Fixed #101 : Implement PLURIAL

Fixed #103 : Implement PlurialNodeParser
Fixed #104 : Implement dynamic concept
Fixed #107 : PrepareEvalxxxEvaluator: context hints are lost on a second evaluation

src/core/builtin_concepts_ids.py

@@ -17,7 +17,7 @@ class BuiltinConcepts:
     EVAL_UNTIL_SUCCESS_REQUESTED = "__EVAL_UNTIL_SUCCESS_REQUESTED"  # PythonEvaluator tries combination until True is found
     EVAL_QUESTION_REQUESTED = "__EVAL_QUESTION_REQUESTED"  # the user input must be treated as question
     EVAL_GLOBAL_TRUTH_REQUESTED = "__EVAL_GLOBAL_TRUTH_REQUESTED"  # the user input is a global truth
-    VALIDATION_ONLY_REQUESTED = "__VALIDATION_ONLY_REQUESTED"  # Validation mode activated. Never evaluate the body
+    EXPRESSION_ONLY_REQUESTED = "__EXPRESSION_ONLY_REQUESTED"  # Do not allow methods with side effect
 
     # possible actions during sheerka.execute() or sheerka.evaluate_rules()
     INIT_SHEERKA = "__INIT_SHEERKA"  #
@@ -53,6 +53,7 @@ class BuiltinConcepts:
     # builtin attributes
     ISA = "__ISA"  # when a concept is an instance of another one
     HASA = "__HASA"  # when a concept has/owns another concept
+    PLURAL = "__PLURAL"  # when multiple occurrence of the concept
     AUTO_EVAL = "__AUTO_EVAL"  # when the concept must be auto evaluated
 
     # object