Make Variables logable by implementing __repr__

run-exp.py

@@ -22,6 +22,12 @@ class Variable(ABC):
     def name(self):
         return self._name
 
+    def __repr__(self):
+        return json.dumps({
+            'name': self.name,
+            'type': str(type(self).__name__),
+        })
+
     @abstractmethod
     def evaluate(self, variable_mapping):
         pass