Experimental parser: use sentinal values for actions

tools/lexer_generator/dfa_optimizer.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 154 matching lines @@
 
     incoming_transitions = {}
     def build_incoming_transitions(state, visitor_state):
       for key, transition_state in state.key_state_iter():
         if not transition_state in incoming_transitions:
           incoming_transitions[transition_state] = []
         incoming_transitions[transition_state].append((key,state))
     dfa.visit_all_states(build_incoming_transitions)
 
     def is_replacement_candidate(state):
-      action = state.action()
-      if not action or not action.match_action():
-        return False
-      if (action.match_action().name() == 'token' or
-          action.match_action().name() == 'harmony_token'):
-        return True
-      return False
+      return (state.action().match_action().name() == 'token' or
+              state.action().match_action().name() == 'harmony_token')
 
     replacements = {}
     for state, incoming in incoming_transitions.items():
       if len(incoming) < 10:
         continue
       if not is_replacement_candidate(state):
         continue
       # check to see if incoming edges are matched by an outgoing edge
       def match_filter((incoming_key, incoming_state)):
         return (incoming_state != state and  # drop self transitions
@@ skipping 42 matching lines @@
           counters['goto_start'] += 1
         else:
           counters['store_token_and_goto'] += 1
           match_action = Term('store_token_and_goto', old_token, state_id)
       elif old_action.match_action().name() == 'harmony_token':
         new_args = list(old_action.match_action().args()) + [state_id]
         match_action = Term('store_harmony_token_and_goto', *new_args)
         counters['store_harmony_token_and_goto'] += 1
       else:
         raise Exception(old_action.match_action())
-      return Action(old_action.entry_action(), match_action,
+      return Action(old_action.entry_action(),
+                    match_action,
                     old_action.precedence())
     # map the old state to the new state, with fewer transitions and
     # goto actions
     def replace_state(state, acc):
       new_state = {
         'transitions' : {},
         'terminal' : state in self.__dfa.terminal_set(),
         'action' : state.action(),
       }
       states[name(state)] = new_state
@@ skipping 40 matching lines @@
         counters['store_harmony_token_and_goto'])
       print 'transitions removed %s' % counters['removals']
       print 'do_stored_token actions added %s' % len(store_states)
     self.__dfa = Dfa(self.__dfa.encoding(), start_name, states)
 
   @staticmethod
   def optimize(dfa, log):
     optimizer = DfaOptimizer(dfa, log)
     optimizer.replace_tokens_with_gotos()
     return optimizer.__dfa