haskell.nix/modules/component-driver.nix

{ config, pkgs, lib, haskellLib, buildModules, ... }:
let
  builder = haskellLib.weakCallPackage pkgs ../builder {
    inherit haskellLib;
    ghc = config.ghc.package;
    buildGHC = buildModules.config.ghc.package;
    inherit (config) nonReinstallablePkgs hsPkgs;
  };

in

{
  options.nonReinstallablePkgs = lib.mkOption {
    type = lib.types.listOf lib.types.str;
  };
  options.reinstallableLibGhc = lib.mkOption {
    type = lib.types.bool;
    default = false;
    description = "Is lib:ghc reinstallable?";
  };

  # Dependencies (with reinstallable-lib:ghc)
  # 
  #              .--------.           .------------------.
  #              | pretty | < ------- | template-haskell |
  #              '--------'           '------------------'
  #                   v                          |
  #              .---------.     .-------.       |
  #              | deepseq | - > | array |       |     
  #              '---------'     '-------'       v 
  #                    v            v         .-------------.
  # .----------.  .----------.  .------.   .- | ghc-boot-th |
  # | ghc-heap |  | ghc-prim |  | base |< -'  '-------------'
  # '----------'  '----------'  '------'  .----------------.
  #       |          v           |  |     | integer-simple |
  #       |       .-----.        |  '-- > |-------or-------|
  #       '---- > | rts | < -----'        | integer-gmp    |
  #               '-----'                 '----------------'
  #
  # without reinstallable-lib:ghc, this is significantly larger.

  config.nonReinstallablePkgs =
    [ "rts" "ghc-heap" "ghc-prim" "integer-gmp" "integer-simple" "base"
      "deepseq" "array" "ghc-boot" "ghc-boot-th" "pretty" "template-haskell" ]
    ++ lib.optional (!config.reinstallableLibGhc) "ghc";

  options.hsPkgs = lib.mkOption {
    type = lib.types.unspecified;
  };

  config.hsPkgs =
    { inherit (builder) shellFor ghcWithPackages ghcWithHoogle;
      buildPackages = buildModules.config.hsPkgs;
    } //
    lib.mapAttrs
      (name: pkg: if pkg == null then null else builder.build-package pkg)
      (config.packages // lib.genAttrs config.nonReinstallablePkgs (_: null));
}