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content/posts/2022-06-09-nix-registry.md

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+---
+title: Nix registry
+date: 2022-06-09
+summary: A quick note about a small trick I implemented in my NixOS configurations.
+---
+
+*A quick note about a small trick I implemented in my NixOS configurations.*
+
+I started using [flakes](https://nixos.wiki/wiki/Flakes) a few months ago, and
+quickly began using them daily. Notably, I moved the NixOS configurations for
+all my machines in a single flake. But there has been a caveat in my workflow:
+using flakes for almost every project I compile made me end up with lots of
+different versions of Nixpkgs lying around. It became very annoying when
+compiling LaTeX documents: two LaTeX projects created a few hours apart could be
+using different versions of Nixpkgs, and thus different versions of TexLive.
+Downloading a few gigabytes every time I set up a LaTeX project was not very
+optimal. I began copying lock files between projects, but it only made me more
+frustrated.
+
+Nix uses a
+[registry](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-registry.html)
+to resolve flake URIs. For instance, it resolves the special flake URI "nixpkgs"
+to "github:nixpkgs/nixos-unstable". We can configure the registry system-wide to
+map "nixpkgs" to a specific revision of the repository. Using the "rev"
+attribute of a flake input, we can even point it to the same revision as the one
+used by our flake-defined configuration.
+
+The module to configure the Nix registry looks like this:
+
+```Nix
+{
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs";
+  };
+
+  outputs = { self, nixpkgs, }: {
+
+    nixosModule = {
+      nix.registry.nixpkgs = {
+        from = {
+          type = "indirect";
+          id = "nixpkgs";
+        };
+        to = {
+          type = "github";
+          owner = "nixos";
+          repo = "nixpkgs";
+          inherit (nixpkgs) rev;
+        };
+      };
+    };
+
+  };
+
+}
+```
+
+The Nix registry can also be configured at the user level, and this module can
+be used as a home-manager module.

content/posts/2023-11-07-flake-template.md

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+---
+title: A Nix Flake Template
+date: 2023-11-07
+summary: I wrote a Nix ❄ Template
+---
+
+I learned to use Nix when flakes were already ubiquitous, and I realized
+recently that by learning Nix through flakes I adopted some bad coding habits. I
+don't think I am the only one that tends to overload their `flake.nix` (the
+flake of [Nix](http://github.com/nixos/nix/blob/master/flake.nix) is over 700
+lines long at the time of writing). Paradoxically, this makes flake expressions
+less discoverable, or at least less flexible. For instance, how do you override
+the package expression defined in a `flake.nix` to try and build it for a system
+that is not explicitly exposed by this flake? In many cases, you can't! Just
+fork the repository and patch the Nix code!
+
+A friend recently told me about [Niv](https://github.com/nmattia/niv), and I
+really liked the way I naturally set up my projects when trying it out, namely
+in a more modular fashion than before. Even if I decided to stick with flakes, I will
+be trying to write them in a more modular way going forward.
+
+If you are interested, I wrote a
+[template](https://github.com/pnmadelaine/flake) that I will be using for medium
+to large projects in the future (it may be a bit ridiculous for smaller flakes).
+For a non-trivial example, you can take a look at
+[Typhon](https://github.com/typhon-ci/typhon) (more on that soon, hopefully!).