Based on your question, why not just use dynamic-wind in combination
with with-handlers? Just keep in mind that the post-thunk could be
called multiple times if there is a continuation jump into value-thunk,
so you should also wrap the whole thing with
call-with-continuation-barrier if it’s important that the post-thunk
only be executed once.
Alexis
> On Jan 24, 2018, at 1:32 PM, Alexander McLin <alex.mc...@gmail.com>
> wrote:
>
> I have a with-handlers expression which handles several exceptions
> appropriately and raises user-error exceptions, I have some additional
> code I'd like to be executed after the exception have been handled,
> analogous to dyanmic-wind's post-thunk argument or like the finally
> clause of a conventional try{}catch{}finally{} structure found in
> other languages.
>
> Documentation has shown that with-handlers and its cousins don't seem
> to have anything like that so I thought I'd wrap my with-handlers
> expression in a call-with-exception-handler to intercept the raised
> user-error exceptions, do additional processing and returns the
> exception to continue its propagation. It's not working and the
> installed exception handler doesn't seem to be called at all.
>
> Here's simplified code.
>
> (call-with-exception-handler
> (lambda (e)
> ...do more work
> e)
> (with-handlers ([exn:a? (lambda (e) (raise-user-error "exception exn:a
> caught"))]
> [exn:b? (lambda (e) (raise-user-error "exception
> exn:b caught"))])
> ...code that may throw either exn:a or exn:b ))
>
> My expectation was that the lambda installed by the
> call-with-exception-handler would run after each user-error is raised.
> I do see the user-error exceptions' messages being printed in the
> terminal so they're being propagated all the way to the uncaught
> exception handler but no work is being done by my own lambda handler.
> What am I doing wrong? More to the point, is there a better way to do
> post with-handlers exception handling processing?
>
> My thinking is that I have a flawed understanding of the meaning of
> dynamic extent of with-handlers and call-with-exception-handler forms.
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