chore: init

templates/haskell/flake.nix

@@ -0,0 +1,57 @@
+{
+  description = "Haskell Environment";
+
+  inputs = {
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+  };
+
+  outputs =
+    inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ inputs.treefmt-nix.flakeModule ];
+
+      perSystem =
+        { pkgs, ... }:
+        let
+          hp = pkgs.haskellPackages;
+          project = hp.callCabal2nix "project" ./. { };
+        in
+        {
+          devShells.default = hp.shellFor {
+            nativeBuildInputs = builtins.attrValues {
+              inherit (pkgs)
+                nil
+                stylish-haskell
+                ghc
+                ;
+              inherit (hp)
+                cabal-install
+                cabal-gild
+                haskell-language-server
+                ;
+            };
+            packages = _: [ project ];
+          };
+
+          packages.default = project;
+
+          treefmt = {
+            programs = {
+              cabal-fmt.enable = true;
+              deadnix.enable = true;
+              hlint.enable = true;
+              nixfmt.enable = true;
+              ormolu.enable = true;
+              statix.enable = true;
+              typstyle.enable = true;
+              yamlfmt.enable = true;
+            };
+            projectRootFile = "flake.nix";
+          };
+        };
+
+      systems = [ "x86_64-linux" ];
+    };
+}