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btw if anyone is genuinely interested in "solving" defaults-affect-inference in Rust, this is the final boss. to the best of my knowledge, if you can make *this* work (and avoid horrible problems with different defaults colliding), then you have completely solved the problem.

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Aria the Cat

@Gankra_

· Apr 25

Replying to @Gankra_ and @UINT_MIN

but here's the problem, this code compiles today: String::from_utf8([1, 2, 3].into_iter().collect()) from_utf8 takes a Vec<u8>, so this is actually unambiguous. But now what happens if String becomes String<A=Global> and wants to make from_utf8 work for all A? Oops! Ambiguous!

Joshua Yanovski

@awesomeintheory

Apr 25

Implicits to the rescue? (I don't know anything about implicits but I do know that Scala 3 is pretty rigorously formalized so maybe they are less terrifying now than they initially appeared?).

Brendan Zabarauskas

@brendanzab

Apr 25

Do you something like Scala 3's context functions? docs.scala-lang.org/scala3/referen - or Scala 2 implicits? IIUC Scala 3 switched to ‘givens’ which are more restricted than implicits.

Joshua Yanovski

@awesomeintheory

Apr 25

I don't think anything more complex than the givens would be needed (from what I can understand). Although, reading a bit, I don't think Scala can implicitly resolve context types this way, only values? Or do I have that wrong? I'm not sure if that changes things fundamentally.

Brendan Zabarauskas

@brendanzab

Apr 25

Hmm ok. I think I was imagining the custom allocator could be a context param. Still unsure what you think Scala 3 would specifically bring to the table here?

Joshua Yanovski

@awesomeintheory

Apr 25

I mostly have just heard that implicits had a lot of theoretical issues in Scala 2 that were resolved in Scala 3, so I figured if Rust were going to learn from an implementation of implicits that would be a better place to start.

Joshua Yanovski

@awesomeintheory

Apr 25

The main reason I'm dubious about allocators as context parameters is what I alluded to elsewhere, I'm not sure how they would play with the borrow checker. We have one implicit context parameter already (for async/await) and it only works in fairly restrictive settings.

Brendan Zabarauskas

@brendanzab

Apr 25

Ahh fair. I would be interested to see experimentation into using Algebraic Effects for allocators, but no clue if that is even possible haha (sounds tricky).

Joshua Yanovski

@awesomeintheory

Apr 25

I'm pretty sure the ambient allocator is more of a coeffect (though I don't know if anyone's specifically called it that before).

Replying to

and

I thought they might have been coeffects (although I didn't use the name) but people disagreed with me – see reply to this:

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Brendan Zabarauskas

@brendanzab

· Jul 23, 2020

So I was wondering: Is there some dual(?) notion to algebraic effects and handlers? Where you inject handlers rather than executing on reified effects after the fact? I think this might look something like how Clean does effects with uniqueness typing: clean.cs.ru.nl/download/html_ 3/3

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10:59 AM · Apr 25, 2022Twitter Web App

Replying to

and

I don't actually see anyone disagreeing with you there, exactly? I could be wrong though. But I know that typeclasses and implicits are both considered coeffects in at least some contexts.

Brendan Zabarauskas

@brendanzab

Apr 25

Ohh I probably misunderstood then (I usually misunderstand stuff eheh 😵‍💫)

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