This is the TXR Lisp interactive listener of TXR 228.
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  1> (with-dyn-lib nil
      (deffi qsort "qsort" void ((ptr (array wstr)) size-t size-t closure))
      (deffi-cb qsort-cb int ((ptr wstr-d) (ptr wstr-d))))
  #:lib-0005
  2> (let ((vec #("the" "quick" "brown" "fox"
                  "jumped" "over" "the" "lazy" "dogs")))
       (prinl vec)
       (qsort vec (length vec) (sizeof wstr)
              [qsort-cb (lambda (a b) (cmp-str a b))])
       (prinl vec))
  #("the" "quick" "brown" "fox" "jumped" "over" "the" "lazy" "dogs")
  #("brown" "dogs" "fox" "jumped" "lazy" "over" "quick" "the" "the")
  #("brown" "dogs" "fox" "jumped" "lazy" "over" "quick" "the" "the")

The lambda is pointless; we could create the FFI closure directly from cmp-str with [qsort-cb cmp-str]. It shows more clearly that we can use any closure.