anchor.diff:        ./b2 -j$NIX_BUILD_CORES -sEXPAT_INCLUDE=${expat.crossDrv}/include -sEXPAT_LIBPATH=${expat.crossDrv}/lib --layout=${layout} --user-config=user-config.jam toolset=gcc-cross variant=${variant} threading=${threading} link=${link} ${cflags} --without-python install
       '';
     };
  -}; in res // { lib = res; }
  +}
  
positive.code:   };
  
    enableParallelBuilding = true;
  
    buildInputs =
      [ icu expat zlib bzip2 python ]
  
negative.code:   withToolset = stdenv.lib.optionalString (toolset != null) " --with-toolset=${toolset}";
  in
  
  stdenv.mkDerivation {
    name = "boost-1.55.0";
  
    meta = {
  