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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/ | More Nix: #community:nixos.org | More Haskell: #haskell-space:matrix.org148 Servers

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3 Jul 2025
@teoc:matrix.orgTeo (he/him) I was profiling eval time of nixpkgs recently and I noticed that a lot of time was spent doing hasPrefix when evalling the haskell package set. I think this is caused by the hasPrefix call to check if stuff is part of amazonka and each call of hasPrefix re-checks if the needle is a path lol https://github.com/NixOS/nixpkgs/issues/419216
We could optimise the hasPrefix call, but maybe we should just add the list of amazonka packages to this file rather than traversing the entire haskell package set?
https://github.com/NixOS/nixpkgs/blob/a44903b927ab16b829a76f51f84bca02a7f89a0f/pkgs/development/haskell-modules/configuration-common.nix#L3352
19:19:35
@alexfmpe:matrix.orgalexfmpe

I was profiling eval time of nixpkgs

how does one even do this? I always wondered

20:24:38
@teoc:matrix.orgTeo (he/him)
In reply to @alexfmpe:matrix.org

I was profiling eval time of nixpkgs

how does one even do this? I always wondered

This is what I used https://github.com/NixOS/nix/pull/13220
20:30:51
@alexfmpe:matrix.orgalexfmpeOoooh20:37:45

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