Resolved some remaining chicken and egg when parsing BNF nodes

src/core/sheerka/Sheerka.py

@@ -8,6 +8,7 @@ from cache.CacheManager import CacheManager
 from cache.DictionaryCache import DictionaryCache
 from cache.IncCache import IncCache
 from cache.ListIfNeededCache import ListIfNeededCache
+from cache.SetCache import SetCache
 from core.builtin_concepts import BuiltinConcepts, ErrorConcept, ReturnValueConcept, BuiltinErrors, BuiltinUnique, \
     UnknownConcept
 from core.concept import Concept, ConceptParts, PROPERTIES_FOR_NEW
@@ -31,6 +32,8 @@ class Sheerka(Concept):
     CONCEPTS_BY_NAME_ENTRY = "Concepts_By_Name"
     CONCEPTS_BY_HASH_ENTRY = "Concepts_By_Hash"  # store hash of concepts definitions (not values)
 
+    CONCEPTS_REFERENCES = "Concepts_References"  # tracks references between concepts
+
     CONCEPTS_BY_FIRST_KEYWORD_ENTRY = "Concepts_By_First_Keyword"
     RESOLVED_CONCEPTS_BY_FIRST_KEYWORD_ENTRY = "Resolved_Concepts_By_First_Keyword"
     CONCEPTS_SYA_DEFINITION_ENTRY = "Concepts_Sya_Definitions"
@@ -215,6 +218,9 @@ class Sheerka(Concept):
         cache = ListIfNeededCache(**params(self.CONCEPTS_BY_HASH_ENTRY))
         register_concept_cache(self.CONCEPTS_BY_HASH_ENTRY, cache, lambda c: c.get_definition_hash(), True)
 
+        cache = SetCache(default=lambda k: self.sdp.get(self.CONCEPTS_REFERENCES, k))
+        self.cache_manager.register_cache(self.CONCEPTS_REFERENCES, cache)
+
         cache = DictionaryCache(default=lambda k: self.sdp.get(self.CONCEPTS_BY_FIRST_KEYWORD_ENTRY, k))
         self.cache_manager.register_cache(self.CONCEPTS_BY_FIRST_KEYWORD_ENTRY, cache)
         self.cache_manager.get(self.CONCEPTS_BY_FIRST_KEYWORD_ENTRY, None)  # to init from sdp