pkgs.nix

{ pkgs ? import <nixpkgs> {}
}:
let
  overrideWith = override: default:
   let
     try = builtins.tryEval (builtins.findFile builtins.nixPath override);
   in if try.success then
     builtins.trace "using search host <${override}>" try.value
   else
     default;
in
let
  # all packages from hackage as nix expressions
  hackage = import (overrideWith "hackage"
                    (pkgs.fetchFromGitHub { owner  = "angerman";
                                            repo   = "hackage.nix";
                                            rev    = "cd21bbd8d8c961793a562d557f9244bd90236961";
                                            sha256 = "03v2fw63xi3l2a7cvz1n9rl0nq9hk65g1k20w8i0gkky7a6cq9yd";
                                            name   = "hackage-exprs-source"; }))
                   ;
  # a different haskell infrastructure
  haskell = import (overrideWith "haskell"
                    (pkgs.fetchFromGitHub { owner  = "angerman";
                                            repo   = "haskell.nix";
                                            rev    = "28a9c6f3528daa57d506d134e137fb617a947985";
                                            sha256 = "0qv0vb5q96sdfi8pwwrswfhcw3ay0qh91a8l2g6bz46q7zmgp75m";
                                            name   = "haskell-lib-source"; }))
                   hackage;

  # the set of all stackage snapshots
  stackage = import (overrideWith "stackage"
                     (pkgs.fetchFromGitHub { owner  = "angerman";
                                             repo   = "stackage.nix";
                                             rev    = "014445d63dcf374f30435e5859e463d2c29b5c4e";
                                             sha256 = "1hma4clx8lslah8l4xpglshbbd42v1vraafhb03ci92dyjscnkdq";
                                             name   = "stackage-snapshot-source"; }))
                   ;

  # our packages
  stack-pkgs = import ./.stack-pkgs.nix;

  # Build the packageset with module support.
  # We can essentially override anything in the modules
  # section.
  #
  #  packages.cbors.patches = [ ./one.patch ];
  #  packages.cbors.flags.optimize-gmp = false;
  #
  pkgSet = haskell.mkNewPkgSet {
    inherit pkgs;
    pkg-def = stackage.${stack-pkgs.resolver};
    modules = [
      stack-pkgs.module
      ({ config, lib, ... }: {
        packages = { hsc2hs = config.hackage.configs.hsc2hs."0.68.3".revisions.default; };
      })
    ];
  };

  packages = pkgSet.config.hsPkgs // { _config = pkgSet.config; };

in packages