Bracket instances for transformers

[durban]

For the various transformers (Kleisli, OptionT, ...) there are Sync instances (if the inner F has a Sync instance). There are also similar MonadError instances for them. However, there doesn't seem to be similar Bracket instances. Is it not possible to define them, or are they simply missing?

[alexandru]

I think the reason there are no instances is because defining instances for these monad transformers is in general complicated. I've lost many hours solving problems for the available instances.

Also it might be challenging because you can't rely on the stack safety of Sync when all you have is Bracket. Not sure if that's important or not.

But try it out. Maybe we can.

[djspiewak]

I would say that this is best tried and experimented with! PRs very much welcome.