syntax-rules bug

[alvatar]

This macro (taken from srfi-67) isn't expanding properly:

(define-syntax if3
  (syntax-rules ()
                ((if3 c less equal greater)
                 (case c
                   ((-1) less)
                   (( 0) equal)
                   (( 1) greater)
                   (else (error "comparison value not in {-1,0,1}"))))))

(define test '(let ((x -1) (y 0)) 
                 (if3 (let ((x0 x)) (set! x (+ x 1)) x0)
                      (begin (set! y (+ y 1))   y)
                      (begin (set! y (+ y 10))  y)
                      (begin (set! y (+ y 100)) y))))

; In REPL:
(expand-macro test)
; =>
(let ((1#x -1) (2#y 0)) (set! 2#y (+ 2#y 1)) 2#y)

; This isn't correct, the expansion should include the case and its clauses.