Haskell in Nixpkgs/NixOS - Public Room Timeline

	Haskell in Nixpkgs/NixOS	710 Members
	For discussions and questions about Haskell with Nix, cabal2nix and haskellPackages in nixpkgs \| Current Docs: https://haskell4nix.readthedocs.io/	140 Servers

Load older messages

Sender	Message	Time
24 Jul 2025
maralorn	@keetonbrewster:matrix.org haskell4nix.readthedocs.io is outdated. It's uptodate version is the nixpkgs manual Haskell section.	06:07:02
maralorn	In reply to @bglgwyng:matrix.org Hello! I'm trying to build a `nixpkgs.haskellPackages` from an arbitrary stackage snapshot. I just found `regenerate-hackage-packages.sh` in nixpkgs and also `hackage2nix` in `cabal2nix`. Is `hackage2nix` enough for my purpose? I don't fully understand how two tools differ. Huh, I don't think we expect downstream users of hackage2nix. I fear that you won't get very far. But if you really want do this the easiest way would probably be to look at the update stackage script in nixpkgs modify it to not use the newest but your desired snapshot, run it and then run the regenerate script. You can think of the regenerate script as running hackage2nix with all correct configuration for nixpkgs in place. Running hackage2nix without it would probably require duplicating parts of it.	06:15:22
bglgwyng	What if I want to avoid making my own version of nixpkgs? I prefer more local apporach such as generating .nix file that can be used to replace `nixpkgs.haskellPackage`. Can I do the same thing using 'regenerate-hackage-packages'?	06:45:03
maralorn	It's not meant to be used that way, no. But maybe you can take it as an inspiration. Maybe you want to have a look at stacklock2nix it might be closer to your needs.	06:47:25
bglgwyng	Do you mean https://github.com/cdepillabout/stacklock2nix this repo?	06:59:05
maralorn	In reply to @keetonbrewster:matrix.org Hi everyone, is there a Haskell specific Nix beginner guide out there? That reminds me. I actually did a talk about that at zurihac. It might be helpful: https://m.youtube.com/watch?v=xOjKAatxD_g&list=PLOvRW_utVPVlFEXuyaIVILO1t_48e4Ai2&index=9&pp=iAQB	06:59:34
bglgwyng	Indeed, I tried an approach using 'plan.json', cabal dry run generates plan.json and nix fetches the source code, however it caused too frequent rebuild of existing library. So I'm looking for a way to pre-bake package set.	07:01:47
maralorn	In reply to @maralorn:maralorn.de That reminds me. I actually did a talk about that at zurihac. It might be helpful: https://m.youtube.com/watch?v=xOjKAatxD_g&list=PLOvRW_utVPVlFEXuyaIVILO1t_48e4Ai2&index=9&pp=iAQB It's sadly not super structured or dense, but I actually think we covered a lot of useful information.	07:04:59
MangoIV	Hey guys. what is the current status of static linking with ghc? Is ghc 9.4.8 still the only supported compiler?	08:51:07
sterni (he/him)	all GHCs work, but TemplateHaskell isn't supported for >= 9.6	10:02:35
Teo (he/him)	out of interest, is there a ticket that tracks this?	10:38:26
Teo (he/him)	found it: https://github.com/NixOS/nixpkgs/issues/275304	10:38:45
MangoIV	teo (they/he): I will try out with your patch and report back. thank you!	12:44:14
25 Jul 2025
iqubic (she/her)	Hmm... I think I might be doing something wrong. So I have this bare-bones starter project of mine: https://github.com/IQubic/mandelbrot	00:10:59
iqubic (she/her)	And entering the `nix-shell` works. But then attempting to run `cabal repl` fails with this: `Resolving dependencies... Error: [Cabal-7107] Could not resolve dependencies: [__0] next goal: mandelbrot (user goal) [__0] rejecting: mandelbrot-0.1.0.0 (conflict: requires GHC2024 which is not supported) [__0] fail (backjumping, conflict set: mandelbrot) After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: mandelbrot`	00:12:02
iqubic (she/her)	Does `cabal` not support GHC2024 yet?	00:12:13
@le:4d2.org	In reply to @mequbic:matrix.org Does `cabal` not support GHC2024 yet? `GHC2024` is only supported if you have at least version 9.10 of ghc, according to a warning when initialising projects with cabal. nix installs 9.8.4 by default though. When I explicitly install a newer version using `nix-shell -p cabal-install haskell.compiler.ghc9122`, which installs ghc version 9.12.2, it works. (Well "works": I get a different error, which could be resolved with changing `base ^>= 4.19.2.0` to `base >= 4.19.2.0` in mandelbrot.cabal, but that's a different topic)	05:49:07
@le:4d2.org	In reply to @le:4d2.org `GHC2024` is only supported if you have at least version 9.10 of ghc, according to a warning when initialising projects with cabal. nix installs 9.8.4 by default though. When I explicitly install a newer version using `nix-shell -p cabal-install haskell.compiler.ghc9122`, which installs ghc version 9.12.2, it works. (Well "works": I get a different error, which could be resolved with changing `base ^>= 4.19.2.0` to `base >= 4.19.2.0` in mandelbrot.cabal, but that's a different topic) To have all of this in your shell.nix, change `myPkg = pkgs.haskellPackages.callCabal2nix "mandelbrot" src {};` to `myPkg = pkgs.haskell.packages.ghc9122.callCabal2nix "mandelbrot" src {};`	05:55:45
aidalgol	I need some help understanding this build failure from PR 424162.	06:12:38
Alex	In reply to @aidalgol:matrix.org I need some help understanding this build failure from PR 424162. It looks like 8 test failures caused by an attempt to run a missing or not found program. Check the source code to see what it's trying to execute and try to add it to the test dependencies. Since these appear to be doctests, they might be failing because the build doesn't have the necessary tools to run doctests available.	08:22:40
MangoIV	teo (they/he): which hadrian needs your patch? The boot compiler or the actual compiler? (the patch only applies to ghc 9.10 but not to 9.12...)	10:59:43
Teo (he/him)	should be actual compiler, I can rebase my patch for ghc-9.12	13:03:01
MangoIV	In reply to @teoc:matrix.org should be actual compiler, I can rebase my patch for ghc-9.12 I fear then it won’t apply to earlier versions. Building with ghc 9.10 but can only continue when my laptop is idle because while it’s building GHCs it’s unusable	13:04:03
MangoIV	😌	13:04:07
MangoIV	In reply to @mangoiv.:matrix.org I fear then it won’t apply to earlier versions. Building with ghc 9.10 but can only continue when my laptop is idle because while it’s building GHCs it’s unusable Okay so applying the patch didn’t do anything, still doesn’t build, with the same error, cc teo (they/he)	14:55:24
Teo (he/him)	thanks for looking! I'll look into this more at some point soon	14:57:21
maralorn	I would like to conceptually grok how cross-compilation works in nixpkgs. My understanding is that "buildPackages" is meant to contain build outputs which are meant to be used on the build system, and they can be used to produce build outputs meant to be run on the target system. What I am wondering is this: When we want to cross-compile to wasm then we need to take a ghc which has wasm als compile target. But that ghc I think runs on the build system and thus belongs to buildPackages right? But when we replace the ghc in buildPackages with a wasm-targeting one, then those haskellBuildPackages are kinda broken because they should be compiled for and usable on the build plattform, so "replacing" the ghc is kinda wrong is it? I am asking because I am trying to understand this line: https://github.com/ners/nix-wasm/blob/795efcfb8f8e98d7084be5da354cbe850f5834da/flake.nix#L48 Which works, but it does e.g. lead to ghcWithPackages not working for wasm cross.	23:24:27
maralorn	But of course the error might be somewhere else. This has all so many moving parts and I am trying to learn the concepts.	23:25:19
26 Jul 2025
emily	`buildPackages` is `pkgsBuildBuild`	01:56:32
emily	packages that run on `buildPlatform` and target (when they are compilers) `buildPlatform`	01:56:44

Show newer messages

Back to Room ListRoom Version: 6