Proposal: Extensible exceptions

[Yitzchak Gale]

Hi Bulat,

I wrote:
>> ...The primitive is block, not bracket.
>> More specifically, blockAsyncExceptions# and unblockAsyncExceptions#.
>> Those are used to implement block, which is used to
>> implement bracket, catch, etc.

Bulat Ziganshin wrote:
> actually it's a catch# used to implement catch used for everything
> else.

Yes, there is also that primitive that is only for IO.
I don't remember this moment whether it might be
possible to work around this one.

> primitives you are mentioned only enable/disable delivering of
> async exceptions

Yes, and they are critical for catch to avoid deadlock.
For this, I didn't find any workaround for the current primitives.

If instead we had

startBlocking :: IO ()
stopBlocking :: IO ()

then we could implement block for other monads. At the time,
Simon Marlow wrote that this could be done, but that we
would lose out on a certain optimization.

Regards,
Yitz