{ nixpkgs ? import <nixpkgs> {}, compiler ? "ghc902", doBenchmark ? false }:

let

  inherit (nixpkgs) pkgs;

  f = { mkDerivation, aeson, base, blaze-html, blaze-markup
      , bytestring, cassava, conduit, conferer, conferer-aeson
      , conferer-warp, conferer-yaml, containers, data-default-class
      , directory, either, exceptions, extra, fmt, hoauth2, http-api-data
      , http-media, insert-ordered-containers, lens, lib, monad-logger
      , mtl, path-pieces, persistent, persistent-postgresql
      , prometheus-client, prometheus-metrics-ghc, protocol-buffers
      , protocol-buffers-descriptor, regex-tdfa, resource-pool, servant
      , servant-docs, servant-server, servant-swagger, servant-websockets
      , shakespeare, stm, swagger2, text, time, timezone-olson
      , timezone-series, transformers, unliftio-core, uri-bytestring
      , uuid, vector, vector-algorithms, wai-extra, warp, websockets
      , yesod, yesod-auth, yesod-auth-oauth2, yesod-core, yesod-form
      , zip-archive
      }:
      mkDerivation {
        pname = "tracktrain";
        version = "0.1.0.0";
        src = ./.;
        isLibrary = false;
        isExecutable = true;
        libraryHaskellDepends = [
          aeson base blaze-html blaze-markup bytestring cassava conduit
          conferer conferer-warp containers either exceptions extra fmt
          hoauth2 http-api-data http-media insert-ordered-containers lens
          monad-logger mtl path-pieces persistent persistent-postgresql
          prometheus-client prometheus-metrics-ghc protocol-buffers
          protocol-buffers-descriptor regex-tdfa resource-pool servant
          servant-docs servant-server servant-swagger servant-websockets
          shakespeare stm swagger2 text time timezone-olson timezone-series
          transformers unliftio-core uri-bytestring uuid vector
          vector-algorithms warp websockets yesod yesod-auth
          yesod-auth-oauth2 yesod-core yesod-form zip-archive
        ];
        executableHaskellDepends = [
          aeson base bytestring conferer conferer-aeson conferer-yaml
          data-default-class directory extra fmt monad-logger
          persistent-postgresql protocol-buffers time wai-extra warp
        ];
        doHaddock = false;
        description = "tracktrain tracks trains on their traintracks";
        license = "unknown";
        mainProgram = "tracktrain";
      };

  haskellPackages = if compiler == "default"
                       then pkgs.haskellPackages
                       else pkgs.haskell.packages.${compiler};

  variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;

  # we can override haskell packages in nix here; but attempt to minimise that
  # since builds get pretty expensive when we do.
  hpkgs = haskellPackages.override {
    overrides = self: super: with pkgs.haskell.lib; {
      # hoauth2 = doDistribute super.hoauth2_2_6_0;
      # cryptonite = doDistribute super.cryptonite_0_30;
      # memory = doDistribute super.memory_0_18_0;
    };
  };

  drv = variant (hpkgs.callPackage f {});

  # this removes the /lib directory from the built derivation, which depends on ghc.
  # this dramatically reduces closure size
  stripLib = drv: pkgs.stdenv.mkDerivation {
    name = drv.name + "-without-lib";
    src = drv.outPath;
    buildPhase = ''
      mkdir -p $out
      cp -r $src/bin $out
    '';
    phases = [ "buildPhase" ];
  };
in stripLib drv