chore: Add flake.nix

Author: jcs090218

flake.nix

@@ -0,0 +1,48 @@
+{
+  description = "Development shell for Common Lisp with Qob";
+
+  inputs.nixpkgs.url = "nixpkgs/nixos-unstable";
+
+  outputs = { self, nixpkgs }:
+    let
+      # Define the systems you want to support
+      systems = [
+        "x86_64-linux"
+        "i686-linux"
+        "x86_64-darwin"
+        "aarch64-linux"
+        "aarch64-darwin"
+      ];
+    in
+      {
+        # Generate devShells for each system
+        devShells = nixpkgs.lib.genAttrs systems (system:
+          let
+            # Get the nixpkgs set for the current system
+            pkgs = nixpkgs.legacyPackages.${system};
+          in
+            {
+              # Define the default development shell for the system
+              default = pkgs.mkShell {
+                buildInputs = [
+                  pkgs.sbcl
+                  pkgs.gnumake
+                ];
+
+                shellHook = ''
+                    echo "Welcome to the Common Lisp development shell with Qob!"
+
+                    # Export `bin` to PATH.
+                    export PATH="$PATH:$PWD/bin"
+
+                    # Install if `bin/qob` is missing
+                    if [ ! -e bin/qob ]; then
+                      make install-ql-no-network
+                      make build
+                    fi
+                    '';
+              };
+            }
+        );
+      };
+}