So, is it still true to say, &quot;You wish you could express your business logic with pure functions. But often you can&#x27;t because the lack of immutability hurts performance in various ways. But ELM creates a &#x27;sandbox&#x27; in which you <i>can</i> do so, by letting you write functions which work over time varying streams instead of stateful callbacks.&quot;<p>If not, which parts changed &#x2F; how would you revise it?