buildHaskell/default.nix


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{ pkgs, ... }:

{
  # Create a nix-shell for Haskell development.
  shell = { deps }: let
    ghc = pkgs.haskellPackages.ghcWithPackages (hpkgs: deps hpkgs);
  in pkgs.mkShell {
    buildInputs = [ghc];
  };

  # Build a Haskell executable. This assumes a project directory with a
  # top-level Main.hs. It also applies a few commonly used language extensions.
  # Here is an overview of the arguments:
  # - `name`: You can find the result at ./result/$name
  # - `srcs`: Will be passed to `srcs` field of `pkgs.stdenv.mkDerivation`.
  # - `deps`: A function that accepts `hpkgs` and returns a list of Haskell
  #   dependencies.
  program = { name, srcs, deps, ghcExtensions }: let
    ghc = pkgs.haskellPackages.ghcWithPackages (hpkgs: deps hpkgs);
  in pkgs.stdenv.mkDerivation {
    name = name;
    buildInputs = [];
    srcs = srcs;
    buildPhase = ''
      ${ghc}/bin/ghc -Wall Main.hs ${pkgs.lib.concatMapStrings (x: "-X${x} ") ghcExtensions}
    '';
    installPhase = ''
      mkdir -p $out && mv Main $out/${name}
    '';
  };
}