chore: initialize project template

nix/modules/flake/devshell.nix

@@ -0,0 +1,19 @@
+{
+  perSystem = { config, pkgs, ... }: {
+    # Default shell.
+    devShells.default = pkgs.mkShell {
+      name = "xmonad-config";
+      meta.description = "Haskell development environment";
+      # See https://community.flake.parts/haskell-flake/devshell#composing-devshells
+      inputsFrom = [
+        config.haskellProjects.default.outputs.devShell # See ./nix/modules/haskell.nix
+        config.pre-commit.devShell # See ./nix/modules/formatter.nix
+      ];
+      packages = with pkgs; [
+        just
+        nixd
+        ghciwatch
+      ];
+    };
+  };
+}

nix/modules/flake/haskell.nix

@@ -0,0 +1,62 @@
+{ root, inputs, ... }:
+{
+  imports = [
+    inputs.haskell-flake.flakeModule
+  ];
+  perSystem = { self', lib, config, pkgs, ... }: {
+    # Our only Haskell project. You can have multiple projects, but this template
+    # has only one.
+    # See https://github.com/srid/haskell-flake/blob/master/example/flake.nix
+    haskellProjects.default = {
+      # To avoid unnecessary rebuilds, we filter projectRoot:
+      # https://community.flake.parts/haskell-flake/local#rebuild
+      projectRoot = builtins.toString (lib.fileset.toSource {
+        inherit root;
+        fileset = lib.fileset.unions [
+          (root + /src)
+          (root + /xmonad-config.cabal)
+          (root + /LICENSE)
+          (root + /README.md)
+        ];
+      });
+
+      # The base package set (this value is the default)
+      # basePackages = pkgs.haskellPackages;
+
+      # Packages to add on top of `basePackages`
+      packages = {
+        # Add source or Hackage overrides here
+        # (Local packages are added automatically)
+        /*
+        aeson.source = "1.5.0.0" # Hackage version
+        shower.source = inputs.shower; # Flake input
+        */
+      };
+
+      # Add your package overrides here
+      settings = {
+        xmonad-config = {
+          stan = true;
+          # haddock = false;
+        };
+        /*
+        aeson = {
+          check = false;
+        };
+        */
+      };
+
+      # Development shell configuration
+      devShell = {
+        hlsCheck.enable = false;
+      };
+
+      # What should haskell-flake add to flake outputs?
+      autoWire = [ "packages" "apps" "checks" ]; # Wire all but the devShell
+    };
+
+    # Default package & app.
+    packages.default = self'.packages.xmonad-config;
+    apps.default = self'.apps.xmonad-config;
+  };
+}

nix/modules/flake/pre-commit.nix

@@ -0,0 +1,32 @@
+{ inputs, ... }:
+{
+  imports = [
+    (inputs.git-hooks + /flake-module.nix)
+    inputs.fourmolu-nix.flakeModule
+  ];
+  perSystem = { config, ... }: {
+    pre-commit.settings = {
+      hooks = {
+        nixpkgs-fmt.enable = true;
+        cabal-fmt.enable = true;
+        fourmolu = {
+          enable = true;
+          package = config.fourmolu.wrapper;
+        };
+        hlint.enable = true;
+      };
+    };
+
+    fourmolu.settings = {
+      indentation = 2;
+      comma-style = "leading";
+      record-brace-space = true;
+      indent-wheres = true;
+      import-export-style = "diff-friendly";
+      respectful = true;
+      haddock-style = "multi-line";
+      newlines-between-decls = 1;
+      extensions = [ "ImportQualifiedPost" ];
+    };
+  };
+}