xo-reader: distinguish interactive sessions

+ allow top-level i64 literals

xo-reader/src/reader/reader.cpp

@@ -4,6 +4,16 @@
 
 namespace xo {
     namespace scm {
+        void
+        reader::begin_interactive_session() {
+            parser_.begin_interactive_session();
+        }
+
+        reader_result
+        reader::end_interactive_session() {
+            return this->read_expr(span_type(nullptr, nullptr), true /*eof*/);
+        }
+
         void
         reader::begin_translation_unit() {
             parser_.begin_translation_unit();