From a23307aabb560c00955f0a7b8df81775c3cb202f Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Sat, 17 Jan 2026 01:05:59 -0500
Subject: [PATCH] xo-expression2: + DVariable

---
 include/xo/expression2/DVariable.hpp | 56 ++++++++++++++++++++++++++++
 src/expression2/CMakeLists.txt       |  1 +
 src/expression2/DVariable.cpp        | 19 ++++++++++
 3 files changed, 76 insertions(+)
 create mode 100644 include/xo/expression2/DVariable.hpp
 create mode 100644 src/expression2/DVariable.cpp

diff --git a/include/xo/expression2/DVariable.hpp b/include/xo/expression2/DVariable.hpp
new file mode 100644
index 00000000..036d88ce
--- /dev/null
+++ b/include/xo/expression2/DVariable.hpp
@@ -0,0 +1,56 @@
+/** @file DVariable.hpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include "DUniqueString.hpp"
+#include "Binding.hpp"
+#include "TypeRef.hpp"
+#include "exprtype.hpp"
+#include <xo/reflect/TypeDescr.hpp>
+
+namespace xo {
+    namespace scm {
+
+        /** @class DVariable*
+         *  @brief syntax for a variable reference
+         **/
+        class DVariable {
+        public:
+            using TypeDescr = xo::reflect::TypeDescr;
+
+        public:
+            DVariable(const DUniqueString & name, const TypeRef & typeref, Binding path)
+                : name_{name}, typeref_{typeref}, path_{path} {}
+
+            const DUniqueString & name() const { return name_; }
+            Binding path() const { return path_; }
+
+            /** @defgroup scm-variable-expression-facet**/
+            ///@{
+
+            exprtype extype() const noexcept { return exprtype::variable; }
+            TypeRef typeref() const noexcept { return typeref_; }
+            TypeDescr valuetype() const noexcept { return typeref_.td(); };
+            void assign_valuetype(TypeDescr td) noexcept;
+
+            ///@}
+
+        private:
+            /** symbol name **/
+            const DUniqueString & name_;
+            /** variable value always has type consistent
+             *  with this description
+             **/
+            TypeRef typeref_;
+            /** at runtime: navigate environemnt via this path to get
+             *  runtime memory location for this variable
+             **/
+            Binding path_;
+        };
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DVariable.hpp */
diff --git a/src/expression2/CMakeLists.txt b/src/expression2/CMakeLists.txt
index bf54ab6a..6b897535 100644
--- a/src/expression2/CMakeLists.txt
+++ b/src/expression2/CMakeLists.txt
@@ -4,6 +4,7 @@ set(SELF_LIB xo_expression2)
 set(SELF_SRCS
     init_expression2.cpp
     DConstant.cpp
+    DVariable.cpp
     TypeRef.cpp
     IExpression_Any.cpp
     IExpression_DConstant.cpp
diff --git a/src/expression2/DVariable.cpp b/src/expression2/DVariable.cpp
new file mode 100644
index 00000000..f589da7b
--- /dev/null
+++ b/src/expression2/DVariable.cpp
@@ -0,0 +1,19 @@
+/** @file DVariable.cpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#include "DVariable.hpp"
+#include "exprtype.hpp"
+
+namespace xo {
+    namespace scm {
+        void
+        DVariable::assign_valuetype(TypeDescr td) noexcept
+        {
+            typeref_.resolve(td);
+        }
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DVariable.cpp */