xo-interpreter2 stack: modularize nth() primitive setup/install

include/xo/procedure2/DPrimitive.hpp

@@ -72,6 +72,7 @@ namespace xo {
         template <typename Fn>
         class Primitive {
         public:
+            using FunctionPtrType = Fn;
             using Traits = detail::PmFnTraits<Fn>;
 
             using ACollector = xo::mm::ACollector;

include/xo/procedure2/ObjectPrimitives.hpp

@@ -0,0 +1,29 @@
+/** @file ObjectPrimitives.hpp
+ *
+ *  @author Roland Conybeare, Mar 2026
+ **/
+
+#pragma once
+
+#include <xo/procedure2/DPrimitive_gco_2_gco_gco.hpp>
+
+namespace xo {
+    namespace scm {
+        /** @brief primitives centered on object2/ data structures.
+         *
+         *  Note: they don't reside in object2/ because DPrimitive
+         *  not available yet at that level
+         **/
+        class ObjectPrimitives {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+
+        public:
+            /** create primitive for fetching nth element of a sequence **/
+            static DPrimitive_gco_2_gco_gco * make_nth_pm(obj<AAllocator> mm);
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end ObjectPrimitives.hpp */

include/xo/procedure2/procedure2_register_primitives.hpp

@@ -10,8 +10,10 @@
 
 namespace xo {
     namespace scm {
-        /** Register gc-aware (AGCObject,DRepr) combinations with garbage collector @p gc **/
-        bool procedure2_register_primitives(obj<xo::mm::AAllocator> gc, InstallSink sink);
+        /** Register primitive-factories **/
+        bool procedure2_register_primitives(obj<xo::mm::AAllocator> gc,
+                                            InstallSink sink,
+                                            InstallFlags flags);
     }
 }