anchor.diff:      platforms = with a.lib.platforms;
         linux;
       license = "bsd";
  -  };
  -  passthru = {
  -    updateInfo = {
  -      downloadPage = "http://code.google.com/p/box2d/downloads/list";
  -    };
  +    inherit version;
     };
   }) x
   
  
positive.code: 
    buildInputs = map (n: builtins.getAttr n x)
      (builtins.attrNames (builtins.removeAttrs x helperArgNames));
    sourceInfo = rec {
      baseName="box2d";
      version="2.1.2";
      name="${baseName}-${version}";
      url="http://box2d.googlecode.com/files/Box2D_v${version}.zip";
      hash="0m5szd74ig8yqazwk2g3zl4z7wwp08k52awawk1pigy6a4z1qd9v";
    };
  in
  rec {
    src = a.fetchurl {
      url = sourceInfo.url;
      sha256 = sourceInfo.hash;
    };
  
    inherit (sourceInfo) name version;
    inherit buildInputs;
  
    phaseNames = ["changeSettings" "doCmake" "doMakeInstall"];
  
negative.code: x@{builderDefsPackage
    , unzip, cmake, mesa, freeglut, libX11, xproto
    , inputproto, libXi, fetchsvn, pkgconfig
    , ...}:
  builderDefsPackage
  (a :  
  