; Returns a generator of streams of random normal deviates.
; http://cap-lore.com/code/Scheme/grnd.txt
(let ((v (fileVal "RC4"))(sc (/ 1. (expt 2 55))))
(lambda (S) (let* ((f #f)(v (ex 'nv (v 'nb S)))(m 0)(gf (lambda () (- (* (v 7) sc) 1))))
  (write (list 'Boo sc))(newline)
    (lambda () (if f (begin (set! f #f) m)
      (let xx () (let* ((x (gf))(y (ex 'gfr (gf)))(s (ex 'd2 (+ (* x x)(* y y)))))
      (if (> s 1.) (xx) (let ((r (sqrt (/ (* -2 (log s)) s))))(set! m (* x r))
            (set! f #t) (* y r))))))))))
 
; tests
(define g1 ((fileVal "RND") "foos"))
(let r ((n 10000)) (if (zero? n) 0 (+ (g1) (r (- n 1))))) ; => -142.48347
(let r ((n 10000)) (if (zero? n) 0 (let ((w (g1))) (+ (* w w) (r (- n 1))))))
; => 9651.553873202625
(let r ((n 10000)) (if (zero? n) 0 (+ (* (g1) (g1)) (r (- n 1)))))
(let r ((n 10000) (s 0)) (if (= n 0) s (r (- n 1) (+ s (g1)))))