| 21 Jul 2025 |
 magic_rb | but not in cabal.project | 10:08:29 |
| magic_rb | and when i was profiling this back then, most of the slowness was in my code because of my custom monad transformer | 10:09:04 |
| magic_rb | im gonna remove the inline pragmas, those didnt seem to be enough last time i tried, which is why i enabled -fexpose-all-unfoldings | 10:10:29 |
| magic_rb | but ill try to removing them again and see if some difference shows up | 10:10:42 |
| magic_rb | okay, same result, im completely confused and have no clue what is going on | 10:19:40 |
 maralorn | I mean, is it a different ghc version than when you added those flags? | 10:20:28 |
| magic_rb | i think i found it | 10:21:36 |
| magic_rb | there was a problem between the keyboard and my chair | 10:21:50 |
| magic_rb | the monkey forgot to use a variable he declared | 10:21:57 |
 Alex | In reply to @magic_rb:matrix.redalder.org
im benchmarking a thing i wrote and im making a nix package out of a cabal file using cabal2nix, however if i change the source cabal file and remove -fllvm, -O2, or -fexpose-all-unfoldings the performance measurements dont seem to change even though im positive they should. Is nixpkgs overwriting my flags somehow? If you're using a profiling build, beware of automatic cost centres (IIRC enabled by default in cabal). | 10:37:54 |
| magic_rb | In reply to @alex:tunstall.xyz
If you're using a profiling build, beware of automatic cost centres (IIRC enabled by default in cabal). Nope, i know about those | 10:49:29 |
| 22 Jul 2025 |
| maralorn | Does anyone here grok/has used the useIntermediates stuff? I have one question: Can it reuse the intermediates of a previous build even when that build had other dependency hashes on the nix side? The argument was that cabal-install does not always have to recompile your project when you modify your nix shell. And the reusing is probably happening based on some cabal level hashing? | 15:02:25 |
 sterni | Well development shell is out anyways since that's Setup.hs which cabal-install won't be able to reuse in any shape or form I think | 18:57:16 |
| maralorn | Are you sure? Maybe the components are similar enough? I mean they have been compiled with the same ghc. Isn’t it basically a dir with .hie and object files in both cases? | 20:55:26 |
| 24 Jul 2025 |
|  Keeton Brewster joined the room. | 00:12:02 |
| Keeton Brewster | Hi everyone, is there a Haskell specific Nix beginner guide out there? | 00:14:32 |
 keypusher | I think it's a bit fragmented depending on your needs / approach as can be seen in this thread https://www.reddit.com/r/haskell/comments/1cqfboq/latest_guidance_on_using_haskell_with_nix/ . Some years ago my searches often ended up here https://haskell4nix.readthedocs.io/ | 00:45:35 |
| keypusher | I would suggest you start wo using these evolved approaches and try to have as few layers on top of "vanilla"/"flakes" nix | 01:09:48 |
| Keeton Brewster | Thank you! | 01:51:31 |
| Keeton Brewster | There seems to be a thousand ways to do it which is confusing for a newbie | 01:56:06 |
|  bglgwyng joined the room. | 05:41:12 |
| bglgwyng | 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. | 05:54:08 |
| 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 |
