build: flake template from the-nix-way

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -21,3 +21,4 @@ cabal.project.local
 cabal.project.local~
 .HTF/
 .ghc.environment.*
+.direnv/

flake.lock

@@ -0,0 +1,25 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1746904237,
+        "narHash": "sha256-3e+AVBczosP5dCLQmMoMEogM57gmZ2qrVSrmq9aResQ=",
+        "rev": "d89fc19e405cb2d55ce7cc114356846a0ee5e956",
+        "revCount": 797896,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.797896%2Brev-d89fc19e405cb2d55ce7cc114356846a0ee5e956/0196c1a7-7ad3-74a9-9d50-1b854aca6d6c/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/NixOS/nixpkgs/0.1"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,39 @@
+{
+  description = "A Nix-flake-based Haskell development environment";
+
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1";
+
+  outputs =
+    inputs:
+    let
+      supportedSystems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      forEachSupportedSystem =
+        f:
+        inputs.nixpkgs.lib.genAttrs supportedSystems (
+          system:
+          f {
+            pkgs = import inputs.nixpkgs { inherit system; };
+          }
+        );
+    in
+    {
+      devShells = forEachSupportedSystem (
+        { pkgs }:
+        {
+          default = pkgs.mkShell {
+            packages = with pkgs; [
+              cabal-install
+              ghc
+              haskell-language-server
+              just
+            ];
+          };
+        }
+      );
+    };
+}