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Lix Development

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(Technical) development of Lix, the package manager, a Nix implementation. Please be mindful of ongoing technical conversations in this channel.135 Servers

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11 Nov 2025
@delroth:delroth.netdelrothif you are having issues accessing git.lix.systems over v4 (timeouts) lmk11:16:51
@shine:proqqul.netTaeer Bar-Yam

that's a historical accident and one that I fail to convince myself you can rely on in good faith to write production Nix code

Clarification: "that" here is referring to functions comparing non-equal when they are, in fact, equal?

I would be in favor of making that comparison true even if it was not before.

I think this is fine as long as it's a one-way ratchet. My concern is that we will make something compare equal (that is equal), people start depending on that behaviour, and then later change the structure again in a way that makes those compare non-equal. This is why I was proposing we mark this feature as unstable (maybe unstable isn't the right word, because there's no intention to make it stable in the future)

I think we're somewhat lucky in that the state of affairs we need to be backward-compatible with at the moment (pointer equality in CppNix), is very weak (in the sense that very few things compare equal), so it's easy to maintain backward compatibility with it. If we add more things to the relation, it will become harder to change things in ways that maintain backward compatibility. (where by backward compatibility i mean things that used to compare equal continue to compare equal, but not necessarily the inverse)

I am quite against reverting the whole thing

Clarification: by "the whole thing" you're referring to pointer equality?

expose builtins to construct your own flavor of pointer equality to pass to the scoped import to make broken code run again.

Wouldn't what we can expose be super dependent on implementation details?

14:47:10
@raitobezarius:matrix.orgraitobezarius

Clarification: "that" here is referring to functions comparing non-equal when they are, in fact, equal?

"that" refers to any (pointer) equality that evaluated to false when it should have evaluated to true

15:02:55
@raitobezarius:matrix.orgraitobezarius

I think this is fine as long as it's a one-way ratchet. My concern is that we will make something compare equal (that is equal), people start depending on that behaviour, and then later change the structure again in a way that makes those compare non-equal. This is why I was proposing we mark this feature as unstable (maybe unstable isn't the right word, because there's no intention to make it stable in the future)

yeah this sounds like a permanent xp feature

15:03:24
@raitobezarius:matrix.orgraitobezarius

Clarification: by "the whole thing" you're referring to pointer equality?

i'm referring to the maximal sharing work that was done in Lix

15:04:01
@raitobezarius:matrix.orgraitobezarius *

Clarification: by "the whole thing" you're referring to pointer equality?

i'm referring to the maximal (well it's not exactly maximal) sharing work that was done in Lix

15:04:09
@raitobezarius:matrix.orgraitobezarius

Wouldn't what we can expose be super dependent on implementation details?

idk, we can formalize what is pointer equality

15:04:28
@raitobezarius:matrix.orgraitobezariuswe can offer recursive pointer equality, one-off pointer equality, sharing pointer equality, etc.15:04:45
@raitobezarius:matrix.orgraitobezariusWe could also consider making functions comparable15:04:53
@raitobezarius:matrix.orgraitobezarius like $$\alpha$$-equivalence of lambda terms via bisimilarity or idk 15:05:10
@raitobezarius:matrix.orgraitobezarius * like $$\alpha$$-equivalence of lambda terms via bisimulation or idk 15:05:16
@kfears:matrix.orgKFears (burnt out)I think there are many various ways to compare functions that can be useful in different contexts (string comparison, signature comparison, evaluated comparison, pointer comparison), and it might be weird to prefer one over another. Maybe having no "default" comparison but having options to choose from would be best?17:42:38
@raitobezarius:matrix.orgraitobezarius I did https://wiki.lix.systems/books/lix-contributors/page/pointer-equality to expand my thoughts and current understanding 18:07:04
@raitobezarius:matrix.orgraitobezariusI feel like there's two directions from the current local optimum (?) we are, kicking function equality out of the language, figuring how far we are willing to go to repair lack of structural equality for complicated types like functions18:08:20
@raitobezarius:matrix.orgraitobezarius pennae are more in favor of kicking the thing out because there's no practical value to offer a real == for fns 18:08:47
@raitobezarius:matrix.orgraitobezarius i was in favor of making == for functions complete, i.e. recursive ptr equality + semantic check if ptr equality fails 18:09:07
@raitobezarius:matrix.orgraitobezariusbut i sat down and looked how to do it and noped out18:09:17
@xokdvium:matrix.orgSergei Zimmerman (xokdvium) Quip: nix eval "github:nixos/nixpkgs?rev=a999c1cc0c9eb2095729d5aa03e0d8f7ed256780#pkgsCross.gnu64.bitwarden" --no-eval-cache. This wasn’t a regression and doesn’t evaluate under any nix impl. It was the case where nixpkgs machinery thought that it was doing this in cross and thus failed to eval 18:09:42
@raitobezarius:matrix.orgraitobezariusaaaaaaaaah thanks18:09:54
@raitobezarius:matrix.orgraitobezariuswell the other thing was a regression no?18:10:00
@raitobezarius:matrix.orgraitobezarius i know something that evals only on lix head now 18:10:06
@xokdvium:matrix.orgSergei Zimmerman (xokdvium)
In reply to @raitobezarius:matrix.org
well the other thing was a regression no?
Yeah, some old nixos config from flake-regressions
18:10:40
@raitobezarius:matrix.orgraitobezariusyeah, ok it was indeed from flake-reg18:11:32
@raitobezarius:matrix.orgraitobezarius (i imagined that and therefore i did yesterday: https://git.lix.systems/raito/flake-regressions) 18:11:48
@raitobezarius:matrix.orgraitobezariusThis is going into the pennae's direction from my understanding18:12:31
@raitobezarius:matrix.orgraitobezarius People can decide to have a cmp fn function they use in their local context 18:12:44
@kfears:matrix.orgKFears (burnt out)
In reply to @raitobezarius:matrix.org
This is going into the pennae's direction from my understanding
Yeah
18:14:11
@shine:proqqul.netTaeer Bar-Yam

no practical value to offer a real == for fns

except backward compatibility, right?

18:29:12
@winter:catgirl.cloudWinter @raitobezarius do you remember the context to https://git.lix.systems/lix-project/nixos-module/commit/a50986cfc71dfd60acaf55d31d1e3e05e9bdde6d ? 18:49:04
@winter:catgirl.cloudWinter working on a semi-related change for nixpkgs and want to know if making nixos-option use config.nix.package would be bad/cause a bunch of rebuilds tm 18:49:29

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