anchor.diff:        shims = if builtins.pathExists ./shims/github.json then fetchFromGitHub (builtins.fromJSON (builtins.readFile ./shims/github.json)) else filterGit ./shims;
         ghcjs = if builtins.pathExists ./ghcjs/github.json then fetchFromGitHub (builtins.fromJSON (builtins.readFile ./ghcjs/github.json)) else filterGit ./ghcjs;
       };
  +    inherit (nixpkgs.stdenv.lib) optionals;
   in with lib;
   let overrideCabal = pkg: f: if pkg == null then null else lib.overrideCabal pkg f;
       exposeAeson = aeson: overrideCabal aeson (drv: {
  
positive.code:   };
  
    inherit ghcjs ghcjsCompiler;
    platforms = [ "ghcjs" "ghc" ];
  
    attrsToList = s: map (name: { inherit name; value = builtins.getAttr name s; }) (builtins.attrNames s);
    mapSet = f: s: builtins.listToAttrs (map ({name, value}: {
  
negative.code:   # The systems that we want to build for on the current system
    cacheTargetSystems = [
      "x86_64-linux"
      "i686-linux"
      "x86_64-darwin"
    ];
  
  