Question

I wrote a function to compute the symmetric difference of two sets (one of the problems on the 4clojure site). The function passed the unit tests, but it’s not as clean as I would like, given that I have duplicated code.

(fn [x y] (set (concat 
  (keep-indexed #(if (nil? (get y %2)) %2) x)
  (keep-indexed #(if (nil? (get x %2)) %2) y))))

Obviously I would prefer something like:

(fn [x y] (set (concat (diff x y) (diff y x))))

Where the diff function is defined and referenced “inline”, but I don’t know how to do that in one fn block.

Answer 1

Use a let or letfn:

(fn [x y]
  (let [diff (... function body here ...)]
   (set
    (concat (diff x y) (diff y x)))))