xo-reader: uncopy: with + exprstate.illegal_input_error()

include/xo/reader/exprstate.hpp

@@ -156,6 +156,13 @@ namespace xo {
                                       exprstatestack * p_stack,
                                       rp<Expression> * p_emit_expr);
 
+        protected:
+            /** throw exception when next token is inconsistent with
+             *  parsing state
+             **/
+            void illegal_input_error(const char * self_name,
+                                     const token_type & tk) const;
+
         protected:
             /** explicit subtype: identifies derived class **/
             exprstatetype exs_type_;