; Copyright (C) 2011 Toby Thain, toby@telegraphics.com.au

(define (primes-up-to n)
  (let
    ((sieve (make-vector (+ n 1) #t)))
    
    (define (test-prime i)
      (define (is-prime? idx)
        (vector-ref sieve idx))
      (define (not-prime! idx)
        (vector-set! sieve idx #f))
      (define (remove-multiples i step)
        (when (<= i n)
          (not-prime! i)
          (remove-multiples (+ i step) step)))
      (if (> i n)
          '()
          (if (is-prime? i)
              (begin
                (remove-multiples i i)
                (cons i (test-prime (+ i 1))))
              (test-prime (+ i 1)))))
    
    (test-prime 2)))