On the delay-recommendation in Hang / Stack Overflow -section

[gspia]

Is there any chances to extend the example so that it would also show, how to apply the delay, at hang-stack-overflow-section?

The delay eats NominalDiffTime and it is not outright obvious, what value it should be given.

I had a this kind of situation, where ev2 <- delay 0 ev1 worked and was required. The runtime errors at ghci referred to "bag -problems in Spider/Internal" and once to "ghc loop" when I was doing changes / trying to find a working combination.

So,

• If there are typical symptons that can be seen, say in ghci, maybe mention those?
• Is it possible to describe, why the given example needs delay? I mean, why the rec-block isn't enough as such as shown at the moment?
• What parameter to give to delay? Is 0 ok?

BTW: it seems that those delays area needed every now and then. If 0 is ok and enough in this kind of situations, is there room for frameDelay = delay 0 in the reflex-lib? (With the idea that it wouldn't confuse the user? The proposed name here probably isn't good.)

[ElvishJerricco]

I have never encountered a scenario where delay 0 was needed to solve a cycle. It's an easy trap to fall in but I think it's bad practice. If delaying solves your problem, it means there's a cycle that simply doesn't need to be there. For instance, in that section of documentation, the cycle is introduced by using a dynamic's own updated event as the second argument to its holdDyn. That means that the only thing triggering the event is itself, which makes no sense.

[ryantrinkle]

Yeah, I would say that any time you're using delay to fix a loop, you still have a bug after doing that. A causality loop is where an Event is able to potentially cause itself to fire, which is a paradox; the correct solution is to figure out why the code creates that paradox, and change it so that it doesn't create it anymore.

[gspia]

Ok thanks @ElvishJerricco @ryantrinkle , luckily the title of this issue is ok as should the whole delay-section/recommendation be revised to reflect what you wrote above? This doc is something that people probably will read and it would be a bit sad if it instructs to apply bad habits.

(Or, is the delay just meant to be a temporary solution to find out where the problem is? Or is there some other way/idea on how to use delay in that kind of situations? If yes, then there probably still is something to re-write/clarify.)

(And now I have to find out where I used that delay and try to fix it.)