restructure nix development environment, now with Hoogle

src/default.nix

@@ -0,0 +1,19 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+let
+  inherit (pkgs) haskellPackages;
+  drv = haskellPackages.callCabal2nix "Hash2Pub" ./Hash2Pub {};
+in
+{
+  my_project = drv;
+  shell = haskellPackages.shellFor {
+    withHoogle = true;
+    packages = p: [ drv ];
+    buildInputs = with pkgs.haskellPackages;
+      [
+        haddock
+        cabal-install
+        hlint
+      ];
+  };
+}

src/shell.nix

@@ -1,11 +1 @@
-let
+(import ./. {}).shell
-  pkgs = import <nixpkgs> {};
-in
-  pkgs.haskellPackages.developPackage {
-    root = ./Hash2Pub;
-    modifier = drv:
-      pkgs.haskell.lib.addBuildTools drv (with pkgs.haskellPackages;
-        [ cabal-install
-          haddock
-      ]);
-    }