Tue Jan 29 13:35:55 CET 2013

Generalize loop

It's probably best to generalize the loop to a proper fold over a
higher order function, then rewrite the current 

The trick is really the binding of the accumulators and the typing,
which still needs to be specified properly.

Basically, the key insight is that the time and space loops are
different.  The time loop is "hardcoded" because the state that is
associated to output feedback operators is hidden, which enables them
to stay purely functional at the stream level: state is an
implementation detail.