You are right, heap sort doesn't need recursion, and is more efficient than shell sort for large arrays. But if you compare the code size, it is hard to beat shell sort. This is a Java version:

    static <T>void shellSort(T[] a, Comparator<T> c) {
        int n = a.length;
        int h = 16, g = 1;
        while (n > g) {
            h = h + h + h / 4 + 16;
            g = (h + 15) / 16;
        }
        do {
            h = (h - 16) * 4 / 9;
            g = (h + 15) / 16;
            for (int i = g; i < n; i++) {
                T t = a[i];
                int j = i;
                for (; j >= g && c.compare(a[j - g], t) > 0; j -= g) {
                    a[j] = a[j - g];
                }
                a[j] = t;
            }
        } while (g > 1);
    }

I was wondering, is there anything as simple as that, and similarly efficient? I doubt it.