Converts a length-pattern to a rhythm-string representation used in timesheets and def-rhythm definitions. All length symbols in the length-pattern are assumed to be of equal size.
(length-to-string '(1/16 -1/16 1/16))
--> "- -"
(length-to-string '(1/4 -1/4 1/4))
--> "- -"
There's no checking if the lengths are of different sizes, and so: