The type of a row

The type of the array

collect_results f acc init a returns f (... (f (f (f acc s1) s2) s3)... ) sN where s1 ... aN are the states when reaching the end of the paths from top to bottom of a such that for all s resulting from the path c1 ; ... ; cK (all paths have this shape) s = E.update (... E.update (E.update (E.update init c1) c2) ...) cK and none of this E.update calls returned a None value (hence the notation abuse of applying E.update to a state instead of a state option in this description).