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Haskell in Nixpkgs/NixOS

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For discussions and questions about Haskell with Nix, cabal2nix and haskellPackages in nixpkgs | Current Docs: https://haskell4nix.readthedocs.io/145 Servers

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18 Mar 2026
@alexfmpe:matrix.orgalexfmpehaskellPackages in particular is 'wrong' in that it generates one derivation per package, not per component05:50:54
@alexfmpe:matrix.orgalexfmpeSo we have to manually break cycles for a bunch of test packages with dontCheck05:51:15
@alexfmpe:matrix.orgalexfmpeSearch for 'cycle' or so in configuration-common.nix for examples05:51:40
@alexfmpe:matrix.orgalexfmpe`nix-build --show-trace` can help find specific cycles since it shows the call stack05:52:47
@alexfmpe:matrix.orgalexfmpe
In reply to @alex:tunstall.xyz
Right, so haskellPackages.ghc is the same as buildPackages.ghc?
I think so, though it seems completely backwards to me
05:53:21
@alexfmpe:matrix.orgalexfmpeI'd expect haskellPackages.foo to always have the same host platform05:53:46
@alexfmpe:matrix.orgalexfmpe* I'd expect pkgsCross.foo.haskellPackages.bar to always have 'foo' as same host platform for all 'bar'05:54:28
@alexfmpe:matrix.orgalexfmpeBut bar=ghc acts special05:54:53
@alexfmpe:matrix.orgalexfmpe
In reply to @alexfmpe:matrix.org
haskellPackages in particular is 'wrong' in that it generates one derivation per package, not per component
Or rather, cabal2nix is wrong, and haskellPackages is based on throwing cabal2nix at hackage
05:55:40
@alex:tunstall.xyzAlex I believe this is due to how ghc is threaded through haskellPackages. So that mkDerivation can find it, it is bound to ghc, but this only works well for native.
It also has weird consequences when you try using other compilers, where you can e.g. end up with haskellPackages.ghc being MicroHs.
06:08:19
@woobilicious:matrix.orgwoobiliciousAhh thanks for the feedback, I don't think manual intervention is practical here, the more I think about it, the more it might be easier to just build dirivation per package, with no "real" dependencies, and then de-duplicate strings some way to prevent infinite loops.07:45:37
@co0o0okies:matrix.orgcookies joined the room.11:01:33
@me:linj.techlinjJust found a new nix interpreter implemented from scratch in Haskell https://github.com/Novavero-AI/nova-nix. Any comments?11:05:00
@b:chreekat.netchreekatBig if true11:20:30
@alexfmpe:matrix.orgalexfmpeAuthor has been announcing it in couple rooms11:29:16
@alexfmpe:matrix.orgalexfmpeSeems like AI slop11:29:25
@alexfmpe:matrix.orgalexfmpe> Hand-rolled recursive descent parser for the full Nix expression language. 13 precedence levels, 18 AST constructors,11:29:30
@alexfmpe:matrix.orgalexfmpe"Now with 30% more precedence levels. Buy 3, take 4"11:30:37
@alexfmpe:matrix.orgalexfmpe* "Now with 30% more precedence levels. Buy 3, get 4"11:31:20
@magic_rb:matrix.redalder.orgmagic_rbIt is AI slop11:32:48
@magic_rb:matrix.redalder.orgmagic_rbIts fully slop-coded, top to bottom11:33:02
@woobilicious:matrix.orgwoobiliciousNothing screams "Haskell" coding like using a probalitistic LLM...11:33:04
@magic_rb:matrix.redalder.orgmagic_rbIndeed, i have interest in reviewing or using slop-coded code in my free time. The code produced is always subtly wrong and weirdly organized, I've better things to do with my life11:34:57
@magic_rb:matrix.redalder.orgmagic_rb * 11:35:09
@morj:morj.menMorj
Nothing screams "Haskell" coding like using a probalitistic LLM...
If it compiles it works, right
12:00:07
@morj:morj.menMorjI remember in chat they were going to use it to distribute their games for windows. If it works for that, that would be cool if horrifying12:09:11
@morj:morj.menMorj* I remember in chat they were going to use the new nix impl to distribute their games for windows. If it works for that, that would be cool if horrifying12:09:20
@mangoiv.:matrix.orgMangoIV

sternimaralorn I would like to invite you to a discussion on coordination of downstream release testing https://gitlab.haskell.org/ghc/ghc/-/issues/27061

I hear that you already had this discussion last ZuriHac with teo (they/he) since the main effort for downstream testing is currently head.hackage but I think we could all benefit for a more coordinated effort across distributors and the GHC maintainers.

Thanks in advance.

12:48:25
@magic_rb:matrix.redalder.orgmagic_rbLets give vibe-coded "programs" root access, what can go wrong12:52:04
@eveeifyeve:matrix.orgeveeifyeveEverything can go wrong.13:18:29

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