Sun Jan 27 19:47:41 CET 2013

Loops in DSP: `feedback' is contextual

* To make things more explicit it should be understood that the
  `feedback' form refers to some kind of "context".  It is nothing
  more than a preprocessing trick to create fold-style loops where
  state feedback dominates.

* Stream processors are an "infinite loop", so the above isn't
  immediately visible (no end, but there is an init that for now has
  been glossed over.  But it makes a lot of sense to have the same
  kind of state feedback mechanism on a local level, i.e. for block
  processing or iterative numerical algorithms.

* The big idea is that the siso system is the unifying structure for
  numerical algorithms that operate on streams of data -- i.e. not the
  'fold', not the 'map'.

In short:

- Syntactical need: Some DSP algorithms can get heavy on local loop
  state.  Removing the need to explicitly name this state helps a lot
  to focus on inter-module dataflow.

- Representation need: Functional representation is good for analysis
  (as opposed to destructive state updates)