; iteration syntax

(define-syntax while
  (syntax-rules ()
    ((_ test-exp e0 e1 ...)
     (letrec
         ((loop (lambda ()
                  (if test-exp (begin e0 e1 ... (loop))))))
          (loop)))))

; while example usage
(define a 1)
(define b 5)

(while (< a b) (set! a (+ a 1)))

;; int fact(int n)
;; {
;;    int m = 1
;;    while (n > 0 ) {
;;         m = m * n;
;;         n = n - 1;
;;     }
;;     return m;
;;  }

(define (fact n)
  (let ((m 1))
    (begin
      (while (> n 0) 
           (set! m (* m n)) 
           (set! n (- n 1)))
      m)))

(define-syntax for
  (syntax-rules ()
    ((_ init-exp test-exp step-exp e0 e1 ...)
     (begin
       init-exp
       (letrec
           ((loop (lambda ()
                    (if test-exp (begin e0 e1 ... step-exp (loop))))))
       (loop))))))

(define i 0)
(define n 10)
(define z 0)

(for (set! i 0) (< i n) (set! i (+ i 1)) (set! z (* i 2)))
i
z