[plt-scheme] handle-evt can wrap handle-evt

From: Robby Findler (robby at cs.uchicago.edu)
Date: Wed Feb 21 22:36:30 EST 2007

On 2/21/07, Dimitris Vyzovitis <vyzo at media.mit.edu> wrote:
> On Wed, 21 Feb 2007, Robby Findler wrote:
> > > The point is to disallow (handle-evt (handle-evt ...) ...)
> > > That's what Matthew meant (I think :) and I don't see any error to it.
> >
> > Matthew's "error" is only that he says that the above should be an
> > error in Scheme! :)
> >
> > I'm saying that it should not be an error. I think it is useful and
> > should not be disallowed.
> If it is allowed how is it different from (handle-evt (wrap-evt ...) ...)?

The break-handling state won't change (which is important sometimes;
generally you don't to disable breaks very often and when you do, you
should be careful about).

Also, you don't have to plan ahead to use wrap-evt if you think
someone else might want to use handle-evt.

> I think that the intent is 'handle-evt proc is a handler that is in tail
> context wrt sync'. This cannot be guaranteed when handle-evts can be nested.

Right. I believe this is a bogus claim. It should be weakened to only
apply when there is a single handle-evt.

(when Matthew and I first discussed this as it was being implemented I
didn't realize it was too strong. I'm glad you pointed this out.)


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