Question

I want to write a closure in Clojure to simulate the following JavaScript code:

var nextOdd = function () {
    var x = 1;
    return function () {
        var result = x;
        x += 2;
        return result;
    }
}();
nextOdd(); //1
nextOdd(); //3
nextOdd(); //5

I know that Clojure supports closures so I could potentially write something like

(defn plusn [x]
    (fn [y] (+ x y)))
(def plus2 (plusn 2))
(plus2 3)

But I need something that will maintain state (i.e. the state of the next odd) every time I call the function… and then there’s the whole immutability thing in Clojure…

Answer 1

This is equivalent in clojure

(def next-odd (let [x (atom -1)]
                (fn []
                  (swap! x + 2))))

(next-odd)
-> 1
(next-odd)
-> 3
(next-odd)
-> 5
(next-odd)
...

Adding to dAni’s example if you need odd number sequence:

(def odd-numbers (iterate (partial + 2) 1))

(take 5 odd-numbers)
-> (1 3 5 7 9)