gen-class

gen-class is a pure-Nix, nixpkgs.lib-free class-share mechanism for the pure-gen module system: partition nodes into classes, compute one shared core per class, and let each member reconstruct itself as a delta against that core.

The problem it owns: a fleet of nodes that are mostly identical shouldn’t pay for their similarity twice — once in config size, once in evaluation. gen-class partitions by a caller-supplied key, computes the core once per class, and hands each member back a merge or extend over that core rather than its own independent copy.

It depends only on gen-prelude, using the tier-1 surface (merge = null). No roster member currently builds on gen-class.

Take it alone

let
  genClass = import (fetchGit "https://github.com/sini/gen-class").outPath {
    prelude = genPrelude;
  };
  inherit (genClass) mkClasses mkCore applyCoreMerge invariantUnder gateCore;
in

classes = mkClasses {
  nodes = { blade = { class = "host"; }; cortex = { class = "host"; }; lonely = { class = "solo"; }; };
  keyOf = name: node: node.class;
};
# ⇒ [ { key = "host"; members = [ "blade" "cortex" ]; archetype = "blade"; … }
#      { key = "solo"; members = [ "lonely" ]; … } ]