"Your implicit wrappers sound like they would be too slippery."
Yeah, I've already changed it since then. It's in a lot of flux right now!
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"I think aw's implicit global variables are somewhat better. Things are only unwrapped once--when a symbol is evaluated--and after that they're first-class values, without the evaluator oppressing them at every turn."
Not true. aw's implicit system is the same as Arc/Nu and Nulan except that ar hardcodes symbol names while Arc/Nu and Nulan use first-class mutable thunks, that's all.
aw's implicit global system works by having a table of symbols. The compiler will look at this table and if it finds a symbol in it, it will wrap it as a function call. In other words... in ar, if 'foo is in the implicit table, this:
(foo bar qux)
Would be compiled into this:
((foo) bar qux)
And then foo is a function that returns the value. This is just like Arc/Nu and Nulan except both Arc/Nu and Nulan handle it in much cleaner ways:
In particular, aw's system hardcodes the symbols, which means it isn't late-bound and works poorly with multiple namespaces. Because Arc/Nu uses values rather than symbols, both of those work perfectly.
As for Nulan... it doesn't have late-bindedness or multiple namespaces (by default), so that's not a problem either way. :P
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"I don't think it can model laziness (since it forces at every step)."
Why not? It may call the implicit thunk repeatedly, but the $lazy vau caches it so the expression is only evaluated once:
$defv! $lazy Env; X ->
$lets: U: uniq
Saved: var U
implicit; ->
$if Saved = U
$set-var! Saved: eval X
Saved
The only issue I see with this is efficiency, which I'm not really worried about right now. That particular problem could be solved by giving a way for the implicit wrapper to mutate itself... then, when evaluating the thunk, it would mutate itself to point directly to the evaluated expression. It would still be slightly inefficient because it would still have to unwrap the implicit, but hey, I can only do so much.
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"There's nothing wrong with pursuing this kind of thing."
There's nothing wrong with any choices. The question is whether you like them or not, whether they support your goals or not.
