We can now use concept sets in BNF definitions

core/builtin_concepts.py

@@ -29,6 +29,7 @@ class BuiltinConcepts(Enum):
     SUCCESS = "success"
     ERROR = "error"
     UNKNOWN_CONCEPT = "unknown concept"  # the request concept is not recognized
+    CANNOT_RESOLVE_CONCEPT = "cannot resolve concept"  # when too many concepts with the same name
     RETURN_VALUE = "return value"  # a value is returned
     CONCEPT_TOO_LONG = "concept too long"  # concept cannot be processed by exactConcept parser
     NEW_CONCEPT = "new concept"  # when a new concept is added
@@ -48,6 +49,7 @@ class BuiltinConcepts(Enum):
     EVALUATOR_PRE_PROCESS = "evaluator pre process"  # used modify / tweak behaviour of evaluators
     CONCEPT_EVAL_REQUESTED = "concept eval requested"
     REDUCE_REQUESTED = "reduce requested"  # remove meaningless error when possible
+    NOT_A_SET = "not a set"  # the concept has no entry in sets
 
     NODE = "node"
     GENERIC_NODE = "generic node"
@@ -79,6 +81,7 @@ BuiltinUnique = [
 BuiltinErrors = [str(e) for e in {
     BuiltinConcepts.ERROR,
     BuiltinConcepts.UNKNOWN_CONCEPT,
+    BuiltinConcepts.CANNOT_RESOLVE_CONCEPT,
     BuiltinConcepts.CONCEPT_TOO_LONG,
     BuiltinConcepts.UNKNOWN_PROPERTY,
     BuiltinConcepts.TOO_MANY_SUCCESS,
@@ -87,6 +90,7 @@ BuiltinErrors = [str(e) for e in {
     BuiltinConcepts.CONCEPT_ALREADY_DEFINED,
     BuiltinConcepts.CONCEPT_EVAL_ERROR,
     BuiltinConcepts.CONCEPT_ALREADY_IN_SET,
+    BuiltinConcepts.NOT_A_SET,
 }]
 
 """
@@ -124,6 +128,16 @@ class ErrorConcept(Concept):
         return f"({self.id}){self.name}: {self.body}"
 
 
+class UnknownConcept(Concept):
+    def __init__(self, metadata=None):
+        super().__init__(BuiltinConcepts.UNKNOWN_CONCEPT, True, False, BuiltinConcepts.UNKNOWN_CONCEPT)
+        self.set_metadata_value(ConceptParts.BODY, metadata)
+        self.metadata.is_evaluated = True
+
+    def __repr__(self):
+        return f"({self.id}){self.name}: {self.body}"
+
+
 class ReturnValueConcept(Concept):
     """
     This class represents the result of a data flow processing