Simplify some things in default.nix

default.nix

@@ -1,8 +1,6 @@
 { compiler    ? "ghc822"
-
 , doProfiling ? false
 , doBenchmark ? false
-
 , rev         ? "ee28e35ba37ab285fc29e4a09f26235ffe4123e2"
 , sha256      ? "0a6xrqjj2ihkz1bizhy5r843n38xgimzw5s2mfc42kk2rgc95gw5"
 , nixpkgs     ? import (builtins.fetchTarball {
@@ -10,41 +8,31 @@
     sha256 = sha256; }) { config.allowBroken = false; config.allowUnfree = true; }
 }:
 
-let
+let inherit (nixpkgs) pkgs;
 
-  inherit (nixpkgs) pkgs;
-
-  haskellPackages = let hpkgs = pkgs.haskell.packages.${compiler}; in
-    hpkgs // {
-      mkDerivation = args: hpkgs.mkDerivation (args // {
-        enableLibraryProfiling = doProfiling;
-        enableExecutableProfiling = doProfiling;
-      });
-    };
-
-  pkg = haskellPackages.developPackage {
-    root = ./.;
-    overrides = with pkgs.haskell.lib; self: super: {
+  haskellPackages = pkgs.haskell.packages.${compiler}.override {
+    overrides = with pkgs.haskell.lib; self: super: rec {
       serialise = dontCheck super.serialise;
     };
-    source-overrides = {
-      insert-ordered-containers = pkgs.fetchFromGitHub {
-        owner  = "mightybyte";
-        repo   = "insert-ordered-containers";
-        rev    = "87054c519b969b62131bcf7a183470d422cbb535";
-        sha256 = "0l0g6ns5bcrcaij0wbdgc04qyl9h0vk1kx9lkzdkwj9v51l26azm";
-      };
-    };
-    modifier = drv: pkgs.haskell.lib.overrideCabal drv (attrs: {
-      testHaskellDepends = attrs.testHaskellDepends ++
-        [
-          pkgs.nix
-          haskellPackages.hpack
-          haskellPackages.cabal-install
-        ];
-      inherit doBenchmark;
-    });
   };
 
+in haskellPackages.developPackage {
+  root = ./.;
 
-in pkg
+  source-overrides = {
+  };
+
+  modifier = drv: pkgs.haskell.lib.overrideCabal drv (attrs: {
+    testHaskellDepends = attrs.testHaskellDepends ++
+      [
+        pkgs.nix
+        haskellPackages.hpack
+        haskellPackages.cabal-install
+      ];
+
+    enableLibraryProfiling    = doProfiling;
+    enableExecutableProfiling = doProfiling;
+
+    inherit doBenchmark;
+  });
+}