(option '("x-accel-redirect") #f #t
(lambda (opt name arg result)
(alist-cons 'x-accel-redirect?
(cond
((member arg '(#f "yes" "true")) #t)
((member arg '("false" "no") #f))
(else
(simple-format
(current-error-port)
"~A: invalid --x-accel-redirect value\n" arg)
(exit 1)))
(alist-delete 'x-accel-redirect? result))))))