Added RET keyword

src/evaluators/RetEvaluator.py

@@ -0,0 +1,40 @@
+from core.builtin_concepts import BuiltinConcepts
+from core.builtin_helpers import ensure_evaluated
+from core.concept import Concept, ConceptParts
+from evaluators.BaseEvaluator import OneReturnValueEvaluator
+
+
+class RetEvaluator(OneReturnValueEvaluator):
+    """
+    The evaluator transform the a concept, using the ret value
+    """
+
+    NAME = "Ret"
+
+    def __init__(self):
+        super().__init__(self.NAME, [BuiltinConcepts.EVALUATION], 10)
+
+    def matches(self, context, return_value):
+        return return_value.status and \
+               isinstance(return_value.value, Concept) and \
+               return_value.value.metadata.ret is not None
+
+    def eval(self, context, return_value):
+        sheerka = context.sheerka
+        concept = return_value.value
+        context.log(f"Processing ret value for concept {concept}.", self.name)
+
+        if not concept.metadata.is_evaluated:
+            evaluated = ensure_evaluated(context, concept)
+            if evaluated.key != concept.key:
+                context.log(f"Failed to evaluate concept '{concept}'")
+                return None
+            ret = evaluated.get_value(ConceptParts.RET)
+        else:
+            ret = concept.get_value(ConceptParts.RET)
+
+        if isinstance(ret, Concept) and sheerka.is_known(ret):
+            return sheerka.ret(self.name, True, ret, parents=[return_value])
+
+        context.log(f"ret '{ret}' is not a concept!")
+        return None