anchor.diff:  lib: pkgs: actuallySplice:
   
   let
  -  defaultBuildBuildScope = pkgs.buildPackages.buildPackages // pkgs.buildPackages.buildPackages.xorg;
  -  defaultBuildHostScope = pkgs.buildPackages // pkgs.buildPackages.xorg;
  -  defaultBuildTargetScope =
  -    if pkgs.stdenv.targetPlatform == pkgs.stdenv.hostPlatform
  -    then defaultBuildHostScope
  -    else assert pkgs.stdenv.hostPlatform == pkgs.stdenv.buildPlatform; defaultHostTargetScope;
  -  defaultHostHostScope = {}; # unimplemented
  -  defaultHostTargetScope = pkgs // pkgs.xorg;
  -  defaultTargetTargetScope = pkgs.targetPackages // pkgs.targetPackages.xorg or {};
   
     spliceReal = { pkgsBuildBuild, pkgsBuildHost, pkgsBuildTarget
                  , pkgsHostHost, pkgsHostTarget
  
positive.code:                    } @ args:
      if actuallySplice then spliceReal args else pkgsHostTarget;
  
    splicedPackages = splicePackages {
      pkgsBuildBuild = defaultBuildBuildScope;
      pkgsBuildHost = defaultBuildHostScope;
      pkgsBuildTarget = defaultBuildTargetScope;
      pkgsHostHost = defaultHostHostScope;
      pkgsHostTarget = defaultHostTargetScope;
      pkgsTargetTarget = defaultTargetTargetScope;
    } // {
      # These should never be spliced under any circumstances
      inherit (pkgs) pkgs buildPackages targetPackages;
      inherit (pkgs.stdenv) buildPlatform targetPlatform hostPlatform;
    };
  
  in
  
  
negative.code:   # `newScope' for sets of packages in `pkgs' (see e.g. `gnome' below).
    callPackage = pkgs.newScope {};
  
    callPackages = lib.callPackagesWith splicedPackagesWithXorg;
  
    newScope = extra: lib.callPackageWith (splicedPackagesWithXorg // extra);
  
    # Haskell package sets need this because they reimplement their own
    # `newScope`.
  