{
  description = "Unison";
  nixConfig = {
    extra-substituters = [ "https://unison.cachix.org" ];
    extra-trusted-public-keys = [
      "unison.cachix.org-1:i1DUFkisRPVOyLp/vblDsbsObmyCviq/zs6eRuzth3k="
    ];
  };
  inputs = {
    haskellNix.url = "github:input-output-hk/haskell.nix";
    nixpkgs.follows = "haskellNix/nixpkgs-unstable";
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
    flake-compat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };
  };
  outputs = { self, nixpkgs, flake-utils, haskellNix, flake-compat, nixpkgs-unstable }:
    flake-utils.lib.eachSystem [
      "x86_64-linux"
      "x86_64-darwin"
      "aarch64-darwin"
    ]
      (system:
        let
          versions = {
            ghc = "928";
            ormolu = "0.5.2.0";
            hls = "2.4.0.0";
            stack = "2.13.1";
            hpack = "0.35.2";
          };
          overlays = [
            haskellNix.overlay
            (import ./nix/haskell-nix-overlay.nix)
            (import ./nix/unison-overlay.nix)
          ];
          pkgs = import nixpkgs {
            inherit system overlays;
            inherit (haskellNix) config;
          };
          haskell-nix-flake = import ./nix/haskell-nix-flake.nix {
            inherit pkgs versions;
            inherit (nixpkgs-packages) stack hpack;
          };
          unstable = import nixpkgs-unstable {
            inherit system;
            overlays = [
              (import ./nix/unison-overlay.nix)
              (import ./nix/nixpkgs-overlay.nix { inherit versions; })
            ];
          };
          nixpkgs-packages =
            let
              hpkgs = unstable.haskell.packages.ghcunison;
              exe = unstable.haskell.lib.justStaticExecutables;
            in
            {
              ghc = unstable.haskell.compiler."ghc${versions.ghc}";
              ormolu = exe hpkgs.ormolu;
              hls = unstable.unison-hls;
              stack = unstable.unison-stack;
              unwrapped-stack = unstable.stack;
              hpack = unstable.hpack;
            };
          nixpkgs-devShells = {
            only-tools-nixpkgs = unstable.mkShell {
              name = "only-tools-nixpkgs";
              buildInputs =
                let
                  build-tools = with nixpkgs-packages; [
                    ghc
                    ormolu
                    hls
                    stack
                    hpack
                  ];
                  native-packages = pkgs.lib.optionals pkgs.stdenv.isDarwin
                    (with pkgs.darwin.apple_sdk.frameworks;
                    [ Cocoa ]);
                  c-deps = with pkgs;
                    [ pkg-config zlib glibcLocales ];
                in
                build-tools ++ c-deps ++ native-packages;
              shellHook = ''
                export LD_LIBRARY_PATH=${pkgs.zlib}/lib:$LD_LIBRARY_PATH
              '';
            };
          };
        in
        assert nixpkgs-packages.ormolu.version == versions.ormolu;
        assert nixpkgs-packages.hls.version == versions.hls;
        assert nixpkgs-packages.unwrapped-stack.version == versions.stack;
        assert nixpkgs-packages.hpack.version == versions.hpack;
        {
          packages = nixpkgs-packages // {
            haskell-nix = haskell-nix-flake.packages;
            build-tools = pkgs.symlinkJoin {
              name = "build-tools";
              paths = self.devShells."${system}".only-tools-nixpkgs.buildInputs;
            };
            all = pkgs.symlinkJoin {
              name = "all";
              paths =
                let
                  all-other-packages = builtins.attrValues (builtins.removeAttrs self.packages."${system}" [ "all" "build-tools" ]);
                  devshell-inputs = builtins.concatMap
                    (devShell: devShell.buildInputs ++ devShell.nativeBuildInputs)
                    [
                      self.devShells."${system}".only-tools-nixpkgs
                    ];
                in
                all-other-packages ++ devshell-inputs;
            };
          };

          apps = haskell-nix-flake.apps // {
            default = self.apps."${system}"."unison-cli:exe:unison";
          };

          devShells = nixpkgs-devShells // {
            default = self.devShells."${system}".only-tools-nixpkgs;
            haskell-nix = haskell-nix-flake.devShells;
          };
        });
}