Make replay consistent with Pyro (#1345)

* make replay consistent with numpyro

* Add docs for apply_stack to clarify its functionality

numpyro/distributions/distribution.py

@@ -762,8 +762,8 @@ def has_enumerate_support(self):
         return self.base_dist.has_enumerate_support
 
     @property
-    def reparameterized_params(self):
-        return self.base_dist.reparameterized_params
+    def reparametrized_params(self):
+        return self.base_dist.reparametrized_params
 
     @property
     def mean(self):

numpyro/handlers.py

@@ -202,14 +202,27 @@ class replay(Messenger):
        >>> assert replayed_trace['a']['value'] == exec_trace['a']['value']
     """
 
-    def __init__(self, fn=None, trace=None, guide_trace=None):
+    def __init__(self, fn=None, trace=None):
         assert trace is not None
         self.trace = trace
         super(replay, self).__init__(fn)
 
     def process_message(self, msg):
         if msg["type"] in ("sample", "plate") and msg["name"] in self.trace:
-            msg["value"] = self.trace[msg["name"]]["value"]
+            name = msg["name"]
+            if msg["type"] in ("sample", "plate") and name in self.trace:
+                guide_msg = self.trace[name]
+                if msg["type"] == "plate":
+                    if guide_msg["type"] != "plate":
+                        raise RuntimeError(f"Site {name} must be a plate in trace.")
+                    msg["value"] = guide_msg["value"]
+                    return None
+                if msg["is_observed"]:
+                    return None
+                if guide_msg["type"] != "sample" or guide_msg["is_observed"]:
+                    raise RuntimeError(f"Site {name} must be sampled in trace.")
+                msg["value"] = guide_msg["value"]
+                msg["infer"] = guide_msg["infer"]
 
 
 class block(Messenger):

numpyro/primitives.py

@@ -18,21 +18,39 @@
 CondIndepStackFrame = namedtuple("CondIndepStackFrame", ["name", "dim", "size"])
 
 
+def default_process_message(msg):
+    if msg["value"] is None:
+        if msg["type"] == "sample":
+            msg["value"], msg["intermediates"] = msg["fn"](
+                *msg["args"], sample_intermediates=True, **msg["kwargs"]
+            )
+        else:
+            msg["value"] = msg["fn"](*msg["args"], **msg["kwargs"])
+
+
 def apply_stack(msg):
+    """
+    Execute the effect stack at a single site according to the following scheme:
+
+        1. For each ``Messenger`` in the stack from bottom to top,
+           execute ``Messenger.process_message`` with the message;
+           if the message field "stop" is True, stop;
+           otherwise, continue
+        2. Apply default behavior (``default_process_message``) to finish remaining
+           site execution
+        3. For each ``Messenger`` in the stack from top to bottom,
+           execute ``Messenger.postprocess_message`` to update the message
+           and internal messenger state with the site results
+    """
     pointer = 0
     for pointer, handler in enumerate(reversed(_PYRO_STACK)):
         handler.process_message(msg)
         # When a Messenger sets the "stop" field of a message,
         # it prevents any Messengers above it on the stack from being applied.
         if msg.get("stop"):
             break
-    if msg["value"] is None:
-        if msg["type"] == "sample":
-            msg["value"], msg["intermediates"] = msg["fn"](
-                *msg["args"], sample_intermediates=True, **msg["kwargs"]
-            )
-        else:
-            msg["value"] = msg["fn"](*msg["args"], **msg["kwargs"])
+
+    default_process_message(msg)
 
     # A Messenger that sets msg["stop"] == True also prevents application
     # of postprocess_message by Messengers above it on the stack

test/test_distributions.py

@@ -894,23 +894,23 @@ def test_sample_gradient(jax_dist, sp_dist, params):
     params_dict = dict(zip(dist_args[: len(params)], params))
 
     jax_class = type(jax_dist(**params_dict))
-    reparameterized_params = [
+    reparametrized_params = [
         p for p in jax_class.reparametrized_params if p not in gamma_derived_params
     ]
-    if not reparameterized_params:
+    if not reparametrized_params:
         pytest.skip("{} not reparametrized.".format(jax_class.__name__))
 
     nonrepara_params_dict = {
-        k: v for k, v in params_dict.items() if k not in reparameterized_params
+        k: v for k, v in params_dict.items() if k not in reparametrized_params
     }
     repara_params = tuple(
-        v for k, v in params_dict.items() if k in reparameterized_params
+        v for k, v in params_dict.items() if k in reparametrized_params
     )
 
     rng_key = random.PRNGKey(0)
 
     def fn(args):
-        args_dict = dict(zip(reparameterized_params, args))
+        args_dict = dict(zip(reparametrized_params, args))
         return jnp.sum(
             jax_dist(**args_dict, **nonrepara_params_dict).sample(key=rng_key)
         )