Macro phasing

phasing.scm

(import (except (rnrs) cons)
        (for (only (rnrs) cons syntax-case lambda
                   display newline syntax) expand (meta 2)))

(define-syntax foo
  (lambda (x)
    (define-syntax expand-phase
      (lambda (x)
        (display (cons 1 2)) (newline)
        #'#t))
    (expand-phase)
    #'#t))

(foo) 
;; prints (1 . 2)

(display (cons 'a 'b)) (newline)
;; should be an error

#|
error:
  Racket (plt-r6rs)
  NMosh  (Andre van Tonder expander)
  Larceny (ditto)

ok:
  Chez
  Mosh (psyntax)
  Ypsilon
  Sagittarius
|#