Utility functions for handling effects

[arybczak]

Supersedes #230.

@michaelpj @ocharles does that work for you?

I decided to go with handleWith instead of interpretWith since the name interpretWith is too close to interpret and might be confusing.

Still reads nicely:

myFunction arg `handleWith_` \case
  NotifyA i -> ...
  NotifyB s -> ...

and won't clash with Control.Monad.Catch.

[arybczak]

Well, actually maybe interpretWith is better? Because then I can also add interposeWith for a flipped interpose. Damn naming 😅

[ocharles]

I think your comment is a good suggestion. Then we don't really introduce any new terms. So I'm +1 on fooWith meaning "flipped foo".

[michaelpj]

Yeah, that would have been what I would have gone for.

[arybczak]

Ok, I added all possible variants, it should be good to go.

[michaelpj]

I'm slightly sceptical of all the variants. With this one I think it's quite likely that runHandlerEs is also quite large, so is it going to make sense to privilege handler as the postfix one? I'm unsure, which makes me wonder if we should omit it for now.

[arybczak]

In my experience runHandlerEs is usually a single internal runner like runReader or runState (maybe both?). In the event that it's an additional setup, like

blah = reinterpret run $ \case
  ...
  where
    run m = do
      x <- setup1
      y <- setup2
      runState x $ runReader y m

reinterpretWith should actually help with this:

blah m = do
  x <- setup1
  y <- setup2
  reinterpretWith (runState x . runReader y) m $ \case
    ...

On the other hand, the handler is almost always multiline, so if you can't partially apply reinterpret, you need to bind the handler separately.

To not look very far, the code from #229 would benefit from reinterpretWith.

Am I missing something? 🙂

[michaelpj]

No, that's convincing!

[michaelpj]

👍

[michaelpj]

Same comment as about reinterpretWith

[michaelpj]

Thanks!