Add simple way of running without entering shell

flake.nix

@@ -10,19 +10,22 @@
     flake-utils.lib.eachDefaultSystem (system:
       let
         overlays = [  ];
-        # see https://github.com/nix-community/poetry2nix/tree/master#api for more functions and examples.
         pkgs = nixpkgs.legacyPackages.${system};
-      in
-        {
-          packages = {
-            default = self.packages.${system}.myapp;
-          };
-
-          devShells.default = pkgs.mkShell {
-            packages = with pkgs; [
+        buildInputs = with pkgs; [
           R
           rPackages.RSiena
         ];
+        name = "run-calc";
+        runCalc = (pkgs.writeScriptBin name (builtins.readFile ./test_rsiena_installation.R));
+      in rec {
+        defaultPackage = packages.runCalc;
+        packages.runCalc = pkgs.symlinkJoin {
+          name = name;
+          paths = [ runCalc ] ++ buildInputs;
+        };
+
+          devShells.default = pkgs.mkShell {
+            packages = buildInputs ++ [runCalc];
           };
         });
 }