Standalone usage (without flake-parts)

haskell-flake can be used without flake-parts via the lib.evalHaskellProject function. This is useful if you have a plain flake or a legacy (non-flakes) Nix setup.

Plain flake

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
    haskell-flake.url = "github:srid/haskell-flake";
  };
  outputs = { self, nixpkgs, haskell-flake, ... }:
    let
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};
      project = (haskell-flake.lib { inherit pkgs; }).evalHaskellProject {
        projectRoot = self;
        modules = [{
          # Same options as haskellProjects.default = { ... }
          settings = {
            mypackage.haddock = false;
          };
          devShell.tools = hp: {
            inherit (hp) fourmolu;
          };
        }];
      };
    in
    {
      packages.${system}.default = project.packages.mypackage.package;
      devShells.${system}.default = project.devShell;
    };
}

API

haskell-flake.lib is a function that takes { pkgs } and returns an attribute set with:

`evalHaskellProject`

{ projectRoot, name ? "default", modules ? [] } -> outputs

projectRoot (required): Path to the project directory containing .cabal or cabal.project files.
name: Project name, defaults to "default".
modules: List of modules with the same options available under haskellProjects.<name> in the flake-parts interface (e.g., packages, settings, devShell, basePackages, otherOverlays).

Returns the project outputs:

Output	Description
`finalOverlay`	The composed Haskell overlay
`finalPackages`	The Haskell package set with all overlays applied
`packages`	Attrset of `{ package, exes }` for each local package
`apps`	Flake apps for each Cabal executable
`devShell`	Development shell derivation
`checks`	Flake checks (e.g., HLS check if enabled)

Without flakes

You can also use haskell-flake from traditional Nix (no flakes):

let
  haskell-flake = builtins.fetchTarball {
    url = "https://github.com/srid/haskell-flake/archive/master.tar.gz";
  };
  pkgs = import <nixpkgs> {};
  project = (import "${haskell-flake}/nix/lib.nix" { inherit pkgs; }).evalHaskellProject {
    projectRoot = ./.;
  };
in
  project.packages.mypackage.package