anchor.diff:  
   { stdenv, writeTextFile, fetchurl, php, unzip }:
   
  -rec {
  +let
     composer = stdenv.mkDerivation {
       name = "composer-1.6.5";
       src = fetchurl {
  
positive.code: 
        extraArgs = removeAttrs args [ "name" "packages" "devPackages" "buildInputs" ];
      in
      stdenv.lib.makeOverridable stdenv.mkDerivation ({
        name = "composer-${name}";
        buildInputs = [ php composer ] ++ buildInputs;
  
  
negative.code:         runHook postInstall
      '';
    } // extraArgs);
  in
  {
    composer = stdenv.lib.makeOverridable composer;
    buildZipPackage = stdenv.lib.makeOverridable buildZipPackage;
    buildPackage = stdenv.lib.makeOverridable buildPackage;
  }
  