Can you describe why you need it? Is it because of real performance concerns or just because it feels better knowing that you don't waste memory space and CPU c

Can you describe why you need it? Is it because of real performance concerns or just because it feels better knowing that you don't waste memory space and CPU cycles? If you really need it, you can always fall back to using mutables for this special list, and use immutables for the rest? This is probably the reason why languages don't implement the Perceus algorithm. If you really needed it you might as well do it by hand.