Sun Aug 2 22:07:01 EDT 2015

fold over sys

Currently fold can't refer to external state.  This is one of the
important properties of RAI: to create state for collections of

So, take a bunch of arrows, and sum their output.
So basically, this should work with fold.

Let's try first to add two signals.

The output of an Arrow forms an applicative.  But this only works for
pure operations.  What about monadic operations?  Basically that's the

So maybe work with signals instead of systems?
Would that work?

EDIT: Applicative is useful.  Just needs join!