anchor.diff:  let
     inherit (stdenv)
       targetSystem;
  -  inherit (stdenv.lib)
  +  inherit (lib)
       boolOn
       concatStringsSep
       elem
       optionals
       platforms;
   
  -  source = (import ./sources.nix { })."${channel}";
  +  sources = {
  +    "stable" = {
  +      version = "2.5";
  +      multihash = "QmSsqLD2yPEuf9CDKgMFEBNSpHYzpE8K2cr6d8aV2icLfB";
  +      sha256 = "2e53259b504a7edb9b21b9800163b1ff4c90e60c74e23e7001d423c69c5d3d17";
  +    };
  +    "head" = {
  +      fetchzipversion = 3;
  +      version = "2017-06-21";
  +      rev = "80c23559084c78c8154ca411ed8e369a07fd7e78";
  +      sha256 = "074441de68a38488af0f4054292783425abe2a119987785225b2af13ecb44b3c";
  +    };
  +  };
  +  source = sources."${channel}";
   
     src =
       if channel == "head" then
  
positive.code:     cmakeFlags = [
        "-DENABLE_CLI=OFF"
        "-DENABLE_SHARED=OFF"
        "-DEXPORT_C_API=OFF"
        "-DHIGH_BIT_DEPTH=ON"
        "-DLINKED_8BIT=OFF"
  
negative.code: , cmake
  , fetchFromBitbucket
  , fetchurl
  , lib
  , ninja
  , yasm
  
  