anchor.diff:  { buildPythonPackage
   , fetchFromGitHub
   , lib
  -
  -# since this is a dependency of pytest, we need to avoid
  -# circular dependencies
  +, flit-core
   , jinja2
   , pytestCheckHook
   , railroad-diagrams
  
positive.code: let
    pyparsing = buildPythonPackage rec {
      pname = "pyparsing";
      version = "3.0.7";
  
      src = fetchFromGitHub {
        owner = "pyparsing";
        repo = pname;
        rev = "pyparsing_${version}";
        sha256 = "sha256-RyvTTbFshAZgyZPgzqcq31E504RlnMZuf16jJYGqDDI=";
      };
  
      # circular dependencies if enabled by default
      doCheck = false;
      checkInputs = [
        jinja2
  
negative.code:     };
    };
  in
  pyparsing
  