Experimental parser: add backtracking

tools/lexer_generator/code_generator.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 275 matching lines @@
     dfa_states = []
     self.__dfa.visit_all_states(lambda state, acc: dfa_states.append(state))
     encoding = self.__dfa.encoding()
     f = lambda state : CodeGenerator.__transform_state(encoding, state)
     dfa_states = map(f, dfa_states)
     id_map = {x['original_node_number'] : x for x in dfa_states}
     dfa_states = []
     start_node_number = self.__dfa.start_state().node_number()
     CodeGenerator.__reorder(start_node_number, id_map, dfa_states)
     # store states
-    eos_states = set([])
+    eos_states = set()
     remap = lambda state_id : id_map[state_id]['node_number']
     def f((key, original_node_number)):
       return (key, remap(original_node_number))
     for state in dfa_states:
       state['transitions'] = map(f, state['transitions'])
       state['unique_transitions'] = {k : remap(v)
           for k, v in state['unique_transitions'].items()}
       if state['omega_transition'] != None:
         state['omega_transition'] = remap(state['omega_transition'])
       if 'eos' in state['unique_transitions']:
@@ skipping 105 matching lines @@
 
     return template.render(
       start_node_number = 0,
       debug_print = self.__debug_print,
       default_action = default_action,
       dfa_states = dfa_states,
       jump_table = self.__jump_table,
       encoding = encoding.name(),
       char_type = char_type,
       upper_bound = encoding.primary_range()[1])