[Haskell-cafe] StateT and ContT
danburton.email at gmail.com
Tue Jan 20 18:34:04 UTC 2015
> And those who do... do they really use it in a way that would manifest
> this breakage?
Never mind, this is obviously the case; I just had to refresh my mind on
what the difference was between the two implementations. (Continuation gets
called with original vs latest state.)
-- Dan Burton
On Tue, Jan 20, 2015 at 10:19 AM, Dan Burton <danburton.email at gmail.com>
> Do people actually *use* the MonadCont class? And those who do... do they
> really use it in a way that would manifest this breakage?
> basically every existing user of the instance is pretty much guaranteed to
>> have breakage.
> It seems the answer to these questions is "yes" and "yes." I'm curious to
> hear more.
> -- Dan Burton
> On Tue, Jan 20, 2015 at 10:02 AM, Ross Paterson <R.Paterson at city.ac.uk>
>> On Wed, Jan 21, 2015 at 12:09:13AM +1100, Ivan Lazar Miljenovic wrote:
>> > This is what I thought: I just wanted to make sure that I wasn't
>> > missing something (especially since there's no real documentation that
>> > I could find as to _how_ liftCallCC' fails to satisfy the laws of a
>> > monad transformer).
>> Any lifting of callCC should satisfy
>> lift (f k) = f' (lift . k) => lift (callCC f) = liftCallCC callCC
>> and liftCallCC' doesn't.
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>> Haskell-Cafe at haskell.org
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