diff --git a/include/xo/reader2/DSyntaxStateMachine.hpp b/include/xo/reader2/DSyntaxStateMachine.hpp
new file mode 100644
index 00000000..4aa35f4d
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+++ b/include/xo/reader2/DSyntaxStateMachine.hpp
@@ -0,0 +1,42 @@
+/** @file DSyntaxStateMachine.hpp
+ *
+ *  @author Roland Conybeare, Jan 2026
+ **/
+
+#pragma once
+
+#include <xo/object2/DArray.hpp>
+
+namespace xo {
+    namespace scm {
+
+        /** @class DSyntaxStateMachine
+         *  @brief static interface for implementing ASyntaxStateMachine
+         *
+         *  Using CRTP to collect methods common to ASyntaxStateMachine
+         *  implementations.
+         *
+         *  Deliberately unusable through base class pointer.
+         *  For runtime polymorphism use something like:
+         *  @code
+         *    Derived * d = ...;
+         *    auto obj = with_facet<ASyntaxStateMachine>::mkobj(d);
+         *    // or
+         *    obj<ASyntaxStateMachine,Derived>(d)
+         *  @endcode
+         **/
+        template<typename Derived>
+        class DSyntaxStateMachine {
+            friend Derived;
+
+            /** arglist is DArray of obj<AGCObejct,DVariable> **/
+            void on_parsed_formal_arglist(this auto&& self, DArray * arglist, ParserStateMachine * p_psm) {
+                p_psm->illegal_parsed_formal_arglist(
+
+            }
+        };
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end DSyntaxStateMachine.hpp */