add flake

flake.nix

@@ -0,0 +1,66 @@
+# https://community.flake.parts/haskell-flake/dependency
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    haskell-flake.url = "github:srid/haskell-flake";
+  };
+  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = nixpkgs.lib.systems.flakeExposed;
+      imports = [ inputs.haskell-flake.flakeModule ];
+
+      perSystem = { self', pkgs, lib, ... }: {
+
+        # Typically, you just want a single project named "default". But
+        # multiple projects are also possible, each using different GHC version.
+        haskellProjects.default = {
+          # The base package set representing a specific GHC version.
+          # By default, this is pkgs.haskellPackages.
+          # You may also create your own. See https://community.flake.parts/haskell-flake/package-set
+          # basePackages = pkgs.haskellPackages;
+
+          # Extra package information. See https://community.flake.parts/haskell-flake/dependency
+          #
+          # Note that local packages are automatically included in `packages`
+          # (defined by `defaults.packages` option).
+          #
+          projectRoot = builtins.toString (lib.fileset.toSource {
+            root = ./.;
+            fileset = lib.fileset.unions [
+              ./src
+              ./haskell-template.cabal
+            ];
+          });
+          packages = {
+            # aeson.source = "1.5.0.0";      # Override aeson to a custom version from Hackage
+            # shower.source = inputs.shower; # Override shower to a custom source path
+          };
+          settings = {
+            #  aeson = {
+            #    check = false;
+            #  };
+            #  relude = {
+            #    haddock = false;
+            #    broken = false;
+            #  };
+          };
+
+          devShell = {
+            # Enabled by default
+            # enable = true;
+
+            # Programs you want to make available in the shell.
+            # Default programs can be disabled by setting to 'null'
+            # tools = hp: { fourmolu = hp.fourmolu; ghcid = null; };
+
+            # Check that haskell-language-server works
+            # hlsCheck.enable = true; # Requires sandbox to be disabled
+          };
+        };
+
+        # haskell-flake doesn't set the default package, but you can do it here.
+        packages.default = self'.packages.HushGP;
+      };
+    };
+}