diff --git a/idl/SyntaxStateMachine.json5 b/idl/SyntaxStateMachine.json5
index 8450b02b..d47656b7 100644
--- a/idl/SyntaxStateMachine.json5
+++ b/idl/SyntaxStateMachine.json5
@@ -10,7 +10,7 @@
         "<xo/type/Type.hpp>",
         "<xo/tokenizer2/Token.hpp>",
         "<xo/reflect/TypeDescr.hpp>",
-        "<xo/alloc2/Collector.hpp>"
+        "<xo/alloc2/GCObjectVisitor.hpp>"
     ],
     // extra includes in SyntaxStateMachine.hpp, if any
     user_hpp_includes: [],
@@ -27,7 +27,7 @@
     ],
     types: [
         { name: "TypeDescr", doc: [ "reflected c++ type" ], definition: "xo::reflect::TypeDescr" },
-        { name: "ACollector", doc: [ "gc interface" ], definition: "xo::mm::ACollector" },
+        { name: "AGCObjectVisitor", doc: [ "gc visitor interface" ], definition: "xo::mm::AGCObjectVisitor" },
         { name: "AGCObject", doc: [ "gc-aware object" ], definition: "xo::mm::AGCObject" },
         // { name: string, doc: [ string ], definition: string },
     ],
@@ -147,11 +147,11 @@
             ],
         },
         {
-            name: "forward_children",
-            doc: ["gc support: move immediate children to to-space and sub forwarding pointer"],
+            name: "visit_gco_children",
+            doc: ["gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each"],
             return_type: "void",
             args: [
-                {type: "obj<ACollector>", name: "gc"},
+                {type: "obj<AGCObjectVisitor>", name: "gc"},
             ],
         }
     ],
diff --git a/include/xo/reader2/DDefineSsm.hpp b/include/xo/reader2/DDefineSsm.hpp
index e372e299..e31c3b2a 100644
--- a/include/xo/reader2/DDefineSsm.hpp
+++ b/include/xo/reader2/DDefineSsm.hpp
@@ -73,7 +73,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DDefineSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -200,7 +200,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc);
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectExprSsm.hpp b/include/xo/reader2/DExpectExprSsm.hpp
index a1ba1c69..e73e1f16 100644
--- a/include/xo/reader2/DExpectExprSsm.hpp
+++ b/include/xo/reader2/DExpectExprSsm.hpp
@@ -6,7 +6,6 @@
 #pragma once
 
 #include "DSyntaxStateMachine.hpp"
-//#include "ParserStateMachine.hpp"
 #include "syntaxstatetype.hpp"
 #include <xo/facet/obj.hpp>
 #include <xo/indentlog/print/ppindentinfo.hpp>
@@ -18,7 +17,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DExpectExprSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -195,7 +194,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectFormalArglistSsm.hpp b/include/xo/reader2/DExpectFormalArglistSsm.hpp
index f28cbac1..954cdc72 100644
--- a/include/xo/reader2/DExpectFormalArglistSsm.hpp
+++ b/include/xo/reader2/DExpectFormalArglistSsm.hpp
@@ -55,7 +55,7 @@ namespace xo {
         class DExpectFormalArglistSsm : public DSyntaxStateMachine<DExpectFormalArglistSsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectFormalArglistSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -130,7 +130,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectQArraySsm.hpp b/include/xo/reader2/DExpectQArraySsm.hpp
index 068a5b93..2ec32eb4 100644
--- a/include/xo/reader2/DExpectQArraySsm.hpp
+++ b/include/xo/reader2/DExpectQArraySsm.hpp
@@ -7,7 +7,6 @@
 
 #include "DSyntaxStateMachine.hpp"
 #include <xo/object2/ListOps.hpp>
-//#include <xo/arena/DArena.hpp>
 #include <xo/facet/obj.hpp>
 
 namespace xo {
@@ -58,7 +57,7 @@ namespace xo {
         class DExpectQArraySsm : public DSyntaxStateMachine<DExpectQArraySsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectQArraySsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -124,7 +123,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectQListSsm.hpp b/include/xo/reader2/DExpectQListSsm.hpp
index c2119c8b..3b9ab53d 100644
--- a/include/xo/reader2/DExpectQListSsm.hpp
+++ b/include/xo/reader2/DExpectQListSsm.hpp
@@ -58,7 +58,7 @@ namespace xo {
         class DExpectQListSsm : public DSyntaxStateMachine<DExpectQListSsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectQListSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -124,7 +124,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectQLiteralSsm.hpp b/include/xo/reader2/DExpectQLiteralSsm.hpp
index f037c7d8..2538fb6f 100644
--- a/include/xo/reader2/DExpectQLiteralSsm.hpp
+++ b/include/xo/reader2/DExpectQLiteralSsm.hpp
@@ -15,7 +15,7 @@ namespace xo {
         class DExpectQLiteralSsm : public DSyntaxStateMachine<DExpectQLiteralSsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectQLiteralSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -129,7 +129,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DExpectSymbolSsm.hpp b/include/xo/reader2/DExpectSymbolSsm.hpp
index 9ca3e1a0..f4c3c156 100644
--- a/include/xo/reader2/DExpectSymbolSsm.hpp
+++ b/include/xo/reader2/DExpectSymbolSsm.hpp
@@ -21,7 +21,7 @@ namespace xo {
         class DExpectSymbolSsm : public DSyntaxStateMachine<DExpectSymbolSsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectSymbolSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -80,7 +80,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
         };
diff --git a/include/xo/reader2/DExpectTypeSsm.hpp b/include/xo/reader2/DExpectTypeSsm.hpp
index 7fae992d..d405e916 100644
--- a/include/xo/reader2/DExpectTypeSsm.hpp
+++ b/include/xo/reader2/DExpectTypeSsm.hpp
@@ -28,7 +28,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DExpectTypeSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -87,7 +87,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DGlobalEnv.hpp b/include/xo/reader2/DGlobalEnv.hpp
index 96cd5771..04605c4c 100644
--- a/include/xo/reader2/DGlobalEnv.hpp
+++ b/include/xo/reader2/DGlobalEnv.hpp
@@ -7,6 +7,7 @@
 
 #include <xo/expression2/DGlobalSymtab.hpp>
 #include <xo/object2/DArray.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 
 namespace xo {
     namespace scm {
@@ -27,8 +28,9 @@ namespace xo {
         public:
             using TypeDescr = xo::reflect::TypeDescr;
             using ACollector = xo::mm::ACollector;
-            using AAllocator = xo::mm::AAllocator;
             using AGCObject = xo::mm::AGCObject;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using AAllocator = xo::mm::AAllocator;
             using MemorySizeVisitor = xo::mm::MemorySizeVisitor;
             using ppindentinfo = xo::print::ppindentinfo;
             using size_type = std::uint32_t;
@@ -70,9 +72,8 @@ namespace xo {
             /** @defgroup scm-globalenv-gcobject-facet **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
             DGlobalEnv * shallow_move(obj<ACollector> gc) noexcept;
-            std::size_t forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
             /** @defgroup scm-globalenv-printable-facet **/
diff --git a/include/xo/reader2/DProgressSsm.hpp b/include/xo/reader2/DProgressSsm.hpp
index 487ba141..372b3af6 100644
--- a/include/xo/reader2/DProgressSsm.hpp
+++ b/include/xo/reader2/DProgressSsm.hpp
@@ -7,7 +7,6 @@
 
 #include "DSyntaxStateMachine.hpp"
 #include "syntaxstatetype.hpp"
-//#include <xo/expression2/Expression.hpp>
 #include <xo/facet/obj.hpp>
 
 #ifdef NOT_YET
@@ -90,7 +89,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DProgressSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -218,7 +217,7 @@ namespace xo {
             /** @defgroup scm-progressssm-gc-support gc support methods **/
             ///@{
 
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DQuoteSsm.hpp b/include/xo/reader2/DQuoteSsm.hpp
index fa598f83..542342ef 100644
--- a/include/xo/reader2/DQuoteSsm.hpp
+++ b/include/xo/reader2/DQuoteSsm.hpp
@@ -65,7 +65,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DQuoteSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -150,7 +150,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
         private:
diff --git a/include/xo/reader2/DSequenceSsm.hpp b/include/xo/reader2/DSequenceSsm.hpp
index e3c699c3..a7819048 100644
--- a/include/xo/reader2/DSequenceSsm.hpp
+++ b/include/xo/reader2/DSequenceSsm.hpp
@@ -29,7 +29,7 @@ namespace xo {
         class DSequenceSsm : public DSyntaxStateMachine<DSequenceSsm> {
         public:
             using Super = DSyntaxStateMachine<DSequenceSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -97,7 +97,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/DToplevelSeqSsm.hpp b/include/xo/reader2/DToplevelSeqSsm.hpp
index b33707e4..4103f45a 100644
--- a/include/xo/reader2/DToplevelSeqSsm.hpp
+++ b/include/xo/reader2/DToplevelSeqSsm.hpp
@@ -40,7 +40,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DToplevelSeqSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -161,7 +161,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/ParserResult.hpp b/include/xo/reader2/ParserResult.hpp
index 73ab38c6..823372da 100644
--- a/include/xo/reader2/ParserResult.hpp
+++ b/include/xo/reader2/ParserResult.hpp
@@ -32,7 +32,7 @@ namespace xo {
 
         class ParserResult {
         public:
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using ppindentinfo = xo::print::ppindentinfo;
 
         public:
@@ -69,7 +69,7 @@ namespace xo {
             bool pretty(const ppindentinfo & ppii) const;
 
             /** gc support: forward gc-eligible children **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
         public:
             /** none|expression|error_description
diff --git a/include/xo/reader2/ParserStack.hpp b/include/xo/reader2/ParserStack.hpp
index 80049a07..e4b414b4 100644
--- a/include/xo/reader2/ParserStack.hpp
+++ b/include/xo/reader2/ParserStack.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include "SyntaxStateMachine.hpp"
+#include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/arena/DArena.hpp>
 #include <xo/facet/obj.hpp>
 #include <xo/indentlog/print/pretty.hpp>
@@ -21,7 +22,8 @@ namespace xo {
          **/
         class ParserStack {
         public:
-            using ACollector = xo::mm::ACollector;
+            //using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -54,7 +56,7 @@ namespace xo {
             /** pretty-printer support **/
             bool pretty(const ppindentinfo & ppii) const;
 
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
         private:
             /** stack pointer: top of stack just before this instance created **/
diff --git a/include/xo/reader2/ParserStateMachine.hpp b/include/xo/reader2/ParserStateMachine.hpp
index cc313660..fedd574d 100644
--- a/include/xo/reader2/ParserStateMachine.hpp
+++ b/include/xo/reader2/ParserStateMachine.hpp
@@ -17,6 +17,7 @@
 #include <xo/object2/DArray.hpp>
 #include <xo/stringtable2/StringTable.hpp>
 #include <xo/alloc2/Allocator.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/arena/ArenaHashMapConfig.hpp>
 #include <xo/arena/DArena.hpp>
 
@@ -39,6 +40,7 @@ namespace xo {
         public:
             using TypeDescr = xo::reflect::TypeDescr;
             using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using ArenaConfig = xo::mm::ArenaConfig;
             using AGCObject = xo::mm::AGCObject;
@@ -352,7 +354,7 @@ namespace xo {
             ///@{
 
             /** update gc-aware exit pointers from this ParserStateMachine **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/QuoteSsm.hpp b/include/xo/reader2/QuoteSsm.hpp
index c0fb5429..801179e9 100644
--- a/include/xo/reader2/QuoteSsm.hpp
+++ b/include/xo/reader2/QuoteSsm.hpp
@@ -6,7 +6,7 @@
 #pragma once
 
 #include "DQuoteSsm.hpp"
-#include "ssm/ISyntaxStateMachine_DQuoteSsm.hpp"
-#include "ssm/IPrintable_DQuoteSsm.hpp"
+#include "quote/ISyntaxStateMachine_DQuoteSsm.hpp"
+#include "quote/IPrintable_DQuoteSsm.hpp"
 
 /* end QuoteSsm.hpp */
diff --git a/include/xo/reader2/SchematikaReader.hpp b/include/xo/reader2/SchematikaReader.hpp
index de3da42f..d70c2c04 100644
--- a/include/xo/reader2/SchematikaReader.hpp
+++ b/include/xo/reader2/SchematikaReader.hpp
@@ -8,17 +8,19 @@
 #include "ReaderConfig.hpp"
 #include "SchematikaParser.hpp"
 #include <xo/tokenizer2/Tokenizer.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 
 namespace xo {
     namespace scm {
         struct ReaderResult {
             using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using span_type = xo::mm::span<const char>;
 
             bool is_tk_error() const { return tk_error_.is_error(); }
 
             /** forward gc-aware pointers (called during gc cycle) **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             /** schematika expression parsed from input **/
             obj<AExpression> expr_;
@@ -40,6 +42,7 @@ namespace xo {
         class SchematikaReader {
         public:
             using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using MemorySizeVisitor = xo::mm::MemorySizeVisitor;
             using span_type = xo::mm::span<const char>;
@@ -107,7 +110,7 @@ namespace xo {
             void reset_to_idle_toplevel();
 
             /** update gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
         private:
             /** tokenizer converts a stream of chars
diff --git a/include/xo/reader2/apply/DApplySsm.hpp b/include/xo/reader2/apply/DApplySsm.hpp
index 64513f0c..f7ee1cce 100644
--- a/include/xo/reader2/apply/DApplySsm.hpp
+++ b/include/xo/reader2/apply/DApplySsm.hpp
@@ -65,7 +65,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DApplySsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -190,7 +190,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/apply/ISyntaxStateMachine_DApplySsm.hpp b/include/xo/reader2/apply/ISyntaxStateMachine_DApplySsm.hpp
index 04c7bddb..db3a147d 100644
--- a/include/xo/reader2/apply/ISyntaxStateMachine_DApplySsm.hpp
+++ b/include/xo/reader2/apply/ISyntaxStateMachine_DApplySsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dapplyssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DApplySsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DApplySsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DApplySsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DApplySsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/define/ISyntaxStateMachine_DDefineSsm.hpp b/include/xo/reader2/define/ISyntaxStateMachine_DDefineSsm.hpp
index 3487a328..d5338cd5 100644
--- a/include/xo/reader2/define/ISyntaxStateMachine_DDefineSsm.hpp
+++ b/include/xo/reader2/define/ISyntaxStateMachine_DDefineSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-ddefinessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DDefineSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DDefineSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DDefineSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DDefineSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/deftype/DDeftypeSsm.hpp b/include/xo/reader2/deftype/DDeftypeSsm.hpp
index a3e4c6cb..b1a6d910 100644
--- a/include/xo/reader2/deftype/DDeftypeSsm.hpp
+++ b/include/xo/reader2/deftype/DDeftypeSsm.hpp
@@ -66,7 +66,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DDeftypeSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -172,7 +172,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/deftype/ISyntaxStateMachine_DDeftypeSsm.hpp b/include/xo/reader2/deftype/ISyntaxStateMachine_DDeftypeSsm.hpp
index f3776f18..9bfdfba5 100644
--- a/include/xo/reader2/deftype/ISyntaxStateMachine_DDeftypeSsm.hpp
+++ b/include/xo/reader2/deftype/ISyntaxStateMachine_DDeftypeSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-ddeftypessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DDeftypeSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DDeftypeSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DDeftypeSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DDeftypeSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp b/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
index 88bc11b1..8e97a792 100644
--- a/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
+++ b/include/xo/reader2/env/IGCObject_DGlobalEnv.hpp
@@ -44,6 +44,7 @@ namespace xo {
             using size_type = xo::mm::AGCObject::size_type;
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -54,8 +55,10 @@ namespace xo {
             // non-const methods
             /** move instance using allocator **/
             static Opaque shallow_move(DGlobalEnv & self, obj<ACollector> gc) noexcept;
-            /** during GC: forward immdiate children **/
-            static void forward_children(DGlobalEnv & self, obj<ACollector> gc) noexcept;
+            /** 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(DGlobalEnv & self, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/reader2/expect_formal_arg/DExpectFormalArgSsm.hpp b/include/xo/reader2/expect_formal_arg/DExpectFormalArgSsm.hpp
index 318e340a..5c7e6dec 100644
--- a/include/xo/reader2/expect_formal_arg/DExpectFormalArgSsm.hpp
+++ b/include/xo/reader2/expect_formal_arg/DExpectFormalArgSsm.hpp
@@ -48,7 +48,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DExpectFormalArgSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -126,7 +126,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/expect_formal_arg/ISyntaxStateMachine_DExpectFormalArgSsm.hpp b/include/xo/reader2/expect_formal_arg/ISyntaxStateMachine_DExpectFormalArgSsm.hpp
index 7e100e40..a880fad3 100644
--- a/include/xo/reader2/expect_formal_arg/ISyntaxStateMachine_DExpectFormalArgSsm.hpp
+++ b/include/xo/reader2/expect_formal_arg/ISyntaxStateMachine_DExpectFormalArgSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectformalargssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectFormalArgSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectFormalArgSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectFormalArgSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectFormalArgSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/expect_listtype/DExpectListTypeSsm.hpp b/include/xo/reader2/expect_listtype/DExpectListTypeSsm.hpp
index 6e7c80b4..eeadd15c 100644
--- a/include/xo/reader2/expect_listtype/DExpectListTypeSsm.hpp
+++ b/include/xo/reader2/expect_listtype/DExpectListTypeSsm.hpp
@@ -62,7 +62,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DExpectListTypeSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -135,7 +135,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
         private:
diff --git a/include/xo/reader2/expect_listtype/ISyntaxStateMachine_DExpectListTypeSsm.hpp b/include/xo/reader2/expect_listtype/ISyntaxStateMachine_DExpectListTypeSsm.hpp
index 153c47a4..9ed4214c 100644
--- a/include/xo/reader2/expect_listtype/ISyntaxStateMachine_DExpectListTypeSsm.hpp
+++ b/include/xo/reader2/expect_listtype/ISyntaxStateMachine_DExpectListTypeSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectlisttypessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectListTypeSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectListTypeSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectListTypeSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectListTypeSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/expect_qdict/DExpectQDictSsm.hpp b/include/xo/reader2/expect_qdict/DExpectQDictSsm.hpp
index 31aa2be3..5ed40fab 100644
--- a/include/xo/reader2/expect_qdict/DExpectQDictSsm.hpp
+++ b/include/xo/reader2/expect_qdict/DExpectQDictSsm.hpp
@@ -63,7 +63,7 @@ namespace xo {
         class DExpectQDictSsm : public DSyntaxStateMachine<DExpectQDictSsm> {
         public:
             using Super = DSyntaxStateMachine<DExpectQDictSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
 
@@ -159,7 +159,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/expect_qdict/ISyntaxStateMachine_DExpectQDictSsm.hpp b/include/xo/reader2/expect_qdict/ISyntaxStateMachine_DExpectQDictSsm.hpp
index 7014238f..c629e07b 100644
--- a/include/xo/reader2/expect_qdict/ISyntaxStateMachine_DExpectQDictSsm.hpp
+++ b/include/xo/reader2/expect_qdict/ISyntaxStateMachine_DExpectQDictSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectqdictssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectQDictSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectQDictSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectQDictSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectQDictSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ifelse/DIfElseSsm.hpp b/include/xo/reader2/ifelse/DIfElseSsm.hpp
index 27043bdf..fd7b8168 100644
--- a/include/xo/reader2/ifelse/DIfElseSsm.hpp
+++ b/include/xo/reader2/ifelse/DIfElseSsm.hpp
@@ -55,7 +55,7 @@ namespace xo {
         class DIfElseSsm : public DSyntaxStateMachine<DIfElseSsm> {
         public:
             using Super = DSyntaxStateMachine<DIfElseSsm>;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -171,7 +171,7 @@ namespace xo {
             /** @defgroup scm-ifelsessm-gc-support gc support methods **/
             ///@{
 
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/ifelse/ISyntaxStateMachine_DIfElseSsm.hpp b/include/xo/reader2/ifelse/ISyntaxStateMachine_DIfElseSsm.hpp
index 8a3991fb..17f6b4cd 100644
--- a/include/xo/reader2/ifelse/ISyntaxStateMachine_DIfElseSsm.hpp
+++ b/include/xo/reader2/ifelse/ISyntaxStateMachine_DIfElseSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-difelsessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DIfElseSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DIfElseSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DIfElseSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DIfElseSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/lambda/DLambdaSsm.hpp b/include/xo/reader2/lambda/DLambdaSsm.hpp
index 1fa1eac9..7b16503b 100644
--- a/include/xo/reader2/lambda/DLambdaSsm.hpp
+++ b/include/xo/reader2/lambda/DLambdaSsm.hpp
@@ -59,7 +59,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DLambdaSsm>;
             using DLocalSymtab = xo::scm::DLocalSymtab;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using TypeDescr = xo::reflect::TypeDescr;
@@ -189,7 +189,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit gc-aware child pointers **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/lambda/ISyntaxStateMachine_DLambdaSsm.hpp b/include/xo/reader2/lambda/ISyntaxStateMachine_DLambdaSsm.hpp
index f10f376e..db67ee9a 100644
--- a/include/xo/reader2/lambda/ISyntaxStateMachine_DLambdaSsm.hpp
+++ b/include/xo/reader2/lambda/ISyntaxStateMachine_DLambdaSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dlambdassm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DLambdaSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DLambdaSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DLambdaSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DLambdaSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/paren/DParenSsm.hpp b/include/xo/reader2/paren/DParenSsm.hpp
index af9daa91..e70ba255 100644
--- a/include/xo/reader2/paren/DParenSsm.hpp
+++ b/include/xo/reader2/paren/DParenSsm.hpp
@@ -50,7 +50,7 @@ namespace xo {
         public:
             using Super = DSyntaxStateMachine<DParenSsm>;
             using TypeDescr = xo::reflect::TypeDescr;
-            using ACollector = xo::mm::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
             using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
             using ppindentinfo = xo::print::ppindentinfo;
@@ -136,7 +136,7 @@ namespace xo {
             ///@{
 
             /** gc support: visit immediate gc-aware children **/
-            void forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
 
diff --git a/include/xo/reader2/paren/ISyntaxStateMachine_DParenSsm.hpp b/include/xo/reader2/paren/ISyntaxStateMachine_DParenSsm.hpp
index c2bbcc21..4dd7ef74 100644
--- a/include/xo/reader2/paren/ISyntaxStateMachine_DParenSsm.hpp
+++ b/include/xo/reader2/paren/ISyntaxStateMachine_DParenSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dparenssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DParenSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DParenSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DParenSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DParenSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/parser/DSchematikaParser.hpp b/include/xo/reader2/parser/DSchematikaParser.hpp
index 07c85e4f..c3de4930 100644
--- a/include/xo/reader2/parser/DSchematikaParser.hpp
+++ b/include/xo/reader2/parser/DSchematikaParser.hpp
@@ -10,6 +10,7 @@
 #include "ParserResult.hpp"
 #include <xo/tokenizer2/Token.hpp>
 #include <xo/alloc2/Allocator.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 
 namespace xo {
     namespace scm {
@@ -164,8 +165,9 @@ namespace xo {
             using ArenaHashMapConfig = xo::map::ArenaHashMapConfig;
             using ArenaConfig = xo::mm::ArenaConfig;
             using ACollector = xo::mm::ACollector;
-            using AAllocator = xo::mm::AAllocator;
             using AGCObject = xo::mm::AGCObject;
+            using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
+            using AAllocator = xo::mm::AAllocator;
             using MemorySizeVisitor = xo::mm::MemorySizeVisitor;
             using ppindentinfo = xo::print::ppindentinfo;
             using size_type = std::size_t;
@@ -292,11 +294,10 @@ namespace xo {
             /** @defgroup scm-schematikaparser-gcobject-methods **/
             ///@{
 
-            std::size_t shallow_size() const noexcept;
             /** not implemented (SchematikaParser not designed to be copyable) **/
             DSchematikaParser * shallow_move(obj<ACollector> gc) noexcept;
             /** forward gc-aware children **/
-            std::size_t forward_children(obj<ACollector> gc) noexcept;
+            void visit_gco_children(obj<AGCObjectVisitor> gc) noexcept;
 
             ///@}
         private:
diff --git a/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp b/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
index 39f61b9b..f2ca67de 100644
--- a/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
+++ b/include/xo/reader2/parser/IGCObject_DSchematikaParser.hpp
@@ -44,6 +44,7 @@ namespace xo {
             using size_type = xo::mm::AGCObject::size_type;
             using AAllocator = xo::mm::AGCObject::AAllocator;
             using ACollector = xo::mm::AGCObject::ACollector;
+            using AGCObjectVisitor = xo::mm::AGCObject::AGCObjectVisitor;
             using Copaque = xo::mm::AGCObject::Copaque;
             using Opaque = xo::mm::AGCObject::Opaque;
             ///@}
@@ -54,8 +55,10 @@ namespace xo {
             // non-const methods
             /** move instance using allocator **/
             static Opaque shallow_move(DSchematikaParser & self, obj<ACollector> gc) noexcept;
-            /** during GC: forward immdiate children **/
-            static void forward_children(DSchematikaParser & self, obj<ACollector> gc) noexcept;
+            /** 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(DSchematikaParser & self, obj<AGCObjectVisitor> fn) noexcept;
             ///@}
         };
 
diff --git a/include/xo/reader2/quote/ISyntaxStateMachine_DQuoteSsm.hpp b/include/xo/reader2/quote/ISyntaxStateMachine_DQuoteSsm.hpp
index 811119c5..35dc5da1 100644
--- a/include/xo/reader2/quote/ISyntaxStateMachine_DQuoteSsm.hpp
+++ b/include/xo/reader2/quote/ISyntaxStateMachine_DQuoteSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dquotessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DQuoteSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DQuoteSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DQuoteSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DQuoteSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ASyntaxStateMachine.hpp b/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
index ead25e24..07d992c1 100644
--- a/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
+++ b/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
@@ -19,7 +19,7 @@
 #include <xo/type/Type.hpp>
 #include <xo/tokenizer2/Token.hpp>
 #include <xo/reflect/TypeDescr.hpp>
-#include <xo/alloc2/Collector.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 #include <xo/facet/obj.hpp>
 #include <xo/facet/facet_implementation.hpp>
 #include <xo/facet/typeseq.hpp>
@@ -46,8 +46,8 @@ public:
     using Opaque = void *;
     /** reflected c++ type **/
     using TypeDescr = xo::reflect::TypeDescr;
-    /** gc interface **/
-    using ACollector = xo::mm::ACollector;
+    /** gc visitor interface **/
+    using AGCObjectVisitor = xo::mm::AGCObjectVisitor;
     /** gc-aware object **/
     using AGCObject = xo::mm::AGCObject;
     ///@}
@@ -90,8 +90,8 @@ public:
     virtual void on_parsed_expression_with_token(Opaque data, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm)  = 0;
     /** update state machine for nested quoted literal @p lit **/
     virtual void on_quoted_literal(Opaque data, obj<AGCObject> lit, ParserStateMachine * p_psm)  = 0;
-    /** gc support: move immediate children to to-space and sub forwarding pointer **/
-    virtual void forward_children(Opaque data, obj<ACollector> gc)  = 0;
+    /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+    virtual void visit_gco_children(Opaque data, obj<AGCObjectVisitor> gc)  = 0;
     ///@}
 }; /*ASyntaxStateMachine*/
 
diff --git a/include/xo/reader2/ssm/IPrintable_DQuoteSsm.hpp b/include/xo/reader2/ssm/IPrintable_DQuoteSsm.hpp
deleted file mode 100644
index 2b969c50..00000000
--- a/include/xo/reader2/ssm/IPrintable_DQuoteSsm.hpp
+++ /dev/null
@@ -1,62 +0,0 @@
-/** @file IPrintable_DQuoteSsm.hpp
- *
- *  Generated automagically from ingredients:
- *  1. code generator:
- *       [xo-facet/codegen/genfacet]
- *     arguments:
- *       --input [idl/IPrintable_DQuoteSsm.json5]
- *  2. jinja2 template for abstract facet .hpp file:
- *       [iface_facet_repr.hpp.j2]
- *  3. idl for facet methods
- *       [idl/IPrintable_DQuoteSsm.json5]
- **/
-
-#pragma once
-
-#include "Printable.hpp"
-#include <xo/printable2/Printable.hpp>
-#include <xo/printable2/detail/IPrintable_Xfer.hpp>
-#include "DQuoteSsm.hpp"
-
-namespace xo { namespace scm { class IPrintable_DQuoteSsm; } }
-
-namespace xo {
-    namespace facet {
-        template <>
-        struct FacetImplementation<xo::print::APrintable,
-                                   xo::scm::DQuoteSsm>
-        {
-            using ImplType = xo::print::IPrintable_Xfer
-              <xo::scm::DQuoteSsm,
-               xo::scm::IPrintable_DQuoteSsm>;
-        };
-    }
-}
-
-namespace xo {
-    namespace scm {
-        /** @class IPrintable_DQuoteSsm
-         **/
-        class IPrintable_DQuoteSsm {
-        public:
-            /** @defgroup scm-printable-dquotessm-type-traits **/
-            ///@{
-            using ppindentinfo = xo::print::APrintable::ppindentinfo;
-            using Copaque = xo::print::APrintable::Copaque;
-            using Opaque = xo::print::APrintable::Opaque;
-            ///@}
-            /** @defgroup scm-printable-dquotessm-methods **/
-            ///@{
-            // const methods
-            /** Pretty-printing support for this object.
-See [xo-indentlog/xo/indentlog/pretty.hpp] **/
-            static bool pretty(const DQuoteSsm & self, const ppindentinfo & ppii);
-
-            // non-const methods
-            ///@}
-        };
-
-    } /*namespace scm*/
-} /*namespace xo*/
-
-/* end */
\ No newline at end of file
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
index d1077f2a..34e7ec84 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
@@ -45,7 +45,7 @@ namespace scm {
         /** integer identifying a type **/
         using typeseq = xo::facet::typeseq;
         using TypeDescr = ASyntaxStateMachine::TypeDescr;
-        using ACollector = ASyntaxStateMachine::ACollector;
+        using AGCObjectVisitor = ASyntaxStateMachine::AGCObjectVisitor;
         using AGCObject = ASyntaxStateMachine::AGCObject;
 
         ///@}
@@ -75,7 +75,7 @@ namespace scm {
         [[noreturn]] void on_parsed_expression(Opaque, obj<AExpression>, ParserStateMachine *)  override;
         [[noreturn]] void on_parsed_expression_with_token(Opaque, obj<AExpression>, const Token &, ParserStateMachine *)  override;
         [[noreturn]] void on_quoted_literal(Opaque, obj<AGCObject>, ParserStateMachine *)  override;
-        [[noreturn]] void forward_children(Opaque, obj<ACollector>)  override;
+        [[noreturn]] void visit_gco_children(Opaque, obj<AGCObjectVisitor>)  override;
 
         ///@}
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectExprSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectExprSsm.hpp
index 79801c00..5ca9f1c0 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectExprSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectExprSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectexprssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectExprSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectExprSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectExprSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectExprSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectFormalArglistSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectFormalArglistSsm.hpp
index 68151e22..04da69bd 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectFormalArglistSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectFormalArglistSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectformalarglistssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectFormalArglistSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectFormalArglistSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectFormalArglistSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectFormalArglistSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQArraySsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQArraySsm.hpp
index cf6ae53d..7b345008 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQArraySsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQArraySsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectqarrayssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectQArraySsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectQArraySsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectQArraySsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectQArraySsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQListSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQListSsm.hpp
index 38a33d20..ea0cb3c2 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQListSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQListSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectqlistssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectQListSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectQListSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectQListSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectQListSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQLiteralSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQLiteralSsm.hpp
index 4cd123f7..4a4bdbfb 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQLiteralSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectQLiteralSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectqliteralssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectQLiteralSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectQLiteralSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectQLiteralSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectQLiteralSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
index 0ed37f25..e3cf7146 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpectsymbolssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectSymbolSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectSymbolSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectSymbolSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectSymbolSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectTypeSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectTypeSsm.hpp
index ea084f51..965212d1 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectTypeSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectTypeSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dexpecttypessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DExpectTypeSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DExpectTypeSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DExpectTypeSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DExpectTypeSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DProgressSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DProgressSsm.hpp
index 24269888..7c12ee39 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DProgressSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DProgressSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dprogressssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DProgressSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DProgressSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DProgressSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DProgressSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DQuoteSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DQuoteSsm.hpp
deleted file mode 100644
index 811119c5..00000000
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DQuoteSsm.hpp
+++ /dev/null
@@ -1,87 +0,0 @@
-/** @file ISyntaxStateMachine_DQuoteSsm.hpp
- *
- *  Generated automagically from ingredients:
- *  1. code generator:
- *       [xo-facet/codegen/genfacet]
- *     arguments:
- *       --input [idl/ISyntaxStateMachine_DQuoteSsm.json5]
- *  2. jinja2 template for abstract facet .hpp file:
- *       [iface_facet_repr.hpp.j2]
- *  3. idl for facet methods
- *       [idl/ISyntaxStateMachine_DQuoteSsm.json5]
- **/
-
-#pragma once
-
-#include "SyntaxStateMachine.hpp"
-#include "SyntaxStateMachine.hpp"
-#include "ssm/ISyntaxStateMachine_Xfer.hpp"
-#include "DQuoteSsm.hpp"
-
-namespace xo { namespace scm { class ISyntaxStateMachine_DQuoteSsm; } }
-
-namespace xo {
-    namespace facet {
-        template <>
-        struct FacetImplementation<xo::scm::ASyntaxStateMachine,
-                                   xo::scm::DQuoteSsm>
-        {
-            using ImplType = xo::scm::ISyntaxStateMachine_Xfer
-              <xo::scm::DQuoteSsm,
-               xo::scm::ISyntaxStateMachine_DQuoteSsm>;
-        };
-    }
-}
-
-namespace xo {
-    namespace scm {
-        /** @class ISyntaxStateMachine_DQuoteSsm
-         **/
-        class ISyntaxStateMachine_DQuoteSsm {
-        public:
-            /** @defgroup scm-syntaxstatemachine-dquotessm-type-traits **/
-            ///@{
-            using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
-            using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
-            using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
-            using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
-            ///@}
-            /** @defgroup scm-syntaxstatemachine-dquotessm-methods **/
-            ///@{
-            // const methods
-            /** identify a type of syntax state machine **/
-            static syntaxstatetype ssm_type(const DQuoteSsm & self) noexcept;
-            /** text describing expected/allowed input to this ssm in current state **/
-            static std::string_view get_expect_str(const DQuoteSsm & self) noexcept;
-
-            // non-const methods
-            /** operate state machine for incoming token @p tk **/
-            static void on_token(DQuoteSsm & self, const Token & tk, ParserStateMachine * p_psm);
-            /** update  stat machine for incoming parsed symbol @p sym **/
-            static void on_parsed_symbol(DQuoteSsm & self, std::string_view sym, ParserStateMachine * p_psm);
-            /** operate state machine for incoming type description @p td **/
-            static void on_parsed_typedescr(DQuoteSsm & self, TypeDescr td, ParserStateMachine * p_psm);
-            /** update state machine for type emitted by nested ssm **/
-            static void on_parsed_type(DQuoteSsm & self, obj<AType> type, ParserStateMachine * p_psm);
-            /** operate state machine for formal emitted by nested ssm **/
-            static void on_parsed_formal(DQuoteSsm & self, const DUniqueString * param_name, TypeDescr param_type, ParserStateMachine * p_psm);
-            /** operate state machine for formal emitted by nested ssm **/
-            static void on_parsed_formal_with_token(DQuoteSsm & self, const DUniqueString * param_name, TypeDescr param_type, const Token & tk, ParserStateMachine * p_psm);
-            /** consume formal arglist emitted by nested ssm **/
-            static void on_parsed_formal_arglist(DQuoteSsm & self, DArray * arglist, ParserStateMachine * p_psm);
-            /** update state machine for nested parsed expression @p expr **/
-            static void on_parsed_expression(DQuoteSsm & self, obj<AExpression> expr, ParserStateMachine * p_psm);
-            /** update state machine @p p_psm for incoming parsed expression @p expr followed by token @p tk **/
-            static void on_parsed_expression_with_token(DQuoteSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
-            /** update state machine for nested quoted literal @p lit **/
-            static void on_quoted_literal(DQuoteSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DQuoteSsm & self, obj<ACollector> gc);
-            ///@}
-        };
-
-    } /*namespace scm*/
-} /*namespace xo*/
-
-/* end */
\ No newline at end of file
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DSequenceSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DSequenceSsm.hpp
index f19601b5..b35d45a1 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DSequenceSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DSequenceSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dsequencessm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DSequenceSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DSequenceSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DSequenceSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DSequenceSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_DToplevelSeqSsm.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_DToplevelSeqSsm.hpp
index b36cbfc6..695da17c 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_DToplevelSeqSsm.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_DToplevelSeqSsm.hpp
@@ -42,7 +42,7 @@ namespace xo {
             /** @defgroup scm-syntaxstatemachine-dtoplevelseqssm-type-traits **/
             ///@{
             using TypeDescr = xo::scm::ASyntaxStateMachine::TypeDescr;
-            using ACollector = xo::scm::ASyntaxStateMachine::ACollector;
+            using AGCObjectVisitor = xo::scm::ASyntaxStateMachine::AGCObjectVisitor;
             using AGCObject = xo::scm::ASyntaxStateMachine::AGCObject;
             using Copaque = xo::scm::ASyntaxStateMachine::Copaque;
             using Opaque = xo::scm::ASyntaxStateMachine::Opaque;
@@ -76,8 +76,8 @@ namespace xo {
             static void on_parsed_expression_with_token(DToplevelSeqSsm & self, obj<AExpression> expr, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for nested quoted literal @p lit **/
             static void on_quoted_literal(DToplevelSeqSsm & self, obj<AGCObject> lit, ParserStateMachine * p_psm);
-            /** gc support: move immediate children to to-space and sub forwarding pointer **/
-            static void forward_children(DToplevelSeqSsm & self, obj<ACollector> gc);
+            /** gc support: visit immediate gc-aware child pointers with @p gc.  Call gc.visit_child() for each **/
+            static void visit_gco_children(DToplevelSeqSsm & self, obj<AGCObjectVisitor> gc);
             ///@}
         };
 
diff --git a/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp b/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
index 13b6d1b7..df1a87f4 100644
--- a/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
+++ b/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
@@ -18,7 +18,7 @@
 #include <xo/type/Type.hpp>
 #include <xo/tokenizer2/Token.hpp>
 #include <xo/reflect/TypeDescr.hpp>
-#include <xo/alloc2/Collector.hpp>
+#include <xo/alloc2/GCObjectVisitor.hpp>
 
 namespace xo {
 namespace scm {
@@ -34,7 +34,7 @@ namespace scm {
         /** integer identifying a type **/
         using typeseq = ASyntaxStateMachine::typeseq;
         using TypeDescr = ASyntaxStateMachine::TypeDescr;
-        using ACollector = ASyntaxStateMachine::ACollector;
+        using AGCObjectVisitor = ASyntaxStateMachine::AGCObjectVisitor;
         using AGCObject = ASyntaxStateMachine::AGCObject;
         ///@}
 
@@ -89,8 +89,8 @@ namespace scm {
         void on_quoted_literal(Opaque data, obj<AGCObject> lit, ParserStateMachine * p_psm)  override {
             return I::on_quoted_literal(_dcast(data), lit, p_psm);
         }
-        void forward_children(Opaque data, obj<ACollector> gc)  override {
-            return I::forward_children(_dcast(data), gc);
+        void visit_gco_children(Opaque data, obj<AGCObjectVisitor> gc)  override {
+            return I::visit_gco_children(_dcast(data), gc);
         }
 
         ///@}
diff --git a/include/xo/reader2/ssm/RSyntaxStateMachine.hpp b/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
index 57cc885e..9c8a8274 100644
--- a/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
+++ b/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
@@ -32,7 +32,7 @@ public:
     using DataPtr = Object::DataPtr;
     using typeseq = xo::reflect::typeseq;
     using TypeDescr = ASyntaxStateMachine::TypeDescr;
-    using ACollector = ASyntaxStateMachine::ACollector;
+    using AGCObjectVisitor = ASyntaxStateMachine::AGCObjectVisitor;
     using AGCObject = ASyntaxStateMachine::AGCObject;
     ///@}
 
@@ -93,8 +93,8 @@ public:
     void on_quoted_literal(obj<AGCObject> lit, ParserStateMachine * p_psm)  {
         return O::iface()->on_quoted_literal(O::data(), lit, p_psm);
     }
-    void forward_children(obj<ACollector> gc)  {
-        return O::iface()->forward_children(O::data(), gc);
+    void visit_gco_children(obj<AGCObjectVisitor> gc)  {
+        return O::iface()->visit_gco_children(O::data(), gc);
     }
 
     ///@}
diff --git a/src/reader2/DApplySsm.cpp b/src/reader2/DApplySsm.cpp
index c465ce1a..1787d560 100644
--- a/src/reader2/DApplySsm.cpp
+++ b/src/reader2/DApplySsm.cpp
@@ -397,10 +397,10 @@ namespace xo {
         }
 
         void
-        DApplySsm::forward_children(obj<ACollector> gc) noexcept
+        DApplySsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&fn_expr_);
-            gc.forward_inplace(&args_expr_v_);
+            gc.visit_poly_child(&fn_expr_);
+            gc.visit_child(&args_expr_v_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DDefineSsm.cpp b/src/reader2/DDefineSsm.cpp
index f9be0335..1ee8e3aa 100644
--- a/src/reader2/DDefineSsm.cpp
+++ b/src/reader2/DDefineSsm.cpp
@@ -692,9 +692,9 @@ namespace xo {
         // ----- gc support -----
 
         void
-        DDefineSsm::forward_children(obj<ACollector> gc)
+        DDefineSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&def_expr_.data_);
+            gc.visit_child(&def_expr_.data_);
         }
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/src/reader2/DDeftypeSsm.cpp b/src/reader2/DDeftypeSsm.cpp
index 3f377113..0007d940 100644
--- a/src/reader2/DDeftypeSsm.cpp
+++ b/src/reader2/DDeftypeSsm.cpp
@@ -271,7 +271,7 @@ namespace xo {
                                              refrtag("expect", this->get_expect_str()));
         }
         void
-        DDeftypeSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DDeftypeSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             static_assert(!DUniqueString::is_gc_eligible());
         }
diff --git a/src/reader2/DExpectExprSsm.cpp b/src/reader2/DExpectExprSsm.cpp
index 6a9d08e7..bce870f6 100644
--- a/src/reader2/DExpectExprSsm.cpp
+++ b/src/reader2/DExpectExprSsm.cpp
@@ -625,7 +625,7 @@ namespace xo {
 #endif
 
         void
-        DExpectExprSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DExpectExprSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             // all members POD, skip
         }
diff --git a/src/reader2/DExpectFormalArgSsm.cpp b/src/reader2/DExpectFormalArgSsm.cpp
index d7e903d8..7a529983 100644
--- a/src/reader2/DExpectFormalArgSsm.cpp
+++ b/src/reader2/DExpectFormalArgSsm.cpp
@@ -265,7 +265,7 @@ namespace xo {
         }
 
         void
-        DExpectFormalArgSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DExpectFormalArgSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             static_assert(!DUniqueString::is_gc_eligible());
         }
diff --git a/src/reader2/DExpectFormalArglistSsm.cpp b/src/reader2/DExpectFormalArglistSsm.cpp
index ab7d19ee..6cbf199a 100644
--- a/src/reader2/DExpectFormalArglistSsm.cpp
+++ b/src/reader2/DExpectFormalArglistSsm.cpp
@@ -358,9 +358,9 @@ namespace xo {
         }
 
         void
-        DExpectFormalArglistSsm::forward_children(obj<ACollector> gc) noexcept
+        DExpectFormalArglistSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&argl_);
+            gc.visit_child(&argl_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DExpectListTypeSsm.cpp b/src/reader2/DExpectListTypeSsm.cpp
index 921c562e..001ff254 100644
--- a/src/reader2/DExpectListTypeSsm.cpp
+++ b/src/reader2/DExpectListTypeSsm.cpp
@@ -204,9 +204,9 @@ namespace xo {
         }
 
         void
-        DExpectListTypeSsm::forward_children(obj<ACollector> gc) noexcept
+        DExpectListTypeSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&elt_type_);
+            gc.visit_poly_child(&elt_type_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DExpectQArraySsm.cpp b/src/reader2/DExpectQArraySsm.cpp
index 3d373783..9e281f8c 100644
--- a/src/reader2/DExpectQArraySsm.cpp
+++ b/src/reader2/DExpectQArraySsm.cpp
@@ -220,9 +220,9 @@ namespace xo {
                                              refrtag("array", array_pr));
         }
         void
-        DExpectQArraySsm::forward_children(obj<ACollector> gc) noexcept
+        DExpectQArraySsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&array_);
+            gc.visit_child(&array_);
         }
 
     }
diff --git a/src/reader2/DExpectQDictSsm.cpp b/src/reader2/DExpectQDictSsm.cpp
index b57887cb..9839ffd2 100644
--- a/src/reader2/DExpectQDictSsm.cpp
+++ b/src/reader2/DExpectQDictSsm.cpp
@@ -267,10 +267,10 @@ namespace xo {
 
 
         void
-        DExpectQDictSsm::forward_children(obj<ACollector> gc) noexcept
+        DExpectQDictSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(const_cast<DString **>(&key_));
-            gc.forward_inplace(&dict_);
+            gc.visit_child(&key_);
+            gc.visit_child(&dict_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DExpectQListSsm.cpp b/src/reader2/DExpectQListSsm.cpp
index 59df8c2c..965351c3 100644
--- a/src/reader2/DExpectQListSsm.cpp
+++ b/src/reader2/DExpectQListSsm.cpp
@@ -215,10 +215,10 @@ namespace xo {
                                              refrtag("list", list_pr));
         }
         void
-        DExpectQListSsm::forward_children(obj<ACollector> gc) noexcept
+        DExpectQListSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&start_);
-            gc.forward_inplace(&end_);
+            gc.visit_child(&start_);
+            gc.visit_child(&end_);
         }
 
     }
diff --git a/src/reader2/DExpectQLiteralSsm.cpp b/src/reader2/DExpectQLiteralSsm.cpp
index b87eff24..c49cf565 100644
--- a/src/reader2/DExpectQLiteralSsm.cpp
+++ b/src/reader2/DExpectQLiteralSsm.cpp
@@ -256,7 +256,7 @@ namespace xo {
                                              refrtag("expect", this->get_expect_str()));
         }
         void
-        DExpectQLiteralSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DExpectQLiteralSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             // cxl_on_rightparen_, cxl_on_rightbracket_: POD, skip
         }
diff --git a/src/reader2/DExpectSymbolSsm.cpp b/src/reader2/DExpectSymbolSsm.cpp
index 0875a044..fa1372b1 100644
--- a/src/reader2/DExpectSymbolSsm.cpp
+++ b/src/reader2/DExpectSymbolSsm.cpp
@@ -146,7 +146,7 @@ namespace xo {
                     );
         }
         void
-        DExpectSymbolSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DExpectSymbolSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             // no gc-aware members
         }
diff --git a/src/reader2/DExpectTypeSsm.cpp b/src/reader2/DExpectTypeSsm.cpp
index b25c9380..47cc5a6c 100644
--- a/src/reader2/DExpectTypeSsm.cpp
+++ b/src/reader2/DExpectTypeSsm.cpp
@@ -198,7 +198,7 @@ namespace xo {
         }
 
         void
-        DExpectTypeSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DExpectTypeSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             // corrected_: POD, skip
         }
diff --git a/src/reader2/DGlobalEnv.cpp b/src/reader2/DGlobalEnv.cpp
index 2893beda..64eabd4f 100644
--- a/src/reader2/DGlobalEnv.cpp
+++ b/src/reader2/DGlobalEnv.cpp
@@ -107,25 +107,17 @@ namespace xo {
 
         // ----- AGCObject facet -----
 
-        std::size_t
-        DGlobalEnv::shallow_size() const noexcept
-        {
-            return sizeof(*this);
-        }
-
         DGlobalEnv *
         DGlobalEnv::shallow_move(obj<ACollector> gc) noexcept
         {
             return gc.std_move_for<DGlobalEnv>(this);
         }
 
-        std::size_t
-        DGlobalEnv::forward_children(obj<ACollector> gc) noexcept
+        void
+        DGlobalEnv::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&symtab_);
-            gc.forward_inplace(&values_);
-
-            return this->shallow_size();
+            gc.visit_child(&symtab_);
+            gc.visit_child(&values_);
         }
 
         // ----- APrintable facet -----
diff --git a/src/reader2/DIfElseSsm.cpp b/src/reader2/DIfElseSsm.cpp
index 03bd1589..f4fd4f88 100644
--- a/src/reader2/DIfElseSsm.cpp
+++ b/src/reader2/DIfElseSsm.cpp
@@ -510,9 +510,9 @@ namespace xo {
         }
 
         void
-        DIfElseSsm::forward_children(obj<ACollector> gc) noexcept
+        DIfElseSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&if_expr_);
+            gc.visit_poly_child(&if_expr_);
         }
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/src/reader2/DLambdaSsm.cpp b/src/reader2/DLambdaSsm.cpp
index d23f04e6..f0fed420 100644
--- a/src/reader2/DLambdaSsm.cpp
+++ b/src/reader2/DLambdaSsm.cpp
@@ -4,16 +4,13 @@
  **/
 
 #include "LambdaSsm.hpp"
-//#include "ssm/ISyntaxStateMachine_DLambdaSsm.hpp"
 #include "ExpectFormalArglistSsm.hpp"
-//#include "ssm/ISyntaxStateMachine_DExpectFormalArglistSsm.hpp"
 #include "DExpectTypeSsm.hpp"
 #include "DExpectExprSsm.hpp"
 #include "ParserStateMachine.hpp"
 #include "syntaxstatetype.hpp"
 #include <xo/expression2/detail/IExpression_DLambdaExpr.hpp>
 #include <xo/expression2/Variable.hpp>
-//#include <xo/expression2/detail/IExpression_DVariable.hpp>
 //#include <xo/expression2/symtab/ISymbolTable_DLocalSymtab.hpp>
 #include <xo/printable2/Printable.hpp>
 #include <xo/alloc2/GCObject.hpp>
@@ -474,15 +471,15 @@ namespace xo {
         }
 
         void
-        DLambdaSsm::forward_children(obj<ACollector> gc) noexcept
+        DLambdaSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&local_symtab_);
+            gc.visit_child(&local_symtab_);
 
             // explicit_return_td not gcobject
             // lambda_td not gcobject
 
-            gc.forward_pivot_inplace(&body_);
-            gc.forward_pivot_inplace(&parent_symtab_);
+            gc.visit_poly_child(&body_);
+            gc.visit_poly_child(&parent_symtab_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DParenSsm.cpp b/src/reader2/DParenSsm.cpp
index 13fb728a..82320cb6 100644
--- a/src/reader2/DParenSsm.cpp
+++ b/src/reader2/DParenSsm.cpp
@@ -459,9 +459,9 @@ namespace xo {
         }
 
         void
-        DParenSsm::forward_children(obj<ACollector> gc) noexcept
+        DParenSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&expr_);
+            gc.visit_poly_child(&expr_);
         }
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/src/reader2/DProgressSsm.cpp b/src/reader2/DProgressSsm.cpp
index 345ba5fd..04c87fac 100644
--- a/src/reader2/DProgressSsm.cpp
+++ b/src/reader2/DProgressSsm.cpp
@@ -1244,10 +1244,10 @@ case optype::op_assign:
         }
 
         void
-        DProgressSsm::forward_children(obj<ACollector> gc) noexcept
+        DProgressSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&lhs_);
-            gc.forward_pivot_inplace(&rhs_);
+            gc.visit_poly_child(&lhs_);
+            gc.visit_poly_child(&rhs_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DQuoteSsm.cpp b/src/reader2/DQuoteSsm.cpp
index 3a665eb5..cbbedc73 100644
--- a/src/reader2/DQuoteSsm.cpp
+++ b/src/reader2/DQuoteSsm.cpp
@@ -212,9 +212,9 @@ namespace xo {
         }
 
         void
-        DQuoteSsm::forward_children(obj<ACollector> gc) noexcept
+        DQuoteSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&expr_);
+            gc.visit_poly_child(&expr_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DSchematikaParser.cpp b/src/reader2/DSchematikaParser.cpp
index e25e76aa..1d5ecea7 100644
--- a/src/reader2/DSchematikaParser.cpp
+++ b/src/reader2/DSchematikaParser.cpp
@@ -184,12 +184,6 @@ namespace xo {
                            );
         }
 
-        std::size_t
-        DSchematikaParser::shallow_size() const noexcept
-        {
-            return sizeof(DSchematikaParser);
-        }
-
         DSchematikaParser *
         DSchematikaParser::shallow_move(obj<ACollector> gc) noexcept
         {
@@ -202,12 +196,10 @@ namespace xo {
             return nullptr;
         }
 
-        std::size_t
-        DSchematikaParser::forward_children(obj<ACollector> gc) noexcept
+        void
+        DSchematikaParser::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            psm_.forward_children(gc);
-
-            return this->shallow_size();
+            psm_.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DSequenceSsm.cpp b/src/reader2/DSequenceSsm.cpp
index f6caeb06..a6d4013b 100644
--- a/src/reader2/DSequenceSsm.cpp
+++ b/src/reader2/DSequenceSsm.cpp
@@ -258,9 +258,9 @@ namespace xo {
         }
 
         void
-        DSequenceSsm::forward_children(obj<ACollector> gc) noexcept
+        DSequenceSsm::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_inplace(&seq_expr_);
+            gc.visit_child(&seq_expr_);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/DToplevelSeqSsm.cpp b/src/reader2/DToplevelSeqSsm.cpp
index 9252c700..e660f780 100644
--- a/src/reader2/DToplevelSeqSsm.cpp
+++ b/src/reader2/DToplevelSeqSsm.cpp
@@ -518,7 +518,7 @@ namespace xo {
                  refrtag("seqtype", seqtype_));
         }
         void
-        DToplevelSeqSsm::forward_children(obj<ACollector> /*gc*/) noexcept
+        DToplevelSeqSsm::visit_gco_children(obj<AGCObjectVisitor>) noexcept
         {
             // seqtype_: POD, skip
         }
diff --git a/src/reader2/ISyntaxStateMachine_Any.cpp b/src/reader2/ISyntaxStateMachine_Any.cpp
index 7d174c5b..a260bdc9 100644
--- a/src/reader2/ISyntaxStateMachine_Any.cpp
+++ b/src/reader2/ISyntaxStateMachine_Any.cpp
@@ -96,7 +96,7 @@ ISyntaxStateMachine_Any::on_quoted_literal(Opaque, obj<AGCObject>, ParserStateMa
 }
 
 auto
-ISyntaxStateMachine_Any::forward_children(Opaque, obj<ACollector>)  -> void
+ISyntaxStateMachine_Any::visit_gco_children(Opaque, obj<AGCObjectVisitor>)  -> void
 {
     _fatal();
 }
diff --git a/src/reader2/ISyntaxStateMachine_DExpectExprSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectExprSsm.cpp
index 75464bcc..0ecc4e24 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectExprSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectExprSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectExprSsm::forward_children(DExpectExprSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectExprSsm::visit_gco_children(DExpectExprSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectFormalArglistSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectFormalArglistSsm.cpp
index 61b219f0..4db6a480 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectFormalArglistSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectFormalArglistSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectFormalArglistSsm::forward_children(DExpectFormalArglistSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectFormalArglistSsm::visit_gco_children(DExpectFormalArglistSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectQArraySsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectQArraySsm.cpp
index b938f1e7..ea8b14cc 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectQArraySsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectQArraySsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectQArraySsm::forward_children(DExpectQArraySsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectQArraySsm::visit_gco_children(DExpectQArraySsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectQListSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectQListSsm.cpp
index 19df0dff..363f9646 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectQListSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectQListSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectQListSsm::forward_children(DExpectQListSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectQListSsm::visit_gco_children(DExpectQListSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectQLiteralSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectQLiteralSsm.cpp
index e6f338fc..61e15926 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectQLiteralSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectQLiteralSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectQLiteralSsm::forward_children(DExpectQLiteralSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectQLiteralSsm::visit_gco_children(DExpectQLiteralSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
index b8e8fed0..c1331ceb 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectSymbolSsm::forward_children(DExpectSymbolSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectSymbolSsm::visit_gco_children(DExpectSymbolSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DExpectTypeSsm.cpp b/src/reader2/ISyntaxStateMachine_DExpectTypeSsm.cpp
index 011edc4f..8daed04c 100644
--- a/src/reader2/ISyntaxStateMachine_DExpectTypeSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DExpectTypeSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectTypeSsm::forward_children(DExpectTypeSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectTypeSsm::visit_gco_children(DExpectTypeSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DParenSsm.cpp b/src/reader2/ISyntaxStateMachine_DParenSsm.cpp
index 6ee6902b..42a199cb 100644
--- a/src/reader2/ISyntaxStateMachine_DParenSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DParenSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DParenSsm::forward_children(DParenSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DParenSsm::visit_gco_children(DParenSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DProgressSsm.cpp b/src/reader2/ISyntaxStateMachine_DProgressSsm.cpp
index 01e1e754..9c5ad07d 100644
--- a/src/reader2/ISyntaxStateMachine_DProgressSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DProgressSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DProgressSsm::forward_children(DProgressSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DProgressSsm::visit_gco_children(DProgressSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DSequenceSsm.cpp b/src/reader2/ISyntaxStateMachine_DSequenceSsm.cpp
index 30e164d8..a6375288 100644
--- a/src/reader2/ISyntaxStateMachine_DSequenceSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DSequenceSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DSequenceSsm::forward_children(DSequenceSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DSequenceSsm::visit_gco_children(DSequenceSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ISyntaxStateMachine_DToplevelSeqSsm.cpp b/src/reader2/ISyntaxStateMachine_DToplevelSeqSsm.cpp
index 73f23da0..47788590 100644
--- a/src/reader2/ISyntaxStateMachine_DToplevelSeqSsm.cpp
+++ b/src/reader2/ISyntaxStateMachine_DToplevelSeqSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DToplevelSeqSsm::forward_children(DToplevelSeqSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DToplevelSeqSsm::visit_gco_children(DToplevelSeqSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/ParserResult.cpp b/src/reader2/ParserResult.cpp
index fa9c9591..609f204f 100644
--- a/src/reader2/ParserResult.cpp
+++ b/src/reader2/ParserResult.cpp
@@ -106,12 +106,12 @@ namespace xo {
         }
 
         void
-        ParserResult::forward_children(obj<ACollector> gc) noexcept
+        ParserResult::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
             // {result_type_, error_src_fn_}: pod, ignore
 
-            gc.forward_pivot_inplace(&result_expr_);
-            gc.forward_inplace(const_cast<DString **>(&error_description_));
+            gc.visit_poly_child(&result_expr_);
+            gc.visit_child(&error_description_);
         }
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/src/reader2/ParserStack.cpp b/src/reader2/ParserStack.cpp
index f40696b2..721b19b4 100644
--- a/src/reader2/ParserStack.cpp
+++ b/src/reader2/ParserStack.cpp
@@ -90,14 +90,14 @@ namespace xo {
         }
 
         void
-        ParserStack::forward_children(obj<ACollector> gc) noexcept
+        ParserStack::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
 
             for (ParserStack * target = this; target; target = target->parent_) {
                 // ParserStack::ckp: skip, POD
 
                 if (target->ssm_)
-                    target->ssm_.forward_children(gc);
+                    target->ssm_.visit_gco_children(gc);
             }
         }
 
diff --git a/src/reader2/ParserStateMachine.cpp b/src/reader2/ParserStateMachine.cpp
index c3d92a0c..6bec1833 100644
--- a/src/reader2/ParserStateMachine.cpp
+++ b/src/reader2/ParserStateMachine.cpp
@@ -907,7 +907,7 @@ namespace xo {
 #endif
 
         void
-        ParserStateMachine::forward_children(obj<ACollector> gc) noexcept
+        ParserStateMachine::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
             //scope log(XO_DEBUG(true));
 
@@ -916,23 +916,23 @@ namespace xo {
 
             //log && log("forward stack_", xtag("addr", stack_));
             if (stack_) {
-                stack_->forward_children(gc);
+                stack_->visit_gco_children(gc);
             }
 
             // static_assert(!expr_alloc_.is_gc_eligible());
             // static_assert(!aux_alloc_.is_gc_eligible());
 
             //log && log("global_symtab_", xtag("addr", global_symtab_.data()));
-            gc.forward_inplace(&global_symtab_);
+            gc.visit_child(&global_symtab_);
 
             //log && log("local_symtab_", xtag("addr", local_symtab_.data()));
-            gc.forward_inplace(&local_symtab_);
+            gc.visit_child(&local_symtab_);
 
             //log && log("global_env_", xtag("addr", global_env_.data()));
-            gc.forward_inplace(&global_env_);
+            gc.visit_child(&global_env_);
 
             //log && log("result_");
-            result_.forward_children(gc);
+            result_.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/SchematikaReader.cpp b/src/reader2/SchematikaReader.cpp
index ba681bab..c9405916 100644
--- a/src/reader2/SchematikaReader.cpp
+++ b/src/reader2/SchematikaReader.cpp
@@ -10,9 +10,9 @@ namespace xo {
 
     namespace scm {
         void
-        ReaderResult::forward_children(obj<ACollector> gc) noexcept
+        ReaderResult::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
-            gc.forward_pivot_inplace(&expr_);
+            gc.visit_poly_child(&expr_);
         }
 
         // ----- SchematikaReader -----
@@ -208,12 +208,12 @@ namespace xo {
         }
 
         void
-        SchematikaReader::forward_children(obj<ACollector> gc) noexcept
+        SchematikaReader::visit_gco_children(obj<AGCObjectVisitor> gc) noexcept
         {
             // tokenizer doesn't contain any gc-aware pointers.
 
-            parser_.forward_children(gc);
-            result_.forward_children(gc);
+            parser_.visit_gco_children(gc);
+            result_.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/IGCObject_DGlobalEnv.cpp b/src/reader2/facet/IGCObject_DGlobalEnv.cpp
index 5c61e9ea..e826c422 100644
--- a/src/reader2/facet/IGCObject_DGlobalEnv.cpp
+++ b/src/reader2/facet/IGCObject_DGlobalEnv.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DGlobalEnv::forward_children(DGlobalEnv & self, obj<ACollector> gc) noexcept -> void
+        IGCObject_DGlobalEnv::visit_gco_children(DGlobalEnv & self, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(fn);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/IGCObject_DSchematikaParser.cpp b/src/reader2/facet/IGCObject_DSchematikaParser.cpp
index 133b3f9c..cd9ec847 100644
--- a/src/reader2/facet/IGCObject_DSchematikaParser.cpp
+++ b/src/reader2/facet/IGCObject_DSchematikaParser.cpp
@@ -21,9 +21,9 @@ namespace xo {
             return self.shallow_move(gc);
         }
         auto
-        IGCObject_DSchematikaParser::forward_children(DSchematikaParser & self, obj<ACollector> gc) noexcept -> void
+        IGCObject_DSchematikaParser::visit_gco_children(DSchematikaParser & self, obj<AGCObjectVisitor> fn) noexcept -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(fn);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DApplySsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DApplySsm.cpp
index daff54de..01f685fe 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DApplySsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DApplySsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DApplySsm::forward_children(DApplySsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DApplySsm::visit_gco_children(DApplySsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DDefineSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DDefineSsm.cpp
index 9867898f..886155c0 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DDefineSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DDefineSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DDefineSsm::forward_children(DDefineSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DDefineSsm::visit_gco_children(DDefineSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DDeftypeSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DDeftypeSsm.cpp
index e6e54b1c..874849ff 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DDeftypeSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DDeftypeSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DDeftypeSsm::forward_children(DDeftypeSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DDeftypeSsm::visit_gco_children(DDeftypeSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DExpectFormalArgSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DExpectFormalArgSsm.cpp
index 059fd4b2..85f8dd7a 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DExpectFormalArgSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DExpectFormalArgSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectFormalArgSsm::forward_children(DExpectFormalArgSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectFormalArgSsm::visit_gco_children(DExpectFormalArgSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DExpectListTypeSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DExpectListTypeSsm.cpp
index b760ac9a..d3b292ad 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DExpectListTypeSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DExpectListTypeSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectListTypeSsm::forward_children(DExpectListTypeSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectListTypeSsm::visit_gco_children(DExpectListTypeSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DExpectQDictSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DExpectQDictSsm.cpp
index 7ee82e82..9f4d74cc 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DExpectQDictSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DExpectQDictSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DExpectQDictSsm::forward_children(DExpectQDictSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DExpectQDictSsm::visit_gco_children(DExpectQDictSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DIfElseSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DIfElseSsm.cpp
index c78464c7..68034ba4 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DIfElseSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DIfElseSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DIfElseSsm::forward_children(DIfElseSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DIfElseSsm::visit_gco_children(DIfElseSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DLambdaSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DLambdaSsm.cpp
index b54d54fc..88e52100 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DLambdaSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DLambdaSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DLambdaSsm::forward_children(DLambdaSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DLambdaSsm::visit_gco_children(DLambdaSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/
diff --git a/src/reader2/facet/ISyntaxStateMachine_DQuoteSsm.cpp b/src/reader2/facet/ISyntaxStateMachine_DQuoteSsm.cpp
index 9624c899..39d26414 100644
--- a/src/reader2/facet/ISyntaxStateMachine_DQuoteSsm.cpp
+++ b/src/reader2/facet/ISyntaxStateMachine_DQuoteSsm.cpp
@@ -78,9 +78,9 @@ namespace xo {
             self.on_quoted_literal(lit, p_psm);
         }
         auto
-        ISyntaxStateMachine_DQuoteSsm::forward_children(DQuoteSsm & self, obj<ACollector> gc) -> void
+        ISyntaxStateMachine_DQuoteSsm::visit_gco_children(DQuoteSsm & self, obj<AGCObjectVisitor> gc) -> void
         {
-            self.forward_children(gc);
+            self.visit_gco_children(gc);
         }
 
     } /*namespace scm*/