"Also, setforms only sends a single argument to sref, so we would need to change that too."
Yeah, I think I noticed that at one point a long time ago, and I consider it to be a bug. (I promptly forgot about it. XD;; ) I never rely on that behavior, but then I don't extend things in the Arc core much either, for cross-implementation compatibility's sake.
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"To be fair, having the key as the last argument is great for slices"
I think that's the reason it is the way it is. I've ended up designing some of my utilities the same way. For instance, I usually give failcall the signature (func fail . args), which is very similar to sref's (func new-value . args). I'd probably call 'sref "setcall" if I were to reinvent it.
I'm not sure I want to reinvent 'sref though: It's kinda bad as a failcallable rulebook, because you can't tell if it will succeed until you've called it, and then you get side effects. I've been thinking about other designs, like a currying-style ((sref func args...) new-value) version or something. But this is kinda specific to a system that uses failcall. In Arc, we can't really recover when an extension doesn't exist, so we don't write code that tries yet.
