xo-expression: + Variable + apply/lambda fixes

src/expression/Variable.cpp

@@ -0,0 +1,17 @@
+/* @file Variable.cpp */
+
+#include "Variable.hpp"
+
+namespace xo {
+    namespace ast {
+        void
+        Variable::display(std::ostream & os) const {
+            os << "<Variable"
+               << xtag("name", name_)
+               << ">";
+        } /*display*/
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end Variable.cpp */