Instantiate haskell template

flake.nix

@@ -0,0 +1,67 @@
+{
+  description = "Haskell Nix Template";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs";
+
+    flake-utils.url = "github:numtide/flake-utils";
+
+    pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";
+    pre-commit-hooks.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, pre-commit-hooks }:
+    flake-utils.lib.eachSystem [ "x86_64-linux" ] (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        overlay = final: prev: {
+          filepack = final.callCabal2nix "filepack" ./. { };
+        };
+
+        haskellPackages = pkgs.haskell.packages.ghc924.extend overlay;
+      in {
+        packages.default = haskellPackages.filepack;
+
+        apps = {
+          default = {
+            type = "app";
+            program = "${self.defaultPackage.${system}}/bin/hello";
+          };
+        };
+
+        checks = {
+          pre-commit-check = pre-commit-hooks.lib.${system}.run {
+            src = ./.;
+            settings = { ormolu.defaultExtensions = [ "GHC2021" ]; };
+            tools.fourmolu = haskellPackages.fourmolu;
+            hooks = {
+              nixfmt.enable = true;
+              fourmolu.enable = true;
+              hpack.enable = true;
+              hlint.enable = true;
+            };
+          };
+        };
+
+        devShells.default = haskellPackages.shellFor {
+          inherit (self.checks.${system}.pre-commit-check) shellHook;
+
+          packages = p: [ p.filepack ];
+
+          withHoogle = true;
+
+          nativeBuildInputs = with pkgs; [
+            haskellPackages.haskell-language-server
+            haskellPackages.fourmolu
+            haskellPackages.hspec-discover
+            haskellPackages.doctest
+            cabal-install
+            ghcid
+            nixfmt
+            hpack
+            hlint
+          ];
+        };
+      });
+}