anchor.diff:  
     kicad = callPackage ../applications/science/electronics/kicad {
       wxGTK = wxGTK30;
  +    boost = boost160;
     };
   
     ngspice = callPackage ../applications/science/electronics/ngspice { };
  
positive.code: 
    gawp = callPackage ../tools/misc/gawp { };
  
    gazeboSimulator = recurseIntoAttrs {
      sdformat = gazeboSimulator.sdformat4;
  
      sdformat3 = callPackage ../development/libraries/sdformat/3.nix { };
  
      sdformat4 = callPackage ../development/libraries/sdformat { };
  
      gazebo6 = callPackage ../applications/science/robotics/gazebo/6.nix { };
  
      gazebo6-headless = callPackage ../applications/science/robotics/gazebo/6.nix { withHeadless = true;  };
  
      gazebo7 = callPackage ../applications/science/robotics/gazebo { };
  
  
negative.code: 
    hxcpp = callPackage ../development/compilers/haxe/hxcpp.nix { };
  
    hhvm = callPackage ../development/compilers/hhvm {
      boost = boost160;
    };
  
    hop = callPackage ../development/compilers/hop { };
  
  