fix flake

flake.nix

@@ -29,7 +29,7 @@
           pkgs.haskell.lib.doJailbreak (pkg.overrideAttrs (_: { meta = { }; }));
 
         packageName = "matebeamter";
-      in {
+      in rec {
         packages.${packageName} = # (ref:haskell-package-def)
           haskellPackages.callCabal2nix packageName self rec {
             mateamt = mateamt-src.defaultPackage.${system};
@@ -37,13 +37,14 @@
 
         defaultPackage = self.packages.${system}.${packageName};
 
-        devShell = pkgs.mkShell {
+        devShell = haskellPackages.shellFor {
+          packages = p: [ defaultPackage ];
+          withHoogle = true;
           buildInputs = with haskellPackages; [
             haskell-language-server
             ghcid
             cabal-install
           ];
-          inputsFrom = builtins.attrValues self.packages.${system};
         };
       });
 }