reader reports tokenizer errors through normal return

include/xo/reader/reader_error.hpp

@@ -0,0 +1,53 @@
+/* reader_error.hpp
+ *
+ * Author: Roland Conybeare, Jul 2025
+ */
+
+#include "xo/tokenizer/tokenizer_error.hpp"
+
+namespace xo {
+    namespace scm {
+        class reader_error {
+        public:
+            using input_state_type = typename tokenizer_error<char>::input_state_type;
+
+        public:
+            /** default ctor represents a not-an-error sentinel object **/
+            reader_error() = default;
+            /** construct to capture parsing error context
+             *  @
+             **/
+            reader_error(const char * src_function,
+                         const char * error_description,
+                         const input_state_type & input_state,
+                         size_t error_pos)
+                : tk_error_{src_function, error_description, input_state, error_pos}
+                {}
+
+            const tokenizer_error<char> & tk_error() const { return tk_error_; }
+
+            /** true, except for sentinel not-an-error object **/
+            bool is_error() const { return tk_error_.is_error(); }
+            /** false, except for object in sentinel state **/
+            bool is_not_an_error() const { return tk_error_.is_not_an_error(); }
+
+            const char * src_function() const { return tk_error_.src_function(); }
+
+            /** print error representation to stream @p os.  Intended for parser/tokenizer
+             *  diagnostics.  For Schematika errors prefer @ref report
+             **/
+            void print(std::ostream & os) const { tk_error_.print(os); }
+
+            /** print human-oriented error report on @p os. **/
+            void report(std::ostream & os) const { tk_error_.report(os); }
+
+        private:
+            /** for parser-level errors, will still use this for
+             *  {src function, error description, input state and error pos}
+             **/
+            tokenizer_error<char> tk_error_;
+        };
+    }
+}
+
+/* end reader_error.hpp */