xo-expression: initial commit (constant + primitive)

src/expression/Expression.cpp

@@ -0,0 +1,15 @@
+/* @file Expression.cpp */
+
+#include "Expression.hpp"
+
+namespace xo {
+    namespace ast {
+        std::string
+        Expression::display_string() const {
+            return tostr(*this);
+        }
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end Expression.cpp */