xo-reader: misc bugfixes + logging [wip, utests not passing]

include/xo/reader/define_xs.hpp

@@ -56,6 +56,11 @@ namespace xo {
             n_defexprstatetype,
         };
 
+        extern const char * defexprstatetype_descr(defexprstatetype x);
+
+        std::ostream &
+        operator<<(std::ostream & os, defexprstatetype x);
+
         /** @class define_xs
          *  @brief state to provide parsing of a define-expression
          **/