anchor.diff:      ++ lib.optional enableFfmpeg ffmpeg
       ++ lib.optionals enableGStreamer (with gst_all_1; [ gstreamer gst-plugins-base ])
       ++ lib.optional enableEigen eigen
  +    ++ lib.optional enableOpenblas openblas
       ++ lib.optionals enableCuda [ cudatoolkit gcc5 ]
       ++ lib.optional enableContrib protobuf3_1
       ++ lib.optionals stdenv.isDarwin [ AVFoundation Cocoa QTKit ];
  
positive.code:   NIX_CFLAGS_COMPILE = lib.optional enableEXR "-I${ilmbase.dev}/include/OpenEXR";
  
    cmakeFlags = [
      "-DWITH_IPP=${if enableIpp then "ON" else "OFF"}"
      (opencvFlag "TIFF" enableTIFF)
      (opencvFlag "JASPER" enableJPEG2K)
      (opencvFlag "WEBP" enableWebP)
  
negative.code: , enableFfmpeg    ? false, ffmpeg
  , enableGStreamer ? false, gst_all_1
  , enableEigen     ? false, eigen
  , enableOpenblas  ? false, openblas
  , enableCuda      ? false, cudatoolkit, gcc5
  , AVFoundation, Cocoa, QTKit
  }:
  