diff --git a/include/xo/expression2/DApplyExpr.hpp b/include/xo/expression2/DApplyExpr.hpp
index bc5cdc47..cb0be70f 100644
--- a/include/xo/expression2/DApplyExpr.hpp
+++ b/include/xo/expression2/DApplyExpr.hpp
@@ -21,8 +21,8 @@ namespace xo {
          **/
         class DApplyExpr {
         public:
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -85,7 +85,7 @@ namespace xo {
             ///@{
 
             DApplyExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-applyexpr-printable-facet **/
diff --git a/include/xo/expression2/DConstant.hpp b/include/xo/expression2/DConstant.hpp
index e81a7b2d..bf901537 100644
--- a/include/xo/expression2/DConstant.hpp
+++ b/include/xo/expression2/DConstant.hpp
@@ -8,7 +8,6 @@
 #include "Expression.hpp"
 #include "TypeRef.hpp"
 #include "exprtype.hpp"
-//#include <xo/alloc2/Collector.hpp>
 #include <xo/alloc2/GCObject.hpp>
 #include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/reflect/TaggedPtr.hpp>
@@ -22,8 +21,8 @@ namespace xo {
         public:
             using TaggedPtr = xo::reflect::TaggedPtr;
             using TypeDescr = xo::reflect::TypeDescr;
-            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
+            using VisitReason = xo::mm::VisitReason;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using typeseq = xo::reflect::typeseq;
@@ -65,7 +64,7 @@ namespace xo {
             ///@{
 
             DConstant * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-constant-printable-facet **/
diff --git a/include/xo/expression2/DDefineExpr.hpp b/include/xo/expression2/DDefineExpr.hpp
index 474a4122..3f0071fd 100644
--- a/include/xo/expression2/DDefineExpr.hpp
+++ b/include/xo/expression2/DDefineExpr.hpp
@@ -26,6 +26,7 @@ namespace xo {
             using ppindentinfo = xo::print::ppindentinfo;
             using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
 
@@ -75,7 +76,7 @@ namespace xo {
             ///@{
 
             DDefineExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-defineexpr-printable-facet **/
diff --git a/include/xo/expression2/DGlobalSymtab.hpp b/include/xo/expression2/DGlobalSymtab.hpp
index b3840a69..4a7fdf93 100644
--- a/include/xo/expression2/DGlobalSymtab.hpp
+++ b/include/xo/expression2/DGlobalSymtab.hpp
@@ -30,9 +30,9 @@ namespace xo {
             using value_type = Binding;
             using ArenaHashMapConfig = xo::map::ArenaHashMapConfig;
             using repr_type = xo::map::DArenaHashMap<key_type, Binding::slot_type>;
-            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using MemorySizeVisitor = xo::mm::MemorySizeVisitor;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -116,7 +116,7 @@ namespace xo {
             ///@{
 
             DGlobalSymtab * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-globalsymtab-printable-facet printable facet **/
diff --git a/include/xo/expression2/DIfElseExpr.hpp b/include/xo/expression2/DIfElseExpr.hpp
index 04a354dd..bc83ccd4 100644
--- a/include/xo/expression2/DIfElseExpr.hpp
+++ b/include/xo/expression2/DIfElseExpr.hpp
@@ -8,7 +8,6 @@
 #include "Expression.hpp"
 #include "TypeRef.hpp"
 #include "exprtype.hpp"
-//#include <xo/alloc2/Collector.hpp>
 #include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/alloc2/Allocator.hpp>
 #include <string>
@@ -21,8 +20,8 @@ namespace xo {
          **/
         class DIfElseExpr {
         public:
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -99,7 +98,7 @@ namespace xo {
             ///@{
 
             DIfElseExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/expression2/DLambdaExpr.hpp b/include/xo/expression2/DLambdaExpr.hpp
index e4b0296d..b7fc76a8 100644
--- a/include/xo/expression2/DLambdaExpr.hpp
+++ b/include/xo/expression2/DLambdaExpr.hpp
@@ -21,8 +21,8 @@ namespace xo {
          **/
         class DLambdaExpr {
         public:
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -88,7 +88,7 @@ namespace xo {
 
             std::size_t shallow_size() const noexcept;
             DLambdaExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-lambdaexpr-printable-facet **/
diff --git a/include/xo/expression2/DLocalSymtab.hpp b/include/xo/expression2/DLocalSymtab.hpp
index 081742b0..b658bbd5 100644
--- a/include/xo/expression2/DLocalSymtab.hpp
+++ b/include/xo/expression2/DLocalSymtab.hpp
@@ -20,8 +20,8 @@ namespace xo {
         public:
             using DArray = xo::scm::DArray;
             using ppindentinfo = xo::print::ppindentinfo;
-            //using ACollector = xo::mm::ACollector;
             using AGCObject = xo::mm::AGCObject;
+            using VisitReason = xo::mm::VisitReason;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             /* note: uint16_t would be fine too */
@@ -100,7 +100,7 @@ namespace xo {
             ///@{
 
             DLocalSymtab * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup xo-localsymtab-printable-facet printable facet **/
diff --git a/include/xo/expression2/DSequenceExpr.hpp b/include/xo/expression2/DSequenceExpr.hpp
index 4a103e0e..e919ae13 100644
--- a/include/xo/expression2/DSequenceExpr.hpp
+++ b/include/xo/expression2/DSequenceExpr.hpp
@@ -23,8 +23,8 @@ namespace xo {
          **/
         class DSequenceExpr {
         public:
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
             using size_type = DArray::size_type;
@@ -75,7 +75,7 @@ namespace xo {
             ///@{
 
             DSequenceExpr * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/expression2/DTypename.hpp b/include/xo/expression2/DTypename.hpp
index 7ddacd21..64ec86bc 100644
--- a/include/xo/expression2/DTypename.hpp
+++ b/include/xo/expression2/DTypename.hpp
@@ -24,8 +24,8 @@ namespace xo {
         class DTypename {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AGCObject = xo::mm::AGCObject;
             using AAllocator = xo::mm::AAllocator;
 
@@ -56,7 +56,7 @@ namespace xo {
             ///@{
 
             DTypename * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-typename-printable-facet **/
diff --git a/include/xo/expression2/DVarRef.hpp b/include/xo/expression2/DVarRef.hpp
index 002e511a..93224199 100644
--- a/include/xo/expression2/DVarRef.hpp
+++ b/include/xo/expression2/DVarRef.hpp
@@ -21,8 +21,8 @@ namespace xo {
         class DVarRef {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
 
@@ -57,7 +57,7 @@ namespace xo {
             ///@{
 
             DVarRef * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-variable-printable-facet **/
diff --git a/include/xo/expression2/DVariable.hpp b/include/xo/expression2/DVariable.hpp
index 5813ae1b..158ef842 100644
--- a/include/xo/expression2/DVariable.hpp
+++ b/include/xo/expression2/DVariable.hpp
@@ -22,8 +22,8 @@ namespace xo {
         class DVariable {
         public:
             using ppindentinfo = xo::print::ppindentinfo;
-            //using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
 
@@ -65,7 +65,7 @@ namespace xo {
             ///@{
 
             DVariable * gco_shallow_move(obj<AGCObjectVisitor> gc) noexcept;
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-variable-printable-facet **/
diff --git a/include/xo/expression2/TypeRef.hpp b/include/xo/expression2/TypeRef.hpp
index f56028ba..c93158fb 100644
--- a/include/xo/expression2/TypeRef.hpp
+++ b/include/xo/expression2/TypeRef.hpp
@@ -26,8 +26,8 @@ namespace xo {
             using TypeDescr = xo::reflect::TypeDescr;
             using type_var = flatstring<20>;
             using prefix_type = flatstring<8>;
-            using ACollector = xo::mm::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using VisitReason = xo::mm::VisitReason;
             using ppindentinfo = xo::print::ppindentinfo;
 
         public:
@@ -75,7 +75,7 @@ namespace xo {
             bool pretty(const ppindentinfo & ppii) const;
 
             /** gc support **/
-            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
+            void visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept;
 
         private:
             TypeRef(const type_var & id, TypeDescr td);
diff --git a/include/xo/expression2/define/IGCObject_DDefineExpr.hpp b/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
index 6a233f92..c07c8e4e 100644
--- a/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
+++ b/include/xo/expression2/define/IGCObject_DDefineExpr.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DDefineExpr & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DDefineExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp b/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
index 399d9398..a1a2fac4 100644
--- a/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DApplyExpr.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DApplyExpr & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DApplyExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DConstant.hpp b/include/xo/expression2/detail/IGCObject_DConstant.hpp
index b2e624be..82783948 100644
--- a/include/xo/expression2/detail/IGCObject_DConstant.hpp
+++ b/include/xo/expression2/detail/IGCObject_DConstant.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DConstant & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DConstant & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp b/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
index 80a49f22..3156fe58 100644
--- a/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DIfElseExpr.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DIfElseExpr & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DIfElseExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp b/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
index 5decc2a0..ec4faded 100644
--- a/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DLambdaExpr.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DLambdaExpr & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DLambdaExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp b/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
index 54bab050..1b927e01 100644
--- a/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
+++ b/include/xo/expression2/detail/IGCObject_DSequenceExpr.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DSequenceExpr & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DSequenceExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/detail/IGCObject_DVarRef.hpp b/include/xo/expression2/detail/IGCObject_DVarRef.hpp
index 98c65aab..085999f9 100644
--- a/include/xo/expression2/detail/IGCObject_DVarRef.hpp
+++ b/include/xo/expression2/detail/IGCObject_DVarRef.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DVarRef & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DVarRef & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp b/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
index 334c0ea9..ee24adfb 100644
--- a/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
+++ b/include/xo/expression2/symtab/IGCObject_DGlobalSymtab.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DGlobalSymtab & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DGlobalSymtab & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp b/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
index c7890a79..cbd98904 100644
--- a/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
+++ b/include/xo/expression2/symtab/IGCObject_DLocalSymtab.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DLocalSymtab & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DLocalSymtab & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/typename/IGCObject_DTypename.hpp b/include/xo/expression2/typename/IGCObject_DTypename.hpp
index e8946864..cdd91734 100644
--- a/include/xo/expression2/typename/IGCObject_DTypename.hpp
+++ b/include/xo/expression2/typename/IGCObject_DTypename.hpp
@@ -43,6 +43,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -57,7 +58,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DTypename & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DTypename & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/expression2/variable/IGCObject_DVariable.hpp b/include/xo/expression2/variable/IGCObject_DVariable.hpp
index 3a31f155..9e173090 100644
--- a/include/xo/expression2/variable/IGCObject_DVariable.hpp
+++ b/include/xo/expression2/variable/IGCObject_DVariable.hpp
@@ -45,6 +45,7 @@ namespace xo {
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
             using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
+            using VisitReason = xo::mm::AGCObject::VisitReason;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -59,7 +60,7 @@ Arguably abusing the word 'visitor' here **/
             /** Invoke fn.visit_child(iface,data) for each child GCObject pointer.
 Context: provides address of data pointer so it can be updated in place
 when @p fn invokes garbage collector reentry point **/
-            static void visit_gco_children(DVariable & self, obj<AGCObjectVisitor> fn) noexcept;
+            static void visit_gco_children(DVariable & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/src/expression2/DApplyExpr.cpp b/src/expression2/DApplyExpr.cpp
index 2776b438..0f9a5c5c 100644
--- a/src/expression2/DApplyExpr.cpp
+++ b/src/expression2/DApplyExpr.cpp
@@ -125,23 +125,16 @@ namespace xo {
         }
 
         void
-        DApplyExpr::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DApplyExpr::visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept
         {
-            typeref_.visit_gco_children(gc);
+            typeref_.visit_gco_children(reason, gc);
 
-            {
-                gc.visit_poly_child(&fn_);
-                //obj<AGCObject> fn_gco = fn_.to_facet<AGCObject>();
-                //gc.forward_inplace(fn_gco.iface(), (void **)&fn_.data_);
-            }
+            gc.visit_poly_child(reason, &fn_);
 
             for (size_type i = 0; i < n_args_; ++i) {
                 obj<AExpression> & arg = args_[i];
 
-                // runtime poly here
-                gc.visit_poly_child(&arg);
-                //obj<AGCObject> arg_gco = arg.to_facet<AGCObject>();
-                //gc.forward_inplace(arg_gco.iface(), (void **)(&arg.data_));
+                gc.visit_poly_child(reason, &arg);
             }
         }
 
diff --git a/src/expression2/DConstant.cpp b/src/expression2/DConstant.cpp
index 19805cb5..441d24a0 100644
--- a/src/expression2/DConstant.cpp
+++ b/src/expression2/DConstant.cpp
@@ -3,8 +3,8 @@
  *  @author Roland Conybeare, Jan 2026
  **/
 
-#include "DConstant.hpp"
-#include "detail/IExpression_DConstant.hpp"
+#include "Constant.hpp"
+//#include "detail/IExpression_DConstant.hpp"
 #include "TypeDescr.hpp"
 #include <xo/object2/DFloat.hpp>
 #include <xo/object2/DInteger.hpp>
@@ -78,11 +78,12 @@ namespace xo {
         }
 
         void
-        DConstant::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DConstant::visit_gco_children(VisitReason reason,
+                                      obj<AGCObjectVisitor> gc) noexcept
         {
-            typeref_.visit_gco_children(gc);
+            typeref_.visit_gco_children(reason, gc);
 
-            gc.visit_child(&value_);
+            gc.visit_child(reason, &value_);
         }
 
         bool
diff --git a/src/expression2/DDefineExpr.cpp b/src/expression2/DDefineExpr.cpp
index ba481805..7bcf817b 100644
--- a/src/expression2/DDefineExpr.cpp
+++ b/src/expression2/DDefineExpr.cpp
@@ -85,11 +85,11 @@ namespace xo {
         }
 
         void
-        DDefineExpr::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DDefineExpr::visit_gco_children(VisitReason reason,
+                                        obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.visit_child(&lhs_var_);
-            //gc.forward_inplace(&rhs_);  // complicated - need to access via GCObject facet
-            gc.visit_poly_child(&rhs_);
+            gc.visit_child(reason, &lhs_var_);
+            gc.visit_poly_child(reason, &rhs_);
         }
 
         bool
@@ -104,9 +104,6 @@ namespace xo {
             if (lhs_var_)
                 assert(lhs.data());
 
-            (void)lhs;
-            (void)rhs;
-
             if (rhs_)
                 assert(rhs.data());
 
diff --git a/src/expression2/DGlobalSymtab.cpp b/src/expression2/DGlobalSymtab.cpp
index f5df4a4c..7b6bd760 100644
--- a/src/expression2/DGlobalSymtab.cpp
+++ b/src/expression2/DGlobalSymtab.cpp
@@ -269,15 +269,22 @@ namespace xo {
         }
 
         void
-        DGlobalSymtab::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DGlobalSymtab::visit_gco_children(VisitReason reason,
+                                          obj<AGCObjectVisitor> gc) noexcept
         {
             // map_ doesn't contain any gc-owned data, can skip
 
+#ifdef __APPLE__
+            // clang not recognizing these as comptime eligible
+            assert(var_map_.is_gc_eligible() == false);
+            assert(type_map_.is_gc_eligible() == false);
+#else
             static_assert(var_map_.is_gc_eligible() == false);
             static_assert(type_map_.is_gc_eligible() == false);
+#endif
 
-            gc.visit_child(&vars_);
-            gc.visit_child(&types_);
+            gc.visit_child(reason, &vars_);
+            gc.visit_child(reason, &types_);
         }
 
         // ----- printable facet -----
diff --git a/src/expression2/DIfElseExpr.cpp b/src/expression2/DIfElseExpr.cpp
index b8758387..6042104b 100644
--- a/src/expression2/DIfElseExpr.cpp
+++ b/src/expression2/DIfElseExpr.cpp
@@ -89,26 +89,15 @@ namespace xo {
         }
 
         void
-        DIfElseExpr::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DIfElseExpr::visit_gco_children(VisitReason reason,
+                                        obj<AGCObjectVisitor> gc) noexcept
         {
-            typeref_.visit_gco_children(gc);
+            typeref_.visit_gco_children(reason, gc);
 
             // GC needs to locate AGCObject iface for each member.
-            {
-                gc.visit_poly_child(&test_);
-                //auto gco = test_.to_facet<AGCObject>();
-                //gc.forward_inplace(gco.iface(), (void **)&(test_.data_));
-            }
-            {
-                gc.visit_poly_child(&when_true_);
-                //auto gco = when_true_.to_facet<AGCObject>();
-                //gc.forward_inplace(gco.iface(), (void **)&(when_true_.data_));
-            }
-            {
-                gc.visit_poly_child(&when_false_);
-                //auto gco = when_false_.to_facet<AGCObject>();
-                //gc.forward_inplace(gco.iface(), (void **)&(when_false_.data_));
-            }
+            gc.visit_poly_child(reason, &test_);
+            gc.visit_poly_child(reason, &when_true_);
+            gc.visit_poly_child(reason, &when_false_);
         }
 
         // ----- printable facet -----
diff --git a/src/expression2/DLambdaExpr.cpp b/src/expression2/DLambdaExpr.cpp
index c73ccc8a..1b512b0c 100644
--- a/src/expression2/DLambdaExpr.cpp
+++ b/src/expression2/DLambdaExpr.cpp
@@ -146,26 +146,15 @@ namespace xo {
         }
 
         void
-        DLambdaExpr::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept {
-            typeref_.visit_gco_children(gc);
-
-            gc.visit_child(&name_);
-            //{
-            //    auto iface = xo::facet::impl_for<AGCObject,DUniqueString>();
-            //    gc.forward_inplace(&iface, (void **)(&name_));
-            //}
+        DLambdaExpr::visit_gco_children(VisitReason reason,
+                                        obj<AGCObjectVisitor> gc) noexcept {
+            typeref_.visit_gco_children(reason, gc);
 
+            gc.visit_child(reason, &name_);
             // type_name_str_
 
-            {
-                gc.visit_child(&local_symtab_);
-                //gc.forward_inplace(&local_symtab_);
-            }
-
-            {
-                gc.visit_poly_child(&body_expr_);
-                //gc.forward_pivot_inplace(&body_expr_);
-            }
+            gc.visit_child(reason, &local_symtab_);
+            gc.visit_poly_child(reason, &body_expr_);
 
             // xxx free_var_set
             // xxx captured_var_set
diff --git a/src/expression2/DLocalSymtab.cpp b/src/expression2/DLocalSymtab.cpp
index 1fa1afd8..9d85a97c 100644
--- a/src/expression2/DLocalSymtab.cpp
+++ b/src/expression2/DLocalSymtab.cpp
@@ -119,11 +119,12 @@ namespace xo {
         }
 
         void
-        DLocalSymtab::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DLocalSymtab::visit_gco_children(VisitReason reason,
+                                         obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.visit_child(&parent_);
-            gc.visit_child(&vars_);
-            gc.visit_child(&types_);
+            gc.visit_child(reason, &parent_);
+            gc.visit_child(reason, &vars_);
+            gc.visit_child(reason, &types_);
         }
 
         // ----- printable facet -----
diff --git a/src/expression2/DSequenceExpr.cpp b/src/expression2/DSequenceExpr.cpp
index a180a5fb..8fdfcf9b 100644
--- a/src/expression2/DSequenceExpr.cpp
+++ b/src/expression2/DSequenceExpr.cpp
@@ -120,11 +120,11 @@ namespace xo {
         }
 
         void
-        DSequenceExpr::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DSequenceExpr::visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept
         {
-            typeref_.visit_gco_children(gc);
+            typeref_.visit_gco_children(reason, gc);
 
-            gc.visit_child(&expr_v_);
+            gc.visit_child(reason, &expr_v_);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/DTypename.cpp b/src/expression2/DTypename.cpp
index da73f28f..c8debab9 100644
--- a/src/expression2/DTypename.cpp
+++ b/src/expression2/DTypename.cpp
@@ -47,15 +47,11 @@ namespace xo {
         }
 
         void
-        DTypename::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DTypename::visit_gco_children(VisitReason reason,
+                                      obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.visit_child(&name_);
-            //gc.forward_inplace(const_cast<DUniqueString**>(&name_));
-            {
-                gc.visit_poly_child(&type_);
-                //auto e = type_.to_facet<AGCObject>();
-                //gc.forward_inplace(e.iface(), (void **)&(type_.data_));
-            }
+            gc.visit_child(reason, &name_);
+            gc.visit_poly_child(reason, &type_);
         }
 
         bool
diff --git a/src/expression2/DVarRef.cpp b/src/expression2/DVarRef.cpp
index 57a39153..b73efe10 100644
--- a/src/expression2/DVarRef.cpp
+++ b/src/expression2/DVarRef.cpp
@@ -65,9 +65,10 @@ namespace xo {
         }
 
         void
-        DVarRef::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DVarRef::visit_gco_children(VisitReason reason,
+                                    obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.visit_child(&vardef_);
+            gc.visit_child(reason, &vardef_);
             //auto iface = xo::facet::impl_for<AGCObject,DVariable>();
             //gc.forward_inplace(&iface, (void **)vardef_.data_);
 
diff --git a/src/expression2/DVariable.cpp b/src/expression2/DVariable.cpp
index 209764cd..066aeb50 100644
--- a/src/expression2/DVariable.cpp
+++ b/src/expression2/DVariable.cpp
@@ -9,7 +9,6 @@
 #include <cstddef>
 
 namespace xo {
-    using xo::mm::ACollector;
     using xo::facet::typeseq;
 
     namespace scm {
@@ -45,9 +44,9 @@ namespace xo {
         }
 
         void
-        DVariable::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        DVariable::visit_gco_children(VisitReason reason, obj<AGCObjectVisitor> gc) noexcept
         {
-            typeref_.visit_gco_children(gc);
+            typeref_.visit_gco_children(reason, gc);
         }
 
         bool
diff --git a/src/expression2/IGCObject_DApplyExpr.cpp b/src/expression2/IGCObject_DApplyExpr.cpp
index d2574d64..610b675b 100644
--- a/src/expression2/IGCObject_DApplyExpr.cpp
+++ b/src/expression2/IGCObject_DApplyExpr.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DApplyExpr::visit_gco_children(DApplyExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DApplyExpr::visit_gco_children(DApplyExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DConstant.cpp b/src/expression2/IGCObject_DConstant.cpp
index be6f583d..20c71341 100644
--- a/src/expression2/IGCObject_DConstant.cpp
+++ b/src/expression2/IGCObject_DConstant.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DConstant::visit_gco_children(DConstant & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DConstant::visit_gco_children(DConstant & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DDefineExpr.cpp b/src/expression2/IGCObject_DDefineExpr.cpp
index f2ea0747..8540ab25 100644
--- a/src/expression2/IGCObject_DDefineExpr.cpp
+++ b/src/expression2/IGCObject_DDefineExpr.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DDefineExpr::visit_gco_children(DDefineExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DDefineExpr::visit_gco_children(DDefineExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DGlobalSymtab.cpp b/src/expression2/IGCObject_DGlobalSymtab.cpp
index 3070a26c..01153218 100644
--- a/src/expression2/IGCObject_DGlobalSymtab.cpp
+++ b/src/expression2/IGCObject_DGlobalSymtab.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DGlobalSymtab::visit_gco_children(DGlobalSymtab & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DGlobalSymtab::visit_gco_children(DGlobalSymtab & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DIfElseExpr.cpp b/src/expression2/IGCObject_DIfElseExpr.cpp
index 6f788e03..22878fea 100644
--- a/src/expression2/IGCObject_DIfElseExpr.cpp
+++ b/src/expression2/IGCObject_DIfElseExpr.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DIfElseExpr::visit_gco_children(DIfElseExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DIfElseExpr::visit_gco_children(DIfElseExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DLambdaExpr.cpp b/src/expression2/IGCObject_DLambdaExpr.cpp
index b4706c56..05bd85a0 100644
--- a/src/expression2/IGCObject_DLambdaExpr.cpp
+++ b/src/expression2/IGCObject_DLambdaExpr.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DLambdaExpr::visit_gco_children(DLambdaExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DLambdaExpr::visit_gco_children(DLambdaExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DLocalSymtab.cpp b/src/expression2/IGCObject_DLocalSymtab.cpp
index 5e37d826..7ccadca0 100644
--- a/src/expression2/IGCObject_DLocalSymtab.cpp
+++ b/src/expression2/IGCObject_DLocalSymtab.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DLocalSymtab::visit_gco_children(DLocalSymtab & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DLocalSymtab::visit_gco_children(DLocalSymtab & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DSequenceExpr.cpp b/src/expression2/IGCObject_DSequenceExpr.cpp
index 1f92c2e2..0cc84faa 100644
--- a/src/expression2/IGCObject_DSequenceExpr.cpp
+++ b/src/expression2/IGCObject_DSequenceExpr.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DSequenceExpr::visit_gco_children(DSequenceExpr & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DSequenceExpr::visit_gco_children(DSequenceExpr & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DTypename.cpp b/src/expression2/IGCObject_DTypename.cpp
index ca21870a..accbfc6e 100644
--- a/src/expression2/IGCObject_DTypename.cpp
+++ b/src/expression2/IGCObject_DTypename.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DTypename::visit_gco_children(DTypename & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DTypename::visit_gco_children(DTypename & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/IGCObject_DVarRef.cpp b/src/expression2/IGCObject_DVarRef.cpp
index 68d6e1d2..e169c37f 100644
--- a/src/expression2/IGCObject_DVarRef.cpp
+++ b/src/expression2/IGCObject_DVarRef.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DVarRef::visit_gco_children(DVarRef & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DVarRef::visit_gco_children(DVarRef & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/
diff --git a/src/expression2/TypeRef.cpp b/src/expression2/TypeRef.cpp
index 961ae148..e3178b7f 100644
--- a/src/expression2/TypeRef.cpp
+++ b/src/expression2/TypeRef.cpp
@@ -102,11 +102,10 @@ namespace xo {
         }
 
         void
-        TypeRef::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
+        TypeRef::visit_gco_children(VisitReason reason,
+                                    obj<AGCObjectVisitor> gc) noexcept
         {
-            //scope log(XO_DEBUG(true), xtag("type", type_.data()), xtag("type.tseq", type_._typeseq()));
-
-            gc.visit_poly_child(&type_);
+            gc.visit_poly_child(reason, &type_);
         }
 
         bool
diff --git a/src/expression2/facet/IGCObject_DVariable.cpp b/src/expression2/facet/IGCObject_DVariable.cpp
index 0a91bfb2..8734ca7a 100644
--- a/src/expression2/facet/IGCObject_DVariable.cpp
+++ b/src/expression2/facet/IGCObject_DVariable.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.gco_shallow_move(gc);
         }
         auto
-        IGCObject_DVariable::visit_gco_children(DVariable & self, obj<AGCObjectVisitor> fn) noexcept -> void
+        IGCObject_DVariable::visit_gco_children(DVariable & self, VisitReason reason, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.visit_gco_children(fn);
+            self.visit_gco_children(reason, fn);
         }
 
     } /*namespace scm*/