get haskell packages from nixpkgs too

shell.nix

@@ -3,21 +3,23 @@ let
                    url = "https://github.com/nixos/nixpkgs/";
                    ref = "refs/tags/24.05";
                  }) {};
-  stdenv = pkgs.overrideCC pkgs.stdenv pkgs.gcc7;
-  # stuck with GCC 7 because Cilk was kicked out in GCC 8,
-  # need OpenCilk packaged in nixpkgs, see
-  # https://github.com/NixOS/nixpkgs/issues/144256
 
-  ghc = pkgs.haskell.compiler.ghc910;
   clang = pkgs.clang_16;
   llvm = pkgs.llvm_16;
   gibbon_dir = builtins.toString ./.;
 in
   with pkgs;
-  stdenv.mkDerivation {
+
+  # we are stuck with GCC 7 because Cilk was kicked out in GCC 8,
+  # OpenCilk needs packaging in nixpkgs, see
+  # https://github.com/NixOS/nixpkgs/issues/144256
+  mkShell.override { stdenv = pkgs.gcc7Stdenv; }  {
+
+    # we use default Haskell toolchain supplied with the chosen nixpkgs; this way we hit their cache
+    inputsFrom = [ (pkgs.haskellPackages.callCabal2nix "gibbon-compiler" ./gibbon-compiler { }).env ];
+
     name = "basicGibbonEnv";
-    buildInputs = [ # Haskell
-                    ghc cabal-install stack
+    buildInputs = [
                     # C/C++
                     clang llvm gcc7 boehmgc uthash
                     # Rust