Implemented a first and basic version of a Rete rule engine

src/sheerkarete/pnode.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from core.rule import Rule
+from sheerkarete.beta import BetaMemory
+from sheerkarete.common import ReteToken
+
+if TYPE_CHECKING:  # pragma: no cover
+    from typing import List
+    from typing import Dict
+    from typing import Any
+    from sheerkarete.common import WME
+    from sheerkarete.common import V
+
+
+class PNode(BetaMemory):
+    """
+    A beta network node that stores the matches for productions.
+    """
+
+    def __init__(self, rule: Rule, **kwargs):
+        super(PNode, self).__init__(**kwargs)
+        self.rules = [rule]
+        self.new: List[ReteToken] = []
+
+    def left_activation(self, token: ReteToken, wme: WME, binding: Dict[V, Any]):
+        new_token = ReteToken(token, wme, node=self, binding=binding)
+        self.items.append(new_token)
+        self.new.append(new_token)
+
+    def pop_new_token(self):
+        if self.new:
+            return self.new.pop()
+
+    def new_activations(self):
+        while self.new:
+            t = self.new.pop()
+            yield t
+
+    @property
+    def activations(self):
+        for t in self.items:
+            yield t