Minils.CtrlNbacGen relies on such type annotations to generat
Controllable-Nbac nodes.  This fix allows the use of ReaX to enforce
contracts of nodes involving merge operations on tuples over multiple
data types, such as:

  (a, b) = merge c
           (true -> ((true when c), (0 when c)))
           (false -> ((false whenot c), (2 whenot c)));

This kind of code previously led to erroneous Controllable-Nbac code.