chore(nix): add nix flake (#14)

.gitignore

@@ -1,2 +1,7 @@
 _build
 *.install
+_build
+# nix ignores
+.direnv
+result
+.envrc

flake.nix

@@ -0,0 +1,39 @@
+{
+  description = "Conditional compilation via attributes for OCaml";
+
+  inputs.minttea.url = "github:leostera/minttea";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" "aarch64-linux" "aarch64-darwin" "x86_64-darwin" ];
+      perSystem = { config, self', inputs', pkgs, system, ... }:
+        let
+          inherit (pkgs) ocamlPackages mkShell;
+          inherit (ocamlPackages) buildDunePackage;
+          name = "config";
+          version = "0.0.1";
+        in
+          {
+            devShells = {
+              default = mkShell {
+                buildInputs = [ ocamlPackages.utop ];
+                inputsFrom = [ self'.packages.default ];
+              };
+            };
+
+            packages = {
+              default = buildDunePackage {
+                inherit version;
+                pname = name;
+                propagatedBuildInputs = with ocamlPackages; [
+                  inputs'.minttea.packages.spices
+                  sedlex
+                  ppxlib
+                ];
+                src = ./.;
+              };
+            };
+          };
+    };
+}