chickadee » srfi-158 » make-unfold-generator

A generator constructor similar to SRFI 1's unfold.

The stop? predicate takes a seed value and determines whether to stop. The mapper procedure calculates a value to be returned by the generator from a seed value. The successor procedure calculates the next seed value from the current seed value.

For each call of the resulting generator, stop? is called with the current seed value. If it returns true, then the generator returns an end-of-file object. Otherwise, it applies mapper to the current seed value to get the value to return, and uses successor to update the seed value. This generator is finite unless stop? never returns true.

(generator->list (make-unfold-generator
                      (lambda (s) (> s 5))
                      (lambda (s) (* s 2))
                      (lambda (s) (+ s 1))
                      0))
  ⇒ (0 2 4 6 8 10)