add examples

examples/woods/opsem_python.py

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+### Operational Semantics - coded in Python ###
+
+import functools
+from examples.semantics.operational.simulator import make_actions_pure, filter_valid_actions
+from examples.woods.common import *
+
+# Action: Time advances, whoever is being attacked dies, bears become hungrier
+def action_advance_time(od):
+    msgs = []
+    clock, old_time = get_time(od)
+    new_time = old_time + 1
+    od.set_slot_value(clock, "time", new_time)
+
+    for _, attacking_link in od.get_all_instances("attacking"):
+        man_state = od.get_target(attacking_link)
+        animal_state = od.get_source(attacking_link)
+        if od.get_type_name(animal_state) == "BearState":
+            od.set_slot_value(animal_state, "hunger", max(od.get_slot_value(animal_state, "hunger") - 50, 0))
+        od.set_slot_value(man_state, "dead", True)
+        od.delete(attacking_link)
+        msgs.append(f"{od.get_name(animal_of(od, animal_state))} kills {od.get_name(animal_of(od, man_state))}.")
+
+    for _, bear_state in od.get_all_instances("BearState"):
+        if od.get_slot_value(bear_state, "dead"):
+            continue # bear already dead
+        old_hunger = od.get_slot_value(bear_state, "hunger")
+        new_hunger = min(old_hunger + 10, 100)
+        od.set_slot_value(bear_state, "hunger", new_hunger)
+        bear = od.get_target(od.get_outgoing(bear_state, "of")[0])
+        bear_name = od.get_name(bear)
+        if new_hunger == 100:
+            od.set_slot_value(bear_state, "dead", True)
+            msgs.append(f"Bear {bear_name} dies of hunger.")
+        else:
+            msgs.append(f"Bear {bear_name}'s hunger level is now {new_hunger}.")
+    return msgs
+
+# Action: Animal attacks Man
+# Note: We must use the names of the objects as parameters, because when cloning, the IDs of objects change!
+def action_attack(od, animal_name: str, man_name: str):
+    msgs = []
+    animal = od.get(animal_name)
+    man = od.get(man_name)
+    animal_state = state_of(od, animal)
+    man_state = state_of(od, man)
+    attack_link = od.create_link(None, # auto-generate link name
+        "attacking", animal_state, man_state)
+    _, clock = od.get_all_instances("Clock")[0]
+    current_time = od.get_slot_value(clock, "time")
+    od.set_slot_value(attack_link, "starttime", current_time)
+    msgs.append(f"{animal_name} is now attacking {man_name}")
+    return msgs
+
+# Get all actions that can be performed (including those that bring us to a non-conforming state)
+def get_all_actions(od):
+    def _generate_actions(od):
+        # can always advance time:
+        yield ("advance time", action_advance_time)
+
+        # if A is afraid of B, then B can attack A:
+        for _, afraid_link in od.get_all_instances("afraidOf"):
+            man = od.get_source(afraid_link)
+            animal = od.get_target(afraid_link)
+            animal_name = od.get_name(animal)
+            man_name = od.get_name(man)
+            man_state = state_of(od, man)
+            animal_state = state_of(od, animal)
+            descr = f"{animal_name} ({od.get_type_name(animal)}) attacks {man_name} ({od.get_type_name(man)})"
+            yield (descr, functools.partial(action_attack, animal_name=animal_name, man_name=man_name))
+
+    return make_actions_pure(_generate_actions(od), od)
+
+# Only get those actions that bring us to a conforming state
+def get_valid_actions(od):
+    return filter_valid_actions(get_all_actions(od))