{
  description = "Advent of Code";
  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";

  outputs =
    { self, nixpkgs }:
    let
      systems = [ "x86_64-linux" ];
      forSystems = function: nixpkgs.lib.genAttrs systems (system: function (import nixpkgs { inherit system; }));
    in
    {
      formatter = forSystems (pkgs: pkgs.nixfmt-tree.override { settings.formatter.nixfmt.options = [ "-w 120" ]; });
      devShells = forSystems (pkgs: {
        default = self.devShells.${pkgs.system}."2015";
        "2015" = pkgs.mkShellNoCC {
          buildInputs = with pkgs; [
            (with beamMinimalPackages; [
              erlang
              erlang-language-platform
              erlfmt
            ])
          ];
        };
      });
    };
}