of getting acquainted with a lot of different ways of doing things and trying them out, while in general looking for ways to apply the existing function library in preference to using recursion and lazy-cat. But in some cases the recursive solution is really great, so it depends on the problem. I'm looking forward to getting the <em>Joy of Clojure</em> book, because I think it will help me a lot with this issue.</p>
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