{ pkgs ? (import (builtins.fetchGit {
  url = "https://github.com/NixOS/nixpkgs-channels.git";
  ref = "nixos-unstable";
  rev = "1e3f09feaa5667be4ed6eca96a984b4642420b83";
}) {}) }:

let
  ghc = ghc'.override {
    overrides = self: super: {
      random = self.random_1_2_0;
      smallcheck = self.smallcheck_1_2_0;
      splitmix = self.splitmix_0_1_0_1;
    };
  };
  ghc' = pkgs.haskellPackages;
in pkgs.stdenv.mkDerivation {
  pname = "haskell-pbil";
  version = "1.0.0";

  src = ./.;

  nativeBuildInputs = [ (ghc.ghcWithPackages (hpkgs: with hpkgs; [
    random
  ])) ];

  buildPhase = ''
    mkdir -p build
    ghc --make \
      -isrc \
      -O2 \
      -outputdir build \
      -o build/haskell-pbil \
      src/Main.hs
  '';

  installPhase = ''
    mkdir -p $out/bin
    mv build/haskell-pbil $out/bin/
  '';

  # Note that `ghc.haskell-language-server` causes an infinite recursion
  # from the overlay.
  shellHook = ''
    export PATH=\
    ${ghc'.haskell-language-server}/bin:\
    $PATH
  '';
}