Experimental parser: use sentinal values for actions

tools/lexer_generator/nfa.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 17 matching lines @@
 from transition_keys import TransitionKey
 from automaton import *
 
 class NfaState(AutomatonState):
 
   def __init__(self):
     super(NfaState, self).__init__()
     self.__transitions = {}
     self.__unclosed = set()
     self.__epsilon_closure = None
-    self.__action = None
+    self.__action = Action.empty_action()
 
   def transitions_to_multiple_states(self):
     return True
 
   def epsilon_closure_iter(self):
     return iter(self.__epsilon_closure)
 
   def set_epsilon_closure(self, closure):
     assert self.is_closed()
     assert self.__epsilon_closure == None
     self.__epsilon_closure = frozenset(closure)
 
   def action(self):
     assert self.is_closed()
     return self.__action
 
   def set_action(self, action):
     assert not self.is_closed()
     assert not self.__action
+    assert isinstance(action, Action)
     self.__action = action
 
   def transitions(self):
     assert self.is_closed()
     return self.__transitions
 
   def __add_transition(self, key, next_state):
     assert key != None
     if next_state == None:
       assert not self.is_closed(), "already closed"
@@ skipping 88 matching lines @@
       f = lambda state: state.transition_state_iter_for_key(key)
       match_states = set(chain(*map(f, nfa_state_set)))
       transition_state = self.__to_dfa(match_states, dfa_nodes, end_node)
       dfa_nodes[name]['transitions'][key] = transition_state
     return name
 
   def compute_dfa(self):
     dfa_nodes = {}
     start_name = self.__to_dfa(set([self.__start]), dfa_nodes, self.__end)
     return (start_name, dfa_nodes)