diff --git a/Makefile b/Makefile
index 7686b3dda..2d6bab619 100644
--- a/Makefile
+++ b/Makefile
@@ -11,6 +11,7 @@ format: FORCE
 
 test: lint FORCE
 	pytest -v test
+	FUNSOR_DEBUG=1 pytest -v test/test_gaussian.py
 	python examples/discrete_hmm.py -n 2
 	python examples/discrete_hmm.py -n 2 -t 50 --lazy
 	python examples/kalman_filter.py --xfail-if-not-implemented
diff --git a/funsor/contract.py b/funsor/contract.py
index e7d374d0e..ef002e875 100644
--- a/funsor/contract.py
+++ b/funsor/contract.py
@@ -3,6 +3,7 @@
 import functools
 from collections import OrderedDict
 
+import funsor.interpreter as interpreter
 import funsor.ops as ops
 from funsor.optimizer import Finitary, optimize
 from funsor.sum_product import _partition
@@ -51,6 +52,7 @@ def contractor(fn):
     """
     Decorator for contract implementations to simplify inputs.
     """
+    fn = interpreter.debug_logged(fn)
     return functools.partial(_simplify_contract, fn)
 
 
diff --git a/funsor/integrate.py b/funsor/integrate.py
index 7799b1aac..fc691f708 100644
--- a/funsor/integrate.py
+++ b/funsor/integrate.py
@@ -3,6 +3,7 @@
 import functools
 from collections import OrderedDict
 
+import funsor.interpreter as interpreter
 import funsor.ops as ops
 from funsor.contract import Contract
 from funsor.terms import Funsor, Reduce, eager
@@ -58,6 +59,7 @@ def integrator(fn):
     """
     Decorator for integration implementations.
     """
+    fn = interpreter.debug_logged(fn)
     return functools.partial(_simplify_integrate, fn)
 
 
diff --git a/funsor/interpreter.py b/funsor/interpreter.py
index bab0205ba..2cdba6834 100644
--- a/funsor/interpreter.py
+++ b/funsor/interpreter.py
@@ -1,5 +1,7 @@
 from __future__ import absolute_import, division, print_function
 
+import functools
+import inspect
 import os
 import re
 import types
@@ -13,6 +15,7 @@
 from funsor.registry import KeyedRegistry
 from funsor.six import singledispatch
 
+_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 _DEBUG = int(os.environ.get("FUNSOR_DEBUG", 0))
 _STACK_SIZE = 0
 
@@ -117,12 +120,38 @@ def _reinterpret_ordereddict(x):
     return OrderedDict((key, reinterpret(value)) for key, value in x.items())
 
 
+if _DEBUG:
+    class DebugLogged(object):
+        def __init__(self, fn):
+            self.fn = fn
+            while isinstance(fn, functools.partial):
+                fn = fn.func
+            path = inspect.getabsfile(fn)
+            lineno = inspect.getsourcelines(fn)[1]
+            self._message = "{} file://{} {}".format(fn.__name__, path, lineno)
+
+        def __call__(self, *args, **kwargs):
+            print('  ' * _STACK_SIZE + self._message)
+            return self.fn(*args, **kwargs)
+
+    def debug_logged(fn):
+        if isinstance(fn, DebugLogged):
+            return fn
+        return DebugLogged(fn)
+else:
+    def debug_logged(fn):
+        return fn
+
+
 def dispatched_interpretation(fn):
     """
     Decorator to create a dispatched interpretation function.
     """
     registry = KeyedRegistry(default=lambda *args: None)
-    fn.register = registry.register
+    if _DEBUG:
+        fn.register = lambda *args: lambda fn: registry.register(*args)(debug_logged(fn))
+    else:
+        fn.register = registry.register
     fn.dispatch = registry.__call__
     return fn
 
diff --git a/funsor/joint.py b/funsor/joint.py
index 6ff1865da..72b93713e 100644
--- a/funsor/joint.py
+++ b/funsor/joint.py
@@ -6,6 +6,7 @@
 from six import add_metaclass
 from six.moves import reduce
 
+import funsor.interpreter as interpreter
 import funsor.ops as ops
 from funsor.delta import Delta
 from funsor.domains import reals
@@ -293,6 +294,7 @@ def _joint_integrator(fn):
     """
     Decorator for Integrate(Joint(...), ...) patterns.
     """
+    fn = interpreter.debug_logged(fn)
     return integrator(functools.partial(_simplify_integrate, fn))
 
 
diff --git a/funsor/registry.py b/funsor/registry.py
index 67b5bb7b4..086b1c35d 100644
--- a/funsor/registry.py
+++ b/funsor/registry.py
@@ -1,4 +1,3 @@
-
 from __future__ import absolute_import, division, print_function
 
 from collections import defaultdict
diff --git a/funsor/terms.py b/funsor/terms.py
index 94938202e..f182f7ff4 100644
--- a/funsor/terms.py
+++ b/funsor/terms.py
@@ -258,7 +258,7 @@ def sample(self, sampled_vars, sample_inputs=None):
         if sampled_vars.isdisjoint(self.inputs):
             return self
 
-        result = self.unscaled_sample(sampled_vars, sample_inputs)
+        result = interpreter.debug_logged(self.unscaled_sample)(sampled_vars, sample_inputs)
         if sample_inputs is not None:
             log_scale = 0
             for var, domain in sample_inputs.items():
@@ -614,7 +614,7 @@ def eager_subs(arg, subs):
     assert isinstance(subs, tuple)
     if not any(k in arg.inputs for k, v in subs):
         return arg
-    return arg.eager_subs(subs)
+    return interpreter.debug_logged(arg.eager_subs)(subs)
 
 
 _PREFIX = {
@@ -647,14 +647,14 @@ def eager_subs(self, subs):
 
 @eager.register(Unary, Op, Funsor)
 def eager_unary(op, arg):
-    return arg.eager_unary(op)
+    return interpreter.debug_logged(arg.eager_unary)(op)
 
 
 @eager.register(Unary, AssociativeOp, Funsor)
 def eager_unary(op, arg):
     if not arg.output.shape:
         return arg
-    return arg.eager_unary(op)
+    return interpreter.debug_logged(arg.eager_unary)(op)
 
 
 _INFIX = {
@@ -730,12 +730,12 @@ def eager_reduce(self, op, reduced_vars):
 
 @eager.register(Reduce, AssociativeOp, Funsor, frozenset)
 def eager_reduce(op, arg, reduced_vars):
-    return arg.eager_reduce(op, reduced_vars)
+    return interpreter.debug_logged(arg.eager_reduce)(op, reduced_vars)
 
 
 @sequential.register(Reduce, AssociativeOp, Funsor, frozenset)
 def sequential_reduce(op, arg, reduced_vars):
-    return arg.sequential_reduce(op, reduced_vars)
+    return interpreter.debug_logged(arg.sequential_reduce)(op, reduced_vars)
 
 
 class NumberMeta(FunsorMeta):