samer@42: % unfolder - arrow to generate sequence by unfolding state
samer@0: %
samer@0: % unfolder ::
samer@0: %    (S -> B, S)  ~'function to state to output and next state',
samer@0: %    S            ~'initial state'
samer@0: % -> arrow({},{B},S) ~'arrow from A to B with state of type S'.
samer@0: 
samer@0: function o=unfolder(fn,s0)
samer@0: 	s.fn=fn; s.s0=s0;
samer@0: 	o=class(s,'unfolder',arrow(0,1));
samer@0: end
samer@0: