feat: add programs.hlint (#33)

style checker for haskell

Author: teto

README.md

@@ -76,6 +76,7 @@ For an example, see [haskell-template](https://github.com/srid/haskell-template)
 * elm-format
 * gofmt
 * gofumpt
+* hlint
 * nixpkgs-fmt
 * ocamlformat
 * ormolu

programs/hlint.nix

@@ -0,0 +1,19 @@
+{ lib, pkgs, config, ... }:
+let
+  cfg = config.programs.hlint;
+in
+{
+  options.programs.hlint = {
+    enable = lib.mkEnableOption "hlint";
+    package = lib.mkPackageOption pkgs "hlint" { };
+  };
+
+  config = lib.mkIf cfg.enable {
+    settings.formatter.hlint = {
+      command = cfg.package;
+      options = [ "-j" ];
+      includes = [ "*.hs" ];
+    };
+  };
+}
+