Changes due to code review by @MegaIng

lark/parser_frontends.py

@@ -34,7 +34,11 @@ def get_frontend(parser, lexer):
                     super(LALR_CustomLexerWrapper, self).__init__(
                         lexer, lexer_conf, parser_conf, options=options)
                 def init_lexer(self):
-                    self.lexer = CustomLexerWrapper(self.lexer_conf)
+                    future_interface = getattr(lexer, '__future_interface__', False)
+                    if future_interface:
+                        self.lexer = lexer(self.lexer_conf)
+                    else:
+                        self.lexer = CustomLexerWrapper(self.lexer_conf)
 
             return LALR_CustomLexerWrapper
         else:

lark/parsers/lalr_parser.py

@@ -2,7 +2,7 @@
 """
 # Author: Erez Shinan (2017)
 # Email : erezshin@gmail.com
-from copy import deepcopy
+from copy import deepcopy, copy
 from ..exceptions import UnexpectedCharacters, UnexpectedInput, UnexpectedToken
 from ..lexer import Token
 
@@ -61,10 +61,13 @@ class ParserState:
             self.lexer, # XXX copy
             self.callbacks,
             self.start,
-            list(self.state_stack),
+            copy(self.state_stack),
             deepcopy(self.value_stack),
         )
 
+    def copy(self):
+        return copy(self)
+
     def feed_token(self, token, is_end=False):
         state_stack = self.state_stack
         value_stack = self.value_stack

lark/parsers/lalr_puppet.py

@@ -41,8 +41,9 @@ class ParserPuppet(object):
 
         return self.parser_state == other.parser_state and self.lexer_state == other.lexer_state
 
-    def __hash__(self):
-        return hash((self.parser_state, self.lexer_state))
+    # TODO Provide with an immutable puppet instance
+    # def __hash__(self):
+    #     return hash((self.parser_state, self.lexer_state))
 
     def pretty(self):
         """Print the output of ``choices()`` in a way that's easier to read."""