Resolved some remaining chicken and egg when parsing BNF nodes

tests/parsers/test_BnfParser.py

@@ -214,3 +214,25 @@ class TestBnfParser(TestUsingMemoryBasedSheerka):
         assert not res.status
         assert context.sheerka.isinstance(res.value, BuiltinConcepts.UNKNOWN_CONCEPT)
         assert res.value.body == ('key', 'foo')
+
+    def test_concept_expression_are_correctly_created_when_isa_concept_is_detected(self):
+        sheerka, context, parser, one, two, number, twenties = self.init_parser(
+            "one",
+            "two",
+            "number",
+            "twenties")
+
+        sheerka.set_isa(context, sheerka.new("one"), number)
+        sheerka.set_isa(context, sheerka.new("two"), number)
+        sheerka.set_isa(context, sheerka.new("twenties"), number)
+
+        sub_context = context.push(BuiltinConcepts.INIT_BNF, twenties)
+
+        expression = "'twenty' number=n1"
+        res = parser.parse(sub_context, Tokenizer(expression))
+
+        assert not parser.has_error
+        assert res.status
+        pexpression = res.value.value
+        assert pexpression == Sequence(StrMatch('twenty'), ConceptExpression(number, "n1"))
+        assert pexpression.elements[1].recurse_id == "1003#n1#1004"