Added support of expansions

lark/load_grammar.py

@@ -451,9 +451,12 @@ class TerminalTreeToPattern(Transformer):
     def expansions(self, exps):
         if len(exps) == 1:
             return exps[0]
-        if len({i.flags for i in exps}) > 1:
-            raise GrammarError("Lark doesn't support joining terminals with conflicting flags!")
-        return PatternRE('(?:%s)' % ('|'.join(i.to_regexp() for i in exps)), exps[0].flags)
+        if not Py36:
+            if len({i.flags for i in exps}) > 1:
+                raise GrammarError("Lark doesn't support joining terminals with conflicting flags!")
+            return PatternRE('(?:%s)' % ('|'.join(i.to_regexp() for i in exps)), exps[0].flags)
+        else:
+            return PatternRE('(?:%s)' % ('|'.join(i.to_regexp() for i in exps)), ())
 
     def expr(self, args):
         inner, op = args[:2]

tests/test_parser.py

@@ -1078,6 +1078,18 @@ def _make_parser_test(LEXER, PARSER):
             self.assertEqual(g.parse("  ").children,["  "])
             self.assertEqual(g.parse("\n ").children,["\n "])
             self.assertRaises(UnexpectedCharacters, g.parse, "\n\n")
+            
+            g = r"""
+                start: A
+                A: B | C
+                B: "b"i
+                C: "c"
+            """
+            g = _Lark(g)
+            self.assertEqual(g.parse("b").children,["b"])
+            self.assertEqual(g.parse("B").children,["B"])
+            self.assertEqual(g.parse("c").children,["c"])
+            self.assertRaises(UnexpectedCharacters, g.parse, "C")
 
 
         def test_lexer_token_limit(self):