anchor.diff: -{ stdenv, fetchurl, ruby, rubyLibs, libiconv, libxslt, libxml2, pkgconfig, libffi, imagemagickBig, postgresql }:
  +{ stdenv, fetchurl, ruby, rubyLibs, libiconv, libiconvOrNull, libiconvOrLibc, libxslt, libxml2, pkgconfig, libffi, glibc, imagemagickBig, postgresql }:
   
   let
     gemspec = map (gem: fetchurl { url=gem.url; sha256=gem.hash; }) (import ./Gemfile.nix);
  
positive.code: 
      bundle config build.nokogiri \
        --use-system-libraries \
        --with-iconv-dir=${libiconv} \
        --with-xslt-dir=${libxslt} \
        --with-xml2-dir=${libxml2} \
        --with-pkg-config \
  
negative.code:   '';
  
    buildInputs = [
      ruby rubyLibs.bundler 
    ] ++ (if (libiconvOrNull != null) then [libiconv] else []) ++ [
      libxslt libxml2 pkgconfig libffi
      imagemagickBig postgresql
    ];
  
  