Reimplemented explain feature

src/core/builtin_concepts.py

@@ -62,6 +62,8 @@ class BuiltinConcepts(Enum):
     PRECEDENCE = "precedence"  # use to set priority among concepts when parsing
     ASSOCIATIVITY = "associativity"  # use to set priority among concepts when parsing
     NOT_INITIALIZED = "not initialized"
+    NOT_FOUND = "not found"  # when the wanted resource is not found
+    FORMAT_INSTRUCTIONS = "format instructions"  # to express how to print the concept
 
     NODE = "node"
     GENERIC_NODE = "generic node"
@@ -73,6 +75,21 @@ class BuiltinConcepts(Enum):
     def __str__(self):
         return "__" + self.name
 
+    def __eq__(self, other):
+        if id(self) == id(other):
+            return True
+
+        if isinstance(other, str):
+            return str(self) == other
+
+        if not isinstance(other, BuiltinConcepts):
+            return False
+
+        return self.value == other.value
+
+    def __hash__(self):
+        return hash(self.value)
+
 
 BuiltinUnique = [
     BuiltinConcepts.BEFORE_PARSING,
@@ -106,7 +123,8 @@ BuiltinErrors = [str(e) for e in {
     BuiltinConcepts.NOT_A_SET,
     BuiltinConcepts.WHERE_CLAUSE_FAILED,
     BuiltinConcepts.CHICKEN_AND_EGG,
-    BuiltinConcepts.NOT_INITIALIZED
+    BuiltinConcepts.NOT_INITIALIZED,
+    BuiltinConcepts.NOT_FOUND
 }]
 
 """