Improved default semantic action.

Converting terminal to a string as a default action.

arpeggio/__init__.py

@@ -706,8 +706,13 @@ class SemanticAction(object):
         This is the default implementation used if no semantic action is
         defined.
         """
+        if isinstance(node, Terminal):
+            # Default for Terminal is to convert to string.
+            retval = str(node)
+        else:
+            retval = node
             # Special case. If only one child exist return it.
-        if len(nodes)==1:
+            if len(nodes) == 1:
                 retval = nodes[0]
             else:
                 # If there is only one non-string child return
@@ -726,7 +731,7 @@ class SemanticAction(object):
                 else:
                     # Return the only non-string child
                     retval = last_non_str
-                # If there is only one non-string child return
+
         return retval