Kinda mind-blowing fibonacci-sequence-producing function.

gistfile1.clj

(defn fib [n]
  (take n (map first (iterate (fn [[a b]] [b (+ a b)]) [1 1]))))

(fib 5) => (1 1 2 3 5)

You can do something similar in JS though it's not as pretty:

function allfibs(end) {
    var x = 0, y = 1, count = 1;
    yield 1;
    while (count++ < end) {
        [x,y] = [y,x + y];
        yield y;
    }
}

function fibs(x) {
    return [ i for (i in allfibs(x)) ]
}

fibs(5) // [1,1,2,3,5]

Wouldn't be hard to write some library functions like take() to get the nth element etc.

@lmarinho - I'd been playing there all morning actually. Thanks for the rec though!

@fogus - Totally agreed. As you covered in your book (which I'm loving), there's something beautifully declarative about saying "this is how you calculate ALL fibs", and then just taking what you need.