diff --git a/xo-expression2/CMakeLists.txt b/xo-expression2/CMakeLists.txt
index fe5cd540..678e5eca 100644
--- a/xo-expression2/CMakeLists.txt
+++ b/xo-expression2/CMakeLists.txt
@@ -32,6 +32,8 @@ xo_add_genfacet(
     OUTPUT_CPP_DIR src/expression2
     )
 
+# ----------------------------------------------------------------
+
 # note: manual target; generated code committed to git
 xo_add_genfacet(
     TARGET xo-expression2-facet-expression
@@ -66,6 +68,20 @@ xo_add_genfacetimpl(
     OUTPUT_CPP_DIR src/expression2
 )
 
+# note: manual target; generated code committed to git
+xo_add_genfacetimpl(
+    TARGET xo-expression2-facetimpl-expression-defineexpr
+    FACET_PKG xo_expression2
+    FACET Expression
+    REPR DefineExpr
+    INPUT idl/IExpression_DDefineExpr.json5
+    OUTPUT_HPP_DIR include/xo/expression2
+    OUTPUT_IMPL_SUBDIR detail
+    OUTPUT_CPP_DIR src/expression2
+)
+
+# ----------------------------------------------------------------
+
 # note: manual target; generated code committed to git
 xo_add_genfacetimpl(
     TARGET xo-expression2-facetimpl-gcobject-uniquestring
diff --git a/xo-expression2/idl/IExpression_DDefineExpr.json5 b/xo-expression2/idl/IExpression_DDefineExpr.json5
new file mode 100644
index 00000000..ff35d6d6
--- /dev/null
+++ b/xo-expression2/idl/IExpression_DDefineExpr.json5
@@ -0,0 +1,12 @@
+{
+    mode: "implementation",
+    includes: [ "\"Expression.hpp\"" ],
+    local_types: [ ],
+    namespace1: "xo",
+    namespace2: "scm",
+    facet_idl: "idl/Expression.json5",
+    brief: "provide AExpression interface for DDefineExpr state",
+    using_doxygen: true,
+    repr: "DDefineExpr",
+    doc: ["doc for IExpression+DDefineExpr" ],
+}
diff --git a/xo-expression2/include/xo/expression2/Binding.hpp b/xo-expression2/include/xo/expression2/Binding.hpp
index 455c1538..5f0f7e27 100644
--- a/xo-expression2/include/xo/expression2/Binding.hpp
+++ b/xo-expression2/include/xo/expression2/Binding.hpp
@@ -15,6 +15,7 @@ namespace xo {
             static constexpr int32_t s_link_global = -1;
 
         public:
+            Binding() : i_link_{-2}, j_slot_{-1} {}
             Binding(int32_t i_link, int32_t j_slot)
                 : i_link_{i_link}, j_slot_{j_slot} {}
 
@@ -32,6 +33,7 @@ namespace xo {
              *  >= 0: number of parent links to traverse
              *        to a fixed-size frame
              *    -1: resolve globally
+             *    -2: sentinel (binding info not computed)
              **/
             int32_t i_link_ = s_link_sentinel;
             /** if @ref i_link_ >= 0, frame offset
diff --git a/xo-expression2/include/xo/expression2/DDefineExpr.hpp b/xo-expression2/include/xo/expression2/DDefineExpr.hpp
new file mode 100644
index 00000000..94a37197
--- /dev/null
+++ b/xo-expression2/include/xo/expression2/DDefineExpr.hpp
@@ -0,0 +1,75 @@
+/** @file DDefineExpr.hpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "DVariable.hpp"
+#include <xo/alloc2/Allocator.hpp>
+
+namespace xo {
+    namespace scm {
+        class DUniqueString; // see DUniqueString.hpp
+
+        /** @class DDefineExpr
+         *  @brief an expression that introduces a variable.
+         *
+         *  Variable may optionally be declared with a type,
+         *  and may come with an expression specifying an initial value
+         **/
+        class DDefineExpr {
+        public:
+            using AAllocator = xo::mm::AAllocator;
+            using TypeDescr = xo::reflect::TypeDescr;
+
+        public:
+            /** create instance: define-expr using memory from @p mm
+             *  with lhs name @p lhs_name and rhs expression @p rhs_expr
+             **/
+            static DDefineExpr * make(obj<AAllocator> mm,
+                                      const DUniqueString * lhs_name,
+                                      obj<AExpression> rhs_expr);
+            /** create empty skeleton. Rely on this for parsing
+             **/
+            static DDefineExpr * make_empty(obj<AAllocator> mm);
+
+            DVariable * lhs() const { return lhs_var_; }
+            obj<AExpression> rhs() const noexcept { return rhs_; }
+
+            const DUniqueString * name() const noexcept;
+
+            void assign_lhs_name(const DUniqueString * name);
+            /** CONCESSION.  will use DUniqueString* once we have StringTable **/
+            void assign_lhs_name(std::string_view name);
+
+            /** @defgroup scm-defineexpr-expression-facet **/
+            ///@{
+
+            exprtype extype() const noexcept { return exprtype::define; }
+            TypeRef typeref() const noexcept { return lhs_var_->typeref(); }
+            TypeDescr valuetype() const noexcept { return lhs_var_->typeref().td(); }
+            void assign_valuetype(TypeDescr td) noexcept;
+
+            ///@}
+
+        private:
+            DDefineExpr(DVariable * lhs_var,
+                        obj<AExpression> rhs);
+
+        private:
+            /** variable being defined by this expression.
+             **/
+            DVariable * lhs_var_ = nullptr;
+
+            /** expression for initial value of this expression
+             **/
+            obj<AExpression> rhs_;
+
+            // std::set<std::string> free_var_set_;
+        };
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DDefineExpr.hpp */
diff --git a/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp b/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp
new file mode 100644
index 00000000..bb668ff3
--- /dev/null
+++ b/xo-expression2/include/xo/expression2/DGlobalSymtab.hpp
@@ -0,0 +1,39 @@
+/** @file DGlobalSymtab.hpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "Binding.hpp"
+
+namespace xo {
+    namespace scm {
+        class DUniqueString;
+
+        /** @class DGlobalSymtab
+         *  @brief symbol table for toplevel environment
+         **/
+        struct DGlobalSymtab {
+        public:
+
+
+        public:
+            /** @defgroup xo-expression2-symboltable-facet symboltable facet**/
+            ///@{
+
+            /** true for global symbol table **/
+            bool is_global_symtab() const noexcept { return true; }
+
+            /** lookup binding for variable @p sym **/
+            Binding lookup_binding(const DUniqueString * sym) const noexcept;
+
+            ///@}
+
+        private:
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DGlobalSymtab.hpp */
diff --git a/xo-expression2/include/xo/expression2/DVariable.hpp b/xo-expression2/include/xo/expression2/DVariable.hpp
index 036d88ce..2208852e 100644
--- a/xo-expression2/include/xo/expression2/DVariable.hpp
+++ b/xo-expression2/include/xo/expression2/DVariable.hpp
@@ -19,15 +19,33 @@ namespace xo {
          **/
         class DVariable {
         public:
+            using AAllocator = xo::mm::AAllocator;
             using TypeDescr = xo::reflect::TypeDescr;
 
         public:
-            DVariable(const DUniqueString & name, const TypeRef & typeref, Binding path)
-                : name_{name}, typeref_{typeref}, path_{path} {}
+            /** create instance
+             *  @p mm      memory allocator
+             *  @p name    variable name
+             *  @p typeref type information for legal values
+             *             (possibly just placeholder when relying on inference)
+             *  @p path    binding path to runtime value.
+             *             This may be computed after parsing;
+             *             mnust be resolved before execution.
+             **/
+            static DVariable * make(obj<AAllocator> mm,
+                                    const DUniqueString * name,
+                                    const TypeRef & typeref,
+                                    Binding path = Binding());
 
-            const DUniqueString & name() const { return name_; }
+            DVariable(const DUniqueString * name,
+                      const TypeRef & typeref,
+                      Binding path);
+
+            const DUniqueString * name() const { return name_; }
             Binding path() const { return path_; }
 
+            void assign_name(const DUniqueString * name) { this->name_ = name; }
+
             /** @defgroup scm-variable-expression-facet**/
             ///@{
 
@@ -40,7 +58,7 @@ namespace xo {
 
         private:
             /** symbol name **/
-            const DUniqueString & name_;
+            const DUniqueString * name_;
             /** variable value always has type consistent
              *  with this description
              **/
diff --git a/xo-expression2/include/xo/expression2/detail/IExpression_DDefineExpr.hpp b/xo-expression2/include/xo/expression2/detail/IExpression_DDefineExpr.hpp
new file mode 100644
index 00000000..3ac7fd49
--- /dev/null
+++ b/xo-expression2/include/xo/expression2/detail/IExpression_DDefineExpr.hpp
@@ -0,0 +1,66 @@
+/** @file IExpression_DDefineExpr.hpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DDefineExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_repr.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DDefineExpr.json5]
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include "Expression.hpp"
+#include "DDefineExpr.hpp"
+
+namespace xo { namespace scm { class IExpression_DDefineExpr; } }
+
+namespace xo {
+    namespace facet {
+        template <>
+        struct FacetImplementation<xo::scm::AExpression,
+                                   xo::scm::DDefineExpr>
+        {
+            using ImplType = xo::scm::IExpression_Xfer
+              <xo::scm::DDefineExpr,
+               xo::scm::IExpression_DDefineExpr>;
+        };
+    }
+}
+
+namespace xo {
+    namespace scm {
+        /** @class IExpression_DDefineExpr
+         **/
+        class IExpression_DDefineExpr {
+        public:
+            /** @defgroup scm-expression-ddefineexpr-type-traits **/
+            ///@{
+            using TypeDescr = xo::scm::AExpression::TypeDescr;
+            using Copaque = xo::scm::AExpression::Copaque;
+            using Opaque = xo::scm::AExpression::Opaque;
+            ///@}
+            /** @defgroup scm-expression-ddefineexpr-methods **/
+            ///@{
+            // const methods
+            /** expression type (constant | apply | ..) **/
+            static exprtype extype(const DDefineExpr & self) noexcept;
+            /** placeholder for type giving possible values for this expression **/
+            static TypeRef typeref(const DDefineExpr & self) noexcept;
+            /** type giving possible values for this expression. Maybe null before typecheck **/
+            static TypeDescr valuetype(const DDefineExpr & self) noexcept;
+
+            // non-const methods
+            /** assing to valuetype member. Useful when scaffolding expressions **/
+            static void assign_valuetype(DDefineExpr & self, TypeDescr td) noexcept;
+            ///@}
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end */
\ No newline at end of file
diff --git a/xo-expression2/include/xo/expression2/exprtype.hpp b/xo-expression2/include/xo/expression2/exprtype.hpp
index 0d5e8299..d64a1191 100644
--- a/xo-expression2/include/xo/expression2/exprtype.hpp
+++ b/xo-expression2/include/xo/expression2/exprtype.hpp
@@ -23,8 +23,10 @@ namespace xo {
 #ifdef NOT_YET
             /** a literal constant that refers to a linkable named function **/
             primitive,
+#endif
             /** variable/function definition **/
             define,
+#ifdef NOT_YET
             /** variable assignment **/
             assign,
             /** function call **/
@@ -55,7 +57,9 @@ namespace xo {
             case exprtype::constant: return "constant";
 #ifdef NOT_YET
             case exprtype::primitive: return "primitive";
+#endif
             case exprtype::define: return "define";
+#ifdef NOT_YET
             case exprtype::assign: return "assign";
             case exprtype::apply: return "apply";
             case exprtype::lambda: return "lambda";
diff --git a/xo-expression2/src/expression2/CMakeLists.txt b/xo-expression2/src/expression2/CMakeLists.txt
index 9194bfa5..0fcd6541 100644
--- a/xo-expression2/src/expression2/CMakeLists.txt
+++ b/xo-expression2/src/expression2/CMakeLists.txt
@@ -6,12 +6,17 @@ set(SELF_SRCS
 
     DConstant.cpp
     DVariable.cpp
+    DDefineExpr.cpp
 
     TypeRef.cpp
 
     IExpression_Any.cpp
     IExpression_DConstant.cpp
     IExpression_DVariable.cpp
+    IExpression_DDefineExpr.cpp
+
+    DLocalSymtab.cpp
+    DGlobalSymtab.cpp
 
     ISymbolTable_Any.cpp
 
diff --git a/xo-expression2/src/expression2/DDefineExpr.cpp b/xo-expression2/src/expression2/DDefineExpr.cpp
new file mode 100644
index 00000000..14d1c52e
--- /dev/null
+++ b/xo-expression2/src/expression2/DDefineExpr.cpp
@@ -0,0 +1,71 @@
+/** @file DDefineExpr.cpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#include "DDefineExpr.hpp"
+#include <xo/indentlog/scope.hpp>
+
+namespace xo {
+    using xo::facet::typeseq;
+
+    namespace scm {
+
+        DDefineExpr::DDefineExpr(DVariable * lhs_var,
+                                 obj<AExpression> rhs)
+          : lhs_var_{lhs_var}, rhs_{rhs}
+        {}
+
+        DDefineExpr *
+        DDefineExpr::make(obj<AAllocator> mm,
+                          const DUniqueString * lhs_name,
+                          obj<AExpression> rhs_expr)
+        {
+            void * mem = mm.alloc(typeseq::id<DDefineExpr>(),
+                                  sizeof(DDefineExpr));
+
+            auto lhs_var = DVariable::make(mm,
+                                           lhs_name,
+                                           rhs_expr.typeref());
+
+            return new (mem) DDefineExpr(lhs_var, rhs_expr);
+        }
+
+        DDefineExpr *
+        DDefineExpr::make_empty(obj<AAllocator> mm)
+        {
+            return make(mm,
+                        nullptr /*lhs_name*/,
+                        obj<AExpression>() /*rhs_expr*/);
+        }
+
+        const DUniqueString *
+        DDefineExpr::name() const noexcept
+        {
+            return lhs_var_->name();
+        }
+
+        void
+        DDefineExpr::assign_lhs_name(const DUniqueString * name)
+        {
+            lhs_var_->assign_name(name);
+        }
+
+        void
+        DDefineExpr::assign_lhs_name(std::string_view name)
+        {
+            scope log(XO_DEBUG(true), "bogus impl - will require unique string");
+            log && log(xtag("name", name));
+
+            //lhs_var_->assign_name(name);
+        }
+
+        void
+        DDefineExpr::assign_valuetype(TypeDescr td) noexcept
+        {
+            lhs_var_->assign_valuetype(td);
+        }
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DDefineExpr.cpp */
diff --git a/xo-expression2/src/expression2/DGlobalSymtab.cpp b/xo-expression2/src/expression2/DGlobalSymtab.cpp
new file mode 100644
index 00000000..c11761d9
--- /dev/null
+++ b/xo-expression2/src/expression2/DGlobalSymtab.cpp
@@ -0,0 +1,27 @@
+/** @file DGlobalSymtab.cpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#include "DGlobalSymtab.hpp"
+#include "DUniqueString.hpp"
+#include <xo/indentlog/scope.hpp>
+
+namespace xo {
+    namespace scm {
+
+        Binding
+        DGlobalSymtab::lookup_binding(const DUniqueString * sym) const noexcept
+        {
+            (void)sym;
+
+            scope log(XO_DEBUG(true), "stub");
+            log && log(xtag("sym", std::string_view(*sym)));
+
+            return Binding();
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DGlobalSymtab.cpp */
diff --git a/xo-expression2/src/expression2/DLocalSymtab.cpp b/xo-expression2/src/expression2/DLocalSymtab.cpp
new file mode 100644
index 00000000..febd1463
--- /dev/null
+++ b/xo-expression2/src/expression2/DLocalSymtab.cpp
@@ -0,0 +1,25 @@
+/** @file DLocalSymtab.cpp
+*
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#include "DLocalSymtab.hpp"
+#include "DUniqueString.hpp"
+#include <xo/indentlog/scope.hpp>
+
+namespace xo {
+    namespace scm {
+
+        Binding
+        DLocalSymtab::lookup_binding(const DUniqueString * sym) const noexcept
+        {
+            scope log(XO_DEBUG(true), "stub impl");
+            log && log(xtag("sym", std::string_view(*sym)));
+
+            return Binding();
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DLocalSymtab.cpp */
diff --git a/xo-expression2/src/expression2/DVariable.cpp b/xo-expression2/src/expression2/DVariable.cpp
index f589da7b..d27c71ef 100644
--- a/xo-expression2/src/expression2/DVariable.cpp
+++ b/xo-expression2/src/expression2/DVariable.cpp
@@ -7,12 +7,34 @@
 #include "exprtype.hpp"
 
 namespace xo {
+    using xo::facet::typeseq;
+
     namespace scm {
+
+        DVariable *
+        DVariable::make(obj<AAllocator> mm,
+                        const DUniqueString * name,
+                        const TypeRef & typeref,
+                        Binding path)
+        {
+            void * mem = mm.alloc(typeseq::id<DVariable>(),
+                                  sizeof(DVariable));
+
+            return new (mem) DVariable(name, typeref, path);
+        }
+
+        DVariable::DVariable(const DUniqueString * name,
+                             const TypeRef & typeref,
+                             Binding path)
+          : name_{name}, typeref_{typeref}, path_{path}
+        {}
+
         void
         DVariable::assign_valuetype(TypeDescr td) noexcept
         {
             typeref_.resolve(td);
         }
+
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/xo-expression2/src/expression2/IExpression_DDefineExpr.cpp b/xo-expression2/src/expression2/IExpression_DDefineExpr.cpp
new file mode 100644
index 00000000..3222eabd
--- /dev/null
+++ b/xo-expression2/src/expression2/IExpression_DDefineExpr.cpp
@@ -0,0 +1,45 @@
+/** @file IExpression_DDefineExpr.cpp
+ *
+ *  Generated automagically from ingredients:
+ *  1. code generator:
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
+ *     arguments:
+ *       --input [idl/IExpression_DDefineExpr.json5]
+ *  2. jinja2 template for abstract facet .hpp file:
+ *       [iface_facet_any.hpp.j2]
+ *  3. idl for facet methods
+ *       [idl/IExpression_DDefineExpr.json5]
+**/
+
+#include "detail/IExpression_DDefineExpr.hpp"
+
+namespace xo {
+    namespace scm {
+        auto
+        IExpression_DDefineExpr::extype(const DDefineExpr & self) noexcept -> exprtype
+        {
+            return self.extype();
+        }
+
+        auto
+        IExpression_DDefineExpr::typeref(const DDefineExpr & self) noexcept -> TypeRef
+        {
+            return self.typeref();
+        }
+
+        auto
+        IExpression_DDefineExpr::valuetype(const DDefineExpr & self) noexcept -> TypeDescr
+        {
+            return self.valuetype();
+        }
+
+        auto
+        IExpression_DDefineExpr::assign_valuetype(DDefineExpr & self, TypeDescr td) noexcept -> void
+        {
+            self.assign_valuetype(td);
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end IExpression_DDefineExpr.cpp */
\ No newline at end of file
diff --git a/xo-facet/include/xo/facet/facet_implementation.hpp b/xo-facet/include/xo/facet/facet_implementation.hpp
index 5669860a..025645e8 100644
--- a/xo-facet/include/xo/facet/facet_implementation.hpp
+++ b/xo-facet/include/xo/facet/facet_implementation.hpp
@@ -92,7 +92,7 @@ namespace xo {
             //static_assert(false && "expect specialization <AFacet,DRepr> which should provide ImplType trait");
         };
 
-        /** Retrieve facet implementation for a (facet, datatype) pair **/
+        /** Retrieve facet implementation for a (facet,datatype) pair **/
         template <typename AFacet, typename DRepr>
         using FacetImplType = FacetImplementation<AFacet, DRepr>::ImplType;
 
diff --git a/xo-interpreter2/include/xo/interpreter2/VirtualSchematikaMachine.hpp b/xo-interpreter2/include/xo/interpreter2/VirtualSchematikaMachine.hpp
index 8bbe6bb4..a149173e 100644
--- a/xo-interpreter2/include/xo/interpreter2/VirtualSchematikaMachine.hpp
+++ b/xo-interpreter2/include/xo/interpreter2/VirtualSchematikaMachine.hpp
@@ -45,6 +45,12 @@ namespace xo {
              **/
             void _do_eval_constant_op();
 
+            /** evaluate a define-expression
+             *  Require:
+             *  - expression in @ref expr_
+             **/
+            void _do_eval_define_op();
+
             /** evaluate a variable expression
              *  Require:
              *  - expression in @ref expr_
diff --git a/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp b/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
index bd29e968..f7131e0a 100644
--- a/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
+++ b/xo-interpreter2/src/interpreter2/VirtualSchematikaMachine.cpp
@@ -45,6 +45,9 @@ namespace xo {
             case exprtype::constant:
                 _do_eval_constant_op();
                 break;
+            case exprtype::define:
+                _do_eval_define_op();
+                break;
             case exprtype::variable:
                 _do_eval_variable_op();
                 break;
@@ -61,6 +64,13 @@ namespace xo {
             this->pc_ = this->cont_;
         }
 
+        void
+        VirtualSchematikaMachine::_do_eval_define_op()
+        {
+            // not implemented
+            assert(false);
+        }
+
         void
         VirtualSchematikaMachine::_do_eval_variable_op()
         {
diff --git a/xo-reader2/idl/SyntaxStateMachine.json5 b/xo-reader2/idl/SyntaxStateMachine.json5
index 2be2a98d..28811512 100644
--- a/xo-reader2/idl/SyntaxStateMachine.json5
+++ b/xo-reader2/idl/SyntaxStateMachine.json5
@@ -43,6 +43,15 @@
         },
     ],
     nonconst_methods: [
+        {
+            name: "on_symbol_token",
+            doc: ["operate state machine for incoming symbol-token @p tk"],
+            return_type: "void",
+            args: [
+                {type: "const Token &", name: "tk"},
+                {type: "ParserStateMachine *", name: "p_psm"},
+            ],
+        },
         {
             name: "on_def_token",
             doc: ["update state machine for incoming define-keyword-token @p tk"],
diff --git a/xo-reader2/include/xo/reader2/DDefineSsm.hpp b/xo-reader2/include/xo/reader2/DDefineSsm.hpp
index 37ccc23d..3bc042c1 100644
--- a/xo-reader2/include/xo/reader2/DDefineSsm.hpp
+++ b/xo-reader2/include/xo/reader2/DDefineSsm.hpp
@@ -8,6 +8,8 @@
 #include "ParserStateMachine.hpp"
 //#include "SyntaxStateMachine.hpp"
 #include "syntaxstatetype.hpp"
+#include <xo/expression2/detail/IExpression_DDefineExpr.hpp>
+#include <xo/expression2/DDefineExpr.hpp>
 #include <xo/facet/obj.hpp>
 
 namespace xo {
@@ -69,21 +71,29 @@ namespace xo {
          **/
         class DDefineSsm {
         public:
+            using AAllocator = xo::mm::AAllocator;
             using DArena = xo::mm::DArena;
 
         public:
             /** @defgroup scm-define-ssm-facet constructors **/
             ///@{
 
-            DDefineSsm();
+            /** constructor; using @p def_expr for initial expression scaffold **/
+            explicit DDefineSsm(DDefineExpr * def_expr);
 
-            /** create instance using memory from @p parser_mm **/
-            static DDefineSsm * make(DArena & parser_mm);
+            /** create instance using memory from @p parser_mm.
+             *  Initial expression scaffold @p def_expr
+             **/
+            static DDefineSsm * make(DArena & parser_mm,
+                                     DDefineExpr * def_expr);
 
             /** start nested parser for a define-expression,
              *  on top of parser state machine @p p_psm
+             *  Use @p parser_mm to allocate syntax state machines,
+             *  and @p expr_mm to allocate expressions
              **/
             static void start(DArena & parser_mm,
+                              obj<AAllocator> expr_mm,
                               ParserStateMachine * p_psm);
 
             ///@}
@@ -98,6 +108,12 @@ namespace xo {
              **/
             std::string_view get_expect_str() const noexcept;
 
+            /** operate state machine for this syntax on incoming symbol-token @p tk
+             *  with overall parser state in @p p_psm
+             **/
+            void on_symbol_token(const Token & tk,
+                                 ParserStateMachine * p_psm);
+
             /** update state for this syntax on incoming token @p tk,
              *  overall parser state in @p p_psm
              **/
@@ -121,6 +137,11 @@ namespace xo {
         private:
             /** identify define-expression state **/
             defexprstatetype defstate_;
+
+            /** scaffolded define-expression.
+             *  This will eventually be the output of this ssm
+             **/
+            obj<AExpression,DDefineExpr> def_expr_;
         };
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-reader2/include/xo/reader2/DExprSeqState.hpp b/xo-reader2/include/xo/reader2/DExprSeqState.hpp
index 1b611aaf..bef2bd68 100644
--- a/xo-reader2/include/xo/reader2/DExprSeqState.hpp
+++ b/xo-reader2/include/xo/reader2/DExprSeqState.hpp
@@ -56,6 +56,11 @@ namespace xo {
              **/
             std::string_view get_expect_str() const noexcept;
 
+            /** operate state machine for this syntax on incoming symbol token @p tk
+             *  with overall parser state in @p p_psm
+             **/
+            void on_symbol_token(const Token & tk, ParserStateMachine * p_psm);
+
             /** update state for this syntax on incoming token @p tk,
              *  overall parser state in @p p_psm
              **/
diff --git a/xo-reader2/include/xo/reader2/ParserResult.hpp b/xo-reader2/include/xo/reader2/ParserResult.hpp
index e179d4bd..39f9c2d1 100644
--- a/xo-reader2/include/xo/reader2/ParserResult.hpp
+++ b/xo-reader2/include/xo/reader2/ParserResult.hpp
@@ -50,6 +50,8 @@ namespace xo {
             std::string_view error_src_fn_;
             const DString * error_description_ = nullptr;
         };
+
+
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/xo-reader2/include/xo/reader2/ParserStateMachine.hpp b/xo-reader2/include/xo/reader2/ParserStateMachine.hpp
index f5293bff..5a7a833f 100644
--- a/xo-reader2/include/xo/reader2/ParserStateMachine.hpp
+++ b/xo-reader2/include/xo/reader2/ParserStateMachine.hpp
@@ -6,6 +6,7 @@
 #pragma once
 
 #include "ParserResult.hpp"
+#include <xo/expression2/DVariable.hpp>
 #include <xo/tokenizer2/Token.hpp>
 #include <xo/alloc2/Allocator.hpp>
 #include <xo/arena/DArena.hpp>
@@ -32,14 +33,14 @@ namespace xo {
 
         public:
             ParserStateMachine(const ArenaConfig & config,
-                               obj<AAllocator> * expr_alloc);
+                               obj<AAllocator> expr_alloc);
 
             /** @defgroup scm-parserstatemachine-accessors accessor methods **/
             ///@{
 
             bool debug_flag() const noexcept { return debug_flag_; }
             ParserStack * stack() const noexcept { return stack_; }
-            obj<AAllocator> * expr_alloc() const noexcept { return expr_alloc_; }
+            obj<AAllocator> expr_alloc() const noexcept { return expr_alloc_; }
             const ParserResult & result() const noexcept { return result_; }
 
             /** true iff state machine is currently idle (at top-level) **/
@@ -65,6 +66,9 @@ namespace xo {
             /** pop syntax state machine from top of @ref stack_ **/
             void pop_ssm();
 
+            /** add variable to current local environment (innermost lexical scope) **/
+            void upsert_var(DVariable * var);
+
             /** reset result to none **/
             void reset_result();
 
@@ -84,10 +88,13 @@ namespace xo {
              **/
             void on_token(const Token & tk);
 
-            /** update state for incoming define-token @p tk **/
+            /** operate state machine for incoming symbol-token @p tk **/
+            void on_symbol_token(const Token & tk);
+
+            /** operate state machine for incoming define-token @p tk **/
             void on_def_token(const Token & tk);
 
-            /** update state for incoming if-token @p tk **/
+            /** operate state machine for incoming if-token @p tk **/
             void on_if_token(const Token & tk);
 
             ///@}
@@ -153,7 +160,7 @@ namespace xo {
              *  scenario, where top-level Expressions can be discarded
              *  once compiled.
              **/
-            obj<AAllocator> * expr_alloc_ = nullptr;
+            obj<AAllocator> expr_alloc_;
 
             /** current output from parser **/
             ParserResult result_;
diff --git a/xo-reader2/include/xo/reader2/SchematikaParser.hpp b/xo-reader2/include/xo/reader2/SchematikaParser.hpp
index 075fb4fc..2f7d6d95 100644
--- a/xo-reader2/include/xo/reader2/SchematikaParser.hpp
+++ b/xo-reader2/include/xo/reader2/SchematikaParser.hpp
@@ -167,7 +167,7 @@ namespace xo {
              *  @p debug_flag  true to enable debug logging
              **/
             SchematikaParser(const ArenaConfig & config,
-                             obj<AAllocator> * expr_alloc,
+                             obj<AAllocator> expr_alloc,
                              bool debug_flag);
 
             bool debug_flag() const { return debug_flag_; }
diff --git a/xo-reader2/include/xo/reader2/SyntaxStateMachine.hpp b/xo-reader2/include/xo/reader2/SyntaxStateMachine.hpp
index 56a8271b..deda9e1d 100644
--- a/xo-reader2/include/xo/reader2/SyntaxStateMachine.hpp
+++ b/xo-reader2/include/xo/reader2/SyntaxStateMachine.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/SyntaxStateMachine.json5]
  *  2. jinja2 template for facet .hpp file:
diff --git a/xo-reader2/include/xo/reader2/ssm/ASyntaxStateMachine.hpp b/xo-reader2/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
index b181fd8d..4f428be5 100644
--- a/xo-reader2/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ASyntaxStateMachine.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/SyntaxStateMachine.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -54,12 +54,14 @@ public:
     virtual std::string_view get_expect_str(Copaque data)  const  noexcept = 0;
 
     // nonconst methods
-    /** update  stat machine for incoming parsed symbol @p sym **/
-    virtual void on_parsed_symbol(Opaque data, std::string_view sym, ParserStateMachine * p_psm)  = 0;
+    /** operate state machine for incoming symbol-token @p tk **/
+    virtual void on_symbol_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  = 0;
     /** update state machine for incoming define-keyword-token @p tk **/
     virtual void on_def_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  = 0;
     /** update state machine for incoming if-keyword-token @p tk **/
     virtual void on_if_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  = 0;
+    /** update  stat machine for incoming parsed symbol @p sym **/
+    virtual void on_parsed_symbol(Opaque data, std::string_view sym, ParserStateMachine * p_psm)  = 0;
     ///@}
 }; /*ASyntaxStateMachine*/
 
diff --git a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
index 046adacb..23b90621 100644
--- a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Any.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/SyntaxStateMachine.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -59,9 +59,10 @@ namespace scm {
         [[noreturn]] std::string_view get_expect_str(Copaque)  const  noexcept override { _fatal(); }
 
         // nonconst methods
-        [[noreturn]] void on_parsed_symbol(Opaque, std::string_view, ParserStateMachine *)  override;
+        [[noreturn]] void on_symbol_token(Opaque, const Token &, ParserStateMachine *)  override;
         [[noreturn]] void on_def_token(Opaque, const Token &, ParserStateMachine *)  override;
         [[noreturn]] void on_if_token(Opaque, const Token &, ParserStateMachine *)  override;
+        [[noreturn]] void on_parsed_symbol(Opaque, std::string_view, ParserStateMachine *)  override;
 
         ///@}
 
diff --git a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DDefineSsm.hpp b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DDefineSsm.hpp
index cfb38fa7..d420ba16 100644
--- a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DDefineSsm.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DDefineSsm.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DDefineSsm.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -53,12 +53,14 @@ namespace xo {
             static std::string_view get_expect_str(const DDefineSsm & self) noexcept;
 
             // non-const methods
-            /** update  stat machine for incoming parsed symbol @p sym **/
-            static void on_parsed_symbol(DDefineSsm & self, std::string_view sym, ParserStateMachine * p_psm);
+            /** operate state machine for incoming symbol-token @p tk **/
+            static void on_symbol_token(DDefineSsm & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming define-keyword-token @p tk **/
             static void on_def_token(DDefineSsm & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming if-keyword-token @p tk **/
             static void on_if_token(DDefineSsm & self, const Token & tk, ParserStateMachine * p_psm);
+            /** update  stat machine for incoming parsed symbol @p sym **/
+            static void on_parsed_symbol(DDefineSsm & self, std::string_view sym, ParserStateMachine * p_psm);
             ///@}
         };
 
diff --git a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
index 44cb6de4..ba8eb0b9 100644
--- a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExpectSymbolSsm.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DExpectSymbolSsm.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -53,12 +53,14 @@ namespace xo {
             static std::string_view get_expect_str(const DExpectSymbolSsm & self) noexcept;
 
             // non-const methods
-            /** update  stat machine for incoming parsed symbol @p sym **/
-            static void on_parsed_symbol(DExpectSymbolSsm & self, std::string_view sym, ParserStateMachine * p_psm);
+            /** operate state machine for incoming symbol-token @p tk **/
+            static void on_symbol_token(DExpectSymbolSsm & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming define-keyword-token @p tk **/
             static void on_def_token(DExpectSymbolSsm & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming if-keyword-token @p tk **/
             static void on_if_token(DExpectSymbolSsm & self, const Token & tk, ParserStateMachine * p_psm);
+            /** update  stat machine for incoming parsed symbol @p sym **/
+            static void on_parsed_symbol(DExpectSymbolSsm & self, std::string_view sym, ParserStateMachine * p_psm);
             ///@}
         };
 
diff --git a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExprSeqState.hpp b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExprSeqState.hpp
index 4da00f95..c1e61b40 100644
--- a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExprSeqState.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_DExprSeqState.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DExprSeqState.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -53,12 +53,14 @@ namespace xo {
             static std::string_view get_expect_str(const DExprSeqState & self) noexcept;
 
             // non-const methods
-            /** update  stat machine for incoming parsed symbol @p sym **/
-            static void on_parsed_symbol(DExprSeqState & self, std::string_view sym, ParserStateMachine * p_psm);
+            /** operate state machine for incoming symbol-token @p tk **/
+            static void on_symbol_token(DExprSeqState & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming define-keyword-token @p tk **/
             static void on_def_token(DExprSeqState & self, const Token & tk, ParserStateMachine * p_psm);
             /** update state machine for incoming if-keyword-token @p tk **/
             static void on_if_token(DExprSeqState & self, const Token & tk, ParserStateMachine * p_psm);
+            /** update  stat machine for incoming parsed symbol @p sym **/
+            static void on_parsed_symbol(DExprSeqState & self, std::string_view sym, ParserStateMachine * p_psm);
             ///@}
         };
 
diff --git a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
index 7de32e25..5a8e2fe3 100644
--- a/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/ISyntaxStateMachine_Xfer.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/SyntaxStateMachine.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -50,8 +50,8 @@ namespace scm {
         }
 
         // non-const methods
-        void on_parsed_symbol(Opaque data, std::string_view sym, ParserStateMachine * p_psm)  override {
-            return I::on_parsed_symbol(_dcast(data), sym, p_psm);
+        void on_symbol_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  override {
+            return I::on_symbol_token(_dcast(data), tk, p_psm);
         }
         void on_def_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  override {
             return I::on_def_token(_dcast(data), tk, p_psm);
@@ -59,6 +59,9 @@ namespace scm {
         void on_if_token(Opaque data, const Token & tk, ParserStateMachine * p_psm)  override {
             return I::on_if_token(_dcast(data), tk, p_psm);
         }
+        void on_parsed_symbol(Opaque data, std::string_view sym, ParserStateMachine * p_psm)  override {
+            return I::on_parsed_symbol(_dcast(data), sym, p_psm);
+        }
 
         ///@}
 
diff --git a/xo-reader2/include/xo/reader2/ssm/RSyntaxStateMachine.hpp b/xo-reader2/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
index f35f4e72..786c83d0 100644
--- a/xo-reader2/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
+++ b/xo-reader2/include/xo/reader2/ssm/RSyntaxStateMachine.hpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/SyntaxStateMachine.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -55,8 +55,8 @@ public:
     }
 
     // non-const methods (still const in router!)
-    void on_parsed_symbol(std::string_view sym, ParserStateMachine * p_psm)  {
-        return O::iface()->on_parsed_symbol(O::data(), sym, p_psm);
+    void on_symbol_token(const Token & tk, ParserStateMachine * p_psm)  {
+        return O::iface()->on_symbol_token(O::data(), tk, p_psm);
     }
     void on_def_token(const Token & tk, ParserStateMachine * p_psm)  {
         return O::iface()->on_def_token(O::data(), tk, p_psm);
@@ -64,6 +64,9 @@ public:
     void on_if_token(const Token & tk, ParserStateMachine * p_psm)  {
         return O::iface()->on_if_token(O::data(), tk, p_psm);
     }
+    void on_parsed_symbol(std::string_view sym, ParserStateMachine * p_psm)  {
+        return O::iface()->on_parsed_symbol(O::data(), sym, p_psm);
+    }
 
     ///@}
     /** @defgroup scm-syntaxstatemachine-member-vars **/
diff --git a/xo-reader2/src/reader2/DDefineSsm.cpp b/xo-reader2/src/reader2/DDefineSsm.cpp
index 8ac919e4..adf9f429 100644
--- a/xo-reader2/src/reader2/DDefineSsm.cpp
+++ b/xo-reader2/src/reader2/DDefineSsm.cpp
@@ -1,9 +1,10 @@
-/** @file DDefineSsm.cpp
+ /** @file DDefineSsm.cpp
  *
  *  @author Roland Conybeare, Jan 2026
  **/
 
 #include "DDefineSsm.hpp"
+#include "DExpectSymbolSsm.hpp"
 #include "ssm/ISyntaxStateMachine_DDefineSsm.hpp"
 
 #ifdef NOT_YET
@@ -328,28 +329,33 @@ namespace xo {
 
         ////////////////////////////////////////////////////////////////
 
-        DDefineSsm::DDefineSsm()
-            : defstate_{defexprstatetype::def_0}
+        DDefineSsm::DDefineSsm(DDefineExpr * def_expr)
+          : defstate_{defexprstatetype::def_0},
+            def_expr_{def_expr}
         {}
 
         DDefineSsm *
-        DDefineSsm::make(DArena & mm)
+        DDefineSsm::make(DArena & mm,
+                         DDefineExpr * def_expr)
         {
             void * mem = mm.alloc(typeseq::id<DDefineSsm>(),
                                   sizeof(DDefineSsm));
 
-            return new (mem) DDefineSsm();
+            return new (mem) DDefineSsm(def_expr);
         }
 
         void
         DDefineSsm::start(DArena & mm,
+                          obj<AAllocator> expr_mm,
                           ParserStateMachine * p_psm)
         {
             //scope log(XO_DEBUG(p_psm->debug_flag()));
 
             assert(p_psm->stack());
 
-            DDefineSsm * define_ssm = DDefineSsm::make(mm);
+            DDefineExpr * def_expr = DDefineExpr::make_empty(expr_mm);
+
+            DDefineSsm * define_ssm = DDefineSsm::make(mm, def_expr);
 
             obj<ASyntaxStateMachine> ssm
                 = with_facet<ASyntaxStateMachine>::mkobj(define_ssm);
@@ -387,7 +393,7 @@ namespace xo {
             case defexprstatetype::def_0:
             case defexprstatetype::n_defexprstatetype:
                 assert(false);  // impossible
-                return nullptr;
+                return "impossible!?";
             case defexprstatetype::def_1:
                 return "symbol";
             case defexprstatetype::def_2:
@@ -409,11 +415,57 @@ namespace xo {
         DDefineSsm::on_parsed_symbol(std::string_view sym,
                                      ParserStateMachine * p_psm)
         {
+            if (this->defstate_ == defexprstatetype::def_1) {
+                this->defstate_ = defexprstatetype::def_2;
+
+                def_expr_.data()->assign_lhs_name(sym);
+
+                // if this is a genuine top-level define (i.e. nesting level = 0),
+                // then we need to upsert so we can refer to rhs later.
+                //
+                // In other contexts (e.g. body-of-lambda) will be rewriting
+                //    {
+                //       def y = foo(x,x);
+                //       bar(y,y);
+                //    }
+                // into something like
+                //    {
+                //       (lambda (y123) bar(y123,y123))(foo(x,x));
+                //    }
+                //
+                // This works in the body of lambda, because we don't evaluate anything
+                // until lambda definition is complete.
+                //
+                // For interactive top-level defs we want to evaluate as we go,
+                // so need incremental bindings.
+
+                if (p_psm->is_at_toplevel()) {
+                    /** remember variable binding in current lexical context **/
+                    p_psm->upsert_var(def_expr_.data()->lhs());
+                }
+
+                return;
+            }
+
             p_psm->illegal_input_on_symbol("DDefineSsm::on_parsed_symbol",
                                            sym,
                                            this->get_expect_str());
         }
 
+        void
+        DDefineSsm::on_symbol_token(const Token & tk,
+                                    ParserStateMachine * p_psm)
+        {
+            // note:
+            // in state def_1, DDefineSsm learns symbol via .on_parsed_symbol().
+            // symbol token arriving here means encountered symbol while
+            // in some other, which can't happen for valid Schematika input
+
+            p_psm->illegal_input_on_token("DDefineSssm::on_symbol_token",
+                                          tk,
+                                          this->get_expect_str());
+        }
+
         void
         DDefineSsm::on_def_token(const Token & tk,
                                  ParserStateMachine * p_psm)
@@ -421,7 +473,8 @@ namespace xo {
             if (this->defstate_ == defexprstatetype::def_0) {
                 this->defstate_ = defexprstatetype::def_1;
 
-                // expect_symbol_xs::start(p_psm->parser_alloc(), p_psm);
+                DExpectSymbolSsm::start(p_psm->parser_alloc(), p_psm);
+                return;
             }
 
             p_psm->illegal_input_on_token("DDefineSsm::on_define_token",
diff --git a/xo-reader2/src/reader2/DExprSeqState.cpp b/xo-reader2/src/reader2/DExprSeqState.cpp
index cca208f6..4afb9608 100644
--- a/xo-reader2/src/reader2/DExprSeqState.cpp
+++ b/xo-reader2/src/reader2/DExprSeqState.cpp
@@ -74,13 +74,48 @@ namespace xo {
             return "impossible-DExprSeqState::get_expr_str";
         }
 
+        void
+        DExprSeqState::on_symbol_token(const Token & tk,
+                                       ParserStateMachine * p_psm)
+        {
+            switch (seqtype_) {
+            case exprseqtype::toplevel_interactive:
+                {
+#ifdef NOT_YET
+                    obj<AExpression,DVariable> var = p_psm->lookup_var(tk.text());
+
+                    if (var) {
+                        DProgressSsm::start(var, p_psm);
+                    } else {
+                        p_psm->unknown_variable_error("DExprSeqState::on_symbol_token",
+                                                      tk,
+                                                      this->get_expect_str(),
+                                                      p_psm);
+                    }
+#endif
+                }
+                break;
+            case exprseqtype::toplevel_batch:
+                break;
+            case exprseqtype::N:
+                assert(false); // unreachable
+                break;
+            }
+
+            p_psm->illegal_input_on_token("DExprSeqState::on_symbol_token",
+                                          tk,
+                                          this->get_expect_str());
+        }
+
         void
         DExprSeqState::on_def_token(const Token & tk,
                                     ParserStateMachine * p_psm)
         {
             (void)tk;
 
-            DDefineSsm::start(p_psm->parser_alloc(), p_psm);
+            DDefineSsm::start(p_psm->parser_alloc(),
+                              p_psm->expr_alloc(),
+                              p_psm);
 
             /* keyword 'def' introduces a definition:
              *   def pi : f64 = 3.14159265
diff --git a/xo-reader2/src/reader2/ISyntaxStateMachine_Any.cpp b/xo-reader2/src/reader2/ISyntaxStateMachine_Any.cpp
index 2076aa5f..44effd57 100644
--- a/xo-reader2/src/reader2/ISyntaxStateMachine_Any.cpp
+++ b/xo-reader2/src/reader2/ISyntaxStateMachine_Any.cpp
@@ -35,7 +35,7 @@ ISyntaxStateMachine_Any::_valid
 // nonconst methods
 
 auto
-ISyntaxStateMachine_Any::on_parsed_symbol(Opaque, std::string_view, ParserStateMachine *)  -> void
+ISyntaxStateMachine_Any::on_symbol_token(Opaque, const Token &, ParserStateMachine *)  -> void
 {
     _fatal();
 }
@@ -52,6 +52,12 @@ ISyntaxStateMachine_Any::on_if_token(Opaque, const Token &, ParserStateMachine *
     _fatal();
 }
 
+auto
+ISyntaxStateMachine_Any::on_parsed_symbol(Opaque, std::string_view, ParserStateMachine *)  -> void
+{
+    _fatal();
+}
+
 
 } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-reader2/src/reader2/ISyntaxStateMachine_DDefineSsm.cpp b/xo-reader2/src/reader2/ISyntaxStateMachine_DDefineSsm.cpp
index 96020a95..34bd4569 100644
--- a/xo-reader2/src/reader2/ISyntaxStateMachine_DDefineSsm.cpp
+++ b/xo-reader2/src/reader2/ISyntaxStateMachine_DDefineSsm.cpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DDefineSsm.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -28,9 +28,9 @@ namespace xo {
         }
 
         auto
-        ISyntaxStateMachine_DDefineSsm::on_parsed_symbol(DDefineSsm & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        ISyntaxStateMachine_DDefineSsm::on_symbol_token(DDefineSsm & self, const Token & tk, ParserStateMachine * p_psm) -> void
         {
-            self.on_parsed_symbol(sym, p_psm);
+            self.on_symbol_token(tk, p_psm);
         }
         auto
         ISyntaxStateMachine_DDefineSsm::on_def_token(DDefineSsm & self, const Token & tk, ParserStateMachine * p_psm) -> void
@@ -42,6 +42,11 @@ namespace xo {
         {
             self.on_if_token(tk, p_psm);
         }
+        auto
+        ISyntaxStateMachine_DDefineSsm::on_parsed_symbol(DDefineSsm & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        {
+            self.on_parsed_symbol(sym, p_psm);
+        }
 
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-reader2/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp b/xo-reader2/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
index b2efaab5..f00b9c2f 100644
--- a/xo-reader2/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
+++ b/xo-reader2/src/reader2/ISyntaxStateMachine_DExpectSymbolSsm.cpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DExpectSymbolSsm.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -28,9 +28,9 @@ namespace xo {
         }
 
         auto
-        ISyntaxStateMachine_DExpectSymbolSsm::on_parsed_symbol(DExpectSymbolSsm & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        ISyntaxStateMachine_DExpectSymbolSsm::on_symbol_token(DExpectSymbolSsm & self, const Token & tk, ParserStateMachine * p_psm) -> void
         {
-            self.on_parsed_symbol(sym, p_psm);
+            self.on_symbol_token(tk, p_psm);
         }
         auto
         ISyntaxStateMachine_DExpectSymbolSsm::on_def_token(DExpectSymbolSsm & self, const Token & tk, ParserStateMachine * p_psm) -> void
@@ -42,6 +42,11 @@ namespace xo {
         {
             self.on_if_token(tk, p_psm);
         }
+        auto
+        ISyntaxStateMachine_DExpectSymbolSsm::on_parsed_symbol(DExpectSymbolSsm & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        {
+            self.on_parsed_symbol(sym, p_psm);
+        }
 
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-reader2/src/reader2/ISyntaxStateMachine_DExprSeqState.cpp b/xo-reader2/src/reader2/ISyntaxStateMachine_DExprSeqState.cpp
index 2279ea88..47c06ba3 100644
--- a/xo-reader2/src/reader2/ISyntaxStateMachine_DExprSeqState.cpp
+++ b/xo-reader2/src/reader2/ISyntaxStateMachine_DExprSeqState.cpp
@@ -2,7 +2,7 @@
  *
  *  Generated automagically from ingredients:
  *  1. code generator:
- *       [/Users/roland/proj/xo-umbrella2/xo-facet/codegen/genfacet]
+ *       [/home/roland/proj/xo-umbrella2-claude1/xo-facet/codegen/genfacet]
  *     arguments:
  *       --input [idl/ISyntaxStateMachine_DExprSeqState.json5]
  *  2. jinja2 template for abstract facet .hpp file:
@@ -28,9 +28,9 @@ namespace xo {
         }
 
         auto
-        ISyntaxStateMachine_DExprSeqState::on_parsed_symbol(DExprSeqState & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        ISyntaxStateMachine_DExprSeqState::on_symbol_token(DExprSeqState & self, const Token & tk, ParserStateMachine * p_psm) -> void
         {
-            self.on_parsed_symbol(sym, p_psm);
+            self.on_symbol_token(tk, p_psm);
         }
         auto
         ISyntaxStateMachine_DExprSeqState::on_def_token(DExprSeqState & self, const Token & tk, ParserStateMachine * p_psm) -> void
@@ -42,6 +42,11 @@ namespace xo {
         {
             self.on_if_token(tk, p_psm);
         }
+        auto
+        ISyntaxStateMachine_DExprSeqState::on_parsed_symbol(DExprSeqState & self, std::string_view sym, ParserStateMachine * p_psm) -> void
+        {
+            self.on_parsed_symbol(sym, p_psm);
+        }
 
     } /*namespace scm*/
 } /*namespace xo*/
diff --git a/xo-reader2/src/reader2/ParserStateMachine.cpp b/xo-reader2/src/reader2/ParserStateMachine.cpp
index c05ab217..2e61be95 100644
--- a/xo-reader2/src/reader2/ParserStateMachine.cpp
+++ b/xo-reader2/src/reader2/ParserStateMachine.cpp
@@ -17,7 +17,7 @@ namespace xo {
 
     namespace scm {
         ParserStateMachine::ParserStateMachine(const ArenaConfig & config,
-                                               obj<AAllocator> * expr_alloc)
+                                               obj<AAllocator> expr_alloc)
             : parser_alloc_{DArena::map(config)},
               expr_alloc_{expr_alloc},
               debug_flag_{config.debug_flag_}
@@ -70,6 +70,13 @@ namespace xo {
             this->stack_ = ParserStack::pop(stack_, parser_alloc_);
         }
 
+        void
+        ParserStateMachine::upsert_var(DVariable * var)
+        {
+            scope log(XO_DEBUG(true), "stub impl");
+            log && log(xtag("var", std::string_view(*(var->name()))));
+        }
+
         void
         ParserStateMachine::reset_result()
         {
@@ -111,6 +118,10 @@ namespace xo {
             }
 
             switch (tk.tk_type()) {
+            case tokentype::tk_symbol:
+                this->on_symbol_token(tk);
+                break;
+
             case tokentype::tk_def:
                 this->on_def_token(tk);
                 break;
@@ -125,7 +136,6 @@ namespace xo {
             case tokentype::tk_i64:
             case tokentype::tk_f64:
             case tokentype::tk_string:
-            case tokentype::tk_symbol:
             case tokentype::tk_leftparen:
             case tokentype::tk_rightparen:
             case tokentype::tk_leftbracket:
@@ -165,6 +175,14 @@ namespace xo {
             }
         }
 
+        void
+        ParserStateMachine::on_symbol_token(const Token & tk)
+        {
+            scope log(XO_DEBUG(debug_flag_), xtag("tk", tk));
+
+            stack_->top().on_symbol_token(tk, this);
+        }
+
         void
         ParserStateMachine::on_def_token(const Token & tk)
         {
@@ -205,7 +223,7 @@ namespace xo {
 
             assert(expr_alloc_);
 
-            auto errmsg = DString::from_view(*expr_alloc_,
+            auto errmsg = DString::from_view(expr_alloc_,
                                              std::string_view(errmsg_string));
 
             this->capture_error(ssm_name, errmsg);
@@ -228,7 +246,7 @@ namespace xo {
 
             assert(expr_alloc_);
 
-            auto errmsg = DString::from_view(*expr_alloc_,
+            auto errmsg = DString::from_view(expr_alloc_,
                                              std::string_view(errmsg_string));
 
             this->capture_error(ssm_name, errmsg);
diff --git a/xo-reader2/src/reader2/SchematikaParser.cpp b/xo-reader2/src/reader2/SchematikaParser.cpp
index 47f6918b..442da75e 100644
--- a/xo-reader2/src/reader2/SchematikaParser.cpp
+++ b/xo-reader2/src/reader2/SchematikaParser.cpp
@@ -19,7 +19,7 @@ namespace xo {
         // ----- SchematikaParser -----
 
         SchematikaParser::SchematikaParser(const ArenaConfig & config,
-                                           obj<AAllocator> * expr_alloc,
+                                           obj<AAllocator> expr_alloc,
                                            bool debug_flag)
             : psm_{config, expr_alloc},
               debug_flag_{debug_flag}
@@ -38,13 +38,13 @@ namespace xo {
 
         void
         SchematikaParser::begin_interactive_session() {
-            DExprSeqState::establish_interactive(*(psm_.expr_alloc()), &psm_);
+            DExprSeqState::establish_interactive(psm_.expr_alloc(), &psm_);
 
         }
 
         void
         SchematikaParser::begin_batch_session() {
-            DExprSeqState::establish_batch(*(psm_.expr_alloc()), &psm_);
+            DExprSeqState::establish_batch(psm_.expr_alloc(), &psm_);
         }
 
         const ParserResult &
diff --git a/xo-reader2/utest/SchematikaParser.test.cpp b/xo-reader2/utest/SchematikaParser.test.cpp
index b333ff0c..6100392a 100644
--- a/xo-reader2/utest/SchematikaParser.test.cpp
+++ b/xo-reader2/utest/SchematikaParser.test.cpp
@@ -27,7 +27,7 @@ namespace xo {
             DArena expr_arena = DArena::map(config);
             obj<AAllocator> expr_alloc = with_facet<AAllocator>::mkobj(&expr_arena);
 
-            SchematikaParser parser(config, &expr_alloc, false /*debug_flag*/);
+            SchematikaParser parser(config, expr_alloc, false /*debug_flag*/);
 
             REQUIRE(parser.debug_flag() == false);
             REQUIRE(parser.is_at_toplevel() == true);
@@ -42,7 +42,7 @@ namespace xo {
             DArena expr_arena = DArena::map(config);
             obj<AAllocator> expr_alloc = with_facet<AAllocator>::mkobj(&expr_arena);
 
-            SchematikaParser parser(config, &expr_alloc, false /*debug_flag*/);
+            SchematikaParser parser(config, expr_alloc, false /*debug_flag*/);
 
             parser.begin_interactive_session();
 
@@ -60,7 +60,7 @@ namespace xo {
             DArena expr_arena = DArena::map(config);
             obj<AAllocator> expr_alloc = with_facet<AAllocator>::mkobj(&expr_arena);
 
-            SchematikaParser parser(config, &expr_alloc, false /*debug_flag*/);
+            SchematikaParser parser(config, expr_alloc, false /*debug_flag*/);
 
             parser.begin_batch_session();
 
@@ -78,20 +78,30 @@ namespace xo {
             DArena expr_arena = DArena::map(config);
             obj<AAllocator> expr_alloc = with_facet<AAllocator>::mkobj(&expr_arena);
 
-            SchematikaParser parser(config, &expr_alloc, false /*debug_flag*/);
+            SchematikaParser parser(config, expr_alloc, false /*debug_flag*/);
 
             parser.begin_batch_session();
 
-            auto & result = parser.on_token(Token::def_token());
+            {
+                auto & result = parser.on_token(Token::def_token());
+
+                // after begin_interactive_session, parser has toplevel exprseq
+                // but is still "at toplevel" in the sense of ready for input
+                REQUIRE(parser.has_incomplete_expr() == true);
+                REQUIRE(result.is_incomplete());
+            }
+
+            {
+                auto & result = parser.on_token(Token::symbol_token("foo"));
+
+                REQUIRE(parser.has_incomplete_expr() == true);
+                REQUIRE(result.is_error());
+            }
 
             // define-expressions not properly implemented
 
-            // after begin_interactive_session, parser has toplevel exprseq
-            // but is still "at toplevel" in the sense of ready for input
-            REQUIRE(parser.has_incomplete_expr() == true);
-            REQUIRE(result.is_error());
 
-            REQUIRE(result.error_description());
+            //REQUIRE(result.error_description());
         }
 
         TEST_CASE("SchematikaParser-interactive-if", "[reader2][SchematikaParser]")
@@ -103,7 +113,7 @@ namespace xo {
             DArena expr_arena = DArena::map(config);
             obj<AAllocator> expr_alloc = with_facet<AAllocator>::mkobj(&expr_arena);
 
-            SchematikaParser parser(config, &expr_alloc, false /*debug_flag*/);
+            SchematikaParser parser(config, expr_alloc, false /*debug_flag*/);
 
             parser.begin_interactive_session();