Experimental parser: make nfa nodes immutable

tools/lexer_generator/nfa_builder.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 230 matching lines @@
       state_iter = lambda node : node.state_iter(key_filter = is_epsilon)
       edge = set(state_iter(node))
       closure = Automaton.visit_states(
           edge, inner, state_iter=state_iter, visit_state=set())
       node.set_epsilon_closure(closure)
     Automaton.visit_states(set([start_state]), outer)
 
   @staticmethod
   def __replace_catch_all(encoding, state):
     catch_all = TransitionKey.unique('catch_all')
-    transitions = state.transitions()
-    if not catch_all in transitions:
+    states = list(state.state_iter_for_key(catch_all))
+    if not states:
       return
     f = lambda acc, state: acc | set(state.epsilon_closure_iter())
-    reachable_states = reduce(f, transitions[catch_all], set())
-    f = lambda acc, state: acc | set(state.transitions().keys())
+    reachable_states = reduce(f, states, set())
+    f = lambda acc, state: acc | set(state.key_iter())
     keys = reduce(f, reachable_states, set())
     keys.discard(TransitionKey.epsilon())
     keys.discard(catch_all)
     keys.discard(TransitionKey.unique('eos'))
     inverse_key = TransitionKey.inverse_key(encoding, keys)
-    if inverse_key:
-      transitions[inverse_key] = transitions[catch_all]
-    del transitions[catch_all]
+    if not inverse_key:
+      inverse_key = TransitionKey.unique('no_match')
+    state.swap_key(catch_all, inverse_key)
 
   @staticmethod
   def nfa(encoding, character_classes, subtree_map, name):
     self = NfaBuilder(encoding, character_classes, subtree_map)
     (start, end, nodes_created) = self.__nfa(name)
     # close all ends
     global_end_to_return = self.__global_end_node or end
     assert global_end_to_return, "no terminal nodes, default tree continues"
     if end and self.__global_end_node:
       end.close(self.__global_end_node)
@@ skipping 66 matching lines @@
     terms = list(NfaBuilder.__flatten_terms(terms, 'OR'))
     assert terms
     return terms[0] if len(terms) == 1 else Term('OR', *terms)
 
   @staticmethod
   def cat_terms(terms):
     terms = NfaBuilder.__flatten_terms(terms, 'CAT')
     terms = list(NfaBuilder.__flatten_literals(terms))
     assert terms
     return terms[0] if len(terms) == 1 else Term('CAT', *terms)