anchor.diff:      XMLSAX
     ]);
   
  +  checkInputs = [ gtest ];
  +
  +  # The build system uses custom logic - defined in
  +  # xs/src/libnest2d/cmake_modules/FindNLopt.cmake in the package source -
  +  # for finding the nlopt library, which doesn't pick up the package in the nix store.
  +  # We need to set the path via the NLOPT environment variable instead.
  +  NLOPT = "${nlopt}";
  +
     prePatch = ''
       # In nix ioctls.h isn't available from the standard kernel-headers package
       # on other distributions. As the copy in glibc seems to be identical to the
       # one in the kernel, we use that one instead.
       sed -i 's|"/usr/include/asm-generic/ioctls.h"|<asm-generic/ioctls.h>|g' xs/src/libslic3r/GCodeSender.cpp
   
  -    # PERL_VENDORARCH and PERL_VENDORLIB aren't detected correctly by the build
  +    # PERL_VENDORARCH and PERL_VENDORLIB aren't set correctly by the build
       # system, so we have to override them. Setting them as environment variables
  -    # doesn't work though, so patching the paths directly in the CMakeLists.txt
  -    # seems to be the easisest way.
  +    # doesn't work though, so substituting the paths directly in CMakeLists.txt
  +    # seems to be the easiest way.
       sed -i "s|\''${PERL_VENDORARCH}|$out/lib/slic3r-prusa3d|g" xs/CMakeLists.txt
       sed -i "s|\''${PERL_VENDORLIB}|$out/lib/slic3r-prusa3d|g" xs/CMakeLists.txt
     '';
  
positive.code:     description = "G-code generator for 3D printer";
      homepage = https://github.com/prusa3d/Slic3r;
      license = licenses.agpl3;
      platforms = platforms.linux;
      maintainers = with maintainers; [ tweber ];
    };
  }
  
negative.code: { stdenv, fetchFromGitHub, makeWrapper, which, cmake, perl, perlPackages,
    boost, tbb, wxGTK30, pkgconfig, gtk3, fetchurl, gtk2, libGLU,
    glew, eigen, curl, gtest, nlopt, pcre, xorg }:
  let
    AlienWxWidgets = perlPackages.buildPerlPackage rec {
      name = "Alien-wxWidgets-0.69";
  