| 18 Mar 2026 |
 woobilicious | I have a questions about the general architecture of haskellPackages, does hackage have dep cycles? and how do you deal with them when generating the package list? I'm working on a little project that generates a package list from a foreign source, but it has cycles, and I'm kinda clueless on how to break cycles up without just removing all dependencies | 04:49:25 |
 Alex | Cross-compiling GHC 9.6+ shouldn't even eval, because of a throw sterni added after we found that Hadrian broke cross. Is there some difference between haskellPackages.ghc and haskell.compiler.ghc? | 05:40:55 |
| Alex | I have not seen anything that suggests that Cabal supports cycles, but you may want to try it out and see whether the dependency solver likes it.
But regardless of what Haskell is doing, I think you would be better off looking at how existing tools that work with the foreign source handle those cycles, since doing the same thing will give your tooling the best chance at doing no worse with weird scenarios you've yet to consider. | 05:46:36 |
 alexfmpe | Not for native | 05:46:36 |
| alexfmpe | In reply to @alexfmpe:matrix.org
Not for native One is cross compiler ghc, the other is cross compiled ghc | 05:47:31 |
| Alex | Right, so haskellPackages.ghc is the same as buildPackages.ghc? | 05:48:13 |
| alexfmpe | In reply to @woobilicious:matrix.org
I have a questions about the general architecture of haskellPackages, does hackage have dep cycles? and how do you deal with them when generating the package list? I'm working on a little project that generates a package list from a foreign source, but it has cycles, and I'm kinda clueless on how to break cycles up without just removing all dependencies You can have package cycles, just not component cycles. For packages A,B it's valid to have libA <- libB <- testA | 05:50:04 |
| alexfmpe | In cabal packages that is | 05:50:24 |
| alexfmpe | haskellPackages in particular is 'wrong' in that it generates one derivation per package, not per component | 05:50:54 |
| alexfmpe | So we have to manually break cycles for a bunch of test packages with dontCheck | 05:51:15 |
| alexfmpe | Search for 'cycle' or so in configuration-common.nix for examples | 05:51:40 |
| alexfmpe | `nix-build --show-trace` can help find specific cycles since it shows the call stack | 05:52:47 |
| alexfmpe | 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 | I'd expect haskellPackages.foo to always have the same host platform | 05:53:46 |
| alexfmpe | * I'd expect pkgsCross.foo.haskellPackages.bar to always have 'foo' as same host platform for all 'bar' | 05:54:28 |
| alexfmpe | But bar=ghc acts special | 05:54:53 |
| alexfmpe | 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 | 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 | Ahh 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 |
|  cookies joined the room. | 11:01:33 |
 linj | Just found a new nix interpreter implemented from scratch in Haskell https://github.com/Novavero-AI/nova-nix. Any comments? | 11:05:00 |
 chreekat | Big if true | 11:20:30 |
| alexfmpe | Author has been announcing it in couple rooms | 11:29:16 |
| alexfmpe | Seems like AI slop | 11:29:25 |
| alexfmpe | > Hand-rolled recursive descent parser for the full Nix expression language. 13 precedence levels, 18 AST constructors, | 11:29:30 |
| alexfmpe | "Now with 30% more precedence levels. Buy 3, take 4" | 11:30:37 |
| alexfmpe | * "Now with 30% more precedence levels. Buy 3, get 4" | 11:31:20 |
 magic_rb | It is AI slop | 11:32:48 |
| magic_rb | Its fully slop-coded, top to bottom | 11:33:02 |
| woobilicious | Nothing screams "Haskell" coding like using a probalitistic LLM... | 11:33:04 |
