Comment by brabel

9 hours ago

A real effect system allows you to do things like NOT continue execution after using the effect (like the error effect does - if you "implement" this by using Exceptions, you're not using effects at all, just using Exceptions with extra steps) or only continuing it after some asynchronous work happens (the Future effect), or even "continue" execution several times. That just cannot be done with "just passing stuff in". You still don't seem to have understood effects.

1 comment

brabel

tome 8 hours ago

Thanks for your response. Perhaps I'm missing some fundamental things. Could you help?

> A real effect system allows you to do things like NOT continue execution after using the effect

Right, Bluefin's Request allows you to do that too. For example here is an example of handling the request by continuing or not, depending on what the value yielded to the Request is.

    example :: Either String ()
    example = runPureEff $ try $ \ex -> do
      forEach
        ( \r -> do
            request r True
            request r True
            request r False
            request r True
            request r True
        )
        ( \case
            True -> pure ()
            False -> throw ex "Stopped"
        )

> if you "implement" this by using Exceptions, you're not using effects at all, just using Exceptions with extra steps

Not sure I follow that. Above you can see I used an exception (Bluefin's Throw capability), but I couldn't have used only an exception because that would have aborted unconditionally. What am I missing here, that makes "using Exceptions" "not using effects at all"?

> only continuing it after some asynchronous work happens (the Future effect)

I'm not really sure what "a Future effect" is, but I don't see how it's not something that can be run as a function call, at least in Haskell.

> or even "continue" execution several times

Right, these are the multishot continuations which Bluefin doesn't support. I haven't discovered many particularly compelling use cases for multishot continuations but would be very interested in finding some. The developer of the Kyo effect system for Scala, Flavio Brasil, suggested parsing, with multiple parse results, which makes sense.

I'm also not entirely sure Bluefin couldn't simulate common use cases of multishot continuations with threads, but I haven't thought about it very hard.

> You still don't seem to have understood effects.

Possibly true, and part of my puzzlement! I'm always happy to try to improve my understanding. Can you help me see what I've missed?