Exceptions vs. Errors (Re: Readline read_history and
simonmarhaskell at gmail.com
Fri Jan 25 04:10:37 EST 2008
Isaac Dupree wrote:
>>> It should really be:
>>> block x = do
>>> IO blockAsyncExceptions#
>>> ret <- x
>>> IO unblockAsyncExceptions#
>>> return ret
>>> in which case we could then supply implementations for
>>> other monads as well.
>> blockAsyncExceptions# has some tricks to restore tail-recursion in
>> some cases (see the paper). But apart from losing that optimisation,
>> I can't think of any reasons why the above couldn't work - one thing
>> you have to worry about is what happens when x raises an exeption, but
>> I think that is handled by the way we save and restore the blocked
>> state in catch.
> what about if the monad is a transformed one with its own error handling
> methods (e.g. ErrorT IO) and so (IO blockAsyncExceptions#) is run but
> (IO unblockAsyncExceptions#) is not? Is that a problem?
Yes, in that case you'd need an exception handler in the above code to
ensure that unblockAsyncExceptions# was called.
More information about the Libraries