xo-reader2 xo-expresion2: work on define-expressions [WIP]

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
              **/