anchor.diff:  
     makeFlags = "VERBOSE=1";
   
  +  preBuild =
  +    /* Work around this:
  +
  +      [ 20%] Generating _msg_handle_simulator.c, _msg_handle_client.c, _msg_handle_server.c
  +      cd /tmp/nix-build-7yc8ghmf2yb8zi3bsri9b6qadwmfpzhr-simgrid-3.5.drv-0/simgrid-3.5/build/teshsuite/gras/msg_handle && ../../../bin/gras_stub_generator msg_handle /tmp/nix-build-7yc8ghmf2yb8zi3bsri9b6qadwmfpzhr-simgrid-3.5.drv-0/simgrid-3.5/teshsuite/gras/msg_handle/msg_handle.xml
  +      ../../../bin/gras_stub_generator: error while loading shared libraries: libsimgrid.so.3.5: cannot open shared object file: No such file or directory
  +      make[2]: *** [teshsuite/gras/msg_handle/_msg_handle_simulator.c] Error 127
  +      make[2]: Leaving directory `/tmp/nix-build-7yc8ghmf2yb8zi3bsri9b6qadwmfpzhr-simgrid-3.5.drv-0/simgrid-3.5/build'
  +
  +    */
  +    '' export LD_LIBRARY_PATH="$PWD/lib:$LD_LIBRARY_PATH"
  +       echo "\$LD_LIBRARY_PATH is \`$LD_LIBRARY_PATH'"
  +    '';
  +
     patchPhase =
       '' for i in "src/smpi/"*
          do
            sed -i "$i" -e's|/bin/bash|/bin/sh|g'
          done
  +
  +       for i in $(grep -rl /usr/bin/perl .)
  +       do
  +         sed -i "$i" -e's|/usr/bin/perl|${perl}/bin/perl|g'
  +       done
       '';
  -
  -  installPhase = "make install-simgrid";
   
     # Fixing the few tests that fail is left as an exercise to the reader.
     doCheck = false;
  
positive.code: { fetchurl, stdenv, cmake, ruby }:
  
  stdenv.mkDerivation rec {
    name = "simgrid-3.4.1";
  
    src = fetchurl {
      url = "https://gforge.inria.fr/frs/download.php/26944/${name}.tar.bz2";
      sha256 = "acd2bb2c1abf59e9b190279b1c38582b7c1edd4b6ef4c6a9b01100740f1a6b28";
    };
  
    /* FIXME: Ruby currently disabled because of this:
  
negative.code:      ld: cannot find -lruby-1.8.7-p72
  
     */
    buildInputs = [ cmake perl /* ruby */ ];
  
    preConfigure =
      # Make it so that libsimgrid.so will be found when running programs from
  