Implemented a first and basic version of a Rete rule engine

src/evaluators/DefConceptEvaluator.py

@@ -2,13 +2,13 @@ import core.utils
 from core.ast_helpers import UnreferencedVariablesVisitor
 from core.builtin_concepts import ParserResultConcept, ReturnValueConcept, BuiltinConcepts
 from core.concept import Concept, DEFINITION_TYPE_BNF, DEFINITION_TYPE_DEF
+from core.global_symbols import NotInit
 from core.sheerka.services.SheerkaExecute import ParserInput
 from core.tokenizer import TokenKind, Tokenizer
 from evaluators.BaseEvaluator import OneReturnValueEvaluator
-from parsers.BaseParser import NotInitializedNode
 from parsers.BnfNodeParser import ParsingExpression, ParsingExpressionVisitor
 from parsers.DefConceptParser import DefConceptNode, NameNode
-from parsers.PythonParser import PythonNode, get_python_node
+from parsers.PythonParser import get_python_node
 
 
 class ConceptOrRuleNameVisitor(ParsingExpressionVisitor):
@@ -70,7 +70,7 @@ class DefConceptEvaluator(OneReturnValueEvaluator):
             part_ret_val = getattr(def_concept_node, prop)
 
             # put back the sources
-            if isinstance(part_ret_val, NotInitializedNode):
+            if part_ret_val is NotInit:
                 continue
             elif isinstance(part_ret_val, NameNode):
                 source = str(part_ret_val)
@@ -107,7 +107,7 @@ class DefConceptEvaluator(OneReturnValueEvaluator):
         concept.init_key(key_source)
 
         # update the bnf definition if needed
-        if not isinstance(def_concept_node.definition, NotInitializedNode) and \
+        if def_concept_node.definition is not NotInit and \
             def_concept_node.definition_type == DEFINITION_TYPE_BNF:
             concept.set_bnf(def_concept_node.definition.value.value)