anchor.diff:  , bison
   , fetchFromGitHub
   , flex
  +, lib
   , libxml2
   , libxslt
   , perl
  
positive.code: }:
  
  let
    version = "19.3";
  
    inherit (stdenv.lib)
      optionals;
  
negative.code:   name = "erlang-${version}";
  
    src = fetchFromGitHub {
      version = 3;
      owner = "erlang";
      repo = "otp";
      rev = "OTP-${version}";
      sha256 = "6f171c1142829fe3a87d584b646668ed98828180162c2ba66bdc6975c2198812";
    };
  
    nativeBuildInputs = [
  