adding flake with sbcl and direnv

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -0,0 +1 @@
+/.direnv/

flake.lock

@@ -0,0 +1,39 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1656928814,
+        "narHash": "sha256-RIFfgBuKz6Hp89yRr7+NR5tzIAbn52h8vT6vXkYjZoM=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "7e2a3b3dfd9af950a856d66b0a7d01e3c18aa249",
+        "type": "github"
+      },
+      "original": {
+        "id": "flake-utils",
+        "type": "indirect"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1657802959,
+        "narHash": "sha256-9+JWARSdlL8KiH3ymnKDXltE1vM+/WEJ78F5B1kjXys=",
+        "path": "/nix/store/v3s2diqbiykxvlfzcgjcpgk9fhbhy9mg-source",
+        "rev": "4a01ca36d6bfc133bc617e661916a81327c9bbc8",
+        "type": "path"
+      },
+      "original": {
+        "id": "nixpkgs",
+        "type": "indirect"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "learning Common Lisp";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let pkgs = nixpkgs.legacyPackages.${system}; in
+        {
+          devShells.default = pkgs.mkShell {
+            buildInputs = [ pkgs.sbcl ];
+          };
+        }
+      );
+  # see https://serokell.io/blog/practical-nix-flakes
+
+}