let
  lib = import ./lib;
  hpkgs = (import ./. {}).haskellPackages;
  suc = lib.filterAttrs (name: value: let res = builtins.tryEval (lib.isDerivation value && builtins.seq value.drvPath true); in res.success && res.value) hpkgs;
  sucCount = lib.length (lib.attrNames suc);
  allCount = lib.length (lib.attrNames hpkgs);
in "Total amount: ${toString allCount}, successful eval: ${toString sucCount}"