{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { self, nixpkgs, ... }@inputs:
    let
      supportedSystems = [
        "aarch64-darwin" "aarch64-linux"
        "x86_64-darwin" "x86_64-linux"
      ];

      each-system = f: nixpkgs.lib.genAttrs supportedSystems (system: f rec {
	pkgs = import nixpkgs {
          inherit system;
        };
	inherit (pkgs) lib;
        inherit system;
      });
    in {
      # Exposed as a REPL convenience.
      _pkgs = each-system ({ pkgs, ... }: pkgs);

      packages = each-system ({ pkgs, ... }: {
        # default = pkgs.callPackage ./default.nix {};
      });

      devShells = each-system ({ pkgs, system, ... }: {
	default = pkgs.haskellPackages.developPackage {
          root = ./.;
          modifier = drv:
            pkgs.haskell.lib.addBuildTools
              drv
              (with pkgs; [
                cabal-install
                qbe
                gcc
              ]);
	};
      });
    };
}