Allow SPA connection to utility nodes.

Closes #190.

This does not allow connections to the basal ganglia input node in this
style because this would require to allow SPA style connections to sliced
inputs which is currently not implemented.

CHANGES.rst

@@ -23,6 +23,13 @@ Release History
 0.6.0 (unreleased)
 ==================
 
+**Added**
+
+- Allow to connect to the utility node returned by `ifmax` with the SPA `>>`
+  operator.
+  (`#190 <https://github.com/nengo/nengo_spa/issues/190>`_,
+  `#194 <https://github.com/nengo/nengo_spa/pull/194>`_)
+
 **Changed**
 
 - Require the ``mapping`` argument for associative memories. In addition to

nengo_spa/actions.py

@@ -6,7 +6,8 @@
 from nengo.utils.compat import is_string
 
 from nengo_spa.ast import dynamic
-from nengo_spa.connectors import ModuleInput, RoutedConnection
+from nengo_spa.connectors import (
+    input_vocab_registry, ModuleInput, RoutedConnection)
 from nengo_spa.exceptions import SpaActionSelectionError, SpaTypeError
 from nengo_spa.types import TScalar
 
@@ -147,7 +148,8 @@ def __len__(self):
 
     def add_action(self, name, *actions):
         assert ActionSelection.active is self
-        utility = nengo.Node(size_in=1)
+        utility = input_vocab_registry.declare_connector(
+            nengo.Node(size_in=1), None)
         if name is not None:
             self._name2idx[name] = len(self._actions)
         self._utilities.append(utility)

nengo_spa/network.py

@@ -46,7 +46,8 @@ def ifmax(name, condition=None, *actions):
     -------
     NengoObject
         Nengo object that can be connected to, to provide additional input to
-        the utility value.
+        the utility value. It is possible (but not necessary) to use SPA style
+        connections of the form ``scalar >> utility`` to this object.
     """
     if not is_string(name):
         if condition is not None:

nengo_spa/tests/test_actions.py

@@ -330,6 +330,13 @@ def test_action_selection(Simulator, rng):
         sim.trange(), sim.data[p_pointer], vocab['E'], skip=2.3, duration=0.2)
 
 
+def test_spa_connections_to_utilities():
+    with spa.Network():
+        with ActionSelection():
+            utility = spa.ifmax(0.)
+        0.1 >> utility
+
+
 def test_does_not_allow_nesting_of_action_selection():
     with spa.Network():
         with ActionSelection():