Configure Aspects

Static Host Config

Set NixOS/Darwin/HM options directly on an aspect:

den.aspects.igloo = {
  nixos = { pkgs, ... }: {
    environment.systemPackages = [ pkgs.hello ];
  };
  homeManager.programs.vim.enable = true;
};

Include Other Aspects

Compose aspects with includes:

den.aspects.tux = {
  includes = [
    den.provides.primary-user
    (den.provides.user-shell "fish")
    den.aspects.base-tools
  ];
};

Context-Aware Includes

Functions in includes receive context and only activate when they match:

den.aspects.igloo.includes = [
  den.aspects.video
];

den.aspects.video = den.lib.take.exactly ({ host, user }: {
  nixos.users.users.${user.userName}.extraGroups = [ "video" ];
});

This runs once per user on the host. A function taking { host } only runs at the host level.

Host Configures Its Users

A host aspect can contribute to user-level settings:

den.aspects.igloo = {
  nixos.networking.hostName = "igloo";
  homeManager.programs.direnv.enable = true;
};

The homeManager config from a host aspect becomes the default for all users on that host.

User Configures Its Host

A user aspect can contribute to the host’s NixOS/Darwin config:

den.aspects.tux = {
  nixos.users.users.tux.description = "cute penguin";
  homeManager = { pkgs, ... }: {
    home.packages = [ pkgs.htop ];
  };
};

The nixos config from a user aspect is applied to every host the user appears on.

Conditional Config by Host/User

Use aspect arguments to specialize:

den.aspects.igloo.includes = [ den.aspects.tuxGit ];

den.aspects.tuxGit = den.lib.take.exactly ({ host, user }:
  if user.userName == "tux"
  then { homeManager.programs.git.enable = true; }
  else { }
);

Global Defaults

Use den.default for settings that apply everywhere:

den.default = {
  nixos.system.stateVersion = "25.11";
  homeManager.home.stateVersion = "25.11";
  includes = [
    den.provides.define-user
    (den.lib.take.exactly ({ host }: {
      nixos.networking.hostName = host.hostName;
    }))
  ];
};

Use den.lib.take.exactly to restrict a function to a specific context shape (e.g., only at host level, not user level).

Compose Named Sub-aspects

Organize aspects hierarchically using provides:

den.aspects.gaming = {
  nixos.programs.steam.enable = true;
  provides.emulation.nixos.programs.retroarch.enable = true;
  provides.streaming = {
    nixos.services.sunshine.enable = true;
    homeManager.programs.moonlight.enable = true;
  };
};

den.aspects.my-pc.includes = [
  den.aspects.gaming
  den.aspects.gaming._.emulation
];

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