Experimental parser: make nfa nodes immutable

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 37 matching lines @@
   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):
+  def state_iter_for_key(self, key):
     assert self.is_closed()
-    return self.__transitions
+    if not key in self.__transitions:
+      return iter([])
+    return iter(self.__transitions[key])
+
+  def swap_key(self, old_key, new_key):
+    'this is one of the few mutations allowed after closing'
+    assert self.is_closed()
+    assert not new_key == TransitionKey.epsilon(), "changes epsilon closure"
+    value = self.__transitions[old_key]
+    del self.__transitions[old_key]
+    self.__transitions[new_key] = value
 
   def __add_transition(self, key, next_state):
     assert key != None
     if next_state == None:
       assert not self.is_closed(), "already closed"
       self.__unclosed.add(key)
       return
     if not key in self.__transitions:
       self.__transitions[key] = set()
     self.__transitions[key].add(next_state)
@@ skipping 19 matching lines @@
       self.__add_transition(key, end)
     if not unclosed:
       self.__add_transition(TransitionKey.epsilon(), end)
 
   def key_state_iter(
     self,
     key_filter = lambda x: True,
     state_filter = lambda x: True,
     match_func = lambda x, y: True,
     yield_func = lambda x, y: (x, y)):
+    assert self.is_closed()
     for key, states in self.__transitions.items():
       if key_filter(key):
         for state in states:
           if state_filter(state) and match_func(key, state):
             yield yield_func(key, state)
 
 class Nfa(Automaton):
 
   def __init__(self, encoding, start, end, nodes_created):
     super(Nfa, self).__init__(encoding)
@@ skipping 44 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)
       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)
     return (start_name, dfa_nodes)