(module version-case mzscheme 
  (require-for-syntax ""
                      (lib "" "syntax"))
  (provide version-case)
  ;; version-case: SYNTAX
  ;; Conditionally include code based on current version number.
  ;; Usage:
  ;; (version-case [clause code] ...
  ;;               [else ...])
  ;; where clause has access to the mzscheme primitives.  In addition,
  ;; the following function is available:
  ;;     version<=: string string -> boolean
  ;; to make it easier to build the conditional clauses.
  (define-syntax (version-case stx)
    (define (eval-condition condition-stx)
      ;; TODO: should we do this more safely or in a more
      ;; controlled fashion?
      (parameterize ([current-namespace (make-namespace)])
        (with-handlers ([exn:fail?
                         (lambda (exn)
                           (raise-syntax-error #f
                                               (format "exn raised during compilation: ~a"
                                                       (exn-message exn))
          (eval `(define version<= ,version<=))
          (eval condition-stx))))
    (syntax-case* stx (else) module-or-top-identifier=?
      [(_ [else code ...])
       (syntax/loc stx
         (begin code ...))]
      [(_ [condition code ...] other-clauses ...)
       (if (eval-condition (syntax condition))
           (syntax/loc stx
             (begin code ...))
           (syntax/loc stx
             (version-case other-clauses ...)))]
       (raise-syntax-error #f "no matching version condition" stx)])))