; UNWIND-PROTECT, as in Common Lisp, implemented in portable Scheme.
;
; Scheme programmers have been using this macro, and similar macros,
; for more than 20 years.

(define-syntax unwind-protect
  (syntax-rules ()
   ((unwind-protect body cleanup ...)
    (dynamic-wind (let ((ok? #t))
                    (lambda ()
                      (if ok? (set! ok? #f) (error))))
                  (lambda () body)
                  (lambda () cleanup ...)))))