anchor.diff:  
     nativeBuildInputs = [
       perl
  -    yasm
  -  ];
  +  ] ++ (
  +    if versionAtLeast source.version "1.6.2" then [
  +      nasm
  +    ] else [
  +      yasm
  +    ]
  +  );
   
     postPatch = ''
       patchShebangs ./build/make/rtcd.pl
  
positive.code:     # master
      "1.999" = {
        fetchzipversion = 3;
        version = "2017-09-27";
        rev = "c493ea1a6b7ade049ac22d8d063b73f12d65bbea";
        sha256 = "e3379632547091c9d162c0970619ae4c262c8364821439e1c3f1b592e1085e5e";
      };
    };
    source = sources."${channel}";
  
negative.code:     "--${boolEn examplesSupport}-examples"
      "--disable-docs"
      #libc
      "--as=${if versionAtLeast source.version "1.6.2" then "nasm" else "yasm"}"
      "${if (sizeLimit != null) then "--size-limit=${sizeLimit}" else null}"
      "--disable-codec-srcs"
      "--disable-debug-libs"
  