Core Principles

The Two Pillars

Den is built on two intertwined principles that together enable a new way of thinking about Nix configurations:

graph LR
  subgraph "1. Context Transformation"
    CT["Declarative context shapes"] --> TP["Pipeline of context transformations"]
  end
  subgraph "2. Context-Aware Aspects"
    CA["Functions of context"] --> CP["Provide Conditional Configs"]
  end
  CT -.-> CA
  CA -.-> CT

1. Context Transformation

Traditional Nix setups wire modules directly: this NixOS module imports that file, this Home-Manager config hardcodes that username.

Den replaces this with a declarative pipeline. You declare entities (hosts, users, homes) and context types (shapes holding them). Den transforms these through a graph of context stages, each producing richer or conditioned data.

The key insight: the flow of data is declared separately from the configurations it produces.

2. Context-Aware Aspects

Aspects are not just bundles of configs — they are functions that inspect context to decide what to produce. A function taking { host, user } naturally adapts to every host-user combination. A function requiring { other } is not used.

The key insight: the shape of the function arguments determines when configs are produced, without explicit conditionals.

Why This Matters

Re-usability

An aspect like define-user works on NixOS, Darwin, and standalone Home-Manager — not because it checks the platform, but because it produces configs for multiple classes and Den picks the relevant class module according to the configuration domain:

{ host, user, ... }: {
  nixos.users.users.${user.userName}.isNormalUser = true;
  darwin.users.users.${user.userName}.home = "/Users/${user.userName}";
  homeManager.home.username = user.userName;
}

Composability

Aspects compose through includes — a directed dependency graph. The parametric functor ensures context flows through the entire graph:

graph TD
  D["den.my-laptop"] --> WS["workspace"]
  D --> DU["common-users-env"]
  WS --> VPN["vpn"]
  WS --> DEV["dev-tools"]
  U["den.aspects.vic"] --> PU["primary-user"]
  U --> SH["user-shell 'fish'"]

Separation of Concerns

Each Dendritic file is focused on a single responsability. Configuring it across all different domains. Configurations are parametrized by data outside of their module config.

The Result

A system where:

• Declaring entities is separate from configuring them
• Configurations are separate from when they apply
• Aspects compose without knowing each other’s details
• Context flows declaratively through a typed pipeline