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den — Aspect-oriented, Context-driven Nix

Write a feature once. Run it on every host, user, and platform you have — and share it with anyone, flake or not.

Den turns Nix configuration into composable features instead of per-host piles of modules. A Den aspect is a plain function: give it context (your hosts and users) and it returns configuration for every Nix class it touches — nixos, darwin, homeManager, hjem, or a class you invent.

# An aspect is a function of context that returns
# configuration for many Nix classes at once.
den.aspects.gaming = { host, user }: {
  nixos       = { pkgs, ... }: { programs.steam.enable = true; };
  darwin      = { pkgs, ... }: { /* ... */ };
  homeManager = { pkgs, ... }: { /* ... */ };

  includes = [ den.aspects.performance ];   # aspects compose
  provides.emulation = { nixos = { /* ... */ }; };  # and nest
};

That one idea — a feature as a function — is what makes the rest possible.

What Den makes possible

• One feature, everywhere, in one place. Stop scattering a single concern across separate nixos, darwin, and homeManager files. An aspect holds all of it together.
• Reuse across hosts, users — and across projects. Share aspects between machines, between people, and between flake and non-flake setups, without forcing everyone to download each other's inputs.
• No mkIf / enable clutter. The shape of the context is the condition — a function that asks for { host, user } simply doesn't run where there's no user. Conditionals disappear.
• Hosts shape their users, users shape their hosts. Cross-entity configuration flows both ways, without coupling them together.
• Add a capability in one line; remove it by deleting that line. Hosts just pick the aspects they want.
• Bring your own classes and whole pipelines. Custom Nix classes, machine fleets, MicroVM guests, terranix, standalone neovim — if you can walk it as data, Den can configure it.

Principles

Four concepts, one job each:

• Entity — what exists: a host, user, or home.
• Aspect — what it does: a feature, spanning Nix classes.
• Policy — how entities relate: topology and routing between them.
• Quirk — structured data aspects share, without coupling.

Feature-first, not host-first. Traditional setups start from hosts and push modules down; Den flips that — features are primary, hosts just select them.

Den embraces your Nix. With or without flakes, flake-parts, or home-manager. Zero dependencies. Every part is optional and replaceable — Den works with the setup you already have, and gets out of the way.

Try it now

# a MicroVM
nix run github:denful/den?dir=templates/microvm#runnable-microvm

# a standalone neovim
nix run github:denful/den?dir=templates/nvf-standalone#my-neovim

# a qemu VM
nix run github:denful/den

Documentation Start here From Zero to Den From Flake to Den Core Principles Go further Custom Nix Classes Homes Integration Batteries Mutual Providers Sharing Namespaces <angle/brackets> Tests as Code Examples Project Motivation Versioning Community Contributing

Templates Pick a starting point and grow from there: default — flake-file + flake-parts + home-manager minimal — flakes, nothing else noflake — npins + lib.evalModules + nix-maid nvf-standalone — neovim apps, no NixOS/Darwin needed microvm — runnable VM + declarative guests flake-parts-modules — third-party perSystem classes example — cross-platform In the wild @vic — fleet-sharing config from Den's author @quasigod — custom namespaces + angle brackets @Gwenodai — path-naming conventions, custom guarded/forwarding classes @adda — multiple hosts, flake-parts + home-manager Den is also running on internal infra at The European Commission. Growing adoption: usage search

What people say

Den takes the Dendritic pattern to a whole new level, and I cannot imagine going back.
— @adda, early Den adopter (after Dendritic flake-parts and Unify)

I'm super impressed with den so far, I'm excited to try out some new patterns that Unify couldn't easily do.
— @quasigod, author of Unify

Massive work you did here!
— @drupol, author of “Flipping the Configuration Matrix”

Thanks for the awesome library and the support for non-flakes… it's positively brilliant! I really hope this gets wider adoption.
— @vczf, at #den-lib:matrix.org

Den is a playground for some very advanced concepts… some of its ideas will play a role in future Nix areas. There are some raw diamonds in Den.
— @Doc-Steve, author of the Dendritic Design Guide

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