anchor.diff:  { stdenv, fetchurl, flex, bison, pkgconfig, zlib, libtiff, libpng, fftw
   , cairo, readline, ffmpeg, makeWrapper, wxGTK30, netcdf, blas
  -, proj, gdal, geos, sqlite, postgresql, mysql, pythonPackages
  +, proj, gdal, geos, sqlite, postgresql, mysql, python2Packages
   }:
   
   stdenv.mkDerivation {
  
positive.code:   postInstall = ''
      wrapProgram $out/bin/grass70 \
      --set PYTHONPATH $PYTHONPATH \
      --set GRASS_PYTHON ${pythonPackages.python}/bin/${pythonPackages.python.executable}
      ln -s $out/grass-*/lib $out/lib
    '';
  
  
negative.code: 
    buildInputs = [ flex bison zlib proj gdal libtiff libpng fftw sqlite pkgconfig cairo
    readline ffmpeg makeWrapper wxGTK30 netcdf geos postgresql mysql.client blas ]
      ++ (with python2Packages; [ python dateutil wxPython30 numpy ]);
  
    configureFlags = [
      "--with-proj-share=${proj}/share/proj"
  