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assumption-free-identifier-equal.rkt (973B)

      1 #lang racket
      2 (require rackunit)
      3 (define-for-syntax outer #f)
      4 (define-for-syntax inner #f)
      5 
      6 (check-equal? (let ([x 1])
      7                 (define-syntax (capture1 stx)
      8                   (set! outer #'x)
      9                   #'(void))
     10                 (capture1)
     11                 (let ([x 2])
     12                   (define-syntax (capture2 stx)
     13                     (set! inner #'x)
     14                     #'(void))
     15                   (capture2)
     16                   (let ([y 3])
     17                     (define-syntax (compare stx)
     18                       (define candidate (datum->syntax #'y 'x))
     19                       ;; check that (datum->syntax #'y 'x) matches the
     20                       ;; inner x, but not the outer x, since they are already
     21                       ;; bound when the macro is executed.
     22                       #`(list #,(free-identifier=? candidate inner)
     23                               #,(free-identifier=? candidate outer)))
     24                     (compare))))
     25               '(#t #f))