anchor.diff:    defaultConfigureFlags = [
       "--verbose" "--prefix=$out" "--libdir=\\$prefix/lib/\\$compiler" "--libsubdir=\\$pkgid"
       (optionalString enableSeparateDataOutput "--datadir=$data/share/${ghc.name}")
  -    (optionalString enableSeparateDocOutput "--docdir=$doc/share/doc")
  +    (optionalString enableSeparateDocOutput "--docdir=${docdir "$doc"}")
       "--with-gcc=$CC" # Clang won't work without that extra information.
       "--package-db=$packageConfDir"
       (optionalString (enableSharedExecutables && stdenv.isLinux) "--ghc-option=-optl=-Wl,-rpath=$out/lib/${ghc.name}/${pname}-${version}")
  
positive.code:     inherit pname version;
  
      isHaskellLibrary = hasActiveLibrary;
  
      env = stdenv.mkDerivation {
        name = "interactive-${pname}-${version}-environment";
  
negative.code:     ''}
  
      ${optionalString enableSeparateDocOutput ''
      for x in ${docdir "$doc"}/html/src/*.html; do
        remove-references-to -t $out $x
      done
      mkdir -p $doc
  