Some experiments with lazy arrays in JavaScript inspired by Clojure's lazy-seq

lazyArray.js

function LazyValue(fn) {
  this.valueOf = fn;
}

function lazyArray(fn) {
  return [new LazyValue(fn)];
}

function cons(item, arr) {
  return [item].concat(arr);
}

function first(arr) {
  var v = arr[0].valueOf();
  return v[1] instanceof LazyValue ? v[0] : v;
}

function rest(arr) {
  return arr[1].valueOf();
}

// Should also be lazy really.
function take(n, arr) {
  return n - 1 > 0 ? cons(first(arr), take(n - 1, rest(arr))) : arr.slice(0, -1);
}

function positiveNumbers(n) {
  return cons(n, lazyArray(function () {
    return positiveNumbers(n + 1);
  }));
}

first(rest(rest(positiveNumbers(10)))); // 12
take(5, positiveNumbers(1)); // [1, 2, 3, 4, 5]