anchor.diff:      nativeBuildInputs = [
         cmake
         ninja
  -      yasm
  -    ];
  +    ] ++ (
  +      if (channel == "head") then [
  +        nasm
  +      ] else [
  +        yasm  # Remove for > 2.6
  +      ]
  +    );
   
       buildInputs = optionals (elem targetSystem platforms.linux) [
         numactl
  
positive.code:     };
      "head" = {
        fetchzipversion = 3;
        version = "2017-09-11";
        rev = "f8ae7afc1f61ed0db3b2f23f5d581706fe6ed677";
        sha256 = "8f844abe9495f6b610c952c14919e9e91cdc440a3d8d6936877daed0148f7452";
      };
    };
    source = sources."${channel}";
  
negative.code:   nativeBuildInputs = [
      cmake
      ninja
      ] ++ (
        if (channel == "head") then [
          nasm
        ] else [
          yasm  # Remove for > 2.6
        ]
      );
  
    buildInputs = [
      libx265-10
  