Clarified comments in minipyro.py to fix #3003 (#3004)

pyro/contrib/minipyro.py

@@ -45,7 +45,7 @@ def __init__(self, fn=None):
         self.fn = fn
 
     # Effect handlers push themselves onto the PYRO_STACK.
-    # Handlers earlier in the PYRO_STACK are applied first.
+    # Handlers later in the PYRO_STACK are applied first.
     def __enter__(self):
         PYRO_STACK.append(self)
 
@@ -162,17 +162,19 @@ def __iter__(self):
 # apply_stack is called by pyro.sample and pyro.param.
 # It is responsible for applying each Messenger to each effectful operation.
 def apply_stack(msg):
+    # PYRO_STACK is reversed so that effect handlers higher
+    # in the stack are first applied.
     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.
+        # it prevents any Messengers below it on the stack from being applied.
         if msg.get("stop"):
             break
     if msg["value"] is None:
         msg["value"] = msg["fn"](*msg["args"])
 
     # A Messenger that sets msg["stop"] == True also prevents application
-    # of postprocess_message by Messengers above it on the stack
+    # of postprocess_message by Messengers below it on the stack
     # via the pointer variable from the process_message loop
     for handler in PYRO_STACK[-pointer - 1 :]:
         handler.postprocess_message(msg)