Truncation and Other Simple Transducers Transducers compute series from series and form the heart of most series expressions.
Mapping is by far the most common transducer.
This section presents a number of additional simple transducers. Let k be the length of the shortest input Si . Let be the position of the first element in the boolean series bools that is not nil or, if every element is nil , the length of bools . The series returned by previous is the same as the input series items except that it is shifted to the right by the positive integer amount . The shifting is done by inserting amount copies of default before items and discarding amount elements from the end of items .