I’ve tried several functional languages (OCaml, Haskell, Racket/Scheme) but Clojure is pure awesomeness.
This is a semi-trivial, not optimized solution to the problem 4 of Project Euler.
Note: you need the pattern-match jar, a wonderful way to bring pattern matching into your Clojure functions.
You can download it from Clojars or adding a dependency in Leningen:
(use 'pattern-match) (defn palindrome? [num-as-string] (match num-as-string  true [x] true [x x] true [x & xs] (if (= x (last xs)) (palindrome? (butlast xs)) false) _ false)) (sort (map (fn [x] (Integer. x)) (filter palindrome? (for [n1 (range 100 999) n2 (range 100 999) :let [k (* n1 n2)]] (str k)))))
In my opinion this version is very readable even if you are a beginner:
- The nested for iter over two range, binding k to (* n1 n2), building a list of strings
- The resulting list is passed to the filter function with the predicate palindrome? that checks if a number is palindrome
- The outer map convert such filtered list in a integer list
- The final sort sort the results because the problem wants the largest palindrome number