anchor.diff: -{ stdenv, lib, fetchFromGitHub, cmake, boost, gmp, mpfr, libedit, python
  +{ stdenv, lib, fetchFromGitHub, cmake, boost, gmp, mpfr, libedit, python3
   , texinfo, gnused, usePython ? true }:
   
   stdenv.mkDerivation rec {
  
positive.code:   outputs = [ "out" "dev" ];
  
    buildInputs = [
      (boost.override { enablePython = usePython; })
      gmp mpfr libedit python gnused
    ];
  
    nativeBuildInputs = [ cmake texinfo ];
  
negative.code:   # however, that would write to a different nixstore path, pass our own sitePackages location
    prePatch = lib.optionalString usePython ''
      substituteInPlace src/CMakeLists.txt \
        --replace 'DESTINATION ''${Python_SITEARCH}' 'DESTINATION "${python3.sitePackages}"'
    '';
  
    installTargets = [ "doc" "install" ];
  