Revert change to default.nix

default.nix

@@ -1,7 +1,32 @@
-{ pkgs ? import <nixpkgs> {} }: pkgs.haskellPackages.developPackage {
+let
+  hostPkgs = import <nixpkgs> {};
+  pinnedPkgs = hostPkgs.fetchFromGitHub {
+    owner = "NixOS";
+    repo = "nixpkgs-channels";
+    rev = "ee28e35ba37ab285fc29e4a09f26235ffe4123e2";
+    sha256 = "0a6xrqjj2ihkz1bizhy5r843n38xgimzw5s2mfc42kk2rgc95gw5";
+  };
+
+in { nixpkgs ? import pinnedPkgs {}
+   , compiler ? "ghc822"
+   , doProfiling ? false
+   , doBenchmark ? false }:
+
+let
+
+  inherit (nixpkgs) pkgs;
+
+  haskellPackages = let hpkgs = pkgs.haskell.packages.${compiler}; in
+    hpkgs // {
+      mkDerivation = args: hpkgs.mkDerivation (args // {
+        enableLibraryProfiling = doProfiling;
+        enableExecutableProfiling = doProfiling;
+      });
+    };
+
+  pkg = haskellPackages.developPackage {
     root = ./.;
     source-overrides = {
-      unordered-containers = "0.2.9.0";
       # Use a particular commit from github
       insert-ordered-containers = pkgs.fetchFromGitHub {
         owner = "mightybyte";
@@ -10,4 +35,10 @@
         sha256 = "0l0g6ns5bcrcaij0wbdgc04qyl9h0vk1kx9lkzdkwj9v51l26azm";
       };
     };
-}
+  };
+
+  variant = if doBenchmark
+            then pkgs.haskell.lib.doBenchmark
+            else pkgs.lib.id;
+
+in variant pkg