(define (backend-nullwrap be)
   (make-storage
      (storage-max-block-size be)
      (storage-writable? be)
      (storage-unlinkable? be)
      (lambda (key data type) ; put!
         ((storage-put! be) key data type))
      (lambda () ; flush!
        ((storage-flush! be)))
      (lambda (key) ; exists?
         ((storage-exists? be) key))
      (lambda (key) ; get
         ((storage-get be) key))
      (lambda (key) ; link!
         ((storage-link! be) key))
      (lambda (key) ; unlink!
         ((storage-unlink! be) key))
      (lambda (tag key) ; set-tag!
         ((storage-set-tag! be) tag key))
      (lambda (tag) ; tag
         ((storage-tag be) tag))
      (lambda () ; all-tags
         ((storage-all-tags be)))
      (lambda (tag) ; remove-tag!
         ((storage-remove-tag! be) tag))
      (lambda (tag) ; lock-tag!
         ((storage-lock-tag! be) tag))
      (lambda (tag) ; tag-locked?
         ((storage-tag-locked? be) tag))
      (lambda (tag) ; unlock-tag!
         ((storage-unlock-tag! be) tag))
      (lambda (command) ; admin!
         ((storage-admin! be) command))
      (lambda () ; close!
         ((storage-close! be)))))

(define (backend-limit-block-size be max-block-size)
   (make-storage
      (min max-block-size (storage-max-block-size be))
      (storage-writable? be)
      (storage-unlinkable? be)
      (lambda (key data type) ; put!
         ((storage-put! be) key data type))
      (lambda () ; flush!
        ((storage-flush! be)))
      (lambda (key) ; exists?
         ((storage-exists? be) key))
      (lambda (key) ; get
         ((storage-get be) key))
      (lambda (key) ; link!
         ((storage-link! be) key))
      (lambda (key) ; unlink!
         ((storage-unlink! be) key))
      (lambda (tag key) ; set-tag!
         ((storage-set-tag! be) tag key))
      (lambda (tag) ; tag
         ((storage-tag be) tag))
      (lambda () ; all-tags
         ((storage-all-tags be)))
      (lambda (tag) ; remove-tag!
         ((storage-remove-tag! be) tag))
      (lambda (tag) ; lock-tag!
         ((storage-lock-tag! be) tag))
      (lambda (tag) ; tag-locked?
         ((storage-tag-locked? be) tag))
      (lambda (tag) ; unlock-tag!
         ((storage-unlock-tag! be) tag))
      (lambda (command) ; admin!
         ((storage-admin! be) command))
      (lambda () ; close!
         ((storage-close! be)))))

(define (backend-debug be name)
   (make-storage
      (storage-max-block-size be)
      (storage-writable? be)
      (storage-unlinkable? be)
      (lambda (key data type) ; put!
         (begin
            (printf "~A: (put! ~A ~A ~A)\n" name key data type)
            ((storage-put! be) key data type)))

      (lambda () ; flush!
        (begin
          (printf "~A: (flush!)\n" name)
          ((storage-flush! be))))

      (lambda (key) ; exists?
         (let ((result ((storage-exists? be) key)))
            (begin
               (printf "~A: (exists? ~A) = ~A\n" name key result)
               result)))
      (lambda (key) ; get
         (let ((result ((storage-get be) key)))
            (begin
               (printf "~A: (get ~A) = ~A\n" name key result)
               result)))
      (lambda (key) ; link!
         (begin
            (printf "~A: (link! ~A)\n" name key)
            ((storage-link! be) key)))
      (lambda (key) ; unlink!
         (let ((result ((storage-unlink! be) key)))
            (begin
               (printf "~A: (unlink! ~A) = ~A\n" name key result)
               result)))
      (lambda (tag key) ; set-tag!
         (begin
            (printf "~A: (set-tag! ~A ~A)\n" name tag key)
            ((storage-set-tag! be) tag key)))
      (lambda (tag) ; tag
         (let ((result ((storage-tag be) tag)))
            (begin
               (printf "~A: (tag ~A) = ~A\n" name tag result)
               result)))
      (lambda () ; all-tags
         (let ((result ((storage-all-tags be))))
            (begin
               (printf "~A: (all-tags) = ~A\n" name result)
               result)))
      (lambda (tag) ; remove-tag!
         (begin
            (printf "~A: (remove-tag! ~A)\n" name tag)
            ((storage-remove-tag! be) tag)))
      (lambda (tag) ; lock-tag!
        (let ((result ((storage-lock-tag! be) tag)))
          (begin
            (printf "~A: (lock-tag! ~A) = ~A\n" name tag result)
            result)))
      (lambda (tag) ; tag-locked?
         (let ((result ((storage-tag-locked? be) tag)))
            (begin
               (printf "~A: (tag-locked? ~A) = ~A\n" name tag result)
               result)))
      (lambda (tag) ; unlock-tag!
         (begin
            (printf "~A: (lock-tag! ~A)\n" name tag)
            ((storage-unlock-tag! be) tag)))
      (lambda (command) ; admin!
         (let ((result ((storage-admin! be) command)))
            (begin
               (printf "~A: (admin! ~A) = ~A\n" name command result)
               result)))
      (lambda () ; close!
         (begin
            (printf "~A: (close!)\n" name)
            ((storage-close! be))))))