(define-syntax my-if
  (syntax-rules (then else)
    [(_ e1 then e2 else e3) (if e1 e2 e3)]
    [(_ e1 then e2) (if e1 e2)]))
(my-if 3 then 4 else 5)
(my-if #f then 4 else 5)

(define-syntax ++
  (syntax-rules ()
    [(_ x) (begin (set! x (add1 x)) x)]))

(define a 5)
(++ a)
a
(define b (+ 3 (++ a)))
a
b

(define-syntax ++post
  (syntax-rules ()
    [(_ x) (let ([orig x])
	     (++ x)
	     orig)]))

(set! b (+ 7 (++post a)))
a
b

(define-syntax my-and
  (syntax-rules ()
    [(_) #t]
    [(_ e) e]
    [(_ e1 e2 ...)
     (if e1
	 (my-and e2 ...)
	 #f)]))

(my-and)
(my-and 3)
(my-and 3 (< 2 1) 7)
(my-and 3 4 5 6)

(define-syntax for
  (syntax-rules (:)
    [(_ ((init ...) : test : update ...)
	body ...)
     (begin
       init ...
       (let for-loop ()
	 (if test
	     (begin
	       body ...
	       update ...
	       (for-loop)))))]))

(for (((define i 0)(define j 1)) :
      (< i 12) :
      (++ i) (set! j (* 2 j)))
     (display i)
     (display "   ")
     (display j)
     (newline))