anchor.diff:  
   stdenv.mkDerivation rec {
     name    = "hhvm-${version}";
  -  version = "3.21";
  +  version = "3.23.2";
   
     # use git version since we need submodules
     src = fetchgit {
       url    = "https://github.com/facebook/hhvm.git";
  -    rev    = "56483773e2edd9e61782f1901ce40e47959e71b8";
  -    sha256 = "0dmdk98nv04m0fv6909gfbsxqlkckn369yi7kadhir0r7vxsj7wa";
  +    rev    = "HHVM-${version}";
  +    sha256 = "1nic49j8nghx82lgvz0b95r78sqz46qaaqv4nx48p8yrj9ysnd7i";
       fetchSubmodules = true;
     };
   
  
positive.code: 
    patches = [
      ./flexible-array-members-gcc6.patch
      (fetchurl {
        url = https://github.com/facebook/hhvm/commit/b506902af2b7c53de6d6c92491c2086472292004.patch;
        sha256 = "1br7diczqks6b1xjrdsac599fc62m9l17gcx7dvkc0qj54lq7ys4";
      })
    ];
  
    enableParallelBuilding = true;
  
negative.code: { stdenv, fetchgit, cmake, pkgconfig, boost, libunwind, libmemcached
  , pcre, libevent, gd, curl, libxml2, icu, flex, bison, openssl, zlib, php
  , expat, libcap, oniguruma, libdwarf, libmcrypt, tbb, gperftools, glog, libkrb5
  , bzip2, openldap, readline, libelf, uwimap, binutils, cyrus_sasl, pam, libpng
  