Recursion Spider Weasel

Combinations.hs

choose :: [a] -> Int -> [[a]]
choose _ 0 = [[]]
choose [] k = []
choose (x:xs) k = thoseWith ++ thoseWithout
  where
    thoseWith = map (x :) (choose xs (k - 1))
    thoseWithout = choose xs k

Combinations.js

function combinations(numArr, choose, callback) {
    var n = numArr.length;
    var c = [];
    var temp = [];
    var inner = function(start, choose_) {
        if (choose_ === 0) {
            c.push(temp.slice());
        } else {
            for (var i = start; i <= n - choose_; i++) {
                temp.push(numArr[i]);
                inner(i + 1, choose_ - 1);
                temp.pop();
            }
        }
    }
    inner(0, choose);
    return c;
}