[plt-scheme] puzzled about multiple value return

hi there,

I have a little helper function that does something like this:

(define (helper thunk)
  (setup)
  (let ((result (thunk))
     (teardown)
      result))

Meaning my helper wraps a call to a thunk with some setup/teardown actions
and returns whatever thunk returned. If thunk raises an error however, I do
not want for teardown to be called.

Assuming I have no control over thunk, how do I make the helper cope with
possible multiple return values from thunk?

Here is my attempt:

(define (helper thunk)
  (let ((success #t))
    (dynamic-wind
        (lambda () (printf "Setup~n"))
        (lambda ()
          (with-handlers (((lambda ex #t)
                           (lambda (exn)
                             (set! success #f)
                             (raise exn))))
            (thunk)))
        (lambda()
          (if success
              (printf "Teardown~n"))))))

> (helper (lambda () (values 1 2 3)))
Setup
Teardown
1
2
3

> (helper (lambda () 1))a
Setup
Teardown
1

> (helper (lambda () (error "Abort") (values 1 2 3)))
Setup
> Abort

This seems to work, but its ugly. Is there a nicer solution?

-pp




-pp
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