Continuations are a feature of languages that allow state to persist.
In functional programming, continuation-passing style (CPS) is a style of programming in which control is passed explicitly in the form of a continuation
example:
; Return a list of all books with at least THRESHOLD copies sold.
(define(best-selling-books threshold)
(filter
(lambda (book)
(>= (book-sales book) threshold))
book-list))