goof-loop/example.scm

(import (goof))
(define (erathostenes n)
  (define vec (make-vector n #t))
  (loop ((:for i (up-from 2 (:to n)))
	 (:when (vector-ref vec i))
	 (:acc lst (listing i))
	 (:for j (up-from (* 3 i) (:to n) (:by (* i 2)))))
    => lst
    (vector-set! vec j #f)))

(define (erathostenes2 n)
  (define vec (make-vector n #t))
  (loop/list ((:for i (up-from 2 (:to n)))
              (:when (vector-ref vec i)))
    ;; Here we set all multiples of i to #f
    (loop ((:for j (up-from (* 3 i) (:to n) (:by (* i 2)))))
      (vector-set! vec j #f))
    i))