Experimental parser: small cleanup

tools/lexer_generator/automaton.py

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 19 matching lines @@
 from transition_keys import TransitionKey
 
 class Action(object):
 
   def __init__(self, entry_action, match_action, precedence = -1):
     for action in [entry_action, match_action]:
       if action == None:
         continue
       assert type(action) == TupleType and len(action)
       assert action[0] != None
+    assert entry_action or match_action
     self.__entry_action = entry_action
     self.__match_action = match_action
     self.__precedence = precedence
 
   def entry_action(self):
     return self.__entry_action
 
   def match_action(self):
     return self.__match_action
 
@@ skipping 127 matching lines @@
   node [shape = doublecircle, style=unfilled]; %s
   node [shape = circle];
 %s
 %s
 }
     ''' % (start_shape,
            start_number,
            " ".join(terminals),
            "\n".join(edge_content),
            "\n".join(node_content))