samer@1: stateful generators:
samer@1: 	unfold    S -> (X,S)                 loop(0 -> 1)
samer@1: 	scan      (Y,X) -> X                 states(loop(1 -> 0))
samer@1: 	mapaccum  (Y,S) -> (X,S)             loop(1 -> 1)
samer@1: 	zipaccum  (Y1,...,S) -> (X,S)        loop(N -> 1)
samer@1: 	iterate   X -> X                     states(loop(0 -> 0))
samer@1: 
samer@1: 
samer@1: signal length?
samer@1: sndfile from shell pipe