Wed Apr 3 18:26:38 EDT 2013

Explicit time loop

Maybe it's time for an explicit time loop.  This would make all the
binding issues fairly simple, i.e. remove the magic.

The `main' function will then do one-time setup + lift anything over
the time loop.

- Make state-feedback explicit: let-feedback : the stub for feedback/n
- fold-time

Combine both?  Essentially, unify feedback (fold) and state variable

Generalizing fold seems to be the most important part.  The problem
here is to initialize the feedback nodes.  How to find out the arity
of a fold?  The syntax of "accumulate" can already do this, since the
number of expressions in the `values' statement is known.