"Were you suggesting that we should highlight things like arc-nu and arcueid?"
Well, I'm suggesting that they share documentation for their common features. If that sharing gives them more or less prominence on the site, I don't mind either way.
I think author intent matters here. If a new so-called "Arc implementation" comes along, sometimes it'll sacrifice improvements for the sake of compatibility (arcueid), and sometimes it'll sacrifice compatibility for the sake of improvements (Semi-Arc). I think this will correlate with our ability to share documentation between projects.
Jarc is an interesting case. It shows how subjective I am: Jarc changes the treatment of unbound variables to make it easier to call Java methods, but this doesn't affect most working Arc programs. Jarc doesn't support continuations, but it would if it could. I consider Jarc to be on the side of compatibility, but maybe only because I've found it easy to write Arc programs that work on Jarc despite these differences. Maybe I would have judged Semi-Arc the same way, if only my programs didn't rely on quite so much hygiene violation and ssyntax manipulation.
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"I would like to be utterly oblivious to compatibility :) "
Yeah. Even though I recommend sharing documentation, I don't look forward to splitting hairs in what amounts to a standardization process.
I see it as work too. Maybe we should reject this rational thinking and focus on something we like.
Personally, I like the idea of jumping ship to Arc/Nu (or merging!). Then we can port the Arc/Nu compiler to Arc/Nu and extend it to compile itself to every platform; who needs other implementations? :-p As I understand it, Arc/Nu has a fully reorganized codebase and very few entrenched users, so it's reasonable to refactor it again and again.
Arc/Nu has a "3.1" folder and a "nu" folder, so the website could introduce the Arc 3.1 documentation as though it's really just documentation for a compatibility mode. ;) Meanwhile, anyone who has a passion for consistency can work on documenting this mode in the same way I described above. :-p
Come to think of it, I might just be outlining more and more work. If Arc/Nu somehow becomes a vibrant community project, it's design by committee, right? I'm going to get some sleep.