chickadee » srfi-1 » span

Span splits the list into the longest initial prefix whose elements all satisfy PRED, and the remaining tail. Break inverts the sense of the predicate: the tail commences with the first element of the input list that satisfies the predicate.

In other words: span finds the intial span of elements satisfying PRED, and break breaks the list at the first element satisfying PRED.

Span is equivalent to

(values (take-while PRED CLIST) 
        (drop-while PRED CLIST))

Span! and break! are the linear-update variants. They are allowed, but not required, to alter the argument list to produce the result.

(span even? '(2 18 3 10 22 9)) =>
  (2 18)
  (3 10 22 9)
 
(break even? '(3 1 4 1 5 9)) =>
  (3 1)
  (4 1 5 9)