Memoize

Memoize already compiled iterators using their toString(). In theory then, something like...

```
$(document.body).click(function () {
$("div").each(function (i) {
if (this.style.color != "blue") {
this.style.color = "blue";
} else {
this.style.color = "";
}
});
});
```

...could benefit from the potential speed improvement of compiled iterators, without any extra effort from developers using the library.

Start by locating the compiled-iterator implementation and the path that turns iterator functions into executable code. Check how iterator identity is currently handled before evaluating the proposed toString()-based memoization. Done means equivalent compiled iterators can reuse prior work without changing the behavior shown in the example.

Written by the indexing model from the issue text.