63 lines
2.8 KiB
Markdown
63 lines
2.8 KiB
Markdown
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---
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title: Transition to NixOS
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author: nek0
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tags: english, administration, programming
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description: My transition to NixOS
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---
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Just recently I made a transition, I was thinking of for quite some time. What
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I'm speaking of is my transition to [NixOS][nixos].
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Two days ago I just installed NixOS on my laptop out of the blue. Now I'm trying
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to get my programming projects to build and work again. On may way to accomplish
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this, I learned a lot about the system and its configuration.
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Overall I must say, that I am quite pleased with the outcome. It is a fairly
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usable system, which holds some cool advantages for me as a Haskell developer
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over my old Debian system setup. Te biggest one is, That I can scrap all cabal
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sandboxes from all my projects and hand the management of the right dependency
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versions over to Nix.
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What I want to share is a small snippet of a nix expression, that lets you
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include local dependencies to your Haskell project's nix shell (like you would
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do with `cabal sandbox add-source`.
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First you need to create a nix shell configuration. There is a handy tool called
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`cabal2nix` which you can install simply by invoking
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`nix-env -iA nixos.cabal2nix`. This is the main work horse for converting any
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Haskell package to nix and it does its job very well.
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To build your Nix shell configuration you call `cabal2nix --shell . > shell.nix`
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from your project directory. This generates the file `shell.nix` for you. Check
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it for any errors. If you want to use a local package, you can add its
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definition to the `shell.nix` file. To get the definition of that package, you
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can again use `cabal2nix`. Simply invoke `cabal2nix file://<path to Package>` and
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copy the resulting block into the `let` block of your existing `shell.nix`
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like this:
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```
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<packageName> = with haskellPackages; callPackage (
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<packageDefinition>
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) {};
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```
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Where `<packageName>` is the variable name for the package inside this Nix
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expression. `<packagDefinition>` is the package definition of the local package
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we just obtained from `cabal2nix`. Then delete the original package name form
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the arguments of the `f` function in the let block of the Nix expression.
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Finally align everything to look nicely, and save the file. To see an example of
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that, you can look at the
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[Nix expression of my latest game project][gamenix].
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To test your setup, just invoke `nix-shell shell.nix` and watch the system build
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a temporary environment for your project and give you a shell to it, if
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everything went well. Now all dependencies of your project, including your local
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ones are installed in this environment, so you only need to invoke
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`cabal build`.
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I hope You find this snippet of my Nix experience helpful, it sure took me some
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time to find out.
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[nixos]: https://nixos.org
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[gamenix]: https://github.com/nek0/tracer/blob/master/shell.nix
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