On Mon, Jul 14, 2014 at 11:16 AM, Gabriel Gonzalez
I don't quite understand your question, but I'll try to give a fuller explanation of the problem I was trying to solve to see if it perhaps answers your question.
I think the suggestion was something like this: -- | The @s@ type is an abstract "heap id" just like in 'ST'. type STSTM s a -- | The second argument allows handling 'BlockedIndefinitelyOnSTM' etc. runSTSTM :: (forall s. STSTM s a) -> (STMError -> b) -> b The idea being that, if the problem with catching BlockedIndefinitelyOnSTM has to do with the fact that all STM variables have global scope and so even if we could catch the exception itself we'd still have problems with cleaning up the collateral damage[1], then that's why it doesn't make sense to allow BlockedIndefinitelyOnSTM to be caught. However, by using an abstract heap-id we can bundle all related STSTM variables together, and we know that once runSTSTM exits they can't be accessed from anywhere else— so even if there's an error, we can still clean up all the variables, threads, and other jetsam associated with this STSTM computation. [1] I don't know if this is actually the reason why why BlockedIndefinitelyOnSTM is uncatchable, rather it sounded like this is what Neil Davies was suggesting to be the reason. Also, I do seem to recall something like this actually being the case; though it's unclear whether the STSTM approach would actually be able to solve the problem. -- Live well, ~wren