Fixed first token recognition when creating bnf concepts

tests/parsers/test_BnfParser.py

@@ -84,6 +84,8 @@ class TestBnfParser(TestUsingMemoryBasedSheerka):
         ("('a'*=x 'b'+=y)=z", Sequence(
             ZeroOrMore(StrMatch("a"), rule_name="x"),
             OneOrMore(StrMatch("b"), rule_name="y"), rule_name="z")),
+        ("'--filter'",
+         Sequence(StrMatch("-", skip_whitespace=False), StrMatch("-", skip_whitespace=False), StrMatch("filter")))
     ])
     def test_i_can_parse_regex(self, expression, expected):
         sheerka, context, parser = self.init_parser()
@@ -141,8 +143,9 @@ class TestBnfParser(TestUsingMemoryBasedSheerka):
         sheerka, context, parser = self.init_parser()
 
         res = parser.parse(context, Tokenizer(expression))
-        ret_value = res.value.value
+        ret_value = res.body.body
         assert parser.has_error
+        assert sheerka.isinstance(res.body, BuiltinConcepts.ERROR)
         assert not res.status
         assert ret_value[0] == error