John Cowan suggested that SRFI 226 should include a version of Common
Lisp's unwind-protect suitable for Scheme.

In [1], I replied after some discussion with the following proposal
for a definition of a Scheme unwind-protect:

(define-syntax unwind-protect
  (syntax-rules ()
    ((unwind-protect protected-form cleanup-form)
     (call-with-continuation-barrier
       (lambda ()
         (dynamic-wind
           (lambda () (values))
           (lambda () protected-form)
           (lambda () cleanup-form)))))))

As I think it is essential to get this famous form right when included
in a fundamental SRFI like SRFI 226, I would like to hear more
opinions on the above form.

(It should be noted, that Scheme procedures like
`call-with-input-file` are not based on unwind-protect semantics.)

Should there be no consensus on unwind-protect, it is probably better
to reserve an extra SRFI for it (which, in turn, can depend on SRFI
226).

Thanks for taking a look,

Marc

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[1] https://srfi-email.schemers.org/srfi-226/msg/20888154/