Quick sort with ECMAScript array comprehensions

qs.clj

(defn qs [lst]
  (let [[head & tail] lst]
    (if (>= 1 (count lst))
      lst
      (flatten [(qs (for [x tail :when (<= x head)] x)) head (qs (for [x tail :when (> x head)] x))]))))

qs.hs

-- Haskell implementation
quicksort [] = []  
quicksort (x:xs) = smallerSorted ++ [x] ++ biggerSorted
    let smallerSorted = quicksort [a | a <- xs, a <= x]  
        biggerSorted = quicksort [a | a <- xs, a > x]

qs.js

// JavaScript implementation
let qs = (arr) => {
  if (!arr || !arr.length) return [];
  let pivot = arr.pop();
  return qs([for (x of arr) if (x <= pivot) x])
    .concat(pivot)
    .concat(qs([for (y of arr) if (y > pivot) y]));
};