wheel-utils/example.scm

(use-modules (srfi srfi-1)
	     (wheel-utils wheel))
;;; Example: fizzbuzz.
;; First we generate out sub-proto-wheels.
(define fizz (every-n-in "fizz" 3))
(define buzz (every-n-in "buzz" 5))

;; Then we merge our proto-wheels
(define proto-wheel (generate-wheel
		     (lambda x
		       (let ((l (filter values x)))
			 (if (null? l)
			     #f
			     (apply string-append l))))
		     fizz
		     buzz))

;; Then we make our wheel circular so that we don't have to check any null.
(define actual-wheel (apply circular-list proto-wheel))

(define (wheel-fizzbuzz n)
  (let loop ((i 1) (wheel actual-wheel))
    (if (> i n)
	'()
	(cons (or (car wheel) i) (loop (+ i 1) (cdr wheel))))))

(define (regular-fizzbuzz n)
  (let loop ((i 1))
    (cond
     ((> i n) '())
     ((eq? 0 (euclidean-remainder i 15))
      (cons "fizzbuzz" (loop (+ i 1))))
     ((eq? 0 (euclidean-remainder i 3))
      (cons "fizz" (loop (+ i 1))))
     ((eq? 0 (euclidean-remainder i 5))
      (cons "buzz" (loop (+ i 1))))
     (else
      (cons i (loop (+ i 1)))))))


;;; Example: prime wheel
;; Here we create a skip wheel that we can use to skip multiples of 2 3 5 and 7.
;; It can be used when implementing, say, the sieve of erathostenes to skip numbers
;; that are already known to be divisors of primes. Removing the first 4 prime-multiples
;; drastically reduces the work that the program needs to do. The first false-positive
;; given by the prime wheel is 11² (121), making this an extremely efficient way to
;; reduce work when trying to find primes.
(define prime-wheel
  (apply circular-list
         (skip-wheel
          (every-n-in 2)
          (every-n-in 3)
          (every-n-in 5)
          (every-n-in 7))))

(display prime-wheel)

(cons* 2 3 5 7 (let loop ((n 11) (wheel (drop prime-wheel 1)))
                 (if (> n 200)
                     '()
                     (cons n (loop (+ n (car wheel)) (cdr wheel))))))