--- a/interpreter.h	Thu May 23 13:42:57 2019 -0400
+++ b/interpreter.h	Thu May 23 17:57:20 2019 -0400
@@ -3,6 +3,8 @@
 
 #include <functional>
 
+#include "parser.h"
+
 namespace calc
 {
   class interpreter
@@ -17,7 +19,9 @@
 
     interpreter& operator = (const interpreter&) = delete;
 
-    ~interpreter (void);
+    ~interpreter (void) = default;
+
+    parser& get_parser (void) { return m_parser; }
 
     int parse_and_execute (const std::string& line);
 
@@ -37,12 +41,14 @@
       return tmp;
     }
 
-    void emit_error (const char *msg);
+    void emit_error (const char *msg) const;
 
-    void emit_result (double value);
+    void emit_result (double value) const;
 
   private:
 
+    parser m_parser;
+
     std::function<void (const char *)> m_error_handler;
     std::function<void (double)> m_result_handler;
   };