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);
     }
 }
 

src/procedure2/CMakeLists.txt

@@ -4,8 +4,10 @@ set(SELF_LIB xo_procedure2)
 set(SELF_SRCS
     init_procedure2.cpp
     init_primitives.cpp
+    procedure2_register_primitives.cpp
     procedure2_register_types.cpp
     procedure2_register_facets.cpp
+    ObjectPrimitives.cpp
     PrimitiveRegistry.cpp
     DPrimitive.cpp
     DSimpleRcx.cpp

src/procedure2/ObjectPrimitives.cpp

@@ -0,0 +1,45 @@
+/** @file ObjectPrimitives.cpp
+ *
+ *  @author Roland Conybeare, Mar 2026
+ **/
+
+#include "ObjectPrimitives.hpp"
+#include "Primitive_gco_2_gco_gco.hpp"
+#include <xo/object2/Sequence.hpp>
+#include <xo/object2/Integer.hpp>
+
+namespace xo {
+    using xo::scm::ASequence;
+    using xo::mm::AAllocator;
+    using xo::mm::AGCObject;
+
+    namespace scm {
+
+        // TODO: seq_gc -> obj<ASequence>
+        //       n_gco -> obj<AGCObject,DInteger>
+        //
+        obj<AGCObject>
+        xfer_nth(obj<ARuntimeContext> rcx,
+                 obj<AGCObject> seq_gco,
+                 obj<AGCObject> n_gco)
+        {
+            scope log(XO_DEBUG(true));
+
+            (void)rcx;
+
+            obj<ASequence> seq = seq_gco.to_facet<ASequence>();
+            auto n = obj<AGCObject,DInteger>::from(n_gco);
+
+            return seq.at(n->value());
+        }
+
+        DPrimitive_gco_2_gco_gco *
+        ObjectPrimitives::make_nth_pm(obj<AAllocator> mm)
+        {
+            return DPrimitive_gco_2_gco_gco::_make(mm, "nth", &xfer_nth);
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end ObjectPrimitives.cpp */

src/procedure2/init_procedure2.cpp

@@ -7,6 +7,7 @@
 #include "init_primitives.hpp"
 #include "procedure2_register_facets.hpp"
 #include "procedure2_register_types.hpp"
+#include "procedure2_register_primitives.hpp"
 
 #include <xo/object2/init_object2.hpp>
 #include <xo/alloc2/CollectorTypeRegistry.hpp>
@@ -14,6 +15,8 @@
 namespace xo {
     using xo::scm::procedure2_register_facets;
     using xo::scm::procedure2_register_types;
+    using xo::scm::procedure2_register_primitives;
+    using xo::scm::PrimitiveRegistry;
     using xo::mm::CollectorTypeRegistry;
 
     void
@@ -22,6 +25,7 @@ namespace xo {
         procedure2_register_facets();
 
         CollectorTypeRegistry::instance().register_types(&procedure2_register_types);
+        PrimitiveRegistry::instance().register_primitives(&procedure2_register_primitives);
     }
 
     InitEvidence

src/procedure2/procedure2_register_primitives.cpp

@@ -0,0 +1,73 @@
+/** @file procedure2_register_primitives.cpp
+ *
+ *  @author Roland Conybeare, Mar 2026
+ **/
+
+#include "procedure2_register_primitives.hpp"
+#include "ObjectPrimitives.hpp"
+#include "Primitive_gco_2_gco_gco.hpp"
+#include <xo/object2/Sequence.hpp>
+#include <xo/object2/Integer.hpp>
+
+namespace xo {
+    using xo::scm::ASequence;
+    using xo::mm::AAllocator;
+    using xo::mm::AGCObject;
+
+    namespace scm {
+        template <typename PrimitiveRepr>
+        bool install_aux(InstallSink sink,
+                         PrimitiveRepr * pm,
+                         InstallFlags flags)
+        {
+            scope log(XO_DEBUG(true));
+
+            if ((flags & InstallFlags::f_generalpurpose) == InstallFlags::f_generalpurpose) {
+                log && log("create primitive", xtag("name", pm->name()));
+
+                return sink(pm->name(),
+                            pm->fn_td(),
+                            obj<AProcedure,PrimitiveRepr>(pm),
+                            flags);
+            } else {
+                log && log("skip primitive", xtag("name", pm->name()));
+
+                return true;
+            }
+        }
+
+        template <typename Primitive>
+        bool install_aux(InstallSink sink,
+                         obj<AAllocator> mm,
+                         std::string_view name,
+                         typename Primitive::FunctionPtrType impl,
+                         InstallFlags flags)
+        {
+            if (flags != InstallFlags::f_none) {
+                auto pm
+                    = Primitive::_make(mm, name, impl);
+
+                return install_aux(sink, pm, flags);
+            } else {
+                return true;
+            }
+        }
+
+        bool
+        procedure2_register_primitives(obj<xo::mm::AAllocator> mm,
+                                       InstallSink sink,
+                                       InstallFlags flags)
+        {
+            scope log(XO_DEBUG(true));
+
+            bool ok = true;
+
+            ok = ok & install_aux(sink, ObjectPrimitives::make_nth_pm(mm), flags);
+
+            return ok;
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end procedure2_register_primitives.cpp */