anchor.diff:  
   let version = "1.2.8"; in
   
  -stdenv.mkDerivation (rec {
  +stdenv.mkDerivation rec {
     name = "zlib-${version}";
   
     src = fetchurl {
  
positive.code:     license = licenses.zlib;
      platforms = platforms.all;
    };
  } // (if stdenv.isDarwin then {
    postInstall = ''
      # jww (2015-01-06): Sometimes this library install as a .so, even on
      # Darwin; others time it installs as a .dylib.  I haven't yet figured out
      # what causes this difference.
      for file in $out/lib/*.so* $out/lib/*.dylib* ; do
        install_name_tool -id "$file" $file
      done
    '';
  } else {}))
  
negative.code:   outputs = [ "dev" "out" "static" "man" ];
    setOutputFlags = false;
  
    preConfigure = ''
      if test -n "$crossConfig"; then
        export CC=$crossConfig-gcc
      fi
    '';
  
    configureFlags = stdenv.lib.optional (!static) "--shared";
  
    postInstall = ''
      _moveToOutput lib/libz.a "$static"
    ''
      # jww (2015-01-06): Sometimes this library install as a .so, even on
      # Darwin; others time it installs as a .dylib.  I haven't yet figured out
      # what causes this difference.
    + stdenv.lib.optionalString stdenv.isDarwin ''
      for file in $out/lib/*.so* $out/lib/*.dylib* ; do
        install_name_tool -id "$file" $file
      done
    '';
  
    # As zlib takes part in the stdenv building, we don't want references
  