While I agree that a functional implementation of something usually copies more, it's a little disingenuous to say that most algorithms return a "fresh copy" of

While I agree that a functional implementation of something usually copies more, it's a little disingenuous to say that most algorithms return a "fresh copy" of a structure. Most of the collections in most of the functional runtimes use clever tricks (hash array mapped tries, hash consing, etc.) to avoid copying the whole structure. In the face of these techniques (and others, e.g. re-structuring things to use zippers and being clever manually or whatever), I suspect the actual amount of redundant data might be quite a bit less than you might think.