rPackages: Implement overlay infrastructure

temporary/all-packages.nix

@@ -18,4 +18,16 @@ self: super: pkgs: with pkgs; {
   python36 = super.python36.override { packageOverrides = pythonOverrides; };
 
   pythonOverrides = import ./python-packages.nix pkgs;
+
+  # same for R as Python (except we have to do the self/super plumbing)
+  rPackages = super.rPackages.override {
+    overrides =
+      let
+        overrides = rOverrides self super.rPackages;
+        self = super.rPackages // overrides;
+      in
+        overrides;
+  };
+
+  rOverrides = import ./r-modules.nix pkgs;
 }

temporary/r-modules.nix

@@ -0,0 +1,3 @@
+pkgs: self: super: with self; {
+
+}