diff --git a/bonobo/execution/contexts/graph.py b/bonobo/execution/contexts/graph.py
index b2362db..2828592 100644
--- a/bonobo/execution/contexts/graph.py
+++ b/bonobo/execution/contexts/graph.py
@@ -148,3 +148,11 @@ class GraphExecutionContext(BaseContext):
     def unregister_plugins(self):
         for plugin_context in self.plugins:
             plugin_context.unregister()
+
+
+    @property
+    def xstatus(self):
+        """
+        UNIX-like exit status, only coherent if the context has stopped.
+        """
+        return max(node.xstatus for node in self.nodes)
diff --git a/bonobo/execution/contexts/node.py b/bonobo/execution/contexts/node.py
index 13c1ff7..b5884a7 100644
--- a/bonobo/execution/contexts/node.py
+++ b/bonobo/execution/contexts/node.py
@@ -123,8 +123,6 @@ class NodeExecutionContext(BaseContext, WithStatistics):
                 self.step()
             except InactiveReadableError:
                 break
-            except Empty:
-                sleep(TICK_PERIOD)  # XXX: How do we determine this constant?
 
         logger.debug('Node loop ends for {!r}.'.format(self))
 
@@ -133,6 +131,8 @@ class NodeExecutionContext(BaseContext, WithStatistics):
             self._step()
         except InactiveReadableError:
             raise
+        except Empty:
+            sleep(TICK_PERIOD)  # XXX: How do we determine this constant?
         except (
                 NotImplementedError,
                 UnrecoverableError,
@@ -294,12 +294,18 @@ class NodeExecutionContext(BaseContext, WithStatistics):
         # Store or check input type
         if self._input_type is None:
             self._input_type = type(input_bag)
-        elif type(input_bag) is not self._input_type:
-            raise UnrecoverableTypeError(
-                'Input type changed between calls to {!r}.\nGot {!r} which is not of type {!r}.'.format(
-                    self.wrapped, input_bag, self._input_type
-                )
-            )
+        elif type(input_bag) != self._input_type:
+            try:
+                if self._input_type == tuple:
+                    input_bag = self._input_type(input_bag)
+                else:
+                    input_bag = self._input_type(*input_bag)
+            except Exception as exc:
+                raise UnrecoverableTypeError(
+                    'Input type changed to incompatible type between calls to {!r}.\nGot {!r} which is not of type {!r}.'.format(
+                        self.wrapped, input_bag, self._input_type
+                    )
+                ) from exc
 
         # Store or check input length, which is a soft fallback in case we're just using tuples
         if self._input_length is None:
diff --git a/bonobo/nodes/aggregation.py b/bonobo/nodes/aggregation.py
new file mode 100644
index 0000000..f09cc17
--- /dev/null
+++ b/bonobo/nodes/aggregation.py
@@ -0,0 +1,16 @@
+from bonobo.config import Configurable, Method, Option, ContextProcessor, use_raw_input
+from bonobo.util import ValueHolder
+
+
+class Reduce(Configurable):
+    function = Method()
+    initializer = Option(required=False)
+
+    @ContextProcessor
+    def buffer(self, context):
+        values = yield ValueHolder(self.initializer() if callable(self.initializer) else self.initializer)
+        context.send(values.get())
+
+    @use_raw_input
+    def __call__(self, values, bag):
+        values.set(self.function(values.get(), bag))