anchor.diff:  { stdenv, lib, fetchurl, fetchpatch, pkg-config, flex, bison, libxslt, autoconf, autoreconfHook
  -, gnome, graphviz, glib, libiconv, libintl, libtool, expat, substituteAll
  +, gnome, graphviz, glib, libiconv, libintl, libtool, expat, substituteAll, vala
   }:
   
   let
  
positive.code:     # so that it can be used to regenerate documentation.
      patches        = lib.optionals disableGraphviz [ graphvizPatch ./gvc-compat.patch ];
      configureFlags = lib.optional  disableGraphviz "--disable-graphviz";
      preBuild       = lib.optionalString disableGraphviz "buildFlagsArray+=(\"VALAC=$(pwd)/compiler/valac\")";
  
      outputs = [ "out" "devdoc" ];
  
  
negative.code:       pkg-config flex bison libxslt
      ] ++ lib.optional (stdenv.isDarwin && (lib.versionAtLeast version "0.38")) expat
        ++ lib.optional disableGraphviz autoreconfHook # if we changed our ./configure script, need to reconfigure
        ++ lib.optionals (stdenv.buildPlatform != stdenv.hostPlatform) [ vala ]
        ++ extraNativeBuildInputs;
  
      buildInputs = [
  