Add a flake file

Author: harendra-kumar

.packcheck.ignore

@@ -1,3 +1,5 @@
 .packcheck.ignore
 .github/workflows/packcheck.yml
-cabal.project
+cabal.project
+flake.lock
+flake.nix

default.nix

@@ -0,0 +1,19 @@
+{
+  description = "Packdiff Development Environment";
+
+  inputs = {
+    basepkgs.url = "git+ssh://git@github.com/composewell/streamly-packages?rev=76420910d9c74e5fc1d92d680499c97e4f94e873";
+    nixpkgs.follows = "basepkgs/nixpkgs";
+    nixpkgs-darwin.follows = "basepkgs/nixpkgs-darwin";
+  };
+
+  outputs = { self, nixpkgs, nixpkgs-darwin, basepkgs }:
+    basepkgs.nixpack.mkOutputs {
+      inherit nixpkgs nixpkgs-darwin basepkgs;
+      name = "packdiff";
+      sources = basepkgs.nixpack.lib.localSource "packdiff" ./.;
+      packages = basepkgs.nixpack.lib.devPackage "packdiff";
+      #sources = import ./sources.nix;
+      #packages = import ./packages.nix;
+    };
+}