Small beginnings

modules/perSystem.nix

@@ -0,0 +1,43 @@
+{ config, lib, self, ... }:
+let
+  inherit (lib)
+    mapAttrs
+    mkOption
+    types
+    ;
+
+  rootConfig = config;
+
+in
+{
+  options = {
+    systems = mkOption {
+      description = "All the system types to enumerate in the flake.";
+      type = types.listOf types.str;
+      default = [ ];
+    };
+
+    perInput = mkOption {
+      description = "Function from system to function from flake to system-specific attributes.";
+      type = types.functionTo (types.functionTo (types.lazyAttrsOf types.unspecified));
+    };
+
+    perSystem = mkOption {
+      description = "A function from system to flake-like attributes omitting the <system> attribute.";
+      type = types.functionTo (types.submoduleWith {
+        modules = [
+          ({ config, system, ... }: {
+            _file = ./perSystem.nix;
+            config = {
+              _module.args.inputs' = mapAttrs (k: rootConfig.perInput system) self.inputs;
+              _module.args.self' = rootConfig.perInput system self;
+            };
+          })
+        ];
+        shorthandOnlyDefinesConfig = false;
+      });
+    };
+  };
+
+  config.perSystem = system: { _module.args.system = system; };
+}