Project Euler With Clojure

I’ve been trying to expand my programming lately by learning some new languages, specifically ones that fill niches that Python doesn’t. These have included Rust, Go, and Clojure, but I think I’m having the most fun with Clojure (though both Rust and Go are also great, they’re just not as much fun.)

(Spoiler Warning: This post contains my solution for Project Euler Problem #2. If you don’t want to be spoiled on a potential strategy for the answer, you should find your own solution before reading the rest of this post.)

As an example, here’s a bit of Clojure I wrote to solve Project Euler problem #2:

(reduce
 +
 (filter
  even?
  (loop [result [1 2]]
    (let [z (reduce + (take-last 2 result))]
      (if (> z 4000000)
        result
        (recur 
          (conj result z))))))

This gives the right answer, but its not exactly great code, is it? Let’s try and improve things a bit.

First thing that jumps out is the lack of reusability. We can fix that by putting the whole thing into a function:

 (defn fib-euler
   "Returns the sum of all the even fibonacci numbers up to the limit
   provided"
   [limit]
   (reduce
    +
    (filter
     even?
     (loop [result [1 2]]
       (let [z (reduce + (take-last 2 result))]
         (if (> z limit)
           result
           (recur 
             (conj result z))))))))

So now we’ve got a reusable function for our problem, and we’ve even added some documentation as well as making the limit a parameter we can pass to the function.