flake-template-hell/templates/haskell/flake.nix

{
  description = "Haskell Project Template";
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    treefmt.url = "github:numtide/treefmt-nix";
  };
  outputs = inputs @ {nixpkgs, ...}: let
    inherit (nixpkgs) lib;
    systems = ["x86_64-linux"];
    forAllSystems = f:
      lib.genAttrs systems (
        system:
          f {
            pkgs = import nixpkgs {
              inherit system;
            };
          }
      );
    treefmtEval = forAllSystems ({pkgs}: inputs.treefmt.lib.evalModule pkgs ./flake/treefmt.nix);
  in {
    packages = forAllSystems ({pkgs}: {
      default = pkgs.callPackage ./flake/package.nix {};
    });
    devShells = forAllSystems ({pkgs}: {
      default = pkgs.callPackage ./flake/shell.nix {};
    });
    formatter = forAllSystems ({pkgs}: treefmtEval.${pkgs.system}.config.build.wrapper);
  };
}