You don't have to re-invent the wheel

I tried to manually implement a simple function but I should have just used existing ones.

I wanted to write a function in clojure to return the nth non nil value in a collection. Like the inexperienced clojure student that I am, I wrote something like this

(defn nth-not-nil
  [n coll]
  (loop [m 0 x (first coll) r (rest coll)]
    (if (nil? x)
      (if (= m n)
        (recur (inc m) (first r) (rest r))))))

First of all, that doesn't work, second of all, it just smells like re-inventing the wheel. Here is a much better way using built in functions:

(nth (filter #(not (nil? %)) coll) n)

It's even a one-liner that, when read out loud, sounds like what I was looking for.

But wait, I want to return nil if the nth not nil value is not found! That's fine, nth allows you to specify a not-found value:

([coll index] [coll index not-found])
  Returns the value at the index. get returns nil if index out of
  bounds, nth throws an exception unless not-found is supplied.  nth
  also works for strings, Java arrays, regex Matchers and Lists, and,
  in O(n) time, for sequences.
(nth (filter #(not (nil? %)) coll) n nil)